U.S. patent number 3,854,772 [Application Number 05/364,101] was granted by the patent office on 1974-12-17 for backrest height adjustment device for office furniture chairs.
This patent grant is currently assigned to All-Steel Inc.. Invention is credited to Dean W. Abrahamson, James W. Lannert.
United States Patent |
3,854,772 |
Abrahamson , et al. |
December 17, 1974 |
**Please see images for:
( Certificate of Correction ) ** |
BACKREST HEIGHT ADJUSTMENT DEVICE FOR OFFICE FURNITURE CHAIRS
Abstract
A backrest height adjustment device for office furniture chairs
of the posture type in which the backrest is applied to a housing
that forms a socket which freely receives the backrest support
member that is conventionally secured to the chair seat, which
housing journals a cam lock member that is received in the socket
and operates with a vertical slot formed in the support member and
about an axis extending transversely of the support member. The cam
lock member includes a pair of oppositely disposed cam lock
portions that are proportioned to make equal but opposite binding
engagement with the respective sides of the slot to fix the
backrest against vertical movement; such cam surface portions that
have a slip fit relation with the slot sides when the cam lock
surfaces are free of such slot sides, to permit height adjustment
of the backrest. The housing also mounts a guide bushing received
in the housing socket end cooperating with a second vertical slot
in the support member to confine the movement of the backrest to up
and down movement relative to its support.
Inventors: |
Abrahamson; Dean W. (Aurora,
IL), Lannert; James W. (Oswego, IL) |
Assignee: |
All-Steel Inc. (Aurora,
IL)
|
Family
ID: |
23433018 |
Appl.
No.: |
05/364,101 |
Filed: |
May 25, 1973 |
Current U.S.
Class: |
297/353;
403/106 |
Current CPC
Class: |
A47C
7/402 (20130101); Y10T 403/32442 (20150115) |
Current International
Class: |
A47C
7/40 (20060101); A47c 001/00 () |
Field of
Search: |
;297/296-298,353,374,376,383,406,407,410,437,345
;248/157,161,295,412 ;403/106,109,110,350 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Mitchell; James C.
Attorney, Agent or Firm: Mann, Brown, McWilliams &
Bradway
Claims
We claim:
1. In a backrest for office chairs including a support member
having its lower end adapted for securement to the chair and a
backrest mounted on the upper end of the support member, a device
for adjusting the backrest vertically of said support member, said
device comprising:
a housing positioned on said support member adjacent the upper end
thereof for movement vertically thereof and having the backrest
secured thereto,
said support member upper end having an elongated slot formed
therein,
said slot extending longitudinally of said support member and being
rectilinear in longitudinal configuration,
said slot defining spaced parallel sidewalls extending
longitudinally of said support member,
and a cam lock member journaled in said housing,
said cam lock member being journaled for pivotal movement about an
axis extending transversely of said support member and said slot
and defining a cam lock portion concentric with said axis and
received in said slot,
said cam lock portion defining a pair of oppositely disposed cam
locking surfaces proportioned transversely of said axis to have
equal but opposite binding engagement with said slot side walls
within said slot when in contact therewith at points lying on radii
extending from said axis that make an angle with the horizontal
having a tangent that is less than the coefficient of static
friction between said cam lock portion and said slot side
walls,
said cam locking surfaces being separated by opposed cam surfaces
proportioned transversely of said axis to have slip fit relation
with said slot side walls whereby the backrest has free sliding
adjustment relative to the support member when said cam locking
surfaces are out of contact with said support member slot side
walls,
means for selectively pivoting said cam lock member about said axis
relative to said housing,
and means for guiding the movement of said housing longitudinally
of said slot when said cam locking surfaces are free of binding
engagement with said slot side walls.
