Calibration device and method of coordinate measuring instrument based on combined ball rod unit

Abstract

The invention discloses a calibration device and method for a coordinate measuring instrument based on a combined ball rod unit, and belongs to the technical field of instrument calibration, the calibration device comprises a combined base, the combined ball rod unit, an anvil structure and a fixed-length rod, and the combined base is provided with a positioning ball seat; the combined cue unit is divided into a rigid combined cue and an elastic combined cue, the rigid combined cue is arranged at the rightmost end, and the elastic combined cue is arranged at other positions; ball positioning mechanisms matched with the standard balls are arranged at the two ends of the fixed-length rod, the fixed-length rod is arranged between the two standard balls, and the positions of the fixed-length rod and the standard balls are self-adaptively calibrated through the ball positioning mechanisms; and the anvil structure is used for applying pre-tightening force to the leftmost elastic combined ball rod. According to the invention, the coordinate measuring instrument with a large measuring range can be calibrated on site, and the calibration efficiency of the coordinate measuring instrument is effectively improved.

Description

Technical Field

[0001] The invention belongs to the technical field of instrument calibration, and in particular relates to a calibration device and method for a coordinate measuring instrument based on a combined ball-bar unit. Background Art

[0002] At present, coordinate measuring machines with a large measuring range, such as three-coordinate measuring machines, articulated arm coordinate measuring machines, laser trackers, laser scanners and camera coordinate measuring machines, all have the problem of difficulty in on-site calibration. For example, a three-coordinate measuring machine with a single-axis measuring range greater than 2m cannot be calibrated using a gauge block (because the longest gauge block is 1m). According to JJF 1064-2010 "Coordinate Measuring Machine Calibration Specification", it is recommended to use a laser interferometer for calibration of three-coordinate measuring instruments with a measuring range greater than 2m. However, the use of laser interferometers can only detect the axial positioning accuracy of the three-coordinate measuring machine, and cannot detect comprehensive errors such as the detection error of the three-coordinate measuring machine. There are similar problems in the on-site calibration of articulated arm coordinate measuring machines with a large measuring range. For example, articulated arm coordinate measuring machines with a measuring range of more than 3m also require a standard of appropriate length (greater than 2.25m according to the calibration specification) for calibration. The calibration of laser trackers, laser scanners and camera coordinate measuring machines also has to be sent to the metrology laboratory for calibration because there is no standard of appropriate length, and cannot be calibrated on the site where the instrument is used. This results in a significant reduction in calibration efficiency, which cannot meet the needs of modern industrial production.

[0003] A ball bat (club) is composed of two or more high-precision spheres and a structure with an extremely low expansion coefficient that connects and fixes these spheres. The spheres are generally made of zirconia or ceramics, and the structure is generally made of carbon fiber or invar steel. The ball center distance of the ball bat is a fixed length. The measurement deviation of the ball center distance indicates the measurement error of the calibrated coordinate measurement system, and can also be used to detect comprehensive errors such as the detection error of the coordinate measuring instrument. However, due to process reasons and the need for easy carrying, the ball bat standard cannot be made too long, and is generally less than 1.5m. This range cannot meet the needs of on-site calibration of coordinate measuring instruments with a large measurement range (greater than 2.25m). Summary of the invention

[0004] Purpose of the invention: In order to overcome the problem that the ball bar in the prior art cannot meet the need for on-site calibration of coordinate measuring instruments with a large measuring range (greater than 2.25m), the present invention provides a calibration device for a coordinate measuring instrument based on a combined ball bar unit.

[0005] Technical solution: To achieve the above purpose, the technical solution adopted by the present invention is: A calibration device for a coordinate measuring instrument based on a combined ball-bar unit comprises a combined base, a combined ball-bar unit, an anvil structure, and a fixed-length rod, wherein: The combined base comprises more than two supports, and two adjacent supports are fixedly connected together through a support fixing structure. A positioning ball seat is arranged on the combined base.

