JPH0438922B2 - - Google Patents

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for controlling a hydraulic drive system, such as one used for hoisting and lifting a suspended load on a crane, and particularly to a method for controlling a hydraulic drive system used for hoisting and lifting a suspended load of a crane. This invention relates to dead zone compensation control for a hydraulic drive system equipped with a plurality of hydraulic pumps.

(Prior Art and its Problems) In a hydraulic drive system used for hoisting and lifting a suspended load of a crane, it is necessary to change the operating speed of the hydraulic actuator depending on the load condition and usage conditions of the drive system. For this reason, the output capacity of the hydraulic pump for driving the hydraulic actuator must have a margin to be able to sufficiently cope with fluctuations in the operating speed of the hydraulic actuator.

However, since hydraulic pumps with a large output capacity are generally large and expensive, it is not applicable to install such a large capacity hydraulic pump in a mobile crane or the like. Therefore, there are many hydraulic drive systems that can drive a hydraulic actuator over a wide range from low speed to high speed by installing multiple hydraulic pumps with normal capacity and changing the number of hydraulic pumps used. It is used.

When a plurality of hydraulic pumps are used in this way, it is ideal that the output of the second hydraulic pump starts rising when the output of the first hydraulic pump is saturated. That is, output control of a hydraulic pump is generally performed by changing the opening area of an oil flow control valve provided corresponding to the pump in accordance with a drive signal. When used, it is ideal to have a characteristic like the synthetic aperture area line CL0 in FIG. 13a.

However, there are variations in the characteristics of hydraulic equipment used in hydraulic drive systems, and even if it is possible to set ideal characteristics as described above for one product, it is difficult to set the control characteristics for other products. In this case, the other products often deviate from the ideal characteristics as described above. Therefore, in reality, the ideal characteristic line CL0 in Figure 13a
There are many cases where it deviates from the

If a deviation occurs such that the saturation a ₁ of the opening area of the oil flow control valve in the first pump is to the right of the point in time a ₂ in the figure when the hydraulic control valve in the second hydraulic pump starts to open. As shown in Fig. 13b, a region Δu _D (hereinafter referred to as the "overlapping region") appears where the hydraulic fluid from the second hydraulic pump begins to merge before the first hydraulic pump becomes saturated. .

In such an overlap region Δu _D , the ratio of change in actuator operation to change in control signal,
In other words, the control sensitivity suddenly changes. Therefore, when a control signal is generated based on manual operation of a control lever, an unintended sudden change in actuator speed is likely to occur, making manual operation difficult.

Therefore, it is necessary to prevent the overlapping region Δu _D from appearing even if there are variations in characteristics between individuals as described above. To do this, it is necessary to set the pressure oil from the second hydraulic pump to start being supplied to the hydraulic actuator after a certain delay from the time when the drive output of the first hydraulic pump is expected to be saturated. It becomes necessary. That is,
As shown in Fig. 13c, the characteristics of the hydraulic control valve of the second pump are set so that the point _a2 at which the hydraulic control valve of the second pump starts to open is to the right of the saturation point _a1 of the first pump. (Specifically, the biasing spring constant of the hydraulic control valve is set so that the above operation occurs).

In this way, even if the saturation point of the output of the first hydraulic pump deviates somewhat from the ideal value due to variations between individual pumps, the overlapping region Δu _D will not appear.

However, if such a setting is made, after the first hydraulic pump becomes saturated and before the hydraulic fluid from the second hydraulic pump starts to merge, that is, in the region c in Fig. 13, there is a difference in Δu _A. In the region shown, the opening degree of the control valve of each hydraulic actuator does not change even if the control signal is increased. As a result, in this region Δu _A , the response sensitivity of the hydraulic actuator's operating speed to the control signal decreases significantly, so in this region Δu _A
becomes a "dead zone".

FIG. 12 is a graph showing such a dead zone from the operating speed characteristics of the hydraulic actuator, and is a region where the hydraulic actuator is driven by one hydraulic pump (hereinafter referred to as the "first speed region"). )
, and indicate a region (hereinafter referred to as "second speed region") in which driving is performed by two hydraulic pumps.

In FIG. 12, when the drive control signal u is continuously increased from 0, the hydraulic flow rate sent from one hydraulic pump to the hydraulic actuator starts to increase after passing through a certain play area, and accordingly The operating speed S of the hydraulic actuator also increases. Then, the speed S reaches the saturation speed S ₀₁ corresponding to the capacity of one hydraulic pump, but after that, the 13th
A dead zone R ₀ according to Δu _A in figure c follows.

As described above, in the dead zone _R0 , the operating speed S of the hydraulic actuator does not change even if the drive control signal u changes.

Further, after passing through this dead zone R ₀ , the first speed region shifts to the second speed region, and driving by the two hydraulic pumps begins.

If such a dead zone R ₀ exists, the control of the hydraulic actuator becomes unstable. For example, in the horizontal movement control of a suspended load in a crane, the control of the hydraulic actuator becomes unstable near the working radius corresponding to the boundary area between the first speed region and the first speed region. There is a problem in that the control deviation becomes large.

Because of this problem, it is desirable that the dead zone R ₀ does not exist, but in reality it is difficult to completely eliminate it. The reason is as follows.

(b) As mentioned above, since there are variations in the characteristics of hydraulic equipment depending on the product, it is not possible to uniformly determine the characteristics that completely eliminate the dead zone for each product.

(b) When the engine speed for driving the pump is low, the flow rate from the first hydraulic pump may be saturated before the opening area of the hydraulic control valve is saturated. Therefore, the width of the dead zone also changes depending on the engine speed.

