U.S. patent number 3,890,907 [Application Number 05/409,360] was granted by the patent office on 1975-06-24 for vertically adjustable overbed table.
This patent grant is currently assigned to Joerns Furniture Company. Invention is credited to Warren J. Peterson.
United States Patent |
3,890,907 |
Peterson |
June 24, 1975 |
Vertically adjustable overbed table
Abstract
A vertically adjustable overbed table including a pedestal, a
horizontal table top mounted at the top of the pedestal and a
horizontal roller-equipped base platform at the lower end of the
pedestal. The pedestal includes an upper outer column which
telescopes over a lower inner column, and a pair of constant force
springs which are mounted within the columns to maintain the
telescoping columns in equilibrium. A clutch assembly is mounted
within the top of the upper column which includes a rotatable
clutch drum, a clutch spring around the clutch drum and a rotatable
spool wound with cable, the spool being connected to the clutch
drum so that both rotate together. A depending loop is formed at an
intermediate portion of the table which engages a pulley wheel at
the lower end of a vertical shaft extending below the clutch
assembly within the columns. One point of the depending cable is
rigidly affixed to the inner column so that the two columns can be
moved telescopically only when the cable spool is free to rotate to
pay out and take up equal amounts of cable. Lever means are
provided for releasing the tension on the clutch spring so that the
clutch drum and the spool are free to rotate so that the table can
be lowered. An override assembly is also provided in conjunction
with the clutch spring which releases the clutch spring tension
when a sufficient downward force is placed on the table top so that
the table top can be lowered without utilizing the tension
releasing lever means. The table top can be raised by exerting an
upward force on the table top sufficient to overcome the
equilibrium effect of the constant force spring.
Inventors: |
Peterson; Warren J. (Stevens
Point, WI) |
Assignee: |
Joerns Furniture Company
(Stevens Point, WI)
|
Family
ID: |
23620142 |
Appl.
No.: |
05/409,360 |
Filed: |
October 24, 1973 |
Current U.S.
Class: |
108/136; 108/146;
248/571 |
Current CPC
Class: |
A47B
23/046 (20130101); A47B 9/02 (20130101); A47B
2023/047 (20130101) |
Current International
Class: |
A47B
9/00 (20060101); A47B 23/00 (20060101); A47B
23/04 (20060101); A47B 9/02 (20060101); A47b
009/02 () |
Field of
Search: |
;108/146,144,136
;248/162,412,337,336 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Parsons, Jr.; Marion
Assistant Examiner: Marquette; Darrell
Attorney, Agent or Firm: Price, Heneveld, Huizenga &
Cooper
Claims
The embodiments of the invention in which an exclusive property or
privilege is claimed are defined as follows:
1. A vertically adjustable overbed table comprising:
a pedestal, a horizontal table top mounted at the top of said
pedestal and a base platform at the lower end of said pedestal;
said pedestal including an outer column and an inner column, said
outer column telescopically engaging said inner column and being
adapted for vertical telescoping movement with respect to said
inner column; at least one spring means associated with said
columns for maintaining the telescoping movement of said outer
column and said inner column in approximate equilibrium; and a
clutch assembly mounted within said pedestal;
said clutch assembly including a rotatable clutch drum, means for
rotating said drum during telescopic movement of said columns, a
tensioned clutch spring means surrounding said drum for permitting
upward movement of one of said columns with respect to the other of
said columns when an upward force is exerted thereon sufficient to
overcome the equilibrium effect of said constant force spring and
for permitting downward movement of said one column with respect to
said other column only when the tension of said clutch spring is
released; and means for releasing the tension of said clutch
spring.
