Vertical back adjust for chairs

A mechanism for vertical adjustability and securement of a backrest of a chair on the upright support of the chair having a housing which includes first and second housing members, and a pair of link assemblies, pivotally connected and movable between a locked position and an unlocked position. A resilient sleeve is carried by one of the link assemblies and is engageable against the upright support when the link assemblies are in the locked position to grip the upright support between the sleeve and a rod to prohibit vertical movement of the housing with respect to the upright support.

BACKGROUND OF THE INVENTION 
Office chairs normally include a vertical adjustment for the chair 
backrest. Such back adjust devices allow for limited movement of the 
backrest up and down on the back upright of a chair. Many such devices are 
difficult to operate as it often requires the release of a locking pin 
secured within a notched slot or similar arrangement in which a pin must 
be disengaged and engaged in the notches of the slot. These arrangements 
provide for a limited number of preset backrest positions. The present 
invention provides a mechanism for easy vertical adjustment and securement 
of a chair backrest and allows placement of the backrest in an infinite 
number of positions. 
SUMMARY OF THE INVENTION 
The present invention provides a mechanism for vertical adjustability and 
securement of a chair backrest which allows for easy adjustability of the 
backrest in an infinite number of positions on the back upright of a 
chair. The mechanism is operative by tilting the cushion of the backrest 
which unlocks the housing and permits relocation and locking of the 
backrest at the desired vertical height. The adjustment mechanism includes 
a housing which has first and second members pivotally attached to each 
other. First and second link assemblies are located within the housing and 
pivotally connected to each other and movable between a locked position 
and an unlocked position. A resilient sleeve member is nonrotatably 
carried by the second link assembly and a rod is carried by the first link 
assembly and spaced apart from the sleeve member to define a gap between 
the sleeve member and the rod. The upright support passes through this 
and, when the housing is in the locked position, is squeezed between the 
sleeve and the rod. A bracket is pivotally connected to the second housing 
member to connect the second housing member to the chair backrest. A 
resilient biasing means is connected between the first link assembly and 
the second link assembly to urge the first and second link assemblies to 
assume the locked position. The bracket includes a stop means which is 
engageable with the first housing member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As best seen in FIG. 1, the mechanism 2 has a housing 4 with a bracket 6 
attached thereto disposed on an upright support 10 of a chair 12. A 
backrest 13 is attached to the bracket 6. As best seen in FIG. 2, the 
housing 4 includes a first member 14 and a second member 16 pivotally 
attached to each other at the upper end. A gap 20 is provided between the 
first and second members extending the entire height of the housing 
through which the upright support 10 of chair 12 passes. The first housing 
member 14 includes a stop member 22 disposed at the bottom end, opposite 
the pivotal end thereof, and a plurality of ribs 26, 27 and 28. These ribs 
26, 27 and 28 insure proper location of the assembly components to be 
described later. The second housing member 16 includes an alignment slot 
30, shown in phantom in FIG. 2 and a sloped recess 32 shown in FIGS. 4 and 
5 in the second housing member 16. 
The bracket, 6 best illustrated in FIG. 4, is attached to the second 
housing member 16 at a pivot point 38 by a pin 40. The bracket 6 includes 
a first end 42 and a second end 44. The first end 42 of the bracket 6 
includes a member 46. The second end 44 of the bracket 6 includes a pair 
of stop feet 48 adapted to extend through a pair of slots 49, shown in 
FIG. 4, in the second housing member 16. Rotating the bracket 6 in a 
clockwise direction about pivot point 38 as viewed in FIG. 2 will result 
in rotational movement only until the feet 48 engage the stop member 22 of 
the first housing member 14 as shown in FIG. 2. This stop action prevents 
the member 46 from contacting the second housing member 16. The bracket 6 
additionally includes a plurality of apertures 50, as best seen in FIG. 4, 
for attachment of the backrest 13 to the bracket 6. 
A first link assembly 60 is disposed in the housing 4 on a first side 62 of 
the upright support 10. A second link assembly 64 is disposed in the 
housing 4 on a second side 66 of the upright support 10. The second link 
assembly 64 is pivotally connected to the first link assembly 60 at a 
pivotal connection 70 by a rod 72. The first and second link assemblies 60 
and 64 are movable between a locked position, as best shown in FIG. 3, and 
an unlocked position as best shown in FIG. 2. 
