JP2803404B2 - Steering control device for autonomous vehicle - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an autonomous vehicle that travels unmanned and autonomously along a reference line such as a white line (center line) provided on a road surface. Related to 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 a travel target point along the reference line,
In some cases, the steering angle is determined so that the vehicle travels toward the traveling target point (see Japanese Patent Application Laid-Open No. 2-48708).

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

[0004]

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

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

[0006]

According to the present invention, an autonomous vehicle traveling along a traveling path d defined by at least two reference lines b and c is described. This is applied to the steering control device of the traveling vehicle a. The above-mentioned object is achieved by an image pickup means e for photographing a road surface ahead of the vehicle a, an image processing means f for calculating the positions of the reference lines b and c based on the image obtained by the image pickup means e, Based on the positions of the reference lines b and c obtained by the means f, the vehicle
a) setting a plurality of target points at a predetermined distance in front of
The tangent angle of a predetermined point on the inner reference line b corresponding to the target point
Based on the calculated tangent angle, the vehicle a is positioned on the inner reference line.
When traveling along the tangential direction of b, the vehicle a
Limit target point distance so as not to protrude from line b
Calculate the separation, and set a plurality of target points and predetermined points on the inner reference line b.
And a predetermined point on the inner reference line b
A traveling route is determined so that the distance becomes the limit target point distance, and a steering control unit g that outputs a steering angle signal for causing the vehicle a to travel along the traveling route; and a steering angle signal obtained by the steering control unit g. This is achieved by providing a steering driving means h for driving the steering device accordingly.

[0007]

The imaging means e photographs the road surface ahead 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 based on the road surface image. Steering control means g
Are located at a predetermined distance in front of the vehicle a based on the positions of the reference lines b and c obtained by the image processing means f.
A point on the inner reference line b corresponding to the target point
Calculate the tangent angle of a fixed point. And based on this tangent angle,
Vehicle a along the tangential direction of the inner reference line b.
Vehicle a does not protrude from the inner reference line b when
Calculate the limit target point distance to perform. In addition, multiple
On a line connecting the target point and a predetermined point on the inner reference line b
The distance to a predetermined point on the inner reference line b is the limit target point distance.
A steering route is determined so as to be separated, and a steering angle signal for causing the vehicle a to travel along the traveling route is output. Drive.

[0008]

Embodiments of the present invention will be described below 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 denotes an autonomous vehicle (hereinafter referred to as an autonomous vehicle).
The vehicle 1 detects a white line (reference line) 3 drawn at both ends of the road surface by photographing a road surface in front of the vehicle with an imaging device 2 provided at a front portion thereof.
By setting a traveling target point along the white line 3 and performing steering control, the vehicle travels along a path along the white line 3 by itself.

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

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

The image processing device 11 extracts white lines 3 drawn at both ends of the road surface by a known image processing method from the road surface image data sent from the imaging device 10, and the position of the white lines 3 in this image. Is calculated 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 the front gazing point. Note that a method for extracting the white line 3 and a method for measuring the distance and the inclination from the forward fixation 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 a route to be traveled. This map data includes, for example, data on nodes and paths on the traveling road. Note that a node is a point at a boundary between a straight part and a curved part of a road, and a path is a distance between adjacent nodes.

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

The steering control device 14 performs a multiple regression of the steering angle when traveling according to a designated route based on the route data output from the traveling control device 13 and the white line data output from the image processing device 11. Calculated by analysis.
The calculated steering angle command value is sent to the steering drive device 15.

The steering driving device 15 operates an actuator according to 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 represents a reference line, the imaging device 10 represents imaging means, the image processing device 11 represents image processing means, and the steering control device 14 represents steering control means. The steering driving device 15 constitutes a steering driving means.

Next, the operation of this embodiment will be described. FIG.
FIG. 4 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 steering control device 14 calculates the travel target point distance t at the forward fixation point L [m] ahead. Then, a steering angle S (x, t) is calculated by the steering controller 14 based on the travel target point distance t and the white line distance data x, and the steering angle data S
Is sent to the steering drive 15. The calculation procedure will be described below, but the description of the white line data calculation method will be omitted as described above.

(1) Standard target point and limit target point A feature of the present embodiment is that, when the vehicle 1 turns, the steering control is performed so that the side of the vehicle 1 does not cross the white line 3 inside due to the inner wheel difference. It is a point. Therefore, a condition for the vehicle 1 not to cross the inner white line 3 when turning will be discussed with reference to FIG.

FIG. 5A shows a case where the curve radius r ₁ of the white line 3 is small, and FIG. 5B shows a case where the curve radius r ₂ is large. Now, when the center of the vehicle is the center of the front wheel tires,
Assuming a case where the vehicle 1 travels so that the side of the vehicle 1 is tangent to the inner white line 3 as shown in FIG.
_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 because the} radius of the curve connecting the innermost part of the vehicle and the center of the curved road is r 2> r ₁ ). Here, the center O ₁ , O ₂ of the front wheels and the center O of the curve of the white line 3
(The radius of the white line 3) and the intersection P of 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 represented by a general formula, w = (k / sinΘ) −r (1) (Θ is a tangent angle, that is, the inclination of the white line 3). This distance w is defined as a limit target point distance W.

On the other hand, when the vehicle 1 travels straight, the vehicle 1 is set to travel in the center of the travel 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. This distance is defined as a standard target point distance T.

