GB2600548A - Apparatus and method for capturing a spatial position of a body - Google Patents

Abstract

The invention relates to an apparatus 10 for capturing a spatial position of a body (measuring element 26), having a first light source 32, which is configured to emit a first light beam; a second light source 34, which is configured to emit a second light beam, which is aligned at an angle that is not equal to 0° with respect to the first light beam; a target element 46 with at least one retroreflector 40, wherein the target element with the at least one retroreflector is configured to reflect the first light beam as a first retroreflected light beam 42 and to reflect the second light beam as a second retroreflected light beam 44; a reception unit 56 with at least one spatially resolving sensor 48,50, wherein the reception unit with the at least one spatially resolving sensor is configured to detect the first retroreflected light beam and to generate, based thereon, a first spatially resolved signal and to detect the second retroreflected light beam and to generate, based thereon, a second spatially resolved signal; and having an evaluation unit 30, which is configured to determine, based on the first and the second spatially resolved signal, the spatial position of the body.

Description

Apparatus and Method for Capturing a Spatial Position of a Body [0001] The present invention relates to an apparatus for capturing a spatial position of a body. The present invention further relates to a measurement appliance having the apparatus according to the invention. The present invention furthermore also relates to a corresponding method for capturing a spatial position of a body.

[0002] An intended field of application of the present invention is the application in measurement appliances for dimensionally measuring measurement objects. For example, the apparatus according to the invention can be used in a coordinate measuring machine to capture the spatial position of a body or component part of the coordinate measuring machine relative to another body or component part of the coordinate measuring machine.

[0003] Measurement appliances, in particular coordinate measuring machines having tactile and/or optical measuring sensors, are typically used in dimensional metrology in order to determine the shape of a workpiece surface, for example by probing. Since dimensional metrology generally finds application in branches of industry in which very high accuracies are required, for example for subsequent processing steps or for quality assurance, error-free implementation of measurements is necessary.

[0004] Coordinate measuring machines for industrial use generally have quite a complex design to reliably ensure the desired accuracies during the measurement. Coordinate measuring machines typically have a plurality of driven shafts having corresponding guides. Typically, measurement standards, which make the determination of absolute and/or relative positions and movement of a moving measuring head of the coordinate measuring machine possible, are assigned in shafts or the guides thereof. In other words, it is thus possible using the measurement standards to ascertain the position of the measuring head, which is usually freely or multidimensionally movable with the aid of the plurality of driven shafts within the measurement volume of the coordinate measuring machine.

[0005] The measuring head has one or more sensors, which can be designed for example as tactile and/or optical sensors, for measuring the measurement object. Frequently, further kinematic systems for moving a part of the sensor or of the sensors are located within the measuring head. To ascertain what is known as the tool centre point (TCP), it is therefore additionally necessary to ascertain the position of a measuring sensor element of the sensor relative to a base part of the measuring head. This base part can be, for example, a part of the measuring head that itself is movable by way of the driven shafts of the coordinate measuring machine, but does not additionally move together with the sensor element of the sensor. Said sensor element can be, for example, a tactile stylus or a part of a measurement optical unit.

[0006] It is thus ultimately possible to uniquely ascertain the position of the tool centre point in any desired coordinate system from the position of the base part of the measuring head, which is ascertainable for example via said measurement standards, and the relative position of the sensor element relative to the base part.

[0007] However, due to the complexity of such coordinate measuring machines, it is never possible to entirely avoid measurement errors in the previously mentioned position ascertainment. By taking corresponding precautions, however, such measurement errors can be minimized (to a few micrometres or even nanometres) using today's coordinate measuring machines.

[0008] Provided that the sensor or probe element is connected to the base part of the measuring head via one or more serially stacked translation or rotation shafts, the tool centre point can be ascertained relatively easily in a conventional manner.

[0009] For various advantageous reasons, however, attempts have been made to replace such serial kinematic systems in the measuring head with parallel kinematic systems. DE 10 2019 115 630 B3 discloses, for example, a swivel probe having a spherical parallel kinematic system.

[0010] Although such parallel kinematic systems offer some advantages when used in a measuring head of a coordinate measuring machine, their use makes the ascertainment of the position of the tool centre point far more difficult. The position must be calculated by a kinematic transformation of the position of the individual axes of the parallel kinematic system. Even if the kinematic system is known as much as possible, some uncertainty when ascertaining the tool centre point must be expected. This is why it is appropriate in such a case to determine the position of the tool centre point directly using an alternative measurement method.

[0011] US 9,599,456 B2 discloses a measurement method and a measurement apparatus, in which the position of a sensor or probe element is ascertained in one direction with a first sensor using an optical method and in a second direction using a distance sensor. Even the application of this method in the abovemenfioned case of using a parallel kinematics system in the measuring head of a coordinate measuring machine is useful only to a limited extent.

[0012] Other methods, such as optical navigation or a multilateration method, are conceivable in general. However, these methods are computationally very intensive and (so far) cannot be evaluated in real time.

[0013] It is therefore an object of the present invention to provide an apparatus and a method for capturing a spatial position of a body, which enables accurate and direct ascertainment of the position of the body in as simple a way as possible. The method according to the invention and the apparatus according to the invention are intended to be suitable in particular for use in the previously mentioned applications but are not intended to be restricted to these applications, and rather generally enable the ascertainment of the spatial position of a body in relation to another one or in relation to a fixed reference point or reference element.

[0014] This object is achieved by an apparatus according to Claim 1, having the following components: a first light source, which is configured to emit a first light beam; a second light source, which is configured to emit a second light beam, which is aligned at an angle that is not equal to 00 with respect to the first light beam; a target element with at least one retroreflector, wherein the target element with the at least one retroreflector is configured to reflect the first light beam as a first retroreflected light beam and to reflect the second light beam as a second retroreflected light beam; a reception unit with at least one spatially resolving sensor, wherein the reception unit with the at least one spatially resolving sensor is configured to detect the first retroreflected light beam and to generate, based thereon, a first spatially resolved signal, and to detect the second retroreflected light beam and to generate, based thereon, a second spatially resolved signal; and an evaluation unit, which is configured to determine, based on the first and the second spatially resolved signal, the spatial position of the body.

