DESCRIPTION

The present invention concerns a measurement device for monitoring robot-guided and tool-based processing of a work piece surface as well as a related alignment method for robot-based alignment of a tool space or processing tool relative to a work piece surface.

US 5,848,859 A discloses a self-normalizing drill head. It comprises a pressure foot for contacting the work piece surface, which is supported by a universally swiveling joint (spherical bearing) on a drill housing, which is guided by a control arm.

US 2009/0018697 A1 discloses a device for positioning an assembly tool (effector) in relation to a surface. The effector is attached to the end of an articulated arm, which is able to apply a force against the surface by means of the effector. The effector comprises a front wall facing toward the surface. A support plate is slideably mounted on the front wall (flat slide bearing) and a nose is supported by a spherical bearing on the support plate.

The prior known techniques are not devised optimally. It is an objective of the present invention, to provide an improved measurement device and an improved alignment method according to the preamble of the respective independent claim. The invention solves this objective with the characterizing features of the independent claims.

The measurement device according to the present disclosure has a nose piece with a frontal contact structure, which is supported by a multi-axial bearing on the main body of the measurement device. The multi-axial bearing allows both a (rotational) tilt movement of the nose piece and a (translational) shift movement of the nose piece along two axes, which are oriented essentially perpendicular to the tool space axis of an elongated tool space, in which a processing tool for processing the work piece surface can be arranged.

By including the two axes for tilt and shift movements in a single multi-axial bearing, the dimensions of the measurement device can be reduced, so that surface processing operations can be performed even in narrow spaces.

The measurement device further comprises a position detection device for determining a relative position of the movable nose piece in respect of a reference position, which is defined in relation to the main body and/or the tool space axis. The measurement device is used in an alignment method according to the present disclosure for robot-based alignment of the tool space or the processing tool relative to the work piece surface. The measurement device is moved (directly or indirectly) by a robot. A tilt movement and/or a shift movement of the nose piece, which occurs while the measurement device is in contact with the work piece surface, is determined based on the measurement result of the position detection device. The robot is controlled based on the determined tilt movement (s) and/or shift movement (s) in such a way, that the movement (s) is/are compensated. So, the tool space or the processing tool is returned to the reference position and/or maintained in the reference position. Grinding marks or other comparable surface deteriorations and misalignment of the processing tool can thus be avoided.

Further advantageous embodiments of the invention are comprised in the dependent claims.

The invention is depicted in the drawings in an exemplary and schematic way. They show:

Figure 1: a schematic view of a robot carrying an effector and a measurement device according to the present disclosure;

Figure 2: a first explosion diagram of a preferred variant of the measurement device comprising a first variant of a multi- axial bearing; Figures 3 and 4:a side view and a semi-cut view of the measurement device;

Figure 5: an enlarged semi-cut view of the measurement device, which is perpendicular to the semi-cut view of Figure 4;

Figure 6: a second explosion diagram of the measurement device;

Figures 7 to 10:schematic diagrams for illustrating an alignment method according to the present disclosure;

Figure 11: a second variant of a multi-axial bearing for the measurement device. The measurement device (1) according to the present disclosure is preferentially guided by a robot (3), as depicted in figure 1. The robot may change its pose, i.e. move its arm members and joints for moving the measurement device (1). The robot (3) can move the measurement device (1) into contact with a work piece surface (6).

The measurement device (1) comprises a main body (4), by which it is attachable or attached to the robot (3) or to an end effector (2) mounted to the robot. Attachment of the measurement device (1) or the main body (4) can thus be based on direct or indirect mounting on the robot. In a preferred embodiment, the measurement device (1) comprises at least on adapter (18) for mounting. As depicted in figures 7 to 10, the measurement device (1) comprises a moveable nose piece (5) with a frontal contract structure (7). This contact structure (7) is designed for contacting the work piece surface (6). It is preferentially an integral part of the nose piece (5). Alternatively, the frontal contact structure (7) may be a separate part, which is permanently or temporally fixed on the nose piece (5). In the following explanation, it will be assumed that the frontal contract structure is an integral part of the nose piece (5). The frontal contact structure (7) at least partially surrounds an elongated tool space (8), where a processing tool (9) can be arranged. The tool space (8) has a tool space axis (X). The tool space axis (X) is used in the following explanation as a main reference criterion for alignment. The tool space axis (X) may in particular be the longitudinal center axis of the measurement device (1) and it may further coincide with a main longitudinal working axis of the end effector (2) or robot (3), to which the measurement device (1) is mounted.

