Note: Descriptions are shown in the official language in which they were submitted.
CA 02412712 2002-11-25
' Lift Truck and Lift Truck Operating Method
The present invention relates to a lift truck, in particular a lift truck for
use in
warehouses. The present invention additionally relates to a method of
operating a lift
truck.
Lift trucks are known and fall into two broad categories, building trucks and
warehouse
type trucks.
Building trucks are used outside to transport material around building sites.
Typically
building trucks will have a mast with vertically moveable forks upon which the
material
can be lifted and carried.
Building sites have contrasting types of terrain, such as soft ground, rough
ground and
surfaces having loose material, in addition to the possibility of the terrain
being wet and
sloping. Therefore building trucks have particular features which enable them
to
negotiate such terrain.
To operate over rough terrain, the building truck must have a suitably high
ground
clearance in addition to the suspension properties of pneumatic tyres. The
tyre footprint
loading of the building truck must be sufficiently low to prevent it from
sinking into
soft ground. Consequently, high flotation tyres are employed, and the weight
of the
building truck is minimised, the weight being determined by the structural
strength
requirements of the truck.
To maintain traction over the various terrain, particularly when conditions
are wet, and
the surface is inclined, building trucks often employ drive t~ all four
wheels. This is
particularly necessary when taking into consideration the low weight of the
building
truck. Furthermore the centre of gravity is located at the approximately the ,
central
position of the building truck to load all four wheels evenly, thus ensuring
each wheel is
capable of providing tractive force.
CA 02412712 2002-11-25
2
Building trucks must also be sufficiently manoeuvrable, and generally have the
ability
to turn the forks and steering up to a maximum of about 45 degrees either side
of the
forward direction (i.e. in a yaw direction). However, angles signiheantly
above 4.5
degrees are not used since they tend to make the building truck unstable.
S
Building trucks are powered by petrol or diesel driven internal combustion
engines
where the harmful emissions are diluted in the atmosphere.
Building trucks are not required to lift loads to very great heights because:-
a) other forms of lifting devices are available e:g. cranes.
b) lifting a load to a significant height, when the building truck is on
uneven ground is
dangerous since the truck may tip over as the load is , raised. This is
particularly
significant on building trucks, which have pneumatic tyres (and hence allow
roll or
pitch of the truck body as the load is raised) and, as mentioned previously,
building
trucks are designed to be light (in line with strength requirements) and have
a relatively
high ground clearance (thus raising the centre of gravity of the truck).
Conversely warehouse type trucks axe required to Lift loads to significant
heights and
thus use a telescopic mast and fork arrangement to load and unload goods in
loading
bays, typically in the aisles of warehouses. To maximise space efficiency in
the
warehouse, the aisles are narrow, and goods are stacked vertically in the
loading bay.
25~ The conditions and he requirements of a lift truck in a warehouse, and the
associated
problems these conditions bring, contrast strongly with those conditions found
on a
building site and the requirements of a building truck.
Warehouses are inside and hence dry, the warehouse floor is generally hard and
smooth,
usually of concrete, as well as being flat. Therefore there are no associated
traction
problems associated with the w arehouse type truck when moving along an aisle,
and for
this reason warehouse type trucks employ drive to the two rear wheels.
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3
Operating inside a warehouse requires warehouse type trucks to be powered by
power
sources where there are no harmful emissions, such as gas fuelled internal
combustion
engines or electric motors. Therefore it would be inappropriate to use a lift
truck
powered by a petrol or diesel fuelled internal combustion engine in a
warehouse.
To maintain the stability of the warehouse type truck, particularly when it is
loading and
unloading goods into the loading bays, extra weight is added to the rear of
the
warehouse type truck. The combined extra weight and the weight of the heavy
goods
exhibits high loading on the tyres of the warehouse type truck, and hence
solid tyres are
used, i.e. non-pneumatic tyres, which do not significantly deform during
loading and
unloading. Such tyres exert high loadings on the ground which must be
sufficiently
strong to resist such loads, hence the use of concrete.
