Coordinate measuring machine

Abstract

Coordinate measuring machine (10) for dimensional measuring of a workpiece (12), wherein the coordinate measuring machine (10) comprises: - a workpiece holder (14) for holding the workpiece (12); - a stand (16), wherein the workpiece holder (14) and the stand (16) are movable relative to one another along a first axis (y); - an arm (18) which is mounted on the stand (16) and is movable relative thereto along a second axis (z) transverse to the first axis (y); - a measuring sensor (26) arranged on the arm (18) and configured to detect a first measuring signal; and - an evaluation unit (28) which is configured to determine coordinates of the workpiece (12) based on the first measurement signal; characterized in that the arm (18) is designed to be foldable and can be unfolded along a third axis (x) transversely to the first and second axes (y, z) into a measuring space volume (32) in order to be extended linearly relative to the stand (16) and retracted into the measuring space volume (32), and can be folded together along the third axis (x) in order to be retracted linearly relative to the stand (16), wherein the arm (18) does not protrude rearwardly from a rear side (38) of the stand (16) facing away from the measuring space volume (32) either during the unfolding or during the folding.

Description

The present invention relates to a coordinate measuring machine for dimensionally measuring a workpiece.Coordinate measuring machines, in particular with tactile and / or optical measurement sensors, are used in dimensional measurement technology in order to determine the shape of a workpiece surface, for example by scanning. Since dimensional measuring technology is generally used in industries in which very high accuracy is required, for example for subsequent processing steps or for quality assurance, a fault-free functioning and attachment of the measuring sensor system and of the workpieces to be measured over the entire service life must be ensured.In particular in industrial coordinate measuring technology, there is an increasing increase in the requirements of accuracy, flexibility and compactness of the measuring devices or of the measurement setup, inter alia because of the versatility in the geometry and dimension of the parts or workpieces to be measured.In particular in vehicle body measurement technology, so-called horizontal arm measuring devices are frequently used. Such horizontal arm measuring devices are usually coordinate measuring devices of stand construction. They have one or more uprights which can be moved generally parallel to the longitudinal axis of the body to be measured. These posts have a height-adjustable mounting. In this mounting, the so-called horizontal arm is again adjustably located, which can be displaced horizontally into the actual measurement space. At the end of this horizontal arm there are one or more measurement sensors for measuring the workpiece. The measurement sensor or sensors are attached to the horizontal arm such that they can rotate about one or also about a plurality of axes. In this way, a five-axis feed is generally realized for the measurement sensor or sensors. The sensor system can thus be adjusted to each point in the volume from each direction (minus the inherent volume of the measurement sensor extended by its working distance, in other words: minus its tool vector).A problem of this construction is the area consumption associated with it and the so-called rear space risk. The danger zone is namely twice as large as the measurement space volume, since the horizontal arm during the movement of the coordinate measuring machine not only moves forward into the measurement space volume, but is also moved rearward out of the stand on the opposite side. If the horizontal arm is, for example, completely pulled back from the measuring space volume, then it protrudes completely rearward out of the stand. This is not only inefficient from the factory area use point of view, but also is considered to be extremely dangerous in terms of safety of operation.From a technical point of view, too, the above-described conventional design of a horizontal arm measuring device is not optimal. Since the accuracy of the system is critically dependent on the accuracy of the knowledge of the sensor position and position, very massive horizontal arms with a constant cross section are typically used. In other words, precision mounting of the horizontal arm would hardly be possible. A conical configuration of the horizontal arm or a wall thickness of the horizontal arm decreasing in the direction of the measurement space volume as a compensation for the aforementioned effect is generally not used. This is not favorable for the dynamic operation of the machine, since a marked mass forward displacement occurs when the horizontal arm is extended.The latter problem could be solved or at least alleviated, under certain circumstances, by the use of horizontal arms of metal foam construction. Such a construction of the horizontal arms would allow the same stiffnesses to be realized with significantly lower masses. The basic problem of rear space risk due to the horizontal arm protruding rearward by the measurement space depth in case of doubt cannot be solved thereby.US 2005 / 0 166 413 A1 discloses a coordinate measuring machine having an articulated arm designed as an exoskeleton, at the free end of which a measurement sensor is arranged.Further exemplary measuring devices are known from the following publications: DE 103 24 833 B3, EP 2 732 934 A2, DE 10 2017 114 713 A1, DE 101 18 392 A1, DE 33 34 460 A1, EP 0 635 697 A2 and DE 10 2017 128 736 A1.It is therefore an object of the present invention to provide a coordinate measuring machine which solves the above-mentioned problems. In this case, it is in particular an object to produce a coordinate measuring machine which solves the above-mentioned problem of rear space risk and nevertheless enables high measurement accuracy.According to one aspect of the present invention, this object is achieved by a coordinate measuring machine for dimensionally measuring a workpiece, wherein the coordinate measuring machine has the following components:a workpiece holder for receiving the workpiece;a stand, wherein the workpiece holder and the stand are movable relative to each other along a