CA1230399A - Vehicle control and guidance system - Google Patents

Abstract

ABSTRACT
A vehicle control and guidance system in which a desired route for the vehicle is stored in the vehicle in the form of co-ordinates in a ground reference frame.
The 'vectors' between these junction points are divided by successive reference points into incremental vectors, the reference points being generated ahead of the vehicle at regular intervals. A dead reckoning system predicts the position of the vehicle at the end of each interval and this estimate is corrected a using a Kalman filter, by an independent fixed-target detection system using a scanning laser. The error between the estimated vehicle position and the local incremental vector provides a steering angle correction for the vehicle and the vehicle speed is dependent upon the lag of the vehicle behind the generation of reference points.

Description

Vehicle Control and Guidance System This invention relates to a vehicle control and guidance system in which one or more vehicles each having its own motive power and steering capability can be accurately moved within a predetermined area. Although the position of a vehicle af par-ticular loca-tions can be precisely determined using on-board sensors and external position markers, difficulties arise in tr~-ing to control accurately the movement of a vehicle between these particular locations in a smooth and economical fashion. Gener-ally, an unmanned vehicle is constrained to move along predeter~mined paths, using either fixed rails which engage the wheels, or cables (or like metallic lines~ buried under the paths to be followed. Such track or cable installations are expensive and unduly permanent since routes are thenceforth determined by the installation.
An object of the present invention is therefore to pro-vide a free ranging un-manned vehicle control system such as to simulate a driver~controlled vehicle with a route to follow.
~ ccording to the present invention there is provided a vehicle control and guidance system comprising- ~A) a vehicle, said vehicle housingo (i) motive power means for driving said vehicle; (ii) dead reckoning means for determining the position and heading of the vehicle; (iii) steering means for controlling the path of the vehicle; (iv) data storage means for storing data defining a desired route for the vehicle; (v) computing means including position comparison means for comparing the ~.~

.~

position of the vehicle as determined by said dead reckoning means with said desired route and controlling said steering means in dependence upon the result of the comparison; (B) an electro-magnetic direction finding system comprising: (i) a plurality of fixed reference targets; (ii) transmitting and receiving means mounted on said vehicle for making periodic determinations of bearing relative to the vehicle of at least one of said fixed reference targets; (C) said computing means further including:
(i) means for periodically receiving from said direction finding system a said bearing of a fixed reference target; (ii) means for storing the locations of said fixed reference targets;
(.iii) means for deriving from said dead reckoning means and from the stored location of the said fixed reference target an estimated bearing of the said fixed reference target; (iv) bear-ing comparison means for comparing the bearing received from said direction finding system with the bearing derived from said dead reckoning means; and (v3 means for correcting the determina-tion of vehicle position and heading provided by said dead reckoning means in dependence upon any bearing error determined by said bearing comparison means.
The data storage means for defining a desired route preferably comprises means for storing the route in terms of a series of straight line segments and the computing means comprises means for converting the junction of the straight line segments into smooth curved transitional segments for storage by the data . storage means.

~ ~3~
-2a-There is preferably provided means for storing fo-- each straight and curved segment, a permissible maximum vehicle speed and a permissible path width, according to the local route conditions.
The dead reckoning means may comprise means for estima-ting the position and heading of the vehicle after each of a series of time or distance increments, from -the position and head-ing of the vehicle at the beginning of the increment and in dependence upon the forward and rotational movement of the vehicle during the increment.
The system preferably comprises means for predicting the bearing of a reference target from the vehicle, on the basis of the estimated position of the vehicle and the last determined position of the reference target.
There may be included means providing a bearing error difference between the predicted bearing of the target and the bearing of the target as determined by the electromagnetic direc-tion finding means, Kalman filter means producing correction products, being products of the bearing error and Kalman gain factors in respect of each of the position coordinate and the vehicle heading, and means for combining the correction products ~tJith ths respective estimates of position and heading provided by the dead reckoning means, the results of the combination being best estimates of the position and heading of the vehicle.
There is preferably provided means for applying the best estimates to the dead reckoning means as a basis from which to estimate the vehicle position and head-ing one increment later. Means may be provided forgenerating sequentially the coordinates of incremental reference points on said segments defining incremental vectors, the distance between such points being equal to the product of the maximum permissible speed for that segment and a basic time increment There may also be provided error detecting means for comparing the best estimates of the vehicle position and heading with the position and heading of the nearest incremental vector and producing distance and heading error signals, and means for producing a steering angle demand signal in dependence upon the distance and heading error signals. This error detecting means preferably comprises means for transforming the coordinates of the best estimates of vehicle position and heading into a refer-ence frame having one coordinate axis in alignment witha local incremental vector and having an origin coinci-dent with the reference point to which the local incre-mental vector is directedO
A speed demand signal for the vehicle may be made dependent upon the number of reference points generated ahead of the vehicle position.
A vehicle control and guidance system in accordance with the invention will now be described,by way of example, with reference to the accompanying drawings, of which:
Figure 1 is a diagrammatic layout of a factory floor area showing a vehicle route;

