Feedback Control of Middle Finger MP Joint Using Functional Electrical Stimulation Based on the Electrical Stimulus Intensity-Joint Torque Relation Model

In this paper, we propose methods to control detailed finger movements by FES (functional electrical stimulation). It is difficult to control the detailed finger movement because the relationship between the electrical stimulus intensity applied to each muscle and the finger joint angle is discrete. However, since the relationship between the electrical stimulus intensity and the joint torque is close to a linear relationship, the relationship between the electrical stimulus intensity and the joint torque can be modeled by the two-piece linear regression model. Then, we propose a method to control the finger joint angle by adjusting the ratio of flexion torque to extension torque by PID control. Though, using the proposed method, it was possible to control to static target joint angle with high accuracy, it was necessary to correct the model by trial and error for some failed controls in some subjects. Therefore, we also propose a new method that can be modeled uniquely based on the relationship between the electrical stimulus intensity to both muscles and the joint angle. This model does not require trial and error model correction and can be modeled routinely. The new proposed model enable to control the finger to static target joint angle with high accuracy, to reduce individual differences, and to reduce the failure probability.