JP4931336B2 - Platform leveling equipment for aerial work platforms - Google Patents

Description

  The present invention relates to a work table leveling device for an aerial work vehicle that holds a work table substantially horizontally regardless of the posture of a boom.

  An aerial work vehicle has a work platform for boarding an operator at the tip of a boom provided on a traveling body, and the work platform is moved to a desired position by moving the boom up and down, expanding and contracting, and turning. It is possible to work at high places. Since the operation of the boom can be performed by operating the boom operation means (lever, etc.) provided on the work table, the worker on the work table must move the work table to a desired position for work. Can do. Further, in order to prevent the boom from operating when the boom operation means is operated by mistake, the boom operation means is operated while operating the switch means (for example, a foot switch operated by stepping on the foot) provided on the work table. The operation input is valid only when the operation is performed.

The workbench can be swung up and down by an expansion and contraction operation of a hydraulic actuator called a leveling cylinder attached to the tip of the boom, and by extending and contracting this leveling cylinder according to the operation of the boom, Therefore, the work table (the floor surface of the work table) can always be made almost horizontal regardless of the posture of the boom. As described above, the expansion and contraction operation of the leveling cylinder is performed in accordance with the operation of the boom as described above, so when the operation of the boom is not performed, for example, when the work is performed with the work table stopped at a certain position. There is no need to supply pressure oil to the leveling cylinder. For this reason, when an unload valve is provided in the oil passage connecting the hydraulic pump and the leveling cylinder and the boom operating means is located at the neutral position, the discharged oil is released to the oil tank, and the boom operating means is moved from the neutral position. A configuration is known in which discharged oil is supplied to a leveling cylinder at the same time (see, for example, Patent Document 1 below). In such a configuration, since the unloading is performed while the work table is stopped, the load on the hydraulic pump can be reduced, power loss can be reduced, and an increase in the oil temperature can be suppressed.
JP-A-11-180695 Japanese Patent Laid-Open No. 9-100804

  However, when the boom operating means is moved from the neutral position to operate the boom as described above, the leveling is performed when the unloading valve is changed from the unloading state to the supply state (the state in which the pressure oil is supplied to the leveling cylinder). Since the spool switching operation of the cylinder control valve (direction switching valve) must be performed after the unloading valve is switched, the actual start of the leveling cylinder is delayed from the start of the boom operation, and the leveling (work platform There was a case in which a follow-up delay of (equilibrium) occurred.

  The present invention has been made in view of such problems, and it is possible to improve leveling responsiveness to boom operation while reducing power loss and preventing oil temperature rise using an unload valve. It is an object of the present invention to provide a work table leveling device for an aerial work vehicle having a possible configuration.

A platform leveling device for an aerial work vehicle according to the present invention includes a traveling body, a boom provided on the traveling body, a boom actuator that receives hydraulic oil supplied from a hydraulic pump for a boom actuator, and operates the boom. , a worktable mounted pivotably up and down at the tip of the boom, the boom operation means for performing operation operation of the boom (e.g., a boom operating lever 71 in the embodiment, the lower boom operation lever 14) and the boom Switch means (for example, foot switch 73 , lower priority switch 16 in the embodiment) provided near the operation means and enabling operation of the boom by operation of the boom operation means only when the operation means is in an ON state. a boom of the hydraulic operating Ri by the boom operating means in the on-state where the switch means is operated is performed Sometimes , the boom actuator is operated to operate the boom, thereby moving the work platform to a desired height position . In addition, a leveling cylinder that swings the work table up and down with respect to the boom by expanding and contracting upon receiving the supply of hydraulic oil, and a leveling hydraulic pump that supplies the hydraulic oil to the leveling cylinder (for example, in the embodiment) The second hydraulic pump P2), the leveling cylinder control valve for controlling the supply amount and direction of the hydraulic oil supplied from the leveling hydraulic pump to the leveling cylinder, and the hydraulic oil discharged from the leveling hydraulic pump to the oil tank and unloading position to allow the working oil is not supplied to the leveling cylinder and the escape, the supply position allowing supply to the leveling cylinder the hydraulic fluid to close the oil passage leading to the oil tank through the leveling cylinder control valve and unloading valve which can be switched between, the switch means is operated A flip the On state, and when the working operation of the boom is performed by the boom operating means, the platform floor by a leveling cylinder control valve drive control to thereby stretch operate the leveling cylinders in accordance with the operation of the boom the leveling control means (e.g., the controller 60 in the embodiment) for holding the horizontal state Ru a. The leveling control means switches the unload valve to the unload position when the switch means is not operated , and releases the hydraulic oil discharged from the leveling hydraulic pump to the oil tank, and the switch means is operated. When the engine is turned on, the unload valve is switched to the supply position so that the hydraulic oil can be supplied to the leveling cylinder via the leveling cylinder control valve . It is preferable that the unload valve is provided in the running body.

