Abstract
Two sets of bellows are located on the same axis in an enclosure which is opened by an exhaust vent to the atmosphere. A nozzle is put on a movable end of one of the sets of bellows (feedback bellows) and faces the movable closed end of the other set (input bellows). The inside of the feedback bellows is connected to a supply chamber, of which the pressure is regulated to a constant value, through an orifice provided in the fixed end of the feedback bellows. The pneumatic circuit which is composed of the nozzle, the orifice and the feedback bellows is so arranged to have bistable transfer characteristics. Another path with a restrictor connects the supply chamber with the inside of the enclosure. The chamber in the feedback bellows is also connected to another set of bellows through an adjustable restrictor built in the fixed end of the bellows, The third bellow is also set in the enclosure and its closed movable end is used to control the flow out area of the exhaust vent.
When a trigger pulse is applied to the input bellows, the nozzle contacts its counterface and the output pressure (in the feedback bellows) jumps from a low level to a high level equal to the supply pressure. Then, the pressure of the third bellows increases gradually with a speed given by the resistance of the adjustable restrictor and the capacity of the bellows. This pressure increase makes the pressure in the enclosure high, because of the resistance increase of the vent. When the pressure in the enclosure reaches a constant level, the nozzle separates abruptly from its counterface by the compressive action of the two sets of bellows and the output pressure falls down to the low level.
