Multi-degree-of-freedom rotation error acquisition method and device, medium and equipment

Abstract

The invention discloses a multi-degree-of-freedom rotation error obtaining method and device, a medium and equipment, and relates to the technical field of precision measurement, and the method comprises the steps: installing a double-ball target on the end face of a rotary table, and obtaining a plurality of different rotation angle images when the double-ball target rotates along with the rotary table; detecting the plurality of images with different rotation angles, determining the three-dimensional coordinates of the sphere center positions of the plurality of double-sphere targets, averaging the three-dimensional coordinates of the sphere center positions of the plurality of double-sphere targets, and generating the motion trails of the sphere centers of the double-sphere targets; fitting the motion trail of the center of the double-ball target by adopting a least square circle method to obtain two base circle center coordinates of the motion trail on a two-dimensional plane, and obtaining a multi-degree-of-freedom rotation error of the rotary table according to the two base circle center coordinates; wherein the multi-degree-of-freedom rotation error comprises an axial rotation error, a radial rotation error and an inclined rotation error, and efficient measurement of the multi-degree-of-freedom rotation error is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of precision measurement, and particularly relates to a method, device, medium and equipment for obtaining multi-degree-of-freedom rotary errors. Background Art

[0002] In equipment such as measuring instruments, numerically controlled machine tools, and medical imaging instruments, rotary components are key mechanical components, such as rotary components of precision turntables, spindles, etc. When they are applied in measuring instruments, their rotary errors will cause the measured object to shift and affect the measurement results; when applied in machine tools, the rotary errors of the spindles will affect the machining quality; when applied in a micro-nano CT system, the rotary errors of the precision turntable will affect its imaging quality. Therefore, the multi-degree-of-freedom rotary errors are measured with the goal of error compensation.

[0003] Traditional rotary error measurement methods include the displacement sensor method, the laser interferometry method, and the vision measurement method. Among them, the displacement sensor method is complex to install, the laser interferometry method is costly, and the simplest and most efficient one under the premise of meeting the measurement accuracy is the vision measurement method. However, the single-objective vision measurement method cannot measure multi-degree-of-freedom rotary errors at one time. Summary of the Invention

[0004] The present invention provides a method, device, medium and equipment for obtaining multi-degree-of-freedom rotary errors to solve the above problems existing in the prior art, that is, the problem of how to efficiently measure multi-degree-of-freedom rotary errors at one time in the prior art. The present invention provides a method for obtaining multi-degree-of-freedom rotary errors, and the method includes: Install a double-ball target on the end face of the turntable, and obtain multiple images of different rotation angles when the double-ball target rotates with the turntable; Detect multiple images of different rotation angles, determine the three-dimensional coordinates of the centers of the multiple double-ball targets, calculate the average value of the three-dimensional coordinates of the centers of the multiple double-ball targets, and generate the motion trajectory of the center of the double-ball target; By projecting the motion trajectory of the center of one of the targets onto a two-dimensional plane, multiple projection points are obtained, and the obtained projection points are subjected to least squares circle fitting to obtain the center coordinates and radius of the base circle of the motion trajectory on the two-dimensional plane. According to the center coordinates and radius of the base circle, the inner and outer envelope circles of the motion trajectory are obtained, and the radial rotary error is obtained according to the inner and outer envelope circles of the motion trajectory; By projecting the motion trajectory of the center of the other target onto a plane perpendicular to the two-dimensional plane, an axial runout curve and the center coordinates of the base circle of the motion trajectory on the plane are obtained, and the maximum amplitude on the axial runout curve is used as the axial rotary error; According to the center coordinates of the two base circles, the line connecting the two centers is used as the average rotation axis when the turntable rotates, and the tilt rotary error is obtained.

[0005] Optionally, the detection of multiple images with different rotation angles specifically includes: By using an edge detection algorithm and a circle detection algorithm, feature extraction and detection are performed on the contour of the target ball in multiple images with different rotation angles.

