JPH0199107A - Electric/hydraulic servo control device - Google Patents

Abstract

PURPOSE:To prevent oscillation to occur at an electrohydraulic system and to simultaneously increase a response by inserting an electric filter into a control device. CONSTITUTION:Between an operational amplifier 16 and a servo amplifier 17, an electric filter 29 is inserted. As the filter 29, for example, a phase delaying filter, a secondary low pass filter, etc., are used. A deviation signal Ve is properly amplified by the operational amplifier 16, becomes a signal VA and the signal VA is modulated so that a prescribed characteristic can be realized by the electrical filter 29, becomes a correcting signal VA' and is given to the servo amplifier 17. Thus, a gain allowance is increased, even when a control object is quickly moved in a step shape, a harmful oscillation does not occur, but, arrives at a target value rapidly, the oscillation to occur at the electrohydraulic system is prevented, and simultaneously the response can be increased.

Description

[Detailed Description of the Invention] [Industrial Field of Application] The present invention is not affected by the characteristics of the mechanical system to be controlled;
Moreover, it relates to an electric/hydraulic servo control device that operates stably and with high response.

[Prior Art] Electric/hydraulic servo systems are used in vibration testing machines, various simulators, and drive parts of industrial machines such as rolling mills and robots. FIG. 9 is an example of this, and shows an electric/hydraulic servo control device for a wrapper roll 3 that is provided in a down coiler that winds up a strip 1 and presses the periphery of the strip that is wound around a mandrel 2. The wrapper roll 3 is attached to the tip of a swing frame 4 that swings around a rotating shaft 7. An angle detector 8 is connected to the rotating shaft 7 to detect the position of the wrapper roll 3. The position is controlled by a hydraulic cylinder 5 that swings the frame 4. The amount of pressure oil supplied to the hydraulic cylinder 5 is controlled by a servo valve 11. In the figure, 6 is a piston, 6a is a piston rod, 9 is a position control target value (set value), and 10
12 and 13 are piping, and 14 are pinch rolls that change the direction of the strip 1.

When the control system of this wrapper roll 3 is modeled, the 10th
As shown in the figure, the movable parts such as the frame 4 and the wrapper roll 3 are moved and positioned through the oil column (spring) of the hydraulic cylinder 5 shown in Fig. 9. In Fig. 10, the spring constant of the oil column of the hydraulic cylinder 5, m is the wrapper roll 3, frame 4, piston 6, piston rod 6a.
This is the mass of the moving parts such as Further, the movable part is subjected to a braking action when the piston 6 moves in oil. This is represented by a dashpot in the figure, and its viscous damping coefficient is C.

By the way, in order to improve the responsiveness and accuracy of positioning of the controlled object, that is, the wrapper roll 3, the following is important.

■ The mass m of the moving part is small.

■ Proper braking, in other words, viscous damping coefficient C
takes an appropriate value.

In other words, even if the piston 6 of the hydraulic cylinder 5 is displaced by X', if a soft spring pushes a heavy moving part, the response will be slow, and if the brake does not work, vibration will continue and the wrapper roll 3 will not reach its target position. It takes a long time to settle on a value.

FIG. 11 shows an example of a response waveform when responsiveness is poor.

In the figure, tR is the response time.

In order to meet the requirements of (1), (2), and (3) above, the following is necessary.

■'Reduce the weight of the machine as much as possible while still providing the necessary strength.

■' Increase the diameter of the hydraulic cylinder 5 and shorten the stroke.

■'Proactively install a damper or other braking mechanism.

However, regarding ■', it is difficult to achieve both weight reduction and maintaining strength, and regarding ■', increasing the diameter increases the amount of oil required for control, which increases costs, and the stroke is mechanically There have been problems such as the fact that it cannot be easily shortened because it is determined by the conditions of use, and the problem of (2) increases the cost.

The above is generally applicable to electric/hydraulic servo systems that use servo valves and hydraulic cylinders to position heavy objects and control force. Solutions have been proposed.

