Method for detecting and evaluating friction conditions on a joint, robot arm and computer program product

Abstract

The invention relates to a method for detecting and evaluating the friction state on at least one joint of a robot arm (9), wherein at least one of a plurality of electric motors (M1-M6) is automatically driven in a first rotational direction within the framework of a brake test program, wherein a first electric motor torque (M_1) on the driven motor is detected during the rotation of the driven motor in the first rotational direction, and then the at least one motor is automatically driven in a second rotational direction opposite to the first rotational direction, wherein a second electric motor torque (M_2) on the driven motor is detected during the rotation of the driven motor in the second rotational direction, and the first motor torque (M_1) and the second motor torque (M_2) are automatically evaluated in order to obtain a friction torque (Mr) of the joint assigned to the driven motor. The invention also relates to a related robot (8) and a related computer program product.

Description

Technical Field

[0001] The present invention relates to a method for detecting and evaluating the friction state on at least one joint of a robot arm, the robot arm having a plurality of joints and a plurality of limbs connecting the joints to each other, wherein the robot arm is connected to a robot controller, which is constructed and designed to control a plurality of electric motors of the robot arm assigned to the joints of the robot arm and the associated brakes of the robot arm in order to move the robot arm. Background Art

[0002] Patent document EP1239354B1 discloses a method for controlling and monitoring a braking device having a rated torque associated with a drive unit of a technical device (e.g., an operating device), wherein a holding current of the drive unit corresponding to the holding torque is measured and stored when the braking device is open, and an axis-specific current value is loaded to the drive unit when the braking device is closed, which current value loads the braking device with a torque equal to or less than the rated torque of the braking device, while monitoring the stationary state of the drive.

[0003] Patent document WO2007 / 008940A2 describes a system for state monitoring and fault diagnosis, the system comprising: a data acquisition function, which acquires a time curve of a variable of one or more selected components; a preprocessing function, which calculates certain features of the time curve; an analysis function, which is used to evaluate the features to generate one or more hypotheses of the state of one or more components; and a demonstration function, which is used to determine the state of one or more components based on the one or more hypotheses. This system for state monitoring and fault diagnosis is particularly configured for robots. Summary of the invention

[0004] The object of the present invention is to automatically detect and evaluate friction conditions in at least one joint of a robot arm in a simple and economical manner.

[0005] The object of the present invention is achieved by a method for detecting and evaluating the friction state on at least one joint of a robot arm, the robot arm having a plurality of joints and a plurality of segments connecting the joints to one another, wherein the robot arm is connected to a robot controller, the robot controller being constructed and designed to actuate a plurality of electric motors of the robot arm assigned to the joints of the robot arm and associated brakes of the robot arm in order to move the robot arm; the method comprising the following steps:

[0006] - automatically executing a brake test method corresponding to a robot arm, the brake test method being provided for controlling the electric motor and brake of the robot arm by means of a robot controller, so as to automatically move the limbs of the robot arm according to a brake test program provided by the brake test method and automatically control the brakes,

[0007] - within the framework of a brake test procedure, automatically driving at least one of the plurality of electric motors in a first rotational direction and detecting a first motor torque on the driven motor during its rotation in the first rotational direction; subsequently automatically driving the at least one motor in a second rotational direction opposite to the first rotational direction and detecting a second motor torque on the driven motor during its rotation in the second rotational direction,

[0008] - Automatically evaluating the first motor torque and the second motor torque in order to obtain the friction torque of the joint belonging to the driven motor.

[0009] In this case, the above detection is carried out without separate dedicated sensors. The above detection is carried out in particular without separate dedicated sensors which are designed and constructed specifically for detecting friction in joints. Instead, the friction state in the individual joints can be detected indirectly, in particular by detecting the current consumption at the electric motors assigned to the joints to be detected and evaluated. Particularly preferably, the current at the individual motors is not detected by means of a separate, dedicated current measurement, but only additionally an evaluation is performed according to the method of the invention of the current at the individual motors which has already been detected within the framework of an already performed brake test method. In this regard, independent, additional measurements of the current at the individual motors can be dispensed with.

