Anomaly detection device and anomaly detection method

Abstract

To detect abnormality, such as tooth jumping of a toothed belt in each shaft of a robot, quickly, surely and with a small computation amount.SOLUTION: In a robot, motors 35A, 35B of respective shafts are driven and controlled by a servo driver 45. In the robot, abnormality is determined to have occurred in a detection object shaft, if an absolute value of a torque command value exceeds a second threshold (a torque command value threshold for tooth jumping detection) b, when a shaft driven by a motor via a toothed belt is a detection object shaft, and a reference point Q is where an absolute value of a torque command value in the servo driver corresponding to a motor of the detection object shaft becomes equal to or less than a first threshold (a torque command value range for drop detection) a, and later exceeds the first threshold.SELECTED DRAWING: Figure 5

Description

[Technical field]

[0001] The present invention relates to an abnormality detection device and an abnormality detection method for detecting abnormalities such as skipping of teeth in a toothed belt for driving an industrial robot. [Background technology]

[0002] In an industrial robot (hereinafter, referred to as a robot) used for transporting a workpiece, a motor for driving each axis is provided, and a transmission mechanism for transmitting the driving force of the motor to the arm of each axis is provided. The transmission mechanism is composed of, for example, a reducer, a pulley, and a toothed belt. In the following, the toothed belt is simply referred to as a belt. In a robot, it is required to be able to detect an abnormality in the transmission mechanism when it occurs. Among the abnormalities in the transmission mechanism, a jump in a belt tooth is a precursor phenomenon of the belt breaking or falling off, and also causes an abnormality in the position of the robot's hand. Therefore, when a jump in a belt tooth occurs, it is necessary to immediately stop driving the robot and activate the brake to prevent the arm of each axis from moving. Therefore, it is required to be able to quickly and reliably detect a jump in a belt tooth that occurs in the transmission mechanism.

[0003] In a robot, a detector such as an encoder attached to the motor detects the position and speed of the motor and feeds back the detected position and speed, and generates a torque command for the motor based on the input position command and the feedback value to control the motor. If, for example, a belt tooth skip occurs on any axis of the robot, the motor of that axis will essentially be in an idling state, and this will also affect the torque command value. Therefore, Patent Document 1 discloses that the torque command signal for the motor is integrated, and if the time it takes to reach a saturation state is longer than a predetermined time, it is determined that a belt tooth skip has occurred.

[0004] As a method for detecting a general fault in a transmission mechanism, Patent Document 2 discloses a method for calculating the input side power and the load side power based on the command angle to each drive shaft of a robot, the actual angle as the motor's position data, and the drive current to the motor, and judging the presence or absence of a fault in the transmission mechanism based on the ratio or difference between these powers. Patent Document 3 discloses a method for detecting an abnormality in a reducer provided on each shaft, and a method for judging the presence or absence of an abnormality in the reducer based on a speed command, a detected speed value, and a detected torque value. The method described in Patent Document 3 is intended to detect an abnormality in the reducer, and cannot be used to detect skipped teeth in a belt. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 5-346812 [Patent Document 2] Japanese Patent Application Publication No. 11-129186 [Patent Document 3] JP 2006-102889 A Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, in a robot, it is required to be able to quickly and reliably detect belt tooth skipping. Focusing on the axis that moves the robot in the vertical direction, i.e., the vertical axis, when the robot is stopped with respect to the vertical axis, the robot's own weight is constantly applied to the vertical axis, so the motor needs to constantly generate a holding torque to support the robot in order to resist the load caused by this own weight. If a tooth skip occurs in the belt of the vertical axis, the robot's own weight is not transmitted to the motor, so the holding torque of the motor of the vertical axis changes to almost 0. On the other hand, even when the robot is accelerating in the vertical axis downward direction as a normal driving condition, the robot's own weight acts, so the torque command value may momentarily become close to 0. The method described in Patent Document 1 cannot distinguish whether the torque command value becomes close to 0 because the holding torque becomes close to 0 due to belt tooth skipping, or because the robot is descending normally, so as a result, there are cases where a tooth skip in the belt of the vertical axis cannot be appropriately detected. The method described in Patent Document 2 has a problem in that the amount of calculation required to detect an abnormality in each axis is large because the calculation is performed using a model.

