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Design of a control system for a mini-automatic transplanting machine of plug seedling
Computers and Electronics in Agriculture 169 (2020) 105226
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Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Design of a control system for a mini-automatic transplanting machine of plug seedling
T
Qizhi Yanga,b, , Guanlong Huanga, Xinyi Shia, Mingsheng Hea, Ibrar Ahmada, Xiaoqi Zhaoa, ⁎ M. Addya,c, ⁎
a
School of Agricultural Equipment Engineering, Jiangsu University, Zhenjiang 212013, PR China Institute of Intelligent Robot, Jiangsu University, Zhenjiang 212013, PR China c Bioproducts and Biosystems Engineering Department, University of Minnesota, USA b
ARTICLE INFO
ABSTRACT
Keywords: Fully-automatic transplanting machine Vegetable seedlings Control system PLC control Microcomputer
In China, vegetable production system has been dominated by small and medium-sized agricultural facilities over the open-field cultivational practices. Low ceiling height and narrow width are dimensional attributes associated with most of these facilities. Due to these dimensional parametric constraints, the application of available field transplanting machinery in such facilities is a problematic subject which leads the vegetable growers towards manual transplanting. In order to meet the needs of small and medium-sized agricultural facilities for automatic vegetable transplanting, a smaller size wireless remote-controlled automatic transplanting machine was designed, which can transplant seedlings quickly in the greenhouse and by considering the stainability of environment electric power was adopted to drive all the mechanisms. In the process of agricultural production, the control system of agricultural machinery plays an important role in the degree of automation of mechanical equipment. Therefore, this paper focuses on the design of the control system of the newly premeditated automatic transplanting machine. The hardware of the control system is separated into three portions: the sensors for signal acquisition, the programmable controller for signal processing, and the driving elements for specific actions. PLC (Programmable logic controller) is adopted as the central control system of the transplanting machines which controls the automatic movement of seedlings tray carrier, seedlings extraction and feeding, and seedlings transmission to the planting units automatically. In order to control the overall movement of seedling transplanting machine, a microcontroller is adapted to control the hub and steering motor. The key driving elements of the control system are solenoid valves and electric motors which controls the action of pneumatic air cylinders and linear movement of different parts of machine respectively. The overall software design of the control system is accomplished, together with coordinated motion between components, control flow design and control program writing. In order to test the motion coordination of each component and the rationality of the control system of the Mini-Automatic transplanting machine, different planting frequencies were set to record the success rate of seedling collection and transplanting. The results of the trials exhibited that at the planting frequencies of 40, 50 and 60 plants/row/min the overall success rates were noted 98.6%, 97.2% and 96.5% respectively. It shows that the key parts of the transplanting machine are synchronized in motion, accurate in positioning, reasonable in assembling the control system and stable in operation, which meets the requirements of transplanting seedlings in the dry land.
1. Introduction With the development of automation in agricultural machinery and gradually improved agricultural economy, the replacement process of manual operation by mechanical automation in agriculture sector of China is growing slowly (Cao., 2019). The planting section of vegetable cultivation system practiced in this piece of land is moving in the
⁎
direction of transplanting seedling with rapid augmentation and shared more than half of total vegetable production (Xiao et al., 2015; Hu et al., 2017). The chines greenhouses which habitually practiced for vegetables cultivation are relatively smaller in size as they compared with other developed countries (Ji et al., 2018). Small and mediumsized arch shed and plastic greenhouse are commonly used for vegetables cultivation and specifications of 1–1.8 m shoulder height, and
Corresponding authors at: School of Agricultural Equipment Engineering, Jiangsu University, Zhenjiang 212013, PR China. E-mail addresses: [email protected] (Q. Yang), [email protected] (M. Addy).
https://doi.org/10.1016/j.compag.2020.105226 Received 14 November 2019; Received in revised form 9 January 2020; Accepted 11 January 2020 0168-1699/ © 2020 Elsevier B.V. All rights reserved.
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1.Transplanting machine chassis 4. Seedling separation unit
2. Seedlings tray carrier 5. Control system
3. Seedling extraction unit 6. Planting unit
Fig. 1. Fully automatic plug transplanting, 1. Transplanting machine chassis, 2. Seedlings tray carrier, 3. Seedling extraction unit, 4. Seedling separation unit, 5. Control system, 6. Planting unit.
the automatic feeding system for pot tray seedlings transplantation. Zhou designed a PLC-based automatic transplanting machine for dryland seedlings in 2015 (Zhou et al., 2015). The main components include the shifting device, the seedling extraction device, the planting device and the PLC control system, which adopts a single seedling extraction method to reduce the seedling separation. Hu developed a twoline fully-automatic transplanting machine for vegetable seedlings in pots and pans in 2017 (Xu et al., 2017). It was well appreciated the fully-automatic functions of seedling supply, seedling collection, seedling separation and seedling transplanting process. Yu developed an automatic transplanting machine for vegetable seedlings in dryland in 2018 (Wang et al., 2018). The machine can automatically complete the transplanting process of seedlings in pots, such as sending, picking, planting and covering soil. Yang proposed a linear reciprocating mobile seedling separation mechanism, which adopted the gear and rack mechanism to accomplish the function of static seedlings throwing and receiving in 2018 (Yang et al., 2018). However, it can be seen from the previous studies that the current automatic vegetable transplanting machines are larger in size, labour intensive, and most of them are powered by the internal combustion engine. The application of this type of engine in small and confined facilities with narrow space availability and poor ventilation, it can easily produce air pollution and affect the quality of vegetables. In China, a small automatic vegetable transplanting machine that meets the requirements for transplanting vegetables in small and mediumsized facilities has not been developed formerly. In this paper, a compact, electric-powered, wirelessly remote controlled and unmanned small automatic vegetable transplanting machine is designed. The transplanting machine uses PLC and microcontroller as programmable processors to realize the whole automation process of seedling extraction, seedlings throwing and soil covering, which provides a possibility to solve the mechanization of vegetable transplanting in medium and small facilities in China.
1.8–3.2 m ridge height associated with smaller size while, mediumsized having 1.2–1.5 m shoulder height, and 1.6–2.5 m ridge height. It is difficult to directly use the available transplanting machinery in such small size greenhouses, therefore, most of the seedlings transplanting operations are performed manually with low working efficiency (Jin et al., 2018). Currently, there is a deficiency of automatic transplanting machine suitable for transplanting vegetables in small and mediumsized facilities. Therefore, it is urgent need to develop a small-automatic vegetable transplanting machine to reduce labor intensity and improve production efficiency. The transplanting technique of vegetable plug seedling was primarily studied in the United States and Japan and during 1920s and 1930s hand-feeding transplanting machines emerged in the horticulture sector. In 1950s, a variety of semi-automatic vegetable transplanting machines with different structures were developed while in the end of 19th century semi-automatic transplanting technology was abundantly established (Wang et al., 2018). In 2002, Choi et al. developed a new seedling device for vegetable transplanting. The seedling device was composed of a gripping pointer, a trajectory generator and a pointer driver. The device was tested with 23-day tomato seedlings, and the transplanting success rate was noted 97% (Zhang et al., 2013). An American company Renaldo developed an automatic vegetable transplanter in 2003 and its working principal was followed negative pressure phenomenon, the grabber could suck the whole root from the plug and send it to the transplanter through a conveying (Han et al., 2011). A global positioning system guided automated rice transplanter was developed by Nagasaka Y and his team from National Agriculture and Food Research Organization, it was guided with only tilt corrected GPS and had advantages of a lower cost and supplementary precise operation (Nagasaka et al., 2013). Academics in China are also in progress to realize the commercial value and advantages of automatic transplanting machine; therefore, the researchers of different fields are working together to develop an efficient automatic transplanting machine (Yin et al., 2016). In the progress of this field of research Yang designed an automatic conveying system for vegetable pot seedlings and PLC was adopted as the central control system of transplanting machine (Yang et al., 2013). The highspeed servo electric cylinder was used to drive the pushrod to push out the seedlings, which realized high-speed, accurate and non-damaging seedling transmission. Han designed an automatic feeding system for a pot tray seedling transplanting machine in 2013 and all the driving parts in the system were driven by pneumatic pressure (Han et al., 2013). The control system was instructed by PLC to govern the action sequence of each cylinder, and it realized the actions and functions of
2. Materials and methods In this study, the structure of the small-scale automatic transplanting machine is shown in Fig. 1. The transplanting machine is mainly composed of the machine chassis, seedlings tray carrier unit, seedling extraction unit, seedling separation unit, planting unit and overall control system.