[0006] Optionally, by projecting the motion trajectory of the center of one target ball onto a two-dimensional plane to obtain multiple projection points, performing least-squares circle fitting on the obtained projection points to obtain the center coordinates and radius of the base circle of the motion trajectory on the two-dimensional plane, and obtaining the inner and outer envelope circles of the motion trajectory based on the center coordinates and radius of the base circle, and obtaining the radial runout error according to the inner and outer envelope circles of the motion trajectory, specifically including: Project the motion trajectory of the ball center onto the xoy plane, and use the following formula to obtain the equation of the circle: ; Construct an objective function according to the equation of the circle: ; where the xoy plane is a plane perpendicular to the connection line of the two base circle center coordinates; According to the objective function, obtain the center coordinates of the base circle of the trajectory on the plane, the radius of the base circle is , draw the inner and outer envelope circles of the trajectory with as the center, the radii are and respectively, and use the following formula to obtain the radial runout error: ; where is the radial runout error.

[0007] Optionally, by projecting the motion trajectory of the center of the other target ball onto a plane perpendicular to the two-dimensional plane, obtaining the axial runout curve and the center coordinates of the base circle of the motion trajectory on the plane, and taking the maximum amplitude value on the axial runout curve as the axial runout error, specifically including: Project the motion trajectory onto the plane to obtain the axial runout curve and the center coordinates of the base circle on the plane, and take the maximum amplitude value on the axial runout curve on the plane as the axial runout error.

[0008] Optionally, according to the two base circle center coordinates, taking the connection line of the two centers as the average rotation axis during the rotation of the turntable, and obtaining the tilt runout error, specifically including: Connect the two centers, and take the connection line of the two centers as the average rotation axis during the rotation of the turntable, and The rotation angle upwards The corresponding points are respectively and , and the tilt rotation error is obtained by using the following formula: ; Wherein, and are respectively and The radial distances from these two points to the average rotation axis, is and The axial distance of the plane where these two points are located, is the tilt rotation error.

[0009] Optionally, the turntable rotates at a speed of 5 degrees per second.

[0010] Optionally, by placing the double-ball target in the center of the binocular camera's field of view and the axis of the double-ball target is in the direction perpendicular to the optical axis of the binocular camera, multiple spatial position images of the double-ball target during rotation with the turntable are obtained.

[0011] The present invention provides a multi-degree-of-freedom rotation error acquisition device, including: An acquisition module, configured to install the double-ball target on the end face of the turntable and acquire multiple different rotation angle images of the double-ball target during rotation with the turntable; A motion trajectory generation module, configured to detect multiple different rotation angle images, determine the three-dimensional coordinates of the centers of the multiple double-ball targets, calculate the average value of the three-dimensional coordinates of the centers of the multiple double-ball targets, and generate the motion trajectory of the centers of the double-ball targets; A multi-degree-of-freedom rotation error determination module, configured to project the motion trajectory of one of the target centers onto a two-dimensional plane to obtain multiple projection points, perform least squares circle fitting on the obtained projection points to obtain the center coordinates and radius of the base circle of the motion trajectory on the two-dimensional plane, obtain the inner and outer envelope circles of the motion trajectory according to the center coordinates and radius of the base circle, and obtain the radial rotation error according to the inner and outer envelope circles of the motion trajectory; project the motion trajectory of the other target center onto a plane perpendicular to the two-dimensional plane to obtain the axial runout curve and the center coordinates of the base circle of the motion trajectory on the plane, and use the maximum amplitude on the axial runout curve as the axial rotation error; according to the two center coordinates of the base circles, use the line connecting the two centers as the average rotation axis during the rotation of the turntable to obtain the tilt rotation error.

[0012] The present invention provides a computer-readable storage medium, and the storage medium stores a computer program, and when the computer program is executed by a processor, the above-mentioned multi-degree-of-freedom rotation error acquisition method is implemented.

