US3611452A

US3611452A - Invalid bed construction

Info

Publication number: US3611452A
Application number: US49672A
Authority: US
Inventors: Michael Turko; Floyd F Mueller
Original assignee: American Hospital Supply Corp
Current assignee: HAMILTON INDUSTRIES Inc
Priority date: 1970-06-25
Filing date: 1970-06-25
Publication date: 1971-10-12
Anticipated expiration: 1988-10-12
Also published as: CA925654A

Abstract

AN INVALID BED HAVING A SCISSORS MECHANISM FOR RAISING AND LOWERING THE PATIENT-SUPPORTING FRAME. MOVEMENT OF TEH PATIENT-SUPPORTING FROME INTO TRENDELENBURG AND REVERSE TRENDELENBURG POSITIONS IS ACHIEVED BY BUCKLING ONE OF THE SCISSORS FRAMES, THEREBY PERMITTING

THE UPPER END OF THAT FRAME TO BE POSITIONED BELOW OR ABOVE THE CORRESPONDING END OF THE OTHER SCISSORS FRAME. POWER DRIVE, COUPLED WITH A LEVER AND CAM ARRANGEMENT, PRODUCES SUBSTANTIALLY CONSTANT-SPEED LIFTING AND LOWERING ACTION OF THE PATIENT-SUPPORTING FRAME REGARDLESS OF THE PARTICULAR ELEVATION OF THAT FRAME.

Description

oct. 12, 1971 QTUR Em 3,611,452

INVALID BED CONSTRUCTION Filed June 25,- 1970 3 Sheets-Sheet 1 FIGI I *-eo 59 11 n 61 AN; R INVENTORS: 153i MICHAEL TURKO FLOYD F. MUELLER ATT'YS Oct. 12, 1971 TURKQ EI'AL INVALID BED CONSTRUCTION FIG. 9 FIG. 8

5o '2 ll H1513: Q I12 30 I 'f- I, I .I I I r II If 52 5 I I INVENTORS: MICHAEL TURKO I FLOYD F. MUELLER ATT'YS Oct. 12, 1971 TURkg, ET AL 3,611,452

INVALID BED CONSTRUCTION Filed June 25, 1970 I) Sheets-Sheet 5 MICHAEL TURKO FLOYD F. MUELLER ATT'YS INVENTORS Umted States Patent 01 fee 3,611,452 INVALID BED CONSTRUCTION Michael Turko, Manitowoc, and Floyd F. Mueller, Two Rivers, Wis., assignors to American Hospital Supply Corporation, Evanston, Ill.

Filed June 25. 1970, Ser. No. 49,672 Int. Cl. A61g 7/00 US. Cl. -62 36 Claims ABSTRACT OF THE DISCLOSURE An invalid bed having a scissors mechanism for raising and lowering the patient-supporting frame. Movement of the patient-supporting frame into Trendelenburg and reverse Trendelenburg positions is achieved by buckling one of the scissors frames, thereby permitting the upper end of that frame to be positioned below or above the corresponding end of the other scissors frame. Power drive, coupled with a lever and cam arrangement, produces substantially constant-speed lifting and lowering action of the patient-supporting frame regardless of the particular elevation of that frame.

BACKGROUND A bed with a scissors mechanism for lifting and lowering a patient-supporting frame is disclosed in co-pending co-owned application Ser. No. 1,222, filed Jan. 7, 1970. As brought out in that application, a scissors mechanism has a number of advantages over other lift mechanisms used in power-operated hospital beds, such advantages including simplicity and strength. However, the use of a scissors mechanism has been found to have an offsetting disadvantage in beds which must be tilted about a transverse horizontal axis into either a Trendelenburg (foot end up) or reverse Trendelenburg (head end up) position. While such positions may be achieved by a construction in which, in effect, an additional frame is interposed between the scissors mechanism and the patient-supporting frame, as disclosed in the aforementioned application, such an additional frame and its associated mechanism not only greatly increases the complexity of the structure but also adds substantially to the total weight of the bed.

SUMMARY The present invention is directed at overcoming the aforementioned problems. Thus, it is an object of this invention to provide an invalid bed construction which utilizes the advantages of a scissors frame while at the same time avoids the disadvantages of using an additional frame (and its associated mechanism) to achieve the Trendelenburg and reverse Trendelenburg positions. Specifically, it is an object to provide a power-operated hospital bed which is relatively strong, light in weight, and uncomplicated in construction, and one which is fully adjustable, with particular reference to Trendelenburg and reverse Trendelenburg adjustments, while at the same time utilizing a scissors lift mechanism.

