METHOD FOR DETECTING AND EVALUATING A FRICTION STATUS AT A JOINT, ROBOTIC ARM AND COMPUTER PROGRAM PRODUCT

Abstract

A method, a robot, and a computer program product for detecting and evaluating a friction status in at least one joint of a robotic arm, wherein, within the scope of a brake test program, at least one motor of a plurality of electric motors is driven automatically in a first rotational direction, wherein a detection of a first motor torque in the driven motor takes place during its rotation in the first rotational direction. The at least one motor is then driven in a second rotational direction opposite the first rotational direction, wherein a detection of a second motor torque in the driven motor takes place during its rotation in the second rotational direction. An automatic evaluation of the first motor torque and the second motor torque takes place in order to obtain the friction torque of the joint associated with the driven motor.

Claims

1-10. (canceled)

11. A method for detecting and evaluating a friction status in at least one joint of a robotic arm that includes a plurality of joints and a plurality of links connecting the joints to each other, wherein the robotic arm is connected to a robot controller that is designed and configured to control a plurality of electric motors and brakes of the robotic arm which are associated with the respective joints in order to move the robotic arm, the method comprising: (a) automatically executing a brake test procedure associated with the robotic arm to control the electric motors and brakes via the robot controller, in order to automatically move the links of the robotic arm in accordance with a brake test program specified by the brake test procedure, and to automatically control the brakes; (b) in accordance with the brake test program, automatically driving at least one motor of the plurality of electric motors in a first rotational direction and detecting a first motor torque in the at least one motor during rotation in the first rotational direction, and subsequently automatically driving the at least one motor in a second rotational direction, opposed to the first rotational direction, and detecting a second motor torque in the at least one motor during rotation in the second rotational direction; and automatically evaluating the first motor torque and the second motor torque in order to obtain a first moment of friction of the respective joint associated with the at least one driven motor.

12. The method of claim 11, wherein automatically evaluating the first motor torque and the second motor torque in order to obtain the first moment of friction comprises calculating the moment of friction as half of the difference between the first motor torque and the second motor torque.

13. The method of claim 11, further comprising automatically assessing the friction status of the at least one joint as defective in response to the obtained first moment of friction exceeding a prespecified maximum torque.

14. The method of claim 13, further comprising: determining the prespecified maximum torque based on a design-dependent rated torque of the brake associated with the joint driven by the at least one motor in which the first motor torque and the second motor torque were detected.

15. The method of claim 14, wherein determining the prespecified maximum torque comprises selecting a value of the prespecified maximum torque between 20 percent and 40 percent of the design-dependent rated torque value of the brake.

16. The method of claim 11, further comprising: comparing the obtained first moment of friction to an original moment of friction determined in a delivery state or commissioning state of the robotic arm; and assessing the friction status of the joint associated with the at least one driven motor as defective in response to a deviation of the obtained first moment of friction from the original moment of friction exceeding a prespecified threshold value.

17. The method of claim 11, further comprising: repeating method steps (a) and (b) at a later point in time; automatically evaluating the first motor torque and the second motor torque obtained at the later point in time in order to obtain a second moment of friction of the respective joint associated with the at least one driven motor. comparing the second moment of friction to the first moment of friction; and assessing the friction status of the joint associated with the at least one driven motor as defective in response to a deviation of the second moment of friction from the first moment of friction exceeding a prespecified threshold value.

18. The method of claim 11, wherein detecting the first motor torque and detecting the second motor torque comprises automatically determining from the first and second motor torques from the respective electric motor currents of the at least one motor during rotation in the first rotational direction and in the second rotational direction, respectively.

19. A robot, comprising: a robotic arm including a plurality of joints connecting a plurality of links that are adjustably positionable relative to one another by the movements of the joints; a plurality of motors and brakes, wherein a respective motor and a respective brake are associated with each joint, and wherein each motor is designed to adjust the respectively associated joint by automatic control of the motor; and a robot controller designed to automatically control the motors in order to adjust the links of the robot arm automatically and individually relative to one another by driven movement of the joints, and to automatically control the brakes to individually brake the joints of the robot arm and hold the brakes in a locked condition; wherein the robot controller is further designed and configured to carry out the method of claim 11.

