WO2019113877A1 - 一种无人车控制方法及无人割草车 - Google Patents

一种无人车控制方法及无人割草车 Download PDF

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WO2019113877A1
WO2019113877A1 PCT/CN2017/116120 CN2017116120W WO2019113877A1 WO 2019113877 A1 WO2019113877 A1 WO 2019113877A1 CN 2017116120 W CN2017116120 W CN 2017116120W WO 2019113877 A1 WO2019113877 A1 WO 2019113877A1
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unmanned
vehicle
steering angle
unmanned vehicle
mower
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PCT/CN2017/116120
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English (en)
French (fr)
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张孝勇
郑友胜
陈寿辉
齐洪豪
谢训鹏
吴添成
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江西洪都航空工业集团有限责任公司
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Publication of WO2019113877A1 publication Critical patent/WO2019113877A1/zh

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    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0212—Control of position or course in two dimensions specially adapted to land vehicles with means for defining a desired trajectory
    • G05D1/0221—Control of position or course in two dimensions specially adapted to land vehicles with means for defining a desired trajectory involving a learning process
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0276—Control of position or course in two dimensions specially adapted to land vehicles using signals provided by a source external to the vehicle
    • G—PHYSICS
    • G05—CONTROLLING; REGULATING
    • G05D—SYSTEMS FOR CONTROLLING OR REGULATING NON-ELECTRIC VARIABLES
    • G05D1/00—Control of position, course, altitude or attitude of land, water, air or space vehicles, e.g. using automatic pilots
    • G05D1/02—Control of position or course in two dimensions
    • G05D1/021—Control of position or course in two dimensions specially adapted to land vehicles
    • G05D1/0276—Control of position or course in two dimensions specially adapted to land vehicles using signals provided by a source external to the vehicle
    • G05D1/0278—Control of position or course in two dimensions specially adapted to land vehicles using signals provided by a source external to the vehicle using satellite positioning signals, e.g. GPS

Definitions

  • the invention relates to an unmanned vehicle and a control method design thereof, in particular to an unmanned vehicle control method and an unmanned mowing vehicle.
  • the unmanned vehicle is an integrated robotic system that integrates various functions such as environment perception, path planning and decision control.
  • the decision control is equivalent to the brain of the unmanned vehicle. Its main function is to make decision decisions based on the information obtained by the sensing system, and then make decisions on the next behavior to control how the vehicle travels. Therefore, decision control technology is a key technology in the unmanned vehicle system.
  • the behavior of decision control systems is divided into reactive, reflective and integrated.
  • the reactive control is a feedback control process, which continuously adjusts the steering wheel angle and the vehicle speed according to the deviation between the current position of the vehicle and the desired path until reaching the destination.
  • the unmanned vehicle simply by obtaining the trajectory tracking control by the positional deviation.
  • the unmanned mower is an application example of the unmanned car technology in a specific occasion, and its main application is in the lawn dressing operation of a large airport.
  • the unmanned mower collects the boundary information of the job map through the GPS satellite navigator, and plans the optimal travel path to traverse the mowing operation in the area. Therefore, how to control the unmanned mower to follow the planned path to achieve full coverage in the area
  • the trajectory tracking control method of the cover traversing mowing operation has become a top priority.
  • the object of the present invention is to provide an unmanned vehicle control method and an unmanned mowing vehicle to solve at least one problem existing in the existing unmanned vehicle and unmanned mower control methods.
  • An unmanned vehicle control method includes the following steps:
  • Step 1 obtaining position information and posture information of the current time of the unmanned vehicle
  • Step 2 Calculate the distance deviation and the angular deviation between the position and the heading of the unmanned vehicle and the planned path at the current time;
  • Step 3 Comparing the distance deviation with the set distance deviation threshold, and combining the angle deviation to obtain a steering angle of the steering mechanism of the unmanned vehicle, specifically including:
  • the steering angle ⁇ is obtained by the following formula (1):
  • ⁇ max is the maximum steering angle of the unmanned vehicle steering mechanism
  • d t is the distance deviation threshold
  • d is the vertical distance between the vehicle-free midpoint and the planned path
  • ⁇ is the current time The angular deviation between the unmanned vehicle and the planned path
  • ⁇ is a positive value indicating a left turn and a negative value indicating a right turn
  • Step four the steering angle of the steering mechanism of the unmanned vehicle obtained is controlled by a command Send to the steering motor of the unmanned vehicle.
