Method and apparatus for determining the coordinates of a workpiece using a coordinate measuring machine

Abstract

Method for determining the coordinates of a workpiece (13) using a coordinate measuring machine, wherein - spatially three-dimensional camera image data of a workpiece (13) are recorded by a 3D camera (10) while the workpiece (13) is located in a measuring volume of the coordinate measuring machine, - by means of an additional coordinate measuring device (12) of the coordinate measuring machine, the workpiece (13) is scanned in the measuring volume, - by evaluating the results of the scanning, the coordinates of the workpiece (13) are determined, - in addition to or as an alternative to the workpiece (13), the 3D camera captures an area of ​​the measurement volume in which the workpiece (13) is not located, and spatially three-dimensional camera image data of the measurement volume are recorded, wherein the camera image data of the measurement volume are evaluated and thereby the presence of an object or body part that is not desired or permitted in the measurement volume is detected, characterized in that - the area of ​​the measurement volume is also measured thermographically and, based on the results of the thermographic measurement, an undesirable or unauthorized body part of a person is detected in the measurement volume, and a corresponding warning signal or control signal is generated if both the results of the thermographic measurement and the evaluation of the camera image data of the measurement volume indicate the presence of the body part.

Description

[0001] The invention relates to a method for determining the coordinates of a workpiece using a coordinate measuring machine. The workpiece is scanned by a coordinate measuring device of the coordinate measuring machine while the workpiece is located in a measuring volume of the coordinate measuring machine. The coordinates of the workpiece are determined by evaluating the results of the scanning. The invention further relates to an arrangement for determining the coordinates of a workpiece, comprising a coordinate measuring machine, a coordinate measuring device of the coordinate measuring machine, and an evaluation device configured to evaluate the results of the scanning of the workpiece and to determine the coordinates of the workpiece.

[0002] Determining the coordinates of a workpiece can also be referred to as measuring the workpiece. A method for the non-contact measurement of object surfaces is described, for example, in DE 4026942 A1. A video camera, which is attached to a measuring arm of a coordinate measuring machine via a rotary / swivel joint, captures camera images of the object from several different positions. The images captured in the different positions are saved and evaluated with respect to the coordinates of characteristic points on the object surface using the spatial forward incision method known from photogrammetry. The position values ​​provided by the scales of the coordinate measuring machine and the angle measurements provided by the rotary / swivel joint are used to determine the camera orientation.In particular, a computer is capable of evaluating camera images from different angular positions and positions of the camera to clearly calculate three-dimensional object coordinates from the supplied position measurement values, the angle measurement values ​​and the image data supplied by an image processing device.

[0003] Although this method allows for reliable, non-contact measurement of objects, the effort required to generate camera images from different positions is relatively high. Furthermore, despite high precision in determining the position and angle measurements, the relationship between the different camera images can only be established with a geometric error. There are also cases where tactile scanning of the workpiece using a probe is preferable. For example, recesses and undercuts can be detected this way.

[0004] WO 02 / 25207 A1 describes a method for measuring an object geometry captured by an optical sensor and displayed as image content. Geometric structures suitable for measuring the object are selected from the image content and then evaluated. When the image content changes, it is automatically searched for geometric structures suitable for measuring the object, and the suitable structures are marked and made available for further analysis.

[0005] In contrast to the method according to DE 4026942 A1, the method according to WO 02 / 25207 A1 not only determines the object geometry from the image data, but also determines the geometric structures suitable for measuring the object. However, the disadvantages described above apply equally.

[0006] DE 10 2012 103 627 A1 describes a method for limiting the movement of a sensor in a coordinate measuring machine. In addition to a measuring sensor, at least one additional sensor is present, which may be a 3D sensor. This is intended to prevent a collision between the coordinate measuring machine or the measuring sensor and a measuring object during measurement.

[0007] DE 10 2010 014 423 A1 describes a method for measuring coordinates of a workpiece, wherein a workpiece arranged in a measuring range of a coordinate measuring machine is automatically detected and a measuring procedure assigned to the detected workpiece is automatically started.

[0008] DE 10 2009 030 644 A1 describes a non-contact detection device for three-dimensionally capturing the surface of an object using a light-capturing camera and a thermographic camera. An evaluation device links the image data from the light-capturing camera with the image data from the thermographic camera. This enables a human observer, e.g., when displaying the image information on a screen, to identify critical and vulnerable areas on operating machines and systems.

[0009] DE 10 2007 053 546 A1 describes a coordinate measuring machine in which a tactile and / or optical sensor extends from a spindle to measure a workpiece. A detection sensor is assigned to the sensor, which detects a possible collision with the sensor.

[0010] DE 102011 119 012 A1 relates to a coordinate measuring system with a portable measuring device that has a stylus for probing a workpiece. The portable measuring device has a position change sensor for recording position change data of the portable measuring device.

[0011] It is an object of the present invention to provide a method for determining the coordinates of a workpiece using a coordinate measuring machine, which enables rapid detection of a workpiece or other objects arranged in the measuring volume of a coordinate measuring machine, while minimizing geometric errors due to the detection. Furthermore, a person's body part should be reliably detected within the measuring volume.

[0012] It is proposed to use, in addition to a coordinate measuring device of the coordinate measuring machine, with which the workpiece is scanned in the measuring volume (optically, tactilely or in another way), a 3D camera by means of which camera image data of a workpiece, a part thereof or at least a partial area of ​​the measuring volume is recorded.

