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In the orchard, a GPS isnt available because the surrounding trees prevent the GPS receiver form being brought into operation. Hence in order to guide the robot tractor, surrounding information is necessary. The objective of this study is to develop the guidance system without GPS in an orchard. This system detects the course which robot drive form surrounding environments. To detect them a laser scanner was adopted in front of the robot tractor. This laser scanner can search distances and angles of the obstacles in the forward. The angle resolution is 1 degree, and the distance range is 80m.

To control the robot tractor, the position and direction information is necessary. So the relative relation between the robot tractor and orchard rows was detected. Hough transform was adopted because it can detect lines certainly even if the points were missed. Using Hough transform, the lateral and direction error between the robot and orchard rows were calculated.

Field test was examined to research the accuracy of this system. The robot tractor ran in the orchard. In this time, the robot tractor loaded RTK-GPS and IMU to compare the result of laser detection. The result of this test, R.M.S of lateral error and direction error was 10cm and 0.7 degree respectively.

In this research, the guidance system in the orchard was established. The accuracy of this system was enough to control the robot tractor.