Active stick control using frictional torque compensation

An active stick which has variable force-feel characteristics is developed. A combined position and force control strategy is mechanized by using a 2-axis built-in force sensor and LVDT. The 2-axis force sensor, which measures the stick force felt by the operator, is developed by using strain gages and appropriate instrumental amplifiers. A mathematical model of the active stick dynamics is derived, and compared with the experimental results. The frictional torque of the stick due to the mechanical contact of several parts causes the experimental frequency responses to be dependent on the magnitude of the excitation signal and the precision closed loop control to be difficult. A friction observer which estimates the frictional torque of the active stick in real time is designed, and applied to the closed loop control. The benefit of using the friction observer is verified through numerical simulation and experiments.