JP4120053B2 - Fluid pressure cylinder, moving body position detection device, industrial vehicle and forklift - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fluid pressure cylinder, a moving body position detection device, an industrial vehicle equipped with the position detection device, and a forklift.
[0002]
[Prior art]
As a forklift, there has been proposed a forklift provided with an automatic control device that automatically moves the fork up and down to a preset lifting position. This type of automatic control device requires a lift detection sensor that continuously detects the lift position of the fork.
[0003]
2. Description of the Related Art Conventionally, a wire take-up reel type sensor is known as a lift detection sensor that can continuously detect a lift. The reel type sensor detects a rotational displacement amount of a reel biased in a rotational direction for winding a wire having a tip connected to an inner mast by a rotational displacement sensor such as a potentiometer.
[0004]
[Problems to be solved by the invention]
However, the reel type sensor has a functional part such as a wire exposed to the outside due to its structure. Therefore, it is easy for an obstacle to hit the wire in the cargo handling operation, the potentiometer may be damaged, or the wire may be cut, and the reliability is not sufficient.
[0005]
In order to solve such a problem, the present applicant has proposed a lift detection device that detects a piston position using an ultrasonic sensor built in a lift cylinder and obtains a lift position from the detected value. Yes. That is, ultrasonic waves are transmitted from the ultrasonic element provided in the lower end of the cylinder body of the lift cylinder toward the end face of the piston, and the ultrasonic waves reflected by the end face of the piston are received again by the same ultrasonic element. Then, as shown in FIG. 5, the distance to the piston, that is, the piston position, is obtained from the elapsed time from the time when the ultrasonic wave is transmitted from the ultrasonic element to the time when the reflected wave is received. Further, the lift position of the fork is obtained from the obtained piston position. According to such an elevation detection device, unlike the reel type sensor, the functional part is hardly damaged, and the reliability is improved.
[0006]
By the way, in order to transmit ultrasonic waves from the ultrasonic sensor, if an oscillation signal is applied to the ultrasonic transducer of the ultrasonic sensor to cause ultrasonic vibration, the ultrasonic transducer's ultrasonic wave can be transmitted even after the application of the oscillation signal is stopped. It is known that the sonic vibration does not stop immediately and there is reverberation that continues for a predetermined time while the ultrasonic vibration is attenuated.
[0007]
As shown in FIG. 5, while the reverberation is present in the ultrasonic vibrator, a voltage signal is generated by the ultrasonic vibration. Therefore, if the reflected wave of the ultrasonic wave transmitted from the ultrasonic transducer is received while the ultrasonic transducer is in the reverberation, the reverberation and the reflected wave cannot be distinguished from each other. Become scarce.
[0008]
And when using the lift detection apparatus using such an ultrasonic element for a forklift, it is possible that the very low lift position when it is very near when a fork is lowered to a minimum cannot be detected.
[0009]
The present invention has been made in order to solve the above-mentioned problems. The first object of the present invention is to continuously detect the position of the piston, and to determine the position of the piston in the entire movement range of the piston. The object is to provide a fluid pressure cylinder that can be detected.
[0010]
The second object is to continuously detect the position of the moving body moved by the fluid pressure cylinder, and to detect the position of the moving body in the entire operating range of the fluid pressure cylinder. An object of the present invention is to provide a position detection device for a moving body.
[0011]
A third object is to provide an industrial vehicle capable of performing control based on the position of a moving body that is continuously detected over the entire operating range of a fluid pressure cylinder.
[0012]
[Means for Solving the Problems]
In order to solve the above problems, the invention according to claim 1 is directed to an ultrasonic transmitter provided to transmit an ultrasonic wave via a working fluid toward a piston of a fluid pressure cylinder, and the ultrasonic transmission. a fluid pressure cylinder reflected wave and ultrasonic receiver arranged to receive via a working fluid each with separately from the ultrasound of the piston child sent, the cylinder of the hydraulic cylinder A sensor body is fixed to the bottom block of the body, and the sensor body includes a transmission side portion and a reception side portion that project into the cylinder body toward the piston, and the transmission side portion and the reception side portion are separated from each other. The ultrasonic transmitter is provided at the piston side end of the transmission side portion, and the ultrasonic receiver is provided at the piston side end of the reception side portion. Wherein the ultrasonic wave transmitting unit having an ultrasonic transmission element and the transmission side, the working fluid is interposed between the ultrasonic wave receiver comprising the ultrasonic receiver and a receiving side.