[0013] A 3D camera is understood to be a camera that is capable of recording a three-dimensional image of the object without changing the relative position of the camera and a recording object. In particular, the 3D camera is designed to capture not only an image value (e.g., gray value of a grayscale corresponding to the intensity of the incident electromagnetic radiation, or e.g., color values ​​corresponding to the intensities of colors in a color space of the incident electromagnetic radiation) for a plurality of sensor elements of a sensor matrix, but also a spatial dimension that corresponds to the viewing direction of the sensor element and thus the 3D camera to the object. For example, the spatial dimension can be specified by a distance value that corresponds to the distance of the sensor element or another reference point or reference plane of the camera (e.g.,the plane of a lens or lens arrangement or a focal point) to the area of ​​the object surface detected by the sensor element. Alternatively, the spatial dimension can be specified, for example, by a value of a depth profile of an object surface of the object, which is normalized to a point on the object surface. If, for example, the camera detects a flat object surface from a viewing direction that is perpendicular to the flat object surface, and the flat surface has a local depression, e.g. in the form of a hole, the sensor elements of the 3D camera that detect the depression would in any case be assigned a greater detected distance or a greater profile depth than the sensor elements that detect the flat area of ​​the surface.

[0014] In particular, the 3D camera has a single, continuous detector surface that is used to capture depth information in addition to the radiation intensity. Therefore, there is no combination of multiple detector surfaces spaced apart from each other perpendicular to the camera's viewing direction. Although depth information could also be determined using multiple detector surfaces according to the stereoscopic principle, this requires at least two sensor elements per image element, which capture the object surface from different viewing angles. This also results in a greater width of the arrangement perpendicular to the viewing direction. Especially with narrow depressions and unfavorable lighting conditions, the depressions cannot be captured with the same reliability in terms of their depth as with a 3D camera with a single detector surface.

[0015] One type of camera that can be used as a 3D camera for the purposes of the invention is commonly referred to as a TOF (Time-Of-Light) camera. In addition to the radiation intensity (e.g., grayscale or color values), the time of flight of radiation is also measured. The time of flight of the radiation is reflected from the 3D camera or a separate radiation source coupled to the camera onto the object to be detected and reflected from the object to the matrix of sensor elements. The time of flight is determined separately for each sensor element to which depth information is to be assigned.

[0016] Another type of 3D camera that can be used, for example, for the purposes of the present invention is the plenoptic camera, also called a light field camera. In this case, the incident radiation intended for an assigned sensor element of the sensor matrix is ​​analyzed with regard to the direction of incidence using optical elements (e.g., lens gratings). For example, an area with multiple sensor elements (e.g., an area with 3 x 3 sensor elements in a square arrangement) is used to analyze the direction of incidence. In the example mentioned, therefore, only a portion of the existing sensor elements of the sensor matrix contribute to the spatial resolution of the camera image perpendicular to the viewing direction. In contrast to stereoscopic arrangements, however, only a single sensor element or a single area of ​​sensor elements is required to determine the radiation intensity.With today's highly integrated semiconductor detector matrices for image acquisition, very high resolutions can still be achieved despite the reduced resolution. In a conventional manner, the desired depth information can be obtained from the areas of sensor elements assigned to a resulting image element.

[0017] In one variant of the light-field camera, different images of the object are projected simultaneously onto one of several sub-areas of the same matrix of sensor elements. The focal point of the projections on the different sub-areas is different. From this, too, the information about the depth (i.e., the spatial dimension in the direction of view of the camera) can be calculated for each individual pixel of the resulting image.

[0018] It is proposed:

[0019] A method for determining coordinates of a workpiece using a coordinate measuring machine, wherein - spatially three-dimensional camera image data of a workpiece are recorded by a 3D camera while the workpiece is located in a measuring volume of the coordinate measuring machine, - the workpiece is scanned in the measuring volume by means of an additional coordinate measuring device of the coordinate measuring machine and - the coordinates of the workpiece are determined by evaluating the results of the scanning, - in addition to or as an alternative to the workpiece, the 3D camera captures an area of ​​the measuring volume in which the workpiece is not located, and spatially three-dimensional camera image data of the measuring volume are recorded, whereby the camera image data of the measuring volume are evaluated and the presence of an object or body part that is not desired or permitted in the measuring volume is detected, - the area of ​​the measuring volume is also measured thermographically and a body part of a person that is not desired or permitted in the measuring volume is detected from the results of the thermographic measurement and a corresponding warning signal or control signal is generated if both the results of the thermographic measurement and the evaluation of the camera image data of the measuring volume indicate the presence of the body part.

[0020] Furthermore, an arrangement for determining coordinates of a workpiece is proposed, the arrangement comprising: - a coordinate measuring machine having a measuring volume in which workpieces can be scanned by means of a coordinate measuring device of the coordinate measuring machine in order to determine the coordinates of the respective workpiece, - a 3D camera for recording spatially three-dimensional camera image data, wherein the 3D camera has a detection area that lies at least partially in the measurement volume, - an evaluation device configured to evaluate both the results of the scanning of the workpiece and the camera image data and to determine the coordinates of the workpiece at least from the results of the scanning of the workpiece, wherein the 3D camera is configured to capture, in addition to or alternatively to the workpiece, an area of ​​the measurement volume in which the workpiece is not located and to record spatially three-dimensional camera image data of the measurement volume, wherein the evaluation device is configured to evaluate the camera image data of the measurement volume and thereby detect the presence of an object or body part that is not desired or permitted in the measurement volume, wherein the arrangement comprises a thermographic measuring device for thermographically measuring the area of ​​the measurement volume and the evaluation device is configured,to detect a body part of a person that is not desired or permitted in the measurement volume from the results of the thermographic measurement, and a signal generating device of the arrangement is designed to generate a corresponding warning signal or control signal if both the results of the thermographic measurement and the evaluation of the camera image data of the measurement volume indicate the presence of the body part.

[0021] A key advantage of using both a 3D camera and an additional coordinate measuring device is the speed of workpiece measurement, including preparation for the measurement process. This is especially true when a non-tactile sensor (e.g., an additional camera) is used for the coordinate measuring device. In particular, the 3D camera can be used to easily document the measurement results obtained by the additional coordinate measuring device and, in particular, to assign them to the correct areas of the workpiece.

