JP3540919B2 - Working height control device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention includes a receiving unit that receives a reference light beam transmitted in a horizontal direction from a transmitting unit that is grounded on a ground working device that is provided to be able to move up and down with respect to a vehicle body, and that is vertically movable with respect to the receiving unit. The target position of the reference light beam is set at the middle position of, and when the reference light beam enters above this target position, the ground work device is raised, and the reference light beam enters below this target position. The work height control device which performs a control operation of lowering the ground work device when the reference light beam is incident on the incident target position when the reference light beam is incident on the incident target position. The control operation when the reference beam cannot be received.
[0002]
[Prior art]
There is a work height control device configured as described above, which is disclosed in Japanese Patent Publication No. 62-25824. In this conventional example, when a receiving unit (light receiver) cannot receive a reference light beam (laser light). The height of the ground working device (blade) is fixed to a level before receiving the reference light beam (laser light) for a set time.
[0003]
[Problems to be solved by the invention]
In the conventional example, when the reference light beam is interrupted, the lifting operation is temporarily stopped to avoid the phenomenon that the ground height of the ground working device is too low or too high, and the reference light beam is received again. In this case, the lifting control can be restarted. However, the conventional transmitting unit is installed on the ground via a tripod, etc., and may not be able to transmit the reference light beam due to overturning due to the wind.In addition, since the battery is used for driving, the standard Sometimes it is not possible to emit light. Furthermore, the vehicle equipped with the ground work device does not always travel on flat ground, and the receiver may not be able to receive the reference beam due to the large inclination of the vehicle on the uneven surface of the ground. Therefore, it is desired to perform appropriate control even in such a situation.
[0004]
That is, as in the conventional example, after the elevating operation of the ground working device is stopped for a predetermined time in a situation where the receiving unit cannot receive the reference beam, the situation where the receiving unit cannot receive the reference beam at the time of starting the control continues. In this case, for example, even if control is performed to maintain a state in which the lifting and lowering of the ground working device is stopped, if this state is continued for a long time, control at an appropriate level cannot be performed, and there is room for improvement. In particular, considering the case where the receiving unit moves up and down greatly due to the inclination of the vehicle body and the reference beam is located above or below the receiving unit, the receiving unit receives the reference beam as in the conventional example. If the lifting / lowering operation of the ground working device is stopped for a predetermined time when it is no longer possible, the height of the ground working device will be maintained at a level deviating from an appropriate height.
[0005]
SUMMARY OF THE INVENTION An object of the present invention is to rationally configure a control device capable of appropriately coping with a case where reception of a reference light beam becomes impossible in lifting and lowering a ground working device based on a reference light beam as described above. On the point.
[0006]
[Means for Solving the Problems]
A first feature of the present invention (claim 1) is that a receiving unit that receives a reference light beam transmitted in a horizontal direction from a transmitting unit that is grounded on the ground is provided to a ground working device that is provided to be able to move up and down with respect to a vehicle body. In addition to the above, a reference light incident target position is set at an intermediate position in the vertical direction with respect to the receiving unit, and when the reference light is incident above the incident target position, the ground operation device is raised and the incident A work height for performing a control operation of lowering the ground work device when the reference light beam is incident on the lower side of the target position, and stopping the elevation operation of the ground work device when the reference light beam is incident on the incident target position. a controlled device, when falling into a situation where not receive the reference light beam by the receiver, determines the position of incidence of the reference beam with respect to the receiving unit immediately before falling into this situation, the incident position of incidence The control direction is set so that the ground work device is raised above the mark position, and the ground work device is lowered if it is below the mark position, and the larger the deviation between the incident position and the target incident position is, the more the ground work is performed. Set the control speed to increase the lifting speed of the device and perform the detection operation ,
If the receiving unit cannot receive the reference light beam due to the elevation operation of the ground operation device by the detection operation, the elevation operation of the ground operation device is stopped when the elevation operation time by the detection operation reaches a preset value. In the state, when the receiving unit cannot receive the reference light beam, the control operation is set so that the ground working device is raised to a preset height and stopped , and the operation and effect are as follows. It is on the street.
