Measuring tillage depth for tractor implement automatic using inclinometer

Nowadays, the motion of agricultural implements in tractors is increasingly controlled by means of electronic systems. Position measurement is a fundamental factor in tractor implement tillage depth automatic control system. The methods of linkage position measuring are divided into two kinds. One is a direct measurement that is based on external-mounted devices, such as a fifth wheel meter, or sliding palm. Another is indirect measurement that uses integrated sensors, such as a potentiometer, or camshaft. A new indirect method is proposed based on the inclinometer in this paper. The inclinometer whose package size is small is mounted on the surface of each side lifting arm. The first step is to get the relations of lifting arm level angle, tillage depth and inclinometer output voltage on the basis of the three-point hitch linkage geometric and inclinometer characteristics. The calibrated data show that the relationship between the sensor voltage output value and tillage depth is approximately linear and can thus be used as an equation to get positions. Once regulated hitch linkage or soil characteristics changes it should be used to re-calibrate the system and obtain a new formula. Compared to other methods of position measurement, by this means the measurement is convenient to be integrated, installed, maintained and calibrated, and the comprehensive precision of sensor is ±1.4 mm. Meanwhile, a virtual terminal display device for tractor implements operation was designed according to the ISOBUS standard. Its interface was classified according to the tractor implements working mode, on which various operating parameters and tillage depth curve reflects the real-time tillage depth control condition during cultivating. With this, if the tillage depth curve fluctuated due to instable working conditions, the operator may adjust set value, change the mode of control and increase or decrease tractor speed in order to achieve the purpose of stable tillage depth. A system of tillage depth measurement and tractor hitch automatic control is established. In position control mode, the field tests showed that the standard deviation is 8.19 when cultivated tillage depth value is -200 mm, and the result is lower than the fifth wheel meter method. That is to say, the inclinometer measurement method is more reliable. When the tillage depth value dropped from -100mm to -200mm, the response time of system was 3.50 s, less than the fifth wheel meter method, and the dynamic characteristic of the system was better. The variation of tillage depth stability coefficient was 3.34% when the tractor implemented actual cultivating that mets the agronomic requirements of 10%. By putting forward the tillage depth measurement, display interface and automatic control system of tractor hitch linkage, this paper has certain reference significance for tractor implement design.