Method and apparatus for providing operating information to an operator of a fork lift truck

A fork lift truck capacity monitor or alerting device informs operators of the weight on the forks and fork height and alerts operators whenever truck speed is above creep with the forks raised above a collapsed height or whenever the forks are raised above a recommended height for a given load. The alerting device includes a control circuit that receives inputs from a speed sensor, a fork height sensor and a weight sensor and reads a memory storing data correlating load weights with maximum recommended fork heights. A truck icon is displayed on a display panel. A plurality of height zone lamps representing the weight of the load on the forks are arranged in a vertical column over the truck icon and selectively illuminated according to the load on the forks. A plurality of lamps represent the height of the forks with the fork height lamps, which include one lamp positioned to represent a lowered position of the forks and a plurality of lamps equal in number to the height zone lamps and placed horizontally opposite therefrom, being selectively illuminated according to the height of the forks. An alarm signal alerts operators whenever the forks are raised above the recommended height for a given load weight, or whenever truck speed exceeds a predetermined maximum speed and the forks are above the collapsed height. The alarm signal may include a combination of an audible signal, a text message, and a flashing lamp.

BACKGROUND OF THE INVENTION 
This invention relates to an improved method and apparatus for providing 
information to a fork lift truck operator regarding the vertical position 
of forks of the truck, the height to which the forks can be raised for a 
given load and the speed of the truck by means of a display and an audible 
alarm. 
Fork lift trucks, such as rider reach lift trucks, are often provided with 
a placard or plate on which capacity information is placed, e.g., 
information as to how high the forks may be raised with various loads on 
the forks. A capacity plate may include a table which states load weight 
versus recommended fork height indicating for a given truck that a load of 
2500 pounds may be lifted to a recommended maximum height of 321 inches, a 
load of 3000 pounds may be lifted to a recommended maximum height of 300 
inches, a load of 4000 may be lifted to a recommended maximum height of 
270 inches, and so forth. It is apparent that such information can be used 
by the operator to determine heights to which a given load can be lifted 
and/or load size which can be lifted to a given height. The center of the 
load is also an important consideration. For example, if a load is moved 
from 24 inches forward of the mast to 34 inches forward of the mast, the 
load capacity may be reduced from 3000 pounds to 2100 pounds. 
There is a need for a more convenient, attention getting, way of providing 
an operator with the information necessary to operate a fork lift truck to 
assist the operator in estimating or determining the weight of the load, 
the height of the forks and the speed of the truck. 
SUMMARY OF THE INVENTION 
In the present invention, the speed of the truck, the weight of the load on 
the forks and the height of the forks are monitored and compared with 
capacity data regarding the truck. A visual display panel is provided to 
make clear to an operator of the truck the maximum recommended fork height 
for an existing load. The invention also provides a visual indication 
whenever the forks are raised above a staging or collapsed height, i.e., 
the top of a lowermost mast member, and alerts the operator using flashing 
lights and audible alarms when certain other conditions are present. 
A display panel includes, among other things, a representation of a lift 
truck, a set of four indicators above the truck representing the load on 
the forks and hence a maximum recommended fork height for that load; a 
second set of five indicators in the form of forks representing the height 
of the forks, one of which represents the forks below the staging or 
collapsed height; and, a visual indicator representing an operator 
correctable error. The truck is also provided with a chime or other 
audible alarm device and a text display screen for providing the operator 
with written instructions, when necessary. 
It is therefore an object of the present invention to provide a method and 
apparatus for displaying information to the operator of a lift truck 
relating to the actual height of the forks and a maximum recommended 
height to which the forks should be raised with an existing load. 
It is another object of the present invention to provide a method and 
apparatus for providing a visual indication whenever the forks are raised 
above the collapsed height; and further, to provide an alarm whenever the 
forks are raised above the collapsed height and the speed of the truck is 
above a predetermined speed. Preferably, the alarm provides both a visual 
and an audible alarm whenever the forks are raised above the collapsed 
height and the speed of the truck is above a predetermined speed. 