[0007] An object of the present invention is to provide an abnormality detection device and an abnormality detection method that can quickly and reliably detect abnormalities such as skipping of belt teeth on each axis of a robot with a small amount of calculation. [Means for solving the problem]

[0008] The abnormality detection device of the present invention is an abnormality detection device that detects abnormalities in a robot in which the motor of each axis is driven and controlled by a servo driver, and is equipped with an abnormality detection unit that determines, as the detection target axis, an axis in the robot driven by a motor via a toothed belt, and determines that an abnormality has occurred in the detection target axis if the absolute value of the torque command value in the servo driver corresponding to the motor of the detection target axis becomes less than or equal to a first threshold value and then exceeds the first threshold value as a reference point, and determines that an abnormality has occurred in the detection target axis if the absolute value of the torque command value exceeds a second threshold value within a predetermined detection application time from the reference point.

[0009] When a tooth skip occurs in the belt when the shaft of the robot is driven by the motor through the belt, the driving force of the motor is at least partially not transmitted to the shaft, so the torque command value for the motor approaches 0. When recovering from the tooth skip, the load on the belt fluctuates suddenly temporarily, so the torque command value jumps up, and then the torque command value converges to a normal value while oscillating. Therefore, by detecting that the torque command value approaches 0, that is, the absolute value of the torque command value becomes equal to or less than the first threshold value, and then the absolute value of the torque command value jumps up within a predetermined period of time to exceed the second threshold value, it is possible to determine that an abnormality in the belt, such as tooth skip, has occurred. Therefore, according to the abnormality detection device of the present invention, an abnormality such as tooth skip in the belt for driving the robot can be quickly and reliably detected with a small amount of calculation.

[0010] In the abnormality detection device of the present invention, when the robot has a vertical axis that moves in the vertical direction, the axis to be detected is, for example, the vertical axis. The motor of the vertical axis of the robot always generates a holding torque due to its characteristic of supporting a load. However, when an abnormality occurs in the belt mechanically connected to the motor, such as tooth skipping, the holding torque becomes almost 0, and the torque command value for the motor also becomes almost 0 correspondingly. Therefore, it can be determined that an abnormality has occurred in the vertical axis when the absolute value of the torque command value is equal to or less than a threshold value. However, even when the vertical axis is normally accelerated downward, the torque command value may approach 0, and there is a risk of erroneous detection when the absolute value of the torque command value is simply compared with the threshold value. The abnormality detection device of the present invention detects a jump in the torque command value after the torque command value becomes almost 0, so that it can reliably detect an abnormality in the belt on the vertical axis without erroneous detection.

[0011] In the abnormality detection device of the present invention, the vertical axis of the robot may be a multi-stage configuration in which each stage is equipped with a motor, and in that case, the abnormality detection unit can determine whether or not an abnormality has occurred for each stage based on the torque command value of the motor for each stage. The abnormality detection device of the present invention makes it possible to accurately detect belt abnormalities even in a robot having a multi-stage vertical axis.

[0012] In the abnormality detection device of the present invention, the robot is, for example, a horizontal articulated robot. When the robot is a horizontal articulated robot, it is possible to detect abnormalities in the belt on the vertical axis and also to detect abnormalities in the belt on axes other than the vertical axis. In a horizontal articulated robot, the axes other than the vertical axis are axes that move the robot horizontally or within a horizontal plane. When belt tooth jump occurs on such an axis, it is generally considered that it occurs when a force is applied to the belt, that is, when a motor generates torque in response to an operation command to drive the axis. When belt tooth jump occurs in such a state, even though an operation command to move the axis is input, a change in the torque command value as described above occurs in the motor of the axis as a precursor, so according to the present invention, it is possible to detect abnormalities in the belt on axes other than the vertical axis of a horizontal articulated robot.

[0013] The abnormality detection method of the present invention is an abnormality detection method for detecting abnormalities in a robot in which the motor of each axis is driven and controlled by a servo driver, and defines an axis in the robot driven by a motor via a toothed belt as the axis to be detected, and defines the time when the absolute value of the torque command value in the servo driver corresponding to the motor of the axis to be detected becomes less than or equal to a first threshold value and then exceeds the first threshold value as a reference point, and determines that an abnormality has occurred in the axis to be detected if the absolute value of the torque command value exceeds a second threshold value within a predetermined detection application time from the reference point.