[0010] This evaluation involves not only a separate consideration of the currents in the individual motors that have already been detected within the framework of the brake test method, but also, if necessary, an evaluation of the currents in the individual motors that go beyond this, for example, a comparison of the current detected in the individual motors with a predetermined maximum torque, with the original friction torque in the starting state or with the friction torque from a previous brake test method, i.e., the stored currents of the individual motors.

[0011] The friction state at at least one joint of the robot arm can therefore be derived from the previously and / or currently detected current at the corresponding motor of the relevant joint.

[0012] The robot comprises a robot arm and a robot controller. With the aid of the robot controller, a plurality of limbs can be adjusted relative to one another by means of movements of the joints of the robot arm, wherein each driven joint is assigned a motor and a brake. The individual motors are configured to adjust the joints assigned to the motors by means of control of the robot controller, more precisely by means of automatic control of the motors. The robot controller is thus configured to automatically control the motors so that the limbs of the robot arm are automatically and independently adjusted relative to one another by means of the driven joint movements. The robot controller is also used to automatically control the brakes so that the joints of the robot arm can be braked individually and held locked. The robot controller also automatically performs a corresponding brake test method according to a brake test program.

[0013] The electric motors may be servomotors which are controlled and driven by the robot controller or by a drive amplifier connected to the robot controller.

[0014] The brake can in particular be an electromechanical brake which can be electrically controlled, ie activated, in order to move electrically driven mechanical brake elements (eg brake pads or brake shoes) which brake and lock the associated joint of the robot arm.

[0015] The brake test program specifies the manner and method in which the braking of the respective joint is tested, ie checked, in order to be able to check the momentary function of the brake.

[0016] In a first step (which has been performed within the framework of a corresponding brake test program), the joint corresponding to the brake to be tested is moved in a first rotational direction. Here, a first motor torque of the driven motor is detected during rotation of the motor in the first rotational direction.

[0017] In a second step (which is also performed in a corresponding brake test program space), the at least one motor is then automatically driven in a second rotational direction opposite to the first rotational direction. Here, a second motor torque of the motor is detected during the rotation of the driven motor in the second rotational direction.

[0018] Depending on the current position of the relevant joint, i.e., depending on the current axis position configuration (Achsstellungskonfiguration) of the robot arm, the joint is loaded once with a directional component in the direction of gravity and once with a directional component opposite to the direction of gravity by a rotation in a first rotational direction and a rotation in a second rotational direction. However, the friction torque is at least approximately the same in both rotational directions. Therefore, the gravity torque can be eliminated from the first total torque in one rotational direction and the second total torque in the other rotational direction. Since the total torque corresponds to the drive torque on the motor and is particularly related to the drive current on the motor, the gravity torque can be calculated and the remaining friction torque of the relevant joint can be determined.

[0019] In a third step, the first motor torque and the second motor torque are automatically evaluated based on this in order to obtain the friction torque of the joint corresponding to the driven motor.

[0020] Brakes are usually provided in robot systems in order to maintain the position of the robot arm in the de-energized state. Therefore, a closed brake on a robot arm joint can be considered a joint with high joint friction. When the brake is open, the robot arm should be able to move as easily as possible in the energized state. Therefore, an open brake on a robot arm joint can be considered a joint with low joint friction.

[0021] Other moving parts, such as spherical bearings, motor shaft bearings and transmission mechanisms, are usually designed to produce the lowest possible friction.

[0022] The situation of brake damage, that is, the brake exerting too little friction torque in the energy-free state, can be determined by a cyclically performed brake test. This ensures that the energy-free system does not accidentally collapse, for example due to the influence of gravity conditions.

[0023] However, there is currently no check for fault situations in which the brake applies too high a torque during operation, for example when the brake is not correctly mechanically released or in the event of a fault in the electrical wiring.

[0024] Therefore, currently the secondary symptoms must be correctly interpreted accordingly, for example by a service technician. The secondary symptoms may include the following types of information occurring: for example "motor overload", "power monitoring", "transmission monitoring".

[0025] There is also currently no direct detection of additional, undesired, high-impact friction occurring during operation, such as bearing friction.

