JP2012055981A - Robot control device and robot control method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stop a servo motor immediately with a dynamic brake and a mechanical brake, while controlling a load on a connection part between the servo motor and a reducer, when an angle sensor falls in an abnormality.SOLUTION: When the abnormality of the angle sensor 160 is detected, a robot control device 200 executes a first braking operation which activates a dynamic brake without activating a mechanical brake, if a total torque value of a braking torque to be generated by the dynamic brake when it is assumed that the dynamic brake has been activated at an estimated rotating speed, and a braking torque to be generated by the mechanical brake 150 when it is assumed that the mechanical brake 150 has been activated exceeds a predetermined upper-limit torque value, and executes a second braking operation which activates the dynamic brake and mechanical brake when the total torque value is equal to or lower than the upper-limit torque value.

Description

  The present invention relates to a technique for controlling a robot equipped with a servo motor, and more particularly, to a technique for stopping a servo motor when an abnormality occurs in an angle sensor connected to the servo motor.

  An angle sensor such as a rotary encoder or a resolver is attached to a servo motor that drives the axis of the robot in order to feedback control the rotation angle. If a failure occurs in the angle sensor or a signal line connecting the angle sensor and the control device is disconnected, the robot axis cannot be accurately driven.

  Therefore, when such an abnormality occurs, it is preferable to stop the servo motor promptly in order to suppress unexpected movement of the robot. In order to stop the servo motor, there are a method of stopping by power generation braking such as a dynamic brake, and a method of stopping by a mechanical brake for maintaining the stop position of the shaft (for example, see Patent Document 1). In order to stop the servo motor more quickly, for example, a dynamic brake and a mechanical brake can be used simultaneously and operated simultaneously.

  However, if the dynamic brake and the mechanical brake are simply operated simultaneously, depending on the rotation speed of the servo motor, the sum of the braking torques of these brakes will increase, and the connection between the servo motor and the reducer will be more than necessary. There was a possibility of burden.

Japanese Patent No. 3494855 Japanese Patent No. 2856253

  In view of the above-mentioned problems, the problem to be solved by the present invention is that when an abnormality occurs in the angle sensor, the load applied to the connecting portion between the servo motor and the speed reducer is suppressed, while the dynamic brake and the mechanical brake are It is to provide a technique for quickly stopping the servo motor using the.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

Application Example 1 A robot control apparatus for controlling a robot including a servo motor, an angle sensor for detecting a rotation angle of the servo motor, and a mechanical brake for stopping the servo motor, The rotation angle of the servo motor is estimated on the basis of a drive control unit that acquires the rotation angle and feedback-controls the drive of the servo motor according to the acquired rotation angle, and an electrical variable of the servo motor. The estimation unit, the abnormality detection unit for detecting whether or not the angle sensor is abnormal, the dynamic brake control unit for controlling the operation of the dynamic brake for the servo motor, and the angle sensor when the abnormality is detected, the estimation It is assumed that the dynamic brake is operated at the determined rotational speed. When the total torque value of the braking torque generated by the dynamic brake and the braking torque generated by the mechanical brake assuming that the mechanical brake is operated exceeds the predetermined torque upper limit value, the mechanical brake is not operated. When the first braking process for operating the dynamic brake is executed and the total torque value is equal to or lower than the torque upper limit value, the second braking process for operating the dynamic brake and the mechanical brake is executed. And a stop control unit.

  According to the above configuration, when an abnormality of the angle sensor is detected, assuming that the dynamic brake is operated at the estimated rotational speed, it is assumed that the braking torque generated by the dynamic brake and the mechanical brake are operated. When the total torque value with the braking torque generated by the mechanical brake exceeds a predetermined torque upper limit value, the dynamic brake is operated without operating the mechanical brake, and the total torque value is equal to or less than the upper torque limit value. To activate the dynamic brake and mechanical brake. Therefore, in the event of an abnormality in the angle sensor, it is possible to stop the servo motor quickly using the dynamic brake and mechanical brake while suppressing the burden on the connection portion between the servo motor and the speed reducer. Become.

