JPH11137019A - Paddy field working machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep a seedling planting apparatus at proper height from field face even pitching of a traveling machine body by providing a specific controller. SOLUTION: This paddy working machine is equipped with a controller for measuring oscillation posture of a ground-leveling float 15 around its shaft center P by a float sensor 47 and carrying out lifting and lowering of a seedling planting apparatus so as to keep the measured result to the control target and an operation wire for forming a part of the shaft center P for supporting a ground-leveling float 15 to be vertically changeable to the seedling planting apparatus and changing over the target posture of the ground-reveling float 15 to forwardly lowered side by an operating sensor body 47A of the float sensor 47 when the part of the shaft center P is changed in the upper direction to perform lowering control frequency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an actuator for connecting a working device to a traveling machine body so as to be able to move up and down, and an actuator for operating the working device up and down. Equipped with a sensing sensor that measures the swinging posture of the ground float that is freely supported, and a sensing spring that biases the front part of the ground float downward, and that the front part of the ground float is displaced upward from the target posture When the sensor is measured by the sensor, the working device is lowered, and when the sensor detects that the front part of the ground float is displaced downward from the target posture, the controller is configured to drive the actuator to lower the working device. Rice paddy working machine
More specifically, the present invention relates to a technique for changing a mode of raising and lowering control of a seedling planting apparatus based on a forward and backward inclination of a body.

[0002]

2. Description of the Related Art As a technique similar to the above-described paddy working machine, there is one disclosed in Japanese Patent Publication No. 3-17607.
This conventional example includes a manual operation system that adjusts the sensitivity of the raising and lowering control of the seedling planting device by changing the attitude of the ground float in accordance with the hardness of the mud in the field scene, and electrically controls the pitching of the traveling machine. And a pitching detecting means including a forward tilt sensing element and a backward tilt sensing element, and the ground float is controlled by electric control based on the pitching detected by the detecting means. And a correction means for automatically adjusting the sensitivity of the elevation control by changing the posture of the camera.

[0003]

However, in the prior art, since the pitching detecting means detects the pitching based on gravity, erroneous detection may occur due to vibration of the body. Further, since the method for correcting the sensitivity of the raising and lowering control of the seedling planting device based on the pitching of the airframe as in the conventional example does not detect the actual posture of the seedling planting device with respect to the field scene, highly accurate correction is performed. Could not be done. In particular, in the conventional example, at the time of pitching of the body, since a proper control sensitivity is obtained after the motor operates by a required amount, a time lag from the occurrence of the pitching to shifting to the appropriate control becomes too large, which is temporary. It is also possible to lower the seedling planting equipment to a large extent to generate a mud push by the grounding float, or to temporarily generate the floating seedlings by holding the seedling planting equipment at a level higher than the target field height. There is room for improvement.

In a conventional rice transplanter control system, the control operation is set such that the larger the deviation between the actual attitude of the grounding float and the target attitude is, the faster the raising and lowering of the seedling planting apparatus is performed. For example, in a situation where the traveling body is restored to the original horizontal posture in a short time even if the traveling body is pitched, such as when traveling on a cultivator in which unevenness is locally present, the raising and lowering operation of the seedling planting apparatus is almost the same. Despite the fact that it is not necessary to do so, when the pitching occurs, the deviation between the target posture and the actual posture of the ground float becomes large, so that the seedling planting device is raised and lowered at high speed, and overshoot due to dynamic inertia causes In some cases, the seedling planting equipment was temporarily set to an inappropriate level.

SUMMARY OF THE INVENTION An object of the present invention is to rationally construct a paddy field working machine capable of maintaining a working apparatus at an appropriate field scene height even when pitching a traveling machine body.

[0006]

According to a first aspect of the present invention, as described at the outset, a working device is connected to a traveling body so as to be able to move up and down, and the working device is moved up and down. An actuator, a sensor for measuring the swinging posture of the grounding float supported swingably around an axis having a lateral posture with respect to the working device, and a sensing spring for biasing the front part of the grounding float downward. When the sensor detects that the front part of the grounding float is displaced upward from the target posture, the working device is lowered, and the sensor detects that the front part of the grounding float is displaced downward from the target posture. In a paddy field working machine equipped with a control device that drives an actuator to lower the working device when measured by a sensor, the position of the axis supporting the grounding float is moved up and down with respect to the working device body. A frequency reducing means which is formed freely and includes an urging means for urging the shaft center portion downward, and the frequency of the lifting / lowering control of the working device is reduced as the shaft center portion is displaced upward. The operation and effect are as follows.

