JP7633075B2 - Anomaly detection device and anomaly detection method - Google Patents

Description

The present invention relates to an abnormality detection device and an abnormality detection method for detecting abnormalities such as breakage of a drive belt in an industrial robot.

Industrial robots (hereafter referred to as robots) used for transporting workpieces, etc., are provided with motors for driving each axis, as well as transmission mechanisms for transmitting the driving force of the motors to the arms of each axis. The transmission mechanisms are composed of, for example, reducers, pulleys, belts, etc. If an abnormality occurs in the transmission mechanism, such as a broken belt, it is necessary to immediately stop the robot from driving and activate the brakes to prevent the arms of each axis from moving. For this reason, there is a demand for the ability to quickly and reliably detect abnormalities in the transmission mechanisms of each axis of the robot.

In a robot, a detector such as an encoder attached to the motor detects the motor's position and speed and feeds back the information. A torque command for the motor is generated based on the input position command and the feedback value, and the motor is controlled. For example, if a belt breaks on one of the robot's axes, the motor will essentially be in an idling state, and this will also have an effect on 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 saturation is longer than a predetermined time, it is determined that the belt has broken.

Patent Document 2 discloses a method for detecting faults in transmission mechanisms in general, which calculates the input power and the load power based on the command angle for each drive shaft of the robot, the actual angle as the motor's position data, and the drive current for the motor, and determines whether or not there is 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, which determines whether or not there is 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 abnormalities in the reducer, and cannot be used to detect belt breakage.

Japanese Patent Application Publication No. 5-346812 Japanese Patent Application Publication No. 11-129186 JP 2006-102889 A

In robots used to transport workpieces, the driving force from the motor of each axis is often transmitted to the arm of that axis via a pulley and a belt, and it is required to be able to detect the breakage of the belt quickly and reliably. Focusing on the axis that moves the robot vertically, 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 in order to resist the load caused by this own weight, the motor must constantly generate a holding torque to support the robot. If the belt of the vertical axis breaks, the robot's own weight is no longer transmitted to the motor, and the holding torque of the vertical axis motor changes to almost zero. 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 zero. The method described in Patent Document 1 cannot distinguish whether the torque command value is near 0 because the holding torque is near 0 due to a broken belt, or because the robot is descending normally, and as a result, it may not be possible to properly detect a broken belt on the vertical axis. The method described in Patent Document 2 uses a model for calculations, which has the problem of a large amount of calculation required to detect an abnormality on each axis.

The 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 a broken belt on each axis of a robot, with a small amount of calculations.

The abnormality detection device of the present invention is an abnormality detection device for detecting an abnormality in a robot having a vertical axis that moves in a vertical direction, and in which the motor of each axis is driven and controlled by a servo driver, and is any one of the first to fourth aspects shown below. These abnormality detection devices include an abnormality detection unit that determines that an abnormality has occurred in the vertical axis when it detects that the absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except for an abnormality detection stop period. The abnormality detection stop period is set during a downward acceleration period in which the vertical axis is accelerated in the downward direction by an operation command to the robot.

The motor of the vertical axis of the robot always generates a holding torque due to its characteristic of supporting a load, but when an abnormality occurs, such as when the belt mechanically connected to the motor breaks, the holding torque becomes almost zero, and the torque command value for the motor also becomes almost zero accordingly. Therefore, it is possible to determine that an abnormality has occurred in the vertical axis when the absolute value of the torque command value is equal to or less than the threshold value. However, even when the vertical axis is normally accelerating downward, the torque command value may approach zero, and there is a risk of erroneous detection if the absolute value of the torque command value is simply compared with the threshold value. Therefore, in the abnormality detection device of the present invention, an abnormality detection stop period is set within the downward acceleration period of the robot, and abnormality detection is not performed during the abnormality detection stop period. In this way, the abnormality detection device of the present invention can prevent erroneous detection.