first axis;an arm mounted on the stand and movable relative to the stand along a second axis transverse to the first axis;a measurement sensor disposed on the arm and configured to detect a first measurement signal; andan evaluation unit configured to determine coordinates of the workpiece based on the first measurement signal;wherein the arm is configured to be foldable and is deployable along a third axis transversely to the first and second axes into a measurement space volume in order to be extended linearly relative to the stand and retracted into the measurement space volume, and is collapsible along the third axis in order to be retracted linearly relative to the stand, wherein the arm, due to its foldability, neither during the deployment nor during the collapsing protrudes rearwardly from a rear side of the stand facing away from the measurement space volume.The term "transverse" is understood here to mean any type of alignment which is not parallel. By "transverse" may, but need not necessarily, be understood as "orthogonal". Other orientations of less than 90° or greater than 90° are also included under the term "transverse".The term "workpiece" should not be interpreted as restrictive in the present case. This can be any type of measurement object.The coordinate measuring machine according to the invention is thus distinguished in particular in that the arm on which the at least one measurement sensor is arranged is designed to be foldable. The arm can thus be extended by folding out into the measurement space volume and can be pulled back or retracted again by folding together from the measurement space volume. Preferably, this extension and retraction of the arm takes place in the manner of an concertina. Other folding mechanisms are equally conceivable, as are link chains with suitable angular stops, which allow horizontal advancement.As a result of this measure, the rear space, that is to say the space opposite the measurement space from the stand point of view, is no longer taken up by the coordinate measuring machine at any point in time during its operation. Due to its foldability, the arm is merely extended forward into the measuring space and withdrawn from the latter again, but without projecting rearward out of the stand. The rear space risk occurring in conventional horizontal arm measuring devices can therefore be completely eliminated with the coordinate measuring device according to the invention.According to a preferred embodiment, the coordinate measuring machine is designed in a stand construction, wherein the first axis, along which the workpiece holder and the stand are movable relative to one another, and the third axis, along which the arm is extendable with respect to the stand, are aligned horizontally, and wherein the second axis, along which the arm is displaceably mounted on the stand, is aligned vertically.According to this construction, the arm is typically referred to as a horizontal arm, as already mentioned above.It should also be mentioned at this point that the workpiece receptacle can in principle be any type of workpiece receptacle. Such a workpiece holder can be any type of base plate or, for example, also a table top of a coordinate measuring machine. Fixed or movable workpiece clamps are also suitable as such workpiece holders. It is also important to mention that the workpiece holder and the stand are movable relative to one another along the third axis. This means that, depending on the exemplary embodiment, there are basically three possibilities for this: 1. workpiece holder moves and stand is stationary; 2. workpiece holder is stationary and stand moves; 3. workpiece holder and stand both move.According to one embodiment, it is provided that the horizontal arm and / or the workpiece holder is / are additionally also rotatable about one, two or three axes. Rotational degrees of freedom for the horizontal arm and / or the workpiece are thus also made possible. This in turn makes it possible to be able to face all the accessible surfaces of the workpiece towards the stand, so that so-called double stand installations are unnecessary.Furthermore, according to one configuration, it is preferred that the arm has a first end which is mounted on the stand and cannot move along the third axis, and that the measurement sensor is arranged at a second, free end of the arm which is opposite the first end and can move along the first, second and third axes.The fixed, first end mounted on the stand therefore moves during operation of the coordinate measuring machine only along the first and the second axis, but not along the third axis. This first end of the arm thus moves "only" with the stand. Only the forwardly projecting parts of the arm are moved along the third axis. This possibility is made possible in particular by the above-described folding mechanism of the arm.According to the invention, the arm can be moved into and out of a measurement space volume along the third axis, and is neither protruding from a rear side of the stand facing away from the measurement space volume nor moved beyond this rear side during the movement in and out.This enables a very compact construction of the coordinate measuring machine, since toward the rear, i.e. beyond the rear side of the stand, the coordinate measuring machine does not require any space in the rear space. In addition to the very compact construction, this has, as already mentioned, above all safety-related advantages.According to one embodiment, the arm can comprise a support structure having a roll-out link chain. For example, the folding mechanism of the arm can be formed by a fold-out link chain which is locked against folding in one direction. Alternatively, the folding mechanism of the arm may comprise a flexible band in which a fixed difference in length between its top and bottom is used to be able to advance it over a fixed support point without tilting down.According to a further embodiment, the arm has a support structure designed as an origami structure. The original structure preferably comprises a plurality of solid state elements.Original structures are mechanical structures that are foldable by a plurality of solid-state elements and thereby remain mechanically stable and resilient even in a case where the original structure in the unfolded state takes up a volume of up to a few 10 cm 