20. A computer program product for detecting and evaluating a friction status in at least one joint of a robotic arm, the computer program product comprising a program code stored on a non-transient, computer-readable medium, the program code, when executed by a robot controller, causing the controller to carry out the method of claim 11.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0057] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate exemplary embodiments of the invention and, together with a general description of the invention given above, and the detailed description given below, serve to explain the principles of the invention.

[0058] FIG. 1 shows an example of a robot in accordance with the present disclosure comprising a robotic arm with a plurality of links and a plurality of joints, wherein a separate motor and a separate brake are associated with each joint, and comprising a robot controller for controlling the robotic arm—in particular, the motors and brakes of the joints,

[0059] FIG. 2 shows a schematic presentation of the basic method in accordance with the present disclosure,

[0060] FIG. 3 shows a schematic presentation of the relationship between gravitational moment, moment of friction, and holding brake torque during the implementation of an exemplary brake test procedure,

[0061] FIG. 4 shows a schematic presentation of a profile of the joint movement during the implementation of an exemplary brake test procedure, in a v/t diagram, and

[0062] FIG. 5 shows a schematic presentation of a representative curve of the total torque at the respective joints during the implementation of an exemplary brake test procedure.

DETAILED DESCRIPTION

[0063] FIG. 1 shows an industrial robot 8 which has a robotic arm 9 and a robot controller 10. In the instance of the present exemplary embodiment, the robot arm 9 comprises several successively arranged links G1 through G7 connected to one another by means of joints L1 through L6 so as to be able to rotate.

[0064] The industrial robot 8 has the robot controller 10 which is designed to execute a robot program and to move the links G1-G7 and joints L1-L6 of the robot arm 9 automatically. One of the several links G1-G7 forms an end link (G7) of the robot arm 9, which has a tool flange 11.

[0065] The robot controller 10 of the industrial robot 8 is designed or configured to execute a robot program via which the links L1 through L6 of the robot arm 9 can be automated or automatically adjusted or moved in rotation in a manual mode in accordance with the robot program. For this purpose, the robot controller 10 is connected to controllable electric drives, the motors M1 through M6, which are designed to move the respective joints L1 through L6 of the robotic arm 9.

[0066] In the instance of the present exemplary embodiment, the links G1 through G7 are a robot base frame 13 and a carousel 14 which is borne so as to be rotatable, relative to the robot base frame 13, about a vertically traveling axis A1. Further elements of the robot arm 9 are a link arm 15, a boom arm 16, and a preferably multi-axis robot hand 17 with a fastening device designed as a tool flange 11 for fastening a tool. The link arm 15 is mounted at the lower end on the carousel 14, i.e., at the link L2 of the link arm 15, which can also be referred to as the pivot bearing head, so as to be pivotable about a preferably horizontal axis of rotation A2.

[0067] At the upper end of the link arm 15, the boom arm 16 is in turn mounted at the one link L3 of the link arm 15 so as to be pivotable about a likewise preferably horizontal axis A3. At its end, said boom arm supports the robot hand 17 with its preferably three axes of rotation A4, A5, A6. The joints L1 to L6 can be driven in a program-controlled manner by a respective one of the electric motors M1 to M6 via the robot controller 10, and can be braked and arrested in place by means of the brakes B1 to B6 associated with the joints L1 to L6 or the motors M1 to M6.

[0068] FIG. 2 illustrates the method for detecting and evaluating a friction status in at least one joint L1 to L6 of the robotic arm 9 having a plurality of joints L1-L6 and a plurality of links G1-G7 connecting the joints L1-L6 to each other, wherein the robotic arm 9 is connected to the robot controller 10, which is designed and configured to control a plurality of electric motors M1-M6 of the robotic arm 9 associated with the joints L1-L6 of the robotic arm 9 and associated brakes B1-B6 of the robotic arm 9 in order to move the robotic arm 9.

[0069] In a first step S1, in the instance of the present exemplary embodiment, a brake test procedure associated with the robotic arm 9 is automatically executed in accordance with a brake test program 1 which is provided to control the electric motors M1-M6 and the brakes B1-B6 of the robotic arm 9 by means of the robot controller 10 in order to automatically move the links G1-G7 of the robotic arm 9 in accordance with the brake test program 1 specified by the brake test procedure, and to automatically control the brakes B1-B6.