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6. Steering mechanism 7. Front axle 8. Drive unit (in-wheel motor) 9. Wheel Fig. 2. Overall structure of the transplanting machine chassis. 1. Electrical cabinet 2. Battery and battery case 3. The frame 4. Planting device assembly 5. Exit board, 6. Steering mechanism 7. Front axle 8. Drive unit (in-wheel motor) 9. Wheel.
2.1. Transplanting machine chassis
the box to prevent the whole tray from being brought up by stickiness during the seedling collection. The whole box is fixed on the frame through two LM shafts at an angle of 60 degrees with the horizontal plane, so that the whole tray can move transversely along the smooth axis (see Fig. 3).
The overall structure of the transplanting machine chassis consisted of chassis frame, front and rear wheels, steering device, and other parts which are listed and shown in Fig. 2. Considering the size limitation of small and medium-sized facilities of agriculture, the lightweight design of the chassis frame of the transplanting machine has been carried out. The mobile mode adopts the method of unmanned ride and wireless remote control, and uses lithium battery to achieve the purpose of energy saving and environmental protection. The chassis of transplanting machine uses hub motor to drive the wheel directly, which simplifies the layout space and improves the extraction efficiency.
2.3. Seedling extraction part The function of the seedling extraction unit is to take off the seedlings from the tray with the help of seedling claws and transport them to seedling separation unit at a specific delivery point. The detailed structure is shown in Fig. 4. The seedling extraction part is mainly composed of large gantry, small gantry, diamond-shaped mechanism, guide rail slider, seedling claws, slide plate, and base fixing plate. The main action of seedling extraction part is seedling extraction and seedling throwing. The action of seedling extraction is realized by flipping while the action of seedling throwing is accomplished by variable pitch.
2.2. Seedlings tray carrier and feeding part The seedlings tray carrier and feeding unit is mainly composed of sprocket chain, LM shaft, box, plug shaft, pressing rod and supporting frame. There are two pairs of sprocket chains symmetrically arranged on both sides of the box, and tension is applied by tensioner and twelve plug shafts are fixed on the chain evenly. The pressure bar is fixed on
5. Seedling claw 6. Slide plate 7. Base fixing plate
1. Sprocket chain 2. LM shaft 3. Plug shaft 4. Box 5. Frame 6. Pressing rod
Fig. 4. Seedling extraction part. 1. Large gantry 2. Small gantry 3. Diamondshaped mechanism 4. Guide rail slider. 5. Seedling claw 6. Slide plate 7. Base fixing plate.
Fig. 3. Seedlings tray carrier and feeding part. 1. Sprocket chain 2. LM shaft 3. Plug shaft 4. Box 5. Frame 6. Pressing rod. 3
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working principle of the automatic transplanting machine for the plug seedlings is as follows: When the transplanting machine starts its operation, the operator places the whole tray on the seedlings tray carrier and feeding unit. Then the operator starts the wireless remote-control transplanting machine to move forward. The tray feeding part starts its motion towards seedlings extraction point and seize its motion at this point. Then the claws of the seedling extraction part turn over, clamp the seedlings and return with the seedlings. When the seedling-taking claws move to the vertical position, the rhombic mechanism pushes out the variable distance, so that the four seedling-taking claws correspond to the four seedlings cups of the seedling-dividing parts one by one, and then the seedling-throwing begins. Seedling extraction part to the seedling guide barrel in the planting part stops directly above the seedling guide barrel after receiving seedlings, the falling seedlings part starts to make the seedlings fall vertically into the ditch opened by the trencher along the seedlings guide barrel, and then cover the soil to suppress and complete the seedlings planting. The transverse and longitudinal feeding of the feeding part, the clamping, turning over and variable distance of the seedling extraction part, the moving of the seedling separation part and the opening and closing of the seedling cups are all controlled by PLC (such as electric machinery, electric actuator, cylinder, etc.). The executing parts and the actions to be performed are shown in Fig. 7.
1. Rack and pinion 2. Connection board 3. Sensor 4. Frame 5. Seedling dropping unit 6. Seedling cup Fig. 5. Seedling separation part. 1. Rack and pinion 2. Connection board 3. Sensor. 4. Frame 5. Seedling dropping unit 6. Seedling cup.
2.4. Seedling separation unit The seedling separation unit adopts the gear-rack base reciprocating moving seedling-dividing mode, which can realize static seedlingthrowing, simplify the seedling-dropping problem and increase the success rate of seedling-throwing. In order to save time, seedling throwing was carried out at one time and increase the overall efficiency. It has the characteristics of quick response, good controllability and is easy to adjust the row spacing. As shown in Fig. 5, the gear is fixed on the shaft of stepping motor and stepping motor is attached with seedlings cups assembly while gear is meshed with rack drive to move the seedlings device in linear manner. When the photoelectric sensors in the left and right position are encountered with seedlings device tracer, the seedling dropping device starts and opens the seedling cup to drop the seedling vertically into the planting parts to complete the seedling planting process.
3. Design of control system hardware The hardware of the control system is divided into three parts: the sensors for signal acquisition, the programmable controller for signal processing, and the driving elements to perform some specific actions. 3.1. Selection of programmable controller The PLC (programmable logic controller) is adopted as central control system of the main mechanisms of machine due to its good reliability and simple operation. The main PLC control system for this machine is shown in Fig. 8. As the core module of the control system, the main function of PLC is to receive the input signal, process the signal, output the signal to
2.5. Working principle of transplanting machine The overall machine motion flow chart is shown in Fig. 6. The
Fig. 6. Machine motion flow chart. 4
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Fig. 7. Component composition and action.
other units, and monitor the information in the process of signal processing. The selection process of PLC has several key parameters, such as the selection of power supply, processing speed, high frequency counting, communication port etc. The most important one is the calculation and distribution of input and output points, that is, the input of sensors and other driving parts of motors and electric cylinders. The input and output points and definitions for detailed PLCs are shown in Table 1. As it can be seen from Table 1, the selected PLC should have at least 16 input points and 11 output points, and two of the output points are pulse output. Therefore, the PLC of XC3-32T-C model was selected as the controller of the implementation part. The specifications of selected PLC are shown in Table 2. The selection of the programmable controller in the chassis part needs to consider the relationship between the wireless remote controller and the hub motor. The output of the remote controller is an analog quantity, and the control of the rotation of the hub motor and the steering motor needs digital quantity, so the core programmable controller is required to have both complex digital quantity as well as analog quantity. Therefore, single-chip computer is selected as the control device, as is shown in Fig. 9. Finally, the MEGA2560 R3 development board of Arduino series is selected as the control part of the chassis control system, and its parameters are shown in Table 3.
3.2. Design of control system hardware circuit To design the circuit of the main part of the transplanting machine, it is necessary to count all the components that need power supply, as is shown in Table 4. Among them, 86 stepping motors and air compressors are powered by 48 V lithium batteries, 57 stepping motors, cylinders and PLCs are powered by 24 V lithium batteries, and the sensors are connected to the input of PLC according to the requirements, as is shown in Fig. 10. The input terminals of the PLC are connected with the switch, the counter photoelectric sensor of the seedlings tray carrier unit, the magnetic switch in the seedling extraction part and the positioning sensor in the seedling separation part. The output terminals are connected with the cylinder of the seedlings tray carrier unit, the longitudinal motor driver, the solenoid valve in the seedling extraction part and the seedling separation motor driver in the seedling separation part. The movement of the chassis part is operated by wireless remote control. The signal is transmitted by wireless remote controller, and it is processed by single chip computer after receiving the signal. Finally, the signal is transferred to the controller of steering motor and hub motor to control the forward, backward and turning movement of whole machine. The hardware circuit design of the chassis is shown in Fig. 11.
Fig. 8. Main PLC control system.
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Table 1 PLC I/O table. Input
Output
X0 X1 X2 X3 X4 X5 X6 X7 X10 X11 X12 X13 X14 X15 X16 X17
Activate switch Stopped switch Manual mode Automatic mode Switch of add 1 Switch of minus 1 Pressure detection Cylinder to origin Cylinder in place 1 Cylinder in place 2 seedlings tray carrier unit in place Highest point of turn cylinder top Turn cylinder will contact Lowest point of turnover cylinder Left limit of seedling separation Right limit of seedling separation
Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y10 Y11 Y12 Y13 Y14 Y15 Y16 Y17
4. Design of control system software
Stepping motor of seedlings tray carrier unit (pulse) Stepping motor of seedling separation motor (pulse) Stepping motor of seedlings tray carrier unit (direction) Stepping motor of seedling separation motor (direction) Cylinders need to reach the origin Cylinder in place 1 Cylinder in place 2 Turn-over cylinder start Variable-pitch cylinder start Taking claw 4 cylinder Dropping seedling 2 cylinder
claws from colliding or directly impacting. After the first removals of seedlings from the seedlings tray, the tray carrier unit should make a judgment. When the number of horizontal feeding is less than 2, the horizontal feeding is carried out. When the number of horizontal feeding is equal to 2, the longitudinal feeding is engaged and the number of horizontal feeding is back to zero. When the number of vertical disc feeding is greater than or equal to 6, withdraw the seedlings tray and put the new seedlings tray quickly. (2) Working synchronization between the seedling extraction part and the seedling separation part, when the seedling extraction part is working, the seedling separation part should move to the waiting position for the reception seedlings. When the seedling extraction parts finished the action and engaged the specific position above the seedling’s cups while the variable-distance mechanism is extended according to the cups position, the claws opened to handover the seedlings to separation unit. The seedling separation part needs to be moved after receiving the seedlings to prevent the seedlings from falling out during the reciprocating movement. (3) Working synchronization between the seedling separation parts and the chassis of the transplanting machine. The walking speed of the chassis should match the seedling speed of the seedling parts to meet the requirements of different plant spacing planting.