3. Original structures use the advantages of solid state joints. The original structure is designed using the original math. This is exemplified in a paper by Tachi, Tomohiro: "Rigid-foldable thick origami", Origami, 2011, 5th Jg., pp. 253-264. Further information on origami structures can be found in Deleo, Antonio A-lessandro et al. in ResearchGate (2018) "COMPOSITE ORIGAMI: FOLDABLE STRUCTURES BASED ON TACHI-MIURA-POLYHEDRON ORIGAMI TECHNIQUE".The term "solid-state joint" is understood to mean a region of a component (which is often subject to material damage and / or a reduction in cross section) which permits a relative movement (rotation) between two rigid body regions of the component by bending. The solid-state joint is therefore not a conventional joint in the sense of a kinematic pair, but rather is based on the principle of elastostatic (elasticity). The function of a solid-state joint is achieved by a region of reduced flexural rigidity relative to two adjacent regions of higher flexural rigidity. The reduced bending stiffness is usually produced by local cross-sectional reduction and / or local material weakening. A flexure hinge can also be compared with a conventional pivot joint having a limited range of rotation without incurring the disadvantages of such a conventional pivot joint. Further details can be found, for example, in the publication Nicolae Lobontiu: Compliant Mechanisms: Design of Flexure Languages. CRC Press, Boca Raton, USA 2002, ISBN 978-0-8493-1367-7.Flexure bearings are particularly advantageous in original structures. In principle, however, it is also possible to produce the support structure designed according to the invention as an original structure with other, conventional joint types, wherein, for example, different joint types can be combined. Solid state joints thus represent a particularly advantageous representative of all joint types in the present case, without excluding or restricting the use of other joint types for producing the origami structure according to the invention.The use of a support structure designed as an original structure in the arm of the coordinate measuring machine brings various advantages. Original structures have one or more exactly defined unfolded states and one or more exactly defined folded states. It is likewise possible to define intermediate states exactly via the original structures. This allows very accurate positioning of the at least one measurement sensor attached to the arm.A further advantage is the very compact construction of such original structures.Furthermore, original structures are superior in stiffness-to-mass ratio to all conventional designs. Accordingly, the original structures in the present field of application can ensure a very high precision with at the same time very low weight.In the above-mentioned preferred embodiment, in which the support structure of the arm comprises an origami structure, the support structure preferably has a multiplicity of plate-shaped segments, of which in each case at least two are integrally connected to one another via a solid joint. The segments can preferably be produced with materials for optimizing specific stiffnesses, such as fiber composite materials, sandwich constructions, foam constructions or optionally high-performance materials, such as technical ceramics. For the production of the support structure designed as an original structure, for example 3D printing methods are suitable, but also conventional material processing methods (such as, for example, CNC milling). An advantage of the 3D printing method for producing the carrier structure is that even highly complex geometries, such as cavities arranged in the interior, can be produced.A further advantage of original structures equipped with flexure joints is their freedom from play in the degree of freedom from buckling or bending. In other words, in contrast to conventional mechanical joints which have a kinematic pair, solid joints do not have any play at the bending point, as is the case, for example, with a conventional articulated joint. Because, in the case of flexure joints, the flexibility at the bending point is achieved by local material weakening and / or cross-sectional reduction, the overall structure is furthermore formed in one piece and the bending point is thus free of play.The support structure designed as an original structure thus has a constant reproducibility even after a plurality of folding movements, for example the repeated extension and retraction of the arm. This in turn has the advantage that the support structure, depending on the geometric structure or on the geometric number of the plurality of flexure bearings in the folded state, preferably comprises very compact dimensions and can nevertheless be folded out reproducibly.The reproducibility of the support structure configured as an original structure is ensured in particular by a predetermined positioning of the plurality of flexure bearings in combination with a dimensioning and geometric configuration of the rigid regions of the support structure adjoining the flexure bearings on both sides.According to a further embodiment, the original structure has a multiplicity of structural elements of different types and / or sizes, wherein structural elements of a first type are larger and / or have a greater wall thickness than structural elements of a second type, and wherein the structural elements of the first type in the unfolded state of the arm have a smaller distance from the stand than the structural elements of the second type.According to this embodiment, the Origami kinematics is therefore embodied with cross sections and / or wall thicknesses and / or surface segment sizes and / or surface segment shapes increasing with respect to the stand. In this way, the rigidity of the support structure can be increased and rolling movement of the arm can be prevented.According to a further embodiment, the arm has a drive which is configured to fold out the arm along the third axis in order to extend the arm relative to the stand and or to fold it together along the third axis in order to retract the arm relative to the stand.The drive is preferably designed as a motor drive. The drive can be integrated into the origami structure. In such a case, the drive preferably has lever, rotation, tension and / or thrust elements which