U.S. patent number RE28,623 [Application Number 05/348,995] was granted by the patent office on 1975-11-25 for push-pull attachment for lift trucks.
This patent grant is currently assigned to Brudi Equipment, Inc.. Invention is credited to Ronald A. Brudi.
United States Patent |
RE28,623 |
Brudi |
November 25, 1975 |
**Please see images for:
( Certificate of Correction ) ** |
Push-pull attachment for lift trucks
Abstract
A novel lazy tongs has offset pivotal connections between the
arms of the linkage allowing the arms to fold together compactly in
vertical positions. The lazy tongs linkage actuates a push frame
for pushing a load off the forks of the lift truck. An adjustable
length connection between the upper forward arm and the push frame
allows the upper end of the push frame to be tilted backward in
extended position of the linkage so that the thrust may be applied
principally at the bottom of the load. Since the adjustable length
arm is vertical in retracted position, the push frame is always
vertical in retracted position regardless of its tilt in extended
position. The rearward tilt of the push frame in extended position
is also advantageous in grasping sheetlike pallets to pull a pallet
load onto the forks of the truck. The lower edge of the push frame
may be equipped with pallet grippers for this purpose.
Inventors: |
Brudi; Ronald A. (Longview,
WA) |
Assignee: |
Brudi Equipment, Inc.
(Longview, WA)
|
Family
ID: |
26687307 |
Appl.
No.: |
05/348,995 |
Filed: |
April 9, 1973 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
015385 |
Mar 2, 1970 |
03640414 |
Feb 8, 1972 |
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Current U.S.
Class: |
414/661 |
Current CPC
Class: |
B66F
9/195 (20130101) |
Current International
Class: |
B66F
9/19 (20060101); B66F 9/12 (20060101); B60P
001/02 () |
Field of
Search: |
;214/514,730,731,700,660,672,673,674,82,77P |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Makay; Albert J.
Attorney, Agent or Firm: Chernoff & Vilhauer
Claims
I claim:
1. In a lift truck having a load carriage mounted for vertical
movement on a mast, a push frame for pushing a load off said
carriage, and a pair of lazy tongs on opposite sides of said
carriage for operating said push frame, each of said lazy tongs
having an arm pivotally connected to a lower portion of said push
frame and an arm movable in a vertical guide in said push frame
above said pivotal connection, said last arm being a straight,
rigid unitary member of a length to tilt said push frame backward
as the push frame is extended, said two arms folding into side by
side positions parallel with each other and parallel with said mast
when the push frame is retracted, causing said push frame to
retract to a position parallel with said mast regardless of the
length of said last arm.
2. The invention of claim 1 including a length adjustment in said
last arm to vary the angle of tilt of said push frame in extended
position.
3. The invention of claim 1, said lazy tongs having four arms
connected together in pairs on offset pivots causing pairs of the
arms to lie flat against each other in a common transverse plane of
contact parallel with said mast, whereby said push frame is
retracted to a position parallel with said mast regardless of its
angle of tilt in extended position.
4. The invention of claim 1 including a cylinder and piston unit
having one end connected with said pivotal connection on said push
frame and its opposite end connected with an arm of said lazy
tongs.
5. The invention of claim 1 including pallet clamp means on the
lower end of said push frame for pulling a sheetlike pallet onto
said load carriages when said push frame is retracted.
