U.S. patent application number 10/179295 was filed with the patent office on 2002-11-07 for chair.
This patent application is currently assigned to Ashfield Engineering Company Wexford Limited. Invention is credited to Hancock, William John.
Application Number | 20020163234 10/179295 |
Document ID | / |
Family ID | 27562981 |
Filed Date | 2002-11-07 |
United States Patent
Application |
20020163234 |
Kind Code |
A1 |
Hancock, William John |
November 7, 2002 |
Chair
Abstract
A chair has a seat (4) and a backrest (5) which are
independently pivotable within limits at extremities. The seat is
biassed upwardly at the front and the backrest is biassed
forwardly. The seat and the backrest have a common pivot joint (8),
under the center of gravity of the occupant. There are no
occupant-operated controls as the chair responds automatically to
the posture of the occupant, providing full support at all relative
positions of the seat and the backrest in a balanced manner for
occupants of a wide range of weights.
Inventors: |
Hancock, William John;
(Wexford, IE) |
Correspondence
Address: |
JACOBSON HOLMAN PLLC
400 SEVENTH STREET N.W.
SUITE 600
WASHINGTON
DC
20004
US
|
Assignee: |
Ashfield Engineering Company
Wexford Limited
|
Family ID: |
27562981 |
Appl. No.: |
10/179295 |
Filed: |
June 26, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10179295 |
Jun 26, 2002 |
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09767944 |
Jan 24, 2001 |
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6422649 |
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09767944 |
Jan 24, 2001 |
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PCT/IE99/00078 |
Jul 27, 1999 |
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Current U.S.
Class: |
297/301.1 |
Current CPC
Class: |
A47C 3/026 20130101;
A47C 7/443 20130101; A47C 1/024 20130101 |
Class at
Publication: |
297/301.1 |
International
Class: |
A47C 001/024 |
Foreign Application Data
Date |
Code |
Application Number |
Jul 27, 1998 |
IE |
980624 |
Oct 29, 1998 |
IE |
980890 |
Oct 29, 1998 |
IE |
980891 |
Oct 29, 1998 |
IE |
980892 |
Oct 29, 1998 |
IE |
980893 |
Dec 23, 1998 |
IE |
S981098 |
Jun 9, 1999 |
IE |
990481 |
Claims
1. A chair comprising a seat, a backrest, and a fixed support for
the seat and the backrest, where the seat and the backrest are each
pivotally mounted for independent pivotal motion and the seat and
the backrest are both biased to provide posture-responsive support
of an occupant.
2. A chair as claimed in claim 1, wherein the chair comprises a
bias means acting to bias the seat upwardly at its front, and a
bias means acting to bias the backrest forwardly whereby the bias
forces are contra-rotational about an occupant's centre of
gravity.
3. A chair as claimed in claim 2, where the backrest bias is
transferred to the seat by abutment of the backrest with the seat
at some relative positions of the seat and the backrest, said bias
transfer acting to bias the seat downwardly at its front.
4. A chair as claimed in claim 1, wherein the seat and the backrest
are pivotally mounted on the fixed support, and wherein the seat is
biased upwardly at its front by a spring acting between the fixed
support and the seat forwardly of the seat pivot axis, and the
backrest is biased forwardly by a spring acting between the fixed
support and the backrest rearwardly of the backrest pivot axis.
5. A chair as claimed in claim 1, wherein the fixed support
comprises a stop means which sets extremities of independent
movement of the seat, and wherein the fixed support comprises a
stop means which sets a rearward extremity of movement of the
backrest, and a forward extremity of the backrest is set by
abutment with the seat.
6. A chair as claimed in claim 1, wherein the seat and the backrest
pivot axes are located with respect to the seat to be substantially
the same vertical plane as the centre of gravity of an occupant
sitting on the chair.
7. A chair as claimed in claim 6, wherein the seat and the backrest
pivot axes are coincident, and extend through the fixed
support.
8. A chair as claimed in claim 4, where the backrest and the seat
are each pivotally mounted on a pivot pin extending through the
fixed support.
9. A chair as claimed in claim 8, wherein the backrest comprises a
pair of lateral supports interconnected by a pivot joint extending
through the fixed support.
10. A chair as claimed in claim 9, wherein the backrest further
comprises a cross-member interconnecting the lateral supports
rearwardly of the pivot joint, and said cross-member is acted upon
by a bias means urging the backrest forwardly.
