Linear actuator with force switch for detecting axial load

摘要

A linear actuator for actuating a valve or other control element. The actuator is characterized by means for measuring the in-line or axial force exerted on a drive sleeve after the valve disk engages the valve seat or back seat. In response to detection of an axial force in excess of a predetermined threshold level, the motor (2) is de-energized. The linear actuator includes a drive sleeve (14) rotatably supported by bearings; a pack of friction springs (18) for axially supporting the drive sleeve; a drive motor (2) for driving rotation of the drive sleeve by way of gearing; a ball screw nut coupled inside and coaxial with the drive sleeve such that the ball screw nut rotates with the drive sleeve; a ball screw which translates axially in response to rotation of the ball screw nut; an anti-rotation device (23) for preventing rotation of the ball screw during its translation; a switch (8) for controlling the ON-OFF state of the motor; and a mechanical assembly for actuating the switch in response to a predetermined amount of axial deflection of the drive sleeve.