Ratchet-type micro-hydraulic actuator to mimic muscle behavior

Piezo actuators are usually found in applications where high precision, high stiffness, but small displacement are required. This makes them the actuation principle of choice for many microand nano-positioning applications. In contrast, animal and human muscles have a comparatively small stiffness, but long displacements. Their force is generated by a ratchet-type mechanism of the actin and myosin cross-bridges. In this paper, we will present a piezohydraulic “ratchet” design, using two valves to mimic the actin-myosin cross-bridges. The actuator is thus able to realize very long linear actuator displacements. The mechanism will be analyzed, and it will be shown that force-velocity and power characteristics of this type of actuator design are highly adaptable, and comparable to muscle tissue. When designing robots for human-robot collaboration, or social machines operating in close proximity to humans, this makes them inherently safe, even when control fails. Measurements from a prototype actuator are shown, demonstrating the practical feasibility of the design.