Evaluation of the Functional Parameters for a Single-Row Seedling Transplanter Prototype

Abstract

The development of an automatic seedling planting system for micro-farms requires testing under laboratory conditions to verify the theoretical relationships between essential functional parameters, working speed and planting time. The constructive dimensional values of the prototype, the results measured in stationary mode directly on the transplanter and the auxiliary equipment and the direct determinations of the working parameters on the soil bin are used. Depending on the characteristics of the soil bin trolley, a range of speeds is chosen at which the machine is tested. The data obtained validate the correct operation of the prototype at speeds close to those determined theoretically for the following indicators: distance between plants per row, planter wheel slippage, misplanted seedlings rate and seedling frequency, with results comparable to existing agronomic standards. Once the appropriate operating speeds of the machine have been obtained, between 0.304 and 0.412 m/s, with planting frequencies between 0.899 and 1.157 s⁻¹ (respectively, 53.94 and 69.42 seedlings per minute), optimizations and adjustments of some machine components can be made, for subsequent testing in real field conditions.

1. Introduction

All over the world, the automation of seedling planting aims to reduce the shortage of skilled labor, to fit the planting operation into the optimal period and to obtain higher quality indicators than manual planting.

The trend is underlined by intensive research and planting machines introduced on horticultural farms in the last 20 years.

There are currently several directions for automated seedling planting. The first is the development of complex, high-productivity, towed or self-propelled automatic machines by companies from Australia, the US, Great Britain, Italy and Sweden. Characteristic of these machines is their low service staff, high travel speed, long autonomy between feedings and adaptability to different planting schemes; purchase and operating prices are high.

The underlying principles of these machines are air-pruning technology for growing seedlings [1,2] and extraction based either on vacuum from the growth cells of the trays [3] or by finger, needle, or combination systems [4,5].

Another direction of research was initiated in Japan by the agricultural divisions of Yanmar Noki, Co., (Osaka, Japan) Kubota Co., Ltd. (Osaka, Japan) and Iseki Noki Co., Ltd. (Matsuyama-shi, Japan), which developed self-propelled automatic seedling planters derived from rice planters for small and medium-sized Japanese farms. They were designed to be serviced by the machine’s sole operator, have a stock of pulp mold cell seedlings trays, use a holding claw seedling extractor and perform a reduced range of planting schemes [6].

The latest approach to plantation automation can be found in research from China and India. Basically, the aim is to use robotic technology to perform the various operations required for planting: seedling extraction from the growing cell [7], seedling distribution [8], selection before planting [9] and guidance of planting machines in greenhouses [10]. Characteristically, in parallel with equipping these planting machines with high-tech components that can be integrated into precision farming, the primary goal remains the trend to develop small-farm-oriented planting systems to achieve better quality and productivity indicators, as illustrated in the mentioned research in India [8] and China [10].

Meanwhile, vegetable farms in Romania are characterized by a preponderance of subsistence micro-farms, of which more than 70% have areas of less than 5 ha; they face a decline in specialized labor and insufficient financial resources for investments on the scale of automatic planting machines and the related standardized seedling production system.

These considerations argue for the need to obtain a seedling technology accessible to small farmers in terms of price and complexity of use, with low and unskilled labor, comprising a simple construction transplanting machine with gravitational extraction, transport and distribution of seedlings with prefabricated Jiffy-type substrate, grown in rigid original plastic trays, in protected shelters. The planting machine is set up as a mono-section, fed with trays of seedlings by an operator, who also drives the aggregate formed by the machine with a walking-behind tractor.

Although it is still aimed at small farms, in comparison with the other approaches presented above, the main feature of the prototype, constructive and functional simplicity, is characterized by certain particularities in all the segments that define the interdependent system of an automatic planting technology: seedling with nutrient substrate, growing medium and automatic planting machine.

