U.S. patent application number 11/256396 was filed with the patent office on 2007-05-10 for seat tilt apparatus for a wheelchair.
This patent application is currently assigned to Permobil AB. Invention is credited to Bo Engman.
Application Number | 20070102615 11/256396 |
Document ID | / |
Family ID | 38002813 |
Filed Date | 2007-05-10 |
United States Patent
Application |
20070102615 |
Kind Code |
A1 |
Engman; Bo |
May 10, 2007 |
Seat tilt apparatus for a wheelchair
Abstract
One aspect of the invention is a seat tilt apparatus for a
wheelchair, which wheelchair comprises a chassis and a seat. The
seat tilt apparatus comprises a base member, a seat supporting
member, a pivotal arm and a linear drive member The base member is
fixable to the chassis and provided with a guide slot. The seat
supporting member is arranged to supportably receive the seat,
movable in relation to the base member and guided by the guide
slot. The pivotal arm is pivotally connected to the base member at
a first point and to the seat supporting member. The linear drive
member is pivotally connected to the base member and to the seat
supporting member, for moving the seat supporting member in
relation to the base member. The guide slot provided in the base
member comprises a first portion which is proximal to the first
point and which has a first general direction of extension. A
second portion of the guide slot, which is distal to the first
point, has a second general direction of extension, which second
general direction of extension is different from the first general
direction of extension.
Inventors: |
Engman; Bo; (Sundsvall,
SE) |
Correspondence
Address: |
HOLLAND & HART, LLP
P.O BOX 8749
DENVER
CO
80201
US
|
Assignee: |
Permobil AB
Timra
SE
|
Family ID: |
38002813 |
Appl. No.: |
11/256396 |
Filed: |
October 21, 2005 |
Current U.S.
Class: |
248/371 ;
280/304.1; 297/325 |
Current CPC
Class: |
A61G 5/1075 20130101;
A61G 5/128 20161101; A61G 5/042 20130101 |
Class at
Publication: |
248/371 ;
297/325; 280/304.1 |
International
Class: |
A47C 1/00 20060101
A47C001/00 |
Claims
1. Seat tilt apparatus for a wheelchair, which wheelchair comprises
a chassis and a seat, which seat tilt apparatus comprises; a base
member, which is fixable to the chassis and which is provided with
a guide slot; a seat supporting member which is arranged to
supportably receive the seat, movable in relation to the base
member and guided by the guide slot; a pivotal arm which is
pivotally connected to the base member at a first point and to the
seat supporting member; and a linear drive member which is
pivotally connected to the base member and to the seat supporting
member, for moving the seat supporting member in relation to the
base member; wherein the guide slot comprises a first portion being
proximal to the first point and having a first general direction of
extension and a second portion being distal to the first point and
having a second general direction of extension, which second
general direction of extension is different from said first general
direction of extension.
2. Seat tilt apparatus according to claim 1, wherein the first
portion of the guide slot is essentially horizontal when mounted on
the chassis and the second portion is angled downwards in relation
to said first portion.
3. Seat tilt apparatus according to claim 1, wherein the first and
second portions of the guide slot are connected by a curved
portion.
4. Seat tilt apparatus according to claim 1, wherein the base
member comprises two side members fixedly connected to each other
in parallel, side by side and at a distance from each other, each
side member being provided with a guide slot; the seat supporting
member comprises two support arms connected to each other by a
first axle, which first axle is guided by both guide slots; and
each support arm is connected to one of said side members by means
of a respective said pivotal arm.
5. Seat tilt arrangement according to claim 4, wherein the linear
drive member is arranged at a first side of a first of said two
side members, which first side is opposite to a second of said two
side members; and the linear drive member is pivotally connected to
the first axle.
6. Seat tilt arrangement according to claim 5, wherein the two
pivotal arms are fixedly connected to a second axle, at slightly
different rotational angles, which second axle is pivotally
connected to the two side members.