  • the obtained steering angle is corrected by the following step function (3):
  • ⁇ ' is the corrected steering angle for this step
  • the fourth step is to send the corrected steering angle to the steering motor of the unmanned vehicle in the form of a control command.
  • the step of correcting the obtained steering angle by the step function further includes:
  • a return function is added on the basis of the step function to correct the obtained steering angle.
  • the steering angle is corrected according to the current speed of the unmanned vehicle, specifically by the following relation (4):
  • a 2 and b 2 are coefficients, and the current speed of the unmanned vehicle.
  • the distance deviation threshold is equal to the maximum vehicle speed of the unmanned vehicle at the current time multiplied by the instruction period.
  • the present invention also provides an unmanned mowing vehicle, which is controlled by the unmanned vehicle control method according to any one of the above, wherein the unmanned mowing vehicle comprises:
  • a first satellite receiving antenna fixedly disposed at a center position of the rear axle of the unmanned mowing vehicle
  • a second satellite receiving antenna fixedly disposed at a center position of the front axle of the unmanned mower
  • a GPS-RTK receiver fixedly disposed on the unmanned mowing vehicle for acquiring the unmanned mower according to information received by the first satellite receiving antenna and the second satellite receiving antenna connected thereto Location information and attitude information at the current time;
  • controller fixedly disposed on the unmanned mowing vehicle, the controller is configured to:
  • the steering angle of the steering mechanism of the unmanned mower is obtained as a control command to the steering motor of the unmanned mower.
  • the controller is further configured to correct the obtained steering angle by a step function, and send the corrected steering angle to the steering motor of the unmanned mower in the form of a control command.
  • the controller is further configured to add a return function based on the step function to correct the obtained steering angle.
  • the controller is further configured to correct the steering angle according to the current speed of the unmanned mowing vehicle.
  • the effective cut width and the actual cut width of the unmanned mower cutting head are determined by the following relationship (5):
  • L is the effective cutting amplitude
  • S is the actual cutting width
  • D is the deviation of the tracking accuracy of the unmanned mowing vehicle.
  • the unmanned vehicle control method and the unmanned mowing vehicle of the invention can obtain the precise position and posture information of the unmanned mower, and the position deviation and the angular deviation calculated by the planned path are more accurate and effective; in addition, according to different situations Different corrective deflection strategies ensure a more rapid return to the correct trajectory.
  • FIG. 1 is a schematic diagram of a small deviation correction deflection direction of an unmanned mower of the present invention
  • FIG. 2 is a schematic diagram of the large deviation correction deflection direction of the unmanned mowing vehicle of the present invention
  • FIG. 3 is another schematic diagram of the large deviation correction deflection direction of the unmanned mowing vehicle of the present invention.
  • FIG. 4 is a schematic diagram showing a step function of a steering angle of an unmanned mower according to the present invention.
  • Figure 5 is a schematic view showing the setting of the steering angle dead zone of the unmanned mower of the present invention.
  • FIG. 6 is a simulation effect diagram of trajectory tracking control of the unmanned mower of the present invention.
  • the invention provides an unmanned vehicle control method (a trajectory tracking control method for an unmanned vehicle), which is a process for controlling the steering angle and speed of an unmanned vehicle to achieve operation along a planned trajectory.
  • a trajectory tracking control method for an unmanned vehicle a process for controlling the steering angle and speed of an unmanned vehicle to achieve operation along a planned trajectory.
  • the satellite receiving antenna is arranged on the unmanned vehicle to obtain the precise position and attitude information of the unmanned vehicle, and the position deviation (ie distance deviation) and angular deviation calculated by the planned path are combined.
  • the trajectory tracking correction algorithm of the unmanned mower is established.
  • the position offset threshold and the angle offset threshold are set.
  • the steering angle within the small deviation range changes linearly continuously. When the threshold range is exceeded.
  • the large steering angle is used to control the unmanned vehicle to return to the correct running track as soon as possible.
  • the unmanned vehicle control method of the present invention can be applied to a plurality of suitable unmanned vehicles as needed; the following description takes an unmanned mower as an example.