• Jiffy pellets seedling growing media have been used for decades for a diverse range of plants for the definite advantages of good workability, compatibility with almost all growing trays, high germination rate and shock-free transplanting. They have been utilized for automated transplanting of seedlings into pots or other growing media in greenhouses, but in this technology, they are intended for obtaining seedlings directly into the tray, used then for direct transplanting in the field. In addition to the constancy of dimensional parameters, an essential advantage for the horticultural micro-farm is the elimination of obtaining different recipes for substrate mixture [8,11,12], with all the inherent difficulties: disinfection of the components, dosing, substrate formation; the first stage is more difficult, due to the thermal or chemical operations required, which sometimes also affect the viability of the seedlings [13].
• The use of the aforementioned mechanically, pneumatically or electrically driven robotic systems for the extraction of seedlings with needles and push forks [7], with L-shaped rotating fingers [8], with clamp-type devices [14], as well as distribution devices with belt-conveyor type with cups [9,15], controlled by an electronic module [16], lead to high qualitative and functional parameters of planting, but with difficulties in operation and maintenance. In the case of the prototype intended for micro-farms in Romania, the solution to eliminate complicated and error-prone seedling extraction and transport systems was the use of exclusively gravitational extraction and multi-stage transport of seedlings with nutrient substrate. Due to the limits to which the substrate can withstand different stresses [17], the verification of Jiffy substrates to transport shocks validates the choice of this simplifying solution.
• Compared to feeding systems from existing high-productivity automatic planters with extraction from universal (Ferrari Growtech, Guidizzolo, Italy) [18] or specialized (Williames Pty Ltd., Warragul, VIC, Australia) [19] trays and transport with different types of conveyors belt types [20,21], the prototype under study comprises a rigid alveolar tray, constructively correlated with the distribution apparatus for simultaneously gravitational discharge of a whole row of seedlings. Thus, intermediate operations performed by third-party systems between the tray and the distribution device are eliminated.
• Existing automatic planters have either a conventional wheel-linked distribution mechanism [7] or an electronically controlled and electrically driven seedling feeding system, independent of the machine’s movement relative to the ground, based on RTK-GPS technology [22]. In both cases, a slip of the machine’s transport system relative to the ground occurs [23], which implies a variation in the distance between plants per row, greater in the first category. The slippage results in non-zero seedling velocities at soil entry, resulting in altered planting depth [24,25] tilting or damage. The designed transplanter has a planting apparatus drive system allowing the zero-speed seedling’s planting in relation to the soil, correlated with the slipping of the planting wheel [26].
• Unlike duckbill [27] or dibble [28]-type planters with an external control mechanism, the system designed for the prototype has seedling release flaps from the planting device, controlled by a cam under the action of its own weight force.

The achievement of this integrated technology for planting seedlings comprises five stages, presented in Figure 1:

–

Determining the need for automated seedling planting technology adapted for Romania;

–

Design and construction of the machine;

–

Laboratory verification of its operation and preliminary calibration of the main working parameters (working speed and planting time);

–

Testing under real conditions in the field, with determination of qualitative, energy and economic parameters, for comparison with current agronomic standards;

–

Technology implementation in practice.

After the design and construction of the prototype, the operating process of the planting machine must be analyzed in terms of two phenomena that take place over interdependent periods of time: the time required to carry out the different operating phases of the feeding system and the time required for the seedling to complete all the stages, from removal from the tray until the entrance into the planting hole. The time intervals involved in the different stages of the planting process are intrinsically linked with the working speed of the machine, which is a defining parameter for machine performance.

These theoretically determined functional characteristics must be verified in practice through calculations and measurements, both at stationary and when operating in the soil bin, to validate the optimum operating values for real operation.

The aim of this paper is to fulfill the second stage of the research:

• Verification of the actual performance of the main operations of the machine: seedling feeding, distribution, insertion and fixing of the seedlings in the soil;
• To determine the range of feasible working speeds and to check that certain quality and energy indicators are within the agronomic limits.

2. Materials and Methods

2.1. Seedling Feeding Times

The schematics of the prototype of the planting machine [26], working at speed V_m, which is planting Jiffy nutritive substrate seedlings at distance d_p between the plants on a row, in a time t_p, is shown in Figure 2.

The machine is shown in the operating position when the feed tube of the planting device (6) is at rest and fed with a seedling from the receiving tube of the distribution apparatus (13). At this moment, when the axis of the planting hole formed in the soil by the spur coincides with the axis of the planting device (6), the control rod (3) actuates the oscillating lever (2) on the portion corresponding to the transport stroke of the AB arc; thus, the sliding rods (5) actuate the planting device (6), which is rolling on the CD curve of the cam guide so the seedling is released when it reaches zero relative speed to the ground (Appendix A). The curve CD equals the fraction of the arc AB corresponding to the transport action (XY arc). The rest of the AB arc corresponds to the pause (BX arc) and return times (AYX arc), respectively; these intervals can be determined according to the position of the control rod on the planter wheel.

Figure 3 shows two combined movements: the distribution apparatus (rotational movement of the distribution apparatus disc with receiving tubes) and the planting device (reciprocating rectilinear movement). The seedling planter travels the corresponding distance d_p between two seedlings in a row while the planting device performs two movements:

–

Movement I is the return action of the planting device from the seedling release position to the rest position for feeding (under the slot of the holding-release screen of the distribution apparatus), partially deployed during the return time (YX arc);

–

Movement II is transporting the seedlings by the planting machine over the same distance during transport time and during the period of initiation of the return movement of the planting device (YA arc).

Between these two movements, the planting device comes to rest in relation to the machine frame (pause time) until the planter wheel control rod comes into contact with the oscillating lever drive profile, initiating the transport stroke (planter wheel XY arc) (Figure 1).

It should be noted that to avoid damaging the seedling, it is necessary that the seedling complete at least part of the gravity fall trajectory from the receiving tube into the planting device tube by the time the seedling transport stroke starts.

