Master of Science

thesisFor those who have suffered stroke or spinal cord injury, rehabilitation is often the answer for improving gait function. Rehabilitative exercises, which often focus on the legs and deemphasize the role of the upper limbs, are done to help stimulate muscles and exploit neuroplasticity for the diminished functions. However, it has been shown that upper limb muscle activity can induce lower limb muscle activity. It has also been shown that proper arm swing is necessary during gait for balance. This thesis presents the design concept and fabricated prototype of a device that swings the arms during gait rehabilitation. The device is low-powered, lightweight, wearable, and capable of assisting the user's arm swing in the sagittal plane and has unhindered kinematics in the remaining unactuated degrees of freedom. The design comprises three key subassemblies: a backpack frame, an underactuated arm-swing mechanism, and a power train to transfer and amplify motor torques to the arm-swing mechanism. Tests are performed to validate the shoulder-angle prediction equations based on the noncollocated motor-angle sensor measurements, to validate the device's ability to provide adequate torque to generate arm-swing in a passive user, and to investigate whether or not the user's active involvement can be observed by examining motor torque or shoulder angles. The results show that the device does provide sufficient torque to move the arms with a factor of safety, but that the model-based shoulder-angle estimates obtained from the motor measurements have nonnegligible error with the current prototype. It is recommended that a Proportional-Derivative (PD) controller with high PD gains be used with the device because of its low root mean square (RMS) tracking error, shoulder-angle amplitude creation, and ability to diagnose user-assistance level (i.e., is the user passive or actively assisting arm swing) online by observing shoulder-angle amplitudes and peak motor torques

A Shoulder Mechanisms for Assisting Upper Arm Function With Distally Located Actuators

This thesis presents a new design for a shoulder assistive device based on a modified double parallelogram linkage (DPL). The DPL allows for active support of the arm motion in the sagittal plane, while enabling the use of a distally located motor that can be mounted around the user’s waist to improve the weight distribution. The development of the DPL provides an unobtrusive mechanism for assisting the movement of the shoulder joint through a wide range of motion. This design contains three degrees-of-freedom (DOFs) and a rigid structure for supporting the arm. The modified DPL uses a cable-driven system to transfer the torque of the motor mounted on the user’s back through the links to the arm. The proposed design assists with the flexion/extension of the arm, while allowing the adduction/abduction and internal/external rotations to be unconstrained. A kinematic analysis of the cable system and linkage interaction is presented, and a prototype is fabricated to verify the proposed concept