Net bed

A bed comprises a flexible web, preferably of mesh or net form, on which a patient is supported and which is slung between two parallel shafts. The ends of the web are respectively wound on to the two shafts which can be turned by end winding handles through drive clutch/brake units of the shafts. At the other ends the shafts have plain bearing assemblies. The drive units are non-rotatably received in support crutches of a frame of the bed, and these crutches can pivot about inclined axes in the manner of the rowlocks of a rowboat. The bearing assemblies are received in fixed crutches formed to allow a permissible range of angularity of the shafts in these crutches when removed from the drive end crutches. Each end of each shaft is retained captive to the frame by a chain or cord of length such that if a shaft is lifted out of the support crutch at one end and lowered to hang on the corresponding cord, while remaining in the crutch at the other end, the shaft is constrained so that the lowering movement lies inside an arc which limits the angularity of the shaft to within a permissible range thereof.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to beds of the type in which a patient is supported 
on a flexible web slung between two generally parallel shafts on to which 
the ends of the web are respectively wound. Thus the shafts can be turned 
in the same direction to transfer the web from one shaft to the other, 
enabling a patient lying on the web to be rolled over for repositioning 
thereon, or they can be turned in opposite directions to raise or lower 
the patient with respect to a conventional mattress or other support 
surface below the web. 
2. Description of the Prior Art 
When the web is of web or net form, as disclosed in U.K. Pat. Specification 
No. 1447163 and U.S. Pat. Specification No. 3905055, such a bed is 
particularly valuable in the prevention and treatment of bed sores. Beds 
of the type concerned are hereinafter referred to generally as "net beds" 
which term where appropriate is to be considered broadly to include a 
flexible web of any form, i.e. not necessarily mesh or net form although 
this is normally preferred. 
Net beds are in general use as attachments for existing hospital beds, 
comprising support framework with four spaced support crutches for the 
rotatable shafts which can normally be lifted out of the crutches so as to 
hang down at the sides of the bed. In U.S. Pat. No. 4,270,234 there is 
disclosed such a net bed arrangement with a collapsible framework which is 
universal, in the sense that it can be used with almost any existing bed 
without the addition of special fittings or adaptors and even without the 
employment of tools. 
With existing beds it is possible for the framework to be damaged if a 
shaft is not lifted "cleanly" out of its two support stirrups. When it is 
engaged only at one end, as may happen when lifted with one hand, it 
functions as a lever which enables very considerable and damaging twisting 
moments to be applied to the stirrup with which it is still engaged, and 
this can seriously damage and distort the framework. 
SUMMARY OF THE INVENTION 
The object of the invention is to provide a shaft and stirrup arrangement 
in which a shaft can be disengaged and lowered at only one end without 
damage to the framework. 
To this end, according to the invention, the shafts of a bed of the type 
concerned each have bearing assemblies demountably supported in spaced 
support crutches of a framework of the bed so as to have at each crutch an 
available permissable range of angular movement. Each end of each shaft is 
held captive with respect to the framework, by means of a chain, cord or 
the like of such length that when one end of a shaft is lifted out of a 
corresponding support crutch and lowered so as to hang freely on the 
corresponding chain or cord it is constrained to move inside an arc such 
that the resultant angular movement at the other end of that shaft, with 
the latter remaining in its associated support crutch, lies within said 
permissible range. 
In the bed disclosed in said U.S. Pat. No. 4,270,234 each shaft comprises 
an assembly including end fittings providing the bearing assemblies. At 
one end a plain bearing assembly has an annular plain bearing member which 
engages directly in a support crutch, whereas the other end fitting is a 
combined bearing and drive clutch/brake unit with a non-circular housing 
which nonrotatably engages in the corresponding crutch. A generally 
similar shaft assembly arrangement can suitably be employed in a bed 
according to the present invention, all that is necessary being to form 
the bearing member, drive housing and/or crutches to provide said 
permissible range of free angular movement. 
So far as the non-drive end of each shaft is concerned the premissible 
range of angular movement can easily be achieved by forming said bearing 
member with adequate clearance relative to the corresponding crutch. 
However, at the drive end it is preferably achieved by suitable formation 
or mounting of the crutch so that the drive housing in the operative shaft 
position remains a good non-rotational fit within the crutch to avoid 
fretting of the engaged surfaces. This can, for example, be achieved in 
simple fashion by using a crutch which is rotatably mounted in the 
framework much in the manner of a rowlock of a rowboat. 
Other features of the invention will be apparent from the following 
description, drawings and claims, the scope of the invention not being 
limited to the drawings themselves as the drawings are only for the 
purpose of illustrating a way in which the principles of the invention can 
be applied. Other embodiments of the invention utilising the same of 
equivalent principles may be used and structural changes may be made as 
desired by those skilled in the art without departing from the present 
invention and the purview of the appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
The net bed illustrated comprises a flexible web 1 of mesh or net form 
slung between two parallel winding shaft asssemblies 2 and 3 on to which 
the ends of the net 1 are respectively wound as clearly shown in FIGS. 1 
and 2. A collapsible support frame 4 which is mainly of tubular 
construction provides spaced support crutches 5 and 6 at one end of the 
frame and similarly spaced support crutches 7 and 8 at the other end of 
the frame. The adjacent ends of the shaft assemblies 2 and 3 are 
respectively supported in these crutches and the frame 4 can be used 
either, as shown in FIG. 1, supported on the base 9 of a conventional bed 
below the mattress (not shown) thereof or in free-standing form as shown 
in FIG. 2. The frame 4 has bottom cross members 10 which in the former 
case, as shown in FIG. 1, extend across and support the net bed on the 
base 9. 
