DE19816785C2 - Method for determining the position and / or guiding a moving object - Google Patents

Description

The invention relates to a method according to the preamble of claim 1 (US Pat. No. 4,727,492 A).

The invention is based on a method that is often used to determine the position of Ob projects or is used for guidance of vehicles without a guide wire. Such a vehicle has its own drive, steering facilities with sensors that monitor the environment capture the exercise of the vehicle and a computer that uses the sensor signals to control the Vehicle.

It is known to use laser navigation to guide vehicles. In U.S. 4,817,000 A the distances to at least three marks are measured with a laser scanner Positions are known. The position of the vehicle and its Rich angle can be calculated.

DE 39 30 109 C1 describes how the angle between the vehicle axle and the laser rays to be measured by the three marks. The brands are at an equal distance attached to a line.

In US Pat. No. 4,847,769 A, the angles are also measured with respect to a number of marks and with an estimate compared that are determined from dead reckoning. From the mistakes between the The measured and estimated angles are corrected using a Kalman filter calculated for the position and the direction angles. For this, the statistics need to be random Errors of the measured quantities must be known. For lack of better knowledge, you will be in a for the Calculation adopted in a workable form.

All of the above-mentioned methods assume that the acquisition of the measured variables from one and takes place from the same position of the vehicle, d. H. the vehicle movement is not taken into account does. In practice, however, this is only approximately permissible, since the vehicle with the The laser scanner moves and the laser can only rotate at a finite speed. Except this often requires a computational time that cannot be neglected for the evaluation, wäh rend that the vehicle covers a distance. Hence, each brand is in a different position recorded. The position errors are only then without taking into account the distance covered low when the vehicle speed is very low and the speed of the Laser scanner is great.

At higher vehicle speeds, however, this also requires a faster one Evaluation device which, due to the complexity of the algorithms, is always a complex computer system. This drives up costs.

No. 4,727,492 A discloses a method for determining the position and guiding a movable Known object with a laser scanner, which rotates around a vertical axis and the Angle to the marks recorded. In addition, a dead reckoning system is provided, which measures the distances between the scan positions, with the position and direction of the Scanners determined by means of the distances covered and corrected with the measuring angles will. Dead reckoning is generally done with incremental encoders and steering angle sensors carried out. Despite the higher effort, errors arise, e.g. B. by slip.

The invention is based on the object of providing a method of the type mentioned at the beginning improve that a position determination and / or guidance of a moving object is possible taking into account the distance covered. The procedure should be if possible get by with little effort and still be relatively accurate.

This object is achieved according to the characterizing part of claim 1. While that Moving an object, the scanner detects various reflective marks under corresponding ones Angles. During this movement he places a corresponding one between each measurement Way back. The position and / or direction calculation takes into account the distance covered Distance between the different scan positions. There is also a certain amount for the calculation If this time is necessary, the distance covered during the computing time can also be used route must be taken into account.

For the guidance of an object is not only the current position but also the direction of the property is important. The scanner is located on the object and is therefore with respect to it ne own axis and on the object axis in a known position. It will be after in the following it is assumed that the direction of the scanner is also used to guide the object or the object is determined, if this is necessary if necessary. In the following general my only spoken of positioning.

The advantages achieved by the invention are in particular that the routes can be detected more or less precisely and who is taken into account for the position of the scanner the. As a result, the position determination is much more accurate than with methods in which in principle it is assumed that during the measurement of the different measuring angles no distance is covered.

In principle, the distances between the scanning positions could also be made with wheel cremes talbers are recorded. However, some of these sensors are very expensive and complex Assembly. Furthermore, they fail when they hatch. Therefore it is beneficial to know the vehicle position more or less accurately estimate. According to claim 2, it is also possible to use the vehicle position to capture or estimate more or less precisely, if the distances between between the measuring angles cannot or cannot be detected directly. Under the assum me that the vehicle moves between the scan positions at approximately the same speed and direction somewhat uniformly and also moved roughly in the same direction or that z. B. the change in direction is uniform and so known when traveling in a circle, the Route continuation can be extrapolated from the old previous values.

The extrapolated values are checked or z. T. also corrected.

According to claim 2 it is generally assumed below that the object is a Vehicle is. This process is particularly interesting for so-called driverless transport vehicles. In internal transport, these vehicles often travel at 1 m / s. Laser scanners often rotate at about ten revolutions per second, so that im at least 100 mm can be covered. However, this route is not suitable for driving with millimeter accuracy more negligible. With the invention, however, it is possible with relatively simple to guide the vehicles with the required accuracy. In principle, scanners could use different frequencies and techniques are used. Laser scanners are, however very advantageous as they are very accurate and relatively inexpensive.

