JPH0569295A - Both sides grinding method using electrolytic dressing and its device - Google Patents

Abstract

PURPOSE:To provide a both-side grinding method using electrolytic dressing and its device by applying the Elid grinding method to the both-side grinding. CONSTITUTION:A both sides grinding device is provided with a first gear 10 to hold a workpiece 2 in a penetrated hole, a second gears 12, 14 which are engaged with the first gear and drive the first gear, a lower side grinding wheel 16 and an upper side grinding wheel 18 which hold the workpiece and are located opposite to each other, a liquid supplying means to supply the conductive liquid into the space between the first gear and the lower side grinding wheel and the space between the first gear and the upper grinding wheel, and a power supplying means to supply the current to the space between the first gear and the lower side grinding wheel and the space between the first gear and the upper grinding wheel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the field of grinding and polishing using electrolytic dressing, and more particularly to a method and apparatus for double-sided grinding using electrolytic dressing.

[0002]

2. Description of the Related Art A conductive grindstone such as a cast iron fiber bonded diamond grindstone is used, and an electrolytic dressing method and apparatus for a conductive grindstone in which a voltage is applied to the grindstone and the grindstone is electrolytically dressed by the same applicant as the present application. Kohei
It has been disclosed in Japanese Patent Application No. 1-188266 (Japanese Patent Application No. 63-12305) and has succeeded in mirror-finishing a semiconductor material such as silicon which is an electronic material. In addition, an electrolytic in-process dressing grinding method (Electrolytic Inproc
ess Dressing: A method and a device called “Elid grinding method” have been developed and announced by the applicant of the present application (RIKEN Symbodium “Latest Technology Trend of Mirror Grinding”, held on March 5, 1991).

In this Elid grinding method, a grindstone having a contact surface with a work, an electrode facing the contact surface, a nozzle for flowing a conductive liquid between the grindstone and the electrode, and a voltage applied between the grindstone and the electrode. A device comprising a power source and a power feeding body for applying a voltage. A voltage is applied between the grindstone and the electrode while the conductive liquid is flowing between the grindstone and the electrode, and the grindstone is dressed electrolytically.

The dressing mechanism by this Elid grinding method is shown in FIG. At the start of grinding of the grindstone (A), the electric resistance between the grindstone and the electrode is small and a relatively large current (5
10A) flows. Thereby, the metal portion (bond) on the surface of the grindstone is dissolved by the electrolytic effect, and the non-conductive diamond abrasive grains are projected. Further, if the power is continued, iron oxide (F
An insulating film mainly composed of e ₂ O ₃ ) is formed on the surface of the grindstone, increasing the electric resistance of the grindstone. This reduces the current,
The dissolution of the bond is reduced, and the protrusion of abrasive grains (grinding of the grindstone) is substantially completed (B). When grinding is started in this state (C), the coating particles release grinding dust, and the diamond abrasive grains wear away as the work is ground. When the grinding is further continued (D), the insulating coating on the surface of the grindstone is removed by abrasion, the electric resistance of the grindstone is lowered, the current between the grindstone and the electrode is increased, the dissolution of the bond is increased, and the protrusion of the abrasive grains (grinding stone Is reopened. Therefore, during grinding by the Elid grinding method, excessive elution of the bond is suppressed by forming / removing the coating as shown in (B) to (D), and the protrusion of the abrasive grains (sharpening of the grindstone) is automatically adjusted. It The above-described cycles shown in (B) to (D) are hereinafter referred to as Elid cycles.

According to the above-mentioned Elid grinding method, since the dressing of the grindstone is performed during the grinding process, the dressing does not interrupt the process and the grindstone does not become clogged. Therefore, compared with the conventional polishing, it was possible to perform high-load grinding by one digit or more, and it was possible to perform mirror finishing with a small surface roughness. However, the Elid mentioned above
Conventionally, the grinding method has been applied only to single-sided processing and not to double-sided processing.