[0013] The present invention provides a computer device, including a memory, a processor, and a computer program stored on the memory and executable on the processor. When the processor executes the program, the above-mentioned multi-degree-of-freedom rotation error acquisition method is implemented.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention provides a multi-degree-of-freedom rotation error acquisition method. By installing a double-ball target for auxiliary measurement on the end face of a precision turntable, collecting images of the double-ball target at multiple positions during one rotation of the device under test, and using image processing technology to calculate the three-dimensional coordinates of the center of the target ball, it is possible to achieve a one-time measurement of the multi-degree-of-freedom rotation error while meeting the measurement accuracy. In addition, the present invention uses binocular vision technology to measure the rotation error, breaking the limitation that traditional vision measurement methods cannot simultaneously measure axial, radial, and tilt rotation errors. It can accurately measure errors in a non-contact manner through image processing algorithms, quickly obtain the three-dimensional spatial information of an object, reduce manual adjustment and operation steps, making the entire measurement process more simple and efficient, and applicable to a variety of devices and environmental conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The accompanying drawings herein are incorporated into the specification and form a part of the specification, showing embodiments consistent with the present invention and used together with the specification to explain the principles of the present invention.

[0016] Figure 1 It is a flowchart of a multi-degree-of-freedom rotation error acquisition method provided by an embodiment of the present invention; Figure 2 It is a technical roadmap of a multi-degree-of-freedom rotation error acquisition method provided by an embodiment of the present invention; Figure 3 It is a schematic diagram of the detection result of a circle detection algorithm provided by an embodiment of the present invention; Figure 4 It is a schematic diagram of the principle of multi-degree-of-freedom rotation error measurement provided by an embodiment of the present invention; Figure 5 It is a schematic diagram of the movement trajectory of the target provided by an embodiment of the present invention; Figure 6 It is a schematic diagram of the structure of a multi-degree-of-freedom rotation error acquisition device provided by an embodiment of the present invention; Figure 7 It is a schematic diagram of the structure of a double-ball target provided by an embodiment of the present invention; Figure 8 It is a schematic diagram of a computer device for a multi-degree-of-freedom rotation error acquisition method provided by an embodiment of the present invention; In the figure, 1 is a backlight; 2 is a double-ball target; 3 is a binocular camera measurement device; 4 is a precision turntable. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0017] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below in conjunction with the accompanying drawings in the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts fall within the scope of protection of the present invention.

[0018] The technical solutions of the present invention and how the technical solutions of the present invention solve the above technical problems will be described in detail below with specific embodiments. These several specific embodiments below can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present invention will be described below in conjunction with the accompanying drawings.

[0019] As Figure 1 and Figure 2 shown, a method for obtaining multi-degree-of-freedom rotational errors shown in this embodiment includes: S1: Mount a double-ball target on the end face of the turntable, and obtain multiple images of different rotation angles of the double-ball target when it rotates with the turntable.

[0020] Exemplarily, by mounting the double-ball target on the end face of the device under test, the device under test selected in this embodiment is a precision turntable, and a backlight is placed behind the target ball. The binocular vision measurement device is placed in front of the target, so that the target is in the center of the camera's field of view. Adjust the distance between the two and the focal length and aperture of the camera to make the image clear; multiple images of the double-ball target at multiple positions when it rotates uniformly for one week with the precision turntable can be collected by using the binocular vision device and stored in the computer.

[0021] The multi-degree-of-freedom rotational errors of the present invention include radial rotational errors, axial rotational errors, and tilt rotational errors.

[0022] Optionally, the axis of the double-ball target is parallel to the axis of the turntable.

[0023] Exemplarily, after the installation and debugging of the binocular vision measurement device are completed, the frame rate of the camera can be set to 1 frame / second, and the rotation speed of the precision turntable can be set to 5 degrees / second, then 72 position images of the target rotating with the precision turntable for one week can be collected.

[0024] S2: Detect multiple images of different rotation angles, determine the three-dimensional coordinates of the centers of the multiple double-ball targets, and calculate the average value of the three-dimensional coordinates of the centers of the multiple double-ball targets to generate the motion trajectory of the center of the double-ball target.

[0025] Exemplarily, multiple spatial position images can be detected to determine the three-dimensional coordinates of the center positions of the double-ball targets, including: detecting the multiple spatial position images by using an edge detection algorithm and a circle detection algorithm to obtain the center coordinates; and obtaining the three-dimensional coordinates of the ball center according to the center coordinates by the principle of triangulation.