[0013]
According to a second aspect of the present invention, in the first aspect of the invention, the sensor body including the ultrasonic transmitter and the ultrasonic receiver is detachably provided on a bottom block of the fluid pressure cylinder. the ultrasonic transmission transducer and ultrasound the receivers is Ru is constructed detachably integrally against the fluid pressure cylinder.
[0014]
According to a third aspect of the present invention, in the fluid pressure cylinder according to the first or second aspect, the ultrasonic transmitter is transmitted to the ultrasonic transmitter, and the ultrasonic transmitter is transmitted to the ultrasonic transmitter. Distance calculating means for obtaining a distance detection value corresponding to an elapsed time from the timing to the reception timing at which the ultrasonic wave receiver receives the reflected wave.
[0015]
According to a fourth aspect of the present invention, in the third aspect of the present invention, the fluid pressure cylinder is a lift cylinder of a forklift provided with a cargo handling attachment as the moving body, and the distance detection value is the load handling value. It is associated with the lift position of the attachment.
[0016]
According to a fifth aspect of the present invention, an industrial vehicle includes the movable body position detection device according to the third aspect, and based on the distance detection value associated with the position of the movable body, Perform position control.
[0017]
According to a sixth aspect of the present invention, the forklift includes the movable body position detection device according to the fourth aspect of the present invention, and is based on the distance detection value associated with the lifted position of the cargo handling attachment. The height of the attachment is controlled.
(Function)
According to the first aspect of the present invention, the ultrasonic wave transmitted from the ultrasonic transmitter is reflected by the piston, and the ultrasonic receiver provided separately from the ultrasonic transmitter has a time corresponding to the position of the piston. Only received late. Therefore, even when the position of the piston is very close to the ultrasonic transmitter and the ultrasonic receiver, the reflected wave is received without the influence of reverberation after ultrasonic vibration.
[0018]
According to the second aspect of the invention, in addition to the operation of the first aspect of the invention, the ultrasonic transmitter and the ultrasonic receiver are integrally attached to and detached from the fluid pressure cylinder. The ultrasonic element can be detached.
[0019]
According to the invention described in claim 3, distance detection corresponding to an elapsed time from when the ultrasonic wave is transmitted from the ultrasonic wave transmitter to the piston until the ultrasonic wave reflected by the piston is received by the ultrasonic wave receiver. The value is obtained by the distance calculation means.
[0020]
According to the fourth aspect of the present invention, the lift position of the cargo handling attachment that is lifted and lowered by the lift cylinder in the forklift is detected.
According to the fifth aspect of the present invention, the position of the moving body that is moved by the fluid pressure cylinder in the industrial vehicle is detected by the position detection device that performs the operation according to the third aspect.
[0021]
According to the invention described in claim 6, in addition to the operation of the invention described in claim 4, the lift position of the fork is continuously detected in the entire lift range moved by the lift cylinder.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment in which the present invention is embodied in a lift height detection device for a forklift will be described with reference to FIGS.
[0023]
As shown in FIG. 3, a forklift 10 as an industrial vehicle includes a mast 12 at the front portion of a vehicle body 11. The mast 12 includes left and right outer masts 13 supported by the vehicle body 11 and an inner mast 14 supported so as to be movable up and down inside the outer mast 13. A lift bracket 16 is attached to the inner mast 14 so as to be movable up and down, and the lift bracket 16 supports a fork 15 as a moving object and a cargo handling attachment. One end of the lift bracket 16 is connected to the cross beam 17 of the outer mast 13 and is suspended by a chain 19 that is hung on a sprocket 18 at the upper end of the inner mast 14.
[0024]
A hydraulic lift cylinder 20 as a fluid pressure cylinder is provided behind the mast 12. In the lift cylinder 20, the cylinder body 21 is fixed to the outer mast 13, and the tip of the piston rod 22 is connected to the upper end of the inner mast 14.
[0025]
As shown in FIG. 1, the cylinder body 21 of the lift cylinder 20 includes a cylinder tube 23, a bottom block 24, and a rod cover 25. The cylinder tube 23 includes a piston 26 to which the lower end of the piston rod 22 is connected. Yes.