Figure 2 is a diagrammatic view of a vehicle to be guided and controlled;
Figures 3 and 4 are diagrams illustrating the position and orientation of the vehicle on the factory floor area in relation to factory coordinate axes;
Figures 5 and 6 show diagrammatically the route of a vehicle, the free path width of the vehicle and bends in the route;
Figure 7 is a block diagram of the system;
Figure 8 is a block diagram of a Kalman filter process of the system;
Figure 9 is a diagram showing displacement and heading errors of the vehicle; and Figure 10 is a diagram showing a transofrmation between 'factory framel coordinates and 'vehicle frame' coordinates for the determination of positional errors.
It will be apparent that, in this specification the term "dead reckoning means" implies means for navigating based on detection of relative movement between vehicle and ground.

3.;~

Referring to the drawings, Figure 1 sho~Js a factory floor area 1 having coordinate axes X and Y marked on it to provide a coordinate system. The coordinates of a location on this area will be referred to as 'factory 5 coordinates' to distinguish from'vehicle coordinates' to be explained subsequently.
A vehicle T, which may be a flat, load bearing truck, is required to move, un-manned, around the area 1 between stations A, B, C & D along a route defined by the factory coordinates of these stations. The route sho~Jn is, of course, purely for purposes of illustration and may in fact be more or less extensive.
Referring also to Figure 2 the vehicle includes driving wheels 3 with any necessary differential gearing and a castor wheel 5 at one or both ends which is controllable in steering angle and which incorporates a steering angle transducer (not shown) and a 'distance-moved' transducer (not shown) for feedback purposes.
The driving wheels 3 are speed-controlled and supplied by way of a gearbox and DC convertor from a battery 7 in known manner.
The essential features of the vehicle are that it has a controllable steering angle and speed controlled driving equipment. The actual mechanical arrangement can obviously be optimised for the purposes of the invention but is not critical. Thus steering may alternatively be achieved by differential control of two driving wheels instead of by driven control of a castor wheel. The mechanical construction of the vehicle equipment need not therefore be detailed further.
Drive control and guidance electronics 9 receive distance and steering angle signals from the castor wheel 5 and provide steering angle control signals and speed control signals as will be explained.
The equipment so far mentioned is necessary for a dead-reckoning navigating system in which the vehicle location is determined on an incremental basis from a knowledge of distance moved and direction taken. Such systems, while satisfactory in some situations where distances are small, can suffer from cumulative faults due to wheel slippage, uneven surfaces, wear etc. Accord-ingly therefore, it is a feature of the present invention that a supervisory referencing and correcting system is provided based upon the detection of fixed reference points and the location of the vehicle relative to them.
The vehicle is provided with a laser source 11 which is mounted to rotate continuously about a vertical axis.
The laser beam is narrow in width and extensive in height so as to form a thin vertical line of radiation incident upon any obstructing target. A number of targets 13 are fixed at various positions around the area so that as far as possible one or more can be ~seen' by the vehicle from any position in the area. Of course, in a factory situation equipment and stores are moved around and are likely to obscure one or more of the targets from certain positions. In such circumstances the dead-reckoning system may be, temporarily at least, 'on its own'.
The targets 13 are formed from retro-reflectors which return incident light in the direction whence it came.
They may be formed from vertical strips of retro-reflective material, the strips being coded by width or by presence and absence to provide an indication of their identity.
They may conveniently be mounted on boards positioned at or above head height to avoid the laser beam being inter-rupted by objects on the floor. The scanning laser beam may be directed upwards accordingly and may have a vertical angular extent sufficient to encompass the targets at ranges in question.