  • the unmanned mowing vehicle of the present invention acquires positioning navigation information by using GPS-RTK technology, and adopts dual receiving antennas; specifically, it may include a first satellite receiving antenna T1, a second satellite receiving antenna T2, a GPS-RTK receiver, and a controller. And other equipment.
  • the first satellite receiving antenna T1 is fixedly disposed at a center position of the rear axle of the unmanned mower; the second satellite receiving antenna T2 is fixedly disposed at a center position of the front axle of the unmanned mower.
  • the GPS-RTK receiver is fixedly disposed at a predetermined position on the unmanned mower, and is mainly used for receiving the letter according to the first satellite receiving antenna and the second satellite receiving antenna connected thereto. Information, calculate the position information and posture information of the current moment of the unmanned mower, and send it to the controller.
  • the controller is fixedly set at a predetermined position on the unmanned mower, and a plurality of known controller devices, such as a single chip microcomputer, a microcomputer, etc., can be selected as needed; wherein the controller is configured to receive according to GPS-RTK
  • the position information and attitude information of the current moment of the unmanned mowing vehicle sent by the machine calculate the distance and the angle deviation between the position and the heading of the unmanned mower at the current moment, and send and control the unmanned mower.
  • Control commands (such as steering angle commands and speed commands).
  • controller is further configured to:
  • the steering angle of the steering mechanism of the unmanned mower is obtained; the steering angle of the obtained unmanned mower steering mechanism is sent to the control command form.
  • the control method of the unmanned mower of the present invention comprises the following steps:
  • Step 1 The GPS-RTK receiver acquires the position information and the posture information of the current time of the unmanned vehicle according to the received information received by the first satellite receiving antenna and the second satellite receiving antenna.
  • the GPS-RTK receiver can solve the current high-precision position signals of the two receiving antennas, and obtain the heading information of the T1 direction in the T2 direction, that is, the current heading posture of the unmanned mowing vehicle. Heading It can be calculated from the T1 position (x 1 , y 1 ) and the T2 position (x 2 , y 2 ):
  • the positional accuracy obtained by GPS-RTK technology is centimeter level. If the accuracy error is s, the heading angle accuracy error is It can be seen that the larger the position of the antennas T1 and T2, the higher the heading angle accuracy.
  • Step 2 The controller calculates the distance deviation and the angular deviation between the position and the heading of the unmanned vehicle and the planned path according to the position information and the posture information of the current time of the unmanned vehicle transmitted by the GPS-RTK receiver.
  • Figure 1 shows the control of the steering angle control of the unmanned mower in the small deviation.
  • the planning path is 1, the arrow indicates the path direction, and the vertical distance between the midpoint of the unmanned mower and the planned path is d, set the distance deviation threshold d t , ⁇ is the angular deviation between the current unmanned mower and the planned path.
  • Step 3 The controller compares the distance deviation with the set distance deviation threshold, and combines the angle deviation to obtain the steering angle of the steering mechanism of the unmanned vehicle, specifically including:
  • a 1 and b 1 are coefficients, which are set according to the actual debugging conditions, and are generally set to 1; ⁇ max is the maximum steering angle of the steering mechanism of the unmanned vehicle. Further, in the present embodiment, it is preferable that the distance deviation threshold d t is equal to the maximum speed V max multiplied by the instruction period T.
  • ⁇ is a positive value indicating a left turn and a negative value indicating a right turn.
  • Step 4 The steering angle of the unmanned vehicle steering mechanism obtained by the controller is sent to the steering motor of the unmanned vehicle in the form of a control command.
  • the unmanned vehicle control method and the unmanned mowing vehicle of the invention can obtain the precise position and posture information of the unmanned mower, and the position deviation and the angular deviation calculated by the planned path are more accurate and effective; in addition, according to different situations Different correction steering strategies ensure a faster return to the correct trajectory.
  • step three After that and before step four, the following steps are also included:
  • the obtained steering angle is corrected by the following step function (3):
  • ⁇ ' is the steering angle corrected for this step; and, in addition, step 4 is that the controller transmits the corrected steering angle to the steering motor of the unmanned vehicle in the form of a control command.
  • a schematic diagram of the steering angle step function is used to discretize the original continuous steering angle output.
  • the unmanned vehicle can avoid the frequent operation of the steering motor during the trajectory tracking process by controlling the steering angle, thereby reducing the steering mechanism loss.
