Automated mechanism to fold and unfold lift truck forks and related process

In an automated process for folding and unfolding a lift truck fork in response to movement of a carriage relative to a supporting mast, the lift truck fork is pivotally supported on the carriage such that under normal conditions a fork tine extends outwardly generally perpendicularly from the carriage. A latch is provided which is connected to the mast and is capable of selectively engaging the lift truck fork. When the carriage is at or near the bottom of the mast, the latch may be selectively caused to engage the lift truck fork. With the latch so engaged, raising of the carriage causes the fork tine to pivot until it lies generally parallel to the carriage. Subsequent lowering of the carriage then causes the fork tine to pivot back to its unfolded position wherein it extends generally perpendicularly from the carriage. The latch is biased to normally remain out of engagement with the lift truck fork so that once the carriage is lowered, the latch disengages from the lift truck fork. The fork then remains unfolded as the carriage is subsequently raised and lowered relative to the mast.

BACKGROUND OF THE INVENTION 
This invention relates generally to fork lift trucks. More specifically, 
the present invention relates to an automated mechanism to fold and unfold 
lift truck forks in response to movement of a carriage relative to a 
supporting mast in a fork lift mechanism. 
Fork lift trucks are used by a wide variety of industries. They are one of 
the most common pieces of equipment used for material handling. Virtually 
all commodities are stacked on pallets at some point in their manufacturer 
or distribution and handled by fork lifts. Sometimes fork lifts are 
carried by delivery trucks to unload their cargos. Such is the case in the 
sod industry. When fork lifts are carried by trucks it is necessary to 
fold the forks in order to meet vehicle code and safety requirements. 
A typical fork lift mechanism includes a generally vertical mast pivotally 
attached to the front of the fork lift truck and connected to one or more 
hydraulic rams which control the angle of inclination of the mast relative 
to a vertical plane. A carriage is slidably supported by the mast and a 
hydraulic mechanism is utilized to selectively raise and lower the 
carriage. The carriage will typically include an upper rail which supports 
a pair of L-shaped forks. In this regard, a fork mounting sleeve is 
provided at an extreme end of each L-shaped fork. The upper rail extends 
through the fork mounting sleeves so that the forks may pivot thereon as 
well as slide laterally. In normal use, a fork back extends downwardly 
from the fork mounting sleeve and then a fork tine extends horizontally 
outwardly from the carriage, generally perpendicularly from the fork back. 
The spacing between the forks may be adjusted by simply sliding the forks 
on the upper rail to the desired position. 
In order to fold the forks in preparation for transporting the fork lift 
truck, a number of steps requiring considerable physical strength are 
necessary. By way of example, each of the forks typically must be slid to 
the respective extreme outside ends of the upper rail. When so positioned, 
each fork must be lifted and pivoted about the upper rail approximately 
180.degree. into a transport position. This process is quite difficult for 
an individual considering that a fork may weigh seventy-five pounds. As an 
alternative procedure, fork lift operators have also utilized a raised 
horizontal surface, such as the bed of a flat bed truck, to assist with 
the fork lift folding process. 
During transport of the fork lift truck, the forks in the folded position 
extend upwardly from the upper rail and rest on brackets provided on each 
side of the mast. To unfold the forks, each must be manually pulled 
forward so as to pivot about the upper rail, and then be restrained from 
falling down onto the carriage. Again, this requires substantial physical 
effort, and some fork lift operators have developed techniques for 
utilizing a raised horizontal surface, such as that provided by a flat bed 
truck, to assist in the process and minimize the amount of manual labor 
required. Nevertheless, whether the forks are strictly manually folded and 
unfolded, or advanced folding and unfolding techniques are utilized, 
multiple steps and considerable physical strength are prerequisites for 
completing the task. 
Accordingly, there is a need for a simple automated mechanical system 
capable of folding and unfolding forks for transport and operation. 
Preferably such an automated system would utilize the fork lift's existing 
hydraulics and be fully actuable from the driver's position on the fork 
lift truck. Additionally, such an automated mechanical system and related 
process is needed which may be adaptable to a wide variety of fork lift 
trucks, and which is easy to maintain and operate. The present invention 
fulfills these needs and provides other related advantages. 
SUMMARY OF THE INVENTION 
The present invention resides in an automated mechanism to fold and unfold 
lift truck forks, and a related process for folding and unfolding the 
forks in response to movement of a carriage relative to a supporting mast. 
