EP2390222B1 - Method for providing information about a current hoisting height and industrial truck for same - Google Patents

Description

The invention relates to a method for providing information about a current lifting height of a load-bearing means of a truck and a truck with an evaluation unit for providing this information. For the safe operation of a truck, it is advantageous if information about the current lifting height is available. For example, when a certain lifting height is exceeded, the maximum driving speed can be reduced in order to prevent the truck from tipping over. If the information about the current lifting height is already available immediately after the truck has been put into operation, the truck is immediately ready for use. In particular, it is then not necessary to detect the current lifting height by initially moving the load-bearing means up and down for the first time.

Known forklifts therefore often use switches for the lifting height detection, which receive their switching state regardless of a power supply, so that the switching state and thus the Hubhöheninformation not be lost when switching off the truck. Frequently used as a reed switch Hubhöhenschalter are used, which provide such a storing function. With reed switches, switching occurs under the influence of a magnetic field, whereby the switch position can be maintained independently of a power supply. In practice, it comes with the use of such Hubhöhenschalter due to their vibration sensitivity and susceptibility to temperature fluctuations to malfunction. In particular, said procedure has proven to be not suitable for cold storage.

From the publication JP2003063791A an industrial truck has become known with which the exceeding of a predetermined maximum lifting height is to be prevented. When the truck is switched off, a lift height information is saved. When switching on the truck, this stored information is read and used as a starting value for the further measurement of the lifting height with a Hubhöhenmessvorrichtung.

From the publication DE 100 54 792 A1 an industrial truck with a device for detecting the lifting height and a method has become known. In the known method, detect at least two transducers, namely an incremental encoder and a potentiometer, the lifting height continuously. The lift height information is stored in an electronic memory so that it remains independent of the supply of the memory with electrical energy. For this reason, it should also be possible to access the measured value generated with the incremental encoder immediately after a startup of the truck.

On this basis, it is the object of the invention to provide a method for providing information about a current lifting height of a load-supporting means of a truck and a Flufförderzeug with an evaluation unit for providing this information available, which is reliable and inexpensive to implement.

This object is achieved by the method having the features of claim 1. Advantageous embodiments are specified in the subsequent subclaims.

• Auslesen einer beim letzten Ausschalten des Flurförderzeugs in einem nicht-flüchtigen Speicher gespeicherten Information über die Hubhöhe,
• Ermitteln einer Information über die aktuelle Hubhöhe auf Grundlage der ausgelesenen Information über die Hubhöhe beim letzten Ausschalten des Flurförderzeugs und des Schaltzustands eines Schaltelements, das keine seinen Schaltzustand unabhängig von einer Energieversorgung erhaltende Funktion aufweist und so angeordnet ist, dass sich sein Schaltzustand ändert, wenn ein Lasttragmittel des Flurförderzeugs eine vorgegebene Hubhöhe passiert.

The method serves to provide information about a current lifting height of a load-bearing means of an industrial truck and comprises the following steps:

• Reading out information about the lifting height stored in a non-volatile memory when the truck was last switched off,
• Determining information about the current lift height based on the read information about the lift height at the last shutdown of the truck and the switching state of a switching element that has no switching state independent of a power supply receiving function and is arranged so that its switching state changes when a Load carrier of the truck passes a predetermined lifting height.

The non-volatile memory stores the information about the current lifting height at the time of switching off the truck. The information is retained during the truck's completely switched-off condition and can be called up immediately after restarting the truck.