[0022] Another advantage of using the 3D camera is that the position and / or orientation of the workpiece within the measurement volume can be determined from the three-dimensional camera image data. This position and / or orientation is essential for the correct execution of measurement sequences, especially predefined measurement sequences, using the additional coordinate measuring device.

[0023] As already mentioned, at least a partial area of ​​the measurement volume can be recorded by the 3D camera as an alternative or in addition to the workpiece, so that corresponding spatially three-dimensional camera image data is obtained. In particular, the recording of camera image data of the workpiece and / or the measurement volume or partial area of ​​the measurement volume can be carried out continuously and / or repeatedly. In this way, changes in the state in the measurement volume can be determined, for example as described in WO 02 / 25207 A1. For example, the workpiece can move in the measurement volume (e.g. when it is moved by a moving device such as a turntable), the 3D camera can move or the recorded area can change due to a zoom process and / or another object (e.g. a person's hand) can enter the measurement volume, move within the measurement volume or leave the measurement volume.

[0024] The spatial three-dimensional camera image data obtained by the 3D camera can therefore be used in different ways to determine the coordinates of the workpiece from the results of scanning the workpiece using the coordinate measuring device.

[0025] In particular, by evaluating the spatial three-dimensional camera image data - the workpiece and / or at least a part of the workpiece is detected or - it is determined that the workpiece and / or part of the workpiece is not present.

[0026] This corresponds to a design of the arrangement, whereby the evaluation device evaluates the spatially three-dimensional camera image data - detects the workpiece and / or at least part of the workpiece or - detects that the workpiece and / or part of the workpiece is not present.

[0027] In particular, the workpiece can be recognized based on structural features. Once a structural feature, e.g. a hole, a projection or a specific shape feature, has been recognized based on the camera image data, an associated process for measuring the workpiece using the coordinate measuring device can be automatically executed by a controller of the coordinate measuring machine. For example, the corresponding process is loaded from a data memory and executed by a computer controller of the coordinate measuring machine. The evaluation of the camera image data can also be used to check an already made selection of a predetermined process sequence for measuring the workpiece using the coordinate measuring device and optionally to correct it or replace it with another process. The process is also understood to mean, in particular, that a part of the coordinate measuring device corresponding to the process is used. e.g.a specific predefined button or optical sensor assigned to the process.

[0028] In particular, by evaluating the camera image data of the workpiece, it is also possible to detect missing features of the workpiece, such as a missing hole. Measures to be taken in such a situation will be described in more detail below. For example, this can prevent a probe of the coordinate measuring machine from being moved into the hole or other recess, which would otherwise collide with the surface of the workpiece at excessively high movement speed due to the missing hole or recess.

[0029] Verifying or automatically selecting a predefined measuring process based on the evaluation of the three-dimensional camera image data of a workpiece is particularly advantageous when manufacturing different types of workpieces. The respective type of workpiece can be automatically identified based on the three-dimensional camera image data. Alternatively or additionally, the position and / or orientation of the workpiece relative to the coordinate measuring device can be automatically identified, and a predefined measuring process can be started and executed according to the identified position and / or orientation. This can significantly reduce personnel costs.

[0030] Generally speaking, when a workpiece and / or at least part of the workpiece is detected, or when it is determined that the workpiece and / or part of the workpiece is not present, information from the camera image data relating to a spatial dimension in the viewing direction of the 3D camera can be compared with prior information about the workpiece (e.g. by the evaluation device). In other words, the above-mentioned depth information is compared with the prior information about the workpiece. In this way, it is possible, in particular, to dispense with or to check complex image data processing methods in which the image values ​​of a two-dimensional image are evaluated with regard to the radiation intensity (e.g. gray values ​​or color values). In order toTo detect object edges, special algorithms must be used which are prone to errors in unfavorable lighting situations or with structural features that are difficult to detect. DE 4026942 A1, for example, mentions evaluation methods for digital image analysis, such as threshold, gradient, or correlation methods (column 5, lines 40 ff. of the document). In contrast, when evaluating the depth information, a depth profile of the workpiece's surface can be directly compared with the prior information. Edges can be extracted directly from the depth profile. It is also possible to compare the information on radiation intensity additionally obtained by the 3D camera (i.e., the image values, such as gray values ​​or color values) with the depth information.If there is an unexpected deviation between the position of the material edge, which was obtained from the information on the radiation intensity, and the position of the edge according to the depth information, a corresponding warning signal can be issued and / or the determination of the position from the radiation intensity can be corrected. For example, the edges of a depression or hole can be reliably determined from the information on the radiation intensity under favorable lighting conditions. However, under unfavorable lighting conditions (e.g., light incidence at large angles to the longitudinal direction of the hole), the depth information of the spatial three-dimensional camera image data is much more reliable. This is particularly true for TOF cameras, where the radiation used to determine the time of flight onto the workpiece falls on the workpiece from the direction of the 3D camera.If the 3D camera is aligned approximately in the direction of the longitudinal axis of the bore, the bore is reliably captured.

[0031] In order to be able to relate the spatially three-dimensional camera image data of the workpiece or at least a partial area of ​​the measurement volume to the coordinate system of the coordinate measuring device, it is preferred that the relationship between the coordinate system of the 3D camera and the coordinate measuring device is known and / or can be determined from the measuring systems of the coordinate measuring machine, which are also used for evaluating the scanning of a workpiece by the coordinate measuring device. Examples of this are given in the aforementioned DE 4026942 A1, in particular column 3, lines 29 ff. In more general terms, the 3D camera can, for example, be attached to a movable part of the coordinate measuring machine to which the coordinate measuring device or a part thereof is also attached. By calibrating the arrangement, e.g.Using a calibration object with a high degree of accuracy regarding its geometry and / or orientation, the relationship between the two coordinate systems, or at least a possible relationship, can be determined. In the latter case, changes in the relationship can then preferably be determined from the measuring systems of the coordinate measuring machine. The determination of the relationship is generally referred to as registration.