[0026] Usually for cost reasons, additional sensors should not be installed in the system which can detect friction directly and thus enable direct evaluation of this sensor value.

[0027] With the invention, the maximum possible automated detection of the second fault situation is achieved without the use of additional sensors.

[0028] By means of the method according to the invention, it is possible to avoid a potential overload of the robot which may go undetected for a long time. Unexpected overloads may lead to increased wear and / or energy consumption. Furthermore, it is possible to avoid the threat of a long-term failure of the robot due to errors of greater impact. The service technician can find out the actual cause of the fault more quickly and replace the defective component more specifically or rectify the fault in another way, for example, make the relevant brake operational again, lubricate the transmission mechanism.

[0029] Error identification can be easily integrated into existing processes and production procedures of robot users, for example by means of an extended evaluation of existing brake tests.

[0030] During regularly performed and prescribed brake tests, in order to evaluate the brake at the beginning of the brake test method, provision can be made for the joint to be initially moved in both directions with the brake open, so that the friction state of the joint in both directions is acquired as long as the brake is not yet closed.

[0031] Based on two test movements, first in one direction of rotation and then in the opposite direction of rotation, the two motor torques measured can then be:

[0032] M + =Mg+Mr and

[0033] M - =Mg+Mr

[0034] Approximately determine the gravity moment Mg and the friction moment Mr:

[0035] Mg=(M + +M - ):2

[0036] Mr=|(M + -M - ):2|

[0037] These data are used to infer the effective braking torque from the switched-in motor torque in the subsequent execution of the brake test method (assuming that the drive does not move during the test).

[0038] According to the invention, the brake test method comprises an extension of the existing evaluation, namely an evaluation of the determined, effective friction torque Mr itself.

[0039] A first approximation for a reasonable, automatically valid limit value may already be the target brake holding torque to be tested itself. The following considerations make sense. If the friction of the system is of the order of magnitude of the friction caused by the brake itself used, then the brake is not necessary. Therefore, the presence of a corresponding amount of friction is an error.

[0040] If the determined friction torque is greater than a limit value which may be configured or which is obtained by means of a percentage value from the test torque of the brake, a targeted error message can be issued at an early stage. Such a targeted error message can be, for example: "Friction too high on axis 3" or "Please check brake / gear".

[0041] By automatically calculating the friction torque as a value that is half the difference between the first motor torque and the second motor torque, the friction torque of the joint assigned to the driven motor can be determined from the first motor torque and the second motor torque.

[0042] In a first embodiment variant, the method can be performed in that the friction state of the at least one joint is automatically evaluated as faulty if the automatically determined friction torque exceeds a predetermined maximum torque.

[0043] That is, first the current friction torque is determined as described above. A simple evaluation can be performed in this way: if the currently detected friction torque exceeds a certain maximum torque, it is judged that there is a fault in the joint. This maximum torque can be determined empirically, for example, by tests. The value of the maximum torque can be specified, for example, so that a certain variation in the actual friction torque is allowed and only values ​​that clearly exceed the average value of the friction torque are considered to be impermissible.

[0044] In order to determine the predetermined maximum torque, in particular the nominal torque of a type-dependent brake which is assigned to a joint driven by a motor at which the first motor torque and the second motor torque can be detected can be taken into account. It can be assumed that the brake provided by the design meets the requirements of the joint of the robot arm with regard to the nominal torque, i.e. the brake is neither oversized nor undersized. In this regard, the nominal torque of the brake assigned to the relevant joint is a good indication of the order of magnitude that the existing friction torque should not reasonably reach. If the actual friction torque is in the order of magnitude of the nominal torque of the brake, the relevant joint may not function properly.

[0045] In particular, a value between 20% and 40% of a nominal torque value of a type-dependent brake which is assigned to a joint driven by a motor at which the first motor torque and the second motor torque can be detected may be considered as the value for the predetermined maximum torque.

[0046] In a second embodiment, the method can be performed as follows: when comparing the automatically determined friction torque with the original friction torque determined in the robot arm delivery state (Auslieferungszustand), if it is determined that the deviation between the automatically determined friction torque and the original friction torque determined in the robot arm delivery state or the robot arm debugging state (Inbetriebnahmezustand) exceeds a predetermined threshold value, the friction state of at least one joint is automatically evaluated as faulty.

