| 摘要 |
An electrically powered window shade with selectively variable shading characteristics is installable within a window opening for selectively blocking (by absorption or reflection), filtering and/or transmitting light through the window shade into a room for purposes of energy control and/or decoration, etc. This window shade comprises an upper roller assembly, a lower roller assembly, and an elongate flexible web wound on the upper and lower roller assemblies, with the web being longer than the spacing between the upper and lower roller assemblies. Each of the roller assemblies comprises an elongate tubular roller, bearings engageable with the end of the roller for rotatably journaling the ends of the roller with respect to the window. The web is scrolled onto and from the rollers as the latter are rotated about their respective longitudinal axes. A drive is provided for each of the rollers so as to drive the rollers in one direction or the other so as to scroll the web from one of the rollers onto the other roller. The drive comprises a gearmotor having an output shaft substantially coaxial with the gearmotor, and with the gearmotor being received within the roller, with the output shaft being coaxial with the roller. The gear motor is fixed against rotation with respect to the frame. Further, each of the gearmotors includes a torsional spring for maintaining the web taut as it is scrolled and unscrolled from one roller to the other, and while the web is stationary and to accommodate changes in rotation rates and roll diameters as the web is scrolled and unscrolled. Specifically, this torsional spring operatively connects the output shaft of each gearmotor with its respective roller. The torsional spring of one of the rollers is wound in one direction (e.g., clockwise), and the other torsional spring associated with the other gearmotor is wound in the other direction (e.g., counterclockwise) so that upon initial energization of one gearmotor or the other, differences in rotational speed and start-up times between the gearmotors will be taken up.
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