EP2617676B1

EP2617676B1 - Industrial truck comprising a control unit

Info

Publication number: EP2617676B1
Application number: EP20120151600
Authority: EP
Inventors: Michael Strand
Original assignee: BT Products AB
Current assignee: Toyota Material Handling Manufacturing Sweden AB
Priority date: 2012-01-18
Filing date: 2012-01-18
Publication date: 2014-10-15
Anticipated expiration: 2032-01-18
Also published as: EP2617676A1

Description

FIELD OF THE INVENTION

The invention relates to an industrial truck in particular to an industrial truck comprising a control unit. More precisely the invention relates to an industrial truck comprising a control unit for controlling a drive control of the industrial truck, wherein the control unit is arranged to receive an indication from a human machine interface of the industrial truck, the control unit is arranged to determine a corresponding desired rotation speed of a drive motor of the industrial truck, based on the indication. The invention also relates to a method and computer program performing said method on an industrial truck of the invention.

BACKGROUND ART

US 3 818 291 discloses an operating system for an electrically driven forklift truck, disclosing a speed of the forklift truck with a non linear variation of the speed as a function of the accelerator pedal angle. The disclosure discloses a particular speed for a particular amount of accelerator pedal angle.

SUMMARY OF THE INVENTION

There is a general problem that an industrial truck is operated in several different operation modes. One mode of operation is when the industrial truck is used for transporting. That is the industrial truck is generally moving from a point A to a point B. This operation is generally performed with transport speeds that are in the higher portion of the possible speed interval of the industrial truck, as the operator desires to be as effective as possible. When the operator enters the loading and lifting operation of the industrial truck he generally applies transport speeds that are in the lower portion of the speed interval. A general problem is then to have good control for all modes of operation
At least one of the problems is solved by the present invention in that the industrial truck comprises a control unit that is arranged to determine if a condition Z is satisfied wherein Z is satisfied if an indication for a desired rotational speed of the industrial truck motor is of a larger magnitude than any previous indication since the last time an indication was received by the control unit indicating the desired rotational speed of the drive motor to zero, and when Z is satisfied the desired rotational speed is determined based on a curve A, and if condition Z is not fulfilled the control unit is arranged to follow a different curve B when determining the desired rotational speed of the drive motor of the industrial truck.
The effect of this is that the industrial truck behaviour is adapted such that the industrial truck can operate with good control both at the higher portion of the speed interval of the industrial truck and in turn it can be adapted such that when needed the industrial has good control in a lower portion of the speed interval. In particular this will make the industrial truck easier to control for the operator. Another advantage is that the performance of the industrial truck will be improved, the better control will decrease incidents, damaged goods etc.
In another embodiment of the industrial truck of the invention curve A and curve B are curves in a diagram with desired rotational speed on the y-axis and indicated magnitude on the x-axis, and said curves A and B are comprised in the control unit preferably as functions or lists of coordinates in said diagrams.
By incorporation of the curves A and B in the control unit itself the control unit need not to address a further device or for performing the determination of condition Z or the desired rotational speed at a given moment in time.
In another embodiment of the invention curve A has a shape with a lower inclination for lower magnitudes of indication and corresponding determinations of desired rotational speed to be sent to the drive control, and a higher inclination for higher magnitudes.
This results in a better control of the rotational speed of the drive motor for the lower portion of the rotational speeds of the drive motor. This also means that in the higher portion of the interval of rotational speeds the altering to a higher desired rotational speed is faster compared to the lower portion of said interval.
