Calibration method

Abstract

This invention provides a calibration method. The calibration method includes the following steps: measuring the ball-to-ball distances of multiple sides of an inspection gauge (100) mounted in a first, second, and third posture using a CMM (200); and calculating calibration values ​​of the ball-to-ball distances between two corresponding balls at both ends of the multiple sides of the inspection gauge by solving a simultaneous equation, which includes: the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the first posture, the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the second posture, the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the third posture, and the measurement error of the CMM (200) at the measurement position.

Description

Technical Field

[0001] This invention relates to a calibration method for inspection gauges used in CMMs. Background Technology

[0002] To check the measurement accuracy of a coordinate measuring machine (CMM), an inspection gauge is used, in which balls are placed at the vertices of a polyhedron or similar object (see, for example, U.S. Patent 6,023,850). The true values ​​of the ball-to-ball distances in the inspection gauge are measured beforehand using a reference instrument such as an optical interferometer. As a method for calibrating gauges with balls as measuring elements (such as tetrahedral gauges and cubic gauges), one known method is to calibrate by comparing the ball-to-ball distances of the gauge with a ball bar having calibration values. Summary of the Invention

[0003] The problem the invention aims to solve

[0004] In the method described in US Patent 6023850, when calibrating inspection gauges, a reference instrument is required to measure the true values ​​of all ball-to-ball distances of the inspection gauge. Therefore, the calibration of the reference instrument is complex.

[0005] This invention focuses on this point, and its purpose is to provide a calibration method that can reduce the time required for calibration operations of inspection gauges.

[0006] Solution for solving the problem

[0007] According to a first aspect of the invention, a calibration method is used to calibrate an inspection gauge in which spheres are arranged at the vertices of a regular tetrahedron. The calibration method includes the following steps: mounting the inspection gauge in a first orientation on a measuring table of a CMM; using the CMM, which identifies measurement errors, measuring the sphere-to-sphere distances of a plurality of sides of the inspection gauge mounted in the first orientation, wherein the measurement errors are at the measurement position of the first side among the plurality of sides of the inspection gauge mounted in the first orientation; after measuring the sphere-to-sphere distances of the plurality of sides, mounting the inspection gauge in a second orientation on the measuring table by rotating the inspection gauge about a first axis of rotational symmetry, wherein in the second orientation, a second side among the plurality of sides, different from the first side, coincides with the measurement position of the first side in the first orientation; and using the CMM to measure the sphere-to-sphere distances of the plurality of sides of the inspection gauge mounted in the second orientation. After measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture, the inspection gauge is mounted on the measuring table in a third posture by rotating it about a second rotational symmetry axis different from the first rotational symmetry axis, in which the third side of the multiple sides, different from the first and second sides, coincides with the measurement position; the CMM is used to measure the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the third posture; and a calibration value for the ball-to-ball distance between two corresponding balls at both ends of the multiple sides of the inspection gauge is calculated by solving a simultaneous equation, which includes the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the first posture, the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the second posture, the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the third posture, and the measurement error of the CMM at the measurement position.

[0008] Measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the first posture may include measuring the ball-to-ball distances of the six sides of the inspection gauge mounted in the first posture; measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture may include measuring the ball-to-ball distances of the six sides of the inspection gauge mounted in the second posture; and measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the third posture may include measuring the ball-to-ball distances of the six sides of the inspection gauge mounted in the third posture.

[0009] Calculating the calibration value of the ball-to-ball distance between two corresponding spheres at the two ends of a plurality of sides of the inspection gauge can include: calculating the calibration value of the ball-to-ball distance of each side of the regular tetrahedron of the inspection gauge by solving the following simultaneous equation 1, as well as the measurement error that occurs when measuring the ball-to-ball distance of each side of the regular tetrahedron of the inspection gauge.

[0010] [Equation 1]

[0011]

[0012] In equation 1, m j This represents the measurement error when measuring the ball-to-ball distance corresponding to the j-th position, where j = 1, 2, ..., 6, and l #i,k This represents the measurement value when measuring the ball-to-ball distance at the k-th position of the inspection gauge arranged in the i-th posture, where i = 1, 2, 3 and k = 1, 2, ..., 6.

[0013] According to a second aspect of the invention, a calibration method is used to calibrate an inspection gauge in which spheres are arranged at the vertices of a regular tetrahedron. The calibration method includes the following steps: mounting the inspection gauge in a first orientation on a measuring table of a CMM; using the CMM, which identifies measurement errors, measuring sphere-to-sphere distances of a plurality of sides of the inspection gauge mounted in the first orientation, wherein the measurement errors are measurement errors at a first measurement position where a first side included in the base of the regular tetrahedron is located, and measurement errors at a second measurement position where a second side not included in the base is located; and after measuring the sphere-to-sphere distances of the plurality of sides of the inspection gauge mounted in the first orientation, rotating the inspection gauge about a rotational symmetry axis orthogonal to the base to a second orientation. Mounted on the measuring platform, in the second posture, a third side, different from the first and second sides, is aligned with the first measurement position of the first side in the first posture, and a fourth side, different from the first, second, and third sides, is aligned with the second measurement position of the second side in the second posture; the CMM is used to measure the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the second posture; and a calibration value for the ball-to-ball distance between two corresponding balls at both ends of the multiple sides of the inspection gauge is calculated by solving simultaneous equations, the simultaneous equations including the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the first posture, the ball-to-ball distances of the multiple sides of the inspection gauge mounted in the second posture, and the measurement error of the CMM at the first and second measurement positions.

