Design and experiment of crank rocker type clamp seedlings mechanism of vegetable transplanter

Abstract: In designing a picking seedling mechanism, it is important to see the compressive characteristic of plug seedlings. So, in this research, the experiments were designed and conducted to get the compressive characteristic of plug seedlings. For more details, in the experiments, 20 pepper plug seedlings with growth period of 40 d were selected randomly. These seedlings were measured, their average height was 140 mm, the average height of the pot was 44 mm, the width of seedlings' leaves was 109.8 mm and the diameter of the seedlings' stem was 2.47 mm. Crank-rocker type seedling clamping mechanism was designed according to corresponding requirements. This mechanism was driven by an adjustable-speed motor and a crank and the movement of the rocker clamper was designed as reciprocating swing. In cooperation with the ejection mechanism, the rocker clamper could capture the seedlings at the right place and move them to the target position. Then, the rocker clamper could accomplish the processing of planting by loosening the 2 plates of the clamper. Also, in this research, an experimental platform of a crank-rocker type seedling clamping mechanism was fabricated and manufactured and with this platform a series of experiments were conducted. In these experiments, 3 experimental factors were set as claw clipping force, clipping claw material and moisture content of plug seedlings. Each experimental factor contained 3 levels and success rate of clamping, expulsion rate of seedlings and broken rate of seedlings were set as 3 test indices. Experiments were repeated by 8 times for each distinct condition, and totally 216 experiments were conducted under 27 different conditions. This research analyzed the mechanical parameters of the crank-rocker type seedling clamping mechanism and the corresponding moisture levels of the seedlings which could lead to the best planting performance. Furthermore, besides the design of the main components of the crank-rocker type seedling clamping mechanism, this research also conducted the mechanical and kinematics analysis on the working process of this seedling clamping mechanism. Also, the movement simulation was conducted with the aid of the simulation software i.e. Solid works COSMOS Motion. In this approach, the structures and the main parameters of the mechanism were properly designed. For more details, the length of the crank, the connecting rod and the swinging rod was respectively designed as 80, 236.22 and 172.5 mm. The test results indicated that when the rocker clamper was metal, the stiffness coefficient was 90 N/m respectively, the expulsion rate and the broken rate of seedlings and the success rate of clamping were 0, 4.2% and 95.8% respectively which meant that the Crank-rocker type seedling clamping mechanism could match the desired performance. The test results showed that when the moisture content of plug seedlings was 60.8%, the plug seedlings had excellent adaptation to different stiffness coefficient and material of clamper, and the average success rate of clamping was 94.4% in this condition. This mechanism could take seedlings from the initial position and put them to the target position by using circular trajectory. The condition of opening and closing of the claw could be controlled by trapezoid track and reset spring. The design was simple and reliable. This mechanism could work with plug seedlings with various shapes and sizes without additional adjustment, and it also contained high adaptability to the seedlings with different moisture levels. Also, it would minimize the damage of the plug seedlings and significantly improved the efficiency of the process of seedling capture and planting.