In another embodiment curve A has an arc shape preferably described by a function that when derived gives an increasing and positive derivative.
This shape of the curves gives a seamless transition from lower desired rotational speed to higher rotational speeds and different inclinations.
In another embodiment of the invention the control unit is arranged to determine the shape of curve B each time the condition Z is fulfilled.
This has the effect that the operation mode of the industrial truck explicitly is transformed into a relation between the indicated magnitude and the rotational speed of the drive motor. This has the effect that the behaviour of the industrial truck is instantly adapted to the desired rotational speed interval. Further the industrial truck will adapt again for other larger magnitudes of indication. Thus the industrial truck will have a dynamic adaptation to the current operation mode. This means that the industrial truck will be more flexible and more effective to the operator.
In another embodiment the control unit is arranged to determine curve B in a point on curve A at the moment when Z is no longer fulfilled.
This has the effect that the control unit need not calculate continuously curve B as a transition takes place along curve A, when indication of higher desired rotational speeds of the drive engine is requested.
In another embodiment of the invention the control unit is arranged to determine curve B by extrapolating a line from the point of the current largest indicated magnitude and its intersection of curve A, to the origin of the diagram comprising curve A.
The effect of this is a simple implementation of the determination of curve B to the control unit. It also provides a linear behaviour to the human machine interface, which will make the control of the industrial truck predicable.
In another embodiment of the invention the curve B has a relation to curve A such that all values of determined desired rotational speed for a indicated magnitude is higher than for corresponding values on the A curve, except for the upper and lower endpoints.
This has the effect that the industrial truck will have a different behaviour when condition Z is not fulfilled than when Z is fulfilled. For example this allows for a particular indicated magnitude to have different desired rotational speeds depending on whether the industrial truck is accelerated by the operator in the beginning of his travel than for an acceleration that occurs after an indication for a lower rotational speed after the first acceleration.
In the preferred embodiment the human machine interface comprises a magnitude input element.
This has the advantage that the magnitude input element is incorporated in the human interface for a convenient control of the industrial truck.
In the preferred embodiment the drive motor is an electric motor.
This has the effect that the industrial truck is very environmentally friendly, and thus is excellent for indoor use.
The preferred industrial truck for the invention is a forklift truck.
The many precision transport operations involved when operating a forklift truck is particularly advantages together with this invention.
The invention also comprises a method for controlling a drive control of an industrial truck, comprising the steps of: a control unit of the industrial truck receives an indication from a human machine interface of the industrial truck, the control unit determines if a condition Z is satisfied, wherein Z is satisfied if the said indication is of a larger magnitude than any previous indication since the last time an indication was received by the control unit indicating the desired rotational speed to zero, and if Z is satisfied the control unit determines desired rotational speed based on a curve A, if the condition Z is not fulfilled the control unit determines the desired rotational speed of the drive motor of the industrial truck , based on a curve B.
In another embodiment of the method it further comprises the step of if condition Z is fulfilled the control unit determines curve B.
The method can in particular be implemented on a industrial truck in the form of a fork lift truck.
The invention also comprises a computer program comprising computer readable instructions which, when executed by a processor of a control unit in an industrial truck according to the above, causes said truck to perform the above method.