2. The overbed table according to claim 1 wherein said outer column
is affixed to said table top, wherein said inner column is affixed
to said base and wherein said clutch assembly is mounted within
said outer column and comprises a horizontally mounted rotatable
clutch drum; a tensioned helical coil spring around said drum; a
horizontally mounted rotatable cable spool adjacent said clutch
drum and connected thereto so as to be rotatable therewith and only
therewith; a cable having its ends wound around said spool in
opposite directions, the ends of said cable being affixed to said
spool and an intermediate portion of said cable extending below
said spool to form a depending cable loop and an intermediate point
of said cable loop being affixed to said inner column; a rigid
member depending within said columns and attached at its upper end
to an upper portion of said outer column and having a pulley wheel
at the lower end thereof receiving said depending cable loop,
whereby said outer column can be telescoped downwardly over said
inner column when a downward force is placed on said outer column
only when said clutch spring tension is released and said spool is
free to rotate to take up cable above said intermediate point of
said depending cable loop and to pay out an equal amount of cable
below said intermediate point of said depending cable loop.
3. The overbed table according to claim 2 wherein one end of said
clutch spring extends outwardly from said spring coil and wherein
said means for releasing the tension on said clutch spring
comprises a trip plate reciprocally mounted on said outer column;
said trip plate having a finger-like extension in engagement with
said one end of said clutch spring so that when said trip plate is
moved in a first direction said clutch spring tension is released
so said table top can be lowered.
4. The overbed table according to claim 3 wherein at least one
upwardly spring-biased lever arm is pivotally mounted on said outer
column adjacent said trip plate and in engagement therewith so that
when said lever arm is depressed downwardly said trip plate will
release the clutch spring tension.
5. The overbed table according to claim 4 which includes a pair of
said lever arms each extending outwardly from said outer column to
opposite sides of said table top.
6. The overbed table of claim 4 wherein said spring means includes
a pair of said constant force springs; each of said constant force
springs comprising a leaf spring rolled around an axle, each said
constant force spring having one end affixed to the lower end of
said rigid member and having its axle horizontally rotatably
mounted at an upper portion of said inner column.
7. The overbed table according to claim 6 which further comprises a
spring-biased override assembly mounted on said outer column
adjacent said clutch assembly in engagement with the other end of
said clutch spring whereby when a downward force is exerted on said
outer column sufficient to overcome the spring biasing of said
override assembly, said override assembly will release the clutch
spring tension so that said table top can be lowered.
8. The overbed table of claim 7 wherein movement of said one end of
said clutch spring is in a direction opposite to said first
direction is restricted by said finger-like extension, wherein the
other end of said clutch spring depends away from said clutch
spring coil and wherein said override assembly comprises an
override lever rotatably mounted adjacent said other end of said
clutch spring having a foot in engagement with said other end of
said clutch spring; said override lever being spring biased against
rotation in a direction in which said foot will tend to be moved by
said other end of said clutch spring when a downward force is
exerted on said outer column whereby when a downward force is
exerted on said outer column sufficient to overcome the
spring-biasing of said override lever, said override lever will be
rotated by said other end of said clutch spring and the clutch
spring tension will thereby be released to permit said table top to
be lowered.
9. The table as set forth in claim 2 wherein said spool includes
two abutting sections, one section being rotatable with respect to
the other to wind cable thereon during assembly of said table.
10. The table as set forth in claim 9 wherein said spool sections
have ratchet faces in abutment with one another permitting one
section to be rotated with respect to the other in a non-working
direction only to wind cable thereon during assembly of said
table.
11. The table as set forth in claim 10 which further comprises
means for resiliently urging said faces together.
12. A vertically adjustable overbed table comprising:
a pedestal, a horizontal table top mounted at the top of said
pedestal and a base platform at the lower end of said pedestal;
said pedestal including an outer column and an inner column, said
outer column telescopically engaging said inner column and being
adapted for vertical telescoping movement with respect to said
inner column; and a clutch assembly mounted within said pedestal
for controlling the telescoping movement of said columns;
said clutch assembly including a rotatable clutch drum, means for
rotating said drum during telescopic movement of said columns, a
tensioned clutch spring means for selectively restraining rotation
of said drum, said spring means permitting free rotation of said
drum in a first direction to permit free upward movement of one of
said columns with respect to the other of said columns when an
upward force is exerted thereon, said spring means restraining
rotation of said drum in a direction opposite to said first
direction to restrain downward movement of said one column with
respect to said other column; and means for releasing the tension
on said clutch spring to permit free rotation of said drum in said
opposite direction.