Importantly, the fork lift mechanism utilizes standard hydraulic systems 
normally associated with fork lift trucks, and the process may be fully 
effected by the driver of the fork lift truck from the driving position. 
In accordance with the invention, the lift truck fork is pivotally 
supported on the carriage such that under normal conditions a fork tine of 
the lift truck fork extends outwardly generally perpendicularly from the 
carriage in an unfolded position. A latch is connected to the mast and 
configured such that it is capable of selectively engaging the lift truck 
fork when the carriage is at or near the bottom of the mast. By raising 
the carriage, the fork tine is caused to pivot until it lies generally 
parallel to the carriage in a folded position. Thus, simply by raising the 
carriage relative to the mast, the lift truck fork may be pivoted from the 
unfolded position to the folded position. When it is desired to later 
unfold the lift truck fork, the carriage is simply lowered on the mast, 
which carriage movement causes the fork tine to pivot back to its unfolded 
position wherein it extends generally perpendicularly from the carriage. 
The latch is typically biased by means of a spring out of engagement with 
the lift truck fork. Thus, the latch must be intentionally and positively 
forced into engagement with the lift truck fork in order to fold the fork 
in response to movement of the carriage. Following the step of lowering 
the carriage, the latch may be disengaged from the lift truck fork so that 
the fork may then remain unfolded as the carriage is subsequently raised 
and lowered relative to the mast. 
The fork lift mechanism itself comprises, generally, a mast, a carriage 
slidably supported by the mast, which carriage includes a backing plate, 
at least one fork pivotally supported by the carriage, including a fork 
tine and a fork back, and at least one latch supported by the mast. The at 
least one mast is capable of selectively engaging the fork back. Under 
normal operating conditions the at least one fork back engages the 
carriage backing plate so that the fork tine extends generally 
perpendicularly outwardly from the carriage as the carriage is moved 
relative to the mast. However, when the at least one latch is caused to 
engage the fork back, the fork back is pulled away from the backing plate 
as the carriage is raised to cause the fork tine to pivot and lie 
generally parallel to the carriage. 
In the illustrated embodiment, a plurality of forks are pivotally supported 
by the carriage. Each fork includes a fork tine, a fork back which extends 
generally perpendicularly to the fork tine, and a mounting sleeve between 
the fork tine and the fork back. A fork mounting shaft supported by the 
carriage extends through the mounting sleeve to permit pivotal movement of 
the fork about the mounting shaft. 
A plurality of latches, corresponding to the plurality of forks, are 
supported by the mast, each latch being pivotable between a fork back 
engaging position and a neutral position. Means are provided for biasing 
the latches toward their neutral position, and further means are provided 
for selectively moving the latches between the engaging and neutral 
positions. The biasing means includes a spring which extends between at 
least one of the latches and the mast. The latch moving means comprises a 
cable linkage which extends from each of the latches rearwardly for 
actuation by a driver of the fork lift truck. 
Other features and advantages of the present invention will become apparent 
from the following more detailed description, taken in conjunction with 
the accompanying drawings which illustrate, by way of example, the 
principles of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
As shown in the drawings for purposes of illustration, the present 
invention is concerned with an improved fork lift mechanism, generally 
designated in the accompanying drawings by the reference number 10. The 
fork lift mechanism 10 is typically associated with a fork lift truck 12, 
and includes a mast 14 that is pivotally supported at a front end of the 
truck 12, and a carriage 16 which is slidably supported by the mast 14. 
The mast 14 is of a generally standard construction and includes a pair of 
side rails 18 connected at their upper and lower ends by connecting beams 
20. A pair of hydraulic rams 22 extend forwardly from a front end of the 
fork lift truck 12 to the mast 14 to permit an operator seated on a seat 
24 on the truck 12 to be able to control the vertical angular orientation 
of the mast 14 about its lower pivot connection to the truck 12. 
