Calibration device and method for a coordinate measuring instrument based on a combined cue unit

Abstract

The present invention discloses a calibration device and method for a coordinate measuring instrument based on a combined ball bar unit, belonging to the technical field of instrument calibration. The device includes a combined base, a combined ball bar unit, an anvil structure, and a fixed-length bar. A positioning ball seat is arranged on the combined base. The combined ball bar unit is divided into a rigid combined ball bar and an elastic combined ball bar. The rigid combined ball bar is arranged at the rightmost end, and the elastic combined ball bars are arranged at other positions. Ball positioning mechanisms matching the standard balls are arranged at both ends of the fixed-length bar. The fixed-length bar is arranged between two standard balls, and the position between the fixed-length bar and the standard balls is self-adaptively calibrated through the ball positioning mechanisms. The anvil structure is used to apply a pre-tightening force to the leftmost elastic combined ball bar. The present invention can calibrate a coordinate measuring instrument with a large measuring range on-site, effectively improving the calibration efficiency of the coordinate measuring instrument.

Description

Technical Field

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

[0002] Currently, coordinate measuring instruments such as coordinate measuring machines with a large measuring range, articulated arm coordinate measuring machines, laser trackers, laser scanners, and photogrammetric coordinate measuring instruments all have the problem of difficult on-site calibration. For example, a coordinate measuring machine with a single-axis measuring range greater than 2m cannot be calibrated using gauge blocks (because the longest gauge block is only 1m). According to JJF 1064-2010 "Calibration Specification for Coordinate Measuring Machines", it is recommended to use a laser interferometer to calibrate coordinate measuring instruments with a measuring range greater than 2m. However, using a laser interferometer can only detect the axial positioning accuracy of the coordinate measuring machine and cannot detect comprehensive errors such as the probing error of the coordinate measuring machine. Similar problems exist in the on-site calibration of articulated arm coordinate measuring machines with a large measuring range. For example, for an articulated arm coordinate measuring machine with a measuring range above 3m, a standard device with a suitable length (greater than 2.25m according to the calibration specification) is also required for calibration. The calibration of laser trackers, laser scanners, and photogrammetric coordinate measuring instruments also has to be sent to a metrology laboratory for calibration due to the lack of a standard device with a suitable length and cannot be calibrated on-site at the instrument usage location. This greatly reduces the calibration efficiency and cannot meet the needs of modern industrial production.

[0003] A ball bar is composed of two or more spheres with high form accuracy and a structure body with an extremely low coefficient of thermal expansion that connects and fixes these spheres. The spheres are generally made of zirconia or ceramics, and the structure body is generally made of carbon fiber or invar steel. The center distance of the ball bar is a fixed length, and the measurement deviation of the center distance of the ball bar also indicates the measurement error of the coordinate measuring system to be calibrated. At the same time, it can also be used to detect comprehensive errors such as the probing error of the coordinate measuring instrument. However, due to technological reasons and the need for convenient portability, the ball bar standard device generally cannot be made too long and is generally less than 1.5m, which cannot meet the need for on-site calibration of coordinate measuring instruments with a large measuring range (greater than 2.25m). Summary of the Invention

[0004] Object 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 object, the technical solution adopted by the present invention is as follows:

[0006] A calibration device for a coordinate measuring instrument based on a combined ball bar unit, comprising a combined base, a combined ball bar unit, an anvil structure, and a fixed-length bar, wherein:

[0007] The combined base includes more than two supports, and adjacent supports are fixedly connected together through a support fixing structure. A positioning ball seat is arranged on the combined base.

[0008] The combined ball bar unit includes more than two combined ball bars, one of the combined ball bars is a rigid combined ball bar, and the remaining combined ball bars are elastic combined ball bars. The combined ball bar includes 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 bar is arranged on the rightmost positioning ball seat on the combined base through the positioning pin, and the elastic combined ball bars are arranged on the other positioning ball seats on the combined base through the positioning pins.