Other objects and advantages of the invention will be apparent from the 
following description, the accompanying drawings and the appended claims.

DETAILED DESCRIPTION OF THE INVENTION 
Reference is now made to the drawings and particularly to FIG. 1, which is 
a view of a display panel 10 on an electric powered lift truck showing 
various indicators for use by an operator of the truck. Included on the 
display panel 10 is a battery voltage level indicator 15 (a type of fuel 
gauge) that is provided with a symbol 20 that represents a battery, a 
symbol 21 that represents a discharged battery and a symbol 22 that 
represents a charged battery. A plurality of indicator lamps 25 show the 
actual state of charge of the battery. It is noted that while the term 
"lamp" is used to refer to indicators which are illuminated or flashed, 
lamp is intended to include light emitting diodes (LED's) and any other 
form of illumination device now in existence or later developed which is 
immediately or remotely associated with the area to be illuminated, for 
example by fiber optics. 
A lift truck representation 28 is formed on the display panel 10. 
Associated with the lift truck representation 28 are a set of disks L1-L4 
that size-wise represent the maximum permissible load at different heights 
of the forks; several height zone indicator lamps C1-C4, which indicate 
the recommended height range to which the forks of the lift truck should 
be raised for a given actual load on the forks; and, fork height lamps 
H1-H4 and 30 which represent the actual height of the forks with the fork 
height lamp 30 indicating when the forks are in a free lift zone beneath 
the collapsed height for the truck. Also on the display panel 10 are an 
operator correctable error indicator 35 (an ISO standard symbol), a 
maintenance needed indicator 40, a performance tune pushbutton 45, a truck 
hour usage pushbutton 50 represented by a stylized hourglass symbol, a 
maintenance pushbutton 55, a text display screen 60, and three push 
buttons 65, 70 and 75 for controlling the input of data to the text 
display screen 60. 
FIG. 2 illustrates a typical rider reach fork lift truck 100, such as 
Series RR or RD lift trucks manufactured by Crown Equipment Corporation, 
the assignee of the present application. The truck 100 includes a power 
unit 110 which houses a battery 115 for supplying power to a traction 
motor (not shown) connected to a steerable wheel 120 and to hydraulic 
motors (not shown) which supply power to several different systems, such 
as mast, fork and reach hydraulic cylinders. An operator's compartment 125 
in the power unit 110 is provided with a steering tiller (not shown) for 
controlling the direction of travel of the truck 100, and a control handle 
135 for controlling travel speed and direction as well as fork height, 
extension, and tilt. The speed of the truck 100 is measured by a 
tachometer, represented at 140, included within the truck 100 in a 
conventional manner. An overhead guard 145 is placed over the operator's 
compartment 125. 
A pair of forks 150 are mounted on a fork carriage mechanism 155 which is 
in turn mounted on a carriage assembly 170. A load back rest 160 is 
provided, as shown. As described in U.S. Pat. No. 5,586,620 which is 
incorporated herein by reference, the carriage assembly 170 is attached to 
an extensible mast assembly 180 by a scissors reach mechanism 175 
extending between the carriage assembly 170 and a reach support 176. The 
reach support 176 is mounted to the mast assembly 180 which includes a 
fixed, lower mast member 182 and nested movable mast members 184 and 186. 
A hydraulic cylinder (not shown) is operated by control handle 135 to 
control the height of the forks 150. As shown in FIG. 2, the mast is 
raised and the reach mechanism 175 is extended. 
The height of the forks 150 is measured by a digital encoder, represented 
at 190, which may be similar to the device shown in U.S. Pat. No. 