[0026]
In the cylinder body 21, an air chamber 27 is formed above the piston 26, and an oil chamber 28 is formed below the piston 26. The air chamber 27 is provided with an exhaust hole 27a communicating with the outside.
[0027]
On the upper side of the bottom block 24, there is formed a regulation stepped portion 24a that abuts on the lower side of the piston 26 and regulates the downward movement, and an ultrasonic distance detector 29 is accommodated below the regulation stepped portion 24a. A chamber 30 is formed. A port 31 for supplying and discharging hydraulic oil to and from the oil chamber 28 is provided on the side of the bottom block 24. The port 31 is connected to a hydraulic oil control valve (not shown) provided on the vehicle body side via a flow regulator valve (not shown).
[0028]
As shown in FIG. 2, the ultrasonic distance detector 29 includes an ultrasonic transmission unit 32 and an ultrasonic reception unit 33. The ultrasonic distance detector 29 includes a sensor body 34 fixed to the bottom block 24. The sensor body 34 includes a transmission side portion 35 and a reception side portion 36. A backing material 37 is provided at the upper end of the transmission side portion 35, and an ultrasonic transmitter 38 is fixed to the upper surface of the backing material 37. Similarly, a backing material 39 is provided at the upper end of the receiving side portion 36, and an ultrasonic receiver 40 is fixed to the upper surface of the backing material 39. The transmission side portion 35, the backing material 37, and the ultrasonic transmitter 38, and the reception side portion 36, the backing material 39, and the ultrasonic receiver 40 are covered with caps 41 in an independent state. The ultrasonic transmission unit 32 includes a transmission side unit 35, a backing material 37, and an ultrasonic transmitter 38, and the ultrasonic reception unit 33 includes a reception side unit 36, a backing material 39, and an ultrasonic receiver 40. Yes.
[0029]
The sensor body 34 is detachably fixed to the bottom wall of the bottom block 24 by screwing. A pair of signal lines 42 are connected to the ultrasonic transmitter 38 from the lower surface of the sensor body 34, and a pair of signal lines 43 are connected to the ultrasonic receiver 40 from the lower surface of the sensor body 34.
[0030]
The transmission surface of the ultrasonic transmitter 38 is opposed to the lower surface of the piston 26, and the reception surface of the ultrasonic receiver 40 is opposed to the lower surface of the piston 26. When an oscillation signal having a predetermined frequency is supplied via the signal line 42, the ultrasonic transmitter 38 vibrates ultrasonically and transmits ultrasonic waves from the transmission surface to the lower surface of the piston 26. The ultrasonic receiver 40 receives the reflected wave from the lower surface of the piston 26 on the receiving surface, and outputs a received signal corresponding to the intensity of the received reflected wave via the signal line 43.
[0031]
As shown in FIG. 1, the signal lines 42 and 43 are connected to a control unit 44 provided on the vehicle body side. The lift cylinder 20 and the control unit 44 constitute a lift detection device.
[0032]
The control unit 44 includes a transmission / reception circuit 45 and a microcomputer 46. In the present embodiment, the microcomputer 46 is provided for automatically controlling the lifting height of the fork 15. Each signal line 42, 43 is connected to a transmission / reception circuit 45, and a microcomputer 46 is connected to the transmission / reception circuit 45. In the present embodiment, the transmission / reception circuit 45 and the microcomputer 46 constitute distance detection means.
[0033]
The transmission / reception circuit 45 has a known circuit configuration, and the transmission side includes an oscillation circuit, an ultrasonic drive circuit, and the like, and the reception side includes an amplification circuit, a bandpass circuit, a detection circuit, a comparison circuit, and the like. An ultrasonic transmitter 38 is connected to the transmission side of the transmission / reception circuit 45 by a signal line 42, and an ultrasonic receiver 40 is connected to the reception side of the transmission / reception circuit 45 by a signal line 43.
[0034]
The transmission / reception circuit 45 outputs an oscillation signal for ultrasonically vibrating the ultrasonic transmitter 38 of the ultrasonic distance detector 29 at a predetermined oscillation frequency only while the control signal output from the microcomputer 47 is input. On the other hand, the transmission / reception circuit 45 outputs a detection signal composed of a pulse signal to the microcomputer 46 when receiving a reception signal of a predetermined level or more from the ultrasonic receiver 40.