[0015] The object is furthermore achieved by a method according to Claim 17, having the steps of: emitting a first light beam; emitting a second light beam, which is aligned at an angle that is not equal to 00 with respect to the first light beam; reflecting the first light beam as a first retroreflected light beam, which has a substantially spatially parallel offset with respect to the first light beam; reflecting the second light beam as a second retroreflected light beam, which has a substantially spatially parallel offset with respect to the second light beam; detecting the first retroreflected light beam and generating a first spatially resolved signal having position information relating to the first retroreflected light beam, based on the first retroreflected light beam; detecting the second retroreflected light beam and generating a second spatially resolved signal having position information relating to the second retroreflected light beam, based on the second retroreflected light beam; and determining the spatial position of the body based on the first and the second spatially resolved signal.

[0016] A further aspect of the present invention relates to a measurement appliance, for example a coordinate measuring machine, a roughness measurement appliance, a microscope, etc., wherein the measurement appliance has an apparatus according to the invention of the aforementioned type.

[0017] The apparatus according to the invention and the method according to the invention are characterized in particular by the following features: At least two light beams, which are preferably each in the form of focused, straight-line (collimated) light beams, are generated via corresponding light sources. The two light beams are aligned at an angle with respect to one another. The two light beams preferably enclose an acute angle. They are aligned towards a target element with at least one retroreflector. This retroreflector reflects the two light beams as retroreflected light beams, which are then detected by a reception unit with at least one spatially resolving sensor. By performing an evaluation within the evaluation unit, the spatial position of the body can be determined from the positions or locations at which the retroreflected light beams are incident on the at least one spatially resolving sensor.

[0018] Preferably, either of the two light sources or the target element with the at least one retroreflector are arranged at the body to be measured, and the respectively other part (the two light sources or the target element) is arranged at a reference part, whose position is known. For example, the two light sources can be arranged at the reference part and the target element with the at least one retroreflector can be arranged at the body to be measured. It is likewise possible for the two light sources to be arranged at the body to be measured and for the target element with the at least one retroreflector to be arranged at the reference part.

[0019] In this way, the relative position of the body to be measured in relation to the reference part can be determined with the aid of the apparatus according to the invention and the method according to the invention. Once the relative position of the reference part, which itself can likewise be moved or is fixed, is known, it is also possible to determine the absolute position of the body to be measured.

[0020] Using the apparatus according to the invention and the method according to the invention, the three-dimensional position of the body is determined preferably as Cartesian or spherical coordinates within any desired reference coordinate system. For ascertaining the orientation and thus the pose of the body, a plurality of such apparatuses or at least a plurality of retroreflectors would be necessary.

[0021] The measurement principle of the apparatus according to the invention and of the method according to the invention is, among other things, based on the fact that the locations at which the two retroreflected light beams are incident on the at least one spatially resolving sensor change both with a change in the relative position and also with a change in the relative orientation between the two light sources and the target element. It is therefore possible, using trigonometric relationships, to calculate the position of the at least one retroreflector in relation to the two light sources from the positions of the two retroreflected light beams on the at least one spatially resolving sensor.

[0022] The angled position of the two light beams relative to one another is necessary for the three-dimensional position determination because two parallel light beams would provide the "same information" and thus lead to an underdetermination of the system of equations used for the calculation.

[0023] Using the apparatus according to the invention and the method according to the invention, very exact measurements can be performed in a comparatively simple and cost-effective way. Owing to the principles involved, the apparatus according to the invention and the method according to the invention are very sensitive with respect to minor displacements or tilts of the at least one retroreflector in relation to the light sources. In the case of greater displacements, the sensitivity of the apparatus according to the invention and of the method according to the invention decrease, however. The method according to the invention is therefore primarily suitable for very exact measurements of the position of a body that moves only slightly or within a relatively small space.

[0024] The at least one retroreflector is configured to reflect the first light beam and the second light beam, independently of an alignment of the at least one retroreflector in relation to the first light beam and the second light beam, in each case such that the first retroreflected light beam has a substantially spatially parallel offset with respect to the first light beam and the second retroreflected light beam has a substantially spatially parallel offset with respect to the second light beam.

[0025] "Substantially spatially parallel" in the present case is understood to mean a parallel alignment that includes minor deviations by +/-3°. This is because retroreflectors, in mathematical terms, reflect the light beams in an exactly spatially parallel manner but this is almost impossible to be realized experimentally. Owing to the construction or to manufacturing tolerances, minor deviations will occur in practice.

[0026] The at least one retroreflector thus has the property of reflecting light in a parallel manner, but not on itself. The retroreflected beam is thus always spatially parallel with respect to the incident beam, and this is independent of how the at least one retroreflector is inclined and/or positioned in relation to the light source.

[0027] Using such a retroreflector, however, rotational information is lost, because a pure rotation of the retroreflector relative to the light beam does not bring about a change in the retroreflected light beam.

[0028] The loss of the rotational information would at first glance actually be considered to be a disadvantage. However, this property has de facto the advantage that the signals generated by the at least one spatially resolving sensor are not "falsified" by rotations of the at least one retroreflector or the light sources. The evaluation of the signals provided by the at least one spatially resolving sensor and the position determination of the body within the evaluation unit are thus more easily possible.

[0029] Such a retroreflector can have a lens element reflector, a cat's eye, a Luneburg lens element, a corner reflector, a triple mirror, a corner cube, a triple prism, a retroreflective film, or a reflex reflector. For example, the retroreflector can have two mutually perpendicular mirrors. A corner cube comprises, for example, three flat, mutually perpendicular mirrors.