11. A chair as claimed in claim 1, wherein the fixed support is of
U-shaped channel construction and the seat comprises a seat support
nested within the fixed support, and wherein the seat support is of
inverted U-shaped channel construction.
12. A chair as claimed in claim 1, wherein the backrest is biased
forwardly by at least two springs, whereby all springs act at a
rearward extremity of the backrest pivotal motion and at least one
spring ceases to act as the backrest moves forward.
13. A chair as claimed in claim 1, further comprising a safety
mechanism comprising means for sensing presence of an occupant in
the chair, and for preventing tilting of the seat downwardly at the
front if the occupant is sitting at the front edge of the seat.
14. A chair comprising: a seat which is pivotally mounted for
rotation about a pivot axis; a backrest which is pivotally mounted
for rotation about a pivot axis, wherein said pivot axis is
substantially coincident with that of the seat, and wherein said
axis are located with respect to the seat to be located
substantially under the centre of gravity of an occupant of the
chair; a fixed support supporting the seat and the backrest and
comprising: stop means to limit downward pivoting of the seat, stop
means to limit forward pivoting of the backrest, and stop means to
limit rearward pivoting of the backrest; a seat bias means urging
upward pivotal movement of the seat at its front about its pivot
axis; and a backrest bias means urging forward pivotal movement of
the backrest about its pivot axis.
15. A chair as claimed in claim 14, wherein the seat and the
backrest are each pivotally mounted on the fixed support.
16. A chair as claimed in claim 14, wherein the seat and the
backrest comprise means for abutting for part of their pivot
movement ranges so that the backrest bias means also acts on the
seat during abutment, and the seat bias means also act on the
backrest during abutment, in which said biases counteract each
other.
17. A chair as claimed in claim 14, wherein the fixed support
comprises stop means to limit upward movement of the seat.
18. A chair as claimed in claim 14, wherein the stop means of claim
17 and the stop means to limit rearward pivoting of the backrest
comprise means for allowing further rearward pivoting of the
backrest after the seat has reached its upper limit position.
19. A chair as claimed in claim 14, wherein the backrest bias means
comprises means for applying reduced bias force for a forward
extremity of pivoting of the backrest.
20. A chair mechanism comprising: a fixed support, a seat support
comprising means for supporting a seat pad, and a backrest support
comprising means for supporting a backrest pad, wherein the seat
support and the backrest support are each pivotally mounted for
independent pivotal motion, and the seat support and the backrest
support are both biased to provide posture-responsive support of an
occupant of a chair incorporating the mechanism.
21. A chair mechanism as claimed in claim 20, wherein the mechanism
comprises a bias means acting to bias the seat support upwardly at
its front, and a bias means acting to bias the backrest support
forwardly.
22. A chair mechanism as claimed in claim 21, wherein the backrest
support abuts with the seat support at some relative positions of
the seat support and the backrest support whereby the backrest
support bias is transferred to the seat support, said bias transfer
acting to bias the seat support downwardly at its front.
23. A chair mechanism as claimed in claim 20, where the seat
support and the backrest support are pivotally mounted on the fixed
support, and wherein the seat support is biased upwardly at its
front by a spring acting between the fixed support and the seat
support forwardly of the seat support pivot axis, and the backrest
support is biased forwardly by a spring acting between the fixed
support and the backrest support rearwardly of the backrest support
pivot axis.
24. A chair mechanism as claimed in claim 20, wherein the fixed
support comprises a stop means which set extremities of independent
movement of the seat support, and wherein the fixed support
comprises stop means which sets a rearward extremity of movement of
the backrest support, and a forward extremity of movement of the
backrest support is set by abutment of the backrest support with
the seat support.
25. A chair mechanism as claimed in claim 20, wherein the seat
support and the backrest support pivot axis are substantially
coincident.
26. A chair mechanism as claimed in claim 25, wherein the backrest
support and the seat support are pivotally mounted on a pivot pin
extending through the fixed support.
27. A chair mechanism as claimed in claim 26, wherein the backrest
comprises a pair of lateral supports interconnected by a pivot
joint extending through the fixed support.
