Coordinate measuring machine

Abstract

The invention relates to a coordinate measuring machine. The coordinate measuring machine comprises: a bracket (12, 30, 31) for supporting and positioning a target end effector (40), the end effector (40) being movable in at least three degrees of freedom and being positioned by the bracket (12, 30, 31); a fixed metrology table (35) as a support for a possible target object; and a control unit, which controls the movement of the end effector (40) by the bracket (12, 30, 31). The CMM further comprises: at least one, in particular at least two, imaging detectors (33) for measuring and determining the position of the possible target object in six degrees of freedom; and an analysis unit for processing electronic signals and / or data transmitted by the imaging detector (33). According to the invention, the imaging detector (33) is firmly mounted to the metrology table (35) and mechanically separated from the bracket (12, 30, 31).

Description

[0001] This application is a divisional application of a patent application with an application date of January 20, 2016, application number 201610037061.4, and invention name “Coordinate Measuring Machine”. Technical Field

[0002] The invention relates to a coordinate measuring machine ("CMM" for short), comprising: a carriage as a support and positioning structure for an end effector (as a target), the end effector being movable in at least three degrees of freedom, in particular up to six degrees of freedom and being positionable by the carriage, a fixed metrology table as a support for a possible target object, and a control unit, which controls the movement of the end effector via the carriage. The CMM further comprises: at least two imaging detectors, in particular at least three imaging detectors, for measuring and determining the position of the possible target object in six degrees of freedom, and an analysis unit for processing electronic signals and / or data transmitted by the imaging detectors. Background Art

[0003] It is common practice to inspect a workpiece immediately after production on a coordinate positioning machine, such as a CMM, in order to check the correctness of predetermined object parameters, such as the size and shape of the object.

[0004] In a conventional 3-D coordinate measuring machine, a probe is supported for movement along three mutually perpendicular axes, in the directions of X, Y and Z. Thus, the probe can be guided to any arbitrary point in space within the CMM's measurement volume, and the object can be measured using a measurement sensor (probe) carried by the probe.

[0005] In a simple form of the machine, suitable transducers mounted parallel to each axis are able to determine the position of the probe relative to the machine base and hence the coordinates of a measurement point located on the object approached by the sensor. To provide for the movability of the probe, a typical coordinate measuring machine may comprise a frame structure in which the probe is arranged and means for moving the frame parts of the frame structure relative to each other.

[0006] Typically, a CMM has a tactile probe or an optical probe for measuring the surface of a target object. The optical or tactile probe is movably fixed to an articulated arm as shown for a tactile probe (i.e., in EP 2283311 A1), or is fixed to a gantry as shown for an optical probe (i.e., WO 2008 / 135530 A1), so that it can be moved on the surface of the target object.

[0007] For measuring surface changes, measuring principles based on the use of tactile sensors and optical sensors are known.

[0008] In general, in order to provide a coordinate measuring machine with a high measuring accuracy, its frame structure is therefore usually designed with a high static stiffness. In order to achieve a stiff and rigid machine design, the frame structure or at least parts thereof are often made of stone materials such as granite. In addition to all the positive effects, such as high thermal stability and good damping properties, granite or other stiff materials also make the machine and the movable frame elements quite heavy. The higher weight on the other side also requires high forces to accommodate suitable accelerations.

[0009] Proper calibration can make such an approach work very well, but all non-repeatable imperfections of the mechanics completely affect the final accuracy. Thus, for example, if there is some play between the first and second axes, the linear scale or angular encoder applied to determine the sensor position will not be able to identify such play.

[0010] As another important aspect, weight reduction is a major topic in relation to novel coordinate measuring machine designs. If machine components are constructed to include less weight (associated with less stiffness), faster positioning of the individual components can be achieved, resulting in fewer forces affecting the coordinate measuring machine. On the other hand, along with the weight reduction of these parts, the impact of machine vibrations and torsions due to reduced stiffness and (faster) moving machine components increases. As a result, the uncertainty of the obtained measurement values ​​and the errors occurring due to such deformations and vibrations increase accordingly.

[0011] Therefore, especially with regard to weight reduction, but also for conventional machines, accurate error handling is an important aspect.

[0012] In industry, measurement time is considered as non-productive time, since no saleable parts are produced during this cycle. The measurement task must therefore be completed as quickly as possible. Thus, high measurement speeds and short preparation times (including fast fixation of the object to be measured and short calibration times of the CMM) are of high commercial importance. In this context, it should be understood that not only the maximum movement speed of the measuring probe relative to the target object is of interest, which is very important for large parts and long distances traveled by the measuring probe, but also the maximum acceleration and deceleration, which are important for small workpieces, since the latter allow the measuring probe to be positioned very quickly at the position of interest relative to the target object.

[0013] Therefore, in order to increase the measurement speed, some measures have been taken in the past. For example, using optical probes instead of tactile probes for measurement can generally increase the measurement rate and avoid the wear effect of the target object surface.

[0014] Another option to increase the measurement rate is to use a camera as a measurement probe and to use it in "flying" mode, which is described in WO 2008 / 135530 A1. During the "flying" measurement mode, the camera is moved continuously over the target object and only takes pictures at the positions of interest, without stopping there. The position data of each image is transmitted from the position encoder and stored together with the corresponding image. Flash illumination of the positions of interest ensures that the pictures are clear, regardless of the movement speed of the camera. Because the camera does not stop at the positions of interest, fewer deceleration and acceleration actions must be performed, thereby reducing the measurement time and avoiding triggering structural vibrations. However, in order to know the positions of interest and in order to move the camera along an optimized trajectory including all the positions of interest, it is usually necessary to calibrate the CMM based on a reference object and to program the subsequent trajectory including the defined positions of interest (the positions where the pictures should be taken).

[0015] However, when used at a magnification sufficient to achieve the necessary accuracy, a normal cost-effective camera using optics of standard size shows a small field of view. Because the field of view is small, it is necessary to take a large number of images, which means a large amount of camera movement in order to see all the features of interest. Therefore, due to its low speed and low acceleration, the throughput of commercial CMMs with articulated arms or gantry structures - whether using "flying" mode or not - is still unsatisfactory. In order to cope with this unsatisfactory situation, many CMMs nowadays have cameras with larger diameter objective lenses, thereby showing a larger field of view for the same magnification. As a result, no movement is required to measure small target objects, and only a small amount of movement and a small number of images are necessary to cover large target objects. However, these CMMs are expensive because cameras with correspondingly large objective lenses are expensive.

[0016] The latest developments attempt to increase the measurement rate by using so-called "Delta robots" instead of gantry machines or articulated arms to move the tactile measurement probe (see Renishaw's brochure "Equator 300 Mess-Systeme", published July 2011).

