JP2003148402A - Hydraulic control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a hydraulic control system capable of performing feedback control based upon a detected value related to hydraulic drive in a stable state. SOLUTION: This hydraulic control system includes a liquid pressure circuit for controlling the hydraulic drive of load 10 by a servo valve 20, and an electronic circuit 40 for performing the control following up a received command Vin for the servo valve 20. The electronic circuit 40 is provided with a correcting means 41 for obtaining a correction value according to a difference between the value of the command Vin and the detected value Vf related to the hydraulic drive, and providing the same for controlling the servo valve 20 according to the command Vin, and the correction value is updated intermittently at time intervals corresponding to the responsiveness of hydraulic drive.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydraulic control system used for driving an industrial machine such as a die-cast machine, and more specifically, a hydraulic control system for electronically controlling a servo valve included in a hydraulic circuit. Regarding

[0002]

2. Description of the Related Art A hydraulic control system, a block diagram of which is shown in FIG. 8A, includes a hydraulic actuator 10 which forms a part of a load or is connected to the load in order to control a driving speed of the load. , A servo valve unit 20 for controlling the hydraulic drive, and a host controller (mother machine) not shown
Receives the speed command Vin from the servo valve unit 2
The controller 30 (electronic circuit) that receives the servo feedback signal Sf from 0 and generates the servo current So and sends it to the servo valve unit 20.

Then, the controller 30 performs proportional calculation (K), voltage-current conversion (V / I), etc., and causes the servo feedback signal Sf to follow the speed command Vin.
The servo valve unit 20 that has generated o increases or decreases the flow rate Q of the pressure liquid supplied from the pressure liquid source of the pressure P to the actuator 10. As described above, conventionally, the speed V of the actuator 10 is controlled by controlling the servo valve to follow the speed command Vin and adjusting the flow rate Q flowing into the actuator 10 by the servo valve.

[0004]

However, the servo feedback signal Sf fed back from the servo valve indicates the state of the servo valve, such as the position of the spool of the servo valve. Therefore, even if the feedback control is performed, the direct control target is the opening degree of the servo valve or the like. The flow rate Q and the speed V are indirectly controlled by interlocking with the opening degree and the like. Such control cannot be said to be feedback control from the viewpoint of the actuator and the load, but is substantially open control / sequence control. Under such control, when the discharge pressure P of the pump and the resistance of the load are different, the influence affects the flow rate Q, so that a deviation ΔV occurs between the speed command Vin and the actual speed V (see FIG. 8B). ).

Then, as a general method for eliminating such a deviation ΔV, the speed V of the load which is the final control target.
It is conceivable that the feedback control is carried out by detecting the above. In that case, the follow-up control of the servo valve goes around the sub and receives the difference ΔV as a command instead of the speed command Vin (see FIG. 9). However, if such a method is simply introduced, in the hydraulic control system, in many cases, hunting or hunting is caused due to the characteristic of the hydraulic actuator such as the hydraulic cylinder that the compression target capacity largely changes in the operating state. Vibration is likely to occur, and it is difficult to make the feedback control always stable.

Further, in the case of the hydraulic system, a large time delay occurs in the response of the actuator to the change in the manipulated variable. Therefore, it is not easy to increase the response speed even when high-speed response is desired. Since the physical quantity of the actuator or the like related to control is not a constant and changes according to the operating state, it cannot be adjusted with a general PID. Therefore,
In order to eliminate the deviation, not only the detection value related to the servo valve but also the detection value related to the hydraulic drive of the load is fed back to perform control, and the control state is stabilized or / and the responsiveness is enhanced during the feedback control. It will be a technical issue to devise such things.

The present invention has been made in order to solve such a problem, and an object thereof is to realize a hydraulic control system capable of performing feedback control in a stable state based on a detection value regarding hydraulic drive. Further, the present invention is
An object of the present invention is to realize a hydraulic pressure control system that can perform feedback control with high response based on a detected value regarding hydraulic drive.