To obtain different planting patterns, the planting machine adjustment by mounting an appropriate equidistantly number of spurs on the planting wheel is based on the fact that the pause time determined by the position of the adjustable control rods on the wheel provides the appropriate time interval for correlating the theoretical distance between plants on ra ow with the interval required for the planting device seedling feeding operation.

These considerations indicate that these times overlap at certain stages of the planting device and distribution apparatus operating process, in varying proportions, depending on the working parameters: distance between plants per row and working speeds.

In conclusion, the following times can be defined as being characteristics of the operation of the planting machine described:

–

Return time t_rev, in which two separate movements occur: that of the drive rod of the planter wheel, with V_m speed on the YA arc, and the completion of the YX arc by the oscillating driving lever, in the opposite direction relative to the wheel movement;

–

Pause time t₀, corresponding to the control rod peripheral movement on the BX arch, with V_m speed;

–

Transport time t_t corresponds to the movement of the control rod and oscillating lever on the XY arc, with a peripheral velocity equal to the V_m speed.

As a result, the planting time t_p is given by the relation:

$$t_p=t_{rev}+t_0+t_t$$

(1)

Planting Device Supplying Time

There are two aspects of the seedlings supply to the planting device: the operation of supplying the planting device with a single seedling from the distribution apparatus and, for every four such supplies, the operation of replenishing the distribution apparatus sectors with sets of four seedlings from each row of the tray (Appendix B). Since the second operation overlaps periodically with the first, only this feeding of the planting device is of interest in determining the planting time.

The planting device supplying time t_al is given by:

$$t_{al}=t_{per}+t_{cd}$$

(2)

where:

–

t_per—The permutation time of the seedling receiving tube from position θ₁ to θ₂ (Figure 2);

–

t_cd—Time of gravitational fall of the seedling from the receiving tube into the planting device, s.

The correct supplying condition is as follows: at the end of the permutation stroke of the seedling receiving tube from position θ₁ to θ₂, the planting device should be at rest position under the slot of the holding-release screen of the distributor; i.e., the return time is lower than the permutation time of the receiving tube, and practically, the planter waits for the gravitational feeding of the seedling during the pause time of the transmission system. The conditions imposed by these factors can be expressed by the relations:

$$t_{rev}\le t_{per}$$

(3)

$$t_{cd}\le t_0$$

(4)

The return t_rev and permutation times are determined experimentally by an electronic control block mounted on a planting section operated in stationary conditions.

The gravitational fall time t_cd was determined with the same electronic control block mounted on an auxiliary installation [26]. The destination of the auxiliary installation is the measurement of the gravitational feed times for the stages of operation of the planting equipment and for simulating the deformation of the substrates during these operations, thus determining the validity of the choice of such transportation, which is the basis of the simple operation of the machine (Appendix C).

The schematic of the electronic system used to measure the components of planting time is shown in Figure 4.

For these determinations, XNote Stopwatch V 1.63 [29] timing software was used, commanded by the micro-switch of the electronic control block, which also allows the measured times to be recorded.

The return time t_rev diagram of the measuring installation, presented in Figure 5, is based on the reciprocating rectilinear movement of the planting device. It is determined by measuring the time from the triggering of the micro-contact by the scotch-yoke device to the shut-off of the infrared beam between the infrared LED and the infrared phototransistor by the same part’s lever returns, which has a synchronous movement with the planting device.

The measurement of the permutation time t_per was based on the step-by-step movement of the distribution apparatus, operated by a ratchet system, as shown in Figure 6. The start of the timer was triggered by the micro-switch through a receiving tube until the infrared beam between the infrared LED and the infrared phototransistor was interrupted by a shutter mounted on the periphery of the distribution apparatus disc.

The seedling’s fall time was measured by triggering a computer timer with a micro-switch when the lever system was actuated, releasing the seedling simulacrum [3]; the timer was stopped when the substrate passed between the infrared LED and photoreceptor, thus interrupting the IR beam. The auxiliary installation is presented in Figure 7.

2.2. Working Speed

Expressing the pause time t₀ as a function of the arc BX leads to:

$$t_0=\frac{\overline{BX}}{V_m}\Rightarrow V_m=\frac{\overline{BX}}{t_0}$$

(5)

where V_m is working speed, m/s, t₀ is pause time, s and the arc length BX, m.

Operating condition (5) allows the determination of the planter’s working speed limit:

$$V_{\lim }\le \frac{\overline{BX}}{t_{cd}}$$

(6)

where V_lim is the theoretical maximum working speed of the machine, m/s.

To calculate the actual range of working speeds of the planting machine, bounded by the theoretically determined speed limit, the definitions of the times mentioned in Section 2.1 were corroborated with the experimentally determined values on the said installations and with the measured constructive parameters of the planter wheel equipped with four spurs.

For the last-mentioned measurement, the arcs BX and XY (Figure 2) were determined with the machine at rest and the wheel immobilized immediately after the control rod released the oscillating lever, which reached the end of the return stroke.