5,103,226 which is incorporated herein by reference. In the illustrated 
embodiment, the height of the forks 150 is also detected by a height 
switch, represented at 191, which is mounted on the reach support 176 and 
actuated whenever the height switch 191 is disengaged from a track (not 
shown) on the mast member 186. The height switch 191 is positioned so that 
it is actuated whenever the top of the load back rest 160 extends above 
the top of the fixed mast member 182, i.e., the collapsed height as shown 
by dashed line 34. As used herein, the term "collapsed height" refers to 
the top of the lower mast member 182 as represented by the dashed line 34. 
Thus, "below the collapsed height" means that neither the back rest 160 
nor either of the mast members 184 or 186 extends above the dashed line 
34. 
The height switch 191 can be mounted on the reach support 176 at a height 
corresponding to the height of the back rest 160 if different height load 
back rests are used. However, it may be preferred to mount the height 
switch 191 at a single position corresponding to the tallest load back 
rest which is provided for a given series of trucks. In this way, the 
switch 191 is ensured to be actuated at or before extension of the back 
rest above the top of the mast member 182 regardless of which back rest 
may be used on a truck. 
The forks 150 may be tilted through a range shown by the arrow 195 by means 
of a hydraulic tilt cylinder 200 located between a bracket attached to the 
forks 150 and the carriage assembly 170, see FIGS. 2 and 3. The weight of 
the load on the forks 150 is measured by a pressure transducer which 
serves as a weight sensor 210 that is attached to a hydraulic line 
connected to the tilt cylinder 200, see FIG. 4. A tilt switch 250 is 
actuated whenever the forks 150 are at their full tilt down or full tilt 
back positions, as will be explained. 
Referring now to FIG. 4, which is a hydraulic schematic diagram for the 
reach, side shift and tilt functions of the fork lift truck 100 shown in 
FIG. 2, hydraulic fluid under pressure is supplied to a hydraulic manifold 
220 in the carriage assembly 170 by hydraulic input lines 222 and 224. 
Within the manifold 220 are a pair of check valves POCV and a solenoid 
valve SVR which controls and directs hydraulic fluid to a pair of reach 
cylinders 226 and 228. 
Hydraulic fluid under pressure is also applied to a manifold 230 which 
includes a solenoid valve SVT for controlling the operation of the tilt 
cylinder 200. A load sensing check valve 242 is included in a return line 
244, which is in turn connected to the input line 222. The weight sensor 
210 is connected to one side of the tilt cylinder 200 to monitor the 
pressure of the hydraulic fluid in the tilt cylinder 200 which pressure is 
a function of the weight being carried by the forks 150, provided, of 
course, that the forks 150 have not reached a mechanical stop (not shown) 
due to tilting movement of the forks 150. Tilting of the forks 150 is 
monitored by the switch 250 which is activated by the forks 150 
immediately prior to the forks 150 reaching the mechanical stop so that 
the tilt switch 250 is actuated whenever the forks 150 are in their full 
tilt down or full tilt back positions. Preferably, the tilt switch 250 
comprises a single switch 250S which is engaged with a plunger/cam 250PC 
which is spring biased to extend outside the tilt switch 250, see FIGS. 3 
and 3A. Advantageously, the switch 250S is activated whenever the plunger 
250PC is forced back into the tilt switch 250 or extended a defined 
distance beyond the tilt switch 250 so that both full tilt down and full 
tilt back positions can be detected using the single switch 250S. 
In this way, the tilt switch 250 is actuated when the weight signal 
generated by the weight sensor 210 may not be accurate due to the forks 
150 being tilted into contact with the mechanical stop. As illustrated in 
FIG. 5, the tilt switch 250 and more particularly the switch 250S includes 
a normally closed contact which is connected in series with the weight 
sensor 210 so that the signal from the weight sensor 210 is interrupted 
whenever the forks 150 are tilted into engagement with the mechanical stop 
and the weight signal is not accurate. Whenever the forks 150 are at 
either the full tilt down position or full tilt back position, as detected 
by the tilt sensor or tilt switch 250, and the weight sensor 210 does not 
accurately reflect the weight of the load on the forks 150, none of the 
indicators of the display panel 10 are energized and the message MONITOR 
DISABLED is displayed on the text display screen 60. 