[0008]

With respect to the first to fourth solving means invented to solve the above problems,
The configuration and action and effect will be described below.

[First Solving Means] The hydraulic control system of the first solving means is, as described in claim 1 at the beginning of the application, a hydraulic circuit for controlling hydraulic driving of a load by a servo valve. In a hydraulic control system including an electronic circuit that controls the servo valve to follow the received command, a correction value is obtained based on a difference between the command value and the detection value related to the hydraulic drive. Is provided in the electronic circuit for controlling the servo valve in accordance with the command, and the correction value is updated intermittently at time intervals corresponding to the response of the hydraulic drive. It is that. Here, "intermittently" means "repeating at discrete points on the time axis".

In the hydraulic control system of the first solving means as described above, the detected value relating to the hydraulic drive is fed back, but the difference between the detected value and the command value is immediately controlled instead of the command. However, the command is still directly input to the control of the servo valve and is used by the main. The detected value is first used for calculating the correction value together with the command value, and then, the correction value is adjusted to the command value, so that it is used by the sub (sub) control of the servo valve. Moreover, since the correction value is updated intermittently at time intervals corresponding to the response of hydraulic drive, it is possible to suppress the occurrence of oscillation and vibration without changing the characteristics of servo valve follow-up control. Becomes

In this way, while maintaining the state that the servo valve follow-up control mainly works, when adding the final target feedback useful for eliminating the deviation, it is combined with sampling (sampling) of a predetermined period. , This feedback is designed to work on the sub side, so that the deviation is eliminated and the destabilization of the control state is avoided. Therefore, according to the present invention, it is possible to realize a hydraulic pressure control system capable of performing feedback control in a stable state based on a detection value regarding hydraulic drive.

[Second Solving Means] In the hydraulic control system of the second solving means, the main valve for controlling the hydraulic drive of the load is pilot-operated by the servo valve as described in claim 2 at the beginning of the application. In a hydraulic control system including a hydraulic circuit for controlling the servo valve and an electronic circuit for performing follow-up control to follow the received command, the electronic circuit is provided with the following responsiveness improving means. . The responsiveness improving means includes a differentiating means for calculating and adding a differential value to the command, a transient determining means for determining a transient state or a stable state based on the differential value, and a result of the determination being a transient state. In this case, the gain switching means for increasing the gain in the follow-up control is provided as compared with the stable state.

In the fluid pressure control system of the second solving means as described above, the response improving means is added, so that a general differential value with respect to the command is generated at the time of a transition requiring a high speed response. In addition to the increase of, the increase by increasing the gain is also added. Therefore, according to the present invention, it is possible to realize a hydraulic control system capable of performing feedback control with high response based on a detection value regarding hydraulic drive.

[Third Solving Means] The hydraulic control system of the third solving means is a combination of the hydraulic control systems of the above first and second solving means. That is, as described in claim 3 at the beginning of the application, in the hydraulic control system including the hydraulic circuit and the electronic circuit, the correcting means and the responsiveness improving means are provided.

In the hydraulic control system of the third solving means as described above, the response speed of the feedback control is increased by the response improving means as described above, but even in such a case, the correction is performed as described above. The feedback control is kept stable by the means. Therefore, according to the present invention, it is possible to realize a hydraulic pressure control system capable of performing feedback control based on a detection value regarding hydraulic drive in a stable state even with high response.

[Fourth Solving Means] The hydraulic control system of the fourth solving means is the hydraulic control system of the above-mentioned third solving means, as described in claim 4 at the beginning of the application. The operation characteristic of the servo valve has a dead zone, and the function calculation means having a dead zone narrower than that is provided in the feedback section from the servo valve in the electronic circuit.

