FR2495797A1 - Laser-optic automatic positioning for electric vehicle - uses fixed reference of three retro-reflectors and measures angle of reflected light to position vehicle - Google Patents

Abstract

The appts. controls an autonomous vehicle which uses optical methods to guide the vehicle to its stopping place and to ensure its correct orientation when it reaches the stopping place. An optical reference is provided by a fixed horizontal strip containing three optical retro-reflectors while a laser and optical detection system on the vehicle determine the angles of each reflection enabling the vehicle control circuit to steer the vehicle towards the reference. The laser light is deflected onto a scanning reflector and light returning from the reference retro-reflectors is focussed onto a photoelectric detector which provides the data for a control circuit to guide the vehicle towards the reference.

Description

AUTOMATIC STEERING SYSTEM OF A LAND VEHICLE
NO ME.

 The present invention, developed at the Center d'Etudes et de Recherches de Toulouse (O.E.R.T.), establishment of 1'O.N.E.R.A., Relates to an automatic piloting system of an autonomous land vehicle towards a determined location.

The term “autonomous” vehicle is understood here to mean an unmanned vehicle provided with its own starting, stopping and steering control means. The invention applies to all autonomous vehicles with traction by electric motor and with directional control Far electric motor and in particular to self-propelled trolleys intended for the picking up, transfer and removal of charyes. The system of the invention more specifically aims on the one hand to guide an autonomous vehicle towards a determined location whatever the distance between them and the initial orientation of the vehicle and on the other hand to ensure a determined orientation said vehicle and its stop when said location is reached. We already know, as such systems
- those which implement distance measurements by periodically determining the duration of the journey of trains of electromagnetic waves (light or ultra-short microwave) exchanged between the vehicle and fixed markers or beacons; the need to measure extremely short durations limits the precision of the guidance and requires the use of bulky, complicated and expensive equipment;
- those implementing the measurement of parameters (intensity, phase) of the electromagnetic field generated by a network of overhead, underground or surface conductors; the measurement must be all the more precise the better the guiding precision sought.

 The automatic pilot system of the invention has none of these drawbacks. It operates by means of triangulation measurements by optical means and requires no other field installation than a very simple reference base. The device on board the vehicle is robust, inexpensive and compact. Finally, the precision of the guidance is largely sufficient for the applications envisaged.

The automatic pilot system of the invention is essentially characterized in that it comprises
- an optical geometric reference base constituted by three retro-reflective optical markers which respectively occupy one end, the middle and the other end of a horizontal segment of determined length and orientation (the term "retro-reflector" qualifying a optical element which, when illuminated by an optical brush, returns in the direction of incidence of this brush at least a fraction of the luminous flux which it receives therefrom) and
a control device on board the vehicle, comprising on the one hand electro-optical means for measuring the angular distances, seen from the vehicle, from one and the other optical end markers relative to the median cctical mark and on the other hand, a control unit which acts on the power supply circuit of the steering control motor to orient the vehicle in motion so that these angular distances tend to increase in equalization and which acts at the end of the journey on the traction motor supply circuit for stopping the vehicle when these angular distances are both equal to a predetermined value.

 The system of the invention therefore effectively operates by triangulation and its precision depends only on the precision of production of the reference base, on the precision of the measurement of the angular distances and of the time of re-re.

response of the vehicle to control orders acting on the supply circuits.

Advantageously
the optical means of the on-board piloting device comprise on the one hand a headlight which delivers a light brush which pivots in a horizontal plane by scanning the base and on the other hand an opto-electronic sensor exposed to the light fluxes sent by the optical markers when these are reached by this light brush and
the control unit comprises means for measuring the deviations of the positions successively occupied by the light brush when the sensor delivers impulse signals corresponding respectively to the light fluxes returned by the three marks.

 The measurements of the angular distances of the three marks are thus reduced to measurements of the angular position of the light brush relative to an axis linked to the vehicle.

 Advantageously, in addition, the headlight comprises a fixed light source (for example a gas laser) delivering a horizontal light brush, a first fixed reflector arranged on the path of this brush to reflect it in a vertical direction and a rotating reflector arranged on the path of the brush thus reflected to return it in a horizontal scanning plane. The light source is thus rigidly linked to the vehicle and the only movable member of the control device is the rotating reflector which is easy to produce with very high precision.

 Advantageously, moreover, the rotating reflector is driven by an electric motor at constant speed (for example provided with a flywheel or else controlled by a synchronization time base) and the means for measuring the angular position deviations are chronometric means which measure the time intervals which separate the instants when the sensor delivers the impulse signals. The angular deviation measurements are thus reduced to chronometric measurements which it is easy to carry out in a very precise manner by means of digital counters.

 It will be noted, in general, that the angular distances measured become all the greater the closer the vehicle is to the base, the relative precision of the angular measurements by the chronometric means increasing in the same proportions. Guidance is more precise as the vehicle approaches its goal. This advantage is particularly precious when this vehicle is a handling trolley provided with automatic means for placing and depositing a load which requires a precise positioning and orientation of the trolley reiatively at the loading and unloading locations.

