WO2009019026A1

WO2009019026A1 - Center-of-gravity tilt-in-space chair

Info

Publication number: WO2009019026A1
Application number: PCT/EP2008/006536
Authority: WO
Inventors: Willis Hetherington
Original assignee: Otto Bock Healthcare Ip Gmbh & Co. Kg
Priority date: 2007-08-07
Filing date: 2008-08-07
Publication date: 2009-02-12

Abstract

Tiltable chair, including a seat structure (18) for supporting a person; a seat carriage (24) on which the seat structure (18) is mounted for tilting about an essentially horizontal first axis; a base structure (12) on which the seat carriage (24) is mounted for linear movement between two end positions along a second axis substantially perpendicular to the first axis; and means (26) for coupling tilt movement of the seat structure (18) and linear movement of the seat carriage (24) whereby the center of gravity of a person when seated in the seat structure (18) upon its tilting will remain substantially fixed at a point in space or within a small locus thereof through linear movement of the seat carriage (24) on the base structure (12). The means for coupling the two movements preferably comprises a mechanical gear (261, 262, 263 and 264) facilitating construction and synchronization of both movements.

Description

Center-of-Gravity Tilt-in-Space Chair

1. Field of the Invention

The present invention relates generally to chairs, and in particular to wheelchairs with an adjustably tiltable seat assembly.

2. Background of the Invention

The invention has been developed primarily for use in wheelchairs, although the concept underlying the invention may find use in stationary chair structures where tilting of a sitting surface with respect to the horizontal (oro another plane of reference) is desired.

It is well known that long term sitting in a fixed position or lying in a prone or similar position can result in blood pooling which can lead to hematological dysfunction such as clotting or musculoskeletal difficulties, including muscular atrophy and frequently the development of bed/pressure sores (ulcers). s Consequently, wheelchairs designed for use by dependent patients (e.g. paraplegic and quadriplegic patients) and their carers will typically include a variety of mechanisms so as to be able to re-position the back rest, seating zone and leg rests of the chair, as well as the chair structure as a whole with respect to it ground support structure, for the occupant to achieve preferred positions during0 the occupant's daily routine and to be positioned to achieve improved health and quality of life outcomes. It is also known to incorporate linear actuators (hydraulic or pneumatic), electric motors as well as passive or manually driven arrangements in wheelchairs that seek to minimize the effort on the part of the wheelchair occupant or attendant in effecting tilting and relative repositioning ofs the seat structure with respect to its wheeled ground support base.

Tilting a wheelchair occupant helps relieves pressure to the wheelchair occupant's contact points with the chair, particularly the ischial tuberosities (buttocks), thus reducing the occurrence of pressure sores and also assists in the re-distribution of blood thereby preventing pooling effects and the associated0 symptoms. In other patient groups such as those with severe spinal deformation, e.g. kyphosis and/or scoliosis, being able to re-position the occupant by using a tilting arrangement may allow the occupant to look forward and interact with their surroundings, thus improving their quality of life. In some extreme situations the need for a tiltable seating arrangement may in fact be required so as to provide adequate positioning to allow proper feeding, respiration and digestion. So called tilt-in space wheel chairs are known that include a seat frame that is mounted to a wheeled base frame at pivot points thereby allowing the seat frame to tilt about a horizontal axis and incline the seated wheelchair occupant while maintaining an essentially orthogonal angle between the occupant's spine and his/her upper legs. The ability to tilt the wheelchair occupant offers the occupant a variety of positions that accommodate their daily schedule, including, for example, an anterior tilt for eating at a table and posterior tilt for resting.

One such tilt-in-space wheelchair is known from US Patent 4,183,578. The chair tilting mechanism layout, however, is such that tilting the occupant involves lifting his or her center of gravity and therefore makes the chair less stable and prone to tipping over as a whole.

One difficulty experienced by the occupant of conventional tilt-in-space wheelchairs during positional changing is the sensation of falling or being tipped over which can be very disconcerting and induce in the occupant untoward feelings and a level of anxiety. This feeling comes about because during positional changing the wheelchair occupant's center of gravity during tilting is moved. This is in part a result of the pivot axis between the base frame and seat frame being typically located towards the rear end of the seat, close to the rear wheels of the chair and away from the occupant's center of gravity.

Furthermore, a carer who might assist in adjusting the occupant's position must use considerable physical effort to effect the tilting and at the same time control the translation of the occupant's mass relative to the occupant's centre of gravity. Because there can be significant displacement of mass in either an anterior or posterior direction relative to the occupant's centre of gravity during these manoeuvres, conventional tilt wheelchairs have been designed with large base frames and anti-tip devices to reduce a loss of balance, the former in particular making such wheelchairs large and bulky and difficult to handle and in conjunction with additional features such as anti-tip devices increases the weight of the chair making them even more difficult to maneuver.

In order to address the wheelchair occupant's discomfort associated with use of conventional tilt-in-space wheelchairs, so called tilt-in-space, constant centre-of-gravity wheel chairs have been devised in which an arrangement is provided whereby the seat frame can be tilted with respect to a support or base frame whilst substantially maintaining the center of gravity ('GG¹) of a typical (or 'standardised') user at a stable point in space or within a locus of such point.

Examples of such types of wheel chairs are described in US patent 7,007,965, and patent documents WO 00027332 A1 and WO 04089268A2.

In one form or another, these wheel chairs utilize arched or otherwise curved guide and/or support rails enabling a curved travel path of the seat frame with respect of the wheeled base frame which ensure a substantially stationary location of the CG of a chair occupier despite tilting of the seat structure. A mayor disadvantage of these structures is the additional weight associated with the curved guide / support rails, and increased bulk of the chair.

With the above background in mind, it is one aim of the present invention to provide a chair, in particular a wheelchair that does not evoke the sensation of being tipped over as consequence of tilting of the seat structure with respect to the supporting, ground engaging chair base frame.

