GB2290281A - Telescopic mast order picker truck - Google Patents

Abstract

A telescopic mast order picker or order picker/stocker truck of the invention controls most movement from a battery powered DC electric motor 11. A controller for the motor 11 has inputs representing a desired motor speed and direction and a sensed motor speed and direction, and an output which is a function of the difference between those inputs. The motor torque being a function of that output. Forks 8 are carried on a cabin 6 also moved via the motor 11. Preferably cables winding onto a winch drum 9 move the most and chains passing round an idler drown move the cabin. Preferably during downward movement the motor is used as a generator. <IMAGE>

Description

TITLE Telescopic Mast Order Picker Truck DESCRIPTION Field of the Invention The invention relates to a telescopic mast order picker truck of the kind that is movable in an aisle of a warehouse between warehouse racking, for placing pallets upon and taking pallets from the racking at any aisle position and any warehouse level.

Background Art Order picker trucks (which term is used in this specification to include order picker/stacker trucks) are well known in themselves. Telescopic mast versions of those trucks utilize hydraulic rams in association with lifting chains to extend the different sections of the telescopic mast, each section relative to the next, so as to raise a cabin platform and associated pallet handling forks or pallet handling platen to different warehouse heights to deliver pallets to or take pallets from the warehouse racking at any warehouse position. One problem associated with such trucks is that the hydraulic rams which raise and lower the cabin platform on the telescopic masts are slow in operation and inefficient.The slow speed of operation is much more of a problem in the taller warehouses, when the time taken to send the cabin from the ground position to the topmost level of racking can be unacceptably long. Typically a high lift telescopic mast truck would have a pair of lifting rams for lifting the movable elements of the telescopic mast, which lifting rams would be extremely long so as to achieve maximum lift, and correspondingly slow in operation.

The inefficiency of the use of hydraulic fluid as the motive source means that the known trucks draw an excessive amount of electrical power from their batteries, with the result that they have to be provided with extremely large battery packs to permit them to function for extended periods without recharge.

For warehouses without overhead obstructions, fixed mast order picker trucks have been proposed. In such trucks, the only lifting and lowering mechanism is that of the cabin platform relative to the truck body. Fixed mast order picker trucks have been proposed which take their motive electrical power directly from the electric mains, applying that power through an AC induction motor or a 500 volt DC shunt wound electric motor. Such trucks operating from an electric mains supply present altogether a simpler control problem than that of a battery operated truck, and the motor control technology cannot readily be applied to telescopic mast trucks operating from a relatively low voltage battery.

It is therefore an object of the invention to provide a battery powered telescopic mast order picker truck having an operating system which is quicker in operation and more economical than the conventional hydraulic mechanisms.

Summary of the Invention The invention provides a telescopic mast order picker truck movable in an aisle of a warehouse between warehouse racking, comprising: a pair of fixed masts upstanding from a truck body; a pair of movable masts vertically movable with respect to the fixed masts; a cabin on a cabin platform supported by and vertically movable relative to the movable masts in response to vertical movement thereof; and pallet handling forks or a pallet handling platen carried by the cabin platform for handling pallets at any warehouse level; wherein a motive force for moving the movable masts is a battery powered DC electric motor operable from within the cabin and controlled by a controller which has inputs representing a desired motor speed and direction and a sensed motor speed and direction, and an output which is a function of the difference between those inputs, the motor torque being a function of that output.

Preferably the movable masts are raised and lowered relative to the fixed masts by a winch and cable driven by the DC electric motor. That is to say, the movable masts are pulled upwards by a pair of cables winding on to a winch drum driven by the motor. That lends itself to the telescopic mast system of the truck being a two-element or three-element system. If a two-element system, then the first element is the pair of fixed masts, generally designed as the outer masts; and the second element is the pair of movable masts, generally designed as the inner masts. The winch drum is advantageously positioned at the bottom of the fixed masts, and the cables arranged to pass over a pair of pulleys at the top of the fixed masts, then under a pair of pulleys at the bottom of the movable masts, to anchorage points at the top of the fixed masts.

If a three-element system, then the first element is the pair of fixed masts, the third element is the pair of movable masts and the second element is a pair of intermediate masts between the fixed masts and the movable masts. The intermediate masts are also movable.

The cabin platform is preferably raised and lowered relative to the movable masts in synchronism with the raising and lowering of the movable masts, by a pair of chains passing around at least one idler wheel. For example, each chain may be anchored at its ends to the fixed mast and the cabin platform, passing between its ends around an idler wheel mounted on the movable mast.

That provides, in the case of the two-element mast described above, a lifting ratio of 2:1 of the winch drum to the movable mast; and a lifting ratio of the movable mast relative to the cabin of 1:2. That is advantageous, because the cabin movement is then tied 1:1 to the rate of playing out or taking in the winch cable.

Raising the cabin is straightforward with a truck according to the invention, and involves simply winding cable on to the winch drum using the DC motor. Such a motor if series wound is capable of high torque at low motor speeds, so at low cabin speeds high loads can be accommodated, without excessive motor current.

