JPH08191635A - Method for holding seeding and device holding the same - Google Patents

Abstract

PURPOSE: To provide the method for holding the seedlings, capable of individually and surely holding them, even when the seedlings are densely cultured in plug trays and even when the stems of the seedlings are inclined, and further to provide the device for holding the same. CONSTITUTION: This method for holding the seedling comprises holding its stem cultured in a container, pulling out the seedling, and simultaneously pressing the culture soil with a press piece, when a pair of claws are lifted to the stem. The holding and pulling treatments of the seedling are performed in an order comprising lowering a pair of the claws 81a, 81b... to positions faced to the ground side part of the seedling → forward moving the claws to positions for nipping the ground side part of the seedling →closing the claws to surround the ground side part of the seedling in a state leaving a margin between the claws and the seedling →lifting the claws to the stem part of the seedling in a stage →further closing the claws in a stage (totally two stages) to hold the stem of the seedling → further lifting the claws in a stage (totally two stages) to pull out the seedling.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and a device for holding young plants. When transplanting a young plant cultivated in a plug tray to another plug tray or the like, when performing root washing or grafting, it is necessary to pull out the young plant from the plug tray and move it to a predetermined position. For example, when grafting seedlings cultivated in plug trays as spikes,
The seedlings are pulled out from each plug one by one and moved to the position where grafting work is to be performed. The present invention relates to a method and a device for gripping a young plant, which holds a young plant cultivated on a plug tray with a pair of claws in the above-described case, and pulls out the held plant and moves it to a predetermined position. It is a thing.

[0002]

2. Description of the Related Art Conventionally, as a means for gripping a young plant, there has been proposed a means provided with a moving actuator, a lifting actuator, an opening / closing actuator, a pair of claws, and a control device for controlling the operation of each of these actuators. (Japanese Patent Laid-Open Nos. 2-2111810 and 3-130015,
JP-A-4-187029). In any of these conventional means, a young plant cultivated in a container is grasped by a pair of nails, and the grasped state is pulled out or cut from the container and moved to a predetermined position. However, these conventional means have a drawback that, in fact, it often happens that individual plantlets cannot be grasped one by one.

When transplanting seedlings, washing roots, grafting, etc., it is necessary to grasp the stems of the seedlings with a pair of nails for convenience of the subsequent work. For example,
When grafting a seedling as a scion, it is necessary to grasp the stalk portion of the seedling at least above the cutting point with a pair of nails. Therefore, in any of the above-mentioned conventional means, the pair of nails is advanced from the beginning to the position where it is sandwiched from both sides aiming at the stem of the seedling and gripping the stem. However, when the seedlings are cultivated relatively densely in the plug tray, even if the seedlings are located near the center of each plug, the stems of the seedlings are often inclined. When the pair of nails advances toward the stem of the seedling that is supposed to be right above the plug, the stem may not be there or there may be a stem of the seedling grown in the adjacent plug. Therefore, the pair of nails may not be able to hold the seedlings or may hold two or more seedlings at the same time.

[0004]

The problem to be solved by the present invention is that it is often the case that the conventional means cannot hold the individual plantlets one by one.

[0005]

SUMMARY OF THE INVENTION The present invention, however, relates to a method for gripping a young plant, which comprises the following first step, second step and third step. First step: The pair of claws supported by the moving actuator descends to a position facing the edge of the seedling cultivated in the plug tray, and then to a position where the edge of the seedling is sandwiched from both sides. Step of advancing Second step: The pair of claws that have been advanced surrounds the edge part of the seedling, while the holding plate moves forward to hold the soil of the seedling, and then the pair of claws Step of rising to the stem of the plant Third step: The pair of raised nails grips the stem of the seedling,
On the other hand, the pressing plate retracts, and then the pair of nails pulls out the seedlings.

