Encoder failure diagnosis method, robot monitoring device, and robot system

Abstract

To provide an encoder failure diagnosis method and a robot monitoring device capable of detecting an encoder failure even when an operation command value to a motor corresponds to stop, and a robot system equipped with the robot monitoring device and having a high safety function.SOLUTION: An encoder failure diagnosis method comprises the steps of: acquiring a power signal of a motor; acquiring an encoder value; determining whether a rotational shaft is rotating on the basis of the power signal; determining whether the rotational shaft is rotating on the basis of the encoder value; and diagnosing that the encoder has failed when it is determined that the rotational shaft is rotating on the basis of the power signal and it is determined that the rotational shaft is stopped on the basis of the encoder value.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present invention relates to a method for diagnosing a fault in an encoder, a robot monitoring device, and a robot system. [Background technology]

[0002] Patent Document 1 discloses a motor control device having an encoder that detects motor operation. This motor control device includes a motor control unit, a drive unit, a cutoff unit, and a safety control unit. The motor control unit generates a command value for motor operation based on an operation command signal for driving the motor and a feedback signal from the encoder. The drive unit supplies a drive current to the motor based on the command value. The cutoff unit cuts off transmission of the drive signal from the motor control unit to the drive unit. When the safety control unit determines that a failure has occurred, it executes a cutoff process for the drive signal via the cutoff unit. This cutoff process is executed based on the result of a comparison between a feedback value calculated from the feedback signal from the encoder and a control calculation value calculated in the process of generating the command value.

[0003] Specifically, if the difference between the feedback value and the control calculation value is outside the allowable range, it means that the feedback signal is not in line with the operating state of the servo motor that it should be in. In this case, the safety control unit described in Patent Document 1 determines that some kind of failure has occurred and executes a cut-off process.

[0004] By providing a safety control unit that executes such a cutoff process, the safety performance of the motor control device can be improved without being restricted by the safety performance of the encoder. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 2018-136696 Summary of the Invention [Problem to be solved by the invention]

[0006] The fault detection method described in Patent Document 1 detects deviation from tracking control by the servo mechanism and determines whether a fault has occurred using a safety control unit. Therefore, this fault detection method functions effectively when a command value is a signal that drives the motor, but when the command value is a signal that does not drive the motor, it is not possible to calculate a control calculation value from the command value. As a result, it is not possible to compare the feedback value with the control calculation value, which poses a problem in that it is not possible to detect a fault in the encoder. [Means for solving the problem]

[0007] A fault diagnosis method for an encoder according to an application example of the present invention includes: A method for diagnosing a fault in an encoder that detects rotation of a rotary shaft of a motor provided at a joint of a robot arm and outputs an encoder value, comprising: obtaining a power signal of the motor; obtaining the encoder value; determining whether the rotary shaft is rotating based on the power signal; determining whether the rotary shaft is rotating based on the encoder value; a step of diagnosing that the encoder is faulty when it is determined that the rotating shaft is rotating based on the power signal and that the rotating shaft is stopped based on the encoder value; It has.

[0008] A robot monitoring device according to an application example of the present invention includes: A robot monitoring device for monitoring the operation of a robot including a robot arm having a joint, a motor provided at the joint, and an encoder that detects rotation of a rotation shaft of the motor and outputs an encoder value, a power signal acquisition unit that acquires a power signal of the motor; an encoder value acquisition unit that acquires the encoder value; a power signal processing unit that determines whether the rotary shaft is rotating based on the power signal; an encoder value processing unit that determines whether the rotary shaft is rotating based on the encoder value; an encoder fault diagnosis unit that diagnoses that the encoder is faulty when the power signal processing unit determines that the rotating shaft is rotating and the encoder value processing unit determines that the rotating shaft is stopped; Equipped with.

[0009] A robot system according to an application example of the present invention includes: Robots and a robot controller for controlling the operation of the robot; A robot monitoring device according to an application example of the present invention; It has. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a perspective view showing a robot system according to a first embodiment. [Figure 2] FIG. 2 is a schematic diagram of the robot shown in FIG. [Figure 3] FIG. 2 is a block diagram showing the main parts of the robot system of FIG. 1. [Figure 4] FIG. 4 is a partially enlarged view of the block diagram shown in FIG. 3. [Figure 5] 4 is a detailed view of a first joint portion shown in FIG. 3 and a functional block diagram of a robot monitoring device. FIG. [Figure 6] 4 is a flowchart illustrating a fault diagnosis method for an encoder according to the first embodiment. [Figure 7] FIG. 10 is a partially enlarged view of a block diagram showing the main parts of a robot system according to a second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a method for diagnosing a fault in an encoder, a robot monitoring device, and a robot system according to the present invention will be described in detail based on the embodiments shown in the accompanying drawings.

[0012] 1. First embodiment First, a robot system according to a first embodiment will be described.

[0013] Fig. 1 is a perspective view showing a robot system according to a first embodiment, Fig. 2 is a schematic diagram of the robot shown in Fig. 1, and Fig. 3 is a block diagram showing the main parts of the robot system of Fig. 1.

[0014] 1 is used for performing tasks on various types of workpieces (objects), such as transport, assembly, and inspection.

[0015] As shown in FIGS. 1 and 3, the robot system 1 includes a base 4, a robot arm 10, a robot 2 including driving units 401 to 406 and driving control units 301 to 306, and a robot control device 8 that controls the operation of the robot 2.

[0016] 1 and 2 is placed on a horizontal floor 101. The base 4 may be placed on a wall, a ceiling, a stand, or the like instead of the floor 101.

[0017] The robot arm 10 shown in FIGS. 1 and 2 includes a first arm 11, a second arm 12, a third arm 13, a fourth arm 14, a fifth arm 15, and a sixth arm 16. An end effector (not shown) can be detachably attached to the tip of the sixth arm 16, and the end effector can grip a workpiece. The workpiece to be gripped by the end effector is not particularly limited, and examples include electronic components and electronic devices. In this specification, the side of the base 4 relative to the sixth arm 16 is referred to as the "base end side," and the side of the sixth arm 16 relative to the base 4 is referred to as the "tip side."

[0018] The end effector is not particularly limited, but examples thereof include a hand that grips a workpiece, a suction head that sucks a workpiece, and the like.

[0019] A force detection unit (not shown) may be provided between the sixth arm 16 and the end effector. The force detection unit detects the force applied to the end effector. An example of the force detection unit is a six-axis force sensor that can detect force components (translational force components) in each of three mutually orthogonal axes and force components (rotational force components) around each of the three axes.

[0020] Furthermore, in addition to the above, the robot system 1 may also include, for example, an image sensor, a depth sensor, an inertial sensor, an ultrasonic sensor, a light curtain, a millimeter wave radar, a laser scanner, and the like.

[0021] 3 includes a robot controller 81, a robot monitoring device 82, a power cutoff unit 85, and a converter unit 86 connected to an AC power supply 9 via the power cutoff unit 85. As will be described later, the robot control device 8 controls the operation of drive control units 301 to 306 to control the operation of the robot 2.

[0022] 1.1.Robots The robot 2 is a single-arm, six-axis, vertically articulated robot in which a first arm 11, a second arm 12, a third arm 13, a fourth arm 14, a fifth arm 15, and a sixth arm 16 are connected in this order from the base end to the tip end to a base 4. Hereinafter, the first arm 11, the second arm 12, the third arm 13, the fourth arm 14, the fifth arm 15, and the sixth arm 16 will also be referred to as "arms." The lengths of the arms 11 to 16 are not particularly limited and can be set as appropriate.