On the other hand, a double-sided polishing apparatus is conventionally known which holds a work on a planetary gear and holds the work between upper and lower grindstones. In such a double-sided polishing machine, although double-sided processing is possible, dressing of the grindstone requires interrupting the polishing operation, so it is necessary to interrupt the processing if the abrasive grains are made fine to improve the surface roughness. The efficiency of the polishing work was poor.

Therefore, there has conventionally been a demand for applying the above-mentioned Elid grinding method to double-sided grinding.

[0008]

However, there are the following problems in applying the Elid grinding method to the above-mentioned double-sided polishing apparatus. (1) It is necessary to hold the planetary gears at a constant distance from the upper and lower grindstones and insulate them.

When an insulating plate is bonded to the surface of the planetary gear to satisfy the demand, the gap is changed by the rapid abrasion of the insulating plate and the supply of the conductive liquid becomes non-uniform. (2) It is necessary to pass an electric current between the planetary gear and the upper and lower grindstones. In order to satisfy such a demand, if the entire planetary gear is made of a conductive material and the power is supplied to the planetary gear through the teeth of the planetary gear, the area through which the current flows becomes too large and the power source becomes large and the gear The intermittent current flow through the tooth causes sparking, prematurely damaging the tooth. (3) It is necessary to uniformly supply the conductive liquid between the planetary gear and the upper and lower grindstones.

In order to satisfy such a demand, in order to constantly fill the space between the planetary gear and the upper and lower grindstones with a conductive liquid, that is, a coolant, it is necessary to provide a liquid tank and immerse the planetary gear therein, which complicates the apparatus. .. Further, the coolant stored in such a liquid tank is liable to rise in liquid temperature due to heat generated by electrolysis, whereby the non-conductive coating formed on the grindstone surface is easily peeled off and the sealant is apt to deteriorate. Further, polishing debris and diamond abrasive grains that have worn away and fallen off are likely to accumulate in the liquid tank and cause scratches.

Therefore, an object of the present invention is to solve the above-mentioned problems, to apply the Elid grinding method to double-sided grinding, and to provide a double-sided grinding method and apparatus using electrolytic dressing.

[0012]

In order to solve the above-mentioned problems, according to the present invention, a second gear that holds a work in a through hole provided in the first gear and meshes with the first gear is provided. The first gear is driven by rotation, the work is sandwiched by a lower grindstone and an upper grindstone facing each other, and a conductive liquid is supplied between the first gear and the lower grindstone and the upper grindstone, respectively. An electric current is supplied between the second gear and each of the lower grindstone and the upper grindstone, whereby both sides of the work are ground while electrolytically dressing the facing surfaces of the lower grindstone and the upper grindstone. A double-sided grinding method using electrolytic dressing is provided.

The first gear is a planetary gear and the second gear is
The gears are preferably sun gears and internal gears arranged concentrically to each other. Further, according to the present invention, the first gear that holds the work in the through hole, the second gear that meshes with the first gear and drives the first gear, and the work that sandwiches the work face each other. Lower grindstone and upper grindstone to
A liquid supply means for supplying a conductive liquid between the gear and the lower grindstone and the upper grindstone, and a power supply means for supplying a current between the first gear and the lower grindstone and the upper grindstone, respectively. Thus, a double-sided grinding device using electrolytic dressing is provided, in which both surfaces of a work are ground while electrolytically dressing the facing surfaces of the lower grindstone and the upper grindstone.

The first gear is a planetary gear and the second gear is
The gears are preferably sun gears and internal gears arranged concentrically to each other. Further, the sun gear is clamped by a disk portion larger than the pitch circle, the internal gear is clamped by a ring portion having an opening smaller than the pitch circle, and the planetary gear is thinner than a work and its tooth tips are the aforesaid. It is preferable that it is sandwiched by both the disk portion and the ring portion, so that a constant gap is maintained between the planetary gear and the lower grindstone and the upper grindstone.

