Litter support having telescoping threaded rod arrangement

A hospital bed includes a base supported by casters, and a lift arrangement vertically movably supports a patient support section on the base. The lift arrangement includes a threaded first member secured to and projecting downwardly from the patient support section, a rotatably supported tubular second member having an internal thread which engages the threaded first member and having an external thread, and a further member which is supported on the base and has a thread engaging the external thread on the tubular second member. In one embodiment, the further member is a nut fixedly supported on the base, and a drive member rotatably supported on the base has an opening through which the second member extends and has a key portion which slidably engages an axially extending slot provided in the second member. In a different embodiment, the further member is itself rotatably supported on the base and has therethrough an opening through which the second member extends, the thread on the further member being an internal thread in the opening.

FIELD OF THE INVENTION 
The present invention relates to a mechanism for moving a movable part of a 
hospital bed and, more particularly, to such a mechanism which moves a 
patient support portion of the bed vertically with respect to a base and 
which has a threaded member rotatably driven by a motor and operatively 
engaging a nut. 
BACKGROUND OF THE INVENTION 
Over the years, various arrangements have been developed to effect movement 
of different parts of a mobile hospital bed with respect to each other. 
For example, upward and downward movement of a patient support litter 
relative to a base has been effected with a pair of spaced hydraulic 
cylinders which have the cylinder housings fixedly mounted on the base and 
which have vertically extending piston rods with their upper ends fixedly 
secured to the patient support portion. However, hydraulic arrangements 
tend to drip oil, which creates a mess and which in some cases presents a 
safety problem when the oil ends up on a floor surface where someone may 
slip on it. In order to be competitive in today's marketplace, a hydraulic 
arrangement must usually include both electrically and manually actuated 
pumps, which tends to render the overall hydraulic system rather complex 
and expensive. Further, if the cylinders each have only a single piston, 
then in order for the lowest position of the patient support litter to be 
reasonably low, the lower end of the hydraulic cylinder must be mounted 
relatively close to the floor, which increases the chance it may fail to 
clear an obstruction when the mobile bed is being moved, resulting in 
possible damage to the hydraulic cylinder and/or a need to manually lift 
the bed over the obstruction. 
As a known alternative to hydraulic cylinders, the patient support litter 
is sometimes supported on the base by a scissors mechanism, which may be 
driven by a electric drive mechanism or by a single small hydraulic 
cylinder. In either case, the scissors mechanism has a number of potential 
points at which a finger or other body part could be caught and pinched, 
which can present a safety problem. Also, scissors mechanisms tend to be 
relatively complex and therefore expensive. Further, the vertical space 
required by a scissors mechanism between a patient support litter and a 
base tends to be sufficiently large that it is difficult to achieve a 
design in which the patient support litter can move to a relatively low 
position. 
Beds often have other movable parts, such as a movable knee support section 
of a patient support assembly. Arrangements of this type are usually 
driven by an electric motor, and the most common approach is to fixedly 
support on the bed frame an electric motor having an elongate rotatable 
shaft which is threaded, to support a nut on the shaft for movement 
therealong relative to the frame, and to use a link mechanism to 
operationally couple the nut to the part to be moved. 
An object of the present invention is to provide an electrically driven 
arrangement for effecting relative movement of two parts of a hospital bed 
which is relatively simple in structure and which is cheaper than known 
arrangements, and in particular which is suitable for effecting vertical 
movement of a patient support litter relative to a base. 
A further object is to provide such an arrangement which has no serious 
pinch points and is thus safer than known scissors mechanisms. 
A further object is to provide such an arrangement which, when used to 
movably support a patient support litter on a base, has a minimal vertical 
height in its collapsed position so that the patient support litter can be 
moved to a relatively low position with respect to the base, and which has 
a relatively large range of movement in comparison to known devices. 
A further object is to provide such an arrangement which is durable and 
reliable. 
SUMMARY OF THE INVENTION 
The objects and purposes of the invention, including those set forth above, 
are met according to one form of the invention by providing a bed which 
includes first and second parts, one of the first and second parts being a 
base portion and the other thereof being a support portion for supporting 
a person, and a selectively actuable first arrangement for effecting 
relative vertical movement of the first and second parts, the first 
arrangement including an elongate, vertically extending threaded member 
which is fixedly connected at one end to the first part, a nut rotatably 
supported on the second part and threadedly engaging the threaded member, 
and a second arrangement for selectively effecting rotation of the nut 
relative to the second part. 