2. In a backrest for office chairs including a support member
having its lower end adapted for securement to the chair and a
backrest mounted on the upper end of the support member, a device
for adjusting the backrest vertically of said support member, said
device comprising:
a housing positioned on said support adjacent the upper end thereof
for movement vertically thereof and having the backrest secured
thereto,
said support member upper end having a pair of elongated slots
formed therein in coplanar relation,
said slots extending longitudinally of said support member in
vertically spaced relation and being rectilinear in longitudinal
configuration,
a bushing mounted in said housing and received in one of said slots
in backrest movement guiding relation therewith,
and a cam lock member journaled in said housing,
said cam lock member being journaled for pivotal movement about an
axis extending transversely of said support member and defining a
cam lock portion concentric with said axis and received in the
other of said slots,
said other slot defining spaced parallel side walls extending
longitudinally of said support member,
said cam lock portion defining a pair of oppositely disposed cam
locking surfaces and proportioned to make equal but opposite
binding engagement with said other slot side walls when in contact
therewith at points lying on radii extending from said axis that
make an angle with the horizontal having a tangent that is less
than the coefficient of static friction between said cam lock
portion locking surfaces and said other slot side walls,
said cam locking surfaces being separated by a pair of opposed cam
portion surfaces having slip fit relation with said other slot side
walls when said cam locking surfaces are free of contact with said
other slot side walls,
and means for pivoting said cam lock member about said axis
relative to said housing to selectively move said cam locking
surfaces into and out of engagement with said other slot side
walls,
whereby said cam lock portion cam locking surfaces when in binding
engagement with said other slot side walls fix the backrest against
movement longitudinally of said support member slots free of
clamping stress applied to said housing.
3. In a backrest for office chairs including a support member
having its lower end adapted for securement to the chair and a
backrest mounted on the upper end of the support member, a device
for adjusting the backrest vertically of said support member, said
device comprising:
a housing positioned on said support member adjacent the upper end
thereof and having the backrest secured thereto,
said housing comprising:
a pair of housing members secured together to define between same a
socket in which said upper end of said support member is
received,
said support member upper end having a pair of elongated
rectilinear slots formed therein disposed in coplanar relation,
said slots extending longitudinally of said support member and each
defining parallel planar side walls extending longitudinally of
said support member,
a bushing carried by said housing and mounted within said socket
and in one of said slots in backrest movement guiding relation with
said one slot,
and a cam lock member mounted in said housing,
said cam lock member being journaled between said housing members
for pivotal movement about an axis extending through said other
slot and transversely of said support member, and defining a cam
lock portion concentric with said axis and disposed in said socket
and said other slot,
said cam lock portion defining a pair of oppositely disposed cam
locking surfaces proportioned radially of said axis to make equal
but opposite binding engagement with said other slot side walls,
respectively, when moved into contact therewith at points lying on
radii extending from said axis that make an angle with the
horizontal having a tangent that is less than the coefficient of
static friction between said cam locking surfaces and said other
slot side walls,
said cam locking surfaces being separated by a pair of oppositely
disposed cam surface portions having slip fit relation with said
other slot side walls when said cam locking surfaces are free of
contact with said other slot side walls,
and a handle member keyed to said cam lock member for pivoting said
cam lock member about said axis relative to said housing to move
said cam locking surfaces into and out of said binding engagement
with said other slot side walls,
whereby said cam lock portion cam locking surfaces when in binding
engagement with said other slot side walls fix the backrest against
movement longitudinally of said support member slots free of
clamping stress applied to said housing.
4. The device set forth in claim 3 wherein:
said cam locking surfaces and said other slot side walls are formed
from steel,
and wherein said angle is no more than about 8.degree..
5. The device set forth in claim 4 wherein:
said support is formed from steel, and said cam lock portion is
formed from powdered metal and has a hardness in the range of 25 -
35 Rockwell C.
6. The device set forth in claim 3 wherein:
said slots are aligned longitudinally of said support member.
7. The device set forth in claim 4 wherein said slip fit cam
surface portions of said cam lock portion are struck on arcs
eccentric with said axis and having a radius exceeding that of said
cam locking surfaces,
with said slip fit cam surface portions smoothly connecting said
cam locking surfaces.
8. The device set forth in claim 3 wherein:
said housing members are each of channel configuration defining
side flanges separated by a web,
said housing members being in nesting relation with their webs
separated to define said socket therebetween,
with one of said housing members being received within the other of
said housing members to provide said nesting relation,
and with the other of said housing members having the backrest
applied thereto,
said cam lock member including a flange exterior of said housing
and concentric with said axis and positioned within said inner
housing member,
said handle member being keyed to said flange for swinging movement
in a plane exterior of said housing.
