Vibration isolating support device

A vibration isolating device comprises a base, a plurality of support members each placed onto the base and comprised of a two series layer of an electroviscous body and an elastomeric body, and a cradle supported through these support members. These support members are provided with circuit for applying voltage to each electroviscous body, respectively.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a support device provided with a vibration 
isolating structure for reducing vibrations transmitted from a vibration 
source side to a vibration isolating side. 
2. Related Art Statement 
In case of transporting or setting precision instruments and the like, or 
in case of setting power machines and the like generating vibration, there 
is a vibration isolating support method as a countermeasure for preventing 
occurrence of such vibrations. 
In general, a vibration isolating support device has a structure supporting 
a cradle together with a rubber isolator, an elastic member such as metal 
spring, air spring or the like, and if necessary, an attenuator and is 
interposed between vibration source and vibration isolating means to shut 
off vibrations. 
Such a vibration isolating support device is schematically shown in FIG. 
16. 
A cradle 03 is supported on a base 01 through a vibration isolating support 
device 02, and an object 04 is placed on the cradle 03. 
Concerning the object 04, there are considered two cases, a first case of 
which being a vibration isolating body such as a precision instrument and 
a second case being a vibration generating body such as motor or the like. 
The vibration isolating support device 02 comprises plural elastic members 
and an attenuator and exhibits constant dynamic properties (spring 
constant K, attenuating factor C) as a whole. 
The frequency characteristic of such a vibration transmission ratio 
(response magnification) in this vibration isolating device is shown in 
FIG. 17. 
As seen from FIG. 17, a large peak of the vibration transmission ratio is 
shown through resonance at a constant resonance frequency of f.sub.0 
=.sqroot.K/M/2n. A vibration isolating area wherein the transmission ratio 
is not more than 1 is a frequency zone of more than .sqroot.2f.sub.0. 
Therefore, the above device has a vibration isolating effect against 
vibrations having a frequency of more than .sqroot.2f.sub.0 and can 
isolate vibrations. 
Moreover, M is a weight on the vibration isolating device 02 (i.e. total 
weight of cradle 03 and object 04). 
The vibration frequency f of vibration source is resonated in the vicinity 
of f.sub.0 to inversely amplify vibrations and transmit toward the 
vibration isolating side, so that it is always required to use the device 
at the vibration isolating zone of more than .sqroot.2f.sub.0. 
That is, the minimum frequency f.sub.min of vibration frequency f of the 
vibration source side and the resonance frequency f.sub.0 are necessary to 
satisfy a relationship of .sqroot.2f.sub.0 &lt;f.sub.min. 
When the weight M and the vibration frequency f of the vibration source 
side are previously known, the resonance frequency f.sub.0 satisfying the 
above relationship is determined, and then the vibration isolating device 
should be designed so as to obtain such a resonance frequency f.sub.0. 
However, when the weight M and vibration frequency f are not known, or 
when they are not constant, it has been difficult to design the optimum 
device. Therefore, the above vibration isolating device is suitable when 
the motor or the like is semi-permanently placed, but is not suitable when 
the loading weight on the cradle is not specified or is varied, or when 
the vibration frequency f always varies. 
For example, in case of a vibration isolating support member for 
transportation of precision instruments or the like and vibration removing 
base, the kind, number and the like of the precision instruments loaded on 
the cradle may vary, so that these devices are designed based on average 
weight M and vibration frequency f. As a result, the optimum design is not 
always obtained, and according to circumstances the vibration frequency f 
may approach to the resonance frequency f.sub.0 to badly exert on the 
precision instrument. 
Therefore, in order to effectively use such a vibration isolating support 
device, the use condition is restricted, and consequently the 
general-purpose use is lacking. 
Because, the spring constant K in the conventional vibration isolating 
device itself is fixed and it is usually difficult to properly change the 
value K adjusted at the designing stage in use. 
For this end, there has hitherto been proposed a method wherein plural 
vibration isolating devices having various spring constants adjusted every 
loading object are provided and used properly as the conventional 
countermeasure. However, such a method has drawbacks in cost and 
efficiency because the plural devices should be used properly. 
