 |
Claims  |
|
|
What is claimed is:
1. A method of controlling the level and vibrations of a vibration control
base suspended by air springs comprising the steps of:
sensing the level of the vibration control base suspended by air springs to
output a level voltage,
comparing the level voltage with a standard level voltage to obtain and
output a difference therebetween,
integrating the difference to obtain an analog integrated value only or
integrating the difference and giving a feedback compensation to the
difference at the same time to obtain a compensated value for accelerating
leveling of the vibration control base,
outputting the analog integrated value only or a value obtained by adding
the analog integrated value and the compensated value as a level control
value,
sensing an acceleration of vibration of a vibration control base in
vertical directions to output a vertical acceleration voltage, and
controlling an air pressure of the air springs in accordance with the level
control value and the vertical acceleration voltage.
2. The method as claimed in claim 1 wherein:
the level control value is obtained by adding a feedforward control value
for a vertical displacement obtained on the basis of predata of the
vertical displacement to the feedback compensation value and the analog
integrated value.
3. The method as claimed in claim 2, further comprising the steps of:
sensing an acceleration of vibration of a vibration control base in
vertical directions to output a vertical acceleration voltage,
giving at least one of integration, differentiation and amplification to
the vertical acceleration voltage or in addition thereto a phase
compensation, so as to carry out a vertical vibration feedback
compensation, and
controlling an air pressure of the air springs in accordance with a level
and vibration control value obtained by summing a vertical vibration
control value obtained by the vertical vibration feedback compensation and
the level control value.
4. The method as claimed in claim 3 wherein: the level and vibration
control value is obtained by adding a feedforward control value for
vertical vibrations obtained on the basis of the predata to a vertical
vibration control value obtained by the vertical vibration feedback
compensation.
5. The method as claimed in claim 1 further comprising the steps of:
giving at least one of integration, differentiation and amplification to
the vertical acceleration voltage or in addition thereto a phase
compensation, so as to carry out a vertical vibration feedback
compensation, and
controlling an air pressure of the air springs in accordance with a level
and vibration control value obtained by summing a vertical vibration
control value obtained by the vertical vibration feedback compensation and
the level control value.
6. The method as claimed in claim 5 wherein:
the level and vibration control value is obtained by adding a feedforward
control value for vertical vibrations obtained on the basis of predata to
a vertical vibration control value obtained by the vertical vibration
feedback compensation.
7. A method of maintaining a lateral position of a vibration control base
suspended by air springs and controlling vibrations of the vibration
control base in horizontal directions comprising the steps of:
sensing a displacement of the vibration control base in horizontal
directions with respect to a standard lateral position thereof to output
an analog lateral position voltage,
comparing the analog lateral position voltage with a standard lateral
position voltage to obtain a difference therebetween,
giving analog integration or feedback compensation for accelerating lateral
positioning of the vibration control base in combination with the analog
integration to the difference so as to output a lateral position control
value to carry out a lateral position control,
sensing an acceleration of vibration of the vibration control base in
horizontal directions to out put a lateral acceleration voltage,
giving at least one of integration, differentiation and amplification to
the lateral acceleration voltage or giving thereto a lateral vibration
control feedback compensation including a phase compensation to output a
lateral vibration control value and carry out lateral vibration control of
the vibration control base, and
controlling an air pressure of air springs in accordance with a lateral
position and lateral vibration control value obtained by summing the
lateral position control value and the lateral vibration control value.
8. A method of controlling a lateral vibration of a vibration control base
suspended by a pair of air springs which are extendable in opposite
lateral directions to one another comprising the steps of:
sensing a displacement of the vibration control base in horizontal
directions with respect to a standard lateral position thereof to output
an analog lateral position voltage,
comparing the analog lateral position voltage with a standard lateral
position voltage to obtain a difference therebetween,
giving analog integration or feedback compensation for accelerating lateral
positioning of the vibration control base in combination with the analog
integration to the difference so as to output a lateral posiiton control
value to carry out a lateral position control,
sensing an acceleration of vibration of the vibraiton control base in
horizontal directions to out put a lateral acceleration voltage,
giving at least one of integration, differentiation and amplification to
the lateral acceleration voltage or giving thereto a lateral vibration
control feedback compensation including a phase compensation to output a
lateral vibration control value and carry out a lateral vibration control
of the vibration control base,
controlling an air pressure of one of the air springs in accordance with a
lateral position and lateral vibration control value obtained by summing
the lateral position control value and the lateral vibration control
value, and
controlling an air pressure of another air spring in accordance with a
value obtained by converting its phase at 180.degree. relative to the
lateral position and lateral vibrating control value.
