Change in telescoping leg strategy with varying walking speed to modulate force advantage.

Human walking consists of two major sequential events (i.e., single- and double-support phases). Although there have been many studies relating to basic principles of the each stage, how the two distinct but continuous phases interact with each other remains to be clarified. We examined the change in walking strategy with varying walking speed on a local reference frame with telescoping and tangential axes; we expect that the telescoping directional dynamics at the end of a single-support phase change with walking speed to facilitate the modulation of the push-off work during a double-support phase. The telescoping directional force and power are calculated using two methods: model simulation and kinematic configuration. The empirical walking data for eight healthy young subjects and the corresponding model parameters obtained from a data-fit optimization were used to investigate the changing trend of each factor (i.e., force and power) with the increase in speed. The resulting force at the end of the single-support phase significantly increased with the walking speed for both methods, whereas the resulting power remained nearly unchanged and was close to zero for the entire range of walking speeds. This result implies that the positive amount of the telescoping directional force at the end of the single-support phase may be a certain type of preparation for the double-support phase, which can contribute to a larger push-off.

Human-mimetic soft robot joint for shock absorption through joint dislocation.

This paper presents a human-mimetic manipulator capable of shock absorption by using dislocation at the soft joint. A one degree-of-freedom (DOF) soft robot joint was developed based on the human elbow-joint structure, especially mimicking the humeroulnar joint in the elbow. Each component of the soft joint is combined by an elastic ligament, which is made up of elastic rubber and is attached to the pivot joint pin positioned at a predetermined place according to a specially designed pin guide. As an external impact is applied to the joint, the elastic ligament is elongated as the pivot joint pin is moved from the predetermined place. This state is defined as a dislocation, which is similar to the dislocation of a human joint when impacted. Dislocation in the proposed soft robot joint occurred when the external impact was larger than the predetermined threshold force. This threshold force can be predicted by the modulus of the elastic ligament and the shape of the pin guide, and the theoretical model was developed in this study. To evaluate the function of dislocation, dynamic and quasi-static impact tests were performed at the 1-DOF soft robot joint. Moreover, the human-mimetic manipulator is proposed based on the 2-DOF soft robot joint. This manipulator can realize four motions of a human arm using the pneumatic artificial muscles: flexion, extension, pronation and supination. Each artificial muscle and bone structure were similar to the human arm structure, and thus the configuration of each bone structure of the manipulator for each motion is similar to the configurations of a human skeletal structure. This manipulator was also capable of dislocation to absorb the external impact. The developed human-mimetic manipulator with a soft joint is expected to be applied to a naturally safe humanoid robot that works with humans in the same space.

Design of a simple, lightweight, passive-elastic ankle exoskeleton supporting ankle joint stiffness.

In this study, a passive-elastic ankle exoskeleton (PEAX) with a one-way clutch mechanism was developed and then pilot-tested with vertical jumping to determine whether the PEAX is sufficiently lightweight and comfortable to be used in further biomechanical studies. The PEAX was designed to supplement the function of the Achilles tendon and ligaments as they passively support the ankle torque with their inherent stiffness. The main frame of the PEAX consists of upper and lower parts connected to each other by tension springs (N = 3) and lubricated hinge joints. The upper part has an offset angle of 5° with respect to the vertical line when the springs are in their resting state. Each spring has a slack length of 8 cm and connects the upper part to the tailrod of the lower part in the neutral position. The tailrod freely rotates with low friction but has a limited range of motion due to the stop pin working as a one-way clutch. Because of the one-way clutch system, the tension springs store the elastic energy only due to an ankle dorsiflexion when triggered by the stop pin. This clutch mechanism also has the advantage of preventing any inconvenience during ankle plantarflexion because it does not limit the ankle joint motion during the plantarflexion phase. In pilot jumping tests, all of the subjects reported that the PEAX was comfortable for jumping due to its lightweight (approximately 1 kg) and compact (firmly integrated with shoes) design, and subjects were able to nearly reach their maximum vertical jump heights while wearing the PEAX. During the countermovement jump, elastic energy was stored during dorsiflexion by spring extension and released during plantarflexion by spring restoration, indicating that the passive spring torque (i.e., supportive torque) generated by the ankle exoskeleton partially supported the ankle joint torque throughout the process.