Field of the Invention

This invention relates to stairlifts

Background to the Invention

Stairlifts, including those travelling in a single direction at a single angle of inclination (straight-line stairlifts), typically comprise a carriage mounted on a stairlift rail for movement along the rail. The carriage includes a drive motor and gearbox and includes some form of drive mechanism, such as a rack and pinion, which contacts the rail to effect movement of the carriage along the rail. Whilst this arrangement is well proven, there is an increasing pressure to reduce the cost of such products whilst not compromising product safety. There is also pressure to provide a drive system which does not require lubrication in the form of grease, since grease may lead to soiling of clothing or other material coming into contact with the rail.

One alternative to a rack and pinion drive system is a friction drive arrangement. Currently proposed friction drive systems have a drive wheel biased into frictional point-contact with the rail and we have found that, in order to ensure reliable drive transfer to the rail, extremely high loads must be applied between the drive wheel and the rail. This, in turn, leads to unacceptably high levels of wear. Further, the surface of the rail must be kept very clean at all times to avoid compromising the ability of the drive wheel to frictionally engage the rail.

It is an object of this invention to provide a straight-line stairlift which goes at least some way in addressing the problems set out above; or which will at least

provide a novel and useful choice.

Summary of the Invention

Accordingly, in one aspect, the invention provides a stairlift including:

a stairlift rail having a drive surface extending along said rail;

a carriage mounted on said rail for movement along said rail;

a drive mechanism within said carriage engageable with said drive surface on the rail to displace said carriage along said rail,

said stairlift being characterised in that said drive mechanism includes a transmission section moveable within said carriage in a direction substantially parallel to said drive surface, and means to maintain said transmission section in engagement with said drive surface such that, upon movement of said transmission section with respect to said carriage, said carriage is driven with respect to said rail.

Preferably said transmission section is embodied in a belt.

Preferably said belt comprises an endless belt supported on a pair of spaced wheels.

Preferably each of said spaced wheels is driven.

Preferably said drive surface and said transmission section include inter- engaging drive elements.

Preferably said drive elements are defined by spaced teeth on said transmission member and spaced recesses on said drive surface configured to receive said teeth.

Preferably said drive mechanism is constructed and arranged such that, at any one time, a plurality of said teeth are engaged with recesses on said drive surface.

Preferably said drive mechanism further includes a follower operable to maintain said teeth in engagement with said recesses.

Preferably each of said wheels on which said endless belt is supported includes at least one side plate, said at least one side plate including projections shaped and positioned to engage with said recesses on said rail in the event of failure of said flexible transmission member.

Preferably said recesses are defined by apertures formed in said rail.

Alternatively said transmission section is constructed and arranged to frictionally engage said drive surface.

Preferably said drive mechanism includes biasing means to bias said transmission section into frictional engagement with said drive surface.

Preferably said drive mechanism is constructed and arranged so that, at any one time, a longitudinal part of said transmission section is in frictional contact with said drive surface.

Many variations in the way the present invention can be performed will present themselves to those skilled in the art. The description which follows is

intended as an illustration only of one means of performing the invention and the lack of description of variants or equivalents should not be regarded as limiting. Wherever possible, a description of a specific element should be deemed to include any and all equivalents thereof whether in existence now or in the future.

Brief Description of the Drawings

Two forms of stairlift incorporating the various aspects of the invention will now be described with reference to the accompanying drawings in which :

Figure 1 : shows an isometric view, from the front, of a first embodiment of stairlift carriage and rail according to the invention;

Figure 2: shows in an isometric view, from the rear, of that which is shown in Figure 1;

Figure 3: shows an end elevation of the stairlift components shown in Figures 1 & 2

Figure 4: shows a rear elevation of the carriage forming part of the stairlift shown in Figures 1 to 3, removed from the stairlift rail;

Figure 5: shows an isometric view, from the front, if a second embodiment of stairlift carriage according to the invention;

Figure 6: shows a rear elevation of the carriage shown in Figure 5, removed from the stairlift rail;

Figure 7: shows a view from the same direction as Figure 6 but of an alternative embodiment of carriage; and

Figure 8: shows a view from the same direction as Figure 6 but of a further alternative embodiment of carriage.