[0023] 1.1.1.Robot Arm As shown in FIG. 2, the base 4 and the first arm 11 are connected via a first joint 171. The first arm 11 is rotatable relative to the base 4 around a first rotation axis O1 that is parallel to the vertical axis. As shown in FIG. 3, the first joint 171 includes a drive unit 401 having a motor 401M and a reducer (not shown), and an angle sensor 411. The first arm 11 rotates when driven by the drive unit 401. The motor 401M generates a driving force that rotates the first arm 11.

[0024] The first arm 11 and the second arm 12 are connected via a second joint 172. The second arm 12 is rotatable relative to the first arm 11 around a second rotation axis O2 that is parallel to the horizontal plane. As shown in FIG. 3, the second joint 172 includes a drive unit 402 having a motor 402M and a reducer (not shown), and an angle sensor 412. The second arm 12 rotates when driven by the drive unit 402. The motor 402M generates a driving force that rotates the second arm 12.

[0025] The second arm 12 and the third arm 13 are connected via a third joint 173. The third arm 13 is rotatable relative to the second arm 12 around a third rotation axis O3 that is parallel to the horizontal plane. As shown in FIG. 3, the third joint 173 includes a drive unit 403 having a motor 403M and a reducer (not shown), and an angle sensor 413. The third arm 13 rotates when driven by the drive unit 403. The motor 403M generates a driving force that rotates the third arm 13.

[0026] The third arm 13 and the fourth arm 14 are connected via a fourth joint 174. The fourth arm 14 is rotatable relative to the third arm 13 around a fourth rotation axis O4 that is parallel to the central axis of the third arm 13. As shown in FIG. 3, the fourth joint 174 includes a drive unit 404 having a motor 404M and a reducer (not shown), and an angle sensor 414. The fourth arm 14 rotates when driven by the drive unit 404. The motor 404M generates a driving force that rotates the fourth arm 14.

[0027] The fourth arm 14 and the fifth arm 15 are connected via a fifth joint 175. The fifth arm 15 is rotatable relative to the fourth arm 14 around a fifth rotation axis O5 that is perpendicular to the central axis of the fourth arm 14. As shown in FIG. 3, the fifth joint 175 includes a drive unit 405 having a motor 405M and a reducer (not shown), and an angle sensor 415. The fifth arm 15 rotates when driven by the drive unit 405. The motor 405M generates a driving force that rotates the fifth arm 15.

[0028] The fifth arm 15 and the sixth arm 16 are connected via a sixth joint 176. The sixth arm 16 is rotatable relative to the fifth arm 15 around a sixth rotation axis O6 that is parallel to the central axis of the tip of the fifth arm 15. As shown in FIG. 3, the sixth joint 176 includes a motor 406M, a drive unit 406 having a reducer (not shown), and an angle sensor 416. The sixth arm 16 rotates when driven by the drive unit 406. The motor 406M generates a drive force that rotates the sixth arm 16.

[0029] Examples of the angle sensors 411-416 include various encoders such as rotary encoders. The angle sensors 411-416 detect the rotation angle of the output shafts of the motors 401M-406M or the output shafts of the reducers of the driving units 401-406. In this specification, detecting the rotation of the output shafts of the motors 401M-406M or the output shafts of the reducers is referred to as "detecting the rotation of the motor's rotation shaft."

[0030] 1.1.2.Drive unit The motors 401M to 406M of the driving units 401 to 406 may be, for example, brushless motors having three-phase coils consisting of U-phase, V-phase, and W-phase. A three-phase brushless motor makes it easy to control the driving of the motors 401M to 406M. The following description will be based on this three-phase brushless motor.

[0031] The reducers of the driving units 401 to 406 may be, for example, planetary gear reducers made up of multiple gears, wave reducers, or the like.

[0032] The driving units 401 to 406 and the angle sensors 411 to 416 are electrically connected to the robot control device 8, respectively.

[0033] The drive control units 301 to 306 are, for example, servo drivers, and control the operations of the drive units 401 to 406 based on operation command values ​​output from the robot control device 8.

[0034] Fig. 4 is a partially enlarged view of the block diagram shown in Fig. 3. Note that Fig. 4 shows in detail only the first joint portion 171 of the first joint portion 171 to the sixth joint portion 176, which are all joint portions located between the arms.

[0035] The first joint 171 is provided with a drive unit 401 including a motor 401M and an angle sensor 411, and a drive control unit 301. The operations of the drive unit 401 and drive control unit 301 will be described below with reference to Fig. 4, but the following description also applies to the drive units 402 to 406 and drive control units 302 to 306.

[0036] 4 includes an encoder 421. The encoder 421 is connected to, for example, the rotation shaft of the motor 401M. The angle sensor 411 may include a plurality of encoders 421. This allows redundancy in the detection of the angular position of the rotation shaft of the motor 401M.

[0037] 4 has a U-phase coil 401u, a V-phase coil 401v, and a W-phase coil 401w. Drive control unit 301 and U-phase coil 401u are connected via a U-phase power line L1u, drive control unit 301 and V-phase coil 401v are connected via a V-phase power line L1v, and drive control unit 301 and W-phase coil 401w are connected via a W-phase power line L1w.

[0038] The encoder 421 may be a safety encoder, but may also be a non-safety encoder.

[0039] A safety encoder is an encoder that has been certified to meet the safety requirements specified in robot safety standards, such as ISO 10218-1:2011 "Robots and robotic devices - Safety requirements for industrial robots - Part 1." These safety requirements require that encoder failures be detected. Note that robot safety standards are not limited to the above standards.

[0040] A non-safety encoder refers to an encoder that has not been certified to meet these safety requirements. Non-safety encoders have a proven track record as encoders for servo motors used in robots, and are therefore stable in quality and inexpensive. Therefore, by using a non-safety encoder, the encoder 421 can be easily procured and the robot system 1 can operate stably. Furthermore, according to this embodiment, even when a non-safety encoder is used, a malfunction of the encoder 421 can be detected by the function of the robot monitoring device 82, which will be described later, and therefore the safety function of the robot system 1 can be sufficiently improved.

[0041] The encoder 421 may be either an absolute encoder or an incremental encoder. An absolute encoder is an encoder that can detect the absolute position of the rotation angle of a rotating shaft. An incremental encoder is an encoder that can detect changes in the rotation angle of a rotating shaft.

[0042] The encoder 421 outputs an encoder value E representing the angular position of the rotation shaft of the motor 401M as position feedback. The drive control unit 301 and the robot controller 81 receive the encoder value E.

[0043] The robot controller 81 outputs, for example, a motion command value M representing a target angular position of the rotation shaft of the motor 401M to the drive control unit 301. Note that the motion command value M is also output when the target angular position of the rotation shaft of the motor 401M is not changed, that is, when the motor 401M is to be kept stopped.

[0044] 1.1.3. Drive control unit Based on the operation command value M and the encoder value E, the drive control unit 301 generates a drive pulse voltage that controls the drive of the motor 401M so that the encoder value E approaches the target angular position specified by the operation command value M. This drive pulse voltage is then output to the motor 401M, controlling the drive of the motor 401M. As a result, the first joint 171 is controlled to a predetermined angle, and the first arm 11 relative to the base 4 is controlled to a predetermined posture.

[0045] The drive control unit 301 shown in FIG. 4 includes an inverter unit 312 and a control circuit 314.

[0046] The inverter unit 312 is a three-parallel push-pull inverter circuit having six switching elements 313. The six switching elements 313 are controlled to be turned on or off by control signals output from a control circuit 314. This causes the inverter unit 312 to apply three-phase drive pulse voltages Vu, Vv, and Vw to the motor 401M.

