scholarly journals Mechanical Simplification of Variable-Stiffness Actuators Using Dielectric Elastomer Transducers

Actuators ◽  
2019 ◽  
Vol 8 (2) ◽  
pp. 44 ◽  
Author(s):  
David P. Allen ◽  
Edgar Bolívar ◽  
Sophie Farmer ◽  
Walter Voit ◽  
Robert D. Gregg
Keyword(s):  
Equilibrium Position ◽  
Variable Stiffness ◽  
Dielectric Elastomer ◽  
Design Approach ◽  
Electrostatic Forces ◽  
Mechanical Stiffness ◽  
Variable Stiffness Actuation ◽  
And Performance ◽  
Variable Stiffness Actuators ◽  
Adjustable Compliance

Legged and gait-assistance robots can walk more efficiently if their actuators are compliant. The adjustable compliance of variable-stiffness actuators (VSAs) can enhance this benefit. However, this functionality requires additional mechanical components making VSAs impractical for some uses due to increased weight, volume, and cost. VSAs would be more practical if they could modulate the stiffness of their springs without additional components, which usually include moving parts and an additional motor. Therefore, we designed a VSA that uses dielectric elastomer transducers (DETs) for springs. It does not need mechanical stiffness-adjusting components because DETs soften due to electrostatic forces. This paper presents details and performance of our design. Our DET VSA demonstrated independent modulation of its equilibrium position and stiffness. Our design approach could make it practical to obtain the benefits of variable-stiffness actuation with less weight, volume, and cost than normally accompanies them, once weaknesses of DET technology are addressed.

Design of a Quadratic, Antagonistic, Cable-Driven, Variable Stiffness Actuator

2021 ◽  
pp. 1-20
Author(s):  
Ryan Moore ◽  
Joseph Schimmels
Keyword(s):  
Linear Relationship ◽  
Equilibrium Position ◽  
Variable Stiffness ◽  
Static Model ◽  
Elastic Behavior ◽  
Good Match ◽  
Elastic Mechanism ◽  
Linear Spring ◽  
Variable Stiffness Actuator ◽  
Variable Stiffness Actuators

Abstract Antagonistically actuated Variable Stiffness Actuators (VSAs) take inspiration from biological muscle structures to control both the stiffness and positioning of a joint. This paper presents the design of an elastic mechanism that utilizes a cable running through a set of three pulleys to displace a linear spring, yielding quadratic spring behavior in each actuator. A joint antagonistically actuated by two such mechanisms yields a linear relationship between force and deflection from a selectable equilibrium position. A quasi-static model is used to optimize the mechanism. Testing of the fabricated prototype yielded a good match to the desired elastic behavior.

Electrothermally Actuated Microbeams With Varying Stiffness

2017 ◽  
Author(s):  
Sherif Tella ◽  
Nouha Alcheikh ◽  
Mohammad I. Younis
Keyword(s):  
Resonance Frequency ◽  
Considerable Increase ◽  
Large Deflection ◽  
Variable Stiffness ◽  
Experimental Results ◽  
Mechanical Stiffness ◽  
Frequency Tunability ◽  
End Conditions ◽  
Variable Stiffness Actuation ◽  
Good Agreement

We present axially loaded clamped-guided microbeams that can be used as resonators and actuators of variable stiffness, actuation, and anchor conditions. The applied axial load is implemented by U-shaped electrothermal actuators stacked at one of the beams edges. These can be configured and wired in various ways, which serve as mechanical stiffness elements that control the operating resonance frequency of the structures and their static displacement. The experimental results have shown considerable increase in the resonance frequency and mid-point deflection of the microbeam upon changing the end conditions of the beam. These results can be promising for applications requiring large deflection and high frequency tunability, such as filters, memory devices, and switches. The experimental results are compared to multi-physics finite-element simulations showing good agreement among them.

scholarly journals Classification of Variable Stiffness Actuators - part 2

2017 ◽  
Vol 21 (2) ◽  
pp. 15-23
Author(s):  
Bartłomiej Kozakiewicz ◽  
Tomasz Winiarski
Keyword(s):  
Variable Stiffness ◽  
Variable Stiffness Actuators

Trajectory control and random vibration control of nonlinear system with dielectric elastomer actuator

2018 ◽  
Vol 29 (11) ◽  
pp. 2424-2436 ◽  
Author(s):  
Yanping Tian ◽  
Yong Wang ◽  
Xiaoling Jin ◽  
Zhilong Huang
Keyword(s):  
Nonlinear System ◽  
Control Strategy ◽  
Primary Structure ◽  
Equilibrium Position ◽  
Random Vibration ◽  
Dielectric Elastomer ◽  
Control Technique ◽  
Dynamic Programming Principle ◽  
Dielectric Elastomer Actuator ◽  
Dielectric Elastomer Actuators

Dielectric elastomer actuators have gained extensive attention in scientific and industrial communities with the rapid development of soft robot technology. There still remain some questions on the control aspect of nonlinear system with dielectric elastomer actuator. The first is whether the soft actuator can successfully drive the primary structure to track an arbitrary prescribed trajectory. The second is how to suppress the random vibration around the equilibrium position when the primary structure is disturbed by external excitation. This article seeks the answers for these two questions. By directly solving the governing equation of motion, an open-loop control technique is designed to track a prescribed trajectory. The effectiveness of the trajectory tracking technique is investigated and the limitation is illustrated by the influence of inertia of the primary structure. Based on the stochastic averaging of energy envelope and stochastic dynamic programming principle, a clipped control strategy is proposed by slightly adjusting the voltage in real time to suppress the random vibration around the equilibrium position. The good effectiveness and high robustness of the clipped control strategy are verified numerically. This work may provide some guidelines for the control aspect of nonlinear systems with dielectric elastomer actuators.

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