JP2011247314A - Active vibration removing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve vibration removing performances in a low frequency region near 1 Hz with a simple configuration in an active vibration removing device.SOLUTION: The active vibration removing device includes: an air spring 21 that supports an object for vibration removal (a surface plate 7, a top plate 27 and a precision device) with respect to a foundation structure 3; a linear motor 23; a controller controlling vibration of the object for vibration removal by driving the linear motor 23; and a displacement sensor 33. The controller 37 includes a displacement feedback control unit 37a, which multiplies a relative displacement X-Xdetected by the displacement sensor 33 and a displacement feedback control gain G to determine a control amount G (X-X) of the linear motor 23. The displacement feedback control unit 37a controls to decrease an apparent spring constant K' represented by a difference between the spring constant K of the air spring 21 and a value proportional to the control gain G, by adjusting the control gain G.

Description

  The present invention relates to a vibration isolator for installing a precision instrument such as a test instrument, an electron microscope, or a semiconductor-related manufacturing apparatus in a state generally insulated from floor vibration, and in particular, using an actuator, the vibration of these instruments is reduced. The present invention relates to an active type vibration isolator that adds a control force to be reduced.

Conventionally, when installing precision instruments such as semiconductor exposure devices and electron microscopes on the floor, so-called passive types that use spring elements such as air springs, coil springs, and anti-vibration rubber to block vibration from the floor A precision device is supported by a vibration isolator (hereinafter also referred to as a passive vibration isolator). An equivalent model of such a passive vibration isolator is represented as shown in FIG. 9A, and the equation of motion of this equivalent model is
M · X ″ + C · (X′−X ₀ ′) + K · (X−X ₀ ) = 0 (Formula 1)
It is expressed. Here, M: weight on spring, C: damping constant, K: spring constant, X ″: acceleration on spring, X ′: speed on spring, X ₀ ′: speed on floor, X: displacement on spring , X ₀ : displacement of the floor.

Then, using the Laplace operator s, the vibration transmissibility of the equivalent model shown in FIG.
_{X 1 / X 0 = (C} · s + K) / (M · s 2 + C · s + K) ... ( Equation 2)
It is expressed.

  FIG. 10 is a graph showing the relationship between the frequency and the vibration transmissibility of the vibration isolator on a logarithmic scale, and the broken line in the figure shows the vibration transmissibility of an example of the passive vibration isolator. In this vibration isolator, a resonance point appears in a low frequency range of 3 Hz to 4 Hz, and it can be seen that the vibration transmissibility at 1 Hz to 5 Hz is 1 (0 dB) or more due to this.

  Thus, in order to obtain a greater vibration isolation effect, the displacement and vibration state of the precision instrument supported by the spring element is detected by a sensor, and the actuator is driven by feeding back the detected state to reduce the vibration of the precision instrument. A so-called active type vibration isolator (hereinafter also referred to as an active vibration isolator) has been proposed that performs positioning and vibration isolation of precision equipment by applying such control force.

  For example, in Patent Document 1, the detected value of the vertical acceleration of the vibration isolation object detected by the acceleration sensor is multiplied by the feedback control gain, and the feedback control gain is set for the speed obtained by integrating the acceleration once. A controller for multiplying the displacement obtained by integrating the acceleration twice and multiplying the displacement by the feedback control gain to determine the control amount of the actuator; Is set corresponding to the closest mass value that is smaller than the actual mass of the object to be isolated, in a map in which the optimum feedback control gain value is obtained by experiment and set. There has been proposed an active vibration control apparatus in which an optimum value is a feedback control gain value.

  According to this active vibration control device, the effect of the so-called skyhook damper can be obtained by speed feedback, the resonance magnification can be reduced without impairing the vibration isolation performance in the high frequency region, and so-called by the displacement feedback It is said that the effect of the skyhook spring can be obtained and the vibration transmissibility can be reduced in a region below the resonance frequency.

Here, the skyhook damper (control) refers to control in which attenuation is obtained without transmitting floor vibration if an object is connected via a damper from a point stationary in the air. The active vibration isolator using the skyhook damper control is represented by an equivalent model shown in FIG. 9B in which an object and a point stationary in the air are connected by a damper. The equation of motion of this equivalent model is
M · X ″ + C · (X′−X ₀ ′) + K · (X−X ₀ ) + C _s · X ′ = 0 (Formula 3)
It is expressed. Here, C _s is an attenuation constant of a skyhook damper connected to a point stationary in the air.

In addition, the vibration transfer characteristic (vibration transmission rate) of this equivalent model is
X / X ₀ = (C · s + K) / {M · s ² + (C + C _s ) · s + K} (Formula 4)
It is expressed.

The solid line in FIG. 10 indicates an active vibration isolator using skyhook damper control based on speed feedback (an example of a passive vibration isolator having a vibration transmissibility indicated by a broken line in FIG. 10 with skyhook damper control added). ) Is shown. In the active vibration isolator using the skyhook damper control, s approaches 0 when the frequency approaches 0, so that X / X ₀ ≈K / K = 1 (0 dB) according to (Equation 4), Even if the frequency is increased, the vibration transmissibility is not deteriorated as in the case of passive with attenuation, and a large vibration isolation effect is obtained in the entire frequency range.

On the other hand, the skyhook spring (control) is a control as if an object is hung on a spring fixed at a point stationary in the air, based on the skyhook theory, like the skyhook damper. The active vibration isolator using the skyhook spring control is represented by an equivalent model shown in FIG. 9C in which an object and a point stationary in the air are connected by a spring. The equation of motion of this equivalent model is
M · X ″ + C · (X′−X ₀ ′) + K · (X−X ₀ ) + K _s · X = 0 (Formula 5)
It is expressed. Here, K _s is a spring constant of a spring connected to a point stationary in the air.