In order to explain such a control solution, we will first explain the electrical and
FIG. 12 shows a general configuration of a hydraulic servo system. 12th
The figure is a block diagram showing an electric/hydraulic servo system. Here, the case of position control will be explained, but the same applies to other cases.

In FIG. 12, the target value (setting value) Vr for positioning the controlled object (for example, the wrapper roll 3 in FIG. 9 corresponds to this) is the signal vX indicating the actual position of the controlled object measured by the displacement meter 22. Comparison and subtraction are performed by the comparator 15 to obtain a deviation signal VQ between the target value vr and the actual displacement signal Vx.
is made. This deviation signal Ve is appropriately amplified by an operational amplifier 16 to become a signal vA, which is converted into a command signal i for driving a servo valve 18 by a servo amplifier 17. Typically, servo valve 18 is driven by a current signal. Thus, the servo valve inputs and outputs fluid q at a flow rate proportional to the current signal i, which is a command signal, and this flows through the pipe 19 to the cylinder 20 (
A fluid flow jlQ' flows into the cylinder 5) of FIG. 9 or flows out through the pipe 19. This fluid flow ff1q'
The piston of the cylinder 20 moves in and out by X',
This controls the position (displacement) X of the mechanical system 21 to be controlled. The position X of the mechanical system 21 at that time is detected by the displacement meter 22 and compared with the target value vr as described above. When the target value ■r and the displacement signal Vχ of the controlled object match, the deviation ve becomes zero, and the fluid flow rate q' flowing into and out of the cylinder 20 becomes zero, so the position X' of the piston of the cylinder 20 becomes stationary. As a result, the positioning of the mechanical system 21 is completed.

When such a system is controlled by simply feeding back the position signal of the controlled object, even if an attempt is made to increase the response speed of the control, the phase delay of the signal in the control loop will be large at frequencies close to the natural frequency of the mechanical system. Therefore, even if you forcefully try to speed up the response, the control system will oscillate. Therefore, the control response speed is limited by the natural frequency of the mechanical system.

In order to increase the natural frequency of a machine, is it necessary to reduce the mass m or increase the spring constant K of the fluid?As mentioned earlier, it is easy to reduce the mass for strength reasons. Moreover, in order to increase the spring constant of the fluid, it is necessary to increase the diameter of the cylinder 20 to increase the effective cross-sectional area or shorten the stroke. However, cylinder 20
If the effective cross-sectional area is increased, the amount of fluid consumed increases, so the capacity of the servo valve 18 and the capacity of the hydraulic pump must be increased more than necessary, resulting in complete waste. In addition, since there are design restrictions on the stroke depending on the equipment, it is usually not possible to arbitrarily shorten the stroke.

Therefore, it can be said that there is no easy means to sufficiently increase the vibration frequency of a mechanical system, as long as practically acceptable economic efficiency is considered.

Similarly, in order to damp vibrations, it is impossible to apply appropriate damping to the movement of the controlled object, that is, to arbitrarily set the viscous damping coefficient C shown in Fig. 10, unless a damper or the like is actively provided. It was possible.

For this reason, the inventors have proposed a method to solve the above problems by feeding back not only the displacement but also the velocity and acceleration of the mass to be controlled, and some methods have already been implemented. FIG. 13 shows a block diagram of the electric/hydraulic servo system when such compensation is performed. Elements in FIG. 13 that are the same as those shown in FIG. 12 are given the same reference numerals.

In Fig. 13, the displacement X of the mechanical system 21 which is the controlled object
In addition, the speed sensor 23 and the acceleration sensor 25 detect the speed sensor 23 and the acceleration sensor 25, respectively, and amplify them appropriately using amplifiers 24 and 26 to obtain the signal VAT.