(c) In order to change the drive from one hydraulic pump to two, the connection of the hydraulic circuit must be changed using a switching valve or the like. In addition, a certain amount of delay tends to occur in the operation of such switching valves and the like. For this reason, even if you try to merge the pressure oil from the second hydraulic pump after the drive output of the first hydraulic pump is saturated, it will not be possible to perform this operation instantly, and the dead zone will be completely closed. Removal is difficult.

(d) Gradually start switching the output of the second hydraulic pump before the drive output of the first hydraulic pump is saturated, and immediately after the first hydraulic pump is saturated, the pressure from the second hydraulic pump is increased. A modification is also conceivable in which oil starts to be supplied to the hydraulic actuator. However, in hydraulic drive systems, the conditions of their use (in the case of cranes,
(boom length, number of hooks, workability, etc.) often change. For this reason, even if the above-mentioned adjustment or control gain correction is performed under specific conditions, it is common for the device to not operate as intended under other conditions. For example, if the hydraulic drive system of a crane is adjusted under certain conditions and the multiplier is doubled, the drive control signal u is simply
It is not possible to eliminate the dead zone simply by doubling the value.

As described above, although it is desirable to completely eliminate the dead zone, it is actually difficult to essentially eliminate the dead zone by adjusting mechanical parts such as the settings of the control valve of the hydraulic pump. Therefore, it is desired to develop a method that assumes the existence of a dead zone in the mechanical part of a hydraulic system and can substantially compensate for such a dead zone by improving the control signal side.

As described above, the conventional control method has a problem in that it is not possible to effectively compensate for the dead zone regardless of the usage conditions.

(Object of the Invention) The present invention is intended to overcome the above-mentioned problems in the prior art, and is a control method capable of effectively compensating for dead zones in a hydraulic drive system equipped with a plurality of hydraulic pumps, regardless of usage conditions. The purpose is to provide

(Means for Achieving the Object) In order to achieve the above-mentioned object, the present invention is configured as follows.

That is, the hydraulic drive system to be controlled by the present invention is a system that satisfies the following conditions a to c.

(a) providing a plurality of hydraulic pumps that drive a predetermined hydraulic actuator; (b) changing the number of hydraulic pumps used and the flow rate of pressure oil sent from the hydraulic pump to the hydraulic actuator; (c) The hydraulic actuator has a dead zone in which the operating speed of the hydraulic actuator does not change even if the value of the control signal is changed when changing the number of the hydraulic pumps used.

In such a hydraulic drive system, the method of the present invention is configured to perform drive control of the hydraulic drive system while compensating for the dead zone.

Specifically, when changing the number of hydraulic pumps to be used, first, the value of the first control signal generated for controlling the flow rate of pressure oil from the hydraulic pump to the hydraulic actuator is changed to The second offset is changed by a predetermined offset amount determined according to the width of the dead zone determined from the relationship between the control signal and the operating speed of the hydraulic actuator.
generates a control signal. By controlling the hydraulic pump using this second control signal, control that compensates for the dead zone is made possible.

(Example) Hereinafter, as an example of the present invention, a method of controlling a hoisting and vertical hydraulic drive system in horizontal movement of a suspended load by a crane will be described. However, this explanation
"Overview of mechanical configuration" about this crane,
"Configuration of hydraulic drive system", "Configuration and operation of control device"
Do it in this order. Finally, a modification of this invention will be mentioned.

A. Overview of Mechanical Configuration of Crane FIG. 1 is a schematic external view showing an overview of the mechanical configuration of a crane incorporating a hydraulic drive system controlled by an embodiment of the present invention. In FIG. 1, this crane 1 has a crane main body 2
and a boom 3 attached to the end of the crane body 2 so as to be able to move up and down. this boom 3
One end of a boom elevating rope 4 is fixed to the tip of the boom elevating rope 4, and the other end of the boom elevating rope 4 is wound around a boom elevating drum 5 provided within the crane body 2. Therefore, by rotating this boom elevation drum 5,
The rope 4 for raising and lowering the boom is wound up and let out, whereby the boom 3 is raised and raised as shown by arrows α and (-α), and the height H of its tip changes.

On the other hand, a hook 7 is suspended from the tip of the boom 3 by a rope 6 for hoisting and lifting. This hoisting/up-down rope 6 is wound around a hoisting/up-down drum 8 provided within the crane body 2. Therefore, by rotating the hoisting/up-down drum 8, the hoisting/up-down rope 6 is wound/unrolled, and the hook 7 is thereby moved in the up/down direction (Z in the figure).
direction). By simultaneously performing the lifting and raising movements of the boom 3 and the hoisting and lifting movements of the hook 7, the load 9 suspended from the hook 7 maintains the height h from the horizontal plane. while moving in the horizontal direction (X direction in the figure).

On the other hand, the crane main body 2 is provided with an engine EG as a power source for the crane, and is also provided with a control device 10 for controlling, which will be described later, and an operation panel 11 for inputting operations by an operator. Further, a boom elevation angle detector 12 is provided near the boom foot of the boom 3 to detect an elevation angle θ of the boom 3 from a horizontal plane. As the boom elevation angle detector 12, an inclinometer type detector (for example, one equipped with a freely movable part and an oil damper) for detecting the angle with respect to the ground is used. A rope winding/feeding amount detector 13 is attached to an idler sheave provided near the tip of the boom 3 and guiding the hoisting/up-down rope 6. This rope winding/feeding amount detector 13 is constituted by a rotary encoder or the like, and is for detecting the winding/feeding amount of the hoisting/up/down rope 6 from the idler sheave rotation angle.