The vehicle incorporates a receiver which receives the reflected beam from a target 13 and provides an indication of the direction of the reflected beam and thus of the target direction relative to the vehicle heading.
This latter parameter is the angle that the vehicle longitudinal axis makes with the X axis of the factory ,~
~;, coordinate system. The 'heading' is not necessarily the direction of travel since the steering wheel may not be straight ahead at the time.
Also included in the vehicle equipment is a micro-processor and data storage facility 19. Amongst the datastored prior to a travel operation is the route 'map' in the form of the coordinates of the point A,B,C & D.
The route may include sections which require reduced vehicle speed and the limiting speed for each straight section (segment or vector ? A to B etc, is specified and stored.
In addition to limitations imposed on the speed along each route vector it may be that the tolerance on transverse vehicle displacement from the route line varies from vector to vector. There is thus in effect a free path width for each vector beyond which the vehicle must not stray and this pathwidth may change at vector junctions. The path width for each vector is also stored prior to each travel operation.
The above information, route identification (co-ordinates of junction points), permissible speed in eachvector and path width for each vector, may be stored in the vehicle data store by manual insertion of a program or may be communicated from a base station 15 to a comm-unication beacon 17 on the vehicle, the beacon accepting and passing on the data to the vehicle data store and micr-oprocessor 19. The communication unit may regularly inform the base station of the current vehicle position or may be interrogated for the same purpose.
The operation and processing involved will be explained with reference to the subsequent Figures additionally. Figure 3 illustrates the vehicle navigation coordinates, the position being given by the x and y 'factory' coordinates, the vehicle heading being the angle ~ , i.e. the angle between the vehicle axis and the X axis, the forward velocity being V, and the rotation rate, i.e.
angular velocity of the vehicle being U.
Figure 4 illustrates the vehicle-target coordinates additionally. The target reflector R, at factory coordinates Xi and Yi is detected at an angle ~i to the vehicle heading, the vehicle itself having position coordinates x and y, and heading ~ , at a particular time 't'.
Figure 5 shows the junction of two vectors where the free path widths as determined by the stored data, are the same. It is essential for smooth operation that the route at vector junctions is continuous rather than angular and a curved path or segment is calculated to fit the intersection. A requirement is that the curvature 10 shall be as small as possible (i.e. maximum radius of curvature) to reduce forces on the vehicle traversing the bend, while at the same time the path width shall nowhere be less than the smaller of the two path widths. In Figure 5 the radius of the curve is therefore half of the common path width. In Figure 6 however, showing junctions between vectors of different path width, the fitted curves have radii pwa/2 and pwb/2 at the points E and F respect-ively.
Referring now to Figure 7 this illustrates in block schematic form the navigation processing performed on the vehicle.
Data indicating the coordinate points on the route and the path widths of the various route vectors are re-ceived and stored (21). The processor then calculates (23) the smooth curves necessary at the vector junctions, as mentioned previously, on the basis of the path widths.
The constant radius curves suggested in Figures 5 and 7 are in fact not possible to achieve since a transition be-tween a straight path and a circular curve would involve 3 an instantaneous change from zero to a finite angular velocity 7 and thus infinite acceleration and force. An ideal curve would involve a linear increase and then decrease of curvature through the bend.
An appro~imation to this curve is provided by the following equation:

2 2 X(~) = (1-~) Xl ~ 2~(1~ ~ ~2 ~ ~3 ... (1) where~ is that fraction into which the bend is divided, i.e. tenths, fifteenths, or whatever~