[0047] The control circuit 314 outputs control signals to each switching element 313 based on the operation command value M and the encoder value E. In this embodiment, the control signals are PWM signals for PWM-controlling (pulse width modulation) the inverter unit 312. Specifically, the PWM signals are set so that equivalent voltages Vue, Vve, and Vwe, which are converted from the voltage values ​​and duties of the three-phase drive pulse voltages Vu, Vv, and Vw, have sinusoidal voltage waveforms with phases shifted by 120°. Using these PWM signals, the control circuit 314 controls the on and off timing of the switching elements 313. As a result, the three-phase drive pulse voltages Vu, Vv, and Vw are applied by the inverter unit 312.

[0048] The phase difference between the three-phase equivalent voltages Vue, Vve, and Vwe causes coil currents to flow through U-phase coil 401u, V-phase coil 401v, and W-phase coil 401w, and the rotating shaft of motor 401M rotates as time changes.

[0049] In this embodiment, the drive control unit 301 also includes voltage value detection units 316u, 316v, and 316w.

[0050] The voltage value detection unit 316u includes a U-phase branch line L2u, an input resistor R1, a shunt resistor R2, a photocoupler PC, an amplifier AMP, and a voltage value measurement unit PWC, and has a function of measuring a voltage value PWu in the U-phase coil 401u.

[0051] The U-phase branch line L2u is a signal line that connects the U-phase power line L1u of the motor 401M to the ground potential GND. The input side resistor R1 and the shunt resistor R2 are resistive elements that are connected in series in this order from the U-phase power line L1u side on the U-phase branch line L2u.

[0052] The input terminal of the photocoupler PC is connected in parallel with the shunt resistor R2. The photocoupler PC shown in FIG. 4 includes a light-emitting element 316L and a light-receiving element 316P. The light-emitting element 316L emits light based on the potential difference between the voltage generated in the U-phase branch wire L2u and the ground potential GND. The light-receiving element 316P receives the light and generates a photocurrent. The amplifier AMP converts the photocurrent into a voltage signal. This allows a voltage signal corresponding to the voltage value PWu to be input to the voltage value measurement unit PWC while electrically isolating the input and output of the photocoupler PC.

[0053] The light-emitting element 316L may be, for example, a light-emitting diode. The light-receiving element 316P may be, for example, a photodiode or a phototransistor. Note that a bipolar photocoupler such as that shown in FIG. 4 is preferably used as the photocoupler PC. Note that a digital isolator may be used instead of the photocoupler PC.

[0054] The voltage value measurement unit PWC receives the voltage signal output from the amplifier AMP and measures the voltage value PWu. This makes it possible to indirectly measure the voltage value PWu. The voltage value measurement unit PWC may be, for example, a counter that has the function of measuring the voltage value of the voltage signal.

[0055] The voltage value detection unit 316v includes a V-phase branch line L2v, an input resistor R1, a shunt resistor R2, a photocoupler PC, an amplifier AMP, and a voltage value measurement unit PWC, and has a function of measuring the voltage value PWv in the V-phase coil 401v.

[0056] The V-phase branch line L2v is a signal line that connects the V-phase power line L1v of the motor 401M to the ground potential GND. Elements of the voltage value detection unit 316v other than the V-phase branch line L2v are the same as those of the voltage value detection unit 316u.

[0057] The voltage value detection unit 316w includes a W-phase branch line L2w, an input resistor R1, a shunt resistor R2, a photocoupler PC, an amplifier AMP, and a voltage value measurement unit PWC, and has a function of measuring a voltage value PWw in the W-phase coil 401w.

[0058] The W-phase branch line L2w is a signal line that connects the W-phase power line L1w of the motor 401M to the ground potential GND. Elements of the voltage value detection unit 316w other than the W-phase branch line L2w are the same as those of the voltage value detection unit 316u.

[0059] The voltage value detectors 316u, 316v, and 316w output the voltage values ​​PWu, PWv, and PWw to the robot monitor device 82.

[0060] 1.2.Robot Control Device The robot control device 8 shown in FIG. 3 includes a robot controller 81, a robot monitoring device 82, a power cutoff unit 85, and a converter unit 86.

[0061] 1.2.1.Robot Controller As shown in Fig. 3, the robot controller 81 controls the operation of the drive control units 301-306, thereby controlling the operation of the robot 2. Specifically, the robot controller 81 outputs an operation command value M to the drive control units 301-306, as shown in Fig. 4, based on the detection results of the angle sensors 411-416 and a force detection unit, image sensor, depth sensor, etc. (not shown). Then, the robot controller 81 controls the operation conditions of the drive units 401-406, such as angular velocity and rotation angle, via the drive control units 301-306, respectively.

[0062] The hardware configuration of the robot controller 81 is not particularly limited, but in Fig. 3 it has a processor 912, a memory 914, and an external interface 916. These are connected to each other via an internal bus so that they can communicate with each other.

[0063] The processor 912 may be, for example, a CPU (Central Processing Unit). The processor 912 executes various programs stored in the memory 914 to realize the functions of the robot controller 81.

[0064] The processor 912 may be a field-programmable gate array (FPGA), an application-specific integrated circuit (ASIC), or the like.

[0065] Examples of the memory 914 include volatile memory such as RAM (Random Access Memory) and non-volatile memory such as ROM (Read Only Memory). Note that the memory 914 is not limited to being non-removable, and may be removable.

[0066] The memory 914 stores various programs as well as various data received by the external interface 916 and various data output from the robot 2.

[0067] Examples of the external interface 916 include a USB (Universal Serial Bus), RS-232C, a wired LAN (Local Area Network), and a wireless LAN.

[0068] 1.2.2. Robotic Monitoring Device The hardware configuration of the robot monitoring device 82 is not particularly limited, but in Fig. 3 it has a processor 922, a memory 924, and an external interface 926. These are connected to each other so that they can communicate with each other via an internal bus.

[0069] The memory 924 and the external interface 926 are similar to the memory 914 and the external interface 916 described above.

[0070] An example of the processor 922 is a CPU. The processor 922 executes various programs stored in the memory 924 to realize the functions of the robot monitoring device 82. The processor 922 may be an FPGA, an ASIC, or the like.

[0071] The robot monitoring device 82 monitors the operation of the robot 2 independently of the robot controller 81, thereby making it possible to further improve the reliability of the functional safety of the robot system 1.

[0072] 1.2.3. Power Cut-Off Section 5 is a detailed view of the first joint unit 171 shown in FIG. 3 and a functional block diagram of the robot monitoring device 82. The configuration of the first joint unit 171 is similar to the configurations of the second joint unit 172, the third joint unit 173, the fourth joint unit 174, the fifth joint unit 175, and the sixth joint unit 176. Therefore, in the following explanation, the first joint unit 171 will be explained as a representative based on FIGS. 4 and 5, and explanations of the other joint units will be omitted.

[0073] The power cutoff unit 85 is provided on a power supply path 91 that electrically connects the AC power source 9 and the first joint unit 171. The drive control units 301 to 306 each receive power supply from the power supply path 91. Therefore, when the power cutoff unit 85 cuts off the power supply path 91, the power supply to the drive control units 301 to 306 is cut off, and the operation of the drive units 401 to 406 can be stopped.

[0074] 5 cuts off the power supply path 91 based on the cutoff signal B. When the power cutoff unit 85 operates, the power supply to all of the drive control units 301 to 306 is cut off. Note that the converter unit 86 and the inverter unit 312 may also function as the power cutoff unit 85.

