Adaptive control

Improvements in CNC machine tools depend on the refinement of adaptive control, which is the automatic monitoring and adjustment of machining conditions in response to variations in operation performance. With a manually controlled machine tool, the operator watches for changes in machining performance (caused, for example, by a dull tool or a harder workpiece) and makes the necessary mechanical adjustments. An essential element of NC and CNC machining, adaptive control is needed to protect the tool, the workpiece, and the machine from damage caused by malfunctions or by unexpected changes in machine behaviour. Adaptive control is also a significant factor in developing unmanned machining techniques.

One example of adaptive control is the monitoring of torque to a machine tool’s spindle and servomotors. The control unit of the machine tool is programmed with data defining the minimum and maximum values of torque allowed for the machining operation. If, for example, a blunt tool causes the maximum torque, a signal is sent to the control unit, which corrects the situation by reducing the feed rate or altering the spindle speed.

Basic principles.

Several other techniques enter into the design of advanced control systems. Adaptive control is the capability of the system to modify its own operation to achieve the best possible mode of operation. A general definition of adaptive control implies that an adaptive system must be capable of performing the following functions: providing continuous information about the present state of the...

Improvements in CNC machine tools depend on the refinement of adaptive control, which is the automatic monitoring and adjustment of machining conditions in response to variations in operation performance. With a manually controlled machine tool, the operator watches for changes in machining performance (caused, for example, by a dull tool or a harder workpiece) and makes the necessary...

http://www.controleng.com/single-article/patent-for-cnc-adaptive-control-system/dcd02f7f852695a253965ee939016628.html s

CNC integrates adaptive control to add productivity

Fanuc iAdapt S adaptive control solution has been integrated into computer numerical controls to improve the

ability for CNC material removal and decrease CNC cycle time. 07/06/2011

anuc Factory Automation America (Fanuc FA America) has integrated its iAdapt S adaptive control solution into the CNC system for increased machine tool productivity. Fanuc iAdapt S improves material removal and minimizes cycle time by automatically optimizing the cutting feedrate based on the actual spindle load. Additionally, integration of the iAdapt S product within the CNC now eliminates the need for mounting space, simplifying installation while improving the capabilities of the original iAdapt product.

The original iAdapt product introduced the concept of roughing cycle productivity to CNC customers.  The “On Demand” control feature simplified the use of the adaptive control by making it easy to setup and operate.

The new iAdapt S has an arsenal of improvements which allows the operator to improve machine cycle time and tool life.  By automatically optimizing the cutting feedrate based on the actual spindle load, iAdapt S improves material removal and minimizes cycle time.  In fact, productivity is increased as cycle times are reduced by up to 40% as every part is automatically optimized in real-time, including the first.  iAdapt S compensates for material and process variations including: material hardness, tool wear, depth of cut and width of cut.  Additionally, feedrate control is 100 times finer which increases the responsiveness and accuracy of the adaptive control.  To view and improve the machining process, a graphing feature has been added, which displays both the spindle load and feedrate override versus time. A new 64-entry setting table has been introduced in iAdapt S which allows easy saving of settings for later use and recall. A new Torque Override feature has been added to allow the operator to dynamically modify the adaptive control set point during the machining cycle.

Additionally, iAdapt S keeps roughing tools fully loaded, putting the heat into the chips rather than the part, thus extending tool life. As a result, there are fewer minor stoppages, which increases productivity and reduces labor costs.

Fanuc Corporation, headquartered at the foot of Mt. Fuji, Japan, is a diversified manufacturer of Factory Automation (FA), Robots and Robomachines. Since its inception in 1956, Fanuc has contributed to the automation of machine tools as a pioneer in the development of computer numerical control equipment. Fanuc is committed to developing efficient, reliable and innovative products.

Fanuc FA America is the exclusive provider of industry leading Fanuc CNC systems and solutions in the Americas, providing a one-stop shop for comprehensive CNC solutions including industry-leading control systems, a complete range of drives and motors and CO2 laser solutions. Fanuc FA America also offers engineering support, genuine parts, repair and factory automation solutions and training programs to machine tool builders, dealers and users. Fanuc FA America has headquarters in Hoffman Estates, IL, and supports 37 offices and service centers in the U.S., Canada, Mexico, Brazil and Argentina.

www.fanucfa.com

http://www.controleng.com/channels/machine-control.html

Patent for CNC adaptive control system

Fanuc Factory Automation America (Fanuc FA America) received a patent for developing on-demand integrated adaptive control for their CNC control system.

06/05/2012

Fanuc Factory Automation America ( Fanuc  FA America) and Jerry Scherer, engineer with  Fanuc  FA America, have been awarded a patent for the development of their CNC Adaptive Control System for on-demand integrated adaptive control of machining operations. This system was developed to increase machine tool productivity with  Fanuc  FA America's iAdaptS adaptive control solution.

Fanuc FA America's patented CNC Adaptive Control System measures the present value of the spindle load and then compares this value to a present value of a target spindle load. The adaptive controller is configured to control the feed rate of the machine tool relative to the workpiece to maintain the present value of the spindle load approximately equal to the present value of the target spindle load using one or more calculations of the first feed rate value, the first feed rate dither adjustment value and the second feed rate dither adjustment value.

This CNC adaptive control system is the base technology in  Fanuc  FA America's iAdaptS solution that improves material removal and minimizes cycle time by automatically optimizing the cutting feedrate based on the actual spindle load. Additionally, integration of the iAdaptS software solution within the CNC now eliminates the need for mounting hardware, simplifying installation while improving the capabilities of the original iAdapt product. The original iAdapt product introduced the concept of roughing cycle productivity to CNC customers. The "On Demand" control feature simplified the use of the adaptive control by making it easy to setup and operate. iAdaptS extends tool life by keeping roughing tools fully loaded, putting the heat into the chips rather than the part. As a result, there are fewer minor stoppages which further increases productivity and reduces labor costs.

Fanuc Factory Automation America

www.fanucfa.com 

- Edited by Chris Vavra, Control Engineering, www.controleng.com 

Also see controleng.com/machinecontrol

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Real-time diagnostics system for micromilling

Control Engineering International: Tool condition monitoring is important for quality of micromilling processes and can be improved with a real-time diagnostics system. Diagnostic signals selection, tool wear inspection algorithm, and proper measuring system selection all help. Testing and validation were completed in operating conditions.