[0032] In particular, by evaluating the spatially three-dimensional camera image data, a digital 3D model of at least part of the surface of the workpiece can be determined, and the results of scanning the workpiece by means of the additional coordinate measuring device can be assigned to areas of the surface of the workpiece using the digital 3D model. In particular, the geometric relationship between the coordinate system of the digital 3D model and the coordinate system of the coordinate measuring device can be used for the assignment. If, for example, a partial area of ​​the surface of the workpiece is scanned using the coordinate measuring device, this known relationship of the coordinate systems can be used to identify a corresponding surface area in the digital 3D model or in additional preliminary information (e.g., a CAD model of the workpiece), and the measurement results in this area can be assigned.

[0033] With regard to the arrangement, this corresponds to the evaluation device determining a digital 3D model of at least part of the surface of the workpiece by evaluating the spatially three-dimensional camera image data and assigning the results of the scanning to areas of the surface of the workpiece by means of the additional coordinate measuring device.

[0034] In particular, the accuracy of the 3D model can be improved by mapping the scan results using the additional coordinate measuring device. For example, if more precise coordinate information has been obtained for a portion of the workpiece surface represented by the 3D model using the coordinate measuring device, this more precise information can be incorporated into the digital 3D model. In this way, the spatial accuracy can be improved and / or the spatial resolution of the model can be refined.

[0035] A digital 3D model created by evaluating the spatial, three-dimensional camera image data can be used alternatively or additionally to define a subsequent process for measuring the workpiece using the coordinate measuring machine. For example, the 3D model can be presented to the user in a visually perceptible manner, allowing the user to define the measuring process and / or select a predefined measuring process based on the visual representation. For example, the measuring process can be defined in the form of a program for a computer control of the coordinate measuring machine, and a predefined measuring program can be selected. Compared to defining a measuring process directly on the workpiece, the effort required by the user is significantly reduced.

[0036] More generally defined, a digital 3D model of at least a portion of the workpiece's surface can be determined by evaluating the spatially three-dimensional camera image data, and the scanning of the workpiece by means of the additional coordinate measuring device can be planned and / or specified based on the 3D model. Regarding the arrangement, this corresponds to the evaluation device being configured to determine and output a digital 3D model of at least a portion of the workpiece's surface by evaluating the spatially three-dimensional camera image data, and to receive user inputs regarding the scanning of the workpiece by means of the additional coordinate measuring device and to control the scanning accordingly.

[0037] Furthermore, alternatively or additionally, the digital 3D model obtained by evaluating the spatially three-dimensional camera image data can be used to represent various areas of the workpiece measured using the coordinate measuring device as measurement results, corresponding to their actual spatial arrangement. This was previously only possible if appropriate prior information, in particular a three-dimensional CAD model, was available. In particular, the areas measured using the coordinate measuring device can be assigned to individual areas of the digital 3D model, thus establishing the geometric relationship between the various measured areas.

[0038] In particular, the 3D camera can be used alternatively or additionally to monitor the measuring volume, e.g. for collision monitoring. For example, the spatial three-dimensional camera image data of the workpiece can be obtained from the 3D camera before and / or during scanning of the workpiece by the coordinate measuring device, and an unintentional collision of the additional coordinate measuring device with the workpiece can be predicted from the camera image data before the collision occurs. An example has already been described above with regard to a bore. In particular, to predict the collision, a predetermined measuring process is evaluated, and from this, the movement of the coordinate measuring device corresponding to the measuring process is determined. However, it can also be determined simply from the fact that an expected structural feature of the workpiece is not present (e.g.the hole mentioned above) and the structural feature is to be scanned, it can be concluded that a collision may occur when attempting to scan the structural feature.

[0039] In one embodiment of the arrangement, the evaluation device is designed to calculate in advance from the spatial three-dimensional camera image data of the workpiece an unintentional collision of the coordinate measuring device with the workpiece before the collision occurs.

[0040] In particular, the above-mentioned digital 3D model, which was determined by evaluating the spatial three-dimensional camera image data, can be used to predict the collision.

[0041] With regard to the arrangement, a design is proposed in which the evaluation device calculates an unintentional collision of the coordinate measuring device with the workpiece from the spatial three-dimensional camera image data of the workpiece before the collision occurs.

[0042] As already mentioned, and according to the appended claims, the 3D camera captures an area of ​​the measuring volume in addition to or alternatively to the workpiece, whereby the area can also be equal to the entire measuring volume or can contain the entire measuring volume. The captured area of ​​the measuring volume is one in which the workpiece is not located. The 3D camera records spatially three-dimensional camera image data of the measuring volume, evaluates the camera image data of the measuring volume and thereby detects the presence of an object or body part that is not desired or permitted in the measuring volume. In particular, additional objects can be located in the measuring volume or at a location in the measuring volume that is unsuitable for a measuring process to be carried out.One example is a holder for a probe or optical sensor, which can be interchangeably mounted on the coordinate measuring machine to measure the workpiece. A probe head with sensors for tactile or optical measurement of the workpiece can also be held by such a holder. This example shows that the coordinate measuring device can have different parts and can also be formed from combinations of several parts. Alternatively or in addition to at least one probe for tactile probing of the workpiece, the coordinate measuring device can, for example, have a probe head, a rotating device (e.g., a rotary / swivel joint) for rotating the probe, the probe head, or the optical sensor, at least one other type of measuring device (e.g., an optical sensor, perhaps another camera), and / or other devices known per se for the coordinate measurement of workpieces.In particular, all these devices can be moved by the coordinate measuring machine relative to the workpiece.

