JP2001198870A - Controller for robot - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a controller stably realizing highly accurate force control even to a hard object and at the same time realizing having a flexible characteristic when contacted in any portion of an arm. SOLUTION: This controller for a robot applies state feedback of position and speed of the robot, and it is provided with a control circuit for a motor driving revolute joints and a force control circuit based upon feedback from a force sensor. It is provided with means 101 and 102 calculating accelerating torque and torque for maintaining speed of the motor from an operation command and/or feedback of the motor, a means 108 adding the accelerating torque and the speed maintaining torque for calculating torque necessary for motion of the motor, a means 109 calculating torque necessary for a correcting operation from a correcting operation command outputted from a force control part 110, and a means 103 limiting generating torque of the robot from the torque necessary for the motion of the motor and the torque necessary for the correcting operation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control device using force sensor feedback in a robot control device, and more particularly to a control device which realizes control suitable for performing a contact work such as an assembly work.

[0002]

2. Description of the Related Art As shown in FIG. 6, a robot 601 may perform a work while applying a force to a work object 604. At this time, according to the information of the force sensor 602 attached to the hand, the work object 6
By controlling the force applied to 04, it is possible to perform the work while applying a desired force. As described above, impedance control is known as one of the force control methods for the robot arm to perform a contact operation on an object. This is shown in FIG.
The movement of the tip of the robot arm is controlled according to the reaction force to the work object 705 so that the dynamic response of No. 4 becomes a mechanical impedance composed of a virtually set inertia 701, viscosity 702, and rigidity 703. Things. In this control, an external force is measured by a force sensor 602 provided at the tip of the robot arm, and a deviation from a target trajectory is calculated by a target impedance model 802 as shown in FIG.
This is a control method in which the sum of the target trajectory and the deviation is given to the servo controller 801 as a motion command. FIG. 9 shows a block diagram of a conventional impedance control. Orbit generator 90
In step 1, an increment value is generated from the designated coordinate system to the reference coordinate system for the current robot command position. Since the reference coordinate system is usually represented by an orthogonal coordinate system centered on the base of the robot, it is converted into an angle increment value of the joint coordinate system of the robot in order to actually perform the operation of the robot. After that, it is sent to the position / speed control unit 902 of each joint as a rotation command to the motor. The reaction force detected by the force sensor 907 attached to the end of the robot arm is coordinate-transformed into force / torque in the working coordinate system, and the impedance control unit 910 creates a correction amount for the target trajectory. The impedance model is represented by equation (1).

(Equation 1) Here, M is virtual inertia, B is virtual viscosity, K is virtual rigidity, x is displacement from the equilibrium point (position correction amount), and F is measured force. A correction amount x is calculated from this equation, and a value obtained by adding the correction amount to the position command value output from the trajectory generation unit 901 is output to the position / speed control unit 902 as a new position command value. The position / velocity control unit 902 outputs a control command to the robot 906 based on the new position command value, and the control command is amplified by the amplifier 905 and then given to the robot 906. Thus, by controlling the position according to the reaction force detected by the robot arm tip, it is possible to control the force applied to the object. In this control method, since the deviation based on the impedance model is input to the servo system as a speed or position command, it can be easily realized by an industrial robot of the current position control method.

[0003]

