Coordinate measuring system with at least two arms

Abstract

A coordinate measuring system having at least two arms. The invention relates to a coordinate measuring machine (CMM) for determining spatial coordinate data of an object point on a workpiece. The CMM includes first and second arms, a detection element, and a coupling interface. The detection element provides detection data regarding an interaction between the sensing area and the object point. A first arm connects the sensing region to the first proximal end. The coupling interface is configured to provide coupling data regarding an interaction between the coupling area and a reference point having a defined spatial relationship with the object point. A second arm connects the sensing region to a second proximal end mechanically constrained to the first proximal end. The CMM is configured to (i) access an actual pose of the sensing region, (ii) access an actual pose of the coupling region, (iii) provide coupling pose change data based on the actual pose of the coupling region and the coupling data, (iv) provide coordinate data of the object point based on the actual pose of the sensing region, the probe data, and the coupling pose change data.

Description

Technical Field

[0001] The invention relates to the structure and operation of a metrological instrument, in particular a coordinate measuring machine (CMM) or a metrological robot. The instrument comprises a first limb on which a detection element is mounted, a second limb on which a coupling interface is mounted. The limb comprises a corresponding set of connecting rods and a set of joints. The CMM provides the actual pose of the detection element and the coupling interface based on sensor readings from sensors associated with the connecting rods and the joints. The invention further relates to a method for determining the spatial coordinates of an object point on a workpiece and a corresponding computer program product for performing the calculation steps of the method. Background Art

[0002] CMM equipment is used in various applications in quality management and quality assurance. CMMs include fixed CMMs, portable CMMs or laser-based CMMs, including laser trackers, laser scanners and total stations. Metrological robots (i.e. CMMs on mobile or airborne chassis) further expand the applicability of the above instruments. For the present invention, CMM should be understood as an instrument configured to provide metrological grade coordinate data. Unless otherwise specified, this definition covers fixed, mobile or airborne instruments as well as tactile and non-contact data acquisition methods.

[0003] A broad example of a basic CMM is a 3-axis system. For example, DE4325347 discloses such a system. Typically, such a CMM includes a base having a measuring table and a movable frame. The workpiece can be positioned or mounted on the measuring table. The movable frame is mounted on the base so that it can move along a first axis. The frame includes an arm movably mounted along a second axis perpendicular to the first axis. The detection element is mounted on the arm so that it can move along a third axis perpendicular to the first axis and the second axis. This structure enables the detection element to be manipulated in all three dimensions, allowing the relevant 3D coordinates of the object to be measured. Contemporary 3-axis systems typically include additional components, such as stacked rotating tables, to provide 5 degrees of freedom regarding the relative posture of the detection element and the workpiece. Throughout this article, unless otherwise expressly specified, position will be used to represent 3D position, while posture represents six-dimensional position and orientation information.

[0004] Another typical embodiment is an articulated arm coordinate measuring machine (AACMM). AACMM comprises a fixed base and an arm having a plurality of arm segments connected by a hinge. The hinge provides mobility to the movable end of the arm opposite to the base. A detection element can be attached to the movable end. Due to design principles, AACMM is not as accurate as the above-mentioned 3-axis system or 5-axis system, but they provide higher flexibility. For example, EP2916099 B1 discloses such an AACMM instrument.

[0005] Conventionally, a high-precision CMM needs to be very stable to withstand the inertial deformations that may occur due to its own operating weight and (especially since fast measurements are also desired) its movement. Therefore, a conventional CMM is a very heavy device that is complex to move and cannot be installed everywhere, for example due to weight restrictions. Especially for portable CMMs, especially due to work safety guidelines regarding manual handling of heavy objects, a lightweight design is preferred.

[0006] In order to achieve the required accuracy, CMMs are usually installed in dedicated metrology laboratories that provide a low-vibration environment and strictly controlled temperature and humidity. However, this means that online control of the workpiece is not possible because the CMM is located in a separate area, usually far away from the manufacturing area. This leads to a slow feedback loop and less frequent quality control, i.e. higher scrap rates.

[0007] It is desirable to provide a lightweight CMM that still allows high-precision measurements. It is also desirable to provide mobility or simplified transportability of the lightweight CMM. Mobile CMMs allow for more efficient industrial processes by reducing the need to place bulky and expensive measurement equipment on each production line. Mobile CMMs can improve the use of raw materials by reducing scrap rates, thus helping to establish a circular economy.

[0008] Some aspects of the CMM will be disclosed using the terminology of a metrology chain and a kinematic chain including corresponding links and joints. Unless otherwise specified, "links" and "joints" should be understood as metrology links and joints. It is assumed that the metrology chain is configured to provide metrology chain data, in particular the relative poses of the end points of the chain with metrology grade accuracy.

[0009] "Metering joints" measure the relative posture or movement of adjacent components of a metering chain. Joints in the sense of the present invention are to be understood in a general manner, i.e., they cover rotational joints and linear joints with one degree of freedom as well as joints with more degrees of freedom, such as spherical joints. In the sense of the present invention, a trackable area that is continuously tracked by an optical tracking instrument can also be a joint. For a metering link, at least the change in geometry (in particular the absolute geometry) is known. In the sense of the present invention, the metering link comprises a rigid component of the arm, in particular a rigid component with a known geometry, or a non-rigid component that provides its geometry. The distance between the sensing area and the object point established, for example, by optical measurement, can also be regarded as a metering link. From here on, it is implicitly assumed that the metering joint and the connecting rod include respective sensors.

[0010] A kinematic chain is a device comprising a set of kinematic links and a set of assembled kinematic joints that transmit forces substantially with negligible deformation. The kinematic links may be rigid, without deformation. The kinematic joints provide movement independent of further components, in particular the movement of other kinematic joints. For the present invention, kinematic links and kinematic joints are to be understood as subtypes of metering links and joints. Rigid and substantially rigid will be used interchangeably and mean that the component is non-deformable under reasonably expected loads.

[0011] The metrology chain may comprise one or more kinematic elements arranged to one or more kinematic chains. The metrology chain may comprise other elements not comprised by the kinematic chain, in particular a measuring path with known geometry and / or spatial relationship of the measuring probe relative to the workpiece. In the sense of the present invention, a metrology loop may be a closed or semi-closed arrangement of one or more metrology chains. For a closed metrology loop, the absolute value of each of the relevant dimensions and arrangements of its components is known. For a semi-closed metrology loop, at least the variation of each of the relevant dimensions and arrangements of its components is known, for example, they may comprise rigid components with unknown absolute dimensions. Summary of the invention

[0012] In view of the above, it is an object of the present invention to provide a CMM having greater flexibility in mounting.

[0013] Another object of the present invention is to improve the accuracy and repeatability of measurements made by a CMM.

[0014] Another object of the present invention is to improve the time efficiency of a CMM by providing a faster measurement option while maintaining accuracy standards.

[0015] The present invention relates to a CMM comprising a first arm, a detection element, a second arm and a coupling element. A CMM in the sense of the present invention encompasses an instrument configured to provide metrological grade coordinate data of an object point on a workpiece. The present invention is applicable to various CMMs, in particular fixed, portable or mobile CMMs. A mobile CMM can be implemented as an unmanned aerial vehicle (UAV) or a wheeled, tracked or legged (e.g., humanoid) robot configured to provide coordinate data of corresponding accuracy.

[0016] The detection element is configured to provide detection data. The detection data includes interaction information between the sensing area of ​​the detection element and the object point. The detection element may include a tactile sensor, and the detection data may include tactile measurement data. For example, the detection data may include information about the relevant forces (particularly contact forces and friction forces) acting between the workpiece and the tactile probe. The detection data may include geometric information about the probe. The detection data may include information about the angle between the probe (particularly the measuring axis of the probe) and the derived workpiece surface and / or the derived measurement path (which includes the object point whose spatial coordinate data has been obtained in the previous step).

[0017] The detection element may be a contactless probe, in particular a laser probe, even more in particular a laser probe configured for distance measurement by triangulation, interferometry or time-of-flight measurement. The detection data may comprise information about the distance between the sensing area, in particular the detector, and the object point. The detection data may comprise information about the optical properties of the workpiece surface. The detection data may comprise information about the angle between the measuring axis of the probe and the derived workpiece surface and / or the derived measurement path, which comprises the object points whose spatial coordinate data have been acquired in a previous step and / or during the actual measuring step.

[0018] The first arm includes a first set of joints and a first set of links. From here on, it is assumed that the first set of sensors are associated with the first set of joints and the first set of links. The first arm connects the detection element to the first proximal end at the sensing end. In particular, for AACMM, the first arm can be foreseen as a structure similar to that of a human arm having a first set of joints that provide substantially rotational mobility. However, the present invention is not limited to this narrow interpretation of the arm, and aspects of the present invention may also be applicable to 3-axis CMMs or 5-axis CMMs. The first set of joints may include sliding joints that represent the movability of these systems.