9. The method as claimed in claim 8 further comprising the step of:
obtaining a feedforward control value for horizontal directions on the
basis of predata for horizontal directions, wherein the lateral vibration
control value is obtained by adding the feedforward control value to the
feedback control value obtained by the feedback compensation in horizontal
directions.
10. An active vibration control apparatus comnprising:
a fixed base,
a vibration control base disposed above the fixed base,
vertical supporters interposed between the fixed base and the vibration
control base to support the vibration control base and having flexibility
in horizontal directions,
a vertical acceleration sensor for sensing vertical vibration accelerations
of said vibration control base,
a level sensor for sensing the level of the vibration control base and
outputting a level voltage,
a lateral position sensor for detecting the displacement of said vibration
control base from a standard lateral position,
vertical direction vibration control means comprising air springs
interposed between the fixed base and the vibration control base via
vertical supporters,
vertical direction control means for using outputs from said level sensor
and from said vertical acceleration sensor to drive the vertical direction
vibration control means for returning to and maintaining the level of the
vibration control base at a standard level position and for controlling
vertical vibrations of said vibration control base,
horizontal direction vibration control means comprising air springs
interposed between the fixed base and the vibration control base, and
horizontal direction control means to drive the horizontal direction
vibration control means for returning to and maintaining the lateral
position of the vibration control base at a standard lateral position and
for controlling horizontal vibrations of said vibration control base.
11. The apparatus as claimed in claim 10 further comprising;
lateral supporters flexible in any direction except axial directions
thereof, wherein the lateral vibration control means is disposed between
the fixed base and the vibration control base via the lateral supporters.
12. The apparatus as claimed in claim 11 wherein:
the vertical and lateral supporters comprise a plurality of rubber plates
and metal plates which are laminated to one another.
13. The apparatus as claimed in claim 11 wherein:
the lateral supporters comprise wires.
14. The apparatus as claimed in claim 10 wherein:
the vertical direction control means comprises a level maintaining circuit,
and a control valve for the air springs, said level maintaining circuit
including a level difference amplifier for comparing the level voltage
with the standard level voltage and outputting a difference therebetween,
an analog integrating amplifier for integrating the level difference from
the level difference amplifier or a feedback compensation circuit for
accelerating levelling of the vibration control base in combination with
the analog integrating amplifier, thereby controlling the control valve
for the air springs for vertical directions in accordance with the output
of the analog integration amplifier and/or the level control value
obtained by summing the output of the analog integrating amplifier and the
output of the feedback compensation circuit.
15. The apparatus as claimed in claim 14 further comprising;
a feedforward control circuit for carrying out feedforward control on the
basis of predata for a level displacement of the vibration control base,
wherein the level control value is obtained by adding a feedforward
control value obtained by the feedforward control circuit to the feedback
compensation value of level displacement and the analog integrated value.
16. The apparatus as claimed in claim 10 further comprising:
the vertical direction control means comprises a vertical vibration control
feedback circuit, and a control valve for the air springs, said vertical
vibration control feedback circuit including at least one of a vertical
vibration integrating amplifier for integrating an output of the vertical
acceleration sensor, a vertical vibration differentiating amplifier for
differentiating the output of the vertical acceleration sensor, and a
vertical vibration proportional amplifier for amplifying the output of the
vertical acceleration sensor or a phase compensation circuit, so as to
obtain a vertical vibration control value therefrom, wherein the control
valve for the air springs is controlled in accordance with the sum of the
vertical vibration control value and the level control value.
17. The apparatus as claimed in claim 16 further comprising;
a feedforward control circuit for carrying out feedforward control on the
basis of predata for vertical vibrations of the vibration control base,
wherein the vertical vibration control value is obtained by adding the
feedforward control value to the feedback compensation value, so as to
control the control valve for the air springs in accordance with the sum
of the vertical vibration control value and the level control value.
