For use as five-finger myoelectric hands in daily living, robotic hands must be 1) lightweight and human sized as well as possess 2) human-like multiple degrees of freedom (DoF) and a high grip force. The compatibility of these requirements is a trade-off; ideal robotic hands have yet to sufficiently satisfy both these requirements. Herein a power allocation mechanism is proposed to improve the grip force without increasing the size or weight of robotic hands using redundant DoF during pinching motions. Additionally, this mechanism is applied to an actual five-finger myoelectric hand, which can make seven types of motions that are necessary for activities of daily living (ADL) and realizes about a 60% improvement in fingertip force, allowing three fingers to pinch objects exceeding 1 kg.

Long-time exposure to repetitive or monotonous work is associated with increased risk for musculoskeletal disorders that are due to muscle fatigue. Previously, researchers reported that muscle fatigue can be estimated using a low-frequency band of an SEMG signal. However, these studies were performed exclusively during static contraction tasks. The objective of the present study was to evaluate and determine the frequency range for a low-frequency band. In addition, the performance during dynamic contraction tasks was analyzed. A group of healthy university students (8 males) was recruited, and endurance handgrip tasks were conducted. SEMG signals were captured from the forearm muscle. The frequency range for the low-frequency band was redefined as 5 - 40 Hz. The results from a dynamic contraction task indicated that a low-frequency band is a reliable method for indexing muscle fatigue from SEMG signals.