[0017] A delta robot is a parallel robot. It consists of a fixed base (mounted above the workspace) fixed to a fixed frame, and three intermediate joint arms extending from the base. The arms, often called "kinematic chains", are connected at their first ends to the base by means of universal joints, and at their second ends to the end effector, which is often constructed in the form of a triangular or circular platform.

[0018] The arm is typically made of a lightweight composite material and is driven by an actuator located in the base. Driven by the actuator, the end effector can move within a motion zone. The motion zone is a three-dimensional space into which the end effector can move to the maximum extent. The boundaries of the maximum movement - and accordingly the boundaries of the motion zone - are defined by the physical limits created by the construction of the kinematic chain and its joint movement linked by the end effector. Actuation can be done with linear or rotary actuators. Because the arm is made of a lightweight composite material, the moving parts of the delta robot have less inertia. This allows very high accelerations and very fast movements, which far exceed the speed of acceleration and movement that can be achieved by traditional gantry machines or articulated arms.

[0019] For the implementation of the Delta Robot as part of a coordinate measuring machine, the degrees of freedom of the Delta Robot have been expanded to up to 6, allowing lateral movement of the end effector in the Cartesian directions X, Y, Z, as well as rotational movement around these axes, resulting in yaw, roll, pitch. Due to their high acceleration / deceleration actions and their high movement speeds, Delta Robots and machines based on Delta Robots are commonly used for pick and pack in packaging plants, medical and pharmaceutical industries; some of them perform up to 300 picks per minute.

[0020] However, despite its applicability in various technical fields, the delta robot is widely considered to be unsuitable for the measurement requirements of coordinate measuring machines. This is due to its sensitivity to temperature fluctuations and strong vibrations during fast movement and rapid acceleration / deceleration actions (caused by its lightweight construction). As a result, the exact position of the end effector cannot be determined accurately enough, and proper focusing is not feasible with conventionally arranged optical devices (such as the optical probe or camera of the CMM).

[0021] The use of a delta robot to move the tactile probe of the CMM, as proposed in the above-mentioned brochure "Equator 300 Mess-Systeme", does not contradict the above statements, but attempts to avoid these problems associated with the delta robot by using a tactile measurement probe. However, since the tactile probe must contact the surface of the target object, the tactile probe determines a measurement speed that is much slower than that allowed by the delta robot. Therefore, the measurement rate is always limited by the tactile probe and its position will thus be able to be determined. Therefore, the possibilities achieved by the delta structure with regard to acceleration and movement speed are not fully developed. In addition, the CMM disclosed in the above-mentioned brochure is again only able to determine the target object with respect to a reference object, which should be measured before measuring the target object. Therefore, calibration must be performed before measurement. As a result, it is impossible to reduce the measurement time during preparation for measurement, and only specially trained personnel will be able to handle the CMM.

[0022] Common to the type of coordinate measuring machine, a proper calibration work can achieve a satisfactory degree of accuracy taking into account the reproducible errors, but all non-repeatable defects in the mechanics completely affect the measurement accuracy obtained. Thus, for example, if there is some play between the first axis and the second axis, neither the linear scale nor the angular encoder applied to determine the position of the CMM probe will have a chance to recognize such play. Other kinds of defects that are often not compensated or require at least great efforts to compensate include, for example: backlash, which has a great influence on the results, and low temperature drift or any other kind of drift that is most of the time not well managed.

[0023] As long as all these negative effects are known, the usual reaction is to choose high-quality and expensive mechanics to minimize backlash or play. Another consequence is that very complex temperature compensation algorithms are applied, which is not a big problem, but always requires a significant data collection phase. Most of the time, the measuring machines have to be calibrated at different temperatures individually, which is long and expensive. Despite all this, the permissible temperature drift is still limited, which practically does not allow application in harsh factory environments. Finally, in order to compensate for low drift or collision effects, a complete recalibration is often performed, usually at least once a year. Summary of the invention

[0024] It is an object of the present invention to provide a coordinate measuring machine which overcomes and preferably completely avoids the above-mentioned accuracy problems.

[0025] A specific object of the present invention is to be able to directly measure the position of an end effector / CMM probe in six degrees of freedom ("6 DOF"). Thus, all geometric imperfections, all clearances, all bounces, and all thermal expansions should be directly included in the 6 DOF position measurement so that they no longer negatively affect the final accuracy.

[0026] These objects are solved by a coordinate measuring machine according to a first aspect.Further developments of the invention are characterized in an alternative or advantageous manner in other aspects.

[0027] The invention relates to a method for determining the position and orientation of an end effector of a coordinate measuring machine (CMM), the coordinate measuring machine comprising a carriage as a support and positioning structure for the end effector, the end effector being movable in at least three, in particular six, degrees of freedom and being positioned by the carriage. The end effector may be realized by a probe capable of determining the exact coordinate position of a possible target object to be measured.

[0028] The CMM further comprises a fixed metrology stage acting as a base or support for a possible target object and at least one imaging detector for capturing an image of at least a portion of a measurement volume defined, in particular, by limiting the mobility of said carriage.

[0029] The method comprises: moving the end effector by the carriage, in particular according to a given part program or measurement path; and capturing images of at least a part of the measurement volume with the imaging detector. Preferably, such images are taken continuously to continuously provide respective position and orientation information of the probe (end effector).

[0030] It should be understood that the area that can be captured with the imaging detector (or more than one corresponding imaging detector) does not correspond to the measurement volume. The measurement volume is defined by the volume within which each position can be reached by individual measurements of the probe of the CMM. The volume imaged by the camera is typically offset to the CMM measurement volume, because the "collaborative target" at the end effector is offset to the tool center point (TCP). There may even be zero overlap between the TCP measurement volume and the capture volume of the photogrammetric positioning system.

[0031] The capture area thus corresponds to a region which can be covered by the imaging detector and in particular at least partially overlaps the measurement volume, and may preferably encompass the entire measurement volume.By such an arrangement, coverage of the end effector with the captured image can be ensured.

[0032] According to the invention, the received image data represent an image covering at least a portion of the end effector (of at least a portion of the measurement volume). The imaging detector may preferably be arranged so that the end effector is covered by the respective images when measuring the target object. Moreover, the image positions of reference points associated with the end effector are determined in the image by image processing, and the position of the end effector is obtained based on the image positions of the reference points. The reference points are arranged on one side of the end effector, for example, by specific markings at the end effector, a defined pattern or by given points of a structure of interest. The positions of these points are determined in a captured image (image position) covering the points.

[0033] Furthermore, the imaging detector is securely mounted to the metrology table and is arranged to be mechanically decoupled from the bracket.

