发明授权
US6120022A Random number selector for overhead projectors 失效
高架投影机的随机数选择器

Random number selector for overhead projectors
摘要:
A spinner for randomly selecting a number has a very low friction bearing between a transparent spinner member and a transparent base plate. In one embodiment the base and spinner are formed of a transparent plastic such as Plexiglas, with a cone point set screw mounted in a threaded hole of the base plate and providing a narrow point for seating of the spinner member. A transparency with annularly arranged numbers may be placed at the bottom side of the transparent base plate, and different numerical arrays or symbol arrays may be selected. The spinner member has a central hole fitted with a central hub that has a recess formed into an internal cone shaped apex. The cone angle of the set screw point is steeper than that in the apex of the hub recess, so that the spinner member rests essentially only on the narrow point of the set screw. When the number selector device is placed on an overhead projector, as in a classroom setting, a gentle turn of the spinner member will generate five or ten revolutions of the spinner arrow, which gradually comes to a stop in the random selection of a number or symbol.
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