[0030] According to a preferred configuration of the present invention, the first and the second light beam enclose an angle of greater than 15°. This increases the stability and robustness of the calculation of the position of the body.

[0031] According to a further configuration, the at least one spatially resolving sensor has a first spatially resolving sensor and a second spatially resolving sensor, wherein the first spatially resolving sensor is configured to detect the first retroreflected light beam and to generate, based thereon, the first spatially resolved signal, and wherein the second spatially resolving sensor is configured to detect the second retroreflected light beam and to generate, based thereon, the second spatially resolved signal.

[0032] Two spatially resolving sensors, that is to say one sensor per light source, have a plurality of advantages compared to only one spatially resolving sensor detecting both light beams. Firstly, it offers a cost advantage, because the two spatially resolving sensors can then have a smaller design, and a plurality of small sensors are cheaper than one large high-resolution sensor. In addition, it is thereby possible to make the installation space of the apparatus according to the invention smaller, because the sum of the surface areas of the two spatially resolving sensors can in this case be smaller than the total surface area of a single spatially resolving sensor.

[0033] If a single spatially resolving sensor is used, much of the sensor surface area is wasted at any rate. Furthermore, a further advantage of using a plurality of individual sensors lies in the fact that each light source or each light beam is assigned a single sensor, which means that there is no need to additionally differentiate between the light beams or retroreflected light beams on the sensors.

[0034] According to a further configuration, the apparatus according to the invention furthermore has a third light source, which is configured to emit a third light beam, wherein the target element with the at least one retroreflector is configured to reflect the third light beam as a third retroreflected light beam, wherein the reception unit with the at least one spatially resolving sensor is configured to detect the third retroreflected light beam and to generate, based thereon, a third spatially resolved signal, and wherein the evaluation unit is configured to determine, based on the first, the second and the third spatially resolved signal, the spatial position of the body.

[0035] Thus, in this configuration, three light sources rather than the previously mentioned two light sources are used. Each further light source adds additional stability in the calculation of the position of the body, because additional position information flows into the calculation by way of the third retroreflected light beam or the third spatially resolved signal that is generated thereby.

[0036] If three light sources are used, it is preferred that the at least one spatially resolving sensor has a first spatially resolving sensor, a second spatially resolving sensor and a third spatially resolving sensor, wherein the first spatially resolving sensor is configured to detect the first retroreflected light beam and to generate, based thereon, the first spatially resolved signal, and wherein the second spatially resolved sensor is configured to detect the second retroreflected light beam and to generate, based thereon, the second spatially resolved signal, and wherein the third spatially resolved sensor is configured to detect the third retroreflected light beam and to generate, based thereon, the third spatially resolved signal.

[0037] Accordingly, it is preferred even in the case of three light sources that each light source or each retroreflected light beam is assigned a spatially resolving sensor in order to, as mentioned previously, save costs and installation space and to more easily differentiate between the retroreflected light beams.

[0038] Independently of the number of the light sources and the associated number of the spatially resolving sensors, it is preferred that the spatially resolving sensors are aligned in each case orthogonally to the retroreflected light beams to be detected. This simplifies the detection and increases the accuracy of the calculation of the position of the body.

[0039] According to a further configuration, provision is made for the first spatially resolving sensor, the second spatially resolving sensor and the third spatially resolving sensor to be arranged at equal distances from one another.

[0040] This again simplifies the calculation of the position of the body.

[0041] According to a further configuration, provision is made for the first light beam to be aligned at a first angle relative to the second light beam and at a second angle relative to the third light beam, wherein the first angle is identical to the second angle.

[0042] For example, two light sources may be aligned at the same angle with respect to one another and the third light source Of provided) may be aligned at a different angle with respect to the two other light sources. This saves space in the arrangement.

[0043] With particular preference when using three light sources, the second light beam is aligned at a third angle relative to the third light beam, wherein the first angle, the second angle and the third angle are identical.

[0044] So, in this case, all three light sources are aligned at an identical angle with respect to one another. This again simplifies the calculation of the position of the body, because it is hereby possible to simplify the trigonometric relationships used for the calculation.

[0045] As was already mentioned in the introductory part, preferably either the at least one retroreflector or the light sources is/are arranged at the body to be measured and the respectively other part (retroreflector or light sources) is arranged at a reference part, whose position is known. With particular preference, the at least one retroreflector is arranged at the body.

[0046] This has the advantage that the body to be measured consequently does not have to be attached to cables, because the at least one retroreflector is typically a passive component part that does not need to be supplied with power. By contrast, the light sources are active component parts that typically need to be supplied with power.

[0047] According to a further configuration, the first light beam has a first coding feature and the second light beam has a second coding feature, which differs from the first coding feature.

[0048] The aforementioned coding features can be, for example, different wavelengths/colours of the light beams. The coding features can likewise be temporally dependent features that are brought about for example due to different timing cycles.

[0049] Independent of the manner in which the coding features are produced, such coding features have the advantage that it is easier to differentiate between the light beams or the retroreflected light beams. This is particularly true in the event that only a single spatially resolving sensor is provided, rather than a spatially resolving sensor being assigned to each individual retroreflected light beam [0050] According to a further preferred configuration, the first and the second light beams each comprise coherent and/or collimated light. It goes without saying that the third light beam (if present) also comprises coherent and/or collimated light. The light sources are preferably laser light sources.

[0051] As already mentioned in the introductory part, the evaluation unit is preferably configured, based on the first and the second spatially resolved signal, by using trigonometric relationships, which include an angle of the first light beam relative to the second light beam, an angle of the first light beam relative to a central axis and an angle of the second light beam relative to the central axis.

[0052] If three light sources or three light beams are used, the trigonometric relationships used for the calculation preferably include the angle of the first light beam relative to the second light beam, an angle of the first light beam relative to the third light beam, and the respective angles of the light beams to the central axis.