The present invention also provides a seedling holding device for holding a young plant cultivated in a container with a pair of nails, pulling out the held plant and moving it to a predetermined position. And a controller for controlling the operation of the gripping section and the transporting section described below, and a gripping apparatus for a young plant body. Gripping part: a moving actuator, a substrate supported by the moving actuator, a lifting actuator mounted on the substrate to move up and down in two steps, an advancing / retreating actuator mounted on the lifting actuator, An opening / closing actuator mounted on the advancing / retreating actuator to close in two stages, and a pair of pawls attached to the opening / closing actuator are provided. The forward movement advances to a position where the ground portion of the seedling is sandwiched from both sides, and then the closing operation of the first stage of the actuator for opening and closing causes the pair of claws surrounding the ground portion of the seedling to move to the first position of the lifting actuator. After ascending to the stem of the seedling by one-step raising operation, the seedling is opened by the second-step closing operation of the opening / closing actuator. Gripper claw pairs of gripping the stem portion of the object is made so as to pull the 該幼 plant by increasing actuation of the second stage of the elevating actuator. Conveying unit: An intermittently driven plug tray placing conveyor, an advancing / retreating actuator attached to the machine frame of the conveyor, and a pressing plate connected to the advancing / retreating actuator, and a seedling in the gripping section When the pair of claws surrounding the above-mentioned ground portion rises up to the stem of the seedling, the pressing plate is advanced to hold down the soil of the seedling.

The important point in the present invention is that the pair of claws descends to a position facing the front part of the seedling body → advances to a position where the ground part of the seedling body is sandwiched from both sides → one stage closes and seedlings Surrounding the land area with a margin between the body and the body → rises by one step and rises up to the stem of the seedling → one step (total 2
Grasp the stems of the seedlings cultivated on the plug tray in the above order, closing and grasping the stems of the seedlings → further raising by one stage (total of 2 stages) to pull out the seedlings. , When the pair of claws surrounding the edge of the seedling rises up to the stem of the seedling while pulling out the seedling, the pressing plate is advancing and the soil of the seedling ( It is a place where the plug soil in which the seedlings are cultivated) is pressed down.

Therefore, unlike the conventional means, the pair of claws do not advance from the beginning by advancing toward the stems of the seedlings, but initially by advancing toward the edge of the seedlings, Is surrounded, and the stalk is grasped after being raised to the stalk in the surrounded state. On the other hand, when the pair of nails rises from the ground portion to the stem portion of the seedling, the holding plate holds down the soil of the seedling. Thus, since the ground portion of the seedlings cultivated in the container is at a substantially predetermined position (almost the center portion of each plug of the plug tray), even if the stem portion is tilted, a pair of claws will be able to move the stem portion. The seedlings can be pulled out from the plug tray by securely grasping. Also, when the pair of nails surrounding the surface of the seedling rises to the stem of the seedling,
If the stalk is abnormally inclined or leaves are protruding in the middle of the process, the pair of claws on the way of ascending may catch on these, resulting in pulling out the seedlings from the plug tray. However, at this stage, since the holding plate holds down the soil of the young plant, such an inconvenient situation can be prevented in advance.

In the present invention, the actuator for moving the gripping portion moves the pair of claws to a position facing the seedlings cultivated in the plug tray from diagonally forward, and the seedlings gripped by the pair of claws and pulled out. It is for moving the body to a predetermined position. As such a moving actuator,
You can use a motor-driven or cylinder-driven system in which an arm with a pair of claws turns, or a system in which a base with a pair of claws moves laterally while being guided by a guide rod. A guide rod, a ball screw pivotally supported by the machine frame, a drive motor connected to the ball screw, for example, a pulse motor, and a base on which the guide rod is slidably fitted and the ball screw is screwed. It is preferable that the base is supported by a substrate on which an elevating actuator to be described later is mounted.

Specifically, since a plug tray is placed on an intermittently driven conveyor and seedlings are cultivated on each plug of the plug tray, machine frames are erected on both sides of the conveyor. Then, two guide rods are mounted on the machine frame, one ball screw is rotatably supported, and a pulse motor is connected to the ball screw. Then, the two guide rods are slidably fitted to each other, and the substrate is supported on a base on which one ball screw is screwed, and an elevating actuator to be described later is attached to the substrate.

In the present invention, the actuator for raising and lowering the gripping portion lowers the pair of claws to the edge of the plug tray in which the seedlings are cultivated, and the actuator of the pair surrounding the edge of the seedling. This is for pulling out the seedling by raising the nail to the stem of the seedling by one step and then raising the pair of nails holding the seedling by one more step. As such an ascending / descending actuator, a type in which a pair of claws are moved up and down by a motor drive or a cylinder drive can be used. However, a main cylinder having a cylinder tube attached to a substrate, and a cylinder rod connected to a cylinder rod of the main cylinder. It is preferable that the auxiliary cylinder be provided with a sub cylinder, a receiving stand attached to the cylinder tube of the sub cylinder, and a guide rod that is installed upright on the receiving stand and slidably fitted into a guide cylinder attached to the substrate. . In this case, the pair of pawls are lowered by the lowering operation of the main cylinder and the sub cylinder, and the pair of pawls are raised by one step by the raising operation of the sub cylinder, and then the pair of pawls are further moved by one step by the raising operation of the main cylinder. To raise.