The processing tool (9) may be any kind of tool, like for example a drilling tool, a riveting tool, a punching tool, a stamping tool, an embossing tool or the like.

The processing tool (9) may be attached to the end effector (2), which may comprise one or several actuators for driving and/or moving the processing tool (9). In particular, the end effector may comprise an actuator for extending the processing tool (9) along the tool space axis (X) for bringing it into contact with the work piece surface (6). Alternatively or additionally, a processing tool (9) and the one or more actuators for driving and/or moving the processing tool (9) may be a part of the measurement device (1).

The main body (4) of the measurement device (1) may have any suitable design. It preferentially has the basic shape of a hollow cylinder or a sleeve. In other words, the measurement device (1) preferentially comprises a sleeve-shaped main body (4). The tool space (8) is preferentially at a pre-defined position and orientation within the main body (4). The longitudinal axis of the main body (4) may preferentially be oriented in parallel to the tool space axis (X). In particular, the tool space axis (X) and the longitudinal axis of the main body (4) may coincide, i.e. have the same orientation and position, which is the assumed case in the following explanation.

The multi-axial bearing (13) may have an arbitrary design. It comprises two axes (A, B), which define the movement (s) of the nose piece (5) and thus the frontal contact structure (7) with respect to the main body (4).

In figures 7 to 10, the multi-axial bearing (13) is depicted in a schematic way. Figures 2, 4, 5 and 6 show a first variant of a multi-axial bearing (13). Figure 11 shows another variant of a multi-axial bearing (13). Beside those variants, any other kind of multi-axial bearing (13) may be used, which allows a tilt movement (Tl, T2) of the nose piece (5) around two axes (A, B), which are essentially perpendicular to the tool space axis (X) and in addition a (translational) shift movement (Si, S2) of the nose piece along the same two axes (A,B).

In other words, the multi-axial bearing (13) is an integrated bearing allowing four degrees of movement, which are defined by the two axes (A, B): One rotational degree of movement and one translational degree of movement are respectively defined by each of the two axes (A, B). Again in other words, each of the two axes (A, B) is both a rotational axis and a translational axis for the movement of the nose piece (5), wherein the two axes (A, B) are integrated in one multi-axial bearing (13). As depicted in figures 2, 4, 5 and 6, the measurement device (1) comprises a detection device (10) for determining a relative position of the moveable nose piece (5) in respect of a reference positon (R). The reference position (R) is depicted in Figures 4, 5 and 7. Figures 8 to 10 illustrate a more or less displaced position (D) of the nose piece (5). The reference position (R) may be defined in relation to the main body (4) and/or in relation to the tool space axis (X).

The position detection device is designed to detect both the tilt movement (s) (Tl, T2) of the nose piece (5) and the shift movement (s) (SI, S2) of the nose piece (5) around and along the two axes (A, B).

In other words, the position detection device (10) is designed for directly determining the relative position of the moveable nose piece (5) in respect of the reference positon (R).

It is thus preferentially not required to separately detect a shift movement by a first detection device and a tilt movement by another detection device and to calculate the overall relative position based on those parameters. However, the positon detection device (10) may comprise two or more sensors (34), which in common determine the relative positon of moveable nose piece in respect of the reference position (R). The sensors (34) may have any arbitrary design. Preferred embodiments for the sensors (34) will be explained further below.

The nose piece (5) preferentially comprises a rear section (12), which moves relative to the main body (4) due to a movement of the frontal contract structure (7). The rear section (12) is preferentially an integral part of the nose piece (5), so that the nose piece (5) (and the frontal contract structure (7)) move in unison with the rear section (12) around the two axes (A, B) (rotational tilt movement) and along the two axes (A, B) (translational shift movement). Alternatively, the rear section (12) may be a separate part, which is temporarily or permanently fixed to the nose piece (5).