At any time from the commissioning of the truck information about the current lifting height is determined. The information read out is used as the basis. As a rule, it can be assumed that immediately after switching on, the current lifting height corresponds to the lifting height read from the non-volatile memory. In order to determine the current lifting height, in particular at a time after the commissioning of the truck, the switching state of a switching element is further considered. The switching element does not have its switching state independent of a power supply maintaining function and therefore can not store information in the switched-off state of the truck. When commissioning the truck, the power supply of the switching element is turned on and the switching element is always in the same ground state. The state of the switching element changes when a load carrying means of the truck passes a predetermined lifting height. The predetermined lift height can be passed both in the "bottom-up" and "top-down" directions by moving the load-bearing member in one of the mentioned directions. In both cases, there is a change in the switching state of the switching element. The switching element may, for example, have only two possible states. However, in a more complicated constructed switching element, a larger number of distinguishable states may be possible. When passing the predetermined lifting height, a change between the two possible states can take place in the sense that before passing a first state and after passing a second state of the switching element is present. Equally well, the switching state during the passage of the load bearing means can change only briefly, for example, while the load carrying means is within a small height range around the predetermined lifting height around, and then return back to the state in which they were before passing the predetermined lifting height Has. In this case, the state of the switching element changes, for example, twice in rapid succession. The truck may be a pedestrian-controlled truck or a ride-on rider. It can have any maximum lifting height and mast construction.

The invention is based on the recognition that many known switches, which have a storing behavior, are expensive and / or error-prone and can cause problems under the operating conditions of an industrial truck. In the invention, instead of a storing switch whose switching state is maintained, a non-volatile memory is used, which stores the information on the lifting height valid at the time of switching off. Although a switching element with non-storing behavior is used in the invention, no switching changes need to be queried before the full function of the truck is released.

In one embodiment, the current lift height information may assume a first value representing a position of the load bearing means below the predetermined lift height, and a second value representing a position of the load bearing means above the predetermined lift height. Thus, only a simple "above / below" information is determined. This is possible in a particularly simple manner with a single switching element which can only assume two switching states. In order to obtain a more accurate information about the lifting height, several switching elements can be combined. These are then arranged so that their switching states change when the load carrying means passes different lifting heights. For example, a first switching element may change its switching state when the load carrying means passes a lifting height of 30 cm, and a second switching element may change its switching state when the load carrying means passes a lifting height of 1.8 m. In the non-volatile memory, an "above / below" information is then stored for each of the predetermined lift heights.

In the invention, the switching element on a sensor which responds to an approach of a counterpart. The counterpart has a magnet. An output signal of the sensor is evaluated and a change of the switching state is triggered according to predetermined criteria. In this way, a contactless switching is possible.

In one embodiment, the switching element has two spaced apart in the direction of movement of a counterpart sensors whose output signals are evaluated to detect a movement of the counterpart on the switching element over and to change the switching state. In particular, a signal difference of the two output signals can be determined in the evaluation of the output signals. This allows a more reliable detection of a passing of the counterpart on the switching element. When using a single sensor may not be reliably distinguished between an approach of the counterpart in a first direction and a subsequent distance in the opposite direction and an actual passing of the counterpart on the sensor. When evaluating the output signals of two spaced apart in the direction of movement of the counterpart sensors this is reliably possible.

In one embodiment, an ascending and / or falling signal edge of at least one output signal is detected during the evaluation of the output signals and evaluated to determine a direction of movement of the counterpart. In particular, from a time coincidence of a rising or falling signal edge of the output signal of a sensor with a 0 or 1 signal of the output signal of the other sensor can be concluded that the movement in the downward or upward direction of the counterpart. As a result, the information about the current lifting height can be determined even more reliable.

In one embodiment, an error message is generated when applied to two inputs of an evaluation unit for determining the current lifting height, which is connected to two complementary outputs of the switching element via two lines, the same signals. The fact that the switching element has two complementary outputs means that the two outputs, each of which can assume two different states, always have opposite states. If the first output provides a 0 signal, the second output will always provide a 1 signal, and vice versa. If the same signals are detected at the inputs of an evaluation unit connected to these outputs, there is either an error in the switching element or an interruption of the connection between the switching element and the evaluation unit. This then leads to an error message, which is displayed for example to a user of the truck and / or stored in an error log and / or acts directly on a control of the truck.

In one refinement, an error message is generated if identical signals are present at two inputs of an evaluation unit for determining the current lifting height, which is connected to two outputs of the switching element via two lines, and an actuating element for the lifting function is actuated for a predetermined period of time. or sink function. In this embodiment, the two outputs are not complementary in the strict sense, but can provide the same signals at a certain lifting height. Only when an operation of the lifting or lowering function for a certain period of time does not change this state, this indicates a malfunction.

