WO2021175929A1

WO2021175929A1 - Method for inspecting an automotive fastening site, method for applying a fastening element to an automotive fastening site, radar assembly and tool head for a robot

Info

Publication number: WO2021175929A1
Application number: PCT/EP2021/055354
Authority: WO
Inventors: Christof CLEMEN; Paul Gianferrara; Luis RODRIGO; Manuel Schneider; Karin Wimmer
Original assignee: Newfrey Llc; Tucker Gmbh
Priority date: 2020-03-06
Filing date: 2021-03-03
Publication date: 2021-09-10
Also published as: DE102020106197A1

Abstract

A method for inspecting and/or measuring a fastening site (14) with a fastening hole (42), by means of a radar assembly (32) which has a transmit antenna arrangement (92, 94) and a receive antenna arrangement (96, 98), the method including the steps of: positioning the radar assembly (32) in relation to the fastening hole (42) on which a fastening process has been conducted or on which a fastening process is to be conducted, such that the fastening hole (42) is located within a coverage of the transmit antenna arrangement (92, 94) and of the receive antenna arrangement (96, 98); emitting at least one radar signal (T) by the transmit antenna arrangement (92, 94); receiving at least one response signal (R) by the receive antenna arrangement (96, 98); and evaluating and/or recording the response signal (R).

Description

Method for inspecting an automotive fastening site, method for applying a fastening element to an automotive fastening site, radar assembly and tool head for a robot

[0001] The present invention relates to a method for inspecting and/or measur ing a fastening hole, particularly an automotive fastening site with a fastening hole.

[0002] Further, the present invention relates to a method for applying a fas tening element to an automotive fastening site, particularly to an automotive vehicle body in white.

[0003] Further, the present invention relates to a radar assembly for attaching to a tool head, and to a tool head for a robot, comprising a fastening tool for conducting a joining process at a fastening site, particularly for applying a fastening element to a fastening site of a workpiece.

[0004] In the automotive field, there is a vast variety of fastening or joining technologies for fastening two workpieces together or for applying fasteners. Particularly, when building an automotive vehicle body in white, there is a huge number of joining methods that are applied depending on shape, material etc. of the workpieces/fasteners.

[0005] The main categories of joining include welding (seam welding, spot welding and stud welding, for example), clinching, riveting (including blind riveting, punch riveting, etc.), screwing, setting, gluing, snap-fitting for example. In the following, the terms fastening and joining are used synonymously.

[0006] When conducting any of the above fastening methods, precision with re gard to positioning is of great importance.

[0007] In the field of manufacturing a vehicle body, therefore, robots are used. The vehicle body is carried by a carrier ( such as a band conveyor), so that its position and attitude is well known to a control system. Further, the robot is controlled such that a tool head for conducting a fastening process is positioned exactly with regard to the position of the fastening site of the vehicle body.

[0008] Quality control is another important factor in the field of automotive manufacturing. Quality control may involve an inspection of a fastening site before a fastening process is conducted. On the other hand, quality control may also involve inspecting a fastening site after a fastening process has been conducted.

[0009] Different methods and tools are used for inspecting and/or measuring a fastening site, such as for instance using a camera or different sensors. Radar sensors have proven to be useful in industrial environments.

[0010] Radar is a detection system that uses radio waves to determine the range, angle, or velocity of objects, for example. In the beginning, radar was mainly used for defense purposes. Modern uses include air and terrestrial traffic control, ocean surveil lance systems, ground-penetrating radar for geological observations, body scanners in airports, and others. In the automotive field, radar systems are used for distance control between vehicles. Therefore, typical applications are forward collision warning, adaptive cruise control, automatic emergency braking, etc.

[0011] Further, radar systems may be used to survey the surroundings of a ve hicle and can therefore be adopted for automated parking systems. In addition, radar systems have been used in the fields of passenger presence detection and breathing motion detetcion within a vehicle passenger compartment.

[0012] EP2637817 uses a radar sensor for detecting the position of an edge at a workpiece for a welding process. To this purpose, it is possible to use several transmit and receive antennas, and to use different polarizations of microwave signals.

DE19931681 discloses a method for monitoring weld beads and weld spots by means of a radar sensor. DE19934068 discloses a device for contactless control of a screw joint. A radar sensor detects vibrations in the screw joint. However, for joining processes having a hole, and notably but not only, blind-rivet element, there is still a need to improve the current methods and tools used for inspecting and/or measuring a fastening site, which is in such cases a hole and therefore requires a particular configuration.

[0013] In view of the above, it is an object of the present invention, to provide an improved method for inspecting and/or measuring a fastening site with a fastening hole, to provide an improved method for applying a fastening element to an automotive fastening hole, and to provide an improved tool head which can be attached to the arm of a robot.

[0014] The above object is achieved by a method for inspecting and/or measur ing a fastening site with a fastening hole, by means of a radar assembly which has a transmit antenna arrangement and a receive antenna arrangement, the method including the steps of: positioning the radar assembly in relation to the fastening hole on which a fastening process is to be conducted, such that the fastening hole is located within a coverage of the transmit antenna arrangement and of the receive antenna arrangement; emitting at least one radar signal by the transmit antenna arrangement; receiving at least one response signal by the receive antenna arrangement; and evaluating and/or recording the response signal.

[0015] The steps of measuring and/or inspecting a fastening site with a fas tening hole are typically performed in a harsh or dirty production environment. Therefore, existing optical methods for inspection and/or measurement needed increased mainte nance attention and have been prone to failures. The above-defined present invention, however, uses a radar assembly for inspecting and/or measuring a fastening hole on which a fastening step is to be conducted. The disclosure also deals with the use of radar imaging and/or of a radar assembly for inspecting a fastening site with a fastening hole or a reference site/feature in a production environment, preferably a fastening hole on an automotive body at which a fastening process is to be conducted.

[0016] It has turned out that a radar assembly is able to provide response sig nals that allow for an accurate inspection and/or measuring of a fastening site with a fastening hole, particularly an automotive fastening hole. [0017] Further, the radar technology is very reliable, particularly in the produc tion line environment. In addition, radar signals and response signals easily penetrate non-metallic housings. Therefore, the radar assembly can be fully encapsulated and may therefore be insensitive to dirt oil, smoke, scratching.

