CH667930A5 - VEHICLE CONTROL AND CONTROL SYSTEM. - Google Patents

Description

DESCRIPTION

The invention relates to a vehicle control and guidance system according to the preamble of claim 1.

Although the position of a vehicle in certain locations can be accurately determined by sensors and external position markers on board, difficulties arise in trying to precisely control the movement of the vehicle in a steady (soft) and economical manner. In general, an unmanned vehicle can only move on a predetermined path using either fixed rails against which the wheels rest or cables buried under the path to be followed. Such devices with rails or cables are expensive and unsuitably durable because the tracks are fixed once and for all.

The invention has for its object to provide a vehicle control and guidance system for a freely maneuverable unmanned vehicle, which enables manual steering of a vehicle on a desired track.

According to the invention, this object is achieved by the characterizing features of patent claim 1.

It is preferably ensured that the device for specifying a desired path has a storage device

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for storing the web in the form of a sequence of rectilinear segments and a device for converting the transition of the rectilinear segments into web-like (soft) curved transition segments.

Furthermore, a device for storing a permissible maximum vehicle speed and a permissible path width can be provided for each straight and curved segment depending on the local path conditions.

The dead reckoning device may include means for estimating the position and heading of the vehicle after each series of time and path increments from the position and heading of the vehicle at the beginning of the increment and depending on the forward and rotational movement of the vehicle during that increment .

The system preferably has a device for predicting the bearing angle of one of the reference targets from the vehicle on the basis of the estimated position of the vehicle and the last determined position of the reference target.

A device for inputting the best estimated values into the dead reckoning device is preferably provided as a basis on which the estimated value of the vehicle position and the vehicle course at the next increment is determined.

Means may also be provided for sequentially generating the coordinates of incremental reference points on the segments which define incremental vectors, the distance between these points being equal to the product of the maximum permissible speed for this segment and a base time increment. In addition, an error detection device can be provided for comparing the best estimates of the vehicle position and the course with the position and the course of the next incremental vector and for generating path and course error signals and a device for generating a steering angle setpoint signal as a function of the path and course error signals.

It can then be ensured that the determining device has a device for transforming the coordinates of the best estimates of the vehicle position and the course into a reference frame with a coordinate axis that coincides with a local incremental vector and has a zero point that coincides with the reference point to which the local incremental vector is directed.

A speed command signal for the vehicle can be made dependent on the number of reference points that are generated before the vehicle position.

A preferred exemplary embodiment of a vehicle control and guidance system according to the invention is described in more detail below with reference to the drawing.

Show it:

1 is a schematic representation of a vehicle track on a limited area of a factory floor,

2 shows a schematic representation of a vehicle which is to be guided and controlled along a predetermined path,

3 and 4 diagrams of the position and orientation of the vehicle on the factory floor surface with respect to factory coordinate axes,

5 and 6 schematically the path of a vehicle, the free path width of the vehicle and turns in the path,

7 is a block diagram of the system;

8 is a block diagram of a Cayman filter process of the system;

9 is a diagram illustrating path and direction errors of the vehicle, and

10 shows a diagram of a transformation between “factory frame” coordinates and “vehicle frame” coordinates for determining position errors.

The term “dead reckoning navigation device” is to be understood here as a device for navigation depending on the detection of a relative movement between the vehicle and the ground.

1 shows a factory floor surface 1 with coordinate axes X and Y forming a coordinate system mounted thereon. The coordinates of a point (or location) on this surface are referred to below as “factory coordinates” in contrast to “vehicle coordinates”.

A vehicle T, which can be a flat transport vehicle, is to travel unmanned on the area 1 between stations A, B, C and D along a path which is determined by the factory coordinates of these stations. The path shown is only for explanation and can be much more complicated.

According to Fig. 2, the vehicle has drive wheels 3 with a differential gear, if necessary, and a pivotable wheel 5 at one or both ends, the steering angle of which is controllable and the one (not shown) steering angle converter and one measuring the distance traveled Has path converter (not shown) for feedback of a distance actual value signal in order to compare it with a distance setpoint.

The drive wheels 3 are speed-controlled and are fed via a gear and a DC / DC converter from a battery 7 in a manner known per se.

