EP2115541A1

EP2115541A1 - Method and system for automatic truck system

Info

Publication number: EP2115541A1
Application number: EP08705369A
Authority: EP
Inventors: Björn Nyberg; Tom Wiberg; Andreas Mellstedt
Original assignee: Helge Nyberg AB
Current assignee: Helge Nyberg AB
Priority date: 2007-02-05
Filing date: 2008-01-28
Publication date: 2009-11-11
Also published as: SE0700280L; EP2115541A4; WO2008097173A1; SE531406C2

Abstract

The present invention is related to a driverless truck system comprising at least one traction vehicle (A) with a guiding system (6, 11) arranged to be able to follow a line- shaped marking (C) arranged on the ground, which traction vehicle (A) comprises a chassis (1), a propulsion system (2), a control unit (4), safety arrangements (5), a superstructure (7) and at least one common 12 or 24 volt battery (1OA, 10B) as energy source, said propulsion system (2) utilising two drive wheels (200, 201) arranged to be able to be driven by one electric motor each (204, 205), independently of each other, said guiding system (6, 11) comprises a sensor part (6) with multiple sensors (601 A- 601G) positioned in the lateral direction of the vehicle and arranged to be able to produce a signal image by aid of which the relative position of the vehicle in relation to the centre line (Cc) of said line-shaped marking (C) can be determined, the same number of signal transmitting units (602A-602G) preferably being used.

Description

METHOD AND SYSTEM FOR AUTOMATIC TRUCK SYSTEM

TECHNICAL FIELD The present invention relates to a driverless truck system comprising at least one traction vehicle with a guiding system arranged to be able to follow a line-shaped marking arranged on the ground, which traction vehicle comprises a chassis, a propulsion system, a control unit, safety arrangements, a superstructure and at least one common 12 or 24 volt battery as energy source, said propulsion system utilising two drive wheels arranged to be able to be driven by one electric motor each, independently of each other.

PRIOR ART

Automatic truck systems have been known for long and are most often called AGV (Automatic Guided Vehicles). An AGV system enables transportation of goods basically without requiring manual input, e.g. for the purpose of supplying different stations of a mounting line in an assembling plant. A traditional AGV system, such as is known from US 5,650,703 e.g., comprises a plurality of traction vehicles/trucks that by aid of advanced technology are guided between different stations along given transport paths by aid of a guiding system that enables each unit to act autonomously. A major drawback of the AGV systems present on the market today is that they are very expensive. The cost per vehicle is usually about EUR 15,000 and as a consequence, a total investment will be very expensive which in turn has limited the number of potential users of such a system, despite the fact that there are many factors that lead to an increased demand for the use of such systems. Among such factors can be mentioned reduction by rationalization of operating steps that are often heavy and tedious, elimination/minimizing of safety risks and the possibility in real time to easier affect and control complex flows.

Many modifications are known for the purpose of creating an AGV system that is less cost demanding, i.e. that means an investment manageable to more. The many systems that have tried to solve this problem have however not been able to create a combination of included part systems that offer adequately good functionality and/or cost reduction. A plausible explanation is that such an AGV system has many interacting part systems included and that it therefore is hard to find a "compromise solution" in which the cost target is fulfilled and in which you at the same time will achieve adequately good functionality in the respective part systems in order to fulfil different types of demands put up by potential users.

Many of these known, modified systems are focused on decreasing/reducing the cost of the drive system and mainly the battery cost. US 2004/025,187 and US 6,498,454 disclose prior art systems intended to optimize the battery charging for such systems in order thereby to be able to maintain a lower cost. This type of systems has however not led to adequate cost reductions all in all.

Other known alternatives have focused on trying to achieve cheaper guide systems. US 6,341,430 discloses an alternative in which the guide system utilises a special type of coding in order to guide an AGV. JP 2005018248 discloses another modification that utilises a guide system with a plurality of distributed signal stations.

