GB2117141A - Vehicle, particularly industrial truck, which is steered along a guide wire without a driver - Google Patents

Abstract

An industrial truck is described in which an additional third sensor remote from the usual two tracking sensors is provided. This is said to improve cornering and reduce swerving during straight line travel. Four modes of travel may be provided i) straight passage between racks ii) straight passage away from racks iii) straight paths where the vehicle is not centred on the track iv) cornering, the operation of the control signal depending on the mode.

Description

SPECIFICATION Vehicle, particularly industrial truck, which is steered along a guide wire without a driver This invention relates to a vehicle, particularly an industrial truck, which is steered along a guide wire without a driver, comprising a load-carrying axle and non-steerable load-carrying wheels provided at a ioad-receiving end and at least one steerable wheel at the other end of the vehicle, two sensors, which consist particularly of coils and are disposed adjacent to one axle, namely, the load-carrying axle or the steerable axle, and serve to generate parameter signals in dependence on the distance from the guide wire, a steering drive for the steerable wheel, which steering drive comprises an actual steering angle signal generator, and a circuit arrangement for processing the parameter signals and generating a desired steering angle signal.

The sensors generally comprise suitable coil arrays, which are either symmetrically spaced from the longitudinal centre line of the vehicle or are provided on the longitudinal centre line and cross each other, so that signals are derived from a field which is generated by the guide wire and are utilized to generate signals representing the position of the vehicle relative to the guide wire, whereafter signals for controlling the steering drive are derived from the latter signals.

In vehicles of the kind described hereinbefore, such coil arrangements are provided either only close to the fixed load-carrying axle or close to a movable, steerable axle.

The reference to a steerable wheel includes also a bilateral wheel arrangement on steerable axles or a movable steerable axle for two wheels.

It can be assumed that a concentrated arrangement of sensors on the rigid load-carrying axle is desirable for aligning the vehicles with a guide wire and permits a cornering in both directions of travel.

But deviations may occur during cornering so that the accuracy of the steering is adversely affected and this imposes limits regarding the speed of travel.

There will also be a danger of swerving movements, even during straight ahead travel, if the steerable wheel is also the driven wheel.

Arrangements are included in which the steerable wheel or the non-steerable load-carrying wheels are driven by motors or other drive means mounted on the vehicle. Both arrangements are known per se in vehicles of the kind described. But the invention preferably relates to a vehicle in which the steerable wheel is driven. If that wheel is disposed at the rear end of the vehicle when the same is travelling with the load-receiving end ahead, that wheel is remote from the sensors so that swerving movements occur, which are undesirable particularly in a narrow passage between racks. For this reason disadvantages must be tolerated in the operation of the known vehicles of that kind or their speed of travel must be so strongly reduced that the economic utilization of the vehicle is rendered more difficult.

It is an object of the invention so to improve a vehicle of the kind described first hereinbefore that the travel performance is improved, particularly in the case of inductive guidance, from one aspect for the travel along a straight path and from another aspect for cornering. That purpose is to be achieved by simple means, particularly circuit means, and simple arrangements on the vehicle.

This object is accomplished particularly for a travel on a straight path in that a third sensor is provided, which is as remote as possible from the axle at which the first and second sensors are provided, and that the circuit arrangement includes a mode-of-travel selector circuit, by which signals from the third sensor can be introduced into the circuit arrangement and which in dependence on measured value signals delivers a desired steering angle signal to the steering drive. It has surprisingly been found that the utilization of signals generated by sensors provided at the forward and rear ends of the vehicle permits a much more accurate travel along a straight guide wire.

Particularly in connection with that concept, a particularly preferred embodiment is arranged to generate an additional set point signal for cornering in dependence on an adjusted steering angle and a time-dependent change of the angle between the center line of the vehicle and the guide wire with utilization of the signals generated by the first and second sensors and representing the distances from the guide wire, and said set point signal for cornering is adapted to be superposed on the desired steering angle signal in dependence on the condition of the mode-of-travel selector circuit. This arrangement results in a much more accurate cornering because in a special embodiment the need for a tachometer is also eliminated.

