Determination of friction and feedforward tuning for a DC servomotor-driven slide table

Feedforward techniques can improve performance of tracking devices which use proportional-integral-differential (PID) controllers. The commercially available controller software used for this project provides an iterative method for determining feedforward gains. This work presents a deterministic method for computing the feedforward gains required to improve performance. The deterministic method can effectively replace the iterative method to save the user time and effort. The deterministic method developed in this paper uses a simple move that consists of a constant acceleration with velocity reversal. With this move, analysis of the controller output with respect to velocity shows the effects of inertia and friction. This information can be directly converted to feedforward gains with knowledge of controller parameters. For a current mode amplifier this information can be converted to physical units for friction and inertia with knowledge of the physical system constants external to the controller. Tests on a slide table driven by DC servomotors show these methods to be effective