Abnormality detection device and abnormality detection method

Abstract

Provided is an abnormality detection device and an abnormality detection method capable of quickly and reliably detecting a tooth skipping or the like of a toothed belt on each axis of a robot with a small amount of computation. In a robot in which motors (35A, 35B) of each axis are driven and controlled by a servo driver (45), an axis driven by a motor via a toothed belt is set as a detection target axis, an absolute value of a torque command value in the servo driver corresponding to the motor of the detection target axis is set as a reference point Q when the absolute value becomes equal to or smaller than a first threshold value (torque command value range for drop detection) a and then exceeds the first threshold value, and in a case where the absolute value of the torque command value exceeds a second threshold value (torque command value threshold value for tooth skipping detection) b within a prescribed detection application time T from the reference point, it is determined that an abnormality has occurred in the detection target axis.

Description

TECHNICAL FIELD

[0001] The present application relates to an abnormality detection device and an abnormality detection method for detecting a tooth jump or the like of a toothed belt for driving in an industrial robot. BACKGROUND

[0002] In an industrial robot (hereinafter referred to as a robot) for carrying a workpiece or the like, a motor for driving each axis is provided, and a transmission mechanism for transmitting the driving force of the motor to an arm of each axis is provided. The transmission mechanism is constituted by, for example, a speed reducer, a pulley, a toothed belt, or the like. Hereinafter, the toothed belt will be simply referred to as a belt. In the robot, it is required to be able to detect an abnormality of the transmission mechanism when it occurs. A tooth jump of the belt, which is one of the abnormalities of the transmission mechanism, is a precursor phenomenon of a break or a fall of the belt, and causes an abnormality such as a positional deviation of a robot finger, so when a tooth jump of the belt occurs, it is necessary to immediately stop the driving of the robot and to actuate a brake to immobilize the arm or the like of each axis. Therefore, it is required to be able to quickly and reliably detect a tooth jump of the belt generated by the transmission mechanism.

[0003] In the robot, the position and the speed of the motor are detected by a detector such as an encoder attached to the motor and are fed back, a torque command for the motor is generated based on an input position command and a feedback value, and the motor is controlled. In a case where a tooth jump of the belt occurs in any one axis of the robot, since the motor of the axis substantially becomes an idle state, the influence thereof is also exhibited on the torque command value. Therefore, Patent Literature 1 discloses that an integral process is performed on a torque command signal for the motor, and in a case where the time until the integral process reaches a saturation state is longer than a prescribed time, it is determined that a tooth jump of the belt has occurred.

[0004] As a method of detecting a general failure of the transmission mechanism, Patent Literature 2 discloses a method of calculating the power on the input side and the power on the load side based on the command angle of each driving axis of the robot, the actual angle which is the position data of the motor, and the driving current of the motor, and determining whether the transmission mechanism has a failure based on the ratio or the difference between these powers. In Patent Literature 3, as a method of detecting an abnormality of a speed reducer provided to each axis, a method of determining whether the speed reducer has an abnormality based on a speed command, a speed detection value, and a torque detection value is disclosed. The method described in Patent Literature 3 is a method for the purpose of detecting an abnormality in the speed reducer, and cannot be used for detecting a tooth jump of the belt.

[0005] [Patent Literature]

[0006] [Patent Literature]

[0007] Patent Literature 1: Japanese Patent Application Laid-Open No. 5-346812

[0008] Patent Literature 2: Japanese Patent Application Laid-Open No. 11-129186

[0009] Patent Literature 3: Japanese Patent Application Laid-Open No. 2006-102889 SUMMARY

[0010] As described above, in a robot, it is required to be able to quickly and reliably detect a skip of a belt. If a vertical shaft, which is a shaft that moves the robot in the vertical direction, is focused on, when the robot is made to be stationary with respect to the vertical shaft, since the weight of the robot is always applied to the vertical shaft, in order to overcome the load due to the weight, the motor needs to always generate a holding torque to support the robot. At this time, when a skip of the belt of the vertical shaft occurs, the weight of the robot is no longer transmitted to the motor, and thus the holding torque of the motor of the vertical shaft substantially changes to 0. On the other hand, as a driving condition of the robot in the normal state, even when accelerating in the lowering direction of the vertical shaft, due to the weight of the robot, the torque command value sometimes becomes around 0 instantaneously. In the method described in Patent Literature 1, since it is not possible to distinguish whether the holding torque becomes around 0 due to a skip of the belt and thus the torque command value becomes around 0, or the torque command value becomes around 0 due to a normal lowering of the robot, as a result, there is a case where a skip of the belt of the vertical shaft cannot be properly detected. The method described in Patent Literature 2 has a problem that the amount of calculation for detecting an abnormality of each shaft becomes large since a model is used for the calculation.

