TMC3in1 – Torch & Motion Controller 3in1texasmicrocircuits.com/...Doc_Vol_02_Plasma_and_THC...They...

Texas MicroCircuits – Vol. 02 Plasma and THC Basics 2017, July 17

th - Rev A - Preliminary

Copyright © 2008-2017 – Texas MicroCircuits www.TexasMicroCircuits.com of 60

TMC3in1 – Torch & Motion Controller 3in1 Plasma THC - 5 Axis Breakout Board - Spindle Controller

Vol. 02: Plasma and THC Basics

Preliminary

For use with TMC3in1 Plugin Rev: ALL

Author: Randall L Ray Very Sr. Engineer Texas MicroCircuits




Table of Contents Table of Contents ................................................................................................... 2

Figures ................................................................................................................... 5

Purpose of this Document ...................................................................................... 6

NOTE 1: RED in text ........................................................................................... 6

NOTE 2: Blue in Text .......................................................................................... 6

NOTE 3: The THC process is simple. ................................................................. 6

Important Plasma Cutting Equipment Players .................................................... 6

Hypertherm ..................................................................................................... 7

Thermal Dynamics .......................................................................................... 7

ESAB .............................................................................................................. 7

Miller ............................................................................................................... 7

Lincoln Electric ................................................................................................ 7

Hobart ............................................................................................................. 7

Definition of Terms used in this Document ............................................................. 8 Torch Height Control - THC ................................................................................ 8 Ethernet Smooth Stepper (ESS) ......................................................................... 8 Variable Frequency Drive (VFD) ......................................................................... 8 Cut Height ........................................................................................................... 8 Pierce Height ...................................................................................................... 9 Pierce Delay ....................................................................................................... 9 Tip Volts or Arc Volts .......................................................................................... 9 Set Voltage or Target Voltage ............................................................................. 9 Resolution ......................................................................................................... 10 PID (Proportional-Integral-Derivative) Controller Algorithm .............................. 10 Anti-Dive ........................................................................................................... 10 G-Code ............................................................................................................. 10 M-code .............................................................................................................. 11 CAD/CAM/Control Program .............................................................................. 11 VCarvePro CAD/CAM Software ........................................................................ 11 SheetCam CAM Software ................................................................................. 11 Mach3/4 Control Program ................................................................................. 12 Torch-On........................................................................................................... 12 Arc OK, Arc Good, or OK-to-Move .................................................................... 12 Kerf Width ......................................................................................................... 12 Cut Order .......................................................................................................... 13 Lead-in and Lead-out ........................................................................................ 13 Charge Pump .................................................................................................... 13 Analog-to-Digital Converter .............................................................................. 13 Voltage Divider ................................................................................................. 14 Opto-Isolator ..................................................................................................... 14 DC-to-DC Converter ......................................................................................... 14 Material Data Base (future enhancement feature) ............................................ 15 TMC3in1 Test Set (near future device - TBD)................................................... 15 Radio Frequency Interference (RFI) or Electromagnetic Interference (EMI) ..... 16 Ground Loops ................................................................................................... 16




Spectrum Analyzer ........................................................................................... 16

Systems Engineering and Architecture ............................................................. 16

Remote Access and Support ............................................................................ 17

Touchstone and Perception- Beware! .................................................................. 17

Touchstone of Performance.............................................................................. 17

Perception of the User ...................................................................................... 18

CNC Plasma Cutting Operation - Simple ............................................................. 19

Firing the Torch ................................................................................................. 19

Torch Height Control Operation Sequence ....................................................... 22

Plasma Cut Quality and what affects it ............................................................. 25

Swirl Gas ....................................................................................................... 26

Shield Gas introduction ................................................................................. 26

Double Arc ........................................................................................................ 27

Double Arc: Conditions causing it ................................................................. 27

Double Arc: Prevention techniques ............................................................... 27

Coning or Why Torch Height is so important .................................................... 30

Dross – Scourge of Plasma Cutting .................................................................. 33

High Speed Dross ......................................................................................... 34

Low Speed Dross .......................................................................................... 35

Corner Dross ................................................................................................. 36

Top Dross ...................................................................................................... 37

Dross Summary ............................................................................................ 37

Other Cutting Characteristics Affected by Torch Height ................................... 38

Top Edge Rounding ...................................................................................... 38

Bevel Angle ................................................................................................... 38

Direction of Cut ............................................................................................. 38

Correct Voltage ............................................................................................. 39

Nitride Contamination .................................................................................... 39

Cut Speed ..................................................................................................... 40

Ideal Cutting Current Control – (machines that will accept control) .................. 40

Clean Air for Optimal Plasma Cutting ............................................................... 40

Anti-Dive Operation (Theory) ............................................................................ 42

Anti-Dive Scenarios to Construct Algorithms .................................................... 43

Scenario 1- Torch Cut Speed Affects Arc Voltage ............................................ 43

Conditions ..................................................................................................... 43

Solution ......................................................................................................... 43

Scenario 2 – Torch Crosses Precut Line .......................................................... 43

Conditions ..................................................................................................... 43

Solution ......................................................................................................... 43

Scenario 3 – Torch Cuts too Close to Edge of Material .................................... 43

Conditions ..................................................................................................... 43

Solution ......................................................................................................... 43

Specification Overview ......................................................................................... 44

System Overview .............................................................................................. 44

Block Diagram of TMC3in1 Hardware .............................................................. 45

Software General Description............................................................................... 46

Software Design Goals ......................................................................................... 46

Overall Software Data Flow from Mach3 through theTMC3in1 ......................... 46




Mach3/4 Operator Screen Enhancements ........................................................ 47

Fire Control Panel – Part of the Fire-by-Wire Project .................................... 48

TMC3in1 Plugin Design – Overview ................................................................. 49

TMC3in1 Firmware Design ............................................................................... 50

Master Microcontroller Firmware Design ....................................................... 50

Spindle Speed Control Design ...................................................................... 50

Plasma Torch Height Control Design ............................................................ 51

THC Operation Simple Process ................................................................. 51

Detailed Process of Changing Torch Height – Then and Now ................... 52

Then (THC301 - circa 2005) ...................................................................... 52

THC Rate ................................................................................................... 53

THC301 Overshoot and Recovery ............................................................. 53

Now (TMC3in1 – circa 2017) ..................................................................... 54

Voltage Range ........................................................................................... 54

Generating Example of Plasma Operation Processes (G-code) .......................... 58

Overview ........................................................................................................... 58

Tools used in Generating Plasma G-code for Mach ......................................... 58

CAD – VcarvePro ............................................................................................. 58

CAM - SheetCam .............................................................................................. 58

Step by Step – From Drawing to Cut Part ......................................................... 58

Main work week 06/19/2017 - TBD ................................................................... 58

Appendix .............................................................................................................. 59

Customer Tests ................................................................................................ 59

Z Axis Speed Limit Test ................................................................................ 59

System Latency Test ..................................................................................... 59

Future Enhancements Wish List........................................................................... 60

Simulator........................................................................................................... 60

Mach3 ............................................................................................................... 60

Mach4 ............................................................................................................... 60

TMC3in1 Plugin ................................................................................................ 60

TMC3in1 General ............................................................................................. 60

Breakout Board ................................................................................................. 60

Torch Height Control ......................................................................................... 60

Spindle Speed Control ...................................................................................... 60




Figures Figure 1 - Plasma Cutting Corrugated Steel ........................................................ 18

Figure 2 - Gas Flow ................................................................................................ 20

Figure 3 – Starting the High Frequency Pilot Arc ............................................... 20

Figure 4 - Pilot Arc to Work Piece ........................................................................ 21

Figure 5 - Transferring the Arc ............................................................................. 21

Figure 6- THC Plasma Sequence 1 of 2 ................................................................ 22

Figure 7- THC Plasma Sequence 2 of 2 ................................................................ 23

Figure 8 - With and Without Swirl Gas ................................................................. 25

Figure 9 - Swirl Gas Difference in Cut (angled sides) ......................................... 26

Figure 10 - Kerf Examples ..................................................................................... 29

Figure 11 - Plasma Arc Shape and Temperature................................................. 30

Figure 12 - Torch Height Too Low ........................................................................ 31

Figure 13 - Torch Height Too High ....................................................................... 31

Figure 14 - Torch Height Just Right ..................................................................... 31 Figure 15 - Another Diagram on How Torch Position Affects Bevel ................. 32 Figure 16 - Showing Dross at Different Speeds .................................................. 33 Figure 17 - High Speed Dross ............................................................................... 34 Figure 18 - Low Speed Dross ................................................................................ 35 Figure 19 - Corner Dross ....................................................................................... 36 Figure 20 - Corner Loops and Triangles .............................................................. 36 Figure 21 - Top Dross ............................................................................................ 37 Figure 22 - Cut Quality – Left and Right Sides .................................................... 38 Figure 23 - Cut Quality - Direction ........................................................................ 39 Figure 24 - Cut Quality - Voltage ........................................................................... 39 Figure 25 - Preferred Method ................................................................................ 41 Figure 26 - Acceptable Method (and most used) ................................................ 41 Figure 27- TMC3in1 System Block Diagram ........................................................ 44 Figure 28- TMC3in1 Hardware Block Diagram..................................................... 45 Figure 29 - Overall Software Data Flow ................................................................ 46 Figure 30 - Mach3 Screen for the TMC3in1 Operations ...................................... 47 Figure 31 - Mach4 Screen for the TMC3in1 Operations ...................................... 47 Figure 32 - Fire-by-Wire Application .................................................................... 48 Figure 33 - TMC3in1 Plugin Screen ...................................................................... 49 Figure 34 - Master Micro Firmware ....................................................................... 50 Figure 35 - Spindle Speed Control Firmware ...................................................... 50 Figure 36 - THC Operation Simple Process ......................................................... 51 Figure 37 - THC Graphical Data for Simple Operation ........................................ 52 Figure 38 - THC301 Guard Band ........................................................................... 52 Figure 39 - THC Rate .............................................................................................. 53 Figure 40 - THC Process for the THC301 showing Overshoot & Recovery ...... 54 Figure 41 - Sample Cut Chart ................................................................................ 55 Figure 42 – Plasma Material Cut Voltage Range ................................................. 56 Figure 43 - Detailed Torch Height Process for TMC3in1 .................................... 57 Figure 44 - VCarvePro Screen............................................................................... 58




Purpose of this Document The purpose of this document is to provide the software developer with: - An understanding of the process flow of a plasma cutting operation - A deeper understanding of the process of a Torch Height Controller - Exceptions in the THC operation and recovery, - Exception logging and actions to help prevent damage to the torch, CNC

machine, and work piece. - A step-by-step plasma cutting example from CAD to cutting steel

NOTE 1: RED in text

Red text entries are either very important messages or “work to be done” TBD.

