30-07-2014, 11:19 AM
COORDINATE MEASURING MACHINE
COORDINATE MEASURING.ppt (Size: 1.42 MB / Downloads: 23)
History
The first coordinate measuring machine appeared at the International Machine Tool exhibition in Paris in 1959 exhibited by the British company Ferranti.
Coordinate Measuring Machine
Developed to speed up inspection of components produced on NC machines.
Can measure including 3D complex shapes with accuracy.
Ex: aero foils, turbine blades
It is Computer controlled.
0.001mm is the accuracy of CMM
Can be Installed on production lines.
Automatic inspection
Minimize operator error
Provide uniform component quality.
Optical measuring system
It consist of polarizer beam splitter, collimating lens, photo cell strips, index grating ,grating are the components.
In this process laser interferometer used by heterodyne method. The displacement of component is calculated from laser signals by analyzing transmitted time(t1) and reflected time(t2) of laser beam.
SOFTWARE:
Measuring software is the most important part of a Coordinate Measuring Machine. Which software takes the least number of keystrokes to measure a feature or a complete part is the better one. CAD is good enough for simple parts
Motor driven CMM: A motor-driven CMM with computer-assisted data processing uses electric motors to drive the probe along the machine axes under operator control. A joystick or similar device is used as the means of controlling the motion
Advantages
Eliminates need for operator calculations and inherent possibility of errors
Machine setup time is greatly reduced
Production increased
Reduces need for operator skill
Eliminates scrap and rework
Most machine tools can be fitted with system
High precision and accuracy.Requires less labor.
Accurate dimensions can be obtained just by knowing the coordinates and distance between the two reference points.
Disadvantages
Initially high in cost.
It needs vacuum chamber for
Highly skilled labour required
Even floor vibration also deviate accuracy of measurement.
Replacement of spare parts not available in case of damage of probe Ruby crystal.
The Coordinate measuring machines are very costly.
The CMMs are less portable.
If the operating software cracks down it is difficult to restart the entire system.
It needs to construct some feature on its own as some parts of the work piece are unreachable by the probe.