WO2017059867A1

WO2017059867A1 - Scissor lift

Info

Publication number: WO2017059867A1
Application number: PCT/DK2016/050324
Authority: WO
Inventors: Hans Balle Christensen
Original assignee: Motion By Balle A/S
Priority date: 2015-10-08
Filing date: 2016-10-07
Publication date: 2017-04-13

Abstract

A wheel chair with a built-in seat hoist comprising a lifting device,the lifting device being configured as a scissor lift is disclosed, wherein a lower frame (1) is provided with a curved track (1.1; 1.2), in which a pressure wheel (7; 7.1) controlling the position of a pressure rod (5) connected to a first lever arm (3) is arranged to roll. Furthermore, a wheel chair with a built-in seat hoist comprising such a lifting device and a method for designing a track for a pressure wheel of such a lifting device are disclosed.

Description

SCISSOR LIFT

The present invention relates to a lifting device, more specifically to a scissor lift, for instance to be mounted in an electric wheel chair for adjustment of the height of the seat thereof. More particularly, the invention relates to a wheel chair with a built-in seat hoist comprising a lifting device.

Background of the invention The use of lifting devices in tables, chairs and beds, etc. is well-known. The majority of such lifting devices operate according to the so-called "scissor principle", in which a lower frame and an upper frame are connected by two lever arms pivotally connected in a configuration similar to the one of the two arms in a pair of scissors. Most often, there are two pairs of such "scissored" lever arms arranged in two opposite sides of the lifting device, respectively.

At their top and bottom ends, these lever arms are connected to the upper and the lower frames, respectively, in such a way that, when the two ends of a pair of lever arms connected to the same frame are moved towards each other, the distance between the two frames is increased. Similarly, when the two ends of the pair of lever arms connected to the same frame are moved away from each other, the distance between the two frames is decreased. The movements of the lever arms can be affected by an actuator such as, for instance, a hydraulic or an electric linear actuator.

Although this lifting principle functions very well and provides many good solutions for lifting devices, however, actuators used in such scissor lifts must typically be somewhat oversized in order to deliver the required force. This is because, especially in the innermost and outermost positions of the scissor lift, the actuator force is not utilized effectively in such known scissor lift configurations. Brief description of the invention

It is an object of the invention to provide a scissor lift, such as a wheel chair with a built-in seat hoist comprising a lifting device configured as a scissor lift, that overcomes at least partly the above-mentioned disadvantages of scissor lifts known in the art.

The present invention relates, such as relates in a first aspect, to a lifting device configured as a scissor lift, such as a wheel chair with a built-in seat hoist comprising a lifting device configured as a scissor lift, comprising a lower frame and an upper frame substantially parallel, such as parallel, to the lower frame, wherein the lower frame and the upper frame are connected by at least one pair of lever arms rotatably connected to each other in a pivotal point in a configuration similar to, such as identical to, the one of the two arms in a pair of scissors, wherein the first lever arm is rotatably connected at its first end to the lower frame in a fulcrum and in sliding or rolling, such as sliding, engagement with the upper frame at its second end, and the second lever arm is rotatably connected at its first end to the upper frame in a fulcrum and in sliding or rolling, such as sliding, engagement with the lower frame at its second end (such as wherein both the connections between lever arms and frames are in sliding arrangement or rolling engagement) in such a way that, when the scissor configuration formed by the two lever arms is opened, the lower frame and the upper frame are forced away from each other, wherein a pressure wheel is suspended in a suspension point on a first end of a pressure rod, the other end of which pressure rod is rotatably connected in a suspension point to a lifting arm fixed to the first lever arm, and wherein a curved track, in which the pressure wheel is arranged to roll (or alternatively slide), is arranged within or fixedly connected to the lower frame in such a way that, when the pressure wheel moves in a first direction along this track, the track controls the path of the pressure wheel and, thereby, the position and orientation of the pressure rod, causing the suspension point of the pressure rod on the lifting arm to move in a direction away from the lower frame, whereby the first lever arm and, in turn, also the second lever arm and the upper frame are forced away from the lower frame.

A possible advantage of the present invention may be that by having a curved track, in which the pressure wheel is arranged to roll, being arranged within or fixedly connected to the lower frame, then it may be possible to keep the height of the lifting device small when in the fully collapsed configuration. This may in turn facilitate an easier integration into a wheel chair, such as enabling a more user-friendly wheel chair.

By 'fully collapsed configuration' may be understood a configuration of the lifting device, wherein the upper frame and the lower frame are as close to each other as possible. By 'an upper frame substantially parallel to the lower frame' may be understood that an angular difference between a plane defined by the upper frame and a plane defined by the lower frame, such as an angular difference between a planar element upon which the lower frame of the lifting device is placed and a planar element placed upon upper frame of the lifting device, may be within 0-10 degrees, such as 0- 5 degrees, such as 0-2 degrees, such as 0-1 degree, such as 0 degrees.