The weight sensor 210 is preferably a transducer which provides an output 
signal proportional to weight. The output signal from the weight sensor 
210 is used to determine the weights of the loads on the forks 150 and 
thereby the height zone lamps C1-C4 to be lighted to indicated recommended 
height ranges for the loads. The weight sensor 210 can also be a simple 
switch, in which case, the only display would be weight above and below 
the threshold level of the switch, or in other words, above and below a 
predetermined level. 
The electrical block diagram of FIG. 5 shows a speed sensor illustrated as 
the tachometer 140, the fork height sensor 190, the weight sensor 210, and 
the tilt switch 250 connected to a control circuit taking the form of a 
microprocessor 80 in the illustrated embodiment which processes the input 
data from these devices in accordance with data representative of the 
truck 100 recorded in a storage device represented by a memory 85. The 
results of this processing are then displayed on the display panel 10, 
and, if necessary, audible alarm 90 is sounded. The microprocessor 
includes a lamp flashing mechanism. 
Referring now to FIGS. 6-8, wherein a second simplified embodiment of a 
display panel 10a for a lift truck without a weight sensor but having a 
sensor that detects when the forks are above the collapsed height 
represented by the dashed line 34 and a truck speed sensor. FIG. 6 shows a 
representation 28 of a lift truck with the forks represented by a fork 
lamp 32 which is not energized when the forks are below the collapsed 
height. In FIG. 7, fork lamp 32 is on or energized when the forks of the 
truck are above the collapsed height line 34 and the vehicle's speed is 
below a predetermined value. FIG. 8 shows the fork lamp 32 flashing and an 
audio alarm 90 sounding when the forks of the truck are above the 
collapsed height 34 and the truck's speed is above a predetermined value. 
Reference is now made to FIGS. 2, 5 and 9-21. The weight of the load on the 
forks 150 is measured by the weight sensor 210 and used by the 
microprocessor 80, together with truck data stored in the memory 85, to 
determine a recommended height to which a load of that weight should be 
lifted. The truck load weight/recommended height data in the illustrated 
embodiment is based on having the load center 24 inches from the back of 
the load back rest 160 and 24 inches above the forks 150. However, in the 
present invention, truck data can be provided for a plurality of load 
centers with the appropriate set of data being manually selected by the 
owner or operator of the truck depending upon specific loads being 
handled. Specific data for one of a plurality of load centers can also be 
selected automatically if a load moment sensor is available on the truck. 
As is well known, the load weight (height of the forks) that is recommended 
to be carried by a fork lift truck is a function of the height of the 
forks (weight of the load); the higher the forks (load weight), the lower 
the recommended load (fork height), as represented by symbols L1-L4 in 
FIG. 1. According to the present invention, the height zone indicators 
C1-C4 are energized to indicate the recommended maximum height or range of 
height to which the forks should be raised for the weight of a sensed load 
on the forks. For example for a truck represented by height/weight 
specification data shown in Table 1, the height zone indicator lamps C1-C4 
are energized as shown. Thus, if the sensed weight on the forks is less 
than or equal to 2500 pounds, for example, all the height zone indicator 
lamps C1-C4 are illuminated since for such weights there is no limitation 
on the recommended height to which the forks can be raised. Therefore, 
when the actual weight is less or equal to 2500 pounds, the maximum 
recommended fork height is 321 inches, the maximum lift height for the 
truck. As another example of interpreting Table 1, if the sensed weight on 
the forks is 3200 pounds, then only lamps C1 and C2 would be illuminated, 
and the maximum recommended fork height is 270 inches. Other examples are 
described below with reference to the drawing figures. 
