GRINDING DEVICE USING ULTRASONIC VIBRATION

Abstract

A grinding device (30) for grinding an object (31) at high accuracy has a support table (32) on which the object (31) is supported and fixed, a vertically movable rotating shaft (34) arranged above the support table, a drive device (35) for vertically moving the rotating shaft, a drive device (36) for rotating the rotating shaft, an elastic body (37) fixed to a base section of the rotating shaft, an annular grind stone (38) provided to a bottom of the elastic body, ultrasonic vibrators (39) arranged on the elastic body, and a transmission unit (41) for transmitting electric energy to the ultrasonic vibrators, in which the elastic body is an annular elastic body and a connection plate (42) is provided between the annular elastic body and the base section of the rotating shaft under such condition that the connection plate and the annular elastic body are connected by connection means (45) having alternately arranged connection sections and space sections and each ultrasonic vibrator is arranged at a predetermined position of the elastic body.

Description

FIELD OF THE INVENTION

This invention relates to a grinding machine utilizing ultrasonic vibration which is employable for grinding a surface of an object such as glass body or silicon body to give a smoothened surface.

BACKGROUND OF THE INVENTION

Heretofore, various substrates such as a glass substrate, a silicon substrate and a silicon nitride substrate are employed for manufacturing thin film electronic devices. These substrates are ground on their surfaces using a grinding machine to give smoothened surfaces. In addition, optical devices such as a lens and a prism can be ground to give smoothened surfaces. It is known that a grinding machine utilizing ultrasonic vibration is employable for grinding these objects on their surface to give smoothened surface or to adjust the thickness of the object by repeated grinding procedures.

FIG. 1 is a front view of a conventional grinding machine illustrated in Japanese Patent Provisional Publication 5-200,659. FIG. 2 is a sectional view of the grinding machine of FIG. 1 which is taken along the I-I line. In FIG. 2, an object 11 to be ground, a support table 12, and a pipe 21 for supply of a grinding liquid are not shown.

In FIGS. 1 and 2, the grinding machine 10 is composed of a rotatable support disc table (work-fixing table) 12 on which an object 11 to be ground is supported and fixed, a grinding shaft 14 arranged above the support table 12, the grinding shaft 14 being vertically and horizontally movable, an elastic body 17 fixed to a base portion of the grinding shaft 14, an annular grind stone 18 provided to the bottom surface of the elastic body, and a pair of laminated piezoelectric actuators 19 placed on a top surface of the elastic body 17. Although the Provisional Publication describes other embodiments, the laminated piezoelectric actuators are placed on a top surface of the elastic body 17 in all embodiments.

The grinding machine 10 is operated as follows. First, the object 11 is fixed onto the support table 12. Subsequently, ultrasonic vibration generated by each laminated piezoelectric actuator 19 is applied to the grind stone 18 via the elastic body 17, so that the object 11 is ground.

The Provisional Publication describes that since the grinding machine 10 employs a laminated piezoelectric actuator 19 (or Langevin vibrator) which can produce an in-plane vibration of standing wave on the grinding surface (bottom surface) of the grind stone 18 or an elliptical vibration perpendicular to the grinding surface, the grind stone 18 can vibrate with a large amplitude and hence the object 11 can be ground with high accuracy in a short period.

The grinding machine can grind an object with high accuracy in a short period. It has been found by the present inventor, however, that a portion of ultrasonic vibration generated by the laminated piezoelectric actuator of the above-mentioned grinding machine is apt to escape into the grinding shaft through the elastic body and hence that a sufficiently large ultrasonic vibration cannot be transmitted to the grind stone. If the ultrasonic vibration transmitted to the grind stone is not sufficiently large, frictional resistance between the grind stone and the object to be ground increases and hence inappropriate mechanical vibration is generated when these are brought into rubbing contact, to decrease the grind accuracy (i.e., the object having been ground has a rough surface).

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a grinding machine utilizing ultrasonic vibration, which can grind an object with high accuracy.

