METHOD AND ARRANGEMENT FOR DETECTING A CALIBRATION OBJECT WITH AN OPTICAL SENSOR DEVICE

Description

[0001] The invention relates to a method and an arrangement for detecting a calibration object with an optical sensor device and in particular to calibrating the sensor device based on this detection.

[0002] It is known to use optical sensor devices for object detection, for example to measure objects three-dimensionally. In particular, three-dimensional coordinates of object points can be determined, wherein these coordinates can be obtained by optically scanning the object using the sensor device. Furthermore, in this context, it is known to attach the optical sensor device to a positioning system and to move it relative to the object. The positioning system can be an articulated arm or robot and / or a coordinate measuring machine. In particular, the relative movement can be generated by means of machine kinematics, e.g. of a coordinate measuring machine, which comprises a plurality of machine axes that can be moved by means of a respective drive device and can position the sensor device in space.The coordinate measuring machine can, for example, be designed as a portal or gantry and move the sensor device relative to a stationary base on which the object is arranged. Additionally or alternatively, the sensor device can be arranged on movement axes, in particular in the form of a so-called rotating / swivel device, which can itself be positioned in space via further axes of the coordinate measuring machine, for example. To record the coordinate values, the assumed axis positions (i.e. the axis position values) of the individual machine axes can be recorded and / or evaluated. Additionally or alternatively, the object can be moved by means of a positioning system which moves the object relative to a stationary or likewise movable sensor device.Such a positioning system can, for example, be a rotary table or a so-called X / Y measuring table, which is movable in two directions of movement that are perpendicular to each other.

[0003] An example of a positioning system in the form of a coordinate measuring machine, in which both the object and the sensor device are actively movable, is the O-INSPECT series from Carl-Zeiss Industrielle Messtechnik GmbH, Oberkochen (Germany). In this variant, the object is placed on a movable X / Y measuring table, and the sensor device is movable in a Z direction orthogonal to the movement directions of this measuring table. All of the aforementioned variants of positioning systems and coordinate measuring machines can also be provided in the present invention.

[0004] One class of optical sensor devices for object detection relates to sensor devices that emit electromagnetic radiation, for example in the form of light comprising radiation components of multiple wavelengths or in the form of substantially monochrome and / or coherent radiation, and in particular laser radiation, along a sensor axis and have at least one focal position on the sensor axis. Furthermore, such sensors can generally generate measurement signals based on detected reflected radiation and depending on the relative arrangement of an object to the focal position (for example, a distance therebetween, in particular along the sensor axis). The electromagnetic radiation does not necessarily have to be visible radiation.

[0005] An example of such a sensor is an interferometric sensor device, in which interference between radiation reflected by an object and a reference radiation, usually coupled out within the sensor device, is determined in order to determine distance information. In this case, radiation can initially be guided in a fiber optic cable and the reference radiation can be coupled out of the sensor device or the fiber optic cable, for example, at an exit area. Radiation reflected by the object can then be coupled back into the fiber optic cable and / or guided to an evaluation unit for superimposition with the reference radiation. In general, in this case, a measuring range can be defined around a focus position of the radiation emitted into the environment, within which analyzable signals can be generated. An example of such a sensor device can be found in DE 102 46 798 B3.

[0006] The sensor axis can, for example, be an axis of a pinhole through which the electromagnetic radiation passes or exits. This axis can be an axis running concentrically through the center and orthogonal to a passage opening of the pinhole, i.e. a center point and / or passage axis. The pinhole can be part of an optics system (sensor optics) of the sensor device and can generally be formed by the exit region and / or the exit opening of an optical fiber through which the electromagnetic radiation is guided. The optical fiber can be an optical fiber, for example a glass fiber. Radiation exiting the pinhole can be converged on the sensor axis and thus focused by means of further optical elements of the sensor optics, such as a converging lens. The sensor optics can therefore, in particular, be a focusing optics system.The focus position may correspond to a point at which rays combined by the sensor optics converge on the sensor axis and, in particular, at which all rays passing through the sensor optics in one exit direction converge.

[0007] Radiation reflected back from the object surface can pass through the sensor optics (in the opposite direction to the radiation emitted by the sensor device) and be directed from there onto the pinhole. In particular, it can at least partially re-enter the light guide and be detected and evaluated by an evaluation device connected to the light guide (for example, comprising a photosensitive unit such as a CCD or CMOS sensor). If the focus position is on an object surface (i.e., the object surface is in the focus of the sensor device), the radiation reflected back from this is thrown back onto the pinhole to a comparatively large extent, so that a high intensity and / or radiant power of the reflected radiation can be detected.If this is not the case, generally a smaller proportion of the reflected radiation from the object surface is reflected back onto the pinhole or imaged onto it, so that only a correspondingly lower or even no intensity and / or radiant power of the reflected radiation can be detected.

[0008] Unless otherwise stated or apparent, in the context of the present disclosure, a (back)reflected radiation can be understood as a (back)reflected radiation detected by the sensor device, ie radiation not arbitrarily reflected into the environment.

[0009] An example of a sensor device of the above-described class is confocal optical sensors. Confocal optical sensors exist that have only a limited number of defined focus positions, and in particular, only one focus position. In this case, the radiation can be monochrome and, in particular, generated as monochrome laser radiation.

[0010] A special type of confocal optical sensor is a chromatic confocal sensor (white light sensor), as described, for example, in DE 10 2015 217 637 A1 and US Pat. No. 5,785,651 A. Compared to other distance sensors (such as capacitive sensors), chromatic confocal sensors are high-resolution and precise distance sensors. White light sensors, for example, are available on the market with a maximum resolution of one hundredth of a micrometer and measuring ranges in the range of several tenths of a millimeter to several tens of millimeters. One example is the confocal white light sensor with the type designation "confocal IDT IFS 2405" from Micro-Epsilon Messtechnik GmbH und Co. KG, Ortenburg, Germany.

[0011] In general, in a white-light sensor, white light (i.e., electromagnetic, not necessarily visible radiation with radiation components of multiple wavelengths) is radiated from a light source onto a sensor optics in the form of a focusing optic. The sensor optics cause dispersion of the radiation, i.e., chromatic aberration occurs. As a result, the radiation components of the different wavelengths are focused at different distances from the sensor optics and thus onto different focus positions. Thus, there are a plurality of wavelength-specific focus positions, with each wavelength having its own focus position (i.e., each focus position is assigned exactly one wavelength, and a wavelength is assigned to only one focus position).If there is an object in one of the focus positions that reflects the radiation back towards the sensor, the sensor detects radiation of the wavelength with maximum intensity and / or radiant power that was reflected in or out of this focus position.

[0012] Furthermore, a white light sensor (e.g., an evaluation device thereof) is typically configured to detect or record an intensity distribution of the reflected radiation across its wavelength spectrum. If one of the focal positions is located directly on the object, a high intensity for radiation with the wavelength associated with this focal position is detected within the intensity distribution. In particular, this can be a single absolute intensity maximum within the detected intensity distribution, and no further local intensity maxima may be present.

[0013] It is also possible for radiation of different wavelengths to be reflected simultaneously at their respective focus positions (for example, when irradiating an at least partially transparent object and reflections at different material interfaces). The sensor then detects a (local) intensity maximum at each of these wavelengths. From the wavelength of the single intensity maximum or from the wavelengths of the intensity maxima, the distance between the sensor and the object surface can be determined if the distance of a focus position from the sensor (e.g., to the focusing optics) is known. However, this knowledge is initially not available and is usually obtained through a reference measurement in which the distance between the sensor and the reflection location is also measured by another means, e.g., using a laser interferometer.

[0014] In particular, a so-called linearization of white light sensors can be performed to obtain meaningful measured values. In detail, distance values ​​to a reference body can be determined by recording distance values ​​using the sensor device to be linearized or an additional measuring device (e.g., a reference sensor with known properties). By comparing these distance values, linearization parameters can be determined. These parameters can be used to determine functional values ​​of a linear mathematical function of the measured value (i.e., the sensor's measurement result) as a function of the object distance from the white light sensor's measurement signals at different object distances.Put simply, the linearization parameters make it possible to convert the sensor's measurement signals (which in particular reflect the intensity distribution of the reflected light received by the sensor across the wavelength spectrum of the reflected (measurement) radiation) into distance measurement values ​​of the object distance in such a way that, for example, if the object distance is doubled, the measured value of the object distance is also doubled.

[0015] Within the scope of linearization, value pairs between sensor measurement signals and the actually existing distance values ​​to an object detected by the sensor device can be determined. However, linearization does not make it possible to determine the actual coordinates of one or all focus positions in a predetermined coordinate system (for example, in a coordinate system of the positioning system, i.e., in device coordinates). Such coordinates can be advantageous in order to be able to position the sensor device and, in particular, its focus position(s) precisely relative to an object. Instead, it has generally been assumed for linearization to date that properties of the sensor device, such as, for example, an orientation in the sense of the alignment of a sensor axis, are known. In the context of the present disclosure, an alignment of the sensor axis can generally be understood as an orientation, for example,in the sense of a twist or rotation in or to the axes of a machine coordinate system (or device coordinate system) or of another coordinate system (e.g. of a sensor carrier) whose orientation is known, for example, relative to the machine coordinate system.

[0016] Information regarding such coordinates is typically determined during a calibration process in the form of a so-called calibration process. In this case, analogous to the calibration of two different sensors in a multi-sensor arrangement and / or two different (particularly tactile) measuring probes, a calibration object (calibrated calibration standard) can be recorded with two different sensor devices. Based on any different measured values ​​obtained in this process, calibration can then take place. For example, one of the sensors and / or measuring probes can be a so-called reference sensor or reference probe, whose properties are known and / or whose measured values ​​can be assumed to be an appropriate reference.Based on the difference between the values ​​acquired with the sensor and / or probe to be calibrated and the reference values, parameters can be determined (e.g., so-called calibration or correction parameters). These can be applied to future measured values ​​obtained from the sensor and / or probe to be calibrated, for example, to correct them.

[0017] In a known manner, for example, a calibration object in the form of a sphere (calibration sphere) can first be measured using a reference sensor device or a reference probe with known properties. For example, a tactile sensor device can be used as a reference, the stylus orientation (in device coordinates), stylus dimensions, and the diameter of any stylus attached to the stylus being known. This tactile sensor device can scan the surface of a calibration sphere at multiple sampling points and, based on these, calculate the coordinates of the sphere's center point (particularly in device coordinates). Subsequently, the surface of the calibration sphere can also be detected using an as yet uncalibrated optical sensor device, and the coordinates of the sphere's center point can also be calculated based on this.

[0018] For this purpose, the optical sensor device can be used, for example, such that a state in which one of a possible plurality of focus positions of the sensor device lies on the sphere's surface is detected as a high intensity of the reflected radiation with the corresponding wavelength (i.e., the wavelength associated with the focus position). In other words, in this state, it can be assumed that a point on the sphere's surface is currently in the focus of the sensor direction, so that, for example, coordinate values ​​for this point can be determined based on a distance value currently determined by the sensor device.For example, the optical sensor direction can be moved in a straight line towards the reference sphere and then, when a maximum intensity is detected (in the case of a chromatic confocal sensor, a maximum intensity for at least one of the plurality of emitted wavelengths), it can be concluded that a point on the sphere surface has been reached.

