Rotary table compensation

Abstract

The invention relates to rotary table compensation. A CMM system and a method for calibrating the same as well as a computer program product are disclosed. The system comprises a CMM, a rotary table and a rotating device. The CMM system is configured to be calibrated by determining a 6 degree of freedom pose of a fixture. The fixture is mountable to at least one component of the rotary table or the rotating device such that a current pose of the fixture is associated with a current pose of the rotary table relative to the CMM. The rotary table is movable into a plurality of poses and the 6 degree of freedom pose of the fixture is measured for each pose. An error map is generated based on angles associated with the poses of the rotary table and a coordinate transformation from a CMM coordinate system to a part coordinate system associated with the rotary table is generated based on the error map. The program code of the computer program product is stored on a machine readable medium or implemented by an electromagnetic wave comprising program code segments and has computer executable instructions which, when run on a CMM system according to the invention, perform a method according to the invention.

Description

Technical Field

[0001] This invention relates to a coordinate measuring machine (CMM) system that measures the geometry of a physical object by sensing features on its surface using sensors. In particular, this invention relates to a CMM system configured to perform a calibration method and a calibration method for the coordinate measuring machine (CMM) system. Furthermore, this invention relates to a computer program product having program code to be stored on the coordinate measuring machine (CMM) or computer data signals for implementing the calibration method. Background Technology

[0002] A coordinate measuring machine (CMM) is a machine configured to measure the 3D coordinates of certain points on the surface of an object. CMMs are important in various industrial sectors and are used, for example, in production measurement techniques to determine, for instance, the deviation of the geometry of a manufactured workpiece from its theoretical model, and to assess whether this deviation is within a defined tolerance range to detect manufacturing defects, determine achievable accuracy in a production process, or measure wear and tear that occurs during the lifespan of an object such as a turbine blade. The object can be, for example, a workpiece suitable for measurement by a CMM.

[0003] Typically, a CMM consists of a main structure, a probing system, and a data collection and processing system. An example of a CMM used in industrial applications (such as production measurement technology) is a 3-axis CMM. A 3-axis CMM is constructed such that the main structure includes three axes of motion to enable the CMM to measure the 3D coordinates of an object. The main structure typically includes: a base with a measuring stage on which the object is positioned; a movable frame mounted to the base such that the movable frame can move along a first axis; and a component, referred to herein as an arm, movably mounted to the movable frame and movable along a second axis nominally perpendicular to the first axis of motion of the frame. The arm contains a probing system, such as a scanning head including sensors, movable along a third axis, for example, where the third axis is nominally perpendicular to the first and second axes of motion of the CMM, thus allowing the sensors to move along all three axes and enabling the CMM to measure the 3D coordinates of the object. Motors are typically built into the CMM to drive each axis. The data collection and processing system typically includes a machine controller, a desktop computer, and application software.

[0004] The detailed construction design was implemented, and the above-mentioned 3-axis variant is only considered as an example of the most common design and principle of CMM.

[0005] To measure surface changes of an object, probes are used, including, for example, tactile sensors or optical sensors. Tactile sensors can be implemented, for example, as spring-loaded steel or ruby ​​ball styluses, and are also referred to as probes in some prior art literature. When the tactile sensor contacts the surface of the object, the stylus is deflected and transmits X, Y, and Z coordinate information to a computer. Another measurement method is to drag the tactile sensor along the surface of the object and measure the 3D coordinates at specified intervals; these tactile sensors are also referred to as scanning probes. This scanning method, for example, is superior to conventional contact probe methods in terms of accuracy and, in most cases, efficiency. Furthermore, optical sensors (such as laser sensors) can be used for distance measurement and thus to determine the 3D coordinates of the object.

[0006] CMMs typically combine different types of sensors and are therefore referred to as multi-sensor measurement machines. This can include various types of sensors, such as tactile sensors or optical sensors, including, for example, lasers, cameras, video, and white light sensors, to provide measurements known as multi-sensor measurements. Depending on the geometry of the object, different sensors can be advantageously used for measurement.

[0007] However, using the traditional 3-axis model of a CMM may make it difficult or impossible to reach some points on the surface of the object, thus slowing down the measurement process or even making the measurement of some 3D points impossible. In many cases, it is necessary to access the object to be measured from all sides, and it is also difficult to reach the points on the object that need to be measured. To simplify the accessibility of each 3D point of the object and accelerate the measurement process, a 5-axis probe can be used, for example. Difficulties arise especially when inspecting parts where the sensors need to be changed multiple times (such as very small and complex parts). Such parts, as well as crankshafts, camshafts, screw compressors, turbine disks, and impeller disks, can be measured, for example, using a rotary table. By reducing the amount of measurement, using a rotary table on a CMM can increase CMM capacity, reduce inspection time, and broaden the application range. Instead of using a single rotary table, stacked rotary tables can also be used, for example, by aligning the object to be measured relative to the sensors. For example, if a multi-sensor system is available, a rotary table can be used to allow vertical probing of the workpiece surface using sensors that are fixedly aligned relative to one of the axes of the CMM. Furthermore, if, for example, one of the sensors is an optical sensor, such as the optical sensor in a camera, the rotary stage also allows the object to be measured to be aligned relative to the focal plane of the camera.

[0008] While offering positive effects, for example, on object accessibility, each additional axis added to a CMM or CMM system (such as a rotary table) is another potential source of error. CMMs or CMM systems are subjected to various error-inducing factors, such as dynamic thermal and mechanical stresses, varying humidity, inconsistent and nonlinear material responses, and inappropriate human input. Therefore, indexing errors, wobbling errors, and eccentricity errors, as well as errors due to the weight of the object mounted on the rotary table, can occur. Consequently, in the prior art, the error map of the rotary table is either factory-calibrated, where the error map can be any well-defined function that provides corrected 3D coordinates of the object for each angular position of the rotary table, or the rotary table is constructed to be long-term stable, leading to increased technology expenditure. Constructing a rotary table to reduce error means that the construction must be long-term stable to avoid frequent remapping and rigid enough to avoid measurement errors due to the load on the object (e.g., workpiece), resulting in high costs.