However, it is known that when the virtual viscosity is reduced, the stability of the control system decreases when the virtual system comes into contact with a hard object. In addition, it is known that a control system becomes unstable when a robot arm to which force control is applied is brought into contact with a highly rigid object without being limited to impedance control. The main reasons for this instability include the following. 1) Contact with an object having high rigidity means that the gain of the force control loop increases, and the contact becomes unstable due to a delay (phase delay) of the response of the robot arm to the force feedback. 2) If the virtual viscosity of the impedance model is reduced,
A sudden phase delay occurs near the resonance frequency. Therefore, in the case of impedance control, it is necessary to set the virtual viscosity to be large in order to stabilize contact, and the degree of freedom in setting is reduced. Also, if the virtual viscosity is large, the responsiveness to an external force is reduced, and the contact force is increased, which may damage the target object or the robot arm. For this reason, it is necessary to make the approach speed to the target sufficiently small. As described above, there has been a problem that the stability is lost and the robot arm rebounds, or an excessive contact force is generated on the target object, thereby making it difficult to perform a highly accurate contact operation. In addition to this, not only impedance control but also other force control methods have similar problems. further,
Because the reaction force cannot be detected by the force sensor at the base of the part than the part where the force sensor is mounted, a large control deviation occurs when the robot arm comes into contact with surrounding objects, and the target object and the robot itself may be damaged was there. Therefore, the present invention provides a control device that realizes stable and high-precision force control even for a hard object, and also has a flexible characteristic even when it comes into contact with any part of the arm. .

[0004]

SUMMARY OF THE INVENTION In order to solve the above problems, the present invention provides a feedback control from a force sensor to a control circuit of a motor for driving a joint by providing a state feedback of the position and speed of a robot. ,
A means for calculating a torque for maintaining the acceleration torque and the speed of the motor from a motor operation command or / and a feedback, and adding the acceleration torque and the speed maintenance torque to a motor necessary for the movement of the motor. Means for calculating a torque, and means for calculating a torque required for the correction operation from a correction operation command output from the force control unit, wherein the torque required for the movement of the motor and the torque required for the correction operation Means for limiting the torque generated by the robot from the above, or means for limiting the torque generated by the robot from the torque required for the movement of the motor, and means for adding the torque required for the correction operation to the torque command. It is assumed that.

[0005]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a first embodiment of the present invention. 101 is a trajectory generation unit, 102 is a position / speed control unit, 103 is a torque limit processing unit, 104 is a gravity compensation torque calculation unit, 105 is an amplifier, 106 is a robot,
107 is a force sensor, 108 is a motion command torque calculator, 1
Reference numeral 09 denotes a corrected operation torque calculation unit, and reference numeral 110 denotes an impedance control unit. The trajectory generation unit 101 generates an increment value converted from the designated coordinate system to the reference coordinate system for the current command position of the robot. Since the reference coordinate system is usually represented by a rectangular coordinate system centered on the base of the robot,
It is converted into an angle increment value of the joint coordinate system of the robot in order to actually perform the operation of the robot. Then, it is sent to the position / speed control unit 102 of each joint as a rotation command to the motor. The processing system of the position / speed control unit 102 performs position control and speed control. In general, proportional control is used in position control, and proportional integral control or the like is used in a speed control system. Here, first, a case where no force is applied to the tip of the robot arm will be described. Motion command torque calculator 10
The control system 8 is a part for calculating the torque required for the motion command. The torque required for normal robot motion is (1) acceleration torque for accelerating the inertial load of both the robot arm and the robot arm tip, and (2) speed maintaining torque for maintaining speed in a normal motion state. 2
Kind. The required acceleration torque is calculated from the product of inertia and acceleration. One of the following methods is used for the information of inertia. 1) A value fluctuating according to the movement of the robot is obtained by calculation. 2) Estimate using a parameter identification technique such as an adaptive observer. 3) Use typical inertia values. The speed maintaining torque is almost equal to the value of the dynamic friction. Therefore, the required torque can be obtained from the relationship between the speed and the friction obtained in advance, based on the current command speed. However, the acceleration torque and the speed maintaining torque are relative to the output of the trajectory generation unit 101 before adding the operation correction amount output from the impedance control unit 110. The added value of the torque calculated by the motion command torque calculation unit 108 is a value substantially equal to the torque at which the robot moves. The calculation result is input to the torque limit processing unit 103.
Here, the position / speed control unit 102 is
Is calculated, and the torque is limited. The limit value can be obtained by providing an appropriate width to the value calculated by the exercise command torque calculator 108. The reason for providing an appropriate width here is that the command torque and the generated torque do not always coincide with each other, so that the error is absorbed and that the time-dependent deviation of the generated torque is absorbed. . Compensation for time deviation means that the torque at the moment when the generated torque is calculated by the command value and the torque generated by the position / speed control unit 102 may cause a time deviation. Absorb by width. This time lag can also be absorbed by inserting a filter for compensating for a time lag into the output of the motion command torque calculator 108. The filter can be adjusted by a general first-order lag filter or a second-order lag filter. The physical effect of providing such a torque limit will be described. In the position / speed control unit 102, when an external force acts on the robot, a position deviation and a speed deviation occur. The position deviation is multiplied by a constant to produce a speed command, and the speed deviation is subjected to proportional integral control, and the output thereof becomes a motor torque command. When a special external force does not act on the robot, two torques to be generated by the motor are acceleration torque and speed maintaining torque. In order for the robot to move in a normal operation, the above torque may be generated. However, when a force acts on the robot from the outside (or the robot itself contacts the outside), the robot operates due to the external force, and the above-described control deviation occurs. Therefore, the command torque at that time deviates from the torque limit range calculated by the motion command torque calculation unit 108. If there is no limit, the maximum possible torque will be generated. If the restriction is moderate, a torque within the restriction is generated, and a deviation is allowed by an external force, that is, the robot moves by an external force.
In a robot moving in the direction of gravity, the gravitational torque is calculated and compensated by the gravitational compensation torque calculation unit 104 according to the posture of the robot. In such a case, the robot arm does not fall due to gravity.

