Disturbance rejection improvement in non-redundant robot arms using bi-articular actuators

Recently, bio-inspired robotic arms equipped with bi-articular muscles, which are actuators that produce torque in two consecutive joints, have been raising interest. Usually bi-articular actuators are present as a redundancy in actuation, which results in advantages such as dramatical increase in range of end effector impedance which can be achieved without feedback, and the ability to produce a homogeneous maximum output force at the end effector. These advantages however are due to the use of bi-articular actuators in addition to the traditional mono-articular ones. Therefore, drawbacks as design complexity and cost are present. In this paper, the role of bi-articular actuators for robot arm that do not present actuator redundancy is investigated. It is shown that for jumping/walking robots, in static conditions the maximum force in the direction parallel to ground is bigger in the configuration with bi-articular actuators. In dynamic conditions, this results in a greater capability of disturbance rejection to forces directed horizontally respect to the ground. As a result, the presence of bi-articular actuators improves the balance capability of jumping/walking robots.