In addition, the vibration transmissibility of this equivalent model is
X / X ₀ = (C · s + K) / (M · s ² + C · s + K + K _s ) (Expression 6)
It is expressed.

The two-dot chain line in FIG. 10 indicates an active vibration isolator using skyhook spring control by displacement feedback (skyhook spring control is added to an example of a passive vibration isolator having a vibration transmissibility indicated by a broken line in FIG. ) Is shown. In the active vibration isolator using the skyhook spring control, s approaches 0 when the frequency approaches 0, and therefore, X ₁ / X ₀ ≈K / (K + K _s ) according to (Equation 6). As a result, in the active vibration isolator using the skyhook spring control, the vibration transmissibility becomes smaller than 1 (0 dB) when the frequency approaches 0, so that a large vibration isolation effect is obtained in a low frequency range lower than the natural frequency. Is obtained.

Japanese Patent No. 4355536

  Incidentally, in recent years, there has been an increasing demand for vibration isolation devices for vibration isolation performance in a low frequency region near 1 Hz. However, in the conventional passive vibration isolator, even if an attempt is made to lower the resonance point (natural frequency) by adjusting the spring element, the vibration isolation performance in the low frequency region near 1 Hz is limited because the limit is slightly less than 1 Hz. It is difficult to increase.

  Moreover, in the thing of the said patent document 1, although the effect of the skyhook damper by the speed feedback is large in the vicinity of a natural frequency, it is small in the low frequency range below 1 Hz. The effect of the skyhook spring by the displacement feedback can be obtained even in a low frequency range of less than 1 Hz. However, since the natural frequency appears in the vicinity of 10 Hz, the vibration isolation performance deteriorates in the vicinity of the natural frequency.

  As described above, to improve the vibration isolation performance in a low frequency region of 1 Hz or less, the skyhook damper control and the skyhook spring control are adopted by the conventional passive vibration isolation device and by feeding back the speed and displacement. This is also difficult with conventional active vibration isolation devices.

  In addition, Skyhook dampers and Skyhook springs integrate acceleration signals, so low frequency noise from sensors and electrical circuits appears as offsets and drifts and cannot be controlled or cut to avoid them. When a high-pass filter is used, the phase changes and the performance is significantly degraded.

  The present invention has been made in view of the above points, and an object of the present invention is to provide a technique for improving vibration isolation performance in a low frequency region near 1 Hz with a simple configuration in an active vibration isolation device. There is.

  In order to achieve the above object, in the present invention, by using the relative displacement actually detected by the displacement sensor, the vibration isolation performance obtained by the effect of the skyhook damper is reduced by reducing the natural frequency of the entire device. The vibration isolation performance different from the vibration isolation performance obtained by the effect of the hook spring is developed.

  Specifically, the first invention is to add a spring element that supports a vibration isolation object to a foundation installed on the floor and a control force that reduces the vibration of the vibration isolation object. And an active vibration isolation device including a control means for driving the actuator to actively control the vibration of the vibration isolation object.

  And a displacement sensor for detecting a relative displacement of the vibration isolation object with respect to the foundation, wherein the control means multiplies the relative displacement detected by the displacement sensor by a displacement feedback control gain to provide feedback of the actuator. A displacement feedback control unit for determining a control amount, and the displacement feedback control unit adjusts the displacement feedback control gain to obtain a spring constant of the spring element and a value proportional to the displacement feedback control gain; The control is performed to reduce the apparent spring constant represented by the difference between the two.

  In the active vibration isolation device according to the first aspect of the present invention, when the floor on which the foundation is installed vibrates, the vibration is transmitted to the vibration isolation object via the foundation and the spring element. In such a vibration isolation device in which a spring element is provided between the vibration isolation object and the foundation, even if it is a passive type vibration isolation device that simply uses a spring element, the vibration of the vibration isolation object is reduced using an actuator. Even if the vibration isolator of the active type is reduced, the spring force generated by the spring element is obtained by multiplying the relative displacement between the object to be isolated and the foundation by the spring constant of the spring element, that is, “spring constant × vibration isolation”. It is represented by the difference between the “displacement of the object” and “spring constant × displacement of the foundation” (see (Expression 1), (Expression 3), and (Expression 5) above). For this reason, the vibration transmissibility expressed by the relationship of “displacement of vibration isolation object” ÷ “floor displacement” naturally includes a spring constant in its denominator and numerator (the above (formula 2)). ), (Formula 4), (Formula 6)).

  Here, according to the first invention, the relative displacement of the vibration isolation object with respect to the foundation is detected by the displacement sensor, and the actually detected value is input to the control means. Then, the displacement feedback control unit multiplies the input detection value by the displacement feedback control gain to determine the feedback control amount of the actuator. Thus, the displacement feedback control gain is multiplied by the relative displacement between the object to be isolated and the foundation, that is, the displacement of the object to be isolated and the displacement of the floor. Will be incorporated into both the denominator and numerator of the rate. As a result, the vibration transmissibility has an “apparent spring constant” represented by “spring constant—a value proportional to the displacement feedback control gain” in both the denominator and the numerator. In other words, in the active vibration isolation device according to the first aspect of the invention, the vibration isolation object is supported by the spring element having the “apparent spring constant” with respect to the foundation. In the present invention, the “value proportional to the displacement feedback control gain” means the displacement feedback control gain or a value obtained by multiplying the displacement feedback control gain by a proportional constant representing the characteristics of the actuator.

