Control of Elasticity and Trajectory of Robot Arm with Redundant Actuators

In mechanical joints applied to robot arms, one actuator is generally required to drive one joint. For the drive of joints on the musculoskeletal system of animal limbs, in which musculi skeleti are used as actuators, there is a pair of bi-articular muscles for driving two joints simultaneously in addition to a pair of monoarticular muscles. By our study with a simple arm model having a 2 degrees of freedom for two joints, the relationship between the compliances of antagonistic muscless at a joint (the muscle coordinate system) and the elastic ellipse at the end of arm (the task coordinate system) has been clarified in connection with the adjustment of the trajectory at the end of arm, which belongs to the task coordinate system, when the bi-articular muscles are made available and when they are made un-available for comparison. The effect of the bi-articular muscles has thus been proved. Then the fact that the trajectory of the arm can be adjusted by means of both an elastic ellipse and the force at the end of the arm has also been clarified. To verify the above, a 2 degrees of freedom robot arm has been adopted. This arm is equipped with two joints having (3-pairs, 6-muscles) pneumatic rubber artificial muscles used as actuators.