are integrated into the original structure and ensure a corresponding transmission of force. The drive preferably has a motor-driven actuator, for example an electric motor, which is coupled to these elements, so that the force generated by the actuator is transmitted via the mentioned elements to the original structure in order to fold out or fold together the arm.For applications in which lower precision requirements are met, it may be sufficient to mount position sensors in or on the drive of the arm, which are designed to determine the respective position of the arm or the respective position of the measurement sensor arranged thereon and thus the tool center point. In general, the precisions of 100 μm and below that customary for dimensional coordinate measuring technology will not be achievable at the tool center point in dynamic operation even with very precise and stiff Origami kinematics.According to a further embodiment, it is therefore provided that the coordinate measuring machine further comprises a monitoring sensor which is configured to acquire a second measurement signal for determining a position and position of the measurement sensor, and that the evaluation unit is configured to determine the position and position of the measurement sensor based on the second measurement signal and to determine the coordinates of the workpiece based on the position and position of the measurement sensor and the first measurement signal.The monitoring sensor is therefore a further sensor which determines or monitors the position of the at least one measurement sensor with which the workpiece is measured. Preferably, the monitoring sensor is a 6D locating system adapted to determine the 6D sample of the free end of the arm. Different approaches can be used for this 6D localization. Preferably, the monitoring sensor comprises one or more optical sensors.According to one embodiment, the measurement sensor is configured to detect the coordinates of the workpiece in a first coordinate system in the form of the first measurement signal, which coordinate system is fixed to the body with respect to the measurement sensor, wherein the monitoring sensor is configured to detect the position and position of the measurement sensor in a second coordinate system in the form of the second measurement signal, and wherein the evaluation unit is configured to determine the coordinates of the workpiece in the second coordinate system on the basis of the first and the second measurement signal.Preferably, the monitoring sensor is precalibrated (intrinsically calibrated) with respect to the second coordinate system, so that the position of the monitoring sensor in the second coordinate system in the measurement space volume is known. If a plurality of monitoring sensors are present, these are preferably calibrated with respect to one another (extrinsically calibrated).The monitoring sensor preferably transmits in real time the position and position of the measurement sensor in the second coordinate system. The monitoring sensor can fundamentally move with respect to the second coordinate system, for example, if the monitoring sensor is arranged on the arm of the coordinate measuring machine. However, the position and position of the monitoring sensor with respect to the second coordinate system should always be known.The measurement sensor determines the coordinates of the workpiece in the first coordinate system, which is stationary with respect to the measurement sensor. The coordinates of the workpiece in the second coordinate system can be determined via the position and position of the measurement sensor in the second coordinate system determined by the monitoring sensor via a coordinate transformation between the first and the second coordinate system. For this purpose, the evaluation unit evaluates both the first and the second measurement signal.According to one embodiment, the monitoring sensor is arranged on or in the arm.For example, the monitoring sensor can have at least three interferometers with fiber-optic feed lines, the exit optics of which are arranged at a free end of the arm, wherein the at least three interferometers generate the second measurement signal.The exit optics are thus preferably arranged at the free end of the arm, on which the at least one measurement sensor is also arranged. The optical fibers and exit optics can be almost neglected in terms of weight. Only the interferometers need to be taken into account in terms of weight. These are therefore preferably arranged in the stand or another stable part of the coordinate measuring machine. Heat input and mass of the monitoring sensor therefore have no influence on the stability of the arm. The interferometers are preferably configured to measure the yaw and pitch angle between the two in addition to the distance of the sensor-side arm end from the stand-side arm end (along the third axis). This can be effected, for example, via the wavelength differences of three triangular interferometer beam paths. At the same time, the interferometer beams can be used to be imaged via beam splitters onto position-sensitive sensor systems (pixel array or even quadrant diodes). In this way, the lateral offset and roll angle can also be determined with the aid of the interferometers.In principle, however, no more than two beams are required for determining the lateral offset and the roll angle. In this respect, the polarized single-mode beams of the interferometer or with pilot beams coupled into the fibers can be used to simultaneously superimpose two of these beams on a single camera with a pole filter array. The positions and relative positions of the two "illuminated spots" registered on this camera then directly result in the lateral position and the roll angle.According to a further embodiment, the monitoring sensor is integrated into the origami structure.The original structure can be incorporated with highly accurate optical or optronic measurement technology, which can serve for locating the position and position of the free arm end or the position and position of the measurement sensor. The enclosure in the original structure protects the monitoring sensor against the influence of the possibly harsh manufacturing environment. On the other hand, it can be advantageous in terms of operating safety if light wavelengths and / or powers and / or