Briefly, the bed consists of a caster-equipped base frame, an upper patient-supporting frame, and an expandable scissors mechanism disposed between the two.

-The scissors mechanism includes a pair of crossed and pivotally-connected scissors frames with their upper ends engaging the patient-supporting frame and their lower ends engaging the base frame. One of the scissors frames is unitary and rigid; the other scissors frame is composed of two sections pivotally connected together for relative movement about a transverse pivot line. Locking means are provided for normally maintaining the two sections in longitudinal alignment; however, when either Trendelenburg or reverse Trendelenburg adjustment is desired, the sections of the second scissors frame are Patented Oct. 12, 1971 pivoted one way or the other with respect to each other. As the second scissors frame buckles in a controlled and gradual manner, the upper ends of the respective scissors frames assume different elevations, thereby causing the patient-supporting frame to tip into a Trendelenburg or reverse Trendelenburg position. This power-operated buckling action is achieved by using the same power means and lifting mechanism normally utilized for raising and lowering the bed. The result is a highly effective and efficient mechanism for a multiple-function poweroperated hospital bed.

Other objects and advantages will appear from the drawings and as the specification proceeds.

DRAWINGS FIG. 1 is a perspective view of the main operating elements of a hospital bed embodying the present invention. For clarity of illustration, a portion of one scissors frame is broken away and the entire patient-supporting frame is illustrated in phantom;

FIG. 2 is a fragmentary perspective View illustrating the releasable locking mechanism for the scissors frames;

FIG. 3 is an enlarged and detailed sectional view showing the locking and release mechanisms and illustrating in diagrammatic fashion the control mechanism for effecting release;

FIG. 4 is a longitudinal sectional view taken along approximately the longitudinal mid line of the bed and illustrating the bed as it approaches a fully raised position. For clarity of illustration, the patient-supporting frame is illustrated in phantom;

FIGS. 5 through 7 are sectional views similar to FIG. 4 but illustrating the bed in Trendelenburg, fully lowered, and reverse Trendelenburg positions, respectively;

FIG. 8 is a fragmentary perspective view illustrating the scissors frame blocking means (used for achieving Trendelenburg position) in operative condition;

FIG. 9 is a fragmentary end elevational view showing the blocking means in inoperative (solid line) and operative (broken line) positions;

FIG. 10 is a fragmentary sectional view showing internal construction of the screw-drive assembly. 7

For clarity of illustration, the motor and screwdrive mechanism for operating the bed, although shown in FIGS. 1, 4, and 10, are omitted from FIGS. 5-7. It is to be understood, however, that such components are part of the embodiment represented in all views. In addition, and as brought out more fully hereinafter, the patientsupporting frame is illustrated in phantom so that its presence will not obscure the scissors mechanism to which this invention is primarily directed.

DESCRIPTION Referring to the drawings, the numeral 10 generally designates a power-operated hospital bed having a base frame A, a patient-supporting frame B, and an intermediate scissors mechanism C. In the illustration given, the base frame A is generally U-shaped in configuration, having a pair of parallel side frame members 11 and an end frame 12. It will be observed that the side frame members 11 are of C-shaped cross section, havinglinwardly-facing channels for guiding movement of 'a scissors frame as the scissors mechanism extends and retracts. At each of its four corners, the base frame is equipped with conventional swivel casters 13. v

The patient-supporting frame B normally extends along a horizontal plane and is therefore usually disposed in parallel relation with respect to base frame A. Like the base frame, the patient-supporting frame has a pair-of inwardly-facing channel frame members 14. extending longitudinally along opposite sides thereof.

Head andfoot panels

15 and 16 are provided atoppositeends offrarne B. Mattress-supporting panels 17-20, illustrated in FIGS. 4-7 but omitted fram FIG. 1 to avoid unnecessary complication of the latter view, constitute part of the patientsupporting frame and are carried by supporting

members

21, 22, 23 and 24. While a patient-supporting frame similar to the structure disclosed in the aforementioned co-pending application has been illustrated here, it is to be understood that any suitable patient-supporting frame may be provided as long as it is equipped with side channels 14 which cooperate with the scissors mechanism. Thus, the size and arrangement of mattress-supporting panels, the mounting of those panels, the means for adjusting such panels into varying positions, constitute no part of the present invention. Since conventional elements may be used in that regard, further description is believed unnecessary herein.