  • the step of correcting the steering angle obtained by the step function further includes:
  • the return function is added on the basis of the step function to correct the obtained steering angle.
  • the schematic diagram of the effect of increasing the return function is to set a dead zone on the edge of the output steering angle change to prevent jitter.
  • step three and before step four the following steps are further included:
  • the steering angle is corrected according to the current speed of the unmanned vehicle, specifically by the following relation (4):
  • a 2 and b 2 are coefficients. According to the field debugging settings, the steering angle will be reduced correspondingly to the higher speed; v the current speed of the unmanned vehicle.
  • the distance L between the two adjacent lines of the unmanned mower is required (ie, effective cutting)
  • the relationship between the actual cut width S and the header is:
  • the grass cover efficiency F of the unmanned mower is:
  • the cutting width of the header is 2.4 meters, and the unmanned mower adopts the above control method to realize the trajectory tracking control, from the deviation -1 m.
  • the position starts running and quickly returns to the planning trajectory.
  • the overshoot is small. At 0.1m. Therefore, it is more suitable to set the effective cutting width L of the unmanned mower to 2m, which can ensure the full coverage of mowing.

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Aviation & Aerospace Engineering (AREA)
  • Physics & Mathematics (AREA)
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Abstract

本发明涉及无人车及其控制方法设计，特别涉及一种无人车控制方法及无人割草车。无人车控制方法包括如下步骤：获取无人车当前时刻的位置信息和姿态信息；计算当前时刻所述无人车的位置和航向与规划路径之间是距离偏差和角度偏差；在距离偏差不小于距离偏差阈值以及大于距离偏差阈值时，分别获取无人车转向机构的转向角度；将获得的所述无人车转向机构的转向角度以控制指令形式发送至无人车。本发明的无人车控制方法及无人割草车，能够获得无人割草车精确位置和姿态信息，结合规划路径计算得到的位置偏差和角度偏差更加精确有效；另外，可以根据不同情形采取不同修正转向策略，能够确保更加迅速的回到正确轨迹上。