Application Example 2 In the robot control apparatus according to Application Example 1, the abnormal stop control unit stores in advance a rotational speed range in which the virtual braking torque total value exceeds the torque upper limit value. Robot control that executes the first braking process when the estimated rotational speed falls within the range, and executes the second braking process when the estimated rotational speed does not fall within the range apparatus.

  With such a configuration, it is easy to execute the first braking process or the second braking process by comparing the estimated rotational speed with a pre-stored rotational speed range. It becomes possible to decide.

[Application Example 3] In the robot control device according to Application Example 2, in the case where the estimated rotation speed is a rotation speed exceeding the range, the abnormal stop control unit is configured so that the estimated rotation speed is When the estimated time to decrease to a rotational speed within the range is estimated, and the estimated time is shorter than the time required for the operation and release of the mechanical brake, the execution of the second braking process is performed. A robot control apparatus that cancels and executes the first braking process.

  With such a configuration, the execution of the braking process can be switched from the second braking process to the first braking process in consideration of the time required for the operation and release of the mechanical brake. When the speed decreases from a high speed to a low speed, it is possible to temporarily suppress the total torque value from exceeding the torque upper limit value.

[Application Example 4] The robot control apparatus according to Application Example 2 or Application Example 3, wherein the abnormal stop control unit performs the estimation when the estimated rotation speed is a rotation speed within the range. Estimating the time when the rotational speed is expected to decrease to a rotational speed lower than the range, and when the estimated time is shorter than the time required for operating the mechanical brake, Robot control device that starts

  With such a configuration, when shifting the braking process from the first braking process to the second braking process, the mechanical brake is operated in consideration of the time required for the actual operation of the mechanical brake. It is possible to start with good timing. Therefore, when the rotational speed is lower than the above range, it is possible to make the braking torques of both the mechanical brake and the dynamic brake work to the maximum torque value.

Application Example 5 In the robot control device according to any one of Application Example 1 to Application Example 4, the torque upper limit value is based on a torque that can be withstood by a reduction gear to which the servo motor is connected. A robot controller that is determined in advance.

  The torque that can be withstood by the reduction gear is, for example, torque that does not cause a shift in a gear that exists at a connection portion between the servo motor and the reduction gear. With such a configuration, it is possible to suppress the occurrence of slipping in the gear that engages the servo motor and the speed reducer. Therefore, for example, when the abnormal state of the angle sensor is recovered and the robot is operated again, it is not necessary to perform recalibration, and the operation can be resumed promptly.

  In addition to the configuration as the robot control device described above, the present invention can be configured as, for example, a robot control method or a computer program for controlling the robot. The computer program may be recorded on a computer-readable recording medium.

It is explanatory drawing which shows schematic structure of the robot system containing a robot control apparatus. It is a block diagram which shows the internal structure of a robot main body and a robot control apparatus. It is a graph which illustrates the variation characteristic of the braking torque of a dynamic brake. It is a flowchart of an abnormal stop process. It is explanatory drawing which shows the example of a 1st threshold value and a 2nd threshold value. It is a flowchart of the abnormal stop process performed in 2nd Example. It is a flowchart of the abnormal stop process performed in 2nd Example. It is explanatory drawing which shows the example of speed fall time and mechanical brake response time.

Hereinafter, embodiments of the present invention will be described based on examples with reference to the drawings.
A. First embodiment:
(A1) Schematic configuration of the robot system:
FIG. 1 is an explanatory diagram showing a schematic configuration of a robot system 10 including a robot control device 200 as an embodiment of the present invention. The robot system 10 is connected to the robot main body 100 configured as an articulated industrial robot, a robot control device 200 for controlling the robot main body 100, and the robot control device 200 to program the operation of the robot main body 100. The teaching pendant 300.

