Position actuator with a load-responsive limit control apparatus.

摘要

A position actuator includes a motor driven low efficiency lead screw (8) with a follower (23) moving in parallel relation to a valve coupler (9) of a valve shaft and a switch operator (62) of a force/torque limit (10) unit. A lever (15) is pivotally coupled to the follower (23), coupler (9) and the operator (62). The lever pivots (15) about the operator (62) to move the valve coupler (9) at a valve limit. The coupler (9) cannot move and the lever pivots (15) about the coupler (9) to move the operator (62) and actuates a switch to signal an alarm and/or another controller. The limit unit includes an elongated coil spring (54) having a low spring rate within a tubular housing (49) having mounting plates (50) for switches. The operator (62) passes through the spring (54) and has retainers abutting the spring ends and the housing (49) to provide a factory spring calibration. The lever couplings (34) include a lever opening with spaced knife-edges (31,32) to provide low friction engagement. In a damper control, limit unit is mounted to a driven sector gear (98) and a lever (104) is secured to a damper shaft (91). At limit condition, the shaft (91) cannot move and sector gear (98) movement moves the operator (102) to actuate the switch. A linear actuator (112) may be connected directly to the operator for in-line movement. The limit unit (10) provides precise identification of the actuator movement (112) and may provide end limit signals for initializing a stepper motor (7) control (118) and/or a constant speed motor control.