Robot control device, robot system and method of controlling robot which carries object in cooperation with person

1. A robot control device for controlling a robot to carry an object in cooperation with a person, the robot control device comprising:

a force acquisition part configured to acquire a force applied from the object to the robot when the robot lifts up the object and before the robot starts an object-carrying operation of carrying the object;

a comparison part configured to compare a force component in a gravity direction of the force acquired by the force acquisition part with a first threshold value predetermined with respect to the force component;

a stop command part configured to maintain the robot in a stopped state so as not to start the object-carrying operation in response to the force component being greater than the first threshold value; and

an operation command part configured to, in response to the force component being smaller than or equal to the first threshold value, generate an operation command to the robot for carrying the object and transmit the operation command to the robot so as to start the object-carrying operation,

wherein, after the operation command part starts the object-carrying operation,

the force acquisition part is configured to acquire a new force applied from the object to the robot,

the comparison part is configured to compare a force component in the gravity direction of the new force acquired by the force acquisition part with the first threshold value, and

the stop command part is configured to stop the object-carrying operation in response to the force component of the new force being greater than the first threshold value.

2. The robot control device according to claim 1 , wherein the operation command part is configured to generate the operation command to the robot for carrying the object in a direction opposite to the gravity direction, in response to the force component of the new force being smaller than or equal to a second threshold value which is smaller than the first threshold value.

3. The robot control device according to claim 1 , wherein the operation command part is configured to generate the operation command to the robot for carrying the object in the gravity direction, in response to the force component of the new force being (i) smaller than or equal to the first threshold value and (ii) greater than or equal to a second threshold value which is smaller than the first threshold value.

4. The robot control device according to claim 1 , wherein the stop command part is configured to stop the robot in response to the force component of the new force being smaller than a second threshold value which is smaller than the first threshold value.

5. The robot control device according to claim 1 , wherein the operation command part is configured to generate the operation command to the robot for carrying the object in a direction intersecting with the gravity direction, in response to a force component in the direction intersecting with the gravity direction of the new force acquired by the force acquisition part.

6. The robot control device according to claim 5 , wherein the stop command part is configured to stop the robot when the force component in a horizontal direction of the new force acquired by the force acquisition part is greater than a threshold value predetermined with respect to the force component in the horizontal direction.

7. A robot system comprising:

a robot; and

a robot control device according to claim 1 configured to control the robot,

wherein the robot includes a force detection part configured to detect a force applied from an object to the robot when the robot lifts up the object.

8. A method of controlling a robot to carry an object in cooperation with a person, the method comprising:

detecting a force applied from the object to the robot when the robot lifts up the object and before the robot starts an object-carrying operation of carrying the object;

comparing a force component in a gravity direction of the detected force with a threshold value predetermined with respect to the force component;

maintaining the robot in a stopped state so as not to start the object-carrying operation in response to the force component being greater than the threshold value;

in response to the force component being smaller than or equal to the threshold value, generating an operation command to the robot for carrying the object, and transmitting the operation command to the robot so as to start the object-carrying operation; and

after starting the object-carrying operation,

acquiring a new force applied from the object to the robot,

comparing a force component in the gravity direction of the acquired new force with the threshold value, and

stopping the object-carrying operation in response to the force component of the new force being greater than the threshold value.

9. The robot control device according to claim 1 , wherein the robot control device is configured to generate a notification to the person in response to the force component in the gravity direction being greater than the first threshold value.

10. The robot control device according to claim 9 , wherein the force acquisition part is configured to acquire a new force applied from the object to the robot after a predetermined time period from the notification to the person.

11. The robot control device according to claim 1 , wherein

when the robot carries the object in cooperation with the person and the person abruptly gets his or her hand off the object causing the force component to sharply increase so as to exceed the first threshold value, the stop command part is configured to generate a command for stopping a servomotor built in the robot and send the command to the servomotor so that the object-carrying operation of the robot is stopped.

12. The robot control device according to claim 4 , wherein

when the robot carries the object in cooperation with the person and an obstacle collides with the object from below causing the force component to sharply decrease so as to be smaller than the second threshold value, the stop command part is configured to generate a command for stopping a servomotor built in the robot and send the command to the servomotor so that the object-carrying operation of the robot is stopped.