[0018] The fastening site is preferably a metal surface, for example a metal sheet of the vehicle body. However, the metal surface may be clean (in white), or may be coated. The metal surface may also be applied with oil, or may be rusty. The term fas tening site is to be understood to have a broad meaning. It could be any site in a produc tion environment, where a fastening process is to be carried out or has been carried out. However, it could also be any reference site where a reference feature is present, which may be used to calibrate the positioning system by means of which the radar assembly is positioned.

[0019] Preferably, a frequency-modulated continuous wave (FMCW) radar is used in the radar assembly. Such radars are based on an integrated oscillator which is linearly tuned in frequency over time. The resulting signal (radar signal) is transmitted, and the returned reflection (response signal) is mixed or correlated with the radar signal. The frequency offset between the radar signal and the response signal is directly connected to the distance of the reflection.

[0020] Looking on the entire spectrum of the detected response signal, not only one, but several targets can be distinguished depending on their distance from the radar assembly and the frequency range used. The higher the bandwidth, the closer objects can be distinguished. The ability to distinguish two reflections (response signals) which are close to each other, is called range resolution. The range accuracy, on the other hand, is the ability to measure the distance of a single object. This is determined by the ability of the radar assembly to measure the frequency offset of a single response signal. Commer cial radar systems operating at approximately 24 GHz only provide a range resolution as low as 60 cm. The accuracy to measure the distance of a single reflector can still go down to millimeter or submillimeter range. [0021] The operating frequency of the radar assembly of the present invention is preferably in a range between 50 GHz and 90 GHz. Higher frequencies may be used, e.g. 120 GHz or 240 GHz. Such frequency bands may be in compliance with certain Directives regarding the use of radar technology (such as provided by the "Bundesnet- zagentur" or "FCC").

[0022] Preferably, the radar assembly of the present invention includes a radar- based 3D imaging module which allows to reconstruct complex structures in several dimensions. For this purpose, several radar channels are preferably used.

[0023] In view of the above, the radar assembly of the present invention prefer ably includes several transmit antennas and several receive antennas (transmitters and receivers), which are located around an inspection axis. The inspection axis is a center axis of the coverage of the antenna arrangements of the radar assembly. In other words, the inspection axis is an axis which is typically normal to a surface of the fastening site (or fastening hole) when the radar assembly is positioned in relation to the fastening site for conducting the inspection and/or measurement method.

[0024] Preferably, the antenna arrangements (transmit and receive) are real ized by radar-on-chip technology. In other words, the antenna elements are preferably located on a printed circuit board, together with integrated circuits (ICs) which are used for signal generation, signal detection and pre-processing of the response signals. Preferably, a microcontroller is provided on the printed circuit board, which microcontroller may be used as an interface between the different radar ICs and a central data port. Further, the microcontroller may be used to conduct additional pre-processing of the response signals, to reduce the data amount before being transmitted over a standard interface (for example Ethernet, ProfiNet, EtherCAT, USB, etc.).

[0025] Further, it is preferred if the reduced data set is transferred via the standard interface to a computer, which calculates the required inspection and/or meas urement data, and provides an interface for the control of the production site (which is used to control for example a robot, a fastening tool, etc.). [0026] The radar ICs and the microcontroller are preferably responsible for at least one of the following steps: signal windowing, pulse compression by a fast Fourier Transformation, demultiplexing, system response compensation, distance calculation and range selection.

[0027] In a computer which is connected to the printed circuit board of the radar assembly, preferably, a surface reconstruction of the fastening site with a fastening hole is conducted, as well as a localization of a fastening feature, for example the localization of the hole. The localization of the fastening feature may be correlation based, phase pattern based, intensity based, etc., or based on combinations of these.

[0028] In some examples, the position of such a fastening feature can be de tected (measured). In further examples, it is possible to measure the orientation of a fastening feature.

[0029] In a preferred embodiment, the fastening feature has a certain sym metry. For example, a circular hole is symmetric with regard to a central axis. On the other hand, a hexagonal hole is symmetric with regard to a plane. The radar assembly prefera bly uses the symmetry to detect the position of the fastening feature with high precision. Therefore, it is also preferred if the transmit antenna arrangement and the receive anten na arrangement are provided so as to be symmetric with regard to a central inspection axis.

[0030] In a preferred embodiment of the method for inspecting and/or measur ing a fastening site with a fastening hole, the radar assembly is positioned within a range of 1 cm to 100 cm in relation to the fastening site.

[0031] Preferably, the range is 1 cm to 50 cm, more preferred 2 cm to 20 cm, and particularly preferred 3 cm to 5 cm.

[0032] Further, it is preferred if the radar assembly is a MIMO radar assembly (multiple input multiple output radar assembly), wherein the transmit antenna arrangement includes multiple transmit antennas and wherein the receive antenna arrangement includes multiple receive antennas, and wherein the emitting step includes emitting different radar signals from each of the transmit antennas.

[0033] MIMO radar is an advanced type of phased array radar employing digital receivers and waveform generators distributed across an aperture. MIMO radar systems preferably transmit mutually orthogonal signals from multiple transmit antennas, and these waveforms can be extracted from each of the receive antennas by a set of matched filters. For example, if a MIMO radar system has three transmit antennas and four receive antennas, twelve signals can be extracted from the receiver because of the orthogonality of the transmitted signals. That is, a twelve-element virtual antenna array is created in this case, using only seven antennas, by conducting digital signal processing on the received signals, thereby obtaining a finer spatial resolution compared with its regular phased array counterpart ("https:\\en. Wikipedia. org/w/index.php?title=mimo_radar+oldid=928753646").

[0034] One of the preferred key features is, therefore, the use of MIMO radar technology for inspecting and/or measuring fastening sites, although other radar technol ogies are feasible as well, e.g. SAR, or a combination of MIMO and SAR.

[0035] Further, it is preferred if the fastening site includes a fastening feature of a vehicle body portion, particularly a fastening hole in a vehicle body sheet portion.