An arrangement is included in which only the so-called first and second sensors provided adjacent to one axle, namely, the load-carrying axle or the steerable axle, and preferably adjacent to the load-carrying axle, are used during cornering and in certain modes of travel the so-called third sensor is enabled or disabled and in one case the additional set point signal for cornering is introduced. It is particularly assumed that the first and second sensors are used during cornering and the third sensor is also used for the control during the transition to a straight ahead travel.

The use of the additional set point signal for cornering is a particularly advantageous feature of the invention, particularly in connection with the selection of different modes of travel.

In a particularly desirable embodiment, that set point signal T2 is generated in accordance with claim 3. That embodiment affords the advantage that optimized constants can be used for the generation also in dependence on the distance between different wheel axles.

According to another advantageous feature of the invention, the additional set point signal for cornering T2 is approximated by the method and composition stated in claim 4. This results in a further simplification, which also produced better results than known embodiments.

In connection with the generation of the set point signal for cornering T2, another advantageous feature resides in its generation in the manner stated in claim 5. In this manner, it can be ensured that that additional set point signal for cornering T2 will not cause the feedback control system to oscillate.

The arrangement which has been described provides the vehicle with a control system which owing to its variability greatly increases the accuracy with which the vehicle can travel along a guide wire in dependence on the conditions of travel.

In a desirable embodiment the mode-of-travel selector circuit comprises at least two mode-oftravel branches for delivering a desired steering angle signal, one mode of travel is used for a straight ahead travel along the guide wire whereas another mode of travel is utilized for cornering, and the modes of travel can be defined by predetermined limits for aistt YV and I as well as T2. This results in an automatie change and a fast adaptation to the path of travel.In a particularly preferred arrangement, four mode-of-travel branches are provided, namely, a first branch for a guidance within a straight passage between racks, a second branch for a guidance along straight paths outside of passages between racks, a third branch for a guidance along straight paths when the vehicle is not exactly centred over the guide wire, and a fourth branch for cornering. This arrangement permits a much more exact adaptation. Regarding the arrangement of the third sensor, one embodiment of the vehicle comprises first and second sensors disposed adjacent to the load-carrying axle and a third sensor which when viewed from the load-carrying axle is disposed beyond the at least one steerable wheel.

This arrangement of the third sensor at the largest possible distance from the two other sensors according to the invention improves the accuracy of the control.

Within the scope of the invention, vehicle parameter signals and measured value signals generated by the third sensor may be superposed in dependence on the mode of travel. This is a particularly advantageous feature of the invention.

In conjunction with the four mode-of-travel branches, a desirable embodiment of the invention provides for the generation of a desired steering angle signal in the manner described in claim 10. That arrangement will result in a particularly accurate control with the aid of all three sensors, during a straight ahead travel. The second branch can be used to ensure an adequate straight ahead travel with a lower expenditure and in a desirable embodiment it is sufficient for that second branch to generate only the desired steering angle signal in the manner described in claim 11. For the third branch a change-over is desirably effected in case of a deviation so that the desired steering angle signal is generated in the manner described in claim 12.This results in a stepped control, which permits an optimum operation of the vehicle in dependence on the path of travel and speed.

The set point signals additionally used for cornering have been mentioned before. In a particularly preferred embodiment, a desired steering angle value generated in the manner described in claim 13 and the signal T2 are used in the so-called fourth branch of the mode-of-travel selector circuit, which branch is used for cornering. This will result in optimum conditions of travel and eliminates the need for a tachometer generator.

The mode-of-travel-selector circuit consists suitably of a multiplexer, in which the corresponding desired steering angle signal SsOz, for the desired mode of travel can be connected to the steering drive.

The invention will be described more in detail hereinafter and the control equations stated in the claims will be summarized. The embodiment will also be explained with reference to the drawing, in which Figure 1 is a top plan view showing the contour of a vehicle for an explanation of the parameters used within the scope of the invention, Figure 2 is a block circuit diagram illustrating the basic interrelations used for the control, and Figures 3 to 9 are block circuit diagrams showing the control circuits which can be assembled as described.Specifically, Figures 3 to 7 show the means for processing the measured value signals generated by the sensors of the vehicle, Figure 8 is a block circuit diagram showing a mode-of-travel selector circuit and Figure 9 is a block circuit diagram illustrating the circuit for generating the desired value signals for the various modes of travel.

