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The development of the finger-tray automatic transplanting system
J. agric. Engng Res. (1991) 50, 51-60
The Development of the Finger-tray Automatic Transplanting System J. VAN DE WERKEN IMAG DIo, P.O. Box 43, 6700AA Wageningen, The Netherlands
(Received 11 October 1988;accepted in revisedform 28 February 1991) The transplanting of plants in the field requires a lot of work to be carried out in a short time. Although there are several types of hand-fed transplanting machines on the market, there is demand for a simple, reliable and economical automatic transplanting system. IMAG has developed such a system. This report deals with the IMAG transplanting system based on the "Finger-tray" invention; several prototypes have now been built and tested. The system has been further developed in cooperation with a machine manufacturer, a grower, a plant raiser, and the plastics industry. The result is an automatic transplanting concept with possibilities for various applications but with some limitations.
1. Introduction The transplanting of plants is one of the major operations carried out by growers. It is therefore very important to minimize the time and labour involved in this process. For the system to be attractive to the grower, it has to be simple in use, reliable, possess a high transplanting capacity with good quality of the transplanting work and must do all this at reasonable cost. In designing an automatic transplanting sytem, consideration must be given to a number of aspects which include the means of raising plants, in modules or trays, the subsequent handling of these and the transplanting system itself. In the past, several attempts have been made to develop an automatic transplanter. The automatic transplanter with a bottomless tray was successfully developed for transplanting large plugs containing plants (Huangl). I M A G has tried applying this system for small plugs, (diam 20 mm, length 40 mm) but was not successful. T o o many plugs got stuck in the tray and the modifications made to the system were too complicated to be practical. The "Finger-tray system" solves this problem.
2. Finger-tray system 2.1 Finger-tray The finger-tray has been developed to a single plastic strip, (600 mm long and 30 mm wide) with 20 holes (Fig. 1). At first two flexible plastic fingers were attached below each hole. The " c o m p a r t m e n t " formed by hole and fingers can be filled with a plug. The fingers grip the plugs and prevent them from falling through the tray. The finger-tray design makes it possible to discharge the plugs from the tray by pulling the plugs, with the plants, through the tray by means of a gripper. An undertray is necessary for transport of the finger-tray strips. One standard growing tray, used as an undertray, contains twelve Presented at AG ENG 88, Paris, France, 2-6 March 1988 51
52
F I N G E R - T R A Y A U T O M A T I C T R A N S P L A N T I N G SYSTEM
Fig. 1. Finger-tray strip strips (Fig. 2). The intention is that the plants are raised in these finger-tray strips. The finger-trays are made of a flexible material so that they can be bent and stretched in the transplanter.
2.2 Finger-tray transplanting concept Fig. 3 shows a diagram of the finger-tray transplanter. A strip containing 20 plants is fed into the machine, after which they are automatically transplanted. The transplanter also collects the empty plastic strips. The transplanting machine consists of a furrow opener (a), with an inbuilt gripper (b) for pulling out the plugs and two press wheels (c), which follow the gripper. The finger-tray strip (d) is fed into the machine at an angle of 45 ° by a mechanism, which provides a steady feed. When the first plant in the strip has reached point (e) on the diagram, the pendulum gripper (b) removes the first plug of the strip and pulls it together with the plant through the hole. Then the gripper pivots 45 ° around point (f) on the
Fig. 2. Twelve finger-trays in a conventional growing tray
53
J. V A N D E W E R K E N
•
?
.
.
Fig. 3. Diagram of the finger-tray transplanting system diagram to a horizontal position, whereupon the plug pusher (h) moves the plug with the plant, in the direction of the press wheels. The gripper can pass the plug pusher strip because the width of this strip is less than the minimum diameter of the plugs. In the meantime the strip has been indexed forward, ready for the next plug to be pulled out by the gripper. This process is repeated until the whole strip has been emptied. The strip then curves through 45 ° to a horizontal position, when it is pushed out and deposited in the empty tray collector (g). The transplanter moves forward at a constant speed. The presswheels firm the plugs in the soil. The feeding of the strips into the machine can be carried out by hand or automatically. Pneumatic cylinders are used for all the positioning and indexing movements. The cylinders are controlled by pneumatic valves. Valve timing is achieved by a camshaft controller one revolution of the shaft corresponds to the planting of one plant in the field. The controller shaft is driven by a variable speed 12 V d.c. motor.