Next, a method of limiting the torque will be specifically described with reference to FIG. FIG. 4 (a) shows the robot arm 1
This is a case where attention is paid to the motion of one joint 401. Joint 40
It is assumed that the motion 1 starts accelerating at time P1, starts at a constant speed at time P2, starts deceleration at time P3, and stops at time P4. A specific motion command for this purpose is given by a motion command for acceleration, constant velocity, and deceleration as shown in FIG. 4 (b). FIG. 4 (c) shows the calculation result of the motion command torque calculator 108 (FIG. 1), and FIG. 4 (d).
FIG. 8 is a diagram showing a result (thick line) of a result obtained by passing a primary filter through an acceleration torque calculation result (dotted line) in consideration of a time delay. The thick line in FIG. 4 (e) is the same as the thick line in FIG. 4 (d) and shows the result after passing through the primary filter, and the thin line is the torque limiting processing unit 1.
The upper limit value and the lower limit value of the torque limit at 03 are shown. In other words, this torque limitation allows the robot arm to flexibly follow the external force according to the external force, even if the robot arm collides with a peripheral object and the control deviation increases, while compensating for the torque for the motion command. Since the torque limit processing unit 103 realizes flexible control without using a sensor, any part of the robot arm can have flexible characteristics. Next, a case where the tip of the robot arm contacts the target will be described. The impedance control unit 110 (FIG. 1) is a block for performing force control by force sensor feedback. The reaction force measured by the force sensor 107 attached to the tip of the robot arm is coordinate-transformed into a working coordinate system, and then a position correction amount is calculated according to a desired impedance model. The position correction amount is converted into an incremental value for each joint of the robot by coordinate conversion, and is added to the incremental value generated by the trajectory generating unit 101. Further, the correction operation torque calculation unit 109
In, the torque for realizing the target impedance is calculated. Here is an example. Here, when the acceleration torque and the speed maintaining torque are calculated in the same manner as in the motion command torque calculation unit 108, the speed and the acceleration itself fluctuate greatly, so that the torque input to the torque limitation processing unit 103 also fluctuates greatly. It will be something. Therefore,
The torque for realizing the impedance is represented by Expression (2).