X2 is a vector representing tAe coordinates of junction point;
xl and ~3 are vectors representing the coordinates of points at the beginning and end of the curve;
and ~ is the general vector representing the coordinates of points on the curve after each fraction~C.
Thus by inserting one-tenth, two-tenths, three-tenths for o4, the coordinates of successive points on the curve are obtained. This process is effected at 23 in Figure 7 using a value ofo~determined as will be explained.
This principle of incremental construction of the curves is in fact common to the straight portions as well, the successive coordinates of points on the straight portion being given by ~ (~) - (1-~) xO ~O~xl where xO and xl are the coordinates of points at the beginning and end of the straight portion.
While the length of the straight portion might commonly be 20 or 30 metres the length of each section, each incremental vector that is, would commonly be perhaps 5 cms. The fractionoCwould then be about 1/500.
This generation of the incremental vectors is per-formed in block 25 and employs initial data (27) defining the speed limits applicable to the various route vectors.
Each incremental vector is defined by the co-ordinates of the point (the 'reference point') at its leading end. The generation of each such reference point occurs once in a basic time interval (at conveniently 20 Hz) which is derived from a clock pulse generator of the system. Since the speed (maximum) for each vector is pre-determined and the time interval is fixed, the maximum length of each incremental vector is determined. At a speed of 1 m/sec therefore, the incremental vector length is 5cms. Having thus determined the maximum length this can be reduced slightly to make the number of incremental vectors in the route vector an integral number, of which o~(above) is the inverse.

3~3~

It will be apparent that if the incremental ~ector length is reduced from its maximum permissible, the speed of the vehicle for that portion of the route will be reduced accordingly. Dynamic control of the speed is thus provided.
In constructing the curve as explained above, by calculation of successive reference points, the incremented reference heading ~ is determined as the angle of the line between successive reference points (relative to the factory X axis)O
The reference points so calculated, which do of course define the required route as opposed to the actual route followed, are generated once per basic interval and stored for comparison with the 'actual1 positions taken by the vehicle. These 'actual' positions are, in fact, estimates derived from the dead reckoning system as checked and corrected by the laser/target reference system.
If the generated reference points advance ahead of the vehicle, due to inertia etc., the difference in position between the latest reference point and the vehicle may be considered as an error distance which the vehicle tries to reduce. The greater this error dist-ance the greater should be the speed of the vehicle (within the limit set for the particular route vector or bend) to try to reduce it. Conversely, the speed should be reduced if the generated reference points are orly just ahead of the vehicle position. This last situation will obtain when the vehicle is approaching a stopping station at the end of a route vector. The number of reference poin~ 'lying in wait' is thus an indication of speed requirement and the vehicle drive motor is controlled accordingly.
The generated reference points and the associated incremental reference heading ~ are passed, one pair at a time, for position and heading error determination ~29).

