JP3378455B2 - Height control device for ground work equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a receiver for receiving a reference light beam horizontally transmitted from a transmitter installed on the ground with respect to a ground work device which is vertically movable with respect to a vehicle body. In addition to the height control device for the ground work device, the height control device for lifting and lowering the ground work device is provided so that the reference light beam is incident on the incident target position set at an intermediate position in the vertical direction of the reception unit. It relates to the control operation when the ray cannot be received.

[0002]

2. Description of the Related Art Conventionally, as a height control device for a ground working device constructed as described above, there is one disclosed in Japanese Patent Publication No. Sho 62-25824, and in this prior art example, a receiver (light receiver) is used as a reference. If you can no longer receive the light beam (laser light),
The height of the ground work device (blade) is fixed to a level before receiving the reference light (laser light) for a set time.

[0003]

In the conventional example, when the reference light beam is blocked, the raising / lowering operation is temporarily stopped so that the ground height of the ground working device is lowered too much or rises too much. In addition to avoiding it, the elevation control can be restarted when the reference light beam is received again. However, the conventional transmitter that emits the reference beam is installed on the ground via a tripod, etc., and it may not be able to emit the reference beam when it falls due to the wind. Depending on the case, the reference ray may not be emitted. Further, the vehicle body equipped with the ground work device does not always run on a flat ground, and the receiving unit cannot receive the reference light beam due to a large inclination of the vehicle body at the uneven surface of the ground. Therefore, it is desired to perform appropriate control even in such a situation.

That is, as in the conventional example, the situation in which the receiving unit cannot receive the reference light beam after the elevating operation of the ground work device is stopped for a predetermined time in the situation in which the receiving unit cannot receive the reference light beam is continued. In such a case, for example, even if control is performed to maintain the state in which the lifting and lowering of the ground work device is stopped, if this state is continued for a long time, proper level control cannot be performed and there is room for improvement. In particular, considering the case where the receiving section moves up and down largely due to the inclination of the vehicle body and falls into the state where the reference ray is located above or below the receiving section, the receiving section receives the reference ray as in the conventional example. If the lifting / lowering operation of the ground work device is stopped for a predetermined time when it becomes impossible, the height of the ground work device is kept out of an appropriate height, and there is room for improvement.

An object of the present invention is to rationalize a control device that raises and lowers a ground work device based on a reference light beam as described above, and makes it possible to take appropriate measures when the reference light beam cannot be received. The point is to configure.

[0006]

The first feature of the present invention (Claim 1) is that it can be raised and lowered with respect to the vehicle body as described at the beginning.
With a receiving portion for receiving the outgoing criteria beam horizontally from the transmitting portion installed on the ground relative to the ground work apparatus coupled to the vertical direction of the intermediate position of the receiving section
So that the reference beam is incident on the incident target position that is set to
A height control device of the ground work apparatus that performs lifting of the ground work apparatus, originating on the reference ray from the transmitter unit如
In the receiving section, it is possible to know what cycle the call was sent from.
It is determined by the incident cycle of the incident reference light and it is also determined that the reference light cannot be received by the receiving unit.
A discriminating unit is provided, and the incident period discriminated by the discriminating unit is
Control mode setting means for setting the control mode based on
And a notification unit for notifying that the reference light beam cannot be received based on the determination result of the determination unit , and its operation is as follows.

A second feature of the present invention (claim 2) is that in claim 1, when the discriminating means cannot receive the reference ray at the receiving portion, the reference ray for the receiving portion immediately before being unable to receive it. When the incident position of is above the incident target position, the ground work device is raised, and when it is below the incident target position, the ground work device is lowered for a predetermined time or a predetermined stroke. The processing unit is configured to determine that the reference light beam cannot be received when the reception unit cannot receive the reference light beam even by the detection control, and its operation is as follows.

A third feature of the present invention (claim 3) resides in that, in claim 1, the notifying means is composed of a processing device which raises the ground work device to an upper limit at high speed. Is as follows.

According to a fourth aspect of the present invention (claim 4), in the control according to claim 3, the discriminating means discriminates that the reference ray cannot be received and the processing device raises the ground work device to the upper limit. When the reference beam is received by the receiving unit during the operation, it is equipped with restarting means for restarting the elevation of the ground work device based on the reference beam, and its action is as follows. is there.