[0011] An object of the present application is to provide an abnormality detection device and an abnormality detection method that can quickly and reliably detect a skip of a belt and the like on each shaft of a robot with a small amount of calculation.

[0012] The abnormality detection device of the present application is an abnormality detection device that detects an abnormality in a robot in which a motor of each shaft is driven and controlled by a servo driver, and includes an abnormality detection section that takes a shaft in the robot that is driven by the motor via a toothed belt as a detection target shaft, takes a point in time when an absolute value of a torque command value in the servo driver corresponding to the motor of the detection target shaft becomes below 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 shaft in a case where the absolute value of the torque command value exceeds a second threshold value within a prescribed detection application time from the reference point.

[0013] When the shaft of the robot is driven by the motor via the belt, if a skip of the belt occurs, the driving force of the motor is not at least partially transmitted to the shaft, so the torque command value of the motor approaches 0. At the time of recovery from the skip, the load applied to the belt temporarily sharply fluctuates, so the torque command value jumps up, and thereafter, the torque command value converges to the value at the time of normality while vibrating. Therefore, by detecting that the torque command value approaches 0, that is, the absolute value of the torque command value becomes below a first threshold value, and then the absolute value of the torque command value jumps up to exceed a second threshold value within a prescribed period, it can be determined that the skip or the like of the belt has occurred. Therefore, according to the abnormality detection device of the present application, the skip or the like of the belt for driving in the robot can be rapidly and reliably detected with a small amount of calculation.

[0014] In the abnormality detection device of the present application, when the robot is provided with a vertical shaft that moves in the vertical direction, the detection target shaft is, for example, the vertical shaft. The motor of the vertical shaft of the robot always generates a holding torque due to the characteristic of supporting a load, but when a skip or the like of the belt mechanically linked to the motor occurs, the holding torque is almost 0, and in correspondence thereto, the torque command value of the motor is also almost 0. Therefore, in a case where the absolute value of the torque command value is below a threshold value, it can be determined that an abnormality has occurred in the vertical shaft. However, when the vertical shaft is normally accelerated in the downward direction, the torque command value also sometimes approaches 0, and in a case where the absolute value of the torque command value is simply compared with the threshold value, it is possible that an abnormality is erroneously detected. The abnormality detection device of the present application detects the jump of the torque command value after the torque command value is almost 0, so it can reliably detect an abnormality of the belt in the vertical shaft without erroneous detection.

[0015] In the abnormality detection device of the present application, the vertical shaft in the robot can be a multi-stage structure in which each stage includes a motor, and in this case, the abnormality detection section can determine whether an abnormality has occurred for each stage based on the torque command value of the motor of each stage. According to the abnormality detection device of the present application, even in a robot having a vertical shaft of a multi-stage structure, an abnormality of the belt can be accurately detected.

[0016] In the abnormality detection device of the present application, the robot is, for example, a horizontal multi-joint robot. In a case where the robot is a horizontal multi-joint robot, an abnormality of the belt in the vertical shaft can be detected, and an abnormality of the belt in a shaft other than the vertical shaft can be detected. In the horizontal multi-joint robot, the shaft other than the vertical shaft is a shaft that moves the robot in the horizontal direction or in the horizontal plane. When a skip of the belt occurs in such a shaft, it is generally considered that the force is applied to the belt, that is, the motor drives the shaft in accordance with the movement command to generate a torque. When a skip of the belt occurs in this state, although the movement command to move the shaft is input, as a precursor, the change in the torque command value as described above occurs in the motor of the shaft, so according to the present application, an abnormality of the belt in the shaft other than the vertical shaft in the horizontal multi-joint robot can also be detected.

[0017] The abnormality detection method of the present application is an abnormality detection method of detecting an abnormality in a robot in which a servomotor drives and controls a motor of each axis, detects an axis driven by a motor via a timing belt as a detection target axis, takes a point in time when an absolute value of a torque command value in the servomotor corresponding to the motor of the detection target axis becomes below 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 in a case where an absolute value of the torque command value exceeds a second threshold value within a prescribed detection application time from the reference point.

