1. Field of the Invention
The present invention relates to automatic methods and systems for steering along row crops and preventing accidents during automatic steering, and more particularly to automatic methods for steering among row crops adapted for use in settings where thicknesses of plants vary.
2. Background Art
Automatic steering methods among row crops are commonly used in harvesting where thicknesses of plants change within a row, and they may be used elsewhere as well. In various applications, a human operator may lack the skills needed to steer efficiently an agricultural machine, e.g., a harvester. In these and other applications, a self-sufficient automatic steering method is indicated. However, if the human operator relies on automatic steering, through inattentiveness or preoccupation with other tasks the operator may miss gaps which occur in rows and allow the machine to overrun a row end, risking serious accident. Hence, a self-sufficient steering method must also be safe.
Conventional methods sense a deviation from a desired, straight ahead course and then correct the deviation so as to steer on a straight course. Several patents show this approach, U.S. Pat. No. 4,367,802 (Stiff et al.), U.S. Pat. No. 4,366,756 (Brum), U.S. Pat. No. 3,797,602 (Sumida), U.S. Pat. No. 3,550,790 (Noble), and U.S. Pat. No. 3,402,784 (Roberson), each using a furrow ploughed in the ground for guidance. U.S. Pat. No. 4,345,659 (Arnold) shows a variation for sod harvesting. Sometimes it is impractical to follow a furrow in the ground. Accordingly, methods employ dual resilient sensing arms which press against the right and left side of a row of crops and then generate on-off correction signals, as U.S. Pat. No. 4,528,804 (Williams) and a companion patent, U.S. Pat. No. 4,505,094 (Demorest) disclose.
The object of all of these methods essentially is to steer straight ahead. To do this, the methods require some sort of feedback which measures a corrective motion so that the tending machine attains a straight ahead course. For instance, this feedback appears in methods employing resilient crop-sensing arms. It takes a form there of a simple expedient of halting turning once the arm loses contact with the crops.
As the thickness of the plants changes, sensing members which press against the left and right sides of the plants may generate contradictory signals. Consequently, a hiatus in sensing may occur, and sometimes a human operator must monitor steering and frequently override an automatic system. Hence, variation in plant thicknesses presents a special kind of problem.
U.S. Pat. No. 4,304,316 (Lang) addresses this problem. It shows left and right resilient arms that generate hydraulic signals X.sub.1 and X.sub.2. These signals indicate a degree of steering error, thus they are quantitative. An arm 40 (or in a separate embodiment, a lever 86) within a hydraulic chamber produces an output hydraulic signal which is the absolute value of a difference X.sub.1 -X.sub.2 between the signals. This process compensates for variations in plant thickness. However, this approach entails some new difficulties. This method includes a step, namely, correlating a corrective motion to a quantity of steering error. Without this step, the machine would not steer on a straight ahead course. To execute this step, this method requires hydraulic equipment, hoses and a valve body. Also, the fact that this method is self-sufficient and that a human operator is disengaged from driving the machine, heightens a need for protection against possible overrunning of row ends.
A type of gap protection as known in grass and grain crop steering methods. U.S. Pat. No. 3,952,828 (Stampfer et al.) shows left and right detectors 86 and 86', which sense the presence or absence of grain. At the end of a field they both generate signals which tell the harvester to halt. However, this process requires a field crop. Row crop steering methods still lack a satisfactory way to protect against overrunning of gaps and row ends.
Signals which an automatic steering system generates when contacting plants in a row, indicate the presence of the row. A gap in these signals can warn of a gap in the row. However, because of the focus of conventional methods on steering straight ahead, wherein an objective is to minimize row contact, the use of contact signals for gap detection is often forgotten. Additionally, hydraulics, or other means of quantitatively correlating corrections with errors, in certain circumstances can complicate the automatic steering process. The state of the art still insists on steering straight ahead only.