Study Of Measurement Method Of Fine-pitch Gear Based On Image Processing

The transmission gears used in high precise apparatuses and instruments are mostly fine-pitch gears that can drive stably. The precision of fine-pitch gear directly affects the working performance and operating time of apparatuses and instruments. Whether a fine-pitch gear is eligible or not just can judged by measuring its peculiarities. But many difficulties are brought in measuring process because of the specialties of a fine-pitch gear, which are listed in the following text. Firstly, low stiffness of the gear makes it to be deformed easily; secondly, small intertooth of the gear makes it difficult to be adjusted and aligned; thirdly, because of large varieties fine-pitch gears used in different conditions and occasions, difficulties are met in fixing and orientation the gear ; otherwise, because of the micro dimension of the gear, the automation of the measuring apparatus is strictly requested, and the mechanical structure of the measuring system is restricted.Because of all the reasons listed before, the testing machines and equipments of the fine-pitch gears are scarce in our country. In order to change the under-developed situation, great emphasis should be put on the development of measuring machines and equipments. Based on the actualities and developing requests of our nation's gear industry, testing and measuring Department of Sichuan University together with Chengdu tool research institute are researching the feasibility of using image processing in testing of the fine-pitch gear, and trying to find a universal way to measure the fine-pitch gear.In this paper, the measuring methods of a fine-pitch gear's common parameters and mismachining tolerance were introduced. Combined with the existent methods, one new technique using image probe to test the fine-pitch gear untouched was put forward. In testing process, after the point coordinates of the involute tooth outline were measured, the involute could be fitted. Using the included angle between the line through the start point of the involute and the centre of base circle and the Y axes' forward direction, other parameters and mismachining tolerances of the fine-pitch gear can be calculated.In the first chapter of this paper, the purpose, meaning and task of this subjectwas expounded, the measuring actuality of fine-pitch gear was introduced; in the second, the involute's formation and characters were introduced, the definitions of the fine-pitch gear' parameters and mismachining tolerances were recommended too. Third, the measuring process of shaft gear, the fitting method of involute and the data processing were introduced. The forth part discussed the image processing method such as the image's edge enhancement, obtaining the pixel axis and converting the pixel axis to mechanical axis, etc. in the fifth chapter a picture was taken as an example in order to explain the data processing and the parameters and mismachining tolerances of shaft gear and pore gear. In succession, chapter 6 analysed the possible error terms in measuring and data processing, and put forward the, method to eliminate or reduce these error terms. Finally the feasibility of this method was analyzed, and the future work was expected.In this project, the PMC650 non-contact three-coordinates measuring machine with image gauge head was used for testing. Using visual C++, the gained pictures were processed and the edge points axis of the gear's tooth outline was obtained. After the data processing, all parameters and error terms can be calculated. Experiments had proved that this method, based on image processing, was feasible to measure the fine-pitch gear.