Error calibration method and device for laser tracker

Abstract

The invention discloses an error calibration method for a laser tracker. The error calibration method comprises the following steps: S1, determining a key error term of the laser tracker; s2, the target ball is arranged at the position where a measuring head of the three-coordinate measuring machine is installed; s3, establishing a system error model according to the structure of the laser tracker; s4, changing the position of the three-coordinate measuring machine, obtaining the center point coordinate of the target ball under the coordinate system of the laser tracker when the three-coordinate measuring machine is at the corresponding position, and obtaining the center point coordinate of the target ball measured by the laser tracker under the coordinate system of the three-coordinate measuring machine when the three-coordinate measuring machine is at the corresponding position; and S5, setting a mathematical model solved in the measurement process, and obtaining the corresponding error value of each key error term in the step S1 through the mathematical model. The method has the beneficial effects that each key error term is quickly decoupled, the method is particularly suitable for quickly decoupling terms with large assembly errors of the laser tracker, and quick calibration of geometric errors of the laser tracker is realized.

Description

Technical Field

[0001] The invention relates to the field of digital measurement, and in particular to a laser tracker error calibration method and device. Background Art

[0002] Laser tracker is a high-precision large-scale spatial coordinate measurement benchmark, and its accuracy calibration is the key to determining the measurement accuracy of the system. Currently, there are two main methods: single parameter calibration and overall parameter calibration. The comprehensive error calibration method uses a modeling method that combines multi-body system dynamics with homogeneous coordinate transformation methods, such as the model established by Conte et al. This method is too complicated, and there are many error couplings between error terms, and it is impossible to achieve accurate calibration of all parameters. Single parameter calibration uses the sum of the effects of single errors on the final measurement accuracy as a model to achieve system accuracy calibration, such as the methods used by Loser, Muralikrishnan, and Zhang Hejun, and the single parameter calibration method is not suitable for calibration with excessive assembly errors. Summary of the invention

[0003] The technical problem to be solved by the present invention is that the current single parameter calibration and overall parameter calibration methods are both unable to calibrate items with large assembly errors of laser trackers. The purpose is to provide a laser tracker error calibration method and device, which can quickly decouple various key error items, and is particularly suitable for quickly decoupling items with large assembly errors of laser trackers, thereby realizing rapid calibration of laser tracker geometric errors.

[0004] The present invention is achieved through the following technical solutions:

[0005] A laser tracker error calibration method comprises the following steps:

[0006] S1, determine the key error terms of the laser tracker;

[0007] S2, setting the target ball at the position where the probe of the coordinate measuring machine is installed;

[0008] S3, establishing a system error model according to the structure of the laser tracker, and transforming the center point coordinates of the target sphere in the reference coordinate system and the center point coordinates of the target sphere in the laser tracker coordinate system through the system error model;

[0009] S4, changing the position of the three-dimensional coordinate measuring machine, obtaining the center point coordinates of the target sphere in the laser tracker coordinate system when the three-dimensional coordinate measuring machine is at the corresponding position, and obtaining the center point coordinates of the target sphere measured by the laser tracker in the three-dimensional coordinate measuring machine's own coordinate system when the three-dimensional coordinate measuring machine is at the corresponding position;

[0010] S5, setting a mathematical model to be solved during the measurement process, and obtaining corresponding error values ​​of each key error term in step S1 through the mathematical model;

[0011] The execution order of step S3 and step S4 can be switched.

[0012] The beneficial effect of the present invention is that by determining the key error terms, the error elements with little influence on the spatial coordinate measurement accuracy are ignored, the coupling of multiple error terms is avoided, and then the target sphere is set at the position where the three-dimensional coordinate measuring machine probe is installed (the probe of the three-dimensional coordinate measuring machine needs to be replaced, and the target sphere is installed at the position where the probe is installed) to position the target sphere, and then a system error model is established according to the structure of the laser tracker. The center point coordinates of the target sphere in the reference coordinate system and the center point coordinates of the target sphere in the laser tracker coordinate system are converted through the system error model, and the changed center point coordinates of the target sphere are substituted into the mathematical model, and each key error term is quickly decoupled, which is particularly suitable for quickly decoupling items with large assembly errors of the laser tracker, so as to realize the rapid calibration of the geometric errors of the laser tracker.