A fifth feature of the present invention (claim 5) is that in claim 1, the notifying means stops the engine of the vehicle body or operates a transmission for traveling the vehicle body to a neutral position. The processing device is configured to perform control for stopping the traveling of the vehicle body, and its operation is as follows.

A sixth feature of the present invention (claim 6) resides in that, in claim 1, the notifying means is composed of a voice generating mechanism such as a buzzer and a speaker. The operation is as follows. is there.

A seventh feature of the present invention (claim 7) resides in that, in claim 1, the notifying means is constituted by a display mechanism such as a lamp and a liquid crystal display, and its operation is as follows. is there.

[Operation] According to the first feature, when the receiving unit cannot receive the reference light beam, the determining unit determines that the state is in this state, and the notifying unit determines based on the determination result. By performing the notification operation, the worker can recognize that the reference light beam cannot be received.

According to the above-mentioned second feature, for example, when the vehicle body is greatly tilted in a short time and the reference ray cannot be received by the receiving section, the reference ray is upward from the incident target position, or Since it is in the unreceivable state after it is displaced to the lower side, when the unreceivable state is entered, the receiving position in the receiving section immediately before that is either the upper side or the lower side from the incident target position. It is possible to estimate the direction in which the reference ray exists by discriminating whether or not it is located on the side of. For this reason, according to the second feature, when the receiving part cannot receive the reference light beam due to the inclination of the vehicle body, the detection is performed based on the incident position of the reference light beam to the receiving part immediately before the reception part becomes unable to receive the reference light beam. By performing the control, it becomes possible to receive the reference light beam, and in such a recoverable situation, the notification means is not operated unnecessarily.

According to the third feature, when the receiving unit cannot receive the reference light beam, the ground work device is raised to the upper limit at high speed, so that the unnecessary lifting control of the ground work device is stopped. At the same time, the worker can recognize that the reference light beam cannot be received based on the state where the ground work device is raised to the upper limit.

According to the fourth feature, when the receiving unit cannot receive the reference light beam and the reference light beam is received while the ground work device is being raised to the upper limit, the restarting means is based on the reference light beam. Since the lifting control is restarted, the work is not interrupted.

According to the fifth feature, when the receiving unit becomes unable to receive the reference ray, the processing device stops the engine or operates the transmission to the neutral position. Since the traveling is stopped, the worker can inevitably understand that the receiving unit cannot receive the reference light beam.

According to the sixth feature, when the receiving unit cannot receive the reference light beam, the receiving unit disables the reference light beam based on the sound from the sound generating mechanism including a buzzer and a speaker. You will be able to understand the situation.

According to the seventh feature, when the receiving unit cannot receive the reference light beam, the receiving unit disables the reference light beam based on the display contents of the display mechanism including a lamp, a liquid crystal display and the like. You will be able to understand the situation.

[0020]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, an engine 4 is mounted on a front portion of a traveling vehicle body 3 having front wheels 1 and rear wheels 2, and power from the engine 4 is applied to front and rear wheels 1 and 2 at a rear portion of the traveling vehicle body 3. The transmission case 5 is provided, the steering wheel 6 and the driver's seat 7 are provided at the center of the traveling vehicle body 3, and the grounding blade 9 as a ground work device is provided at the rear end position of the traveling vehicle body 3 via the link mechanism 8 so as to be vertically movable. To form an agricultural tractor.

A lift cylinder 10 as an actuator is arranged above the mission case 5, and a pair of left and right lift arms 11 which are vertically moved by the lift cylinder 10 and the link mechanism 8 are provided via a lift rod 12. The landing blade 9 can be raised and lowered by the operation of the lift cylinder 10 by connecting the lift arm 1 and the lift arm 1.
1 is equipped with a potentiometer-type lift arm sensor 13 for measuring the height of the rotary tiller 9 with respect to the vehicle body from the swing amount of the lift arm 11, and the upper surface of the leveling blade 9 is received via a column 14. A level sensor S as a unit is provided.

A leveling blade 9 is provided on the side of the driver's seat 7.
A position lever 15 for controlling the raising and lowering of the position lever 15 is arranged, and a potentiometer-type position setter 16 for measuring the operating position of the lever 15 is provided at the base end of the position lever 15. When the elevation control of the ground leveling blade 9 is performed in the position control mode, the lift arm sensor 13 indicates that the lift arm 11 is 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.