3. System development 3.1 Finger-tray emptier For the development of the finger-tray transplanting system the step by step method was adopted. First, a stationary finger-tray emptier, with a six row finger-tray was designed and tested. The tray consisted of a 3 mm thick plastic board with 25 mm diameter holes and a test rig was built for the configuration (Fig. 4 and 5). Two metal wire springs were attached at each hole, the springs acting as tray "fingers". The initial plan was to index the whole tray, so it could be emptied with one plug gripper. At a later stage, the tray design evolved to a single row strip (Fig. 1). For easy adjustment of the oscillating speed, a hydraulic crankdrive was used to drive the pendulum gripper. Both the plug gripper and the tray feeder were equipped with pneumatic cylinders. To control the forward movement of the tray and gripper timing, a cam controller was connected to the crankshaft. This controller actuated the electropneumatic valve for the cylinders. ! During prototype testing the tray was filled with plugs and plants by hand. The plants had been raised in a conventional tray. It was found that the prototype gripper could handle one plant per second to a predetermined location. Two possibilities presented
54
FINGER-TRAY
AUTOMATIC
TRANSPLANTING
SYSTEM
Fig. 4. Finger-tray emptyer
themselves: (1) to use the described system as a plant feeder device for any manually fed transplanter; and (2) to transplant the plants from this position directly into the soil. It was decided to follow the second option.
Fig. 5. Close-up gripper
J. VAN DE W E R K E N
55
4. Development finger-tray Because the design of the transplanting unit had to be as narrow as possible, the original 12-row tray was modified into the single row finger-tray strip. This type of strip was developed by the plastics industry. The shape of the strip made it difficult to manufacture. The final product is shown in Fig. 1. For plants with a low product value, such as cabbage plants which were used during trials, the strip proved to be too expensive for one-off use. For plants with a higher intrinsic value, however, this strip might be commercially viable. Re-use of the strips several times is possible, but the consequences are that the strips must be collected carefully, transported and cleaned. During the development period, attempts were made to design a strip with the same performance as the finger-tray strip but which could be produced easier and cheaper. This was the so-called "kartel-tray". The kartel-tray has no fingers but instead of these a notched edge grips the plug, because the flexibile inner diameter of the notched edge is smaller than the plug diameter. The edge has the shape of a bonbon package.
5. Field performance Field tests have been carried out with the prototype transplanter described under Section 2.2. At first the device was tested to see how it would perform in the field. Particular attention was given to: (a) transplanting quality, regular distance in the row, individual position of the plants in the soil; (b) transplanting capacity; (c) mechanical performance of the different machine parts; and (d) machine clogging and obstructions. The tests were made on a dry and sandy soil. This easy type of soil was cultivated about 80 mm deep. Forward speed of the tractor was 2-5 km/h. After a number of adjustments were made, satisfactory results were achieved for the points (a), (b), and (c) but "(d), clogging of the machine, was a problem. Each time that a plug with a plant was pulled through the tray, a small amount of soil accumulated inside the furrow-opener and clogged up the mechanism. The position of the plug push cylinder was modified so that the bottom of the furrow-opener stayed free of soil, thus solving this problem. The prototype was fitted with standard available presswheels of diameter 400mm, width 60mm. However, with this type of presswheel the edges were compressed too much. So it was decided to fit double-width presswheels. Later in the growing season, more extensive tests were performed. Points for research were again, transplanting quality, plant-distance, effect of different weights on the wider presswheels and the effect of pulling the plants through the finger-tray on the quality of the final product. These tests also took place in sandy soil (Fig. 6). The finger-tray transplanter worked with three different loads on the presswheels, 100, 250 and 500 N. Two tests were made; the first one with cauliflower plants and the second with Brussels sprouts. The plants were grown in the standard growing trays, then manually transferred into the handmade finger-tray strips immediately before transplanting, so there were no "misses" in the field. After transplanting, the distances between the plants in the row were measured as well as the force required to pull plants out of the soil. The measuring equipment used consisted of a force measuring device provided with a string. The string was attached to a plant leaf and the measuring device was pulled by hand to determine the uprooting force needed.