[0014] According to the anomaly detection method of the present invention, it is possible to quickly and reliably detect anomalies in a belt while preventing erroneous detection. In addition, since the method checks for signs of breakage or falling off, it can also be used for preventive maintenance. Furthermore, when a control device (robot controller) that drives and controls the robot is provided, this anomaly detection method can be realized by simple arithmetic processing in the control device without providing additional hardware, and if the control device is software-controlled, it can be realized by modifying the software.

[0015] In the anomaly detection method of the present invention, when a robot has a vertical axis that moves in a vertical direction, the axis to be detected is, for example, the vertical axis. In the vertical axis of the robot, the torque command value for the motor may approach 0 as the robot operates normally, and there is a risk of erroneous detection if belt anomalies are detected only based on the torque command value approaching 0. By applying the anomaly detection method of the present invention to the vertical axis of the robot, belt anomalies can be reliably detected without the risk of erroneous detection.

[0016] In the abnormality detection method of the present invention, the vertical axis of the robot may be a multi-stage configuration in which each stage is equipped with a motor, in which case the presence or absence of an abnormality can be determined for each stage based on the torque command value for the motor for each stage. In other words, the abnormality detection method of the present invention makes it possible to accurately detect belt abnormalities even in a robot having a multi-stage vertical axis.

[0017] In the abnormality detection method of the present invention, the robot is, for example, a horizontal articulated robot. When the robot is a horizontal articulated robot, it is possible to detect an abnormality in the belt on the vertical axis as well as an abnormality in the belt on an axis other than the vertical axis. Effect of the Invention

[0018] According to the present invention, abnormalities such as skipped teeth of a belt on each axis of a robot can be detected quickly and reliably with a small amount of calculation. [Brief description of the drawings]

[0019] [Figure 1] 1A and 1B are diagrams showing a robot to which an anomaly detection method according to an embodiment of the present invention is applied, in which (a) is a schematic side view and (b) is a plan view. [Diagram 2] FIG. 2 is a diagram illustrating a configuration of a lifting mechanism. [Diagram 3] FIG. 2 is a block diagram showing a configuration for operational control and abnormality detection. [Figure 4] FIG. 4 is a waveform diagram showing a change in speed and a change in a torque command value corresponding to the speed. [Diagram 5] FIG. 4 is an enlarged view showing a change in a torque command value. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows a robot to which an anomaly detection method according to an embodiment of the present invention is applied, with (a) being a schematic side view and (b) being a plan view. The robot 10 is configured as a horizontal articulated robot, with the objective of transporting a workpiece such as a glass substrate. The robot 10 is electrically connected to a control device (robot controller) 40 via a cable, which receives an operation command for the robot 10 from outside and drives and controls the robot 10 based on the operation command. The control device 40 also functions as an anomaly detection device based on the present invention. For ease of understanding, the control device 40 and the cable connected thereto are not shown in FIG. 1(b).

[0021] The robot 10 is configured as a so-called double-handed robot equipped with two hands 13A and 13B each holding a workpiece 60 (not shown in FIG. 1(a)). The control device 40 includes a control unit 41 that receives an operation command and detects the occurrence of an abnormality, and a drive circuit 42 that is provided for each motor of each axis provided in the robot 10 and includes a servo driver 45 (see FIG. 2) and the like for driving the motor. The detailed configuration of the control device 40 will be described later. Since the robot 10 of this embodiment is used to transport the workpiece 60, the operation command is basically a movement operation command for moving the hands 13A and 13B to a certain position. The control unit 41 generates an internal command including a speed for each axis of the robot 10 based on the operation command, and the drive circuit 42 actually drives the motor of each axis of the robot 10 based on the internal command for each axis.

