In recent years, there is a proposed method for controlling changing the position and posture of a grasped object related to gripper (in-hand manipulation) by using a multi-fingered gripper (e.g., Japanese Patent No. 4890199). Japanese Patent No. 4890199 proposes a technique of carrying out an in-hand manipulation while maintaining balance of the object by measuring actual contact points (contact positions) between the object and the gripper as well as actual force vectors (contact force vectors) acting on the object by using tactile sensors attached to the fingers. This method adjusts the magnitude and direction of each contact force to let the total force and the total moment generated by these forces become zero. To achieve this, they remove several contacted fingers from the object and reposition those fingers to touch the object again in new positions and directions to get desired contact forces.
Another proposed method creates a series of complicated motion plans to execute state transitions using a two-fingered gripper, to reposition an object through multiple steps (e.g., Japanese Patent No. 6057862).
Furthermore, there is another proposed control method which lifts up an object, holds it and changes its posture, only using the degree-of-freedom of the robot arm to which the gripper is attached. However, it does not use the degree-of-freedom of the gripper (e.g., Japanese Patent No. 5289179).
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