WO2002098207A1

WO2002098207A1 - Equipment for a glasshouse, harvesting vehicle for use with such an equipment, and stabilizing element for such a vehicle

Info

Publication number: WO2002098207A1
Application number: PCT/NL2002/000376
Authority: WO
Inventors: Frederik Steenks
Original assignee: Freek Steenks Service V.O.F.
Priority date: 2001-06-07
Filing date: 2002-06-07
Publication date: 2002-12-12
Also published as: NL1019820C2

Abstract

The invention relates to an apparatus for performing operations in a glasshouse such as harvesting of cultivated crops, comprising: a transport path, guide means and a harvesting vehicle (20), which harvesting vehicle (20) is provided with: a frame (22) and at least four support wheels supporting the frame, which support wheels are adApted to co-act with the transport path, and at least one stabilizing element (21) connected to the frame for stabilizing the vehicle, which stabilizing element (21) is adapted to co-act with the guide means. The invention also relates to a harvesting vehicle for use in such an apparatus. The invention further relates to a stabilizing element for use in such a harvesting vehicle.

Description

EQUIPMENT FOR A GLASSHOUSE, HARVESTING VEHICLE FOR USE WITH SUCH AN EQUIPMENT, AND STABILIZING ELEMENT FOR SUCH A VEHICLE

5 The invention relates to an apparatus for performing operations in a glasshouse such as harvesting of cultivated crops, comprising: a transport path, guide means and a harvesting vehicle, which harvesting vehicle is provided with: a frame and at least four support wheels supporting the frame, which support wheels are adapted to co-act with the transport path, and at least one stabilizing element connected to the frame for 10 stabilizing the vehicle, which stabilizing element is adapted to co-act with the guide means. The invention also relates to a harvesting vehicle for use in such an apparatus. The invention further relates to a stabilizing element for use in such a harvesting vehicle.

15 In glass horticulture plants, fruit and vegetables are cultivated in glasshouses, also referred to as greenhouses. The glasshouses are generally equipped with a heating pipe system for conditioning the temperature present in the glasshouse. Some of the heating pipes forming part of the heating pipe system are usually positioned close to the floor of the glasshouse. The usual diameters of the heating pipes amount to 45 or 51 millimetres.

20 The heating pipes positioned close to the ground are usually positioned in one or more pairs of two heating pipes running parallel to each other. The mutual distance between two heating pipes forming part of a pair generally amounts to 42 or 55 centimetres. One or more crops can be cultivated on at least one side, preferably on two sides, of each pair of heating pipes. A pair of heating pipes is often multi-functional as it can also be

25 used as guide over which a harvesting vehicle, also known as pipe rail trolley, is displaced for harvesting cultivated crops. Such multi-functional heating pipes are usually referred to as pipe rails in the technical jargon. The height of the harvesting vehicle is generally adjustable, whereby crops can be harvested (manually) at different heights. A great drawback of the known harvesting vehicles is that the working height

30 of the harvesting vehicle is only adjustable up to 3 metres (above the pipes), while the cultivated crops sometimes reach heights of more than 3 metres. The assumption is that the harvesting vehicle is (still) sufficiently stable at a working height of a maximum of 3 metres, and thus safe for a user. At greater heights the stability of the harvesting vehicle declines sharply, whereby users, with a view to required safety standards, may not reach such heights because of the great hazard of the harvesting vehicle tilting at such working heights. The considerable height/width ratio of the harvesting vehicle is in significant part the cause of the limited stability of the harvesting vehicle at working heights above 3 metres. It should be apparent that the harvesting vehicle can be used not only to harvest crops but can also be employed in the tending of crops and in other activities such as maintenance of the glasshouse, fastening of tensioning wires and so on.

The above stated drawback is partially resolved by a harvesting system described in the American patent US 5,438,794 for crops in a glasshouse in which pipe rails are arranged. Cars provided with support wheels are displaceable over the pipe rails, wherein the support wheels engage on the pipe rails. In an embodiment variant additional stabilizing wheels are positioned on a side of the pipe rails remote from the support wheels in order to stabilize the car on the pipe rails. A significant drawback of the cars described in the American patent publication is that such cars provided with additional stabilizing wheels can only be used on the shown C-shaped pipe rails. On other types of pipe rail, such as for instance pipe rails as described in the Netherlands patent NL 1016095, wherein support on the fixed components takes place using support elements forming the shortest connection between the pipe rails and the fixed components, such cars are not usable since the support elements obstruct the passage of the stabilizing wheels during transport of the car over the pipe rails.