[0022] The robot 10 includes a base 22 movable on a pair of parallel rails 21 arranged in a straight line on the floor surface, a rotating table 23 arranged on the base 22 and rotated in a horizontal plane around a rotating shaft 31 by a motor 35TH built into the base 22, and a lifting mechanism 24 arranged to stand upright relative to the rotating table 23. A cover 25 is attached to the rail 21. A motor 35X for moving the base 22 horizontally along the rail 21 is provided on the base 22, and the motor 35X constitutes and drives a horizontal movement mechanism that moves the robot 10 together with the base 22 horizontally along the rail 21. The motor 35TH and the rotating table 23 constitute a rotation mechanism that rotates the lifting mechanism 24 relative to the base 22 around the vertical rotating shaft 31, and this rotation mechanism is driven by the motor 35TH.

[0023] The lifting mechanism 24 includes a fixed part 24A attached to the rotating table 23 and a moving part 24B that moves up and down in a vertical direction relative to the fixed part 24A by a motor. FIG. 2 is a diagram showing the structure of the lifting mechanism 24. Although only one motor may be used in the lifting mechanism, in order to move a robot with a large mass at high speed and with a large lift amount, it is effective to use multiple motors to configure the moving mechanism 24 in multiple stages. In this embodiment, the lifting mechanism is configured in two stages, with a first stage Z-axis motor 35ZA provided in the fixed part 24A and a second stage Z-axis motor 35ZB provided in the moving part 24B. The Z-axis motor 35ZA attached to the housing of the fixed part 24A rotates and drives the ball screw 54A via a belt 52A. A slider 55 that moves up and down with the rotation of the ball screw 54A is attached to the ball screw 54A. The housing of the moving part 24B is attached to the slider 55, and the second-stage Z-axis motor 35ZB in the moving part 24B rotates and drives the ball screw 54B via the belt 52B. The arm support part 26, which is a slider that rises and falls with the rotation of the ball screw 54B, is attached to the ball screw 54B. Of course, the lifting mechanism 24 can be configured with three or more stages. In the multi-stage lifting mechanism 24, a motor, a ball screw, a belt stretched between the motor and the ball screw, and a slider that rises and falls with the rotation of the ball screw are provided for each stage. The belts 52A and 52B provided in the lifting mechanism 24 are toothed belts.

[0024] The arm support 26 is a member that holds the horizontal multi-joint mechanism, and is provided so as to extend in the horizontal direction as shown in Fig. 1. Two sets of horizontal multi-joint mechanisms are attached to the tip of the arm support 26 in a vertically arranged manner. The lifting mechanism 24 is driven by motors 35ZA and 35ZB to raise and lower the arm support 26 relative to the base 22. The upper horizontal multi-joint mechanism includes a first arm 11A that is attached to the arm support 26 and can rotate in a horizontal plane around a common shaft 32, and a second arm 12A that is attached to the tip of the first arm 11A and can rotate in a horizontal plane around a shaft 33A, and a hand 13A is attached to the tip of the second arm 12A. Similarly, the lower horizontal multi-joint mechanism comprises a first arm 11B attached to the arm support portion 26 and rotatable in a horizontal plane around a common axis 32, and a second arm 12B attached to the tip of the first arm 11B and rotatable in a horizontal plane around an axis 33B, and a hand 13B is attached to the tip of the second arm 12B.

[0025] The hands 13A and 13B are fork-shaped with multiple rod-shaped members arranged in parallel so that the plate-shaped workpiece 60 can be transported while being kept horizontal by holding it from below. The hands 13A and 13B move forward or backward with respect to the workpiece 60 when taking out the workpiece 60 stored in a cassette or load lock chamber of a processing device and holding it on the hands 13A and 13B, or storing the held workpiece 60 in a cassette or the like. The direction in which the hands 13A and 13B move forward or backward coincides with the direction in which the rod-shaped members extend. The width of the hands 13A and 13B in the left-right direction, i.e., the direction perpendicular to the front-rear direction, is shorter than the left-right width of the workpiece 60 to be transported.