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

Now, consider a case where the vehicle 1 is traveling from a straight portion to a curved portion of the travel path as shown in FIG.
A plurality of forward fixation points, for example, d ahead of the vehicle 1 in the traveling direction
_i-1, d _i, sets the d i _{+ 1,} if provided the travel target point T _g in the transverse direction in the forward gaze point d _i, the distance from the travel target point T _g to the inner white line 3 ( Hereinafter, referred to as a travel 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 an absolute value of X) where θ (i−1 ), Θ (i), θ (i + 1) are the tangent angles of the white line 3 at the respective forward fixation points, γ is the offset value, and ε is the proportionality constant.

Equation (2) is a difference (differential) equation. When the traveling road is a straight line, the differential value of the tangent angle (that is, the slope) of the white line 3 is 0, so that t (n) = T. but, t (n) <T becomes closer to the entrance of the curved portions, the travel target point the T _g gradually approaches toward 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) changes accordingly. Then, t (n) increases as the traveling path 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 separates from the inner curve 3 and again becomes t (n) in the linear portion. ) = T.

When viewed from above the vehicle 1 at t (n) = W + γ, its side portion contacts the inside white line 3. Then, when t (n) becomes smaller than W + γ in the 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 the forward gaze point d _i-1, d i of the white line 3 in _{+ 1} distance data x (i-1), x (i + 1) and inclination data θ (i-1), θ (i + 1)
, But 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 filed an application for the details (Japanese Patent Application No. 3-68571), only the outline will be described in this embodiment.

In the curved portion of the traveling road, a change in the steering angle appears as a similar change later than a 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 a multiple regression analysis based on a change in the distance data of the white line 3 at that time. In the multiple regression equation, this data can be defined innumerably, but as a result of the experiment, the present, the past (1), and the previous past (2)
Has been found to be sufficient. Therefore, the values to be input include the current white line distance data x (n), the data x (n-1) one control cycle before, and the data x (n-n) two control cycles before.
2). In this case, a 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 and k ₂ , k ₃ and d are constants, and n is a discrete time). These constants are derived by a multiple regression analysis method based on the actual white line distance data and the actual steering angle.

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

Therefore, according to the present embodiment, the steering control is performed such that the side of the vehicle 1 comes into contact with the inside white line 3 when the vehicle 1 turns, so that even when the vehicle 1 travels on a meandering road as in the prior art, Therefore, the route on which the vehicle travels does not cross a reference line such as a center line or a roadway boundary line, so that the present invention can be applied to an actual road or the like whose curvature changes variously.

Further, as compared with a 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 increase the steering angle in the curved portion. Power can be reduced. Therefore, the acceleration acting in the lateral direction of the vehicle 1 during turning can be reduced, and the running speed during turning can be increased to the limit of the vehicle stable region. Furthermore, the traveling distance can be reduced 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 apparatus 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 using the inclination data of the white line. For example, if the vehicle speed is v and the standard vehicle speed is V, 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 by the following equation. As is apparent from the equation (5), the vehicle speed v is v = V when the vehicle 1 is traveling in a straight line portion, gradually decreases as the vehicle 1 approaches the entrance of the curved portion, and reaches the exit of the curved portion. When it approaches, it accelerates again and becomes v = V.

[0033]

As described in detail above, according to the present invention, the inner base is provided so that the vehicle does not protrude from the inner reference line.
A driving route that travels along the tangential direction of the quasi-line is determined, and steering control is performed so that the vehicle travels along this traveling route, so it can be applied to actual roads with various curvatures. Become. Moreover, as compared with the case where the vehicle simply travels 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 increase the steering angle, so that the steering holding force at the time of turning the vehicle can be reduced. For this reason, the acceleration acting in the lateral direction of the vehicle at the time of turning can be reduced, and the running speed at the time of turning can be increased to the limit of the vehicle stable region. Furthermore, the traveling distance can be reduced as compared with the case of traveling in the middle of the road, which is also effective for energy saving traveling.

[Brief description of the drawings]

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

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

FIG. 3 is a schematic diagram illustrating an appearance of an autonomous traveling 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 the steering control of the vehicle according to one embodiment.

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

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

FIG. 10 is a diagram showing an example of a set position of a target traveling point in a conventional autonomous traveling vehicle.

[Explanation of symbols]

 Reference Signs List a Vehicle b, c Reference line d Running path e Imaging means f Image processing means g Steering control means h Steering drive means 1 Autonomous traveling vehicle 2, 10 Imaging device 3 White line 11 Image processing device 12 Map information device 13 Travel control device 14 Steering Control device 15 Steering drive

Claims (1)

(57) [Claims] 1. A steering control device for an autonomous vehicle that travels along a traveling path defined by at least two right and left reference lines, wherein: an imaging unit that captures an image of a road surface in front of the vehicle; Image processing means for calculating the position of the reference line based on the obtained image; and the vehicle based on the reference line obtained by the image processing means.
A plurality of target points are set at predetermined distances in front of both,
Calculates the tangent angle of a given point on the inner reference line corresponding to the target point
Out, and based on the calculated tangent angle,
When traveling along the tangential direction of the reference line, the vehicle
Limit target point so that it does not protrude from the side reference line
Calculate the distance, on the plurality of target points and the inner reference line
On the line connecting the predetermined point, on the inner reference line
A steering control means for obtaining a travel route so that the distance to the predetermined point is the limit target point distance, and outputting a steering angle signal for causing the vehicle to travel along the travel route; and And a steering drive means for driving a steering device in accordance with the steering angle signal.