WO2016202852A1

WO2016202852A1 - Coordinate measuring machine and method for calibrating same using a time-of-flight camera

Info

Publication number: WO2016202852A1
Application number: PCT/EP2016/063740
Authority: WO
Inventors: Dominik DOMINIK SEITZ; Rainer Sagemüller; Tobias TOBIAS HELD; Jochen Burger
Original assignee: Carl Zeiss Industrielle Messtechnik Gmbh
Priority date: 2015-06-16
Filing date: 2016-06-15
Publication date: 2016-12-22
Also published as: DE102015109612A1; DE102015109612B4

Abstract

Disclosed is a CMM (10), comprising: a contact probe (28) for probing an object (32, 62) to be measured within a fixedly defined measurement volume (33), which is assigned to the CMM (10) and which defines a CMM-specific coordinate system; an evaluation and control unit (36, 38, 39); and a TOF camera (70), wherein the TOF camera (70) is configured to illuminate and record at least one TOF image of a scene in the measurement volume (33), wherein the TOF image defines a TOF-specific coordinate system which differs from the CMM-specific coordinate system and wherein the scene has a characteristic feature (28-1, 32, 62), the geometry and/or position of which in relation to the CMM-specific coordinate system is/are known; wherein the evaluation and control unit (36, 38, 39) is configured to identify the characteristic feature (28-1, 32, 62) in the TOF image and determine the geometry and/or position of the identified characteristic feature (28-1, 32, 62) in the TOF-specific coordinate system; and wherein the evaluation and control unit (36, 38, 39) is furthermore configured to determine an imaging function for referencing the CMM-specific coordinate system to the TOF-specific coordinate system, or vice versa, on the basis of the geometries and/or positions of the characteristic feature in the CMM-specific coordinate system and in the TOF-specific coordinate system.

Description

Coordinate measuring machine and method for calibrating the same

with a time-of-flight camera

The present invention relates to a coordinate measuring machine with a button, a

Evaluation and control unit and a time-of-flight camera. The invention further relates to a method for referencing a coordinate measuring machine-foreign coordinate system to a coordinate measuring machine-specific coordinate system.

The document US 2014/0286536 A1 discloses a method for determining a

Position and alignment of a known article with six degrees of freedom. Document DE 196 18 283 A1 discloses an image pickup device and a method for three-dimensional non-contact measurement. The document US 2015/0049186 A1 discloses a coordinate measuring machine including a camera. The document US 201 1/01 19025 A1 discloses a manipulation aid for coordinate measurement. The document DE 10 2006 039 000 A1 discloses a stylus holder. The document US 2013/0010070 A1 discloses an information processing apparatus and a method for processing information.

The document DE 101 24 493 A1 describes a correction method for

Coordinate measuring machines, ie for devices with a measuring head, which are inside a (fixed) defined measuring volume is movable relative to a workpiece that measure

shall be. Measuring points on the workpiece are measured with the measuring head.

Often, the measuring head for this purpose has a probe element, in particular in the form of a probe with a stylus and a stylus, with the desired measurement points on the workpiece are physically touched. Therefore, such a measuring head is often referred to as a probe. Alternatively, there are measuring heads with which defined measuring points on a workpiece can be measured without contact, in particular with optical sensors (for example laser scanners).

A control and evaluation determines from the position of the measuring head within the measuring volume and possibly from the position of the probe relative to the measuring head when probing the workpiece spatial coordinates that represent the touched measuring point. Determining the spatial coordinates at a plurality of measurement points, one can measure geometric properties of the workpiece, such as a diameter of a bore or a spatial distance of two geometric elements on the workpiece. In addition, you can determine with a variety of coordinates measuring curves that represent the spatial shape or surface contour of individual geometric elements or even the spatial shape of the entire workpiece. Frequently, geometric dimensions, such as the diameter of a bore or the distance between two geometric elements, are determined based on the measurement curves.

The economics of a coordinate measuring machine is almost always determined by two factors in metrology, namely the accuracy and speed. In this context, the question often arises as to how many measuring points can be obtained in which time and with what accuracy. In the measurement of smaller workpieces (less than 0.5 dm ³ ) usually the accuracy is more in the foreground, since these types of workpieces are subject to very small tolerances. To meet this requirement, it is thus usually tactile measured. If larger components (eg parts or complete vehicle bodies) are measured, a sensor with μm accuracy is less important. However, the focus is more on the measuring speed. The characteristics of a vehicle body should be able to be measured in an equally acceptable time, which in turn would allow the use of tactile sensors, even in the scanning ning operation, excludes. Thus, sensors are used for such applications, which both in time and space have a very high density of points.