B. Configuration of Hydraulic Drive System FIG. 2 is a hydraulic circuit diagram showing the configuration of a hydraulic drive system for raising and raising the boom 3 and hoisting and raising the hook 7. In FIG. 2, this hydraulic drive system includes first and second main hydraulic pumps 21a and 21b that are rotationally driven by an engine EG (not shown in FIG. 2). Of these, hydraulic pressure from the first main hydraulic pump 21a is applied to the boom elevation hydraulic motor 23a via the boom elevation direction control valve 22a. This boom elevating hydraulic motor 23a is for rotationally driving the boom elevating drum 5 shown in FIG. Also, the first
The respective hydraulic pressures from the main hydraulic pumps 21a and 21b are used to rotate the hoisting drum 8 shown in FIG. Hydraulic motor 23 for hoisting and lifting
It is also given to b.

Among these control valves 22a to 22c, the pilot portion of the boom elevation control valve 22a has secondary side circuits 2 for a boom-raising proportional electromagnetic pressure reducing valve 26a and a boom-lowering electromagnetic proportional pressure reducing valve 27a.
4a and 25a are connected. Similarly, the pilot parts of the hoisting and lowering directional control valves 22b and 22c are provided with respective secondary circuits 2 of the hoisting electromagnetic proportional pressure reducing valve 26b and the hoisting lowering electromagnetic proportional pressure reducing valve 27b.
4b and 25b are connected.

Among these, the electromagnetic proportional pressure reducing valves 26a, 27a
The primary side of the boom elevation remote control valve 32a is connected to secondary side circuits 30a and 31a, respectively. The boom elevation remote control valve 32a is equipped with a pair of variable pressure reducing valves (not shown), and controls the secondary pressure to be applied to the secondary circuit 30a or 31a according to the operating direction and operating amount of the boom operating lever 33a. It has the function of controlling.

Further, boom lever pilot pressure detectors 36 and 37 for detecting the respective secondary pressures are provided in the secondary side circuits 30a and 31a of the boom elevation remote control valve 32a. And this boom lever pilot pressure detector 36, 37
Accordingly, the operating direction and operating amount of the boom operating lever 33a can be detected.

On the other hand, electromagnetic proportional pressure reducing valve 2 for hoisting and lowering
The primary sides of 6b and 27b are electromagnetic switching valves 28 and 29.
are connected to the secondary side of each. And, on the primary side of these electromagnetic switching valves 28, 29, secondary side circuits 30b, 31 of remote control valve 32b for winding/up/down are connected.
b is switchably connected to a secondary circuit 35 of a pilot hydraulic pump 34 driven by the engine EG. The remote control valve 32b for hoisting and lowering is equipped with a pair of variable pressure reducing valves (not shown), like the remote control valve 32a for raising and lowering the boom. Side circuit 3
This is for controlling the secondary pressure applied to 0b or 31b. In addition, in the figure, CV indicates a check valve.

An outline of the drive operation of the hydraulic drive system having such a configuration during horizontal movement is as follows. That is, when horizontally moving the suspended load 9 of FIG. 1, first, a mode changeover switch (not shown) provided on the operation panel 11 of FIG. 1 is switched to the horizontal movement control mode. Then, the electromagnetic switching valves 28 and 29 in FIG. 2 are urged upward in the figure, and hydraulic pressure from the secondary circuit 35 of the pilot hydraulic pump 34 is applied to the primary sides of the electromagnetic proportional pressure reducing valves 26b and 27b. Therefore, at this time, the operation of the winding/up/down operation lever 33b becomes irrelevant to drive control.

When the operator operates the boom operation lever 33a, hydraulic pressure corresponding to the direction and amount of operation is applied from the boom elevation remote control valve 32a to the primary side of the electromagnetic proportional pressure reducing valves 26a and 27a.

Electromagnetic proportional pressure reducing valves 26a, 27a and 26b,
27b operates in response to drive control signals V and U (not shown in FIG. 2) from a control system to be described later,
Thereby, the secondary circuits 24a, 25a, 24
The oil pressure inside b and 25b changes. These oil pressures are applied to the respective pilot portions of the boom elevation directional control valve 22a and the first and second hoisting/up/down directional control valves 22b, 22c.

Then, the boom elevation direction control valve 22a is gradually switched to the boom up (or boom down) position, and pressure oil from the main hydraulic pump 21a is supplied to the boom elevation hydraulic motor 23a. As a result, the hydraulic motor 23a rotationally accelerates, and the boom elevating drum 5 shown in FIG. 1 rotates. As a result, the boom elevating rope 4 shown in FIG. 1 is wound up or let out, and the boom 3 is raised or lowered.

On the other hand, the hoisting and up-down directional control valves 22b, 2 in FIG.
2c, the spring constant of the biasing spring of the first directional control valve 22b for hoisting and up-down is set smaller than the spring constant of the biasing spring of the second directional control valve 22c for hoisting and up-down. For this reason, the electromagnetic proportional pressure reducing valve 26b,
When the control signal U applied to 26c is small, only the first hoisting/lowering directional control valve 22b is switched to the hoisting (or hoisting/lowering) position, whereby the pressure oil from the main hydraulic pump 21a is changed to the hoisting/lowering hydraulic pressure. It is supplied to the motor 23b. As a result, the hydraulic motor 23b rotates and accelerates, the hoisting/up-down drum 8 shown in FIG. 1 rotates, and the hoisting/up-down rope 6 is wound up or let out. As a result, the hook 7 is raised or lowered.