7. Wheelchair comprising a chassis, a seat and a seat tilt
apparatus, wherein the seat is tiltable in relation to the chassis
by means of the seat tilt apparatus, which seat tilt apparatus
comprises; a base member, which is fixable to the chassis and which
is provided with a guide slot; a seat supporting member which is
arranged to supportably receive the seat, movable in relation to
the base member and guided by the guide slot; a pivotal arm which
is pivotally connected to the base member and to the seat
supporting member; and a linear drive member which is pivotally
connected to the base member at a first point and to the seat
supporting member, for moving the seat supporting member in
relation to the base member; wherein the guide slot comprises a
first portion being proximal to the first point and having a first
general direction of extension and a second portion being distal to
the first point and having a second general direction of extension,
which second general direction of extension is different from said
first general direction of extension of said first portion.
8. A wheelchair according to claim 7, wherein the chassis comprises
a seat lift device having a first part stationary relative to the
chassis and a second part vertically movable in relation to the
chassis, for vertical movement of the seat in relation to the
chassis; and the seat tilt apparatus is fixed to the second part of
the seat lift device.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] The present invention relates generally to wheelchairs and
particularly to an apparatus for tilting the seat of a wheelchair
in relation to the chassis of the wheelchair. The invention also
relates to a wheelchair provided with such an apparatus.
BACKGROUND OF THE INVENTION
[0002] Wheelchairs, especially electrically driven wheelchairs
often have means for adjusting the position of the seat in relation
to the chassis. These means may comprise a seat lift for vertically
adjusting the height of the seat and a backrest tilt arrangement
for tilting the backrest of the seat in relation to the bottom of
the seat, i.e. for changing the angle between the backrest and the
bottom of the seat.
[0003] Modern wheelchairs may additionally be provided with an
electrically driven seat tilt apparatus, by which the entire seat,
including the bottom and backrest may be tilted in relation to the
chassis of the wheelchair. Such seat tilt apparatuses are provided
for facilitating changing the body weight of the wheelchair
occupant, to thereby avoid injuries, numbness and other
inconveniences otherwise caused by static positioning of the
occupant.
[0004] At one known type of seat tilt apparatuses the entire seat
is tilted around a transverse horizontal axis, which axis is
stationary in relation to the chassis. While allowing easy change
of the occupant's body weight, this known type of seat tilt causes
the center of gravity of the seat and occupant to move backwards
during tilting. Such backward movement of the center of gravity is
disadvantageous since it decreases the stability of the wheelchair
and may even cause the wheelchair to fall over.
[0005] In order to solve this problem different so-called constant
center of gravity seat tilt devices have been suggested At these
types of seat tilt arrangements the axis around which the seat is
tilted moves forwardly during the tilting operation. U.S. Pat. No.
6,032,976 discloses one such apparatus, comprising a seat frame
which, at a rear end, is pivotally connected to a transverse
support member. The support member is guided in opposing horizontal
linear slots arranged in a base frame of the wheelchair. The seat
frame is also connected to the base frame by means of a tilt
linkage, which is formed of two bars that are pivotally connected
to opposing sides of the seat frame, forward of its rear end, and
to the base frame. An electrical drive member is at a forward end
connected to the base frame and at a rear end connected to the
transverse support member. By actuating the drive member, the
support member and the rear part of the seat frame is moved
forwardly while being guided by the linear slots in the base
member. During this movement, the two bars force the seat frame to
tilt upwards around the pivot axis, which is defined by the
opposing pivotal connections between the rear end of the seat frame
and the transverse support member.
[0006] The arrangement according to U.S. Pat. No. 6,032,976 thus
enables tilting the seat while keeping the center of gravity of the
seat and occupant essentially unchanged. However, this known
arrangement also entails some disadvantages. It is often desired to
keep the overall dimensions of a wheelchair as small as possible.
