JPH0546241A - Steering controller for autonomously travelling vehicle - Google Patents

Abstract

PURPOSE:To provide the steering controller of an autonomously travelling vehicle which can perform the general purpose application to a real road having various curvatures. CONSTITUTION:By an image pick-up means (e) provided in the front part of a vehicle (a), the road surface in the forward direction of the vehicle (a) is photographed, and based on the road surface image, the position of reference lines (b) and (c) provided in the right and left is counted by an image processing means (f). Next, based on the position of the reference lines (b) and (c) obtained by the image processing means (f), a travelling channel in which at the time of the turning of the vehicle (a), the side part of the vehicle (a) becomes the tangent direction near an inside reference line (b) is obtained, a steering angle signal to travel the vehicle (a) along the travelling channel is counted by a steering control means (g) and in accordance with the steering angle signal obtained by the steering control means (g), the steering device of the vehicle is driven by a steering driving means (h).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autonomous vehicle which is self-propelled along a reference line such as a white line (center line) provided on a road surface, and more specifically, to steering control of the autonomous vehicle. Regarding the device to perform.

[0002]

2. Description of the Related Art As a conventional autonomous vehicle, a road surface in front of the vehicle is photographed by an image pickup device, and a reference line such as a center line provided on the road surface is extracted from an image of the image pickup device by image processing. Set the travel target point along the reference line,
There has been a technique in which the steering angle is determined so that the vehicle travels toward this traveling target point (see Japanese Patent Application Laid-Open No. 2-48708).

In the example disclosed in Japanese Unexamined Patent Publication No. 2-48708, the traveling target point is set inward by a predetermined distance from the reference line at the left end, or when the width of the road is narrow, the traveling target point is set at the center of the road. The steering angle is set so that the vehicle travels toward the travel target point. Furthermore, when traveling on a winding road when the vehicle speed is in a high speed region exceeding a preset threshold value, as shown in FIG. 10, the lateral acceleration acting on the vehicle is reduced as much as possible. The running target point OC with a gentle curvature was set.

[0004]

However, in the above-mentioned conventional autonomous vehicle, only the reduction of the lateral acceleration acting on the vehicle when traveling at a high speed on a winding road is taken into consideration. Since the travel target point OC having a gentle curvature is set, the route on which the vehicle actually travels may exceed the reference line such as the center line or the roadway boundary line. Therefore, the conventional autonomous vehicle is
It was difficult to apply to actual roads with various curvatures.

An object of the present invention is to provide a steering control device for an autonomous traveling vehicle which can be applied to an actual road by setting a traveling route that does not exceed the inner reference line when the vehicle turns. It is in.

[0006]

The invention will be described with reference to FIG. 1, which is a diagram corresponding to claims, in which the present invention is an autonomous vehicle that travels along a traveling path d defined by at least two reference lines b and c on the left and right. It is applied to the steering control device of the traveling vehicle a. Then, the above-mentioned purpose is to image capturing means e for capturing the road surface in front of the vehicle a, and image processing means f for calculating the positions of the reference lines b and c based on the image obtained by the image capturing means e.
Based on the positions of the reference lines b and c obtained by the image processing means f, the vehicle a travels such that the side portion of the vehicle a is in the tangential direction near the inner reference line b when the vehicle a turns. Steering control means g for obtaining a route and outputting a steering angle signal for causing the vehicle a to travel along the traveling route, and steering drive means for driving a steering device according to the steering angle signal obtained by the steering control means g. It is achieved by providing h and.

[0007]

The image pickup means e photographs the road surface in front of the vehicle a, and the image processing means f calculates the positions of the reference lines b and c provided on the left and right sides of the image based on the road surface image. Steering control means g
Based on the positions of the reference lines b and c obtained by the image processing means f, when the vehicle a turns, the side portion of the vehicle a is in the tangential direction in the vicinity of the inner reference line b. Then, a steering angle signal for causing the vehicle a to travel along this travel route is output, and the steering drive means h drives the steering device according to the steering angle signal obtained by the steering control means g.

[0008]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a block diagram showing an embodiment of a steering control device for an autonomous traveling vehicle according to the present invention, and FIG. 3 is a schematic diagram showing an appearance of the autonomous traveling vehicle.

In FIG. 3, reference numeral 1 is an autonomous vehicle (hereinafter,
This vehicle 1 captures an image of the road surface in front of the vehicle by an image pickup device 2 provided at the front of the vehicle 1 and detects white lines (reference lines) 3 drawn at both ends of the road surface.
By setting the traveling target point along the white line 3 and controlling the steering, the vehicle travels along the white line 3 by itself.