The essential features of the vehicle are that it has a drive device which controls or regulates the steering angle and the speed. The mechanical setup can be optimized, but is not critical. Steering can alternatively also be effected by differential control of the two drive wheels instead of by drive control of a pivotable wheel. The mechanical structure of the vehicle equipment therefore need not be described in more detail.

Drive control and steering electronics 9 receive path and steering angle signals from the pivotable wheel 5 and generate steering angle control signals and speed control signals, as will be described in more detail.

The device described so far is a dead reckoning device, in which the vehicle location is determined on an incremental basis from the known size of a path covered and a direction taken. With such systems, although in some applications where the paths are small, cumulative errors due to wheel slip, uneven surfaces, wear, etc. can occur. According to a further exemplary embodiment of the invention, a monitoring reference and correction device is therefore provided, which is based on the establishment of fixed reference points and the location of the vehicle with respect to them. The vehicle is provided with a laser source 11 which is mounted in such a way that it constantly rotates about a vertical axis. The laser beam has a narrow width and extends in height, so that a thin vertical line of illumination is created on a target that enters the beam path. Several targets 13 are permanently installed on the surface 1 in different positions, so that the vehicle can - as far as possible - "see" one or more targets from any location on the surface. Of course, in a factory, facilities and storage devices can be moved around and cover one or more targets from specific locations. In such cases, the dead reckoning device can be "left alone" for at least a short time.

The targets 13 are formed from retro reflectors which reflect incident light in the direction of incidence. They can be made from vertical strips of retroflective material that are coded in width or by presence and absence to represent their identifier. Conveniently, they are arranged on shelves at or above head height in order to

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prevent the laser beam from being interrupted by objects on the floor. The scanning laser beam can accordingly be directed upwards and have such a large vertical angular extent that it can detect targets at the distances in question.

The laser scanning device is the subject of GB patent application 8 313 339 and is therefore not described in more detail here.

The vehicle is equipped with a receiver which receives the beam reflected from a target 13 and forms a sign representing the direction of the reflected beam and thus the target direction relative to the vehicle course.

The last-mentioned parameter is the angle that the vehicle longitudinal axis encloses with the X axis of the factory coordinate system. The "course" is not necessarily the direction of travel since the steering wheel does not have to stand straight at the moment in question.

The vehicle system also contains a microprocessor and data storage device 19. The data stored before the start of a journey includes a train "map" in the form of the coordinates of the points A, B, C and D. The train can have sections in which a reduced Vehicle speed is required and the limit speed for each straight section (segment or vector) A to B etc. is prescribed and stored.

In addition to speed limits along each trajectory vector, the tolerances of a vehicle's lateral deviation from the trajectory may change from vector to vector. There is practically a “free” (freely available) web width for each vector, which the vehicle must not exceed, and this web width can change in vector transitions. For each vector, the web width is also saved before each trip.

The above information, orbit data (coordinates of transition points), allowable speed for each vector, and orbit width of each vector can be stored in the vehicle data memory by manually inputting a program or transmitted from a base station 15 to a communication antenna 17 on the vehicle T, the Antenna receives the data and transmits it to the vehicle data storage and microprocessor device 19. The transmission or communication unit can regularly transmit the current vehicle position to the base station or be queried for the same purpose.

The computing and processing operations carried out here are additionally explained below with reference to the following figures. Fig. 3 shows the vehicle navigation coordinates, where the position is given by the "factory" coordinates x and y, the vehicle course the angle \ y, i.e. the angle between the vehicle axis and the X axis, the forward speed V and the rotational speed, i.e. Angular velocity of the vehicle, U is.

Fig. 4 also shows the vehicle target coordinates. The target reflector R with the factory coordinates Xi and yi is determined at an angle 0 to the vehicle course, the vehicle itself at a certain time t the position coordinates x and y and has the course y.

