Origami Structured Compliant Actuator (OSCA)

As a perhaps unintended consequence of their design, soft actuators typically store significant elastic energy as they expand under fluid pressure. Certain applications rely on a limited power budget. For example, we are interested in transmitting body power from a less impaired joint to assist in generating motions of an impaired joint. Thus stored elastic energy is not useful in our application. In this paper, we introduce the Origami Structured Compliant Actuator (OSCA), in which a fluid chamber is surrounded with rigid faces connected through hinges that guide the expansion of the chamber. The OSCA design ensures that no elastic energy is stored and expansion in off-axis directions is in fact converted to on-axis forces or torques. The OSCA design also features a kinematic singularity that gives rise to a significant mechanical advantage over certain ranges of motion. The typical advantages of soft actuators such as backdriveability, lightweight construction, and compatibility with a fluid transmission are preserved. We present the design of a bending actuator as an example of OSCA. Experimental results from prototypes support the model-based performance predictions.