[0018] According to the abnormality detection method of the present application, it is possible to prevent false detection and to rapidly and reliably detect an abnormality of a belt. In addition, since it checks a precursor to a breakage or a shedding, the abnormality detection method can also be used for preventive maintenance. Furthermore, in a case where a control device (robot controller) that drives and controls a robot is provided, the abnormality detection method can be realized by a simple arithmetic processing in the control device without providing additional hardware, and if the control device is a software-based device, it can be realized by a modification of software.

[0019] In the abnormality detection method of the present application, in a case where the robot has a vertical axis that moves in a vertical direction, the detection target axis is, for example, the vertical axis. On the vertical axis of the robot, an absolute value of a torque command value of a motor sometimes approaches 0 as it normally operates, and if only the torque command value approaching 0 is used to detect an abnormality of a belt, there is a possibility of false detection. By applying the abnormality detection method of the present application to the vertical axis of the robot, it is possible to reliably detect an abnormality of a belt without worrying about false detection.

[0020] In the abnormality detection method of the present application, the vertical axis of the robot can also be a multi-stage structure in which each stage includes a motor, and in this case, it is possible to determine whether or not an abnormality has occurred for each stage based on a torque command value of the motor of each stage. That is, according to the abnormality detection method of the present application, it is possible to accurately detect an abnormality of a belt even in a robot having a vertical axis of a multi-stage structure.

[0021] In the abnormality detection method of the present application, the robot is, for example, a horizontal multi-joint robot. In a case where the robot is a horizontal multi-joint robot, it is possible to detect an abnormality of a belt on a vertical axis and to detect an abnormality of a belt on an axis other than the vertical axis.

[0022] According to the present application, it is possible to rapidly and reliably detect an abnormality typified by a belt skip on each axis of a robot with a small amount of arithmetic processing. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1The diagram shows a robot applying an anomaly detection method according to one embodiment of the present invention, (a) is a simplified side view, and (b) is a top view.

[0024] Figure 2 This is a diagram schematically showing the structure of the lifting mechanism.

[0025] Figure 3 This is a block diagram showing the structure used for motion control and anomaly detection.

[0026] Figure 4 It is a waveform diagram showing the change in speed and the change in the torque command value corresponding to the speed.

[0027] Figure 5 It is a magnified graph showing the changes in the torque command value. Detailed Implementation

[0028] The embodiments of the present invention will now be described with reference to the accompanying drawings. Figure 1 This diagram illustrates a robot employing an anomaly detection method according to one embodiment of the present invention. (a) is a simplified side view, and (b) is a top view. The robot 10 is configured as a horizontal, multi-jointed robot for transporting workpieces such as glass substrates. The robot 10 is electrically connected to a control device (robot controller) 40 via cables. The control device 40 receives motion commands for the robot 10 from the outside and drives and controls the robot 10 based on these motion commands. The control device 40 also functions as an anomaly detection device based on the present invention. Furthermore, for ease of understanding, in… Figure 1 (b) does not depict the control device 40 and the cable connected to it.

[0029] Robot 10 is configured to hold workpieces 60 ( Figure 1 (a) is a so-called two-handed robot with two hands 13A and 13B (not shown in the diagram). The control device 40 includes: a control unit 41 that inputs motion commands and detects the occurrence of abnormalities; and a drive circuit 42 that is provided for each motor of each axis of the robot 10, and includes a servo driver 45 (see reference) for driving the motor. Figure 2 The detailed structure of the control device 40 will be described later. In this embodiment, the robot 10 is used for transporting the workpiece 60; therefore, the motion commands are essentially commands to move the hands 13A and 13B to a specific position. The control unit 41 generates internal commands containing speed information for each axis of the robot 10 based on the motion commands, and the drive circuit 42 actually drives the motors of each axis of the robot 10 according to the internal commands for each axis.

[0030] The robot 10 is provided with a base 22 that is movable on a pair of rails 21 that are arranged in parallel in a straight line on the ground, a rotary table 23 that is provided on the base 22 and rotates in a horizontal plane about a rotary shaft 31 by a motor 35TH built in the base 22, and a lifting mechanism 24 that is provided in an upright manner with respect to the rotary table 23. A cover 25 that covers the rails 21 is attached to the rails 21. A motor 35X for moving the base 22 in the horizontal direction along the rails 21 is provided on the base 22, and the motor 35X and the base 22 constitute and drive a horizontal moving mechanism that moves the robot 10 in the horizontal direction along the rails 21. In addition, the motor 35TH and the rotary table 23 constitute a rotating mechanism that rotates the lifting mechanism 24 about the vertical rotary shaft 31 with respect to the base 22, and the rotating mechanism is driven by the motor 35TH.

