Note: Descriptions are shown in the official language in which they were submitted.
~2359~3,3
-- 1 --
"TILTING MECHANISM FOR A C~AIR"
This invention relates to tilting mechanisms for
chairs, of a kind comprising two parts, for connection,
in use, to the chair seat and chair back respectively,
said two parts being pivotally connected together for
relative pivotal movement about a horizontal axis,
means being provided for securing the two parts of the
mechanism in a required relative angular position,
whereby, in use, the angle of the chair back with
respect to the chair seat can be adjusted. Such a
mecbanism is frequently used in what are commonly
referred to as "typists" chairs.
In one known form of mechanism of this type, the part
for connection to the chair bacl~ is provided with a
fixed extension which lies in a vertical plane,
projects forwardly and is formed along its forward edge
with an arcuate row of notches centred about the axis
of pivoting of the chair back. Engageable with the
notches is part of an operating arm mounted for
horizontal swinging movement on the chair seat, a
spring being provided to urge the ar~ rearwardly into
engagement with the extension. Thus, the angle of the
chair back in relation to the seat may be adjusted by
swinging the arm forwardly out of engagement with the
extension, against the action of the spring, tilting
the chair back to the required angle and then releasing
t'ne arm so that it is urged by the spring into
engagement wit'n a new notch in the extension.
Such an arrangement 'nas the advantage that it provides
for positive location of the chair b~ck with respect to
t'ne seat, and does not rely on frictional engagement as
is the case in other known designs. However, the
described arrangement suffers from two major
disadvantages. ~irstly, in order to provide a row of
notc'nes of sufficient length, the dimensions of the
~L235993
extension projects beyond the chair seat part at the
upper and lower limits of its pivoting movement. The
upward projection must be accommodated in the design of
seat, whereas the downward projection of the extension
below the seat makes for an unsightly appearance.
Secondly, the horizontal swinging movement of the
operating ar~, necessitated by the up-and-down swinging
movement of the extension, means that there is, in
practice, a risk of accidentally knocking the arm out
of engagement with the notched extension so that the
chair back is free to fall backwards under the weight
of a person sitting in the chair. Also, any weakening
or failure of the spring urging the operating arm into
engagement t~ith the extension may also permit the arm
to slip out of engagement with the notches, again
permitting movement of the chair bac~.
The object of the present invention is to provide a
chair tilting mechanism which enables a chair back rest
to be tilted easily and reliably, provides for positive
location of the chair back, and is relatively
inexpensive to produce, but which overcomes the above-
mentioned disadvantages.
According to the invention a tilting mechanism for a
chair comprises two parts, for connection, in use, to
the chair seat and chair back respectively, said tr~o
parts being pivotally connected together for relative
pivotal movement about a horizontal axis, characterized
by said parts being connected by linkage means
pivotally connected to one of the parts and also
pivotally connected to a member movably mounted on the
other of said parts, releasable stop means being
provided for movement bet~een a locking position, in
~hich the movable member is engaged by the stop means
123~j993
to lock the movabLe member in a required position on
said other part, thereby to determine a relative
angular position of the two parts, and a release
position, in which the stop means are dis-engaged from
said movable member to allow relative angular movement
between said two parts to define a different relative
angular position thereof, such movement being
transmitted through said linkage means to move said
movable member reltive to said other part, the
arrangement bein~ such that when said different
relative angular position i5 reached, the stop means
are moved to said loc1~ing position to lock said movable
member relative to said other part.
Since the me~ber which is loc~ed in the required
position is not an extension pivotable with said one
part of the mechanism, as in the earlier known arrange-
ment described above, but is instead a separate member
connected thereto by a link, the movable member may be
movably mounted on the other part of the mechanism in
any convenient fashion so as to overcome the disadvan-
tages referred to above.
Thus the movable member may be pivotally mounted on
said other part, said link being pivotally connected to
the movable member at a point spaced from the pivotal
mounting of the member. Preferably the movable meQber
is mounted on the part of the mechanism for connection
to the chair seat.
The invention will now be described, by way of example,
with reference to the accompanying drawings, in which:
Figure 1 is a schematic perspective view of a chair
fitted with a tiling mechanism construct~d in
aceordance with the present invention,
- 123~393
-- 4 --
Figure 2 is a side elevational cross-sectional view of-
the tiling mechanism,
Figure 3 is a cross-sectional view on the line 3-3 in
Figure 2, with a torsion spring of the mechanism
omitted for the sake of clarity;
Figure 4 is a view similar to Figure 2 but showing the
backrest in an alternative, tilted position.
Figure 5 is a diagrammatic cross-section through an
alternative form of tilting mechanism of the invention;
and
Figure 6 is a top plan view of the mechanism of Figure
5.