Bogdan Broel-Plater, Krzysztof Pietrusewicz, Paweł Waszczuk

07/11/2012 Share

With wider use of miniature components in all industries, attention to quality in micromilling of various materials has become more important. A real-time diagnostics system for micromilling allows tool condition monitoring and improves metal component production quality. A monitoring system ensures accuracy, quality, and most of all, microcutting process stability.

Selecting a proper signal that provides the best information about process conditions is crucial. Due to availability, simplicity of use, and price, accelerometers are the most common sensing choice. Sensors placed in key areas of a micromilling machine ensure that an acceleration signal processing algorithm can create reliable and useful information about the process.

It’s also important to measure microcutting process cutting forces. Because of the nature of micromilling, cutting force amplitude can be very low (<1N) and hard to measure. Like information about vibration, cutting force information is extremely helpful for diagnostics.

Measurements, diagnostics

Selecting an appropriate measuring system is an important issue during development of a diagnostics system. A real-time diagnostics system for micromilling was created based on National Instruments hardware and software: cRIO-9022 PAC controller and analog modules with dynamic signal acquisition for making high-accuracy frequency measurements from an integrated electronic piezoelectric (IEPE) accelerometer. The controller includes a reconfigurable field-programmable gate array (FPGA) chassis, which allows analog signal acquisition up to 51.2 kHz. Data are filtered then processed in real time to provide determinism and stability of the monitoring algorithms. Depending on need, acquired data can be written on a device’s hard drive

or visualized by the user interface panel on a computer screen. Additionally, the system can communicate with the micromilling machine drives controller.

Thanks to the flexibility of the measurement equipment used, a monitoring system was created and specially adapted for microcutting processes. The FPGA module and LabVIEW Real-Time System allow development of deterministic data acquisition and data processing algorithms.

As for other technologies, motion control uses Aerotech linear nano-modules (250 ns movement resolution); force measurement is based on Kistler dynamometer for small forces; and PCB Piezoelectronics is used for acceleration measurement.

The main assumption of the diagnostic procedure was to process obtained signals using an FFT algorithm. An inspection program based on rotational speed of the electric spindle observed adequate spectrum section of acceleration and cutting force signals at all three axes. In case of additional frequencies near the excitation frequency, the monitoring algorithm immediately informs the operator via the user interface panel and sends appropriate notification to the micromilling machine drives controller.

During microcutting operations, the device’s hard drive stores data to analyze all diagnostic signal variations. If necessary, a quick implementation of new algorithms is possible, to gain measurement variety. Relatively small dimensions and rugged design permit use in a wide range of applications.

18,000 rpm

To test the real-time diagnostics system for micromilling, a set of experiments on carbon steel 18G2 and two-bladed, 0.61mm diameter tool was prepared. Spindle rotational speed was set to 18,000 rpm, with step size of 6 µm and milling depth of 10 µm. Accelerometers were attached to the electro spindle, based on prior experiments. A 3-axis dynamometer was placed on the vertical axis of the micromilling machine. The work piece was attached on top of the dynamometer. Experiments were performed for five tool passes through the entire work piece, during which the tool condition was monitored. Before and after every operation, tool images were made using a digital microscope (500X magnification).

During experiments, significant degradation of the tool and surface quality deterioration were observed. Power spectrum analysis of recorded acceleration and cutting force signals shows a similar relationship. Figure 3 compares diagnostic signal power spectrum graphs of a new and a worn tool. The excitation frequency of spindle rotational speed (600 Hz) is clearly dominant. In the case of a worn tool, additional undesirable frequencies occur, indicating damaging vibrations that can have a negative impact on micromilling process quality.

The real-time diagnostics system developed for micromilling is an interesting solution for any application where accuracy and improved quality are required. Due to modularity, it can be quickly reconfigured to fit various conditions. Small dimensions and ruggedness allow use in a wide range of applications. The intuitive user interface can be adapted to operator needs. Implementing a real-time diagnostics system for micromilling in industrial applications helps save time and money.

- Bogdan Broel-Plater, Krzysztof Pietrusewicz, and Paweł Waszczuk are with West Pomeranian University of Technology, Control Engineering Poland. Edited by Mark T. Hoske, content manager CFE Media, Control Engineering and Plant Engineering, mhoske(at)cfemedia.com

www.controlengpolska.com

Szczecin University of Technology 

ONLINE extra - More about the authors

- Bogdan Broel-Plater, PhD, is with the West Pomeranian University of Technology, Szczecin, Faculty of Electrical Engineering. His research work involves artificial intelligence utilization within the digital control and supervision systems.

- Krzysztof Pietrusewicz, PhD, is with the West Pomeranian University of Technology, Szczecin, Faculty of Electrical Engineering. He is also an editor for Control Engineering Poland. His research work involves robust open architecture controls and integrated condition monitoring approach for machine tools.

- Paweł Waszczuk, PhD student, is with the West Pomeranian University of Technology, Szczecin, Faculty of Electrical Engineering. His research interests include real-time condition monitoring systems for machine tools as well as micromilling.

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Domestic machine tool manufacturer facility expansion drives new opportunities

Brian Papke, president of Mazak Corp., talks about how a large expansion to the company's Florence, Ky. facility is driving new opportunities for the company in the U.S.

08/17/2012 Share

Mazak Corp. has announced a large expansion of its Florence, Ky., manufacturing facility to handle the rapid growth in the domestic machine tool business. Brian Papke, president of Mazak Corp., talks about how that growth is driving new opportunities for the company in the U.S.

PE: What have the last three years been like for Mazak? Have you been able to invest in R+D while serving the existing customer base?

Papke: Our incoming orders in 2010 were up 100%, last year up 60% (on a calendar year basis), and this year are up 20% thus far. Also during the past 3 years, we continued to develop new, innovative products, as opposed to simply meeting the increases in demand with existing older machine models.

