CN107544520B - Control method for automatic driving of four-wheel carrier - Google Patents
Control method for automatic driving of four-wheel carrier Download PDFInfo
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Abstract
The invention discloses a control method for automatic driving of a four-wheel carrier, which mainly comprises the following steps: s1) setting the initial state of the system, planning the driving path in advance, and measuring vehicle parameters including the wheel track of the guide wheel and the wheel track of the vehicle body; s2) measurementMeasuring the real-time position of the vehicle and measuring the real-time angle of the guide wheel on any side; s3) calculating real-time errors of the vehicle and the planned path, including position errors and angle errors; s4) calculating a target angle: s5) calculating the required rotation angle of the tire; s6) controlling tire rotationAnd (4) an angle. According to the invention, the foresight distance is associated with the speed, the foresight distance is determined according to the real-time vehicle speed, and the target point corresponding to the path is calculated according to the foresight distance, so that the path tracking stability under the complex driving speed can be met, meanwhile, the algorithm complexity is low, the operation time of a program is greatly reduced, and good real-time performance is provided for the system.
Description
Technical Field
The invention relates to an automatic control system of a vehicle, in particular to an intelligent control method for unmanned driving and automatic driving of the vehicle.
Background
The unmanned vehicle is a typical four-wheel mobile robot, relates to numerous interdisciplinary knowledge, is a product of high combination and development of contemporary computer science, pattern recognition and control technology, senses the surroundings of the vehicle by using sensors with different functions, plans a safe and collision-free path according to road, vehicle position and obstacle information obtained by sensing, and controls the speed and steering of the vehicle, thereby enabling the vehicle to safely drive on the road autonomously.
The rapid development and wide application of the unmanned vehicle technology will bring profound effects and great benefits to people's daily life. The active research and development of the unmanned vehicle technology have important significance for taking a favorable position in the fierce international competition of China.
The motion control of the unmanned vehicle is to make the unmanned vehicle move along a desired path by adjusting the moving speed and moving direction of the vehicle, and the motion control is one of the most critical problems in the system research of the unmanned vehicle, because all that is needed is the precise running of the unmanned vehicle to ensure the target of the upper layer.
The unmanned control mainly comprises a transverse control part and a longitudinal control part, wherein the transverse control mainly refers to the control of a vehicle steering system. Path tracking is one of the primary applications of intelligent vehicle lateral control. The path tracking means that the actual running path of the vehicle can be consistent with the planned path according to the position information in the geodetic coordinate system and a certain control strategy on the premise that an expected path is obtained.
The existing widely used algorithm for tracking the path of the unmanned intelligent vehicle basically realizes the tracking of the path by adjusting the deviation between the actual path and the planned path in real time. The method is characterized by comprising the following steps of comparing commonly used path tracking algorithms such as a Steiner algorithm, a circular preview algorithm and the like. The problems that the adjusting time is long, the tracking stability is poor, the dynamic adjustment cannot be related to the speed and the like exist at present.
Disclosure of Invention
The invention aims to provide a path tracking control method related to speed, which determines a target point at each moment according to real-time vehicle speed so as to improve the adjustment response of a system and reduce the time required by adjustment; meanwhile, the forward looking distance is adjusted at any time according to the changing speed, the stability under path tracking is improved, and the stability of the vehicle in straight lines and curved lines is ensured; meanwhile, the algorithm is low in complexity, the operation time of a program is greatly reduced, and the good real-time performance of the system is guaranteed.
The technical scheme adopted by the invention for solving the technical problems is as follows:
a control method for automatic driving of four-wheel vehicle features that the forward-looking distance of system is dynamically regulated in relation to speed to shorten regulation time and increase tracking stability of system.
The control method comprises the following steps:
s1) setting the initial state of the system, planning the driving path in advance, measuring the vehicle parameters including the wheel track b of the guide wheel and the wheel base of the vehicle body. The travel path is a straight path or a curved path.
S2) measuring the real-time position of the vehicle, and measuring eitherReal-time angle of side guide wheel。
S3) calculating real-time errors of the vehicle and the planned path, including position errors and angle errors:
s3.1) determining the forward looking distance according to the running speed of the four-wheel vehicle, and recording the forward looking distanceThe forward looking distance needs to be adjusted at any time according to the changing speed;
s3.2) judging the position relation between the four-wheel carrier and the planned driving path;
and S3.3) determining a target point according to the position relation and the forward looking distance.