[0006] The combined ball club unit includes more than two combined ball clubs, one of which is a rigid combined ball club, and the remaining combined ball clubs are elastic combined ball clubs, the combined ball clubs include a standard ball, a support rod, and a positioning pin, the upper end of the support rod is fixedly connected to the standard ball, and the lower end is fixedly connected to the positioning pin. The rigid combined ball club is set on the rightmost positioning ball seat on the combined base through the positioning pin, and the elastic combined ball club is set on other positioning ball seats on the combined base through the positioning pin.

[0007] Ball positioning mechanisms matching the standard ball are arranged at both ends of the fixed-length rod. The fixed-length rod is arranged between two adjacent elastic combination ball rods and between the rigid combination ball rod and the adjacent elastic combination ball rod. The fixed-length rod and the standard ball are adaptively calibrated in position through the ball positioning mechanism.

[0008] The anvil structure is fixedly mounted on the left end of the combined base, and is used to apply a pre-tightening force to the leftmost elastic combined club.

[0009] Preferably, the ball positioning mechanism comprises more than three positioning support pieces, the curvature of the positioning support pieces is adapted to the spherical curvature of the standard ball, and the arc surface formed by the more than three positioning support pieces matches the spherical surface of the standard ball.

[0010] Preferably, a positioning boss is provided between the support rod and the positioning pin, a positioning hemisphere is provided on the positioning boss, and a positioning groove corresponding to the positioning hemisphere is provided on the base.

[0011] Preferably, the support rods in the elastic combination golf club are elastic support rods, and the support rods in the rigid combination golf club are rigid cylindrical support rods.

[0012] Preferably: the anvil structure comprises an anvil, a preload spring, an anvil handle and a support; the support is fixedly mounted at the rightmost end of the combined base; one end of the preload spring is fixedly connected to the anvil, and the other end is fixedly connected to the anvil handle; the anvil handle is mounted on the support via a threaded connection.

[0013] Preferably: the support fixing structure includes a connecting steel bar and a fixing bolt. The support is provided with a screw hole one, and the connecting steel bar is provided with a screw hole two. After adjacent supports are spliced ​​and docked, the fixing bolt is passed through the screw hole two and the screw hole one in turn, so that the connecting steel bar fixes the two adjacent supports together.

[0014] Another object of the present invention is to provide a calibration method for a coordinate measuring instrument based on a combined ball-bar unit, comprising the following steps: Step 1: First, assemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit in the laboratory, and then use a standard coordinate measuring machine to take multiple sampling points on the surface position of the standard ball to obtain the position coordinates of multiple sampling points on the surface of each standard ball, which are recorded as standard measurement position coordinates.

[0015] Step 2, according to the standard measurement position coordinates, the center coordinates of each sphere of the standard measurement are obtained by a sphere center optimization method based on the energy equation.

[0016] Step 3, calculate the distance between the centers of any two balls based on the coordinates of each center of the ball measured by the standard, and record it as the standard value of the distance between the centers of the balls.

[0017] Step 4, during calibration, first disassemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit and bring it to the calibration site, and assemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit at the calibration site. Then use the calibrated coordinate measuring instrument to take multiple sampling points on the surface of the standard ball to obtain the coordinates of the multiple sampling points on the surface of each standard ball collected by the calibrated coordinate measuring instrument, which are recorded as the coordinates of the measurement position to be calibrated. The calibrated coordinate measuring instrument uses the algorithm carried by the calibrated coordinate measuring instrument itself to calculate the coordinates of the center of each ball to be calibrated based on the collected coordinates of the measurement position to be calibrated, and calculates the distance between the centers of any two balls based on the coordinates of the center of each ball to be calibrated, which is recorded as the measurement value of the distance between the centers of the balls.

[0018] Step 5: compare the standard value of the sphere center distance with the measured value of the sphere center distance. If the difference is within the allowable error range, the accuracy of the calibrated coordinate measuring instrument meets the use requirements. If the difference exceeds the allowable error range, the accuracy of the calibrated coordinate measuring instrument does not meet the use requirements.

[0019] Preferably, the sphere center optimization method based on the energy equation is as follows: Step 21: Determine the initial value of the sphere center coordinates based on the collected standard measurement position coordinates .