[0009] To correct for errors, the corresponding isometric transformations from the part coordinate system fixed relative to the object being measured and the CMM coordinate system associated with the CMM must be known. Together with the known orientation of the rotary table, the object coordinates can then be determined. Based on the existing state, transformation parameters can be derived from the known geometric mechanical setup, the positioning of one or more rotary tables within the CMM system, and feedback on the rotational position within each rotary table. In the prior art, error maps of individual components (e.g., rotary table rotary joints) are typically factory-calibrated. However, the measurement accuracy of the rotary table is limited due to systematic errors (e.g., translational and angular errors). In other words, the errors of the CMM and the rotary table are determined; however, the measurement inaccuracies caused by the mechanical connection between the rotary table and the CMM are not considered, and therefore such measurement inaccuracies still exist. Summary of the Invention

[0010] Therefore, the object of the present invention is to provide a coordinate measuring machine (CMM) system including a rotary table and a method that allows for improved accuracy and overall measurement robustness.

[0011] Furthermore, the object of the present invention is to provide a coordinate measuring machine (CMM) system and method including a rotary table, which, compared with the prior art, reduces technical expenditure and / or provides higher measurement accuracy.

[0012] Another object of the present invention is to provide a coordinate measuring machine (CMM) system and method including a rotary table, which can improve measurement accuracy even if further rotational axes are added to the system and thus error sources are added.

[0013] These objectives are achieved by implementing at least some of the features described below. Other aspects describe features that further develop the invention in alternative or advantageous ways.

[0014] Feature section

[0015] This invention relates to a method that allows users to easily and frequently perform autonomous calibration of a rotary table and / or rotating mechanism in a CMM system. Therefore, the CMM system and method of this invention provide the possibility of frequent error adjustment by frequently generating error maps. In these error maps, the 3D coordinates of the 6-DOF orientation of the fixture are determined using the CMM's sensors by measuring the deviation of the fixture at various rotation angles, thereby generating a coordinate transformation from the part coordinate system (fixed relative to the rotary table) to the CMM coordinate system (fixed relative to the CMM's base) to register the deviation between the actual measured 6-DOF (6 DOF) orientation of the fixture and the theoretically assumed 6-DOF of the fixture. The CMM system of this invention generates an isometry from the part coordinate system to the CMM coordinate system (or from the CMM coordinate system to the part coordinate system) with high precision, and thus allows for error correction of measurements. The method of this invention also allows for the installation of low-precision and lower-cost bearings, while still achieving higher measurement accuracy compared to using higher-precision bearings in conjunction with existing calibration conditions. Furthermore, the method of this invention allows for overall calibration of the entire CMM system, including not only error compensation for the rotary table but also compensation for the entire setup or mechanical fixation on the CMM. Besides enabling overall calibration of the entire CMM system, the method of this invention leads to cost reduction because, for example, oscillation and eccentricity errors of the rotary table can be frequently measured and corrected by the user. Since the method of this invention uses the CMM itself as a reference system, the calibration procedure requires only low-cost fixtures. Moreover, the fixture itself does not need to be precisely known; the only requirement is that it is geometrically stable during the calibration process, or that the behavior of the fixture is known during the calibration procedure.

[0016] More specifically, the present invention relates to a coordinate measuring machine (CMM) system operable to measure an object, the CMM system comprising: a coordinate measuring machine (CMM) associated with a coordinate measuring machine coordinate system fixed relative to the CMM, the CMM including a computing unit and at least one sensor, particularly a tactile sensor or an optical sensor, for determining the three-dimensional coordinates of the object; a rotary table having means for holding the object and associated with a part coordinate system fixed relative to the rotary table; a rotating device configured to move the rotary table to different orientations relative to the CMM by rotational movement; and a fixture configured to determine the 6-DOF (6 degrees of freedom) orientation of the fixture using the at least one sensor of the CMM, and relative to the rotary table. The fixture is arranged such that the current orientation of the fixture is associated with the current orientation information of the rotary table relative to the coordinate measuring machine, particularly wherein the fixture is part of or can be mounted to the rotary table. The coordinate measuring machine system is characterized by being configured to perform, in particular automatically, a calibration procedure comprising: moving the rotary table into multiple orientations by setting different angular positions with respect to the rotational movement; measuring the 6-DOF orientation of the fixture using the coordinate measuring machine for each of the multiple orientations of the rotary table; generating an error map using the calculation unit based on the angles associated with the different angular positions and the associated 6-DOF orientation of the fixture; and determining, in particular automatically, a coordinate transformation from the coordinate measuring machine coordinate system to the part coordinate system using the calculation unit based on the error map.

[0017] The rotary table can be directly mounted to the base or mounted to the base via an intermediary component. According to one embodiment of the invention, the coordinate measuring machine (CMM) system is characterized in that the rotary device is configured as a single-axis device, wherein the rotary table is mounted to the base, the base is mounted to the coordinate measuring machine, and the setting of different angular positions includes rotating the rotary table about a first rotation axis relative to the base.

[0018] An intermediary component is mounted to the base. According to one embodiment of the invention, the coordinate measuring machine (CMM) system is characterized in that the rotary device is configured as a single-axis device, wherein the rotary table is mounted to the base, the base is mounted to the coordinate measuring machine, and the setting of different angular positions includes rotating the rotary table about a first rotation axis relative to the base.

[0019] According to another embodiment of the invention, the coordinate measuring machine (CMM) system according to the invention is characterized in that the rotating device is configured as a dual-axis device, wherein the rotating table is mounted to a base via an intermediate rotating arm, wherein the rotating arm is mounted to the base and is rotatable relative to the base about a first rotation axis; the rotating table is mounted to the rotating arm and is rotatable about a second rotation axis, wherein the rotating arm is configured such that the first rotation axis and the second rotation axis are nominally perpendicular to each other, wherein moving the rotating table to a plurality of postures includes rotating the rotating arm and / or the rotating table about the first rotation axis or the second rotation axis respectively.

