Control properties of a two-joint link mechanism equipped with mono- and bi-articular actuators

When a two-joint link mechanism was installed with an antagonistic pair of bi-articular actuators in addition to antagonistic pairs of mono-articular actuators the two-joint link mechanism could demonstrate perfect human-like control properties at the endpoint. First, only a single command signal informing the target point could control any desired output force direction at the endpoint via a simple spinal level neural network. Second the existence of three antagonistic pairs of actuators made it possible to control three parameters of a viscoelastic ellipse exerted at the endpoint independently, and consequently to induce coincidence of trajectory and output force exerted at the endpoint. Thus, the mechanism could lead smooth, rapid and precise movements without use of positional feedback signal from the endpoint, i.e. open loop control.