13. The overbed table according to claim 12 wherein said outer
column is affixed to said table top, wherein said inner column is
affixed to said base and wherein said clutch assembly is mounted
within said outer column and comprises a horizontally mounted
rotatable clutch drum; a tensioned helically coiled spring
positioned around said drum, said spring having one end thereof
arrested from movement and being positioned around said drum such
that the spring tends to tighten radially under the influence of
attempted rotation of said drum in said opposite direction, a
horizontally mounted rotatable cable spool adjacent said clutch
drum and connected thereto so as to be rotatable therewith and only
therewith; a cable having its ends wound around said spool in
opposite directions, the ends of said cable being affixed to said
spool and an intermediate portion of said cable extending below
said spool to form a depending cable loop and an intermediate point
of said cable loop being affixed to said inner column; a rigid
member depending within said columns and attached at its upper end
to an upper portion of said outer column and having a pulley wheel
at the lower end thereof receiving said depending cable loop,
whereby said outer column can be telescoped downwardly over said
inner column when a downward force is placed on said outer column
only when said clutch spring tension is released and said spool is
free to rotate to take up cable above said intermediate point of
said depending cable loop and to pay out an equal amount of cable
below said intermediate point of said depending cable loop.
14. The table as set forth in claim 12 wherein said releasing means
comprises a lever which is moveable downwardly to release the
tension of said clutch spring.
Description
BACKGROUND OF THE INVENTION
This invention relates to overbed tables and more particularly to a
vertically adjustable overbed table which can be raised or lowered
from either side of the table.
Overbed tables are most often used in hospitals to provide an
eating and work surface for bed-ridden patients. Although some such
overbed tables are rigid structures, many are vertically adjustable
so that the patient or nurse can raise or lower the table to the
most convenient height. While a variety of mechanisms have been
employed in such vertically adjustable overbed tables, most of such
adjustable tables are crank-operated, spring-biased or a
combination of the two. In the crank-operated tables, the crank
must be operated to either raise or lower the table. In the
spring-biased tables, a brake lock is generally employed in
conjunction with a spring. When the brake is released, the table is
free to move either upwardly or downwardly to the desired position
at which time the brake lock is again engaged. The disadvantages of
these overbed tables are that the crank-operated tables are
impractical when used with electric powered beds; may offer a
hazard to the patient when the bed is elevated, necessitate the
rather tedious cranking task, which is sometimes arduous to a weak,
sickly patient and, in the case of the spring-biased tables bearing
objects of moderate to heavy weight, the danger of the table
lowering too quickly when the brake is released creating the danger
of dropping on the patient, spilling food, and the like.
Some more recent overbed tables have employed a combination of
crank operation and spring biasing. For example, in U.S. Pat. No.
3,504,643, an overbed table is disclosed which is spring-assisted
for raising the table and which must be cranked to lower the table.
Although such an overbed table minimizes the risk of injury to the
patient from the table dropping on him, it still involves the
tedious task of operating the crank to lower the table. In
addition, overbed tables of the spring-bias type now on the market
are at best difficult to service and at worse, dangerous to
servicing personnel because constant force springs are usually
inaccessible inside the telescoping columns, as well as the other
mechanism necessary for operation of the table.
Thus, there has been a need for a vertically adjustable overbed
table which is easy to raise and lower and which can be safely
controlled during lowering; and a need that such a table can be
easily and safely serviced when necessary.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a vertically
adjustable overbed table which does not utilize a crank assembly
and which can be easily raised or lowered with no possibility of
being accidentally lowered too quickly even when overloaded,
thereby eliminating any chance of possible injury to a bed-ridden
patient, spilled food and the like. The overbed table of the
present invention comprises a pedestal column with a horizontal
table top and a horizontal, roller-equipped base platform, the
pedestal being located at the same side of each of the table
platform and base platform. The pedestal includes an upper, outer
column which telescopes over a lower inner column. The height of
the table is a function of the degree to which the lower inner
column telescopes into the upper outer column.