During the downturn prior to the manufacturing upswing, we continued to reinvest in our factory and in our R+D resources to ensure that we could competitively produce new products that were receptive to the market when the economy was back on track in 2010. Even though business is now good for most manufacturers, they must still strengthen their competitiveness, and doing so requires truly new, innovative, and productive equipment, not technology that’s as much as 5 years old.

And Mazak, like other manufacturers, is under the same pressure, which is why we continually improve our technology and invest in new equipment for our own production-on-demand manufacturing operations to increase our productivity and competitiveness. Our customers, like us, want the latest and greatest technology that will increase their productivity better than anything else on the market and better than what their competitors are using.

A favorable business climate doesn’t imply that a company will automatically be successful. You still have to be competitive or you will lose that success. Our customers are very receptive to the products we develop because they consistently provide more productivity and a competitive advantage.

PE: As IMTS approaches, what are you hearing from your customers about what they need to continue to grow their business?

Papke: As IMTS approaches, our customers are seeking new technology that will give them the competitive advantage and improve their business. Additionally, they are quite concerned with how those products will help reduce the labor content in operations—not in an effort to necessarily reduce labor costs, but instead to improve production without increasing their dependency on skilled labor.

To reduce their reliance on skilled labor, manufacturers are also seeking to automate as many operations or processes as possible. Such automation can take different forms besides the commonly thought-of stand-alone robot. For instance, a multitasking machine combines enough different processing capability that, in itself, automates production because parts are loaded in the machine once and come out completed.

PE: Conversely, what do they say are the barriers to growing their business?

Papke: The biggest barrier to our customers’ abilities to grow is the current lack of skilled labor. Recruiting, training, and maintaining skilled employees on an ongoing basis are proving increasingly challenging for these manufacturers. Therefore, we continue to strengthen our efforts in providing not only highly productive machines and fully automated solutions that will ease the need for skilled labor, but also providing customers with various training programs as part of our Pyramid of Learning and through our regionally located technology centers.

PE: Mazak is a global company. What are the secrets to being both global and local today, and why is that of benefit to manufacturing?

Papke: There is really no big secret, except for the fact that a company has to be committed. Being a successful company on both a global and local level simply takes a strong commitment to being where your customers are and having a well-established presence in those areas.

We are not only a company that sells machine tools, but one that also works closely with its customers to develop complete turnkey manufacturing solutions that provide them the lowest possible cost of ownership and the fastest return on their investment. But equally important, these solutions optimize their operations and increase equipment utilization rates.

In the machine tool business, those who survive, prosper, and grow over long periods of time are the ones that are completely committed to providing innovative technology and unmatched customer support. Ultimately, our desire is to always have our customers tell us that they’ve improved their profitability as a result of investing in Mazak equipment. We want them to grow and prosper, and in the process, we want to grow as partners with them.

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http://www.slideshare.net/guestac67362/adaptive-control-systems-paper-presentation

Adaptive Control Systems Paper Presentation — Document Transcript

1. www.studentyogi.com www.studentyogi.com co om Adaptive control system with knowledge server system m in CNC system gi. .c oogi ntyy eent ADAPTIVE CONTROL SYSTEM WITH KNOWLEDGE t t dd SERVER IN INTELLEGENT CNC SYSTEM ssuu w. . w ABSTRACT: ww ww In an ideal scenario of intelligent machine tools the human mechanist was almost replaced by the controller. During the last decade many efforts have been made to get closer to this ideal scenario, but the way of information processing within the CNC did not change too much. The paper summarizes the requirements of an intelligent CNC evaluating the advancement of technology in this field using different adaptive control systems. In this paper a low cost concept for artificial intelligence named www.studentyogi.com www.studentyogi.com

2. www.studentyogi.com www.studentyogi.com Knowledge Server for Controllers (KSC) is introduced. It allows more devices to solve their intelligent processing needs using the same server that is capable to process intelligent data. The KSC concept is used in an open CNC environment to build up an intelligent CNC. om Key words: Intelligent CNC, knowledge server, adaptive control systems i.c og nty de 1. INTRODUCTION: stu There are many definitions of the intelligent machine tools. In a well known book Wright and Bourne said that “We must therefore acknowledge that the degree of intelligence can be gauged by the complexity of the input and/or the difficulty w. of ad hoc in-process problems that get solved during a successful operation. Our unattached, fully matured intelligent machine tool will be able to manufacture accurate aerospace components and get a good part right the first time”. They told that an ww intelligent machine tool had the CAD data, the materials and the set-up plans as inputs and could produce correctly machined parts with quality control data as outputs. 2 It is clear that adaptive control techniques are necessary to apply if one wants intelligent CNC machine, but - of course - the usage of them is not adequate in intelligent behavior. www.studentyogi.com www.studentyogi.com

3. www.studentyogi.com www.studentyogi.com Table 1 summaries the features of an intelligent CNC (Wright and Bourne collected them more than ten years ago) and shows two further things: the positive changes done in the recent years and the still existing gaps where - according to the scientific community – adaptive control systems offers solutions with its information om processing methods. Analyzing the above list, it is clear that many features do not require direct adaptive control methods. We can state that the main reasons of the advancement were: i.c (1) The development of the hardware elements (more sensitive sensors, more precise actuators, quicker and stronger computers etc.) even in higher requirements. og (2) The development of the software and the methodology mainly in the preparation phases of the manufacturing (in design, planning, scheduling, resource management etc.) and in the user interface issues (more comfortable and informative 'windows-like' screens nty and Menus). de Table 1. Commercial needs

for the intelligent machine tools: stu Features (forecasted in 1988) Big Artificial advance intelligence by 2001 methods still needed w. 1. Reduce the number of scrap parts following initial setup. ww 2. Increase the accuracy with which parts are made. 3. Increase the predictability of machine tool operations. 4. Reduce the manned operations in the machine tool environment. www.studentyogi.com www.studentyogi.com