  The robot body 100 includes, for example, a base portion 101 fixed in a factory, a shoulder portion 102 supported by the base portion 101 by a shaft that can be turned in a horizontal direction, and a shoulder portion 102 by a shaft that can be turned in a vertical direction. The lower arm 103 is supported at the lower end thereof, the upper arm 104 is supported at the front end of the lower arm 103 by a shaft that can pivot in the vertical direction, and the tip of the upper arm 104 by the shaft that can pivot in the vertical direction. And a wrist 105 supported by the head. A flange portion 106 that is rotatable in the circumferential direction of the wrist 105 is provided at the tip of the wrist 105. For example, a hand (not shown) that holds a workpiece is attached to the flange portion 106.

  The joint portion connecting the parts of the robot main body 100 described above is provided with a servo motor and a speed reducer for driving the shaft, and an angle sensor for detecting the rotation angle and rotation speed of the servo motor is incorporated. It is. The robot control apparatus 200 according to the present embodiment includes a function (hereinafter also referred to as an emergency stop function) for quickly stopping the servo motor when an abnormality occurs in the angle sensor. Hereinafter, a configuration and processing for realizing the emergency stop function will be described in detail.

(A2) Internal configuration of robot main body and robot control device:
FIG. 2 is a block diagram showing the internal configuration of the robot body 100 and the robot control device 200. The robot body 100 transmits a servo motor 110 configured as a three-phase AC brushless DC motor, a rotary encoder 162 connected to the rotation shaft of the servo motor 110, and power of the servo motor 110 to a joint and a hand. 1 and a mechanical brake 150 that mechanically holds the rotational position of the servo motor 110.

  An angle converter 164 is connected to the rotary encoder 162. The angle converter 164 receives a signal corresponding to the rotation of the servo motor 110 from the rotary encoder 162, and generates angle information representing the rotation angle of the servo motor 110 based on this signal. The angle information generated by the angle converter 164 is input to the robot controller 200 and used as a feedback signal for performing feedback control described later. In the following description, the rotary encoder 162 and the angle converter 164 are collectively referred to as “angle sensor 160”. In this embodiment, the rotation angle of the servo motor 110 is detected by the rotary encoder 162, but may be detected by using a resolver.

  The robot control device 200 includes an inverter 120 that supplies three-phase AC power to the servo motor 110 of the robot main body 100, a drive circuit 140 that performs switching control of the inverter 120 based on a command from the drive control unit 211, And a current detector 130 for detecting a current value of a current flowing between the servo motor 110 and the servo motor 110. The robot control apparatus 200 includes a CPU 210, a ROM 230, and a RAM 240. The CPU 210 loads a predetermined control program 235 stored in the ROM 230 into the RAM 240 and executes it, so that the drive control unit 211, the abnormality detection unit 212, the abnormal stop control unit 213, the rotation speed estimation unit 214, and the dynamic brake control unit 216 and the mechanical brake control unit 217.

  The drive control unit 211 outputs a pulse signal for driving the servo motor 110 to the drive circuit 140 based on the trajectory data 245 stored in the RAM 240. At this time, the drive control unit 211 acquires angle information from the angle sensor 160 of the robot body 100, and feedback-controls the drive of the servo motor 110 based on the angle information. The drive circuit 140 drives the inverter 120 based on the pulse signal input from the drive control unit 211 and rotates the servo motor 110.

  The abnormality detection unit 212 detects whether or not an abnormality has occurred in the angle sensor 160. The abnormality detection unit 212 is large when the angle information cannot be acquired from the angle sensor 160 due to, for example, the disconnection of the signal line between the robot main body 100 and the robot control device 200 or when the command value output by the drive control unit 211 is large. When a different rotation angle or rotation speed is acquired, or when an error signal is received from the angle sensor 160, it is determined that an abnormality has occurred in the angle sensor 160.

  The abnormal stop control unit 213 executes an abnormal stop process for urgently stopping the servo motor 110 when the abnormality detection unit 212 detects an abnormality of the angle sensor 160. Details of the abnormal stop process will be described later.

  The dynamic brake control unit 216 causes the servo motor 110 to operate a dynamic brake (also referred to as a short circuit brake) in response to a command from the abnormal stop control unit 213. Specifically, the dynamic brake control unit 216 controls the switching element of the inverter 120 through the drive circuit 140 and forcibly shorts the terminals of the servo motor 110. Then, since the rotational energy of the servo motor 110 is consumed by the heat generated by the servo motor 110 itself, the servo motor 110 can be stopped.