[0020] According to one embodiment, multiple rotary tables may also be stacked on top of each other directly or via an intermediary member, wherein the rotation axes of the multiple rotary tables are preferably nominally perpendicular to at least one of the rotation axes of the other rotary tables of the CMM system.

[0021] The calibration procedure can be performed, for example, in an automated manner, as automation further simplifies the calibration process for the user, leading to a further reduction in time and a decrease in the tendency for errors to arise due to operational mistakes. According to one embodiment of the invention, the coordinate transformation from the CMM coordinate system to the part coordinate system generated by the calibration procedure is described by an angle-dependent matrix that takes into account errors of the rotation axis, such as, for example, indexing errors, wobbling errors, and translation errors. If the rotation device is configured according to the single-axis device, then this matrix is ​​CT. α , where α is the rotation angle of the rotary table about the first rotation axis; or if the rotary device is configured according to the dual-axis device, then the matrix is ​​CT. α,β α is the rotation angle of the rotating arm about the first rotation axis, and β is the rotation angle of the rotating table about the second rotation axis. CT α or CT α，β It is the sum of a 3×3 angle-dependent rotation matrix multiplied by a 3x1 vector with applied coordinate transformation, plus a 3x1 translation vector. For example, if the rotation device is configured as a dual-axis device: CT α，β =R α，β x+t α，β , where R α，β It is a rotation matrix, x is the vector to which the rotation matrix is ​​applied, and t is the vector to which the rotation matrix is ​​applied. α，β It is a translation vector.

[0022] In some cases, coordinate measuring machine (CMM) systems already include application software for prior art coordinate transformations, which may even account for index errors. To apply the method of this invention, the prior art coordinate transformation must first be reversed. This can be done, for example, by removing the application software and instead performing the prior art coordinate transformation. Another possibility is to first reverse the prior art coordinate transformation by multiplying it inversely with a pre-installed prior art coordinate transformation before applying the coordinate transformation of this invention to the measured values. The combination of the coordinate transformation of this invention with prior art coordinate transformations allows for the integration of the coordinate transformation of this invention into existing workflows.

[0023] According to one embodiment of the invention, the coordinate measuring machine system includes software that has stored coordinate transformations described by a dependent angle matrix CT, wherein the rotational movement is assumed to be provided by an ideally aligned, perfectly aligned axis of rotation, wherein, for the calibration procedure, the coordinate transformation from the coordinate measuring machine coordinate system to the part coordinate system is described by a dependent angle matrix that takes into account errors of the axis of rotation: if the rotational device is configured according to the single-axis device, then the matrix is ​​CT. α , where α is the rotation angle of the rotary table about the first rotation axis; or if the rotary device is configured according to the dual-axis device, then the matrix is ​​CT. α,β Where α is the rotation angle of the rotating arm about the first rotation axis, and β is the rotation angle of the rotating table about the second rotation axis, and wherein, respectively, by providing error diagrams... or The coordinate transformation CT α or CT α,β Embedded into the software. The angle-dependent matrix CT can describe an isometry, where rotational movement is assumed to be provided by an ideally aligned, perfectly aligned axis of rotation. However, the angle-dependent matrix CT can also describe any pre-installed error compensation, which is inverted and replaced by the isometry or coordinate transformation of the present invention, respectively. The CT can be, for example, a matrix in which the axis of rotation of the rotating device is estimated.

[0024] Not only the weight and dimensions of the components of the rotating device, but also the weight and dimensions of the objects mounted on the rotary table are potential sources of error. If, for example, the rotating device is configured as a dual-axis device (where the rotary table is mounted to the base via an intermediate rotating arm, and a heavy object is mounted on the rotary table), the axes may tilt, lean, and / or shift compared to the original configuration. To compensate for the mounted weight, the resulting error can be determined by performing measurements without attaching any additional weight, then mounting different types of weights onto the rotary table, performing the calibration process of the present invention without any weight mounted on the rotary table, and generating a weight-dependent error map accordingly for each mounted weight. The weight of the mounted object can be determined, for example, by using an integrated balance, thereby determining the weight directly on the coordinate measuring machine, or the user can manually input the weight of the mounted object. The weight-dependent error map then leads to even more accurate coordinate transformations.

[0025] In some cases, only partial calibration is required. From the multiple degrees of freedom associated with the movement of the rotating device, at least one parameter is assumed to be constant, and the calibration procedure is performed based on at least one assumed variable parameter. If, for example, the rotating device is configured as a two-axis device (where the rotary table is mounted to the base via an intermediate rotary arm), and the intermediate rotary arm is known to be the largest source of error, then rotating only the rotary arm to generate an error map dependent only on the first axis of rotation, and ignoring errors caused by the rotation of the rotary table or rotation about the second axis of rotation, can provide a reasonable error map while reducing time compared to full calibration. Therefore, at least one of the actuation axes remains constant, and the parameters associated with that actuation axis are determined. According to one embodiment, the coordinate measuring machine system is characterized in that the calibration procedure depends on multiple parameters.

[0026] A reasonable error map can be provided while reducing time compared to full calibration. Therefore, at least one actuation axis remains constant, and the parameters associated with that actuation axis are determined. According to one embodiment, the coordinate measuring machine system is characterized in that the calibration procedure depends on multiple parameters.

[0027] In some cases, it may be beneficial to perform partial calibration only with respect to weight. For example, if the rotary device is configured as a dual-axis device (where the rotary table is mounted to a reference via an intermediate rotary arm), and the intermediate rotary arm is known to be the largest source of error with respect to weight variation, then the weights can also be mounted onto the rotary arm. These weights can also be mounted onto any other component of the rotary device. Performing this type of partial calibration is particularly advantageous if the largest source of error with respect to weight is known, and because it reduces the time required for partial calibration compared to full calibration, compared to all other errors.

