A Primary-secondary Approach to Mitigate the Effects of Force Fight Between Parallel Redundant Electromechanical Actuators

In this research, a primary-secondary control technique is developed for parallel redundant electromechanical actuators (EMAs) that are employed in the actuation of a primary flight control surface. Redundant EMAs must be all operated in active mode, which leads to force fight and has prevented EMAs from being used efficiently for flight control. Under the proposed primary-secondary control strategy, one of the EMAs is designated as the primary and is position controlled. The remaining EMA is treated as a secondary and is torque controlled with the joint torque of the primary as the commanded input. The proposed control technique avoids simultaneous position control and bypasses the position sensor of the secondary channel, which is effective in reducing force fight as position measurement error contributes greatly to force fight. The developed primary-secondary control technique has been theoretically analyzed and computer simulated, showing a decrease of 50.0% and 99.8% for dynamic and static force fight, respectively.