(Equation 2) Here, T _imp is the torque for realizing the impedance, T _fric is the torque for the friction of each joint, J ^T is the transposed matrix of the Jacobian matrix, and F _ref is the force for the impedance (inertia, viscosity, rigidity). . F _ref can be calculated according to the impedance model set by the impedance control unit 110. Also, T _fric
Is calculated at the speed of the output of the impedance control unit 110, since the speed is not stable, for example,
Based on carrying out calculation with the information of the F _ref. Here, by inputting the value output from the correction operation torque calculating section 109 to the torque limiting processing section 103, the torque limiting processing section 10
In 3, an upper limit and a lower limit torque limit values, which are obtained by adding the motion command torque and the correction operation torque, are generated. Next, the function of the torque limit processing unit 103 will be described. When the work is performed by the tip of the robot arm being in contact with the target object, if the target object is a hard object, it will be in a controlly unstable state such as rebound and vibration. As described above, if the torque is not limited at this time, as much torque as possible is generated, and large bounces and vibrations occur. When the torque command is output from the position / speed control unit 102 when the torque command is moderately limited by the torque limit processing unit 103, the torque command is stuck to the upper or lower torque limit value, or even if the torque command is vibrated, the torque Since the value falls within the range, stable contact is realized. Further, since a certain width is provided, it is possible to absorb a calculation error of torque for realizing the impedance according to the equation (2).

FIG. 2 shows a second embodiment.
201 is a trajectory generator, 202 is a position / velocity controller, 20
Reference numeral 3 denotes a torque limit processing unit, 204 denotes a gravity / friction compensation torque calculation unit, 205 denotes an amplifier, 206 denotes a robot, 207 denotes a force sensor, 208 denotes a motion command torque calculation unit, 209 denotes a correction operation torque calculation unit, and 210 denotes impedance control. Department. In the first embodiment, the output of the correction operation torque calculation unit 109 is input to the torque limitation processing unit 103, but here, as shown in FIG.
It is characterized in that the output at step S09 is directly added to the command torque after the torque limiting process. Also in this case, the position / speed control unit 2
Since the torque of the torque command from 02 is limited by the torque limitation processing unit 203, the same effect as described above can be expected. That is, precise force control can be performed while maintaining contact stability. FIG. 3 shows a third embodiment. 301 is a trajectory generation unit, 302 is a position / speed control unit, 303 is a torque limit processing unit, 304 is a gravity / friction compensation torque calculation unit, 305 is an amplifier, 306 is a robot,
307 is a force sensor, 308 is a motion command torque calculator, 3
Reference numeral 09 denotes a correction operation torque calculation unit, and reference numeral 310 denotes an impedance control unit. Here, the feature is that in 304, in addition to the gravity compensation torque calculation unit 108 of FIG. 1, a friction compensation torque calculation unit is added by state feedback from the robot. In consideration of this, the speed maintaining torque is calculated by the motion command torque calculating unit 308. By adding friction compensation in this way, there is an effect that the flexibility of each joint is improved. Here, the impedance control has been described as an example, but the same problem can be solved by various force controls using the force feedback of the force sensor.

FIG. 5 shows a hardware configuration used in each of the above embodiments. Trajectory generation unit 10 in FIG.
1 corresponds to the trajectory generation block 500 and the trajectory generation block 510 in FIG. In the trajectory generation block 500, data taught by the teaching pendant is stored in the nonvolatile memory 506. The mechanical and control parameters of the robot are also stored in this non-volatile memory, and are shared by the bus. The function of orbit generation is realized by the CPU 503 executing a program stored in the ROM 504. Orbit generation block 5
In 10, the trajectory generation and coordinate conversion functions are stored in the ROM 5.
13 is realized by the CPU 512 executing the program stored in the CPU 13. Also, the position / speed control unit, the motion command torque calculation unit 108, the impedance control unit 110, the correction operation torque calculation unit 109, the torque limit processing unit 103, and the like in FIG. 1 are realized as software of the motion control block 520 in FIG. Is done. FIG. 1, FIG. 2, FIG.
The position / speed control and force control in the figure are programmed in the ROM 523 in the servo board 521 of the motion control block 520. When the CPU 522 reads and executes this program, the torque limiting process is actually performed, and the result is output to the servo amplifier 526. Also, the force sensor and force information are taken in by the sensor block 53.
0. The detection signal from the force sensor 536 is read by the AD conversion unit 533 in the sensor
The CPU 532 processes the detection signal according to the instruction of M534, and the position correction amount or the like is output to the bus conversion unit 535 by force control means such as impedance control. Since the blocks 500, 510, 520, and 530 are connected by the shared bus 550, the sensor block 5
The position correction amount from 30 is sent to the motion control block 520 via the shared bus 550 and enters the CPU 522 via the bus conversion unit 525. The CPU 522 reads the position correction amount, executes a torque limiting process, and
The result is output to the servo amplifier 526 via 24. The servo amplifier 526 drives the robot 540, and the rotation status of the motor of the robot is fed back to the servo amplifier 526 by the servo motor encoder 541.