Reference is made first to Figure 1, also for explanation of the formula stated in the control equations. The contour of a vehicle 1 is shown, which has a load-receiving end 2, on which a loadcarrying fork 4 is guided by a lifting frame or another guiding means 3. The load-carrying axle 5 provided with non-steerable load-carrying wheels 6,7 is mounted near that end 2. Also near that loadreceiving end 2, two sensors are associated with the load-carrying axle 5 and are symmetrically arranged with respect to the longitudinal axis 10 of the vehicle. These sensors consist of a first sensor 8 and a second sensor 9 and may comprise two coils each. The first sensor 8 is disposed between the load-receiving end 2 and the load-carrying axle 5 at a distance 1 1 (a,) from the load-carrying axle 5 and the second sensor 9 is disposed on the other side of the load-carrying axle 5 at a distance 12 (a2) therefrom.

Close to the other end 14 of the vehicle, a steerable wheel 1 6 is mounted on a vertical steering shaft 15 and has a center spacing 13 (b) from the load-carrying axle 5. The so-called third sensor 17 is disposed behind that steerable wheel when viewed from the load-carrying axle 5 and is adapted to be enabled or disabled. The third sensor 1 7 is spaced from the load-carrying axle by the distance 18 (a3).

In the position shown, the steerable wheel 1 6 is inclined to the longitudinal centre line of the vehicle. The angle 19 is represented by the signal iSt.

In Figure 1, the guide wire 20 is disposed on one side of the longitudinal centre line 10 of the vehicle. The distances from the guide wire to the centre of each of the three sensors 8, 9, 17 and to the centre line of the vehicle are designated 21(Y1), 22(Y2) and 23 (Y3), respectively.

The speed of travel v of the vehicle is represented by the arrow 24 in front of the steerable wheel 1 6 and is stated in this explanation as the circumferential velocity'of that steerable driven wheel.

For this purpose a tachometer is provided, the output signal of which is related to the diameter of the steerable wheel.

The desired steering angle 8soII which is to be adjusted is computed from the three distances Y1, Y2 and Y3, the adjusted steering angle S,st and the speed v.

In the embodiment shown by way of example, a drive motor 25 and a steering drive 26 are associated with the steerable wheel 16. That steering drive delivers via a functional link 27 an actual steering angle signal to a circuit arrangement 28, which via another functional link 29 delivers a desired steering angle signal 0soII to the steering drive.

The above-mentioned measured value signals which represent the outputs of the sensors and of the steering drive and the speed are delivered to the circuit arrangement by an input bus generally designated 30. The vehicle parameters 11, 12 and 18 are thus taken into account. This is stated only for a formal explanation.

That input bus 30 receives the input signals represented in Figures 3 and 4 as well as the output signal of the above-mentioned tachometer, and these signals are processed in the amplifier which is shown in Figure 4 and in which the speed is related to the centre spacing 13.

When the load-carrying end 2 of the vehicle is in front and the vehicle is disposed on the right of the guide wire 20, as is shown in Figure 1, the Y values are regarded as positive values in the following description and the steering angle to the left which is shown is regarded as a positive angle.

The four modes of travel are determined by the criteria stated above. The first mode of travel is used for a travel within a straight passage between racks. For such an exact control, signals from the sensors are used. The following formulae are applicable to that so-called first mode: #soll=K1xYh+K2x|#h|xsign{#Yh} (1) wherein 1 a2 a3 a, a3 a, a2 Yh= (Y1( + )+Y2( + )+Y3( - ) (2) 3 a,+a2 a,+a3 a,+a2 a3-a2 a3+a, a3-a2 |#h|=1x|Yh-Y3| (3) a3 a3 dYh Yh= (4) dt dYh AYh dt K1, K2=constants.