18. The apparatus as claimed in claim 10 wherein:
the horizontal direction control means includes:
lateral air springs for generating a horizontal standard load for loading
substantially a constant lateral load onto the vibration control base or a
connecting member connected thereto and for generating a control load for
loading same onto the vibration control base or a connecting member
connected thereto in an opposite direction to the horizontal standard
load,
an analog level position sensor for sensing a level displacement of the
vibration control base from a standard level position thereof and
outputting an analog level position voltage,
a level difference amplifier for comparing the analog level position
voltage with a standard level position voltage and for outputting a
difference therebetween,
an integrating amplifier for integrating the difference or the integrating
amplifier and a feedback compensation circuit for accelerating levelling
of the vibration control base, so as to obtain a lateral position control
value,
at least one of an analog horizontal acceleration sensor for sensing an
acceleration of horizontal vibrations of the vibration control base, a
horizontal vibration integrating amplifier for integrating an output of
the analog horizontal acceleration sensor, a horizontal vibration
differentiating amplifier for differentiating the output of the analog
horizontal acceleration sensor, a horizontal vibration proportional
amplifier for amplifying the output of the analog horizontal acceleration
sensor or a vibration feedback compensation circuit for a phase
compensation, so as to obtain a horizontal vibration control value,
an adder for adding the horizontal vibration control value to the lateral
position control value, and
a control valve for controlling an air pressure of the lateral air springs
in accordance with a value output from the adder.
19. The apparatus as claimed in claim 10 wherein
the horizontal direction control means includes:
lateral air springs for generating a horizontal force and for loading same
onto the vibration control base or a connecting member connected thereto
in an opposite direction to one another,
an analog level position sensor for sensing a level displacement of the
vibration control base from a standard level position thereof and
outputting an analog level position voltage,
a level difference amplifier for comparing the analog level position
voltage with a standard level position voltage and for outputting a
difference therebetween,
an integrating amplifier for integrating the difference or the integration
amplifier and a feedback compensation circuit for accelerating levelling
of the vibration control base, so as to obtain a lateral position control
value,
at least one of an analog horizontal acceleration sensor for sensing an
acceleration of horizontal vibrations of the vibration control base, a
horizontal vibration integrating amplifier for integrating an output of
the analog horizontal acceleration sensor, a horizontal vibration
differentiating amplifier for differentiating the output of the analog
horizontal acceleration sensor, a horizontal vibration proportion
amplifier for amplifying the output of the analog horizontal acceleration
sensor or a vibration feedback compensation circuit for a phase
compensation, so as to obtain a horizontal vibration control value,
an adder for adding the horizontal vibration control value to the lateral
position control value,
a control valve for controlling an air pressure of the lateral air springs
in accordance with a value output from the adder, and
a phase converting circuit for converting a phase of the value output from
the adder at 180.degree., thereby the air pressure of the air springs is
controlled in response to an output from the phase converting circuit. |
|
 |
|
 |
Claims |
|
|
|
Description |
|
|
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of controlling positions and
vibrations and an active vibration control apparatus therefor for carrying
out a precise vibration control for any kind of precision machines and
precision instruments such as a holographic instrument, an electron
microscope, apparatus for producing semiconductors, a laser measuring
machine, a super precision measuring machine and so sorth.
2. Description of the Prior Art
A floor receives any kind of vibrations such as strong and weak vibrations,
horizontal and vertical vibrations and any range of frequencies of
vibrations from high frequency to low frequency. Therefore, these
vibrations are propagated to a precision machine or instrument which is
mounted on the floor.
For instance where a measuring instrument mounted on the floor provides
driving means and when a work piece to be measured by the instrument is
moved, vibrations occur and inclination of the instrument may sometimes be
occurred.
In the case that the instrument or the machine is an ordinary machine tool,
it is not necessary to consider influence of such vibrations propagated to
the machine. However, in the case that the instrument or machine is such
as a jig boring machine, a super precision machine tool an apparatus for
producing a super LSI, or a laser measuring machine, such vibrations give
a fatal influence to those instruments.