28. A chair mechanism as claimed claim 27, wherein the backrest
support further comprises a cross-member interconnecting the
lateral supports rearwardly of the pivot joint, and wherein the
cross member is acted upon by a bias means urging the backrest
support forwardly.
29. A chair mechanism as claimed in claim 20, wherein the fixed
support is of U-shaped channel construction and the seat support is
nested within the fixed support, and wherein the seat support is of
inverted U-shaped channel construction.
30. A chair mechanism as claimed in claim 20, wherein the backrest
support is biased forwardly by at least two springs, whereby all
springs act at a rearward extremity of the backrest support pivotal
motion and at least one spring ceases to act as the backrest
support moves forwardly.
31. A chair mechanism as claimed in claim 20, further comprising a
safety mechanism comprising means for sensing presence of an
occupant and for preventing tilting of the seat support downwardly
at the front if an occupant is sitting at a front edge of the seat.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a chair of the type which allows
movement of its backrest and seat.
PRIOR ART DISCUSSION
[0002] Typically, chairs have been designed with functional details
of the chair parts and the mechanism in mind rather than response
to health or supportive movement of the occupant. While is approach
tends to provide a chair which is reasonably reliable and conforms
to safety standards, the chair is typically not particularly
comfortable and supportive. Also, this approach does little to
reduce the risk of repetitive strain injury caused by a mainly
static support system.
[0003] European Patent Specification No. 22933 (Grammer) describes
a chair having a seat and a backrest which are set to positions to
provide static support. The gas struts appear to act as dampers
which are set to positions according to occupant movement of an
actuating lever. Forward movement of the lever adjust the seat gas
strut and rearward movement adjusts the backrest gas strut U.S.
Pat. No. 4,521,053 describes a chair in which a backrest part has a
front seat portion. These chairs appear to do little to respond to
the posture of the occupant and both require adjustment to suit the
particular occupant.
[0004] PCT patent specification No. WO87/06810 (Savo) describes a
chair in which the seat and the backrest are curved where they join
and they overlap each other so that their pivot axes are through an
imaginary axis of the hip joint of the occupant. While this
approach is undoubtedly an improvement because it takes into
account the anatomy of the occupant, it appears that the mechanism
would be relatively complex to manufacture because of the need for
the backrest and the seat to overlap each other and rotate without
the benefit of a conventional pivotal joint. Also, this chair does
not appear to provide comprehensive support of the torso and legs
for different postures.
[0005] In general, a major problem with chairs is that they require
the occupant to actively and consciously control the chair using
actuators to achieve a supportive and comfortable configuration of
the chair. A example is the adjustment of a strong spring at the
front of a chair to set a required pressure according to the weight
of the occupant. Further, the configuration which is reached is
either static or provides synchronised seat and backrest tilting.
If static, RSI may be a problem. If synchronised, the chair
effectively imposes a range of seat/backrest configurations
irrespective of the natural posture of the occupant.
OBJECTS OF THE INVENTION
[0006] It is therefore an object of the invention, to provide a
chair which actively provides comprehensive support and promotes
and induces joint movement of the user at all times (is
"posture-responsive"), while the role played by the occupant is
passive (there is no need for actuators or for the occupant to
become actively involved in any way).
[0007] Another object is to provide a chair having a very simple
and robust construction.
SUMMARY OF THE INVENTION
[0008] According to the invention, there is provided a chair
comprising a seat, a backrest, and a fixed support, wherein the
seat and the backrest are independently pivotable and are biassed
to provide posture-responsive support of an occupant.
[0009] In one embodiment, the seat is biassed upwardly at the front
and the backrest is biassed forwardly whereby the bias forces are
contra-rotational about an occupant's centre of gravity.
[0010] In one embodiment, the backrest bias is transferred to the
seat by abutment of the backrest within the seat at some relative
positions of the seat and the backrest.
[0011] In one embodiment, the seat and the backrest are pivotally
mounted on the fixed support.
[0012] In one embodiment, the seat is biassed upwardly at the front
by a spring acting between the fixed support and the seat forwardly
of the seat pivot axis, and the backrest is biassed forwardly by a
spring acting between the fixed support and the backrest rearwardly
of the backrest pivot axis.
[0013] In another embodiment, the fixed support comprises a stop
means which sets extremities of independent movement of the
seat.
[0014] In one embodiment, the fixed support comprises a stop means
which sets a rearward extremity of movement of the backrest and a
forward extremity of the backrest is set by abutment within the
seat.
