## 2 Materials and Methods
### Field Harvesting Experiment  
In order to test the performance of the optimized harvester in the field, a field harvesting trial was conducted in June 2022 at the planting base of Fritiariae ussuriensis maxim in Heilongjiang Infinity Forest Town Green Organic Agriculture Development Co. Ltd. The basic conditions for planting Fritiariae ussuriensis maxim at the base are as follows: the bottom of the border is 1200 mm wide, the border is 1100 mm wide, the border height is 50 mm, the walkway ditch is 500 mm wide, and the average thickness of the mulch layer is 10 mm; the average thickness of the mixed layer of Fritiariae ussuriensis maxim and soil was 30 mm, the diameter of flat maidenhair was 2.5-18 mm, and the moisture content of the soil was 17.8%; the soil was loose, the black soil layer was thick, the humus content was high, the soil structure was good, and the nutrients were rich. The supporting power of the Fritiariae ussuriensis maxim harvester is the Dongfanghong (First Tractor) LX904 wheeled tractor with power of 66.2 kW and operation speed of 1.65 km/h, one step slower, as shown in Figure 11.  
Figure 11: Field experiment of improved prototype.  
Figure 10: Static simulation analysis of bulldozer.  
The main indicators of harvesting performance of the harvesting machine are the removal rate of bulbs, the damage rate of bulbs, the soil content rate, and the harvesting efficiency. The damage rate of bulbs directly affects the market value of Fritilariae ussuriensis maxim and the harvesting efficiency is the main index of economic performance of harvester. According to the conclusion of the optimized design of the excavation shovel, adjust the angle \(\alpha\) of entry of the shovel blade into the soil, with reference to the national standards \"General Provisions for the Determination of Agricultural Machinery Test Conditions\" (GB/T5262-2008), \"Agricultural Machinery Production Test Methods\" (GB5667-2008), and the harvesting test methods of other underground cash crops [18], three sets of tests with the entry angle \(\alpha\) of 20\({}^{\circ}\), 25\({}^{\circ}\), and 30\({}^{\circ}\) were set in turn, and the specific data of the three sets of tests are shown in Table 2.  
As seen from Table 2, the excavation depth gradually increased when the entry angle \(\alpha\) is 20\({}^{\circ}\), 25\({}^{\circ}\), and 30\({}^{\circ}\). With the increase in excavation depth, the collection rate of bulbs of Fritilariae ussuriensis maxim increased from 93.5% to 99.2%. At the same time, the soil content in the mixture of Fritilariae ussuriensis maxim's bulbs and soil increased with the increase in excavation depth, resulting in the increase in soil content from 12.9% to 18.6%. With the increase in excavation depth, the chance of direct contact between the excavation shovel and Fritilariae ussuriensis maxim's bulbs decreased, so the damage rate of bulbs decreased from 5.6% to 1.2%. The gradual increase in digging depth also leads to the gradual increase in digging resistance, resulting in the decrease in harvesting efficiency from 0.15 hm\({}^{2}\)-h\({}^{-1}\) to 0.10 hm\({}^{2}\)-h\({}^{-1}\). Considering all the indicators of the test, it can be concluded that the field operation performance of the harvester is most ideal when the angle \(\alpha\) of digging shovel into the soil is 25\({}^{\circ}\).