[0009] Both ends of the fixed-length bar are provided with a ball positioning mechanism matching the standard ball. The fixed-length bar is arranged between two adjacent elastic combined ball bars and between the rigid combined ball bar and the adjacent elastic combined ball bar, and the position between the fixed-length bar and the standard ball is self-adaptively calibrated through the ball positioning mechanism.

[0010] The anvil structure is fixedly installed at the left end of the combined base, and the anvil structure is used to apply a pre-tightening force to the leftmost elastic combined ball bar.

[0011] Preferably: The ball positioning mechanism includes more than 3 positioning support pieces, the radian of the positioning support piece is adapted to the spherical radian of the standard ball, and the arc surface formed by more than 3 positioning support pieces matches the spherical surface of the standard ball.

[0012] Preferably: A positioning boss is arranged between the support rod and the positioning pin. A positioning hemisphere is arranged on the positioning boss, and a positioning groove corresponding to the positioning hemisphere is arranged on the base.

[0013] Preferably: The support rod in the elastic combined ball bar is an elastic support rod, and the support rod of the rigid combined ball bar is a rigid cylindrical support rod.

[0014] Preferably: The anvil structure includes an anvil, a pre-tightening spring, an anvil handle, and a support. The support is fixedly installed at the rightmost end of the combined base. One end of the pre-tightening spring is fixedly connected to the anvil, and the other end is fixedly connected to the anvil handle; the anvil handle is installed on the support through a threaded connection.

[0015] Preferably, the support fixing structure includes connecting steel bars and fixing bolts. There is a first screw hole on the support, and a second screw hole on the connecting steel bar. After adjacent supports are spliced and butted, the connecting steel bars fix the adjacent two supports together by passing the fixing bolts through the second screw hole and the first screw hole in sequence.

[0016] Another object of the present invention is to provide a calibration method for a coordinate measuring instrument based on a combined ball bar unit, including the following steps:

[0017] Step 1, first assemble the calibration device for the coordinate measuring instrument based on the combined ball bar unit in the laboratory, and then use a standard coordinate measuring machine to perform multi-point sampling on the surface positions of the standard balls to obtain the coordinate positions of multiple sampling points on the surface of each standard ball, denoted as standard measurement position coordinates.

[0018] Step 2, obtain the center coordinates of each ball in the standard measurement through the ball center optimization method based on the energy equation according to the standard measurement position coordinates.

[0019] Step 3, calculate the center distance between any two balls according to the center coordinates of each ball in the standard measurement obtained, denoted as the standard value of the center distance.

[0020] Step 4, during calibration, first disassemble the calibration device for the coordinate measuring instrument based on the combined ball bar unit and take it to the calibration site, and then assemble the calibration device for 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 perform multi-point sampling on the surface positions of the standard balls to obtain the coordinate positions of multiple sampling points on the surface of each standard ball collected by the coordinate measuring instrument to be calibrated, denoted as the coordinates of the positions to be calibrated for measurement. The coordinate measuring instrument to be calibrated calculates the center coordinates of each ball to be calibrated for measurement according to the coordinates of the positions to be calibrated for measurement collected by using the algorithm carried by itself, and calculates the center distance between any two balls according to the center coordinates of each ball to be calibrated for measurement, denoted as the measured value of the center distance.

[0021] Step 5, compare the standard value of the center distance with the measured value of the center distance. If the difference is within the allowable error range, the accuracy of the coordinate measuring instrument to be calibrated meets the usage requirements; if the difference exceeds the allowable error range, the accuracy of the coordinate measuring instrument to be calibrated does not meet the usage requirements.

[0022] Preferably, the ball center optimization method based on the energy equation is as follows:

[0023] Step 21, determine the initial value of the center coordinates according to the collected standard measurement position coordinates .

[0024] Step 22, set the basic objective function according to the collected standard measurement position coordinates:

[0025] ;

[0026] Among them, is the basic objective function, , is the total number of points, is the variable of the center coordinate of the sphere, is the variable of the coordinate of the measurement point.

