JPH08219229A - Vibration isolator - Google Patents

Abstract

PURPOSE: To increase the response speed of a vibration isolator when a control object supported by an air spring is floated up. CONSTITUTION: A PI control part 11 which controls an electro-pneumatic analog valve for feeding vertical deviation control force to a control object supported by an air spring so that the analog valve may follow the target value rk of a floating-up quantity of the control object by means of PI action, and a feed forward control part 12 for outputting an operational quantity N.rk previously set on the basis of the target value rk of the floating-up quantity are provided, so that the electro-pneumatic analog valve may be controlled by using the operational quantity fPI(ek ) obtained by the PI control part 11 and the operational quantity N.rk obtained by using the feed forward control part 12. Therefore, the floating-up time of the control object can be shortened an also realized by a simple logic, so that deterioration of control performance and increase in the cost can be prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an anti-vibration device applied to an anti-vibration table, and more particularly to an anti-vibration device for levitating a controlled object by any one of PI control, PD control and PID control.

[0002]

2. Description of the Related Art Conventionally, in order to obtain precision required for precision equipment represented by semiconductor manufacturing / inspection equipment, electron microscopes, optical measuring instruments, etc.,
An anti-vibration device is used to support and isolate these facilities from the effects of vibration from the installation foundation or floor. In order to support vibration isolation, such a vibration isolation device supports an object to be controlled such as a surface plate on which precision equipment is mounted with an air spring. This air spring is feedback-controlled so that when the controlled object is levitated to a predetermined position, the floating amount (controlled amount) of the controlled object matches the target value. This feedback control includes, for example, PID (proportional / integral / derivative) control.

The PID control circuit performs arithmetic operation of control operation by adding P operation, I operation and D operation. P
The operation, the I operation, and the D operation are added because the flying height and the target value cannot be perfectly matched only by the P operation, and an offset (steady deviation) may remain. This offset can be prevented by adding the I operation, but it has a drawback that it takes a long time to respond and control is delayed. Therefore, although D motion is added to compensate for this, side effects such as overshoot and hunting may occur. Here, the overshoot is an overshoot amount, which is a phenomenon in which the target value is exceeded during control.

When the controlled object is levitated to a predetermined levitating position by the vibration isolator thus constructed, it takes time from the start of control to the levitating as shown in FIG. In addition,
It goes without saying that the same problem will occur even if the PI control circuit for PI control and the PD control circuit for PD control are connected to the feedback circuit. In addition, if the target value is known in advance, there is a control method that adds an operation amount commensurate with the offset that occurs during feedback control, but whenever the target value changes, the operation amount commensurate with the offset is changed. There was a difficulty that it had to be.

[0005]

An object of the present invention is to solve such a conventional problem, and it is possible to speed up the response speed when a controlled object supported by an air spring is levitated. The purpose is to provide.

[0006]

The vibration isolator according to the present invention which achieves such an object is a PI actuator for a vertical actuator for injecting a vertical displacement control force into a controlled object supported by an air spring. Control means for outputting a manipulated variable for controlling so as to follow the target value of the flying height of the controlled object by either control or PID control, and a feed for outputting the manipulated value preset based on the target value of the flying height. Forward control means, and a control system for controlling the vertical actuator by the operation amount obtained by the feedforward control means and the operation amount obtained by the control means.

[0007]

According to this vibration isolator, the operation amount of the vertical actuator is obtained by adding the operation amount obtained by any one of PI control, PD control and PID control means and the operation amount obtained by the feedforward control means. By operating with the operation amount, the controlled object is levitated to a predetermined flying height. As a result, the flying height can be quickly reached to the target value even when the control is started or the target value changes. Further, since side effects such as overshoot and hunting can be prevented, the control system can be kept in a stable state.