I am giving feedback as VA2. Signal VA+, V
A24; t, Comparison operator 27.28 Comparison operation is performed with the signal vA from the amplifier 1G, VA - VA 1 - VA2
becomes an input to the servo amplifier 17. The subsequent operation is the first
This is the same as in Figure 2.

The principle of a method for improving the characteristics of a mechanical system to be controlled by feeding back the velocity and acceleration k of the mechanical system together with the displacement
It is explained in detail in the specification of No. 52658.

However, this compensation law is either very strong or has the following problems.

(2) As can be seen from FIG. 13, compensation by velocity feedback and acceleration feedback acts on the cylinder 20 and mechanical system 21 through the servo valve 18 and piping 19. Therefore, the response of the servo valve 18 may be poor, or the piping 19 may have poor response.
If the time required to act on the cylinder 20 is delayed due to a long time, the above-mentioned improvement effect will be limited due to the time lag between the actual movement of the mechanical system 21 and the correction input. On the other hand, if this time lag becomes large, the speed feedback and acceleration feedback will adversely affect the control, causing the response time tR to become longer and vibrations to occur.

(2) In order to perform velocity feedback and acceleration feedback, a detector for detecting each or a device for calculating velocity and acceleration from position signals is required, which increases costs.

■ If a speed detector or acceleration detector is installed,
Maintenance and other efforts are required, which increases running costs.

[Problems to be Solved by the Invention] On the other hand, the inventors of the present application have obtained signals corresponding to velocity and acceleration signals from displacement signals by simple calculations without using the velocity detector 23 and the acceleration detector 25. Although we have already proposed a method for creating and using it for compensation, the above problem (2) still remains.

The present invention has been developed in view of the above circumstances, and is designed to prevent continuous vibration from occurring in a mechanical system without particularly using velocity, acceleration, or signals corresponding to these.As a result, high response, The aim is to realize a high-precision electric/hydraulic servo system, and also to do this easily and inexpensively.

[Means for solving the problem] The present invention calculates a deviation by comparing an input signal that is a target value and a quantity to be controlled that is an output signal of a controlled object,
In an electric/hydraulic servo control device that sends the deviation to a servo valve through a servo amplifier and operates the servo valve, and controls the output flow rate and direction of the servo valve to reduce the deviation, an electric filter is installed in the control device. It is designed to prevent vibrations generated in the electric/hydraulic system and improve response at the same time.

[Operation] The deviation obtained by comparing the input signal, which is the target value, and the quantity to be controlled, which is the output signal of the controlled object, is appropriately amplified, and then sent from the servo amplifier to the servo valve, and the deviation is The output flow rate and direction of the servo valve are controlled so that No harmful vibrations occur even when moving rapidly in steps, and the target value is quickly reached.

[Example] Hereinafter, an example of the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows one embodiment of the present invention, and the same reference numerals in FIG. 1 as those shown in FIG. 12 are given the same reference numerals.

In the electric/hydraulic servo control device shown in FIG. 1, an electric filter 29 is inserted between the operational amplifier 16 and the servo amplifier 17.
It has exactly the same configuration as the one in Figure 2. filter 2
As 9, for example, a phase lag filter or a second-order low-pass filter is used.

Next, the reason why the characteristics of the control system are improved by inserting the filter 29 as described above will be explained.

Generally, when the frequency characteristics of the open-loop transfer function of the electric/hydraulic servo system shown in FIG. 12 without the filter 29 are expressed in a Boat diagram, a peak may appear in the gain curve as shown in FIG. 14.

Here, the -cyclic transfer function is ``the transfer function of an open circuit that occurs when a closed circuit is cut at an arbitrary point'' (from ``Automatic Control Terminology Dictionary'' published by Ohm Co., Ltd.), and as shown in Figure 12, For example, it refers to the characteristics from Ve to vx. In addition, a Bode diagram is a set of pairs in which the frequency ω is plotted on a logarithmic scale log+oω on the horizontal axis, and the gain (dB) and phase (degrees) of a system or element are plotted separately on the ordinate. This is a diagram. When the gain is G, the vertical axis is often graduated in decibels [dB], but (omitted)...
The phase is normally scaled by degl. The abscissa is the frequency in Hz
(cycle 7 seconds), cycle 7 minutes, etc., or take the frequency divided (normalized) by a specific reference frequency. ”
(from the same text).