6. In a lift truck having a load carriage mounted for vertical
movement on a mast, a push frame for pushing a load off said
carriage, a pair of lazy tongs on opposite sides of said carriage
for operating said push frame, each of said lazy tongs having four
arms connected together in pairs on offset pivots causing pairs of
the arms to lie flat against each other in a common transverse
plane of contact parallel with said mast, one of said arms being
pivotally connected to a lower portion of said push frame and
another of said arms being movable in a vertical guide above said
pivotal connection, said last arm consisting of two parts which are
adjustable relative to each other to either lengthen or shorten the
arm to tilt said push frame either forward or backward in the
extended position of the lazy tongs, and a cylinder and piston unit
having one end connected with said pivotal connection on said push
frame and its opposite end connected with an arm of said lazy tongs
for extending and retracting said push frame. .Iadd. 7. In a lift
truck having a load carriage mounted for vertical movement and
means for selectively tilting said load carriage forwardly or
backwardly with respect to said truck, a push frame movable
forwardly and rearwardly relative to said carriage for pushing a
load off said carriage and selectively extensible and retractable
linkage means coupling said push frame and said carriage for
operating said push frame, said linkage means comprising a pair of
arms extending forwardly and rearwardly between said carriage and
said frame and pivoted to one another at a point intermediate the
ends thereof, each said arm having an upper coupling and a lower
coupling respectively on either side of said pivot point for
coupling said arm between said carriage and frame, the length of
one of said arms between its upper coupling and said pivot point
being less than the length of said other arm between its lower
coupling and said pivot point so as to cause backward tilting of
said push frame relative to said carriage in response to the
extension of said linkage means..Iaddend..Iadd. 8. The invention of
claim 7 including pallet clamp means on the lower end of said push
frame for engaging a sheetlike pallet when said frame is extended
and for pulling said pallet onto said load carriage by the
retraction of said push frame..Iaddend. .Iadd. 9. An attachment for
a lift truck load carriage comprising a push frame adapted to move
forwardly and rearwardly relative to said carriage for pushing a
load off said carriage and selectively extensible and retractable
linkage means for coupling said push frame with said carriage and
operating said push frame, said linkage means comprising a pair of
arms adapted to extend forwardly and rearwardly between said
carriage and said frame and pivoted to one another at a point
intermediate the ends thereof, each said arm having an upper
portion and a lower portion respectively on either side of said
pivot point and coupling means on each of said portions for
coupling said arm between said carriage and said push frame, the
upper portion and coupling means of one arm connected to the push
frame being less extensive in the extended position from the
intermediate pivot than the respective bottom portion and coupling
means of the other arm thereby causing backward tilting of said
push frame relative to said carriage automatically upon extension
of said linkage means and independently of any force exerted
against said push frame by said load..Iaddend. .Iadd. 10. The
invention of claim 9 including pallet clamp means on the lower end
of said push frame for engaging a sheetlike pallet when said frame
is extended and for pulling said pallet onto said load carriage by
the retraction of said push frame..Iaddend.
Description
BACKGROUND OF THE INVENTION
This invention relates to an improved push-pull attachment for lift
trucks and has particular reference to an improved lazy tongs
linkage for tilting a push frame backward in pushing a load off the
forks of the truck and in grasping a sheetlike pallet to pull a
load onto the forks.
In pushing a load off the forks of a lift truck it is often
desirable to apply the major thrust at the bottom of the load in
order to avoid pushing the top of the load forward out of vertical
alignment, especially when the load is of a deformable nature such
as stack of boxes or the like. On the other hand, it is not
desirable to mount the push frame in a permanently backward tilted
position because then the push frame will not retract compactly
against the back of the fork lift carriage. Compact folding of the
pusher linkage is essential in order to position the load as close
to the front wheels of the truck as possible in carrying and
lifting the load. When the push frame is not retracted compactly
against the back of the lift carriage, the center of gravity of the
load is located farther forward from the wheels causing the truck
to overbalance and thereby reducing the carrying capacity of the
truck. For this reason it has heretofore been considered
impractical to tilt the push frame backward, with the result that
the top of the load is frequently pushed forward out of vertical
alignment, particularly if the mast and forks of the truck are
tilted slightly forward when the load is discharged.
A similar problem arises in pulling a load onto the forks of the
truck by means of a sheetlike pallet. In order to adapt a lift
truck for the use of sheetlike pallets, a gripper is mounted at the
lower edge of the push frame to grasp a protruding edge of the
pallet sheet. To perform this manipulation, it is usually necessary
to tilt the mast of the truck forward in order to place the
grippers within an inch or so of the floor. But when the mast is
tilted forward, a normally vertical push frame is also tilted
forward, causing the upper end of the push frame to encounter the
load before the grippers are close enough to the bottom of the load
to grasp the pallet sheet. This makes it quite difficult to use
sheetlike pallets with a conventional lift truck notwithstanding
the great advantage of such pallets for handling certain types of
merchandise.
Objects of the invention are, therefore, to provide an improved
extending and retracting mechanism for tilting the push frame on a
lift truck in extended position without any sacrifice of space in
retracted position, to provide means for tilting the push frame
backward when extended and then returning the push frame to
vertical position when retracted, to provide an improved lazy tongs
linkage for such purpose and to provide a push-pull mechanism which
is better adapted to handle sheetlike pallets.
SUMMARY OF THE INVENTION
According to the present invention, the push frame is extended and
retracted by a pair of vertical lazy tong linkages on opposite
sides of the lift carriage. The pivotal connections between the
arms of each lazy tongs are offset so that all the arms fold
compactly in vertical positions when the push frame is retracted.