With respect to the multi-axial bearing (13), the frontal surface structure (7) extends essentially along the tool space axis (X) toward the work piece processing space, whereas the rear section (12) is orientated toward the end effector (2) / the robot (3). A frontal end or frontal direction is thus a distal end/distal direction (pointing away from the robot/end effector). A rear end or rear direction is correspondingly a dorsal end or dorsal direction (pointing towards the robot/end effector). The position detection device (10) is preferentially designed for combined determination of the translational shift movement (s) (SI, S2) and the rotational tilt movement (s) (Tl, T2) of the nose piece (5), as explained above. It is particularly preferred that this combined determination is based on measuring local distances (dl, d2, d3, d4) of the rear section (12) with respect to the main body (4). Alternatively, any other measuring scheme may be applied. The rear section (12) may have the shape of a sleeve or a cup, which at least partially envelopes or surrounds the main body (4). This is best visible in figures 4 and 5.

The local distances (dl-d4) may be measured between the outer cylinder wall surface of the main body (4) and an inner surface of the rear section (12) of the movable nose piece (5). The inner surface of the rear section (12) may also have a cylinder shape. Alternatively, it may have any other suitable shape.

The position detection device (10) may comprise any suitable number and kind of sensors (34) for the above mentioned purpose.

Optionally, the measurement device (1) and/or the position detection device (10) may comprise one or several emitters (33), which support the sensors (34). The sensors (34) may be inductive sensors, conductive sensors, field sensors, ultra-sonic sensors, radiation sensors or the like. The one or several emitters (33) may correspondingly be magnetic emitters, (electric) field emitters, ultra-sonic emitters, radiation emitters or the like.

In the examples of figure 5 and 6, a plurality of magnetic field sensors (34) (inductive sensors) is arranged on the circumferential outer surface of the main body (4). The sensors (34) are directed in a radial direction toward the inner surface of the rear section (12) of the movable nose piece (5). They are designed for measuring a distance (dl-d4) between a sensor (34) and a corresponding emitter (33), which is arranged at or on the movable nose piece (5). In the examples of figures 5 and 6, the emitters (33) are magnetic field emitters (e.g. permanent magnets or electric magnets).

According to a preferred embodiment, the sensors (34) and emitters (33) are arranged such, that - when the nose piece (5) is in the reference position (R), a respective emitter (33) is arranged in the measurement direction opposite to a sensor (34).

The arrangement of sensors (34) and emitters (33) may be reversed with respect to the aforementioned example. Alternatively, both sensor and corresponding emitter may be arranged on the same part i.e. both on the main body (4) or both on the rear section (12) of the nose piece

(5).

Preferentially, at least two sensors (34) are present, which measure a distance (dl-d4) of the rear section (12) with respect to the main body (4) next to each other. The pair of neighboring sensors may thus measure in two different directions, which are both essentially perpendicular to the tool space axis (X). In a pair of sensors (34), the two sensors may be arranged next to each other along the tool space axis (X). The pair of sensors may be arranged on a common sensor support, e.g. a common board (printed circuit board), as depicted in Figures 5 and 6.

It has been found that very precise determination of both tilt movements (Tl, T2) and shift movements (SI, S2) can is possible by arranging single sensors (34) or pairs of sensors (34) at 90 degree distances around the tool space axis (X).

In the example of figure 5, a shift movement (SI) along the first axis (A) and a tilt movement (T2) around the second axis (B) can be determined very precisely based on the various differences between the measured distances (dl, d2, d3, d4), which are determined on both sides of the main body (4). In an analogues way, further distances may be measured essentially perpendicular to the distances (dl-d4) shown in figure 5 (compare Figure 4, where however the measured distances are not depicted). Figures 2, 4, 5 and 6 illustrate a first preferred embodiment of the multi-axial bearing (13). Figure 11 shows a second preferred embodiment.

In both variants, the multi-axial bearing (13) comprises a first bearing member (30) connected with the main body (4), an intermediate bearing member (31) and a second bearing member (32) connected with a nose piece (5). The intermediate bearing member (31) can be tilted and shifted with respect to the first bearing member (30) around and along an axis (B). It can further be tilted and shifted with respect to the second bearing member (32) around and along the other axis (A). As a result, the first bearing member (30) can be moved in a combined tilt and shift movement both around and along the axis (A) and around and along the axis (B).

In other words, one of the two axes (A) is arranged between the first bearing member (30) and the intermediate bearing member (31), allowing tilt (Tl) and shift (SI) movement of the intermediate member (31) relative to the main body (4); and the other of the two axes (B) is arranged between the intermediate member (31) and the second bearing member (32), allowing tilt (T2) and shift (S2) movement of the nose piece (5) relative to the intermediate member (31) and thus also relative to the main body (4).