For the compilation of control system there is a need of corresponding software which has synchronization with control hardware. The core programming software used in this paper is XCPPro V3.1 version of the PLC programming software provided by Xinjie Company. In comparison with the common C language programming, the ladder diagram programming has more perception and correspondence, and is easy to operate and monitor. 4.1. Design of control system process According to the requirements of the project, the main function of the transplanting machine is to robotically take the seedlings from seedlings tray and plant them in the ridge with 40–60 plants/min/row planting frequency during working operation. According to the analysis of the mechanism and working principle of the transplanting machine, each action is divided into some modules: the feeding parts of the transplanting machine can complete the functions of quick feeding, transverse feeding and longitudinal feeding; the seedling extraction parts can complete the functions of seedling-taking, variable-distance and seedling-throwing; the seedling separation parts can complete the functions of seedling-receiving, and seedling-dropping and finally planting parts complete the functions of ditching, seedling planting and soil covering. In the process of planting, each unit should be able to work independently, but also can cooperate with each other and without any interference. The coordination relationship of each unit is described in the following:
Taking 60 plants/min/behavior as an example, this transplanting machine is a two-row transplanting machine, which can plant two potted seedlings at the same time. Therefore, 120 seedlings need to be picked up by the seedling extraction mechanism within 1 min. The seedling extraction mechanism of this machine has four claws. Therefore, four potted seedlings can be picked up at the same time. It means that the seedling extraction mechanism needs to complete 30 cycles for seedling picking up and transporting within 1 min. It takes 2 s for the seedling separation mechanism to complete a complete action of taking and throwing seedlings. Based on the synchronized action of each part of the transplanting machine, i.e. the feeding mechanism of the transplanting machine box, the seedling separation mechanism finishes a complete action for 2 s. The time sequence of each part is shown in Table 5. According to the function of each component and the action to be achieved, and taking the synchronized relationship of component motions into consideration, the overall control process of the transplanting
(1) Operational synchronization between the feeding part and the seedling extraction part, as the feeding part transports the seedlings tray to the seedling extracting position, the claws of the seedling extraction part are inserted into the case of seedlings tray to clamp the seedling. At this time, the variable pitch mechanism of the seedling extraction part should be in a compressed state, and the four seedling claws correspond to the four holes in the row of the hole tray. In the process of seedlings taking, the tray carrier unit should remain stationary, and cannot move until the fingernails are completely separated from the seedlings tray, so as to prevent the Table 2 PLC parameter table. I/O Points
High frequency pulse output
Type of input
Type of output
Type of power
Communication Port
Capacity of program
32(18/14)
2
NPN
Transistor
DC24V
2
96 K
6
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Fig. 9. Chassis MCU control system.
machine was designed, as is shown in Fig. 12. After pressing the starting button, the chassis moves forward and the box moves quickly to push the hole tray into the seedling point to be taken, and the seedling separation part also moves the cup to the seedling point until the seedling falls into the cup. After the seedling extraction part completes the turning, clamping, returning, variable-pitch and throwing, the box keeps moving to feeding which is in the process of variable-pitch returning, and at the same time, the seedling separation parts are reversed to start, and the seedling separation action is started. The seedling separation parts are circulated to stop pressing buttons in turn, and the planting is finished. Using XCPPro V3.1 software to write control program is to classify the modules of each part, to program each action into a single subroutine, and then call it when the general program runs. The detailed subroutines are shown in Fig. 13. Program execution flow: starting work, program backs to zero, at the same time, the tray carrier part begins to feed longitudinally and after being detected by the photoelectric sensor, the longitudinal motor stops its working. In the program execution flow, the seedling extraction part begins its movement to perform seedling taking accomplishment. After clamping the plug seedlings from the seedlings tray it retains its initial position above the cup’s assembly where the highest point of the sliding slot is detected by the magnetic switch. Then the variable-pitch cylinder is started to complete the waiting cycle of extending variable-pitch and after transferring the seedlings to separation unit the seedling extraction unit moves towards next cycle of seedlings extraction. At the same time, the seedling separation cylinder opens and closes after the seedling separation parts are connected to complete the distribution and planting of two seedlings, and then moves the seedlings to the second seedling delivery point. In the moving process of seedling separation parts, the number of times of tray carrier part is judged, and the transverse or vertical movements are carried out according to the working schedule of operation. At the same time, the seedling extraction parts start to work, and then complete the next cycle until finishing the planting.
5.2. Test of transplanting machine control system 5.2.1. Aims The success rate of seedling taking and seedling throwing under different planting frequencies was used to investigate the motion coordination of each part of the automatic transplanting machine and the rationality of the control system (see Figs. 15–18). 5.2.2. Conditions (1) Test equipment: The small-sized tray seedling automatic transplanting machine, camera and laser range finder developed in this paper. (2) Seedling selection: 72-hole tray cucumber seedlings, with a seedling age of about 20 days, with two leaves, one core or three leaves and one core, the average seedling height is about 13.5 cm. 5.2.3. Steps (1) Turn on the switch, inflate the gas tank with the air compressor, charge 0.5 MPa to the working cylinder, wait for the transplanting machine to start. (2) Connect the PLC to the transplanting machine to set different planting frequencies, specifically 40 strains/min/row, 50 strains/ min/row, 60 strains/min/row. (3) When finish the experiment, the success rate of seedlings taking and throwing under different planting frequencies were calculated, and the overall success rate was tallied. 5.2.4. Results and analysis The overall success rate of seedling-taking and seedling-throwing is an important parameter to measure the coordination and rationality of the components of the automatic vegetable transplanting machine. In order to reflect the working efficiency of each component more intuitively, according to the working process of each component, S is used to express the overall success rate of seedling-taking and seedlingthrowing. While, a denotes the number of failed seedling removal trays, such as the case where the seedling claws break the pot seedlings and fail to take them out of the hole tray; b denotes the number of failures in putting seedlings into cups, such as seedling dropping in pots during seedling transportation; c indicates the number of damaged seedlings during transportation, and the breakage of seedlings stems caused by damaged seedlings. N is the total number of seedlings. The formula is expressed as:
5. Test of transplanting machine control system 5.1. Transplanting machine control system In this paper, the control system components of the transplanting machine are fitted in the electric cabinet which is positioned at the rear portion of the chassis. The power supply (lithium battery) is installed at the left and right ends of the rear wheel bracket. The control sub-unit of the transplanting machine is installed at the position of the executing elements of the components. The signals from the controller are transmitted to each unit controller through the shielding line, and control the movement of the powering units. The physical diagram of the control system is shown in Fig. 14.
