| 摘要 |
PROBLEM TO BE SOLVED: To provide an AC clock for mechanically changing the frequency without depending on an electric circuit. SOLUTION: A driving gear 4 is fixed to an output shaft 3a of a synchronous motor using an AC power supply. The driving gear 4 is rotated at two speeds in synchronization with two different frequencies of the AC power supply. Two intermediate gears 8, 9 are selectively engaged with the driving gear 4. An output gear 5 is engaged with the intermediate gears 8, 9. The output gear 5 to which the rotation of the driving gear 4 is transmitted from one of the intermediate gears 8, 9 is always rotated at a constant speed. The rotating speed of the output gear 5 is reduced via a reducing gear 10 in driving a pointer of a clock. Each of the intermediate gears 8, 9, the number of teeth of which is set such that two rotating speeds of the driving gear 4 are changed to a constant rotating speed of the output gear 5 to be transmitted, is rotatably provided on a supporting plate 6 to be oscillated around the output gear 5. A spring 11 is latched to the supporting plate 6 for energizing the intermediate gears 8, 9 to two stable positions where they are selectively engaged with the driving gear 4.
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