On the other hand, if the control signal U applied to the electromagnetic proportional pressure reducing valves 26b and 26c is larger than a certain level,
When the first hoisting/up/down directional control valve 22b is turned on fully, switching in the second hoisting/up/down directional control valve 22c is started. As a result, the pressure oil from the first and second main hydraulic pumps 21a, 21b is combined and applied to the hoisting/lowering hydraulic motor 23b.
Therefore, in this case, the winding up/down drum 8 in FIG. 1 rotates at high speed, and the hanging load 9 is hoisted up or lowered at high speed. However, at this time, as will be understood from the explanation of the control system to be described later, the raising and raising motion of the boom 3 is also performed at high speed.

Stable horizontal movement of the suspended load 9 is realized by adjusting and controlling the relationship between the lifting and raising movements of the boom 3 and the hoisting and lifting movements of the hook 7 using a control device that will be described later. However, in these operations, the rotational speed of the hydraulic motors 23a, 23b (therefore, the boom elevation drum 5 and the hoisting/up/down drum 8) is controlled by the electromagnetic proportional pressure reducing valves 26a, 27a, and 2.
It is defined by the magnitude of drive control signals V and U given to 6b and 27b.

C. Configuration and Operation of Control Device FIG. 3 is a block diagram showing the configuration of a control device for controlling the hydraulic drive of the crane. This control system includes a boom elevation control system and a hoist up/down control system, of which the hoist up/down control system includes a feed forward control system and a feedback control system. Further, this control system is provided with means for compensating for a dead zone in the hoist vertical drive system, corresponding to the features of the present invention. The configuration and operation of these will be explained below.

(C-1) Boom elevation control system First, in the boom elevation control system, the detection value _D1 of the boom lever pilot pressure detectors 36 and 37 explained in FIG. 2 is used as a control input, and this input is used as shown in FIG. It is applied to the multiplier 42. As another input of this multiplier 42, boom elevation suppression pattern data _D2 (described later) stored in the boom elevation suppression pattern storage device 41 is given.
Then, a boom elevation signal D ₃ obtained by multiplying the detection value D ₁ and this suppression pattern data D ₂ is obtained.
is given to the boom elevation electromagnetic proportional pressure reducing valve 43 as an elevation drive control signal V. However, this boom elevation proportional electromagnetic pressure reducing valve 43 corresponds to the boom raising proportional electromagnetic pressure reducing valve 26a and the boom lowering proportional electromagnetic pressure reducing valve 27a shown in FIG.

By applying such an elevation drive control signal V to the boom elevation electromagnetic proportional pressure reducing valve 43, the boom elevation drive control signal V, which is configured by the boom elevation direction control valve 22a, the boom elevation hydraulic motor 23a, etc. shown in FIG. The boom elevation drive system 44 shown in Figure 3 is connected to the engine.
It operates based on the driving force of EG. As a result, the second
Depending on the operating direction and operating amount of the boom operating lever 33a shown in the figure, the boom 3 starts to be raised and raised.

Here, the boom elevation suppression pattern data _D2 shown in FIG. 3 mentioned above will be explained. During the horizontal movement of the hanging load 9, hunting is most likely to occur during the period immediately after the horizontal movement is started.
Therefore, in this embodiment, pattern data as shown in FIG. 4 is given as the boom elevation/height suppression pattern data _D2 , with the elapsed time t from the start of horizontal movement as a parameter. Then, even if the operator suddenly operates the boom operating lever 33a at the start of horizontal movement and the detected value _D1 of the boom lever pilot pressure detectors 36, 37 becomes a large value, the suppression pattern data in FIG. By multiplying this detected value _D1 by the value of the rising portion R1 of _D2 (<1), the boom elevation signal _D3 becomes a value smaller than _the detected value _D1 . Therefore, during the period corresponding to the rising portion _R1 in FIG. 4, the directional control valves 22a and 22b are gradually switched, so the upward and downward movement of the boom 3 is slow, and when the horizontal movement starts Hunting is prevented.

Then, after the horizontal movement starts, a certain amount of time t ₀
In the steady portion _R2 after (Fig. 4) has elapsed, the pattern data _D2 becomes "1", and the detected value _D1 corresponding to the operation amount of the boom operation lever 33a becomes the elevation drive control signal V as it is. .

Therefore, at the start of horizontal movement, hunting is prevented by slow boom raising and lowering movements.
As time elapses, the boom's elevation is accelerated, and in a steady state, the boom's elevation and elevation are realized as intended by the operator.

(C-2) Hanging cargo up/down control system Next, the hanging cargo up/down control system will be explained. As mentioned above, this hoist up/down control system has a feedforward control system and a feedback control system. Of these, in the feedforward control system, first, the detected value _D1 detected by the boom lever pilot pressure detectors 36 and 37 shown in FIG. 3 is applied to the multiplier 45. This multiplier 45
As another input, feedforward rise pattern data _D4 stored in the feedforward rise pattern memory 46 is given.

This feedforward startup pattern data
D ₄ is data prepared in order to prevent a sudden change in operation at the start of horizontal movement, similar to the boom elevation suppression pattern D ₂ described above, and is the same as the boom elevation suppression pattern D 2 described above in FIG. It has a similar pattern. Then, the multiplier 45 converts these data into
Data D ₅ obtained by multiplying D ₁ and D ₄ is provided to the arithmetic unit 47 .

This calculator 47 includes a boom elevation angle detector 1
The value of the boom elevation angle θ detected in step 2 is also input. Then, the calculator 47 calculates the value of K _F = K _ff cos θ (1) based on the feed forward gain K _ff set in the method described later and the boom elevation angle θ. , this value K _F is multiplied by the data D ₅ to obtain the feed forward amount u _f .

In addition, the factor "cos θ" is included in the above equation (1) because the boom elevation angle θ is (θ + Δθ).
Since the amount of elevation of the tip of the boom 3 when changing from This is due to the fact that it has to be done.