For the second mode of travel along straight paths outside passages between racks, the following conditions are applicable in the simplified form: 8,,,,=K,Y,+K,x19,1 xsignIhY,j (5) wherein a2 a, Yv=Y1 +Y2 (6) a1+a2 a1+a2 xIY1-Y21 (7) a1 +a2 dYv #Yv= (8) dt The following control equation is applicable to the third mode, in which only the first and second sensors are used, just as in the second mode: #soll=K12Yv+K22x|#v|xsign{#Yv} (9) The constants K,2 and K22 should be optimized for centring.

The following control equation is applicable to the so-called fourth mode of travel, i.e., to cornering, when only the first and second sensors are used and the centre distance is also taken into account.

O901i=Ki3Yv+ K23 x |#vlxsi9 njAY} + K3T2 (10) wherein b d T2=arc sinjsin #ist±x-(|#v|xsign{#Yv})} (11) lvi dt and K13, K23 and K3 are optimized constants.

In general the parameter T2 can be approximated by the equation d T2=t0iSt+K4X(liVlxsign{Ayv}) (12) dt and in another embodiment with use of only discrete values by the condition A1+A1+1 T2= forA < T2 < A,+, i=1,2. . . n (13) 2 A,=discrete step values.

In the equations, the speed of travel v is suitably stated as the circumferential velocity of a driven wheel. The desired value #soll is computed from that speed of travel v and the three distances Y1, Y2, Y3 in conjunction with the adjusted steering angle 0ist.

During an inductive guidance in accordance with the above control equations, the mode of travel is selected in consideration of the fact that the first and second modes provide for an exact guidance along a straight guide wire. The mode selection is effected in dependence on whether or not the lateral deviation of the centre of the load-carrying axle from the guide wire, the angle # between the longitudinal centre line of the vehicle and the guide wire, and the adjusted steering angle 0ist are smaller in magnitude than corresponding limits YrmaXt #1max and #1max. These limits are fixed in a circuit arrangement so that the automatic connection to effect an optimum guidance is ensured.

The first mode of travel is not selected until l0istlt IYVI and lVvl are lower than the corresponding limits values #1max, Y1max and Pi1max When mode 1 has been selected, it cannot be abandoned until the magnitudes Of #ist|, lYvi and |#v| exceed predetermined limits #2max, Y2maX and #2max.

Unless the requirements for the first and second modes of travel are met, the third or fourth mode and travel will be selected. This selection will be effected by monitoring circuits in response to measured value signals which are received. Particularly for the fourth mode of travel used for cornering, the parameter T2 will be superposed only when its magnitude exceeds a predetermined limit T2 min This will avoid disturbances which may occur when approximate values occur.

It is known in the art that the values Y, to Y3 and #ist are known and that the angle # between the longitudinal centre line of the vehicle and the guide wire can be computed from the Y values.

Figure 3 shows how the signals Yh and #h are generated. The inputs Y, Y2, Y3 are applied to amplifiers 31 to 33, the constants of which are apparent from the formula 2 stated above. For this purpose the outputs of all three sensors 8, 9, 1 7 are combined. The amplifiers 31 to 33 feed via leads 34 to 36 an anlog adder which embodies the above-mentioned formula and at its output terminal 38 generates the signal Yh. From the lead connected to the output terminal 38 of the analog adder 37, a branch lead is connected to a second difference-forming circuit 39, which also receives the input Y3 via a lead 143. That difference forming circuit 39 is connected as an inverted analog adder and computes the difference Yh minus Y3. This constitutes a parameter used in computing Vh (formula 3).

The difference-forming circuit 39 is succeeded by a magnitude-computing circuit 41 and the latter is succeeded by an amplifier 42, the constant gain of which equals the amount 1/a3 from formula 3. The amplifier 42 is succeeded by a multiplier 43, which is fed from the branch lead 40 via a branch line 44.

In the branch line 44, a differentiator 45 and a sign detector 46 for rA are connected in series. As a result, the parameter h=l hlxsign (AYh) is computed in the multiplier 43.

The signal ttrh thus appears at the output terminal 47.

