Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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TITLE: IMPROVEMENTS IN TILT CONTROLS FOR CHAIRS
FIELD OF THE INVENTION
[0001] The invention relates generally to tilt mechanisms for chairs
such as office chairs.
BACKGROUND OF THE INVENTION
5[0002] A typical office chair includes a seat/back assembly which is
coupled to a chair base by a mechanism that allows controlled tilting of the
seat/back assembly with respect to the base. The base usually has an
upright post which carries a lower, stationary housing part of the tilt
mechanism. Pivoted to the stationary housing part is an upper housing part
that carries the seat/back assembly. The back may or may not be movable
with respect to the seat. A spring extends between the two housing parts of
the tilt mechanism and normally maintains the parts in a rest position with
respect to one another. When a person sitting on the chair leans back, the
upper housing part tilts with respect to the lower housing part and the spring
is
compressed, cushioning the tilting movement. The spring tension is
adjustable to vary the degree of cushioning.
[0003] CA 2,446,654 discloses a chair spring tension control having a
side operated actuator that is accessible to a person seated on a chair fitted
with the control. CA 2,301,933 discloses a chair seat tilt lock mechanism.
SUMMARY OF THE INVENTION
[0004] An object of the present invention is to provide a number of
improvements in tilt mechanisms for chairs.
[0005] A mechanism in accordance with the present invention includes
upper and lower housing parts adapted to be coupled respectively to a chair
seat/back assembly and to a chair base, the parts being pivoted together for
movement with respect to one another to permit tilting of the seat/back
assembly with respect to the base in use. A compression spring is coupled
between the upper and lower housing parts so as to normally maintain the
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parts in a rest position and to be compressed when the upper housing part
tilts with respect to the lower housing part in use.
[0006] In one aspect of the invention, stop means is provided between
the upper and lower housing parts and defines the rest position of those
parts.
The stop means includes a plurality of stop surfaces and is moveable to bring
different ones of those surfaces selectively into an operative position
between
the housing parts, defining respectively different angular positions of the
housing parts with respect to one another. The mechanism also includes an
operator controlled actuator for moving the stop means.
[0007] The stop means may be a slide profiled to define the plurality of
stop surfaces at positions spaced along the slide or a rotary stop with stop
surfaces at different radial positions with respect to an axis about which the
stop can be turned.
[0008] In the case of a rotary stop, the actuator may be a simple rotary
shaft that extends transversely of the mechanism so as to project outwardly to
one side of the seat of the chair when the mechanism is installed. A handle is
provided on the outer end of the shaft, so that the shaft can conveniently be
turned by a person seated on the chair, turning the rotary stop means to
different positions. Conveniently, the stop means comprise a pair of rotary
cam-like structures, one at each side of the tilt mechanism. The shaft is
carried by the upper housing part and the cam-like structures, one at each
side, rest on respective stop surfaces on the lower housing part.
10009] The stop means provides a convenient way of defining different
rest positions of the tilt mechanism. For example, in a typical mechanism, the
cam-like structures are profiled to define three stop surfaces at different
radial
positions with respect to the shaft, one defining a 1.5 degree forward tilt,
another defining a 6.5 degree forward tilt and the third defining a 3.5 degree
backward tilt.
[0010] Of course, the number of stop surfaces and the degree of tilt can
vary.
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[0011] In another aspect of the invention, an anti kick-back feature is
provided; that is, a feature that prevents release of the mechanism in such a
way as to allow uncontrolled return of the housing parts to their rest
position
under the effect of the compression spring. For example, if a chair has been
set at a particular tilt using a locking device and the device is released, if
there
is no anti kick-back control, the seat back will be propelled rapidly forward
and
possibly even hit the user of the chair. If the chair is unoccupied, this can
cause the chair to "kick" in an uncontrolled fashion, and possibiy even fall
over.
[0012] In accordance with this aspect of the invention, the tilt
mechanism includes anti kick-back control means comprising a tongue carried
by one of the housing parts and a rack carried by the other housing part and
having teeth for receiving the tongue. The rack is curved about a pivot axis
between the upper and lower housing parts of the chair and the tongue is
moveable between extended and retracted positions by a tension member in
one direction and a tension spring that is extended for biasing the tongue to
its extended position in engagement with the rack.
[0013] The compression spring between the housing parts provides a
biasing force that causes the tongue to bind in the tooth of the rack in which
it
is received and prevents retraction of the tongue until a force counter to the
biasing force is applied to the housing parts.
[0014] In a practical situation in which the tilt mechanism is installed in
a chair, this counter force will be provided by a person who leans back in the
chair against the force of the compression spring to so to speak "unbind" the
tongue. In other words, by leaning back in the chair, the user moves the
housing parts to a position in which the tongue is free to retract. Since the
user is seated in the chair at the time and pushing back on the chair back,
the
user's body effectively controls return movement of the housing parts under
the effect of the compression spring and there is no "kick" or uncontrolled
movement.