  For this reason, as the value proportional to the displacement feedback control gain is adjusted to approach the spring constant, the apparent spring constant becomes smaller. Therefore, “the natural frequency of the entire device is proportional to the half power of the apparent spring constant. "Can be lowered to a low frequency region (for example, around 0.2 Hz) that is significantly lower than 1 Hz, and the vibration transmissibility in the low frequency region around 1 Hz can be lowered. Thereby, in the active vibration isolator, the vibration isolation performance in a low frequency region near 1 Hz can be improved with a simple configuration.

  Further, when determining the feedback control amount of the actuator, since the relative displacement directly detected by the displacement sensor is used, not the displacement obtained by integrating the acceleration of the vibration isolation object detected by the acceleration sensor twice. If the first invention is applied to a passive type vibration isolator, it is not necessary to use a filter with a large time constant in order to cut the DC component due to gravitational acceleration, and the sensor output may become infinitely large due to integration. It can be avoided that the phase is largely shifted due to the repetition of the cut and amplification of the DC component, the control cannot be performed, and the performance is remarkably deteriorated.

  On the other hand, if the first invention is applied to the conventional active type vibration isolator, the vibration isolation performance can be further improved in combination with the vibration isolation effect by speed feedback or the like. Specifically, the second invention further comprises a vibration sensor for detecting a vibration state of the vibration isolation object in the first invention, wherein the control means is the vibration isolation object detected by the vibration sensor. It further has a feedback control unit that determines a feedback control amount of the actuator based on an acceleration or a speed of an object.

  According to the second aspect, the vibration isolation performance in the low frequency region near 1 Hz is enhanced by the displacement feedback control unit, and a large vibration isolation effect is obtained in the high frequency region by feedback such as speed and acceleration. High vibration isolation performance can be obtained from the low frequency range to the high frequency range.

  According to a third invention, in the first or second invention, the actuator is a linear motor disposed between the vibration isolation object and the foundation.

  According to the third invention, by using a linear motor having excellent responsiveness, the time delay of the control system is reduced, and the control of the first and second inventions is applied to vibrations in a wider frequency range. be able to.

  According to a fourth invention, in the first or second invention, the spring element is a gas spring, and the gas spring has a control force by controlling a servo valve for adjusting a pressure state of the gas spring. It is also used as the actuator for adding.

  According to the fourth invention, by supporting the vibration isolation object by the gas spring, it is possible to improve the basic vibration isolation performance in a state in which the spring force is very soft and no control force is applied. it can. Further, by using the gas spring as an actuator, it is not necessary to separately provide an actuator, and a relatively large force can be easily obtained as a characteristic of the gas spring.

  According to the active vibration isolation device of the present invention, the displacement feedback control unit multiplies the relative displacement of the vibration isolation object with respect to the foundation, that is, the displacement feedback control gain for both the vibration isolation object displacement and the floor displacement. Thus, since the feedback control amount of the actuator is determined, the displacement feedback control gain is incorporated into the denominator and numerator of the vibration transmissibility expressed by the relationship of “displacement of vibration isolation object” ÷ “floor displacement”.

  Thus, in a vibration isolator in which a spring element is provided between the vibration isolation object and the foundation, the spring constant is naturally included in the denominator and numerator of the vibration transmissibility. The vibration transmissibility includes an “apparent spring constant” expressed by “spring constant—a value proportional to the displacement feedback control gain” in its denominator and numerator.

  As a result, in the active vibration isolator according to the present invention, the vibration isolation object is supported by the spring element having the “apparent spring constant” with respect to the foundation, and a value proportional to the displacement feedback control gain. Since the “apparent spring constant” becomes smaller as the spring constant becomes closer to the spring constant, the natural frequency of the entire active vibration isolator can be lowered to a low frequency range significantly lower than 1 Hz with a simple configuration. It is possible to reduce the vibration transmissibility.

1 is a perspective view showing a schematic configuration of a precision vibration isolation table according to the present invention. It is a figure which shows schematic structure of the active vibration control apparatus which concerns on Embodiment 1. FIG. It is a block diagram showing typically a physical phenomenon in linear motor control. It is a graph which shows the relationship between a frequency and a vibration transmissibility. It is a figure which shows schematic structure of the active vibration control apparatus which concerns on Embodiment 2. FIG. It is a block diagram showing typically a physical phenomenon in linear motor control. It is a figure which shows schematic structure of the active vibration control apparatus which concerns on Embodiment 3. FIG. It is a block diagram showing typically a physical phenomenon in air pressure control. It is a figure which shows the equivalent model of a vibration isolator, The figure (a) is a passive type, The figure (b) is an active type using a skyhook damper, The figure (c) ) Is an active type using a skyhook spring. It is a graph which shows the relationship between the frequency and vibration transmissibility in the conventional passive type and active type vibration isolator.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

(Embodiment 1)
FIG. 1 shows an example of a precision vibration isolation table according to Embodiment 1 of the present invention. This precision vibration isolation table 1 is, for example, a semiconductor-related manufacturing apparatus, test equipment, atomic force microscope (AFM), or laser microscope. Like precision measuring instruments such as the above, they are equipped with precision devices that are easily affected by vibrations, and are installed in a state that is insulated from floor vibrations as much as possible. More specifically, the illustrated precision vibration isolation table 1 is a basic structure that is installed on a floor (not shown) via levelers 19, 19, 19, 19 for height adjustment, more specifically, on a dedicated table or table. A surface plate 7 provided with a portion (foundation) 3 and air spring units 5, 5, 5, 5 respectively disposed at four corners of the upper surface thereof and supported by these four air spring units 5, 5,. A precision device (not shown) is mounted on the top.