pulse energies are used in the monitoring sensor, which could represent a risk for the environment.According to a further embodiment, the monitoring sensor is configured to detect at least one optical marker on the measurement sensor and / or in its environment, wherein the evaluation unit is configured to determine the position and position of the measurement sensor based on the at least one optical marker.If the monitoring sensor is arranged on the arm, it can look into the surrounding space starting from the arm and can determine its own position preferably on the basis of reference objects (e.g. optical markers) known in the surrounding space. If the relative position between the monitoring sensor and the measurement sensor is then known and this remains constant, for example, the position of the measurement sensor is also known. As already mentioned above, the coordinates of the workpiece can thus be determined by adding the first measurement sensor generated by the measurement sensor.It is likewise possible for the monitoring sensor not to be arranged on the arm and to look, so to speak, from the outside onto the arm and onto the measurement sensor arranged thereon. In such a case, it is advantageous if one or more optical markers are arranged on the arm and / or on the measurement sensor, which the monitoring sensor detects from the outside for position determination.Other possibilities for the realization of the monitoring sensor are likewise conceivable. The monitoring sensor can have, for example, a Hartmann-Schack sensor system or wavefront measurement technique. In addition, it is conceivable for the monitoring sensor to have a lidar (light detection and ranging) or ladar (laser detection and ranging) device in combination with markers or light spots on position-sensitive detectors. Furthermore, the monitoring sensor can have a modem-coupled laser for distance measurement. Further measurement principles which can be used as the basis for the monitoring sensor are laser tracking and white light interferometric surface "remote probing" of a correspondingly structured target at the free end of the arm, which is structured for 6D localization.It is likewise possible to combine the above-mentioned measurement principles with conventional absolute encoders on the arm actuator system.According to a further embodiment, the coordinate measuring machine can furthermore have a temperature sensor which is configured to detect a temperature of the arm in the form of a temperature signal, wherein the evaluation unit is configured to determine the coordinates of the workpiece also on the basis of the temperature signal.By means of the temperature sensor or a plurality of temperature sensors, a temperature distribution of the support structure of the arm can preferably be monitored. Thus, a mathematical position correction of the support structure of the arm can be carried out, by means of which temperature-related expansions of the support structure are corrected. This is particularly advantageous if the carrier structure is designed as an origami structure, since the origami structure typically has a very large ratio of surface area to material to be heated through (a low wall thickness). Thus, the strain response of the support structure to temperature changes is rapidly reported. Such thermographic monitoring can, however, also be carried out from the outside by means of optical sensors or cameras.It is understood that the features mentioned above and those still to be explained below can be used not only in the respectively specified combination, but also in other combinations or alone, without departing from the scope of the present invention.Exemplary embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. The following are shown: FIG. 1 shows a schematic view of a first exemplary embodiment of a coordinate measuring machine according to the present invention in a first state; FIG. 2 shows a schematic view of the exemplary embodiment of the coordinate measuring machine according to the invention shown in FIG. 1 in a second state; FIG. 3 shows a schematic view of a second exemplary embodiment of the coordinate measuring machine according to the invention; and FIG. 4 shows a schematic view of a third exemplary embodiment of the coordinate measuring machine according to the invention.FIGS. 1 and 2 show a first exemplary embodiment of the coordinate measuring machine according to the invention in two different operating states. The coordinate measuring machine is identified therein in its entirety by the reference numeral 10.The coordinate measuring machine 10 serves for the dimensional measurement of a measurement object. In the figures, a cuboidal workpiece 12 is illustrated purely schematically and by way of example as a measurement object. The workpiece 12 is arranged on a workpiece holder 14. This workpiece holder 14 is designed as a workpiece table in the present case. This table is frequently also referred to as a measurement table. For example, this may be a stable garnet plate. However, it is also conceivable to use other types of workpiece receptacles, for example a workpiece clamping means or a base plate lying directly on the floor.The coordinate measuring machine 10 further comprises a stand 16 which is movable relative to the workpiece holder 14 along a first axis designated as y-axis in the figures. It is understood that it would likewise be conceivable to move the workpiece holder 14 along the y-axis relative to the stand 16. The y-axis preferably extends in the horizontal direction independently thereof. The y-axis is generally referred to herein as a "first axis.".The stand 16, which can also be referred to as a column in principle, extends substantially along a second axis, which is referred to as the z-axis in the figures. This second axis (z-axis) extends orthogonally to the first axis (y-axis), preferably in the vertical direction.An arm 18 is mounted on the stand 16 so as to be height-adjustable in the z direction. The bearing 20 is illustrated only schematically in FIG. 1 by means of dashed lines. The arm 18 itself extends substantially along a third axis, which is designated in the drawings as the x-axis and preferably extends orthogonally to the first two axes (y-axis and z-axis). Accordingly, the arm 18 preferably extends in the horizontal direction. The arm 18 is