[0053] On this basis alone it becomes evident that the trigonometric relationships and thus also the entire calculation can be simplified, as mentioned above, by arranging the light sources at equal distances and at identical angles with respect to one another.

[0054] The apparatus according to the invention is preferably used in a measurement appliance for measuring a measurement object. For example, the measurement appliance can be a coordinate measuring machine, a roughness measurement appliance or a microscope. Further measurement appliances for dimensionally measuring a measurement object are likewise conceivable.

[0055] The measurement appliance preferably has a base part and a measurement element for measuring a geometric property of the measurement object, wherein the measurement element is movable with respect to the base part, and wherein the first and the second light sources are arranged at the base part and the at least one retroreflector is arranged such that it moves together with the measurement element with respect to the base part.

[0056] Said base part consequently corresponds to the previously mentioned reference part, whose position in space is permanently known, with the result that, in this case, the apparatus according to the invention can be used to calculate the relative position of the measurement element with respect to the base part and thereby the absolute position of the measurement element in space is known. The measurement element can be, for example, a tactile measurement element, such as a stylus, or an optical measurement element (for example a camera).

[0057] If used in a coordinate measuring machine, the apparatus according to the invention can be arranged, for example, in a measurement sensor that is used for the tactile and/or optical measurement of a measurement object and is arranged at a free end of a quill. In this case, the light sources and the spatially resolving sensors can be arranged, for example, at the base part of the measurement sensor that moves along with the quill, whereas the at least one retroreflector is fixedly connected to the tactile and/or optical measurement element.

[0058] It goes without saying that the aforementioned features and those yet to be explained below can be used not only in the combination specified in each case but also in other combinations or on their own, without departing from the scope of the present invention.

[0059] It also goes without saying that the previously mentioned features mentioned in relation to the apparatus according to the invention also relate, in an equivalent manner, to the measurement appliance having the apparatus according to the invention. The features defined in the dependent claims in relation to the apparatus according to the invention also relate, in an equivalent manner, to the method according to the invention. The method according to the invention consequently has the following equivalent design possibilities.

[0060] According to a configuration, the first and the second light beam enclose an angle of greater than 15°.

[0061] According to a further configuration, the first retroreflected light beam is detected by a first spatially resolving sensor and the second retroreflected light beam is detected by a second spatially resolving sensor.

[0062] According to a further embodiment, the method additionally has the steps of: emitting a third light beam; reflecting the third light beam as a third reflected light beam, which has a substantially spatially parallel offset with respect to the third light beam; detecting the third retroreflected light beam and generating a third spatially resolved signal having position information relating to the third retroreflected light beam, based on the third retroreflected light beam; and determining the spatial position of the body based on the first, the second and the third spatially resolved signal.

[0063] According to a further configuration, the first retroreflected light beam is detected by a first spatially resolving sensor, the second retroreflected light beam is detected by a second spatially resolving sensor and the third retroreflected light beam is detected by a third spatially resolving sensor.

[0064] According to a further configuration, the three spatially resolving sensors are arranged at equal distances from one another.

[0065] According to a further configuration, the light sources emitting the light beams are arranged at equal distances from one another.

[0066] According to a further configuration, the first light beam is aligned at a first angle relative to the second light beam and at a second angle relative to the third light beam, wherein the first angle is identical to the second angle. According to a further configuration, the second light beam is aligned at a third angle relative to the third light beam, wherein the first angle, the second angle and the third angle are identical.

[0067] According to a further configuration, the first light beam has a first coding feature and the second light beam has a second coding feature, which differs from the first coding feature.

[0068] According to a further configuration, the light beams each comprise coherent and/or collimated light.

[0069] According to a further configuration, the spatial position of the body is determined based on the first and the second spatially resolved signal, by using trigonometric relationships, which include an angle of the first light beam relative to the second light beam, an angle of the first light beam relative to a central axis and an angle of the second light beam relative to the central axis.

[0070] Exemplary embodiments of the disclosure are illustrated in the drawings and will be explained in more detail with reference to the following description. In the drawings: Fig. 1 shows a schematic illustration of a first exemplary embodiment of a measurement appliance, in which the apparatus according to the present invention can be used; Fig. 2 shows a perspective view of a second exemplary embodiment of the apparatus according to the invention used in a swivel probe having a parallel kinematic system; Fig. 3 shows a schematic view for illustrating the basic setup of the apparatus according to the invention in accordance with an exemplary embodiment; Fig. 4 shows a schematic view for illustrating the schematic setup of the apparatus according to the invention in accordance with a further exemplary embodiment; Fig. 5 shows a top view of the schematic diagram illustrated in Fig. 4; Fig. 6 shows a schematic illustration of the effective principle of a retroreflector used in the apparatus according to the invention; and Fig. 7 shows a block diagram for illustrating the procedure of the method according to the invention.

[0071] Fig. 1 shows a coordinate measuring machine as an example of a measurement appliance, in which the apparatus according to the invention can be used. The coordinate measuring machine is denoted as a whole by the reference sign 100. The apparatus according to the invention, which acts as an integral part of said coordinate measuring machine 100, is denoted as a whole by the reference sign 10.

[0072] The coordinate measuring machine 100 has a base 12. A gantry 14 is arranged on the base 12 such that it is displaceable in the longitudinal direction. The base 12 is preferably a stable plate, which is produced from granite, for example. The gantry 14 serves as a movable carrier structure. The gantry 14 has two columns projecting upward from the base 12, which are connected by a crossbeam and have an inverted U-shape overall.

[0073] The direction of movement of the gantry 14 in relation to the base 12 is usually referred to as the Y-axis. A carriage 16, which is displaceable in the transverse direction, is arranged on the upper crossbeam of the gantry 14. This transverse direction is usually referred to as the X-direction. The carriage 16 carries a quill 18, which is movable in the Z-direction, that is to say perpendicularly to the base 12.