  The base structure portion 3 is a structure in which structural members of a steel square pipe are assembled so as to have a substantially rectangular parallelepiped shape. Reference numeral 9 denotes a leg portion, and reference numerals 11 and 13 denote beam portions. Reference numeral 15 denotes a horizontal plate on which the air spring unit 5 is disposed, and reference numeral 17 denotes a caster. In this figure, the controller 37 of the air spring unit 5 is not shown.

  As schematically shown in FIG. 2, the air spring unit 5 includes an air spring (gas spring (spring element)) 21 and a linear motor (actuator) 23 disposed on a base plate 25. The air spring 21 elastically supports the top plate 27 that receives the load of the surface plate 7 and the mounted device (precision device), and controls vibration (control force) that reduces the vibration of the top plate 27. ) Is added by the linear motor 23. The surface plate 7, the top plate 27, and the precision device mounted thereon are the vibration isolation objects in the active vibration isolation device according to the present embodiment. Thus, by supporting the object for vibration isolation with the gas spring 21, the spring characteristics can be made very soft, and the basic vibration isolation performance in the state where no control force is applied can be improved.

  The air spring 21 is, for example, a diaphragm type that includes an air chamber 21a filled with air and a piston 31 that is airtightly inserted into an opening of an upper wall of the air chamber 21a via a diaphragm 29. Further, a gimbal mechanism can be incorporated in the piston 31 so that a very soft spring characteristic can be obtained in the horizontal direction. A bellows type air spring 21 can also be used.

Further, the air spring unit 5 includes a displacement sensor 33 for detecting a relative displacement of the vibration isolation object with respect to the foundation structure 3, more specifically, a relative displacement X−X ₀ of the top plate 27 with respect to the base plate 25. Is provided. An output signal from the displacement sensor 33 is input to a controller (control means) 37.

  The controller 37 is configured to drive the linear motor 23 disposed between the vibration isolation object and the foundation structure 3 to actively control the vibration of the vibration isolation object. More specifically, the controller 37 outputs a control signal (current) to the linear motor 23 for each air spring unit 5 and applies a control force to the top plate 27 so as to reduce its vibration. That is, active vibration control is performed to reduce the vibration of the surface plate 7 and the equipment mounted thereon. The linear motor 23 includes a coil and a magnet (not shown), and generates an attractive force or a repulsive force between the magnetic force generated by supplying current to the coil and the magnetic force of the magnet. The coils are attached to the top plate 27 and the magnets are attached to the base plate 25 respectively. However, since there is a gap between them and they are not in contact with each other, the vibration of the foundation structure part 3 is transmitted via the linear motor 23. It is not transmitted to the object of vibration isolation.

  .., The linear motor 23, the displacement sensor 33, and the controller 37 constitute an active vibration isolation device for the precision vibration isolation table 1. In the active vibration isolator according to the present embodiment, it is not necessary to use acceleration sensors for detecting the vibration states of the base plate 25 and the top plate 27 as in the conventional active vibration isolator, and thus the apparatus configuration is greatly simplified. can do. FIG. 2 shows only the vertical displacement sensor 33 and the vertical linear motor 23 of the air spring unit 5, but a horizontal displacement sensor and linear motor are also provided. The control in the horizontal direction is also performed in the same manner as the control in the vertical direction described below.

Although not shown in detail, the controller 37 is a digital controller having a conventionally known structure including a microcomputer, an I / O interface, a data bus, and a memory such as a RAM, ROM, or HDD, and is output from the displacement sensor 33. In response to this, a control signal is output to the linear motor 23 for each air spring unit 5. Specifically, the controller 37, based on a signal from the displacement sensor 33 recognizes the relative displacement X-X ₀ of the top plate 27 with respect to the base plate 25, the platen 7, counteracts the vibrations of the top plate 27 and a precision device Such a feedback control amount is determined, and a displacement feedback control unit 37a that drives the linear motor 23 to generate a control force based on the determined feedback control amount is provided. With respect to the basic control of the linear motor 23 by the displacement feedback control unit 37a, only the control for reducing the vertical vibration will be described in detail below with reference to FIG.

FIG. 3 is a block diagram schematically showing a physical phenomenon in the linear motor control in the vertical direction by the displacement feedback control unit 37a. More specifically, the symbol P in this block diagram indicates that the object of vibration isolation of the sprung weight M is supported by the air spring 21 having the damping constant C and the spring constant K, and the symbol FB1 is , feedback control amount G · obtained by multiplying the displacement feedback control gain G of the relative displacement X-X ₀ to (X-X _0), via the linear motor 23, represented by K _L, subject such vibration damping This means that the object acts as a control force. Note that the damping constant C and the spring constant K of the air spring 21 are values that can be set in advance or obtained by measurement, and the sprung weight M is obtained by actually mounting a precision device on the surface plate 7. It is a determined value. The relative displacement to be used in determining the feedback control amount is not a distance object to be vibration-isolated against the substructure 3, the difference in variation from the initial value of X and X _0, in fact, When the value directly output from the displacement sensor or the output signal includes a DC component that is a certain deviation, a value obtained by subtracting the DC component is used, but for the sake of convenience, it is expressed as (X−X ₀ ) below. .

