Chairs and seats – Movable back
Reexamination Certificate
2000-08-18
2001-10-09
Nelson, Jr., Milton (Department: 3636)
Chairs and seats
Movable back
Reexamination Certificate
active
06299253
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to telescopic positioning mechanisms and more particularly to a telescopic positioning mechanism for chair backrest so as to adjust the height of the backrest relative to chair seat.
BACKGROUND OF THE INVENTION
Office chairs are widely used throughout the world. In general, such chair is equipped with a padded backrest and even a pair of armrests for providing a degree of comfort to the seated person. Further, some backrests in such chairs are height adjustable as detailed below.
A conventional height adjustable backrest is disclosed in, for example, U.S. Pat. No. 4,639,039 entitled “Height Adjustable Mechanism For Chair Backrest”. Such mechanism
12
comprises a guide
24
secured to support
18
and a channel
28
secured to backrest
22
and mounted for vertical sliding movement on guide
24
. In operation, bias latch pin
36
of latch bar
32
along slot
38
for engaging latch pin
36
with one of notches
51
through
56
so as to lock backrest
22
in one of height positions H
1
through H
6
.
But this is unsatisfactory for the purpose for which the invention is concerned for the following reasons:
1. The positioning of torsion spring
40
is not well maintained. As such, torsion spring
40
is prone to disengage from the predetermined position thus failing the mechanism
12
.
2. The biasing of latch bar
32
is made possible totally by virtue of the spring force of legs
64
,
66
of torsion spring
40
. This may cause fatigue to torsion spring
40
after a short period of time of intensive use, resulting in a malfunction of torsion spring
40
.
3. It is possible that latch bar
32
is over headed in operation when torsion spring
40
is malfunctioned.
In view of the foregoing, it is desirable to provide an improved telescopic positioning mechanism for chair backrest in order to overcome the above drawbacks of prior art.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a telescopic positioning mechanism mountable on a chair such that backrest of chair can be manually raised or lowered to one of a plurality of vertical positions relative to the chair seat in a simple reliable manner.
To achieve the above and other objects, the telescopic positioning mechanism of present invention comprises a guide rigidly secured to a support of a chair and a channel rigidly secured to a backrest wherein channel comprises a notched member consists of a plurality of notches in a side of slot, a top ramp in the top end of slot, a bottom ramp in the bottom end of slot, and two vertically extending grooves on opposite sides; guide comprises a center section, two side tongues for slidably engaging with the grooves, a plurality of horizontal and vertical flanges on the rear side, a plurality of horizontal grooves defined by the flanges, a recess adjacent the groove, a stud, and a torsion spring put on stud; latch member is biased by the torsion spring to engage with one notch in a locked position, the latch member comprises a ratchet bar, two posts engaged with the grooves, and a projection; a bottom ramp is sloped downwardly from the lowest notch; and a top ramp is sloped upwardly from the highest notch. In operation, pull backrest up in adjusting the height of channel with respect to guide. In turn, the locked latch member is pushed rightward to clear from the notch. Latch member is biased leftward to move into engagement with the next adjacent notch by virtue of torsion spring. In a highest position, ratchet bar passes over the lowest notch to cause the latch member to move along the bottom ramp to a free sliding position wherein projection is engaged with recess. Then pushes down backrest to cause it to reach its lowest position with the ratchet bar passing over the highest notch such that latch member moves along top ramp to a free sliding position wherein projection is out of engagement with recess. Latch member is again locked by notched member by virtue of torsion spring.
The above and other objects, features and advantages of the present invention will become apparent from the following detailed description taken with the accompanying drawings.
REFERENCES:
patent: 4639039 (1987-01-01), Donovan
patent: 5649741 (1997-07-01), Beggs
patent: 5685609 (1997-11-01), Miotto
patent: 5951107 (1999-09-01), Tornero
patent: 6155643 (2000-12-01), Gorgi et al.
Jr. Milton Nelson
Pro-Techtor Inter-national Services
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