[0026] Exemplarily, through image processing in a computer, the three-dimensional coordinates of the center position corresponding to each group of images are calculated, and the motion trajectories are formed based on the three-dimensional coordinates of the two target balls, including: using image processing technology in the computer for edge detection and feature detection to obtain the center coordinates, and then calculating the three-dimensional coordinates of the center based on the parallax and the camera internal parameters by the principle of triangulation to obtain the motion trajectories.

[0027] Exemplarily, the and pixel coordinates of the center points on two images and are calculated through edge detection and feature detection. As Figure 3 shown, the detection results obtained by the circle detection algorithm are used. Then, based on the parallax and the camera internal parameters, the three-dimensional coordinates of the ball center and are calculated. The three-dimensional coordinates of the ball centers at all the collected positions of and are calculated, and the motion trajectories of and are drawn according to the actual rotation angles of 72 positions. Figure 4 In and , the and are the motion trajectories of the ball centers

[0028] S3: By projecting the motion trajectory of one of the target ball centers onto a two-dimensional plane to obtain multiple projection points, performing least-squares circle fitting on the obtained projection points to obtain the center coordinates and radius of the base circle of the motion trajectory on the two-dimensional plane, obtaining the inner and outer envelope circles of the motion trajectory according to the center coordinates and radius of the base circle, and obtaining the radial runout error according to the inner and outer envelope circles of the motion trajectory.

[0029] Exemplarily, based on the and motion trajectories obtained in the above S2, the radial, axial, and tilt runout errors of the device are calculated. As Figure 5 shown, the motion trajectory is projected onto the plane, and the projected points are . All the points are subjected to least-squares circle fitting, that is:

[0030] The equation of the circle can be expressed as: Establish the objective function: Solve for the center of the least-squares circle , which is the coordinate of the base circle center of the trajectory on the plane. The radius of the base circle is . Draw the inner and outer envelope circles of the trajectory with as the center, and the radii are and respectively. The radial runout error is: where is the radial runout error.

[0031] S4: By projecting the movement trajectory of the center of another target ball onto a plane perpendicular to the two-dimensional plane, obtain the axial runout curve and the coordinate of the base circle center of the movement trajectory on the plane. Take the maximum amplitude value on the axial runout curve as the axial runout error.

[0032] As shown in Figure 5 , project the movement trajectory onto the plane. Then, the axial runout curve can be seen on the plane, and the axial runout error is the maximum amplitude value on the curve .

[0033] S5: According to the coordinates of the two base circle centers, take the line connecting the two centers as the average rotation axis when the turntable rotates, and obtain the tilt runout error.

[0034] As shown in Figure 4 , after obtaining the movement trajectories and of the centers of and respectively, find the coordinates of the base circle centers of and respectively. The line connecting the two centers is used as the average rotation axis when the precision turntable rotates. and The points corresponding to the rotation angles on are and respectively. Then, the tilt runout error can be expressed as: where and are the radial distances from and these two points to the average rotation axis respectively, is and The axial distance of the plane where these two points are located is the tilt rotation error.

[0035] The above is the method for obtaining multi-degree-of-freedom rotation error provided by one or more embodiments of this specification. Based on the same idea, this specification also provides a corresponding device for obtaining multi-degree-of-freedom rotation error, including: An acquisition module, configured to install a double-ball target on the end face of a turntable, and acquire multiple images of different rotation angles when the double-ball target rotates with the turntable; A motion trajectory generation module, configured to detect multiple images of different rotation angles, determine the three-dimensional coordinates of the centers of the multiple double-ball targets, calculate the average value of the three-dimensional coordinates of the centers of the multiple double-ball targets, and generate the motion trajectory of the center of the double-ball target; A multi-degree-of-freedom rotation error determination module, configured to project the motion trajectory of the center of one of the targets onto a two-dimensional plane to obtain multiple projection points, perform least-squares circle fitting on the obtained projection points to obtain the center coordinates and radius of the base circle of the motion trajectory on the two-dimensional plane, obtain the inner and outer envelope circles of the motion trajectory based on the center coordinates and radius of the base circle, and obtain the radial rotation error according to the inner and outer envelope circles of the motion trajectory; project the motion trajectory of the center of the other target onto a plane perpendicular to the two-dimensional plane to obtain the axial runout curve and the center coordinates of the base circle of the motion trajectory on the plane, and take the maximum amplitude on the axial runout curve as the axial rotation error; according to the center coordinates of the two base circles, take the line connecting the two centers as the average rotation axis when the turntable rotates, and obtain the tilt rotation error.