In the first aspect of the abnormality detection device, when the robot has a vertical axis equipped with motors arranged in multiple stages, the abnormality detection unit determines that an abnormality has occurred for the lowest stage motor when it detects that the absolute value of the torque command value is equal to or less than a threshold value even during an abnormality detection stop period. The lowest stage motor of a multi-stage vertical axis has a large load, so the torque command value may not approach 0 even during a normal descent acceleration period. In such a case, by constantly monitoring the torque command value for the lowest stage motor, it becomes possible to more quickly detect a break in the belt, etc.

In the abnormality detection device of the second aspect , the abnormality detection stop period starts after a predetermined delay time has elapsed after the start of the downward acceleration period . Since the torque command value is far from 0 if the torque command value is in a normal state immediately after the start of the downward acceleration period, by delaying the start of the abnormality detection stop period, it is possible to quickly detect an abnormality immediately after the start of the downward acceleration period.

In the abnormality detection device of the third aspect , the robot is a horizontal articulated robot. When the robot is a horizontal articulated robot, the abnormality detection unit determines that an abnormality has occurred in an axis when it detects that the absolute value of a torque command value in a servo driver for a motor of a shaft other than a vertical axis of the horizontal articulated robot is equal to or less than a threshold value during execution of control to move that axis . In a horizontal articulated robot, an axis other than the vertical axis is an axis that moves the robot horizontally or within a horizontal plane. If, for example, a belt breaks in such an axis, the torque command value of that axis approaches 0 even though an operation command to move that axis is input, and it is therefore possible to detect the occurrence of an abnormality in that axis by detecting that the absolute value of the torque command value is equal to or less than a threshold value.

In the fourth aspect of the abnormality detection device, the abnormality detection unit detects that the absolute value of the torque command value is equal to or less than the threshold value when the absolute value of the torque command value is equal to or less than the threshold value for a predetermined detection duration . By configuring in this manner, it is possible to eliminate the influence of noise and the influence of variations when setting the abnormality detection stop period.

The abnormality detection method of the present invention is an abnormality detection method for detecting an abnormality in a robot having a vertical axis for vertical movement, the motor of each axis being driven and controlled by a servo driver, and is any one of the following first to fourth aspects. In these abnormality detection methods, an abnormality detection stop period is set during a downward acceleration period in which the vertical axis is accelerated in a downward direction by an operation command for the robot, and it is determined that an abnormality has occurred in the vertical axis when it is detected that the absolute value of the torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except for the abnormality detection stop period.

According to the anomaly detection method of the present invention, when detecting an anomaly in the vertical axis because the torque command value for the vertical axis motor approaches 0, an anomaly detection stop period is set within the descent acceleration period, and erroneous detection can be prevented by not detecting an anomaly during the anomaly detection stop period. Furthermore, when a control device (robot controller) that drives and controls the robot is provided, this anomaly detection method can be realized by simple calculation 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.

In the first aspect of the abnormality detection method, when a robot has a vertical axis with motors arranged in multiple stages, it is determined that an abnormality has occurred in the lowest stage motor when it is detected that the absolute value of the torque command value is equal to or less than a threshold value even during an abnormality detection stop period. Since the load of the lowest stage motor of a multi-stage vertical axis is large, the torque command value may not approach 0 even during a normal descent acceleration period. In such a case, by constantly monitoring the torque command value of the lowest stage motor, it becomes possible to more quickly detect a break in the belt, etc.

In the abnormality detection method of the second aspect , the abnormality detection stop period is started after a predetermined delay time has elapsed after the start of the downward acceleration period . Since the torque command value is far from 0 if the torque command value is in a normal state immediately after the start of the downward acceleration period, by delaying the start of the abnormality detection stop period, it is possible to quickly detect an abnormality immediately after the start of the downward acceleration period.

