## 1 Introduction  
Recently, pneumatic actuators are used in various robot systems due to their high mass power ratio and flexibility. To realize the positioning of pneumatic actuators with high precision and short response, many studies on pneumatic servo systems are conducted to date [1; 2; 3; 4; 5]. In pneumatic servo systems including pneumatic robot systems, pneumatic servo valves are important components that determine the overall performance of the system. The most commonly used servo valves are broadly divided into nozzle flapper-type servo valves and spool-type servo valves [6], whose overall structures are shown in Figures 1 and 2. The structure of the nozzle flapper-type servo valve is such that atmospheric release exists at all times, and thus, air consumption is high. The spool-type servo valve consumes less air as compared to the nozzle flapper-type servo valve. However, there is loss due to leakage from the sliding portion gap of the spool. When you try to use a small compressor, which can be embedded in the pneumatic system, the leakage amount can be a significant problem. Therefore, when a large number of servo valves are used in the systems that requires small compressors (for e.g., multi-degree-of-freedom robot systems), the consumption of air due to leakage from valves becomes a significant problem. Decreases in leakage from the servo valve and air consumption of the complete system aid in solving these problems and saving energy. Previous studies have developed a servo valve that reduces leakage by increasing the amount of overlap of the spool-type valve [7]. However, the structure of such valves consists of a sliding part in the flow path, and thus, it is difficult to completely eliminate the leakage. Studies on valves have also examined using vibration-driven poppets as valves without leakage to the exterior [8; 9; 10]. However, it is difficult to adjust the vibration-driven flow rate in such valves, and they are not suitable for a robot system that requires precise control. Alternatively, it is conceivable to use a peristaltic pump or pinch-type valve by using an elastic tube to suppress leakage to the exterior. In a pneumatic robot system, controlling enough flow rate with high speed is required, and it is not better to use pumps. On the other hand, various valves are already available as products to adjust the amount of tube blockage by a motor or a solenoid and are widely used in applications where blood and chemical liquids are controlled, and contamination is not permitted. In the microfluidics field, pinch valves that do not use tubes are actively examined [11; 12]. However, none of the valves are intended for use in high-speed and high-precision pneumatic servo systems, and characteristics in the flow rate control are not clarified. Additionally, any existing valve corresponds to a two or three-way valve, and it is unable to control a double acting pneumatic actuator used for robot systems by using a single valve. A four-way valve is required to drive the double-acting pneumatic cylinder as a single unit, and a high-speed and high-accuracy response is required to operate it as a servo system. As a research example, [PERSON] et al. developed a pinch-type servo valve by using the bending of a tube [13]. Although it was wearable and exhibits low mass, its responsiveness is insufficient for use in a precise robot system. Therefore, we have developed a four-way pinch type pneumatic servo valve using a cam mechanism to realize a leakage free, precise, and high-response pneumatic servo valve that is suitable for use in a robot system [14]. However, the sensitivity of the flow rate relative to the cam angle was low around the neutral cam position. Additionally, the actual reduction effect of the air consumption was not evident, and the durability of the tube was a concern. In the present study, we newly develop a four-way pinch valve with an improved cam mechanism and a fine offset tuner.