[0013] In some embodiments, the step S1 further includes establishing a coordinate system of each component of the laser tracker, wherein the coordinate system of each component of the laser tracker includes a horizontal axis coordinate system. 0 (x 0 ,y 0 , z 0 ), pitch axis coordinate system O 1 (x 1 ,y 1 , z 1 ), optical axis coordinate system O 2 (x 2 ,y 2 , z 2 ) and the target sphere coordinate system O 3 (x 3 ,y 3 , z 3 ), the horizontal axis coordinate system O 0 (x 0 ,y 0 , z 0 ) is the reference coordinate system.

[0014] In some embodiments, the key error terms include the perpendicularity E_AOY between the horizontal axis and the vertical axis, the intersection E_XO between the horizontal axis and the vertical axis, the reference deviation dd between the optical axis and the pitch axis along the X direction, the intersection E_OY between the optical axis and the pitch axis along the Y direction, the intersection E_OZ between the optical axis and the pitch axis in the opposite direction of Z, the perpendicularity E_COX between the optical axis and the pitch axis along the Y direction, and the perpendicularity E_BOX between the optical axis and the pitch axis along the Z direction, so as to calibrate the above key error terms, ignore the error elements that have little influence on the accuracy of spatial coordinate measurement, and avoid the coupling of multiple error terms.

[0015] In some embodiments, the system error model is:

[0016]

[0017] Among them, the transformation formula of T_α in the system error model is,

[0018] The transformation formula of T_AOY in the system error model is:

[0019]

[0020] The transformation formula of T_XO in the system error model is:

[0021] The system error model The transformation formula is,

[0022] The transformation formula of T_OY in the system error model is:

[0023] The transformation formula of T_OZ in the system error model is:

[0024] The transformation formula of T_COX in the system error model is:

[0025]

[0026] The transformation formula of T_BOX in the system error model is:

[0027]

[0028] The transformation formula of T_d in the system error model is:

[0029] E_AOY is the perpendicularity between the horizontal axis and the vertical axis, E_XO is the intersection between the horizontal axis and the vertical axis, dd is the reference deviation between the optical axis and the pitch axis along the X direction, E_OY is the intersection between the optical axis and the pitch axis along the Y direction, E_OZ is the intersection between the optical axis and the pitch axis in the opposite direction of Z, E_COX is the perpendicularity between the optical axis and the pitch axis along the Y direction, E_BOX is the perpendicularity between the optical axis and the pitch axis along the Z direction, α is the horizontal axis rotation angle of the laser tracker, is the pitch axis rotation angle, d is the length measured by the laser tracker, (x c ,y c , z c ) is the center point coordinate of the target sphere measured in the laser tracker coordinate system, so as to realize the conversion between the center point coordinate of the target sphere in the reference coordinate system and the center point coordinate of the target sphere in the laser tracker coordinate system.

[0030] In some embodiments, a second conversion relation is set to obtain the coordinates (x mc ,y mc , z mc ), the second conversion relation is:

[0031]

[0032] Among them, (x c ,y c , z c ) is the center point coordinate of the target sphere measured in the laser tracker coordinate system.

[0033] In some embodiments, a homogeneous coordinate transformation matrix is ​​set to transform the homogeneous coordinates of the six parameters existing in the coordinate system of the three-dimensional coordinate measuring machine and the reference coordinate system. The homogeneous coordinate transformation matrix is ​​as follows:

[0034]

[0035] Among them, R represents the rotation transformation matrix, and P represents the translation transformation matrix.

[0036] In some embodiments, the mathematical model is:

[0037]

[0038] Among them, (x m ,y m , z m ) is the coordinate of the center point of the target ball in the coordinate measuring machine's own coordinate system, (x mc ,y mc , z mc) is the center point coordinate of the target sphere measured by the laser tracker in the coordinate measuring machine’s own coordinate system. The solution obtained by the error model is substituted into the mathematical model to quickly solve the seven geometric error parameters of the laser tracker.