A different form of the present invention involves the provision of an 
apparatus which includes first and second parts supported for relative 
movement and an arrangement for effecting relative movement of the first 
and second parts, such arrangement including an elongate member supported 
on the first part, an elongate tube having the elongate member extending 
thereinto, the elongate member and elongate tube being rotatable relative 
to each other about a common axis, the elongate tube being rotatable 
relative to a further member which is supported on the second part so as 
to be held against axial movement with respect to the second part, an 
arrangement responsive to relative rotation of the tube and the elongate 
member for effecting relative lengthwise movement thereof, an arrangement 
responsive to relative rotation of the tube and further member for 
effecting lengthwise movement of the tube relative to the further member, 
an arrangement for effecting rotation of the tube relative to the elongate 
member, and means for effecting rotation of the tube relative to the 
further member.

DETAILED DESCRIPTION 
FIG. 1 is a side view of a mobile hospital bed or stretcher 10. The bed 10 
has a base 12 movably supported in a conventional manner on several 
casters 13, and has a conventional patient support litter 16 vertically 
movably supported on the base 12 by two spaced pedestals 17 and 18. The 
pedestal 18 includes two laterally spaced screw lift mechanisms, one of 
which is visible in FIG. 1, and the pedestal 17 includes a single screw 
lift mechanism which is shown in detail in FIG. 2 and is described in 
detail below. All of the screw lift mechanisms in the pedestals 17 and 18 
are substantially identical, and therefore only the screw lift mechanism 
in the pedestal of FIG. 17 is described in detail. 
Referring to FIGS. 1 and 2, the patient support litter 16 has secured to 
the underside thereof a laterally extending horizontal plate 21. The base 
12 has two laterally spaced upward projections 23, one of which is visible 
in FIG. 1, and a rectangular metal support plate 24 extends between and is 
secured to the upper ends of the portions 23. The plate 24 has in it a 
rectangular opening 27, and a rectangular metal bottom plate 31 is 
provided on the plate 24 with its peripheral edge portions supported on 
top of the plate 24 and its central portion extending across the opening 
27 so as to cover the opening 27. As shown in FIG. 2, a cylindrical metal 
guide portion 32 projects downwardly from the underside of the plate 31, 
and a cylindrical opening 33 extends concentrically and vertically through 
the cylindrical guide portion 32 and plate 31. At the upper end of the 
opening 33 is an annular recess 36 having a diameter greater than that of 
the opening 33, and an annular nut 37 having a helical internal thread is 
disposed in the annular recess 36. The thread on nut 37 projects radially 
inwardly into the opening 33 from a cylindrical surface on the nut which 
has a diameter at least as large as the diameter of opening 33. 
As shown in FIGS. 2 and 3, metal spacer blocks 41 and 42 are provided on 
top of the plate 31 at opposite ends thereof, and a metal top plate 43 
extends between and has its ends supported on top of the spacer blocks 41 
and 42. Several bolts 46 each extend through aligned openings in the top 
plate 43, spacer block 41 or 42, bottom plate 31 and support plate 24, and 
each threadedly engage a nut 47 so as to fixedly secure the plates and 
spacer block together. 
The top plate 43 has a cylindrical metal guide portion 51 projecting 
upwardly from the upper side thereof, and concentrically and vertically 
extending through the guide portion 51 is a cylindrical opening 52 which 
is equal in diameter to and is coaxially aligned with the cylindrical 
opening 33 through the guide portion 32. 
As shown in FIG. 2, an electric motor 56 has a flange 57 which is disposed 
against the underside of the plate 31 near the guide portion 32, the 
flange 57 being fixedly secured to the plate 31 by four bolts 58 which 
extend through holes in the flange and engage threaded holes in the plate 
31. The motor 56 is a conventional and commercially available reversible 
motor. The motor 56 has an upwardly projecting rotatable shaft 61 which 
extends concentrically through a vertical opening 62 in the plate 31, the 
opening 62 having a diameter larger than that of the shaft 61. A pinion 63 
is fixedly secured to the upper end of the shaft 61, the axial length of 
the pinion being slightly less than the distance between the plates 31 and 
43 so that the pinion 63 can rotate between the plates with no significant 
frictional engagement therewith. 