Errors in the underlying speed or direction lead, in particular, to length ren driving distances to a no longer negligible inaccuracy in the Positioning. Much better values are obtained again when the vehicle drives very slowly or even stops.

With the method according to claim 3, new ones can also be used in an existing system previously unknown brands are measured. Assuming the scanner Cannot measure distances directly, the angle to the new mark must be at two or more points measured from the desired route or other known measuring points will. The data can therefore be relative in relation to the route or absolute in relation to a Coordinate system can be detected. In principle, the calibration can be carried out during a so-called teach be done in-drive. The vehicle is then usually guided on this teach-in route. It It is of course also possible to program or control the vehicle so that it is controlled by the Teach-in distance deviates.

According to claim 4, the measuring angles do not have to be taken from three different brands will. In principle, it is also possible for the position of the vehicle to be more or less is determined or estimated when the vehicle is out of driving after the next Rotation of the scanner measures the angle at the same mark. In extreme cases, during while driving, the angles are always measured to the same mark. This can then be used in one to a certain extent the deviations from the position are checked.

Embodiments of the invention are shown in the following drawings and are described in more detail below. Show it

Fig. 1, the variables and parameters for determining the position in motion,

Fig. 2 is a functional structure of the system,

Fig. 3 shows the positioning of new brands,

Fig. 4 Estimation of the position at a single mark,

Fig. 5 Estimation of the position without a distance measuring device.

The essential fundamentals of the measurement method are illustrated in FIG. 1. For the sake of simplicity, it is assumed below that the object is a vehicle and that the distances covered by the vehicle are ideal straight lines.

A scanner 3 located on a vehicle (not shown further) moves through points P ₁ to P ₄ . The continuously revolving scanning beam detects the vehicle axis at point P _1, the mark M ₁ , at the measurement angle θ ₁ , at the position P _2, the mark M ₂ under the measurement angle θ ₂ and at position P _3, the mark M ₃ below the measuring angle θ ₃ . The position P ₃ can be calculated according to the invention if the three angles θ ₁ , θ ₂ and θ ₃ between the direction of movement of the vehicle and the marks and the distance between the points P ₁ , P ₂ and P ₃ , given by the distances s ₁ and s ₂ , are known. The distances s ₁ and s ₂ can be estimated. Since computing time is required to determine the result, it is only available at point P ₄ . But since the vehicle speed and the computing time are known or can be easily determined, the distance s ₃ or point P _{4 can be} determined.

The three scanning beams do not intersect in one point, but in A, B, C, which the Zwi between angles α and β are assigned. The path of the scanner in the considered section has the direction angle ϕ with respect to the x-axis of the reference system. The task of the Position system is to determine the x and y coordinates of the scanner as well as this Directional angle ϕ.

This task is solved analytically here. To do this, the following variables must be known:

• - the route sections s ₁ , s ₂ and s ₃
• - the positions of the brands M ₁ , M ₂ and M ₃
• - the scanning angles θ ₁ , θ ₂ and θ ₃ measured by the scanner.

The brand positions are known a priori because they are fixed brands. The Strec kenanschnitte s ₁ , s ₂ and s ₃ must be estimated during the scanning process. Here s _{3 means} the route section that the vehicle covers while evaluating the data. The position is therefore only available at point P ₄ .

In any triangle, the sides a, b, c and the angles η ₁ , η ₂ and η ₃ can be calculated if the coordinates of the corner points are known. The points M ₁ , M ₂ and M ₃ mean three retroreflective marks whose coordinates (x ₁ , y ₁ ), (x ₂ , y ₂ ) and (x ₃ , y ₃ ) are known in the Cartesian coordinate system.

With the coordinates of the marks M ₁ , M ₂ and M ₃ , the sides a, b and c as well as the angles η ₁ , η ₂ and η ₃ can be calculated as follows:

In the triangle M ₁ M ₂ M ₃ applies

Using the measured angles θ ₁ and θ ₃ as well as the distances s ₁ and s ₂ , the side P ₃ B of the triangle P ₁ P ₃ B can be calculated. According to the sine law, the following applies

The calculation is only for angles θ ₃ - θ ₁ ≠ 2. n. π is possible because for n = 0, 1, 2, 3. . . division by zero takes place. In addition, only the calculation of η _{7 is} required to determine the position of P _3. With the help of η ₆ , however, a quick check of the calculation results is possible, please include, since the sum of the angles in each square is 2π, ie in the square M ₁ M ₂ M ₃ B applies

η ₂ + η ₆ + η ₇ + α + β = 2π. (4)

Fig. 1 also shows the need for the calculation of η η ₆ and ₇ sizes.

a = M₁M₂ m = M₂P₂ α = θ ₂ - θ ₁ (5a)

b = M₂M₃ t = AC β = θ ₃ - θ ₂ (5b)

c = M₁M₃ n = AP₂ α + β = θ ₃ - θ ₁ (5c)

