Technical Field
This invention relates to a motorised truck having a tiller-controlled steerable wheel.
The invention is especially, but not exclusively, applicable to pedestrian-operated
pallet carriers, forklift trucks and order pickers.
Background Art
Many materials are stored in warehouses on pallets, either on the ground or above
ground on racking. Aisles between the palletised materials allow the operator of
pedestrian-operated forklift trucks to select whatever pallet they require. However,
the aisles need to have a certain minimum width to allow unrestricted operation of
the trucks. This will now be described with reference to Figs, l a and lb.
Fig. l a is a schematic top plan view of a conventional pedestrian-operated forklift
truck. The truck comprises a chassis 10 having left and right non-steerable, nondriven
front wheels 12L, 12R respectively and a steerable rear drive wheel 14
disposed centrally between, but rearwardly displaced, relative to the front wheels.
The chassis 10 carries a conventional lifting mechanism such as a mast 16 and lift
forks 18. In some trucks with tillers the lift forks are replaced by lift platforms. The
rear wheel 14 is directly or indirectly connected to a steering tiller 20 by a
mechanical, hydraulic, electrical or other coupling. The truck is controlled from a
tiller head 22, mounted at the free rear end of the tiller 20, by a pedestrian operator
24. A traction motor (not shown in Figs, l a and lb) drives the steerable rear wheel
14 in forward or reverse directions about a horizontal rotation axis 26 under the
control of manually operable control members (also not shown) on the tiller head 22.
The rear wheel 14 is steerable by rotation about a substantially vertical axis by
rotation of the tiller 20. The connection between the tiller 20 and the rear wheel 14
is such that when the tiller 20 is rotated through a certain angle the rear wheel 14
follows suit so that the rear wheel 14 is always in line with the tiller 20; i.e. the
horizontal rotational axis 26 of the rear wheel 14 is always normal to a vertical plane
containing the tiller 20.
Conventional pedestrian-operated forklift trucks as described above normally
operate in an aisle 30 (Fig. lb) between two parallel rows 32 of palletised product. In
order to pick up any particular pallet the truck needs to be initially positioned at right
angles to the row 32 with the tiller 20 extending directly to the rear, as shown in Fig.
lb. This means that the aisle 30 must have a minimum width W equal to the total
length of the truck. The required steering space Sis necessary but effectively wasted
storage space.
Disclosure of the Invention
According to the present invention there is provided a motorised truck with tiller
comprising:
(a) a chassis having a plurality of ground-engaging wheels, at least one of which is
steerable to steer the truck;
(b) a drive motor for driving at least one of the wheels to move the truck across
the ground;
(c) a tiller rotatably connected to the chassis which may be swung from side to
side to steer the truck;
(d) a steering motor for varying the angle of the steerable wheel;
(e) a steering motor controller which, in a normal mode of operation, receives as
an input an indication of the tiller angle and which outputs in response thereto
a control signal to the steering motor to vary the angle of the steerable wheel
such that the angle between the tiller and steerable wheel maintains a
predetermined angular offset;
wherein the angular offset between the tiller and steerable wheel may be adjusted
and the adjusted angular offset subsequently used as the predetermined
angular offset.
This allows greater manoeuvrability compared to conventional trucks where the tiller
is in fixed alignment with the drive wheel. It further allows the truck to be driven
straight ahead forward or backwards with the tiller offset by a considerable amount,
such as with the operator and tiller offset to the side of the truck.
The steering motor controller may be integral with the steering motor or separate
therefrom. It may be implemented in hardware, firmware, or in software running on
a suitable processing apparatus. It can be implemented as logic circuitry which may
be programmable or dedicated to the task. Where the steering motor controller is
implemented using programming, the apparatus on which it runs or into which it is
programmed may perform additional functions related or unrelated to steering.
Preferably, the steering motor controller is further operable, in a realignment mode
of operation, to steer the wheel so as to change said predetermined angular offset.
In particular, by allowing for a realignment mode of operation the tiller can be offset
from the steering direction, or viewed another way, the steered wheel can be
realigned along a different axis when the tiller is positioned off to one side.
A particularly preferred embodiment permits automatic alignment of the steered
wheel with either of two major axes of interest, namely the tiller axis and a major
axis of the truck chassis, i.e. the normal front-rear axis or the axis along which the
tiller is aligned when in a neutral steering position.
Preferably, therefore, in said realignment mode of operation the steering motor
controller is operable to change said predetermined angle between (i) a zero tiller
angle wherein the wheel is aligned parallel to the tiller and (ii) a zero chassis angle
wherein the wheel is aligned parallel to an axis of the chassis and offset from the
tiller by the same angle as the tiller is offset from the chassis during the realignment
mode of operation.
The axis of the chassis is, as mentioned above, preferably an axis defined by the axis
of the tiller when the tiller is in a neutral steering position. It may be the front-rear
axis, the left-right axis, an axis defined by forks provided on the truck (e.g. on a pallet
carrier or forklift truck, etc.
Preferably, the steering motor controller receives as an input an indication of the
tiller angle relative to one or more of the chassis, the steerable wheel, or the steering
motor.
Further, preferably, the steering motor controller receives as an input an indication of
the steerable wheel's steering angle relative to one or more of the chassis, the tiller,
or the steering motor.
The received indication of tiller angle may be an absolute measurement or may be an
indication that the angle has changed by a detected amount.
Preferably, the truck further includes an angular sensor system of one or more
sensors which detect and output an indication or indications of the relative angle
between two or more of the tiller, the steerable wheel, the steering motor, and the
chassis.
Any suitable sensor system may be used to provide the required output. Preferably
the sensor system comprises one or more rotary encoders which sense the relative
angle between two or more components. The skilled person will appreciate that if,
for example, the steering motor is fixed to the chassis and two angular sensors are
provided, with one sensor providing the angle of the steered wheel relative to the
motor housing, and the other providing the angle between the tiller and the motor
housing (or chassis), then it is trivial to calculate the relative angle between the tiller
and steered wheel as a sum or difference of the angles adjusted by an offset.
Further, preferably, the indication or indications output by said angular sensor
system provide the steering motor controller with information to determine, during
said realignment mode of operation, the angle between the tiller and the steerable
wheel and/or the angle between the steerable wheel and the chassis.