By 'sliding engagement' may be understood that the first lever arm and/or second lever arm is, at their respective second ends, able to 'slide' along a surface of the upper frame, respectively, the lower frame. By 'rolling engagement' may be understood that the first lever arm and/or second lever arm is, at their respective second ends, able to 'roll' along a surface of the upper frame, respectively, the lower frame, e.g. by means of a wheel. It may be restricted from movement in other directions. The sliding or rolling engagement may, e.g. be facilitated by, respectively, rollers or sliders according to embodiments of the present invention. By 'curved track' may be understood a non-rectilinear track, such as a track comprising tangents being non-parallel, such as tangents with angular differences - with respect to each other - of at least 0.1 degrees, such as at least 1 degree, such as at least 2 degrees, such as at least 5 degrees. If the tangents are projected onto a plane (such as a plane corresponding to the plane of the paper in figures 1-5) spanned by a line traced by a point of contact between the first lever arm and the upper frame when the upper frame is forced away from the lower frame and a line traced by pivotal point (E) when the upper frame is forced away from the lower frame, such projected tangents may have angular differences - with respect to each other - of at least 0.1 degrees, such as at least 1 degree, such as at least 2 degrees, such as at least 5 degrees. The curved track may be confined within a plane (such as a plane corresponding to the plane of the paper in figures 1-5) spanned by a line traced by a point of contact between the first lever arm and the upper frame when the upper frame is forced away from the lower frame and a line traced by pivotal point (E) when the upper frame is forced away from the lower frame.

By 'pressure wheel' may in general be understood a wheel, such as a wheel capable of enduring the pressures exerted on the wheel during use. By 'pressure rod' may in general be understood a rod, such as a rod capable of enduring the pressures exerted on the rod during use.

By the pressure wheel being 'arranged to roll' may be understood that the pressure wheel is arranged to move smoothly, e.g. by rotating, i.e. turning over and over.

It may be understood that when the pressure wheel moves along this curved track, thereby forcing the upper frame away from the lower frame, the pressure wheel moves in a 'first direction' . By 'lifting arm' may be understood a structural element within or (rigidly) fixed to the first lever arm serving to provide a separation of the suspension point (C) and an axis of the first lever arm (such as said axis being a line traversing both the fulcrum (A) connecting the first lever arm and the lower frame and the suspension point for roller or slider on first lever arm), wherein said separation is at least in a

circumferential direction (such as 'around the axis') with respect to the rotation of the first lever arm around the fulcrum (A) connecting the first lever arm and the lower frame), such as in the direction of rotation when the upper frame is forced away from the lower frame (such as in front of the axis of the first lever arm during such movement). By 'fixed to the first lever arm' may be understood that the 'lifting arm' is connected, such as rigidly connected, to the first lever arm, such as the lifting arm and first lever arm being separated structural elements or the first lever arm and the lifting arm being a single structural element, such as a single monolithic structural element. A possible advantage of having a separation of the suspension point (C) and an axis of the first lever arm may be that it enables having an improved ratio between a necessary force applied on the pressure wheel in order to move the upper frame away from the lower frame and a distance, which the upper frame moves. For example, this ratio may be substantially constant, such as constant throughout the movement from fully collapsed to fully unfolded.

By 'whereby the first lever arm and, in turn, also the second lever arm and the upper frame are forced away from the lower frame' may be understood that at least the centre of gravity moves away from the lower frame. For example, the first lever arm is rotatably connected via fulcrum (A) to the lower frame, and as such rotates around (the respective) fulcrums of the first lower frame, but the centre of gravity of the first lever arm moves away from the lower frame. Similarly, the second lever arm may remain in contact with the lower frame, but rotates so that the centre of gravity moves away from the lower frame.

In an embodiment of the invention, the curved track is designed in such a way that when the pressure wheel moves in a first direction along the curved track, there is a substantially constant, such as constant, ratio between the lifting height, i.e. the change in distance between the lower frame and the upper frame, and the distance which the pressure wheel has moved along the curved track. This presents the advantage that, if the pressure wheel is e.g. caused to move along the curved track by a motor, e.g. in a toothed gear-arrangement or using a linear actuator, this motor can be effectively dimensioned, as the force required to cause the pressure wheel to move does not vary significantly, such as does not vary at all, from one end of the curved track to the other. This means that a less powerful motor may be used. By

'substantially constant ratio' between lifting height and the distance which the pressure wheel has moved along the curved track may be understood that a minimum ratio between lifting height and length of stroke (at a point within the lifting range) is within 80-100 %, such as within 90-100 %, such as within 95-100 %, such as within 98-100 %, with respect to a maximum ratio between lifting height and length of stroke (at a point within the lifting range).

In an embodiment of the invention, a power source, such as a linear actuator, is rotatably connected at its first end to the lower frame in a fulcrum and rotatably connected at its second end in a suspension point to the first end of the pressure rod nearby or coinciding with the suspension point of the pressure wheel on the pressure rod, and wherein the motion of the pressure wheel in the first direction along the curved track is caused by extending the length of the power source, and the track is designed in such a way that there is a substantially constant, such as constant, ratio between the lifting height, i.e. the change in distance between the lower frame and the upper frame, and the length of stroke, i.e. the change in the length, of the power source, throughout the full lifting range of the lifting device. By 'substantially constant ratio' between lifting height and length of stroke may be understood that a minimum ratio between lifting height and length of stroke (at a point within the lifting range) is within 80-100 %, such as within 90-100 %, such as within 95-100 %, such as within 98-100 %, with respect to a maximum ratio between lifting height and length of stroke (at a point within the lifting range). With a construction like this, it is possible to use close to 100 % of the capacity of the power source along the full lifting height, which means that a less powerful, and therefore smaller and/or less expensive power source can be used than in scissor lifts known in the art. Furthermore, the construction is relatively simple and very rigid, which ensures a reliable and safe function of the lifting device. In an embodiment of the invention, the angle, through which the power source rotates for a full lift from a totally collapsed to a totally unfolded configuration of the lifting device is less than 20°, preferably less than 15° and most preferred less than 10°. The fact that the power source does not move forth and back as a pendulum during operation of the lifting device, which is the case for many known solutions within the art, means that the power of the power source can be utilized maximally.