As a result of studies by the inventor, it has been discovered that when the annular elastic body having a grind stone on the bottom surface is connected to a base portion of the rotating shaft for rotating the grind stone with a connection plate having a connection means comprising alternately formed connection sections and space sections on a bottom surface thereof, portions of the elastic body between the adjoining connection sections show larger ultrasonic vibration than portions in the vicinity of the connection sections. It has been further discovered that if a ultrasonic vibrator is placed on the former portions to generate ultrasonic vibration, the ultrasonic vibration hardly escapes to the rotating shaft and hence most of the ultrasonic vibration are transmitted to the grind stone through the annular elastic body to increase grind accuracy.

Accordingly, the present invention resides in a grinding machine comprising a support table on which an object to be ground is supported and fixed, a vertically movable rotating shaft arranged above the support table, a drive device for vertically moving the rotating shaft, a drive device for rotating the rotating shaft, an elastic body fixed to a base section of the rotating shaft, an annular grind stone provided to a bottom of the elastic body, ultrasonic vibrators arranged on the elastic body, and a transmission unit for transmitting electric energy to the ultrasonic vibrators, wherein

the elastic body is an annular elastic body, a connection plate having connection means comprising alternately formed connection sections and space sections on a bottom surface thereof is provided between the annular elastic body and the base section of the rotating shaft under the condition that the connection sections are bonded to a top surface of the annular elastic body, and the ultrasonic vibrators are placed on the top surface of the annular elastic body in an area facing the space sections or on an inner or outer side surface of the annular elastic body in a area adjacent to the area facing the space sections, or

the elastic body is an annular elastic body, a connection plate having connection means comprising alternately formed connection sections and space sections on an outer side surface thereof is provided between the annular elastic body and the base section of the rotating shaft under the condition that the connection sections are bonded to an inner side surface of the annular elastic body, and the ultrasonic vibrators are placed on the inner side surface of the annular elastic body in an area facing the space sections or on a top surface or an outer side surface of the annular elastic body in a area adjacent to the area facing the space sections.

Preferred embodiments of the present invention are set forth below.

(1) The connection plate and connection sections are made of elastic material.

(2) The connection plate and connection sections are made of elastic material, and the connection plate, connection sections and annular elastic body are formed as a single unit.

(3) A ratio of a length of the connection section and a length of the space section is in the range of 1:1 to 1:20, the length being determined along a periphery of the connection plate.

(4) The transmission unit for transmitting electric energy to the ultrasonic vibrators is a rotary transformer.

(5) The connection sections are arranged symmetrically around the rotating shaft and the space sections of the connection means are arranged symmetrically around the rotating shaft.

(6) The ultrasonic vibrators are arranged symmetrically around the rotating shaft.

(7) The support table is rotatable, and the rotatable support table is equipped with a drive unit driving the support table.

The grinding machine of the invention has a connection plate between an annular elastic body having a grind stone on its bottom surface and a base portion of a rotating shaft for rotating the grind stone, under such condition that the annular elastic body is connected to the connection plate through connection means comprising alternately formed connection sections and space sections. Ultrasonic vibrations generated by a plurality of ultrasonic vibrators placed on the annular elastic body at the predetermined positions hardly escape into the rotating shaft through the connection sections (and connection plate) and a most portion of the ultrasonic vibrations are transmitted to the grind stone through the annular elastic body because the elastic body vibrates with a larger amplitude in areas facing the space sections than in areas connected to the connection sections. Therefore, the grinding machine of the invention can grind an object with high accuracy.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a front view of a grinding machine according to prior art.

FIG. 2 is a sectional view of the grinding machine 10, taken along the line I-I shown in FIG. 1, in which the object 11 to be ground, support table 12 and pipe 21 for supply an abrasive liquid are not shown.

FIG. 3 is a front view of a grinding machine according to the invention.

FIG. 4 is an enlarged view illustrating the grinding tool 40 of the grinding machine 30 of FIG. 3 which comprises a connection plate 42, connection means 45, annular elastic body 37, ultrasonic vibrators 39 and grind stone 38.

FIG. 5 is a perspective exploded view of the grinding tool 40 of FIG. 4.

