Fig. 10

Passive compliance of the antagonistic joint. (1) Nature length of a hydraulic muscle. (2) Horizontal position with the same internal pressure \(P_{\text{avg}} \). (3) Certain initial position with different internal pressures. (4) Passive torque \(\tau _{\text{pass}} \) generated from angular displacement \(\Delta \theta _{\text{dis}} \) caused by external torque \(\tau _{\text{ext}} \) and gravitational torque \(\tau _{\text{sel}} \) received