The amount of feed forward obtained in this way
u _f is added to the feedback amount u _b in an adder 48 to form a winding/up/down signal u. After this hoisting/up/down signal u undergoes dead band compensation in a compensator 56 (to be described later), it becomes a hoisting/up/down control signal U, and this signal U is given to the hoisting/up/down electromagnetic pressure reducing valve 49 as a pressure reducing control signal. This electromagnetic pressure reducing valve 49 for hoisting up and down is the electromagnetic proportional pressure reducing valve 2 for hoisting shown in FIG.
6b and the hoisting electromagnetic proportional pressure reducing valve 27b.

The hoisting hoist up/down drive system 50 shown in FIG. 3, which is composed of the hoisting/up/down directional control valve 22b in FIG. Based on the rate, the first
The winding/unwinding rope 6 shown in the figure is caused to wind up/feed out.

The above is the configuration and operation of the feed forward control system.

Next, the feedback control system will be explained. In this feedback control system, first,
The rope winding/feeding amount detector 13 shown in the figure detects the actual winding/feeding amount l of the winding/lowering rope 6. On the other hand, the value of the boom elevation angle θ detected by the boom elevation angle detector 12 described above is also given to the calculator 51. This calculator 51 calculates a target value l' of the winding/feeding amount of the hoisting/lowering rope 6 required to maintain the suspended load 9 at a predetermined height h, based on the value of the boom elevation angle θ. Calculation formula: l′=l _bppn (sinθ−sinθ ₀ ) ...(2). However, l _bppn is the length of the boom 3, and θ ₀ is the boom elevation angle at the start of horizontal movement.

The target value l' obtained in this way and the actual winding/unwinding amount l detected as described above are given to a subtractor 52, and in this subtractor 52, the deviation between them: Δh =l'-l...(3) is obtained.

This deviation Δh is input to the calculator 53, which calculates the sum of the proportional control component: K _p Δh and the integral control component: K _I ∫Δhdt=K _I Δh/s. However, s represents a Laplace operator. The feedback amount u _b thus obtained is added to the feedback amount u _f in the adder 48 as described above, and the winding/up/down control is executed based on the sum u.

Note that the calculator 53 calculates the boom lever pressure detection value.
It also has a function to determine whether it is horizontal retraction (boom up) or horizontal extrusion (boom down) based on D ₁ , and in the case of horizontal extrusion, it inverts the sign of the feedback signal u _b and outputs it. are doing. This is related to the fact that during horizontal extrusion, the electromagnetic proportional pressure reducing valve 26b for the hoist is operated, and during horizontal retraction, the electromagnetic proportional pressure reducing valve 27b for the hoist is operated. That is, for example, the hanging load 9
When the height of the rope becomes higher than the target value, it is necessary to increase the "lowering amount" of the hoisting/lowering rope 9 for horizontal retraction, but it is necessary to decrease the "hoisting amount" for horizontal extrusion. It is. In this way, horizontal retraction and horizontal extrusion are reverse operations.
As is well known.

That is, here, feedback control is performed based on the deviation between the target value l' of the rope winding/unwinding amount and the actual value l, and the combination of the feedback control described above and this feedback control is performed. Accordingly, the hoisting/lowering rope 6 is wound/reeled in accordance with the upward and downward movements of the boom 3. As a result, the suspended load 9 is moved horizontally.

(C-3) Dead Zone Compensation Next, dead zone compensation in this embodiment will be explained. As already explained, when controlling the speed of the hoisting drum 8 using a plurality of hydraulic pumps 21a and 21b, the dependence of the rotational speed S of the hoisting drum 8 on the hoisting/uploading drive control signal u is as follows. The result is as shown by the characteristic line C ₀ in FIG. Therefore, when the hoisting/up/down drive control signal u shown in FIG. Dead band in the speed part corresponding to ₀₁
R ₀ (Figure 5) occurs.

Therefore, in this embodiment, when changing the number of hydraulic pumps used, the hoisting/up/down drive control signal u is changed by a predetermined offset amount Δu to reduce the dead zone R ₀
substantially reduces the range of That is, when the winding/up/down drive control signal u is sequentially changed, there is a jump between points _P1 and _P2 on the characteristic line _C0 in FIG.
The aim is to reduce the range that remains above the dead zone _R0 . Furthermore, in this embodiment, compensation is also made for the dead zone E ₀ of the starting portion due to mechanical play or the like. This compensation is performed by jumping between the origin O and the point _P0 .

Hereinafter, a method for specifically performing such compensation will be explained with reference to the flowchart shown in FIG. 6. This compensation operation is the third
This is the operation when the compensation device 56 shown in the figure is configured by a microcomputer or the like. In addition, in this operation, hysteresis is provided in the compensation, and the offset amount Δu corresponding to the compensation amount is set smaller than the width of the dead zone _R0 , resulting in "incomplete compensation." The reason for performing such processing will be described later.

Note that in the following explanation, steps S6 and S9 of the flowchart in FIG. 6 and related text explanations will be based on the point P ₀ in FIG. 5 as the value of the signal u.
For convenience, the value expressed as a standard is used.
Therefore, for example, the value of u at point P ₀ in FIG. 5 is zero, and the value of u at P ₁ is (u ₀ +
w). It is obvious from FIG. 5 that in order to rewrite the value of u to a value based on the origin O in FIG. 5, it is sufficient to add Δu to the value of u.

First, in step S1 of Fig. 6, flag F is set to "0".
shall be. Then, in the next step S2, the engine speed is detected by the engine speed detector 54 shown in FIG.
Detect the rotation speed N. And step S3
Then, the data representing the engine speed N is applied to the offset amount setter 55 shown in FIG. 3, thereby determining the offset amount Δu.