In the third aspect of the abnormality detection method, when a robot has an in-horizontal axis for moving the robot in a horizontal plane, if it is detected that the absolute value of the torque command value in the servo driver for the motor of the in-horizontal axis is equal to or less than a threshold value during execution of control to move the in-horizontal axis, it is determined that an abnormality has occurred in the in-horizontal axis. If, for example, a belt breaks in the in-horizontal axis, the torque command value of the in-horizontal axis approaches 0 even though a motion command to move the in-horizontal axis is input, and by detecting that the absolute value of the torque command value is equal to or less than the threshold value, it is possible to detect the occurrence of an abnormality in the in-horizontal axis.

In the fourth aspect of the anomaly detection method, the anomaly detection unit detects that the absolute value of the torque command value is equal to or less than the threshold value when the absolute value of the torque command value is equal to or less than the threshold value for a predetermined detection duration . By configuring in this manner, it is possible to eliminate the influence of noise and the influence of variations when setting the anomaly detection stop period.

The present invention makes it possible to quickly and reliably detect abnormalities, such as a broken belt on each axis of a robot, with a small amount of calculations.

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 FIG. 4A and 4B are diagrams showing the details of the configuration of a lifting mechanism. FIG. 2 is a block diagram showing a configuration for operational control and abnormality detection. FIG. 4 is a waveform diagram showing a change in speed and a change in a torque command value corresponding to the speed. FIG. 4 is an enlarged view showing a change in a torque command value.

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, and is intended to transport workpieces such as glass substrates. The robot 10 is electrically connected to a control device (robot controller) 40 via a cable, which receives operation commands for the robot 10 from outside and drives and controls the robot 10 based on the operation commands. The control device 40 also functions as an anomaly detection device based on the present invention. Note that, to make the explanation easier to understand, the control device 40 and the cable connected thereto are not shown in FIG. 1(b).

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)). FIG. 1(a) shows the state in which the horizontal articulated mechanism of the robot 10 is raised. 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 includes a servo driver 45 (see FIG. 2) and the like provided for each motor of each axis provided in the robot 10 to drive 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 to move the hands 13A and 13B to a certain position. The control unit 41 generates an internal command including the 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.

The robot 10 is equipped with a base 22 that can move on a pair of parallel rails 21 that are arranged in a straight line on the floor surface, a rotating table 23 that is arranged on the base 22 and rotates in a horizontal plane around a rotating shaft 31 by a motor 35TH built into the base 22, and an elevating mechanism 24 that is arranged to stand upright relative to the rotating table 23. A cover 25 is attached to the rail 21. A motor 35X is provided on the base 22 for moving the base 22 horizontally along the rail 21, 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 also constitute a rotation mechanism that rotates the elevating mechanism 24 relative to the base 22 around the vertical rotating shaft 31, and this rotation mechanism is driven by the motor 35TH.

The lifting mechanism 24 includes a fixed part 24A attached to the rotating table 23 and a moving part 24B that moves vertically relative to the fixed part 24A by a motor. FIG. 2 is a diagram showing the internal structure of the lifting mechanism 24. Although one motor may be used to lift the moving part 24B relative to the fixed part 24A, it is effective to use multiple motors to form a multi-stage configuration in order to move a robot with a large mass at high speed and with a large lift amount. In this embodiment, a three-stage configuration is used. The Z-axis motor 35ZA at the lowest stage is provided on the housing of the fixed part 24A, and this Z-axis motor 35ZA rotates and drives a ball screw 54A fixed to a pulley 53C via a belt 52A and a pulley 53C that are attached to a pulley 51A. A lifting table 55A that moves up and down with the rotation of the ball screw 54A is attached to the ball screw 54A. The lifting platform 55A is provided with a second-stage Z-axis motor 35ZB. The second-stage Z-axis motor 35ZB also rotates and drives a ball screw 54B via a pulley 51B, a belt 52B, and a pulley 53B, and a lifting platform 55B that rises and falls along with the ball screw 54B is attached to the ball screw 54B. The third-stage Z-axis motor 35ZC is provided to this lifting platform 55B. The third-stage Z-axis motor 35ZC also rotates and drives a ball screw 54C via a pulley 51C, a belt 52C, and a pulley 53C, and a lifting platform 55C that rises and falls along with the ball screw 54C is attached to the ball screw 54C. The moving part 24B of the lifting mechanism 24 is attached to the third-stage lifting platform 55C.