[0074] Measurement devices on the basis of which the X-, Y-and Z-positions of the gantry 14, the carriage 16 and the quill 18 can be determined are denoted by the reference signs 20, 20', 20". The measurement devices 20, 20', 20" are typically glass rulers, which serve as measuring scales. These measuring scales are designed in conjunction with corresponding reading heads (not shown here) to determine the respectively current position of the gantry 14 in relation to the base 12, the position of the carriage 16 in relation to the upper crossbeam of the gantry 14 and the position of the quill 18 in relation to the carriage 16.

[0075] A measuring head 22 is disposed at a lower, free end of the quill 18. The measuring head 22 has a measurement sensor 24 having a measurement element 26 for probing a measurement object 28 that is to be measured. The measurement sensor 24 in the present exemplary embodiment is a tactile measurement sensor 24 having a tactile stylus 26 as measurement element, on the lower end of which a probe ball 52 is arranged with which the measurement object 28 is probed. The probe ball 52 is produced from a ruby sphere, for example.

[0076] When contact-probing a multiplicity of measurement points on the measurement object 28, position information is transmitted either wirelessly or using one or more cables by the measuring head 22 to a control unit 30 of the coordinate measuring machine 100. The control unit 30 is also designated as evaluation unit. It determines the spatial coordinates of the respective measurement point, with the result that the geometry of the measurement object 28 can be calculated for example by evaluating a multiplicity of measurement points.

[0077] In the exemplary embodiment shown in Fig. 1, the apparatus 10 according to the invention serves for determining the spatial position of the measurement element 26 relative to the gantry 14. However, it goes without saying that this is merely one arbitrary application out of numerous possible applications of the apparatus 10 according to the invention.

[0078] Associated with the apparatus 10 according to the invention are a first light source 32 and a second light source 34. The two light sources 32, 34 can each be laser light sources, for example. They each generate a straight-lined light beam 36, 38.

[0079] The two light sources 32, 34 are aligned with respect to one another such that the first light beam 36 produced by the first light source and the second light beam produced by the second light source 34 are aligned at an angle to one another (i.e. are not parallel). The two light beams 36, 38 are aligned towards a retroreflector 40, which in the exemplary embodiment shown in Fig. 1 is arranged at the tactile measurement element 26 and is fixedly connected thereto.

[0080] The retroreflector 40 has the property that it reflects back the incident light beams 36, 38 largely independently of the direction of incidence and the alignment of the retroreflector 40 substantially in a manner such that they have a spatially parallel offset. In other words, the retroreflector 40 reflects the first light beam 36 as a first retroreflected light beam 42, which is substantially spatially parallel to the first light beam 36. In the same way, the second light beam 38 is reflected back by the retroreflector 40 as a second retroreflected ray 44, which is substantially spatially parallel to the second light beam 38. In other words, the two light beams 36, 38 are reflected back by the retroreflector 40 in each case in the same direction but not in themselves, but in each case parallel to the incident rays. Details concerning the setup and principle of the retroreflector 40 will be mentioned below with reference to Fig. 6.

[0081] The retroreflector 40 is part of a target element 46 of the apparatus 10. In principle, this target element 46 can also have a plurality of retroreflectors 40. In the exemplary embodiment shown in fig.1, the target element 46, however, has only one retroreflector 40. In this case, the target element 46 even consists of the retroreflector 40. However, it goes without saying that further attachments or fastening means can belong to the target element 46.

[0082] The light beams 42, 44 reflected by the retroreflector 40, which are referred to as the first and second retroreflected light beams 42, 44, are each incident on a spatially resolving sensor 48, 50. The spatially resolving sensors 48, 50 are preferably in each case a photodetector, which can have, for example, one or more CMOS sensors. In other words, it is a two-dimensional area detector (for example a camera chip), which makes it possible to accurately determine the respective position at which the retroreflected light beam 42 or 44 is incident on the sensor 48, 50. The two retroreflected light beams 42, 44 thus generate in each case a spatially resolved signal on the spatially resolving sensors 48, 50.

[0083] These spatially resolved signals are transmitted wirelessly or using one or more cables to the evaluation unit 30. The evaluation unit 30 is configured to determine, based on these spatially resolved signals, the spatial position of the target element 46 and thus of the measurement element 26 in relation to the gantry 14. In the exemplary embodiment shown in Fig.1, the measurement element 26 is thus the body whose position is determined with the aid of the apparatus 10 according to the invention.

[0084] This position determination can take place for example instead of or in addition to the position determination that is performed with the aid of the measurement devices 20, 20', 20". For example, the apparatus 10 according to the invention can be used to correct or check the coordinates that are measured with the aid of the measurement devices 20, 20', 20". It is likewise conceivable that the measurement element 26 is a swivel probe that can be swivelled with respect to the quill in one or more further degrees of freedom. In such a case, the absolute position of the measurement ball 52 can be determined with the aid of the apparatus according to the invention.

[0085] The apparatus 10 according to the invention is particularly advantageous if a swivel probe with a parallel kinematic system is used in the measuring head 22. Such an exemplary embodiment is shown schematically in Fig. 2. In this case the apparatus 10 according to the invention is used to determine the position of the measurement element 26, or more specifically of the measurement ball 52, in relation to the base part 54 of the measurement sensor 24 fastened to the quill 18.

[0086] Unlike in the first exemplary embodiment shown in Fig. 1, the target element 46, which has the retroreflector 40, and the light sources 32, 34, and also the reception unit 56, which has the two spatially resolving sensors 48, 50, are then located at the measuring head 22. The apparatus 10 according to the invention in this exemplary embodiment is thus entirely integrated into the measuring head 22. This in particular has the advantage that in this case significantly smaller deflections and shifts in position need to be measured than is the case in comparison with the first exemplary embodiment. This in turn is particularly advantageous because the apparatus 10 according to the invention is suitable in particular for an exact measurement of comparatively smaller positional changes.