Among other things such small dimensions facilitates access to
narrow places, maneuvering and handling such as storage of the
wheelchair. For achieving such small overall dimensions it is of
great importance to keep the constructional height of the seat tilt
apparatus as small as possible. However, the geometrical
requirements of linkage systems, Such as the one described in U.S.
Pat. No. 6,032,976 often constitute a limit of how much the
constructional height of the linkage system may be reduced. In the
above mentioned known apparatus the tilting movement is achieved by
two linkages, each being articulated at three points. For the above
mentioned constructional reasons it would be desirable to keep the
vertical distance of these three articulated points as low as
possible, when the seat is in its horizontal position. However, if
all three points where to bee aligned on a horizontal line, the
linkage would interlock and the drive member would not be able to
initiate the tilting movement from the horizontal position.
Therefore, at least one of the articulate points needs to be
arranged at a distance from a straight line connecting the other
two articulate points. In the above mentioned known apparatus the
articulate point between the base frame and the pivotal bar is
arranged below a straight line connecting the other two articulate
points. At this arrangement any reduction of the distance between
said articulate point and a line aligning the other two points
needs to be compensated by a correspondingly increased force
applied by the drive member to overcome the gravitational force
acting on the seat frame in front of the articulate point between
the seat frame and the pivotal bar. Hence, with the described known
arrangement a reduction of the constructional height of the tilt
apparatus will require a correspondingly more powerful drive member
in order for it to be able to initiate tilting from the horizontal
position. Such powerful drive members are not only expensive but
also comparatively large, whereby the drive member per se adds to
the total constructional height of the tilt apparatus.
SUMMARY OF THE INVENTION
[0007] It is therefore an object of the present invention to
provide a seat tilt apparatus for a wheelchair, which seat tilt
apparatus may be constructed with a comparatively small
constructional height.
[0008] Another object is to provide such a seat tilt apparatus,
which allows for use of a comparatively weak and small drive
member.
[0009] It is a further object to provide such a seat tilt apparatus
by which the fore required for initiating tilting of a seat from a
horizontal position is reduced.
[0010] A still further object is to provide such a seat tilt
apparatus which is strong and reliable in use.
[0011] One aspect of the invention is therefore a seat tilt
apparatus for a wheelchair, which wheelchair comprises a chassis
and a seat. The seat tilt apparatus comprises a base member, a seat
supporting member, a pivotal arm and a linear drive member. The
base member is fixable to the chassis and provided with a guide
slot. The seat supporting member is arranged to supportably receive
the seat, movable in relation to the base member and guided by the
guide slot. The pivotal arm is pivotally connected to the base
member at a first point and to the seat supporting member. The
linear drive member is pivotally connected to the base member and
to the seat supporting member, for moving the seat supporting
member in relation to the base member. The guide slot provided in
the base member comprises a first portion which is proximal to the
first point and which has a first general direction of extension. A
second portion of the guide slot, which is distal to the first
point, has a second general direction of extension, which second
general direction of extension is different from the first general
direction of extension.
[0012] By this arrangement of the guide slot, with two different
portions being arranged at an angle to each other it is achieved
that the drive member will act on the seat supporting member under
two different gear ratios, when the seat member is guided to move
along the two different portions of the guide slot movement of the
seat supporting member along the second distal portion, corresponds
to the initial phase of the tilting action, from the horizontal
position, where the required power is at its greatest. This portion
of the guide slot may thus be arranged with a lower gear ratio,
such that a comparatively weak drive member may still be able to
initiate the tilting action from the horizontal position. When the
tilting action has been initiated and the seat supporting member
moves along the second portion, the required power for continuing
the tilting is lowered. This portion of the guide slot may thus be
arranged with a higher gear ratio, whereby the comparatively weak
drive member may continue the tilting action at a comparatively
higher and satisfying speed of the tilting motion.
[0013] Hence, with the seat tilt apparatus according to the
invention it is possible to keep the three articulate points at a
comparatively small vertical distance from each other, to thereby
reduce the overall constructional height of the seat tilt apparatus
and the entire wheelchair. According to the invention this may
further be achieved while utilizing a comparatively weak drive
member, which still is capable of initiating the tilting motion and
completing the motion at a desirable speed.
