*3.4. Design of the Separation Devices*

Separation is an important process to separate dandelion seeds from pappi so as to obtain dandelion seeds [23]. The separation devices include an impurity removal mechanism, a cap, a concave board for separation, and a separation drum. Figure 11 shows the 3D structure of the separation devices.

After entering the separation devices, dandelion seeds with pappi are separated from pappi under the action of the separation elements [24]. The separated seeds fall in the seed storage tank through the concave board, as shown in Figure 12. Finally, pappi are discharged from the harvester via the impurity removal mechanism, thus completing the seed–pappus separation stage. This overcomes the difficulty in seed–pappus separation, addresses low separation efficiency, and reduces the potential for harm to operators often caused during the manual separation of pappi.

**Figure 11.** The 3D structure of the separation devices. 1. Impurity removal mechanism; 2. Cap; 3. Concave board for separation; 4. Separation drum.

**Figure 12.** Schematic diagram of separation process of grain and crown hair. (**a**) Before separation. (**b**) During separation. (**c**) After separation.

#### 3.4.1. Design of the Separation Drum

Optimal design of the separation drum can promote efficient seed–pappus separation [25,26]. Seeds with pappi are light and easily affected by the wind as they float. This makes it difficult to bring the seeds into contact with the separation drum to separate seeds from pappi. Therefore, the separation drum is designed as a closed drum (Figure 13), which narrows the space available to the seeds with pappi and to some extent solves the problems of floating, small contact areas with the separation drum and concave board, and low contact probability of seeds [27]. It also improves the separation efficiency of pappi and seeds, increases the separation rate, and reduces impurities in the harvest.

**Figure 13.** The 3D structure diagram of separation drum. 1. Impurity removal mechanism; 2. Wireloops; 3. Hairbrush; 4. Closing drum.

Through comparison with separation devices of other harvesters and through combining the special material characteristics of dandelion seeds, the separation elements were designed as hairbrushes and wire-loops. Dandelion seeds with pappi were separated from pappi by the wire-loops and hairbrushes distributed on the drum, thus yielding pure dandelion seeds. The layouts of the separation elements exert a significant influence on the

separation effect of pappi and seeds. To explore the optimal layout of separation elements, three element layouts (Figure 14) were designed to select the better combination through pre-testing. Figure 14a–c separately shows the spiral layouts of only wire-loops distribution, only brush distribution, and cross distribution of bow tooth brushes [28,29].

**Figure 14.** Separation element combination mode. (**a**). Only wire-loops distribution. (**b**). Only brush distribution (**c**). Cross distribution of bow tooth brushes.

Furthermore, the selection of materials for producing the hairbrushes and wire-loops can also heavily influence the separation effect of pappi and seeds. Commonly used materials to produce hairbrushes include polybutylene terephthalate (PBT) fibers, bristles, nylon fibers, polypropylene (PP) fibers, and metal wires. Among them, PBT fibers and bristles are so soft that the separation effect cannot meet the operation requirement; PP fibers show poor elasticity and cannot recover all imposed long-term deformations, hindering the separation of pappi and seeds; metal wires are hard; and nylon fibers exhibit moderate hardness, favorable elasticity, and cost-effective performance, so nylon was also used to fabricate hairbrushes on the separation devices. Wire-loops are commonly made with metal (steel or iron). In the present study, steel was selected to produce the wire-loops.

The length of the separation drum is closely related to its separation capacity: the longer the drum, the longer the separation time and the higher the separation rate [30]. The length of the separation drum in the separation part is calculated using the following formula:

$$L \geq \frac{q}{q\_0} \tag{5}$$

where *L* represents the length of the separation drum (m); *q* denotes the feed quantity of the separation devices (kg/s) and is set to 0.5 kg/s in the present research; and *q0* is the designed allowable feed quantity per unit length of the separation drum (kg/(s·m)) and is set to 0.5~0.8 kg/(s·m).

From Equation (2), the length *L* of the separation section of the separation drum is 0.63~1.0 m and it is set to 1.0 m here. Therefore, the length of the separation section of the drum is 1.0 m.

If the diameter of the separation drum is too small, only small amounts of seed–pappus mixtures are allowed to enter the drum, and the contact area between the mixtures and the concave board narrows [31], reducing the time taken for the separation of dandelion seeds from pappi. At present, the diameter of commonly used separation drums is 550~650 mm. The greater the diameter, the greater the feed quantity that can be sustained, although the heavier the load. Compared with the harvesting of wheat and rice, the feed quantity of dandelion is not that large. The diameter *Dz* of the separation drum satisfies

$$D\_z = D\_\mathcal{X} + 2h\_z \tag{6}$$

where *Dg* is the tooth root diameter of the drum (mm) and *hz* is the height of the high separation elements (mm).

Generally, *Dg* ≥ 300 mm. Considering the separation effect and the feed quantity of dandelion seed–pappus mixtures, *Dg* was determined to be 300 mm. To avoid collisions of wire-loops with bafflers on the cap, the heights of wire-loops and hairbrushes were separately set to be 35 and 50 mm. The diameter of the separation drum was then calculated to be 400 mm using Equation (3).

By conducting pre-tests on the separation drum, the separation effects of the separation drums with the three different element layouts were verified. The results show that the combined layout of hairbrushes and wire-loops allows the optimal separation effect of the separation drum and the significant separation effect of seeds and pappi. That is, the combined layout of hairbrushes and wire-loops was selected for separation elements on the separation drum; the length of the drum separation section is 1.0 m, and the diameter of the separation drum is 400 mm.

#### 3.4.2. Design of the Concave Board

The concave board mainly consists of a perforated screen, a connecting plate with the upper cap, and an arcuate side-plate [32,33]. Holes are distributed uniformly on the perforated screen (Figure 15). To enable better contact of seed–pappus mixtures with the drum and convenient separation of seeds from pappi, the wrap angles of the concave board for separation are designed to be 180◦; that is, the concave board is hemi-cylindrical. One end of the concave board is connected to the transmission pipeline, while the other end is connected to the impurity-removal device to coordinate with the separation drum to separate pappi from seeds and allow seeds to pass through the holes in the screen. In the meantime, pappi are retained on the concave board and discharged from the harvester via the impurity removal mechanism during the rotation of the separation drum.

**Figure 15.** The 3D structure diagram of separation concave plate. 1. Connecting plate with the upper cap; 2. Perforated screen; 3. Arcuate side-plate; 4. Bolt hole.

The screening effect of the perforated screen is closely related to porosity of the screen, which is influenced by the hole shape, size, and layout. Dandelion seeds resemble paddy rice in appearance, both of which are elliptic. Considering the shape and passing performance of seeds through the perforated screen, round screen holes were designed; because dandelion seeds are generally 0.30~0.47 cm long, the screen holes are circular with a diameter of 0.5 cm.

The more porous the screen, the better the screening effect and the more seeds that pass through the screen. Therefore, screen holes are distributed in the form of equilateral triangles that enable high porosity (Figure 16). If the hole diameter *d* is 0.5 cm and the spacing between two adjacent holes *l* is 0.1 cm, the center-to-center spacing of two adjacent holes *l*<sup>1</sup> is 0.6 cm. The porosity *K* of the screen is

$$K = \frac{\pi d\_0^2}{2\sqrt{3}l\_1^2} \times 100\% = 63\% \tag{7}$$

where *K* is the porosity of the screen (%); *d* is the hole diameter on the screen (cm); and *l*<sup>1</sup> is the center-to-center spacing between two adjacent holes (cm).

**Figure 16.** Schematic diagram of sieve arrangement.