Figure 4 explains the generation of the signal Yv appearing at the output terminal 48 and the signal v appearing at the output terminal 49. Only the signal Y, and Y2 are applied as inputs to amplifiers 50, 51, the constants of which are apparent from the above formula 6, namely, the input Y and for the amplifier 51 the parameter Y2 from formula 6. The output terminals are connected by the leads shown to the analog adder 52, which delivers the output 48.

Two function leads 58, 59 are branched from the leads for the inputs Y1 and Y2 and feed a difference-forming circuit, which embodies formula 7. That difference-forming circuit 60 is succeeded by a magnitude-computing circuit 61 and the latter is succeeded by an amplifier 62 which has a gain corresponding to the constant from formula 7 and feeds a multiplexer 63. From the lead connected to the output terminal 48, the multiplexer 63 is fed by a branch line 64, in which a differentiator 65 and a sign detector 66 are connected in series. the signal for v according to formula 7 appears at the output terminal 49.

The generation of the various parameters for T2 is diagrammatically explained in Figures 5 to 7.

The operation represented by the above-mentioned equation 11 is illustrated in Figure 5. The signal for Vv is delivered from the output terminal 49 to the input terminal 67. Another input terminal 68 receives a measured value signal 0Ist from the steering drive. The input 67 is succeeded by a differentiator 69 and the latter by an amplifier 70. The parameter v is differentiated in 69 and is amplified in accordance with formula 11 in the amplifier having the gain b/(vl.

The signal H,st fed to the input terminal 68 is converted in a circuit 72 to a sine function and is then applied in that form to a succeeding analog adder, in which the signals are added to each other.

The output terminal of the analog adder 71 is connected to a unit 73, in which an arc sin term of the characteristic curve is formed in accordance with equation 11 so that the signal T2 generated in accordance with that equation appears at the output terminal 74.

Figure 6 shows how T2 is generated in accordance with the above formula 1 2 from corresponding inputs and by means of a differentiator 69', which corresponds to the unit 69. The differentiator 69' is preceded by an amplifier 75 having a constant gain K4.Thhe measured value signal flst is applied from the input terminal directly to the analog adder 76, which delivers at its output terminal 77 the approximate signal T2 for cornering.

In the arrangement shown in Figure 7, the signal T2 appearing at the output terminal 74 or 77 is delivered to a unit 78 and is processed therein in accordance with the above equation 1 3 in that the signal T2 is adjusted to one of the discrete step values so that a conversion to discrete steps is effected and the signal appearing at the output terminal 79 will not cause succeeding feedback control circuits to oscillate if the signal is used further, such as is the case with the signals appearing at the output terminal 74 or 77.

Figure 8 shows the mode-of-travel selector circuit and illustrates that inputs delivered by the previously described circuit arrangements are converted to output signals, which are adapted to be fed to the steering drive as a Sso signal for use as control signals for the first to fourth modes of travel.

Figure 8 shows input terminals 80 for v, 81 for Yv, 82 for 0iso' 80', 811 and 82' for the corresponding inputs, and 83 for Y3. All input terminals are connected to comparators 84 to 90 in the arrangement shown from top to bottom. The comparators 85 to 89 are window comparators. The window comparators 85 and 86 define the threshold values which must exceed the input for a selection of the modes of travel 1 and 2, respectively. A succeeding AND gate 91 controis the set input terminal 92 of a succeeding RS flip-flop 93, the reset input terminal 94 of which receives the output of the AND gate 95. The input terminals of the latter are connected to the window comparators 87 to 89.

In this way the RS flip-flop is reset. Such RS flip-flops are known. The flip-flop produces a low output in response to a high signal applied to its set input terminal and a low signal applied to its reset input terminal and produces a high input in response to a high signal applied to its reset input terminal. It is assumed that two high inputs are not applied at the same time and that the flip-flop will not change its state when low signals are applied to both inputs. This permits a distinction between the first and second modes of travel. For this purpose the input terminal 83 for Y3 is used, which is succeeded by the window comparator 90 and an AND gate 96. A so-called passage signal "vehicle in passage" is applied to a second input terminal 97 of the AND gate 96. The output of the AND gate 96 is either delivered by a link 98 to an inverter 99 or by another link 100 to an AND gate 101, which at its second input terminal is connected to the Q output terminal of the RS flip-flop. As a result, the AND gate 101 presents at its output terminal 102 a variable signal for selecting the first mode.