Further, it is preferable that the power feeding means has a power feeding plate fixed to the sun gear and contacting the planetary gear. Further, it is preferable that an electrode for electrolytic dressing which is long in the radial direction and is thinner than the work and thicker than the planetary gear is embedded in the planetary gear. Further, it is preferable that the liquid supply means has a circumferential groove provided on the inner surface of the ring portion, and a plurality of radial grooves communicating from the circumferential groove to the tip of the internal gear.

Further, it is preferable that the double-sided grinding apparatus further comprises adjusting means for relatively adjusting the vertical positions of the sun gear, the internal gear and the lower grindstone.

[0017]

According to the method and apparatus of the present invention described above, the first
A conductive liquid is respectively supplied between the gear and the lower grindstone and the upper grindstone, and an electric current is respectively supplied between the first gear and the lower grindstone and the upper grindstone via the conductive liquid, whereby, The facing processing surfaces of the lower grindstone and the upper grindstone are electrolytically dressed. Therefore, both sides of the work can be ground while electrolytically dressing both the lower grindstone and the upper grindstone by the Elid grinding method. Therefore, since the dressing of the grindstone is performed during the grinding process, the dressing does not interrupt the process and the clogging of the grindstone does not occur. As a result, compared with the conventional double-sided polishing, it is possible to perform high-load grinding by one digit or more, and it is possible to perform mirror-finishing with a small surface roughness.

Further, when the first gear is a planetary gear and the second gear is a sun gear and an internal gear arranged concentrically with each other, an insulator or the like is interposed between the lower and upper grindstones. Since a constant gap is maintained on the upper and lower surfaces of the planetary gear without causing such a change, there is no risk of a change in the gap due to wear, and the conductive liquid can be smoothly flown into this gap.

Further, by providing the power feeding plate which is in contact with the planetary gear, the power feeding to the planetary gear can be performed without interruption. Further, the electrode for electrolytic dressing which is long in the radial direction and is thinner than the work and thicker than the planetary gear is embedded in the planetary gear, whereby the current density for electrolytically dressing can be maintained at a high density.

Further, by flowing the conductive liquid through the groove provided on the inner surface of the ring portion, the conductive liquid can be uniformly supplied to the gap between the upper and lower surfaces of the planetary gear, and the whole planetary gear is submerged in the conductive liquid. No need.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a plan view of a double-sided grinding machine using electrolytic dressing according to the present invention, in which the upper grindstone is omitted for clarity. In addition, FIG.
It is sectional drawing in line AA of FIG.

The double-sided grinding machine according to the present invention comprises a planetary gear 1
0, and a sun gear 12 and an internal gear 14 that mesh with the planetary gear 10 and are arranged concentrically with each other around a vertical axis 1.
A lower grindstone 16 and an upper grindstone 18 facing each other are provided. The sun gear 12 is connected to a drive shaft 20 via a sun gear support plate 13, and the drive shaft 20 is configured to rotate about a shaft center 1 by a drive device (not shown).
Further, the internal gear 14 is connected to the main body 22 via the internal gear support plate 15.
The main body 22 is fixed to a base (not shown). The main body 22 has a recess 22a for accommodating the lower grindstone 16 on the upper surface, and the lower grindstone 16 having a central opening 16a is placed in the recess 22a via an appropriate insulating support material 24.

A planetary gear 10 is arranged on the upper surface of the lower grindstone 16, a through hole 10a is provided in the planetary gear 10, and a substantially rectangular parallelepiped workpiece 2 is held in the through hole 10a. The shape of the through hole 10a is substantially the same as the outer shape of the work 2 so that the work 2 can slide in the vertical direction without resistance. The number of the through holes 10a may be only one for each planetary gear 10 or may be plural. On the upper part of the planetary gear 10, an upper grindstone 18 having a central opening 18a is placed,
The work 2 is held between the lower grindstone 16 and the upper grindstone 18. It is preferable that the lower grindstone 16 and the upper grindstone 18 are conductive grindstones containing abrasive grains on at least opposing surfaces, and preferably cast iron fiber bond diamond grindstones.
The lower grindstone 16 and the upper grindstone 18 may have the same grindstone grain size or different grain sizes.