Here, the displacement feedback control unit 37a may determine the feedback control of the linear motor 23 by multiplying the displacement feedback control gain G of the relative displacement X-X ₀ detected by the displacement sensor 33 G · (X-X 0 ) However, the feedback control amount G · (X−X ₀ ) mentioned here is a current, and the linear motor 23 generates a force when the current flows as described above. The control force to be applied is proportional to the control amount G · (X−X ₀ ). Then, the proportional constant and K _L, expressed such physical phenomena in a formula, the equation of motion of object to be vibration-isolated in the case of performing the vertical feedback control by the displacement feedback control unit 37a is
M · X ″ + C · (X′−X ₀ ′) + K · (X−X ₀ ) −G · K _L · (X−X ₀ ) = 0 (Expression 7)
It is expressed. Here, X ″: acceleration of the vibration isolation object, X ′: speed of the vibration isolation object, X ₀ ′: speed of the foundation structure 3, X: displacement of the vibration isolation object, X ₀ : foundation structure 3 displacement.

And using the Laplace operator s, the vibration transmissibility of the active vibration isolator is
X / X ₀ = (C · s + K−G · K _L ) / (M · s ² + C · s + K−G · K _L ) (Expression 8)
It is expressed.

Furthermore, the apparent spring constant K ′ is
K ′ = K−G · K _L (Formula 9)
When substituting into (Equation 8), the vibration transmissibility of the active vibration isolator is
X / X ₀ = (C · s + K ′) / (M · s ² + C · s + K ′) (Expression 10)
It is expressed.

That is, the fact that the feedback control in the vertical direction by the displacement feedback control unit 37a is performed is based on the object of vibration isolation with the weight M, as is clear from comparing (Expression 2) and (Expression 10). , By supporting the spring element with the damping constant C and the apparent spring constant K ′, and by adjusting the displacement feedback control gain G, as apparent from (Equation 9), It means that 'can be changed freely. In other words, the displacement feedback control section 37a, by adjusting the displacement feedback control gain G, and the spring constant K of the air spring 21, proportional to the product (displacement feedback control gain G of the displacement feedback control gain G and proportional constant K _L Control to reduce the apparent spring constant K ′ represented by the difference between the value and the value.

The natural frequency f _n of the active vibration isolator is expressed as f _n = (K ′ / M) ^1/2 / 2π. By adjusting the displacement feedback control gain G, the natural frequency f _{n is obtained.} Can be lowered. Thus, if it is possible to reduce significantly the natural frequency f _n, it is possible to extend the possible range vibration damping lowers the lower limit of the vibration isolation possible frequencies than previously possible anti-vibration eigenfrequency Vibration isolation performance at high frequencies can also be improved. Not only if extremely brought closer to the product of the displacement feedback control gain G and proportional constant K _L a spring constant K, the natural frequency f _n to realize a vibration control device close to zero as possible, in other words, the ideal It becomes possible to realize no vibration of a certain vibration isolation object.

  FIG. 4 is a graph showing a simulation result in which the relationship between the frequency and the vibration transmissibility is expressed on a logarithmic scale. The solid line in the figure indicates the vibration transmissibility of the active vibration isolator of the present embodiment, and the broken line indicates the passive. The vibration transmissibility of the vibration isolator is shown, and the two-dot chain line shows the vibration transmissibility of the conventional active vibration isolator. From the figure, according to the active vibration isolator according to the present embodiment, unlike the passive vibration isolator, the natural frequency of the entire apparatus can be easily reduced to a low frequency region (for example, around 0.2 Hz) that is significantly lower than 1 Hz. It can be lowered, and it can be seen that the vibration isolation performance is significantly improved in the low frequency region around 1 Hz as compared with the conventional one.

  Moreover, since the resonance point appears in the active vibration isolator according to the present embodiment at 0.3 Hz to 0.4 Hz, the vibration transmissibility exceeds 1 (0 dB) in an extremely low frequency region lower than 0.5 Hz. It can also be seen from the figure that the vibration transmissibility is significantly smaller in the frequency range higher than that of the conventional active vibration isolator. That is, according to the active vibration isolator according to the present embodiment, the vibration isolation performance in the low frequency region near 1 Hz, which is not obtained by the effect of the skyhook damper or the skyhook spring in the conventional active vibration isolator. Can be reliably improved.

Further, unlike a conventional active vibration isolator using a double integral of acceleration as a displacement value used for displacement feedback, the relative displacement X− between the base plate 25 and the top plate 27 detected by the displacement sensor 33. the active anti-vibration apparatus according to the present embodiment using X _0, the following advantages.

That is, firstly, in a vibration isolation table that controls fine vibrations, it is necessary to greatly amplify the signal (1000 times or more) of an acceleration sensor that detects vibrations. However, since the acceleration of gravity (1G at 0Hz) always acts as a DC component in the acceleration sensor in the vertical direction, and the gravitational acceleration of 1G is very large compared to the vibration, all sensor outputs including such DC components are amplified. Then, the signal is saturated and the acceleration information of the minute vibration is lost. For this reason, it is necessary to apply a high-pass filter with a large time constant to cut the DC component due to gravitational acceleration, and then amplify the signal. That is, if in the case of amplifying the acceleration detected by the acceleration sensor when to large high-pass filter become necessary constants, using the relative displacement X-X ₀ detected by the displacement sensor 33, the filter Is no longer necessary.

Secondly, in order to use the skyhook damper control or the like, when integrating the acceleration detected by the acceleration sensor, it is necessary to remove the gravitational acceleration from the sensor output with a high-pass filter and greatly amplify it. Causes a DC offset component. For this reason, even when a small DC offset component occurs, the sensor output becomes infinitely large when integrated, and does not hold as a numerical value for control. In contrast, in the case of using the relative displacement X-X ₀ detected by the displacement sensor 33 has the advantage of avoiding to amplify the DC offset component according to not integrating to infinity.

Thirdly, when DC cut and amplification are repeated with a high-pass filter, the phase is greatly shifted and the control is hindered. On the other hand, the relative displacement XX ₀ detected by the displacement sensor 33 is present. Is used, there is an advantage that the occurrence of such a phase shift can be avoided.