[0087] The probe shown in Fig. 2 is designed as a swivel probe 25. This swivel probe 25 allows an additional movement of the stylus 26 or of the probe ball 52 in relation to the base part 54. This additional movement of the probe ball 52, which takes place in addition to the movements of the gantry 14, of the carriage 16 and of the quill 18, is determined with the aid of the apparatus 10 according to the invention. The component parts of the apparatus 10 used for this purpose are the same as the component parts explained previously with respect to the exemplary embodiment shown in Fig. 1.

[0088] The swivel probe 25 has a rotor part 58 that is movable with respect to the base part 54. The probe element 26 is fastened to the rotor part 58 or is integrally connected thereto. The rotor part 58 is coupled to the base part 54 via a spherical parallel kinematic system 60. The rotor part 58 and thus the probe element 26 can be swivelled three-dimensionally in space with respect to the base part 54 almost arbitrarily with the aid of said spherical parallel kinematic system.

[0089] Unlike in sequentially constructed, linear kinematic systems, a position determination of the probe element 26 or of the probe ball 52 in such spherical parallel kinematic systems, but also in other parallel kinematic systems, is possible only to a very limited extent or with difficulty. Typically, an attempt is made in this case to determine the position of the probe ball 52 based on the signals of the position transmitters, which are integrated into the drives of the parallel kinematic system. However, this requires an exact kinematic model and a corresponding calibration of the spherical parallel kinematic system. Nevertheless, such conventional position measurements are accurate only to a highly limited extent and are typically hardly suitable for use in highly precise coordinate measuring machines.

[0090] The advantage of the use of the apparatus 10 according to the invention is thus that it can be used to measure the position of the rotor part 58 in relation to the base part 54 "directly" and, consequently, highly accurately. The body, whose position is measured with the aid of the apparatus 10 in this exemplary embodiment, is thus the rotor part 58 with the probe element 26 arranged thereon.

[0091] The two light sources 32, 34 are for this purpose arranged at the base part 54. The reception unit 50 with the two spatially resolving sensors 48, 50 is likewise also arranged at the base part 54. The target element 46 with the retroreflector 40, by contrast, is fixedly connected to the rotor part 58 or the probe element 26.

[0092] The principle of measurement remains unchanged. As is summarized in the block diagram from Fig. 7, the two light beams 36, 38 are emitted by the light sources 32, 34 and directed onto the retroreflector 40 (steps Si and S2). These light beams 36, 38 are then reflected back in a substantially spatially parallel manner as retroreflected light beams 42, 44 (steps 33 and 34). The retroreflected light beams 42, 44 are detected by the spatially resolving sensors 48, 50, wherein the sensors 48, 50 generate corresponding spatially resolved signals (steps 35 and 36). These spatially resolved signals are dependent on the position of the retroreflector 40. The positions at which the retroreflected rays 42, 44 are incident on the sensors 48, 50 thus change in other words with the position and orientation of the retroreflector 40. Using trigonometric relationships, it is thus possible in step S7 to determine the spatial position of the retroreflector 40 and thus also of the rotor part 58 or of the probe element 26 including the probe ball 52 from the spatially resolved signals generated by the sensors 48, 50.

[0093] Fig. 3 again shows the measurement setup of the apparatus 10 according to the invention in a schematic illustration. As can be seen, the two spatially resolving sensors 48, 50 are aligned preferably orthogonally to the respective direction of the retroreflected light beams 42, 44. The stars 60 indicated on the sensors 48, 50 each indicate the point of incidence of the respective retroreflected light beam 42, 44 on the respective sensor 48, 50. These points of incidence 60 change as soon as the position of the retroreflector 40 changes. By contrast, the points of incidence 60 do not change if the retroreflector 40 rotates about its central axis 62. In other words, changes only occur in the case of tilting or translational displacements of the retroreflector. Purely rotational information of the retroreflector 40 is thus lost, but this is generally advantageous because the generated spatially resolved signals are not falsified by the rotation of the retroreflector 40 and the position evaluation is thus easier.

[0094] Fig. 6 shows a basic illustration from which it becomes clear how the position of the point of incidence of the first retroreflected light beam 42 on the first spatially resolving sensor 48 changes if the position of the retroreflector 40 changes. Fig. 6 shows the retroreflector 40 in two different positions, wherein it is denoted by the reference sign 40' in its second position. The second position of the retroreflector 40' differs from the first position of the retroreflector 40, among other things, in a translational offset, denoted by the distance d. Due to the properties of the retroreflector 40, 40', a translational change in position of the retroreflector 40, 40' by the distance d leads to a change in position of the point of incidence 60 on the spatially resolving sensor 48 that is twice as large. So, if the retroreflector 40, 40' is translafionally displaced along an axis, the retroreflected light beam 42, 42' or the point of incidence on the spatially resolving sensor 60, 60' is displaced by twice the distance. This property must correspondingly be taken into account in the position calculation according to the invention.

[0095] A calculation example for calculating the position will be explained below with reference to a third exemplary embodiment, which is schematically illustrated in Fig. 4 and 5. In contrast to the previously mentioned exemplary embodiment, a third light source 64 is provided here, which emits a third light beam 66, which is reflected by the retroreflector 40 as a third retroreflected light beam 68. The position of the third retroreflected light beam 68 is detected by a third spatially resolving sensor 70. All three spatial resolving sensors 48, 50, 70 are, as before, aligned preferably perpendicularly to the respective retroreflected light beams 42, 44, 68. The light sources 32, 34, 64 are preferably arranged at equal distances from one another. The light sources 32, 34, 64 are preferably arranged such that the light beams 36, 38, 66 are mutually aligned at the same angle. All three light beams in this exemplary embodiment are inclined with respect to the central axis or the perpendicular 62 at an angle f3= 22.5° (see Fig. 3). As is clear from the top view shown in Fig. 5, the three light beams 36, 38, 66 are offset with respect to one another by in each case 120° in the top view. The angle between the first light beam 36 and the second light beam 38 is denoted below by (112 and the angle between the first light beam 36 and the third light beam 66 is denoted below by (p3. A further angle, which is the rotation angle for the first light beam 36 about the central axis 62, is the angle pi, which, however, is not shown in Fig. 5 because the direction of the first light beam 36 in this calculation example is used as a reference direction and the angle (Nis thus 00.