More preferably, when said steering motor controller is operating to change said
predetermined angle to a zero tiller angle it receives as an input from the angular
sensor system information sufficient to determine the angle between the tiller and
the steerable wheel, and when said steering motor controller is operating to change
said predetermined angle to a zero chassis angle it receives as an input from the
angular sensor system information sufficient to determine the angle between the
steerable wheel and the chassis.
The drive motor is preferably operable to drive the steered wheel. It is operable
regardless of whether the wheel is aligned with the tiller or the chassis or some other
alignment. It may optionally be disabled during the realignment mode of operation
but this is not critical.
In a preferred configuration the chassis supports the tiller at a rear end and forks at a
front end, and the steered wheel is at the rear end, with one or more unsteered
wheels (which may be driven or not) at the front end.
A particularly preferred configuration is a three-wheeled truck with two front wheels
which are undriven and not steered, and a single driven, steered, rear wheel which is
positioned generally beneath the rotation axis of the tiller.
The axis of rotation of the tiller is preferably vertical or includes a substantial vertical
component (> 45 degrees from horizontal , more preferably > 60 degrees, even more
preferably > 75 degrees and most preferably 85 to 90 degrees from horizontal) such
that when the tiller is rotated about the axis it swings sideways and not simply
vertically (as it would about a horizontal axis).
In a preferred embodiment the tiller has a tiller head at its free end, the tiller head
having one or more manual controls which when actuated engage the realignment
mode of operation.
In a particularly preferred embodiment, the manual controls can select between at
least two states, namely a zero tiller angle and a zero chassis angle as described
above.
Preferably, when the steering motor controller is in said realignment mode of
operation the tiller is decoupled from the steerable wheel.
Preferably, when the steering motor controller in said realignment mode of operation
has completed steering the wheel so as to change said predetermined angular offset,
the steering motor controller reverts to said normal mode of operation to steer said
wheel to follow the tiller based on the new predetermined angular offset achieved in
the realignment mode.
The realignment mode of operation may be implemented by storing a new
predetermined angular offset which the steering motor then implements in a normal
steering operation by matching the actual offset to the new stored offset.
In a further independent aspect of invention, there is provided a pedestrian-operated
motorised truck with tiller, having a tiller-controlled steerable drive wheel, wherein
the tiller can be selectively de-coupled from and re-coupled to the drive wheel to
allow rotation of the tiller independently of the steering angle of the drive wheel,
whereby the tiller can be fixed at different angular positions relative to the drive
wheel.
This allows greater manoeuvrability compared to conventional trucks where the tiller
is in fixed alignment with the drive wheel.
Preferably, the drive wheel is motorised and can be driven both with the tiller aligned
with the wheel and with the tiller offset from the driving direction of the drive wheel.
This allows the truck to be manoeuvred in tight spaces, such as in warehouse aisles,
with the operator and the tiller at an offset angle. In particular the truck can be
driven forwards or backwards into or out of a loading space with the tiller offset and
the operator standing to the side rather than in line with the driving direction.
In a preferred embodiment the tiller has a tiller head at its free end, the tiller head
having a manually operable control member which when placed in one state de
couples the tiller from the drive wheel and when placed in a second state re-couples
the tiller to the drive wheel.
The truck preferably has a steering motor for varying the steering angle of the drive
wheel.
Further, preferably, the truck has a steering motor controller which receives as an
input an indication of tiller angle and which outputs a control signal to the steering
motor to change the steering angle in accordance with detected changes in the tiller
angle.
Preferably, while the tiller is selectively decoupled from the drive wheel, changes in
the tiller angle are either not received as an input or are not converted to output
control signals to the steering motor.
The truck preferably further comprises a tiller angle sensor which senses the angle of
the tiller relative to one of the drive wheel and a chassis of the truck with tiller and
which provides an indication of said angle as an input to the steering motor
controller.
The truck preferably further comprises an operator steering control to selectively
engage the steering motor and vary the steering angle relative to the tiller.
In a preferred embodiment the steering motor controller is operable to receive as an
input a selection of a specific angular relationship between the tiller and the drive
wheel and to output a control signal to the steering motor to change the steering
angle to said selection.
Preferably the truck is provided with a specific control input to enable selection of a
particular angular relationship between the tiller and truck.
Preferably, the steering motor controller is operable to receive as an input an
indication of the current steering angle and to compare the current steering angle
with a desired angle stored in a memory or register accessible to the steering motor
controller, and to output to the steering motor a control signal to change the steering
angle to match said desired angle.
Preferably, the truck further comprises said memory or register.
Further, preferably, said desired angle is reset to match a current detected angle
when the tiller is re-coupled to the drive wheel.
The steering motor controller may be implemented as hardware control circuitry
which is designed to implement the or each function ascribed to it above, or the
functionality may be implemented in logic circuits or programmable logic, or a
processor executing software instructions in any suitable code format. Where a
memory or register is employed to store a desired angle, that memory or register
may be integral with the control circuitry, logic, or processor, or may be separate to
and addressable by the control circuitry, logic, or processor.
Preferably the tiller may be offset from the drive wheel by an angle of 75 degrees or
greater, more preferably, 90 degrees or greater.
The motorised truck with tiller may preferably be a forklift truck, a pallet carrier or an
order picker.
There is also provided a method of manoeuvring a motorised truck with tiller,
comprising the steps of:
(a) driving the truck within an aisle with the tiller substantially aligned with a
steerable wheel of the truck;
(b) positioning a front end of the truck adjacent a space into which the truck is to be
manoeuvred along the aisle;
(c) adjusting the angular offset between the tiller and steerable wheel such that the
steerable wheel is offset from the line of the tiller by more than 45 degrees; and
(d) driving front of the truck into said space while maintaining the offset of greater
than 45 degrees between the steerable wheel and the tiller.
By "substantially aligned" is meant that the wheel is aligned to the tiller sufficiently
for it to be perceived to steer true, i.e. it need not be in exact alignment.
An alternative t o steps (c) and (d) is that in step (c) the tiller is offset from the neutra l
steering position by an amount at least equa l t o the angle required for the end of the
tiller t o be level with or forwa rd of the back of the truck, and for the wheel t o then be
aligned with the major axis of the chassis, this defining an offset angle between tiller
and wheel which is maintained as the front of the truck is driven into the space.