[0036] As Figure 6 shown, target 2 is a double-ball target with a precise interface. The schematic diagram of the double-ball target is as Figure 7 shown. The device under test is a precision turntable 4, and the rotation speed can be set. In the present invention, a double-ball target 2 is installed on the end face of the precision turntable 4. The target 2 has a precise installation interface to ensure that the axis of the target is parallel to the axis of the precision turntable. A backlight 1 is placed behind the target, and a binocular vision measurement device 3 is placed in front of the target to make the target in the center of the camera's field of view. Adjust the distance between the two and the focal length and aperture of the camera to make the image clear.

[0037] For the specific limitations of the device for obtaining multi-degree-of-freedom rotation error, reference can be made to the limitations of the method for obtaining multi-degree-of-freedom rotation error in the above text, which will not be elaborated here. Each module in the above device for obtaining multi-degree-of-freedom rotation error can be implemented in whole or in part through software, hardware, and their combination. The above modules can be embedded in or independent of the processor in the computer device in the form of hardware, or stored in the memory of the computer device in the form of software, so that the processor can call and execute the operations corresponding to the above modules.

[0038] The present invention also provides a computer-readable storage medium storing a computer program, which can be used to execute the multi-degree-of-freedom rotation error acquisition method provided above.

[0039] The present invention also provides Figure 8 a schematic structural diagram of the computer device shown in Figure 8 As shown, at the hardware level, the computer device includes a processor, an internal bus, a network interface, a memory, and a non-volatile memory. Of course, it may also include other hardware required for other services. The processor reads the corresponding computer program from the non-volatile memory into the memory and then runs it to implement the multi-degree-of-freedom rotation error acquisition method provided in the above embodiments.

[0040] The technical features of the above embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered as the scope recorded in the present invention.

Claims

1. A method for obtaining multi-degree-of-freedom rotation error, characterized in that: include: The double-ball target is mounted on the end surface of the turntable, and multiple images of the double-ball target at different rotation angles are obtained when the double-ball target rotates with the turntable; Detect multiple images with different rotation angles, determine the three-dimensional coordinates of the center positions of multiple double-ball targets, average the three-dimensional coordinates of the center positions of multiple double-ball targets, and generate the motion trajectory of the center of the double-ball target; The motion trajectory of one of the target sphere centers is projected onto a two-dimensional plane to obtain a plurality of projection points, and the obtained projection points are fitted with a least squares circle to obtain the base circle center coordinates and base circle radius of the motion trajectory on the two-dimensional plane. The inner and outer envelope circles of the motion trajectory are obtained based on the base circle center coordinates and base circle radius. The radial rotation error is obtained based on the inner and outer envelope circles of the motion trajectory. By projecting the motion trajectory of the center of another target sphere onto a plane perpendicular to the two-dimensional plane, an axial runout curve and the coordinates of the center of the base circle of the motion trajectory on the plane are obtained, and the maximum amplitude on the axial runout curve is taken as the axial rotation error; According to the coordinates of the centers of the two base circles, the line connecting the two centers is used as the average rotation axis when the turntable rotates to obtain the tilt rotation error.

2. The method for obtaining multi-degree-of-freedom rotation error according to claim 1, characterized in that: The detecting of multiple images at different rotation angles specifically includes: By adopting edge detection algorithm and circle detection algorithm, the feature extraction and detection of target ball contour in multiple images with different rotation angles are performed.

