Research On Straightness Error Measurement Of Positioning Platform Based On Binocular Vision

As the key parts of many precision machining or precision testing equipment,positioning platform provides precision positioning platform for manufacturing and measurement fields.Moving axis is the main component of the positioning platform,moving axis along the axis will produce straightness error,for precision machining,straightness error is one of the very important geometric errors,which will directly affect the positioning accuracy of the positioning platform.In a variety of straightness measurement equipment,the most widely used is the laser interferometer,however,laser interferometer installation and adjustment is difficult,general industrial use of ordinary laser interferometer,an installation adjustment can only measure one error,measurement efficiency is low and the price is expensive.Visual measurement has been widely used in error measurement due to its advantages of non-contact,fast measurement,high precision and low cost,which conforms to the current development trend of intelligent manufacturing.Therefore,the straightness error measurement of positioning platform based on binocular vision is proposed in this paper.By analyzing the structure of the positioning platform and the straightness error of the positioning platform's moving axis,combining the measurement principle of binocular vision and the straightness determination method,a synchronous measurement method of horizontal and vertical straightness of the positioning platform based on binocular vision was proposed.On this basis,the hardware and software system of binocular vision measurement of moving axis straightness was built,and the transformation of 2D pixel coordinate system and 3D coordinate system of vision system was completed by Zhang Zhengyou calibration method.The transformation from visual coordinate system to positioning platform coordinate system is completed by hand-eye calibration.An efficient and accurate method for locating the center of the circle is studied.A multi-scale and multi-structure morphological pixel edge detection method was used for coarse edge location.Based on coarse edge location,the improved Zernike moment was used for sub-pixel location of coarse edge points.Finally,the method of locating the center of concentric circles is established,which improves the precision of locating the center and the anti-noise performance.Meanwhile,the edge detection method combining coarse and fine edges improves the efficiency of edge detection.The straightness of Y axis of the positioning platform was measured experimentally.Firstly,according to the established binocular vision measurement system,the straightness of the positioning platform in two directions within the 20 mm travel of the Y axis was measured synchronously.The laser interferometer was used to evaluate the vision measurement accuracy,and the measurement deviations of the straightness errors in horizontal and vertical directions were 11.85% and 10.61% respectively.Aiming at the problems of small field of view of the vision measurement system and large total travel of Y axis to be measured,the measurement method of large travel straightness splicing and reconstruction was adopted to carry out the vision measurement of two straightness errors of total travel of Y axis 300 mm,and the laser interferometer was used to verify the measurement accuracy.The horizontal and vertical straightness errors of the 300 mm total stroke were 16.43% and 15.18%,respectively,which verified the effectiveness and accuracy of the vision measurement system.