GB2143969A

GB2143969A - Vehicle guidance

Info

Publication number: GB2143969A
Application number: GB08417806A
Authority: GB
Inventors: Fritz Von Ballmoos; Peter Von Ballmoos
Original assignee: Mannesmann AG
Current assignee: Vodafone GmbH
Priority date: 1983-07-14
Filing date: 1984-07-12
Publication date: 1985-02-20
Also published as: GB2143969B; FR2549252A1; DE3325413A1; IT8421893A1; FR2549252B3; GB8417806D0; IT8421893A0; IT1196191B

Abstract

A vehicle 2 travels parallel to a track 1 in reliance upon information provided by indicia 7, 7A and 8 arranged at intervals along the track and observed by detectors 4 on the vehicle. The indicia 7 and 7A result in the detectors generating signals which are used by an on-board computer to make periodic course corrections. The indicia 8 in the form of bar codes provide the computer with information which is used to plan subsequent manoeuvres. <IMAGE>

Description

SPECIFICATION Vehicle guidance It is well known to guide a vehicle across the floor of a factory or warehouse, or over an open expanse of ground, by using a detector on the vehicle to follow an electrical conductor buried in the ground. The conductor can only be introduced at considerable expense and the path which it defines cannot easily be changed.

The present proposal avoids the need for a continuous guide conductor by providing indicia which are arranged at distances from each other along the path to be followed by the vehicle. A vehicle proceeds along the path by moving from each indicium to the next, which is of a sufficiently large size to be reached by the vehicle even if the latter deviates from its intended course. The indicia used may be arranged simply to restore or direct the vehicle on to a desired linear course (or a nonlinear course formed by linear segments), or to provide information for use by an on-board computer which steers the vehicle along a more complex course.At least two detectors may be arranged on the vehicle, and be spaced apart from one another in the transverse direction, the detectors being directed downwardly so as to respond to indicia arranged on or in the floor and having an output to the computer. The computer may also receive feed-back signals from the steering system and the vehicle drive or running wheels. To this end a distance measuring device, for example, an incremental pick-up provided with light barriers, is connected to the drive system of the vehicle or to a running wheel, and measures the rotations through which the wheel turns in order to provide an indication to the computer of the distance travelled by the vehicle. The incremental pickup can have two light barriers, one of which is responsive to forward travel and the other to rearward travel.Responsive to the input from the pick-up, the computer is able to determine the distance which the vehicle has travelled from the indicium last encountered, and can determine from the absence within a predetermined time of a signal from the next indicium to be encountered that the vehicle has strayed off course. Two incremental pick-ups can be provided, one on each side of the vehicle, each being associated for example with a respective rear wheel. Because the wheels rotate at different speeds as the vehicle travels around a curve being steered in accordance with signals from the computer, feedback from the two pick-ups enables the computer to determine and correct any deviation from the desired curve.By employing two pick ups the computer is better able to determine the vehicle's position in two dimensions and the indicia may be arranged at distances greater than if only one pick up is employed.

To restore the vehicle to a desired path when it has deviated to one side or the other, use may be made of a bar-like symbol which has a straight edge arranged perpendicular to the desired path. If the vehicle approaches such an edge along a line which is other than normal to the edge, non-simultaneous signals are generated by the detectors, and the computer makes a correction to the course accordingly.

An alternative may take the form of a triangle, and the vertices of all of the triangles point to the same side of the desired path.

Use is preferably made of obtuse angled triangles with an angle of about 120 . The hypotenuse of the triangle is arranged downstream in the direction of travel. Although right angled triangles may be used, by instead making use of an obtuse angled triangle, there is less risk of a detector of a vehicle which approaches the triangle obliquely travelling laterally out of the triangle prematurely and thereby producing a false correction pulse.

The length of the path followed by each detector across the triangular symbol is indicative of the distance between the detector and the apex of the triangle, and thus of the deviation of the detector from its desired path across the symbol. This information is taken into account by the computer in determining the correction.

The incremental pick-up provides feed-back as to the distance travelled by the vehicle along a corrected course, and the microprocessor can extract the next value from a table or make calculations in accordance with a program in order to complete the entire correction manoeuvre.

Preferably, the indicia are arranged along a track which is spaced from the paths followed by the wheels of the vehicle, so that the visually discernable indicia are protected as far as possible from contamination. Materials handling vehicles often have three wheels, so that the track is arranged adjacent to the longitudinal centre line of the vehicle, and the detectors are arranged on the vehicle so as to be located one on each side of the track.

Instead of, or in addition to, symbols such as those described above which simply enable the computer to restore the vehicle to the path which it should be following, the indicia may be so arranged as to feed data to the computer concerning the manoeuvres to be performed by the vehicle in following a more complex course. By providing for each of the triangular symbols to be preceded by data imparting indicia, the course of the vehicle is not adjusted if it travels along the track in the reverse direction. The track may therefore be a two-way track. The data imparting indicia are thus invariably arranged in front of the triangular or other symbols and may consist of conventional bar diagrams formed from paper symbols attached to the floor.

