Part auxiliary clamping method based on three-dimensional measurement

Abstract

The invention provides a part auxiliary clamping method based on three-dimensional measurement. Comprising the following steps: 1, calibrating a rotation matrix of a measurement coordinate system relative to a machine tool coordinate system; 2, calibrating a translation vector of the measurement coordinate system relative to a machine tool coordinate system; 3, acquiring a surface point cloud of the to-be-processed blank in the measurement coordinate system; and 4, determining the moving path of the cutter according to the position of the blank and the CAD design model of the part. Unification of a part design model coordinate system and a machine tool coordinate system is achieved mainly through the three-dimensional point cloud of the blank and the conversion relation between all the coordinate systems, operation is easy, the method is suitable for machining of various parts, good stability is achieved, clamping of the blank can be assisted, and the efficiency and reliability of part machining of the machine tool are effectively improved.

Description

Technical Field

[0001] The invention relates to a parts auxiliary clamping method, and specifically to the field of three-dimensional point cloud data acquisition and processing, and in particular to measurement system calibration and grating fringe three-dimensional scanning. Background Art

[0002] When using CNC machine tools to process parts, you first need to determine the position of the blank in the machine tool coordinate system before planning the tool movement path. If the clamping position of the blank is not accurately positioned, problems such as insufficient machining allowance may occur; at the same time, if the positioning takes too long, it will seriously affect the processing efficiency of the CNC machine tool. In order to improve the quality and efficiency of CNC machine tool processing, it is necessary to use a part auxiliary clamping method to quickly provide the machine tool with accurate clamping position information of the blank.

[0003] The current auxiliary clamping method mainly relies on the contact probe installed on the machine tool to detect whether the surface of the blank is parallel to a certain coordinate axis of the machine tool coordinate system. If it is not parallel, the blank is rotated and tested again until the surface of the blank is parallel to the coordinate axis of the machine tool coordinate system. This method obtains a small amount of data, is inefficient, and is only applicable to blanks with regular shapes. Summary of the invention

[0004] In order to solve the problems of low efficiency and small application scope of traditional auxiliary clamping methods, the present invention discloses a part auxiliary clamping method based on three-dimensional measurement, which uses marker points and a ball standard to realize the calibration of the measurement coordinate system relative to the machine tool coordinate system, and realizes the planning of the machine tool tool processing path by measuring and transforming the surface point cloud of the blank part and aligning the design model, and includes the following steps:

[0005] (1) Calibrate the rotation matrix of the measurement coordinate system relative to the machine tool coordinate system.

[0006] First, fix the 3D measurement system on the machine tool, keep its position unchanged relative to the machine tool, then paste the backlight reflection mark point on the machine tool axis, take a picture of the mark point using the 3D measurement system, and calculate the 3D coordinates of the mark point in the measurement coordinate system based on the principle of binocular stereo vision. Control the machine tool axis to move along the X, Y, and Z axes of the machine tool coordinate system respectively, and use the 3D measurement system to measure the position change of the mark point before and after moving along each axis, so as to obtain the direction vectors n_x, n_y, and n_z of the three axes of the machine tool coordinate system in the measurement coordinate system, and calculate the rotation matrix R = [n_x, n_y, n_z] between the two coordinate systems.

[0007] (2) Calibrate the translation vector of the measurement coordinate system relative to the machine tool coordinate system.

[0008] Continue to keep the position of the 3D measurement system relative to the machine tool unchanged, fix the ball standard on the machine tool, use the 3D measurement system and the machine tool contact probe to measure the surface point cloud of the ball standard and fit the spherical surface, and obtain the coordinates of the center of the ball in the measurement coordinate system and the machine tool coordinate system, which are x_1 and x_2 respectively. Based on this, calculate the translation vector T = x_1-R·x_2 between the origins of the two coordinate systems.

[0009] (3) Perform three-dimensional measurement to obtain the surface point cloud of the blank to be processed in the measurement coordinate system.