A spring of the "constant force" type is mounted in association
with the outer and inner columns to place the telescoping thereof
in equilibrium when no external force is exerted on the table top.
The table top is raised by exerting a slight upward force to
overcome the telescoping equilibrium produced by the constant force
spring.
A clutch assembly which is mounted in the upper portion of the
upper outer column controls the lowering of the table. The clutch
assembly, in the preferred embodiment of the invention, comprises a
rotatable drum including a spool portion and a clutch portion. The
clutch portion of the drum is engaged by a peripheral helical
clutch spring which is mounted and tensioned so that the drum can
be freely rotated in one direction but not in the other direction
until the spring tension is overtly released. A cable is wound
around the spool portion of the drum with an intermediate depending
loop portion engaging a pulley wheel at the lower end of a
depending shaft. The shaft is rigidly mounted at its upper end to
an upper portion of the outer column and extends axially downwardly
within the two telescoping columns. An intermediate portion of the
depending loop of the cable is rigidly attached to the lower inner
column so that telescoping movement of the outer column either
upwardly or downwardly is possible only when the spool is free to
rotate. Thus, since the clutch spring permits rotation of the drum
in one direction without an overt release of tension, the cable is
directionally wound around the spool with respect to the attachment
of the intermediate portion of the depending cable loop to the
inner column so that the upper outer column can be raised without
overtly releasing the tension on the clutch spring. However, since
the spool is not free to rotate in the opposite direction unless
the clutch spring tension is overtly released, the table cannot be
lowered unless the clutch spring tension is so released.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a perspective view of an overbed table constructed
according to the present invention;
FIG. 2 is an end elevation view of the overbed table of FIG. 1;
FIG. 3 is an exploded perspective view of the pedestal column
assembly of the overbed table of FIG. 1;
FIG. 4 is a perspective view of the clutch assembly of the overbed
table of FIG. 1;
FIG. 5 is an end elevation view of the clutch assembly of FIG. 4
showing the override assembly thereof;
FIG. 6 is an exploded perspective view of the clutch, override,
cable and constant force spring assembly components of the overbed
table of FIG. 1;
FIG. 7 is a plan view of the clutch and override assembly of the
overbed table of FIG. 1;
FIG. 8 is a cross-sectional view of the pedestal of the overbed
table of FIG. 1 taken along the plane VIII--VIII of FIG. 1;
FIG. 9 is a fragmentary end elevational view of the actuator lever
arm assembly on the pedestal of the overbed table of FIG. 1;
FIG. 10 is a cross-sectional view taken along the plane X--X of
FIG. 2;
FIG. 11 is a cross-sectional view of the pedestal of the overbed
table of FIG. 1 taken along the plane XI--XI of FIG. 2; and
FIG. 12 is a fragmentary, perspective view of the mechanism
utilized to lock the cable to the inner column.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to the drawings in more detail, FIGS. 1 and 2 are
respectively perspective and end elevational views of the overbed
table of the present invention which includes table top 10, base
11, and pedestal 20. Table top 10 is rigidly attached to a metal
tubular horizontal frame 12 which is welded or otherwise rigidly
affixed to the top of the pedestal 20.
Pedestal 20 includes an upper, outer column 21 which telescopes
over a lower inner column 22 which is rigidly connected at its
lower end to base 11. A pair of lever arms 40 and 41 are pivotally
connected at the upper portion of outer column 21 and extend
outwardly in opposite directions. The end handles 42 and 43, which
are affixed normally to arms 40 and 41, respectively, are
accessible at the sides of table top 10. Lever arms 40 and 41 are
depressible to permit lowering of table top 10 when desired, as
will be explained more fully hereinafter. By providing a lever arm
at each side of the table top 10, it will be appreciated that table
top 10 can be placed over a patient from either side and in either
case a lever arm will be accessible to both the patient and to the
nurse.