BRIEF EXPLANATION OF THE DRAWINGS

Fig. 1 discloses an industrial truck of the invention
Fig. 2 discloses curves A and B according to one embodiment of an industrial truck according to the invention.
Fig. 3 discloses curves A and B according to one embodiment of an industrial truck according to the invention.
Fig. 4 discloses a magnitude input element of one embodiment of an industrial truck according to the invention.
Fig. 5 discloses a magnitude input element of one embodiment of an industrial truck according to the invention.
Fig. 6 discloses a method according to the invention.
Fig. 7 discloses an industrial truck of another type than in fig. 1 still according to the invention.
Fig. 8 discloses the embodiment according to fig. 1 with added arrows for explanation.

DETAILED DESCRIPTION

In fig. 1 a preferred embodiment of the industrial truck 3 is disclosed wherein it comprises a control unit 1 a drive control 5 and the control unit 1 controls is arranged to control the drive control 5. The control unit 1 is arranged to receive an indication m, such as by way of example in fig. 2, m1, m2, m3, from a human machine interface 4 of the industrial truck 3. The control unit 1 is arranged to determine a corresponding desired rotation speed d based on the indication m, where d is represented by examples of specific values in fig 2, d1, d2, d3. And the control unit 1 is arranged to determine if a condition Z is satisfied wherein Z is satisfied if the said indication m is of a larger magnitude than any previous indication since the last time an indication was received by the control unit 1 indicating the desired rotational speed to zero d0, and when Z is satisfied the desired rotational speed is determined based on a curve A, and if condition Z is not fulfilled the control unit 1 is arranged to follow a different curve B when determining the desired rotational speed of the drive motor of the industrial truck 3.
The industrial truck 3 generally comprises an industrial truck computer. The industrial truck computer comprises a processor, a RAM and a ROM memory. The industrial truck computer has a comprehensive ability to control the remaining electronic components of the industrial truck. The industrial truck computer is hierarchically at the top of the industrial truck as far as the electronics are concerned and can be compared with a brain. It has the ability to store software and can execute this. According to what is mentioned above the industrial truck computer is central and can comprise the said control unit 1. It should also be understood that the control unit 1 as comprised in the industrial truck computer, can be constituted by instructions and logic instructions stored in the industrial truck computer. The control unit 1 can also be a separate control unit. The control unit 1 can be positioned at a suitable position in the industrial truck. A suitable position is generally close to a human machine interface 4 of the industrial truck. The control unit 1 can also be positioned elsewhere in the industrial truck such as in the industrial truck's body.
The drive control 5 is to be understood as primarily being engaged in controlling the drive motor 2 of the industrial truck 3. The drive control 5 is arranged to take instructions from the control unit 1. The drive control 5 is responsible for transforming the instructions, in form of signals, from the control unit 1, into rotational speed instructions sent to the drive motor 2. The drive control 5 generally can handle the very large current intensities needed to control the drive motor 2.
The human machine interface 4 is generally arranged in dependence of what type of industrial truck 3 it is applied to. The human machine interface 4 is for a tiller arm truck, fig. 1, comprised in the handle of the tiller arm. In a larger reach truck, see fig 7, the human machine interface can be comprised of a steering wheel and a control panel and also pedals for the feet of an operator.
The general concept of the invention is that the control unit 1 receives an indication m exemplified in figures 2-3 and 8 by m1, m2, m3 from the human machine interface 4. This indication is generally in form of a signal coming from the human machine interface 4. The indication is construed by the control unit 1 before passing it to the drive control 5 as signals of desired rotational speeds d, exemplified by d1, d2, and d3. The control unit 1 thus uses the indication m to determine a corresponding desired rotational speed d for the drive motor 2 of the industrial truck. When determining the corresponding rotational speed of the drive motor 2 the control unit 1 checks whether a condition Z is satisfied or not. The check of condition Z is thus performed by the control unit 1 independently.
The check of condition Z can be performed in several possible ways. One possible way is that the control unit 1 stores the information of maximum values of magnitudes of indication m, as exemplified by m1, m2, corresponding to rotational speeds d, as exemplified by d1, d2 being determined by means of the A curve. This means that the control unit 1 stores the current highest m value, and compares this with the current m value.