[0014] According to another aspect of the invention the first
proximal portion of the guide slot is essentially horizontal and
the second distal portion of the guide slot is arranged at a
downward angle in relation to the first portion. By this
arrangement the rear part of the seat supporting member is somewhat
lifted during the initial phase of the tilting, when the seat
supporting member is guided by the angled portion Since the rear
part of the seat supporting member then moves vertically at the
same time as the forward portion of the seat supporting member, the
rotational motion of the seat supporting movement around the
connection between the seat supporting member and the pivotal arm
is reduced. Thereby, the load on the drive member caused by the
gravitational force acting on the forward portion of the seat
supporting member, in front of the articulate connection between
the seat supporting member and the pivotal arm is reduced.
[0015] The two portions of the guide slot may preferably be
connected by an intermediate curved portion. By this means, the
acceleration of the tilting motion when the seat supporting member
moves from the first to the second portion of the guide slot is
reduced to thereby avoid any unpleasant abrupt change of speed.
[0016] Preferably, the seat tilt apparatus comprises two sets of
seat supporting members and pivotal arms arranged in parallel to
each other and being connected to a base member with two guide
slots each having a first and a second portion as described above.
By this means a well-balanced seat tilt apparatus is achieved which
may withstand and manage considerable loads.
[0017] In order to further minimize the constructional height of
the seat tilt apparatus and the entire wheelchair, especially when
the seat tilt apparatus is fixed to a centrally positioned seat
lift of the wheelchair chassis, the drive member may be arranged
asymmetrical at one side of the base member.
[0018] At such an asymmetrical positioning of the drive member
there might be a tendency that one of two seat supporting members
arranged in parallel moves slightly before the other. I order to
compensate for any such unbalanced motion the two pivotal arms may
be fixed to the second axle at slightly different rotational
angles.
[0019] A further aspect of the invention is a wheelchair comprising
a seat tilt apparatus as described.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic front perspective view of a wheelchair
provided with a seat tilt apparatus according to the invention.
[0021] FIG. 2 is a front perspective view of the seat tilt
apparatus schematically illustrated in FIG. 1
[0022] FIG. 3 is a front perspective view of a base member forming
part of the seat tilt apparatus shown in FIG. 2
[0023] FIGS. 3a-c are side views showing the seat tilt apparatus in
different positions, corresponding to the seat being horizontal,
partially tilted and fully tilted.
DETAILED DESCRIPTION OF THE INVENTION
[0024] FIG. 1 shows an electrical wheelchair comprising a chassis
1, a seat 2 and a seat tilt apparatus 3 according to the invention.
The chassis supports two front wheels 4, which are driven by
electrically powered motors and a pivotal rear wheel 5. The chassis
also comprise an electrical seat lift device (not shown) for
vertical movement of the seat 2. In the figure, the seat lift is in
its lowest position.
[0025] The seat 2 comprises a seat bottom 7, a backrest 8 and arm
rests 9, which armrests are connected to the backrest 8. In the
shown embodiment the backrest 8 is fixedly connected to the seat
bottom 7. The backrest 8 may however also be pivotal in relation to
the seat bottom by means of a backrest tilt arrangement, which is
known per se to the skilled person. The seat bottom 7 is further
fixed to a seat frame 6, which also supports a leg rest 10.
[0026] As will be described more in detail below, the seat frame 6
is fixed to the seat tilt apparatus 3 and the seat tilt apparatus
is in turn fixed to a vertically movable part of the seat lift
device.
[0027] With reference to FIGS. 2 and 3, the seat tilt apparatus
comprises a base member 11, which is shown separately in FIG. 3.
