U.S. patent application number 10/959332 was filed with the patent office on 2005-02-24 for polishing apparatus.
This patent application is currently assigned to Governor of Akita prefecture. Invention is credited to Akagami, Yoichi, Satou, Yukichi, Yamamoto, Chikayoshi.
Application Number | 20050040050 10/959332 |
Document ID | / |
Family ID | 19128974 |
Filed Date | 2005-02-24 |
United States Patent
Application |
20050040050 |
Kind Code |
A1 |
Akagami, Yoichi ; et
al. |
February 24, 2005 |
Polishing apparatus
Abstract
A polishing apparatus for polishing a workpiece by utilizing a
fluid including abrasive particles having a dielectric property.
The polishing apparatus includes an electrode for applying
processing pressure to the abrasive particles on the workpiece and
having electrode elements for collecting and arranging the abrasive
particles by a Coulomb force produced by application of an
alternating-current voltage to the electrode, and a driving device
for driving the electrode.
Inventors: |
Akagami, Yoichi;
(Akita-city, JP) ; Satou, Yukichi; (Honjyo city,
JP) ; Yamamoto, Chikayoshi; (Ohta-ku, JP) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
Governor of Akita
prefecture
Akita city
JP
|
Family ID: |
19128974 |
Appl. No.: |
10/959332 |
Filed: |
October 7, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10959332 |
Oct 7, 2004 |
|
|
|
10054937 |
Jan 25, 2002 |
|
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Current U.S.
Class: |
205/662 |
Current CPC
Class: |
B24B 37/04 20130101;
B23H 5/08 20130101 |
Class at
Publication: |
205/662 |
International
Class: |
B23H 003/00 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 5, 2001 |
JP |
2001-309902 |
Claims
What is claimed as new and desired to be sucured by Letters Patent
of the United States is:
1. A polishing apparatus for polishing a workpiece by utilizing a
fluid including abrasive particles having a dielectric property,
comprising: an electrode configured to apply processing pressure to
the abrasive particles on the workpiece and having a plurality of
electrode elements configured to collect and arrange the abrasive
particles by a Coulomb force produced by application of an
alternating-current voltage to the electrode; and a driving device
for driving the electrode.
2. A polishing apparatus according to claim 1, wherein the
plurality of electrode elements are cylindrical, having different
diameters and disposed in a concentric circular formation and
mutually separated by insulative material.
3. A polishing apparatus according to claim 1, wherein different
voltages are applied to the plurality of electrode elements.
4. A polishing apparatus according to claim 2, wherein different
voltages are applied to the plurality of electrode elements.
5. A polishing apparatus according to claim 2, wherein the
plurality of electrode elements include inner and outer electrode
elements, and a lower voltage is applied to the inner electrode
elements and a higher voltage is applied to the outer electrode
elements.
6. A polishing apparatus according to claim 3, wherein the
plurality of electrode elements include inner and outer electrode
elements, and a lower voltage is applied to the inner electrode
elements and a higher voltage is applied to the outer electrode
elements.
7. A polishing apparatus according to claim 4, wherein the
plurality of electrode elements include inner and outer electrode
elements, and a lower voltage is applied to the inner electrode
elements and a higher voltage is applied to the outer electrode
elements.
8. A polishing apparatus according to claim 1, wherein the
electrode comprises a cylindrical electrode having a film-shaped
conductor and an insulative layer that are wound around a spindle
so that the conductor and insulative layer are alternated around
the spindle.
9. A polishing apparatus according claim 1, further comprising an
insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
10. A polishing apparatus according to claim 2, further comprising
an insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
11. A polishing apparatus according to claim 3, further comprising
an insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
12. A polishing apparatus according to claim 4, further comprising
an insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
13. A polishing apparatus according to claim 5, further comprising
an insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
14. A polishing apparatus according to claim 6, further comprising
an insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
15. A polishing apparatus according to claim 7, further comprising
an insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
16. A polishing apparatus according to claim 8, further comprising
an insulative tube positioned to supply a fluid containing a
dispersion of said abrasive particles to the workpiece and
electrodes provided around the insulative tube to adjust fluid flow
from the insulative tube.