JP 2000309276 discloses another prior art attempt of decreasing the costs, which suggests the utilisation of a special type of attachment vehicle that is to enable cost reducing lifts and transports.

JP 2005088814 discloses a system in which lifts and traction ability are limited and part systems with a decreased functionality, which is inflexible in the guide system and yet relatively expensive.

Furthermore, JP 2001175331 discloses a concept that focuses on the use of compact and cheap driverless trucks that have relatively cheap part systems. It is suggested to use relatively cheap 12 volt batteries as a drive source, to use a relatively small vehicle chassis of relatively low weight, to use a drive system of relatively limited traction ability, a relatively simple guide/control system of limited functionality and a relatively simple tracking system that utilises tape, thus enabling low costs as compared with many of the other known concepts of guiding such trucks. However, the system according to JP 20001175331 has a major drawback in that it only enables 90° turns or straight movement, which drastically reduces the field of applications for the system. A system according to JP 20001175331 also has other drawbacks, e.g. in terms of safety aspects, which is most likely an explanation for the fact that the system has not entered the market, at least not to any appreciable extent. BRIEF ACCOUNT OF THE INVENTION

It is an object of the present invention to be able to provide a method and a system that eliminate or at least minimize some of the above mentioned drawbacks, which is achieved by a driverless truck system according to claim 1.

Thanks to the solution according to the invention, a driverless truck system is achieved that with good functionality achieves most of the market demands on such a system, at a cost that is considerably lower than the cost of existing systems on the market. As an example, it can be mentioned that the purchase price for a driverless truck according to the present invention can be reduced by more than 80% compared to a common existing driverless truck system on the market today.

According to further aspects of the invention: braking is automatically achieved by the transmission, - a guide system is enabled that senses the relative position of the vehicle, •

- a particularly cost efficient solution can be achieved in terms of the guide/sensor unit,

- a particularly flexible and cost-efficient track marking, a stable construction optimized from a weight point of view, - a minimized risk of soiling the track marking, achievement of a particularly cost-efficient safety arrangement.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the invention will be described in greater detail with reference to the attached drawing figures, of which:

Fig. 1 shows a side view over parts of a driverless truck according to the invention and a trailer intended to be pulled by the same,

Fig. 2 shows a view in perspective as seen obliquely from above, of a driverless truck according to the invention,

Fig. 3 shows a planar view as seen from below, of a driverless truck according to the invention,

Fig. 4 shows the same view as in Fig. 2 but without the superstructure,

Fig. 5 shows a view in perspective as seen obliquely from above and obliquely from behind in which not only the superstructure but also parts of the supporting frame structure have been removed in order to show parts of the transmission according to the invention, Fig. 6 shows the card with IR-transmitter and IR-sensor, according to one embodiment of the invention and also indicates a guide tape according to the invention,

Fig. 7 schematically shows the signal reading of the IR sensor when the driverless truck travels centred above a guide tape according to the invention, Fig. 8 shows the corresponding signal image when the truck has moved such that its centre line is positioned at the right of the centre line of the tape, and Fig. 9 shows a display unit according to one embodiment of the invention.

DETAILED DESCRIPTION

Fig. 1 shows parts of a driverless truck A according to the invention, which pulls a trailer B that is normally used in this transport system. The trailer B is of traditional construction, comprising a platform Bl arranged with/at a frame construction provided with wheels B3. A draw bar B4 is provided with a towing eyelet for coupling to the driverless truck A. By the wheel pair B2 that is coupled to the part with the draw bar B4 being arranged to pivot at the trailer B, the trailer will follow the movements of the driverless truck. By providing the rear end of the trailer B with a coupling device B5, additional trailers can be connected to form a train.