Lowering the cabin requires more extensive control, as the forks or platens may be carrying a heavily loaded pallet, such that downward movement can create massive inertial loads. The controller in the truck according to the invention is capable of applying the necessary control, in conjunction with a brake for the winch drum.

Advantageously, the brake automatically brakes the winch drum when the drum is stationary, and releases the brake when the relevant controller input demands motor movement.

When the controller acts to control the downward movement of the cabin platform from rest, it applies the following control sequence: (i) applying a cabin platform lifting torque to the motor and simultaneously releasing the brake; (ii) reducing the lifting torque to permit controlled downward movement of the cabin platform under gravity; and (iii) utilizing the motor as a generator and directing the generated output as an output current through a resistance load such as a diode connected across the armature or as a back EMF to recharge the batteries.

Directing the generated output current through a resistance load is known as rheostatic braking or plug braking, and is used only at low speeds of cabin descent because of the high currents involved.

Directing the generated output as a back EMF to recharge the batteries is known as regenerative braking. If desired, step (iii) in the above control sequence may involve plug braking up to a predetermined threshold cabin descent rate followed by regenerative braking when the cabin descent rate exceeds that predetermined threshold.

During plug braking or regenerative braking the motor functions as a generator so that the armature is rotating in the reverse direction to that of a motor. Control of the braking effort is possible by controlling the pulsing of the main thyristor as a percentage on time in response to the desired speed of descent signal input to the controller.

The trucks of the invention are capable of substantially faster cabin movement than conventional telescopic mast trucks which utilize hydraulics for mast raising and lowering, and are substantially more economical in their use of battery power. Those economies are further augmented by the partial recharging of the batteries when regenerative braking is utilized as described above. The above control sequence for downward movement of the cabin is a preferred feature of the invention, but provides a singularly reliable control of cabin descent, which meets all of the safety requirements currently demanded of and met by hydraulically actuated telescopic mast trucks.

Nevertheless fail-safe safety chains, such as are provided on hydraulically actuated telescopic mast trucks, will be specified in trucks according to the invention so as to comply with manufacturing and operating safety requirements. Also a mechanical overspeed device is fitted to provide independent braking of the telescopic moving mast sections relative to the fixed sections.

Drawings A preferred embodiment of the invention is described below with reference to the drawings, of which Figure 1 is a side view of a telescopic mast order picker/stacker truck according to the invention; Figure 2 is an exploded view of a winch and cable mechanism for raising and lowering the movable masts of the truck according to Figure 1; Figure 3 is a schematic illustration of the interconnection between the elements of the telescopic mast and the cabin platform of the truck of Figures 1 and 2, illustrating the means of obtaining a linear relationship between cable movement and the movement of the cabin platform; and Figure 4 is a block diagram illustrating the operation of the controller in the truck of Figures 1 to 3.

The truck of Figure 1 comprises a truck body movable on wheels along an aisle of a warehouse. A telescopic mast assembly 2 is upstanding from the body of the truck, and is a two-element system comprising a pair of outer masts 3 which are fixed relative to the truck body and a pair of inner masts 4 which are vertically movable.

Carried on the inner masts 4 and movable relative thereto, is the cabin platform 5 carrying an operator cabin 6 and a pallet fork mechanism 7. The fork mechanism 7 includes means for moving a pair of pallet lifting forks 8 laterally of the cabin platform 5 to enter the racking system of the warehouse at either side of the aisle to deposit or retrieve a pallet (not shown).

A winch drum 9 controls the raising and lowering of the cabin platform 5, and is powered by a series wound DC electric motor which takes current from a substantial rechargeable battery pack 10 on the truck 1, typically delivering 72 volts.

Figure 2 illustrates the raising and lowering of the inner masts 4 of the telescopic mast assembly 2, using the winch drum 9. The DC electric motor is shown in Figure 2 as 11, and drives the winch drum 9 through a gearbox 12. A pair of high tensile steel cables 13 is wound onto the winch drum 9, each cable 13 passing over a high level pulley 14 towards the top of the fixed outer masts 3, then beneath a low level pulley 15 near the bottom of the movable inner masts 4, before being anchored at an anchorage point 16 at a high level on the fixed outer masts 3. That is sufficient to provide a 1:2 lifting ratio for the inner masts of the telescopic mast assembly, relative to the rate at which the winch drum 9 draws on or releases the cables 13.

The cabin platform 5 can travel up and down the pair of inner masts 4 in direct response to the movement of the winch drum 9. Figure 3 illustrates schematically the driving connection between the telescopic mast assembly 2 and the cabin platform 5. It must be understood that Figure 3 is schematic only and does not attempt to show the actual relative sizes and dispositions of the various components. For example, it will be understood from Figure 2 that the pulley wheels 14 and 15 are in mutually perpendicular planes, but for illustrative purposes only they are shown in Figure 3 in the same plane so that the relative paths of the cables 13 and chains 17 can be understood.The connection between the mast assembly 2 and the cabin platform 5 comprises a pair of chains 17 and idler wheels 18, each chain being anchored at one end at 17a to the cabin platform 5, and at its other end at 17b to a respective fixed outer mast 3. Between its ends, each chain 17 passes over a high level idler wheel 18 carried by the respective movable inner mast 4. This arrangement provides a 2:1 lifting ratio between the inner masts 4 and the cabin platform 5. That 2:1 ratio, taken with the 1:2 ratio referred to above, provides a linear 1:1 ratio between the winch movement and the cabin movement.