FIG. 6 is a top view illustrating the annular elastic body 37, ultrasonic vibrators 39 and grind stone 38 which constitute the grinding tool 40 of FIG. 4.

FIG. 7 is a sectional view illustrating the annular elastic body 37, ultrasonic vibrators 39 and grind stone 38 taken along the line II-II shown in FIG. 6.

FIG. 8 is a top view of the rotary transformer of FIG. 3.

FIG. 9 is a sectional view of the rotary transformer taken along the line III-III shown in FIG. 8.

FIG. 10 is a front view showing another embodiment of a grinding tool to be used in the grinding machine of the invention.

FIG. 11 is a perspective exploded view of the grinding tool 100 of FIG. 10.

FIG. 12 is a perspective view illustrating a further embodiment of a grinding tool to be used in the grinding machine of the invention.

FIG. 13 is a perspective view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention.

FIG. 14 is a front view of a ultrasonic vibrator 39 to be used in the grinding tool 130 of FIG. 13.

FIG. 15 is a top view of a ultrasonic vibrator 39 to be used in the grinding tool 130 of FIG. 13.

FIG. 16 is a front view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention.

FIG. 17 is a top view of the grinding tool of FIG. 16.

FIG. 18 is a sectional view of the grinding tool taken along the line IV-IV shown in FIG. 17.

FIG. 19 is a perspective view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention.

FIG. 20 is a sectional view of the grinding tool 190 taken along the line V-V shown in FIG. 19.

FIG. 21 is a top view of a ultrasonic vibrator 39 to be used in the grinding tool 190 of FIG. 19.

FIG. 22 is a front view of a ultrasonic vibrator 39 to be used in the grinding tool 190 of FIG. 19.

FIG. 23 is a top view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention.

FIG. 24 is a sectional view of the grinding tool taken along the line VI-VI shown in FIG. 23.

FIG. 25 is a top view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention.

FIG. 26 is a perspective view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention.

The numerals mean the following:

10 grinding machine, 11 object to be ground, 12 support table, 14 grinding shaft, 17 elastic body, 18 grind stone, 19 laminated piezoelectric actuator, 21 pipe, 30 grinding machine, 31 object to be ground, 32 support table, 33 drive device, 34 rotating shaft, 35 drive device, 36 drive device, 37 annular elastic body, 38 grind stone, 38a grind stone (piece), 39 ultrasonic vibrator, 39a, 39b, 39c, 39d electrode, 39e piezoelectric element, 40 grinding tool, 41 transmission unit (rotary transformer), 42 connection plate, 43 connection section, 43a connection section, 44 space section, 44a through hole, 45 connection means, 51 substrate, 52 rotation driving unit, 52a rotating shaft, 53 feed screw, 53a nut, 54 pole, 55 bearing, 56 arm, 57 bearing, 58 rotation driving device, 58a rotating shaft, 59a, 59b pulley, 60 belt, 61a, 61b nozzle, 62a, 62b screw hole, 63 bolt, 64a, 64b, 64c electric wiring, 65 power source, 66a power supply unit, 66b power receiving unit, 67a stator core, 67b rotor core, 68a stator coil, 68b rotor coil, 100, 120, 130, 160, 190, 230, 250, 260 grinding tool

DETAILED DESCRIPTION OF THE INVENTION

The grinding machine of the invention is described below, referring to the attached drawings.

FIG. 3 is a front view of a grinding machine according to the invention. FIG. 4 is an enlarged view illustrating the grinding tool 40 of the grinding machine 30 of FIG. 3 which comprises a connection plate 42, connection means 45, annular elastic body 37, ultrasonic vibrators 39 and grind stone 38. FIG. 5 is a perspective exploded view of the grinding tool 40 of FIG. 4. FIG. 6 is a top view illustrating the annular elastic body 37, ultrasonic vibrators 39 and grind stone 38 which constitute the grinding tool 40 of FIG. 4. FIG. 7 is a sectional view illustrating the annular elastic body 37, ultrasonic vibrators 39 and grind stone 38 taken along the line II-II shown in FIG. 6.

