The Research On Hole Roundness' Automatic Measurement System

The rapid developments of the computer and sensor technology have brought about a new revolutionary change in the measuring instrument. The measuring instrument is tending to be multi-functions,integrated and intelligent. Hole parts is one kind of components which is widely used in modern machine. Researching and developing this kind of measuring instrument for improving the assembling accuracy, extend the life of equipment is of great importance. This paper take the locomotive engine crankshaft hole as research object, and has developed a round aperture of automatic detection system.Based on the analysis of trends in the development of automatic detection system and the basis of follow principles that concluded convenience, practical and economical, the hardware and software of the system is designed. System hardware core adapts a cost-effective PC and the PLC. The hardware design took modern sensory technology and signal treatment technology as the scheme support. Choose eddy current sensor to gather the signals and realize high accuracy gathering of the data. And choose PLC,step-motor that can control the data acquisition accuracy. In addition, the paper determined high accuracy automatic detection system device principle which according to the principle of the eddy current sensor and step-motor. The paper describes design method and application of various modules forming the software system in detail. Meanwhile a corresponding program is developed. This program realizes good man-machine interface function quickly and reliability signal processing function strongly date signal storage and transact function.Finally, four roundness error's evaluation methods and basic principles are stated in this paper. Those methods include the minimum circumscribed circle,the least square circle method,the maximum inscribed circle and the minimum region method. Based on the principle of least square method, the roundness error is evaluated by least square circle method. A new method that can location the centre of a circle is proposed on the above basis. In order to improve the calculation speed of roundness error evaluation, the paper have summarized a variable step iterative algorithm, which can accelerate the data processing.Compared with traditional instrument, the measuring instrument designed in the papers has great advantages in the measurement method, data processing methods and so on.Using this system to measure roundness, can get a high reliability, real-time, and accuracy has also increased substantially.