scholarly journals A Compact Adjustable Stiffness Rotary Actuator Based on Linear Springs: Working Principle, Design, and Experimental Verification

Actuators ◽  
2020 ◽  
Vol 9 (4) ◽  
pp. 141
Author(s):  
Cong Phat Vo ◽  
Van Du Phan ◽  
Thanh Ha Nguyen ◽  
Kyoung Kwan Ahn
Keyword(s):  
Elastic Energy ◽  
Sliding Mode ◽  
Fast Transient Response ◽  
Output Torque ◽  
Rotary Actuator ◽  
Simultaneous Control ◽  
Sliding Mode Controllers ◽  
Output Element ◽  
Working Principle ◽  
Stiffness Control

Inspired by improving the adaptive capability of the robot to external impacts or shocks, the adjustable stiffness behavior in joints is investigated to ensure conformity with the safety index. This paper proposes a new soft actuation unit, namely Adjustable Stiffness Rotary Actuator (ASRA), induced by a novel optimization of the elastic energy in an adjusting stiffness mechanism. Specifically, a stiffness transmission is configured by three pairs of antagonistically linear springs with linkage bars. The rotational disk and link bars assist the simplified stiffness control based on a linear transmission. To enhance the elastic energy efficiency, the force compressions of the linear springs are set to be perpendicular to the three-spoke output element, i.e., the output link direction. Besides, the ASRA model is also formed to investigate the theoretical capabilities of the stiffness output and passive energy. As a simulated result, a high passive energy storage ability can be achieved. Then, several experimental scenarios are performed with integral sliding mode controllers to verify the physical characteristics of the ASRA. As trial results, the fast transient response and high accuracy of both the position and stiffness tracking tests are expressed, in turn, independent and simultaneous control cases. Moreover, the real output torque is measured to investigate its reflecting stiffness.

Sliding Mode Impedance and Stiffness Control of a Pneumatic Cylinder

2019 ◽  
Author(s):  
Jonathon E. Slightam ◽  
Eric J. Barth ◽  
Mark L. Nagurka
Keyword(s):  
Motion Control ◽  
Sliding Mode ◽  
Impedance Control ◽  
Pneumatic Cylinder ◽  
Control Methods ◽  
Control Applications ◽  
Compliant Motion ◽  
Simultaneous Control ◽  
Stiffness Control ◽  
Virtual Impedance

Abstract Pneumatic double acting cylinders are able to provide inherent stiffness and force control for compliant motion control applications. Impedance control methods allow for a broad spectrum of mechanical properties of actuators to be achieved. The range of this spectrum can be increased by simultaneously controlling the actuator’s inherent stiffness and impedance, a concept explored in this paper. Presented here is a sliding mode impedance and stiffness controller for a servo-pneumatic double acting cylinder. Two proportional servo-valves are employed for simultaneous control of the virtual impedance and inherent stiffness of the pneumatic cylinder. Experimental results of tracking trajectories and contact are reported and discussed with respect to different approaches in the literature.

Comparing model-based control methods for simultaneous stiffness and position control of inflatable soft robots

2020 ◽  
pp. 027836492091196
Author(s):  
Charles M. Best ◽  
Levi Rupert ◽  
Marc D. Killpack
Keyword(s):  
Dynamic Models ◽  
Position Control ◽  
Sliding Mode ◽  
Joint Stiffness ◽  
Variable Stiffness ◽  
Soft Robots ◽  
End Effector ◽  
Simultaneous Control ◽  
Stiffness Model ◽  
Stiffness Control

Inflatable robots are naturally lightweight and compliant, which may make them well suited for operating in unstructured environments or in close proximity to people. The inflatable joints used in this article consist of a strong fabric exterior that constrains two opposing compliant air bladders that generate torque (unlike McKibben actuators where pressure changes cause translation). This antagonistic structure allows the simultaneous control of position and stiffness. However, dynamic models of soft robots that allow variable stiffness control have not been well developed. In this work, a model that includes stiffness as a state variable is developed and validated. Using the stiffness model, a sliding mode controller and model predictive controller are developed to control stiffness and position simultaneously. For sliding mode control (SMC), the joint stiffness was controlled to within 0.07 Nm/rad of a 45 Nm/rad command. For model predictive control (MPC) the joint stiffness was controlled to within 0.045 Nm/rad of the same stiffness command. Both SMC and MPC were able to control to within 0.5° of a desired position at steady state. Stiffness control was extended to a multiple-degree-of-freedom soft robot using MPC. Controlling stiffness of a 4-DOF arm reduced the end-effector deflection by approximately 50% (from 17.9 to 12.2cm) with a 4 lb (1.8 kg) step input applied at the end effector when higher joint stiffness (40 Nm/rad) was used compared with low stiffness (30 Nm/rad). This work shows that the derived stiffness model can enable effective position and stiffness control.

Robust cascade control of electrical drives using discrete-time chattering-free sliding mode controllers with output saturation

2021 ◽  
Author(s):  
Milutin P. Petronijević ◽  
Čedomir Milosavljević ◽  
Boban Veselić ◽  
Branislava Peruničić-Draženović ◽  
Senad Huseinbegović
Keyword(s):  
Discrete Time ◽  
Sliding Mode ◽  
Cascade Control ◽  
Electrical Drives ◽  
Sliding Mode Controllers ◽  
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