If there is a risk of coloured symbols becoming contaminated, metal symbols may be used instead which are arranged to cooperate with magnetic sensors. Metal indicia can be arranged beneath a floor covering. Of course, any other suitable sensors may be used instead, for example, dielectric sensors. Because a vehicle may be diverted from the desired path by an obstacle, it may go astray and fail to encounter the next indicium. Reflectors may be arranged adjacent selected indicia, and the vehicle may be provided with a locator which responds to the nearest reflector and can provide an input to the computer which overrides its operation and causes the computer to guide the vehicle towards the reflector and hence towards the nearest indicium. The reflectors are preferably radiation reflectors.If the locator is arranged sufficiently high up on the vehicle, the reflector need not project above the indicia. Normally, the locator is disenabled so that the reflectors do not affect the operation of the control system. It is also possible to arrange for the locator to be enabled and provide normal guidance in the event of particularly bad road conditions. Deviations from linear travel can also be compensated by means of further geometric figures, two parallel bars or a bar and triangle being used for this purpose.

In the drawings: Figure 1 is a diagrammatic phantom perspective view showing a vehicle and guidance devices therefor, Figure 2 is a plan view of a factory floor showing guide paths for vehicles, Figure 3 is a plan view illustrating a corrected path for a vehicle, and, Figure 4 shows the path of a vehicle through guidance devices whereby a deviation in travel is obtained.

Referring to Fig. 1, a vehicle 2 which may be used to transport loads within a factory has a chassis supported on three wheels 3. The leading wheel is driven in rotation by an electric motor 10 and steered by a motor 1 2.

The motor 10 is associated with a pick-up and signal transmitter 11 and the motor 1 2 with a pick-up and signal transmitter 1 3 for providing signals indicative of the distance travelled by the wheel and its angular position. Information concerning the distance and direction through which the vehicle has travelled may be derived from these signals. As an alternative to the transmitters 11 and 12, the rear wheels 3 of the vehicle may be associated with incremental pick-ups and signal transmitters 15.1 and 15.2. Signals obtained from these transmitters may be processed to provide the same information.A control computer 6 provides control signals for actuating the motors 10 and 1 2 utilising data obtained from the transmitters and from a pair of detectors 4 arranged in line with the axles of the rear wheels and from a locator 5 mounted at the front of the vehicle.

The detectors 5 are arranged one on each side of an axis spaced laterally from its longitudinal centre line. When the vehicle is correctly on course, this axis coincides with a track 1 through the factory or warehouse. In one embodiment, the detectors 4 consist of optical sensors or laser scanners responsible to visually discernable indicia and are directed at the ground, and in another magnetic sensors are employed which respond to metal indicia laid on or under the floor. Each sensor generates signals as it passes over indicia on the floor. The indicia employed consists of a number of different types, including surfaces 8 marked with bar codes, triangular surfaces 7 and rectangulr surfaces or bars 7A.Because the track 1 is located to one side of the leading wheel 3 the wheels 3 do not normally pass over the indicia which consequently remain relatively clean.

Associated with some of the information carrying surfaces are reflectors 9 which the locator 5 seeks after the vehicle has travelled a predetermined distance without encountering any of the information surfaces. The locator is movable vertically and horizontally for the purpose, and transmits signals to the computer which processes them to guide the vehicle to the reflector. In Fig. 1 the various information surfaces are shown closer together than is the case in practice.

The wide bars 7A are used by the computer periodically to restore the vehicle to a linear path along its course following travel along an oblique course resulting from discrepancies caused by jolting. When the vehicle passed over the bars 7A, signals are generated by the detectors 4. Provided the signals occur simultaneously, the vehicle is determined by the computer to be on course and the computer takes no corrective action. In the event that the signals do not coincide, the vehicle makes a steering correction, the sense of which depends upon the order of receipt of the signals and the magnitude of which depends upon the magnitude of the discrepancy. A complete system of guide tracks for vehicles 2 is shown in Fig. 2 where main guide tracks 1a and intersecting tracks 1 b are depicted, the surfaces 7 and 8 being shown in a simplified form.

The triangular surfaces 7 are used by the computer to restore the vehicle to the correct course from an incorrect but parallel course.

An example of how this is done is shown in Fig. 3. The triangle has its side 7.1 perpendicular to the track 1, its hypotenuse 7.2 arranged obliquely to this path, and its shortest side 7.3 alongside the path 1. The triangle is so arranged that the sensors 2 first encounter the side 7.1 as they scan across the triangle.

