Evaluation and development of a method for compensating the positioning error of computer numeric control equipment

Abstract

In the manufacturing process, Computer Numerical Control is widely used to process products that require a high level of accuracy. It is found that during product processing, Computer Numerical Control is still unable to fully counteract the influence of vibration and the presence of uneven product surfaces. In this paper, the stabilization mechanism developed, known as the Modified Stewart platform, which has a 3 Degrees of Freedom and can rotate around the X and Y axes and move translationally along the Z axis. This platform can be used to improve the accuracy and stability of the Computer Numeric Control tool. In this research, the positioning accuracy of the Modified Stewart platform has been evaluated. In this research, a mock-up or prototype and a simulation model of the Modified Stewart platform was developed. The data to be studied is the inclination angle of the platform. In the experiment, to determine the positioning error, the variable being changed acquires not only the linear movement, but also the angle of the X-Y plane. By changing the angle contained in the X-Y plane, it can be seen the influence of the X-Y angle on the position error or angle of the Z-A plane. The simulation was carried out on MATLAB. The mathematical model in this study is to find the platform position or angle. To simplify the calculation, the Modified Stewart platform was depicted in the form of a trapezoid. The results of the angle in the simulation will be compared with the result of the angle on the mock-up Modified Stewart platform. The trapezoidal parameter used in the simulation corresponds to the parameters on the mock-up modified Stewart platform. The simulation provided information about the angle of inclination, height, length of its sides, and the relative length of sides. It was found that the position or angle movement of the platform is in accordance with the calculation or simulation model that has been developed, and the positioning error data of the platform is very small and it changes constantly. It should be noted that the presented method can be used to evaluate the platform positioning error and consequential calibration of the mechanisms with spatial kinematic. The positioning error at various mobile links positions is changing, but during the movement in just one direction it remains almost constant. The position error caused by the platform mechanism can be minimized by redesigning the platform and using components that can provide a much more precise movement, moreover, using the preliminary measurements it is possible to build a table containing corrections for the control program to access the correct position of the moving platform. The accuracy and the stability of its movement can be improved and the platform can be applied to Computer Numerical Control. The method developed allows to estimate the moving platform positioning error of the mechanism with spatial kinematic. Thus, the method developed can be eliminated or compensated. It is possible to calibrate the moving platform movements in automatic mode as well.