17. A method of polishing a workpiece comprising: supplying a fluid
including abrasive particles having a dielectric property to the
workpiece; providing an electrode configured to apply processing
pressure to the abrasive particles on the workpiece and having a
plurality of electrode elements configured to collect the abrasive
particles; and applying an alternating-current voltage to the
electrode to produce a Coulomb force.
18. A method according to claim 17, wherein said providing includes
providing the plurality of electrode elements which are cylindrical
having different diameters and disposed in a concentric circular
formation and mutually separated by insulative material.
19. A method according to claim 17, wherein said applying includes
applying different voltages to the plurality of electrode
elements.
20. A method according to claim 18, wherein the plurality of
electrode elements include inner and outer electrode elements, and
said applying includes applying a lower voltage to the inner
electrode elements and applying a higher voltage to the outer
electrode elements.
21. A method according to claim 17, wherein said providing includes
providing a cylindrical electrode having a film-shaped conductor
and an insulative layer by winding the film-shaped conductor and
the insulative layer around a spindle alternately.
22. A method according to claim 17, further comprising: providing
an insulative tube configured to supply a fluid containing a
dispersion of the abrasive particles to the workpiece; and
providing electrodes around the insulative tube to adjust fluid
flow from the insulative tube.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a polishing apparatus in
which polishing of a workpiece is effected using dielectric
abrasive particles located at a position at which processing
pressure is applied by a Coulomb force produced when a voltage is
applied across electrodes.
[0003] 2. Description of the Prior Art
[0004] Polishing apparatuses having various configurations have
been proposed. A polishing apparatus generally has a polishing pad
holding abrasive particles that is affixed to a surface plate, and
effects polishing by moving one of the plate and the workpiece with
respect to the other. In recent years, progress has been made with
research into functional fluids that respond to an electrical field
or a magnetic field, and there are polishing apparatuses that
utilize such functional fluids.
[0005] In processing such as polishing and surface finishing, for
example, use has been made of magnetic fluids, which are fluids
containing a dispersion of angstrom-order magnetic particles. When
used on their own, such a fluid has almost no polishing effect, so
abrasive particles are added to the fluid for polishing
applications. The magnetism induced in the magnetic fluid by a
magnetic field causes the abrasive particles to be pressed against
the workpiece surface by the fluid. Although polishing using a
magnetic fluid is suitable when the workpiece to be polished has a
spherical or other such special shape, magnetic fluid polishing has
a number of problems. For example, magnetic fluid induction
produces a small processing pressure that results in a low
polishing efficiency. In addition, a magnetic substance prevents
the polishing process to suppress the effect of enhancing surace
roughness. Other problems include scratching caused by fragments of
removed material that become entrained in the magnetic fluid, and
the fact that in the case of a magnetic workpiece, movement of the
abrasive particles is constrained, making it impossible to achieve
the required polishing effect. Such problems have limited the
application of polishing using magnetic fluids.
[0006] Magnetically responsive (MR) fluids are fluids containing a
dispersion of iron powder or other such ferromagnetic particles
having micrometer-order sizes. When a magnetic field is applied to
such a fluid that also contains abrasive particles, it sets up a
strong interparticle attraction that causes the ferroparticles to
rapidly aggregate into thick magnetic column formations that can be
used to apply a powerful processing force to the workpiece surface,
ensuring a high processing efficiency. However, because it has been
considered difficult to control the shape, position and apparent
viscosity of the formations, it is thought that there is a high
risk that applying pressure to the formations will produce
scratching of the workpiece surface. Thus, it has been considered
that these MR fluids are usable for primary rough grinding but are
not readily usable for fine and finish polishing. The large size of
the iron particles generally used in the MR fluids has posed
another obstacle to their use for fine and finish polishing.
[0007] FIG. 12 shows an example of a prior art polishing apparatus.