  Further, in the active vibration isolator of the present embodiment, the linear motor 23 having excellent responsiveness is used as the actuator, so that the time delay of the control system is reduced and the control of the present invention is applied to vibrations in a wider frequency range. Can be applied.

(Embodiment 2)
This embodiment is different from the first embodiment in that a control method by the controller 37 and an acceleration sensor 35 are provided. Hereinafter, differences from the first embodiment will be described.

FIG. 5 shows the air spring unit 5 in the precision vibration isolation table 1 according to the second embodiment of the present invention. As schematically shown in FIG. 5, the air spring unit 5 includes not only the displacement sensor 33 for detecting the relative displacement X−X ₀ of the top plate 27 with respect to the base plate 25, but also the vibration state of the vibration isolation object, Specifically, an acceleration sensor (vibration sensor) 35 for detecting the vibration state of the top plate 27 is provided. Thus, output signals from the displacement sensor 33 and the acceleration sensor 35 are input to the controller 37, respectively.

  The controller 37 outputs a control signal to the linear motor 23 for each air spring unit 5 and applies a control vibration (control force) that reduces the vibration to the top plate 27, that is, a constant value. Active vibration control for reducing vibrations of the board 7, the top plate 27, and the precision device is performed. In other words, the air springs 21 of the air spring units 5, 5,..., The linear motor 23, the acceleration sensor 35 and the displacement sensor 33, and the controller 37 constitute an active vibration isolation device for the precision vibration isolation table 1. ing.

  In addition to the displacement feedback control unit 37a, the controller 37 includes a first feedback control unit 37b that determines the feedback control amount of the linear motor 23 based on the acceleration of the vibration isolation object detected by the acceleration sensor 35. Yes. More specifically, the first feedback control unit 37b recognizes the acceleration X ″ of the top plate 27 based on a signal from the acceleration sensor 35, and cancels vibrations of the surface plate 7, the top plate 27, and the precision device. A linear feedback control amount is determined, and the linear motor 23 is driven to generate a control force based on the determined feedback control amount. In FIG. 5, only the vertical acceleration sensor 35, the displacement sensor 33, and the vertical linear motor 23 of the air spring unit 5 are shown, but in addition to this, a horizontal displacement sensor, an acceleration sensor, and a linear sensor are shown. A motor is also provided, and horizontal control is performed in the same manner as vertical control described below.

With respect to the basic control of the linear motor 23 by the displacement feedback control unit 37a and the first feedback control unit 37b, only the control for reducing the vertical vibration will be described in detail below with reference to FIG. Explained. FIG. 6 is a block diagram schematically showing physical phenomena in the linear motor control in the vertical direction by the displacement feedback control unit 37a and the first feedback control unit 37b. As in the first embodiment, the symbol P indicates that the vibration isolation object is supported by the air spring 21, and the symbol FB1 indicates the feedback control amount G determined by the displacement feedback control unit 37a. · a (X-X _0), which represents that by acting on the object to be vibration-isolated as a control force via the linear motor 23.

Furthermore, part of the sign FB2 in Figure 6, anti-vibration vertical acceleration X '' to multiply the feedback control gain G _m, the acceleration X 'of the object' once integrating the speed X 'in the feedback control obtained Feedback control amounts G _m · X ″, G _c · X obtained by multiplying the displacement X obtained by multiplying the gain G _c and integrating the acceleration X ″ twice by the feedback control gain G _k ', the G k _· X, via the linear motor 23, represented by K _L, indicates that to act as control force in such a vibration damping target. Thus, the vibration state (acceleration X ″) of the vibration isolation object after the control force is applied is fed back again from the control object including the vibration isolation object and the air spring 21.

When this physical phenomenon is expressed by a mathematical expression, the equation of motion of the vibration isolation object when the vertical feedback control is performed by the displacement feedback control unit 37a and the first feedback control unit 37b is as follows:
(M + _Gm · K _L ) · X ″ + (C + G _c · K _L ) · X′−C · X ₀ ′ + (K + G _k · K _L −G · K _L ) · X− (K−G · K _L ) · X ₀ = 0 (Formula 11)
It is expressed.

And using the Laplace operator s, the vibration transmissibility of the active vibration isolator is
X / X ₀ = (C · s + K−G · K _L ) / {(M + G _m · K _L ) · s ² + (C + G _c · K _L ) · s + (G _k · K _L + K−G · K _L ) } (Formula 12)
It is expressed.

As apparent from (Equation 12), multiplying the acceleration X ″ by the control gain G _m and feeding back is substantially equivalent to increasing the mass of the vibration system, and this can lower the resonance frequency. . In addition, the so-called skyhook damper effect is obtained by feedback of the speed X ′, and the resonance magnification can be reduced without impairing the vibration isolation performance in the high frequency range. Further, the so-called skyhook spring effect is obtained by the feedback of the displacement X, and the vibration transmissibility can be lowered in the region below the resonance frequency.

Further, as apparent from comparing (Equation 12) with the above (Equation 4) and (Equation 6), the feedback control amount G ···· obtained by multiplying the relative displacement X−X ₀ by the displacement feedback control gain G is as follows. By applying a control force proportional to (X−X ₀ ), the apparent spring constant can be greatly reduced, and the passive natural frequency can be reduced. When active control by the first feedback control unit 37b is added to the passive vibration isolation table having a low natural frequency, the active vibration control is performed in a state where the natural frequency is high and the displacement feedback control is not performed. Therefore, the vibration isolation performance is remarkably excellent.