4. www.studentyogi.com www.studentyogi.com 5. Reduce the skill level required for machine setup and operations. 6. Reduce total costs for part fabrication. om 7. Reduce machine downtime. 8. Increase machine throughput. 9. Increase the range of materials that can be both setup and i.c machined. 10. Increase the range of possible og geometries for the part 11. Reduce tooling through better operation planning nty 12. Reduce number of operations required for setup 13. Reduce setup time bydesigning parts for ease of setup de 14. Reduce the time between part design and fabrication stu 15. Increase the quantity of information between the machine 16. control and part design w. operations ww Even there is a big advance in the technology of the CNCs, the Knowledge processing and other adaptive control methods have not appeared within the Intelligent Open CNC System Based on the Knowledge Server Concept 3controllers, so in some points there is no real development. Special heuristic rules, problem-solving strategies, learning capabilities and knowledge communication features are still missing www.studentyogi.com www.studentyogi.com

5. www.studentyogi.com www.studentyogi.com from the recent controllers available on the market. It is also true for many new, open or PC-based CNC s, where DSP add-on-boards provide the necessary computation power and speed. Further requirements of intelligent CNC s can be find out and defined. (Table 2.): The second column indicates whether the different adaptive control om techniques (mainly rule base systems, neural nets and fuzzy logic) would provide methods and solutions. One can find positive answers to all these issues in the resent literature: i.c og nty de Table2. Future requirements of an intelligent CNC: stu Table 2. Future requirements of an intelligent CNC w. Further features Artificial intelligence methods ww would help www.studentyogi.com www.studentyogi.com

6. www.studentyogi.com www.studentyogi.com • Model based on-line path generation • Automatic tool selection • Technological based settings of the operational parameters • Automatic compensation of machine limits • Automatic back-step strategies om • Detection and compensation of geometrical deflection • On-line selection of control algorithms • Intelligent co-operation with other devices to solve problems i.c together • Detection and correction of tool wear and breakage • Automatic handling of rejected work pieces og • Detection and managing of emerging situations of the machine tool • Complex self-diagnostics nty The list may be continued with the learning capabilities and others. In the users' point of view these features rough in a controller, that "recognizes the problem" and de "efficiently and reasonable solves them" with minimal disturbance of the environment of the controller. stu w. 2. RESULTS IN INTELLIGENT CNC s: ww On the one hand in the recent literature one can find many different topics related to intelligent CNCs. Unfortunately they often do not mean intelligent behaviors but the application of intelligent methods. Sometimes it is the case that authors call their devices “intelligent" if one module of the system contains based method. On the other hand (2) the key controller vendors leave everything to the users or machine tool builders offering

PC/Windows based CNCs. With these systems any software modules (e.g. even www.studentyogi.com www.studentyogi.com

7. www.studentyogi.com www.studentyogi.com adaptive control based ones) can be coupled into the controller but they do not offer J real solutions or methodologies, but only software possibilities. The following list summarizes the most important active research topics in this field. A real intelligent CNC would contain most of these issues. om 1) Fuzzy logic based concurrent control of some operating parameters (E.g. cutting speed, depth of cut, feed rate) independently from the Given tool and the work piece. i.c 2) Neural nets and fuzzy rules in the CNC's control algorithms. Optimal path planning, real-time correction of the trajectory.3) og 4). Compensation of temperature (and other) deformations. Life time management of the tools and other parts of the machine5) Tool including self-diagnostics. nty 6) Tool breakage detection (maybe forecasting) and tool wear Monitoring (maybe compensation) with AI methods. 7) The utilization of CNC management (setup, orders, etc.) via Intelligent agents. de Intelligent parts of a CNC can be classified into three groups, namely: stu (1) Tool monitoring, (2) operation/machine tool modeling and (3) Adaptive control. w. A general problem in all the three groups is that the adaptive control based solutions are typically limited and valid only in a very narrow field. If one changes some parameters of the operation or the environment, the earlier successful methods become ww false. A special type of adaptivity partly helps on this hard and well-known problem. If it is possible to replace the different modules of the controller time by time, than one can guarantee, that a given adaptive control module can run within its limitation, and over it another module (e.g. a much simpler one) covers the same functionality. It can be realized (among others) if the controller is open to allow this replacement. www.studentyogi.com www.studentyogi.com

8. www.studentyogi.com www.studentyogi.com 3. Adaptive Control System : In adaptive control, the operating parameters automatically adapt themselves to conform to new circumstances such as changes in the dynamics of the particular process and any arise. The adaptive would check load conditions, adapt an appropriate desired braking om profile (for ex: antilock brake system and traction control), and then use feed back to implement it. With advanced adaptive controllers the gain may vary continuously with changes in operating condition. i.c Purpose of adaptive control: 1. to optimize production rate 2. to optimize product cost og 3. to minimize cost The functions common to adaptive control systems are the following: 1. Determine the operating conditions of the process, including measures of nty performance. Thos typically achieved by using sensors which measure process parameters (such as force, torque, vibration, and temperature). 2. Configure the process control in response to the operating conditions. Large changes de in the operating conditions may provoke a decision to make a major switch in control strategy. More modest alterations may be the modifications of process parameters (such as changing the speed of operation or the feed in manufacturing). stu 3. continue to monitor the process, making further changes in controller when and As needed. In an operation such as turning on lathe, the adaptive control system senses real – w. time cutting forces, torque, temperature, tool-ware, tool chipping or tool fracture, and surface finish of the work piece. The system then converts this information into commands that modify the process parameters on the machine tool to hold them ww constant (or with in certain limits) or to optimize the cutting operation. 4. DIFFERENT APPROACHES OF KNOWLEDGE SERVERS: www.studentyogi.com www.studentyogi.com

9. www.studentyogi.com www.studentyogi.com The features of World Wide Web led to introduce knowledge server to easier solve the installation and version control problems of expert systems and to provide a web based interface of the knowledge base for the different users. Some advanced knowledge based systems are based on this concept. There are some applications of knowledge servers in manufacturing. In the HPKB (High Performance Knowledge Environment) om some hundred thousand rules are performed in an intelligent knowledge environment. In this project the different intelligent components are called knowledge servers. The components are communicating with each other via the OKBC (Open Knowledge Base Connectivity) protocol specified at Stanford. i.c On communication networks, the protocol named MAP uses a bus configuration, broad band transmission, a token passing access scheme and data Transmission rate of og 10mbps. MAP is based on specification defined by the identical standard organizations (ISO) called the open system interconnection (OSI) reference model. nty The seven layer structure of MAP standard the first four layers are connected with the inter connection functions, and the top three layers are connected with inter working functions. The application layer (seventh layer) is the highest layer in MAP at the time of de this writing. It is possible that this layer may be sub divided into multiple layers as applications of communication protocol and computer techniques evolve in future. stu w. ww 5. KNOWLEDGE SERVER FOR CONTROLLERS: Knowledge Server for Controllers (KSC) is defined as a server providing capability of intelligent data processing for other systems. It allows the basic system to reach external intelligent processing resources, because it does not have any. The KSC contains a high performance reasoning tool, and different knowledge based modules. All www.studentyogi.com www.studentyogi.com

