Taking the sensor as the probe, the problem of roundness error measurement of large precision parts which is not suitable for measuring on roundness instrument is solved by using the error separation technology of multiple positioning method or multiple probe method [1]. This method uses computer for real-time processing to realize clinical measurement. The sampling data (that is, the input signal) is transformed and processed in time domain and frequency domain to suppress the interference signal and improve the signal-to-noise ratio, so as to separate the error and improve the measurement accuracy and stability. Among them, the three-probe method is widely used, and the three sensors are arranged on the same radial section of the measured part and intersect with the center of the coordinate system at a certain angle. The system structure block diagram of the measuring device is shown in Figure 6.

It can be seen that error separation is the key technology to improve the measurement accuracy of roundness error. Error separation method has developed into a comprehensive application of sensing technology, digital technology, control technology, computer technology and electronic technology.

3 evaluation of roundness error

3. 1 Common evaluation methods

The following table lists the evaluation methods of common roundness errors:

(See Table 2)

The above method conforms to GB7235-87.

3.2 Computer data processing

3.2. 1 Basic ideas

As can be seen from the above table, no matter which evaluation method is adopted, although the reference circle is different, the key technology for evaluating roundness error is to determine the center of the reference circle, that is, to determine the coordinate position of the evaluation reference center, and to complete the benchmark conversion of test data from the measurement center to the evaluation center. In this way, the radial direction of each point on the actual measurement contour with the center of the evaluation reference circle as the coordinate origin is obtained, and the difference between the maximum value and the minimum value is the required roundness error value. All kinds of computer solutions are basically based on this idea to program and process data. There are many research examples in this field [2] [3] [4].

Some of these solutions are based on rectangular coordinates and some are based on polar coordinates; There are directly applicable mathematical formulas.

Some are solved, and some are charts based on calculation; Some use successive approximation method, some use optimization method and so on.

program flow chart

We designed data processing subroutines with various evaluation methods, and extended the above programs to merge the subroutines into a whole program. A friendly man-machine interface is designed. By selecting the switch, multiple evaluation methods can be arbitrarily selected for the same set of measurement data. The results can be output as data and graphics respectively.

This paper introduces and analyzes various methods of measuring and evaluating roundness error, and points out the key technologies of measuring and evaluating roundness error. Combined with working practice, the accuracy and applicability of measuring roundness error with CMM are discussed. The computer processing method for evaluating roundness error is given.

Computer aided tolerance design and geometric measurement (CAT) is a hot technology in international and domestic academic circles, and it is an inevitable trend of tolerance theory and practice development. It is of great theoretical and practical value to study and explore the measurement and evaluation method of roundness error along this direction.

References:

[1] Cui Shaoliang, et al. Error separation and data processing of roundness measurement. National University Interchangeability and Measurement Technology Research Association 1994 Proceedings

[2] Tian, et al. Further discussion on the "universal algorithm" for roundness error evaluation. Metrology, 200 1

[3] A fast electric algorithm for calculating roundness error value under the minimum conditions such as Yang Xue. Measurement, 200 1.

Tian. Simplified algorithm for roundness error evaluation. Measurement, 200 1.4.