[0034] The direct benefit of the method of the invention showing the above features is that the mechanical mass (i.e. vibration resistance) and other mechanical instabilities associated with a typical CMM are made less important for the measurements to be obtained using the CMM. The main remaining constraint of the carriage is that high-frequency movements (such as vibrations) are avoided, since the frame rate supplied by the imaging detector is typically only a few hundred hertz at most, while vibrations can reach frequencies in the kilohertz range or even beyond. To some extent, such fast movements can also be measured using additional sensors (such as inertial measurement units IMU, gyroscopes and magnetometers). However, in this case, it will be necessary to integrate the low-frequency image signals and high-speed signals of such additional sensors (see below).

[0035] Even more advantageously, according to a specific embodiment of the present invention, one or more imaging detectors are mounted to the metrology stage for capturing images of the end effector. By arranging more cameras and jointly using the image information of these cameras, the accuracy of the position determination of the end effector is significantly increased.

[0036] To this end, the coordinate measuring machine comprises at least two, in particular three imaging detectors, wherein the method for determining the position and orientation of the end effector comprises: capturing an image of at least a portion of the measurement volume with at least two imaging detectors; and receiving image data representing the captured images, each image being captured with a different imaging detector and covering at least a portion of the end effector.

[0037] Furthermore, the image position of a reference point associated with the end effector is determined in each image by image processing, and the position of the end effector is derived based on the image position of the reference point. By doing so, the derived image positions of some images are used for the position (and orientation) determination of the end effector, resulting in a higher accuracy. Moreover, the at least two imaging detectors are firmly mounted to the metrology table and are arranged to be mechanically separated from the bracket.

[0038] In particular, for synchronization purposes, images are acquired by the imaging detector at certain time instances.

[0039] According to a preferred embodiment, the position determination is based on images from all imaging detectors which were recorded in the same position, in particular simultaneously, from a possible target object and / or the end effector.

[0040] This ensures that the target position is reliably determined based on the images of all applied imaging detectors, even if the target is moving. In other words: All imaging detectors will take pictures of the same target, ensuring very coherent information. If the cameras would not be perfectly synchronized, the physical position of the target would be different on the images taken by different detectors, resulting in a worse accuracy of the position determination.

[0041] However, even if the imaging detectors were to be triggered with a common external signal, it would be difficult to guarantee from the detector manufacturer that an accurate waiting time could be ensured between a certain flank of the trigger signal and effective image acquisition. Again, such uncertainty could reduce the accuracy of positioning.

[0042] To overcome these limitations, a defined shutter time of the imaging detectors may be triggered (e.g. by a control unit of the CMM) such that a temporally common image acquisition cycle is provided to the imaging detectors, the end effector may be illuminated for a defined illumination period during the common image acquisition cycle, and images of image data may be acquired with the imaging detectors, each imaging detector representing the end effector in a defined (same) state corresponding to the illumination period. In other words, each captured image represents an alternative perspective image (pose) formed by the end effector in its defined illumination state.

[0043] In particular, the end effector is illuminated in a pulsed manner, with an illumination frequency and an illumination period, the illumination frequency being synchronized with the shutter time (and / or frame rate) of the imaging detector. Alternatively, the end effector can also be illuminated aperiodically (without a fixed frequency), but still synchronized with the camera exposure time.

[0044] The flash light source illuminates the end effector during the shutter open time of the imaging detector / camera (in particular, synchronized with the respective frame rate). Thus, even if the detector shutter does not open and close in the same time interval after the trigger signal, the acquired image is dominated by the flash duration, which provides that the intensity of the flash is much stronger than the ambient light intensity. As a result, the corresponding acquired images appear completely synchronized.

[0045] According to a more specific embodiment, the movement of the end effector is synchronized with the frame rate of the imaging detector such that images are taken only when the carriage remains stationary during an acquisition cycle, in particular wherein high frequency movements faster than 200 Hz are avoided.

[0046] Concerning the calibration of the entire measuring system, the reference marks arranged at the fixed metrology stage can be covered by at least one image of the image data, the positions of the respective marks can be determined in the at least one image by image processing, and the respective poses of the respective imaging detectors are obtained based on the mark positions (for example by a geometric cut-out method). By doing so, in particular, a calibration of the pose of the imaging detector with respect to the reference marks is provided.

[0047] The invention also relates to a coordinate measuring machine (CMM), comprising: a bracket, which serves as a supporting and positioning structure for an end effector, which can move in up to six degrees of freedom and is positioned by the bracket; a fixed metrology table, which serves as a support for a possible target object; and a control unit, which controls the movement of the end effector achieved by the bracket and controls the image acquisition using an imaging detector.

[0048] A tool holder may be included in or attached to the end effector, such tool holder being configured to accommodate various measurement probes. In particular, the end effector is represented by a probe head including a probe element, such as a stylus having a probe tip at a distal end.

[0049] The movement and positioning of the end effector may be achieved by means of any kind of positioning system, under the control of a control unit which may be located in the base or remotely, providing sufficient positioning accuracy for the CMM.

[0050] The CMM further comprises at least one imaging detector for capturing an image of at least a part of the measurement volume (motion zone) and an analyzing unit for processing electronic signals and / or data transmitted by said imaging detector.

[0051] The analysis unit typically comprises storage means for storing the transmitted images and comprises a circuit unit for processing the images.

[0052] According to the invention, the imaging detector is firmly mounted to the metrology table and mechanically separated from the bracket. Moreover, the analysis unit is configured to determine the position (and orientation) of the end effector in six degrees of freedom by receiving image data representing an image covering at least a portion of the end effector, determining an image position of a reference point associated with the end effector in the image by image processing, and deriving the position of the end effector in six degrees of freedom based on the image position of the reference point.

[0053] According to one embodiment of the invention, the coordinate measuring machine comprises at least two, in particular three, imaging detectors, which are firmly mounted to the metrology table and mechanically separated from the carriage. Here, the analysis unit is configured to determine the position of the end effector in six degrees of freedom by receiving image data representing images, each image being captured by a different imaging detector and covering at least a portion of the end effector, determining the image position of a reference point associated with the end effector in each image, and deriving the position of the end effector based on the image position of the reference point (in a set of images).

[0054] The use of at least two, in particular three, cameras and the processing of the image data generated by these cameras for determining the position of the end effector results in a greater accuracy with regard to the position determination.

[0055] According to one embodiment, the control unit is designed and configured so that the image data are generated at the same position for all acquired images, in particular by capturing images with each imaging detector of the end effector at the same time. The image thus represents the end effector in a constant and identical state and provides an accurate basis for further processing the image data and determining the position and orientation of the end effector.

[0056] In particular, the position determination is based on images from all (at least two) imaging detectors in order to provide improved position accuracy.

