*2.2. Design of the Main Components of the Hazelnut Harvester*

The hazelnut harvester achieves separation of the picking device and the wind selection device by using the unloading device, so that the wind of the two devices does not interfere with each other. At the same time, the mixture from the picking device can be transported to the wind sorting device for secondary wind sorting. When the pick-up device picks up, the mixture collides with the screen plate and breaks up the material. The dust-like impurities are sucked out by the negative-pressure air flow of the centrifugal fan, and the rest of the hazelnut mixture will fall into the discharge device and further fall into the wind selection box device for secondary wind selection. The hazelnuts slide down to the hazelnut collection box by gravity, and the remaining leaves and other debris are windselected to the miscellaneous collection box by the sieve leaf plate under positive-pressure wind. The angle and position of the sieve plate at each level inside this hazelnut harvester can be freely adjusted to harvest different kinds of nuts. The working principle is shown in Figure 2.

**Figure 2.** Hazelnut harvester gas–material flow trajectory diagram: 1. material picking device, 2. wind sorting device, 3. discharge device.

The designed multi-purpose picking head device includes a harvesting device, transmission device, support device, collection device, and other structural components. The

pick-up device includes eccentric vibration ring, brush head, and other structural components. The collection device includes a fan, collection box, and collection funnel structural components. The transmission device includes a 57 series three-phase hybrid stepper motor, transmission shaft, and other structural components. The support device includes frame, bearing seat, front and rear part of the grip handle, and other structural components. When the hazelnut harvester is working, the handheld multifunctional picking head can pick hazelnuts on the tree, and the brush head part can rotate under eccentric vibration, relying on inertia to remove the hazelnut fruits from the tree. In addition, a small fan on the multi-purpose picking head is designed to provide cooling for the working motor and to help the brush head get rid of twisted branches. This fan can also blow away impurities at any time during the working process and blow down the already combed hazelnut fruit into the collection pipe for the next sorting step of the hazelnut harvester.

The main components of said hazelnut harvester also include structural components such as a picking device, wind selection device, power device, and support device. The picking device includes structural components such as a picking duct, deflector, air regulating valve, fish scale sieve plate (primary sieve plate), and cylindrical roller brush. The wind sorting device includes structural components such as the unloading device, the sieve leaf plate (secondary sieve plate), the hazelnut collection box, and the impurity collection box. The power and support device includes a centrifugal fan, clutch, diesel engine, battery, frame, universal wheel, and other structural components. The hazelnut harvesting machine structure display is shown in Figure 3.

**Figure 3.** Hazelnut harvesting machine structure diagram: 1. machine outer casing, 2. air regulating valve, 3. conveying pipeline, 4. cylinder roller brush, 5. centrifugal fan, 6. sieve leaf plate, 7. vibrating screens, 8. positive-pressure fan, 9. gasoline engine, 10. storage battery.

The discharging device mainly consists of a cavity shell, a fixed blade, and an adjusting blade, as shown in Figure 4. Six cavities of equal volume are formed inside the discharge device, and the regulating blades are made of rubber to prevent damage to the hazelnuts. When working, the particle mixture falls into the discharge device, and when the cavity is opposite to the lower outlet, hazelnuts and fallen leaves are discharged from the discharge device.

**Figure 4.** Discharge device structure and hazelnut collision schematic: 1. material feed inlet, 2. chamber housing, 3. adjusting blades, 4. material outlet.

The discharging device mainly plays the role of conveying the particle mixture and locking the gas, and the discharging device has an important influence on the working performance of the hazelnut harvesting machine. If discharging is too slow, it can cause hazelnuts and leaves to accumulate in the picking device and reduce conveying efficiency. If discharging is too fast, it is easy to cause the particle mixture to be too late for sorting, and also cause the pressure loss at the connection between the discharge device and the harvester to increase. During the design process, it was found that most of the particle mixture fell on the right side of the cavity shell after hitting the screen plate. When the blade rotates clockwise, the blade, the right damage point, and hazelnuts touch more at the same time. When the blade rotates counterclockwise, the hazelnuts, the left damage point, and the blade touch less at the same time, so the discharging device uses counterclockwise rotation to discharge. The discharging device structure and hazelnut collision are shown in Figure 4.

The discharge volume of the discharge device should meet the requirements of pneumatic conveying volume, which can be calculated by using Formula (1).

$$\mathbf{G} \mathbf{s} = 0.06n\mathbf{\hat{Y}} \, i\gamma \, \text{s} \tag{1}$$

In the formula, *Gs* is the discharge volume, kg/h; *n* is the impeller speed, 25 r/min; and Ψ is the impeller filling factor, 0.6~0.8.

The value of 0.8 for is granular materials; *i* is the effective discharge volume of the impeller, m3; and *γs* is the capacity of the conveyed material, 850 kg/m3.

$$\dot{m} = (R - r) \left[ \pi (R + r) - \xi z \right] \tag{2}$$

In the formula, *R* is the radius of the outer edge of the impeller, 0.14 m; *r* is the radius of the root of the impeller, 0.06 m; *ξ* is the thickness of the blade, 0.01 m; *z* is the number of blades, 6; and *L* is the blade length, 0.23 m.