NOTE 2: Blue in Text

In some sentences in this document, some words, phrases, or sentences will appear in blue denoting that this is important and directly related to proper torch height.

NOTE 3: The THC process is simple.

It is the response and exception handling that differentiates the TMC3in1 from its competitors. You will learn many details about plasma cutting in this document. The TMC3in1 cannot counteract all of the issues. However, understanding how the process works, the many pitfalls, and specific THC operation and adjustments to the inaccuracies, will give us huge edge over our competition. RR A couple of video to watch for plasma operation (non-CNC) is on YouTube: https://www.youtube.com/watch?v=n2XmlFNc7L4 https://www.youtube.com/watch?v=mJJydOxHwZU Another video that shows how well a THC should work is this one: https://www.youtube.com/watch?v=txGP-Qbii2E Impressive cutting up to 6.25” stainless steel block: https://www.youtube.com/watch?v=ZSlH9TOay7A

Important Plasma Cutting Equipment Players

Plasma cutting was accidently discovered right after WWII in the US defense industry. Good, clean operation was hampered by “double arc” (explained later in this document). Plasma cutting remained an “industry” tool until Hypertherm and Thermal Dynamics (Thermadyne) produced less expensive machines for the smaller shops and “weekend welder” in the late 1980s and early 1990s.




Hypertherm Hypertherm is one (if not the) largest plasma cutting manufacturers in the world. It was formed in 1968 when founder Dick Couch invented a process of injecting water in the nozzle to produce better cuts and almost no “double arc” (explained later) Thermal Dynamics Incorporated in 1957, Thermal Dynamics (ThermaDyne, now Victor Technologies) has been one of the pioneers in plasma cutting systems. ESAB ESAB is a welding company founded in 1904. They produce and sell plasma cutting equipment. Miller Miller is a welding company founded in 1929. They produce and sell plasma cutting equipment Lincoln Electric Lincoln Electric is a welding company founded in 1895. They produce and sell plasma cutting equipment Hobart Hobart is a welding company founded in 1917. They produce and sell plasma cutting equipment. Each plasma cutter power supply (i.e. Hypertherm, Thermal Dynamics, Hobart, Miller, to name a few) comes with a user manual. Each manual, for the particular make/model, will have a table showing plasma settings for a particular material to cut. These setting include: - Material (steel, stainless steel, aluminum) - Thickness (20ga, 1/8”, ¼”, ½” to name a few) - Amp setting directly proportional to thickness of material - Pierce delay (defined in next section) - Cutting speed - Air pressure and flow rate for air flowing through the torch - And most important is the voltage used by a Torch Height Control to

determine height of the torch above the material being cut. These setting differ with each type of material, thickness and speed of cut for each model of plasma cutter.




Definition of Terms used in this Document Definitions and terminology are important as it gives the developers and users a basis in their understanding of the TMC3in1 function and operation. Below are several terms we use in this document and the definitions as we see them.

Torch Height Control - THC

Plasma machines use a constant current power supply for cutting. The power supply can range from 10 to 400 amps (or more) selected from the plasma machine control panel. A constant current supply keeps the cutting current at the user selected value by changing the cutting voltage as the load changes. The load changes as the distance from the torch tip to the metal you are cutting changes. The TMC3in1 torch height control monitors this “Tip Voltage” and adjusts the torch height to maintain Tip Voltage to within + or – 0.125v (hopefully better) of the user Set Voltage. NOTE: In this document, “THC” refers to the Torch Height Control function of the TMC3in1.

Ethernet Smooth Stepper (ESS)

The Ethernet Smooth Stepper (http://www.warp9td.com/) is a 6 axis motion control device that connects to the Ethernet port of a computer. It accepts commands from a trajectory planner (i.e. Mach3/4) and produces a very high quality pulse train to stepper and servo motors (accepting Step/Direction pulses). When used with Mach3/4, the Ethernet Smooth Stepper can act as a replacement for up to three printer ports, both in terms of function and connections. It can be viewed as a super printer port. If your system is currently using Mach3/4 with one, two, or three printer ports, changing to the Smooth Stepper should be very easy. The Smooth Stepper allows computers with no printer ports, such as laptops, to control motion with Mach3/4. More information on the ESS is explained later in this document.

Variable Frequency Drive (VFD)

A variable-frequency drive (VFD) (also termed adjustable-frequency drive, variable-speed drive, AC drive, micro drive or inverter drive) is a type of adjustable-speed drive used in electro-mechanical drive systems to control AC motor speed and torque by varying motor input frequency and voltage. This is the device that controls the spindle and communicates with the TMC3in1 Spindle Speed microcontroller.

Cut Height

The Cut Height is the optimum distance from the tip of the torch to the top of the metal being cut while cutting. The optimum Cut Height depends on many variables such as type of material, thickness, rate of cut, and cutting amperage. This distance is known as the “sweet spot” for optimum cutting of the specific material and




therefore it is crucial to keep the tolerances of this distance to an absolute minimum while cutting.

Pierce Height

The Pierce Height is approximately 2 times the distance of the Cut Height. The torch is set to the Pierce Height when the torch is about to fire and pierce the metal to begin cutting. This extra distance helps prevent molten metal blowback from damaging the torch tip when the torch is fired and is piercing the metal.

Pierce Delay

The pierce delay is the time allowed when the torch is fired (and Arc OK is active) until the X/Y starts moving. This allows the arc to pierce the material before the actual cutting starts. The pierce delay is usually set in in G-code (i.e. SheetCam) for each “tool” and is dependent on the material being pierced, thickness, and current used. For thin materials such as those 1/8” and below, the pierce delay is usually 0.0 seconds. Thicker materials, such as 3/16”, 0.5 seconds should do. Even thicker requires more delay. Use this as a rule-of-thumb.

Tip Volts or Arc Volts

Tip Voltage or Arc Voltage is the voltage measured from the tip of the torch to the metal while being cut. This voltage can range from 0 to 255 volts DC. In special cases, the TMC3n1 can be calibrated to reach beyond 255vdc, but only a max of 255 is used by any plasma cutter. This voltage is directly proportional to the distance (Cut Height) between the torch tip and the metal being cut. In THC operations, it is the Tip Volts that is set in reference to the Cut Height. This proportional Tip Volts to Cut Height is slightly different from machine to machine so each machine needs to be “calibrated” by cutting different materials and adjusting the Set Voltage to assure the “sweet spot” for that particular material being cut and the machine being used to make the cut. The suggested setting in the machine’s user guide is only a starting point.

Set Voltage or Target Voltage

The Set Voltage is the “target” voltage you wish to have the THC maintain while cutting and can be adjusted from the main screen Mach3/4 application or from the optional THC3in1 encoder knob. The Set Voltage (adjusted by the user using the TMC3in1 optional encoder knob or the horizontal slider on the Mach3/4 app) is compared to the Tip voltage and the THC function tells Mach3/4 to adjust the Z axis up or down until the Tip voltage equals the Set voltage. Maintaining this Tip Voltage helps insure a constant distance between the tip and the metal being cut. This is the main purpose of the THC function.




Resolution

The THC will maintain the Tip Volts at + or – 0.125v of the Set Volts (target). The THC will only display readings in tenths of volts (XXX.x) but the internal resolution is kept in thousandths of volts (XXX.xxx). An algorithm called a Proportional-Integral-Derivative (PID) is a generic control loop feedback mechanism (controller) widely used in industrial control systems and is incorporated to help smooth out the adjustment of the delta of Tip Volts to Set Volts. This PID algorithm is self-tuning so it adjusts to the rate of cut of the material.

PID (Proportional-Integral-Derivative) Controller Algorithm

A PID controller is a control loop feedback mechanism (controller) widely used in industrial control systems. A PID controller calculates an error value as the difference between a measured process variable and a desired set point. The controller attempts to minimize the error by adjusting the process through use of a manipulated variable. In the TMC3in1, PID (or variation) algorithms are used in the THC, Spindle Speed, The PID controller algorithm involves three separate constant parameters, and is accordingly sometimes called three-term control: the proportional, the integral and derivative values, denoted P, I, and D. Simply put, these values can be interpreted in terms of time: P depends on the present error, I on the accumulation of past errors, and D is a prediction of future errors, based on current rate of change. The weighted sum of these three actions is used to adjust the process via a control element such as the position of a control valve, a damper, the power supplied to a heating element, or, in our case, a PID algorithm for the THC control and a PID algorithm for the Spindle Speed control. For more detailed information see: http://en.wikipedia.org/wiki/PID_controller

Anti-Dive

The automatic Anti-Dive feature in the THC prevents the torch from “diving” toward the metal being cut when crossing previous cut areas or when cutting tight arcs and small circles. There are other situations that cause “diving” and their prediction and prevention is the “intellectual property” or “trade secrets” of THC designers.