The present invention has for its object to provide an improved apparatus for performing operations in a glasshouse, such as the harvesting of cultivated crops, with which it is also possible to operate safely at working heights above 3 metres.

The invention provides for this purpose an apparatus of the type stated in the preamble, with the feature that the relative orientation of at least a part of the stabilizing element and the frame can be changed. Since the relative orientation of at least a part of the stabilizing element can be changed relative to the frame, very great freedom is obtained in using the harvesting vehicle. The harvesting vehicle according to the invention can in fact be applied on a very wide range of guide means, irrespective of the positioning and geometry of one or more support elements for supporting the guide means on the fixed components. Changing the relative orientation can be understood to mean: displacing, in particular pivoting, or rotating the stabilizing element relative to the frame. Changing of the said orientation will generally occur particularly during engagement of the stabilizing element on the support element of the guide means, whereby continuous stabilized transport of the harvesting vehicle can take place on generally any type of guide means. As stated, the presence of the stabilizing element contributes in significant part toward the stability of the harvesting vehicle during standstill as well as during transport. If there is a danger of an unstable situation of the harvesting vehicle occurring, the stabilizing element engages on the guide means such that further inclination of the harvesting vehicle relative to the horizontal is countered. Inclination of the harvesting vehicle relative to the horizontal is thus bounded by the stabilizing element. The bounding is such that no unsafe situations can occur for a user of the harvesting vehicle. Tilting of the harvesting vehicle can also be countered and/or prevented. The working height at which it is still possible for the user to work safely is considerably higher than 3 metres due to the controlled stabilization, whereby crops can also be harvested which grow to a height considerably higher than 3 metres.

Maintenance on the roof of a glasshouse thus also becomes possible using the apparatus according to the invention. During normal use and in an ideal situation there is preferably a (limited) free space present between the stabilizing element and the guide means to counter friction and energy loss.

During normal use the support wheels must preferably make contact with the transport path. Rails and the like can be applied as transport path. The transport path is preferably formed by pipe rails, whereby heating pipes placed close to the floor of a glasshouse have two functions: conditioning the temperature prevailing in the glasshouse and forming a guide over wliich the harvesting vehicle can be transported. As already noted above, the harvesting vehicle can also be utilized for maintenance activities and the like on crops, the glasshouse or the equipment in the glasshouse. The guide means are preferably integrated with the rails so that the rails form the transport path as well as the guide means. Other variants can however also be envisaged wherein there is provided a separate, for instance concrete transport path and/or separate guide means in the form of for instance a standing edge arranged specifically for this purpose.

The guide means are preferably formed by the transport path. In such a preferred embodiment the stabilizing element is adapted to engage on the transport path on which the support wheels also engage. Since use can be made of an already existing infrastructure of pipe rails in a glasshouse, no additional modifications need be made, whereby cost and time can be saved. In specific situations it may nevertheless be desirable to use a separate second guide, for instance in the form of a rail.

The stabilizing element is preferably adapted to engage on a side of the guide means substantially remote from the frame. Such a positioning of the stabilizing element provides a certain measure of locking of the harvesting vehicle relative to the transport path. Such a positioning is also very advantageous during stabilizing of the harvesting vehicle, as stabilizing can take place simply but effectively in this manner. The most ideal engaging position for the stabilizing element on the guide means lies in line with the direction in which the support wheels tend to become detached from the transport path in an unstable situation of the harvesting vehicle.

In another preferred embodiment at least a part of the stabilizing element is adapted for substantially form-fitting co-action with the guide means. Such a design of the stabilizing element can result in a high degree of stabilization of the harvesting vehicle as parts of the stabilizing element can engage at different positions on the guide means. The total load on the stabilizing element engaging on the guide means can moreover be distributed over a number of parts of the stabilizing element, whereby the concentrated load can be kept relatively low.

The stabilizing element preferably engages under bias on the guide means. Such an 'active' stabilizing gives the harvesting vehicle a high measure of stability. If the harvesting vehicle is about to incline more than is permissible as maximum, or even threatens to tilt, the stabilizing element engages on the guide means. The stabilizing element further exerts forced pressure on the guide means in order to correct the unstable disorientation of the harvesting vehicle relative to the transport path such that a stable orientation of the harvesting vehicle relative to the transport path is (again) brought about.

The invention also provides a harvesting vehicle for use in such an apparatus, wherein the stabilizing element is adapted, as already stated, to stabilize the harvesting vehicle in controlled manner, so that working heights of considerably more than 3 metres can also be reached in a safe manner.

