Note: Descriptions are shown in the official language in which they were submitted.
7~14~
F'IELD OF THE INVEMTION
The invention rela-tes to a caster swivel lock
device for preventing swiveling of a caster relative to the
leg of the equipmen-t -to which it is attached, and to a
locking caster which incorporates such device.
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BACKGROUND OF THE INVENTION
Casters for mobile equipment, especially hospitalbeds, normally consist of a wheel housing for receiving a
wheel, a stem for insertion in-to a leg socket, and a
swiveling mechanism which enables the wheel housing to
swivel rela-tive -to -the leg of the hospi-tial bed or o-ther
piece of mobile equipmen-t. Casters exist which contain a
~` brake mechanism enabling both the swivel and wheel movement
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` to be simultaneously locked or unlocked by a simple foot
operation. However, it has been found that swivel movement
can s-till occur under certain circumstances, despite the
action of such brake mechanism, because in some cases, -the
stem rotates relative -to the socket in the -tubular leg of
the mobile equipment, causing swiveling of the entire
~caster. The inevltable result lS tha-t injuries occur when,
for~example, pa-tients lean against hospital beds or attempt
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to climb into ~'locked" hospital beds, assuming -tha-t the bed
will remain stationary.
To overcome this problem, some manufacturers
cross-drill the stem. However, this solution requires
cus-tomers to inser-t a fastener through the hole in the stem,
which is inconvenient. A second solution involves
manufacturing a special key-way stem which is designed to
mate with a matching socket having a key protruding into the
centre thereof. The problem with this approach, however, is
that the circular s-tems and sockets are common to the trade,
with bed manufacturers providing the sockets, so customers
are not amenable to purchasing a caster with a stem that
requires a special socket. Also, a square stem could be
used to prevent the unwanted rotation, but again, this would
require a depar-ture from the standard socket having a
circular aperture therein.
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~ 20 SUMMARY OF THE INVENTION
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The present invention provides a swivel lock
device ~or use with locking casters which are installed on
~ ~the tubular legs of~mobile platforms. Such tubular legs
: ~ 25 ~ typically have inserted therein a socket having a
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non-circular flange extending from the bottom of the tubular
leg, each socke-t being provided with an axial aperture of
circular cross-section. Typical locking casters include a
wheel housing for receiving a wheel rotatable about a
horizontal axis, swiveling means coupled to -the top of the
wheel housing for enabling the wheel housing to swivel about
a vertical axis, and brake means for preventing the wheel
from rotating and the wheel housing from swiveling. The
subject swivel lock device comprises a stem rigidly coupled
to the swiveling means so as to extend along the aforesaid
ver-tical axis, -the stem having an upper portion shaped and
dimensioned for insertion into the socket aperture, and
interlocking means comprises a plate rigidly secured to the
- stem having coupling means for coupling the pla-te to the
; outer edges of socket flange so as to prevent the plate from
rotating rela-tive to the socket flange. The plate is
preferably secured to the stem by means of an aperture
therein configured for mating wi-th a portion of the stem of
non-circular cross-sectlon.
` In a preEerred embodiment, the stem has one flat
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on it, and the pl`ate has a D-shaped opening which mates with
the flat on the stem and two pairs of diametrically opposed
.~ ~ locking ears which curve upward to engage the edge of -the
socket flange. The plate thus engages both the stem and the
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socke-t, when the socket is inserted into a hollow tubular
leg of a mobile platform, thereby preven-ting rotation of the
stem relative to -the socket when the brake means is
deployed. As a result, swiveling of the caster relative to
5 the leg of -the mobile platform is prevented, when the caster
~: is locked.
BRIEF DESCRIPTION OF THE DRAWINGS
1 0
The invention will now be described by way of
example only, with reference to the following drawings, in
which like numerals refer to like parts, and in which;
:
Figure l is a side view of a caster embodying the
swivel lock device of the present invention, shown ins-talled
on a tubular leg;
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Figure 2 is a cross-sectional view of a caster
(without wheel) incorporating the subject swivel lock
" device; and
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Figure 3 is an exploded perspective view of the
: subject invention.:
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7~14;3
DETAILED DESCRIPTION OF THE PREF_RRED E BOnIMENT
Referring firs-t to Figures 1. and 2, il.lustra-ting
: -the caster oE -the present invention, caster 10 comprises a
wheel housing 12 having an axle aperture 14 for receiving an
axle 16 and wheel 18 rota-table about a horizontal axis, a
s-tem 20 for insertion in-to a socket 22 of leg 24, swiveling
means shown generally as 26, a brake mechanism shown
- generally as 28, and interlocking plate 30. Swiveling means
.~ 10 26 comprises upper raceway 32 and lower raceway 34, bo-th of
which are rigidly secured to s-tem sleeve 36, two sets of
ball bearings 38, 40, and raceway cover 42. Ball bearings
38, 40 ride against wheel housing flange 44, and stem 20 is
orbit riveted to the base of s-tem sleeve 36. The result is
1.5 that stem 20 is capable of swiveling freely relative to
wheel housing 12 about a vertical axis. Brake mechanism 28
comprises brake pedal 45 and brake arm 46 having protrusions
48 for bearing against the tire of wheel 18 and a -tang 50
~ for engaging with peripheral slots 52 in the bottom surface
: 20 of lower raceway 34. When brake mechanism 28 is activated
;` by depressing brake pedal 45, protrusions 48 prevent
rotation of the wheel, while tang 50 simul-taneously prevents
swiveling of wheel housing 12 relative to lower raceway 34.