3. The method for obtaining multi-degree-of-freedom rotation errors according to claim 1, characterized in that: The method projects the motion trajectory of one of the target sphere centers onto a two-dimensional plane to obtain a plurality of projection points, performs least squares circle fitting on the obtained projection points, obtains the base circle center coordinates and base circle radius of the motion trajectory on the two-dimensional plane, obtains the inner and outer envelope circles of the motion trajectory according to the base circle center coordinates and the base circle radius, and obtains the radial rotation error according to the inner and outer envelope circles of the motion trajectory, specifically including: Project the trajectory of the center of the sphere onto the xoy plane and use the following formula to get the equation of the circle: ； Construct the objective function based on the equation of a circle: ； Among them, the xoy plane is a plane perpendicular to the line connecting the coordinates of the centers of the two base circles; According to the objective function, the trajectory is Coordinates of the center of the base circle on the surface , the base circle radius is ,by Draw the inner and outer enveloping circles of the trajectory as the center of the circle, and the radii are and , the radial rotation error is obtained using the following formula: ； in, is the radial rotation error.

4. The multi-degree-of-freedom rotation error acquisition method according to claim 1, characterized in that: The method projects the motion trajectory of the center of another target ball onto a plane perpendicular to the two-dimensional plane, obtains an axial runout curve and the coordinates of the center of the base circle of the motion trajectory on the plane, and takes the maximum amplitude on the axial runout curve as the axial rotation error, specifically including: Project the motion trajectory onto On the surface, get The axial runout curve and base circle center coordinates on the surface are The maximum value on the axial runout curve on the surface is taken as the axial rotation error.

5. The method for obtaining multi-degree-of-freedom rotation errors according to claim 1, characterized in that: The method of obtaining the tilt rotation error by taking the line connecting the two base circle centers as the average rotation axis when the turntable rotates according to the coordinates of the centers of the two base circles specifically includes: Connect the two centers and use the line connecting the two centers as the average rotation axis when the turntable rotates. and The angle of rotation The corresponding points are and , the tilt rotation error is obtained using the following formula: ； in, and They are and The radial distances of these two points from the mean axis of rotation are for and The axial distance between the two points in the plane is is the tilt rotation error.

6. The multi-degree-of-freedom rotation error acquisition method according to claim 1, characterized in that: The turntable rotates at a speed of 5 degrees / second.

7. The multi-degree-of-freedom rotation error acquisition method according to claim 1, characterized in that: By placing the double-ball target in the center of the binocular camera's field of view, with the double-ball target axis in a direction perpendicular to the binocular camera's optical axis, multiple spatial position images of the double-ball target are acquired when the double-ball target rotates with the turntable.

8. A multi-degree-of-freedom rotation error acquisition device, characterized in that: include: An acquisition module is used to mount the double-ball target on the end surface of the turntable and acquire multiple images of the double-ball target at different rotation angles when the double-ball target rotates with the turntable; A motion trajectory generation module is used to detect multiple images with different rotation angles, determine the three-dimensional coordinates of the center positions of multiple double-ball targets, average the three-dimensional coordinates of the center positions of multiple double-ball targets, and generate a motion trajectory of the center of the double-ball target; The multi-degree-of-freedom rotation error determination module is used to project the motion trajectory of one of the target sphere centers onto a two-dimensional plane to obtain multiple projection points, perform least squares circle fitting on the obtained projection points, obtain the base circle center coordinates and base circle radius of the motion trajectory on the two-dimensional plane, obtain the inner and outer envelope circles of the motion trajectory based on the base circle center coordinates and the base circle radius, and obtain the radial rotation error based on the inner and outer envelope circles of the motion trajectory; project the motion trajectory of the other target sphere center onto a plane perpendicular to the two-dimensional plane to obtain an axial runout curve and the base circle center coordinates of the motion trajectory on the plane, and use the maximum amplitude on the axial runout curve as the axial rotation error; and use the line connecting the two base circle centers as the average rotation axis when the turntable rotates based on the two base circle center coordinates to obtain the tilt rotation error.

9. A computer-readable storage medium, characterized in that: The storage medium stores a computer program, and when the computer program is executed by a processor, the multi-degree-of-freedom rotation error acquisition method described in any one of claims 1 to 7 is implemented.

10. A computer device, characterized in that: The method comprises a memory, a processor and a computer program stored in the memory and executable on the processor, wherein when the processor executes the program, the method for acquiring multi-degree-of-freedom rotation errors as described in any one of claims 1 to 7 is implemented.

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