The support wheels are preferably provided with a flanged edge projecting from the supporting surface. Support wheels with a flange have the advantage that they may be suitable for transporting the harvesting vehicle over different types of transport path, such as rails, pipe rails and a made-up road. The harvested crops do not therefore have to be transferred immediately outside the glasshouse where generally no (pipe) rails are placed, to a(n) (other) transport vehicle, but the harvesting vehicle can itself be transported over a made-up road.

In another preferred embodiment the harvesting vehicle is provided with at least two stabilizing elements. The stabilizing elements are preferably positioned such that stabilizing of the harvesting vehicle can take place in at least two preferably opposing directions. In order to realize such a high measure of stability of the harvesting vehicle, the stabilizing elements can for instance be positioned on either side of the guide means. The distance between the stabilizing elements is preferably continuously adjustable. Since the dimensions and geometry of the guide means can vary, it may be advantageous to allow the distance between the stabilizing elements to be continuously adjustable. The harvesting vehicle hereby acquires a certain adaptability in that the same harvesting vehicle could be applied with different types of guide means.

The distance between two support wheels positioned on opposite sides of the frame is preferably continuously adjustable. A transport path, preferably pipe rails, of different dimensions is often used in a glasshouse, wherein the distance between the pipe rails can also vary. The most usual mutual distances between two pipe rails are 42 centimetres and 55 centimetres. According to the previous preferred embodiment, an adaptability can be advantageous in enabling use of the harvesting vehicle on pipe rails with differing mutual distances.

In a preferred embodiment the distance between a part of the frame and the ground bearing the harvesting vehicle is adjustable. The person using the harvesting vehicle can therefore reach any desired working height within a determined range. Characteristic of the invention is that working heights higher than 3 metres can be reached without unsafe situations occurring here for the user.

In yet another preferred embodiment the stabilizing element is positioned at least close to two sides forming part of the frame and positioned perpendicularly of each other. In order to stabilize the harvesting vehicle with the lowest possible load on the stabilizing element (in respect of wear and the like), it is important to maximize the moment of the stabilizing element relative to a tilt axis of the harvesting vehicle.

The stabilizing element is preferably connected pivotally to the frame. In a preferred embodiment this can be under bias, whereby the stabilizing element, in a situation of overload on the stabilizing element by the guide means, can be displaced in a direction away from the guide means. In another preferred embodiment the stabilizing element as a whole is fully pivotable relative to the frame under determined conditions. This may be desirable during transport on for instance a made-up road, as the stabilizing element cannot cause any steric hindrance in such a swivelled-away orientation. The stabilizing element is preferably (also) displaceable relative to the frame. The relative orientation of the stabilizing element and the frame is thus adjustable, which can be advantageous - as already stated above - during transport of the harvesting vehicle on a made-up road and/or positioning of the harvesting vehicle on the guide means. Damage to the stabilizing element can hence be prevented or at least countered by the presence of the stabilizing element pivotable and/or displaceable relative to the frame. In a special preferred embodiment the frame comprises locking means for fixing a desired position of the stabilizing element relative to the frame.

In a preferred embodiment the stabilizing element is coupled releasably to the frame. An advantage of such a construction is that the stabilizing element can be uncoupled when the harvesting vehicle is placed on and taken off the transport path and/or guide means, whereby the chance of damaging the stabilizing element during performing of such operations can be prevented. Another advantage of the releasable couplings of the stabilizing element to the frame is that the type and geometry of the stabilizing element can be adapted to already present guide means. The harvesting vehicle therefore acquires an adaptability and, through the use of different stabilizing elements, can co- act with different types of guide means. The releasable coupling is preferably formed by coupling means forming part of the stabilizing element, which coupling means co-act with mating coupling means forming part of the frame. The (mating) coupling means applied are already known in the prior art. A screw connection or a bayonet fitting can for instance be envisaged as possible couplings. The invention further relates to a stabilizing element for use in such a harvesting vehicle. When conventional guide means are used, the stabilizing element is preferably provided with a stabilizing wheel. As already described above, in an ideal situation the stabilizing wheel does not quite make contact with the guide means so as prevent and/or counter friction and therefore energy loss. Only in less stable situations does the stabilizing wheel engage on the guide means. In practice however, the stabilizing wheel will generally engage, possibly continuously, on the guide. In the case of deformation of the stabilizing wheel and/or change in the position of the stabilizing wheel relative to the frame, the stabilizing wheel can engage more frequently on the second guide. The advantage of the stabilizing wheel is that the friction drag created during engagement (with increased frequency) is minimized because the stabilizing wheel can co-rotate in the transport direction of the harvesting vehicle. In addition to a stabilizing wheel, other types of stabilizing elements can also be envisaged, such as brackets and beams fixed under the frame.

