Robot arm control method and control device

• US 7,102,315 B2
• Filed: 07/02/2004
• Issued: 09/05/2006
• Est. Priority Date: 07/29/2003
• Status: Active Grant

• Current Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Original Assignee: Matsushita Electric Industrial Company Limited (Panasonic Holdings Corporation)
• Inventors: Hashimoto, Atsumi, Nakata, Hiroyuki, Mukai, Yasushi, Masunaga, Naoto
• Primary Examiner(s): Ro, Bentsu
• Application Number:
  US10/546,712
• Publication Number:
  US 20060071625A1
• Time in Patent Office: 795 Days
• Field of Search: 318/567, 318/568.1, 318/568.11, 318/568.17, 318/568.18, 318/568.21, 318/568.22, 318/609, 318/610, 318/619, 318/621, 318/632, 901/9, 901/23, 901/25, 901/45, 901/49
• US Class Current: 318/568.22
• CPC Class Codes: B25J 9/1633 compliant, force, torque control, e.g. combined with position control
• CPC Class Codes: B25J 9/1676 Avoiding collision or forbidden zones
• CPC Class Codes: G05B 19/4061 Avoiding collision or forbidden zones
• CPC Class Codes: G05B 2219/39355 Observer, disturbance observer
• CPC Class Codes: G05B 2219/40226 Input control signals to control system and to model, compare their outputs
• CPC Class Codes: G05B 2219/42288 Limit, stop drive current if axis obstructed, blocked, force against stop

Abstract

When either a command value or an actually measured value is appropriately selected as an angular velocity used for the frictional torque calculation, the frictional compensation can be made valid at all times in both the case in which a robot is actively operated according to an angular velocity command and the case in which the robot is passively operated being pushed by an external force. In the case where a motor rotating direction and a collision direction are reverse to each other after a collision has been detected, the control mode is switched from the positional control to the electric current control and a torque, the direction of which is reverse to the direction of the motor rotation is generated by the motor, so that the motor rotating speed can be reduced and the collision energy can be alleviated. After that, when the motor rotating speed is reduced to a value not more than the setting value, the control mode is switched to the compliance control and the distortion caused in a reduction gear is dissolved. On the other hand, in the case where the motor rotating direction and the collision direction are the same, the control mode is directly switched from the positional control to the compliance control without passing through the electric current control. When the robot is operated whole following a collision force, the collision force can be alleviated.

Claims

1. A method of controlling a robot arm comprising:

a step of detecting a rotary angle of a motor to drive the robot arm;

a step of calculating an actually measured angular velocity from the rotary angle;

a step of calculating a command angular velocity from a command value given to the motor;

a step of calculating a frictional torque according to one of the command angular velocity and the actually measured angular velocity, wherein an absolute value of the command angular velocity and an absolute value of the actually measured angular velocity are compared with each other and the angular velocity of a higher absolute value is used for calculating the frictional torque; and

a step in which a value corresponding to the frictional torque is added to the command value given to the motor when the motor is driven according to the command value.

2. A method of controlling a robot arm according to claim 1, further comprising:

a step in which at least one of the command angular velocity and the actually measured angular velocity is multiplied by a weighting factor or alternatively the weighting factor is added to at least one of the command angular velocity and the actually measured angular velocity.

3. A method of controlling a robot arm according to claim 1, further comprising:

a step in which at least one of the command angular velocity and the actually measured angular velocity is multiplied by a friction compensation rate.

4. A method of controlling a robot arm driven by a motor via a reduction gear, comprising:

a step of calculating a generation torque generated by the motor;

a step of calculating a frictional torque, which includes at least a dynamic frictional torque of the reduction gear necessary for an output of the reduction gear, from the torque by an inverse dynamic calculation;

a step of increasing a dynamic torque of the reduction gear according to the frictional torque necessary for the output of the reduction gear; and

a step of calculating an external force by subtracting the increased frictional torque from the generated torque.

5. A method of controlling a robot arm driven by a motor via a reduction gear,

comprising:

a step of conducting a motor output torque compensation by feedforward control according to an inverse dynamic calculation of the robot for finding a torque necessary for the reduction gear output and according to a dynamic frictional torque calculation of the reduction gear,

wherein the dynamic frictional torque of the reduction gear is increased in proportional to the torque necessary for the reduction gear output in the case of conducting feedback control.