  As described above, according to the present embodiment, the vibration isolation effect by the displacement feedback control unit 37a and the vibration isolation effect by the first feedback control unit 37b are combined to extend from a low frequency range to a high frequency range. High vibration isolation performance can be obtained.

(Embodiment 3)
The present embodiment is different from the second embodiment in that the air spring 21 instead of the linear motor 23 is used as an actuator for applying a control force. Hereinafter, differences from the second embodiment will be described.

  As shown in FIG. 7, each air spring 21 is connected to a servo valve 39 via a pipe 43, and the servo valve 39 receives a control signal from a controller 37 to open and close to each air spring 21. The supply / discharge flow rate of air to the air spring 21 for each unit 5 is adjusted, and the air pressure of the air spring 21 is quickly changed. In other words, the air spring 21 is used as an actuator for applying control vibration (control force) to the object to be isolated by controlling the servo valve 39 for adjusting the pressure state of the air spring 21. Yes. Thus, by using the gas spring 21 as an actuator, it is not necessary to separately provide the linear motor 23 as in the first and second embodiments, and a relatively large force can be easily obtained as a characteristic of the gas spring 21. be able to.

  The servo valve 39 is connected to a reservoir tank 41 that stores compressed air. An electric pump (not shown) is connected to the reservoir tank 41, and the operation of this electric pump causes the air pressure in the reservoir tank 41 to reach a predetermined value. To be maintained. FIG. 7 shows only the vertical acceleration sensor 35 and the displacement sensor 33 of the air spring unit 5, but in addition to this, a horizontal displacement sensor and an acceleration sensor are also provided. The horizontal control is performed in the same manner as the vertical control described below.

  The controller 37 recognizes the acceleration X ″ of the top plate 27 based on a signal from the acceleration sensor 35 in addition to the displacement feedback control unit 37a, and cancels vibrations of the surface plate 7, the top plate 27, and the precision device. A second feedback control unit 37c that adjusts the air pressure of the air chamber 21a of the air spring 21 by determining such a feedback control amount and operating the servo valve 39 based on the determined feedback control amount. Yes. With respect to the basic control of the air spring 21 by the displacement feedback control unit 37a and the second feedback control unit 37c, only the control for reducing the vertical vibration will be described in detail below with reference to FIG. Explained.

  FIG. 8 is a block diagram schematically showing a physical phenomenon in the vertical air pressure control by the displacement feedback control unit 37a and the second feedback control unit 37c. As described above, the reference numeral P indicates that the vibration isolation object is supported by the air spring 21.

The part of the symbol FB1 is obtained by multiplying the object to be isolated by the feedback control amount determined by the displacement feedback controller 37a by (1 + T _V · s) / (K _V · A _m ). It is shown that the value is applied via the servo valve 39 whose characteristic is expressed by K _V · A _m / (1 + T _V · s). Here, _{K V} is a gain, _{T V} is the time constant, _{A m} is the pressure receiving area of the air spring 21.

More specifically, the feedback control amount G · (X−X ₀ ) is the same current as in the first and second embodiments, but unlike the linear motor 23 in which the control force is proportional to the feedback control amount, In this case, the servo valve 39 is controlled by the feedback control amount G · (X−X ₀ ) so that air is taken in and out of the air chamber 21a of the air spring 21 and the pressure is changed so that the object of vibration isolation is obtained. The control force is added to. Therefore, when the air spring 21 is used as an actuator as in this embodiment, the opening degree of the servo valve 39 is proportional to the feedback control amount G · (X−X ₀ ), and the internal pressure of the air spring 21 is since proportional to approximate the integral of the feedback control quantity _{G · (X-X 0)} , and a control force feedback control amount _{G · (X-X 0)} , a relationship of a first-order lag without proportional.

Then, if the feedback control amount G · (X−X ₀ ) is used as it is, it is approximated by K _V · A _m / (1 + T _V · s) which is the first order lag element. The feedback control amount G · (X−X ₀ ) is multiplied by the inverse of the characteristic of the servo valve 39. As a result, the control force applied to the vibration isolation object by the air spring 21 is proportional to the feedback control amount G · (X−X ₀ ) without being in a first-order lag relationship.

Further, reference numeral FB3 in FIG. 8 indicates feedback control in the vertical direction by the second feedback control unit 37c. However, when the air spring 21 is used, the differential value, the proportional value, and the integral value of the acceleration X ″ are fed back in consideration of the fact that the force is proportional to the approximate integral value of the feedback control amount as described above. . Specifically, part of the sign FB3 is 'multiplied by the feedback control gain G _c on the detected value of acceleration X' vertical acceleration X 'of the top plate 27 detected by the acceleration sensor 35' by integrating once Obtained by multiplying the speed X ′ obtained by the feedback control gain G _k and multiplying X ′ ″ obtained by differentiating the acceleration X ″ once by the feedback control gain G _m . Feedback control quantity _{G m · X ''',} G c · X'', the _G k · X', which indicates that the action on the object to be vibration-isolated through the servo valve 39.

Then, as described above, since the control force is proportional to the internal pressure, acting feedback control amount _G m · _{X ''} through a ', G c · X'' , the servo valve 39 to _G k · X' in the air spring 21 As a result, the control force applied to the vibration isolation object is approximated as follows.
G _m · X ′ ′ · {K _V · A _m / (1 + T _V · s)} ≈G _m · X ′ ′ (Equation 13)
G _c · X ′ · {K _V · A _m / (1 + T _V · s)} ≈G _c · X ′ (Expression 14)
G _k · X ′ · {K _V · A _m / (1 + T _V · s)} ≈G _k · X (Equation 15)
Thus, the equation of motion of the vibration isolation object when the vertical feedback control is performed by the displacement feedback control unit 37a and the second feedback control unit 37c is as follows:
_{(M + G m) · X} '' + (C + G c) · X'-C · X 0 '+ (K + G k -G) · X- (K-G) · X 0 = 0 ... ( Equation 16)
It is expressed.