[0036] The fastening hole may be a hole for receiving a blind rivet element, such as a blind rivet, a blind rivet stud, blind rivet nut, or may be a hole behind which another fastening feature is provided on which a fastening step is to be carried out. The latter example applies for example to fastening of a clip to a plastic fastening rib.

[0037] The hole in the body sheet portion may be a circular hole. In other em bodiments, the hole is a polygonal hole, for example a hexagonal hole. Further, the hole may have any symmetrical or non-symmetrical shape, including any polygonal shapes with rounded or sharp edges and/or corners, or a shape that combines round features and polygonal features. [0038] Further, it is preferred if the radar assembly is carried by a robot and if the evaluation step includes determining at least one position feature of the fastening site.

[0039] The position feature may be a center location of the fastening hole, the diameter of a fastening feature, the coordinates of the fastening hole and/or the attitude angles of the fastening hole. Particularly, if the fastening hole is provided by a sheet portion which is generally flat, the position feature may include the coordinates of one point of the sheet portion (for example a center of the hole), measured in x, y, and z coordinates, as well as attitude angles of the surface of the sheet portion around the respective x-axis, y-axis and z-axis (angles a, b, g).

[0040] In some cases, the position feature is just the center of a hole (the diam eter of which is known in advance), wherein the center location is defined by its coordi nates x, y, z. This will be sufficient for the identification of circular holes. If a hexagonal hole is to be identified, it is, typically, also necessary to determine an angle around the inspection axis (angle g around the z-axis).

[0041] Further, it is preferred if the evaluating step includes calculating a 2D ra dar image or a 3D radar image of the fastening site from the at least one response signal. Also, the images may be combined in a motion picture or video (4D).

[0042] A 2D radar image is typically sufficient if a center position of a hole is to be detected. However, a 3D radar emitter will allow to see whether the surface of the sheet portion is slanted, for example. On the other hand, a 3D radar image also allows to inspect three-dimensional fastening sites.

[0043] The evaluating step, further, may calculate more dimensions or other da ta, including for example intensity, phase, time, etc..

[0044] The above object is also achieved by a method for applying a fastening element to an automotive fastening site with a fastening hole, particularly of an automotive vehicle body , including: positioning a fastening tool at a fastening tool position in relation to the fastening site with a fastening hole; evaluating whether the fastening tool position is correct, using a radar assembly, particularly by conducting the method for inspecting and/or measuring of the present invention as described above; re-positioning the fas tening tool in dependence on the outcome of the evaluation step; and applying the fas tening element to the fastening site.

[0045] This method for applying a fastening element to an automotive fastening site with a fastening hole allows to conduct the step of applying the fastening element to the fastening site with high accuracy, even in a dirty environment such as a production line.

[0046] As previously mentioned, the fastening element is for instance a blind rivet element such as a blind rivet nut to be set in the fastening hole.

[0047] The difference between a diameter of the fastening hole and an outer diameter of a shaft of the blind rivet element is typically very small, so that the blind rivet element needs to be inserted into the fastening hole with high precision. Therefore, the evaluation of the fastening tool position, using the radar assembly, allows to conduct this insertion step with high precision.

[0048] In an alternative embodiment, the fastening site with a fastening hole in cludes a fastening rib which may be arranged within or behind the fastening hole in a body sheet portion, wherein the fastening element is a clip, particularly trim clip or a high retention fastening clip, or a U-base clip to be applied to the fastening rib. Such clips may be used for instrument panels carriers, for example.

[0049] The fastening rib is typically a plastic rib, and the clip is a metal element which may include dedicated winglets that form a locking engagement with the plastic rib. In some cases, such a fastening rib is arranged within or behind a fastening hole in a body sheet portion, so that insertion of the fastening element through the fastening hole must be done with high precision. [0050] In the prior art, such a step has been done by hand , because the instal lation needs exact positioning.

[0051] The above object is further achieved by a radar assembly for attaching to a tool head which includes a fastening tool, comprising a housing which can be at tached to a front end of the fastening tool, the housing having a central through hole, a circuit carrier arrangement located within the housing so as to surround the central through hole, and a transmit antenna arrangement and a receive antenna arrangement which are arranged on the circuit carrier arrangement.

[0052] While it is generally conceivable to use a radar assembly for inspecting and/or measuring a fastening site with a fastening hole such that an inspection axis of the radar assembly is displaced in parallel with respect to a fastening axis of the fastening tool, the radar assembly of the present invention allows to arrange the radar assembly in a manner concentric with respect to the fastening axis. In other words, the fastening axis and the inspection axis may be the same.

[0053] The housing of the radar antenna has a central through hole. Therefore, a part of the fastening tool may be guided through the central through hole for conducting the fastening process. The central through hole is dimensioned such that, preferably, a fastening element can be guided through the central through hole.

[0054] Preferably, the central through hole has an inner diameter of at least 5 mm, preferably at least 8 mm. Typically, the diameter is not greater than 50 mm, prefer ably not greater than 40 mm.

[0055] The housing is preferably made of a plastic material through which radar waves can penetrate without significant interference therewith. Therefore, the housing can be sealed against the environment. [0056] The housing is preferably attached to a front end of the fastening tool, such that the housing forms a foremost portion of the fastening tool, so as to provide the radar assembly with an unobstructed view on the fastening site.

[0057] The fastening tool may be a setting tool for blind rivet elements or clips.

[0058] The circuit carrier arrangement carries a radar antenna arrangement, as described below. However, the circuit carrier arrangement preferably carries also radar chipsets (ICs, particularly MMICs), and optionally a processing unit like a microcontroller, and further optionally memory for storage of data derived from the at least one response signal.

[0059] The transmit antenna arrangement may include a round or at least par tially circular antenna array, which is preferably arranged concentrically with respect to the fastening/inspection axis.

[0060] Preferably, the transmit antenna arrangement comprises two transmit antenna arrays and the receive antenna arrangement comprises preferably two receive antenna arrays.

[0061] The antenna arrays are preferably linear arrays. The number of transmit antennas within each antenna array is preferably in a range between 2 and 20, particularly in a range between 2 and 16, resulting in 8 to 256 individual antennas. The number of antenna elements in the transmit antenna arrays and in the receive antenna arrays may be the same. However, the number can be different, as explained above.