In one embodiment the control unit 1 performs the determination by a time log for when the last time the indication from the human machine interface 4 was null. That is the human machine interface 4 didn't send any indication. For example it could be possible that a delay is incorporated such that if the indication of the desired rotational speed is at least a certain time period, condition Z is fulfilled. Thus consequently if the indication for a desired rotational speed is a short time period, the control unit 1 can determine that condition Z is not fulfilled. Thus the control unit 1 will continue to apply curve B for determinations of desired rotational speeds d as exemplified by d3, of the drive motor 5. The control unit 1 will thus determine that condition Z is fulfilled or not. If fulfilled the control unit 1 will determine a new curve A when construing the signal corresponding to the magnitude of the signal m and determine a corresponding desired rotational speed d for the drive motor of the industrial truck 3. The new curve A is determined such that it at the current m value has an intersection with the B curve, such that any jerks when switching curves does not jeopardize the security of the industrial truck. This signal corresponding to d is then sent to the drive control 5 of the industrial truck 3.
If the control unit 1 determines that the condition Z was not fulfilled, the control unit 1 will use curve B. Curve B generally is different from Curve A for all embodiments. It should however be understood that intersection points or smaller portions of the two curves cold be the common.
Condition Z is thus a condition of comparative nature. The maximal value of since the last time the indication indicated m0 a desired speed to be zero d0, should be understood in general terms as the last time the human interface was not actuated. It could be that the human interface 4 delivers no signal to the control unit 1 in this case, and this should be understood as the desired rotational speed is zero d0. However it could also mean that the control unit 1 sends a signal for an indication that the desired speed is zero, even though the human interface 4 is not actuated. It should also be understood that condition Z is a condition of choice between curves. The control unit 1 determines how to proceed forward with the indication received that for different moments in time can be different for the very same indication received from the human machine interface 4.
Curve A and Curve B are curves in a diagram with magnitude of indication of the human machine interface 4 on the x-axis and the desired rotational speed of the drive engine 5 on the y-axis.
Curve A could generally be considered as a maximal curve. That is curve A is a curve that is implemented each time a maximal value of indication is received. Thus curve A should be understood as not to be used for any determination when desired rotational speeds d such as d3 fig. 2 and fig. 3, has been lowered but not zeroed.
Curve B could generally be considered to be the curve that is actually implemented for the control of the rotational speed in the interval between the latest maximal point (m1, d1), (m2, d2) on the A curve, see fig 2, fig3, and the origin (m0, d0) which should be understood as when zero rotational speed is desired. That is curve B could generally be considered to be the curve to be implemented whenever a lowering of the rotational speed is desired.
With regard to the application of the wording curves it should be understood that this should be considered as descriptive of underlying mathematical functions from describing the relation between indicated magnitudes of the human machine interface 4 and the desired rotational speed of the drive engine. However it should not be construed as limited to mathematical functions, the curves could be stored in the control unit 1 as a list of coordinates that describes a stepwise curve that could be more difficult to describe as a simple mathematical function. This is applicable for both A and B curves.
Curve A can have any optional shape. In one embodiment the curve A has an inclination for lower values of magnitudes of indication that has a low inclination, and for higher values of magnitudes of indication has an inclination that is higher. This gives the advantage that for lower values where condition Z is fulfilled the rotational speed increases more slowly, i.e. with greater precision, than for higher values where the condition Z is fulfilled.
In one embodiment the curve A has an arc shape according to fig. 2.
Curve B in its simplest form has a straight line form from the current maximal value on the A curve to the origin of the diagram.
In one embodiment the curve B is determined each time condition Z is fulfilled. An example of this is can be seen in fig 2 and 3, where the intersection between curve B and curve A describes the value for which the Z value is fulfilled for m1 and m2. However these are points and according to the embodiment the determination is made continuously during the transition between m1, and m2. In fig. 8, one can follow a transition, see arrow 13 from a magnitude that is m1 to m2 where a new B curve with higher inclination is determined. One can also follow a transition from m1 to m3, see double arrow 12, which is of a lower indicated magnitude. Thus m3 is used by the control unit 1 to determine a corresponding desired rotational speed d3 that is based on the B curve determined through the m1 indication. This is in contrast to the m2 indication which demonstrates a new maximal value of indication, thus fulfilling the Z condition, and consequently a new curve B is determined. For a better understanding, see mentioned fig. 8 where arrow 11 as said discloses a transition along curve A as Z is fulfilled. Arrow 12 discloses a transition, having reached (m1, d1) where Z is no longer is fulfilled. And as can be seen any transition for m < m1 follows curve B, in both directions. This does not include the origin, which if reached, will lead to a transition according to arrow 11 along curve A. Arrow 13 discloses a transition along curve A for new magnitudes of indication m > m1. And Arrow 14 discloses transitions along curve B up and down as long as condition Z is not fulfilled. A transition from point m3, d3 to point (m2, d2) would for the first part of the transition follow curve B and for the second part, when condition Z is fulfilled follow curve A.