[0026] In the robot 10, the horizontal articulated mechanism is configured such that the hands 13A, 13B move forward and backward in a linear motion along a direction perpendicular to the direction in which the arm support 26 extends, by a link mechanism incorporated in the first arms 11A, 11B and the second arms 12A, 12B. That is, both hands 13A, 13B move forward and backward in the same direction. The movement of the tips of the hands 13A, 13B away from the central axis 32 is the forward movement, and the movement in the opposite direction to the forward movement is the backward movement. The first arms 11A, 11B and the second arms 12A, 12B perform bending movements as a whole, and in order to keep the orientation of the hands 13A, 13B constant in the horizontal plane, the hands 13A, 13B are attached at the tips of the second arms 12A, 12B so as to be rotatable in the horizontal plane around the wrist axes 34A, 34B, respectively. In the upper horizontal articulated mechanism, the link mechanism is driven by a motor 35RU provided on the arm support section 26, whereby the first arm 11A and the second arm 12A move, and the hand 13A moves in a direction perpendicular to the extension direction of the arm support section 26 while maintaining its orientation. Similarly, in the lower horizontal articulated mechanism, the link mechanism is driven by a motor 35RD provided on the arm support section 26, whereby the first arm 11B and the second arm 12B move, and the hand 13B moves in a direction perpendicular to the extension direction of the arm support section 26 while maintaining its orientation. In this robot 10, the hands 13A and 13B can be moved forward and backward independently. The forward and backward movement of the hands 13A and 13B by the bending motion of the first arms 11A and 11B and the second arms 12A and 12B is called arm extension and contraction.

[0027] In conclusion, the movement of the robot 10 shown in FIG. 1 can be divided into horizontal movement along the rail 21 (this is the X-axis or travel axis movement), rotation around the rotation axis 31, which is an axis oriented in the vertical direction, relative to the base (this is the θ-axis or rotation axis movement), horizontal forward and backward movement of the hands 13A and 13B, i.e., extension and contraction movement of the arms (this is the R-axis movement), and vertical lifting and lowering of the arm support part 26 by the lifting mechanism 24 (this is the vertical axis or Z-axis movement). Since two horizontal multi-joint mechanisms are provided corresponding to the two hands 13A and 13B, in this robot 10, the R-axis is divided into the RU-axis corresponding to the upper hand 13A and the RD-axis corresponding to the lower hand 13B. The RU-axis and the RD-axis are independent of each other. The X-axis, θ-axis, RU-axis, and RD-axis are driven by the motors 35X, 35TH, 35RU, and 35RD corresponding to the respective axes via pulleys and belts. The X-axis, θ-axis, RU-axis, and RD-axis are axes that move the robot 10 in a horizontal plane, and are therefore horizontal-plane movement axes. The Z-axis, which is a vertical axis, is driven by two-stage motors 35ZA and 35ZB via belts 52A and 52B. The robot 10 executes an operation of moving only one of these axes or an operation of moving two or more axes simultaneously, by drive control based on an internal command from the control device 40 in response to an operation command. When driving the Z-axis, basically the two-stage motors 35ZA and 35ZB are driven simultaneously. As described above, the belts 52A and 52B of the vertical axes are toothed belts, but the belts of the X-axis, θ-axis, RU-axis, and RD-axis are also toothed belts.

[0028] FIG. 3 is a block diagram showing the control system of the robot 10 to explain the operation control and abnormality detection of the robot 10 in this embodiment. As described above, the robot 10 is provided with three motors 35ZA and 35ZB for driving the lifting mechanism 24, which is a vertical axis, motors 35RU and 35RD for driving the extension and contraction of arms corresponding to the upper and lower hands 13A and 13B, a motor 35X for driving the horizontal movement mechanism, and a motor 35TH for driving the rotation mechanism, as motors for each axis. All of these motors are motors with encoders, and are servo-controlled by a servo driver 45 provided for each motor in a drive circuit 42 in the control device 40. The servo driver 45 for each axis is supplied with an internal command for each axis from the control unit 41 in the control device 40, and drives the corresponding motor in response to the internal command. In addition, a signal indicating a torque command value for the corresponding motor is also output from the servo driver 45 for each axis.

[0029] An operation command for causing the robot 10 to perform a desired operation is input to the control unit 41 of the control device 40. The operation command is generated, for example, as a result of teaching the robot, and includes, as an example, a start point and an end point of the movement of the hand 13A. The control unit 41 is provided with a trajectory calculation unit 43 that analyzes the input operation command to generate a trajectory of the robot, calculates the movement required for each axis based on the trajectory, and generates an internal command for each axis. The internal command output by the trajectory calculation unit 43 includes at least one of a position command and a speed command for the motor of each axis.