The vehicle 1 has an image pickup device 1 as shown in FIG.
0, an image processing device 11, a map information device 12, a travel control device 13, a steering control device 14, and a steering control device 15.

The image pickup device 10 is, for example, a TV camera,
As described above, the road surface image that is fixed to the front part of the vehicle 1 and is in front of the vehicle 1 is captured. The photographed road surface image data is sent to the image processing apparatus 11.

The image processing device 11 extracts the white lines 3 drawn at both ends of the road surface from the road surface image data sent from the image pickup device 10 by a known image processing method, and the position of the white line 3 in this image. Based on, the distance from a predetermined front gazing point provided in front of the vehicle 1 to the white line 3 and the inclination of the white line 3 with respect to the vehicle 1 at this front gazing point are calculated. The method of extracting the white line 3 and the method of measuring the distance and the inclination from the front gazing point to the white line 3 are well known,
The description is omitted. The calculated white line distance data and white line inclination data are sent to the steering control means 14.

The map information device 12 stores data such as map data on routes to be traveled. This map data includes, for example, data such as nodes and paths on the road. A node is a boundary point between a straight line portion and a curved line portion of a road, and a path is a distance between adjacent nodes.

The traveling control device 13 determines route data according to the designated route based on the data stored in the map information device 12. This route data includes, for example, traveling vehicle speed, traveling distance, traveling route (where to turn at a branch point), turning radius of a curved portion, and the like. The determined route data is sent to the steering control device 14.

Based on the route data output from the traveling control device 13 and the white line data output from the image processing device 11, the steering control device 14 multiple regressions the steering angle when traveling along the designated route. Calculated by analysis.
The calculated steering angle command value is sent to the steering drive device 15.

The steering drive device 15 operates the actuator in accordance with the steering angle command value obtained by the steering control device 14 to drive the steering device.

In the correspondence between the embodiment and the claims, the white line 3 is the reference line, the image pickup device 10 is the image pickup means, the image processing device 11 is the image processing means, and the steering control device 14 is the steering control means. The steering driving device 15 constitutes steering driving means.

Next, the operation of this embodiment will be described. Figure 4
FIG. 6 is a diagram showing a data flow in the present embodiment. In FIG. 4, the white line data (x, θ) calculated by the image processing means 11 is sent to the steering control device 14, and the standard target point distance T and the limit target point distance W are calculated based on the white line data. 14 is calculated. These standard target point distance data T and limit target point distance data W,
Then, based on the white line inclination data θ, the traveling target point distance t at the forward gazing point ahead of L [m] is calculated by the steering control device 14. Then, the steering angle S (x, t) is calculated by the steering control device 14 based on the travel target point distance t and the white line distance data x.
Is sent to the steering drive device 15. Hereinafter, each of the calculation procedures will be described, but the description of the white line data calculation method will be omitted as described above.

(1) Standard target point, limit target point The present embodiment is characterized in that steering control is performed so that the side portion of the vehicle 1 does not cross the white line 3 on the inside when the vehicle 1 is turning due to the difference in the inner wheels. That is the point. Therefore, the conditions for the vehicle 1 not to cross the inner white line 3 when turning will be examined with reference to FIG.

FIG. 5A shows the case where the curve radius r ₁ of the white line 3 is small, and FIG. 5B shows the case where the curve radius r ₂ is large. Now, when the center of the vehicle is the center of the front tires,
As shown in FIG. 5, assuming that the side of the vehicle 1 travels along the tangent to the inner white line 3, the front wheel center O
_1, the distance w ₁ from O ₂ to the white line 3, w ₂ are _{w 1 = (k / sinα)} -r 1 w 2 = (k / sinβ) -r 2 (k: front wheel - tread between the rear wheels, alpha , Β: steering angle) (in this case, w ₁ > w ₂ since the curve radius connecting the innermost portion of the vehicle and the center of the curved road is r 2> r ₁ ). Here, the front wheel centers O ₁ and O ₂ and the curve center O of the white line 3
An intersection P of the line connecting the line (that is, the radius of the white line 3) and the white line 3
_1, the tangent c _1, the angle between c ₂ white lines 3 in P ₂ (tangent angle), the steering angle as shown in FIG. 5 alpha, because equal and β is geometrically be demonstrated, using the relationship When the distance w is expressed by a general formula, w = (k / sin Θ) -r (1) (Θ is a tangent angle, that is, the inclination of the white line 3). This distance w is set as the limit target point distance W.

