Figure 7
From: Design of a series visco-elastic actuator for multi-purpose rehabilitation haptic device
System can exhibit passivity with suitable selection of P and b, for desired V. If proportional gain of the controller P is higher than 1.9, Re(Z(jw)) becomes negative and therefore the system does not exhibit passivity. When emulating a LOW impedance environment (V = 0 N/m), damping of at least b ≥ 190 Ns/m is needed, while for a HIGH impedance environment, damping of at least b ≥ 780 Ns/m is needed.