  FIG. 3 is a graph illustrating the fluctuation characteristics of the braking torque of the dynamic brake. The horizontal axis of this graph represents the rotational speed of the servo motor 110, and the vertical axis represents the braking torque of the dynamic brake corresponding to the rotational speed. As shown in this graph, in general, the braking torque of the dynamic brake operated by the servo motor 110 for the robot becomes higher as the rotation speed of the servo motor 110 increases, and a certain rotation speed (in the case of FIG. 3). Has a characteristic of gradually lowering above about 800 rpm).

  The mechanical brake control unit 217 (FIG. 2) operates the mechanical brake 150 of the robot body 100 in response to a command from the abnormal stop control unit 213. The mechanical brake control unit 217 has a function of maintaining the rotational position of the servo motor 110 by operating the mechanical brake 150 even when the power of the robot system 10 is turned off regardless of the command from the abnormal stop control unit 213.

The rotation speed estimation unit 214 acquires a current value from the current detector 130 when the dynamic brake is operated by the dynamic brake control unit 216, and estimates the rotation speed of the servo motor 110 according to the current value. At this time, the current value acquired from the current detector 130 is referred to as a dynamic brake current value. The rotational speed of the servo motor 110 can be estimated by referring to a map or table in which the relationship between the dynamic brake current value and the rotational speed of the servo motor 110 is recorded in advance. In addition, the rotational speed of the servo motor 110 can also be estimated based on other electrical variables generated with the rotation of the servo motor 110, such as a voltage change of the servo motor 110. Further, the rotation angle (electrical angle) of the servo motor 110 is estimated from the dynamic brake current value, and the amount of change of the estimated rotation angle within a certain time is calculated as shown in the following equation (1): It is also possible to estimate the rotational speed.
Rotation speed = (Rotation angle at n-1 o'clock -Rotation angle at n o) / Fixed time (1)

  2 shows the internal configuration of the robot body 100 and the internal configuration of the robot control apparatus 200 for one joint portion, the other joint portions also have the same internal configuration. Note that one set of CPU 210, ROM 230, and RAM 240 is provided for each robot control device 200, and each functional unit 211 to 217 realized by the CPU 210 is provided for each joint.

(A3) Abnormal stop processing:
FIG. 4 is a flowchart of the abnormal stop process executed by the abnormal stop control unit 213 of the robot control apparatus 200 in order to realize the emergency stop function described above. This abnormal stop process is a process executed when an abnormality of the angle sensor 160 is detected by the abnormality detection unit 212.

  When the abnormal stop process is started, first, the abnormal stop control unit 213 starts to acquire the rotation speed estimated from the rotation speed estimation unit 214 (step S100). Then, the abnormal stop control unit 213 determines whether or not the estimated value is included in a range between the first threshold Th1 and the second threshold Th2 (Step S105).

  FIG. 5 is an explanatory diagram illustrating an example of the first threshold Th1 and the second threshold Th2. FIG. 5 shows the braking torque of the dynamic brake (see FIG. 3) according to the rotational speed of the servo motor 110, and the braking torque of both when assuming that the dynamic brake and the mechanical brake 150 are operated simultaneously. The total value is shown according to the rotation speed of the servo motor 110. Further, in FIG. 5, a torque upper limit value TL that can be withstood by the reduction gear 170 is indicated by a thick horizontal line. This torque upper limit value TL represents the upper limit value of the braking torque at which no slip occurs between the rotating shaft of the servo motor 110 and the fastening portion (gear) of the speed reducer 170 due to abrupt braking of the servo motor 110.