When the drive shaft 20 is rotated by the above-mentioned structure, the planetary gear 10 rotates while the sun gear 12 rotates.
Revolve around. Since the weight of the upper grindstone 18 acts on the work 2, the work 2 is ground by the lower grindstone 16 and the upper grindstone 18 while repeating the planetary motion. Unlike the above-described configuration, for example, the sun gear 12 may be fixed and the internal gear 14 may be driven, or the planetary gear may be driven via a known carrier, or the lower grinding wheel 16 and / or the upper grinding wheel. 18 may be driven. Further, a well-known pressing device for pressing the upper grindstone 18 downward, for example, a pressure cylinder, a jack, or the like may be provided so that the pressing pressure can be adjusted.

The sun gear 10 has a disk portion larger than its pitch circle, that is, the sun gear support plate 13 and the sun gear fixing plate 2.
It is sandwiched between 1. Further, the internal gear 14 is sandwiched by a ring portion having an opening smaller than the pitch circle, that is, the internal gear support plate 15 and the internal gear fixing plate 23. Planetary gear 1
0 is thinner than the thickness of the work 2, and the tooth tips of the planetary gear 10 are clamped by both the disk portion and the ring portion, whereby the planetary gear 10 and the lower grinding wheel 16 and the upper grinding wheel 18 are respectively separated. A constant gap is maintained.

Between the sun gear support plate 13 and the drive shaft 20,
Between the inner gear support plate 15 and the main body 22, means for adjusting the vertical position, that is, the spacer 25 is provided.
By inserting a and 25b and adjusting the thickness, the vertical position of the sun gear and the internal gear can be adjusted. A drive device for moving the lower grindstone 16 up and down may be provided without using the spacer.

Further, between the planetary gear 10 and the lower grindstone 16 and the upper grindstone 18, there are provided liquid supply means for respectively supplying a weakly conductive cutting liquid, that is, a coolant. As shown in FIG. 2, the liquid supply means includes circumferential grooves 15b and 23b provided on the inner surface of the ring portion, that is, the internal gear support plate 15 and the internal gear fixing plate 23, and the circumferential groove 15b.
b, 23b to the tooth tips of the internal gear 14 and a plurality of radial grooves 15c, 23c. Radial groove 15c,
Reference numeral 23c has a shape such that the tooth tips of the planetary gear 10 do not interfere with each other, and serves as a coolant ejection port. Also,
The internal gear 14 is provided with a plurality of through holes 14a so that the circumferential grooves 15b and 23b communicate with each other. Further, the internal gear fixing plate 23 has a supply port 23a for supplying the coolant to the circumferential groove 23b.

With the above-described structure, by flowing the coolant through the supply port 23a, the coolant flows through the donut-shaped circumferential grooves 15b and 23b shown by the broken line in FIG. 23 c and is jetted out uniformly in the gap between the upper and lower surfaces of the planetary gear 10.
The coolant is supplied from the respective jet outlets to the gap between the upper and lower surfaces of the planetary gear 10, and then stored in the coolant tank 30 through the opening 22b provided in the lower portion of the recess 22a of the main body 22 to collect chips and abrasive grains. The debris and the like are removed, and the circulation pump 32 supplies the supply again to the supply port 23a. Such a coolant circulation system is liquid-tightly configured by a known means such as an O-ring and packing.

Further, power supply means for supplying a current between the planetary gear 10 and the lower grindstone 16 and the upper grindstone 18 is provided. This power feeding means is a means known to the sun gear 12,
For example, the power supply plate 26 is fixed by bolting and contacts the planetary gear 10. The power supply plate 26 is a substantially circular phosphor bronze conductive metal plate, the outer peripheral portion of which is divided into a plurality of arc portions by radial slits, and each arc portion is bent so as to contact the planetary gear 10. There is. Therefore, due to the elasticity of the arc portion, the power supply plate 26 is always in contact with the peripheral portion of the planetary gear 10. It is preferable that the power supply plate 26 directly contacts an electrode provided on a planetary gear described later, but the present invention is not limited to this. Further, the power feeding plate 26 may have a configuration different from the above configuration, for example, a perfect disc or a cup shape without slits, and may be biased downward by a spring or the like.