Scissors mechanism C comprises a pair of

scissors frames

25 and 26. Each scissors frame is generally rectangular in configuration, frame 25 having a pair of spaced parallel side frame members 27 and a pair of

end frame members

28 and 29. While scissors frame 26 similarly has a pair of

end frame members

30 and 31, each of its side frame members 32 is composed of upper and

lower sections

32a and 32b. As a result, scissors frame 26 is as a whole divided into upper and

lower sections

26a and 26b. In the illustration given, the upper and lower sections of the scissors frame 26 are connected by pivots 33 for relative pivotal movement about the same transverse axis about which the respective scissors frames 25 and 26 pivot. Also, it will be observed that there is substantial overlap between the side members of scissors frame 26; that is, frame members 32b extend upwardly beyond the pivots so that the

respective members

32a and 32b have

portions

34 and 35 in laterallydisplaced or side-by-side relation.

To permit proper scissors action resulting in movement of the patient-supporting frame B between raised and lowered positions, certain ends of the scissors frames must be pivotally connected to the base and patientsupporting frames and other ends of the scissors frames must be slidably or movably connected thereto. In the context of this application, the term sliding movement is intended to mean translatory movement of one part relative to another and is therefore to be understood as including members which shift longitudinally upon each other even though frictional resistance may be reduced by means of rollers.

In the embodiment illustrated in the drawings, the lower end member 28 of scissors frame 25 is pivotally connected to the side members 11 of the base frame A. The opposite or upper end of the scissors frame 25 is equipped with rollers 36 (FIG. 1) which travel in the channels 14 of the patient-supporting frame B. Similarly, the upper end member 31 of scisors frame 26 is provided with laterally projecting pivots 31a which are rotatably received in openings in the side members 14 of the patientsupporting frame whereas the lower end of scissors frame 26 is equipped with rollers 37 (FIG. 1) which ride in the channels defined by the side members of base frame A. As the scissors mechanism is retracted horizontally (or extended vertically) to raise the patient-supporting frame, the ends of the scissors frames adjacent the head end of the bed pivot while the opposite ends of the respective scissors frames slide or shift longitudinally towards the beds head end. Conversely, when the scissors mechanism extends horizontally (or retracts vertically) to lower the bed, the

rollers

36 and 37 of the respective scissors frames travel in channels 14 and 11 towards the foot end of the bed.

Operation of the scissors mechanism is achieved by drive means which, in the particular embodiment illustrated, comprises a lever assembly 38 and a motor 39. The lever assembly includes a pair of lever arms 40 which have their lower ends pivotally secured to the side members of scissors frame 25 intermediate end member 28 and pivot shaft 33. Preferably, to increase the length of ,4 the lever arms, each side member 27 of scissors frame 25 is provided with depending projections 41 to which the lower ends of the lever arms are pivotally secured.

The upper ends of the parallel lever arms are secured together by transverse shaft 42, the shaft extending beneath the upper section of scissors frame 26 and being equipped with rollers 43 (FIG. 1) which ride along the surfaces of cam members '44. As shown most clearly in FIGS. 1 and 4, each cam 44 comprises a guide member mounted along the underside of one of the members 32a of the upper section of scissors frame 26. The underside of each guide member defines a camsurface which extends longitudinally of the scissors frame, then slopes downwardly and forwardly away from that frame, and finally reverses in direction, curving upwardly and rearwardly with respect to such frame. The distinctive configuration of each cam surface results in a bed which will raise or descend at substantially constant speed and at substantially constant motor loading throughout its entire range of vertical movement. In addition, the reverse curvature of the cam surfaces at the front ends thereof assures that the lever assembly will remain in proper engagement with the cams even when the bed is fully lowered (FIG. 6).

The lever assembly is operatively connected to motor 39 by means of a pair of upstanding plates 45 which serve as a clevis and which are connected at their upper ends to an internally threaded tube assembly 46. Such assembly comprises a tube 46a equipped with a nut 46b (FIG. 10) The nut threadedly receives the threaded drive shaft 47 of the reversible motor 39, the motor in turn being mounted upon end member 29 of scissors frame 25 by means of a pair of supporting brackets 48. Therefore, as motor 39 operates to rotate threaded shaft 47 in one direction, the cooperative action between the lever assembly and the cam assembly causes the scissors mechanism to contract and lift the patient-supporting frame B into the raised position illustrated in FIGS. 1 and 4, whereas rotation of the shaft in the opposite direction causes the scissors mechanism to expand and lower the patientsupporting frame into the fully lowered position illustrated in FIG. 6.

