Coordinate Measuring Machine

(CMM)

ContentsO Types of CMMO Application of CMMO Advantages and DisadvantagesO Parts descriptionO Probing :

O TypesO FunctionO Selection criterionsO Probes calibration

INTRODUCTIONA 3D device for measuring the physical geometrical

characteristics of an object.

This machine may be manually controlled by an

operator or it may be computer controlled

Types of CMM

CANTILEVER TYPE BRIDGE TYPE

Only suitable for small measuring ranges since the projecting part of the column must have short length

due to its rigidity

They are used for measuring tasks even when high precision is

required, because they encompass the entire range of machine tools.

Four basic types are:

COLUMN TYPE GANTRY TYPE

Column type (horizontal arm type) are used predominantly, owing to their very large measuring range, for checking sheet metal, cast iron and steel parts in the automotive industry, aircraft construction and

shipbuilding

Gantry type are used for measurements of very large parts

in system manufacturing and heavy machine construction, but also in

the car body and mold making sectors of the automotive industry, for example when measuring wind

tunnel models.

The ApplicationO Dimensional MeasurementO Profile MeasurementO Angularity or OrientationO Depth MappingO Digitizing or ImagingO Shaft measurement

The Advantages and Disadvantages

ADVANTAGES DISADVANTAGESO High precision and

accuracyO Requires less labor O Accurate dimensions can

be obtained just by knowing the coordinates and distance between the two reference points

O Robustness against external force and error accumulation

O The Coordinate measuring machines are very costly

O The CMMs are less portableO If the operating software

cracks down it is difficult to restart the entire system.

O It needs to construct some feature on its own as some parts of the workpiece are unreachable by the probe.

Description of PartTECHNICAL DETAILS

PARTS

PARTS MAIN

STRUCTUREPROBING

DATA COLLECTION

1. MAIN STRUCTURE• The main structure which

include three axes of motion2. PROBING• Probing system3. DATA COLLECTION• Data collection and reduction

system - typically includes a machine controller, desktop computer and application software

Main Structure

• Main structure of CMM is made of cast iron, contains a granite table, housings

and slider of bridge carrying probhead

• It contains 3 digit no. which shows the max. dimension measured by it along X,Y,Z

axis respectively in multiples of 100mm.

Probing System

• It is international standard to use

probhead

• It has function of half and full rotation about X and Z axis respectively.

• A clamp is provided to lock the probhead.

• In probe, the bolt type structure is fixed called module, which provides

recess for prob.

• Actually, prob consist of two parts, one is

extension and other is styli.

• Ruby diamond is attach to styli for contact

measurement. It has spring inside it for shock

absorption.

Data Collection (Software

Specification)

• On average, most CMM’s in many industries runs

on DELCAM software

• Program which needs to be installed in computer

to operate CMM is POWER INSPECTOR.

CMM Reference Sphere

• The calibration sphere is used to perform

calibration of probe system. Standard sizes are: Ø25.4 mm (1.000") with ⅜-16 thread mount for surface plate inserts

(M10 Optional).

• It is fixated into the recess provided in

granite table

ProbingTHE PROBING SYSTEM

Types of ProbesHard Contact:• Make contact manually

Soft Contact (electronic probes)• Including probe head, probe and stylus• Can record movement directions 4-way, 5-way, 6-way

probes• Use soft probes: compare as zero point & standard: null

process, standard = built-in scale

Non-contact type probes:• Avoid deforming objects by stylus• Light beam stylus, microscope and optical probes

Probe Head SelectionO The response speed of the probe system must be

compatible with the CMM controller.

O Where possible the same probe body should be used for a complete measuring application.

O The probe body should be able to accommodate all the styli to be used for the application.

Probes Calibration

Question & AnswerDo not hesitate to ask