G-Code

“G-code (also RS-274), which has many variants, is the common name for the most widely used numerical control (NC) programming language. It is used mainly in computer-aided manufacturing (CAM) for controlling automated machine tools. G-code is sometimes called G programming language. In fundamental terms, G-code is a language in which people tell computerized machine tools how to make something.” See http://en.wikipedia.org/wiki/G-code




M-code

Mx (“x” is usually a numerical value) refers to an M (Miscellaneous function…..sometimes referred to as a “Macro”) is used by the G-code for plasma cutting operations for special operations such as “Torch On, Torch Off, and other special functions. (i.e. M3, M5, M6, etc.) Add new TMC3in1 Macros overview

CAD/CAM/Control Program

Though this entry is a multiple definition, it is important to understand the difference between CAD, CAM, and the G-code Control Program and how they are used in plasma cutting by the TMC3in1.

- CAD or Computer Aided Design is a method of using a computer to create a drawing of a component design into an electronic form that can later be used by CAM software to make it “manufacturable”.

- CAM or Computer Aided Manufacturing is a method of using a computer to take a CAD file and generate a file with all the necessary “tool and material information” producing a “G-code” file. This file is then fed to a G-code Control Program that operates a CNC (Computer Numerical Control) machine to make the component.

- Control Program – The machine Control Program runs a G-code file generated specifically for and operates the CNC machine, tools used, and material being processed in order to produce the component. This program usually runs on a PC running either Windows or Linux operating system. It is configured to run a particular CNC machine, though many can be reconfigured to run many different CNC machines.

VCarvePro CAD/CAM Software

VCarvePro by Vectric (www.vectric.com) is a CAD/CAM software program that is known for its “intuitive” ease of use and included “nesting” of parts. There are many CAD programs on the market today and this is just one example and the one used by us at Texas MicroCircuits for all of our CAD work in plasma cutting, routing, and engraving. It also contains a CAM element that we use for routing and engraving but does not have the capability to produce the CAM file needed for plasma cutting. For that “missing” piece, we, and most CNC plasma cutting customers use SheetCam.

SheetCam CAM Software

SheetCam by Stable Design (www.sheetcam.com) is the CAM program of choice for almost all of the plasma users of our THCs. SheetCam provides tool definitions for plasma specific operations including kerf width (and compensation), automatic cut order, pierce delay time, and ramp piercing. It can also provide lead-ins and lead-outs and a host of other options beneficial to plasma cutting.




Mach3/4 Control Program

The TMC3in1 (currently) is designed to work exclusively with the Mach3/4 control program (www.artsoftcontrols.com), though that may change in future firmware releases. The X, Y, Z, A, B, and C axes are controlled by the ESS parallel port 3 and the THC function works through the ESS parallel port 3 and through the ESS expansion port.

Torch-On

The Mach3 control program uses the G-code macro “M3” to generate the “Torch-On” command to the THC. This turns on the “Torch-On” “led” on the Mach3/4 screen. Next the THC picks the “Torch-On” relay, telling the plasma cutter to fire the torch. The G-code macro “M5” turns the torch off.

Arc OK, Arc Good, or OK-to-Move

When the Mach3/4 fires the torch, a small “pilot” arc is generated out of the tip of the torch and tries to electrically connect with the work piece (that has the work (ground) clamp attached to it). This pilot arc produces an ionized stream of air that is highly conductive. The pilot arc (and highly conductive, ionized stream of air) connects with the work piece. This arc “transfers” from a pilot arc to a cutting arc producing the full current flow set by the current adjustment on the plasma cutter. This “main” cutting arc is what generates the intense heat used to vaporize the metal in the work piece and pierces through it starting a cut. At this point or arc transfer, the plasma cutter generates a signal known by several names (Arc-OK, Arc Good, or OK-to-Move). This signal tell the THC to start looking at the Tip Volts and making plans to tell Mach3 when to move the Z-axis up or down to match the Set Volts. It also sends the “Arc-OK” signal to Mach3 to signal that it is “OK” for Mach3 to move the X and Y axis per the G-code program (after a “Pierce Delay) set up in the G-code.

Kerf Width

The kerf is a machining term that refers to the material removed during cutting. In plasma cutting, the width of the kerf is dependent on the cutting current, material being cut, height of plasma tip to material, cutting speed, plasma torch tip, direction of cut, etc. The proper CAM software should compensate for this kerf (once the proper kerf width is input for the “cutting tool”) when cutting the part. Normally, the kerf width of normal plasma cutting operations is between 0.035” and 0.080” with all of the above mentioned factors affecting the kerf width. That’s why we recommend taking the time to cut material, varying the parameters to find the “sweet spot” and making a “plasma tool” from these parameters for the CAM software to use.




Cut Order

The “cut order” of the different cuts to make a part in plasma cutting is usually very important. If you are making a square plate with 4 holes for the bolts of a caster plate, for instance, it is critical that your G-code is written such that the 4 holes are cut first before the outside square is cut. Think about it. Most of us have ruined parts just because the cut order was not correct. SheetCam has an automatic cut order option that is very helpful as it will determine which cuts need to be made first and which cuts are “inside” cuts and which are “outside” cuts, providing kerf compensation.

Lead-in and Lead-out

Lead-ins and Lead-outs are starts and ends of plasma cuts that occur in material that is part of the waste. For a hole, the lead-in (and lead-out) is located in the inner material of the hole that will drop out once the hole is cut. The lead-in is important because the piercing will not leave a “divot” in the hole circumference. The lead-out will help insure a “bump” is not left in the circumference if the lead-ins and lead-out overlap (overcut) properly.

Charge Pump

The “charge pump” is a circuit that has as its input a “pulse train” and produces an active signal when this pulse train is present. The purpose of the charge pump is to insure that Mach3 control program has full control of the parallel ports. When Windows is booted, it goes through a series of resets to the parallel ports and many of the output bits are “glitched” until Windows fully loads the parallel drivers. This “glitching” can cause such things as the plasma torch firing indiscriminately while Windows is booting up and before Mach3 takes over. By placing a charge pump circuit in the THC and using it to disable all control signals if the “pulse train” is not present (about 12.5Khz), then the THC will not be active until Mach3 is in charge of the parallel ports and generates the charge pump pulse train. Once this pulse train is sensed by the charge pump, the THC can be made “Ready”. This charge pump is also present in most all “breakout boards” as well. However, by using the ESS, the charge pump is unnecessary, but it is still generated anyway to keep with the charge pump scheme as some breakout boards and THCs rely on it to operate.

Analog-to-Digital Converter

If the analog-to-digital converter (A/D) is the hardware heart of the THC, the firmware is the soul. The A/D converts the Tip Volts from the plasma cutter (directly proportional to the height of the torch above the material being cut) to a digital value. This digital value is compared to the Set Volts generated by the slide control on the Mach3/4 screen or the optional encoder knob connected to the TMC3in1 board. The




outcome of the comparison determines whether an “UP” or “Down” signal is sent to Mach3/4 by the THC to bring the height of the torch (Tip volts) back in line with the Set Volts adjustment. In the THC301 THC, the A/D has a resolution of 12 bits (about + or – 0.5v) whereas the TMC3in1 uses a 16 bit A/D giving the TMC3in1 16 times better resolution or theoretically + or – 0.03v or 30 millivolts. The high end plasma cutters only require about + or – 0.125v or 1/8th of a volt and the TMC3in1 can easily maintain this.

Voltage Divider

The voltage divider circuit is provided by the plasma cutter. The voltage divider will take the raw Tip Volts from the plasma cutter and divide it down to a safe voltage the THC can measure. Usually this is in the ratio of 16.6:1. Other divider options are 20:1, 25:1, 30:1 and 50:1. We recommend using the 16.6:1 as it makes the output voltage more noise immune to the Radio Frequency (RF) noise that is inherent to the plasma arc. Our TMC3in1 will adapt (via software selection) to the divider in the plasma cutter. We need more discussion on this and our A/D circuit in the TMC3in1. RR

Opto-Isolator

An opto-isolator is an electronic device provides galvanic isolation for the transmission of digital signals so that high (or noisy) voltages are not transferred from the plasma cutter or CNC gantry back to the THC. This prevents any spurious damaging voltage spikes from getting into and damaging the internal THC (and PC) hardware. You will see these opto-isolators used in the block diagrams in an earlier section of this manual.

DC-to-DC Converter

A DC-to-DC converter is an electrical device that electrically isolates the transmission of power and is the “other half” of circuit isolation. Not all DC-to-DC converters are electrically isolated. An opto-isolator is a great device for its purpose, but if the same power supply (or ground) is used on each side of the opto-isolator, then the electrical isolation is defeated. These two devices go “hand-in-hand” and, in most cases, one without the other provides no electrical isolation at all. Plasma cutters, by design, are notorious high voltage and RF noisy devices and proper isolation of signals and power are critical to proper operation and protection of expensive equipment such as PCs and THCs. You will see these DC-to-DC converters used in the block diagrams in an earlier section of this manual.




Material Data Base (future enhancement feature)

The Material Data Base (MDB) is a crucial part of the Fire-by-Wire philosophy (Fire-by-Wire is explained in detail later in this document). The MDB is a database of almost all of the major plasma cutters on the market and their specific cut parameters that are published with each machine model. These parameters include such things as:

- Material - Thickness of material - Cutting current used - Rate of cut - Pierce delay - Tip Volts

There are also proprietary parameters for each entry determined by Texas MicroCircuits and experimental results using the different models of TMC3in1. Once the operator has chosen the type and thickness of material from the database along with any custom parameters for the type of parts being cut, this information is loaded into the THC and it is set up for the optimum operation. The MDB is crucial to the Fire-by-Wire philosophy explained in more detail later in this document.

TMC3in1 Test Set (near future device - TBD)

The text below was about my THC test set I had for the THC301unit. It saved me a ton of emails and calls…….I left it for us to think about what we can provide for the TMC3in1. The THC (THC301) Test Set will be mentioned in this document so it is being explained here. The THC Test Set was designed and documented for 4 main purposes:

- Allow the user to “bench test” the THC301 and its components (Sensor board and cables) independent of a Mach3 or plasma connection.