It would be beneficial also to devise a mechanism for use or incorporation in a wheel chair that may reduce the effort required on the part of a wheel chair occupant or a carer to tilt the chair occupant, preferably by providing for an arrangement that avoids lifting or lowering of the wheelchair occupant's center of gravity during a tilting operation.

It is also desirable to provide an embodiment according to the invention wherein weight distribution between the front and rear wheels of a wheel chair is not substantially affected as consequence or during tilting of the seat frame with respect to the ground-supporting base frame. Another aim would be to simplify the mounting arrangement between seat frame and its supporting base frame of a wheel chair. 3. Summary of the Invention

In accordance with a broad aspect of the invention there is provided a tiltable chair that has a seat structure for supporting a person, a seat carriage on which the seat structure is mounted for tilting about an essentially horizontal first s axis, a base structure on which the seat carriage is mounted for linear movement between two end positions along a second axis substantially perpendicular to the first axis, and means for coupling tilt movement of the seat structure and linear movement of the seat carriage whereby the center of gravity of a person when seated in the seat structure upon its tilting will remain substantially fixed at a pointo in space or within a small locus thereof through linear movement of the seat carriage on the base structure.

In another aspect of the present invention, there is provided a wheelchair, including a base structure, two rear and at least one, but preferably two front wheels supported at the base structure, a seat carriage on which a seat structure5 for supporting a person is mounted for tilting about an essentially horizontal first axis, the seat carriage being mounted to the base structure for linear movement between a forward and a rearward end position along a second axis substantially perpendicular to the first axis, and means for coupling tilt movement of the seat structure and linear movement of the seat carriage in such manner that the0 center of gravity of a person when seated in the seat structure will remain substantially fixed at a point in space or within a small locus thereof in that tilting of the seat structure will cause linear movement of the seat carriage relative to the base structure.

In accordance with a preferred aspect of the invention, a (wheel) chair5 arrangement is proposed that includes three discrete sub-assemblies (ie the seat structure or frame, the base structure or frame and the seat carriage that mounts the former to the latter structure) which are motionally coupled such that tilting of the seat frame about its (horizontal) tilting axis, which in and by itself would lead to a shifting in space of the CG of an occupier seated in the seat frame relative to0 the base structure, is accompanied by an appropriately measured movement of the seat frame supporting carriage relative to the base structure (and thus the tilt axis defined between seat carriage and seat structure) to counter-adjust the horizontal displacement of the occupier's CG that would otherwise follow would such linear movement not be superimposed onto the seat structure. Such arrangement enables to maintain the CG of the chair user substantially unchanged between the front and rear wheels of the chair, preferably centered between the wheel pairs, thereby assuring balance and stability during the tilting operation. The proposed arrangement is also such as to prevent lifting or lowering of the CG during tilting and linear movement of the seat frame, which minimizes possible tipping over of the chair occupant.

Preferably, the seat frame (or structure) is articulated or pivoted solely to the carriage structure, preferably at a location sharing a common vertical alignment axis with the CG of a notional person seated in the upright seat structure. Such arrangement is intended to provide for an indifferent attitude of the chair structure to rotate about its pivot axis at the carriage structure, and therefore minimizes the effort required to tilt the seat with respect to the wheeled base frame on which the carriage is mounted for linear movement between the front and rear wheels of the chair.

In a preferred embodiment, the motion coupling means include a gear mechanism arranged to translate tilting movement of the seat structure into linear movement of the seat carriage and/or vice versa. Such mechanical motion coupling of the movable chair components simplifies the movement synchronization measures required to achieve substantial positional retention of the CG of the chair user during the tilting operation.

In one form, the gear mechanism may include a rack and pinion gear operative between the base structure and the seat carriage, wherein preferably a rack bar or track is secured to the base structure and a pinion wheel is received at the seat carriage, providing a constructionally simple and compact gear arrangement.

The gear mechanism would then further include a tilt gear set operative between the seat structure and the seat carriage to fully couple the tilting movement of the seat structure with the linear displacement (or motion) of its supporting carriage on the base structure. Particularly simple in layout, the tilt gear set could be embodied in a first gear wheel which is received at the seat carriage and a counter gear member that meshes with the first gear wheel and which is held stationary at the seat structure, the counter gear member being a sturdy plate member having an arched peripheral edge with gear teeth indexed with the first gear wheel.

Indexing of the tilt gear set is preferably chosen such that a seating surface present at the seat structure may be tilted within an angular range of preferably -10° to +60° with respect to a horizontal reference plane. It is hereby preferred that gear teeth are provided on the counter gear member only along an arc extension on the edge spanning this angular range, thereby providing a positive stop that would prevent unpleasant or undesired over-tilting of the seat structure with respect to the base structure.

Positive motion coupling between the tiltable and the linear displaceable constituents of the chair assembly is further enhanced by arranging the pinion wheel and the first gearwheel in a gear cluster supported at the seat carriage.

The respective gear ratios of the tilt gear set and the rack and pinion gear set can be chosen to accommodate a desired degree of horizontal movement of the seat carriage on its supporting base structure required to accommodate the horizontal shifting of the CG of a user that would be caused by tilting of the seat structure about the tilt axis at the seat carriage. In essence, the specific geometric values of wheel chair track and wheel gauges can be determined by the skilled worker in this field to meet operational and safety requirements.

To minimize friction loses at the mount between seat carriage and base structure, provision can be made for a low friction support assembly operative between the seat carnage and the base structure to secure the former to the latter in a removable manner. A preferred low friction support assembly may include a pair of rail members (for example of tubular configuration/circular cross section) secured in fixed arrangement parallel spaced-apart relationship on the base structure (or provided by the two structural, longitudinally extending tubular frame members of the base structure), and a plurality of roller wheel assemblies at the seat carriage by means of which the seat carriage is displaceably but otherwise securely mounted onto the rails (and thus the base) and guided at the rail members. Advantageously, one pair of roller wheel assemblies is provided per rail member, e.g. at or near the forward and the rearward end, respectively, of the carriage.