[0075] 1.2.4.Converter section The converter unit 86 is provided on the power supply path 91 between the power cutoff unit 85 and the first joint unit 171. The converter unit 86 shown in FIG. 4 is an AC-DC converter that has a bridge diode 862 and a smoothing capacitor 864 and converts alternating current into direct current. The converter unit 86 then supplies the direct current voltage to the inverter unit 312. Note that, depending on the type of power source, the converter unit 86 may be omitted or may be replaced with another converter.

[0076] 1.3. Functions of the Robot Monitoring Device The robot monitoring device 82 shown in FIG. 5 includes, as functional units, a power signal acquisition unit 820, an encoder value acquisition unit 822, a power signal processing unit 824, an encoder value processing unit 826, an encoder fault diagnosis unit 828, and an interruption signal output unit 830.

[0077] The power signal acquisition unit 820 acquires the voltage values ​​PWu, PWv, and PWw output from the drive control unit 301 as power signals. Note that the power signals are not limited to the voltage values ​​PWu, PWv, and PWw, and other measured values ​​may be used as long as they are voltage measured values. The power signals may be current values ​​instead of voltage values.

[0078] The encoder value acquisition unit 822 acquires the encoder value E output from the encoder 421 .

[0079] The power signal processing unit 824 stores in advance stop determination conditions related to the voltage values ​​PWu, PWv, and PWw for determining that the motor 401M is stopped. When the voltage values ​​PWu, PWv, and PWw acquired by the power signal acquisition unit 820 satisfy the stop determination conditions, the power signal processing unit 824 determines that the rotating shaft of the motor 401M is stopped. On the other hand, when the voltage values ​​PWu, PWv, and PWw do not satisfy the stop determination conditions, the power signal processing unit 824 determines that the rotating shaft of the motor 401M is rotating.

[0080] The encoder value processing unit 826 stores in advance a judgment condition for determining whether or not the rotary shaft of the motor 401M is rotating, which is a judgment condition related to the encoder value E output from the encoder 421. By comparing the encoder value E with the judgment condition described above, the encoder value processing unit 826 determines whether or not the rotary shaft of the motor 401M is rotating.

[0081] The encoder fault diagnosis unit 828 diagnoses that the encoder 421 is faulty when the power signal processing unit 824 determines that the rotating shaft of the motor 401M is rotating and the encoder value processing unit 826 determines that the rotating shaft of the motor 401M is stopped.

[0082] The shutdown signal output unit 830 outputs a shutdown signal B based on the diagnosis result by the encoder failure diagnosis unit 828 .

[0083] 1.4. Encoder fault diagnosis method Next, a fault diagnosis method for an encoder according to the first embodiment will be described. In the following description, a method using the functions of the robot monitoring device 82 described above will be taken as an example. In the following description, a fault diagnosis method for the encoder 421 provided in the first joint 171 will be described as a representative example, but the fault diagnosis method for the encoders provided in the second joint 172 to the sixth joint 176 is similar to the following.

[0084] FIG. 6 is a flowchart for explaining the encoder fault diagnosis method according to the first embodiment.

[0085] 6 includes a power signal acquisition step S102, an encoder value acquisition step S104, a power signal processing step S106, an encoder value processing step S108, an encoder fault diagnosis step S110, and a power cut-off step S112. Note that the order of the steps is not limited to this and may be reversed.

[0086] 1.4.1. Power signal acquisition process In the power signal acquisition step S102, the power signal acquisition unit 820 acquires the voltage values ​​PWu, PWv, and PWw as power signals. Specifically, the power signal acquisition unit 820 acquires the voltage values ​​PWu, PWv, and PWw detected by the voltage value detection units 316u, 316v, and 316w.

[0087] 1.4.2. Encoder value acquisition process In the encoder value acquisition step S104, the encoder value acquisition unit 822 acquires the encoder value E output from the encoder 421. The encoder value E is rotation information of the rotary shaft of the motor 401M.

[0088] 1.4.3. Power signal processing process In the power signal processing step S106, the power signal processing unit 824 performs processing to determine whether the voltage values ​​PWu, PWv, and PWw satisfy a stop determination condition. The stop determination condition is, for example, a range for the voltage values ​​PWu, PWv, and PWw, and when the voltage values ​​PWu, PWv, and PWw are within this range, the rotating shaft of the motor 401M can be considered to be stopped.

[0089] When the voltage values ​​PWu, PWv, and PWw satisfy the stop determination conditions, the power signal processing unit 824 determines that the rotating shaft of the motor 401M is stopped.

[0090] On the other hand, when the voltage values ​​PWu, PWv, and PWw do not satisfy the stop determination conditions, the power signal processing unit 824 determines that the rotary shaft of the motor 401M is rotating.

[0091] Examples of stop determination conditions include (a) voltage values ​​PWu, PWv, and PWw, and (b) voltage change amounts TPWu, TPWv, and TPWw. The stop determination conditions (a) and (b) will be explained below in order. Note that the stop determination conditions may be conditions other than those listed below.

[0092] (a) Voltage values ​​PWu, PWv, PWw The voltage values ​​PWu, PWv, and PWw are the amplitudes of voltage changes occurring in the three-phase coils. The stop determination condition for the voltage values ​​PWu, PWv, and PWw is expressed, for example, by the following formula (1). |PWu|<α, and |PWv|<α, and |PWw|<α … (1)

[0093] In the above formula (1), α is, for example, the minimum voltage value required to rotate the rotating shaft of the motor 401M. α can be found through experiments, simulations, etc. By providing a range for the stop determination conditions in this way, it is possible to suppress instability in the fault diagnosis process due to detection errors of the voltage values ​​PWu, PWv, and PWw.

[0094] If two of the voltage values ​​PWu, PWv, and PWw can be obtained, the remaining one can be found by calculation. Therefore, in the power signal obtaining step S102, it is sufficient to obtain two or more of the voltage values ​​PWu, PWv, and PWw as the power signal.

[0095] (b) Changes TPWu, TPWv, TPWw The variations TPWu, TPWv, and TPWw are time variations in the voltage values ​​PWu, PWv, and PWw generated in the three-phase coils. The stop determination condition for the variations TPWu, TPWv, and TPWw in voltage is expressed, for example, by the following formula (2).

[0096] -β <TPWu<+β、かつ、-β<TPWv<+β、かつ、-β<TPWw<+β … (2)

[0097] In the above formula (2), β is set appropriately depending on the switching sequence that changes the coil current. β can be found through experiments, simulations, etc. As an example, β is set to less than half the minimum step width of the switching sequence. For example, when the change period of the three-phase voltage values ​​PWu, PWv, and PWw is 360° and the minimum step width is 30°, β can be set to less than 15°.

[0098] If two of the variations TPWu, TPWv, and TPWw can be obtained, the remaining one can be found by calculation. Therefore, in the power signal acquisition step S102 described above, it is sufficient to acquire two or more of the variations TPWu, TPWv, and TPWw as power signals.

[0099] The stop determination conditions used in the power signal processing step S106 may include both of the above (a) and (b).

[0100] 1.4.4. Encoder Value Processing Steps In the encoder value processing step S108, a process is performed to determine whether or not the rotary shaft of the motor 401M is rotating based on the encoder value E.

[0101] For example, if the rotation angle represented by the encoder value E is equal to or greater than the minimum detection angle of the encoder 421, that is, if rotation can be detected, it is determined that the rotation shaft is rotating.

[0102] On the other hand, if the rotation angle represented by the encoder value E is less than the minimum detection angle, that is, if rotation cannot be detected, it is determined that the rotating shaft is stopped.

