JPH1059686A - Control method and control device for hoisting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a suspending cargo from being stopped since it cannot be hoisted or from being lowered by controlling a delivery of a hydraulic pump so that rotating speed of a hoisting drum is held at prescribed speed or more in hoisting operation. SOLUTION: Rotating speed of a hoisting drum 1 is detected, and an electric current signal of a level to obtain a delivery of a minimum flow sent to a hydraulic motor 3 from a pump 5 so that this rotating speed V does not become (V<V MIN) to the lowest rotating speed V MIN, is inputted to a solenoid proportional pressure reducing valve 9 from a controller 14, and when an operation quantity of an operation lever 10 is small and a bleed-off quantity inside of a directional control valve 4 is large and the rotating speed V of the hoisting drum 1 does not reach the lowest rotating speed V MIN, a level of an electric current signal outputted to solenoid proportional pressure reducing valves 7 and 8 is increases to reduce the bleed-off quanrity. Therefore, even when weight of a suspending cargo is large, the occurrence of stopping and a stall of the hoisting drum 11 can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a control method and a control device for a hoisting device driven by a hydraulic motor.

[0002]

2. Description of the Related Art In general, hydraulic systems are often used as power for hoisting devices such as mobile cranes. Such a hydraulic hoist includes a hydraulic pump, a hydraulic motor, and a direction switching valve that controls the flow rate and direction of hydraulic oil supplied to the hydraulic motor. Also, as a hydraulic pump or a hydraulic motor, an axial piston pump or a piston motor is often used. By changing the tilt angle of the swash plate or the swash axis, respectively, the lifting and lowering of the hoisting device is performed. The speed is adjustable.

When the load of the hoisting device is large or very large, or when the position of the hoisting load is adjusted, the hoisting device must be driven at a very slow speed, that is, at a very low speed. Therefore, the conventional hoisting device fixes the tilt angle of the swash plate or the inclined shaft of the hydraulic pump to a minimum value, and provides a low-speed switch for minimizing the flow rate of hydraulic oil supplied from the hydraulic pump to the hydraulic motor. Slow speed operation has been made possible by providing a small amount or operating the operation lever.

[0004]

However, as in the above-described conventional hoisting apparatus, the tilt angle of the swash plate or the swash shaft of the hydraulic pump is fixed to a minimum value, or the operating lever is operated by a very small amount to achieve a very low speed. When performing operations, if the load applied to the hoisting device is large due to the heavy load, the stall (compared to the load) Insufficient oil pressure or flow rate of the hydraulic oil supplied to the hydraulic motor causes rotation in the direction opposite to the hoisting direction), and the suspended load may not be hoisted or slip off. Such a movement of the suspended load against the intention of the operator at the time of hoisting not only impairs the operability but also is extremely dangerous, and has become a factor that gives anxiety to the operator.

The holding pressure of the hydraulic motor is calculated using the rope tension calculated by the overload prevention device, the actual holding pressure is detected, and the calculated holding pressure is compared with the detected actual holding pressure. There has been proposed a load drop prevention device for a hoisting device (Japanese Utility Model Laid-Open No. 5-37884) in which the brake is not released until the two pressures match only during hoisting. However, the load drop prevention device of the hoisting device described in Japanese Utility Model Laid-Open No. 5-37884 prevents slipping when switching from holding by the brake at the start of hoisting to holding by the hydraulic motor. Does not take into account stalls caused by insufficient supply of hydraulic oil to the hydraulic motor during driving of the hydraulic motor.

SUMMARY OF THE INVENTION The present invention solves the above-mentioned problem. By preventing the hoist drum from being stalled while the hydraulic motor is being driven, the hoisting load cannot be hoisted during hoisting and stops or rolls down. An object of the present invention is to provide a control method and a control device for a hoisting device which prevent such a situation from occurring and are excellent in safety and operability.

[0007]

SUMMARY OF THE INVENTION The present invention provides a hydraulic pump, a hydraulic motor, a directional switching valve interposed between the hydraulic pump and the hydraulic motor, and the directional switching valve according to the operation amount of the operating means. Valve control means for controlling a valve, discharge amount control means for controlling the discharge amount of the hydraulic pump according to the operation amount of the operation means, and a hoisting drum which is driven to rotate by the hydraulic motor and winds up a suspended load. In the hoisting device provided, during the hoisting operation according to the operation amount of the operating means, the rotational speed of the hoisting drum is detected, and the detected rotational speed is maintained at a preset speed or higher. The discharge amount of the hydraulic pump is controlled (claim 1).

According to this method, the rotating speed of the hoist drum is detected during the hoisting operation according to the operation amount of the operating means, and the detected rotating speed is maintained at a preset speed or higher. By controlling the discharge amount of the hydraulic pump as described above, it is possible to prevent the suspended load from becoming unwound and stopping or winding down during hoisting.

Further, in the control method of the hoisting device according to the first aspect, the detected rotation speed is compared with the set speed, and when the detected rotation speed becomes equal to or less than the set speed, the hydraulic pump is discharged. In this case, the minimum discharge amount of hydraulic oil is increased.

According to this method, during the hoisting operation according to the operation amount of the operating means, the rotational speed of the hoist drum is detected, and the detected rotational speed is compared with the set speed. When the speed is below the set speed, the minimum discharge amount of hydraulic oil discharged from the hydraulic pump increases, so that even if the weight of the suspended load is heavy, the suspended load will not be It will be prevented from dropping.

A hydraulic pump, a hydraulic motor, a directional control valve interposed between the hydraulic pump and the hydraulic motor, and valve control means for controlling the directional control valve in accordance with the amount of operation of the operating means. A hoisting device comprising: a discharge amount control unit that controls a discharge amount of the hydraulic pump according to an operation amount of the operation unit; and a hoisting drum that is rotatably driven by the hydraulic motor and winds up a suspended load. During the hoisting operation according to the operation amount of the operating means, the inlet pressure of the hydraulic motor and the discharge pressure of the hydraulic pump are detected, and the ratio of the discharge pressure of the hydraulic pump to the inlet pressure of the hydraulic motor is calculated. The discharge amount of the hydraulic pump is controlled so that the calculated ratio is maintained at or above a preset ratio (claim 3).

According to this method, the inlet pressure of the hydraulic motor and the discharge pressure of the hydraulic pump are detected during the hoisting operation according to the operation amount of the operating means, and the ratio of the discharge pressure of the hydraulic pump to the inlet pressure of the hydraulic motor is detected. Is calculated, and the discharge amount of the hydraulic pump is controlled so that the calculated ratio is maintained at a preset ratio or more. Is prevented from rolling down.

