We show a calculation formula for obtaining θ from the cosine theorem in Eq.(7), and equation for obtaining the foot reaction force N by moment balancing in Eq.(8).
\(\cos\theta=\frac{q^2+r^2-p^2}{2qr}\) (7)
\(N=\frac{F\sin\theta\cdot r}{R}\) (8)
Calculating based on these equations revealed that strokes of 43.6mm in the pushing direction and 98.2mm in the pull direction are required.
The thrust of the cylinder can be obtained by (pressure receiving area) × (internal pressure of the cylinder). Originally, we should have chosen a reciprocating cylinder. However, since this study covers with ankle spasm of cerebral infarction patients, portability must be achieved through size and weight reduction. For the reason, we chose a single acting cylinder for only dorsiflexion operation.
In the selected cylinder (M24D 150, Airpel Corp.) , As a result of the calculation, 39.4 N was obtained at 0.1 MPa, the thrust obtained by the experiment was 40.1 N, which was a satisfactory value and the accuracy of the calculation formula was confirmed.
3.3 Design for control system
To realize the rehabilitation operation of a physical therapist by control design, an ankle rehabilitation device designed with the control system to switch from position control to force control. In this control, training for the target angle is repeated for the healthy person or the users with weak contracture of the ankle by position control. Even if position control is performed by contracture, for patients who do not reach the target angle, position control is switched to the force control. A flowchart is shown in Figure 5.