[0019] Typically, with an already linearized sensor, a distance value is specified and the sensor device is positioned relative to the reference sphere, e.g. as part of distance-dependent position control of the CMM axes, in such a way that this distance value is measured. Once this condition is reached, coordinates for a surface point of the reference sphere can be determined on the basis of the determined distance. If a plurality of points on the sphere surface are detected in this way (e.g. at least three), coordinates for the sphere center can be calculated from them. Calibration parameters for the optical sensor device can then be determined from the difference between the sphere center coordinates determined in each case (i.e. the coordinates determined with the reference probe and the coordinates determined with the optical sensor device).

[0020] However, it has been shown that this approach does not always achieve the desired accuracy. In particular, it can be difficult to determine the exact coordinates of an optically detected contact point on the sphere's surface in directions perpendicular to a calibration direction (i.e., perpendicular to a direction along which the sensor device is moved toward the calibration object, for example, and / or which corresponds to an at least presumed orientation of the sensor axis), since the sensor axis may be tilted relative to the calibration direction (i.e., an actually scanned point lies adjacent to, and thus radially offset from, the calibration direction).

[0021] Furthermore, the desired accuracy cannot always be achieved by simply optically probing points on a spherical surface. Due to the small angle of incidence (to the sensor axis) of the rays directed onto the curved spherical surface, only a small proportion of the reflected radiation can be imaged, for example, onto a pinhole of the sensor device. Despite arranging a focus position directly on the spherical surface, it is therefore not always possible to record the maximum intensity of the reflected radiation. This means that the sensor device may not recognize that it is already located on the spherical surface and, for example, calculate incorrect coordinates and, in particular, incorrect center coordinates during the calibration process described above. As a result, incorrect calibration parameters may be determined and values ​​output by the sensor device and, if applicable,Measured values ​​calculated using these calibration parameters do not reflect the actual conditions. In particular, when detecting spherical surface points, only small spherical segments can usually be detected (i.e., the detectable surface points are located close to one another). This results in a significant mathematical uncertainty when using the surface points for a sphere calculation or for determining sphere center coordinates.

[0022] DE 10 2006 017 401 A1 also discloses a method for optically determining the center of a transparent sphere. A focal point is positioned at the center of the sphere and light reflected from the sphere's inner surface is measured. The incident radiation is intended to pass through the transparent sphere into its interior and be reflected back from an inner wall, passing through the sphere's center again.

[0023] The document ZOU XICONG ET AL: "Non-contact on-machine measurement using a chromatic confocal probe for an ultra-precision turning machine", THE INTERNATIONAL JOURNAL OF ADVANCED MANUFACTURING TECHNOLOGY, SPRINGER, LONDON, Vol. 90, No. 5, October 10, 2016 (2016-10-10), pages 2163-2172, XP036227824, ISSN: 0268-3768, DOI: 10.1007 / S00170-016-9494-3 discloses a sphere-based calibration of a chromatic confocal sensor device.

[0024] US 7,436,520 B1 discloses a method for calibrating an interferometer device.

[0025] An object of the present invention is therefore to improve the accuracy of the calibration of optical sensor devices for object detection.

[0026] This object is achieved by a method and an arrangement according to the appended independent claims, which define the scope of protection. Advantageous developments are specified in the dependent claims. Furthermore, it is understood that the features mentioned in the introductory description can also be provided individually or in any combination in the presently disclosed solution, unless otherwise stated or apparent.

[0027] According to a basic concept of the invention, during the calibration process, the at least one focus position of an optical sensor device is not (or at least not exclusively) directed at a surface of a calibration object (or measurement object). Instead, this focus position is positioned at a distance from a calibration object. This means that the angle of incidence of the emitted radiation relative to the surface can increase, in particular compared to the case where the focus position is arranged directly on the surface itself. As explained below, the distance can be selected in particular such that a predetermined and in particular maximally pronounced (detectable) backreflection can be achieved.

[0028] Furthermore, according to the invention, contrary to previously known solutions, it can be provided not only to move the sensor device in a straight line towards the calibration object in one calibration direction, but also to enable further movements. In particular, it was recognized that an additional shift of the focus position relative to the calibration object (but at a distance therefrom) compared to the calibration direction enables even more precise detection of the calibration object. In particular, this can ensure with a high degree of reliability that the focus position is directed towards a desired predetermined point inside or outside the calibration object(s), wherein coordinates for this predetermined point have preferably been determined and / or are known using a reference sensor device. A final calibration based on a comparison of coordinates determined for this point can therefore be particularly precise.

[0029] A further basic idea and advantage of the method according to the invention is that the focus position can be directed, for example, only to a single predetermined point in or outside the calibration object(s) and not to a plurality of points on the sphere's surface. This shortens the calibration time and the measurement uncertainty associated with detecting multiple contact points and, based on these, only indirectly calculating, for example, sphere center coordinates. In particular, the method can achieve greater accuracy because radiation reflected by an entire surface segment is evaluated (i.e., the detectable radiation reflected by the surface as a whole when the focus position is positioned at a distance from the surface) and not just from individual surface points. Dimensions and, in particular, a radius of the calibration object can be known or determined.

[0030] In detail, a method for detecting a calibration object with an optical sensor device is proposed, wherein the sensor device is configured to emit electromagnetic radiation with at least one wavelength and to focus this radiation in a focus position along a sensor axis (ie the sensor device has at least one focus position), the method comprising: Radiating electromagnetic radiation along the sensor axis onto a curved surface of a calibration object (which is opaque to the radiation according to the invention) and detecting radiation reflected by the calibration object; arranging the sensor device and the calibration object relative to one another such that the focus position is arranged at a distance from the curved surface and a target state is reached in which, according to a first alternative according to the invention, a detected reflected radiation power of the wavelength associated with the focus position or, according to a second alternative according to the invention, an interference property determined on the basis of the detectable reflected radiation fulfills a predetermined condition (e.g., reaches or exceeds a threshold value).

[0031] The calibration object can be a so-called calibration standard. The curved surface can form a segment or region of the total surface of the calibration object. In general, the curved surface can be convexly curved and preferably convexly curved in the direction of the sensor device, or concavely curved and in particular concavely curved in a direction facing away from the sensor device. For example, the curved surface of the calibration object can be an outer spherical surface or an (outer) surface segment of a spherical calibration object or an (outer) surface segment of, for example, a hemispherical recess. The calibration object can be arranged in a fixed position (i.e. stationary) relative to the sensor device or it can be movable by means of a positioning system (e.g. a measuring table).

[0032] The reflection detected according to the invention can originate predominantly or exclusively from an outer curved surface (outer surface) of the calibration object or occur on this. Reflections from inner surfaces, where the radiation must first penetrate into the calibration object through at least one material boundary and / or exit again, cannot be provided for and are generally not preferred, since these can be subject, for example, to optical refraction effects explained below. Undesired interference effects could also occur if radiation components reflected from different surfaces overlap one another at least partially along a common radiation path (for example, along a radiation path between the calibration object and the sensor device). The invention can provide that the radiated radiation (e.g.after leaving the sensor device) does not pass through a material boundary before and / or after a reflection on the calibration object.

[0033] According to the invention, it is provided to use a calibration object material that is largely or completely opaque to the incident radiation. This allows the reflection of the radiation at the outer surface, and preferably exclusively at the outer surface, without the incident radiation penetrating the calibration object or being reflected by areas of the calibration object other than the outer surface (for example, not being reflected by an inner surface of the calibration object after passing through material boundaries as discussed above).

[0034] This avoids optical refraction effects that would occur with at least partial transparency. This is particularly relevant because the optical refraction properties of materials, especially (partially) transparent materials, can be temperature-dependent, which would result in additional losses in accuracy. Furthermore, these refraction properties may not be distributed evenly across the material, for example, due to mechanical stresses resulting from the manufacturing process.

[0035] Furthermore, the use of opaque materials has the advantage that the calibration object's mounts (e.g., pin-shaped mounts for known calibration spheres) can be optically concealed by the calibration object. The influence of such mounts, particularly on the sensor-detected reflection process, can thus be suppressed. Furthermore, there is greater freedom in arranging the mounts than if a material that is at least partially transparent to radiation were used. In the latter case, radiation could pass through the calibration object and hit the mount, which would then produce reflections that would distort the measurement result. The mount would therefore always have to be positioned appropriately to avoid interactions with the radiation penetrating the calibration object.

[0036] The advantageous opacity of the calibration object is preferably achieved by using common ceramic calibration spheres, which also saves costs, as readily available ceramic calibration spheres can be used. These can then also be used for tactile measurements, for example, with a reference probe.

[0037] According to the invention, it can generally be provided to irradiate the same curved surface in the manner described herein, but also to measure it tactilely (for example, with a reference probe and / or for calibration purposes). In this case, too, a surface made of non-transparent material, and in particular of materials used in common calibration spheres (e.g., ceramic), is advantageous, as these typically possess both the desired reflective and non-transparent properties as well as sufficient surface hardness for repeated tactile probing. Material that is too soft and / or transparent could scratch during tactile probing, which in turn negatively affects the reflective properties.

[0038] Furthermore, it is generally preferred that a radius of curvature of the curved surface is smaller than a distance of the focus position from the sensor device and / or sensor optics. In the case of a plurality of focus positions, the radius of curvature is preferably smaller than the shortest distance of one of the focus positions from the sensor optics and / or sensor device, or smaller than the distance of at least a plurality of the focus positions from the sensor optics. By appropriately selecting the radius of curvature, it is possible to arrange the focus position within the calibration object, and in particular in the region of any center of curvature of the curved surface, in such a way that meaningful measured values ​​are generated.For example, this can ensure that the sensor optics can still be positioned at a distance from the curved surface and thus can guide the radiation in the desired manner, but at the same time the focus position can be arranged to a desired extent (or at a desired depth) within the calibration object (for example, on the center of the curvature).

[0039] The optical sensor device can be configured to be coupled to a coordinate measuring machine or another positioning system. This means that, in particular, the movement of the sensor device relative to the calibration object according to the invention can be effected by moving the sensor device coupled and / or attached to a coordinate measuring machine or robot by a movement device of the coordinate measuring machine or robot. The movement device can, in particular, have at least one drive, such as an electric motor.

[0040] In particular, after detecting the calibration object with the optical sensor device, a measurement of a measurement object that is not the calibration object can be performed with the sensor device coupled and / or attached to the coordinate measuring machine or the robot, wherein the results of detecting the calibration object with the optical sensor device are taken into account, in particular at least one of the results described below. In particular, the sensor device is not decoupled or removed from the coordinate measuring machine or the robot between detecting the calibration object and detecting the measurement object. The results of the detection, in particular calibration information, are therefore valid for the current state of the coupling or attachment.

[0041] The scope of the invention therefore also includes a coordinate measuring machine or a robot to which the optical sensor device is arranged, in particular coupled and / or attached, wherein the coordinate measuring machine or the robot is designed to carry out the method in one of the embodiments described in this description. In particular, the coordinate measuring machine or the robot therefore has the evaluation device described below. The evaluation device or another computing device (for example, a commercially available computer with software) can in particular be designed to process calibration information from the detection of the calibration object with the optical sensor device.