As shown in FIGS. 2 and 3, a fuel level gauge 21, an engine tachometer 22, a cooling water thermometer 23, and a laser as will be described later are provided on a meter panel 20 in front of the driver's seat 7. A start switch 24 that is turned on when starting the raising / lowering control of the leveling blade 9 using the light L, and a level setter 25 operated by a dial 25D to change the control target by software during the raising / lowering control. , Dial 26 to set the sensitivity of the lifting control during this lifting control.
An alarm lamp 27 constituting a sensitivity setting device 26 operated by D and an informing means E which is activated when the level sensor S cannot detect the laser light L during the elevation control.
And a buzzer 28, and a display device D indicating the operating state of the leveling blade 9 at the time of elevation control using the laser light L is attached to the upper position of the meter panel 20.
Further, the display device D shows that the grounding blade 9 is in a descending operation with respect to the case 29 and the green neutral lamp 30 showing a state where the leveling blade 9 is maintained at an appropriate height and the lifting operation is stopped. It is provided with a red descending lamp 31 and a red ascending lamp 32 indicating that the leveling blade 9 is ascending.

The level sensor S, as shown in FIG.
A laser beam L as a reference light beam which is arranged on a horizontal plane by arranging a large number of light receiving elements 34 in an area of about 250 mm in the vertical direction with respect to the outer surface of the case 33 in the portrait orientation.
It has a capability of sensing the vertical position of the with a resolution of about 5 mm, and is configured to convert the sensing result into a voltage signal and output it.

As shown in FIG. 1, the laser lighthouse T is a main body 3 supported by a tripod 35 as a transmitting portion for horizontally sending out the laser light L to be received by the level sensor S.
6 is provided with a light source (not shown) that horizontally emits a beam-shaped laser beam L, and a reflecting mirror or a prism in the main body 36 is rotated around a longitudinal axis Y to emit light. An electric motor (not shown) for rotating the beam-shaped laser light L is provided. Further, as the laser lighthouse T, either one of two types, that is, one in which the rotation speed of the laser light L is 600 rotations per minute (600 rpm) and one in which the rotation speed is 300 rotations per minute (300 rpm) is used.

As shown in FIG. 5, a control unit 38 having a microprocessor (not shown) built therein is provided to form a control system for controlling the elevation of the leveling blade 9. In this control system, the control unit 38 is provided. On the other hand, the level sensor S, start switch 24, level setting device 25, sensitivity setting device 26, position setting device 16, lift arm sensor 13
An input system for signals from each of them is formed, and an output system for an electromagnetically operated control valve V for controlling the lift cylinder 10, the alarm lamp 27, the buzzer 28, and the display device D is formed. . Further, the control valve V obtains the opening degree corresponding to the current value supplied to the electromagnetic solenoid,
A so-called electromagnetic proportional type is used, and the control device 38 supplies to the control valve V by changing the duty ratio of the intermittent signal supplied to the electromagnetic solenoid (not shown) of the control valve V (PWM type control). It is configured to adjust the power.

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 level sensor S is set at the vertical center. By adjusting the ground height of the laser lighthouse T and turning on the start switch 24 so that the laser light L from the laser lighthouse T is incident on the incident target A, the height of the ground leveling blade 9 changes during the work. Even if the control device 38 receives the laser light L at the incident target position A of the level sensor S, the solenoid valve V is operated to adjust the leveling blade 9.
As a result of raising and lowering, a wide field can be accurately leveled on a horizontal surface, and the raising and lowering control operation will be described below.

As shown in the flow chart of FIG. 6, at the start of control, first, the period of incidence of the laser light L on the level sensor S is discriminated, and control parameters are set based on the discrimination result (# 101, # 102 steps). ).
This control parameter is used to determine which of the above-described two types the turning period of the laser light L emitted from the laser lighthouse T is, and to switch the control mode based on the determination result. The operating speed of the lift cylinder 10 is changed by switching the mode.

That is, when the laser beam L is incident on the level sensor S, the data (value of "1") indicating that the laser beam L is incident is held for about 150 milliseconds and then cleared (" The flag means of the microprocessor and the memory of the control device 38 constitute the memory means M (see FIG. 5) so as to hold the value "0"), and as shown in the timing chart of FIG. When inputting to the sensor S at a cycle of 0.2 seconds (the rotation speed of the laser light L by the laser lighthouse T is 300 rpm), the data in the storage means M is always cleared at the timing when the laser light L is incident. In addition, as shown in the timing chart of FIG.
When the data is input at a cycle of 2 seconds (the turning speed of the laser light L by the laser lighthouse T is 600 rpm), the data in the storage means M is always in the data holding state at the timing when the laser light L is incident. From this, the control device 38 determines the presence or absence of the data in the storage means M at the timing when the laser light L is incident, and if the AND condition is simply satisfied, the incidence period of the laser light L is 0.1 second. If the AND condition is not satisfied, it is determined that the incident period of the laser light L is 0.2 seconds.