In one embodiment, when determining the information about the current lifting height, the position of an actuating element for a lifting function of the industrial truck is taken into account. Basically it is possible and sufficient, the current Lift height based solely on a previous information about the current lifting height and determine a change of the switching state to determine. By additionally taking into account the position of the actuating element, a plausibility check can be carried out. For example, a change in the state of the switching element during execution of the lift function indicates an abnormality when the current lift height information indicates a position of the load bearing means "above" the given lift height. Such irregularities can be detected by considering the position of the actuator.

In one embodiment, information about the current lifting height is only changed if a change in the switching state of the switching element is detected during or shortly after an actuation of the lifting function. A change in the switching state is thus observed only if it occurs in temporal relation to an actuation of the lifting or lowering function.

In one embodiment, a change in the information about the current lift height from the first value (representing a position of the load bearing means below the predetermined lift height) to the second value (representing a position of the load bearing means above the predetermined lift height) is made only when a change in the Switching state of the switching element is detected during or shortly after an actuation of the lifting function. In a further embodiment, it is provided that a change in the information about the current lift height from the second value to the first value is only made if a change in the switching state of the switching element is detected during or shortly after an actuation of the sink function. Both measures result in a faulty information about a current lifting height being automatically corrected at a subsequent passing of the load-carrying means at the given lifting height.

The o.g. The object is also achieved by a truck with the features of claim 10. Advantageous embodiments are specified in the subsequent subclaims.

The hall equipment has an evaluation unit for providing information about a current lifting height of a load supporting means of the truck and a switching element which is connected to the evaluation unit and arranged so that its switching state changes when a load carrying means of the truck passes a predetermined lifting height, a not Volatile memory available and the evaluation unit is designed so that when switching off the truck information about the lifting height is stored in the non-volatile memory, and wherein the switching element has no switching state independent of a power supply maintaining function. With regard to the already explained in connection with the inventive method features and the particular advantages, reference is made to the above explanations of the method. The evaluation unit is an electronic device that can be designed as a separate device or preferably as part of a vehicle control system.

Preferably, the switching element with respect to the mast is fixedly arranged and a counterpart, which causes a change in the switching state, is fixedly disposed relative to the load supporting means. In principle, a reverse arrangement is conceivable. In addition, the counterpart or the switching element instead of the load bearing means on a jointly with the load support member moving element, such as a lifting chain or a moving element of a telescopic mast, be attached.

In the invention, the switching element on a sensor which responds to an approach of a counterpart. In particular, a magneto-resistive Sensor that responds to a magnetic field can be used. Such sensors are inexpensive and very robust. In particular, they are insensitive to temperature fluctuations and shocks. A well-suited example of a mapeto-resistive sensor is a Hall sensor.

In one embodiment, the switching element has two outputs which are each connected to an input of the evaluation unit. As a result, an automatic error detection is enabled in particular, as already explained in connection with the method according to the invention. The two outputs may in particular be complementary.

In one embodiment, the switching element on two sensors that respond to approach of a counterpart and are spaced apart in the direction of movement of the counterpart. This allows, as already explained in connection with the method, a more reliable detection of the switching element passing the counterpart.

In one embodiment, an actuating element for a lifting function is connected to the evaluation unit. In this way, the position of the actuating element can be taken into account in determining the information about the current lifting height, which offers the advantages already explained.

In one embodiment, the evaluation unit is designed so that the method is carried out according to one of claims 4 to 9. The truck is thus designed so that said process steps are executable and actually executed. This training of the truck can in particular consist in a corresponding programming a controller or the evaluation of the truck.

Fig. 1

ein deichselgeführtes Flurförderzeug gemäß der Erfindung,

Fig. 2

das Schaltelement, die Auswerteeinheit und ein Betätigungselement des Flurförderzeugs aus Figur 1 in einer schematischen Darstellung,

Fig. 3

ein Zustandsdiagramm zur Erläuterung des erfindungsgemäßen Verfahrens,

Fig. 4

ein Diagramm zum Verlauf der Ausgangssignale eines weiteren Schaltelements.

