Patent ID: 8485177

Claim:
A drive control mechanism for a vertically retractable down draft vent system, the drive control mechanism comprising: a first switch that interrupts a drive circuit that supplies power to a drive motor, the first switch interrupting the drive circuit when a framework of the vent system encounters a downwardly directed force equal to or greater than a threshold force; a second switch that interrupts the drive circuit when the framework of the vent system encounters an upwardly directed force equal to or greater than the threshold force; and an actuating element that is connected to the framework, the actuating element moving in response to the downwardly directed force equal to or greater than the threshold force to actuate the first switch to interrupt the drive circuit when the framework reaches a fully extended position, and the actuating element moving in response to the upwardly directed force equal to or greater than the threshold force to actuate the second switch to interrupt the drive circuit when the framework reaches a fully retracted position, wherein the actuating element is positioned in a non-contact position when the framework encounters no downwardly directed force or a downwardly directed force less than the threshold force and the framework encounters no upwardly directed force or an upwardly directed force less than the threshold force, the first switch does not interrupt the drive circuit when the actuating element is in the non-contact position, the second switch does not interrupt the drive circuit when the actuating element is in the non-contact position, the first or second switch continues to interrupt the drive circuit while the framework encounters a force equal to or greater than the threshold force, and when the actuating element returns to the non-contact position from a position in which the first or second switch interrupted the drive circuit, the drive circuit is completed and the drive motor operates in a direction in which it was operating before the drive circuit was interrupted by the first or second switch.