On the other hand, when the vehicle 1 travels straight, it is set to travel in the center of the traveling path, and the average value of the distance data of the white lines on the left and right of the vehicle 1 is set as the target point distance of the vehicle 1. Let this distance be the standard target point distance T.

(2) Travel Target Point FIG. 6 is a diagram for explaining the procedure for setting the travel target point when the vehicle 1 is turning. In FIG. 6, if the standard target point distance T is the traveling target point distance t, the vehicle 1
Indicates that the vehicle travels with the traveling target point set on the route indicated by the dotted line in the figure, but in the present embodiment, when the vehicle 1 turns, the vehicle approaches the inner white line 3 gradually and demarcates the middle point of the curved portion. Then, this time, the traveling target point is set on a route (one-dot chain line in the figure) that gradually moves away from the inner white line 3.

Now, let us consider a case where the vehicle 1 is traveling from a straight portion to a curved portion of a traveling path as shown in FIG.
A plurality of forward gaze points, for example, d in front of the traveling direction of the vehicle 1.
_{If i−1} , d _i , and d _{i + 1} are set and the traveling target point T _g is provided in the lateral direction at the front gazing point d _i , the distance from the traveling target point T _g to the inner white line 3 ( Hereinafter, the running target point distance) t (n) is given by the following equation. t (n) = T- | [{θ (i) -θ (i-1)} + {θ (i + 1) -θ (i)}] / 2 ｜ × ε (t (n)> W + γ) (2) t (n) = W + γ (t (n) ≦ W + γ) (3) (where | X | represents the absolute value of X) where θ (i-1 ), Θ (i), and θ (i + 1) are tangent angles of the white line 3 at the respective forward gaze points, γ is an offset value, and ε is a proportional constant.

The equation (2) is a difference (differential) equation, and when the traveling road is a straight line portion, the differential value of the tangent angle (that is, the inclination) of the white line 3 is 0, so t (n) = T. However, t (n) <T becomes closer to the entrance of the curved portion, and the traveling target point T _g gradually approaches the inner white line 3. Further, since the differential value of the tangent angle of the white line 3 is determined by the curvature of the curve, if the curvature of the curve changes, t (n) also changes accordingly. Then, t (n) increases as the traveling road approaches the exit of the curved portion with the middle point of the curved portion as a boundary, and the traveling target point T _g gradually deviates from the inner curve 3 and again t (n) in the straight portion. ) = T.

When t (n) = W + γ, when viewed in plan from above the vehicle 1, its side portion contacts the inner white line 3. Therefore, if t (n) becomes smaller than W + γ in equation (2),
(3) limit is applied to the travel target point T _g is not approach more inward white line 3 by formula.

The curve radius r of the white line 3 in the equation (1) is
Is distance data x (i-1), x (i + 1) and inclination data θ (i-1), θ (i + 1) of the white line 3 at the forward gazing points d _i-1 , d _{i + 1} .
However, the calculation procedure is omitted.

(3) Steering Angle In this embodiment, the steering angle S is calculated by multiple regression analysis. Since the present inventor has already applied for the details (Japanese Patent Application No. 3-68571), only the outline thereof will be described in the present embodiment.

In the curved portion of the traveling road, the change in the steering angle appears as a similar change after the change in the distance data of the white line 3 in front of the vehicle. Therefore, an appropriate value can be obtained by estimating the steering angle S after a predetermined time by the multiple regression analysis based on the change in the distance data of the white line 3 at that time. This data can be defined infinitely in the multiple regression equation, but as a result of the experiment, present, past (1), and past (2)
Has been confirmed to be sufficient. Therefore, the values to be input are the current white line distance data x (n), the data x (n-1) one control cycle before and the data x (n-two control cycle before.
2). In this case, the relational expression (regression function expression f) indicating the steering angle S after a predetermined time is: S = k ₁ × (x (n) -t) + k ₂ × (x (n-1) -t) + k ₃ × (x (n-2) -t) = k 1 × x (n) + k 2 × x (n-1) + k 3 × x (n-2) + d ...... (4) ( where, k _1, k ₂ , k ₃ , d are constants, and n is a discrete time). These constants are derived by the multiple regression analysis method based on the actual white line distance data and the actual steering angle.