[0031] The lifting mechanism 24 is provided with a fixed portion 24A attached to the rotary table 23 and a moving portion 24B that is lifted in the vertical direction with respect to the fixed portion 24A by a motor. Figure 2 is a view showing the structure of the lifting mechanism 24. The lifting mechanism can use only one motor, but in order to move a robot having a large mass at a high speed and with a large lifting amount, it is effective to use a plurality of motors to make the moving mechanism 24 a multi-stage structure. In the present embodiment, a two-stage structure is adopted, and a first-stage Z-axis motor 35ZA is provided on the fixed portion 24A, and a second-stage Z-axis motor 35ZB is provided on the moving portion 24B. The Z-axis motor 35ZA attached to the housing of the fixed portion 24A rotates a ball screw 54A via a belt 52A. A slide 55 that is lifted in accordance with the rotation of the ball screw 54A is attached to the ball screw 54A. A housing of the moving portion 24B is attached to the slide 55, and a second-stage Z-axis motor 35ZB inside the moving portion 24B rotates a ball screw 54B via a belt 52B. An arm support portion 26 that is a slide that is lifted in accordance with the rotation of the ball screw 54B is attached to the ball screw 54B. Of course, the lifting mechanism 24 can also adopt a three-stage or more structure. In the multi-stage lifting mechanism 24, a motor, a ball screw, a belt provided between the motor and the ball screw, and a slide that is lifted in accordance with the rotation of the ball screw are provided for each stage. The belts 52A and 52B provided on the lifting mechanism 24 are toothed belts.

[0032] The arm support portion 26 is a member that holds a horizontal multi-joint mechanism, like Figure 1The arm support section 26 is provided in a manner extending in the horizontal direction as shown. Two sets of horizontal multi-joint mechanisms are installed in the up-and-down direction on the front end of the arm support section 26. The lifting mechanism 24 is driven by the motors 35ZA, 35ZB to lift the arm support section 26 relative to the base 22. The upper horizontal multi-joint mechanism has a first arm 11A installed to the arm support section 26 and rotatable in the horizontal plane about a common shaft 32, and a second arm 12A installed to the front end of the first arm 11A and rotatable in the horizontal plane about a shaft 33A, with a hand 13A installed to the front end of the second arm 12A. Similarly, the lower horizontal multi-joint mechanism has a first arm 11B installed to the arm support section 26 and rotatable in the horizontal plane about the common shaft 32, and a second arm 12B installed to the front end of the first arm 11B and rotatable in the horizontal plane about a shaft 33B, with a hand 13B installed to the front end of the second arm 12B.

[0033] The hands 13A, 13B are formed in a fork-like shape with a plurality of rod-like members arranged in parallel, so as to be able to hold a plate-like workpiece 60 in a horizontal state and convey it by holding it from below. The hands 13A, 13B advance or retreat relative to the workpiece 60 when taking out the workpiece 60 housed in a cassette or a load lock chamber of a processing device, or the like, and holding it on the hands 13A, 13B, or housing the held workpiece 60 in a cassette, or the like. The direction of advance or retreat of the hands 13A, 13B coincides with the extending direction of the rod-like members. The width of the hands 13A, 13B in the left-and-right direction, that is, the direction orthogonal to the front-and-rear direction, is shorter than the width of the workpiece 60 to be conveyed in the left-and-right direction.

[0034] In the robot 10, the horizontal multi-joint mechanism is configured so that the hands 13A, 13B perform advancing and retreating movements by linear motion in a direction orthogonal to the direction in which the arm support portion 26 extends, through the link mechanisms assembled to the first arms 11A, 11B and the second arms 12A, 12B. That is, the hands 13A, 13B perform advancing and retreating in the same direction. The movement of the tips of the hands 13A, 13B away from the center axis 32 is advancing movement, and the movement in the opposite direction to the advancing movement is retreating movement. The first arms 11A, 11B and the second arms 12A, 12B perform bending movement as a whole, but in order to keep the orientations of the hands 13A, 13B constant in the horizontal plane, the hands 13A, 13B are respectively installed in a manner capable of rotating in the horizontal plane about the wrist axes 34A, 34B at the tips of the second arms 12A, 12B. In the upper horizontal multi-joint mechanism, the first arm 11A and the second arm 12A are moved by driving the link mechanisms by the motor 35RU provided on the arm support portion 26, and the hand 13A is moved in a direction orthogonal to the direction in which the arm support portion 26 extends while keeping its orientation. Similarly, in the lower horizontal multi-joint mechanism, the first arm 11B and the second arm 12B are moved by driving the link mechanisms by the motor 35RD provided on the arm support portion 26, and the hand 13B is moved in a direction orthogonal to the direction in which the arm support portion 26 extends while keeping its orientation. In the robot 10, the hand 13A and the hand 13B can be independently advanced and retreated. The movement of the hands 13A, 13B by the bending movement of the first arms 11A, 11B and the second arms 12A, 12B to advance or retreat is referred to as the extension and contraction of the arms.