[0057] According to one embodiment, the carriage is constructed as or comprises a delta robot.Alternatively, the carriage is represented by a gantry of a gantry CMM or by an articulated arm.

[0058] The motion zone of the end effector (corresponding to the measurement volume) together with any components comprised therein or attached thereto may thus be defined and limited by the arm (ie the kinematic chain) of the delta robot, at the end of which the end effector is linked.

[0059] According to one embodiment, the delta robot comprises three arms, each arm having a first portion joined to a second portion, the first portion being connected to a fixed base and the second portion being connected to the end effector.

[0060] A delta robot according to a recently developed CMM typically has a fixed base fixed to a fixed frame and comprises a kinematic chain, which is an intermediate joint arm. As usual, the joint can be provided with an angle encoder (also called position sensor) to transmit a corresponding angle signal so that the current position of the end effector with a camera can be obtained and used by the analysis unit and the control unit.

[0061] Advantageously, the imaging detector may have a field of view encompassing at least 20% of the motion area.

[0062] It is also advantageous if the imaging detector is a high speed detector capable of taking pictures / images very quickly, i.e. more than 360 frames per second. Advantageously, the imaging detector is controlled in such a way that pictures are taken at a high clock rate, e.g. 500 frames per second or even more. In particular, the camera is designed and controlled such that the image acquisition is twice as fast as the highest mechanical characteristic frequency that may be excited (at the CMM), so that interpolation (of the image data) can be efficient.

[0063] According to a preferred embodiment, the imaging detector is embodied as a camera.

[0064] According to another embodiment, the end effector is illuminated, in particular by means of an LED array. In general, the light source may comprise a plurality of independent light sources under common control. The light source may be attached to a base. However, the light source may also be integrated into the end effector or attached to the imaging detector.

[0065] In the case of pulsed illumination, the flash light source illuminates the end effector and / or the target object or cooperative target during the shutter open time (frame rate) of the imaging detector / camera. Thus, even if the detector shutter does not open and close in the same time interval after the trigger signal, the acquired image is dominated by the flash duration, which provides for a flash intensity that is much stronger than the ambient light intensity. As a result, the corresponding acquired images appear completely synchronized.

[0066] According to another embodiment, the CMM is additionally provided with a sensor unit comprising a plurality of sensors, wherein, in particular, the sensor unit is supported by the end effector and the plurality of sensors are dedicated to relative position determination and / or displacement determination. In particular, the plurality of sensors are embodied as multi-axis acceleration sensors and / or inertial measurement units IMU and / or gyroscopes and / or magnetometers, in particular capable of acquiring signals at high frequencies.

[0067] Using the signal of the acceleration sensor allows for a position determination with improved accuracy by largely eliminating vibration influences.Another option is to provide tilt sensors for the horizontal x-axis and y-axis in the sensor unit in order to determine the position even more accurately.

[0068] Preferably, a sensor fusion algorithm, in particular a Kalman filter, is used to perform integration of signals of multiple sensors of the sensor unit, in particular integration of high-frequency signals, and integration of signals of the imaging detector, in particular integration of low-frequency signals originating from absolute position measurement in six degrees of freedom.

[0069] It is further preferred that reference marks are arranged on the metrology stage in the area where possible target objects are placed, in particular enabling calibration of the position of the camera for these reference marks, whereby it is assumed that the reference marks are within the field of view of the camera. Based on these features, by combining the signals from the plurality of sensors of the sensor unit and the signals from the imaging detector, also by utilizing reference marks, a system calibration and compensation of slow drifts is enabled.

[0070] According to another embodiment, the end effector is provided with a geometric pattern providing reference points and / or is provided with one or more reference marks. Thus, an automatic calibration of the end effector, in particular for a camera, including the reference marks, is enabled.

[0071] According to another embodiment, the end effector comprises a cooperation target having a triangular shape and provided with a triangular or chessboard-like geometric pattern and provided with markings for orienting and positioning the cooperation target.

[0072] This means that the "end effector" can also be identical to the "cooperation target".

[0073] In the case of using "only" one imaging detector, a 3D target can be arranged at the end effector to provide various reference points, based on which the precise position and orientation of the end effector can be calculated. By doing so, the reference points do not lie completely in a common plane, thus enabling precise localization of the target.

[0074] Preferably, the cooperating target and / or the structure carrying the reference marker is arranged in a material having a low and / or stable coefficient of thermal expansion CTE. In the latter case, "stable CTE" means a dimensional change proportional to a temperature change, the temperature sensor being advantageously arranged so that dimensional changes due to temperature changes can be easily taken into account in the calculation for compensation purposes.

[0075] According to one embodiment, the cooperative target is made of Borofloat glass. Borofloat glass is low cost and has a low CTE. According to another embodiment, the cooperative target is made of a material specially designed to have a low CTE, such as microcrystalline glass or Invar (CTE is close to zero).

[0076] Advantageously, the geometric pattern of the cooperating target is printed with high image quality, in particular with low gloss, high contrast and high definition, for example on extra-matt "fine art" paper (or any other high-quality paper with a gloss close to zero and a flat surface structure) for gluing to a support, in particular made of Borofloat glass.

[0077] Another aspect of the invention relates to the effect of the drive system / positioning on the stability of the mechanical system. As already mentioned above, a vibration-free movement is mandatory to achieve the required accuracy, therefore, the drive system of the carriage is critical. In order to keep the size of the motor small enough (not only significant for system size / weight, but also for costs) and to use it at an efficient operating speed, it is usually necessary to have a reduction between the motor shaft and the drive shaft. Some technical solutions are known, for example when using gear mechanisms, but most of them are associated with some play or some rebound. Technical solutions using belts are usually not very rigid or generate vibrations when using toothed belts.

[0078] Therefore, according to another embodiment of the invention, the drive system of the carriage comprises a motor shaft and a drive shaft, wherein a speed reduction is provided between the motor shaft and the drive shaft, in particular by means of a cable reduction.

[0079] This friction-based solution for speed reduction is associated with the following advantages:

[0080] High stiffness;

[0081] Absolutely no gaps;

[0082] Easy and cheap to manufacture. BRIEF DESCRIPTION OF THE DRAWINGS

[0083] The invention will be described in more detail below with reference to examples of possible embodiments. Identical elements in the figures are indicated by the same reference numerals. It should be understood that the drawings are diagrammatic representations of such example embodiments and accordingly, neither limit the scope of the invention nor are the drawings necessarily drawn to scale. The drawings schematically show:

[0084] Figure 1a is a "gantry" or "bridge" CMM, as the first example of a prior art coordinate measuring machine CMM;

[0085] Figure 1b It is an articulated arm CMM according to the latest state of the art;

[0086] Figure 2 is a CMM according to the invention having a delta robot as a support structure;

[0087] Figure 3 Illustration of target flash illumination and use according to Figure 2 Synchronization between the exposure times of the imaging detectors in the CMM;

[0088] Figure 4 is another embodiment of yet another embodiment of a CMM according to the present invention;

[0089] Figure 5a It is a feasible design for the end effector / collaboration target;

[0090] Figure 5b It is another feasible design for the end effector / collaboration target;

[0091] Figure 6a is a cable reduction for a drive system of a CMM according to the invention; and

[0092] Figure 6b is based on Figure 6a Detailed view of the various parts of the cable reducer. DETAILED DESCRIPTION

[0093] Figure 1a A "gantry" or "bridge" CMM 20 is shown as a first example of a prior art coordinate measuring machine CMM.

