Eddy-Current Linear-Rotary Position Sensor for an Implantable Total Artificial Heart

This paper presents an eddy-current linear-rotary position sensor for ShuttlePump, an implantable total artificial heart based on a linear-rotary actuator. The sensor is obtained by extending a commercially available rotary position sensor with appropriate data processing by also capturing the information about the linear position. In fact, with changing linear distance of the target, the amplitudes of the sine and cosine sensor outputs change. Furthermore, the commercial IC serving as interface for the rotary sensor adjusts its excitation frequency due to the changing coupling between the sensor and the linearly moving target. Hence, there are two options to additionally measure the linear position, which are analyzed theoretically with finite element simulations, validated experimentally and compared in terms of achievable sensitivity, bandwidth and linearity. Both options allow to reach z-resolutions below the required 100 mu m and phi-accuracy in the 5 degrees range while meeting the specified 100 Hz bandwidth requirement and can hence be used for feedback position control of ShuttlePump.