S=
N
a
b N
c
× 100%
(5.1)
The Success rate of tests were carried out on the automatic feeding, seedling taking and seedling throwing system. Point Tray Seedlings
Table 3 Single chip microcomputer parameter table. Input voltage
Output voltage
I/O Digital input /Output pins
I/O Analog Input /Output Pins
PWM terminal
FLASH capacity
DC 7–12 V
5 V/3.3 V
54
16
14
256 K
7
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Table 4 Main hardware design name and model. Project
Name
Type
Voltage
Number
Signal acquisition element
Opposite photoelectric sensor Magnetic switch Photoelectric positioning Sensor PLC Longitudinal motor Transverse cylinder Electromagnetic valve Seedling separation motor Lithium battery
G12A-M100(1/2) AL-03R E3F-DS30C4 XC3-32T-C 85BYGH450B-06D RSW-10-100 4 V210-08 86HBS120 BN4824CD
24 24 24 24 24 24 24 48 48
1 3 2 1 1 1 8 1 3
Central control element Driving element
Power
with 72 holes were used to carry out seedling taking and throwing experiments at different planting frequencies. The number of plug seedlings not clamped out of the tray, the number of pot seedlings not put into the cup, and the number of damaged pot seedlings during transportation were recorded, as is shown in the Table 6. Table 6 shows that when planting frequency is 40 plants/min/row, only one plant has not been taken out, that is, the success rate of seedling taking is 99.3%. All the potted seedlings taken out are put into the seedling cup (excluding the damage of potted seedlings), that is, the success rate of seedling throwing is 100%, and the overall success rate of seedling extraction and separation is 98.6%. When planting frequency is 60 plants/min/row, the success rate of seedling taking is 98.6%, the success rate of seedling throwing is 98.6%, and the overall success rate is 96.5%. It shows that the main parts of the transplanting machine in this paper are synchronized accurate in positioning, reasonable in compiling control system and stable in operation. It can be seen from the table that with the increase of planting frequency, the overall success rate of taking and throwing seedlings has decreased. The reasons for this phenomenon are as follows: With the increase of planting frequency, the time availability for
V V V V V V V V V/24 V
each part to complete its working cycle gradually decreases, allowing to the acceleration of the intermediate movement process, resulting in the reduction of waiting time for seedling collection of seedling-division parts, the second cycle of seedling was started again before it was picked up, and the seedlings were not fully put into the cup. The overall amount of movement remained unchanged, and accelerating the movement speed of the parts increased which will contribute to increase the vibration and shock produced by the moving parts, which leads towards in the decrease of the stability of the operation, the failure of clamping the seedlings in the seedling extraction parts, the breakage and falling off of the seedlings in the transportation process, and finally the overall success rate of the seedling taking and throwing will decrease with the increase of the planting frequency. 6. Conclusion To meet the requirements of vegetable transplanting in small and medium-sized facilities, a small automatic vegetable transplanting machine with electric drive and wireless remote control was designed. The transplanting machine is mainly composed of chassis, feeding unit
Fig. 10. Main control system circuit schematic.
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Fig. 11. Chassis control system circuit schematic.
Table 5 Transplanting movement schedule. Schedule seedlings tray carrier unit Seedling extraction part Seedling separation part
Completing a horizontal or vertical feed in 2 s Turning over and clamp seedlings Moving and variable distance 0.7 s 0.5 s Falling seedlings Moving 0.3 s 0.7 s
Throwing and dropping seedlings 0.3 s Falling seedlings 0.3 s
Fig. 12. Overall control process chart.
9
Moving and variable distance 0.5 s Moving 0.7 s
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Fig. 15. Put the plug into the seedlings tray carrier.
Fig. 13. PLC subroutine.
of hole tray, seedling extraction unit, seedling separation unit, planting parts and control system. In this paper, the structure and function of the transplanting machine and the working principle are introduced in detail. Aiming at the complexity of transplanting machine control system, this paper introduces the control system in detail from two aspects of hardware design and software design. The hardware of the control system is divided into three parts: the sensors for signal acquisition, the programmable controller for signal processing, and the driving elements for specific actions. Photoelectric sensor and magnetic switch are used in the as sensing devices. The selection of programmable controller is completed cautiously, the main part of the transplanting machine is controlled by PLC to realize automatic movement of plugs tray, automatic seedling extraction, seedling throwing, seedling separation and planting. In the chassis part, microcontroller is selected as the control unit to realize the forward, backward and steering movement of the machine. Powering units include solenoid valves and motors. The software design of the control system includes the coordinated movement of each component, the design of control action process and the compilation of control program.
Fig. 16. The plug begins to move.
In order to test the motion coordination of each part and the rationality of the control system of the mini-automatic transplanting machine, different planting frequencies were set up to record the success rate of seedling taking and throwing. The results showed that when the planting frequency was 40 plants/min/row, the overall success rate
1.The tray feed motor driver 2. The steering motor driver 3. The seedling motor driver 4.PLC 5. Single chip microcomputer 6. Hub motor driver 7. Electric cylinder driver 8. Wireless signal receiver Fig. 14. Control system physical picture. 1. The tray feed motor driver 2. The steering motor driver 3. The seedling motor driver 4. PLC 5. Single chip microcomputer 6. Hub motor driver 7. Electric cylinder driver 8. Wireless signal receiver. 10
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Supervision. Guanlong Huang: Software, Writing - review & editing. Xinyi Shi: Formal analysis, Investigation. Mingsheng He: Validation. Ibrar Ahmad: Writing - original draft. Xiaoqi Zhao: Data curation. M. Addy: Visualization. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work is supported by the National Natural Science Foundation of China (51675239), the construction work of dominant subjects of higher education of Jiangsu Province, China (SU CAI (2014) No. 37); A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD-2018-87); The Natural Science Project of Jiangsu Higher Education Institutions (19KJA430018-2019-2022); The Research and Development Program of Zhenjiang (NY2019015).
Fig. 17. Take out the seedlings.
References Cao, J., 2019. Current situation and countermeasures of vegetable industry [J]. Seed Sci. Technol. 37 (03), 18–21. Han, C.J., Yang, W.Z., Zhang, X.J., et al., 2013. Design and test of automatic feeding system for pot tray seedling transplanter [J]. J. Agric. Eng. 29 (8), 51–61. Han, C.J., Zhang, X.J., et al., 2011. Present status and analysis of dry-land auto-transplanting seedling technique [J]. Agric. Mechanization Res. 33 (11), 238–240. Hu, W.Y., Zhang, Y.X., Huang, B., et al., 2017. Soil environmental quality in greenhouse vegetable production systems in eastern China: current status and management strategies[J]. Chemosphere 170, 183–195. Ji, H., Huang, Z., 2018. Introduction of greenhouse types and performance in facility agriculture [J]. Modern Rural Sci. Technol. 9, 103. Jin, X., Li, D.Y., Ma, H., et al., 2018. Development of single row automatic transplanting device for potted vegetable seedlings[J]. Int. J. Agric. & Biol. Eng. 11 (3), 67–75. Nagasaka, Y., et al., 2013. A global positioning system guided automated rice transplanter [J]. Ifac Proceedings Volumes 46 (18), 41–46. Wang, J.Q., Fu, Z.T., Zhang, B., et al., 2018a. Decomposition of influencing factors and its spatial-temporal characteristics of vegetable production: a case study of China[J]. Inform. Process. Agric. 5 (4), 477–489. Wang, Y.W., He, Z.L., Wang, J., et al., 2018b. Performance test of vegetable pot seedling automatic transplanter in Dryland[J]. J. Agric. Eng. 34 (3), 19–25. Xiao, T.Q., He, C.X., Chen, Q.M., et al., 2015. Cost-benefit analysis of vegetable production based on agricultural mechanized production[J]. Trans. Chinese Soc. Agric. Machinery 46 (5), 75–82. Xu, F., Mao, H.P., Hu, J.P., et al., 2017. Space coordination design and test of feeding and taking-off device of automatic transplanter [J]. Res. Agric. Mech. 9, 88–92. Yang, C.H., Fang, X.F., Yang, X.J., et al., 2013. Automatic conveying device of vegetable pot seedling transplanter based on PLC [J]. J. Agric. Mach. 44, 19–23. Yang, Q.Z., Xu, L., Shi, X.Y., et al., 2018. Design of seedlings separation device with reciprocating movement seedling cups and its controlling system of the fully-automatic plug seedling transplanter[J]. Comput. Electron. Agric. 147, 131–145. Yin, H., 2016. Development trend of vegetable transplanting machinery in China [J]. New Technol. Product. China 9, 172–173. Zhang, Z.G., Cao, W.B., et al., 2013. Development and prospect of plug seedlings automatic transplanter. J. Agric. Mechanization Res. 5, 237–241. Zhou, Y., Sun, L., 2015. Design of control system for automatic transplanter of dried-land seedlings based on PLC [J]. Modern Agric. Sci. Technol. 21, 199–200.
