Construction of a selective Head-forming Vegetables Harvester with a Microcomputer Controlled Sensor

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An experimental selective harvester for lettuce was constructed. It equipped with a selector which detected maturity and size of lettuce heads and a microcomputer which processed the selector output signals. The harvester consisted of a detector, a microcomputer and a knife driven by a hydraulic system. These elements were all mounted on a subframe and it was mounted on the three-point linkage of the smaller four-wheel drive tractor. This harvester could select and cut lettuce heads of single-row, and its travelling speed was 0.1 meter per second.Two types of detectors were developed. One was that of mechanically compression and the other was of electro-static capacity measurement.The mechanical detector had compression and selection rollers between which lettuces passed. The first action of detection was that the compresion rollers which were loaded by a spiral spring compressed the surrounding leaves of lettuce against the head and gaged size of the lettuce head. The second action wa … More s that the selection rollers which was loaded by a helical spring compressed the lettuce head and measured firmness of the head. On the other hand the dielectric detector had a couple of electrode plates to which high-frequency voltage applied. Apparent density of lettuce head could be measured as output signals of the detector.As a result of field tests on selective harvesting of lettuces, the experimental selective harvester operated satisfactorily. However, performance of the harvester almost depended on that of the detector. In case of the mechanical detector stronger correlation was observed between the measured size of lettuce and the diameter of the head, and fairly good correlation between the measured firmness and the apparent density of the head. In case of the dielectric detector selection accuracy was influenced significantly by the shape of electrode plates, and the electrode of curved plates fitted to the curvature of the lettuce head detected much accurately than that of flat plates. Less