[0013] In the control method of the hoisting device according to claim 3, the calculated ratio is compared with the set ratio.
When the calculated ratio is equal to or less than the set ratio, the minimum discharge amount of hydraulic oil discharged from the hydraulic pump is increased (claim 4).

According to this method, the calculated ratio is compared with the set ratio, and when the calculated ratio becomes equal to or less than the set ratio, the minimum discharge amount of the hydraulic oil discharged from the hydraulic pump increases. Even when the weight of the suspended load is large, it is possible to prevent the suspended load from becoming unwound and stopping or rolling down during the hoisting.

Further, in the control method of the hoisting device according to any one of claims 1 to 4, the directional control valve is further controlled during the hoisting operation according to the operation amount of the operating means. (Claim 5).

According to this method, during the hoisting operation according to the operation amount of the operating means, the rotational speed of the hoisting drum is maintained at or above a preset speed, or the inlet pressure of the hydraulic motor is controlled. The directional control valve is controlled so that the ratio of the discharge pressure of the hydraulic pump to the hydraulic pump is maintained at or above a preset ratio. Is more reliably prevented.

A hydraulic pump, a hydraulic motor, a directional control valve interposed between the hydraulic pump and the hydraulic motor, and valve control means for controlling the directional control valve in accordance with the amount of operation of the operating means. A hoisting device comprising: a discharge amount control unit that controls a discharge amount of the hydraulic pump according to an operation amount of the operation unit; and a hoisting drum that is rotatably driven by the hydraulic motor and winds up a suspended load. A stall prevention control means for preventing a stall of the hoist drum during a hoisting operation according to an operation amount of the operating means (claim 6).

According to this structure, the hoist drum is prevented from being stalled during the hoisting operation according to the operation amount of the operating means, so that the hoisting load does not become hoisted during the hoisting, and the hoisting drum stops or stops. It is prevented from falling.

The stall prevention control means includes a rotation speed detection means for detecting a rotation speed of the hoist drum;
Storage means for storing a preset set speed; and second discharge rate control means for controlling the discharge rate of the hydraulic pump so that the rotational speed is maintained at or above the set speed. (Claim 7).

According to this structure, the rotation speed of the hoist drum is detected, and the discharge amount of the hydraulic pump is controlled so that the rotation speed is maintained at a preset speed or higher, thereby making it possible to carry out the winding operation. In addition, it is possible to prevent the suspended load from becoming unwound and stopping or being rolled down.

The stall prevention control means further includes second valve control means for controlling the direction switching valve such that the rotation speed is maintained at or above the set speed. 8).

According to this configuration, the directional control valve is further controlled so that the rotation speed of the hoist drum is maintained at a preset speed or higher, so that the suspended load is lifted during hoisting. Stopping and rolling down due to disappearance are more reliably prevented.

The stall prevention control means includes a discharge pressure detection means for detecting a discharge pressure of the hydraulic pump, an inlet pressure detection means for detecting an inlet pressure of the hydraulic motor, and stores a preset set ratio. Storage means, and second discharge amount control means for controlling the discharge amount of the hydraulic pump such that the ratio of the discharge pressure to the inlet pressure is maintained at or above the set ratio. Item 9).

According to this configuration, the discharge pressure of the hydraulic pump and the inlet pressure of the hydraulic motor are detected, and the discharge amount of the hydraulic pump is maintained so that the ratio of the discharge pressure to the inlet pressure is maintained at a predetermined ratio or more. Is controlled, it is possible to prevent the suspended load from becoming unwound and stopping or being rolled down during hoisting.

According to a ninth aspect of the present invention, in the control device for the hoisting device, the flow rate of the hydraulic oil provided to the direction switching valve and supplied from the hydraulic pump to the hydraulic motor in accordance with the load pressure of the hydraulic motor. (Flow rate control valve) for controlling the pressure (claim 10).

According to this configuration, since the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic motor is controlled according to the load pressure of the hydraulic motor, the ratio of the discharge pressure to the inlet pressure is set in advance. The discharge amount of the hydraulic pump is controlled so as to be maintained at or above the set ratio, during hoisting, the suspended load does not wind up and stops,
Rolling down is more reliably prevented.

The control device for a hoisting device according to claim 9 or 10, wherein said directional control valve is controlled such that a ratio of said discharge pressure to said inlet pressure is maintained at or above said set ratio. It is provided with a valve control means (claim 11).

According to this configuration, the directional control valve is further controlled so that the ratio of the discharge pressure to the inlet pressure is maintained at or above the set ratio. Stopping or rolling down is more reliably prevented.

[0029]

FIG. 1 is a hydraulic circuit diagram of a first embodiment of a hoist to which the present invention is applied. The hoisting device includes a hoisting drum 1 for hoisting and lowering a suspended load,
A brake device 2 for braking the hoisting drum 1, a hydraulic motor 3 for driving the hoisting drum 1 to rotate, a hydraulic pilot type directional switching valve 4 for controlling the rotation direction and rotation speed of the hydraulic motor 3, Electromagnetic proportional pressure reducing valves 7 and 8 for controlling the operating positions of a hydraulic pump 5 as a hydraulic pressure supply source for the motor 3, a relief valve 6 of a hydraulic circuit, and a direction switching valve 4.
And an electromagnetic proportional pressure reducing valve 9 for controlling the tilt angle of the hydraulic pump 5
An operation lever 10 for an operator to operate, an operation amount detector 11 for detecting an operation amount of the operation lever 10,
A low-speed command switch 12 for minimizing the tilt angle of the hydraulic pump 5, a rotation speed detector 13 for detecting the rotation speed of the hoisting drum 1, and a controller 14 for controlling the operation of the hoisting device. A tank 15 for storing hydraulic oil,
A counterbalance valve 17 provided in a hydraulic drive circuit 16 between the hydraulic motor 3 and the direction switching valve 4, and auxiliary hydraulic sources 7 a, 8 a connected to the electromagnetic proportional pressure reducing valves 7, 8 are provided.

The operating lever 10 is used by an operator to instruct lifting and lowering of a suspended load, and its speed and stop. The operation amount detector 11 detects the operation direction and lever angle of the operation lever 10, that is, the operation amount, converts the operation amount into a voltage signal of a level corresponding to the operation amount, and converts the voltage signal into a voltage corresponding to the operation amount.
To be sent.