[0030] In order to detect abnormalities in each axis of the robot 10, particularly abnormalities such as belt tooth skipping in the transmission mechanism of each axis, the control unit 41 is also provided with an abnormality detection unit 44. The abnormality detection unit 44 receives command output information indicating what internal command is currently being output to the servo driver 45 of each axis from the trajectory calculation unit 43, and also outputs a signal indicating a torque command value from each servo driver 45. Instead of the command output information, the internal command for each servo driver 45 may be directly provided to the abnormality detection unit 44. The process of abnormality detection by the abnormality detection unit 44 will be described below.

[0031] When a motor drives a robot shaft via a belt, if the belt is slipping, particularly when the belt is slipping due to tooth skipping, the driving force from the motor is at least partially not transmitted to the shaft, the load on the motor is reduced, and the motor is in an idling state, so the torque command value for the motor approaches 0. When the belt recovers from the slip, that is, when the belt teeth are re-engaged, the load on the belt temporarily changes suddenly, so the torque command value jumps up. After the belt recovers from the slip, the torque command value converges to a normal value while oscillating. Therefore, the abnormality detection unit 44 applies the abnormality detection method based on the present invention, and determines that an abnormality has occurred in the shaft when the torque command value of the motor of a certain axis of the robot approaches 0, that is, when the absolute value of the torque command value becomes equal to or less than a first threshold value and then exceeds the first threshold value as a reference point Q, and when the absolute value of the torque command value exceeds a second threshold value within a predetermined detection application time from the reference point Q. The abnormality detection method described here is a method for detecting belt tooth skipping, which is considered to be a precursor phenomenon of belt breakage and falling off, and can therefore also be used for preventive maintenance of the belt.

[0032] The abnormality detection unit 44 detects the occurrence of an abnormality in the belt by applying the abnormality detection method based on the present invention to at least the vertical axis among the axes of the robot 10. When detecting abnormalities such as belt tooth skipping for the vertical axes ZA and ZB, the above-mentioned first threshold is particularly called the torque command value range for detecting a fall. The second threshold is also called the torque command value threshold for detecting tooth skipping. When the abnormality detection method based on the present invention is applied to the vertical axes of the robot, the jump in the torque command value when recovering from a slip is a jump in the upward direction in the torque command value, so when the torque command value for rotating the motor in the upward direction is set to a positive value, the torque command value itself may be used instead of the absolute value of the torque command value when comparing with the second threshold. When the torque command value for rotating the motor in the upward direction is set to a negative value, the second threshold may be set to a negative value, and the torque command value may be determined to be smaller than the second threshold. In the anomaly detection method according to the present invention, an anomaly in the belt is detected not only by detecting the torque command value approaching 0 but also by detecting a sudden increase in the torque command value after the torque command value approaches 0, so that it is possible to prevent erroneous detection of an anomaly, particularly with respect to the vertical axis, due to only detecting that the torque command value approaches 0. As will be described later, the values ​​of the first and second thresholds and the length of the detection application time are determined in advance based on the configuration and operating conditions of robot 10.

[0033] The abnormality detection unit 44 can also detect abnormalities in the X-axis, θ-axis, RU-axis, and RD-axis, which are the axes moving in the horizontal plane. In the case of an axis moving in the horizontal plane, if the torque command value for the motor of the axis is almost 0 even though the internal command to move the axis is output from the trajectory calculation unit 43, it can be determined that an abnormality such as a tooth jump of the belt has occurred. Therefore, when the abnormality detection unit 44 detects that the absolute value of the torque command value in the servo driver 45 for the motor of the axis moving in the horizontal plane is equal to or less than a threshold value when an internal command to move a certain axis moving in the horizontal plane is output in the command output information from the trajectory calculation unit 43, the abnormality detection unit 44 determines that an abnormality has occurred in the axis moving in the horizontal plane. Alternatively, the abnormality detection unit 44 may also detect the occurrence of an abnormality in the belt for the axis moving in the horizontal plane by applying the abnormality detection method based on the present invention described above. When it is determined that an abnormality exists in the vertical axis or in the horizontal axis, the abnormality detection unit 44 outputs a signal to the outside to notify that an abnormality has been detected.

