Abstract
Wearable robots use batteries as a power source; therefore, the efficiency of the actuation mechanism must be improved to increase their operation time. Soft wearable robots using fabric-type soft actuators (FSA) have attracted much interest recently. In FSAs, the actuator itself is soft, flexible, and lightweight, and energy must be continuously supplied to support the load and hold the actuation state. In particular, when maintaining a particular posture, such as holding an object, constant energy supply is needed to enable the actuator to support the load. To reduce the energy consumption of the holding motion in FSAs, this study proposes a locking–unlocking mechanism (LUM) that can maintain the FSA’s contraction state without sustained energy supply. The LUM is fixed to the FSA’s upper end; it consists of a ratchet-pawl mechanism, pawl rotating actuators (PRA) with shape memory alloy springs, and a wire encoder. The PRA enables the pawl to lock and unlock the ratchet. One end of the wire encoder connected to the ratchet’s rotary shaft is fixed at the bottom part of the FSA, thereby maintaining the FSA contraction state and measuring the contraction length. The LUM’s displacement controller can control the FSA to a specific displacement length. This paper presents the design procedure, operating test, and performance evaluation for energy efficiency improvement of the LUM. When the LUM is applied, FSA can maintain the contraction state while supporting the load, making energy consumption unnecessary. As a result, we expect that applying the LUM with FSAs to soft wearable robots can improve the operation time by at least two times.
Published Version
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