[0094] The bridge CMM comprises a base 8 (metrology table) and a frame structure (carriage of the CMM) for linking a tool carriage 6 (end effector) to the base 8. The first frame part is a gantry with two gantry legs 1 and 2, the upper ends of which are connected by a bridge 3. Driven by a drive mechanism (not shown), the frame part can move along the longitudinal side of the base 8. This direction corresponds to the direction Y.

[0095] The X-carriage 4 is arranged on the bridge 3 of the frame part in a movable manner in the X direction. The movement of the carriage 4 (which should be regarded as another frame part) can also be realized by a rack and pinion. The vertical rod 5 (sleeve, Z-jack) constituting another frame part is incorporated in the carriage 4 in a movable manner. At the bottom of the vertical rod 4, a tool bracket 6 is provided to hold the attached stylus 7. The stylus can be understood as also being part of the end effector.

[0096] The tool carrier 6 can be moved to any desired point in the measurement volume (working area) of the coordinate measuring machine 20 along the directions X, Y and Z. The measurement volume is defined by the base 8 and the frame parts 1, 2, 3, in particular by the range of movability of the support 4. The three spatial directions X, Y and Z are preferably orthogonal to each other, but this is not essential to the invention. It should be noted that the drive mechanism and the controller for driving the frame parts (and thus for driving the tool carrier 6) are not shown.

[0097] In the embodiment shown, the base 8 may comprise a table with a granite surface plate, in particular the base is made of granite for supporting an object to be measured and on which the spatial coordinates of at least one measuring point are intended to be determined.

[0098] Not shown is a control and processing unit which is designed to actuate the motor drive of the coordinate measuring machine 20 so that the end effector 6 is moved to a predetermined measuring point. The control and processing unit comprises a processor and a memory.

[0099] Figure 1b An articulated arm CMM 21 according to the state of the art is shown. Here, the arm corresponds to the carriage of the CMM. The CMM is designed to determine the measuring position of the probe 7. Therefore, the articulated arm CMM 21 comprises a base 13, which forms a support for the CMM and can be positioned on a surface, in particular a floor or a workbench. In the sense of the present invention, the base 13 and / or the surface represent a fixed metrology table. Some arm parts 15a-15g connected to the base 13 are linked by hinges and swivel joints 18a-18d, so that the arm parts 15a-15g can move relative to each other. The joints 18a-18d provide a rotational movability that is essentially free of resistance and support forces to achieve an accurate measurement of the actual relative setting of each joint.

[0100] The first arm part 15a is linked to the base 13 and can move relative to it, the second arm part 15b is linked to the first arm part 15a and can move relative to it, etc. Finally, the arm part 15g (end effector) forms the end of the articulated arm and can be connected to the base 13 in terms of its functionality. Figure 1a Compared with the stylus holder 6 of FIG. 1 , ie, a probe 7 is attached, which can thus move freely within a given volume. For example, the probe 7 can be manually operated by a user and can be designed as a ruby ​​ball for contacting a surface point to be measured.

[0101] Furthermore, detection units 19a-19d are assigned to the hinges and swivel joints 18a-18d, which are formed for measuring the actual relative setting of each joint 18a-18d. Thus, for example, the detection units 19a-19d are installed in the housing of the respective joint 18a-18d. For example, a photoelectric angle sensor is used as the detection unit for measuring the actual angle α, β, γ, δ, ε between two arm parts 15a-15g linked by the respective joint 18a-18d.

[0102] The measured actual settings of each joint 18a-18d are sent to the calculation unit 17. By combining the relative settings of each joint 18a-18d, the calculation unit 17 calculates the internal position of the probe 7 relative to the base 13 of the coordinate measuring machine 21—the position of the point touched by the probe 7, respectively. The coordinates of the calculated internal position relative to the base 13 can be displayed on a display of the calculation unit 17, for example.

[0103] Figure 2A coordinate measuring machine 22 (CMM) according to the invention is shown having a carriage embodied as a delta robot 12 as a support structure.

[0104] The delta robot 12 comprises a fixed frame 30 supporting a fixed base 31, and three arms, also referred to as kinematic chains. The frame 30 may be embodied as a massive construction. Each arm has two parts 32a, 32b linked by an intermediate joint 32c. A first part 32a of each arm is connected to the fixed base 31, while a second part 32b is connected to an end effector 40, which can move with three degrees of freedom (3 DOF) by means of the components of the delta robot 12. However, parasitic movements may occur in up to six degrees of freedom, such as rotations caused by one arm being warmer than the others. In this case, the end effector 40 is constructed in the form of a triangle, but may also be embodied as, for example, a circular plate, for example designed to support tools, probes, etc. In particular, the end effector 40 is constructed so that any attached elements are interchangeable. The end effector 40 may include a geometric pattern 45 for providing a reference point (see also Figure 5a and Figure 5b ).

[0105] A stationary measuring platform or metrology table 35 is used as support and for positioning a possible target object or a so-called “cooperative target.” The metrology table 35 may have the shape of a disc.

[0106] At least two (in the preferred case shown three) imaging detectors 33 are here embodied as cameras and are arranged to accurately determine the position of the end effector 40, in particular the position of the geometric pattern. The number of imaging detectors / cameras is designed and arranged (positioned) so as to enable a fully detailed view of the entire cooperative target.

[0107] To determine the position of the end effector, the camera acquires an image of the pattern 45 at the effector 40. A large number of reference points, in particular represented by the black / white contrast provided by the triangular pattern 45, are provided with the end effector 40, whose positions are determined in the acquired image and the image position is obtained (using image processing). Based on the image position of the reference points, the relative position and orientation of the end effector 40 with reference to the coordinate system of the CMM 22 can be calculated. The more reference points are provided and identified, the more accurate such a determination will be.

[0108] According to the invention, the imaging detector 33 is securely mounted to a metrology stage 35 which is mechanically separate from the carrier (delta robot 12). According to an embodiment of the invention, furthermore the metrology stage 35 is completely mechanically separate from the carrier.

