The document discusses Coordinate Measuring Machines (CMM), which are electromechanical systems used for coordinate metrology to measure the physical geometrical characteristics of objects. It outlines the components, types, features, applications of CMM, and probes used, including the potential causes of measurement errors due to alignment, calibration, and environmental factors. Various CMM types, such as cantilever, moving bridge, and gantry, are highlighted for their specific advantages and applications.

1. BAHIR DAR UNIVERSITY
BAHIR DAR INSTITUTE OF TECHNOLOGY (BiT)
FACULTY OF MECHANICAL AND INDUSTRIAL
ENGINEERING
Rapid Prototyping & Reverse Engineering
[MEng6123]
Reverse Engineering
Coordinate Measuring Machine (CMM)

2. Coordinate Measuring Machines (CMM)
• A Coordinate Measuring Machine (CMM)
is an electromechanical system designed
to perform coordinate metrology.
• CMM is a device for measuring the
physical geometrical characteristics of
an object.

3. Components of 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
Coordinate Measuring Machines (CMM)

4. 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
• Threaded table inserts
Coordinate Measuring Machines (CMM)

5. 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
Coordinate Measuring Machines (CMM)

6. CMM Applications
Metrology
• Linear Measurement
• Angular Measurement
• 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
Coordinate Measuring Machines (CMM)

7. Types of CMM
• Cantilever Type
• Moving bridge type
• Fixed bridge type
• Column type
• Gantry type
• Horizontal arm type
• Portable type

8. 1. Cantilever Type of CMM
Easy access to work and it has high desk volume.
It suitable for measuring the long and thin part.
Major disadvantage is bending caused by cantilever design
Types of CMM
Application:
• For checking sheet metal, cast iron and steel
parts in the automotive industry, aircraft
construction and shipbuilding.

9. 2. Moving Bridge type
•Most widely used
•Disadvantage- with this design, the phenomenon of yawing
(sometimes called walking) can occur- affect the accuracy
•Advantage- reduce bending effect
Types of CMM
Application:
• For medium to large measuring range

10. 3.Fixed bridge type
• This type of CMM supported for Large and Medium components.
• It has better rigidity.
• It has Higher Accuracy than Horizontal arm CMM.
• It has Limited work area.
Types of CMM
Application:
• For medium to large measuring range

11. 4. Column type CMM
• It has Good Rigidity and High accuracy.
• That commonly known as a universal measuring machine.
• It is similar to drilling and vertical milling machine
Types of CMM
Application:
• In precision measurements on gages
and master parts

12. 5. Horizontal arm type CMM
• That has large work volume and free from obstruction.
• That CMM accessibility for large objects like dying, car bodies.
Types of CMM

13. 6. Gantry type CMM
• It can measure a large object.
• It has more accuracy than all other CMM.
Types of CMM
Application:
• Heavy machinery construction, car
body and mold making sectors of
the automotive industry

14. 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
Types of CMM

15. Types of Probe
• Contact probe
• Hard probe
• Switching probes
• Measuring probes
• Non-contact probes
• Laser probe
• Vision probe

16. 1. Hard Probe
 It has a variety of probe tip shape and size based on the application.
 Ball/Spherical shape probe used for establishing surface locations.
 Tapered or conical probe used for locating holes.
 Cylindrical probe used for checking slots and holes in sheet metal.
Types of Probe
Contact Probe

17. 2. Switching Probes
• It is also called as Trigger type probe system.
• The “Buckling mechanism” is a three point bearing it
arranged at 120º around and circumference.
• Switching probe mostly used when an object has to be
measured very fast by a single point.
Types of Probe
Contact Probe

18. 3. Measuring Probes
• It used for the large bridge type of CMM.
• It has also a “Buckling mechanism”
• It is a three dimensional probe.
• Stylus able to deflect in any direction
Types of Probe
Contact Probe

19. 1. Laser Probe
The single-spot laser triangulation method.
This method uses low-powered laser beam for distance measurement.
A light sensitive detector at an angle of approximately 25º.
Types of Probe
Non-Contact Probe

20. 2. Vision Probe
• A charge-coupled device (CCD) is usually employed in the camera.
• It consists of matrix arrays.
• It measured by computer ‘Count’ of pixels.
• The analog voltage value of each pixel converts to a digital value.
Types of Probe
Non-Contact Probe

21. CAUSES OF ERRORS IN CMM
• If the table and probes are in imperfect alignment;
• the probes may have a degree of run out and move up and down in the
Z-axis may occur perpendicularity errors.
• Therefore CMM should be calibrated with master plates before using
the machine.
• Dimensional errors of a CMM is influenced by;
• Straightness & perpendicularity of the guide ways.
• Scale division and adjustment.
• Probe length.
• Probe system calibration, repeatability, zero point setting and reversal error.
• Error due to digitization.
• Environment

22. • The length of the probe should be minimum to reduce deflection.
• The weight of the work piece may change the geometry of the guide
ways and therefore, the work piece must not exceed maximum
allowable weight.
• Variation in temperature of CMM, specimen and measuring lab influence
the uncertainly of measurements.
• Translation errors occur from error in the scale division and error in
straightness perpendicular to the corresponding axis direction.
• Perpendicularity error occurs if three axes are not orthogonal.
CAUSES OF ERRORS IN CMM