[0035]
The microcomputer 46 includes a central processing unit (CPU) 47, a read only memory (ROM) 48, a writable and readable memory (RAM) 49, a counter 50, and the like. The ROM 48 stores various data such as a control processing program executed by the CPU 47.
[0036]
The CPU 47 outputs a control signal to the transmission / reception circuit 45 so that the ultrasonic transmitter 38 continuously transmits ultrasonic waves for a predetermined transmission period for a predetermined time. This transmission cycle is the time required for the ultrasonic wave transmitted from the ultrasonic transmitter 38 to be reflected by the lower surface of the piston 26 and received by the ultrasonic receiver 40 when the stroke of the lift cylinder 20 is maximum. Is set to a longer time.
[0037]
Further, the CPU 47 uses the counter 50 to measure the elapsed time from the transmission timing at which the ultrasonic wave is transmitted to the reception timing at which the detection signal output from the transmission / reception circuit 45 is input, for each transmission cycle.
[0038]
The CPU 47 obtains a distance detection value corresponding to the elapsed time from the count value of the counter 50. Further, the CPU 47 associates the distance detection value with the lifted position of the fork 15. Associating the distance detection value with the lift position, the distance detection value may be used as it is, or a lift detection value corresponding to the lift position may be obtained using a predetermined relational expression.
[0039]
The CPU 47 controls the lift cylinder 20 with a predetermined control content based on the distance detection value or the lift detection value, and controls the lift position of the fork 15.
Next, the operation of the lift cylinder and the lift detection device configured as described above will be described.
[0040]
When the forklift 10 is started, the microcomputer 46 of the control unit 44 is activated. When the lift lever is raised, the hydraulic oil is supplied to or discharged from the oil chamber 28 of the lift cylinder 20 by the hydraulic oil control valve, and the piston 26 is raised or lowered. Then, the inner mast 14 is raised or lowered by the lift cylinder 20, and the lifted position of the fork 15 is raised or lowered.
[0041]
When the CPU 47 causes the ultrasonic transmitter 38 to transmit an ultrasonic wave, the ultrasonic wave transmitted from the ultrasonic transmitter 38 is transmitted through the hydraulic oil in the oil chamber 28 and reaches the lower surface of the piston 26. It is reflected, transmitted again in the hydraulic oil, and received by the ultrasonic receiver 40. At this time, the ultrasonic wave is received by the ultrasonic wave receiver 40 with a time delay corresponding to the position of the piston 26, that is, the lifted position of the fork 15. When receiving the reflected wave, the ultrasonic receiver 40 outputs a reception signal to the transmission / reception circuit 45, and the transmission / reception circuit 45 outputs a detection signal to the microcomputer 46 based on the reception signal. The CPU 47 uses the counter 50 to measure the elapsed time from the transmission timing at which the ultrasonic transmitter 38 transmits ultrasonic waves to the reception timing at which the detection signal is input. And CPU47 calculates | requires the distance detection value to piston 26 from elapsed time.
[0042]
When the lifting height position of the fork 15 is set to the lower limit, the position of the piston 26 is very close to the ultrasonic transmission unit 32 and the ultrasonic reception unit 33. When an ultrasonic wave is transmitted from the ultrasonic transmitter 38 in this state, the reflected wave from the piston 26 is received by the ultrasonic receiver 40 in a state where the ultrasonic transmitter 38 has reverberation after ultrasonic vibration. The As shown in FIG. 4, the timing at which the reception signal is generated by the reflected wave at the ultrasonic receiver 40 overlaps the timing at which the voltage signal due to reverberation is generated at the ultrasonic transmitter 38. However, since the reflected wave from the piston 26 is received by the ultrasonic receiver 40 provided separately from the ultrasonic transmitter 38, a voltage signal based on reverberation does not enter the transmitter / receiver circuit 45. A reception signal based only on the reflected wave from is output. Therefore, even if the piston 26 is located at a position very close to the ultrasonic distance detector 29 such that a reflected wave returns when the ultrasonic transmitter 38 has reverberation, the position is reliably detected.
[0043]
As described above in detail, according to the lift cylinder and the lift detection device of the present embodiment, the following effects can be obtained.
