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Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The generation of power shift tractor promotes the automatic driving of agricultural machinery to the direction of unmanned, and the automatic obstacle avoidance of agricultural machinery has become a key issue to be solved. Most of the existing obstacle avoidance path planning adopts the shortest tangent method, which has the advantages of fast and simple path generation and short track, but the curvature of the path curve is discontinuous and there are corner inflection points, which make the tractor front wheel angle suddenly change and affect the obstacle avoidance accuracy. In this paper, for the curvature discontinuity of the shortest tangent path curve, poor tracking control accuracy and low precision of agricultural machinery model, the third-order bezier curve optimization method was used to form a continuous smooth agricultural machine obstacle avoidance path. The optimized curve curvature was continuous and the obstacle avoidance path was smooth with no turning points, which was conducive to the control of agricultural machinery driving. The linear control model of agricultural machinery movement was established by chain control theory, and the PI controller was used for corner compensation to improve the accuracy of agricultural machinery obstacle avoidance. The simulation of the path tracking control method was completed. The simulation results showed that the heading error angle of the agricultural machinery was mostly in the range of - 0.06-0.06 rad, the lateral position error was less than 13 cm, and the front wheel steering angle changed gently with no significant mutation, indicating that the control method of the obstacle avoidance path control method had a high precision, and the agricultural machinery can drive according to the preset trajectory. The ploughing operation test was carried out, and the Dongfanghong LF954-C power shift tractor was used, which can automatically start, stop, shift, and implement the lifting operation of the farm. The tractor was equipped with the Beidou agricultural autopilot with the straight running accuracy of ±2.5 cm. Ultrasonic radar and image recognition technology were used to perceive obstacles in the working environment. The farm implement was a 250 cm wide plow. A haystack obstacle was set on the machine working path with a contour radius smaller than the minimum turning radius of the tractor. The results of the plowing operation test showed that the machine can automatically complete the straight-line driving, farm implement lifting, automatic obstacle avoidance, farm implement falling, and continuous straight-line operation. The obstacle avoidance accuracy of the bezier curve was 5.21 cm, and the tracking control effect of the curve path was well. The accuracy of the agricultural machine continuing to travel in a straight line after obstacle avoidance was 1.98 cm, which indicated that the path tracking control method can ensure the tractor straight-line automatic driving after obstacle avoidance. The above results showed that the obstacle avoidance path and control method showed good robustness and adaptability in uneven ploughing land and can meet the obstacle avoidance requirements of tractor operation. [ABSTRACT FROM AUTHOR]

Copyright of Transactions of the Chinese Society of Agricultural Engineering is the property of Chinese Society of Agricultural Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Soil subsoiling is currently the most widely used method for soil loosening, which can break the hard bottom of soil. At present, soil subsoiling operations mainly use shovel subsoiler, which has common problems like poor subsoiling effect, uneven soil disturbance and high energy consumption. In this context, a new subsoiling technology, gas explosion subsoiling, is studied in this paper, which injects high pressure gas into the soil to cause fissures, thereby breaking the bottom soil and achieving the purpose of subsoiling. In order to clarify the subsoiling effect of gas explosion on soil, an orthogonal test with the gas explosion parameters like pressure, depth and volume was designed. The soil block used in test was in standard size of 100 cm × 50 cm (diameter × height). The soil fissures and disturbance situation on the soil section were observed through the cross-sectional treatment method, and the influence of gas explosion parameters on soil fissure extension was analyzed. Then, the soil fissure trace equation and soil disturbance model were established based on the 9 orthogonal test results calculated by OriginPro software and Auto2Fit software. The effect of soil damage form on the impact of soil subsoiling was discussed based on Mohr-Coulomb soil strength theory and Rankine's earth pressure theory. The orthogonal experiment results showed that the greater the gas explosion pressure, the deeper the gas explosion depth; the more the gas volume, the better the soil subsoiling effect. The soil fissure trace equation was a quadratic function and the soil disturbance area was parabolic. This research provided a model and method for studying the soil fissure trace equation, and the soil hardness in the equation could be used as a variable for the soil type, so the soil fissure trace equation was applicable to most types of soils. The soil was mainly subjected to pulling damage when the gas explosion depth was less than 25 cm, the soil surface tended to rise at the gas splitting force of 0.17 MPa and the disturbance coefficient of 50%, and the center of soil fissure was the gas explosion center. The soil was mainly subjected to shear damage when the gas explosion depth was more than 25 cm, the soil surface elevation was not obvious at the gas splitting force of 0.39 MPa and the soil disturbance coefficient of more than 50%, and meanwhile the center of soil fissure moved downward, and the downward displacement increased with the increase of gas explosion pressure. What was more, the effect of shear damage on soil subsoiling was better than that of pulling damage. Therefore, soil shear damage should occur as much as possible in design of gas explosion technological parameters, which played a significant role in promoting the expansion of soil fissures and increasing the degree of soil loosening. When the gas explosion depth was 25 cm, the soil damage would be the joint action of pulling and shear, and the degrees of these 2 kinds of damages were equivalent, which was conducive to the horizontal expansion of soil fissures. In addition, the gas explosion pressure was not as high as possible, and higher pressure gas source had a higher technical requirement on gas storage and booster device, and also a longer time for gas collection, which was not conducive to long-term working operation. The data optimization results showed that 1 MPa gas explosion pressure and 30 cm gas explosion depth were more appropriate, and under the condition the soil subsoiling effect was remarkable with the soil disturbance coefficient of 79.5%. The results can provide theoretical basis for the optimization of gas explosion subsoiling parameters. [ABSTRACT FROM AUTHOR]