Examples of sensors with temporally and spatially very high point density are laser line scanner or strip projectors that are regularly used for measuring tasks on the above workpieces. Line scanners project a laser line onto the workpiece for distance measurement. This line is then recorded with a camera and triangulation calculations can then be used to determine the distance to the sensor and thus the surface of the workpiece. Although this type of sensor has a high temporal and spatial point density, but has disadvantages due to the design. It must be moved to measure the surface of a laser line over the workpiece. Since the projected strip can not be arbitrarily large, this leads to a proportional increase in the measuring time.

An alternative to the line scanner are strip projectors. To determine the

Surface of the workpiece is projected to a black and white line pattern on the workpiece. The strip pattern is then detected by a camera and the surface of the workpiece is calculated by triangulation, comparable to the evaluation on the line scanner. These types of sensors have disadvantages because the surface of the workpiece to be measured can be diffusely reflective.

Therefore, tactile is often measured. In a tactile measurement, however

Preliminary information eg about the type and orientation of the used probe, the position / orientation of a fixed on the coordinate measuring machine axis of rotation or the position / orientation of a located on the coordinate measuring workpiece required. This preliminary information must currently be created by a manual operation of the user in a pre-measurement step. For this purpose, either the position of a calibration ball is roughly measured manually (probe calibration), the space axis of the rotation axis is measured manually or the position of the workpiece is measured roughly by hand. As soon as this rough, manual calibration has taken place, the respective feature can then be measured automatically again in an automated step, with a correspondingly adapted strategy or correspondingly adapted number of support points being used. It is an object of the present invention to provide a coordinate measuring system (KMB) which simplifies this type of measurement.

This object is achieved by a CMM comprising: a probe for probing an object to be measured within a fixed measuring volume, which is assigned to the CMM and which defines a CMM-specific coordinate system; an evaluation and control unit; and a ToF camera, wherein the ToF camera is arranged to illuminate and record at least one ToF image of a scene in the measurement volume, the ToF image defining a ToF-specific coordinate system different from the CMM-specific coordinate system, and the scene having a characteristic feature whose geometry and / or attitude with respect to the CMM-specific coordinate system is known; wherein the evaluation and control unit is set up to recognize the characteristic feature in the ToF image and to determine the geometry and / or position of the recognized characteristic feature in the ToF-specific coordinate system; and wherein the evaluation and control unit is further configured, based on the geometries and / or positions of the characteristic feature in the CMM-specific coordinate system and in the ToF-specific coordinate system, a mapping function for referencing the CMM-specific coordinate system to the ToF-specific coordinate system, or vice versa, to determine.

The ToF camera provides the above-mentioned preliminary information, so that a manual rough pre-measurement is unnecessary. All measurement steps can be automated. The geometry and position of a previously unknown probe can be roughly measured automatically. The position of a rotation axis can be roughly calculated automatically. The position of a workpiece can be roughly measured automatically.

In one embodiment, the evaluation and control unit is further configured to determine in the ToF-specific coordinate system a geometry and / or position of an unknown object from a ToF image, which shows the unknown object within the measurement volume, and based on the thus determined geometry and / or location of the unknown object, a test plan in the CMM-specific coordinate system for the Unknown object to be determined without the unknown object was pre-measured manually coarse in the CMM-specific coordinate system.

Under a test plan below is a roadmap for the button of

Coordinate measuring device understood. This schedule defines the movement paths of the probe during an automated measurement. This roadmap also defines the touch points (on the object to be measured) that correspond to interpolation points.

According to a further embodiment, the unknown object is a replaceable, with respect to its construction unknown button, which has at least one stylus, each of the stylus has at least one connecting element and a Tastkugel, which is provided at a free end of the corresponding stylus, and where the test plan represents a calibration of the unknown probe.

The buttons are often assembled depending on the application by the user. The manufacturers of the CMM provide probe kits for this purpose. The probe kits have connecting elements, joint pieces and probe balls. These elements can be present in different dimensions. Thus, a variety of different buttons can be configured by the user himself. Before using the self-configured button, it is necessary for the CMM to know the structure of the self-configured button. Otherwise, no exact coordinate determination is possible. Therefore, these self-configured pushbuttons must be calibrated. The above configuration allows the probe calibration.

According to another embodiment, the ToF image of the scene shows both the

unknown probe as well as a Einmesskugel whose dimensions are known and which is fixed, and preferably permanently arranged at a known position of a base of the CMM, as a characteristic feature.

Further, it is preferred that the characteristic feature rotates about a rotation axis, which is not visible in the ToF image itself, wherein the evaluation and control unit is further adapted to a plurality of staggered ToF images according to a respective position of the characteristic feature in each ToF image with respect to a position of the axis of rotation in the CMM-specific coordinate system to evaluate.

In particular, the characteristic feature stationary fixed and permanent in

Measuring volume may be provided, wherein the evaluation and control unit is further configured to cause the ToF camera cyclically recurring to record a new ToF image including the characteristic feature, and wherein the evaluation and control unit is further configured, at least two of the new ToF To evaluate images with respect to a respective position of the characteristic feature in the ToF-specific coordinate system and to determine a drift in the CMM-specific coordinate system in the event that the respective position of the characteristic feature in the ToF-specific coordinate system changes significantly.