[0103] In these cases, the presence or absence of rotation may also be determined based on a value slightly larger than the minimum detection angle.

[0104] 1.4.5. Encoder fault diagnosis process In the encoder fault diagnosis process S110, if it is determined in the power signal processing process S106 that the rotating shaft of the motor 401M is rotating and in the encoder value processing process S108 that the rotating shaft of the motor 401M is stopped, the two determination results are different, and therefore the encoder 421 is diagnosed as faulty.

[0105] The determination in the power signal processing step S106 is based on power signals such as voltage values ​​PWu, PWv, PWw and variation amounts TPWu, TPWv, TPWw. These power signals can be said to accurately reflect the rotational state of the rotating shaft. On the other hand, the determination in the encoder value processing step S108 is based on the encoder value E.

[0106] In light of the above, if the determination in the power signal processing step S106 determines that the rotating shaft is rotating, but the determination in the encoder value processing step S108 determines that the rotating shaft is not rotating (is stopped), it can be assumed that the rotational state of the rotating shaft is not correctly reflected in the encoder value E. In this case, it can be said that there is a high probability that the encoder 421 is malfunctioning. Therefore, in this case, the encoder malfunction diagnosis unit 828 diagnoses that the encoder 421 is malfunctioning.

[0107] If a failure of the encoder 421 can be determined using the above process, a failure of the encoder 421 can be diagnosed based on the power signal and the encoder value E, without relying on the operation command value M. Therefore, even in a special situation where, for example, an operation command value M that does not rotate the rotating shaft is output from the robot controller 81 and the rotating shaft unintentionally rotates, the voltage and coil current generated by the rotation of the rotating shaft can be obtained as a power signal. This makes it possible to detect whether the rotating shaft is rotating based on both the power signal and the encoder value E. Therefore, a failure of the encoder 421 can be accurately diagnosed based on the difference in the results of the above determination. In other words, even in the rare case where the encoder 421 fails when the operation command value M commands a stop and the determination based on the power signal indicates rotation, a failure of the encoder 421 can be detected. As a result, a failure of the encoder 421 can be accurately diagnosed even when a non-safety encoder is used as the encoder 421.

[0108] The above-described event has a significant impact on safety because it is an event in which the rotary shaft of the motor 401M rotates when the encoder 421 is not outputting the correct encoder value E. Therefore, if a failure of the encoder 421 can be accurately detected under conditions in which such an event may occur, the safety of the robot system 1 can be more reliably ensured. An example of such an event is an event in which the first arm 11 attached to the rotary shaft of the motor 401M rotates in a direction that causes it to fall due to its own weight, causing the rotary shaft of the motor 401M to rotate accordingly.

[0109] Furthermore, according to the fault diagnosis process for the encoder 421 as described above, it is possible to detect a fault in the encoder 421 even when a non-safety encoder is used as the encoder 421. Therefore, according to the robot monitoring device 82, even when combined with a non-safety encoder, it is possible to realize the SOS (Safely operating stop, stop monitoring) function and the SS2 (Safely stop 2, controlled stop without interruption) function, which are among the safety functions defined in the European safety standard EN ISO13849-1:2008 Category 3 PLd. In other words, even when a non-safety encoder is used as the encoder 421, the robot monitoring device 82 can provide safety functions that comply with the safety requirements stipulated in the robot safety standard.

[0110] If it is diagnosed that the encoder 421 has failed, the flow may be ended, but in this embodiment, the flow proceeds to a power cut-off step S112. The encoder failure diagnosis unit 828 outputs the diagnosis result to the robot controller 81 as necessary. Based on the diagnosis result, the robot controller 81 may notify the user that the encoder 421 has failed.

[0111] Also, if it is determined in the power signal processing step S106 that the rotating shaft of the motor 401M is stopped and it is determined in the encoder value processing step S108 that the rotating shaft of the motor 401M is rotating, the encoder 421 may be diagnosed as faulty since the two determination results are different.

[0112] On the other hand, if it is determined in the power signal processing step S106 that the rotating shaft of the motor 401M is rotating, and it is also determined in the encoder value processing step S108 that the rotating shaft of the motor 401M is rotating, the two determination results are the same, and therefore the encoder 421 is diagnosed as normal.

[0113] Similarly, if it is determined in the power signal processing step S106 that the rotating shaft of the motor 401M is stopped, and it is also determined in the encoder value processing step S108 that the rotating shaft of the motor 401M is stopped, the two determination results are the same, so the encoder 421 is diagnosed as normal.

[0114] In this step, if it is determined that the encoder 421 is normal, the flow returns to the power signal acquisition step S102.

[0115] In addition, even if the two determination results are the same in the power signal processing step S106 and the encoder value processing step S108, if there is another problem with the encoder 421, the encoder may not be diagnosed as normal.

[0116] 1.4.6. Power Cut-Off Process As shown in FIG. 6, the fault diagnosis method for an encoder according to this embodiment includes an optional power cut-off step S112.

[0117] In the power cut-off step S112, the cut-off signal output unit 830 outputs the cut-off signal B based on the diagnosis result output from the encoder failure diagnosis unit 828. That is, when the diagnosis result indicates that the encoder 421 is at fault, the cut-off signal B is output.

[0118] 5 receives this cutoff signal B and cuts off the power supply path 91. This stops the operation of the driving units 401 to 406. As a result, it is possible to prevent the driving units 401 to 406 from continuing to operate when it has been determined that the encoder 421 has failed, thereby improving the safety function of the robot system 1.

[0119] Furthermore, the above-described encoder fault diagnosis method may be executed at a timing corresponding to the operation command value M.

[0120] For example, if the operation command value M is a value that rotates the rotation shaft (a value that changes the position), the operation command value M becomes a significant value. In this case, it is possible to determine whether the rotation shaft is rotating based on the operation command value M. Then, by comparing the determination result based on the operation command value M with the determination result based on the encoder value E, it is possible to diagnose whether the encoder 421 is malfunctioning.

[0121] On the other hand, if the operation command value M is a value that does not rotate the rotary shaft (a value that does not change the position), then as described above, it is sufficient to determine whether the rotary shaft is rotating or not based on the power signal. This makes it possible to diagnose a fault in the encoder 421 even if the operation command value M is not a significant value. In this case, the operation command value M is used in addition to the power signal described above as a comparison target for comparing with the determination result based on the encoder value E. This increases the reliability of fault diagnosis compared to when using only the power signal.

[0122] Furthermore, as described above, the computational load required for fault diagnosis can be reduced by switching the comparison target in accordance with the operation command value M. In other words, since judgment based on the operation command value M requires a small amount of computation, it is possible to reduce the computational resources occupied by fault diagnosis in the robot monitoring device 82.

[0123] 2. Second embodiment Next, a fault diagnosis method for an encoder, a robot monitoring device, and a robot system according to a second embodiment will be described.

[0124] Fig. 7 is a partially enlarged block diagram showing the main parts of the robot system 1 according to the second embodiment. Of the first joint 171 to sixth joint 176, all of which are joints located between the arms, Fig. 7 shows only the first joint 171 in detail. In Fig. 7, the same components as those in the first embodiment are denoted by the same reference numerals.

[0125] The second embodiment will be described below, but the following description will focus on the differences from the first embodiment, and a description of similar points will be omitted.

[0126] The robot system 1 according to the second embodiment is similar to the robot system 1 according to the first embodiment, except that the drive control unit 301 is configured to acquire the coil current flowing through the motor 401M as a power signal.