In the example of figures 2, 4, 5 and 6 the axes (A, B) are formed by pairs of grooves (39), which are arranged in the front and rear surfaces (with respect to the tool space axis (X)) of the main body (4)/first bearing member (30), the intermediate bearing member (31) and the nose piece (5)/second bearing member (32). The grooves (39) have an orientation, which is essentially perpendicular to the tool space axis (X), when the nose piece (5) is in the reference position (R). The grooves for forming the first axis (A) of the multi- axial bearing (13) are further essentially perpendicular to the grooves (39) for forming the second axis (B).

Balls (38) are arranged between two corresponding grooves (39) of the neighboring parts (first bearing member (30) to intermediate member (31)/intermediate member (31) to second bearing member (32)). As can be seen in the semi-cut views of Figure 4 and

Figure 5, the balls (38) may be held within the grooves (39) along the axes (A, B) on the one hand by abutment against an inner surface of the nose piece (5) or against the main body (4) and on the other hand by an outer limitation member, as for example the displayed fixation ring (28). In other words, the stroke of the balls (38) along the axis (A, B) may be limited by at least one suitable limitation member, which is arranged at or on the inner end and/or the outer end of the respective groove (39). The measurement device (1) according to the present disclosure may comprise one or several locking devices (15, 15') for locking the momentary position of the movable nose (5) with respect to the main body (4) and/or the tool space (8).

A first variant of a locking device (15) is shown in figures 2, 4, 5 and 6. It comprises a pair of locking surfaces (36), wherein one of the locking surfaces (36) is arranged (directly or indirectly) on the movable nose piece (5) and the other locking surface is arranged

(directly or indirectly) on the main body (4). At least one of the locking surfaces (36) may be arranged on a movable or displaceable structure. In the displayed examples, one locking surface (36) is arranged on the inner front surface (with respect to the tool space axis (X)) of a ring-shaped flange cap (37), which may be attached to the rear section (12) of the nose piece (5).

Another locking surface (36) is arranged on a rear surface of a ring-shaped moveable skid (26), which is slideably arranged on the main body (4).

When the skid (26) is urged in the rear direction (i.e. away from the nose piece (5)), the locking surfaces (36) are pressed against each other, which causes the locking of the momentary positon of the moveable nose (5) with respect to the main body (4). When the skid (26) is however moved in the front direction (i.e. toward the nose piece (5)), the locking surfaces (36) are separated from each other, so that the nose piece (5) is again released for movement. In the example of figure 11, the axes (A, B) of the multi-axial bearing (13) are formed by studs (41), on which sleeve bearings / glide bearings (42) can slide and rotate. In the depicted example, the studs (41) are an integral part of or attached to the intermediate bearing member (31), whereas the sleeve bearings (42) are arranged on the first and second bearing members (30, 32) / the main body (4) and the nose piece (5). However the arrangement of studs (41) and sleeve bearings (42) with respect to the bearing members (30, 31, 32) may be changed or replaced, such that sleeve bearings (42) may also be arranged on the intermediate bearing member (31) and studs (41) may be arranged on the main body (4) / first bearing member (30) and the nose piece (5) / second bearing member (32). The multi-axial bearing (13) as depicted in Figure 11 can be of the cardan joint type. The intermediate bearing member (31) preferentially has a hollow center.

In the example of figure 11, a locking device (15') (displayed only once for axis (B)) may be a clamping device, in particular a pair of clamping jaws, which are arranged next to any of the sleeve bearings (32) and designed for clamping the respective stud (41). When at least one stud (41) for each of the axes (A, B) is clamped, the nose piece (5) is locked in its momentary position with respect to the main body (4), i.e. in an analogues way to the example explained above with reference to figures 4 and 5.

Activation and deactivation of any of the locking devices (15, 15) may be done in any arbitrary way and by any suitable activation or deactivation member. According to a first variant, the locking device may have a self- locking effect. The self-locking effect may be created by a resilient member, in particular a spring (43), which urges the locking device (15) into an active state or active position. In the example of figures 4 and 5, a spring (43) is arranged between a collar on the main body (4) and the movable skid (26). The spring (43) is pre compressed and urges the skid (26) and the respective locking surface (36) into contact with the flange cap (37), where the other locking surface (36) is arranged.