6. A method of controlling a robot in a stopping operation conducted after the detection of a collision of the robot driven by a motor, in an axis in which a motor rotary direction and a collision torque direction are reverse to each other, when a control mode is switched from a positional control, in which an electric current command to make an actual position follow a positional command is generated, to an electric current control in which an electric current to generate a torque, the direction of which is reverse to the rotary direction of the motor, by the motor is commanded, a motor rotating speed is decreased, and when the motor rotating speed is decreased to a value not more than a setting value, the control mode is switched to a compliance control in which the robot follows a collision force direction;

and

in an axis in which the motor rotary direction and the collision torque direction are the same, the control mode is switched from the positional control to the compliance control.

7. A method of controlling a robot according to claim 6, wherein in an axis in which a collision detecting torque is lower than the setting value, irrespective of the motor rotary direction and the collision torque direction, the control mode is switched from the positional control to the electric current control, and when a torque, the direction of which is reverse to the direction of the motor rotation, is generated by the motor, the motor rotating speed is reduced, and when the motor rotating speed is reduced to a value not more than the setting value, the control mode is switched to the compliance control.

8. A method of controlling a robot according to claim 6, wherein when the electric current control is conducted in which a torque, the direction of which is reverse to the motor rotary direction, is generated by the motor in an axis in which the motor rotary direction and the collision torque direction are reverse to each other and the motor rotating speed and the collision torque detection value exceed the setting values, after the motor rotating speed is reduced, a torque in the reverse direction is kept being impressed until the speed direction is inverted, and when the motor rotating speed is increased to a value not less than the setting value, the control mode is switched to the compliance control in which the robot follows the collision force direction.

9. A method of controlling a robot according to claim 6, wherein when the electric current control, in which a torque, the direction of which is reverse to the direction of motor rotation, is generated by the motor, is conducted after the collision detection, an electric current to generate the maximum torque of the motor is commanded.

10. A device of controlling a robot comprising:

a collision torque detecting means for detecting an intensity and direction of torque given to a motor, which drives an arm of the robot, by a collision force given to the arm of the robot;

a collision judgment means for judging a collision by comparing the collision torque detecting value with the threshold value of the collision torque which has been set;

a motor rotation detecting means for detecting a rotating speed and a rotating direction of the motor;

a collision direction discriminating means for comparing the collision torque detecting direction with the motor rotary direction; and

a motor deceleration judging means for confirming a deceleration of the motor by comparing the motor rotating speed with the threshold value which has been set, wherein in an axis in which a motor rotary direction and a collision torque direction are reverse to each other, when a control mode is switched from a positional control, in which an electric current command to make an actual position follow a positional command is generated, to an electric current control in which an electric current to generate a torque, the direction of which is reverse to the rotary direction of the motor, by the motor is commanded, a motor rotating speed is decreased, and when the motor rotating speed is decreased to a value not more than the setting value, the control mode is switched to a compliance control in which the robot follows a collision force direction,

a device of controlling a robot further comprising a control mode switching means for switching from a positional control means to a compliance control means in an axis in which the motor rotary direction and the collision torque direction are the same.

11. A device of controlling a robot according to claim 10, further comprising:

a collision torque threshold value judging means for comparing the collision torque detection value with a collision direction discriminating torque threshold value; and

a control mode switching means for switching the control mode from the positional control means to the electric current control means in an axis, in which the collision torque detection value is lower than the collision direction discriminating torque threshold value, irrespective of the motor rotary direction and the collision torque direction and for switching the control mode to the compliance control means when the motor rotating speed is reduced by generating a torque, the direction of which is reverse to the direction of the motor rotation, by the motor so as to reduce the rotating speed of the motor and the rotating speed of the motor is reduced to a value not more than the setting value.

12. A device of controlling a robot according to claim 10, wherein when the electric current control is conducted in which a torque, the direction of which is reverse to the motor rotary direction, is generated by the motor in an axis in which the motor rotary direction and the collision torque direction are reverse to each other and the motor rotating speed and the collision torque detection value exceed the setting values, after the motor rotating speed is reduced, a torque in the reverse direction is kept being impressed until the speed direction is inverted, and when the inverted motor rotating speed is increased to a value not less than the setting value, the control mode is switched to the compliance control in which the robot follows the collision force direction.

13. A device of controlling a robot according to claim 10, further comprising:

an electric current control means for commanding an electric current to generate the maximum torque by the motor, the direction of which is reverse to the direction of the motor rotation, when the electric current control means is selected by the control mode switching means after the collision has been detected.