JP3616399B2 - Active vibration isolator - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an active vibration isolator having vibration isolation, seismic isolation, and vibration control functions, and more particularly to an active vibration isolator including a servo sensor that can obtain a phase difference and gain optimal for active control.
[0002]
[Prior art]
Conventionally, precision instruments represented by semiconductor manufacturing / inspection equipment, electron microscopes, optical application equipment, etc., vibrate from the foundation of installation or the floor in order to make their functions and specifications highly integrated, high resolution, and ultra-precision. It is necessary to shut off.
[0003]
For this reason, a spring with a soft spring coefficient (anti-vibration rubber, spring, air spring) and a dash pot with a viscous damping constant are used, and a mass controlled object in which precision equipment is mounted on a surface plate supported by the spring. 2. Description of the Related Art Passive type vibration isolation tables that perform passive vibration control are known.
[0004]
In this passive vibration isolation table, the region where the vibration is greater than the vibration of the foundation or floor (resonance region) and the region where vibration can be attenuated (vibration isolation region) coexist and the damping constant is small When the normalized frequency is 1 or more, the vibration isolation effect is large, but the resonance becomes large. When the attenuation constant is large, the resonance approaches 0 dB, but the vibration isolation effect at a normalized frequency of 1 or more is reduced. Moreover, when trying to suppress the resonance by adding viscous damping, the vibration isolation effect was reduced and the two-way reciprocity could not be destroyed.
[0005]
As a development of these passive vibration isolation tables, a vertical spring (vibration-proof rubber, spring, air spring) having a spring coefficient k and a dash of a viscous damping constant c are used as a vertical uniaxial (Z-axis) model shown in FIG. The vibration of the mass m itself of the controlled object on which the precision device is mounted on the surface plate supported by the spring system of the pot is monitored by the vibration sensor SE, the phase is inverted by the compensation circuit, and the drive signal is created by the drive circuit. By applying an actuator ACT provided separately from the system to the controlled substance quantity m with precision equipment mounted on the surface plate, an active type vibration isolation table with no vibration phenomenon and high vibration isolation effect can be obtained. It has been developed and reported in JP-A-61-2228137, JP-A-61-224015 and the like.
[0006]
In this active vibration isolation table, the vibration sensor SE is directly fixed to a control object (for example, a surface plate) to be actively controlled for vibration (FIG. 4).
[0007]
As the vibration sensor SE, a speed type sensor or an acceleration type sensor is used, but the servo type acceleration sensor is frequently used because the gain in the low frequency region (f ≦ 5 Hz) is flat and the phase characteristic is flat. Has been.
[0008]
Furthermore, it is desirable that the natural frequency of the vibration isolation table is in the order of 1 to 4 Hz, and the output of the vibration sensor does not decrease in this frequency band.
[0009]
As shown in FIG. 5, the servo acceleration sensor includes a pendulum weight 30 having a mass m supported by a spring 30 having a spring coefficient k and a damper 31 having a viscous damping constant D provided in the case, A position detection unit 32 that detects displacement from the equilibrium point, a drive unit 33 that generates an electrical restoring force to constantly return the weight to the equilibrium point, and a servo amplifier that is interposed between the position detection unit and the drive unit 34. When the displacement y occurs in the space and acceleration is applied to the weight 30 and the displacement x is displaced from the equilibrium point by the position detection unit 32, this displacement is detected by the servo amplifier 34 and the drive unit 33. , To generate an electrical restoring force proportional to the flow. The acceleration is not measured from the displacement of the conventional weight, but the current i supplied to the drive unit 33 is measured by the voltage drop v of the resistor R.
[0010]
[Problems to be solved by the invention]
(1) In an active vibration isolation table equipped with such a servo-type acceleration sensor, the ratio of output vibration to input vibration of the vibration isolation table = vibration transmissibility (Board diagram) is as shown in FIG. The natural frequency is maximum (for example, 10 dB), and the phase is delayed by 90 ° at the natural frequency fo, and the phase is −180 ° at higher frequencies. In this vibration transmissibility, if the spectrum of vibration acceleration on the floor ER (FIG. 4) is constant at a certain level (ndB) (FIG. 7), the spectrum of vibration acceleration on the controlled object (surface plate) is Trace the curve of vibration transmissibility.