The added extra weight results in the centre of gravity being located towards
the rear of
the truck. Thus, the stability of the truck is improved when steering at high
steer angles.
Storage space is generally at a premium in warehouses and hence goods are
stacked to a
very significant height and aisles between rows of goods can be narrow.
Consequently,
it is difficult for a lift truck to retrieve and deposit goods that are
located at right angles
to the truck's direction of travel. If the goods are located at some height
above the
position of the lift truck driver this manoeuvre is further complicated by the
difficulty
of the driver in seeing whether the forks are at the correct height and
lateral position to
enter a pallet or the like upon which the goods are stored.
Prior art trucks have attempted to overcome his problem by employing pallet
forks
mounted on a traversing arrangement at 90° ao the truck"s direction of
travel. The
arrangement permits the forks to move into a pallet and retrieve the pallet
with no
movement of the remainder of the truck occurring. Such truck designs limited
to
working at this 90° angle; may suffer from stability problems at
height, and can be
relatively complex tb manufacture.
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!~.
The present invention seeks to overcome; or at least mitigate, the problems of
the prior
art.
One aspect of the present invention provides a lift truck comprising a first
portion
having a carriage mounted on a carriage mast and one or more first wheels, and
a
second portion distinct from the first and comprising a cab mounted on a cab
mast to
enable the raising of the cab and one or more second wheels, the first portion
being
pivotally mounted 'relative to the steering of the truck being capable of
being effected
by adjusting the angle of the first portion relative to the second, :wherein
substantially
all controls for controlling the functioning of the truck during depositing
and pickup of
goods are arranged so as to permit the raising thereof together with the cab.
A second aspect of the present invention provides a method of operating a lift
truck
comprising a first portion having a carriage mounted on a carriage mast and
one or
more first wheels, and a second portion distinct from the first and comprising
a cab
mounted on a cab mast to enable the raising of the cab and one or more second
wheels,
the first portion being pivotally mounted relative to the steering of the
truck being
capable of being effected by adjusting the angle of the first portion relative
to the
second, wherein substantially all controls for controlling the functioning of
the truck
during depositing and pickup of goods are arranged so as to permit the raising
thereof
together with the cab comprising the steps of
i) positioning the carriage at the required height to engage goods to be
picked
up;
ii) manoeuvring the entire truck into the required position to engage the
goods by
25~ driving at least one of the first or second truck wheels;
iii) raising the carriage to pick up the goods.
Embodiments of the present invention will now be described, by way of example
only,
with reference to the accompanying drawings, in which:
FIGURE 1 is a side view of a lift truck according to an embodiment of the
present
invention; and
CA 02412712 2002-11-25
FIGURE 2 is a plan view of the lift ruck of Figure 1.
Referring to the figures, a warehouse type lift: truck indicated generally at
10 comprises
a first portion 12 and a second portion 14 that are pivotally mounted together
by a pin
34 arranged along a vertical axis.
The first portion 12 comprises a mast 16, than may be raised telescopically
using any
suitable known means such as hydraulic rams: The mast 16 is shown in unbroken
lines
in its retracted position and in broken lines in its extended position. The
mast 16 shown
in the figures is a two-stage mast but in other embodiments other suitable
mast
arrangements may be provided (cg three stage masts).
A carriage 15 is provided on the front face at the top of the mast 16 and is
arranged to
mount pallet forks 18 or other suitable attachments such as spikes or grabs
{not shown).
Suitable arrangements comprising hydraulic rams (not shown) are preferably
provided
to enable the entire,mast 16 to be tilted (i.e. pitched) backwards and
forwards andlor the
carriage 15 to be tipped forwards and backwards relative to the mast.
A pair of wheels 32 are provided to support the first portion and are arranged
in a fixed
position relative to each other by an axle (not shown). The axle is preferably
arranged to
pivot about a horizontally arranged pivot pin 36 to permit the wheels to ride
over
uneven ground. The wheels 32 are driven by electric motors (not shown), but in
other
classes of embodiment; hydraulic or other suitable motors may be employed.