The invention will be explained in more detail with reference to an embodiment shown in three figures. Show it:

Fig. 1

a drawbar-guided industrial truck according to the invention,

Fig. 2

the switching element, the evaluation and an actuator of the truck FIG. 1 in a schematic representation,

Fig. 3

a state diagram for explaining the method according to the invention,

Fig. 4

a diagram for the course of the output signals of another switching element.

The truck off FIG. 1 has a mast 10, on which a load supporting means 12 is guided. Via a lifting drive 14, the lifting height of the load supporting means 12 can be controlled. This purpose, a control unit 16 which is connected to a magneto-resistive switching element 18 which is fixed to the mast 10. Furthermore, the control unit 16 is connected to an actuating element 20 of an operating unit 22. The actuator 20 has a rest position, a position for actuating the lifting function and another position for actuating the lowering function. Of course, this can also be provided for several separate actuators. The load bearing means 12, a counterpart 24 is fixed, which has a magnet.

If the load carrying means 12 passes the predetermined lifting height 26, the counterpart 24 is moved past the switching element 18.

Further details will be given by the FIG. 2 explains that the switching element 18, an evaluation 28, which has an evaluation and signal processing unit 30 and is integrated into the control unit 16, and the actuator 20 schematically represents.

The switching element 18 has two magneto-resistive sensors 32, 34, which are arranged spaced apart in the direction of movement of a counterpart 24 having a magnet. The magnetoresistive sensors 32, 34 respond to an approximation of the counterpart 24. The two magneto-resistive sensors 32, 34 are connected to two switching outputs S1, S2 of the switching element 18. In between, signal conditioning steps may be performed which are not shown in the figure. The two switching outputs S1 and S2 are complementary to each other and each output a 0-signal or a 1-signal. Whenever the counterpart 24 passes on the switching element 18, the two outputs S1, S2 change state ( FIG. 4 ). Also in the FIG. 2 a connection 38 for a supply voltage of the switching element 18 and a ground terminal 40 of the switching element 18 is shown.

The transmitter 28 has a voltage source 42 which is connected to the terminal 38 of the switching element 18 and the switching element 18 is energized. Furthermore, the transmitter 28 has a ground terminal 44 which is connected to the ground terminal 40 of the switching element 18. The transmitter 28 has two digital inputs 46 and 48 which are connected to the outputs S1 and S2, respectively. The actuating element 20 comprises an arbitrary interface, which is connected via a suitable interface 50 of the evaluation electronics 28 with its evaluation and signal conditioning unit 30. Also connected to the evaluation and signal conditioning unit 30 is a non-volatile memory 52, in which when switching off the truck information about the current lift height at this time is stored.

The evaluation and signal processing unit 30 has a state machine which provides information about the current lifting height. In doing so, it takes into account the information stored in the non-volatile memory 52 of the lift height present at the last switch-off of the industrial truck and the signals of the switching element 18 present at the inputs 46, 48. Furthermore, the position of the actuating element 20 is taken into account by the evaluation unit 30.

Based on the state diagram of FIG. 3 will be explained in more detail how the evaluation and signal processing unit 30 determines the information about the current lifting height. In the diagram, possible states are illustrated by ellipses, accessible transitions between the states by arrows.

The ellipse 54 shown on the top left corresponds to the state of the load bearing means 12 above the predetermined lifting height 26. The underlying ellipse 56 corresponds to the state of the load supporting means 12 below the predetermined lifting height 26. The ellipse 58 represents the information stored in the non-volatile memory on the Lifting height at the time of the last shutdown of the truck dar. The arrow 60 shows the initialization of the system in the event that in the non-volatile memory 58 as the last present lifting height information is stored "above the specified lifting height". In this case, the system is in state 54. The second arrow 62 originating from the non-volatile memory 58 leads to the state 56 in the event that the information "below the predetermined lifting height" is stored in the non-volatile memory. A change from state 54 to state 56 is shown by the arrow 64. This change of state is only made if at the entrances 46, 48, a change is detected and in temporal context so that the position "lowering" of the actuating element 20 is present. Accordingly, a change from state 56 to state 54 is made only if at the entrances 46, 48 a change is determined and in temporal relation therewith the position "lifting" of the actuating element 20 is present, as illustrated by the arrow 66.