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[0015] In a further embodiment, the tilt mechanism includes a tension
control for the compression spring between the housing parts, comprising co-
operating wedges having confronting sliding surfaces so that movement of the
wedges in one direction with respect to one another increasing spring tension
while movement in the opposite direction reduces spring tension. In a
minimum position, the spring is fully relaxed so that it can be removed and
installed by hand, without the need for any special tools.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] In order that the invention may be more clearly understood,
reference will now be made to the accompanying drawings which illustrate
preferred embodiments of the aspects of the invention. In the drawings:
[0017] Fig. 1 is a side elevational view of a typical office chair fitted with
a chair control in accordance with the invention, with the control shown
partly
in cross-section;
[0018] Fig. 1 a is an enlargement of the chair control of Fig. 1;
[0019] Figs. 2 to 5 are general assembly drawings showing respectively
a side elevational view; a perspective view; a plan view; and an end
elevational view of a chair tilt mechanism in accordance with the present
invention;
[0020] Fig. 6 is a view similar to Fig. 3 but with parts removed so as to
illustrate only the forward tilt stop mechanism;
[0021] Fig. 6A is a detail perspective view of part of Fig. 6;
[0022] Figs. 7, 8 and 9 are side elevational views corresponding to Fig.
6 illustrating three different stop positions of the mechanism;
[0023] Fig. 10 is a view similar to Fig. 4 illustrating a slightly modified
embodiment of the invention in which a pair of parallel tension control
springs
are used instead of a single spring;
[0024] Fig. 11 is a partial view similar to Fig. 10, in which the springs
are shown separate from the chair control, prior to installation;
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[0025] Fig. 12 is a sectional view on line A-A in Fig. 11;
[0026] Fig. 13 is a perspective view of the control mechanism
illustrating the anti kick-back feature; and,
[0027] Fig. 14 is a fragmentary cross-sectional view of the tongue and
rack arrangement.
DETAILED DESCRIPTION OF THE INVENTION
[0028] Referring first to Fig. 1, a tilt mechanism in accordance with the
invention is shown generally at 20 installed between a typical chair base 22
and a chair seat and back assembly including a seat 24 and a back 26. The
seat 24 and back 26 may be in fixed angular relationship with respect to one
another. However, reference numeral 27 denotes a known clutch mechanism
which allows the back to be tilted and locked with respect to the seat. Since
the mechanism is known it will not be described.
[0029] The tilt mechanism 20 includes an upper housing part 28 and a
lower housing part 30 coupled together for pivotal movement about a
transverse pivot axis indicated at 32 in Fig. 1. The upper housing part 28
carries the seat/back assembly 24, 26. Assuming the tilt mechanism is not
locked, when a person sitting on the seat 24 pushes against the back 26, the
upper housing part moves in the clockwise direction about pivot axis 32
considering the mechanism as seen in Fig. 1.
[0030] Fig. 2 shows the tilt mechanism 20 of Fig. 1 separate from the
chair components. As indicated previously, Figs. 2 to 5 are general assembly
drawings and as such include components not directly relevant to the present
invention. Accordingly, only the principal components of the mechanism will
be described.
[0031] It is important to note that the mechanism includes one or more
compression springs 34 coupled between the upper and lower housing parts
so as to normally maintain those parts in a rest position and which is
compressed when the upper housing part 28 tilts with respect to the lower
housing part 30 in use. In Fig. 2, for example, the spring is mostly hidden
but
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from Figs. 1 and 1 a it can be seen that the spring effectively acts between
one
end 36 of the lower housing part 30 and a transverse pin 38 that extends
between the side walls of the upper housing part 28 and is received in
elongate openings in side walls of the lower housing part 30. Accordingly, if
the upper housing part 28 is rotated clockwise from the position shown about
pivot pin 32, pin 38 moves to the left and compresses the spring.
[0032] A tension adjustment mechanism is provided for the spring and
comprises a wedge arrangement somewhat similar to that disclosed in
Canadian Patent Application No. 2,446,654 referred to previously, but
incorporating improvements to be described. The mechanism is actuated by
a shaft indicated at 40 in Figs. 3 and 4 which projects laterally below the
seat
of the chair and which has a handle 40a that can conveniently be turned by a
person seated on the chair, to adjust spring tension.
[0033] Figs. 1, 1 a and 2 also show a rotary stop 42 that is carried by
the upper housing part and that bears against a surface 44 on the lower
housing part to define the rest position of the two housing parts with respect
to
one another. This stop is a component of the three-position tilt stop
mechanism of the invention and is illustrated in more detail in Figs. 6 to 9.