Minimising the rotation of the power source also minimises the space requirements and, thereby enables the producer of the lifting device to obtain a very low installation height of the lifting device, which is often required if the lifting device is to be used, for instance, as a built-in seat hoist in a wheel chair.

In an embodiment of the invention, both the track for pressure wheel and the pressure wheel are toothed and arranged to engage with one another so that, when a power source, such as for instance a step motor, causes the toothed pressure wheel to rotate, the toothed pressure wheel moves relatively to the toothed track and the scissor lift to move. With this configuration, a very precise configuration of the scissor lift can be obtained through controlling the rotational position of the pressure wheel carefully.

In an embodiment of the invention, the lifting device is comprising a power source, such as a linear actuator or a step motor, arranged to apply a force to the pressure wheel so as to move the pressure wheel in the first direction, wherein a force applied by the power source is applied directly at the pressure wheel. An advantage of this may be that no force transmitting elements between power source and pressure wheel cause loss of energy. Another possible advantage may be that the lifting device may be kept compact. By "a force applied by the power source is applied directly at the pressure wheel" may be understood that the power source acts directly on the pressure wheel or an axle of the pressure wheel, such as without intervening hinges or toothed wheels or other force transmitting elements. In an example, the power source is a linear actuator wherein the axis of the linear actuator substantially intersects (such as intersects within 20 mm, such as within 10 mm, such as within 5 mm, such as intersects) the axis of the pressure wheel and wherein the moving part of the linear actuator is connected to the axis of the pressure wheel. In another example, the power source (for example a step motor) generates rotary motion around a motor axis wherein said motor axis coincides (such as coincides within 20 mm, such as within 10 mm, such as within 5 mm, such as coincides) with the axis of the pressure wheel and wherein the power source motor axis is connected to the axis of the pressure wheel,

In an embodiment of the invention, the contact surface of the pressure wheel (such as the contact surface facing the curved track) and/or the contact surface the curved track (such as the contact surface facing the pressure wheel) comprises an aluminium based alloy, such as the 7075 aluminium alloy, such as an alloy having a composition which includes 5.6-6.1 % zinc, 2.1-2.5 % magnesium, 1.2-1.6 % copper, and less than a half percent of silicon, iron, manganese, titanium, chromium, and other metals. The aluminium based alloy may be EN AW 7075.

In an embodiment of the invention, the sliding engagement between the first lever arm and the upper frame and between the second lever arm and the lower frame is obtained by means of rollers or sliders suspended in suspension points at the second ends of the respective lever arms. In an embodiment of the invention, the lifting device is able to lift a load of at least 180 kg, preferably at least 250 kg, over a range of at least 250 mm, preferably at least 300 mm, and wherein the height of the lifting device in a fully collapsed

configuration is less than 125 mm, preferably less than 90 mm.

In a further embodiment of the invention, the height of the lifting device in a fully collapsed configuration is less than 125 mm, preferably less than 90 mm. This may be advantageous as the lifting device may then be more easily integrated in a wheel chair for adjustment of the height of the seat thereof, such as without such integration resulting in the dimensions of the wheel chair being significantly larger and/or without requiring substantial modifications of the design of the wheel chair.

By 'height of the lifting device' may be understood the size of the lifting device in a direction of movement of the upper frame when the upper frame moves away from the lower frame.

A lifting device with such characteristics is very suitable for being used in applications with demand for a high lifting capacity like, for instance, as a built-in seat hoist in a wheel chair.

In an aspect of the invention, such as a first aspect, it relates to a wheel chair with a built-in seat hoist comprising a lifting device as described above.

In an aspect of the invention, such as a second aspect, it relates to a method for designing a track for a pressure wheel of a lifting device, such as a lifting device of a wheel chair, as described above, which method comprises the steps of:

A. dividing the maximum lifting height of the lifting device into a plurality of height steps

B. for each of these height steps: determining the position of the first lever arm and, thereby, the position of the suspension point of the pressure rod on the lifting arm of the first lever arm at this height step

determining, for the determined position of the suspension point and taking into consideration the geometry of the lifting device, one or more possible positions of the pressure wheel near the lower frame choosing, according to certain predefined criteria, the preferred position of the pressure wheel for this height step, thereby defining a point on the path followed by the pressure wheel through the track

C. fitting a curve through the defined points, thus determining the path to be followed by the pressure wheel through the track

D. designing the track to cause the pressure wheel to follow this curve

In an embodiment of the invention, step B comprises: determining the fraction of the maximum lifting height constituted by the given height step

- determining the length of a power source corresponding to a length of stroke corresponding to a similar fraction of the full stroke length - taking into account the determined length of the power source when

determining the one or more possible positions of the pressure wheel near the lower frame.

In an embodiment of the invention, the maximum lifting height of the lifting device is divided into between 3 and 20 height steps, preferably into between 5 and 10 height steps. In an embodiment of the invention, the distance between any neighbouring height steps is the same. In an embodiment of the invention, step B is performed at least partly using geometrical drawings corresponding to each of the different height steps. The method as described in different embodiments here above is a reliable and safe way of reaching the optimal result independently of the geometrical construction and structure of the lifting device.