Fig. 2 shows a view as seen obliquely from above, over a driverless truck A according to the invention. The reference numbers in the drawing indicate various included parts/part systems of the driverless truck A, with the purpose of providing a lucid structure for the reference numbers used below. Reference number 1 refers to the chassis of the vehicle, reference number 2 refers to the propulsion system/transmission of the vehicle, reference number 3 refers to the traction arrangement of the vehicle, reference number 4 refers to the control panel and associated safety arrangements of the vehicle, reference number 5 refers to the built-in safety system for automatic arresting at any hinders, reference number 6 (see Fig. 3) refers to the guide/sensor system of the vehicle, reference number 7 refers to the superstructure/carriage body of the vehicle, reference number 8 refers to the supporting structure of the vehicle for a directly carried load, reference number 9 refers to the safety audio system of the vehicle (ultrasound and signal horn), reference number 10 refers to the energy source/battery system of the vehicle, and finally reference number 11 refers to the automated control mechanism/system of the vehicle. The vehicle is designed to be very compact. According to a preferred embodiment of the invention, the taction vehicle A has a width in the range 75-90 cm, a total length including draw bar of 100-140 cm, a height to the control panel 4 in the range of 60-80 cm, a ground clearance in the range 1-5 cm, a wheel base in the range 45-60 cm and a weight inclusive batteries in the range 100-150 kg. The maximum load on the loading device 8 is suitably in the range of 30-70 kg, its maximum safe pull is 400-600 kg, its maximum speed is in the range 2-4 km and its maximum speed during start up is 20- 50% of its maximum speed.

Fig. 3 shows an image from underneath the vehicle A. It is shown that the chassis 1 is founded on a base plate 100 that consists of a relatively thick- walled panel, suitably in the range of 8 to 12 mm, having a width of about 55 cm (preferably in the range of 40- 70 cm) and a length of about 90 cm (preferably in the range of 70-110 cm). The base plate is essentially solid, which results in a cost-efficient and compact way of achieving an adequate weight in order for the vehicle to be able to stop quickly, i.e. with the purpose of having a relatively high friction between the ground and the wheels 200, 201. Preferably, the base plate is given a total weight in the range of 25 kg to 35 kg. The base plate 100 is furthermore shown to be provided with a number of recesses, among other reasons for easy and safe mounting of chassis parts welded to the base plate, such as a box construction 110-114 (described in detail in connection with Fig. 4). The total weight of the entire chassis is suitably in the range 40-50 kg.

One recess 101, that is centrally positioned in respect of the centre line C_A of the vehicle and in the front portion of the base plate 100, is arranged to enable transmitter and sensor signals to pass through the plate. An arrangement of transmitter units 602 and an arrangement of receiver units 601 are arranged at the sensor card (see Fig. 4). A second recess 102 is arranged in the vicinity of said first recess 101, which second recess is circular with the purpose of being able to give 360° free revolving of a front support wheel 250 that is centrally journalled in bearings about a vertical bearing 251, inside the recess 102. In its turn, the bearing 251 is fixed at a U-shaped cross bar 252 that is attached at the base plate 100 (preferably all attachments of the chassis are welded). The reason for the cross bar 252 being U-shaped is for the attachment 252 for the wheel 250 suitably to be at a higher level than the plate 100 in order to give a lower clearance. According to a preferred embodiment of the invention, the ground clearance is in the range 15-30 cm. As is clear from Fig. 3, the vertical swinging axle for the support wheel 250 is arranged at a distance from the centre line C_A of the vehicle and the sensor device 6, respectively. Thanks to this "non-centred" positioning of the support wheel 250, the wheel will not soil the marking, such as a tape strip (see Fig. 7), that is used for the guiding of the vehicle A.

It is also shown that there are symmetrical recesses 103, 104 in the rear part of the vehicle, intended to accommodate the drive wheels 200, 201, such that the outer sides of the wheels are essentially aligned with the side edges of the bottom plate. Moreover, the bottom plate 100 has a number of smaller recesses 105 shaped as grooves, with the purpose of enabling stable anchoring of different parts to be attached on top of the bottom plate 100, which is beneficial from a mounting as well as a strength point of view. Finally, additional recesses 106, 107 are shown in the bottom plate, which are arranged between the wheels 200, 201 and have the purpose of providing space for drive motors 204, 205 and transmission 202, 203, respectively, to extend down through the bottom plate.