TABLE 1 
______________________________________ 
Indicator Weight (pounds) 
Max. Height (inches) 
______________________________________ 
C4 .ltoreq.2500 
321 
C3 .ltoreq.3000 
300 
C2 .ltoreq.4000 
270 
C1 .ltoreq.4500 
240 
______________________________________ 
If the interrelated specifications for load weight, fork height and truck 
speed are violated, the microprocessor 80 lights certain lamps on the 
display panel 10 or 10a. The microprocessor 80 may also make some lamps 
flash, sound an audible alarm, and in some cases, generate a text message 
on the text display screen 60, as illustrated in the flow chart of FIG. 21 
and shown in Table 2 for the illustrated embodiment. 
TABLE 2 
______________________________________ 
HEIGHT/WEIGHT 
SPEED LAMP 
LIMITS LIMIT 35 ALARM 90 
TEXT 60 
______________________________________ 
Under Spec &lt;Creep Off Off None 
Under Spec .gtoreq.Creep 
Off On None 
Over Spec &lt;Creep On On CHECK LOAD 
Over Spec .gtoreq.Creep 
On On CHECK LOAD 
______________________________________ 
The microprocessor 80 continuously processes the signals coming in from the 
weight sensor 210, the fork height sensor 190 and the speed sensor 140. 
While these signals can be processed in a number of ways for the present 
invention, FIG. 21 illustrates a currently preferred processing flow. In 
FIG. 21, the current weight signal is read and used to calculate the 
recommended fork height for the corresponding weight and the number of 
height zone indicator lamps C1-C4 or icons which should be illuminated to 
advise the truck operator of the recommended maximum fork lift height, see 
block B1. The corresponding height zone indicator icons are then 
illuminated, see block B2. 
A check is then made to determine whether the forks 150 have been tilted to 
the point that they contact the mechanical rest as indicated by actuation 
of the tilt switch 250. If the tilt switch 250 is actuated, the signal 
from the weight sensor 210 is interrupted which is sensed at block B3 by 
the value of the weight signal from an analog to digital (A/D) converter 
is equal to zero. If so, all weight icons and other indicators are turned 
off and a MONITOR DISABLED message is displayed on the text display screen 
60, see block B4. 
The current fork height signal is read and used to determine which one of 
the fork height lamps H1-H4 or icons to illuminate to indicate to the 
operator of the truck the height or height zone of the forks 150, see 
block B5. The determined fork height icon is then illuminated, see block 
B6. Next, the fork height is compared to the recommended fork height based 
on the weight of the load on the forks 150 as determined in block B1, see 
block B7. If the fork height is greater than or equal to the recommended 
fork height based on load weight or weight level, a CHECK LOAD message is 
displayed on the text display screen 60 and the operator correctable error 
indicator 35 is illuminated, see block B8. If the fork height is less than 
the weight level, no such action is taken. 
The fork height is then compared to the staging or collapsed height for the 
truck and the signal from the truck speed sensor 140 is read, see block 
B9. If the fork height is greater than the collapsed height for the truck 
and the travel speed is greater than a predetermined maximum value, for 
example 1.5 miles per hour (mph), also known as creep speed, then the 
illuminated fork icon is flashed and the audible alarm 90 is sounded, see 
block B10. This processing sequence is then repeated to maintain the 
alerting system of the present invention up to date for current truck 
operating conditions. These operations will be clarified by the following 
examples which represent specific truck operating conditions and how the 
alerting system responds. 
In operation, when the fork lift truck 100 is initially turned on, the 
microprocessor 80 initiates a self check procedure which causes each of 
the lamps in the display to be energized, displays the word TEST on the 
text display screen 60, and causes the audible alarm 90 to sound briefly 
as shown in FIG. 9. The indicator lamps shown in FIGS. 6 to 20 may be off, 
on or flashing. In the drawings, when off, a lamp is represented by an 
outline, for example as shown by H1-H4 in FIG. 10; when on, a lamp is 
represented by a solid shape, for example as shown by C1-C4 in FIG. 10; 
when flashing, a lamp is represented by cross-hatching, for example as 
shown by H1 in FIG. 14. 
