Session: 06-12-03: Robotics, Rehabilitation

Paper Number: 114054

114054 - Development of an Assistive Ankle-Foot Exoskeleton With Sensorized Silicone-Based Insole 

Lower-limb exoskeletons are wearable devices designed to assist and augment human mobility, specifically for those with lower-limb impairments. These devices have been employed increasingly as a means of enhancing rehabilitation, reducing the risk of injury, and improving the quality of life for individuals with lower-limb disabilities. Lower-limb exoskeletons work by providing external mechanical support for the legs, allowing users to stand, walk, and even climb stairs with enhanced ease and stability. As a result, these devices have the potential to revolutionize the way we think about mobility and accessibility. This will offer new possibilities for individuals with mobility impairments to engage in activities that were previously out of reach. In this research work, a soft, wearable ankle-foot exoskeleton is designed, fabricated, and tested for assisting individuals with disabilities in lower-limb activities such as walking, sit-to-stand movements, and climbing stairs. 

The components of this ankle-foot exoskeleton include a pressure silicone mold insole where pressure sensors are embedded, an inertial measurement unit (IMU) sensor for the foot, an ankle-foot brace that transmits the actuation torque to the ankle joint from a DC motor attached to the upper torso part using a cable-driven system, and the mechatronics setup with a mini-PC, microcontroller, battery, and intermediate boards. The pressure insole design consists of a flexible insole with five ground-contact sensors that measure the ground reaction force (GRF) and its distribution along the foot. This insole is designed to fit inside a normal shoe and can be configured for various foot sizes and shapes. The insole is made of silicone (Ecoflex 00-30 from Smooth-On, Inc) as a soft, moldable, and biocompatible material that can house the sensors and allow them to take accurate measurements while providing adequate comfort for the user’s feet. The data from the pressure and IMU sensors is transmitted wirelessly by implementing C++ codes on a mini-PC and a microcontroller (ESP32).

The prototype of this ankle-brace exoskeleton is modeled and analyzed in SolidWorks. The brace is designed to extend from the base of the foot to the calf muscle. The top of the ankle brace is secured to the leg using fabric Velcro straps that wrap around the center section of the shank. The ankle brace is fabricated in three separate pieces to be modular and adjustable to accommodate different wearers’ body sizes. This fabricated prototype is experimentally tested to verify the design objectives and assess the product functionality in different ankle movements. In the control software, the measured data from the IMU and the pressure insole devices is retrieved and analyzed in real-time and the desired position commands are sent to the DC motor (AK80-9 model from T-Motor) to actuate the ankle joint with a high sampling rate of 250 kHz. To evaluate the robustness and flexibility of this exoskeleton, a series of tests consisting of stance and swing phases in walking, climbing, and sitting-to-stand transitions were conducted.

Presenting Author: Mojtaba Sharifi San Jose State University

Presenting Author Biography: Mojtaba Sharifi is an Assistant Professor at the Department of Mechanical Engineering, San Jose State University, San Jose, California, USA. Prior to that, he was a postdoctoral research fellow at the Department of Electrical and Computer Engineering and the Department of Medicine, University of Alberta, Canada. He received his B.Sc. and M.Sc. degrees in Mechanical Engineering from Shiraz University and Sharif University of Technology, Iran, in 2010 and 2012, respectively. He conducted a collaborative research project in the Telerobotic and Biorobotic Systems Lab of the University of Alberta, Canada, from 2015 to 2016, and earned his Ph.D. degree from Sharif University of Technology, Iran, in 2017. His interdisciplinary research includes intelligent design, control, and dynamics of robots (in biomedical applications: rehabilitation, surgery, and imaging), human-robot interaction (using impedance control and learning), wearable and assistive robotics (exoskeleton, prosthesis, and orthosis), haptics, collaborative robotics, and telerobotics (using bilateral and multilateral control), control and modeling of musculoskeletal systems, and biological systems.

Authors:

Tc Cheng San Jose State University
Mojtaba Sharifi San Jose State University