[0028] According to one embodiment, the coordinate measuring machine (CMM) system is characterized in that different types of weights are mounted onto the rotary table or a portion of the rotary device, wherein the CMM is configured to measure, in particular automatically, the 6-DOF attitude of the fixture for different weights, wherein, for each weight, the 6-DOF attitude of the fixture is measured for at least a subset of the different angular positions, and the CMM is configured to provide weight-dependent corrections to the coordinate transformation, specifically, wherein, in the case of the rotary device configured according to the dual-axis device, the subset of the different angular positions includes the rotation of the rotary arm about the first rotation axis and / or the rotation of the rotary table about the second rotation axis. For the example of a dual-axis device, this means that for each rotation angle about the first or second rotation axis and for each type of weight, the deviation of the fixture's 6-DOF attitude is mapped, thereby generating an angle- and weight-dependent error map.

[0029] An error map can typically be any well-defined function that provides corrected 3D coordinates of an object for each angular position of the rotary table. According to one embodiment, the coordinate measuring machine system is characterized by using harmonic expansion, polynomial expansion, or lookup tables to implement the error map.

[0030] A fixture is an object having features that allow for the determination of at least a portion of the 6-DOF orientation of a rotating device. According to one embodiment, the coordinate measuring machine system is characterized in that the fixture is a modular component that can be mounted to the rotary table, or the fixture is fixedly mounted to the rotary table.

[0031] According to one embodiment, the coordinate measuring machine system is characterized in that the fixture is geometrically stable during the calibration procedure, or the characteristics and behavior of the fixture are stored and considered in the computing unit during the calibration procedure. The fixture may be, for example: a plate, with at least three spheres mounted to the plate; a triangle on the plate, particularly a metal triangle on the plate; a pattern on the plate, particularly a checkerboard pattern on the plate; or identical to the worktable or a portion of the worktable. If, for example, a portion of the worktable is used as the fixture, the 6-DOF orientation of the worktable can be determined by considering the edges of the worktable. If, for example, a metal triangle on the plate is used as the fixture, determining the orientation of two edges of the triangle is sufficient to determine the 6-DOF orientation of the fixture. If, for example, a random non-planar surface on the plate is used as the fixture, surface mating can be used to determine the 6-DOF orientation of the fixture. Furthermore, a pattern (e.g., a checkerboard) can be used as the fixture, and the 6-DOF orientation of the fixture can then be determined from an image captured by a camera. For example, the rotating worktable itself can also be used as the fixture when scanning the sides, top, and preferably additional markers that break rotational symmetry. Geometric stability refers to the properties of a fixture that make it constant, or that variations in the fixture's size and / or shape can be ignored. Geometric stability can thus relate to two-dimensional fixtures (e.g., a checkerboard pattern) or three-dimensional fixtures (e.g., embodied as a sphere). Among the properties that can be stored on a computing unit, this property can be, for example, the coefficient of thermal expansion, which defines the expansion of an object with respect to temperature changes. Knowing the coefficient of thermal expansion of the material used to manufacture the fixture allows for the prediction of the actual expansion of the fixture during the calibration process.

[0032] The expansion of an object with respect to temperature changes is defined. Knowing the coefficient of thermal expansion of the material used to manufacture the fixture allows for prediction of the actual expansion of the fixture during the calibration procedure.

[0033] According to one embodiment, the coordinate measuring machine system is characterized in that a rotary table is implemented as a fixture, structural data of the rotary table is stored on the coordinate measuring machine, and the coordinate measuring machine is configured to perform a calibration procedure using at least a portion of the structural data of the rotary table, particularly automatically performing the calibration procedure.

[0034] According to another embodiment, the coordinate measuring machine system is characterized in that the rotating device is configured according to the dual-axis device, and the fixture includes at least two spheres, wherein at least one sphere is mounted to the rotating arm near the base, and at least one sphere is mounted to the rotating arm near the rotary table. "Near the base" can, for example, mean that the sphere mounted to the rotating arm near the base is mounted such that the distance between the sphere and the base is shorter than the distance between the sphere and the rotary table. Therefore, "near the rotary table" can mean that the distance between the sphere and the rotary table is shorter than the distance between the sphere and the base. The rotating arm can be L-shaped. For an example of an L-shaped rotating arm, "near the base" can mean that the sphere is mounted on a straight portion of the rotating arm that is closer to the base than a straight portion of the rotating arm that is closer to the rotary table. More specifically, for an example of an L-shaped rotating arm, "near the base" also means that the sphere is mounted on a straight portion of the rotating arm that is mounted to the base directly or via an intermediary member.

[0035] According to another embodiment, the coordinate measuring machine system is characterized in that the rotary device is configured as a dual-axis device, and the fixture includes at least three balls, wherein at least one ball is mounted to the rotary arm near the base, at least one ball is mounted to the rotary arm near the rotary table or to an intermediary member between the rotary arm and the rotary table, and at least one ball is mounted to the rotary table directly or via an additional member.

[0036] Depending on the object being measured and the fixture, different sensors may be advantageous for different fixtures or different measurement conditions. According to one embodiment, a coordinate measuring machine system is characterized in that the coordinate measuring machine includes multiple sensors for determining the three-dimensional coordinates of the object, one of which is particularly a tactile sensor or an optical sensor.

