1. CMM Coordinate-Measuring MachineBy
Prof. A.U.Awate
Department of Mechanical Engineering
PRMIT & R Badnera-Amravati

2. CMM is a 3D device for measuring the physical geometrical characteristics of an object.
CMM is a machine which takes readings in six degrees of freedom and displays these readings in mathematical form.
CMM is a specialized form of  industrial robot

3. Parts CMM include three main components: 1.Main Structure
which include three axes of motion
2. Probing system
3. Data collection and reduction system
Application software
Machine controller
Desktop computer

4. 1.Main Structure
Gantry type
Advantage:
Measurement of large size parts 
Disadvantage:
Geometric changes caused by non-uniform temperature distribution owing to their large size.
Application:
Heavy machine construction,
car body and mold making sectors
of the automotive industry,
measuring wind tunnel models.

5. Maximum accessibility Disadvantage:
1.Main Structure
Cantilever type
Advantage:
Large measuring range
Maximum accessibility
Disadvantage:
Bending of the cantilever above the measuring area
Application:
For checking sheet metal, cast iron and steel parts in the automotive industry, aircraft construction and shipbuilding.

6. High accelerations and speeds owing to the large supporting base
1.Main Structure
Column type
(horizontal arm type)
Advantage:
High accelerations and speeds
owing to the large supporting base
of the column and its low weight 
Disadvantage:
Suitable for small measuring ranges
only since the projecting part of the column must have short length due to its rigidity.
Application:
In precision measurements
on gages and master parts.

7. 1.Main Structure
Bridge type   
Advantage:
Most widely used
High rigidity  owing to compact bridge design and thus small measuring deviations.
Disadvantage:
Limited accessibility caused by the bridge.
Application:
For medium to large measuring range

8. Portable CMM
Have six rotary axes with rotary encoders,
instead of linear axes.
Less accurate than a bridge type CMM
Use angular measurements taken at the
joints of the arm to calculate the position
of the stylus tip.
Can reach the insides of complex parts
Applications:
Reverse engineering, rapid prototyping,
and large-scale inspection of low-volume parts
are ideally suited for portable CMMs

9. CMM Features
Granite Table
Structurally and thermally stable material
Low porosity
Low moisture absorption
Low coeff. of thermal expansion
Superior strength
Uniformity of texture
Non-glaring surface
M8 threaded table inserts

10. CMM Features
Air bearings
Provided for ensuring friction free travel to all axes
Compressed air is forced through a series of very small holes in a flat bearing surface to provide a smooth but controlled air cushion on which the CMM can move in a frictionless manner

11. CMM Features
Each axis is fitted with a reference system and a linear measurement transducer for positional feedback.
(0.5 micron resolution)
Passive vibration damping system isolates external vibrations
FEA designed bridge beam extrusion provides optimum M.I. for minimum deflection when operating at high accelerations

12. 2. Probing system
The touch probe forms the sensing device on the end of the quill
Mechanical probe
Contact type
Soldering a hard ball to the end of a shaft
No control on measuring pressure
Electronic touch trigger probe
Stylus is spring-loaded with ruby ball at the tip
As the probe touched the surface of the component the stylus deflected and simultaneously sent the XYZ coordinate information to the computer
Optical probes and Laser probes
Non-Contact type
White light/ Laser beam is projected against the surface of the part
Better for scanning

13. Pre-travel variation (PTV) Pre-travel is the amount of stylus bending
2. Probing system
Pre-travel variation (PTV)
Pre-travel is the amount of stylus bending
at the point that a trigger occurs.
Pre-Travel depends on
Contact Force FC needed to overcome
Spring Force FS
Length L and stiffness of the stylus
Direction of measurement R
Pre-travel in the Z direction tends to be small
despite the higher forces
Pre-travel can be compensated by probe calibration.
A datum feature (of known size and position) is
measured to establish the average pre-travel

14. 2. Probing system
Stylus modules

15. Correction for Tip Radius
2. Probing system
Qualifying Probe Tips
Correction for Tip Radius
CMM detects dimension from and to the center of the tip (ruby ball) which calls for correction for tip radius.
Each recorded value is corrected for tip radius.

16. Application software PC-DMIS CMM PC-DMIS PRO PC-DMIS CAD PC-DMIS CAD++
3. Data collection and reduction system
Application software
PC-DMIS CMM
Dimensional Measuring Interface Standard is the world’s leading metrology software
PC-DMIS PRO
Full-featured metrology software system
without CAD capabilities.
PC-DMIS CAD
It adds CAD capabilities to PC-DMIS PRO.
It allows import and export CAD modules
Possible to develop, test and debug part programs directly on CAD models
Compares the measured data directly to the CAD model
Lets graphically test and debug inspection routines
PC-DMIS CAD++
Handles difficult scanning tasks (contact & non contact type)
and supports sophisticated scanning devices 

17. Application software Modules
3. Data collection and reduction system
Application software Modules
PC-DMIS CMM
PC-DMIS Planner
PC-DMIS Gear
PC-DMIS Blade
PC-DMIS NC
PC-DMIS Portable
PC-DMIS Vision

18. 3. Data collection and reduction system
Application software
Alignment
PC-DEMIS mathematically relates the Part Coordinate System and Machine Coordinate System.

19. Measured and Constructed Features
3. Data collection and reduction system
Application software
Measured and Constructed Features

20. Controller is the heart of CMM Provides precise control of the
3. Data collection and reduction system
CMM controller
Controller is the heart of CMM
Provides precise control of the
motion of the machine
Interfacing to sensors and
with the metrology software.

21. CMM Applications Metrology
Linear Measurement (Measured and Constructed Features)
Angular Measurement (Measured and Constructed Features)
Geometrical Features
Profile Checking
Stages of Inspection
Receiving
In-proses
Final
Mode of Inspection Operation
Manual
Automated (DCC)
Purpose of Inspection
First-piece approval
Process Control
Pre-assembly qualification of parts
Reverse Engineering
Location of Inspection
Standard Room
Machine Shop
on Site