  The first threshold value Th1 and the second threshold value Th2 are set to rotation speeds at which the sum of the braking torques of the dynamic brake and the mechanical brake 150 matches the torque upper limit value TL. That is, when the rotational speed of the servo motor 110 is included in the range between the first threshold Th1 and the second threshold Th2, if both the dynamic brake and the mechanical brake 150 are operated, the total braking torque is obtained. The value exceeds the torque upper limit value TL that the speed reducer 170 can tolerate. On the other hand, when the rotational speed of the servo motor 110 is equal to or higher than the second threshold Th2 or equal to or lower than the first threshold Th1, the braking torque is applied even if both the dynamic brake and the mechanical brake are operated. Is equal to or lower than the torque upper limit value TL that the reduction gear 170 can tolerate.

  In step S105, when it is determined that the estimated value of the rotational speed is included in the range between the first threshold value Th1 and the second threshold value Th2, the abnormal stop control unit 213 includes the dynamic brake control unit. 216 is controlled and the 1st braking process which operates only a dynamic brake is performed (Step S110). On the other hand, when it is determined that the estimated value of the rotational speed is equal to or less than the first threshold Th1 or equal to or greater than the second threshold, the abnormal stop control unit 213 includes the dynamic brake control unit 216 and the mechanical brake. The controller 217 is controlled to execute a second braking process for operating both the dynamic brake and the mechanical brake 150 (step S115).

  When the first braking process or the second braking process is executed as described above, the abnormal stop control unit 213 determines whether the servo motor 110 has stopped (step S120). Whether or not the servo motor 110 has stopped can be determined that the servo motor 110 has stopped when the rotation speed estimated by the rotation speed estimation unit 214 becomes zero. If it is determined that the servo motor 110 has not stopped, the abnormal stop control unit 213 returns the process to step S105 and repeatedly executes the series of processes described above. On the other hand, if it is determined that the servo motor 110 has stopped, the abnormal stop control unit 213 ends the abnormal stop process. According to the abnormal stop process described above, for example, if the rotation speed of the servo motor 110 is 3000 at the time when the abnormality occurs in the angle sensor 160, the torque fluctuation as shown by the one-dot chain line in FIG. Thus, braking to the servo motor 110 is performed.

  According to the robot control apparatus 200 of the present embodiment described above, even when the abnormality occurs in the angle sensor 160, even if the dynamic brake and the mechanical brake 150 are simultaneously operated, the total value of the braking torque is reduced by the speed reducer 170. If the allowable torque upper limit value TL is not exceeded, both brakes are operated simultaneously. On the other hand, when these brakes are operated simultaneously, if the total value of the braking torque exceeds the torque upper limit value TL that the speed reducer 170 can tolerate, only the dynamic brake is operated. Therefore, the servo motor 110 can be quickly stopped without imposing a burden on the reduction gear 170 more than necessary. In addition, by controlling the dynamic brake and the mechanical brake 150 as described above, it is possible to prevent the speed reducer 170 from being burdened more than necessary. The shift of the gear is suppressed from occurring. Therefore, it is not necessary to recalibrate the rotation angle when the robot system 10 is re-operated, and the operation can be resumed promptly. The mechanical brake 150 is basically a brake for maintaining the posture of the robot body 100 in a stationary state, and therefore the braking force is not so strong. On the other hand, in the case of the dynamic brake, when the rotational speed of the servo motor 110 decreases to a rotational speed (second threshold Th2) at which the total value of the braking torques of both brakes exceeds the torque upper limit value TL, the braking torque (See FIG. 5). Therefore, even if the mechanical brake 150 is released and the overall braking force temporarily decreases, the braking force of the dynamic brake is expected to return to a value close to the original braking force (the total braking torque value of both brakes). it can. Therefore, even if the mechanical brake 150 is temporarily released, the braking force of the dynamic brake is sufficient, so that the braking force for decelerating the servo motor 110 is not critically insufficient.

