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Quantitative analysis of stability-efficiency relationship in redundant quadruped locomotion

2026-06-30T15:00:00Z

Title: Quantitative analysis of stability-efficiency relationship in redundant quadruped locomotion Author(s): Song, Jinhyeok; Lim, Seunghyun; Jeong, Yeongjoon; Kim, Taehwan; Yun, Dongwon Abstract: Legged robots often face a trade-off between stability and energy efficiency, as postures that improve stability typically increase energy consumption, particularly in unstructured environments such as disaster response or exploration sites. While additional appendages can introduce a synergy between stability and efficiency, they also increase hardware and control complexity. In this study, we show that the strategic use of intrinsic kinematic redundancy through posture modulation can provide a stability-efficiency synergy. We design a stability-enhanced gait for a redundant quadruped robot that independently modulates body height z(s )and foot orientation n(y) under fixed foothold conditions, and experimentally evaluate its energetic performance. As evaluation metrics, we use the minimum normalized energy stability margin (NESM) over a gait cycle to quantify static stability and the cost of transport (CoT) to assess energy efficiency. Under quasi-static, no-slip, slope-walking conditions, experimental results reveal a strong negative correlation between the minimum NESM and CoT ( rho=-0.86,p<0.001 ). In particular, configurations with a lower body height and a foot orientation slightly exceeding the slope angle increased the maximum slope from 10 degrees to 20 degrees (100%) and reduced CoT by up to 27.7%. These results suggest that NESM can serve as a design-level indicator for selecting energy-efficient and stable gaits based on kinematic posture alone, offering a practical guideline for redundant legged robots operating under limited sensing and computational resources.

Supercritical Sliding-Mode Control for Position Tracking of PMSM With Disturbance Rejection

2025-12-31T15:00:00Z

Title: Supercritical Sliding-Mode Control for Position Tracking of PMSM With Disturbance Rejection Author(s): Kim, Jisu; Choi, Sunghyun; Yun, Dongwon Abstract: In highly dynamic environments, such as industrial automation systems with frequent load changes or electric vehicles, ensuring both robustness and high-precision control remains challenging, particularly in the position control of permanent magnet synchronous motors. Sliding-mode control (SMC) is widely used for its robustness, but traditional SMC methods often suffer from chattering and slow convergence, limiting overall system performance. To address these limitations, this study proposes a robust SMC approach incorporating a novel nonlinear sliding surface inspired by the supercritical pitchfork bifurcation concept. Additionally, a new reaching law is introduced to attenuate chattering and ensure fast convergence of the sliding variable to zero within a finite time. The proposed method also integrates a proportional-integral observer (PIO) with the equivalent-input disturbance (EID) framework to enhance disturbance rejection under both matched and mismatched uncertainties. The stability of the proposed controller was verified using Lyapunov stability analysis, and its performance was validated through simulations and real-world experiments. Comparative evaluations demonstrated that the proposed reaching law significantly reduces chattering amplitude by over 50 % and improves convergence speed by approximately 5.6 times faster than conventional methods. Furthermore, the system's disturbance-rejection capability under matched and mismatched uncertainties is enhanced through the PIO+EID structure. These results confirmed the robust performance of the controller under unknown disturbances. This paper is accompanied by a video that demonstrates the proposed control strategy and provides a comparison with traditional controllers. © 2025 Elsevier B.V., All rights reserved.

형상 적응 파지를 위한 소형 부족 구동 기반 그리퍼 개발

2025-09-30T15:00:00Z

Title: 형상 적응 파지를 위한 소형 부족 구동 기반 그리퍼 개발 Author(s): 금재영; 김동현; 정영준; 송진혁; 윤동원 Abstract: This paper proposes a wire-driven gripper that actuates three fingers using a single motor, aiming to enable stable object manipulation in confined and unstructured environments such as battlefields and disaster sites. Unmanned robots operating in such scenarios are increasingly required to perform missions including reconnaissance, search, rescue, and hazardous material removal. To fulfill these tasks, compact and reliable gripper systems are essential. Conventional grippers are categorized into soft grippers, which offer excellent shape adaptability through flexible materials, and rigid grippers, which provide structural strength. However, soft grippers are unsuitable for field environments due to limited stiffness, while rigid grippers lack adaptability for irregular objects. The proposed gripper enhances adaptability by leveraging wire-driven mechanism and reduces size and complexity through single-motor actuation. The design was validated through workspace analysis and motor torque estimation, and grasping experiments confirmed its performance. This paper demonstrates that the proposed gripper is well-suited for unmanned robots tasked with hazardous material handling and rescue operations in constrained environments.

A twisted string actuator using a shape memory alloy for dual actuation

2025-10-31T15:00:00Z

Title: A twisted string actuator using a shape memory alloy for dual actuation Author(s): Nam, Yoonsoo; Choi, Sunghyun; Kim, Bongju; Yun, Dongwon Abstract: A Twisted String Actuator (TSA) is a type of linear actuator that converts rotational motion into linear motion. Due to its lightweight structure and high energy efficiency, TSA has been extensively studied in various fields. In particular, the speed-mode TSA offers the advantage of increasing both actuation range and speed through a simple mechanism. However, a critical drawback of the speed-mode TSA is its relatively low force transmission efficiency. To overcome this limitation, this study proposes a novel actuator concept: the SMA-TSA, which replaces the traditional TSA string with Shape Memory Alloy (SMA). By incorporating SMA, which can generate actuation independently, the SMA-TSA enables dual actuation. This provides an additional driving force alongside the conventional twisted-string mechanism. We designed the SMA-TSA to facilitate dual actuation and experimentally validated its performance. The results demonstrated that the SMA-TSA achieved an additional 14.42 mm of contraction and force output of 95.96 N. Furthermore, when applied to a robotic finger, the SMA-TSA increased the finger tip force by approximately 6.38 N, suggesting its potential for future applications in robotics. © 2025