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The graduator is a very important standard device in the optical angular measuring instrument, which determines the
measure precision of the measuring instrument. A new graduator test method is discussed in this paper.
This test method is a dual dynamic imaging measurement method with dual digital microscope system, which acquires
the images of the graduator rotated by a rotating motor.
Here is the introduction of this method with more detail. At first, fix a graduator to be measured on a rotary stage, this
stage will be driven by a high precision programmable motor. Make the stage rotate with a constant angular velocity ω.
Then place the digital microscope system upon the graduator. The digital microscope system includes two digital
microscopes, which placed in the opposite diameter direction. Each digital microscope is made up of optical lens and a
CMOS electro-ocular. The sampling frequency f can be set in the control software of the elector-ocular. The two digital
microscopes make up a dual dynamic image acquire system. This system can acquire two images of the moving
graduator at the same time with the sampling frequency f. Then, a serial of the graduator images can be acquired after a
period of rotation, and there is a constant angular difference ω/f between every adjacent image. Each image of the
graduator includes several graduation lines, identify these lines and get the position of the lines with image processing
method. The measuring value of the rotate angle can be calculated from the adjacent line positions. Use the angular
difference ω/f as a standard value of the rotate angle. Compare the measuring value and the standard value with the
"comparing method of graduator measurement" formula. A compare result will be given to judge the graduator is good or
not at last.
The whole system is divided into four functional units: 1,the motion control unit;2,the dual dynamic imaging unit; 3, the
image processing unit; 4,the data analysis unit.
The measurement principle is introduced in the first part of the paper. In this part, the background of graduator
measurement and the theories of graduator measurement are referred. According to the measurement principle a system
design is made in the second part of the paper. In this part, the whole measure system is described: the structure of the
system, the function of each component and the specifications for the key components. An experiment system is build up
under the design, and some measurement data is obtained, the error analyses of the measure data is given at the last of
the paper.
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