S3.4) calculating a position error:
the position error is a straight line parallel to the four-wheel vehicle body and marked as a straight line a when the target point is crossed, and the position error is a distance between the straight line a and the four-wheel vehicle body and marked as d.
S3.5) calculating an angle error:
the angle error is a tangent line of a planned driving path made by passing a target point and is marked as a straight line b, and the angle error is an angle formed by the straight line b and the heading of the four-wheel carrier head and is marked as an angle。
S4) calculating a target angle:
where gamma is the target angle of the wheel, d is the position error, as found in step 3.4,for the angular error to be derived from step 3.5,is the wheel base of the vehicle, is actually measured,forward looking distance, from step 3.1.
S5) calculating the required rotation angle of the tire:
since the angle of the guide wheel on one side is measured in real time, it is recorded asThe angle of the guide wheel on the other side is calculated and recorded as2, according to ackermann kinematics principles:
Angle of rotation required for tyreIs the difference between the target angle and the current vehicle body steering angle, so
WhereinFor the angle the tire needs to be turned, and for the result d is the position error, derived from step 3.4,for the angular error to be derived from step 3.5,the angle of the guide wheel on one side is obtained by actual measurement, b is the wheel track of the guide wheel of the vehicle is obtained by actual measurement,the wheel base of the vehicle is actually measured,forward looking distance, from step 3.1.
the vehicle can be ensured to run along the planned path by executing the steps more than once in each control period.
The forward looking distance has a certain relation with the running speed of the four-wheel carrier, the increase of the forward looking distance can prolong the path tracking time, the larger forward looking distance can enable the four-wheel carrier to approach the target point along an arc line with smaller radian, and conversely, the four-wheel carrier can approach the target point along an arc line with larger radian.
And the target point is positioned at the intersection point of a circle which takes the center point of the four-wheel carrier as the center of the circle and the forward looking distance as the radius and the planned driving path, and if the number of the intersection points is more than 1, the target point is determined according to the position relation in the step S3.2).
The relation between the forward looking distance and the running speed of the four-wheel vehicle is=1.5 × running speed of the four-wheel vehicle.
The invention has the beneficial effects that:
the invention relates the foresight distance and the speed, is different from the foresight distance fixed by other algorithms, determines the foresight distance according to the real-time vehicle speed, and calculates the target point corresponding to the path according to the foresight distance, thereby meeting the path tracking stability under the complex driving speed, having low algorithm complexity, greatly reducing the operation time of the program and providing good real-time performance for the system.
Drawings
Fig. 1 shows an ackerman vehicle kinematics model.
FIG. 2 shows a vehicle trajectory update diagram.
Fig. 3 shows a control algorithm flow chart.
Fig. 4 shows a geometric schematic of the control algorithm motion model.
Detailed Description
While the invention will be described in conjunction with the examples, it will be understood that they are not intended to limit the invention to these examples. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. Well-known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the present invention.
As shown in fig. 1, the ackerman vehicle kinematics model is assumed that the positioning angles of the front wheels of the vehicle are all equal to zero, the traveling system is rigid, and no lateral force is generated during the traveling of the vehicle, and the steering characteristic is characterized in that:
(1) when the automobile runs in a straight line, the axes of the 4 wheels are parallel to each other and are vertical to the longitudinal central plane of the automobile
(2) In the steering driving process of the automobile, all wheels need to roll around an instantaneous central point in a circle, and the corners of a front inner wheel and a front outer wheel meet the following relation:
As shown in fig. 2, which is a schematic diagram of vehicle trajectory update, assuming that a control cycle is a very short time, the speed of the vehicle can be considered to be constant in one cycle, and then the trajectory update becomes a pure geometric problem, assuming that the radian of the vehicle around the center of a circle in one cycle is β, the motion trajectory of the vehicle in one update cycle can be determined, and further, the coordinates (x) that the vehicle finally reaches in the vehicle body coordinate system can be obtained0,y0) The following formula can be derived:
wherein s is the arc length of the vehicle motion track in a period, which can be simply regarded as a straight line in a period, v is the running speed of the current vehicle, t is the duration of a control period, beta is the central angle corresponding to the vehicle track arc in a period, and R is the turning radius, so that the following two formulas are combined to obtain the vehicle motion track, namely:
fig. 3 shows a control flow of the control method.
Step S1: an ideal path for the vehicle to be unmanned or automatically driven is planned manually.