[0020] Step 22, set the basic objective function according to the collected standard measurement position coordinates: ; in, is the basic objective function, , is the total number of points, is the variable of the sphere center coordinates, Variables for measuring point coordinates.

[0021] Step 23, construct an energy equation based on the basic objective function, the energy equation is: ; make ,but: ; in, is the energy function, is the basic objective function matrix.

[0022] Step 24, set exist There is an increment ,right Performing a first-order Taylor expansion, we obtain: ; in, For the The variables of the sphere center coordinates of the collected points, For the The variable-based objective function matrix of the spherical center coordinates of the collected points, for exist The Jacobian matrix at is: ; Step 25: Expand the formula obtained by Taylor to Taking the derivative equal to 0, we get: ; Solving this equation, we get The increment equation is: .

[0023] Step 26, iteratively calculate steps 22 to 25 according to the set increment threshold to determine the variables of the sphere center coordinates, that is, to obtain the coordinates of each sphere center of the standard measurement.

[0024] Preferably, a method for iteratively calculating the variables of the sphere center coordinates according to a set increment threshold is as follows: Step 241, the formula for setting the increment threshold is as follows: ; in, To set the increment threshold, is the maximum allowable error.

[0025] Step 242, if , then stop the calculation and get the variables of the sphere center coordinates The value of .

[0026] Step 243, if , then let , and continue to iteratively solve the problem in the sphere center optimization method based on the energy equation.

[0027] Preferably, the sampling point positions include the sphere top and the equatorial positions, wherein there is one sphere top and four equatorial positions, and the initial values ​​of the sphere center coordinates are determined by the sampling point coordinates of the sphere top and the equatorial positions.

[0028] Compared with the prior art, the present invention has the following beneficial effects: The calibration device of the coordinate measuring instrument based on the combined ball-bar unit of the present invention realizes the on-site assembly and restoration of the ball-bar with high-accuracy ball-center distance, and its measurement error is 10 μm, which meets the needs of on-site calibration of coordinate measuring instruments with a large measuring range (greater than 2.25 m), makes it possible to calibrate the coordinate measuring instruments with a large measuring range on-site, and effectively improves the calibration efficiency of the coordinate measuring instruments. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 Schematic diagram of the calibration system structure of the coordinate measuring instrument.

[0030] Figure 2 It is a schematic diagram of the structure of a standard ball structure unit with elastic support rods.

[0031] Figure 3 It is a schematic diagram of a standard ball structure unit with elastic supports.

[0032] Figure 4 Schematic diagram of the standard spherical structural unit with rigid cylindrical supports.

[0033] Figure 5 Schematic diagram of the anvil structure and fixed-length rod.

[0034] Figure 6 Flow chart of a calibration method for a coordinate measuring instrument.

[0035] Figure 7 This is a schematic diagram of the locations of 5 dispersed sampling points.

[0036] Among them, 1 is a combined base, 11 is a first support, 12 is a second support, 3 is an anvil structure, 31 is an anvil, 32 is a preload spring, 33 is an anvil handle, 34 is a support, 4 is an elastic combined ball rod, 41 is a standard ball, 42 is an elastic support rod, 43 is a positioning pin, 44 is a positioning hemisphere, 45 is a positioning boss, 5 is a rigid combined ball rod, 52 is a rigid cylindrical support rod, 6 is a fixed length rod, 61 is a ball positioning mechanism, , , , , are the positions of the first five measurement points. DETAILED DESCRIPTION

[0037] The present invention is further explained below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. After reading the present invention, various equivalent forms of modifications to the present invention by those skilled in the art all fall within the scope defined by the claims attached to this application.

[0038] Example 1 This embodiment provides a calibration device for a coordinate measuring instrument based on a combined ball-bar unit, such as Figure 1-6 As shown, it includes a combined base 1, a combined ball-bar unit, an anvil structure 3, and a fixed-length rod 6, wherein: The combined base 1 includes more than two supports, and two adjacent supports are fixedly connected together by a support fixing structure. In another embodiment, the number of the supports is two, respectively denoted as a first support 11 and a second support 12, and the first support 11 and the second support 12 are connected to each other. In another embodiment, the number of the supports is three. The support is generally 1.5m-1.6m, and multiple supports can be spliced ​​to form a long base (combined base 1) of 3m-8m. The specific length can be freely combined as needed, and the length of the combined base 1 can be spliced ​​and lengthened according to actual needs. There are positioning ball seats on the combined base 1, and the positioning ball seats are evenly spaced at intervals of 500mm.