Accordingly, vibration control becomes a very important element in keeping
a high recision for the super precision machine. Since the vibrations
propagated to the super precision machine on the floor involve many kinds
of frequencies and sometimes the machine resonates according to a certain
frequency, and an ordinary spring cannot control such vibrations.
Therefore, instead of the conventional idea of the vibration control
system, it is introduced an active vibration control system which converts
the vibrations propagated from the floor into electronic signals so as to
control a vibration control base by means of an active vibration control
apparatus.
For example, Japanese Patent Application No. 63-35829, discloses a
vibration control apparatus for controlling vibrations and maintaining a
level of a vibration control base by means of a digital control system,
which is shown in FIG. 28.
The apparatus provides a digital level control circuit 100 for controlling
a level. The digital control circuit detects a value of level displacement
of a vibration control base 131 by means of a level sensor 120 and the
output of the level sensor 120 is compared with a standard level voltage
by means of a comparator 132 and the difference obtained thereby is input
to a pulse generator 121 so that the generator generates analog signals in
accordance with the value of the displacement and then inputs the analog
signals into a displacement pulse generator 121. Constant pulses are
generated by the displacement pulse generator 121 in synchronism with a
clock 122, which is provided therewith, during the period of generation of
the analog signals and the constant pulses are input to an adder 123. The
adder 123 counts the input signals and then outputs same as the
displacement signals and thereby the value of level displacement may be
sized digitally.
Next, vertical micro-vibrations may be controlled by means of a digital
vibration control circuit 101. Micro-vibrations of a vibration control
base 131 propagated from a floor or vibrations of a precision instrument
on the base, are detected by a vibration sensor 124 and vibration signals
from the vibration sensor 124 are input to an arithmetic circuit 125 via a
lowpass filter 133. The phases of the detected signals output from the
arithmetic circuit 125 are inverted at 180.degree. by means of a phase
inverter 126. The signals inverted by the phase inverter 126 are input to
a level displacement and micro-vibration adder 127 after they are changed
to analog signals. By means of the level displacement and micro-vibration
adder 127, the phase inverting signals are added to the level displacement
signals output from the adder 123 of the level control circuit 100 and
disturbance control is carried out together with a levelling correction.
The outputs from the level displacement and micro-vibration adder 127 are
input to a drive circuit 128 so as to control a control valve 129 in order
to control a pressure of an air spring 132. An compression air is supplied
to the control valve 129 from an air pressure source 110 via a regulator
112 so as to control an air pressure of the air spring 132.
According to the digital level control circuit 100, the drive circuit 128
outputs a raising signal to the control valve 129 in order to lift up the
vibration control base 131 by means of the air spring 132 when the
vibration control base 131 goes down below a standard level H, and when
the vibration control base 131 becomes positioned above the standard level
H, a lowering signal is output.
While the raising signal is output, the output signals of the displacement
pulse generator 121 are added by means of the adder 123 and subtracted
thereby when the lowering signal is output. The added or subtracted
signals are finally converted to analog signals via a D/A converter 130
and then output. The addition and subtraction is continued while the
vibration control base 131 is not accorded with the standard level H.
Such a digital control system cannot, however, evade hunting (raising and
lowering) of the vibration control base 131 around the standard level H
since the raising and lowering signals are changed on the basis of a
single point of the standard level. Therefore, it is required to add
another means to the digital control system so as to stop counting of the
adder 123 within a range which is limited at very short distances in up
and down directions from the standard level. However, in such a manner,
the vibration control base 131 is freely raised and lowered within the
limited range so that a level error frequently occurs within the limited
range. In other words, the digital control system includes a control
precision of .+-.X % at the standard level H.
To minimize the error and increase the precision of levelling, it is
necessary to use a D/A converter 130 having a great number of bits.
However, such a converter increases a cost of the apparatus.
SUMMARY OF THE INVENTION
The present invention has an object to provide a method of controlling a
level of a vibration control base precisely so as to be returned to and
maintained at a predetermined level without hunting.
To achieve the object, the method of controlling a level according to the
present invention comprises the steps of sensing a level of a vibration
control base suspended by air springs to output a level voltage, comparing
the level voltage with a standard level voltage to obtain and output a
difference therebetween, integrating the difference to obtain an analog
integrated value only or integrating the difference and giving a feedback
compensation to the difference at the same time to obtain a compensated
value for accelerating levelling of the vibration control base, outputting
the analog integrated value only or a value obtained by adding the analog
integrated value and the compensated value as a level control value, and
controlling an air pressure of the air springs in accordance with the
level control value.