[0042] In particular, by detecting the calibration object with the optical sensor device, coordinates of the calibration object can be determined and these coordinates can be used as calibration information when measuring the measurement object.

[0043] In the case of an at least partially spherical calibration object, the sphere center coordinates can be determined as calibration information. The sphere center coordinates can then be used in the same way as known from the prior art. In particular, calibration parameters for the optical sensor device can be determined from the difference between the sphere center coordinates determined in each case (i.e., the coordinates determined with a reference probe and the coordinates determined with the optical sensor device).

[0044] The optical sensor device can comprise sensor optics (focusing optics) by means of which electromagnetic radiation can be radiated into the environment and radiation reflected from the environment can be detected. The optical sensor device can also comprise a light guide or light guide section in which electromagnetic radiation generated by a radiation generating device (for example, a light source or lamp of a confocal sensor) and / or reflected back from the environment is guided. In particular, electromagnetic radiation can be directed from the light guide onto the focusing optics and from there onto the calibration object.

[0045] Furthermore, the reflected radiation can be guided back into the optical fiber by means of the sensor optics and from there to an evaluation device (for example, a controller of the coordinate measuring machine or the robot). The radiation generation device, evaluation device, and at least that section of the optical fiber that is not directly coupled to and / or accommodated in the optical sensor device can be provided separately from the optical sensor device (or at least a movable sensor head thereof). For example, these units can be stationary and arranged, for example, on a base of the coordinate measuring machine, whereas the optical sensor device can be movable in space by means of the axes of the coordinate measuring machine. In this case, in particular, the sensor device can be designed or referred to as a sensor head.In principle, however, it can also be provided that at least one of the radiation generating device and evaluation unit is integrated into the optical sensor device or forms a component thereof.

[0046] According to the first alternative according to the invention, the optical sensor device is a confocal sensor device or a chromatic confocal sensor device (i.e., a white light sensor) or, according to the second alternative according to the invention, an interferometric sensor device. If a confocal sensor device is provided, the focus position and a wavelength can refer to the only focus position or, preferably, the only emitted (or only evaluable emitted) wavelength of this sensor device. If a chromatic confocal sensor device is provided, the above or following references to a focus position and / or wavelength can refer to at least one of the plurality of focus positions and / or associated wavelengths of this sensor device. This can, in particular, be a predetermined focus position including the associated wavelength.In particular, in the case of a chromatic confocal, it can be assumed that a clear relationship between focus positions and wavelengths exists and is preferably also known.

[0047] As described in the introduction, the sensor axis can be an axis concentric with a pinhole (or the exit opening of a fiber optic cable), along which the radiation is guided within the sensor optics and on which the focus position is located. Generally, the sensor axis is a virtual axis that can be moved in space together with the optical sensor device and, in particular, the exit opening of the fiber optic cable. The location of the focus position can be defined as a virtual point on the sensor axis by selecting the optical elements of the sensor optics, particularly their dimensions, optical properties, and / or arrangement.

[0048] The detection of the retro-reflected radiation can in particular comprise imaging the retro-reflected radiation onto the pinhole (e.g. in the form of the exit opening of a light guide) using the sensor optics. From there, the retro-reflected radiation (or at least the portion of the radiation imaged onto the pinhole) can be guided to an evaluation device. This can, for example, determine the radiant power and in particular an intensity (i.e., radiation flux density) of the retro-reflected radiation (detected, for example, during an exposure period). In the case of a chromatic-confocal sensor, the intensity distribution over the entire emitted wavelength spectrum can also be detected, for example during an exposure period. In a manner known per se, the evaluation device for detecting the radiant power, intensity and / or intensity distribution can comprise a photosensitive unit such as a CCD or CMOS sensor.

[0049] The measurement signals and / or measured values ​​of the sensor device can therefore relate to or indicate the radiation power, the intensity, and / or an intensity distribution. In other words, the sensor device can thus detect several different measured values ​​relating to different properties of the retroreflected radiation, or even just one measured value. However, the evaluation device can also be configured to determine further measurement information and, in particular, distance values ​​based on such measurement signals or measured values. For this purpose, it can use the linearization parameters and / or calibration parameters described above. The evaluation device can be implemented as a computing unit and, for example, comprise a processor on which program instructions for evaluating the measurement signals or measured values ​​can be executed.

[0050] Alternatively or additionally, the measurement signals or measured values ​​may also relate to a time period required to record a predetermined radiation intensity integrated over time and, in particular, an integrated minimum intensity.

[0051] In general, the arrangement of the sensor device and the calibration object can initially comprise a rough arrangement (i.e. a rough arrangement or rough positioning). In this case, for example, the results of a pre-calibration explained below can be used. In this way, an attempt can be made to achieve a relative arrangement which already approximates the target state as closely as possible. In particular, the focus position can be arranged at a distance from the object surface (e.g. in the object volume) and / or generally in such a way that impact on the surface as a result of further expected relative movements is excluded with a high degree of probability. Subsequently, a fine arrangement or fine positioning can take place, in which additional relative movements of the sensor device and the calibration object can be carried out until the target state is reached.

[0052] Arranging the sensor device and the calibration object can comprise a linear relative movement of the sensor device and the calibration object. In particular, it can be provided that the sensor device is moved along a linear direction of movement (calibration direction) relative to and / or toward the calibration object. Simultaneously, the acquired measurement signals, which can indicate, in particular, the intensity (and / or intensity distribution) of the reflected radiation, are preferably monitored.

[0053] According to a variant of the method and arrangement, the achievement of a desired distance of the focus position to the curved surface and in particular the achievement of a (virtual) plane at which this distance exists is detected based on the intensity or radiant power of the reflected radiation. This can be relevant, for example, if the alignment of the sensor axis is determined in advance (i.e., as part of a pre-calibration before carrying out the actual method) and the calibration direction is preferably selected along the sensor axis. The alignment can, for example, be estimated based on the design of the sensor device and / or its attachment, for example, on a coordinate measuring machine. Alternatively, such an alignment can be estimated from individual measurements on, for example, a calibration sphere. For example, distance values ​​can be specified to which adjustment is to be made (i.e.,The sensor device is to be positioned at these distances relative to, for example, a calibration sphere. The orientation of the sensor axis can then be estimated from the positions assumed when the distance values ​​are reached (i.e., the respective positions can be considered to lie on the sensor axis, so that the (presumed) sensor axis can be calculated from them).

[0054] It should be noted that intensity maxima can generally be detected when a focus position is on the surface, but also when this is positioned at a predetermined distance from it (e.g., at a center of curvature as explained below). The latter represents a preferred condition for the solution presented here. To ensure that detected radiation outputs actually relate to the latter condition and not to positioning on the surface, a rough positioning can be carried out as explained below, which excludes with a high degree of probability that the surface is reached by the focus position. Additionally or alternatively, a manual (i.e., performed by an operator) plausibility check can take place and / or can (in each case manually or automatically), for examplea distance signal, known information on the object position and / or dimensions, a CMM position or information on an approximately known sensor geometry can be used for a plausibility check to differentiate whether the focus position has reached the preferred distance or the object surface.

[0055] According to one variant of the method and arrangement, the position of the focus position (e.g. as the distance of the focus position to the sensor device) is known approximately (i.e. at least roughly or approximately), in particular in device coordinates, and has been determined in advance, for example, as part of a pre-calibration. Furthermore, the position of a predetermined point or a predetermined plane inside or outside the calibration object can also be known at least approximately, whereby the point or plane can, for example, have a defined relationship with the curved surface. For example, it can be a center of curvature or a plane encompassing this point, or generally a plane or a point which the focus position must at least approximately reach in order to achieve the target state. Such information can preferably again be present in device coordinates.

[0056] The position of the predetermined plane or point can be determined, for example, by tactile probing of the calibration object (or generally detecting the calibration object using a reference sensor device), whereupon a position of the plane and / or a predetermined point located therein can be calculated based on the measured values ​​acquired in this process. The position of the focus position can be determined, for example, within the scope of the described pre-calibration by optically measuring a reference sphere and comparing the measured values ​​obtained with measured values ​​obtained by detecting the same sphere using a reference probe.

[0057] Consequently, the focus position can be positioned at least approximately in the predetermined plane or at the predetermined point by specifying movement instructions to a positioning system (and in particular to the axes of a coordinate measuring machine). In this way, or in other ways (e.g., based solely on estimates or empirical values), a first rough arrangement of the sensor device and calibration object can be established, which is preferably refined by further relative movement of the sensor device and calibration object until the target state is reached.

[0058] More precisely, the coordinates of the focus position and the predetermined plane or point can be used to derive the necessary movement instructions to position the focus position in the plane, and in particular at a predetermined point within it. Whether or to what extent this positioning was actually successful and whether the target state was thereby achieved can be checked and / or corrected, for example, by changing the relative arrangement of the sensor device and the calibration object and, in particular, by moving the focus position in the plane.

[0059] Alternatively, a pre-calibration can be carried out in which the position of the sensor axis (for example in device coordinates) is determined at least approximately (i.e. roughly or approximately). The sensor device can be aligned such that the (determined) sensor axis intersects a center of curvature determined, for example, using a reference probe, or at least a plane containing this point, or the sensor axis can be determined such that it intersects this center point. The sensor device can then be moved along the sensor axis and measurement signals can be monitored in parallel until they indicate that, for example, the center of curvature or the plane and / or the target state have been at least approximately reached. The calibration direction can thus be aligned along the determined position of the sensor axis.A rough arrangement can also be carried out in this way and, as described below, additional relative movements of the sensor device and the calibration object can then be carried out in order to achieve the target state.

[0060] The optional precalibrations, which can generally be provided as separate method steps of the method according to the invention and / or can be carried out by the arrangement according to the invention, offer the advantage that at least a rough initial arrangement of the focus position and calibration object close to the target state can be carried out comparatively quickly and precisely. In particular, it is not necessary to proceed entirely iteratively or manually in order to arrange the focus position in a suitable manner relative to the calibration object and / or to at least roughly approximate the target state. However, such an iterative or manual initial arrangement would in principle also be possible, so that performing a precalibration represents a purely optional measure.

[0061] If, following an initial (rough) alignment, further relative movements of the sensor device and the calibration object are to occur (e.g., for fine positioning), these movements can be selected in directions different from any calibration direction. In particular, only relative movements of the sensor device and the calibration object can occur in directions orthogonal to the calibration direction (and / or the sensor axis). Again, the measurement signals of the sensor device, and in particular their changes, can be monitored in parallel. Additionally or alternatively, these relative movements can occur along at least two directions of movement in a common plane, wherein the directions of movement are at an angle to one another and preferably orthogonal to one another.

[0062] The target state, the achievement of which is checked and / or continuously monitored during this change using the measurement signals, can be a state in which a predetermined and in particular maximum reflection behavior of the radiation by the calibration object occurs (at least in relation to the at least one wavelength). This can be correspondingly recognizable using the measurement signals. This can in particular be a maximum extent and in particular a maximum detectable reflected radiation power of at least one wavelength of the retro-reflected radiation, wherein this wavelength belongs to the focus position (i.e. radiation with this wavelength is focused in the focus position). An intensity, a time duration for detecting an integrated intensity and / or an intensity distribution can be considered as an indication of the presence of a corresponding radiation power, as explained in more detail below.