Description
This invention relates to a backrest height adjustment arrangement
for posture chairs, and more particularly, to an arrangement for
mounting the backrest on its support that permits ready height
adjustment relative to the chair seat.
The prior art dealing with backrest height adjustments reveals a
wide variety of devices of this type, many of which are concerned
with some type of clamping arrangement either at the connection of
the backrest to its support, or the connection of the support to
the chair chassis, to permit height adjustment and sometimes
lateral adjustment forwardly and rearwardly of the user. In devices
of this type, the familiar screw clamp or over center cam lock
lever type device usually provides the clamping action for binding
several relatively movable parts together that, when released,
permit the height adjustment desired.
A principal object of the present invention is to provide a
backrest adjustment arrangement that avoids the clamping approach
of the prior art, and uses instead a simple cam lock device that
confines the locking stress to the backrest support.
Another principal object of the invention is to provide a backrest
adjustment arrangement that not only provides a firm securement of
the backrest support, but also is readily loosened for adjustment
purposes without leaving the seat and provides for infinite or
stepless adjustment within the range of adjustment allowed.
Other objects of the invention are to provide a backrest adjustment
arrangement that is of few and simple parts, that is economical of
manufacture, and that is reliable and long lived in use.
In accordance with this invention, the backrest height adjustment
device comprises a housing to which the backrest is secured that
defines a socket that freely receives the backrest support member,
which is in the form of a bar suitably mounted in upright relation
on the chair chassis. The support member is formed with a pair of
rectilinear vertically spaced and vertically extending slots, with
the portion of the support member defining such slots being
received in the housing socket. The housing journals a cam lock
member that is received in the socket and operates within the upper
vertical slot and about an axis extending transversely of the
support member. The cam lock member includes a pair of oppositely
disposed cam lock portions that are concentric with said operating
axis and are proportioned to make equal but opposite binding
engagement with the respective sides of the upper slot to fix the
backrest against movement, with such cam lock surface portions
being separated by a pair of opposed surface portions that have a
slip fit relation with the upper slot sides when the cam lock
surfaces are free of such sides, to permit height adjustment of the
backrest. The housing also mounts a guide bushing that is received
in the housing socket and cooperates with the second slot to
confine movement of the backrest relative to its support member to
up and down movement when adjustment is desired.
The result is that the locking action desired is applied to the
backrest support to the exclusion of the device housing and no
clamping together of relatively movable parts is required.
Other objects, uses, and advantages will be obvious or become
apparent from a consideration of the following detailed description
and the application drawings.
In the drawings:
FIG. 1 is a perspective view of a posture chair of the secretarial
type to which the invention is applied;
FIG. 2 is a rear view of the backrest support showing the height
adjustment device in elevation and the backrest in phantom;
FIG. 2A is a perspective view of the backrest support;
FIG. 3 is a sectional view through the height adjustment mechanism
taken substantially along line 3--3 of FIG. 2;
FIG. 4 is a view of the height adjustment mechanism similar to that
of FIG. 2 but on an enlarged scale and with parts broken away
showing the device in locked position;
FIG. 5 is similar to that of FIG. 4 but showing the device in its
released position;
FIG. 6 is a plan view of the cam lock component employed in
connection with the present invention, on an enlarged scale;
and
FIG. 7 is a diagram of the cam lock device on an enlarged scale
bringing out basic features of the invention.
However, it is to be understood that the drawing illustrations
provided are supplied primarily to comply with the requirements of
the Patent Laws, and that the invention may have other embodiments
which will be obvious to those skilled in the art, and which are
intended to be covered by the appended claims.
GENERAL DESCRIPTION
Reference numeral 10 of FIG. 1 generally indicates a posture chair
of the type to which the invention is especially concerned, that
shown being of the secretarial type (although the invention is
equally applicable to executive and other types of posture chairs).
