Pneumatic actuator

A pneumatic actuator comprising:

• a drive pin coupled to a rotatable drive shaft;
• a diaphragm housing formed by an upper housing and a lower housing;
• a resilient diaphragm;
• a cap-shaped diaphragm cam rigidly attached to said resilient diaphragm, said resilient diaphragm being mounted in said housing for restraining torsional movement of said diaphragm cam wherein said diaphragm cam is provided with a pair of opposed arcuate drive slots which engage said drive pin so as to be rotatable in said drive slots such that a linear motion of said diaphragm cam produces a rotational movement of said drive pin and said drive shaft;
• said diaphragm cam having at least one correction slot of a particular shape cut through the cam wall at the bottom edge thereof and
• said lower housing having at least one correction cam formed at the bottom wall thereof and projecting from same, and beneath said correction slot, said correction cam and said correction slot being normally disengaged from one another, said correction cam having the shape of said correction slot, said correction cam and said correction slot having respective engagable oblique surfaces,
• whereby said correction cam is firmly seated in said correction slot when said diaphragm cam descends within said housing;
• and
• whereby rotational movement of said diaphragm cam is corrected and precise rotation of said drive shaft is produced.