Method For Detecting A Collision Of A Robot Arm With An Object, And A Robot With A Robot Arm

Abstract

A method for detecting a collision of a robot arm with an object and a correspondingly configured robot. The robot arm is a part of the robot and includes a plurality of serially arranged links mounted relative to respective axes, and position sensors allocated to the individual axes are provided for determining the poses of any two adjacent links relative to one another. The robot further includes an electronic control device connected to the positioning devices, and actuators controlled by the electronic control device for automatically moving the links. The method includes evaluating whether at least one invariant for a target movement of the robot arm is satisfied by an actual movement of the robot arm and, when the evaluation results in a non-satisfaction of the at least one invariant, then indicating a collision of the robot arm with the object and initiating a safety function of the robot.

Claims

1-12. (canceled)

13. A method for detecting a collision of a robot arm with an object, wherein the robot arm is a part of a robot that includes a plurality of serially arranged links mounted relative to respective axes, and position sensors assigned to the individual axes and provided for determining the positions of each two adjacent links relative to one another, wherein a tool center point is allocated to the robot arm and the robot further includes an electronic control device in communication with the position sensors, and drives controlled by the electronic control device for the automatic movement of the links of the robot arm relative to one another, the method comprising: automatically moving the links controlled by the electronic control device, such that the robot arm performs an actual movement associated with a target movement of the robot arm; during the actual movement of the robot arm with the electronic control device based upon the signals emitted by the position sensors, evaluating whether at least one invariant for the target movement of the robot arm is satisfied by the actual movement of the robot arm, based upon the actual poses and/or derived values of the actual poses of the links relative to one another, and/or based upon the actual position and/or at least one derived value of the actual position of the tool center point; and when the evaluation results in a non-satisfaction of the at least one invariant, then: indicating a collision of the robot arm with the object, and initiating of a safety function of the robot, controlled by the electronic control device.

14. The method of claim 13, further comprising determining the target movement of the robot arm, wherein the target movement is determined by: using a path planning performed by the electronic control device; or evaluating, with the electronic control device, the movement of the tool center point or the links at the start of an actual movement of the robot arm, and extrapolating this movement in order to obtain the target movement of the robot arm.

15. The method of claim 13, wherein the invariant relates to whether the target movement is smooth, and wherein a collision of the robot arm with the object is indicated when: the third derivative of the actual position of the tool center point according to time or a time rate of change of the actual acceleration of the tool center point exceeds a predetermined value; or the third derivatives of the actual positions of the links relative to one another according to time or a time rate of change of the actual accelerations of the actual positions of the links relative to one another exceed a predetermined value.

16. The method of claim 15, further comprising operating the robot arm using admittance control or force control, wherein the predetermined value depends upon the rigidity of the admittance control or force control.

17. The method of claim 13, wherein: the at least one invariant is associated with target positions of the tool center point during the target movement, the actual positions of the tool center point are evaluated during the actual movement of the robot arm, and the invariant is not satisfied if at least one of the actual positions deviates from the corresponding target position of the tool center point by a predetermined value; or the at least one invariant is associated with target poses of the links relative to one another during the target movement, the actual poses of the links relative to one another are evaluated during the actual movement of the robot arm, and the invariant is not fulfilled if at least one of the actual poses deviates from the corresponding target pose by a predetermined value.

18. The method of claim 13, wherein: the at least one invariant is associated with a constant target velocity of the tool center point during its movement, the actual velocity and/or the actual acceleration of the tool center point is determined and evaluated as at least one derived value of the actual position of the tool center point during the actual movement of the robot arm, and the invariant is not satisfied if the actual velocity of the tool center point deviates by a predetermined value and/or the magnitude of the actual acceleration of the tool center point exceeds a predetermined value; or the at least one invariant is associated with a constant target acceleration of the tool center point during its movement, the actual acceleration and/or the time rate of change of the actual acceleration of the tool center point is determined and evaluated as at least one derived value of the actual position of the tool center point during the actual movement of the robot arm, and the invariant is not satisfied if the actual acceleration of the tool center point deviates by a predetermined value and/or the magnitude of the time rate of change of the actual acceleration of the tool center point exceeds a predetermined value.

