HydroBone and Variable Stiffness Exoskeleton with Knee Actuation

The HydroBone is a variable stiffness load-bearing element, which utilizes jamming of granular media to achieve stiffness modulation, controlled by the application of positive pressure. Several compressive tests were conducted on the HydroBone in order to quantify the load-bearing capability of the system. It was determined that the stiffness of the HydroBone was a function of the internal pressure of the system. A controller was modeled based on this function to achieve automatic stiffness modulation of the HydroBone. An exoskeleton was designed based on the HydroBone and various actuators for the exoskeleton were considered. The HydroMuscle, a soft linear actuator was selected to provide knee actuation for the exoskeleton, based on several efficiency and force output test conducted. A knee brace was designed, capable of producing 15Nm of torque on the knee, actuated using Bowden cables coupled to the HydroMuscles

A Soft-Inflatable Exosuit for Knee Rehabilitation: Assisting Swing Phase During Walking

In this paper, we present a soft-inflatable exosuit to assist knee extension during gait training for stroke rehabilitation. The soft exosuit is designed to provide 25% of the knee moment required during the swing phase of the gait cycle and is integrated with inertial measurement units (IMUs) and smart shoe insole sensors to improve gait phase detection and controller design. The stiffness of the knee joint during level walking is computed using inverse dynamics. The soft-inflatable actuators, with an I cross-section, are mechanically characterized at varying angles to enable generation of the required stiffness outputs. A linear relation between the inflatable actuator stiffness and internal pressure as a function of the knee angle is obtained, and a two-layer stiffness controller is implemented to assist the knee joint by providing appropriate stiffness during the swing phase. Finally, to evaluate the ability of the exosuit to assist in swing motion, surface-electromyography (sEMG) sensors are placed on the three muscle groups of the quadriceps and two groups of the hamstrings, on three healthy participants. A reduction in muscle activity of the rectus femoris, vastus lateralis, and vastus medialis is observed, which demonstrates feasibility of operation and potential future usage of the soft inflatable exosuit by impaired users

Exploiting a Simple Asymmetric Pleating Method to Realize a Textile Based Bending Actuator

This work presents the design, modeling and control of an asymmetrically pleated textile actuator (APTA). The presented actuator utilizes a simple inflatable beam which is constrained asymmetrically using a pleat that is fixed only to a single side. Due to the difference in length between the constrained side and the unconstrained side, a bend at the pleat is generated upon inflation. This method utilizes sewing and/or heat sealing to create bending, making it easy to manufacture compared to many soft actuators and further allows for the creation of complex 3D structures in conjunction with methods presented in literature due to the in-plane bending generated by the presented pleating method. The design, fabrication and modeling of the APTA are presented and the actuator characterization in the form of bending angle, quasi-static torque and hysteresis tests are performed. A maximum normalized output torque of 400 Nm/kPa.m3 was demonstrated by the presented APTA. An empirical model for the APTA using the collected data was derived to predict torque output throughout the actuator range of motion. A controller using the empirical model was designed to track desired torque profiles. Single and Multiple step response experiments were conducted to evaluate the efficacy of the controller for burst-like actuation which could have implications in physical assistance for biological systems and in shape forming deployable structures. Further, we present several potential applications to this actuator in the form of 3D inflatable structures, a continuum module segment, and a wearable elbow device