3.2 Selection of the cylinder
We chose a cylinder that satisfies the required stroke and thrust from the geometrical relationship between the cylinder and footrest. The required specification is the stroke necessary to rotate 20 degrees in the dorsiflexion direction from the axis of rotation of the footrest and the thrust which gives a force of 40 N, which is the average value of the female hand pressing force [24] on the sole of the foot. We investigated and compared calculated values and actual measurements, which is the relationship between the ankle joint angle, the thrust and the force applied to the soles of the foot. Parameters used for calculations in Figure 4: N signifies the foot reaction force; F represents the cylinder thrust; R denotes the distance from the axis of rotation of the footrest to the measurement position; r stands for the distance from the axis of rotation of the footrest to the attachment part of the cylinder rod and footrest from the rotation axis of the footrest; p expresses the distance from the cylinder mounting part to the rotation axis; q is the cylinder length; θ is the angle between q and r. Here, R, r and p are invariable even when the footrest rotates. They are known parameters. Calculating based on these equations revealed that strokes of 43.6mm in the pushing direction and 98.2mm in the pull direction are required. It was found that a stroke of 43.6 mm in the pushing direction and 98.2 mm in the pulling direction is necessary since a range of movement of 20 degrees in the dorsiflexion direction and 45 degrees in the dorsiflexion direction is necessary.