[0063] In general, the condition for the radiation output can be defined as the achievement of a maximum value, which can also be a merely local maximum value in a detected intensity distribution of the reflected radiation. As explained below, an exposure time, preferably automatically controlled for achieving a predetermined integrated intensity value, can also be considered, wherein the condition is the achievement of a minimum value or lower threshold value of this exposure time. According to the second alternative according to the invention, a contrast explained below is determined as the interference property, which must be maximized to fulfill the condition.

[0064] A further development of the method and arrangement provides that the sensor device is calibrated on the basis of at least one measured value which is determined when the target state is reached. For example, the measured value can be a distance value from the sensor device to the curved surface and / or to a predetermined plane inside or outside the calibration object (and / or a predetermined point located therein) or can be based on this distance value. When the target state is reached, for example, the current distance value determined by the (preferably linearized) sensor device can be determined and added to a known dimension (e.g. a radius) of the calibration object. From this, a distance of a sensor coordinate system and / or a sensor interface of the positioning system to a predetermined point on the calibration object can be determined.In particular, coordinates of a center of curvature can be determined based on this, e.g., in device coordinates. The measured value can therefore generally indicate coordinates relative to the calibration object, e.g., of its curved surface, of the predetermined plane, and / or of a predetermined point located therein (or generally of a center of curvature).

[0065] The measured value can be used to determine a difference from coordinates for the calibration object determined, for example, using a reference probe (in particular from a center of curvature). This difference can be used in a manner known per se to determine calibration parameters. More precisely, the calibration of the sensor device can comprise determining calibration parameters with which measurement information (or measured values) obtained from the sensor device in the future can be calculated and / or transformed. This can be done analogously to the known approaches discussed in the introduction, according to which the calibration parameters are determined based on a difference from reference measurement signals and / or reference measurement information, for example when the same calibration object (and in particular the same plane and / or the same predetermined point or center of curvature arranged therein) is measured with a reference sensor device.

[0066] Generally speaking, information, in particular in the form of distance or coordinate values, can be determined as the at least one measured value or on the basis of the at least one measured value, which can form the basis for calibrating the sensor device.

[0067] According to a further embodiment of the method and arrangement, the target state is achieved when the focus position is positioned at a center of curvature of the curved surface (or, in other words, lies on the center of curvature). The curved surface can be formed, for example, by at least one segment of a cylindrical surface or spherical surface of the calibration object. In the case of a spherical calibration object, the center of curvature would correspond to the center of a sphere. In the case of a cylindrical calibration object (preferably with a circular base), the center of curvature can lie on a cylinder axis (in particular, a cylinder longitudinal axis). In this way, directional dependencies of the acquired measurement information can be reduced or even eliminated entirely.Furthermore, if the at least one focus position is positioned at the center of the curvature, a preferred and easily detectable reflection behavior (in particular, a maximum detectable radiant power of the retroreflected radiation) can be reliably achieved. Furthermore, measured values ​​(e.g., coordinates) for the center of the curvature can also be determined precisely and easily using a reference probe or a reference sensor device, which can then be compared with at least one measured value determined by the sensor device for calibration purposes.

[0068] The predetermined condition can be met, particularly in connection with the center of curvature, when a maximum of the reflected radiant power is reached. This can be a local maximum with respect to the distance of the sensor device from the curved surface (or viewed as a function of this distance). For example, it would also be possible to achieve maximum radiant power if the focus position is on the curved surface but not at the center. In other words, depending on the calibration object, several states can be achieved in which the reflected radiant power assumes a maximum value. Positioning the focus position at the center of curvature can correspond to one of these states.

[0069] In a further development of the method and arrangement, the radiation radiated onto the calibration object comprises a beam path that runs at least partially at an angle to the sensor axis. In particular, this beam path comprises at least (or exactly) two beams that converge towards one another in the direction of the focus position. Furthermore, the target state is preferably achieved when the radiation reflected back by the calibration object is reflected along this beam path. In other words, the target state can be achieved when beams radiated onto the calibration object are reflected back into themselves and / or are perpendicular to the curved surface of the calibration object. This can particularly relate to any converging beams of the beam path that can accordingly strike the curved surface perpendicularly.Once such a state is reached, the detectable radiant power of the reflected radiation can be particularly high, and in particular, at its maximum. This allows for precise determination of whether the target state has been reached, allowing for a correspondingly accurate calibration of the sensor device.

[0070] In one embodiment of the method and the arrangement, the radiation incident on the calibration object in a solid angle range from different directions (i.e. each radiation or each radiation component or each individual beam) has a radiation path incident on the curved surface at an angle (which can also be 0°) to the sensor axis, and the target state is achieved when the radiation reflected back by the calibration object in the solid angle range is each reflected back from the curved surface along the same radiation path. The solid angle range can be the entire area in which the sensor device radiates radiation onto the curved surface (e.g. if the calibration object is spherical). If the calibration object is cylindrical, the solid angle range can be a circular, line-like area or such an area can be encompassed by the solid angle range.In the case of a partially spherical surface, the solid angle range would only contain the corresponding spherical sub-area. For all of the calibration objects mentioned above, a corresponding solid angle range can be defined and a target state can be achieved in which at least a local maximum of the reflected radiation power is achieved.

[0071] The inventors have recognized that the state of maximum reflection and / or self-reflection of the incident rays is achieved in particular when the focus position is arranged at a predetermined distance relative to a curved surface of the calibration object. For example, this can be achieved by arranging the focus position in a plane containing any center of curvature, and in particular the center of a sphere, inside or outside the calibration object and / or by lying directly on such a center. For example, with a surface of the calibration object that is convexly curved relative to the center of curvature, it can then occur that the radiation radiated by the sensor device is at least partially perpendicular to an irradiated surface segment, whereby a correspondingly increased or maximum reflection of the radiation by the calibration object can be achieved.One advantage of positioning at the center of the curvature is that it can be reliably detected (e.g., as the maximum value of the reflected radiant power). Compared to an intensity distribution, this results in a narrow intensity peak or narrow scatter or distribution around the maximum value. Relative displacements to the center of the curvature can thus be reliably detected as significant intensity changes.

[0072] The target state can thus generally be associated with a predetermined relative arrangement of the focus position and the calibration object, or it can only be achieved with a correspondingly unambiguous relative arrangement. The achievement of this relative arrangement can thus be precisely detected by detecting the achievement of the target state, and vice versa.

[0073] In a further development of the arrangement and method, the coordinates (and / or the position) of the focus position and a center of curvature of the curved surface in a predetermined coordinate system are at least approximately known, and the sensor device and the calibration object are arranged relative to one another based thereon (for example, as part of a first arrangement and / or to define an initial state from which the target state is to be reached). This can correspond to a rough arrangement or positioning as explained above. It is therefore understood that further changes to the relative arrangement and, in particular, the execution of relative movements of the focus position and the calibration object can be provided to achieve the target state. As described, the position of the focus position and the center of the sphere can be determined, for example, by means of a previously performed calibration by scanning a spherical surface.The coordinate system can be a device coordinate system. By specifying movement instructions to the positioning system based on the known coordinates, the focus position and the calibration object can then be arranged relative to one another, in particular such that the focus position is at least approximately positioned on the center of curvature. In particular, it can be provided that the sensor device is arranged at the beginning of a process, the end of which is the achievement of the target state, such that the approximately known focus position and the approximately known center of curvature coincide.

[0074] A further variant of the method and the arrangement provides that the focus position is shifted in a plane to achieve the target state (e.g., by shifting the sensor device relative to the calibration object and / or changing an orientation of the sensor device relative to the calibration object). The plane can be a cross-sectional plane of the calibration object or a plane outside the calibration object, which plane is opposite the curved surfaces, for example. In particular, it can be a plane that contains at least one predetermined point, for example, the center of curvature and, in particular, a sphere center of a spherical calibration object. The focus position can be positioned in this plane, for example, as part of a coarse arrangement or positioning.

[0075] Whether this has occurred and / or whether a possibly predetermined focal point in this plane has been reached can be determined, for example, based on the measurement signals of a particularly confocal sensor device. The measurement signal corresponding to a predetermined wavelength or focal position can be monitored during movement of the sensor device along a calibration direction (which, for example, runs along an approximately determined sensor axis) as well as during further movements of the focal position relative to the calibration object or the curved surface in this plane, in particular during movements in at least two directions extending at an angle to one another.In parallel, the measurement signals of the sensor device (in particular the detectable reflected radiation power) can be monitored again and if these meet the predetermined condition and in particular reach a local or absolute maximum value (for example in an intensity distribution), it can be concluded that the target state has been reached.

[0076] Particularly when using a confocal or interferometric sensor, an iterative approach is possible, for example, by performing multiple movements along the sensor axis (e.g., to various points along this axis) and also transversely to it. In other words, iterative displacement can be performed in several preferably parallel planes. From the totality of the recorded values, it is then possible to conclude whether the target state has been reached, e.g., by identifying a maximum or minimum value or by reaching threshold values. If a chromatic confocal sensor is used, iterative attempts can also be made, for example, to reach the target state with a specific focus position.Alternatively, during a coarse positioning, one of the plurality of focus positions may presumably already be positioned in the above-mentioned plane, so that a shift relative to the sensor axis results in the target state being reached with this focus position.

[0077] In this context, it can further be provided that the plane runs orthogonally to the (preferably at least approximately or roughly known) sensor axis. In other words, the focus position can thus be shifted radially and / or orthogonally to the sensor axis. This can be achieved by changing the relative arrangement of the sensor device and the calibration object, wherein at least one of the sensor device and the calibration object can be moved (e.g., by means of a positioning system or coordinate measuring machine). This can be particularly relevant if the position of the sensor axis was at least approximately determined, e.g., during pre-calibration.

[0078] Alternatively or additionally, it can be provided that the plane in which the focus position is shifted runs orthogonal to an axis (e.g. a calibration axis) along which the sensor device is moved, in particular in order to arrange the focus position in the plane for the first time. This can be a rectilinear movement axis along which the sensor device is moved, for example, until the focus position has reached the plane is detected on the basis of the measurement signals from the sensor device (e.g. because a radiation output is maximum). As explained, it is advantageous for robustness and, in particular, for shortening the measurement time if a rough positioning is carried out based on available information and does not have to be carried out primarily iteratively.

[0079] Shifting the focus position in the plane, and in particular in the orthogonal directions explained above, offers the advantage that this enables a more precise arrangement of the focus position within the plane and in particular relative to and optionally to a predetermined point in the plane. The inventors have recognized that, in interaction with the irradiated curved surface of the calibration object, shifts within the cross-sectional plane can be accompanied by reliably detectable states of the arrangement and / or reliably detectable process states. This applies, for example, because the extent of detectable back reflections can vary depending on the distance of the focus position from a predetermined area or point within the plane. In particular, the angle of incidence relative to the curved surface of the calibration object can also change depending on this distance.Only when the predetermined point has been reached can the maximum degree of reflection be achieved, since the radiation radiated onto the curved surface then exhibits a predetermined and preferably perpendicular angle relative to this surface. Thus, by shifting the focus position in the plane and by preferably parallel monitoring and / or evaluating the measurement signals, it can be precisely determined whether the plane and / or a predetermined point within it is in focus.