[0039] In some embodiments, the data measured by the laser tracker is interferometric length measurement data, and the three-coordinate measuring machine is a long-stroke high-precision three-coordinate measuring machine. In the measurement process, the interferometric length measurement data of the laser tracker is used, and in the measurement process, a long-stroke high-precision three-coordinate measuring machine is used, so that a more accurate error value can be obtained.

[0040] The present invention also provides a laser tracker error calibration device, comprising a three-coordinate measuring machine, a target ball and a laser tracker, wherein the target ball is arranged at the position where the probe of the three-coordinate measuring machine is installed; and the laser tracker is arranged on the three-coordinate measuring machine. It is convenient to use the three-coordinate measuring machine as an on-site precision calibration device to reduce the difficulty of solving the key error items of the laser tracker.

[0041] In some embodiments, the three-dimensional coordinate measuring machine further includes a workbench, and the laser tracker is arranged on the workbench to improve the measurement accuracy.

[0042] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0043] 1. By determining the key error terms, ignoring the error elements that have little influence on the spatial coordinate measurement accuracy, avoiding the coupling of multiple error terms, and then setting the target sphere at the position where the three-dimensional coordinate measuring machine probe is installed to locate the target sphere, and then establishing a system error model according to the laser tracker structure, the center point coordinates of the target sphere in the reference coordinate system and the center point coordinates of the target sphere in the laser tracker coordinate system are converted through the system error model, and the changed center point coordinates of the target sphere are substituted into the mathematical model, and the key error terms are quickly decoupled, which is especially suitable for quickly decoupling the items with large assembly errors of the laser tracker, so as to realize the rapid calibration of the geometric errors of the laser tracker.

[0044] 2. Use a three-coordinate measuring machine as on-site precision calibration equipment to reduce the difficulty of solving key error terms of the laser tracker. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the technical solutions of the exemplary embodiments of the present invention, the following briefly introduces the drawings required for use in the embodiments. It should be understood that the following drawings only illustrate certain embodiments of the present invention and should not be regarded as limiting the scope. For those of ordinary skill in the art, other relevant drawings can be obtained based on these drawings without creative work. In the drawings:

[0046] Figure 1 It is a structural diagram of the device of the present invention;

[0047] Figure 2 The schematic diagram of the method of the present invention.

[0048] Marks and corresponding parts names in the attached drawings:

[0049] A three-dimensional coordinate measuring machine 10 , a workbench 12 , a target sphere 20 , and a laser tracker 30 . DETAILED DESCRIPTION

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with embodiments and drawings. The exemplary embodiments of the present invention and their description are only used to explain the present invention and are not intended to limit the present invention.

[0051] Throughout the specification, references to "one embodiment," "an embodiment," "an example," or "an example" mean that a particular feature, structure, or characteristic described in conjunction with the embodiment or example is included in at least one embodiment of the present invention. Therefore, the phrases "one embodiment," "an embodiment," "an example," or "an example" appearing in various places throughout the specification do not necessarily all refer to the same embodiment or example. In addition, particular features, structures, or characteristics may be combined in one or more embodiments or examples in any suitable combination and / or sub-combination. In addition, it will be appreciated by those of ordinary skill in the art that the figures provided herein are for illustrative purposes and that the figures are not necessarily drawn to scale. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0052] In the description of the present invention, the directions or positional relationships indicated by terms such as “front”, “rear”, “left”, “right”, “up”, “down”, “vertical”, “horizontal”, “high”, “low”, “inside” and “outside” are based on the directions or positional relationships shown in the accompanying drawings and are only for the convenience of describing the present invention and simplifying the description. They do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction. Therefore, they should not be understood as limiting the scope of protection of the present invention.

[0053] The terms "first" and "second" used in the present invention are only used to distinguish the corresponding components for the sake of clarity of description, and are not intended to limit any order or emphasize importance, etc. In addition, the term "connected" used in this article can be directly connected or indirectly connected via other components without special explanation.