Therefore, according to the method, the following advantages may be
obtained.
(1) Comparing with the conventional digital vibration control system, there
occurs no error range wherein the vibration control base becomes free in
up and down directions around a standard (initial) level and so it becomes
possible to stop and maintain the vibration control base at the standard
(initial) level precisely.
(2) It becomes possible to simplify the levelling control circuit and to
lower its cost in spite of grading up the precision of levelling control.
(3) There is little noise disturbance in comparison with the conventional
digital control system.
(4) In addition to the analog integration, where the feedback compensation
takes place, it becomes possible to accelarate levelling of the vibration
control base by speeding up an integral action time.
(5) Further, where the vibration includes a frequency higher than a time
constant of the air spring, a component of the difference differentiated
by the feedback compensation, is input to the adder and so as to take
place a feedback control. As the results, it becomes possible to control
the displacement of the vibration control base in the up and down
directions within a high frequency vibration.
(6) Further, where the vibrations include frequencies lower than a time
constant of the air spring, a component of the difference differentiated
by the feedback compensation, is input to the adder and so that a feedback
control may take place. As the results, it becomes possible to control the
displacement of the vibration control base in the up and down directions
within a low frequency vibration.
(7) The vertical vibrations are memorized as predata and a feedfoward
control may be carried out on the basis of the predata.
(8) In addition to the levelling control, it may carry out a feedback
compensation with respect to vertical vibrations so that the vibration
control base in the up and down directions may be controlled.
The second object of the present invention is to provide a method of
controlling vibrations of a vibration control base in horizontal
directions without influence of high and low frequencies of the horizontal
or lateral vibrations.
To achieve the second object, the method of controlling vibrations
comprises the steps of sensing a displacement of a vibration control base,
which is suspended by air springs, in a horizontal direction with respect
to a standard level position so as to output an analog level position
voltage, comparing the analog level position voltage with a standard level
position voltage to obtain and output a difference therebetween,
integrating the difference to obtain an integrated value only or
integrating the difference and giving a feedback compensation to the
difference at the same time to obtain a compensated value for accelerating
levelling control of the vibration control base, outputting the integrated
value only or a value obtained by adding the integrated value and the
compensated value as a level control value, sensing an acceleration of
vibration of the vibration control base in a horizontal direction so as to
output an accelaration voltage of horizontal directions, giving at least
one of integration, differentiation and amplification to the accelaration
voltage of horizontal direction or combining a phase compensation
therewith to output a horizontal vibration control value so as to carry
out a feedback compensation for vibrations in horizontal directions, and
controlling an air pressure of the air springs in accordance with a level
and vibration control value obtained by summing the level control value
and the horizontal vibration control value.
Accordingly, it becomes possible to control vibrations in horizontal
directions while maintaining the vibration control base at the standard
level position so that vibrations may be controlled precisely. For
instance, the method may be applied for an apparatus for producing
semiconductors.
The third object of this invention is to provide an active vibration
control apparatus for controlling any kind of vibrations propagated from a
floor to a machine or apparatus set on a vibration control base which
vibrations include high and low frequencies, strong and weak vibrations
and vibrations in any directions.
To achieve the third object of this invention, the active vibration control
apparatus comprises a fixed base, a vibration control base disposed above
the fixed base, vertical supporters interposed between the fixed base and
the vibration control base to support the vibration control and having
flexibility in horizontal directions, vertical direction vibration control
means interposed between the fixed base and the vibration control base via
the vertical supporters, vertical direction control means for returning
and maintaining a level of the vibration control base at a standard level
position and for controlling vertical vibrations to drive the vertical
direction vibration control means, horizontal direction vibration control
means interposed between the fixed base and the vibration control base,
and horizontal direction control means for returning and maintaining a
lateral position of the vibration control base at a standard lateral
position and for controlling horizontal vibrations to drive the horizontal
direction vibration control means.