In Fig. 4, the vehicle A is shown as seen in perspective obliquely from above, without the carriage body/superstructure 7. Here, the bumper mechanism 5 is clearly shown. Its front part 50 consists of a curved plate-shaped part with a larger total width than the rest of the vehicle. It is designed to prevent cutting or scraping damages from easily occurring by contact with the front part 50. At its rear side surface, the front part 50 is attached to a first 51 and a second 52 bumper rod that are able to slide in brackets 53, 55. Accordingly, the front part 50, with the bumper rods 51, 52, can be moved from its front position to a position in which it is in contact with the vehicle's front part of the bottom plate 100 (or some other part), by the rods 51, 52 sliding through the holes that are arranged in said brackets 53, 55. At the rear end of the respective bumper rod 51, 52 (see also Fig. 5), there is an end surface 56 intended to interact with a breaker unit 57, 58. The breaker unit 57, 58 comprises a swivelling breaker arm 57 that cuts the current when it is swivelled away from its unaffected position (in Fig. 4 in its lower position) and thereby initiates the breaking of the drive wheels 201, 202. The safety system is preferably supplemented by an ultrasound sensor 9, in addition to the bumper mechanism 5.

At the front of the bottom plate 100, the card 6 with the transmitter and sensor units is arranged, which card 6 will be described in greater detail in connection with Fig. 6. A control and governor unit 11 is arranged in direct connection with this position, in the form of a compact unit that accommodates hardware and software for controlling various functions of the vehicle. The above mentioned box is arranged behind this and on top of the bottom plate 100, which box construction consists of two side panels 110, a rear panel 114, an oblique front panel 112 and a panel 111 that forms the upper part of the box, the panel thickness suitably being in the range 2-5 mm, i.e. considerably thinner than the plate 100. This box construction 110-114 forms a support structure for the attachment of most of the various included load/force carrying details of the construction, such as the wheels 200, 201, the bumper mechanism 5, the drive motors 204, 205 and struts 82/84; 83/85 (that are suitably also welded to be part of the chassis) for the loading arrangement 8. Recesses are arranged in the upper panel 111 and adapted to accommodate two 12 volt batteries 1OA, 1OB that are preferably coupled in series in order to make use of a 24 volt system, among other things for driving the motors 204, 205.

Fig. 5 shows a view in perspective as seen obliquely from above and from behind in order more clearly to show the transmission according to this embodiment of the invention. Only the right motor 204 is described since the construction is basically exactly the same on both sides. The motor 204 is positioned such that its rotor shaft (not shown) is arranged at an acute angle in relation to the horizontal plane of the bottom plate. The output rotor shaft transmits via a self-braking worm gear accommodated in a gear box housing 203. The gear change is suitably in the range 40:1 - 60:1, preferably about 50:1, which at a maximum motor rotation of 3000 rpm will give a maximum drive wheel 200, 201 rotation of 60 rpm. The output shaft from the transmission part 203 transmits the rotation to the wheel's drive shaft 215 arranged coaxially therewith. The transmission part 203 and the wheel/shaft 215 are fixed to the chassis via shaft brackets 211 welded to the side panels 110 (see Fig. 4). It may be noted that the second motor 205 is positioned reversely in relation to the first motor 204 by interacting with the first transmission part 202 on its upper side instead of the on its lower side. The reason for this is that it is desired for the motors to have the same driving direction and thereby in a simple way to achieve a desired driving direction for the wheels.