According to a second feature of the present invention (claim 2), in claim 1, the sensing sensor is rotated by a sensor main body and an operation shaft rotatably provided with respect to the sensor main body. In addition to being configured as an operation type, a linkage for rotating the operation shaft is formed in conjunction with the vertical displacement of the ground float, and the frequency reduction means is configured to displace the shaft core upward. In that it is provided with an operating member that changes the attitude of the sensor main body so as to displace the target attitude of the ground float in the forward and downward directions in conjunction with the operation of the sensor body.
And the effect is as follows.

[0008] A third feature of the present invention (claim 3) is that, according to claim 1, further comprising a displacement sensor for measuring the amount of vertical displacement of the portion of the shaft center, and wherein the frequency reducing means measures the displacement by the displacement sensor. The control in which the control operation is set such that the target posture of the ground float is changed to the forward-lower side as the amount of upward displacement of the portion of the shaft center is increased, or the width of the dead zone of the elevation control is increased. The operation and effects are as follows.

[Action]

According to the first feature, when pitching in the direction in which the front portion of the traveling machine body is lifted during work, the entire work apparatus is displaced in a direction approaching the field scene, and the grounding float is moved to the field scene. As a result, the portion of the shaft supporting the grounding float is displaced upward, and the frequency reduction means reduces the frequency of the elevating control in conjunction with this displacement. Is suppressed. That is, since the form of the elevation control is switched based on the relative state change of the working device with respect to the field scene, when pitching occurs in the traveling body, quick control corresponding to the occurrence of pitching becomes possible, As a result, it becomes possible to perform control in a state in which erroneous control due to vibration of the traveling body is suppressed as compared with the case where the traveling body has a sensor.

More specifically, in a conventional rice transplanter in which the portion of the axis of the grounding float cannot be vertically displaced, as shown in FIG. In the case where pitching in the direction in which the front part of the traveling machine body is lifted as shown in FIG. Although a force in the lifting direction from the field scene S acts on the rear end of the landing float 15 to cause a phenomenon of pushing down the front end of the landing float 15 downward, control for lowering the working device may be performed. According to the second feature, at the time of pitching, the entire work apparatus is displaced in a direction approaching the field scene, and the portion of the shaft supporting the ground float is displaced upward by the pressure from the field scene, whereby the ground float is displaced. At the same time as the amount of downward movement of the front part can be reduced, the operating member operates the sensor body in conjunction with this displacement to displace the target attitude of the ground float to the forward downward side, so if this pitching angle is not so large, Can match the target attitude of the grounding float with the attitude of the grounding float at the time of pitching to prevent the lowering control of the working device.

According to the third feature, for example, when pitching occurs in the direction in which the front part of the traveling machine body is lifted, the entire working device is displaced in a direction approaching the field scene and is subjected to pressure from the field scene. The displacement of the front part of the grounding float can be reduced by displacing the part of the shaft core that supports the grounding float upward, and at the same time, the displacement sensor measures the amount of displacement, and the control device grounds based on the measurement result. The target attitude of the float is changed to the forward and downward sides, or the width of the dead zone of the elevation control is increased.If this pitching angle is not so large, the target attitude of the grounding float and this pitching It is possible to prevent the descent control of the work equipment by matching the attitude of the grounding float, or by putting the attitude of the grounding float at the time of this pitching within the dead zone. That.

[Effect of the Invention] Therefore, even if the front part of the traveling machine body is pitched in the lifting direction, the grounding float sinks into the field scene by rapid control based on the change in the relative positional relationship between the field scene and the work equipment. A paddy field working machine capable of avoiding the phenomenon and maintaining the working device at an appropriate height with respect to the field scene was rationally configured (claim 1). Further, when the front part of the traveling machine body is pitched in the lifting direction, useless mechanical lifting operation of the working device can be suppressed by mechanical and reliable operation, and the level of the working device with respect to the field scene can be maintained. 2) In addition, when the front part of the traveling body is pitched in the lifting direction, useless moving operation of the working device is suppressed by an electric control operation that does not use the movable member so much that the working device is used in a field scene. The level can be maintained (claim 3).