[0096] The positions of the points of incidence 60 of the retroreflected light beams 42, 44, 68 on the sensors 48, 50, 70 will be indicated in the following calculation example in each case in two-dimensional x-, y-coordinates and denoted by x,,n and ys,n, wherein "n" is the respective sensor number. The sensor 48 is given the sensor number n = 1; the sensor 50 is given the sensor number n = 2; and the sensor 70 is given the sensor number n = 3. The origin of the sensor coordinate system is here respectively selected to be in the sensor centre. The origin of the sensor system is here for each of the sensors 48, 50, 70 preferably selected such that, at a retroreflector position x = 0, y = 0, z = 0 of the retroreflector 40, the retroreflected light beams 42, 44, 68 are incident on the sensors 48, 50, 70 in the respective origins of the sensor coordinate system.

[0097] In the following calculation example, the retroreflector 40 moves in a coordinate system in which the sensors 48, 50, 70 are considered to be "fixed". The coordinate system of the retroreflector 40 thus does not move in relation to the sensors 48, 50, 70. The movement of the retroreflector 40 in the retroreflector coordinate system is indicated by xp, yp and zp along the respective axes of the coordinate system.

[0098] For the definition of the system of equations to be solved, it is firstly described how the reflected ray 42, 44, 68 detected on the respective sensor 48, 50, 70 mathematically comes into existence. Based on the geometric relationships, the reflected ray 42, 44, 48 detected on the respective sensor can be calculated from the following relationships.

= 2 * (xp * cos(q) + Yp * sin(Pn)) , and ysin = 2 * ((-xp sin(con) + yp cos((pn)) cos(f3) + zp sin(f0) [0099] The factor 2 in the above relationships is due to the fact that the respective retroreflected rays 42, 44, 68 are displaced, as previously mentioned with reference to Fig. 6, by twice the offset d of the retroreflector 40.

[00100] Rewritten, the above equations give the following system of equations: 2 * cos(q) 2 * sin(con) 0 xP sin() * cos() 2 * cos((pn) * cos() sin(p)). (zYP) [00101] The unknowns to be ascertained here are thus xp, yp and zp. In the abovementioned arrangement with yl = 0°, (p2 = 120° and cp3 = 240° and with fJ = 22.5°, at a position of the retroreflector 40 [0.2, -0.3, 0.5], the following sensor signals are obtained xs,1 = 0.4, ys,i = -0.937, Xs2 = -0.7196, ys2 = -0.4256, xs,3 = 0.3196, ys,3 = 0.2145, and the system of equations to be solved thus reads as follows: /2 0 1.8478 1.7321 -0.9239 -1.7321 -0.9239 0 \ * (P / 0.4000 \ I -0.9370 -0.7196 -0.4256 0 -0.7654 Yp) = z 0.3196 / -1 0 \ 0.2145 / -1.6 -0.7654 -1 0 \ 1.6 -0.7654/ [00102] Solving this system of equations gives the previously mentioned position of the retroreflector 40 [0.2, -0.3, 0.5]. As can be seen, the system of equations is overdetermined. The same system of equations or calculation principle can therefore also be used with only two light sources and two light beams, as are shown in Fig. 1-3. To solve the abovementioned overdetermined system of equations, it is recommended to use known strategies for solving overdetermined systems of equations, such as Newton-Gauss, Levenberg-Marquardt or Householder, which will not be discussed in more detail here.

[00103] In the abovementioned calculation example it is assumed that the inclination angle f3 of each light beam 36, 38, 66 and the rotation angles (pn and of course the sensor signals of the spatially resolving sensors 48, 50, 70 are known. In practice, the inclination and rotation angles p, (pn can be ascertained for example by a prior calibration of the apparatus 10. The sensor signals are actively measured.

[00104] In the abovementioned calculation example, it was assumed that the spatially resolving sensors 48, 50, 70 do not move. However, this need not necessarily be the case. The variation of the sensor position and the variation of the sensor/light beam viewing direction can likewise be incorporated in the calculation, if necessary. This is merely a further known factor that can be ascertained by calibration.

[00105] It should likewise be pointed out that, in the apparatus 10 according to the invention, not necessarily every retroreflected light beam must be assigned a dedicated spatially resolving sensor. In principle, a single spatially resolving sensor may also detect all retroreflected light beams. This does not change the abovementioned system of equations. Merely a slightly different origin of the sensor coordinate system is then selected. Preferably, this origin is then selected in the intersection point of the central axis 62 with the sensor. In such an event of using merely a single sensor, it is furthermore advantageous to colour-code, or code in a different way, the individual light beams so as to be able to uniquely differentiate between them on the sensor.

[00106] In addition, it should also be noted that the alignment of the spatially resolving sensors orthogonally to the retroreflected light beams to be detected in each case does not necessarily have to be orthogonal if a plurality of sensors are used. An inclined position of said sensors can easily be taken into account in the abovementioned calculation.

[00107] Finally, it should be noted that the apparatus according to the invention can be used in numerous further exemplary applications. It is not limited to being used in coordinate measuring machines. The purpose of use within a coordinate measuring machine can also be different than was indicated in the abovementioned exemplary embodiments.