The following tables give examples of the temporal development of the current position. In the first column, the signal at the output S1, in the second column, the signal at the output S2 of the switching element 18 is entered. The third column represents the information stored in the non-volatile memory information about the lifting height when last switching off the truck. In the fourth column is referred to as "internal info" is the position of the actuator 20, as the evaluation and signal processing unit 30 is available. The fifth column is overwritten with "current position" and shows the result of the evaluation by the evaluation and signal conditioning unit 30 again. <b> Table 1: </ b> S 1 S2 Position when last switched off Internal Info Actual position 0 1 below the switching point hibernation below the switching point 0 1 below the switching point To lift below the switching point 1 0 below the switching point To lift above the switching point 1 0 below the switching point Reduce above the switching point 0 1 below the switching point Reduce below the switching point S1 S2 Position when last switched off Internal Info Actual position 0 1 below the switching point hibernation below the switching point 0 1 below the switching point Reduce below the switching point 1 0 below the switching point Reduce below the switching point 1 0 below the switching point To lift below the switching point 0 1 below the switching point To lift above the switching point S1 S2 Position when last switched off Internal Info Actual position 0 1 above the switching point hibernation above the switching point 0 1 above the switching point To lift above the switching point 1 0 above the switching point To lift above the switching point 1 0 above the switching point Reduce above the switching point 0 1 above the switching point Reduce below the switching point S1 S2 Position when last switched off Internal Info Actual position 0 1 above the switching point hibernation above the switching point 0 1 above the switching point Reduce above the switching point 1 0 above the switching point Reduce below the switching point 1 0 above the switching point To lift below the switching point 0 1 above the switching point To lift above the switching point

All four tables begin in the first line with a given immediately after switching on the truck state in which the switching element 18 is in a ground state, wherein at the output S 1 is applied a 0-signal and at the output S2 a 1-signal. Likewise in all tables, the actuating element 20 is in the first step in the idle state, as indicated in each case in the fourth column under "internal info".

In the case shown in Table 1, when the truck was last switched off, the load-carrying means 12 was below the predetermined lifting height or wording of the table, below the switching point. This information is stored in non-volatile memory 52 and remains unchanged during the considered period. As a result, the current position of the load bearing means 12 in the first row of the table is also below the switching point.

In the next considered time, represented in the second line of Table 1, the actuator 20 has been brought into the "lifting" position. However, the switching state of the switching element 18 has not changed, which can be seen on the 0 signal at the output S1 and the 1 signal at the output S2. Consequently, the current position of the load bearing means is unchanged "below the switching point".

In the next step, the outputs S1 and S2 indicate a change of the switching state, wherein furthermore the actuating element 20 is in the position "lifting". It is from the evaluation and signal conditioning unit 30 thus a state change according to the in FIG. 3 determined by 66 arrow and the current position changes to "above the switching point".

In the table given in the fourth line step, the actuator 20 is placed in the "sink" position, a change of the switching state can not be determined. Accordingly, the current position remains "above the switching point".

In the last step of Table 1, in turn, a change of the switching state is detected. The position of the actuating element 20 is further "sinking", so that a state transition according to the in FIG. 3 64 indicated arrow in the state "below the switching point" is determined.

