A STAIR LIFT AND A SUPPORTING UNIT FOR A STAIR LIFT The invention relates to a stair lift comprising a supporting unit and a rail system, wherein said rail system comprises a rail having a guiding surface substantially in the form of an arc of a circle, seen in cross-sectional view, on which the tread of a wheel of the supporting unit, which is for example provided with a seat, can roll, which wheel has a radially extending centre plane, in which plane the tread diameter is smaller than the tread diameter at some distance from said centre plane, wherein the tread comprises a concave, substantially arced portion, seen in longitudinal sectional view through the axis of the wheel.

A stair lift of this kind is known from WO 96/20125, wherein such a diabolic wheel, which rolls on a circular tube, is for example indicated at 27 in Figure 4. A wheel of this kind provides very good guidance when moving a supporting unit on which the wheel mounted, as long as the tubular guide rail extends in a straight path. When the guide rail does not extend in a straight path, but rather comprises a curved portion which forms a bend, it must be ensured that the axis of rotation (central axis) of the diabolic wheel remains perpendicular to the local longitudinal direction of the tubular rail. Especially when the supporting unit moves over the tubular rail with two spaced-apart diabolic wheels, said wheels will have to be steered individually in such a manner that their correct position, with the central axis extending perpendicularly to the local longitudinal direction of the rail, is maintained. A mechanism which provides such steering is known per se.

The objective of the invention is to provide a stair lift whose supporting unit is guided over a rail, for example in the form of a circular tube, with at least one diabolic wheel, wherein said diabolic wheel is formed so that proper guidance of the supporting unit is provided, also when the central axis of the diabolic wheel includes an acute angle with the local longitudinal direction of the guide rail.

In order to accomplish that objective, the wheel tread is substantially in the form of an arc of a circle, seen in axial longitudinal sectional view of the wheel, whose radius is larger than that of the arced guiding surface.

Whilst it is usual to have the radius of said circular arc equal half the outside diameter of the tube, it has surprisingly become apparent in practice that a small increase of said radius, preferably between 0.05 mm and 1.5 mm, more preferably between 0.2 mm and 1 mm, already enables a displacement of the central axis of the wheel through an angle of more than 20°, or even 30°, when a tube having a usual diameter (for example of 45-75 mm) is used, whilst the difference between the radius of the circular arc on the one hand and the half-diameter of the tube on the other hand is so small that proper guidance will be provided at all times.

The quality of the guidance of a supporting unit on the rail largely depends on the degree to which the seat of the supporting unit feels stable. Even if proper and safe guidance is provided per se, said guidance does not satisfy the requirements if the user perceives the seat as not being completely stable. This is the reason for the preconceived notion that the radius of said circular arc must exactly equal the half-diameter of the guide tube and should not be selected any larger.

In practice it has become apparent that a comparatively small increase of the radius of the circular arc, namely an increase which causes a hardly perceptible decrease of the stability of the supporting unit, already enables a considerable angular displacement of the central axis of the diabolic wheel relative to the longitudinal direction of the guide rail.

In one preferred embodiment, the tread form, seen in a coaxial plane (longitudinal sectional view), is such that the radius thereof in said centre plane is larger than the radius thereof at some distance from said centre plane. Said form, which is essentially the form of a circular arc, is slightly ellipsoidal, for example. The wheel form may be essentially cylindrical near the centre plane thereby.

In another preferred embodiment, the tread comprises two concave, substantially arced portions, which are arranged symmetrically with respect to said centre plane, and whose facing, spaced-apart ends are substantially in line. The centres of the two arced portions are positioned some distance apart thereby. The two arced portions may have a radius which equals half the outside diameter of the tube, whilst said ends are interconnected by a substantially straight portion, so that the wheel has a substantially cylindrical tread in said centre plane. Said cylindrical tread may have a small length of 0.1-3 mm, preferably of 1-2.5 mm, which small length already enables a considerable displacement of the central axis of the wheel.

With this latter embodiment, wherein two arced portions of the tread have a radius which equals half the outside diameter of the guide rail, proper guidance is obtained in the straight portions of the rail, whereby a circular arc abuts against the circular guide tube without any distortion of the material.