The moving section 24B is provided with an arm support section 26 that holds the horizontal multi-joint mechanism extending horizontally, and two sets of horizontal multi-joint mechanisms are attached to the tip of the arm support section 26 in a vertical arrangement. The lifting mechanism 24 is driven by motors 35ZA, 35ZB, and 35ZC to raise and lower the arm support section 26 relative to the base 22. The upper horizontal multi-joint mechanism includes a first arm 11A attached to the arm support section 26 and rotatable in a horizontal plane around a common axis 32, and a second arm 12A attached to the tip of the first arm 11A and rotatable in a horizontal plane around an axis 33A, and a hand 13A is attached to the tip of the second arm 12A. Similarly, the lower horizontal articulated mechanism includes a first arm 11B attached to the arm support 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, with a hand 13B attached to the tip of the second arm 12B.

The hands 13A and 13B are fork-shaped with multiple rod-shaped members arranged in parallel so that they can transport the plate-shaped workpiece 60 while keeping it horizontal by holding it from below. The hands 13A and 13B move forward or backward relative 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-back direction, is shorter than the left-right width of the workpiece 60 to be transported.

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

In the end, the movements of the industrial 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 vertical axis 31 relative to the base (this is the θ-axis or rotation axis movement), horizontal forward and backward movements of the hands 13A and 13B, i.e., the extension and contraction of the arms (this is the R-axis movement), and vertical lifting and lowering of the arm support 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, 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 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 movement axes. The Z-axis, which is a vertical axis, is driven by three-stage motors 35ZA, 35ZB, and 35ZC via pulleys 51A, 51B, 51C, 53A, 53B, and 53C and belts 52A, 52B, and 52C. The robot 10 executes an operation to move only one of these axes or an operation to move two or more axes simultaneously, by drive control based on an internal command from the control device 40 in response to a motion command. When driving the Z-axis, the three-stage motors 35ZA, 35ZB, and 35ZC are basically driven simultaneously.

Figure 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, 35ZB, and 35ZC for driving the lifting mechanism 24, which is the vertical axis, motors 35RU and 35RD for driving the extension and contraction of the arms corresponding to the upper and lower hands 13A and 13B, motor 35X for driving the horizontal movement mechanism, and 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 servo drivers 45 provided for each motor in the drive circuit 42 in the control device 40. The servo drivers 45 for each axis are supplied with internal commands for each axis from the control unit 41 in the control device 40, and drive the corresponding motors in response to the internal commands. In addition, the servo drivers 45 for each axis also output signals indicating torque command values for the corresponding motors.

Operation commands for causing the robot 10 to perform a desired operation are input to the control unit 41 of the control device 40. The operation commands are generated, for example, as a result of teaching the robot, and include, as an example, the start and end points of the movement of the hand 13A. The control unit 41 is provided with a trajectory calculation unit 43 that analyzes the input operation commands to generate a trajectory for 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.

In order to detect abnormalities in each axis of the robot 10, particularly abnormalities such as a broken belt 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 from the trajectory calculation unit 43 indicating what internal command is currently being output to the servo driver 45 of each axis, and also outputs a signal indicating the 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 given to the abnormality detection unit 44. Then, when the abnormality detection unit 44 detects that the absolute value of the torque command value in the servo driver 45 for the motors 35ZA, 35ZB, and 35ZC of the vertical axes ZA, ZB, and ZC is equal to or less than a threshold value except for the abnormality detection stop period, it determines that an abnormality has occurred in that axis. Here, the abnormality detection stop period is a period set in the downward acceleration period in which the vertical axis is accelerated in the downward direction by the operation command to the robot 10, and is, for example, a period that starts after a predetermined delay time has elapsed from the start of the downward acceleration period. As described below, the length of the delay time and the abnormality detection stop period are determined in advance based on the configuration and operating conditions of the robot 10. When the abnormality detection unit 44 learns that the descent acceleration period has started based on the command output information from the trajectory calculation unit 43, it recognizes the point at which the delay time has elapsed from that time as the start of the abnormality detection stop period, and does not perform abnormality detection based on the absolute value of the torque command value during the abnormality detection stop period. Once the abnormality detection stop period has elapsed, the abnormality detection unit 44 resumes abnormality detection based on the absolute value of the torque command value.