[0035] As a result, Figure 1The actions of the robot 10 shown can be divided into: movement in the horizontal direction along the rail 21 (action of the X axis or traveling axis); rotation relative to the base with respect to the rotation axis 31 that is an axis in the direction of the vertical (action of the θ axis or rotation axis); forward and backward movement of the hands 13A, 13B in the horizontal direction, i.e., extension and retraction movement of the arms (action of the R axis); and raising and lowering of the arm support portion 26 in the vertical direction by the raising and lowering mechanism 24 (action of the vertical axis or Z axis). By providing two horizontal multi-joint mechanisms corresponding to the two hands 13A, 13B, in this robot 10, the R axis is divided into an RU axis corresponding to the upper hand 13A and an RD axis corresponding to the lower hand 13B. The RU axis and the RD axis are independent of each other. The X axis, the θ axis, the RU axis, and the RD axis are driven by the motors 35X, 35TH, 35RU, and 35RD corresponding to the respective axes via pulleys or belts. The X axis, the θ axis, the RU axis, and the RD axis are axes that move the robot 10 in the horizontal plane, and thus are horizontal plane movement axes. The Z axis that is the vertical axis is driven by the 2-stage motors 35ZA, 35ZB via the belts 52A, 52B. The robot 10 performs an action that moves only one of these axes and an action that moves two or more axes simultaneously by drive control based on internal commands from the control device 40 corresponding to the action commands. When the Z axis is driven, the 2-stage motors 35ZA, 35ZB are driven substantially simultaneously. As described above, the belts 52A, 52B that are the vertical axes are toothed belts, but the belts of the X axis, the θ axis, the RU axis, and the RD axis are also toothed belts.

[0036] Figure 3 A block diagram of the control system of the robot 10 is shown in order to explain the action control and abnormality detection of the robot 10 in this embodiment. As described above, in the robot 10, as the motors of the respective axes, there are provided: the 3-stage motors 35ZA, 35ZB that drive the raising and lowering mechanism 24 that is the vertical axis; the motors 35RU, 35RD that drive the extension and retraction of the arms corresponding to the upper and lower hands 13A, 13B, respectively; the motor 35X that drives the horizontal movement mechanism; and the motor 35TH that drives the rotation mechanism. These motors are all motors with encoders, and in the drive circuit 42 in the control device 40, servo control is performed by the servo driver 45 provided for each motor. The servo driver 45 of each axis provides an internal command for each axis from the control section 41 in the control device 40, and drives the corresponding motor in accordance with the internal command. In addition, a signal showing the torque command value for the corresponding motor is output from the servo driver 45 of each axis.

[0037] An action instruction for causing the robot 10 to perform a desired action is input to the control section 41 of the control device 40. The action instruction is generated, for example, as a result of an instruction to the robot, and contains, as an example, a start point and an end point of movement of the hand 13A. An orbit calculation section 43 is provided in the control section 41, which analyzes the input action instruction to generate an orbit of the robot, and calculates a motion required for each axis from the orbit to generate an internal instruction for each axis. The internal instruction output from the orbit calculation section 43 contains at least one of a position instruction and a speed instruction for a motor of each axis.

[0038] In order to detect an abnormality of each axis of the robot 10, particularly a skip tooth of a belt in a transmission mechanism of each axis or the like, an abnormality detection section 44 is further provided in the control section 41. The instruction output information of what internal instruction is currently output to each servo driver 45 of each axis is input from the orbit calculation section 43 to the abnormality detection section 44, and a signal showing a torque instruction value from each servo driver 45 is also output. Instead of the instruction output information, the internal instruction of each servo driver 45 can be directly supplied to the abnormality detection section 44. The processing of abnormality detection by the abnormality detection section 44 will be described below.