[0043] With regard to the arrangement, this corresponds to an embodiment in which the 3D camera is aligned, in addition to or alternatively to the workpiece, to an area of ​​the measuring volume in which the workpiece is not located, wherein the evaluation device is designed to evaluate the camera image data of the measuring volume and thereby to detect the presence of an object or body part that is not desired or permitted in the measuring volume.

[0044] Even if an object or body part that is not desired or permitted in the measuring volume is detected, the collision with the object or body part can be predicted. With regard to possible embodiments of the prediction, reference is made to the embodiments already described in connection with a collision between a coordinate measuring machine and a workpiece. As in this case, the collision with an object other than the workpiece or a body part can be avoided by the evaluation device that predicts the collision outputting a signal to the control of a movement device of the coordinate measuring machine in order to carry out the movement differently or to stop it. Alternatively, the signal can be output from the evaluation device to a central control of the coordinate measuring machine, which can, for example,Movement sequences for measuring the workpiece are calculated in advance and, after receiving the signal, a movement sequence is calculated that does not lead to a collision.

[0045] In particular, in general terms, a warning signal or control signal can be generated if a collision has been predicted and / or an unwanted object or unauthorized object or body part has been detected in the measuring volume.

[0046] For monitoring the measurement volume and / or for collision monitoring, at least one additional 3D camera can optionally be used. This camera is located at a different position relative to the measurement volume and is oriented in a different viewing direction. This allows, for example, the measurement volume to be completely monitored and / or the workpiece to be captured from multiple sides by 3D cameras. However, regardless of whether one or more 3D cameras are used, it is preferred that at least one 3D camera be mounted on the same movable part of the coordinate measuring machine where the additional coordinate measuring device is located.Therefore, the 3D camera and the additional coordinate measuring device of the coordinate measuring machine can be moved simultaneously and in the same way, so that the 3D camera can continuously capture an area that has a defined and, in particular, fixed geometric relationship to the detection area of ​​the coordinate measuring device. In particular, the 3D camera can thus continuously capture an area of ​​the measuring volume in which the coordinate measuring device can scan a workpiece. Collisions between the coordinate measuring device and the workpiece can be reliably detected in this way, even without pre-calculating the movement of the coordinate measuring device. For example,By evaluating the three-dimensional camera image data generated by the 3D camera, wherein the evaluation is preferably carried out repeatedly using the most recent camera image data, it can be determined that the coordinate measuring device has fallen below a minimum distance from the workpiece. Optionally, an additional condition can be defined that must be met so that the detection of the minimum distance being fallen below leads to the generation of a signal that prevents the collision (e.g. switch-off signal for the movement device of the coordinate measuring machine or a signal to reverse the movement of the coordinate measuring device). This additional condition can, for example, consist of the speed of the coordinate measuring device being above a limit value. This prevents an unintentional collision from being falsely detected when the workpiece is tactilely probed at a lower speed.

[0047] With regard to the arrangement, this corresponds to an embodiment in which a movement device is provided which is designed to move the 3D camera simultaneously with the additional coordinate measuring device of the coordinate measuring machine, so that the 3D camera continuously captures an area in which the coordinate measuring device can scan a workpiece.

[0048] In particular, spatially three-dimensional camera image data of the workpiece and / or the measurement volume can be repeatedly recorded, and changes between older and more recent camera image data can be determined (e.g., by the evaluation device) to detect the collision or to recognize the object or body part. With the exception of the evaluation of the depth information, which leads to additional options for action and / or enables a review of the results obtained from the image intensities, the evaluation of older and more recent camera image data or the consideration of changes in the scene captured by a camera is described in the aforementioned WO 02 / 25207 A1, e.g., on page 2 of the document. According to the present invention, however, the depth information can also be evaluated.

[0049] The measurement volume, or a portion thereof, in particular the workpiece or an area around the workpiece, is additionally measured thermographically. Temperature values ​​can be assigned to the spatially three-dimensional camera image data. Accordingly, the arrangement can generally comprise a thermographic measuring device for measuring the workpiece, and the evaluation device can be configured to assign temperature values ​​to the spatially three-dimensional camera image data.

[0050] In particular, the temperature of the workpiece can be recorded in this way and / or a human body part can be detected in the measurement volume in a simple and particularly reliable manner. When recording the workpiece temperature, a correction can be made, for example, by correlating the thermographic images or the temperature with the workpiece coordinates (or with corresponding raw information) also recorded at different times using the coordinate measuring device or using different coordinate measuring devices. In particular, the assignment of the spatially resolved thermographic measurement results to the camera image data of the 3D camera allows a correction of the workpiece measurement using the coordinate measuring devices depending on the location on the workpiece surface.In particular, thermographic measurement eliminates the need for temperature sensors that are in contact with the workpiece and only measure the temperature representatively for a specific part of the workpiece. More generally, a combination of the 3D camera and the thermographic, spatially resolved measurement of the workpiece can easily capture the spatial temperature distribution of the workpiece.

[0051] According to the invention, thermographic measurement is additionally considered for the detection of body parts in the measurement volume. Thus, the area of ​​the measurement volume to be monitored (including the entire measurement volume) is also measured thermographically (in the case of the arrangement by a thermographic measuring device), and an undesired or prohibited body part in the measurement volume is detected from the results of the thermographic measurement (e.g., by the evaluation device). A corresponding warning signal or control signal is generated (e.g., by a signal generation device) if both the results of the thermographic measurement and the evaluation of the camera image data of the measurement volume indicate the presence of the body part. The arrangement, and in particular the evaluation device of the arrangement, are designed accordingly.This is based on the idea that surfaces of body parts typically have temperatures of at least 23°C and this is typically above the temperature in the measuring volume.