[0019] The detection element and the first arm are functionally defined, in particular they are defined with respect to the actual measurement task. The first arm can have an extension, in particular an extension with an alternative detection or coupling element. Such an extension can be part of the same physical component, for example a rigid part with branches. Multiple first arms can be used sequentially or in parallel during the measurement task. By way of example here, only an embodiment with a single first arm is discussed in detail. Details of other embodiments can apply accordingly.

[0020] The present invention is applicable to a CMM with a single detection element having a single sensing area arranged on the sensing end of the arm. The present invention is equally applicable to a CMM with multiple sensing units arranged to different positions on a single arm and / or to multiple arms. For the present invention, the interaction surface of the sensing element providing detection data (in particular the detector surface and / or the ruby ​​sphere or diamond) is considered to be the sensing area, while one or more first arms connect these sensing areas to the first proximal end. The CMM of the present invention with multiple sensing elements can provide detection data without using individual sensing units, in particular the sensing units can provide connection data.

[0021] The connection interface is configured to provide connection data including interaction information between the connection area and the reference point. The object point has a defined spatial relationship with the reference point. The reference point can be included by the workpiece. In particular, it is assumed that the workpiece is rigid under the influence of the forces and moments experienced during the measurement process. The workpiece may include a mounting temporarily arranged on the workpiece. The connection interface can provide a mechanical connection, that is, the connection interface can be locked to the workpiece. The connection interface can be configured to move the workpiece. Alternatively, the connection interface can provide a metrological connection, that is, the relative posture of the connection area and the reference point is known, and its accuracy corresponds to the accuracy of the CMM measurement. Unless otherwise specified, from here on, the connection is used in the sense of a six-degree-of-freedom connection. Specific features of other types of connection interfaces / data may be applied accordingly.

[0022] The second arm comprises a second set of links and / or a second set of joints. From here on, it is assumed that the second set of sensors is associated with the second set of joints and the second set of links. The second arm connects the coupling interface to the second proximal end at the coupling end. The second proximal end is mechanically constrained to the first proximal end. That is, the movement of one of the proximal ends causes the movement of the other. For some embodiments, the second arm may consist of a single joint or a single link. The second arm may include multiple joints and links and is similar to the first arm, in particular, the same as the first arm. The coupling interface may be a detection element. As an example only, an embodiment in which the second arm is similar to the first arm will be discussed in detail. Specific features of embodiments with different types of second arms may be applied accordingly. The arm provides a metering chain between the coupling / sensing area and the proximal end and provides metering chain data based on the sensor readings of the set of sensors.

[0023] The support structure can connect the first proximal end and the second proximal end. Unlike other auxiliary components (e.g., a mobile chassis), the support structure is considered to be part of the metering loop. For a closed or semi-closed measurement loop, the first arm and the second arm and the support structure are functionally defined. To some extent, whether a specific physical component is assigned to the first arm, the second arm or the support structure is a matter of interpretation. The CMM (in particular, the controller of the CMM) is configured to (i) determine the actual posture of the sensing area, in particular based on the sensor readings of the first group of sensors to determine the actual posture of the sensing area, (ii) determine the actual posture of the connection area, in particular based on the sensor readings of the second group of sensors to determine the actual posture of the connection area, (iii) provide connection posture change data based on the actual posture of the connection area and the connection data, and (iv) provide coordinate data of the object point based on the detection data, the actual posture of the sensing area and the connection posture change data. It goes without saying that the use of numbers and letters does not indicate, for example, the order in which the steps are performed. These and all other numbers do not represent time and space connections, not even in the form of a preferred order, and are only used for readability purposes.

[0024] In some embodiments, the first proximal end and the second proximal end coincide. In other words, at least a portion of the joints is comprised by both the first set of joints and the second set of joints, or at least a portion of the connecting rods is comprised by both the first set of connecting rods and the second set of connecting rods. Alternatively, a substantially rigid support structure may connect the first proximal end and the second proximal end. Such embodiments are beneficial because the metering circuit can be decoupled from environmental influences, in particular from vibrations.

[0025] In some embodiments, each joint in the first group of joints includes (i) a proximal side connected to the first proximal end by a corresponding proximal portion of the first arm, (ii) a distal side connected to the sensing area by a corresponding distal portion of the first arm, and (iii) a joint sensor unit configured to provide first joint sensor data about the relative posture and / or posture change between the proximal and distal sides of the joint. The proximal and distal sides, especially for joints with more than one degree of freedom, can be represented by multiple equivalent models. The present invention is not limited to a given representation of a metrology chain, in particular a joint. Each joint in the second group of joints includes (i) a proximal side connected to the second proximal end by a corresponding proximal portion of the second arm, (ii) a distal side connected to the coupling area by a corresponding distal portion of the second arm, and (iii) a joint sensor unit, which is configured to provide second joint sensor data about the relative posture and / or posture change between the proximal and distal sides of the joint. As an example only, an embodiment in which the joints in the second group of joints are substantially similar to the first group of joints is discussed in detail. Specific features of the alternative embodiments may apply accordingly, in particular where a portion of the joints in the second set of joints are less accurate and / or simpler than the joints in the first set of joints.

[0026] In some embodiments, the CMM is configured to access computer-generated or operator-input data about the desired posture or movement of the sensing area. A subset of the first group of joints (particularly each joint) includes a first drive unit, which is configured to provide a relative posture and / or posture change between the proximal and distal sides of the joint. In other words, at least one joint in the first group of joints can be a kinematic joint. The CMM is configured to provide a steering command for the first drive unit based on the desired posture or movement and the actual posture of the sensing area.

[0027] In some embodiments, the CMM is configured to access computer generated or operator input data about the desired posture or movement of the joint area. A subset of the second group of joints (particularly each joint) includes a second drive unit, which is configured to provide a relative posture and / or posture change between the near side and the far side of the joint. That is, at least one joint in the second group of joints can be a kinematic joint. The CMM is configured to provide a steering command for the second drive unit based on the desired posture or movement and actual posture of the joint area.

[0028] In some specific embodiments, the drive unit and the sensor unit are integrated into a common module including a motor circuit board, a stator and a rotor. The rotor is configured to rotate around a rotation axis relative to the stator, wherein the rotor is controlled by the motor circuit board. The common module may include a gearbox to convert the rotational motion of the rotor around the rotation axis into the rotational motion of the gearbox output component around the rotation axis according to a defined gear ratio. The motor circuit board and the stator are axially arranged on one side of the gearbox relative to the rotation axis, represented as the gearbox input side. The gearbox output component engages with the gearbox from the other side of the gearbox represented as the gearbox output side. The common module also includes a connecting portion, which extends from the gearbox output side to the gearbox input side and is configured to pick up the rotation of the gearbox output component in a rigid manner, thereby providing a rotation of the connecting portion consistent with (e.g., identical to) the rotation of the gearbox output component. The common module also includes a rotary encoder, which is configured to detect the rotation of the gearbox output component around the rotation axis. The rotary encoder is arranged on the gearbox input side and is configured to provide a rotation for measuring the connecting portion around the rotation axis. It is also possible to combine two of the above common modules into a dual-axis common module.

[0029] In some embodiments, the CMM is configured to (i) store first arm calibration parameters and second arm calibration parameters, (ii) determine the actual pose of the sensing area based on the first arm calibration parameters, and (iii) determine the actual pose of the coupling area based on the second arm calibration parameters. The calibration parameters may include data on the dynamic behavior of the CMM, in particular the set of deformations of the links and / or joints when movements of the CMM are performed with high acceleration and / or under the influence of gravity. The calibration parameters may also include information on the thermal behavior of the respective arms, for example, information on the effects of thermal gradients.

[0030] In some embodiments, the CMM includes an internal calibration object and a reference-free calibration function. The reference-free calibration function includes (i) providing a calibration pose of the internal calibration object, (ii) providing first calibration data including spatial coordinates of the internal calibration object in the calibration pose based on first arm calibration parameters, (iii) providing second calibration data including spatial coordinates of the internal calibration object in the calibration pose based on second arm calibration parameters, (iv) providing deviation data based on the first calibration data and the second calibration data, in particular wherein the deviation data is proportional to the difference in spatial coordinates, and (v) updating the first arm calibration parameters and / or the second arm calibration parameters based on the deviation data.