Assuming that the vehicle is on course, path 1.1 followed by a point midway between the two sensors 4 coincides with the track 1, and the sensors will scan across the triangle at equal distances from the path 1. Each sensor will generate a signal which represents the distance which it has travelled across the triangle, having regard to the speed at which the vehicle is travelling. Taking into account signals from the transmitters and from the sensors, the computer will ascertain that the vehicle is on course. If the vehicle is travelling to one side of its course, the signals will be of lesser or greater duration. In the event that the discrepancy exceeds an acceptable value, the computer may make an adjustment and the motor 1 2 operated to steer the vehicle back towards its course.Fig. 3 illustrates specifically how the vehicle may be travelling at,an angle to its desired course, so that the sensors follow paths across the triangle of length 4.1 and 4.2. The computer interprets this data as showing that the vehicle is to the right of its desired course and applies a correction to cause the vehicle to follow the path 1.1 and return to the desired path. The magnitude of the error as indicated by the lengths 4.1 and 4.2 influences the magnitude of the correction applied by the computer to restore the vehicle towards the desired path, the correction being progressively reduced as the path 1 is approached.

Fig. 4 shows how this principle may be used to steer the vehicle along a relatively complex course. Whereas, in Fig. 3, the side 7.1 of the triangle is perpendicular to track 1, in Fig. 4 it is arranged obliquely to this track so as to cause the vehicle to deflect and head towards the triangle 7b. Upon encounter with this latter triangle, the vehicle is re-deflected and directed towards the information carrying surface 8 and the triangle 7c.

In an alternative arrangement, the triangle is obtuse having an angle of 120 so that the side 7.3 diverges from the track to lessen the risk of the paths 4.1 and 4.2 failing to cross the slide 7.2.

The information carrying surface 8 bears a bar code and is arranged in front of the triangle 7c. The code contains information which is transmitted from the sensors to the computer. This information may specify: An identifying code for the surface 8, Identification from information exchange point, Distance to the next surface 8, Radius of the next curve to be traversed, and, Information relevant to steering the vehicle along a track composed of straight lines and curves.

The information carrying surfaces may also give commands to the vehicle, for example: Stop, whereupon the vehicle stops and must be manually restarted in order to travel further.

Reduce speed, Increase speed, Pause for a predetermined time, Turn to the right through, for example, 90 or 180 , Turn to the left through, for example, 90 or 180 .

The information may also specify the radius of the turn so that the vehicle can return along a parallel route at a predetermined distance from its outward route.

It is not always necessary for the triangular or rectangular surfaces 7 and 7A to be preceeded by the bar codes, the latter codes being required only when it is necessary to impart information to the vehicle computer to give commands other than course corrections.

The triangular and rectangular surfaces may therefore be provided alone at various locations in order to restore the vehicle to its desired course. In all cases, the corrections to travel are calculated taking into account the measured values 4.1 and 4.2 either directly after measurement by means of a microprocessor, or the corresponding values are calculated beforehand and read from a table stored in the processor. After measuring the values 4.1 and 4.2, the individual correction values are located and interpolated. The correction values are emitted as set values, the movement performed being reported back, monitored and if necessary corrected in response to feed back from incremental and measured value pick-ups. Even relatively bad contamination of the indicia does not affect the reading of the values 4.1 and 4.2.Nevertheless, to increase reliability, more sensors (for example five) may be arranged next to each other so that multiple measurements may be taken.

The ability of the detectors to read the triangle is increased markedly by using a number of detectors, the reading being made transversely of the direction of travel. Because, in general, all or most of the sensors will encounter the triangle 7 as the vehicle passes over it, the reliability of sensor operation and signal generation is increased compared with the known systems in which an uninterrupted guideline is scanned, in which case at regular intervals monitoring is difficult to ensure.

A further advantage of the present proposal is that the entire control device may be disconnected after the course has been corrected and until the detectors detect subsequent indicia. Energy can be saved in this way and the vehicle does not oscillate continuously around the set course if its deviation from the predetermined track 1 is negligible. For example, with an interval between individual surfaces 7 of three metres, the surface having a size of one half of an A4 sheet, a correction is only required if the deviation exceeds 3 cm.

Claims

1. A method wherein a vehicle is guided by using a detector on the vehicle to detect indicia on the floor or ground over which the vehicle travels, the indicia being spaced from one another along a path which the vehicle is intended to follow.

2. A method as claimed in claim 1, wherein the indicia are detected by at least two downwardly directed detectors spaced from each other in the direction transversely of the vehicle.

3. A method as claimed in claim 1 or claim 2, wherein the distance traversed by the vehicle from the indicium most recently encountered is measured.

4. A method as claimed in claim 3, wherein distance is measured using an incremental pick-up provided with light barriers.

5. A method as claimed in claim 4, wherein the incremental pick-up has two light barriers, one of which measures forward travel and the other measures rearward travel.