Detailed Description of Working Embodiments

Referring firstly to Figures 1 to 4, according to the invention a stairlift assembly 10 is provided, the assembly 10 including a stairlift rail 11 and a carriage 12 mounted for movement along the rail. Included within the carriage 12 is a novel drive mechanism which will be described in greater detail below.

In the form shown the rail 11 is formed from a combination of folded sheet metal sections and comprises a first section 14 and a second section 16, the two sections being fixed together by, for example, rivets 17. The first section 14 includes an upright centre web 18, an upper flange 20, and a lower flange 22. The flanges 20 and 22 are substantially parallel and the upper flange 20 has strengthening rib 21 extending along the outer edge thereof whilst the lower flange 22 has an angled strengthening rib 23 extending along the outer edge thereof.

As can be seen in Figures 1 & 2, the upper flange 20 has included therein, or itself defines, a drive surface. In this particular embodiment the drive surface has formed therein, a series of spaced recesses, preferably in the form of evenly-spaced slotted apertures 24. These apertures may be laser-cut into the flange 20 although other methods of forming the slots will be known to those

skilled in the art. After formation of the apertures, the edges thereof may be smoothed off and/or tailored more closely to the profile of the driving transmission member by, for example, applying a punch to each aperture.

The second section 16 of the rail includes a centre web 26, and a bottom flange 28 having a angled strengthening rib 29 extending along the outer edge thereof. When the sections 14 and 16 are fixed together in the intended manner, the flanges 22 and 28 are aligned and form mirror images about the centre-line of the rail 11.

The rail 11 as described above, can be readily formed using conventional sheet-metal forming techniques which do not require expensive tooling investment.

It should be appreciated, however, that the rail need not be formed as two components, or formed from sheet metal, as described above. The rail could, for example, be extruded and the apertures 24 post- formed by punching or ^• other suitable technique.

The carriage 12 has a central chassis member 30 which may be cast, or machined from a solid block of metal. The chassis member might also be formed from other materials including injection moulded plastics.

A number of rollers are provided to support the chassis on the rail 11 and, in the form shown, include two spaced, vertical, support rollers 32a and 32b which are in rolling contact with the flange 22 of the rail; and a plurality of horizontal rollers arranged to resist rotation of the carriage about the rail. As shown the horizontal rollers include a spaced pair 34a and 34b which bear against rib 21, and a spaced pair 36a and 36b which bear against the upper

margin of centre web 18. The rollers 34 are mounted at opposite edges of the main chassis 30 whilst the rollers 36 are mounted on brackets 38 extending from, but fixed to, the rear surface of the chassis 30.

The horizontal roller set is completed by central bottom roller 40 which is positioned to bear against the rib 23 of first rail section 14.

A characteristic feature of the stairlift according to the invention is the drive mechanism included within the carriage 12 to displace the carriage 12 along the rail 11. This drive mechanism includes a transmission section which, when the carriage is mounted on the rail, is parallel to the drive surface 20 on the rail, and is held in contact with the drive surface 20. The transmission section is preferably flexible in form and, in this embodiment, is provided with drive elements arranged to engage with the apertures 24 on the rail in such a way that displacement of the transmission section with respect to the carriage, effects displacement of the carriage along the rail.

As is best seen in Figure 4, the flexible transmission section is advantageously incorporated in an endless belt 44 having drive elements in the form of teeth 46 and 48 extending from the inner and outer faces, respectively, thereof. The teeth 48 extending from the outer surface of the belt 44 are configured and arranged to engage with the apertures 24 in the rail. The teeth 46 are selected to engage with, or determine, the toothed peripheries (not shown) of spaced drive wheels 50a and 50b on which the belt 44 is mounted and supported.

The belt 44 is preferably a readily available, off-the-shelf, timing belt. These are typically rubber/plastics/synthetic/fabric composite items manufactured by Gates amongst others. A particular feature of these belts is that they operate without the need for any lubrication.