With regard to the determination of curve B this could thus be performed by the control unit 1 continuously during a transition on curve A, i.e. where condition Z is fulfilled. However this could also be performed in a preferred way by the control unit 1 in the point where a transition along curve A is stopped. This means that curve B is determined by the control unit 1 in a point. In this embodiment the fig. 2, fig. 3 and fig. 8 should be construed as the determination of B is performed in the disclosed points corresponding to m1 and m2, as these represent points where a transition on the A curve is stopped.
In one preferred embodiment the curve B is positioned above curve A for all vales as can be seen in fig. 2 and fig. 3. This means that when an operator accelerates his industrial truck he will slow down, after reaching a magnitude m as exemplified in fig. 2,3 and 8 by m1, m2, in a more moderate way than should he have followed the A curve. This is especially favourable at high rotational speeds.
The shape of curve B can alter; see fig. 3, which discloses a shape of curve B different from the shape of curve B in fig. 2. I should also be understood that as seen in fig. 3, curve B for a first determination, can have a different shape, than a curve B for a later determination. Difference in shape of B curve will have the effect that the behaviour of the industrial truck 3 can be adapted more precisely for different magnitudes of indication m when condition Z is fulfilled.
The human machine interface 4 comprises a magnitude input element 6.
The magnitude input element can be constructed as a toggle switch 6a which can easily be actuated by a thumb of the operator, see fig. 4. This is the preferred embodiment. The toggle switch 6a has a spring which returns the toggle switch to a position giving a magnitude that corresponds to desired rotational speed of the drive engine that is zero. In fig 2, the magnitudes that are correspondingly disclosed in fig. 4 are disclosed. Thus the magnitude input element 6a is a spring actuated rotating device optimized for actuation by a finger of the operator, preferably a thumb, wherein said device is arranged by means of said spring such that when released it attains a zero magnitude. The effect of the toggle switch is that the operation is easy and the zero desired speed is conveniently attained by means of the spring and the easy removal of the operator's finger from the input element.
The magnitude input element 6 can be constructed in any suitable way, such as a hand operated element in fig. 7, or as a (non disclosed) pedal in an industrial truck. See fig. 7 for an example of an industrial truck that could be using pedals as means indication desired rotational speed of the drive engine of the industrial truck 3. The preferred pedal is an accelerator pedal.
The magnitude input element (6b) can also be of a spring actuated linear type, fig. 5, optimized for actuation by a finger of the operator. This device is arranged by means of said spring such that when released it attains a zero magnitude. The magnitude input element is preferably a slide switch as can be seen in fig. 5. Corresponding values of magnitude m1, m2, m3 to curves of fig. 2, 3 and 8 are disclosed in fig. 5. The magnitude element comprises a loop on a bar, to be actuated by a finger. The advantage of the linear type design is that the magnitude input element is easily readable.
One particular embodiment comprises a digital magnitude input element. This can function in any appropriate way, such as a clicking and holding it down corresponds to an indication of a magnitude of m3, see fig 2-3. A double clicking could mean a magnitude of m1, holding down could mean another magnitude etc. The advantage for a digital magnitude input element is that the magnitude input element is more robust, and can be easily actuated.
It should be understood that for all embodiments the indicated magnitude can for the magnitude input element of fig 4 and fig. 5 generally be transferred by a position of the toggle switch or the loop on a bar. This is not possible for the digital input element where the magnitude is determined by the way of clicking operations.
Desired rotational speed of the drive motor should be understood as to correspond to the desired industrial truck travel speed. Generally the gear of industrial trucks is fixed thus a rotational speed of the drive motor 5 corresponds directly by mechanical transmission to a wheel rotation speed. Thus if the wheel does not slide on the base surface the rotational speed of the drive engine corresponds directly to the travel speed of the industrial truck.
The discussed embodiments above discuss desired rotational speed d of the drive motor 5. It should be understood that desired rotational speed d is not the same as actual rotational speed of the drive motor 5 for all moments in time. The actual rotational speed is of course depending on the momentum of the industrial 3 in motion. And if the operator indicates a magnitude m corresponding to zero d0 desired speed and then decides to indicate a magnitude m corresponding to a higher desired speed the actual rotational speed of the drive motor 5 will never reach zero. However in line with the invention the control unit 1 will in this determine that condition Z is fulfilled and apply curve A for determining this higher desired rotational speed.
The embodiments above for the industrial truck 3 are also to be understood as a method for controlling a drive control 5 of an industrial truck 3, comprising the steps of:

a control unit 1 of the industrial truck receives an indication m from a human machine interface 4 of the industrial truck 3,
the control unit 1 determines if a condition Z is satisfied, wherein Z is satisfied if the said indication m is of a larger magnitude than any previous indication since the last time an indication was received by the control unit 1 indicating the desired rotational speed to zero, and
if Z is satisfied the control unit 1 determines desired rotational speed d based on a curve A,
if the condition Z is not fulfilled the control unit 1 determines the desired rotational speed d of the drive motor 2 of the industrial truck 3, based on a curve B.

The method can further comprise steps that uses the described construction it the industrial truck discussed above. One such example is that the control unit 1, if condition Z is fulfilled determines curve B.
It should be understood that it is possible to implement the above describe embodiments in an existing industrial truck, which then becomes a modified industrial truck according to the invention.
The method is preferably implemented in an industrial truck in the form of a forklift truck.
The embodiments above described as having the following; a control system for control of the desired rotational speed of the industrial truck drive motor 2 comprising the control unit 1, the drive control 5, and magnitude input element 6 of the human machine interface 4, wherein the magnitude input element 6 is arranged to generate and send an operator indication signal to the control unit 1, and wherein the control unit 1 is arranged to receive the operator indication signal from the magnitude input element 6 and transmit a control command to the drive control 5, wherein the drive control 5 is arranged based on the control command to send a control signal to the drive motor 2 for a desired rotational speed.
It should also be understood that the industrial truck can comprise a control unit 1 that comprises a computer program comprising computer readable instructions which, when executed by a processor of a control unit 1 in an industrial truck performs the method above.
The invention described above is thus adapted for industrial trucks 3. An example of such an industrial truck 3 is disclosed in fig. 1, and another in fig.7. These figures disclose industrial trucks in the form of forklift trucks. In the meaning of forklift truck is intended trucks that are material handlers. It has a load handling section and a drive section. The load handling section has generally a mast, but can also be without a mast, as the exemplified forklift truck 3 of fig. 1. The load handling section comprises a fork pair. Generally two forks, but the fork pair should be interpreted as one or several forks. The fork pair can be lifted or lowered to handle a load. The lifting and lowering function is performed by means of hydraulic pistons. The fork pair is generally positioned on a fork carriage, but can also be designed such that a fork carriage is not needed, for example on a low lifting forklift truck. On certain forklift trucks the fork pair can be moved sideways. To push the forks sideways there are hydraulic pistons. On certain forklift trucks the gap between the forks can optionally be adjusted. In this case this is also performed by means of a hydraulic piston or hydraulic pistons. On certain forklift trucks the load handling section comprises an operator cage. The operator cage can also have a function of movement in its entirety. Preferably this movement is performed by hydraulic pistons. Generally this movement is horizontal. In a variant of forklift trucks the fork pair can also be rotated essentially horizontally.
The driving section comprises functions for driving the forklift truck. For all embodiments above, the forklift drive motor 2 is preferably an electric motor. In case of an electric drive motor 2 it is supplied from an energy source in the form of a battery, or other forms of suitable electric energy sources, such as fuel cells, or supply from an electric network. The energy source could also be of another type, such as gasoline, diesel, gas or the like, in combination with a combustion drive engine. However the invention is primarily intended for electrically powered forklift trucks having a battery as an energy source.
The driving section comprises at least one drive motor 2. The drive motor 2 is connected to one or several of the truck's wheels. Generally there is a gear between the drive motor and the drive wheel. As mentioned above the most common way of arranging the gear is with a direct transmission from the drive motor 2 to the wheel. Generally the drive motor is an electric motor 5, as in the forklift truck of fig. 1 and fig. 7.
The driving section generally comprises human machine interfaces as control devices for manoeuvring the forklift truck. These can be constituted of a tiller arm, a wheel or the like. To this adds devices for manoeuvring of the load handling section, these can be constituted of devices for lifting and lowering, tilting, and side movement of the forks, there can also be devices for changing the spread of the forks. The devices can be bars, wheels, buttons or the like. They can be separate for each function alternatively several functions are gathered in the same device. For larger forklift trucks, a driver compartment can be arranged. For smaller forklift trucks, fig. 1, such as tiller arm trucks, the driver walks with the forklift truck alternatively, travels on a platform behind the forklift truck. The features for controlling the different functions of forklift trucks in general, add up to the human machine interface 4.
This particular invention could also be implemented on an industrial truck in the form of a towing tractor, not disclosing any load lifting capability, by means of for example forks and other hydraulic lifting mechanisms.