In another preferred embodiment, the supporting unit is provided with at least two wheels, which roll on the same guiding surface in spaced-apart relationship, and which each rotate about an axis, whereby said axes include an acute angle with each other, preferably an angle of more than 1 degree, more preferably an angle of more than 3 degrees, and in a preferred embodiment an angle of 3-8 degrees. The two wheels roll on the same guiding surface in spaced-apart relationship, and their axes of rotation lie in a plane parallel to the central axis of the rail. As a result of the sloping position which the two wheels occupy relative to each other, said wheels roll in a direction which includes an angle with the radial surface of the wheel, at least when the wheels roll on a straight portion of the rail. Said rolling of the wheels in a"sloping"position is made possible by the aforementioned difference in the radii of the substantially circular portions of the wheels and the rail, respectively.

The sloping position of two wheels with respect to each other makes it possible to form the rail with a more acute angle in the direction in which the axes of the two wheels converge than in the other direction. This possibility can be utilized

with a stair lift because a bend in the rail in one direction is generally larger than in the other direction. Said one direction, which includes the larger bend, is the outside bend relative to the staircase, and said other direction is the inside bend.

In the inside bend, the supporting unit rotates backwards if the supporting unit is provided with a seat fitted with a back support which is directed towards the rail.

The arrangement of the two wheels in a sloping position, so that their axes of rotation include an angle with each other, can be considered to constitute an invention by itself, independently of the various wheel forms.

The axes of rotation of the two wheels which roll over the same guiding surface in spaced-apart relationship may lie in a plane parallel both to the central axis of the rail and to a horizontal line perpendicularly to said central axis. In a preferred embodiment, however, the axis of rotation of a wheel includes an angle with said plane, preferably an angle of more than 1 degree, more preferably of more than 3 degrees, so that the axis of rotation slopes downwards from the supporting unit, in particular in a portion of the rail system wherein the rail extends horizontally.

The invention furthermore relates to a supporting unit for a stair lift, which is provided with the above-described diabolic wheel, and also to a wheel having the above-described diabolic form.

The invention furthermore relates to a method for manufacturing a wheel and to a method for guiding an object along a rail as defined in the claims.

Further aspects will be described by means of embodiments, which are schematically illustrated in the figures, and which are defined in the claims.

Figure 1 shows a cross-sectional view of a tubular rail and an elevation of a wheel; Figure 2 shows a sectional view and an elevation corresponding with those of Figure 1; Figure3 is a plan view of that which is shown in Figure 2;

Figure 4 shows an alternative embodiment, which corresponds with the embodiment of Figure 2; and Figures 5-7 show the device according to Figure 3 with a curved rail and with a straight rail.

Figure 1 shows a circular tube 1 in cross-sectional view, which tube makes up the guide rail or part of the guide rail for a stair lift. A wheel 2, which can rotate about a central axis 3 and which is mounted on the supporting unit 10 (not shown in Figure 1) of a stair lift, rolls on said tube 1. Wheel 2 is shown in elevation, it consists of two cylindrical parts 4 and a substantially concave tread 5, which, seen in longitudinal sectional view of central axis 3 of wheel 2, has essentially the form of an arc of a circle. Said form slightly deviates from that of an arc of a circle, however, since the curved form in fact consists of two arced portions 6, each having a radius r, and a straight portion having a length d in the middle.

From Figure 1 it is apparent that wheel 2, whose central axis 3 extends perpendicularly to the longitudinal direction of tube 1, precisely abuts against circular tube 1 in an arc of a circle 7 which lies on one side of the radial centre plane of wheel 2. On the other side (the right-hand side in the figure) of said centre plane, tread 5 of wheel 2 does not abut against the outer surface of tube 1.

The illustrated embodiment is constructed so that when a lateral force (to the right in the figure) is exerted on wheel 2 on a straight portion of rail 1, which is a situation wherein the guide is heavily loaded, there is a good contact between wheel 1 and tube 1, since the two abut against each other with their complementary forms.