In the present invention, the actuator for advancing and retracting the gripping portion is for advancing the pair of nails to a position where the ground portion of the seedling is sandwiched from both sides. As such an advancing / retreating actuator, a method of advancing / retreating a pair of claws by driving a motor or a cylinder can be used, but an advancing / retreating cylinder in which a cylinder tube is attached to the pedestal of the elevating actuator described above is preferable.

In the present invention, the actuator for opening and closing the gripping part encloses the ground part of the seedling with a pair of claws, and the pair of claws is raised to the stem part of the seedling by one step while being surrounded. For gripping the stem of the seedling. As such an opening / closing actuator, a type in which a pair of claws are opened / closed by a motor drive or a cylinder drive can be used. However, the case attached to the cylinder rod of the advance / retreat cylinder and the slidably housed in the case A pair of racks, and a pinion that engages the pair of racks,
A drive motor for rotating the pinion, for example, one having a pulse motor is preferable. In this case, the pair of racks are respectively engaged with the pinions, and both the pinions have different numbers of teeth on the circumferential surface. More preferably, both pinions are mounted on the same rotary shaft of the drive motor. The forward rotation of the first stage of the drive motor causes the pair of racks to close by one step through the pinion, and the second stage of forward rotation of the drive motor causes the pair of racks to close through the pinion by another stage.

In the present invention, the pair of claws of the gripping portion are for surrounding the edge portion of the seedling and gripping the stem of the seedling. When using a combination of a pair of racks and a pinion that engages with them as an opening / closing actuator, one pawl is attached to one rack and the other pawl is attached to the other rack. Although attached, in this case, it is preferable that the inner circumference of one claw is formed in an arc shape and the inner circumference of the other claw is formed in a V shape. This is because so-called center alignment is surely performed. By the closing operation of the first stage of the rack, the pair of claws surrounds the ground part of the seedling, and the enclosed pair of claws is raised to the stem of the seedling by the raising operation of the first stage of the lifting actuator. After that, the second pair of closing operations of the rack cause the pair of claws to grip the stem of the seedling.

In the present invention, the conveyer of the carrying section mounts a plug tray in which seedlings are cultivated on each plug, and the plug tray is intermittently arranged in units of one row of a plurality of plugs provided therein. It is for moving. It is preferable that the intermittent movement is performed by using a pulse motor as a conveyor driving motor and intermittently driving the pulse motor with a pulse signal.

In the present invention, the advancing / retreating actuator of the conveying section advances the pressing plate to the upper part of the soil of the seedlings cultivated in each plug of the plug tray in relation to the operation of the pair of claws in the gripping section. It is also for retreating to the original position. As such an advancing / retreating actuator, an actuator that moves a pressing plate forward / backward by driving a motor or a cylinder can be used, but an advancing / retreating cylinder having a cylinder tube attached to the machine frame of the conveyor is preferable.

In the present invention, the pressing plate of the conveying section holds down the soil of the seedling when the pair of nails surrounding the edge of the seedling rises up to the stem of the seedling. It is for storing. The pressing plate is mounted slidably in the width direction of the conveyor (perpendicular to the rotation direction of the conveyor) slightly above the plug tray placed on the conveyor. It is preferable that a plurality of recesses corresponding to the plugs in the width direction are formed narrower than the plugs. In this case, the pressing plate presses the soil of a plurality of plugs provided on the plug tray at a time in a row unit.

In the present invention, the above-mentioned moving actuator, lifting actuator, advancing / retreating actuator and opening / closing actuator of the gripping portion, and the conveyor driving motor and advancing / retreating actuator of the conveying portion are all connected to the control portion. The operation of each actuator and the like is controlled by a time-dependent command signal from the control unit.