[0008]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the vibration isolator according to the present invention will be described below with reference to the drawings. As shown in FIG. 2, the vibration isolation device includes an air spring 2 of bellows type, diaphragm type, etc., and a vibration isolation device supported by the air spring 2 via a support 6 on an installation surface 10 which is a foundation or a floor. The table or control object 3 and the control circuit 4 for controlling the control object 3 via the air spring 2 are provided. The air spring 2 is supplied and exhausted by an electro-pneumatic analog valve 5 which is a vertical actuator driven by a control signal from the control circuit 4. Air compressed by an air pressure source such as a compressor (not shown) is applied to the electro-pneumatic analog valve 5. The electro-pneumatic analog valve 5 supplies air to the air spring 2 and exhausts air from the air spring 2 based on a control signal from the control circuit 4.

Here, the controlled object 3 is not only a mass to be oscillated such as a surface plate, but also a semiconductor manufacturing IC such as a stepper (reduction projection type exposure machine) mounted on this, a semiconductor.
It includes precision equipment such as inspection equipment, electron microscopes, and optical application equipment. As shown in FIG. 1, the control circuit 4 included in the control system 1 of the vibration isolator has, for example, a PI control unit 11 that is a PI control unit that is used together with an integral operation to cancel an offset (steady deviation), and a preset value. And a feedforward control unit 12 that is a feedforward control unit that outputs a manipulated variable that is set based on the flying height target value r _k that is set in the unit 8. The controlled object 13 controlled by the control system 1 is not limited to the controlled object 3 defined in the present embodiment, but includes the air spring 2.

The PI control unit 11 performs PI control calculation based on the control deviation e _k obtained by subtracting the flying height (control amount) y _k from the target value r _k of the flying height of the controlled object 3. , The operation amount from the PI control unit 11 is u _1k = f
It becomes _PI (e _k ). In addition, the feedforward control unit 1
Reference numeral 2 denotes a target value r _k of the flying height of the controlled object 3 multiplied by a feedforward constant N, and the operation amount from the feedforward control unit 12 is u _2k = N · r _k . Accordingly, each operation amount are added by the summing _{point, u k = u 1k + u} 2k = N · r k becomes the control output (manipulated variable) as input to the electric pneumatic analog valve 5.

Here, if the arithmetic expression of PI control is digital control,

[0012]

[Equation 1]

Is represented by Here, u _k is an operation amount for operating the controlled object 3, K _p is a proportional sensitivity, θ is a sampling time, and T _I is an integration time. The flying height y _k can be obtained by the vertical displacement sensor 7 that detects the vertical displacement of the controlled object 3 and outputs a vertical displacement signal. The vertical displacement sensor 7 may be, for example, an eddy current element, a differential transformer, an LED, a laser element, or the like, and is mounted on either the controlled object 3 or the support 6.

It is preferable that such a vibration isolation device be controlled by a digital control device such as a microcomputer.
In that case, the feedforward constant N is stored in the memory circuit of the digital controller. The operation of the vibration isolator thus configured will be described below. Control object 3 now
When the position control is started by the control circuit 4 in order to levitate the target value r _k of the flying height set by the setting unit 8,
A vertical displacement signal having a flying height y _k obtained by a vertical displacement sensor 7 mounted on either the controlled object 3 or the support 6 is read into the control circuit 4. The feedback control by the flying height y _k becomes vertical displacement signal is started, the control circuit 4 compares the flying height y _k is read and the target value r _k, the r _k -y _k, the target value r _k The control deviation e _k which is the deviation from is calculated.