10. www.studentyogi.com www.studentyogi.com the modules have their special rules and procedures. The client system calls these modules, passes them specific data if necessary, and the KSC module can collect data if the knowledge processing requires. All the data acquisition and user interaction is done by the client system. It is clear that in KSC the clients have much more tasks than a simple browser based user interface and in the applications listed in the previous chapter. om It should be stated that KSC does not deal with fuzzy and neural net based adaptive control modules. The computing power and the necessary software costs and complexity of these methods are less than the rule or model based ones. (In the case of the neural nets it is true only if the net is not trained on-line.) . i.c The KSC allows the different modules to run independently, to cooperate as agents or to control each other. The third case means that one module is started by another one og because either the second one uses the results of the first one or the inference of the first one led to the need of the second module. Generally the resources of the KSC can use more clients (controllers) nty simultaneously. It leads to a cost effective AI solution, because one costly AI tool can solve all the intelligent problems in a distributed environment. The overhead of the KSC (network connection, one more computer, some delay etc.) is much less comparing to the advantages (adaptive control tool licensing, less computing power in the de clients/controllers, one server module may used by more clients etc.). Using the KSC together with the component based software technology (e.g. stu CORBA) gives a very adaptive software frame to solve complex problems. In the Fig. 1 a CNC with an embedded PLC controls a machine tool. The modules of both controllers are open and some of them are also clients of a knowledge server (KSC). It means that these modules can run special adaptive control Intelligent

Open w. CNC System Based on the Knowledge Server Concept methods during their work that is an independent service is implemented in the KSC. ww www.studentyogi.com www.studentyogi.com

11. www.studentyogi.com www.studentyogi.com om i.c og nty 6. PROTOTYPE INTELLIGENT CNC BASED ON KSC: In an early prototype of the intelligent open CNC that is using KSC, Adaptive de control system was implemented An advance axis tester is put on the top of this. Axis Test module handles all the tests but it gets the necessary position and velocity values from a stu knowledge based general tester running as an application on the KSC. The KB tester determines some goal positions and motion speeds, that the Axis Test module executes with the axis using jog commands. The results (execution time, tuning in errors etc.) are w. sent to the KSC that analyses and qualifies the axis. In the prototype the modules are built in CORBA, the controller and the HMI is programmed in Java. ww www.studentyogi.com www.studentyogi.com

12. www.studentyogi.com www.studentyogi.com 7. CONCLUSIONS: The controllable parameters in machining by using micro controller i.e. adaptive om control system are cutting force, torque, vibrations, feed and depth of cut. The controllable parameters in machining by using artificial intelligenceModel based on-line path generation • Automatic tool selection i.c • Technological based settings of the operational parameters • Automatic compensation of machine limits og • Automatic back-step strategies • Detection and compensation of geometrical deflection • On-line selection of control algorithms nty • Intelligent co-operation with other devices to solve problems together • Detection and correction of tool wear and breakage • de Automatic handling of rejected work pieces • Detection and managing of emerging situations of the machine tool By introducing an interface between micro controller of adaptive control system stu and the data base of artificial intelligence we can control all the above parameters by communicating with knowledge server. The features of KSC were discussed and an early prototype was introduced. w. References: ww Adaptive control system -------- Bernard wplrow,Samuel D.stearns Manufactureing Engg and technology by Serope Kalpak Jain, Steven R. schmid Computer integrated manufacturing---------------- James A Regh, Henry w scrab Manufacturing system Engg -------------------- katsundo Hitoni www.studentyogi.com www.studentyogi.com

http://my.safaribooksonline.com/book/manufacturing/9780132441889/computer-controls-in-nc/ch09lev1sec7#X2ludGVybmFsX0ZsYXNoUmVhZGVyP3htbGlkPTk3ODAxMzI0NDE4ODklMkZjaDA5bGV2MXNlYzg=

9.7. Adaptive Control Machining Systems

Adaptive control (abbreviated AC) machining originated out of research in the early 1960s sponsored by the U.S. Air Force at the Bendix Research Laboratories. The initial adaptive control systems were based on analog control devices, representing the state of technology at that time. Today, AC uses microprocessor-based controls and it is typically integrated with an existing CNC system. Accordingly, the topic of adaptive control is appropriate to include in this chapter on computer controls in NC.

For a machining operation, the term adaptive control denotes a control system that measures certain output process variables and uses these to control speed and/or feed. Some of the process variables that have been used in adaptive control machining systems include spindle deflection or force, torque, cutting temperature, vibration amplitude, and horsepower. In other words, nearly all the metal-cutting variables that can be measured have been tried in experimental adaptive control systems. The motivation for developing an adaptive machining system lies in trying to operate the process more efficiently. The typical measures of performance in machining have been metal removal rate and cost per volume of metal removed.

Where to use adaptive control

One of the principal reasons for using numerical control (including DNC and CNC) is that NC reduces the nonproductive time in a machining operation. This time savings is achieved by reducing such elements as workpiece handling time, setup of the job, tool changes, and other sources of operator and machine delay. Because these nonproductive elements are reduced relative to total production time, a larger proportion of the time is spent in actually machining the workpart. Although NC has a significant effect on downtime, it can do relatively little to reduce the in-process time compared to a conventional machine tool. The most promising answer for reducing the in-process time lies in the use of adaptive control. Whereas numerical control guides the sequence of tool positions or the path of the tool during machining, adaptive control determines the proper speeds and/or feeds during machining as a function of variations in such factors as work-material hardness, width or depth of cut, air gaps in the part geometry, and so on. Adaptive control has the capability to respond to and compensate for these variations during the process. Numerical control does not have this capability.