The roller wheel assemblies are designed and arranged to cooperate with the rail members at the base structure whereby the seat carriage, in normal operation of the chair, is prevented from jumping the base structure guide tracks (or rails) whilst allowing reciprocating (linear) movement of the carriage along the rails to effect CG movement compensation in a secure manner.

The roller wheel assemblies are preferably mounted onto a seat carriage base plate such that the guide rails are received between the wheel members of each roller wheel assembly and between each facing pair of the latter.

In one embodiment, each roller wheel assembly will include two, preferably identical, roller wheels supported on a common axle, whereby the periphery of the rollers has such a configuration that a channel is defined between the adjacent-located wheels, the channel serving to receive the associated one of the guide rails in sideways engagement. So for example, the carriage may include a total of four roller wheel assemblies, each having one wheel axle extending perpendicular from the plane in which the rails extend and the gauge of the wheel assemblies may be chosen such that the wheels engage with the parallel rails from an outer side or an inner side of the rail pairs.

Alternatively, each roller wheel assembly may include at least two rollers whose respective axles extend above and below the plane spanned by the rails in such manner to prevent upward and downward motion (ie jumping) of the carriage as ft travels along the rails. A side guide wheel may assist against sideways rattling of the carriage as it is moved along the rails.

The peripheral surface of the rollers will advantageously have a complementary profile to match the rails' cross-section, e.g. channeled profile roller wheels, in addition to or instead of the optional side guide wheel, compare for example roller coaster wheel bogies. In order to facilitate mounting (and if desired maintenance removal) of the seat carriage to (from) the base structure, it is preferred to have means for adjusting the gauge between the roller wheel assemblies that cooperate to maintain the seat carriage secured to the guide rails at the base structure, or the gauge between the parallel-spaced apart rail members themselves. The adjustment means could include eccentric adaptor bushings in which are received the axles of some or all of the respective ones of the roller wheel assemblies. This mechanism allows for fine adjustment also of the pressure exerted by the wheel assemblies onto the rails.

The mount for the roller wheels may include a C- or U-bracket or housing at which the wheel axles are secured, the brackets then being mounted in fixed (or adjustable) manner on both width-ward sides of the carriage base plate member, such that each bracket in effect straddles the associated guide rail.

A spring or other biasing mechanism could be incorporated into the roller wheel assemblies to provide positive bias of the roller wheels' periphery onto the guide rails.

As per conventional tilt-in space wheel chairs (or as a matter of fact as is the case with stationary chair designs as well), the seat structure may include a back rest portion and a seat portion angularly adjustable relative to each other, wherein however, in accordance with a further aspect of the invention, a (horizontally extending) axle carried at an underside of the seat portion a predetermined distance away from a rearward end thereof, provides a mounting which enables the seat structure to be pivotally supported solely at the seat carriage structure through said axle. Preferably, the location of the axle will coincide with a vertical line passing through the CG of a user seated upright in the seat structure, such as to maintain a neutral moment of inertia that facilitates ease of tilting of the seat structure at its carriage support. A simple seat carriage assembly is composed of a pedestal protruding from a base plate, the pedestal having coaxially aligned bushes in which is received the support axle mounting the seat structure to the seat carriage. The pedestal itself may be composed of two, parallel-spaced apart upright, triangular plates, that may be braced together if desired to increase stiffness of the seat support.

As per conventional practice, chairs in accordance with the present invention will typically include means for releasably locking the tilt-position of the seat structure with respect to the seat carriage. When the chair also utilizes the above described and preferred gear cluster arrangement to positively couple the tilt and linear motions that the relevant constituent structures (or sub-assemblies) perform, given the positive mechanical coupling employed, use of a locking mechanism operative on the seat structure gear set for locking of the tilt position of the seat structure will automatically also lock the relative position of the seat carriage with respect to the base construction. Consequently, in such case, it is also possible to instead use a locking mechanism operative to lock and release linear movement of the carriage on its supporting base structure. A preferred locking means may include linear actuators pivoted at opposite ends thereof to the seat carriage and the seat structure, respectively, wherein the linear actuators may include hydraulic or pneumatic cylinder-piston rods.

A particularly advantageous additional feature of a preferred embodiment of the invention resides in the provision of one or more hydro-pneumatic rams coupled / articulated with one end thereof to the carriage structure and with another end thereof to the chair structure in such manner that tilting of the chair structure into an occupant backward reclining position is aided by the occupants weight and effected against pneumatic pressure build-up in the ram(s) pneumatic circuit, thereby providing a 'cushioned' or feathered (and controlled) reclining motion, and tilting of the chair structure from a backward reclining position into an upright position is aided by the pneumatic circuit acting on the hydraulic circuit of the ram(s) whereby hydraulic circuit pressure is used in aiding in the tilt movement of the chair structure into its upright position. The hydro-pneumatic ram(s) can themselves provide the tilt position locking mechanism. The number and/or pressure specification of the ram(s) will be chosen to match specific chair user (occupant) weight ranges, eg two 180 N pneumatic pressure charge rams may be employed for wheel chairs intended for users having a body weight of 70 Kg, whereas four 120 N rams may be mounted to cater for 90 kg wheel chair users. A wheel chair incorporating the above described pedestal mounting of the chair structure to the carriage structure at the wheeled base, with mechanical gear arrangement for coupling the tilt and the linear motion of chair structure and carriage, and tilt motion assisting and controlling rams provides for a wheel chair design that will not require additional motorized actuators to assist in backward and forward tilting of the chair structure, as the components ae designed to cooperate in minimizing the effort / force required by a carer and/or chair occupant in effecting the tilt movement. In the following, preferred embodiments of a wheelchair in accordance with the present invention will be described in more detail with reference to the accompanying drawings.