[0027] Step 23: Construct an energy equation according to the basic objective function. The energy equation is:

[0028] ;

[0029] Let , then:

[0030] ;

[0031] Among them, is the energy function, is the basic objective function matrix.

[0032] Step 24: Assume has an increment at . Perform a first-order Taylor expansion on , and obtain:

[0033] ;

[0034] Among them, is the variable of the center coordinate of the sphere at the th acquisition point, is the basic objective function matrix of the variable of the center coordinate of the sphere at the th acquisition point, is at The Jacobian matrix at, that is:

[0035] ;

[0036] Step 25: Take the derivative of the expression obtained by the Taylor expansion with respect to and set it equal to 0, and obtain:

[0037] ;

[0038] Solve this equation to obtain the increment equation for :

[0039] .

[0040] Step 26: Iteratively calculate the variables of the ball center coordinates according to the set increment threshold in Steps 22 - 25, that is, obtain the ball center coordinates of each standard measurement.

[0041] Preferably, the method for iteratively calculating the variables of the ball center coordinates according to the set increment threshold:

[0042] Step 241: The formula for the set increment threshold is as follows:

[0043] ;

[0044] where, is the set increment threshold, is the maximum allowable error.

[0045] Step 242: If , stop the calculation and obtain the value of the variable of the ball center coordinates.

[0046] Step 243: If , then let , and continue to iteratively solve in the ball center optimization method based on the energy equation.

[0047] Preferably, the sampling positions include the ball top and the equator positions. Among them, there is 1 ball top and 4 equator positions. The initial values of the ball center coordinates are determined through the sampling coordinates of the ball top and the equator positions.

[0048] Compared with the prior art, the present invention has the following beneficial effects:

[0049] 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 a ball bar with a highly accurate ball center distance. Its measurement error is within 10 μm, meeting the need for on-site calibration of coordinate measuring instruments with a relatively large measurement range (greater than 2.25 m), making it possible to calibrate coordinate measuring instruments with a relatively large measurement range on-site and effectively improving the calibration efficiency of coordinate measuring instruments. Brief Description of the Drawings

[0050] Figure 1 is a schematic structural diagram of the calibration system of the coordinate measuring instrument.

[0051] Figure 2 is a schematic structural diagram of the standard ball structural unit with an elastic support rod.

[0052] Figure 3 is a front schematic diagram of the standard ball structural unit with an elastic support rod.

[0053] Figure 4 is a schematic structural diagram of the standard ball structural unit with a rigid cylindrical support rod.

[0054] Figure 5 Schematic diagram of the anvil structure and the fixed-length rod.

[0055] Figure 6 Flow chart of the calibration method for the coordinate measuring instrument.

[0056] Figure 7 Schematic diagram of the positions of five scattered sampling points.

[0057] Among them, 1 is the combined base, 11 is the first support, 12 is the second support, 3 is the anvil structure, 31 is the anvil, 32 is the pre-tightening spring, 33 is the anvil handle, 34 is the support, 4 is the elastic combined ball rod, 41 is the standard ball, 42 is the elastic support rod, 43 is the positioning pin, 44 is the positioning hemisphere, 45 is the positioning boss, 5 is the rigid combined ball rod, 52 is the rigid cylindrical support rod, 6 is the fixed-length rod, 61 is the ball positioning mechanism. , , , , Are the positions of the first five measurement points. Specific implementation mode

[0058] The present invention will be further clarified below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. After reading the present invention, various equivalent forms of modification by those skilled in the art fall within the scope defined by the appended claims of this application.

[0059] Embodiment 1

[0060] This embodiment provides a calibration device for a coordinate measuring instrument based on a combined ball rod unit, as Figures 1-6 shown, including a combined base 1, a combined ball rod unit, an anvil structure 3, and a fixed-length rod 6, where:

[0061] The combined base 1 includes more than two supports, and adjacent supports are fixedly connected together through a support fixing structure. In another embodiment, the number of supports is two, denoted as the first support 11 and the second support 12 respectively, and the first support 11 and the second support 12 are connected to each other. In another embodiment, the number of supports is three. The supports are generally 1.5m - 1.6m, and multiple supports can be spliced together to form a long base (combined base 1) of 3m - 8m. The specific length can be freely combined according to needs, 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 distributed at intervals of 500mm.