When the gain margin (Gain Margin, abbreviated as CM) and phase margin (Phase Margin, abbreviated as PM) are read from the Bode diagram of the open-loop transfer function in FIG. 14, they become GM-5dBSPM-77 degrees. in general,
In a servo mechanism, the gain margin is often set at 12 to 20 dB, and the phase margin is set at about 40 to 60 degrees, and in the example shown in FIG. 14, the gain margin is extremely small. The gain margin is small from 30Hz to 40Hz in the gain curve in Figure 14.
This is because of the peaks seen during the period. When the characteristics (called closed loop transfer function) from the input to the output (vr to Vx in Figure 12) of an electric/hydraulic servo system with such characteristics are drawn on a Bode diagram, it becomes as shown in Figure 15. Become.

The gain curve in Figure 15 shows the O between 30Hz and 40Hz.
There is a peak of dB or more. This peak is equivalent to 5 dB from the figure, and from 55-201o+o G, the transfer function G is G
-1.78.

That is, when an input having a frequency of 30-odd Hz is applied to an electric/hydraulic servo system having the characteristics shown in FIG. 15, its amplitude will be amplified 1.78 times as much as the input amplitude. In other words, the machine will move more than the target value. When a step force is applied to the electric/hydraulic servo system in such a state, the step-like signal contains various frequency components, so the 30-odd Hz component is emphasized, resulting in the step response shown in Figure 18. As shown, a poorly damped persistent oscillation of several 30 Hz occurs around the target value r.

Here, the gain margin is defined as ``the phase of the -cyclic transfer function is -18
At an angular frequency of 06, its gain is 1 (Note:
A value that shows how much margin there is for (equivalent to OdB)
, and the phase margin is [a value that indicates how much margin there is for the phase with respect to -180'' at the angular frequency where the gain of the heating wave number transfer function is 1'' (published by Ohm Co., Ltd. (From “Control Terminology Encyclopedia”).

The object of the present invention is to use a simple method to suppress poorly damped vibrations at a certain frequency, which occur due to reasons such as weak rigidity of a machine to be controlled by an electric/hydraulic servo system, as described above. For this purpose, consider installing an electrical filter and lowering the gain value when the phase is 1180 degrees, or shifting the frequency at which the phase is -180 degrees. By doing this, the gain margin is increased as a result.

Figure 2 shows the frequency characteristics of the round transfer function of the electric/hydraulic servo system calculated by computer and expressed in a Bode diagram when a phase lag filter is used as the electrical filter 29 shown in Figure 1. . The phase delay element is expressed by a transfer function of (T2S+1)/(T+S+1), and T, . . . T2 are selected so as to increase the gain margin on the Bode diagram in FIG. 14. From the Bode diagram of the open-loop transfer function in Figure 2 obtained in this way, the gain margin GM
, when reading the phase margin PM, GM-12dB, PM
-[i9 degrees.

The output (from the input to the electric/hydraulic servo system), which has characteristics as a round-trip transfer function as shown in the Bode diagram in Figure 2, is
When the characteristic (closed loop transfer function) from vr to Vx in FIG. 1 is expressed in a Bode diagram, it becomes as shown in FIG. 3. The gain curve in FIG. 3 also has a peak between 30 Hz and 40 Hz, but this peak is equivalent to -3 dB as shown in the figure, and the gain G is 1 or less. That is, even if an input having a frequency of 30-odd Hz is applied to an electric/hydraulic servo system having the characteristics shown in FIG. 3, the amplitude of the output will be smaller than the amplitude of the input. Therefore, the mechanical system 21 is less likely to move beyond the target value. When a step input is applied to an electric/hydraulic servo system in such a state, even if the step signal contains various frequency components, the 30-odd Hz component will not be emphasized, and the 4th frequency component will not be emphasized. As shown in the step response in the figure, the vibration damps rapidly with respect to the target value r, so that the vibration no longer persists, and the control characteristics of the electric/hydraulic servo system are improved.