  In this embodiment, when the dynamic brake and the mechanical brake 150 are simultaneously operated, the total brake torque exceeds the torque upper limit value TL that the speed reducer 170 can tolerate. Instead, activate the dynamic brake. Therefore, even in such a situation, the rotational speed of the servo motor 110 can be accurately estimated based on the dynamic brake current value. As a result, the timing at which the mechanical brake 150 can be actuated can be obtained accurately due to the decrease in the rotational speed. Therefore, when the rotational speed of the servo motor 110 decreases, not only the dynamic brake but also the mechanical brake 150 is operated simultaneously. Therefore, the braking torque characteristic of the dynamic brake, in which the braking torque becomes weak when the rotational speed is low, can be compensated by the braking torque of the mechanical brake 150.

  Further, in this embodiment, when the dynamic brake and the mechanical brake 150 are simultaneously operated, the total value of the braking torque exceeds the torque upper limit value TL that the speed reducer 170 can tolerate. Is stopped and braking is performed only by dynamic braking. Therefore, measures such as newly adding dynamic brake resistance for each axis to suppress the total braking torque, and measures to secure holding force at each arm stop position while introducing a mechanical brake with weak braking torque. There is no need to do. Therefore, the braking torque at the time of emergency stop can be easily controlled without increasing the cost and size of the robot body 100.

  In the present embodiment, the abnormal stop process described above can be executed by a function realized by the CPU 210 without newly installing special hardware in the robot body 100. Therefore, the above-described emergency stop function can be easily added to an existing robot system that is already arranged in the production facility.

B. Second embodiment:
In the first embodiment described above, the dynamic brake and the mechanical brake 150 depend on whether or not the estimated rotation speed of the servo motor 110 is included in the range between the first threshold Th1 and the second threshold Th2. Was controlled. In contrast, in the second embodiment, the dynamic brake and the mechanical brake are controlled in consideration of the time during which the mechanical brake 150 is mechanically operated. The apparatus configuration of this embodiment is the same as that of the first embodiment.

  6 and 7 are flowcharts of the abnormal stop process executed in the second embodiment. Hereinafter, the abnormal stop process will be described with reference to FIG. FIG. 8 is an explanatory diagram illustrating an example of a speed reduction time and a mechanical brake response time, which will be described later. In this embodiment, when this abnormal stop process is executed, first, the abnormal stop control unit 213 starts to acquire the rotational speed estimated from the rotational speed estimation unit 214 (step S200). And it is judged whether this estimated value is larger than 2nd threshold value Th2 (step S205).

  When the estimated value is larger than the second threshold Th2, the abnormal stop control unit 213 estimates the time DT1 (see FIG. 8) until the rotation speed decreases to the second threshold Th2 (step S210). . This time DT1 (hereinafter referred to as “speed reduction time DT1”) can be calculated based on, for example, the relationship between the current rotational speed and the inertia of the arm or workpiece. When the abnormal stop control unit 213 estimates the speed reduction time DT1, the speed reduction time DT1 and the time required for the mechanical brake 150 to be mechanically operated and released (hereinafter referred to as “mechanical brake response time x”). 8), it is determined whether or not the estimated speed reduction time DT1 is shorter than the mechanical brake response time x (step S215). The mechanical brake response time x can be set in advance by actually measuring the time for operating and releasing the mechanical brake 150, for example.

  When the speed decrease time DT1 is shorter than the mechanical brake response time x, even if the mechanical brake 150 is operated at the current rotational speed, the mechanical brake 150 is not yet reduced until the rotational speed decreases to the second threshold Th2. Will not be released in time. That is, there is a possibility that both the dynamic brake and the mechanical brake 150 are temporarily activated immediately after the rotation speed is lowered from the second threshold Th2. Therefore, when the mechanical brake response time x is longer than the estimated speed reduction time DT1, the abnormal stop control unit 213 is a case where the estimated rotational speed exceeds the second threshold Th2. However, the first braking process for operating only the dynamic brake is executed (step S220). On the other hand, when the mechanical brake response time x is shorter than the speed reduction time DT1, the speed reduction time DT1 has a margin. A second braking process for simultaneously operating the mechanical brake 150 is executed (step S225).