Generally, a large-sized servo valve having no dead band in operating characteristics and less energy loss increases the manufacturing cost. Therefore, when a servo valve having less energy loss is manufactured at a low cost, a dead zone appears in the operating characteristics. Although unavoidable, the presence of such dead zones usually has a negative effect on the characteristics of the tracking control. On the other hand, in the fluid pressure control system of the fourth solving means, the feedback operation from the servo valve is provided with the function calculating means, and the narrow dead zone is provided to the function calculating means. Will be alleviated by various electronic calculation processes. Therefore, according to the present invention, it is possible to inexpensively realize a hydraulic pressure control system that can perform feedback control based on a detection value related to a large flow rate hydraulic drive in a stable state even with a high response.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION A concrete mode for carrying out the hydraulic control system of the present invention achieved by the above-mentioned means will be described with reference to the following first to third embodiments. The first embodiment shown in FIG. 1 embodies the first solving means described above, and the second embodiment shown in FIGS. 2 to 6 is the second and third solving means described above. The third embodiment shown in FIG. 7 embodies the above-mentioned fourth solving means.

[0019]

First Embodiment A specific configuration of the first embodiment of the hydraulic control system of the present invention will be described with reference to the block diagram of FIG.

This hydraulic control system comprises an actuator 10 and a servo valve unit 20 similar to the conventional one, and a controller 40 (electronic circuit) obtained by expanding the conventional controller 30. The actuator 10 is a hydraulic cylinder or hydraulic motor connected to a load, and its speed V
A sensor for detecting is attached to the rod or the load, and the detection speed Vf obtained thereby is fed back to the controller 40 as a detection value regarding hydraulic drive.

The servo valve unit 20 is equipped with an electronically controllable servo valve for controlling the hydraulic drive of the actuator 10, and is discharged to the actuator 10 at a pressure P from a fixed or variable piston pump or the like. The flow rate Q of the pressure liquid is variable. The servo valve is
The opening of the oil passage is changed by moving the spool in accordance with the servo current So, and the LVDT detects the position of the spool so that feedback control can be performed.
Sensors such as are attached, and the servo feedback signal Sf obtained thereby is fed back to the controller 40.

The controller 40 may be an analog type electronic circuit or a digital circuit mainly including a digital signal processor, but here, it is described as an analog circuit. The controller 40 uses the servo current So that causes the servo feedback signal Sf to follow the speed command Vin.
In order to generate
An addition / subtraction calculation unit 46 that subtracts the servo feedback signal Sf from the speed command Vin, a proportional calculation unit that amplifies with a constant gain K, and a voltage-current conversion unit (V / I) that converts the calculation result into a servo current So and outputs it. It is equipped with Although the speed command Vin is directly input to the addition / subtraction calculation unit 46 immediately before the proportional calculation unit (K), as in the conventional case (see FIG. 8), it is different from the expansion mode in the general method (see FIG. 8). 9).

This controller 40 is the controller 30
The difference (see FIG. 1) is that a correction circuit 41 for adding the speed command Vin and the detected speed Vf to calculate the correction value y is added. The correction value y is sent to the addition / subtraction calculation unit 46 so as to be added to the speed command Vin, and added there. The correction circuit 41 uses the speed command Vin
It comprises a subtraction circuit for subtracting the detected speed Vf from the difference ΔV and a sampling means for taking in the deviation ΔV in a predetermined cycle. The value held by the sampling means is appropriately amplified by a gain (Ka). , A correction value y is generated.

The sampling period of the deviation ΔV by the sampling means is about 10 ms, typically 5 to 15 ms, which is set to be almost the same as the settling time of the step response waveform of the speed V. This cycle is orders of magnitude longer than the time interval in which the digital signal processor inputs and outputs signals. With such sample-and-hold, the correction value y is updated intermittently at time intervals corresponding to the response of hydraulic drive.

The usage mode and operation of the hydraulic control system of the first embodiment will be described with reference to the drawings. FIG. 1B shows the typical signal waveform.