Adaptive control (AC) is not appropriate for every machining situation. In general, the following characteristics can be used to identify situations where adaptive control can be beneficially applied:

Sources of variability in machining

The following are the typical sources of variability in machining where adaptive control can be most advantageously applied. Not all of these sources of variability need be present to justify the use of AC. However, it follows that the greater the variability, the more suitable the process will be for using adaptive control.

1. Variable geometry of cut in the form of changing depth or width of cut. In these cases, feed rate is usually adjusted to compensate for the variability. This type of variability is often encountered in profile milling or contouring operations.

2. Variable workpiece hardness and variable machinability. When hard spots or other areas of difficulty are encountered in the workpiece, either speed or feed is reduced to avoid premature failure of the tool.

3. Variable workpiece rigidity. If the workpiece deflects as a result of insufficient rigidity in the setup, the feed rate must be reduced to maintain accuracy in the process.

4. Toolwear. It has been observed in research that as the tool begins to dull, the cutting forces increase. The adaptive controller will typically respond to tool dulling by reducing the feed rate.

5. Air gaps during cutting. The workpiece geometry may contain shaped sections where no machining needs to be performed. If the tool were to continue feeding through these so-called air gaps at the same rate, time would be lost. Accordingly, the typical procedure is to increase the feed rate by a factor or 2 or 3, when air gaps are encountered.

Two types of adaptive control

In the development of adaptive control machining systems, two distinct approaches to the problem can be distinguished. These are:

1. Adaptive control optimization (ACO) 2. Adaptive control constraint (ACC)

Operation of an ACC System

Typical applications of adaptive control machining are in profile or contour milling jobs on an NC machine tool. Feed is used as the controlled variable, and cutter force and horsepower are used as the measured variables. It is common to attach an adaptive controller to an NC machine tool. Numerical control machines are a natural starting point for AC for two reasons. First, NC machine tools often possess the required servomotors on the table axes to accept automatic control. Second, the usual kinds of machining jobs for which NC is used possess the sources of variability that make AC feasible. Several large companies have retrofitted their NC machines to include adaptive control. One company, Macotech Corporation in Seattle, Washington, specializes in retrofitting NC machine tools for other manufacturing firms. The adaptive control retrofit package consists of a combination of hardware and software components. The typical hardware components are:

1. Sensors mounted on the spindle to measure cutter deflection (force).

2. Sensors to measure spindle motor current. This is used to provide an indication of power consumption.

3. Control unit and display panel to operate the system.4. Interface hardware to connect the AC system to the existing NC or CNC control unit.

Benefits of adaptive control machining

A number of potential benefits accrue to the user of an adaptive control machine tool. The advantage gained will depend on the particular job under consideration. There are obviously many machining situations for which it cannot be justified. Adaptive control has been successfully applied in such machining processes as milling, drilling, tapping, grinding, and boring. It has also been applied in turning, but with only limited success. Following are some of the benefits gained from adaptive control in the successful applications.

1. Increased production rates. Productivity improvement was the motivating force behind the development of adpative control machining. On-line adjustments to allow for variations in work geometry, material, and tool wear provide the machine with the capability to achieve the highest metal removal rates that are consistent with existing cutting conditions. This capability translates into more parts per hour. Given the right application, adaptive control will yield significant gains in production rate compared to conventional machining or numerical control.

The production rate advantage of adaptive control over NC machining is illustrated in Table 9.1 for milling and drilling operations on a variety of work materials. Savings in cycle time reported in this table range from 20% up to nearly 60% for milling and 33 to 38% for drilling.

Table 9.1. Comparison of Machining Times—NC versus Adaptive Control

Operation DescriptionWork

materialNC

time AC timePercent saving

Profile milling

Aircraft flap ribs Aluminum 152 min 81 min 46

Profile milling

Aircraft flap ribs Aluminum 641 min 319 min

50

Profile milling

Aerospace component Stainless steel 9.6 h 7.5 h 22

Table 9.1. Comparison of Machining Times—NC versus Adaptive Control

Operation DescriptionWork

materialNC

time AC timePercent saving

Profile milling

Aerospace component Stainless steel 11.8h 9.4 h 20

Profile milling

Space shuttle engine ring Inconel 718 35

Profile milling

Engine Mounting ring Inconel 718 45

Profile milling

Aircraft component Titanium 64 min 35 min 48

End milling Aerospace component 4330 Steel 61 min 25 min 59

Drilling 0.433″ diameter × 1.0″ deep 1019 Steel 8 s 5 s 38

Drilling 0.433″ diameter × 1.75″ deep

Cast iron 10.5 s 7 s 33

Source: Data courtesy of Macotech Corp.

2. Increased tool life. In addition to higher production rates, adaptive control will generally provide a more efficient and uniform use of the cutter throughout its tool life. Because adjustments are made in the feed rate to prevent severe loading of the tool, fewer cutters will be broken.

3. Greater part protection. Instead of setting the cutter force constraint limit on the basis of maximum allowable cutter and spindle deflection, the force limit can be established on the basis of work size tolerance. In this way, the part is protected against an out-of-tolerance condition and possible damage.

4. Less operator intervention. The advent of adaptive control machining has transferred control over the process even further out of the hands of the machine operator and into the hands of management via the part programmer.

5. Easier part programming. A benefit of adaptive control which is not so obvious concerns the task of part programming. With ordinary numerical control, the programmer must

plan the speed and feed for the worst conditions that the cutter will encounter. The program may have to be tried out several times before the programmer is satisfied with the choice of conditions. In adaptive control part programming, the selection of feed is left to the controller unit rather than to the part programmer. The programmer can afford to take a less conservative approach than with conventional NC programming. Less time is needed to generate the program for the job, and fewer tryouts are required.

