Song, Yang, and Zhang Shumin. “Design and Parameter Optimization of Flexible Comb-Type Grass Seed Metering Device”. International Journal of Agricultural and Biological Engineering, vol. 8, no. 1, Feb. 2015, pp. 9-16, https://ijabe.migration.pkpps06.publicknowledgeproject.org/index.php/ijabe/article/view/1294.