7 to 9 are diagrams showing simulation results of steering control by the present inventor. As a condition,
Road width is 4 [m], radius of curvature r = 15 [m], vehicle speed is 10
[km / h], and simulations were performed for three types of t = 2, 4, 0 [m]. As shown in these figures, t
It can be understood that the vehicle is running faithfully at the designated position of t simply by changing the value of.

Therefore, according to the present embodiment, when the vehicle 1 is turning, the steering control is performed so that the side portion of the vehicle 1 contacts the inner white line 3. Therefore, even when the vehicle 1 is traveling on a winding road as in the conventional case. Moreover, the route on which the vehicle travels does not exceed a reference line such as a center line or a roadway boundary line, and therefore, the present invention can be applied to an actual road or the like in which the curvature changes variously.

Moreover, as compared with the case where the vehicle is simply driven in the middle of the road, the route in the curved portion becomes closer to a straight line, and it is not necessary to set a large steering angle in the curved portion. Power can be lowered. Therefore, the lateral acceleration of the vehicle 1 at the time of turning can be reduced, and the traveling speed at the time of turning can be increased to the limit of the vehicle stability range. Further, the traveling distance can be shortened as compared with the case of traveling in the middle of the road, which is also effective for energy-saving traveling.

The details of the steering control device for an autonomous vehicle according to the present invention are not limited to the above-described embodiment, and various modifications are possible. As an example, in the above-described embodiment, only the steering angle of the steering device is controlled,
It is also possible to control the vehicle speed by using the inclination data of the white line. For example, if the vehicle speed is v and the standard vehicle speed is V, then v = V- | [{θ (i) -θ (i-1)} + {θ (i + 1) -θ (i)} / 2] | × ε ′ (v> 0) (5) (where ε ′ is a proportional constant), the vehicle speed v can be controlled. As is apparent from the equation (5), the vehicle speed v is v = V when the vehicle 1 is traveling on a straight line portion, and the vehicle speed decelerates gradually as it gets closer to the curved line entrance, When approaching, it accelerates again and becomes v = V.

[0033]

As described in detail above, according to the present invention, when the vehicle turns, the vehicle is caused to travel along a traveling route in which the vehicle side portion is in the tangential direction in the vicinity of the inner reference line. Since such steering control is performed, it can be applied to an actual road or the like whose curvature changes variously. Moreover, as compared with the case of simply traveling in the middle of the road, the route at the time of turning becomes closer to a straight line, and it is not necessary to set a large steering angle, so that the steering holding force at the time of turning of the vehicle can be reduced. Therefore, the acceleration acting in the lateral direction of the vehicle at the time of turning can be reduced, and the traveling speed at the time of turning can be increased to the limit of the vehicle stable range.
Further, the traveling distance can be shortened as compared with the case of traveling in the middle of the road, which is also effective for energy-saving traveling.

[Brief description of drawings]

FIG. 1 is a diagram corresponding to a claim of the present invention.

FIG. 2 is a block diagram showing a circuit configuration of a steering control device for an autonomous traveling vehicle that is an embodiment of the present invention.

FIG. 3 is a schematic view showing an appearance of an autonomous vehicle.

FIG. 4 is a diagram showing a data flow of one embodiment.

FIG. 5 is a diagram for explaining a method of calculating a limit target point distance.

FIG. 6 is a diagram for explaining a method of calculating a travel target point distance.

FIG. 7 is a diagram showing a simulation result of vehicle steering control according to an embodiment.

FIG. 8 is a view similar to FIG. 7.

9 is a view similar to FIG. 7. FIG.

FIG. 10 is a diagram showing an example of setting positions of target traveling points in a conventional autonomous vehicle.

[Explanation of symbols]

 a vehicle b, c reference line d traveling path e imaging means f image processing means g steering control means h steering driving means 1 autonomous traveling vehicle 2, 10 imaging device 3 white line 11 image processing device 12 map information device 13 traveling control device 14 steering Control device 15 Steering drive device

Claims (1)

[Claims] 1. A steering control device for an autonomously traveling vehicle that travels along a traveling path defined by at least two left and right reference lines, the imaging means capturing an image of a road surface in front of the vehicle, and the image capturing means. Based on the image obtained, based on the position of the reference line obtained by the image processing means for calculating the position of the reference line, the image processing means,
Steering control means for determining a traveling route such that the vehicle side portion is in the tangential direction in the vicinity of the inner reference line when the vehicle is turning and outputting a steering angle signal for traveling the vehicle along the traveling route; A steering control device for an autonomous traveling vehicle, comprising: a steering drive device that drives a steering device according to a steering angle signal obtained by the steering control device.