Therefore, according to the apparatus, the vertical direction vibration
control means does not interfere with the horizontal direction control
means almost since the vertical direction vibration control means is
supported by the vertical supporters which are flexible in horizontal
directions and as the result both of the vertical and horizontal direction
means are unified in a sole apparatus.
Accordingly, it becomes possible to control vibrations including all of the
directions, high and low frequencies and strong and weak vibrations by a
sole apparatus. This does not mean that it is necessary to arrange the
vertical direction vibration control means independently from the
horizontal direction control means as in the above mentioned conventional
art.
Contrary to the conventional art, the apparatus of this invention becomes
compact and does not occupy to much space.
BRIEF DESCRIPTION OF THE DRAWINGS
The drawings show embodiments of an active vibration control apparatus and
a method of controlling positions and vibrations according to the present
invention in which:
FIG. 1 is a block diagram used for maintaining a level and removing
micro-vibrations,
FIG. 2 is a block diagram used for maintaining a standard level and
controlling vibrations in horizontal directions,
FIG. 3 is a block diagram modifying the block diagram of FIG. 2,
FIG. 4 is a block diagram used for a standard air spring instead of a metal
spring in controlling a level,
FIG. 5 is a block diagram for a push-pull control in controlling a level,
FIG. 6 is a partial side view of the air springs arranged to be directed in
an opposite direction as those of the air springs in FIG. 5,
FIG. 7 is a partial side view showing the air springs in FIG. 5 arranged to
be located on both of the sides of vibration control base,
FIG. 8 is a plan view of the vibration control base,
FIG. 9 is a cross sectional view of the apparatus of the first embodiment,
FIG. 10 is a sectional side view of the apparatus in FIG. 9,
FIG. 11 is a block diagram of the first embodiment for controlling the
vibration control base vertically and horizontally,
FIG. 12 is a block diagram of the second embodiment of controlling the
vibration control base vertically and horizontally by means of a push-pull
control,
FIG. 13 is a sectional view of the vibration control apparatus of the
second embodiment,
FIG. 14 is a sectional view of the vibration control apparatus of the third
embodiment,
FIG. 15 is a cross sectional view of the vibration control apparatus of the
fourth embodiment,
FIG. 16 is a sectional side view of the apparatus in FIG. 15,
FIG. 17 is a cross sectional view of the vibration control apparatus of the
fifth embodiment,
FIG. 18 is a sectional side view of the apparatus in FIG. 17,
FIG. 19 is a cross sectional view of the vibration control apparatus of the
sixth embodiment,
FIG. 20 is a sectional view of the vibration control apparatus of the
seventh embodiment,
FIG. 21 is a sectional view of the vibration control apparatus of the
eighth embodiment,
FIG. 22 is a sectional view of the vibration control apparatus of the ninth
embodiment,
FIG. 23 is a cross sectional view of the vibration control apparatus of the
tenth embodiment,
FIG. 24 is a sectional side view of the vibration control apparatus of the
tenth embodiment,
FIG. 25 is a cross sectional view of the vibration control apparatus of the
eleventh embodiment,
FIG. 26 is a sectional side view of the vibration control apparatus of the
eleventh embodiment,
FIG. 27 is a sectional side view of the vibration control apparatus of the
twelfth embodiment,
FIG. 28 is a block diagram used for a conventional digital control.
DETAILED DESCRIPTION OF THE EMBODIMENTS
The embodiments of the present inventional will be described below in
detail with reference to the drawings.
A vibration control base 2 is so constructed as to mount thereon precision
instruments such as a holographic instrument, an electron microscope,
apparatus for producing semiconductors. To support the vibration control
base 2, four active vibration control devices A as well as an active
vibration control circuit are provided.
The vibration control device A includes a vertical vibration control means
and a horizontal vibration control means as a unit to form like a block.
As shown in FIG. 8, where four vibration control devices A are used, they
are arranged in such a manner that horizontal control directions of each
of the vibration control devices A, which are adjacent to one another, are
perpendicular to one another. Where there vibration control devices A are
used, they are arranged to make the same horizontal control directions
perpendicular to the center of gravity of the vibration control base and
to hold an angle of 120.degree. therebetween or arranged to have their
directions toward the center of gravity and hold an angle of 120.degree.
therebetween.