It will be appreciated that the upper span 52 of the mounted belt engages the under-surface of the flange 20, and thus the teeth 48 engage with apertures 24 from below. In this way, the moving belt is kept out of contact with the exterior of the stairlift assembly. The span 52 of the belt is vertically supported by, and maintained in contact with flange 20, by a static rubbing block or follower 54 which is positioned within the loop defined by the mounted belt. The follower ensures that the section of belt which, at any time defines the upper span 52, cannot sag and allow the teeth 48 thereon to become disengaged from the slots 24.

A particular feature of the drive mechanism herein described is that a plurality of the teeth 48 are engaged in slots 24 at any given time. The number of teeth 46 engaged in slots 24 is determined by the length of the upper span 52 of the belt. By way of example, with a span of 230mm, 23 teeth are fully engaged in slots 24, each tooth 48 having a width of about 5mm. The fact that more than one tooth 48 is engaged with the rail, reduces the loading on the individual teeth and thus reduces the likelihood of tooth failure. The relatively low loading on each tooth also enables the use of non-metallic materials.

As a further safety precaution, a slackness monitor 56 is preferably provided which acts against the bottom span 58 of the belt and determines if the span 58 becomes slack due to, for example, breakage of the belt 44. In the event the monitor 56 senses slackness of the belt 44, an internal switch is broken cutting power to the carriage drive.

Whilst a toothed flexible belt as described above is the preferred form of flexible transmission member, other drives are possible without departing from the scope of the invention. For example, a chain based drive system could be provided having teeth or the like, projecting from the individual chain links, to engage in apertures 24 in the rail. Similarly, the belt or chain

need not engage with the slots or apertures 24, as shown. In place of the slots or apertures 24, a downwardly facing arrangement, more in the nature of a rack, could be provided - either formed integrally with flange 20, or as a separate component mounted thereon. That is to say, downwardly facing teeth or like projections could engage with the teeth 48 of the drive belt. The rack could be machined from metal, moulded from plastics, or punched from sheet material in the manner described in greater detail in our co-pending British Patent Application No. 0523027.1.

Toothed wheels 50a and 50b are preferably, but not necessarily, both driven. To this end, the wheels are mounted on the output shafts of two motor/gearbox units 60a and 60b. The units 60a and 60b are mounted on the front face of the chassis 30 but so that the output shafts thereof pass through the chassis. The units 60a and 60b are preferably selected so as to be self-sustaining. That is to say, the units will not free-wheel whilst not energised and subjected to a displacing force. The self-sustaining feature overcomes the necessity to provide separate braking for the carriage.

Batteries 62a and 62b are clamped to the rear of the chassis 30 to provide power for the motor/gearbox units and for the other electrical based functions of the stairlift, the latter being under the control of an electronic control unit (ECU)-based control system 64 provided on the upper edge of the chassis 30.

To further enhance safety, another aspect of the invention provides that each of the drive wheels 50a and 50b may be provided with side plates 51 which not only serve to maintain the belt 44 from slipping sideways off the wheels 50, but may also be provided with peripheral projections or teeth 61, some of which are shown on wheel 50a. The teeth 61 are shaped and spaced to protrude within apertures 24 but not, normally, to engage the edges of the

apertures and provide a drive function. However, in the event of the belt 44 loosing tension or breaking, power is cut to the motor/gearbox units 60 and the teeth 61 may then engage the edges of the apertures 24 and lock the carriage in position.

Finally, a boss 66 is mounted to project from the front surface of the chassis 30 to provide a mounting point for a chair interface.

Referring now to Figures 5 and 6, a second embodiment 110 of stairlift is shown which, in most respects, is identical to the stairlift 10 described above. The rail 111 of this embodiment is identical in all respects with the rail 11 described above, but for the fact that the drive surface 120 is not necessarily formed with the recesses or apertures of drive surface 20 of the rail 11. Similarly, the structure of carriage 112, and the roller arrangement for supporting the carriage 112 on the rail 111, is identical to that described above.