As illustrated in Fig. 7, this means that the engine
Since the width of the dead zone _R0 changes depending on the rotational speed N of the EG, this process is for setting the offset amount Δu according to the rotational speed N. However, the vertical axis in FIG. 7 indicates the drum rotational speed normalized by the maximum rotational speed S _nax of each of the hoisting and lowering drums 8 at the angular rotational speed N of the engine EG.

For this purpose, a table expressing the correspondence between the engine rotational speed N and the offset amount Δu is written in advance in a memory (not shown) in the offset amount setter 55 shown in FIG. As can be seen from FIG. 7, as the engine speed N increases, the width of the dead zone R ₀ becomes narrower, so the relationship between N and Δu is set as shown in FIG. 8, for example.

Returning to FIG. 6, in step S4, the third
The value of the winding/up/down drive control signal u before compensation is taken from the adder 53 in the figure. In the next step S5, F=0
It is determined whether F=
Since the value is 0, the process proceeds to step S6, where the magnitude relationship between the value of the winding/up/down drive control signal u and a predetermined value _u0 is determined. As shown in Figure 5, the value of u ₀ corresponds to the width in the horizontal axis direction from the rising position P ₀ of the characteristic line C ₀ to the point P ₃ set near the left end of the dead zone R ₀ . do. As will be understood from the following explanation, this value u ₀ is related to the jump position of the winding/up/down drive control signal u. Therefore, depending on the engine speed N,
If it is desired to change the value of u ₀ as well, it is sufficient to provide a correspondence table between N and u ₀ in the offset amount setter 55 shown in FIG.

This value u ₀ is related to the end position of the dead zone R ₀ and indirectly to the saturation point of the first main hydraulic pump 21a. That is, from driving one hydraulic pump 21a to driving two hydraulic pumps 21a, 21
The switching to the drive of b is performed by the first hydraulic pump 21a.
This is done in anticipation of the saturation of the first main hydraulic pump 21a, resulting in a dead zone _R0 , so the value _u0 is determined according to the saturation point of the first main hydraulic pump 21a.

However, it is not necessary to detect the saturation point of the first main hydraulic pump 23a during execution of the control according to this embodiment. The reason is that once the system to be controlled is specified, it is possible to know by prior measurement the output state and the point at which the first main hydraulic pump 23a becomes saturated. This is because the value u ₀ can be determined by referring to the saturation point that can be known in advance. The same applies to the width of the dead zone _R0 , which is referred to when determining the offset amount Δu, which will be described later, in advance.

Specifically, before shipping the crane, the control signal u
The value of the control signal u is increased while monitoring the value of and the operating speed of the crane. The value of the control signal u at which the increase in the operating speed of the crane begins to slow down significantly is the saturation point of the hydraulic pump 21a. Further, the width of the dead zone can be determined from the value of the control signal u at the time when the operating speed of the crane starts to increase again and the above-mentioned saturation point. Even when determining values such as u ₀ and the width of the dead zone R ₀ according to the engine speed, the engine speed may be changed to several levels and the above measurements may be performed for each speed.

That is, in the method of this embodiment, it is assumed that the outline of the characteristic C ₀ shown by the solid line in FIG. 5 is known, and from this characteristic C ₀ (the dead zone is compensated for) the characteristic line C Control is executed so that the characteristic line C is obtained (characteristic line C will be described in detail later).

However, as explained in the "Prior Art" section,
The width of the dead zone is not constant, and its value changes depending on the situation. However, even if errors occur due to such fluctuations, they can be dealt with by employing incomplete compensation, which will be described later. For this reason, it is not necessary to know exactly the width of the dead zone, etc.
You just need to know the outline.

Although the outline of the characteristic C ₀ is thus specified in advance, this measurement itself can be realized within the range of known techniques.

If no improvements are made as in this example,
It is a well-known fact that a characteristic like the characteristic C ₀ shown by the solid line in Fig. 5 occurs as the number of hydraulic pumps is changed, and the solid characteristic line C ₀ shows this in detail. (Characteristic line C ₀ in Figure 5)
is the same as the characteristic line in FIG. 12 explained in the prior art section).

Returning to FIG. 6, considering the case where the winding/vertical drive control signal u is started from 0, since initially u<u ₀ , the process moves from step S6 to S7 and the winding/vertical drive control signal u is increased. The offset amount Δu ₀ is added to generate the compensated winding/up/down drive control signal U. however,
This offset amount Δu ₀ is the point from the origin O in Figure 5.
This is the interval width up to P ₀ . Therefore, as shown in FIG. 9, u=0 is converted to U=Δu ₀ .
After setting the flag F to "1" in step S7, the hoisting/up/down drive control signal U is outputted to the hoisting/up/down electromagnetic proportional control valve 49 shown in FIG. 3 in step S8.

In the next processing cycle, since F=1,
The process goes from step S4 to S9 via S5. Then, in step S9, the values of the winding/up/down drive control signal u before compensation and (u ₀ +w) are compared. However, w is a predetermined hysteresis width.

In the period when u < (u ₀ + w), the step
Proceeding to S10, the above-mentioned Δu ₀ is added to the winding/vertical drive control signal U to generate the winding/vertical drive control signal U, which is output in step S8. These steps S4, S5,
The processes of S9, S10, and S8 are repeated until u≧(u ₀ +w).

When u≧(u ₀ +w), the process moves from step S9 to step S11, where two types of offset amounts Δu ₀ and Δu are added to the winding/up/down drive control signal u to generate a compensated winding/up/down drive control signal U. . After setting F=0, the winding/up/down drive control signal U is output in step S8. Therefore, as shown in FIG.
=u ₀ +w, a jump occurs in the relationship between the winding and vertical drive control signals u and U before and after compensation.