The upper forward arm of each lazy tongs is provided with a length
adjustment adjacent a sliding connection with the upper part of the
push frame. By means of this length adjustment the push frame may
be caused to assume a conventional vertical position when fully
extended or it may be caused to tilt backward so that the principal
thrust in discharging a load from the lift forks is applied at the
bottom of the load. Since the adjustable length arms are vertical
when fully retracted, this length adjustment does not disturb the
vertical position of the push frame in retracted position. Thus,
regardless of the tilt of the push frame when extended, it always
returns to compact vertical position when retracted.
A backward tilting push frame is especially advantageous in pulling
a load onto the lift forks by means of a sheetlike pallet. A
backward tilt of the push frame places the pallet grippers at the
lower edge of the push frame close to the bottom of the load even
when the mast is tilted forward to place the grippers and the
forward ends of the forks as close to floor level as possible. The
tilt adjustment of the push frame thereby provides a two-fold
advantage in the use of lift trucks equipped with the
invention.
The invention will be better understood and additional objects and
advantages will become apparent from the following description of
the preferred embodiment illustrated in the accompanying drawings.
Various changes may be made in the details of construction and
arrangement of parts and certain features may be used without
others. All such modifications within the scope of the appended
claims are includes in the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a side elevation view with parts broken away, showing a
lift truck embodying the invention wherein the push frame mechanism
is extended to grasp a sheetlike pallet;
FIG. 2 is a view on the line 2--2 in FIG. 1;
FIG. 3 is a view similar to FIG. 1 but with the push frame
retracted; and
FIG. 4 is a front elevation view of FIG. 3 with parts broken
away.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The numeral 10 designates generally a conventional lift truck
having front wheels 11 and a mast 12 and equipped with a cylinder
and piston rod 9 for tilting the mast. As shown in FIG. 1, the mast
is tilted forward through a small angle 13 with respect to vertical
line 14. As is understood by persons skilled in the art, the mast
may be moved to vertical position 14 and it may also be tilted
backward behind vertical line 14 for carrying and lifting a
load.
The load is carried on forwardly extending forks 15 on a lift
carriage 16 which moves vertically on mast 12. In most cases the
mast 12 is an extension type of mast having telescoping, vertically
sliding sections which may be raised to considerable height for the
purpose of stacking and unstacking merchandise or other objects. In
FIG. 1, carriage 16 is in its lowermost position whereby the
forward tilt of the mast causes the front ends of forks 15 to be
depressed to the floor level 17.
The invention resides in a novel and improved lazy tongs linkage 20
for extending and retracting a vertical or near vertical push frame
21 which is arranged to push a load 22 off the forks 15. Push frame
21 is supported at its opposite sides by a pair of the lazy tongs
20, one on each side of the truck. The lazy tongs, in turn, are
supported by a vertical frame 25 on the lift carriage 16.
Each lazy tongs linkage comprises four arms 31, 32, 33 and 34. Arms
31 and 32 are pivotally connected together intermediate their ends
by pins 35, and arms 33 and 34 are pivotally connected together
intermediate their ends by pins 36. The forward end of arm 31 is
pivotally connected to the rear end of arm 33 by a pin 37, and the
forward end of arm 32 is pivotally connected to the rear end of arm
34 by pin 38.
Pin 37 passes through a central tongue 40 on arm 33 and a pair of
ears on arm 31 which straddle the tongue 40. Similarly, the pin 38
passes through a central tongue 42 on the arm 32 and a pair of ears
43 on the arm 34 which straddle the tongue 42. Arms 31 and 33 are
disposed in a common vertical plane and arms 32 and 34 are disposed
in a common vertical plane alongside arms 31 and 33.
Pins 37 and 38 are offset relative to the arms so that the axis of
pin 37 lies in the plane of an underneath flat side 44 of arm 31
and also in the plane of an underneath flat side 45 of arm 33.
Similarly, the axis of pin 38 is offset so that it lies in the
plane of an upper flat side 46 on arm 32 and an upper flat side 47
on arm 34. Thus, the lazy tongs linkage is adapted to fold
compactly together as shown in FIG. 3 with flat surface 45 lying
against flat surface 44 and flat surface 47 lying against flat
surface 46, all of these surfaces being disposed in a common
transverse plane parallel with the planes of supporting frame 25
and mast 12. This compact folding feature is of particular
advantage when lift carriage 16 is equipped with a side shifting
mechanism which occupies some additional space between the mast and
the load, spacing the load farther forward from wheels 11.
