A Novel User-Controlled Assisted Standing Control System for a Hybrid Neuroprosthesis

Spinal cord injury (SCI) is a serious condition with 17,000 new cases each year and an estimated total of 282,000 people in the United States who have SCI. Some people with SCI who have paraplegia suffer from paralysis, muscle spasticity, bone changes, chronic pain and other problems. Active orthoses such as the ReWalk, EXPOS, and Ekso have improved the quality of life of people with SCI. The hybrid neuroprosthesis is an active orthosis that uses functional electrical stimulation (FES) at the quadriceps and has two main purposes: restoring mobility in people with SCI and providing physical therapy for the user outside of a clinical setting. To mobilize people with SCI, the neuroprosthesis must provide assisted movement for a sitting to standing motion. A standing control system developed by the Pitt Neuromuscular Control and Robotics Laboratory (NCRL) before this proposed system did not give enough control of the movement to the user and FES alone did not provide enough torque at the knees for standing. The NCRL neuroprosthesis was modified to include a harmonic gearmotor at the knees, a thumb joystick for user control, and a force sensing walker. A control system using a finite state machine (FSM) was designed to perform hybrid standing in the neuroprosthesis. The FSM is divided into 3 states and uses 5 separate controllers: a tracking controller for forward leaning during sitting, a tracking controller to synchronize the knees, a tracking controller to lock the knees during standing, a hip tracking controller, and openloop FES. Four experiments were performed on subjects to analyze control performance, power usage, and energy consumption during motors only and hybrid standing. A subject with SCI successfully performed several trials of hybrid standing. The controllers performed sufficiently accurately, and several minor control problems were fixed. The highest average energy consumption at the knee motors was 88.4 joules during experiment 1. The hybrid standing experiment demonstrated a modest energy reduction of 15% in a subject with SCI. The hybrid standing demonstrated a high energy reduction of 74% in the right knee in experiment 2, through hybrid actuation and a slower standing speed

Control Methods for Compensation and Inhibition of Muscle Fatigue in Neuroprosthetic Devices

For individuals that suffer from paraplegia activities of daily life are greatly inhibited. With over 5,000 new cases of paraplegia each year in the United States alone there is a clear need to develop technologies to restore lower extremity function to these individuals. One method that has shown promise for restoring functional movement to paralyzed limbs is the use of functional electrical stimulation (FES), which is the application of electrical stimulation to produce a muscle contraction and create a functional movement. This technique has been shown to be able to restore numerous motor functions in persons with disability; however, the application of the electrical stimulation can cause rapid muscle fatigue, limiting the duration that these devices may be used. As an alternative some research has developed fully actuated orthoses to restore motor function via electric motors. These devices have been shown to be capable of achieving greater walking durations than FES systems; however, these systems can be significantly larger and heavier. To develop smaller and more efficient systems some research has explored hybrid neuroprostheses that use both FES and electric motors. However, these hybrid systems present new research challenges. In this dissertation novel control methods to compensate/inhibit muscle fatigue in neuroprosthetic and hybrid neuroprosthetic devices are developed. Some of these methods seek to compensate for the effects of fatigue by using fatigue dynamics in the control development or by minimizing the amount of stimulation used to produce a desired movement. Other control methods presented here seek to inhibit the effects of muscle fatigue by adding an electric motor as additional actuation. These control methods use either switching or cooperative control of FES and an electric motor to achieve longer durations of use than systems that strictly use FES. Finally, the necessity for the continued study of hybrid gait restoration systems is facilitated through simulations of walking with a hybrid neuroprosthesis. The results of these simulations demonstrate the potential for hybrid neuroprosthesis gait restoration devices to be more efficient and achieve greater walking durations than systems that use strictly FES or strictly electric motors