2.3. Soil Bin Studies

The prototype was tested on a soil bin in order to verify the correct functioning of the component systems and to evaluate the constructive, functional and energetic parameters; one of the parameters investigated was the working speed of the equipment. The speed values for which planting of the seedlings is performed properly can be compared with the current values for existing automatic and semi-automatic planting machines; in particular, the maximum value at which proper planting can be performed may provide information regarding the assumptions that led to the theoretical determination of the maximum working speed.

The soil bin shown in Figure 8 [30] was equipped with a trolley on which the tested prototype was mounted. The horizontality and working depth of the planting equipment may be adjusted using screw mechanisms.

The towing cable is coupled to the trolley by two LAUMAS Model SL C3 1000 daN tension load cells, allowing for an average tensile force value to be displayed by a controller.

The rotation speed of the electric motor (5.5 kW and 1000 rpm) may be adjusted by means of a frequency converter (type OMRON Hitachi JX Inverter) to vary the frequency of the supply current between 3 Hz and 50 Hz, allowing the working speed to be modified within wide limits, from 0.1 m/s to 1.55 m/s (0.36…5.58 km/h); it is also possible to control the return movement of the trolley for a new test run on the channel [30].

All these adjustment possibilities will allow the determination of preliminary speeds for prototype testing.

Four indicators were analyzed, with a direct correlation with working speed:

1. A first quality indicator, the relative deviation of the distance between seedlings per row, by measuring the distance between the seedlings on the row’s axis, between the stems points of insertion in the substrate, with a roller; the arithmetic mean was taken:

$$d_{pm}=\frac{{\displaystyle \sum _{i=1}^y{d}_{pi}}}{y}$$

(7)

where:

–

y = z − 1 is the number of intervals between z planted seedlings.

–

d_p—Distance between plants per row, m.

The relative deviation of the distance between plants from the arithmetic mean A_d was calculated with the usual relation:

$$A_d=\frac{\sqrt{\frac{{\displaystyle \sum _{i=1}^y{(d_{pm}-d_{pi})}^2}}{y-1}}}{d_{pm}}\cdot 100$$

(8)

2. A second qualitative index, the misplanted rate; seedlings that do not survive after planting are in one of the following situations: broken at the stem insertion into the substrate, with the substrate not inserted into the soil, buried in the soil and sloped. Regarding the simulacrum seedlings, these situations are similar, except that the real stem breaking is replaced by stem wire bending. The percentage of misplanted M_s seedlings is:

$$M_s=\frac{s_w}{s}\cdot 100$$

(9)

where:

–

s_w is the number of the misplanted seedlings.

–

s is the total number of planted seedlings.

3. An energetic indicator, the slip coefficient of the planter wheel; knowing the theoretical value between plants per row d_pt (for four spurs on the planter wheel), the wheel slip α was calculated with the relation:

$$\alpha =\frac{d_{pm}-d_{pt}}{d_{pm}}\cdot 100$$

(10)

4. A qualitative economic exploitation indicator, planting frequency; F_s represents the number of seedlings distributed per second and is determined by the speed of the machine traveling the average distance between seedlings per row:

$$F_s=\frac{V_m}{d_{pm}}$$

(11)

The agronomic indicators of automatic seedling planting to be met by the four mentioned indicators are taken from the literature and are presented in

Table 1. Agronomic requirements for seedling planting.

Agronomic Planting Indicator	Relative Deviation Ad (%)	Misplanted Rate Ms (%)	Planter Wheel Slippage α (%)	Planting Frequency Fs (s−1)
Value	5–10 1	6–10 2	10–15 3	0.83–5 4

¹ Maximum values [8,10,31,32,33,34,35]; ² Maximum values [24,35,36,37]; ³ Maximum values [36,38]; ⁴ Extended values range [10,24,31,33,35,39].

.

Due to the relatively small number of seedlings planted along the active length of the soil channel (10 seedlings), three repetitions were performed for each selected speed.

3. Results

3.1. Stationary Collected Data

In order to determine the return time of the planting device and the permutation time of the distribution apparatus, the transplanter prototype was mounted on a suitable stationary stand, which allowed the planter wheel to be driven, with the rotational speed measured by means of a version of the same electronic control block, with the micro-switch triggered by the control rods of the wheel. The rotational speeds of the planter wheel, ranging from 0.47 to 2.38 rev/s, correspond to the calculated working speeds of the transplanter between 0.1 and 0.5 m/s, by the relation:

$$V=\omega \cdot R$$

(12)

where:

–

V is the working transplanter speed, m/s;

–

ω is the rotational speed, rev/s;

–

R is the planter wheel radius, m.

Since the planter wheel has four spurs for making planting holes, eight complete wheel rotations are required to make a number of repetitions equal to the number of seedlings contained in a planting tray (32 seedlings).

3.1.1. The Planting Device Return Time Determination

The return times of the planting device for each machine’s working speed and planter wheel rotational speed, determined on installation shown in Figure 9, were processed by calculating the standard deviation from the arithmetic mean (

Table 2. Planting device return time *.