  In the work platform leveling device for an aerial work platform according to the present invention, when the switch unit is operated and the boom operation input is performed by the boom operation unit, the control unit operates the actuator to operate the boom, In a configuration in which the leveling cylinder is expanded and contracted to maintain the horizontal posture of the work table, an unload valve is provided in an oil passage connecting the hydraulic pump and the leveling cylinder. The unload valve is switched to an unload state in which the oil discharged from the hydraulic pump is released to the oil tank when the operator is not operating the switch means, and is hydraulic when the operator is operating the switch means. It is possible to switch to a supply state in which pump discharge oil is supplied to the leveling cylinder. In such a configuration, when the leveling cylinder is not in operation, the hydraulic pump can be unloaded to reduce power loss and prevent the oil temperature from rising. Since the leveling cylinder can be already activated at the stage of operating the switch means, it becomes possible to operate the leveling cylinder simultaneously with the start of the operation of the boom operation means, and the leveling for the operation of the boom (the work table (Equilibrium) response can be improved. Further, if the unloading valve is provided in the traveling body, the work table can be made lighter than when the unloading valve is provided in the work table.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows an aerial work platform 1 equipped with a work table leveling device according to an embodiment of the present invention. Before describing the work table leveling device according to the present invention, the configuration of the aerial work vehicle 1 will be described first.

  The aerial work vehicle 1 is provided with traveling wheels 11,..., A truck type traveling body 10 that can be traveled from a driving cabin 12, a swivel base 20 provided on the traveling body 10, and the swivel base. A boom 30 having a base end supported on an upper portion of a support column 21 extending upward from 20 via a foot pin 22, and a work board 40 for boarding an operator attached to the distal end of the boom 30. It is configured.

  The swivel base 20 is attached to the rear part of the traveling body 10 so as to be rotatable 360 degrees around the vertical axis. A boom turning motor (hydraulic motor) 23 is provided inside the traveling body 10, and by rotating the boom turning motor 23, the turntable 20 can be horizontally turned through a gear (not shown). . The boom 30 includes a base boom 30a, an intermediate boom 30b, and a distal boom 30c. The boom 30a, 30b, and 30c are moved relative to each other by a telescopic operation of a boom telescopic cylinder (hydraulic cylinder) 31 provided therein. The entire boom 30 can be expanded and contracted in the axial direction. A boom hoisting cylinder (hydraulic cylinder) 24 is provided between the base end boom 30a and the column 21 of the swivel base 20, and the boom hoisting cylinder 24 is extended and contracted to move the entire boom 30 up and down. Can be undulated.

  A vertical post holding metal fitting 32 is attached to the tip of the tip boom 30c, and a lower end portion of the vertical post 33 is pivotally supported on the vertical post holding metal fitting 32. A work table support plate 34 is fixed to the upper end portion of the vertical post 32, and the work table 40 is provided on the upper surface side of the work table support plate 34. The worktable support plate 34 is connected to the vertical post holding bracket 32 by a leveling cylinder (hydraulic cylinder) 35, and the vertical post 33 (worktable 40) is swung up and down by operating the leveling cylinder 35 to extend and contract. be able to. For this reason, the leveling cylinder 35 is telescopically operated in accordance with the hoisting operation of the boom 30 (the telescopic operation of the boom hoisting cylinder 24), the telescopic operation (the telescopic operation of the boom telescopic cylinder 31) or the pivoting operation (the rotational operation of the boom pivoting motor 23). By doing so, regardless of the posture of the boom 30, it is possible to always keep the vertical post 33 in the vertical posture and keep the work table 40 (the floor surface of the work table 40) horizontally. Note that the leveling cylinder 35 operates in the expansion and contraction operation of the boom 30 when the extension amount of the boom 30 increases and the boom 30 is bent downward, and the leveling cylinder 35 operates in the turning operation of the boom 30. This is the case when the boom 30 is turned from the state in which the traveling body 10 is located on the slope.