In an embodiment of the invention, the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of the space occupied by the lifting device when fully collapsed.

In this way, the shape of the lifting track may be used to optimise the compactness of the lifting device on top of its primary purpose relating to ensuring a constant ratio between the lifting height and the stroke length as described above.

In an embodiment of the invention, the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of distance from the centre of the lifting wheel to a centre line along the longitudinal axis of the first lever arm.

A simpler shape and, thereby, an easier manufacturing of the track is obtained, if, for the different height steps, the positions of the pressure wheel closest to the centre line of the lower frame is chosen, because this, all things being equal, results in as linear a track as possible.

In an aspect of the invention, such as a third aspect, it relates to use of a wheel chair with a built-in seat hoist comprising a lifting device according to the first aspect for elevating a seat of the wheel chair by having the upper frame being forced away from the lower frame, such as for elevating a person, such as a person having a mass of at least 50 kg, such as at least 75 kg, such as at least 100 kg, such as at least 150 kg, such as at least 180 kg, such as at least 250 kg, sitting in the seat.

In an aspect of the invention, it relates to a method for elevating a seat of a wheel chair (such as for elevating a person, such as a person having a mass of at least 50 kg, such as at least 75 kg, such as at least 100 kg, such as at least 150 kg, such as at least 180 kg, such as at least 250 kg, sitting in the seat), said method comprising providing a wheel chair with a built-in seat hoist comprising a lifting device according to the first aspect and elevating the seat (such as the seat and the person) of the wheel chair by having the upper frame being forced away from the lower frame.

The drawing

In the following, a few exemplary embodiments of the inventions are described in more detail with reference to the drawing, of which

Fig. 1 is a principle sketch of a scissor lift according to an embodiment of the invention in a fully collapsed configuration, Fig. 2 is a principle sketch of the same scissor lift in a partly unfolded

configuration,

Fig. 3 is a principle sketch of the same scissor lift in a fully unfolded

configuration,

Fig. 4 is a schematic illustration of a method used for constructing a track for the pressure wheel of a scissor lift according to an embodiment of the invention, and Fig. 5 is a principle sketch of a scissor lift according to another embodiment of the invention in a partly unfolded configuration. Detailed description of the invention

Figs. 1-3 are principle sketches of a scissor lift according to an embodiment of the invention in a fully collapsed, in a partly unfolded and in a fully unfolded

configuration, respectively.

A first lever arm 3 and a second lever arm 4, which are rotatably connected to each other in a pivotal point E, forms a scissor configuration. In practice, there is such a scissor configuration in both sides of the lifting device. For the sake of explanation, however, the following section explains the function of one such scissor

configuration only.

When the scissor configuration, which constitutes a primary part of the lifting mechanism, is opened, two substantially parallel frames, namely a lower frame 1 and an upper frame 2, are forced away from each other. If the lower frame 1 is placed on a more or less horizontal surface, this means that the upper frame 2 (and whatever might be placed thereupon) is lifted when the scissor configuration is opened.

The first lever arm 3 is rotatably connected at its first end to the lower frame 1 in a fulcrum A and in sliding engagement with the upper frame 2 at its second end by means of a roller 8, which is suspended in a suspension point I on the first lever arm 3. Similarly, the second lever arm 4 is rotatably connected at its first end to the upper frame 2 in a fulcrum B and in sliding engagement with the lower frame 1 at its second end by means of a roller 9, which is suspended in a suspension point H on the second lever arm 4.

A power source 6, such as a linear actuator, is suspended between a fulcrum G on the lower frame 1 and a suspension point F on a pressure rod 5 near a first end thereof. The other end of the pressure rod 5 is suspended from a suspension point C on a lifting arm 3.1 fixedly connected to the first lever arm 3. A pressure wheel 7 is suspended from a suspension point D on the pressure arm 5. In the illustrated embodiment, this suspension point D coincides with the suspension point F of the power source 6 on the pressure arm 5. A curved track 1.1, in which the pressure wheel 7 is arranged to roll, is arranged within or in fixed connection to the lower frame 1.

When the length of the power source 6 is extended, the pressure wheel 7 moves along the track 1.1 changing the position and orientation of the pressure arm 5 in such a way that its suspension point C on the lifting arm 3.1 is pressed in a direction away from the lower frame 1, which forces the first lever arm 3 to rotate upwards around its fulcrum A.

The connection in the pivotal point E between the first lever arm 3 and the second lever arm 4 forces the second lever arm 4 to follow the first lever arm 3 upwards by rotating around its fulcrum B. The opening of the scissor configuration by this rotation of the first lever arm 3 and the second lever arm 4 in relation to the lower frame 1 and the upper frame 2 causes the upper frame 2 to be lifted away from the lower frame 1, while the rollers 8 and 9 move along the upper frame 2 and the lower frame 1, respectively, towards the fulcrum B of the first lever arm 3 and the fulcrum A of the second lever arm 4, respectively.