It is also clear from Fig. 5 that the draw bar 310 is attached to the bottom plate 100 by aid of a spacer bracket 312 and that a bolt device 311 is arranged through a hole at its outer end with the purpose of easy attachment of a carriage or the like. As is shown already, the main traction arrangement 300 is arranged more centrally in the vehicle. Its attachment to the bottom plate 100 is preferably arranged centrally between the drive wheels 200, 201, on (or near) the line of the drive shaft, in order to minimize moment influence when turning. The traction arrangement consists of a rod-shaped part 302 that is fixed at the bottom plate and that extends straight up, in order to arrange the actual coupling part 300 at adequate height above the superstructure 7. The actual coupling part 300 has a conical shape such that it is thicker close to the top than at the level where the eyelet of the draw bar rests. Thereby it is "automatically achieved" that the bar will not come off in connection e.g. with a forceful braking. Thanks to this, no additional "locking mechanism" is needed and thanks to choosing a low maximum speed for the vehicle, the gap (resulting from the "wide top") between the towing eyelet and the coupling part 300, will not result in problems, e.g. in the form of vibrations, during operation.

Fig. 6 shows a schematic view of the underside of parts of a control card 6 according to the invention and also a tape C, preferably 15-25 mm wide, more preferred about 20 mm, to be used according to a preferred embodiment for controlling the vehicle. It is clear that the control card 6 is provided with a transmitter portion 602 and a sensor portion 601. The transmitter portion 602 consists of a plurality of IR diodes 602 A- 602G, preferably at least 5, more preferred 7 as is shown in the drawing, which are suitably positioned 10-20 mm from each other. At a tape width of 20 mm, a distance t_s of about 13 mm is to be preferred, meaning that a diode in the middle can be centrally positioned at the same time as the two adjacent diodes have about one half above the tape and the other half outside the tape C. An equally large number of photo-diodes 601A-601G are arranged just behind (preferably in the range 5-10 mm) the transmitter portion, which photo-diodes compose a measuring/signal-receiving portion. It is hence a major advantage that the distance t_s between two adjacent IR diodes is less than the width t_c of the tape C. Accordingly, at least two IR diodes will be positioned above the tape at the same time, such that adequately good accuracy is achieved in the positioning of the control card 6 and thereby of the vehicle A in relation to the tape C. Thanks to multiple transmitters/receivers, the relative position of the vehicle in relation to the centre line C_c of the tape is easy to achieve in a simple and cost-efficient manner. The drawing shows that the centre line C₆ of the control card 6 (and thereby of the vehicle) is somewhat displaced in relation to the centre line C_c of the tape. It is also clear that the centre lines of the control card C₆ and the vehicle C_A are suitably the same but it is realised that this is not necessary since it is easy to compensate for a non-centrally positioned control card by programming.

Figs. 7 and 8 illustrate the basic function of the control mechanism according to the invention. Fig. 7 shows an example in which the control card 6 is centrally positioned in relation to the tape C and Fig. 8 shows an example in which the control card (and naturally thereby the vehicle) is positioned somewhat displaced to the right of the centre line of the tape. The function of the control card is such that IR light is transmitted by switching on one of the IR diodes 602A-602G in a rolling sequence. The transmitted and via the tape C reflected IR light is measured by the photo-diodes 601 A-601G, one photo-diode at the time being activated and such that when the first IR diode 602A is active the first photo-diode 601 A too is active. In a manner that is conventional per se, the signals received by the photo-diodes are amplified and transmitted in the form of analogous signals to A/D conversion and digital processing. As is shown in Fig. 7, the look of the analogous signal when the sensor is centred at the tape is such that the middle analogous signal, i.e. the one obtained by the middle photo-diode, is considerably much higher than all other and that the other signals on either side are positioned successively lower. Hence, a kind of stepped structure is formed by aid of which it can be read off that the vehicle A is centred above the tape C. Fig. 8 on the contrary shows a corresponding signal image when there is a certain displacement to the right. A stronger signal image will then be obtained on one side of the middle sensor 60 ID, such that the steps are asymmetrical. The control and governor unit 11 can, by aid of a correction algorithm (preferably in the form of software), compensate to the right in order to reposition the vehicle centrally above the tape C (the same function can also be achieved by a digital solution by simply using the signal difference between the channels on either side of the middle sensor).