Chair 10 generally comprises a suitable base 12 equipped with the
usual pedestal 14 provided with legs 16 riding on suitable casters
18. Suitably mounted on the pedestal 14 is a chair seat 20 that may
be of any conventional type, and that is equipped with backrest
support 22 to which backrest 24 is applied in accordance with this
invention.
The support 22 has its lower end 26 angled as at 28 for adjustable
securement to the chair seat 20 in any suitable manner.
The backrest 24 is applied to the upper end 30 of the support 22 by
employing height adjustment device 32 to which the backrest 24 is
suitably secured.
The height adjustment device 32 generally comprises a housing 34 in
the form of a pair of channel members 36 and 38 associated in
nested relation to define a socket 40 (see FIG. 3) into which
extends the upper end 30 of the backrest support member 22.
The backrest support member 22 at its upper end 30 is formed with a
pair of rectilinear slots 42 and 44 that are in aligned vertically
disposed and vertically spaced relation, with the slots 42 and 44
being identical in configuration and length. Slot 42 defines
opposed planar side walls 46 and 48 while slot 44 defines opposed
planar side walls 50 and 52.
The housing 34 journals a bushing 54 which is received in the
socket 40 and is disposed in guiding relation in the slot 44
between its side walls 50 and 52.
The housing 34 also journals cam lock member 56 that includes a cam
lock portion 58 received in the socket 40 and extending through
slot 42 for operative cooperation with the side walls 46 and 48 of
the slot 42.
The cam lock member 56 is journaled in the housing 34 for pivotal
movement about axis 61 that extends transversely of the housing 34
and backrest support member 22. The cam lock portion 58 comprises a
pair of opposed cam lock surfaces 60 and 62 that are concentric
with the axis 61 and are each struck on an arc that proportions
opposite portions of the cam lock portion 58 to make equal but
opposite binding engagement with the respective slot sides 46 and
48 of the slot 42 to lock the backrest against vertical movement
relative to the support 22. In the form shown, cam lock surfaces 60
and 62 are separated by surfaces 64 and 66 that are struck on arcs
which proportion the corresponding areas of cam lock portion 58
between surfaces 60 and 62 to have slip fit relation with respect
to the sides 46 and 48 of the slot 42 when the cam lock member 56
is positioned to dispose surfaces 60 and 62 out of engagement with
slot side walls 46 and 48, respectively (see FIG. 5). The surfaces
60, 62, 64 and 66 are contoured to merge consecutively about cam
lock portion 58 where indicated at cam surface portions 68 (see
FIG. 6) in a smoothly contoured manner.
Cam lock member 56 has operating handle 70 keyed thereto for
pivoting the cam lock member 56 between the positions of FIGS. 4
and 5, it being understood that the handle 70 when pivoted
clockwise of FIG. 5 will lock the device 22 against adjustment.
The arrangement is such that when handle 70 is moved clockwise of
FIG. 5 toward the position of FIG. 4, the cam lock portion 58 at
approximately the locations of cam surface portions 68 makes equal
but opposite binding engagement with the respective sides 46 and 48
of the slot 42 to lock the backrest against vertical movement.
It will thus be seen that when the handle 70 of device 32 is in the
position of FIG. 5, the backrest 24 may be suitably adjusted
vertically of the support member 22 to the position desired by the
user of the chair, and by the user moving the arm 70 clockwise of
FIG. 5 sufficiently to bring the cam lock portion 58 into binding
engagement with the respective sides 46 and the slot 42, the device
32 is fixed against vertical movement relative to its support
22.
SPECIFIC DESCRIPTION
The support member 22 is suitably formed from bar stock to define
the general shape included in the drawings, including angled lower
end 26 that is slotted as at 74 for application to the chair seat
chassis in any suitable manner that may provide for adjustment of
support member 22 forwardly and rearwardly of the chair. Slots 42
and 44 are formed in any suitable manner, as by punching.
As the backrest 24 per se is conventional, it is only
diagrammatically illustrated. In practice it comprises a
polystyrene backing plate 77 (see FIG. 1) to which suitable cushion
material 79 and a decorative cover 81 are suitably applied over the
forward side of same, and an outer back shell 83 of plastic
material on the backside of the backing plate that masks the
housing 34; the backing plate 77 and shell 83 are suitably secured
together as by employing fasteners about their marginal edges that
are masked by molding 85.