Again, for the sake of comparison with the conventional example, if the speed command Vin changes stepwise, in this case as well, at first, it operates as if it were stable with the deviation ΔV remaining as in the conventional case. But eventually (time t in FIG. 1B)
The correction value y is updated by the correction circuit 41. Then, even if the speed command Vin does not change,
The correction value y changes stepwise, and this changes
Therefore, since it is added to the speed command Vin, the servo valve unit 20 is equivalent to a slight change in the control target value.

Then, the detected speed Vf shows a small step response toward the speed command Vin (see the time between t1 and t2 in FIG. 1B). Then, after a predetermined time interval (see time t2 in FIG. 1B), when the waveform of the detected speed Vf is likely to be stable,
The correction value y is updated again by the correction circuit 41.
Then, even if the speed command Vin does not change, the correction value y
Changes stepwise, and the detected speed Vf becomes the speed command Vin
A step response is shown toward (see between time t2 and t3 in FIG. 1B). This waveform change is smaller than the previous one.

Further, after a predetermined time interval (see FIG.
(Refer to the time t3 in (b)), the correction value y is updated by the correction circuit 41, and the correction value y is updated.
The detected speed Vf shows a step response toward the speed command Vin due to the step change of (see time t in FIG. 1B).
See 3 and later). This waveform change is even smaller.
Then, while such updating of the correction value y is repeated, the deviation ΔV between the speed command Vin and the detected speed Vf disappears.

In this way, the conventional response waveform is followed by the initial response waveform that defines the basic and basic parts of the applied operation, while the deviation disappears from the subsequent response waveforms, unlike the conventional response waveform. Moreover, at that time, the response waveform is not disturbed.
At least there is no factor that makes it more unstable than before. Therefore, this hydraulic pressure control system can be used in the same manner as in the conventional case, and even in that case, the hydraulic drive can be performed more accurately than in the conventional case. Therefore, the present invention can be easily applied not only to newly developed application devices but also to modification and improvement of existing application devices.

[0030]

Second Embodiment A specific configuration of a second embodiment of the hydraulic control system of the present invention will be described with reference to the drawings. 2 is a block diagram of the overall configuration, FIG. 3 is a block configuration diagram of the electronic control unit among them, FIG. 4 is a signal waveform diagram relating to the response improving means, and FIG.
Is a block diagram of the correction circuit 41, and FIG.
It is the typical signal waveform diagram.

This hydraulic control system differs from that of the first embodiment described above in that it is clearly shown that the actuator 10 is a large cylinder (see FIG. 2), and the servo valve unit 20 is large. Main valve 2 for driving at flow rate
1 and a servo valve 22 that pilot-operates it (see FIG. 2), and a controller 40
Is that the response improving means 42 + 43 + 44 is added (see FIGS. 3 and 4), and the correction circuit 41 is further improved (see FIG. 5).

The actuator 10 (see FIG. 2) is a hydraulic cylinder used in a large die casting machine or a press machine, and the oil storage amount is almost zero between stroke ends.
It greatly changes from L to 20 L, for example. Therefore, the parameters for determining stability of the control state such as compressibility / capacity component are changed significantly. Further, the control parameters such as the back pressure and the resistance component also greatly vary depending on the filling condition of the filling material and the state of the injection port.

The main valve 21 (see FIG. 2) has a maximum of 3000 to 20 necessary for hydraulically driving the actuator 10.
A large seat valve that can flow a large flow rate of 000 L / min is adopted.
A sensor such as an LVDT that detects the position of the spool or the like is additionally provided, and the main valve feedback signal Qf obtained thereby is fed back to the controller 40.

The controller 40 (see FIG. 3) divides the gain K of the proportional operation section into a gain Kp and a gain Kp2 before and after, and feeds back the servo feedback signal Sf during both operations, and calculates the gain Kp operation section ( By feeding back the main valve feedback signal Qf before the gain switching circuit 44, which also serves as this (described later), the flow rate Q of the pressure liquid supplied to the actuator 10 can be varied. Further, a dither which is a minute oscillation signal is added or pulled between the operation unit of the gain Kp2 and the voltage / current conversion unit (V / I) in order to prevent stick slip.