Figure 5 shows the transition (junction) of two vectors where the free web widths determined by the stored data are the same. It is essential for «soft» operation that the path at vector transitions is continuous and not angled. Therefore, a curved path or a curved segment (curve) is calculated to adjust the intersection accordingly. Here, the curvature must be as small as possible, i.e. the radius of curvature should be as large as possible in order to keep the forces acting on the vehicle in the curve (turning) as small as possible and at the same time to ensure that the web width is nowhere smaller than the smaller of the two web widths. 5, the radius of curvature is therefore equal to half the common web width. According to FIG. 6, which shows vector transitions with different web widths, the adapted curves at points E and F each have a radius of pwa / 2 and pwb / 2.

7 illustrates in the form of a block diagram the navigation processing operations performed on the vehicle.

The data representing the coordinate points on the path and the path widths of the different path vectors are received and stored (21). The processor then calculates (23) the smooth curves required at the vector transitions based on the web widths, as previously mentioned. The curves with a constant radius shown in FIGS. 5 and 6 cannot be achieved in practice since the transition from a straight path to a circular path means an instantaneous change in the angular velocity from zero to a finite value and thus an infinitely high acceleration and force would. With an ideal curve, the curvature should increase and then decrease linearly.

This curve can be approximated by realizing the following equation:

x (a) = (l-a) 2Xi + 2a (l-a) x2 + a2X3 (1)

Where a is the fraction into which the turn is divided, i.e. Tenths, fifteenths or any other fraction,

x2 a vector representing the coordinates of a transition point,

x2 and i? 3 vectors representing the coordinates of the points at the beginning and end of the curve, and x the running vector representing the coordinates of the points on the curve after each fraction a.

By inserting tenths, two tenths, three tenths, etc. for a, the coordinates of successive points on the curve are obtained. This process is carried out in the device 23 in FIG. 7 with a value for a, which is determined in the manner explained below.

This principle of an incremental composition of the curves also applies to the straight sections, whereby for the coordinates of successive points on the straight section applies x (a) = (1 - a) xo + xi where xo and xi are the coordinates of points at the beginning and end of the straight section.

While the length of the straight sections can be approximately 20 to 30 m, each incremental vector can have a length of approximately 5 cm. The fraction a is then 1/500.

The incremental vectors are formed in a target bearing predictor 25 from the initial data (27), which represent the speed limit values for the different path vectors.

Each incremental vector is determined by the coordinates of the point (the "reference point") at its front end. The reference point is determined once per basic time period (at approximately 20 Hz), which is determined by a clock pulse generator of the system. Since the (maximum) speed for each vector is predetermined and the time period is fixed, the maximum length of each incremental vector is determined. The length of the incremental vector is therefore 5 cm at a speed of 1 m / s. After the maximum length has been determined in this way, it can be reduced somewhat to obtain an even number of incremental vectors in rail traffic, of which a represents the reciprocal.

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If the length of the incremental vector is chosen to be less than its maximum permissible value, the speed of the vehicle in this section of the path decreases accordingly. This results in a dynamic regulation of the speed.

When composing the curve in the manner mentioned by calculating successive reference points, the incremented reference course \ | / r is determined as the angle that the line between successive reference points includes the factory X-axis.

The reference points calculated in this way, which represent the desired path in contrast to the path actually tracked, are generated once per base time period and stored for comparison with the actual positions assumed by the vehicle. These actual positions are practical estimates that are determined by the dead reckoning device 35, 39 after checking and correction by the laser target reference system.

If the generated reference points run in front of the vehicle due to inertia, etc., the position difference between the last reference point and the vehicle can be regarded as a path error that the vehicle is trying to reduce. The greater this path error, the greater the speed of the vehicle should be (within the limit specified for the path vector or bend in question) in order to reduce it. Conversely, the speed should be reduced if the generated reference points are immediately in front of the vehicle position. This latter case occurs when the vehicle approaches a stop at the end of a path vector. The number of reference points that are "waiting" is therefore a measure of the required speed and the vehicle drive motor is controlled accordingly.

The generated reference points and the associated incremental reference course \ | / are passed for position and course error determination (29), one pair at a time.

The estimated value of the vehicle position and the vehicle course is determined by a Cayman filter device 37 according to FIG. 7. Target determination input signals 0 (FIG. 4), which were formed by the target determination device 33, are used. The signals represented by the vehicle and the steering angle are formed by the already mentioned converter 35 according to FIG. 7. The Cayman filter device 37 itself is shown in greater detail in FIG. 8.