4. Brief description of the Drawings

Fig.1 is a perspective top and side view of a wheel chair frame prototype in accordance with a first, non-motorised version of the present invention;

Fig. 2a is a side view of the wheel chair of fig. 1 but in which the rear small diameter wheels have been replaced with large diameter wheels that allow a wheel chair occupant to self-propell the chair;

Fig 2b is another isometric view of the wheel chair of fig.1 , but from a bottom angle, with some components / subassemblies removed for improved clarity of illustration purposes.;

Figure 3a and 3b are side views of the wheel chair of fig. 1 , illustrating the seat structure of the chair in an upright and and in a backward tilted position, respectively, and the fixed positioning in space of the CG of a notional chair occupant during tilting ;

Figure 4a and 4b are respectively top plan views of two embodiments of a base structure of the wheel chair of fig. 1 , incorporating one of the gear components of the tilt mechanism for the seat support structure shown in fig.

6 as weel as some of the guide elements to enable linear movement of the seat with respect to the base structure;

Figure 5a and 5b are respective perspective views of the base structures of fig. 4a and 4b, with wheel support frame members mounted thereto;

Figure 6 is a perspective view of a seat support frame as used in the chair of fig. 1; Figure 7 is a perspective view of one seat side support subassembly as used in the chair of fig. 1 ;

Figure 8a, 8b and 8c are respectively a perspective, a side and a front plan view of a first embodiment of a seat carriage and support structure, with a gear cluster of the tilt mechanism for the seat structure (not shown) to be mounted thereon;

Figure 8d and 8e are respectively a side and a front plan view of a • second embodiment of a seat carriage and support structure, with a gear cluster of the tilt mechanism for the seat structure (not shown) to be mounted thereon; and

Figure 9a, 9b and 9c are respectively a perspective illustrative view, and two side illustrative views of the base structure of fig. 4a, the seat structure of fig. 6, and the seat carriage structure of fig. 8a/b, in an assambled state, with movement synchronisation gear elements and a tilt assisting ram pair.

5. Description of preferred Embodiment

Referring first to Figures 1, 2a and 2b, a center-of-gravity tilt-in-space wheelchair 10 is shown to be assembled form a number of subassemblies, as is customary with modular wheel chairs, to cater for different user / occupant body specifications. Herein below, as well as above, relative terms of reference such as forward, rear- or backward, width, height, as well as indicators such as horizontal and vertical, are employed to provide reference context to facilitate understanding of the invention, and are not intended to limit the scope of the otherwise structurally disclosed and described components and assemblies. The chair 10 includes a base structure 12 (see also figures 4a, 4b and 5) to which are removably mounted two front wheel support assemblies 14a and 14b, each mounting identical front wheels 16a for castoring about a vertical axis, and a rear wheel subassembly, genetically identified at 15, and which includes two rear wheels 16b journaled for rotation about a horizontal axis; a seat support structure 18 (see also figure 6) to which are removably mounted two seat side support frames 20a and 20b (see figure 7) which themselves are disposed to support between them a non-illustrated seat cushion or capsule for supporting the buttocks and upper legs of an occupant and in between which is also articulated / pivoted a back rest assembly 22 that receives a non-illustrated back rest surface for supporting the spine / back of the occupant; a seat carriage and support subassembly 24 (see also figures 8) mounted to the base structure 12 for linear horizontal motion between the front and rear wheels 16a and 16b as will be described below, and to which is mounted the seat support structure 18 (see eg figures 9a to c) for tilting about a horizontal axis; and a mechanical gear 26 which couples tilting movement of the seat support structure 18 with respect to the seat carriage structure subassembly 24 and linear movement of the carriage structure 24 with respect to the base structure 12 as is described below.

As may be gleaned from figures 4 to 8 in particular, the base, wheel support, seat support, back rest and seat side support structures 12, 14, 18, 20 and 22 consist of tubular aluminum or steel-alloy members that are welded together or otherwise fixed to one another into framework structures, the dimensions of the tubular members being chosen such that telescopic insertion of the respectively cooperating subassemblies is enabled, the relative insertion position being fixable using fasteners as is known in the industry. The respective subassemblies will be described below.

Turning next then to fig. 4a, there is illustrated a first embodiment of the base structure 12; similar reference numerals have been used in figs. 4a and 4b to identify similar components in both base frame versions. In the embodiment of fig. 4a, structure 12 is made up of two longitudinally extending rectangular tubular support members 120, 121 welded in parallel-spaced apart position in orthogonal relation to and between two parallel-spaced apart circular tubular traverse members 122, 123. Three rectangular cross-section, equidistantly parallel-spaced apart bracing members 124 to 126 are welded to also extend between support members 120, 121. A toothed gear track 261 that forms part of the movement synchronization gear 26 described in greater detail below is removably bolted to the top of bracing members 124 to 126. Two rectilinear carriage support tracks 127, 128 are mounted in parallel to and secured by means of a number of bolts

129 on to a respectively one of the support members 120 and 121. The support tracks 127 and 128 will have a suitable polygonal or even semi-circular ceoss- section and provide rolling surfaces for guide roller assemblies mounted to the seat carriage and support subassembly 24 as is described below in reference to figures 8a to c.

The base structure 12 embodiment illustrated in figure 4b is essentially similar to that of fig. 4a, but uses circular tubular, longitudinal support members s 120, 121 extending between and welded endwise to traverse tubular traverse members 122, 123. This embodiment dispenses with separate track members as described with reference to fig 4a, and the rolling surfaces for the guide roller assemblies, as will be described below, are defined along part of the peripheral surface of support tubes 120, 121 , compare also fig 8e. Furthermore, in order too reduce weight, traverse bracing members are dispensed with, and the toothed gear track 261 that forms part of the movement synchronization gear 26 described in greater detail below is removably suspended and supported by means of a total of four ear plates (two pairs 124' and 125') welded pairwise to the respective traverse members 122, 123a; gear track 261 again extendss parallel about the middle between the longitudinal support members 120, 121 and is secured to ears 124', 125' using conventional bolts 129. The gear track 261 will be mounted to ear plates 124' under incorporation of a biasing mechanism (not shown), eg a spring mount, which serves to provide positive bias to maintain engagement between the teeth of track 261 and gear wheel 2620 illustrated in fig 9a, for example.