[0015] In one embodiment, the seat and the backrest are pivotally
mounted and the pivot axes are located substantially in the same
vertical plane as the centre of gravity of an occupant sitting on
the chair.
[0016] In a further embodiment, the seat and the backrest pivot
axes are coincident.
[0017] Preferably, the pivot axes extend through the fixed
support.
[0018] In one embodiment, the backrest and seat pivot axes comprise
a pivot pin extending through the fixed support.
[0019] In one embodiment, the backrest comprises a pair of lateral
supports interconnected by a pivot joint extending trough the fixed
support.
[0020] In one embodiment, the backrest further comprises a
cross-member interconnecting the lateral supports rearwardly of the
pivot joint.
[0021] In one embodiment, the cross-member is acted upon by a bias
means urging the backrest forwardly.
[0022] In another embodiment, the fixed support is of U-shaped
channel construction and the seat comprises a seat support nested
within the fixed support.
[0023] In one embodiment, the seat support is of inverted U-shaped
channel construction.
[0024] In one embodiment, the backrest is biassed forwardly by at
least two springs, whereby all springs act at a rearward extremity
of the backrest and at least one spring ceases to act as the
backrest moves forward.
[0025] In one embodiment, the chair further comprises a safety
mechanism comprising means for preventing tilting of the seat
downwardly at the front if the occupant is sitting at the front
edge of the seat.
[0026] According to another embodiment, the invention provides a
chair mechanism comprising:
[0027] a fixed support, a seat support comprising means for
supporting a seat pad, and a backrest support comprising means for
supporting a backrest pad, wherein the seat support and the
backrest support are independently pivotable and are biassed to
provide posture-responsive support of an occupant of a chair as
defined above.
DETAILED DESCRIPTION OF THE INVENTION
Brief Description of the Drawings
[0028] The invention will be more clearly understood from the
following description of some embodiments thereof, given by way of
example only with reference to the accompanying drawings in
which:
[0029] FIG. 1 is a diagrammatic side view of a chair of the
invention showing two seat and backrest positions;
[0030] FIG. 2 is a rear view of a chair mechanism of the chair;
[0031] FIG. 3 is an underneath plan view of the mechanism;
[0032] FIG. 4 is a diagrammatic cross-sectional side view showing
the chair mechanism at mid (start) positions of the seat and
backrest and showing a passive safety lock of the chair;
[0033] FIG. 5 is a diagrammatic cross-sectional side view showing
the mechanism for seat-rearward and back-rearward positions;
[0034] FIG. 6 is a diagrammatic cross-sectional side view for
seat-forward and back-forward positions;
[0035] FIG. 7 is a diagrammatic cross-sectional side view for a
forward seat position and a mid backrest position; and
[0036] FIG. 8 is a diagrammatic cross-sectional side view for a
forward position of the seat and a rearward position of the
backrest.
DESCRIPTION OF THE EMBODIMENTS
[0037] Referring to the drawings, there is shown a chair 1 having a
mechanism 2. The chair 1 comprises a pedestal 3, a seat 4, and a
backrest 5. The mechanism 2 comprises a fixed support 6 having a
socket 7 for receiving the chair pedestal 3.
[0038] A pivot pin 8 extends rough the fixed support 6. The pivot
pin 8 is part of a backrest support of the backrest 5. The backrest
support also comprises a cross-bar 9 which extends through the
fixed support 6. A pair of laterally spaced-apart arms 5(a) at the
sides of the mechanism are interconnected by the pivot pin 8 and
the cross bar 9. These arms extend upwardly at the back to support
a backrest pad 5(b).
[0039] The mechanism 2 also comprises a seat support 10 which
rotates about the pivot pin 8. The seat support 10 comprises an
arcuate slot 11 through which the cross-bar 9 of the backrest
support extends. As shown in FIGS. 2 and 3, the seat support 10
comprises upper lateral fixing brackets 12 connected to a seat
pad.
[0040] Nylon stops 13 are mounted in the fixed support 6 to limit
downward movement of the seat support 10 at the back. Also, the
fixed support 6 has a planar nylon stop 16 at its front base. The
stop 16 sets the lower limit for the seat at the front, and the
stops 13 set the lower limit at the back.
