| 摘要 |
PURPOSE:To obtain sufficient assistance effect by constructing a rotation ring to roll along a V-shaped guide face in a cover. CONSTITUTION:When a rotation shaft 2 starts to drive, a cover 3, that is, a V-shaped guide face 21 also starts to rotate in the same direction and at the same speed, thereby, a rotation ring 4 starts to roll in the same direction along the V-shaped guide face 21 at a lowest position of the cover 3. When the rotation ring 4 rolls along the V-shaped guide face 21, contact points between ridges 19 of dovetail plates 12 and inclined faces 20 of the V-shaped guide face 21 continuously shifts to the next dovetail plates 12 sequentially. Force is applied, accordingly, from the rotation ring 4 in a direction so as to assist the rotation of the cover 3, to the cover 3 through the contact points between dovetail projections 12 and the V-shaped guide face 21. |
