Control of articulated robots by biarticular actuation has recently attracted great attention in the research field of robotics. Although many of studies concerned with this issue deal with legged robots or robot arms kinetically interacting with environment such as a floor or an object, motion control of an articulated robot arm with no kinetic interaction is also an interesting topic of biarticular actuation. In the motion control, a major issue is how it is possible for biarticular actuation to contribute to improvement of control; however, showing a clear finding for this issue seems to be considerably difficult. This paper considers a study for exploring that issue. Biarticular actuation usually constitutes a redundant actuation system; therefore, control of a robot arm to a desired posture can be achieved by many combinations of actuator forces. Based on this feature, this paper considers three typical combinations of actuator forces. Point-to-point control of the robot is performed for each of the combinations in simulation, and control performances of the combinations are compared with each other. In addition, the performances are compared with that of monoarticular actuation. In those comparisons, two of the three combinations show similar control performances, which suggests possibility of major contribution of biarticular actuators to motion control of a robot arm. On the other hand, control performance of the other combination is similar to that of monoarticular actuation, rather than those of other two combinations.
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