[0031] In some specific embodiments, multiple calibration poses of the internal calibration object are provided. If the CMM has L>1 arms, D degrees of freedom of movement for each arm, A poses of the end effector connected together, and C calibration parameters for each arm, the number of unknowns is U=L×C+A×6, and the number of knowns is K=L×A×D. If K>>U, that is, the number of knowns significantly exceeds the number of unknowns, self-calibration can be performed without a reference system. This self-calibration is particularly suitable if one of the arms is not as accurate as the other, for example due to a collision. In addition, this self-calibration can provide feedback on the calibration state of the arm. In some embodiments, the reference-free calibration function also includes mechanically interlocking the first arm and the second arm. Or in other words, during calibration, only constrained movements are allowed, where the calibration state is represented by a deviation of zero.

[0032] In some embodiments, the internal calibration object is (i) a sensing area, (ii) a coupling area, (iii) a second arm calibration object arranged on the second arm, in particular a calibration pattern of multiple calibration objects with a known spatial arrangement, or (iv) a first arm calibration object arranged on the first arm, in particular a calibration pattern of multiple calibration objects with a known spatial arrangement. The above list is non-exclusive, and other embodiments of the present invention may utilize different internal calibration objects. In addition, the internal calibration objects can be alternated during the calibration routine. This is particularly useful for a two-step calibration routine, where the first step involves calibration of a first portion of the first arm and the second step involves calibration of a second portion that is partially different from the first portion.

[0033] In some embodiments, the coupling interface is configured to provide a rigid mechanical coupling between the coupling region and the reference point. The coupling data includes data about the presence of the rigid mechanical coupling. In some specific embodiments, the coupling interface is configured to clamp the workpiece. The CMM is configured to provide a steering command for the second arm, in particular the second drive unit, based on the actual posture of the coupling region and the relative coordinate data of the reference point.

[0034] In some specific embodiments, the coupling interface includes a first locking element, and the workpiece includes a second locking element associated with the reference point. The first locking element and the second locking element are configured to provide a releasable, substantially rigid mechanical contact, in particular a permanent magnetic contact, and / or an electromagnetic contact, and / or a single ball connection, and / or a three-ball connection, and / or a key contact and / or a bolt connection.

[0035] In some specific embodiments, when a rigid mechanical connection is provided between the connection area and the reference point, the mobility of a part of the second group of joints is further reduced. In particular, an immobile state of each joint in the second group of joints is established. In such an embodiment, the entire second arm can be considered as a rigid element. The advantage of this method is that the second arm does not have an impact, especially measurement noise. In addition, the measurement task is simplified because only the first arm must be controlled, which is particularly advantageous during manual measurement under direct operator control. However, the present invention is applicable when the second arm is not fixed or a rigid mechanical connection is not established between the connection interface and the workpiece.

[0036] In some embodiments, the workpiece includes a traceable pattern, in particular an optically traceable pattern, more particularly a QR code. The pose of the reference point is associated with the traceable pattern. The CMM is configured to (i) identify the traceable pattern, for example by pattern recognition, and (ii) provide the relative pose of the connection area and the reference point, for example by optical distance measurement. The connection data includes the relative pose of the connection area and the reference point. Such embodiments are advantageous because they allow the measurement loop to be closed without contacting the workpiece. Non-contact measurement is beneficial for non-rigid workpieces in the absence of force applied to the workpiece because it reduces the risk of deformation of the workpiece during measurement. In the sense of the present invention, tracking and tracing provide similar effects and can be used interchangeably. The connection data can be provided by optically tracing the traceable pattern, for example, by performing structure from motion analysis on the acquired image.

[0037] In some embodiments, each joint in the first group of joints and the second group of joints is a rotary joint, and each connecting rod in the connecting rod has a generally cylindrical shape, and the posture change between the corresponding base and the distal side is a rotation around one or more axes, and the corresponding joint sensor data includes rotation angle data. In other words, CMM has followed the design of contemporary AACMM. In the sense of the present invention, generally cylindrical means that the connecting rod does not include kinks, bends, branches or similar structures, but they can include recesses, cavities, notches or similar structures. Connecting rods and / or joints can include associated auxiliary components that provide increased mechanical stability. Generally cylindrical can also mean, for example, prismatic or conical.

[0038] In some embodiments, the detection element includes a tactile sensor, and the detection data includes contact and / or friction information between the sensing area and the object point. Such an embodiment provides higher accuracy and precision, but the present invention is not limited thereto.

[0039] In some embodiments, the first and second sets of links, the support structure and the workpiece are mechanically rigid, in particular the CMM is configured to access a defined spatial relationship between an object point and a reference point. Such embodiments can be advantageously combined with a rigid mechanical connection between the workpiece and the connection interface and tactile detection. That is, the measurement circuit comprises only rigid elements and joints, in particular joints providing one or more rotational degrees of freedom.

[0040] In some embodiments, each connecting rod has a sensor associated with them. The associated sensor is configured to provide geometric data about the corresponding connecting rod, in particular about the length and / or bending of the corresponding connecting rod. Instead of an ideal rigid connecting rod that only realizes the movement of the rigid body, the geometry of the connecting rod can also be provided by sensor measurement. This geometric data can be further supported by computer modeling of the CMM.

[0041] In some embodiments, the CMM further comprises a contactless tracking unit, in particular a laser and / or image-based tracking unit, for determining the posture of the sensing area and / or the joint area. Such a contactless tracking unit may alternatively or additionally provide the posture of the sensing area and / or the joint area. In particular, the contactless tracking unit may provide verification measurements on the joint sensor data.

[0042] In some embodiments, the first arm and / or the detection element comprises a first six-degree-of-freedom trackable area associated with the posture of the sensing area, in particular a retroreflector or a visual marker. Alternatively or additionally, the second arm and / or the coupling interface comprises a second six-degree-of-freedom trackable area associated with the posture of the coupling area, in particular a retroreflector or a visual marker.

[0043] Six degrees of freedom trackable areas are advantageous because they allow full pose characterization of the detection element and / or the coupling interface. However, for many applications, it is sufficient to obtain the position of the component, and in some alternative embodiments, the detection element and / or the coupling interface includes a three-degree-of-freedom trackable area. Having an area configured to be cooperatively tracked by a contactless tracking unit provides benefits for the stability and / or accuracy of tracking, and the present invention is not limited to embodiments having a trackable area.

[0044] In some embodiments, the CMM (particularly the support structure) is configured to be mounted to a mobile chassis. The mobile chassis is configured to transport the CMM from a first location to a second location. The mobile chassis can be an unpowered trolley, a manned or unmanned ground vehicle, a UAV, or a mobile robot. Alternatively, the CMM can be portable.

[0045] In some embodiments, the CMM exhibits a transmission mode and a measurement mode. In the transmission mode, a portion of the first arm and / or the second arm is fixed, in particular the first arm and the second arm are interlocked. That is, the mobility or total freedom of the first arm and / or the second arm is reduced relative to the mobility in the measurement mode. The CMM is locked to the mobile chassis. This transmission mode is beneficial because delicate joint drivers and sensors are protected from vibration and / or impact events experienced during transmission. Alternatively, a portion of the joint, in particular each joint, can be idling. In addition, the detection element can be moved to a parking position and / or unloaded during the transmission mode. In the measurement mode, the CMM is mechanically separated from the mobile chassis so that the mechanical vibration between the mobile chassis and the CMM is damped. The advantage of this separation is that even if the CMM is still arranged to the mobile chassis, it can perform high-accuracy measurements. Mechanical separation can be achieved, for example, by passive or active pneumatic damping elements between the support structure and the mobile chassis.

[0046] The present invention further relates to a method for determining spatial coordinate data of an object point on a workpiece by means of a CMM, in particular a CMM according to one of the above-mentioned embodiments. The method comprises the following steps: (i) providing an actual posture of a sensing area associated with a sensing end of an arm comprising a first set of links and a first set of joints, (ii) providing detection data comprising interaction information between the sensing area and the object point, (iii) providing an actual posture of a connection area associated with a connection end of a second arm comprising a second set of links and / or a second set of joints, (iv) providing connection data comprising interaction information between the connection area and a reference point, in particular a reference point on the workpiece, (v) deriving connection posture change data based on the actual posture of the connection area and the connection data, and (vi) providing coordinate data of the object point based on the actual posture of the sensing area, the detection data and the connection posture change data. The object point has a defined spatial relationship with the reference point. A first proximal end of the first arm opposite to the sensing end and a second proximal end of the second arm opposite to the connection end are mechanically constrained to each other.