8, the first process to be performed is to estimate the position and course at the end of a base period (At) from the actual or estimated forward and turning speeds of the vehicle during that period and the position at the beginning of that period.

The signals entered by the converter 35 in the position prediction process represent the steering angle 0 measured by the pivotable wheel and the path covered by the pivotable wheel (steering wheel), represented in the form of path counting pulses. The path increment and the increment At give the speed in the direction of the swiveling wheel, from which the forward speed V of the vehicle in its course direction is determined by multiplication by the cosine of the steering angle 0. The angular speed U of the vehicle is determined by multiplying the steering wheel speed by the sine of the steering angle 0 in accordance with the geometry of the vehicle wheels. The speeds V and U are calculated in each time period on the assumption that the speeds and the steering angle are constant in this (short) time period At.

The equations implemented in the process of the position predictor 39 according to FIG. 8 are derived below: For example, the following equations can be given for the rates of change of the position coordinates x and y and the course angle y using FIG. 3:

y = U

5 X = V COS \ | /

y = V sin co

Integrating these three equations over time At gives the following equations:

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\ | / (t + At) = v (t) + U-At x (t + At) = x (t) + V (sin (\ | / (t) + U- At) -sin (\ | / (t))) At / U * At y (t + At) = y (t) -V (cos (\ | / (t) + U-At) -cos (\ | / (t))) At / U-At

15 According to the first of these equations, the value y at time (t + At) is equal to the value of \) / at time t plus the angle through which the vehicle has turned in the time period At. In the second and third equations, t and (t + At) have the same meaning as in the first equation.

20 These equations can be rewritten for the estimates to:

<(jr (t + At | t) = <pr (t | t) + U-At x (t + A111) = x (t 11) + V (sin (<j> (t 11) + UA t) -sini |> (t | t)) / U 25 y (t + At jt) = y (t | t) -V (cos (\ jf (t 11) + UAt) -cos \ J / (t | t )) / U

The circumflex over a parameter denotes an estimate, and the symbol «11» means «evaluated at time« t ».

30 As can be seen, these equations are sufficient to estimate the position and course of the vehicle at the time (t + At) if the estimated position and the estimated course at time t are known. The output signals of block 39 are therefore the estimated coordinates x and y and the estimated course \ j / of the 35 vehicle after a further time period At, which apart from input variable 41 are based only on the dead reckoning system of the path covered and the angle passed.

4, the estimated angle of a target reflector R in the form of the vehicle course y and the coordinates of the vehicle and the target can be determined using the following equation:

0i (t + At 11) = tan "

[yi-y

Xi-X

• y (t + At | t)

■ x (t + At | t)

- i | / (t + At 11)

In this equation, 0; the estimated target angle at time (t + At), evaluated at time t. The coordinates Xi and yi of the target are predetermined by the arrangement of the targets on the factory Bo-50. The estimated values x and y of the vehicle and the estimated value \ | f of the course are determined in the process 39. The equation is thus processed in a target bearing predictor 43, which forms the output variable Si.

The output signal of the target error detection device 33 is a precise representation of the target angle 0i, which is compared with the estimated value 0i in a process 45 in order to determine a target estimate error 0i-0i.

This error signal is processed by a Kalman amplifier 47, which multiplies the error by Kalman gain 60 factors kr, kx and ky, respectively. The correction products are then added in a process 49 to the predictions of the dead reckoning position predictor 39 according to the following equations in order to obtain corrected estimates of the vehicle course and position:

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<j> (t + At | t + At) = v (t + At | t) + kr (0i — Sj)

x (t + At 11 + At) = x (t + At 11) + kx (0i — 0i)

y (t + At | t + At) = y (t + Atjt) + ky (0i-00

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The derivation of the Cayman correction products and the mode of action of the Cayman filters are specified in the book "Optimization of Stochastic Systems" by M. Aoki, published by Acade-mic Press 1967.