[0011]
(2) When this output vibration (vibration on the surface plate) is measured by a servo-type acceleration sensor, an acceleration sensor signal obtained by tracing the output vibration pattern is output as shown in FIG. The phase difference of the output signal of the servo type acceleration sensor with respect to the vibration on the surface plate is 0 ° and in phase as shown in FIG.
[0012]
(3) In order to actively attenuate the resonance region in the shaded area in the vibration transmissibility of FIG. 6, a high gain and phase inversion near the resonance point are required as the output of the vibration sensor.
[0013]
(4) Phase inversion is adjusted by inverting +/- of the vibrometer output signal and connecting it to the phase compensation circuit (FIG. 4). High gain is achieved by electrically amplifying the output signal of the vibration sensor over the entire frequency band (FIG. 9).
[0014]
(5) In many cases, the signal adjusted and amplified according to the above item (4) causes phase shift and gain increase in the frequency band of 100 Hz or more due to resonance of the vibration isolation member constituting the vibration isolation table, resulting in poor control. It becomes stable and oscillates. For this purpose, gain adjustment is performed by inserting a high-pass filter (HPF) and a low-pass filter (LPF) acting on a specific frequency band. This gain adjustment causes a phase shift, making optimal adjustment very difficult.
[0015]
(6) The evaluation of the above items (1) to (5) is performed by a single open loop transfer function (open loop transfer function). That is, in order to intentionally vibrate the surface plate, the force actuator ACT is transmitted with a known signal (Vin) and each element (force actuator, vibration isolation table, vibration sensor, compensation circuit) when it vibrates with this signal. Controllability is checked using the entire transfer function based on the ratio (gain, phase) to the signal (Vout) at the compensation circuit exit through the function (frequency characteristics, phase characteristics) (FIG. 10).
[0016]
To summarize the issues described above, the requirements for an active vibration isolation table are:
a) How to keep the vibration near the resonance point low b) Return to passive vibration so as not to exceed passive vibration near 20-30 Hz c) Stabilize so as not to oscillate at 100 Hz or higher. Is shown in FIG.
[0017]
Therefore, the output signal measured by the acceleration sensor with respect to the vibration acceleration on the surface plate shown in FIGS.
a) How to increase the gain in the vicinity of the resonance point b) High frequency range (> 30 Hz) where vibration of the vibration isolation member (a surface plate as a controlled object, precision equipment mounted on it, a frame of the vibration isolation table, etc.) is likely to occur The problem is how to keep the gain of) low.
[0018]
[Means for Solving the Problems]
In order to solve these problems, according to the active vibration isolator of the present invention, a vibration isolation table including a passive spring element that supports a control object on an installation surface such as a foundation, a floor, or a ground, and a control target A sensor for detecting vibration of an object, a control circuit for generating a drive signal for active vibration isolation from the detected vibration signal of the controlled object, and an actuator for applying a damping force to the controlled object by the drive signal The sensor comprises a servo type acceleration sensor mounted on a controlled object via a resonance table having a natural frequency substantially matching the natural frequency of the vibration isolation table. those having a gain of the phase difference and + 10～40DB substantially 90 ° in the natural frequency of the table.
[0019]
[Action]
An object to be controlled is supported by a passive spring element of a vibration isolation table on an installation surface such as a foundation, a floor, or the ground.
[0020]
The vibration of the controlled object is detected by a sensor. The detected control object vibration signal is amplified by an amplifier in the control circuit, the phase compensation circuit performs phase compensation of the control object vibration signal, and a drive signal for active vibration isolation is generated in the drive circuit. The A damping force is applied to the controlled object by the pneumatic actuator by the drive signal.
[0021]
This sensor is composed of a servo-type acceleration sensor, and is mounted on a controlled object via a resonance table. The resonance table has a natural frequency that substantially matches the natural frequency of the vibration isolation table. Since the servo-type acceleration sensor mounted on the controlled object has a phase difference of substantially 90 ° and a gain of +10 to 40 dB at the natural frequency of the vibration isolation table, the gain in the resonance region is selectively selected. The output signal can be attenuated in a frequency band (100 Hz or higher) in which resonance can occur in the vibration isolation member of the vibration isolation table. In this way, the optimum phase difference and gain for active control can be obtained.
[0022]
【Example】
Hereinafter, a preferred embodiment of an active vibration isolator according to the present invention will be described with reference to the drawings.