[0007]
A second feature of the present invention (claim 2) is that a receiving unit that receives a reference light beam transmitted in a horizontal direction from a transmitting unit that is grounded on the ground is provided to a ground working device that is provided to be able to move up and down with respect to a vehicle body. In addition to the above, a reference light incident target position is set at an intermediate position in the vertical direction with respect to the receiving unit, and when the reference light is incident above the incident target position, the ground operation device is raised and the incident A work height for performing a control operation of lowering the ground work device when the reference light beam is incident on the lower side of the target position, and stopping the elevation operation of the ground work device when the reference light beam is incident on the incident target position. Control device,
When the receiving unit falls into a situation where the reference beam cannot be received, the incident position of the reference beam to the receiving unit immediately before entering the situation is determined, and it is determined that the incident position is above the incident target position. The control direction is set so that the work equipment is raised and the ground work equipment is lowered when the work equipment is on the lower side, and the elevation speed of the ground work equipment is increased as the deviation between the incident position and the incident target position is larger. Set the speed and perform the detection operation,
If the receiving unit cannot receive the reference light beam due to the elevation operation of the ground operation device by the detection operation, the elevation operation of the ground operation device is stopped when the elevation operation time by the detection operation reaches a preset value. In the state, when the receiving unit cannot receive the reference light beam, the control operation is set so that the ground working device is raised to a preset height and stopped , and the operation and effect are as follows. It is on the street.
[0008]
[Action]
According to the first feature, in the state where the reference light beam is received by the receiving unit, the ground work device is raised and lowered in a direction in which the reference light beam is received at the incident target position, so that the ground work device has a ground height. Height can be maintained at the target height, and when the receiving unit falls into a situation where the reference beam cannot be received, the position where the reference beam is incident on the receiving unit immediately before the situation where the receiving beam cannot be received. In addition to setting the vertical direction of the ground working device based on the target and the incident target, the detecting operation is performed by setting the vertical speed of the ground working device based on the deviation between the incident position of the reference light beam and the incident target. .
[0009]
In other words, for example, when the posture of the vehicle body changes greatly in a short time, such as when working in a rough field, the deviation between the incident position and the incident target immediately before the reference beam falls into a state where reception is not possible. By operating the ground work device at a high speed, the time required to receive the reference light beam at the receiving unit is shortened.For example, in a control state in which the ground work device is raised and lowered by a small amount, the reference light beam is blocked by rain. When the reference beam cannot be received temporarily as in the case where the reference beam immediately before entering the unreceivable state has a small deviation between the incident position and the incident target, so the ground working device is slightly moved up and down at a low speed. The reference light beam can be received, and the ground work apparatus does not need to be moved up and down greatly.
[0010]
Then, when the reference light beam cannot be received by the detection operation, the ground operation device is raised and lowered by a predetermined lifting and lowering operation amount and stopped, thereby suppressing useless lifting and lowering operation.
Further , according to the second feature, when the reference light beam cannot be received by the detection operation, the ground work device is raised and lowered for a preset time and stopped, thereby suppressing useless lifting operation.
[0011]
Further, if the reference light beam cannot be received within a set time in a state where the lifting and lowering of the ground work device is stopped after the detection operation, the ground work device is determined based on the reference light, such as the vehicle body being located at an abnormal level. It is considered that there was a situation in which control to raise and lower the vehicle was not possible, or a situation in which the reference beam could not be transmitted due to a failure on the transmitter side.Therefore, the work load on the vehicle body was increased by raising the ground work equipment to the set height. At the same time, the worker can recognize that proper work is not being performed due to the rise of the working device.
[0012]
〔The invention's effect〕
Therefore, according to the first and second aspects of the present invention, even if the reference light beam cannot be received, the control device can detect the reference light beam in a short time and shift to the lifting / lowering control of the ground working apparatus based on the reference light beam. The device was configured. When the reference beam cannot be received, wasteful lifting energy is reduced by suppressing useless elevating operation, and when control based on the reference beam is impossible, the load on the engine is reduced while the load is improperly determined. By raising the ground working device to a proper working height, the worker is made aware that the work is impossible, and the wasteful working time is reduced.
[0013]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
As shown in FIG. 1, an engine 4 is mounted on a front portion of a traveling body 3 having a front wheel 1 and a rear wheel 2, and power from the engine 4 is transmitted to front and rear wheels 1 and 2 at a rear position of the traveling body 3. A transmission case 5 is provided. A steering handle 6 and a driver's seat 7 are provided at a central position of the traveling vehicle body 3, and a leveling blade 9 as a ground working device is provided at a rear end position of the traveling vehicle body 3 via a link mechanism 8 so as to be able to move up and down. To form an agricultural tractor.