The stabilizing element is preferably axially rotatable. As already indicated above, the ability of the stabilizing element to rotate generally reduces to a considerable extent the friction drag and the associated wear.

In a preferred embodiment the stabilizing element is provided with a support rod, which support rod is provided at least close to a free end with coupling means adapted for co- action with mating coupling means forming part of the frame, and which support rod is provided on an opposite end with at least one projecting stabilizing member. The above construction is particularly suitable when guide means are used which are held a distance from the ground by a plurality of substantially straight support elements which during normal use are positioned substantially parallel to at least one part of the projecting stabilizing member. When the stabilizing element is coupled to the frame of the harvesting vehicle, the rod is preferably rotatable in fully axial manner. When a harvesting vehicle is displaced along the above mentioned guide means provided with the substantially straight support elements, unilateral stabilizing of the harvesting vehicle will take place, whereby tilting of the harvesting vehicle can be prevented or at least countered. When there is contact between the stabilizing member and one of the support elements, rotation of the support rod will generally take place, whereby displacement of the stabilizing member round the support element will take place. The use of a stabilizing wheel as stabilizing element on the described guide means provided with the substantially straight support elements is usually impractical as the stabilizing wheel will generally collide with the support element when it passes the support element.

In a particular preferred embodiment the support rod is provided on a free end remote from the coupling means with a plurality of stabilizing members projecting relative to the support rod, wherein the stabilizing members mutually enclose substantially the same angle with each other. An advantage of applying a plurality of stabilizing members is a relatively good (continuous) stabilizing during rotation of the stabilizing members. When a stabilizing member rotates away during contact with a support element, another stabilizing member will be positioned on a side of the guide means remote from the substantial part of the frame, thereby ensuring continuous stabilization of the harvesting vehicle. Use of the stabilizing members together with the stabilizing wheel in a single stabilizing element can also be envisaged.

In another particular preferred embodiment the support rod is provided with a stabilizing disc positioned at a distance from the stabilizing member. During normal use of a stabilizing element connected to the frame, the stabilizing member is situated on a side of the guide means remote from the substantial part of the frame and the stabilizing disc on a side of the guide means directed toward the substantial part of the frame, whereby a bilateral stabilization is present. It will be apparent that the stabilizing disc can also be provided with recesses, thereby creating one or more members resembling the stabilizing members. The advantage of using a disc is that a disc can generally withstand a relatively high load.

In yet another particular preferred embodiment the stabilizing element is provided with positioning means for positioning the stabilizing member relative to the guide means. The stabilizing member can thus always be positioned in a desired preferred position in order to allow the rotation of the stabilizing member relative to the support elements to proceed in optimal manner. A possible realization of such a preferred embodiment is mounting of the stabilizing member on the frame under bias, for instance by applying a mechanical spring.

The invention will be further elucidated with reference to the non-limitative embodiments shown in the following figures. Herein: figure 1 shows a side view of a first preferred embodiment of an apparatus according to the invention, figure 2 shows a cross-section through the apparatus of figure 1, figure 3 shows a cross-section of a second preferred embodiment of an apparatus according to the invention, figure 4 is a perspective view of a preferred embodiment of a part of a harvesting vehicle, in particular a stabilizing element, according to the invention, and figure 5 is a perspective view of another preferred embodiment of a part of a harvesting vehicle, in particular a stabilizing element, according to the invention.