[0054] Example 1

[0055] Due to manufacturing errors in parts processing, assembly errors in the installation of optical and mechanical components, and environmental changes, there is a deviation between the coordinate values ​​of the target point measured by the laser tracker and the actual coordinate values. Taking into account the size and randomness of the laser tracking system error, the key error elements in the error model are identified, the error elements that have a small impact on the spatial coordinate measurement accuracy are ignored, and the error model is simplified to solve the key errors. To this end, the present invention provides a laser tracker error calibration method, see Figure 1 and Figure 2 , including the following steps:

[0056] S1, determining the key error terms of the laser tracker 30;

[0057] S2, setting the target ball 20 at the probe position of the three-dimensional coordinate measuring machine 10; (it is necessary to replace the probe of the three-dimensional coordinate measuring machine and install the target ball).

[0058] S3, establishing a system error model according to the structure of the laser tracker, and transforming the center point coordinates of the target sphere 20 in the reference coordinate system and the center point coordinates of the target sphere 20 in the laser tracker coordinate system through the system error model;

[0059] S4, changing the position of the three-dimensional coordinate measuring machine 10, obtaining the center point coordinates of the target sphere 20 in the laser tracker coordinate system when the three-dimensional coordinate measuring machine 10 is at the corresponding position, and obtaining the center point coordinates of the target sphere 20 measured by the laser tracker 30 in the three-dimensional coordinate measuring machine's own coordinate system when the three-dimensional coordinate measuring machine 10 is at the corresponding position;

[0060] S5, setting a mathematical model to be solved during the measurement process, and obtaining corresponding error values ​​of each key error term in step S1 through the mathematical model;

[0061] The implementation order of step S3 and step S4 can be interchanged. By determining the key error terms, ignoring the error elements that have little influence on the spatial coordinate measurement accuracy, avoiding the coupling of multiple error terms, and then setting the target sphere 20 at the position where the probe of the three-dimensional coordinate measuring machine 10 is installed to locate the target sphere 20, and then establishing a system error model according to the structure of the laser tracker, through the system error model, the center point coordinates of the target sphere 20 in the reference coordinate system and the center point coordinates of the target sphere 20 in the laser tracker coordinate system are converted, and the changed center point coordinates of the target sphere 20 are substituted into the mathematical model, and each key error term is quickly decoupled, which is particularly suitable for quickly decoupling the items with large assembly errors of the laser tracker, so as to realize the rapid calibration of the geometric error of the laser tracker.

[0062] See also Figure 2The step S1 also includes establishing the coordinate system of each component of the laser tracker, wherein the coordinate system of each component of the laser tracker includes a horizontal axis coordinate system O 0 (x 0 ,y 0 , z 0 ), pitch axis coordinate system O 1 (x 1 ,y 1 , z 1 ), optical axis coordinate system O 2 (x 2 ,y 2 , z 2 ) and the target sphere coordinate system O 3 (x 3 ,y 3 , z 3 ), the horizontal axis coordinate system O 0 (x 0 ,y 0 , z 0 ) is the reference coordinate system.

[0063] See also Figure 2 The key error terms include the perpendicularity E_AOY between the horizontal axis and the vertical axis, the intersection E_XO between the horizontal axis and the vertical axis, the reference deviation dd between the optical axis and the pitch axis along the X direction, the intersection E_OY between the optical axis and the pitch axis along the Y direction, the intersection E_OZ between the optical axis and the pitch axis in the opposite direction of Z, the perpendicularity E_COX between the optical axis and the pitch axis along the Y direction, and the perpendicularity E_BOX between the optical axis and the pitch axis along the Z direction, so as to calibrate the above key error terms and avoid the coupling of multiple error terms.

[0064] Specifically, the system error model is:

[0065]

[0066] Among them, the transformation formula of T_α in the system error model is,

[0067] The transformation formula of T_AOY in the system error model is:

[0068]

[0069] The transformation formula of T_XO in the system error model is:

[0070] The system error model The transformation formula is,

[0071] The transformation formula of T_OY in the system error model is:

[0072] The transformation formula of T_OZ in the system error model is:

[0073] The transformation formula of T_COX in the system error model is:

[0074]

[0075] The transformation formula of T_BOX in the system error model is:

[0076]

[0077] The transformation formula of T_d in the system error model is:

