Abstract
A better understanding of how actuator design supports locomotor function may help develop novel and more functional powered assistive devices or robotic legged systems. Legged robots comprise passive parts (e.g., segments, joints and connections) which are moved in a coordinated manner by actuators. In this study, we propose a novel concept of a hybrid electric-pneumatic actuator (EPA) as an enhanced variable impedance actuator (VIA). EPA is consisted of a pneumatic artificial muscle (PAM) and an electric motor (EM). In contrast to other VIAs, the pneumatic artificial muscle (PAM) within the EPA provides not only adaptable compliance, but also an additional powerful actuator with muscle-like properties, which can be arranged in different combinations (e.g., in series or parallel) to the EM. The novel hybrid actuator shares the advantages of both integrated actuator types combining precise control of EM with compliant energy storage of PAM, which are required for efficient and adjustable locomotion. Experimental and simulation results based on the new dynamic model of PAM support the hypothesis that combination of the two actuators can improve efficiency (energy and peak power) and performance, while does not increase control complexity and weight, considerably. Finally, the experiments on EPA adapted bipedal robot (knee joint of the BioBiped3 robot) show improved efficiency of the actuator at different frequencies.
Highlights
In the biological body, different muscles have similar general functionality but vary in contraction properties
We examined two different static and dynamic models and presented a new model to identify our pneumatic artificial muscle (PAM) dynamic behavior to be employed in electric-pneumatic actuator (EPA)
To derive a precise model of EPA, we have developed our experimental setup including an electric motor (EM) in series with a PAM
Summary
Different muscles have similar general functionality but vary in contraction properties (e.g., maximum contraction speed and maximum isometric force). VIAs are usually constructed by adding another EM (e.g., a direct drive servo motor) to the actuator design to control spring stiffness (e.g., via changing the lever arm or preloading of the spring) [16] It improves the controllability of the output which is useful for enabling legged robots to cope with changing ground conditions and changing the motion speed efficiently. We tested how PAM compliance adjustment (by setting the air pressure) can reduce energy consumption in periodic movement required in legged locomotion. This last experiment was performed in a knee joint of a bioinspired bipedal robot (BioBiped3 [21])
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