[0047] Some embodiments of the method include providing a rigid mechanical connection between the connection area and the reference point. In some specific embodiments, the rigid mechanical connection is provided by clamping the workpiece with a second arm and / or a connection interface. Alternative methods of providing a rigid mechanical connection are also within the meaning of the present invention. A non-exclusive list of these alternatives includes permanent magnetic contact, and / or electromagnetic contact, and / or a single ball connection, and / or a three-ball connection, and / or a lock-and-key contact, and / or a bolt connection. Some specific embodiments of the method further include reducing the mobility of the arm, such as by fixing the joint to reduce the mobility of the arm.

[0048] Some specific embodiments of the method include mechanically separating the workpiece from the environment, such as by lifting the workpiece through a second arm and / or a coupling interface. For example, such an embodiment is beneficial when the workpiece is located on a production line (e.g., on a conveyor belt). In this case, the measurement is performed with higher accuracy after the workpiece is separated from the environment. After the measurement is completed, the second arm can place the workpiece in a different position. That is, the CMM can be included by a robot that performs further tasks.

[0049] In some embodiments of the method, the actual pose of the sensing region is provided based on the first arm calibration parameters, and the actual pose of the coupling region is provided based on the second arm calibration parameters.

[0050] In some embodiments of the method, the actual posture of the sensing area is provided by deriving first metrology chain data. Deriving the first metrology chain data includes (i) accessing first geometric data of each link in the first group, in particular by processing sensor readings associated with the corresponding link, (ii) accessing first joint sensor data about the relative posture between a proximal side and a distal side of a corresponding joint, wherein the proximal side is connected to the first proximal end through a corresponding proximal portion of the first arm, and the distal side is connected to the sensing area through a corresponding distal portion of the first arm, and (iii) deriving the actual posture of the sensing area based on the first geometric data and the first joint sensor data.

[0051] In some embodiments of the method, the actual posture of the connection area is provided by deriving second metrology chain data. Deriving the second metrology chain data includes: (i) accessing second geometric data of each link in the second group, in particular by processing sensor readings associated with the corresponding link, (ii) accessing second joint sensor data about the relative posture between a proximal side and a distal side of the corresponding joint, wherein the proximal side is connected to the second proximal end through a corresponding proximal portion of the second arm, and the distal side is connected to the connection area through a corresponding distal portion of the second arm, and (iii) deriving the actual posture of the connection area based on the second geometric data and the second joint sensor data.

[0052] In some embodiments, the method includes another measurement phase. The other measurement phase includes: (i) selecting an object point from a set of measured object points as a second reference point, (ii) providing the actual posture of the sensing area relative to the other reference point, (iii) providing additional connection data including interaction information between the sensing area and the other reference point, (iv) deriving additional connection posture change data based on the actual posture of the sensing area and the additional connection data, (v) providing the actual posture of the connection area, (vi) providing additional detection data including interaction information between the connection area and another object point on the workpiece, and (vii) providing coordinate data of another object point based on the actual posture of the connection area, the additional detection data and the additional connection posture change data. In other words, in this other measurement phase, the effects of the sensing area and the connection area and the first arm and the second arm are opposite. Such an embodiment is advantageous during the measurement of large workpieces by moving the CMM. This measurement can be performed as a set of chain link measurements, in which one of the object points will be regarded as a reference point for the next measurement from the set of chain link measurements.

[0053] The invention further relates to a computer program product for a CMM which, when executed by a computing unit and / or a controller, in particular a controller of a CMM according to the invention, causes the calculation steps of selected embodiments of the measurement method to be automatically performed. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] By way of example only, specific embodiments of the present invention will be described more fully hereinafter with reference to the accompanying drawings, in which:

[0055] Figure 1a A prior art three-axis CMM is schematically shown.

[0056] Figure 1b A prior art articulated arm inspection unit is shown schematically.

[0057] Figure 2a A prior art CMM performing measurements is schematically depicted.

[0058] Figure 2b The metrology chain during a prior art CMM measurement is shown.

[0059] Figure 3a The CMM of the invention is schematically depicted with a first arm and a second arm, the object point and the reference point coinciding during the measuring step.

[0060] Figure 3b Depicted is a metrology chain of a CMM of the invention with a first arm and a second arm, the object point and the reference point coinciding during the measuring step.

[0061] Figure 4a The CMM of the invention is schematically depicted with a first arm and a second arm during a common measurement step.

[0062] Figure 4b A metrology chain of the CMM of the invention is depicted with a first arm and a second arm during a common measurement step.

[0063] Figure 5a Depicted is a flow chart of a method in which a CMM of the present invention establishes a mechanical connection between a connection interface and a workpiece.

[0064] Figure 5b A flow chart of a method is depicted in which the CMM of the present invention establishes a contactless connection between a connection interface and a workpiece.

[0065] Figure 6a and Figure 6b The CMM of the invention is schematically depicted mounted to a moving chassis in transmission mode and measurement mode.

[0066] Figure 7a , Figure 7b and Figure 7c A schematic measurement process of a large object is depicted, wherein the CMM has an arm that sequentially functions as a first arm and a second arm.

[0067] Figure 8a and Figure 8b The portable CMM of the invention is schematically depicted in transport mode and during measurement of a workpiece.

[0068] Figures 9a to 9c A schematic diagram depicting a connection based on gesture determination relative to a QR code.

[0069] Fig.10a A schematic calibration using a calibration object arranged to the second arm is depicted.

[0070] Fig.10b A schematic calibration using sensing regions and coupling regions is depicted.

[0071] Fig.11 A flow chart representation of the calibration of the arm is depicted. DETAILED DESCRIPTION

[0072] Figure 1aA prior art three-axis CMM 1 is schematically shown. The CMM 1 comprises a measuring table supporting a workpiece 20, the measuring table serving as a support structure 2. Although not shown, the measuring table 2 may include elements that assist in positioning, clamping or otherwise securing the workpiece 20. Such additional elements may be temporarily mounted to the measuring table 2. The measuring table 2 is typically a heavy, inert object and is assumed to be stable during measurement.

[0073] A movable frame is mounted on the measuring table 2 so that a girder 31 can be moved along a first axis depicted as the x-axis by a first set of motors 32. The frame comprises rods 310 rigidly mounted between the beams 31. A carriage 33 is mounted on the rods 310 so that it can be moved by a second set of motors 34 along a second axis perpendicular to the first axis (depicted as the y-axis). A probe mount 35 is mounted on the carriage 33 so that it can be moved by a third set of motors 36 along a third axis perpendicular to both the first and second axes (depicted as the z-axis). A detection element 5 is mounted on the probe mount 35. The depicted detection element 5 is a non-contact probe having a beam emitter 51 that emits a primary beam 52 and a receiver 53 that receives a secondary beam 54 returned from the workpiece 20, in particular from the object point 25. In the sense of the present invention, the receiver 53 can be considered as a sensing area, the first set of joints can be identified as a sliding joint comprising a motor (e.g., 35) and an associated sliding element (e.g., 36), and the beam 31 is a connecting rod. It is clear to those skilled in the art that Figure 1a The basic three-axis setup depicted in can be extended with further components providing further degrees of freedom, in particular rotational degrees of freedom. To ensure the required accuracy of a typical prior art CMM 1, the table 2 is heavier than the first arm 3, while the workpiece 20 has negligible size and weight compared to the table 2.

[0074] To further improve accuracy, such CMM 1 is usually installed in a dedicated metrology laboratory with air conditioning 81, which operates under strict regulations (e.g., ±1°C and ±10% humidity). This is not only disadvantageous for cost and production efficiency reasons, but also requires further energy consumption and may therefore lead to increased greenhouse gas emissions.

[0075] Figure 1bAnother typical embodiment of a prior art CMM 1 as an articulated arm coordinate measurement / inspection unit is depicted. The depicted CMM 1 is placed next to a conveyor system 29, where a workpiece 20 travels towards the next station. The CMM comprises a support structure 2 and a first arm 3 coupled to a first proximal end 402 located on the support structure 2. The detection element 5 comprises a tactile sensor 55 having a ruby ​​ball as a sensing area 56. The tactile sensor 55 typically establishes direct mechanical contact between the sensing area 56 and the object point 25. The cylindrical links 38 of the first set of links and the joints 37 of the first set of joints provide a first metrology chain between the sensing area 56 and the first proximal end 402. The depicted joints 36 provide at least one relative rotational degree of freedom.

[0076] It is clear to a person skilled in the art that there are many combinations and alternatives to the depicted embodiments, and in particular that the detection element 5 can be modified without modifying the first arm 3 . Figure 1a to Figure 1b The embodiments depicted in are for illustrative purposes only. The presently claimed invention is not limited to a particular type of CMM and may be applied to any reasonable design.