Deactivation or lessoning of the locking effect may be achieved by external or internal actuation. Internal actuation may be achieved by providing an actuator (not displayed) at or on the measurement device (1), in particular on the main body (4), on the intermediate bearing member (31) or on the nose piece (5). The actuator may be designed for directly or indirectly exerting a retraction force on the locking device (15,

15'). The retraction force may be controlled or switched. External actuation may be achieved by providing an entry space (25) at or on the measurement device (4), where an external actuation member can be broad into contact with the locking device (15). In the example of figures 4 and 5, such an entry space (25) is arranged on the outer circumferential surface of the main body (4) and in the rear direction (with respect to the tool space axis (X)) next to the rear surface of the moveable skid (26).

As displayed in figure 5, an external actuation element or external actuator, which is here exemplarily displayed as a fork (35), may be positioned in the entry space (25). The external actuator (35) may be moved in a release direction for directly or indirectly deactivating the locking device (15) and/or for lessoning the locking effect. In Figure 5, when the fork (35) moves in the frontal direction, as displayed with a small arrow, it will get into contact with the skid (26), so that a counterforce against the spring (43) is applied to the skid (26). Through this counterforce, the pressing between the locking surfaces (36) can be reduced, or when the counterforce is larger than the resilient force exerted by the spring (43), the locking surfaces (36) can be separated. As a result, the external actuator or actuation device (35) can lessen or release the locking effect, which is created between the locking surfaces (36).

In an analogues way, in the example of figure 11, resilient members (not depicted) could be arranged for urging the clamping jaws of the locking device (15') into the closed position. A counterforce against those resilient members or a release movement of the clamping jaws could be created or affected by an external actuator or actuation device, which directly or indirectly exerts a counterforce on the clamping jaws, in particular through a suitable transmission. Alternatively, one or several internal actuators may be arranged on the measurement device (1) for retracting one or several of the clamping jaws.

Alternatively, or in addition to the locking device, the measurement device (1) may comprise one or several centering devices (41, 41') for exerting a bias force, which urges the nose piece (5) into or towards the reference position (R).

In the example of figures 4 and 5, the centering device (41) may comprise the same elements, which have been explained above for the locking device (15). In particular, the surfaces (36) may - depending on their form and inclination angles - either create a locking effect or a centering effect.

In the example of Figures 5 and 6 the locking surfaces (36) have a conical shape. The inclination angle of the locking surfaces (36) with respect to the outer circumferential surface of the main body (4) is an obtuse angle, in particular an angle between 55 degrees and 80 degrees. This causes a locking-effect. When the inclination angle is instead an acute angle, in particular an angle between 10 degrees and 35 degrees, instead of the locking effect a centering effect is created. Instead of having only one skid (26) as depicted in figures 4 and 5, two or more skids or a multi-part skid can be arranged on the measurement device (1) for creating two or more pairs of locking surfaces (36) or centering surfaces (not depicted). Those surfaces may either be conical surfaces, spherical surfaces or ball shaped surfaces or any suitable inter-combination of those. The skilled person may select a number and combination of surfaces, which is suitable for creating the desired locking effect and/or centering effect based on the specific geometry of the measurement device (1).

In an analogues way to above examples on a locking device (15, 15'), a centering device (20, 20') may be activatable or de-activatable. Likewise, the centering effect may be lessened or released by an internal or external actuator.

In the example of figure 11, various elastic members (40) are arranged in the movement space between the bearing members (30, 31, 32) for urging the nose piece (5) into the reference position (R). A first set of elastic members (40), in particular springs, may be arranged on one or several of the studs (41), in order to exert a bias force on the sleeve bearings (42) for returning them to the reference position (R) or holding them in the reference position (R). Another set of elastic members, in particular springs (43), may be placed on the one hand between the front surface or rear surface of the first and second bearing members (40, 42) and a holding plate, which is rigidly arranged on the intermediate bearing member (31) and between the springs (43).

An alignment method for robot-based alignment of a tool space (8) or a processing tool (9) relative to a work piece surface (6) is now explained by taking reference to figures 1 and 7 to 10.

As can be seen in figure 1, a robot (3) may carry the measurement device (1) according to the present disclosure, which may be attached directly or indirectly to the robot (3). In particular, the measurement device (1) may be attached to an end effector (2), which is carried by the robot (3).

The tool space (8) or processing tool (8), which is used or intended for a processing of the work piece surface (6), has a tool axis (X), which is comprised in the measurement tool according to above explanations.