[0014]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, a drive-type front wheel 1 and a drive-type rear wheel 2 that are steered.
The engine 4 is mounted on the front of the traveling body 3 provided with a transmission body 5 and the transmission case 5 in which the power from the engine 4 is transmitted to the front of the traveling body 3 via a belt-type continuously variable transmission V. In addition, a steering wheel 6 and a driver seat 7 are arranged at the center of the traveling body 3 and a parallel quadruple link that is driven up and down by a lift cylinder 8 as an actuator at the rear end of the traveling body 3. A seedling planting device A as a working device is connected via a mechanism 9 to constitute a rice planting machine as a paddy working machine.

The seedling planting apparatus A includes a transmission case 10 to which the power from the traveling machine body 3 is transmitted, a plurality of chain cases 11 to which the power from the transmission case 10 is transmitted, and a rear portion of each of the chain cases 11. And a seedling table 14 on which a mat-shaped seedling W is placed, and a plurality of leveling floats 15 as grounding floats. At the time of planting operation, the planting claw provided on the planting arm 13 cuts out the seedlings one by one from the lower end of the mat-shaped seedling W placed on the seedling placing stand 14 and the plant scene S
It is configured to perform an operation of planting in a plant.

On the right side of the driver's seat 7, there is provided a lifting lever 16 for raising and lowering the seedling planting device A and turning on and off a planting clutch (not shown) built in the transmission case 5. A main shift lever 17 is provided on the left side of the meter panel at the front position. As shown in FIG. 2, an accelerator lever 18 and a sub shift lever 19 for setting the rotation speed of the engine 4 are provided at the right position of the meter panel. It is arranged. The main shift lever 17 is configured to mechanically perform forward / backward switching and forward / backward two-step switching by operating a gear type transmission of the transmission case 5.
The sub-transmission lever 19 is configured to perform a speed-change operation of the continuously variable transmission V.

As shown in FIG. 3, the continuously variable transmission V includes
An output pulley 21 provided on the output shaft 4A of the engine 4 and having a variable belt winding diameter, and an input shaft 5A of the transmission case 5
, An endless belt 23 wound around each of them, an operation mechanism 24 for simultaneously adjusting the belt winding radius of both pulleys 21 and 22, and a rod And an electric cylinder 26 that is operated via a transmission 25, and a potentiometer type shift sensor 27 is interposed at an intermediate position of the shift system.

Of the plurality of leveling floats 15, one at the center in the left-right direction is configured as a grounding float for measuring the relative height of the seedling planting apparatus A with respect to the field scene S.
As shown in FIGS. 4 to 6, the swinging end of the arm 30 swinging integrally with the planting depth adjusting shaft 29 is provided with an intermediate support shaft 31 in a lateral posture.
A displacement member 32 is provided so as to swing freely around the displacement member 3.
A support member 34 at a rear position of the leveling float 15 is supported at a rear end position of the float 15 by a support member 34 swingably supported around a support shaft 33 in a lateral posture. Arm 30
As a biasing means for setting the posture of the displacement member 32 with respect to the arm, a vine-winding neutral spring 35 is disposed so as to sandwich the lateral piece 30A at the rear end of the arm 30 and the shaft 36 fixed to the displacement member 34, This leveling float 15 is used in the field scene S
When the contact member is grounded with an appropriate pressure, the displacement member 32 is maintained at the neutral position shown in FIG. Further, by providing a bending and stretching type link member 39 between the bracket 37 provided at the front position of the leveling float 15 and the frame 38 of the seedling planting apparatus A, the relative height of the field scene S to the seedling planting apparatus A is increased. The ground leveling float 15 is configured to swing up and down around the axis P of the support shaft 33 when the height changes.

A planting depth adjusting lever 41 for rotating the planting depth adjusting shaft 29 is provided, and the lever 41 is engaged with a locking piece 41A provided on the planting depth adjusting lever 41. Is held by the frame 38 of the seedling plant A via the intermediate plate 43. A support plate 45 is provided at a front position of the intermediate plate 43 via a parallel quadruple link mechanism 44 so as to be vertically movable, and a pin 46 provided at the base end of the planting depth adjusting lever 41 and a link mechanism are provided. 44, the support plate 45 is raised in conjunction with the rise of the leveling float 15 which is linked with the operation of the planting depth adjusting lever 41, and conversely, the support plate 4 is linked with the descent of the leveling float 15
5 is set to descend. Further, the sensor body 47A and the operation shaft 47 are supported with respect to the support plate 45.
B and a float sensor 47 (an example of a sensing sensor) of a potentiometer type. The float sensor 47 is configured such that the sensor main body 47A is connected to the support plate 45 via the intermediate member 48 with the axis Q of the operation shaft 47B. It is supported rotatably around the coaxial core. Also, the float sensor 47
An operation rod 50 for transmitting the vertical operation of the terrain float 15 is interposed between the operation arm 49 connected to the operation shaft 47B of the bracket and the bracket 37 in an inclined position positioned rearward toward the upper end. A compression coil type sensing spring 51 for urging the operation arm 49 downward between the upper end position of the sensor arm 45 and the upper end 45 is provided.