Description

一种无人车控制方法及无人割草车 技术领域
本发明涉及无人车及其控制方法设计，特别涉及一种无人车控制方法及无人割草车。
背景技术
随着科学技术的快速发展，无人车发展越来越受到关注，国内外各大汽车厂商和科技公司都投入大量精力到无人车研发中。无人车是一个集环境感知、路径规划和决策控制等多种功能于一体的综合机器人系统。
其中，决策控制相当于无人车的大脑，其主要功能是依据感知系统获得的信息来进行决策判断，进而对下一步的行为进行决策，控制车辆如何行进。因此，决策控制技术是无人车系统中的关键性技术。决策控制系统的行为分为反应式、反射式和综合式。其中，反应式控制是一个反馈控制的过程，是根据车辆当前位置与期望路径的偏差，不断调节方向盘转角和车速，直到到达目的地。但是，仅仅简单通过位置偏差获得轨迹跟踪控制还无法顺畅控制无人车。
为了解决上述问题，目前的一些无人车，是通过高清摄像机、激光扫描仪和雷达传感器等来观察周边道路和障碍物信息，从而建立轨迹跟踪控制算法，但此类方法算法复杂，实现难度大，且不是适合在野外场合使用。
另外，无人割草车是无人车技术在特定场合的应用实例，其主要应用在大型机场草坪修整作业中。无人割草车通过GPS卫星导航仪采集作业地图边界信息，并规划最优行进路径在区域内进行遍历割草作业。因此，如何控制无人割草车按照规划的路径行进实现区域内全覆 盖遍历割草作业的轨迹跟踪控制方法成为重中之重。
发明内容
本发明的目的是提供了一种无人车控制方法及无人割草车，以解决现有无人车及无人割草车控制方法存在的至少一个问题。
本发明的技术方案是：
一种无人车控制方法，包括如下步骤：
步骤一、获取无人车当前时刻的位置信息和姿态信息；
步骤二、计算当前时刻所述无人车的位置和航向与规划路径之间是距离偏差和角度偏差；
步骤三、通过将所述距离偏差与设置的距离偏差阈值进行比较，并结合所述角度偏差，获取所述无人车转向机构的转向角度，具体包括：
当所述距离偏差不小于距离偏差阈值时，通过如下公式(1)获得转向角度θ：
Figure PCTCN2017116120-appb-000001
其中，a1、b1为系数，θmax为无人车转向机构的最大转向角度，dt为所述距离偏差阈值，d无车中点与规划路径之间的垂直距离，α为当前时刻无人车与规划路径之间的角度偏差；
当所述距离偏差大于距离偏差阈值时，通过如下关系式(2)获得转向角度θ：
Figure PCTCN2017116120-appb-000002
其中，θ为正值表示左转向，为负值表示右转向；
步骤四、将获得的所述无人车转向机构的转向角度以控制指令形 式发送至无人车的转向电机。
可选的，在所述步骤三之后且在所述步骤四之前还包括如下步骤：
通过如下阶梯函数(3)对获得的转向角度进行修正：
Figure PCTCN2017116120-appb-000003
其中，θ’为此步骤修正后的转向角度；
另外，所述步骤四是将所述修正后的转向角度以控制指令形式发送至无人车的转向电机。
可选的，在所述阶梯函数对获得的转向角度进行修正步骤中还包括：
在所述阶梯函数基础上增加回型函数，从而对获得的转向角度进行修正。
可选的，在所述步骤三之后且在所述步骤四之前还包括如下步骤：
根据无人车当前时刻车速情况对转向角度进行修正，具体是采用如下关系式(4)进行修正：
Figure PCTCN2017116120-appb-000004
其中，a2、b2为系数，v无人车当前时刻车速。
可选的，所述距离偏差阈值等于无人车当前时刻最大车速乘以指令周期。
本发明还提供了一种无人割草车，采用上述任一项所述的无人车控制方法进行控制，其中，所述无人割草车包括：
第一卫星接收天线，固定设置在所述无人割草车后轮轴中心位置；
第二卫星接收天线，固定设置在所述无人割草车前轮轴中心位置；
GPS-RTK接收机，固定设置在所述无人割草车上，用于根据与其连接的所述第一卫星接收天线和第二卫星接收天线接收到的信息，获取所述无人割草车当前时刻的位置信息和姿态信息；
控制器，固定设置在所述无人割草车上，所述控制器用于：
根据所述无人割草车当前时刻的位置信息和姿态信息，计算当前时刻所述无人割草车的位置和航向与规划路径之间是距离偏差和角度偏差；
通过将所述距离偏差与设置的距离偏差阈值进行比较，并结合所述角度偏差，计算所述无人割草车转向机构的转向角度；
将获得的所述无人割草车转向机构的转向角度以控制指令形式发送至所述无人割草车的转向电机。
可选的，所述控制器还用于通过阶梯函数对获得的转向角度进行修正，将所述修正后的转向角度以控制指令形式发送至无人割草车的转向电机。