[0077] Figure 2a A schematic prior art AACMM 1 performing measurements on a workpiece 20 is shown. The AACMM 1 is mounted on a support structure 2 (e.g., a measuring table), and the workpiece 20 is placed on the same structure. The AACMM includes links 371, 373, 375, 35 and joints 382, ​​384, 386. For transparency reasons, joints 382, ​​384, 386 are depicted as having only a single rotational degree of freedom. The first arm may include specific components to determine the geometric data of the links 371, 373, 375, 35. The depicted AACMM includes a tactile probe 55, that is, the object point 25 is in contact with the sensing area 56 of the probe 55.

[0078] Figure 2bA first metrology chain 4 representing the same measurement process is depicted. The metrology chain 4 has a first proximal end 402 at a support structure and a sensing end 456 representing the location of the sensing area. For reasons of simplicity and transparency, the links 371, 373, 375, 35 are considered rigid. Alternative embodiments including modeling and / or measuring certain deformations also exist in the prior art. Each joint (joint 384 shown as an example) has a proximal side 483 connected to the first proximal end 402 by a corresponding proximal part 42 and a distal side 485 connected to the sensing end 456 by a corresponding distal part 45. A joint sensor (not shown) measures the posture and / or posture change between the proximal side 483 and the distal side 485, such as a rotation around a single axis. A drive unit (not shown) can provide a relative posture and / or posture change between the proximal side 483 and the distal side 485. The metrology chain 4 depicted is not closed, that is, the accuracy of the measurement depends on the assumption that the closed part 41 of the loop provided by the workpiece and the measuring table is mechanically rigid. To ensure this, the measuring table is ideally heavy and the workpiece is ideally clamped.

[0079] The above requirements can be met according to Figure 1a However, the CMM can be realized by using the CMM of the embodiment, but at the expense of the volume of the CMM. Figure 1b The coordinate measurement operation of the system depicted in cannot meet these requirements, let alone using a lightweight mobile CMM. Even if the measurements are performed during the phases where the conveyor is stationary, the inertia of the support structure and the conveyor system cannot be guaranteed, as such a system must meet other design criteria.

[0080] Figure 3a The AACMM 1 of the present invention is schematically depicted performing measurements on a workpiece 20. The AACMM 1 is mounted on a chassis component 24 (e.g., a measuring table) that is not part of a measurement circuit. The AACMM 1 includes a first set of links 371, 373, 375, 35 and a first set of joints 382, ​​384, 386. The depicted AACMM 1 includes a tactile probe 55, that is, the object point 25 is in contact with the sensing area 56 of the probe 55. The AACMM 1 of the present invention includes a second arm 6. The depicted second arm includes a link 671 and a joint 682. The second arm 6 may include additional joints and links. The second arm 6 may include specific components to determine geometric data of the link 671. A coupling interface 7 is mounted to the second arm 6. The depicted coupling interface 7 also includes clamping, clamping or suitable alternative components to provide a rigid connection between the reference point 27 on the workpiece 20 and the coupling area 76. This enables, for example, measurements to be performed on the depicted lifted workpiece 20. However, the invention is also applicable without a rigid connection between the workpiece 20 and the connection region 76. Figure 3aIn the depicted embodiment, the reference point 27 interacting with the coupling region 76 and the object point 25 interacting with the sensing region 56 are substantially the same. This is for illustrative purposes only.

[0081] Figure 3b A first metrology chain 4 and a second metrology chain 9 are depicted representing the same measurement process. The first metrology chain 4 has a first proximal end 402 and a sensing end 456 representing the location of the sensing area. Similarly, for Figure 2b , the connecting rods 371, 373, 375, 35 are considered rigid. The second metering chain 9 has a second proximal end 902 and a coupling end 976 indicating the location of the coupling area. Figure 3a In the particular geometry depicted in FIG, the proximal ends 402 / 902 of the first metering chain 4 and the second metering chain 9 coincide with the sensing end 456 or the coupling end 976, respectively. In general, the posture of the respective proximal ends 402 and 902 is mechanically constrained. Since both the first metering chain 4 and the second metering chain 9 are open, the respective distal ends 456, 976 are not constrained, i.e., the depicted situation represents the situation when the closed measurement loop contains only the metering chains 4, 9.

[0082] Figure 4a and Figure 4b The first arm 3 and the second arm 6 both comprise a plurality of links and joints. The depicted detection element 5 is an optical probe configured to detect a secondary beam 54 returning from the workpiece 20. A sensing area 53 is defined as a receiver of the detection element 5. Figure 4a An intermediate stage of the measurement is shown consisting of a number of measurement events along the measurement path 252. The spatial relationship between the actual object point 25 and the initial object point 251 is known. During the measurement process, the pose difference 257 between the reference point / joint region 27 / 76 and the initial object point 251 is fixed, even if unknown.

[0083] Figure 4b A corresponding semi-closed measurement loop is depicted. The first part of the measurement loop between the first proximal end 402 and the sensing end 453 is the first metrology chain 4. The second part between the sensing end 453 and the actual object point 25 is provided by the known spatial relationship established by the optical detection 540. The third part between the actual object point 25 and the initial object point 251 is provided by the known spatial relationship established by the measurement path 252. The fourth part 257 between the initial object point 251 and the coupling end 976 of the second metrology chain 9 is provided by the fixed but unknown attitude difference between the coupling area and the initial object point 251. In the depicted embodiment, there is a direct point-shaped mechanical connection between the coupling end 976 and the reference point. The fifth closed part between the coupling end 976 and the second proximal end 902 is provided by the second metrology chain 9.

[0084] exist Figure 3a and Figure 3b as well as Figure 4a and Figure 4b Many alternatives to the embodiments depicted in . A non-exclusive list of alternatives includes, for example, a second arm that is structurally and functionally equivalent to the first arm providing metrology grade data. The pose of the reference point and / or the change in pose of the connection area relative to the reference point can be determined by measurement (particularly non-contact measurement). Other reference points having a known spatial relationship to the initial reference point can be defined. The first proximal end and the second proximal end can be connected by a support structure, particularly by a substantially rigid support structure. The listed and further alternatives can be combined with each other.

[0085] Figure 5a A flow chart representation of a measurement process utilizing the CMM of the present invention is depicted. Command / flow lines are shown in bold and data lines are shown as dashed arrows. The depicted flow chart focuses on the features of the claimed invention, and actual embodiments include other elements not depicted, particularly command or data elements and / or data transmission lines. In addition, for reasons of clarity and brevity, command or data modules may be depicted in simplified form. In the depicted embodiment, the first arm and the second arm include corresponding kinematic chains to manipulate the sensing area and the coupling area.

[0086] In the depicted process, a mechanical connection between the workpiece and the connection interface is established by (i) providing 776 a steering command for the joint of the second arm to provide the mechanical connection, and (ii) providing 711 data regarding the existence of a mechanical connection 710 between the connection interface and the workpiece. When the mechanical connection exists, a steering command is provided 325 for the joint of the first arm to approach the object point. The actual measurement includes (i) providing 701 connection data 700, the connection data 700 including interaction information 720 between the connection area and the reference point, (ii) providing 761 the actual posture 760 of the connection area, (iii) providing 763 connection posture change data 762 based on the actual posture 760 of the connection area and the interaction data 720 between the connection area and the reference point, (iv) providing 501 detection data 500, the detection data 500 including interaction information 520 between the sensing area and the object point, (v) providing 561 the actual posture 560 of the sensing area, and (vi) providing 201 coordinate data 200 of the object point based on the actual posture 560 of the sensing area, the detection data 500 and the connection posture change data.

[0087] Figure 5bA flow chart representation of a measurement process utilizing a CMM of the present invention is depicted, wherein a connection is provided by a non-contact connection method. In the depicted process, a non-contact connection between a workpiece and a connection interface is established by (i) providing 776 a steering command for a joint of a second arm to approach a reference point, and (ii) identifying 741 a traceable pattern associated with the reference point and providing identification data 740 about the traceable pattern. When the traceable pattern is identified, a steering command for a joint of a first arm to approach the object point is provided 325. The actual measurement includes (i) providing 701 connection data 700, the connection data 700 including the interaction information 720 between the connection area and the reference point and the relative posture 750 between the connection area and the reference point, (ii) providing 761 the actual posture 760 of the connection area, (iii) providing 763 connection posture change data 762 based on the actual posture 760 of the connection area and the relative posture 750 of the connection area and the reference point, (iv) providing 501 detection data 500, the detection data 500 including the interaction information 520 between the sensing area and the object point, (v) providing 561 the actual posture 560 of the sensing area, and (vi) providing 201 coordinate data 200 of the object point based on the actual posture 560 of the sensing area, the detection data 500 and the connection posture change data 762.

