US3831996A

US3831996A - Stretcher support arrangement especially for ambulances

Info

Publication number: US3831996A
Application number: US00321043A
Authority: US
Inventors: S Layer
Original assignee: Binz GmbH and Co
Current assignee: Binz GmbH and Co
Priority date: 1972-01-08
Filing date: 1973-01-04
Publication date: 1974-08-27
Anticipated expiration: 1991-08-27
Also published as: FR2167805A1; CH549387A; SE374490B; DE2200814C2; DE2200814B1; NL7300047A; FR2167805B1; GB1377041A

Abstract

A stretcher support arrangement for ambulances in which a stretcher support frame is mounted movable between a substantially horizontal rest position located within the ambulance and an extended position partly outwardly withdrawn therefrom and with the outwardly extending end downwardly tilted on frame means fixed to the floor of the ambulance. Links guided in guide rails are connected to the stretcher support frame to move the latter automatically to its tilted position when the support frame is pulled towards its extended position.

Description

United States Patent [191 Layer Aug. 27, 1974 [75] Inventor: Siegfried Layer, Lorch/Wuerttemberg, Germany [73] Assignee: Binz &Co., Lorch/Wuerttemberg,

Germany.

22 Filed: Jan. 4, 1973 [2]] Appl. No.: 321,043

[30] Foreign Application Priority Data Jan 8. l972 Germany 2200814 [52] US. Cl. 296/19 [51] Int. Cl A6lg 1/00 [58] Field of Search 296/19 [56] References Cited UNITED STATES PATENTS 3.630.565 l2/l97l Lehmann 296/19 FOREIGN PATENTS OR APPLICATIONS l l66.4l5 3/1964 Germany 296/19 Primary ExaminerPhilip Goodman Attorney, Agent, or Firm-Michael S. Striker ABSTRACT A stretcher support arrangement for ambulances in which a stretcher support frame is mounted movable between a substantially horizontal rest position located within the ambulance and an extended position partly outwardly withdrawn therefrom and with the outwardly extending end downwardly tilted on frame means fixed to the floor of the ambulance. Links guided in guide rails are connected to the stretcher support frame to move the latter automatically to its tilted position when the' support frame is pulled towards its extended position.

14 Claims, 5 Drawing; Figures PATENIED 3.881 .996 sum ear 3 STRETCHER SUPPORT ARRANGEMENT ESPECIALLY FOR AMBULANCES BACKGROUND OF THE INVENTION The present invention relates to a stretcher support arrangement, especially for ambulances, with a stretcher support frame which can be moved from a substantially horizontal rest position in longitudinal direction to an extended inclined position with the outwardly extending end moved in downward direction, and back from the extended, inclined to the horizontal rest position. The inclined or tilted position of the stretcher support frame greatly facilitates to place a stretcher on this frame and to remove a stretcher therefrom.

Stretcher support arrangement for ambulances are already known in which the stretcher support frame is tiltable about an axis extending transverse to the longitudinal direction of the frame permitting to place the head end of the frame into a lower position, and in which the head end of the frame is appropriately guided.

This known stretcher support arrangement, does not permit the stretcher support frame to .tilt in its outwardly extended position in such a manner that the outer end of the frame is moved downwardly.

SUMMARY OF THE INVENTION It is an object of the present invention to provide for a stretch support arrangement, especially for ambulances, in which an elongated support frame adapted to support a stretcher thereon is movable relative to a support adapted to be fixed to the ambulance between a substantially horizontal rest position and an outwardly extended position, in which the stretcher support frame can be moved easily between the two positions thereof while being properly guided during such movement.

It is a further object of the present invention to provide for such a stretcher support arrangement which is composed of relatively few and simple parts so that the stretcher support arrangement can be manufactured at reasonable cost and will stand up properly under extended use.

With these and other objects in view, which will become apparent as the description proceeds, the stretcher support arrangement according to the present invention mainly comprises support means adapted to be mounted in fixed position in an ambulance, an elongated support frame adapted to support a stretcher thereon superimposed on the support means, means guiding the support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with the support means and an extended position extending with an end portion thereof beyond the support means. support link means pivotally conneeted at one end to the support frame at a region of the end of the latter which is opposite said one end por* tion, and longitudinally extending guide rail means for guiding the support link means and for releasing the one end thereof from the guide means when the support frame is in its extended position so that the support link means may be tilted about the other end thereof in upward direction to thereby tilt the support frame correspondingly.

The support link means therefore serve to guide the support frame during its movement in longitudinal direction and to tilt the latter in its extended position.

