| 摘要 |
PURPOSE:To enable the opening operations of an upper unit to be performed smoothly all the time by allowing a return spring to perform its energizing action under well-balanced conditions from the beginning to the end of the opening operations of the upper unit. CONSTITUTION:A cam 26 has a length sufficient to be constantly in close contact with a roller 60 which rolls along with the opening operation of an upper unit 20. When the upper unit 20 is in a state in which it is closed to a lower unit 30, a return spring 50 is in a state to be energized to store sufficient elastricity. Thereby, when a locking device is released to cause the upper unit 20 to be opened by a hinging device 40 so as to return clockwise, an elastic force energized by the return spring 50 to store a sufficient energy acts as an angular moment, and accordingly, the weight of the upper unit 20 is decreased so that its opening operation can be performed very easily.
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