The estimated vehicle position and heading is provided by a Kalman filter predictor process37 in Figure 7. This employs target detection inputs 3i ~Figure 4) derived from the laser/reflector system 33.
Distance moved by the vehicle and steering angle signals are obtained from transducers referred to previously and indicated in Figure 7 at 35. The Kalman predictor process itself (37) is illustrated in greater detail in Figure 8.
Referring to Figure 8, the first process to be performed is the estimation of position and heading at the end of one basic time interval (~t) given the ~orward and rotational speeds of the vehicle during that interval and the position, either actual or estim-ated, at the beginning of the interval.
The transducer inputs to the position predictor process are the steering angle ~ picked off the steer-ing castor, and the distance travelled by that castor ~heel produced as distance-counting pulses. The distance increment and the increment 4t give the speed in the direction of the castor wheel from which the forward speed V of the vehicle, along its heading, is obtained as a product with the cosine of the steering (castor) angle ~. The angular velocity of the vehicle, U, is derived from the products of the castor wheel velocity and the sine of the steering angle in accordance with the geometry of the vehicle wheels.
These velocities V and U are calculated in each time interval on the assumption that the velocities and steer-ing angle are constant for the (short) time interval ~ t .
The equationsused in the process of the positionpredictor 39 of Figure 8 are derived as follows. The rates of change of the position coordinates x and y, and of the heading angle ~ can be seen from inspection of Figure 3 to be given by:
~= U
x = V cos y = V sin , By the integration of these equations over the period ~t the following equations are derived:
~(t+~t) = ~(t)+U.~t x(t+at) = x(t)~V(sin(~(t)~U.~t)-sin(~(t)))~ t/U.~t y(t+~t) = y(t)-V(cos(~(t)+U.~t)-cos(~(t)3) .~t/U.~t The first of these is expressed as: the value of ~V at time (t+~t) is equal to the value of ~ at time t plus the angle through which the vehicle has rotated in the time interval ~ t. In the second and third equations t and (t+4t) have the same significance as in the first.
These equations may be re-written for estimated values as:
~t+~tlt) = ~ (tlt)+~.~t X (t~t~t) =x (t~t)+V(sin ~(t¦t)+U~t)-sin~(tlt~/U
~ (t+~t¦t) = y(t¦t)-v(cos(~(t¦t)+u.dt)-cos~(t¦t)) /U
The 'hat' over a parameter indicating an estimated value, and the symbol" t t" meaning "evaluated at time t".
It may be seen that these equations are sufficient to estimate the position and heading of the vehicle at time (t~Qt) knowing the estimated position and heading at time t. The output of block 39 is thus the estimated coordinates x and y and the estimated heading ~ of the vehicle after a further time interval~ t, and 9 but for the input 41, based only on the dead reckoning system of distance travelled and angle moved through.
From Figure 4 theestimate~ angle of a target reflector R may be obtained in terms of the vehicle head-ing ~ and the coordinates of the vehicle and the target [xi-x ( t+~t I t ~
where ei is the estimated target angle at time (t+~t) evaluated at time t. The coordinates xi and Yi of the target are predetermined from the layout of the targets on the factory floor. The estimated values x and y of the vehicle are derived from process 39 and also the estimated value ~ of the heading. The equation is thus ~ ~lg~

processed in a target bearing predictor 43 which produces the output 0i-The output of the laser target detection system 33provides an accurate observation of the target angle ~i which is differenced with the estimated value ei in a process 45 to give a target estimation error 9i~
This error signal is processed by the Kalman filter 47 which effectively produces products of the error ~ith respective ~21man gain factors k~, kx, and k~. These correction products are then added in process 49 to the dead-reckoning predictions of process 39 in accordance ~ith the following equations to give corrected estimates of the vehicle heading and position:
~ (t~4tlt~at) = r(t~tlt) ~ k~ 9i) x (t+~tlt~t) = ~ (t~t~t) + k (~
(t+~t~t~t) = ~(t~tlt) + ky(~i-~i) The derivation of Kalman correction products and the operation of Kalman filters is given in the book "Optimisation of Stochastic Systems" by M. Aoki,published by Academic Press 1967.
Thus corrected estimates of heading and position at time (t+~t) evaluated at that time are obtained from estimates of heading and position obtained at time t and corrected by the Kalman filter process. These best estimateS are output to the error determining process 29 of Figure 7 but are also applied as 'present' inputs (41) to the position predictor 39 of Figure 8 from which to predict the next reference point. Thus in the absence of one or more target reference corrections, due, for example, to obscuring of the targets, the next reference point is predicted by dead reckoning from the last reference point that had the benefit of target-detection correction.
Referring back to Figure 7, the determination of distance and heading errors will now be described. The two inputs to process 29 are (a) the generated series of reference points defining the ideal route, and (b) the best estimate of vehicle heading and position derived from the Kalman process of Figure 8.