As is illustrated in FIGS. 3 to 7, the grinding machine 30 comprises a support table 32 on which an object 31 to be ground is supported and fixed, a vertically movable rotating shaft 34 arranged above the support table 32, a drive device 35 for vertically moving the rotating shaft 34, a drive device 36 for rotating the rotating shaft 34, an elastic body 37 fixed to a base section of the rotating shaft 34, an annular grind stone 38 provided to a bottom of the elastic body 37, ultrasonic vibrators 39 arranged on the elastic body 37, and a transmission unit 41 for transmitting electric energy to the ultrasonic vibrators 39.

In the grinding machine 30 of the invention, the above-mentioned elastic body 37 is an annular elastic body, a connection plate 42 having connection means 45 comprising alternately formed connection sections 43 and space sections 44 on its bottom surface is provided between the annular elastic body 37 and the base section of the rotating shaft 34 under the condition that the connection sections 54 are bonded to a top surface of the annular elastic body 37, and the ultrasonic vibrators 39 are placed on the top surface of the annular elastic body 37 in an area facing the space sections 44.

There are no specific limitations with respect to the objects to be ground by the grinding machine 30. The objects can be glass substrates, silicon substrates (silicon wafers), silicon nitride substrates and lithium niobate substrates.

The object 31 to be ground is fixed and supported on the surface of the support table 32, for instance, using a hot-melt adhesive. The object can be placed in a holder and the holder is fixed to the support table. Thus, the object can be indirectly fixed and supported on the support table. The holder can be fixed onto the support table, for instance, by a bolt or electromagnetic power.

The support table 32 can be arranged above a substrate 51, preferably, via a drive device (e.g., motor) 33 connected to the lower surface of the table 32, for rotating the support table 32. The support table 32 is generally rotated at a 50 to 500 r.p.m. The support table 32 can be connected to the drive device 33 via a power transmission unit such as gear or belt. In addition, the support table can be arranged to move reciprocally in its plane.

The support table 32 takes a circular or polygonal form so that the table 32 can be rotated stably.

The rotating shaft 34 arranged above the support table 32 can be vertically moved in a reciprocal mode by the drive device 35 and rotated by the drive device 36.

The drive device 35 comprises a rotation driving unit 52 placed on the substrate 51, a feed screw 53 connected to a rotating shaft 52a of the rotation driving unit 52, a bearing 55 which is connected to a nut 53 of the feed screw 53 and can be moved vertically along a pole 54 standing on the substrate 51, nut 53a of the feed screw 53, an arm connected to the nut 53a of the feed screw 53, and a bearing 57 which is arranged in the vicinity of the front end of the arm 56 and supports the rotating shaft 34. The bearing 57 can support the rotating shaft 34 under such condition that the rotating shaft 34 can rotate but cannot move vertically with reference to the bearing 57.

Therefore, when the rotation driving unit 52 of the drive device 35 is actuated to drive the rotating shaft 52a to rotate in a normal direction or an opposite direction, the nut 53a of the feed screw 53 connected to the rotation driving unit 52 and the bearing 55 can move along the pole 54 upwardly and downwardly, whereby the rotating shaft 54 supported by the bearing 57 attached to the arm 56 which is connected to the nut 53a moves upwardly or downwardly.

The drive device 36 comprises a rotation driving device 58 fixed to the nut 53a of the feed screw 53 of the drive device 35, a pulley 59a fixed to the lower end of the rotating shaft 58a of the rotation driving device 58, a pulley 59b arranged around the rotating shaft 34, and a belt 60 connecting the pulley 59a to the pulley 59b. The drive device 36 applies a power driving the rotation driving device 58 to the driving shaft 34 via the belt 60, whereby the rotating shaft 34 supported by the bearing 57 is rotated. The rotating shaft generally rotates at 1,000 to 10,000 r.p.m.

To the base portion of the rotating shaft 34 are fixed the connection plate 42 and the annular elastic body 37 via the connection means 45. The annular elastic body 37 has an annular grind stone 38 on the bottom surface.

The annular grind stone 38 can be produced by binding abrasive grains (such as diamond grains) with a metal bond or a resin bond. The abrasive grains generally have a mean size in the range of 0.1 to 50 μm.