Abutments means are preferably provided in the region of that end of the guide means which face the one end portion of the support frame and the other end of the guide link means abuts against this abutment means during movement of the support frame from the rest towards the extended position. The guide rail means and the abutment means are constructed and arranged in such a manner so that a force acting in longitudinal direction of the support frame for moving the latter to the extended position will first cause movement of the support frame in this direction while the support link means are guided in the guide means and, after the other end of the support link means engages the abutment means, upward tilting of the support link means and thereby a corresponding tilting of the support frame.

The support link means preferably comprises a pair of guide members respectively arranged on opposite ends of the support link means and the guide rail means has guide faces including an upper guide face for guiding the support members substantially along the length of the guide rail means. The upper guide face is provided with an opening intermediate the opposite ends of the guild rail means permitting movement of the guide member at said one end of the support link means upwardly through this opening and upward tilting of the support link means about the other guide member. The guide rail means preferably has a downwardly inclined end portion facing said one end portion of the support frame so that during movement of the support frame towards its extended position the support frame will assume an already partly inclined position so that only a limited further inclination will be necessary at the end of the movement of the support frame towards its extended position. By use of elements with rolling friction for guiding the support link means and for guiding the support frame at its outwardly movable end portion, the movement of the support frame between the positions thereof will be additionally facilitated.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation together with additional objects and advantages, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a perspective view of the stretcher support arrangement according to the present invention and showing the stretcher support frame in its rest position;

FIG. 2 is a perspective view drawn to a slightly smaller scale in which the stretcher support frame is shown in its extended and tilted position;

FIG. 3 is a partial end view of the stretcher support arrangement as viewed in the direction indicated by the arrow 3 of FIG. 2;

FIG. 4 is a schematic side view of the stretcher support arrangement showing the stretcher support frame in its rest position; and

FIG. 5 is a schematic side view showing the stretcher support frame in its extended and tilted position.

DESCRIPTION OF THE PREFERRED EMBODIMENT As shown in the drawing, the stretcher support arrangement according to the present invention preferably comprises a base frame adapted to be connected to the floor or to an intermediate member on the floor of an ambulance, now shown in the drawing, which is for instance movable in the direction of the arrow f shown in FIG. 5. In the embodiment illustrated, an intermediate frame 20 is mounted by means of rubber buffers or the like on the base frame 10, preferably adjustable so that the end of the intermediate frame 20 facing in the moving direction may be lowered with respect to the opposite end. Guide rail means, comprising a pair of elongated guide rails 11, are connected at opposite ends to opposite sides of a vertical longitudinal plane of symmetry of the aforementioned frames to the intermediate frame 20 or, when the latter is omitted, directly to the base frame 10. Each of the guide rails 11 is U-shaped in cross section and has a longer, from its connected end upwardly extending, portion 11a and a shorter, to its connected end downwardly extending portion 1 lb. The arrangement includes further support link means comprising a pair of elongated support links 12, each having in the region of opposite ends thereof guide members, preferably rollers, 13 and 14 which extend from the open side of the U-shaped cross section of each guide rail into the latter so that the support links 12 are respectively guided in the two guide rails 11 for movement in longitudinal direction thereof. The support link means 12 serve to guide and to prop a stretcher support frame 15 which is pivotally connected adjacent its right end, as viewed for instance in FIG. 2, to the support link means 12 at the axis of the guide roller 14.

One. or a pair of rollers 16 are provided at the left end, as viewed in the drawing, corresponding to the rear end as viewed in the driving direction f, on the base frame 10 for further support of the stretcher support frame 15 such that the support frame 15 may move in longitudinal direction along the one, or the pair of rollers 16. A pair of lateral guide rollers 19 mounted turnably about vertical axes and connected to the base frame 10, respectively the intermediate frame 10. are preferably provided to rollingly engage the support frame 15 onopposite sides thereof to prevent lateral movement of this frame.

As best shown in FIGS. 4 and 5, each of the guide rails 11 is provided in its upper guide face 17, that is in the upper leg of the U-shaped cross section of each guide rail. with an opening 18 which is arranged in the region of the junction of the two oppositely inclined guide rail portion 11a and llb.

The downwardly inclined guide rail portion 11b has a length which substantially corresponds to the length of the support link 12 guided therein such that in the position 12' of the support link indicated in dashed-dot lines in FIG. 5, the upper end of the support link with its guide roll 14 may pass through the opening 18 and be tilted in the direction of the arrow y into the position 12, shown in full lines in FIG. 5, whereby the support frame 15 will be correspondingly tilted from the position 15 shown in dashed-dot lines in FIG. 5, to the position 15 shown in full lines in FIG. 5.

