拖拉机转向轮转角位移式和四连杆式间接测量方法对比试验.

Wheel swivel angle is regarded as a critical parameter in agriculture automatic navigation system, and it can always be measured by using angle sensor. In engineering practice, angle sensor is difficult to fix, and the shaft is easily broken. In order to solve the problem, displacement indirect measurement method and four-bar indirect measurement method are proposed in this paper. Wheel rotation depends on steering cylinder piston movement, and the movement of steering cylinder piston causes the movement of steering trapezoidal mechanism. Therefore it is available to apply displacement sensor in measuring the position of the steering cylinder piston rod, and the displacement sensor is parallel fixed with the steering cylinder. Referring to the motion of steering trapezoidal mechanism, it is proposed to use the front axle, knuckle arm, connecting rod and pendulum rod to form a four-bar linkage. According to the fixed location of the displacement sensor and four-bar angle sensor, it is available to establish measurement models for those 2 indirect measurement methods, and calibrate the relation between sensor measurement and wheel swivel angle, but those 3 measurement methods are incapable to measure the real wheel swivel angle. In the 2 kinematic models of wheel vehicle, wheel swivel angle is the angle between wheel axis and vehicle body axis, and thus Ackerman transformation must be used for converting the test angle into wheel swivel angle. However, different vehicles are different in the transformation of Ackerman, and the ideal Ackerman transformation cannot be used. In fact, the rotation angles of left and right wheels have little bias with the wheel swivel angle when the wheel swivel angle is being in a small range in the middle of the pair. Therefore it is supposed that the measurement angle is the wheel swivel angle. Through automatic navigation precision comparison experiment, the advantages and disadvantages of different measurement methods are compared. The experiment is performed on basis of the LOVOL tractor M800, in which the self developed automatic navigation system was used, and an experiment platform was built. The experiment is completed on the asphalt pavement and the field, and the platform can be utilized to compare the accuracy of 3 measurement methods of wheel swivel angle and compare the accuracy of navigation through statistical analysis. The result shows that the four-bar angle sensor can provide the highest angle measurement accuracy and navigation accuracy. When the vehicle keeps the speed of about 4.2 km/h, the mean value of lateral deviation is -0.028 2 cm by using the four-bar angle sensor in the field, and the mean value of lateral deviation is -0.014 6 cm by using the hall angle sensor and 0.109 0 cm by using the displacement sensor in the same experiment environment. Therefore the four-bar indirect measurement method offers almost a navigation accuracy equal with the direct angle measurement, but the standard deviation of lateral deviation for automatic navigation of the four-bar indirect measurement method is 1.297 5 cm, which is less than the direct measurement method. But considering the displacement sensor wear, when the sensor has been used for about 50 h in the same environment, the mean value of lateral deviation is -0.656 1 cm. Thus the displacement angle measurement is incapable of replacing the direct angle measurement, while the four-bar angle sensor is capable to replace direct angle measurement method and can be further applied in practice, which is easily fixed and protected. [ABSTRACT FROM AUTHOR]