The annular grind stone 38 of the grinding machine 30 can have a height of 5 to 10 mm and a width of 3 to 10 mm.

The annular grind stone can embrace a grind stone formed of plural pieces of grind stone arranged in the form of ring. If the annular grind stone is formed of the plural pieces of grind stone, the production of the annular grind stone, particularly a large annular grind stone, can be facilitated. Further, stress produced in the grind stone by applied ultrasonic vibration or thermal expansion caused by friction with the object to be ground is reduced, whereby damage (such as production of cracks) of the grind stone can be obviated.

The annular elastic body 37 supporting the grind stone 38 can be made of known metallic materials showing good transmission of ultrasonic vibration, such as aluminum, bronze, stainless steel, or duralumin.

The connection plate 42 arranged between the annular elastic body 37 and the rotating shaft 34 can be made of the metallic material mentioned above for the elastic body 37 or other metallic material such as titanium or iron.

If the connection plate 42 is made of material other than the material used for the annular elastic body 37, the connection plate 42 is preferably made of titanium, iron or stainless steel having high rigidity (high mechanical strength). The connection plate 42 having high rigidity is effective to stably support the annular elastic body 37 by the rotating shaft 34.

In addition, the connection plate 42 is preferably made of material which has an acoustic impedance greatly differing from that of the annular elastic body 37. For instance, if the annular elastic body 37 is made of aluminum (acoustic impedance: 17.3×10⁶ Ns/m³), and the connection plate 42 is made of stainless steel (acoustic impedance: 45.7×10⁶ Ns/m³), escape of the ultrasonic vibration generated by the ultrasonic vibrator 39 into the rotating shaft 34 via the annular elastic body 37, connection means 45 and connection plate 42 is effectively reduced.

The bottom surface (i.e., lower surface) of the periphery of the connection plate 42 is connected to the top surface (i.e., upper surface) of the annular elastic body 37 via the connection means 45 comprising alternately formed plural connection sections 43 and space sections 44. The connection plate 42, connection sections 43 of the connection means 45, and the annular elastic body 37 are connected to each other by screw holes 62a and bolts 63. The connection means 43 can be made of those described for the connection plate 42.

There are no specific limitations with respect number of the connection sections 43 (and space sections 44) of the connection means 45. However, the connection means 45 preferably has 3 to 30 connection sections (and space sections). If only less than 3 connection sections are formed, the connection plate 42 cannot support the annular elastic body 37 stably, whereby grind accuracy decreases. On the other hand, it is not easy to form more than 30 connection sections.

The ultrasonic vibrators 39 generating ultrasonic vibration to be applied to the grind stone 38 is arranged on the top surface of the annular elastic body 37 under such condition that each of the ultrasonic vibrators 39 faces each of the space sections 44 of the connection means 45 (that is, each of the ultrasonic vibrators 39 is placed between the adjacent connection sections).

The ultrasonic vibrator 39 can comprises a piezoelectric element being curved along the annular elastic body 37 and a pair of electrodes each of which is placed on the top or bottom surface of the piezoelectric element. The piezoelectric element can be made of piezoelectric ceramic material such as lead zirconium titanate. The piezoelectric element can be polarized in the thickness direction. The electrode can be made of silver or phosphor bronze.

The ultrasonic vibrators 39 can be placed on the top surface of the annular elastic body 37 under such condition that ultrasonic vibrators arranged adjacently to each other have opposite polarization directions, that is, upwardly polarized vibrator is arranged adjacently to downwardly polarized vibrator.

Each ultrasonic vibrator 39 can be fixed to the annular elastic body by epoxy resin. The epoxy resin serves to insulate the lower electrode of the ultrasonic vibrator 39 from the annular elastic body 37. In addition, each ultrasonic vibrator 39 can be coated with an insulating paint, whereby the pair of electrodes of the ultrasonic vibrator cannot be connected to each other when the vibrator is brought into contact with a cooling liquid (e.g., water) in the course of grinding procedures.