The bed will now be described with specific reference to the structure responsible for shifting the patient-supporting frame into the Trendelenburg position illustrated in FIG. 5. As previously mentioned, raising and lowering of the bed is accompanied by horizontal movement of end member 30 along side frame members 11 of base frame A. In other words, if the bed were to be lowered from the raised position illustrated in FIG. 4, end member 30 would slide or shift towards the foot end of the bed as the scissors mechanism expands. To achieve a Trendelenburg position, means are provided to block such rearward translation of end member 30; thereby causing a buckling of scissors frame 26 about shaft 33 as the lever assembly 38 continues to pivot downwardly.

Referring to FIG. 8, it will be observed that the rear member 12 of base frame A supports a blocking member 50, the blocking member having a curved forward surface which conforms to the contour of end member 30 of scissors frame 26 when the blocking member is in the operative position shown. A shaft 51 extends horizontally (and longitudinally of the bed) beneath frame member 12 and is rotatably mounted thereon by means of a bracket 52. The front portion of the shaft is secured to the underside of the blocking member to one side of the vertical mid plane thereof. At its rear end, the shaft 51 extends upwardly and outwardly to define an operating handle 53.

The position of the block illustrated in FIG. 8 is not a stable one, even though the handle engages stop 53a, because of the off-center support provided by shaft 51. Therefore, unless the block is restrained against tipping movement, it will swing by its own weight into the lowered or inoperative position illustrated in solid lines in FIG. 9. In that position, the block is disposed at a level beneath the path of travel of end member 30 of scissors frame 26. A

projection 54 engages handle 53 and normally holds the blocking assembly in the inoperative position shown in FIGS. 9 and 4.

Starting from the raised position of the bed illustrated in FIG. 4, if an operator wishes to shift the bed into the Trendelenburg position of FIG. then handle 53 is simply swung into the raised position illustrated in FIGS. 5 and 8 (and in broken lines in FIG. 9) to position blocking member 50 in the path of movement of end member 30 as the bed begins to descend. Blocking member 50 therefore prevents further rearward movement of end member 30 and, consequently, prevents further lowering of the rear or foot end of the bed. However, since scissors frame 26 is jointed, continued downward movement of lever assembly 38 permits the forward or second section 26a of the scissors frame 26 to pivot downwardly about shaft 33 (FIG. 5).

The extent of downward pivotal movement of scissors frame section 26a is controlled by a suitable limit switch (not shown) which simply interrupts operation of motor 39. A pair of stop members 56 mounted on portions 34 of scissors frame members 32a are engageable with portions 35 of frame members 32b to positively limit the extent of downward buckling of the scissors frame 26 should any failure in the operation of the limit switch occur.

Movement of the bed out of the Trendelenburg position of FIG. 5 is accomplished simply by reversing the steps described above; that is, the motor 39 is reversed to cause upward pivoting of lever arm assembly 38 to raise scissors frame section 26a and, when the two sections of scissors frame 26 are in planar alignment, to cause elevation of the patient-supporting frame into the fully raised position of FIG. 4. Because of the ofl-center mounting of blocking member 50, movement of end member 30 away from the blocking member results in automatic movement of the blocking member into the inoperative position of FIG. 9.

Upward buckling of scissors frame 26 as the bed is raised is normally prevented by releasable locking means in the form of pivotal butterfly arm 57. As shown most clearly in FIG. 2, each butterfly arm comprises a plate element disposed beneath the second or upper section 32a of each side member 32 of scissors frame 26. An upstanding shaft 58 supports each butterfly arm for rotational or pivotal movement about a generally vertical axis. In normal locking position, each butterfly arm has a wing or end portion 57a disposed beneath the upper end portion 35 of frame section 32b (FIG. 1), thereby preventing independent upward movement of upper section 32a.

