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.
Evaluation of buckling load and dynamic performance of steel shear wall retrofitted with strips made of shape memory alloy
One of the most imperfections of the steel shear wall is out of plane displacements that cause severe damage in both structural and non-structural elements. In this paper, the effects of shape-memory alloys on steel shear walls are investigated. First, a numerical analysis using the finite element method in ABAQUS software has been carried out according to an experimental test. The results of the numerical analysis have been verified with experimental results. Next, shape-memory alloy fibers have been added vertically and horizontally to various parts of the steel shear wall. The results show that retrofitting with the shape-memory alloy reduces the out-of-plane displacement of the steel shear wall under both cyclic and seismic loadings. Besides, the buckling load in the steel shear wall increases when it is retrofitted with the shape-memory alloy. Also, the total out-of-plane movement (accumulated absolute displacements) of the steel shear wall and non-structural damage are controlled by the characteristic of a shape-memory alloy material called “super-elastic”.