Return Time Speed Rotational/Working	trev1 (s)	trev2 (s)	trev3 (s)	trev4 (s)	trev5 (s)
	ω1 = 0.47 rev/s V1 =0.1 m/s	ω2 = 0.95 rev/s V2 = 0.2 m/s	ω3 = 1.42 rev/s V3 = 0.3 m/s	ω4 = 1.90 rev/s V4 = 0.4 m/s	ω5 = 2.38 rev/s V5 = 0.5 m/s
X = $\overline{x}\pm {\sigma }_{\overline{x}}$	0.3506 ± 0.0025	0.3496 ± 0.0035	0.3478 ± 0.0021	0.3406 ± 0.0018	0.3328 ± 0.0027

* The table with all measured data can be found in Appendix D, Table A4.

).

3.1.2. The Distribution Apparatus Permutation Time Determination

The distribution apparatus permutation time was determined, as shown in Figure 10, at the same working and rotational speeds; the measured and processed values are shown in

Table 3. Distribution apparatus permutation time **.

Permutation Time Speed Rotational/Working	tper1 (s)	tper2 (s)	tper3 (s)	tper4 (s)	tper5 (s)
	ω1 = 0.47 rev/s V1 = 0.1 m/s	ω2 = 0.95 rev/s V2 = 0.2 m/s	ω3 = 1.42 rev/s V3 = 0.3 m/s	ω4 = 1.90 rev/s V4 = 0.4 m/s	ω5 = 2.38 rev/s V5 = 0.5 m/s
X $=\overline{x}\pm {\sigma }_{\overline{x}}$	0.7784 ± 0.0052	0.7762 ± 0.0050	0.7765 ± 0.0067	0.7734 ± 0.0070	0.7718 ± 0.0055

** The table with all measured data can be found in Appendix D, Table A5.

.

3.1.3. The Gravitational Fall Time Determination

To avoid growing a large number of seedlings for experiments, Jiffy’s substrate seedling simulacrum is used, consisting of a real Jiffy substrate and a wire stem with plastic leaves imitation seedling, presented in Figure 11, made according to the model exposed by Hallonborg, U. [3]. The parameters of a 32-simulacrum set are measured after two-phase watering of the substrate according to the Jiffy manufacturer’s instructions [40] and are presented in

Table 4. Seedling simulacra mean parameters *.

Seedling Height [mm]	Stem Height [mm]	Substrate Height [mm]	Substrate Diameter [mm]	Weight [g]	Foliage Diameter [mm]	Leaves Number [pcs.]
157 ± 0.1045	79 ± 0.1254	40.28± 0.1411	41.11 ± 0.2374	58 ± 0.3236	45 ± 1.175	2–4

* The data are the parameters of seedling simulacra after the first gravitational transport presented in Appendix C.

.

The auxiliary system, shown in Figure 12, was adjusted to measure the gravitational fall time of the seedling simulacrum for the distribution apparatus supply stage from the lower end of the receiving tube (13) into the planting device (6) (as shown in Figure 2), where at the bottom end of the tube, a retention system keeps the substrate seedling until the last operation, the gravitational transport to the planting hole in the soil. The exact height of the tube of the planting device (6), which is 228 mm, represents the actual gravitational fall height for this stage of the planting machine supply operation.

The values determined, and the results regarding the standard deviation from the arithmetic mean are shown in

Table 5. Seedlings fall time values.

No.	tcd (s)	No.	tcd (s)	No.	tcd (s)	No.	tcd (s)
1	0.27	9	0.22	17	0.29	25	0.26
2	0.22	10	0.29	18	0.29	26	0.21
3	0.25	11	0.25	19	0.28	27	0.25
4	0.22	12	0.27	20	0.31	28	0.28
5	0.22	13	0.28	21	0.29	29	0.28
6	0.29	14	0.27	22	0.22	30	0.29
7	0.29	15	0.24	23	0.25	31	0.24
8	0.24	16	0.22	24	0.28	32	0.23
$\mathrm{X}=\overline{x}\pm {\sigma }_{\overline{x}}$	0.2590 ± 0.045

.

3.2. Soil Bin Test Data

After the soil preparation operations in the bin with the plow attached to the trolley and by processing with the mini-tiller, the degree of soil granulation was analyzed using a metric frame, a set of sieves and a precision balance to determine the percentages of soil components, as shown in Figure 13a. The determinations of the degree of soil compaction and soil moisture at the planting depth of 0–0.150 m were made using the handheld Eijkelkamp cone penetrometer, with humidity electrical conductivity soil sensor ThetaProbe type ML2x (using the software mentioned in Supplementary Materials), as illustrated in Figure 13b.

Following the two types of determinations, the soil in the test bin can be described as a chernozem having a loam-clay texture with 38% clay, 32% silt and 30% sand, with aggregates below 20 mm, moisture content of 19% and compaction of 0.28–0.32 MPa.

