| 摘要 |
A door operated drive assembly comprising an electric drive motor mechanically connected to a door pulling device by a transmission in the form of a belt drive or the like, utilizes an extension of a plate that is swingable in response to deviations of application pressure of the drive belt on belt guide pulleys carried thereby to trigger a switching arrangement utilized to trigger stopping or reversal of the drive motor. In order to make actuation of the switching arrangement a function of the degree of pressure applied by the drive belt, the plate is elastically loaded toward a middle position of its range of swingable movement. The elastic loading of the plate in accordance with a first embodiment is by way of two-arm springs positioned at opposite sides thereof, and in a second embodiment is produced by helical springs which act via actuators, on opposite sides of the plate extension. In both embodiments, the extension reaches to a position adjacent the switching arrangement, but, in the first embodiment, the extension comprises a pair of shields and the switching arrangement comprises a single photoelectric arrangement disposed therebetween, while, in the second embodiment, the extension is a straight projecting arm and the switching arrangement is a pair of switches disposed at opposite sides thereof. In accordance with a feature common to either embodiment, the drive arrangement is mounted in a multiple-component housing that comprises two components which are shiftable relative to each other between an operating position in which the drive motor is mechanically connected to a door pulley means, and a disconnected position in which the mechanical connection is interrupted.
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