An idler gear 66 disposed between the plates 31 and 43 also has an axial 
length slightly less than the distance between the plates, the idler gear 
66 being rotatably supported on a vertically extending cylindrical pin 67 
having its ends disposed in blind holes in the plates 31 and 43. The idler 
gear 66 has teeth which meshingly engage teeth on the pinion 63. 
Also disposed between the plates 31 and 43 is a drive gear 71 which has a 
substantially larger diameter than either the pinion 63 or idler 66, the 
drive gear 71 having an axial length which is slightly less than the 
distance between the plates 31 and 43 so that it can rotate therebetween 
with minimal friction. The drive gear 71 has teeth on its periphery which 
meshingly engage the teeth on the idler gear 66. The drive gear 71 also 
has a cylindrical central opening 73 extending vertically therethrough, 
the opening 73 being equal in diameter to and being coaxially aligned with 
the openings 33 and 52 in the guide portions 32 and 51. The drive gear 71 
also has in one side of the central opening 73 a rectangular axial groove 
74 which serves as a keyway. 
An elongate, cylindrical, tubular outer screw member 77 is made of metal 
and has a helical thread 78 extending along its outer surface. The outside 
diameter of the screw member 77, including the thread, is slightly less 
than the diameters of the openings 33 and 52 in the guide portions 32 and 
51, so that the screw member 77 can move axially within the openings 
without significant friction and with negligible radial play. The outer 
screw member 77 extends through the openings 33 and 52, and the thread 78 
thereon engages the thread of the nut 37. The screw member 77 has in an 
external surface thereof an axially-extending slot 81 (FIG. 3) of 
rectangular cross section. A rectangular metal key 82 is provided between 
the plates 31 and 43 in engagement with the keyway 74 in drive gear 71 and 
the slot 81 in outer screw member 77. The key 82 is held against axial 
movement by the plates 31 and 43, but is axially slidable within the slot 
81 in the outer screw member 77. Although the key 82 is a separate 
structural part in the preferred embodiment, it will be recognized that it 
could alternatively be an integral part of the drive gear 71. 
A central opening 83 through the outer screw member 77 is cylindrical, and 
an annular rectangular groove 86 is provided in the surface of the opening 
83 at a location spaced from the upper end of outer screw member 77 by a 
distance which is approximately a quarter of the axial length of the 
member 77. A sleeve-like nut 87 is disposed within the groove 86, a 
helical internal thread on the nut 87 projecting radially inwardly into 
the opening 83 from an inner surface of the nut which has a diameter equal 
to or slightly greater than the diameter of the opening 83. 
The outer screw member 77 also has an annular groove 88 provided in the 
exterior surface thereof at a location spaced a short distance above the 
lower end of member 77. An annular ring 89 is disposed in the groove 88, 
the outer diameter of the ring 89 preferably being slightly greater than 
the outer diameter of the thread 78 on member 77, so that the ring 89 
rather than the thread slidably engages the inner surface of opening 33. 
In the preferred embodiment, the ring is made of polytetrafluoroethylene 
(which is commonly referred to with the trademark Teflon), but there are 
other materials which would also be suitable. 
An elongate, cylindrical, inner metal screw member 92 has a helical thread 
93 extending along an exterior surface thereof, the outside diameter of 
the screw member 92, including thread 93, being slightly less than the 
diameter of the central opening 83 through the outer screw member 77, so 
that the screw member 92 can move axially within the opening 83 without 
significant friction and with negligible radial play. The inner screw 
member 92 extends within the central opening 83 in the outer screw member 
77, the helical thread 93 engaging the thread on nut 87. An annular groove 
96 is provided in the exterior surface of the inner screw member 92 a 
short distance above the lower end thereof, and an annular ring 97 is 
disposed within the groove 96, the ring 97 preferably being made of the 
same material as the ring 89. The outside diameter of the ring 97 
preferably is slightly larger than the outside diameter of the thread 93 
on the screw member 92. 
At the upper end of the screw member 92 is an upwardly tapering 
frustoconical surface 101. A metal fitting 102 has a cylindrical stem 103 
with a diameter substantially equal to the outside diameter of the thread 
93 on the inner screw member 92, and has at the upper end of the 
cylindrical stem 103 a radially outwardly projecting annular flange 106. 