The abnormality detection unit 44 also detects abnormalities in the horizontal movement axes, the X-axis, the θ-axis, the RU-axis, and the RD-axis. In the case of an axis moving in a horizontal plane, if the torque command value for the motor of that axis is nearly 0 even though an internal command to move that axis is output from the trajectory calculation unit 43, it can be determined that an abnormality such as a broken 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 a certain axis moving in a horizontal plane is equal to or less than a threshold value when an internal command to move that axis moving in a 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 that axis moving in a horizontal plane.

When it is determined that there is an abnormality in the vertical axis or in the horizontal axis of movement, the abnormality detection unit 44 outputs a signal to the outside to notify that an abnormality has been detected. In order to avoid the effects of noise and the effects of variations when setting the abnormality detection stop period, it is preferable that the abnormality detection unit 44 detects that the absolute value of the torque command value of the corresponding axis is equal to or less than the threshold value when the absolute value of the torque command value of the corresponding axis is equal to or less than the threshold value for a predetermined detection duration.

The detection of an abnormality 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 axis, ZB axis, and ZC axis, 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, the dashed line shows the change in the ZB axis, and the dashed line shows the change in the ZC 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 graph of the speed, the speed waveform of the ZB axis and the speed waveform of the ZC axis overlap. In the upward phase, the robot first accelerates and then reaches a constant speed (constant speed section), and then decelerates and stops. And when it descends, there is first a period of acceleration (a descending acceleration period), followed by a constant speed section, and finally a period of deceleration (a descending deceleration period).

In the torque command value graph, the ZA, ZB, and ZC axes all have upward torque command values 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 differs from the horizontal movement axis in that the torque command value is not 0 even when the robot is stopped. However, as shown in area P in the figure, the torque command values of the ZB and ZC axes approach 0 during the downward acceleration period. If an abnormality such as a broken belt occurs on the vertical axis, the torque command value approaches 0, so the presence or absence of an abnormality can be determined by detecting this, but if the torque command value approaches 0 even when the robot is operating normally, it is not possible to determine that an abnormality exists based on whether the torque command value approaches 0. Therefore, in this embodiment, as described above, an abnormality detection stop period is set within the downward acceleration period, and during the abnormality detection stop period, even if the torque command value approaches 0, it is not determined that an abnormality exists, thereby preventing erroneous detection. This makes it possible to quickly and reliably detect abnormalities in the vertical axis with a small amount of calculation. For the ZA axis, which is at the bottom, the torque command value does not approach 0 even during the descent acceleration period. This is thought to be because the ZA axis has a larger load weight than the ZB and ZC axes. Therefore, for the ZA axis, if the torque command value approaches 0 even during the abnormality detection stop period, it can be determined that an abnormality has occurred.

Next, the detection of an abnormality and the setting of the abnormality detection stop period will be described with reference to FIG. 5. FIG. 5 is an enlarged view of region P in FIG. 4. In this embodiment, a positive constant a is used as a threshold, and when the torque command value is between +a (this is the upper threshold) and -a (this is the lower threshold), that is, when the absolute value of the torque command value is equal to or less than a, it is determined that the torque command value is approaching 0 and an abnormality has occurred. In practice, the detection duration is set taking into consideration the effects of noise and variations in the abnormality detection stop period, and an abnormality is determined to have occurred when the absolute value of the torque command value is equal to or less than the threshold for the detection duration. The length of the detection duration is, for example, sufficiently shorter than the length of the abnormality detection stop period.