The end of the outer wire 53A of the push-pull type operation wire 53 as the operation member is connected to the arm 30.
And the end of the inner wire 53B of the operation wire 53 is supported by the arm 32A of the displacement member 32. The outer wire 53A on the other end side of the operation wire 53
Is supported on the support plate 45, and the inner wire 53B
Is connected to an arm 47C formed on the sensor main body 47A, so that when the rear end of the leveling float 15 is displaced upward, the sensor main body 47A is rotated about the axis Q to swing the swing end of the operation arm 44. Is switched to the downward attitude (switching to the attitude in which the target attitude of the terrain float 15 changes to the forward-lowering side), thereby changing the target attitude of the grounding float 14 to the forward-lowering side to increase the control relationship so as to increase the control sensitivity. Is set. Further, when the leveling float 15 is displaced downward, the control sensitivity is reduced by rotating the sensor main body 47A in a direction opposite to that described above by the operation force from the operation wire 53. The system having the operation wires 53 constitutes the frequency reduction unit.

In this rice transplanter, the seedling planting apparatus A is moved up and down so that the swinging posture of the leveling float 15 around the axis P of the support shaft 33 is maintained at the target posture. A control device 55 for maintaining the surface height is provided. That is,
The control device 55 includes a microprocessor,
A lever sensor 56 for measuring the operation position of the elevating lever 16 with respect to the control device 55, a potentiometer type sensitivity setting device 58 which is rotated by a dial 57, the float sensor 47, the shift sensor 27, the accelerator lever An input system for receiving a signal from each of a potentiometer type engine speed sensor 59 for measuring the set position of the motor 18 is formed, an electromagnetically operated control valve 60 for controlling the lift cylinder 8, and the electric cylinder 26.
And an output system for outputting a signal to the relay switch 61 for controlling the power to the power supply. It should be noted that the control valve 60 is configured to obtain an opening corresponding to the current value for the solenoid, and the control device 55 controls the PW by changing the duty cycle.
The control operation is set so that the opening of the control valve 60 can be adjusted by controlling the current value of the control valve 60 to the electromagnetic solenoid in the M type.

The control unit 55 controls the lifting and lowering as follows based on a preset program. That is, as shown in the flowchart of FIG. 12, first, the actual traveling speed of the body 3 is determined based on the signal from the engine speed sensor 59 and the signal from the shift sensor 27, and the correction value is set (# 101 to # 101). 1
03 steps). Next, a signal from the sensitivity setting device 58 is input, a control target is set based on the input signal and the correction value, and a dead zone formed based on the control target and a signal value from the float sensor 47 are calculated. In comparison, when the signal from the float sensor 47 is within the dead zone, the elevation control is not performed. When the signal is outside the dead zone, the opening degree of the control valve 60 is determined by comparing the signal from the float sensor 47 with the control target. The larger the deviation is, the larger the deviation is set, and the control of the control valve 60 is performed to raise and lower the seedling plant A (steps # 104 to # 108).

As shown in FIG. 8, the control target corresponds to the target attitude E of the leveling float 15 around the axis P of the support shaft 33 (the swing attitude e of the operating arm 49 of the float sensor 47 and the control attitude). As shown in FIG. 9, the posture of the terrain float 15 is changed to the target posture E by swinging around the axis P.
When it is displaced to the front ascending side, the float sensor 47 measures the displacement, and in a state where this posture has reached outside the dead zone, the seedling planting apparatus A is to be raised, and conversely, When the posture of the leveling float 15 is displaced forward and downward from the target posture E (not shown), the displacement is measured by the float sensor 47, and when the posture is out of the dead zone, seedlings are planted. The control direction is set so as to lower the device A. The target posture E is set based on the set value of the sensitivity setting device 58. When the dial 57 is set to the "dull" side, the target posture E of the terrain float 15 is changed to the forward ascending side. Then, the urging force acting on the leveling float 15 from the sensing spring 51 is increased to suppress the swing of the leveling float 15, and the dial 57 is set to “quick”.
In the case of setting on the leveling float 15, the biasing force acting on the leveling float 15 from the sensing spring 51 is reduced by changing the target attitude E of the leveling float 15 to the front downward side.
Swinging easily occurs. From this, when the mud of the field scene S is hard, the dial 57 of the sensitivity setting device 58 is set to the “dull” side to thereby set the field scene S.
When the mud in the field scene S is soft, the level change of the field scene S is set by setting the dial 57 of the sensitivity setting device 58 to the “sensitive” side when the mud of the field scene S is soft. Lifting control can be performed with high sensitivity.

