Force Controlled Actuator
Built around a rotating arm with parallel leaf spring, the Force-Controlled Actuator generates force profiles by controlling the displacement of its spring. The mass of the leg and backlash are minimized by transfering torque from the motor to the joint through a belt, cable and crankshaft system. This simplifies modeling the actuator. The leg is approximated to be massless with a zero moment of intertia.
Three 13-bit magnetic encoders measure the absolute angle of the leg and spring. One of these encoders measures the angle of the arm directly at the arm axle. This angle provides a course approximation for the arm position, which is used to initialize the values of the remaining two encoders. Each of these encoders is geared down 5:1 with a cable and pulley system, thus providing five times the resolution of the encoder reading directly from the arm axle.
The high resolution encoders measure the arm and spring angle. The difference of these angle is the displacement of the spring, and is used to determine the spring force.