[0070] In a second step S2, in the instance of the present exemplary embodiment, and within the scope of the brake test program 1, at least one motor of the plurality of electric motors M1-M6 is automatically driven in a first rotational direction, and a first motor torque M_1 is detected in the driven motor during its rotation in the first rotational direction, and subsequently the at least one motor is automatically driven in a second rotational direction opposed to the first rotational direction, and a second motor torque M_2 is detected in the driven motor during its rotation in the second rotational direction.

[0071] In the third step S3, in the instance of the present exemplary embodiment the first motor torque M_1 and the second motor torque M_2 are automatically evaluated in order to obtain the moment of friction Mr of the joint associated with the driven motor.

[0072] The moment of friction Mr of the joint associated with the driven motor can be determined from the first motor torque M_1 and the second motor torque M_2 in that the moment of friction Mr is automatically calculated as the absolute value of half of the difference between the first motor torque M_1 and the second motor torque M_2.

[0073] The friction status of the at least one joint is automatically assessed as defective if, for example, the automatically determined moment of friction Mr exceeds a prespecified maximum torque.

[0074] To determine the prespecified maximum torque, the design-dependent rated torque can be used of that brake which is associated with the joint which is driven by the motor in which the first motor torque M_1 and the second motor torque M_2 were detected.

[0075] For example, a value between 20 percent and 40 percent of the design-dependent rated torque value of that brake which is associated with the joint which is driven by the motor in which the first motor torque M_1 and the second motor torque M_2 were detected can be used as the value of the prespecified maximum torque.

[0076] The friction status of the at least one joint can be automatically assessed as defective when, for example, upon a comparison of the automatically determined moment of friction Mr with an original moment of friction determined in the delivery state of the robotic arm 9, a deviation of the automatically determined moment of friction Mr from the original moment of friction determined in the delivery state of the robotic arm 9 or commissioning state of the robotic arm 9 is identified which exceeds a prespecified threshold value.

[0077] The friction status of the at least one joint can be automatically assessed as defective when, for example, upon a comparison of a later moment of friction, determined automatically within the scope of an execution of a second brake test procedure at a later point in time, with an earlier moment of friction, determined automatically within the scope of an execution of a first brake test procedure at an earlier time, a deviation of the later determined moment of friction from the earlier determined moment of friction is identified which exceeds a prespecified threshold value.

[0078] The first motor torque M_1 of the driven motor and the second motor torque M_2 of the driven motor can be determined automatically from the respective electric motor currents of the motor during its rotation in the first rotational direction and in the second rotational direction.

[0079] Shown in FIG. 3 is a schematic presentation of the relationship between gravitational moment, moment of friction, and holding brake torque during the implementation of an exemplary brake test procedure. The gravitational moment Mg always acts with the same magnitude and in the same direction. The braking torque Mb increases in the one rotational direction up to a maximum value. Then, a switch is made to the other rotational direction in that the braking torque Mb is continuously reduced. The moment of friction corresponds to half of the torque difference in the one direction and in the other rotational direction. This is also illustrated in particular in FIG. 5.

[0080] FIG. 4 shows a schematic presentation of a profile of the joint movement during the implementation of an exemplary brake test procedure in a v/t diagram. The motor is first started up—i.e., it is accelerated—in order then to move the joint at a constant speed in the first rotational direction. Subsequently, it is braked and accelerated in the other rotational direction in order to then move the joint at a correspondingly opposite constant speed in the other rotational direction. In accordance with this acceleration and speed profile of the brake test procedure, a curve of the total torque in the motor is established, as is shown schematically in FIG. 5.

[0081] Shown in FIG. 5 is a schematic presentation of a representative curve of the total torque M in the respective joint during the implementation of an exemplary brake test procedure. The different heights of the plateau phases of the total torque M result in that the gravitational moment acts in the same way both upon the rotational movement in the first rotational direction and upon the opposite rotational movement in the second rotational direction. The torque difference between the two plateau phases of the total torque M corresponds to twice the moment of friction.

[0082] 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 de-tail. 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.