Fig. 18. Injecting seeds into the cup. Table 6 Test results of the success rate of seedlings taking and throwing. Planting frequency (plant/min/ row)
Total Number of seedlings N
Number not taken out a
Number of uncupped cups b
Number of damages c
Overall success rate S
40 50 60
144 144 144
1 2 2
0 0 1
1 2 2
98.6 97.2 96.5
was 98.6%. When planting frequency was 50 plants/min/row, the overall success rate of taking and putting in was 97.2%. When the planting frequency was 60 plants/min/row, the overall success rate was 96.5%. It shows that the main parts of the transplanting machine are coordinated in motion, accurate in positioning, reasonable in compiling the control system and stable in operation, which meets the requirements of transplanting seedlings in dry land. CRediT authorship contribution statement Qizhi
Yang:
Conceptualization,
Methodology,
Resources,
11
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Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag
Design of a control system for a mini-automatic transplanting machine of plug seedling
T
Qizhi Yanga,b, , Guanlong Huanga, Xinyi Shia, Mingsheng Hea, Ibrar Ahmada, Xiaoqi Zhaoa, ⁎ M. Addya,c, ⁎
a
School of Agricultural Equipment Engineering, Jiangsu University, Zhenjiang 212013, PR China Institute of Intelligent Robot, Jiangsu University, Zhenjiang 212013, PR China c Bioproducts and Biosystems Engineering Department, University of Minnesota, USA b
ARTICLE INFO
ABSTRACT
Keywords: Fully-automatic transplanting machine Vegetable seedlings Control system PLC control Microcomputer
In China, vegetable production system has been dominated by small and medium-sized agricultural facilities over the open-field cultivational practices. Low ceiling height and narrow width are dimensional attributes associated with most of these facilities. Due to these dimensional parametric constraints, the application of available field transplanting machinery in such facilities is a problematic subject which leads the vegetable growers towards manual transplanting. In order to meet the needs of small and medium-sized agricultural facilities for automatic vegetable transplanting, a smaller size wireless remote-controlled automatic transplanting machine was designed, which can transplant seedlings quickly in the greenhouse and by considering the stainability of environment electric power was adopted to drive all the mechanisms. In the process of agricultural production, the control system of agricultural machinery plays an important role in the degree of automation of mechanical equipment. Therefore, this paper focuses on the design of the control system of the newly premeditated automatic transplanting machine. The hardware of the control system is separated into three portions: the sensors for signal acquisition, the programmable controller for signal processing, and the driving elements for specific actions. PLC (Programmable logic controller) is adopted as the central control system of the transplanting machines which controls the automatic movement of seedlings tray carrier, seedlings extraction and feeding, and seedlings transmission to the planting units automatically. In order to control the overall movement of seedling transplanting machine, a microcontroller is adapted to control the hub and steering motor. The key driving elements of the control system are solenoid valves and electric motors which controls the action of pneumatic air cylinders and linear movement of different parts of machine respectively. The overall software design of the control system is accomplished, together with coordinated motion between components, control flow design and control program writing. In order to test the motion coordination of each component and the rationality of the control system of the Mini-Automatic transplanting machine, different planting frequencies were set to record the success rate of seedling collection and transplanting. The results of the trials exhibited that at the planting frequencies of 40, 50 and 60 plants/row/min the overall success rates were noted 98.6%, 97.2% and 96.5% respectively. It shows that the key parts of the transplanting machine are synchronized in motion, accurate in positioning, reasonable in assembling the control system and stable in operation, which meets the requirements of transplanting seedlings in the dry land.
1. Introduction With the development of automation in agricultural machinery and gradually improved agricultural economy, the replacement process of manual operation by mechanical automation in agriculture sector of China is growing slowly (Cao., 2019). The planting section of vegetable cultivation system practiced in this piece of land is moving in the
⁎
direction of transplanting seedling with rapid augmentation and shared more than half of total vegetable production (Xiao et al., 2015; Hu et al., 2017). The chines greenhouses which habitually practiced for vegetables cultivation are relatively smaller in size as they compared with other developed countries (Ji et al., 2018). Small and mediumsized arch shed and plastic greenhouse are commonly used for vegetables cultivation and specifications of 1–1.8 m shoulder height, and
Corresponding authors at: School of Agricultural Equipment Engineering, Jiangsu University, Zhenjiang 212013, PR China. E-mail addresses: [email protected] (Q. Yang), [email protected] (M. Addy).
https://doi.org/10.1016/j.compag.2020.105226 Received 14 November 2019; Received in revised form 9 January 2020; Accepted 11 January 2020 0168-1699/ © 2020 Elsevier B.V. All rights reserved.
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1.Transplanting machine chassis 4. Seedling separation unit
2. Seedlings tray carrier 5. Control system
3. Seedling extraction unit 6. Planting unit
Fig. 1. Fully automatic plug transplanting, 1. Transplanting machine chassis, 2. Seedlings tray carrier, 3. Seedling extraction unit, 4. Seedling separation unit, 5. Control system, 6. Planting unit.
the automatic feeding system for pot tray seedlings transplantation. Zhou designed a PLC-based automatic transplanting machine for dryland seedlings in 2015 (Zhou et al., 2015). The main components include the shifting device, the seedling extraction device, the planting device and the PLC control system, which adopts a single seedling extraction method to reduce the seedling separation. Hu developed a twoline fully-automatic transplanting machine for vegetable seedlings in pots and pans in 2017 (Xu et al., 2017). It was well appreciated the fully-automatic functions of seedling supply, seedling collection, seedling separation and seedling transplanting process. Yu developed an automatic transplanting machine for vegetable seedlings in dryland in 2018 (Wang et al., 2018). The machine can automatically complete the transplanting process of seedlings in pots, such as sending, picking, planting and covering soil. Yang proposed a linear reciprocating mobile seedling separation mechanism, which adopted the gear and rack mechanism to accomplish the function of static seedlings throwing and receiving in 2018 (Yang et al., 2018). However, it can be seen from the previous studies that the current automatic vegetable transplanting machines are larger in size, labour intensive, and most of them are powered by the internal combustion engine. The application of this type of engine in small and confined facilities with narrow space availability and poor ventilation, it can easily produce air pollution and affect the quality of vegetables. In China, a small automatic vegetable transplanting machine that meets the requirements for transplanting vegetables in small and mediumsized facilities has not been developed formerly. In this paper, a compact, electric-powered, wirelessly remote controlled and unmanned small automatic vegetable transplanting machine is designed. The transplanting machine uses PLC and microcontroller as programmable processors to realize the whole automation process of seedling extraction, seedlings throwing and soil covering, which provides a possibility to solve the mechanization of vegetable transplanting in medium and small facilities in China.
1.8–3.2 m ridge height associated with smaller size while, mediumsized having 1.2–1.5 m shoulder height, and 1.6–2.5 m ridge height. It is difficult to directly use the available transplanting machinery in such small size greenhouses, therefore, most of the seedlings transplanting operations are performed manually with low working efficiency (Jin et al., 2018). Currently, there is a deficiency of automatic transplanting machine suitable for transplanting vegetables in small and mediumsized facilities. Therefore, it is urgent need to develop a small-automatic vegetable transplanting machine to reduce labor intensity and improve production efficiency. The transplanting technique of vegetable plug seedling was primarily studied in the United States and Japan and during 1920s and 1930s hand-feeding transplanting machines emerged in the horticulture sector. In 1950s, a variety of semi-automatic vegetable transplanting machines with different structures were developed while in the end of 19th century semi-automatic transplanting technology was abundantly established (Wang et al., 2018). In 2002, Choi et al. developed a new seedling device for vegetable transplanting. The seedling device was composed of a gripping pointer, a trajectory generator and a pointer driver. The device was tested with 23-day tomato seedlings, and the transplanting success rate was noted 97% (Zhang et al., 2013). An American company Renaldo developed an automatic vegetable transplanter in 2003 and its working principal was followed negative pressure phenomenon, the grabber could suck the whole root from the plug and send it to the transplanter through a conveying (Han et al., 2011). A global positioning system guided automated rice transplanter was developed by Nagasaka Y and his team from National Agriculture and Food Research Organization, it was guided with only tilt corrected GPS and had advantages of a lower cost and supplementary precise operation (Nagasaka et al., 2013). Academics in China are also in progress to realize the commercial value and advantages of automatic transplanting machine; therefore, the researchers of different fields are working together to develop an efficient automatic transplanting machine (Yin et al., 2016). In the progress of this field of research Yang designed an automatic conveying system for vegetable pot seedlings and PLC was adopted as the central control system of transplanting machine (Yang et al., 2013). The highspeed servo electric cylinder was used to drive the pushrod to push out the seedlings, which realized high-speed, accurate and non-damaging seedling transmission. Han designed an automatic feeding system for a pot tray seedling transplanting machine in 2013 and all the driving parts in the system were driven by pneumatic pressure (Han et al., 2013). The control system was instructed by PLC to govern the action sequence of each cylinder, and it realized the actions and functions of
2. Materials and methods In this study, the structure of the small-scale automatic transplanting machine is shown in Fig. 1. The transplanting machine is mainly composed of the machine chassis, seedlings tray carrier unit, seedling extraction unit, seedling separation unit, planting unit and overall control system.
2
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6. Steering mechanism 7. Front axle 8. Drive unit (in-wheel motor) 9. Wheel Fig. 2. Overall structure of the transplanting machine chassis. 1. Electrical cabinet 2. Battery and battery case 3. The frame 4. Planting device assembly 5. Exit board, 6. Steering mechanism 7. Front axle 8. Drive unit (in-wheel motor) 9. Wheel.