Referring to Figure 9, this shows successive incremental vectors IV1 and IV2 and their associated ref-erence points RP1 and RP2 as generated in accordance with process 25 (Figure ~7). Errorq in the navigation of the vehicle T are determined as the perpendicular distance de between the centre of the vehicle and the local incremen-tal vector, and the angular error ~e between the heading of the vehicle and the direction of the local increm-ental vector.
Measurement of these errors de and 9e are achieved by a kransformation of the actual vehicle position in factory coordinates to a position in a vehicle reference frame in which the origin is at the reference point of the local incremental vector and the new X axis coincides with the local incremental vector. This transformation is illustrated in Figure 10 in which X and Y are the factory coordinate axes, X* and Y* are the vehicle frame axes, xr and y are the coordinates in the factory frame of the local incremental vector reference point, x, y are the coordinates of the vehicle in the factory frame and x* y* are the vehicle coordinates in the vehicle frame.
The angle ~r is the heading of the incremental vector relative to the factory frame. From Figure 9 the following transformations are derived by simple geometry:
( r) ~ r (Y Yr) lYr Y (Y Yr)CS~r ~ (x-xr)sin~i/r In this vehicle r~ference frame it may be seen that the distance error de is the y* coordinate of the vehicle centre and the angle error ~e is the transformation angle ~ r directly.
When the vehicle passes the local reference point r Yr the polari~y of x* will change from negative to positive. This change will initiate discarding of the current vehicle reference frame and re-establishing it with origin on the succeeding reference point and x*
axis aligned with the next incremental vector. It will be seen therefore that the vehicle frame steps alon~
synchronously with the vehicle.
The error values de and 9e are then used to derive a steering-angle-demand signal ~d as a direct 5 function of these error values. The demanded angular velocity ~d is first derived as:
Ud = Kl de + K2 ~e where Kl and K2 are gain functions defined by the dynamics of the vehicle itself. The demand steering angle is then 10 calculated from the vehicle geometry and the demanded forward speed of the vehicle.
As mentioned above, speed of the vehicle is controlled by measuring the number of incremental vectors between the vehicle and the last one generated. This 15 last generated one will always be ahead of the vehicle and will appear to 'pull' the vehicle along as if an elastic band connects the vehicle to the last position reference generated.
From a stationary position the reference points 20 will be generated at a linear rate away from the 'rest' station and will in effect stretch the above mentioned elastic. The vehicle will accelerate in accordance with the error distance to the latest reference point and dependent upon its inertia and power, and gradually the 25 error will reduce until a steady state is reached where the vehicle speed is equal to the rate of advance of the reference points.
Reference point speed and therefore vehicle speed can be altered dynamically during travel along a defined 30 trajectory by altering the incrementing distance (i.e.by varyingOCin algorithm (1) above) bet~een successive reference points.
When the generation of incrementing vectors and reference points is complete, the final incrementing vector will terminate Gn the final stopping position demanded by the original route specified in coordinate ~I3f~ 7 position defining route vectors. The vehicle speed will slow down as the distance error decreases. By shaping the distance-error/demanded~speed relationship the speed is controlled so that the final point is reached without overshoot. The vehicle frame is again directly applicable here as the x* coordinate is the 'distance-to-go' in that frame and this can be monitored without further calculation.
The electromagnetic direction-finding means is, in the above embodiment a laser system providing direction sensing by means of a narrow laser beam scanning in azimuth.
It is however envisaged that radar beams could be employed providing accurate direction finding by phase comparison techniques. In addition 7 the reflectors above could be replaced by transponders with coded emissions.

Claims (22)

1. A vehicle control and guidance system comprising:
(A) a vehicle, said vehicle housing:
(i) motive power means for driving said vehicle;
(ii) dead reckoning means for determining the position and heading of the vehicle;
(iii) steering means for controlling the path of the vehicle;
(iv) data storage means for storing data defining a desired route for the vehicle;
(v) computing means including position comparison means for comparing the position of the vehicle as determined by said dead reckoning means with said desired route and controlling said steering means in dependence upon the result of the comparison;
(B) an electromagnetic direction finding system comprising:
(i) a plurality of fixed reference targets;
(ii) transmitting and receiving means mounted on said vehicle for making periodic determinations of bearing relative to the vehicle of at least one of said fixed reference targets;
(C) said computing means further including:
(i) means for periodically receiving from said direction finding system a said bearing of a fixed reference target;
(ii) means for storing the locations of said fixed reference targets;
(iii) means for deriving from said dead reckoning means and from the stored location of the said fixed reference target an estimated bearing of the said fixed reference target;
(iv) bearing comparison means for comparing the bearing received from said direction finding system with the bearing derived from said dead reckoning means;
and (v) means for correcting the determination of vehicle position and heading provided by said dead reckoning means in dependence upon any bearing error determined by said bearing comparison means.