[0039] In a case where a motor drives an axis of a robot via a belt, when the belt slips, particularly when a skip tooth performs tooth slip, at least a part of the driving force from the motor is not transmitted to the axis, the load of the motor decreases to become an idling state, and thus the torque instruction value of the motor approaches 0. When the slip is recovered, that is, when the teeth of the belt are engaged again, the load applied to the belt temporarily sharply changes, and thus the torque instruction value jumps. After the slip is recovered, the torque instruction value converges to a value at a normal time while vibrating. Therefore, the abnormality detection section 44 applies an abnormality detection method based on the present application, takes a point in time when the torque instruction value of the motor of a certain axis of the robot approaches 0, that is, when the absolute value of the torque instruction value exceeds a first threshold value after becoming equal to or smaller than the first threshold value as a reference point Q, and in a case where the absolute value of the torque instruction value exceeds a second threshold value within a prescribed detection application time from the reference point Q, determines that an abnormality has occurred in the axis. The abnormality detection method described here is a method of detecting a skip tooth of a belt, which is considered to be a precursor phenomenon at the time of a belt breakage or the like, and thus can also be used for preventive maintenance of the belt.

[0040] The abnormality detection section 44 applies the abnormality detection method based on the present application to at least the vertical axes among the axes of the robot 10 to detect the occurrence of an abnormality in the tape. In the case of detecting an abnormality such as a skip in the tape with respect to the ZA axis and the ZB axis that are the vertical axes, the above-mentioned first threshold value is particularly referred to as a torque command value range for drop detection. The second threshold value is also referred to as a torque command value threshold value for skip detection. In the case where the abnormality detection method based on the present application is applied to the vertical axes of the robot, since the jump in the torque command value at the time of recovery from slip is a jump in the upward direction of the torque command value, in the case where the torque command value that causes the motor to rotate in the upward direction is set to a positive value, the absolute value of the torque command value can not be used in the comparison with the second threshold value, and the torque command value itself can be used. In the case where the torque command value that causes the motor to rotate in the upward direction is set to a negative value, the second threshold value can be set to a negative value, and the determination can be made by the torque command value being smaller than the second threshold value. In the abnormality detection method based on the present application, not only the case where the torque command value approaches 0 is detected, but also the jump in the torque command value after the torque command value approaches 0 is detected, and thus, particularly with respect to the vertical axes, false detection of an abnormality caused by the detection of only the torque command value approaching 0 can be prevented. As described later, the values of the first threshold value and the second threshold value, and the length of the detection application time are determined in advance based on the structure of the robot 10 and the conditions of the operation.

[0041] The abnormality detection section 44 can also perform detection of an abnormality with respect to the X axis, the θ axis, the RU axis, and the RD axis that are the axes of movement in the horizontal plane. In the case of the axes of movement in the horizontal plane, although an internal command to move the axis is output from the track calculation section 43, if the torque command value with respect to the motor of the axis is substantially 0, it can be determined that an abnormality such as a skip in the tape has occurred. Thus, when the abnormality detection section 44 detects that the absolute value of the torque command value in the servo driver 45 with respect to the motor of the axis of movement in the horizontal plane is equal to or smaller than a threshold value while an internal command to move the axis of movement in the horizontal plane is output from the track calculation section 43, it is determined that an abnormality has occurred with respect to the axis of movement in the horizontal plane. Alternatively, with respect to the axes of movement in the horizontal plane, the abnormality detection section 44 can apply the abnormality detection method based on the present application to detect the occurrence of an abnormality in the tape. When it is determined that an abnormality exists with respect to the vertical axes, or when it is determined that an abnormality exists with respect to the axes of movement in the horizontal plane, the abnormality detection section 44 outputs a signal to the outside that indicates that an abnormality has been detected.

[0042] Hereinafter, the abnormality detection on the vertical axes of the robot 10 in the present embodiment will be described in more detail. Figure 4is a waveform chart showing the change in speed on the ZA axis and the ZB axis when the lifting mechanism 24 located at a certain position is raised, temporarily stopped, and then lowered to return to the original position, and the change in torque command value corresponding to the change in speed. (a) shows the change in speed, and (b) shows the change in torque command value. The solid line shows the change on the ZA axis, and the broken line shows the change on the ZB axis. In the graph of the torque command value, the upward direction and the downward direction of the vertical axis show whether the torque command value is such that the motor rotates in the upward direction or in the downward direction. In the case of upward movement, the motor first accelerates and then becomes a constant speed (constant speed interval), and then decelerates, and the robot stops. Also, in the case of downward movement, there is also an acceleration period (downward acceleration period) first, then a constant speed interval, and finally a deceleration period (downward deceleration period).