Figure 7 shows a situation, where the measurement device (1) is pre-positioned next to a work piece surface (6).

On the work piece surface (6), there is a processing area (14), where the processing actually shall be performed.

The processing area (14) may for example be a spot, where a hole shall be created by drilling or where a rivet shall be placed.

The alignment of the tool space (8) or processing tool (9) is performed relative to a predefined direction with respect to the surface (6) of the work piece. This may in particular be a normal direction (N) to the center of the processing area (14).

When the measurement device (1) is brought into contact with the work piece surface (6), the frontal contact structure (7) will get a direct contact (touch) with the work piece surface (6) in a contact zone (11). The frontal contact structure (7) may have a ring-form. Alternatively, it may have the form of one or several ring segments or any other suitable shape. The form of the frontal contact structure (11) may be selected based on the work piece geometry and a free space around the processing area (14).

A robot (3) is usually well capable of precise pre positioning the work piece axis (X) of the measurement device (1) (or a processing tool) directly above the processing area (14), in particular above the center of the processing area (14). The pre-positioning may be supported detecting the processing area (14) on the work piece surface (6) and by regulating the robot movement in such a way, that the tool space axis (X) is positioned in the desired location with respect to the processing area (14). In particular, a camera-based detection device may be provided for the detection of the processing area (14).

In the transition from figure 7 to figure 8 the measurement device (1) is brought into initial contact with the work piece surface (6). Furthermore, the robot (3) may be commanded to apply a pressing force towards the work piece surface (6). This pressing force may in particular be exerted via the frontal contact structure (7) of the nose piece (5). In both situations of making the initial contact and of applying or increasing a pressing force, the positioning of the work piece axis (X) with respect to the processing area (14) may be subject to impreciseness for various reasons. On the one hand, a (precise) detection of the processing area (14) may not be possible anymore, once it is covered due to the contact between the measurement device (1) and the work piece surface (6), so that no further regulation of the robot movement is possible. On the other hand, as the robot (3) has an elastic structure, its pose may slightly change depending on the momentary orientation of its arm pieces and joints and counter forces resulting from the contact with the work piece surface (6). Therefore, already making the initial contact and also the exertion of a pressing force may result in elastic transverse forces, which again cause a misalignment and/or offset with respect to the processing area (14).

Additionally, the real position (location and orientation) and/or the surface quality (flatness) of the work piece may be subject to tolerances and deviate from an expected state. In particular, the actual orientation of the work piece surface (6) may differ from an expected orientation or target orientation, which is for example defined in the control data for the robot (3). When or while the measurement device (1) is contact with the work piece surface (6), a tilt movement (Tl, T2) and/or a shift movement (SI, S2) of the nose piece (5) may occur, as has been explained above. In particular, the movement of the nose piece (5) may comprise one or two tilt movements (Tl, T2) and one or to shift movements (SI, S2) of the nose piece (5) with respect to the tool space axis (X) around and along the two axes (A, B) of the multi-axial bearing (13).

In the example of figure 8, a first shift movement (SI) and a first tilt movement (Tl) are depicted.

Those tilt movements and/or shift movements are determined based on the measurement result of the position detection device (10) of the measurement device (1). As it has been explained above, the robot (3) can be controlled to compensate those determined tilt movement (s) and/or shift movement (s) in such a way, that the tool space (8) or the processing tool (9) is returned to and/or maintained in the reference position (R). The determination of the movements (Tl, T2, Si, S2) and the control of the robot can be performed in any arbitrary way.

The reference position (R) may be re-calibrated, once the initial contact has been established. A newly set or re calibrated reference position (R) may in particular allow a residual shift (Si') of the tool space axis (X) with respect to the (center of) the processing area. However, the re-calibrated reference position (R) may stipulate that the tool space axis (X) is in a defined angle with respect to the work piece surface (6), in particular oriented parallel to the normal direction (N) on the processing area (14).

Figures 9 and 10 show states of the measurement device (1), in which such a re-calibrated reference position (R) is maintained, while a pressing force is increased and/or the processing tool (9) is moved into contact the work piece surface (6). Of course, it is also possible to compensate also the residual shift (Si') and return the nose piece into or maintain it in the original reference position (R).