Turning next to figures 5a and 5b, these illustrate the base structures 12 in accordance with fig. 4a and 4b, respectively, with the two wheel support assemblies 14a, 14b received at and secured thereto, each of the assemblies 14a, 14b comprising a straight longitudinally extending tubular member 141 thats supports at a terminal, bent forward end thereof a vertical tubular bush mounting 142 for receiving and rotatably securing an axle of the front castor wheel 16a (see fig. 1 ). A total of two tubular insertion members 143 (at the front), 144 (at the rear) are welded in longitudinally parallel-spaced apart locations to member 141 such that these can be telescopically and fittingly inserted into and secured at0 discrete insertion depths at the respective traverse members 123, 122 of base structure 12, which thus provides a range adjustment for the desired wheelchair width. The rear wheel subassembly 15 comprises two parallel-spaced apart rear wheel mounting brackets or plates 145 that are detachably affixed to tubular longitudinal members 141, respectively, by means of bolts which are received in two of a plurality of mounting bores that are located in spaced-apart relationship at the rear portion of member 141 ; this arrangement provides a range of adjustment for the desired wheel base length. A bracing tube 146 is suitably secured to and spans the distance between the bracket pair 145 mounted to each member 141, thereby increasing the overall stiffness of the base structure 12 at the mounting location of the rear wheels 16b. At 147 is illustrated one of a plurality of wheel axle mounting holes which provide not only for height adjustability of the rear wheel mounting points 148 at the base frame 12, but also provides different axis points for a selection of rear wheel diameters.

Whilst the relatively small diameter rear wheel 16b illustrated in figs. 1 and

2 is of a type used in non-self-propelled wheel chairs, it will be appreciated that the different height mounting points 147 provided at bracket 145 enable use of large diameter rear wheels, that are preferably driven wheels which may be manually driven or power driven.

Figure 6 illustrates the make-up of the seat support structure 18, which together with two mirror-symmetric seat side support assemblies as the one illustrated in fig. 7 and the back rest assembly 22 illustrated in figure 1 and 2 make up the tiltable seat unit carried by the seat carriage subassembly 24 in movable and tiltable manner on the wheeled base structure 12.

The seat support structure 18 is comprised of two straight tubular members 181, 182 extending in lengthwise direction of the wheel chair 10 in parallel-spaced apart relationship and which are welded at their respective terminal ends into a self-supporting frame between two tubular traverse members 183, 184. Two parallel spaced apart ram mounting ears 185 are welded onto an outside of the traverse member 184 of the frame 12 which will, when the chair is assembled, be located towards the rear of the wheel chair 10. A gear member anchoring ear 186 is located between the ram mounting ears 185 but onto a frame-inside facing side of the same rear traverse member 184. Finally, a through hole 187 is provided on each tubular member 181,182 along a common axis that extends parallel to the axis of traverse members 183, 184, and which serves to receive and anchor a support axle by means of which the support structure frame 18 is mounted onto the seat carriage and support subassembly 24 as described below.

The mirror-symmetric seat side support assemblies 20 (a and b), one of which is illustrated in fig 7, consist of a straight tubular side bar 201 to which are welded in parallel spaced apart relationship and orthogonally thereto, two tubular insertion members 202, 203 dimensioned for telescopic and fitting insertion into the seat support structure's traverse tubular members 183 and 184, respectively.

A number of positioning through-holes provide a range of insertion depth adjustment and fixing points for the seat side support assemblies 20a and 20b at the seat support frame 18 to allow modular chair assembly that caters for different desired wheelchair widths, in similar manner as was described above in relation to the base and wheel support subassemblies 12, 14a and 14 b, compare fig. 5. It will thus be appreciated that indexing of the respective fastening through hole rows at the respective, transversely extending insertion members 143, 144 and 202, 203 of the seat side support assemblies and wheel support assemblies will be the same.

Reverting to figure 7, a backrest support plate 204 is removably affixed to the rear end of side bar 201 using two mounting bolts 205. The backrest support plate 204 has a mounting hole 206 near an upper terminal end for receiving a pivot bolt 208 (see fig 1 ) that serves to secure in pivoting manner the backrest subassembly 22 between the two support plates 204 of the seat side support assemblies 20a and 20b when inserted and secured to the respective opposite width-ward sides of the seat support frame 18. Backrest support plate 204 also has a plurality of angularly spaced-apart, backrest inclination position adjustment holes 207 that provide for a range of adjustment positions for the backrest subassembly 22 (described below) in relation to the seat support structure 18, the angle of inclination being fixable by locking pins 221 carried at the back rest subassembly 22. The backrest assembly 22 includes two straight tubular side frame members 222a, 222b, the lower terminal end portions of which are bent backwards and provided with traverse trough holes indexed in accordance with the spacing of the through holes at backrest support plate 204, for reception and securing of the backrest angle locking pins 221 and backrest pivot bolts 208, respectively. A traverse coupling tubular rod 223 is telescopically received between and inserted fittingly into transversely extending, bent receptacle tube stumps 224a and 224b that are welded to the side tubes 222a and 222b, respectively. As is the case with the other, telescopically adjustable tube components, chair width indexed through holes in coupling rod 223 cooperate with receptacle holes and position fixing pins (not reference in figure 1 ) to allow width adjustment of the backrest assembly 22.