A first embodiment of the invention will now be
described with reference to Figures 1 to 4 of the
accompanying drawings.
The type of chair to which the mechanism of the present
invention is usually applied is that conventionally
referred to a typists' chair. Such a chair is shown in
Figure 1. The chair has a base comprising five castor-
supporting legs 10 extending radially outwardly from
the bottom of an upright, cylindrical support column
11, The legs are equi-angularly spaced around the
column in the form of a star. The column 11 has
conventional gas spring height adjustment means for
raising or lowering a seat 12 of the chair in
accordance with the users requirements. ~ backrest 13
of the chair is connected to the seat 12 by means of an
oval section tube 14. By way of the tube 14 the
backrest is spaced a~ove and somewhat behind the seat
12. In addition to the facility for vertical
adjustment, t'ne column may have provision for rotary
movement relative to the part of the base formed by the
five legs 10.
~Z 35 ~9 3
Considering now the tilting mechanism itself, Figures 1
to 4 show a frame 15 on which an upholstered seat pad
would be fitted. This frame 15 constitutes a first
part of the mechanism. The tube 14 is enga~ed in a
socket in which it can be adjusted vertically to alter
the position of the backrest 13 in a vertical direction
relatively to the seat 12. This adjustment facility is
provided by way of a resilient sleeve 16 surrounding
the tube 14. The sleeve 16 is carried in a bracket 17
in which is engaged a locking bar. The bar has a head
at one end and an operating lever portion at the otber
end. Within the bracket 17, which is of generally
U-shaped configuration as shown best in Figure 3, the
locking bar has an eccentric portion which can engage
and press against the sleeve 16 and thus trap the tube
14. Locking and unlocXing are carried out by an
overcentre action and the bar engages in the bracket 17
through enlarged holes as seen in Figure 2 to allow
freedom of movement of the bar in its released position.
The U-shaped bracket 17 is therefore normally secured
relatively to the backrest but the latter can be
adjusted in the vertical direction as described.
The frame 15 carrying the seat 12 is an elongated
inverted channel and the bracket 17 is pivotally
connected to the frame 15 by means of a horizontal
pivot pin 18 extending through registering holes in the
side flanges of the frame 15 and of the bracket 17.
The bracket 17 constitutes a second part of the tilting
mechanism.
Between the flanges of the frame 15 towards the
opposite end tbereof from the pivot pin 18, is welded a
socket member 19 into which the upper end of a support
post 20 fitted in the top of the column ll is received
in conventional manner.
1;;~3543
-- 6
Surrounding the pivot pin 18 is a coiled torsion spring
21 having one limb engaging the base of the inverted
channel of the frame 15 and t'ne other limb engaging a
second pivot pin 22 at the lower e~remity of the
bracket 17. Connected to the pivot pin 22 are two
levers 23, 24 making up a linkage mechanism, the
linkage mechanism being retained in a fixed axial
position on t~e pivot pin 22 by means o~ a cylindrical
sleeve 22a also carried on the pivot pin 22. Each
lever is made up of a first straight part and a shorter
second straight part integrally connected by a short
step portion. The two first straight parts of the
respective levers are parallel and interconnected by a
short integral lug 25. The shorter second straight
parts of the respective levers are also parallel and
lie close to opposite sides of a sector or quadrant
shaped angularly movable member 26. These shorter
straight parts of the respective levers are pivotally
connected together through a pivot pin 27 to said
corner of the movable member 25. Since the bracket 17
is deeper than the frame 15, the pivot 22 is below the
side flanges of the frame 15.
The movable member 25 lies in a vertical plane and is
pivotally mounted on a pivot pin 28 which extends
between the two side flanges of the frame 15. The upper
edge of the movable member 26 opposite the pivot pin 27
is formed with a series of recesses or teeth 29 lying
along an arc of which the centre coincides with the
pivot pin 28 for the member 26. In this arrangement the
pivot pin 27 is located remote from the recesses 29
behind the pivot pin 28.
~ locking bar 30 can engage in any one of the recesses
29 in the member 26. This iocking bar is pivotally
engaged at 31 in one of the side flanges of the frame
~2359~33
-- 7
15 and is secured thereto by an appropriate locking
device which may be a split pin or otber fastening
arrangement. The ot'ner end of the locking bar extends
through a slot in the other side flange of the frame 15
so as to allow the bar to move up and down to a limited
extent. As shown in Figure 1, the free end of the bar
30 is formed with a handle and is of such a length that
the handle is accessible by a person sitting on the
chair, as are also t~e operating portion of the locking
bar for raising and lowering t~e backrest, and the
operating means for raising or lowering the seat 12
relative to the base of the chair. The arrangement of
the spring 21 is such that it biases the movable me~ber
to the position shown in Figure 2, wherein the
backrest is generally upright. A coiled tension spring
32 is connected between the bar 30 and t'ne pivot pin 28
so as to urge the bar 30 downwardly into engagement
with t~e member 26, and in particular into one of the
recesses 29, so as to lock the member 26 relative to he
frame 15 and thus to fix the frame 1~ and bracket 17 in
a particular relative angular orientation.
