In order to improve the seeding performance of pneumatic cylinder-type precision direct seed-metering device for rice, the single factor and central composite experimental experiments were conducted in this paper. The effects of the main working parameters (rotational speed of seeding cylinder, vacuum degree in vacuum gas chamber, air-blowing velocity and clearing blockage positive pressure of chamber) on seeding performance of the direct seed-metering device were analyzed by means of the JPS-12 type performance test rig of metering device. The study object was "Huanghuazhan", which was pre-germinated and its moisture was 21.65%-23.73% (wet basis). Qualified rate, miss-seeding rate, replay rate, average hole distance and variation coefficient of hole distance were regarded as the performance evaluation indexes. The result of single factor experiments showed that rotational speed of seeding cylinder, vacuum degree in vacuum gas chamber and air-blowing velocity had significant influence on the qualified rate, miss-seeding rate and replay rate of metering device, respectively. The clearing blockage positive pressure of chamber had no significant influence on qualified rate, miss-seeding rate, replay rate, the average hole distance and the variation coefficient of hole distance of metering device, respectively. So, it was only necessary to provide the positive pressure chamber with suitable strength of clearing blockage positive pressure to ensure the suction hole not be blocked during the metering device working. The three-factor and five-level quadratic regression rotation design optimization experiment of the 3 influence significant factors on metering device showed that the order affecting qualified rate was rotational speed of seeding cylinder > vacuum degree in vacuum gas chamber > air-blowing velocity, and the order affecting miss-seeding was vacuum degree in vacuum gas chamber > rotational speed of seeding cylinder > air-blowing velocity. The variance analysis of experimental results had a significant affecting of experimental factors on performance evaluation indexes. Through the analysis of effect of various factors on the metering device, the seeding performance of the metering device was better under the condition of low rotational speed of seeding cylinder, high vacuum degree in vacuum gas chamber and higher air-blowing velocity. The optimal combination working parameters of metering device were seeding cylinder rotational speed with 10 r/min, vacuum degree in vacuum gas chamber with 4.6 kPa and air-blowing velocity with 21.88 m/s. All of those were obtained by optimization solution of all factors by use of quadratic regression model equation of performance evaluation indexes in the range of experimental parameters constraints. The results of verification test were consistent with the results of optimization solution. Under the condition of the optimal combination working parameters, the qualified rate, miss-seeding rate, cavity rate and replay rate were 87.73%, 2.93%, 0.53% and 9.34%, respectively. Meanwhile, the seed breakage rate was 0.91%, the average hole distance was 200.07 mm (theoretical hole distance was 200.00 mm), the variation coefficient of hole distance was 4.75%, the apiece row consistency variation coefficient of seeding quantity was 3.07%, the stability variation coefficient of the full seeding quantity was 2.08%. This seeding quality met the direct seeding requirements of hybrid rice. The field sowing experiment of the direct seed-metering device was carried out in the modern agricultural science and technology experiment base of Huazhong Agricultural University. When the average forward speed was about 1.79 km/h of direct seeder, the average vacuum degree in vacuum gas chamber was about 4.6 kPa and the average air-blowing velocity was about 21.88 m/s, the qualified rate, miss-seeding rate, cavity rate and reseeding rate were 79.42%, 15.11%, 3.88% and 5.47%, respectively. Meanwhile, the average hole distance was 175.61 mm, the variation coefficient of hole distance was 20.03%.The study provided the scientific basis for the structure and working parameter optimization of pneumatic cylinder-type precision direct seed-metering device for rice and the improvement of its seeding performance. © 2017, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
