Height adjusting mechanism for chair back

An adjustable mechanism for use with an office chair, such as a secretarial chair, to allow vertical adjustment of the seat back. The mechanism includes a slide which is mounted on the chair back and is vertically slidably supported on an upright which projects from the seat portion of the chair. The slide has a latching lever pivotally mounted thereon and spring-urged into engagement with one of a series of notches formed along one side of an elongated slot formed in the upright. The notches, together with the latching projection formed on the lever, are defined by upper and lower edge surfaces which are individually generated about a centerpoint which is coincident with the pivot axis of the lever to maintain the chair back securely latched when either upward or downward external forces are imposed thereon.

FIELD OF THE INVENTION 
This invention relates to an improved height adjusting mechanism for 
permitting the back of a chair, such as a secretarial chair, to be 
selectively vertically adjusted, while at the same time providing a secure 
latching of the chair back to prevent accidental release of same due to 
upward or downward external forces being imposed thereon. 
BACKGROUND OF THE INVENTION 
Commercial or office chairs, and specifically those commonly referred to as 
secretarial chairs, are generally provided with an adjustment structure 
for permitting the vertical position of the back to be adjusted to 
accommodate the user. In the past, many chairs employed a threaded handle 
arrangement mounted on the chair back and creating a frictional engagement 
with an upright for vertically adjusting but fixedly securing the chair 
back. These threaded handle arrangements have been extensively utilized, 
but have been recognized as being not only unreliable, but more 
importantly extremely unsightly in view of their protrusion from the rear 
of the chair back. 
Accordingly, in recent years manufacturers have attempted to provide height 
adjusting mechanisms which are more effectively hidden within the interior 
of the chair back. Most of these mechanisms, however, have been bulky 
and/or structurally and mechanically complex. More importantly, most of 
these mechanisms have been unable to provide secure latching of the chair 
back to the upright, particularly when the chair back is subjected to an 
external vertical load, and hence have permitted the chair back to be 
released permitting undesired vertical displacement of the chair back 
either upwardly or downwardly. For example, a person standing adjacent a 
chair may lean against the chair back and hence impose a rather 
substantial downward force thereon, which force often causes release of 
the adjusting mechanism, whereupon the chair back moves suddenly 
downwardly, and hence creates a situation which can cause possible harm to 
the person or at the least annoyance and inconvenience. Similarly, it has 
also been discovered that many of the adjusting mechanisms permit the 
chair back to be released when the chair is lifted upwardly by the back, 
and again this causes annoyance and inconvenience, and also creates a 
situation where possible injury can occur. 
In recognition of the above problem, and specifically the safety hazard 
created when the chair back releases upon application of a 
downwardly-directed external force, the association representing 
manufacturers of office furniture have required that all chairs employing 
a vertically adjustable back must be capable of withstanding a downward 
external load on the back of at least 300 pounds without permitting 
release of the back. Many known adjusting mechanisms are unable to 
withstand such load, and while others are capable of withstanding this 
load, nevertheless even these others are generally of substantial 
complexity and/or require excessive spring forces which make manual 
release of the mechanisms extremely difficult. Thus, these known 
mechanisms are still considered deficient in many respects. 
One attempt to provide an improved height-adjusting mechanism is 
illustrated by U.S. Pat. No. 4,012,158 issued to Harper. The adjusting 
mechanism disclosed in this patent employs a latching lever pivotally 
mounted on a support secured to the chair back, which latching lever is 
spring-urged so that a small tooth thereon is selectively engageable with 
one of a plurality of notches formed along the outer edge of the upright. 
These notches slope downwardly as they project toward the outer edge of 
the upright, and are provided with straight sidewalls. While this known 
mechanism is desirable in view of its compact and simple structure, 
nevertheless it has been observed that forming the mechanism with 
straight-sided notches employing a lever and notch arrangement having the 
positional arrangement disclosed in this patent is unsatisfactory, since 
this type mechanism is believed to permit the latching lever to 
automatically disengage from the notch when an external downward force of 
substantial magnitude is imposed on the chair back. In addition, the 
latching finger associated with the lever is extremely small and 
undersized relative to the notches, so that substantial vertical looseness 
exists between the latching finger and the notches. This is also 
undesirable when an upward external force is imposed on the chair back, 
such as the chair being lifted by the back, since this results in at least 
a small upward movement of the back so that the finger impacts against the 
upper sidewall of the notch, and this can cause accidental release of the 
latching finger and hence release of the chair back. 