Referring now to FIG. 3, the telescoping of outer column 21 over
inner column 22 is controlled by means of an internal lift assembly
23. Lift assembly 23 includes clutch assembly 50 and override
assembly 80 mounted on mounting bracket 24 which has side flanges
25 for rigidly mounting the lift assembly to the upper inside
portion of upper column 21 through bolt holes 26. Depending from
mounting bracket 24 is a rigid member 27 which is slightly longer
than the length of outer column 21. The lower end of member 27 is
provided with a horizontal foot portion having a rubber bumper 28
which limits the telescoping travel of the outer column in both up
and down directions. It contacts the bottom wall of inner column 22
when outer column 21 is telescoped downwardly over inner column 22
to the fullest extent. It contacts the arrest bracket 122 when
outer column 21 is at the limit of its upward reach.
Toward the lower end of member 27, one end of each of a pair of
rolled constant force leaf springs 29 is attached to opposite sides
of member 27. The other end of each of the constant force springs
is attached to rotatable spindles 30 which extend outwardly from
the rolled constant force leaf spring sufficient to be seated in
corresponding slots 31 in the top portion of inner column 22. The
spindle sections 30' are molded from plastic and the bore thereof
has a thin depressible circumferential lip molded about the
interior at 30". These lips 30" depress radially outwardly when the
spindle sections 30' are forced over the axles, returning to their
initial configuration in the central, reduced-diameter groove in
the axle. These lips retain the assemblies as an integral unit once
they have been assembled.
The adjacent faces of spool sections 30' come into abutment or near
abutment during assembly. The spool sections roll on axles 30, the
axles being held stationary by the squared lugs on their
extremities which fit into and mate in non-rotatable fashion with
slots 31 in inner column 22.
A pulley wheel 32 is positioned near the lower end of member 22.
The depending loop of cable 59 is looped about this wheel as will
be explained more fully hereinafter.
To avoid frictional drag when outer column 21 is telescoped over
inner column 22, a pair of rollers 33 is provided on each side of
the upper portion of inner column 22. The axes of rollers 33 are
offset with respect to the minor width of column 22 and/or the
rollers are slightly undersized so that as column 21 is raised or
lowered telescopically over column 22, rollers 33 will bear the
sliding movement between one inside surface of outer column 21 and
the adjacent outside surface of inner column 22. The contact
between rollers 33 and the inside surface of outer column 21 is
more clearly shown in FIG. 10.
Referring now to FIGS. 4-7, the detailed construction of the clutch
and override assemblies is shown. Clutch assembly 50 includes a
rotatable drum horizontally rotatably mounted on mounting bracket
24 on axle 51. The rotatable drum consists of a clutch drum section
52 and an adjacent spool section 53. Although a single-piece
rotatable drum can be employed, in the preferred embodiment, as
shown in FIG. 6, spool section 53 consists of a pair of spool
halves 54 and 55 each of which has a set of ratchet teeth 56 and
57, respective, on the inner, stepped-down diameter axial face
thereof. Teeth 56 and 57 mesh and lock together in the working
direction when the spool halves are brought together to interlock
the two spool halves so that they rotate together as a single
spool. The ratchet teeth permit relative rotation of the spool
halves in the non-working direction such that cable 59 can be wound
into working position during assembly of the mechanism by merely
turning splined face 63', and thus spool half 53, with a
conventional open-end wrench counterclockwise as viewed in FIG. 6.
The inner axle extensions of spool halves 54 and 55 are preferably
interlocked axially through a spool hub 58 to avoid any fouling of
cable 59 when wound around the spool. Cable-retaining slots 60 and
61 are provided in the periphery of spool halves 54 and 55,
respectively, in which the two ends of cable 59 are secured, as
will be more fully explained hereinafter.