(1) The reflected wave from the piston 26 of the ultrasonic wave transmitted from the ultrasonic transmitter 38 is received by the ultrasonic receiver 40 provided separately from the ultrasonic transmitter 38. Therefore, even when the piston 26 is located very close to the ultrasonic distance detector 29, a correct distance detection value can be obtained without being affected by the reverberation of the ultrasonic transmitter 38. As a result, the lift position of the fork 15 moved by the lift cylinder 20 can be continuously detected, and the lift position of the fork 15 can be correctly detected in the entire operating range of the lift cylinder 20. .
[0044]
(2) Since the ultrasonic transmitter 38 and the ultrasonic receiver 40 are provided so as to be detachable integrally with the lift cylinder 20, both the ultrasonic elements 38 and 40 can be attached and detached at a time. Therefore, the attachment / detachment to / from the lift cylinder 20 can be easily performed.
[0045]
The embodiment is not limited to the above embodiment, and may be modified as follows.
The ultrasonic transmitter 38 and the ultrasonic receiver 40 are provided in separate sensor bodies, and the ultrasonic elements 38 and 40 are separately attached to and detached from the lift cylinder 20.
[0046]
○ A transmission / reception circuit and a microcomputer are integrally provided in the ultrasonic distance detector 29. The distance detection value is directly output from the ultrasonic distance detector sensor. With this configuration, it is possible to reduce the burden on the microcomputer of the control unit that is provided on the vehicle body and that automatically controls the lift based on the distance detection value.
[0047]
The present invention is not limited to the lift height detection device for the fork 15 in the forklift 10, and is applied to the tilt angle detection device for the mast 12. In this case, the distance detection value is associated with the tilt angle of the mast 12. In this configuration, the tilt angle of the mast 12 can be detected continuously, and the tilt angle of the mast 12 can be detected in the entire operating range of the tilt cylinder. In addition, the mast 12 can be made less likely to be damaged than the case where the tilt angle of the mast 12 is detected by a potentiometer provided outside the tilt cylinder, and the reliability can be increased.
[0048]
The cargo handling attachment is not limited to the fork 15 as long as it is lifted and lowered by the lift cylinder 20. For example, any of fork devices such as side shift forks, hinged forks, and rotating forks, bale clamps, clamp devices such as roll clamps, and ram devices may be used.
[0049]
The industrial vehicle is not limited to the forklift 10 as long as it has a fluid pressure cylinder and a moving body moved by the fluid pressure cylinder. In addition, for example, the present invention can be applied to a position detection device such as a tractor excavator whose bucket is controlled by a cylinder and an aerial work vehicle whose boom elevation angle is controlled by a telescopic cylinder.
[0050]
○ Implemented in a position detection device for moving objects that are moved by hydraulic cylinders other than hydraulic cylinders.
Moreover, it implements to the position detection apparatus of the moving body moved with a pneumatic cylinder.
[0051]
Hereinafter, the technical idea grasped from the embodiment and another example of the embodiment to which previous mentioned described along with the effects.
(1) In the invention according to claim 3, the fluid pressure cylinder is a tilt cylinder of a forklift provided with a mast as the moving body, and the distance detection value is associated with a tilt angle of the mast. Yes. According to such a configuration, the tilt angle of the mast can be continuously detected in the forklift, and the tilt angle of the mast can be detected in the entire operating range of the lift cylinder. Further, it is possible to make the mast tilt angle harder to be damaged than in the case where the mast tilt angle is detected by a potentiometer provided outside the tilt cylinder, and the reliability can be increased.
[0052]
(2) A forklift that includes the movable body position detection device according to (1) and performs tilt angle control of the mast based on the distance detection value associated with the tilt angle of the mast. According to such a configuration, the lift height of the fork can be continuously detected over the entire operating range of the tilt cylinder, and the lift height of the fork can be controlled based on the detected lift position.
[0053]
(3) An ultrasonic transmitter that transmits ultrasonic waves toward the piston of the fluid pressure cylinder that moves the moving body, an ultrasonic receiver that receives reflected waves from the piston, and an ultrasonic wave to the ultrasonic transmitter A distance calculation means for obtaining a distance detection value corresponding to an elapsed time from a transmission timing at which the ultrasonic transmitter transmits an ultrasonic wave to a reception timing at which the ultrasonic receiver receives a reflected wave; The position detection apparatus of the moving body provided with. According to such a configuration, the position of the moving body moved by the fluid pressure cylinder can be continuously detected, and the position of the moving body can be detected in the entire operating range of the fluid pressure cylinder. .
