Purpose: Yield monitoring systems are an essential component of precision agriculture. They indicate the spatial variability of crop yield in fields, and have become an important factor in modern harvesters. The objective of this paper was to review research trends related to yield monitoring sensors for grain crops. Methods: The literature was reviewed for research on the major sensing components of grain yield monitoring systems. These major components included grain flow sensors, moisture content sensors, and cutting width sensors. Sensors were classified by sensing principle and type, and their performance was also reviewed. Results: The main targeted harvesting grain crops were rice, wheat, corn, barley, and grain sorghum. Grain flow sensors were classified into mass flow and volume flow methods. Mass flow sensors were mounted primarily at the clean grain elevator head or under the grain tank, and volume flow sensors were mounted at the head or in the middle of the elevator. Mass flow methods used weighing, force impact, and radiometric approaches, some of which resulted in measurement error levels lower than 5% (R 2 = 0.99). Volume flow methods included paddle wheel type and optical type, and in the best cases produced error levels lower than 3%. Grain moisture content sensing was in many cases achieved using capacitive modules. In some cases, errors were lower than 1%. Cutting width was measured by ultrasonic distance sensors mounted at both sides of the header dividers, and the errors were in some cases lower than 5%. Conclusions: The design and fabrication of an integrated yield monitoring system for a target crop would be affected by the selection of a sensing approach, as well as the layout and mounting of the sensors. For accurate estimation of yield, signal processing and correction measures should be also implemented.

Real time sensing of crop yield is critical for a successful implementation of precision agriculture. Yield monitoring system is an optional component of a 55 kW multipurpose combine harvester, developed in Korea, for both domestic and global markets, especially Asian countries where field sizes are relatively small. The aim of the present study was to fabricate and evaluate the performance of a grain flow sensor suitable to the mid-sized full-feed type combine for rice, soybean, and barley. Firstly, commercially available non-contact type sensing modules (optical, ultrasonic, laser, and microwave modules) were chosen for alternative candidates, to be further tested in a laboratory bench. Through the laboratory tests, the ultrasonic module was selected as a potential approach and the performance was improved by increasing the number of modules and their layout. Finally, the improved grain flow sensor was evaluated during field harvesting operation. Field tests with the improved grain flow sensor showed a good potential for rice (R 2 =0.85, RMSE=126.14 g/s), soybean (R 2 =0.78, RMSE=43.87 g/s), and barley (R 2 =0.83, RMSE=37.39 g/s). Further research would be necessary for improvement and commercialization, through various signal processing and field tests under different field and crop conditions.

High performance small and mid-sized tractors are required for dryland and orchard operations. A power transmission system is the most important issue for the design of high performance tractors. Many operations, such as loading and lifting, use hydraulic power. In the present study, a hydraulic power transmission system for the 3-point hitch of a 50 kW narrow tractor was developed and its performance was evaluated. First, major components were designed based on target design parameters. Target operations were spraying, weeding, and transportation. Main design parameters were determined through mathematical calculation and computer simulation. The capacity of the hydraulic cylinder was calculated taking the lifting force required for the weight of the implements into consideration. Then, a prototype was fabricated. Major components were the lifting valve, hydraulic cylinder, and 3-point hitch. Finally, performance was evaluated through laboratory tests. Tests were conducted using load weights, lift arm sensor, and lift arm height from the ground. Test results showed that the lifting force was in the range of 23.5 -29.4 kN. This force was greater than lifting forces of competing foreign tractors by 3.9 -4.9 kN. These results satisfied the design target value of 20.6 kN, determined by survey of advanced foreign products. The prototype will be commercialized after revision based on various field tests. Improvement of reliability should be also achieved.

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