2.2.2. Recovery Shovel
The factors affecting the performance of the recovery shovel include: the width of the shovel body (
B), the shovel angle (
α), and the length of the shovel body (
L). According to the agronomic requirements of the central and western regions of Inner Mongolia, potatoes are often planted in double rows on large ridges, with one drip irrigation tape laid on each ridge. The distance between two drip irrigation tapes is generally less than 800 mm. After the potatoes are harvested, the drip irrigation tapes laid in the fields have a degree of randomness in their placement width. To avoid missing any drip irrigation tapes, the width of the shovel body (
B) is set to 1050 mm. Cultivation patterns in west-central Inner Mongolia are shown in
Figure 4.
When the recovery shovel is in operation, the force on the soil on the shovel face is as depicted in
Figure 5. From the force analysis, the Equation (1) can be derived:
In the equation: F is the working resistance experienced by the recovery shovel, N; FN is the pressure exerted on the recovery shovel by the drip irrigation tape and soil, N; α is the shovel angle, °; G is the gravitational force of the drip irrigation tape and soil, N; f is the frictional force between the drip irrigation tape and soil on the recovery shovel, N; µ is the coefficient of friction between the shovel face and the soil.
Wherein:
ƒ =
μFN from the aforementioned equation, the calculation Equation (2) for the shovel angle can be derived:
Based on the expected functional requirements of the recovery shovel, an analysis and calculation of Equations (1) and (2) determined that the shovel angle should be between 8–16 degrees. This range ensures that the drip irrigation tape can be shoveled up smoothly while shoveling up only a small amount of soil, while also avoiding issues such as increased recovery resistance due to excessively large angles of the recovery shovel.
During the recycling process, it is common for stones to get caught between the recovery shovel and the conveyor chain. Therefore, a hinged transition plate that can move is installed behind the shovel. The length of the recovery shovel is designated as (L1), the length of the transition plate as (L2), and the total length of the shovel body as (L), such that L = L1 + L2.
According to literature reviews and field observations, it has been noted that after potato harvest, some of the drip irrigation tape is left lying on top of the soil while some is slightly buried, with the burial depth generally ranging from 3 to 20 mm [
16,
17]. Based on the distribution of the drip irrigation tape, the depth at which the recovery shovel should enter the soil should be controlled between 20 to 70 mm and be adjustable. The Equation (3) for calculating the length of the recovery shovel is:
By substituting the shovel angle α = 8–16° into the above equation, the range of values for (L1) is calculated to be 109–290 mm. Considering the positional relationship between the recovery shovel and the conveying mechanism, and taking all factors into account, the length of the recovery shovel (L1) is determined to be 200 mm.
Incorporating the principle of conservation of energy, the Equation (4) for calculating the length of the transition plate segment (
L2) is:
From this, the Equation (5) for calculating the total length of the shovel body is:
In the equation: h1 is the depth of recovery operation, mm; α is the shovel angle, °; v is the machine forward speed, and mm/s; φ is the friction angle between the soil and the shovel face, °.
Substituting the data into the calculation, the value range of (
L2) is determined to be 72 mm to 143 mm. After consulting the “Agricultural Machinery Design Manual” [
18] and considering the actual design situation, the final length of the transition plate is determined to be 107 mm. Therefore, the length of the shovel body (
L) is 307 mm.
2.2.3. Conveying Mechanism
After the recovery shovel digs up the drip irrigation tape and soil mixture, it needs to continue to transport the drip irrigation tape to the rear collection box and separate it from the soil. Therefore, a conveying mechanism with two rows of conveyor chains is set up behind the recovery shovel (
Figure 6). During operation, the drip irrigation tape is clamped and conveyed to the rear by the double-row conveyor chains. The power for the conveyor chains is transmitted from the rear power output shaft through a reduction gearbox and chains. During the conveying process, the soil falls back to the ground through the gaps between the rods (6). To increase the friction between the conveyor chain and the drip irrigation tape, finger-shaped rubber roller sleeves (5) are fitted on the rods (6) of the conveyor chain. These rubber roller sleeves not only increase friction with the drip irrigation tape but also prevent the tape from becoming entangled with the rods (6) during the recycling process. This prevents congestion or entanglement of the drip irrigation tape due to insufficient friction and machine vibration during the lifting process.