As seen in the figures, the track 1.1 curves relatively much in the beginning of the lift, i.e. when the pressure wheel 7 is in the positions shown in Figs. 1 and 2, whereas it becomes more linear near the maximum lifting height as illustrated by the position of the pressure wheel 7 in Fig. 3. This means that, if the track 1.1 is properly designed, the rotation of the first lever arm 3 is adjusted to the length of the power source 6 in such a way that there is a substantially constant ratio between the lifting height, i.e. the change in distance between the lower frame 1 and the upper frame 2, and the length of stroke, i.e. the change in the length, of the power source 6, throughout the full lifting range of the lifting device. When the length of the power source 6 is shortened, the motion of the different parts of the lifting device goes in the opposite direction towards a collapsed configuration of the lifting device. As can be seen from Fig. 1, the different parts of the lifting device are packed very tight, when the lifting device is fully collapsed. To a certain degree, the design of the track 1.1 can contribute to obtaining as compact a packing of the parts in the collapsed configuration as possible, thereby minimising the necessary installation height corresponding to the minimum height of the lifting device. When

appropriately designed, it has been proven possible to obtain a minimum height of less than 90 mm for a lifting device capable of lifting a load of at least 250 kg over a range of at least 300 mm.

A number of choices must be made when a lifting device according to the present invention is to be designed, even though some of the variables, such as the maximum height in a fully collapsed configuration, the desired maximum lifting height, the maximum weight to be lifted, etc. are often given. For instance, it must be decided, through which angle the power source 6 is allowed to rotate for a full lift from a totally collapsed to a totally unfolded configuration of the lifting device. In preferred embodiments, this angle is less than 10°. Especially, the desired minimum height of the lifting device must be taken into consideration, when determining the actual design and positioning of the individual moving parts of the lifting device.

When the primary design choices have been taken, the optimal shape of the track 1.1 can, for instance, be determined through a step-by-step method, in which a number of distinct points on the desired path of the pressure wheel 7 are found, after which the shape is determined by fitting a suitable curve through these points. Fig. 4 illustrates schematically a construction drawing used for such a step-by-step approach to designing a track 1.1. As mentioned above, the goal is to obtain a substantially constant ratio between the lifting height and the length of stroke throughout the full lifting range of the lifting device. In the illustrated example, the lifting range may for instance be 300 mm and the maximum stroke length of the power source 6 may be 120 mm, which means that the ratio between the lifting height and the stroke length should be close to 2.5 throughout the full lifting range.

In this case, the lifting range is divided into six steps of 50 mm each corresponding to steps of the stroke length of 20 mm each. Now, for each of the lifting heights 0 mm, 50 mm, 100 mm, ... , 300 mm, a schematic drawing can be made with the appropriate stroke length of the power source 6 for identifying the ideal position of the pressure wheel 7 relative to the suspension point C of the pressure arm 5 on the lifting arm 3.1. Fig. 4 illustrates schematically the position of the first lever arm 3-0, 3-1, ... , 3-6 for each of the seven lifting heights as defined above as it rotates about its fulcrum A. For the initial position (lifting height 0 mm), the figure also illustrates the position of the second lever arm 4-0 and the pivotal point E-0 between the first 3-0 and the second 4-0 lever arm in this position.

For this initial position, the position of the suspension point F-0 for the power source 6-0 on the pressure arm 5-0 and thereby the position of the suspension point D-0 of the pressure wheel 7-0 is determined by the chosen geometry of the scissor lift. In a similar way, the positions of the suspension points F-l, F-2, ... F-6 for the power source 6 on the pressure arm and the corresponding suspension points D-l, D-2, D-6 of the pressure wheel 7 are identified for each of the lifting heights 50 mm, 100 mm, ... , 300 mm by repeating the above procedure while increasing the length of the power source by 20 mm for each new iteration. During this repeated procedure with increasing lifting heights, the position and orientation of the pressure arm 5 changes, and the power source 6 rotates first slightly anticlockwise and then slightly clockwise about its fulcrum G.

The seven suspension points D-0, D-l, ... , D-7 defines a curve, from which the track 1.1 can be designed, when the dimensions of the pressure wheel 7 are known.

When choosing the geometry of the scissor lift, thereby defining the initial positions 3-0, 4-0, C-0, D-0, and F-0 in Fig. 4, several parameters may be taken into consideration. These parameters include minimisation of the minimum height of the lifting device, keeping the track 1.1 as linear as possible for manufacturing purposes, etc.

Fig. 5 shows another embodiment of a scissor lift according to the invention in a partly unfolded configuration similar to the one illustrated in Fig. 2. The main differences between the two embodiments are that, in the embodiment illustrated in Fig. 5, both the track for pressure wheel 1.2 and the pressure wheel 7.1 have been toothed so that they engage with one another, and that the length- varying power source has been replaced by a power source, such as for instance a step motor, which is arranged to rotate the toothed pressure wheel 7.1. Thereby it causes the toothed pressure wheel 7.1 to move relatively to the toothed track for pressure wheel 1.2 and the scissor lift to move towards a collapsed or unfolded configuration, depending on the direction of the rotation of the toothed pressure wheel 7.1.

