System and method for providing steering control for autonomous vehicle

• US 5,414,625 A
• Filed: 04/01/1992
• Issued: 05/09/1995
• Est. Priority Date: 04/01/1991
• Status: Expired due to Fees

• Current Assignee: Nissan Motor Co., Ltd.
• Original Assignee: Nissan Motor Co., Ltd.
• Inventors: Hattori, Akira
• Primary Examiner(s): Chin, Gary
• Application Number:
  US07/862,610
• Time in Patent Office: 1,133 Days
• Field of Search: 364/424.01, 364/424.02, 318/587, 180/167-169, 348/113, 348/118
• US Class Current: 701/27
• CPC Class Codes: G05D 1/0246 using a video camera in combination with image processing means
• CPC Class Codes: G05D 1/0274 using mapping information stored in a memory device navigation using map-matching G01C21/30

Abstract

A system and method for providing a steering control for an autonomous vehicle are disclosed in which a plurality of measuring points for determining distances therefrom to respective points on an imaged white line are set, a membership function for each measuring point is set which gives a reliability μl_i (j) to the other measuring points so that an effective range to the input values of the respective measuring points is expanded, and a control equation sl_i (or sr_i) at each measuring point toward which the input values to the other measuring points are reflected.

Claims

1. A system for providing a steering control for an autonomous vehicle, comprising:

a) first means, disposed on the vehicle so as to face toward a vehicular forward direction, for monitoring a presence of a road contour index extended in the vehicular forward direction;

b) second means for setting a plurality of measuring points for a plurality of predetermined distances set toward the vehicular forward direction ahead of a vehicular center on a vehicular coordinate system;

c) third means for defining positions of the monitored road contour index and outputting the position data of the monitored contour index defined with respect to the respective measuring points;

d) fourth means for setting a membership function for each measuring point which gives predetermined reliabilities to input values of the position data for the measuring points mutually adjacent to the corresponding one of the measuring points to which the membership function is set; and

e) fifth means for calculating a steering angle through which a steering mechanism of the vehicle is steered for each measuring point with the position data for the respective measuring points as input parameters, said fifth means calculating the steering angle for each measuring point, the input parameters of the other measuring points being included in the calculation of the steering angle for any one of the measuring points according to the reliabilities given to the other measuring points, said system providing the steering control for the steering mechanism of the autonomous vehicle on the basis of the calculated steering angle.

2. A system for providing a steering control for an autonomous vehicle as set forth in claim 1, which further includes sixth means for actuating the steering mechanism.

3. A system for providing a steering control for an autonomous vehicle, as set forth in claim 2, wherein said road contour index is a white line placed along a side edge of a running road and wherein said first means includes a camera for photographing the white line, and said second and third means include an Image processing block for measuring the positions of the white line to the respective measuring points.

4. A system for providing a steering control for an autonomous vehicle as set forth in claim 3, wherein said third means outputs the position data x_i (i=1, 2, 3, --, n) which indicate relative position distances of the white line from the respective measuring points l_i (i=1, 2, 3, --, n) on the vehicular coordinate system L_i ahead of the vehicular center corresponding to a position of the actuator of the steering mechanism.

5. A system for providing a steering control for an autonomous vehicle as set forth in claim 4, wherein said fifth means sets a control equation for each measuring point expressed as sl_i =Fl_i (x_i) according to each measuring point, wherein Fl_i (x_i) is set as a displacement deviation function from a running reference line on which the vehicular center is moved and expressed as Fl_i (x_i)=α

_i ·

(X_i -x_i), wherein X_i denotes the running reference line for each measuring point and α

_i denotes a coefficient for each measuring point.

6. A system for providing a steering control for an autonomous vehicle as set forth in claim 4, wherein said fourth means sets the membership function denoted by M_i and M_i gives the reliability as μ

l_i (j) (j=1, 2, 3, --, n) to the input values of the position data for the respective measuring points.

7. A system for providing a steering control for an autonomous vehicle as set forth in claim 5, wherein said fifth means calculates the control equation sl_i for each measuring point on the basis of a weight mean method of a fuzzy inference.

8. A system for providing a steering control for an autonomous vehicle as set forth in claim 7, wherein said fifth means calculates a final steering angle S through which the steering mechanism is steered using a gross mean of a derived control equation.

9. A system for providing a steering control for an autonomous vehicle as set forth in claim 8, wherein a membership function M₁ which gives a reliability of 1.0 to the input value of the position data for one measuring point l₁ gives the reliability of 0.5 to the second measuring point l₂.

10. A system for providing a steering control for an autonomous vehicle as set forth in claim 9, wherein the control equation sl₂ for the second measuring point is expressed as follows:

space="preserve" listing-type="equation">sl.sub.2 =(0.5×

Fl.sub.2 (x.sub.1)+1.0×

Fl.sub.2 (x.sub.2)+0.5×

Fl.sub.2 (x.sub.2))/(0.5+1.0+0.5).