Claims

An industrial truck (3) comprising a control unit (1) for controlling a drive control (5) of the industrial truck (3), the control unit (1) being arranged to receive an indication (m) from a human machine interface (4) of the industrial truck (3), the control unit (1) is arranged to determine a corresponding desired rotation speed (d) of a drive motor (2) of the industrial truck (3), based on the indication (m),
characterised in that
the control unit (1) is arranged to determine if a condition Z is satisfied
wherein Z is satisfied if the said indication (m) is of a larger magnitude than any previous indication since the last time an indication was received by the control unit (1) indicating the desired rotational speed (d) to zero (d0), and
when Z is satisfied the desired rotational speed (d) is determined based on a curve A, and
if condition Z is not fulfilled the control unit (1) is arranged to follow a different curve B when determining the desired rotational speed (d3) of the drive motor of the industrial truck (3).
The industrial truck (3) according to claim 1, wherein curve A and curve B are curves in a diagram with desired rotational speed on the y-axis and magnitude of indication on the x-axis, and said curves A and B are comprised in the control unit (1) preferably as functions or lists of coordinates in said diagrams.
The industrial truck (3) according to claim 1 or 2, wherein the curve A has a shape with a lower inclination for lower magnitudes (m) of indication and corresponding determinations of desired rotational speed to be sent to the drive control (5), and a higher inclination for higher magnitudes (m).
The industrial truck (3) according to any of the claims 1 - 3, wherein curve A has an arc shape preferably described by a function that when derived gives an increasing and positive derivative.
The industrial truck (3) according to any of the claims 1-4, wherein the control unit (1) is arranged to determine the shape of curve B each time the condition Z is fulfilled.
The industrial truck (3) according to any of the claims 1 - 4 , wherein the control unit (1) is arranged to determine curve B in a point on curve A at the moment when Z is no longer fulfilled.
The industrial truck (3) according to claim 5 or 6, wherein the control unit (1) is arranged to determine curve B by extrapolating a line from the point of the current largest indicated magnitude (m) and its intersection of curve A, to the origin of the diagram comprising curve A.
The industrial truck (3) according to any of the claims above, wherein curve B has a relation to curve A such that all values of determined desired rotational speed (d) for a indicated magnitude (m) is higher than for corresponding values on the A curve, except for the upper and lower endpoints.
The industrial truck (3) according to any of the claims above wherein the human machine interface (4) comprises a magnitude input element (6).
The industrial truck (3) according to any of the claims above, wherein the drive motor (2) is an electric motor.
The industrial truck (3) according to any of the claims above, wherein the industrial truck (3) is a forklift truck (3).
A method for controlling a drive control (5) of an industrial truck (3), comprising the steps of:
- a control unit (1) of the industrial truck receives an indication (m) from a human machine interface (4) of the industrial truck (3),

- the control unit (1) determines if a condition Z is satisfied, wherein Z is satisfied if the said indication (m) is of a larger magnitude than any previous indication since the last time an indication was received by the control unit (1) indicating the desired rotational speed to zero, and

- if Z is satisfied the control unit (1) determines desired rotational speed (d) based on a curve A,

- if the condition Z is not fulfilled the control unit (1) determines the desired rotational speed (d) of the drive motor of the industrial truck (3), based on a curve B.
The method of claim 12, wherein it further comprises the step of:
- if condition Z is fulfilled the control unit determines curve B.
The method according to any of the claims 12 -13, wherein the industrial truck is a forklift truck.
Computer program comprising computer readable instructions which, when executed by a processor of a control unit (1) in an industrial truck (3) according to any of the claims 1-11, causes said industrial truck (3) to perform the method according to any of the claims 12 - 14.