The project has built upon our initial work focused on the development of a cable actuated glove for stroke rehabilitation that was followed up with work on developing a cable actuated elbow and wrist. The goal of our work in soft robotics is to develop a wearable rehabilitation device that would allow patients suffering from hemiparesis to perform repetitive motion therapy in their homes. This therapy is commonly used in restoring lost motor skills by helping the brain rebuild neural pathways lost as a result of disease or trauma such as stroke. In removing the need for a physical therapist to conduct these exercises, the patients would be able to devote more time to their therapy at a lower cost while achieving a greater level of independence.
Our soft robotics work by actuating the user's joints with pairs of antagonistic cables (as one shortens the other extends) with one cable of each pair responsible for flexion and the other for extension. These cables are routed with the use of a Bowden cable system and are actuated by DC motors, each with a spool specially sized to reel in, and let out, the needed amount of cable for that joint. 3D printed cable guides are attached to the fingers and arm to turn cable tension into joint torque. The goal is to eventually package all components into a backpack allowing the system to be mobile either by carrying it on the person or on the back of a wheelchair.
The highly geared DC motors we employ for actuation allow for the development of an inexpensive system with high torque and power densities and allow for the potential of a portable system. Some of the drawbacks include the inherent non-compliance of the actuators. To increase safety, comfort, and effectiveness of the design we are exploring means of adding compliance and developing active stiffness control. For elbow actuation, we are employing series elastic actuators to introduce mechanical compliance and allow for accurate sensing of joint torque. For finger actuation we are looking into using a damper with variable damping coefficient placed in series with the motor. This method has the potential for higher bandwidth and higher fidelity force tracking over series elastic actuators as well as being better suited to adapting to various load impedances. With this control we will look to develop effective exercise routines which can safely and naturally actuate the user's joints.
To add feedback for the control of the orthotic we will be incorporating flex sensors, pressure sensors, and EMG surface electrodes. We plan to use EMG signals to determine grasp and elbow flexion intent allowing for user input to the control. In collaboration with Prof. Ted Clancy's group at WPI we are working to incorporate the surface mount electrodes featured in the robotic rehabilitation devices into a standalone system that could be worn by any user and be able to accurately read their electromyograpic signals. The project is being focused around standardizing the electrodes used for sEMG work from previous rehab projects and adapting them such that they can be mounted in a soft compliant housing that the user can put on and be used without any major set up or accommodations being needed to use.
Graduate Students Involved