The previous mentioned steps describe the learningmode of the computer (Manual lead through in DCCProgramming).If other similar parts wer^ to be measured they areclamped on the table ih approximately the sameposition as the first part.Accurate positioning iscommand is given via

lot necessary, the correctthe computer and the

measuring process is repeated by the machine (DCCmeasuring machines).When combined with rotary tables, most complexshapes can be measured.These machines are very expensive and are onlyeconomic where used for measurement of largequantities and complex shapes. 25

5. Automatic Handling of Measuring Instrumentsand Workpieces

:

• Measurement and test equipment are integrated intothe material flow of production applications.

• Especially useful if various! workpieces and productionfeatures must be measured in a short period of time.

• Fully automated measurements requires fullyautomated handling of measurement instruments andworkpieces.

0

• A measurement station which is automated throughthe use of robots, can be made available duringassembly to acquire tre data needed for theworkpiece selection. It can control the material flowdepending on the selection and provide ideally pairedworkpieces for the assemb y process. 26

Industrialrobot

Measurement stationfor inner and outerdiameter

palettetransportsysteta

Digitate/analoguemodules forinput &output

computer

Processor system wttH analogue/digital connectionsbetween separate measurement stations

6. Interfacing Production Machines and MeasuringSystems

• One of the problems with conventional machinetools is that the leadscrews, which cause the

, slideway to move, are also expected to beresponsible for measuring the motion.

• In C.N.C. machine tools;, the distance moved ismeasured by a device cjompletely separate fromthe actuator that caused' that movement. °

• A C.N.C. machine will produce conforming partsas long as the processthe part's tolerance.

variability is better than

28

• Tool wear, for example, changes the initialsetting of the C.N.C. machine and accordinglythe process variability.

• Therefore a separate product measuringsystem, for the product,! is still required but maybe fitted to the machine.

• The measured data may be fed to a computer toperform the following:

Perform necessary borrections to machinemotion.

Establishment and updating of control charts.

29

Video Link:->

https://www.dropbox.cdm/s/vndtd5titt4g2ft/CMM.mp4

30

Virtual Metrology

Virtual Metrology (predictive Metrology)'

• When each workpiece on ithe production line shouldbe measured, a significant number of metrologytools and procedures is required.

• Production cycle time is, accordingly, significantlyincreased.

• (VM) is a technology to predict metrology variablesusing information about tpe state of the process forevery workpiece.

: '•

1. Development Phase• A range of production runs is

prediction model that correlaprocess data.

• The model is refined until theshow a reasonable correlation.

used to develop an empiricales actual measurements with

Dredicted measurement values

liCorrelati n of Predicted vs.

Observed Values

2. Production Phaset

• The model is used during production to estimatemeasurement values for the parts being produced.

• Variations from desired product parameters are used toupdate the,process parameters.

• Adjustments in process parameters can be made on aproduct-to-product basis wimeasurement set-up.

Actual measurements are still

hout requiring a separate

made in the production flow,

[ the primary tools used to

but their role has shifted to trjat of calibrating/updating theprediction model.

» Actual measurements are nocontrol the process.

i• Control, at the single product level, reduces within-lot

variability thus increasing proceiss capability index.

Challengesiii

Large number of procesjs variables need to bemanaged to provide prediction of a few qualityparameters .(which process variables are mostimportant?).

iAccuracy and reliability problems.

INoise and accuracy of VM prediction may make it notpractical or usable.

Benefits

• Reduction of metrology costs.

• Control, at the single prodtict level, reduces within-lotvariability thus increasing process capability index.

• Reduces cycle time.

• Eliminates stand-alone metrology steps when the results canbe accurately predicted.

• Provides cost-effective alternative to integrated metrologyfor processes that exhibit hard to predict variation within theprocess run.

• Lowers the number of sampled products thus increasingproduction efficiency.

• Prediction model transparenmaintenance).

:y (Ex. Being updated after

VM Versus Integrated Metro

> Both, VM and IM, are used to

ogy (IM)

reduce process variability andimprove the control of a produ :tion process.

• VM is an algorithm technique requiring no in situmeasurements.

t

• IM includes measurement harcware that can be incorporatedinto the production equipment to provide measured valuesduring production.

• IM may include special software to calibrate the obtainedreadings with reference artifacts.

• In IM the hardware portion represents most of theinvestment required.

• In IM there is a tradeoff be1measurement.

ween speed and accuracy of