The power feeding means is further provided with a power source 28, which applies a + voltage to the lower grinding wheel 16 and the upper grinding wheel 18 to supply the power feeding plate 2
A negative voltage can be applied to the planetary gear 10 via 6. The power source 28 may be a pulse power source or a power source in which pulse and DC are mixed. The power supply 28 and the upper grindstone 18 are directly connected by an appropriate electric wire, and the power supply 28 and the lower grindstone 16 are connected via an appropriate current introduction terminal 29 provided in the main body 22. As illustrated, the lower grindstone 16 and the upper grindstone 18 are the planetary gears 1
0, the main body 22, the drive shaft 20, and the like, and the lower grindstone 16 is insulated from the main body 22 by an insulating support material 24. The power supply plate 26 is slidably connected to a power source 28 via a brush 27.

With the above-described structure, a positive voltage can be applied to the lower grinding wheel 16 and the upper grinding wheel 18 and a negative voltage can be applied to the planetary gear 10 via the power feeding plate 26 without the occurrence of sparks or the like. .. FIG. 3 shows the planetary gear part in detail. As can be seen from FIGS. 1 and 3, in the planetary gear 10, an electrode 34 for electrolytic dressing, which is long in the radial direction, thinner than the work 2, and thicker than the planetary gear 10, is embedded similarly to the work 2. The electrode 34 is made of a material having higher electric conductivity than the planetary gear 10, for example, copper, is fitted in the through hole 10b provided in the planetary gear 10, and is soldered or brazed to the planetary gear 10. It is joined. The area of the electrode 34 is determined so that an appropriate current density is generated between the lower grindstone 16 and the upper grindstone 18. Further, the shape of the electrode 34 is preferably trapezoidal or fan-shaped which spreads outward from the center of the planetary gear. As a result, the degree of concentration of current density, the size of the electrode area, etc. are configured in a well-balanced manner, the thickness of the insulating film formed on the grindstone surface is maintained at an appropriate level, and the protrusion of diamond abrasive grains is evenly distributed over the front surface of the grindstone. Can be secured. Further, when the grain sizes of the upper and lower grindstones are different, the electrode areas may be different between the upper and lower sides. Furthermore, without using the electrode 34, the entire planetary gear 10 may be made of a suitable electrically conductive material, or the electrode 34 may be bonded to both surfaces of the planetary gear 10.

4 and 5 show a second embodiment according to the present invention. In this figure, parts common to those in FIGS. 1 to 3 are indicated by the same numbers. FIG. 4 is a plan view of the second embodiment, in which the silicon wafer, that is, the work 2 is formed in the through hole 10.
A first spur gear 10 held in a is shown. The first spur gear 10 is rotatably mounted around a shaft 40 passing through its center and is rotated by a second spur gear 42 meshing with the shaft 40. 1st spur gear 1
Electrode 34 is attached to 0 as described above.

FIG. 5 is a side sectional view of FIG. In this figure, the lower grindstones 16 that sandwich the workpiece 2 and face each other
And the upper grindstone 18 has a spacer 25b on the top of the main body 22.
Is laid horizontally through. A liquid tank for accumulating the coolant is provided in the main body 22, and the coolant is supplied to the first spur gear 10 through an opening hole 40a and an ejection port 40b provided in the shaft 40 by a pump 32 provided in the main body. A conductive liquid is supplied between the lower grindstone 16 and the upper grindstone 18.