Fig. 9 shows a view as seen from above of a preferred embodiment of a control panel 4 according to the invention. It shows a keyboard 40, a flash bulb 41, a stop button 42, a manoeuvring button for reverse drive 43, a manoeuvring button for left drive 44, a manoeuvring button for forward drive 45 and a manoeuvring button for right drive 46. The keyboard is intended to be used in order by codes to initiate different types of functionalities of the vehicle A. Thanks to the use of codes, only authorised users are allowed to start the truck. This functionality can also be supplemented, i.e. making the drive even safer, by requiring the giving of a personal code before any manoeuvring commands can be given.

The driverless truck A according to the invention is accordingly a kind of automated carriage tractor primarily intended for internal handling of light goods material. By aid of the truck, a load can be transported on carriages B. Thanks to the manoeuvrability and the flexibility of the truck it can be used almost anywhere where any type of carriages are used today. By using an adhesive tape C with a suitable reflecting upper surface (preferably it is made use of 3M Scotchlite Diamond Grade™ or a corresponding type of highly reflecting surface) and a suitable over and over sticky adhesive on the underside, such as an acrylic adhesive. It will accordingly be easy and cheap to change the track to be followed by the truck, as compared with most other known systems. Thanks to the support wheel being non-centrally arranged, the risk is also minimized that the tape C is soiled. According to what has already been shown, the vehicle A is suitably started manually but is arranged to be able to stop automatically at marked end stations. The end station is thereby suitably marked e.g. by applying three pieces of tape abreast, whereby a large number of photo-diodes will give the same type of output signal, which means that a signal image is obtained that clearly deviates from the stepped pattern, and thereby the control unit receives signal(s) to stop the vehicle A. Suitably, the control and governor unit 11 is programmed to have a derailment function which means that when the sensor unit 6 loses contact with the tape C, there will be an automated search for the loop, first by a search of e.g. 45° in the direction from which it came and then once in the opposite direction. If it does not find its way back to the loop C, it is suitably programmed to stop. The minimum turning radius for the tape is suitably in the range 1-2 m, suitably about 1,5 m, with the purpose of achieving adequately good reliability (in order to avoid derailment) at the same time as a beneficial cost-efficiency it achieved in respect of the sensor system. Suitably, the unit is programmed such that the keyboard 40 is only allowed to cut the manoeuvre current to the motor drive and that the emergency stop 42 cuts the current from the batteries. Naturally, the master switch will also cut the current from the batteries.

The invention is not limited to what has been described above but may be varied within the scope of the claims. Moreover, many of the described part systems can be made the subject of individual patent protections, since it is realised that they can constitute efficient technical solutions also in other contexts. The above described guiding system need for example not necessarily be coupled to use in connection with an automated truck according to the above and especially not in all situations with a truck of such rigorous safety systems, e.g. when trucks move about in surroundings in which humans are not allowed. Under such circumstances it is realised e.g. that a bumper mechanism need not be used. Accordingly, it is realised that the bumper mechanism is not an essential combination for many of the part systems that are described above and that are coupled with the bumper mechanism in the dependent claims. Therefore, the right is reserved of filing divisional applications concerning many of these described part systems, without the coupling to a bumper mechanism. Moreover, the person skilled in the art will realise that there are many obvious alternative mechanical and electronic constructions that can be used as alternatives for the above described mechanical and electronic constructions and that without inventive work can be used by the person skilled in the art, still employing the basic function according to the invention. In other words, it is realised that the combinatory solution described according to the invention and the beneficial technical effect provided thereby, especially in terms of cost reductions, can be achieved with certain different part solutions that are obvious alternatives to the person skilled in the art when he has studied the overall concept according to the above. Such an obvious deviation is to use another type of sensor mechanism and to use magnetic tape in combination with inductive sensors instead of reflecting tape.