  Thereafter, the abnormal stop control unit 213 repeats the processes in steps S205 to S225 described above until the estimated rotation speed becomes equal to or less than the second threshold Th2. In step S205, when it is determined that the estimated rotation speed is equal to or less than the second threshold Th2, the abnormal stop control unit 213 determines whether or not the estimated rotation speed is greater than the first threshold Th1. Is determined (step S230). If the estimated rotation speed is greater than the first threshold Th1 (that is, if the estimated rotation speed is within the range of the first threshold Th1 and the second threshold Th2), the abnormal stop control unit 213 A time DT2 (see FIG. 8) until the rotation speed decreases to the first threshold Th1 is estimated (step S235). This time DT2 (hereinafter referred to as “speed reduction time DT2”) can also be calculated based on, for example, the relationship between the current rotational speed and the inertia of the arm or workpiece, similarly to the speed reduction time DT1. When the abnormal stop control unit 213 estimates the speed reduction time D2, the speed reduction time D2 and the time required for the mechanical brake 150 to be mechanically operated (hereinafter referred to as “mechanical brake response time y”). 8), it is determined whether or not the estimated speed reduction time DT2 is shorter than the mechanical brake response time y (step S240). The mechanical brake response time y can be set in advance, for example, by measuring the time from when the operation start command is given to the mechanical brake 150 until the actual braking torque is applied.

  When the speed decrease time DT2 is shorter than the mechanical brake response time y, the abnormal stop control unit 213 gives an operation start command for the mechanical brake 150 to the mechanical brake control unit 217 (step S245). . By doing so, the braking torque of the mechanical brake 150 can be applied in a timely manner at the same time as the rotational speed reaches the first threshold value Th1. On the other hand, when the speed reduction time DT2 is longer than the mechanical brake response time y, the abnormal stop control unit 213 executes a first braking process that activates only the dynamic brake (step S250). If it is determined in step S230 that the estimated rotational speed is smaller than the first threshold value Th1, the abnormal stop control unit 213 operates the second braking process for operating both the dynamic brake and the mechanical brake 150. Is executed (step S255). The abnormal stop control unit 213 repeatedly executes the processes in steps S230 to S255 described above until it is determined that the servo motor 110 has stopped (step S260).

  According to the abnormal stop process of the second embodiment described above, the same effect as that of the first embodiment can be obtained, and the mechanical brake 150 is actually used when the rotational speed becomes lower than the second threshold Th2. In consideration of the time for activation and release, switching from the second braking process to the first braking process can be performed. For this reason, it is possible to prevent both the mechanical brake 150 and the dynamic brake from being activated immediately after the estimated rotational speed becomes equal to or less than the second threshold Th2. In addition, according to the present embodiment, when switching from the first braking process to the second braking process, an operation start command is given to the mechanical brake 150 in consideration of the time during which the mechanical brake 150 is actually operated. be able to. Therefore, when the estimated rotation speed becomes lower than the first threshold Th1, the braking torque of the mechanical brake 150 can be applied with good timing. As a result, when the rotational speed is lower than the first threshold value Th1, the braking torque of both the mechanical brake 150 and the dynamic brake can be applied using the full range up to the torque upper limit value. Note that either the processing based on the mechanical brake response time x and the speed reduction time DT1 or the processing based on the mechanical brake response time y and the speed reduction time DT2 can be omitted.

C. Variations:
As mentioned above, although several Example of this invention was described, this invention is not limited to these Examples, A various structure can be taken in the range which does not deviate from the meaning. For example, a function realized by software may be realized by hardware and vice versa. In addition, for example, the following modifications are possible.

  In the above embodiment, it is determined whether to execute the first braking process or the second braking process by comparing the estimated rotation speed with a predetermined threshold (rotation speed). On the other hand, the first braking process and the second braking process are performed by estimating the rotational speed, obtaining a braking torque corresponding to the rotational speed, and comparing the braking torque with a predetermined threshold (torque). It may be determined which to execute.

  In the above embodiment, the mechanical brake is not used at all when the estimated rotational speed is within the range between the first threshold Th1 and the second threshold Th2. On the other hand, for example, the dynamic brake is operated and the mechanical brake is operated in a time-sharing manner so that the temporal average value of the braking torque may be controlled so as not to exceed the torque upper limit value TL. .