And using the Laplace operator s, the vibration transmissibility of the active vibration isolator is
_{X / X 0 = (C ·} s + K-G) / {(M + G m) · s 2 + (C + G c) · s + (G k + K-G)} ... ( Equation 17)
It is expressed.

As is clear from comparison between the above (Equation 17) and (Equation 12), the difference between the vibration transmissibility in the case of pneumatic control and the vibration transmissibility in the case of linear motor control depends on the control gains G and G. _{m, G} c, because _{G k} to proportional constant _{K L} is only whether it is multiplied, in the case of pneumatic control, by adjusting the control gain _G, G _m, G c, a _{G k} As in the second embodiment, the resonance magnification is decreased without impairing the vibration isolation performance in the high frequency range, the vibration transmissibility is decreased in the region below the resonance frequency, or the passive natural frequency is decreased. It is possible to easily reduce the transmission rate. Therefore, also in the pneumatic control, the vibration isolation effect by the displacement feedback control unit 37a and the vibration isolation effect by the second feedback control unit 37c are combined to provide high vibration isolation performance from the low frequency range to the high frequency range. Can be obtained.

  Further, since the servo valve 39 has very high responsiveness and can control a minute air flow rate, the internal pressure of the air spring 21 can be changed with high accuracy without delay with respect to minute vibrations of the vibration isolation object. it can. Thereby, stable vibration control with high convergence can be realized.

(Other embodiments)
The present invention is not limited to the embodiments, and can be implemented in various other forms without departing from the spirit or main features thereof.

  In each said embodiment, although the air spring 21 was used as a spring element, not only this but a coil spring and vibration-proof rubber may be used, for example.

  In the second and third embodiments, the vibration state of the vibration isolation object is detected using the acceleration sensor 35. However, the present invention is not limited to this, and the vibration state may be detected using a speed sensor.

  Furthermore, in each said embodiment, although the air spring unit 5 used what was provided with the air spring 21, the linear motor 23, the base plate 25, the top plate 27, the diaphragm 29, and the piston 31, In addition, a mechanical leveling valve for maintaining the top plate 27 at a preset height may be provided. The mechanical leveling valve has a function of automatically supplying compressed air when the top plate is lowered and exhausting it when the top plate is raised to keep the position of the top plate constant. Although it seems to be contradictory to provide such a mechanical leveling valve and to determine the feedback control amount of the actuator based on the relative displacement, the mechanical leveling valve is 0.1 mm to 1.0 mm. The active vibration isolator of the present invention acts on the extremely small vibration that is the dead band of the mechanical leveling valve, while the dead band of the present invention does not react to small vibration such as floor vibration. There is no contradiction.

  In each of the above embodiments, the feedback feedback control amount obtained by multiplying the acceleration X ″, velocity X ′, and displacement X of the top plate 27 detected by the acceleration sensor 35 by the feedback control gain is excluded. Although it was made to act with respect to the shaking object, it is not restricted to this, For example, you may make any one of these or any two act.

  Furthermore, in Embodiments 2 and 3, the feedback control is performed based on the sensor signal of the acceleration sensor 35 provided in the air spring unit 5. However, the present invention is not limited to this. For example, another acceleration sensor is placed on the floor. The feedforward control based on the sensor signal may be added.

  Further, as the actuator, the linear motor is used in the first and second embodiments and the air spring is used in the third embodiment. However, the actuator is not limited to this, and an actuator such as a piezoelectric element may be used.

  As described above, the above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the present invention is useful for an active vibration isolator for installing a precision instrument in a state generally insulated from floor vibration.

3 basic structure (basic)
7 Surface plate (object for vibration isolation)
21 Air spring (gas spring (spring element), actuator)
23 Linear motor (actuator)
27 Top plate (object for vibration isolation)
33 Displacement sensor 35 Acceleration sensor (vibration sensor)
37 Controller (Control means)
37a Displacement feedback control unit 37b First feedback control unit 37c Second feedback control unit 39 Servo valve

Claims (4)

A spring element that supports the object to be vibration-isolated against the foundation installed on the floor, an actuator for adding a control force to the object to be anti-vibrated to reduce the vibration, and driving the actuator An active vibration isolator having a control means for actively controlling vibration of a vibration isolation object,
A displacement sensor for detecting a relative displacement of the vibration isolation object with respect to the foundation;
The control means includes a displacement feedback control unit that determines a feedback control amount of the actuator by multiplying the relative displacement detected by the displacement sensor by a displacement feedback control gain.
The displacement feedback control unit adjusts the displacement feedback control gain to reduce an apparent spring constant represented by a difference between a spring constant of the spring element and a value proportional to the displacement feedback control gain. An active vibration isolator characterized by performing control. The active vibration isolator according to claim 1.
A vibration sensor for detecting a vibration state of the vibration isolation object;
The active vibration isolating apparatus, wherein the control means further includes a feedback control unit that determines a feedback control amount of the actuator based on an acceleration or a speed of a vibration isolation object detected by the vibration sensor. . The active vibration isolator according to claim 1 or 2,
An active vibration isolation device, wherein the actuator is a linear motor disposed between the vibration isolation object and the foundation. The active vibration isolator according to claim 1 or 2,
The spring element is a gas spring;
The active vibration isolation device, wherein the gas spring is also used as the actuator for adding a control force by controlling a servo valve for adjusting a pressure state of the gas spring.

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