When the actual running speed of the body 3 is high, the leveling float 1 is pushed by the pushing force from the mud in the field scene S.
The force that lifts the front of 5 acts strongly,
The target spring E is corrected from the sensing spring 51 to the leveling float 1 by correcting the target attitude E so that the attitude change of the leveling float 15 due to the lifting is suppressed.
The correction value in the above-mentioned flowchart is set so as to increase the urging force acting on the front part of the fifth embodiment.

In operation, as shown in FIG. 13B, when the front wheel 1 rides on the convex portion of the plow G and the front part of the traveling machine body 3 is pitched in the lifting direction, Since the rear end of the planting device A is displaced in the direction approaching the field scene S and the rear end of the leveling float 15 is pressed against the field scene S, the urging force of the neutral spring 35 is applied as shown in FIG. As a result, the displacement member 32 swings upward, and the portion of the axis P that supports the terrain float 15 is displaced upward.
3 rotates the sensor body 47A of the float sensor 47 to the high sensitivity side around the axis Q, so that the front end position of the leveling float 15 is lowered as shown in FIG. The target posture E (strictly, a target posture based on the position of the axis P assuming that the displacement member 32 is at the neutral position) is changed to a forward lower side from the target posture set by the sensitivity setting device 58. As a result, the lowering control of the seedling planting apparatus A is suppressed. In particular, when the rear end side of the seedling planting device A is displaced in a direction approaching the field scene S, the portion of the axis P that supports the leveling float 15 is displaced upward, so that the front of the leveling float 15 is The descending amount is reduced, and the descending control is favorably suppressed.

On the contrary, FIG.
As shown in (c), when the front wheels 1 are fitted into the recesses of the cultivator G and pitching in a direction in which the front part of the traveling machine body 3 is lowered occurs, as shown in FIG. Since the rear end side of A is displaced away from the field scene S, the displacement member 32 swings downward by its own weight of the leveling float 15 against the biasing force of the neutral spring 35, and the shaft supporting the leveling float 15 The portion of the core P is displaced downward, and the operation wire 53 is connected to the float sensor 47 in conjunction with this displacement.
As a result of rotating the sensor body 47A around the axis Q to the low sensitivity side, the front end position of the leveling float 15 is lifted as shown in FIG. The target posture based on the position of the axis P assuming that the displacement member 32 is at the neutral position is changed to a position on the front side higher than the target posture set by the sensitivity setting device 58, and seedling planting is performed. The control for raising the apparatus A is suppressed. In particular, when the rear end side of the seedling planting device A is displaced in a direction away from the field scene S, the portion of the axis P supporting the leveling float 15 is displaced downward, so that the front portion of the leveling float 15 is displaced downward. The lifting amount is reduced, and the lifting control is favorably suppressed.

As described above, in the rice transplanter of this configuration, when the traveling body 3 is pitched, based on the relative positional relationship of the rear end portion of the leveling float 15 to the field scene S,
The rear end portion of the leveling float 15 is moved up and down to reduce the swing amount of the leveling float 15, and at the same time, the seedling is planted in a direction opposite to the direction of the raising and lowering control of the seedling planting apparatus A caused by the swing of the leveling float 15. Since the control sensitivity is automatically changed so that the apparatus A is moved up and down, the frequency of the up and down control is reduced and unnecessary use of the up and down control is not performed.

[Other Embodiments] The present invention can be configured as shown in FIGS. 14 and 15 in addition to the above embodiment. That is, a potentiometer-type displacement sensor 63 that measures the amount of vertical displacement of the rear end of the leveling float 15 without the operation wire 53 as in the above-described embodiment is provided (specific structure is not described in detail), The target attitude of the terrain float 15 can be changed by an electric process based on the measurement result from the displacement sensor 63. With the same numbers and signs.)