Preferably, the ToF camera during a referencing operation is at least fixedly disposed at a position outside the measurement volume and preferably detects the entire measurement volume.

In another embodiment, the characteristic feature comprises: a

Reference sphere; a part of a machine frame that moves the stylus within the measuring volume; a reference button; and / or a probe magazine.

Further, the object is achieved by a method for referencing a non-CMM coordinate system to a CMM-specific coordinate system, comprising the following steps: taking a ToF image with a ToF camera of a CMM, the ToF camera for Illuminating and picking up the ToF image, the ToF image defining a ToF-specific coordinate system different from the CMM-specific coordinate system and showing a scene in a measurement volume of the CMM (10) having a characteristic feature whose geometry and / or location is known in the CMM-specific coordinate system; Recognizing the characteristic feature in the ToF image by means of image recognition, which is performed by an evaluation and control unit of the CMM; Determining a geometry and / or location of the detected characteristic feature in the ToF image; and a mapping function by the evaluation and control unit based on the geometries and / or positions of the characteristic feature in the CMM-specific coordinate system and in the Tof-specific coordinate system to reference the coordinate systems to each other.

Preferably, the method further comprises the steps of: determining a geometry, in particular a construction, and a position of an unknown probe and at least one layer of a known calibration sphere from a ToF image; Determining the corresponding geometries and positions in the CMM-specific coordinate system; Determining a test plan in the CMM-specific coordinate system, in particular for a probe calibration, for the unknown probe, without the unknown probe having been manually roughed in advance in the CMM-specific coordinate system.

In particular, the method further comprises the steps of: rotating the characteristic feature about a rotation axis in the measurement volume; Generating multiple, staggered ToF images; Determining a respective location of the characteristic feature from the ToF images; and evaluating the respective positions of the characteristic feature with respect to an orientation of the axis of rotation in the CMM-specific coordinate system.

In particular, the method further comprises the steps of: permanent stationary fixation of the characteristic feature in the measurement volume; cyclically recording a new ToF image that always contains the characteristic feature; Evaluating at least two of the new ToF images for a respective position of the characteristic feature in the ToF specific coordinate system; and determining a drift in the CMM-specific coordinate system in the event that the respective position of the characteristic feature in the ToF-specific coordinate system substantially changes.

It is understood that the features mentioned above and those yet to be explained below can be used not only in the particular combination given, but also in other combinations or in isolation, without departing from the scope of the present invention. Embodiments of the invention are illustrated in the drawings and are explained in more detail in the following description. Show it:

1 is a perspective view of a coordinate measuring machine in exemplary gantry design,

Fig. 2 shows several different buttons;

Fig. 3 shows a reference key and an unknown new key;

4 shows a scanning of a calibration sphere within a measuring volume, wherein the calibration sphere is kept spatially fixed by a clamping;

FIG. 5 shows a conventional probe (FIG. 5A) and a probe for scanning undercuts (FIG. 5B);

Fig. 6 is a flowchart of a referencing method;

FIG. 7 is a flowchart of a method for roughly determining coordinates of a workpiece; FIG. and

8 is a flowchart of a method for probe calibration.

In Fig. 1, a coordinate measuring machine is shown by way of example in the gantry design and designated in its entirety by the reference numeral 10. The coordinate measuring machine 10 (hereinafter also referred to as "CMM" for short) has a base 12 on which a portal 14 is arranged. A traverse of the portal 14 carries a carriage 16, on which a quill 18 is arranged. The CMM further comprises one or more, preferably electric, drives (not shown here) with which the portal 14 in the direction of an arrow 20 is horizontally movable relative to the base 12. Furthermore, the carriage 16 can be moved along an arrow 22 on the portal 14 horizontally, and preferably perpendicular to the first direction 22. The quill 18 can in the direction of an arrow 24 be moved vertically relative to the carriage 18. The directions 20, 22 and 24 preferably form a Cartesian coordinate system. At the base 12, the portal 14 and the quill 18 in each case scales 26 may be arranged, with the aid of a current position of the portal 14, the carriage 16 and / or the sleeve 18 can be determined.

At a lower free end of the sleeve 18, a button 28 is arranged, which carries a stylus 30 with a Tastkugel 31. The pushbutton 28 can be moved with one or more, preferably electrical, drives of the CMM 10, which are not shown here, within a measuring volume 33, which here by the movement axes and areas (20-24) of the portal 14, the carriage 16th and the sleeve 18 is spanned and is illustrated with a dashed auxiliary line. The stylus 30 with its probe ball 31 is used for probing a workpiece 32, which is fixedly arranged on the base 12 of the CMM 10. The base 12 thus also serves as a workpiece holder.