Prefera bly, in steps (a) and (b) said wheel is aligned with the line of the tiller t o within
10 degrees or less, more prefera bly 5 degrees or less, and most prefera bly within 3
degrees or less. Most prefera bly, the wheel follows substa ntia lly the same angle as
the tiller within the control limits of the steering motor and controller.
Prefera bly in steps (c) and (d) the steera ble wheel is offset from the line of the tiller
by 60 degrees or more, more prefera bly 80 degrees or more. A particula rly preferred
implementation of the method has an offset defined when the wheel is aligned t o
the chassis and the tiller rotated by an amount sufficient t o bring the end of the t iller
level with or forwa rd of the rea rmost point of the truck body.
Brief Description of the Drawings
Em bodiments of the invention will now be descri bed, by way of exa mple, with
reference t o the accom panyi ng drawi ngs, in which :
Figs, l a and l b (previously described) are schematic top pla n views of a
conventiona l pedestria n-operated forklift truck.
Figs. 2a and 2b are schematic top pla n views of an embodi ment of motorised
truck with t iller accordi ng t o the invention as it manoeuvres through a
typical series of operations in an aisle.
Figs. 3a t o 3c are perspective views of the steering mecha nism of the truck of
Fig 2.
Fig. 4 is a block diagram of the control circuit for the truck of Fig. 2.
Fig. 5 is a flowchart of operation of a steering motor controller for use in a
motorised truck with tiller according t o the invention, when in an "align
t o tiller" mode.
Fig. 6 is a second flowchart of operation of a steering motor controller for use in
a motorised truck with tiller according t o the invention, when in an "align
t o chassis" mode.
Figs. 7a t o 7f are schematic top plan views of another embodiment of motorised
truck with tiller according to the invention, and a typical sequence of operations.
Figs. 8 to 11 are flowcharts detailing the operation of a steering controller in
various modes of operation.
Fig. 12 is a block diagram of the control circuit for the forklift truck.
Detailed Description of Preferred Embodiments
In the drawings the same reference numerals have been used for the same or
equivalent components.
Referring t o Figs. 2a and 2b, a pedestrian-operated forklift truck or pallet carrier is
shown successively in five positions denoted 1, 2, 3, 4, 5 (position 3 is repeated at the
end of Fig. 2a and at the start of Fig. 2b for continuity) as it is manoeuvred into a
space 11 in an aisle 30 between two rows of palletised products. The truck is
generally of the same configuration as described above in relation t o Figs, l a and l b
and thus like parts such as chassis 10, tiller 20, steerable wheel 14, etc.) are denoted
by like reference numerals and need not be described specifically again.
The aisle is of a width which is not much greater than the length of the truck plus its
load 13, as can be seen from position 3 in Figs. 2a and 2b. Nevertheless the truck can
be manoeuvred into and out of the space 11 with ease where such space would not
permit a conventional truck with tiller t o be operated.
In position 1 (leftmost image of truck in Fig. 2a), the truck is operating in a normal
mode of operation, with the rear, steerable wheel aligned t o the axis of the tiller 20.
In conventional manner the operator manoeuvres the truck t o position 2 (centre
position, Fig. 2a) where the load 13 is almost aligned with the space 11 and then t o
position 3 (rightmost position of Fig. 2a and leftmost of Fig. 2b).
While a conventional truck could be manoeuvred into position 3 it could not be
driven into the space 11 because the steering direction of wheel 14 is perpendicular
t o the desired direction of travel.
The truck of Fig. 2a and 2b, however, is provided with the functionality t o change the
angle between the wheel and the tiller t o a non-zero offset. In particular it can be
changed t o an angle where it is aligned parallel with the major front-rear direction of
the chassis, this being the position with respect t o the chassis as shown in position 4
(centre, Fig. 2a). The same axis can also be defined as the axis in which the tiller is in a
neutral steering position (see position 1), or the axis defined by the direction of the
forks.
The offset angle can be changed using a steering motor which turns the wheel
relative t o the chassis and/or tiller, or using a ratcheting action in combination with a
mechanism t o selectively decouple the tiller from the wheel and recouple it t o the
wheel, both of which are described below.
On attaining the position shown in Fig. 4, the operator is now alongside the truck
with the tiller 20 offset from the wheel 14 by about 90 degrees (it could be more or
less). The tiller head is provided again with drive controls which when activated allow
the truck to be driven forward or in reverse, including when the tiller is offset. Thus,
the operator engages the forward drive and the front of the truck and its load 13
enters the space 11 where the load can be unloaded.
The angle need not be 90 degrees. For the truck to work within its minimum operable
aisle width, the tiller needs to be rotated so that the end of the tiller and tiller head is
level with or forward of the rearmost point of the truck body, as can be seen in
position 3. Depending on the truck layout this minimum amount of rotation could be
significantly less than or greater than 90 degrees.
At no point in positions 4 and 5 does the tiller need to be straightened, and the
steering of the truck can be adjusted and fine tuned in the normal way by steering
the tiller from side to side. The steering motor responds as normal, i.e. when the tiller
is rotated about its axis 15 (see position 3, Fig. 2b) by say 5 degrees clockwise, the
steering motor will rotate the wheel 14 also by 5 degrees clockwise so that the wheel
continues to follow the tiller but with a different angular offset from normal, i.e. a
non-zero angle which in this case is about 90 degrees.
The removal of a pallet or load from the rows is accomplished in reverse. The empty
truck is manoeuvred into the row to engage and pick up the load using the steps
already described . With the operator and tiller alongside the truck (position 5), the
truck is driven in reverse back to the row behind the truck (position 4). The steerable
wheel is then rotated to the position where it is aligned with the tiller, and again this
can be done manually or using a steering motor and a steering motor can
automatically align to the tiller or can align to the tiller under operator control of the
steering motor. When the wheel and tiller are aligned (position 3) the operator is free
to manoeuvre the truck back to positions 2 and 1.
Figs. 3a t o 3c show the traction motor, steering motor and associated com ponents of
the truck. Only a sma ll part of the truck chassis 10 on which these com ponents are
mounted is shown, but the rest of the truck is as described above.
