Qin Zhang

Agricultural automatic guidance research in North America

Abstract A review of the recent research in agricultural vehicle guidance automation in North America is presented. A conceptual framework of an agricultural vehicle guidance automation system includes navigation sensors, navigation planner, vehicle motion models, and steering controllers.

DYNAMIC CALIBRATION AND IMAGE SEGMENTATION METHODS FOR MULTISPECTRAL IMAGING CROP NITROGEN DEFICIENCY SENSORS

Site-specific variable-rate nitrogen application is one of the core operations in precision crop management. The ndetermination of an appropriate nitrogen application rate relies greatly on the capability of assessing crop nitrogen stress. nA machinery-mounted multispectral imaging sensor has been developed for real-time crop nitrogen deficiency detection on nthe sprayer during fertilization operations. While field tests indicated that this image-based sensor was capable of detecting ncrop nitrogen deficiency “on the go,” the test results also showed that this sensor was very sensitive to ambient light changes nand needed a considerably long image processing time to extract crop nitrogen deficiency data. To solve these problems, the nresearch has developed a dynamic calibration method to compensate for ambient illumination variation on crop canopy reflectance, nan image segmentation algorithm to eliminate the soil background noise, and a correlation model to estimate the nSPAD values from the calibrated multispectral crop canopy reflectance. Field validation tests demonstrated that the developed nsensor calibration and image processing algorithms improved the performance of the multispectral sensor on detecting ncorn nitrogen stress. Using the modified sensor resulted in a reasonable correlation between the estimated and measured nSPAD values (R2 > 0.72). This research confirmed that it is technically feasible to design a machinery-mounted multispectral nimaging sensor to detect crop nitrogen stress reliably and accurately.

Hardware-in-the-loop simulator of an off-road vehicle electrohydraulic steering system.

The design of electrohydraulic (E/H) steering control systems for off-road vehicles should consider the ncharacteristics of physical components, steering system dynamics, and a variety of other factors including vehicle ndynamics and soil stiffness. A computer-controlled hardware-in-the-loop (HIL) E/H steering simulator has been ndeveloped as a tool for steering dynamics and controller research. The HIL simulator integrated a dynamic model of the nsteering system, an actual E/H steering actuator and control interface, and an independently controlled steering loader. nThis article describes the design of the HIL simulator, the development of dynamic model of a tractor E/H steering system, nand the validation of this system. Results indicated that the HIL simulator was a valuable tool for investigating the ndynamics and interface characteristics of E/H steering systems and evaluating real-time steering controller performance nin a laboratory recreated environment for off-road vehicles with loading conditions representative of the field application. nThe HIL simulator provided an effective tool for E/H steering dynamics research, E/H steering system design and E/H nsteering controller development.

A DYNAMIC PERFORMANCE EVALUATION METHOD FOR DGPS RECEIVERS UNDER LINEAR PARALLEL-TRACKING APPLICATIONS

GPS (Global Positioning System) receivers have been widely used as position sensors in precision agriculture. Many GPS manufacturers report GPS accuracy using stationary test data. However, most agricultural applications, such as tillage, planting, spraying, and harvesting, in which GPS receivers are used under dynamic conditions, are mobile operations. In this study, we developed a method to evaluate the GPS dynamic position accuracy under linear parallel-tracking applications. It is proposed that the pass-to-pass accuracy is the most important criterion in evaluating a receivers dynamic performance for those applications. Eight commercially available DGPS receivers were tested during the spring of 2002 under different dates, times of the day, and travel speeds. As examples of using the proposed method, the dynamic performance of these receivers was evaluated. It was found that the dynamic performance of a receiver was extremely variable from test to test. The cumulative frequency distribution of the pass-to-pass average error provided a good statistical measure of the GPS dynamic accuracy.

Development of Robot Tractor Based on RTK-GPS and Gyroscope

This study developed a field robot for an agricultural operating environment. The nnavigation sensor consisted of an RTK-GPS, a fiber optic gyroscope (FOG), and an inertial nmeasurement unit (IMU). A sensor fusion algorithm was used to identify FOG bias and ncompensate for location error in real-time, thus providing sufficient navigation information to nsupport accurate robot guidance in the field. The guidance system could guide the agricultural nrobot automatically to follow either straight or curve paths including crop rows at a speed of 2.5 nm/s. This RMS position error of the desired pathway in the field was less than 3 cm. The results nindicated that the navigation system was capable of guiding an agricultural robot accurately and nrobustly under normal agricultural operations.

