SUMMARYA multimodal actuator was proposed to achieve a more agile power-assisted exoskeleton in uncertain complex walking environments. A power-assisted knee exoskeleton prototype based on a multimodal actuator was constructed. With this multimodal actuator, several modes of operation in the power-assisted knee exoskeleton during a motion cycle are actuated, including series elastic actuation, stiff position control, and energy storage and release. Also, a control strategy for power-assisted knee exoskeleton motion control based on a state machine is developed. The ability of the power-assisted knee exoskeleton to follow human motion was tested, and the results showed that the angle error of the knee exoskeleton followed the human motion is not more than 0.4˚, and the response time error of the knee exoskeleton followed the human motion is not more than 0.2 s.
A multimodal actuator is proposed to fulfil the different walking patterns of a power-assisted knee exoskeleton. With this actuator, the exoskeleton leg can realize several modes of operation, including series elastic actuation, stiff position control and energy storage and release. The energy amplification characteristics of the multimodal actuator in the series elastic mode are analysed. A dynamics model was established to study how series elasticity and the equivalent mass of transmission influence a power source, such as an electric motor. The results, in both simulation and experiment, show that series elasticity can amplify actuator power output, and the power output of a multimodal actuator is greater when the equivalent mass of the transmission mechanism is smaller. This research into multimodal actuator energy amplification supplies important insights into the design of artificial systems that can more closely approximate the performance of biological systems.
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