[0014] Measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the first posture may include measuring the ball-to-ball distances of the six sides of the inspection gauge mounted in the first posture, and measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture may include measuring the ball-to-ball distances of the six sides of the inspection gauge mounted in the second posture.

[0015] Calculating the calibration value of the ball-to-ball distance between two corresponding spheres at the ends of multiple edges of the inspection gauge can include: calculating the calibration value of the ball-to-ball distance between two corresponding spheres at the ends of each edge of the regular tetrahedron of the inspection gauge, and the measurement error that occurs when measuring the ball-to-ball distance, by solving the following simultaneous equation 2.

[0016] [Equation 2]

[0017]

[0018] In equation 2, m j This represents the measurement error when measuring the ball-to-ball distance corresponding to the j-th position, where j = 1, 2, ..., 6, l #i,k This represents the measurement value when measuring the ball-to-ball distance at the k-th position of the inspection gauge arranged in the i-th posture, where i = 1, 2, 3 and k = 1, 2, ..., 6, g k This represents the calibration value obtained by calibrating the ball-to-ball distance between two corresponding balls at the two ends of the k-th side of the inspection gauge, where k = 1, 2, ..., 6, l 2,scl This represents the value obtained by identifying the measurement error when measuring the ball-to-ball distance at the first measurement position, and l 5,scl This represents the value obtained by identifying the measurement error when measuring the ball-to-ball distance at the second measurement position.

[0019] Calculating the calibration value may include using the least squares method. The calibration method may also include the step of using a laser interferometer to identify measurement errors.

[0020] The effects of the invention

[0021] According to the present invention, the time required for calibration of inspection gauges can be reduced. Attached Figure Description

[0022] Figures 1A to 1C Each shows an outline of the calibration method according to the first embodiment.

[0023] Figure 2 This shows the CMM configuration.

[0024] Figure 3 This demonstrates how the identification unit identifies measurement errors.

[0025] Figure 4 This shows an example of inspecting the j-th position of a gauge.

[0026] Figures 5A to 5C Each example shows the position of the edge of the inspection gauge corresponding to the subscript.

[0027] Figure 6 This is a flowchart illustrating the process for calibrating the ball-to-ball distance of the inspection gauge in the first embodiment.

[0028] Figure 7A and Figure 7B Each shows an outline of the calibration method according to the second embodiment.

[0029] Figure 8 This is a flowchart illustrating the process for calibrating the ball-to-ball distance of the inspection gauge in the second embodiment.

[0030] Explanation of reference numerals in the attached figures

[0031] 21 Ministry of Communications

[0032] 22 detector units

[0033] 23 Display Department

[0034] 24 Storage Department

[0035] 25 Control Department

[0036] 31 orbits

[0037] 32 Slider

[0038] 33 Test subjects

[0039] 34 Reflectors

[0040] 35 Laser Interferometer

[0041] 100 Inspection Gauges

[0042] 200 CMM

[0043] 251 Measurement Department

[0044] 252 Identification Department

[0045] 253 Computing Department

[0046] 254 Display Control Unit Detailed Implementation

[0047] <First Embodiment>

[0048] [Overview of Calibration Method]

[0049] The calibration method according to the first embodiment is a method for calibrating a check gauge used to check the measurement accuracy of a coordinate measuring machine (CMM). Figures 1A to 1C Each of the first embodiment of the calibration method is illustrated in summary. In this calibration method, an inspection gauge is mounted on a CMM such that some edges of the inspection gauge are aligned with positions on the CMM as identified by a reference instrument such as a laser interferometer. Then, in multiple postures obtained by rotating the inspection gauge around a predetermined axis of rotational symmetry a predetermined number of times, the distance between spheres at the ends of each edge of the inspection gauge is measured using the CMM. When using a CMM, since the distance can be automatically measured simply by pre-setting the positions to be measured, the calibration time required can be reduced compared to setting the reference instrument according to the number of edges to be calibrated by this calibration method.

[0050] In the calibration method according to the first embodiment, for each of the three postures, the length of one side (the distance between the balls at the two ends of the side) is measured at the position of the CMM calibrated by the reference instrument, and the distance between the balls at the two ends of at least some other sides is measured at the uncalibrated position in the CMM, thereby calibrating the inspection gauge. In this calibration method, the CMM is used to measure the ball-to-ball distance of each side for each of the following postures: (i) the first posture, (ii) the second posture after the inspection gauge has been rotated only once from the first posture about a first rotational symmetry axis, and (iii) the third posture after the inspection gauge has been rotated only once from the second posture about a second rotational symmetry axis. Figure 1A This shows how to install the inspection gauge 100 in the first position. Figure 1B This shows how to install the inspection gauge 100 in the second position. Figure 1C This shows how to install the inspection gauge 100 in the third position.

[0051] like Figure 1A As shown, the inspection gauge 100 has a tetrahedral shape, and the measuring elements (spheres A to D) are arranged at each vertex of the tetrahedron. Figure 1A In the example, assume that the inspection gauge 100 is mounted on the measuring table of the CMM in a first orientation. Measuring elements with shapes other than spheres can be arranged at the various vertices of the inspection gauge 100. Assume that the measuring elements are capable of using the CMM to measure the coordinates of feature points such as the center or edge of a sphere.