During several runs of the soil bin trolley with the planting machine mounted and performed at different speeds without seedling planting, time was measured and divided by the active length of the stand; the speeds obtained are listed in

Table 6. Soil bin speed selection.

Parameters/Runs	1	2	3	4	5	6	7	8	9
Frequency (Hz)	10	14.6	19.9	21.7	28.3	31.5	35.4	40.3	48.2
Electrical resistance (KΩ)	1.0	3.0	4.5	5.0	6.5	7.0	7.5	8.0	8.5
Speed Vm (m/s)	0.102	0.150	0.208	0.227	0.285	0.304	0.353	0.412	0.528

.

With the machine mounted on the soil bin trolley, with the planting wheel engaged into the soil and with the same adjustment of the fixing skids, at speeds close to those used to determine the planting time components, planting runs were executed (Figure 14). The distances between the planted seedlings simulacra were then measured, as shown in Figure 15; both raw and processed data are presented in

Table 7. Measured and calculated indicators.

No.	Working Speed Vm (m/s)	Seedlings Distance Per Row dp (m)				Relative Deviation Ad (%)	Misplanted Rate Ms (%)	Wheel Slip α (%)	Planting Frequency Fs (s−1)
		Min	Max	Mean	St Dev
1	V1 = 0.102	0.308	0.396	0.333	0.0151	4.534	10	3.60	0.306
2	V2 = 0.208	0.323	0.352	0.335	0.0080	2.388	0	4.179	0.620
3	V3 = 0.304	0.324	0.356	0.338	0.0086	2.544	3.33	5.029	0.899
4	V4 = 0.412	0.331	0.382	0.356	0.0141	3.960	3.33	9.831	1.157
5	V5 = 0.528	0.333	0.394	0.370	0.0160	4.324	13.33	13.24	1.427

Underlined values: exceeded agronomic limits.

and Figure 16.

3.3. Wheel Planter Construction Parameters

Measuring the circle arcs of the planting driving wheel (with diameter D = 0.420 m) under the conditions mentioned in Section 2.2 produced the following results:

$$\overline{XY}=0.085; \overline{BX}=0.138$$

(13)

where the length of the arc XY, m.

Based on experimental results, it was possible to use the arithmetic mean of the fall time corresponding to transport II from Table 3, i.e.,

t_cd = t₂ = 0.2590

(14)

It therefore follows:

$$V_{\lim }\le \frac{\overline{BX}}{t_{cd}}\iff V_m\le 0.533$$

(15)

Thus, for the theoretical maximum limit speed obtained (without slip) of 0.533 m/s (1.918 km/h) and for the theoretical distance between plants per row d_pt = 0.321 m, determined for the mentioned planting wheel configuration, the planting time t_p can be calculated with the relation:

$$t_p=\frac{d_p}{V_m}$$

(16)

The resulting planting time is greater than or at most equal to the minimum limit value, obtained as follows:

$$t_p\ge t_{p\lim }=0.602$$

(17)

The relationship (1) of the seedling planting time allows the study of the component times.

Thus, the t_rev return times obtained from the experimental tests (Table 1) have very close values, with arithmetic averages differing by a few tenths of a second, indicating that the recovery springs provide sufficient force to overcome resistances that arise during machine operation at different speeds; the fact that the times are inversely proportional to the five rotational speeds of the planting wheel shows that, at very low speeds, the fraction of the return time corresponding to running the YA arc at the planting wheel speed for a correspondingly longer time changes the composition of the planting time. This influence is less pronounced at high speeds, given the small size of the said arc.

For the calculation of the planting time, the measured return time corresponding to the working speed close to the calculated maximum speed V_lim shall be chosen, i.e., t_rev = t_rev5 = 0.3328 s.

The pause time t₀, corresponding to the XB arc preceding the operation of the planting machine, is given by the relation:

$$t_0=\frac{\overline{BX}}{V_m}=0.259$$

(18)

The time corresponding to the transportation of the seedling by the planting device on the curve CD, t_t, can be deduced by measuring its length or by using the size of the arc XY, equal to CD; thus, it results in the following:

$$t_t=\frac{\overline{DC}}{V_m}=0.159$$

(19)

So, planting time can be expressed as the sum of its components:

$$t_{p\min }=t_{rev}+t_0+t_t=0.750$$

(20)

It can be seen that the value obtained, which is the minimum real planting time of a seedling, calculated with the limited maximum working speed of the machine, follows a relation (17), where the theoretical planting time does not take into account the partial overlapping of some components of the planting and distribution times, an essential element in the machine functioning in different operating modes.

4. Discussion

The data measured for different working speeds provide the possibility of evaluating the constructive and functional factors involved in the indices’ variations in Table 7.