[0009]

As described above, according to the present invention, it is possible to realize a stable contact even with a hard object by limiting the torque set up and down, thereby realizing a highly accurate contact work. A control device can be provided. Furthermore, since a flexible operation may be performed in which a portion that cannot be detected by the force sensor may come into contact, a safe robot can be provided even if it collides with a peripheral object. As described above, the advantages of both high-precision force control using a force sensor and flexible control without a force sensor can be enjoyed by the control device of the present invention.

[Brief description of the drawings]

FIG. 1 is a control block diagram showing a first embodiment of the present invention.

FIG. 2 is a control block diagram showing a second embodiment of the present invention.

FIG. 3 is a control block diagram showing a third embodiment of the present invention.

FIG. 4 shows the operation of the present invention.

FIG. 5 is a diagram showing a hardware configuration used in each embodiment.

FIG. 6 is a diagram showing a concept of a contact work assumed in the present invention.

FIG. 7 is a diagram showing a concept of an impedance mechanism applied to the present invention.

FIG. 8 is a diagram showing a concept of impedance control applied to the present invention.

FIG. 9 is a conventional impedance control block diagram.

[Explanation of symbols]

 101, 201, 301 Trajectory generator 102, 202, 302 Position / velocity controller 103, 203, 303 Torque limiter 104, 204, 304 Gravity compensation torque calculator 105, 205, 305 Amplifier 106, 206, 306 Robot 107 , 207, 307 Force sensor 108, 208, 308 Motion command torque calculator 109, 209, 309 Corrected operation torque calculator 110, 210, 310 Impedance controller 500 Trajectory generation block 510 Trajectory generation block 520 Motion control block 530 Sensor block 540 Robot 550 shared bus

 ────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Hideo Nagata 2-1 Kurosaki Castle Stone, Yawatanishi-ku, Kitakyushu-shi, Fukuoka F-term (reference) 3F059 AA03 DA07 DC04 DE03 FB13 FB29 FC03 5H269 AB22 AB33 BB03 CC09 EE01 GG02 NN07

Claims (2)

[Claims] 1. A robot control device comprising: a control circuit for a motor that drives a joint by performing state feedback on the position and speed of a robot; and a control device for a robot that includes a force control circuit based on feedback from a force sensor. Means for calculating the torque for maintaining the acceleration torque and the speed of the motor from the feedback and the feedback, means for calculating the torque required for the movement of the motor by adding the acceleration torque and the torque for maintaining the speed, and output from the force control unit. Means for calculating a torque required for the correction operation from the correction operation command to be performed, a torque required for the movement of the motor, and a means for limiting the torque generated by the robot from the torque required for the correction operation. Characteristic robot controller. 2. A robot control apparatus comprising: a control circuit for a motor that drives a joint by performing state feedback on the position and speed of a robot; and a control device for a robot that includes a force control circuit based on feedback from a force sensor. Means for calculating the torque for maintaining the acceleration torque and speed of the motor from the feedback and feedback; means for calculating the torque required for the movement of the motor by adding the acceleration torque and the torque for maintaining the acceleration; and output from the force control unit. Means for calculating the torque required for the correction operation from the correction operation command to be performed; means for limiting the torque generated by the robot from the torque required for the movement of the motor; and adding the torque required for the correction operation to the torque command. Means for controlling a robot, comprising: