Pneumatic actuators

Claim 1

In a pneumatic actuator having a double acting assembly of interconnected first pistons forming in a common chamber, a series of individually expansible chambers with independent, respective strokes and arranged to provide for an end connector a plurality of possible discrete positions differently spaced from a datum, a rack mounted for lengthwise movement with said end connector, said rack being provided with a plurality of teeth with recesses between said teeth, a plunger arranged to cooperate with the rack to secure the rack and end connector in at least some of the said positions, one end of the plunger being shaped for engagement with said recesses, a second piston for moving said plunger relative to the rack, to engage and disengage from the rack, and a plurality of valves for connecting selected ones of said chambers to an air supply, wherein the improvement comprises counter means including a first light source and a first photocell disposed adjacent said rack so that on opposite sides of the path of said teeth the illumination by the light source is interrupted by the passage of the teeth of the rack, thereby to cause said photocell to produce, when said rack is moved, an output having a number of successive interruptions, the number of interruptions providing an indication of the extent of movement of the rack.