With the help of the law of sine the following relationships result:
In the triangle M ₂ M ₃ A applies

and thus

In the triangle M ₁ M ₁ C applies

and thus

From the two equations for m one obtains a determining equation for t = CA:

From Eq. (4) either η ₆ or η _{7 can be} optional:

η ₆ = 2π - (α + β + η ₂ + η ₇ ) (7)

η ₇ = 2π - (α + β + η ₂ + η ₆ ) (8)

The following mathematical relationships are used for the sine:

sin (2π - x) = -sinx

sin (x + y) = sinxcosy + sinycosx (9)

If η _{6 is replaced} in Eq. (6), the following relationship is obtained:

With the help of Eq. (9) becomes from it

The sine and cosine _{terms of η 7} are combined

The angles α and β are according to Eq. (5a and b) determined by the measured angles θ ₁ , θ ₂ and θ ₃ . The distance t can now be calculated from the measured quantities s ₁ and s ₂ as well as the three angles θ ₁ , θ ₂ and θ ₃ . It follows from the triangles P ₁ P ₂ C and P ₂ P _{3 A}

Thus, from Eq. (12) the angle η ₇ , can be calculated. Eq. (12) has the form

t = G. sinη ₇ + H. cosη ₇ (14)

with

Eq. (12) has two solutions for η ₇

The decision as to which of the two solutions to use can be made using the angle η ₆ . With Eq. (8), Eq. (10) can be written as follows:

This leads to a determining equation for η ₆

This equation now has the form -t = J. sinη ₆ + K. cosη ₆ with the parameters

The two solutions for η ₆ are

From the solutions for η ₆ and η ₇ , Eq. (4) the right ones selected.

The further calculation then takes place in the triangle M ₁ M ₃ B. Here the distance M₃B is calculated with the sine law in the triangle M ₁ M ₃ B.

This allows the distance M₃P₃ according to the relationship

M₃P₃ = M₃B - P₃B (20)

to calculate. The Eqs. (19) and (3) are used.

The sum of the angles in the triangle M ₃ DE gives:

It follows:

The angle ϕ ₄ results from

ϕ ₄ = η ₇ - η ₃ - ϕ ₃ (23)

Since the coordinates of the mark M _{3 are} known, it is sufficient to calculate the following differences:

Δx = M₃P₃sinϕ ₄ Δy = M₃P₃cosϕ ₄ (24)

The coordinates you are looking for are closed

x _P3 = x ₃ - Δx y _P3 = y ₃ - Δy (25)

The coordinates of the vehicle at point P ₄ after completion of the calculations can now be found from the vehicle speed v and the computing time t _r and the angle ϕ:

This results in the coordinates of point P ₄ in the form

x _P4 = x _P3 + v. t _r . cosϕ y _P4 = y _P3 + v. t _r . sinϕ (27)

Fig. 2 shows a functional structure of the system for position determination and Winkelbestim determination. The scanner 3 detects n scan angles θ _i (but at least 3) to n marks. In the brand evaluator 2 , all possible brands are read from the list of the brand memory 1 and then the cheapest three brands are selected and the position _{data of these three brands M 1,} M ₂ and M ₃ including the associated scan angles θ ₁ , θ ₂ and θ _{3 passed} to the position determination 6 for the analytical determination of position and direction angle. In principle, it is possible for the scanner 3 to determine the distances s ₁ , s ₂ and s ₃ in distance measurement 5 using a distance measurement method, e.g. B. counting the wheel increments 8 with wheel sensors. The disadvantage, however, is the increased effort. In general, it can be assumed that the vehicle, not shown here, or the scanner 3 here, is moving in the same way as before due to the inertial mass, the relatively low speed and the relatively fast mark detection. For short scan times, the route sought can be determined relatively precisely by multiplying the old speed with the scan time, so that the distance measurement 5 and the wheel increments 8 are then no longer required.

The estimated routes are managed in position determination 6 . It first calculates the position of the system at point P ₃ on the basis of analytical equations and then extra polishes the position data on point P _{4 on the basis of the direction angle and the distance s 3} . The exact coordinates x, y and the direction angle ϕ are available for this point P _4. The data are made available to a vehicle controller 10 via a data interface.

To identify and optimally select the marks, the mark evaluator 2 uses the position of the scanner that the position determination 6 determined in the previous calculation. At the start of operation, the starting position x _a , y _a and ϕ _{a is} therefore the system from the outside, z. B. via a control terminal 9 , passed.

In addition to the scanner 3 , the functional structure according to FIG. 2 also consists of further modules. In practice, the assignment of functions is fluid. It has advantages to use extra computers for the vehicle control and the operating terminal. Thus, the functions of mark evaluator, mark memory, path measurement and position determination are carried out by the computer for position and direction determination. Of course, other assignments are also possible.