[0039] In another embodiment, the support fixing structure includes a connecting steel bar and a fixing bolt, the support is provided with a first screw hole, and the connecting steel bar is provided with a second screw hole. After adjacent supports are spliced ​​and docked, the fixing bolts are passed through the second screw hole and the first screw hole in sequence, so that the connecting steel bar fixes the two adjacent supports together. A positioning ball seat is provided on the combined base 1.

[0040] The combined club unit includes more than two combined clubs, one of which is a rigid combined club 5, and the remaining combined clubs are elastic combined clubs 4. The combined club includes a standard ball 41, a support rod, and a positioning pin 43. The upper end of the support rod is fixedly connected to the standard ball 41, and the lower end is fixedly connected to the positioning pin 43. The rigid combined club 5 is arranged on the rightmost positioning ball seat on the combined base 1 through the positioning pin 43, and the elastic combined club 4 is arranged on other positioning ball seats on the combined base 1 through the positioning pin 43. By inserting the positioning pin 43 into the positioning ball seat, the combined club is fixedly installed on the base. In another embodiment, the positioning ball seat is arranged along a straight line on the combined base 1, thereby realizing that the elastic combined club 4 is arranged along a straight line on the combined base 1. A positioning boss 45 is arranged between the support rod and the positioning pin 43. A positioning hemisphere 44 is arranged on the positioning boss 45, and a positioning groove corresponding to the positioning hemisphere 44 is arranged on the base. First, the combined ball bar is installed on the positioning ball seat through the positioning pin 43, and then the positioning hemisphere 44 is positioned in the positioning groove through the mutual cooperation of the positioning hemisphere 44 and the positioning groove, so as to realize the high-precision positioning of the combined ball bar on the combined base 1 and ensure the accuracy of the installation direction.

[0041] The two ends of the fixed-length rod 6 are provided with ball positioning mechanisms 61 that match the standard ball 41. The fixed-length rod 6 is arranged between two adjacent elastic combination ball rods 4 and between the rigid combination ball rod 5 and the adjacent elastic combination ball rod 4 (that is, the fixed-length rod 6 is arranged between two standard balls 41), and the fixed-length rod 6 and the standard ball 41 are adaptively calibrated in position through the ball positioning mechanism 61. The fixed-length rod 6 has excellent rigidity and is not easy to deform. The ball positioning mechanism 61 is adaptively calibrated in position, so it can ensure that the elastic combination ball rod 4 is disassembled from the combined base 1. After assembly, the distance between the two standard balls 41 remains unchanged. In another embodiment, the ball positioning mechanism 61 includes more than three positioning support plates, the curvature of the positioning support plates is adapted to the spherical curvature of the standard ball 41, and the arc surface formed by the more than three positioning support plates matches the spherical surface of the standard ball 41. When the fixed-length rod 6 is set between two standard balls 41, a three-point support can be formed. Under the action of gravity, preload force and the support force of the ball positioning mechanism 61, the fixed-length rod 6 can be adaptively located on the line connecting the centers of the two standard balls 41, that is, all fixed-length rods 6 can be located on the line connecting the centers of all standard balls 41, preventing positioning deviations of the fixed-length rod 6, ensuring the uniqueness of the installation, and improving the positioning accuracy between the standard balls 41.