56
FINGER-TRAY AUTOMATIC TRANSPLANTING SYSTEM
Fig. 6. Testing the finger-tray transplanter
6. Results o f field tests
From Table 1 it can be seen that the finger-tray transplanting system achieved a high degree of positioning accuracy. It was found that with the "Auto 50" machine, weight 500 N on the presswheels, the plants stood looser in the soil than with "Auto 10" (100 N). This had to do with the position of the presswheels in relation to each other. The plant pull tests were carried out by pulling on the leaves first, one day after transplantation then again after 19 days. The forces varied from 0-8 to 10 N directly after transplanting, and from 1.6 to 30 N when tested 19 days after transplanting. There were several reasons for this, but the most significant one was again the incorrect position of the presswheels relative to each other. After some testing, it was found that a parallel position of the presswheels ensured the best results. After this adjustment, the main problems were solved. The plants did not seem to have been planted in the correct, vertical position. They sometimes stood at an Table 1 Positioning accuracy (of transplanting) Cauliflower Machine
Number o f measurements
Mean spacing, cm
Standard error, cm
Auto 10 Auto 25 Auto 50
92 95 95
64-0 63.0 64.0
0-33 0.27 0.22
Brussels sprouts Machine
Number o f measurements
Mean spacing, cm
Standard error, cm
Auto 10 Auto 25 Auto 50
110 108 110
52.5 52.3 51.4
0.22 0.19 0.22
J. VAN DE W E R K E N
57
angle of approximately 20° with the vertical in the direction of travel. This was caused by the presswheels having a kind of milling effect, slightly rotating the soil and plant between the wheels. This problem was solved by mounting the plug guide plate (which pushes the plugs into the soil) at a 20 ° backwards sloping angle, which counteracted the forward effect of the presswheels on the plants. The physical extraction of the cabbage plants through the finger-tray holes had no detrimental effects on the plant growth or finished quality. It was found that with the finger-tray transplanting system a transplanting capacity could be achieved of at least one plant per second per element, independent of the spacing of the plants in the row within limits up to 70 cm. One operator can easily feed a two-row machine by hand with finger-tray strips. Commercial hand-fed transplanters vary in capacity from 0.6 to 0-8 plants per second with one operator per element. The length of the furrow-opener of the prototype finger-tray transplanter was longer than usual. This can be a disadvantage when the tractor does not move in a straight line, thus creating a wider furrow than desirable. It is possible to shorten the length of the furrow-opener by re-arranging the gripper and the plug pusher in later models. 7. Sorting
The fingertray strips were 100% hand-filled with plants for the transplanting tests carried out in Section 6. This allowed all of the available ground planting locations to be utilized. In practice this is not the case, as up to 10% or more plugs may not contain a plant, leaving open spaces in the field. There are two approaches to solving this problem: (a) sort the seedlings in thesreenhouse, filling up the empty spots in the tray by hand or automatically (Brewer~); or (b) detect the empty spots in the finger-tray on the transplanting machine and modify the finger-tray indexing mechanism.
Fig. 7. Sorting device on the transplanter
58
F I N G E R - T R A Y A U T O M A T I C T R A N S P L A N T I N G SYSTEM
The first solution was considered; but because growers do not appreciate any disturbance to their production lines, we opted for (b), developing a sorting device on the finger-tray transplanter itself.