[0078] E_AOY is the perpendicularity between the horizontal axis and the vertical axis, E_XO is the intersection between the horizontal axis and the vertical axis, dd is the reference deviation between the optical axis and the pitch axis along the X direction, E_OY is the intersection between the optical axis and the pitch axis along the Y direction, E_OZ is the intersection between the optical axis and the pitch axis in the opposite direction of Z, E_COX is the perpendicularity between the optical axis and the pitch axis along the Y direction, E_BOX is the perpendicularity between the optical axis and the pitch axis along the Z direction, α is the horizontal axis rotation angle of the laser tracker, is the pitch axis rotation angle, d is the length measured by the laser tracker, (x c ,y c , z c ) is the center point coordinate of the target sphere 20 measured in the laser tracker coordinate system, so as to realize the conversion between the center point coordinate of the target sphere 20 in the reference coordinate system and the center point coordinate of the target sphere 20 in the laser tracker coordinate system.

[0079] See also Figure 2 , set the second conversion relationship to obtain the coordinates (x mc ,y mc , z mc ), the second conversion relation is:

[0080]

[0081] Among them, (x c ,y c , z c ) are the center point coordinates of the target sphere 20 measured in the laser tracker coordinate system.

[0082] Specifically, a homogeneous coordinate transformation matrix is ​​set to transform the homogeneous coordinates of the six parameters existing in the coordinate system of the three-dimensional coordinate measuring machine and the reference coordinate system. The homogeneous coordinate transformation matrix is ​​as follows:

[0083]

[0084] Among them, R represents the rotation transformation matrix, and P represents the translation transformation matrix.

[0085] Specifically, the mathematical model is:

[0086]

[0087] Among them, (x m ,y m , z m ) is the center point coordinate of the target ball 20 in the coordinate measuring machine's own coordinate system, (x mc ,y mc , z mc ) is the center point coordinate of the target sphere 20 measured by the laser tracker 30 in the coordinate measuring machine's own coordinate system. The solution obtained by the error model is substituted into the mathematical model to quickly solve the seven geometric error parameters of the laser tracker 30. The laser tracker 30 is error compensated to improve the measurement accuracy of the laser tracker 30.

[0088] See also Figure 1 The data measured by the laser tracker 30 is interferometric length measurement data, and the three-dimensional coordinate measuring machine 10 is a long-stroke high-precision three-dimensional coordinate measuring machine. Using the interferometric length measurement data of the laser tracker 30 and using a long-stroke high-precision three-dimensional coordinate measuring machine during the measurement process can obtain a more accurate error value.

[0089] Example 2

[0090] The present invention also provides a laser tracker error calibration device, see Figure 1 , including a three-dimensional coordinate measuring machine 10, a target sphere 20 and a laser tracker 30, wherein the target sphere 20 is arranged at the position where the probe of the three-dimensional coordinate measuring machine 10 is installed; and the laser tracker 30 is arranged on the three-dimensional coordinate measuring machine 10. It is convenient to use the three-dimensional coordinate measuring machine 10 as an on-site precision calibration device to reduce the difficulty of solving the laser tracker 30.

[0091] See also Figure 1 The three-dimensional coordinate measuring machine 10 also includes a workbench 12, and the laser tracker 30 is arranged on the workbench 12 to improve the measurement accuracy.

[0092] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A laser tracker error calibration method, characterized in that: The steps include: S1, determine the key error terms of the laser tracker; S2, setting the target ball at the position where the probe of the coordinate measuring machine is installed; S3, establishing a system error model according to the structure of the laser tracker, and transforming the center point coordinates of the target sphere in the reference coordinate system and the center point coordinates of the target sphere in the laser tracker coordinate system through the system error model; S4, changing the position of the three-dimensional coordinate measuring machine, obtaining the center point coordinates of the target sphere in the laser tracker coordinate system when the three-dimensional coordinate measuring machine is at the corresponding position, and obtaining the center point coordinates of the target sphere measured by the laser tracker in the three-dimensional coordinate measuring machine's own coordinate system when the three-dimensional coordinate measuring machine is at the corresponding position; S5, setting a mathematical model to be solved during the measurement process, and obtaining corresponding error values ​​of each key error term in step S1 through the mathematical model; The execution order of step S3 and step S4 can be switched.