[0109] In the example shown, a camera as imaging detector 33 is attached to a columnar support 34, which is mounted on the metrology table in a circular arrangement, for example at a height of 550 mm above the level of the metrology table 35. Reference numeral 36 denotes a 440 mm radius of the camera field of view projected onto the metrology table 35. A light source 37, embodied, for example, as an LED array, can be used for illumination of the end effector 40 and / or a possible cooperative target / target object. As Figure 2 In an embodiment, the light source 37 may be attached to the base 31. However, the light source 37, which may include a plurality of independent light sources, may also be integrated into the end effector 40 or attached to the imaging detector 33.

[0110] The end effector 40 may additionally include sensors such as accelerometers for measuring acceleration and / or deceleration in the X-, Y-, and Z-directions, gyroscopes for measuring rotation, or a full 6-DOF inertial measurement unit IMU, although generally this is not necessarily required by the present invention.

[0111] A direct benefit of the CMM 22 according to the invention is that the mechanical mass (i.e. its resistance to mechanical drift and vibration) is in particular no longer of substantial importance, since the position of the end effector 40 itself can be measured directly, preferably in a coordinate measuring system related to the object to be measured. The only remaining constraint on the mechanical properties of the carriage is that high-frequency movements (such as high-frequency vibrations) must be avoided, since the frame rates supplied by the camera are usually only at most a few hundred hertz, while vibrations can reach the kilohertz range or even exceed. To some extent, these fast movements can also be measured using IMUs, gyroscopes and magnetometers. However, in this case, the integration of the relevant measurement signals can occur (for example when using accelerometers to obtain the position) during the data evaluation, and the results of the additional sensors only mean displacements, not absolute positions. Therefore, the measurement results transmitted by such additional sensors can be considered and regarded as complementary data. However, it is advantageous to bridge the gap between the absolute position data extracted from the imaging detector 33 and such complementary measurement data, also subject to drift. Accordingly, as another development form of the invention, a sensor fusion algorithm, in particular including a Kalman filter, is applied during the data evaluation and analysis.

[0112] In case the positioning system described here is time synchronized with any end-effector mounted sensor (such as a camera, distance sensor or tactile probe), then the vibration requirements are greatly relaxed since no interpolation is required. The vibration must then only be low enough to make the setup "motionless" (stationary) during the exposure time of the measurement.

[0113] Obviously, the columnar support 34 of the imaging detector 33 must be stable relative to the metrology stage 35. Because the assembly (comprising the metrology stage 35, columnar support 34 and camera 33) contains no moving parts and is separate from the delta robot 12, however, the mechanical stability of the assembly is easier to achieve than the carriage / delta robot 12.

[0114] The use of some cameras to determine the position of an object is well known and widely described in the field of photography. For all such solutions for position determination based on camera images, one of the first prerequisites is to extract the relative positions of the different cameras. There are some solutions, but the arrangement association implemented by the present invention has significant advantages. Known cooperating targets (reference marks) or geometric patterns at the metrology table can be used to determine the relative positions of the cameras 33, and the patterns can be easily moved to different locations in order to repeat the position estimation, which reduces any resulting uncertainty. The system operates in an automatic manner, and the appropriate number of iterations to accurately determine the camera positions is only limited by the processing time. In any case, the measurement of some different positions greatly improves the final accuracy.

[0115] However, for a good position determination based on the camera image with the coordinate measuring machine according to the invention, further important prerequisites must be met:

[0116] 1. All cameras 33 must capture images of the same target at the same location to ensure information consistency. - This condition is relatively easy to meet, but is far from sufficient.

[0117] 2. All camera images for the same position determination must be taken at exactly the same time, since most of the time the target is moved by the carriage / delta robot. — To meet this condition, a complete synchronization of the cameras should be established in order to ensure that the physical position of the target is indeed the same in all commonly assigned images.

[0118] 3. Finally, even if the camera 33 is triggered by a common external signal, the camera manufacturer cannot guarantee the exact waiting time between the determined flank of the trigger signal and the effective image acquisition. Again, this uncertainty reduces the position determination accuracy.

[0119] Figure 3 The solution to this last proposed problem is illustrated by using a flash light source 37 to illuminate the end effector, for example a geometric pattern at the end effector, during the shutter opening time of the camera (between "33 open" and "33 closed"). Although the shutter opening time of each camera is not started at the exact time after the trigger signal S(tr) ​​and does not have the exact same length, as Figure 3Obviously, however, the individual images acquired are primarily dependent on the light generated by LED 37, as it is much stronger than the ambient light I(a), resulting in the effective exposure time of all three cameras being the same and correspondingly acquiring perfectly synchronized images during the flash "37 on" period.

[0120] After the improvements associated with the above-mentioned other developments of the invention, the photographic results are excellent, but the system still cannot identify any internal drift of the system. Such internal drift may occur, for example, due to thermal sources, with thermal expansion of the columnar support 34, and falsified results will become apparent when the next system calibration is to be performed. In order to overcome this problem, Figure 4 A solution is presented: reference marks 39 are provided on the measurement stage 35 and additional reference marks 38 are provided on the probe or end effector, in the field of view of the camera 33 indicated by arrows 39a, 39b. Thus, the camera 33 and the probe marks 38 can be calibrated relative to each other and the position of the camera 33 can be recalibrated online relative to the reference marks 39 of the metrology stage 35. According to one embodiment, the reference marks are provided in a material that brings the coefficient of thermal expansion CTE close to zero, but also any other material with low uncertainty (i.e. stable CTE in combination with a temperature sensor).

[0121] Furthermore, the design of the end effector and / or its geometry also has a strong influence on the final accuracy of the camera measurement results. It is important to have enough reference points, but all of them with enough space between them to account for single meaning differences, especially when the target is tilted (non-perpendicular) with respect to the optical axis of the camera field of view.

[0122] Figure 5a A possible design of a geometric pattern 45' is shown, which may also be referred to as a "reference plate". A triangular ground shape with a lateral extension of, for example, 150 mm is subdivided into small triangles with a base length of, for example, 13.6 mm, resulting in an x ​​number of corners per side, for example 9, corresponding to a total of 45 corners. The small triangles arranged subsequently / adjacent to each other are arranged in black and white in an alternating manner. The cut corners and white edges indicated by the reference symbol "y" reduce the risk of false positive angle determination. In this case, two external target orientation marks 42 are printed in black, supporting the correct orientation when positioning the reference plate. In addition, two internal orientation marks 41 are provided in this case.