7.1 Design of the sorting device on the transplanting machine Our main aim was to design a device which would detect the presence of a plant just before the plug gripper has reached top position. If a plant is detected, the finger-tray feeder stops indexing, but if there is no plant, the finger-tray feeder continues feeding the strip until a plant is detected. This means that there will be no "misses" in the field. Figs 7 and 8 show the tray-feeding correction device. The finger-tray strips are fed by means of a pneumatic cylinder (a) with a stroke of 100 mm. The pitch between the plugs in the strip is 30 mm. The cylinder rod is provided with a toothrack with three teeth (b), pitch 30 mm. A second cylinder (c) is mounted on the machine and actuates an interrupting latch (d). When this "stop" cylinder is extended, it interrupts the movement of the feeding cylinder by means of a racktooth contacting the latch mechanism on the stop cylinder. A standard commercial photoelectric reflex type optical sensor used as a plant detector (e) generates a signal which activates the cylinder. If there is no plant, the stop cylinder remains in the retracted position. In other words, the stroke of the feeding cylinder is controlled by means of the stop cylinder which corrects the feeding of the finger-tray. Satisfactory results have been obtained with this system, although one limitation is that the presently used sensor does not detect plants with bent stems.
2: :
."
-7
Fig. 8. Finger-tray index interrupter
J. V A N D E W E R K E N
59
8. Raising plants in finger-trays Plant raising tests have been carried out using the finger-tray strips. Twelve finger-tray strips were laid into standard growing trays. The trays were filled in the usual way with the pre-pressed plugs and the plants were raised by a grower in the normal way (Fig. 9). It was possible to raise good quality plants in finger-tray strips which were placed in conventional growing trays. Growing tests were also performed using finger-tray strips which were placed in the so-called "slide tray" as an undertray, which should be used for automatic feeding of the finger-tray strips into the transplanter. These tests have not yet been successful. The plugs dry out and do not remain in the finger-tray, resulting in poor quality plants. Further development is needed in this area. Kartel-trays were also tested in the same way as the finger-tray strips, with the kartel-trays placed in the standard trays, filled with pre-pressed plugs. These tests gave good results, with the good plants firmly attached to the edges of the kartel-trays.
9. Necessary alteration in the tray filling line If the finger-tray (kartel-tray) is used in a plant production system, certain modifications have to be made to the tray filling method (Fig. 10). In a conventional tray filling line, the growing trays are destacked (a), filled with the plugs (b), seeded (c) then stacked again (d) for transport to the nursery area of the greenhouse. Using the finger-trays or kartel-trays, they must be inserted into the undertrays directly after they are destacked (e). IMAG has built a prototype device for this operation, which is ready for further development.
10. Conclusions 1. The finger-tray transplanting system is able to automatically transplant seedlings raised in finger-trays, or "kartel"-trays. The transplanting capacity is a minimum one plant per second. Only one operator is needed to feed a two-row machine with finger-tray strips. 2. The system is simple. 3. The large-scale raising of plants using finger-trays on a slide tray, has some problems that need further attention.
~.
...
Fig. 9. Raising plants in finger-trays
60
FINGER-TRAY
AUTOMATIC TRANSPLANTING
SYSTEM
b
Fig. I0. Finger-tray msert mechanism in a tray filling line
4. Acceptable plants can be raised in the finger or "kartei"-trays placed in a growing tray. 5. With the finger-tray transplanting concept, plugs without plants can be detected and sorted out. 6. The finger-tray system device can be used as an automatic feeding system for conventional hand-fed machines. 7. The fingertray system could be developed further for various applications, such as on a potting machine. 8. The finger-tray transplanting system ensures a high degree of positional accuracy.
Acknowledgement We wish to thank all the participants in this project for all their help and cooperation in developing and testing the finger-tray system.
References Huang, B. K. Systems Engineering in Precision Automatic transplanting. Vol. 14 No. 1 1983 Agricultural Mechanization in Asia, Africa and Latin America. 2 Brewer, H. L. Design challenges in developing an automatic seedling sorter. ASAE Summer Meeting Paper No. 85-1085.