11. A system for providing a steering control for an autonomous vehicle as set forth in claim 10, wherein the control equation sl_i =Fl_i (x_i) applies to the case when the white line corresponding to the measuring point l_i and when the white line is not viewed from the camera.

12. A system for providing a steering control for an autonomous vehicle as set forth in claim 11, wherein both reliabilities to the measuring points l_i-1 and l_i+1 are 0.5 and the reliability to the measuring point l_i is zero.

13. A system for providing a steering control for an autonomous vehicle as set forth in claim 4, wherein said fifth means sets a control equation sl_i for each measuring point l_i as follows:

space="preserve" listing-type="equation">sl.sub.i =α

.sub.i ·

xl.sub.i (N)+β

.sub.i ·

xl.sub.i (N-1)+γ

.sub.i ·

xl.sub.i (N-2)+δ

.sub.i

wherein N, N-1, and N-2 denote discrete times, α

, β

, γ

, and δ

denotes multiple regression coefficients estimated during the run of the vehicle, sl_i denotes the control equation in a case where the steering control following up the white line placed along a left side edge of the running road as viewed from the camera is executed and xl_i denotes the position data on the left side white line at the measuring points l_i.

14. A system for providing a steering control for an autonomous vehicle as set forth in claim 13, said fifth means calculates the instantaneous steering angle S₀ supposing that the distance from the white line placed along the right side edge of the running road which is vertical to the vehicular forward direction to the measuring point L meters ahead of the vehicle center O₀ placed at a position V₀ as follows:

##EQU4## wherein x₀, x_-1, and x_-2 denotes the position data on the white line at the present time of control, the position data thereon at a previous control period, and the position data thereon at two previous control periods

and said fifth means calculates all of the steering angles for all measuring points from a predetermined start position to a predetermined end position of a route of travel and estimates the values of α

, β

, γ

, and δ

through a multiple regression analysis using all steering angles S.

15. A system for providing a steering control for an autonomous vehicle as set forth in claim 14, wherein said fifth means calculates the final steering angle S_F as follows when the vehicle runs on a road segment having a radius of curvature of 15 meters at a vehicle speed of 10 Km/h with L being 5 meters:

space="preserve" listing-type="equation">S.sub.F =-0.84581·

x.sub.0 -7.13965·

x.sub.-1 +0.21617·

x.sub.2 +15.4842.

16. A system for providing a steering control for an autonomous vehicle as set forth in claim 4, wherein said fifth means sets a control equation sr_i for each measuring point l_i as follows:

space="preserve" listing-type="equation">sr.sub.i =α

.sub.i ·

xr.sub.i (N)+β

.sub.i ·

xr.sub.i (N-1)+γ

.sub.i ·

xr.sub.i (N-2)+δ

.sub.i

wherein N, N-1, and N-2 denote discrete times, α

, β

, γ

, and δ

denotes multiple regression coefficients estimated during the run of the vehicle, sr_i denotes the control equation in a case where the steering control following up the white line placed along a right side edge of the running road as viewed from the camera is executed, and xr_i denotes the position data of the right side white line at the measuring points l_i.

17. A system for providing a steering control for an autonomous vehicle as set forth in claim 16, wherein said fifth means sets another control equation sl_i for each measuring point l_i as follows:

space="preserve" listing-type="equation">sl.sub.i =α

.sub.i ·

xl.sub.i (N)+β

.sub.i ·

xl.sub.i (N-1)+γ

.sub.i ·

xl i(N-2)+δ

,

wherein N, N -1, and N -2 denote discrete times, α

, β

, γ

, and δ

denotes multiple regression coefficients estimated during the run of the vehicle, sl_i denotes the control equation in a case where the steering control following up the white line placed along a left side edge of the running road as viewed from the camera is executed and xl_i denotes the position data on the left side white line at the measuring points l_i, and wherein said fifth means sets still another control equation s_i for each measuring point 1_i

wherein the control equation s_i is set according to the equation;

s_i =(sl_i +sr_i)/2, wherein s_i denotes the control equation in a case where the steering control following up both white lines placed along both side edges of the running road.

18. A system for providing a steering control for an autonomous vehicle as set forth in claim 17, wherein said fifth means determines and outputs the final steering angle S(n) using the white line distance data x(n) L meters ahead of the vehicular center as follows:

calculating an n-order equation related to the left side white line y =L (x) from the white line distance data (x₁, t₁)L₁, (x₂, t₂)L₂ at the front positions denoted by L₁ and L₂ ahead of the vehicular center;

calculating the output steering angle S(n)'"'"' as follows using an equation of x=L^-1 (y) and X_L^-1 (0) as evaluation values of vehicle movement;

S(n)'"'"'=S(n)+δ

when a value of the distance of the vehicle to the white line>

|X_L^-1 | and

-S(n)'"'"'=S(n)-δ

when a value of the distance of the vehicle to the white line≦

|X_L^-1 |

updating old S(0) from among N+1 data of S(0)˜

S(N) after deriving S(n)'"'"', x₀ (n), x_-1 (n), x_-2 (n), --

updating the values of α

, β

, γ

, and δ

through the multiple regression analysis

and calculating the final steering angle S(N) on the basis of the derived steering angle S(n)'"'"'.