[0047] That is, in the second embodiment variant, the friction torque automatically determined within the framework of the brake test method is not compared statically with a fixed predetermined maximum value, but with a friction torque determined at a point in time assuming that the brake and the joint are in a normal state. This safe and correct state can thus be associated with the commissioning state of the robot arm.

[0048] In a third embodiment, the method can be performed as follows: when comparing a later friction torque automatically determined at a later time point within the framework of a second braking test method with a previous friction torque automatically determined at a previous time point within the framework of a first braking test method, if it is determined that the deviation between the later determined friction torque and the previously determined friction torque exceeds a predetermined threshold value, the friction state of at least one joint is automatically evaluated as faulty.

[0049] That is, in the third embodiment variant, the friction torque automatically determined within the framework of the brake test method is not statically compared with a fixed predetermined maximum value, nor is it compared with the (static) friction torque in the normal state, but is compared with any friction torque determined at a previous point in time during the operation of the robot arm. A plurality of previously determined friction torques can be taken into account, which are detected at different points in time. Thus, it is even possible to deduce trends as to the extent to which the friction torque at the joint deteriorates and the speed at which the friction torque at the joint deteriorates. This allows an automated recommendation as to when maintenance should be performed or how long the robot arm can continue to operate without maintenance.

[0050] In all embodiments, the first motor torque of the driven motor and the second motor torque of the driven motor can be automatically determined from the respective motor currents of the motor during its rotation in the first rotational direction and in the second rotational direction.

[0051] The friction state in the individual joints can thus be detected indirectly, and in particular by detecting the current consumption at the electric motors associated with the joints to be detected and evaluated. It is particularly advantageous if the current at the individual motors is not detected by a dedicated, separate current measurement, but only additionally the current at the individual motors already detected within the framework of the already performed brake test method is evaluated according to the method according to the invention. In this respect, an independent, additional measurement of the current at the individual motors can be omitted.

[0052] The purpose of the present invention is also achieved by a robot, which has a robot arm, the robot arm has multiple joints and multiple limbs, which can be adjusted relative to each other by the movement of the joints of the robot arm, wherein each driven joint is assigned a motor and a brake, wherein each motor is constructed to adjust the joint assigned to the motor, more precisely by automatically controlling the motor; and the robot also has a robot controller, which is constructed to: automatically control the motor so that the limbs of the robot arm are automatically and independently adjusted relative to each other through the movement of the driven joints; and automatically control the brake so that the joints of the robot arm can be braked individually and locked, wherein the robot controller is constructed and designed to perform the method described in one or more of the above-mentioned embodiments.

[0053] The object of the present invention is also achieved through a computer program product, which has a machine-readable carrier on which a program code is stored, and the program code can be read by the robot controller as described above, and the robot controller is constructed and / or designed to perform the method described in accordance with one or more of the above-mentioned embodiments when the robot controller executes the program code.

[0054] The computer program product may be, for example, a CD, a DVD or a USB stick. However, the computer program product may also be a control card with an integrated microprocessor. However, the computer program product may also be implemented in the form of a download, which may be provided and sold via the Internet or other networks.

[0055] Therefore, the machine-readable carrier can be a CD, DVD or microprocessor having the program code stored therein. The machine-readable carrier can also be a hard disk or SSD drive, to which the program code has been downloaded, for example, by downloading, in particular in the form of a data packet.

[0056] The program code may be represented by a compiled program and / or data stored on a machine-readable carrier.

[0057] By reading the edited program and / or data, the robot controller after reading is constructed and / or designed to be able to execute the method according to the present invention.

