Sensor-Based Decoupling Control in a SCARA-Type Robot (1st Report)

Control Method

Abstract

In a SCARA-type robot, coupling forces act between the joints. To improve the dynamic behavior and to reduce the time of a working cycle, it is necessary to compensate for the force generated between the joints. The active coupling torque of the arm is expressed by the sum of acceleration-coupling terms due to the nondiagonal element in an inertia matrix and the Coriolis and centrifugal forces. If the exact angular acceleration θ is known, the coupling torque is easily estimated without calculating the complex inverse dynamic mechanics. This paper describes the decoupling control in a SCARA-type robot using acceleration sensors for the estimation of these terms. In an experiment servotype acceleration sensors having high resolution and linearity at low frequency were installed to the arms. A simple control algorithm that can decouple the joints by applying a nonlinear compensation feedback control is proposed. The proposed method showed satisfactory results even for the stepwise input signal of a velocity command. It could reduce the position errors to less than 47% when compared with the traditional PI control.