[0019]

The plug tray in which the seedlings are cultivated is placed on each plug at a predetermined position on the conveyor, and the conveyor is driven to move the plug tray to the predetermined position. In this state, first, the pair of claws is moved to the position where the seedlings cultivated in the plug at the end of the first row out of the plurality of plugs are viewed from diagonally above by the operation of the moving actuator. Next, the lowering operation of the lifting actuator lowers the pair of claws to a position facing the ground portion of the seedlings cultivated in the plugs at the end of the first row from the horizontal direction, and then the forward movement operation of the forward and backward actuators. Thus, the pair of claws advances to a position where the claw of the seedling is sandwiched from both sides. Subsequently, the pair of claws surrounds the ground portion of the seedling by the first-stage closing operation of the opening / closing actuator, and then the first-stage raising operation of the lifting / lowering actuator causes the pair of claws to grow in the surrounded state. It rises to the stem of the body. On the other hand, immediately before the pair of claws surrounding at least the ground portion of the seedling body starts to move up to the stem portion of the seedling body in the first stage, the pressing plate is moved by the forward movement of the advancing / retreating actuator of the transport unit. To move forward and press the first
Hold down the soil of the plug at the end of the row. Then, after the pair of claws grips the stem portion of the seedling by the second-stage closing operation of the opening / closing actuator, the pair of claws moves the second-stage ascending operation of the raising / lowering actuator in the gripped state. Pull out from the plug. On the other hand, at least immediately before the pair of claws holding the stems of the seedlings start to move up in the second stage to pull out the seedlings, the pressing plate is moved by the backward movement of the advancing / retreating actuator of the transport unit. Move it back to its original position. The pair of claws moves the seedlings to a predetermined position by operating the movement actuator while holding the stem portion of the seedlings that was finally pulled out. Although not described, each actuator after operation has returned to its original position. Thus, after pulling out the seedlings cultivated in the plugs at the end of the first row, the same operation is repeated thereafter to sequentially pull out the seedlings cultivated in the plugs in the first row. Then, after pulling out all the seedlings cultivated in the plugs of the first row, the conveyor is driven to move the plugs of the second row to a predetermined position, and the same operation is repeated to make the plugs of the second row. The cultivated seedlings are pulled out sequentially from the end.
The following is a repeat of this.

Even when the seedlings are densely cultivated on the plug tray, the seedlings are located at the center of each plug, so the target plug should be aimed at. The pair of advanced claws can surely surround the edge of the seedling. Then, since the pair of claws ascends to the stalk in the surrounded state and grips the stalk, even if the stalk of the seedling is tilted and not directly above the target plug, or adjacent plugs Even if the stalks of the seedlings cultivated in the above are tilted and are directly above the target plug, it is possible to reliably grip only the stalks of the seedlings cultivated in the target plug. it can. Also, when the pair of nails surrounding the seedlings of the seedlings rises to the stem of the seedlings, the holding plate holds down the soil of the seedlings. Even if the seedlings are caught on the stems or leaves of the seedlings, the seedlings will not be pulled out. According to the present invention, it is possible to surely grasp the seedlings one by one.

[0021]

1 is a perspective view showing an embodiment of the present invention, FIG.
1 is a side view showing the same embodiment as FIG. 1 with a part of the gripping part omitted, and FIG. 3 omits part of the relationship between the opening / closing actuator of the gripping part and a pair of claws for the same embodiment as FIG. FIG. In the illustrated embodiment, as the actuator for moving the grip portion, the one in which the base screwed with the ball screw is horizontally moved while being guided by the guide rod by the rotation of the ball screw, but both cylinder rods are connected as the lifting actuator. The main cylinder and the sub-cylinder are used as the advancing / retreating actuators, the advancing / retreating cylinders are used as the opening / closing actuators, and a pair of racks and pinions that are screwed into these racks are used. And a cylinder for advancing and retreating are used as actuators for advancing and retreating, respectively, and the control unit for controlling the operation of each actuator and the driving of the belt conveyor is omitted.

First, the transport section will be described. A drive roller 12a and a floating roller 12b are axially supported by the machine frame 11, and an endless belt 13 is tightly engaged between the drive roller 12a and the floating roller 12b.
2a is connected to a pulse motor (not shown).

A plug tray 21 is placed on the belt 13, and the plug tray 21 is sandwiched between a guide plate 14a and a guide plate 14b provided upright on the machine frame 11. A cylinder tube 22 a of a forward / backward moving cylinder 22 is attached to the machine frame 11, and a cylinder rod 2 of the forward / backward moving cylinder 22 is attached.
A pressing plate 23 is connected to 2b. The pressing plate 23 is located slightly above the plug tray 21, and is slidably fitted to the machine frame 11 on both sides of the belt 13. Holding plate 2
3, the recesses 23a are formed at intervals and in a number corresponding to the plugs 21a in each row provided on the plug tray 21, and the width of the recesses 23a is narrower than the width of the plugs 21a.