Furthermore, in order to use the device at a vibration isolating zone of 
more than .sqroot.2f.sub.0, it is considered that the spring constant K is 
designed to a considerably low value so as to render the resonance 
frequency f.sub.0 into a low initial value. In this case, there is no 
problem when the weight of the loading object is light, but as the weight 
becomes heavy, the sinking down of the elastomer in the vibration 
isolating device 02 or deformation under loading becomes considerably 
large and hence there is caused a problem in the strength and durability 
of the vibration isolating device 02. 
As a result, the weight of the loading object itself is restricted. 
SUMMARY OF THE INVENTION 
Under the above situations, the invention is to provide a vibration 
isolating support device which can always obtain an optimum vibration 
isolating effect by varying spring constant in accordance with the weight 
of the loading object. 
According to the invention, there is the provision of a vibration isolating 
device, characterized in that a plurality of support members each 
comprised of a two series layer of an electroviscous body and an 
elastomeric body are placed onto a base in parallel with each other, and a 
cradle is supported through these support members, and said support 
members are provided with means for applying voltage to each 
electroviscous body, respectively. 
In the electroviscous body, the viscosity increases through the application 
of the voltage, and properties as a rigid body are exhibited at a voltage 
above a certain value. 
That is, the spring constant of the device as a whole can easily be 
adjusted by selectively applying voltage to the electroviscous body in the 
plural support members each comprised of the two series layer of 
electroviscous body and elastomeric body and supporting the cradle. 
Therefore, the voltage is controlled in accordance with the weight of the 
loading object and the vibration frequency of vibration source side to 
adjust the spring constant, whereby the optimum vibration isolating effect 
can be obtained and also the desired strength can be maintained even 
against a heavy object.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
An embodiment of the vibration isolating support device according to the 
invention will be described with reference to FIG. 1 to FIG. 7. 
FIG. 1 is a side view of the vibration isolating support device 1 according 
to the first embodiment as a whole, and FIG. 2 is a plan view thereof. 
In this device, rectangular plate-like base 2 and cradle 3 are positioned 
upward and downward to face to each other, and four vibration isolating 
support members 4 are interposed therebetween at four corner portions to 
support the cradle 3. 
The inner structure of the vibration isolating support member 4 is shown in 
FIGS. 3 and 4. 
The vibration isolating support member 4 is comprised of upper and lower 
layers. The lower layer is a cylindrical rubber body 5, and the upper 
layer is a square pillar-like bag 7 containing an electroviscous fluid 6 
therein. 
Plural electrode plates 10, 11 vertically protrude from upper and lower 
conductive substrates 8, 9 in opposite directions and arranged in the 
electroviscous fluid 6. These electrode plates 10, 11 are alternately 
arranged so as to oppose a part thereof to each other. 
Lead wires 14 are drawn out from the upper and lower substrates 8, 9 and 
connected to each other through a direct current source 12 and a switch 
13. 
The electroviscous fluid 6 is generally obtained by dispersing particles of 
silica gel or the like into an insulating oil such as silicone oil or the 
like, and has a property that the viscosity changes in accordance with an 
intensity of electric field applied and the response thereof is very fast. 
FIG. 5 shows a change of viscosity to electric field, wherein an abscissa 
is an electric field (KV/mm) and an ordinate is a viscosity (CP). 
As seen from FIG. 5, when the electric field exceeds a certain value, the 
viscosity rapidly increases to provide properties as a rigid body. 
In the embodiment according to the invention, the electroviscous fluid has 
a viscosity to a certain extent at a state of applying no voltage and a 
spring constant smaller than that of the rubber body 5. 
Therefore, when the switch 13 is closed to apply a voltage between the 
electrode plates 10 and 11 as shown in FIG. 3, the viscosity of the 
electroviscous fluid 6 considerably increases to act as a rigid body 
against vibrations between the base 2 and the cradle 3. Consequently the 
rubber body 5 mainly has a vibration isolating effect and spring component 
is substantially determined by the spring constant of the rubber body 5. 
On the other hand, when the switch 13 is opened to stop the application of 
voltage between the electrode plates 10 and 11 (see FIG. 4), the viscosity 
of the electroviscous fluid 6 becomes smaller than that of the rubber body 
5, consequently the electroviscous fluid 6 mainly has a vibration 
isolating effect and also the value of spring constant becomes small. 