[0041] The backrest support cross-bar 9 is inserted rough nylon
bushings 14 which are aligned with nylon stops 15 in the fixed
support 6. Thus, the stops 15 in the fixed support limit the
rearward movement of the backrest by abutment with the bushings
14.
[0042] An important aspect of the mounting of the seat and the
backrest is that the seat has independent movement within the
extremities set by the stops 13 and 16 on the fixed support The
backrest has independent movement between a rearward extremity set
by abutment of the bushings 14 with the stops 15 and a forward
extremity set by abutment of the bushings 14 with the seat support
10. Thus, the forward extremity of the backrest occurs with
abutment of the seat support 10 with the stop 16. However, before
this happens, the bias on the backrest acts upon the seat also to
counter-balance the bias on the seat. This is now described in more
detail.
[0043] The fixed support 6 is generally U-shaped construction
having upwardly-directed side walls. The seat support 10 is of
inverted U-shaped construction having generally
downwardly-depending side walls and is nested within the fixed
support. The seat support 10 is biassed upwardly at the front in
the clockwise direction as viewed in the drawings about the pin 8
by a spring 20. The spring 20 is a helical spring anchored on the
base wall of the fixed support 6 and pressing upwardly against the
web of the seat support 10 forwardly of the pivot pin 8.
[0044] The backrest support is urged in the anti-clockwise
direction about the pin 8 by an outer spring 21 and an inner spring
22. These springs are anchored on the base web of the fixed support
6 rearwardly of the pin 8. The springs 21 and 22 press upwardly
against the cross-bar 9 to urge the backrest support in the
anti-clockwise direction as viewed in the drawings. The spring 20
is retained in position by retainers 25, and the springs 21 and 22
are retained by retainers 26.
[0045] It will be appreciated that the backrest and the seat are
interconnected so that they actively induce and promote movement of
the occupant's joints at any given position of the occupant's
centre of gravity. The axes of these two supports are generally
directly under the centre of gravity of the occupant and in this
embodiment the axes are coincident. This is very important for
ensuring balanced posture-responsive movement of the seat and the
backrest whereby the bias forces are contra-rotational about an
occupant's centre of gravity.
[0046] It is important that the seat is biassed upwardly at the
front and the backrest is biassed forwardly. The forward bias of
the backrest also imparts a bias upwardly on the seat at the rear
when the backrest bushings 14 abut the seat support 10. Thus, the
seat and the backrest together have a positive and proactive
nesting/enclosing action around the occupant. This avoids the need
for any user-operated control mechanism and the occupant has a
totally passive role. The chair is thus inherently
posture-responsive.
[0047] Referring to FIGS. 4 to 8 inclusive, some positions of the
chair are illustrated. These are "snapshots" of particular
positions during dynamic movement, given for clarity of
understanding.
[0048] Referring to FIG. 4, a start position is illustrated. In is
position, force exerted by the spring 20 matches that exerted by
the springs 21 and 22 so that the chair is in a balanced position
ready for an occupant. As illustrated, the seat is approximately
horizontal as measured from the upper surface of the seat support
10. The backrest support, as measured by a line between the centres
of the pin 8 and the cross-bar 9 is tilted very slightly
rearwardly. These represent mid positions for the seat and the
backrest. At this position both the spring 20 and the springs 21
and 22 are acting on the seat in opposed directions about the pin
8.
[0049] Referring now to FIG. 5, when the occupant shifts his or her
weight rearwardly, the springs 21 and 22 are compressed. This
movement may aided by action of the spring 20. In the position
shown in FIG. 5, neither the backrest or the seat are at their
extreme positions. This position is simply set by the desired
posture of the occupant. The springs 20, 21, and 22 provide
excellent support to the occupant at this self-selected
position.
[0050] Referring now to FIG. 6, the seat is at a forward extremity
at which the seat support 10 abuts against the pad 16 on the lower
web of the fixed support 6. If the occupant begins with the
position of FIG. 5, the position of FIG. 6 is reached by the
occupant shifting his or her weight forwardly so that the spring 20
is compressed and the action is aided by the bias of the springs 21
and 22. The movement passes through a position at which the forces
are equal and subsequently as the occupant shifts weight further
forwardly, the spring 20 is further compressed. At this stage, the
spring 22 begins to work independently of the spring 21 to urge the
backrest forward with less force.