[0052] CMM measures the ball-to-ball distance between two spheres. CMM measures the distance between two spheres on multiple sides of a regular tetrahedron in the inspection gauge 100. Figure 1AThe thick line in the diagram represents the first ball-to-ball distance between balls B and C at the two ends of the side (hereinafter also referred to as the first side) corresponding to the measurement position (position A indicated by the dashed arrow). It is assumed that the measurement error in the case where the CMM measures the ball-to-ball distance at this measurement position will be pre-identified by a method described later. The CMM also measures the ball-to-ball distances corresponding to the five sides of the inspection gauge 100, excluding the first side, mounted in the first orientation.

[0053] After the CMM has measured multiple ball-to-ball distances of the inspection gauge 100 mounted in the first position, the inspection gauge 100 is mounted on the measuring table in the second position, as follows: Figure 1A As indicated by the arrow, this second pose is obtained by rotating about the first axis of rotational symmetry. The inspection gauge 100 is mounted in the same position as the first pose in the CMM coordinate system. The first axis of rotational symmetry is an axis passing through sphere A and orthogonal to the plane including spheres B, C, and D.

[0054] Figure 1B This illustrates how to mount the inspection gauge 100 in a second orientation. In the second orientation, one of the edges of the regular tetrahedron of the inspection gauge 100 that differs from the first edge (the edge sandwiched between spheres B and D, also referred to hereinafter as the second edge) moves to align with the measurement position of the first edge in the first orientation. The CMM measures the second ball-to-ball distance between spheres B and D at both ends of the second edge of the inspection gauge 100 mounted in the second orientation. The CMM measures the ball-to-ball distances corresponding to the five edges of the inspection gauge 100 mounted in the second orientation, excluding the second edge.

[0055] After the CMM has measured the ball-to-ball distances of multiple sides of the inspection gauge 100 mounted in the second orientation, the inspection gauge 100 is mounted on the measuring table in a third orientation obtained by rotating about the second axis of rotational symmetry. The inspection gauge 100 is mounted in the same position in the CMM coordinate system as in the second orientation. The second axis of rotational symmetry differs from the first axis of rotational symmetry. The second axis of rotational symmetry is located in... Figure 1B The middle is represented by a dashed line. Figure 1B In the example, the second axis of rotational symmetry passes through sphere D and is orthogonal to the plane that includes spheres A, B, and C.

[0056] Figure 1CThis illustrates how to mount the inspection gauge 100 in a third position. In the third position, one of the edges of the regular tetrahedron of the inspection gauge 100 that differs from the first and second edges (the edge sandwiched between spheres C and D, also referred to hereinafter as the third edge) is moved to a position consistent with the measurement position. The CMM measures the third ball-to-ball distance between spheres C and D at both ends of the third edge of the inspection gauge 100 mounted in the third position. The CMM also measures the ball-to-ball distances corresponding to the five edges of the inspection gauge 100 mounted in the third position, excluding the third edge.

[0057] The CMM 200 calculates calibration values ​​obtained by calibrating the ball-to-ball distances between two corresponding spheres at the ends of multiple edges of the inspection gauge 100. The CMM 200 calculates these calibration values ​​by solving a simultaneous equation to calibrate the ball-to-ball distances between two corresponding spheres at the ends of multiple edges. This simultaneous equation includes: (i) the ball-to-ball distances of the multiple edges of the inspection gauge 100 when mounted in a first orientation; (ii) the ball-to-ball distances of the multiple edges of the inspection gauge 100 when mounted in a second orientation; (iii) the ball-to-ball distances of the multiple edges of the inspection gauge 100 when mounted in a third orientation; (iv) the calibration values ​​(unknowns) obtained by calibrating the ball-to-ball distances between two corresponding spheres at the ends of multiple edges; and (v) the pre-identified measurement error of the CMM at the measurement location. Details will be described later. By employing this calibration method, the user does not need to use a laser interferometer or similar equipment to measure all ball-to-ball distances of the inspection gauge 100, thus reducing the time required for calibration operations on the inspection gauge 100.

[0058] [CMM 200 Configuration]

[0059] Figure 2 The configuration of CMM 200 is shown. CMM 200 includes a communication unit 21, a detector unit 22, a display unit 23, a storage unit 24, and a control unit 25. The control unit 25 includes a measurement unit 251, an identification unit 252, a calculation unit 253, and a display control unit 254.

[0060] The communication unit 21 is a communication interface for communicating with other devices such as laser interferometers. For example, the communication unit 21 communicates with other devices via wireless communication such as Wi-Fi (registered trademark). The communication unit 21 can also communicate with other devices via cables such as a local area network (LAN).

[0061] The detector unit 22 includes a detector for contacting the object under test, a sensor for detecting that the detector has contacted the object under test, and a motor for moving the detector or changing its orientation. The detector unit 22 measures the three-dimensional coordinates of the detector's end point when the detector contacts the object under test. The detector unit 22 inputs the measured three-dimensional coordinates to the measurement unit 251. The display unit 23 displays characters or images, etc.

[0062] The storage unit 24 includes a storage medium such as a read-only memory (ROM), random access memory (RAM), or a hard disk. The storage unit 24 stores the program executed by the control unit 25. The control unit 25 functions as a measurement unit 251, an identification unit 252, a calculation unit 253, and a display control unit 254 by executing the program stored in the storage unit 24.

[0063] The measuring unit 251 uses the detector unit 22 to measure the ball-to-ball distance of the inspection gauge 100. More specifically, the measuring unit 251 measures the coordinates of the center of the ball by measuring the three-dimensional coordinates of multiple contact points of the detector with the ball of the inspection gauge 100.

