| 摘要 |
PROBLEM TO BE SOLVED: To precisely control the speed of closing an upper frame by providing the variable braking force imparting mechanism capable of increasing the braking force corresponding to the progress of the closing operation. SOLUTION: In this device, on starting the closing operation of the upper frame 12 by applying the lock releasing force to the upper frame 12, the top end 301 of a lever 302 slides on a stepped part 122b of a turning transmission gear 122 in company with the turning work of the turning transmission gear 122. When the closing operation of the upper frame 12 is progressed and the top end 301 of the lever 302 is allowed to pass a position AP2, the braking force applied corresponding to the closing operation of the upper frame 12 is increased, in company with the closing operation. Moreover, when the operation of closing the upper frame 12 progresses and becomes to just before the completion of closing, the range from a rotary shaft 121 to the stepped part 122b rapidly becomes longer, therefore the braking force by a coil spring 305 rapidly becomes weaker. In such a manner, by making the braking force by the coil spring 305 weakened in the finally closing stage, an operator can close the upper unit without applying the force stronger than needed. |