Stops, not shown in the drawing, which may for instance be provided on the support links 12 and cooperating with the upper faces of the intennediate frame are preferably provided for limiting tilting of the support links 12 beyond the position shown in full lines in FIG. 5.

To arrest the support frame 12 in its rest as well as in its extended tilted position latch means are provided, preferably including first latch means 21 mounted for instance on the intermediate frame 20 or on any other stationary part of the support arrangement and second latch means comprising two

latch members

22 and 23 mounted for instance spaced from each other in longitudinal direction of the support frame 15 on the latter and arranged in such manner that the latch means 21 will cooperate with the latch member 22 on the support frame to arrest the latter in the rest position, whereas in the extended and tilted position the latch means 21 will cooperate with the latch member 23 to arrest the support frame 15 in its extended and tilted position. The aforementioned latch means may be constructed in any well known manner and may comprise for instance a movable bolt arranged on the latch means 21 and insertable in corresponding bores formed in the

latch members

22 and 23 or the latch means may comprise for instance a yieldable member mounted on one of the latch means and automatically snapping in the other latch means when the support frame 15 is either in the rest or the extended tilted position. The arrangement preferably includes further

tiltable hooks

24 and 25 in order to maintain the intermediate frame 20, which may at one end be liftable or lowerable by means of a device not shown in the drawing, in an adjusted position relative to the base frame 10.

The stretcher support frame 15 is shown in FIGS. 1 and 4 in its rest position in which the frame 15 is maintained in a substantially horizontal position. The

rollers

13 and 14 on opposite ends of each support link 12 are located in this position in the respective guide rail 11 with the rollers 14 at the forward, that is the right ends, as viewed in FIGS. 1 and 4 of the guide rail sections 110. The support frame 15 rests with its rear, that is with its left end as viewed in FIGS. 1 and 4, on the guide rollers 16 and is arrested against movement in longitudinal direction on the intermediate frame 20 by the

latch

21 and 22.

When the support frame 15 is to be brought into its loading position, that is to its rearward extended and tilted position, the latch member 22 will first be disengaged from the latch member 21 so that the frame 15 may be moved rearwardly in the direction of the arrow .r, indicated in FIG. 5. During the first part of this movement, the frame 15 is guided by means of the support links 12 in the portion 11a of the guide rails to move from the position as shown in FIG. 4 toward a position as shown in FIG. 5 whereby the rollers 13 will move over the highest portion of the guide rail into the downwardly inclined guide rail portion 1112 until the support link will reach the position 12' and the support frame the position 15, shown in dash-dot lines in FIG. 5. In this position of the support links, the rollers 13 will engage an abutment at the lower end of the guide rail portion 11b whereas the other roller will be in the position 14' so that during further pulling on the support frame 15 in the direction of the arrow x, the roller 14 in the position 14' will pass through the opening 18 in the upper leg of the U-shaped guide rail 11 and move in the direction indicated by the arrow y rearwardly, that is toward the left, as viewed in FIG. 5, whereby the support links will tilt about the lower rollers 13 from the position 12, indicated in dash-dot lines in FIG. 5, to the position shown in full lines in this FIGURE causing thereby the support frame to tilt from the slightly inclined position 15 indicated in dash-dot lines in FIG. 5, to the further inclined position, shown in full lines in this FIGURE, in which the support frame 15 is arrested by the cooperating

latch members

21 and 23 not shown in FIG. 5.

As shown in the drawing, each guide rail 11 is U- shaped in side view, and its downwardly inclined portion 11b is inlined at such an angle that a pulling force acting on support frame 15 in the direction of the arrow .r will cause movement of the frame in longitudinal direction by means of the support links 12 in the guide rails 11 from the rest position shown in FIG. 4 first to the an intermediate position shown dash-dot lines in FIG. 5 and subsequently thereto, by a corresponding component of this force, the tilting of the support links 12 from the position 12, shown in dash-dot lines in FIG. 5, to the position 12, shown in full lines in this FIGURE, with a corresponding further tilting of the support frame 15.

