References and Acknowledgments
Most of the content of this article is reproduced from the following articles. First of all, I would like to thank the original author. I hope that I can summarize and improve on the basis of these predecessors.
1. The connection and difference between motion planning/path planning/trajectory planning
https://blog.csdn.net/wx545644217/article/details/54175035
1. Basic Concepts
Motion Planning
Path Planning
Trajectory Planning
Motion planning consists of path planning (space) and trajectory planning (time). The sequence of points or curves connecting the starting position and the ending position is called a path, and the strategy that constitutes a path is called path planning.
Path planning is one of the main research contents of motion planning.
A path is a certain sequence of robot poses, regardless of the time-varying factors of robot pose parameters.
Path planning (generally referred to as position planning) is to find a series of waypoints to pass through, the waypoints are the positions or joint angles in space, and the trajectory planning is to give the path time information.
Motion planning, also known as motion interpolation, is to insert a sequence of intermediate points for control between given path endpoints to achieve smooth motion along a given path.
Motion control mainly solves the problem of how to control the target system to accurately track the command trajectory, that is, for a given command trajectory, select the appropriate control algorithm and parameters, generate output, and control the target to accurately track the given command trajectory in real time.
The goal of path planning is to make the distance between the path and the obstacle as far as possible and the length of the path as short as possible;
The main purpose of trajectory planning is to make the running time of the robot as short as possible or the energy as small as possible in the movement of the robot joint space.
Trajectory planning adds time series information on the basis of path planning, and plans the speed and acceleration of the robot when it performs tasks to meet the requirements of smoothness and speed controllability.
Here are the highlights:
In addition, according to the content of the book Model Predictive Control of Unmanned Vehicles, the connections and differences between path and trajectory, path planning and trajectory planning, path tracking and trajectory tracking are as follows:
For an intelligent vehicle, the global waypoint only needs to contain spatial position information, and it can also contain attitude information, and it does not need to be related to time, but in local planning, time information can be considered.
It is stipulated here that the track point is also a kind of way point, that is, when the time constraint is added to the way point information, it can be called the track point.
From this perspective, trajectory planning is a kind of path planning. When the path planning process needs to satisfy the longitudinal and lateral dynamic constraints of the unmanned vehicle, it becomes trajectory planning.
Path planning and trajectory planning can be represented both in state space and in Cartesian coordinates.
In the process of path tracking, the reference path curve can be independent of time parameters. During tracking control, it can be assumed that the unmanned vehicle moves at a constant speed at the current speed, and the driving path is made to approach the reference path with a certain cost rule;
During trajectory tracking, the reference path curve is related to both time and space, and the unmanned vehicle is required to reach a preset reference path point within a specified time.
Different from trajectory tracking, path tracking is not subject to time constraints, and only needs to track the reference path within a certain error range.
Motion control in path tracking is to find a bounded sequence of control inputs to get the unmanned vehicle from an initial position to a set desired position.