19. A system for providing a steering control for an autonomous vehicle as set forth in claim 18, wherein the value of X_L^-1 (0) is estimated from the equation of y=L(x) when y=0.

20. A system for providing a steering control for an autonomous vehicle as set forth in claim 17, which further includes calculating means for deriving an instantaneous vehicle speed and the multiple regression coefficients α

, β

, γ

, and δ

are determined for each classified vehicle speed V_CLASS which is classified according to a magnitude of the vehicle speed.

21. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index, comprising:

a) first means having a video camera, the video camera being disposed on the vehicle so as to face toward a vehicle forward direction, for photographing a white line serving as the road contour index extending along a side edge of a running road and outputting an image signal indicating a presence of the white line;

b) second means, including an image processing block, for setting a plurality of measuring points for a plurality of predetermined distances set toward the vehicular forward direction ahead of a vehicular center on a vehicular coordinate system and for defining positions of the white line with respect to the respective measuring points and outputting the position data of the white line at the respective measuring points and outputting the defined position data;

c) third means for setting a running reference line on which the vehicle is to run autonomously;

d) fourth means for setting a membership function for each measuring point which at least gives predetermined reliabilities to input values of the position data for the measuring points mutually adjacent to the corresponding one of the measuring points to which the membership function is set; and

e) fifth means for calculating a steering angle through which a steering mechanism of the vehicle is steered for each measuring point with the position data for the respective measuring points and output from the third means as input steering values, said fifth means calculating the steering angle for each measuring point on a basis of a weight mean method in which reliabilities are multiplied by the position data for the respective measuring points and outputting a final steering angle which is calculated using a gross mean of the calculated steering angle and said system providing the steering control through the steering mechanism of the vehicle on the basis of the calculated final output steering angle of the fifth means so as to run the vehicle in parallel to the road contour index.

22. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index as set forth in claim 21, which further includes a steering drive block having an actuator of said steering mechanism and which actuates the actuator to steer the vehicle through the final steering angle calculated by the fifth means.

23. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index as set forth in claim 22, wherein said second means outputs the position data, which said position data indicates relative distances of the white line from respective measuring points.

24. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index as set forth in claim 23, wherein said fifth means sets a control equation for each measuring point expressed as sl_i =Fl_i (x_i) according to each measuring point, wherein Fl_i (x_i) is set as a displacement deviation function from the running reference line on which the vehicular center is moved and expressed as Fl_i (x_i)=α

_i ·

(X_i -x_i), wherein X_i denotes the running reference line for each measuring point and α

_i denotes a predetermined coefficient for each measuring point.

25. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index as set forth in claim 24, wherein said fourth means sets the membership function denoted by M_i and M_i gives the reliability as μ

l_i (j) (j=1, 2, 3, --, n) to the input values of the position data for the respective measuring points.

26. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index as set forth in claim 25, wherein said fifth means calculates the control equation sl_i for each measuring point on the basis of the weight mean method on a fuzzy inference.

27. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index as set forth in claim 26, wherein said fifth means calculates the control equation for each measuring point.

28. A system for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index as set forth in claim 27, wherein said fifth means calculates the final steering angle S through which the steering mechanism is steered using a weighted mean method.

29. A method for providing a steering control for an autonomous vehicle so as to run the vehicle in parallel to a road contour index, comprising the steps of:

a) monitoring a presence of a road contour index extending in the vehicular forward direction;

b) setting a plurality of measuring points for a plurality of predetermined distances set toward the vehicular forward direction ahead of a vehicular center on a vehicular coordinate system;

c) defining positions of the monitored road contour index with respect to the respective measuring points and outputting the position data of the monitored contour index defined with respect to the respective measuring points;

d) setting a membership function for each measuring point which gives predetermined reliabilities to input values of the position data for the measuring points mutually adjacent to the corresponding one of the measuring points to which the membership function is set;

e) calculating a steering angle through which a steering mechanism of the vehicle is steered for each measuring point with the position data for the respective measuring points as input steering values; and

(f) calculating the steering angle for each measuring point, the input values of the other measuring points being included in the calculation of the steering angle for any one of the measuring points according to reliabilities given to the other measuring points, said method providing the steering control for the steering mechanism of the autonomous vehicle on the basis of the calculated steering angle.