Figure 1. Working Principle of Internal Exhaust Air Recirculation (IEAR). a The working principle of IEAR. ①Inlet to inflate the chamber ②Outlet to deflate the chamber ③Branch for internal recirculation ④Branch to the atmosphere ⑤Closed branch for external recirculation. We have DIDO(①②④), IEAR (①②③④), and EEAR (①②⑤). IEAR recirculates compressed air by a valve island. Compared with DIDO, IEAR recycles compressed air and recovers the energy of the system. Compared with EEAR, IEAR does not require an air buffer and air recompression by the pump. b The pressure-volume relationship (constant temperature, open system). In such a system \(\int pdV=W_{load}+W_{material}+W_{dissipation}\), plays a metric of the input work. With IEAR, exhaust air is directly transmitted and recirculated between chambers through a specialized valve island, thereby shortening the working cycle (the arrow path) and reducing the required input work. c Traditionally, compressed air directly inlet and directly outlet (DIDO) the chambers of m-SPAs, leading to markedly energy loss and poor actuation performance (speed, energy efficiency, supplied pressure, system power, etc.).