Further, the main body 2 is provided around the first spur gear 10.
The ring 14 'is sandwiched by the ring fixing plate 23' on the upper part of the spacer 2 via the spacer 25b. The ring 14 'is a C-shaped annular plate with the second spur gear 42 side cut out,
The plate thickness is thicker than that of the second spur gear 42. Above the ring fixing plate 23 ', a power feeding plate 26 similar to that of the first embodiment is provided.
Is fixed, and a − voltage can be applied to the first spur gear 10 via the power supply plate 26, and a + voltage can be applied to the lower grindstone 16 and the upper grindstone 18 as in the first embodiment. Thus, the power supply means is provided.

With the above structure, it is possible to perform double-sided grinding with a simple structure without using a planetary gear mechanism. The drive system is not limited to the gears described above, and a pulley, a friction wheel, or the like may be used. Example 1 Double-sided grinding according to the present invention was tested using the experimental equipment and conditions shown in Table 1. Here, the size of the planetary gear is the outer diameter 1
The size of the electrode is 44 mm and the thickness is 5 mm.
mm, upper side 3.5 mm, lower side 8.5 mm trapezoid,
The thickness was 5.5 mm. Zirconia is used as the work, and its dimensions are 9 mm in length, 30 mm in width, and 6 m in height.
It was m. The test results are shown in FIG.

[0036]

[Table 1]

FIG. 6 is a diagram showing the machinability of zirconia with a cobalt bond grindstone by the Elid grinding method. The machinability changes (circle) according to the present invention and the machinability changes when Elid grinding is not used (● (Indicated by a mark). When Elid grinding is not used, that is, when electrolysis is not applied, the grindability of the grindstone surface causes the machinability to drop in about 10 minutes, and the machinability sharply deteriorates. On the other hand, Elid
In the case of the present invention using grinding, it can be seen that the machinability does not decrease over time, the machinability becomes almost constant, and good grinding is maintained.

The machinability is higher in the case where Elid grinding is not used than in the case of the present invention, but this is because the test conditions, that is, the initial setting condition of the grindstone, etc. are different. It was due to. Further, as is clear from the figure, the machinability corresponds to about 1 μm / min or more, that is, 10 μm in 10 minutes, for example, and a result higher by one digit or more than that obtained by ordinary polishing was obtained. The surface roughness obtained was a good mirror surface with Rmax of 0.08 μm on both surfaces.

In the conventional Elid grinding method, a weakly conductive coolant is used, but in the present invention, a coolant having a high degree of electrolysis can be used. This is because the decrease in the electrolytic current value did not appear so large that the insulating coating being processed was formed relatively thin. That is, since the grindstone used in the present invention has a large diameter unlike a normal narrow grindstone, and the electrolysis is uniformly applied to a wide area, and the electrolytic dressing is performed while always applying a load between the upper and lower grindstones and the work. ,
This is because an insulating coating having an appropriate thickness is formed and maintained.

[0040]

According to the above-described method and apparatus of the present invention, the conductive liquid is supplied between the first gear and the lower grindstone and the upper grindstone, respectively. Electric currents are respectively supplied between the lower grindstone and the upper grindstone, so that the facing processing surfaces of the lower grindstone and the upper grindstone are electrolytically dressed. Therefore, both sides of the work can be ground while electrolytically dressing both the lower grindstone and the upper grindstone by the Elid grinding method. Therefore,
Since the dressing of the grindstone is performed during the grinding process, the dressing does not interrupt the process and the grindstone is not clogged. As a result, compared with the conventional double-sided polishing, it is possible to perform high-load grinding by one digit or more, and it is possible to perform mirror-finishing with a small surface roughness.

Further, when the first gear is a planetary gear and the second gear is a sun gear and an internal gear arranged concentrically with each other, an insulator or the like is interposed between the lower and upper grindstones. Since a constant gap is maintained on the upper and lower surfaces of the planetary gear without causing such a change, there is no risk of a change in the gap due to wear, and the conductive liquid can be smoothly flown into this gap.

Further, by providing the power feeding plate which is in contact with the planetary gear, it is possible to feed power to the planetary gear without interruption. Further, the electrode for electrolytic dressing which is long in the radial direction and is thinner than the work and thicker than the planetary gear is embedded in the planetary gear, whereby the current density for electrolytically dressing can be maintained at a high density.