As mentioned above, the spring constant of the vibration isolating support 
member 4 can be changed into large and small values by on-off of the 
switch 13. 
The voltage applied is dependent upon the distance between opposed 
electrode plates 10 and 11 and the type of the electroviscous fluid, but 
it is sufficient to an extent of largely changing the viscosity and is 
usually several kV. 
Furthermore, when the electrode plates 10, 11 are conductive, the material 
is not particularly restricted. They are desirable to sufficiently ensure 
durability during the use in the electroviscous fluid 6. For example, use 
may be made of metals such as gold, silver, copper, iron and the like. 
Moreover, the shape of the electrode plate is not particularly restricted, 
but it is sufficient to have opposed faces between the electrode plates 10 
and 11. 
The distance between the opposed electrode plates 10 and 11 is preferably 
0.1-100 mm, more particularly 1-11 mm. 
In this embodiment, plural electrode plates 10, 11 are alternately arranged 
to produce an approximately constant electric field in the whole of the 
electroviscous fluid 6 to cause the viscosity change at once. 
In this case, however, it is necessary that each top of the electrode 
plates 10, 11 should always hold a certain distance from the substrates 9, 
8 so as not to come into contact therewith. For this purpose, a stopper 
may be arranged to support the cradle 3. 
The experimental results on the vibration isolating support device 1 will 
be described below. 
The experiment was made by placing the vibration isolating support device 1 
onto a vibration applying apparatus 20 and a vibration isolating object 21 
onto the cradle 3 of the device 1 as shown in FIG. 6. Vibrations input to 
the vibration applying apparatus 20 are white noise. 
Onto the base 2 and the cradle 3 are attached sensors 22 and 23 for the 
measurement of vibration acceleration rate, respectively. The acceleration 
signals detected by the sensors 22 and 23 analyzed by a frequency 
analyzing machine to obtain acceleration rate x.sub.55 0 of the base 2 and 
acceleration rate x.sub. 1 of the cradle 3, from which a ratio of both 
rates or response magnification .vertline.x.sub. 1 x.sub. 0 .vertline. is 
calculated. 
At first, the experiment was made by applying voltage to all of four 
vibration isolating support members 4. 
In this case, the viscosity of electroviscous fluid 6 in all of four 
vibration isolating support members 4 increases and the spring constant of 
the device becomes large state as a whole. As shown by a solid line in 
FIG. 7, the vibration transmission ratio shows a maximum peak at a 
frequency of about 20 Hz as a resonance frequency and the vibration 
isolating zone is more than 20.sqroot.2 Hz. 
Then, the voltage was applied to only two of four vibration isolating 
support members 4. In this case, the spring constant of the device as a 
whole becomes small, and the maximum peak of vibration transmission ratio 
is shifted as a resonance frequency of about 15 Hz as shown by dotted 
lines in FIG. 7. Hence, the vibration isolating zone is widened to more 
than 15.sqroot.2 Hz. 
As mentioned above, the spring component can easily be changed by 
selectively applying the voltage to the vibration isolating support 
members. 
Therefore, the spring constant is adjusted by selectively applying the 
voltage to the vibration isolating support members in accordance with the 
weight of the vibration isolating object 21 and the input vibrations, 
whereby the optimum vibration isolating effect can easily be obtained 
while maintaining the required strength. 
In the above embodiment, the electroviscous fluid 6 in the vibration 
isolating support member 4 is square pillar-like and the flat plate-like 
electrode plates 10, 11 are arranged side by side inside the 
electroviscous fluid 6 as shown in FIGS. 3 and 4. Another embodiment of 
such a structure is shown in FIGS. 8 and 9. 
In a vibration isolating support member 30 of this embodiment, a lower 
layer of rubber body 31 and an electroviscous fluid 32 enclosed in an 
upper layer of bag body 33 are cylindrical. Also, electrode plates 36, 37 
vertically arranged from upper and lower substrates 34, 35 in the 
electroviscous fluid 32 are cylindrical. 
In this case, two cylindrical electrode plates 36 having different radii 
are vertically arranged from the upper substrate 34 at the same central 
axis, while a rod-like electrode 38 is vertically arranged in the above 
central axis, wherein the lower ends of these electrodes are same level. 