Backrest assembly 22 further includes a multi-piece handle assembly 27 consisting of two tubular insertion members 271a and 271b dimensioned for telescopic fitting insertion into the (upper) free ends of side frame members 224a ad 224b, respectively, the telescopic extension being adjustable and fixed by means of lever-operated friction brackets 272 or any other suitable mechanism. A transversely extending joiner tube 273 with indexed through holes is telescopically received in and between two bent tubular handle members 274a and 274b the other end of which is coupled through a lever operable and frictionally fixable knee joint connector 275 with the insertion members 271a and

271b, respectively. The adjustable knee-joint clamps 275 and friction brackets

272 allow a range of adjustment positions for backrest height and angle of the push handle assembly.

As can be best seen in figures 1, 2a and 7, the seat side support assemblies 20a and 20b are also designed to carry at a front terminal end of each side tube 201 , in telescopically adjustable manner, a leg rest subassembly 28a and 28b. The leg rest subassemblies include each an insertion and fixing tube 209 (see fig 7) having a plurality of through holes into selected ones of which are insertable fixing bolts 210 by means of which the insertion depth of the assembly can be fixed relative to the seat support structure 18. This provides for a range of adjustment longitudinally for the seat length and correct leg rest length position, ie upper leg length adjustment of a wheel chair user. Leg rest angle position adjustment is provided by a lever-operable, knee joint fixture 211 carried at the front terminal end of fixing tube 209. Equally, arm rest structures 29a and 29b are secured in height adjustable manner by means of mounting brackets to the side members 201 of the seat side support assemblies 20a and 20b. Referring next to figure 8a to 8c, a first embodiment of a seat carriage and support subassembly 24 is illustrated in simplified representation in order to permit appreciation of the main components which in a true representation of an actual carriage 24 would be hidden or obscured. Subassembly 24 is intended for use with the base structure 12 of fig. 4a, and consists of a base plate member 241 on a top surface of which are welded two identical, upright, triangular pedestal plate members 242, 243 in parallel-spaced apart relationship, and two pairs of low-friction linear roller assemblies 244, 245 having roller axes of rotation which extend perpendicular to the plane of the plate 241 (and thus the plane in which the guide rails (see figs 4a, 4b) extend). Each subassembly 244, 245 is secured in a receptacle hole, four of which are provided near a respective one of the four comers of plate 241 , on a bottom facing side of plate 241.

The pedestal plates 242 and 243 have at an upper free portion respective through holes in which are received respective low-friction, high-strength bush members 246 that are coaxially aligned to themselves receive a not illustrated support axle whose terminal ends extend beyond the pedestal plates 242 and 243 to be respectively received and secured against axial displacement in the mounting through holes 187 provided on the tubular members 181,182 of the seat support frame 18, see eg fig. 9a. Consequently, the seat support frame 18 is mounted / supported on the pedestal for rotation solely about a horizontal axis defined by the axle.

The two pairs of low-friction support roller assemblies 244 and 245 serve to mount the seat carriage subassembly 24 onto the track members 127 and 128 of the base structure 12 illustrated in figure 4a, such that the carriage 18 is secured against lateral (or width-ward) movement, but enabled to linearly translate towards the front and rearward sides of the base frame 12. Enhanced load bearing and guidance characteristics are provided by using roller wheel assemblies 244, 245 that each comprise a pair of wheels or roller members 246, 247 having a geometrically defined outer periphery, eg triangular or rounded, and which are supported in spaced-apart relationship along a common axle such as to define with their peripheries a channel 248 into which the respective guide rail member 127, 128 protrudes. The axis of rotation of the wheels 246, 247 thus extends perpendicular to a longitudinal axis of the guide rails (or track members) 127, 128; that is, one pair of rollers 244 is supported and guided at one rail 127, and the other pair 245 at the other rail 128. In order to facilitate mounting (and if desired maintenance removal) of the seat carriage 24 to (from) the base structure 12, and to simultaneously provide for track guidance adjustment, it is preferred to have means for adjusting the gauge between the opposing roller wheel assembly pairs that cooperate to maintain the seat carriage secured to the guide rails at the base structure. In the carriage illustrated in figs. 8a and 8b, these adjustment means are provided by eccentric adaptor bushings in which are received the axles of the roller wheel assembly pair 245 only, whereas the axles of roller wheel pair 244 are fixed spatially with respect to the receptacle holes in the base plate 241. This mechanism allows for fine adjustment also of the pressure exerted by the wheel assemblies 244, 245 onto the rails as each such pair in effect straddles the two rails.

Figures 8d and 8e illustrate an alternative embodiment of not only the seat carnage subassembly, here referred to as 1024, but also in particular the roller wheel assemblies 1244 which engage with the guide surfaces provided by the structural longitudinal support members (tubes) 120, 121 of the base structure 12 illustrated in fig. 4b.

It will be noted that there are a total of four parallel-spaced apart pedestal frame members 1242a and b, 1243 a and b, whereby only the central pair 1242a and 1243a illustrate the presence of support bushings 1246 for the not illustrated axle of the seat structure assembly 18 of figure 6, see also fig. 9a, the axle there at 189. The light weight but otherwise stiff central frame members 1242a and 1243a are welded or otherwise secured to the top surface of the carriage base plate 1241 , whereas the outer pedestal frame members 1242b and 1243b are welded or otherwise mounted to a top outer surface of respective, identical roller wheel assembly housings 1249 of two roller wheel assemblies 1244 secured by means of fastening bolts 1250 to both width-ward longitudinal sides (or edges) to the underside of plate 1241, as best seen in fig. 8e, respectively. Roller wheel assembly housing 1249 essentially consists of two pressed and/or bent sheet metal sections 1249a, 1249 that define in cross-section (as per fig. 8e) a C- or U- bracket open to the lower end of carriage 1024. Each roller wheel assembly 1244 incorporates a total of four rollers or wheels 1246 and 1247 arranged pair wise near a front and a rear end of carriage 1024, respectively, with their axles 1251a and 1251b respectively extending horizontally above and bellow the support member (hinted at 120 in fig 8e) on which the assemblies 1244 engage for safe tracking of the carriage on the base structure 12. This mount type effectively restrains jumping of the carriage 1024 from its guide rails as it travels along the rails during CG adjustment, see below. The peripheral surface of the rollers 126, 1247 have a complementary peripheral profile to match the guide rails' cross-section, e.g. semi-circular channeled profile roller wheels, again, as best seen in fig 8e. Of course, suitable gauge and roller pressure adjustment arrangements or mechanisms can be incorporated at the roller wheel mounting locations within the housing 1249 and/or the housing 1249 as a whole with respect to the base plate 1241.