Synchronized operation of the butterfly arms on opposite sides of the bed is achieved by means of a transverse tube or cylinder 59 extending between frame member sections 32a and rotatably mounted thereon. As the tube is rotated in a counterclockwise direction (as viewed in FIGS. 1-3), pins 60, which project upwardly from wing portions 57b of the butterfly arms and which are received in longitudinal slots 60a in tube 59, are urged towards the foot end of the bed to pivot such arms and withdraw wing portions 57a from beneath the lower members 32b of the split scissors frame 26 (FIG. 2). Such rotational movement of the tube may be achieved by any suitable control means 61 such as, for example, an operating cable connected to the tube, such cable being retracted either manually or electrically, as by means of a solenoid. A return force to urge the tube and the butterfly arms back into their original positions may be conveniently provided by simply weighing the tube with a suitable internal weight 62. (FIG. 3). It is to be understood, however, that any suitable means for urging thetube into its original position and for swinging the butterfly arms into their normal locking positions may be provided.

FIGS. 6 and 7 illustrate the steps for shifting the bed into a reverse Trendelenburg position. As the patientsupporting frame B moves towards its fully lowered position the upper end of scissors frame 25that is, the end of the frame adjacent end member 2.9engages upwardly-projecting stop elements 63 mounted upon base frame A. Such engagement occurs before the lever assembly 38 has completed its descent. Consequently, continued downward travel of the lever assembly permits the upper or second section 26a of scissors frame 26 to pivot downwardly about the axis of shaft 33 while the first or lower section of that frame is held stationary. A slight downward buckling of scissors frame 26 occurs. As illustrated in FIG. 6, such buckling is slight; in fact, the head end of the patient-supporting frame B drops only an inch or less lower than the foot end of that frame. However, such buckling is enough to lower the butterfly arms 57 out of contact with the side members of scissors frame section 26b. By manipulating or energizing control 61, an operator may thus rotate tube 59 to swing the butterfly arms away from the end of scissors frame section 261) so that when motor 39 is reversed to pivot lever assembly 38 upwardly, the butterfly arms will clear the end of scissors frame section 26b and will therefore permit upward buckling of scissors frame 26 as illustrated in FIG. 7.

The extent of such upward buckling action is limited by stop members 64. Such members, illustrated most clearly in FIGS. 1, 2, and 7, are secured to the side members of scissors frame section 26b and have inwardly projecting terminal portions 64a which extend into the path of movement of scissors frame section 26a and which engage. the top surfaces of side members 32a to lock the sections of scissors frame 26 against further buckling action.

FIG. 7 illustrates the bed in its full reverse Trendelenburg position. It is to be noted, however, that the inclined position will be maintained even if the driving motor is operated to continue the lifting action of lever assembly 38. In other words, if the lever assembly is lifted towards the vertical from the position shown in FIG. 7, the patient-supporting frame will move upwardly without changing the angle of inclination shown.

The bed is shifted from reverse Trendelenburg position into its normal horizontal position by simply reversing the steps described. As the bed returns to its fully lowered position of FIG. 6, the butterfly arms clear the ends of frame members 32b and automatically swing into their original locking positions (FIG. 1) under the influence of weighted tube 59.

It will be observed from FIG. 10 that threaded drive shaft 47 has an unthreaded terminal portion 47a. Normally nut 46b does not run off of the threads and onto the unthreaded terminal portion, even when the bed is in the fully lowered position of FIG. 6, because a limit switch (not shown) interrupts operation of the motor 39' when that position is achieved. However, should there ever be a failure in the operation of the switch resulting in a running-on of the motor 39 after the bed is fully lowered, damage to the drive mechanism (as by buckling of the drive tube assembly 46) and other components of the bed will be avoided because the nut will simply ride the slight additional distance necessary to carry it off of the end of the threaded portion of shaft 47 and onto the unthreaded terminal portion 47a where it will remain until the operation of the motor is reversed and the force of helical compression spring 64 (interposed between nut 46b and terminal flange 65 of shaft 47) will cause it to reengage the threads of the shaft. Relative rotation between nut 46b and the tube 46a is prevented by a stud or guide pin 66 which is affixed to the nut and which projects radially through longitudinal guide slot 67 in the tube wall. Therefore, the nut may move longitudinally within the tube, to the limited extent permitted by the slot and stud, until it becomes unthreaded from the shaft, thus preventing damage which might otherwise occur should the limit switch fail.

From the above description, it is believed apparent that the operating mechanism is relatively simple in structure and light in weight, and that the same driving mechanism not only moves the patient-supporting frame between raised and lowered positions but also operates to shift such frame into Trendelenburg or reverse Trendelenburg positions as desired.