Provision, not s'nown, is made for securing the pivot
pins 18, 22, 27 and 28 in the appropriate component to
prevent endwise movement. Split pins, locking t~ashers
or other devices ~ay be used for this purpose.
When it is required to adjust the angle of the chair
back in relation to the seat, the bar 30 is raised to
disengage it from its recess 29 in the member 26. This
raising of the bar 30 takes place against the action of
the spring 32. Pressure can then ~e applied to the
backrest of the chair to move it for~ardly or rear-
wardly to the desired position. The pivoting movement
of the bracket 17 on which t'ne backrest is mounted
takes place about the pivot pin 18 against the action
of the spring 21, and this pivoting movement is
~:359~33
transmitted through the links 23, 24 to the sector or
quadrant shaped member 26 which swings about its pivot
pin 28 to bring a new recess beneath the bar 30. I~hen
the back rest of the chair is in the desired new
position, the bar 30 is released and is pulled
downwardly by the action of the spring 32 so that it
engages in the appropriate recess beneath it. As shown
the sides of the recesses 29 are generally arcuate so
that downward mo~ment of the bar 30 can effect any
slight necessary movement of the member 26 so that the
bar can enter to the full dept~ oE the appropriate
recess.
Figure 2 shows t'ne backrest in its most upright
position with t'ne bar 30 in its locking position in a
recess 29 in the member 25. Figure 4 shows the bar 30
released from the member 26, with the backrest tilted
slightly rearwardly so that a different one of the.
recesses is now under the bar. As can be seen from
Figures 2 and 4 slightly raised portions of the member
26 are provided at opposite ends of the row of
recesses, thereby to limit the permitted swinging
movement of the member 26.
The tilting mechanism described provides a simple
adjustment and is relatively inexpensive to produce.
In addition it overcomes the disadvantages of the prior
art referred to. In particular the member 26 lies
wholly within the channel of the fra~e 15 during the
whole of its possible movement. ~oreover any weakening
of the spring 25 will not render the mechanism
inoperative or release the backrest since the bar 30 is
urged downwardly by gravity into engagement with the
recesses 29. ~loreover accidental release of the bar 30
is unlikely as it would have to be moved upwardly
against the action of the spring 32.
- 1235993
Figures 5 and 6 show an alternative form of mechanisQ,
although mostly this is of a form quite similar to that
shown in Figures 1 to 4. In Figures S and 6 the same
numerals have been used for parts whic~ are the same as
those described in Figures 1 to 4.
The main difference with this further embodiment of the
invention, concerns the positioning of the pivot pin 27
on the movable member 26. As described in Figures 1 to
4, this pivot pin 27 is disposed remote from the
recessès 29 behind the pivot pin 28. However as shown
in Figure j it can be seen that in this alternative
arrangement the pivot pin 27 is disposed approximately
midway between the pivot pin 28 and the recesses 29.
This has t'ne effect of reversing the direction of
movement of the member 26 relative to the movement of
the backrest 13. In the example of Figures 1 to 4,
rearward tilting of the backrest will cause the member
26 to pivot towards t'ne brac'~et 17. However with t'ne
example of Figures 5 and 6 rearward tilting of t'ne
backrest will cause the member 26 to pivot towards the
end of the frame 15 remote from the bracket 17.
Another difference in t'ne embodiment of Figures 5 and 6
concerns the spring means which bias the bac~rest to a
rest position. In Figures 1 to 4 the torsion spring 21
is provided. However with the alternative embodiment
of Figures 5 and 5 a helical tension spring 33 is
connected between the pivot pins 18 and 27. As can be
seen from Figure 5 this tends to bias the backrest
towards the seat 12. ~lternatively the tension spring
33 may be connected between the pivot pin 22 and one
flange of the channel shaped frame 15.
In both embodiments, instead of the member 26 being
pivotally mounted, it could be movably mounted on the
lZ35993
- 10 -
frame 15 by other means; for example it may comprise a
member slidably movable along the channel-shaped frame
15. However the pivoted arrangement shown is preferred
since it magnifies the movement of the recessed portion
of the movable member 26. It will be appreciated that
many alternative shapes of recesses in the movable
member, and of the co-operating lock bar, may be
provided instead of the arrangement shown. The member
26 could of course be provided on the bracket 17
instead of the frame 15.