Movement of the support frame 15 from the extended tilted position to the horizontal rest position will occur in the opposite sequence, that is during push on the support frame 15 in a direction opposite to the direction indicated by the arrow x, the support links 12 will first be tilted in a direction opposite to the direction indicated by the arrow y to the position indicated in dash-dot lines in FIG. 5, whereby the support frame 15 will reach the position 15 likewise indicated by dash-dot lines in the FIGURE, and the roller 14 will enter through the opening 18 into the guide rail 11 so that during further pushing of the support frame 15 in the direction opposite to the direction indicated by the arrow each support link will be guided by both

rollers

13 and 14 in the respective guide rail to its end position as shown in FIG. 4.

It will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of stretcher support arrangement especially for ambulances differing from the types described above.

While the invention has been illustrated and described as embodied in a stretcher support arrangement including an elongated support frame movable between a substantially horizontally rest position and an extended inclined position facilitating placing and removing a stretcher on the support frame, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the pres ent invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore such adaptations should and are intended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended:

l. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in a fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon, said elongated support frame having opposite ends and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end thereof beyond said support means: support link means pivotally connected at one end to said support frame in the region of the other end of the latter; and guide rail means extending in the longitudinal direction of said support frame for guiding said support link movable with said support frame in the longitudinal direction of the guide rail means as said support frame moves from said rest to an intermediate position and for releasing said one end of said support link means from said guide rail means as said support frame moves from said intermediate to said extended position to thereby tilt said support link means about the other end thereof in upward direction with corresponding tilting of said support frame.

2. A stretcher support arrangement as defined in claim 1, and including abutment means in the region of that end of said guide rail means which faces said one end of said support frame, and other end of said guide link means abutting against said abutment means in said intermediate position of said support frame, said guide rail means and said abutment means being constructed and arranged so that a force acting in longitudinal direction of said support frame for moving the latter toward the extended position will first cause movement of said support frame in this direction while said support link means are guided in said guide rail means and after said other end of said support link means engages said abutment means upward tilting of said support link means and thereby corresponding tilting of said support frame.

3. A stretcher support arrangement as defined in claim 2, wherein said guide rail means has a downwardly inclined end portion facing said one portion of said support frame.

4. A stretcher support arrangement as defined in claim 1, wherein said support link means comprise a pair of guide members respectively arranged on opposite ends of said support link means, and wherein said guide rail means has guide faces for guiding said guide members along said guide rail means, said guide faces including an upper guide face having an opening intermediate the opposite ends of said guide rail means permitting movement of the guide member at said one end of said support link means upwardly through said opening and upward tilting of said support link means about the other guide member.

5. A stretcher support arrangement as defined in claim 4, wherein said guide members are rollers.

6. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end thereof beyond said support means; support link means pivotally connected at one end to said support frame in the region of the other end of the latter, said support link means comprising a pair of guide members respectively arranged at opposite ends of said support link means; and longitudinally extending guide rail means having guide faces for guiding said guide members along said guide rail means, said guide faces including an upper guide face having an opening intermediate the opposite ends of said guide rail means permitting movement of the guide member at one end of the support link means upwardly through said opening and upward tilting of said support link means about the other guide member with corresponding tilting of said support frame, said opening in said upper guide face being spaced from the end of said guide rail means which faces said one end of said support frame a distance which is substantially equal to the spacing between said pair of guide members from each other.

7. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end thereof beyond said support means; support link means pivotally connected at one end to said support frame in the region of the other end of the latter, said support link means comprising a pair of guide members respectively arranged at opposite ends of said support link means; and longitudinally extending guide rail means having guide faces for guiding said guide members along said guide rail means, said guide faces including an upper guide face having an opening intermediate the opposite ends of said guide rail means permitting movement of the guide member at said one end of said support link means upwardly through said opening and upward tilting of said support link means about the other guide member with corresponding tilting of said support frame, said guide rail means having an end portion facing said one end of said support frame and being downwardly inclined with respect to the remainder of said guide rail means, said opening being located at the region of the junction of said downwardly inclined end portion with the remainder of said guide rail means.

8. A stretcher support arrangement as defined in claim 7, wherein said remainder of said guide rail means extends upwardly inclined to said junction.

9. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end thereof beyond said support means; support link means pivotally connected at one end to said support frame in the region of the other end of the latter, said support link means comprising a pair of guide members respectively arranged at opposite ends of said support link means; and longitudinally extending guide rail means having guide faces for guiding said guide members along said guide rail means. said guide faces including an upper guide face having an opening intermediate the opposite ends of said guide rail means permitting movement of the guide member at said one end of the support link means upwardly through said opening and upward tilting of said support link means about the other guide member with corresponding tilting of said support frame, said guide rail means having a U-shaped cross-section in which said guide members are guided, said upper guide face with said opening being formed in the upper leg of said U-shaped cross-section.

10. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end beyond said support means, said guide means including roller guide means mounted on said support means adjacent said one end of said support frame in the rest position of the latter, said roller guide means including a pair of rollers mounted on said support means turnable about a vertical axis and respectively engaging said support frame on opposite sides; support link means pivotally connected atone end to said support frame at a region of the other end of the latter; and longitudinally extending guide rail means for guiding said support link means and for releasing said one end thereof from said guide rail means when said support frame is in said extended position so that said support link means may be tilted about the other end thereof in upward direction to thereby tilt said support frame correspondingly.

11. A stretcher support arrangement as defined in claim 1, wherein said support means comprise a base frame adapted to be fixedly mounted in an ambulance and an intermediate frame adjustably mounted on said base frame above the latter, said guide rail means being fixedly connected to said intermediate frame.

12. A stretcher support arrangement as defined in claim 11, and including roller guide means mounted on that end of one of said frames constituting said support means which is adjacent said one end of said support frame in the rest position of the latter.

13. A stretcher support arrangement as defined in claim 1, and including a latch arrangement for securing said support frame in said rest and in the extended position.

14. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extended with one end portion thereof beyond said support means; support link means pivotally connected at one end to said support frame at a region of an end of the latter which is opposite said end portion; longitudinally extending guide rail means for guiding said support link means and for releasing said one end thereof from said guide rail means when said support frame is in said extended position so that said support link means may be tilted about the other end thereof in upward direction to thereby tilt latching position, one of said latch means comprising two substantially identical latch members spaced in longitudinal direction of said support frame from each other and engageable with the other latch means in the rest, respectively in said extended position of said support frame.

Claims

1. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in a fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon, said elongated support frame having opposite ends and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end thereof beyond said support means: support link means pivotally connected at one end to said support frame in the region of the other end of the latter; and guide rail means extending in the longitudinal direction of said support frame for guiding said support link movable with said support frame in the longitudinal direction of the guide rail means as said support frame moves from said rest to an intermediate position and for releasing said one end of said support link means from said guide rail means as said support frame moves from said intermediate to said extended position to thereby tilt said support link means about the other end thereof in upward direction with corresponding tilting of said support frame.

9. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end thereof beyond said support means; support link means pivotally connected at one end to said support frame in the region of the other end of the latter, said support link means comprising a pair of guide members respectively arranged at opposite ends of said support link means; and longitudinally extending guide rail means having guide faces for guiding said guide members along said guide rail means, said guide faces including an upper guide face having an opening intermediate the opposite ends of said guide rail means permitting movement of the guide member at said one end of the support link means upwardly through said opening and upward tilting of said support link means about the other guide member with corresponding tilting of said support frame, said guide rail means having a U-shaped cross-section in which said guide members are guided, said upper guide face with said opening being formed in the upper leg of said U-shaped cross-section.

10. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extending with one end beyond said support means, said guide means including roller guide means mounted on said support means adjacent said one end of said support frame in the rest position of the latter, said roller guide means including a pair of rollers mounted on said support means turnable about a vertical axis and respectively engaging said support frame on opposite sides; support link means pivotally connected at one end to said support frame at a region of the other end of the latter; and longitudinally extending guide rail means for guiding said support link means and for releasing said one end thereof from said guide rail means when said support frame is in said extended position so that said support link means may be tilted about the other end thereof in upward direction to thereby tilt said support frame correspondingly.

14. A stretcher support arrangement, especially for ambulances, comprising support means adapted to be mounted in fixed position in an ambulance; an elongated support frame adapted to support a stretcher thereon and being superimposed on said support means; means guiding said support frame movable in longitudinal direction between a substantially horizontal rest position coextensive with said support means and an extended position extended with one end portion thereof beyond said support means; support link means pivotally connected at one end to said support frame at a region of an end of the latter which is opposite said end portion; longitudinally extending guide rail means for guiding said support link means and for releasing said one end thereof from said guide rail means when said support frame is in said exteNded position so that said support link means may be tilted about the other end thereof in upward direction to thereby tilt said support frame correspondingly; and a latch arrangement for securing said support frame in said rest and in said extended position, said latch arrangement comprising first latch means mounted on said support frame and second latch means on said support means, said first and said second latch means being movable relative to each other between a latching and an unlatching position, one of said latch means comprising two substantially identical latch members spaced in longitudinal direction of said support frame from each other and engageable with the other latch means in the rest, respectively in said extended position of said support frame.