2.1. Transplanting machine chassis
the box to prevent the whole tray from being brought up by stickiness during the seedling collection. The whole box is fixed on the frame through two LM shafts at an angle of 60 degrees with the horizontal plane, so that the whole tray can move transversely along the smooth axis (see Fig. 3).
The overall structure of the transplanting machine chassis consisted of chassis frame, front and rear wheels, steering device, and other parts which are listed and shown in Fig. 2. Considering the size limitation of small and medium-sized facilities of agriculture, the lightweight design of the chassis frame of the transplanting machine has been carried out. The mobile mode adopts the method of unmanned ride and wireless remote control, and uses lithium battery to achieve the purpose of energy saving and environmental protection. The chassis of transplanting machine uses hub motor to drive the wheel directly, which simplifies the layout space and improves the extraction efficiency.
2.3. Seedling extraction part The function of the seedling extraction unit is to take off the seedlings from the tray with the help of seedling claws and transport them to seedling separation unit at a specific delivery point. The detailed structure is shown in Fig. 4. The seedling extraction part is mainly composed of large gantry, small gantry, diamond-shaped mechanism, guide rail slider, seedling claws, slide plate, and base fixing plate. The main action of seedling extraction part is seedling extraction and seedling throwing. The action of seedling extraction is realized by flipping while the action of seedling throwing is accomplished by variable pitch.
2.2. Seedlings tray carrier and feeding part The seedlings tray carrier and feeding unit is mainly composed of sprocket chain, LM shaft, box, plug shaft, pressing rod and supporting frame. There are two pairs of sprocket chains symmetrically arranged on both sides of the box, and tension is applied by tensioner and twelve plug shafts are fixed on the chain evenly. The pressure bar is fixed on
5. Seedling claw 6. Slide plate 7. Base fixing plate
1. Sprocket chain 2. LM shaft 3. Plug shaft 4. Box 5. Frame 6. Pressing rod
Fig. 4. Seedling extraction part. 1. Large gantry 2. Small gantry 3. Diamondshaped mechanism 4. Guide rail slider. 5. Seedling claw 6. Slide plate 7. Base fixing plate.
Fig. 3. Seedlings tray carrier and feeding part. 1. Sprocket chain 2. LM shaft 3. Plug shaft 4. Box 5. Frame 6. Pressing rod. 3
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working principle of the automatic transplanting machine for the plug seedlings is as follows: When the transplanting machine starts its operation, the operator places the whole tray on the seedlings tray carrier and feeding unit. Then the operator starts the wireless remote-control transplanting machine to move forward. The tray feeding part starts its motion towards seedlings extraction point and seize its motion at this point. Then the claws of the seedling extraction part turn over, clamp the seedlings and return with the seedlings. When the seedling-taking claws move to the vertical position, the rhombic mechanism pushes out the variable distance, so that the four seedling-taking claws correspond to the four seedlings cups of the seedling-dividing parts one by one, and then the seedling-throwing begins. Seedling extraction part to the seedling guide barrel in the planting part stops directly above the seedling guide barrel after receiving seedlings, the falling seedlings part starts to make the seedlings fall vertically into the ditch opened by the trencher along the seedlings guide barrel, and then cover the soil to suppress and complete the seedlings planting. The transverse and longitudinal feeding of the feeding part, the clamping, turning over and variable distance of the seedling extraction part, the moving of the seedling separation part and the opening and closing of the seedling cups are all controlled by PLC (such as electric machinery, electric actuator, cylinder, etc.). The executing parts and the actions to be performed are shown in Fig. 7.
1. Rack and pinion 2. Connection board 3. Sensor 4. Frame 5. Seedling dropping unit 6. Seedling cup Fig. 5. Seedling separation part. 1. Rack and pinion 2. Connection board 3. Sensor. 4. Frame 5. Seedling dropping unit 6. Seedling cup.
2.4. Seedling separation unit The seedling separation unit adopts the gear-rack base reciprocating moving seedling-dividing mode, which can realize static seedlingthrowing, simplify the seedling-dropping problem and increase the success rate of seedling-throwing. In order to save time, seedling throwing was carried out at one time and increase the overall efficiency. It has the characteristics of quick response, good controllability and is easy to adjust the row spacing. As shown in Fig. 5, the gear is fixed on the shaft of stepping motor and stepping motor is attached with seedlings cups assembly while gear is meshed with rack drive to move the seedlings device in linear manner. When the photoelectric sensors in the left and right position are encountered with seedlings device tracer, the seedling dropping device starts and opens the seedling cup to drop the seedling vertically into the planting parts to complete the seedling planting process.
3. Design of control system hardware The hardware of the control system is divided into three parts: the sensors for signal acquisition, the programmable controller for signal processing, and the driving elements to perform some specific actions. 3.1. Selection of programmable controller The PLC (programmable logic controller) is adopted as central control system of the main mechanisms of machine due to its good reliability and simple operation. The main PLC control system for this machine is shown in Fig. 8. As the core module of the control system, the main function of PLC is to receive the input signal, process the signal, output the signal to
2.5. Working principle of transplanting machine The overall machine motion flow chart is shown in Fig. 6. The
Fig. 6. Machine motion flow chart. 4
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Fig. 7. Component composition and action.
other units, and monitor the information in the process of signal processing. The selection process of PLC has several key parameters, such as the selection of power supply, processing speed, high frequency counting, communication port etc. The most important one is the calculation and distribution of input and output points, that is, the input of sensors and other driving parts of motors and electric cylinders. The input and output points and definitions for detailed PLCs are shown in Table 1. As it can be seen from Table 1, the selected PLC should have at least 16 input points and 11 output points, and two of the output points are pulse output. Therefore, the PLC of XC3-32T-C model was selected as the controller of the implementation part. The specifications of selected PLC are shown in Table 2. The selection of the programmable controller in the chassis part needs to consider the relationship between the wireless remote controller and the hub motor. The output of the remote controller is an analog quantity, and the control of the rotation of the hub motor and the steering motor needs digital quantity, so the core programmable controller is required to have both complex digital quantity as well as analog quantity. Therefore, single-chip computer is selected as the control device, as is shown in Fig. 9. Finally, the MEGA2560 R3 development board of Arduino series is selected as the control part of the chassis control system, and its parameters are shown in Table 3.
3.2. Design of control system hardware circuit To design the circuit of the main part of the transplanting machine, it is necessary to count all the components that need power supply, as is shown in Table 4. Among them, 86 stepping motors and air compressors are powered by 48 V lithium batteries, 57 stepping motors, cylinders and PLCs are powered by 24 V lithium batteries, and the sensors are connected to the input of PLC according to the requirements, as is shown in Fig. 10. The input terminals of the PLC are connected with the switch, the counter photoelectric sensor of the seedlings tray carrier unit, the magnetic switch in the seedling extraction part and the positioning sensor in the seedling separation part. The output terminals are connected with the cylinder of the seedlings tray carrier unit, the longitudinal motor driver, the solenoid valve in the seedling extraction part and the seedling separation motor driver in the seedling separation part. The movement of the chassis part is operated by wireless remote control. The signal is transmitted by wireless remote controller, and it is processed by single chip computer after receiving the signal. Finally, the signal is transferred to the controller of steering motor and hub motor to control the forward, backward and turning movement of whole machine. The hardware circuit design of the chassis is shown in Fig. 11.
Fig. 8. Main PLC control system.
5
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Table 1 PLC I/O table. Input
Output
X0 X1 X2 X3 X4 X5 X6 X7 X10 X11 X12 X13 X14 X15 X16 X17
Activate switch Stopped switch Manual mode Automatic mode Switch of add 1 Switch of minus 1 Pressure detection Cylinder to origin Cylinder in place 1 Cylinder in place 2 seedlings tray carrier unit in place Highest point of turn cylinder top Turn cylinder will contact Lowest point of turnover cylinder Left limit of seedling separation Right limit of seedling separation
Y0 Y1 Y2 Y3 Y4 Y5 Y6 Y7 Y10 Y11 Y12 Y13 Y14 Y15 Y16 Y17
4. Design of control system software
Stepping motor of seedlings tray carrier unit (pulse) Stepping motor of seedling separation motor (pulse) Stepping motor of seedlings tray carrier unit (direction) Stepping motor of seedling separation motor (direction) Cylinders need to reach the origin Cylinder in place 1 Cylinder in place 2 Turn-over cylinder start Variable-pitch cylinder start Taking claw 4 cylinder Dropping seedling 2 cylinder
claws from colliding or directly impacting. After the first removals of seedlings from the seedlings tray, the tray carrier unit should make a judgment. When the number of horizontal feeding is less than 2, the horizontal feeding is carried out. When the number of horizontal feeding is equal to 2, the longitudinal feeding is engaged and the number of horizontal feeding is back to zero. When the number of vertical disc feeding is greater than or equal to 6, withdraw the seedlings tray and put the new seedlings tray quickly. (2) Working synchronization between the seedling extraction part and the seedling separation part, when the seedling extraction part is working, the seedling separation part should move to the waiting position for the reception seedlings. When the seedling extraction parts finished the action and engaged the specific position above the seedling’s cups while the variable-distance mechanism is extended according to the cups position, the claws opened to handover the seedlings to separation unit. The seedling separation part needs to be moved after receiving the seedlings to prevent the seedlings from falling out during the reciprocating movement. (3) Working synchronization between the seedling separation parts and the chassis of the transplanting machine. The walking speed of the chassis should match the seedling speed of the seedling parts to meet the requirements of different plant spacing planting.
