an autonomous institution · 2019. 10. 8. · • advantage- a fixed table allows good...

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CMM

M&M/ UNIT- 3 CMM/ K.KUGAN, III MECH B, SNSCE

KUGAN.KIII MECH B

SNSCE

SNS COLLEGE OF ENGINEERINGKurumbapalayam (Po), Coimbatore – 641 107

AN AUTONOMOUS INSTITUTIONAccredited by NBA – AICTE and Accredited by NAAC – UGCwith ‘A’ Grade

Approved by AICTE, New Delhi & Affiliated to Anna University, Chennai

22/08/2019

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Coordinate Measuring Machine (CMM)

Measuring machine consisting of a contact probe and a mechanism to position the probe in three dimensions relative to surfaces and features of a work part

• The probe is fastened to a structure that allows movement relative to the part

• Part is fixture on worktable connected to structure

• The location coordinates of the probe can be accurately recorded as it contacts the part surface to obtain part geometry data

M&M/ UNIT- 3 CMM/ K.KUGAN, III MECH B, SNSCE22/08/2019

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TYPES OF MEASURING MACHINES

1. Length bar measuring machine.

2. Newall measuring machine.

3. Universal measuring machine.

4. Co-ordinate measuring machine.

5. Computer controlled co-ordinate measuring

machine.

22/08/2019 M&M/ UNIT- 3 CMM/ K.KUGAN, III MECH B, SNSCE

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Length Bar measuring Machine

• https://www.youtube.com/watch?v=TO8SeVbsXv0


https://www.youtube.com/watch?v=TO8SeVbsXv0

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• https://www.youtube.com/watch?v=DxdFiIDrFBc


https://www.youtube.com/watch?v=DxdFiIDrFBc

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Measuring machine consisting of a contact probe and a

mechanism to position the probe in three-dimensions

relative to surfaces and features of a work part

The probe is fastened to a structure that allows movement

relative to the part

Part is fixture on worktable connected to structure

The location coordinates of the probe can be accurately

recorded as it contacts the part surface to obtain part

geometry data 22/08/2019 M&M/ UNIT- 3 CMM/ K.KUGAN, III MECH B, SNSCE

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Coordinate Measuring Machines

• A CMM consists of a constant probe that can be

positioned in 3D space relative to the surface of a

work part, and the x, y, and z coordinates of the probe

can be accurately and precisely recorded to obtain

dimensional data concerning the part geometry


accomplish measurements in 3D, a basic CMM is composed of

the following components:

Probe head and probe to contact the work part surface.

Mechanical structure that provides motion of the probe in

three Cartesian axes and displacement transducers to

measure the coordinate values of each axis.

• In addition, many CMM have the following components:

Drive system and control unit to move each of the three

axes

Digital computer system with application software.

Coordinate Measuring Machines


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CMM

CMM – Coordinate Measuring

Machine

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ACTIVITY


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CMM Mechanical Structure

(d) Horizontal Arm (e) Gantry

(f) Column


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CMM Mechanical Structure

(a) Cantilever (b) Moving bridge (c)

Fixed bridge22/08/2019 M&M/ UNIT- 3 CMM/ K.KUGAN, III MECH B, SNSCE

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Cantilever type

• A vertical probe moves in the z-axis

• Carried by a cantilevered arm that moves in the y-

axis

• This arm also moves laterally through the x-axis

• Advantage- a fixed table allows good accessibility

to the work piece

• Disadvantage- the bending caused by the cantilever

design

• The cantilever design offers a long table with

relatively small measuring ranges in the other two

axis.

• Suitable for measuring long, thin part


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Column type

• Often referred to as universal measuring

machine instead of CMM

• The column type CMM construction

provides exceptional rigidity and

accuracy

• These machines are usually reserved for

gauge rooms rather than inspection


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Fixed bridge type

• In the fixed bridge

configuration, the bridge is

rigidly attached to the machine

bed

• This design eliminates the

phenomenon of walking and

provides high rigidity22/08/2019 M&M/ UNIT- 3 CMM/ K.KUGAN, III MECH B, SNSCE

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Moving bridge type

• Most widely used

• Has stationary table to support work

piece to be measured and a moving

bridge

• Disadvantage- with this design, the

phenomenon of yawing (sometimes

called walking) can occur- affect the

accuracy

• Advantage- reduce bending effect


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Horizontal arm type

• Unlike the previous machines, the

basic horizontal arm-type CMM

• Also referred to as layout machine

• Has a moving arm, and the probe is

carried along the y-axis

• Advantage- provides a large area,

unobstructed work area

• Ideal configuration for measurement

of automobile parts


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Gantry type

• The support of work piece is independent of

the x and y axes, both are overhead, supported

by four vertical columns rising from the floor

• This setup allows you to walk along the work

piece with the probe, which is helpful for

extremely large pieces


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CMM Advantages

• Higher productivity - a CMM can perform complex inspection procedures in much less time than traditional manual methods

• Greater inherent accuracy and precision than conventional methods

• Reduced human error

• Versatility - a CMM is a general purpose machine that can be used to inspect a variety of part configurations


an autonomous institution · 2019. 10. 8. · • advantage- a fixed table allows good...

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