Having regard next also to figures 3a, 3b and 9a to c in particular, a motion coupling mechanism 26 arranged to translate and/or couple the tilting movement of the seat support structure 18 about the axle 189 which supports it at the pedestal plates 242, 243 of carriage and support subassembly 24 (and 1024) into / with the linear movement which the seat carriage subassembly 24 is able to carry out with respect to the base structure 12, and/or vice versa. Synchronization of these two motions by means of a mechanical gear mechanism enables achievement of substantial positional retention of the CG of a 'notional' (or reference) chair user during tilting of the seat support frame 18 (and herewith associated seat side support and backrest assemblies) with respect to a reference plane defined by the base frame 12. The mechanical gear mechanism 26 includes a rack and pinion gear operative between the base structure 12 and the seat carriage 24 (hereinafter this reference numeral also covering the embodiment 1024 of fig 8d and 8e), the rack bar being the afore referenced track 261 of the base frame structure 12, and a herewith cooperating pinion wheel 262 being secured against rotation on a carrier axle 263 that extends between and is itself run on appropriately dimensioned bearings received in through holes near a bottom zone of the pedestal plates 242, 243 of carriage subassembly 24, compare also fig. 8; it will be noted that pinion wheel 262 will extend with its periphery through an opening in base plate 241 of the carriage 24 so as to mesh with the track rack bar 261 at the base structure 12, compare fig. 9a and b. Consequently, rotation of pinion wheel 262 (about the axis define by axle 189 and as per arrow R in fig. 3), which is otherwise held in a fixed position on the carriage structure 24, will cause the carriage structure 24 to be displaced linearly along the track rails on base structure 12 along arrows F and B shown in fig. 3

The gear mechanism 26 further includes a tilt gear set operative between the seat support structure 18 and the seat carriage 24 to fully couple the tilting movement about R of the seat structure 18 with the linear displacement (or motion) along F and B of its supporting carriage 24 on the base structure 12. The tilt gear set includes a gear wheel 264 (fig 8c) secured against rotation on carrier axle 263, which is dimensioned to mesh with a counter gear member 266 which is held stationary at the seat support structure 18. As will be noted from figures 10a to c, the counter gear member 266 is a sturdy plate member secured at one end to gear member anchoring ear 186 of frame 18 by means of a suitable bolt, and supported at a through hole 190 at an opposite upper end on the seat support axle 189 that spans between the pedestal plates 242, 244, see figure 9a.

The counter gear member 266 has an arched peripheral edge with gear teeth indexed to match / mesh with the first gear wheel 264 in such fashion that a seating surface present at the seat support structure 18 can be tilted within an angular range of -10° to +60° with respect to a horizontal reference plane. It is hereby preferred that gear teeth are provided on the counter gear member only along an arc extension on the edge spanning this angular range, thereby providing a positive stop that would prevent unpleasant or undesired over-tilting of the seat structure with respect to the base structure.

The respective gear ratios of the tilt gear set and the rack and pinion gear set can be chosen to accommodate a desired degree of horizontal movement of the seat carriage 24 on its supporting base structure 12 required to accommodate the horizontal shifting of the CG of a user that would be caused by tilting of the seat structure 18 about the tilt axis (provided by axle 189) at the seat carriage pedestal 242, 243. As may be best seen in figures 2a, 2b, 3a, 3b and 9b and c, a pair of tilt movement assistance and movement restriction rams 29 are operative between the rear end of seat support structure 18 and a forward end of seat carriage structure 24. To this end, a pair of double arm side support brackets 291 (only one visible in the referenced figures) are mounted in parallel-spaced apart relationship on carriage base plate member 241 to extend in forward direction thereof and having mounting holes for articulating and securing the terminal ends of ram push rods 292 of rams 29 to the carriage assembly 24. The respective opposite ends of the cylinder 293 of the hydro-pneumatic rams 29 are articulated and secured to ram mounting ears 185 provided at the seat support frame 18. As may be noticed by comparing the different tilt and carriage position end settings respectively illustrated in figures 9b and 3a vs 9c and 3b, the ram's stroke length is chosen such as to limit the rotation of seat support structure 18 to a desired angle of inclination, eg between 0° and 55°, or even a slight forward inclination of -5° with respect to the horizontal plane, which will effectively also limit the linear travel path of the carriage structure 24 on the base structure 12 to a specified value, eg 240mm, due to the mechanical gear coupling between the three sub- assemblies 12, 18 and 24.

The geared carriage assembly 24, 26 allows tilt angle movement of the seat support frame 18 whilst traveling back and forth with respect to the base frame 12. As may be gleaned from figures 3 and 9, the appropriate geometric dimensions and relationships between the rotation axles and travel path that enable and provide constant balance between the wheeled base structure 12 with a focal point P that is adapted to be coincident with or within an acceptable locus area about the center of gravity (CG) of a 'standardised' or real wheelchair occupant can be determined as required. Dimensioning of the gas pressure values as well as the hydraulic circuit of the rams 29, which provide additional support between the seat support assembly 18 and the gear carriage 24 is also within the skill level of a competent engineer. The hydro-pneumatic (or other type) rams are essentially provided to assist the upright-tilting action of the seat structure 18 out of its fully tilted position shown in fig 3b and 10c to achive the attitude illustrated in figs. 3a and 10b; the rams can also be used to lock the tilt position of the seat structure 18 in space, and can be adjusted to permit the overall tilt angle and movement range.