[0052] Optionally, a pattern can be projected onto the workpiece or another object located in the measurement volume using electromagnetic radiation, to which the 3D camera is sensitive. The projected pattern can be changed for different, consecutively recorded camera image data from the 3D camera. For example, the position of the pattern relative to the workpiece surface can be changed, the width of structures in the pattern (e.g., stripes) can be varied, and / or the direction of structural elements with respect to the course of the structural elements on the surface of the workpiece can be changed. By evaluating the camera image data at different points in time, which depict the different pattern projections, the resolution with regard to the depth information can be further increased. The process of projecting patterns is already known for 2D cameras.In the three-dimensional camera image data, the detection of the time-varying patterns only affects the detected radiation intensity, so the same evaluation methods can be applied as for 2D camera image data. The additional depth information captured in the 3D camera image data now enables verification of the results of the pattern projections and / or vice versa. One depth information is obtained directly from the 3D camera, the other indirectly by evaluating the pattern projection.

[0053] Embodiments of the invention will now be described with reference to the accompanying drawings. The individual figures of the drawing show: Fig. 1 in perspective view, but schematically, a coordinate measuring machine in gantry design, with a rotary / swivel joint arranged on the spindle of the device, which carries a 3D camera and a tactile probe for probing a workpiece, Fig. 2 schematically shows an arrangement with a 3D camera directed at a surface of a workpiece with a bore, Fig. 3 a table explaining the assignment of both intensity values ​​and depth information to image elements of a camera image of a 3D camera and Fig. 4 schematically shows an arrangement with a 3D camera, a data processing device of a coordinate measuring machine, a database and the drive system of the coordinate measuring machine.

[0054] Fig. Figure 1 shows a coordinate measuring machine (hereinafter referred to as CMM) in gantry design, which has a base 1. A gantry of the CMM is movable in a straight direction (e.g. y-direction) relative to the base 1. The corresponding drive system is shown in Fig. 1 is not shown in detail. This also applies to additional drives for executing other movements of the CMM. To measure the relative position of the gantry 2 and the base 1, a first scale 4 is arranged on the side of the base 1, for example. Measured values ​​of the relative position are fed to a central evaluation and control unit 28 of the CMM.

[0055] A carriage 7, movable in a second horizontal direction (e.g., the x-direction), is arranged on a bridge of the gantry 2. To determine the relative position of the carriage 7 and the gantry 2, a second scale 5 is arranged on the side of the bridge of the gantry 2. Position values ​​read from the scale 5 (or corresponding values, e.g., pulses from a grating) are also fed to the central unit 28 of the CMM.

[0056] A quill 3 of the CMM is movable relative to the carriage 7 in the vertical direction (e.g., z-direction). To determine the relative position of the carriage 7 and the quill 3, a third scale 6 is arranged on the quill 3. Corresponding values ​​of the relative positions are also fed to the central unit 28.

[0057] At the lower end of the sleeve 3, in the exemplary embodiment, a rotary / swivel joint 8 is arranged, which enables rotary movements about two mutually perpendicular axes of rotation A, B. At the free end of the rotary / swivel joint 8, a unit 9 is arranged, which has a 3D camera 10 and a probe head 12 that is immobile relative to the 3D camera 10. On the probe head 12, in turn, a stylus 14 with a probe ball 15 is arranged as a probe element. In the foreground of the Fig. 1, a holder 35 is located on the base 1, which holds interchangeable parts 9' 40, which can be coupled to the spindle 3 instead of the rotary / swivel joint 8 and / or instead of the unit 9. In particular, the unit 9' is another combination with a 3D camera 10' with a probe head 12', which in turn carries a probe pin 14' with a probe ball 15'. The interchangeable part 40 is, for example, a probe or a probe head with a coupled probe.

[0058] The parts coupled to the quill and the interchangeable parts mentioned are merely examples. Devices for scanning a workpiece (tactile or non-contact scanning) that are customary or known from the technical field of coordinate measuring machines can be coupled to the quill 3 of the CMM. Unit 9 or unit 9' can also enable relative movement between the 3D camera and the probe head. Furthermore, it is possible for the probe head or probe to be coupled directly to the rotary / swivel joint or directly to the quill 3, and for the 3D camera to be coupled to the quill 3 or to other parts of the assembly in another way. For example, a separate mount for the 3D camera can be mounted on the base 1.However, the joint movement of the 3D camera and an additional measuring device for measuring the coordinates of a workpiece is preferred if the spatial area in which the coordinate measuring device can acquire measured values ​​of the surface of a workpiece is to be continuously or repeatedly captured by the 3D camera. If the coordinate measuring device is aligned differently, the 3D camera is automatically aligned accordingly. The illustration of such a joint arrangement of the 3D camera and the coordinate measuring device in the embodiment of the . Fig. 1 is merely schematic. For clarity, the 3D camera is shown relatively large and with its optics projecting toward the probe sphere 15 or 15'. Alternatively, the optics of the 3D camera can be integrated into the common unit of the 3D camera and the coordinate measuring device or, for example, into a probe head. Light field cameras are particularly suitable for integration into a probe head if several lenses are arranged around the area to which a stylus is coupled or to which the stylus is attached. In this case, the lenses are objectives whose optical axes are aligned approximately parallel to the longitudinal axis of a stylus shaft. Optionally, with additional lenses, the lenses each project an image of the scene to be observed (e.g., workpiece or area of ​​the measurement volume) onto a separate sub-area of ​​the 3D camera's sensor matrix.As is well known, the focal length of the various lenses or lens systems that create images of the scene is different.

[0059] Fig. 1 further shows a workpiece 13 held on the base by a workpiece holder 32. The 3D cameras 10 and the longitudinal axis of the stylus 14 are aligned with a region of the surface of the workpiece 13.

[0060] In addition, on the left in Fig. 1 depicts an input / output device (here: keyboard and monitor) 29, by means of which interaction between a user and the arrangement is possible. In particular, an image generated by the 3D camera 10 can be displayed on the monitor, and the user can specify the operation of the CMM using the keyboard or other input devices. The unit 29 is connected to the CMM's central control and evaluation device 28.