[0080] A further development of the method and arrangement provides that the radiant power, and in particular the possible fulfillment of the condition, is detected indirectly. In particular, a detected intensity (e.g., during an exposure period), an intensity distribution, or a time period for reaching a predetermined intensity threshold can be used for this purpose (see also the following aspect), from which an existing radiant power can be inferred. Thus, it can also be provided that no exact value for the radiant power is determined.

[0081] According to a further aspect of the method and arrangement, the predetermined condition is one of the following and / or the reaching or exceeding of a radiation power limit is detected as follows: An intensity of the detected reflected radiation with the at least one wavelength, detected for example during a defined exposure time, reaches a predetermined threshold value (in particular an at least local maximum value) and / or is maximum; A time period required to reach a predetermined integrated intensity value of detected reflected radiation with the at least one wavelength reaches a predetermined threshold value (in particular an at least local minimum value) and / or is minimum; The detected retroreflected radiation power can be assigned to only one of a plurality of focus positions and / or only to the at least one wavelength; The contrast determined as an interference property of an interference signal determined on the basis of the reflected radiation is maximum and / or reaches a predetermined threshold value.

[0082] Combinations are also possible, for example, to detect the fulfillment of the condition in multiple (i.e., redundant) and thus particularly reliable ways. Where reference is made here to maximum or minimum values, these can be determined depending on the relative movement of the focus position to the object and the resulting value curves. This means that they can also only refer to local maxima / minima within a corresponding value curve and not necessarily absolute maxima / minima, since such values ​​can depend significantly on the irradiated calibration object.

[0083] For (interference) contrast, the reference beam and the measurement beam (i.e., the beam emitted into the environment and reflected by the sample) are superimposed to form an interference signal. Different, controlled phase shifts are introduced between the reference beam and the measurement beam, and the resulting modulated intensity of the superimposed radiation or interference signal is evaluated as a function of the phase shift. The contrast is typically defined as the ratio of (maximum - minimum) / (maximum + minimum) relative to the intensity of the interference signal detected during the phase shifts. The interference signal is thus generated based on the detected reflected radiation or the phase of the reflected radiation.

[0084] The time required to reach the predetermined integrated intensity value can be determined, for example, by means of an evaluation device and / or output directly as a measurement signal from the sensor device. In this case, the intensity of the detected reflected radiation can be integrated over time, and when this intensity reaches a predetermined threshold value, the elapsed time can be determined. If the determined time is short, this means that the intensity of the reflected radiation and thus the radiant power is comparatively high. If this time period elapses after a predetermined threshold and, in particular, minimum value, it can also be detected that a maximum degree of radiation reflection and, in particular, a radiant power above a predetermined limit value is present.In one variant, the system first waits for a maximum intensity (as a predetermined material-independent threshold) to be reached, and then sets a reduced exposure time as an upper limit. Additionally or alternatively, a minimum exposure time determined during a measurement process for reaching the predetermined intensity value can be determined, indicating that the condition has been met.

[0085] With a constant exposure time, however, a maximum can be determined from the total intensity values ​​determined during a measurement process, which indicates that the condition has been reached.

[0086] The case in which the detected retroreflected radiation can be assigned to only one of a plurality of focus positions is particularly relevant for chromatic confocal sensor devices. In this case, a measurement signal can, for example, comprise an intensity distribution with a plurality of local maximum intensities, and each local maximum can be assigned to a specific focus position and wavelength of the radiation. If, in such a case, a state is reached in which there is only a single intensity maximum within the distribution, it can be concluded that the only radiation currently being retroreflected is that can be assigned to a specific wavelength and the associated focus position. This is due to the fact that the radiation is reflected back to the sensor devices (for example, any optical fiber) to the greatest possible extent.This also means that the recorded radiant power of the reflected radiation is particularly high and in particular reaches or exceeds a maximum value.

[0087] A further development of the arrangement and method provides that the described procedure with regard to the arranging of focus position and calibration object for reaching the target state is carried out for at least two different focus positions. In detail, the sensor device can have a plurality of focus positions and the method can be carried out for at least two different focus positions, wherein in each method pass, position information is determined when the target state is reached and an alignment of the sensor axis is determined based on the overall position information determined. In particular, for each of the focus positions, for example, the position of the sensor device at which the predetermined state is reached can be recorded as position information and an alignment of the sensor axis can be determined based on the overall position information determined (i.e. across all method passes).

[0088] The position information can be a position of the sensor device (e.g., an origin of a sensor coordinate system thereof) in device coordinates. Alternatively, position information regarding the calibration object can be determined based on the measurement signals of the sensor device, e.g., regarding the position of a center of curvature or a sphere. For example, the position information can relate to the center of curvature coordinates determined during a respective process run.

[0089] If at least two pieces of position information are determined, a straight line can be determined that extends through points and / or coordinates defined on the basis of the position information, whereby this straight line can approximate the sensor axis.

[0090] One embodiment of the method and arrangement provides that an alignment of the sensor axis and the coordinates of a center of curvature of the curved surface in a predetermined coordinate system are at least approximately known, and the sensor device and the calibration object are arranged relative to one another based thereon. This can again be a rough arrangement or rough positioning, which is followed by further relative movements to reach the target state. Additionally or alternatively, the (particularly confocal) sensor device can be moved along the sensor axis toward the calibration object, and measurement signals can be monitored, preferably in parallel, for example, until they reach a maximum value, for example, based on the value curve determined during the movement (for example, when the measurement signals relate to the radiation power and / or radiation intensity).This can be considered a state in which the focus position has reached a plane containing the center of curvature. Subsequently, the relative arrangement of the sensor direction and the calibration object can be further adjusted, or in other words, refined, until the target state is reached (in particular, by shifting the focus position in the plane). The orientation of the sensor axis can be determined according to one of the variants below. The coordinates of the center of curvature can be determined, for example, by scanning the curved surface with a reference probe.

[0091] The invention further relates to an arrangement comprising: a positioning system (in particular a coordinate measuring machine), a calibration object (in particular a calibration sphere) which has at least one curved surface; an optical sensor device which is designed to emit electromagnetic radiation with at least one wavelength along a sensor axis and to focus this radiation in a focus position along a sensor axis (iethe sensor device has at least one focus position); and a control device which is configured to cause (or, in other words, control) the arrangement to carry out the following measures: radiating electromagnetic radiation along the sensor axis onto a curved surface of a calibration object and detecting radiation which is reflected by the calibration object; arranging the sensor device and the calibration object relative to one another such that the focus position is arranged at a distance from the curved surface and a target state is reached in which detectable radiation, in particular reflected radiation power of the wavelength associated with the focus position (or, in other words, of reflected radiation with a wavelength associated with the focus position) or an interference property determined on the basis of the detectable reflected radiation fulfils a predetermined condition.

[0092] The arrangement may include any further development and any further feature to provide or perform all of the above or below steps, operating states, and functions. In particular, the arrangement may be configured to perform a method according to any of the above or below aspects.

[0093] An embodiment of the invention is explained below with reference to the accompanying schematic figures. Features that are identical in type and / or function may be provided with the same reference numerals throughout the figures. They depict: Fig. 1: a view of an arrangement according to the invention with which the methods according to the invention can be carried out; Figs. 2 - 3: optical detections of a spherical calibration object according to the prior art; Fig. 4: a detection of a spherical calibration object with the arrangement of Figure 1; Fig. 5: a change of a relative arrangement of a sensor device to the calibration object with the arrangement of Figure 1 ; Fig. 6 a representation of the effects of changing the relative arrangement from Figure 5 ; Fig. 6a shows an example of detecting an alternative calibration object; and Fig. 7 shows an example of a pre-calibration for determining the position of a sensor axis.

[0094] The Figure 1 and 2The arrangement shown comprises a coordinate measuring machine (CMM) 211 in gantry design, which has a measuring table 201, above which columns 202, 203 are arranged to be movable in the Y direction of a Cartesian coordinate system. The columns 202, 203, together with a cross member 204, form a gantry of the CMM 211. The cross member 204 is connected at its opposite ends to the columns 202 and 203, respectively. Electric motors (not shown in detail) cause the linear movement of the columns 202, 203 in the Y direction, along the movement axis, which runs in the Y direction. For example, each of the two columns 202, 203 is assigned an electric motor. The cross member 204 is combined with a cross slide 207, which is movable, for example, on air bearings, along the cross member 204 in the X direction of the Cartesian coordinate system. The current position of the cross slide 207 relative to the cross member 204 can be determined using a scale division 206.The movement of the cross slide 207 along the movement axis in the X direction is driven by at least one further electric motor (not shown). A vertically movable quill 208 is mounted on the cross slide 207. At its lower end, the quill is connected via a mounting device 210 and a rotating device 205 to a change interface 209, to which a sensor device in the form of a white light sensor 215 is coupled via an angled holder. Due to the angle, the measuring direction of the white light sensor 215 runs approximately parallel to the XY plane. Driven by a further electric motor, the change interface 209 can be moved relative to the cross slide 207 in the Z direction, along the Z movement axis, of the Cartesian coordinate system.The electric motors of the CMM allow the white light sensor 215, which is coupled to the interchangeable interface 209, to be moved into virtually any position in the area below the cross member 204. Furthermore, the rotating device 205 can rotate the white light sensor 215 about the Z-axis, allowing the white light sensor 215 to be oriented in different directions. Alternatively, a rotating device can be used instead of the rotating device 205, allowing other degrees of freedom of movement, e.g., additional rotational mobility about a rotation axis perpendicular to the vertical (Z-direction).

[0095] The CMM 211 forms a positioning system for adjusting and varying a relative arrangement of the white light sensor 215 to the stationary measuring table 201 and the components that can be arranged thereon, as explained below.

[0096] Also shown is an evaluation device 220, which receives the measurement signals of the white light sensor 215 via a schematically shown connection 230. The connection 230 can be, for example, a light guide such as a fiber optic cable. Although the connection 230 is Figure 1 and 2 not necessarily recognizable directly connected to the white light sensor 215.

[0097] Furthermore, in Figure 1 and 2 A control device 222 of the CMM 211 is shown schematically, which in particular controls the drives (e.g., the aforementioned electric motors). In particular, the control device 222 is capable of moving the white light sensor 215 to a desired position by controlling the drives and also controlling the rotating device 205 in order to align the white light sensor 215 in a desired measuring direction.

[0098] The control device 222 is further combined with a data memory 221, in which information about a relationship between measurement signals of the confocal white light sensor 215 and an actual distance of the white light sensor 215 from a measurement object 235 (and also the calibration object explained below) is stored. As explained below, however, it is not mandatory for the invention that such information be available from the outset. In particular, an optional precalibration can also take place without a linearization having already taken place.