The first link assembly 60 includes a pair of links 77A and 77B which are 
spaced apart and disposed parallel to each other as best seen in FIG. 5. 
Links 77A and 77B each include a pivotal end 80 and a tensioning end 82 
disposed opposite thereto. The tensioning end 82 of each link 77A and 77B 
includes a notch 84. The second link assembly 64 includes links 79A and 
79B which are spaced apart and disposed parallel to each other, as best 
seen in FIG. 5. Links 79A and 79B each include a pivotal end 90, a 
tensioning end 92 and a central portion 94 disposed therebetween and are 
generally L-shaped in configuration. The tensioning end 92 of each link 
79A and 79B includes a notch 96. 
A tension spring 100 is connected between the links 77A and 79A at the 
tension ends 82 and 92 in the notches 84 and 96. A spring 101 similarly 
connects links 77B and 79B to provide a biasing means to urge the first 
and second link assemblies 60 and 64 to assume the locked position of FIG. 
3. 
A grooved rod 106 extends between and through the links 79A and 79B of the 
second link assembly 64 at the central portion 94 thereof and is 
nonrotatable with respect thereto. The grooved rod 106 is positioned on 
the second side 66 of the upright support 10 opposite the rod 72. The 
grooved rod 106 is adapted to sit in the sloped recess 32 in the second 
housing member 16 when the link assemblies 60 and 64 are in the locked 
position. The sloped recess 32 allows for unobstructed movement of the 
ends of the grooved rod 106 when the link assemblies 60 and 64 are moved 
from the locked position to the unlocked position. A resilient sleeve 
member 110 is nonrotatably carried by the grooved rod 106. A gap 111 is 
formed between the rod 72 and the sleeve member 110 to allow for passage 
of the upright support 10 therethrough. The sleeve member 10 is engageable 
against the second side 66 of the upright support 10 when the first and 
second link assemblies 60 and 64 are in the locked position to squeeze the 
support 10 between the sleeve 110 and the rod 72 to prohibit vertical 
movement of the housing 4 with respect to the upright support 10. 
A roller 112 is disposed between links 77A and 77B of the first link 
assembly 60 on a rod 116 at the first side 62 of the upright support 10. 
The roller 112 provides for easy vertical adjustability of the housing 4 
and backrest 13 with respect to the upright support 10 when the housing is 
in the unlocked position. 
An alignment pin 120 extends between and through the links 79A and 79B of 
the second link assembly 64 on the second side 66 of the upright support 
10 opposite the roller 112. The alignment pin 120 is adapted to engage the 
alignment slot 30 in the second housing member 16 to provide for movement 
of the second link assembly 64 when the second housing member 16 is 
pivoted with respect to the first housing member 14. 
In operation, when adjustment of the vertical position of the backrest is 
desired, the backrest 13 of chair 12 is grasped by a user, preferably with 
one hand on either side thereof, and the backrest is pulled away from the 
upright support 10. The pin 40 becomes the force applying member and 
causes pivotal movement of the bottom of the second housing member 16 away 
from the first housing member 14. As the second housing member 16 pivots, 
the second link assembly 64 attached thereto at the alignment slot 30 is 
pivoted with respect to the first link assembly 60 into the unlocked 
position as shown in FIG. 2, such that the sleeve member 110 disengages 
from the second side 6 of the upright support 10. This allows vertical 
repositioning of the housing 4 with respect to the upright support 10 in 
any of an infinite number of locations. When the feet 48 engage the stop 
22, no further pivoting is permitted. During normal use, the backrest 13 
pivots about the axis 38 while adjusting to the user's back shape and 
position. The stop 22 prevents the upper member 46 from contacting the 
upper surface of the second housing 16 and causing separation of the 
housing members and inadvertent unlocking of the mechanism. When vertical 
repositioning is completed, the backrest 13 is released and the springs 
100 and 101 urge the first and second link assemblies 60 and 64 to assume 
the locked position, as shown in FIG. 3. The upright support 10 is gripped 
between the resilient sleeve member 110 and the rod 72, thereby preventing 
vertical movement of the housing 4 with respect to the upright support 10. 
Various features of the invention have been shown and described in 
connection with the illustrated embodiments of the invention. However, it 
must be understood that these particular arrangements merely illustrate, 
and that the invention is to be given the fullest interpretation within 
the terms of the appended claims.