The Development of the Finger-tray Automatic Transplanting System J. VAN DE WERKEN IMAG DIo, P.O. Box 43, 6700AA Wageningen, The Netherlands
(Received 11 October 1988;accepted in revisedform 28 February 1991) The transplanting of plants in the field requires a lot of work to be carried out in a short time. Although there are several types of hand-fed transplanting machines on the market, there is demand for a simple, reliable and economical automatic transplanting system. IMAG has developed such a system. This report deals with the IMAG transplanting system based on the "Finger-tray" invention; several prototypes have now been built and tested. The system has been further developed in cooperation with a machine manufacturer, a grower, a plant raiser, and the plastics industry. The result is an automatic transplanting concept with possibilities for various applications but with some limitations.
1. Introduction The transplanting of plants is one of the major operations carried out by growers. It is therefore very important to minimize the time and labour involved in this process. For the system to be attractive to the grower, it has to be simple in use, reliable, possess a high transplanting capacity with good quality of the transplanting work and must do all this at reasonable cost. In designing an automatic transplanting sytem, consideration must be given to a number of aspects which include the means of raising plants, in modules or trays, the subsequent handling of these and the transplanting system itself. In the past, several attempts have been made to develop an automatic transplanter. The automatic transplanter with a bottomless tray was successfully developed for transplanting large plugs containing plants (Huangl). I M A G has tried applying this system for small plugs, (diam 20 mm, length 40 mm) but was not successful. T o o many plugs got stuck in the tray and the modifications made to the system were too complicated to be practical. The "Finger-tray system" solves this problem.
2. Finger-tray system 2.1 Finger-tray The finger-tray has been developed to a single plastic strip, (600 mm long and 30 mm wide) with 20 holes (Fig. 1). At first two flexible plastic fingers were attached below each hole. The " c o m p a r t m e n t " formed by hole and fingers can be filled with a plug. The fingers grip the plugs and prevent them from falling through the tray. The finger-tray design makes it possible to discharge the plugs from the tray by pulling the plugs, with the plants, through the tray by means of a gripper. An undertray is necessary for transport of the finger-tray strips. One standard growing tray, used as an undertray, contains twelve Presented at AG ENG 88, Paris, France, 2-6 March 1988 51
52
F I N G E R - T R A Y A U T O M A T I C T R A N S P L A N T I N G SYSTEM
Fig. 1. Finger-tray strip strips (Fig. 2). The intention is that the plants are raised in these finger-tray strips. The finger-trays are made of a flexible material so that they can be bent and stretched in the transplanter.
2.2 Finger-tray transplanting concept Fig. 3 shows a diagram of the finger-tray transplanter. A strip containing 20 plants is fed into the machine, after which they are automatically transplanted. The transplanter also collects the empty plastic strips. The transplanting machine consists of a furrow opener (a), with an inbuilt gripper (b) for pulling out the plugs and two press wheels (c), which follow the gripper. The finger-tray strip (d) is fed into the machine at an angle of 45 ° by a mechanism, which provides a steady feed. When the first plant in the strip has reached point (e) on the diagram, the pendulum gripper (b) removes the first plug of the strip and pulls it together with the plant through the hole. Then the gripper pivots 45 ° around point (f) on the
Fig. 2. Twelve finger-trays in a conventional growing tray
53
J. V A N D E W E R K E N
•
?
.
.
Fig. 3. Diagram of the finger-tray transplanting system diagram to a horizontal position, whereupon the plug pusher (h) moves the plug with the plant, in the direction of the press wheels. The gripper can pass the plug pusher strip because the width of this strip is less than the minimum diameter of the plugs. In the meantime the strip has been indexed forward, ready for the next plug to be pulled out by the gripper. This process is repeated until the whole strip has been emptied. The strip then curves through 45 ° to a horizontal position, when it is pushed out and deposited in the empty tray collector (g). The transplanter moves forward at a constant speed. The presswheels firm the plugs in the soil. The feeding of the strips into the machine can be carried out by hand or automatically. Pneumatic cylinders are used for all the positioning and indexing movements. The cylinders are controlled by pneumatic valves. Valve timing is achieved by a camshaft controller one revolution of the shaft corresponds to the planting of one plant in the field. The controller shaft is driven by a variable speed 12 V d.c. motor.