[0043] In the graph of the torque command value, the ZA axis and the ZB axis both become torque command values in the upward direction in substantially the entire region, because the vertical axis is the axis that supports the weight of the robot 10 and the weight of the workpiece 60, and even if there is no movement in the vertical direction (for example, during "stop" in the figure), the motor needs to generate a holding torque. Even if the robot stops, the torque command value becomes non-zero, which is a point of difference from the horizontal movement axis. However, as shown by the region P in the figure, during the downward acceleration period, the torque command value of the ZB axis approaches zero. If an abnormality such as a skip tooth of the belt occurs on the vertical axis as well, the torque command value approaches zero, so if this situation is detected, it is possible to determine the presence or absence of an abnormality, but if the torque command value also approaches zero when the robot is operating normally, it is not possible to determine an abnormality based on whether the torque command value approaches zero. Therefore, in the present embodiment, as described above, by detecting whether the torque command value skips after the torque command value approaches zero, it is possible to prevent false detection, and to rapidly and reliably detect an abnormality in the belt of the vertical axis with a small amount of computation.

[0044] Next, the use of the first threshold value and the second threshold value will be described. Figure 5 The detection of an abnormality and the setting of the first threshold value, the second threshold value, and the detection application time in the present embodiment will be described. Figure 5is a graph showing a change in the torque command value in a case where a skip of the toothed belt occurs on the vertical axis. Since it is the vertical axis, a constant torque command value in the rising direction is generated in order to generate the holding torque. Here, it is assumed that a skip of the toothed belt occurs. In the graph, the skip occurs in the vicinity of the time axis 100 ms. In the skip, tooth slip first occurs as a phenomenon, and thus the torque command value approaches 0 as shown in a tooth slip section S. A first threshold value (torque command value range for drop detection) is set to be able to detect a case where the torque command value approaches 0 due to the tooth slip. In the example shown here, a positive value smaller than the torque command value corresponding to the holding torque is set to a, and a is set to the first threshold value. Thus, when the torque command value becomes a value between +a and -a, that is, when the absolute value of the torque command value becomes the first threshold value a or less, it is determined that the torque command value approaches 0.

[0045] With the progress of the skip of the belt, then, engagement of the teeth of the belt is again made. At this time, a jump of the torque command value in the rising direction is generated. Thus, in order to detect whether or not the jump is made in the torque command value, when the absolute value of the torque command value exceeds the first threshold value a after the absolute value of the torque command value becomes the first threshold value a or less, it is taken as a reference point Q, and it is determined whether or not the absolute value of the torque command value exceeds a second threshold value (torque command value threshold value for skip detection) b within a prescribed detection application period T from the reference point Q. In the example shown here, as shown by a point R, the absolute value of the torque command value exceeds the second threshold value b, and thus it is determined that the skip occurs. The torque command value which jumps due to the engagement of the teeth again converges to a value corresponding to the holding torque while vibrating thereafter. Figure 5 The example shown here, as shown by a point R, the absolute value of the torque command value exceeds the second threshold value b, and thus it is determined that the skip occurs. The torque command value which jumps due to the engagement of the teeth again converges to a value corresponding to the holding torque while vibrating thereafter. Figure 5 The case where the rise and fall on the vertical axis are not made and only the holding torque is applied to the vertical axis is shown, but actually when the rise and fall on the vertical axis is made, it is also necessary to detect the skip. Thus, the detection application period T is determined based on a timing at which the jump of the torque command value caused by the skip is considered to occur, considering conditions such as the shape and interval of the teeth in the belt, the speed of the belt accompanying the rise and fall of the vertical axis. In addition, the second threshold value is also determined to be able to distinguish the torque command value or the change thereof which can be generated at the time of normal operation, and the jump of the torque command value caused by the skip.

[0046] Figure 5 The detection of the abnormality of the belt on the vertical axis of the robot 10 is explained, but as for the horizontal plane moving axis of the robot 10, if the belt is abnormal when the axis is driven, the torque command value in the motor of the axis is considered to change as shown in Figure 5 the same as shown, and thus as in the case of the vertical axis, it is possible to detect the occurrence of the abnormality in the belt. When the horizontal plane moving axis is the object, according to the forward and reverse rotation directions of the motor of the axis, the torque command value is considered to change as shown in Figure 5The upward direction and the downward direction in the belt are replaced by the positive direction and the reverse direction. If the teeth jump when the shaft is driven by the torque command value in the positive direction, the direction of the jump of the torque command value after the teeth slip is the positive direction, and conversely, if the teeth jump when the shaft is driven by the torque command value in the reverse direction, the direction of the jump of the torque command value after the teeth slip is the reverse direction.