The stem 103 extends through a circular opening 107 provided in the plate 
21 of the frame 16 (FIG. 1), the diameter of the hole 107 being 
approximately equal to the diameter of the stem 103. The flange 106 is 
disposed against the upper surface of the plate 21, and is fixedly secured 
thereto by a welding bead 108. Extending into the fitting 102 from a lower 
end of the stem 103 is an upwardly tapering frustoconical hole 111 which 
receives the frustoconical upper end of the inner screw member 92. A screw 
112 has a shank extending downwardly through a central opening in the 
fitting 102 and threadedly engaging a vertical threaded hole 113 provided 
in the upper end of the inner screw member 92. Thus, the screw 112 and 
fitting 102 rigidly secure the inner screw member 92 to the plate 21 and 
prevent relative rotation therebetween. 
An alternative embodiment of the inventive apparatus is shown in FIG. 5. In 
most respects, the embodiment of FIG. 5 is identical to the embodiment 
just described, and thus only the differences are described in detail. 
Components in FIG. 5 which correspond directly to components in FIGS. 1-4 
are identified with the same reference numerals. 
The embodiment of FIG. 5 lacks a nut equivalent to that shown at 37 in FIG. 
4, and lacks a key equivalent to that shown at 82 in FIG. 4. Instead, the 
drive gear 171 in FIG. 5 has therethrough a central opening 172 which is 
threaded and which directly cooperates with the helical thread 178 on the 
outer screw member 177. In addition, the outer screw member 177 has an 
annular groove provided in the exterior surface thereof a short distance 
below its upper end, and disposed in the annular groove 184 is an annular 
ring 185. The annular ring 185 is preferably made of the same material as 
the annular rings 89 and 97. The outer diameter of the annular ring 185 
preferably is slightly greater than the outer diameter of the thread 178 
on outer screw member 177. 
OPERATION 
Assume that, with the various illustrated components in the operational 
positions of FIG. 2, the motor 56 is energized in a manner effecting 
rotation of the shaft 61 is a forward rotational direction. The pinion 63 
rotates with the shaft 61 and rotates the idler gear 66, which in turn 
rotates the drive gear 71. The key 82 causes the outer screw member 77 to 
rotate synchronously with the drive gear 71, and the rotation of the outer 
screw member 77 relative to nut 37 causes the outer screw member 77 to 
move upwardly relative to the nut 37, gear 71 and plates 31 and 43. As the 
outer screw member 77 moves upwardly, the key 82 slides within the 
lengthwise slot 81 in the outer screw member 77. 
Meanwhile, since the inner screw member 92 is fixedly held against rotation 
relative to the plate 21 by the screw 112 and fitting 102, the outer screw 
member 77 and the nut 87 thereon necessarily rotate relative to the 
stationary inner screw member 92. The relative rotation between nut 87 and 
inner screw member 92 causes the inner screw member 92 to move upwardly 
relative to the rotating outer screw member 77. In short, while the outer 
screw member 77 is moving upwardly relative to the gear 71 and plates 43 
and 31, the inner screw member 92 is simultaneously moving upwardly 
relative to the outer screw member 77. Thus, the litter 16 (FIG. 1) is 
moved upwardly relative to the base 12 of the bed 10. If at some point the 
motor 56 is stopped, rotational movement of the outer screw member 77 and 
vertical movement of the inner and outer screw members 77 and 92 will 
halt, thereby maintaining the spacing between the litter 16 and base 12 
which was present at the point in time when the motor stopped. 
Alternatively, if the motor continues to run, then as shown in FIG. 4 the 
ring 89 on the outer screw member 77 will eventually reach the nut 37 and 
the ring 97 on inner screw member 92 will eventually reach the nut 87. 
Since the rings 89 and 97 have diameters large enough to physically 
prevent them from moving into the nuts, rotation of the outer screw member 
77 is forcibly halted in the position shown in FIG. 4 in order to prevent 
the telescoping lift mechanism from becoming overextended. It will be 
noted that, in this position, approximately 1/4 to 1/3 of the inner screw 
member 92 is still disposed within the upper end of the outer screw member 
77, and approximately 1/4 to 1/3 of the outer screw member 77 is disposed 
within the guide arrangement defined by the guide portions 32 and 51. 
Thus, even in the extended position of FIG. 4, there is little or no 
radial play between the inner screw member 92 and the outer screw member 
77, and likewise there is little or no radial play between the outer screw 
member 77 and the guide portions 32 and 51. Consequently, the litter 16 is 
steadily supported on the base 12 with no significant play or wobble. 