[0058] The method according to the invention is carried out when the robot controller actually executes the program code, ie the edited program, and / or actually processes the data accordingly. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The specific embodiments of the present invention are described in detail below with reference to the accompanying drawings. The specific features of these exemplary embodiments can be considered to represent the general features of the present invention individually or in combination when necessary, regardless of where they are specifically mentioned in this article. Among them:

[0060] Figure 1 An exemplary robot is shown, comprising a robot arm with a plurality of limbs and a plurality of joints, wherein each joint has its own motor and brake, and a robot controller for operating the robot arm, in particular the motors and brake joints,

[0061] Figure 2 A schematic diagram showing the basic method according to the present invention is shown,

[0062] Figure 3 A schematic diagram showing the relationship between gravity torque, friction torque and brake holding torque during the execution of an exemplary brake test method,

[0063] Figure 4 A schematic diagram showing the joint motion process during the execution of the exemplary brake test method is shown as a v / t diagram, and

[0064] Figure 5 A schematic diagram showing a representative course of total torques on various joints during execution of an exemplary brake testing method is shown. DETAILED DESCRIPTION

[0065] Figure 1 An industrial robot 8 is shown, which has a robot arm 9 and a robot controller 10. In the case of the present embodiment, the robot arm 9 includes a plurality of joints G1 to G7 which are arranged in sequence and rotatably connected to one another via joints L1 to L6.

[0066] The industrial robot 8 has a robot controller 10, which is configured to execute a robot program and automatically move the joints G1 to G7 and joints L1 to L6 of the robot arm 9. One of the joints G1 to G7 constitutes an end joint (G7) of the robot arm 9, which has a tool flange 11.

[0067] The robot controller 10 of the industrial robot 8 is constructed or designed to execute a robot program, whereby the joints L1 to L6 of the robot arm 9 can be automatically adjusted or automatically rotated according to the robot program or in manual operation. To this end, the robot controller 10 is connected to controllable electric drives, namely motors M1 to M6, which are constructed to adjust the individual joints L1 to L6 of the robot arm 9.

[0068] In the present exemplary embodiment, the members G1 to G7 comprise a robot base 13 and a turntable 14 which is rotatably mounted relative to the robot base 13 about an axis A1 extending vertically. The other members of the robot arm 9 comprise a rocker arm 15, a cantilever arm 16 and a preferably multi-axial robot hand 17 which has a fastening device configured as a tool flange 11 for fastening a tool. The rocker arm 15 is pivotally mounted on the turntable 14 at the lower end, i.e. at the joint L2 of the rocker arm 15 (which can also be referred to as the rocker arm bearing head), about a preferably horizontal rotation axis A2.

[0069] At the upper end of the rocker 15, a cantilever arm 16 is also pivotably mounted on the joint L3 of the rocker 15 about an axis A3 which is also preferably horizontal. The cantilever arm carries a robot hand 17 at the end with its preferably three rotation axes A4, A5, A6. The joints L1 to L6 can be driven in a program-controlled manner by an electric motor M1 to M6 via the robot controller 10, and can be braked and locked by means of brakes B1 to B6 assigned to the joints L1 to L6 or electric motors M1 to M6.

[0070] Figure 2 A method for detecting and evaluating the friction state on at least one joint L1 to L6 of a robot arm 9 is shown, the robot arm having a plurality of joints L1 to L6 and a plurality of joints G1 to G7 connecting the joints L1 to L6 to each other, wherein the robot arm 9 is connected to a robot controller 10, and the robot controller is constructed and designed to control a plurality of electric motors M1 to M6 of the robot arm 9 assigned to the joints L1 to L6 of the robot arm 9 and brakes B1 to B6 of the assigned robot arm 9 in order to move the robot arm 9.

[0071] In the first step S1, in the case of the present embodiment, a braking test method assigned to the robot arm 9 is automatically executed according to a braking test program 1, and the braking test method is configured to control the electric motors M1 to M6 and brakes B1 to B6 of the robot arm 9 through the robot controller 10, so that the joints G1 to G7 of the robot arm 9 are automatically moved according to the braking test program 1 set by the braking test method, and the brakes B1 to B6 are automatically controlled.

[0072] In the second step S2, in the case of the present embodiment and within the framework of the brake test procedure 1, at least one of the multiple electric motors M1 to M6 is automatically driven along a first rotational direction, and a first motor torque M_1 on the motor is detected during rotation of the driven motor along the first rotational direction; then the at least one motor is automatically driven along a second rotational direction opposite to the first rotational direction, and a second motor torque M_2 on the motor is detected during rotation of the driven motor along the second rotational direction.