List of reference numbers

1. Lower frame

1.1 Track for pressure wheel

1.2 Toothed track for pressure wheel

2. Upper frame

3. First lever arm

3.1 Lifting arm of first lever arm

4. Second lever arm

5. Pressure rod

6. Power source

7. Pressure wheel

7.1 Toothed pressure wheel

8. Roller or slider on first lever arm

9. Roller or slider on second lever arm

A. Fulcrum for first lever arm on lower frame

B. Fulcrum for second lever arm on upper frame

C. Suspension point for pressure rod on lifting arm of first lever arm

D. Suspension point for pressure wheel on pressure rod

E. Pivotal point between first and second lever arm

F. Suspension point for power source on pressure rod

G. Fulcrum for power source on lower frame

H. Suspension point for roller or slider on second lever arm

I. Suspension point for roller or slider on first lever arm

In alternative embodiments E1-E14, there is presented:

El . A lifting device configured as a scissor lift comprising a lower frame (1) and an upper frame (2) substantially parallel to the lower frame, wherein the lower frame and the upper frame are connected by at least one pair of lever arms (3, 4) rotatably connected to each other in a pivotal point (E) in a configuration similar to the one of the two arms in a pair of scissors, wherein the first lever arm (3) is rotatably connected at its first end to the lower frame in a fulcrum (A) and in sliding engagement with the upper frame at its second end, and the second lever arm (4) is rotatably connected at its first end to the upper frame in a fulcrum (B) and in sliding engagement with the lower frame at its second end in such a way that, when the scissor configuration formed by the two lever arms is opened, the lower frame and the upper frame are forced away from each other, wherein a pressure wheel (7; 7.1) is suspended in a suspension point (D) on a first end of a pressure rod (5), the other end of which pressure rod is rotatably connected in a suspension point (C) to a lifting arm (3.1) fixed to the first lever arm, and wherein a curved track (1.1; 1.2), in which the pressure wheel is arranged to roll, is arranged within or fixedly connected to the lower frame in such a way that, when the pressure wheel moves in a first direction along this track, the track controls the path of the pressure wheel and, thereby, the position and orientation of the pressure rod, causing the suspension point (C) of the pressure rod on the lifting arm to move in a direction away from the lower frame, whereby the first lever arm and, in turn, also the second lever arm and the upper frame are forced away from the lower frame.

E2. The lifting device according to embodiment El, wherein a power source (6), such as a linear actuator, is rotatably connected at its first end to the lower frame in a fulcrum (G) and rotatably connected at its second end in a suspension point (F) to the first end of the pressure rod (5) nearby or coinciding with the suspension point (D) of the pressure wheel (7) on the pressure rod, and wherein the motion of the pressure wheel in the first direction along the curved track (1.1) is caused by extending the length of the power source, and the track is designed in such a way that there is a substantially constant ratio between the lifting height, i.e. the change in distance between the lower frame and the upper frame, and the length of stroke, i.e. the change in the length, of the power source, throughout the full lifting range of the lifting device.

E3. The lifting device according to embodiment El or E2, wherein the angle, through which the power source rotates for a full lift from a totally collapsed to a totally unfolded configuration of the lifting device is less than 20°, preferably less than 15° and most preferred less than 10°.

E4. A lifting device according to embodiment El, wherein both the track for pressure wheel (1.2) and the pressure wheel (7.1) are toothed and arranged to engage with one another so that, when a power source, such as for instance a step motor, causes the toothed pressure wheel to rotate, the toothed pressure wheel moves relatively to the toothed track and the scissor lift to move. E5. The lifting device according to any of the preceding embodiments, wherein the sliding engagement between the first lever arm and the upper frame and between the second lever arm and the lower frame is obtained by means of rollers or sliders (8, 9) suspended in suspension points (I, H) at the second ends of the respective lever arms. E6. The lifting device according to any of the preceding embodiments, which is able to lift a load of at least 180 kg, preferably at least 250 kg, over a range of at least 250 mm, preferably at least 300 mm, and wherein the height of the lifting device in a fully collapsed configuration is less than 125 mm, preferably less than 90 mm. E7. A wheel chair with a built-in seat hoist comprising a lifting device according to any of the preceding embodiments.

E8. A method for designing a track (1.1; 1.2) for a pressure wheel (7) of a lifting device according to any of embodiments E1-E6, which method comprises the steps of: A. dividing the maximum lifting height of the lifting device into a plurality of height steps

B. for each of these height steps:

- determining the position of the first lever arm (3) and, thereby, the

position of the suspension point (C) of the pressure rod (5) on the lifting arm (3.1) of the first lever arm at this height step

determining, for the determined position of the suspension point (C) and taking into consideration the geometry of the lifting device, one or more possible positions of the pressure wheel (7; 7.1) near the lower frame (1) choosing, according to certain predefined criteria, the preferred position of the pressure wheel for this height step, thereby defining a point on the path followed by the pressure wheel through the track C. fitting a curve through the defined points, thus determining the path to be followed by the pressure wheel through the track

D. designing the track to course the pressure wheel to follow this curve E9. The method according to embodiment E8, wherein step B comprises: determining the fraction of the maximum lifting height constituted by the given height step

determining the length of a power source (6) corresponding to a length of stroke corresponding to a similar fraction of the full stroke length

- taking into account the determined length of the power source when determining the one or more possible positions of the pressure wheel (7) near the lower frame (1). E10. The method according to embodiment E8 or E9, wherein the maximum lifting height of the lifting device is divided into between 3 and 20 height steps, preferably into between 5 and 10 height steps. El l . The method according to any of embodiments E8-E10, wherein the distance between any neighbouring height steps is the same.

E12. The method according to any of embodiments E8-E11, wherein step B is performed at least partly using geometrical drawings corresponding to each of the different height steps.

El 3. The method according to any of embodiments E8-E12, wherein the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of the space occupied by the lifting device when fully collapsed.

E14. The method according to any of embodiments E8-E13, wherein the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of distance from the centre of the pressure wheel to a centre line along the longitudinal axis of the lower frame.

For the above embodiments El -El 4, it may be understood that reference to preceding 'embodiments' may refer to preceding embodiments within embodiments E1-E14.