Step S2: the wheel track of the guide wheel of the vehicle is measured,denoted b. The vehicle wheelbase is measured and is denoted as l. The current speed of the vehicle is obtained through GPS or visual identification, the forward-looking distance is adjusted at any time according to the changed speed, the forward-looking distance = speed x 1.5, and the appropriate forward-looking distance at the current speed can be calculated. The forward looking distance has a relationship with the speed of travel of the vehicle, and an increase in forward looking distance increases the path tracking time because a larger forward looking distance causes the vehicle to approach the target point along an arc of smaller arc, whereas the vehicle approaches the target point along an arc of larger arc.
Step S3: as shown in fig. 4, the position relationship between the vehicle and the ideal path is determined by comparing the current actual position of the vehicle with the manually planned ideal path.
Step S4: and taking the center of the vehicle as the center of a circle, taking the front sight distance as the radius to make a circle, and taking the intersection point of the front sight distance and the track as a vehicle driving target point. If the number of the target points is larger than 1, the target points need to be determined according to the position relationship, and usually, the points located in the direction of the vehicle head are the target points.
Step S5: the line parallel to the vehicle body is marked as the line laThe position error is a straight line laThe distance from the vehicle body is denoted as d. Making a tangent line of the planned driving path at the target point, and marking the tangent line as a straight line lbThe angle error is a straight line lbThe angle formed with the vehicle head orientation is noted β.
Step S6: as shown in fig. 4, define: VXgThe horizontal coordinate of the target point in the vehicle body coordinate system is shown; VYgThe longitudinal coordinate of the target point in the vehicle body coordinate system is shown; gamma is the turning curvature of the agricultural machinery, is a signed number, and specifies that the turning curvature when the vehicle runs anticlockwise is positive (gamma is more than 0) and the turning curvature when the vehicle runs clockwise is negative (gamma is less than 0); r is the instantaneous turning radius of the vehicle; d is the lateral position error of the vehicle relative to the path, and is a signed number, which specifies that the lateral position error of the vehicle is positive (d > 0) when the vehicle is on the right side of the ideal path in the forward direction, and the lateral position error of the vehicle is negative (d < 0) when the vehicle is on the left side of the ideal path0) (ii) a Ld is the forward looking distance; Ψ e is the error between the current heading of the vehicle and the heading of the path at the target point; Φ is the heading change angle of the vehicle as it reaches the target point along the steering arc. According to the geometric relation, the horizontal and vertical coordinates of the target point in the vehicle body coordinate system can be obtained as
In the triangular PNG, there is the following relationship:
combining the formula in step 3 can obtain:
meanwhile, the following relations exist:
by combining the two formulas, the final wheel target angle can be obtained as follows:
step S7: calculating the required rotation angle of the tire:
since the angle of the guide wheel on one side is measured in real time, it is recorded asThe angle of the guide wheel on the other side is calculated and recorded as2, according to ackermann kinematics principles:
Angle of rotation required for tyreIs the difference between the target angle and the current vehicle body steering angle, so
WhereinThe angle the tire needs to be turned, and for the result d is the position error, derived from step 5,in order for the angle error to be derived from step 5,for the forward looking distance, it comes from step 2,the angle of the guide wheel on one side is obtained by actual measurement, b is the wheel track of the guide wheel of the vehicle,the actual measurement is obtained, the vehicle wheel base is obtained, and the actual measurement is obtained.
Controlling tire rotationAngle when the tire is rotatingAfter the angle, the tire angle is now the target angle γ, and this is one complete control cycle. Since the position and the state of the vehicle are continuously changed, the vehicle can be ensured to run along the planned path by circularly executing more than one step in each control period.