[0042] The anvil structure 3 is fixedly mounted on the left end of the modular base 1. The anvil structure 3 is used to apply a preload force to the leftmost elastic combination ball rod 4, and then apply a preload force to the remaining elastic combination ball rods 4 through the transmission effect of the fixed-length rod 6 until it is offset by the rigid combination ball rod 5. The anvil structure 3 includes an anvil 31, a preload spring 32, an anvil handle 33, and a support 34. The support 34 is fixedly mounted on the rightmost end of the modular base 1. One end of the preload spring 32 is fixedly connected to the anvil 31, and the other end is fixedly connected to the anvil handle 33. The anvil handle 33 is installed on the support 34 through a threaded connection. The end of the anvil 31 away from the preload spring 32 points to the standard ball 41. By rotating the anvil handle 33, the anvil 31 spirally moves forward due to the effect of the thread. When the anvil 31 contacts the standard ball 41, the anvil handle 33 is further rotated, and the preload spring 32 is compressed, so that the preload force is applied to the standard ball 41.

[0043] like Figure 2-4 As shown, the support rod in the elastic combination ball bar 4 is an elastic support rod 42, and the support rod of the rigid combination ball bar 5 is a rigid cylindrical support rod 52. The elastic support rod 42 can undergo a certain swing deformation along the vertical direction of the spring sheet surface when subjected to force, and the rigid cylindrical support rod 52 has excellent rigidity and will not deform after being subjected to force. Only one rigid cylindrical support rod 52 is required, and it is placed in the last position. The elastic support rod 42 is located on the elastic combination ball bar 4 between the elastic combination ball bar 4 closest to the top anvil structure 3 and the elastic combination ball bar 4 second farthest from the top anvil structure 3, and the rigid cylindrical support rod 52 is located on the rigid combination ball bar 5 farthest from the top anvil structure 3.

[0044] After the connection base is assembled, the elastic combined ball bar 4 with the elastic support rod 42 can be inserted from the first positioning ball seat in sequence, but the last positioning ball seat must be inserted with the rigid combined ball bar 5 with the rigid cylindrical support rod 52. Then, the fixed length rod 6 is placed between the standard balls 41 and the standard balls 41. After the fixed length rod 6 is installed, the top anvil of the top anvil structure 3 is used to press the first standard ball, so that the entire spliced ​​ball bar is squeezed toward the last rigid combined ball bar 5 as a whole. In this way, the assembly of the entire combined ball bar device is completed.

[0045] When calibrating a coordinate measuring instrument with a large measuring range (greater than 2.25m), before using this embodiment for on-site calibration, the device must be assembled in the laboratory first, and then the assembled device must be assigned values ​​to obtain the standard value of each segment of the spherical center distance and the standard value of multiple segments. The assembled device is then brought to the calibration site. Due to the special structural design of this device, its measurement error is 10μm, ensuring that the spherical center distance after assembly can be restored to the standard value in the laboratory within a very small error range, and the special structural design of this device also ensures that the standard value of multiple segments can also be restored and used, meeting the needs of on-site calibration of coordinate measuring instruments with a large measuring range (greater than 2.25m).

[0046] Example 2 This embodiment provides a calibration method for a coordinate measuring instrument based on a combined ball-bar unit, such as Figure 6 As shown, the following steps are included: Step 1: First, assemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit in the laboratory, and then use a standard coordinate measuring machine to take multiple sampling points on the surface position of the standard ball to obtain the position coordinates of multiple sampling points on the surface of each standard ball, which are recorded as standard measurement position coordinates.

[0047] In another embodiment, when sampling points, the first five points are scattered at the top of the sphere and the equator, such as Figure 7 As shown, there is one point on the top of the ball , 4 points on the equator , , , , try to distribute them evenly. The positions of the first five measurement points are as follows Figure 7 As shown, is the top position of the ball, i.e. point location, , , , There are four equatorial positions, namely points , , , Then take any number of points, and the total number of points is n .generally n The value should be between 15 and 25.

[0048] Step 2, according to the standard measurement position coordinates, the center coordinates of each sphere of the standard measurement are obtained by a sphere center optimization method based on the energy equation.

[0049] The sphere center optimization method based on the energy equation is as follows: Step 21: Determine the initial value of the sphere center coordinates based on the collected standard measurement position coordinates In another embodiment, the initial value of the sphere center coordinates is determined by sampling point coordinates at the sphere top and equator.

[0050] Step 22, set the basic objective function according to the collected standard measurement position coordinates: (1) in, is the basic objective function, , is the total number of points, is the variable of the sphere center coordinates, Variables for measuring point coordinates.