The abnormality detection stop period can be determined by determining the period during which the absolute value of the torque command value is equal to or less than the threshold during the downward acceleration period when the robot 10 is in a normal state. In the example shown in FIG. 5, the period from elapsed time t0 to t3 is the downward acceleration period. Focusing on the torque command value of the ZC axis, this torque command value is equal to or less than the upper threshold value + a during the period from elapsed time t1 to t2. Therefore, the period from elapsed time t1 to t2 can be determined as the abnormality detection stop period. The period from elapsed time t0 to t1 is the delay time from the start of the downward acceleration period to the start of the abnormality detection stop period. Once the abnormality detection stop period and delay time are determined for the robot 10 according to its mechanism and operating conditions, the abnormality detection stop period and delay time can be used thereafter to quickly find abnormalities in the vertical axis without false detection.

In the anomaly detection method described above, the anomaly detection stop period is determined based on the start of the downward acceleration period. Therefore, if it is not known when the downward acceleration period starts, an anomaly cannot be detected accurately. The start of the downward acceleration period may be determined, for example, by monitoring the speed command on the vertical axis and determining when the speed command value changes, or it may be determined based on the change in the rotation speed of the motor by actually measuring the rotation speed.

According to the present embodiment described above, with regard to the vertical axis, it is possible to quickly detect the occurrence of an abnormality without false detection and with a small amount of calculation. With regard to the horizontal movement axis as well, it is possible to quickly detect the occurrence of an abnormality with a small amount of calculation.

The inventors constructed an experimental device consisting of a motor, an inertia ring attached to the motor's rotating shaft, a belt wound around the inertia ring, and a weight attached to the end of the belt, so as to mimic the vertical axis of a transport robot 10. They then conducted an experiment in which a servo driver was used to apply a holding torque to the motor and in that state the belt was instantly cut. As a result, within about 100 milliseconds, the absolute value of the torque command value fell below the threshold value, enabling the occurrence of an abnormality to be detected. It was demonstrated that the occurrence of an abnormality can be quickly determined by detecting that the torque command value for the vertical axis is approaching 0.

10...Robot; 11A, 11B...First arm; 12A, 12B...Second arm; 13A, 13B...Hand; 21...Rail; 22...Base; 23...Rotary base; 24...Lifting mechanism; 24A...Fixed part; 24B...Moving part; 25...Cover; 26...Arm support part; 31...Rotary axis; 32...Common axis; 33A, 33B...Axis; 34A, 34B...Wrist axis; 35RD, 35RU, 35TH, 35X, 35ZA, 35ZB, 35ZC...motor; 40...control device; 41...control unit; 42...drive circuit; 43...trajectory calculation unit; 44...abnormality detection unit; 45...servo driver; 51A, 51B, 51C, 53A, 53B, 53C...pulley; 52A, 52B, 52C...belt; 54A, 54B, 54C...ball screw; 55A, 55B, 55C...lifting platform; 60...work.

Claims (8)