[0088] Figure 6a A schematic CMM 1 mounted to a mobile carrier 21 is depicted. By way of example, the mobile carrier 21 comprises three wheel axles. The invention is not limited to the depicted embodiments. The CMM 1 according to the invention may be adapted for any reasonable implementation of a mobile carrier, a non-exclusive list including alternative wheel arrangements, tracking, legged or flying / hovering carriers or even portable CMM 1.

[0089] The mobile carrier 21 and / or the chassis component 24 may include a vibration damping element 23, such as a pneumatic element. In the depicted embodiment, the first arm 3 and the second arm 6 are directly connected. That is, the chassis component 24 is not part of the measurement circuit. The chassis component 24 may include a support structure that provides a rigid connection between the proximal ends of the first arm 6 and the second arm 6. This support structure is part of the measurement circuit. The mobile carrier 21 and / or the chassis component 24 may include a fixing element 22, which is configured to lock the chassis component 24 to the mobile carrier 21, in particular to lock the chassis component 24 to the mobile carrier 21 in the depicted transmission mode. In addition, the first group of joints 382, ​​384, 386 and the second group of joints 682, 684 may also be partially (in particular, as depicted, completely) fixed in the transmission mode. In the depicted embodiment, the detection head 5 includes a tactile sensor 55, and the coupling interface 7 is interlocked with the tactile sensor 55. Different types of interlocking of the first arm 3 and the second arm 6 are within the meaning of the present invention.

[0090] Figure 6b The same CMM 1 is shown performing measurements in measurement mode. The chassis part 24 is now connected to the mobile carrier 21 only via the vibration damping element 23, i.e. the CMM 1 is separated from the environment. As an example, the mobile carrier 21 stands on uneven ground, which is also compensated by the vibration damping element 23, however the invention is equally applicable without such compensation. The first group of joints 382, ​​384, 386 exhibits complete mobility in measurement mode, and to date other requirements (in particular requirements for improved accuracy) would not actuate the fixation of one or more joints. The second group of joints 682, 684 is fixed to provide improved accuracy. The connection interface 7 provides a rigid mechanical connection to the workpiece 20. The invention is not limited to the depicted embodiment and can be equally applied if the connection interface 7 does not provide a rigid mechanical connection to the workpiece but provides connection data including interaction information between the connection area and a reference point (in particular the relative posture of the connection area and the reference point).

[0091] Figure 7a A pipeline as a large workpiece 20 to be inspected by a mobile CMM 1 is depicted. A support structure 2 connecting a first arm 3 and a second arm 6 is mounted on a mobile chassis 21, which is depicted as a track drive. The support structure 2 is part of a measurement circuit, however, the mobile chassis 21 is not included by the measurement circuit. The depicted first arm 3 and second arm 6 include the same structural and functional elements and are distinguished only by their use. Alternatively, the first arm 3 and second arm 6 may be substantially similar. As an example, the two arms include corresponding tactile sensors 55, 75. The tactile sensor 55 of the first arm 3 serves as a detection element 5 providing detection data, while the sensing area 56 depicted as a ruby ​​ball is guided along the measurement path 252. The tactile sensor 75 of the second arm 6 serves as a connection interface 7 providing connection data, i.e., the connection area 76 remains in contact with the reference point 27 and provides a relative posture change between the connection area 76 and the reference point 27. The detection element 5 and the connection interface 7 may also include additional physical components that provide a rigid mechanical connection to the workpiece 20. The depicted CMM 1 also comprises further sensors 82, such as a camera, to provide at least a rough positioning of the workpiece 20. It is within the meaning of the invention to provide further similar or alternative sensors.

[0092] Figure 7bThe transition to the next measurement phase is depicted. The first phase is completed and the measurement path 252 has reached its end. The ruby ​​ball 56 of the tactile sensor 55 remains in contact with the other reference point 270. In other words, the first arm 3 will provide the "function of the second arm". Since the CMM 1 is separated from the mobile chassis 21, i.e. the metrology circuit is not closed by the mobile chassis 21, a repositioning of the CMM 1 according to the invention is also possible.

[0093] Figure 7c The next measurement phase is depicted, in which the second arm 6 guides the connection area 76 along another measurement path 253 of the next phase and provides coordinate data of another object point 254. That is, the second arm 6 provides the function of the "first arm". The detection element 5 and the first arm 3 provide additional connection data. By performing multiple such transitions, large workpieces 20 can be accurately measured. In the depicted embodiment, the borehole 202 is used as a reference. The workpiece 20 may have a specified connection partner, for example, a single ball connection, a three-ball connection, a jig or an electromagnetic connection partner. Such a connection partner may have an identifier that can be detected by the detection element 5 and / or the connection interface 7 and / or one or more additional sensors 82.

[0094] Figure 8a A lightweight, portable CMM 1 is depicted in a transfer mode. The depicted CMM 1 includes a support structure 2 and an output element 84, the support structure 2 connecting a first arm 3 and a second arm 6, and featuring an input element 83 depicted as a pair of joysticks for receiving operator input and an output element 84 depicted as a screen. The first arm 3 has a plurality of joints and links. A tactile sensor 55 having a ruby ​​ball as a sensing area 56 is mounted on the first arm 3. The second arm 6 is substantially similar to the first arm 3. A coupling interface 7 configured to provide a releasable rigid mechanical coupling via an electromagnetic element is mounted on the second arm 6. In the depicted transfer mode, the first arm 3 and the second arm 6 are interlocked by the coupling element 7.

[0095] Figure 8bThe same portable CMM 1 is depicted measuring, for example, a ferromagnetic workpiece 20 in a measuring mode. A releasable rigid mechanical connection is established between the connection area 76 and a reference point 27 located on the workpiece 20. That is, the pose of the workpiece 20 is locked to the pose of the second arm 6. The second arm 6 can also be locked during measurement. Alternatively, the second arm 6 can provide a controlled pose change for the workpiece 20. Therefore, a semi-closed metrology loop is provided by the second arm 6, the support structure 2, the first arm 3 and the workpiece 20. The operator provides commands regarding the desired movement of the sensing area 56 along the measurement path 252 via the input interface 83. Due to the semi-closed metrology loop, in particular when the second arm 6 is locked, the accuracy of the derived pose of the sensing area 56 determines the accuracy of the measurement.

[0096] Figure 6a and Figure 6b as well as Figures 7a to 7c Aspects of embodiments of the mobile CMM may be related to Figure 8a and Figure 8b The invention also combines aspects of a portable CMM. Furthermore, the CMM according to the invention can also be transported by a legged robot or UAV as a mobile carrier and / or transport vehicle. Neither the detection element nor the connection interface is limited to the depicted embodiments. Alternative components, operating principles or methods of use are within the meaning of the invention.

[0097] Figure 9a , Figure 9b and Fig.9c A method for deriving connection posture change data through the connection interface 7 based on a non-contact principle is described. The connection interface is located at the connection end of the second arm 6. For example, a reference point on the workpiece 20 is associated with a QR code as a traceable pattern 275. The present invention can be applied in combination with patterns other than QR codes. The pattern can be text, areas with different reflectivities, surface roughness. The pattern can also be a functional feature of the workpiece 20, such as one or more drill holes and / or screw heads, and / or edges and / or corners. The present invention is applicable to any suitable combination or alternative of the above non-exclusive list.

[0098] The depicted coupling interface 7 is configured to acquire imaging data, in particular camera images, from the field of view 765. The coupling pose change data is based on the relative position and / or movement of the trackable pattern 275 in the field of view 765. Figure 9a , Figure 9b and Fig.9c Some example relative positions are depicted. The bottom row shows the second arm 6 relative to the workpiece 20. The top row shows the pattern 275 in the field of view 765. Figure 9a , pattern 275 is first aligned with field of view 765. Since the present invention only requires determining the relative pose change of the joint area and the reference point, many alternative alignments are possible as a first alignment. Figure 9b It is depicted that a relative lateral movement 751 occurs between the workpiece 20 and the coupling interface 7. As a result, the pattern 275 moves relative to the field of view 765. Fig.9c An example is depicted in which the distance between the workpiece 20 and the coupling interface 7 has changed 752. As a result, the size of the pattern 275 relative to the field of view 765 has changed. Based on the image data, coupling pose change data can be determined. Relative rotations have respective effects.