[0014]
A lift cylinder 10 as an actuator is arranged at the upper part of the transmission case 5. A pair of left and right lift arms 11, which are operated by the lift cylinder 10, are connected to the link mechanism 8 via a lift rod 12. The lift cylinder 10 is operated to lift and lower the leveling blade 9, and a potentiometer type is provided at the base end of the lift arm 11 for measuring the height of the rotary tillage device 9 with respect to the vehicle body from the swing amount of the lift arm 11. , And a level sensor S as a receiving unit is provided on the upper surface of the grading blade 9 via a support post 14.
[0015]
A position lever 15 for controlling the elevation of the ground leveling blade 9 is disposed on the side of the driver's seat 7, and a potentiometer type position setting device for measuring the operation position of the lever 15 is provided at the base end of the position lever 15. 16 is provided. When raising and lowering the leveling blade 9 in the position control mode, the lift arm sensor 13 detects that the lift arm 11 has moved up and down to a position corresponding to the set position of the lever 15 by manually operating the position lever 15. The operation of driving the lift cylinder 10 is performed until the measurement is performed.
[0016]
As shown in FIG. 2, the level sensor S includes a large number of photodiodes, phototransistors, and the like over a region of about 250 millimeters in a vertical direction with respect to three or more parts in the circumferential direction of the outer surface of the case 21 in the vertical posture. By arranging the light receiving elements 22 in a strip shape, the laser beam L as a reference light beam can be received even if it is incident from any direction on the horizontal plane, and the receiving position is set to about 5 mm in the vertical direction. It has the capability of sensing at a resolution and is configured to convert the sensing result into a voltage signal and output it. In the level sensor S, a reception area Z is formed in a vertical region in which the light receiving elements 22 are arranged, and an incident target position A is set at an intermediate position of the reception area Z.
[0017]
As shown in FIG. 1, a laser lighthouse T is configured as a transmitting unit that horizontally sends out a laser beam L to be received by the level sensor S. The laser lighthouse T has a beam shape on a main body 24 supported by a tripod 23. A light emitting source (not shown) for transmitting the laser light L in the horizontal direction, and a reflecting mirror or a prism in the main body 24 is rotated around a vertical axis Y to form a beam from the light emitting source. An electric motor (not shown) for turning the laser light L is provided. As the laser lighthouse T, either a laser light L that rotates 600 times per minute (600 rpm) or a laser light L that rotates 300 times per minute (300 rpm) is used.
[0018]
As shown in FIG. 4, a control system for controlling the elevation of the grading blade 9 by including a control device 25 having a microprocessor is formed. In this control system, a potentiometer type level setter 27 operated by a dial 26, a potentiometer type sensitivity setter 29 operated by a dial 28, and a position An input system for signals from the lift arm sensor 13 and the activation switch 30 is formed, and an output system for each of the electromagnetically operated control valve V for controlling the lift cylinder 10, the display device D, and the buzzer 31 is formed. ing. The control valve V is of a so-called electromagnetic proportional type that obtains an opening corresponding to the current value supplied to the electromagnetic solenoid, and the control device 25 is provided with an electromagnetic solenoid (not shown) of the control valve V. The power supplied to the control valve V can be adjusted by changing the duty ratio of the supplied intermittent signal (PWM type control). The display device D includes a neutral lamp 32, a rising lamp 33, a descending lamp 34, and a working state lamp 35, as shown in FIG.
[0019]
When performing the work, the leveling height of the leveling blade 9 is set to a target value by operating the position lever 15, and in this state, the incident target A set at the center of the level sensor S in the vertical direction is set. By turning on the start switch 30 by adjusting the ground height of the laser lighthouse T so that the laser light L from the laser lighthouse T is incident, even if the height of the leveling blade 9 fluctuates slightly during work. As a result of the control device 25 operating the control valve V to receive the laser beam L at the incident target position A of the level sensor S and raising and lowering the leveling blade 9, it is possible to level a wide field with high accuracy on a horizontal plane. The lifting control operation will be described below.