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~ 25 The subject swivel lock device comprises stem 20
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and lnterlocking plate 30. The other componets of caster 10
are conventional.
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Referring now to Figures 2 and 3, stem 20 has an
upper por-tion 2l dimensioned to fit in-to a standard socket
and a lower portion 23 of smaller diameter dimensioned to
fi-t into stem sleeve 36. Upper portion 21 of stem 20 is
provided with a grip ring 54 for preventing stem 20 from
falling out of socket 22 and a circumferen-tial flat 58 for
ma-ting wi-th interlocking plate 30. Flat 58 preferably
extends only par-t way up upper portion 21 of stem 20. The
height of fla-t 58 is preferably approximately equal to the
thickness of plate 30, so tha-t plate 30 will be snugly
sandwiched between upper por-tion 21 of stem 20 and the top
of stem sleeve 36 during assembly.
As best shown in Figure 3, interlocking plate 30
has a centrally located D-shaped aperture 60, and four
upwardly curving peripheral portions in the form of equally
~ spaced locking ears 62. The D-shaped aperture 60 of
;~ interlocking plate 30 is configured and dimensioned to mate
,
~j wi-th flat 58 of stem 20. Locking ears 62 are configured to
:~ 20 engage the outside edges of square flange 64 of socket 22.
; Interlocking plate 30 is slipped onto stem 20 before the
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stem 20 is passed through the stem sleeve 36 and riveted
together with the bottom of stem sleeve 36 to lower raceway
34. It should be apparent that when stem 20 is inserted
into socket 22, socket flange 64 is engaged by locking ears
~ 62 of interlocklng plate 30. Consequently, when an attempt
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7~43
is made -to rotate stem 20, lock:ing ears 62 bind against the
corners of socket flange 62, thus preven-ting plate 30 from
rotating rela-tive to socket flange 64.
In operation, a cas-ter 10 is attached to a
hospital bed or other mobile equipment having tubular legs
24 of square cross-section, by firs-t inserting a s-tandard
square socket 22 into the bot-tom of a leg. The upper
portion 21 of stem 20 is then inserted into the circular
aperture of socket 22. Once installed, -the stem 20 is
prevented from swiveling rela-tive to socket 22 when a torque
is applied to the stem, since locking ears 62 of
interlocking plate 30 bind against the corners of socket
flange 64, preven-ting plate 30 from rota-ting relative to
flange 64. Thus, when brake mechanism 28 is deployed, there
is no opportunity for the swiveling of stem 20 relative to
socket 22j as socket 22 and stem 20 are firmly interlocked
by interlocking plate 30.
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The upper portion 21 of -the stem 20 is dimensioned
to be lnserted into a socket~22 wlth a circular aperture of
standard diameter. However, the diameter of the stem 20
could be varied so that it can be fltted to sockets having
non-standard apertures.
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Whi]e the preferred embodimen-t of -the invention
includes a s-tem having a single flat, -the cross-sec-tion of
stem 20 at the bo-t-tom of upper portion 21 could assume some
other non-circular shape, provided -tha-t aperture 60 of plate
30 is shaped to mate -therewith. For example, stem 20 could
be provided with two or more flats, e.g. a pair of
diametrically opposed flats, in which case, interlocking
plate 30 would have to be provided with an aperture
configured to mate with such flats, having two straight
sides. Also, the fla-t could extend the en-tire length of
stem, or the plate could be secured to the stem by other
means, such as spot welding or by matching -threads, although
a single flat on stem 20 and a matching aperture in plate 30
are believed to be the simplest and least expensive means of
securing plate 30 to stem 20.
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Interlocking plate 30 is preferably stamped from a
~,! round washer. However, there are a number of alternative
ways of making such plate. For example it could be die
cast, or formed from a pair of criss-crossed welded-together
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~ ~ metal s-trips, having up-turned edges configured to conform
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that plate 30 be made from metal, it could be made of molded
plastic.
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It will -thus be apparen-t to those skilled in the
; art that while the subject invention as been described and
illus-trated with respect to various preferred and
alternative embodiments, various modifications of these
embodiments may be made withou-t departing from the subject
inven-tion, the scope of which is defined in -the appended
claims.
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