[0054]
【The invention's effect】
According to the first and second aspects of the invention, the reflected wave can be received regardless of the reverberation of the ultrasonic vibration, so that the piston position can be continuously detected, and the entire piston can be detected. It is possible to detect the position of the piston within the moving range.
[0055]
According to the second aspect of the present invention, both the ultrasonic elements can be detached and attached to the fluid pressure cylinder body easily.
According to the third, fourth, and fifth aspects of the invention, the position of the moving body moved by the fluid pressure cylinder can be continuously detected, and the entire operating range of the fluid pressure cylinder can be detected. The position of the moving body can be detected at. In the industrial vehicle, the control based on the position of the moving body can be correctly performed in the entire operation range of the fluid pressure cylinder.
[0056]
According to the fourth and sixth aspects of the present invention, the lift position of the cargo handling attachment can be continuously detected in the forklift, and the lift position of the cargo handling attachment can be detected in the entire operating range of the lift cylinder. Can be detected. In a forklift, control based on the lifted position of the cargo handling attachment can be correctly performed over the entire operating range of the lift cylinder.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a lift detection device.
FIG. 2 is a schematic cross-sectional view of a main part of a lift cylinder.
FIG. 3 is a schematic side view of a forklift.
FIG. 4 is a graph of voltage signals generated in an ultrasonic transmitter and a receiver.
FIG. 5 is a graph of a voltage signal generated in an ultrasonic transceiver.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 10 ... Forklift as an industrial vehicle, 15 ... Fork as attachment for moving body and cargo handling, 20 ... Lift cylinder as fluid pressure cylinder, 26 ... Piston, 38 ... Ultrasonic transmitter, 40 ... Ultrasonic receiver, 45 ... A transmission / reception circuit constituting a distance calculation means, 46...

Claims (6)

An ultrasonic transmitter provided to transmit ultrasonic waves through the working fluid toward the piston of the fluid pressure cylinder ;
Wherein a fluid pressure cylinder ultrasonic transmitter transducer is separately provided, respectively and ultrasonic receiver arranged to receive via the working fluid reflected waves from the piston of the ultrasonic wave transmitted,
A sensor body is fixed to a bottom block of a cylinder body of the fluid pressure cylinder, and the sensor body includes a transmission side portion and a reception side portion that project into the cylinder body toward the piston, and the transmission side portion and the reception side portion. The sides are provided apart from each other,
The ultrasonic transmitter is provided at the piston side end of the transmission side portion, and the ultrasonic receiver is provided at the piston side end of the reception side portion,
A fluid pressure cylinder in which a working fluid is interposed between an ultrasonic transmission unit including the ultrasonic transmitter and a transmission side part and an ultrasonic reception unit including the ultrasonic receiver and a reception side part . By the said sensor body with an ultrasound transmission transducer and ultrasonic receiver are provided removably in the bottom block of said hydraulic cylinder, said ultrasonic transmission element and ultrasound the receivers is against the fluid pressure cylinder fluid pressure cylinder according to claim 1 that consists detachably integrally Te. The fluid pressure cylinder according to claim 1 or 2,
A distance corresponding to an elapsed time from a transmission timing at which the ultrasonic transmitter transmits ultrasonic waves to the ultrasonic transmitter to a reception timing at which the ultrasonic receiver receives a reflected wave. A position detection apparatus for a moving body, comprising: distance calculation means for obtaining a detection value. The fluid pressure cylinder is a lift cylinder of a forklift equipped with a cargo handling attachment as the moving body,
The position detection apparatus of the moving body according to claim 3, wherein the distance detection value is associated with an elevation position of the cargo handling attachment. An industrial vehicle comprising the position detection device for a moving body according to claim 3 and performing position control of the moving body based on the distance detection value associated with the position of the moving body. A forklift comprising the position detection device for a moving body according to claim 4, wherein the lift control of the cargo handling attachment is performed based on the distance detection value associated with the lift height position of the cargo handling attachment.

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