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1. A Balanced Hybrid Active-Passive Actuation Approach for High-Performance Haptics

   https://doi.org/10.1109/WHC.2019.8816146  

   Parthiban, Chembian; Dills, Patrick; Fufuengsin, It; Colonnese, Nick; Agarwal, Priyanshu; Zinn, Michael (July 2019, 2019 IEEE World Haptics Conference (WHC))

   Hybrid actuation approaches for haptic interfaces generally suffer from asymmetry in active and passive torque capabilities. This paper describes the design of a high-performance balanced hybrid haptic device, which addresses the asymmetry by combining a high-power, low-impedance active compliant actuation (series-elastic actuator) with energy absorbing high-force passive actuation in parallel with a fast, low-power secondary active actuation. We describe the actuation, design and control approaches and experimentally validate the approach with a one degree-of-freedom testbed. The performance is compared with active only approach and results show significant improvements in stability and rendering range of the device. 

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2. A Hybrid Active-Passive Actuation and Control Approach for Kinesthetic Handheld Haptics

   https://doi.org/10.1109/HAPTICS45997.2020.ras.HAP20.12.af578b0a  

   Dills, Patrick; Colonnese, Nick; Agarwal, Priyanshu; Zinn, Michael (March 2020, 2020 IEEE Haptics Symposium (HAPTICS))

   Handheld haptic devices are often limited in rendering capability, as compared to traditional grounded devices. Strenuous design criteria on weight, size, power consumption, and the ungrounded nature of handheld devices, can drive designers to prioritize actuator force or torque production over other components of dynamic range like bandwidth, transparency, and the range of stable impedances. Hybrid actuation, the use of passive and active actuators together, has the potential to increase the dynamic range of handheld haptic devices due to the large passive torque capability, the stabilizing effects of passive actuators, the high bandwidth of conventional DC servomotors, and the synergy between actuators. However, to date the use of hybrid actuation has been limited due to the highly nonlinear torque characteristics of available passive actuators that result in poor rendering accuracy. This paper describes a hybrid actuation approach and novel control topology which aims to solve actuation challenges associated with nonlinear passive actuators in hybrid and handheld haptic devices. The performance of the device is assessed experimentally, and the approach is compared to existing handheld devices. 

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3. Design and Validation of a Powered Knee–Ankle Prosthesis With High-Torque, Low-Impedance Actuators

   https://doi.org/10.1109/TRO.2020.3005533  

   Elery, Toby; Rezazadeh, Siavash; Nesler, Christopher; Gregg, Robert D. (July 2020, IEEE Transactions on Robotics)

   In this article, we present the design of a powered knee–ankle prosthetic leg, which implements high-torque actuators with low-reduction transmissions. The transmission coupled with a high-torque and low-speed motor creates an actuator with low mechanical impedance and high backdrivability. This style of actuation presents several possible benefits over modern actuation styles in emerging robotic prosthetic legs, which include free-swinging knee motion, compliance with the ground, negligible unmodeled actuator dynamics, less acoustic noise, and power regeneration. Benchtop tests establish that both joints can be backdriven by small torques ( ∼ 1–3 N ⋅ m) and confirm the small reflected inertia. Impedance control tests prove that the intrinsic impedance and unmodeled dynamics of the actuator are sufficiently small to control joint impedance without torque feedback or lengthy tuning trials. Walking experiments validate performance under the designed loading conditions with minimal tuning. Finally, the regenerative abilities, low friction, and small reflected inertia of the presented actuators reduced power consumption and acoustic noise compared to state-of-the-art powered legs. 

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4. Stability and Rendering Limitations of a Parallel Hybrid Active-Passive Haptic Interface

   https://doi.org/10.1109/HAPTICS52432.2022.9765621  

   Dills, Patrick; Dawson-Elli, Alexander; Gruben, Kreg; Adamczyk, Peter; Zinn, Michael (March 2022, IEEE Haptics Symposium 2022 (HAPTICS))

   Impedance based kinesthetic haptic devices have been a focus of study for many years. Factors such as delay and the dynamics of the device itself affect the stable rendering range of traditional active kinesthetic devices. A parallel hybrid actuation approach, which combines active energy supplying actuators and passive energy absorbing actuators into a single actuator, has recently been experimentally shown to increase the range of stable virtual stiffness a haptic device can achieve when compared to the active component of the actuator alone. This work presents both a stability and rendering range analysis that aims to identify the mechanisms and limitations by which parallel hybrid actuation increases the stable rendering range of virtual stiffness. Increases in actuator stability are analytically and experimentally shown to be linked to the stiffness of the passive actuator. 

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5. Dynamic Modeling and Robust Torque Control of a Discrete Variable Stiffness Actuator

   https://doi.org/10.1115/DETC2023-115235  

   Yu, Ziqing; Fu, Jiaming; Yao, Bin; Chiu, George; Voyles, Richard; Gan, Dongming (August 2023, American Society of Mechanical Engineers)

   Abstract Collaborative robots, or cobots, have been developed as a solution to the growing need for robots that can work alongside humans safely and effectively. One emerging technology in robotics is the use of Discrete Variable Stiffness Actuators (DVSAs), which enable robots to adjust their stiffness in a fast-discrete manner. This enables cobots to work in both low and high stiffness modes, allowing for safe collaboration with human workers or operation behind safety barriers. However, achieving good performance with different stiffness modes of DVSAs is a challenging problem. This paper proposes a method to provide force control of a DVSA by exploiting the dynamic model and the discrete stiffness levels. The two-mass dynamic model, a widely accepted model of flexible systems, is used to model and analyze the DVSA. The proposed method involves using Gain-scheduling and Deterministic Robust Control (DRC) controllers as modelbased control algorithms for the DVSA to achieve high-precision force control. We also conducted a comparison with the commonly used proportional integral derivative (PID) control algorithms. The paper presents a detailed analysis of the dynamic behavior of the DVSA and demonstrates the effectiveness of the proposed control algorithms through simulation with different scenario comparisons, even in the presence of external disturbances. 

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