[0034] The detection of anomalies in the vertical axis of the robot 10 in this embodiment will be described in more detail below. FIG. 4 is a waveform diagram showing the change in speed on the ZA and ZB axes and the change in the torque command value corresponding to the change in speed when the lifting mechanism 24 is lifted from a certain position, stopped once, and then lowered back to the original position. (a) shows the change in speed, and (b) shows the change in the torque command value. The solid line shows the change in the ZA axis, and the dashed line shows the change in the ZB axis. In the graph of the torque command value, the upward and downward directions of the vertical axis indicate whether the torque command value rotates the motor in the upward direction or the downward direction. In the upward phase, the robot first accelerates and then reaches a constant speed (constant speed section), and then decelerates and stops. In the downward phase, there is also a period of acceleration (downward acceleration period), followed by a constant speed section, and finally a period of deceleration (downward deceleration period).

[0035] In the graph of the torque command value, both the ZA axis and the ZB axis have torque command values ​​in the upward direction in almost the entire range because the vertical axis is an axis that supports the weight of the robot 10 and the weight of the workpiece 60, and the motor needs to generate a holding torque even when the robot is not moving in the vertical direction (for example, during the "stop" period in the figure). The vertical axis is different from the horizontal movement axis in that the torque command value is not 0 even when the robot is stopped. However, as shown in the region P in the figure, the torque command value of the ZB axis approaches 0 during the downward acceleration period. If an abnormality such as a tooth jump occurs in the belt on the vertical axis, the torque command value approaches 0, so the presence or absence of an abnormality can be determined by detecting this. However, if the torque command value approaches 0 even when the robot is operating normally, it is not possible to determine the abnormality based on whether the torque command value approaches 0. Therefore, in this embodiment, as described above, by detecting whether the torque command value jumps up after the torque command value approaches 0, erroneous detection is prevented, and an abnormality in the belt of the vertical axis can be quickly and reliably detected with a small amount of calculation.

[0036] Next, the detection of an abnormality in this embodiment and the setting of the first threshold, the second threshold, and the detection application time will be described with reference to FIG. 5. FIG. 5 shows the change in the torque command value when a tooth jump occurs in the toothed belt on the vertical axis. Since it is a vertical axis, a constant torque command value in the upward direction is generated to generate a holding torque. It is assumed that a tooth jump occurs in the toothed belt here. In the figure, the tooth jump occurs near 100 ms on the time axis. In the tooth jump, tooth slip occurs first as a phenomenon, so that the torque command value approaches 0 as shown in the tooth slip section S. The first threshold (torque command value range for drop detection) is set so that it can be detected that the torque command value approaches 0 due to tooth slip. In the example shown here, a positive value smaller than the torque command value corresponding to the holding torque is set as a, and a is set as the first threshold. Therefore, when the torque command value becomes a value between +a and -a, that is, when the absolute value of the torque command value becomes equal to or less than the first threshold a, it is determined that the torque command value approaches 0.

[0037] When the belt tooth jump progresses, the belt teeth are re-engaged. At this time, the torque command value jumps upward. In order to detect the presence or absence of the jump in the torque command value, the time when the absolute value of the torque command value becomes equal to or less than the first threshold value a and then exceeds the first threshold value a is set as a reference point Q, and it is determined whether the absolute value of the torque command value exceeds a second threshold value (torque command value threshold value for detecting tooth jump) b within a predetermined detection application period T from the reference point Q. In the example shown in FIG. 5, since the absolute value of the torque command value exceeds the second threshold value b as shown by point R, it is determined that tooth jump has occurred. The torque command value that jumps up due to the re-engagement of the teeth then oscillates and converges to a value corresponding to the holding torque. FIG. 5 shows a case where the vertical axis is not raised or lowered and only the holding torque is applied to the vertical axis, but in reality, it is necessary to be able to detect tooth jumping even when the vertical axis is raised or lowered. Therefore, the detection application time T is determined based on the timing at which a jump in the torque command value due to tooth jumping is expected to occur, taking into consideration conditions such as the shape and interval of the teeth on the belt and the speed of the belt accompanying the raising and lowering of the vertical axis. The second threshold value is also determined so as to be able to distinguish between a torque command value or a change therein that may occur during normal operation and a sudden increase in the torque command value due to a tooth jump.

