| 摘要 |
A pocket member is fixed or adapted to be fixed to the seat plate of a chair. A horizontal shaft is rotatably mounted in said pocket member. A bearing member and a pinion are corotationally mounted on said shaft. A holder is pivoted to said pocket member on a horizontal axis and connected or adapted to be connected to the back rest of said chair. A gear segment is carried by said holder and in mesh with said pinion. A nonrotatable ratchet ring is coaxial with said shaft and secured to said pocket member and carries internal teeth. Two symmetrically opposite locking pawls are pivoted to said bearing member on axes which are parallel to said shaft. Each of said locking pawls has a toothed outer side which faces said internal teeth and is engageable therewith in such a manner that one of said locking pawls is engageable with said internal teeth to hold said bearing member and shaft against rotation in one, and only one, direction, and the other of said locking pawls is engageable with said internal teeth to hold said bearing member and shaft against rotation in the opposite, and only in the opposite, direction. Spring means urge said locking pawls into engagement with said internal teeth. Two cam followers are provided, each of which is generally parallel to said shaft and carried by one of said locking pawls. A hand wheel is freely rotatably mounted on said shaft and provided with first cam faces which are adapted to engage said cam follower of that of said locking pawls which normally holds said bearing member against rotation in the direction in which the hand wheel is being rotated, and with two spaced apart second cam faces. An additional cam follower is carried by said bearing member and extends with a backlash between said second cam faces. |