2. A vehicle control and guidance system comprising:
(A) a vehicle, said vehicle housing:
(i) motive power means for driving said vehicle;
(ii) dead reckoning means for determining the position and heading of the vehicle;
(iii) steering means for controlling the path of the vehicle;
(iv) data storage means for storing data defining a desired route for the vehicle;
(v) computing means including position comparison means for comparing the position of the vehicle as determined by said dead reckoning means with said desired route and controlling said steering means in dependence upon the result of the comparison;
(B) a laser target detection system comprising:
(i) a plurality of fixed reference target reflectors;
(ii) laser beam scanning means mounted on said vehicle;
(iii) laser beam detection means mounted on said vehicle for detecting laser beam reflections from said target reflectors, said computing means including means for determining from the scanning direction at the instant of detection of a said laser beam reflection the bearing of a said target reflector;
(C) said computing means further including:
(i) means for periodically receiving from said laser target detection system a said bearing of a said target reflector;
(ii) means for storing the locations of said fixed reference targets;
(iii) means for deriving from said dead reckoning means and from the stored location of the said fixed reference target an estimated bearing of the said fixed reference target;
(iv) bearing comparison means for comparing the bearing received from said target detection system with the bearing derived from said dead reckoning means; and (v) means for correcting the determination of vehicle position and heading provided by said dead reckoning means in dependence upon any bearing error determined by said bearing comparison means.

3. A vehicle control and guidance system according to Claim 2 , wherein said data storage means for defining a desired route comprises means for storing said route in terms of a series of straight line segments, and said computing means comprises means for converting the junction of said straight line segments into smooth transitions for storage by said data storage means.

4. A vehicle control and guidance system according to Claim 3, wherein said data storage means comprises means for storing, for each of said straight line segments, a permissible maximum vehicle speed and a permissible path width, according to the local route conditions.

A system according to Claim 4 wherein said means for converting said junction into smooth transitions comprises means for calculating the radius of curvature of a transition as not less than half the value of the path width and, where there are different path widths at the junction, half the value of the greater of the two path widths.

6. A system according to Claim 2, wherein said dead reckoning means comprises means for estimating the position and heading of the vehicle after each of a series of time increments, the position and heading of the vehicle after each time increment being estimated from the position and heading of the vehicle at the beginning of the said time increment and in dependence upon the forward and angular velocities of the vehicle during the said time increment.

7. A system according to Claim 6, wherein said computing means comprises means for predicting the bearing of a said target reflector from the vehicle at the end of a said time increment, on the basis of the said estimated position of the vehicle at the end of said time increment and the known position of said target reflector.

8. A system according to Claim 7, wherein said computing means comprises means providing a bearing error difference be-tween the predicted bearing of said target and the bearing of said target as determined by said laser target detection system, Kalman filter means for producing correction products, said cor-rection products being products of the said bearing error and Kalman gain factors in respect of coordinates of the vehicle position and the vehicle heading, and means for combining said correction products with the respective estimates of vehicle position and heading provided by said dead reckoning means, the results of the combination being best estimates of the position and heading of the vehicle.

9. A system according to Claim 8, wherein said best esti-mates of the position and heading of the vehicle are employed by said dead reckoning means as current vehicle position and head-ing for estimation of vehicle position and heading one said time increment later.

10. A system according to Claim 4, wherein said computing means comprises means for generating sequentially the coordinates of reference points on said straight line segments defining incremental vectors, each such reference point being generated in a time increment corresponding to -the maximum permissible speed of the vehicle over a said incremental vector.

11. A system according to Claim 4, wherein said computing means comprises means for generating sequentially the coordinates of reference points on said straight line segments defining incremental vectors, each such reference point being generated in a time increment corresponding to the maximum permissible speed of the vehicle over a said incremental vector, error detecting means for comparing the said corrected vehicle position and heading with the position and heading of the nearest incremental vector and producing distance and heading error signals, and means for producing a steering angle demand signal in dependence upon said distance and heading error signals.

12. A system according to Claim 11, wherein said error detecting means comprises means for transforming the coordinates of said corrected vehicle position and heading into a reference frame having one coordinate axis in alignment with a local incremental vector and having an origin coincident with the reference point to which the local incremental vector is directed.