[0062] In another embodiment, the support fixing structure includes connecting steel bars and fixing bolts. A first screw hole is provided on the support, and a second screw hole is provided on the connecting steel bar. After adjacent supports are spliced and butted, the fixing bolts sequentially pass through the second screw hole and the first screw hole, so that the connecting steel bar fixes two adjacent supports together. A positioning ball seat is provided on the combined base 1.

[0063] The combined cue unit includes more than two combined cues. One of the combined cues is a rigid combined cue 5, and the remaining combined cues are elastic combined cues 4. The combined cue 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 cue 5 is arranged on the positioning ball seat at the rightmost end on the combined base 1 through the positioning pin 43, and the elastic combined cue 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 cue is fixedly installed on the base. In another embodiment, the positioning ball seats are arranged in a straight line on the combined base 1, so as to realize the straight-line arrangement of the elastic combined cues 4 on the combined base 1. 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. First, the combined cue is installed on the positioning ball seat through the positioning pin 43, and then through the mutual cooperation of the positioning hemisphere 44 and the positioning groove, the positioning hemisphere 44 is positioned in the positioning groove, realizing the high-precision positioning of the combined cue on the combined base 1 and ensuring the accuracy of the installation direction.

[0064] Both ends of the fixed-length rod 6 are provided with a ball positioning mechanism 61 that matches the standard ball 41. The fixed-length rod 6 is arranged between two adjacent elastic combined cue rods 4 and between the rigid combined cue rod 5 and the adjacent elastic combined cue rod 4 (that is to say, the fixed-length rod 6 is arranged between two standard balls 41). And the position between the fixed-length rod 6 and the standard ball 41 is self-adaptively calibrated through the ball positioning mechanism 61. The fixed-length rod 6 has excellent rigidity and is not easily deformed. And through the self-adaptive calibration of the position by the ball positioning mechanism 61, it can ensure that the elastic combined cue 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 3 positioning support pieces. The radian of the positioning support piece is adapted to the spherical radian of the standard ball 41. The arc surface formed by more than 3 positioning support pieces matches the spherical surface of the standard ball 41. When the fixed-length rod 6 is arranged between two standard balls 41, three-point support can be formed. Under the action of gravity, pre-tightening force and the supporting force of the ball positioning mechanism 61, the fixed-length rod 6 is self-adaptively located on the connection line of the centers of the two standard balls 41. That is, all the fixed-length rods 6 can be located on the connection line of the centers of all the standard balls 41, preventing deviation in the positioning of the fixed-length rod 6, ensuring the uniqueness of installation, and improving the positioning accuracy between the standard balls 41.

[0065] The anvil structure 3 is fixedly installed at the left end of the combined base 1. The anvil structure 3 is used to apply a pre-tightening force to the leftmost elastic combined cue rod 4. Then, through the transmission of the fixed-length rod 6, a pre-tightening force is applied to the remaining elastic combined cue rods 4 until it is offset by the rigid combined cue rod 5. The anvil structure 3 includes an anvil 31, a pre-tightening spring 32, an anvil handle 33, and a support 34. The support 34 is fixedly installed at the rightmost end of the combined base 1. One end of the pre-tightening 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 by threaded connection. The end of the anvil 31 away from the pre-tightening spring 32 points to the standard ball 41. By rotating the anvil handle 33, due to the effect of the thread, the anvil 31 advances in a spiral manner. When the anvil 31 contacts the standard ball 41, continue to rotate the anvil handle 33, and the pre-tightening spring 32 is compressed to apply a pre-tightening force to the standard ball 41.

