Operating agricultural vehicle such as tractors and harvesters often requires highly repetitive operations. Due to the repetitive nature of the work, and irregularities in the terrain, gaps and overlaps in the rows of crops can occur. This can result in damaged crops, overplanting, or reduced yield per acre. Additionally, it is often desirable for a vehicle to follow a set path pattern over an area, for example when planting a field, conducting a search, or to reproduce a previously created path pattern at a later date. For example, a field may be ploughed, then sowed or planted, fertilized, sprayed and harvested. Following the same path pattern over the field each time ensures that each subsequent action is targeted to the correct area. It is therefore known to pre-plan the paths that a vehicle will follow. As the size of agricultural vehicles and farming implements continues to increase, precisely controlling their motion becomes more important.
Guidance systems are increasingly used for controlling agricultural and environmental management equipment and operations such as road side spraying, road salting, and snow plowing where following a previously defined route is desirable. This allows more precise control of the vehicles than is typically realized than if the vehicle is steered by a human.
In one known method of planning a plurality of desired paths for a machine to traverse, the path planning system may receive information including the physical dimensions of the machine. A first reference path may be traced using position sensing means, and this path used to plan subsequent paths, which may be either straight or curved.
The perimeter of a work area may be established by driving the perimeter whilst generating positioning signals, storing the positioning signals and then planning a pattern of work paths to cover the area contained by the perimeter. The desired pattern can be chosen after considering factors which may include the area covered during one pass, the turning radius of the machine or the size of the work area. A GPS system is particularly appropriate for this application.
Projected paths may be used to guide a robotically controlled vehicle directly, or transmitted to an on-board display to be followed by a human operator. Systems of course-correction may be used to minimize cross-track and offset if the vehicle deviates from a pre-projected path. Gain tuning may also be applied to the auto-steering system in order to approximate the differences in human steering when the vehicle is traveling at different speeds.
However, the current systems for planning a path pattern encounter problems when the desired path follows a concave curve. For example, in subsequent parallel paths, the curve typically becomes progressively sharper until the radius of the planned turn is too sharp for the vehicle to physically perform. It may then become necessary for a driver to manually stop and turn the vehicle to realign it with the planned path pattern. Typically, this manually determined path correction is not reproducible at a later date.
There are known methods of determining whether a curve is too tight. In one method, when a curve is identified as being too tight, that path is abandoned, and a fresh one drawn. This results in complicated path patterns which are difficult to drive.
Another current method for planning a curved path projects a path by looking ahead of the current position either a set amount of time or distance and creating a heading based on the predicted location at that time. This is neither repeatable nor reliable.