In order to lower the litter 16 relative to the base 12, the motor 56 is 
simply energized so that the shaft 61 rotates in a reverse direction, and 
the illustrated structure telescopically contracts in a manner opposite 
but analogous to the above-described telescopic extension thereof. The 
motor 56 can be stopped at any point. If it continues to run, the plate 21 
will eventually engage the upper end of the guide portion 51 as shown in 
FIG. 2 in order to forcibly halt movement of the screw members 77 and 92. 
It will be recognized that the groove 88 and ring 89 could be omitted in 
the embodiment of FIGS. 1-4. Since the screw members 92 and 77 move 
synchronously, engagement of the ring 97 with the nut 87 will halt 
rotation of screw member 77 and thus halt axial movement of both of the 
screw members 92 and 77. It would also be possible to omit the ring 97 and 
groove 96, in which case the inner screw member 92 would stop moving 
upwardly when its lower end reached the top of nut 87, there being enough 
remaining axial overlap of the members 92 and 77 to keep the member 92 
properly vertically supported by member 77. Likewise, the outer screw 
member 77 would stop moving upwardly when its lower end reached the top of 
nut 37, and then the guide portion 51 would continue to maintain the 
member 77 in a proper vertical orientation. 
Turning to the alternative embodiment of FIG. 5, the operation is slightly 
different from that just described for the embodiment of FIGS. 1-4. In 
particular, when the drive gear 171 is rotated in a direction which will 
extend the telescoping screw members, the inner screw member 92 and outer 
screw member 177 tend to move sequentially rather than simultaneously. 
Depending on frictional characteristics in the engagement of the various 
threaded portions within the system, the outer screw member 177 may 
initially rotate with the drive gear 171, during which rotation the outer 
screw member 177 does not move upwardly relative to the drive gear 171. 
However, this rotation of the outer screw member 177 causes the nut 87 
thereon to rotate relative to the stationary inner screw member 92, so 
that the inner screw member 92 moves upwardly relative to the outer screw 
member 177. Eventually, the annular ring 97 on the inner screw member 92 
will engage the nut 87 and prevent further rotation of the outer screw 
member 177 relative to the inner screw member 92. Thereafter, since the 
outer screw member 177 does not rotate, the drive gear 171 rotates 
relative to the outer screw member 177, which causes the outer screw 
member 177 to move upwardly. If the motor continues to run, the annular 
ring 89 will eventually engage the drive gear 171 in order to forcibly 
halt upward movement of the outer screw member 177. 
Alternatively, if the frictional characteristics are such that the drive 
gear 171 initially does rotate relative to the outer screw member 177, the 
outer screw member 177 will move upwardly relative to the drive gear 171 
without rotating. Eventually, the annular ring 89 will engage the drive 
gear 171 and thereby force the outer screw member 177 to stop moving 
upwardly and to begin rotating with the drive gear 171. This rotation of 
the outer screw member 177 causes the nut 87 thereon to rotate around the 
stationary inner screw member 92, and thus the inner screw member 92 will 
move upwardly relative to the outer screw member 177. Eventually, the 
annular ring 97 will engage the nut 87 and thus forcibly halt movement of 
the illustrated components. 
In order to telescopically collapse the structure illustrated in FIG. 5, 
the motor is operated in an opposite direction and the components will 
return to their original positions in a manner opposite but analogous to 
that described above for telescopic extension thereof. Again, depending on 
frictional characteristics, the outer screw member 177 may initially move 
downwardly relative to the rotating drive gear 171 until the annular ring 
185 engages the drive gear 171, after which the inner screw member 92 will 
move downwardly relative to the outer screw member 177 until the plate 21 
engages the upper end of the outer screw member 177. Under different 
frictional characteristics, the outer screw member 177 may initially 
rotate with the rotating drive gear 177 so that it does not move 
downwardly but instead the inner screw member 92 moves downwardly relative 
to the outer screw member 177 until the plate 21 engages the upper end of 
outer screw member 177, after which the outer screw member 177 will be 
held against rotation and thus will move downwardly relative to the 
rotating drive gear 171 until the annular ring 185 engages the drive gear 
171 and halts movement of the illustrated components. 
Two preferred embodiments of the present invention have been disclosed in 
detail for illustrative purposes, but it will be recognized that there are 
variations and modifications of the disclosed mechanisms, including the 
rearrangement or reversal of parts, which lie within the scope of the 
present invention.