Position and force control of an electrohydraulic manipulator in the presence of friction

A work cell for decapitation of salmon has been developed in the authors´ Industrial Automation Laboratory. An X-Y electrohydraulic manipulator is used to quickly move a sharp blade to its desired position in the horizontal plane. This blade slides on two lubricated metal guideways. Precise, fast and smooth positioning of the blade is considered here. A quintic polynomial approach is used to generate a smooth reference trajectory. A novel friction-compensating control strategy is proposed to improve tracking performance of the manipulator. The approach is based on an acceleration feedback control law. According to the experimental results, this controller outperforms the classical PD (Proportional+Derivative) controller. In the force control domain, it is experimentally verified that force control is possible as long as no motion is involved. In other words, the reference force is below the static friction break-away force. PD control is used for this purpose. This type of force control can be used to compensate for disturbance force before it actually affects movement of the manipulator