The response improving means 42 + 43 + 44 (see FIGS. 3 and 4) receives the speed command Vin, generates a differential value Da, and outputs the differential value Da to the addition input of the addition / subtraction calculating unit 46, and the differential value. Input Da, which is the predetermined threshold S
A transition determination circuit 43 that generates a determination result signal Db that takes an ON value that indicates a transient state when it exceeds L and an OFF value that indicates a stable state when it is below L, and sends this to the gain switching circuit 44, and an addition / subtraction calculation unit 46. And a gain switching circuit 44 for inputting a value obtained by adjusting the main valve feedback signal Qf and performing a proportional operation of the gain Kp on the input value. The gain switching circuit 44 almost doubles the gain Kp when the discrimination result signal Db is on rather than when it is off.

In the correction circuit 41 (see FIG. 5A), the sampling means is more precise. Specifically, 3
With two sample and hold circuits S1, S2, S3,
The deviation &Dgr; V is sampled by the sample & hold circuit S1, and the added value of the sampling value &Dgr; V 'and the sampling value x held by the sample & hold circuit S3 is sampled by the sample & hold circuit S2.
The hold value of the hold circuit S2 is sampled and held by the sample and hold circuit S
The sampling is performed at 3, and the correction value y is generated by the proportional calculation of the gain Ka or the like.

Those sampling periods are (FIG. 5 (b))
Reference), both are the same as in the first embodiment described above,
The sample & hold circuits S1, S2 and the sample & hold circuit S3 are shifted by a half cycle. In addition to this, the sampling and holding circuit S3 feeds back the sampling value x with respect to the sampling and holding circuit S2, so that the correction value y for eliminating the deviation ΔV can be calculated more quickly.

The usage and operation of the hydraulic control system of the second embodiment will be described with reference to the drawings. FIG. 6 shows the typical signal waveform. When the speed command Vin changes stepwise, the response waveform indicated by the speed V of the actuator 10 is the response improving means 42+.
Without 43 + 44 and the correction circuit 41, it tries to stabilize at a distance ΔV from the speed command Vin as in the conventional case (see FIG. 6 (a)), but in this case, the response improving means 42 + 43 + 44 works first to The rising edge of is determined to be in a transient state and its responsiveness is temporarily enhanced, so that the speed V quickly reaches the speed command Vin (see FIG. 6 (b)).

Of course, if the speed V exceeds the speed command Vin by itself, it will attempt to stabilize (Fig. 6).
(Refer to (b)) After that, since the correction circuit 41 also works, the improvement of the control state continues. That is, (see FIG. 6C), after the transitional state has elapsed, the correction value y is updated by the correction circuit 41 at a predetermined cycle, and the speed V approaches the speed command Vin each time, and the two eventually match. Thus, also in this case,
The first response waveform that defines the basic and basic parts of the applied operation follows the conventional waveform, while the deviation disappears from the subsequent response waveforms, unlike the conventional one. Moreover, at that time, the response waveform is not disturbed.

[0040]

[Third Embodiment] A specific configuration of a third embodiment of the hydraulic control system of the present invention will be described with reference to the drawings. FIG. 7 shows the structure of the main part, (a) is a block diagram, (b) is a sectional view of the main part of the pilot valve,
(C) is a characteristic diagram of the pilot valve, and (d) is a function form of the function calculating means.

This hydraulic control system differs from that of the second embodiment described above in that the servo valve unit 20 has a pilot valve 23 interposed between a main valve 21 and a servo valve 22. Regarding the controller 40, the function calculation circuit 45 is inserted in the line (feedback section) of the servo feedback signal Sf.