25~
The second portion 14 comprises a cab 22 mounted on a'second mast 20. The mast
20
is shown in a retracted position in unbroken lines and an extended position in
broken
lines. The cab is provided with a safety cage 28, a seat for the thick
operator 24 and a
plurality of controls 26 (including: a steering wheel 27) to control the speed
and
direction of the truck, as well as to enable the carnage 15 and cab 22 to be
lifted. As can
be seen from Figure 1, the entire cab 22 including the seat 24 and controls 26
may be
CA 02412712 2002-11-25
raised by the mast 20. The controls lifted with the cab include at least those
for
controlling the manoeuvring of the truck l0 and controls for lifting the fork
carriage 15.
The second portion further comprises a pair of wheels 30 mounted in a
substantially
fixed position relative to the second portion 14 and weights 25 to improve the
stability
of the truck 10, particularly when the masts 16 and 20 are raised. A
proportion of this
weight may be provided by batteries provided in the truck to store the energy
required
to power the motors.
In operation,, the truck operator drives down a warehouse aisle to the
location from
which he/she wishes to retrieve some palletised goods (not shown). If the
goods are
above ground level, he/she raises the pallet forks 18 to the required Level
and preferably
also raises the cab 22 to a position Where he/she has a good view of the
pallet forks 18.
Since the necessary truck controls 26 are raised with the cab, it is still
possible for the
truck manoeuvring and lifting functions to be operated. In a preferred
embodiment, the
cab 22 is automatically raised simultaneously with the forks 18 (e.g. under
the control
of a microprocessor controller or the like). Once the forks 18 are at the
correct height,
the operator turns the first portion 12 through 90° in direction A to
the position shown
in Figure 2. This is preferably achieved by independent motors (not shown)
driving
wheels 32 in opposite directions under the influence of an input from a
control 26 (e.g.
steering wheel 27) controlled by the driver. Of course, the first portion is
capable of
pivoting through 90° in the opposite direction to that shown in Figure
2 (i.e. the first
portion can be turned through 90° to the right or left of the straight
ahead position
shown in broken lines in figure 2). A suitable controller (e.g. A
microprocessor
~ controller) may be provided to convert inputs from the steering wheel 27
into the
appropriate relative angular velocities of the wheels.
Both wheels 32 may then be driven forward to enable the pallet forks 18 to
interengage
with a pallet (not shown) in a stack. The operator may then lift the pallet
and optionally
tilt the pallet backwards to ensure that it is held stably on the truck. To
remove the
pallet he/she then reverses the drive to wheels 32 so that the pallet is clear
of the stack
before again causing the wheels to be driven in opposite directions thereby
rotating the
CA 02412712 2002-11-25
forks I8 back to a straight-ahead position. Both of the forks 18 and the cab
22 may then
be re-lowered so that the goods stacked on the pallet may be transported
safely to their
desired location and deposited.
One advantage of the Lift truck of the present invention is that it requires
fewer
components than prior art trucks that permanently have the fork carriage 15
mounted at
90° to the vehicle's normal direction of travel, and which use a
separate "traverse"
mechanism to withdraw and deposit goods from a stack. Additionally, the truck
of the
present invention is more flexible in its operation than such prior art
trucks.
Furthermore, by ensuring that wheels 32 remain close to the forks l8 in a
fixed relative
direction at all times, the stability of the truck 10 may be improved.
It should be understood that numerous changes may be made within the scope of
the
present invention. The cab 22 or seat 24 may be arranged so as to rotate
together with
I S the forks I B. The truck may be driven by any suitable power unit such as
electric
motors, gas or diesel engines. Steering may be effected by alternative means,
such as
hydraulic rams) or the like mounted between the first and second portions, for
example. The truck may be rear wheel drive or four wheel drive (as
alternatives to front
wheel drive), and in which cases the rear wheels may be driven in opposite
directions to
permit the truck to be steered.