For the compilation of control system there is a need of corresponding software which has synchronization with control hardware. The core programming software used in this paper is XCPPro V3.1 version of the PLC programming software provided by Xinjie Company. In comparison with the common C language programming, the ladder diagram programming has more perception and correspondence, and is easy to operate and monitor. 4.1. Design of control system process According to the requirements of the project, the main function of the transplanting machine is to robotically take the seedlings from seedlings tray and plant them in the ridge with 40–60 plants/min/row planting frequency during working operation. According to the analysis of the mechanism and working principle of the transplanting machine, each action is divided into some modules: the feeding parts of the transplanting machine can complete the functions of quick feeding, transverse feeding and longitudinal feeding; the seedling extraction parts can complete the functions of seedling-taking, variable-distance and seedling-throwing; the seedling separation parts can complete the functions of seedling-receiving, and seedling-dropping and finally planting parts complete the functions of ditching, seedling planting and soil covering. In the process of planting, each unit should be able to work independently, but also can cooperate with each other and without any interference. The coordination relationship of each unit is described in the following:
Taking 60 plants/min/behavior as an example, this transplanting machine is a two-row transplanting machine, which can plant two potted seedlings at the same time. Therefore, 120 seedlings need to be picked up by the seedling extraction mechanism within 1 min. The seedling extraction mechanism of this machine has four claws. Therefore, four potted seedlings can be picked up at the same time. It means that the seedling extraction mechanism needs to complete 30 cycles for seedling picking up and transporting within 1 min. It takes 2 s for the seedling separation mechanism to complete a complete action of taking and throwing seedlings. Based on the synchronized action of each part of the transplanting machine, i.e. the feeding mechanism of the transplanting machine box, the seedling separation mechanism finishes a complete action for 2 s. The time sequence of each part is shown in Table 5. According to the function of each component and the action to be achieved, and taking the synchronized relationship of component motions into consideration, the overall control process of the transplanting
(1) Operational synchronization between the feeding part and the seedling extraction part, as the feeding part transports the seedlings tray to the seedling extracting position, the claws of the seedling extraction part are inserted into the case of seedlings tray to clamp the seedling. At this time, the variable pitch mechanism of the seedling extraction part should be in a compressed state, and the four seedling claws correspond to the four holes in the row of the hole tray. In the process of seedlings taking, the tray carrier unit should remain stationary, and cannot move until the fingernails are completely separated from the seedlings tray, so as to prevent the Table 2 PLC parameter table. I/O Points
High frequency pulse output
Type of input
Type of output
Type of power
Communication Port
Capacity of program
32(18/14)
2
NPN
Transistor
DC24V
2
96 K
6
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Fig. 9. Chassis MCU control system.
machine was designed, as is shown in Fig. 12. After pressing the starting button, the chassis moves forward and the box moves quickly to push the hole tray into the seedling point to be taken, and the seedling separation part also moves the cup to the seedling point until the seedling falls into the cup. After the seedling extraction part completes the turning, clamping, returning, variable-pitch and throwing, the box keeps moving to feeding which is in the process of variable-pitch returning, and at the same time, the seedling separation parts are reversed to start, and the seedling separation action is started. The seedling separation parts are circulated to stop pressing buttons in turn, and the planting is finished. Using XCPPro V3.1 software to write control program is to classify the modules of each part, to program each action into a single subroutine, and then call it when the general program runs. The detailed subroutines are shown in Fig. 13. Program execution flow: starting work, program backs to zero, at the same time, the tray carrier part begins to feed longitudinally and after being detected by the photoelectric sensor, the longitudinal motor stops its working. In the program execution flow, the seedling extraction part begins its movement to perform seedling taking accomplishment. After clamping the plug seedlings from the seedlings tray it retains its initial position above the cup’s assembly where the highest point of the sliding slot is detected by the magnetic switch. Then the variable-pitch cylinder is started to complete the waiting cycle of extending variable-pitch and after transferring the seedlings to separation unit the seedling extraction unit moves towards next cycle of seedlings extraction. At the same time, the seedling separation cylinder opens and closes after the seedling separation parts are connected to complete the distribution and planting of two seedlings, and then moves the seedlings to the second seedling delivery point. In the moving process of seedling separation parts, the number of times of tray carrier part is judged, and the transverse or vertical movements are carried out according to the working schedule of operation. At the same time, the seedling extraction parts start to work, and then complete the next cycle until finishing the planting.
5.2. Test of transplanting machine control system 5.2.1. Aims The success rate of seedling taking and seedling throwing under different planting frequencies was used to investigate the motion coordination of each part of the automatic transplanting machine and the rationality of the control system (see Figs. 15–18). 5.2.2. Conditions (1) Test equipment: The small-sized tray seedling automatic transplanting machine, camera and laser range finder developed in this paper. (2) Seedling selection: 72-hole tray cucumber seedlings, with a seedling age of about 20 days, with two leaves, one core or three leaves and one core, the average seedling height is about 13.5 cm. 5.2.3. Steps (1) Turn on the switch, inflate the gas tank with the air compressor, charge 0.5 MPa to the working cylinder, wait for the transplanting machine to start. (2) Connect the PLC to the transplanting machine to set different planting frequencies, specifically 40 strains/min/row, 50 strains/ min/row, 60 strains/min/row. (3) When finish the experiment, the success rate of seedlings taking and throwing under different planting frequencies were calculated, and the overall success rate was tallied. 5.2.4. Results and analysis The overall success rate of seedling-taking and seedling-throwing is an important parameter to measure the coordination and rationality of the components of the automatic vegetable transplanting machine. In order to reflect the working efficiency of each component more intuitively, according to the working process of each component, S is used to express the overall success rate of seedling-taking and seedlingthrowing. While, a denotes the number of failed seedling removal trays, such as the case where the seedling claws break the pot seedlings and fail to take them out of the hole tray; b denotes the number of failures in putting seedlings into cups, such as seedling dropping in pots during seedling transportation; c indicates the number of damaged seedlings during transportation, and the breakage of seedlings stems caused by damaged seedlings. N is the total number of seedlings. The formula is expressed as:
5. Test of transplanting machine control system 5.1. Transplanting machine control system In this paper, the control system components of the transplanting machine are fitted in the electric cabinet which is positioned at the rear portion of the chassis. The power supply (lithium battery) is installed at the left and right ends of the rear wheel bracket. The control sub-unit of the transplanting machine is installed at the position of the executing elements of the components. The signals from the controller are transmitted to each unit controller through the shielding line, and control the movement of the powering units. The physical diagram of the control system is shown in Fig. 14.