In other words, the reference position (R) is a position, in which the tool space axis (X) or the processing tool (9) is parallel to a normal direction (N) of the work piece surface (6) and/or a position in which the tool space axis (X) or the processing tool (9) is additionally centered in a pre-determined processing area (14) on the work piece surface (6).

According to a preferred embodiment, the measurement device (1) comprises a controller (17) (measurement device controller), which is designed for analyzing the signals of the various sensors (34), in order to determine the momentary position of the nose piece (5). The measurement device controller (17) may be arranged in a controller housing (23), which is attached to the measurement tool (1). It may be connected (e.g. through the connector (24) and a cable or through a wireless connection) with a robot controller (16). The robot controller (16) may take information from the measurement device controller as an input parameter, defining an actual momentary position of the tool space axis (X). The robot controller (16) may calculate commands for a movement of the robot (3), which will bring or return the tool space axis (X) into an orientation, which is normal to the work piece surface (6), i.e. for returning or maintaining it in the reference position (R).

The commands, which are calculated for the robot (3), will control the robot in such a way that the tool space axis (X) or respectively the tool space (8) or the processing tool (9) is returned to and/or maintained in the (original or re-calibrated) reference position (R). In some applications, it is more important to align the orientation of the tool space axis (X) in a specific angle with respect to the work piece surface (6) than to keep the tool space axis (X) in the center of the processing area (14). In other words, orientation precision may be more important than centering precision. I such cases, it may be best to re-calibrate the reference position (R).

On the other hand, it may be required for a good processing quality that a strong pressing force is exerted on the work piece surface (6).

In such cases, or also in other situations, it may be preferred to lock the position of the nose piece (5), as soon as a specific pressing force level has been reached. Due to the locking, which may be effected by any of the locking devices (15, 15') as explained above, the pressing force can be distributed in a desired form on the frontal contact structure (7) or respectively the contact zone (11). The pressing force may in particular be uniformly distributed.

Locking of the nose piece (5) may in particular be performed, while the processing tool (9) is actuated for performing the surface processing (see Figure 10), i.e. while a drill is extended for plunging into the work piece or while a riveting tool is extended for driving a rivet into the work piece and the like. Depending on the desired surface processing method, the locking of the nose piece (5) may be lessened or deactivated during or after the actuation of the processing tool (9). For the alignment method of the present disclosure, the following steps may be performed. The measurement device (1) is moved into initial contact with the work piece surface (6), wherein the frontal contact structure (7) touches a contact zone (11) that is located next to or surrounding the processing area (14). The robot (3) is commanded to compensate one or several determined tilt movements (Tl, T2) and/or one or several shift movements (SI, S2) of the nose piece (5). The robot (3) may then be commanded to apply a pressing force towards the work piece surface (6), wherein possibly one or several further tilt movements (Tl, T2) and/or one or several further shift movements (SI, S2) are determined while the pressing force is established or maintained or increased.

The robot may further be commanded, while the pressing force is established or maintained or increased, to change its pose or otherwise move in such a way, that the determined further tilt movement (s) (Tl, T2) and/or the determined further shift movement (s) (SI, S2) is/are compensated. As an optional step, the nose piece (5) may be locked in a momentary position, which may in particular be the (original or re-calibrated) reference position (R), which is maintained or reached due to above alignment operations of the robot (3). The locking is preferentially performed, when a predefined pressing force level is reached or exceeded. Variations of the invention are possible in various ways. In particular, all features that are claimed, depicted or described with respect to a specific embodiment or variant, may be combined with or replaced by any feature of the other embodiments or variants. The main body (4) of the measurement device (1) may have a cylinder shaped inner surface, by which the main body (4) can be slideably mounted on a cylinder-shaped circumferential surface of an adapter (18). By doing so, the main body (4) may be freely rotatable on the adapter (18), which is illustrated in figure 6 by the rotation error (K). Two or more adapters (18) may be provided, which are designed for fixation on different end effectors (2) and/or robots (3)

A separate fixation means (19) may be used for fixing the main body (4) of the measurement device (1) on the adapter (18). In the drawings, this fixation means is exemplary formed by a screw. Alternatively, any other suitable fixing means may be used, which can be operated manually or by an actuator. As depicted in Figure 4, the fixation means / screw (19) may be arranged in a suitable part of the measurement device (1), in particular in the controller housing (23), which is attached to the main body (4). The front end of the screw (19) can be brought into direct contact with a collar (22) on the adapter (18). When the screw (19) is tightened, the relative position of the main body (4) with respect to the adapter (18) is locked.