therefore also referred to as a horizontal arm.The stand-side end of the horizontal arm 18 (not visible in FIG. 1 ) is fixedly connected to a slide 22, which is height-adjustable in the z-direction by means of the aforementioned bearing arrangement 20 within the stand 16. The opposite free end 24 can also be produced along the x-axis in a manner to be described further below with respect to the stand-side end of the horizontal arm 18. Accordingly, the free end 24 of the horizontal arm 18 can be moved along all three spatial directions.A measurement sensor 26 is arranged at the free end 24 of the horizontal arm 18. The measurement sensor 26 serves for measuring the workpiece 12, and the measurement sensor 26 is configured to acquire a first measurement signal, on the basis of which the coordinates of various surface points of the workpiece 12 can be determined. The evaluation of this measurement signal, which is referred to herein as "first measurement signal", takes place in an evaluation unit 28.The evaluation unit 28 is preferably a computer on which a corresponding measurement software is stored, which serves for evaluating the measurement signal mentioned. The evaluation unit 28 is coupled to the measurement sensor 26 via a data connection 30. This data connection 30 can be configured as a wired or also as a wireless data connection.The evaluation unit 28 typically serves not only for evaluating the measurement signal generated by the measurement sensor 26, but also for controlling the coordinate measuring machine 10, i.e. for example for controlling the actuators, with the aid of which the stand 16 and the horizontal arm 18 are moved along the mentioned axes. The evaluation unit 28 is therefore frequently also referred to as an evaluation and control unit.In the exemplary embodiment shown here, the measurement sensor 26 is designed as an optical measurement sensor. This optical sensor 26 can be designed, for example, as a laser scanner. Alternatively, the optical measurement can be carried out with the aid of fringe light projection or a photogrammetric evaluation.Instead of an optical sensor, however, a tactile sensor can also be used as the measurement sensor 26 without departing from the scope of the present invention. It is also possible to use a combination of a tactile and an optical sensor as the measurement sensor 26. Likewise, multiple (two, three or more) sensors may be disposed at the free end 24 of the horizontal arm 18.Preferably, the at least one measurement sensor 26 is articulated on the free end 24 of the horizontal arm 18. In this way, the measurement sensor 26 can be pivoted about one, two or three axes relative to the horizontal arm 18. Overall, a 6-dimensional measurement system can be generated in this way.The measurement sensor 26 can be moved in and out along the x-axis with the aid of the horizontal arm 18 with respect to the stand 16 in order thus to be brought to any desired point within the measurement space volume 32 in addition to the movements of the stand 16 and of the slide 22. The measurement space volume 32 refers to the volume that can basically be detected by the coordinate measuring machine 10 by measurement technology. In the case shown here, the measurement space volume is limited, for example, to a volume above the measurement table 14. The measurement space volume 32 is thus located on the left of the stand 16 in FIGS. 1 and 2.The horizontal arm 18 is configured to be foldable according to the invention. The horizontal arm 18 can be unfolded along the x-axis in order to be extended relative to the stand 16 and moved into the measurement space volume 32. Conversely, the horizontal arm 18 can be folded together in order to be retracted relative to the stand 16 and at least partially withdrawn from the measurement space volume 32. FIG. 2 shows a state of the coordinate measuring machine 10 in which the horizontal arm 18 is retracted or folded further compared to the state shown in FIG. 1.This folding mechanism of the horizontal arm 18 has the particular advantage that the horizontal arm 18 does not move into the so-called rear space 36 during its inward and outward movement. The rear space is the space which is opposite the measurement space volume 32 with respect to the stand 16. The rear space 36 is thus located on the rear side 38 of the stand 16 facing away from the measurement space volume 32.Due to the foldability of the horizontal arm 18, it does not project beyond the rear side 38 either during its retraction movement or during its extension movement or when the coordinate measuring machine 10 is at a standstill. This proves to be advantageous not only with regard to reducing the installation space of the coordinate measuring machine 10, but also with regard to the so-called rear space risk. An introduction of parts of the coordinate measuring machine 10, in particular an introduction of the horizontal arm 18 into the rear space 36, can namely be avoided as a result. Persons moving in this rear space 36 are therefore not endangered by the operation of the coordinate measuring machine 10.The horizontal arm 18 is preferably moved via a drive 40, which is only schematically depicted in FIGS. 1 and 2. This drive 40 is preferably an electric motor which is configured to fold out the horizontal arm 18 along the x-axis in order to extend the horizontal arm 18 relative to the stand 16. Accordingly, the drive 40 is also configured to fold the horizontal arm 18 along the x-axis in order to retract the horizontal arm 18 relative to the stand 16.The horizontal arm 18 preferably has a support structure 42 designed as an original structure. This support structure 42, which is configured as an origami structure, is also referred to herein as origami kinematics. It preferably has a plurality of flexure joints 44, by means of which the original structure 42 or the horizontal arm 18 can be unfolded and folded in an exactly predefined manner. The support structure 42 of the horizontal arm 18 designed as an origami structure is designed according to origami mathematical relationships and represents, for example, a highly complex 3D geometry. This geometry of the support structure 42 is illustrated only schematically and greatly simplified in FIGS. 1 and 2.In principle, it is possible to determine the position and position (pose) of the measurement sensor 26 on the