A second-order low-pass filter can also be used as the electrical filter 29 shown in FIG.

The frequency characteristics of the open-loop transfer function of the electric/hydraulic servo system in this case are expressed in a Bode diagram as shown in FIG. The second-order low-pass filter is ωn2/(S”+2ζωnS+ω
n2), and ω is selected so that the gain margin increases on the Bode diagram in FIG. 14. Reading the gain margin GM and phase margin PM from the Bode diagram of the open-loop transfer function in Fig. 5, GM-10,5d
B, PH will be -64 degrees.

The input to output (
When the characteristic (closed loop transfer function) from V to Vx in FIG. 1 is expressed in a Bode diagram, it becomes as shown in FIG. 6. The gain curve in Figure 6 also has a frequency of 30Hz, similar to the gain curve described above.
There is a peak between 40 Hz and 40 Hz, but this peak is equivalent to -7 dB as shown in the figure, and the gain G is 1 or less.

Therefore, the output at 30-odd Hz in this case becomes even smaller than in the case of Fig. 3, and it attenuates even more rapidly toward the target value r than in the case of Fig. 4, and the characteristics of the electric/hydraulic servo system become even more Becomes good.

Next, the operation of the electric/hydraulic servo control device shown in FIG. 1 will be explained. For example, the target value (set value) Vr for controlling the wrapper roll 3 shown in FIG. is compared with the signal vx indicating the actual position of
e is appropriately amplified by the operational amplifier 16 to become a signal vA, and this signal VA is passed through an electric filter 29 to the signal shown in FIG.
The modified signal VA' is modulated so as to realize the characteristics shown in the Bode diagram in FIG. 5, and is applied to the servo amplifier 17. The following operation is the same as that of the electric/hydraulic servo system shown in FIG. 12, so a description thereof will be omitted.

As described above, in the present invention, when a poorly damped vibration system exists in the control loop of the electric/hydraulic servo system, the gain curve at a certain frequency as seen in the Bode diagram of the open-loop transfer function in FIG. We focused on the characteristic that a peak occurs in the oscillation system, resulting in a significant decrease in gain margin.We suppressed this inherent characteristic caused by the vibration system by inserting an electric filter into the control device, and as a result, we developed a vibration-proof system. I try to do that. Since vibration is suppressed, operational amplifier 1 in Figure 1
It is possible to increase the amplification factor (generally called gain) of
Shorten R. )be able to. Therefore, in the present invention,
Even if the controlled object is moved in steps using an electric/hydraulic servo system, harmful vibrations will not occur and the target value can be quickly reached.

The electric/hydraulic servo control device shown in FIG. 1 can be applied to systems other than the control system for wrapper rolls as shown in FIG. 9. That is, FIG. 8 shows an example of the configuration of the present electric/hydraulic servo control device for controlling a hydraulic rolling mill. This rolling mill is equipped with a hydraulic reduction cylinder 31 on the lower back-up roll 30 side, a reduction screw 33 on the upper back-up roll 32 side, and the reduction cylinder 31
The rolling force of the rolled material 43 by the upper and lower work rolls 3B and 37 is adjusted by controlling the servo valve 34 and the rolling screw drive motor 35.

Therefore, this rolling mill is equipped with a rolling screw position detector 38.
, a load cell 39 and a hydraulic pressure reduction cylinder position detector (displacement meter) 40 arranged on the movable part of the cylinder 31. These detection signals are input into the control device 41, into which the filter shown in FIG. 1 is inserted. 42 in the diagram
is the target value for position control.