[0127] 2.1. Drive control unit The drive control unit 301 shown in FIG. 7 includes current value detection units 317u, 317v, and 317w.

[0128] The current value detector 317u includes a shunt resistor R3, a U-phase current detection line L3u, and an isolated A / D converter ADC, and has a function of measuring a current value Iu of a coil current flowing through the U-phase power line L1u.

[0129] The shunt resistor R3 is a resistive element inserted in the U-phase power line L1u. The isolated A / D converter ADC is connected in parallel with the shunt resistor R3 via the U-phase current detection line L3u. The isolated A / D converter ADC may be, for example, a device incorporating elements such as a ΔΣ modulator, an isolation element (photocoupler), and a digital filter.

[0130] It should be noted that various current sensors, such as a cored current sensor or a coreless current sensor, may be used in place of the shunt resistor R3 and the isolated A / D conversion unit ADC.

[0131] The current value detector 317v includes a shunt resistor R3, a V-phase current detection line L3v, and an isolated A / D converter ADC, and has a function of measuring the current value Iv of the coil current flowing through the V-phase power line L1v.

[0132] The current value detector 317w includes a shunt resistor R3, a W-phase current detection line L3w, and an isolated A / D converter ADC, and has a function of measuring a current value Iw of a coil current flowing through the W-phase power line L1w.

[0133] The current value detectors 317u, 317v, and 317w output the coil current values ​​Iu, Iv, and Iw to the robot monitor device 82.

[0134] 2.2. Encoder fault diagnosis method Next, a fault diagnosis method for an encoder according to the second embodiment will be described. In the following description, a method using the functions of the robot monitoring device 82 described above will be described as an example with reference to Fig. 6. In the following description, a fault diagnosis method for the encoder 421 provided in the first joint 171 will be described as a representative example, but the fault diagnosis method for the encoders provided in the second joint 172 to the sixth joint 176 is also similar to the method described below.

[0135] 2.2.1. Power signal acquisition process In the power signal acquisition step S102, the power signal acquisition unit 820 acquires, as power signals, the current values ​​Iu, Iv, and Iw of the coil currents output from the drive control unit 301A. Specifically, the power signal acquisition unit 820 acquires the current values ​​Iu, Iv, and Iw detected by the current value detection units 317u, 317v, and 317w.

[0136] Furthermore, the power signal acquisition step S102 preferably includes a process of acquiring the power signal while flowing coil currents through the U-phase coil 401u, the V-phase coil 401v, and the W-phase coil 401w (three-phase coils) so that the excitation component exceeds zero even when the torque component of the motor 401M is zero. By performing such a process, it becomes easier to ensure the signal strength of the power signal. This makes it possible to increase the S / N ratio (signal-to-noise ratio) of the power signal.

[0137] Furthermore, by performing the above-described processing, it is possible to obtain a significant power signal even when, for example, the operation command value M output from the robot controller 81 is a value that does not rotate the rotation axis. The reason why such an effect is obtained will be explained below.

[0138] First, the torque component of the coil current flowing through the motor 401M is defined as Iq, and the excitation component is defined as Id. The torque component Iq and excitation component Id of the coil current are calculated from the three-phase coil current through various transformations. Specifically, the three-phase coil current is first transformed into two-phase currents Iα and Iβ using Clarke transformation. The currents Iα and Iβ are currents in stationary coordinates, and these axes are orthogonal to each other. Next, the currents Iα and Iβ in the stationary coordinates are transformed into the excitation component Id and torque component Iq in rotating coordinates using Park transformation.

[0139] The excitation component Id and the torque component Iq are obtained by decomposing the coil current into two orthogonal components on the rotational coordinate system. Typically, as the coil current approaches zero, both the excitation component Id and the torque component Iq approach zero. In contrast, in this embodiment, when the coil current approaches zero, the control circuit 314 controls the operation so that the torque component Iq approaches zero while the excitation component Id exceeds zero. Because the excitation component Id is a component that generates magnetic flux, the three-phase coil currents are controlled so that the excitation component Id exceeds zero. This ensures that the magnetic flux necessary to detect a significant power signal is generated even when the torque component Iq becomes zero. As a result, the signal strength of the power signal can be maintained, and the S / N ratio of the power signal can be improved. This allows for more accurate detection of a fault in the encoder 421, even when the torque component Iq of the coil current is zero.

[0140] 2.2.2. Encoder value acquisition process In the encoder value acquisition step S104, the encoder value acquisition unit 822 acquires the encoder value E output from the encoder 421, as in the first embodiment.

[0141] 2.2.3. Power signal processing process In the power signal processing step S106, the power signal processing unit 824 performs processing to determine whether the current values ​​Iu, Iv, and Iw of the coil currents satisfy a stop determination condition. The stop determination condition is, for example, a range for the current values ​​Iu, Iv, and Iw, and when the condition is met, the rotating shaft of the motor 401M can be considered to be stopped.

[0142] When the current values ​​Iu, Iv, and Iw satisfy the stop determination conditions, the power signal processing unit 824 determines that the rotating shaft of the motor 401M is stopped.

[0143] On the other hand, when the current values ​​Iu, Iv, and Iw do not satisfy the stop determination conditions, the power signal processing unit 824 determines that the rotary shaft of the motor 401M is rotating.

[0144] In this embodiment, the stop determination conditions include (c) the current values ​​Iu, Iv, and Iw of the coil current, and (d) the amounts of change TIu, TIv, and TIw of the coil current. The stop determination conditions (c) and (d) will be explained in order below. Note that the stop determination conditions may be conditions other than those listed below.

[0145] (c) Coil current values ​​Iu, Iv, Iw This stop determination condition is particularly effective when the torque component Iq of the current approaches zero or has become zero, and the excitation component Id also approaches zero. The current values ​​Iu, Iv, and Iw of the coil currents are the amplitudes of the time changes of the coil currents flowing through the three-phase coils. The stop determination condition for the current values ​​Iu, Iv, and Iw is expressed, for example, by the following equation (3): |Iu|<γ, and |Iv|<γ, and |Iw|<γ … (3)

[0146] In the above formula (3), γ is, for example, the minimum current value required to rotate the rotating shaft of the motor 401M. γ can be found through experiments, simulations, etc. By providing a range for the stop determination condition in this way, it is possible to suppress instability in the fault diagnosis process due to detection errors of the current values ​​Iu, Iv, and Iw, etc.

[0147] If two of the current values ​​Iu, Iv, and Iw can be obtained, the remaining one can be found by calculation. Therefore, in the power signal obtaining step S102 described above, it is sufficient to obtain two or more of the current values ​​Iu, Iv, and Iw as the power signal.

[0148] Furthermore, Clarke transformation is performed on the current values ​​Iu, Iv, and Iw to convert them into stationary coordinates. This determines the two-phase current values. Then, the stop determination condition may be set based on these current values.

[0149] (d) Coil current change amount TIu, TIv, TIw The coil current variations TIu, TIv, and TIw are the time variations of the current values ​​Iu, Iv, and Iw of the coil currents flowing through the three-phase coils. The stop determination condition for the coil current variations TIu, TIv, and TIw is expressed, for example, by the following equation (4).

[0150] -δ <TIu<+δ、かつ、-δ<TIv<+δ、かつ、-δ<TIw<+δ … (4)

[0151] In the above formula (4), δ is set appropriately depending on the switching sequence that changes the coil current. δ can be found through experiments, simulations, etc. As an example, δ is set to less than half the minimum step width of the switching sequence. For example, when the change period of the three-phase coil current is 360° and the minimum step width is 30°, δ can be set to less than 15°.