That is, the threshold value (Δu _{0 +} w) and the control signal (the first By comparing the first control signal u with the first control signal u, it is determined that the first control signal u has a signal value belonging to the dead zone _R0 . If it belongs to the dead zone R ₀ , the offset amount Δu is added to the first control signal u, thereby obtaining the second control signal U that is actually used for drive control (the other offset Since the amount Δu ₀ is added before entering the dead zone R ₀ , the essential offset amount in compensation for the dead zone R ₀ is Δu).

Thereafter, as the winding/up/down drive control signal u increases further, the process moves from step S4 to step S8 via S5, S6, and S12. In step S12, the step
Similar to S11, two types of offset amounts Δu ₀ and Δu are added to u.

Therefore, as the hoisting/up/down drive control signal u increases from 0, the value of the hoisting/up/down drive control signal U after compensation changes along the locus of FIG. 9: H ₁ , H ₂ , H ₃ , H ₄ I will go there. Therefore, in the interval 0≦u≦(u ₀ +w), (u+Δu ₀ ) is given as the actual winding/up/down drive control signal U, and the fifth
As shown by the characteristic line C in the figure, processing equivalent to shifting the section from P ₀ to P ₁ of the original characteristic line C ₀ toward the origin O side by Δu ₀ is performed. However, points _Q0 to _Q2 correspond to points _P0 to _P2, respectively. Also, the section from point P ₁ to P ₂ in FIG. 5 is effectively short-circuited by the jump in locus H ₃ in FIG. 9. Then, for the part on the right side of the characteristic line C ₀ from point P ₂ , (Δu ₀ + Δu)
This is equivalent to shifting to the left by As a result, the illustrated characteristic line C is obtained.

Next, the winding/up/down drive control signal u changes from a large value to 0.
Consider the case where the value decreases toward . At this time,
As can be seen by following the flowchart of FIG. 6 in the same manner as above, in the section where u≧u ₀ , two types of offset amounts Δu ₀ and Δu are added to the winding/up/down drive control signal u. When u< _u0 , only the offset amount _Δu0 is added to the winding/up/down drive control signal u.

Therefore, in this case, the characteristic line C ₀ in FIG.
is uniformly shifted to the left by Δu ₀ , and then the point
Regarding the section to the right of P ₃ , for each point on the characteristic line C ₀ , the point located to the right of each point by Δu is the apparent relationship between the winding/up/down drive control signal u and the rotation speed S. This is the point that indicates Therefore, even when the winding/up/down drive control signal u decreases from a large value toward 0, the apparent characteristic line is
This corresponds to characteristic line C described above.

As is clear from the figure, the characteristic line C obtained in this way has a shape obtained by truncating the section R _u in the dead zone R ₀ of the original characteristic line C ₀ . and,
This process is executed regardless of the usage conditions of the hydraulic drive system. Therefore, the dead zone R ₀ is effectively compensated, and stable hydraulic system control can be performed.

Next, the effects of hysteresis and incomplete compensation will be explained.

Hysteresis As can be seen from the flowchart in Figure 6, when the winding/up/down drive control signal u increases, u=
A jump occurs at (u ₀ +w), and when the winding/up/down drive control signal u decreases, a jump occurs at u=u ₀ . Therefore, in the latter case, the winding up/down drive control signals u, _{U before and after} compensation are
The relationship changes, and hysteresis as shown occurs. However, since this hysteresis generating operation occurs in the dead zone R ₀ in Fig. 5, it appears as follows.
No hysteresis appears in the characteristic line C.

The reason for providing such hysteresis is as follows. That is, first, when hysteresis is not provided (w=0), when the winding/up/down drive control signal u fluctuates around _u0 , a jump by the offset amount Δu frequently occurs in the control system. Then, the control signal level fluctuates rapidly, and the third
The operating state of the electromagnetic proportional pressure reducing valve 49 for lifting and lowering the cargo load shown in the figure becomes unstable. As a result, the hoisting vertical drive system 5
The operation of 0 also becomes unstable, and there is a possibility that the drive response, which should originally have the characteristics as shown in FIG. 5, collapses. Therefore, hunting of the suspended load 9 may occur near u= _u0 .

On the other hand, when hysteresis is provided as described above, the movement of the winding/up/down drive control signal U and the drive system does not become unstable, and stable control can be performed.

Incomplete Compensation In the embodiment described above, the magnitude of the offset amount Δu in FIG. 5 is made smaller than the width of the dead zone R ₀ to some extent. Therefore, some dead zone remains in the apparent characteristic line C. On the other hand, if the offset amount Δu is made equal to the width of the dead zone _R0 , the dead zone can be completely compensated for, but in this case, the following situation may occur. In other words, even if the dead zone compensation is completely performed to obtain the characteristic line _C1 shown in Figure 10a, the shape of the original characteristic line C (Figure 5) may change due to the following reasons. There is a shift in the
As a result, a jump ΔS in the speed S may occur at the connection boundary between the first speed region and the second speed region, as illustrated by the characteristic line _C2 in FIG. 10b.
Examples of reasons why such a situation occurs are as follows.

(a) Individual differences in hydraulic systems and drive mechanical systems (b) Individual differences in electromagnetic proportional pressure reducing valves and the electric circuits that drive them (c) Changes in characteristics due to differences in the weight of suspended loads (d) Changes in engine speed Characteristic changes due to the difference (However, if the magnitude of the offset amount Δu is changed according to the rotational speed N as in the above embodiment, this effect becomes smaller.) Furthermore, the step-like change ΔS as described above When this occurs, there is a possibility that an overshoot will occur in the output of the electromagnetic proportional pressure reducing valve or in the position change of the main spool of the directional control valve.