The example of Table 2 begins in line 1 with the initial state explained with reference to Table 1. In the second step, a lowering of the load carrying means takes place, the current position still remaining "below the switching point". In the step shown in the third row of Table 2, a change of the switching state is detected. This is possible starting from a current position "below the switching point" only if the load carrying means has been moved up past the switching point. In the example, however, the actuator 20 is in the "sink" position. Accordingly, both are not for a state transition according to one of the arrows 64 or 66 of FIG FIG. 3 required conditions, so that no change of the current position takes place and this is further provided as "below the switching point". These procedures can be explained by the fact that the initial state in the first row of Table 2 is not reproduced correctly. In fact, when the truck is switched on, the load carrying means has not been below the switching point, as stored in the non-volatile memory 52, but above the switching point. This is conceivable, for example, after maintenance work. Line 3 of the table shows that in this case an automatic correction of the current position takes place, because after the change of the switching state determined in the third line, the load carrying means 12 is actually again below the switching point, and this state is determined as the current position. The fourth and fifth lines of the table show readily understandable steps, which proceed analogously to the processes explained in Table 1.

Table 3 shows another peculiarity. Starting point is line 1, in which the switching element 18 is in the initial state and is stored as the last position of the load supporting means 12 when switching off the truck, the value "above the switching point" in the non-volatile memory 52. The current position of the load bearing means 12 is determined as "above the switching point". In the second step, a further lifting of the load carrying means 12, as at the corresponding Detect position of the actuator 20. A change of the switching state does not take place and also the current position remains unchanged.

In the third line, although the lifting function is still active, a change in the switching state is detected. However, a corresponding change of the current position to the value "below the switching point" does not take place, because the conditions of the transition to be traversed according to arrow 64 from FIG. 3 not both are fulfilled. In fact, this process is explained by the fact that the initially determined current position was not correct, because the load carrier was lowered below the predetermined height during the switched-off condition of the truck. From the third step of Table 3, in turn, an automatic correction of the determined current position has taken place and the information about the current lifting height applies in all subsequent steps.

The next two steps, which are listed in Table 3, are again readily understandable.

The further example shown in Table 4 is also based on the state diagram of FIG FIG. 3 easily comprehensible.

In the FIG. 4 the course of two output signals S1 and S2 of a further switching element when passing a counterpart 24 to two sensors of the switching element is illustrated. In this example, the two switching outputs S1, S2 are strictly not complementary to each other, but each associated with a sensor. At the two switching outputs S1 and S2, either a 0-signal or a 1-signal can be present. At the switching output S1 is a 0-signal when the counterpart 24 is located at a greater distance from the switching element. In the area between the switching points denoted by F1 and F3, the counterpart 24 is so close to the switching output S1 associated sensor that this provides a 1-signal. The switching output S2 is associated with a second sensor, which is arranged in the direction of movement of the counterpart 24 at a distance in front of the first sensor. The signal applied to this switching output signal always has a 1 value when the counterpart 24 is located at a greater distance from the switching element 18. Only between the two switching points F2 and F4 is present at the switching output S2, a 0-signal. The distances indicated by double arrows 68 between the switching points F1 to F4 may be, for example, a few millimeters, preferably about 3 mm.

When evaluating the signals at the switching outputs S1 and S2, rising and falling signal edges are taken into account. As can be deduced from the figure, a rising or falling signal edge at one of the two switching outputs S1 or S2 in conjunction with a specific switching state at the other switching output is a clear indication of a specific direction of movement of the counterpart 24. If, for example, a rising Signal edge observed and is at the same time at the switching output S2 to a 1-signal, then moves the counterpart 24 in the FIG. 4 from left to right, which may correspond, for example, to an upward movement of the load carrying means, past switching point F1. If a 0 signal arrives at the switching output S2 at the same time as a rising signal edge at the switching output S1, this indicates that the counterpart 24 is moving past the switching point F3 in the opposite direction.

Table 5 reproduced below shows further possible combinations of the signals at the switching outputs S1 and S2. <b> Table 5: </ b> switching point S1 S2 direction F1 Rising edge 1 up F2 1 Falling edge up F3 Falling edge 0 up F4 0 Rising edge up F1 Falling edge 1 down F2 1 Falling edge down F3 Rising edge 0 down F4 0 Falling edge down

As is also apparent FIG. 4 results, the signals at the switching outputs S1 and S2 are not always complementary. For example, both switching outputs S1 and S2 have a 1-signal between the switching points F1 and F2. However, this does not indicate an error, but merely that the counterpart 24 is just between the two switching points mentioned. However, if it is determined at the same time that the lifting or lowering function has been actuated for a certain period of time, there is a malfunction because the load carrying means with the counterpart 24 would otherwise have already left this narrow spatial area again. It therefore makes sense to output an error message.

