Shanhai Jin

Real-Time Quadratic Sliding Mode Filter for Removing Noise

Abstract This paper presents a sliding mode filter for removing noise. It effectively removes impulsive noise and highfrequency noise, producing a smaller phase lag than linear filters. In addition, it is less prone to overshoot than previous sliding mode filters and it does not produce chattering. It is computationally inexpensive and thus suitable for real-time applications. The proposed sliding mode filter employs a quadratic surface as its sliding surface, which is designed so that the output converges to the input in finite time when the input value is constant. Its algorithm is derived by using the backward Euler discretization, which can be used to prevent chattering. The effectiveness of the filter was shown by experiments using an ultrasonic sensor and an optical encoder.

Experimental Evaluation of Energy Efficiency for a Soft Wearable Robotic Suit

This paper presents a new soft wearable robotic suit for energy-efficient walking in daily activities for elderly persons. The presented robotic suit provides a small yet effective assistive force for hip flexion through winding belts that include elastic elements. In addition, it does not restrict the range of movement in the lower limbs. Moreover, its structure is simple and lightweight, and thus wearers can easily take the device on and off by themselves. Experimental results on nine elderly subjects (age = 74.2±3.7 years) show that the robotic suit worn and powered on (PON) significantly reduced energy expenditure by an average of 5.9% compared with the condition of worn but powered off (POFF). Furthermore, compared with the POFF condition, there was a significant improvement in gait characteristics in the PON condition for all subjects.

Improving velocity feedback for position control by using a discrete-time sliding mode filtering with adaptive windowing

In position control of mechatronic devices, velocity feedback is important for injecting additional damping to avoid low-frequency fluctuation around desired trajectories. In practice, velocity signal is often obtained by finite difference of position signal from an optical encoder. However, such a numerical differentiation produces high-frequency noise by magnifying quantization error contained in the position signal. As a result, the controller may produce high-frequency vibration. This paper presents a new noise-reduction discrete-time filter based on sliding mode and adaptive windowing. The presented filter is an improved version of a sliding mode filter by Jin et al. (2012), with including adaptive windowing of which the window size is determined in a similar way to that of a discrete-time adaptive windowing differentiator by Janabi-Sharifi et al. (2000). The presented filter is then applied to a position control of a mechatronic device for improving velocity feedback. Experimental results show that the presented filter provides better velocity feedback than its previous version, Janabi-Sharifi et al.’s differentiator, and combinations of these two filters. Graphical Abstract

Discrete-time velocity estimator based on sliding mode and adaptive windowing

In position control of mechatronic devices, velocity feedback is necessary for injecting additional damping to avoid low-frequency fluctuation around desired trajectories. In practice, velocity signal is often obtained by performing Euler discretization on position signal from an optical encoder. However, due to the limited encoder resolution, the obtained velocity signal is corrupted by high-frequency noise that may result in high-frequency vibration of the controlled device. This paper presents a discrete-time velocity estimator based on sliding mode and adaptive windowing for position control. Experimental results show that the presented estimator rather improves velocity feedback compared to a sliding mode filter by Jin et al. (2012), an adaptive windowing filter by Janabi-Sharifi et al. (2000), and the cascades of these two filters.

Effects of a soft wearable robotic suit on metabolic cost and gait characteristics in healthy young subjects

This paper experimentally evaluates the effects of a soft wearable robotic suit, which is developed for energy-efficient walking in daily activities, in healthy subjects. The robotic suit provides a small but effective assistance for hip flexion. Moreover, it is lightweight and it does not restrict the motion range of the lower limbs. Experimental results on two healthy subjects show that the robotic suit worn and powered on (PON) reduced oxygen uptake by an average of 3.6 % compared with the condition of worn but powered off (POFF). Moreover, compared with the POFF condition, walk ratio was improved by an average of 2.6 % in the PON condition.