Fail-safe attachment for an actuator

A part-turn actuator having a rotatable output member and a cam plate mounted on said output member for rotation therewith to actuate at least one switch for the control of the actuator, said actuator having a fail-safe mechanism comprising:

• a rotatable spring operated cam plate coupling;
• means for manually setting said spring and for rotating said cam plate coupling in one direction of rotation to an inoperative position;
• latch means for holding said cam plate coupling in said inoperative position;
• said fail-safe mechanism being independent of the normal operation of the actuator when said cam plate coupling is held in its inoperative position;
• said latch means comprising:
• a first movable lever positioned by electrical means;
• a second movable lever having one end engageable with said first movable lever, a pawl pivotally mounted to said lever;
• said electrical means, when energized, holding said first movable lever in an inoperative position urging said second movable lever in a direction for engaging said pawl to said cam plate coupling, latching it in an inoperative position, said pawl being pivotally movable to allow rotation of said cam plate coupling in said one direction of movement to latch said cam plate coupling by said pawl in its inoperative position, said mechanism being rendered operative by an interruption of electrical current to said electrical means, the deenergization of said electrical means releasing said first movable lever to allow movement of said first movable lever from its inoperative position to a position for releasing said second lever disengaging said pawl, whereby said cam plate coupling is released so as to rotate in its other direction to engage drivably the switch cam plate moving the output member of the actuator to a predetermined fail-safe position by the stored energy of the spring force.