The upper electrodes of the ultrasonic vibrators 39 are electrically connected to each other via wiring 64a, and the lower electrodes are electrically connected to each other via wiring 64b.

In the grinding machine 30, a rotary transformer is employed as a transmission unit 41 for transmitting electric energy to the ultrasonic vibrators 39.

FIG. 8 is a top view of the rotary transformer (transmission unit) of FIG. 3, and FIG. 9 is a sectional view of the rotary transformer 41 taken along the line III-III shown in FIG. 8.

The constitution and operation of the rotary transformer 41 is described below by referring to FIGS. 3 to 9.

The rotary transformer 41 is placed for supplying electric energy generated by a power source 65 to the ultrasonic vibrators 39 which rotate with the annular elastic body 37 when the object 31 is ground.

The rotary transformer 41 comprises a power supply unit 66a and a power receiving unit 66b adjacently arranged to each other with a small space. Both of the power supply unit 66a and power receiving unit 66b are in an annular form. The power supply unit 66a comprises an annular stator core 67a and a stator coil 68a, and the power receiving unit 66b comprises an annular rotor core 67b and a rotor coil 68b. Each of the stator core 67a and rotor core 67b is made of magnetic material such as ferrite and has annular grooves arranged along the periphery of the core. Each of the stator coil 68a and rotor coil 68b comprises a conductive wiring coiled along the annular grooves formed on each of the stator core 67a and rotor core 67b.

To the stator coil 68a of the power supply unit 66a is electrically connected a power source 65, and to the rotor coil 68b of the power receiving unit 66b is electrically connected each ultrasonic vibrator 39 via an electric wiring 64c. The electric wiring 64c is connected to the rotor coil 68b at its upper end, while it is electrically connected to the ultrasonic vibrators 39 at its lower end via a hollow space of the rotating shaft 34 and a through-hole of the connection plate 42.

When an electric energy generated by the power source 65 is supplied to the stator coil 68a of the rotary transformer 41, the stator coil 68a and the rotor coil 68b are magnetically coupled to each other. For the reason, the electric energy supplied to the stator coil 68a is transmitted to the rotor coil 68b when the rotor coil 68b (together with the power receiving unit 66b) is rotated simultaneously with the rotating shaft 34. Hence, the electric energy generated by the power source 65 can be transmitted to each ultrasonic vibrator 39 rotating together with both of the rotating shaft 34 and annular elastic body 37 when the object 31 is being ground.

Since the electric energy (e.g., a.c. voltage) generated by the power source 65 is transmitted to each ultrasonic vibrator 39 (in more detail, each electrode of the piezoelectric vibrator serving as ultrasonic vibrator), the ultrasonic vibrator 39 generates ultrasonic vibration which is then applied to the annular grind stone 38 via the annular elastic body 37.

The rotary transformer serving as a transmission unit for transmitting the electric energy to ultrasonic vibrator can be replaced with a slip ring. The rotary transformer is advantageous in that the rotary transformer can stably transmit the electric energy to the ultrasonic vibrator rotating together with the rotating shaft at a rotation rate up to 10,000 r.p.m., because the electric energy is transmitted through the power supply unit and power receiving unit which are arranged with no contact. On the other hand, the slip ring cannot stably transmit the electric energy to the rotating ultrasonic vibrator when the rotation rate exceeds approx. 5,000 r.p.m.

The procedures for grinding the object 31 by means of the grinding machine 30 are described below.

The object 31 is temporarily fixed, for instance, to an iron-made holder using a hot-melt adhesive. The holder to which the object 31 is fixed is then fixed on the support table 32 of the grinding machine 30, for instance, by means of magnetic force.

Thereafter, the drive device 36 is actuated to rotate the rotating shaft, for instance, at 5,000 r.p.m. The electric energy generated by the power source 65 is transmitted to the ultrasonic vibrators 39 of the grinding tool 40 via the rotary transformer 41, whereby each ultrasonic vibrator 39 generates ultrasonic vibration. The generated ultrasonic vibration is then transmitted to the annular grind stone 38 via the annular elastic body 37.