The control parameter is that the incident period is 0.1.
In the case of seconds, a large numerical value is given and the incident period is 0.2
In the case of seconds, a control unit 38 is provided so that a small value is given.
Is set, and the duty ratio of the intermittent signal for driving the electromagnetic solenoid of the electromagnetic valve V is set as described later.

Next, the incident target A in the level sensor S is set based on the signal from the level setter 25,
Processing for setting the control sensitivity based on the signal from the sensitivity setting device 26 is performed (steps # 103, # 104). That is, when the dial 25D of the level setter 25 is set to the "standard" position, as shown in FIG. 9A, the vertical position H in the sensing area Z of the level sensor S is 1/2 the incident target. A, and the dial 25D of the level setting device 25
When is operated to the “deep” side, as shown in FIG.
When the incident target A is displaced upward with reference to the position H and the dial 25D of the level setting device 25 is operated to the "shallow" side, the incident target A is reversed with respect to the position H, contrary to the above. When the control operation of the control device 38 is set so as to be displaced downward and the dial 26D of the sensitivity setting device 26 is set to the "standard" position, the incident target A is used as a reference as shown in FIG. In the case where the width U of the dead zone formed in the area equal to the upper side and the lower side has a standard value and the dial 26D of the control sensitivity setting device 26 is set to the "sensitive" position,
As shown in (b), the width U of the dead zone formed on the basis of the incident target A is narrowed, and the dial 2 of the control sensitivity setting device 26 is set.
When 6D is set to the "blunt" position, the control operation of the control device 38 is set to expand the width U of the dead zone formed on the basis of the incident target A, contrary to the above.

Next, it is judged whether or not data (value of "1") is written in the memory means M, and if data (value of "1") is written in the memory means M, level is determined. Since the sensor S is in the state of receiving the laser beam L, the ascending / descending operation routine is executed and the operation status of the ground leveling blade is displayed on the display device (# 105, # 20).
0, step # 106). The lifting operation routine is set in the form of a subroutine as shown in FIG. That is, the operation determines whether or not the detection value of the level sensor S exists within the dead zone U formed with the incident target A as a reference, and when it exists within the dead zone U, the elevation control is not performed, and the operation exists outside the area. In this case, the deviation is obtained from the comparison between the voltage value (target voltage value) corresponding to the incident target A and the detection value (detection voltage value) of the level sensor, and the larger the deviation is, the ON the intermittent signal for driving the solenoid valve V is turned ON. The numerical value of the characteristic for increasing the time is obtained, the above-mentioned parameter is multiplied by the numerical value thus obtained to obtain the duty ratio of the intermittent signal for driving the control valve V, and the intermittent signal of the duty ratio thus obtained is obtained. Is used to drive the control valve V (# 20
1- # 204 steps). Further, the determination means E is configured in the step of determining whether or not the laser light L is received, as in step # 105.

The control parameter is the laser light L.
Lift cylinder 1 when the incident cycle of 0.1 seconds
When 0 is operated at a standard speed and it is determined that the incident period of the laser light L is 0.2 seconds, the control valve V is compared with the case where the incident period of the laser light L is 0.1 second. Is set to 1/2 and the lift cylinder 10 is operated at a speed of 1/2 of the standard speed, and is short when the incident period of the laser light L is 0.1 seconds. The laser light L can be controlled with high accuracy by measuring the laser light L at intervals, and the incident period of the laser light L is 0.
In the case of 2 seconds, the shift cylinder 10 is operated smoothly to enable the operation without generating a shock.

Further, the notification operation in the notification device D is performed by the neutral lamp 3 when the ground leveling blade 9 is not moved up and down.
When 0 is continuously turned on and the control for lowering the leveling blade 9 is being performed, the descending lamp 31 is blinked (may be continuously turned on), and control for raising the leveling blade 9 is performed. In this case, the rising lamp 32 is made to blink (it may be continuously turned on).