Claims (13)

1. A method for providing information about a current lifting height of a load support means (12) of an industrial truck, with the following steps:

   • reading an information about the lifting height which was memorised in a non-volatile memory (52) when the industrial truck was switched off at last,

   • determining an information about the current lifting height based on the read-out information about the lifting height when the industrial truck was switched off at last, and about the switching state of a switch element (18) which does not comprise any function for maintaining its switching state independently from an energy supply, and is arranged such that its switching state changes when the load support means (12) of the industrial truck passes through a given lifting height (26), characterised in that the switch element (18) comprises a sensor (32, 34) which responds to the approach of a counterpart (24) comprising a magnet.
2. The method according to claim 1, characterised in that the information about the current lifting height can assume a first value which represents a position of the load support means (12) below the given lifting height (26), and a second value which represents a position of the load support means (12) above the given lifting height (26).
3. A method according to any one of claims 1 to 2, characterised in that the switch element (18) has two sensors (32, 34) spaced apart from each other in the direction of the movement of a counterpart (24), whose output signals are analysed in order to detect a movement of the counterpart (24) along the switch element and to change the switching state.
4. The method according to claim 3, characterised in that in the analysis of the output signals, an increasing and/or falling signal flank of at least one output signal is registered and analysed for the detection of a direction of the movement of the counterpart (24).
5. A method according to any one of claims 1 to 4, characterised in that an error message is generated when equal signals are present on two inputs (46, 48) of an analysing unit for determining the current lifting height that is connected to two complementary outputs (S1, S2) of the switch element (18) via two lines.
6. A method according to any one of claims 1 to 4, characterised in that an error message is generated when equal signals are present on two inputs (46, 48) of an analysing unit for determining the current lifting height that is connected to two outputs (S1, S2) of the switch element (18) via two lines, and an actuation element for the lifting function indicates an actuation of the lifting- or lowering function for a given time duration.
7. A method according to any one of claims 1 to 6, characterised in that the position of an actuation element (20) for a lifting function of the industrial truck is taken into account in the determination of the information about the current lifting height.
8. The method according to claim 7, characterised in that an information about the current lifting height is changed only then when a change of the switching state of the switch element (18) is detected during or shortly after an actuation of the lifting function.
9. The method according to claim 8, characterised in that a change of the information about the current lifting height from the first value to the second value is performed only then when a change of the switching state of the switch element (18) is detected during or shortly after an actuation of the lifting function, and/or that a change of the information about the current lifting height from the second value to the first value is performed only then when a change of the switching state of the switch element (18) is detected during or shortly after an actuation of the lowering function.
10. An industrial truck with an analysing unit (30) for providing information about a current lifting height of a load support means (12) of the industrial truck, and a switch element (18) which is connected to the analysing unit (30) and arranged such that its switching state (18) changes when a load support means (12) of the industrial truck passes along a given lifting height, wherein there is a non-volatile memory (52) and the analysing unit (30) is made such that when the industrial truck is switched off, information about the lifting height is stored in the non-volatile memory (52), and that the switch element (18) does not comprise any function for retaining its switching state independently from an internal energy supply, characterised in that the switch element (18) comprises a sensor (32, 34) which responds to the approach of a counterpart (24) which comprises a magnet.
11. The industrial truck according to claim 10, characterised in that the switch element (18) has two outputs (51, 52), each of which is connected to one input (46, 48) of the analysing unit (30) at a time.
12. An industrial truck according to claim 10 or 11, characterised in that the switch element (18) has two sensors (32, 34), which respond to the approach of a counterpart (24) and are spaced apart from each other in the direction of the movement of the counterpart (24).
13. An industrial truck according to any one of claims 10 to 12, characterised in that an actuation element (20) for a lifting function is connected to the analysing unit (30).

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