ISAT 303 Mod 1-1 1997-2001 M. Zarrugh Module I Sensors and Measurements in MFG The objectives of...

ISAT 303 Mod 1-1 1997-2001 M. Zarrugh

Module ISensors and Measurements in MFG

The objectives of this module are to

– understand the role which sensors and measurements play in manufacturing

– describe sensors used in detecting objects

– introduce object identification through bar codes and RFID tags

– discuss measurements used to describe conditions of a process

– briefly describe sensors used in machine tool and robotic applications


Sensing and Measuring Sensing - determination of process condition by

automatic means. Measurement - implies the automatic and real-time

determination of process values» Values include pressure, temperature, velocity, no. of parts, etc..


Automation & Shop Floor Control contd. CONTROL IMPLIES:

» sensing current conditions

» analyzing them and then

» effecting changes in the process [ACT]


Automation & Shop Floor Control It is Necessary to:

– gather information in real-time and– use the information to make “timely decision”. E.G..:

» secure production equipment

» move assembly materials and components

» move material handling equipment as needed e.g.. robots, AGVS, LGVS, conveyors.


Sensing and Measurement are Critical Elements of Feedback Control Systems

ControllerSystem orProcess

ActualBehavior

DesiredBehavior

Open-Loop Control

Closed-Loop (Feedback) Control

ControllerSystem orProcess

ActualBehavior

DesiredBehavior

Sensing &Measurement


Feedback Control Systems:An Example

Furnace Room

Thermometerin Thermostat

Heatq

ActualTemperature

TDesiredTemperature

Td

On/Offsignal

Actuator

Space Heating System

System

Sensor

Thermo-stat

Controller


Role of Instrumentation & Measurementin Manufacturing Statistical Process Control: manufacturing process data

must be collected and transmitted to the control computer which prepares the control charts and alerts the operator to serious deviations.

Dedicated Digital Control: programmable logic controllers need status data of the tasks and events being controlled.

Numerical Control of Machine Tools: positions of the cutting tool relative to the part must be fed back to the control computer to insure accurate cutting.


Role of Instrumentation & Measurementin Manufacturing Adaptive Control: cutting conditions, such as noise,

vibrations, temperature and force data need to be measured so that the controllers can adapt cutting parameters to changing conditions.

Shop Floor Control: real-time data on the status of resources (people and machines) and parts need to be monitored so that timely decisions can be made.

Manufacturing Cell: supervisory computer needs status data of the operations and events being controlled so that these are sequenced properly.


Types of Measurements in the Factory

Object detection

Object identification

Measurement of condition

Sensing for machine tools and robots


Object Detection Limit Switches: mechanical contact closes or opens when an

object trips the switch. (cheap, simple, but slow)– single pole (SP) normally open (NO)– single pole (SP) normally closed (NC)– double pole (DP) normally open (NO)

Photoelectric Sensors: object interrupts light or IR beam which causes on/off action in sensing circuit.– hysteresis: light threshold level for “on” or “off” setting

Proximity Sensor: non-contacting sensors that respond to the presence of material: inductive and magnetic sensors for metallic material and capacitive devices for all materials


Object Identification Necessary for tracking materials, parts and final products in the

factory. Bar codes (sequences of light and dark bands) are most

common:– Universal Product Code (UPC) for consumer items (numbers only)

xxx xxx xxx xxx12 Digits

MFR Item ParityCodeKey

4 bars per digit

– Code 39 provides 44 alphanumeric characters: most common in manufacturing: more versatile and flexible than the UPC code. There are 9 bars per character.


Measurement of Conditions:Transducers Transducers are devices which generate an electrical

output from other forms of input energy. Basic transducer types

by physics of operation:


Sensing for Machine Tools Basic sensing associated with motion control of the machine tool

itself will be discussed in module III. Other types of sensing needed for machining are

Part dimensions:– Coordinate measurement machines (CMMs)– Optical gaging: laser, video camera

Tool wear (indirect):– increased cutting forces– increased power consumption

Axial motion:– Optical encoders

Sequencing:– proximity or limit switches


Robot Sensing Basic sensing associated with motion control of the robot itself

is similar to that of machine tools and will be discussed in module III. Other types of sensors needed to provide tactile, visual or force feedback to the robot are

Touch sensors:– Skin-like sensors: arrays of strain or pressure transducers– Spatial (hepatic) perception: wrist force measurement

Vision: – Video camera: record images which are analyzed to recognize part

shapes and orientations and to detect defects Voice recognition:

– Speech recognition are used for programming robots and for issuing commands from busy operators or from disabled persons using the robots as assistive devices.


Sensing & MeasuringSensing & Measuringin Manufacturingin Manufacturing

ObjectObjectIdentificationIdentification

ObjectObjectDetectionDetection

ConditionConditionDetectionDetection

Sensing forSensing forMach/RobotsMach/Robots

bar codesbar codesmagnetic stripesmagnetic stripesRF devicesRF devicesvision/voicevision/voice

limit switcheslimit switchesprox. detectorsprox. detectorssensorssensors

transducerstransducerst/ct/claser systemslaser systemstv camerastv cameras

opticaloptical encodersencoderstactile tactile sensorssensors

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ISAT 303 Mod 1-1 1997-2001 M. Zarrugh Module I Sensors and Measurements in MFG The objectives of...

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