Claims (1)

1. Claims 1. Apparatus (10) for capturing a spatial position of a body (26, 58), having: a first light source (32), which is configured to emit a first light beam (36); a second light source (34), which is configured to emit a second light beam (38), which is aligned at an angle that is not equal to 0° with respect to the first light beam (36); a target element (46) with at least one retroreflector (40), wherein the target element (46) with the at least one retroreflector (40) is configured to reflect the first light beam (36) as a first retroreflected light beam (42) and to reflect the second light beam (38) as a second retroreflected light beam (44); a reception unit (56) with at least one spatially resolving sensor (48, 50), wherein the reception unit with the at least one spatially resolving sensor (48, 50) is configured to detect the first retroreflected light beam (42) and to generate, based thereon, a first spatially resolved signal, and to detect the second retroreflected light beam (44) and to generate, based thereon, a second spatially resolved signal; and an evaluation unit (30), which is configured to determine, based on the first and the second spatially resolved signal, the spatial position of the body (26, 58) 2. Apparatus according to Claim 1, wherein the at least one retroreflector (40) is configured to reflect the first light beam (36) and the second light beam (38), independently of an alignment of the at least one retroreflector (40) in relation to the first light beam (36) and the second light beam (38), in each case such that the first retroreflected light beam (42) has a substantially spatially parallel offset with respect to the first light beam (36) and the second retroreflected light beam (44) has a substantially spatially parallel offset with respect to the second light beam (38).3. Apparatus according to Claim 1 or 2, wherein the first and the second light beam (36, 38) enclose an angle of greater than 15°.4. Apparatus according to one of Claims 1-3, wherein the at least one spatially resolving sensor has a first spatially resolving sensor (48) and a second spatially resolving sensor (50), wherein the first spatially resolving sensor (48) is configured to detect the first retroreflected light beam (42) and to generate, based thereon, the first spatially resolved signal, and wherein the second spatially resolving sensor (50) is configured to detect the second retroreflected light beam (44) and to generate, based thereon, the second spatially resolved signal.5. Apparatus according to one of Claims 1-3, which furthermore has a third light source (64), which is configured to emit a third light beam (66), wherein the target element (46) with the at least one retroreflector (40) is configured to reflect the third light beam (66) as a third retroreflected light beam (68), wherein the reception unit (56) with the at least one spatially resolving sensor (48, 50, 70) is configured to detect the third retroreflected light beam (68) and to generate, based thereon, a third spatially resolved signal, and wherein the evaluation unit (30) is configured to determine, based on the first, the second and the third spatially resolved signal, the spatial position of the body (26, 58).6. Apparatus according to Claim 5, wherein the at least one spatially resolving sensor has a first spatially resolving sensor (48), a second spatially resolving sensor (50) and a third spatially resolving sensor (70), wherein the first spatially resolving sensor (48) is configured to detect the first retroreflected light beam (42) and to generate, based thereon, the first spatially resolved signal, and wherein the second spatially resolving sensor (50) is configured to detect the second retroreflected light beam (44) and to generate, based thereon, the second spatially resolved signal, and wherein the third spatially resolving sensor (70) is configured to detect the third retroreflected light beam (68) and to generate, based thereon, the third spatially resolved signal.7. Apparatus according to Claim 6, wherein the first spatially resolving sensor (48), the second spatially resolving sensor (50) and the third spatially resolving sensor (70) are arranged at equal distances from one another.8. Apparatus according to one of Claims 5-7, wherein the first light source (32), the second light source (34) and the third light source (64) are arranged at equal distances from one another.9. Apparatus according to one of Claims 1-8, wherein the first light beam (36) is aligned at a first angle relative to the second light beam (38) and at a second angle relative to the third light beam (66), and wherein the first angle is identical to the second angle.10. Apparatus according to Claim 9, wherein the second light beam (38) is aligned at a third angle relative to the third light beam (66), and wherein the first angle, the second angle and the third angle are identical.11. Apparatus according to one of Claims 1-10, wherein the at least one retroreflector (40) is arranged at the body (26, 58).12. Apparatus according to one of Claims 1-11, wherein the first light beam (36) has a first coding feature and the second light beam (38) has a second coding feature, which differs from the first coding feature.13. Apparatus according to one of Claims 1-12, wherein the first and the second light beams (36, 38) each comprise coherent and/or collimated light.14. Apparatus according to one of Claims 1-13, wherein the evaluation unit (30) is configured, based on the first and the second spatially resolved signal by using trigonometric relationships, which include an angle of the first light beam (36) relative to the second light beam (38), an angle of the first light beam (36) relative to a central axis (62) and an angle of the second light beam (38) relative to the central axis (62).15. Measurement appliance (100) for measuring a measurement object (28), wherein the measurement appliance (100) has an apparatus (10) according to one of Claims 1 to 14.16. Measurement appliance according to Claim 15, which furthermore has a base part (54) and a measurement element (26) for measuring a geometric property of the measurement object (28), wherein the measurement element (26) is movable with respect to the base part (54), and wherein the first and the second light sources (32, 34) are arranged at the base part (54) and the at least one retroreflector (40) is arranged such that it moves together with the measurement element (26) with respect to the base part (54).17. Method for capturing a spatial position of a body (26, 58), having the steps of emitting (Si) a first light beam (36); emitting (52) a second light beam (38), which is aligned at an angle that is not equal to 0° with respect to the first light beam (36); reflecting (53) the first light beam (36) as a first retroreflected light beam (42), which has a substantially spatially parallel offset with respect to the first light beam (36); reflecting (54) the second light beam (38) as a second retroreflected light beam (44), which has a substantially spatially parallel offset with respect to the second light beam (36); detecting (55) the first retroreflected light beam (42) and generating a first spatially resolved signal having position information relating to the first retroreflected light beam (42), based on the first retroreflected light beam (42); detecting (S6) the second retroreflected light beam (44) and generating a second spatially resolved signal having position information relating to the second retroreflected light beam (44), based on the second retroreflected light beam (44); and determining (S7) the spatial position of the body (26, 58) based on the first and the second spatially resolved signal.