Rack and pinion pneumatic actuator with counter-pressure control and damping device

A pneumatic rotary actuator comprising:

• a hollow body (10) defining first and second piston chambers (11, 12) having their longitudinal axes arranged parallel in the hollow body, and also having an air pressure inlet port (27, 28) arranged at one end of each of the piston chambers;
• a single acting rack and piston assembly reciprocable in each of the piston chambers, each of the assemblies having a rack (13, 14) provided with piston members (20, 24;
• 19, 23) at opposite ends thereof;
• an output shaft (16) having a gear pinion (15) meshing with the rack and pinion assemblies;
• an air pressure-actuated cushioning means including:
• a flow restricting control valve (42, 44) offset from a longitudinal axis of each of the piston chambers;
• and
• a counter-pressure actuated dampening means (30, 31, 36, 48) including:
• tightly closable counter-pressure chamber means (25, 26) at another end of each of the piston chambers, said another end being opposite to the air-pressure inlet port;
• duct means (30) axially extending between the opposite ends of each rack and piston assembly, to communicate between both sides of each piston chamber, one end of said duct means opening to and being in direct communication with the air pressure inlet port of the piston chamber;
• and
• a check valve (31) to keep normally another end of the duct means closed with respect to the piston chamber;
• interacting sealing means (36, 48) coaxially arranged at the other end of the duct means and at the other end of the piston chamber, respectively, to close communication of the duct means with each of the piston chambers defining the counter-pressure means when the rack and piston assemblies approach one end of their strokes;
• and
• check valve actuating means (36) coaxially arranged with respect to each of the piston chambers and the interacting sealing means, said check valve actuating means having a thrust pin member (36) protruding into each of the piston chambers and into the duct means through said interacting sealing means;
• said thrust pin member acting to open the check valve to communicate rapidly with and bring both sides of each piston chamber to equal air pressures shortly before the sealing means interact to close the duct means and before venting the counter-pressure chamber means through the flow restricting control valve.