Similarly, two cylindrical electrode plates 37 having different radii are 
vertically arranged from the lower substrate 35 at the same central axis. 
The upper ends of these electrodes are at the same level. 
The radii of these upper and lower cylindrical electrode plates 36, 37 are 
alternately arithmetical progression, and the lower portions of the upper 
electrode plates 36 are concentrically overlapped with the upper portions 
of the lower electrode plates 37. 
According to the above structure, when the voltage is applied, the 
viscosity change can be given to the whole of the cylindrical 
electroviscous fluid 32. 
The experiment using such a cylindrical vibration isolating support member 
30 will be described below. 
FIG. 10 shows a side view of a vibration isolating support device 40 using 
the above cylindrical vibration isolating support member 30, and FIG. 11 
is a plan view thereof. 
In the vibration isolating support device 40, 16 vibration isolating 
support members 42 are vertically arranged on a floor 41 as a base in four 
rows and four columns at a distance of 0.25 m, and support a rectangular 
plate-like honeycomb table 43 (1 m.times.1 m) as a cradle. 
Each of the vibration isolating support members 42 has a switch capable of 
applying voltage independently. 
Onto the honeycomb table 43 is placed an object 44 assumed as a precision 
instrument. 
Furthermore, a rotating machine 45 as a vibration source is placed on the 
floor 41. 
The rotating machine 45 is driven at a revolution number of 1200 rpm, which 
can mainly give vibrations of 20 Hz to the floor 41. 
Moreover, pick-up sensors for acceleration rate 46, 47 are attached onto 
the floor 41 and the object 44, respectively. The signals detected by 
these sensors are indicated in form of time series wave through charge 
amplifiers. 
Under the above setting conditions, when the voltage was applied to all of 
the 16 vibration isolating support members 42 and the object 44 of 100 kg 
was placed onto the honeycomb table 43, the resonance frequency was 10 Hz 
as measured from the transmission function. Since the frequency of the 
rotating machine 45 as a vibration source was 20 Hz, the above resonance 
frequency was sufficiently included in the vibration isolating zone of 
more than 10.sqroot.2 Hz. 
When the time series waves of vibration acceleration rates in the floor 41 
and the object 44 were measured by driving the rotating machine 45, the 
results shown in FIGS. 12 and 13 were obtained, from which it is 
understood that the vibrations of the object 44 are sufficiently isolated 
while suppressing the width of the object 44 against the floor 41 to not 
more than 1/3. 
Moreover, the strength was sufficiently held because the spring constant of 
the device itself became large by applying the voltage to all of the 
vibration isolating support members 42. 
Then, when the weight of the object 44 was changed into 25 kg under a state 
that the voltage was applied to all of 16 vibration isolating support 
members 42, the vibration acceleration rate of the object showed an 
amplitude larger than the vibration acceleration rate of the floor (see 
FIG. 12) as shown in FIG. 14, and the vibrations were amplified. 
This is due to the fact that the resonance frequency f.sub.0 was 20 Hz and 
was coincident with the input vibration to cause resonance because the 
weight of the object 44 was changed to 1/4. 
Now, when the weight of the object 44 was changed to 1/4 and the voltage 
was applied to only four vibration isolating support members 42 among the 
16 members, the resonance frequency f.sub.0 was 10 Hz, and the input 
vibration of 20 Hz was included in the vibration isolating zone. 
In the latter case, the vibration acceleration rate of the object 44 
significantly reduced its amplitude as shown in FIG. 15. 
Moreover, the strength is low as compared with that of the previous 
experiment because the voltage is applied to only the four vibration 
isolating support members 42, but the weight of the loading object becomes 
small, so that there is no problem on the strength itself. 
As mentioned above, the vibration isolating support device according to the 
invention can always be used in the vibration isolating zone by 
selectively applying the voltage to the vibration isolating support 
members in accordance with the weight of the loading object, so that it is 
rich in the general-purpose use. 
According to the invention, the spring component can easily be changed by 
selectively applying the voltage to the vibration isolating support 
members utilizing the electroviscous fluid, so that the optimum vibration 
isolating effect can always be obtained in accordance with the weight of 
the loading object and the kind of the input vibration.