The rotation speed detector 13 is fixed to the rotating shaft of the hoisting drum 1 and has a pulse plate provided with a number of slits at equal intervals on a circumference having the same radius from the center of the shaft. An optical encoder consisting of a light-emitting unit such as an LED arranged on one side and a photo-interrupter consisting of a light-receiving unit such as a photodiode arranged on the other side. Is sent from the photointerrupter to the controller 14.

The controller 14 is composed of a microcomputer or the like and has a memory 14a. The controller 14 sends a current signal of a level corresponding to the operation direction and the lever angle of the operation lever 10 to the electromagnetic proportional pressure reducing valves 7 and 8. When the operation direction of the operation lever 10 is lowering, the current signal is sent to the electromagnetic proportional pressure reducing valve 7 and when the operation lever 10 is winding up, the current signal is transmitted to the electromagnetic proportional pressure reducing valve 8. Further, the controller 14 controls the operation lever 1
When 0 is the neutral position, the minimum current signal sp _{0 is} set in advance so that the discharge amount of the hydraulic pump 5 is equal to or less than the minimum flow rate.
Is output to the electromagnetic proportional pressure reducing valve 9.

Further, the controller 14 controls the operation lever 1
A current signal having a level corresponding to the operation amount of 0 is sent to the electromagnetic proportional pressure reducing valve 9 and when the fine speed command switch 12 is turned on, the upper limit value sp _MAX set in advance to the electromagnetic proportional pressure reducing valve 9 is set to the upper limit. To send the hydraulic pump 5
Is set to a minute angle set in advance to minimize the discharge amount of hydraulic oil.

At this time, the controller 14 calculates the rotation speed V of the hoisting drum 1 using the detection signal from the rotation speed detector 13 during the winding, as described later, and also calculates the calculated rotation speed. V is compared with a preset minimum rotation speed V _MIN, and when V ≦ V _MIN , the electromagnetic proportional pressure-reducing valve 8 has a minimum compensation reference value sv ₀ or more so that stall does not occur in the hoisting drum 1. A current signal having a level equal to or higher than the minimum compensation reference value sp ₀ is sent to the level and electromagnetic proportional pressure reducing valve 9.

The minimum rotation speed V _MIN is set to a value at which the hoist drum 1 does not stall.

The memory 14a stores the upper limit value sp _MAX , the minimum current signal sp _MIN , the minimum rotation speed V _MIN, and other preset values described later.

The electromagnetic proportional pressure reducing valves 7 and 8 are connected to the controller 1
The opening is adjusted to an opening corresponding to the level of the current signal supplied from the auxiliary signal source 4, and the pilot pressure from the auxiliary hydraulic sources 7 a, 8 a according to the opening is supplied to the direction switching valve 4. The directional control valve 4 is operated by switching between three positions of a hoisting position A, a neutral position B, and a lowering position C by the pilot pressure supplied from the electromagnetic proportional pressure reducing valves 7 and 8.

The operation of the hoist will now be described. When the operation lever 10 is operated by the operator, the operation amount detector 11 converts the operation signal into a voltage signal having a level corresponding to the operation amount and sends the voltage signal to the controller 14. The lowering and the magnitude of the speed are determined.

For example, in the case of hoisting, a current signal of a level corresponding to the hoisting speed is output from the controller 14 to the electromagnetic proportional pressure reducing valve 8, and the pilot signal supplied from the electromagnetic proportional pressure reducing valve 8 to the direction switching valve 4. The directional control valve 4 moves to the right by the pressure, and hydraulic oil is sent from the hydraulic pump 5 to the hydraulic motor 3 in the direction of the arrow in the hydraulic drive circuit 16 in the figure.

When the operation amount of the operation lever 10 increases, the pilot pressure supplied from the electromagnetic proportional pressure reducing valve 8 to the directional control valve 4 also increases, and the hydraulic oil returned to the tank 15 by bleed-off inside the directional control valve 4. As the flow rate decreases, the flow rate sent to the hydraulic motor 3 increases. At the same time, a current signal of a level corresponding to the operation amount is output from the controller 14 to the electromagnetic proportional pressure reducing valve 9, and the discharge amount of the hydraulic oil discharged from the hydraulic pump 5 also increases. Thereby, the hoisting speed and the driving force of the hoisting drum 1 increase.

On the other hand, in the case of lowering, the controller 14 similarly controls the electromagnetic proportional pressure reducing valve 7 and the electromagnetic proportional pressure reducing valve 9.
, The directional control valve 4 moves to the left, hydraulic oil is sent from the hydraulic pump 5 through the hydraulic drive circuit 16 to the hydraulic motor 3 in the direction opposite to the arrow in FIG. The hoisting drum 1 rotates at the lowering speed according to the operation amount of.

When the low-speed command switch 12 is turned on, the level of the current signal output from the controller 14 to the electromagnetic proportional pressure reducing valves 7 and 8 varies according to the operation amount of the operation lever 10. However, the electromagnetic proportional pressure reducing valve 9
Is set to a level such that the discharge amount of the hydraulic pump 5 becomes a preset minimum flow rate.

At this time, the rotation speed V of the hoisting drum 1 is detected by a procedure described later, and the pump 5 is controlled so that the rotation speed V does not satisfy V ≦ V _MIN with respect to the minimum rotation speed V _MIN . A current signal at a level at which a required minimum flow rate of the discharge amount sent to the hydraulic motor 3 is obtained is output from the controller 14 to the electromagnetic proportional pressure reducing valve 9.

The operation amount of the operation lever 10 is small,
If the bleed-off amount inside the direction switching valve 4 is large and the rotation speed V of the hoisting drum 1 does not reach the minimum rotation speed _VMIN , the electromagnetic proportional pressure reducing valve 7 is used to reduce the bleed-off amount. , 8 are also increased.

Thus, even when the weight of the suspended load is large, it is possible to prevent the hoisting drum 1 from stopping during the hoisting operation and from causing a stall.

FIG. 2 is a flowchart showing a control procedure of the electromagnetic proportional pressure reducing valves 7 and 8. The control of the electromagnetic proportional pressure reducing valves 7 and 8 is repeatedly performed by the controller 14 every predetermined sampling cycle.

First, it is determined whether or not the operation lever 10 is in the neutral position (step # 10). If it is in the neutral position (YES in step # 10), the electromagnetic proportional pressure reducing valves 7, 8
Is not performed, the operation flag FLG1 indicating that the operation is being performed is reset to 0 (step # 150), and the process returns to step # 10.