In alternative embodiments Fl-Fl 1, there is presented: Fl . A lifting device configured as a scissor lift comprising a lower frame (1) and an upper frame (2) substantially parallel to the lower frame, wherein the lower frame and the upper frame are connected by at least one pair of lever arms (3, 4) rotatably connected to each other in a pivotal point (E) in a configuration similar to the one of the two arms in a pair of scissors, wherein the first lever arm (3) is rotatably connected at its first end to the lower frame in a fulcrum (A) and in sliding engagement with the upper frame at its second end, and the second lever arm (4) is rotatably connected at its first end to the upper frame in a fulcrum (B) and in sliding engagement with the lower frame at its second end in such a way that, when the scissor configuration formed by the two lever arms is opened, the lower frame and the upper frame are forced away from each other, wherein a power source (6), such as a linear actuator, is rotatably connected at its first end to the lower frame in a fulcrum (G) and rotatably connected at its second end in a suspension point (F) to a first end of a pressure rod (5), the other end of which pressure rod is rotatably connected in a suspension point (C) to a lifting arm (3.1) fixed to the first lever arm, wherein a pressure wheel (7) is suspended in a suspension point (D) on the pressure rod nearby or coinciding with the suspension point (F) of the power source on the pressure rod, and wherein a curved track (1.1), in which the pressure wheel is arranged to roll, is arranged within or fixedly connected to the lower frame in such a way that, when the length of the power source is extended, this track controls the path of the pressure wheel and, thereby, the position and orientation of the pressure rod, causing the suspension point (C) of the pressure rod on the lifting arm to move in a direction away from the lower frame, whereby the first lever arm and, in turn, also the second lever arm and the upper frame are forced away from the lower frame, said track being designed in such a way that there is a substantially constant ratio between the lifting height, i.e. the change in distance between the lower frame and the upper frame, and the length of stroke, i.e. the change in the length, of the power source, throughout the full lifting range of the lifting device. F2. The lifting device according to embodiment Fl, wherein the sliding engagement between the first lever arm and the upper frame and between the second lever arm and the lower frame is obtained by means of rollers or sliders (8, 9) suspended in suspension points (I, H) at the second ends of the respective lever arms.

F3. The lifting device according to any of the preceding embodiments, wherein the angle, through which the power source rotates for a full lift from a totally collapsed to a totally unfolded configuration of the lifting device is less than 20°, preferably less than 15° and most preferred less than 10°.

F4. The lifting device according to any of the preceding embodiments, which is able to lift a load of at least 180 kg, preferably at least 250 kg, over a range of at least 250 mm, preferably at least 300 mm, and wherein the height of the lifting device in a fully collapsed configuration is less than 125 mm, preferably less than 90 mm.

F5. A wheel chair with a built-in seat hoist comprising a lifting device according to any of the preceding embodiments.

F6. A method for designing a track (1.1) for a pressure wheel (7) of a lifting device according to any of embodiments F1-F4, which method comprises the steps of:

B dividing the maximum lifting height of the lifting device into a plurality of height steps

C for each of these height steps:

determining the position of the first lever arm (3) and, thereby, the position of the suspension point (C) of the pressure rod (5) on the lifting arm (3.1) of the first lever arm at this height step

determining the fraction of the maximum lifting height constituted by this height step determining the length of the power source corresponding to a length of stroke corresponding to a similar fraction of the full stroke length determining, for the determined position of the suspension point (C) and the determined length of the power source and taking into consideration the geometry of the lifting device, one or more possible positions of the pressure wheel (7) near the lower frame (1)

choosing, according to certain predefined criteria, the preferred position of the pressure wheel for this height step, thereby defining a point on the path followed by the pressure wheel through the track

D. fitting a curve through the defined points, thus determining the path to be followed by the pressure wheel through the track

E. designing the track to course the pressure wheel to follow this curve

F7. The method according to embodiment F6, wherein the maximum lifting height of the lifting device is divided into between 3 and 20 height steps, preferably into between 5 and 10 height steps. F8. The method according to embodiments F6 or F7, wherein the distance between any neighbouring height steps is the same.

F9. The method according to any of embodiments F6-F8, wherein step B is performed at least partly using geometrical drawings corresponding to each of the different height steps.

F10. The method according to any of embodiments F6-F9, wherein the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of the space occupied by the lifting device when fully collapsed. Fl 1. The method according to any of embodiments F6-F10, wherein the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of distance from the centre of the pressure wheel to a centre line along the longitudinal axis of the lower frame. For the above embodiments F 1 -F 11 , it may be understood that reference to preceding 'embodiments' may refer to preceding embodiments within embodiments Fl-Fl 1.