The CMM 10 is shown here in the form of a typical example. However, the invention is not limited to gantry type coordinate measuring machines and may equally be used with coordinate measuring machines of a different type and other devices for measuring workpieces, such as coordinate measuring machines in horizontal arm construction.

In the present exemplary embodiment, the workpiece 32 has, by way of example, two bores 34a, 34b whose position, shape, depth, and diameter are to be measured by means of the CMM 10. The bores 34a, 34b are typical geometric features of the workpiece 32, which can be measured by means of coordinate measuring machines. Other geometric features may be, for example, cylindrical or non-cylindrical protrusions, trunnions or recesses, undercuts, edge lengths or even a complex spatial shape, such as the topographies of a turbine blade. Depending on the geometries to be measured, different probes 28 are often used, as will be explained in more detail below with reference to FIGS. 2 to 5. Reference numeral 36 denotes a controller which controls the drives of the CMM 10

controls. In many cases, the controller 36 is a programmable logic controller (PLC).

The reference numeral 38 denotes e.g. a computer on which a measuring or

Evaluation software 39 is executed. The computer or computer 38 determines with the software 39 a current position of the portal 14, the carriage 16 and / or the quill 18, in particular taking into account the scales 26. The measured values provided by the controller 36 are evaluated by the software 39 (eg Transformation into a workpiece-own coordinate system). In particular, the software 39 generates a measurement protocol 40, which includes a measurement curve 42 and a numerical output of the measurement values 44 by way of example. Together, the controller 36 and the computer 38 with the measurement or evaluation software 38 form an evaluation and control unit.

In principle, it is conceivable to realize the evaluation and control unit with only one computer 38 or with only one controller 36, wherein the respective other functionality is then integrated by hardware and / or software. For example, on a computer 38, a programmable logic controller 36 could be implemented in the form of appropriate software. For this reason, the illustration in FIG. 1 with a controller 36 and a separate (evaluation) computer 38 is only one of several implementation variants.

The controller 36 in this example has a first memory 46 in which measurement parameters (e.g., key metrics) for the measurement of the workpiece 32 are stored. The measurement parameters in memory 46 may include i.a. determine the movements of the probe 28 within the measuring volume 33. In particular, they can define a trajectory and the speeds and accelerations of the probe 28 during a measurement process.

The reference numeral 48 denotes a second memory or memory area are stored in the second measurement parameters that define a modified movement of the probe 28 within the measuring volume 33. The first measurement parameters in memory 46 are typically determined by the user with the aid of the measurement and evaluation software 39 before the start of an actual measurement run. This is in particular a probe calibration.

Since different probes 28 are used, each of the probes 28 must be calibrated prior to use, i. be measured. In this case, position and size differences of the probe 28, preferably in comparison to a reference probe of the CMM 10, determined. A reference key is a key 28 supplied with the CMM 10 and specially marked, the dimensions of which the CMM 10 has deposited in one of its memories 46, 48. In order for the correct measured value 44 to be displayed on the computer 38, the controller 36 or the software 39 can still take into account the following data: key type, probe direction, stylus type, radius of the probe ball and the like.

The core of the CMM 10 is the probe 28. There are switching and measuring probes 28. In FIG. 2, four different probes 28-1 to 28-4 are shown. 3 shows a detailed view of a (reference) button 28-1 and a star-shaped button 28-4. The following description is made with simultaneous reference to FIGS. 2 and 3.

The CMM 10 always determines the same location or the same position, no matter which type of stylus is used and from which (probing) direction 50 (see FIG. 2), the workpiece 32 is touched.

The structure and dimensions of the reference probe 28-1 are known and stored in at least one of the memories 46 or 48. A button 28 may be modular. The reference probe 28-1 has, for example, a single stylus 30, at the free end of the Tastkugel 31 is attached. The stylus 30 has a single connecting element 52, which connects the Tastkugel 31 with a Tastschaft 54. The dimensions of the connecting element 52 and the Tastkugel 31 and their orientations are known. However, CMMs 10 often also have stylus kits, from the components of which application-specific buttons 28 are assembled by the user himself. can be built. In addition to the connecting elements 52, pivot pieces 56 belong to the button assembly sets. The buttons 28-2 and 28-3 of Fig. 2 each have two links 56-1 and 56-2. The pushbutton 28-2 and the pushbutton 28-3 each have four connecting elements 52 as an example. Both buttons 28-2 and 28-3 each have two styli 30-1 and 30-2. The styli 30-1 and 30-2 of the probe 28-2 are L-shaped, wherein the connecting elements 52 each enclose an angle of 90 °. The styli 30-1 and 30-2 of the probe 28-3 are angled (angle not equal to 90 °) formed.

The button 28-4 is star-shaped and has in Fig. 2, five pins 30 which

are mounted at right angles to each other on the probe shaft 54.

