Controle motor de movimentos funcionais empregando sistema de estimulação elétrica em malha fechada

Abstract

Introduction: Spinal cord injury can affect several areas of the human body. Mobility, proprioception and tactile sensitivity are consequences of the disability. Adaptations are required to perform daily activities. Functional electrical stimulation (FES) is an effective rehabilitation resource for these persons because it allows the control of functional movements. This study aims to develop a motor control strategy using closed-loop FES to generate functional movements in the lower limbs of persons who have suffered spinal cord injury. This motor control strategy involves the agonist and antagonist muscle groups of the impaired lower limb. Methodology: The quadriceps muscle group is stimulated in combination with the hamstring muscle group to assess the feasibility of knee position control for the construction of a future neuroprosthesis. Written in C language, the PI controller algorithm was implemented using Raspberry Pi and ATmega328. The pulses generated by the stimulator follow the recommendations of the literature regarding the signal profile, frequency, duration, and amplitude. The FES system was tested on 10 volunteers, seven of then with spinal cord injuries, one with stroke sequelae, one with transverse myelitis, and one with polio (uninjured leg). The domain frequency method was used to find stable parameters for the PID controller. Results: In vivo tests have shown that control over knee range of motion has the same tendency among volunteers, but is also strongly dependent on the individual. The time taken to achieve the goal or the predicted range of motion was inversely proportional to the controller gain (Kc), whereas the overshooting was directly proportional to Kc. Settling time and target showed a tendency to follow the controller time constant (Tc). Conjugated stimulation between quadriceps and hamstrings accentuates the response observed with relation to stimulation of the quadriceps exclusively. When the parameters of the controller are appropriately chosen for the quadriceps, the combined stimulation improves the performance of the control, such as reducing overshoot and the time to reach the target extension. Conclusions: It is concluded that FES can be used to control the range of motion of the knee of people with spinal cord injury, being able to reach a predefined range safely. Controller parameters can be adjusted to suit the characteristics of each volunteer’s, making it possible to reach the target extension with greater or lesser speed, reduce overshoot and even minimize undesirable oscillations. The combined stimulation of the quadriceps and hamstring muscle groups, with the parameters of the controller properly chosen, promotes better control of the extension.