In this way, complete compensation may lead to control instability, but in the above example, the offset amount Δu is set to be smaller than the dead band R ₀ to some extent, so there is a margin for characteristic fluctuations. Therefore, a jump like that shown in FIG. 10b does not occur.

Therefore, in this embodiment, preferable dead zone compensation is performed.

Figures 11a and 11b show the winding/lowering amount deviation and the winding/vertical drive control signal U (current) over time t, respectively.
FIG. 3 is a diagram showing changes in the conventional control method without dead zone compensation (broken line) and the above embodiment (solid line). As can be seen from this figure, by performing dead band compensation, it is possible to shift from the first speed region to the second speed region.
The deviation near the transition to the high speed region is significantly reduced, and stable control is performed.

D Modification Examples The embodiments of this invention have been described above, but
This invention is not limited to the above-mentioned embodiment, and the following modifications are also possible, for example.

In the above embodiment, a case is considered in which changes in the individual hydraulic outputs of the two main hydraulic pumps 21a and 21b and changes in the number of main hydraulic pumps to be used are controlled based on one control signal u. The present invention is also applicable to the case where the output of each hydraulic pump and the number of hydraulic pumps to be used are changed by separate control signals.

Although the effect is further improved by employing the above hysteresis and incomplete compensation, it is not necessary to employ these in a hydraulic drive system in which changes in characteristics do not need to be taken into consideration much. Also,
When the engine rotational speed (generally the rotational speed of a power source that provides rotational power to a hydraulic pump) is constant, there is no need to change the offset amount in response to changes in the rotational speed.

The hydraulic actuator in this invention may be a direct-acting actuator (such as a hydraulic cylinder), and the number of hydraulic pumps may be any number as long as they are plural. The present invention can be applied to a wide range of applications such as hydraulic drive systems for cranes, various transportation equipment, processing equipment, and hydraulic drive systems for large robots.

(Effects of the Invention) As explained above, according to the present invention, when changing the number of hydraulic pumps that drive the hydraulic actuator, the hydraulic pressure generated to control the hydraulic flow rate sent from the hydraulic pump to the hydraulic actuator is A second control signal is generated by changing the value of the first control signal by a predetermined offset amount determined according to the width of a dead zone determined from the relationship between the first control signal and the operating speed of the hydraulic actuator. However, since the hydraulic pump is controlled by this second control signal, the dead zone can be effectively compensated for in a hydraulic drive system including a plurality of hydraulic pumps, regardless of usage conditions.

[Brief explanation of drawings]

Fig. 1 is a schematic external view of a crane to which an embodiment of the present invention is applied, Fig. 2 is a hydraulic circuit diagram of the hydraulic drive system of the crane shown in Fig. 1, and Fig. 3 is a control used in the embodiment. A block diagram of the system, FIG. 4 is a diagram showing an example of suppression pattern data, FIG. 5 is a diagram showing characteristic changes of the winding/up/down drive control signal u and rotational speed S in the embodiment, and FIG. A flowchart showing the operation, Fig. 7 is an explanatory diagram of characteristic changes depending on engine speed, Fig. 8 is a diagram showing the relationship between engine speed and offset amount, and Fig. 9 shows compensation of the winding/up/down drive control signal. Graph, Fig. 10 is an illustration of incomplete compensation, Fig. 11 is an illustration of the effect of the embodiment, Fig. 12 is an illustration of dead zone, and Fig. 13 is an explanation of problems when using multiple pumps. This is a diagram for 1... Crane, 2... Crane body, 3...
Boom, 4... Rope for boom elevation, 6... Rope for winding up and down, 9... Hanging load, 12... Boom elevation angle detector, 21a, 21b... Main hydraulic pump, 2
2a...Boom elevation directional control valve, 22b, 22
c... Directional control valve for winding and lowering, 26a, 26b, 2
7a, 27b...Solenoid proportional pressure reducing valve, 32a, 32
b... Remote control valve, 33a... Boom operation lever, 33b... Winding/up/down operation lever, 36, 37
...Boom lever pilot pressure detector, 54...
...Engine speed detector, 55...Offset amount setting device, 56...Compensation device.

Claims (1)

[Scope of Claims] 1. The hydraulic actuator is equipped with a plurality of hydraulic pumps that drive a predetermined hydraulic actuator, and the number of hydraulic pumps used and the flow rate of pressure oil sent from the hydraulic pump to the hydraulic actuator are changed. As the operating speed of
In a hydraulic drive system having a dead zone in which the operating speed of the hydraulic actuator does not change even if the value of the control signal is changed when changing the number of the hydraulic pumps used, the hydraulic drive system is driven while compensating for the dead zone. A control method for controlling, when changing the number of hydraulic pumps used, a value of a first control signal generated for controlling the flow rate of the pressure oil sent from the hydraulic pump to the hydraulic actuator. , generating a second control signal by varying it by a predetermined offset amount determined according to the width of the dead zone determined from the relationship between the first control signal and the operating speed of the hydraulic actuator; A method for controlling a hydraulic drive system, comprising controlling the hydraulic pump using a control signal. 2. The first control signal is a control signal that is used in common to control changes in the flow rate of pressure oil from the hydraulic pump and to control changes in the number of hydraulic pumps used, and the offset amount The method of controlling a hydraulic drive system according to claim 1, wherein the control method is determined according to the rotational speed of a power source that provides rotational power. 3. The method of controlling a hydraulic drive system according to claim 1 or 2, wherein the hydraulic drive system is a system for hoisting and vertically driving a cable-shaped body on which a suspended load is suspended in a crane.