Environmental position actuator apparatus having load responsive limit

Abstract

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