Accordingly, this invention relates to an improved height-adjusting 
mechanism for a chair back, which mechanism overcomes the aforementioned 
disadvantages. 
More specifically, the improved height-adjusting mechanism of this 
invention is desirably simple and compact, and can be effectively hidden 
within the interior of the chair back so as to not detract from the 
appearance thereof. At the same time, this improved mechanism permits the 
chair back to be securely latched or locked in any one of a selected 
number of discrete vertical positions, with the mechanism maintaining the 
chair back securely locked even when a substantial upward or downward 
external load (such as at least 300 pounds) is imposed on the chair back. 
The adjusting mechanism of this invention coacts with, and in fact includes 
part of, the upright which projects upwardly from the chair seat. The 
upright has an elongated slot extending vertically thereof, and a slide 
member mounted on the chair back is slidably accommodated within the slot. 
One of the inner edges of the slot has a series of vertically spaced 
notches formed therein, which notches open into the slot. An adjustment 
lever is pivotally mounted on the slide for swinging movement about a 
substantially horizontal axis, and is spring-urged toward a position of 
engagement with one of the notches. The latching lever has, at its upper 
end, a sidewardly-projecting finger for engagement within one of the 
notches. This latching finger, and each of the notches, is defined by 
opposed upper and lower edges which are generated on radii which are 
centered on the pivot axis of the lever, and the finger is sized to snugly 
fit within and substantially totally fill the notch, whereby imposition of 
upward or downward external forces on the chair back causes these forces 
to be resisted over a substantial peripheral area between the latching 
finger and the notch, which resisting forces are directed radially 
relative to the pivot axis. This enables the latching lever to be securely 
maintained in its latched position, even when upward or downward external 
forces of substantial magnitude are imposed on the chair back. 
Other objects and purposes of the invention will be apparent to persons 
familiar with structures of this type upon reading the following 
specification and inspecting the accompanying drawings.

Certain terminology will be used in the following description for 
convenience in reference only, and will not be limiting. For example, the 
words "upwardly," "downwardly," "leftwardly" and "rightwardly" will refer 
to directions in the drawings to which reference is made. The words 
"upwardly " and "downwardly" will also have reference to the direction of 
movement of the chair back relative to the upright. The words "inwardly" 
and "outwardly" will refer to directions toward and away from, 
respectively, the geometric center of the apparatus and designated parts 
thereof. Said terminology will include the words specifically mentioned, 
derivatives thereof, and words of similar import. 
DETAILED DESCRIPTION 
FIG. 1 illustrates a chair 11 having a seat portion 12 supported in the 
conventional manner by a pedestal or leg structure 13. An upright 14 is 
connected to the rear of the seat 12 and projects upwardly therefrom. A 
conventional seat back 16 is connected to and supported by the upright 14. 
This seat back 16, in the illustrated embodiment, includes an exterior 
cushion 17 which overlies an inner support shell 18, the latter being 
spaced from but suitably joined to a rear support shell 19. These shells 
18 and 19 define therein an interior region into which projects the 
upright 14, and the improved height-adjusting mechanism 21 is provided for 
joining the chair back 16 to the upright 14. 
The height-adjusting mechanism 21, as illustrated by FIGS. 2-5, includes a 
slide 22 which defines thereon a pair of forwardly-projecting tabs 23 
which, through pivots 24, are joined to suitable supports 26, the latter 
being secured to the inner shell 18. This arrangement enables the chair 
back 16 to be tiltable about the pivot 24, such as is conventional with 
secretarial chairs, although it will be appreciated that the chair back 
can be fixed if desired, in which case the slide 22 would be fixedly 
related to the inner shell 18. 
The slide 22 includes a pair of relatively flat but thin plate members 27 
and 28 disposed in opposed but slightly spaced relationship. The plate 
member 27 has a pair of blocklike offset portions 29 formed therein, which 
offset portions are seated against the plate 28 so that the major portion 
of the plates 27-28 are maintained in parallel but spaced relationship. 
Suitable screws 31 and 32 are provided for rigidly joining the plates 
27-28 together. 