[0123] As material for such a reference plate, Borofloat glass material can be used, which has both low cost (e.g. lower than Invar or glass-ceramic) and a very low coefficient of thermal expansion, and can therefore also be used as a reference length artifact (corresponding to the real length of the triangular base) for calibrating camera pixels. In order to achieve the required high image quality (low gloss, high contrast and high definition), the pattern itself can preferably be inkjet printed on super matt art paper. For the example shown, the latter is glued directly to the Borofloat plate.

[0124] This example benchmark board shows the following performance:

[0125] The triangular shape allows the use of all surfaces for disposal in the delta structure;

[0126] 170 corner features (algorithms for locating larger numbers of features are now fast and accurate);

[0127] Excellent image quality;

[0128] Easy to calibrate due to flat shapes and scale-invariant features (e.g. using machine vision);

[0129] Different orientation markings facilitate correct calibration of orientation.

[0130] Figure 5b An alternative embodiment of a reference plate or cooperating target 45" is shown. In this case, a square pattern is used to facilitate image recognition when viewing the target under perspective (oblique vision), as the square pattern is useful to avoid errors due to camera non-linearity.

[0131] In order to achieve the required measurement accuracy, a further aspect is important.

[0132] As already mentioned above, vibration-free movement is mandatory to achieve the required accuracy, therefore, the drive system of the carriage is critical. In order to keep the size of the motor small enough and to operate the drive system at a speed that allows sufficient efficiency, it is necessary to reduce the speed between the motor shaft and the drive shaft. Some solutions for this purpose are known, but most of them are associated with some play or some backlash, for example when using a gear mechanism. Belt-based solutions to the problem usually do not provide sufficient rigidity or generate vibrations when using a toothed belt.

[0133] In the context of the present invention, Figure 6a and Figure 6b As shown, cable deceleration is proposed. A cable 54 (some turns) is wrapped around a motor shaft 52, which is driven by a motor 51, and around a drive shaft 53, which has a much larger diameter than the motor shaft 52 to provide the required deceleration (see Figure 6a ). Figure 6b The notches 56 shown in detail facilitate guiding the cable 54 from one groove 55 to the next. This solution allows machining all grooves 55 as a single circular groove without having to make a complex spiral along the entire drive axis.

[0134] This friction-based solution for deceleration is associated with the following advantages:

[0135] High stiffness;

[0136] Absolutely no gaps;

[0137] Easy and cheap to manufacture.

[0138] It should be noted that the above solutions for deceleration (such as Figure 6a and Figure 6b The illustrated embodiment has only a limited working angle, however, this is not a problem for the purposes of the present invention.

[0139] In summary, the present invention is distinguished by the following advantages:

[0140] • Precise measurement and position determination of the target object position can be performed with 6 degrees of freedom while avoiding negative effects of the bracket (e.g. due to bounce, play, bending, thermal expansion, instability in time...).

[0141] • The above ability to measure accurately allows for relaxation of the stability requirements of the bracket, thus reducing the price.

[0142] • The present invention is able to perform position measurement and determination at low frequency in 6 degrees of freedom using imaging detectors / cameras when this is required in combination with high frequency measurement of relative displacement through the use of IMUs, gyroscopes and / or magnetometers.

[0143] • Cooperative targets (geometrical reference patterns) made of materials with low or at least stable thermal expansion coefficients are subject to automatic system calibration, in particular their integration into the overall system control and operation.

[0144] - Especially cooperative targets in optimal lighting are imaged by all (three) cameras at the same position, leading to excellent photographic results.

[0145] • The cooperative target, in particular embodied as a reference plate with a characteristic geometric pattern, allows compensation of slow drift effects, such as temperature-induced drifts.

[0146] • Mechanical reduction of the drive system with high stiffness, lack of play and low cost is implemented in the system according to the invention.

[0147] The present invention can be generally applied to all types of coordinate measuring machines (e.g. Figure 1a and Figure 1b As shown), that is, the CMM is designed as a parallel kinematic machine and the CMM has linear or serial motion. Exemplarily, the CMM can be designed as a bridge type, L-bridge type, horizontal arm type, cantilever type or gantry type machine.

[0148] Although the invention has been illustrated above, partly with reference to some specific embodiments, it must be understood that many modifications and combinations of embodiments of the different features may be made and that the different features may be combined with calibration principles and / or coordinate measuring machines known from the prior art.

Claims

1. A method for determining a position of an end effector of a coordinate measuring machine (20, 21, 22), the coordinate measuring machine (20, 21, 22) comprising: a bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31), the bracket serving as a support and positioning structure for the end effector (6, 7, 15g, 40, 40'), the end effector (6, 7, 15g, 40, 40') being movable in at least three degrees of freedom and being positioned by the bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30), and a fixed metering table (8, 35) which serves as a support for possible target objects, Wherein, the method comprises: the end effector (6, 7, 15g, 40, 40') is moved by the carriage (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31), and capturing an image of at least a portion of the measurement volume with an imaging detector (33), It is characterized in that receiving image data representing said image covering at least a portion of said end effector (6, 7, 15g, 40, 40'), determining the image position of a reference point associated with the end effector (6, 7, 15g, 40, 40') in the image by image processing, and · obtaining the position of the end effector based on the image position of the reference point, in, The coordinate measuring machine comprises at least one imaging detector (33) which is securely mounted to the metrology table (8, 35) and arranged to be mechanically separated from the bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31), and the metrology table is mechanically separated from the bracket, and the movement of the end effector (6, 7, 15g, 40, 40') is synchronized with the frame rate of the imaging detector (33) so that images are captured only when the carriage remains stationary during an acquisition cycle, And among them The end effector (6, 7, 15g, 40, 40') is provided with a geometric pattern (45, 45', 45") providing the reference point and comprises a cooperation target having a triangular shape, The cooperation target is arranged in a triangular or chessboard-like geometric pattern, and The collaboration goals include: Cut corners and white edges to reduce the risk of false positive angle determination; and / or Markers (41, 42) for orienting and locating the cooperation target.

2. The method according to claim 1, characterized in that The movement of the end effector (6, 7, 15g, 40, 40') is synchronized in time with any end effector mounted sensors.

3. The method according to claim 2, characterized in that The carriage remains stationary during the exposure time of the measurement of the end effector mounted sensor.

4. The method according to any one of claims 1 to 3, characterized in that Avoid high frequency movements faster than 200Hz.

5. The method according to any one of claims 1 to 3, characterized in that The coordinate measuring machine (20, 21, 22) comprises at least two imaging detectors (33), wherein the method comprises: capturing an image of at least a portion of the measurement volume using the at least two imaging detectors (33), receiving said image data representing said images, each image being captured with a different imaging detector (33) and covering at least a portion of said end effector (6, 7, 15g, 40, 40'), determining the image position of the reference point in relation to the end effector (6, 7, 15g, 40, 40') in each image by image processing, and · obtaining the position of the end effector based on the image position of the reference point, Wherein, the imaging detector (33) is firmly mounted to the metering table (8, 35) and is arranged to be mechanically separated from the bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31).