In the control operation, as shown in the flow chart of FIG. 15, first, the actual traveling speed of the body 3 is obtained based on the signal from the engine speed sensor 59 and the signal from the speed change sensor 27 to perform the first correction. Set the value and set the displacement sensor 6
3 to set a second correction value (# 20).
1 to # 205 steps). The first correction value is set to a value that corrects the attitude of the terrain float 15 from the control target to the front as the traveling speed of the body 3 increases, and the second correction value is the upward displacement of the terrain float 15. The value which corrects the attitude of the leveling float 15 from the control target to the forward downward side as the value is larger, and conversely, corrects the attitude of the leveling float 15 from the control target to the forward side as the downward displacement of the leveling float 15 increases Is set. Next, a signal from the sensitivity setting device 58 is input, a control target is set based on the input signal, the first correction value, and the second correction value, and a dead zone and a float sensor 47 formed based on the control target are set. And the signal value from the float sensor 4
When the signal from 7 is within the dead zone, the elevation control is not performed. When the signal is outside the dead zone, the opening degree of the control valve 60 is set to be larger as the deviation between the signal from the float sensor 47 and the control target is larger. The setting is made larger so that the control valve 60 is controlled to move the seedling planting apparatus A up and down (steps # 206 to # 210).

Further, in the present invention, besides the above embodiment, for example, it is also possible to set a control program of the control device so as to increase the width of the dead zone in order to lower the sensitivity.

[Brief description of the drawings]

FIG. 1 is an overall side view of a rice transplanter.

FIG. 2 is a plan view of a meter panel.

FIG. 3 is a schematic diagram of a continuously variable transmission.

FIG. 4 is a side view of an operation system of the float sensor.

FIG. 5 is a plan view of the rear part of the float.

FIG. 6 is a front view of an operation system of the float sensor.

FIG. 7 is a block circuit diagram of a control system.

FIG. 8 is a side view showing an operation state of the sensor when the leveling float is in a target posture.

FIG. 9 is a side view showing an operation state of the sensor when the leveling float is in a front-up position;

FIG. 10 is a side view showing the operation state of the sensor when the rear part of the leveling float is raised.

FIG. 11 is a side view showing an operation state of the sensor when the rear part of the leveling float is lowered.

FIG. 12 is a flowchart showing a lifting control routine;

FIG. 13 is a side view showing three states of a relationship between the attitude of the traveling machine body and the seedling planting apparatus.

FIG. 14 is a block circuit diagram of a control system according to another embodiment.

FIG. 15 is a flowchart showing a lifting control routine according to another embodiment;

[Explanation of symbols]

 Reference Signs List 3 traveling machine body 8 actuator 15 ground float 35 urging means 47 sensing sensor 47A sensor body 47B operating shaft 51 sensing spring 53 operating member 55 control device 63 displacement sensor A working device P shaft center

Claims (3)

[Claims] An actuator for connecting a working device to a traveling body so as to be able to move up and down, and an actuator for operating the working device up and down, and a ground float supported to be swingable about an axis centered in a lateral posture with respect to the working device. A sensing sensor that measures the swinging posture of the ground float, and a sensing spring that biases the front part of the grounding float downward, and measures that the front part of the grounding float is displaced upward from the target posture by the sensing sensor. Then, the paddy field working machine is provided with a control device that lowers the working device and, when the sensor detects that the front part of the grounding float has been displaced downward from the target posture, drives the actuator to lower the working device. Urging means for forming a portion of the shaft supporting the grounding float so as to be vertically displaceable relative to the working device body, and for urging the shaft center downward. It includes also paddy working machine site of this axis is provided with the frequency reduction means for reducing the frequency of elevation control of the working device as displaced upward. 2. The sensor according to claim 1, wherein the sensing sensor is configured to be a rotating operation type including a sensor main body and an operation shaft rotatably operated with respect to the sensor main body, and is interlocked with the vertical displacement of the ground float. Then, a linkage for rotating the operation shaft is formed, and the frequency reducing means displaces the target attitude of the grounding float forward and downward in conjunction with the upward displacement of the shaft center portion. The paddy working machine according to claim 1, further comprising an operation member for changing a posture of the sensor main body. 3. The apparatus according to claim 1, further comprising a displacement sensor for measuring an amount of vertical displacement of the portion of the shaft center, wherein the frequency reducing means increases the amount of upward displacement of the portion of the shaft center measured by the displacement sensor. 2. The paddy field working machine according to claim 1, wherein the control device is configured to control the control operation so as to change a target posture of the grounding float to a forward lowering side or to increase a width of a dead zone of the elevation control. 3.