[0020]
That is, the basic operation of the control operation is set as shown in the flowchart of FIG. 5, and when this control is started, the incident target position A in the level sensor S is set based on the signal from the level setter 27, and the sensitivity is set. Processing for setting the control sensitivity based on the signal from the setting unit 29 is performed (# 101, # 102 steps). Specifically, when the dial 26 of the level setting device 27 is set to the “standard” position, as shown in FIG. Is the incident target position A, and when the dial 26 of the level setting device 27 is operated to the "deep" side, the incident target position A is displaced upward with respect to the position H as shown in FIG. When the dial 26 of the level setting device 27 is operated to the “shallow” side, the control operation of the control device 25 is set so that the incident target position A is displaced downward with respect to the position H, contrary to the above. When the dial 28 of the sensitivity setting device 29 is set to the "standard" position, as shown in FIG. The width U of the dead zone becomes a standard value. When 28 is set to the "sensitive" position, as shown in FIG. 3B, the width U of the dead zone formed based on the incident target position A is reduced, and the dial 28 of the control sensitivity setting device 29 is turned. When the position is set to the “dull” position, the control operation of the control device 25 is set so that the width U of the dead zone formed based on the incident target position A is increased, contrary to the above.
[0021]
Next, it is determined whether or not the level sensor S is receiving the laser beam L. If the laser beam L is being received, an ascending / descending operation routine is executed, and the operation status of the grading blade 9 is displayed on the display device D. (Steps # 103, # 200, # 104). The raising / lowering operation routine (step # 200) is set in a subroutine as shown in FIG. 6, and the operation is such that the position where the laser beam L is received by the level sensor S is formed based on the incident target position A. It is determined whether it is within the range of U. If it is within the range, no elevation control is performed. If it is outside the range, the voltage value (target voltage value) corresponding to the incident target position A and the level sensor S The deviation direction and the deviation are determined from the comparison with the detected value (detected voltage value), and the operating direction of the lift cylinder 10 is set from the deviation direction, and the opening of the control valve V is set from the deviation (# 201 to # 201). # 205 step). Further, the proportionality is set so that the opening degree of the control valve V becomes larger as the deviation is larger. When setting the opening degree, the ON time of the intermittent signal for driving the solenoid valve V is adjusted (the duty ratio is adjusted). When the ON time of the intermittent signal is prolonged, the opening of the control valve V increases and the elevating speed increases, and when the ON time is shortened, the opening of the control valve V decreases. As a result, the elevating speed decreases.
[0022]
In addition, when the level sensor S receives the laser beam L and the proper ascent / descent control is performed as described above, the work state lamp 35 of the display device D is continuously lit, and the elevating / lowering of the terrain blade 9 is performed. Is stopped, the neutral lamp 32 is lit, the ascending lamp 33 is lit when the grading blade 9 is ascending, and the descending lamp 34 is lit when the grading blade 9 is ascending, and the operating status is given to the worker. Is recognized (the process of step # 104).
[0023]
Next, when it is determined in step # 103 that the laser beam L has not been received, before the elapse of 10 seconds after falling into the unreceivable state, a set time (less than 1 second) after falling into the unreceivable state The detection operation routine is performed until the elapse of a short period of time, or until the lift arm sensor 13 measures that the lift arm 11 has been operated by a set amount (to the extent that it does not reach the operation limit) after falling into the reception disabled state. Then, the display operation is performed by the display device D (# 105 to # 107, # 200, and # 108 steps).
[0024]
The detection operation routine is set in the form of a subroutine as shown in FIG. 7. In this processing, the reception position of the level sensor S immediately before the reception becomes impossible is determined, and the reception position and the incident target position A are compared. It is determined whether the receiving position is within the dead zone U formed with reference to the incident target position A. If the receiving position is within the range, the elevation control is not performed. The deviation is obtained, and the operation direction of the lift cylinder 10 is set based on the deviation direction, and the opening of the control valve V is set based on the deviation (steps # 301 to # 306), similarly to the above-described elevating operation routine. That is, the detection operation is a process for receiving the laser beam L by the level sensor S in the elevation control in the direction in which the laser beam L is presumed to be present. It is determined whether the incident position of the laser light L on the level sensor S immediately before the laser beam L has been received has been received on the upper end side or the lower end side of the sensing area Z of the level sensor S. If the signal is received at the upper end of Z, the laser light L is likely to be present above the level sensor S, so the terrain blade 9 is actuated upward, and conversely, received at the lower end of the sensing area Z. In this case, the operation direction is set so as to operate the grading blade 9 on the descending side, and the larger the deviation between the receiving position and the incident target position A, the higher the speed at which the laser is moved up and down. Light L It has become a thing that may be received.