Claims

1. A driverless truck system comprising at least one traction vehicle (A) with a guiding system (6, 11) arranged to be able to follow a line-shaped marking (C) arranged on the ground, which traction vehicle (A) comprises a chassis (1), a propulsion system (2), a control unit (4), safety arrangements (5), a superstructure (7) and at least one common 12 or 24 volt battery (1OA, 10B) as energy source, said propulsion system (2) utilising two drive wheels (200, 201) arranged to be able to be driven by one electric motor each (204, 205), independently of each other, characteri s ed in that said guiding system (6, 11) comprises a sensor part (6) with multiple sensors (601A-601G) positioned in the lateral direction of the vehicle and arranged to be able to produce a signal image by aid of which the relative position of the vehicle in relation to the centre line (Cc) of said line-shaped marking (C) can be determined, the same number of signal transmitting units (602A-602G) preferably being used.

2. A driverless truck system according to claim 1, characte ri s ed in that the distance (t_s) between two adjacent sensors (60 IA - 601G) is less than the width (t_c) of said line-shaped marking (C), i.e. t_s < t_c, preferably t_s < 0.8 t_c, even more preferred ts = 0.7 tc ± 15%.

3. A driverless truck system according to claim 2, characteri s ed in that said transmitter units (602A-602G) are IR diodes and that said sensor units (601 A- 601G) are photo diodes.

4. A driverless truck system according to any one of the preceding claims, characteri s e d in that said line-shaped marking (C) is constituted by a reflecting tape arranged to be able to be moved, preferably having a width t_c of 15-25 mm, preferably about 20 mm.

5. A driverless truck system according to any one of the preceding claims, characteri s e d in that said chassis ( 1 ) comprises a bottom plate (100) consisting of a plate arranged directly and/or indirectly to constitute a basis for the attachment of the plurality of, preferably all, load-bearing structures in the vehicle (A), preferably with the purpose of giving the vehicle enough weight to achieve a desired friction between the drive wheels (200, 201) and the ground.

6. A driverless truck system according to any one of the preceding claims, c haracteri s e d i n that said propulsion system (2) comprises a self-braking transmission, preferably in the form of a worm gear (203) with a gear change in the range of 20:1-100:1, more preferred at least 30:1 and most preferred in the range of 40:1-60:1.

7. A driverless truck system according to any one of the preceding claims, characteri s e d i n a support wheel (250, 251) that is freely revolving in the horizontal direction and that is longitudinally displaced in relation to said drive wheels (200, 201), whereby three contact points are achieved, said support wheel (250, 251) preferably being positioned in relation to the centre line C_A of the vehicle at another distance than the centre line C₆ for the position of the sensor unit (6) that is used.

8. A method in connection with the control/governing of a driverless track comprising arranging a guiding system (6, 11) at a traction vehicle (A), arranging a line-shaped marking (C) that can be read/followed by said guiding system, arranging a control unit (4) at the traction vehicle (A), arranging at least one safety arrangement (5) at the traction vehicle (A), arranging an energy source in the form of at least one common 12 or 24 volt battery (1OA, 10B), and arranging a propulsion system (2) comprising two drive wheels (200, 201) arranged to be able to be driven by one electric motor each (204, 205), independently of each other, characteri s ed in that a self-braking transmission (202, 203) is arranged between said drive wheels (200, 201) and said electric motors (204, 205), whereby the vehicle will come to a standstill by stopping and/or down-ramping said electric motors (204, 205).

9. A method according to claim 8, c haracteri s ed in that said guide system (6, 11) is arranged to allow for starting of said traction vehicle (A) only when manually influenced, preferably in combination with the giving of a code, preferably comprising an authorisation code, via a keyboard (40) at said control panel (4).

10. A method according to claim 8 or 9, characteri s e d i n that said guiding system (6, 11) is arranged to allow for automatic stopping of the traction vehicle

(A), preferably by a change in the width (t_c) of said line-shaped marking (C).