6. The method according to claim 5, characterized in that triggering the shutter time of the imaging detector (33) so as to provide the imaging detector (33) with a temporally common image acquisition cycle, illuminating the end effector (6, 7, 15g, 40, 40') for a defined illumination period during the common image acquisition cycle, and Acquiring images of the image data using the imaging detector (33), each image representing the end effector (6, 7, 15g, 40, 40') in a defined state corresponding to an illumination period.

7. The method according to claim 6, characterized in that The end effector (6, 7, 15g, 40, 40') is illuminated in a pulsed manner with an illumination frequency that is synchronized with a shutter time of the imaging detector (33).

8. The method according to any one of claims 1 to 3, characterized in that Overlaying a reference mark arranged at the stationary metering table (8, 35) by at least one image of the image data, determining the corresponding marking position in each of the at least one image by image processing, and Based on the marker positions, the corresponding postures of the imaging detectors (33) are obtained.

9. The method according to claim 8, characterized in that Calibration of the pose of the imaging detector (33) relative to the reference marker (39) is provided.

10. A coordinate measuring machine (20, 21, 22), comprising: a bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31), the bracket serving as a support and positioning structure for an end effector (6, 7, 15g, 40, 40'), the end effector (6, 7, 15g, 40, 40') being movable in at least three degrees of freedom and being positioned by the bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30), a fixed metering table (8, 35) which serves as a support for possible target objects, a control unit (17) which controls the movement of the end effector (6, 7, 15g, 40, 40') by the carriage (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31) and controls image acquisition by an imaging detector (33), and an analysis unit for processing the electronic signals and / or data transmitted by the imaging detector (33), It is characterized in that the coordinate measuring machine comprises at least one imaging detector (33) for capturing images, the imaging detector (33) being securely mounted to the metrology table (8, 35) and mechanically decoupled from the carriage (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31), and the metrology table being mechanically decoupled from the carriage, and The analysis unit is configured to determine the position of the end effector (6, 7, 15g, 40, 40') in six degrees of freedom by: o receiving image data representing an image covering at least a portion of the end effector (6, 7, 15g, 40, 40'), o determining an image position of a reference point associated with the end effector (6, 7, 15g, 40, 40') in the image, and o obtaining the position of the end effector (6, 7, 15g, 40, 40') based on the image position of the reference point, wherein the movement of the end effector (6, 7, 15g, 40, 40') is synchronized with the frame rate of the imaging detector (33) so that images are captured only when the carriage remains stationary during an acquisition cycle, And among them The end effector (6, 7, 15g, 40, 40') is provided with a geometric pattern (45, 45', 45") providing the reference point and comprises a cooperation target having a triangular shape, The cooperation target is arranged in a triangular or chessboard-like geometric pattern, and The collaboration goals include: Cut corners and white edges to reduce the risk of false positive angle determination; and / or Markers (41, 42) for orienting and locating the cooperation target.

11. The coordinate measuring machine (20, 21, 22) according to claim 10, characterized in that The cooperation target is embodied as an external mark (42) and / or an internal orientation mark (41).

12. The coordinate measuring machine (20, 21, 22) according to claim 10 or 11, characterized in that The coordinate measuring machine (20, 21, 22) comprises a sensor unit comprising a plurality of sensors which are dedicated for relative position determination and / or displacement determination.

13. The coordinate measuring machine (20, 21, 22) according to claim 12, characterized in that The sensor unit enables signal acquisition at high frequencies.

14. The coordinate measuring machine (20, 21, 22) according to claim 12, characterized in that The signals from the plurality of sensors of the sensor unit and the signal from the imaging detector (33) are integrated.

15. The coordinate measuring machine (20, 21, 22) according to claim 14, characterized in that The signals from the plurality of sensors include high frequency signals and / or the signals from the imaging detector (33) include low frequency signals from absolute position measurements in six degrees of freedom.

16. The coordinate measuring machine (20, 21, 22) according to claim 14, characterized in that The integration is performed using a sensor fusion algorithm.

17. The coordinate measuring machine (20, 21, 22) according to claim 12, characterized in that The sensor unit is embodied as a multi-axis acceleration sensor and / or an inertial measurement unit and / or a gyroscope and / or a magnetometer.

18. The coordinate measuring machine (20, 21, 22) according to claim 12, characterized in that The sensor unit is supported by the end effector (6, 7, 15g, 40, 40').

19. The coordinate measuring machine (20, 21, 22) according to claim 10, characterized in that The geometric pattern (45, 45', 45") is provided in a material having a low and / or stable coefficient of thermal expansion.

20. The coordinate measuring machine (20, 21, 22) according to claim 10, characterized in that The cooperation target is made of Borofloat glass and / or the geometric pattern of the cooperation target is printed with high image quality and has low gloss, high contrast and high clarity.

21. The coordinate measuring machine (20, 21, 22) according to claim 10 or 11, characterized in that the coordinate measuring machine (20, 21, 22) comprises at least two imaging detectors (33) which are securely mounted to the metrology table (8, 35) and mechanically separated from the bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 30, 31), and The analysis unit is configured to determine the position of the end effector (6, 7, 15g, 40, 40') in six degrees of freedom by: o receiving said image data representing images, each image being captured by a different imaging detector (33) and covering at least a portion of said end effector (6, 7, 15g, 40, 40'), o determining the image position of the reference point in relation to the end effector (6, 7, 15g, 40, 40') in each image, and · Obtaining the position of the end effector (6, 7, 15g, 40, 40') based on the image position of the reference point.

22. The coordinate measuring machine (20, 21, 22) according to claim 21, characterized in that The control unit (17) is designed and constructed so that the image data is generated by acquiring an image at the same position using each imaging detector (33) of the end effector (6, 7, 15g, 40, 40'), and / or • Position determination is based on images from all imaging detectors (33).

23. The coordinate measuring machine (20, 21, 22) according to claim 22, characterized in that The images are acquired simultaneously using each imaging detector (33) of the end effector (6, 7, 15g, 40, 40').

24. The coordinate measuring machine (20, 21, 22) according to claim 10 or 11, characterized in that The driving system of the bracket (1, 2, 3, 4, 5, 12, 13, 15a, 15b, 15c, 15d, 15e, 15f, 15g, 30, 31) includes a motor shaft (52) and a driving shaft (53), and provides a reduction in speed between the motor shaft (52) and the driving shaft (53).

25. The coordinate measuring machine (20, 21, 22) according to claim 24, characterized in that Speed ​​reduction between the motor shaft (52) and the drive shaft (53) is provided by means of a cable speed reduction (50).

Images