On the other hand, if the operating lever 10 is not at the neutral position (NO in step # 10), the operator is performing the operation of hoisting or lowering, and the operating lever 10 to be output to the electromagnetic proportional pressure reducing valves 7 and 8 is operated. A current signal sv of a level corresponding to the operation amount is calculated (step # 20).

Next, it is determined whether the operating direction of the operating lever 10 is hoisting or lowering (step #).
30) In the case of lowering (NO in step # 30),
The calculated current signal sv is output as it is to the electromagnetic proportional pressure reducing valve 7 (step # 120), and proceeds to step # 140.

On the other hand, in the case of winding (step # 30)
Is YES), and the operation flag FLG1 is determined (step # 4)
0), if the operation flag FLG1 = 1, that is, if the operation lever 10 is operated in the previous cycle (NO in step # 40), the process proceeds to step # 60, where the operation flag FLG1 = 0,
That is, if the operation lever 10 has not been operated in the previous cycle (YES in Step # 40), Step # 2
Using the current signal sv calculated at 0, the minimum compensation reference value sv ₀
Is set (step # 50).

Next, the rotation speed V of the hoisting drum 1 is calculated using the detection signal from the rotation speed detector 13 (step # 60), and the magnitude of the rotation speed V and the minimum rotation speed V _MIN are determined (step # 60). (Step # 70) If V> V _MIN (NO in Step # 70), the process proceeds to Step # 90,
On the other hand, if V ≦ V _MIN (YE in step # 70)
S), a predetermined amount Δsv ₀ stored in the memory 14a is added to the minimum compensation reference value sv ₀ and sv ₀ = sv ₀ + Δ
sv ₀ is set (step # 80).

[0052] Then, step # 20 the magnitude of the current signal sv calculated minimum compensation reference value sv ₀ is discriminated in (step # 90), if sv <sv ₀ (in step # 90 N
O), a current signal sv ₀ is output to the electromagnetic proportional pressure reducing valve 8 (step # 110), and the process proceeds to step # 140. If sv ≧ sv ₀ (YES in step # 90), in step # 20 The calculated current signal sv is output to the electromagnetic proportional pressure reducing valve 8 (Step # 100).

Next, the operation flag FLG1 is set to 1 (step # 140), and the process returns to step # 10.

FIG. 3 is a flowchart showing a control procedure of the electromagnetic proportional pressure reducing valve 9. The control of the electromagnetic proportional pressure reducing valve 9 is performed by the controller 14 similarly to the electromagnetic proportional pressure reducing valves 7 and 8 in FIG.
Is repeated every predetermined sampling period.

First, it is determined whether or not the operation lever 10 is at the neutral position (step # 210). If it is in the neutral position (YES at step # 210), the minimum current signal
sp _MIN is output to the proportional pressure reducing valve 9 (step # 36).
0), the operation flag FLG2 indicating that the operation is being performed is reset to 0 (Step # 380), and Step # 210
Return to

On the other hand, if the operation lever 10 is not at the neutral position (NO in step # 210), the operator is performing the hoisting or lowering operation, and the operation amount of the operating lever 10 to be output to the electromagnetic proportional pressure reducing valve 9 Is calculated (step # 220).

Next, it is determined whether or not the slow speed command switch 12 is turned on (step # 225). If it is not turned on (NO in step # 225), the process proceeds to step # 260 and is turned on. If (YES in step # 225), an upper limit value sp _MAX that minimizes the tilt angle of pump 5 is set (step # 230).

Next, the magnitude of the current signal sp calculated in step # 220 and the upper limit value sp _MAX is determined (step # 220).
240), if sp ≦ sp _MAX (N in step # 240)
O) The process proceeds to step # 260. On the other hand, if sp> sp _MAX (YES in step # 240), the upper limit value sp _MAX is set as the current signal sp (step # 250).

Subsequently, it is determined whether the operation direction of the operation lever 10 is hoisting or hoisting (step #).
260), in the case of lowering (N in step # 260)
O), the current signal sp is output to the electromagnetic proportional pressure reducing valve 9 (Step # 350), and the process proceeds to Step # 370.

On the other hand, in the case of winding (step # 26)
0 and YES), and the operation flag FLG2 is determined (step #)
270), if the operation flag FLG2 = 1, that is, if the operation lever 10 has been operated in the previous cycle (step # 2)
(NO at 70), proceeds to step # 290 to operate flag FL
G2 = 0, i.e. if it is not operated the operating lever 10 in the previous cycle (YES in Step # 270), the minimum compensation reference value sp ₀ by using the current signal sp is set (Step # 280).

Next, the rotation speed V of the hoisting drum 1 is calculated using the detection signal from the rotation speed detector 13 (step # 290), and the rotation speed V and the minimum rotation speed V _MIN are calculated.
Is determined (step # 300), and if V> V _MIN (NO in step # 300), step # 320
If V ≦ V _MIN (step # 300)
YES), a predetermined amount Δsp ₀ stored in the memory 14a is added to the minimum compensation reference value sp ₀ , and sp ₀ = s
p ₀ + Δsp ₀ is set (step # 310).

Next, the current signal sp and the minimum compensation reference value sp ₀
Magnitude is determined in (Step # 320), if the sp <sp ₀ (NO at step # 320), the current signal sp ₀ is output to the solenoid proportional pressure reducing valve 9 (Step # 340), the step # 370 On the other hand, if sp ≧ sp ₀ (YES in step # 320), the current signal sp
(Step # 330).

Next, the operation flag FLG2 is set to 1 (step # 370), and the process returns to step # 210.

As described above, according to the first embodiment, during winding, the rotation speed V of the hoisting drum 1 is detected, and when this rotation speed V becomes equal to or lower than the preset minimum rotation speed V _MIN , Since the minimum compensation reference values sv ₀ and sp ₀ of the current signals output to the proportional pressure reducing valves 8 and 9 are increased, it is possible to reliably prevent the hoisting drum 1 from stopping or causing a stall. . Thereby, safety and operability of the hoisting device can be improved.

FIG. 4 shows a second embodiment of the hoisting device to which the present invention is applied.
It is a hydraulic circuit diagram of an embodiment. The hoisting device according to the second embodiment includes pressure detectors 18 and 19 instead of the rotation speed detector 13 according to the first embodiment. The pressure detector 18 detects the discharge pressure of the hydraulic pump 5 and sends a voltage signal of a level corresponding to the detected discharge pressure to the controller 14. The pressure detector 19 detects an inlet pressure when the hydraulic motor 5 is hoisted, and sends a voltage signal of a level corresponding to the detected inlet pressure to the controller 14.

