Mechanical design and energy storage efficiency research of a variable stiffness elastic actuator

Bo Liu,Bowei Li,Wenjie Ge,Zhihua Zou,Donglai Zhao

doi:10.1177/1729881420930950

Abstract

The energy storage efficiency is an important performance of a robot or a man–machine interaction device. This article will introduce the process of design and energy storage research of a variable stiffness elastic actuator with a two-elements and one actuator mod. Firstly, the principle model will be present to analyze the operation theory. Then, the simulation and experiment model will be described to calculate the characteristics of the device. The stiffness ratio of the two springs constituting the elastic element of the device will be studied in detail, and the results can present the rule of the energy storage value. Finally, the performance of the device, the error of the experiment, and a special mechanism which presented at the extreme shape condition of the ratio will be discussed. The conclusion is that the maximum energy that the device can store is 1.415 J at the stiffness ratio equaling 0.46, and the energy storage efficiency is 1.3608 at the ratio equaling 0.45, when the weight of the device is 3.54 kg and the apparent stiffness is about 3450 N/m.

Highlights

The ratio of the energy storage of an elastic element in a robot to the total amount of energy output of the actuator is the efficiency of energy storage (EOES), which is so important that it can significantly affect the motion capability of legged robots.To increase the EOES of the robots, a variable stiffness elastic actuator (EA), realized by the variable length of linkage, has been designed by Visser and his team,1,2 and the design theory of their mechanism has been verified with simulation and experiment
Brown has presented a passiveassist device,3–5 which consisted of actuator and elastic element, and introduced the optimization method of the spring and the results of the experiments to verify that EOES of the parallel elastic actuator (PEA) is higher than other mechanisms
The maximum energy storage is increasing with the increase of k, and lMAX at max value of each curve is decreasing during this process

Summary

Introduction

The ratio of the energy storage of an elastic element in a robot to the total amount of energy output of the actuator is the efficiency of energy storage (EOES), which is so important that it can significantly affect the motion capability of legged robots. The mechanical structure in this figure is not the final design of the TE-VSEA, but a diagram to explain the working principle This device contains two springs, one hydro-cylinder, two loads, and one locking mechanism. Form the calculation and analyze of simulation model, the max value of energy storage and the max ratio of EOES are existed at the l 1⁄4 0.46 and l 1⁄4 0.45, respectively (as shown in Figures 12 and 15). This result is obtained from the fact that the sum of loads is constant and the apparent stiffness of the system is unchanged.

Findings

Discussion

Conclusion and future work