This apparatus includes a rotary electrode 1 and a polishing pad 2
directly under the rotary electrode 1. The abrasive comprises
abrasive particles dispersed in silicon oil or a lubricant having
electrically insulating properties. Applying an alternating-current
voltage between a conductive specimen 3 and the rotary electrode 1
causes the abrasive particles to be alternatively attracted to, and
repelled by, the electrode. The electrode 1 is supported so that it
can be rotated in the direction indicated by arrow A by a drive
means (not shown).
[0008] FIG. 13 illustrates the effect of the prior art electrode.
The application of an electrical field causes the abrasive
particles 4 to cluster together into chain formations having a
perpendicular alignment with respect to the conductive specimen 3.
In this case, there is a mutual repulsion between adjacent
clusters, and in order to maintain a certain spacing, the
positioning of the abrasive particles can readily become uneven,
giving rise to non-uniformity in the surface roughness of the
polished surface.
[0009] With the polishing apparatus of the prior art thus
configured, the movement of the abrasive particles from the rotary
electrode 1 onto the conductive specimen 3, and the uneven
positioning of the abrasive particles, makes it difficult to
achieve a high-quality polished surface in the case of large
products. Moreover, having to apply a voltage between the rotary
electrode and a conductive workpiece makes it difficult to apply
the apparatus to insulating materials. That is, the thickness of a
workpiece having insulation properties has the same effect as an
air-gap, so a high polishing effect cannot be obtained without
using an electrical field strength that is high enough to control
the position of the abrasive particles, which means the work is
dangerous and there is a risk of the workpiece being damaged by an
electrical discharge.
[0010] Also, centrifugal force generated by the rotation of the
polishing part tends to cause the abrasive particles to accumulate
around the periphery of the polishing area, reducing polishing
efficiency. In response, prior art polishing apparatuses have
sought to achieve a uniform distribution of abrasive particles with
respect to the workpiece by again utilizing Coulomb force to return
the abrasive particles to the polishing area, using the fact that
the particles to which an electrical field has been applied have a
high dielectric constant. However, the aforementioned spacing
between adjacent clusters of abrasive particles has made it
impossible to achieve a highly uniform arrangement of the
particles.
[0011] An object of the present invention is therefore to provide a
polishing apparatus that can polish insulative materials and can
readily control the uniformity of the abrasive particle
arrangement.
SUMMARY OF THE INVENTION
[0012] To attain the above object, the present invention provides a
polishing apparatus, comprising an electrode comprised of a
plurality of electrode elements, a driving means for driving the
electrode, and abrasive particles having a dielectric property
disposed between the electrode and a workpiece at a position at
which processing pressure is applied by a Coulomb force produced by
application of an alternating-current voltage to the electrode.
That is to say, the present invention relates to an apparatus that
utilizes a Coulomb force to collect on a sample abrasive particles
while dispersing the abrasive particles onto te sample and applies
a processing pressure to the collected abrasive particles, thereby
performing the polishing process.
[0013] The electrode can be configured as a plurality of electrode
elements having different diameters that are disposed in a
concentric circular formation and mutually separated by insulative
material.
[0014] The electrode can be configured so that different voltages
are applied to the plurality of electrode elements. For example,
the voltage applied to the electrode elements gradually increases
going outwards from the center elements.
[0015] The electrode can be a cylindrical electrode comprised of a
film-shaped conductor and an insulative layer that are wound around
a spindle so that the conductor and insulative layer are alternated
around the spindle.
[0016] The apparatus can include electrode provision around an
insulative tube used to supply a fluid containing a dispersion of
abrasive particles to the workpiece, and application of a
low-frequency alternating-current electrical field having a
frequency of 0.1 to 10 Hz and an electrical field strength of 1.5
to 3 kV/mm.