[0073] In a third step S3 , in the present exemplary embodiment, the first motor torque M_1 and the second motor torque M_2 are automatically evaluated in order to determine the friction torque Mr of the joint assigned to the driven motor.

[0074] The friction torque Mr of the joint assigned to the driven motor can be determined as a function of the first motor torque M_1 and the second motor torque M_2 as follows: The friction torque Mr is automatically calculated as a value that is half the difference between the first motor torque M_1 and the second motor torque M_2 .

[0075] For example, when the automatically determined friction torque Mr exceeds a predetermined maximum torque, the friction state of the at least one joint is automatically evaluated as faulty.

[0076] To determine the predetermined maximum torque, the nominal torque of a type-dependent brake which is assigned to the joint driven by a motor at which the first motor torque M_1 and the second motor torque M_2 can be detected can be taken into account.

[0077] For example, a value between 20% and 40% of the nominal torque value of a type-related brake can be considered as the value of the predetermined maximum torque, which brake is assigned to a joint driven by a motor, on which a first motor torque and a second motor torque can be detected, and on which a first motor torque M_1 and a second motor torque M_2 are detected.

[0078] For example, when comparing the automatically determined friction torque Mr with the original friction torque determined in the delivery state of the robot arm 9, if it is determined that the deviation between the automatically determined friction torque Mr and the original friction torque determined in the delivery state of the robot arm 9 or the debugging state of the robot arm 9 exceeds a predetermined threshold, the friction state of at least one joint can be automatically evaluated as faulty.

[0079] For example, when comparing a later friction torque automatically determined at a later time point within the framework of a second braking test method with a previous friction torque automatically determined at a previous time point within the framework of a first braking test method, if it is determined that the deviation between the later determined friction torque and the previously determined friction torque exceeds a predetermined threshold, the friction state of at least one joint can be automatically evaluated as faulty.

[0080] A first motor torque M_1 of the driven motor and a second motor torque M_2 of the driven motor can be automatically determined based on the respective motor currents of the motors during their rotation in the first rotational direction and in the second rotational direction.

[0081] exist Figure 3 A schematic diagram of the relationship between the gravity torque, the friction torque and the brake holding torque during the execution of an exemplary brake test method is shown in FIG. The gravity torque Mg always acts with the same magnitude and the same direction. The braking torque Mb increases to a maximum value in one rotational direction. Then it changes to the other rotational direction, in which the braking torque Mb continuously decreases. The friction torque is equal to half of the torque difference in the one rotational direction and in the other rotational direction. This is also Figure 5 Specifically shown in.

[0082] Figure 4 The process of the joint movement during the execution of the exemplary braking test method is schematically shown in a v / t diagram. First, the motor is started, that is, it is accelerated so that the joint then moves in a first rotational direction at a constant speed. Next, it is braked and accelerated in another rotational direction so that the joint then moves in another rotational direction, i.e., the second rotational direction, at a correspondingly opposite constant speed. Based on the acceleration and speed curves of the exemplary braking test method, a curve of the total torque on the motor is established, such as Figure 5 As schematically shown in .

[0083] exist Figure 5 A schematic diagram of a representative course of the total torque M on each joint during the execution of an exemplary braking test method is shown in FIG. The plateau stages of the total torque M at different heights are obtained in the following way: the gravity torque acts in the same way in the rotational movement along the first rotational direction and in the reverse rotational movement along the second rotational direction. The torque difference between the two plateau stages of the total torque M corresponds to twice the friction torque.