The slide 22 is positioned directly adjacent and vertically slidably 
supported on the upright 14. This upright 14, in the illustrated 
embodiment, comprises an elongated rearwardly-opening U-shaped channel 
having a base web 33 provided with an elongated narrow slot 34 extending 
longitudinally thereof. This slot 34 is positioned centrally of web 33 and 
has a width which is relatively narrow relative to the overall width of 
the web. The offset portions 29 associated with slide 22 are sized so that 
they snugly but slidably fit within the slot 34, substantially as 
illustrated by FIG. 5, whereby the individual slide plates 27-28 are thus 
disposed substantially coplanar with but on opposite sides of the web 33. 
To facilitate displacement of slide 22 vertically (that is longitudinally) 
along the upright 14, the upper and lower ends 36 of plates 27-28 are 
preferably tapered slightly outwardly. The slide plate 28, which is 
disposed adjacent the outer side of web 33, is also provided with tabs or 
flanges 37 on opposite sides thereof, which flanges are bent inwardly at 
right angles and hence slidably embrace the upright 14 therebetween. 
The height-adjusting mechanism 16 includes an adjustment or latching lever 
38 hingedly supported on the slide 22. This lever 38, in the illustrated 
embodiment, is hingedly supported on the lower screw 32 and hence is 
pivotally swingable about a hinge axis 39 defined by this screw. The lever 
38 is formed from a thin platelike element and includes an elongated 
handle 41 which is positioned adjacent the front or outer side of the 
channel web and projects downwardly from the hinge axis 39, which handle 
41 preferably projects downwardly so that the lower end thereof projects 
slightly below the cushion 17. The lower exposed end of handle 41 
preferably has a finger-engaging tab 42 thereon so that the lever can be 
suitably manually actuated, while at the same time the lever is positioned 
so as to be virtually hidden and hence not detract from the overall 
appearance of the chair. 
The adjustment lever 38 has a latching or locking portion 43 which projects 
inwardly from the hinge axis 39 and, at its upper free end, is provided 
with a latching finger or projection 44 which extends sidewardly a 
substantial distance beyond the adjacent side edge 46 of the lever. This 
latching finger 44, as most clearly illustrated in FIG. 6, is defined by 
upper and lower side edges 47 and 48, respectively, each of which is 
formed as a partial cylindrical surface generated about a common center 
defined by the pivot axis 39. That is, the outer edge 47 is cylindrical, 
being formed on a radius R.sub.o generated about the pivot axis 39, with 
the inner edge 48 being formed on a radius R.sub.i generated about the 
same axis 39. The latching finger 44 also terminates in a rounded outer 
edge or nose 49, which preferably comprises a substantially 
semi-cylindrical surface which extends between and merges smoothly with 
the side edges 47 and 48. 
The latching finger 44 is designed for cooperation with a toothed rack 51 
which is fixedly associated with, and in fact is integrally formed on, the 
upright 14. This toothed rack 51 is directly associated with the web 33 
and is disposed directly along the side edge 52 of slot 34. The rack 51 
includes a plurality of identical notches or recesses 53 which are 
vertically spaced from one another and which individually communicate 
directly with the slot 34 and open into the web 33 through the side edge 
52. These notches 53 are separated by intermediate enlarged portions 54 
which resemble teeth, which portions have the free end surfaces 56 thereof 
being part of the side edge 52. 
As illustrated by FIG. 6, each notch 53 is sized so as to snugly 
accommodate therein the latching finger 44. For this reason, the notch 53 
is defined by upper and lower edges 56 and 57, respectively, which open 
outwardly through the slot side edge 52, with the notch edges 56 and 57 
being joined by a rounded bottom wall 59 of substantially semi-cylindrical 
configuration which merges smoothly with the edges 56 and 57. The upper 
edge 56 is of a partial cylindrical configuration, and in fact is formed 
by being generated on a radius R.sub.o about a center 63 which lies on a 
reference line 58, which line 58 extends through the longitudinal center 
of slot 34. The lower edge 57 also of a partial cylindrical configuration 
and is formed on a radius R.sub.i which is also generated about the 
centerpoint 63. Each of the notches 53 are formed in an identical manner 
and, since the radii used for generating the upper and lower edges of each 
notch 53 correspond with the radii used for generating the upper and lower 
edges of the latching finger 44, the center 63 used for generating the 
edges of the respective notch 53 is hence aligned with the pivot axis 33 
when the lever 38 is disposed so that its latching finger 44 projects into 
the respective notch. Of course, a minimal clearance is provided between 
the edges of the notch and the edges of the latching finger, but this 
clearance is normally in the order of several one-thousandths of an inch, 
and hence for all practical purposes the radii used for generating the 
notch and latching finger are identical. 