  The work table 40 is attached to the upper surface side of the work table support plate 34 so as to be rotatable about the vertical axis, and a work table turning motor (hydraulic motor) 36 provided in the work table support plate 34 is rotated. Thus, the work table 40 can be horizontally swung around the vertical post 33 via a gear (not shown).

  The work table 40 is provided with an upper operation device 70, in which a boom operation lever 71 for performing the raising / lowering, expanding / contracting and turning operations of the boom 30 and a work table operation for performing a horizontal turning operation of the work table 40. A lever 72 is provided. The boom operation signal output by the operation of the boom operation lever 71 and the worktable operation signal output by the operation of the worktable operation lever 72 are respectively input to the controller 60 installed in the traveling body 10 (see FIG. 3). ). The controller 60 controls the first control valve 51 corresponding to the boom hoisting cylinder 24, the second control valve 52 corresponding to the boom telescopic cylinder 31, and the boom turning motor 23 based on the boom operation signal output by the operation of the boom operation lever 71. Each spool (not shown) of the corresponding third control valve 53 is electromagnetically driven. Further, the controller 60 electromagnetically drives a spool (not shown) of the fourth control valve 54 corresponding to the worktable turning motor 36 based on a worktable operation signal output by operating the worktable operation lever 72.

  The floor surface of the work table 40 is provided with a foot switch 73 that is operated by the operator OP stepping on the work table 40 with his / her foot (this foot switch 73 is also a part of the upper operation device 70). The foot switch 73 is a switch that enables the boom 30 to be operated by operating the boom operation lever 71 only when the foot switch 73 is being operated. In the on state (operating state) in which the operator OP is stepped on with a foot, a signal ( This is used as a switch operation signal), and the switch operation signal is not output in the off state (non-operation state) in which the depression is released. The switch operation signal output from the foot switch 73 is input to the controller 60 as shown in FIG. 3, and the controller 60 operates the boom operation lever 71 only when the switch operation signal is output from the foot switch 73. Each of the boom operation signal output by the operation table and the work table operation signal output by the work table operation lever 72 is treated as valid.

  A first hydraulic pump P1 provided in the traveling body 10 is rotationally driven by an engine E (or an electric motor or the like), and the boom hoisting cylinder 24 is passed through the first to fourth control valves 51, 52, 53, 54. Then, pressure oil is supplied to the boom telescopic cylinder 31, the boom turning motor 23, and the worktable turning motor 36. Therefore, the boom hoisting cylinder 24, the boom telescopic cylinder 31 and the boom turning motor 23 can be operated as desired by operating the boom operation lever 71, and the worktable turning motor 36 is operated as desired by operating the worktable operation lever 72. be able to. However, as described above, even if the operator OP on the workbench 40 operates the boom operation lever 71 or the workbench operation lever 72, the foot switch 73 is depressed (the foot switch 73 is turned on). Since the operation is not effective unless it is performed in the state), the operator OP must first depress the foot switch 73 and then operate the boom operation lever 71 or the worktable operation lever 72. . Since the aerial work platform 1 has the above-described configuration, the operator OP who has boarded the work platform 40 moves the work platform 40 by operating the boom operation lever 71 and the work platform operation lever 72 to work at any height location. Can be done.

  As shown in FIGS. 2 and 3, a lower operation device 13 is provided on the traveling body 10. Like the boom operation lever 71 of the upper operation device 70, the boom 30 is raised and retracted, A lower boom operation lever 14 for performing a turning operation, and a lower worktable operation lever 15 for performing a horizontal turning operation of the worktable 40 as well as a worktable operation lever 72 of the upper operation device 70 are provided. The boom operation signal output by the operation of the lower boom operation lever 14 and the work platform operation signal output by the operation of the lower work platform operation lever 15 are respectively input to the controller 60 (see FIG. 3). Based on the boom operation signal output by the operation of the boom operation lever 14, the spools of the first control valve 51, the second control valve 52, and the third control valve 53 are electromagnetically driven to move the boom 30 up and down, expand and contract, and turn. It is supposed to let you. Further, the controller 60 electromagnetically drives the spool of the fourth control valve 54 based on the work table operation signal output by the operation of the lower work table operation lever 15, thereby causing the work table 40 to perform a horizontal turning operation.