- This allowed for getting used to the operation of the THC301 without actually having to connect it up to the PC or plasma equipment

- It also allowed the user to prove the integrity (proper operation) of the THC301 system with the complexities of the PC/Mach/Plasma cutter getting mixed in the equation.

- If the THC system DID have a problem, using the Quick Start manual, the user could perform “problem isolation” each component on the THC system using a “building block” approach, whereby “building” on the previous proper operation of a component to help determine the status of the next component under test. This Test Set was shipped with every THC301 and proved to be invaluable in the field in isolating failing components improving support for the OEMer and manufacturer in getting the problem resolved quickly.

In the same but more integrated manner, the function of the THC Test Set will be designed into each TMC3in1 along with extensive diagnostics to help the support




team (OEM or TMC) to isolate the failure and provide solution fixes in a quicker amount of time to get the customer back up and running.

Radio Frequency Interference (RFI) or Electromagnetic Interference (EMI)

RFI also called EMI is electrical disturbance that affects electrical circuits due to either electromagnetic induction or electromagnetic radiation emitted from an external source. In simpler words, this is noise induced by a plasma or even welding system in close proximity to electronic hardware such as THCs and PCs. It is this type of noise that we strive to suppress by directing the users of plasma systems to properly ground their tables and equipment.

Ground Loops

A ground loop is a condition where an unintended connection to ground is made through an interfering electrical conductor. Generally ground loop connection exists when an electrical system is connected through more than one way to the electrical ground. Ground loops are notorious for causing “hum” in audio and video systems but also cause problems in computer connections and associated hardware (i.e. THCs). Though most of the time, the noise is “line frequency” (60Hz in North America and 50Hz in Europe), it can also be frequencies generated by the RF frequencies produced by a plasma cutter or nearby welder (especially TIG welders). There are methods to eliminate ground loops both in the THC equipment and in the complete plasma system.

Spectrum Analyzer

A Spectrum Analyzer is an expensive piece of equipment used to measure Radio Frequency (RF) and Electromagnetic Interference (EMI) that is present, not only in the air, but coming in the cables of the THC system and causing “noise” problems. The primary use is to measure the power of the spectrum of known and unknown signals. At TMC we use a spectrum analyzer that measures from 1 Hz to over 4 GHz in the testing of our THCs, plasma, and welding systems to see what frequencies (and harmonics) are generated and provide filtering and installation procedures to eliminate them from our systems.

Systems Engineering and Architecture

In the past, THCs were designed to be a piece of hardware that performed a particular function. Recently the functional requirements for THC subsystems has become complex enough that any new THCs must be developed from a systems engineering and architecture point-of-view. Using systems architecture to “map” out the THC subsystem means designing with 3 distinct “components” in mind;




Hardware, Software/Firmware, and multi-level User Operational Capability (used to be called “user friendly” but more complex now). Though there is much more to this than explained here, it basically says that the hardware is designed to be more robust and full of features that can be used at a later date by newer versions of software/firmware and that the user interface is designed to accommodate these changes. The THC subsystems will evolve primarily through newer software/firmware versions that the hardware is able to respond to.

Remote Access and Support

One of the most important features that our OEMers and our support team need (thus providing the end user with quicker and more accurate support) is being able to remotely access, observe, and control the THC from our local support centers. At best, in the past, the support teams could only look at the operation of the PC and the Mach3/4 program, but never into the internal operation of the THC. From a “ground up” approach using System Engineering and Architecture methodologies, we are designing the Fire-by-Wire family of THC subsystems with these remote access and support features.

Touchstone and Perception- Beware! Probably remove this section on Touchstone… It is important, when manufacturing and marketing a product, to understand both the touchstone of performance and the perception of the user. In many cases the touchstone of performance is a “test” that is not necessarily indicative of the overall or even general operation of the product. Sometimes the user’s perception (defined as “customer expectations”) of the operation or specifications of a product are either meaningless or, at best, only partially significant. Unfortunately, the customer’s perception and touchstone are what, in his mind, are the deciding factors in comparing and purchasing the product. If the developer(s) and marketer(s) (many times the same people) understand this, they can provide what the customer expects. Though it may have little bearing on the true performance of the product, by understanding that these factors will be significant to the user, we can truthfully make sure these factors or “specifications” are represented in the product.

Touchstone of Performance

Definition: Touchstone – “a standard or criterion by which something is judged or recognized”. Each “discriminating” plasma customer has his “touchstone of performance” that he uses to measure and compare the performance of a THC. In almost all cases, the touchstone of performance for a Torch Height Controller is how well the torch height (or Z axis) responds when cutting corrugated steel. To be truthful, almost no one cuts corrugated steel as a production item. The only reasons they use this is:

-




- They heard someone say “Hey, if it cuts corrugated, then it does what all THCs must do. The best THCs will cut corrugated.” (this is only partially true).

- They think that is the best way to show the response of the THC is it riding the “nap of the land” going up and down the “sine wave” of the corrugated steel. A PID loop, well-tuned for the corrugated “sine wave” would demonstrate the “excellent performance” of the THC in question but it would be a case of “tuning for touchstone” and not of the “real world”. The “myth” that cutting corrugated is the best way to demonstrate (and compare) THC operation is mostly false. Cutting corrugated steel only shows the THC operation in moving the Z axis in response to the predictable changing arc voltage as the torch moves across the “sine wave” of the corrugated steel. The torch tries to adjust its height proportionally with the ever changing arc voltage as the material “moves” up and down in the “torch’s point of view”.

Though this does show the torch correcting for the changing height of the material in relation to the cutting direction, it does nothing to demonstrate any of the many “exception handling processes” (i.e. anti-diving algorithms, correction for false arc to height inconsistencies, etc.) that are built into a very well designed THC (or its firmware). However, this “cutting of corrugated” continues to be the “touchstone of performance” and, therefore, must be shown to those users in their “comparison” of THCs.

Z Axis

Cut Direction CorrugatedSteel

“theoretical” Cut Height(determined by arc voltage)

Figure 1 - Plasma Cutting Corrugated Steel

Perception of the User

Definition: Perception – “a way of regarding, understanding, or interpreting something; a mental impression”.




Specifications of a product are important for two reasons: 1. It states the qualifications and limits of the product. It is a detailed description

of the design and materials used to make a product. 2. This second reason is the specifications are sometimes “adjusted” or

“manipulated” in such a way that they can be slightly misinterpreted or misleading to a customer.

The second reason is used in most products because the marketing folks know that a potential customer may use the specifications as a final “tie-breaker” when comparing two products (all other considerations being equal). Unfortunately, if one product’s specifications show a condition or qualifier that is just 1 point “better”, no matter how insignificant that qualifier is, the chances that the customer chooses the product with the “better” qualifier over the “inferior” product is very high. Case in point: If the A/D converter of one THC is 12bit and the A/D of another THC is 16bit, (all other “specs” being equal) it seems the obvious “better” one is the THC that has the 16bit A/D. However, as an overall picture would show, the 16bit A/D may be wasted if the resolution of the complete “torch control loop” (arc voltage, A/D, any latency, and mechanical function of the Z axis mechanism) if well below any benefit the extra 4 bits of A/D resolution would bring. But the “perception of the user” is that the 16bit A/D THC is the better one. And because this is the case with most potential customers, our THC must have 16bit A/D because it is the customer’s perception that will decide the THC selection……even if 16bit A/D is an insignificant spec. In summary, no matter the specification, if the user perception is that a particular spec is the deciding factor, we must provide that “better” spec, even if it has little bearing on the total performance of the THC.

CNC Plasma Cutting Operation - Simple Now we are finally getting to the point of explaining just how plasma cutting works and the processes it takes to complete an operation. I want to remind you that this really will help pull things together when developing firmware for the TMC3in1.

Firing the Torch

A start input signal is sent to the power supply. This simultaneously activates the open circuit voltage and the gas flow to the torch. Open circuit voltage can be measured from the electrode (-) to the nozzle (+). Notice that the nozzle is connected to positive in the power supply through a resistor and a relay (pilot arc relay), while the metal to be cut (work piece) is connected directly to positive. Gas flows through the nozzle and exits out the orifice. There is no arc at this time as there is no current path for the DC voltage.




Figure 2 - Gas Flow

After the gas flow stabilizes, the high frequency circuit is activated. The high frequency breaks down between the electrode and nozzle inside the torch in such a way that the gas must pass through this arc before exiting the nozzle. Energy transferred from the high frequency arc to the gas causes the gas to become ionized, therefore electrically conductive. This electrically conductive gas creates a current path between the electrode and the nozzle, and a resulting plasma arc is formed. The flow of the gas forces this arc through the nozzle orifice, creating a pilot arc.

Figure 3 – Starting the High Frequency Pilot Arc

Assuming that the nozzle is within close proximity to the work piece, the pilot arc will attach to the work piece, as the current path to positive (at the power supply) is not restricted by a resistance as the positive nozzle connection is. Current flow to the work piece is sensed electronically at the power supply. As this current flow is sensed, the high frequency is disabled and the pilot arc relay is opened. Gas ionization is maintained with energy from the main DC arc.




Figure 4 - Pilot Arc to Work Piece

The temperature of the plasma arc melts the metal, pierces through the work piece and the high velocity gas flow removes the molten material from the bottom of the cut kerf. At this time, torch motion is initiated (Arc OK signal is sent to the controller) and the cutting process begins.

