| 摘要 |
A drive for opening and closing air flow control devices, such as ventilation curtains, in a poultry house or the like includes a ball screw drive which is automatically disengaged during a power failure to allow the air flow control devices to drop open partially or fully. Upon restoration of power, the air flow control device is automatically restored to a set position. A digital controller receives inputs from a thermostat and/or pressure sensor which cause periodic actuation of a gear motor that rotates the ball screw and thereby moves a block to which one or more ventilation curtains are attached by means of lifting cables. An electromagnetically actuated brake is attached to the motor which holds its output shaft in position during normal operation. Upon occurrence of a power failure, the brake is deenergized so that the output shaft of the motor, and therefore the ball screw, are allowed to rotate freely, thereby allowing the ventilation curtains to drop to a partially opened position under the force of gravity. Alteratively, an electromagnetic clutch is placed between the motor shaft and the ball screw which disengages upon the occurrence of a power failure, and allows the ventilation curtains to drop open a substantial amount by decoupling the motor, which has inherent frictional resistance, from the ball screw. The use of the ball screw drive in conjunction with a heavy duty thrust bearing positioned between the ball screw and the motor provides a greatly increased lifting capacity over prior art power drives.
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