2. The laser tracker error calibration method according to claim 1, characterized in that: The step S1 also includes establishing coordinate systems of various components of the laser tracker, and the coordinate systems of various components of the laser tracker include a horizontal axis coordinate system O0 (x0, y0, z0), a pitch axis coordinate system O1 (x1, y1, z1), an optical axis coordinate system O2 (x2, y2, z2) and a target sphere coordinate system O3 (x3, y3, z3). The horizontal axis coordinate system O0 (x0, y0, z0) is a reference coordinate system.

3. The laser tracker error calibration method according to claim 1, characterized in that: The key error terms include the perpendicularity E_AOY between the horizontal axis and the vertical axis, the intersection E_XO between the horizontal axis and the vertical axis, the reference deviation dd between the optical axis and the pitch axis along the X direction, the intersection E_OY between the optical axis and the pitch axis along the Y direction, the intersection E_OZ between the optical axis and the pitch axis in the opposite direction of Z, the perpendicularity E_COX between the optical axis and the pitch axis along the Y direction, and the perpendicularity E_BOX between the optical axis and the pitch axis along the Z direction.

4. The laser tracker error calibration method according to claim 1, characterized in that: The system error model is: Among them, the transformation formula of T_α in the system error model is, The transformation formula of T_AOY in the system error model is: The transformation formula of T_XO in the system error model is: The system error model The transformation formula is, The transformation formula of T_OY in the system error model is: The transformation formula of T_OZ in the system error model is: The transformation formula of T_COX in the system error model is: The transformation formula of T_BOX in the system error model is: The transformation formula of T_d in the system error model is: E_AOY is the perpendicularity between the horizontal axis and the vertical axis, E_XO is the intersection between the horizontal axis and the vertical axis, dd is the reference deviation between the optical axis and the pitch axis along the X direction, E_OY is the intersection between the optical axis and the pitch axis along the Y direction, E_OZ is the intersection between the optical axis and the pitch axis in the opposite direction of Z, E_COX is the perpendicularity between the optical axis and the pitch axis along the Y direction, E_BOX is the perpendicularity between the optical axis and the pitch axis along the Z direction, α is the horizontal axis rotation angle of the laser tracker, is the pitch axis rotation angle, d is the length measured by the laser tracker, (x c ,y c , z c ) is the center point coordinate of the target sphere measured in the laser tracker coordinate system.

5. The laser tracker error calibration method according to claim 4, characterized in that: Set the second conversion relationship to obtain the coordinates (x mc ,y mc , z mc ), the second conversion relation is: Among them, (x c ,y c , z c ) is the center point coordinate of the target sphere measured in the laser tracker coordinate system.

6. The laser tracker error calibration method according to claim 5, characterized in that: Set the homogeneous coordinate transformation matrix to transform the homogeneous coordinates of the six parameters existing in the coordinate system of the three-dimensional coordinate measuring machine and the reference coordinate system. The homogeneous coordinate transformation matrix is ​​as follows: Among them, R represents the rotation transformation matrix, and P represents the translation transformation matrix.

7. The laser tracker error calibration method according to claim 6, characterized in that: The mathematical model is: Among them, (x m ,y m , z m ) is the coordinate of the center point of the target ball in the coordinate measuring machine's own coordinate system, (x mc ,y mc , z mc ) is the center point coordinate of the target sphere measured by the laser tracker in the coordinate measuring machine's own coordinate system.

8. The laser tracker error calibration method according to claim 1, characterized in that: The data measured by the laser tracker are interferometric length measurement data, and the three-coordinate measuring machine is a long-travel and high-precision three-coordinate measuring machine.

9. A laser tracker error calibration device, characterized in that: The laser tracker error calibration method according to any one of claims 1 to 8 is implemented, comprising: A three-dimensional coordinate measuring machine and a target ball, wherein the target ball is arranged at a position where a probe of the three-dimensional coordinate measuring machine is installed; A laser tracker is arranged on the three-dimensional coordinate measuring machine.

10. The laser tracker error calibration device according to claim 9, characterized in that: The three-dimensional coordinate measuring machine also includes a workbench, and the laser tracker is arranged on the workbench.

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