[0061] The 3D camera 10 from Fig. 1 or another 3D camera is in accordance with Fig. 2 is aligned with a surface 21 of a workpiece, which may be, for example, the workpiece 13 according to Fig. 1. The surface 21 has flat regions 22a, 22b into which a depression 23, e.g. a bore, is introduced. Consequently, the bottom 24 of the depression 23 is further away from the camera 10 than the flat surface regions 22. The 3D camera 10 also captures the bottom 24 of the depression 23 because it is correspondingly aligned with the surface 21. Pixels or corresponding sensor elements assigned to the depression 23 in the camera image generated by the camera 10 have distance information or depth information corresponding to the bottom 24 or generate this distance information or depth information. Other image elements or sensor elements assigned to the flat surface regions 22 contain other depth information or distance information that correspond to the smaller distance to the camera 10 or generate this information.

[0062] If a recess 23 is provided on the workpiece 23 (e.g., according to a CAD design of the workpiece 13) but is not implemented, this will be reliably detected by the camera 10. The same applies, of course, to other shape features of a workpiece that influence the depth profile of a three-dimensional camera image.

[0063] Image data from 2D cameras typically consists of arrays of image elements, usually arranged in rows and columns. The image values ​​(e.g., gray values ​​or color values) of the image elements can therefore be entered into a table whose rows and columns correspond to the rows and columns of the 2D camera image. For example, for a camera image with n rows and m columns (n, m are positive integers), a table as shown in Fig. 3, in which the intensity values ​​g are entered. In addition, the table in Fig. 3, however, the depth information of a camera image from a 3D camera, where the values ​​of the depth information are denoted by d. The indices of the intensity values ​​g and the depth values ​​d represent the number of the row followed by the number of the column. For simplicity, in the table in Fig. 3 only the corner elements are shown, i.e. the values ​​of the image element in the first row and first column, the image element in the first row and m-th column, the image element in the n-th row and first column and the image element in the n-th row and m-th column.

[0064] The representation of the Fig. Figure 3 illustrates that the camera image data of the 3D camera does not contain information about volume areas, as is the case with computer tomography, but rather three-dimensional courses of surfaces or other areas.

[0065] Based on Fig. 4 will now explain various combinations of units and their functionality, which can be part of an arrangement for determining the coordinates of a workpiece. Therefore, not all of the units in Fig. 4, the units or parts of the arrangement shown are mandatory. For example, the thermographic sensor TH on the right in the figure can be omitted if thermographic measurement is not desired. Additional units, such as a second 3D camera, can also be present.

[0066] In the Fig. In the embodiment shown in Figure 4, a 3D camera K is provided, which captures at least a partial area of ​​a measurement volume of a CMM. Camera image data from the 3D camera K are fed to an evaluation device COMP, which is part of the central evaluation and control device of the CMM and, for example, in Fig. 1 is designated by the reference numeral 28. However, all variants of the arrangement and their functions explained here can also be used with other types of coordinate measuring machines than in Fig. 1. The Fig. The cameras 10 and probe heads 12 shown in Figure 1 can be arranged on other types of coordinate measuring machines, e.g. at the free end of a horizontally extending arm of a so-called horizontal arm CMM.

[0067] Optionally, the evaluation device COMP also receives the measurement signal from the CMM measuring systems, e.g., the readings of scales 4, 5, 6 in Fig. 1 plus the measuring signals of the probe when contacting the workpiece and (if available) the rotary position signals of a rotary device. In the case of Fig. 1, a rotary / swivel joint 8 is provided, and therefore measurement signals are transmitted to the unit 28, which make it possible to determine the rotational positions about the rotational axes A, B. Therefore, if the unit COMP receives both the camera images and the measurement signals from the coordinate measuring systems, the unit COMP can establish the spatial relationship of the coordinate system of the 3D camera image to a coordinate system in which the coordinates of the measured workpiece are specified.

[0068] In any case, the COMP unit can generate a digital three-dimensional model of the workpiece captured by the camera(s) from at least one camera image of a 3D camera, and in particular from multiple camera images of at least one 3D camera. Furthermore, the COMP unit can optionally place this digital model of the surface of the workpiece in spatial relationship to a coordinate system of the coordinate measuring machine and / or the workpiece. For example, prior information contained in a database DB can be used, e.g., prior information about the workpiece (e.g., a CAD model). In this case, it is possible to determine from the camera image whether features of the workpiece are planned but not present, or whether additional, unplanned features are present.If the camera image(s) only depict a portion of the workpiece surface and therefore the digital model only relates to a portion of the workpiece, this partial area can be placed in a spatial relationship to the other areas of the workpiece by using the prior information. If prior information is not used or the digital model generated by the COMP unit is not compared with prior information, the digital model can be used to plan and / or prepare the measurement of the workpiece using the additional coordinate measuring device. User input may also be possible for this purpose, e.g., according to the arrangement shown in . Fig. 1 via the unit 29, which is connected to the unit 28 and thus to the unit COMP. Even without user input or in addition to user input, an automatic alignment of at least one predefined measuring sequence for measuring the workpiece by means of the additional coordinate measuring device can take place. These predefined sequences can be stored in the database DB and retrieved therefrom by the device COMP and transferred to a control CONTR of the unit 28. The control CONTR controls the movement of the coordinate measuring device in a manner known per se by outputting corresponding control signals to the drive system 11 of the CMM, which, for example, executes the movements according to the Fig. 1 described movement possibilities.

