Research On Vision Measurement Technology Of Rectangular Spline Shaft Based On Line Structure Light

As a typical shaft tooth part,the rectangular spline shaft is widely used in mechanical transmission.Its shape and size error directly affect the friction,wear and matching nature between parts.Since the shape characteristics and measurement indexes of the rectangular spline shafts combine the typical geometric elements and geometric tolerances of most mechanical parts,the visual non-contact measurement technology of the rectangular spline shaft is studied,which can be used not only for the dimensional measurement of spline shafts in production,but also can be directly or slightly modified used for dimensional inspection of most other mechanical parts.In this paper,a line structured light vision measurement system is built by line structure light laser,industrial camera,computer and measurement experiment rig.According to the geometric characteristics of the spline shafts,a full-size measurement method of spline shafts based on line structure light vision is proposed.The full-size includes: diameter of the spline shaft(large and small diameter),concentricity error,key width,and position error of each key.Firstly,this paper studies the strip center point detection algorithm and the line structure light calibration algorithm in the line structure light optical vision system.The paper determines the light bar area in the image based on pyramid down sampling and gray value matching method.In this area,the Steger algorithm is used to obtain the pixel coordinates of the center point in the light strip.The method improves the detection speed of the center point of the light strip under the premise of ensuring the detection accuracy.In the line structure light calibration algorithm,this paper uses the spatial geometric relationship to establish the error point determination condition,and filters the data points of the participating structure light calibration to overcome the limitation of using the image gray information to judge the error point.Secondly,according to the geometric characteristics of the rectangular spline shafts,when the beam plane projected by the line laser(collectively referred to it as the light plane in this paper)intersects the spline shafts,the large and small diameters of the spline shaft on the intercepting surface correspond to the short axis diameters of the two spatial ellipse,using this geometric relationship,the measurement model of spline shaft large,small diameter and coaxiality is established respectively.In the diameter measurement model,a plane parallel to the light plane is used as a coordinate plane to establish a local coordinate system.With this coordinate system,the spatial ellipse fitting problem can be transformed into a plane ellipse fitting problem.Using the intersection of the spline shaft and the light plane,and by calculating the distance from the center point of the light strip to the intersection point on the surface of the spline shaft,the center point of different regions of the spline shafts is automatically divided,which lays a foundation for the automatic measurement of the spline shafts.In the coaxiality measurement,the translation rig is used to obtain the intersection planes of multiple light planes and spline shafts.The total least squares is used to obtain the axis equation of the small diameter corresponding cylinder,and calculate the distance from the center point of the ellipse corresponding to the large diameter to the axis on each section,then the concentricity error is obtained based on the principle of minimum containment.Once more,in this paper,the measurement model of the key width and the position of each key is proposed by using the center point of the light stripe on both sides of the spline.In the key width measurement,the spline shaft is rotated and the rotation angle is recorded.The coordinate transformation relationship can be used to restore the center point of all the light strips on the side of the spline to the initial position of the rotation,and establish a projection plane perpendicular to the axis.All the center points on the side of the spline are projected onto the plane,the line is fitted by using the center point on one side,and the distance from the center point of the other side to the line is calculated to obtain the width of each key.Based on the measurement of the key width,according to measurement method of using three-coordinate instrument to obtain the position error of spline,this paper proposes a spline position measurement algorithm using distance iteration.Finally,through the linear structured light measurement system and the measurement algorithm of size and tolerance,the actual measurement of the rectangular spline shaft is carried out,and the measurement results are compared with the measurement results obtained by the three-coordinate measuring machine,and the correctness and feasibility of the measurement method in this paper are verified.