[0017] Constituting the electrode as a plurality of electrode
elements having different diameters that are arranged in a
concentric circular formation and mutually separated by an
insulative material enables uniform polishing, unaffected by the
workpiece material or thickness. Also, by applying different
voltages to the plurality of electrode elements and adjusting the
thickness of the insulative material, it is possible to reduce
scattering of abrasive particles by the centrifugal force generated
by the rotation of the electrode. Moreover, applying a voltage that
increases going outward from the center elements helps to provide
uniform polishing. It is easy to manufacture the electrode
comprised of a film-shaped conductor and an insulative layer that
are wound around a spindle so that the conductor and insulative
layer are alternated around the spindle, and reducing the thickness
of the insulative material makes it possible to use a lower applied
voltage, thus providing an energy-saving effect.
[0018] Further features of the invention, its nature and various
advantages will be more apparent from the accompanying drawings and
following detailed description of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
[0019] FIG. 1 is a diagram of a rotary electrode according to a
first embodiment of the polishing apparatus of the present
invention.
[0020] FIG. 2 is a vertical sectional view of the principle parts
of the electrode of FIG. 1.
[0021] FIG. 3 is a bottom view of the electrode of FIG. 1.
[0022] FIG. 4 is a vertical sectional view of the principle parts
of a rotary electrode according to a second embodiment of the
invention.
[0023] FIG. 5 shows a layer structure used to form a rotary
electrode according to a third embodiment of the invention.
[0024] FIG. 6 illustrates the method of fabricating the rotary
electrode using the layer structure of FIG. 5.
[0025] FIG. 7 shows a polishing apparatus that uses the rotary
electrode of FIG. 6.
[0026] FIG. 8 shows an example of a machining head application of
the rotary electrode of the invention.
[0027] FIG. 9(a) is a perspective view of a rotary electrode
according to a fourth embodiment of the invention, and FIG. 9(b)
shows the electrode portion of the rotary electrode of FIG.
9(a).
[0028] FIG. 10 is a perspective view of the principle parts of a
fifth embodiment.
[0029] FIG. 11 illustrates an example of supplying an abrasive
fluid in the polishing apparatus of the invention.
[0030] FIG. 12 shows a prior art polishing apparatus electrode.
[0031] FIG. 13 illustrates the effect of the prior art polishing
electrode of FIG. 12.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0032] The invention is described below with reference to the
drawings. FIG. 1 shows a rotary electrode 11 of a polishing
apparatus 10 according to a first embodiment of the invention, FIG.
2 shows a vertical cross-section of the main parts of the
electrode, and FIG. 3 is a bottom view of the electrode. In the
polishing apparatus 10, the rotary electrode 11 is rotated by a
drive device (not shown), and a fluid comprising a lubricating oil
containing a dispersion of electrically insulative abrasive
particles 13 is dripped between the rotary electrode 11 and a
workpiece 12. Application of a processing pressure to the collected
abrasive particles enables effective polishing. By applying an
alternating-current voltage to the rotary electrode 11, a Coulomb
force is produced that is used to align the abrasive particles 13
into pearl chain formations between a polishing pad 17 and the
workpiece 12. It is desirable for the applied electrical field to
have a field strength of .+-.1 to 10 kV/mm and a frequency of 0.1
to 1000 Hz. When there is a large amount of polishing involved, it
is better to use a square waveform with a good rise, while in the
case of a small amount of polishing work, it is better to use a
sinusoidal waveform with a smooth rise that contains no noise
component.
[0033] The rotary electrode 11 is comprised of a support spindle
14, a backplate 15, a column-shaped electrode section 16, a
disk-shaped polishing pad 17, and so forth. The support spindle 14
is supported so that it can be rotated in the direction of arrow A
in FIG. 1 by a drive means (not shown). The backplate 15 is affixed
to the support spindle 14 and supports the electrode section 16.
The polishing pad 17 has substantially the same diameter as the
electrode section 16 and is impregnated or supplied with the
abrasive particles 13 dispersed in the low-viscosity lubricating
oil having an electrically insulative property. An
alternating-current voltage is applied to the rotary electrode 11
via a carbon feeder 18.