Further, by flowing the conductive liquid through the groove provided on the inner surface of the ring portion, the conductive liquid can be uniformly supplied to the gap between the upper and lower surfaces of the planetary gear, and the whole planetary gear is submerged in the conductive liquid. No need. Therefore, the Elid grinding method can be applied to double-sided grinding to provide a double-sided grinding method and apparatus using electrolytic dressing.

Although the present invention has been mainly described with respect to a rectangular parallelepiped shape work, it is obvious that the present invention can be applied to double-sided grinding of a circular work, especially a silicon wafer.

[Brief description of drawings]

FIG. 1 is a plan view of a double-sided grinding device according to the present invention.

2 is a cross-sectional view taken along the line AA in FIG.

FIG. 3 is a detailed view showing a portion of a planetary gear.

FIG. 4 is a plan view of a second double-sided grinding device according to the present invention.

5 is a side sectional view of FIG.

FIG. 6 is a diagram showing test results according to the present invention.

FIG. 7 is an explanatory diagram showing an Elid cycle in an Elid grinding method.

[Explanation of symbols]

 2 Work 10 Planetary Gear 12 Sun Gear 14 Internal Gear 16 Lower Grinding Stone 18 Upper Grinding Stone 20 Drive Shaft 22 Main Body 24 Insulation Supporting Material 26 Power Supply Plate 27 Brush 28 Power Supply 34 Electrode

Claims (9)

[Claims] 1. A work is held in a through hole provided in a first gear, and the first gear is driven by the rotation of a second gear meshing with the first gear so that the works face each other. It is sandwiched between a lower grindstone and an upper grindstone, a conductive liquid is supplied between the first gear and the lower grindstone and the upper grindstone, and an electric current is applied between the second gear and the lower grindstone and the upper grindstone. A double-sided grinding method using electrolytic dressing, characterized in that both sides of the work are ground while electrolytically dressing the facing surfaces of the lower grindstone and the upper grindstone. 2. The method according to claim 1, wherein the first gear is a planetary gear and the second gear is a sun gear and an internal gear arranged concentrically with each other. 3. A first gear that holds a work in a through hole, a second gear that meshes with the first gear and drives the first gear, and a lower side that sandwiches the work and faces each other. A grindstone and an upper grindstone, a liquid supply unit that respectively supplies a conductive liquid between the first gear and the lower grindstone and the upper grindstone, and an electric current is supplied between the first gear, the lower grindstone, and the upper grindstone. A double-sided grinding machine using electrolytic dressing, characterized in that it is configured to supply power to each of them, and grinds both sides of the work while electrolytically dressing the facing surfaces of the lower grindstone and the upper grindstone. 4. The apparatus according to claim 3, wherein the first gear is a planetary gear, and the second gear is a sun gear and an internal gear arranged concentrically with each other. 5. The sun gear is clamped by a disc portion larger than its pitch circle, the internal gear is clamped by a ring portion having an opening smaller than its pitch circle, and the planetary gear is thinner than a workpiece. 5. The tip is clamped by both the disc portion and the ring portion, whereby a constant gap is maintained between the planetary gear and the lower grindstone and the upper grindstone, respectively. The device according to. 6. The apparatus according to claim 5, wherein the power feeding means has a power feeding plate fixed to the sun gear and in contact with the planetary gear. 7. The apparatus according to claim 6, wherein an electrode for electrolytic dressing, which is long in the radial direction and is thinner than the work and thicker than the planet gear, is embedded in the planetary gear. 8. The liquid supply means has a circumferential groove provided on the inner surface of the ring portion, and a plurality of radial grooves communicating from the circumferential groove to the addendum of the internal gear. The device according to claim 7, characterized in that 9. The apparatus according to claim 8, wherein the double-sided grinding apparatus further comprises adjusting means for relatively adjusting the vertical positions of the sun gear, the internal gear, and the lower grindstone.