3. System development 3.1 Finger-tray emptier For the development of the finger-tray transplanting system the step by step method was adopted. First, a stationary finger-tray emptier, with a six row finger-tray was designed and tested. The tray consisted of a 3 mm thick plastic board with 25 mm diameter holes and a test rig was built for the configuration (Fig. 4 and 5). Two metal wire springs were attached at each hole, the springs acting as tray "fingers". The initial plan was to index the whole tray, so it could be emptied with one plug gripper. At a later stage, the tray design evolved to a single row strip (Fig. 1). For easy adjustment of the oscillating speed, a hydraulic crankdrive was used to drive the pendulum gripper. Both the plug gripper and the tray feeder were equipped with pneumatic cylinders. To control the forward movement of the tray and gripper timing, a cam controller was connected to the crankshaft. This controller actuated the electropneumatic valve for the cylinders. ! During prototype testing the tray was filled with plugs and plants by hand. The plants had been raised in a conventional tray. It was found that the prototype gripper could handle one plant per second to a predetermined location. Two possibilities presented
54
FINGER-TRAY
AUTOMATIC
TRANSPLANTING
SYSTEM
Fig. 4. Finger-tray emptyer
themselves: (1) to use the described system as a plant feeder device for any manually fed transplanter; and (2) to transplant the plants from this position directly into the soil. It was decided to follow the second option.
Fig. 5. Close-up gripper
J. VAN DE W E R K E N
55
4. Development finger-tray Because the design of the transplanting unit had to be as narrow as possible, the original 12-row tray was modified into the single row finger-tray strip. This type of strip was developed by the plastics industry. The shape of the strip made it difficult to manufacture. The final product is shown in Fig. 1. For plants with a low product value, such as cabbage plants which were used during trials, the strip proved to be too expensive for one-off use. For plants with a higher intrinsic value, however, this strip might be commercially viable. Re-use of the strips several times is possible, but the consequences are that the strips must be collected carefully, transported and cleaned. During the development period, attempts were made to design a strip with the same performance as the finger-tray strip but which could be produced easier and cheaper. This was the so-called "kartel-tray". The kartel-tray has no fingers but instead of these a notched edge grips the plug, because the flexibile inner diameter of the notched edge is smaller than the plug diameter. The edge has the shape of a bonbon package.
5. Field performance Field tests have been carried out with the prototype transplanter described under Section 2.2. At first the device was tested to see how it would perform in the field. Particular attention was given to: (a) transplanting quality, regular distance in the row, individual position of the plants in the soil; (b) transplanting capacity; (c) mechanical performance of the different machine parts; and (d) machine clogging and obstructions. The tests were made on a dry and sandy soil. This easy type of soil was cultivated about 80 mm deep. Forward speed of the tractor was 2-5 km/h. After a number of adjustments were made, satisfactory results were achieved for the points (a), (b), and (c) but "(d), clogging of the machine, was a problem. Each time that a plug with a plant was pulled through the tray, a small amount of soil accumulated inside the furrow-opener and clogged up the mechanism. The position of the plug push cylinder was modified so that the bottom of the furrow-opener stayed free of soil, thus solving this problem. The prototype was fitted with standard available presswheels of diameter 400mm, width 60mm. However, with this type of presswheel the edges were compressed too much. So it was decided to fit double-width presswheels. Later in the growing season, more extensive tests were performed. Points for research were again, transplanting quality, plant-distance, effect of different weights on the wider presswheels and the effect of pulling the plants through the finger-tray on the quality of the final product. These tests also took place in sandy soil (Fig. 6). The finger-tray transplanter worked with three different loads on the presswheels, 100, 250 and 500 N. Two tests were made; the first one with cauliflower plants and the second with Brussels sprouts. The plants were grown in the standard growing trays, then manually transferred into the handmade finger-tray strips immediately before transplanting, so there were no "misses" in the field. After transplanting, the distances between the plants in the row were measured as well as the force required to pull plants out of the soil. The measuring equipment used consisted of a force measuring device provided with a string. The string was attached to a plant leaf and the measuring device was pulled by hand to determine the uprooting force needed.