The pilot valve 23 (see FIG. 7 (a))
The servo valve 22 is smaller than the main valve 21 but larger than the servo valve 22, and the servo valve 22 is mounted as a pilot operated valve so that its hydraulic output is power-amplified and sent to the pilot portion of the main valve 21. It has become. The pilot valve 23 is also provided with a sensor such as an LVDT, and the spool position of the pilot valve 23 detected by the sensor is used for the servo feedback signal Sf. The pilot valve 23
Since the land of the spool 23a and the port of the body 23b slightly overlap each other (see FIG. 7 (b)), the relationship between the displacement of the spool and the opening degree of the valve, which represents the operating characteristic of the land (see FIG. 7 (c)). )) There is a dead zone at the center of the displacement range, and the valve is kept closed there even when the spool 23a is displaced.

The function operation circuit 45 (see FIG. 7A)
A function value Sf ′ is generated from the servo feedback signal Sf and is sent to the addition / subtraction calculation unit with the output of the gain switching circuit 44 in place of the servo feedback signal Sf, and the pilot valve 23 is used for the function calculation. The dead zone is narrower than the dead zone in the operating characteristics of. Specifically (Fig. 7
(D)) In the relationship between the servo feedback signal Sf and the function value Sf ′, the inclination of the inclined portion is the same as the inclination of the inclined portion in the relationship between the spool displacement of the pilot valve 23 and the valve opening. When the dead band widths are compared after expansion and contraction, the dead band in the characteristic graph of the function calculation of the function calculation circuit 45 is slightly narrower than the dead band in the operation characteristic graph of the pilot valve 23.

In this case, the difference between the opening of the pilot valve 23 and the servo feedback signal Sf caused by the presence of the dead zone in the operating characteristic of the pilot valve 23 by the calculation of the function calculation circuit 45 is the function value Sf '. Since the size becomes smaller, the feedback control based on the servo feedback signal Sf is smoothly performed even if the pilot valve 23 is not the underlap type like the servo valve 22 but the overlap type. Further, since the dead zone on the side of the function calculation circuit 45 does not exceed the dead zone on the side of the pilot valve 23, the control system does not become unstable even if the function calculation accompanied by the dead zone is used together.

[0045]

[Others] In each of the above embodiments, the hydraulic circuit has been described as a specific example, but the application of the present invention is not limited to this, and may be applied to hydraulic equipment or other hydraulic devices. The servo valve is not limited to the spool valve type described above, but may be a seat valve type such as a so-called cartridge valve. Further, the function calculation circuit 45 may be capable of variably setting the width of the dead zone in the function form and adjusting it according to the actual machine. Further, the application destination of the present invention is not limited to a press or a die casting machine, and various industrial equipment such as an injection molding machine and a large-sized testing machine can be cited.

[0046]

As is apparent from the above description, in the hydraulic control system according to the first solution of the present invention, the final target of the servo valve can be maintained while maintaining the state in which the follow-up control is mainly performed. By adding feedback so that it works in combination with sampling, the deviation is eliminated without impairing the stability of the control state, and as a result, feedback control based on the detected value related to hydraulic drive can be performed in a stable state. There is an advantageous effect that the hydraulic control system can be realized.

Further, in the hydraulic control system according to the second solution of the present invention, not only the general differential value but also the step-up value of gain is added to the command at the time of transition, so that It is possible to realize the hydraulic pressure control system capable of performing the feedback control based on the detected value related to the pressure drive with high response.

Further, in the hydraulic pressure control system of the third means for solving the problems of the present invention, by introducing the specific response improving means and the specific correcting means together, it is based on the detected value relating to the hydraulic pressure drive. There is an advantageous effect that a hydraulic control system capable of performing feedback control in a stable state even with high response was realized.

Further, in the hydraulic control system according to the fourth solution of the present invention, the adverse effect of the dead zone of the operating characteristic of the servo valve on the follow-up control characteristic is alleviated by the narrow dead zone in the function calculation. By doing so, there is an advantageous effect that it is possible to inexpensively realize a hydraulic control system that can perform feedback control based on a detection value related to a large flow rate hydraulic drive in a stable state even with a high response.