The rea r wheel 14 is driven in forwa rd or reverse directions by a traction motor 50
under the control of control mem bers (not shown in Figs. 3a t o 3c but shown and
described below in relation t o Fig. 8) on the tiller head 22, as previously described.
This is well-known. While it is preferred t o drive the rea r wheel, additiona l or
alternative wheels could be driven instead.
The steering angle of the rea r wheel 14 relative t o the chassis 10 is adjusted by
rotation of the wheel 14 about a vertica l axis - this is effected by a steering motor 52.
The steering motor is prefera bly an electric motor in the embodiment shown, but
may equa lly be hydra ulic, pneumatic, or of any other suita ble type.
A sensor 54 determines the angula r position of the tiller 20 relative t o the chassis 10.
A steering motor controller 60, responsive t o the sensor 54, actuates the steering
motor 52 so that the rea r wheel 14 rotates about a vertica l axis by the same angle
and in the same direction as the tiller 20. In other words, the steeri ng angle of the
rea r wheel 14 relative t o the chassis 10 increases or decreases as the angle of the
tiller 20 relative t o the fore-aft direction of the chassis 10 increases or decreases, by
the same amount and in the same direction of rotation. Thus any angula r offset
between the tiller 20 and the rea r wheel 14 which was previously set is maintained.
Fig. 3a shows the steering mecha nism when the tiller 20 is in line with the rea r wheel
14, i.e. the offset angle is zero, Fig. 3b shows the steering mecha nism when the offset
angle between the t iller 20 and rea r wheel 14 is 45 degrees, and Fig. 3c shows the
steeri ng mecha nism when the offset angle is 90 degrees.
Referring next t o Fig. 4, a schematic of the steering components shown in Figs 3a t o
3c is shown as a block diagram. The wheel 14 rotates on an axis 26 when it is driven
by a traction motor 50 using conventional operator controls (not shown). Steering
about a vertical axis is accomplished by the steering motor 52 under the control of
the steering motor controller 60. As previously described the tiller angle with respect
t o the chassis is provided as an input from the tiller angle sensor 54.
The tiller angle sensor may be any sensor whose output is effective t o allow the
steering motor controller either t o determine the absolute angle t o the tiller relative
t o a chassis axis, or t o determine changes in the tiller angle as it is moved about its
rotation axis. Thus, where the tiller angle sensor is a rotary encoder, it may be of the
type known as an absolute encoder or a relative encoder. Sensors can be digital (e.g.
mechanical absolute encoders), optical (such as a source and detector which are
separated by a patterned disc), magnetic (e.g. using a Hall-effect sensor t o sense
strips of magnetised material on a disc) or analogue (such as a synchro, resolver,
rotary variable differential transformer (RVDT) or rotary potentiometer).
A further angular sensor 61 is provided on the steering motor, which senses the angle
of the output shaft from the motor (and hence the angle of the steerable wheel
mounted on that shaft) relative t o the motor housing (and hence the chassis t o which
the housing is mounted).
Also shown are operator controls including an "align t o tiller" button 63 and an "align
t o chassis" button 65, which are typically provided on the tiller head, for example at
the position shown at 40 in Figs. 3a t o 3c.
Figs. 5 and 6 illustrate the operation of the steering motor controller in a particularly
preferred embodiment which allows the operator t o engage either of two modes t o
automatically align the steered wheel with either the axis of the tiller in one mode, or
the main front-rear axis of the chassis in the other mode (i.e. from position 2 t o
position 3 in Fig. 2b and vice versa, in accordance with the operator selecting buttons
63 or 65). Fig. 5 shows the operation of the controller on system start-up and when in
the "align t o tiller" mode, while Fig. 6 shows the operation of the controller in the
"align t o chassis" mode.
In Fig, 5 the controller 60 starts up in a normal mode of operation, step 200, and by
default the controller will keep the steerable wheel aligned t o the tiller, step 202.
The controller has stored in an internal or external register or a memory accessible t o
it (not shown) a predetermined angular offset which initially is set t o zero and which
is always reset t o zero when the controller reverts t o the "align t o tiller" mode and
the flowchart of Fig. 5 is restarted, step 204. This means that the controller is
configured t o keep the wheel 14 aligned with the tiller 20, i.e. with a zero degree
offset, as is shown in e.g. Fig. 2a, positions 1, 2 and 3.
The controller, after initialising or resetting the stored value t o zero, operates in a
feedback loop. This loop can be interrupted at any point by the operator pressing the
"align t o chassis button". For the purposes of the flowchart illustration, this
interruption is indicated by the controller, on each iteration, making a check t o see if
the button 65 has been operated, step 206. In actual operation, the feedback loop
used for normal steering may not explicitly check for this input in step 206, as it will
be configured t o receive an interrupt signal, and the steering feedback loop will
comprise steps 208, 210, 212 as will now be described.
In step 208, the inputs from the tiller angle sensor and the wheel angle sensor are
received. In a preferred embodiment, each sensor will return a voltage value which
varies from a minimum at one extreme of rotation, through a midpoint at the neutral
straight ahead position (of the tiller or wheel respectively), t o a maximum at the
other extreme of rotation. As indicated previously, this type of sensor is simply one
option that may be used. Digital or other analogue sensors can equally provide inputs
as to the absolute position or amount of rotation of the tiller or the wheel relative to
one another, to the chassis, or to any other component of the truck or the external
environment. The inputs from the two sensors are appropriately calibrated to one
another so that the controller can interpret each input as being indicative of the
angle at which the tiller or wheel is positioned relative to the chassis, and by simple
comparison or subtraction, from one another.
In step 210 this comparison is conducted, and the difference between the angles is
compared to the stored offset which in this case is zero. If the tiller and wheel are
offset by a zero angle, no action is needed, and the process then reverts to steps 206
and 208. If however there is a mismatch, then in step 212 the steering motor is
provided with an output to rotate the wheel until the angles match.
Steering is accomplished by the operator turning the tiller about its vertical axis. This
will lead to the controller detecting and correcting a mismatch between the detected
tiller angle and wheel angle. Because the process operates in a feedback loop, the
wheel should closely follow the tiller except in cases of violent movement of the tiller
and the operator should not notice any appreciable lag.