  The lower boom operation lever 14 and the lower work table operation lever 15 are mainly for operating the boom 30 and the work table 40 in a state where the operator does not get on the work table 40, such as inspection before starting work. By operating the lower priority switch 16 provided in 13 with the lower priority switch 16 turned on, the operation signal becomes valid. That is, it plays the same role as the foot switch 73 in the upper operating device 70. However, in the state where the lower priority switch 16 is turned on, even if there is an operator OP on the work table 40 and the foot switch 73 is depressed (even if the foot switch 73 is turned on), The operation signal output by the operation of the boom operation lever 71 and the work table operation lever 72 in the upper operation device 70 becomes invalid (the operation from the lower operation device 13 has priority).

  Further, the controller 60 prevents the traveling body 10 from falling due to the overturning moment generated by extending the boom 30 or the like so that the tip of the boom 30 is not positioned at a position where the traveling body 10 is toppled. The operation control of the boom 30 is performed while restricting. The controller 60 is provided at the base end portion of the boom 30 and detects a undulation angle detector 61a that detects the undulation angle of the boom 30, a boom length detector 61b that is provided in the boom 30 and detects the length of the boom 30, and travel. Based on detection information from three detectors of a boom turning angle detector 61c that is provided in the body 10 and detects a turning angle of the boom 30 with respect to the running body 10 (of the swivel base 20). The position of the tip of the boom 30 is calculated, and the spool operation of the first to third control valves 51, 52, 53 is performed so that the position of the tip of the boom 30 is within the allowable work range set in advance in the controller 60. Control. In addition, outrigger jacks 50, 50,... That project downward (extend and operate) and stably support the traveling body 10 are provided at four positions on the front, rear, left, and right sides of the traveling body 10 (see FIG. 2). .

  Next, a work table leveling device provided in the aerial work platform 1 will be described. As shown in FIG. 1, the work table leveling device of the aerial work vehicle 1 includes the boom operation lever 71, the foot switch 73, the controller 60, the leveling cylinder 35, the work table tilt angle detector 62, and the second hydraulic pump. P2, a leveling cylinder control valve 55, an unload valve 56, and a double pilot check valve 57 are configured.

  The work table tilt angle detector 62 is attached to the work table 40, detects the tilt angle of the work table 40 (the floor surface of the work table 40) with respect to the ground G, and outputs the detected information to the controller 60. As shown in FIG. 3, the second hydraulic pump P <b> 2 is driven by the engine E similarly to the first hydraulic pump P <b> 1 and supplies pressure oil to the leveling cylinder 35. The leveling cylinder control valve 55 is a direction switching valve interposed in the oil passages L1 and L2 that connect the second hydraulic pump P2 and the leveling cylinder 35. The spool 60 is electromagnetically driven by the controller 60, so that the second hydraulic pressure is controlled. Supply (including direction switching) and stop of the discharge oil from the pump P2 to the leveling cylinder 35 are performed. The unload valve 56 is interposed at a position upstream of the boom 30 in the oil passages L1 and L2 (specifically, in the traveling body 10), and discharge oil from the second hydraulic pump P2 is supplied to the oil tank T. It is possible to switch between an unloading position 56a for releasing and a supply position 56b for supplying the discharge oil of the second hydraulic pump P2 to the leveling cylinder 35. The double pilot check valve 57 is interposed at a position downstream of the boom 30 (specifically, in the work table 40) in the oil passages L1 and L2, and pressure oil is supplied to the leveling cylinder 35. It functions to lock the leveling cylinder 35 so that it does not expand and contract due to external force when it is not. Further, the double pilot check valve 57 prevents the work table 40 from swinging downward due to its own weight even when one of the oil passages L1, L2 between the leveling cylinder control valve 55 is damaged. It also works.

  When an operation input of the boom 30 is performed by the boom operation lever 71, the controller 60 operates the actuators (the boom hoisting cylinder 24, the boom telescopic cylinder 31, and the boom turning motor 23) to raise, lower, extend, and rotate the boom 30. The horizontal posture of the work table 40 is maintained by operating and leveling cylinder 35 extending and contracting. That is, the work table 40 is leveled (balanced) in accordance with the operation of the boom 30. More specifically, the leveling cylinder control valve 55 is electromagnetically driven based on the detection information from the work table tilt angle detector 62 to cause the leveling cylinder 35 to extend and contract, thereby detecting the work table tilt angle detector 62. The tilt angle of the work table 40 is set to be substantially zero.