9.8. Trends and New Developments in NC

We will conclude these three chapters on numerical control by discussing some of the important trends and new developments in NC technology. Without question, the most important general trend in NC involves the expanding use of computer technology. The use of computers has already provided significant improvements in part programming procedures (e.g., computer-assisted programming, interactive graphics, and voice programming). The control of NC machinery has also been dramatically enhanced through computer technology (e.g., CNC, DNC, and adaptive control). We have covered these topics in Chapter 8 on programming and in the current chapter on computerized NC. In the following sections, we discuss some additional topics likely to influence the future evolution of numerical control.

http://www.moldmakingtechnology.com/articles/optimize-cnc-machining-with-add-on-adaptive-controls

Optimize CNC Machining With Add-On Adaptive Controls The use of CNC adaptive controls can help moldmakers not only reduce cycle times, but also extend the life of their cutting tools.

While CNC technology coupled with CAD/CAM has long helped to introduce flexibility in batch production, there still remain some major inefficiencies inherent in most machining processes.

Present day CNC technology relies on the programmers' input of appropriate cutting parameters - even when sophisticated software systems are used to generate NC programs. The fact is that NC programming is based on predetermined and unchanged conditions.

The control mechanisms of CNC machines are limited to geometry and kinematics. As such, they follow pre-programmed and constant speed and feedrates during each cutting segment. Consequently, they do not have the flexibility required for adapting to the dynamic changes that occur during cutting. This inflexibility would be acceptable if cutting conditions were uniform

during machining. In practice, however, cutting conditions tend to continuously vary for many of the following reasons:

Uneven workpiece surface. Gradual tool wear. Material hardness varies within each workpiece. Workpiece dimensions vary from piece to piece. Temperature variations in material during cutting. The fixture's stability may be affected during cutting. NC programs may contain errors.

Advances in CAD/CAM technology have caused machinists to focus most of their attention to "defining the required geometry" and ignore the need to consider the rest of the previously mentioned conditions. However, with all of the those deviations in mind, NC programmers have no alternative but to be conservative in determining cutting parameters - resulting in safer but more inefficient cutting processes. No matter how optimized NC programs may be, they cannot take into account these dynamic variations encountered during cutting. At best, long NC programs may be created with different feedrates for each segment. However, these programs still cannot modify cutting parameters in real time in order to adapt to unexpected conditions that may occur during cutting.

Dynamic Optimization Solution

CNC machining can be fully optimized through the implementation of add-on adaptive control systems, which continuously monitor cutting conditions in real time. Such optimization and machine automation technology systems are indispensable if expensive CNC machines are ever to run at their full capacity and if cutting tools are to be utilized up to their maximum life rather than incurring in-process catastrophic breakage and production disruption. Similarly, machine operators will not be required to intervene in the machining process to watch and manually fine-tune the process. In this way, true automation is made a reality and programmers may be more aggressive, knowing that the adaptive controls will adjust the feedrate based on the load.

Manufacturers require optimization features that can be added on to their existing CNC machinery. Add-on adaptive control systems connect directly to the CNC machine controller; sense and monitor actual cutting load conditions; and adjust feedrates to optimal levels in real time. This ensures a constant cutting load, which takes into account the variations in the cutting conditions during the cut. In this way, these systems ensure that machine cycle times are minimized and that the machines run at the maximum permissible capacity for each tool.

One of the most attractive features of these systems is that they apply the optimal feedrate in real time based on the most basic parameters for each specific tool and material. These parameters may be input, if necessary, from an external tool library. The operator is not required to know specific load threshold for each tool, as the internal expert system determines these limits for itself.

This enhancement allows NC programmers to be aggressive and program feeds as though the tools are new and sharp. During cutting, the adaptive controls automatically compensate for tool wear since feedrates are automatically and continuously adjusted partly as a function of the extent of tool wear. The system also gives operators a quantitative indication of tool wear during the cut. Based on the system's indication, operators can get ready to replace the worn tools in time without actually incurring costly and disruptive tool breakage or replacing the tool much sooner than necessary.

In addition to detecting tool wear, the devices also protect tools from breakage through their sensitivity to the spindle load. Fewer broken tools also reduce scrap and the need for rework. Breakage protection is provided in the form of an alarm system that alerts the machine operator/supervisor when acute overload conditions occur in the cutting process and, if necessary, automatically stops the machine.

Adaptive control systems ensure automatic optimization of the machining process to reduce cycle times, increase tool utilization and prevent tool breakage, thus lowering machining costs and increasing machine capacity.

These adaptive control systems are applicable on CNC milling, turning and drilling applications. Typical applications include rough milling when the material and workpiece surface hardness vary, die and mold manufacturing, blade manufacturing an

Cnc, dnc & adaptive control — Presentation Transcript

1. CNC, DNC &Adaptive Control Arvind Deshpande 2. Problems with Conventional NC1. Partprogramming mistakes2. Nonoptimal speeds

and feeds3. Punched tape4. Tape reader5. Controller6. Management information4/10/2012 Arvind Deshpande(VJTI) 2

3. Conventional hard- wired NC controllerComputer Numerical Control unit NC system that utilizes stored programs inreplaced by computer. a dedicated computer to perform some or Soft-wiredall NC functions Flexibility4/10/2012 Arvind Deshpande(VJTI) 3

4. CNC4/10/2012 Arvind Deshpande(VJTI) 4 5. Functions of CNC1. Machine tool control Hybrid CNC –Hard-wired logic circuits for

functions like feed rate generation , circular interpolation etc. in addition to computer Mass production of circuits and less expensive computer Straight CNC – Computer to perform all NC functions4/10/2012 Arvind Deshpande(VJTI) 5

6. Hybrid CNC4/10/2012 Arvind Deshpande(VJTI) 6 7. Straight CNC4/10/2012 Arvind Deshpande(VJTI) 7 8. Functions of CNC2. In-process compensation – Dynamic correction of machine tool

motion for changes or errors that occur during processing Adjustment of errors sensed

by in-process inspection probes and gauges Recomputation of axis positions when an inspection probe is used to locate a datum reference on the work part Offset adjustments for tool radius and length Adaptive control adjustments to sped and feed Computation of predicted tool life and selection of alternate tooling when indicated.4/10/2012 Arvind Deshpande(VJTI) 8

