Modeling Vacuum Bellows Soft Pneumatic Actuators with Optimal Mechanical Performance

This paper presents the concept and model of "Vacuum Bellows," a cylindrical membrane-reinforced contractile vacuum soft pneumatic actuator (V-SPAs). These actuators consist of a tubular membrane connected to a series of interior rigid rings periodically spaced along its length. Our model shows how the rings can be spaced to achieve a desired actuator force profile. For example, the contraction ratio can be maximized by spacing the rings one diameter apart inside the tube. The work output of the actuator can be concentrated in the initial portion of the stroke by increasing the ring spacing. And, usefully, an approximately constant force-to-pressure relationship can be created by spacing the rings a fraction of a diameter apart. Our experimental results highlight the utility of the model and some practical considerations for actuator fabrication and use. The experimental results demonstrate how the ring spacing can be used to achieve high peak forces per unit pressure (three times greater than an equivalent-diameter piston achieved experimentally) or large contractions (achieved contraction to 30% of the extended length). Our model suggests that this performance can be improved with improved fabrication techniques.