[0064] The measuring unit 251 measures the coordinates of the centers of the centers of each of the four spheres of the inspection gauge 100 mounted in the first posture. The measuring unit 251 calculates the distances between the centers of the four spheres as sphere-to-sphere distances. Among these distances, the measuring unit 251 calculates the sphere-to-sphere distance between two corresponding spheres at the ends of the first side corresponding to the measurement position as the first sphere-to-sphere distance. The measuring unit 251 also calculates the sphere-to-sphere distances corresponding to the five sides of the inspection gauge 100 mounted in the first posture, excluding the first side.

[0065] Similarly, the measuring unit 251 calculates the ball-to-ball distances between the centers of the four balls arranged at each vertex of the inspection gauge 100 mounted in the second posture. Among these distances, the measuring unit 251 calculates the ball-to-ball distance between two corresponding balls at the ends of the second side corresponding to the measurement position as the second ball-to-ball distance. The measuring unit 251 also calculates the ball-to-ball distances corresponding to the five sides of the inspection gauge 100 mounted in the second posture, excluding the second side.

[0066] Similarly, the measuring unit 251 calculates the ball-to-ball distances between the centers of the four balls arranged at each vertex of the inspection gauge 100 mounted in the third posture. Among these distances, the measuring unit 251 calculates the ball-to-ball distance between the two corresponding balls at the ends of the third side corresponding to the measurement position as the third ball-to-ball distance. The measuring unit 251 also calculates the ball-to-ball distances corresponding to the five sides of the inspection gauge 100 mounted in the third posture, excluding the third side. The measuring unit 251 outputs information indicating the measured ball-to-ball distances to the calculation unit 253.

[0067] [Identification of Measurement Errors]

[0068] The identification unit 252 communicates with the laser interferometer via the communication unit 21. The identification unit 252 pre-identifies the measurement error of the CMM 200 at the measurement position. Figure 3 This illustrates how the identification unit 252 identifies measurement errors. The identification unit 252 uses two devices (i.e., detector unit 22 and laser interferometer 35) to measure the same distance at the measurement location. By comparing the measurement results from these two devices, the identification unit 252 identifies the measurement errors made by detector unit 22.

[0069] exist Figure 3 In the example, track 31 is installed at the measurement position of the CMM 200 measuring platform. Figures 1A to 1C At the same location. Assume that the slider 32, which is movable on track 31, moves along the measurement position. The object under test 33 and the reflector 34 are fixed to the slider 32. The laser interferometer 35 is arranged such that its optical axis is aligned with the direction in which track 31 extends. The optical axis of the laser interferometer 35 is defined by the center of the spherical portion at the end of the object under test 33 and the center of the reflector plate of the reflector 34.

[0070] First, assume that the slider 32 is in a first reference position on the track 31. With the slider 32 in the first reference position, the position of the spherical portion of the test object 33 is compared to the position of the ball B positioned at one end of the first side when the inspection gauge 100 is arranged in the first posture (see...). Figure 1A The coordinates are roughly the same. With the slider 32 in the first reference position, the identification unit 252 uses the detector unit 22 to measure the coordinates of the spherical portion of the object under test 33. For example... Figure 3 As shown by the dashed arrow, with the slider 32 in the first reference position, the distance from the laser interferometer 35 to the reflector 34 is measured using the laser interferometer 35. The recognition unit 252 obtains the measurement result of the distance from the laser interferometer 35 to the reflector 34 when the slider 32 is in the first reference position from the laser interferometer 35.

[0071] Next, the slider 32 moves to the second reference position on the track 31. With the slider 32 in the second reference position, the position of the spherical portion of the test object 33 is relative to the position of the ball C positioned at one end of the first side when the inspection gauge 100 is arranged in the first posture (see...). Figure 1AThe coordinates are roughly the same. With the slider 32 in the second reference position, the recognition unit 252 uses the detector unit 22 to measure the coordinates of the spherical portion of the object under test 33. With the slider 32 in the second reference position, the distance from the laser interferometer 35 to the reflector 34 is measured using the laser interferometer 35. The recognition unit 252 obtains the measurement result of the distance from the laser interferometer 35 to the reflector 34 when the slider 32 is in the second reference position from the laser interferometer 35.

[0072] The identification unit 252 is based on (i) the distance from the laser interferometer 35 to the reflector 34 when the slider 32 is in the first reference position. Figure 3 The difference between (ii) the distance from the laser interferometer 35 to the reflector 34 when the slider 32 is in the second reference position is used to calculate the reference distance from the first reference position to the second reference position as the calibration value.

[0073] The identification unit 252 is not limited to the example of measuring the calibration value of the reference distance using the laser interferometer 35. For example, the identification unit 252 can use a ball bar (not shown) to measure the calibration value of the reference distance.

[0074] The identification unit 252 calculates the measured value of the reference distance from the first reference position to the second reference position based on the difference between (i) the coordinates of the object under test 33 measured by the detector unit 22 when the slider 32 is in the first reference position and (ii) the coordinates of the object under test 33 measured by the detector unit 22 when the slider 32 is in the second reference position.

[0075] In this example of the invention, the measurement accuracy of the laser interferometer 35 is higher than that of the detector unit 22. Therefore, the identification unit 252 assumes that the difference between the calibration value measured by the laser interferometer 35 and the measurement value measured by the detector unit 22 is caused by the measurement error of the detector unit 22. Based on the difference between the calibration value of the reference distance measured by the laser interferometer 35 and the measurement value of the reference distance measured by the detector unit 22, the identification unit 252 identifies the measurement error of the measurement value measured by the detector unit 22 at the measurement position. The identification unit 252 outputs the identified measurement error to the calculation unit 253.