[0062] Further, it is preferred if the two transmit antenna arrays and the two re ceive antenna arrays are each arranged so as to be normal with respect to an axis of the through hole.

[0063] The antenna arrays are preferably skewed with respect to the axis of the through hole, i.e. do not intersect the axis. Preferably, the antenna arrays are arranged at a short distance from the central through hole, for example in a range from 1 mm to 10 mm.

[0064] In this case, it is ensured that the housing can be realized with small di mensions in directions traverse to the axis of the through hole.

[0065] In other words, the housing of the radar assembly can be attached to the front end of the fastening tool without increasing the front end dimensions of the fastening tool significantly, so as to avoid creating interference contours.

[0066] The axial length of the housing is preferably in a range from 5 mm to 40 mm. The extension of the housing in a direction transverse to the axis of the through hole is preferably in a range from 20 mm to 100 mm, preferably in a range from 30 mm to 60 mm.

[0067] In a preferred embodiment, the two transmit antenna arrays are ar ranged on opposite sites of the through hole, and the two receive antenna arrays are arranged on opposite sides of the through hole.

[0068] Further, it is preferred if the two transmit antenna arrays are arranged so as to be orthogonal to the two receive antenna arrays.

[0069] In this case, it is preferred if the two transmit antenna arrays and the two receive antenna arrays form a perimeter of a rectangle, preferably the perimeter of a square which is arranged concentric to an axis of the central through hole.

[0070] On the circuit carrier arrangement, the antenna arrays are preferably ar ranged close to the central through hole, and radar ICs are preferably arranged on a side of the antenna arrays which faces away from the central through hole.

[0071] The above object is further achieved by a tool head for a robot, particu larly for attaching to an arm of a robot, comprising a fastening tool for conducting a joining process at a fastening site with a fastening hole, particularly for applying a fastening element to a fastening site with a fastening hole of a workpiece; a tool controller adapted to position the tool head in relation to a position feature of the fastening site; a radar assembly comprising a transmit antenna arrangement, a receive antenna arrangement and a radar controller, and adapted to emit a radar signal in the direction of the fastening site and to receive a response signal, particularly a radar assembly according to the invention as described above; wherein the radar controller is further adapted to evaluate the position feature of the fastening site on the basis of the at least response signal, and to re-position the tool head, if necessary.

[0072] Preferably, a housing of the radar assembly is attached to a front end of a fastening tool of the tool head.

[0073] The joining process may be used to connect two workpieces together. However, in many cases, the joining process includes the fastening of a fastener to the fastening site provided with a fastening hole.

[0074] It will be understood that the features of the invention mentioned above and those yet to be explained below can be used not only in the respective combination indicated, but also in other combinations or in isolation, without leaving the scope of the present invention.

[0075] Exemplary embodiments of the invention are explained in more detail in the following description and are represented in the drawings, in which is:

Fig. 1 a schematic view of a fastening system in a production environment;

Fig. 2 a schematic view of an unset blind rivet nut;

Fig. 3 a schematic view of a U-base clip to be attached to a fastening rib locat ed behind a through hole of a sheet portion; Fig. 4 a schematic view of a fastening tool positioned in relation to a fastening site, wherein a radar assembly is arranged concentrically to the fas tening tool;

Fig. 5 a perspective view of an embodiment of a tool head with a fastening tool and a radar assembly;

Fig. 6 a perspective view of a blind rivet nut to be set by the fastening tool of Fig. 5;

Fig. 7 a sectional view of the blind rivet nut of Fig. 6;

Fig. 8 an explosive view of the fastening tool and the radar assembly of Fig. 5;

Fig. 9 a front view of the fastening tool of Fig. 8, with the radar assembly at tached thereto;

Fig. 10 a sectional view along a plane XII-XII in Fig. 9, showing a state where a blind rivet nut has been supplied to a front end of the fastening tool;

Fig. 11 a view similar to Fig. 10 wherein a spindle has been screwed into the blind rivet nut;

Fig. 12 a view similar to Fig. 10, wherein the blind rivet nut has been guided out of a central through hole of the radar assembly, so that the blind rivet nut is inserted into a fastening hole of a fastening site like a body sheet;

Fig. 13 a view similar to Fig. 10, wherein the blind rivet nut has been set in the fastening hole of the body sheet. Fig. 14 is a schematic planar view of a circuit carrier arrangement of a radar as sembly.

Fig. 15 a flow chart of a process for applying a fastening element to an automo tive fastening site;

Fig.16 a perspective view of a U-base clip; and

Fig. 17 a perspective view of a fastening rib to which the U-based clip of Fig. 16 is to be applied.

[0076] In Fig. 1, an automotive manufacturing site is schematically shown and designated by 10.

[0077] The automotive manufacturing site 10 is used to manufacture or assem ble a vehicle body 12 of an automobile. The vehicle body 12 may be a vehicle body in white.

[0078] The vehicle body 12 includes at least one fastening site 14 with a fas tening hole. The fastening site 14 is a location at the vehicle body 12, where a fastening process is to be conducted. However, the fastening site may be a reference site/feature as well.

[0079] Examples for such fastening processes are riveting (including blind rivet ing), placing a plastic clip on a carrier, etc.

[0080] The manufacturing site 10 includes a robot arrangement 16. The robot arrangement 16 comprises a robot 18 with at least one arm. A tool arrangement 20 is attached to an end of the robot arm.

[0081] Further, the robot arrangement 16 includes a tool supply unit 22 which may be carried by a movable carriage. The tool supply unit 22 includes a tool controller 24 which is connected to the tool arrangement 20. The tool controller 24 provides control signals for the tool arrangement 20, and may also provide energy for actuating the tool arrangement 20, including, for example, electrical energy, pneumatic energy, etc.

[0082] In case that the tool arrangement 20 is used for applying a fastener to the fastening site, the tool supply unit 22 preferably comprises a fastener supply 26. The fastener supply 26 is connected via a hose or the like to the tool arrangement 20. Fasten ers, for example rivets etc. can be supplied from the fastener supply 26 to the tool ar rangement 20 via the hose, using for example pressurized air.