[0066] As Figures 2-4As shown, the support rod in the elastic combined cue 4 is an elastic support rod 42, and the support rod of the rigid combined cue 5 is a rigid cylindrical support rod 52. The elastic support rod 42 can undergo a certain swinging deformation in the vertical direction of the elastic surface under force, while the rigid cylindrical support rod 52 has excellent rigidity and will not deform under force. Only one rigid cylindrical support rod 52 is required and is placed at the last position. The elastic support rod 42 is located on the elastic combined cue 4 between the elastic combined cue 4 closest to the anvil structure 3 and the second farthest elastic combined cue 4 from the anvil structure 3, and the rigid cylindrical support rod 52 is located on the rigid combined cue 5 farthest from the anvil structure 3.

[0067] After the connection base is assembled, the elastic combined cue 4 with the elastic support rod 42 can be inserted into the first positioning ball seat in sequence, but the last positioning ball seat must be inserted with the rigid combined cue 5 with the rigid cylindrical support rod 52. Then, a fixed-length rod 6 is placed between the standard balls 41 and 41. After the fixed-length rod 6 is installed, use the anvil of the anvil structure 3 to press the first standard ball, so that the whole assembled cue is squeezed towards the last rigid combined cue 5. In this way, the assembly of the whole combined cue device is completed.

[0068] When calibrating a coordinate measuring instrument with a large measurement range (greater than 2.25 m), before using this embodiment for on-site calibration, the device needs to be assembled in the laboratory first, and then the assembled device is assigned values to obtain the standard values of the center distances of each section and the standard values of multiple sections. Then, the assembled device is taken to the calibration site. Due to the special structural design of this device, its measurement error is within 10 μm, ensuring that the 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 values of multiple sections can be restored for use, meeting the needs of on-site calibration of coordinate measuring instruments with a large measurement range (greater than 2.25 m).

[0069] Embodiment 2

[0070] This embodiment provides a calibration method for a coordinate measuring instrument based on a combined cue unit, as Figure 6 shown, including the following steps:

[0071] Step 1, first assemble the calibration device for the coordinate measuring instrument based on the combined cue unit in the laboratory, and then use a standard coordinate measuring machine to perform multi-point sampling on the surface position of the standard ball to obtain the coordinate values of multiple sampling positions on the surface of each standard ball, denoted as standard measurement position coordinates.

[0072] In another embodiment, when sampling, the first 5 points are scattered at the ball top and the equator positions, as Figure 7 shown, 1 point at the ball top and 4 points on the equator , , , , and distribute them as evenly as possible. The positions of the first 5 measurement points are as shown in Figure 7 . is the position of the ball top, that is, the position of point . , , , are respectively the 4 equatorial positions, that is, the positions of points , , , . Then, take multiple points arbitrarily, and the total number of points is n . Generally, it is appropriate that the value of n reaches 15 - 25.

[0073] Step 2: Obtain the center coordinates of each standard measurement through the center optimization method of the sphere based on the energy equation according to the standard measurement position coordinates.

[0074] The center optimization method of the sphere based on the energy equation is as follows:

[0075] Step 21: Determine the initial value of the center coordinates according to the collected standard measurement position coordinates . In another embodiment, the initial value of the center coordinates is determined through the sampling coordinates of the ball top and the equatorial positions.

[0076] Step 22: Set the basic objective function according to the collected standard measurement position coordinates:

[0077] (1)

[0078] where is the basic objective function, , is the total number of points, is the variable of the center coordinates, is the variable of the measurement point coordinates.

[0079] Step 23: Construct the energy equation according to the basic objective function, and the energy equation is:

[0080] (2)

[0081] Let , then:

[0082] (3)

[0083] where is the energy function, is the basic objective function matrix.