[0010] The 3D measurement system consists of two cameras and a phase fringe projector. The projector projects multi-frequency phase-shifted sinusoidal grating fringes at multiple brightnesses onto the surface of the part to be measured. Multiple fringes of different frequencies are selected at each brightness, and N vertical fringe patterns with a phase difference of 2π / N are projected at each frequency. The left and right cameras of the 3D measurement system are triggered to take pictures each time the projection is performed. After the continuous phase image of the projected part surface is obtained through phase solution and phase expansion, the same-name points are matched and 3D reconstructed according to the polar line constraint relationship between the two cameras to obtain the 3D point cloud data of the surface of the blank to be processed.

[0011] (4) Determine the tool movement path based on the blank position and part design model.

[0012] Assume that the coordinate of a point on the surface of the blank in the measurement coordinate system is p_1, and the corresponding point coordinate in the machine tool coordinate system is p_2. According to the rotation matrix R and translation vector T between the two coordinate systems, p_2 = R^(-1)·(p_1+T). The blank surface point cloud in the measurement coordinate system is transformed to the machine tool coordinate system, and the CAD design model of the part is aligned to the transformed blank surface point cloud. The moving path of the CNC machine tool tool is planned according to the position of the CAD design model of the part after alignment.

[0013] The present invention mainly utilizes the three-dimensional point cloud of the blank and the conversion relationship between each coordinate system to realize the unification of the part design model coordinate system and the machine tool coordinate system. It is simple to operate, has a wide range of applications, has good stability and repeatability, can assist in the clamping of the blank, and effectively improves the efficiency and reliability of CNC machine tool processing parts. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 A flowchart of a part auxiliary clamping method based on three-dimensional measurement is provided in an embodiment. DETAILED DESCRIPTION

[0015] In order to better understand the present invention, the technical solution of the present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0016] See attached Figure 1, a part auxiliary clamping technology based on three-dimensional measurement, including the following steps:

[0017] (1) Calibrate the rotation matrix from the 3D measurement system coordinate system to the machine tool coordinate system.

[0018] First, fix the 3D measurement system on the machine tool and keep the posture unchanged. Fix a plane target with a circular mark point on the machine tool axis so that the normal of the target points to the 3D measurement system for easy measurement. Then control the machine tool axis to drive the target to translate along the X, Y, and Z axes of the machine tool coordinate system. Before and after each movement, use the binocular camera of the 3D measurement system to take pictures of the circular mark points on the target and extract the coordinates of the center of the circle. Use the principle of binocular stereo vision to achieve 3D reconstruction of the center of the mark point. According to the change of the 3D coordinates of the mark point before and after the movement of the machine tool axis, calculate the 3D vector corresponding to the coordinate axis in the machine tool coordinate system in the measurement coordinate system. Assume that the direction vectors obtained by moving the machine tool axis three times are n respectively. x 、n y and n z , then there are two rotation matrices between the coordinate systems R = [n x , n y , n z ].

[0019] (2) Calibrate the translation vector from the 3D measurement system coordinate system to the machine tool coordinate system.

[0020] Keep the three-dimensional measurement system fixed, fix a spherical standard within the measurement field of view of the three-dimensional measurement system, use the three-dimensional measurement system and the machine tool contact probe to measure the surface point cloud of the spherical standard and fit the spherical surface, and obtain the coordinates of the center of the sphere in the measurement coordinate system as x1, and the coordinates of the center of the sphere in the machine tool coordinate system as x2, thereby calculating the translation vector T = x1-R·x2 between the origins of the two coordinate systems.

[0021] (3) Clamp the blank to be processed on the machine tool, and use the 3D measurement system to measure the 3D point cloud of the surface of the blank.

[0022] The blank to be processed is fixed within the field of view of the 3D measurement system on the machine tool. The projector of the 3D measurement system is controlled to project sinusoidal grating stripes at multiple brightnesses onto the surface of the part to be measured. Three groups of sinusoidal stripes with spatial periods of 15, 16, and 17 pixels are projected at each brightness. Four vertical stripe images with a phase difference of π / 2 are projected at each frequency. The left and right cameras of the 3D measurement system are triggered to take pictures each time the projection occurs. After the continuous phase image of the projected part surface is obtained through phase solution and phase expansion, the same-name points are matched and 3D reconstructed according to the polar constraint relationship between the two cameras to obtain the 3D point cloud data of the surface of the blank to be measured.