Next, when it is determined in step # 105 that the laser light L is not received, specifically, the storage means M is used.
If the data (value of "1") is written in the storage means M and the data (value of "1") is not written in the storage means M (if the value is "0"), If the level sensor S receives the laser beam L in the detection operation for 0.5 seconds or less, the process moves to the control flow for performing the above-described lifting operation routine (# 200 step), and the detection operation is performed. If the level sensor S cannot receive the laser beam L even if the operation is continued for 0.5 seconds or more, the operation of forcibly raising the leveling blade 9 to the upper limit is started (steps # 107 to # 109). In addition, even when this forcible ascending operation is performed, it is determined whether the level sensor S receives the laser beam L by the same processing as in step # 105.
When the level sensor S receives the laser beam L during the ascending operation, the ascending / descending operation routine (# 200
If the level sensor S does not receive the laser light L during the ascending operation, the lift arm sensor 13 detects that the leveling blade 9 has reached the upper limit at the timing when the lift arm sensor 13 detects the lift. Cylinder 10
Is stopped, the alarm lamp 27 is turned on, the buzzer 28 is operated, and the descending lamp 31 and the ascending lamp 30 of the display device D are simultaneously blinked. These controls are continued until they are reset. (Steps # 110 to # 114).

That is, the detection operation is a control operation for receiving the laser light L by the level sensor S by performing the elevation control in the direction in which the laser light L is presumed to exist, and the control operation is the level sensor S. It is determined whether the incident position of the laser light L on the level sensor S immediately before the laser light L cannot be detected is the upper end side or the lower end side of the sensing area Z of the level sensor S that is detecting the laser light L. However, for example, when it is detected at the upper end side of the sensing area Z, there is a high possibility that the laser light L exists above the level sensor S, so the leveling blade 9 is actuated to the ascending side, and conversely When it is detected at the lower end side of Z, the control operation is set to operate the leveling blade 9 on the lower side, and when the level sensor S receives the laser beam L by this detection operation, If the laser beam L cannot be detected even if the raising / lowering operation routine is performed and the detection operation is continued for 0.5 seconds, the solenoid valve V is set to the front open state regardless of the value of the control parameter. Then, the lift cylinder 10 is operated in the ascending direction at the highest speed, and is stopped when the grounding blade 9 reaches the upper limit position by the signal from the lift arm sensor 13, which causes a slight shock to the operator. On the other hand, let's feel the abnormal occurrence by feeling,
At the same time, the alarm lamp 27 is turned on and the buzzer 2
8 is activated to blink the descending lamp 31 and the ascending lamp 30 of the display device D at the same time, so that the occurrence of abnormality can be visually and audibly recognized.

When the position lever 15 is operated to adjust the height of the grounding blade 9 with respect to the vehicle body, the descending lamp 31 of the display device D, or
By blinking any of the rising lamps 32, it is possible for the operator to recognize that the position control mode is in effect.

As described above, in the present invention, the level sensor S
When the laser beam L cannot be received by the control, the operation for detecting the laser beam L is performed for a short time, and when the laser beam L can be detected by this detection operation, the control is performed by shifting to an appropriate control operation. If the level sensor S cannot receive the laser beam L even by this detection operation, the leveling blade 9 is raised to the upper limit at a high speed, so that the leveling blade 9 is unsuitable. The user can easily recognize that the laser beam L cannot be received because the operator can feel the shock caused by the ascending operation of the grounding blade 9 while avoiding the state in which the laser beam L is set. , And the alarm lamp 2
7, the blinking of the buzzer 28 and the lamp of the display device D inevitably allows the operator to recognize that the laser beam L cannot be received. The control device 38 that performs the control operation of raising the leveling blade 9 to the upper limit in this way is also used as the processing device as the notification unit F.

[Other Embodiments] In addition to the above-described embodiments, the present invention can use, for example, a rotary tiller, a plow or the like as a ground work device.

Further, in the present invention, when the laser beam L cannot be received by the level sensor S as the receiving section, the engine 4 of the vehicle body 3 is stopped as an informing means for informing of this situation, or Mission case 5
By forcibly operating the shift position of the vehicle to the neutral position, the vehicle body 3
It is also possible to configure with a processing device that stops the traveling of.

Further, according to the present invention, the notifying means can be composed of a liquid crystal display for outputting characters and images, and the notifying means can receive the reference light beam in human words by using a PCM sound source or the like. It is also possible to be configured to notify that the disabled state has been entered.