S=
N
a
b N
c
× 100%
(5.1)
The Success rate of tests were carried out on the automatic feeding, seedling taking and seedling throwing system. Point Tray Seedlings
Table 3 Single chip microcomputer parameter table. Input voltage
Output voltage
I/O Digital input /Output pins
I/O Analog Input /Output Pins
PWM terminal
FLASH capacity
DC 7–12 V
5 V/3.3 V
54
16
14
256 K
7
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Table 4 Main hardware design name and model. Project
Name
Type
Voltage
Number
Signal acquisition element
Opposite photoelectric sensor Magnetic switch Photoelectric positioning Sensor PLC Longitudinal motor Transverse cylinder Electromagnetic valve Seedling separation motor Lithium battery
G12A-M100(1/2) AL-03R E3F-DS30C4 XC3-32T-C 85BYGH450B-06D RSW-10-100 4 V210-08 86HBS120 BN4824CD
24 24 24 24 24 24 24 48 48
1 3 2 1 1 1 8 1 3
Central control element Driving element
Power
with 72 holes were used to carry out seedling taking and throwing experiments at different planting frequencies. The number of plug seedlings not clamped out of the tray, the number of pot seedlings not put into the cup, and the number of damaged pot seedlings during transportation were recorded, as is shown in the Table 6. Table 6 shows that when planting frequency is 40 plants/min/row, only one plant has not been taken out, that is, the success rate of seedling taking is 99.3%. All the potted seedlings taken out are put into the seedling cup (excluding the damage of potted seedlings), that is, the success rate of seedling throwing is 100%, and the overall success rate of seedling extraction and separation is 98.6%. When planting frequency is 60 plants/min/row, the success rate of seedling taking is 98.6%, the success rate of seedling throwing is 98.6%, and the overall success rate is 96.5%. It shows that the main parts of the transplanting machine in this paper are synchronized accurate in positioning, reasonable in compiling control system and stable in operation. It can be seen from the table that with the increase of planting frequency, the overall success rate of taking and throwing seedlings has decreased. The reasons for this phenomenon are as follows: With the increase of planting frequency, the time availability for
V V V V V V V V V/24 V
each part to complete its working cycle gradually decreases, allowing to the acceleration of the intermediate movement process, resulting in the reduction of waiting time for seedling collection of seedling-division parts, the second cycle of seedling was started again before it was picked up, and the seedlings were not fully put into the cup. The overall amount of movement remained unchanged, and accelerating the movement speed of the parts increased which will contribute to increase the vibration and shock produced by the moving parts, which leads towards in the decrease of the stability of the operation, the failure of clamping the seedlings in the seedling extraction parts, the breakage and falling off of the seedlings in the transportation process, and finally the overall success rate of the seedling taking and throwing will decrease with the increase of the planting frequency. 6. Conclusion To meet the requirements of vegetable transplanting in small and medium-sized facilities, a small automatic vegetable transplanting machine with electric drive and wireless remote control was designed. The transplanting machine is mainly composed of chassis, feeding unit
Fig. 10. Main control system circuit schematic.
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Fig. 11. Chassis control system circuit schematic.
Table 5 Transplanting movement schedule. Schedule seedlings tray carrier unit Seedling extraction part Seedling separation part
Completing a horizontal or vertical feed in 2 s Turning over and clamp seedlings Moving and variable distance 0.7 s 0.5 s Falling seedlings Moving 0.3 s 0.7 s
Throwing and dropping seedlings 0.3 s Falling seedlings 0.3 s
Fig. 12. Overall control process chart.
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Moving and variable distance 0.5 s Moving 0.7 s
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Fig. 15. Put the plug into the seedlings tray carrier.
Fig. 13. PLC subroutine.
of hole tray, seedling extraction unit, seedling separation unit, planting parts and control system. In this paper, the structure and function of the transplanting machine and the working principle are introduced in detail. Aiming at the complexity of transplanting machine control system, this paper introduces the control system in detail from two aspects of hardware design and software design. The hardware of the control system is divided into three parts: the sensors for signal acquisition, the programmable controller for signal processing, and the driving elements for specific actions. Photoelectric sensor and magnetic switch are used in the as sensing devices. The selection of programmable controller is completed cautiously, the main part of the transplanting machine is controlled by PLC to realize automatic movement of plugs tray, automatic seedling extraction, seedling throwing, seedling separation and planting. In the chassis part, microcontroller is selected as the control unit to realize the forward, backward and steering movement of the machine. Powering units include solenoid valves and motors. The software design of the control system includes the coordinated movement of each component, the design of control action process and the compilation of control program.
Fig. 16. The plug begins to move.
In order to test the motion coordination of each part and the rationality of the control system of the mini-automatic transplanting machine, different planting frequencies were set up to record the success rate of seedling taking and throwing. The results showed that when the planting frequency was 40 plants/min/row, the overall success rate
1.The tray feed motor driver 2. The steering motor driver 3. The seedling motor driver 4.PLC 5. Single chip microcomputer 6. Hub motor driver 7. Electric cylinder driver 8. Wireless signal receiver Fig. 14. Control system physical picture. 1. The tray feed motor driver 2. The steering motor driver 3. The seedling motor driver 4. PLC 5. Single chip microcomputer 6. Hub motor driver 7. Electric cylinder driver 8. Wireless signal receiver. 10
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Supervision. Guanlong Huang: Software, Writing - review & editing. Xinyi Shi: Formal analysis, Investigation. Mingsheng He: Validation. Ibrar Ahmad: Writing - original draft. Xiaoqi Zhao: Data curation. M. Addy: Visualization. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work is supported by the National Natural Science Foundation of China (51675239), the construction work of dominant subjects of higher education of Jiangsu Province, China (SU CAI (2014) No. 37); A Project Funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions (PAPD-2018-87); The Natural Science Project of Jiangsu Higher Education Institutions (19KJA430018-2019-2022); The Research and Development Program of Zhenjiang (NY2019015).
Fig. 17. Take out the seedlings.
References Cao, J., 2019. Current situation and countermeasures of vegetable industry [J]. Seed Sci. Technol. 37 (03), 18–21. Han, C.J., Yang, W.Z., Zhang, X.J., et al., 2013. Design and test of automatic feeding system for pot tray seedling transplanter [J]. J. Agric. Eng. 29 (8), 51–61. Han, C.J., Zhang, X.J., et al., 2011. Present status and analysis of dry-land auto-transplanting seedling technique [J]. Agric. Mechanization Res. 33 (11), 238–240. Hu, W.Y., Zhang, Y.X., Huang, B., et al., 2017. Soil environmental quality in greenhouse vegetable production systems in eastern China: current status and management strategies[J]. Chemosphere 170, 183–195. Ji, H., Huang, Z., 2018. Introduction of greenhouse types and performance in facility agriculture [J]. Modern Rural Sci. Technol. 9, 103. Jin, X., Li, D.Y., Ma, H., et al., 2018. Development of single row automatic transplanting device for potted vegetable seedlings[J]. Int. J. Agric. & Biol. Eng. 11 (3), 67–75. Nagasaka, Y., et al., 2013. A global positioning system guided automated rice transplanter [J]. Ifac Proceedings Volumes 46 (18), 41–46. Wang, J.Q., Fu, Z.T., Zhang, B., et al., 2018a. Decomposition of influencing factors and its spatial-temporal characteristics of vegetable production: a case study of China[J]. Inform. Process. Agric. 5 (4), 477–489. Wang, Y.W., He, Z.L., Wang, J., et al., 2018b. Performance test of vegetable pot seedling automatic transplanter in Dryland[J]. J. Agric. Eng. 34 (3), 19–25. Xiao, T.Q., He, C.X., Chen, Q.M., et al., 2015. Cost-benefit analysis of vegetable production based on agricultural mechanized production[J]. Trans. Chinese Soc. Agric. Machinery 46 (5), 75–82. Xu, F., Mao, H.P., Hu, J.P., et al., 2017. Space coordination design and test of feeding and taking-off device of automatic transplanter [J]. Res. Agric. Mech. 9, 88–92. Yang, C.H., Fang, X.F., Yang, X.J., et al., 2013. Automatic conveying device of vegetable pot seedling transplanter based on PLC [J]. J. Agric. Mach. 44, 19–23. Yang, Q.Z., Xu, L., Shi, X.Y., et al., 2018. Design of seedlings separation device with reciprocating movement seedling cups and its controlling system of the fully-automatic plug seedling transplanter[J]. Comput. Electron. Agric. 147, 131–145. Yin, H., 2016. Development trend of vegetable transplanting machinery in China [J]. New Technol. Product. China 9, 172–173. Zhang, Z.G., Cao, W.B., et al., 2013. Development and prospect of plug seedlings automatic transplanter. J. Agric. Mechanization Res. 5, 237–241. Zhou, Y., Sun, L., 2015. Design of control system for automatic transplanter of dried-land seedlings based on PLC [J]. Modern Agric. Sci. Technol. 21, 199–200.
Fig. 18. Injecting seeds into the cup. Table 6 Test results of the success rate of seedlings taking and throwing. Planting frequency (plant/min/ row)
Total Number of seedlings N
Number not taken out a
Number of uncupped cups b
Number of damages c
Overall success rate S
40 50 60
144 144 144
1 2 2
0 0 1
1 2 2
98.6 97.2 96.5
was 98.6%. When planting frequency was 50 plants/min/row, the overall success rate of taking and putting in was 97.2%. When the planting frequency was 60 plants/min/row, the overall success rate was 96.5%. It shows that the main parts of the transplanting machine are coordinated in motion, accurate in positioning, reasonable in compiling the control system and stable in operation, which meets the requirements of transplanting seedlings in dry land. CRediT authorship contribution statement Qizhi
Yang:
Conceptualization,
Methodology,
Resources,
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