6. A method as claimed in claim 5, wherein the distance traversed by the vehicle is measured by two incremental pick-ups, each associated with a respective side wheel of the vehicle.

7. A method as claimed in any preceding claim wherein the vehicle is guided by signals obtained from an on-board control computer, input data for which is obtained from the detectors.

8. A method as claimed in claim 7, wherein data for the computer is also obtained from a pick-up associated with the vehicle steering system.

9. A method as claimed in any preceding claim, wherein an indicium is constituted by a symbol, an edge of which facing the approaching vehicle is a straight line, and the time difference between signals generated by the detectors is used to provide a steering control signal.

10. A method as claimed in claim 9, wherein the edge of the symbol facing away from the approaching vehicle is a straight line, and the distance between the two lines varies along the length of the symbol and signals responsive to the distances travelled by the detectors between the lines are used to produce the steering control corrections.

11. A method as claimed in claim 10, wherein the symbol is a triangle, and all such triangles have vertices pointing to the same side of the track.

12. A method as claimed in claim 11, wherein the triangles are obtuse angled triangles.

13. A method as claimed in claim 12, wherein the angle is approximately 120 .

14. A method as claimed in any preceding claim, wherein the indicia are spaced from the tracks of the vehicle wheels.

15. A method as claimed in claim 14 wherein the detectors are related to an axis spaced from the central longitudinal axis of the vehicle.

16. A method as claimed in any preceding, claim wherein the indicia include differing information carrying symbols, data from which is input to the computer and used as the basis for subsequent manoeuvres.

17. A method as claimed in any preceding claim, wherein the indicia include bar codes.

1 8. A method as claimed in claim 17, wherein each bar code is arranged ahead of a triangular symbol.

19. A method as claimed in any preceding claim, wherein the indicia consist of or are provided on metal surfaces arranged on the ground.

20. A method as claimed in any preceding claim, wherein the indicia consist of or are provided on metal surfaces arranged in the ground.

21. A method as claimed in any preceding claim, wherein the vehicle has locators which detect reflectors arranged along the path to be followed by the vehicle and the computer causes the vehicle to be steered towards a selected reflector.

22. A method as claimed in claim 21, wherein the reflectors are arranged adjacent to indicia.

23. A method as claimed in claim 21, wherein the reflectors are radiation reflectors.

24. A method as claimed in claim 22, or claim 23, wherein the reflectors do not project beyond the indicia.

25. A method as claimed in claim 24, wherein the reflectors are curved.

26. A method as claimed in claim 21, wherein the locator is arranged on the front of the vehicle adjacent its upper side.

27. A method as claimed in any preceding claim, including indicia consisting of two parallel bars.

28. In combination, a vehicle provided with downwardly directed detectors and a path therefor marked at spaced apart intervals with indicia.

29. A vehicle including a steering system, a computer for sending signals to the steering system, and laterally spaced apart downwardly directed optical detectors arranged to transmit signals to the computer.

30. A vehicle as claimed in claim 29, wherein the vehicle has at least two down-, wardly directed detectors spaced from each other in the direction transversely of the vehicle.

31. A vehicle as claimed in claim 29, including means for measuring the distance traversed by the vehicle is measured.

32. A vehicle as claimed in claim 31, including an incremental pick-up provided with light barriers.

33. A vehicle as claimed in claim 32, wherein the incremental pick-up has two light barriers, one of which is arranged to measure forward travel and the other to measure rearward travel.

34. A vehicle as claimed in claim 33, wherein the two incremental pick-ups are arranged on the axis of the wheels of the vehicle, one on each side thereof.

35. A vehicle as claimed in any of claims 30 to 34, including an on-board control computer, data for which is obtained from the detectors.

36. A vehicle as claimed in claim 35, including an input for the computer from a pick-up associated with the vehicle steering system.

37. A track arranged to be followed by a vehicle claimed in claim 30, the track being marked at spaced apart intervals with visually detectable indicia, wherein the indicia includes a symbol, an edge of which facing the approaching vehicle is a straight line perpendicular to the track.

38. A track as claimed in claim 37, wherein the edge of the symbol facing away from the approaching vehicle is a straight line, and the distance between the two lines varies along the length of the symbol.

39. A track as claimed in claim 38, wherein the symbol is a triangle, and all such triangles have vertices pointing to the same side of the track.

40. A track as claimed in claim 39, wherein the triangles are obtuse angled triangles.

41. A track as claimed in claim 40, wherein the angle is approximately 120 .

42. A track as claimed in claim 38 wherein the indicia include bar codes.

43. A track as claimed in claim 42, wherein each bar code is arranged ahead of a triangular symbol.

44. A vehicle guidance system substantially as hereinbefore described with reference to and as illustrated in the drawings.