Figure 5 - Transferring the Arc




Torch Height Control Operation Sequence

Figure 6- THC Plasma Sequence 1 of 2

Both the Mach3 and SheetCam settings overview will be discussed later (TBD). The below explanation is a simplified sequence of events. Assuming Mach3 is set up properly for THC Plasma operation and a G-Code “cut file” has been properly generated from SheetCam, the sequence of events follows when plasma cutting:

1. The Plasma Torch is at some “retract” height above the work metal.

2. Pressing Start on Mach3 (with the THC On/Off button activated on the Mach3 screen will, eventually, put the Z axis under Torch Height Control) causes the torch to move to the requested X/Y position. The beginning G-code will perform a (Touch-off). The Z axis moves down and the “floating head switch” or ohmic sensor detects the work piece with the tip of the torch. The Z DRO will be set to “0”. We have now referenced the Z axis.

3. Mach3 then raises the torch to the Pierce Height (also G-Code determined by settings in SheetCam) – P=Pierce Height

4. Mach3 (M3) then turns on the TORCH light under Torch Height Control and tells the THC to fire the torch (Torch On signal). The THC triggers the Torch relay which sends the “torch on” signal to the plasma cutter. Gas flow (shop air in most cases) begins. The Z axis is still under G-code control.




Figure 7- THC Plasma Sequence 2 of 2

5. The plasma pilot arc initiates via the plasma machine. The pilot arc transfers to the cutting arc and cutting arc connects with the work piece. Arc OK signal is sent to the THC via either an “Arc OK or “Arc Good” signal from the plasma cutter. The “Arc OK” signal is received by the THC where it sends it to Mach3 via ESS. Mach3 then turns on the ARC OK square “LED” on the screen in the Torch Height Control section. If there is a Pierce Time Delay that was set in SheetCam for this operation, then the Mach3 delays moving the torch until the delay has ended. It is at this point (Arc OK) that the THC takes “assists” in control of the Z axis (via Torch UP and Torch Down signals to Mach3).

6. Now Mach3 working with the THC moves the torch down to the Cut Height. The THC compares the Arc Voltage to the Set Voltage (Set Voltage is the number the user set in the THC by adjusting the optional encoder knob or the slider on the Mach3 screen) and tells Mach3 to adjust the Z axis to compensate. Mach3 now tells the torch to move and start cutting.

7. As the torch moves and cuts the work piece the Tip Voltage may change if the metal warps or is not perfectly flat. This necessitates movement of the Z axis to maintain the proper cut height. The THC tells Mach3 to move the Z axis up if the Set Voltage is higher than the Tip Voltage or down if the Set Voltage is lower than the Tip Voltage. If they are equal, then no Z axis motion is performed. These actions are reflected in both the UP and DOWN lights on the modified Mach3 screen.




8. When the cut is finished, Mach3 stops X/Y movement, tells the THC to turn the torch off, whereas the THC loses Arc OK, and Mach3 raises the Z axis to the “retract” height. If there is more to cut, then Mach3 will move the torch to the next X/Y position and the process will start over.

NOTE: SheetCam can be programmed to perform a Z axis touch-off on every cut, or when the distance from the last touch-off is over 500mm. These options will be discussed later.




Plasma Cut Quality and what affects it

For arc cutting, we take advantage of the fact that Plasma is electrically conductive. Being so hot, not even its own atoms can remain unaffected and they get ionized, that is they emit free electrons which can then freely move from one atom to the other and the atoms themselves are left with a positive charge. Positively and negatively charged particles give plasma its electro-conductive property. What do we have here? We have an excessively hot gas mass than can also conduct electricity. The idea of forming a jet of this gassy mass to attack and melt metals was only one step ahead. For this idea to be realized, some kind of a "plasma gun" should be produced. It should be enough heat resistant to contain the plasma and designed in a way to be able to target it at the metal to be cut. Because no material would remain intact at 22000 degrees C (40,000 degrees F), there was only one way out: Design a "gun" in such a way that the ionized gas be "enveloped" in a much cooler gassy "container", the parts involved provided with constant cooling and make sure they be made of a material of the highest possible melting point. Additionally, it should constrict the plasma jet so that its thermal energy would concentrate on a small area of the target material, for better results. A plasma torch uses a copper alloy nozzle to constrict the ionized gas stream to focus the energy to a small cross section. The high velocity gas jet ejected through the nozzle transfers electric current to the plate we wish to cut which is melted and the molten material is driven away by the very plasma jet. In our drawing below you will see a Plasma torch design with or without Swirl Gas, about which we explain right underneath:

- A. Coolant entry (in most small machine this is shop air), - B. Coolant exit, - C. Plasma Gas, - D. Swirl Gas, - E. Cutting direction and - F. Cut surface.

Figure 8 - With and Without Swirl Gas




Swirl Gas

The introduction of Swirl Gas technology assists cutting in many ways. To begin with, gas swirling helps cooling. The non-ionized atoms of the gas are heavier and cooler than the ionized ones and, when forced to swirl, are distributed on the outer layer of the swirling gas "column". This lower temperature layer protects the copper alloy nozzle. The higher the current, the greater the percentage of ionized atoms, so that the "ideal ratio" of 30% plasma, 70% cool gas gets higher, increasing the eating of the nozzle and reducing its cooling. Nozzles are designed and manufactured to function within a given range of current amperage. Swirl gas improves cut quality. If plasma jet is not swirling, both kerf sides would be beveled, sometimes to an extent that makes work-pieces useless. Please check drawing below:

- A. Straight gas flow, cut surface beveled on both sides. - By swirling the gas, the plasma jet is distributed on one side evenly,

therefore this cut surface is "square" - B. Swirled gas jet, square cut surface. If swirling direction is changed

(clockwise instead of anti-clockwise), the square side changes diametrically. The swirling gas jet attacks one side of the sheet to be cut vertically in its full thickness. Cutting energy is distributed evenly over the full thickness of the work-sheet, resulting in a cut surface perpendicular to the one of the work-sheet. This is the cut edge to use; the one across the kerf is inclined at an angle of some 5 to 8 degrees.

Figure 9 - Swirl Gas Difference in Cut (angled sides)

Shield Gas introduction The introduction of Shield Gas can further constrict the jet and cool the nozzle. This gas is injected in the plasma jet in the last stages of its flow through the torch, after it is ionized, at the nozzle tip.




Double Arc

This topic is described only because it is sometimes blamed (by the customer) as “diving” and it is good to understand why it is not diving.

Double Arc: Conditions causing it Double Arc is created when the nozzle remains connected to the power generator, and this can happen under very special conditions. As previously described, the nozzle should stay isolated from the cutting Arc circuit and only be connected to it during the Pilot Arc creation stage. In case it fails to disconnect and it carries the cutting high amperage, it gets damaged. Double Arcing can be caused by:

Standing Pierce. The torch must be positioned to such a distance from the plate that the Pilot Arc has a chance to come in contact with it; otherwise the Main Arc will fail to start. Molten metal slag, splashes towards all directions during the initial stages of piercing but, as the hollow becomes deeper, the jet blowing through the nozzle orifice is "reflected" upwards carrying slag against the very nozzle. If this slag comes to form a connecting "bridge" between the nozzle and the plate, being electrically conductive, it keeps the nozzle connected to the main Arc circuit even after the nozzle relay opens to isolate it. Such a malfunction could destroy the whole of the front end of the torch and not just the nozzle.

Torch touching the plate. Thin material cutting. All systems of automatic torch positioning make use of some THC (Torch Height Control) method to determine the right distance between the nozzle tip and the work-plate. One such method is the "Touch and Retract" one. The torch is lowered slowly until it touches the plate lightly and retracts to the right height driven by the CNC automation. If the sensor fails to accurately judge the distance (floating-head sensor too strong and deflects thin metal instead of moving floating head switch) or anything else goes wrong, the torch may stay in contact with the plate because of its springing up or warping. In this case the nozzle will stay in the cutting amperage circuit and it will get damaged.

Pilot Arc Malfunction. Sometimes the nozzle relay fails to isolate it. This may be due to a relay short circuit or some shorted resistor. Also in this case the nozzle has to face a much higher amperage than it is designed for and it is damaged.

Double Arc: Prevention techniques Double Arc mainly occurs during the piercing process. There follow some methods to help avoid it:

Creep Torch move. The machine is configured so that the torch is in slow motion during the Main Arc Transfer stage. Torch velocity is approximately 5% to 10% of the normal cutting velocity (Mach3 “THC Rate”), and this slowing down only takes place for a short time. Pierce slag cannot




accumulate on the nozzle, since the latter is moving, drastically reducing the chances for Double Arcing.

Slow rising of the torch during piercing. If we prefer to do standing pierce, during the main arc initiation, the torch slowly rises away from the work-sheet, and spatter cannot easily damage the nozzle. The torch continues to move upwards for the pre-configured time period and then, when the machine starts moving the cutting head at normal velocity, it moves down to the normal cutting height.

Initial Standing pierce with the torch positioned higher than normal. With the torch distanced from the work-sheet longer than normally, it gets more difficult for spatter to build a "bridge" between the nozzle and the sheet, drastically reducing Double Arcing chances. This last preventive method is the least effective of the three.

Plasma Cutting Process parameters Maximum productivity, maximum cut quality and maximum consumables life depend on a series of important cutting parameters, all of which should be carefully considered and controlled to balance. Α. Gas purity – Using other than “Dry Shop Air” Gas purity is a variable of fundamental importance as far as high cut quality and long consumables life are concerned. Minimum purity required for Nitrogen is 99.995% and for Oxygen 99.5%. If purity levels are below the minima recommended, the following malfunctions can occur:

The arc may fail to penetrate thin materials regardless the amperage Excessively shortened Electrode longevity Uneven cut quality, depending on the gas contamination degree. When cutting with N2, we get a thin blackish layer on the nozzle orifice and

the electrode; the higher the contamination degree, the thicker the residue layer. When the gas is pure, the electrode and the nozzle have a somehow sand-blasted appearance

Β. Gas pressure and Flow velocity Each nozzle is designed and manufactured to perform at an optimal amperage matching a given gas pressure and flow. Raising the pressure results in shortening the electrode’s life duration. In this case the electrode tungsten core develops a drilled appearance. If we work with Nitrogen, we may have difficulty with starting the torch. If the torch fails to start, we may notice that the Pilot Arc comes sputtering. This sort of problem occurs when there is too high gas pressure. With too low gas flow we get double arcs.