[0099] In the following, the information stored in the data memory 221 is referred to as "linearization parameters," although the term "linearization parameters" merely denotes a specific type of such information. Alternatively or additionally, information of a different type than linearization parameters concerning the relationship between the measurement signals of the white light sensor 215 and the actual distance of the white light sensor 215 from a measurement object can be stored in the data memory 221. In each case, the stored information is assigned to a specific white light sensor 215, i.e., even white light sensors 215 of the same type are assigned separate information, which is referred to below as "linearization parameters."

[0100] When operating confocal white light sensors 215, the sensor measurement signals are typically linearized with respect to the actual distance of the white light sensor 215 from a measurement object 235. Typically, a reference measurement is performed by the manufacturer of the white light sensor 215 or in a certified measurement laboratory. During linearization, value pairs are recorded, each consisting of a sensor signal (i.e., measurement signal) or multiple sensor signals and the associated distance measurement value of an additional distance measurement system. In particular, the linearization is performed by a model that describes the behavior of the white light sensor 215 depending on the object distance. The model can be, for example, a mathematical model, for example, with polynomials and / or splines that describe the behavior. Alternatively or additionally, it can be a physical model, for exampledescribes the function of the focusing optics of the white light sensor 215. Typically, the linearization result is stored in the data memory of a control unit of the white light sensor system. The control unit and white light sensor 215 are delivered to the user together, with the control unit also being integrated into the evaluation device 220 or the control device 222. Figure 1 can be integrated.

[0101] In contrast to the linearization at the manufacturer or in the test laboratory, in the example shown a reference measurement is carried out using a coordinate measuring machine 211, while the white light sensor 215 is coupled to the CMM 211. This is described in DE 10 2015 217 637 A1 with reference to the Figures 1 and 2explained in more detail. For this purpose, the white light sensor 215 is coupled to the spindle sleeve 208 via the interchangeable interface 209. A reference body 231, e.g., a plane-parallel glass pane, is located on the measuring table 201, wherein the reference body 231 is supported on the measuring table 201 via a support 232. In the exemplary embodiment, the reference body 231 remains stationary relative to the measuring table 201 during the reference measurement. In contrast, the white light sensor 215 is preferably brought into different positions relative to the measuring table 201, and thus also relative to the reference body 231, exclusively by moving the columns 202, 203 in the Y direction. Figure 1The white light sensor 215 is shown in one of these relative positions. A dashed arrow indicates that the white light sensor 215 is aligned with the reference body 231. In each relative position, the white light sensor 215 radiates its measuring radiation onto the reference body 231, the measuring radiation is reflected at least at the front side facing the white light sensor 215, and the measuring radiation reflected back to the white light sensor 215 is detected by the latter.

[0102] In addition, for each of the relative positions from the position measuring system of the CMM 211, the position of the white light sensor 215 is determined (ie, determined in device coordinates). Before, or alternatively after the reference measurement, the position of the reference body 231 is determined with respect to the measuring table 201 or with respect to another reference location in the coordinate system of the CMM 211 (ie, determined in device coordinates). It is possible, for example, that before or after the Figure 1 In the illustrated coupled state of the white light sensor 215 on the sleeve 208, another sensor (e.g., a tactile probe) is coupled to the sleeve 208. The other sensor can be referred to as a reference probe or a reference sensor device. The tactile probe is then used to probe the surface of the reference body 231, thus determining the exact position at least in the Y direction and preferably also in the X and Z directions.

[0103] Via a signal line not shown, the control device 222 receives the results of the position determination by the position measuring system of the CMM 211, both during the reference measurement and optionally during probing by a tactile probe or during scanning by another sensor coupled to the CMM 211. Furthermore, the evaluation device 220 receives the measurement signals from the sensor 215 during the reference measurement. For example, both the results of the position measurement and the measurement signals from the white light sensor 215 (or signals further processed therefrom) can be provided with additional information that enables the position measurement results to be assigned to the measurement signals from the white light sensor 215 or to the further processed signals. An example of this is consecutive numbering of the value pairs or the addition of a timestamp that represents the measurement time.

[0104] The evaluation device 220 or the control device 222 determines the relationship between the measurement signals of the confocal white light sensor 215 and the actual distance of the white light sensor 215 from a measurement object 235 for the operating state of the white light sensor system, which exists when the white light sensor 215 is coupled to the CMM, from the measurement data recorded during the reference measurement, which were obtained from the measurement signals of the white light sensor 215 and from the position measuring system of the CMM 211. The linearization parameters, i.e., the results of this relationship, are stored in the data memory 221, preferably with additional information that uniquely identifies the associated white light sensor 215 for which the reference measurement was performed.

[0105] In a later measuring operation (or the calibration methods or operations explained below) of the CMM 211, a measurement object 235 or calibration object 10 is measured using the white light sensor 215 coupled to the quill 208. During measuring operation, the white light sensor 215 measures at least a distance of a surface point of the measurement object 235, and the position measuring system of the CMM 211 determines the associated position and orientation of the sensor 215, e.g., in a coordinate system (device coordinates) of the CMM 211 that is stationary with respect to the measuring table 201. The distance measured by the white light sensor 215 to the measurement object 235 is determined by the evaluation device 220, which generates at least one distance measurement value from the measurement signals of the white light sensor 215 using the linearization parameters stored in the data memory 221.This at least one measured value is then transmitted, in particular, from the evaluation device 220 to the control device 222, which also receives the position measured values ​​from the position measuring system of the CMM 211 and calculates the coordinates of the surface point of the measurement object 235 from them. An analogous procedure can also be used within the scope of the calibration method below, although a calibration object 10 is detected instead of a general measurement object 235.

[0106] Above, a linearization of the white light sensor 215 in a state directly mounted on a coordinate measuring machine 211 was explained. However, for the present calibration procedure, it is also possible to use a white light sensor 215 that has already been linearized by a manufacturer.

[0107] Not shown in Figure 1is also a calibration object in the form of a calibration sphere 10, explained in the following figures. This is positioned on the measuring table 201 of the CMM 211 instead of the reference body 231.

[0108] Furthermore, in the measuring operation described above, it was assumed that the position measuring system of the CMM 211 knows or can determine the position and orientation of the white light sensor 215 and thus also the coordinates of one or all of its focus positions, for example in device coordinates. This requires the white light sensor 215 to be calibrated as precisely as possible, in particular such that the coordinates of a measured object point for which a distance value was determined can be transformed into device coordinates (i.e., can be traced back to CMM coordinates). Figuratively speaking, calibration can be used to achieve a precise transformation of the sensor coordinate system, in which, for example, the distance value and / or a coordinate of the detected object point can be determined, into the device coordinate system, regardless of which focus position currently lies on an object area to be measured.The calibration can result in coordinates of an object point in a device coordinate system, which are recorded with different sensors (for example with the sensor device 215 to be calibrated and a reference probe), matching with sufficient accuracy.

[0109] First, based on Fig. 2 A calibration procedure is explained as it is currently common in the state of the art. Figures 2 to 5 only a section of the arrangement Fig. 1 shown, where the perspective corresponds to a top view of the measuring table 201. Furthermore, the components shown are different from the illustration in Fig. 1 partially cut and / or simplified.

[0110] In Fig. 2 First, individual components of the white light sensor 215 can be recognized without its Fig. 1recognizable bend and / or cylindrical housing parts are shown. One can see a section of the fiber optic connection 230 leading into the white light sensor 215, which is concentric to its Fig. 1 horizontally angled area. The optical fiber connection 230 has a comparatively small circular exit opening 238 with a diameter of a few micrometers. The shown section of the connection 230 defines a longitudinal axis L, along which the electromagnetic (measurement) radiation also exits, albeit at least partially at an angle thereto. The longitudinal axis L corresponds to a sensor axis of the white light sensor 215 and is perpendicular to a surface of the exit opening 238.

[0111] The white light sensor 215 further comprises sensor optics in the form of focusing optics 240. This comprises a converging lens 242, which focuses the radiation expanding from the exit opening 238. More precisely, the measuring radiation is recombined by the converging lens 242 onto the sensor axis L, specifically in such a way that it converges onto a common focus position 12 or a focus point on the sensor axis L. Both the sensor axis L and the focus position 12 are virtual or imaginary features of the sensor 215, the position and / or orientation of which, however, can be defined and / or determined via the sensor optics 240.

[0112] Since the white light sensor 215 shown is a chromatic confocal white light sensor, several focus positions 12 along the sensor axis L are defined via the sensor optics 240, namely several focus positions 12, each of which is assigned to a single wavelength of the measuring radiation and combines radiation with the corresponding wavelength in the associated focus position 12. In other words, a plurality of wavelength-specific focus positions 12 are defined. Fig. 2 By way of example, only two such focus positions 12 are shown, one of which is located exactly on the surface of the calibration sphere 10.

[0113] It can also be seen that for each of the focus positions 12, there is a beam path emanating from the exit opening 238 with at least two separately shown beams that run at an angle to the sensor axis L. The beams initially diverge until they strike the converging lens 242 and are converged by the latter onto the sensor axis L or focus position 12.

[0114] To calibrate the white light sensor 215 according to the prior art, the measuring radiation of the white light sensor 215 is directed onto the calibration sphere 10 shown in section, which forms a calibration object or calibration standard. The calibration sphere 10 is mounted on the measuring table 201 made of Fig. 1positioned and lies opposite the white light sensor 215. Analogous to the detection of the reference body 213 described above, the white light sensor 215 can be moved towards the calibration sphere 10 until a predetermined intensity of the reflected radiation is determined for a wavelength by the evaluation device 220. If this is the case, a focus position 12 associated with this wavelength lies exactly on the surface of the calibration sphere 10. The incident radiation is then at least partially reflected back onto the converging lens 242 of the focusing direction 240 and from there imaged onto the exit opening 238 and guided back into the light guide 230 and in the direction of the evaluation device 220. As described in the introduction, this is disadvantageous compared to the solution disclosed herein because, for example, radiation is detected and evaluated that is only reflected by a single point and not by a surface segment.

[0115] If a focus position 12 is positioned directly on the curved spherical surface 13, there is a high degree (and more precisely a high intensity and / or radiant power) of reflected radiation detectable by the white light sensor 215. This particularly applies to radiation with a wavelength associated with this focus position 12. If, however, the focus position 12 is not located on the spherical surface, but above it, only a smaller degree of the incident radiation is imaged back onto the opening 238 of the light guide 230. This condition is shown in Fig. 3shown, in which both focus positions 12 are located above the sphere surface 10 and, as indicated by corresponding arrows, a large portion of the irradiated measuring radiation is no longer reflected back onto the converging lens 242 and thus is not imaged onto the opening 238. Variants in which the focus position 12 is located at a distance from the measuring sphere 10 and, for example, in a cross-sectional plane thereof, have not yet been provided for in the prior art.