Even with such a configuration, the work roll 3 is
6.37 servo control can be performed.

Note that the electric/hydraulic servo control device of the present invention can be applied to various hydraulic devices other than the above-mentioned hydraulic down coiler and hydraulic reduction type rolling mill, and has a wide range of application. Further, the filter may be constructed of either hardware such as an electronic circuit or software using a computer. Further, in the above description, for convenience, the case where the position of the controlled object is controlled has been taken up, but the present invention can also be applied to cases where the speed or force is controlled.

[Effects of the Invention] As explained above, according to the electric/hydraulic servo control device of the present invention, harmful vibration elements are suppressed by a simple filter, and as a result, it is possible to suppress the influence of the characteristics of the controlled object. An excellent effect can be achieved in that less servo control can be realized.

[Brief explanation of the drawing]

Fig. 1 is a control block diagram of an embodiment of the electric/hydraulic servo control device of the present invention, and Fig. 2 is a Bode line representing the frequency characteristics in an open loop when the filter of the device of Fig. 1 is a phase delay filter. Figure 3 is a Bode diagram showing the frequency characteristics in a closed loop when the filter of the device shown in Figure 1 is a phase lag filter, and Figure 4 is a Bode diagram showing the frequency characteristics of the device shown in Figure 1.
A diagram showing the step response state of a mechanical system when the filter in the device shown in the figure is a phase lag filter, and Figure 5 shows the frequency characteristics in an open loop when the filter in the device shown in Figure 1 is a second-order low-pass filter. Figure 6 is a Bode diagram representing the frequency characteristics in a closed loop when the filter of the device shown in Figure 1 is a second-order low-pass filter, and Figure 7 is a Bode diagram representing the frequency characteristic of the device shown in Figure 1 as a second-order low-pass filter. A diagram showing the step response state of the mechanical system when used as a filter, Fig. 8 is an explanatory diagram when the electric/hydraulic servo control device of the present invention is applied to a hydraulic reduction type rolling mill, and Fig. 9 is a down coiler wrapper. An explanatory diagram of the roll's electric/hydraulic servo system. Figure 10 is an explanatory diagram of a modeled version of the device in Figure 9. Figure 11 shows how the device in Figure 9 can be used to control the wrapper roll without inserting a filter. A diagram showing the step response state when the
A control block diagram of a conventional electric/hydraulic servo system when controlling the wrapper roll position of the device shown in the figure, Figure 13 is a control block diagram when feeding back the same speed signal and acceleration signal, and Figure 14 is a control block diagram of the conventional electric/hydraulic servo system when controlling the wrapper roll position. Figure 15 is a Bode diagram representing the frequency characteristics in the open loop of the control system.
FIG. 2 is a Bode diagram showing the frequency characteristics in the closed loop of the control system, and FIG. 16 is a diagram showing the step response state of the mechanical system in the control system of FIG. In the figure, 15 is a comparator, 17 is a servo amplifier, 18 is a servo valve, 19 is piping, 20 is a cylinder, 21 is a mechanical system,
22 is a displacement meter, and 29 is a filter.

Claims (1)

[Claims] 1) Compare and calculate the input signal, which is the target value, and the quantity to be controlled, which is the output signal of the controlled object, to find the deviation, and send the deviation to the servo valve through the servo amplifier. In the electric/hydraulic servo control device that operates the servo valve and controls the output flow rate and direction of the servo valve to reduce deviation, an electric filter is inserted into the control device to suppress vibrations generated in the electric/hydraulic system. An electric/hydraulic servo control device characterized in that it is configured to prevent the problem and at the same time increase response. 2) An electric/hydraulic servo control device according to claim 1, wherein the electric filter is incorporated into an electric/hydraulic servo control device for a wrapper roll of a down coiler. 3) The electric filter according to claim 1), wherein the electric filter is incorporated into a hydraulic pressure reduction control device of a rolling mill.
Hydraulic servo control device.