Other provisions, relating in particular to the constitution of the control unit, will be set out in the following description of an exemplary embodiment of the control system of the invention. This description refers to the accompanying drawings in which
- Figure 1 is a general view of the system showing in profile a vehicle equipped with the steering device and in perspective the reference base;
- Figure 2 is a block diagram showing the essential elements of the control unit of the control device;
FIG. 3 is a diagram of time measurement pulse signals;
- Figure 4 is a geometric diagram;
- Figure 5 is a kinetic diagram.

 In Figures 1 and 2 are shown only the provisions necessary for understanding the invention.

The vehicle, in particular, is reduced to its driving organs and to the organs of the steering device.

 We first consider Figure 1. The vehicle or carriage 10 comprises a plate 11 supported by a rear drive axle with two wheels such as 12 and by a crazy front steering wheel 13. The axle of the wheels 12 is driven by a motor electric 14 while the steering pivot 131 of the wheel 13 is actuated by means of a geared motor 15 with two operating directions. accumulator electr ~ i- que 16 supplies the motor 14 via a supply control circuit 17 and the motor 15 via a supply control circuit 18.

The on-board piloting device 20 is housed in a turret 21 fixed to the front of the platform 11. It includes
a continuous-illumination laser 22 located at the top of the turret 21 and projecting a light brush P horizontally,
a first fixed reflector 23 returning this light brush vertically downwards,
a rotating reflector 24 returning this light brush in a horizontal plane and supported by the vertical axis of an electric motor 25,
a second fixed reflector 26 which is disposed between the reflectors 23 and 24, oriented so as to reflect towards the rear of the carriage the light fluxes successively collected by the rotating mirror 24 during its rotation and in which a transparent window 261 is formed which allows the light brush P to be transmitted between the reflectors 23 and 24,
a first opto-electronic sensor or transducer 27 on which an optic 271 focuses the return flows collected by the reflector 24 and deflected by the reflector 26,
a second opto-electronic sensor 28 on which an optic 281 focuses the brush P when the latter is reflected towards this optic at each turn of the reflector 24,
finally, a control unit 40 which receives by links 401 and 402 the respective output signals from the sensors 27 and 28 from which it generates control signals transmitted respectively to the supply circuits 17 and 18.

 As for the optical reference base 60, it is constituted by a horizontal rule 61 resting on the ground by a stand 65 or fixed to a structure not shown (for example a storage locker). This reyle carries three optical marks 62, 63 and 64 which are retro-reflectors, that is to say which, when they receive a light flux, reflect at least a fraction of this flux in the direction of incidence. These three marks could be achieved by means of small areas of a reflective and diffusing coating (possibly fluorescent), but, for reasons of light output, it is advantageous to constitute them by retro-reflectors, which allows the system to operate in natural or artificial mood lighting. The reperdes 62 and 64 are each arranged at one end of the rule 61, the mark 63 being placed in the middle of this rule, equidistant from the other two.

FIG. 2 shows the essential elements of the control unit 40, at least those which contribute to the steering control of the vehicle. These are - a circuit for shaping (width and amplitude) of the output pulses of the sensors 27 and 28, - a time acQaisition circuit 42 constituted by three digital counters (not shown) which are all synchronized by a base time 43; which are all three re-initial.i.séa: at each turn of the reflector 24 by the output pulse of the sensor 28 and which are respectively stopped by the three successive output pulses of the sensor 27 which correspond to the light pulses returned by the base 60, - a programmable digital computer 44 which generates, from the data supplied by the circuit 42, control signals which are transcribed analogically by an interface circuit 45 and which are supplied to the control circuit 17 of the motor 14 by an amplifier 46 (if it is a question of controlling the start or stop of the vehicle) and to the control circuit 18 of the engine 15 by amplifiers 47 (if it is a question of bending the direction of the vehicle)
FIG. 3 illustrates the fact that the durations Tvl, TV2 and TV3 respectively measured by the three counters of the circuit 42 from the origin determined at each revolution of the mirror 24 by the sensor 28 (VO pulse) provide by difference to the computer 44 the durations which separate the pulses V1, V2 and V3 successively delivered by the sensor 27 on reception of the light pulses successively returned by the references 62, 63 and 64.

We now consider Figure 4. We find there, seen from above and very schematically, on the one hand the carriage 10 with its plate 11, its rear drive wheels 12 and its steering wheel 13, on the other hand the base 60 with its three reflectors 62, 63 and 64 carried by the rule 61. It is assumed that the axis of the vertical pivot of the wheel 13 is coincident with the axis of rotation of the mirror 24 (fig. 1) and that the sensor 28 is aligned with the longitudinal axis of the carriage.
d: the distance from the axis of the mirror 24 to the reflector 63,
b: (base length) the distance between the refl
teurs 62 and 64,
I: the angle of incidence of the soft brush reflected by
the mirror 24 when it strikes the reflector 63 (angle
done with normal NN),
A1 and A2: the angular distances (seen from the mid-axis
see 24) which respectively separate the reflector 62
of the reflector 63 and the latter of the reflector 64, it is verified by calculation that the state of the vehicle at a given instant, defined by the variables d and I, can be known by the values of Al and A2 since
2 tg I = cotg A2 - cotg Al (1) and d = b cos I (cotg A2 + cotg A1) / 4 (2)
Consequently, for a determined base length b and a determined wheelbase E of the vehicle, the computer is able to correct after each rotation of the mirror 24 the turning angle R of the wheel 13 since the value of the angles Al and A2 itself is given by the time differences
(TV2 - TV1) and (TV3 - TV2). The program assigned to it must be such that, at the end of the trajectory, the longitudinal axis LL of the vehicle coincides with the normal EN and that the values of the angles Al and A2 are both equal to a predetermined value which fixes the location where said vehicle must park.