Claims

1. A wheel chair with a built-in seat hoist comprising a lifting device, the lifting device being configured as a scissor lift comprising a lower frame (1) and an upper frame (2) substantially parallel to the lower frame, wherein the lower frame and the upper frame are connected by at least one pair of lever arms (3, 4) rotatably connected to each other in a pivotal point (E) in a configuration similar to the one of the two arms in a pair of scissors, wherein the first lever arm (3) is rotatably connected at its first end to the lower frame in a fulcrum (A) and in sliding or rolling engagement with the upper frame at its second end, and the second lever arm (4) is rotatably connected at its first end to the upper frame in a fulcrum (B) and in sliding or rolling engagement with the lower frame at its second end in such a way that, when the scissor configuration formed by the two lever arms is opened, the lower frame and the upper frame are forced away from each other, wherein a pressure wheel (7; 7.1) is suspended in a suspension point (D) on a first end of a pressure rod (5), the other end of which pressure rod is rotatably connected in a suspension point (C) to a lifting arm (3.1) fixed to the first lever arm, and wherein a curved track (1.1; 1.2), in which the pressure wheel is arranged to roll, is arranged within or fixedly connected to the lower frame in such a way that, when the pressure wheel moves in a first direction along this track, the track controls the path of the pressure wheel and, thereby, the position and orientation of the pressure rod, causing the suspension point (C) of the pressure rod on the lifting arm to move in a direction away from the lower frame, whereby the first lever arm and, in turn, also the second lever arm and the upper frame are forced away from the lower frame.

2. The wheel chair according to claim 1, wherein the curved track is designed in such a way that when the pressure wheel moves in a first direction along the curved track, there is a substantially constant ratio between the lifting height, i.e. the change in distance between the lower frame and the upper frame, and the distance which the pressure wheel has moved along the curved track.

3. The wheel chair according to claim 1, wherein a power source (6), such as a linear actuator, is rotatably connected at its first end to the lower frame in a fulcrum (G) and rotatably connected at its second end in a suspension point (F) to the first end of the pressure rod (5) nearby or coinciding with the suspension point (D) of the pressure wheel (7) on the pressure rod, and wherein the motion of the pressure wheel in the first direction along the curved track (1.1) is caused by extending the length of the power source, and the track is designed in such a way that there is a substantially constant ratio between the lifting height, i.e. the change in distance between the lower frame and the upper frame, and the length of stroke, i.e. the change in the length, of the power source, throughout the full lifting range of the lifting device.

4. The wheel chair according to claim 1 or 2 or 3, wherein the angle, through which the power source rotates for a full lift from a totally collapsed to a totally unfolded configuration of the lifting device is less than 20°, preferably less than 15° and most preferred less than 10°.

5. The wheel chair according to any of claims 1 or 2, wherein both the track for pressure wheel (1.2) and the pressure wheel (7.1) are toothed and arranged to engage with one another so that, when a power source, such as for instance a step motor, causes the toothed pressure wheel to rotate, the toothed pressure wheel moves relatively to the toothed track and the scissor lift to move.

6. The wheel chair according to any of the preceding claims, wherein the lifting device is comprising a power source (6) arranged to apply a force to the pressure wheel so as to move the pressure wheel in the first direction, wherein a force applied by the power source is applied directly at the pressure wheel.

7. The wheel chair according to any one of the preceding claims, wherein the contact surfaces of the pressure wheel and the curved track comprises an aluminium based alloy, such as EN AW 7075.

8. The wheel chair according to any of the preceding claims, wherein the sliding engagement between the first lever arm and the upper frame and between the second lever arm and the lower frame is obtained by means of rollers or sliders (8, 9) suspended in suspension points (I, H) at the second ends of the respective lever arms.

9. The wheel chair according to any of the preceding claims, wherein the height of the lifting device in a fully collapsed configuration is less than 125 mm, preferably less than 90 mm.

10. The wheel chair according to any of the preceding claims, wherein the lifting device is able to lift a load of at least 180 kg, preferably at least 250 kg, over a range of at least 250 mm, preferably at least 300 mm, and wherein the height of the lifting device in a fully collapsed configuration is less than 125 mm, preferably less than 90 mm.

11. A method for designing a track (1.1; 1.2) for a pressure wheel (7) of a lifting device of a wheel chair according to any of claims 1-10, which method comprises the steps of:

B. for each of these height steps: determining the position of the first lever arm (3) and, thereby, the position of the suspension point (C) of the pressure rod (5) on the lifting arm (3.1) of the first lever arm at this height step

determining, for the determined position of the suspension point (C) and taking into consideration the geometry of the lifting device, one or more possible positions of the pressure wheel (7; 7.1) near the lower frame (1) choosing, according to certain predefined criteria, the preferred position of the pressure wheel for this height step, thereby defining a point on the path followed by the pressure wheel through the track

D. designing the track to cause the pressure wheel to follow this curve

12. The method according to claim 11, wherein step B comprises: determining the fraction of the maximum lifting height constituted by the given height step

- determining the length of a power source (6) corresponding to a length of stroke corresponding to a similar fraction of the full stroke length - taking into account the determined length of the power source when determining the one or more possible positions of the pressure wheel (7) near the lower frame (1).

13. The method according to claim 11 or 12, wherein the maximum lifting height of the lifting device is divided into between 3 and 20 height steps, preferably into between 5 and 10 height steps.

14. The method according to an of claims 11-13, wherein the distance between any neighbouring height steps is the same.

15. The method according to any of claims 11-14, wherein step B is performed at least partly using geometrical drawings corresponding to each of the different height steps.

16. The method according to any of claims 11-15, wherein the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of the space occupied by the lifting device when fully collapsed.

17. The method according to any of claims 11-16, wherein the predefined criteria for choosing the preferred position of the pressure wheel for a given height step includes minimisation of distance from the centre of the pressure wheel to a centre line along the longitudinal axis of the lower frame.

18. Use of a wheel chair with a built-in seat hoist comprising a lifting device according to any one claims 1-10 for elevating a seat of the wheel chair by having the upper frame being forced away from the lower frame, such as for elevating a person sitting in the seat.