The derivation process and principles regarding the guide wheel mean angle and target angle are as follows:
according to the Ackerman angle principle, the turning angles of the inner wheels and the outer wheels have certain difference when the vehicle turns, the deflection angle of the inner wheels is larger than that of the outer wheels, and the ideal formula relationship is as follows:
whereinRespectively are the outer wheel corner and the inner wheel corner, b is the distance between the inner wheel and the outer wheel,for the wheel base, the average angle of the guide wheels of the four-wheel vehicle is calculated as follows:
The derivation process of the target angle calculation process is as follows:
according to the ackermann kinematics model, the four-wheel vehicle has the following motion constraints:
whereinThe included angle between the heading direction of the four-wheel carrier and the north direction is specifiedAnd the angle of the guide wheel of the four-wheel carrierAll taking the counterclockwise direction as positive, the kinematic model of the vehicle can be obtained as follows:
whereinIf only the motion of the four-wheel vehicle on a two-dimensional plane is considered, the following formula can be obtained:
whereinFor the forward looking distance, R is the radius of curvature of the circular arc path of travel, and the above formula is taken together:
and the Ackerman vehicle kinematics model can obtain:
whereinAs the wheel base of the vehicle,for the target turning angle, the above two formulas are combined to obtain:
Obtaining by simultaneous method:
Claims (4)
1. A control method for automatic driving of a four-wheel vehicle is characterized by comprising the following steps: the forward-looking distance of the system is dynamically adjusted in a speed-related mode to shorten the system adjusting time and increase the tracking stability of the system, and the control method comprises the following steps:
s1) setting the initial state of the system, planning a driving path in advance, and measuring vehicle parameters including a guide wheel track b and a vehicle body wheel base l; the driving path is a straight path or a curve path;
s2) measuring the real-time position of the vehicle and the real-time angle 1 of the guide wheel on any side;
s3) calculating real-time errors of the vehicle and the planned path, including position errors and angle errors:
s3.1) determining a forward looking distance according to the running speed of the four-wheel vehicle, and recording the forward looking distance as LdThe forward looking distance needs to be adjusted at any time according to the changing speed;
s3.2) judging the position relation between the four-wheel carrier and the planned driving path;
s3.3) determining a target point according to the position relation and the forward looking distance;
s3.4) calculating a position error:
the position error is a straight line which is parallel to the four-wheel vehicle body and is marked as a straight line a when the target point is crossed, and the position error is the distance between the straight line a and the four-wheel vehicle body and is marked as d;
s3.5) calculating an angle error:
the angle error is a tangent line of a planned driving path at the target point and is marked as a straight line b, and the angle error is an angle formed by the straight line b and the head orientation of the four-wheel vehicle and is marked as psie;
S4) calculating a target angle:
where γ is the target angle of the wheel, d is the position error, derived from step 3.4, ψeFor angular error originating from step 3.5, L is the actual measurement of the wheelbase of the vehicle, LdForesight distance, from step 3.1;
s5) calculating the required rotation angle of the tire:
since the angle of the guide wheel on one side is measured in real time, as 1, according to ackermann kinematics:
R=l/tan1
R+b=l/tan2
The angle delta theta of the tire required to rotate is the difference between the target angle and the current steering angle of the vehicle body, so
Where Δ θ is the angle the tire needs to be rotated, and d is the position error for the result, derived from step 3.4, ψeFor angular error from step 3.5, 1 is the angle of the leading wheel on one side, as actually measured, 2 is the angle of the leading wheel on the other side, b is the track width of the leading wheel of the vehicle, as actually measured, L is the wheel base of the vehicle, as actually measured, LdForesight distance, from step 3.1;
s6) controlling tire rotation by an angle Δ θ:
the vehicle can be ensured to run along the planned path by executing the steps more than once in each control period.
2. A control method for automatic driving of a four-wheel vehicle according to claim 1, wherein: the forward looking distance has a certain relation with the running speed of the four-wheel carrier, the increase of the forward looking distance can prolong the path tracking time, the larger forward looking distance can enable the four-wheel carrier to approach the target point along an arc line with smaller radian, and conversely, the four-wheel carrier can approach the target point along an arc line with larger radian.
3. A control method for automatic driving of a four-wheel vehicle according to claim 1 or 2, characterized in that: and the target point is positioned at the intersection point of a circle which takes the center point of the four-wheel carrier as the center of the circle and the forward looking distance as the radius and the planned driving path, and if the number of the intersection points is more than 1, the target point is determined according to the position relation in the step S3.2).
4. The control method as claimed in claim 1, wherein the relation between the forward looking distance and the driving speed of the four-wheel vehicle is Ld1.5 x the running speed of the four-wheel vehicle.
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Address after: 201702 Room 201, building 1, China Beidou Industrial Park, 99 Lane 215, Gaoguang Road, Qingpu District, Shanghai Patentee after: Shanghai Lianshi Navigation Technology Co.,Ltd. Address before: 201702 Beidou innovation base, No.99, Lane 215, Gaoguang Road, Xujing Town, Qingpu District, Shanghai Patentee before: SHANGHAI LIANSHI NAVIGATION TECHNOLOGY Co.,Ltd. |