Accordingly in the normal operating mode, and when the align to tiller function is
active, the steering motor rotates the wheel to "follow" the tiller under the direction
of the steering motor controller. That controller is continually trying to maintain a
predetermined zero degree offset between the wheel and tiller.
Now, assuming that the tiller is aligned with the wheel, i.e. the predetermined offset
angle stored in memory is zero, we next look at what happens when the operator
depresses the "align to chassis" button 65, as would occur when the operator is
seeking to rotate the wheel so that it is no longer aligned with the tiller (position 3)
but rather is aligned with the chassis (position 4). As indicated in step 206 of Fig. 6
this interrupts the normal steering operation and the controller instead starts t o
implement the process of Fig. 6.
In Fig. 6, the align t o chassis mode is active, step 214. Although not shown in Fig. 6, a
safety check may be conducted before implementing the align t o chassis operation. If
the truck is moving at a speed where it would be unsafe t o suddenly change the
steered wheel angle (this may be a function of the motor speed, and optionally the
current tiller angle) then the command t o align t o chassis may be ignored and the
process may revert t o Fig. 5. Assuming however that the truck is at a safe speed, i.e.
a low speed or stopped, the controller will firstly realign the wheel t o the chassis axis
and will then allow normal steering but with the tiller offset from the wheel.
Thus, in step 216, the controller detects the wheel angle (with respect t o the chassis).
In most cases when this occurs the wheel will currently be aligned t o the tiller, and
the tiller will be at a non-zero angle to the main front-rear chassis axis. The steering
controller realigns the wheel by engaging the steering motor until the input from the
wheel angle sensor indicates a zero angle with respect t o the chassis, step 218. At
this point the tiller may have remained in the same position or may have been moved
by the operator by a smaller or larger amount. In either case, once the wheel and
chassis axis are aligned, the current tiller angle is detected with respect t o the
chassis, step 220, with the intention of now "locking" the steering of the wheel t o the
tiller with this offset. The detected angle (or a value such as a voltage or digital
quantity indicative of the angle) is stored in the memory or register available t o the
controller, step 222. This value denotes the offset of the tiller with respect t o both
the chassis and the wheel, given that the latter two are aligned.
Once this is achieved, the controller actually works in the same way as was described
with respect t o Fig. 5, steps 208, 210, 212 but with the exception that rather than the
controller using feedback t o ensure the wheel follows the tiller with a zero degree
offset, the controller in the further operation of Fig. 6 will act t o ensure the wheel
follows the tiller's steering movements with the same constant offset as was present
when the steering motor had aligned the wheel t o the chassis in step 218.
As with Fig. 5, the controller's operation can be interrupted by detection of the "align
t o tiller" command, step 224. Also, and not shown for clarity, the controller's
operation can also be interrupted by the receipt of a further "align t o chassis"
command. The operator, having aligned the wheel t o the chassis and manoeuvred
the truck, may want t o resume conventional steering, in which case the align t o tiller
command will be used, or may want t o align the wheel t o the chassis with a new
offset, perhaps more or less extreme, or with the tiller offset t o the other side of the
truck body. Therefore the "align t o chassis" command is available t o realign the
wheel even though the truck may be operating in the align t o chassis mode already.
Assuming no such interruption is received in step 224, the steering operation
continues by detecting the angles of both the tiller and the wheel with respect t o the
chassis, step 226.
By comparison and subtraction, the controller determines the angle of offset
between the tiller and wheel and checks, step 228, whether the offset is as desired,
i.e. equal t o the predetermined offset value stored in memory in step 222. If so, no
steering output is needed and the process reverts t o step 224. If however there is a
discrepancy, then the steering motor is engaged until the desired offset is restored or
reached, step 230.
If in step 224 the controller detects that the align t o tiller mode has been selected
once again, the process moves back t o Fig. 5. This has the result that the current
offset angle stored in memory is overwritten with a zero degree offset (Fig. 5, step
204) and the controller then, in accordance with the normal steering operation (steps
208, 210, 212) rectifies the mismatch between the detected tiller-wheel offset and
the desired offset of zero.
The skilled person will appreciate that the steering operation in both Figs. 5 and 6,
after correction of a mismatch as described immediately above in Fig. 5, or after the
alignment t o the chassis in Fig. 6, operates in precisely the same way: it has a desired
offset value which it is seeking t o maintain and responds t o tiller inputs by moving
the wheel t o maintain the desired predetermined offset. When acting in this way, it is
said t o be in a normal mode of operation, and while varying the offset angle t o zero
with respect t o the tiller or the chassis, it is said t o be in a realignment mode of
operation.
A further embodiment will now be described with reference t o Figs. 7 t o 12. The
embodiment of Figs. 7 t o 12 below, and the embodiment of Figs. 2 t o 6 above, are
united by the fact that, in a normal mode of operation, the controller controls the
steering motor t o maintains a predetermined angular offset between the tiller and
wheel, and in that the angular offset between the tiller and steerable wheel may be
adjusted and the adjusted angular offset subsequently used as the predetermined
angular offset.
While the adjustment preferable happens automatically as described above in
relation t o Figs. 4, 5 and 6 and below in relation t o Fig. 11, or semi-automatically (i.e.
with powered steering but under a manual control) as described below in relation t o
Fig. 10, it can also occur manually as described below in relation t o Figs. 7 and 9.
Referring t o Figs. 7a t o 7e, an alternative embodiment of pedestrian-operated forklift
truck has a tiller 20 which can be selectively de-coupled and re-coupled to the rear
wheel 14. This allows selective rotation of the tiller 20 independently of the rear
wheel 14 t o allow the tiller t o be fixed at different angular positions relative t o the
rear wheel. As seen in Figs. 3a t o 3e the tiller head 22 has a push button (which may
also be located at position 40 and will be referred t o as push button 40) which when
pressed down de-couples the tiller 20 from the rear wheel 14 and, while being held
pressed down, allows the tiller t o be rotated through any selected angle (within the
design limits of the truck) while the steering angle of the rea r wheel 14 relative t o the
truck chassis 10 remains fixed. When the operator 24 has moved the tiller t o a
desired angula r offset from the rea r wheel 14, the button 40 is released and the tiller
20 is re-coupled t o the rea r wheel. From this point on, until the button 40 is next
pressed, and as described previously, rotation of the tiller 20 through any angle in
either direction will rotate the rea r wheel 14 through the same angle in the same
direction, whi le retai ning the selected angula r offset.