Clutch drum 52 is bored centrally and includes a series of notches
62 spaced at 90.degree. intervals around the inside wall of the
bore. Notches 62 receive corresponding radial splines 63 on the
outer stepped-down diameter axial extension 64 of spool half 54 so
that clutch drum 52 is rotated whenever spool portion 54 is
rotated. It will be noted that spool half 55 also has an outer
axial extension with a plurality of radial splines 63'. This
intelligence is functional not only during assembly of the device
but permits spool halves 54 and 55 to be identical, thus
simplifying manufacturing.
Ratchet faces 56 and 57 are resiliently forced together by means of
a spring washer 34 sandwiched within bracket 24. Shaft 51, retained
against bracket 24 at one end by trip plate 81, is grooved at its
opposite extremity to receive a snap ring 35 to retain the clutch
assembly together. Stepped-down section 64 of spool half 54 is
axially elongated with respect to clutch drum 52 and, when
fabricated from molded plastic as in the preferred form of this
invention, serves as a thrust bearing against the interior sidewall
of bracket 24.
The base of bracket 24 has two slots formed therein through which
cable 59 passes from opposite sides of spool 53. A U-shaped spring
clip closely enveloping the side portions of the cable drum, is
snapped into the opposed exterior edges of these slots and insures
proper take-up and release of cable 59 by spool assembly.
A peripheral helically coiled clutch spring 65 having ends 66 and
67 is provided around clutch drum 52. End 66 is formed to extend
generally horizontally and is retained against upward movement by
upper finger-like extension 71 of trip plate 70 as is discussed
more fully below. However, end 66 is free to move downwardly. End
67 is formed to extend vertically downward and is retained against
movement to the left (FIG. 5) by the lower horizontal foot 82 of
the spring-biased trip plate 81 of override assembly 80 as will be
discussed hereinafter. End 67 is retained from movement to the
right, as viewed in FIG. 5, by its abutment with edge 83' of
aperture 83.
Beginning at end 66, clutch spring 65 is coiled clockwise in the
direction of end 67. Clutch spring 65 is tensioned and sized so
that clutch drum 52 cannot be rotated in the direction of arrow "A"
in FIGS. 4 and 6 because of the coil tightening and gripping effect
when clutch drum 52 is rotatably urged in that direction and the
retention of end 67 against foot 82. However, when clutch drum 52
is rotated in the opposite direction, end 66 is free to move
downwardly while end 67 is fixed due to its abutment with wall 83'.
This slightly uncoils clutch spring 65 so that no coil tightening
and gripping effect is produced. Therefore, clutch drum 52 can be
rotated within clutch spring 65 in a direction opposite to arrow
A.
Referring to FIGS. 4, 8 and 11, the function of cable 59 is most
clearly shown with table top 10 being almost at its lowest position
in FIGS. 8 and 11 with constant force springs 29 nearly completely
unrolled. As shown in FIG. 4, each end of cable 59 is provided with
an anchoring or locking bead 68 and 69 which is received in cable
slots 60 and 61, respectively, of the spool halves 54 and 55.
Starting from locking bead 69, cable 59 is wound in one direction
around spool portion 54, and starting from locking bead 68, cable
59 is wound around spool portion 55 in the opposite direction until
a depending loop remains which is just long enough to be received
around pulley 32 at the lower end of shaft 27. This winding can be
easily accomplished, as noted previously, by free-wheeling spool
half 53 counterclockwise as shown in FIG. 6. This procedure is
continued until the depending loop is tensioned around pulley 32.
Final tightening can be accomplished by placing an end wrench into
engagement with splines 63'. Ratchet faces 56 and 57, resiliently
urged together by washer 34, will thereafter prevent unwinding of
the cable except when an equal amount is wound up on the opposite
side of spool 53.
One of the features of the overbed table disclosed herein resides
in the ability to assemble the components illustrated in FIG. 6 as
an integral unit prior to insertion of the same into column 22. The
constant force springs, clutch assembly, overload protection means,
cable depending loop portion; and all other internal mechanism
employed in the counter balance and height control, more
particularly, is constructed as a separate, removable lift assembly
and is removed and serviced as a total unit. Because trip plate 70,
to be discussed hereinafter, is part of the outer column assembly,
and because finger-like extension engages clutch spring 65 above
the horizontal end 66, when the two bolts 26' are removed the
entire outer column assembly with lever arms and trip plate intact
may be removed to give access to the lift assembly as a unit.