DESCRIPTION OF SYMBOLS 10 ... Robot system 100 ... Robot main body 101 ... Base part 102 ... Shoulder part 103 ... Lower arm 104 ... Upper arm 105 ... Wrist 106 ... Flange part 110 ... Servo motor 120 ... Inverter 130 ... Current detector 140 ... Drive circuit 150 ... Machine Brake 160 ... Angle sensor 162 ... Rotary encoder 164 ... Angle converter 170 ... Reducer 200 ... Robot controller 210 ... CPU
211 ... Drive control unit 212 ... Abnormality detection unit 213 ... Abnormal stop control unit 214 ... Rotational speed estimation unit 216 ... Dynamic brake control unit 217 ... Mechanical brake control unit 230 ... ROM
235 ... Control program 240 ... RAM
245 ... Track data 300 ... Teaching pendant

Claims (6)

A robot control device for controlling a robot comprising a servo motor, an angle sensor for detecting a rotation angle of the servo motor, and a mechanical brake for stopping the servo motor,
A drive control unit that obtains the rotation angle from the angle sensor and feedback-controls the drive of the servo motor according to the obtained rotation angle;
An estimation unit for estimating a rotation speed of the servo motor based on an electrical variable of the servo motor;
An abnormality detection unit for detecting the presence or absence of abnormality of the angle sensor;
A dynamic brake control unit for controlling the operation of a dynamic brake for the servo motor;
When abnormality of the angle sensor is detected, when it is assumed that the dynamic brake is operated at the estimated rotational speed, and the braking torque generated by the dynamic brake and the mechanical brake are operated When a torque total value with a braking torque generated by the mechanical brake exceeds a predetermined torque upper limit value, a first braking process for operating the dynamic brake without operating the mechanical brake is executed, and the torque total When the value is equal to or lower than the torque upper limit value, an abnormal stop control unit that executes a second braking process for operating the dynamic brake and the mechanical brake;
A robot control device comprising: The robot control device according to claim 1,
The abnormal stop control unit stores in advance a rotational speed range in which the total torque value exceeds the torque upper limit value, and the first braking process is performed when the estimated rotational speed falls within the range. A robot controller that executes and executes the second braking process when the estimated rotational speed does not fall within the range. The robot control device according to claim 2,
The abnormal stop control unit estimates a time during which the estimated rotation speed is expected to decrease to a rotation speed within the range when the estimated rotation speed exceeds the range, and the estimation A robot control device that cancels the execution of the second braking process and executes the first braking process when the set time is shorter than the time required to activate and release the mechanical brake; The robot control device according to claim 2 or 3, wherein
The abnormal stop control unit estimates a time when the estimated rotation speed is expected to decrease to a rotation speed lower than the range when the estimated rotation speed is a rotation speed within the range, A robot control device that starts the operation of the mechanical brake when the estimated time becomes shorter than the time required for the operation of the mechanical brake. The robot control device according to any one of claims 1 to 4, wherein:
The robot control apparatus, wherein the torque upper limit value is determined in advance based on a torque that can be withstood by a reduction gear connected to the servo motor. A control method for a robot comprising a servo motor, an angle sensor for detecting a rotation angle of the servo motor, and a mechanical brake for stopping the servo motor,
(A) obtaining the rotation angle from the angle sensor, and feedback controlling the drive of the servo motor according to the obtained rotation angle;
(B) detecting the presence or absence of abnormality of the angle sensor;
(C) when an abnormality of the angle sensor is detected, estimating a rotation speed of the servo motor based on an electrical variable of the servo motor;
(D) braking torque generated by the dynamic brake when the servo motor is operated at the estimated rotational speed, and braking generated by the mechanical brake when the mechanical brake is operated. Executing a first braking process for operating the dynamic brake without operating the mechanical brake when a total torque value with a torque exceeds a predetermined torque upper limit value;
(E) executing a second braking process for operating the dynamic brake and the mechanical brake when the total torque value is equal to or less than the torque upper limit value;
A control method comprising:

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