[0083] The tool arrangement 20 includes a tool head 28 which has a fastening tool 30 attached thereto. In some cases the fastening tool 30 is a joining apparatus. Preferably, however, the fastening tool 30 is used to apply a fastener to the fastening site 14. To this purpose, the fastening tool 30 may include a riveting tool (e.g. a blind riveting tool), etc.

[0084] The tool head 28, further, comprises a radar assembly 32. The radar as sembly 32 is used for inspecting and/or measuring the fastening site 14 with a fastening hole. To this purpose, the tool arrangement 20, which includes the radar assembly 32, can be placed at a certain distance from the fastening hole, using the robot arrangement 16. Subsequently, the radar assembly 32 is actuated. The response signal of a transmitted radar signal is received and is subsequently evaluated and/or recorded.

[0085] In the evaluation step, the information about the fastening site might be used to re-position the tool arrangement 20 before a fastening process is conducted. In other cases, after a fastening process has been conducted, the information provided by the radar assembly can simply be recorded, in order to establish a quality protocol.

[0086] The information provided by the radar assembly 32 can either be used to automatically re-position the fastening tool, or can be provided for recording the response signal or information procured on the basis thereof, or can be shown on a monitor 36, which may be assigned to the tool supply unit 22. [0087] If the response signal is recorded, this is meant to include recording the response signal itself and/or information derived therefrom, e.g. a 2D or 3D radar image.

[0088] In Fig. 2 and Fig. 3, different fasteners are shown. For example, Fig. 2 shows a body sheet portion 40 of the vehicle body 12, wherein the sheet portion 40 has a fastening hole 42. Fig. 2 shows that a blind rivet nut 44 is inserted with its shaft into the fastening hole 42, before a blind rivet setting step is conducted.

[0089] Fig. 3 shows a sheet portion 40 with a hole 42"'. Another sheet portion 40b is located approximately parallel to the sheet portion 40. A fastening rib 48 is attached to the additional sheet portion 40b, such that the fastening rib 48 is located in alignment with and behind the fastening hole 42"'. The fastener, here, is a U-base clip 44'" made of metal, which can be fastened to the fastening rib 48, by inserting the U-base clip through the fastening hole 42'".

[0090]

[0091] Fig. 4 is a schematic view of an embodiment of a tool head 28'. The tool head 28' includes a fastening tool 30 for fastening a fastener 44 to a fastening site 14, particularly to a fastening hole 42. The fastener 44 may, for example, be a blind rivet, particularly a blind rivet nut (for instance as depicted in Fig. 6 and Fig. 7).

[0092] The fastening tool 30 defines a fastening axis 45 which is typically nor mal to a surface of the sheet portion 40 and is defined by the direction in which the fastener 44 is applied to the fastening site 14.

[0093] The tool head 28, further, comprises a radar assembly 32' which is ar ranged concentrically to the fastening tool. The radar assembly 32 includes a radar assembly through hole which is coaxial to the fastening axis 45. The through hole 50 is formed such that at least the fastener 44, but preferably also a part of the fastening tool 30 can be moved through the through hole 50. [0094] The radar assembly 32' is adapted to emit at least one radar signal T and to receive at least one response signal R. As such, the radar assembly 32' is able to provide at least one response signal from which a radar image of the fastening site 14 can be derived. To this purpose, the tool head 28 is positioned in relation to the fastening site within a range H of 1 cm to 100 cm, preferably 1 cm to 20 cm, particularly preferred 2 cm to 10 cm, and in particular 3 cm to 5 cm.

[0095] The antenna arrangement provided within the radar assembly 32' is po sitioned such that the fastening site 14 is located within a coverage or footprint of the antenna arrangement, which includes a transmit antenna arrangement and a receive antenna arrangement.

[0096] An evaluation of the image derived from the at least one response signal R allows to re-position the tool head 28' in relation to the fastening site 14. Fig. 4 schemat ically shows that the tool head 28' has a position that can be defined by coordinates XT, yi and Z_T. Further, the tool head 28' has an attitude which is defined by attitude angles at around the x-axis, bt around the y-axis and gt around the z-axis.

[0097] Similarly, a position of the fastening site 14 can be defined by its coordi nates XF, y_F, ZF, and the attitude of the fastening site 14 can be defined by an angle CXF around the x-axis, an angle P_F around the y-axis and an angle JF around the z-axis.

[0098] Further characteristic position features of the fastening site may include a center CF of the fastening hole 42, a diameter DF of the fastening hole, and a thickness t_F of the sheet portion 40.

[0099] When a fastening element 44 is to be fastened to the fastening site 14, the tool head 28' with the fastening tool 30 is positioned in relation to the fastening site 14. Subsequently, the radar assembly 32' is activated so as to produce at least one response signal R from which at least one position feature regarding the fastening site can be derived. On the basis thereof, it is evaluated whether the fastening tool position is correct. Subsequently, the fastening tool is re-positioned, in case that the evaluation step has revealed that the fastening tool 30 was not correctly positioned and aligned with the fastening site 14. Only then the fastening process is conducted, including applying the fastening element 44 to the fastening hole.

[00100] In Figs. 5 to 13, another tool head 28" with a fastening tool 30" for set ting blind rivet nuts 44^IV in fastening holes 42 is shown. The design and function of the tool head 28” correspond to those of the above described tool heads. Same reference numer als are used, therefore. Mainly the differences are described below.

[00101] The fastening tool 30" includes a tool front end 52 which is attached to the tool head 28". The tool front end 52 includes a fastener supply channel 54 through which fasteners (e.g. blind rivet nuts 44^IV) are supplied, for example by means of pressur ized air.

[00102] Further, the fastening tool 30 includes a tool drive system 56 which is aligned with the tool front end 52 along the fastening axis 45.

[00103] The blind rivet nuts 44^IV that can be fastened by means of the fastening tool 30" are shown in Figs. 8 and 9.