Next, the grip portion will be described. Machine frames 31a and 31b, one of which is attached to the machine frame 11 of the transport unit and the other of which is attached to another machine frame (not shown) (however, the machine frame 31b
(Not shown, the same applies hereinafter) is mounted with a guide rod 32a, a ball screw 32b is rotatably supported on the machine frames 31a and 31b, and a pulse motor (not shown) is connected to the ball screw 32b. . The guide rod 32a is slidably fitted to the base 33, and the base 33 has a ball screw 3
2b is screwed together.

A substrate 41 is supported on the base 33,
The cylinder cylinder 51 a of the main cylinder 51 is attached to the substrate 41. The cylinder rod 51b of the main cylinder 51 is connected to the cylinder rod 52b of the sub cylinder 52, and the pedestal 53 is attached to the cylinder cylinder 52a of the sub cylinder 52. There are two guide rods 53 on the pedestal 53.
a and 53b are provided upright, and guide rods 53a and 53b are provided.
Is slidably fitted into guide cylinders 41a and 41b attached to the substrate 41.

A cylinder tube 61a of a forward / backward movement cylinder 61 is attached to the receiving base 53, and a case 71 is attached to a cylinder rod 61b of the forward / backward movement cylinder 61. Two guide rods 71a and 71b are extended from the case 71, and the guide rods 71a and 71b are slidably fitted to a guide cylinder (not shown) attached to the pedestal 53.

A pair of racks 72a and 72b guided by rails (not shown) are housed in the case 71, and the racks 72a and 72b have pinions 73 having different numbers of teeth on their peripheral surfaces.
a and 73b are engaged with each other, and the pinion 73
a and 73b are attached to the same rotary shaft 74a of the pulse motor 74.

One claw 81a is attached to the rack 72a, and the other claw 81b is attached to the rack 72b.
The claw 81b is composed of two claws provided with a gap, and the pair of claws 81a and 81b are taken out of the case 71. One claw 81a is formed in an arcuate inner circumference, and the other claw 81b is formed in a V-shaped inner circumference so that the claw 81a fits into the gap between the two claws 81b. ing.

In the gripping portion of the illustrated embodiment, the base 33
Lateral movement → descending operation of the main cylinder 51 and the sub cylinder 52 → advancing operation of the advancing / retreating cylinder 61 (a pair of claws 81a, 8a).
1b advances to a position where it sandwiches the ground part of the seedlings cultivated on the plug 21a of the plug tray 21 from both sides) → the first closing operation of the racks 72a, 72b (paired claw 81a,
81b surrounds the ground part of the seedling) → The raising operation of the sub-cylinder 52 (the paired claws 81a and 81b rise to the stem of the seedling in the enclosed state) → the second stage of the racks 72a and 72b Closing operation (paired claws 81a, 81b grip the stem portion of the seedling) → raising operation of the main cylinder 51 (paired claws 81a, 81b pull out the seedling from the container in the gripped state) → base 33 Lateral movement of (moving the extracted seedlings to a predetermined position) becomes the operation sequence. Further, in the illustrated transporting section of the embodiment, at least the pair of nails 8 surrounding at least the ground portion of the seedlings 8
Immediately before 1a and 81b rise to the stem, the pressing plate 23 presses the soil of the plug 21a in which the seedling is cultivated by the forward movement of the advancing / retreating cylinder 22, and conversely at least the stem of the seedling. Pair of claws 81a and 81b that grip the
Just before pulling out the seedlings, the forward / backward moving cylinder 22
The pressing plate 23 is returned to the original position by the retreating operation of.

[0030]

EFFECTS OF THE INVENTION As is apparent, according to the present invention described above, even if seedlings are densely cultivated in the plug tray and the stems of the seedlings are inclined, There is an effect that each young plant can be reliably gripped one by one.

[Brief description of drawings]

FIG. 1 is a perspective view showing an embodiment of the present invention.

FIG. 2 is a side view showing the same embodiment as in FIG. 1 with a part of the gripping portion omitted.

FIG. 3 is an enlarged perspective view showing the same embodiment as FIG. 1 with a part of the relationship between the opening / closing actuator of the grip portion and a pair of claws omitted.