  Further, the controller 60 sets the unload valve 56 to the unload state (to the unload position 56a) when the foot switch 73 is not depressed by the operator OP and no switch operation signal is output from the foot switch 73. When the foot switch 73 is depressed and the switch operation signal is output from the foot switch 73, the unload valve 56 is switched to the supply state (supply position 56b). Therefore, when the operator OP does not intend to operate the boom 30 or the work table 40 and does not depress the foot switch 73, the unload valve 56 is in an unload state (located at the unload position 56a). Therefore, the discharge pressure of the second hydraulic pump P2 is not supplied to the leveling cylinder 35 and is released to the oil tank T as it is. That is, the second hydraulic pump P2 is unloaded (no load operation). In this state, even if the boom operation lever 71 or the work table operation lever 72 is operated, the operation becomes invalid, so that the boom 30 and the work table 40 do not actually operate.

  On the other hand, when the operator OP intends to operate the boom 30 or the work table 40 and the foot switch 73 is depressed before the boom operation lever 71 or the work table operation lever 72 is operated, the unload valve 56 is Since it is in the supply state (located at the supply position 56b), the discharge oil of the second hydraulic pump P2 is supplied to the leveling cylinder 35. In this state, the leveling cylinder 35 can be expanded and contracted by control from the controller 60. In this state, the operation of the boom operation lever 71 or the work table operation lever 72 is effective, and the boom 30 and the work table 40 are actually operated. Then, the work table 40 is leveled in accordance with the operation of the boom 30.

  As described above, the work table leveling device provided in the aerial work platform 1 has the controller 60 when the foot switch 73 is depressed (operated) and the operation input of the boom 30 by the boom operation lever 71 is performed. In the configuration in which the actuator (the boom hoisting cylinder 24, the boom telescopic cylinder 31 and the boom turning motor 23) is operated to operate the boom 30, and the leveling cylinder 35 is expanded and contracted to maintain the horizontal posture of the work table 40. 2 An unload valve 56 is provided in the oil passages L1 and L2 connecting the hydraulic pump P2 and the leveling cylinder 35. The unload valve 56 is in an unload state in which the discharged oil of the second hydraulic pump P2 is released to the oil tank T (unload position) when the operator OP has not depressed the foot switch 73 (not operated). 56a), and when the operator OP is stepping on (operating) the foot switch 73, it is switched to the supply state (to the supply position 56b) in which the discharge oil of the second hydraulic pump P2 is supplied to the leveling cylinder 35. It is like that.

  In such a configuration, when the leveling cylinder 35 is not operated, the second hydraulic pump P2 can be unloaded to reduce the power loss and prevent the oil temperature from rising. Since the leveling cylinder 35 can be already in an operable state at the step of stepping on the foot switch 73 (step of operating the foot switch 73) performed before the operation of the leveling cylinder 35, the leveling cylinder 35 is started simultaneously with the operation of the boom operation lever 71. The leveling response to the operation of the boom 30 can be improved. Further, the unload valve 56 can be provided on the downstream side of the boom 30, that is, on the work table 40, but as shown in FIG. 1, if provided on the traveling body 10 on the upstream side of the boom 30, this The work table 40 can be made lighter than when the unload valve 58 is provided in the work table 40.

  Further, the controller 60 enables the switch operation signal output from the foot switch 73 when the lower priority switch 16 is turned off, and the unload valve 56 according to the output / non-output of the switch operation signal from the foot switch 73. While the position is switched, the unload valve 56 is switched to the supply position 56b while invalidating the switch operation signal from the foot switch 73 when the lower priority switch 16 is turned on. For this reason, the aerial work vehicle 1 has a configuration in which the position of the unload valve 56 is switched according to the on / off state of the foot switch 73 as described above, but the unloading operation is not performed regardless of the on / off operation of the foot switch 73. A means for switching the load valve 56 to the supply position 56b is provided. When the boom 30 is operated by operating the lower boom operating lever 14, the lower boom operating lever 14 is operated without the on / off operation of the foot switch 73. The work table 40 can be leveled according to the operation.