Thus, for the lowest speed V₁, difficult planting machine operations occur due to component inertia (oscillating lever-driving rod level, distribution apparatus disc), leading to an increased number of wrongly planted seedlings: tilted and insufficiently fixed (Figure 17a) and displaced, as in Figure 17b and, hence, the results in a higher value of the deviation of the distance between plants per row, even if it is well below the permissible limit. Although the misplanted rate is at the upper acceptable limit, and the wheel slip has a low value, what eliminates V₁ working speed is the very low planting frequency, below the accepted range, even for semi-automatic planting machines.

The V₂ speed ensures a more constant operation of the distribution system, which has resulted in no planting errors and the lowest deviation of planting distances per row. The low travel speed (about 0.75 km/h) leads to reduced slippage but also to a low planting frequency, below the limit mentioned in the literature.

In the case of the V₃ speed, the distribution and planting machine operations are optimal, the only planting fault being the bent seedling simulacrum stem, shown in Figure 18, which would not necessarily compromise planting in a real seedling case. The distance per row deviation, the misplanted rate percentage and the planter wheel slip are within the accepted limits, while the planting frequency, 0.899 s⁻¹ or 53.94 seedlings/minute, exceeds the lower accepted value for the first time. Thus, V₃ = 0.304 m/s or 1.094 km/h is the first speed at which the operating parameters specific to an automatic seedling planter are reached.

For the V₄ speed, the working parameters are in normal values for the planting process, with the slip index towards the upper allowed limit. The only planting fault is a buried seedling, presented in Figure 19; the planting frequency has a good value for a process with automatic distribution, 1.157 s⁻¹ or 69.42 seedlings per minute, falling well within the range indicated by the literature.

For the V₅ speed, the relative deviation index of the distance between seedlings per row is in the normal range and the planting frequency is high, 1.427 s⁻¹ or 85.62 seedlings per minute; however, the exceeded value of the wheel slip and, in particular, the high percentage of planting errors (such as buried and insufficiently fixed seedlings, as in Figure 20a,b) make this working speed not a viable option for machine operation in this prototype design variant.

The resulting soil profile is noticeable with a raised area on the planted row, bordered by two furrows, a phenomenon responsible for some of the planting defects produced.

The relative deviation of the distance between seedlings per row, although generally increasing slightly with working speed, remains, for all five speeds, below the agronomic limit indicated in the literature.

The exception, for V₁, with the highest value of these indicators among the five variants, is precisely due to the defective distribution, which led to the change in the distance between the two affected seedlings, visible on the graph in Figure 16a as a sudden variation of large amplitude.

The rate of planting faults has a similar variation, increasing with working speed, with the same exception due to planting faults at V₁, where the agronomic upper limit is reached; at V₅, however, there is a net overshoot of this indicator due to multiple planting faults, which are not only due to distribution deviations at extreme speeds but also to seedlings poor fixation by winged skids in the soil.

The most influential energy indicator is the slip coefficient of the planting wheel; in practice, its increase with the working speed is the factor that directly determines the identical variation of the distance between plants per row and indirectly the number of misplanted seedlings by altering the interaction of the fixing skids with the soil and the way the planting wheel spurs makes holes in the soil.

Planting frequency is the main indicator that selects the working speeds for future field trials, among those where planting parameters fall within the agronomic limits for automatic transplanters. From the processing of the measured data, the speeds V₁ and V₂ will not be selected for further testing, even if in V₁ tests there was only one indicator at the upper limit, but not exceeded, and there were no misplanted seedlings in V₂; the planting frequency for these two speeds is too low, even for manually fed machines.

In the case of speed V₅, there is a net overshoot of the slip value, and hence, as pointed out, a high misplanted rate, which also eliminates this speed, even if a very good planting frequency is achieved.

Speeds V₃ and V₄, with good values of the other indicators, are selected as guideline speeds for field tests precisely because of the planting frequency, acceptable for V₃ (according to some cited expert sources, others indicating as a minimum limit a frequency of 1 s⁻¹, i.e., 60 seedlings per minute) and good for V₄.

Future Research Directions

Looking at these results, it can be seen that the range of eligible speeds is relatively narrow, and ways need to be found to expand it. While we have shown that it is not feasible from qualitative and economic points of view to choose low speeds, it is logical to eliminate the shortcomings found to achieve higher working speeds.

As shown in relation 15, the theoretical maximum working speed of the machine V_lim = 0.533 m/s and the theoretical maximum planting frequency deduced is 1.66 s⁻¹ or 99.62 seedlings/minute (neglecting both aspects related to the real deployment of some feeding times and wheel slip). The V₅ speed has a value close to the limit speed, and obviously, this will be the target working speed if some adjustments or constructive and functional aspects of the prototype are modified.

For this last working speed V₅, it should be noted that the process of supplying and transporting the seedlings works correctly; the planting faults are due to the process of introduction and fixing into the soil: incorrectly formed hole, altered (tilted) fixation, and buried seedlings.

Thus, four systems need to be modified to remove or mitigate these shortcomings to achieve higher working speeds in the future.

