Presentation on Cmm

8/3/2019 Presentation on Cmm

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PRESENTATION ON CMM

BY

DAVINDER KUMAR

CONDUCTED BY Dr.THOMAS TIEN-I LIUME-238


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INDEX

Introduction

Types of CMM

Parts of CMM

Uses of CMM

Features of CMM

Brief description

CMM Operation

Programming And Data Analysis

New probing System

Conclusion

Questions


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Coordinate Measuring MachineIntroduction

This is one of the most important type of sensortechnology for automated inspection

This is contact type inspection method

It is a device for measuring the physicalgeometrical characteristics of an object

This machine may be manually controlled by an

operator or it may be computer controlled


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Introduction Page 2

Measurements aredefined by a probeattached to the third

moving axis of thismachine

Probes may bemechanical, optical,

laser, or white light,among others.


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Types of CMM

Manual control

Manual computer- assisted

Motorized computer assisted Direct computer control


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Technical detailsParts

Coordinate-measuring machines includethree main components:

The main structure which include three

axes of motion Probing system

Data collection and Reduction system -

typically includes a machine controller,desktop computer and applicationsoftware.


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Uses

They are often used for:

Dimensional measurement

Profile measurement Angularity or orientation measurement

Depth mapping

Digitizing or imaging Shaft measurement


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Featuers

They are offered with features like:

Crash protection

Offline programming

Reverse engineering Shop floor suitability

SPC software and temperature compensation.

CAD Model import capability Compliance with the DMIS standard

Controller compatibility


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Brief Description

The coordinate measuringmachine ranges from smallhighly accurate machines usedfor small to average sizedparts, such as gears or bearing

races, to large machines thatcan measure automobilebodies. One of the mostcommon CMMs used is themoving bridge CMM, whichconsists of a fixed table with a

bridge system that containstwo other axes of motion. Thebridge itself moves along thetable and is the third axis ofmotion.


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Conti.

A similar machine is the fixed bridge machine and as itsname implies the bridge system is fixed with the tablemoving as the third axis. The other two axes are on thebridge as with the moving bridge scheme. An example of

a fixed bridge coordinate measuring machine is shown inFigure .The cantilever style machine incorporates twoaxes of motion riding on a cantilever that moves along afixed table (in most cases). The horizontal arm CMM issimilar to the cantilever machine in layout, but has a

column that moves for axis, a horizontal arm that slidesvertically on the column for another axis, and a movingtable to provide the third axis of motion.


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Conti

The last machine configuration that is thegantry style machine. This machineconsists of two bridges and a sliding

crossbeam. The motion of the slidingbeam creates one axis of motion while aram and another slide on the crossbeam

provide the other axes.


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CMM Operation

Having discussed the different types of axisconfigurations available it now becomesimportant to understand the method in whichdata is retrieved from the machine. The probe

head attached to the axis system of the CMM isthe sensor, which tells the controller where thesurface of the part is with respect to the machinecoordinate system.There are two principal typesof contact probe heads available. The first is the

touch trigger probe. This probe incorporates astylus mounted via kinematic mounts onto theaxes of the CMM. The kinematic mounts act asswitches


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CMM Operation

When the stylus comes into contact with the surface of the part theswitch is flipped and a data point is taken.The second type ofcontact probe is the scanning analog probe.This probe head utilizesa set of stacked flexures that are compliant in one direction. Theflexures are oriented such that each flexure is compliant in differentdirections, similar to the axes of the CMM.The stylus is mounted on

the probe head and balanced. Some form of displacementtransducer monitors the deflection of the flexures is a depiction ofthe probe head used on a Brown&Sharpe.The stylus is brought intocontact with the surface until a constant force is detected. Themachine then moves along keeping the stylus in contact with thesurface reading data at the prescribed interval. In essence, this typeof probe head is another coordinate measuring machine


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Programming and Data Analysis

Each brand of coordinate measuring machinehas its own software, which allows for thecreation of mathematical models of the trueshape of the part. The data collected during a

measurement is fit to mathematicalrepresentation of the shape being measured byan algorithm.The mathematical model used iscalled the substitute geometry and is what thesoftware uses as the reference when comparing

the sampled data. There are many differenttypes of fitting algorithms that can be used, suchas least squares, maximum inscribed, minimumcircumscribed, and Chebychev.


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New Probing System

There are newer models that have probes that drag along thesurface of the part taking points at specified intervals, known asscanning probes. This method of CMM inspection is often moreaccurate than the conventional touch-probe method and most timesfaster as well.

The next generation of scanning, known as non-contact scanning

includes high speed laser single point triangulation[1], laser linescanning[2], white light scanning[3], is advancing very quickly. Thismethod uses either laser beams or white light that are projectedagainst the surface of the part. Many thousands of points can thenbe taken and used to not only check size and position, but to createa 3D image of the part as well. This "point-cloud data" can then be

transferred to CAD software to create a working 3D model of thepart. These optical scanners often used on soft or delicate parts orto facilitate reverse engineering.
http://en.wikipedia.org/wiki/Coordinate-measuring_machinehttp://en.wikipedia.org/wiki/Coordinate-measuring_machinehttp://en.wikipedia.org/wiki/Coordinate-measuring_machinehttp://en.wikipedia.org/wiki/Coordinate-measuring_machine


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Conclusions

Coordinate measuring machines are complexinstruments that require a generous amount ofknowledge if accurate and reliable results are tobe obtained. The performance tests eluded too

in this paper are only a fraction of the requiredtesting needed to qualify a machine. The reasonfor showing examples of the is to inform thereader of the types of challenges that need to bewell thought-out with the aim of making quality

measurements. A basic understanding of themachine operation and mechanical configurationis necessary for the optimal use of suchinstruments.


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QUESTIONS?

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Presentation on Cmm