[0099] Fig.10a Schematic steps of reference-free calibration using a calibration object 61 arranged on the second arm 6 as an internal calibration object are depicted. The detection element 5 in the depicted embodiment comprises a tactile sensor 55 having a ruby ​​ball as a sensing area 56. The detection element 5 also has a vision sensor 82 arranged thereon, which can be a positioning aid, for example, by providing visual data about the attitude of the sensing area 56 and the workpiece. The vision sensor 82 can also be a metrology grade sensor providing coordinate data by non-tactile measurement. The first arm 3 is mounted on the support structure 2 and comprises a first set of joints 382, ​​384, 386 and connecting rods 371, 373, 375. For reasons of transparency, only a single first drive unit 484, a single joint sensor unit 366 and a single sensor 355 associated with the connecting rod 375 are depicted. The first arm 3 provides a corresponding metrology chain with the required sensors 355, 366. An embodiment in which the first arm 3 comprises a kinematic chain to provide a set attitude of the probe is advantageous. The first arm calibration parameters may comprise free parameters to be determined with respect to the sensor data provided by the sensors 355, 366. The depicted degrees of freedom of the sensors and drive units are for illustrative purposes and should not be interpreted in a limiting manner. The invention is also not limited to the depicted arrangement of the first arm 3. The second arm 6 is mounted on the support structure 2 in a different position than the first arm 3. Alternative embodiments in which the first arm 3 and the second arm 6 comprise common components are also within the meaning of the invention.

[0100] The depicted second arm 6 comprises a second set of joints 682, 684 and a second set of links 671, 673, 675. For reasons of transparency, only a single second drive unit 982 and a single joint sensor unit 664 are depicted, however the second arm 6 provides a corresponding metering chain. A coupling interface 7 (depicted as a three-ball gauge) having a coupling region 76 is arranged to the second arm 6. The link 673 comprises a calibration pattern of a plurality of calibration objects 61 arranged in a known space. The depicted arrangement is advantageous because the joint 682 provides a plurality of calibration postures with a posture uncertainty caused by a single joint for the calibration object. That is, the posture accuracy of the calibration object 61 may exceed the posture accuracy of the sensing region 56. Arranging the calibration object to a link further away from the support structure 2 provides the benefit of increased flexibility. The present invention is not limited to any particular design.

[0101] The depicted calibration comprises the step of contacting the sensing area 56 with the calibration object 61. By recording sensor data, for example, from the joint sensor unit 366, the measured pose of the sensing area 56, i.e., first calibration data, can be derived using the first arm calibration parameters. The second metrology chain provides second calibration data, i.e., the actual pose of the calibration object 61, based on the second arm calibration parameters. The calibration parameters can be updated based on the deviation between the actual pose of the calibration object 61 and the measured pose of the sensing area 56. The complete calibration process may involve a set of individual calibration measurements with multiple poses of the calibration object 61. Similar calibrations apply to contactless sensors.

[0102] Fig.10b Schematic steps of a method for calibrating arm calibration parameters by measuring the pose of an object point 25 associated with a coupling area 76 of a coupling interface 7 by a detection element 5 are depicted. The detection element 5 in the depicted embodiment comprises a tactile sensor 55 having a ruby ​​sphere as a sensing area 56. The detection element 5 comprises a first six-degree-of-freedom trackable area 85 depicted as a visual marker, which is associated with the pose of the sensing area 56. The second arm 6 comprises a second six-degree-of-freedom trackable area 86 associated with the pose of the coupling area 76, which is depicted as a visual marker. A non-contact tracking unit 87 depicted as a laser tracker is mounted on the support structure 2. The tracking unit 87 tracks the markers 85, 86 using a laser beam 88 to determine the pose of the sensing area 56 and the coupling area 76. The laser tracker 87 can provide supplementary pose information about the pose of the sensing area 56 or the coupling area 76. The depicted calibration method can also be used to provide updates for set calibration parameters of the laser tracker 87.

[0103] The first arm 3 is mounted on the support structure 2 and comprises a first set of joints 382, ​​384, 386 and a first set of connecting rods 371, 373, 375. For reasons of transparency, only a single first drive unit 482 is depicted and no joint sensor unit is depicted. The depicted second arm 6 comprises a second set of joints 682, 684 and a second set of connecting rods 671, 673, 675. For reasons of transparency, only a single second drive unit 982 and a single joint sensor unit 664 are depicted. A coupling interface 7 (depicted as a three-ball gauge) with a coupling area 76 is arranged to the second arm 6. An object point 25 is associated with the pose of the coupling interface 76.

[0104] The depicted calibration includes placing the coupling interface 76 in a calibration posture. The second metrology chain provides second calibration data based on the sensor data of the second set of sensors and the second arm calibration parameters. Based on the sensor data of the first set of sensors, the first arm calibration parameters can be used to derive the measurement posture of the sensing area 56, i.e., the first calibration data.

[0105] In particular, alternative embodiments in which the coupling interface 7 and the probe 5 are interlocked are within the meaning of the present invention. Such embodiments are particularly beneficial because they enable continuous constrained movement, in which the posture of the coupling area 76 and the sensing area 25 can be derived for multiple first arm movements and / or second arm movements. One of the arms 3, 6 can provide the driving force, and at least a portion of the joint 382, ​​384, 386, 682, 684 of the other arm can be idle.

[0106] Fig.11 Depicted Fig.10a and Fig.10b. A flow chart representation of a calibration of a probe is shown. In a first step, a probe calibration pose with associated nominal coordinate data is selected 600 from a stored set of probe calibration poses 60. A steering command for a corresponding joint of a second arm is provided 610 to bring the calibration object into the calibration pose. Second calibration data 601 of the calibration object are provided 611 by the second metrology chain using second arm calibration parameters 602. Then, first calibration data 301 of the calibration object are provided 311 by measuring the first calibration data 301 of the calibration object with a detection element (i.e., by the first metrology chain) using the first arm calibration parameters 302. Deviation data 306 are provided by comparing 316 the first calibration data 301 and the second calibration data 601. Based on the deviation data 306, updated first arm calibration parameters 302 and second arm calibration parameters 602 are provided 320. It will be clear to a person skilled in the art that a typical calibration involves multiple calibration poses. It is within the meaning of the present invention that the deviation data includes data from multiple calibration object poses and / or different parts of the calibration object. Other reasonable variations of calibration, in particular where measured coordinate data about the same calibration object pose is provided by alternative joint poses of the first set of joints, are also within the meaning of the invention. Furthermore, a CMM according to the invention may allow further calibration object poses to be derived based on model calculations or measurements.

[0107] The described calibration method assumes that the second arm comprises a kinematic chain and that the calibration pose is provided by said kinematic chain. It is clear to a person skilled in the art that the claimed invention is not limited to this embodiment. The invention can be implemented by embodiments in which both arms are driven or in which a part of the joint is idle, for example.

[0108] Although the present invention has been described in the foregoing with reference to some specific embodiments, it must be understood that various modifications and combinations of different features of the embodiments are possible. All such modifications are within the scope of the appended claims.

Claims

1. A coordinate measuring machine (CMM) (1), the CMM (1) being used to determine spatial coordinate data (200) of an object point (25) on a workpiece (20), the CMM (1) comprising a first arm (3) and a detection element (5), wherein: - the first arm (3) comprises a first set of joints (35, 37, 382, ​​384, 386), a first set of connecting rods (38, 371, 373, 375), and connects the detection element (5) at the sensing end (453, 456) to the first proximal end (402), - the detection element (5) is configured to provide (501) detection data (500), the detection data (500) comprising interaction information (520) between the sensing area (53, 56) of the detection element (5) and the object point (25), and - the CMM (1) is configured to determine (561) the actual pose (560) of the sensing area (53, 56), It is characterized in that The CMM (1) comprises a second arm (6) and a connection interface (7), wherein: - the second arm (6) comprises a second set of links (671, 673, 675) and / or a second set of joints (682, 684) and connects the coupling interface (7) to a second proximal end (902) at a coupling end (976), wherein the second proximal end (902) is mechanically constrained to the first proximal end (402), the connection interface (7) being configured to provide (701) connection data (700), the connection data (700) comprising interaction information (720) between a connection area (76) of the connection interface (7) and a reference point (27), wherein the object point (25) has a defined spatial relationship with the reference point (27), in particular wherein the reference point (27) is comprised by the workpiece (20), and The CMM (1) is further configured as follows: - determining (761) the actual posture (760) of the joint area (76), - providing (763) joint posture change data (762) based on the actual posture (760) of the joint area (76) and the joint data (700), and - providing (201) the coordinate data (200) of the object point (25) based on the detection data (500), the actual posture (560) of the sensing area (53, 56) and the joint posture change data (762).

2. The CMM according to claim 1, wherein: The first proximal end (402) and the second proximal end (902) coincide with each other, or a substantially rigid support structure (2) connects the first proximal end (402) and the second proximal end (902).