The inverter 99 feeds another AND gate 103, which is also connected by a lead 104 to the lead 105 between 93 and 101 so that a variable signal for selecting the second mode of travel appears at the output 106.

When the first and second modes are not selected as a result of the comparison with the threshold values, the signal T2 which has been generated in accordance with one of the abovementioned formulae is delivered to an additional input terminal 107 and checked by the succeeding window comparator 108 and is then applied to the AND gate 109 having an output terminal 110 for the selection of the third mode or to an AND gate 111, which is succeeded by another AND gate 112 presenting at its output terminal 1 13 a signal for selecting the fourth mode of travel. Both AND gates 109, 14 receive via a lead 114 the Q output of the RS flip-flop 93.

In this connection, reference is also made to the above control equations 1, 5, 9, 10. This permits the generation of signals for controlling the travel in various modes.

In accordance with Figure 9, the outputs described hereinbefore are delivered to a multiplexer circuit 11 5 having the input terminals designated 102, 106, 1 3 and 110. These reference numbers have also been used for output terminals. The transmission of these input signals through the multiplexer 11 5 is controlled by the signals Yh at the input terminals 11 6, h at the input terminal 11 7, Yv at the input terminal 118, Siv at the input terminal 119, Yv at the input terminal 118', v at the input terminal 119', Yy at the input terminal 118", Vv at the input terminal 119", and T2 at the input terminal 107.The magnitudes of these signals have been determined as described hereinbefore with reference to Figures 3 to 7.

The input terminals are succeeded by the amplifiers 120 to 128, each of which has the abovementioned steering parameters or constant gains K1, K2 or the optimized constant gains K,2, K22 and K13, K23 and K3. The outputs of the amplifiers 120, 121 are combined in an analog adder 129, those of the amplifiers 122, 123 in an analog adder 130, those of the amplifiers 124, 125 in an analog adder 131 and those of the amplifiers 126, 128 in an analog adder 132. As a result, the above-mentioned functions are utilized for setting the multiplexer for the transmission of variable signals for selecting respective modes of travel. The analog adders are connected by respective leads 133, 134, 135, 136 to respective input terminals which are associated with the first to fourth modes of travel, respectively, and arranged to be sampled, so that the multiplexer presents at its output terminal 141 the signal Oslo, which is defined by the above-mentioned equations for the various conditions.

Claims (15)

Claims

1. A vehicle, particularly an industrial truck, which is steered along a guide wire without a driver, comprising a load-carrying axle and non-steerable load-carrying wheels provided at a load-receiving end and at least one steerable wheel at the other end of the vehicle, two sensors, which consist particularly of coils and are disposed adjacent to one axle, namely, the load-carrying axle or the steerable axle, and serve to generate parameter signals in dependence on the distance from the guide wire, a steering drive for the steerable wheel, which steering drive comprises an actual steering angle signal generator, and a circuit arrangement for processing the parameter signals and generating a desired steering angle signal, characterized in that a third sensor is provided, which is as remote as possible from the axle at which the first and second sensors are provided, and that the circuit arrangement includes a mode-of-travel selector circuit, by which signals from the third sensor can be introduced into the circuit arrangement and which in dependence on measured value signals delivers a desired steering angle signal to the steering drive.

2. A vehicle, particularly according to claim 1, characterized in that an additional desired value signal for cornering is generated in dependence on an adjusted steering angle and a time-dependent change of the angle between the center line of the vehicle and the guide wire with utilization of the signals generated by the first and second sensors and representing the distances from the guide wire, and said set point signal for cornering is adapted to be superposed on the desired steering angle signal in dependence on the condition of the mode-of-travel selector circuit.