With respect to this control deviation e _k , the PI control unit 11 of the control circuit 4 performs a PI control calculation to obtain a control output which is an operation amount u _1k . In addition, in the case of the present embodiment, since the arithmetic expression of PI control is digital control,

[0016]

[Equation 2]

## EQU1 ## On the other hand, in addition to such PI control, the feedforward control unit 12 performs a feedforward control calculation to obtain a control output which is an operation amount of u _2k = N · r _k . The control output u _1k from the PI control unit 11 and the control output u _2k from the feedforward control unit 12 are added at the addition point,

[0018]

(Equation 3)

The electropneumatic analog valve 5 is controlled by the control output u _k . Specifically, a control signal of the control output u _k is input to the electro-pneumatic analog valve 5, and the electro-pneumatic analog valve 5 driven based on this control signal causes the air spring 2 to inject the vertical displacement control force. The controlled object 3 is levitated to a predetermined flying height. As a result, even if the response by the PI control unit 11 is slow, the operation amount corresponding to the target value r _k is immediately PI by the feedforward control unit 12.
Since it is added to the operation amount from the control unit 11, for example, as shown in FIG.
When the feedforward constant N = 6000 as shown in FIG. 3, the controlled object 3 quickly levitates from the control start point S, and the dynamic characteristics during levitating can be made favorable. Further, as shown in FIG. 4, even if the target value r _k is changed, the characteristic before the change can be obtained without changing the feedforward constant N = 6000. In this vibration isolator 1, for example, if the feedforward constant N is increased as shown in FIG. 5, (N = 730
0), the levitation time can be further shortened, but the levitation dynamic characteristic causes overshoot (overshoot amount).

Therefore, by changing the feedforward constant N, it is possible to obtain an arbitrary levitation dynamic characteristic. Further, since the feedforward term refers to the target value, even if the target value changes, the feed There is no need to readjust the forward constant N. Further, in the present embodiment, the control means is PI control, but the present invention is not limited to this, and PD control or PID control may be used. In PD control, PD control calculation is performed by the control circuit 4, f
_The control output, which is the manipulated _{variable PD} (e _k ), is output to the addition point, and the PID control calculation is performed by the control circuit 4 in the PID control, and the control output, which is the manipulated _variable f _PID (e _k ) is the addition point. Is output to.

[0021]

As is apparent from the above description, the vibration isolator according to the present invention performs PI control and PD control on the vertical actuator for injecting the vertical displacement control force into the controlled object supported by the air spring. And a PID control, the control means outputs an operation amount for controlling so as to follow the target value of the flying height of the controlled object, and a feedforward that outputs the operation amount preset based on the target value of the flying height. Since the control system includes a control unit and controls the vertical actuator by the operation amount obtained by the feedforward control unit and the operation amount obtained by the control unit, the levitation time of the controlled object can be shortened. . Moreover, since it can be realized by a simple logic, it does not impose a burden on the hardware, and it is possible to prevent a decrease in control performance and an increase in cost.

[Brief description of drawings]

FIG. 1 is a block diagram showing a position control system of a vibration isolation device according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram of a vibration isolation device according to the present invention.

FIG. 3 shows the time obtained by the vibration isolator according to the present invention-
The graph which shows the relationship of flying height.

FIG. 4 shows the time obtained by the vibration isolation device according to the present invention.
The graph which shows the relationship of flying height.

FIG. 5: Time obtained by the vibration isolator according to the present invention-
The graph which shows the relationship of flying height.

FIG. 6 is a graph showing the relationship between time and flying height obtained by a conventional vibration isolation device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Vibration isolation apparatus 2 ... Air spring 3 ... Control object (control object) 5 ... Electro-pneumatic analog valve (vertical direction actuator) 11 ... PI control part (control means) 12 ... Feedforward control part (feedforward control means) ) r _k ... floating amount of the target value u _1k ... operation amount obtained by the operation amount u _2k ... feedforward controller obtained by the PI control unit u _k ... operation amount that has been added by the adding point

Claims (1)

[Claims] 1. A vertical actuator for injecting a vertical displacement control force into a controlled object supported by an air spring is a PI.
Control means for outputting an operation amount for controlling so as to follow the target value of the flying height of the controlled object by any one of control, PD control and PID control, and an operation preset based on the target value of the flying height A feedforward control means for outputting a quantity, and a control system for controlling the vertical actuator according to the operation quantity obtained by the feedforward control means and the operation quantity obtained by the control means. Vibration isolation device.