The carriage 16 includes a pair of track members 26 that are configured to 
slide vertically within the side rails 18 of the mast 14. A carriage 
superstructure 28 is connected to the track members 26 and extends 
forwardly therefrom to lie generally adjacent to a forward side of the 
mast 14. The superstructure 28 includes a pair of side support members 30 
which extend vertically generally adjacent to the track members 26, and a 
pair of backing plates 32 which extend laterally between the side support 
members 30. Connected to and extending downwardly from the lower one of 
the backing plates 32 are a pair of lower support brackets 34 which are 
equidistantly spaced from the respective side support members 30. A fork 
mounting shaft 36 is supported between each lower support bracket 34 and 
its adjacent side support member 30, and it is these shafts 36 which 
provide the primary pivotal support for the lift truck forks 38. Of course 
it will be understood by those of skill in the art that modifications to 
the above-described structure may be made. For example, the lower support 
brackets 34 could be eliminated and a single fork mounting shaft 36 
provided which extends the entire width of the carriage superstructure 28 
between the opposing side support members 30. 
A lifting hydraulic ram 40 is fixed to the mast 14. Specifically, a lower 
end of the ram 40 is secured to a lower one of the connecting beams 20. 
The hydraulic ram 40 is of standard construction and includes a lower 
cylinder 42 and an upper piston 44. The upper end of the piston 44 is 
fitted with a carriage lifting chain guide 46 through or over which a 
carriage lifting chain 48 extends. A lifting chain anchor 50, in the form 
of a bar, extends laterally across the mast 14 and is fixed to the side 
rails 18. One end of the lifting chain 48 is secured to the anchor 50. The 
other end of the lifting chain is secured to the carriage superstructure 
28, and specifically to an upper one of the backing plates 32. As the 
piston 44 is raised relative to the cylinder 42, the lifting chain 48 will 
pull the carriage 16 upwardly relative to the mast. Conversely, as the 
piston 44 is lowered relative to the cylinder 42, the lifting chain 46 
will permit the carriage 16 to be lowered relative to the mast 14, all in 
a standard fashion. 
The lift truck forks 38 carried by the carriage 16 include a fork tine 52 
configured to extend forwardly and generally perpendicularly outwardly 
from the carriage under normal operating conditions, a fork back 54 which 
extends generally perpendicularly to the fork tine, and a mounting sleeve 
56 between the fork tine and the fork back. The mounting sleeve 56 is 
positioned and configured to receive therein a respective one of the fork 
mounting shafts 36 supported by the carriage 16 to permit pivotal movement 
of the lift truck forks 38 between an unfolded position (wherein the fork 
tine 52 extends outwardly generally perpendicularly to the carriage--FIG. 
1) and a folded position (wherein the fork tine is pivoted about the fork 
mounting shaft 36 to lie generally parallel to the carriage--FIG. 8). 
Extending rearwardly from each fork back 54, near an upper end thereof, 
are a pair of latch brackets 58 that support a latch pin 60 therebetween. 
The latch pins 60 of the lift truck forks 38 may be selectively engaged by 
a latch 62 supported by the mast 14 to automate the folding and unfolding 
of the lift truck forks 38 relative to the carriage 16. 
The latches 62, which correspond to the lift truck forks 38, each include a 
lower sleeve 64 and an upper hook 66. The lower sleeve 64 pivots about a 
latch pivot pin 68 that is secured to the lower mast connecting beam 20 by 
means of a pair of latch pivot pin supporting brackets 70. Each latch 62 
is configured so that the upper hook 66 is capable of capturing a 
respective latch pin 60 associated with each fork back 54 when an operator 
of the fork lift truck 12 desires to hold the lift truck forks 38. Under 
normal operating conditions, however, it is desired to keep the latches 62 
pivoted away from the latch pins 60 to allow the lift truck forks 38 to 
remain in their unfolded position as the carriage 16 is raised and lowered 
relative to the mast 14. To help accomplish this, a spring 72 is provided 
to help bias the latches 62 out of engagement with the lift truck forks 
38. Further, a cable linkage 74 that is actuable by an operator of the 
fork lift truck 12 from the seat 24 thereof is provided to permit the 
operator to positively selectively control the positioning of the upper 
hook portion 66 of the latches 62 between a fork back engaging position 
(FIGS. 4-7) and a neutral position (FIG. 2). 
More particularly, a connecting arm 76 extends from each latch 62 in a 
manner to interconnect the latches 62 to ensure that the latches are each 
in the same pivotal orientation about the latch pivot pins 68. A linkage 
arm 78 extends rearwardly from the connecting arm 76 to a control knob 80 
which the operator of the fork lift truck 12 may grasp to positively and 
selectively position the latches 62 as desired. 
In operation, the lift truck forks 38 are normally in their unfolded 
position as illustrated in FIG. 1. In this position the fork tines 52 
extend perpendicularly outwardly from the carriage 16 and the mast 14. 