[0084] Step 24, set At has an increment , for perform a first-order Taylor expansion to obtain:

[0085] (4)

[0086] wherein, is the variable of the center-of-sphere coordinates of the th acquisition point, is the variable-based objective function matrix of the center-of-sphere coordinates of the th acquisition point, is at the Jacobian matrix, that is:

[0087] (5)

[0088] Step 25, Equation (4) is a quadratic function with as the variable. Take the derivative of the equation (4) obtained by Taylor expansion with respect to and set it equal to 0 to obtain:

[0089] (6)

[0090] Solve this equation to obtain the increment equation for :

[0091] (7)

[0092] That is:

[0093] (8)

[0094] Step 26, according to the set increment threshold, perform iterative calculations on Steps 22 - 25 to determine the variables of the center-of-sphere coordinates, that is, obtain the center-of-sphere coordinates of each standard measurement.

[0095] Method for determining the variables of the center-of-sphere coordinates by performing iterative calculations according to the set increment threshold:

[0096] Step 241, according to the actual working conditions, for high-precision application scenarios, such as calibration of high-precision coordinate measuring machines with a maximum allowable error ( MPE ) less than 5 μm, can be set to 0.001; for general-precision application scenarios, such as calibration of general-precision coordinate measuring machines with a maximum allowable error ( MPE ) greater than 5 μm and less than 20 μm, 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:

[0097] (9)

[0098] in, To set the increment threshold, is the maximum allowable error.

[0099] Step 242, if , then stop the calculation and get the variables of the sphere center coordinates The value of .

[0100] Step 243, if , then let , and continue to iteratively solve the problem in the sphere center optimization method based on the energy equation.

[0101] 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.

[0102] 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.

[0103] 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).

[0104] 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.

[0105] 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.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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 method for a calibration device of a coordinate measuring instrument using a combined cue unit, characterized in that On-site calibration of a coordinate measuring instrument with a measuring range greater than 2.25 m. A calibration device for a coordinate measuring instrument based on a combined ball bar unit includes a combined base (1), a combined ball bar unit, an anvil structure (3), and a fixed-length bar (6), where: The combined base (1) includes two or more supports, and adjacent supports are fixedly connected together through a support fixing structure; a positioning ball seat is provided on the combined base (1); The combined ball bar unit includes two or more combined ball bars. One of the combined ball bars is a rigid combined ball bar (5), and the remaining combined ball bars are elastic combined ball bars (4). The combined ball bar 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 ball bar (5) is arranged on the positioning ball seat at the rightmost end on the combined base (1) through the positioning pin (43), and the elastic combined ball bar (4) is arranged on other positioning ball seats on the combined base (1) through the positioning pin (43); the support rod in the elastic combined ball bar (4) is an elastic support rod (42), and the support rod of the rigid combined ball bar (5) is a rigid cylindrical support rod (52); Both ends of the fixed-length bar (6) are provided with a ball positioning mechanism (61) matching the standard ball (41). The fixed-length bar (6) is arranged between two adjacent elastic combined ball bars (4) and between the rigid combined ball bar (5) and the adjacent elastic combined ball bar (4), and the position of the fixed-length bar (6) and the standard ball (41) is adaptively calibrated through the ball positioning mechanism (61); The anvil structure (3) is fixedly installed at the left end of the combined base (1), and the anvil structure (3) is used to apply a pre-tightening force to the leftmost elastic combined ball bar (4); Including the following steps: Step 1, first assemble the calibration device for the coordinate measuring instrument based on the combined ball bar unit in the laboratory, and then use a standard coordinate measuring machine to perform multi-point sampling on the surface position of the standard ball to obtain the coordinates of multiple sampling positions on the surface of each standard ball, denoted as the standard measurement position coordinates; Step 2, obtain the center coordinates of each ball in the standard measurement through the ball center optimization method based on the energy equation according to the standard measurement position coordinates; Step 3, calculate the center distance between any two balls according to the obtained center coordinates of each ball in the standard measurement, denoted as the standard value of the center distance; 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. 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 perform multi-point sampling on the surface position of the standard ball, and obtain the coordinates of multiple sampling positions 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 positions to be calibrated. The coordinate measuring instrument to be calibrated calculates the center coordinates of each ball to be calibrated using the algorithm carried by itself according to the obtained coordinates of the measurement positions to be calibrated, and calculates the center distance between any two balls according to the center coordinates of each ball to be calibrated, which is recorded as the measured center distance value. Step 5: Compare the standard center distance value with the measured center distance value. If the difference is within the allowable error range, the accuracy of the coordinate measuring instrument to be calibrated meets the usage requirements; if the difference exceeds the allowable error range, the accuracy of the coordinate measuring instrument to be calibrated does not meet the usage requirements.

