## 1 Introduction  
Plug seedling transplanting technology can enable economic crops to overcome unfavorable factors during the growth stage, improve the seedling survival rate, and save planting costs [1; 2; 3]. With the increasing maturity of this technology, it has been gradually applied to the large-scale planting of economic crops such as vegetables (peppers, tomatoes, eggplants) and fruits (strawberries, watermelons), and can effectively shorten the growing period of crops, alleviate the contradiction of planting seasons, and improve the land replanting index and crop yield [4; 5]. At present, the transplanting technology of vegetables in China is still immature and is a mainly semi-automatic transplanting technology. Due to the manual single seedling picking and seedling launching process, its labor intensity is high, and the operation efficiency is low, generally not exceeding 40 plants/(min \(\cdot\) row) [6; 7; 8]. An automatic transplanting machine eliminates the manual seedling-picking process and adds an automatic seedling-feeding plate, seedling picking, and seedling dropping mechanism to the original device, and the single-row transplanting planting efficiency can reach 70-140 plants/(min \(\cdot\) row). Therefore, to improve the planting efficiency, it is of great significance to develop a fully automatic transplanting machine [9; 10; 11]. Developed countries such as Europe, the United States, and Japan, where research on seedling transplanting technology started earlier, have gradually applied PLC, single chip microcomputer, and Fuzzy-PID compound control technology with automatic transplanting technology and replaced the manual seedling method with automatic seedling feeding systems, reducing the labor intensity and improving economic efficiency [12; 13; 14; 15]. For the requirements of agricultural cultivation in China, to implement efficient mechanized vegetable cultivation, Chinese scholars have carried out relevant research on automatic seedling supply, seedling collection, and seedling dropping in the whole process of transplanting cavity tray seedlings. Based on a semi-automatic transplanter, fully automatic planting was achieved by combining electric, pneumatic, and hydraulic intelligent control technologies [16; 17; 18]. According to the number of seedlings harvested at one time, the seedling harvesting process can be divided into single-seedling harvesting and whole-row seedling harvesting. Whole-row seedling picking is relatively efficient, but it needs to enter the lower planting device through a seedling splitting device to solve the problem of single-plant delivery of whole-row potted seedlings. A rotating seedling cup is a common solution for seedling separation [19]. The seedling cup rotates circularly along the horizontal track to catch the pot seedlings. The seedling cup opens the bottom opening at a specific position, and the pot seedlings fall into the lower planting device for seedling separation. It is generally suitable for pot seedlings taken out in a vertical posture, such as clamping stems, and is widely used because of its simple structure and reliable operation. However, limited by its volume and seedling cup open position, a single set of rotating seedling cups has the following limitations: it is suitable for single-row or double-row transplanting and cannot be used for multiple-row planting; it has a large moment of inertia during operation and is not suitable for high-speed planting operations [20; 21; 22]; and it requires a high seedling docking time and it is difficult to cooperate it with the lower planting device during the seedling dropping period [23]. To further improve the working efficiency of seedling pickup and seedling dropping and to reduce the size of the machine, a seedling cup fixing device was designed based on the idea of rotating seedling cups with spaced openings to achieve a whole row of potted seedlings by using a seedling support plate at the bottom of the cam-spaced openings of the seedling cups.