Error Averaging Effect in Parallel Mechanism Coordinate Measuring Machine
Error averaging effect is one of the advantages of a parallel mechanism when individual errors are relatively large. However, further investigation is necessary to clarify the evidence with mathematical analysis and experiment. In the developed parallel coordinate measuring machine (PCMM), which is based on three pairs of prismatic-universal-universal joints (3-PUU), error averaging mechanism was investigated and is analyzed in this report. Firstly, the error transfer coefficients of various errors in the PCMM were studied based on the established error transfer model. It can be shown how the various original errors in the parallel mechanism are averaged and reduced. Secondly, experimental measurements were carried out, including angular errors and straightness errors of three moving sliders. Lastly, solving the inverse kinematics by numerical method of iteration, it can be seen that the final measuring errors of the moving platform of PCMM can be reduced by the error averaging effect in comparison with the attributed geometric errors of three moving slides. This study reveals the significance of the error averaging effect for a PCMM.
Kinematic solution of 3-PSS parallel mechanism and its application in parallel CMM
A new style coordinate measuring system based on 3-PSS parallel mechanism was proposed to overcome the drawbacks and weaknesses of traditional Coordinate Measurement Machines(CMMs) and articulated arm CMMs and to realize 3D measurement with only one linear grating and one precision guide.A measurement model,a measuring error model as well as the error averaging effort of the parallel mechanism were investigated.Firstly,a 6-bar measurement model was achieved based on the theory of parallel kinematic mechanism.Then,the influence of bar length error and reading error from the liner grating were analyzed in detail and the hypostasis why parallel structure posses error averaging effort was revealed mathematically.Finally,the prototype CMM was introduced to its design,manufacturing and assemble and the experiment result was provided too.Results indicate that the measuring errors before compensation and instrument calibration in three dimensions are about 0.029 mm in x direction,0.045 mm in y direction and 0.058 mm in z direction.Obtained results can provide the direction for the design of new CMM protypes.
High-resolution multidimensional displacement monitoring system
The possibility of using quadrant detectors to develop a new optical system that can monitor all six degrees of freedom of mechanical workpieces with very high resolution is investigated. A prototype system based on this approach has been designed and built. Although the system is not fully optimized, our proposed system has already demonstrated some promising results. Using a thermally compensated laser source together with a pinhole spatial filtering system, we have demonstrated that lateral resolution better than 50 nm and angular displacement resolution better than 0.25 ?rad is achievable with this system.