An official website of the United States government
Abstract This article introduces a novel compact discrete variable stiffness actuator, distinguished by its design topology enabling compactness and independent stiffness adjustment regardless of position, without relying on complex stiffness tuning mechanisms. The compactness is achieved through a rotary spring module comprising six linear springs. Variation in stiffness is attained by adjusting the number of engaged elastic elements (springs) using linear actuators. The article comprehensively covers the design, modeling, prototyping, and control of the actuator. A mathematical model, encompassing stiffness and dynamic aspects of the system, is developed and analyzed. Robust controllers are devised to ensure stability across different stiffness levels and under varying loads. Simulation and experimental findings provide empirical validation of the effectiveness of this innovative compact actuation system, underscoring its suitability for diverse applications across sectors such as manufacturing, healthcare, and assistive robotics.
more »
« less
This content will become publicly available on October 29, 2027
A Discrete Variable Stiffness Actuator for Safe and Adaptive Human–Robot Interaction
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
- PAR ID:
- 10700697
- Publisher / Repository:
- IEEE IROS 2026
- Date Published:
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract The demand for flexible grasping of various objects by robotic hands in the industry is rapidly growing. To address this, we propose a novel variable stiffness gripper (VSG). The VSG design is based on a parallel-guided beam structure inserted by a slider from one end, allowing stiffness variation by changing the length of the parallel beams participating in the system. This design enables continuous adjustment between high compliance and high stiffness of the gripper fingers, providing robustness through its mechanical structure. The linear analytical model of the deflection and stiffness of the parallel beam is derived, which is suitable for small and medium deflections. The contribution of each parameter of the parallel beam to the stiffness is analyzed and discussed. Also, a prototype of the VSG is developed, achieving a stiffness ratio of 70.9, which is highly competitive. Moreover, a vision-based force sensing method utilizing ArUco markers is proposed as a replacement for traditional force sensors. By this method, the VSG is capable of closed-loop control during the grasping process, ensuring efficiency and safety under a well-defined grasping strategy framework. Experimental tests are conducted to emphasize the importance and safety of stiffness variation. In addition, it shows the high performance of the VSG in adaptive grasping for asymmetric scenarios and its ability to flexible grasping for objects with various hardness and fragility. These findings provide new insights for future developments in the field of variable stiffness grippers.more » « less
-
This paper introduces a novel observer-based dynamic event-triggered control (ETC) approach for 2 × 2 linear hyperbolic PDEs with collocated sensing and actuation. The proposed method guarantees global exponential stability (GES) under ETC using PDE backstepping, with stability estimates provided in the spatial L2 norm of the states. The triggering mechanism explicitly enforces a lower bound on the time interval between consecutive events, ruling out the possibility of Zeno behavior, and introduces a dynamic variable with appropriate switching dynamics. Events are triggered when the dynamic variable crosses zero from positive, after which the variable is immediately reset to an appropriate nonnegative value. By employing a novel Lyapunov functional that incorporates the L2 norms of the observer and observer error target system states, the switching dynamic variable, and a state-independent dynamic reset variable modulated by the square of the control input sampling error, the GES of the closed-loop system is established under the zero-order hold application of the backstepping control between events. The well-posedness of the closed-loop system is also proven. A simulation study is conducted to illustrate the theory.more » « less
-
In this paper, an integral sliding mode current controller (SMC) is proposed for mutually coupled switched reluctance motors (MCSRM) using asymmetric bridge converters aiming to achieve constant switching frequency and lower sampling rate. A generalized state-space model is built and then the design of a sliding mode controller along with the stability analysis of the closed-loop system are presented. The effectiveness of SMC is verified using simulation studies with a three-phase, sinusoidal excitation 12/8 MCSRM over a wide speed range. Compared to the hysteresis current control, the proposed SMC-based design approach demonstrates a comparable response in terms of currents ripples, the root-mean-square error of current and torque while achieving a constant switching frequency and lower sampling rate.more » « less
-
In this paper, an integral sliding mode current controller (SMC) is proposed for mutually coupled switched reluctance motors (MCSRM) using asymmetric bridge converters aiming to achieve constant switching frequency and lower sampling rate. A generalized state-space model is built and then the design of a sliding mode controller along with the stability analysis of the closed-loop system are presented. The effectiveness of SMC is verified using simulation studies with a three-phase, sinusoidal excitation 12/8 MCSRM over a wide speed range. Compared to the hysteresis current control, the proposed SMC based design approach demonstrates a comparable response in terms of currents ripples, the root-mean-square error of current and torque while achieving a constant switching frequency and lower sampling rate.more » « less