[0076] [Calculation of the calibration value for ball-to-ball distance]

[0077] The calculation unit 253 calculates the calibration value by measuring the ball-to-ball distance between two corresponding spheres at the two ends of each side of the calibration gauge 100. The calculation unit 253 calculates the calibration values ​​g1 to g6 of the ball-to-ball distances of each side of the regular tetrahedron of the calibration gauge 100, as well as the measurement errors m1 to m6 that occur when the measuring unit 251 measures the ball-to-ball distances of each side of the regular tetrahedron of the calibration gauge 100, by solving the following equation 3.

[0078] [Equation 3]

[0079]

[0080] In equation 3, m j (j = 1, 2, ..., 6) represents the measurement error (unknown) when the detector unit 22 measures the ball-to-ball distance corresponding to the j-th position in the measurement coordinate system of CMM 200.

[0081] Figure 4 This illustrates an example of the j-th position in the measurement coordinate system of the CMM 200. The inspection gauge 100 is mounted such that the vertices of the regular tetrahedron of the inspection gauge 100 are aligned with the coordinates of the first, second, and third positions. Figure 4 Positions P1, P2, and P3 are aligned as shown.

[0082] Figure 4 The j-th (j = 1, 2, ..., 6) position in the measurement coordinate system of CMM 200 is shown.

[0083] In equation 3, l #i,k (i = 1, 2, 3 and k = 1, 2, ..., 6) represents the ball-to-ball distance obtained by measuring the k-th position of the inspection gauge 100 arranged in the i-th posture by the measuring unit 251. Figures 5A to 5C Each example shows the position of the edge corresponding to the subscript k of the inspection gauge 100. Figure 5A The position of the edge of the inspection gauge 100 corresponding to the subscript k (k = 1, 2, ..., 6) is shown when the inspection gauge 100 is arranged in the first posture (i = 1). Figure 5A The arrow in the figure indicates the direction of rotation of the inspection gauge 100 when it is installed in the second position.

[0084] Figure 5B The position of the edge of the inspection gauge 100 corresponding to the subscript k (k = 1, 2, ..., 6) is shown when the inspection gauge 100 is arranged in the second posture (i = 2). Figure 5B The dashed line in the figure indicates the second axis of rotational symmetry around which the inspection gauge 100 rotates when it is installed in the third position. Figure 5B The arrow in the figure indicates the direction of rotation of the inspection gauge 100 when it is installed in the third position. Figure 5C This shows the position of the edge of the inspection gauge 100 corresponding to the subscript k (k = 1, 2, ..., 6) when the inspection gauge 100 is arranged in the third posture (i = 3). k(k = 1, 2, ..., 6) indicates the calibration value (unknown) obtained by calibrating the ball-to-ball distance between the two corresponding balls at the two ends of the kth side of the calibration gauge 100.

[0085] In equation 3, l 2,scl The indication recognition unit 252 identifies the value of the measurement error when the measurement unit 251 measures the ball-to-ball distance at the measurement position. The calculation unit 253 calculates the calibration value g of the ball-to-ball distance by solving the simultaneous equations corresponding to the matrix shown in Equation 3. k and measurement error m j In an example of the present invention, the calculation unit 253 calculates the calibration value g of the ball-to-ball distance using the least squares method. k Similarly, the calculation unit 253 calculates the measurement error m of the ball-to-ball distance using the least squares method. j In this way, the calculation unit 253 can calculate the most probable value as the calibration value g. k The calculation unit 253 will indicate the calibration value g of the calculated ball-to-ball distance. k and measurement error m j The information is output to the display control unit 254.

[0086] The display control unit 254 displays characters or images on the display unit 23. The display control unit 254 displays the calibration value g of the ball-to-ball distance calculated by the calculation unit 253. k and measurement error m j .

[0087] [Inspect the calibration process of the gauges]

[0088] Figure 6 This is a flowchart illustrating the process for calibrating the ball-to-ball distance of the inspection gauge 100 in the first embodiment. First, the inspection gauge 100 is mounted in a first orientation on the measuring platform of the CMM 200, where the measurement error at the measurement position of the first side is identified (S101). The measuring unit 251 measures each ball-to-ball distance between two corresponding balls at both ends of the plurality of sides of the inspection gauge 100 mounted in the first orientation (S102). The inspection gauge 100 is then rotated 120 degrees around a first axis of rotational symmetry and mounted in a second orientation (S103). The measuring unit 251 measures each ball-to-ball distance between two corresponding balls at both ends of the plurality of sides of the inspection gauge 100 mounted in the second orientation (S104).

[0089] Next, the inspection gauge 100 is rotated 120 degrees around the second axis of rotational symmetry and installed in a third posture (S105). The measuring unit 251 measures each ball-to-ball distance among the ball-to-ball distances between two corresponding balls at both ends of the plurality of sides of the inspection gauge 100 installed in the third posture (S106). The calculation unit 253 calculates the calibration value of the ball-to-ball distance by solving a simultaneous equation (S107) and ends the process. The simultaneous equation includes: (i) the ball-to-ball distances of the plurality of sides of the inspection gauge 100 measured when installed in the first posture, (ii) the ball-to-ball distances of the plurality of sides of the inspection gauge 100 measured when installed in the second posture, (iii) the ball-to-ball distances between the plurality of sides of the inspection gauge 100 measured when installed in the third posture, (iv) the calibration value obtained by calibrating the ball-to-ball distances corresponding to the plurality of sides of the inspection gauge 100, and (v) the measurement error at the pre-identified measurement position.