The types of keys shown in FIGS. 2 and 3 can therefore be designed differently. The connecting elements 52 and the Taststifte 30 may have different lengths, since e.g. deeper holes 34 require longer styli 30. If the holes 34 have a certain inclination, you need to their measurement appropriately inclined Taststifte to reach an inside of the bore 34 well. However, each of the buttons 28 requires a probe calibration. For each of the buttons 28, it is necessary to know where the probes 31 of the styli 30 are located and what radii the probes 31 have. Once these data are determined once for each of the styli 31 and for each button 28 and then stored, the button 28 can be changed without costly remeasurement. The software 39 can then automatically consider which of the buttons 28 is being used.

Thus, in a measuring operation different buttons 28 with a wide variety

Configurations of the probe pins 30 provide the same measurement results, the computer 38 must know in advance the relative spatial arrangement of the styli 30, the dimensions of the styli 30 and the radii of the Tastkugeln 31. These parameters are determined during probe calibration. After calibration, the computer 38 knows the center distances of the Tastkugeln 31 -4 to the center 60 of the ball 31 -1 of the reference button 28-1 (see FIG. 3). The diameter of the Tastkugeln 31 -4 is then known or calculated. As a standard of determination, a dimensionally accurate sphere is usually used for the calibration, as shown by way of example in FIG. 4. FIG. 4 shows such a ball standard or a calibration ball 62. The metering ball 62 is positioned at an arbitrary position on the base 12 of the CMM 10. For this purpose, a clamping 64 can be used, which represents an interference contour for measurements within the measuring volume 33. In the following, a probe calibration will now be described.

In a first step, the control and evaluation unit brings the position of the

Einmesskugel 62 within the measuring volume 33 in experience. Usually, the calibration ball 62 is touched with the reference key 28-1, whose position and geometry the computer 38 knows, from several sides according to a defined strategy (manually). The computer 38 determines therefrom the center of the calibration sphere. With each further button 28 (in Fig. 4, another button 28-2 is shown), which is to be used, the calibration ball is now also touched, the calibration ball 62 of course remains at its metered position. From the data thus obtained, correction quantities are calculated for the (unknown) push-button 28-2. In a next step, the computer 38 calculates a location difference of the button 28-2 to the reference button 28-1. From the probing a ball and its center are calculated. Of course, the calculated center is correct only for the reference key 28-1. However, based on this data, the correction amount needed for the button 28-2 can be determined. In a further step, the radius of the probe ball 31 of the probe 28-2 can be determined. The radius of the detection ball 62 determined by the computer 38 using the probe 28 is larger by the probe ball radius than the known exact radius of the calibration ball 62. The probe ball radius can therefore be determined as the difference between the measured ball radius and the stored radius of the calibration ball 62.

The coarse preliminary sensing required for the probe calibration is conventionally accomplished by manual control of the probes 28 by the measurement volume 33.

However, the probe calibration described above can also be automated. To this

The purpose is a time-of-flight camera shown in FIG. 1 (hereinafter referred to briefly as ToF camera) 70 used. The KMG10 includes the ToF camera 70. The ToF camera 70 is connected to controller 36 and / or computer 38 (hardwired and / or wireless) for signal and data exchange. The ToF camera 70 is positioned so that preferably the entire measuring volume 33 can be detected. The ToF camera 70 may be movably formed relative to the base 12. However, a (picking) position of the ToF camera 70 is known. From the images taken by the ToF camera 70, positions, positions and dimensions of objects located in the measurement volume 33, such as the probe or buttons 28, the calibration ball 62, the clamping 64 and the like can be determined at least roughly by the control and evaluation unit be determined. The later, exact probing movements required in connection with the probe calibration can be automated on the basis of this data. Unlike the conventional approach, an approach of the probe 28 to the Einmesskugel 62 is no longer required by a manual control, even if the buttons 28 are constructed very complex. By way of example, it should be noted in this context button 28, with which undercuts are vermessbar. Such a button 28-5 is shown in Fig. 5B, whereas Fig. 5A shows a "simple" reference button 28-1. With the reference button 28-1 of FIG. 5A, horizontal undercuts can not be measured. This can only be the button 28-5 of Fig. 5B.

In general, a ToF camera 70 is a 3D camera system, which by means of a

Runtime method (time-of-flight method) Measures distances. For this purpose, a scene, such as the measuring volume 33, is illuminated with a light pulse. The light pulses are e.g. produced with LED or laser diodes, which are modulated sufficiently fast, so that a camera sensor can perfectly measure transit times. A pulse duration moves in the nanosecond range. The lighting is usually emitted in the near infrared range. The ToF camera 70 measures for each pixel the time it takes the light to reach the object and back again. The time required is directly proportional to the distance. The camera 70 thus provides for each pixel the distance of the object imaged thereon.

