Control method for robot apparatus, computer readable recording medium, and robot apparatus

1. A control method for a robot apparatus, the robot apparatus including a robot arm having an end effector located at an end of the robot arm, the robot arm including a plurality of links coupled one to another by one or more joints, and a control device, the joint including a motor, an input-side encoder, and an output-side encoder, the control method comprising:

driving, by the motor, the joint via a reduction gear;

detecting, by the input-side encoder, an angle of an input drive shaft of the reduction gear;

detecting, by the output-side encoder, an angle of an output drive shaft of the reduction gear; and

selecting, by the control device, the semi-closed control or the fully closed control to control the joint, the semi-closed control being control in which an angle of an output drive shaft is controlled in accordance with an output of the input-side encoder, the fully closed control being control in which an angle of the output drive shaft is controlled in accordance with an output of the output-side encoder.

2. The control method for a robot apparatus according to claim 1 , wherein the selecting includes

performing a test run a plurality of times in which the control device causes the robot arm to operate while performing semi-closed control on the joint, and

selecting either the semi-closed control or the fully closed control in accordance with a result, which is obtained by the control device evaluating the tip position of the robot arm at a specific point using outputs of the output-side encoder obtained in the test runs.

3. The control method for a robot apparatus according to claim 2 , wherein in a case where semi-closed control is used to control the joint during operation, the control device calculates the bias of the tip position of the robot arm at specific points using the outputs of the output-side encoder obtained in the test runs and performs semi-closed control on the joint using a driving distance based on a correction value for correcting this bias.

4. The control method for a robot apparatus according to claim 2 , wherein in the selecting step, the control device selects either semi-closed control or fully closed control for use to control the joint in accordance with the variation in the tip position of the robot arm at the specific point, the variation being calculated using the outputs of the output-side encoder obtained in the test runs.

5. The control method for a robot apparatus according to claim 2 , wherein in the selecting step, the control device converts a variation in a joint angle of the joint, the variation being calculated using the outputs of the output-side encoder of the joint obtained in the test runs, into a variation in the tip position of the robot arm at a specific point, selects the semi-closed control for use to control the joint in a case where the variation satisfies a user's desired accuracy, and selects the fully closed control for use to control the joint in a case where the variation does not satisfy the user's desired accuracy.

6. The control method for a robot apparatus according to claim 2 , wherein the specific point is a target position point to which the tip position of the robot arm is to be moved.

7. The control method for a robot apparatus according to claim 1 , wherein the controlling includes

determining the content of a task that the robot arm is to be caused to perform,

selecting either the semi-closed control or the fully closed control for use to control the joint in accordance with the content of the task that is determined in the determining step and that the robot arm is to be caused to perform, and

performing a certain operation using the semi-closed control or the fully closed control on the joint, which is selected in the selecting step.

8. The control method for a robot apparatus according to claim 7 , wherein in the selecting step, the control device selects either the semi-closed control or the fully closed control for use to control the joint in accordance with an object that the end effector is to be caused to operate.

9. The control method for a robot apparatus according to claim 8 , wherein in the selecting step, the control device selects the fully closed control in a case where the object is an object applying random external forces to the robot arm.

10. The control method for a robot apparatus according to claim 8 , wherein in the selecting step, in a case where, as the object, a plurality of objects are present that are identically shaped but made of different materials, the control device selects the fully closed control.

11. The control method for a robot apparatus according to claim 8 , wherein in the selecting step, in a case where the object is an object whose center of gravity changes when the object is operated by the end effector, the control device selects the fully closed control.

12. The control method for a robot apparatus according to claim 7 , wherein in the selecting step, the control device selects either the semi-closed control or the fully closed control for use to control the joint in accordance with an operation that the robot arm is to be caused to perform.

13. The control method for a robot apparatus according to claim 7 , wherein in the selecting step, in a case where a target value of a joint angle of the joint is in a range of looseness or hysteresis of a system constituting the joint, the control device selects the fully closed control.

14. The control method for a robot apparatus according to claim 1 ,

wherein the control device is configured to select either the semi-closed control or the fully closed control of the joint in accordance with a content of a task that the robot arm is to perform, and to cause the robot arm to operate while performing the selected semi-closed control or fully closed control on the joint.

15. The control method for a robot apparatus according to claim 1 , further comprising:

causing, by the control device, the robot arm to perform the selected semi-closed control or fully closed control on the joint.

16. A non-transitory computer readable recording medium storing a control program for a robot apparatus, the robot apparatus including a robot arm having an end effector located at an end of the robot arm, the robot arm including a plurality of links coupled one to another by one or more joints, and a control device, the joint including a motor, an input-side encoder, and an output-side encoder, the control program causing the robot apparatus to perform a control method comprising:

driving, by the motor, the joint via a reduction gear;

detecting, by the input-side encoder, an angle of an input drive shaft of the reduction gear, the semi-closed control being control in which an angle of the joint is controlled in accordance with an output of the input-side encoder;

detecting, by the output-side encoder, an angle of an output drive shaft of the reduction gear, the fully closed control being control in which an angle of the joint is controlled in accordance with an output of the output-side encoder; and

selecting, by the control device, the semi-closed control or the fully closed control to control the joint.

17. A robot apparatus comprising:

a robot arm having an end effector located at an end of the robot arm,

the robot arm including a plurality of links coupled one to another by one or more joints; and

a control device configured to selectively perform semi-closed control or fully closed control on the joint,

the joint including

a motor configured to drive the joint via a reduction gear,

an input-side encoder configured to detect an angle of an input drive shaft of the reduction gear, and

an output-side encoder configured to detect an angle of an output drive shaft of the reduction gear, the semi-closed control being control in which an angle of the joint is controlled in accordance with an output of the input-side encoder, the fully closed control being control in which an angle of the joint is controlled in accordance with an output of the output-side encoder,

wherein the control device is configured to select and use either semi-closed control or fully closed control to control the joint.

18. The robot apparatus according to claim 17 , wherein the control device is configured to perform a test run a plurality of times in which the control device

causes the robot arm to operate while performing semi-closed control on the joint,

evaluates the tip position of the robot arm at a specific point using outputs of the output-side encoder obtained in the test runs,

selects either the semi-closed control or the fully closed control for use to control the joint in accordance with a result, and

causes the robot arm to operate while performing the selected semi-closed control or fully closed control on the joint.

19. The robot apparatus according to claim 17 ,

wherein the control device is configured to select either the semi-closed control or the fully closed control of the joint in accordance with a content of a task that the robot arm is to perform, and to cause the robot arm to operate while performing the selected semi-closed control or fully closed control on the joint.