[00104] The blind rivet nut 44^IV includes a blind rivet nut head 60 having a di ameter DH which is larger than the diameter DF of the fastening hole 42. Further, the blind rivet nut 44^IV includes a blind rivet nut shaft 62 extending from the nut head 60. The outer diameter Ds of the nut shaft 62 corresponds to the diameter DF of the fastening hole 42, such that the shaft 62 can be inserted into the fastening hole 42.

[00105] The nut shaft 62 comprises at one end thereof an inner thread (nut thread 64). Further, in an area between the nut thread 64 and the nut head 60, the nut shaft 62 includes a deformation region 66. The deformation region 66 is deformed during a blind rivet nut setting process, such that a rivet bead can be formed which engages a blind side of a sheet portion 40, so that the sheet portion 40 is arranged between the nut head 60 and the bead. [00106] In Fig. 8, the fastening tool 30" is shown in more detail. The fastening tool 30" includes a spindle 70.. The spindle 70 can be rotated by the tool drive system 56, and can be axially displaced by the tool drive system 56. These two motions may be combined, preferably synchronized to a thread pitch of a thread of a blind rivet nut.

[00107] The tool front end 52 includes at its foremost end a nut holding portion 72. In the nut holding portion 72, a blind rivet nut 44^IV can be held in a rotationally fixed manner, so that an outer thread of the spindle 70 can be screwed into the nut thread 64.

[00108] The foremost end of the tool front end 52 is closed by a separation pate 74, which separates the tool front end 52 from the radar assembly 32".

[00109] The foremost end of the tool front end 52 has a rectangular shape. The shape of the radar assembly 32" corresponds to that of the foremost end of the front end 52. Particularly, the radar assembly 32" has, in a planar view, a rectangular shape, with a long side A and a short side B. The length of the long side A is within a range from 2 cm to 10 cm, particularly in a range from 3 cm to 6 cm.

[00110] The length of the short side B is in a range from 1 cm to 6 cm, particular ly from 2 cm to 5 cm. The thickness T of the radar assembly 32" is in a range from 1 cm to 4 cm, particularly in a range from 1 cm to 3 cm.

[00111] The radar assembly 32" is encased by a radar assembly housing 76 having the above dimensions A, B, T. Further, a housing protrusion 78 is provided at one of the long sides of the radar assembly housing 76. The housing protrusion 78 serves to provide the circuitry of the radar assembly 32" inside the housing 76 with energy and with a bi-directional signal interface (e.g. Ethernet).

[00112] Fig. 9 is a front view of the tool front end 52 and shows the radar as sembly 32" and the through hole 50 which is arranged concentrically to the fastening axis 45. The diameter DR of the through hole is larger than the outer diameter of the largest dimension of the fastener, particularly larger than the outer diameter D_H of the blind rivet nut head 60.

[00113] Figs. 10 to 13 each show sectional views along a plane XII-XII in Fig. 9, and show different steps during a fastening process.

[00114] Particularly, Fig. 10 shows that the spindle 70, at its front end, comprises a thread portion 80 with an outer thread corresponding to the nut thread 64 of the blind rivet nut 44^IV.

[00115] Further, in a portion adjacent to the thread portion 80, the spindle 70 is provided with a sleeve 82. The sleeve 82 is arranged concentrically with the sleeve 70. The sleeve 82 is axially displaceable with respect to the spindle 70. At its front end, the sleeve 82 comprises a setting portion adapted to engage the upper side of the blind rivet nut head 60 during a setting process.

[00116] Fig. 10 also shows the fastener supply channel 54 through which fas teners 44 are supplied by pressurized air. One fastener 44B is held in a waiting position (offset from the fastening axis) by means of a movable nose extending into the channel 54. Further, Fig. 10 shows a fastener 44A which is held in the nut holding portion 72. Between the waiting position and the nut holding portion 72, there is provided a sensor 84 which senses that a fastener 44A has passed and must therefore be provided in the nut holding portion 72. In the nut holding portion 72, the fastener 44A may be held rotationally fixed by means of jaws 86. In Fig. 10, the jaws are in a released position.

[00117] In Fig. 10, the thread portion 80 is retracted so as to allow fasteners 44 to pass fromthe channel 54 into the nut holding portion 72.

[00118] Starting from Fig. 10, a force F_A is applied on the spindle 70 so as to move the thread portion 80 into the direction of the fastener 44A held in the nut holding portion 72. [00119] As is shown in Fig. 11, the spindle 70 is rotated by means of a force FR so as to screw the thread portion 80 into the nut thread 64, until the setting portion of the sleeve 82 abuts the rivet nut head 60. During this process, the jaws 86 are in a closed position so as to rotationally fix the fastener 44A.

[00120] When the fastener 44A is in the nut holding portion 72, it does not pro trude from the central hole 50.

[00121] In Fig. 12, it is shown that the spindle 70 is moved further forward so that the fastener 44A is moved out of the through hole of the radar assembly 32". To this purpose, the jaws 86 are briefly released. As soon as the rear part of the sleeve 82 has passed the jaws 86, they are driven into their closed position again, so that, as is shown in Fig. 12, the sleeve 82 abuts the jaws 86 and cannot be retracted again.

[00122] In the position shown in Fig. 12, the shaft 62 of the fastener 44A has been inserted into a fastener hole 42 of a sheet portion (not shown in Fig. 12).

[00123] For the process of setting the blind rivet nut 44A, the spindle 70 is re tracted by a force Fs, as shown in Fig. 13. The front setting portion of the sleeve 82 engages the nut head 60, and the spindle 70 acts as a blind rivet mandrel which draws the portion of the nut shaft which is provided with the nut thread, backwards, such that the deformation region 66 deforms and forms a bulge 66', as is shown in Fig. 13. The bulge 66' engages the blind side of the sheet portion 40, such that the blind rivet nut 44A is securely fastened to the sheet portion 40. Subsequently, the spindle 70 is rotated into a direction opposite to the one of Fig. 11, so as to release the spindle from the nut thread. In the following, the claws 86 are released, and the spindle 70 is withdrawn again into the position shown in Fig. 10, such that the next fastener 44B can be blown into the nut holding portion 72 for conducting another blind rivet nut setting process as described above.