[0034] The electrode section 16 comprises a plurality of
concentric, cylindrical conductive electrode elements 16a (FIGS. 2
and 3), to each of which a different electrical field can be
applied. For example, a high electrical field is applied to the
peripheral portion where there is a strong centrifugal force at
work, and lower voltages are applied going towards the center. The
carbon feeder 18 comprises a carbon electrode 18a and a support
section 18b. In the electrode section 16, the conductive electrode
elements 16a are alternated with insulative members 16b.
[0035] As the fluid containing abrasive particles that impregnates
or is supplied to the polishing pad 17, there can be used kerosene
and silicone oil and other such electrically insulative fluids
having a kinetic viscosity in the order of 1 to 10000 mm.sup.2/s.
Single-crystalline or polycrystalline diamond, cerium oxide
(CeO.sub.2), alumina (Al.sub.2O.sub.3), lanthanum oxide
(La.sub.2O.sub.3), praseodymium oxide (Pr.sub.6O.sub.11), neodymium
oxide (Nd.sub.2O.sub.3), fluorides, calcium oxide, and cubic boron
nitride (CBN) can be used for the dispersion particles.
[0036] The operation and effect of the polishing apparatus using
the rotary electrode, according to the above-described
configuration of the invention, will now be explained. First, the
polishing pad 17 is impregnated with the abrasive particles
dispersed in the lubricating oil and an alternating-current voltage
is applied to the electrode section 16 provided with the
concentrically arranged electrode elements 16a. The voltages are
set so that higher voltages are applied to the peripheral electrode
elements 16a and lower voltages to the inner elements. The rotary
electrode 11 is rotated by a drive means that is not shown. To make
it easier to roll the abrasive particles, the workpiece 12 is
rotated in the opposite direction to the rotary electrode 11. The
rotary electrode 11 and workpiece 12 could instead be rotated in
the same direction at different speeds.
[0037] The rotary electrode 11 is pressed toward the workpiece 12
by the application of a constant pressure. When the workpiece 12 is
thus polished, there is no need to apply a voltage between the
rotary electrode 11 and the workpiece 12, so the workpiece 12 does
not have to be conductive. This makes it possible to polish even
ceramic or glass workpieces. For example, in 15 minutes the surface
roughness of glass (BK-7) was improved from 1.5 .mu.m Ry to 0.1
.mu.m Ry, using a processing load of 18 kgf, an applied electrical
field frequency of 0.8 Hz and an electrical field strength of 1.8
kV/mm.
[0038] FIG. 4 is a vertical sectional view of the main parts of a
rotary electrode according to a second embodiment of the invention.
In this case, the electrode section 16 comprises the electrode
elements 16a wound around the support spindle 14 in a stepped,
spiral arrangement, with insulative members 16b interposed between
the electrode elements 16a. An electric-field-applying carbon
feeder 18 in contact with the outer side of each of the electrode
elements 16a is used to apply a voltage. Taking the centrifugal
force of the rotary electrode 11 into consideration, the abrasive
particles can be uniformly positioned by adjusting the voltage
applied to each electrode element, making it possible to achieve an
evenly-polished surface. The abrasive particles 13 are aligned
parallel to the workpiece surface as shown in FIG. 2, and there is
no behavior that the abrasive particles 13 are projected from the
electrode and beat and roll on the workpiece between the electrodes
to enhance the polishing characteristics. As a result, it is
possible to achieve high-quality polished surfaces. Also, the
difference between the specific inductive capacities of the
polishing debris and of the abrasive particles gives rise to a
Coulomb force that makes it possible to separate and remove the
debris. Since an electrical field is not applied between the rotary
electrode 11 and the workpiece 12, there is no discharge damage to
the workpiece 12.
[0039] The above-described configuration enables the electrical
field strength to be increased at peripheral portions where there
is a strong centrifugal force. The ability to apply different field
voltages to each of the electrode elements 16a makes it possible to
achieve a uniformly polished surface. For example, voltages of 1
kV/mm, 2 kV/mm and 3 kV/mm can be applied to the innermost, middle
and outermost electrode elements 16a, respectively.
