Control of industrial robots that have transmission elasticity

A control scheme is presented for electrically driven, industrial robots that have transmission elasticity. Some feedback structures that have been described in the past have an inner control loop to cancel the elastic coupling torque between motor and link. An outer feedback loop is then used for the control of the arm position. A refinement of such a control scheme is analyzed using singular perturbation methods. A broad spectrum of control algorithms that were originally designed under the assumption of ideal, rigid joints can now be extended to the elastic transmission case with minor modifications. One contribution is that exact cancellation of the elastic torque is not necessary. In fact, the elasticity effects in some robots can be adequately damped by simply adding only a term that is proportional to the differential speed (difference between link velocity and motor velocity). Experimental results are also presented