19. The method of claim 13, wherein: a linear movement of the tool center point is associated with the target movement of the robot arm; or automatically moving the links comprises linearly moving the links of the robot arm based upon the target movement of the robot arm.

20. The method of claim 13, wherein the tool center point is intended to move along a target path based upon the target movement of the robot arm, and the tool center point moves along an actual path based upon the actual movement of the robot arm.

21. The method of claim 20, wherein: the target path is a curved path of the tool center point and the invariant is associated with a maximum curvature of the curved path; and a collision of the robot arm with the object is indicated if evaluation of the signals from the position sensors results in the curvature of the actual path exceeding a predetermined value.

22. The method of claim 20, wherein: the target path is a circular path of the tool center point with a predetermined curvature and the invariant indicates the predetermined curvature; and a collision of the robot arm with the object is indicated if evaluation of the signals from the position sensors shows that the curvature of the actual path deviates from the predetermined curvature by a predetermined value.

23. The method of claim 21, wherein the indication of a collision of the robot arm with the object further depends upon the velocity of the tool center point during the movement along the actual path.

24. The method of claim 22, wherein the indication of a collision of the robot arm with the object further depends upon the velocity of the tool center point during the movement along the actual path.

25. A robot comprising: a robot arm having an assigned tool center point and which comprises a plurality of serially arranged links mounted relative to respective axes; position sensors allocated to the respective axes and configured to determine angle settings of any two adjacent links relative to one another; an electronic control device in communication with the position sensors; and actuators controlled by the electronic control device for automatic movement of the links relative to one another; wherein the electronic control device is configured to detect a collision of the robot arm with an object according to the method of claim 13.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0058] The accompanying drawing, which is incorporated in and constitutes a part of this specification, illustrates an exemplary embodiment of the invention and, together with a general description of the invention given above, and the detailed description given below, serves to explain the principles of the invention.

[0059] FIG. 1 is a robot in a perspective view, and

[0060] FIG. 2 is a table.

DETAILED DESCRIPTION

[0061] FIG. 1 shows a robot 1 comprising a robot arm 2 and an electronic control device 10. The robot arm 2 comprises multiple links arranged behind one another and connected using joints. The links are, in particular, a stationary or adjustable frame 3 and a carousel 4 mounted rotatably about an axis A1 which extends vertically relative to the frame 3. In the case of the present exemplary embodiment, further links of the robot arm 2 are a link arm 5, a boom arm 6, and a preferably multi-axial robot hand 7 with a fastening device configured, for example, as a flange 8 for fastening an end effector 11.

[0062] The link arm 5 is mounted at the bottom end to, for example, a pivot bearing head, not shown in greater detail, on the carousel 4 pivotably about a preferably horizontal axis of rotation A2. At the upper end of the link arm 5, the boom arm 6 is also mounted pivotably about a likewise preferably horizontal axis A3. At its end, said boom arm holds the robot hand 7 with its preferably three axes A4, A5, A6.

[0063] In order to move the robot 1 and its robot arm 2, said robot comprises actuators connected to the electronic control device 10 (robot control) in the generally known manner. The actuators are, in particular, electric actuators comprising the electric motors 9. At least the motors and the electric motors 9 are arranged and fastened in or on the robot arm 2. FIG. 1 shows only a few of the electric motors 9. The actuator[s] are preferably controlled electric actuators.

[0064] Power electronics of the electric actuators are arranged, for example, within a housing of a control cabinet, not shown in greater detail, in which, for example, the electronic control device 10 is also arranged. In the case of the present exemplary embodiment, the electric motors 9 are three-phase motors, for example three-phase synchronous motors. However, the power electronics can also be arranged in and/or on the robot arm 2. The electronic control device 10 comprises, for example, a processor, not shown in greater detail, and can also be configured as, for example, a computer.