Stop 42 is shown in each of Figs. 7, 8 and 9 but in respectively different
angular positions corresponding to different stop positions of the housing
parts. For example, in Fig. 7 the stop position is designated at 1.5 degrees
forward tilt, in Fig. 8 as 6.5 degrees forward tilt and in Fig. 9 as 3.5
degrees
backward tilt. In this embodiment, the stop 42 has three stop surfaces 46, 48
and 50 shown respectively in Figs. 7, 8 and 9 in their "operative" rest
position-
defining orientations. Of course, there is no limitation to three surfaces
only.
The surfaces 46, 48 and 50 are at respectively different radial distances from
an axis 52 about which the stop is turnable.
[0034] Fig. 6A shows a plunger 53, in the form of a spring loaded steel
ball, that is provided on each stop 42 for engagement in one of three detents
53a in the adjacent sidewall of the lower housing part 30 for defining the
three
angular positions of the stops.
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[0035] Axis 52 is defined by a transverse shaft 54 shown in Fig. 6.
Shaft 54 carries a second rotary stop similar to stop 42 at the far side of
the
lower housing part in Fig. 6. The second stop is identical with stop 42 and is
in the same angular position about the shaft. The second stop co-operates
with a surface portion of the lower housing part corresponding to surface 44,
so that the upper housing part is supported equally at both sides. Shaft 54
also projects laterally from the mechanism so as to extend below the seat of a
chair in which the mechanism is installed and be conveniently accessible to a
person seated in the chair. Again, a handle or knob 54a is provided so that
shaft 54 can be turned easily.
[0036] The tilt mechanism of the invention may have only a single
compression spring 34. However, the drawings in fact show an embodiment
in which a pair of compression springs denoted 34' and 34" are used side-by-
side. The upper ends of the springs 34', 34" as seen in Fig. 10 bear against a
pair of cylindrical blocks 56 that form spring seats. The blocks are carried
by
a tube 57 through which pin 38 extends (see Fig. 13). The lower ends of the
springs as seen in Fig. 10 bear against a top surface of a wedge element 58
that is moveable towards and away from pin 38 to control the tension in the
springs 34', 34" and hence the degree of cushioning that is encountered when
a person seated on the chair leans back. Element 58 provides respective
spring seats for the lower ends of springs 34', 34".
[0037] Tension adjustment is accomplished by a sliding wedge
arrangement that is perhaps best seen in Figs. 11 and 12. The mechanism
essentially comprises wedge element 58 and a pair of co-operating wedge
elements 60, 62 that are adjustable laterally of the mechanism towards and
away from one another by turning the shaft 40 that projects laterally from the
mechanism below the seat of the chair. Shaft 40 extends through bushings in
the side walls 30a and 30b of the lower housing part 30. Between those side
walls, the shaft extends through aligned plain bores in the respective wedge
elements 60, 62. The external surface of the shaft is screw-threaded and
carries a nut 63 received in a slot in the bottom of wedge element 62. A
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corresponding slot 64 in wedge element 60 is empty. A shoulder 40b on shaft
40 bears against the outer face of wedge element 60. Turning shaft 40 in
one rotational direction moves the wedge elements 60, 62 towards one
another by virtue of shoulder 40b moving wedge element 60 to the right in
Figs. 11 and 12 and nut 63 drawing element 62 to the left.
[0038] Wedge element 58 is located between the two wedge elements
60, 62 and the springs 34, 34" of the tension control mechanism bear against
element 58. Wedge element 58 is symmetrical about a longitudinal centerline
of the chair control mechanism and has a pair of inclined faces 58a, 58b that
bear against corresponding parallel faces of wedge element 60, 62. Those
faces are in fact formed by channel-shaped grooves in the respective wedge
elements and the wedge element 58 is received between opposite faces of
those grooves so that the wedge elements are positively located with respect
to one another in the vertical direction.
[0039] It will of course be appreciated that, if the shaft 40 is turned in
the appropriate rotational direction to move the wedge elements 60, 62
towards one another, wedge element 64 will be forced upwardly in Fig. 11,
compressing the springs 34', 34". Turning of shaft 40 in the opposite
rotational direction will allow the wedge elements 60, 62 to move apart under
the influence of in the springs 34', 34", as those springs relax.
[0040] The mechanism is designed so that, when the wedge elements
60, 62 are at the maximum spacing as shown in Fig. 11, there is no tension in
the springs 34', 34". In fact, the mechanism is designed so that there is a
slight clearance c (Fig. 11) between the springs (shown in exploded positions
at S in Fig. 11) and the spring seats at opposite ends of the springs, when
the
wedge elements 60, 62 are fully spaced apart and the springs are fully
relaxed. This greatly facilitates assembly of the mechanism in that the
springs
can be simply dropped into place without any need for pre-compression or
forcing the springs into place.