 We will not give here an example of a calculation program since this program depends on the constitution of the calculator and in particular, if it is a microcomputer whose arithmetic and logical unit is constituted by a microprocessor , the instruction set available for it. Such a program is also available to any specialist with the necessary information. It will only be noted that, in order to improve the operating stability of the system, it is advantageous to shift the axis of the mirror 25 to the rear with respect to the axis of the steering wheel 13 or even to introduce a parameter simulating such a shift.

 FIG. 5 illustrates an example of the results obtained using the system of the invention. The curve T represents the trajectory of the vehicle between the starting point 01 and the base 60, in a coordinate system (XI, Y). The corresponding values of the angles R (steering) and A (angular deviation of the axis LL from the straight line which joins the axis of the wheel 13 in the middle of the base 60) are indicated with respect to an axis of the abscissae 02 -X2.We can see that, at the end of the course, these two angles cancel each other out simultaneously, which means that the vehicle is placed perpendicular to the middle of base 60.

 To complete the present description, it will be noted that, given the constitution of the system of the invention, this can easily be applied to the piloting of vehicles already provided with devices for recognizing address of charges of the known type which implement the remote reading of codes consisting of alignments of optical markers.

Claims (7)

CLAIMS. 1. Autopilot system of an autonomous vehicle fitted with an electric traction motor, an electric motor for steering control and supply circuits for these motors, characterized in that it comprises, for directing the vehicle (1G) to a specific location and to stop it in a specific orientation when it has reached this location:  - an optical geometric reference base (60) constituted by three retro-reflective optical references (62,63,64) which respectively occupy one end, the middle and the other end of a horizontal segment of determined length and orientation and  - a control device on board the vehicle, comprising on the one hand electro-optical means (20) for measuring the angular distances, seen from the vehicle, from either of the optical end mark relative to the median optical mark and on the other hand a control unit (40) acting on the supply circuit (18) of the steering control motor (15) to orient the vehicle in motion so that these angular distances tend to increase by equalizing and sliding at the end of the journey on the supply circuit (17) of the traction motor (15) to stop the vehicle when these angular distances have both become equal to a predetermined value. 2. Control system according to claim 1, characterized in that  - Said electro-optical means (2gui comprise on the one hand a headlight (22,23,24) which delivers a light brush which pivots in a horizontal plane by scanning the base 60 and on the other hand an opto-electronic sensor (27 ) exploded to the luminous flux returned by the optical markers (62,63,64) when these are reached by the luminous brush and  - in that the control unit (40) comprises means for measuring the deviations of the angular positions occupied successively by the scanning light brush when the sensor 27 delivers impulse signals corresponding respectively to the light fluxes returned by the first reference mark end - that is to say the first encountered during a sweep - (62) by the middle mark (63) and by the second end mark (64). 3. Piloting system according to claim 2, characterized in that the headlight comprises a light source (22) delivering a horizontal light brush, a first fixed reflector (23) disposed on the path of this brush to reflect it in a vertical direction and a rotating reflector (24) arranged on the path of the brush thus reflected to return it in a horizontal scanning plane. 4. Scanning system according to claim 3, characterized in that the rotating reflector (24) is driven by an electric motor at constant speed (25) and in that the means for measuring said deviations from the angular positions of the scanning light brush are chronometric means (42) which measure the time intervals separating the instants when the sensor (27) delivers said signals. 5. Piloting system according to claim 3 or claim 4, characterized in that the piloting device further comprises a second fixed reflector (26) interposed between the fixed reflector (23) and the pivoting reflector (24), comprising a transparent window crossed by the light brush reflected by the reflector (23) and inclined so that it reflects towards the sensor (27) the light flux collected by said pivoting reflector (24). 6. control system according to claim 4 or according to claim 4 and claim 5 characterized in that the control device further comprises a second opto-electronic sensor (28) disposed in the plane of the light brush reflected by the rotating reflector (24) and delivering to the control unit (40) an original time measurement signal when it is reached by said light brush. 7. Control system according to claim 4 or according to claim 4 and claim 5 or according to claim 6, characterized in that the control unit (40) comprises digital pulse counters constituting the chronometric means (22 a digital computer (44s developing digital control signals from the digital signals transmitted by said counters and an interface (45) transforming said digital control signals into analog control signals intended for supply circuits (15,18).