The ToF camera 70 can be used in a distance range of a few decimeters to about

40 m are used. A distance resolution is about 1 cm. A lateral resolution reaches about 200 x 200 pixels. The camera 70 can take up to 160 images per Deliver second. A core element of the ToF camera 70 is the image sensor, which measures the run time separately for each pixel. This image sensor resembles a chip for digital cameras, but with the difference that a pixel is much more complicated. It does not just have to be able to collect the incoming light, but also to measure the runtime. It can image sensors are used, which have a resolution of preferably up to 204 x 204 pixels with an edge length of 45 μηη.

By means of the ToF camera 70, it is possible geometries, alignments,

To determine topographies, feature complexes of workpieces to be measured, positions and positions in a CMM-specific coordinate system - at least roughly. The CMM-specific coordinate system is defined by the measurement volume 33 (see FIG. 1). The images that the ToF camera 70 provides, i. So the ToF images, define a ToF camera-specific or ToF-specific coordinate system. In the following, with reference to Fig. 6 will be described how the two coordinate systems are referenced to each other. A "reference" is generally understood as a reference system. "Referencing" generally means "referring to something".

6 shows a flowchart of a method for referencing the CMM-specific coordinate system to the ToF-specific coordinate system (or vice versa).

In a first step S10, the ToF camera 10 is moved relative to the measuring volume 33,

preferably outside of it, positioned. The ToF camera 70 is positioned so that it has, in particular, the entire measuring volume 33 in its field of vision. It is understood that the ToF camera 70 could also be arranged within the measuring volume 33. Further, it will be understood that the ToF camera 70 may be positioned at different locations to also illuminate and record shadows of objects located in a scene within the field of view of the ToF camera 70. The scene is composed of the objects within the measurement volume 33 that the ToF camera 70 sees. The scene may also include, for example, the portal and / or the button 28. In a step S12, the ToF image of the scene is taken and in shape

corresponding data transmitted to the evaluation and control unit. The evaluation and control unit determines, by means of stored recognition algorithms (preferably image recognition algorithms), the objects contained in the scene (step S14). At least one of the objects is known in terms of its geometry and / or position in the CMM-specific coordinate system. For example, the gauge ball 62 (see FIG. 4) is e.g. in a lower left corner of the base 12 of the CMM 10 - at least during the duration of the recording - stationary fixed. The geometry of the calibration ball 62, and possibly the clamping 64, are stored in the memory 46 (see FIG. 1) as data in the CMM-specific coordinate system. The same applies to the position or position of the calibration ball 62 and / or the clamping 64 within the measuring volume 33.

Since at least one object contained in the scene of the ToF image is known, specific identifying features of the object within the ToF image can be identified (see step S16). Once the specific identifier is identified, in step S18 the corresponding coordinates of the identifier can be determined in the ToF specific coordinate system. Preferably, these coordinates are also stored in the memory 46. In a step S22, the coordinates of the same recognition feature with respect to the CMM-specific coordinate system are retrieved from the memory 46. In a step S24, an imaging function is then determined that maps the coordinates of the specific recognition feature from the coordinate system of the CMM 10 into the coordinate system of the ToF camera 70. This completes the referencing process.

Assuming that the position of the ToF camera 70 with respect to the rest

Components (portal, base, buttons, etc.) of the CMM 10 is not changed and that the referencing method described in connection with FIG. 6 is completed, further special applications can be performed, which will be described below with reference to FIGS. 7 and 8 to be discribed.

Fig. 7 shows a flowchart of a method with which the position of a

(unknown) workpiece 32 - at least roughly - on the basis of a ToF image in the CMM specific coordinate system is determined (see step S26). Alternatively or additionally, the orientation of the workpiece 32 can also be determined. Once the workpiece 32 is roughly located, the evaluation and control unit may determine a measurement or testing plan for the probe 28 (step S28). The test plan consists of any number of support points (contact points between button 28 and workpiece 32). The probe 28 automatically runs the workpiece 32 along a test curve to fine-tune the coordinates of the workpiece 32 in the CMM-specific coordinate system (see step S30).

The same applies to the above-described probe calibration, the below

Referring to the flowchart of Fig. 8 will be described. FIG. 8 shows a flow chart for a method for probe calibration. In a first step S32, roughly a geometry of an unknown probe 28 (compare buttons 28-2 to 28-4 in FIG. 2) is determined on the basis of a (referenced) ToF image. In a step S34, the stylus pens 30 of the unknown button 28, e.g. identified by means of image recognition. The image recognition algorithm knows the components from which the buttons 30 can be constructed. The image recognition algorithm thus knows e.g. the various types of fasteners 52, the configuration of the links 56 and the like. By means of the image recognition, the orientations of the stylus pins 30 can also be recognized at least roughly. Also, the stylus balls 31 can be identified (step S36). This also applies to the diameter of the stylus balls 31. Once the geometry and / or position or position of the (unknown) button on the basis of ToF image is roughly determined, again a measurement or test plan for this specific button 28 Taststastekalibrierung be determined (step S38).