[0041] The mechanism can easily be hand assembled by positioning
the wedge elements 60, 62 at their full outward spacing against respective
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sidewalls 30b, 30c of the lower house part and without the shaft 40 in place.
The shaft is then inserted through the aligned openings in the sidewalls of
the
housing part and bores in the wedge elements and is fitted at its distal end
with a retaining collar 66, after the springs have been placed into the
mechanism. The shaft can then be turned to move the wedge elements
towards one another and apply some compression to the springs 34', 34".
[0042] Collar 66 is screw threaded onto shaft 40 and has a hexagonal
outer surface so that it can be adjusted on the shaft to apply any desired pre-
load to springs 34', 34". The collar is then secured to the shaft by adhesive
(e.g. LOCTITET'").
[0043] In summary, the particular tension adjustment mechanism
provided in accordance with the invention is both easy to assemble without
the need for any special tools or spring tensioning, and also provides for
convenient tension adjustment by a person seated on the chair, who merely
has to reach down and turn the shaft 40 until a comfortable tension level is
achieved.
[0044] Reference will finally be made to Figs. 13 and 14 in describing
the anti kick-back feature of the chair control. As best seen in Fig. 14, a
curved rack element 68 extends downwardly from a top wall 28a of the upper
housing part 28. As the upper housing part tilts with respect to the lower
housing part 30 when a person leans back in the chair, the rack 68 moves in
an arcuate path with respect to the lower housing part. In fact, the rack 68
is
curved to follow a radius centered on the pivot pin 32 between the two
housing parts. A slide 70 carried by the lower housing part includes a tongue
72 that can be retracted to allow free movement of the rack 68 with respect to
the slide, or projected into a selected one of the teeth of the rack to lock
the
two housing parts in respective angular positions. In Fig. 13, the tongue 72
is
shown in a projected position in engagement with one of the teeth of the rack.
[0045] Tongue 72 is slideably mounted between upper and lower plates
74, 76 of slide 70 so that the tongue moves generally on a radial line
centered
on pivot shaft 72. A tension spring 78 extends between the tongue 72 and
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the top plate 74 so that the spring is in tension (i.e. stretched) for urging
the
tongue 72 to the locking position in which it is shown in Fig. 13. As best
seen
in Fig. 14, spring 78 is a simple coil spring having hooked portions at its
respective ends that are engaged in openings in the top plate 74 and in a
projecting end portion of the tongue 72. The tongue can be retracted against
the biasing effect of spring 78 by a further spring 80 (Fig. 13). A hooked
portion at one end of spring 80 is engaged in an opening in tongue 72 while
an "eye" formation at the opposite end of the tension element extends around
a vertical limb 84 of an L-shaped actuating member. The member has a
horizontal limb that extends laterally of the chair control and projects
outwardly to one side thereof as shown at 88 in Fig. 4. A paddle 90 on limb
88 allows limb 88 to be turned angularly, moving the vertical limb 84 of the
member back and forth generally on the longitudinal centerline of the chair
control. As best seen in Fig. 11, limb 86 extends between a pair of resilient
jaws 92 having detent positions 94, 96 at opposite ends, in either of which
the
limb is retained in an extreme end position. In other words, by depressing or
lifting the paddle 90 at the outer end of the horizontal limb 88, the vertical
limb
86 can be caused to "snap" between extreme end positions to project or
retract the tongue 72.
[0046] As mentioned previously, the tongue and rack arrangement just
described provides a so-called anti kick-back feature that prevents release of
the chair control in such a way as to allow uncontrolled return of the housing
parts to their rest position under the effect of the compression springs 34',
34".
Thus, if the chair control has been set at a particular tilt by engaging the
tongue 72 in an appropriate one of the teeth of the rack 68, the compression
springs 34', 34", acting between the upper and lower housing parts 28, 30
respectively cause the tongue 72 to bind in the rack so that the tongue and
rack will remain engaged even if the paddle 90 is moved in a direction to
retract the tongue. Retraction can take place only when the user of the chair
leans back against the force of the compression springs so that the tongue 72
no longer binds in the rack and is free to retract. Since the user is seated
in
the chair at this time and is pushing back on the chair back, the user's body
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effectively controls return movement of the housing parts under the effect of
the compression springs and there is no "kick" or uncontrolled movement.
[0047] It will of course be understood that the preceding description
applies to particular preferred embodiments of the invention and that many
modifications are possible within the broad scope of the invention. For
example, the aspects of the invention described previously may be embodied
in a single tilt mechanism, but are not necessary used together. Referring in
particular to the anti kick-back feature, it is of course to be understood
that
other or different linkages or mechanisms can be used to retract the tongue
72 and that the particular mechanism shown is not essential.