[0116] To calibrate the sensor device 215, according to the state of the art, Fig. 2In the manner explained, several different points on the sphere's surface are recorded and saved as coordinate values. In particular, it can be recognized that a focus position 12 lies on the sphere's surface. In this state, a distance value to the calibration sphere 10 and, from this, coordinates of the recorded point on the sphere's surface can be determined (i.e., the white light sensor 215 has already been linearized for the calibration process). To determine the coordinates, a known sphere position and, in particular, a center point position as well as a sphere center calculated from the recorded points are used, and the initially recorded point coordinates can be adjusted based on a ratio (in particular, a difference) between the known and calculated position values.If corresponding coordinate values ​​are determined for at least three different points on the sphere surface, the sphere center point coordinates of the calibration sphere 10 can be calculated from these.

[0117] In addition, the calibration sphere 10 can be made analogously to the reference body 231 Fig. 1 scanned by a known reference probe. In this way, too, coordinates of, for example, at least three surface points of the calibration sphere 10 can be determined and the coordinates of a sphere center can be calculated. The sphere center corresponds at least approximately to the actual conditions, since the properties (in particular the position and orientation) of the reference probe are known in device coordinates, and thus the coordinates of the surface points can be precisely determined.

[0118] Calibration parameters can be determined from the difference between the sphere center coordinates determined with the optical sensor device to be calibrated, in the form of the white light sensor 215, and the sphere center coordinates determined with the reference probe. In particular, the calibration parameters can be used to correct distance values ​​and / or point coordinates determined with the white light sensor 215 and / or to transform them into device coordinates. The quality of the calibration depends, for example, on the accuracy of the determined or assumed sensor direction and the linearization. Furthermore, it is known that a so-called zero position can be defined for linearized sensors (usually the center of their measuring range, where the measuring range encompasses the spectrum of detectable distance values, but in principle also any distance value within the measuring range).The zero position is further defined in such a way that its position relative to a reference point of the system is known (e.g., in the form of a difference vector), which can be determined, for example, during calibration. Measurements taken outside the zero position can be shifted in the sensor direction by the measured distance value (or its difference from the zero position distance value), for example, to determine their position in device coordinates. The farther away from the zero position the measurement is taken, the greater the influence of errors due to inaccurate linearization and / or direction determination.

[0119] However, it has been shown that this method does not always allow for sufficiently accurate calibration. Firstly, when irradiating the surface of a calibration sphere 10 (but also another calibration object with a curved surface, for example, a cylinder with a circular base), the angle of incidence W (acceptance angle) enclosed by the measuring radiation and the sensor axis L is comparatively small (see Figure 2 This can result in only a small proportion of radiation being imaged back onto the opening 238, and reaching the sphere's surface may not be immediately detected. Furthermore, the possibly only limited accuracy of detecting a plurality of points on the sphere's surface and indirectly calculating the sphere's center based on this can lead to undesirable losses in accuracy.

[0120] The embodiments of the invention described below instead provide for optically detecting a calibration object 10 having a curved surface 13 in a different way and in particular in such a way that the focus position 12 is arranged as a virtual (or imaginary) point at a distance from the curved surface 13.

[0121] This is illustrated by the representation of Fig. 4 . In simplified form, only a single focus position 12 for a single wavelength is shown there, although, analogous to the previous figures, multiple wavelengths and associated focus positions 12 are also provided. Sensor 215 is therefore again designed as a chromatic confocal sensor. Furthermore, a radius of curvature of calibration sphere 10 is smaller than a distance of focus position 12 from sensor object 240 and, in particular, converging lens 242.

[0122] You can first recognize the Figures 2 and 3explained components of the sensor device designed as a white light sensor 215 in the form of the connection 230 and the focusing optics 240. Furthermore, it can be seen, however, that the focus position 12 (or at least one of the plurality of focus positions 12) was directed or positioned on a sphere center M of the calibration sphere 10. This is equivalent to reaching a target state. The focus position 12 is thus arranged at a distance from the curved surface 13 of the calibration sphere 10. The sphere center M corresponds to a center of curvature of the spherical surface 13 convexly curved around this sphere center M. The measuring radiation thus still strikes the curved surface 13 of the calibration sphere 10, which forms the calibration object.However, in this case, the focus positions 12 are no longer located directly on the sphere surface 13, but rather a radiation component located in front of this focus position 12, this radiation being reflected by the entire irradiated surface segment of the calibration sphere 10.

[0123] In Fig. 4 It is particularly emphasized that when the focus position 12 (or one of the focus positions 12) coincides with the sphere center M, an angle R between the radiation component falling on the sphere surface 13 and this sphere surface 13 is essentially 90°. In other words, the radiation in this case strikes the sphere surface essentially perpendicularly, which, as can be seen from Figure 2 This is not the case when a focus position 12 is directly positioned on the spherical surface 13 (see angle R' in Figure 2 ). In addition, the angle of incidence to the sensor axis increases.

[0124] The inventors have recognized that with a correspondingly perpendicular alignment of the incident radiation to the object surface, a maximum radiant power of the detected retroreflected radiation is present, which can be defined as a target state (i.e., reaching the maximum value of the radiant power can be defined as a predetermined condition, the fulfillment of which indicates that the target state is reached). In the case of multiple emitted wavelengths, including the associated focus positions 12, the radiation intensity of the radiation that can be assigned to the focus position 12 that currently lies at the sphere center M is detected as the maximum.

[0125] Furthermore, in the target state according to Figure 4It can happen that radiation is reflected back into itself, for example, along the illustrated outer rays of the beam path, i.e., it is reflected along the same beam path or beam path with which these rays were directed onto the calibration sphere 10. This also results in the radiation reflected by the calibration object 10 being imaged to a maximum extent onto the opening 238, and thus a maximum radiation power can be detected.

[0126] In the target state Figure 4The sphere center coordinates can then be precisely determined. For example, the current distance value of the white light sensor 215, which was linearized during this measurement process and whose direction (i.e., orientation of the sensor axis) is known, can be calculated to obtain a vector, e.g., starting from a CMM sensor interface to the sphere center. For this purpose, one can take advantage of the fact that, as explained above, in a recorded intensity distribution of the reflected radiation, the signal for the wavelength whose focus position is in the sphere center is maximum. The distance value associated with the determined sensor measurement value or the intensity distribution and determined as part of the linearization therefore also refers to the distance to the sphere center.Preferably, the radius of the calibration sphere 10 is further selected such that, when one or all focus positions 12 are positioned close to the sphere center, no detectable radiation is reflected from it (i.e., so that the center lies outside the detection range of the sensor). If the white light sensor 215 is not linearized (but also generally when it is linearized), it can be brought into the target state with its distance value defined as the reference point (usually, the center of the measuring range explained above is defined as the zero position and thus represents the reference point). The difference between the sphere center coordinates detected at its zero results in the difference from the sphere center coordinates determined with the reference probe.

[0127] As generally explained above, the sphere center coordinates can also be determined using a reference probe or a reference sensor device and then a difference between the respectively determined sphere center coordinates can be determined in order to determine calibration parameters for the white light sensor 215 based thereon.

[0128] In the following, variants are explained with which the target state from Figure 4 can be achieved.

[0129] According to one variant, the white light sensor 215 can be moved in a straight line toward the calibration sphere 10 as part of the calibration process according to the invention. The white light sensor 215 (and / or its at least one focal point 12) can be moved along a presumed sensor axis L or an approximately determined sensor axis L by means of the precalibration explained below. This sensor axis L (or the calibration direction or axis along the approximately determined sensor axis L) can be selected such that it intersects a sphere center M determined, for example, using a reference probe. In parallel, the measurement signals of the white light sensor 215 can be monitored. If these have a predetermined and, in particular, maximum intensity and / or radiant power for the wavelength associated with the focal position 12, it can be concluded that the focal position 12 has reached a plane Q containing the sphere center M.It can also be moved iteratively multiple times in the sensor direction and at different positions perpendicular to it. This allows the reaching of plane Q and, in particular, the reaching of a center of curvature therein to be determined, e.g., from a maximum measured value determined across all movement processes. This variant is particularly relevant for purely confocal or interferometric sensor devices or if a predetermined focus position of a white light sensor 215 is to be arranged at the center of curvature M, although this is not mandatory.

[0130] Alternatively, for example, based on a rough calibration (i.e., an at least approximately known sphere center M and / or an at least approximately known focus position 12), the sensor device 215 can be positioned directly relative to the calibration sphere 10 without moving in the calibration direction and monitoring intensity changes, and this can be assumed to be a sufficiently accurate arrangement of the focus position 12 in the plane Q.

[0131] In the example shown, the plane Q is a virtual cross-sectional plane of the calibration sphere 10, which contains the sphere center M. This plane Q is orthogonal to the assumed sensor axis L or the direction of movement of the white light sensor 215. Movements within the cross-sectional plane Q are therefore always orthogonal to the direction of movement (or calibration direction) and / or to the sensor axis L. In this way, a first rough arrangement of the sensor device 215 and the calibration sphere 10 can be carried out, whereby, for example, a state analogous to the one explained below Figure 5 can be achieved.

[0132] Alternatively, during a pre-calibration, the position of the focus position 12 can be determined at least approximately or roughly, preferably in device coordinates. This can be done using the calibration from Figure 2 The same applies to the coordinates of the sphere center M, which are calculated analogously to the procedure of Fig. 2can be calculated by scanning the sphere surface 10 with a reference probe. As part of the calibration process of Fig. 4 the coordinate measuring machine 211 can be controlled in such a way that the (assumed or approximately known) focus position 12 is at least approximately located on the (assumed or approximately known) center point M of the calibration sphere 10. In this way, a first rough arrangement of the sensor device 215 and the calibration sphere 10 can also be carried out, whereby, for example, a state analogous to the one explained below Figure 5 can be achieved.

[0133] If, after the corresponding first (rough) arrangement of the sensor device 215, the coordinate measuring machine 211 detects, for example, a maximum detectable intensity of the radiation with the wavelength associated with the focus position 12, it can be assumed that the pre-calibration was already so precise that the focus position 12 was positioned directly on the center point M. In such a case, further process steps would not be absolutely necessary. Particularly in cases in which no information on the level of an absolute maximum detectable intensity (which may, for example, also depend on the properties of the calibration object) is stored, it can be provided that additional travel movements of the focus position 12 take place even with a high measured initial intensity or in principle as a result of each rough positioning. From the total determined, for example,the maximum radiation intensity and / or minimum exposure time are determined and then the achievement of the target state is detected.

[0134] However, due to the limited accuracy of the pre-calibration, there will usually be a certain offset between the focus position 12 and the sphere center M, as shown in Figure 5 This particularly concerns a lateral offset V within the cross-sectional plane Q of the calibration sphere 10 containing a sphere center M, as shown in Figure 5 is shown.

[0135] In Fig. 5 It can be seen that due to the offset V, the radiation indicated by dashed lines, which is directed to the focus position 12, is not completely imaged onto the opening 283 of the light guide connection 230, but is offset relative to it (in Fig. 5(shown significantly exaggerated). Such an offset, which enables the detection option discussed below, occurs in particular due to the inventive positioning of the focus position 12 at a distance from the surface. If the focus position 12 were positioned on the surface, a decrease in the intensity of radiation with a wavelength belonging to the focus position 12 would be detectable in the event of an offset, e.g., relative to an ideal point of incidence at a vertex of the sphere. However, it would not be possible to determine such an offset as a function of the intensity profile and in particular the possible presence of several local maxima within this profile for a large number of wavelengths, as is the case with the detection option explained below.