ETHANOL-DIESEL BLENDS: A STEP TOWARDS A BIO-BASED FUEL FOR DIESEL ENGINES

The global fuel crises in the 1970’s generated awareness amongst many countries of their nvulnerability to oil embargoes and shortages. Considerable attention was focused on the development of nalternative fuel sources, with particular reference to the alcohols. Blends of ethanol and diesel fuel were ninvestigated and found to be technically feasible, however, the high costs of ethanol production meant nthat the fuel could only be considered in cases of fuel shortages. In the last two decades of the 20th ncentury, major advances in engine technology have occurred, leading to greater fuel economy in vehicles. nThe reduction of emissions from engines has become a major factor in the development of new engines nand manufacturers are trying to meet the requirements specified by EPA. As a result the use of nalternative fuels as a means of meeting these requirements has generated much attention. Today the neconomics are much more favorable in the production of ethanol and it is able to compete fairly well with nstandard diesel. Hence there has been renewed interest in the ethanol-diesel blends with particular nemphasis on emissions reductions. When considering an alternative fuel for use in diesel engines, a nnumber of issues are important. This purpose of this paper is to review these issues with particular nreference to safety and distribution, integrity of the fuel being delivered to the engine, emissions, engine nperformance and durability.

KALMAN FILTERING OF DGPS POSITIONS FOR A PARALLEL TRACKING APPLICATION

A Kalman filter was developed to improve the DGPS position estimates for a parallel tracking application. nApplying Kalman filtering to raw DGPS measurement data effectively removes the DGPS noise and reduces the nroot–mean–squared (RMS) positioning error. In our study, the maximum cross–tracking error (XTE) was reduced from 9.83 m nto 2.76 m by Kalman filtering. The Kalman filter also reduced the root–mean–squared XTE from 0.58 m to 0.56 m. In the ndirection of travel, the Kalman filter had much smaller positioning error than the mean filter; the RMS positioning errors in nthe direction of travel were 1.35 m for the mean filter and 0.26 m for the Kalman filter. The GPS bias error was the major nsource of the cross–tracking error. Further study is recommended to estimate and reduce the GPS bias error for parallel ntracking applications.

FUZZY CONTROL OF ELECTROHYDRAULIC STEERING SYSTEMS FOR AGRICULTURAL VEHICLES

This paper presents the development of a fuzzy steering controller for wheel–type agricultural vehicles with an nelectrohydraulic (E/H) steering system. The fuzzy controller,which consisted of a variable fuzzifier, an inference engine with na steering control rulebase, and a control signal defuzzifier, was developed based on a common–sense model of agricultural nvehicle steering. The controller implemented steering corrections based upon the desired steering rate and the error between nthe desired and the actual wheel angles. Test results indicated that this controller could be used on vehicles with similar nsteering actuating mechanisms. Limited tuning on fuzzy membership functions was used to account for physical differences nbetween vehicles. This fuzzy controller achieved prompt and accurate steering performance on both a hardware–in–the–loop nelectrohydraulic steering simulator and on an agricultural tractor. The adoption of this fuzzy controller can significantly nreduce the time and costs in the design of steering controllers for agricultural vehicles.

ON-FARM EVALUATION OF DIESEL FUEL OXYGENATED WITH ETHANOL

The benefits of burning an ethanol-diesel blend in a diesel engine primarily include lower nemissions and the use of a renewable bio-based product. Specially formulated additives can effectively novercome problems of fuel separation, reduced cetane number and reduced fuel lubricity. Laboratory-based ntests have shown that these blends can fuel diesel engines without damaging the engine. The nobjective of this work is to evaluate the effects of E diesel (a blend containing 10% ethanol, an additive nand diesel) on selected tractors and combines working under normal field conditions. Two tractors and ntwo combines were instrumented with data loggers that collected data through the CAN bus. One of each nvehicle type was fueled with E diesel and the other with no.2 diesel. Comparisons showed that increases nin fuel consumption of approximately 4 to 5% occurred on average with both the tractor and the combine, nwhich was equivalent to the reduced energy content of the blend. Timeliness penalties increased as the nengine loading increased, but were mostly negligible. The operators reported no differences between the nvehicles running on the respective fuels while performing the daily tasks.

Computational modelling of NOx emissions from biodiesel combustion

A detailed numerical spray atomisation, ignition, combustion and NOx formation model was developed for direct injection diesel engines using KIVA-3V code that could be applied to biodiesel fuels and this model was used to investigate the NOx emissions mechanisms of biodiesel compared with diesel fuel. In addition, computational modelling was applied to evaluate strategies for reducing NOx emissions from biodiesel combustion. The physical and thermodynamic properties of biodiesel used in the model were based on fatty acid composition. The model was verified with experimental data from an engine fuelled with diesel fuel, soyabean methyl ester, Yellow Grease Methyl Ester (YGME) and genetically modified soyabean methyl ester. Strategies for reducing NOx emissions from biodiesel combustion were evaluated with the aid of the model. Increasing spray cone angle, retarding start of injection, applying Exhaust Gas Recirculation (EGR) and charge air cooling were all effective approaches to reducing NOx emissions from biodiesel fuel.