[Explanation of symbols]

11, 31a ... Machine frame, 13 ... Belt, 22, 6
1 ... Forward / backward actuator, 23 ... Pressing plate,
33 ... Base, 32a, 53a, 53b, 71a, 7
1b ... guide rod, 32b ... ball screw, 41.
..Substrate, 51 ... Main cylinder, 52 ... Sub cylinder, 53 ... Cradle, 71 ... Case, 72a, 72
b ... rack, 73a, 73b ... pinion, 81
a, 81b ... claws

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsutoshi Hosoi 23-23 Ando-cho, Kuroiso-shi, Tochigi Prefecture (72) Inventor Hideo Akutsu 2557-6 Terako Oto, Nasu-machi, Nasu-gun, Tochigi Prefecture

Claims (11)

[Claims] 1. A method for gripping a young plant, which comprises the following first step, second step and third step. First step: The pair of claws supported by the moving actuator descends to a position facing the edge of the seedling cultivated in the plug tray, and then to a position where the edge of the seedling is sandwiched from both sides. Step of advancing Second step: The pair of claws that have been advanced surrounds the edge part of the seedling, while the holding plate moves forward to hold the soil of the seedling, and then the pair of claws Step of rising to the stem of the plant Third step: The pair of raised nails grips the stem of the seedling,
On the other hand, the pressing plate retracts, and then the pair of nails pulls out the seedlings. 2. A seedling holding device for holding a young plant cultivated on a plug tray with a pair of claws, pulling it out in a gripped state, and moving it to a predetermined position, comprising the following gripping part: A grasping device for a young plant characterized by comprising the following conveying section and a control section for controlling the operation of the grasping section and the conveying section. Gripping part: a moving actuator, a substrate supported by the moving actuator, a lifting actuator mounted on the substrate to move up and down in two steps, an advancing / retreating actuator mounted on the lifting actuator, An opening / closing actuator mounted on the advancing / retreating actuator to close in two stages, and a pair of pawls attached to the opening / closing actuator are provided. The forward movement advances to a position where the ground portion of the seedling is sandwiched from both sides, and then the closing operation of the first stage of the actuator for opening and closing causes the pair of claws surrounding the ground portion of the seedling to move to the first position of the lifting actuator. After ascending to the stem of the seedling by one-step raising operation, the seedling is opened by the second-step closing operation of the opening / closing actuator. Gripper claw pairs of gripping the stem portion of the object is made so as to pull the 該幼 plant by increasing actuation of the second stage of the elevating actuator. Conveying unit: An intermittently driven plug tray placing conveyor, an advancing / retreating actuator attached to the machine frame of the conveyor, and a pressing plate connected to the advancing / retreating actuator, and a seedling in the gripping section When the pair of claws surrounding the above-mentioned ground portion rises up to the stem of the seedling, the pressing plate is advanced to hold down the soil of the seedling. 3. The moving actuator in the gripping portion moves while a ball screw rotates to guide a base screwed with the actuator, and the base plate is attached to the base. 2. The seedling-holding device according to 2 above. 4. An elevating actuator in the gripping part is attached to a main cylinder having a cylinder cylinder attached to a substrate, a sub cylinder having a cylinder rod connected to a cylinder rod of the main cylinder, and a cylinder cylinder of the sub cylinder. 4. The seedling body according to claim 2 or 3, further comprising: a pedestal, the pedestal being moved up and down while being guided by a guide rod with respect to the substrate by an up-and-down operation of the main cylinder and / or the sub-cylinder. Gripping device. 5. The seedling holding apparatus according to claim 4, wherein the advancing / retreating actuator in the gripping portion is an advancing / retreating cylinder having a cylinder tube attached to a pedestal. 6. A case in which an actuator for opening and closing in a grip portion is attached to a cylinder rod of a cylinder for advancing and retracting, a pair of racks slidably accommodated in the case, and a pinion that engages with the pair of racks. The holding device for a young plant according to claim 5, further comprising: a drive motor that rotates the pinion. 7. A pair of racks are respectively engaged with pinions, both pinions having different numbers of teeth on their peripheral surfaces, and both pinions are attached to the same rotary shaft of a drive motor. A device for holding a young plant described in the above. 8. The seedling according to claim 6, wherein among the pair of claws and racks, one claw is attached to one rack and the other claw is attached to the other rack. Body gripping device. 9. The grasping device for a young plant according to claim 8, wherein one of the inner circumferences of the pair of claws is formed in an arc shape and the other is formed in a V shape. 10. The seedling holding device according to claim 1, wherein the advancing / retreating actuator in the conveying section is an advancing / retreating cylinder having a cylinder tube attached to a machine frame of a conveyor. 11. A pressing plate is mounted slidably above the plug tray in the width direction of the conveyor, and a plurality of recesses corresponding to the plugs in the width direction of the plug tray are narrower than the plug. The holding device for a young plant according to claim 10, wherein the device is formed in a width.