[0037] The present invention also relates to a calibration method for a coordinate measuring machine (CMM) system, the CMM system comprising: a coordinate measuring machine (CMM) associated with a coordinate measuring machine coordinate system fixed relative to the CMM, the CMM including a computing unit and at least one sensor, particularly a tactile sensor or an optical sensor, for determining the three-dimensional coordinates of an object; a rotary table having means for holding the object and associated with a part coordinate system fixed relative to the rotary table; a rotating device configured to move the rotary table to different orientations relative to the CMM by rotational movement; and a fixture configured to determine the six freedoms of the fixture using at least one of the sensors of the CMM. The method involves determining the 6-DOF (6 degrees of freedom) orientation of the fixture and arranging it relative to the rotary table such that the current orientation of the fixture is associated with the current orientation information of the rotary table relative to the coordinate measuring machine (CMM), particularly wherein the fixture is part of or can be mounted to the rotary table. The method includes the following steps: moving the rotary table into multiple orientations by setting different angular positions with respect to the rotational movement; measuring the 6-DOF orientation of the fixture using the CMM for each of the multiple orientations; generating an error map using the computing unit based on the angles associated with the different angular positions and the associated 6-DOF orientation of the fixture; and determining a coordinate transformation from the CMM coordinate system to the part coordinate system using the computing unit based on the error map. For example, the rotary table can be automatically moved into multiple orientations using software stored on the computing unit, meaning that to move the rotary table into multiple orientations, the rotary table is rotated about its axis of rotation around multiple predetermined angles, wherein the 6-DOF orientation of the fixture is measured when a preset orientation is set. The measurement of the 6-DOF orientation of the fixture can also be performed automatically. Based on the measurements of the fixture's 6-DOF orientation, the computational unit can automatically generate an error map. The computational unit can then automatically determine the coordinate transformation from the coordinate measuring machine coordinate system to the part coordinate system. While individual steps are preferably performed automatically, the entire calibration process is not required to be automated. However, the entire calibration method can also be implemented such that all process steps are fully automated, rather than automating only each individual process step.

[0038] An error map is generated; and the coordinate transformation from the coordinate measuring machine coordinate system to the part coordinate system is determined using the calculation unit based on the error map. For example, the rotary table can be automatically moved into multiple postures using software stored on the calculation unit. This means that in order to move the rotary table into multiple postures, the rotary table is rotated around its axis of rotation by multiple predetermined angles, wherein the 6-DOF posture of the measuring fixture is set when a preset posture is established. The 6-DOF posture of the measuring fixture can also be executed automatically. Based on the measured values ​​of the 6-DOF posture of the fixture, the error map can be automatically generated by the calculation unit. Then, the calculation unit can automatically determine the coordinate transformation from the coordinate measuring machine coordinate system to the part coordinate system. Although it is preferred to perform individual steps automatically, it is not mandatory to perform the entire calibration process automatically. However, the entire calibration method can also be implemented such that the process steps of the calibration method are fully automated, rather than automating only each individual process step.

[0039] According to one embodiment, a calibration method for a coordinate measuring machine system is characterized in that the rotating device is configured as: a single-axis device, wherein the rotary table is mounted to a base, the base is mounted to the coordinate measuring machine, and setting different angular positions includes rotating the rotary table about a first rotation axis relative to the base; or a dual-axis device, wherein the rotary table is mounted to the base via an intermediate rotating arm, wherein the rotating arm is mounted to the base and is rotatable about a first rotation axis relative to the base; the rotary table is mounted to the rotating arm and is rotatable about a second rotation axis, wherein the rotating arm is configured such that the first rotation axis and the second rotation axis are nominally perpendicular to each other, wherein moving the rotary table to multiple postures includes rotating the rotating arm and / or the rotary table about the first rotation axis or the second rotation axis.

[0040] The rotary table is mounted to the rotary arm and is rotatable about a second rotation axis, wherein the rotary arm is configured such that the first rotation axis and the second rotation axis are nominally perpendicular to each other, wherein moving the rotary table to a plurality of postures includes rotating the rotary arm and / or the rotary table about the first rotation axis or the second rotation axis.

[0041] According to another embodiment of the invention, the calibration method is characterized in that it is computer-implemented and includes: providing software for the coordinate measuring machine (CMM) system, the software having stored coordinate transformations described by a dependent angle matrix CT, wherein the rotational movement is assumed to be provided by an ideally aligned, perfectly aligned axis of rotation; wherein, for the calibration procedure, the dependent angle coordinate transformation from the CMM coordinate system to the part coordinate system is described by a matrix that takes into account the tilt error of the rotation axis; if the rotational device is configured according to the single-axis device, then the matrix is ​​CT. α , where α is the rotation angle of the rotary table about the first rotation axis; or if the rotary device is configured according to the dual-axis device, then the matrix is ​​CT. α,β Where α is the rotation angle of the rotating arm about the first rotation axis, and β is the rotation angle of the rotating table about the second rotation axis; by providing an error diagram or The coordinate transformation CT α or CT α,β Embedded into the software.

[0042] According to another embodiment of the invention, the method is characterized in that it further includes: mounting a weight onto the rotary table or a part of the rotary device and repeating the steps of the invention; performing the process / cycle for different types of weights; and providing a weight-dependent correction to the coordinate transformation.

[0043] A computer program product comprising program code stored on a machine-readable medium or implemented by electromagnetic waves including program code segments, and having computer-executable instructions for performing the method according to the invention, particularly when run on a coordinate measuring machine of the invention. Attached Figure Description

[0044] The aspects of the invention will now be described or explained in more detail by way of example only, with reference to the schematic examples shown in the accompanying drawings. In the drawings, the same elements are labeled with the same reference numerals. The described embodiments are generally not shown to scale and should not be construed as limiting the invention. Specifically:

[0045] Figure 1 This is one embodiment of the present invention, wherein the rotating device is configured as a single-axis device.

[0046] Figure 2 This is one embodiment of the invention in calibration settings, wherein the rotating device is configured as a biaxial device.

[0047] Figure 3 This is an embodiment of the calibration setup of the present invention, wherein the rotating device is configured as a biaxial device.

[0048] Figure 4 This is an embodiment of the CMM system of the present invention, wherein the rotating device is configured as a dual-axis device.

[0049] Figure 5 This describes the workflow of an implementation of the method of the present invention. Detailed Implementation

[0050] Figure 1 An embodiment of the invention is shown, wherein the rotating device is configured as a single-axis device. A rotary table 2 is mounted to a base 1 and is rotatable about a first rotation axis 6. Different angular positions are achieved by rotating the rotary table 2 about the first rotation axis 6 relative to the base 1. A part coordinate system 4 is fixed relative to the rotary table 2 and is defined, for example, such that the z' axis is coaxial with the first rotation axis, and the x'-y' plane lies on the surface of the rotary table 2. Furthermore, the rotary table has means for holding the workpiece 5, for example, a fastener, implemented herein as a simple hole 3.