During the hoisting operation, the controller 14 controls the discharge pressure Pp of the hydraulic pump 5 input from the pressure detector 18 and the discharge pressure Pp of the hydraulic motor 5 input from the pressure detector 19, as described later. And the ratio Pr = Pp / Ph of the discharge pressure to the inlet pressure using the inlet pressure Ph
In order to keep the calculated ratio Pr equal to or higher than the theoretical pressure ratio PR, which is a device-specific value, the electromagnetic proportional pressure reducing valve 8 supplies a current signal having a level equal to or higher than the minimum compensation reference value sv ₀ and the electromagnetic proportional pressure reducing valve 9 supplies a minimum value. A current signal having a level equal to or higher than the compensation reference value sp _{0 is} transmitted.

Further, the memory 14a of the second embodiment is provided with a predetermined constant for giving a certain width to the theoretical pressure ratio PR and the theoretical pressure ratio PR instead of the minimum rotation speed V _MIN. A and the preset maximum value sv _MAX of the compensation reference value sv ₀ for performing the stall prevention control in the electromagnetic proportional pressure reducing valve 8 are stored, and the upper limit value sp _MAX , the minimum current signal sp _MIN, and the later described Other preset values and the like are stored.

FIG. 5 shows an electromagnetic proportional pressure reducing valve 7 according to the second embodiment.
8 is a flowchart illustrating a control procedure of No. 8; The control of the electromagnetic proportional pressure reducing valves 7 and 8 is repeatedly performed by the controller 14 every predetermined sampling cycle.

First, it is determined whether or not the operating lever 10 is at the neutral position (step # 410). If the operating lever 10 is at the neutral position (YES at step # 410), the output to the electromagnetic proportional pressure reducing valves 7, 8 is not performed. , The operation flag FLG1 indicating that the operation is being performed is reset to 0 (step # 64)
0), returning to step # 410.

On the other hand, if the operating lever 10 is not in the neutral position (NO in step # 410), the operator is performing the lifting operation or the lowering operation, and the operation lever 10 to be output to the electromagnetic proportional pressure reducing valves 7 and 8 is operated. A current signal sv of a level corresponding to the operation amount is calculated (Step # 420).

Next, it is determined whether the operating direction of the operating lever 10 is hoisting or lowering (step #).
430), in the case of lowering (N in step # 430)
O), the calculated current signal sv is output as it is to the electromagnetic proportional pressure reducing valve 7 (step # 610), and step # 630
Proceed to.

On the other hand, in the case of winding (step # 43)
0 and YES), and the operation flag FLG1 is determined (step #)
440), if the operation flag FLG1 = 1, that is, if the operation lever 10 has been operated in the previous cycle (step # 4)
(NO at 40), the process proceeds to step # 460, and the operation flag FL
If G1 = 0, that is, if the operating lever 10 has not been operated in the previous cycle (YES in step # 440), the minimum compensation reference value sv ₀ is set using the current signal sv calculated in step # 420. (Step # 450).

Next, the pump discharge pressure is detected from the pressure detector 18.
At the same time as Pp is taken in, the motor inlet pressure Ph is taken in from the pressure detector 19 (Step # 460), and the ratio Pr = Pp / Ph of the pump discharge pressure Pp to the motor inlet pressure Ph is calculated (Step # 470).

Next, the calculated ratio Pr and the theoretical pressure ratio PR
And PR × A are discriminated (steps # 480, # 480).
490), if Pr <PR (YE in step # 480)
S), proceeding to step # 500, if PR ≦ Pr ≦ PR × A (NO in step # 480 and NO in step # 490), proceed to step # 520, and if PR × A <Pr (step NO at # 480 and Y at step # 490
ES), and proceeds to step # 540.

Then, in step # 500, Pr <
Since PR may cause a stall, the subtraction flag FL
G3 is reset to 0, then a set amount? SV ₁ set in advance is stored in the memory 14a is added to the minimum compensation reference value sv _0, the minimum compensation reference values a new sv ₀ = sv ₀ +
Δsv ₁ is calculated (Step # 510), and Step # 5
Proceed to 60.

In step # 520, it is determined whether the subtraction flag FLG3 is set. If the subtraction flag FLG3 is set to 1 (step # 52).
0, NO). In this case, since the minimum compensation reference value sv ₀ is excessive, the minimum compensation reference value sv _{0 is} subtracted from the minimum compensation reference value sv ₀ by the set amount Δsv ₁ to obtain a new minimum compensation reference value sv ₀ = sv ₀ −Δsv. ₁ is calculated (Step # 530), and the process proceeds to Step # 560.

On the other hand, if the subtraction flag FLG3 has been reset to 0 in step # 520 (step # 52)
0, YES), the process proceeds to step # 560 while keeping the minimum compensation reference value sv _{0 as it} is.

[0078] Further, in step # 540, the subtraction flag FLG3 is set to 1, then the minimum compensation reference value sv ₀ in this case is excessive, subtracted from the minimum compensation reference value sv ₀ set amount? SV ₁ And the new minimum compensation reference value s
v ₀ = sv ₀ −Δsv ₁ is calculated (step # 550), and the process proceeds to step # 560.

Next, in step # 560, the magnitude of the minimum compensation reference value sv ₀ and the maximum value of the compensation reference value sv _MAX are determined. If sv ₀ <sv _MAX (N in step # 560)
O), proceeding to step # 580, if sv ₀ ≧ sv _MAX (YES in step # 560), the maximum value sv of the compensation reference value
_MAX is set as the minimum compensation reference value sv ₀ (step # 570), and then the magnitude of the current signal sv calculated in step # 420 and the minimum compensation reference value sv ₀ is determined (step # 58).
0).

If sv <sv ₀ (step # 5)
(NO at 80), the current signal sv ₀ is output to the electromagnetic proportional pressure reducing valve 8 (step # 600), and the process proceeds to step # 630, while if sv ≧ sv ₀ (YE at step # 580).
S), the current signal sv calculated in Step # 420 is output to the electromagnetic proportional pressure reducing valve 8 (Step # 590).

Next, the operation flag FLG1 is set to 1 (step # 630), and the process returns to step # 410.

FIGS. 6 and 7 are flowcharts showing the control procedure of the electromagnetic proportional pressure reducing valve 9 of the second embodiment. The control of the electromagnetic proportional pressure-reducing valve 9 is repeatedly performed by the controller 14 every predetermined sampling period, similarly to the electromagnetic proportional pressure-reducing valves 7 and 8 in FIG.