basis of conventional material measures, as are typically used in coordinate measuring machines. Such measuring embodiments can also be provided in the horizontal arm 18. Although the Origami kinematics integrated in the horizontal arm can basically be embodied with high precision, it is nevertheless advantageous to determine the pose of the free end 24 of the horizontal arm 18 and thus the pose of the measurement sensor 26 even more accurately by one or more additional sensors.According to the second exemplary embodiment shown schematically in FIG. 3, the coordinate measuring machine 10 has a monitoring sensor 46 for this purpose, which is configured to record a second measurement signal for determining the pose of the measurement sensor 26 and to pass it on to the evaluation unit 28. In this case, the evaluation unit 28 determines the pose of the measurement sensor 26 on the basis of the second measurement signal generated by the monitoring sensor 46. It is thus possible for the evaluation unit 28 to determine the coordinates of the workpiece 12 on the basis of the determined pose of the measurement sensor 26 and the (first) measurement signal generated by the measurement sensor 26 itself. The measurement sensor 26 is preferably configured to record the coordinates of the workpiece in a first coordinate system in the form of the first measurement signal, which coordinate system is fixed to the body with respect to the measurement sensor 26. The monitoring sensor 46 is configured to detect the pose of the measurement sensor 26 in a second coordinate system in the form of the second measurement signal. The evaluation unit 28 is configured to determine the coordinates of the workpiece 12 in the second coordinate system on the basis of the first and the second measurement signal.In the second exemplary embodiment shown in FIG. 3, the monitoring sensor 46 is at least partially integrated into the horizontal arm 18. Preferably, the monitoring sensor 46 is integrated into the original structure 42 of the horizontal arm 18. The original structure 42 serves as a housing or enclosure for a plurality of optical measurement elements. The monitoring sensor 46 has three interferometers 48 which, in the exemplary embodiment shown in FIG. 3, are arranged in the slide 22 of the stand 16. These three interferometers 48 are connected to three fiber optic feed lines 50, the exit optics 52 of which are arranged at the free end 24 of the horizontal arm 16. The three interferometers 48 are configured to measure not only the x-distance of the stand-side end of the horizontal arm 18 from the free end 24 of the horizontal arm 18 but also the yaw pitch and roll angles and the lateral offset of the horizontal arm 18.In the third exemplary embodiment of the coordinate measuring machine 10 according to the invention shown in FIG. 4, the horizontal arm 18 again has a support structure 42 designed as an original structure. The original structure here, however, has a multiplicity of components of different types and / or sizes. Components 54 of a first type are designed to be larger and / or have a greater wall thickness than components of a second type 56 which are at a greater distance from the stand 16 than the components 54 of the first type. Components 58 of a third type are configured to be even smaller in comparison with the components 54, 56 of the first two types and / or have an even smaller wall thickness than these. In this exemplary embodiment, the original structure 42 is therefore designed with cross sections and / or wall thicknesses and / or surface segment sizes and / or surface segment shapes increasing with respect to the stator 16. This further improves the stability of the horizontal arm 18 and prevents rolling thereof.Furthermore, the coordinate measuring machine 10 according to the third exemplary embodiment shown in FIG. 3 also has a temperature sensor 60 which is configured to detect a temperature of the horizontal arm 18 and to pass on this temperature signal to the evaluation unit 28 for the evaluation thereof. The evaluation unit 28 is configured to use this temperature signal in order to correct the calculation of the pose of the measurement sensor 26 and thus the calculation of the coordinates of the workpiece 12. Temperature-induced deformations of the horizontal arm 18 can thus be compensated purely by calculation.In the third exemplary embodiment of the coordinate measuring machine 10 shown in FIG. 4, the monitoring sensor 46' is configured differently from the monitoring sensor 46 shown in FIG. 3, but the monitoring sensor 46' ultimately serves the same purpose, namely the determination of the pose of the measurement sensor 26. For this purpose, the monitoring sensor 46' comprises one or more cameras. The camera images can be evaluated photogrammetrically within the evaluation unit 28, for example, in order to calculate the pose of the measurement sensor 26 using this photogrammetric evaluation on the basis of the known positions of the optical markers 62.A similar principle of calculating the pose of the measurement sensor 26 can also be realized in that such a monitoring sensor 46' is not arranged on the horizontal arm 18 itself, but is fixed in the vicinity of the coordinate measuring machine 10 at a known location and is aligned with the horizontal arm 18. In this case, it is advantageous if the optical markers 62 are arranged distributed on the horizontal arm 18. The position of the horizontal arm 18 or the pose of the measurement sensor 26 could then also be determined by means of the optical markers 62 on the basis of the images supplied by the monitoring sensor 46' within the evaluation unit 28.Finally, it should be mentioned that in FIGS. 1-4, the drive 40, the interferometers 48 and the temperature sensor 60 are each arranged at the same location for the sake of simplicity. However, this is not intended to mean that the corresponding components replace one another. This merely serves for simplified illustration. It is understood that the components 40, 46 and 60 can generally also be combined with one another in one and the same exemplary embodiment. This also applies to the remaining components of the coordinate measuring machine 10 according to the individual exemplary embodiments, which can be combined with one another without departing from the scope of the present invention.

