Fig. 3

Engagement and disengagement of the exoskeleton mechanical apparatus during different phases of a walking stride. The upper portion of the figure shows the action of the exoskeleton during a stride and the lower portion provides a detailed view of the knee mechanism. Red arrows indicate the direction that ropes r1, r2 and r3 are moving during a specific phase (in panel E, red arrows are also used to indicate the extension of the linear springs). a During Mid-Swing, r2 begins to stretch due to knee extension and pulls the central pin. This knee extension movement continues until (b) Terminal Swing, and results in the rotation of the block which, in turn, compresses the springs. r3 also undergoes tension and causes the counterclockwise rotation of the case during Terminal Swing (considering the lateral side of the right leg). c During the Loading Response, both r2 and r3 become slack as the hip extends, which causes clockwise rotation of the central pin and case, respectively. d During Mid-Stance, r3 is stretched again as the hip rotates over the ankle and the case is locked so that there is no additional counterclockwise rotation. e During Terminal Stance, r1 is stretched due to hip extension, which pulls the pawl out of the ratchet, and allows the linear springs to extend and release their stored elastic energy. In this way, the block rotates clockwise and pulls on r3, which provides assistance during ankle powered plantarflexion. f At the subsequent Initial Swing only r1 is still stretched, while all of the other components of the device are disengaged