[0023] (4) Determine the tool movement path based on the blank position and part design model.

[0024] According to the rotation matrix R and translation vector T of the measurement coordinate system converted to the machine tool coordinate system, the coordinate transformation relationship is p2 = R -1 (p1+T), where p1 is the coordinate of a point on the blank surface in the measurement coordinate system, and p2 is the coordinate of the corresponding point in the machine tool coordinate system. After obtaining the 3D point cloud of the blank surface in the measurement coordinate system, convert it to the machine tool coordinate system according to the coordinate transformation formula, and then align the CAD design model of the part to the inside of the 3D point cloud of the blank surface, and plan the tool movement path of the CNC machine tool according to the position of the CAD design model of the part after alignment.

Claims

1. A parts auxiliary clamping method based on three-dimensional measurement, characterized in that The conversion from the part design model coordinate system to the machine tool coordinate system is realized through the 3D measurement system, so as to plan the tool movement path, including the following steps: (1) Calibrate the rotation matrix of the measurement coordinate system relative to the machine tool coordinate system; (2) Calibrate the translation vector of the measurement coordinate system relative to the machine tool coordinate system; (3) Obtaining a surface point cloud of the blank to be processed in a measurement coordinate system; (4) Determine the tool movement path based on the blank position and part design model.

2. The method for auxiliary clamping of parts based on three-dimensional measurement according to claim 1, characterized in that: The (1) method fixes the position of the three-dimensional measurement system relative to the machine tool coordinate system, pastes the backlight reflection mark point on the machine tool motion axis, controls the machine tool to translate the mark point along the X, Y, and Z axes of the machine tool coordinate system, and uses the three-dimensional measurement system to measure the position change of the mark point before and after moving along each axis, thereby obtaining the direction vector n of the three axes of the machine tool coordinate system in the measurement coordinate system. x 、n y and n z , based on which the rotation matrix R between the two coordinate systems is calculated = [n x , n y , n z ].

3. The method for auxiliary clamping of parts based on three-dimensional measurement according to claim 1, characterized in that: The (2) method keeps the posture of the three-dimensional measurement system fixed relative to the machine tool coordinate system, clamps a spherical standard on the machine tool, uses the three-dimensional measurement system and the machine tool contact probe to measure the surface point cloud data of the spherical standard and fit the spherical surface, and obtains the coordinates of the center of the sphere in the two coordinate systems, which are x1 and x2 respectively, and calculates the translation vector T = x1-R·x2 between the origins of the two coordinate systems.

4. The method for auxiliary clamping of parts based on three-dimensional measurement according to claim 3 is characterized in that: The (3) described above uses a three-dimensional measurement system composed of a binocular camera and a phase fringe projector. The projector of the three-dimensional measurement system projects multi-frequency phase-shifted sinusoidal grating stripes at multiple brightnesses onto the surface of the part to be measured. Stripes with different frequencies are selected for use at each brightness. N vertical fringe patterns with a phase difference of 2π / N are projected at each frequency. The left and right cameras of the three-dimensional measurement system are triggered to take pictures each time projection occurs. After a continuous phase map of the projected part surface is obtained through phase solution and phase expansion, the same-name point matching and three-dimensional reconstruction are performed based on the polar line constraint relationship between the two cameras to obtain complete point cloud data of the surface of the blank.

5. The method for auxiliary clamping of parts based on three-dimensional measurement according to claim 1, characterized in that: The above (4) assumes that the coordinates of a point on the surface of the blank in the measurement coordinate system are p1, and the corresponding point coordinates in the machine tool coordinate system are p2. According to the rotation matrix R and translation vector T between the two coordinate systems, p2 = R -1 (p1+T), based on which the surface point cloud of the blank in the measurement coordinate system is converted to the machine tool coordinate system, and the CAD design model of the part is aligned to the surface point cloud of the blank. The moving path of the CNC machine tool tool is planned according to the position of the CAD design model of the part after alignment.

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