[0051] Figure 2 An embodiment of the invention in a calibration setup is shown, wherein the rotating device is configured as a dual-axis device. As an example, a rotary table 2 is mounted to an intervening member 9, which forms a base for the rotary table 2, which is rotatable relative to the intervening member 9 about a second rotation axis 12. The intervening member 9 is fixedly mounted to a rotating arm 10. The rotating arm 10 is rotatably mounted to the base 1 via a rotary table 11 and is rotatable about a first rotation axis 6. Furthermore, the rotating arm 10 is configured such that the first rotation axis 6 and the second rotation axis 12 are nominally perpendicular to each other. A jig consisting of a circular plate 7 mounted on the rotary table 2 and three spheres 8 mounted on the plate 7 is used for the full calibration procedure. Measurements of the 3D coordinates of the three spheres 8, and thus the six DOF orientations of the jig, generate information about indexing errors, tilt and translation errors of the rotation axes, and wobbling errors.

[0052] Figure 3An embodiment of the calibration setup is shown, in which the rotary device is configured as a dual-axis device. One or more spheres 8 serve as fixtures or part of a clamp to perform full or partial calibration. The dual-axis device is configured such that the rotary table 2 includes holes 3 for mounting a workpiece or fixture. The rotary table 2 is rotatably mounted to an intervening member 9, which is fixedly mounted to a rotary arm 10. The rotary arm 10 is rotatably mounted to the base 1 of the CMM via a rotary table 11. The rotary arm 10 is configured such that a first axis of rotation and a second axis of rotation (not shown in the figure) are nominally perpendicular to each other. The fixture is a modular component that can be mounted to the rotary table 2, such as for the two spheres 8 fixedly mounted to the L-shaped intervening member, while the fixture is only mounted to the rotary table 2 for calibration of the rotary arrangement and is removed for workpiece measurement. The fixture can also be fixedly mounted to a part of the rotary device, such as for the spheres 8 mounted to the intervening member 9, or for the spheres 8 fixedly mounted to the rotary arm 10.

[0053] In some cases, partial calibration may be sufficient. If the rotary arm 10 is known to be the largest source of error and the error caused by the rotary table 2 can be ignored, the fixture, implemented herein as a sphere 8, can also be fixedly mounted to the rotary arm 10 or the intervening component 9. For example, a sphere 8 attached to the stationary part (here, the intervening component 9) on which the rotary table 2 is mounted can be used to calibrate the assembly of the rotary arm 10 and the rotary table 11. Since the rotary table 2 has a smaller tendency for wobbling and translation errors than the rotary arm 10 and the rotary table 11, a single sphere 8 on the rotary table 2 can provide sufficiently accurate results.

[0054] Figure 4 An embodiment of the CMM system of the present invention is shown, wherein the rotation device is configured as a dual-axis device. The CMM is associated with a CMM coordinate system 13, which is fixed relative to the CMM. The CMM includes a measuring stage 16 as part of a base 1, a frame 14, and an arm 15 including a probe with a sensor 17. In this example, the sensor 17 is implemented as a tactile sensor. The measuring stage 16 is fixed relative to the CMM coordinate system 13. The frame 14 is mounted to the base 1, thereby being movable along the x-axis. The arm 15 is mounted to the frame 14, such that the arm 15 is movable along the Y-axis. The probe with the sensor 17 attached is mounted to the arm 15 and is movable along the z-axis. The CMM thus provides three translational degrees of freedom.

[0055] The CMM system of the present invention includes a rotating device and a rotary table, the rotating device being introduced, for example, in paragraph

[0041] and... Figure 3The rotating device shown is attached to the base 1 of the CMM, and the rotary table is moved to different orientations relative to the CMM by means of the rotating device. A rotating arm is mounted to the base 1 and is rotatable relative to the base 1 about a first rotation axis 6, and the rotary table is mounted to the rotating arm and is rotatable about a second rotation axis 12, wherein the rotating arm is configured such that the first rotation axis 6 and the second rotation axis 12 are nominally perpendicular to each other. In this embodiment, the part coordinate system 4 is defined such that in the initial position, the second rotation axis 12 is coaxial with the z' axis of the part coordinate system 4, and the first rotation axis 6 is parallel to the y' axis of the CMM coordinate system 13. Therefore, the combination of the rotary table and the rotating device provides two additional degrees of freedom.

[0056] In the calibration procedure of this invention, the rotary table is moved into multiple postures by rotating the rotary table around the second rotation axis 12 at different angles, or by rotating the rotary arm around the first rotation axis 6 at different angles, or by both. In each posture, the 3D coordinates of the sphere are measured, so that the 6-DOF posture of the fixture can be determined. Based on multiple angle-dependent measurements of the 6-DOF posture of the fixture in different angular positions, an error map is generated, i.e., a map of all geometric errors of the combination of the rotary table and the rotating device. Based on this error map, a coordinate transformation from the part coordinate system 4 to the CMM coordinate system 13 is generated.

[0057] Figure 5 The workflow of an embodiment of the method of the present invention is illustrated. A CMM system of the present invention is provided, in this embodiment of the system including a rotary device configured as a dual-axis device (a). A fixture may, for example, be mounted to a rotary table for calibration only and may be removed for actual measurement (b), or the fixture may, for example, be fixedly mounted to a portion of a rotary arm or an intervening component (b'). After arranging the fixture relative to the rotary table such that the current orientation of the fixture is associated with the current orientation information of the rotary table relative to the CMM, the rotary table is moved into multiple orientations by setting different angular positions with respect to rotational movement (c). In this embodiment, when the rotary device is configured as a dual-axis device, moving the rotary table into multiple orientations includes rotating the rotary arm and / or the rotary table about a first rotation axis or a second rotation axis, respectively. For each of the multiple orientations of the rotary table, a 6-DOF orientation of the fixture is measured using at least one sensor included in the CMM (d). An error map (e) is generated based on the measured 6-DOF orientation of the fixture and the angles associated with the different angular positions or orientations of the rotary table. Based on this error diagram, the coordinate transformation (f) from the CMM coordinate system to the part coordinate system is determined.