[0023]
In FIG. 1, the active vibration isolator of the present invention comprises a vibration isolation table 13 in which a control object 12 is supported by a passive spring element 11 on an installation surface 10 such as a foundation, a floor or the ground. .
[0024]
Here, the controlled object 11 is not only a vibration-isolated mass such as a surface plate, but also an IC such as a stepper (reduction projection type exposure machine) mounted thereon, an LSI semiconductor manufacturing / inspection apparatus, an electronic A precision instrument 14 such as a microscope or an optical application apparatus is included.
[0025]
This passive spring element 11 constitutes a known passive vibration isolator composed of an air spring and a dashpot.
[0026]
A control object 12 including the precision device 14 is equipped with a sensor 15 that detects vibration of the control object 12.
[0027]
In addition, a control circuit 16 that generates a drive signal S2 for active vibration isolation from the detected control object vibration signal S1, and a pneumatic actuator 17 that applies a damping force f to the control object 12 by the drive signal S2. And are provided.
[0028]
The control circuit 16 includes an amplifier 18 that amplifies the controlled object vibration signal S1 detected by the sensor 15, a phase compensation circuit 19 that performs phase compensation of the amplified controlled object vibration signal S1, and a drive from the phase compensated signal. The driving circuit 20 generates the signal S2. A servo valve 21 for supplying and exhausting air to the pneumatic actuator 17 by a drive signal S2 from the drive circuit 20 is provided. As the pneumatic actuator, the servo valve 21 can be omitted, and a linear motor (voice coil motor) can be used, which can be electrically driven directly by the drive signal S2.
[0029]
According to a feature of the present invention, the sensor 15 comprises a servo type acceleration sensor (FIG. 5). The servo type acceleration sensor is mounted on the control object 12 via the resonance table 22 (FIG. 1).
[0030]
As shown in FIG. 2 (a), the resonance table 22 is configured by a mass type m1 of a servo acceleration sensor supported by a passive spring element of an air spring having a spring coefficient k1 and a dashpot having a viscous damping constant c1. Yes.
[0031]
The anti-vibration table 13 that supports the controlled object 12 includes a precision device mounted on a surface plate supported by an air spring having a spring coefficient k and a passive spring element 11 having a dash pot having a viscous damping constant c. Due to the mass m, it has a natural frequency fo (FIG. 3). The resonance table 22 has a natural frequency that substantially matches the natural frequency of the vibration isolation table 13. In order to match the natural frequency of the resonance table 22 with that of the vibration isolation table 13, the spring coefficient k1 of the air spring in the passive spring element used, the viscosity damping constant c1 of the dashpot, the mass m1 of the servo acceleration sensor, or the servo It is adjusted by the auxiliary mass m2 (FIG. 2B) provided between the type acceleration sensor and the passive type spring element.
[0032]
Thus, the servo-type acceleration sensor mounted on the controlled object 12 via the resonance table 22 has a phase difference of substantially 90 ° and +10 to 40 dB, preferably +10 to 10 at the natural frequency fo of the vibration isolation table 13. It has a gain of 20 dB (FIG. 3).
[0033]
As a result, the output of the acceleration sensor (m1) shown in FIG. 2 becomes as shown in FIG. 3 with respect to the vibration shown in FIGS. The output signal can be attenuated in a frequency band (100 Hz or more) where resonance of the vibration isolation member of the vibration isolation table 13 occurs. In addition, by changing the viscosity attenuation constant c1 of the dashpot shown in FIG. 2 to c10 and c20, the degree of amplification in the resonance region and the attenuation in the frequency band where the resonance occurs as shown in FIG. Can do.
[0034]
The output of the output signal of the acceleration sensor is delayed by 90 ° in the natural frequency region with respect to the vibration acceleration of the surface plate due to the resonance stage equipped with the vibration acceleration sensor.
[0035]
In the active vibration isolator configured as described above, the control object 12 is supported by the passive spring element 11 of the vibration isolation table 13 on the installation surface 10 such as a foundation, a floor, or the ground.
[0036]
The vibration of the controlled object 12 is detected by the sensor 15. The detected control object vibration signal S1 is amplified by the amplifier 18 in the control circuit 16, the phase compensation circuit 19 performs phase compensation of the control object vibration signal S1, and the drive circuit 20 performs active vibration isolation. Drive signal S2 is generated. A damping force f is applied to the controlled object 12 by the pneumatic actuator 17 by the drive signal S2.