[0025]
When the detection operation is performed in this manner, the operation state lamp 35 of the display device D is switched to a blinking state, so that the operator can recognize that the laser beam L is in a state in which reception is impossible, and at the same time, By turning on the neutral lamp 32, the ascending ramp 33, or the descending ramp 34 in accordance with the operation of the leveling blade 9, the operator can recognize the operation state of the leveling blade 9 (step # 108). Processing).
[0026]
When the laser beam L is received by the level sensor S by the processing of this detection operation routine, the flow proceeds from step # 103 to step # 200 (elevation operation routine) and shifts to an appropriate processing. . Conversely, if the set time of step # 106 has elapsed, or if any of the conditions of operation by the set amount of step # 107 is satisfied, the control valve V is set to the neutral position and the leveling blade is set. Only when the raising and lowering of the landslide 9 is stopped and the process of lowering the landslide blade 9 until the stop is performed is performed, the returning process of raising the landslide blade 9 by の of the descending amount is performed, and the display device D (Steps # 109 to # 111).
[0027]
This processing is to suppress excessive raising and lowering of the leveling blade 9, and to avoid a situation where the leveling blade 9 is maintained at a position deeper than the target plowing depth when the leveling blade 9 is lowered and stopped. In order to avoid overloading the engine 4, the leveling blade 9 is raised by 1/2 of the descending amount. When the lifting operation is stopped in this way, the operating state of the display device D By switching the ramp 35 to the blinking state and blinking the ascending ramp 33 and the descending ramp 34 at the same time, the operator can recognize that the elevation of the terrain blade 9 has stopped (step # 111). . These processes are continued until reset (# 112 step).
[0028]
Next, when the state in which the laser beam L cannot be received by the level sensor S has passed for 10 seconds (at this time, the elevation of the grading blade 9 is stopped), the grading blade 9 is forcibly moved to the upper limit at a high speed. In addition to performing the raising process, the display device D performs the display operation and performs the alarm operation by the buzzer 31. After that, even if the laser beam L is incident on the level sensor S, the lifting operation is not performed. ing.
[0029]
That is, when the state in which the laser beam L cannot be received continues for 10 seconds or more, it is possible to determine that the laser lighthouse T is out of order or that the field is at an inappropriate height for the work. Work is stopped for the purpose of suspending the work and for the purpose of eliminating the harmful effect that the leveling blade 9 is set and maintained at an inappropriate height for an extended period of time. By raising at a relatively high speed, the worker can feel the shock at the time of stopping the lifting, and can sense that the work has been interrupted. When the leveling blade 9 is forcibly raised, the operating state lamp 35 and the ascending lamp 33 of the display device D are simultaneously blinked, and even after the forcible ascent, the display state is continued. By operating the buzzer 31, the operator can visually and audibly recognize that the leveling blade 9 has been forcibly controlled to rise in addition to the above-described bodily sensation.
[0030]
As described above, according to the present invention, when the level sensor S cannot receive the laser light L, the lifting operation to the side for detecting the laser light L for a short time or a predetermined amount immediately before the reception becomes impossible. Since the detection is performed at a speed based on the deviation of the receiving position, quick detection is enabled. When the laser light L can be detected by this detection operation, the control is shifted to an appropriate control operation to perform the control. If the laser beam L cannot be received by the level sensor S even by the raising and lowering operation for this detection, the leveling blade 9 can be operated after a set time (10 seconds) has elapsed. Is raised at a high speed to the upper limit, so that the inconvenience that the leveling blade 9 is maintained at an improper height can be quickly avoided, and at the same time, the operator can feel the shock caused by the raising operation of the leveling blade 9 and feel the laser It becomes easy to recognize that the reception of the laser beam L has been disabled, and furthermore, it is inevitable for the operator to disable the reception of the laser beam L by the blinking of the lamp of the display device D and the operation of the buzzer 31. It is recognizable.