In the example of figure 4, the adapter (18) has a thread on the inside of the collar (22), by which it can be screwed on a holding section of a drilling end effector (2). The measurement device (1) can slide on the adapter

(18). By sliding the main body (4) on the adapter (18), the measurement device (1) can be brought into a desired basic position, in which for example the axes (A, B) of the multi-axial bearing (13) are in a specific relation to the end effector (2) or the mounting flange of the robot (3).

Once the measurement device (1) is positioned and locked on the adapter (18), the measurement device (1) may be initialized. For this, the nose piece can be brought into the reference position (R), e.g. by activating the centering device (41, 41'). As an optional step, the measurement device (1) can be moved by the robot (3) into a referencing device, which may for example contain a test surface with a precisely known surface orientation. The measurement device can be brought into contact with this test surface once or several times and in particular by using different poses of the robot (3) and/or positions of the end effector (2). Based on the contact with the test surface, the measurement device controller (17) performs a calibration, which is based on the signals of the sensors (34) and the known orientation of the testing surface. All method steps and actions that have been explained above for the alignment method and/or the robot controller (16) and/or the measurement device controller (17) may be distributed in any desired form to the named controller devices (16, 17) or other controllers, like for example an external production plant controller. In particular, the robot controller (16) and the measurement device controller (17) may be integrated into a single controller, which may be arranged on the robot (3), on the end effector (2) or on the measurement device (1). Alternatively, this separate controller may be arranged as an external controller.

LIST OF REFERENCES

Measurement device Messeinrichtung End effector / robot Endeffektor / guided tool Robotergefuhrtes

Werkzeug

Robot Roboter Main body Hauptkorper

Movable nose piece Bewegliches Nasenstdck Work piece surface Werkstuckoberflache Frontal contact Vorderseitige structure Kontaktstruktur Tool space Werkzeugraum Processing tool Bearbeitungswerkzeug Position detection Positionserfassungs- device einrichtung

Contact zone Kontaktzone Rear section Ruckwartiger Ausschnitt Multi-axial bearing Mehrachsiges Lager Processing Area Bearbeitungsflache Locking device Sperrvorrichtung Locking device Sperrvorrichtung Controller / robot Steuerung / controller Robotersteuerung Controller / Steuerung / measurement device Messeinrichtungs- controller steuerung Adaptor / mounting Adapter / sleeve Befestigungshulse Fixation means / Befestigungsmittel /

Screw Schraube

Centering device Zentriereinrichtung Centering device Zentriereinrichtung Fixing member Befestigungsmittel- reception aufnahme Collar Kragen

Controller housing Steuerungsgehause

Connector Stecker

Entry space Zugangsraum

Skid Schlitten

Cover Abdeckung

Fixation ring Fixierring Suction hole / Air Saugoffnung / Luft- inlet or outlet Einlass Oder Auslass First bearing member Erste Lagerelement / / main body side Hauptkorper Seite Intermediate bearing Zwischengelagertes member Lagerelement

Second bearing member Zweites Lagerelement / / nose piece side Nasenkorper Seite Emitter / Magnet / Emitter / Magnet / field generator Felder zeuger Sensor Sensor

Actuator / Fork Aktuator / Gabel Locking surface Sperr-Oberflache (conical / spherical (konisch / kugelig / / ball-shaped) ballig)

Flange cap Flanschkappe 38 Ball Kugel

39 Groove Rille / Nut

40 Elastic member Elastisches Element

41 Stud Bolzen

42 Sleeve bearing / Hulsenlager / Gleitlager glide bearing

43 Resilient member / Riickstell-Element /

Spring Feder dl Distance Abstand d2 Distance Abstand d3 Distance Abstand d4 Distance Abstand

A First axis Erste Achse

B Second axis Zweite Achse

D Displaced position Verlagerte Position

K Free rotation Freie Rotation

N Normal direction NormaIrichtung

R Reference position Referenzlage si, Shift movement along Versatzbewegung entlang

SI' first axis erster Achse

S2 Shift movement along Versatzbewegung entlang second axis zweiter Achse

T1 Tilt movement around Kippbewegung um erste first axis Achse

T2 Tilt movement around Kippbewegung um zweite second axis Achse

X Tool space axis Werkzeugraum-Achse