Claims

Coordinate measuring machine (10) for dimensionally measuring a workpiece (12), wherein the coordinate measuring machine (10) has: - a workpiece holder (14) for holding the workpiece (12); - a stand (16), wherein the workpiece holder (14) and the stand (16) are displaceable relative to one another along a first axis (y); - an arm (18) which is mounted on the stand (16) and is displaceable with respect thereto along a second axis (z) transversely to the first axis (y); - a measurement sensor (26) which is arranged on the arm (18) and is configured to record a first measurement signal; and - an evaluation unit (28) which is configured to determine coordinates of the workpiece (12) on the basis of the first measurement signal; characterized in that the arm (18) is designed to be foldable and can be deployed along a third axis (x) transversely with respect to the first and the second axis (y, z) into a measurement space volume (32) in order to be extended linearly with respect to the stand (16) and retracted into the measurement space volume (32), and can be folded together along the third axis (x) in order to be retracted linearly with respect to the stand (16), wherein the arm (18), on account of its foldability, neither during the deployment nor during the folding together protrudes rearwardly out of a rear side (38) of the stand (16) which is remote from the measurement space volume (32).The coordinate measuring machine according to claim 1, wherein the coordinate measuring machine (10) is configured in a stand construction, the first and third axes (y, x) are horizontally oriented and the second axis (z) is vertically oriented.Coordinate measuring machine according to Claim 1 or 2, wherein the arm (18) has a first end which is mounted on the stand (16) and is immovable along the third axis (x), and wherein the measurement sensor (26) is arranged at a second, free end (24) of the arm (18), which is opposite the first end and is displaceable along the first, second and third axes (x, y, z) and / or rotatable about the first, second or third axis (x, y, z).Coordinate measuring machine according to one of Claims 1-3, wherein the arm (18) has a carrier structure designed as an original structure (42).The coordinate measuring machine of claim 4, wherein the origami structure (42) comprises a plurality of flexure bearings (44).Coordinate measuring machine according to Claim 4 or 5, wherein the original structure (42) has a multiplicity of structural elements (54, 56, 58) of different types and / or sizes, wherein structural elements (54) of a first type are larger and / or have a greater wall thickness than structural elements (56) of a second type, and wherein the structural elements (54) of the first type, in the unfolded state of the arm (18), have a smaller distance from the stand (16) than the structural elements (58) of the second type.Coordinate measuring machine according to one of Claims 1-6, wherein the arm (18) has a drive (40) which is configured to fold out the arm (18) along the third axis (x) in order to extend the arm (18) with respect to the stand (16) and to fold together along the third axis (x) in order to retract the arm (18) with respect to the stand (16).Coordinate measuring machine according to one of Claims 1 - 7, wherein the coordinate measuring machine (10) furthermore has a monitoring sensor (46, 46'), which is configured to record a second measurement signal for determining a position and position of the measurement sensor (26), and wherein the evaluation unit (28) is configured to determine the position and position of the measurement sensor (26) on the basis of the second measurement signal and to determine the coordinates of the workpiece (12) on the basis of the position and position of the measurement sensor (26) and the first measurement signal.Coordinate measuring machine according to Claim 8, wherein the measurement sensor (26) is configured to record the coordinates of the workpiece (12) in a first coordinate system in the form of the first measurement signal, which coordinate system is fixed to the body with respect to the measurement sensor (26), wherein the monitoring sensor (46, 46') is configured to record the position and position of the measurement sensor (26) in a second coordinate system in the form of the second measurement signal, and wherein the evaluation unit (28) is configured to determine the coordinates of the workpiece (12) in the second coordinate system on the basis of the first and the second measurement signal.The coordinate measuring machine according to claim 8 or 9, wherein the monitoring sensor (46, 46') is arranged on or in the arm (18).Coordinate measuring machine according to one of Claims 4-6 and one of Claims 8-10, wherein the monitoring sensor (46) is integrated into the original structure.Coordinate measuring machine according to one of Claims 8 - 11, wherein the monitoring sensor (46) has at least three interferometers (48) with fiber-optic feed lines (50), the exit optics (52) of which are arranged at a free end (24) of the arm (18), wherein the at least three interferometers (48) generate the second measurement signal.Coordinate measuring machine according to one of Claims 8 - 11, wherein the monitoring sensor (46') is configured to record at least one optical marker (62) on the measurement sensor (26) and / or in the environment thereof, and wherein the evaluation unit (28) is configured to determine the position and position of the measurement sensor (26) on the basis of the at least one optical marker (62).Coordinate measuring machine according to one of Claims 1 - 13, wherein the coordinate measuring machine (10) furthermore has a temperature sensor (60) which is configured to record a temperature of the arm (18) in the form of a temperature signal, and wherein the evaluation unit (28) is furthermore configured to determine the coordinates of the workpiece (12) also on the basis of the temperature signal.

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