More Like this

1. An Investigation of a Balanced Hybrid Active-Passive Actuator for Physical Human-Robot Interaction

   https://doi.org/10.1109/LRA.2021.3064497  

   Dills, Patrick; Dawson-Elli, Alexander; Gruben, Kreg; Adamczyk, Peter G.; Zinn, Michael (July 2021, IEEE Robotics and Automation Letters)

   null (Ed.)

   Cooperative robots or “cobots” promise to allow humans and robots to work together more closely while maintaining safety. However, to date the capabilities of cobots are greatly diminished compared to industrial robots in terms of the force and power they are able to safely produce. This is in part due to the actuation choices of cobots. Low impedance robotic actuators aim to solve this problem by attempting to provide an actuator with a combination of low output impedance and a large bandwidth of force control. In short the ideal actuator has a large dynamic range. Existing actuators success and performance has been limited. We propose a high force and high power balanced hybrid active-passive actuator which aims to increase the actuation capability of low impedance actuators and to safely enable high performance larger force and workspace robots. Our balanced hybrid actuator does so, by combining and controlling a series elastic actuator, a small DC motor, and a particle brake in parallel. The actuator provides low and high frequency power producing active torques, along with power absorbing passive torques. Control challenges and advantages of hybrid actuators are discussed and overcome through the use of trajectory optimization, and the safety of the new actuator is evaluated. 

   more » « less
2. A Discrete Variable Stiffness Actuator for Safe and Adaptive Human–Robot Interaction

   Fu, J; Yu, Z; Guo, Q; Zhang, X; Gan, D (October 2026, IEEE IROS 2026)

   This paper presents a Discrete Variable Stiffness Actuator (DVSA) based on a Variable Stiffness Parallel Beam (VSPB), where stiffness modulation is achieved through block insertion and cross-sectional reconfiguration. The actuator employs a solenoid-driven planar push-push mechanism to enable rapid and synchronized switching among three discrete stiffness levels. A theoretical stiffness model is established and validated through comparisons among analytical calculations, simulation results, and experimental measurements. The results demonstrate that the proposed model provides high predictive accuracy within practical parameter ranges. A prototype actuator is fabricated, and torque control experiments are conducted under different stiffness configurations. The system achieves a stiffness variation ratio of 78. A PID-based closed-loop controller ensures stable torque tracking performance. By introducing a rollback-assisted strategy, online stiffness switching is realized under closed-loop operation without compromising system stability. Owing to its compact structure, low energy consumption, and reconfigurable stiffness capability, the proposed DVSA is suitable for safety-critical cobots and humanoid robotic systems, providing an effective solution for applications requiring both compliance and high stiffness. 

   more » « less
3. Toward Tradeoff Between Impact Force Reduction and Maximum Safe Speed: Dynamic Parameter Optimization of Variable Stiffness Robots

   https://doi.org/10.1115/1.4046839  

   Song, Siyang; She, Yu; Wang, Junmin; Su, Hai-Jun (October 2020, Journal of Mechanisms and Robotics)

   Abstract Variable stiffness robots may provide an effective way of trading-off between safety and speed during physical human–robot interaction. In such a compromise, the impact force reduction capability and maximum safe speed are two key performance measures. To quantitatively study how dynamic parameters such as mass, inertia, and stiffness affect these two performance measures, performance indices for impact force reduction capability and maximum speed of variable stiffness robots are proposed based on the impact ellipsoid in this paper. The proposed performance indices consider different impact directions and kinematic configurations in the large. Combining the two performance indices, the global performance of variable stiffness robots is defined. A two-step optimization method is designed to achieve this global performance. A two-link variable stiffness link robot example is provided to show the efficacy of the proposed method. 

   more » « less
4. An Energy-Based Framework for Robust Dynamic Bipedal Walking Over Compliant Terrain

   https://doi.org/10.1115/1.4064094  

   Karakasis, Chrysostomos; Poulakakis, Ioannis; Artemiadis, Panagiotis (March 2024, Journal of Dynamic Systems, Measurement, and Control)

   Abstract Bipedal locomotion over compliant terrain is an important and largely underexplored problem in the robotics community. Although robot walking has been achieved on some non-rigid surfaces with existing control methodologies, there is a need for a systematic framework applicable to different bipeds that enables stable locomotion over various compliant terrains. In this work, a novel energy-based framework is proposed that allows the dynamic locomotion of bipeds across a wide range of compliant surfaces. The proposed framework utilizes an extended version of the 3D dual spring-loaded inverted pendulum (Dual-SLIP) model that supports compliant terrains, while a bio-inspired controller is employed to regulate expected perturbations of extremely low ground-stiffness levels. An energy-based methodology is introduced for tuning the bio-inspired controller to enable dynamic walking with robustness to a wide range of low ground-stiffness one-step perturbations. The proposed system and controller are shown to mimic the vertical ground reaction force (GRF) responses observed in human walking over compliant terrains. Moreover, they succeed in handling repeated unilateral stiffness perturbations under specific conditions. This work can advance the field of biped locomotion by providing a biomimetic method for generating stable human-like walking trajectories for bipedal robots over various compliant surfaces. Furthermore, the concepts of the proposed framework could be incorporated into the design of controllers for lower-limb prostheses with adjustable stiffness to improve their robustness over compliant surfaces. 

   more » « less
5. Development and analysis of a cable-driven serial robot with a full actuation

   https://doi.org/10.1177/09544062251406281  

   Xiu, Guodong; Cheng, Jinsai; Shen, Tao (January 2026, Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science)

   Cable-driven serial robots, with their lightweight structure and flexibility, show great potential for development in fields such as healthcare, aerospace engineering, and architectural engineering. However, compared to traditional serial robots, cable-driven serial robots have motion coupling issues, where the movement of one joint affects another due to the interconnected cables, making precise control difficult. Moreover, their force and torque distributions have special characteristics due to the presence of cables, which will have a significant impact on their dynamic modeling. Current research mainly focuses on decoupling mechanisms and analysis of cable-driven parallel robots. This paper presents the design, analysis, and control of a 2-degree of freedom (DOF) cable-driven serial robot based on the non-circular pulley. Denavit-Hartenberg (DH) convention and the Newton-Euler method were used to analyze kinematics and special dynamics. A model-based control strategy is developed based on the above analyses. And validation is conducted by comparing the proposed dynamic control method with dynamic controller of a traditional serial robot and a PID position controller. The results show the proposed model-based method can achieve the smallest position errors in the comparison, demonstrating the correctness of kinematics and dynamics, and effectiveness of the controller. 

   more » « less