Figure 10 - Kerf Examples

C. Kerf Cut Kerf is the width of the material removed by the cutting process. Three major variables are involved in Kerf forming:

a. Cutting Speed (Feed Rate). When cutting speed is higher (keeping the rest of the parameters constant), kerf gets narrower. It will keep getting narrower, up to the point that loss of arc will occur See drawing above: A. Narrow Kerf, failed cut,

B. Wider Kerf, Cut accomplished. b. Cutting Amperage. If we increase the Cutting current, keeping the rest of

the parameters constant, the kerf gets wider. If we keep on increasing the amperage, the kerf will continue getting wider until the nozzle is destroyed. Decreasing the amperage, the kerf gets narrower and the cut angle gets more positive until arc penetration fails.

c. Standoff. Standoff (Cut Height) is the distance between the nozzle tip and the work-sheet surface while the cutting job is in progress, after the piercing stage is over. By increasing the arc voltage, standoff is increased and kerf gets wider. Excessive standoff values result in loss of cutting ability. By decreasing standoff, the kerf gets narrower and eventually cutting ability is likewise lost.

D. The Arc Voltage The Arc voltage depends on a multitude of parameters:

a. Cutting Current Amperage b. The diameter of the nozzle orifice c. Gas Flow d. Cutting Height e. Cutting Velocity

Standard plasma cutters use dry shop air for all cutting. Higher quality machines may use other gases during different phase of cutting. The gases generally needed to perform a plasma cutting job are of three kinds: A start gas, a cut gas and a shield gas. In some cases an extra shield gas may be needed. There are some parameters that should be taken into consideration when we plan a cutting job:

Type and thickness of the material Cutting duration




Cut quality and Production costs

The choice of the gases to work with depends on the specific job or the torch type. Generally speaking, different cutting results are achieved with different combinations of Oxygen, Nitrogen, Air, Methane and H-35 (a combination of 65% argon - 35% hydrogen); Argon is also used for engraving jobs. For detailed info please refer to your machine's manual.

Coning or Why Torch Height is so important

“Coning” is one of the pitfalls of obtaining quality parts when plasma cutting. Below is a drawing of a plasma arc shape and temperature. At the top of the arc, the flame is expanding outward. In the middle of the arc (for a large portion), the flame is stable in size and temperature. At the bottom of the arc, the flame shrinks inward and the temperature drops. The “Sweet Spot” is the middle of the arc that is most perpendicular with the work piece. Higher Arc Voltage will proportionally make the “Sweet Spot” longer for better cuts though thicker materials.

Figure 11 - Plasma Arc Shape and Temperature




If a torch is cutting too close to the material (work piece), the final piece cut will have beveled edges. The bevel will appear along the bottom of the piece because the arc is expanding in the “cut zone” (the distance between the top of the work piece and the bottom. This “beveling” is also known as “coning”. Coning out on the bottom shown in the figure below.

Figure 12 - Torch Height Too Low

If a torch is cutting too far away from the material, the final piece will have beveled edges. The bevel will appear along the top of the piece because the arc is starting to shrink in the “cut zone”. The coning out on the top is shown in the figure below.

Figure 13 - Torch Height Too High

When the torch is at the proper “cut height”, the long, relatively stable middle of the flame is in the “cut zone” and we get a straight cut without the conning in either direction shown in the figure below.

Figure 14 - Torch Height Just Right




Figure 15 - Another Diagram on How Torch Position Affects Bevel




Dross – Scourge of Plasma Cutting

Dross is molten metal that does not blow away during the cutting process and instead adheres to the bottom or top of the part in a re-solidified state. There are many factors that can contribute to the accumulation of dross. The most common are: cutting speed, torch standoff height or damaged consumables. In most instances, dross can be reduced or eliminated completely by adjusting the cutting speed to the optimum condition as prescribed in the operator’s manual. However, there may be times when a simple speed adjustment is not possible or will have little effect, such as when the thickness of the material or the cutting amperage requires a slow cutting speed. In this case, dross accumulation is inevitable and cannot be eliminated. Also, the quality, grade and composition of the material are factors that can increase the likelihood of dross and are outside of the control of cutting parameters. For example, a lower quality sheet of carbon steel may be more susceptible to dross buildup due to the increased level of impurities. Finally, as the temperature of the plate increases from the plasma cutting process, dross is more likely to stick to the bottom even with optimum parameters.

Figure 16 - Showing Dross at Different Speeds

Note: High speed dross need grinding. Low speed dross usually chips off.




High Speed Dross

Figure 17 - High Speed Dross

Cause: When the programmed cutting speed is too fast for the amperage being used or the material thickness being cut, the bottom of the arc will lag behind the top. When this happens, the high pressure gas found at the orifice of the nozzle is not as effective at material removal, allowing small amounts of dross to form on the bottom of the plate. High speed dross is typically dotted in appearance and cannot be removed easily by scraping with a hand tool. It must be removed by grinding or machining the finished part. Solution: Verify the cutting speed matches that of published cutting charts for the selected amperage, material type and thickness. If it already does, decrease the cutting speed in small increments (5-10 inches per minute) until the best result is achieved. Select a lower cutting amperage. The optimum cutting amperage for a given material thickness ideally is where the thickness is located near the middle of the range in the cutting chart. Examine the electrode and nozzle for excessive wear and replace as needed.




Low Speed Dross

Figure 18 - Low Speed Dross

Cause: If the cutting speed is too slow for the material thickness or selected amperage, a solid line of dross that resembles a weld bead will form on the bottom of the part. To understand why, remember that the plasma cutting process is electrical in nature. When the torch is moving too slowly, the arc begins to expand in an effort to maintain contact with the edge of the kerf in order to keep its path to ground through the plate. As the arc widens, the distance from the cut edge to the high pressure section of the plasma jet increases to the point where the gas is no longer able to blow away the material effectively. Low speed dross is easily removed with a hand scraping tool. Solution: Verify the cutting speed matches that of published cutting charts for the selected amperage. If it already does, increase the cutting speed in small increments (2-5 in. per minute) until the best result is achieved. Select a higher cutting amperage and adjust the parameters accordingly. Examine the nozzle and shield cap for damage and replace as needed.




Corner Dross

Figure 19 - Corner Dross

Cause: Dross will intermittently form in the corners of a part due to the speed reduction required for a cutting machine to perform an extreme change in direction, such as a right angle. The likelihood of this occurring varies depending on the thickness of the material, cutting amperage, and material composition. Solution: This is a normal occurrence and cannot be avoided without altering the part drawing to include options such as corner loops or triangles. Fortunately, the amount of dross this condition presents is minimal and is easily removed with a hand scraping tool. Corner “loops” and “triangles” are also used to get perfectly squared corners. These methods don’t require the torch feedrate to be slowed when using these methods, producing better corners and almost no dross.

Figure 20 - Corner Loops and Triangles




Top Dross

Figure 21 - Top Dross

Cause: Occasionally, small amounts of dross will form on the top of the part when the programmed cutting speed is too fast or the torch standoff distance is too high. This is caused by the plasma arc’s inability to blow all the molten metal through the bottom of the kerf when the tip of the nozzle is too high above the plate. Top dross is normally a very light accumulation that can be removed easily with a scraping tool. Solution: 1. Reduce cutting speed in 5 in. per minute increments, while monitoring for the introduction of low speed dross. 2. Lower the arc voltage setting in 2 volt increments. 3. Check the nozzle for damage and replace as needed. Dross Summary Most plasma cutting will produce some amount of dross. Keeping it to a minimum will produce better parts and reduce labor costs to produce those parts. Proper torch height above the material, at all times, along with proper feedrate and plasma current will help minimize dross. In the above section we have given several different examples of plasma dross and even steps to reduce the amount of dross accumulated. It is important to know the critical role proper torch height plays in elimination of dross in CNC plasma cutting.




Other Cutting Characteristics Affected by Torch Height

Top Edge Rounding Caused by the heat of the plasma arc at the top surface of the cut. Proper torch height control can minimize or eliminate top edge rounding. Excessive top edge rounding is often a sign that torch cutting height should be lower. See drawing below. Bevel Angle Precision cut processes produce bevel angle in the 0-3° range. Conventional plasma cutting will produce larger bevel angles. Proper torch height control will produce the smallest bevel angle, as well as improved kerf width and minimal top edge rounding. A slower cut speed can be used when cutting circles and corners to reduce bevel.

Figure 22 - Cut Quality – Left and Right Sides

Direction of Cut The plasma has a clockwise swirl as it exits the torch tip. Considering the direction of torch travel, the right side of the cut will always show less bevel and top edge rounding than the left side. Program cuts so that the right side will be on the finished part and the left side will be scrap.




Figure 23 - Cut Quality - Direction

Correct Voltage This may seem like a “no-brainer” if one uses only the voltage specified in the User Manual for the plasma cutter model. However, this voltage “suggestion” is only a starting point and each system (plasma cutter, torch, motion controller, gas quality, etc.) determine the proper voltage for that system. In other words, the voltage in the chart should be sued as a starting point and several cuts in specific material adjusting parameters until the best cut is produced for the selected speed (feed rate). Some examples of voltage changes are seen below.

Figure 24 - Cut Quality - Voltage

Nitride Contamination Air plasma cutting will produce nitride contamination of the cut face on carbon steel and stainless steel. Nitride contaminated surfaces will require grinding before welding to eliminate weld porosity. The depth of the contamination will be close to the Heat Affected Zone, between .005 and .010" in depth. Nitride contamination can be eliminated by using a process other than air plasma; oxygen plasma for carbon steel, H35 or nitrogen/WMS for non-ferrous materials.




