Binocular vision-based 3D method for detecting high dynamic and wide-range contouring errors of CNC machine tools

Abstract

Periodic checking for contouring error in unloading conditions can effectively evaluate the dynamic performance of machining centers. Existing measurement devices have limitations in the high accuracy three-dimensional (3D) measurement of arbitrary contouring errors (e.g. ballbar and cross-grid encoder). Thus, in this paper, a cost-effective binocular vision-based 3D method for detecting high dynamic and wide-range contouring error of computer numerical control machine tools is proposed. With this method, the strobe lighting method is first presented to suppress the blurring effect of the newly designed 1024 coded targets that were embedded in the measurement fixture. Thereafter, an encoding and decoding method based on finding the optimal initial non-encoding region is proposed to automatically identify, match, and reconstruct the time-varying targets. Then, to enhance the performance of the vision system, a calculated method based on three visible non-collinear coded targets is presented to deduce the dynamic and large-scale contouring error. Finally, contouring error detection experiments are carried out in a self-built five-axis machine tool to validate the advantages of the method. Both the proposed vision method and cross-grid encoder are used to measure contouring errors of three types of trajectories under different feed rates. By comparing the difference between the two trajectories measured by the two devices, the experimental results illustrate that the mean vision detection error at 7 m min−1 is about 4.3 µm, which verifies the accuracy and effectiveness of the proposed vision measurement method.

Metrology and Measurement Systems

“…After the image processing, the pixel coordinates of the needle tip in the two cameras are extracted accurately and satisfy the epipolar constraint. The corresponding image plane coordinates denoted by p 1 = (x 1 , y 1 ), p 2 = (x 2 , y 2 ) arere calculated by equation (7). The camera coordinates of both cameras are P c1 (x c1 , y c1 , z c1 ) and P c2 (x c2 , y c2 , z c2 ) respectively from which the information on the depth z c1 , z c2 needs to be calculated.…”

“…Stereo vision, as a typical measurement technology, is widely used in many areas, such as geometry measuring, robot path correction, and quality inspection [4][5][6][7][8][9][10][11][12][13]. Xiang et al [14] used the binocular vision technology and the relative measurement principle to determine the bayonet sizes of large automobile brake pads.…”

Possibilities of Evaluating the Dimensional Acceptability of Workpieces Using Computer Vision

“…Three-dimensional surface roughness parameters are compared with texture parameters. Contouring errors of CNC machine tools are investigated in paper [20]. Binocular vision-based 3D method for detecting high dynamic and wide-range contouring errors of CNC machine tools has been successfully proposed.…”

Error analysis of precision measurement with monocular vision

“…These systems can generally be categorized into three groups: monocular, binocular, and multi-camera vision systems. Compared with binocular [11,12] and multi-camera systems [13,14], monocular vision systems employ a single camera to capture target images and then use algorithms to determine the pose relationship between the target coordinate system and the camera coordinate system. This approach has several advantages, including lower cost, greater flexibility, mature algorithms, high accuracy, and reliability.…”