[00124] Fig. 14 shows a schematic view of a printed circuit board 90 of a radar assembly 32'". [00125] The printed circuit board 90 has a rectangular shape, with a long side a and a short side b. The length of the long side a corresponds to the long side A of the housing 76 in Fig. 8. The length of the short side b corresponds to the length of the short side B of the housing 76 in Fig. 8.

[00126] The circuit board 90 has a central hole 50"'. In Fig. 14, the central hole 50"' has a rectangular shape with a long side c and a short side d. However, the shape of the central hole 50'" may be circular as well.

[00127] The radar assembly 32'" includes a first transmit antenna array 92 and a second transmit antenna array 94. Each of the transmit antenna arrays 92, 94 includes a number of 2 to 16 transmit antennas which are linearly aligned in parallel to one of the sides of the printed circuit board 90. In the present case, the two transmit antenna arrays 92, 94 are arranged in parallel to the long sides a of the printed circuit board 90.

[00128] The two transmit antenna arrays 92, 94 are arranged on opposite sides of the central through hole 50'".

[00129] Further, the radar assembly 32'" includes a first receive antenna array 96 and a second receive antenna array 98. The receive antenna array 96, 98 each include a number of receive antenna elements, wherein the number may be in a range from 2 to 16. The number may be smaller than that of the number of transmit antenna elements in each of the arrays 92, 94.

[00130] The two receive antenna arrays 96, 98 are arranged on opposite sides of the central through hole 50'" and are arranged orthogonal to the transmit antenna arrays 92, 94, so that the antenna arrays 92 to 98 form the perimeter of a rectangle.

[00131] The length of the transmit antenna arrays 92, 94 is shown at e. The length of e is smaller than the length of the long side a of the printed circuit board 90, but is longer than the length of the long side c of the central through hole 50’”. Further, each of the receive antenna arrays 96, 98 have a length f which is smaller than the length b of the short side of the printed circuit board 90 and larger than the short side d of the through hole 50"'.

[00132] The rectangular shape of the printed circuit board 90 may be a square shape, in which case the central through hole may also have a square shape or a circular shape. In this case, it follows a = b and e = f.

[00133] The printed circuit board 90 also includes transmit circuitry 100 with in tegrated circuits (ICs) which are assigned to the antenna elements of the transmit antenna arrays 92, 94. The transmit circuitry is arranged between the respective transmit antenna arrays 92, 94 and the outer side of the printed circuit board 90.

[00134] Similarly, the printed circuit board 90 includes receive circuitry 102 in cluding ICs connected to the antenna elements of the receive antenna arrays 96, 98. In each case, the receive circuitry 102 is arranged between the respective receive antenna array 96, 98 and the outer side of the printed circuit board 90.

[00135] The above antenna arrangement of the radar assembly 32"' allows to operate the radar assembly 32'" as a MIMO radar (multiple-input-multiple-output).

[00136] In a MIMO radar system, each transmit antenna element is assigned an individual waveform generator of the transmit circuitry 100, which provides an individual signal for this antenna element. This individual signal is the basis for assigning return signals to its source.

[00137] For a more effective radar signal processing, each individual transmit signal may be changed ("adaptive waveform") with the target, to improve the signal noise ratio.

[00138] Fig. 15 is a flow chart 110 of a fastening process which can be conduct ed in the automotive manufacturing site 100 described above, using for example the tool head 28 of Fig. 5. [00139] The process starts at S2. In a subsequent step S4, a robot moves the tool head 28 to a certain position.

[00140] Into the next step S6 it is enquired whether the robot is in position. If no, the process returns to step S4. If the robot is in position (yes in step S6), the process proceeds to step S8. In step S8, the robot sends a start signal to the radar assembly 32, so that at least one transmit signal T is emitted.

[00141] In step S10, it is enquired whether a at least one receive signal R has been received. If the answer is no in step S10, the process returns to step S8. If the answer is yes, the process proceeds to step S12. In step S12, an evaluation is conducted whether the robot position is correct, on the basis of an evaluation of the at least one response signal. If the robot position is determined to be correct in step S12 (yes), the process proceeds with step S14 so as to initiate the fastening process.

[00142] In step S16, it is enquired whether the fastening process has been com pleted. If the answer is no, the process proceeds to step S17 in which a timer is enquired. If the elapsed time is larger than a threshold (yes in step S17), a fault signal is generated in step S19. Thereafter the process ends at step S30. On the other hand, if the answer in step S17 is no, the process returns to step S16. If the answer in step S16 is yes (fastening process completed), the fastening tool sends an acknowledgement signal to the robot in step S18.

[00143] In step S20, an enquiry is made as to whether another fastening process is to be conducted. If the answer is yes, the process returns to step S22, in which a counter is incremented. After step S22, the process returns to step S4.

[00144] If the answer in step S20 is no, the process is stopped at step S30.

[00145] On the other hand, if the evaluation in step S12 has revealed that the robot position is not correct, a robot relocation or re-positioning is initiated in step S24. [00146] In subsequent step S26, an enquiry is made whether the robot is at the relocated position. If the answer is no, step S26 inquires whether a timer has reached a certain threshold. If the answer is yes, the process releases the fault signal of step S19.

On the other hand, if the timer has not yet reached the threshold, the process returns to step S26.

[00147] If the answer in step S26 is yes (robot has been relocated to new posi tion), the process returns to step S8, so that the radar assembly is started again. The process the proceeds through steps S10 to S20, in order to complete the fastening process.

[00148] While above a system for setting a blind rivet nut has been described in detail, the teaching can be applied to other fastening processes as well.

[00149] Fig. 16 shows for example a fastener 44^v, which is a U-base fastener made of metal. The fastener 44^v is adapted to be placed on a fastening rib48^v made of plastic material, as shown in Fig. 17.

[00150] The fastener 44^v has to be positioned on the fastening rib 48^v with high precision. In some cases, the fastening rib 48^v is located behind a hole, as is shown at 42"' in Fig. 3.