Claims

1. A coordinate measuring machine system capable of operating to measure an object (5), the coordinate measuring machine system comprising: A coordinate measuring machine associated with a coordinate measuring machine coordinate system (13) fixed relative to the coordinate measuring machine, the coordinate measuring machine including a computing unit and at least one sensor (17) for determining the three-dimensional coordinates of an object (5), wherein the coordinate measuring machine includes a base (1) fixed relative to the coordinate measuring machine coordinate system (13), the base (1) being mounted to the coordinate measuring machine, and wherein the at least one sensor is implemented as a tactile sensor and / or an optical sensor and is configured to measure surface changes of the object; A rotary table (2) having a device (3) for holding an object (5) and associated with a part coordinate system (4) fixed relative to the rotary table (2); A rotating device, which is attached to the base (1) and configured to move the rotary table (2) to different orientations relative to the coordinate measuring machine by means of the rotational movement by setting different angular positions with respect to the rotational movement; A fixture is configured to determine the 6-DOF orientation of the fixture using at least one sensor (17) of the coordinate measuring machine, and the fixture is arranged relative to the rotary table (2) such that the current orientation of the fixture is associated with the current orientation information of the rotary table (2) relative to the coordinate measuring machine, wherein the fixture is an object (5) exhibiting geometric features that allow for the determination of at least a portion of the 6-DOF orientation of the rotating device. The coordinate measuring machine system provides a calibration procedure that defines a process in which the rotating device moves the rotary table (2) into multiple orientations via the rotational movement, and the calibration procedure is configured to be automatic. For each of the plurality of postures of the rotary table (2), the 3D coordinates of the geometric features of the fixture are measured using at least one sensor of the coordinate measuring machine, and the 6-DOF posture of the fixture is determined for each of the plurality of postures of the rotary table based on the measured 3D coordinates. Based on the angles associated with the different angular positions and the associated 6-DOF attitude of the fixture, an error map is generated using the computing unit; and The calculation unit uses the error diagram to determine the coordinate transformation from the coordinate measuring machine coordinate system (13) to the part coordinate system (4).

2. The coordinate measuring machine system according to claim 1, characterized in that, The rotating device is configured as follows: ○ A single-axis device, wherein the rotary table (2) is mounted on the base (1), and the setting of different angular positions includes rotating the rotary table (2) about a first rotation axis (6) relative to the base (1). or ○ Dual-axis device, wherein the rotary table (2) is mounted to the base (1) via an intermediate rotary arm (10), wherein: The rotating arm (10) is mounted to the base (1) and is rotatable relative to the base (1) about a first rotation axis (6); The rotary table (2) is mounted to the rotary arm (10) and is rotatable about the second rotation axis (12), wherein the rotary arm (10) is configured such that the first rotation axis (6) and the second rotation axis (12) are nominally perpendicular to each other. Moving the rotary table (2) to multiple postures includes rotating the rotary arm (10) and / or the rotary table (2) around the first rotation axis (6) or the second rotation axis (12) respectively.

3. The coordinate measuring machine system according to claim 2, characterized in that, The coordinate measuring machine system includes software that has stored coordinate transformations described by a CT-dependent angle matrix, wherein the rotational movement is assumed to be provided by perfectly aligned rotational axes (6, 12). The calibration procedure is described by a dependent angle matrix, which accounts for the error of the rotation axes (6, 12). ○ If the rotating device is configured according to the single-axis device, then the matrix is ​​CT. α Where α is the rotation angle of the rotary table (2) around the first rotation axis (6); or ○ If the rotating device is configured according to the dual-axis device, then the matrix is ​​CT. α, β α is the rotation angle of the rotating arm about the first rotation axis (6), and β is the rotation angle of the rotating table (2) about the second rotation axis (12); and Among them, by providing error diagrams respectively The coordinate transformation CT α or CT α,β They are respectively embedded into the software.

4. The coordinate measuring machine system according to any one of claims 1 to 3, characterized in that, Different types of weights are mounted on the rotary table (2) or on a part of the rotary device, wherein the coordinate measuring machine is configured to measure the 6-DOF attitude of the fixture for different weights, wherein for each weight, the 6-DOF attitude of the fixture is measured for at least a subset of the different angular positions, and the coordinate measuring machine is configured to provide weight-dependent correction to the coordinate transformation.

5. The coordinate measuring machine system according to any one of claims 1 to 3, characterized in that, The error graph can be implemented using harmonic expansion, polynomial expansion, or lookup tables.

6. The coordinate measuring machine system according to any one of claims 1 to 3, characterized in that, The clamp is a modular component that can be mounted to the rotary table, or the clamp is fixedly mounted to the rotary table.

7. The coordinate measuring machine system according to any one of claims 1 to 3, characterized in that, The fixture is geometrically stable during the calibration procedure, or the mechanical properties and behavior of the fixture during the calibration procedure are stored in and taken into account by the computing unit.

8. The coordinate measuring machine system according to any one of claims 1 to 3, characterized in that, The coordinate measuring machine includes multiple sensors (17) for determining the three-dimensional coordinates of the object (5).

9. The coordinate measuring machine system according to any one of claims 1 to 3, characterized in that, The fixture is: A plate, at least three spheres (8) are mounted to the plate; The triangle located on the board; The pattern on the board; or It is the same as the worktable (2) or a part of the worktable (2).

10. The coordinate measuring machine system according to any one of claims 1 to 3, characterized in that, The calibration procedure depends on a number of parameters, assuming that at least one of the parameters is constant, and is performed based on at least one parameter that is assumed to be variable.

11. The coordinate measuring machine system according to claim 1, characterized in that, The fixture is part of the rotary table (2) or can be mounted to the rotary table (2).

12. The coordinate measuring machine system according to claim 4, characterized in that, The coordinate measuring machine is configured to automatically measure the 6-DOF attitude of the fixture for different weights.

