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.
Error modelling and validation of a high-precision five degree of freedom hybrid mechanism for high-power high-repetition rate laser operations
The accuracy, repeatability and speed requirements of high-power laser operations demand the employment of five degree of freedom motion control solutions that are capable of positioning and orientating the target with respect to the laser(s)-target interaction point with high accuracy and precision. The combined serial and parallel kinematic (hybrid) mechanism reported in this paper is a suitable candidate for this purpose; however, a number of error sources can affect its performance. A kinematic model to analyse the errors causing the positional and orientational deviations of the target is described considering two rotational degrees of freedom of the hybrid mechanism. Strategies are outlined to simplify the error analysis and to determine the error parameters of the mechanism using the error model and an experimental technique.
Assessing geometrical errors of multi-axis machines by three-dimensional length measurements
In this paper a method is presented for assessing geometrical errors of multi-axis machines based on volumetric three-dimensional length measurements. A universal machine error model is proposed since a large variety of machine configurations exists. Such models can be used for software error compensation techniques in order to improve the machine’s positioning behaviour as well as for diagnostic purposes. Length measurements are chosen for the measurement of the positioning errors of a multi-axis machine because these measurements can be executed in a short period of time in a relatively simple way combined with a high accuracy. In order to get comparable results for the geometrical errors as measured with conventional techniques, i.e., laser interferometry, the design of the measurement setup as well as the formulation of the machine error model (including parameter correlation effects) appeared to be of major importance and are subject of this paper.