56
FINGER-TRAY AUTOMATIC TRANSPLANTING SYSTEM
Fig. 6. Testing the finger-tray transplanter
6. Results o f field tests
From Table 1 it can be seen that the finger-tray transplanting system achieved a high degree of positioning accuracy. It was found that with the "Auto 50" machine, weight 500 N on the presswheels, the plants stood looser in the soil than with "Auto 10" (100 N). This had to do with the position of the presswheels in relation to each other. The plant pull tests were carried out by pulling on the leaves first, one day after transplantation then again after 19 days. The forces varied from 0-8 to 10 N directly after transplanting, and from 1.6 to 30 N when tested 19 days after transplanting. There were several reasons for this, but the most significant one was again the incorrect position of the presswheels relative to each other. After some testing, it was found that a parallel position of the presswheels ensured the best results. After this adjustment, the main problems were solved. The plants did not seem to have been planted in the correct, vertical position. They sometimes stood at an Table 1 Positioning accuracy (of transplanting) Cauliflower Machine
Number o f measurements
Mean spacing, cm
Standard error, cm
Auto 10 Auto 25 Auto 50
92 95 95
64-0 63.0 64.0
0-33 0.27 0.22
Brussels sprouts Machine
Number o f measurements
Mean spacing, cm
Standard error, cm
Auto 10 Auto 25 Auto 50
110 108 110
52.5 52.3 51.4
0.22 0.19 0.22
J. VAN DE W E R K E N
57
angle of approximately 20° with the vertical in the direction of travel. This was caused by the presswheels having a kind of milling effect, slightly rotating the soil and plant between the wheels. This problem was solved by mounting the plug guide plate (which pushes the plugs into the soil) at a 20 ° backwards sloping angle, which counteracted the forward effect of the presswheels on the plants. The physical extraction of the cabbage plants through the finger-tray holes had no detrimental effects on the plant growth or finished quality. It was found that with the finger-tray transplanting system a transplanting capacity could be achieved of at least one plant per second per element, independent of the spacing of the plants in the row within limits up to 70 cm. One operator can easily feed a two-row machine by hand with finger-tray strips. Commercial hand-fed transplanters vary in capacity from 0.6 to 0-8 plants per second with one operator per element. The length of the furrow-opener of the prototype finger-tray transplanter was longer than usual. This can be a disadvantage when the tractor does not move in a straight line, thus creating a wider furrow than desirable. It is possible to shorten the length of the furrow-opener by re-arranging the gripper and the plug pusher in later models. 7. Sorting
The fingertray strips were 100% hand-filled with plants for the transplanting tests carried out in Section 6. This allowed all of the available ground planting locations to be utilized. In practice this is not the case, as up to 10% or more plugs may not contain a plant, leaving open spaces in the field. There are two approaches to solving this problem: (a) sort the seedlings in thesreenhouse, filling up the empty spots in the tray by hand or automatically (Brewer~); or (b) detect the empty spots in the finger-tray on the transplanting machine and modify the finger-tray indexing mechanism.
Fig. 7. Sorting device on the transplanter
58
F I N G E R - T R A Y A U T O M A T I C T R A N S P L A N T I N G SYSTEM
The first solution was considered; but because growers do not appreciate any disturbance to their production lines, we opted for (b), developing a sorting device on the finger-tray transplanter itself.