[0040] FIG. 5 shows a layer structure used to form the rotary
electrode in a third embodiment of the invention, and FIG. 6 shows
how the layer structure of FIG. 5 is used to manufacture the rotary
electrode. A rotary electrode 20 is formed by forming a conductor
20a on an insulative member 20b to form an internal electrode
element and winding the internal electrode of layered structure in
a spiral arrangement around a spindle 21 and holding the wound
layers in place by means of an electrode holder 23 that is an
external cylindrical electrode element of conductive material.
Vapor deposition, coating, adhesive or other such means can be used
to apply a conductive substance to an insulative film to form a
layered structure of the conductor 20a and the insulative member
20b. The polishing apparatus shown in FIG. 7 uses an electrode 20
thus fabricated.
[0041] The applied voltage can be kept down, ensuring safety, by
using a rotary electrode comprised, as shown in FIG. 6, by layers
of thin, film-shaped strips of the insulative member 20b and the
conductor 20a shown in FIG. 5 wound in a spiral. The operation and
effect of this embodiment thus configured will now be explained. To
start with, the rotary electrode 20 can be readily fabricated by
simply winding the electrode layers around the spindle 21. An
alternating-current voltage having a rectangular or sinusoidal
waveform is applied to the rotary electrode 20 having the
spirally-wound, film-shaped conductor 20a. The rotary electrode 20
is rotated by a drive means that is not shown. A rotary surface
plate 22 rotates the workpiece 12 in the opposite direction to the
rotary electrode 20.
[0042] In the case of this embodiment, the thickness of the
insulative member 20b can be reduced, which makes it possible to
keep the applied voltage down to the required level. In the case of
an insulative film that is 0.1 mm thick, for example, an applied
voltage of 200 to 300 volts can be used. The ability to use a lower
applied voltage makes a high-voltage apparatus unnecessary, and
also facilitates attachment to the head of machine tools such as
machining centers and general-purpose milling machines. Therefore,
electrical power consumption can be reduced. Thus, there is no need
for a special high-voltage power supply, which helps to simplify
the system configuration and reduce the cost. The lining up of the
abrasive particles parallel to the workpiece surface makes it
possible to achieve a high-quality polished surface even with fluid
compositions containing a low concentration of abrasive particles,
which helps to reduce costs and makes it unnecessary to use a
polishing pad.
[0043] FIG. 8 shows an example of the rotary electrode 20 of the
invention used on a machining head. The electrode 20 is affixed to
the head 32 of the machining center, enabling the workpiece 12 to
be polished on the rotary surface plate 22.
[0044] FIG. 9 shows an electrode according to a fourth embodiment
of the invention, that is used to polish a three-dimensional
workpiece making use of a Coulomb force attracting the abrasive
particles to to the electrodes, with FIG. 9(a) being a perspective
view of the electrode and FIG. 9(b) showing the electrode portion.
The electrode body 30 comprises a pliant, porous member and
electrode elements shaped like the teeth of a comb. As shown in
FIG. 9(b), the electrode elements 31a and 31b shaped like the teeth
of a comb are mutually opposed, with the teeth portions being
mutually offset with a prescribed spacing therebetween. An
alternating-current voltage is applied to the electrode elements
31a and 31b. Changes in the field polarity imparted by a
low-frequency alternating-current electrical field are used to
effect dressing by producing contact and collisions of the abrasive
particles, and are also effective for removing polishing debris and
preventing clumping of the abrasive particles. Sponge, foamed resin
and so forth can be used to form the pliant, porous member. The
apparatus thus configured was used to polish a workpiece having a
surface processed to a roughness of 10 .mu.m Ry by an electrical
discharge machine. Polishing for 30 minutes at a processing force
of 500 gf and an applied electrical field strength of .+-.2.0 kV/mm
resulted in a mirror-surface roughness of 0.2 .mu.m Ry.