The shaft assemblies 2 and 3 each comprise a tubular shaft member, around 
which the corresponding end of the net 1 is wound, extending between end 
fittings 11, 12 or 13, 14. Each of the end fittings 12 and 14 includes a 
winding handle 15 by which the shaft is turned through a drive 
clutch/brake unit 16 or 17. The units 16 and 17 have housings of square 
external profile so as to engage non-rotatably in the corresponding 
support crutches 5 and 6. The shaft assemblies 2 and 3 are handed in the 
sense that they can only be fitted, respectively, at the left-hand and 
right-hand sides of the frame 4. To this end the housings of the units 16 
and 17 are of different size so that the larger one thereof can only be 
fitted in the correct support crutch 5 or 6. 
The end fittings 11 and 13 are identical and each comprises an annular 
plain bearing member which rests in the corresponding support crutch 7 or 
8 and allows free rotation of the corresponding shaft when the associated 
handle 15 is turned. The end fittings 11, 12, 13 and 14 of the shaft 
assemblies 2 and 3 and the end support crutches 7 and 8 are generally as 
described in detail in said U.S. Pat. No. 4,270,234, to which reference 
should be made if further detailed description is required. The end 
fittings 11 and 13 rest loosely in the support crutches 7 and 8 so as to 
allow either of the end fittings 12 or 14 to be lifted out of the support 
crutch 5 or 6 and lowered to an inoperative side position in which it 
hangs down at the side of the frame 4 on a length of cord 18 or 19 by 
which the corresponding end of the shaft assembly concerned is held 
captive to the frame 4. The fit of the end fittings 11 and 13 in the 
support crutches 7 and 8 is such as to accommodate the angularity of a 
shaft assembly as it is lifted out of the corresponding support crutch 5 
or 6 and lowered so as to hang on the corresponding cord 18 or 19 without 
a damaging twisting moment being applied to the corresponding end support 
crutch 7 or 8 by the lever which the corresponding shaft provides. 
The end fitting/support crutch arrangements at the other end of the frame 4 
are also such as to accommodate the angularity of the shaft assemblies 2 
and 3 if they are lifted out of the corresponding support crutches 7 and 8 
and lowered on the attachment cords 20 shown in FIG. 1. However, in view 
of the drive/brake function performed by the end units 16 and 17 these 
cannot be a fit such as to allow the required angular movement within the 
support crutches 5 and 6 themselves if fretting of the housings is to be 
avoided. Accordingly the support crutches closely receive the fitting 
rectangular housings of the drive/brake units 16 and 17 and are rotatably 
mounted in corner fittings 21 of the frame 4 in the manner of a rowlock of 
a rowboat. This, and the carefully chosen lengths of the cords 18, 19 and 
20 are the important features of difference of the arrangement as compared 
with the otherwise functionally similar arrangement disclosed in said U.S. 
Pat. No. 4,270,234. 
The novel crutch arrangement is illustrated in detail in FIGS. 2 to 5 of 
the drawings, the support crutch 6 here being illustrated. The crutch has 
a rectangular support recess 22 which closely receives the rectangular 
housing 17a of the corresponding unit 17 (shown in broken lines in FIG. 
3). Apart from the "handed" size of this recess 22 the crutches 5 and 6 
are identical. The crutch 6 has a pivot spindle 23 which is rotatably 
received in a bearing bush 24 in the corresponding angular corner fitting 
21 of the frame 4. Axial retention is achieved by a location washer 25 
fixed to the end of the spindle 23 by a retaining bolt 26 which engages a 
central screw-threaded blind bore 27 in the spindle 23. A thrust bearing 
washer 28 is fitted between the crutch 6 and the fitting 21, and another 
such washer 29 is fitted between the fitting 21 and the washer 25. 
The corner fitting 21 is of symetrical form with two mutually inclined and 
projecting limbs 30 and 31 which are bored out to receive, respectively, a 
top frame tube member 32, which in the frame 4 directly interconnects the 
two corner fittings 21, is disposed horizontally providing an inclined 
pivot axis 34 for the crutch 6, this axis being inclined at an angle of 
about 55.degree. to the horizontal. 
As shown in the detail views of FIGS. 4 to 6 the crutch recess 22 is 
defined by flat parallel side faces 35 and a flat bottom face 36 so that 
the housing 17a of the corresponding unit 14 is closely received and seats 
firmly in the support crutch 6 without any relative fretting movement when 
the corresponding handle 15 is turned. 
FIG. 7 illustrates a modification which provides a preset degree of 
frictional loading to the pivot bearings of the support crutches 5 and 6. 
As compared with the view of FIG. 3, FIG. 7 shows that the modification 
introduces a "wavy" spring washer 40 between the location washer 25 and 
the thrust washer 29. This washer 40 is under axial preload such as to 
provide a preset fictional restraint in the bearing so that the crutch 6 
(or 5) does not spin freely and hence stays where it is placed. This 
assists fitting of a shaft assembly, leaving a nurse fitting up the bed 
with both hands free to handle each shaft assembly as it is fitted. To 
control the axial preload of the washer 40, the extended spindle 23 of the 
crutch has a reduced diameter end extension, providing a step 41 against 
which the washer 40 seats and is held by the washer 25. The washer 40 may 
be of beryllium copper with thrust washers 28 and 29 of nylon, for example 
.