A more sophisticated control pad for use on a tiller head is described below in
relation t o Fig. 12. It is t o be understood that the push button, or any other control
interface, need not necessa rily be located on the tiller head, but for operator
convenience, it is preferable to locate this within easy reach of the operator and the
tiller head is therefore preferred.
Fig. 7a shows the forklift truck positioned at right angles t o a row 32 of palletised
product with the rea r wheel 14 in a fore-aft steering position in line with the tiller 20
which extends directly t o the rea r. This is equiva lent t o the situation shown in Fig. l b
and, as described, the steering space Sis wasted storage space.
In Fig. 7b, the operator 24 has de-coupled the tiller 20 from the rea r wheel 14 by
pressing the button 40, and while holding the button 40 pressed has moved the tiller
clockwise through nea rly 90 degrees. The rear wheel 14 stays in its origina l fore-aft
orientation.
Next, Fig. 7c, the operator backs the truck towa rds the row 32, the rea r wheel 14
remaining in the fore-aft orientation. This movement is accom plished by operating a
control (not shown in Figs. 3a t o 3e but visible in the control pad of Fig. 12 described
below) on the tiller head t o actuate a drive motor driving the rea r wheel 14. Now the
truck can approach the row 32 much closer since the tiller 20 is off t o one side,
requiring a much sma ller steering space. While backing the truck the tiller 20 can
stay de-coupled from the rea r wheel 14 (traction control operates irrespective of
whether the tiller and rea r wheel are coupled or not), or it can be re-coupled t o the
rea r wheel 14 by releasing the button 40.
To return t o the norma l steering configuration (i.e. rea r wheel in line with the tiller)
the tiller is " ratcheted" back and forth through a sma ll angle, the button 40 being
held pressed during anti-clockwise movements when the tiller arm is decoupled, and
released during clockwise movements when the tiller arm is coupled t o the rea r
wheel 14. This will gradua lly bring the rea r wheel 14 into line with the tiller 20, Fig.
7e, after which norma l steering of the truck can be resumed, Fig. 7f.
Although the drawings show the tiller 20 being offset clockwise relative t o the rea r
wheel 14, it is capable of being offset either clockwise or anti-clockwise.
Referring next t o the flowcha rts of Figs. 8 t o 11 and the control circuit of Fig. 12,
further details of the operation of an alternate steering motor controller 60 are
shown. Figs. 8-11 show in flowcha rt form the progra mmed operation of a steering
motor controller which can be seen in Fig. 12, in various modes of operation.
As seen in Fig. 12 the steering motor controller 60 is connected t o the steering motor
52 such that appropriate control signa ls may be output from the controller 60 t o the
steering motor 52 t o rotate the steering angle of the wheel 14 relative t o the til ler or
chassis.
A control pad 62, prefera bly provided on the tiller head (not shown in Fig. 12)
contains four control areas, namely a traction motor control area, a de-couple/recouple
control area 70; a manua l steeri ng area 74; and an auto-a lign control area 78.
The traction motor control area 64 is provided with forwa rd and reverse control
buttons 66,68 and is directly connected t o the traction motor. When the buttons
66,68 are depressed, control signa ls are sent t o the traction motor t o drive the wheel
about its axis 26 in the forwa rd or reverse direction respectively. Although as shown
the traction control is a single-speed control, the skilled person will be awa re of
control mecha nism allowing for graduated speed control, for example a dia l could be
employed allowing any degree of speed between full speed forwa rd and full speed
reverse, or a low speed toggle switch could be employed in com bination with sim ple
forwa rd/reverse control buttons of the type shown in Fig. 12 t o allow for slower
manoeuvring in tight spaces.
Referring additiona lly t o Fig. 8, a "norma l" mode of operation is described, in which
the operator is sim ply operating the traction control area 64, and not the additiona l
control areas 70, 74, 78.
In step 100 the truck is in the norma l operation mode. It remains in this mode
provided that the de-couple mode is not activated (decision 102, leading t o Fig. 9);
the manua l steer mode is not activated (decision 104, leading t o Fig. 10); and the
auto-a lign mode is not activated (decision 106, leading t o Fig. 11). In the norma l
mode the operator uses the forwa rd and reverse buttons t o drive the truck forwa rd
and in reverse. Steering is accom plished by turning the tiller about its vertica l axis
and as previously described an angle sensor determines the relative angle between
the drive wheel (a bout its vertical axis) and the t iller. This signa l is received in step
108.
A register or memory area (not shown) provided in or accessible t o the controller
stores a "desired angle" for the sensor signa l . In most cases, and on initia lising the
system, the desired angle is zero, i.e. the tiller and wheel are in alignment and any
movement of the tiller causes a requirement for the wheel t o be rotated about its
vertica l axis t o regain alignment and t o revert t o the desired angle of zero.
Thus, a feedback loop is operated wherein the sensor signa l is received in step 108,
and a check is made, decision 110, whether the detected angle is the same as the
desired angle stored in memory. If so, step 112, there is no output t o the steering
motor and the feedback process reverts t o step 108.
If however a discrepa ncy is noted, i.e. the tiller has moved t o a different angle tha n
that desired, an output is provided t o the steering motor in step 114 t o rotate the
wheel about its vertical axis unti l the desi red angle is once again regained.
As previously described, the tiller can be decoupled from the wheel by depressing
button 40 in the embodiment of Figs. 3a t o 3c, or in Fig. 12 if one refers t o the de
couple/re-couple control area 70, this is provided with a single on/off button 72
which when depressed simila rly de-couples the tiller from the wheel and when
released re-couples the t iller to the wheel. This button 72 directly replaces the button
40 shown in Figs. 3a t o 3c.