One serious problem faced by the inventors of this telescopic mast order picker truck is the control of downward movement of the cabin platform from rest. The pallet forks 8 may be empty, or may have picked or be about to pick up a heavily loaded pallet. Figure 4 illustrates a preferred system of controlling the cabin platform movement. The weight of the pallet can, if desired, be rapidly sensed by a load cell 21, so that the motor can be controlled by a controller 22 to operate at higher torque when the loads are heavy. Two other inputs to controller 22 are a signal 23 from a joystick 24 in the cabin 6 indicating a desired speed and direction of cabin movement, and a signal 25 from a sensor 26 which represents the sensed speed and direction of cabin movement. The output of the controller 22 is a function of the difference between the input signals 23 and 25, and directly controls the torque generated by the motor. The controller also controls the release or application of a brake for the motor. Preferably, however, the load cell 21 is omitted and the truck of the invention is controlled even in the absence of a signal representing a sensed load on the platform. The control, for a platform descending from a rest position, is as follows.

(1) A cabin platform lifting torque is applied by the motor 11 and simultaneously a winch brake 27 is released by the controller 22.

(2) The lifting torque of the motor 11 is then progressively reduced to permit controlled downward movement of the cabin platform 5 under gravity.

(3) In a preferred control sequence, plug braking then commences. The motor is utilized as a generator, and under the control of the controller the generator output current is sent through a diode connected across the armature. The plug braking step in the sequence is, however, optional.

(4) When the winch movement is sufficient, regenerative braking of the winch drum 9 commences, in which the motor 11 is still used as a generator, but its output is applied as a back EMF to the rechargeable battery pack 10. The generator output is controlled by the controller in response to the operator control of desired descent rate.

Although Figure 2 shows a brake release lever 28 which can be operated from ground level, that is a safety feature only in case the operator is unable to control the truck from the cabin 6. Apart from such necessary safety considerations, all truck movement is controlled from the cabin 6, and the vertical movement of the cabin platform relative to the ground is preferably achieved by a single control lever or joystick (represented in Figure 4 by box 24), providing the input to the controller representing the desired motor speed and direction. That single joystick input 23, together with a second input 25, indicating a sensed motor speed and direction, is sufficient to provide full control of motor torque, and control of the brake 27, to achieve proper and safe raising and lowering of the cabin 6 irrespective of the pallet loads being carried by the forks 8. The sensor 26 may be a tachometer connected to the winch drum 9 as shown in Figure 2, producing an analog output, or a digitizer, producing an output that is a digital representation of speed and direction. The third input to the controller 22, from the load cell 21 and representing sensed loads on the pallet forks, is purely optional.

Claims (10)

1. A telescopic mast order picker truck movable in an aisle of a warehouse between warehouse racking, comprising: a pair of fixed masts upstanding from a truck body; a pair of movable masts vertically movable with respect to the fixed masts; a cabin on a cabin platform supported by and vertically movable relative to the movable masts in response to vertical movement thereof; and pallet handling forks or a pallet handling platen carried by the cabin platform for handling pallets at any warehouse level; wherein a motive force for moving the movable masts is a battery powered DC electric motor operable from within the cabin and controlled by a controller which has inputs representing a desired motor speed and direction and a sensed motor speed and direction, and an output which is a function of the difference between those inputs, the motor torque being a function of that output.

2. A truck according to claim 1, wherein the motor is a series wound DC electric motor.

3. A truck according to claim 1 or claim 2, wherein the movable masts are raised or lowered relative to the fixed masts by a pair of cables winding onto a winch drum that is driven by the DC electric motor.

4. A truck according to claim 3, wherein the cabin platform is raised or lowered relative to the movable masts by a pair of chains each passing around at least one idler wheel.

5. A truck according to claim 4, wherein each chain passes around an idler wheel mounted on the movable mast, and is secured at its opposite ends to the fixed mast and to the cabin platform respectively.

6. A truck according to any preceding claim, wherein the lifting ratio of the winch drum to the movable mast is 2:1 and the lifting ratio of the movable mast relative to the cabin is 1:2.

7. A truck according to any preceding claim, wherein the controller also controls a brake which automatically brakes the winch drum when the drum is stationary and releases the brake when the relevant controller input demands motor movement.

8. A truck according to claim 7, wherein the DC motor is powered by rechargeable batteries carried by the truck.

9. A truck according to claim 8, wherein the controller acts to control the downward movement of the cabin platform from rest by applying the following control sequence: (i) applying a cabin platform lifting torque to the motor and simultaneously releasing the brake; (ii) reducing the lifting torque to permit controlled downward movement of the cabin platform under gravity; (iii) utilizing the motor as a generator and directing the generated output as an output current through a resistance load; and/or as a back EMP to recharge the batteries.

10. A telescopic mast order picker truck substantially as described herein with reference to the drawings.