[0152] If two of the variations TIu, TIv, and TIw can be obtained, the remaining one can be found by calculation. Therefore, in the power signal acquisition step S102, it is sufficient to acquire two or more of the variations TIu, TIv, and TIw as the power signal.

[0153] The stop determination conditions used in the power signal processing step S106 may include both of the above (c) and (d).

[0154] In addition, when the torque component Iq of the current approaches zero, or even when it becomes zero, if the excitation component Id is controlled to exceed zero, in addition to the fault diagnosis based on the stop judgment condition described above, a fault diagnosis based on the following equation (5) may be performed. Iα 2 +Iβ 2 >η 2 … (5)

[0155] In the above formula (5), η is set to a measurable value that is smaller than the coil current when the excitation component Id is controlled so as not to become zero. When the excitation component Id is controlled so as to exceed zero, if the above formula (5) is not satisfied, it can be assumed that normal control is not being executed, and therefore the encoder 421 may be diagnosed as having a malfunction.

[0156] 2.2.4. Encoder Value Processing Steps In the encoder value processing step S108, a process is performed to determine whether or not the rotary shaft of the motor 401M is rotating based on the encoder value E. This step is the same as in the first embodiment.

[0157] 2.2.5. Encoder fault diagnosis process In the encoder fault diagnosis process S110, as in the first embodiment, when it is determined in the power signal processing process S106 that the rotating shaft of the motor 401M is rotating and when it is determined in the encoder value processing process S108 that the rotating shaft of the motor 401M is stopped, the encoder 421 is diagnosed as faulty.

[0158] The determination in the power signal processing step S106 is based on power signals such as the coil current values ​​Iu, Iv, Iw and the variations TIu, TIv, TIw. These power signals accurately reflect the rotational state of the rotating shaft. On the other hand, the determination in the encoder value processing step S108 is based on the encoder value E.

[0159] In light of the above, if the determination in the power signal processing step S106 determines that the rotating shaft is rotating, but the determination in the encoder value processing step S108 determines that the rotating shaft is stopped, it can be assumed that the rotational state of the rotating shaft is not correctly reflected in the encoder value E. In this case, it can be said that there is a high probability that the encoder 421 is malfunctioning. Therefore, in this case, the encoder malfunction diagnosis unit 828 diagnoses that the encoder 421 is malfunctioning.

[0160] 2.2.6. Power Cut-Off Process The encoder fault diagnosis method according to this embodiment also includes the optional power cut-off step S112, similar to the first embodiment. In the second embodiment as described above, the same effects as in the first embodiment can be obtained.

[0161] 3. Effects of the above embodiment As described above, the encoder fault diagnosis method according to the embodiment is a method for diagnosing a fault in the encoder 421 that detects rotation of the rotary shaft of the motor 401M provided in the first joint 171 of the robot arm 10 and outputs an encoder value E, and includes a power signal acquisition step S102, an encoder value acquisition step S104, a power signal processing step S106, an encoder value processing step S108, and an encoder fault diagnosis step S110. In the power signal acquisition step S102, a power signal of the motor 401M is acquired. In the encoder value acquisition step S104, the encoder value E is acquired. In the power signal processing step S106, it is determined whether the rotary shaft is rotating based on the power signal. In the encoder value processing step S108, it is determined whether the rotary shaft is rotating based on the encoder value E. In the encoder fault diagnosis process S110, when it is determined that the rotating shaft is rotating based on the power signal and that the rotating shaft is stopped based on the encoder value E, it is diagnosed that the encoder 421 is faulty.

[0162] With this configuration, even when the operation command value M for the motor 401M is a value corresponding to stop, it is possible to diagnose a failure of the encoder 421 based on the power signal and the encoder value E. As a result, for example, even when an operation command value M that does not rotate the rotation shaft is output from the robot controller 81 and an event occurs in which the rotation shaft rotates, it is possible to accurately detect a failure of the encoder 421. In other words, even in the rare case where the operation command value M commands stop and the determination based on the power signal is rotation, a failure of the encoder 421 can be detected. As a result, even when a non-safety encoder is used as the encoder 421, it is possible to accurately diagnose a failure of the encoder 421, thereby providing an encoder failure diagnosis method that can ensure the safety of the robot system 1.

[0163] In the encoder fault diagnosis method according to the embodiment, the motor 401M is a brushless motor having three-phase coils consisting of U-phase, V-phase, and W-phase. With this configuration, the driving of the motor 401M can be easily controlled.

[0164] In the encoder fault diagnosis method according to the embodiment, the power signal acquisition step S102 (a step of acquiring a power signal) includes a process of acquiring a power signal while flowing coil current through the U-phase coil 401u, the V-phase coil 401v, and the W-phase coil 401w (three-phase coils) so that the excitation component Id exceeds zero when the torque component Iq of the motor 401M is zero.

[0165] This configuration ensures the signal strength of the power signal and increases the S / N ratio of the power signal, making it possible to more accurately detect a failure in the encoder 421 even when the torque component Iq of the coil current is zero.

[0166] In the encoder fault diagnosis method according to the embodiment, the power signal is composed of two or more of the voltage value PWu in the U-phase coil 401u, the voltage value PWv in the V-phase coil 401v, and the voltage value PWw in the W-phase coil 401w.

[0167] With this configuration, it is possible to diagnose a failure in the encoder 421 based on the voltage values ​​PWu, PWv, and PWw in the three-phase coils.

[0168] In the encoder fault diagnosis method according to the embodiment, the power signal is composed of two or more of the voltage change amount TPWu in the U-phase coil 401u, the voltage change amount TPWv in the V-phase coil 401v, and the voltage change amount TPWw in the W-phase coil 401w.

[0169] According to this configuration, it is possible to diagnose a failure in the encoder 421 based on the amounts of change TPWu, TPWv, and TPWw in the voltages of the three-phase coils.

[0170] In the encoder fault diagnosis method according to the embodiment, the power signal is composed of two or more of the current value Iu of the coil current flowing through the U-phase coil 401u, the current value Iv of the coil current flowing through the V-phase coil 401v, and the current value Iw of the coil current flowing through the W-phase coil 401w.

[0171] According to this configuration, it is possible to diagnose a failure in the encoder 421 based on the current values ​​Iu, Iv, and Iw of the coil currents flowing through the three-phase coils.

[0172] In the encoder fault diagnosis method according to the embodiment, the power signal is composed of two or more of the change in coil current TIu flowing through the U-phase coil 401u, the change in coil current TIv flowing through the V-phase coil 401v, and the change in coil current TIw flowing through the W-phase coil 401w.

[0173] According to this configuration, it is possible to diagnose a failure in the encoder 421 based on the amounts of change TIu, TIv, and TIw in the coil currents flowing through the three-phase coils.

[0174] The robot monitoring device 82 according to the embodiment monitors the operation of a robot 2 that includes a robot arm 10 that includes a first joint 171, a motor 401M that is provided in the first joint 171, and an encoder 421 that detects rotation of the rotation shaft of the motor 401M and outputs an encoder value E. The robot monitoring device 82 includes a power signal acquisition unit 820, an encoder value acquisition unit 822, a power signal processing unit 824, an encoder value processing unit 826, and an encoder fault diagnosis unit 828.

[0175] The power signal acquisition unit 820 acquires the power signal of the motor 401M. The encoder value acquisition unit 822 acquires the encoder value E. The power signal processing unit 824 determines whether the rotating shaft is rotating based on the power signal. The encoder value processing unit 826 determines whether the rotating shaft is rotating based on the encoder value E. The encoder fault diagnosis unit 828 diagnoses that the encoder 421 is faulty when the power signal processing unit 824 determines that the rotating shaft is rotating and the encoder value processing unit 826 determines that the rotating shaft has stopped.