[0051] Step 23, construct an energy equation based on the basic objective function, the energy equation is: (2) make ,but: (3) in, is the energy function, is the basic objective function matrix.

[0052] Step 24, set exist There is an increment ,right Performing a first-order Taylor expansion, we obtain: (4) in, For the The variables of the sphere center coordinates of the collected points, For the The variable-based objective function matrix of the spherical center coordinates of the collected points, for exist The Jacobian matrix at is: (5) Step 25, equation (4) is a is a quadratic function of the variable, and the Taylor expansion of equation (4) is Taking the derivative equal to 0, we get: (6) Solving this equation, we can get The increment equation is: (7) Right now: (8) Step 26, iteratively calculate steps 22 to 25 according to the set increment threshold to determine the variables of the sphere center coordinates, that is, to obtain the coordinates of each sphere center of the standard measurement.

[0053] The method of iteratively calculating the variables of the sphere center coordinates according to the set increment threshold is as follows: Step 241, according to the actual working situation, high-precision application scenarios, such as for the maximum allowable error ( MPE ) Calibration of high-precision coordinate measuring machines with a precision of less than 5 μm, It can be set to 0.001; general precision application scenarios, such as the maximum allowable error ( MPE ) Calibration of general precision coordinate measuring machines with a range of greater than 5μm and less than 20μm, It can be set to 0.005; for applications where accuracy is not high, such as for the maximum allowable error ( MPE ) Calibration of optical scanners greater than 20 μm, It can be set to 0.01 or larger. The formula for setting the increment threshold is as follows: (9) in, To set the increment threshold, is the maximum allowable error.

[0054] Step 242, if , then stop the calculation and get the variables of the sphere center coordinates The value of .

[0055] Step 243, if , then let , and continue to iteratively solve the problem in the sphere center optimization method based on the energy equation.

[0056] Step 3, calculate the distance between the centers of any two balls based on the coordinates of each center of the ball measured by the standard, and record it as the standard value of the distance between the centers of the balls.

[0057] Step 4, during calibration, first disassemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit and bring it to the calibration site, and assemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit at the calibration site. Then use the calibrated coordinate measuring instrument to take multiple sampling points on the surface of the standard ball to obtain the coordinates of the multiple sampling points on the surface of each standard ball collected by the calibrated coordinate measuring instrument, which are recorded as the coordinates of the measurement position to be calibrated. The calibrated coordinate measuring instrument uses the algorithm carried by the calibrated coordinate measuring instrument itself to calculate the coordinates of the center of each ball to be calibrated based on the collected coordinates of the measurement position to be calibrated, and calculates the distance between the centers of any two balls based on the coordinates of the center of each ball to be calibrated, which is recorded as the measurement value of the distance between the centers of the balls.

[0058] When calibrating the coordinate measuring instrument to be calibrated on site, use the coordinate measuring instrument to be calibrated to collect points on the surface of each standard ball. The coordinate measuring instrument to be calibrated can be contact type (such as three-coordinate measuring machine, articulated arm coordinate measuring machine, laser tracker) or non-contact type (laser scanner and camera coordinate measuring machine). Then use the software that comes with the coordinate measuring instrument to fit the collected points to the center of the ball and calculate the distance between each ball (ball center distance).

[0059] Step 5: compare the standard value of the sphere center distance with the measured value of the sphere center distance. If the difference is within the allowable error range, the accuracy of the calibrated coordinate measuring instrument meets the use requirements. If the difference exceeds the allowable error range, the accuracy of the calibrated coordinate measuring instrument does not meet the use requirements.

[0060] By comparing the standard value of the sphere center distance with the measured value of the sphere center distance, it can be determined whether the indication error of the calibrated coordinate measuring instrument is qualified, thereby determining whether the accuracy of the calibrated coordinate measuring instrument meets the requirements.