The base member 11 comprises a central mounting plate 12 with a
plurality of mounting holes 13 for being secured by screws or the
like to the vertically movable part of the seat lift or to a
stationary part of the chassis. Hence, the seat lift may be omitted
if desired. The base member 11 also comprises two side members 14
extending downwards from the mounting plate 12 in parallel to each
other and perpendicular to the mounting plate 12. In the shown
embodiment the side members 14 are separate parts fixedly secured
to the mounting plate 12. The mounting plate 12 and side members
may however also form an integral part. A seating 15 for a bearing
is formed in a forward lower portion of each side member 14. A
guide slot 16 is formed in each side member 14. Each guide slot
comprises a first forward portion 16a which is proximal to the
seating 15 and a second rear portion 16b which is distal to the
seating 15. The first 16a and second 16b portions are connected by
an intermediate third portion 16c. The first portion 16a is
generally horizontal and essentially longer than the combined
length of the second 16b and third 16c portion.-The second portion
16b is angled downward to the right as seen in the figure at an
angle of approximately 45.degree..
[0028] One of the side members 14 further comprises a shaft journal
17, which protrudes sideways, perpendicularly from an upper forward
portion of the side member.
[0029] As best seen in FIG. 2 the seat tilt apparatus also
comprises a seat supporting member 20. The seat supporting member
comprises two support arms 21. The support arms 21 are provided
with mounting holes 23 for fixation of the seat frame 6. Both
support arms 21 are fixed to a first axle 22, which extends in the
transverse direction through both guide slots 16. The first axle 22
is displaceable in the longitudinal direction of the guide slots 16
and guided in the vertical direction by the edges of the guide
slots 16. The first axle 22 is also pivotal relative to the base
member 11, around its own axis for allowing the support arms 21 to
pivot around the axis of the first axle 22. Both support arms 21
are fixed from rotation in relation to the first axle 22, whereby
the rotational angle between the two support arms 21, in relation
to the first axle 22 is fixed. In the shown embodiment the two
support arms are parallel to each other, i.e. the rotational angle
them between, in relation to the first axle is zero.
[0030] The seat tilt apparatus 3 further comprises two pivotal arms
24. Both pivotal arms 24 are, at a first proximal end, connected to
a common second axle 25, which is journalled in bearings received
in the seatings 15 (se FIG. 3). The second distal end of each
pivotal arm 24 is pivotally connected to an upper portion of one of
the supporting arms 21, by means of a screw and nut combination 26
extending through corresponding through holes in the respective
supporting arm 21 and pivotal arm 24.
[0031] A linear drive member 27 is at a first forward end 27a
pivotally connected to the shaft journal 17 of the base member 11.
A second rear end 27b of the drive member 27 is pivotally connected
to a portion of the first axle 22, which portion extends sideways
from the guide slot, in the same direction as the shaft journal.
This portion of the first axle 22 is received by a cylindrical bore
arranged at the rear end of the linear drive member. This portion
of the first axle 22, being in engagement with the cylindrical
bore, is slightly cambered. By this means a slight angular
adjustment of the first axle 22 is allowed without causing a
corresponding angular adjustment of the drive member 27 when the
drive member acts on the first axle 22 under load Such an angular
adjustment of the drive member could otherwise cause damage to the
drive member. The linear drive member 27 further comprises an
electrical motor 28 and a transmission unit 29 for retracting and
expelling the second end 27b of the linear drive member in relation
to the first end 27a.
[0032] In FIG. 4a the seat tilt apparatus is shown when the seat
supporting member is in a first horizontal position. In this
position the first axle 22 is received by the downwardly angled
distal portion 16b of the guide slots 16 in both side members 14.
When the electrical motor 28 is actuated for rotation at a constant
speed in a first direction, the rear end 27b (covered in FIG. 4a)
of the drive member 27 is retracted towards the forward end 27a.