[0176] This configuration provides a robot monitoring device 82 that can diagnose a fault in the encoder 421 based on the power signal and the encoder value E, without based on the operation command value M. With this robot monitoring device 82, for example, even if an operation command value M that does not rotate the rotation shaft is output from the robot controller 81 and an event occurs in which the rotation shaft rotates, it can detect a state in which the encoder 421 is faulty. As a result, even if a non-safety encoder is used as the encoder 421, it is possible to accurately diagnose a fault in the encoder 421, and a robot monitoring device 82 that can ensure the safety of the robot system 1 can be realized.

[0177] The robot system 1 according to the embodiment includes a robot 2, a robot controller 81 that controls the operation of the robot 2, and a robot monitoring device 82 according to the embodiment.

[0178] Such a robot system 1 is a system that can provide safety functions that comply with the safety requirements stipulated in the robot safety standard, even when a non-safety encoder is used as the encoder 421. Furthermore, this safety function is realized in the robot monitoring device 82 without relying on the robot controller 81. Therefore, a robot system 1 with high safety functions can be realized.

[0179] Although the encoder fault diagnosis method, robot monitoring device, and robot system of the present invention have been described above based on the illustrated embodiments, the present invention is not limited to the above embodiments.

[0180] For example, the robot monitoring device and robot system of the present invention may be configured such that the configuration of each part of the above-described embodiment is replaced with any configuration having similar functions, or may be configured such that any other components are added to the above-described embodiment.

[0181] Furthermore, the encoder fault diagnosis method of the present invention may be configured by adding any desired process to the above-described embodiment. [Explanation of symbols]

[0182] 1...Robot system, 2...Robot, 4...Base, 8...Robot control device, 9...AC power supply, 10...Robot arm, 11...First arm, 12...Second arm, 13...Third arm, 14...Fourth arm, 15...Fifth arm, 16...Sixth arm, 81...Robot controller, 82...Robot monitoring device, 85...Power cut-off unit, 86...Converter unit, 91...Power supply path, 101...Floor, 171...First joint unit, 172...Second joint unit, 173...Third joint unit, 174...Fourth joint unit, 175...Fifth joint unit, 176...Sixth joint unit, 301...Drive control unit, 301A...Drive control unit, 302...drive control unit, 303...drive control unit, 304...drive control unit, 305...drive control unit, 306...drive control unit, 312...inverter unit, 313...switching element, 314...control circuit, 316L...light-emitting element, 316P...light-receiving element, 316u...voltage value detection unit, 316v...voltage value detection unit, 316w...voltage value detection unit, 317u...current value detection unit, 317v...current value detection unit, 317w...current value detection unit, 401...drive unit, 401M...motor, 401u...U-phase coil, 401v...V-phase coil, 401w...W-phase coil, 402...drive unit, 402M...motor, 403... Drive unit, 403M...motor, 404...drive unit, 404M...motor, 405...drive unit, 405M...motor, 406...drive unit, 406M...motor, 411...angle sensor, 412...angle sensor, 413...angle sensor, 414...angle sensor, 415...angle sensor, 416...angle sensor, 421...encoder, 820...power signal acquisition unit, 822...encoder value acquisition unit, 824...power signal processing unit, 826...encoder value processing unit, 828...encoder fault diagnosis unit, 830...shutdown signal output unit, 862...bridge diode, 864...smoothing capacitor Denser, 912...Processor, 914...Memory, 916...External interface, 922...Processor, 924...Memory, 926...External interface, ADC...Insulated A / D conversion unit, AMP...Amplifier, B...Shutdown signal, E...Encoder value, GND...Ground potential, Iu...Current value, Iv...Current value, Iw...Current value, L1u...U-phase power line, L1v...V-phase power line, L1w...W-phase power line, L2u...U-phase branch line, L2v...V-phase branch line, L2w...W-phase branch line, L3u...U-phase current detection line, L3v...V-phase current detection line, L3w...W-phase current detection line, M...Operation command value,O1...first rotating shaft, O2...second rotating shaft, O3...third rotating shaft, O4...fourth rotating shaft, O5...fifth rotating shaft, O6...sixth rotating shaft, PWC...voltage value measurement unit, PWu...voltage value, PWv...voltage value, PWw...voltage value, R1...input side resistor, R2...shunt resistor, R3...shunt resistor, S102...power signal acquisition process, S104...encoder value acquisition process, S106...power signal processing process, S108...encoder value processing process, S110...encoder fault diagnosis process, S112...power cut-off process, TIu...amount of change, TIv...amount of change, TIw...amount of change, TPWu...amount of change, TPWv...amount of change, TPWw...amount of change, Vu...drive pulse voltage, Vv...drive pulse voltage, Vw...drive pulse voltage,

Claims

1. A method for diagnosing a fault in an encoder that detects rotation of a rotary shaft of a motor provided at a joint of a robot arm and outputs an encoder value, comprising: obtaining a power signal of the motor; obtaining the encoder value; determining whether the rotary shaft is rotating based on the power signal; determining whether the rotary shaft is rotating based on the encoder value; a step of diagnosing that the encoder is faulty when it is determined that the rotating shaft is rotating based on the power signal and that the rotating shaft is stopped based on the encoder value; A fault diagnosis method for an encoder, comprising:

2. 2. The encoder fault diagnosis method according to claim 1, wherein the motor is a brushless motor having three-phase coils consisting of U-phase, V-phase, and W-phase.

3. 3. The encoder fault diagnosis method according to claim 2, wherein the step of acquiring the power signal includes a process of acquiring the power signal while flowing a coil current through the three-phase coils so that an excitation component exceeds zero when a torque component of the motor is zero.

4. 4. The encoder fault diagnosis method according to claim 1, wherein the power signal is composed of two or more of a voltage value in the U-phase coil, a voltage value in the V-phase coil, and a voltage value in the W-phase coil.

5. 4. The encoder fault diagnosis method according to claim 1, wherein the power signal is composed of two or more of the amount of change in voltage in the U-phase coil, the amount of change in voltage in the V-phase coil, and the amount of change in voltage in the W-phase coil.

6. 4. The encoder fault diagnosis method according to claim 1, wherein the power signal is composed of two or more of the current value of the coil current flowing in the U-phase coil, the current value of the coil current flowing in the V-phase coil, and the current value of the coil current flowing in the W-phase coil.

7. 4. The encoder fault diagnosis method according to claim 1, wherein the power signal is composed of two or more of the amount of change in coil current flowing through the U-phase coil, the amount of change in coil current flowing through the V-phase coil, and the amount of change in coil current flowing through the W-phase coil.

8. A robot monitoring device for monitoring the operation of a robot including a robot arm having a joint, a motor provided at the joint, and an encoder that detects rotation of a rotation shaft of the motor and outputs an encoder value, a power signal acquisition unit that acquires a power signal of the motor; an encoder value acquisition unit that acquires the encoder value; a power signal processing unit that determines whether the rotary shaft is rotating based on the power signal; an encoder value processing unit that determines whether the rotary shaft is rotating based on the encoder value; an encoder fault diagnosis unit that diagnoses that the encoder is faulty when the power signal processing unit determines that the rotating shaft is rotating and the encoder value processing unit determines that the rotating shaft is stopped; A robot monitoring device comprising:

9. Robots and a robot controller for controlling the operation of the robot; The robot monitoring device according to claim 8; A robot system comprising:

Images