As illustrated by FIG. 4, the upper latching portion 43 of the lever 38 is 
provided with a transverse offset 61 therein which results in this 
latching portion 47 having a substantially Z-shaped configuration. The 
offset 61 extends through an opening 62 formed in the slide plate 28, 
whereby the free end part of the lever, namely that part having the 
latching finger 44 thereon, is hence slidably enclosed between the plates 
27 and 28, whereby the latching finger 44 is thus closely sidewardly 
confined and hence can be swingably moved into engagement with the 
respective notch 53. The finger 44 is thus positively sidewardly retained 
within the notch so that a sideward disengagement between the notch and 
the latching finger is effectively prevented. 
The height-adjusting mechanism is also provided with a low-force tension 
spring 64, one end of which is anchored to the handle 41, and the other 
end of which is anchored to a tab provided on the slide plate 28. This 
spring 64 continuously urges the lever 38 toward a latched position, that 
is, the lever is always urged clockwise in FIGS. 2 and 5 so that the 
latching finger 44 is urged into one of the notches 53. 
OPERATION 
During normal utilization of the chair, the back 16 is securely latched to 
the upright 14 in the desired adjusted vertical position due to the 
latching finger 44 associated with lever 38 being maintained in latching 
engagement within a selected one of notches 53. The latching lever is 
continuously urged into this latched position due to urging of spring 64. 
When adjustment in the height of chair back 16 is desired, the operator 
can manually engage the handle 41 and easily pivot same counterclockwise 
in FIG. 5 against the urging of spring 46, thereby releasing the lever as 
indicated by the dotted position in FIG. 5. The chair back can then be 
manually slid upwardly or downwardly along the upright 14, which slidable 
movement is accomplished by the slide 22 being slidably displaced 
vertically along the upright web 33, being guided by the slot 34. When the 
desired vertical position of chair back 16 is reached, then the lever 38 
is manually released, and the spring 64 automatically returns the latching 
lever into a latching position wherein the finger 44 projects into the 
selected notch 53. In the event that finger 44 is not initially aligned 
with one of the notches, then the nose of finger 44 will bear against the 
free tooth edge 56 until the chair back is slightly displaced a small 
vertical extent, whereupon the spring then causes the finger 44 to 
automatically enter into and engage the adjacent notch 53. 
Once the latching finger 44 is engaged within the respective notch 53, the 
chair back is fixedly and securely latched to the upright 14. Further, 
this latched relationship is maintained even though a substantial external 
force, whether directed upwardly or downwardly, is imposed on the chair 
back 16. This secure latching of the chair back on the upright is achieved 
due to the configuration of the latching finger 44 and the mating or 
corresponding configuration of the notches 53, coupled with the positional 
relationship of the notches 53 along the adjacent side edge 52 of the 
slot. More specifically, since the upper and lower edges 47-48 and 56-57 
associated with the latching finger 44 and notch 53 are formed as partial 
cylindrical surfaces which are generated about substantially the same 
radii R.sub.o and R.sub.i which are generated about a common centerpoint 
which also defines the pivot axis 39, any upwardly or downwardly directed 
external force imposed on the chair back 16 is thus resisted due to the 
engagement between either the upper or lower edge 47-48 of finger 44 
bearing against the respective upper or lower edge 56-57 associated with 
the notch 53. Since these edges are generated about the pivot axis 39, the 
resistance or reaction force between the upright 14 and finger 44 is thus 
generated over a substantial area, and the reaction force is also directed 
predominantly along a line of action which projects radially through the 
pivot axis 39, and hence has little tendency for causing the latching 
lever 38 to swing away from its latched position. The latching lever is 
hence able to remain in this latched position even though upwardly or 
downwardly directed external forces of substantial magnitude are imposed 
on the chair back 16. Further, this desirable reaction between the upright 
and the latching lever operates effectively for both upwardly and 
downwardly directed external forces, and also enables the spring 64 to be 
of minimal size and force since it is no longer necessary to rely on the 
spring for creating the dominant torque required for maintaining the 
latching lever in its latched position. The spring force can hence be 
greatly minimized, which thus simplifies manual adjustment of the chair 
back. 
Although a particular preferred embodiment of the invention has been 
disclosed in detail for illustrative purposes, it will be recognized that 
variations or modifications of the disclosed apparatus, including the 
rearrangement of parts, lie within the scope of the present invention.