The online adaptation of exoskeleton control based on muscle activity sensing offers a promising approach to personalizing exoskeleton behavior based on the user's biosignals. While electromyography (EMG)-based methods have demonstrated improvements in joint torque estimation, EMG sensors require direct skin contact and extensive post-processing. In contrast, force myography (FMG) measures normal forces resulting from changes in muscle volume due to muscle activity. We propose an FMG-based method to estimate knee and ankle joint torques by integrating joint angles and velocities with muscle activity data. We learn a model for joint torque estimation using Gaussian process regression (GPR). The effectiveness of the proposed FMG-based method is validated on isokinetic motions performed by ten participants. The model is compared to a baseline model that uses only joint angle and velocity as well as a model augmented by EMG data. The results indicate that incorporating FMG into exoskeleton control can improve the estimation of joint torque for the ankle and knee joints in novel task characteristics within a single participant. Although the findings suggest that this approach may not improve the generalizability of estimates between multiple participants, they highlight the need for further research into its potential applications in exoskeleton control.

Ankle exoskeletons can assist the ankle joint and reduce the metabolic cost of walking. However, many existing ankle exoskeletons constrain the natural 3 degrees of freedom (DoF) of the ankle to limit the exoskeleton’s weight and mechanical complexity, thereby compromising comfort and kinematic compatibility with the user.This paper presents a novel ankle exoskeleton frame design that allows for 3 DoF ankle motion using a symmetric parallel frame design principle resulting in a strong frame while weighing 1.8 kg. Furthermore, a cable routing method is proposed to actuate the plantarflexion of the ankle. The kinematic compatibility of the proposed exoskeleton frame is evaluated in straight- and curve-walking scenarios with four users. The study demonstrates that the exoskeleton frame adapts to the natural 3 DoF ankle motion and the range of motion (RoM) during walking. The actuation in plantarflexion is evaluated in a stationary torque experiment demonstrating the ability of the frame to transfer large torque loads of up to 57.4 Nm. This work contributes to the design and development of more flexible and adaptable ankle exoskeletons for walking assistance.

While existing literature encompasses exoskeleton-assisted sit-stand tasks, the integration of energy recovery mechanisms remains unexplored. To push the boundaries further, this study introduces a portable pneumatic knee exoskeleton that operates in both quasi-passive and active modes, where active mode is utilized for aiding in standing up (power generation), thus the energy flows from the exoskeleton to the user, and quasi-passive mode for aiding in sitting down (power absorption), where the device absorbs and can store energy in the form of compressed air, leading to energy savings in active mode. The absorbed energy can be stored and later reused without compromising exoskeleton transparency in the meantime. In active mode, an air pump inflates the pneumatic artificial muscle (PAM), which stores the compressed air, that can then be released into a pneumatic cylinder to generate torque. All electronic and pneumatic components are integrated into the system, and the exoskeleton weighs 3.9 kg with a maximum torque of 20 Nm at the knee joint. The paper describes the mechatronic design, mathematical model and includes a pilot study with an able-bodied subject performing sit-to-stand tasks. The results show that the exoskeleton can recover energy while assisting the subject and reducing mean muscle activity by ~31%. Further results highlight air regeneration’s potential for energy saving in portable pneumatic exoskeletons, showing that the proposed device extends exoskeleton operation by ~27%.