| Parallel mechanism is widely applied in various fields in recent30years, such asthe intelligent robot, parallel tools and micro-nano motion stage, on account of itsadvantages including high degree of modularization, rapid motion velocity andsimple structure. This project is supported by NSFC, which aimed at transplantingparallel mechanism to coordinate measuring machine design. A new CMM withparallel mechanism was proposed here, which will partly compensate the inherentshortcomings and limitations in traditional CMM with series mechanism, andimprove measuring accuracy and efficiency, especially when machine works in highspeed.The novel coordinate measuring system based on a spatial3-PSS parallelmechanism, which allows3-DOF of pure translation and could build the traditionalorthogonal coordinate system in accordance with the actual measurement. Due tothe symmetrical weakly-coupled property, it is easy to establish contractedmeasurement model and error model, control measurement system conveniently anduse software to compensate precision. This CMM could realize3D measurementwith only one linear grating, one precise guide and three reading heads.Firstly, the prototype CMM is introduced to its foundations. The kinematics modeland error mode are carried out by the coordinate transformation method and thetheory of the spatial mechanics. Then, the workspace is verified by computersimulation and the optimization methods of workspace are given. After the inversekinematics equation is solved, the Jacobian matrix is obtained. It is used to foundall singularity points of workspace. Thirdly, the sources of the errors in the wholesystem are analyzed. The mechanical errors and the input parameter affecting theprobe position accuracy are focus on too. Then, the hardware and the software ofmeasuring system are discussed in detail. The function test of the data acquisitionis finished in the end. Experiment results indicate that the performance index of thecurrent prototype meets the expected specifications. |
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