A diabolic wheel as shown in this embodiment also appears to function considerably better when the guide rail consists of a tube which does not have an exactly circular outside diameter all over. With such a tube, a small increase of the diameter, seen in vertical direction, will hardly be noticeable, whilst a slight increase of the diameter in horizontal direction will not have any negative effects, either, when the above-described diabolic wheel is used. With the usual wheel,

wherein the tread, seen in the longitudinal direction of the wheel, exactly describes a arc of a circle, whose radius equals the half-diameter of the guide tube, a slight increase of the diameter in horizontal direction will cause a considerable increase of the friction of the guide system, whilst also the diabolic wheel will be heavily loaded in that case.

Figure 2 shows a tubular rail 1 with two wheels 12,13 present on either side of the rail. Wheels 12 rolls on the upper side and wheel 13 rolls on the underside of rail 1. Figure 2 also shows part of supporting unit 10.

Figure 3 is a plan view of Figure 2, so that wheel 14 is shown, which wheel 14 rolls on the same guiding surface of rail 1, at some distance from wheel 13. A fourth wheel, which rolls on the underside of rail 1, namely at the location of wheel 14, is not shown in the figures. Wheels 12 and 13 are rotatably mounted on a frame 20, as are wheel 14 and the wheel that is not shown. Both frames 20 are mounted, whether or not capable of rotating movement, on mounting unit 15, which is mounted in bearings in supporting unit 10, in such a manner that it can rotate about axis 16. Wheels 12,13,14 can rotate about axes of rotation 17,18, 19. Figure 2 shows axes 17 and 18 to extend substantially parallel to each other, whilst Figure 3 shows axes 18 and 19 to extend at an acute angle to each other.

Said axes 18,19 converge in a direction away from the supporting unit. When wheels 13,14 run on a straight rail 1, as is shown in Figure 3, the radial centre plane of each wheel includes an angle with the longitudinal axis (central axis) of the rail, so that wheels 13,14 will roll obliquely forwards. Since the"average" radius of the respective tread of each wheel (tread 5, see Figure 1), which has essentially the form of an arc of a circle, is larger than the radius of the guiding surface of tubular rail 1, a proper abutment of wheel 13,14 against rail 1 is obtained in spite of the sloping position of wheel 13,14.

Figure 4 shows an embodiment wherein the axes of rotation 17,18 of wheels 12, 13 include an angle with axis of rotation 16 of mounting unit 15, seen in a transverse plane with respect to rail 1. Frame 20 is wedge-shaped to that end, so that wheels 12,13 are slightly tilted backwards with respect to supporting unit 10,

which in practice results in an improved abutment of wheels 12,13 against rail 1, especially in helical bends of rail 1. Axis of rotation 16 of mounting unit 15 intersects the central axis of tubular rail 1, as is the case in Figure2.

The placing of the axes of rotation 17,18 of wheels 12,13 at an angle with respect to axis of rotation 16 of mounting unit 15 may be considered to constitute an invention by itself.

Figures5,6 and 7 show an advantage of the sloping position of axes of rotation 18,19 as discussed with reference to Figure 3, namely the fact that a"backward" bend of the rail can be more acute than a"forward"bend, due to said sloping position. Figure 5 shows a backward bend, and Figure 6 shows a forward bend. In this embodiment, the diameter of the tubular rail is 45 mm, and the angle between the two axes of rotation 18,19 of wheels 13,14 equals 6 degrees. The tread 5 of each wheel 13,14, seen in cross-sectional view, comprises a cylindrical portion having a length of 1.1 mm, and furthermore the radius of the tread, seen in an axial plane of the wheel, equals the radius of the outer surface of tubular rail 1.

In this embodiment, the tread of the wheel practically abuts against the guiding surface of rail 1 in an"inside bend" (Figure 5) having a radius R of 250 mm and in an"outside bend" (Figure 6) having a radius R of 400 mm. When rail 1 is straight (Figure 7), the amount of play between the rail and the wheel on one side of the rail will be 1 mm at most. Said amount of play appears to be acceptable in practice.

It will be apparent that if the rail 1 of the stair lift is mounted on one side of the staircase, a"backward"bend will generally be more acute than a"forward"bend.

With the illustrated sloping position of wheels 13,14, it is possible to take both bends with wheels 12,13,14 whose axes of rotation occupy a fixed position with respect to mounting unit 15.