Design and experiment of a multi-body constant-orientation rotary cabbage seedling picking device

Fully automatic transplanting has been one of the pressing needs in cabbage cultivation. However, the existing seedling-picking device is also confined to low efficiency and high damage rates. In this study, the horizontal constant-orientation rotary seedling picking device was developed with the multi-body array for high speed with low damage rates during transplanting. Firstly, a stem compression test was conducted to optimize the device. The optimal cushioning material was selected for the seedling-picking end. The mechanical damage was then minimized after seedling picking. In addition, a stem bending test was carried out to determine the clamping speed range of the actuator during seedling picking. Furthermore, the stem-clamping seedling picking was performed to verify the feasibility of the device. Secondly, a seedling-picking device was designed for high speed and low damage rates. Multiple whole-row seedling picking and distribution modules were equipped with servo motor individuals. A seedling delivery mechanism was also employed as the horizontal constant-orientation rotary. The stem bending damage was effectively minimized under the posture changes during the delivery of plug seedlings. Thereby the whole-row seedling picking was facilitated to ensure the evenly distribution of spaced seedlings. Various influencing factors were optimized after mechanical damage during seedling picking. Ultimately, the mechanical damage to plug seedlings was reduced for the high-speed and low-damage seedling retrieval after the low-frequency rotation of the whole-row seedling picking and distribution modules. Furthermore, the performance of the seedling-picking device was enhanced to calculate the key parameters related to the critical components, including the seedling-picking end effector, a multi-stage scissor-type seed-ling distribution mechanism, a structural diagram of the horizontal orientation mechanism, and limit side plates. Additionally, a control system for the test bench was developed as the "stepper motor" and "servo motor" control system. Finally, the test subjects were selected as the 128-cell plug seedlings of the cabbage variety "Zhonggan 11". The experimental factors included the seedling picking frequency, servo motor rotation time, and servo motor rotation angle. The evaluation indicators comprised the seedling picking success rate and respiration intensity of the damaged pot-plate seedling. A response surface method (RSM) was employed for the experimental design using Box-Behnken Design (BBD). Multiple objective optimization was then carried out after variance analysis and response surface design. A bench test was conducted on the performance of the whole-row seedling picking and distribution modules. The results showed that an optimal combination of parameters was achieved: a seedling picking frequency of 56 seedlings/min, a servo motor rotation time of 438 ms, and a rotation angle of 83°. The bench tests demonstrated that the average success rate of seedling picking was achieved at 96.30% under these optimal parameters, while the respiration intensity of the damaged pot-plate seedling measured at 4.40‰; The relative errors were only 0.82 percentage points and 0.20 permillage points, respectively, compared with the predictions from regression models. The multi-body constant-orientation rotary device effectively improved the success rates and mechanical damage, compared with the existing devices. The seedling-picking device can be expected to serve as the fully automatic transplanters for cabbage. The finding can also provide an innovative reference to assess the damage rates of seedling picking.