[0136] The condition of Figure 5leads to the fact that initially a lower than the actually expected maximum detectable radiation power of the reflected radiation is detected. In order to position the focus position 12 exactly on the sphere center M, the sensor device 215 and thus the focus position 12 can be moved relative to the calibration sphere 10 and its sphere center M by means of the coordinate measuring machine 211. In particular, the focus position 12 can be shifted within the plane Q and thus perpendicular to the sensor axis L. This continues until the target state from Figure 4 is achieved by detecting the reaching of the center point M, for example, as a maximum intensity of the detected reflected radiation with the wavelength of the focus position 12. However, if the target state is not reached, the pre-calibration can be repeated and / or the focus position 12 can be repositioned in the plane Q.

[0137] As described, the present embodiment assumes that the achievement of the target state is indicated by the presence of a maximum detectable radiant power, which in turn is signaled by the presence of a maximum intensity within a defined exposure time. Alternatively, however, the time required to reach a predetermined integrated minimum intensity can also be considered, which, for example, indicates the achievement of a maximum detectable reflected radiant power when a minimum time period is present.

[0138] Another way to recognize the achievement of the target state is described below using Figure 6 Here, one can once again see the effects of the offset V between the focus position 12 and the sphere center M, as shown in Fig. 5is shown. Due to this offset V, at a plurality of focus positions 12, as shown in the chromatic-confocal sensor device 215, radiation components with several different wavelengths enter the optical fiber connection 230 or its opening 238. In Fig. 6 only the upper part of the sensor device 215 is made of the Figures 4 and 5 shown (ie in particular not the measuring sphere 10 and the measuring radiation directed towards it).

[0139] It can be seen that due to the offset V from Figure 5Radiation belonging to a currently viewed focus position 12 is not imaged again onto the opening 238 of the optical fiber connection 230 (see the corresponding arrangement of the imaged or reflected focus position 12' relative to the opening 238). Instead, however, radiation of other wavelengths and even several different wavelengths enters the optical fiber connection 230. This involves radiation with wavelengths belonging to other focus positions and in particular to the focus positions 12b', 12c' imaged in the area of ​​the opening 238.

[0140] As stated in DE 10 2015 217 637 A1 in connection with the Fig. 4As explained, the evaluation device 220 would interpret the detection of such a plurality of reflected radiation components with different wavelengths as a reflection at different material interfaces. Within the scope of the shift of the focus position 12 in the plane Q provided according to the invention, however, it can be achieved that, analogous to the state from Fig. 4 only radiation is imaged onto the opening 238 which can be assigned to a single focus position 12 (ie only radiation with a single wavelength is imaged back onto the opening 238). From the perspective of the evaluation device 220, instead of a plurality of local intensity maxima in a detected intensity distribution of the reflected radiation, as in the case of Fig. 5present, only a single intensity maximum is present within the entire distribution. If this is the case, it can be concluded that the detected reflected radiant power can only be assigned to a single focus position 12, namely the focus position 12 that was positioned at the sphere center M. This corresponds to the state from Fig. 4 .

[0141] In summary, this can be seen from the Figures 4 and 5The method described proposes determining the position (or coordinates) of at least one of the focus positions 12 of the white light sensor 215 in device coordinates as part of an optional pre-calibration. Furthermore, the position and / or coordinates of the cross-sectional plane Q and preferably of the sphere center M can also be determined, which can also be done in device coordinates. Subsequently, as part of the actual (main) calibration process, a predetermined focus position 12 of the white light sensor 215 is positioned at the sphere center M by controlling the axes of the coordinate measuring machine 211. The measurement signal acquired in this state is then evaluated and monitored, while the focus position 12 is shifted within the cross-sectional plane Q. This continues until the achievement of a predetermined state is detected based on the measurement signals. This state corresponds to the arrangement of the focus position 12 at the sphere center M.Possibilities for detecting the achievement of this state based on the measurement signals have been explained above and relate, for example, to the level of the detected reflected intensity, a time period for reaching a predetermined integrated intensity, or the number of maxima in a determined intensity distribution. Once this state is reached, sphere center coordinates (ie, sphere center coordinates detected by the optical sensor device 315) can be determined.

[0142] It should also be mentioned that in the case of an interferometric sensor device with a lateral offset as in Fig. 6 Similar problems can occur in the sense of insufficient coupling. This manifests itself in a decrease in the contrast of the interference signal, as explained above.

[0143] If sphere center coordinates are calculated in the manner described for a plurality of focus positions 12 (ie by arranging a plurality of focus positions 12 in the sphere center M and determining the coordinates based thereon), a straight line can be formed through these focus position-specific sphere center coordinates to approximate the sensor axis L.

[0144] In Figure 6a The achievement of the target state is shown for an alternative, sectioned calibration object 10. This has a hemispherical recess 100, the base of which forms a (hemispherically) curved surface 13, which, however, still represents an outer surface of the calibration object 10. A center of curvature M is therefore located above the recess 100 and outside the calibration object 10. However, if the focus position 12 is arranged in the corresponding center of curvature M, similar reflection properties result as based on Figure 4 explained. Coordinates of this center of curvature M can also be determined by detecting the recess 100 with a reference probe, and a calibration can be performed based on the difference between the respective coordinates.

Claims

1. Method for capturing a calibration object (10) using an optical sensor device (215), which is a confocal or chromatic-confocal optical sensor device, wherein the sensor device (215) is configured to emit electromagnetic radiation at at least one wavelength and focus said radiation on a focus position (12) along a sensor axis (L), wherein the method comprises: - radiating electromagnetic radiation along the sensor axis (L) onto a curved surface (13) of the calibration object (10) and capturing radiation reflected off the curved surface (13) of the calibration object (10), the curved surface (13) being an outer surface of the calibration object (10) and the calibration object (10) being non-transparent to the radiation, - moving the sensor device (215) and the calibration object (10) relative to each other while monitoring the measurement signals created by the sensor device until the focus position (12) is arranged at a distance from the curved surface (13) and a target state is reached, in which a capturable reflected radiation power of the wavelength of the electromagnetic radiation associated with the focus position (12) fulfils a predetermined condition.

2. Method for capturing a calibration object (10) using an optical sensor device (215), which is an interferometric sensor device, wherein the sensor device (215) is configured to emit electromagnetic radiation at at least one wavelength and focus said radiation on a focus position (12) along a sensor axis (L), wherein the method comprises: - radiating electromagnetic radiation along the sensor axis (L) onto a curved surface (13) of the calibration object (10), and capturing radiation reflected off the curved surface (13) of the calibration object (10), the curved surface (13) being an outer surface of the calibration object (10) and the calibration object (10) being non-transparent to the radiation, - moving the sensor device (215) and the calibration object (10) relative to each other while monitoring the measurement signals created by the sensor device until the focus position (12) is arranged at a distance from the curved surface (13) and a target state is reached, in which a contrast ascertained on the basis of the capturable reflected radiation is maximal.

3. Method according to Claim 1 or 2, wherein the sensor device (215) is calibrated on the basis of at least one measured value that is ascertained when the target state is reached.

4. Method according to any of Claims 1 to 3, wherein the target state is reached when the focus position (12) is positioned at a centre of curvature (M) of the curved surface.

5. Method according to any of the preceding claims, wherein the radiation incident on the calibration object from different directions in a solid angle range has a radiation path that in each case is incident on the curved surface (13) at an angle to the sensor axis (L) and the target state is reached when the radiation reflected back off the calibration object (10) into the solid angle range is in each case reflected back from the curved surface (13) along the same radiation path.

6. Method according to any of the preceding claims, wherein the coordinates of the focus position (12) and of a centre of curvature (M) of the curved surface are known at least approximately in a predetermined coordinate system, and the sensor device (215) and the calibration object (10) are arranged relative to each other on the basis thereof.

7. Method according to any of the preceding claims, wherein the focus position is displaced in a plane (Q) in order to reach the target state.

8. Method according to Claim 7, wherein the plane (Q) extends orthogonally to the sensor axis (L); and / or wherein the plane (Q) extends orthogonally to an axis along which the sensor device (215) is moved in order to arrange the focus position (12) in the plane (Q).

9. Method according to any of the preceding claims, wherein the predetermined condition is one of the following: - an intensity of the captured reflected radiation at the least one wavelength reaches a predetermined threshold value and / or is maximal; - a time required to achieve a predetermined integrated intensity value of captured reflected radiation at the at least one wavelength reaches a predetermined threshold value and / or is minimal; - the captured reflected radiation power can be assigned to only one of a plurality of focus positions (12) and / or to only the at least one wavelength; - the contrast of an interference signal ascertained on the basis of the reflected radiation, which is ascertained as an interference property, is maximal and / or reaches a predetermined threshold value.

10. Method according to any of the preceding claims, wherein the sensor device (215) comprises a plurality of focus positions (12), and the method is performed for at least two different focus positions (12), and wherein position information is ascertained during each iteration of the method when the target state is reached, and an alignment of the sensor axis (L) is determined on the basis of all of the ascertained position information.

11. Method according to any of the preceding claims, wherein an alignment of the sensor axis (L) and the coordinates of a centre of curvature (M) of the curved surface (13) are known at least approximately in a predetermined coordinate system, and the sensor device (215) and the calibration object (10) are arranged relative to each other on the basis thereof.

12. Arrangement, having: - a positioning system (211), - a calibration object (10) having at least one curved surface (13); - an optical sensor device (215) which is a confocal or chromatic-confocal optical sensor device and configured to emit electromagnetic radiation at at least one wavelength and focus said radiation on a focus position (12) along a sensor axis (L); and - a control device that is configured to cause the arrangement to perform the following measures: • radiating electromagnetic radiation along the sensor axis (L) onto a curved surface (13) of the calibration object (10), and capturing radiation reflected off the curved surface (13) of the calibration object (10), the curved surface (13) being an outer surface of the calibration object (10) and the calibration object (10) being non-transparent to the radiation, • moving the sensor device (215) and the calibration object (10) relative to each other while monitoring the measurement signals created by the sensor device until the focus position (12) is arranged at a distance from the curved surface (13) and a target state is reached, in which a capturable reflected radiation power of the wavelength of the electromagnetic radiation associated with the focus position (12) fulfils a predetermined condition.

13. Arrangement, having: - a positioning system (211), - a calibration object (10) having at least one curved surface (13); - an optical sensor device (215) which is an interferometric sensor device and configured to emit electromagnetic radiation at at least one wavelength and focus said radiation on a focus position (12) along a sensor axis (L); and - a control device that is configured to cause the arrangement to perform the following measures: • radiating electromagnetic radiation along the sensor axis (L) onto a curved surface (13) of the calibration object (10), and capturing radiation reflected off the curved surface (13) of the calibration object (10), the curved surface (13) being an outer surface of the calibration object (10) and the calibration object (10) being non-transparent to the radiation, • moving the sensor device (215) and the calibration object (10) relative to each other while monitoring the measurement signals created by the sensor device until the focus position (12) is arranged at a distance from the curved surface (13) and a target state is reached, in which a contrast ascertained on the basis of the capturable reflected radiation is maximal.