[0090] [Second Embodiment]

[0091] In the first embodiment, an example of the measuring unit 251 measuring the ball-to-ball distance of the inspection gauge 100 installed in a first, second, and third posture has been described. On the other hand, in the second embodiment, in each of the two postures, the inspection gauge 100 is calibrated by measuring (at two locations on the CMM calibrated with a reference instrument) the length of (i) one side of the bottom surface and (ii) one side of a surface other than the bottom surface, and by measuring the distance between the balls at both ends of at least one other side at an uncalibrated location in the CMM. That is, the process of installing the inspection gauge 100 in the third posture is omitted, and the measuring unit 251 measures the ball-to-ball distance of the inspection gauge 100 installed in the first and second postures.

[0092] Figure 7A and Figure 7B Each shows a summary of a calibration method according to a second embodiment of the present invention. Figure 7A This shows the state in which the inspection gauge 100 is installed in the first position. Figure 7B This shows the state in which the inspection gauge 100 is installed in the second position.

[0093] Similar to the first embodiment, the inspection gauge 100 is mounted on the measuring table of the CMM 200 in a first orientation. In the second embodiment, it is assumed that the identification unit 252 pre-identifies the measurement unit 251 in the same manner as in the first embodiment. Figure 7AThe measurement error is shown by the thick line in the diagram when measuring ball-to-ball distances at the first measurement position (position A indicated by the dashed arrow) and the second measurement position (position B indicated by the dashed arrow). The measuring unit 251 measures the first ball-to-ball distance between balls B and C at the two ends of the first side corresponding to the first measurement position among the plurality of sides of the inspection gauge 100 mounted in the first posture. Similarly, the measuring unit 251 measures the second ball-to-ball distance between balls A and C at the two ends of the second side corresponding to the second measurement position. The measuring unit 251 also measures the ball-to-ball distances corresponding to the four sides of the plurality of sides of the inspection gauge 100 mounted in the first posture, excluding the first and second sides.

[0094] After the measuring unit 251 has measured the ball-to-ball distances of multiple sides of the inspection gauge 100 installed in the first posture, as follows: Figure 7A As indicated by the arrow, the inspection gauge 100 is mounted on the measuring table in a second posture, with the inspection gauge 100 rotated about its axis of rotational symmetry. The axis of rotational symmetry is... Figure 7A An axis extending approximately in the depth direction is defined. This axis of rotational symmetry passes through sphere A and is orthogonal to a plane including spheres B, C, and D. In the example of the second embodiment, when the plane orthogonal to the axis of rotational symmetry in the inspection gauge 100 (the plane including spheres B, C, and D) is the bottom surface, the first side corresponding to the first measurement position is included in the bottom surface, but the second side corresponding to the second measurement position is not. By arranging the first measurement position, the second measurement position, and the axis of rotational symmetry for rotating the inspection gauge 100 in this manner, the user can limit rank deficiency (where a non-uniquely determined solution occurs) when calculating sphere-to-sphere distances using the equations described later.

[0095] Figure 7B This illustrates how to mount the inspection gauge 100 in a second position. In the second position, one of the edges of the regular tetrahedron of the inspection gauge 100 that differs from the first and second edges (the edge sandwiched between spheres B and D, also referred to hereinafter as the third edge) moves such that it aligns with the first measurement position where the first edge is positioned in the first position. At this time, one of the edges of the regular tetrahedron of the inspection gauge 100 that differs from the first, second, and third edges (the edge sandwiched between spheres A and B, also referred to hereinafter as the fourth edge) aligns with the second measurement position where the second edge is positioned in the first position.

[0096] The measuring unit 251 measures the third ball-to-ball distance between balls B and D at both ends of the third side of the inspection gauge 100, which is mounted in the second posture and corresponds to the first measuring position. The measuring unit 251 also measures the fourth ball-to-ball distance between balls A and B at both ends of the fourth side of the inspection gauge 100, which is mounted in the second posture and corresponds to the second measuring position. The measuring unit 251 further measures the ball-to-ball distances corresponding to the four sides of the inspection gauge 100, excluding the third and fourth sides.

[0097] The calculation unit 253 calculates the calibration value by solving a series of equations to calibrate the ball-to-ball distance between two corresponding balls at the ends of multiple sides of the inspection gauge 100. The series of equations includes: (i) the ball-to-ball distance of multiple sides of the inspection gauge 100 when installed in a first posture, (ii) the ball-to-ball distance of multiple sides of the inspection gauge 100 when installed in a second posture, (iii) the calibration value (unknown) obtained by calibrating the ball-to-ball distance between two corresponding balls at the ends of multiple sides of the inspection gauge 100, and (iv) the measurement error of the CMM at the first measurement position and the second measurement position identified by the identification unit 252.

[0098] The calculation unit 253 uses the following equation 4 to calculate the calibration values ​​g1 to g6 of the ball-to-ball distance between two corresponding spheres at the two ends of each side of the regular tetrahedron of the inspection gauge 100, as well as the measurement errors m1 to m6 that occur when the measurement unit 251 measures the ball-to-ball distance.