The distinction between the two embodiments lies in the drive arrangement. As with the first embodiment, the core of the drive arrangement of this second embodiment is an endless belt 144. However, unlike the belt 44 described above, the belt 144 does not include teeth 48 on the outer surface thereof. In this embodiment the outer surface 148 of the belt 144 is plane and arranged to frictionally interact with the drive surface 120. The inner surface of the belt 144 is provided with teeth 146 to engage the surfaces of toothed drive wheels 150a and 150b. As shown, these drive wheels are both driven, by motor/gearbox units 160a and 160b, though one only may be driven.

The benefit of a friction drive system as shown in Figures 4 and 5 is that the frictional interaction between the carriage 112 and the rail 111 is generated

and maintained over the length of the span 152 of the belt 144. This substantially reduces the high point loading and high wear of existing friction drive stairlifts.

Some form of biasing means is preferably provided to maintain the full length of the span 152 in contact with the drive surface 120 of the rail. In the particular form shown, this biasing means comprises a plurality of rollers 170 mounted on a support bracket 172. The support bracket 172 is, in turn, biased toward the underside of the span 152 by springs 174. If desired, the peripheries of the rollers 170 may be slotted to received the teeth 146 on the inner surface of the belt 144.

It will be appreciated that many alternatives may be provided, for upwardly biasing the belt 144 into contact with the drive surface 120, without departing from the scope of this invention. Two such alternatives are shown in Figures 7 and 8 and involve drawing the belt span 152 upwards into contact with drive surface 120 by application of a biasing force from above the drive surface.

In the embodiment shown in Figure 7, two supplementary rollers 180 bear against the outer part 121 of that section of the rail whose underside defines drive surface 120. In so doing, the rollers 180 maintain the drive belt 144 in contact with the drive surface 120. To increase the interaction between the drive belt 144 and the drive surface 120, the rollers 180 are biased towards the rail by compression springs 182 or the like. This, of course, has the effect of drawing the drive wheels 50 and thus the drive belt 144, up towards the drive surface 120. The degree of interaction can be varied by changing the strength of springs 182.

A further alternative is shown in Figure 8. In this embodiment supplementary rollers 186 are provided, the rollers 186 being positioned to bear against

surface 121 of the rail. In this embodiment, however, the rollers are rotatably mounted on rockers 188 and the rockers, themselves are pivotally mounted to the chassis at 190. The upper ends of the rockers are interconnected by a biasing link 192 which can vary the spacing between the rockers and thus adjust the bias of the rollers 186 against the rail. It will be appreciated that this affects the degree to which the drive belt 144 is drawn up into contact with the drive surface 120.

The biasing link 192 may comprise a manual adjustment with or without additional spring bias. Alternatively, the link 192 may be configured to provide bias which is dependent on passenger weight, substantially as shown in our published International Patent Application No. WO 02/05617.

As with the first embodiment described above, a slackness monitor 156 may be provided to monitor the tension in the belt 144 and activate the necessary safety systems to halt the carriage in the event that this tension falls below a pre-determined minimum level.

It will thus be appreciated that the present invention provides a simple yet effective form of stairlift assembly which, at least in the case of the embodiment above described, is believed to have the following advantages:

a) The assembly has a particularly simple form of carriage which is compact, provides low seat height, and creates greater scope for chair and interface design.

b) The chassis, being extremely simple and robust in form, lends itself to simplified manufacturing techniques including plastics injection moulding.

c) The use of two drive systems reduces the required power and torque rating of each individual motor. This in turn means that there is a greater range of available units from which to choose.

d) The combination of two self-sustaining motor/gearbox units in combination with the follower 54 or biasing rollers 170, and slackness monitor 56, 156 provides all the required safety systems and is believed to obviate the need for an over-speed governor.

e) The belt-based drive system is highly efficient and the fact that such a length thereof is in contact with the rail means than, whether interacting teeth/recesses or a friction drive is chosen, the loading on the drive elements is low. The rubber/plastics based belt also obviates the need for additional lubrication to be added to the drive system.

f) The rail, being unhanded and having the drive surface formed integrally therewith, is ready to be mounted for every installation. The step of positioning and fixing the rack has been eliminated.

g) The rail configuration and drive system opens the possibility of the stairlift being installed by non-expert technicians.