[0038] FIG. 5 describes detection of belt abnormality in the vertical axis of the robot 10, but as for the axis moving in the horizontal plane of the robot 10, if an abnormality occurs in the belt while the axis is being driven, the torque command value of the motor of the axis is considered to change in the same manner as shown in FIG. 5, so that the occurrence of an abnormality in the belt can be detected in the same manner as in the case of the vertical axis. When the axis moving in the horizontal plane is the subject, the upward and downward directions in FIG. 5 can be interpreted as forward and reverse directions according to the forward and reverse rotation direction of the motor of the axis. If a tooth jump occurs while the axis is being driven by a forward torque command value, the direction of the jump in the torque command value after the tooth slip will be forward, and conversely, if a tooth jump occurs while the axis is being driven by a reverse torque command value, the direction of the jump in the torque command value after the tooth slip will be reverse.

[0039] The detection of abnormalities and the setting of the first threshold value, the second threshold value, and the detection applicable time have been explained above assuming that the belt is a toothed belt. However, even if the belt is not a toothed belt, it is believed that belt slippage and recovery from slippage are precursors to breakage or falling off. Therefore, by setting the first threshold value, the second threshold value, and the detection applicable time in the same manner as described above, abnormalities in the belt such as breakage or falling off can be detected.

[0040] According to the present embodiment described above, it is possible to quickly find an abnormality with a small amount of calculation without erroneous detection for the vertical axis. It is also possible to quickly find an abnormality with a small amount of calculation for the horizontal axis. [Explanation of symbols]

[0041] 10...robot; 11A, 11B...first arm; 12A, 12B...second arm; 13A, 13B...hand; 21...rail; 22...base; 23...rotating table; 24...lifting mechanism; 24A...fixed part; 24B...moving part; 25...cover; 26...arm support part; 31...rotating axis; 32...common axis; 33A, 33B...axis; 34A, 34B...wrist axis; 35RD, 35RU, 35TH, 35X, 35ZA, 35ZB...motor; 40...control device; 41...control part; 42...drive circuit; 43...trajectory calculation part; 44...abnormality detection part; 45...servo driver; 52A, 52B...belt; 54A, 54B...ball screw; 55...slider; 60...work.

Claims

1. An abnormality detection device for detecting an abnormality in a robot in which motors of each axis are driven and controlled by a servo driver, an abnormality detection device comprising: an abnormality detection unit that determines, as an axis to be detected, an axis driven by the motor in the robot via a toothed belt, and determines that an abnormality has occurred in the axis to be detected, when an absolute value of a torque command value in the servo driver corresponding to the motor of the axis to be detected becomes equal to or less than a first threshold value and then exceeds the first threshold value as a reference point, and when the absolute value of the torque command value exceeds a second threshold value within a predetermined detection application time from the reference point.

2. The robot has a vertical axis for vertical movement; The anomaly detection device according to claim 1 , wherein the axis to be detected is the vertical axis.

3. In the robot, the vertical axis has a multi-stage configuration, each stage having the motor, The abnormality detection device according to claim 2 , wherein the abnormality detection unit determines whether or not the abnormality has occurred for each stage based on the torque command value of the motor for each stage.

4. The abnormality detection device according to claim 1 , wherein the robot is a horizontal articulated robot.

5. An abnormality detection method for detecting an abnormality in a robot in which motors of each axis are driven and controlled by a servo driver, comprising: an axis driven by the motor in the robot via a toothed belt is defined as an axis to be detected, and a reference point is defined as a point when an absolute value of a torque command value in the servo driver corresponding to the motor of the axis to be detected becomes equal to or less than a first threshold value and then exceeds the first threshold value, and if the absolute value of the torque command value exceeds a second threshold value within a predetermined detection application time from the reference point, it is determined that an abnormality has occurred in the axis to be detected.

6. The robot has a vertical axis for vertical movement; The method of claim 5 , wherein the axis to be detected is the vertical axis.

7. In the robot, the vertical axis has a multi-stage configuration, each stage having the motor, The abnormality detection method according to claim 6 , further comprising the step of determining whether or not the abnormality has occurred for each stage based on the torque command value of the motor for each stage.

8. The abnormality detection method according to claim 5 , wherein the robot is a horizontal articulated robot.

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