[0047] In the above, the detection of an anomaly and the setting of the first threshold value, the second threshold value, and the detection application time have been described as a case where the belt is a toothed belt, but even in a case where the belt is not a toothed belt, it is considered that slippage of the belt and recovery from the slippage will be caused as a precursor to breakage and shedding, and thus by determining the first threshold value, the second threshold value, and the detection application time in the same manner as described above, it is possible to detect an anomaly such as breakage and shedding of the belt.

[0048] According to the present embodiment described above, with respect to the vertical axis, it is possible to quickly find the occurrence of an anomaly with a small amount of computation without false detection. With respect to the horizontal in-plane moving axis, it is also possible to quickly find the occurrence of an anomaly with a small amount of computation.

[0049] Symbol Explanation

[0050] 10 … robot; 11A, 11B … first arm; 12A, 12B … second arm; 13A, 13B … hand; 21 … rail; 22 … base; 23 … rotary table; 24 … lifting mechanism; 24A … fixed portion; 24B … moving portion; 25 … cover; 26 … arm support portion; 31 … rotary shaft; 32 … common shaft; 33A, 33B … shaft; 34A, 34B … wrist shaft; 35RD, 35RU, 35TH, 35X, 35ZA, 35ZB … motor; 40 … control device; 41 … control portion; 42 … drive circuit; 43 … rail calculation portion; 44 … anomaly detection portion; 45 … servo driver; 52A, 52B … belt; 54A, 54B … ball screw; 55 … slide; 60 … workpiece.

Claims

1. An abnormality detection device that detects an abnormality in a robot in which a motor of each axis is driven and controlled by a servo driver, characterized by comprising an abnormality detection section that takes, as a detection target axis, an axis in the robot that is driven by the motor via a cogged belt, takes, as a reference point, a time when an absolute value of a torque command value in the servo driver corresponding to the motor of the detection target axis exceeds a first threshold value after the absolute value of the torque command value becomes the first threshold value or less, and determines that an abnormality has occurred in the detection target axis in a case where the absolute value of the torque command value exceeds a second threshold value within a prescribed detection application time from the reference point, the first threshold value is a positive value that is smaller than a torque command value corresponding to a holding torque generated by the motor of the detection target axis, the detection application time is determined based on a timing at which a jump of the torque command value caused by cog skipping is considered to have occurred, and the second threshold value is a cog skipping detection torque command value threshold value.

2. The abnormality detection device according to claim 1, characterized in that the robot has a vertical axis that moves in a vertical direction, and the detection target axis is the vertical axis.

3. The abnormality detection device according to claim 2, characterized in that in the robot, the vertical axis is a multi-stage structure in which each stage includes the motor, and the abnormality detection section determines, for each stage, whether or not the abnormality has occurred, based on the torque command value of the motor of the stage.

4. The abnormality detection device according to any one of claims 1 to 3, characterized in that the robot is a horizontal multi-joint robot.

5. An abnormality detection method that detects an abnormality in a robot in which a motor of each axis is driven and controlled by a servo driver, characterized by taking, as a detection target axis, an axis in the robot that is driven by the motor via a cogged belt, taking, as a reference point, a time when an absolute value of a torque command value in the servo driver corresponding to the motor of the detection target axis exceeds a first threshold value after the absolute value of the torque command value becomes the first threshold value or less, and determining that an abnormality has occurred in the detection target axis in a case where the absolute value of the torque command value exceeds a second threshold value within a prescribed detection application time from the reference point, the first threshold value is a positive value that is smaller than a torque command value corresponding to a holding torque generated by the motor of the detection target axis, the detection application time is determined based on a timing at which a jump of the torque command value caused by cog skipping is considered to have occurred, and the second threshold value is a cog skipping detection torque command value threshold value.

6. The abnormality detection method according to claim 5, characterized in that the robot has a vertical axis that moves in a vertical direction, and the detection target axis is the vertical axis.

7. The abnormality detection method according to claim 6, characterized in that in the robot, the vertical axis is a multi-stage structure in which each stage includes the motor, and the abnormality detection section determines, for each stage, whether or not the abnormality has occurred, based on the torque command value of the motor of the stage.

8. The abnormality detection method according to any one of claims 5 to 7, characterized in that the robot is a horizontal multi-joint robot. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​

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