3. A vehicle according to claim 2, characterized in that the additional set point signal for cornering T2 is generated in accordance with the formula bd T2=arc sintsin Oj5t±x-(i(liixsigniAY1)1 Ivl dt wherein Ojst=desired steering angle b=distance from load-carrying axle to vertical axis of rotation of steerable wheel v=speed of travel livl= x lY, a,+a2 dYv AYv= dt a2 a1 Yv=Y1 +Y2 a1+a2 a1+a2 Y1=distance from centre of first sensor, viewed from the load-receiving end of the vehicle, to the guide wire Y2=distance from centre of second sensor, viewed from the load-receiving end, which sensor is disposed behind the load-carrying axle, to the guide wire a,=distance from the first sensor at the load-receiving end of the vehicle to the load-carrying axle a2=distance from the second sensor, disposed on the other side of the load-carrying axle, to the load-carrying axle.

4. A vehicle according to claim 2, characterized in that the additional set point signal for cornering T2 is generated in accordance with the formula d T2=O8+K4x-((lixsignfAY}) dt wherein said symbols have the same meanings as in claim 3.

5. A vehicle according to claim 2, characterized in that the additional set point signal for cornering T2 is generated in accordance with the formula A+Aj+, T2= forA1 < T2 < A1+1 i/1, 2...n 2 wherein Aj=discrete step values.

6. A vehicle according to any of claims 1 to 5, characterized in that the mode-of-travel selector circuit comprises at least two mode-of-travel branches for delivering a desired steering angle signal, one mode of travel is used for a straight ahead travel along the guide wire whereas another mode of travel is utilized for cornering, and the modes of travel can be defined by predetermined limits for #ist, Yv and |#| as well as T2.

7. A vehicle according to claim 6, characterized in that four mode-of-travel branches are provided, namely, a first branch for a guidance within a straight passage between racks, a second branch for a guidance along straight paths outside of passages between racks, a third branch for a guidance along straight paths when the vehicle is not exactly centred over the guide wire, and a fourth branch for cornering.

8. A vehicle according to claim 1, in which the first and second sensors are disposed adjacent to the load-carrying axle, characterized in that the third sensor when viewed from the load-carrying axle is disposed beyond the at least one steerable wheel.

9. A vehicle according to claim 1, 8 or 7, characterized in that vehicle-dependent parameter signals and measured value signals from the third sensor are superposed in dependence on the mode of travel.

10. A vehicle according to claim 7, characterized in that a desired steering angle signal for the first branch is generated in accordance with the formula #soll=K1 =K1xYh+K2x|#h|x#h|xsign{#Yh} and that the three sensors are used and 1 a2 a3 a1 a3 a1 a2 Yh= (Y1( + )+Y2( + )+Y3( - ) 3 a1+a2 a,+a3 a1+a2 a3-a2 a3+a1 a3-a2 #h=1x|Yh-Y3| a3 dYh Yh dt a1 and a2 have the same meanings as in claim 3, a3=distance from the third sensor disposed at the other end of the vehicle from the axle adjacent to which the first and second sensors are disposed K1, K2=constants.

11. A vehicle according to claim 6, characterized in that a desired steering angle signal for the second branch is generated in accordance with the formula #soll=K1Kv+K2xsign{#Yv} wherein Yv, Y1, a1, a2, #' and bYV and Y2 and the meanings stated in claim 3.

12. A vehicle according to claim 6, characterized in that a desired steering angle signal for the second branch is generated in accordance with the formula #soll=K12Yv+ K22x|#v|xsign{#Yv} wherein the symbols have the meanings stated above and K,2 and K22 are constants which exceed K, and K2.

13. A vehicle according to claim 6, characterized in that the desired steering angle signal for the branch used for cornering is generated in accordance with the formula Osoii=K13Yv+K23Xl(livI xsign(AY}+KJ2 wherein the symbols have the same meanings as in claims 3 to 5 and K,3, K23 and K3 are constants which are optimized with respect to K, and K2.

14. A vehicle according to any of claims 1 to 13, characterized in that the mode-of-travel selector circuit consists of a multiplexer, in which the corresponding desired steering angle signal îSO for the desired mode of travel can be connected to the steering drive.

15. A vehicle according to claim 1, substantially as described hereinbefore with reference to the accompanying drawings.