Throwing operations by manipulator with a 2-DOF variable viscoelastic joint using pneumatic artificial muscles and a magnetorheological brake

The performance of a robot can be enhanced by increasing its output. However, increasing the output of rigid actuators such as motors and hydraulic actuators will likely increase the weight of the robot. Conversely, organisms such as human beings achieve high output within a short time by accumulating and releasing the elastic energy stored in their muscles (thus providing an instantaneous force). Moreover, the viscoelastic properties of muscle enable organisms to control their instantaneous force outputs and their overall movements. Therefore, in this study, we developed a manipulator with a 2-degree-of-freedom (DOF) variable viscoelastic joint. The manipulator comprises a straight-fiber-type artificial muscle and a magnetorheological (MR) brake. The ability of the manipulator to generate controlled movement from an instantaneous force was tested in a throwing operation. This simple 2-DOF variable viscoelastic manipulator with apparent viscosity control by the MR brakes achieved successful throwing motions.