关键词: 自动泊车, 车头泊入, 路径规划, 样条理论, 多约束

Abstract:

With the continuous increase in the number of electric vehicles in China and the increasingly narrow parking spaces in cities, how to park safely has become one of the problems that troubles the people. Traffic accidents caused by parking errors are also common in traffic accidents. As an important component of autonomous driving, automatic parking has always had excellent market prospects and is also a hot research topic in the field of autonomous driving and automotive intelligence technology.

At present, automatic parking has relatively complete technological development, but it still has the following obvious drawbacks. Firstly, the existing automatic parking systems are all based on reversing, while electric vehicles in China have been in a high-speed development stage in recent years. For many electric vehicles, the charging ports are installed at the front of the vehicle, which will lead to the problem of charging cables being too short to charge when the driver operates reverse parking. Even if the charging cable is long enough, there is a risk of safety hazards caused by excessive stretching of the cable. Therefore, the existing parking methods based on reversing are not suitable for some electric vehicles. It is necessary to develop a parking method based on front parking. Secondly, the existing automatic parking systems do not comprehensively consider vehicle steering, braking constraints and initial dynamic posture conditions in the path planning process. This can lead to the need for in situ steering in the planned path, which increases the wear of the tires and the steering equipment. Additionally, there are potential problems in the planned reference path, such as curvature discontinuity and inconsistency with the initial posture characteristics of real vehicles. These potential issues may all affect the tracking performance of actual vehicles.

Aiming at the problems in the existing parking system, this paper designs a new parking method. The main contents are as follows. Aiming at the characteristics of the charging ports of most new electric vehicles installed in the front of the vehicle, a new parking method based on the constraint optimization model of polynomials and the B-spline curve is proposed to optimize the front parking of a vehicle. This paper analyzes the trajectory curves of the forward and backward stages during the parking process, and calculates the parking point and attitude of the car during the transition between the two stages. Based on the possible collision points during the parking process, as well as the vehicle parameter constraints such as steering and braking constraints, a polynomial multi-constraint equation for the parking planning path is established, effectively changing potential issues such as a mismatch of the initial pose characteristics of the vehicle with the pose characteristics of the starting point of the planning path. In order to ensure that the planned path can meet the continuous change of the vehicle steering wheel speed, it is necessary to optimize the parking path through four fifth order B-spline curves to solve the curvature discontinuity problem of the parking path, reduce the parking time and improve the parking efficiency. This paper proposes to use Matlab software to obtain trajectory control points using nonlinear constraint optimization functions, and obtain trajectory curves that meet the constraint conditions. The experimental results show that the path planned by combining spline theory and multi-constraint equations can achieve collision free parking and positioning of vehicles, meet the requirements of curvature continuity, and avoid problems such as turning in place.