Referring now t o Fig. 9, when button 72 is depressed this results in a "de-couple"
signa l being received by the controller 60, step 116. The controller then cancels
norma l mode (i.e. the operation as shown in Fig. 8), step 118 with the result that the
auto-a lign and manua l steer functiona lity is no longer availa ble, step 120; there is no
further output t o the steering motor, step 122; and input from the steering angle
sensor is ignored, step 124 (or the sensor tem pora rily deactivated until the controller
re-enters norma l mode). The truck is now in the de-coupled mode.
In this mode, until the de-couple signa l is deactivated, or a re-couple signa l received -
this depending on the design and mecha nism used for the de-couple button - the
tiller is rotata ble independently of the wheel. In this mode the traction motor
controls are still active and unaffected. As described earlier the till can thus be offset
relative t o the wheel and no attempt is made t o realign the wheel with the til ler as
long as the two are decoupled.
Once the decoupling is deactivated or a recoupling signa l is received, step 126, the
sensor signa l is again received and processed, step 128. In most cases the tiller will
have been offset while in the decoupled mode and will no longer be at the desired
angle. So for example if the initia l desired angle was zero with the tiller and wheel
aligned, and the tiller was then decoupled and rotated 90 degrees counter-clockwise
out of alignment from the wheel, the sensor will report a wheel angle of 90 degrees
clockwise rotation relative t o the tiller. This initia l indication of the new tiller-wheel
angula r relationship is used t o reset the desired angle stored in memory t o this new
angle, step 130, and the truck is then returned t o the norma l mode of operation, step
132.
From this poi nt on the norma l mode of operation reverts t o the process of Fig. 8 as
previously described, but with a desired angle now set at 90 degrees, so that the
feedback loop between the sensor, controller and motor now strives t o maintain the
offset at this same 90 degree angle. In other words the tiller and wheel are now
"locked" 90 degrees out of align ment.
When the steering is the tiller is " ratcheted" back and forth through a sma ll angle as
previously described, the steering controller repeatedly flips between the norma l
mode of Fig. 8 (button released and tiller locked t o wheel) and de-coupled mode of
Fig. 9 (tiller free and rotata ble independently of wheel), with the desired angle being
reset t o the new angular relationshi p every t ime the button is released.
Referring now t o Fig. 10, and additiona lly t o the manua l steering control area 74 of
Fig. 12, it can be seen that a toggle switch 76 is provided which is biased t o a neutra l
position as shown in Fig. 12 but which can be rotated clockwise or anti-clockwise t o
actuate manua l steering of the wheel 14 (simi la r in action t o turni ng a key in either
direction in a spring-loaded lock). When the switch is toggled in either direction, a
manua l steer signa l (clockwise or anti-clockwise depending on how the switch was
toggled) is received by the steering controller, step 134.
The controller cancels norma l mode, step 136 and deactivates the auto-a lign and
decoupli ng functionality of the control pad, step 138. The truck is now in manua l
steeri ng mode.
In this mode, the steering motor controller outputs left and right (or clockwise and
anti-clockwise steering signa ls t o the steering motor for as long as the manua l steer
signa ls are received from the toggle switch 76. It will be appreciated that in place of a
sim ple toggle switch, a steering wheel, left/right paddle controls, or any other known
and suita ble steering control could be used to independently rotate the wheel about
its vertica l axis.
When the manua l steering signa l stops, step 142, a sensor angle indication is
received, step 144, and the desired angle is reset t o the new angula r relationship
between tiller and wheel, step 146. The truck is then returned t o norma l mode, step
148.
Using this mecha nism, the driven wheel can be rotated t o a new angle without
ratcheting or manipulating the tiller. This is useful, for example, in rea ligning the
wheel t o the tiller. Again the traction control is fully active when in the manua l
steeri ng mode.
Fig. 11 shows the functiona lity of the auto-a lign control area 78 of Fig. 12. The autoalign
control area 78 is provided with three buttons namely an "align t o tiller" button
80, a "90 deg. Right" button 82, and a "90 deg left" button 84. The operator can use
these buttons t o align the wheel automatica lly t o the tiller or at an offset of 90
degrees left or right. Obviously one could provide additiona l or alternative controls if
it were desired t o frequently offset the tiller from the wheel at different angles such
as 45 degrees, 60 degrees or 80 degrees. One could additionally or alternatively place
a dial or clockface with angular markings and allow an operator t o select an angle
from a continuous range or by switching a rotary knob t o any of several preset
angular positions.
In Fig. 11, the truck is in normal mode, step 110, when one of the three buttons 80,
82, 84 (Fig. 12) is depressed, resulting in an auto-align signal being received from the
control pad, step 150. A different signal is received depending on which of the three
buttons is selected by the operator.
The steering controller cancels the normal mode, step 152, and deactivates the de
couple and manual steer functions described above, step 154. Then, in dependence
on which button has been chosen, decision 156, a different result occurs. (In reality
the programmed or hardwired logic according t o which the controller operates may
not implement a decision at this point but instead will have three parallel functions
for the three buttons. Of course any of the flowcharts of Figs. 8-11 may be
implemented in several alternative ways and the particular flowcharts describe the
best known method of implementing different functions which the system designer
may choose t o use, modify, or leave out entirely in a given product.)
If the "Align with tiller" button was selected, step 158, the controller resets the
"desired angle" stored in memory or a register assigned t o that purpose, t o a value
corresponding t o a zero degree angle. Similarly, if the 90 degree right button was
selected, step 160, or the 90 degree left button, step 162, the desired angle is set
accordingly t o a value equivalent t o the wheel being offset by the selected angle.
(Whether the terminology used is "right/left", "clockwise/anti-clockwise", a graphical
indication of the angle, or any other terminology, is at the preference of the system
designer, as is also the choice of convention as t o whether it is the offset rotational
direction of the tiller or of the wheel.)
In any event, after setting the desired angle in steps 158, 160, 162, t o the appropriate
value t o match the desired offset chosen by the operator, the controller then returns
t o normal mode, step 164.
Assuming that the tiller is not already at the offset specified (e.g. suppose the tiller is
offset from the wheel direction by 10 degrees when the operator chooses "align with
tiller"), the effect of normal mode is t o follow steps 108, 110 and 114 as described in
relation t o Fig. 8 t o output a signal t o the steering motor until the sensed angle
matches the angle stored in memory. This results in the flowchart of Fig. 11 being
used t o reset the desired angle and the flowchart of Fig. 8 then making the steering
correction until the tiller is aligned with (or offset by 90 degrees etc.) the wheel.