Another application, which is not shown in the form of a special flow chart, can be seen in the correction of a so-called zero-point drift. Due to external influences (eg temperature), an absolute zero point of the CMM-specific coordinate system can change over time. This means that an absolute location of the zero point in the frame of reference of the CMM 10 may change over time. With the ToF camera 70 fixed points within the measuring volume 33 can be cyclically measured - and thus monitored. Such a fixed point can be represented by the measuring ball 62, which in this case is permanently stationary within the measuring volume 33 remains installed. Since the actual position of the fixed point does not change over time, but the position changes in the image over time due to the drift, it is clear that there is a drift effect that can be corrected by calculation. Such a check is particularly useful for long inspection plans that require, for example, an hour or more to measure all the required points of a workpiece. In this case, for example, cyclic measurements of the fixed points can be carried out every five minutes. If the position of the fixed point does not change over time in the ToF image, then there is no drift.

Another advantage of using a ToF camera 70 is the fact that

Interference contours, such as the clamping 64 (see FIG. 4), can be detected and taken into account in the determination of the test plan (measuring curve along which the probe 28 is moved during a measuring operation).

The ToF image may also replace a CAD model of the workpiece 32. If e.g.

Freeform surfaces are to be scanned tactile, it is necessary for higher web speeds of the probe 28 that the direction of a surface normal is known in advance. This information is usually extracted from CAD model data. But if no CAD model is available, it has been necessary to scan very slowly so far. However, the required surface normal can at least roughly be derived from the data of the ToF image.

Furthermore, a working volume (measuring volume 33) of the CMM can be achieved with the ToF camera 70

10 with regard to device safety.

Another possible application of the ToF camera 70 can be seen in a fast rotation axis measurement. Even without knowing the orientation of the axis of rotation, the axis of rotation in the coordinate system of the CMM 10 can be determined on the basis of the ToF images. For this purpose a known object (eg the calibration ball 62) is attached to the axis of rotation. Subsequently, several ToF images are recorded at different (known) rotation angles. The calibration ball 62 is identifiable in each of the ToF images. From the familiar contour of the calibration sphere visible in the ToF image 62 can be closed back to the respective position of the center of the Einmesskugel 62. From the different positions of the centers at the different angular positions can be deduced on a trajectory of the center during rotation. The trajectory in turn defines an area on which the axis of rotation is perpendicular. Thus, the orientation of the axis of rotation can be calculated from the ToF images.

In summary, it can therefore be stated that the use of a ToF camera 70 offers the advantage that the CMM 10 does not provide any preliminary information, for example about the type and orientation of a new pushbutton 28, the position and orientation of an axis of rotation fastened on the CMM 10 or the position and Orientation of a located on the CMM 10 workpiece 32 is needed. This preliminary information is conventionally provided by manual operation of the user in a pre-measurement step of the CMM 10. In this case, either the position of the calibration ball is manually roughly measured (probe calibration), the spatial axis of the installed rotary axis is manually roughly measured or the position of the workpiece is measured roughly by hand. Once this rough manual measurement has been carried out, the respective feature can then be measured again in an automated step. The use of the ToF camera 70 makes the manual pre-measurement superfluous.

LIST OF REFERENCE NUMBERS

10 coordinate measuring machine / CMM

12 base

14 portal

16 sleds

18 quill

20-24 arrows / directions

26 standards

28 buttons

30 stylus

31 probe ball

32 workpiece

33 measuring volume

34a / 34b holes

36 control

38 computers

39 software

40 measurement protocol

42 trace

44 measured values

46 1. Storage

48 2. Memory

50 Antastrichtung

52 extension element

54 probe shaft

56 joint piece

58 center distance

60 center point

62 ball standard / calibration ball

64 clamping

70 ToF camera

Claims

claims

CMM (10) with:

a probe (28) for probing an object to be measured (32, 62) within a fixed measuring volume (33) associated with the CMM (10) and defining a CMM-specific coordinate system;

an evaluation and control unit (36, 38, 39); and

a ToF camera (70), wherein the ToF camera (70) is adapted to illuminate and record at least one ToF image of a scene in the measurement volume (33), the ToF image defining a ToF specific coordinate system which is from the CMM-specific coordinate system, and wherein the scene has a characteristic feature (28-1, 32, 62) whose geometry and / or attitude with respect to the CMM-specific coordinate system is known;

wherein the evaluation and control unit (36, 38, 39) is set up to recognize the characteristic feature (28-1, 32, 62) in the ToF image and to determine the geometry and / or position of the recognized characteristic feature (28-1, FIG. 32, 62) in the ToF-specific coordinate system; and

wherein the evaluation and control unit (36, 38, 39) is further arranged based on the geometries and / or positions of the characteristic feature in the CMM-specific coordinate system and in the ToF-specific coordinate system, a mapping function for referencing the CMM-specific coordinate system to the ToF-specific coordinate system, or vice versa, to determine.

