This paper proposes a new variable gain sliding mode filter augmented by variable windowing for achieving smooth and reactive response over a broad range of input frequencies. The proposed filter can be seen as a synergistic combination of Kikuuwe et al.'s [1] sliding mode filter with varying gain and sliding surfaces and a novel varying-length moving-window algorithm. In all schemes, the estimated input speed is employed for rendering the filter parameters between low and high settings. The discrete-time algorithm of the proposed filter does not suffer from chattering due to implicit (backward) Euler method. The effectiveness of the proposed filter in achieving better trade-off between noise attenuation and signal preservation is validated in both simulation and experimental scenarios by using the velocity signal obtained by differentiation of quantized position data.

This paper presents three contributions in the filed of medical imaging applications using hand-held ultrasound probe: 1) a new type of belt-driven mechanism for force-controlled ultrasound probe (FCUS) and 2) a safe and precise position controller and 3) a new algorithm for endpoint avoidance in the limited motion range. To enhance the image quality, the probe-patient contact force is controlled. In such case, to achieve both safe contact within limited range of motion and accurate positioning, proxy-based sliding mode control augmented with friction compensation is proposed. Due to proxy-based sliding mode control, the proposed controller is advantageous in that it guarantees overdamped response and the system model, which is difficult to obtain for probe-patient interaction system, does not appear in the controller. Due to friction compensation, the controller provides accurate positioning. The new algorithm for endpoint avoidance enables continuous motion in the limited motion range. The proposed controller is validated experimentally.