[0099] [Equation 4]

[0100]

[0101] In equation 4, m j (j = 1, 2, ..., 6) represents the measurement error (unknown) when detector unit 22 measures the ball-to-ball distance corresponding to the j-th position in the measurement coordinate system of CMM 200. In equation 4, l #i,k (i = 1, 2, 3 and k = 1, 2, ..., 6) represents the ball-to-ball distance obtained by measuring the k-th position of the inspection gauge 100 arranged in the i-th posture using the measuring unit 251. k (k = 1, 2, ..., 6) represents the calibration value (unknown) obtained by calibrating the ball-to-ball distance between the two corresponding balls at the two ends of the k-th side of the gauge 100. In equation 4, l 2,scl This indicates the value identified by the recognition unit 252 for the measurement error when the measurement unit 251 measures the ball-to-ball distance at the first measurement position. In equation 4, l 5,sclThe value identified by the identification unit 252 is for the measurement error when the measurement unit 251 measures the ball-to-ball distance at the second measurement position.

[0102] [Inspect the calibration process of the gauges]

[0103] Figure 8 This is a flowchart illustrating the process for calibrating the ball-to-ball distance of the inspection gauge 100 in the second embodiment. First, the inspection gauge 100 is mounted in a first posture on the measuring table of the CMM 200, where measurement errors have been identified at a first measurement position and a second measurement position (S201). The measuring unit 251 measures each ball-to-ball distance among the ball-to-ball distances between two corresponding balls at both ends of a plurality of sides of the inspection gauge 100 mounted in the first posture (S202).

[0104] Next, the inspection gauge 100 is rotated 120 degrees around its axis of rotational symmetry and mounted in a second posture (S203). The measuring unit 251 measures each ball-to-ball distance among the ball-to-ball distances between two corresponding balls at the two ends of the plurality of sides of the inspection gauge 100 mounted in the second posture (S204).

[0105] The calculation unit 253 calculates the calibration value (S205) by solving a series of equations to calibrate the ball-to-ball distance between two corresponding balls at both ends of multiple sides of the inspection gauge 100, and then ends the process. The series of equations includes: (i) the ball-to-ball distance of multiple sides of the inspection gauge 100 installed in a first posture, (ii) the ball-to-ball distance of multiple sides of the inspection gauge 100 installed in a second posture, (iii) the calibration value obtained by calibrating the ball-to-ball distance corresponding to the multiple sides of the inspection gauge 100, and (iv) the measurement error at the pre-identified measurement position.

[0106] In the first and second embodiments, examples have been described of the calculation unit 253 of the CMM 200 calculating calibration values ​​obtained by calibrating the ball-to-ball distances corresponding to multiple edges of the inspection gauge 100. However, the present invention is not limited to the example of the CMM 200 including the calculation unit 253. For example, a calibration device (not shown) different from the CMM 200 may be provided with a calculation unit, and this calculation unit may be able to calculate calibration values ​​obtained by calibrating the ball-to-ball distances corresponding to multiple edges of the inspection gauge 100.

[0107] In the first embodiment, an example has been described where the measuring unit 251 measures the ball-to-ball distance of the inspection gauge 100 mounted in a first, second, and third posture. However, the invention is not limited to this, and the user can increase the number of times the posture of the inspection gauge 100 is changed. For example, the measuring unit 251 can measure the ball-to-ball distance of the inspection gauge 100 mounted in a first, second, third, and fourth posture. In this way, the calculation unit 253 can increase the redundancy of the calibration value of the ball-to-ball distance of the inspection gauge 100 to be calculated, and reduce the influence of measurement noise in the calculation of the calibration value.

[0108] [Effects of the calibration method of the present invention]

[0109] According to the calibration method of the present invention, the calculation unit 253 calculates the calibration value of the ball-to-ball distance by solving a series of equations. By adopting this calibration method, the user does not need to use a laser interferometer 35 or the like to measure all the ball-to-ball distances of the inspection gauge 100, thereby reducing the time required for calibration work on the inspection gauge 100.

[0110] This invention is explained based on exemplary embodiments. The scope of this invention is not limited to the scope explained in the above embodiments, and various changes and modifications can be made within the scope of this invention. For example, all or part of the device can be configured to be functionally or physically distributed and integrated in any unit. Furthermore, new exemplary embodiments generated by any combination thereof are included in the exemplary embodiments of this invention. The effects of the new embodiments resulting from the combination have the same effects as the original embodiments together.

Claims

1. A calibration method for calibrating an inspection gauge, said inspection gauge being used to check the measurement accuracy of a coordinate measuring machine (CMM) and having a regular tetrahedral shape, with spheres A, B, C, and D respectively arranged at each vertex of the tetrahedron, the calibration method comprising the following steps: The inspection gauge is mounted on the measuring table of the CMM in a first position; The CMM, which identifies measurement errors, is used to measure the ball-to-ball distances of multiple sides of the inspection gauge mounted in the first posture, wherein the measurement errors are the measurement errors at the measurement position of the first side of the multiple sides of the inspection gauge mounted in the first posture. After measuring the ball-to-ball distances of multiple sides, the inspection gauge is mounted on the measuring table in a second posture by rotating it around a first axis of rotational symmetry. In the second posture, the second side, which is different from the first side among the multiple sides, is in the same measurement position as the first side in the first posture. The first axis of rotational symmetry is an axis that passes through ball A and is orthogonal to the plane including ball B, ball C, and ball D. The CMM is used to measure the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture; After measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture, the inspection gauge is mounted on the measuring table in a third posture by rotating the inspection gauge about a second rotational symmetry axis different from the first rotational symmetry axis. In the third posture, the third side, which is different from the first and second sides, is aligned with the measurement position. The second rotational symmetry axis is an axis that passes through the ball D and is orthogonal to the plane including the ball A, the ball B, and the ball C. The CMM is used to measure the ball-to-ball distances of multiple sides of the inspection gauge mounted in the third posture; as well as The calibration value of the ball-to-ball distance between two corresponding balls at both ends of a plurality of sides of the inspection gauge is calculated by solving a simultaneous equation, which includes the ball-to-ball distances of the plurality of sides of the inspection gauge installed in the first posture, the ball-to-ball distances of the plurality of sides of the inspection gauge installed in the second posture, the ball-to-ball distances of the plurality of sides of the inspection gauge installed in the third posture, and the measurement error of the CMM at the measurement position.