可选的，所述控制器还用于在所述阶梯函数基础上增加回型函数，从而对获得的转向角度进行修正。
可选的，所述控制器还用于根据无人割草车当前时刻车速情况对转向角度进行修正。
可选的，所述无人割草车割台的有效割幅与实际割幅采用如下关系式(5)进行确定：
L≤S-2·D   (5)；
其中，L为有效割幅，S为实际割幅，D为无人割草车轨迹跟踪控制精度偏差。
发明效果：
本发明的无人车控制方法及无人割草车，能够获得无人割草车精确位置和姿态信息，结合规划路径计算得到的位置偏差和角度偏差更加精确有效；另外，可以根据不同情形采取不同纠偏转向策略，能够确保更加迅速的回到正确轨迹上。
附图说明
图1是本发明无人割草车小偏差纠偏转向示意图；
图2是本发明无人割草车大偏差纠偏转向的一个示意图；
图3是本发明无人割草车大偏差纠偏转向的另一示意图；
图4是本发明无人割草车转向角度阶梯函数示意图；
图5是本发明无人割草车转向角度死区设置示意图；
图6是本发明无人割草车的轨迹跟踪控制仿真效果图。
具体实施方式
为使本发明实施的目的、技术方案和优点更加清楚，下面将结合本发明实施例中的附图，对本发明实施例中的技术方案进行更加详细的描述。在附图中，自始至终相同或类似的标号表示相同或类似的元件或具有相同或类似功能的元件。所描述的实施例是本发明一部分实施例，而不是全部的实施例。下面通过参考附图描述的实施例是示例性的，旨在用于解释本发明，而不能理解为对本发明的限制。基于本发明中的实施例，本领域普通技术人员在没有作出创造性劳动前提下所获得的所有其他实施例，都属于本发明保护的范围。下面结合附图对本发明的实施例进行详细说明。
在本发明的描述中，需要理解的是，术语“中心”、“纵向”、“横向”、“前”、“后”、“左”、“右”、“竖直”、“水平”、“顶”、“底”、“内”、 “外”等指示的方位或位置关系为基于附图所示的方位或位置关系，仅是为了便于描述本发明和简化描述，而不是指示或暗示所指的装置或元件必须具有特定的方位、以特定的方位构造和操作，因此不能理解为对本发明保护范围的限制。
下面结合附图1至图6对本发明无人车控制方法及无人割草车做进一步详细说明。
本发明提供了一种无人车控制方法(无人车的轨迹跟踪控制方法)，是控制无人车的转向角度及速度使其达到沿规划轨迹运行的过程。采用GPS-RTK卫星导航技术，在无人车上布置卫星接收天线来获取无人车精确位置和姿态信息，结合规划路径计算得到的位置偏差(即距离偏差)和角度偏差。以位置偏差和角度偏差为基础建立无人割草车轨迹跟踪纠偏算法，设定多个位置偏移阈值和角度偏移阈值，在小偏差范围内的转向角度线性连续变化，在超出阈值范围时，采用大转向角度控制无人车尽快返回到正确运行轨迹上。针对不同转向执行机构可以选择性在转向角度控制上增加阶梯函数、回型函数和速度函数来优化转向角度。
需要说明的是，本发明的无人车控制方法可以根据需要应用到多种适合的无人车上；下面以无人割草车为例进行详细说明。
本发明的无人割草车采用GPS-RTK技术获取定位导航信息，采用双接收天线；具体地，可以包括第一卫星接收天线T1、第二卫星接收天线T2、GPS-RTK接收机以及控制器等设备。其中，第一卫星接收天线T1固定设置在无人割草车后轮轴中心位置；第二卫星接收天线T2固定设置在无人割草车前轮轴中心位置。
GPS-RTK接收机固定设置在无人割草车上预定位置，主要用于根据与其连接的第一卫星接收天线和第二卫星接收天线接收到的信 息，计算获得无人割草车当前时刻的位置信息和姿态信息，并发送给控制器。
控制器固定设置在无人割草车上预定位置，可以根据需要选择已知的多种适合的控制器设备，例如单片机、微型计算机等等；其中，控制器配置成用于根据GPS-RTK接收机发送的无人割草车当前时刻的位置信息和姿态信息，计算当前时刻无人割草车的位置和航向与规划路径之间是距离偏差和角度偏差，并发送控制无人割草车的控制指令(例如转向角度指令和速度指令)。
进一步，控制器还配置成用于：
通过将距离偏差与设置的距离偏差阈值进行比较，并结合角度偏差，获取无人割草车转向机构的转向角度；将获得的无人割草车转向机构的转向角度以控制指令形式发送至无人割草车的转向电机；通过阶梯函数对获得的转向角度进行修正，将所述纠偏后的转向角度以控制指令形式发送至无人割草车转向电机；在阶梯函数基础上增加回型函数，从而对获得的转向角度进行修正；根据无人割草车当前时刻车速情况对转向角度进行修正。
本发明的无人割草车的控制方法包括如下步骤：