The first aspect, even if it has mainly occurred at low speeds, the operating deviations due to the high inertia of the distribution apparatus disc, behaving like a flywheel when actuated by the ratchet mechanism, with intermittent movement at low rotational speeds, require its modification or a more efficient immobilization system.

The second issue concerns the shape of the spurs on the wheel (Figure 21a) for forming planting holes, which at high speeds with high slippage tend to form elongated holes, shown in Figure 21b, which can favor the tilting of the seedling in the direction of the row.

The third aspect relates to the fixation of seedlings in the soil by winged fixing skids, presented in Figure 22. It was noted that to standardize the conditions for determining working speeds, the distance and angle of the skid wings are kept constant.

It is obvious that, in addition to changing these parameters according to the soil characteristics in field tests, even at the level of the soil bin where the soil has relatively constant properties, adjustments are necessary because soil flow behavior changes between the skid wings at different working speeds. Thus, because increasing the working speed leads to an increase in the misplanted seedlings number, as shown in Figure 16, it is necessary to increase the distance and decrease the angle between the wings to avoid displacing too vigorously and too much soil, as happened at V₅ speed, Figure 20a. In this way, it can be reduced the process of tilting or burial of seedlings already planted in the soil in the fixing process, as shown in Figure 23.

The elongated holes can also favor tilting the seedling in the direction of the row.

The fourth direction is aimed at reducing the wheel slip to the maximum—this factor is the most influential on the behavior of the planting machine. Given that control rods of the distribution system are at the base of some of the anti-slip profiles shown in Figure 21a, the change in their number and profile must be made in accordance with the normal operation of the distribution and, also with the new shape of the spurs, in order not to create variations of wheel adhesion to the ground.

In addition to the prototype testing environment, it should be noted that when testing on the soil bin, there are issues that could interfere with the functioning of the prototype and, therefore, with some of the calculated indicator values. The most important considerations in this situation are as follows:

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The slippage is exacerbated due to the soil structure damage after repeated crossings;

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Some events, such as misplanted seedlings, have a higher frequency at the ends of the run (where the soil has more unevenness: moisture, compaction, different grain sizes), observable in the context of a bin run with 10 seedlings planted.

The weight of these influences can only be assessed in actual field tests.

5. Conclusions

The paper presents the test on the soil bin of an automatic seedling planting machine prototype, designed to be attached to a walk-behind tractor, intended for vegetable micro-farms. The work aims at how the transplanter works and the optimal range of speeds for future field tests.

The most important aspects of this research stage are:

• The results indicate that the chosen speeds, which are below the upper limit of the calculated theoretical working speed, allow for the prototype’s testing, which provides indications of the correctness of the planting operation under near-real conditions.
• The chosen speeds at which the planting parameters comply with agronomic indicators are comparable to those of existing automatic planting machines.
• The working speeds suitable for this configuration of the automatic seedling transplanter prototype are within the range given by the speeds V₃ and V₄, respectively, 0.304 and 0.412 m/s, which have demonstrated the fulfillment of the agronomic indicators imposed by the literature.
• The prototype achieves seedling planting frequencies of 0.899 and 1.157 s⁻¹, 53.94 and 69.42 seedlings per minute at the mentioned speeds.

At this point, it should be noted that there are no viable working speeds below 0.304 m/s, given the planting frequency towards the lower agronomic limit obtained for V₃, which is 0.899 s⁻¹ (nearly 54 seedlings per minute). Still, there are probably working speeds higher than V₄ = 0.412 m/s in accordance with the fact that theoretical calculated speed limit (with real planting and distribution times taken into account), given by the relations (16) and (20), is 0.428 m/s.

In order to achieve higher working speeds and thus higher quality and economic indicators, in particular higher planting frequencies, following the analysis of the deficiencies found, directions for improvement of the seedling planter prototype were established for future field trials:

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Some low mass inertia components, such as the distribution apparatus disc, should be made to avoid malfunctions at low speeds;

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The shape of the spurs should be modified (e.g., by adopting a double-circular arc profile design) to obtain appropriate openings over the whole speed range;

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The anti-slip profiles need resizing and reconfiguration to minimize planter wheel slip and improve self-cleaning of soil that tends to stick;

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The setting of the fixing skid wings must be correlated with the soil type, moisture content, and working speed, a priority being establishing an appropriate relationship for effective adjustment.

6. Patent

Applicant:

Universitatea de Știinţe Agricole şi Medicină Veterinară “Ion Ionescu de la Brad” [Ro]-Iasi University of Life Sciences (IULS).

Inventor:

Vlahidis Virgil, “Ion Ionescu de la Brad”Iasi University of Life Sciences (IULS), Faculty of Agriculture, Department of Pedotechnics, Romania [RO]

Title:

Equipment for automatically planting seedlings with nutritive pots

Registered by:

OSIM-State Office for Inventions and Trademarks Romania

Priorities:

RO201500134A·2015-02-24

Published as:

RO130295 on 30.03.2022