In closing it should be noted that the wheel chair 10 may also incorporate wheel brake devices as well as other components typically present in manually operated wheel chairs. The present invention is particularly suited for non- motorised wheel chair types, in that (a) the pedestal mounting of the seat support structure for rotation about a single support axle of the pedestal, coupled with (b) the mechanical gear which is arranged to translate and synchronize tilt movement of the seat support frame at the pedestal into and with linear displacement of the seat carriage support structure at the base structure, and (c) the presence of tilt motion supporting / aiding rams provide an improved wheel chair design which minimizes the effort required for a carer or a wheel chair occupant to tilt and readjust the upright position of the seat structure, whilst providing a compact and simple wheel chair design of minimized overall weight as compared eg to some of the prior art wheel chairs referred to at the outset of this specification.

Claims

1. Tiltable chair, including a seat structure for supporting a person; s a seat carriage on which the seat structure is mounted for tilting about an essentially horizontal first axis; a base structure on which the seat carriage is mounted for linear movement between two end positions along a second axis substantially perpendicular to the first axis; and o means for coupling tilt movement of the seat structure and linear movement of the seat carriage whereby the center of gravity of a person when seated in the seat structure upon its tilting will remain substantially fixed at a point in space or within a small locus thereof through linear movement of the seat carriage on the base structure. 5

2. A wheelchair, including a base structure to which are secured two rear and at least one front wheel; a seat structure for supporting a person; a seat carriage on which the seat structure is mounted for tilting about an0 essentially horizontal first axis, the seat carriage being mounted to the base structure for linear movement between a forward and a rearward end position along a second axis substantially perpendicular to the first axis; and means for coupling tilt movement of the seat structure and linear movement of the seat carriage in such manner that the center of gravity of a person5 when seated in the seat structure will remain substantially fixed at a point in space or within a small locus thereof in that tilting of the seat structure will cause linear movement of the seat carriage relative to the base structure.

3. Chair according to claim 1 or 2, wherein the coupling means include a gear0 mechanism arranged to translate tilting movement of the seat structure into linear movement of the seat carriage and/or vice versa.

4. Chair according to claim 1 , 2 or 3, wherein the gear mechanism includes a rack and pinion gear operative between the base structure and the seat carriage.

5. Chair according to claim 4, wherein a rack bar or track is secured to the base structure, and wherein a pinion wheel is received at the seat carriage.

6. Chair according to any one of claims 3 to 5, wherein the gear mechanism further includes tilt gear set operative between the seat structure and the seat carriage.

7. Chair according to claim 6, wherein the tilt gear set includes a first gear wheel which is received at the seat carriage and a counter gear member that meshes with the first gear wheel and which is held stationary at the seat structure.

8. Chair according to claim 7, wherein the counter gear member is a plate member having an arched peripheral edge with gear teeth.

9. Chair according to claim 7 or 8, wherein the pinion wheel and the first gear wheel are comprised in a gear cluster supported at the seat carriage.

10. Chair according to any one of claims 1 to 9, further including a low friction support assembly operative between the seat carriage and the base structure to secure the former to the latter, preferably in removable manner.

11. Chair according to claim 10, wherein the low friction support assembly includes a pair of guide rails secured in parallel spaced-apart relationship to or otherwise defined and provided by structural / load-bearing members of the base structure, and two or more roller wheel assemblies mounted to the seat carriage and operatively associated with the guide rails, the roller wheel assemblies being devised to guide and support the seat carriage at the guide rails and prevent the carriage from jumping off the rails.

12. Chair according to claim 11 , wherein each roller wheel assembly includes a pair of wheels which are received along a common axle or parallel-spaced apart, separate wheel roller axles in such manner that outer peripheral profiles of the two wheel rollers define between them a guide channel for the guide rails.

13. Chair according to claim 12, wherein the axis of rotation of the roller wheels extend perpendicular to a longitudinal axis of the guide rails, and wherein the wheels are journalled at locations on the seat carriage such that the guide rails are received either in between width-ward separated roller wheel assemblies or on width-ward outer sides of the guide rails.

14. Chair according to claim 11 , wherein each roller wheel assembly includes at least two rollers whose respective axles extend above and below the plane spanned by the guide rails in such manner as to prevent jumping off of the carriage as it travels along the rails

15. Chair according to claim 10, further including means for adjusting the rail gauge between the roller wheel assemblies that cooperate to maintain the seat carriage secured to the guide rails at the base structure.

16. Chair according to claim 15, wherein the adjustment means include eccentric adaptor bushings in which are received the axles of one or more of the roller wheels of the roller wheel assemblies.

17. Chair according to any one of claims 1 to 16, wherein the seat structure is pivotally supported solely at the seat carriage structure.

18. Chair according to any one of claims 1 to 17, further including tilt-position locking means for releasably locking the tilt-position of the seat structure with respect to the seat carriage.

19. Chair according to claim 18, wherein the locking means include linear actuators pivoted at opposite ends thereof to the seat carriage and the seat structure, respectively.

s 20. Chair according to claim 19, wherein the linear actuators include hydraulic or pneumatic cylinder-piston rods.

21. Chair according to any one of claims 17 to 20, wherein the seat carriage includes a pedestal protruding from a base plate, the pedestal havingo coaxially aligned bushes in which is received a support axle mounting the seat structure to the seat carriage.

22. Chair according to claim 21 , wherein the seat structure has a rearward end and includes a back rest portion and a seat portion angularly adjustable5 relative to each other, and wherein the supporting axle is mounted to an underside of the seat portion a predetermined distance away from the rearward end.