[0065] In the case of the present exemplary embodiment, the electronic control device 10 is configured such that it comprises a first control functionality and a second control functionality. The first control functionality undertakes the object of a safety control, the second control functionality undertakes the remaining controls of the robot 1.

[0066] On the electronic control device 10, a computation program, a so-called user program, runs, using which the control device 10 controls the actuators in an automatic operation within the scope of the work object, such that, if so ordered, if the robot arm 2 and the flange 8 of the robot 1 and a Tool Center Point TCP allocated to the robot arm 2 perform a predetermined movement. This is performed, for example, by the second control functionality.

[0067] Based upon the target movement of the robot arm, the Tool Center Point is intended to move along a target path. During the actual movement of the robot arm, the Tool Center Point moves along an actual path.

[0068] It can also be provided that the electronic control device 10 also controls the end effector 11 fastened to the flange 8 using the user program in the normal operation of the robot 1.

[0069] The robot 1 and its robot arm 2 further comprise multiple position sensors 12 preferably configured as resolvers. In the case of the present exemplary embodiment, the position sensors 12 are configured in safe technology and are configured in order to determine the actual angle poses of any two neighboring links 3-8 relative to one another.

[0070] The position sensors 12 are connected to the electronic control device 10, such that said device can evaluate the signals emitted by the position sensors 12. In the case of the present exemplary embodiment, this occurs using the first control functionality.

[0071] In particular, at least one position sensors 12 is allocated to each of the axes A1-A6 such that, in the normal operation of the robot 1, the electronic control device 10 receives a notification regarding the actual angle poses of each of the links 3-8 of the robot arm 2 relative to its neighboring link 3-8 based upon the signals emitted by the position sensors 12. It is thus also possible, in particular, for the electronic control device 10 to determine the actual position and, if applicable, also the actual orientation of the Tool Center Points TCP in the frame.

[0072] It is also possible, for example through differentiation or repeated differentiation and derivation according to time or repeated derivation according to time of the determined actual position of the Tool Center Point TCP and/or the determined individual actual angle poses, for the electronic control device 10 to determine the current velocity, the current acceleration, and/or the change of the current acceleration of the Tool Center Point TCP and/or the individual links 3-8.

[0073] In the case of the present exemplary embodiment, the robot 1 and its electronic control device 10 are configured, during an actual movement of the robot arm 2, in particular during the movement of the Tool Center Point TCP along an actual path, to check, based upon the signals emitted by the position sensors 12, whether, based upon the actual angle poses and/or derived values of the actual angle poses, and/or based upon the actual position, and/or at least one derived value of the actual position of the Tool Center Point, at least one applicable invariant is fulfilled for the target movement of the robot arm allocated to the actual movement, and/or for the movement of the Tool Center Point TCP along the target web for the actual movement of the robot arm and/or for the movement of the Tool Center Points TCP along the actual path, respectively. If the invariant for the actual movement is not fulfilled, then the electronic control device 10 concludes that the robot arm 2 has collided with an object 13 and initiates a safety function of the robot.

[0074] In the case of the present exemplary embodiment, it can be provided that the invariant indicates that the target movement is jerk-free. The electronic control device 10 then indicates a collision of the robot arm 2 with an object 13 if the third derivation of the actual position of the Tool Center Point TCP according to time or a time rate of change of the actual acceleration of the Tool Center Point TCP exceeds a predetermined value. Alternatively, it is also possible for a collision of the robot arm 2 with the object 13 to be indicated if the third derivations of the actual angle poses according to time or a time rate of change of the actual accelerations of the actual angle poses exceed a predetermined value.

[0075] In the case of the present exemplary embodiment, it can be provided that the electronic control device 10 controls the robot arm 2 using an admittance or force control. The predetermined value can then depend upon the rigidity of the admittance or force control.

