Depth control system is important in bulb crop harvester. The higher the depth causes the greater amount of soil entering to harvesting system. A proper depth control leads to optimize energy consumption. A four-bar mechanism was used in order to move the blade of the machine and to control the operation depth while a DC electrical motor provided the movement of the blade. The four-bar mechanism consisted of a power screw, linkage bars, moveable pin and a blade. A control system was used to follow the uneven ground surface and control the displacement of the blade by sending commands to the DC electrical motor. The tests were carried out in laboratory on artificial uneven ground in sinuous curves as well as square and triangle shapes. The displacement of the blade was recorded by a digital camera and converted to image and analyzed using Matlab software. All the tests were replicated three times. The photo sensor responded better than the capacitive sensor for all obstacle shapes.