The rear end of arm 31 is pivotally mounted on a pin 49 in the
lower end of a vertical channel track 50 mounted on frame 25. The
rear end of arm 32 is equipped with a roller 51 which rides in the
channel track. Similarly, the front end of arm 33 pivots on a pin
52 in the lower end of a vertical channel track 55 on push frame 21
and the front end of arm 34 carries a roller 56 which travels in
the channel track.
The linkage geometry is such that pins 37 and 38 always remain in a
common transverse plane parallel with channel track 50, but the
length of arm 34 is adjustable so that push frame 21 in extended
position may be made parallel to frame 25 or tilted relative
thereto as desired. The forward ends of arms 34 in the two lazy
tongs are stabilized by a slightly offset transverse tie rod
37.
Any suitable form of length adjustment may be provided for the arms
34, a preferred embodiment being illustrated in FIG. 2. Roller 56
is mounted on a bar 60 which telescopes in hollow arm 34. Bar 60 is
provided with a series of tapped holes 61 to receive cap screws 62
in selected holes 63 in arm 34.
When bar 60 is adjusted to make arm 34 the same effective length as
arm 33, push frame 21 will remain parallel to the plane of support
frame 35 in all positions of the lazy tongs linkage. By adjusting
bar 60 to shorten the effective length of arm 34 it will be
apparent that push frame 21 in extended position may be tilted
backward relative to support frame 25 as shwon in FIG. 1. However,
when the linkage is folded to its FIG. 3 position both arms 33 and
34 become parallel with support frame 25 and a transverse plane
through the axes of pin 52 and roller 56 is parallel with frame 25.
Hence, in fully retracted position, push frame 21 is always
parallel with support frame 25 regardless of the length adjustment
of arm 34 because any variation in length merely shifts the roller
56 up or down parallel with frame 25.
In order to handle sheetlike pallets 70, the lower end of push
frame 21 is equipped with a lower stationary clamp jaw 71 extending
across the width of the push frame. An upper clamp jaw 72 is
actuated by piston rods 73 in one or more fluid pressure cylinders
74.
In approaching a load 22 on a pallet sheet 70, the mast 12 may be
tilted forward to cause lower clamp jaw 71 to pass under an
upfolded edge on the pallet sheet 70 as shown in FIG. 1. Then by
causing claim jaw 72 to grip the pallet sheet, the load may be
drawn onto forks 15 by operation of a fluid pressure cylinder 80 in
each lazy tongs. When push frame 21 cannot be tilted back to
vertical position as shown, the upper end of the forward tilted
push frame encounters the side of load 22, before the clamp jaws
are close enough to grasp the pallet sheet.
One end of cylinder 80 is connected to pivot 52 and a piston rod 81
extending from the opposite end of the cylinder is pivotally
connected to a pin 82 in the arm 31. Drawing piston rod 81 into the
cylinder folds the lazy tong linkage into its FIG. 3 position and
pulls the load onto the forks 15. Extension of piston rod 81 from
cylinder 80 causes push frame 21 to push the load off the forks
15.
By appropriate length adjustment of the arms 34 of the two lazy
tongs the thrust exerted by the two piston rods 81 will be applied
to the lower part of the load, even though the mast 12 is tilted
forward as shown in FIg. 1. The connection of cylinder 80 directly
to pin 52 is advantageous in providing direct thrust against the
lower portion of push frame 21 and thereby minimizing stress on the
linkage. This permits a lightweight construction of the linkage
arms which also makes for a compact assemblage when folded.
Similarly, in pulling the load onto forks 15, the pull is exerted
on pin 52, close to clamp jaws 71 and 72, minimizing stress on the
linkage.
Clamp jaws 71 and 72 may be omitted when elevated pallets are used
instead of sheetlike pallets.
FIG. 3 illustrates the necessity for compact folding of the lazy
tongs linkage. Dimension 90 indicates the space occupied by the
push frame attachment in front of the back plate of lift carriage
16. Dimension 91 indicates the distance of the lift carriage back
plate ahead of the front wheel axis. The sum of these two
dimensions is equal to dimension 92 which measures the distance
from the wheel axis to the back side of the load. It will be
apparent that any reduction in dimension 90 places the center of
gravity of the load that much closer to the wheel axis, thereby
increasing the load which the truck may safely carry without danger
of overbalancing.
* * * * *