The invention is not limited t o the embodiments described herein which may be
modified or varied without departing from the scope of the invention.
Claims
1. A motorised truck with tiller comprising:
(a) a chassis having a plurality of ground-engaging wheels, at least one of which is
steerable to steer the truck;
(b) a drive motor for driving at least one of the wheels to move the truck across
the ground;
(c) a tiller rotatably connected to the chassis which may be swung from side to
side to steer the truck;
(d) a steering motor for varying the angle of the steerable wheel;
(e) a steering motor controller which, in a normal mode of operation, receives as
an input an indication of the tiller angle and which outputs in response
thereto a control signal to the steering motor to vary the angle of the
steerable wheel such that the angle between the tiller and steerable wheel
maintains a predetermined angular offset;
wherein the angular offset between the tiller and steerable wheel may be adjusted
and the adjusted angular offset subsequently used as the predetermined
angular offset.
2. A motorised truck with tiller according to claim, wherein said adjustment of
the angular offset is carried out by said steering motor controller in a realignment
mode of operation, in which the steering motor controller outputs a control signal to
the steering motor to steer the wheel to a different angular offset.
3. A motorised truck with tiller according to claim 2, wherein the steering motor
controller is operable, in said realignment mode of operation, to perform automatic
alignment of the steerable wheel to be parallel with either of two major axes of
interest, namely the tiller axis and a major axis of the truck chassis.
4. A motorised truck with tiller according to claim 2 or 3, wherein the steering
motor controller is opera ble, in said rea lignment mode of operation, to cha nge said
predetermined angle between (i) a zero tiller angle wherein the wheel is aligned
parallel to the tiller and (ii) a zero chassis angle wherein the wheel is aligned parallel
to an axis of the chassis and offset from the tiller by the same angle as the tiller is
offset from the chassis during the rea lignment mode of operation.
5. A motorised truck with tiller according to claim 3 or 4 wherein said axis of the
chassis is selected from an axis defined by the axis of the tiller when the tiller is in a
neutra l steering position; a front-rea r axis of the truck; a left-right axis of the truck;
and, where the truck is provided with lifting forks, an axis defined by said lifting forks.
6. A motorised truck with tiller according to any of claims 2-5, further com prising
one or more manua l controls which when actuated engage the rea lignment mode of
operation.
7. A motorised truck with tiller according to claim 6, wherein the manua l
controls can select between at least two states, namely (i) a zero tiller angle wherein
the wheel is aligned parallel to the tiller and (ii) a zero chassis angle wherein the
wheel is aligned parallel to an axis of the chassis and offset from the tiller by the
same angle as the tiller is offset from the chassis during the rea lignment mode of
operation.
8. A motorised truck with tiller according to claim 6 or 7, wherein the tiller has a
tiller head at its free end, the tiller head being provided with said manua l controls.
9. A motorised truck with tiller according to any of claims 2-8, wherein when the
steering motor controller is in said rea lignment mode of operation the tiller is
decoupled from the steera ble wheel.
10. A motorised truck with tiller according to any of claims 2-9, wherein the
steering motor controller is configured to automatically revert from said realignment
mode to said normal mode of operation following completion of the operation to
steer the wheel so as to change said predetermined angular offset, and further
wherein upon reverting to said normal mode from said realignment mode, the
predetermined angular offset is updated in accordance with the offset achieved in
the realignment mode.
11. A motorised truck with tiller according to any preceding claim, wherein the
steering motor controller receives as an input an indication of the tiller angle relative
to one or more of the chassis, the steerable wheel, or the steering motor.
12. A motorised truck with tiller according to any preceding claim, further
comprising an angular sensor system of one or more sensors which detect and
output an indication or indications of the relative angle between two or more of the
tiller, the steerable wheel, the steering motor, and the chassis.
13. A motorised truck with tiller according to claim 12, wherein the indication or
indications output by said angular sensor system provide the steering motor
controller with information to determine, during a realignment mode of operation,
the angle between the tiller and the steerable wheel and/or the angle between the
steerable wheel and the chassis.
14. A motorised truck with tiller according to claim 12 or 13, wherein when said
steering motor controller is operating to change said predetermined angle to a zero
tiller angle it receives as an input from the angular sensor system information to
determine the angle between the tiller and the steerable wheel, and when said
steering motor controller is operating to change said predetermined angle to a zero
chassis angle it receives as an input from the angular sensor system information to
determine the angle between the steerable wheel and the chassis.
15. A motorised truck with tiller according to any preceding claim, further
comprising a memory accessible to the steering motor controller in which is stored
an indication of said predetermined offset angle.
16. A motorised truck with tiller as claimed in any preceding claim, wherein the
motorised truck with tiller is selected from a forklift truck, a pallet carrier and an
order picker.
17. A motorised truck with tiller according to any preceding claim, wherein the
chassis supports the tiller at a rear end and the truck further comprises forks located
at a front end of the chassis, and wherein the steered wheel is at the rear end.
18. A motorised truck with tiller according to any preceding claim, wherein the
truck is a three-wheeled truck with two front wheels which are undriven and not
steered, and a single driven, steered, rear wheel which is positioned generally
beneath the rotation axis of the tiller.
19. A method of manoeuvring a motorised truck with tiller, comprising the steps
of:
(a) driving the truck within an aisle with the tiller substantially aligned with a
steerable wheel of the truck;
(b) positioning a front end of the truck adjacent a space into which the truck is to be
manoeuvred along the aisle;
(c) adjusting the angular offset between the tiller and steerable wheel such that the
steerable wheel is offset from the line of the tiller by more than 45 degrees; and
(d) driving front of the truck into said space while maintaining the offset of greater
than 45 degrees between the steerable wheel and the tiller.
20. The method of claim 19, wherein in steps (a) and (b) said wheel is aligned with
the line of the tiller to within 5 degrees or less.
21. The method of claim 20, wherein in steps (c) and (d) the steerable wheel is
offset from the line of the tiller by 60 degrees or more, more preferably 80 degrees or
more.