Once such assembly has been completed, the unit may be easily
inserted into the lower column by merely wedging foot 28 under
arrest bracket 122, seating the axles of constant force spring
spindles into slots 31 and thereafter bolting the upper column 21
to the bracket 24 via apertures 26 on flanges 25. During this
assembly process, the one point on cable 59 is fixedly attached to
the upper extremity of inner column 22.
To this end, an intermediate lug 101 is provided on cable 59. This
lug is engaged by a bifurcated retaining clip 102 having a planar
section 103 containing a screw aperture 104, a rearwardly
projecting bifurcated section 105, and a forwardly curved
bifurcated section 106. Once the assembly shown in FIG. 6 is
inserted into the inner column 22, the bifurcated sections of clip
102 are protruded into opening 107 and lug 101 engaged in the
manner shown in FIG. 12. Clip 102 is then secured in the position
shown in FIG. 10 by means of a screw, bolt or the like. Sufficient
clearance is provided between the inner and outer columns so that
the presence of clip 102 and its attachment screw does not
interfere with smooth telescoping of the inner and outer
columns.
With point 101 of cable 59 fixed with respect to inner column 22 in
this manner, the only way that outer column 21 can be moved
upwardly or downwardly is for spool portion 53 to rotate and unwind
or pay out a portion of cable 59 from one side while taking up an
equal portion from the other side. Therefore, when clutch spring 65
is tensioned, clutch drum 52 and consequently spool portion 53 will
not be able to rotate in the direction of arrow A and accordingly
upper column 21 cannot be telescoped downwardly over column 22.
However, since clutch drum 52 can be rotated in the direction
opposite arrow A, because of the uncoiling effect permitted by end
66 of clutch spring 65, outer column 21 can be raised upwardly
since spool portion 53 will be free to rotate to pay out and take
up an equal amount of cable 59.
To release the tension of clutch spring 65 on clutch drum 52 so
that spool portion 53 will be free to rotate in the direction of
arrow A to lower the table top, either a downward force is exerted
on end 66 of clutch spring 65 tending to unwind clutch spring 65 or
end 67 is permitted to move to the left (FIG. 5) by override
assembly 80 so that no gripping action will result when clutch drum
52 is rotatably urged in the direction of arrow A. To relieve the
tension of clutch spring 65 on clutch drum 52 by a downward force
acting on clutch spring end 66, a vertically reciprocable trip
plate 70 (FIGS. 7, 9 and 11) is mounted adjacent the upper outer
side of outer column 21. Trip plate 70 has a finger-like extension
71 which extends through an elongated slot 72 in outer column 21 to
be in depressing engagement with horizontal end 66 of clutch spring
65. Trip plate 70 also has a lower finger-like extension 74 to
engage lever arms 40 and 41 as explained hereinafter.
Lever arms 40 and 41 are pivotally connected at the upper portion
of outer column 21 by means of a pivot bolt 44 passing through the
end of lever arm 40 into outer column 21 and by a pivot bolt 45
passing through the end of lever arm 41 into outer column 21. Lever
arms 40 and 41 are mounted so that the ends thereof overlap. Bolt
44 also passes through a vertically elongated aperture 46 in lever
arm 41 and bolt 45 passes through a vertically elongated aperture
47 in lever arm 40 to control the degree of pivoting of the lever
arms about their pivot points. A spring 48 interconnects depending
ears provided on lever arms 40 and 41 to bias the lever arms in
their full upper position (FIG. 9). Thus, when the lever arms are
depressed to the fullest extent permitted by elongated apertures 46
or 47 and then released, they will be automatically returned to
their upper position.