7.1 Design of the sorting device on the transplanting machine Our main aim was to design a device which would detect the presence of a plant just before the plug gripper has reached top position. If a plant is detected, the finger-tray feeder stops indexing, but if there is no plant, the finger-tray feeder continues feeding the strip until a plant is detected. This means that there will be no "misses" in the field. Figs 7 and 8 show the tray-feeding correction device. The finger-tray strips are fed by means of a pneumatic cylinder (a) with a stroke of 100 mm. The pitch between the plugs in the strip is 30 mm. The cylinder rod is provided with a toothrack with three teeth (b), pitch 30 mm. A second cylinder (c) is mounted on the machine and actuates an interrupting latch (d). When this "stop" cylinder is extended, it interrupts the movement of the feeding cylinder by means of a racktooth contacting the latch mechanism on the stop cylinder. A standard commercial photoelectric reflex type optical sensor used as a plant detector (e) generates a signal which activates the cylinder. If there is no plant, the stop cylinder remains in the retracted position. In other words, the stroke of the feeding cylinder is controlled by means of the stop cylinder which corrects the feeding of the finger-tray. Satisfactory results have been obtained with this system, although one limitation is that the presently used sensor does not detect plants with bent stems.
2: :
."
-7
Fig. 8. Finger-tray index interrupter
J. V A N D E W E R K E N
59
8. Raising plants in finger-trays Plant raising tests have been carried out using the finger-tray strips. Twelve finger-tray strips were laid into standard growing trays. The trays were filled in the usual way with the pre-pressed plugs and the plants were raised by a grower in the normal way (Fig. 9). It was possible to raise good quality plants in finger-tray strips which were placed in conventional growing trays. Growing tests were also performed using finger-tray strips which were placed in the so-called "slide tray" as an undertray, which should be used for automatic feeding of the finger-tray strips into the transplanter. These tests have not yet been successful. The plugs dry out and do not remain in the finger-tray, resulting in poor quality plants. Further development is needed in this area. Kartel-trays were also tested in the same way as the finger-tray strips, with the kartel-trays placed in the standard trays, filled with pre-pressed plugs. These tests gave good results, with the good plants firmly attached to the edges of the kartel-trays.
9. Necessary alteration in the tray filling line If the finger-tray (kartel-tray) is used in a plant production system, certain modifications have to be made to the tray filling method (Fig. 10). In a conventional tray filling line, the growing trays are destacked (a), filled with the plugs (b), seeded (c) then stacked again (d) for transport to the nursery area of the greenhouse. Using the finger-trays or kartel-trays, they must be inserted into the undertrays directly after they are destacked (e). IMAG has built a prototype device for this operation, which is ready for further development.
10. Conclusions 1. The finger-tray transplanting system is able to automatically transplant seedlings raised in finger-trays, or "kartel"-trays. The transplanting capacity is a minimum one plant per second. Only one operator is needed to feed a two-row machine with finger-tray strips. 2. The system is simple. 3. The large-scale raising of plants using finger-trays on a slide tray, has some problems that need further attention.
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Fig. 9. Raising plants in finger-trays
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FINGER-TRAY
AUTOMATIC TRANSPLANTING
SYSTEM
b
Fig. I0. Finger-tray msert mechanism in a tray filling line
4. Acceptable plants can be raised in the finger or "kartei"-trays placed in a growing tray. 5. With the finger-tray transplanting concept, plugs without plants can be detected and sorted out. 6. The finger-tray system device can be used as an automatic feeding system for conventional hand-fed machines. 7. The fingertray system could be developed further for various applications, such as on a potting machine. 8. The finger-tray transplanting system ensures a high degree of positional accuracy.
Acknowledgement We wish to thank all the participants in this project for all their help and cooperation in developing and testing the finger-tray system.
References Huang, B. K. Systems Engineering in Precision Automatic transplanting. Vol. 14 No. 1 1983 Agricultural Mechanization in Asia, Africa and Latin America. 2 Brewer, H. L. Design challenges in developing an automatic seedling sorter. ASAE Summer Meeting Paper No. 85-1085.