[0076] The electronic control device 10 can receive data based upon non-safe technology. These are processed with the second control functionality. Data used or produced for a control, for example, do not fulfill the criterion of safe data. These data are used, for example, for the current movement of the robot arm 2. These data and information thus cannot be evaluated in the safety control, because they originate from, for example, the non-safe user program. In some cases, however, it is nonetheless also possible, on the basis of available safe data regarding assumptions/models, to obtain the information in safe technology that is otherwise only available in the non-safe control.

[0077] According to a further configuration, a linear movement of the Tool Center Point TCP is allocated to the target movement of the robot arm 2.

[0078] In the case of the present exemplary embodiment, it can be provided that the target movement of the robot arm 2 occurs using a path planning performed by the electronic control device 10. This path planning is performed, in particular, using the second control functionality.

[0079] According to this embodiment, it can be provided that the second control functionality transmits a notification to the first control functionality that a planned linear movement of the Tool Center Point TCP is imminent. This notification comprises, in particular, information about the target start and target end point of the Tool Center Point, whereby the first control functionality receives as an invariant the notification that the target positions of the Tool Center Point of the imminent target movement will run on the straight lines determined by the target start and target end points. If at least one of the actual positions of the corresponding target position deviates from these straight lines by the predetermined value during the movement, then the first control functionality identifies the collision.

[0080] In addition to the collision detection, there is also the possibility of detecting an erroneous performance of the movement of the robot arm, i.e. also in the event that no collision has appeared but the robot arm does not move as expected. This is illustrated in the table shown in FIG. 2.

[0081] If the information transmission between the two control functionalities is error-free, a collision will be reliably detected, and no safety function will be initiated if no collision is detected.

[0082] By contrast, if the information transmission between the two control functionalities is erroneous, then the electronic control device 10 will identify a collision, even if there is none. If there additionally is a collision, then two errors will result.

[0083] It is thus ensured that no safety function is initiated only when the transmission between the two control functionalities is error-free and no collision has been indicated.

[0084] In the case of the present exemplary embodiment, it can also be provided that the electronic control device 10, in particular its first control functionality, evaluates the movement of the Tool Center Point TCP at the start of a movement, in order to obtain through extrapolation of this movement the target path.

[0085] In this case, it is provided, in particular, that no information is exchanged between the first and second control functionalities. At the start of the performance of the movement, for example in an acceleration phase, the first control functionality can record the movement of the Tool Center Point TCP or the links 3-8 at the start of an actual movement of a robot arm 2, during a preferably predetermined period of time, and extrapolate from this the future target movement of the robot arm 2. The basis of the extrapolation can be a notification of which types of path are possible in principle, for example linear paths or circular paths.

[0086] The extrapolation should preferably be completed before the velocity of the Tool Center Point TCP or the robot arm 2 becomes so high that potential collisions become dangerous.

[0087] In the case of the present exemplary embodiment, it can be provided that the target path is a curved path. The invariant then indicates a maximum curvature of the curved path, such that a collision of the robot arm 2 with the object 13 is indicated if an evaluation of the signals from the position sensors 12 shows that the curvature of the actual path exceeds a predetermined value.

[0088] It can also be provided that the target path of the Tool Center Point TCP is a circular path of the Tool Center Point TCP with a predetermined curvature, and the invariant indicates the predetermined curvature. A collision of the robot arm with the object is then indicated if an evaluation of the signals from the position sensors shows that the curvature of the actual path deviates from the predetermined curvature by a predetermined value.

[0089] Additionally, the local curvature can be related to the velocity, such that the initiation of the safety function based upon a greater curvature only occurs if the velocity also exceeds a predetermined value. This means that relatively large curvatures are only permissible with relatively low velocities.

[0090] A further invariant can be that the actual path cannot be pulled out backwards. Thereby, at least those collisions that are oriented parallel to the path tangent can be detected if they are oriented opposite to the direction of movement.

[0091] While the present invention has been illustrated by a description of various embodiments, and while these embodiments have been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. The various features shown and described herein may be used alone or in any combination. Additional advantages and modifications will readily appear to those skilled in the art. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and method, and illustrative example shown and described. Accordingly, departures may be made from such details without departing from the spirit and scope of the general inventive concept.