While in the foregoing, an embodiment of the invention has been disclosed in considerable detail for purposes of illustration, it will be understood by those skilled in the art that many of these details may be varied without departing from the spirit and scope of the invention.

We claim:

1. An invalid bed having normally parallel base and patient-supporting frames, and a scissors mechanism therebetween for adjusting the elevation of said patient-supporting frame relative to said base frame, said scissors mechanism comprising a pair of crossed and pivotally-connected scissors frames having their upper ends engaging said patient-supporting frame and their lower ends engaging said base frame, the improvement wherein:

one of said scissors frames is jointed for buckling action about a transverse horizontal line, and means for upwardly and downwardly buckling said one scissors frame about said transverse line for selectively varying the elevation of the upper end of said one scissors frame independently of the elevation of the upper end of the other scissors frame, whereby, said patientsupporting frame is selectively shifted into Trendelenburg or reverse Trendelenburg positions by the controlled buckling of said one scissors frame in opposite directions.

2. The structure of claim 1 in which said jointed scissors frame has first and second sections pivotally connected along said transverse line for relative pivotal movement thereabout, said means including a lever assembly having a lever arm movable between raised and lowered positions and engaging one of said sections for pivoting the same relative to the other of said sections.

3. The structure of claim 2 in which said means includes power-driven means for moving said lever arm between raised and lowered positions.

4. The structure of claim 2 in which said first section has an end engaging said base frame and said second section has an end engaging said patient-supporting frame, said lever arm extending between said second section and a portion of said other scissors frame therebelow.

S. The structure of claim 4 in which said lever arm has its lower end pivotally connected to said portion of said other scissors frame and the opposite end of said lever arm movably engages a cam member provided by said second section.

6. The structure of claim 5 in which said means includes motor means for pivoting said lever arm between raised and lowered positions.

7. The structure of claim 5 in which said cam comprises at least one guide member mounted along the underside of said second section and defining a curved cam surface engaged by said lever arm.

8. The structure of claim 7 in which said cam surface is reversely turned to retain the adjacent end of said lever arm in engagement therewith.

9. The structure of claim 2 in which locking means are provided for normally maintaining said first and second sections in generally planar alignment.

10. The structure of claim 9 in which said first and second sections have lateral portions thereof in side-byside relation, said locking means for normally maintaining said sections in planar alignment being mounted on said lateral portions.

11. The structure of claim 10 in which one of said lateral portions has stop means engageable with the other of said lateral portions for limiting the extent of buckling of said one scissors frame in at least one direction.

12. The structure of claim 11 in which said stop means includes a stop member secured to one of said lateral portions and having an extension disposed in the path of movement of said other of said lateral portions.

13. The structure of claim 4 in which each of said scissors frames has an end slidably engaging one of said patient-supporting and base frames for horizontal sliding movementas said scissors mechanism expands and contracts, and blocking means for selectively restraining sliding movement of said one scissors frame as said lever arm is moved from a raised to a lowered position, whereby, downward movement of said lever arm while said one scissors frame is restrained against sliding movement results in downward buckling of said one scissors frame about said transverse line.

14. The structure of claim 13 in which said first section of said one scissors frame slidably engages said base frame and said second section is pivotally connected to said patient-supporting frame, said blocking means comprising a stop block movably mounted upon said base frame for movement between an operative position for blocking endwise sliding movement of said first section and an inoperative position permitting endwise movement thereof.

15. The structure of claim 14 in which said stop block is biased for movement into said inoperative position.

16. An invalid bed having normally parallel base and patient-supporting frames, and a scissors mechanism therebetween for adjusting the elevation of said patient-supporting frame relative to said base frame, said scissors mechanism comprising a pair of crossed and pivotallyconnected scissors frames having their upper ends engaging said patient-supporting frame and their lower ends engaging said base frame, the improvement wherein:

one of said scissors frames is jointed for buckling action about a transverse horizontal line coincident with the line of pivotal connection between said pair of scissors frames, and means for upwardly and downwardly buckling said one scissors frame about said transverse line for selectively varying the elevation of the upper end of said one scissors frame independently of the elevation of the upper end of the other scissors frame, whereby, said patient-supporting frame is selectively shifted into Trendelenburg or reverse Trendelenburg positions by the controlled buckling of said one scissors frame in opposite directions.