[Brief description of drawings]

FIG. 1A is a block diagram and FIG. 1B is a signal waveform diagram of a first embodiment of a hydraulic control system of the present invention.

FIG. 2 is a block diagram of the overall configuration of a second embodiment of the hydraulic control system of the present invention.

FIG. 3 is a block configuration diagram of an electronic control unit.

FIG. 4 is a signal waveform diagram relating to response improving means.

FIG. 5A is a block diagram of the correction means, and FIG. 5B is a signal waveform diagram.

FIG. 6A to FIG. 6C are signal waveform diagrams for explaining operating states.

FIG. 7 is a block diagram of a third embodiment of the hydraulic control system of the present invention, FIG. 7B is a sectional view of a main portion of a pilot valve, FIG. 7C is a characteristic diagram of the pilot valve, and FIG. )
Is the function form of the function calculation means.

FIG. 8 is a block diagram and a signal waveform diagram of a conventional hydraulic control system.

FIG. 9 is a configuration example in which feedback is multiplexed by a general method.

[Explanation of symbols]

10 Actuator (hydraulic cylinder / motor, load drive unit, hydraulic circuit) 20 Servo valve unit (hydraulic servo circuit, hydraulic drive control unit, hydraulic circuit) 21 Main valve 22 Servo valve 23 Pilot valve 23a Spool (valve body) 23b Body (main body) 30 Controller (speed / pressure control unit, arithmetic processing unit, electronic circuit) 40 Controller (speed / pressure control unit, arithmetic processing unit, electronic circuit) 41 Correction circuit (correction means with sampling) 42 Differentiation circuit (differentiation means, response improvement means) 43 Transient determination circuit (transition determination means, response improvement means) 44 Gain switching circuit (gain switching means, response improvement means) 45 Function calculation circuit (calculates a function with dead zone) Function calculation means) 46 Addition / subtraction calculation unit (addition circuit, subtraction circuit)

Claims (4)

[Claims] 1. A hydraulic control system comprising: a hydraulic circuit for controlling hydraulic drive of a load by a servo valve; and an electronic circuit for controlling the servo valve to follow a received command. A correction unit is provided in the electronic circuit to obtain a correction value based on the difference between the command value and the detection value related to the hydraulic drive, and to provide the correction value for controlling the servo valve according to the command, and the correction value is updated. Is intermittently performed at time intervals corresponding to the response of the hydraulic drive. 2. A hydraulic circuit for pilot-operating a main valve for controlling hydraulic drive of a load by a servo valve, and an electronic circuit for performing follow-up control for following a command received on the servo valve. In the hydraulic control system, differentiating means for calculating and adding a differential value to the command, transient distinguishing means for judging a transient state or a stable state based on the differential value, and a result of the determination is a transient state. The hydraulic control system is characterized in that the electronic circuit is provided with a gain switching means for increasing the gain in the follow-up control sometimes than in a stable state. 3. A hydraulic circuit for pilot-operating a main valve for controlling hydraulic drive of a load by a servo valve, and an electronic circuit for performing follow-up control for following a command received by the servo valve. In the hydraulic control system, a correction value is obtained based on a difference between a value of the command and a detection value related to the hydraulic drive, and the correction value is supplied to the control of the servo valve in accordance with the command and the correction value is updated. Correcting means intermittently performed at time intervals corresponding to the responsiveness of hydraulic drive, and a differential value of the command is calculated and added, and a transient state or a stable state is determined based on the differential value. A hydraulic control system comprising: a response improving means for increasing the gain in the follow-up control when the determination result is in a transient state, compared to a stable state, in the electronic circuit. 4. The servo valve has a dead zone in its operating characteristics, and function calculating means having a dead zone narrower than that is provided in a feedback section from the servo valve in the electronic circuit. The hydraulic control system according to claim 3.