Air springs, piezo-electric crystal, or linear motors may be provided with
the vibration control devices A. In this embodiment, air springs 3 are
used for the vertical vibration control means and the horizontal vibration
control means of the vibration control device A. Further, laminated
supporters 7 are used for vertical direction supporters B2 and wires 8 are
used for horizontal direction supporters B1.
In FIGS. 9 through 12, the apparatus are controlled in two directions, i.e.
vertical and horizontal directions. As shown in FIGS. 15 and 16, the
apparatus may of course be controlled in three directions, i.e. vertical
and two horizontal directions.
Now, the embodiment will be described with reference to FIGS. 8 through 11.
As shown in FIGS. 9 and 10, one of the four vibration control devices A is
referred to in order to simplify the description of this embodiment.
The active vibration control device provides a vertical air spring 3e,
vertical direction supporters B2, which in this embodiment comprise a
laminated supporter 7, a pair of horizontal air springs 3a and 3b, a level
sensor 9, a vertical acceleration sensor 10, a lateral position sensor 1
and a horizontal acceleration sensor 11.
The vertical air spring 3e and the horizontal air springs 3a and 3b
comprise a diaphram section 5 and air tanks 4 which are communicated with
the diaphram section 5, respectively. The outer periphery of the diaphram
section 5 is bolted to a fixed base 25 connected to the air tank 4 or a
partition plate 26 via a fixed seat 24 of ring form and circular seats
24a, 27b, 27c and 27d are fitted in a center movable portion of thereof.
The air tanks 4 for the horizontal air springs 3a and 3b are arranged
independently from each other on right and left sides of a center
partition plate 26'. In this embodiment, the horizontal air springs 3a and
3b are separated to be a controllable spring and a standard spring and the
standard spring 3a is connected to an air pressure source 16 via a precise
regulator 19. On the other hand, the controllable air spring 3b is
connected to the air pressure source 16 via a control valve 6a and the
control valve 6a is controlled by means of an active vibration control
circuit.
As is clear from FIG. 9, the horizontal air springs 3a and 3b are enclosed
with a casing 30 and the circular seats 27a and 27b are secured to the
inside wall of the casing 30. The casing 30 and the vibration control base
2 are connected to each other by means of fine wires 8. The connecting
manner of the wires 8 is as follows. As shown in FIG. 9, an arm 29 is
projected from each of the outer sides of the casing 30 and the wires 8
arranged to bridge the side walls 2a, are secured to the arms 29. On the
other hand, as shown with phantom lines in FIG. 9, the wires 8 projecting
from a center portion of the casing 30, may be secured to the sid e wall
2a of each of the vibration control base 2.
The vertical air spring 3e is mounted on the vertical direction supporters
B2 which are mounted on the fixed base 25. The vertical direction
supporters B2 comprise laminated supporters 7. Each of the laminated
supporters 7 comprises a number of a rubber plate 31 and a metal plate 32
which are laminated one another, and it is flexible in horizontal
directions, but not compressed almost in vertical directions.
In this embodiment, the vertical direction supporters B2 are arranged to be
two stories.
The active vibration control device or means A is used to be positioned at
four corners of a base 28, as shown in FIG. 8. The arrangement of the
devices are, as shown with arrows in FIG. 8, is such that the horizontal
air springs 3a and 3b adjacent to each other are cross in their extending
directions.
Next, a horizontal or lateral position maintaining circuit of the
horizontal direction control section or means will be described.
A lateral position sensor 1 and a horizontal direction acceleration sensor
11 are attached to the arm 29 of the vibration control device A in FIG. 9,
which arm is movable in forward and backward, right and left and rotatable
together with the vibration control base 2. However, their attachments may
be changed to another place. As shown in FIG. 11, the lateral position
sensor 1 is so constructed as to detect a displacement of the vibration
control base 2 from a standard lateral position So immediately and input a
value of the displacement into an input terminal of a lateral position
difference amplifier 12a. For instance, a non-contact analog output sensor
is used for the lateral position sensor 1.