9. Functions of CNC3. Improved programming and operating features Use of tape and tape reader only once On-line editing of part programs at the machine Special canned cycles. Graphic display of tool path to verify the tape Various types of interpolation: circular, parabolic, cubic Support of various units. Conversion from one unit to another unit. Use of specially written subroutines or macros Manual data input (MDI) Several part programs in bulk can be stored.4/10/2012 Arvind Deshpande(VJTI) 9

10. Functions of CNC4. Diagnostics – Equipped with diagnostic capability to assist in maintaining and repairing the system Identification of reason for downtime Indication of imminent failure of certain component Redundancy of components4/10/2012 Arvind Deshpande(VJTI) 10

11. Direct Numerical Control A manufacturing system in which no. of machines are controlled by a computer through direct connection and in real time.4/10/2012 Arvind Deshpande(VJTI) 11

12. DNC with satellite computer4/10/2012 Arvind Deshpande(VJTI) 12 13. DNC – Drip Feeding very large NC programVery complex part shapes NC

controller memory may not handle HUGE part program computer feeds few blocks of NC program to controller When almost all blocks executed, controller requests more blocks4/10/2012 Arvind Deshpande(VJTI) 13

14. Behind the Tape Reader (BTR) Computer is linked directly to regular NC controller unit The connection is made behind the tape reader Two temporary storage buffers Less cost4/10/2012 Arvind Deshpande(VJTI) 14

15. Special Machine Control Unit Regular NC controller is replaced by special MCU More accuracy in circular interpolation and fast material removal rates than BTR systems Most CNC machines are sold with computer4/10/2012 Arvind Deshpande(VJTI) 15

16. NC, CNC and DNC4/10/2012 Arvind Deshpande(VJTI) 16 17. Functions of DNC1. NC without punched tape2. NC part program storage Programs

must be made available for downloading to CNC machine tools Part program can be uploaded after editing from CNC machine Entry of new programs. Editing of programs , deletion of programs Tool management Tool offsets can be downloaded in to MCU Postprocessor Data processing and management functions Primary storage and secondary storage Syntax checking and graphic proving of programs on CNC computer CNC can be operated directly from DNC computer Flexibility in shop floor scheduling Part program preparation Machinability database for calculating speed/feed4/10/2012 Arvind Deshpande(VJTI) 17

18. Functions of DNC3. Data collection, Processing and reporting Monitor production in the factory Data processing and report generation by DNC computer Getting the data about health of the machine in the form of sensor signals or diagnostic messages which can be used for preventive/predictive maintenance Metrological data in the form of dimensional acceptance4. Communications Central computer and machine tools Central computer and NC part programmer terminals Central computer and bulk memory, which stores the NC programs CAD system Shop floor control system

Corporate data processing Remote maintenance diagnostics system4/10/2012 Arvind Deshpande(VJTI) 18

19. Justification of DNC Interconnected CNC machines are large in Very large programnumber size. Can not be accommodated in the part program Largememory of MCU variety of part programs and small Frequent changes inbatch sizes program designs4/10/2012 Arvind Deshpande(VJTI) 19

20. Advantages of DNC1. Elimination of punched tape and tape reader2. Greater computational capability and flexibility3. Convenient storage of NC part programs in computer files4. Programs stored as CLFILE5. Reporting of shop performance6. Establishes the framework for evolution of future computer automated factory (CIM)7. 2-5 % increase in operational efficiency of CNC machine tools. Cost of DNC installation can be recovered quickly.4/10/2012 Arvind Deshpande(VJTI) 20

21. Combined CNC/DNC systems Development of hierarchical computer systems in manufacturing Flexibility Ability to gradually build the system More versatile and economic approach Distributed Numerical System Part program downloaded only once Redundancy Improved communication between central computer and shop floor4/10/2012 Arvind Deshpande(VJTI) 21

22. Adaptive Control A control system that measures certain output process variables like spindle deflection, force, torgue, cutting temperature, vibration amplitude, horse power and uses them to control speed or feed NC reduces non productive time in a machining operation AC determines proper speeds and feeds during machining as a function of variation in work piece hardness, width or depth of cut, air gaps in part geometry etc. Increased metal removal rate and reduced cost per volume of metal removed4/10/2012 Arvind Deshpande(VJTI) 22

23. Where to use adaptive control?1. In-process time consumes significant portion of the machining cycle time. (>40%)2. Significant sources of variability in the job3. Higher cost of operation of machine tool4. Work material – steel, titanium, high strengh alloys4/10/2012 Arvind Deshpande(VJTI) 23

24. Sources of variability in machining1. Variable depth/width of cut2. Variable workpiece hardness and variable machinability3. Variable workpiece rigidity4. Toolwear5. Air gaps during cutting4/10/2012 Arvind Deshpande(VJTI) 24

25. Adaptive Control Optimization(ACO) Index of performance is a measure of overall process performance such as production rate or cost per volume of metal removed. Objective is to optimize the index of performance by manipulating speed or feed in the operation IP = MRR/TWR MRR – Material removal rate TWR – Tool wear rate Sensors for measuring IP not available4/10/2012 Arvind Deshpande(VJTI) 25

26. Adaptive control Constraint (ACC) Less sophisticated and lessNearly all AC systems is of this type expensive Objective is to manipulate speedthan research ACO systems or feed so that measured process variables are maintained at or below their constraint limit values.4/10/2012 Arvind Deshpande(VJTI) 26

27. Operation of ACC system Profile or contour milling on NC machine tool Feed is controlled variable Cutter force and horsepower are used as measured variables Hardware components1. Sensors mounted on the spindle to measure cutter force2. Sensors to measure spindle motor current3. Control unit and display panel to operate the system4. Interface hardware to connect the AC system to existing NC/CNC system4/10/2012 Arvind Deshpande(VJTI) 27

28. Relationship of AC software to APTprogram4/10/2012 Arvind Deshpande(VJTI) 28 29. Operation of ACC system duringmachining process4/10/2012 Arvind

Deshpande(VJTI) 29 30. Benefits of AC1. Increased production rate2. Increased tool life3. Greater part

protection4. Increases machine life5. Less operator intervention6. Easier part programming4/10/2012 Arvind Deshpande(VJTI) 30