Figure 1 shows a side view of a first preferred embodiment of an apparatus 1 according to the invention. Apparatus 1 comprises a pipe rail trolley 2 and two pipe rails 3 positioned parallel to each other and carrying pipe rail trolley 2. Pipe rail trolley 2 is displaceable along pipe rails 3. Pipe rail trolley 2 can be used to harvest crops 4 and/or perform other operations on crops 4 or a glasshouse. Pipe rail trolley 2 comprises a frame 5, four flanged wheels 6 supporting frame 5 and four stabilizing wheels 7. These latter are adapted to engage substantially laterally - and therefore substantially perpendicularly of the transport direction of pipe rail trolley 2 - on pipe rails 3. The stabilizing wheels 7 shown in figure 1 are in fact situated between pipe rails 2. Pipe rails 2 are held a distance from the ground by a plurality of support elements 8. Frame 5 comprises a scissor mechanism 9 and a work platform 10 connected to scissor mechanism 9. Work platform 10 is provided with a control panel 11 for operating pipe rail trolley 2, and a safety bar 12. Should pipe rail trolley 2 make a determined angle of inclination with the horizontal, stabilizing wheels 7 then engage on pipe rails 3 such that further inclination of pipe rail trolley 2 is countered. As a result of such a stabilizing provision the maximum working height which can be reached in safe manner can amount to considerably more than 3 metres. Figure 2 shows a cross-section of apparatus 1 according to figure 1. The stabilizing wheels 7 connected to frame 5 are embodied substantially form-fittingly relative to pipe rails 3. Stabilizing wheels 7 are preferably freely rotatable and positioned such that the distance between stabilizing wheels 7 and the ground is greater than the distance of at least a part of the flanged wheels 6 to the ground. Flanged wheels 6 are formed such that a(n) (inner) part of flanged wheels 6 is adapted to engage on pipe rails 3 and a(n) (outer) part of flanged wheels 6 is adapted to engage on another type of transport path such as a made-up road. The mutual distance between stabilizing wheels 7 and the mutual distance between flanged wheels 6 are preferably continuously adjustable.

Figure 3 shows a cross-section of a second preferred embodiment of an apparatus 13 according to the invention. Apparatus 13 comprises a vehicle 14, which vehicle 14 is provided with a frame 19, flanged wheels 15 connected to frame 19 and a stabilizing element 16 connected to frame 19. Flanged wheels 15 engage on two pipe rails 17. Stabilizing element 16 comprises two members, the mutual distance of which is adjustable. Stabilizing element 16 is adapted to engage on a guide 18. Guide 18 can also form a pipe rail. Stabilizing of vehicle 14 relative to pipe rails 17 takes place through engagement of stabilizing element 16 on guide 18, whereby possible tilting of vehicle 19 can be prevented and/or countered.

Figure 4 is a perspective view of a preferred embodiment of a part of a harvesting vehicle 20, in particular a stabilizing element 21, according to the invention. Stabilizing element 21 is releasably connected by coupling means (not shown) to mating coupling means (not shown) forming part of a frame 22. Stabilizing element 21 comprises an axially rotatable support rod 23, a stabilizing disc 24 connected to the support rod and four stabilizing members 25 positioned on a free end of support rod 23 remote from the coupling means. Stabilizing members 25 enclose a substantially equal (right) angle with each other. In the shown preferred embodiment the harvesting vehicle 20 is positioned on a guide 26 which is provided with a guide rail 27 and a plurality of substantially straight support elements 28 connected to guide rail 27. Support elements 28 form the shortest connection between guide rail 27 and the ground supporting guide rail 27. During contact of a stabilizing member 25 with support element 28 the support rod will begin to rotate, whereby an adjacent stabilizing member 25 will be positioned on a side of guide rail 27 remote from frame 22. The stabilizing member rotating away from the guide 26 is then replaced by an adjacent stabilizing member 25, whereby stabilizing of harvesting vehicle 20 can generally always take place. Stabilizing disc 24 also provides for stabilizing of harvesting vehicle 20, whereby bilateral stabilizing of harvesting vehicle 20 can take place. Stabilizing members 25 are shown here in rod form and project at least substantially perpendicularly relative to support rod 23. It is also conceivable to design stabilizing members 25 in another way, such as for instance as circle segment (see for instance figure 5) or as cone segment, and/or to connect them at an angle to support rod 23. In another embodiment the support rod 23 can also be connected at an angle to a frame forming part of a harvesting vehicle.