*Gs* = 640 kg/h is obtained by Equations (1) and (2). Considering that impurities are picked up together with the picking process, the unloading volume should be 1.2~1.5 times the pneumatic conveying volume, and the obtained *Gs* value meets the design requirements.

The wind sorting device is one of the main structures of the hazelnut harvester. In order to improve the net fruit rate of the wind sorting device, the air flow sorting device with negative-pressure picking and positive-pressure cleaning was designed according to the fluid flow principle. The picking device mainly consists of a fish scale sieve plate and air regulating valve. The fish scale sieve plate is at a 30◦ angle, and according to the size of the picking chamber design the rectangular fish scale sieve plate length is 600 mm and the width is 250 mm. The aperture of the fish scale sieve is a 15 mm, 15 × 10 arrangement. According to the characteristics of the material through mechanical analysis, it is concluded that the screen leaf plate is at an angle of 55◦ with the bottom. The aperture of the vibrating screen plate is a 17 mm, 15 × 30 arrangement, mainly to distinguish the size of the hazelnuts. In order to explore the mechanical mechanism affecting the hazelnut picking and sorting process, the critical velocity of the sucking up and sorting of hazelnuts and fallen leaves is calculated according to the principle of gas–solid two-phase flow, as follows.

$$F\_{\mathbf{x}} = \frac{1}{8} \Pi \mu \rho y^2 v\_q^2 \tag{3}$$

$$F\_z = \Pi \text{g} \rho x y^2 \tag{4}$$

$$G = m\_{\text{max}} \mathcal{g} \tag{5}$$

$$G = F\_x + F\_z \tag{6}$$

Simplification of Equations (3) and (6) of critical conditions for hazelnut suspension velocity:

$$v\_{\eta} = \sqrt{\frac{8m\_{\max}\mathcal{g} - 2\Pi\lg\rho\chi\eta^2}{\Pi\mu\rho\eta^2}}\tag{7}$$

$$v = kv\_q \tag{8}$$

In the formula, *F*<sup>x</sup> is the attractive force (N); *Fz* is the resistance (N); *μ* is the resistance constant; *<sup>ρ</sup>* is the air density (kg·m−3); *<sup>x</sup>* is the short axis diameter of the material (mm); *y* is the long axis diameter of the material (mm); *vq* is the flow velocity of the theoretical air flow (m·s−1); *<sup>v</sup>* is the flow velocity of the actual air flow (m·s−1); *<sup>m</sup>* is the mass of the material (g); *mmax* is the maximum mass of the material (g); *g* is the acceleration of gravity (m·s<sup>−</sup>2); and *<sup>k</sup>* is the reliability coefficient.

According to the test that measured the average mass of hazelnuts, *m* is 3.61 g, the average mass of fallen leaves is 2.3 g, the drag coefficient *C* is 0.6, the projected area of hazelnut in the direction of motion *S* is 3.1 mm2 and fallen leaves is 12.56 mm2, the critical condition of hazelnut suspension speed that can be calculated from the above formula is 15.6 m·s<sup>−</sup>1, and the critical value of fallen leaves suspension speed is 4.92 m·s<sup>−</sup>1.

To verify the theoretical calculation value, the suspension speed experiment was conducted at the Agricultural Machinery Laboratory of Shenyang Agricultural University. The instruments used were the material suspension speed test bench of model PS-20 and an electronic balance (BS200S-MEI). In order to ensure the accuracy of the test, each group of materials was tested five times repeatedly, three measurement points were selected and averaged for each group of tests, and the final suspension speed of each material was similar to the theoretical calculated value, which can be used as a basis for design.

The hazelnut gravitational component force *gcosθ* can be considered to be balanced with the Magnus effect force *FM*; in the direction of hazelnut motion by the joint action of the differential pressure force generated by the air flow and *gsinθ*, the differential equation for the motion of the hazelnut is obtained according to D'Alembert's principle:

$$\frac{dv\_{sx}}{dt} = \frac{F\_M}{m} + g\cos\theta\tag{9}$$

$$\frac{dv\_{sy}}{dt} = \frac{k\rho S(v - v\_s)^2}{m} - gsin\theta \tag{10}$$

In the equation, *FM* is the Magnus effect (N) and *vs* is the hazelnut velocity (m·s<sup>−</sup>1).

In the sorting process, hazelnuts will be in contact with the sieve plate, in addition to the above forces, but are also affected by the sieve plate support force *FN* and friction resistance *Ff*, according to D'Alembert's principle to obtain the differential equation of hazelnut motion, as follows:

$$F\_f = \mu F\_N \tag{11}$$

$$\frac{dv\_{sx}}{dt} = \frac{F\_M + F\_N}{m} + g\cos\theta \tag{12}$$

$$\frac{dv\_{sy}}{dt} = \frac{k\rho S(v - v\_s)}{m} - \mathfrak{g}\sin\theta + \frac{\mu F\_N}{m} \tag{13}$$

According to Equation (13), the velocity of hazelnut movement in the sorting device is influenced by the average velocity of gas flow *v*, the initial average velocity of hazelnut *vs*, and the angle *θ* between the sieve plate and the horizontal direction. Therefore, the factors affecting hazelnut sorting mainly include gas flow velocity and sieve plate angle, which are controlled by fan speed and sieve plate angle in the experiment. The theoretical analysis of fluid dynamics provides the theoretical basis for the simulation and experimental design.