[0061] The present invention obtains each sphere center coordinate of the standard measurement and each sphere center coordinate to be calibrated by a sphere center optimization method based on an energy equation, then obtains a standard value of the sphere center distance and a measured value of the sphere center distance according to each sphere center coordinate of the standard measurement and each sphere center coordinate to be calibrated, and finally calibrates the calibrated coordinate measuring instrument by comparing the measured value of the sphere center distance and the measured value of the sphere center distance. Therefore, the present invention is not only easy to solve the sphere center coordinates, but also has high calibration accuracy for the calibrated coordinate measuring instrument.

[0062] During calibration, the present invention uses the calibrated coordinate measuring instrument to collect points on the surface of each standard sphere, and then uses the software provided by the calibrated coordinate measuring instrument to fit the collected points to the sphere center, and obtains the measurement values ​​of each sphere center distance. The measured values ​​of each sphere center distance are compared with the standard values ​​of each sphere center distance obtained by laboratory measurement. If the difference is within the allowable error range, the accuracy of the calibrated instrument meets the use requirements. If the difference exceeds the allowable error range, the accuracy of the calibrated instrument does not meet the use requirements.

[0063] The present invention realizes on-site assembly and restoration of a ball-bar device with a high-accuracy ball-center distance, makes it possible to calibrate a coordinate measuring instrument on-site, and effectively improves the calibration efficiency of the coordinate measuring instrument.

[0064] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A calibration device for a coordinate measuring instrument based on a combined ball-bar unit, characterized in that: It comprises a combined base (1), a combined ball-bar unit, an anvil structure (3), and a fixed-length rod (6), wherein: The combined base (1) comprises more than two supports, and two adjacent supports are fixedly connected together via a support fixing structure; a positioning ball seat is provided on the combined base (1); The combined ball club unit comprises more than two combined ball clubs, one of the combined ball clubs is a rigid combined ball club (5), and the remaining combined ball clubs are elastic combined ball clubs (4). The combined ball clubs comprise a standard ball (41), a support rod, and a positioning pin (43). The upper end of the support rod is fixedly connected to the standard ball (41), and the lower end is fixedly connected to the positioning pin (43). The rigid combined ball club (5) is arranged on the rightmost positioning ball seat on the combined base (1) through the positioning pin (43), and the elastic combined ball club (4) is arranged on other positioning ball seats on the combined base (1) through the positioning pin (43). Ball positioning mechanisms (61) matching the standard ball (41) are provided at both ends of the fixed-length rod (6); the fixed-length rod (6) is arranged between two adjacent elastic combination ball rods (4) and between a rigid combination ball rod (5) and an adjacent elastic combination ball rod (4); and the fixed-length rod (6) and the standard ball (41) are adaptively calibrated in position via the ball positioning mechanisms (61); The anvil structure (3) is fixedly mounted on the left end of the combined base (1), and the anvil structure (3) is used to apply a pre-tightening force to the elastic combined ball rod (4) on the far left.

2. The calibration device for coordinate measuring instrument based on combined ball-bar unit according to claim 1, characterized in that: The ball positioning mechanism (61) comprises more than three positioning support pieces, the curvature of the positioning support pieces is adapted to the spherical curvature of the standard ball (41), and the arc surface formed by the more than three positioning support pieces matches the spherical surface of the standard ball (41).

3. The calibration device of the coordinate measuring instrument based on the combined ball-bar unit according to claim 2, characterized in that: A positioning boss (45) is provided between the support rod and the positioning pin (43); a positioning hemisphere (44) is provided on the positioning boss (45), and a positioning groove corresponding to the positioning hemisphere (44) is provided on the base.

4. The calibration device for coordinate measuring instrument based on combined ball-bar unit according to claim 3, characterized in that: The support rod in the elastic combined golf club (4) is an elastic support rod (42), and the support rod in the rigid combined golf club (5) is a rigid cylindrical support rod (52).

5. The calibration device for coordinate measuring instrument based on combined ball-bar unit according to claim 4, characterized in that: The anvil structure (3) comprises an anvil (31), a preload spring (32), an anvil handle (33), and a support (34); the support (34) is fixedly mounted at the rightmost end of the combined base (1); one end of the preload spring (32) is fixedly connected to the anvil (31), and the other end is fixedly connected to the anvil handle (33); the anvil handle (33) is mounted on the support (34) by means of a threaded connection.