The CMM (10) according to claim 1, wherein the evaluation and control unit (36, 38, 39) is further set up in the ToF-specific coordinate system a geometry and / or position of an unknown object (28-2, 28-3, 28). 4, 32) from a ToF image showing the unknown object (28-2, 28-3, 28-4, 32) within the measurement volume (33) and based on the geometry and / or location thus determined of the unknown object (28-2, 28-3, 28-4, 32) a test plan in the CMM-specific coordinate system for the unknown object (28-2, 28- 3, 28-4, 32), without the unknown object having been manually roughed in advance in the CMM-specific coordinate system.

The CMM (10) of claim 2, wherein the unknown object (28-2, 28-3, 28-4, 32) is a replaceable button of unknown construction (28-2, 28-3, 28-4, 32). with at least one stylus (30), each of the styli (30) having at least one connector (52) and a stylus (31) provided at a free end of the corresponding stylus (30), and wherein the test plan a calibration of the unknown button (28-2, 28-3, 28-4, 32) represents.

The CMM (10) of claim 3, wherein the ToF image of the scene includes both the unknown probe (28-2, 28-3, 28-4, 32) and a calibration sphere (62) whose dimensions are known and the fixed, and preferably permanently positioned at a known position of a base (12) of the CMM (10), as a characteristic feature.

The CMM (10) of claim 1, wherein the characteristic rotates about an axis of rotation not seen in the ToF image, and wherein the evaluation and control unit is further configured to provide a plurality of staggered ToF images at a respective position of the characteristic Feature in the respective ToF image with respect to a position of the axis of rotation in the CMM-specific coordinate system.

The CMM (10) according to claim 1, wherein the characteristic feature is stationary fixed and permanent in the measurement volume (33), wherein the evaluation and control unit is further configured to cyclically cause the ToF camera (70) to generate a new ToF Including image including the characteristic feature, and wherein the evaluation and control unit is further configured to evaluate at least two of the new ToF images with respect to a respective position of the characteristic feature in the ToF-specific coordinate system and to determine a drift in the CMM-specific coordinate system in the event that the respective position of the characteristic feature in the ToF-specific coordinate system substantially changes.

7. The CMM (10) according to any one of claims 1 to 6, wherein the ToF camera (70) during a referencing at least at a fixed position outside the measuring volume (33) is arranged and preferably the entire measuring volume (33) detected.

The CMM (10) of any one of claims 1 to 7, wherein the characteristic feature comprises: a calibration ball (62); a part of a machine frame which moves the probe within the measuring volume (33); a reference key (28-1); and / or a probe magazine.

9. A method of referencing a non-CMM coordinate system to a CMM specific coordinate system comprising the steps of:

Capturing a ToF image with a ToF camera (70) of a CMM (10), the ToF camera (70) being positioned to illuminate and capture the ToF image, the ToF image defining a ToF specific coordinate system, which differs from the CMM-specific coordinate system and shows a scene in a measurement volume (33) of the CMM (10) having a characteristic feature (28-1, 32, 62) whose geometry and / or position in the CMM specific coordinate system is known or are;

Recognizing the characteristic feature in the ToF image by means of image recognition performed by an evaluation and control unit of the CMM (10);

Determining a geometry and / or location of the detected characteristic feature in the ToF image; and Determining an imaging function by the evaluation and control unit based on the geometries and / or positions of the characteristic feature in the CMM-specific coordinate system and in the Tof-specific coordinate system to reference the coordinate systems to each other.

10. The method of claim 9, further comprising:

Determining a geometry, in particular a construction, and a position of an unknown probe (28-2, 28-3, 28-4) and at least one layer of a known calibration sphere (62) from a ToF image;

Determining the corresponding geometries and positions in the CMM-specific coordinate system;

Determining a test plan in the CMM-specific coordinate system, in particular for a probe calibration, for the unknown probe (28-2, 28-3, 28-4) without the unknown probe (28-2, 28-3, 28-4) previously measured roughly coarsely in the CMM-specific coordinate system.

1 1. The method of claim 9, further comprising:

Rotating the characteristic feature about an axis of rotation in the measuring volume (33);

Generating multiple, staggered ToF images;

Determining a respective location of the characteristic feature from the ToF images; and

Evaluating the respective positions of the characteristic feature with respect to an orientation of the axis of rotation in the CMM-specific coordinate system.

12. The method of claim 9, further comprising:

permanent stationary fixation of the characteristic feature in the measurement volume (33); cyclically recording a new ToF image that always contains the characteristic feature;

Evaluating at least two of the new ToF images for a respective position of the characteristic feature in the ToF specific coordinate system; and

Determining a drift in the CMM-specific coordinate system in the event that the respective position of the characteristic feature in the ToF-specific coordinate system changes significantly.