2. The calibration method of the calibration device of the coordinate measuring instrument using the combined cue unit according to claim 1, characterized in that: The ball positioning mechanism (61) includes more than 3 positioning support pieces. The radian of the positioning support piece is adapted to the spherical radian of the standard ball (41), and the arc surface formed by more than 3 positioning support pieces matches the spherical surface of the standard ball (41).

3. The calibration method of the calibration device of the coordinate measuring instrument using the combined ball bar unit according to claim 2, characterized in that: 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.

4. The calibration method of the calibration device of the coordinate measuring instrument using the combined cue unit according to claim 3, characterized in that: The anvil structure (3) includes an anvil (31), a pre-tightening spring (32), an anvil handle (33), and a support (34). The support (34) is fixedly installed at the rightmost end of the combined base (1). One end of the pre-tightening 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) by threaded connection.

5. The calibration method of the calibration device of the coordinate measuring instrument using the combined cue unit according to claim 4, characterized in that: The support fixing structure includes a connecting steel bar and a fixing bolt. A first screw hole is arranged on the support, and a second screw hole is arranged on the connecting steel bar. After adjacent supports are spliced and butted, the connecting steel bar fixes the adjacent two supports together by passing the fixing bolt through the second screw hole and the first screw hole in sequence.

6. The calibration method of the calibration device of the coordinate measuring instrument using the combined ball bar unit according to claim 5, characterized in that, The method for optimizing the center of the ball based on the energy equation is as follows: Step 21, determine the initial value of the spherical center coordinates according to the collected standard measurement position coordinates ; Step 22: Set the basic objective function according to the collected standard measurement position coordinates. ； Among them, is the basic objective function, , is the total number of points, is the variable of the center-of-sphere coordinates, is the variable of the measurement-point coordinates; Step 23: Construct an energy equation according to the basic objective function. The energy equation is: ； Let , then: ； Among them, is the energy function, is the basic objective function matrix; Step 24, set At there is an increment , for perform a first-order Taylor expansion to obtain: ； Among them, is the variable of the center-of-sphere coordinates of the th acquisition point, is the variable-based objective function matrix of the center-of-sphere coordinates of the th acquisition point, is at the Jacobian matrix at this point, that is: ； Step 25, take the derivative of the expression obtained by Taylor expansion with respect to and set it equal to 0, obtaining: ； Solve this equation to obtain the incremental equation for : ； Step 26: Perform iterative calculation on Steps 22 - 25 according to the set increment threshold to determine the variables of the center coordinates of the ball, that is, obtain the center coordinates of each ball for standard measurement.

7. The calibration method of the calibration device of the coordinate measuring instrument using the combined club unit according to claim 6, characterized in that, The method for determining the variables of the center coordinates of the ball by performing iterative calculation according to the set increment threshold: Step 241: The formula for setting the increment threshold is as follows: ； Among them, is the set increment threshold value, is the maximum allowable error; Step 242, if , then stop the calculation and obtain the value of the variable of the center coordinates of the sphere; Step 243, if , then let , and continue to iteratively solve in the sphere center optimization method based on the energy equation.

8. The calibration method of the calibration device of the coordinate measuring instrument using the combined cue unit according to claim 7, characterized in that: The sampling positions include the ball top and the equator positions. Among them, there is 1 ball top and 4 equator positions. The initial value of the center coordinates of the ball is determined by the sampling coordinates of the ball top and the equator positions.

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