2. The calibration method according to claim 1, wherein, Measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the first posture includes measuring the ball-to-ball distances of all six sides of the inspection gauge mounted in the first posture. Measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture includes measuring the ball-to-ball distances of all six sides of the inspection gauge mounted in the second posture. Measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the third posture includes measuring the ball-to-ball distances of all six sides of the inspection gauge mounted in the third posture.

3. The calibration method according to claim 1 or 2, wherein, Calculating the calibration values ​​for the ball-to-ball distances between two corresponding spheres at the ends of multiple edges of the inspection gauge includes: calculating the calibration values ​​for the ball-to-ball distances of each edge of the regular tetrahedron of the inspection gauge by solving the following simultaneous equation 1, and the measurement errors that occur when measuring the ball-to-ball distances of each edge of the regular tetrahedron of the inspection gauge. Equation 1 … (1) In equation 1, m j Let represent the measurement error when measuring the ball-to-ball distance corresponding to the j-th position, where j = 1, 2, ..., 6, l #i,k This represents the measurement value when measuring the ball-to-ball distance at the k-th position of the inspection gauge arranged in the i-th posture, where i = 1, 2, 3 and k = 1, 2, ..., 6, g k This represents the calibration value obtained by calibrating the ball-to-ball distance between the corresponding balls at the two ends of the k-th side of the inspection gauge, where k = 1, 2, ..., 6, and l 2,scl This represents the value obtained by identifying the measurement error when measuring the ball-to-ball distance at the measurement location.

4. A calibration method for calibrating an inspection gauge, said inspection gauge being used to check the measurement accuracy of a coordinate measuring machine (CMM) and having a regular tetrahedral shape, with spheres A, B, C, and D respectively arranged at each vertex of the tetrahedron, the calibration method comprising the following steps: The inspection gauge is mounted on the measuring table of the CMM in a first position; The CMM, which identifies measurement errors, is used to measure the ball-to-ball distances of multiple sides of the inspection gauge mounted in the first posture. The measurement errors are the measurement errors at a first measurement position where the first side of the multiple sides of the inspection gauge mounted in the first posture is included in the bottom surface of the regular tetrahedron, and the measurement errors at a second measurement position where the second side is not included in the bottom surface. After measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the first posture, the inspection gauge is mounted on the measuring table in a second posture by rotating the inspection gauge about a rotational symmetry axis orthogonal to the bottom surface. In the second posture, a third side, which is different from the first side and the second side, coincides with the first measurement position of the first side in the first posture, and a fourth side, which is different from the first side, the second side, and the third side, coincides with the second measurement position of the second side in the first posture. The rotational symmetry axis is an axis that passes through the ball A and is orthogonal to the plane including the ball B, the ball C, and the ball D. The CMM is used to measure the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture; as well as The calibration value of the ball-to-ball distance between two corresponding balls at two ends of a plurality of sides of the inspection gauge is calculated by solving a simultaneous equation, which includes the ball-to-ball distances of the plurality of sides of the inspection gauge mounted in the first posture, the ball-to-ball distances of the plurality of sides of the inspection gauge mounted in the second posture, and the measurement error of the CMM at the first measurement position and the second measurement position.

5. The calibration method according to claim 4, wherein, Measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the first posture includes measuring the ball-to-ball distances of all six sides of the inspection gauge mounted in the first posture, and Measuring the ball-to-ball distances of multiple sides of the inspection gauge mounted in the second posture includes measuring the ball-to-ball distances of all six sides of the inspection gauge mounted in the second posture.

6. The calibration method according to claim 4 or 5, wherein, Calculating the calibration values ​​for the ball-to-ball distances between corresponding spheres at both ends of multiple edges of the inspection gauge includes: calculating the calibration values ​​for the ball-to-ball distances between two corresponding spheres at both ends of each edge of the regular tetrahedron of the inspection gauge by solving the following simultaneous equations 2, as well as the measurement error that occurs when measuring the ball-to-ball distances. Equation 2 … (2) In equation 2, m j Let represent the measurement error when measuring the ball-to-ball distance corresponding to the j-th position, where j = 1, 2, ..., 6, l #i,k This represents the measurement value when measuring the ball-to-ball distance at the k-th position of the inspection gauge arranged in the i-th posture, where i = 1, 2 and k = 1, 2, ..., 6, g k This represents the calibration value obtained by calibrating the ball-to-ball distance between the corresponding balls at the two ends of the k-th side of the inspection gauge, where k = 1, 2, ..., 6, l 2,scl This represents the value obtained by identifying the measurement error when measuring the ball-to-ball distance at the first measurement position, and l 5,scl This represents the value obtained by identifying the measurement error when measuring the ball-to-ball distance at the second measurement position.

7. The calibration method according to any one of claims 1, 2, 4 and 5, wherein, Calculating the calibration value includes using the least squares method.

8. The calibration method according to any one of claims 1, 2, 4 and 5 further includes the step of using a laser interferometer to identify measurement errors.

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