[00151] It is to be understood that the fastening tool for placing the fastener 44^v onto the fastening rib 48^v is different from the fastening tool shown for example in Fig. 5 to 13. However, the same principles apply. Here, the shape of the central through hole 50 in the radar assembly 32 may in fact be rectangular and not circular. Further, the fastening hole 42"' may also be rectangular and not circular. Reference numerals:

Automotive manufacturing site vehicle body fastening site robot arrangement robot with arm tool arrangement tool supply unit tool controller fastener supply tool head fastening tool radar assembly monitor body sheet portion fastening hole fastener fastening axis/inspection axis48 fastening rib radar assembly through hole tool front end fastener supply channel tool drive system blind rivet nut head blind rivet nut shaft blind rivet nut thread deformation region spindle nut holding portion separation plate radar assembly housing housing protrusion thread portion 70 82 sleeve 70

84 sensor

86 jaws

90 printed circuit board

92 first transmit antenna array

94 second transmit antenna array

96 first receive antenna array

98 second receive antenna array

100 transmit circuitry

102 receive circuitry

104 radar image

106 processed radar image

108 virtual MIMO antenna

110 flow chart

T radar signal

R response signal

X_T,y-r,Z_T tool coordinates a^t, bt, gt tool attitude angles

XF.yF.zp fastening site coordinates

OF, br, YF fastening site attitude angles

CF fastening site center

DF fastening site diameter

DH rivet nut head diameter

DS rivet nut shaft diameter

DR radar assembly hole diameter

FR rotation threading force

FA axial force

FS setting force tF sheet thickness H distance 28/14 along 45 a long side of 90 b short side of 90 c long side of 44’” d short side of 44’” e length transmit antenna arrays f length receive antenna arrays

A long side of 76

B short side of 76

T thickness of76’

Claims

1. A method for inspecting and/or measuring a fastening hole (42), by means of a radar assembly (32) which has a transmit antenna arrangement (92, 94) and a re ceive antenna arrangement (96, 98), the method including the steps of: positioning the radar assembly (32) in relation to the fastening hole (42) on which a fastening process is to be conducted, such that the fastening hole (42) is located within a coverage of the transmit antenna arrangement (92, 94) and of the receive antenna arrangement (96, 98); emitting at least one radar signal (T) by the transmit antenna arrangement (92, 94); receiving at least one response signal (R) by the receive antenna arrange ment (96, 98); and evaluating and/or recording the response signal (R).

2. The method of claim 1, wherein the radar assembly (32) is positioned within a range (H) of 1 cm to 100 cm in relation to the fastening hole (42).

3. The method of claims 1 or 2, wherein the radar assembly (32) is a MIMO radar assembly, wherein the transmit antenna arrangement (92, 94) includes multiple transmit antennas and wherein the receive antenna arrangement (96, 98) includes multiple receive antennas, and wherein the emitting step includes emitting different radar signals from each of the transmit antennas.

4. The method of any of claims 1 to 3, wherein the fastening site (14) includes a fastening feature (42) of a vehicle body portion (40).

5. The method of any of claims 1 to 4, wherein the radar assembly (32) is carried by a robot (18) and wherein the evaluating step includes determining at least one po sition feature (CF, DF, XF F.ZF, OF, br, YF) of the fastening hole (42).

6. The method of any of claims 1 to 5, wherein the evaluating step includes calculat ing an 2D radar image or an 3D radar image of the fastening hole (42) from the at least one response signal (R).

7. A method for applying a fastening element (44) to an automotive fastening hole (42), particularly of an automotive vehicle body (12) in white, including: positioning a fastening tool (30) at a fastening tool position in relation to the fastening site (14) ; evaluating whether the fastening tool position is correct, using a radar as sembly (32), and by conducting the method according to any one of claims 1 to 6; re-positioning the fastening tool (30) in dependence on the outcome of the evaluating step; and applying the fastening element (44) to the fastening hole (42).

8. The method of claim 7, wherein the fastening element (44) is a blind rivet element to be set in the fastening hole (42).

9. A tool head (28) for a robot (18), comprising a fastening tool (30) for conducting a joining process at a fastening site (14), particularly for applying a fastening element (44) to a fastening site (14) of a workpiece (40); a tool controller (24) adapted to position the tool head (28) in relation to a position feature (C_F, D_F, X_{F F}.Z_F, O_F, br, Y_F) of the fastening site (14); a radar assembly (32) comprising a transmit antenna arrangement 92, 94), a receive antenna arrangement (96, 98) and a radar controller, and adapted to emit a radar signal (T) in the direction of the fastening site (14) and to receive a response signal (R), particularly a radar assembly (32) ac cording to any one of claims 10 to 14; wherein the radar controller is further adapted to evaluate the position feature of the fastening site (14) on the basis of the response signal (R), and to re-position the tool head (28), if necessary.

10. Tool head (28) for a robot (18) according to claim 9, comprising: a housing (76) which can be attached to a front end (52) of the fastening tool (30), the housing (76) having a central through hole (50), a circuit carrier arrangement (90) located within the housing (76) so as to surround the central through hole (50), a transmit antenna arrangement (92, 94) and a receive antenna arrange ment (96, 98) which are arranged on the circuit carrier arrangement (90).

11. Tool head (28) of claim 10, wherein the transmit antenna arrangement (92, 94) comprises two transmit antenna arrays (92, 94) and wherein the receive antenna arrangement (96, 98) comprises two receive antenna arrays (96, 98).

12. Tool head (28) of claim 11, wherein the two transmit antenna arrays (92, 94) and the two receive antenna arrays (96, 98) are each arranged so as to be normal with respect to an axis (45) of the through hole (50).

13. Tool head (28) of any of claims 10 to 12, wherein the two transmit antenna arrays (92, 94) are arranged on opposite sides of the through hole (50), and wherein the two receive antenna arrays (96, 98) are arranged on opposite sides of the through hole (50).

14. Tool head (28) of any of claims 10 to 13, wherein the two transmit antenna arrays (92, 94) are arranged so as to be orthogonal to the two receive antenna arrays (96, 98).

15. The use of radar imaging and/or of a radar assembly (32) for inspecting a fas tening site (14) or a reference site in a production environment, preferably a fas tening site on an automotive body (12) at which a fastening process is to be con ducted or has been conducted.