[0051] As illustrated in FIGS. 7 and 8, the seat remains at the
forward position. However, the occupant has shifted his or her
weight rearwardly so that his or her legs maintain the seat 4 at
the forward position but the torso urges the backrest support
rearwardly through a mid position shown in FIG. 7 to a limit
position shown in FIG. 8 set by abutment against the stops 15.
Again, the springs provide excellent support. It will be noted that
the occupant can leave his or her feet on the ground even though
the bulk of his or her weight leans back against the backrest. The
chair provides excellent support through the full range of
positions as the occupant changes posture. The pivot pin 8 is
located approximately under the centre of gravity of the user at a
mid position and the springs provide a balancing effect.
[0052] Referring again to FIG. 4, a passive safety mechanism 30 of
the chair 1 is illustrated. It is illustrated only in FIG. 4 to
avoid repetition and enhance clarity of the drawings. The safety
mechanism 30 senses occupants weight rearwardly of the pin 8. A
weight sensor 31 is depressed when the occupant's weight bears down
on it. This rotates an arm 32, causing it to pull a cable 33, which
in turn activates a bolt 34 to prevent locking the seat with
respect to the fixed support 6.
[0053] When the sensor 31 does not sense weight, the bolt 34
remains in a default locked position to provide a safe and
supportive seat if the occupant is sitting on the front edge only
of the seat. The safety mechanism 30 thus prevents the seat from
tilting to a forward extremity when the occupant is sitting in an
towards the front. This in turn prevents the chair from becoming
unbalanced. Again, user actuation is not required as the mechanism
30 actively operates unbeknownst to the occupant and the occupant's
role is again totally passive.
[0054] It will be appreciated that the invention provides a chair
which inherently changes its support configuration in a
posture-responsive manner without a need for any actuators. The
role of the occupant is totally passive. This is a dramatic advance
over the prior art, in which it has been regarded that actuators
are necessary to achieve different seat and backrest configurations
for occupant support, or that it has been necessary to mechanically
link the backrest and the seat so that they tilt in forced
synchronism, irrespective of the desired posture of the
occupant.
[0055] The chair automatically and actively supports the occupant
during postural movements while promoting and inducing joint
movement. This support is achieved with the occupant having an
entirely passive role. He or she does not need to know how the
chair operates and does not need to operate any actuators. This is
achieved irrespective of the weight of the occupant and without the
need for adjustment of a tension device. A combination of seat and
backrest bias, seat and backrest individual freedom of movement
and, and the location of the seat and backrest pivot axes provide
his effect. It is also important that the pivot axes are directly
under the centre of gravity of the occupant and the bias forces are
contra-rotational about the occupant's centre of gravity.
[0056] In essence, the invention represents a radical departure, in
which the occupant has an entirely passive role. Indeed, in
practice, many occupants do not know how to operate actuators and
many who do know do not bother. The invention solves these problems
by avoiding the need for actuators.
[0057] Another advantage is that the chair has much fewer parts
than in conventional chairs. Therefore, the chair is generally much
more robust and reliable than conventional chairs.
[0058] These features of the chair provide very significant
advantages in practice. The avoidance of a need to operate
actuators and to adjust the chair also makes "hot-desking" much
easier because the different users do not need to adjust each time.
Another very significant advantage is ergonomic use--the constant
movement (however small it may be) helps to avoid repetitive strain
injury (RSI). The chair allows the occupant's body to move
naturally whilst still being supported. Indeed, the chair actively
and dynamically promotes movement at the occupant's joints. This,
in turn, ensures that the occupant's muscles are kept in motion at
all times without the occupant having to act or even think about
it.
[0059] The configuration of the chair involves a backrest which
extends downwardly and forwardly to the sides of the mechanism. The
backrest arms at the sides are interconnected by the pin 8 and the
cross-bar 9. These arms provide excellent foundations for support
of auxiliary chair parts such as armrests. For a manufacturer, this
makes provision of the option of armrests very simple, with the
same basic chair construction being used.
[0060] The invention is not limited to the embodiments described,
but may be varied in construction and detail. For example, the
backrest may comprise a pivot pin having a splined and keyed
arrangement for pressing against a spring. This would avoid the
need for a cross-bar 9. Also, the springs may be of any other
suitable type such as of polyurethane material.
* * * * *