步骤一、GPS-RTK接收机根据接收的第一卫星接收天线和第二卫星接收天线接收到的信息，获取无人车当前时刻的位置信息和姿态信息。
具体地，GPS-RTK接收机可以解算获得当前两接收天线高精度位置信号，并获得T1指向T2方向的航向信息，即为无人割草车的当前航向姿态。航向角
Figure PCTCN2017116120-appb-000005
可通过T1位置(x1,y1)与T2位置(x2,y2)计算获得：
Figure PCTCN2017116120-appb-000006
采用GPS-RTK技术获得的位置精度为厘米级，假设其精度误差为s，则航向角精度误差为
Figure PCTCN2017116120-appb-000007
可知天线T1和T2位置越大，航向角精度越高。
步骤二、控制器根据GPS-RTK接收机传输的无人车当前时刻的位置信息和姿态信息，计算当前时刻无人车的位置和航向与规划路径之间是距离偏差和角度偏差。
如图1所示给出了无人割草车在小偏差修正转向角度控制示意图，其中规划路径为1，箭头表示路径方向，无人割草车中点与该规划路径之间的垂直距离为d，设置距离偏差阈值dt，α为当前无人割草车与规划路径之间的角度偏差。
步骤三、控制器通过将距离偏差与设置的距离偏差阈值进行比较，并结合角度偏差，获取无人车转向机构的转向角度，具体包括：
1)当距离偏差不小于距离偏差阈值时(即d≤dt时)，通过如下公式(1)获得转向角度θ：
Figure PCTCN2017116120-appb-000008
其中，a1、b1为系数，根据实际调试情况设定，一般情况下设定为1；θmax为无人车转向机构的最大转向角度。另外，本实施例中，优选距离偏差阈值dt等于最大速度Vmax乘以指令周期T。
2)当距离偏差大于距离偏差阈值时(即d>dt)，通过如下关系 式(2)获得转向角度θ：
Figure PCTCN2017116120-appb-000009
其中，θ为正值表示左转向，为负值表示右转向。
步骤四、控制器将获得的无人车转向机构的转向角度以控制指令形式发送至无人车的转向电机。
本发明的无人车控制方法及无人割草车，能够获得无人割草车精确位置和姿态信息，结合规划路径计算得到的位置偏差和角度偏差更加精确有效；另外，可以根据不同情形采取不同修正转向策略，能够确保更加迅速的回到正确轨迹上。
进一步，由于转向电机在每个指令周期都会得到新的转向角度指令，频繁的给定转向指令，将会对转向机构造成损害，因此，本发明无人割草车的控制方法中，在步骤三之后且在步骤四之前还包括如下步骤：
通过如下阶梯函数(3)对获得的转向角度进行修正：
Figure PCTCN2017116120-appb-000010
其中，θ’为此步骤修正后的转向角度；另外，步骤四是控制器将修正后的转向角度以控制指令形式发送至无人车的转向电机。
如图4所示为转向角度阶梯函数示意图，即将原本连续的转向角度输出离散化。无人车在控制转向角度实现轨迹跟踪过程中则可避免频繁操作转向电机，从而降低转向机构损耗。
进一步，在阶梯函数的边界值时依然存在转向机构抖动现象，为消除抖动现象，在本发明无人割草车的控制方法中，在阶梯函数对获得的转向角度进行修正步骤中还包括：
在阶梯函数基础上增加回型函数，从而对获得的转向角度进行修正。如图5所示为增加回型函数效果示意图，即在输出转向角度变化边沿设置死区，防止抖动。
进一步，在本发明无人割草车的控制方法中，无人割草车执行轨迹跟踪算法输出转向角度时，应当考虑当前车速情况。具体地，在步骤三之后且在步骤四之前还包括如下步骤：
根据无人车当前时刻车速情况对转向角度进行修正，具体是采用如下关系式(4)进行修正：
Figure PCTCN2017116120-appb-000011
其中，a2、b2为系数，根据实地调试设定，使得速度越大执行转向角度会相应减小；v无人车当前时刻车速。
在本发明无人割草车中，若无人割草车轨迹跟踪控制精度偏差为D，则要求设定的无人割草车两条相邻线路之间的距离L(即有效割幅)与割台实际割幅S之间的关系为：
L≤S-2·D   (5)；
这样能够使得无人割草车全覆盖，不发生漏割现象。此时，无人割草车割草覆盖效率F为：
Figure PCTCN2017116120-appb-000012
如图6所示，在本发明无人割草车中的一个具体实施例中，其割台割幅为2.4米，无人割草车采用上述控制方法后实现轨迹跟踪控制，从偏差-1m位置开始运行，很快回到规划轨迹线上运行，超调偏差小 于0.1m。因此，无人割草车有效割幅L设置为2m较为合适，能保证全覆盖割草作业。