[0037]
In this case, the sensor 15 is composed of a servo-type acceleration sensor, and this servo-type acceleration sensor is mounted on the controlled object 12 via the resonance table 22, and the resonance table 22 is substantially equal to the natural frequency of the vibration isolation table 13. The servo-type acceleration sensor mounted on the controlled object 12 via the resonance table 22 has a phase difference of substantially 90 ° at the natural frequency fo of the vibration isolation table 13 and Since it has a gain of +10 to 40 dB, the gain in the resonance region can be selectively amplified, and the output signal can be attenuated in the frequency band (100 Hz or more) in which the vibration isolation member of the vibration isolation table 13 is generated.
[0038]
【The invention's effect】
As is clear from the above embodiments, according to the active vibration isolator of the present invention, the vibration isolation table is composed of a passive spring element that supports a controlled object on an installation surface such as a foundation, a floor, or the ground. And a sensor that detects vibration of the control target, a control circuit that generates a drive signal for active vibration isolation from the detected control target vibration signal, and a damping force applied to the control target by the drive signal And a sensor comprising a servo type acceleration sensor mounted on a controlled object via a resonance table having a natural frequency substantially matching the natural frequency of the vibration isolation table. , by having the phase difference and + gain 10~40dB substantially 90 ° at the natural frequency of the vibration isolation table, selectively increase or decrease the output of the acceleration sensor in the frequency axis, Accession It is possible to provide a maximum gain in the resonance region where the active power is most necessary and a sufficient filter function (vibration isolation function) to stabilize the control in the subsequent high frequency band. Optimal phase difference and gain are obtained, and ideal active control shown in FIG. 11 is achieved.
[0039]
In addition, the resonance stage has a mechanical filter function, and the burden on the electrical phase compensation circuit 19 in the subsequent stage is reduced. Alternatively, the control stability in the high range increases, so that the gain in the resonance range can be further increased with this circuit.
[0040]
Further, since the phase is automatically shifted by the resonance stage so as to be optimally active, the subsequent phase inversion is unnecessary.
[0041]
Furthermore, the rate of change in the gain and phase shift of the output signal can be adjusted by making the damping force of the damper of the resonance table variable.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of an active vibration isolator according to an embodiment of the present invention. FIGS. 2A and 2B are configurations of a vibration isolation table and a resonance table used in the active vibration isolation device according to the present invention. Fig. 3 is a diagram showing elements. Fig. 3 is a diagram showing gain of an output of an acceleration sensor with respect to acceleration on a surface plate. Fig . 4 is an explanatory diagram of a conventional active vibration isolator. Fig. 5 is used for an active vibration isolator. Fig. 6 is a graph showing the frequency-vibration transmission rate obtained by a conventional active vibration isolator. Fig. 7 is a diagram showing vibration on the floor surface in a conventional active vibration isolator. FIG. 8 is a graph showing the frequency-vibration transmissibility obtained when measured with a servo type acceleration sensor in a conventional active vibration isolator. Phase output signal of servo type acceleration sensor in vibration isolator FIG. 10 is a graph showing a frequency-vibration transmissibility in which high gain amplification is obtained. FIG. 10 is a diagram showing a method for checking controllability by an open loop transfer function in a conventional active vibration isolator. Graph schematically showing passive vibration isolation, active vibration isolation, and ideal vibration isolation in a vibration isolator
10 …… Installation surface 11 …… Passive spring element 12 …… Control object 13 …… Vibration isolation table 15 …… Sensor (servo type acceleration sensor)
16... Control circuit (18... Amplifier 19... Phase compensation circuit 20... Drive circuit)
17 …… Actuator 22 …… Resonance table f …… Damping force fo …… Natural frequency S1 of vibration isolation table …… Control object vibration signal S2 …… Drive signal

Claims (1)

From a vibration isolation table made of a passive spring element that supports a control object on an installation surface such as a foundation, floor, or ground, a sensor that detects vibration of the control object, and a detected control object vibration signal A control circuit for generating a drive signal for active vibration isolation, and an actuator for applying a damping force to the object to be controlled by the drive signal, wherein the sensor matches the natural frequency of the vibration isolation table A servo type acceleration sensor mounted on the object to be controlled through a resonance table having a natural frequency, and the servo type acceleration sensor has a phase difference of 90 ° and +10 to +10 at the natural frequency of the vibration isolation table. An active vibration isolator having a gain of 40 dB.

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