Claims

1. A method for detecting and evaluating a friction state on at least one joint of a robot arm (9), the robot arm having a plurality of joints (L1-L6) and a plurality of limbs (G1-G7) connecting the joints (L1-L6) to one another, wherein the robot arm (9) is connected to a robot controller (10), the robot controller being constructed and designed to control a plurality of electric motors (M1-M6) of the robot arm (9) assigned to the joints (L1-L6) of the robot arm (9) and an assigned brake (B1-B6) of the robot arm (9) in order to move the robot arm (9), the method comprising the following steps: - automatically executing a brake test method corresponding to the robot arm (9), the brake test method being provided for controlling the electric motor (M1-M6) and the brake (B1-B6) of the robot arm (9) through the robot controller (10) so as to automatically move the limbs (G1-G7) of the robot arm (9) according to a brake test program (1) provided by the brake test method, and automatically controlling the brake (B1-B6), - within the framework of the brake test procedure, automatically driving at least one of the plurality of electric motors (M1-M6) in a first rotational direction and detecting a first motor torque (M_1) on the driven motor during rotation of the driven motor in the first rotational direction; subsequently automatically driving the at least one motor in a second rotational direction opposite to the first rotational direction and detecting a second motor torque (M_2) on the driven motor during rotation of the driven motor in the second rotational direction, - automatically evaluating the first motor torque (M_1) and the second motor torque (M_2) in order to obtain the friction torque (Mr) of the joint belonging to the driven motor, Characterized in that the friction torque (Mr) of the joint belonging to the driven motor is determined from the first motor torque (M_1) and the second motor torque (M_2) by automatically calculating the friction torque (Mr) as a value of half the difference between the first motor torque (M_1) and the second motor torque (M_2), and when the automatically determined friction torque (Mr) exceeds a predetermined maximum torque, the friction state of the at least one joint is automatically evaluated as faulty, and When comparing a later friction torque (Mr) automatically determined at a later time point within the framework of executing a second braking test method with a previous friction torque (Mr) automatically determined at a previous time point within the framework of executing a first braking test method, if it is determined that the deviation between the later determined friction torque (Mr) and the previously determined friction torque (Mr) exceeds a predetermined threshold value, the friction state of the at least one joint is automatically evaluated as faulty.

2. The method according to claim 1, characterized in that To determine the predetermined maximum torque, a type-dependent nominal torque of a brake that is assigned to a joint driven by the motor for which the first motor torque (M_1) and the second motor torque (M_2) are detected is used.

3. The method according to claim 2, characterized in that A value between 20% and 40% of a type-dependent nominal torque value of a brake assigned to a joint driven by a motor for which the first motor torque (M_1) and the second motor torque (M_2) are detected is used as the value for the predetermined maximum torque.

4. The method according to claim 1, characterized in that: When comparing the automatically determined friction torque (Mr) with the original friction torque determined in the delivery state of the robot arm (9), if it is determined that the deviation of the automatically determined friction torque (Mr) from the original friction torque determined in the delivery state of the robot arm (9) or in the debugging state of the robot arm (9) exceeds a predetermined threshold value, the friction state of at least one joint is automatically evaluated as faulty.

5. The method according to any one of claims 1 to 4, characterized in that A first motor torque (M_1) of the driven motor and a second motor torque (M_2) of the driven motor are automatically determined as a function of the respective motor currents of the motor during its rotation in the first rotational direction and in the second rotational direction.

6. A robot having a robot arm (9), the robot arm having a plurality of joints (L1-L6) and a plurality of limbs (G1-G7), the limbs being adjustable relative to each other by the movement of the joints (L1-L6) of the robot arm (9), wherein each driven joint (L1-L6) is assigned a motor (M1-M6) and a brake (B1-B6), wherein each motor (M1-M6) is constructed to adjust the joint (L1-L6) assigned to the motor and is adjusted by automatically controlling the motor (M1-M6); the robot also having a mechanical A robot controller (10) is constructed to automatically control the motors (M1-M6) so that the joints (G1-G7) of the robot arm (9) are automatically and independently adjusted relative to each other through the movement of the driven joints (L1-L6), and the robot controller is also constructed to automatically control the brakes (B1-B6) so that the joints (L1-L6) of the robot arm (9) can be braked individually and held in a locked manner, wherein the robot controller (10) is constructed and designed to perform the method according to any one of claims 1 to 5.

7. A computer program product having a machine-readable carrier on which a program code is stored, the program code being readable by a robot controller (10) of a robot (8) according to claim 6, and the robot controller being constructed and / or designed to execute a method according to any one of claims 1 to 5 when the program code is executed by the robot controller (10).

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