The position of not yet registered marks can be determined as shown in FIG. 3. The mark is preferably measured while the scanner is standing at the two scan positions P ₁ and P ₂ , the coordinates of which and thus the distance s are known, at the angles θ ₁ , θ ₂ . Then the coordinates x _m , y _{m of} the mark M result from the following calculation:

k = s - 1 (28)

1 . tanθ ₂ = k. tan (π - θ ₁ ) (29)

It then follows

Analogously to this results

In the triangle, the following applies in general

h ² = 1. k (32)

so that the side f results over the Pythagoras

f = √k² + h² (33)

The coordinates of point M can now be calculated as follows:

x _m = x ₁ + f. cos (ϕ + θ ₁ - π) y _m = y ₁ + f. sin (ϕ + θ ₁ - π) (34)

Fig. 4 shows that the position can be determined even when two or even all three measurement angles to while driving with respect to a mark M to be measured. One must then assume, however, that one can determine the routes according to their lengths and directions by a reliable assumption.

It can be seen that the angles θ change if the roadway would run through the points P _1P to P _{4P instead of through the desired points P 1} to P _4. The angles θ change in the same way if the direction of the roadway is _{rotated in P 1} , so that the twisted roadway would run through the points P ₁ , P _2D , P _3D , P _4D . Such errors could be detected.

The situation is different, however, if the route rotated around the mark M as the center point. It then runs through P _1K to P _4K . Such an error could not be detected. Since all angles θ _{1 are the} same as the angles θ _1K , the vehicle would then drive in the wrong direction. A prerequisite for this, however, is that both the position and the direction have _{already been incorrect in P 1K.}

In practice, you can use a single brand as an alternative, up to one or more other brands appear that allow a more reliable position fix to be performed can be.

FIG. 5 explains that in many cases it is possible to drive with sufficient precision even without distance measuring devices.

The travel of the vehicle begins in P ₁ with the coordinates Y ₁ , X ₁ , and the measurement angle θ ₁ with respect to the mark M ₁ .

With the ideal course of the target route, the vehicle would measure the mark M _{2 after s 1s} in P _2s with the angle θ _2s. After continuing the journey with the desired route s through point P _3s , the vehicle finally arrives at the desired point P _{4s after route s 3s} . In P _3s the scanner will read the mark M ₁ at the angle θ _3s.

The desired target positions can be checked to a certain extent. Assuming that the direction of travel was correct, but the length of the distance s _{1s was} estimated to be too short, the mark M _{2 is} measured at point P _2R at an angle θ _2R which is smaller than θ _2s .

The situation is different if, in this unfavorable position of the mark M ₂ , the length of the route s _{1s is} equal to s _1i , but the vehicle moves from the ideal lane z. B. deviates to the right. At point P _2l , mark M ₂ is measured at approximately the same angle θ _2l as in _{setpoint position P 2s} at angle θ _2s . The deviation could not yet be detected with this measurement.

Assuming that the vehicle maintains the same directional error to the right, it would at the correct length of the path _2l s (corresponding to the length of segment s _2s) closing Lich arrive at the point P _3l. The deviation can be determined here, however, since the angle θ _3l at which the mark M _{1 is} measured is greater than the angle θ _3s . The result is available when the vehicle has reached position P _4l .

Because the errors are detected, the actual actual position of the vehicle can ge can be calculated more precisely. This applies even if there is no measuring device available.

Claims (4)

1. A method for determining the position and / or guiding a moving object using stationary reflective marks and a scanner with a computer on the object, wherein

• - the beam of the scanner rotates around a vertical axis and records the angles to the marks,
• - the distances between the scan positions at which the angles were measured are estimated, characterized in that,
• - That the position of the vehicle is initially known and the vehicle continues to move substantially at an undiminished speed and in a known direction or that changes in speed and / or direction are known, so that the distances between the scan positions and those covered during the computation time Distance can be estimated and
• - That thus the position and / or direction of the scanner is determined without a measuring device.

2. The method according to claim 1, characterized in that

• - that a token memory holds the location data of the tokens,
• - that the scanner is a laser scanner,
• - That the object is a vehicle and
• - that the scanner is firmly mounted on the vehicle,
• - That the position and / or direction determination of the scanner by means of the estimated distances is only carried out as an aid until the vehicle itself can carry out a reliable position and / or direction determination at a standstill or when driving very slowly.

3. The method according to any one of the preceding claims, characterized in that

• - That the position of unknown marks can be determined by the scanner and added to the database in the mark memory.

4. The method according to any one of the preceding claims, characterized in that

• - That at least two of the three measuring angles are measured and used one after the other with respect to the same mark to determine the position of the scanner.