以上所述，仅为本发明的具体实施方式，但本发明的保护范围并不局限于此，任何熟悉本技术领域的技术人员在本发明揭露的技术范围内，可轻易想到的变化或替换，都应涵盖在本发明的保护范围之内。因此，本发明的保护范围应以所述权利要求的保护范围为准。

Claims (10)

  1. 一种无人车控制方法，其特征在于，包括如下步骤：
    步骤一、获取无人车当前时刻的位置信息和姿态信息；
    步骤二、计算当前时刻所述无人车的位置和航向与规划路径之间是距离偏差和角度偏差；
    步骤三、通过将所述距离偏差与设置的距离偏差阈值进行比较，并结合所述角度偏差，获取所述无人车转向机构的转向角度，具体包括：
    当所述距离偏差不小于距离偏差阈值时，通过如下公式(1)获得转向角度θ：
    Figure PCTCN2017116120-appb-100001
    其中，a1、b1为系数，θmax为无人车转向机构的最大转向角度，dt为所述距离偏差阈值，d无车中点与规划路径之间的垂直距离，α为当前时刻无人车与规划路径之间的角度偏差；
    当所述距离偏差大于距离偏差阈值时，通过如下关系式(2)获得转向角度θ：
    Figure PCTCN2017116120-appb-100002
    其中，θ为正值表示左转向，为负值表示右转向；
    步骤四、将获得的所述无人车转向机构的转向角度以控制指令形式发送至无人车的转向电机。
  2. 根据权利要求1所述的无人车控制方法，其特征在于，在所述步骤三之后且在所述步骤四之前还包括如下步骤：
    通过如下阶梯函数(3)对获得的转向角度进行修正：
    Figure PCTCN2017116120-appb-100003
    其中，θ’为此步骤修正后的转向角度；
    另外，所述步骤四是将所述修正后的转向角度以控制指令形式发送至无人车的转向电机。
  3. 根据权利要求2所述的无人车控制方法，其特征在于，在所述阶梯函数对获得的转向角度进行修正步骤中还包括：
    在所述阶梯函数基础上增加回型函数，从而对获得的转向角度进行修正。
  4. 根据权利要求3所述的无人车控制方法，其特征在于，在所述步骤三之后且在所述步骤四之前还包括如下步骤：
    根据无人车当前时刻车速情况对转向角度进行修正，具体是采用如下关系式(4)进行修正：
    Figure PCTCN2017116120-appb-100004
    其中，a2、b2为系数，v无人车当前时刻车速。
  5. 根据权利要求1所述的无人车控制方法，其特征在于，所述距离偏差阈值等于无人车当前时刻最大车速乘以指令周期。
  6. 一种无人割草车，其特征在于，采用如权利要求1-5任一项所述的无人车控制方法进行控制，其中，所述无人割草车包括：
    第一卫星接收天线，固定设置在所述无人割草车后轮轴中心位置；
    第二卫星接收天线，固定设置在所述无人割草车前轮轴中心位置；
    GPS-RTK接收机，固定设置在所述无人割草车上，用于根据与其连接的所述第一卫星接收天线和第二卫星接收天线接收到的信息，获取所述无人割草车当前时刻的位置信息和姿态信息；
    控制器，固定设置在所述无人割草车上，所述控制器用于：
    根据所述无人割草车当前时刻的位置信息和姿态信息，计算当前时刻所述无人割草车的位置和航向与规划路径之间是距离偏差和角度偏差；
    通过将所述距离偏差与设置的距离偏差阈值进行比较，并结合所述角度偏差，计算所述无人割草车转向机构的转向角度；
    将获得的所述无人割草车转向机构的转向角度以控制指令形式发送至所述无人割草车的转向电机。
  7. 根据权利要求6所述的无人割草车，其特征在于，所述控制器还用于通过阶梯函数对获得的转向角度进行修正，将所述修正后的转向角度以控制指令形式发送至无人割草车的转向电机。
  8. 根据权利要求7所述的无人割草车，其特征在于，所述控制器还用于在所述阶梯函数基础上增加回型函数，从而对获得的转向角度进行修正。
  9. 根据权利要求8所述的无人割草车，其特征在于，所述控制器还用于根据无人割草车当前时刻车速情况对转向角度进行修正。
  10. 根据权利要求6所述的无人割草车，其特征在于，所述无人割草车割台的有效割幅与实际割幅采用如下关系式(5)进行确定：
    L≤S-2·D  (5)；
    其中，L为有效割幅，S为实际割幅，D为无人割草车轨迹跟踪控制精度偏差。
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