If the weight of the load on the forks 150, as detected by the weight 
sensor 210, is below the weight permitted for elevation of the forks to 
full height, and the forks are below the collapsed height, then the 
display will be as shown in FIG. 10. All of the height zone indicator 
lamps C1-C4 are illuminated indicating that the operator may raise the 
forks 150 to their maximum height. It is to be understood that while four 
zones are described, the display may include any reasonable number of 
zones greater than four or less than four. The lamp 30 is also energized 
to indicate that the forks are in a free lift zone beneath the collapsed 
height for the truck. 
If the weight of the load on the forks 150 exceeds the weight recommended 
for full height extension of the forks, then the display will appear as 
shown in FIGS. 11 and 12. In FIG. 11, the weight of the load on the forks 
150 is less than or equal to 3000 pounds so that the forks 150 should not 
be raised above the height represented by height zone indicator C3 and, 
accordingly, the height zone indicators C1-C3 are illuminated while the 
height zone indicator C4 is not illuminated. Similarly, in FIG. 12, if 
additional weight is added to the forks 150, the maximum height should be 
limited to the height represented by illumination of only the height zone 
indicator C1. 
When the forks 150 are moved above the collapsed height represented by the 
dashed line 34 in FIG. 2, then the lamp 30 is extinguished. The actual 
fork height (in zones) is represented by energizing one of the fork height 
indicator lamps H1-H4. Thus, in FIG. 13-16, the forks 150 are shown as 
being raised above the collapsed height, and therefore the forks and/or 
mast of the truck extends above the collapsed height, i.e., dashed line 
34, which represents the minimum height of the truck, and into the first 
zone, H1. In FIG. 13 the weight of the load permits full height extension 
of the mast or maximum height of the forks, as shown by illumination of 
all of the height zone indicator lamps C1-C4, and the speed of the truck, 
as monitored by speed sensor or tachometer 140, is below 1.5 mph, creep 
speed. FIG. 14 is similar to FIG. 13 except that the truck's speed is 
equal to or greater than 1.5 mph, creep speed. As shown, the lamp H1 is 
flashing and an audible alarm 90, typically a chime, is sounding to alert 
the operator to the operating conditions. 
FIGS. 15 and 16 are similar to FIG. 13 and 14, but the load on the forks is 
greater so that a lower maximum fork height is recommended. That is, the 
maximum recommended fork height is limited to the height zone indicated by 
the height zone indicator C2. Accordingly, to be in compliance with 
recommend truck operation, the forks 150 should only be raised to the 
height represented by height zone lamp C2, or fork height zone H2. Of 
course, the operator can move the forks to any height since the invention 
of the present application does not control or limit truck operation but 
only alerts the operator to operating conditions which should be of 
concern to the operator. 
If the load on the forks is greater than the recommended maximum for the 
truck, with the forks 150 in the lowermost position, then the display 10 
appears as shown in FIG. 17. None of the lamps C1-C4 are energized, since 
the weight on the forks is above the maximum for even zone C1, the 
operator correctable error indicator 35 is energized, and a message CHECK 
LOAD is displayed on the text display screen 60. 
Similarly, if the forks are raised above the recommended height based on 
the sensed weight of the load on the forks 150, the display appears as 
shown in FIG. 18. In both FIGS. 17 and 18, the speed of the truck is less 
than the predetermined creep speed. If the speed is increased to equal or 
exceed the so-called creep speed, then the display will appear as shown in 
FIG. 19 where the fork height indicator lamp H3 is flashing and the 
audible alarm 90 is sounding. 
Having thus described the invention of the present application in detail 
and by reference to preferred embodiments thereof, it will be apparent 
that modifications and variations are possible without departing from the 
scope of the invention defined in the appended claims.