A Study On A Novel Geometric Parameter And Thread Measuring System For Revolving Workpieces

In this paper a coordinate measuring machine(CMM) for measuring inner and outer surfaces of bodies of rotation has been designed and developed. This new type of measuring machine measures not only dimensions, form and position errors, functional diameters of the threads of thin-walled parts online, but also can be modified to meet the changes of the measured pieces and can be used as a common CMM.The CMM can measure inner and outer features of rotational parts automatically. The whole measuring process is automatic. The measured data are stored and analyzed. A safety protection system is built in the CMM and can prevent accidents effectively. The key technologies solved in the thesis include the measurement of the functional diameters of threads, measurement of inner and outer surfaces of the part simultaneously, collision avoidance issues, unification of coordinate systems of the inner, outer measuring devices and the rotary table, calibration and error compensation techniques, accuracy assurance etc. In order to solve the above mentioned problems, a set of collision avoidance measures and calibration techniques are creatively developed. Safety is one of the most important problems in the design of the machine. Safety and reliability measures are taken from all possible aspects. Supplemental measures come into action once any of the protection measures fails. The calibration, adjustment and performance evaluation approaches of the measuring machine are studied in detail. A large number of experiments have been carried out to verify the performance of the measuring machine. Errors sources are analyzed and error compensation is introduced to make the machine meet the design requirements.The main creative ideals and innovations of the thesis include the follows.1. A special structure of the CMM for measuring bodies of rotation with high accuracy and high efficiency has been realized in the cylindrical coordinate system. A multi-column and multi-probe construction is developed to enhance the efficiency of the measuring process. The interference problem of the multiple contact probes has been solved successfully.2. A probe and method for measuring the functional diameters of threads have been developed successfully. A floating probe with a self- orientating full thread measuring tip is adopted. An approach for automatic aiming at and meshing with the thread of the workpiece has been developed. The measurement is carried out under the rotation of the workpiece and the linear motion of the probe in the axial direction of the workpiece to simulate the meshing process of the thread gage with the part. The functional diameter of the thread is measured directly and numerical value of the functional diameter and the orientation of the thread axis are obtained.3. A new method of thermal deformation error compensation has been put forward. A new idea which states the central position of the probe during bidirectional measurement is independent of the diameter of the measured workpiece is put forward. The thermal error compensation has been realized successfully under the workshop environment. It is much simpler and more accurate than the common practice based on thermal model and measuring the temperatures by mounting a large number of thermistors on the CMM.The developed CMM can measure and evaluate all the inner and outer features, including thread functional diameters, of the workpiece in a single mount. It possesses the advantages of high efficiency, high accuracy, high reliability, and meets the requirement of that the measurement is carried out under the same conditions as the part functions. It is a high efficient and high accurate shop floor CMM.