Figure 5 shows a perspective view of another preferred embodiment of a part of a harvesting vehicle 29, in particular a stabilizing element 30, according to the invention. Stabilizing element 30 is preferably releasably connected to a frame 31 forming part of harvesting vehicle 29. The stabilizing element is provided with a axially rotatable support rod 32. Support rod 32 is provided with two stabilizing members 33 which are positioned during normal use on a side of guide rail 34 directed toward frame 31. On a free end of support rod 32 remote from frame 31 the support rod 32 is provided with a circle segment-shaped stabilizing disc 35 provided with a recess. Support rod 32 is also provided with positioning means (not shown) which can for instance be formed by a mechanical spring, which positioning means are also coupled during normal operation to frame 31. Owing to the presence of the positioning means the support rod 32 will situate itself in a preferred position relative to frame 31 during an unloaded, non- stabilizing situation. If the recess of stabilizing disc 33 comes into contact with a support element 36 supporting guide rail 34, the support rod will rotate about a determined angle. After passage of support element 36 through the stabilizing element, support rod 32 will be carried by the positioning means back into the original preferred orientation. During the passage of a support element the support rod 32 will thus displace each time through substantially the same angle. Complete, i.e. 360E, rotation of support rod 32 on its own axis will generally not therefore occur. An advantage of the positioning means is that stabilizing disc 35 can generally always make initial contact with support element 36 in optimal manner, whereby a halting displacement of harvesting vehicle 29 or damage to the components shown in figure 5 can be prevented or at least countered.

Claims

1. Apparatus for performing operations in a glasshouse such as harvesting of cultivated crops, comprising: - a transport path,

- guide means, and

- a harvesting vehicle, which harvesting vehicle is provided with:

- a frame,

- at least four support wheels supporting the frame, which support wheels are adapted to co-act with the transport path, and

- at least one stabilizing element connected to the frame for stabilizing the vehicle, which stabilizing element is adapted to co-act with the guide means, characterized in that the relative orientation of at least a part of the stabilizing element and the frame can be changed.

2. Apparatus as claimed in claim 1 , characterized in that the transport path is formed by pipe rails.

3. Apparatus as claimed in either of the foregoing claims, characterized in that the guide means are integrated with the transport path.

4. Apparatus as claimed in any of the foregoing claims, characterized in that the stabilizing element is adapted to engage on a side of the guide means substantially remote from the frame.

5. Apparatus as claimed in any of the foregoing claims, characterized in that at least a part of the stabilizing element is adapted for substantially form-fitting co-action with the guide means.

6. Apparatus as claimed in any of the foregoing claims, characterized in that the stabilizing element engages under bias on the guide means.

7. Harvesting vehicle for use in an apparatus as claimed in any of the claims 1-6.

8. Harvesting vehicle as claimed in claim 7, characterized in that the support wheels are provided with a flange projecting from the supporting surface.

9. Harvesting vehicle as claimed in either of the claims 7-8, characterized in that the harvesting vehicle is provided with at least two stabilizing elements.

10. Harvesting vehicle as claimed in claim 9, characterized in that the distance between the stabilizing elements is continuously adjustable.

11. Harvesting vehicle as claimed in any of the claims 7-10, characterized in that the distance between two support wheels positioned on opposite sides of the frame is continuously adjustable.

12. Harvesting vehicle as claimed in any of the claims 7-11, characterized in that the position of the support wheels relative to the frame is adjustable.

13. Harvesting vehicle as claimed in any of the claims 7-12, characterized in that the stabilizing element is positioned at least close to two sides forming part of the frame and positioned perpendicularly of each other.

14. Harvesting vehicle as claimed in any of the claims 7-13, characterized in that the stabilizing element is connected pivotally to the frame.

15. Harvesting vehicle as claimed in any of the claims 7-14, characterized in that the stabilizing element is coupled releasably to the frame.

16. Harvesting vehicle as claimed in any of the claims 7-15, characterized in that the releasable coupling is formed by coupling means forming part of the stabilizing element, which coupling means co-act with mating coupling means forming part of the frame.

17. Stabilizing element for use in a harvesting vehicle as claimed in any of the claims 7-16.

18. Stabilizing element as claimed in claim 17, characterized in that the stabilizing element is provided with a stabilizing wheel.

19. Stabilizing element as claimed in either of the claims 17 or 18, characterized in that the stabilizing element is axially rotatable.

20. Stabilizing element as claimed in any of the claims 17-19, characterized in that the stabilizing element is provided with a support rod, which support rod is provided at least close to a free end with coupling means adapted for co-action with mating coupling means forming part of the frame, and which support rod is provided on an opposite end with at least one projecting stabilizing member.

21. Stabilizing element as claimed in claim 20, characterized in that the support rod is provided on a free end remote from the coupling means with a plurality of stabilizing members projecting relative to the support rod, wherein the stabilizing members enclose substantially the same angle with each other.

22. Stabilizing element as claimed in claim 20 or 21, characterized in that the support rod is provided with a stabilizing disc positioned at a distance from the stabilizing member.

23. Stabilizing element as claimed in any of the claims 20-22, characterized in that the stabilizing element is provided with positioning means for positioning the stabilizing member relative to the guide means.