In this way, corrected estimates of the course and position at time (t + At), evaluated at that time, are determined from the estimates of the course and position, which were determined at time t and corrected by the Kalman filter process. These best estimates are entered in the error determination process in the Kalman filter device 37 according to FIG. 7 and also as “instantaneous” input variables 41 in the position predictor 39 according to FIG. 8 in order to predict the next reference point from these. Therefore, if one or more target reference corrections fail, for example because the targets are covered, then the next reference point is precalculated by means of dead reckoning from the last reference point at which a target determination correction was carried out.

The determination of path and course errors is described below with reference to FIG. 7. The two inputs to the process in predicator 39 are a) the generated sequence of reference points that define the ideal trajectory, and b) the best estimate of the course and the position of the vehicle determined by the Kalman process of FIG. 8.

FIG. 9 shows successive incremental vectors IVI and IV2 and their associated reference points RP1 and RP2, which were determined after the process in the reference point generator 25 (FIG. 7). Errors in the navigation of the vehicle T are shown in the form of the vertical distance de of the vehicle center from the local incremental vector and as an angle error 0e between the vehicle course and the direction of the local incremental vector.

These errors de and 0e are measured by transforming the actual value of the vehicle position in factory coordinates into a position in a vehicle reference frame in which the zero point with the reference point of the local incremental vector and the new X axis with the local one incremental vector coincides. This transformation is shown in Fig. 10, in which X and Y are the factory coordinate axes, X * and Y * are the vehicle frame axes, xr and yr are the coordinates of the local incremental vector reference point in the factory frame, x and y are the coordinates of the vehicle in the factory frame and x * and y * are the vehicle coordinates in the vehicle frame.

The angle * | / r is the course or the direction of the incremental vector relative to the factory frame. The following transformation equations can be derived from FIG. 9 by simple geometric considerations:

x * = (x-xr) cos \ j / r + (y-yr) sinyr y * = (y-yr) cos * | / r - (x-xr) sin \ | / r

In this vehicle reference frame, the distance or path error de is the y * coordinate of the vehicle center and the angle error 0C is the direct transformation angle \ | / r.

When the vehicle passes the local reference point xr, yr, the sign of x * changes from minus to plus. This change triggers deletion of the current vehicle reference frame and its re-formation in such a way that its zero point coincides with the following reference point and the x * axis with the next incremental vector. It can therefore be seen that the vehicle frame progresses synchronously with the vehicle.

The error values dc and 0e are therefore used to derive a steering angle setpoint signal 0d as a direct function of these error values (directly proportional to these error values). The nominal value of the angular velocity Ud is first determined as:

Ud = Kl de + Kz 0e in which Ki and K2 are gain functions (gain factors) that are determined by the dynamics of the vehicle itself. The setpoint of the steering angle is then calculated from the vehicle geometry and the setpoint of the forward speed of the vehicle.

As previously mentioned, vehicle speed is controlled by measuring the number of incremental vectors between the vehicle and the last one generated. The last one created always lies in front of the vehicle and seems to "move on", as if an elastic band connects the vehicle to the last determined reference position.

From a stationary position, the reference points are formed at a linear speed away from the "resting" station, so that they practically stretch the "elastic band" mentioned. The vehicle T is accelerated according to the distance from the last reference point and depending on its inertia and power, so that the error is gradually reduced until a steady state is reached in which the vehicle speed is equal to the propagation speed of the reference points.

The reference point speed, and thus the vehicle speed, can be changed dynamically during travel on a predetermined path by changing the increment length [i.e. by changing a in equation (1)] between successive reference points.

When the generation of increment vectors and reference points is completed, the last incremental vector ends at the last stop position, which is prescribed by the original path, which in turn is specified in coordinate position determination path vectors. The vehicle speed decreases with decreasing distance or path errors. By influencing the ratio of distance error to speed setpoint, the speed is regulated so that the end point is reached without overshoot. Here, too, the vehicle frame can be used immediately, since the x * coordinate is the path to be covered in the frame, and this can be monitored without further calculation.

In the above exemplary embodiment, the electromagnetic bearing device 33 is a laser system, by means of which a direction measurement is effected by means of an azimuthally scanning thin laser beam. Instead, however, radar beams can also be used, which enable an exact bearing using phase comparison methods. Furthermore, the reflectors can be replaced by transponders (answering devices) with coded emissions.