17. The structure of claim 16 in which said jointed scissors frame has first and second sections pivotally connected along said transverse line for relative pivotal movement thereabout, said means including a lever assembly having a lever arm movable between raised and lowered positions and engaging one of said sections for pivoting the same relative to the other of said sections.

18. The structure of claim 17 in which said means includes power-driven means for moving said lever arm between raised and lowered positions.

19. The structure of claim 17 in which said first section has an end engaging said base frame and said second section has an end engaging said patient-supporting frame, said lever arm extending between said second section and a portion of said other scissors frame therebelow.

20. The structure of claim 19 in which said lever arm has its lower end pivotally connected to said portion of said other scissors frame and the opposite end of said lever arm movably engages a cam member provided by said second section.

21. The structure of claim 20 in which said means includes motor means for pivotaing said lever arm between raised and lowered positions.

22. The structure of claim 20 in which said cam comprises at least one guide member mounted along the underside of said second section and defining a curved cam surface engaged by said lever arm.

23. The structure of claim 22 in which said cam surface is reversely turned to retain the adjacent end of said lever arm in engagement therewith.

24. The structure of claim 17 in which locking means are provided for normally maintaining said first and second sections in generally planar alignment.

25. The structure of claim 24 in which said first and second sections have lateral portions thereof in side-byside relation, said locking means for normally maintaining said sections in planar alignment being mounted on said lateral portions.

26. The structure of claim 25 in which one of said lateral portions has stop means engageable with the other of said lateral portions for limiting the extent of buckling of said one scissors frame in at least one direction.

27. The structure of claim 26 in which said stop means includes a stop member secured to one of said lateral portions and having 'an extension disposed in the path of movement of said other of said lateral portions.

28. The structure of claim 19 in which each of said scissors frames has an end slidably engaging one of said patient-supporting and base frames for horizontal sliding movement as said scissors mechanism expands and contracts, and blocking means for selectively restraining sliding movement of said one scissors frame as said lever arm is moved from a raised to a lowered position, whereby downward movement of said lever arm while said one scissors frame is restrained against sliding movement results in downward buckling of said one scissors frame about said transverse line.

29. The structure of claim 28 in which said first section of said one scissors frame slidably engages said base frame and said second section is pivotally connected to said patient-supporting frame, said blocking means comprising a stop block movably mounted upon said base frame for movement between an operative position for blocking endwise sliding movement of said first section and an inoperative position permitting endwise movement thereof.

30.. The structure of claim 29 in which said stop block is biased for movement into said inoperative position.

31. An invalid bed having normally parallel base and patient-supporting frames, and a scissors mechanism therebetween for adjusting the elevation of said patient-supporting frame relative to said base frame, said scissors mechanism comprising a pair of crossed and pivotallyconnected scissors frames having their upper ends engaging said patient-supporting frame and their lower ends engaging said base frame, one of said scissors frames having upper and lower sections pivotally joined along a transverse line for movement between aligned relation and buckled relation with respect to each other, said sections including pairs of longitudinal frame members having adjacent end portions in juxtaposition when said sections are aligned, one of said end portions terminating at a substantial distance from said transverse line, and a locking arm movably mounted upon the other of said end portions and being movable between a locking position wherein said arm engages said one of said end portions adjacent the termination thereof to limit relative movement between said sections and a releasing position wherein said arm is retracted to permit such movement, and means for shifting said arm between said locking and releasing positions.'

32. The structure of claim 31 in which means are pro-" vided for normally urging said arm into said locking position.

33. The structure of claim 32 in which said arm is pivotally movable between said locking and releasing positions.

34. The structure of claim 33 in which said arm has a top surface engageable with the underside of said one end portion when said arm is in its locking position, said top surface being displaced from beneath said underside when said arm is in its releasing position.

35. The structure of claim 34 in which said means for shifting said locking arm includes a rotatable member mounted upon said one of scissors frame, means operatively connecting said rotary member to said locking arm for movement of the latter between locking and unlocking position as said rotary member is turned in opposite directions.

36. The structure of claim 35 in which said means for normally urging said arm into its locking position comprises a weight carried by said rotary member and normally urging said rotary member to rotate in one direction to direct said locking member into its locking position.

References Cited UNITED STATES PATENTS 2,445,258 7/1948 Beem 5-62 UX 2,833,587 5/1958 Saunders 5-63 X JAMES C. MITCHELL, Primary Examiner U.S. Cl. X.R. 563; 108-8