13. The coordinate measuring machine system according to claim 2 or 3, characterized in that, Different types of weights are mounted to the rotary table (2) or to a part of the rotary device, wherein the coordinate measuring machine is configured to measure the 6-DOF attitude of the fixture for different weights, wherein for each weight, the 6-DOF attitude of the fixture is measured for at least a subset of the different angular positions, and the coordinate measuring machine is configured to provide weight-dependent correction to the coordinate transformation, wherein, in the case of the rotary device configured according to the dual-axis device, the subset of the different angular positions includes the rotation of the rotary arm (10) about the first rotation axis (6) and / or the rotation of the rotary table (2) about the second rotation axis (12).

14. The coordinate measuring machine system according to claim 8, characterized in that, One of the multiple sensors (17) is a tactile sensor or an optical sensor.

15. The coordinate measuring machine system according to claim 9, characterized in that, The triangle is a metal triangle located on the plate.

16. The coordinate measuring machine system according to claim 9, characterized in that, The pattern is a chessboard pattern.

17. The coordinate measuring machine system according to claim 10, characterized in that, The parameters are multiple degrees of freedom associated with the movement of the rotating device.

18. A calibration method for a coordinate measuring machine system, the coordinate measuring machine system comprising: A coordinate measuring machine associated with a coordinate measuring machine coordinate system (13) fixed relative to the coordinate measuring machine, the coordinate measuring machine including a computing unit and at least one sensor (17) for determining the three-dimensional coordinates of an object (5), wherein the coordinate measuring machine includes a base (1) fixed relative to the coordinate measuring machine coordinate system (13), the base (1) being mounted to the coordinate measuring machine, and wherein the at least one sensor is implemented as a tactile sensor and / or an optical sensor and is configured to measure surface changes of the object; A rotary table (2) having a device (3) for holding an object (5) and associated with a part coordinate system (4) fixed relative to the rotary table (2); A rotating device, which is attached to the base (1) and configured to move the rotary table (2) to different orientations relative to the coordinate measuring machine by means of the rotational movement by setting different angular positions with respect to the rotational movement; A fixture, configured to determine the 6-DOF orientation of the fixture using at least one of the sensors (17) of the coordinate measuring machine, and the fixture is arranged relative to the rotary table (2) such that the current orientation of the fixture is associated with the current orientation information of the rotary table (2) relative to the coordinate measuring machine, the fixture being an object (5) exhibiting geometric features that allow for the determination of at least a portion of the 6-DOF orientation of the rotating device. The method includes the following steps: The rotary table (2) is moved into multiple postures by the rotational movement; For each of the plurality of postures of the rotary table (2), the 3D coordinates of the geometric features of the fixture are measured using at least one sensor of the coordinate measuring machine; The 6-DOF orientation of the fixture is determined for each of the plurality of orientations of the rotary table using the measured 3D coordinates of the geometry of the fixture. Based on the angles associated with the different angular positions and the associated 6-DOF attitude of the fixture, an error map is generated using the computing unit; and The calculation unit uses the error diagram to determine the coordinate transformation from the coordinate measuring machine coordinate system (13) to the part coordinate system (4).

19. The calibration method for a coordinate measuring machine system according to claim 18, characterized in that, The rotating device is configured as follows: ○ A single-axis device, wherein the rotary table (2) is mounted on the base (1), and the setting of different angular positions includes rotating the rotary table (2) about a first rotation axis (6) relative to the base (1). or ○ Dual-axis device, wherein the rotary table (2) is mounted to the base (1) via an intermediate rotary arm (10), wherein: The rotating arm (10) is mounted to the base (1) and is rotatable relative to the base (1) about a first rotation axis (6); The rotary table (2) is mounted to the rotary arm (10) and is rotatable about the second rotation axis (12), wherein the rotary arm (10) is configured such that the first rotation axis (6) and the second rotation axis (12) are nominally perpendicular to each other. Moving the rotary table (2) to multiple postures includes rotating the rotary arm (10) and / or the rotary table (2) around the first rotation axis (6) or the second rotation axis (12).

20. The method according to claim 19, characterized in that, This method is implemented by a computer and includes: Software is provided for the coordinate measuring machine system, the software having stored coordinate transformations described by matrix CT, wherein the rotational movement is assumed to be provided by perfectly aligned rotational axes (6, 12); The calibration method for the coordinate measuring machine system is performed, wherein the angular coordinate transformation from the coordinate measuring machine coordinate system (13) to the part coordinate system (4) is described by a matrix that takes into account the tilt error of the rotation axes (6, 12): ○ If the rotating device is configured according to the single-axis device, then the matrix is ​​CT. α Where α is the rotation angle of the rotary table (2) around the first rotation axis (6); or ○ If the rotating device is configured according to the dual-axis device, then the matrix is ​​CT. α, β , where α is the rotation angle of the rotating arm about the first rotation axis (6), and β is the rotation angle of the rotating worktable (2) about the second rotation axis (12); By providing error graphs separately The coordinate transformation CT α or CT α, β They are respectively embedded into the software.

21. The method according to claim 18 or 19, characterized in that, The method also includes: The weight is attached to the rotary table (2) or a part of the rotary device, and the steps described in claim 18, 19 or 20 are repeated; Perform the previous step / loop for different types of weight; Provide weight-dependent correction to the coordinate transformation.

22. The method according to claim 18, characterized in that, The fixture is part of the rotary table (2) or can be mounted to the rotary table (2).

23. The method according to claim 20, characterized in that, The method also includes: The weight is attached to the rotary table (2) or a part of the rotary device, and the steps described in claim 18, 19 or 20 are repeated; Perform the previous step / loop for different types of weight; Provide weight-dependent correction to the coordinate transformation.

24. A computer program product comprising program code stored on a machine-readable medium or implemented by an electromagnetic wave comprising program code segments, and having computer-executable instructions for performing the method according to any one of claims 18 to 23 when operated on a coordinate measuring machine system according to any one of claims 1 to 17.

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