Cut Speed Cut charts specify a cut speed that will produce high quality cut performance. Any plasma system can cut at faster or slower speeds, but cut performance will be affected. Cut speed should be reduced for corners and tight curves to reduce bevel and corner rounding. Optimum cut speeds produce a trailing arc which will be visible in the slight arc lines visible in the cut face. Arc lines are useful for evaluating cut speed on mild steel, but less so for aluminum and stainless steel. Arc lines that trail at less than 15° indicate that cut speed is in the optimum range when air or oxygen plasma processes are used. Optimum cut quality in precision cutting processes will result in arc lines that are near vertical. A slow cut speed may show arc lines that angle forward and a fast cut speed will show arc lines at a sharper angle relative to the top of the plate.

Ideal Cutting Current Control – (machines that will accept control)

The cutting current must be controllable to automatically lower amperage whenever the cutting speed slows down. If it is not, a bigger quantity of material will be melted and removed from the actual point than necessary to achieve an optimal cut. At the same time, a minimum Plasma density should be maintained, for the arc to stay alive and the cutting process active. The whole system must be balanced to avoid time consuming and consumables damaging interruptions. CNC control over the source current is also indispensable for Pulse Piercing to be feasible. New macro controls current for power supplies that allow remote current control.

Clean Air for Optimal Plasma Cutting

With the recent advancements in plasma cutting technology and torch design, fabricators are now able to cut parts with unprecedented precision. For instance, some “high definition” systems can achieve edge angularity of two degrees or less with virtually no dross build-up. The benefits of such a system are less post-process work and reduced labor costs. However, there are several factors that can reduce the effectiveness of such an advanced plasma cutting system. One of the easiest to overlook is compressed air quality. Typical shop compressors convert shop atmospheric air to pressures upwards of 130 psi, which is then supplied to the plasma system through a series of metal piping or hoses. The pressurized air cools naturally on its way to the plasma torch, resulting in moisture contamination. Most compressor holding tanks have a release valve that can be activated to purge water buildup, but additional filtration is required to completely remove all remaining moisture in the transport lines. In addition to moisture buildup, most compressors that are motor-driven have a tendency to contaminate the air with lubricating oil. Standard particulate filters may catch the liquid oil in the lines, but additional specialized filters should be added to prevent any remaining oil aerosols from reaching the torch. Using compressed air




without the right filtration can result in reduced cut quality, or even catastrophic torch failure. The best way to prevent contaminated air and ensure the absolute best cut quality is to use compressed cylinders of air with a purity of 99.9%; however, if shop air is used, it must be cleaned to ISO 8573.1 Class 1.4.1 Standards. This can be achieved by using filter types AO, AA, and ACS in conjunction with a water separator and dryer. Below are diagrams of each of these methods. The equipment shown is only representational and is not meant to specify any manufacturer.

Figure 25 - Preferred Method

Figure 26 - Acceptable Method (and most used)

Grade AO – High Efficiency General Purpose Protection Used for the removal of particles down to 1 micron including water and oil aerosols, providing a maximum remaining oil aerosol content of 0.6 mg/m3 @ 21 °C. Grade AA – High Efficiency Oil Removal Filtration Used for the removal of particles down to 0.01 micron including water and oil aerosols, providing a maximum remaining oil aerosol content of 0.01 mg/m3 @ 21°C. Grade ACS – Activated Carbon Filtration Used for the removal of oil vapor and hydrocarbon odors providing a maximum remaining oil vapor content of 0.003 mg/m3 (excluding methane) @ 21°C.




Anti-Dive Operation (Theory)

“Diving” is the unwanted process of the machine torch moving toward the work piece and attempting to crash, damaging the torch and possible the work piece. The normal torch height control process is relatively simple as you have seen in the previous section. Unlike oxy/fuel CNC cutting, plasma claims to have an arc voltage that is “directly proportional” to the height of the torch above the work piece. Unfortunately, this is not always true……sort of. Two common examples of the torch diving toward the work piece are explained below. In each case, “anti-diving” algorithms should prevent the torch from diving in error. The third example is a “perceived” case of diving, but it actuality, is not. Example 1: When plasma cutting is a straight line, the arc voltage is somewhat directly proportional to the height of the torch. However, when the cutting goes into a tight arc (small holes, or just around tight corners), the arc voltage will grow yet the torch is still the same distance from the work piece. This unreliable arc voltage change forces the THC to think it is higher than it should be and will correct by sending the z axis down, thus causing a diving motion. Example 2: The torch is cutting along on a flat surface and the THC is making minimal adjustments. Suddenly, the torch crosses a recut line in the work piece and the arc voltage spikes (because the arc jumps from the side it was cutting from to the other side of the precut line). This causes the THC to try and compensate by driving the Z axis down……diving into the work piece. Example 3: The torch is cutting and moving along and the THC is adjusting the height based on the delta between the Set Volts and the Tip Volts. A good THC does this as fast as possible within the mechanical limits of the Z axis, however, if the Z axis cannot move fast enough (up) when the work piece is sloped up (warpage), then the torch will crash into the work piece appearing to be “diving” , but that is not the case. These are but 3 examples of either “diving” or perceived “diving” that need to be addressed when developing firmware for THC operation. There are many conditions of “diving” and almost happen because the arc voltage we depend on for telling us the height of the torch above the work piece is inaccurate. Later in this manual, we will explain the “old methods” of preventing diving conditions as well as we will need to collect current data to help us prevent these conditions.




In summary, the arc voltage is the only “reliable” way we have to measure the height of the torch above the work piece….but, it is not accurate in all cases and we must build algorithms to help us keep the torch from diving.

Anti-Dive Scenarios to Construct Algorithms

A lot of this is explained in detail starting on page 52 through about 60. I will still come back here this week and flesh this out.

Scenario 1- Torch Cut Speed Affects Arc Voltage

Conditions Solution TBD

Scenario 2 – Torch Crosses Precut Line


Scenario 3 – Torch Cuts too Close to Edge of Material





Specification Overview

System Overview

Mach3 Plugin ESS TMC3in1 THC(portion)

TMC3in1

Figure 27- TMC3in1 System Block Diagram

A standard plasma cutting system using the TMC3in1 will have a “data/control path” shown in the picture above. TMC3in1 configuration will be set via the plugin screen and display/control will be shown on a modified Mach3 screen (defined later in this manual). Control of the “Set Volts” by the user is available as a “slider” (or data entry DRO) on the Mach3 front panel; however, an optional encoder (and knob) will be available as any users want the “feel” and control of a multi-turn knob.




Block Diagram of TMC3in1 Hardware

Figure 28- TMC3in1 Hardware Block Diagram

Diagram needs updating The TMC3in1 board is actually 2 boards but is addressed as 1 board because they are: - Tightly coupled (literally) - One can’t function without the other - Are not sold separately - It is easier to refer to them as 1 board for the purposes of this document.




Software General Description Finally we get to the meat of the software design goals and specifications. In the sections below, we will present the necessary processes that are required for the firmware development. It is compartmentalized as much as possible with overlap where needed. Hopefully it is specified what is needed and some suggestions on how to do it. I emphasize the “what to do” and make “suggestions on how it might be accomplished” as just one way to resolve it. It is left to the developer to choose the coding strategy for the best performance and most flexibility.

Software Design Goals The design goals are separated into 3 sections: - Mach3/4 screen enhancements…showing the necessary items that are

required to be displayed on the Mach3/4 screen with the absence of the THC301 front panel display (Set/Tip volts display, several LED states, and user “knob” for dialing in Set Volts.

- TMC3in1 plugin requirements and screen design…..mainly the minimum needed now and later enhancements TBD.

- Finally, the TMC3in1 firmware design. It is further divided into 6 sections (but will grow to 7 or more)

o Overall software data from Plugin through the ESS to the TMC3in1 o Master microcontroller requirements o THC control requirements o Spindle Speed control requirements o External THC encoder requirements o External relay board communication requirements o TOCD – future

Overall Software Data Flow from Mach3 through theTMC3in1

This is a simplified diagram of the data flow from the Mach3/4 program through the ESS and finally through the TMC3in1 board. We will expand on these units in future sections. Re-evaluate

Figure 29 - Overall Software Data Flow




Mach3/4 Operator Screen Enhancements

Update to newest screen

Figure 30 - Mach3 Screen for the TMC3in1 Operations

Place holder for Mach4 screen (better resolution coming from Brian Barker) Figure 31 - Mach4 Screen for the TMC3in1 Operations




Fire Control Panel – Part of the Fire-by-Wire Project NOT to be released to end users…….. The Fire-by-Wire control panel below was an application called “Fire Control” that was part of the old Fire-by-Wire THC project. The TMC3in1 will use elements of this panel in the Mach3 and Mach4 panel because, like the Fire-by-Wire system, the TMC3in1 has no physical front panel like the THC301 unit had. Critical elements will be transferred asap with other elements following as needed. The critical elements are: - Set Volts DRO - Tip Volts DRO - Set Volts user “slider’ on knob to input the Set Volts to the system - “Ready” LED - “Torch On” LED - “Arc OK” LED - “UP” LED - “DOWN” LED

Later elements to be developed for the Mach3 and Mach4 screens (not all of these elements will make it to both screens) - “Speedometer” showing “delta” of Set Volts vs Tip Volts - Graphical “torch” states - Safe-Z, Touch-off, Piercing, and Cutting. - Number of pierces since tip was changed – DRO - Vectorscope (data from future TOCD) - “Running linear graph” showing Set volts, Tip volts

Figure 32 - Fire-by-Wire Application




TMC3in1 Plugin Design – Overview

The ESS plugin screen below is only a place holder for the TMC3in1 plugin screen. Update this week.