A lateral standard position voltage corresponding to the lateral standard
position So of the vibration control base 2 is input to another input
terminal of the lateral position difference amplifier 12a, FIG. 2. Each of
output terminals of the lateral position difference amplifier 12a is
connected to a lateral position control analog integrating amplifier 13a,
a feedback compensation circuit XFb and a feedforward control circuit XFf
which is connected to a drive circuit 17 and described in detail
hereinafter, and on the basis of an output of the drive circuit 17, the
air spring 3b is controlled via an adder Ka. The feedforward compensation
circuit XFb means that it comprises a lateral position proportional
amplifier 14a and a lateral position differentiating amplifier 15a or the
lateral position proportional amplifier 14a and/or a phase compensation
circuit 15a', which are refferred to hereinafter.
The feedforward control circuit XFf is constructed to facilitate
controlling of vibrations in the beginning of vibration on the basis of
predata concerning lateral displacements of the vibration control base 2
by receiving an output of the lateral position control analog integrating
amplifier 13a, or the sum of the output and an output of the feedback
compensation circuit XFb.
Where only the lateral position control analog integrating amplifier 13a is
used, the vibration control base 2 is returned to the standard lateral
position So according to a time constant of the integrating amplifier 13a
and its returning speed is rather slow. However, where the lateral
position control analog integrating amplifier 13a and the feedback
compensation circuit XFb are used in combination, its returning speed goes
up.
As shown in FIG. 11, the feedback compensation circuit XFb comprises a
lateral position proportional amplifier 14a and/or a lateral position
differentiating amplifier 15a as a first example, and as a second example,
the feedback compensation circuit XFb comprises the lateral position
proportional amplifier 14a and a phase compensation circuit 15a'.
As the first example, their combinations are as follows:
(1) The lateral position integrating amplifier 13a and the lateral position
proporational amplifier 14a.
(2) The lateral position integrating amplifier 13a and the lateral position
differentiating amplifier 15a.
(3) The lateral position integrating amplifier 13a and the lateral position
proportional amplifier 14a and the lateral position differentiating
amplifier 15a.
As the second example, their combinations are as follows:
(1) The lateral position integrating amplifier 13a and the lateral position
proportional amplifier 14a and the phase compensation circuit 15a'.
As mentioned hereinbefore, it becomes possible to speed up positioning and
returning of the vibration control base 2 toward a standard or inital
position by accelerating a time constant of integration by adding the
proportional amplification, the differentiating amplification and the
phase compensation other than the analog integration to a relative
displacement.
Further, it becomes possible to effectively carry out a relative
displacement control by taking a feedback of a differentiated value where
the vibration frequencies are higher than a time constant of the air
spring 3, for instance, over 0.1 H.sub.z. and on the contrary where the
vibration frequencies are lower than the time constant, it may take a
feedback of a proportional value. According to the feedback controls, it
becomes possible to control vibration displacements in low frequencies
which are gentle vibrations of the vibration control base 2 in horizontal
directions around the standard lateral position So during returning to the
standard lateral position. It is very difficult to control such vibration
displacements only by taking a feedback of the data obtained by a
horizontal direction acceleration sensor 11 which will be referred to
hereinafter.
Further, it is limited to reduce an initial response with respect to a
disturbance only by using the feedback control for horizontal vibration
directions and to improve the disadvantage it is effective to add a
feedforward control to the feedback control. The feedforward control
circuit XFf will be described in detail below.
The feedforward control circuit XFf may be used in a first manner as
follows. Namely, level displacements of the vibration control base 2,
which occur due to driving of instruments or apparatus to be controlled,
are memorized with for instance a CPU in advance by patterning the lateral
displacements. When the lateral displacements occur, it catches initial
signals of the lateral displacementds and choose a most preferable pattern
immediately and then control a control valve 6a in accordance with the
pattern. The second manner is carried out by detecting or measuring an
amount of lateral displacement of the vibration control base 2 just before
entering control of the vibration control base 2 without memorizing and
patterning the lateral displacements and then operating the detected value
so as to control the control valve 6a with real time. As the result, it
may improve a disadvantage of the feedback control that the lateral
position control is not carried out sufficiently in the beginning of
vibrations.
The control valve 6a is connected to the air tank 4 of the control air
spring 3b and the standard air spring 3a is connected to the air pressure
source 16 via the regulator 19. The control valve 6a is controlled with a
current like | | |
