| 摘要 |
PURPOSE:To realize silent operation and high time precision by making an annular balance of metal and an engaging piece and an escape wheel of resin. CONSTITUTION:The escape wheel 9 is rotated with the energizing force of a mainspring and the annular balance reciprocates. The engaging piece 23 fitted to the annular balance 16 engages and disengages the escape wheel 9 and teeth 10 with and from each other repeatedly to turn the escape wheel 9 stepwise, thus controlling the rotation of the escape wheel 9 to a specific speed. For the purpose, the annular balance 16 is made of metal and the engaging piece 23 implanted therein and the escape wheel 9 are made of resin to attain the engagement and is engagement silently, thereby realizing low-noise operation. Even if the ambient temperature varies to cause the annular balance 16 and escaping wheel 9 to move closely to or away from each other relatively owing to their difference in percentage of elongation or contraction, an extension piece 25 extends or contracts and the engaging piece 23 moves toward or away from the escape wheel 9, thereby canceling the relative movement between the annular balance 15 and escape wheel 9. Therefore, the depth of the engagement between the engaging piece 23 and teeth 10 of the escape wheel 9 is made constant regardless of temperature condition and the time precision is held high. |