First, it is determined whether or not the operation lever 10 is at the neutral position (step # 710). If it is the neutral position (YES at step # 710), the minimum current signal
sp _MIN is output to the proportional pressure reducing valve 9 (step # 94).
0), the control flag FLG5 indicating that the stall prevention control is being performed is reset to 0, indicating that the vehicle is in the normal control state (step # 960), and the process returns to step # 710.

On the other hand, if the operation lever 10 is not at the neutral position (NO in step # 710), the operator is performing the operation of raising or lowering, and the operation amount of the operation lever 10 to be output to the electromagnetic proportional pressure reducing valve 9 Is calculated (step # 720).

Next, it is determined whether or not the slow speed command switch 12 is turned on (step # 725). If it is not turned on (NO in step # 725), the process proceeds to step # 760 and is turned on. If (YES in step # 725), the upper limit value sp _MAX that minimizes the tilt angle of the pump 5 is set (step # 730).

Next, the magnitude of the current signal sp calculated in step # 720 and the upper limit sp _MAX is determined (step # 720).
740), if sp ≦ sp _MAX (N in step # 740)
O), the process proceeds to step # 760. On the other hand, if sp> sp _MAX (YES in step # 740), the upper limit value sp _MAX is set as the current signal sp (step # 750).

Subsequently, it is determined whether the operating direction of the operating lever 10 is hoisting or hoisting (step #).
760), in the case of lowering (N in step # 760)
O), the current signal sp is output to the electromagnetic proportional pressure reducing valve 9 (Step # 930), and the process proceeds to Step # 960.

On the other hand, in the case of winding (step # 76)
0, YES), a determination similar to that of step # 560 in FIG. 5,
That is, the minimum compensation reference value sv ₀ for the electromagnetic proportional pressure reducing valve 8
And the maximum value sv _MAX of the compensation reference value are determined (step # 770). If sv ₀ <sv _MAX (step # 770)
NO), the stall prevention control is performed only by the electromagnetic proportional valve 8 without being performed by the electromagnetic proportional valve 9, and the process proceeds to step # 930.

On the other hand, in step # 770, sv ₀ ≧ s
If v is _MAX (YES in step # 770), the stall prevention control cannot be performed only by the electromagnetic proportional pressure reducing valve 8, so that the process proceeds to step # 780 and the stall prevention control is also performed by the electromagnetic proportional pressure reducing valve 9.

At step # 780, the control flag FL
If G5 is determined and the control flag FLG5 = 1, that is, if the stall prevention control has been performed in the previous cycle (NO in step # 780), the process proceeds to step # 800, while the control flag FLG5 = 0, that is, If the stall prevention control is not performed in the cycle (Y in step # 780)
ES), the minimum compensation reference value sp ₀ is set using the current signal sp (step # 790).

Next, the pump discharge pressure is detected from the pressure detector 18.
At the same time as Pp is taken in, the motor inlet pressure Ph is taken in from the pressure detector 19 (Step # 800), and the ratio Pr = Pp / Ph of the pump discharge pressure Pp to the motor inlet pressure Ph is calculated (Step # 810).

Next, the calculated ratio Pr and the theoretical pressure ratio PR
And PR × A are determined (steps # 820 and # 820).
830), if Pr <PR (YE in step # 820)
S), proceeding to step # 840, if PR ≦ Pr ≦ PR × A (NO in step # 820 and NO in step # 830), proceed to step # 860 and if PR × A <Pr (step NO in # 820 and Y in step # 830
ES), and proceeds to step # 880.

Then, in step # 840, Pr <
Since PR may cause a stall, the subtraction flag FL
G4 is reset to 0, then a set amount whose ASP ₁ set in advance is stored in the memory 14a is added to the minimum compensation reference value sp _0, a new minimum compensation reference value sp ₀ = sp ₀ +
Δsp ₁ is calculated (Step # 850), and Step # 9
Go to 00.

In step # 860, it is determined whether or not the subtraction flag FLG4 is set. If the subtraction flag FLG4 is set to 1 (step # 86)
0 NO), the minimum compensation reference value sp ₀ in this case is excessive, set amount Δsp only is subtracted from the minimum compensation reference value sp _{0 1,} a new minimum compensation reference value sp ₀ = sp ₀ -Δsp ₁ is calculated (Step # 870), and the routine proceeds to Step # 900.

On the other hand, if the subtraction flag FLG4 has been reset to 0 in step # 860 (step # 86)
(0 and YES), the process proceeds to step # 900 with the minimum compensation reference value sp ₀ unchanged.

[0096] Further, in step # 880, the minimum compensation reference value sp ₀ in this case is excessive, the subtraction flag FLG4 is set to 1, then subtracted from the minimum compensation reference value sp ₀ set amount whose ASP ₁ Then, a new minimum compensation reference value sp ₀ = sp ₀ −Δsp ₁ is calculated (Step # 890).
Proceed to step # 900.

Next, in step # 900, the magnitude of the current signal sp and the minimum compensation reference value sp ₀ is determined, and sp <sp ₀
If (NO in step # 900), the current signal sp ₀ is output to the electromagnetic proportional pressure reducing valve 9 (step # 920),
Proceeding to step # 950, if sp ≧ sp ₀ (YES in step # 900), a current signal sp is output to the electromagnetic proportional pressure reducing valve 9 (step # 910).

Next, the control flag FLG5 is set to 1 (step # 950), and the process returns to step # 710.

As described above, according to the second embodiment, the pump discharge pressure Pp and the motor inlet pressure Ph are detected during hoisting,
Ratio of pump discharge pressure Pp to motor inlet pressure Ph: Pr = Pp / Ph
When this ratio Pr becomes equal to or less than the theoretical pressure ratio PR, the minimum compensation reference value sv of the current signal output to the electromagnetic proportional pressure reducing valve 8 is calculated.
_{Since 0} is increased, it is possible to prevent the hoisting drum 1 from stopping or causing a stall.

When the increased minimum compensation reference value sv ₀ is equal to or greater than the set maximum value sv _MAX , the minimum compensation reference value sp ₀ of the current signal output to the electromagnetic proportional pressure reducing valve 9 is further increased. Therefore, it is possible to reliably prevent the hoisting drum 1 from stopping or causing a stall. Thereby, safety and operability of the hoisting device can be improved.

The present invention is not limited to the above embodiment, but can adopt the following modifications (1) to (6).