This linear retraction is also effected under a constant linear
speed. The first axle 22 is guided by the distal portion 16b of the
guide slot 16 to move diagonally up to the left as seen in the
figures. During this diagonal movement, the speed of the first axis
in the horizontal forward direction is lower than the linear speed
of the drive member rear end 27b. It is only motion of the first
axle 22 in the horizontal direction which causes the seat
supporting member 20 to pivot around the articulate points 26
between the seat supporting member 20 and the pivotal arms 24.
Thereby, the comparatively low speed in the horizontal direction
constitutes a low gear ratio between the movement of the drive
member and the horizontal movement of the first axle 22 which
causes the seat member 20 to tilt. This in turn lowers the load on
the drive member 27, whereby a comparatively weak and small drive
member suffices for achieving a satisfactory initiation of the tilt
action, even if the seat is occupied by a heavy person.
[0033] The fact that the first axle 22, during this initial phase,
moves in a vertical direction further accomplishes that the rear
portion of the seat supporting member 20 is lifted at the same time
as the forward portion. The decreased pivotal movement of the seat
supporting member around the connections 26 further lowers the load
on the drive member, which load is caused by the gravitational
force acting on the forward portion of the seat supporting member
in front of the articulate points 26 and the lever arm constituted
by this forward portion of the seat support member 20.
[0034] In FIG. 4b a partly tilted position is illustrated. At this
position the first axle 22 has entered the intermediate curved
portion 16c of the guide slot 16. During its movement in this
curved portion the first axle 22 gradually increases its speed in
the horizontal direction and the vertical speed is gradually
decreased correspondingly. This change of speed in the horizontal
direction corresponds to an increase of the gear ratio between the
drive member 27 and the seat supporting member 20. At this phase of
the tilting motion, the load on the drive member is lower than in
the initial phase, whereby the comparatively weak drive member
still is capable to continue the tilting motion in spite of the
increased gear ration.
[0035] In FIG. 4c the seat supporting member 20 has reached its
fully tilted position. As seen in the figure the first axle 22 has
then been displaced horizontally along the first proximal portion
16a of the guide slot 16. During this displacement the first axle
22 has moved at its full horizontal speed, which horizontal speed
is essentially the same as the linear speed of the drive member,
due to the small angle between the horizontal portion 16a of the
guide slot and the longitudinal extension of the drive member 27.
At this final movement the load on the drive member 27 is
comparatively low and the tilting motion may be completed at
swiftly at a desired speed.
[0036] According to an embodiment which is not shown in the
figures, the two pivotal arms 21 of the supporting member 20 may be
fixed to the second axle 25 with a small rotational angle them
between. Especially a first pivotal arm being arranged at the
opposite side of the base member in relation to the linear drive
member, may be slightly displaced in the clockwise direction as
shown in the figures, in relation to a second pivotal arm arranged
adjacent to the drive member. When the seat supporting member is in
the horizontal position, the free end of a first supporting arm
connected to the first pivotal arm will thereby be at a slightly
higher level than the free end of the second supporting arm
connected to the second pivotal arm. When the drive member acts on
the first axle under heavy load there might be a tendency of
angular adjustment of the first axle. Such an angular adjustment of
the first axle could then cause the supporting arm being adjacent
to the drive member to move slightly before the other supporting
arm. With an angular arrangement of the pivotal arms according to
this embodiment, any such unbalanced movement of the two supporting
arms is compensated for and the two arms will be leveled under the
load from the seat.
[0037] According to the embodiments described above the seat tilt
apparatus comprises a double linkage having two supporting arms,
two pivotal arms and two guide slots. It is however also
contemplated that for some applications it might suffice for the
seat tilt apparatus to comprise a single linkage, whereby one
supporting arm, one pivotal arm and one guide slot may be omitted.
The skilled person also realizes that the seat tilt apparatus may
comprise a multiple linkage with several sets of supporting arms,
pivotal arms and guide slots arranged in parallel to each
other.
[0038] Above, exemplifying embodiments of the invention have been
described and illustrated. However, the invention should not be
seen as limited to these embodiments but may be varied within the
scope of the attached claims.
* * * * *