Further downward rotation of the fork tines 52 is prevented by engagement 
between the fork backs 54 and the lower carriage backing plate 32 (FIGS. 
2-4). With the latches 62 pulled rearwardly by the cable linkage 74 and as 
biased by the spring 72 into the neutral position (FIG. 2), the operator 
may raise and lower the carriage 16 relative to the mast in a normal 
fashion. 
To pivot the lift truck forks 38 to the folded position (FIG. 8), the 
carriage is first fully lowered (FIG. 2). The operator then pushes 
forwarding on the cable linkage control knob 80 which, in turn, causes the 
linkage arm 78 and the connecting arm 76 to move forwardly to pivot the 
latches 62 so that the upper hook 66 of each latch 62 is positioned 
directly over a respective latch pin 60 mounted on the fork backs 54. The 
carriage 16 may then be raised using the conventional fork lift hydraulics 
(the lifting ram 40). As the carriage 16 is first lifted upwardly, the 
upper hooks 66 will engage the latch pins 60. Further upward movement of 
the carriage causes the lift truck forks 38 to pivot about the fork 
mounting shafts 36 (FIGS. 5 and 6) until the fork tines 52 are rotated 
from the horizontal position (FIG. 2) to the vertical position (FIG. 7). 
Once the lift truck forks 38 have been fully folded (FIGS. 7 and 8), the 
carriage 16 cannot be raised in any further and the raising hydraulics 
circulate through a hydraulic valve pressure bypass. When the hydraulic 
valve is placed in neutral the forks remain in the vertical transport or 
folded position. 
It has been found that once the forks 38 are placed in the folded position 
and the fork lift truck is shut down, the forks may, slowly over the 
course of several hours, unfold back into the horizontal operating 
position. This is typically caused by normal hydraulic leakage inside the 
mast/carriage ram control valve. To overcome this problem, a hydraulic 
pressure accumulator and a pilot operated check valve in the hydraulic 
circuit that controls the mast/carriage ram is provided. The check valve 
stops the leakage and the accumulator maintains pressure in the hydraulic 
system when the fork lift truck is shut down. 
To unfold the lift truck forks 38 for operation, the hydraulic valve is 
actuated to lower the piston 44 and thus the carriage 16. The forks, and 
specifically the fork tines 52, automatically unfold until they reach the 
horizontal or unfolded position (FIGS. 1 and 2). As the carriage 16 lowers 
further, the upper hooks 66 of the latches 62 disengage from the latch 
pins 60. The operator may then grasp the control knob 80 to pull the cable 
linkage 74 rearwardly to clear the latch pins 60 of the latches 62. At 
this point the fork lift mechanism 10 is ready for operation in a standard 
fashion and the carriage 16 can be raised and lowered as needed relative 
to the mast, without engaging the folding mechanism until desired. 
From the foregoing it will be appreciated that the present invention 
requires only the operation of the fork lifts' existing hydraulics and an 
additional cable linkage to permit much faster and easier fork folding and 
unfolding in comparison with the manual methods now required. The process 
for folding and unfolding the lift truck forks 38 in response to movement 
of the carriage 16 relative to the mast 14 has been greatly simplified. In 
this regard the process comprises the steps of pivotally supporting the 
lift truck fork on the carriage such that under normal conditions the fork 
tines 52 extend outwardly generally perpendicularly from the carriage 16 
in an unfolded position, causing the latches 62 to engage the lift truck 
forks 38 when the carriage is at or near the bottom of the mast, raising 
the carriage to cause the fork tines 52 to pivot until they are caused to 
lie generally parallel to the carriage in a folded position, and 
subsequently lowering the carriage to cause the fork tines to pivot back 
to their unfolded position wherein they extend generally perpendicularly 
from the carriage. 
Although a particular embodiment of the invention has been described in 
detail for purposes of illustration, various modifications may be made 
without departing from the spirit and scope of the invention. For example, 
one of skill in the art would readily appreciate that modifications may be 
made to the spring and the cable linkage 74 to permit the operator to 
quickly and easily engage or disengage the latch pins 60 associated with 
the fork backs 54. Moreover, other types of latches 62 may be 
advantageously utilized in connection with the invention, including 
electrically actuated solenoids and the like. Accordingly, the invention 
is not to be limited, except as by the appended claims.