(1) In the first and second embodiments, the rotation speed V of the hoisting drum 1 is set to the predetermined minimum rotation speed V
_When the pressure becomes equal to or less than _MIN (first embodiment) or when the pressure ratio Pr becomes equal to or less than the theoretical pressure ratio PR (second embodiment), the minimum compensation reference value s of the current signal output to the electromagnetic proportional pressure reducing valves 8 and 9 is obtained.
Although the levels of v ₀ and sp ₀ are each increased by the set amount, similar effects may be obtained by using PID control or other known control methods.

(2) In the first and second embodiments, the rotation speed V of the hoisting drum 1 is set to the predetermined minimum rotation speed V
_When the pressure becomes equal to or less than _MIN (first embodiment) or when the pressure ratio Pr becomes equal to or less than the theoretical pressure ratio PR (second embodiment), the minimum compensation reference value s of the current signal output to the electromagnetic proportional pressure reducing valves 8 and 9 is obtained.
Although the levels of v ₀ and sp ₀ are each increased by a set amount, normal control is performed on the electromagnetic pressure reducing valve 8, and the minimum compensation reference value of the current signal output to the electromagnetic proportional pressure reducing valve 9 is obtained. Only the level of sp ₀ may be increased by the set amount. Also in this case, the stall of the hoisting drum 1 can be prevented to some extent.

(3) In the first and second embodiments,
A potentiometer operated by an operator may be provided instead of the slow speed command switch 12, and when the level input from the potentiometer to the controller 14 is equal to or less than a predetermined level, it may be determined that the slow speed is commanded.

(4) In the first and second embodiments,
Means for controlling the directional control valve 4 includes electromagnetic proportional pressure reducing valves 7 and 8
Not limited to For example, the operating lever may be constituted by a hydraulic pilot valve or the like, an electromagnetic proportional pressure reducing valve may be disposed between the pilot valve and the hydraulic pump, and the pilot pressure may be reduced by the electromagnetic proportional pressure reducing valve. In this case, the operation direction and the operation amount of the operation lever may be determined by disposing a pressure switch between the pilot valve and the electromagnetic proportional pressure reducing valve or by providing a limit switch on the pilot valve. .

(5) In the first and second embodiments,
As shown in FIG. 8, a flow control valve 20 that controls the flow rate of hydraulic oil supplied from the hydraulic pump 5 to the hydraulic motor 3 according to the load pressure of the hydraulic motor 3 may be provided to the direction switching valve 4. Good.

In this case, normal control is performed on the electromagnetic proportional pressure reducing valve 8 to increase only the level of the minimum compensation reference value sp ₀ of the current signal output to the electromagnetic proportional pressure reducing valve 9 by the set amount. Thus, stall of the hoisting drum 1 can be prevented.

(6) In the first embodiment, the rotation speed detector 13 is not limited to the above-described optical encoder, and the gear fixed to the rotation shaft of the hoisting drum 1 and the proximity switch are opposed to each other. Alternatively, a magnetic encoder configured to detect a rotational speed by detecting a change in magnetic flux generated in the groove may be used.

Further, it is connected to the rotating shaft of the hoisting drum 1 and
It is also possible to use a potentiometer that changes the output voltage by rotation and detects the rotation speed of the hoisting drum 1 based on the amount of voltage change per unit time.

[0110]

As described above, according to the present invention,
During the hoisting operation according to the operation amount of the operating means, the rotational speed of the hoist drum is detected, and the discharge amount of the hydraulic pump is controlled so that the detected rotational speed is maintained at a preset speed or higher. Thus, during hoisting, it is possible to prevent the suspended load from becoming unwound and stopping or being rolled down. Thereby, the movement of the suspended load against the operator's intention is eliminated, and operability and safety can be improved.

Further, the detected rotation speed of the hoist drum is compared with the set speed, and when the detected rotation speed becomes equal to or lower than the set speed, the minimum discharge amount of the hydraulic oil discharged from the hydraulic pump is increased to thereby increase the lifting speed. Even if the weight of the load is large, it is possible to prevent the suspended load from becoming unwound and stopping or rolling down during hoisting,
Thereby, the movement of the suspended load contrary to the operator's intention is eliminated, and operability and safety can be improved.

During the hoisting operation according to the operation amount of the operating means, the inlet pressure of the hydraulic motor and the discharge pressure of the hydraulic pump are detected, and the ratio of the discharge pressure of the hydraulic pump to the inlet pressure of the hydraulic motor is calculated. However, since the discharge rate of the hydraulic pump is controlled so that the calculated ratio is maintained at a preset ratio or more, during hoisting, the suspended load does not wind up and stops or rolls down. Can be prevented. Thereby, the movement of the suspended load against the operator's intention is eliminated, and operability and safety can be improved.

Further, the calculated ratio is compared with the set ratio,
When the calculated ratio is equal to or less than the set ratio, by increasing the minimum discharge amount of hydraulic oil discharged from the hydraulic pump, even if the weight of the suspended load is large, the suspended load does not wind up and stops during the hoisting. It is possible to prevent the hanging load from rolling down, thereby preventing the movement of the suspended load against the operator's intention, thereby improving operability and safety.

Further, during the hoisting operation according to the operation amount of the operating means, the direction switching valve is further controlled to prevent the suspended load from being hoisted and stopping or winding down during hoisting. Can be prevented more reliably.

Further, by detecting the rotation speed of the winding drum and controlling the discharge amount of the hydraulic pump so that the rotation speed is maintained at a preset speed or higher, the rotation speed of the winding drum can be reduced. Since the speed is always maintained at or above the set speed, it is possible to prevent the suspended load from becoming unwound and stopping or being rolled down during hoisting. Thereby, the movement of the suspended load against the operator's intention is eliminated, and operability and safety can be improved.

Further, by controlling the directional control valve so that the rotation speed of the hoisting drum is maintained at a preset speed or more, during hoisting, the suspended load can no longer be hoisted and stopped. , That it rolls down,
It can be prevented more reliably.

The discharge pressure of the hydraulic pump and the inlet pressure of the hydraulic motor are detected, and the ratio of the discharge pressure of the hydraulic pump to the inlet pressure of the hydraulic motor is maintained at or above a preset ratio. Since the discharge amount is controlled, it is possible to prevent the suspended load from becoming unwound and stopping or being rolled down during hoisting. Thereby, the movement of the suspended load against the operator's intention is eliminated, and operability and safety can be improved.

