A Cable-Driven Portable Fitness Chair with Programmable Resistance for Effective Muscle Training.

The COVID-19 pandemic has changed the lifestyle of society and the interest in health and fitness has greatly increased, accordingly. Recently, motorized devices that allow fine and automatic adjustment of resistance without physically changing the applied weight have been released to the market. In fact, these devices have eased the resistance-changing process. However, such devices are still not portable as they must be mounted on the wall and their resistance control needs to be improved to increase the efficiency of strength training. This study introduces a portable chair-shaped fitness device that allows inducing various resistance profiles. A compact, light, and robust cable-driven actuation module design was achieved by implementing a derailing prevention mechanism. The actuator covers resistance up to 120 N for each left and right arm separately. Exercise can be conducted by pulling the elastic handle connected to cable. The controller of the proposed device allows variation of resistance according to the joint range-of-motion (ROM) to make the workout more challenging but still safe through the full ROM. Viscous resistance, ascending resistance, and descending resistance profile can be provided. The experimental results shows that various muscle activation patterns can be provided by changing the resistance profile, which is important for effective training. The device can be used anywhere, at home or office, to perform various upper and lower body exercises or for physical self-care.

RNN-Based On-Line Continuous Gait Phase Estimation from Shank-Mounted IMUs to Control Ankle Exoskeletons.

Several research groups have developed and studied powered ankle exoskeletons to improve energetics of healthy subjects and the mobility of elderly subjects, or to reduce asymmetry in gaits induced by strokes. To achieve optimal effect, the timing of assistive torque has been proved to be of crucial importance. Previous studies estimated the onset timings mostly by extrapolating the time horizon from past gait events observed with sensors. Such methods have inherently limited performance when subjects are not walking at steady frequencies. To overcome such limitation and allow the use of exoskeletons in various scenarios in a daily life, we propose to estimate the gait phase as a continuous variable progressing over a gait cycle, hence allowing immediate response to frequency changes rather than iteratively correcting it after each cycle. Our method uses recurrent neural networks to estimate gait phases out of an inertial measurement unit (IMU) every 10 ms. By replacing foot sensors with an IMU we can obtain rich enough information to estimate gait phase continuously as well as avoid physical damage in sensors from ground impacts. Our preliminary tests with 2 healthy subjects showed qualitatively positive outcomes regarding the gait phase estimation and the assistive torque control.

Compact Hip-Force Sensor for a Gait-Assistance Exoskeleton System.

In this paper, we propose a compact force sensor system for a hip-mounted exoskeleton for seniors with difficulties in walking due to muscle weakness. It senses and monitors the delivered force and power of the exoskeleton for motion control and taking urgent safety action. Two FSR (force-sensitive resistors) sensors are used to measure the assistance force when the user is walking. The sensor system directly measures the interaction force between the exoskeleton and the lower limb of the user instead of a previously reported force-sensing method, which estimated the hip assistance force from the current of the motor and lookup tables. Furthermore, the sensor system has the advantage of generating torque in the walking-assistant actuator based on directly measuring the hip-assistance force. Thus, the gait-assistance exoskeleton system can control the delivered power and torque to the user. The force sensing structure is designed to decouple the force caused by hip motion from other directional forces to the sensor so as to only measure that force. We confirmed that the hip-assistance force could be measured with the proposed prototype compact force sensor attached to a thigh frame through an experiment with a real system.