The rotation accuracy evaluation methods for the high-speed spindle of machining robots
High speed machining robots is designed for a number of high speed machining applications, the precision of which is one of the essential features. To increase precision of the robots, the study of accuracy evaluation methods is important. First, according to the demands for robots, key information of high-speed spindle of machining robots is determined, then it will be extracted by sensors and data acquisition card. Second, four different evaluating methods are introduced to assess the rotation accuracy, the results respectively solved by which are compared in detail. Furthermore, the particle swarm algorithm based on simulated annealing (SA-PSO) is introduced and theory analysis about the impact of simulated annealing factor is carried on to provide basis for giving the parameter better value. Finally, through the contrast between the evaluation results obtained by the proposed method and other optimization methods, the availability and precision of the SA-PSO is verified.
Applying particle swarm optimization algorithm to roundness error evaluation based on minimum zone circle
Abstract Minimum zone circle (MZC) method and least square circle (LSC) method are two most commonly used methods to evaluate roundness, but only the MZC method complies with the standard definition and can obtain the minimum roundness error value. The determination of the center of MZC is a nonlinear optimization problem which is suitable to be solved by particle swarm optimization (PSO) algorithms. In this paper, the standard PSO algorithm was introduced and theory analysis about the impact of value selection of some important parameters, such as inertia weight ω , on the algorithm’s stability and convergence was carried on so as to provide basis for giving these parameters better values. Furthermore, the superiority of making ω decrease linearly with iterations was verified through a computation experiment in terms of stability and accuracy, compared with the other three cases of ω  = 1, 0.5, 0. Based on the analysis, the novel PSO algorithm, with ω decreasing linearly from 0.9 to 0.4 and the LSC center as the initial positions of the particles, is implemented to obtain MZC-based roundness errors of sampling points collected from circular section profiles by a coordinate measuring machine (CMM). By comparing the novel PSO–MZC results with the LSC-based results, it is concluded that the former are a little smaller than the latter, which verifies that the novel PSO algorithm is feasible to calculate roundness error and the fact that a LSC-based one is generally larger than a MZC-based result; the values of the two roundness errors are both related to sample size and increase with an increase in the sample size with a decreasing increment.
Magnetic properties of Lu2Fe17 crystals
Abstract We present the results of crystal structure and magnetization studies of three single crystals grown from melts of different nominal compositions in the vicinity of the Lu2Fe17 stoichiometry. The ferromagnetic state of the crystals is strongly dependent on the real sample composition and the local atomic ordering. A drastic difference is observed in the behaviour of the ferro–antiferromagnetic transition, even in crystals for which almost identical composition and crystal parameters were determined by microprobe and X-ray analysis.