6. The calibration device for coordinate measuring instrument based on combined ball-bar unit according to claim 5, characterized in that: The support fixing structure includes a connecting steel bar and a fixing bolt. The support is provided with a screw hole 1, and the connecting steel bar is provided with a screw hole 2. After adjacent supports are spliced ​​and connected, the fixing bolt is passed through the screw hole 2 and the screw hole 1 in sequence, so that the connecting steel bar fixes the two adjacent supports together.

7. A calibration method using the calibration device of the coordinate measuring instrument based on the combined ball-bar unit according to claim 1, characterized in that: The following steps are involved: Step 1, first assemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit in the laboratory, and then use the standard coordinate measuring machine to take multiple sampling points on the surface position of the standard ball to obtain the position coordinates of multiple sampling points on the surface of each standard ball, which are recorded as standard measurement position coordinates; Step 2, according to the standard measurement position coordinates, the coordinates of each sphere center of the standard measurement are obtained by a sphere center optimization method based on an energy equation; Step 3, calculating the distance between the centers of any two balls according to the coordinates of the centers of each ball measured by the standard, and recording it as the standard value of the distance between the centers of the balls; Step 4, during calibration, first disassemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit and bring it to the calibration site, and assemble the calibration device of the coordinate measuring instrument based on the combined ball-bar unit at the calibration site; then use the coordinate measuring instrument to be calibrated to collect multiple points on the surface of the standard ball, and obtain the coordinates of the multiple points collected on the surface of each standard ball collected by the coordinate measuring instrument to be calibrated, which are recorded as the coordinates of the measurement position to be calibrated; the coordinate measuring instrument to be calibrated calculates the coordinates of the center of each ball to be calibrated based on the collected coordinates of the measurement position to be calibrated using the algorithm carried by the coordinate measuring instrument to be calibrated, and calculates the distance between the centers of any two balls based on the coordinates of the centers of each ball to be calibrated, which is recorded as the measurement value of the distance between the centers of any two balls; Step 5: compare the standard value of the sphere center distance with the measured value of the sphere center distance. If the difference is within the allowable error range, the accuracy of the calibrated coordinate measuring instrument meets the use requirements. If the difference exceeds the allowable error range, the accuracy of the calibrated coordinate measuring instrument does not meet the use requirements.

8. The calibration method according to claim 7, characterized in that: The sphere center optimization method based on the energy equation is as follows: Step 21: Determine the initial value of the sphere center coordinates based on the collected standard measurement position coordinates ; Step 22, set the basic objective function according to the collected standard measurement position coordinates: ； in, is the basic objective function, , is the total number of points, is the variable of the sphere center coordinates, is the variable of the measurement point coordinates; Step 23, construct an energy equation based on the basic objective function, the energy equation is: ； make ,but: ； in, is the energy function, is the basic objective function matrix; Step 24, set exist There is an increment ,right Performing a first-order Taylor expansion, we obtain: ； in, For the The variables of the sphere center coordinates of the collected points, For the The variable-based objective function matrix of the spherical center coordinates of the collected points, for exist The Jacobian matrix at is: ； Step 25: Expand the formula obtained by Taylor to Taking the derivative equal to 0, we get: ； Solving this equation, we get The increment equation is: ； Step 26, iteratively calculate steps 22 to 25 according to the set increment threshold to determine the variables of the sphere center coordinates, that is, to obtain the coordinates of each sphere center of the standard measurement.

9. The calibration method according to claim 8, characterized in that: The method of iteratively calculating the variables of the sphere center coordinates according to the set increment threshold is as follows: Step 241, the formula for setting the increment threshold is as follows: ； in, To set the increment threshold, is the maximum allowable error; Step 242, if , then stop the calculation and get the variables of the sphere center coordinates The value of Step 243, if , then let , and continue to iteratively solve the problem in the sphere center optimization method based on the energy equation.

10. The calibration method according to claim 9, characterized in that: The sampling point positions include the sphere top and the equatorial positions, of which there is one sphere top and four equatorial positions. The initial values ​​of the sphere center coordinates are determined by the sampling point coordinates at the sphere top and the equatorial positions.

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