Coordinate Measuring Machine (CMM)
Nov 03, 2014
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