Figure 2. m-SPAs with two chambers-Double Bellows. a Structure of the Double Bellows. b Arc-shape deformation geometry of the Double Bellows. c Equivalent section force diagrams of the Double Bellows. d Working flow chart of DIDO. When the conditions along the arrows are satisfied, the actuator moves to the next stage. e Working flow chart of IEAR. f Experimental pressures and theoretical pressures of DIDO and IEAR in 0-3 s. \(p_{low}\)= 10 kPa, \(\Delta p\) =10 kPa. g Steady-state actuation frequency with \(p_{high}\) from 50 to 100 kPa. h Steady-state energy consumption per cycle with \(p_{high}\) from 50 to 100 kPa.