3. The CMM (1) according to any one of claims 1 to 2, wherein: - Each of the first group of connectors (35, 37, 382, ​​384, 386) comprises: o a proximal side (483), said proximal side (483) being connected to said first proximal end (402) via a corresponding proximal portion (42) of said first arm (3), o a distal side (485) connected to the detection element (5) via a corresponding distal portion (45) of the first arm (3), and o a joint sensor unit (366) configured to provide first joint sensor data regarding a relative posture and / or a posture change between the proximal side (483) and the distal side (485) of the joint (35, 37, 382, ​​384, 385); Each of the second set of connectors (682, 684) comprises: o a proximal side, which is connected to the second proximal end (902) by a corresponding proximal portion of the second arm (6), o a distal side, which is connected to the coupling interface (7) via a corresponding distal portion of the second arm (6), and o a joint sensor unit (664) configured to provide second joint sensor data regarding a relative posture and / or a posture change between the proximal side and the distal side of the joint; In particular, a subset of the first set of joints (35, 37, 382, ​​384, 386) comprises a first drive unit (482, 484) configured to provide the relative posture and / or posture change between the proximal side (483) and the distal side (485) of the joints (35, 37, 382, ​​384, 386), - the CMM (1) is configured as follows: o accessing computer generated data or operator input data regarding a desired pose or movement of the sensing region (53, 56), o providing (325) a steering command to the first drive unit (482, 484) based on the desired pose or movement and the actual pose (560) of the sensing area (53, 56), a subset of the second set of joints (682, 684) comprises a second drive unit (982) configured to provide the relative posture and / or the posture change between the proximal side and the distal side of the joints (682, 684), and - the CMM (1) is configured as follows: o access to computer generated data or operator input data regarding a desired posture or movement of the articulation region (76), and o Providing a steering command for the second drive unit (982) based on the desired posture or movement of the joint area (76) and the actual posture (760).

4. The CMM (1) according to claim 3, wherein: Each joint in the first set of joints (35, 37, 382, ​​384, 386) and the second set of joints (682, 684) is a revolute joint, and each connecting rod (38, 371, 373, 375, 671, 673, 675) has a generally cylindrical shape, In particular, - the change in posture between the respective proximal side and the distal side is a rotation about one or more axes, - the corresponding joint sensor data includes rotation angle data, and The detection element (5) comprises a tactile sensor (55), and the detection data (500) comprises contact force information and / or friction force information between the sensing area (53, 56) and the object point (25).

5. The CMM (1) according to any one of the preceding claims, the CMM (1) being configured as: - storing first arm calibration parameters (302) and second arm calibration parameters (602), - determining the actual pose (560) of the sensing area (53, 56) based on the first arm calibration parameters (302), and - determining the actual pose (760) of the articulation region (76) based on the second arm calibration parameters (602).

6. The CMM (1) according to claim 5, comprising an internal calibration object and a reference-free calibration function, wherein the reference-free calibration function comprises: - providing (600) a calibration pose of said internal calibration object, - providing (311) first calibration data (301) comprising spatial coordinates of the internal calibration object in the calibration pose based on the first arm calibration parameters (302), - providing (611) second calibration data (601) comprising the spatial coordinates of the internal calibration object in the calibration pose based on the second arm calibration parameters (602), - providing (316) deviation data (306) based on the first calibration data (301) and the second calibration data (601), in particular wherein the deviation data (306) is proportional to the difference of the spatial coordinates, and - updating the first arm calibration parameter (302) and / or the second arm calibration parameter (602) based on the deviation data (306), In particular, - providing (600) a plurality of calibration poses of said internal calibration object, - the reference-free calibration function further comprises mechanically interlocking the first arm (3) with the second arm (6).

7. A CMM (1) according to any one of the preceding claims, wherein: - the coupling interface (7) is configured to provide a rigid mechanical coupling between the coupling area (76) and the reference point (27), and - said connection data (700) comprises data on the presence of said rigid mechanical connection (710), In particular, - the coupling interface (7) is configured to clamp the workpiece (20), and - the CMM (1) is configured to provide (776) a steering command for the second arm (6) based on the actual pose (760) of the joint area (76) and the relative coordinate data (720) of the reference point (27).

8. The CMM (1) according to claim 7, wherein: The coupling interface (7) comprises a first locking element, and the workpiece (20) comprises a second locking element associated with the reference point (27), wherein the first locking element and the second locking element are configured to provide a releasable, substantially rigid mechanical coupling (710), In particular, providing the rigid mechanical connection (710) between the connection area (76) and the reference point (27) further reduces the mobility of a portion of the second group of joints (682, 684), and in particular places each joint in the second group of joints (682, 684) in a fixed state.

9. The CMM (1) according to any one of claims 1 to 6, wherein: - the workpiece (20) comprises a traceable pattern (275), in particular an optically traceable pattern, more particularly a QR code, wherein the pose of the reference point (27) is associated with the traceable pattern (275), - the CMM (1) is configured to identify (741) the traceable pattern (275), and o providing a relative posture (750) of the connection area (76) and the reference point (27); and The joint data (700) include a relative pose (750) of the joint area (76) and the reference point (27).

10. The CMM (1) according to any one of the preceding claims, comprising a contactless tracking unit (87) for determining (561) the pose (560) of the sensing area (53, 56) and / or the coupling area (76), In particular, - the contactless tracking unit (87) is configured to determine the gesture based on laser and / or image based tracking, and - the first arm (3) and / or the detection element (5) comprises a first six-degree-of-freedom trackable area (85) associated with the pose (560) of the sensing area (53, 56), and / or - the second arm (6) and / or the coupling interface (7) comprises a second six-degree-of-freedom trackable area (86) associated with the pose (760) of the coupling area (76).

11. A CMM (1) according to any one of the preceding claims, the CMM (1) being configured to be mounted to a mobile chassis (21), the mobile chassis (21) being configured to transport the CMM (1) from a first position to a second position, In particular, the CMM (1) exhibits a transmission mode and a measurement mode, wherein: - in the transport mode, a part of the first arm (3) and / or the second arm (6) is fixed, in particular, the first arm (3) and the second arm (6) are interlocked, and the CMM (1) is locked to the mobile chassis (21), and - In the measurement mode, the CMM (1) is mechanically decoupled from the mobile chassis (21), so that mechanical vibrations between the mobile chassis (21) and the CMM (1) are damped.

12. A method for determining spatial coordinate data (200) of an object point (25) on a workpiece (20) by means of a CMM (1), in particular a method for determining spatial coordinate data (200) of the object point (25) on the workpiece (20) by means of a CMM (1) according to any one of claims 1 to 11, the method comprising the following steps: - providing (561) an actual pose (560) of a sensing area (53, 56) associated with a sensing end (453, 456) of a first arm (3) comprising a first set of links (38, 371, 373, 375) and a first set of joints (35, 37, 382, ​​384, 386), - providing (501) detection data (500), the detection data (500) comprising interaction information (520) between the sensing area (53, 56) and the object point (25), - providing (761) an actual posture (760) of the joint region (76) associated with the joint end (976) of the second arm (6) comprising the second set of links (671) and / or the second set of joints (682, 684), - providing (701) connection data (700), the connection data (700) comprising interaction information (720) between the connection area (76) and a reference point (27), in particular interaction information (720) between the connection area (76) and a reference point (27) on the workpiece (20), - deriving (763) joint posture change data (762) based on the actual posture (760) of the joint area (76) and the joint data (700), and - providing (201) coordinate data (200) of the object point (25) based on the actual posture (560) of the sensing area (53, 56), the detection data (500) and the joint posture change data (762).

13. The method according to claim 12, further comprising providing a rigid mechanical connection between the connection area (76) and the reference point (27), In particular, - providing said mechanical connection by clamping said workpiece (20) with said second arm (6) and / or said connection interface (7), and / or - the method further comprises mechanically separating the workpiece (20) from the environment, in particular by lifting the workpiece (20) by the coupling interface (7), and / or - The method further comprises reducing the mobility of the second arm (6).

14. The method according to claim 12 or 13, comprising a further measurement phase, wherein: The further measurement phase comprises: - selecting an object point (25) from a set of measured object points as a further reference point (270), - providing (561) an actual pose (560) of the sensing area (53, 56) relative to the further reference point (270), - providing further connection data comprising interaction information between said sensing area (53, 56) and said further reference point (270), - deriving further joint pose change data based on the actual pose (560) of the sensing area (53, 56) and the further joint data, - providing (761) said actual posture (760) of said joint area (76), - providing further detection data including interaction information between the connection region (76) and another object point (253) on the workpiece (20), and - providing coordinate data of the further object point (253) based on the actual pose (760) of the joint area, the further detection data and the further joint pose change data.

15. A computer program product which, when executed by a computing unit and / or a controller, in particular a controller for a CMM (1) according to any one of claims 1 to 11, enables automatic execution of the calculation steps of the method according to any one of claims 12 to 14.

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