1. An abnormality detection device for detecting an abnormality in a robot having a vertical axis for moving in a vertical direction, in which a motor for each axis is driven and controlled by a servo driver, and the vertical axis is provided with motors each provided in a plurality of stages,
an abnormality detection unit that determines that an abnormality has occurred in the vertical axis when it detects that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during an abnormality detection stop period;
the abnormality detection stop period is set during a downward acceleration period in which the vertical axis is accelerated in a downward direction by a motion command to the robot,
The abnormality detection device, wherein the abnormality detection unit determines that the abnormality has occurred for the motor in the lowest stage when it detects that the absolute value of the torque command value is equal to or less than the threshold value even during the abnormality detection stop period. An abnormality detection device for detecting an abnormality in a robot having a vertical axis for moving in a vertical direction, the motor of each axis being driven and controlled by a servo driver, comprising:
an abnormality detection unit that determines that an abnormality has occurred in the vertical axis when it detects that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during an abnormality detection stop period;
the abnormality detection stop period is set during a downward acceleration period in which the vertical axis is accelerated in a downward direction by a motion command to the robot,
The abnormality detection device, wherein the abnormality detection stop period starts after a predetermined delay time has elapsed after the start of the downward acceleration period. An abnormality detection device for detecting an abnormality in a horizontal articulated robot having a vertical axis for moving the robot in a vertical direction, the motors of which are driven and controlled by servo drivers, comprising:
an abnormality detection unit that determines that an abnormality has occurred in the vertical axis when it detects that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during an abnormality detection stop period;
the abnormality detection stop period is set during a downward acceleration period in which the vertical axis is accelerated in a downward direction by a motion command to the robot,
The abnormality detection device, wherein when the abnormality detection unit detects that the absolute value of the torque command value in the servo driver for the motor of an axis other than the vertical axis of the horizontal articulated robot is below the threshold value during execution of control to move the axis other than the vertical axis, it determines that an abnormality has occurred in the axis. An abnormality detection device for detecting an abnormality in a robot having a vertical axis for moving in a vertical direction, the motor of each axis being driven and controlled by a servo driver, comprising:
an abnormality detection unit that determines that an abnormality has occurred in the vertical axis when it detects that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during an abnormality detection stop period;
the abnormality detection stop period is set during a downward acceleration period in which the vertical axis is accelerated in a downward direction by a motion command to the robot,
The abnormality detection device, wherein the abnormality detection unit detects that the absolute value of the torque command value is equal to or less than the threshold value when the absolute value of the torque command value is equal to or less than the threshold value for a predetermined detection duration. 1. A method for detecting an abnormality in a robot having a vertical axis for moving in a vertical direction, in which a motor for each axis is driven and controlled by a servo driver, and the vertical axis is provided with motors provided in multiple stages , the method comprising the steps of:
setting an abnormality detection stop period during a downward acceleration period in which the vertical axis is accelerated in a downward direction by an operation command for the robot;
determining that an abnormality has occurred in the vertical axis when it is detected that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during the abnormality detection stop period;
With respect to the motor in the lowest stage, the abnormality detection method determines that the abnormality has occurred when it is detected that the absolute value of the torque command value is equal to or less than the threshold value even during the abnormality detection stop period. 1. A method for detecting an abnormality in a robot having a vertical axis for moving in a vertical direction, the motor of each axis being driven and controlled by a servo driver, comprising:
setting an abnormality detection stop period during a downward acceleration period in which the vertical axis is accelerated in a downward direction by an operation command for the robot;
determining that an abnormality has occurred in the vertical axis when it is detected that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during the abnormality detection stop period;
The abnormality detection method includes starting the abnormality detection stop period after a predetermined delay time has elapsed after the start of the downward acceleration period. 1. A method for detecting an abnormality in a robot having a vertical axis for moving in a vertical direction, the motor of each axis being driven and controlled by a servo driver, comprising:
an abnormality detection stop period is set during a downward acceleration period in which the vertical axis is accelerated in a downward direction by an operation command for the robot;
determining that an abnormality has occurred in the vertical axis when it is detected that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during the abnormality detection stop period;
The abnormality detection method determines that an abnormality has occurred in the horizontal axis of movement when the robot has an axis of movement in a horizontal plane that moves the robot in a horizontal plane and detects that an absolute value of a torque command value in the servo driver for the motor of the axis of movement in a horizontal plane is equal to or less than the threshold value during execution of control for moving the axis of movement in a horizontal plane. 1. A method for detecting an abnormality in a robot having a vertical axis for moving in a vertical direction, the motor of each axis being driven and controlled by a servo driver, comprising:
setting an abnormality detection stop period during a downward acceleration period in which the vertical axis is accelerated in a downward direction by an operation command for the robot;
determining that an abnormality has occurred in the vertical axis when it is detected that an absolute value of a torque command value in the servo driver for the motor of the vertical axis is equal to or less than a threshold value except during the abnormality detection stop period;
The method of detecting an abnormality further comprises detecting that an absolute value of the torque command value is equal to or less than the threshold value when the absolute value of the torque command value is equal to or less than the threshold value for a predetermined detection duration.

Images