Design and optimization of a new terrain-adaptive hitch mechanism for hilly tractors

In view of the problems of poor working quality and low efficiency caused by traditional hitch mechanisms,which cannot make farm implements adapt to hillside fields for terrain-adaptive working after leveling the body of hilly tractors,a new type of terrain-adaptive hitch mechanism was designed which can adjust the transverse posture of farm implements to meet the ploughing requirements of complicated terrain in hilly and mountainous areas.The mechanism was mainly composed of the original hitch device and the newly added rotating device.The kinematic model of each sub-mechanism was established,as well as the mathematical relation of significant performance indexes of the whole mechanism,such as lifting capacity,transverse inclination angle and tillage depth.Genetic algorithm was used to optimize the lifting performance of this hitch mechanism in Matlab,so that the minimum vertical lifting force at the center of gravity of farm implements increased by 14.1%,which met the requirements of national standards.Through ADAMS simulation calculation,it was found that different working slopes had a certain influence on the external load of each component,and terrain-adaptive hitch mechanism had little effect on the vibration characteristics of hilly tractors.The fatigue analysis and optimization design of the key component,rotating shaft,were carried out in ANSYS Workbench,and the mass of this part reduced by 64%.A real vehicle test platform was set up to test and verify the power lifting range and working slope range of terrain-adaptive hitch mechanism.The test results showed that the actual power lifting ranged in 185-857 mm,and the maximum error from the theoretical range was only 3.1%,while the actual working slope range was from–25.9°to+23.2°,and the maximum error from the theoretical range was only 4.5%.Therefore,the terrain-adaptive hitch mechanism can meet the requirements of power lifting performance,and simultaneously can adjust the transverse posture of farm implements for adapting to hillside fields of no less than 20°.

Tractor path tracking control based on binocular vision

In the process of field operation management,determining how to accurately realize crop row identification and path tracking control is an essential part of tractor automatic navigation.According to the linear operation in the process of cotton field management,the tractor path tracking control system was designed based on binocular vision and the pure pursuit model.A new crop row detection method based on the Census transform and the PID control algorithm with dead zone were used.First,the upper computer software was developed by C++with the functions of parameter setting and image acquisition and processing.Second,an automatic steering controller was developed based on microprocessor MC9S12XS128 of Freescale.The control program was developed based on modular design using CodeWarrior during development of the PID-based automatic steering control strategy.Finally,a field experiment platform of tractor path tracking control was built,and field experiments under the actual cotton were conducted.The optimal visibility distance was determined by several previous experiments.When the tractor tracks the path with the optimal visibility distance in the growth environment of actual cotton crops,the mean absolute deviation of course angle was 0.95°,and the standard deviation was 1.26°;the mean absolute deviation of lateral position was 4.00 cm,and the standard deviation was 4.97 cm;the mean absolute deviation of front wheel angle was 2.99°,and the standard deviation was 3.67°.The experimental results show that(1)the crop row detection method based on Census transform can identify the crop line and plan the navigation path well,and(2)the tractor path tracking control system based on binocular vision has good stability and high control precision;thus,the control systemcan realize the automatic path tracking control of cotton line operation and meets the agricultural requirements of cotton field operation management.

Factorial significance on tractor stability under variation of terrain roughness employing the Taguchi method

Tractor rollover accidents remain an issue with the development of agricultural mechanization.Adopting the scale-model-based experimental approach,this study investigated the three most influential geometric factors of tractor in various agricultural ground conditions with improved configuration of force sensing system.The initiation of tractor rollover,associated with the tire-ground contact status,was investigated for various front tire types,ballast weights,and rear track widths.Employing the Taguchi method,the ground reaction forces applied to the tractor’s uphill wheels were measured and evaluated using stability indicators.By taking this approach,the effects and statistical significance of the three factors and their interactions were examined under various agricultural ground conditions.Results showed that the ballast weight significantly affected the ground contact status of the uphill front tire.The significance of the front tire type gradually increased as the road roughness increased,but dramatically decreased for an extremely rough road surface.Furthermore,none of the factors or interactions,except the factor of the rear track width for relatively rough roads,was statistically significant.The study revealed that not all commonly discussed factors consistently affect tractor stability.The results of the present study are thus expected to provide a reference explaining how to explore the necessity and feasibility of parameter adjustment before reconfiguring a tractor for higher stability.

Path-tracking control based on a dynamic trigonometric function

With the rapid development of the modern vehicle industry,the automated control of new vehicles is in increasing demand.However,traditional course control has been unable to meet the actual needs of such demand.To solve this problem,more precise pathtracking control technologies have attracted increased attention.This paper presents a new algorithm based on the latitude and longitude information,as well as a dynamic trigonometric function,to improve the accuracy of position deviation.First,the algorithm takes the course deviation and adjustment time as the optimization objectives and the given path and speed as the constraints.The controller continuously adjusts the output through a cyclic“adjustment and detection”process.Second,through an integration of the steering,positioning,and speed control systems,an experimental platform of a path-tracking control system based on the National Instruments(NI)myRIO controller and LabVIEW was developed.In addition,path-tracking experiments were carried out along a linear path,while changing lanes,and on a curved path.When comparing and analyzing the experimental results,it can be seen that the average deviation in lateral displacement along the linear and curved paths was 0.32 and
0.8 cm,and the standard deviation of the lateral displacement was 2.65 and 2.39 cm,respectively.When changing lanes,the total adjustment time for the vehicle close to the target line to reach stability was about 1.5 s.Finally,the experimental results indicate that the new algorithm achieves good stability and high control accuracy,and can overcome directional and positional errors caused by road interference while driving,meeting the precision requirements of automated vehicle control.