This paper has determined that the width of the recovery shovel (
B) is 1050 mm. Therefore, the width of the conveying mechanism should be the same as the width of the recovery shovel. According to relevant references [
19,
20], the lifting angle range of the conveyor chain is 18–34°, and the height of the collection box is 300 mm. The relative position between the front recovery shovel and the conveyor chain has been determined. Based on the lifting angle of the conveyor chain, the distance between the two shafts of the conveyor chain is calculated to be 536–971 mm. To ensure the efficiency of the conveying mechanism and that it has the ability to funnel down soil, this paper sets the distance between the front and rear shafts of the conveying mechanism at 750 mm.
When the potato drip irrigation tape recycling machine is operating stably, the amount of soil conveyed by the conveying mechanism per unit time should equal the amount of soil shoveled by the recovery shovel. Therefore, the following Equation (6) can be derived:
In the equation: h1 is the depth of the recovery shovel into the soil during operation, mm; h2 is the width of the gap between the two conveyor chains during operation, mm; L is the working width of the machine, mm; v1 is the forward linear speed of the machine, mm/s; v2 is the linear speed of the conveyor chain, and mm/s; t is the working time of the machine, s.
The collation leads to Equation (7):
Therefore, the ratio of the depth of the recovery shovel in the soil to the width of the gap between the two conveyor chains is equal to the ratio of the linear speed of the conveyor chain to the linear speed of the machine. According to the relevant literature [
21,
22], when the machine forward speed is between 0.56 m/s and 1.11 m/s, the overall recovery effect of the drip irrigation tape is relatively good. Thus, the linear speed range of the conveyor chain can be determined to be approximately 0.99 m/s to 1.55 m/s. According to the Equation (8):
In the equation: n is the conveyor sprocket speed, r/min; r is the diameter of the driven sprocket of the conveyor chain, mm.
Given that the diameter of the driven sprocket of the conveyor chain is 90 mm, substituting this into the equation, the conveyor sprocket speed should be in the range of 210–330 r/min.
2.2.5. Collection Mechanism
After dewatering the drip irrigation tape through the guiding effect of the leading tape plate (1) into the collection box, after collecting a full drip irrigation tape, open the rear side tape plate (2) to remove the drip irrigation tape. The collection mechanism is shown in
Figure 8.
Combined with the “Agricultural Machinery Design Manual” about the box class capacity calculation [
18], this article used the pre-experiment on the round trip to recover a full drip irrigation tape to determine the necessary size of the collection box. We performed multiple experiments to determine the volume factor for the collection box that holds recycled drip irrigation tape. From this, Equation (9) can be developed:
In the equation: V1 is the collection box capacity, m3; V2 is the volume of drip irrigation tape recovered per second, m3; V3 is the amount of soil recovered per second, m3; η is the volume factor for the collection box’s recycled drip irrigation tape; and T is the machine operating time, h.
Inner Mongolia’s central and western regions mostly use single-wing labyrinth drip irrigation tape. The potato drip irrigation tape recycling machine can recycle two drip irrigation tapes at the same time. The capacity of the collection box is 0.21 m3, and the operating distance of the potato drip irrigation tape recycling machine per second is 0.56 m–1.11 m. The value of η is 0.5. Only a very small amount of soil enters into the collection box during the recycling process, and the substitution of the formula yields the operating time of the machine to be 1.8–3.6 h, which meets the reference operation quality standard.
The technical parameters of the potato drip irrigation tape recycling machine are shown in
Table 1.