Further, in the present invention, the ground leveling blade 9 is based on the signal from the lift arm sensor 13 for performing the detection operation.
It is also possible to set the control operation so as to move up and down by a preset stroke.

[0043]

Therefore, the control device is reasonably configured so that the operator can appropriately recognize that the situation where the reference light beam cannot be received based on the notification operation of the notification means and take appropriate action. There is (claim 1). Also, if it is possible to return to proper control such as when the reference beam cannot be received due to the tilt of the vehicle body, the reference beam is actively detected and proper control is performed in a short time. It becomes possible to return (claim 2), and by raising the ground work device to the upper limit, it makes sure that the worker can recognize that the reception of the reference light beam has become impossible, and at the same time work at an incorrect height. (Claim 3), when the receiving part receives the reference light beam when raising the ground work device in this way, the control moves to the elevation control based on the reference light beam and returns to the proper control. (Claim 4), which surely makes the operator aware that the reception of the reference ray has become impossible due to the stop of the traveling of the vehicle body, and at the same time avoids the work at an incorrect height. Next (Claim 5), from the voice generating mechanism That it's impossible reception of the reference beam on the basis of the voice reliably recognized to those with it to workers (Claim 6),
The worker can be made sure to recognize that the reception of the reference light beam from the display content of the display mechanism has become impossible (claim 7).

[Brief description of drawings]

FIG. 1 is a side view of a tractor in a working state.

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

FIG. 3 is a plan view showing an arrangement of control system operating devices.

FIG. 4 is a perspective view of a level sensor.

FIG. 5 is a block circuit diagram of a control system.

FIG. 6 is a flowchart of control operation

FIG. 7 is a flowchart of a lifting operation routine.

FIG. 8 is a timing chart showing a relationship between two types of laser light reception periods and a signal of a storage unit.

FIG. 9 is a side view showing a relationship between an incident target position of the level sensor and a dead zone with respect to operating positions of the level setting device and the sensitivity setting device.

[Explanation of symbols]

3 car body 4 engine 9 Ground work device 27 Display mechanism 28 Voice generation mechanism A incident target position E discrimination means F notification means S receiver L reference ray T transmitter

Claims (7)

(57) [Claims] 1. A receiving unit for receiving a reference light beam horizontally transmitted from a transmitting unit installed on the ground with respect to a ground work device that is vertically movable with respect to a vehicle body, and the receiving unit. is a height control device of the ground work apparatus that performs lifting of the ground work apparatus so that the vertical direction of the reference light beam to the incident target position is set to an intermediate position is incident, originating on the reference ray from the transmitter unit Departure at what cycle
The reference light that is incident on the receiving unit to determine whether it is received
Equipped with a discrimination means for discriminating according to the incident period of the rays and determining that the reference ray cannot be received by the receiving section.
The control mode is based on the incident period determined by the determining means.
A height control device for a ground work device , comprising: a control mode setting means for setting a mode; and a notifying means for notifying that reception of a reference light beam has become impossible based on the discrimination result of the discrimination means . 2. When the discriminating unit cannot receive the reference light beam at the receiving unit, when the incident position of the reference light beam to the receiving unit immediately before being unable to receive is above the incident target position, it is grounded. When the work device is raised and the ground work device is lowered when the position is below the incident target position, the detection control is performed for a predetermined time or for a predetermined stroke, and the reference beam cannot be received by the receiving unit even by this detection control. The height control device for a ground work device according to claim 1, wherein the height control device comprises a processing device that determines that the reference light beam cannot be received. 3. The height control device for a ground work device according to claim 1, wherein said notifying means is constituted by a processing device for raising said ground work device to an upper limit at high speed. 4. When the reference unit receives the reference light beam during the control operation for raising the ground work device to the upper limit by the processing device by determining that the reference light beam cannot be received. 4. The height control device for a ground work device according to claim 3, further comprising restarting means for restarting the lifting and lowering of the ground work device based on the reference light beam. 5. The informing means is constituted by a processing device for stopping the traveling of the vehicle body such as stopping the engine of the vehicle body or operating a transmission for traveling the vehicle body to a neutral position. The height control device for a ground work device according to claim 1. 6. The height control device for a ground work device according to claim 1, wherein said notifying means is constituted by a voice generating mechanism such as a buzzer and a speaker. 7. The height control device for a ground work device according to claim 1, wherein the notifying means comprises a display mechanism such as a lamp or a liquid crystal display.