13. A system according to Claim 11, wherein said computing means comprises means for providing a speed demand signal for the vehicle dependent upon the number of reference points generated ahead of the vehicle position.

14. A vehicle control and guidance system comprising:
(A) a vehicle, said vehicle housing:
(i) motive power means for driving said vehicle;
(ii) steering means for controlling the path of the vehicle;
(iii) data storage means for storing data defining a desired route for the vehicle;
(iv) computing means; and (v) dead reckoning means comprising (a) transducer means for providing a vehicle displacement signal, (b) transducer means for providing a vehicle heading signal, and (c) position and heading estimating means comprised within said computing means and responsive to said displacement signal and to said heading signal for estimating the position and heading of the vehicle after each of a series of time increments, the position and heading of the vehicle after each time increment being estimated from the position and heading of the vehicle a', the beginning of the said time increment and in dependence upon the forward and angular velocities of the vehicle during the said time increment;
(B) a laser target detection system comprising:
(i) a plurality of fixed reference target reflectors;
(ii) laser beam scanning means mounted on said vehicle;
(iii) detection means mounted on said vehicle for detecting laser beam reflections from said target reflectors;
(iv) bearing determination means comprised within said computing means for determining from the scanning direction at the instant of detection of a said laser beam reflection the bearing of a said target reflector;
(C) said computing means including:
(i) location storage means for storing the locations of said fixed reference target reflectors;
(ii) bearing prediction means for providing a predicted bearing of a said target reflector from the vehicle at the end of a said time increment, said bearing prediction means employing the said estimated position and heading of the vehicle at the end of said time increment and the location of said target reflector derived from said location storage means;
(iii) bearing error detection means for determining the bearing error between said predicted bearing and the detected bearing determined by said bearing determination means; and (iv) Kalman filter processing means comprising:
(a) means for producing correction products, said correction products being products of the said bearing error and Kalman gain factors in respect of coordinates of the vehicle position and the vehicle heading, and (b) means for combining said correction products with the respective estimates of vehicle position and heading provided by said dead reckoning means, the results of the combination being best estimates of the position and heading of the vehicle; and (D) said computing means including means for comparing said best estimates of the position and heading of the vehicle with said desired route and controlling said steering means accordingly.

15. A vehicle control and guidance system according to Claim 14, wherein said data storage means for defining a desired route comprises means for storing said route in terms of a series of straight line segments, and said computing means comprises means for converting the junction of said straight line segments into smooth transitions for storage by said data storage means.

16. A vehicle control and guidance system according to Claim 15, wherein said data storage means comprises means for storing, for each of said straight line segments, a permissible maximum vehicle speed and a permissible path width, according to the local route conditions.

17. A system according to Claim 16, wherein said means for converting said junction into smooth transitions comprises means for calculating the radius of curvature of a transition as not less than half the value of the path width and, where there are different path widths at the junction, half the value of the greater of the two path widths.

18. A system according to Claim 14, wherein said best estimates of the position and heading of the vehicle are employed by said dead reckoning means as current vehicle position and heading for estimation of vehicle position and heading one said time increment later.

19. A system according to Claim 16, wherein said computing means comprises means for generating sequentially the coordinates of reference points on said straight line segments defining incremental vectors, each such reference point being generated in a time increment corresponding to the maximum permissible speed of the vehicle over a said incremental vector.

20. A system according to Claim 19, wherein said computing means further comprises error detecting means for comparing said best estimates of the vehicle position and heading with the position and heading of the nearest incremental vector and producing distance and heading error signals, and means for producing a steering angle demand signal in dependence upon said distance and heading error signals.

21. A system according to Claim 20, wherein said error detecting means comprises means for transforming the coordinates of said best estimates of vehicle position and heading into a reference frame having one coordinate axis in alignment with a local incremental vector and having an origin coincident with the reference point to which the local incremental vector is directed.

22. A system according to Claim 20, wherein said computing means comprises means for providing a speed demand signal for the vehicle dependent upon the number of reference points generated ahead of the vehicle position.