Further, a flow control valve for controlling the flow rate of the hydraulic oil supplied from the hydraulic pump to the hydraulic motor in accordance with the load pressure of the hydraulic motor is attached to the direction switching valve, so that the discharge pressure relative to the inlet pressure can be reduced. By controlling the discharge amount of the hydraulic pump so that the ratio is maintained at a preset ratio or more, during hoisting, it is more sure that the suspended load does not roll up and stops or rolls down. Can be prevented.

Further, by controlling the directional control valve so that the ratio of the discharge pressure of the hydraulic pump to the inlet pressure of the hydraulic motor is maintained at or above a preset ratio, the lifting load during the hoisting is controlled. Can be more reliably prevented from stopping and rolling down due to no longer winding up. Thereby, operability and safety can be reliably improved.

[Brief description of the drawings]

FIG. 1 is a hydraulic circuit diagram of a first embodiment of a hoisting device to which the present invention is applied.

FIG. 2 is a flowchart illustrating a control procedure of the electromagnetic proportional valves 7 and 8 according to the first embodiment.

FIG. 3 is a flowchart illustrating a control procedure of the electromagnetic proportional valve 9 of the first embodiment.

FIG. 4 is a hydraulic circuit diagram of a second embodiment of a hoisting device to which the present invention is applied.

FIG. 5 is a flowchart showing a control procedure of the electromagnetic proportional valves 7 and 8 of the second embodiment.

FIG. 6 is a flowchart showing a control procedure of the electromagnetic proportional valve 9 of the second embodiment.

FIG. 7 is a flowchart showing a control procedure of the electromagnetic proportional valve 9 of the second embodiment.

FIG. 8 is a diagram showing a main part of a hydraulic circuit of a modified form of the hoisting device to which the present invention is applied.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Hoisting drum 2 Brake device 3 Hydraulic motor 4 Direction switching valve 5 Hydraulic pump 6 Relief valve 7, 8 Electromagnetic proportional pressure reducing valve (valve control means, second valve control means) 7a, 8a Auxiliary hydraulic pressure source 9 Electromagnetic proportional pressure reducing valve (Discharge amount control means, second discharge amount control means) 10 Operation lever 11 Operation amount detector 12 Slow speed command switch 13 Rotation speed detector (rotation speed detection means) 14 Controller (valve control means, second valve control means) ,
Discharge amount control means, second discharge amount control means) 14a memory (storage means) 15 tank 16 hydraulic drive circuit 17 counter balance valve 18 pressure detector (discharge pressure detection means) 19 pressure detector (inlet pressure detection means) 20 Flow control valve

Claims (11)

[Claims] 1. A hydraulic pump, a hydraulic motor, a direction switching valve interposed between the hydraulic pump and the hydraulic motor, and valve control means for controlling the direction switching valve in accordance with an operation amount of an operation means. A hoisting device comprising: a discharge amount control unit that controls a discharge amount of the hydraulic pump according to an operation amount of the operation unit; and a hoisting drum that is rotatably driven by the hydraulic motor and winds up a suspended load. During the hoisting operation according to the operation amount of the operating means, the rotational speed of the hoist drum is detected, and the discharge amount of the hydraulic pump is adjusted so that the detected rotational speed is maintained at a preset speed or higher. A method for controlling a hoisting device, wherein the method is controlled. 2. The control method according to claim 1, wherein the detected rotation speed is compared with the set speed.
A control method for a hoisting device, wherein the minimum discharge amount of hydraulic oil discharged from the hydraulic pump is increased when the detected rotation speed is equal to or lower than the set speed. 3. A hydraulic pump, a hydraulic motor, a direction switching valve interposed between the hydraulic pump and the hydraulic motor, and valve control means for controlling the direction switching valve according to an operation amount of an operation means. A hoisting device comprising: a discharge amount control unit that controls a discharge amount of the hydraulic pump according to an operation amount of the operation unit; and a hoisting drum that is rotatably driven by the hydraulic motor and winds up a suspended load. During the hoisting operation according to the operation amount of the operating means, the inlet pressure of the hydraulic motor and the discharge pressure of the hydraulic pump are detected, and the ratio of the discharge pressure of the hydraulic pump to the inlet pressure of the hydraulic motor is calculated.
A control method for a hoisting device, wherein the discharge amount of the hydraulic pump is controlled so that the calculated ratio is maintained at or above a preset ratio. 4. The method according to claim 3, wherein the calculated ratio is compared with the set ratio, and when the calculated ratio is equal to or less than the set ratio, an operation discharged from the hydraulic pump. A method for controlling a hoisting device, wherein the minimum discharge amount of oil is increased. 5. The hoist control method according to claim 1, wherein the directional control valve is further controlled during the hoisting operation according to the operation amount of the operating means. A method for controlling a hoisting device. 6. A hydraulic pump, a hydraulic motor, a direction switching valve interposed between the hydraulic pump and the hydraulic motor, and valve control means for controlling the direction switching valve according to an operation amount of an operation means. A hoisting device comprising: a discharge amount control unit that controls a discharge amount of the hydraulic pump according to an operation amount of the operation unit; and a hoisting drum that is rotatably driven by the hydraulic motor and winds up a suspended load. A control device for a hoisting device, comprising stall prevention control means for preventing a stall of the hoist drum during a hoisting operation according to an operation amount of an operation means. 7. The stall prevention control means includes: a rotation speed detection means for detecting a rotation speed of the hoist drum; a storage means for storing a preset set speed; 7. The control device for a hoisting device according to claim 6, further comprising second discharge amount control means for controlling the discharge amount of said hydraulic pump so as to be held. 8. The stall prevention control means further comprises second valve control means for controlling the direction switching valve such that the rotation speed is maintained at or above the set speed. The control device for a hoisting device according to claim 7, wherein 9. The stall prevention control means includes a discharge pressure detection means for detecting a discharge pressure of the hydraulic pump, an inlet pressure detection means for detecting an inlet pressure of the hydraulic motor, and stores a preset set ratio. Storage means, and second discharge amount control means for controlling the discharge amount of the hydraulic pump so that the ratio of the discharge pressure to the inlet pressure is maintained at or above the set ratio. The control device for a hoisting device according to claim 6, wherein 10. The control device for a hoisting device according to claim 9, wherein a flow rate of hydraulic oil provided to said directional switching valve and supplied from said hydraulic pump to said hydraulic motor in accordance with a load pressure of said hydraulic motor. A control device for a hoisting device, comprising a flow control valve for controlling the pressure. 11. The control device for a hoisting device according to claim 9, wherein the direction switching valve is controlled such that a ratio of the discharge pressure to the inlet pressure is maintained at or above the set ratio. A control device for a hoisting device, comprising a valve control means.