The housing member 36 comprises web 80 separating spaced side walls
82 and 84 (see FIG. 3), with the side walls 82 and 84 respectively
being provided with the respective wing flanges 86 and 88. The web
80 of channel member 36 is formed with opening 90 that receives
mounting screw 92 which journals cam lock member 56 in housing 34,
as by having its threaded end 94 applied to suitable conventional
weld nut 96 affixed to the web 80 exteriorily of the socket 40,
such that its shoulder 95 is firmly against web 80, and its head 97
engages handle 70.
The web 80 is also formed with a second opening (not shown) spaced
longitudinally of member 22 through which screw 100 extends for
application to a second weld nut 102 (see FIGS. 4 and 5) affixed to
the web 80 exteriorily of the socket 40 and below the weld nut
96.
The housing member 38 comprises web 104 separating spaced side
walls 106 and 108 (see FIG. 3) that are respectively equipped with
the respective wing flanges 110 and 112. As indicated in FIG. 3,
the channel member 38 is nested within the channel member 36 to
define the socket 40 as well as operating channel 113 within which
handle 70 acts, and these two members 36 and 38 are suitably fixed
together, as by spot welding at 114 (see FIGS. 4 and 5). The wing
flanges of the channel members 36 and 38 are suitably formed with
aligned openings 116 to receive suitable fasteners for securing the
housing 34 to the aforementioned backing plate 77 of the backrest
24.
The web 104 of member 38 is formed with opening 120 through which
extends the cam lock portion 58 of cam lock member 56. The web 104
is formed with a second opening 122 through which the bushing 54 is
applied within the socket 40 and slot 44.
The cam lock member in the form illustrated is of hub configuration
comprising sleeve portion 124 defining bore 126 through which the
journalling screw 92 extends, and the respective surfaces 60, 62,
64 and 66. Integral with sleeve portion 124 is flange portion 128
defining a pair of spaced apart openings 130 and 132 which
respectively receive pins 134 and 136 that are fixedly carried by
handle 70. Handle 70 is secured to the flange 128 by the screw 92
to keep the pins 134 and 136 seated in their respective openings
130 and 132.
As indicated in FIG. 3, the flange 128 of the cam lock member 56 is
proportioned from the standpoint of thickness to dispose the
operating plane of the handle 70 within its operating channel 113,
and thus substantially in the plane of the wing flanges 110 and 112
of channel member 38.
Handle 70 at its end 140 is formed with right angled projection 142
that projects rearwardly of the backrest 24 and beneath but closely
adjacent the portion of the molding 85 that lies along the lower
edge of the backrest, for easy gripping by the user when seated in
the chair, and also to provide a handle for the chair user to hold
up and move vertically the backrest when the cam lock member 56 is
freed from binding engagement with support member 22.
The support 22 is preferably formed from a suitable steel such as
SAE 1018, while cam lock member 56 is formed from a suitable
composition of powdered metal, such as steel, having a hardness of
25 to 35 Rockwell C. In one successful form of the invention, the
slots 42 and 44 are .620 inch in width and have sufficient length
to permit approximately 2 inches of vertical height adjustment. Cam
lock surfaces 60 and 62 are struck on arcs concentric with the axis
61 and have a dimension of 0.320 inch. Surfaces 64 and 66 are
struck on arcs about centers 150 and 152 that are offset from axis
61 and have a radius longer than the radius of surfaces 60 and 62.
Thus, arc 64 is struck on an arc about center 150 and having a
radius of 0.406 inch, while surface 66 is struck on an arc about
center 152 having the same radius.
An important aspect of the invention is that cam lock portion 58
should be proportioned radially thereof relative to the width of
slot 42 such that when the cam lock portion 58 is being moved to
locking relation with the sides of slot 42, the cam lock portion 58
makes engagement with the respective slot surfaces 46 and 48 at
positions where the cam contact points 155 and 157 (FIG. 7)
involved lie along radii 159 and 161 from axis 61 that make angles
with respect to the horizontal having a tangent which is less than
the coefficient of static friction between the slot and cam
surfaces involved.