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Claims (13)

667 930 2nd PATENT CLAIMS 1. Vehicle control and guidance system with a vehicle having a motion drive (3, 7), a steering device (5, 9) for controlling the vehicle along a track, a dead reckoning device (35, 39) for calculating the position and the course of the vehicle on an incremental basis, means (19) for specifying a desired path (ABC) of the vehicle, means (29) for controlling the vehicle motion drive and steering means (3, 5, 7, 9) for guiding the vehicle along the desired path, one Means (43) for determining the bearing angle of the target (13) from the calculated position and the path of the vehicle, an electromagnetic bearing device (33) for determining the bearing angle of the reference target (13) relative to the vehicle, a device (45) for comparison the determined bearing angle (0;) with the predetermined bearing angle (0;) and a device (47, 49) for correcting the control of the vehicle motion drive and the steering ng of the vehicle depending on the bearing angle error (0i - 0i). 2. Installation according to claim 1, characterized in that the device (47, 49) for correcting the control comprises a Kalman filter device (37) for the formation of correction products, which are products of the bearing angle error and Kalman amplification factors in all Position coordinates and the vehicle course, and means for summing the correction products and the respective estimates of the position and the course, which are output by the dead reckoning device (35, 39), the sums forming the best estimates of the position and the course of the vehicle. 3. Installation according to claim 1, characterized in that the device (19) for specifying the desired path (AB-CD), a memory device (21) for storing the path in the form of a sequence of straight-line segments (EF) and a device (23) for converting the transition of the straight-line segments (EF) into continuously curved transition segments. 4. Installation according to claim 3, characterized by a device (27) for storing the permissible maximum vehicle speed and the permissible web width for each straight and curved segment depending on the local web conditions. 5. Installation according to claim 4, characterized in that the means (23) for converting the transition into curved transition segments means for calculating the radius (ra, rt,) of the curvature of a curved segment as not less than half the value of the web width (pwa) and, if there are different web widths at the transition (E), half the value of the larger of the two web widths. 6. System according to claim 2, characterized in that the dead reckoning device (35, 39) a device for estimating the position and the course of the vehicle after each sequence of time and path increments from the position and the course of the vehicle at the beginning of the increment and depending on the forward and rotational movement of the vehicle during this increment. 7. System according to claim 6, characterized by a target bearing predictor (25) for predicting the bearing angle of one of the reference targets from the vehicle on the basis of the estimated position of the vehicle and the last determined position of the reference target. 8. System according to claim 2, characterized by a device (33) for entering the best estimates in the dead reckoning device (35, 39) as a basis on which the estimate of the vehicle position and the vehicle course is determined at the next increment. 9. Installation according to one of claims 3, 4 or 5, characterized by a device (25) for sequentially generating the coordination of incremental reference points on the segments that define incremental vectors, the distance between these points being equal to the product of the maximum permissible speed for this segment and a base time increment. 10. System according to claim 2, characterized by a device (27) for storing a permissible maximum vehicle speed and a permissible path width for each of the straight and curvilinear segments depending on local path conditions, means (25) for sequentially generating the coordinates of incremental reference points the segments defining incremental vectors, the distance between these points being equal to the product of the maximum allowable speed for that segment and a base time increment, target error detection means (33) for comparing the best estimates of the vehicle position and course with the position and the Course of the next incremental vector and for generating path and course error signals and a device (28) for generating a steering angle setpoint signal as a function of the path and course error signals. 11. Plant according to claim 10, characterized in that the target error detection device (33) has a device for transforming the coordinates of the best estimates of the vehicle position and the course into a reference frame with a coordinate axis which coincides with a local incremental vector and has a zero point which coincides with the reference point to which the local incremental one Vector is directed. 12. System according to claim 10 or 11, characterized by a device (30) for forming a speed setpoint signal for the vehicle (T) depending on the number of reference points that are generated before the vehicle position. 13. System according to one of the preceding claims, characterized in that the direction finding device (33) a laser beam source (11) which effects an azimuthal scanning and a device for determining the bearing angle of a target reflector relative to the course of the vehicle (T) based on the direction of the reflected beam.