Figure 33 - TMC3in1 Plugin Screen




TMC3in1 Firmware Design

May remove this section The TMC3in1 firmware design is divided into 3 sections. Each section has its own microcontroller and each is responsible for a specific set of functions. These functions will be listed under each section with a flowchart helping to describe each function. Master Microcontroller Firmware Design The Master microcontroller is the “traffic cop” of the TMC3in1. It has full control of communications between the THC micro, the Spindle Speed micro and the ESS via the expansion port and Port 3. It is also the communications path for the external relay board(s) and interfaces with the external encoder for THC manual control. I’ll come back to this after I describe the processes for the THC part of this spec.

Figure 34 - Master Micro Firmware

Spindle Speed Control Design The Spindle Speed microcontroller is responsible for control and monitoring of the VFD (Variable Frequency Drive) spindle I’ll come back to this after I describe the processes for the THC part of this spec.

Figure 35 - Spindle Speed Control Firmware




Plasma Torch Height Control Design THC Operation Simple Process The basic THC operation is simple: - THC is idle (but ready) - Mach sends a “Torch On” signal - THC “fires” the torch - THC checks for Arc OK - If “True” then send sig back to Mach - Make decision if Tip volts is =, >, or < Set Volts - Act accordingly (THC Up, THC Down, nothing) - Go back and check for “Arc Ok” - That’s it.

In any case, once the THC begins adjusting the Z axis (torch), the goal is Set Volts = Tip Volts, it must always check to see if it still has: - “Arc OK” signal……and if not, - Does it have “Torch On” command from Mach - If not, then quit.

Figure 36 - THC Operation Simple Process




The graphical data will be gathered in the next few weeks….dummy data

Figure 37 - THC Graphical Data for Simple Operation

Detailed Process of Changing Torch Height – Then and Now When Mach3 processes a G-code X/Y move, it uses the “Motor Tuning” parameters in Mach to provide acceleration and deceleration to the X and Y motors as saved in Motor Tuning and Setup. The Z axis motor is also operated the same way as long as it is movement from a G-code command to the Z. Any commands involving “THC Up” or “THC Down” from the THC will NOT use the acceleration or deceleration parameters, but instead will move (or try to move) the Z axis motor at full speed….using MAX acceleration. If the user did not set his Z axis “Motor Tuning” parameters such that it would be required to move with MAX acceleration, then the motor may stall. That’s another story. Just remember that when the “THC Up” or “THC Down” signal is sent to Mach by the THC, Mach will move the Z axis at full

speed. Then (THC301 - circa 2005) In the current THC301, there is a “guard band” or “no man’s land” of + or – 0.5v (see drawing below). In the year in which was designed (c 2005), this was “good enough” then but is hardly good enough now.

Figure 38 - THC301 Guard Band




To make matters worse, when the Tip volts was detected outside the “guard band”, the “THC Up” or “THC Down” signal was switched on and left on until the Tip volts equaled Set Volts….many times overshooting to the other side of the guard band, creating oscillations. There was no PID algorithm. THC Rate Updating when I get Andy updates The only “mechanism” to stop this oscillating was to set a “THC Rate” in Mach (see below).

Figure 39 - THC Rate

The THC Rate was a setting that dictated that the Z axis (torch) was only allowed to move a “percentage” of the current Feedrate. In most cases, a THC Rate of 5% was used for the Mach PC using a parallel port for machine control. Mach PCs that used an ESS could go up to around 20% because the ESS drastically reduced the latency from the time the THC Up/Down signal was sent to Mach to the time that Mach responded with step pulses to the Z motor. Even then, 20% really reduced the speed that the Z axis could move in relation to the X/Y feedrate. When setting up their Z axis for plasma cutting, most users would increase this THC Rate until their Z axis oscillated or stalled (lost steps), whichever came first. This was still a crude way to operate the Z axis with a THC, but it was “best practice” of the day. THC301 Overshoot and Recovery Below is a drawing showing the Tip volts wandering “out of band”, the THC reacting, and the overshoot that occurred most times. Because of the way THC Up/Down worked, it was “all or nothing”. If the Tip volts got “out of band” just a little (maybe +0.51v plus Set volts), the reaction by Mach was the same as if it had been “out of band” a lot (+2.0v plus Set volts).




Figure 40 - THC Process for the THC301 showing Overshoot & Recovery

Now (TMC3in1 – circa 2017) With the new TMC3in1 we have the opportunity to provide much tighter control over the height control process because: - We have much faster microcontroller(s) - We have a much higher quality and resolution A/D converter - A superb software developer extraordinaire! - We will use a PWM for Torch Up/Down control - We have a better understanding of the plasma cutting process and arc

voltage inconsistencies

Voltage Range The TMC3in1 is designed to cover the different cutting voltage ranges for almost all plasma cutters. Plasma manufactures publish a “cut chart” for each machine. This chart contains cutting parameters for each type and thickness of material the specific plasma machine is capable of cutting. See the example below of a Thermadyne A80, cutting at 80 amps, mild steel and using shop air:




Figure 41 - Sample Cut Chart

Plasma cutters from different manufacturers publish “preferred” cut voltages for specific materials. Each machine has a voltage “range” it uses that includes the material type (i.e. mild steel), material thickness (i.e. 0.025”), and cut speed (i.e. 100 ipm). For instance, the Hypertherm PowerMax 45 uses voltages between 96v and 148v for a total range of 52v. While the Hypertherm MaxPro200 uses cut voltages from 90v to 206v for a range of 116v. Because the TMC3in1, as yet, doesn’t know the specific plasma cutter being used, it has to cover the total range of all the plasma cutters. A pretty good sampling is shown in the chart below. It shows that we need to provide torch adjustment from 60v to 210v over a 150v range of the arc voltage.




Plasma Material Cut Voltage Range Power Supply Min Max Range

Hypertherm 45 96 148 52

65 68 146 78

85 68 146 78

800 102 130 28

1000 63 154 91

1650 63 169 106

HT2000 108 188 80

Max100 65 170 105

Max200 105 185 80

MaxPro200 90 206 116

HPR260xd 63 202 139

ThermaDyne A80 95 160 65

A120 95 172 77

Lowest Min, Highest Max 63 206 143

Round off 60 210 150 Figure 42 – Plasma Material Cut Voltage Range

Remove PWM references Remember back when we defined the term “THC” and we said the TMC3in1 needed to be accurate (Set Volts = Tip Volts) to + or – 0.125v (or better)? Well, if we use the cut voltage range of 150v and our A/D circuit resolution is a solid 12 bits (probably better since it is a 16bit A/D), then over 150v range we are able to read in increments of 0.036v (150/4095). That’s a resolution of nearly 4 times better than we need. In reality, once the torch pierces the material, the THC receives “Arc OK” and after relaying the signal to Mach, g-code moves the torch to “cut height”, our Tip volts should be very near (within + or - 1.00v of) the Set volts (because at “cut height”, Tip Volts should be equal to Set Volts per the manufacturer cut chart). When the THC adjusts the torch to where Tips Volts is actually equal to Set Volts for the first time, any A/D reading which is more than +/- X.xxv (TBD from live captured data) from the last reading, (assuming greater than 1kHz read cycle), will be a “false” read or invalid Tip volts. Because in the TMC3in1 design we are using both PWMs to operate the THC Up/Down and a PID algorithm, we will be better able to control the Z axis when we see the Tip Volts approaching the edge of the guard band and longer Up/Down pulses if it gets outside the guard band.




Referring to the drawing below, we see that at point “A” the Tip volts is approaching the upper inside edge of the guard band. The actions of the PID controller will give us a short pulse (per THC Down PWM) to attempt to keep it “in band”. In the same manner, point “B” shows the opposite action when the Tip volts approaches the lower inside edge of the guard band. Notice the same thing happening at point “C”, however, this “small pulse” action is not enough to keep the Tip volts inside the guard band so the PWM initiates a longer pulse because the Tip volts is further away from Set volts. This still does not keep the Tip volts (for whatever reason) headed back for the guard band, so the PWM initiates a much stronger pulse since now the Tip volts is far away for inside the guard band. This last action works and the Tip volts once again is “corralled” inside the guard band. Points “F” and “G” mimic the same actions as “A” and “B”.

Figure 43 - Detailed Torch Height Process for TMC3in1

We expect the PWM to give short pulses when the Tip volts is close but not equal to the Set volts. As the Tip volts wanders further from the Set volts, we expect longer pulses. The PID controller, we expect, is to “foresee” the Tip volts starting to wander outside the guard band based on history of early readings and sends PWM pulse accordingly.




Generating Example of Plasma Operation Processes (G-code)

Overview

Tools used in Generating Plasma G-code for Mach

CAD – VcarvePro

Figure 44 - VCarvePro Screen

CAM - SheetCam

Figure 45 - SheetCam Screen 1



Step by Step – From Drawing to Cut Part

Main work week 06/19/2017 - TBD




Appendix

Customer Tests

Greg and I came up with some customer tests that will help us determine the limitations for the customers system so that we don’t get blamed for problems that are not in the THC. More work in this area soon. More work here. Z Axis Speed Limit Test THC customer test: Prereqs: No THS involved.

1. Test the limits of the Z axis – touch-off Z….raise up…… Run Z sine wave…….Touch-off and measure delta of actual vs DRO……raise sine frequency……repeat process. This determines z limit.

System Latency Test

2. Cut straight line at given speed, on flat metal…changing z height in sine wave ever increasing frequency (but not exceeding Test 1 limit) until measured arc voltage does not follow true sign which means plasma cutter has enough latency to interfere with operation.




Future Enhancements Wish List

Simulator

Mach3

Mach4

TMC3in1 Plugin

TMC3in1 General

Breakout Board

Torch Height Control

Spindle Speed Control

TMC3in1 – Torch & Motion Controller 3in1texasmicrocircuits.com/...Doc_Vol_02_Plasma_and_THC...They...

Documents

Transcript of TMC3in1 – Torch & Motion Controller 3in1texasmicrocircuits.com/...Doc_Vol_02_Plasma_and_THC...They...