In other words, the angle A should be such that its tangent is less
than the coefficient of static friction between cam lock portion 58
and slot surfaces 46 and 48. Where cam lock portion 58 and support
22 are formed from steel, angle A should be a maximum of 8.degree..
In this connection it is dry or unlubricated static friction that
governs as any lubricant on the surfaces involved would be squeezed
out under the application forces involved.
Thus, cam lock portion 58 makes contact with surfaces 46 and 48 at
or adjacent cam surface portions 68, depending on the state of wear
of cam lock portion 58, to effect the binding locking action
contemplated by this invention.
It is understood, of course, that the usual manufacturing
tolerances are permitted, and, of course, specific dimensions
employed may be varied to suit special purposes, it only being
important that the cam lock portion 58 and slot surfaces 46 and 48
have the relationships indicated, and the surfaces 64 and 66 permit
ready slip fit relation between the cam lock member 56 and the
sides 46 and 48 of slot 42 when the cam lock portion 58 is moved
out of engagement therewith. The concentric relation of the cam
surfaces 60 and 62 is a convenient way of forming these surfaces
for the purpose intended.
Bushing 54 may be formed from a suitable antifriction material such
as nylon and is proportioned to have slip fit relation with side
walls 50 and 52 of slot 44. In the embodiment referred to above,
the bushing 54 has an outer diameter of 0.618 inch.
To operate the device 32, the chair user, when seated in the chair
10, merely reaches around to the backside of the support 22 at the
level of the lower edge of backrest 24 to grasp handle 70, and in
particular its rearwardly projecting end portion 142, and swings
handle 70 to its released position of FIG. 5 to free cam lock
member 56 from binding engagement with the sides 46 and 48 of slot
42. The backrest may then be freely moved vertically as desired and
relocked at the desired position by swinging handle 70 clockwise of
FIG. 5 to approximately the position of FIG. 4 to bring cam lock
portion 58 into equal but opposite binding engagement relation with
slot side walls 46 and 48 that effects the backrest locking action
of this invention. Thus, handle 70 is approximately vertically
disposed in the locked relation of device 32. Any wearing of
surfaces 60 and 62 will result in additional movement to the left
of FIG. 4 to achieve the locking action desired.
As it is desired that the handle 70 be an unobstructive as
reasonably possible, handle 70 is confined in its movement to
channel 113, and its range of swinging movement limited by such
channel 113 so that projection 142 may be disposed closely adjacent
the lower margin of molding 85. The corners 160 and 162 of housing
34 serves as stops that form the ultimate limits of the permissible
range of movement of handle 70.
While the arrangement of handle 70 and cam lock member 56 that is
shown is preferred (single locking direction operation), handle 70
can be keyed relative to cam lock member 56 so as to be vertically
disposed in the released position of same, whereby handle 70 could
be swung clockwise or counterclockwise to effect the locking action
desired. Handle 70 may also be suitably spring biased to its
locking position.
It will therefore be seen that in accordance with this invention,
the backrest 24 is secured relative to its support 22 by a lock
device which involves no clamping together of relatively movable
parts, but rather the binding of a cam member with opposed sides of
an operating slot in an equal but opposite manner whereby the parts
subjected to stress are limited to the cam lock member and the
support 22, to the exclusion of housing 34. The cam lock member 56
is readily moved into and out of its locking relation to permit
ready height adjustment of the backrest. The positioning of handle
70 is such that the chair user can readily reach and operate same
without rising from his seat.
It is also to be noted that within the range of height adjustment
permitted, stepless or infinite positioning is available. There are
no set locations or fixed series of height adjustment locations to
contend with. The device 32 is generally flat in configuration with
its thickness dimension minimized to be consistent with the slim
trim overall appearance of the backrest and its support.
The foregoing description and the drawings are given merely to
explain and illustrate the invention and the invention is not to be
limited thereto, except insofar as the appended claims are so
limited, since those skilled in the art who have the disclosure
before them will be able to make modifications and variations
therein without departing from the scope of the invention.
* * * * *