Development of two-axis arm motion generator using active impedance

In this research a two-dimensional arm motion generator, composed of two linear motors, was developed. The inertia, damping and/or stiffness characteristics of the motion generator can be changed on the real-time basis by properly regulating the force generated by the linear motors. That is, active impedance is implemented without actual change in the physical structure of the motion generator. Control of the motor force is carried out by regulating the input currents supplied to the linear motors by using a common voltage-driven driver. In the control system, the time delay due to A/D conversion of the current output has an adverse effect on the stability of the system. Furthermore, disturbances caused by characteristics of the motion generator also exist. To cope with these difficulties, a 2-DOF controller combined with LQ-servo and H-infinity controllers was used. The gains of the controller are selected so that disturbance rejection, stability guarantee and tracking performance may be achieved. This motion generator can be used to measure kinesthetic sense associated with the human arm and thus leads to developing the products for which the kinesthetic sense is taken into account.