  Although the preferred embodiments of the present invention have been described so far, the scope of the present invention is not limited to those described in the above embodiments. For example, the boom operation means for inputting the operation of the boom is a lever (boom operation lever 71) in the above-described embodiment, but this is not limited to the lever, and may be another operation means such as a knob. Moreover, although the boom 30 was a telescopic boom, it may be a boom of another form, such as a bent-boom boom. At this time, the controller 60 operates the leveling cylinder 35 in accordance with the bending and extending operation of the boom. Further, the switch means that enables only the operation input of the boom operation means performed in the state of being turned on by the operator OP is a foot switch 73 that is operated by the operator OP stepping on with a foot in the above-described embodiment. However, other switch means, for example, provided that it is provided in the vicinity of the boom operating means and can operate the boom by operating the boom operating means only when operated. It may be a lever or button switch operated by hand.

  Further, in the above-described embodiment, the controller 60 determines whether or not a switch operation signal by the operation of the switch means is output, so that the controller 60 outputs a switch operation signal from the foot switch 73. Only the boom operation signal output by the operation of the boom operation lever 71 and the work table operation signal output by the work table operation lever 72 are treated as valid. A switch mechanism that is opened and closed by the operation of a foot switch is installed in each of the intermediate portion of the signal line connecting between 60 and 60 and the intermediate portion of the signal line connecting between the worktable operation lever 72 and the controller 60. The switch mechanism closes both signal lines only when the Zooming operation signal and the platform control signal may be set to be valid.

It is a block diagram which shows the structure of the worktable leveling apparatus which concerns on one Embodiment of this invention. It is a side view which shows one Embodiment of an aerial work vehicle provided with the said work-table leveling apparatus. It is a block diagram which shows a part of structure of the power transmission system in the aerial work vehicle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Aerial work vehicle 10 Running body 23 Boom turning motor (actuator)
24 Boom hoisting cylinder (actuator)
30 Boom 31 Boom telescopic cylinder (actuator)
35 Leveling cylinder 40 Working table 60 Controller (control means)
55 Leveling cylinder control valve 56 Unload valve 56a Unload position 56b Supply position 71 Boom operation lever (boom operation means)
73 Foot switch (switch means)
P2 Second hydraulic pump (hydraulic pump)
L1, L2 oil passage

Claims (2)

A traveling body, a boom provided on the traveling body, a boom actuator for operating the boom upon receiving hydraulic oil supplied from a hydraulic pump for a boom actuator, and swingable up and down at the tip of the boom a worktable mounted, a boom operation means for performing operation operation of the boom, provided in the vicinity of the boom operating means, said boom by the operation of the boom operating means only when the oN state of being operated and a switch means for allowing the operation, when the working operation of the boom Ri by said boom operating means is performed in the on-state in which the switch means is operated to actuate the boom actuator A platform leveling device for an aerial work platform that moves the platform to a desired height position by operating the boom. ,
A leveling cylinder that swings the work table up and down with respect to the boom by extending and contracting by receiving supply of hydraulic oil;
A leveling hydraulic pump for supplying hydraulic oil to the leveling cylinder;
A leveling cylinder control valve for controlling a supply amount and a supply direction of hydraulic oil supplied from the leveling hydraulic pump to the leveling cylinder;
The hydraulic fluid the hydraulic oil discharged from the leveling hydraulic pump is closed and the unload position to allow the hydraulic fluid to the escape into the oil tank is not supplied to the leveling cylinder, an oil passage leading to the oil tank and unloading valve which can be switched between a supply position allowing supply to the leveling cylinder via the leveling cylinder control valve,
When the switch means is in an ON state and the boom operation means is operated by the boom, the leveling cylinder control valve is driven to control the leveling in accordance with the operation of the boom. Leveling control means for holding the floor surface of the work table in a horizontal state by operating the cylinder to extend and contract,
The leveling control means switches the unload valve to the unload position when the switch means is not operated, and releases hydraulic oil discharged from the leveling hydraulic pump to an oil tank, and the switch When the means is operated to be in the on state, the unload valve is switched to the supply position so that the hydraulic oil can be supplied to the leveling cylinder via the leveling cylinder control valve. A platform leveling device for aerial work platforms.   The platform leveling device for an aerial work platform according to claim 1, wherein the unloading valve is provided in the traveling body.

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