[0045] FIG. 10 is a perspective view of the principal parts of a
fifth embodiment. Here, an electrode body 34 comprises a central
electrode body formed of a porous member 35 that has an electrode
member 34c inserted therein and is flanked at each end by electrode
elements 34a and 34b. When an alternating-current electrical field
is applied, the abrasive particles are disposed between a workpiece
36 and the electrode body 34. The workpiece 36 is processed by
applying a processing force to the workpiece 36 via the electrode
body 34 and effecting reciprocating movement of traveling surface
plates 40 and 41 along the X and Y axes, respectively, producing a
relative motion that rolls the abrasive particles. The plates 40
and 41 can also be moved horizontally at 0.1 to 30 Hz by means of a
linear motor or the like. The electrode body 34 and the traveling
surface plates move in sync at right-angles. For example, the plate
40 moves along the X axis in fine increments at 5 to 30 Hz and the
plate 41 moves along the Y axis in fine increments at 0.1 to 15
Hz.
[0046] Using the above configuration, an electrical field is
applied to the electrode elements 34a and 34b while applying a
processing pressure. The Coulomb force that is thus generated
causes the abrasive particles to accumulate on the processing
surface of the porous member 35, which sweeps back and forth along
the Y axis, flexing pliantly like a broom. This makes it easy to
roll the abrasive particles, making it possible to keep the
processing pressure low. This enables high-quality polishing
without changing the properties of the processed layer. Because the
porous member 35 can be pushed up at right-angles to the surface,
it is also possible to apply a uniform processing pressure to
curved surfaces. Also, the low processing pressure reduces
roll-over on angled portions.
[0047] FIG. 11 illustrates an embodiment that uses the polishing
apparatus of the invention to effectively form a good polished
surface. Parts that are the same have been given the same reference
numerals, and further description thereof is omitted. Via an
insulative tube 38, a fluid 39 comprising a dispersion of abrasive
particles in lubricating oil is supplied onto the top of the
workpiece 12. Electrodes 37a and 37b provided midway along the tube
38 are used to apply an alternating-current electrical field. This
increases the viscosity of the fluid flowing between the electrodes
37a and 37b, and therefore can be used to adjust the amount of the
fluid 39 that is supplied to the workpiece 12. The application of
the electrical field across the electrodes 37a and 37b also
prevents the abrasive particles from clumping together, thus
ensuring delivery of a stable dispersion fluid. As a result, a
high-quality polished surface can be achieved.
[0048] As described in the foregoing, in the polishing apparatus
using a rotary electrode according to the present invention, the
electrode is divided into a plurality of elements, which makes it
possible to effect polishing without regard to the shape, material
or, in particular, the thickness of the workpiece. When the unitary
type electrode of the prior art is used to polish an insulative
workpiece, the workpiece thickness acted as an air-gap,
necessitating the use of a high application voltage to accomplish
the polishing. Such an operation carried with it runs a high risk
of discharges and was unsafe. However, with the multi-element
electrode configuration used by this invention, the abrasive
particles contained in silicone oil, on the polishing pad are
aligned parallel with the surface being polished and moved in
accordance with the frequency of the applied voltage, making it
possible to also polish insulative materials.
[0049] Thus, the workpiece can be uniformly polished regardless of
the material. In particular, since a voltage is not applied to the
workpiece, both conductive and insulative workpieces can be
polished. For example, it is possible to polish insulative, brittle
materials such as ceramics and glass. Thus, the polishing apparatus
does not impose a restriction on the workpiece materials that can
be polished. The multi-element electrode produces fine and coarse
abrasive particle areas parallel to the surface being polished, in
accordance with the disposition of the electrode. In addition to
the dressing effect produced by the movement of the abrasive
particles in response to the frequency of the applied voltage,
polishing debris is discharged from the coarse areas. The uniform
disposition of the abrasive particles is facilitated by controlling
the voltages applied to the plurality of electrode elements,
thereby enabling control of the surface roughness.
* * * * *