According to the agronomic requirements of rapeseed planting, the amount of rapeseed sowing varies in different regions and different sowing dates. Aiming at such production practice, a cam-rocker sowing rate adjusting mechanism for rapeseed precision direct seeding machine with a speed ratio of 0-0.45 was designed. The Newton-Simpson algorithm was used to draw the mechanism diagram at each moment and the basic motion principle of the adjusting mechanism was analyzed. Based on the principle of graphic method, a kinematics mathematical model of the mechanism was established with closed-loop vector equations, and the equations of speed and acceleration were determined to solve the transcendental equations. Combining with the swing law of the active crank of the linkage mechanism and the variation coefficient of travel speed of the cam, the sine varying putter motion law of push rod and cam profile curves were determined. The cam profile curve of the cam-rocker mechanism and the follower motion law were analyzed, the results showed that the cam profile curve was spindle shape, follower displacement curve was a spiral curve, the follower speed curve was a curve with one peak and three column points, and the angular velocity changing curve of the follower was a combination of two different sine curves with different amplitudes and frequencies. During the entire moving process of the follower, the speed and acceleration of follower were continuous, which avoided rigid impact. The cam had a rapid return characteristic and meet the design requirements. The tests of transmission accuracy of sowing rate adjusting mechanism and influence on seeding performance were carried out on JPZS-12 seed-meter test platform. The test results showed that when the rotation speed of input shaft of sowing rate adjusting mechanism ranged from 20 to 100 r/min, comparing with the ratio ranged from 0.1 to 0.2, the relative errors of the output rotation speed of the sowing rate adjusting mechanism was small at the speed ratio ranged from 0.2 to 0.45, the average error was less than 3.8%. Comparing with the sowing rate of adjusting mechanism uninstalled, the relative change of the qualified index of the sowing rate adjusting mechanism was installed at different rotation speeds and forward speeds was less than 0.5 percentage points, the change trend of qualified index was similar, the cam-rocker sowing rate adjusting mechanism meet the different sowing rate requirements of rapeseed. Precision broad width no-tillage planter for rapeseed was selected to conduct filed experiments using sowing rate adjusting mechanism, the sowing rate was set to 5 500 and 6 720 g/hm2. In field experiments, 8 rows of the rapeseed in different areas were selected to measure the plants in 1 m, each rows chose 5 measure points, respectively. The field experiment results showed that the average numbers of plants within 1 m were 16 and 20, respectively, which meet the preset sowing rate. The coefficient of variation were 6.48% and 8.19%, respectively, which meet the rapeseed variable sowing quality requirements of precision broad width no-tillage planter for rapeseed. © 2020, Editorial Department of the Transactions of the Chinese Society of Agricultural Engineering. All right reserved.