[0031]
[Another embodiment]
In the present invention, in addition to the above-described embodiment, for example, a rotary tillage device, a plow, or the like can be used as a ground working device.
[0032]
Further, as the control mode, the opening degree of the control valve V corresponding to the deviation in the lifting operation routine and the opening degree of the control valve V corresponding to the deviation in the detection operation routine may be the same. It is possible to set the opening degree of the control valve V in the detection operation routine to be larger than the opening degree of the control valve V in the elevating operation routine, or to set the opening degree to be the opposite relation.
[Brief description of the drawings]
FIG. 1 is a side view of a tractor in a working state; FIG. 2 is a perspective view of a level sensor; FIG. 3 is a side view showing a relationship between an incident target position of the level sensor and a dead zone with respect to operation positions of a level setting device and a sensitivity setting device. FIG. 4 is a block diagram of a control system. FIG. 5 is a flowchart of a control operation. FIG. 6 is a flowchart of a lifting operation routine. FIG. 7 is a flowchart of a notification operation routine.
3 Body 9 Ground work equipment A Incident target L Reference ray S Receiver

Claims (2)

A receiving unit (S) for receiving a reference light beam (L) transmitted in a horizontal direction from a transmitting unit (T) grounded to the ground with respect to a ground working device (9) provided to be able to move up and down with respect to the vehicle body (3). And an incident target position (A) of the reference light beam (L) is set at an intermediate position in the vertical direction with respect to the receiving unit (S), and the reference light beam (L) is located above the incident target position (A). When the light is incident, the ground operation device (9) is raised, and when the reference light beam (L) is incident on the lower side of the incident target position (A), the ground operation device (9) is lowered, A work height control device for performing a control operation for stopping the elevation operation of the ground work device (9) when the reference light beam (L) is incident on the incident target position (A);
When the receiving unit (S) falls into a situation where the reference beam (L) cannot be received, the incident position of the reference beam (L) to the receiving unit (S) immediately before entering the situation is determined, and the incident position is determined. The control direction is set so that the ground working device (9) is raised when the position is above the target incident position (A), and the ground working device (9) is lowered when the position is below the target position (A). and have rows detection operation by setting the control speed to increase the lifting speed of the incident target position (a) as the ground work apparatus deviation is large and (9),
If the receiving unit (S) cannot receive the reference light beam (L) due to the lifting / lowering operation of the ground work device (9) by the detection operation, the ground work is performed when the amount of vertical movement by the detection operation reaches a preset value. When the lifting and lowering of the device (9) is stopped, and the receiving unit (S) cannot receive the reference light beam (L) in this stopped state, the ground work device (9) is raised to a preset height and stopped. Work height control device in which the control operation is set . A receiving unit (S) for receiving a reference light beam (L) transmitted in a horizontal direction from a transmitting unit (T) grounded to the ground with respect to a ground working device (9) provided to be able to move up and down with respect to the vehicle body (3). And an incident target position (A) of the reference light beam (L) is set at an intermediate position in the vertical direction with respect to the receiving unit (S), and the reference light beam (L) is located above the incident target position (A). When the light is incident, the ground operation device (9) is raised, and when the reference light beam (L) is incident on the lower side of the incident target position (A), the ground operation device (9) is lowered, A work height control device for performing a control operation for stopping the elevation operation of the ground work device (9) when the reference light beam (L) is incident on the incident target position (A);
When the receiving unit (S) falls into a situation where the reference beam (L) cannot be received, the incident position of the reference beam (L) to the receiving unit (S) immediately before entering the situation is determined, and the incident position is determined. If the position is above the target incident position (A), the control direction is set so that the ground work device (9) is raised, and if the position is below the target target position (A), the ground work device (9) is lowered. The detection operation is performed by setting the control speed so that the deviation between the ground work device (9) and the incident target position (A) is increased as the deviation becomes larger.
If the receiving unit (S) cannot receive the reference light beam (L) due to the elevation operation of the ground work device (9) by the detection operation, the ground operation is performed when the elevation operation time by the detection operation reaches a preset value. When the lifting and lowering of the device (9) is stopped, and the receiving unit (S) cannot receive the reference light beam (L) in this stopped state, the ground work device (9) is raised to a preset height and stopped. Work height control device in which the control operation is set .

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