At the lower end of trip plate 70, an outwardly extending finger 74
extends through overlying apertures 49 through lever arms 40 and
41. Thus, when either of the lever arm handles are depressed, trip
plate 70 will be moved downwardly to depressing end 66 of spring 65
to produce a spring uncoiling effect which releases the tension
thereof on clutch drum 52. As long as one of the lever arm handles
is kept depressed to maintain the released clutch spring tension on
clutch drum 52, the table top can be lowered by a slight downward
force since spool 53 will be free to rotate in the direction of
arrow A to pay out and take-up corresponding amounts of cable 59.
Generally, the downward force exerted on the lever arm handle is
sufficient to provide the necessary downward force needed to
overcome the upward biasing force of constant force spring 29 to
achieve downward movement for telescoping of outer column 21 over
inner column 22. As soon as the lever arm is released, spring means
48 will cause it to automatically return to its fullest upper
position thereby raising trip plate 70 and end 66 of spring 65
resulting in tension again being placed on clutch drum 52 by clutch
spring 65. Thus, a positive continued downward force is required on
one of the lever arms to maintain a downward movement of the table
top, and consequently, there is no possibility of the table top
being lowered faster than desired since as soon as downward force
exertion by the operator on the lever arm ceases, the table will
cease its lowering action. Cessation of the downward force will
occur whenever the table top "catches up" to the operator's hand
thus insuring that the table top will not lower further or more
quickly than desired.
Table top 10 can also be lowered without depressing one of the
lever arms by exerting a large downward force directly on the table
top such as might be experienced if someone were to fall upon it.
The primary function of this feature is to prevent damage to the
table in such a loading situation. This is accomplished by means of
override assembly 80 which is most clearly shown in FIG. 5.
Override assembly 80 includes spring-biased override lever 81 which
is rotatably mounted on mounting bracket 24 at one end of axle 51.
Lever 81 has a lower horizontal foot portion 82 which extends
through an opening 83 in the sidewall of mounting bracket 24 to
contact vertical end 67 of clutch spring 65. A spring means such as
coil spring 85 extends between the top portion of side flange 25
and a top outwardly extending horizontal extension 84 on lever 81
to bias foot 82 against edge 83" of opening 83. By this
arrangement, when a large downward force is exerted on the table
top in the direction of arrow A clutch drum 52 will be rotatably
urged with sufficient force to overcome the tension of override
spring 85. Lever 81 will then rotate slightly in a clockwise
direction (FIG. 5) permitting movement of spring end 67 to the left
(FIG. 5) -- and permitting spring end 66 to engage fingerlike
extension 71 of trip plate 70 -- to release the tension of clutch
spring 65 on clutch drum 52. As long as this requisite downward
force is maintained, spool 53 will be free to rotate in the
direction of arrow A and table top 10 can be lowered. However, as
with the action of the lever arm, when the downward force on the
table top 10 is discontinued or diminished to such an extent that
the force of spring means 85 is no longer overcome and override
lever 81 rotates back to the original position thereby again
placing clutch spring 65 under tension, the downward movement of
table top 10 will stop. The spring constant of spring 85 should be
chosen, as will be readily apparent to those skilled in the art,
such that override lever 81 will be permitted to rotate only when
the table top experiences an atypical loading.
It will be apparent to those skilled in the art from a reading of
the foregoing specification and study of the accompanying drawings
that this invention has provided a novel and unobvious vertically
adjustable overbed table. The table may be raised merely by
exerting an upward force thereagainst. Once it has been raised to a
predetermined position, it will be locked from downward movement by
action of the unique clutch assembly. The table may be lowered from
this position only by the actuation of the override assembly in an
"atypical" loading situation or by depression of the clutch lever
arms. There is no danger, during such downward movement, of the
table top "running away" downwardly since a constant downward force
must be maintained either on the table top or the lever arms for
continued downward movement.
While a preferred embodiment of the present invention has been
described and illustrated, it will be understood to those skilled
in the art that changes and modifications can be made without
departing from the spirit of the invention. Accordingly, the scope
of the present invention is deemed to be limited only by the
following appended claims.
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