[0069] Regardless of whether the COMP unit creates a digital model from at least one camera image from camera K, the COMP unit can monitor the measurement volume based on at least one camera image. For example, successively recorded camera images are evaluated for differences, and from this, a movement of at least part of the CMM (including the coordinate measuring machine) and / or a body part of a person in the measurement volume is detected. In this case, advance information from the database DB is preferably used. In particular, this information relates to the position of obstacles to the movement of the part of the CMM being monitored, or to sub-areas of the measurement volume in which no body part may be present at a given time or within a given period of time, for safety reasons. However, the aforementioned model can also be generated from the camera image data and used for monitoring. For example,The model can be used to determine that a certain feature of the workpiece is expected but not present, or that an unexpected feature is present. From this, the COMP unit can calculate a collision before it occurs.

[0070] If the COMP unit determines during monitoring that the CONTR controller needs to be instructed to execute, modify, or not execute a specific movement sequence, the COMP unit sends a corresponding signal to the CONTR controller. Alternatively or additionally, the COMP unit can also send a warning signal via a signal connection not shown, e.g., to the Fig. 1 shown unit 29.

[0071] If the optional TH thermographic measuring device is present, it can output the results of the thermographic measurement of the workpiece, a part of it, and / or the measuring device to the COMP unit. This thermographic information can be linked to the camera image data, linked to the measurement results of the CMM's M measuring systems, linked to preliminary information from the DB database, and / or evaluated and / or processed separately. In particular, the thermographic measurement results can be used to correct the coordinate measurement with respect to the temperature of the workpiece and / or the temperature of the coordinate measuring device. Alternatively or additionally, the thermographic measurement results can be used to identify features of the workpiece and / or to detect body parts within the measurement volume.Depending on the evaluation and / or processing of the thermographic measurement results, the COMP unit can output a signal to the CONTR controller, which then controls the CMM's drive systems 11 accordingly. The COMP unit can also output a warning signal.

Claims

[1] Method for determining coordinates of a workpiece (13) using a coordinate measuring machine, wherein - spatially three-dimensional camera image data of a workpiece (13) are recorded by a 3D camera (10) while the workpiece (13) is located in a measuring volume of the coordinate measuring machine, - the workpiece (13) is scanned in the measuring volume by means of an additional coordinate measuring device (12) of the coordinate measuring machine, - the coordinates of the workpiece (13) are determined by evaluating the results of the scanning, - in addition to or as an alternative to the workpiece (13), the 3D camera detects an area of ​​the measuring volume in which the workpiece (13) is not located, and spatially three-dimensional camera image data of the measuring volume are recorded, wherein the camera image data of the measuring volume are evaluated and thereby the presence of an object or body part that is not desired or permitted in the measuring volume is detected, characterized by , that - the area of ​​the measuring volume is also measured thermographically and a body part of a person that is not desired or permitted in the measuring volume is detected from the results of the thermographic measurement and a corresponding warning signal or control signal is generated if both the results of the thermographic measurement and the evaluation of the camera image data of the measuring volume indicate the presence of the body part. [2] Method according to claim 1, wherein by evaluating the spatially three-dimensional camera image data - the workpiece (13) and / or at least a part of the workpiece (13) is detected or - it is determined that the workpiece (13) and / or part of the workpiece (13) is not present. [3] Method according to claim 2, wherein during the recognition or detection, information of the camera image data relating to a spatial dimension in the viewing direction of the 3D camera (10) is compared with prior information about the workpiece (13). [4] Method according to one of the preceding claims, wherein a digital 3D model of at least part of the surface (21) of the workpiece (13) is determined by evaluating the spatially three-dimensional camera image data and the results of the scanning by means of the additional coordinate measuring device (12) are assigned to regions of the surface of the workpiece (13). [5] Method according to claim 4, wherein an accuracy of the 3D model is improved by the assignment of the results of the scanning by means of the additional coordinate measuring device (12). [6] Method according to one of the preceding claims, wherein a digital 3D model of at least part of the surface (21) of the workpiece (13) is determined by evaluating the spatially three-dimensional camera image data and the scanning of the workpiece (13) by means of the additional coordinate measuring device (12) is planned and / or specified on the basis of the 3D model. [7] Method according to one of the preceding claims, wherein the spatially three-dimensional camera image data of the workpiece (13) are obtained by the 3D camera (10) before and / or during a scanning of the workpiece (13) by the coordinate measuring device and an unintentional collision of the additional coordinate measuring device (12) with the workpiece (13) is predicted from the camera image data before the collision occurs. [8] Method according to one of the preceding claims, wherein the 3D camera (10) is moved simultaneously with the additional coordinate measuring device (12) of the coordinate measuring machine, so that the 3D camera (10) continuously captures an area in which the coordinate measuring device (12) can scan a workpiece (13). [9] Arrangement for determining coordinates of a workpiece (13), the arrangement comprising: - a coordinate measuring machine having a measuring volume in which workpieces (13) can be scanned by means of a coordinate measuring device (12) of the coordinate measuring machine in order to determine coordinates of the respective workpiece (13), - a 3D camera (10) for recording spatially three-dimensional camera image data, wherein the 3D camera (10) has a detection range which lies at least partially in the measurement volume, - an evaluation device (COMP) which is designed to evaluate both the results of the scanning of the workpiece (13) and the camera image data and to determine the coordinates of the workpiece (13) at least from the results of the scanning of the workpiece (13), wherein the 3D camera is designed, in addition to or alternatively to the workpiece (13), to capture an area of ​​the measuring volume in which the workpiece (13) is not located, and to record spatially three-dimensional camera image data of the measuring volume, wherein the evaluation device is designed to evaluate the camera image data of the measuring volume and thereby detect the presence of an object or body part that is not desired or permitted in the measuring volume, characterized by , that the arrangement comprises a thermographic measuring device for thermographically measuring the area of ​​the measuring volume and the evaluation device is designed to detect, from the results of the thermographic measurement, a body part of a person that is not desired or not permitted in the measuring volume and a signal generating device of the arrangement is designed to generate a corresponding warning signal or control signal if both the results of the thermographic measurement and the evaluation of the camera image data of the measuring volume indicate the presence of the body part.

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