Inverted Pendulum Standing Apparatus for Investigating Closed-Loop Control of Ankle Joint Muscle Contractions during Functional Electrical Stimulation

Figure 3

Examples of the pendulum fluctuation (angle and torque) during the four different conditions (single subject): (1) voluntary control—NOstim (top graph); (2) adequate controller—PDstimLD (second graph from top, using a P-gain of 100 Nm/rad and a D-gain of 85 Nm·s/rad); (3) inadequate controller—PDstimSD (third graph from top, using a P-gain of 100 Nm/rad and a D-gain of 30 Nm·s/rad); and (4) constant stimulation—CONSTstim (bottom graph, using a stimulation amplitude of 33 mA). The left column shows the angular displacements and the right column the measured torque. Positive angles and torques in the panels correspond to plantarflexor contractions of the subject. For the CONSTstim and PDstimSD conditions, the pendulum movement was interrupted by the built-in safety stoppers after approximately 10 seconds into the trials.

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