When the grinding procedures are carried out, a cooling liquid (e.g., water) is sprayed from the nozzle 61a onto the object 31 which is moved below the nozzle 61a by the rotation of the support table 32. The cooling liquid serves to reduce frictional resistance between the grind stone 38 and the object 31 whereby reducing unnecessary mechanical vibrations. Moreover, the cooling liquid is effective to obviate temperature elevation of the object caused by the friction with the grind stone, whereby increasing grinding accuracy. Similarly, the nozzle 61b drops a cooling liquid into an inner space of the rotating shaft 34. The cooling liquid runs through the inner space of the rotating shaft 34 into the through-hole formed in the central part of the connection plate 42 and finally drops onto the object 31 which is moved below the rotating shaft 34 by the rotation of the support table 32.

The drive device 33 is actuated to rotate the support table 32, for instance, at 300 r.p.m, and the rotating shaft 34 is downwardly moved by actuating the drive device 35, so that the bottom of the grind stone 38 to which the ultrasonic vibration is applied is brought into contact with the object at a peripheral area and subsequently into contact with the whole top surface of the object 31, whereby the object 31 is ground. The grinding procedure is continued until the object has the predetermined thickness by further moving the rotating shaft 34 downwardly.

As is described above, in the grinding machine 30 of the invention, a connection plate 42 is arranged between the annular elastic body 37 having the grind stone 38 on its bottom surface and the rotating shaft 34 for rotating the grind stone 38. The connection plate 42 is connected to the annular elastic body 37 with the connection means 45 which comprises alternately formed connection sections 43 and space sections 44. The ultrasonic vibrator is arranged on the annular elastic body 37 in the predetermined position (in the area between the adjacent connection sections 43). Therefore, the annular elastic body 37 in the areas between the adjacent connection sections 43 is easily vibrate in the ultrasonic vibration mode as compared with the annular elastic body 37 in the areas connected to the connection sections 43, and hence the ultrasonic vibration hardly escapes to the rotating shaft 34 by way of the connection sections 43 (and the connection plate 42) and most of the ultrasonic vibration is transmitted to the grind stone 38 via the annular elastic body 37. For the reasons, the grinding machine of the invention can grind an object with high accuracy.

In the grinding machine of the invention, a ratio of length of the connection section and length of the space section (both lengths are determined along the periphery of the connection plate) preferably is in the range of 1:1 to 1:20. The above-mentioned grinding machine 30 has a ratio of approx. 1:8 (L₁ of the connection section 43:L₂ of the space section 44). If a ratio (L₂/L₁) of the length of the space section 44 (L₂) to the length of the connection section 43 (L₁) is less than 1, the connection plate 42 is firmly fixed to the annular elastic body 37, and both are apt to vibrate in the ultrasonic vibration mode in the united structure, and hence the ultrasonic vibration generated by each ultrasonic vibrator 39 easily escapes to the rotating shaft 34 via the connection section 43 of the connection means 45 and the connection plate 42. Therefore, an enough amount of the ultrasonic vibration may not be transmitted to the grind stone 38, and hence the grind accuracy may decrease. On the other hand, if the ratio (L₂/L₁) exceeds 20, rigidity of each connection section 43 decreases, and the grind stone 38 may not be stably supported by the rotating shaft 34. Therefore, the grind accuracy may decrease.

Further, it is preferred that the connection sections 43 (as well as the space sections 44) are arranged symmetrically around the rotating shaft (FIG. 3, 34). A combination of the arrangement of the connection sections 43 and an appropriate adjustment of frequency of the ultrasonic vibration generated by each ultrasonic vibrator 39 can cause ultrasonic vibration of the annular elastic body 37 in such mode (free vibration, named inplane bending vibration) as vibrating as indicated by the long dashed double-short dashed line from the reference line indicated by the dashed dotted line, as illustrated in FIG. 6. The ultrasonic vibration showing the mode shown in FIG. 6 as the long dashed double-short dashed line subsequently shows a mode opposite to the long dashed double-short dashed line (shown in FIG. 6) with reference to the dashed dotted line after a half-period of the vibration period.

It is preferred that the ultrasonic vibrators 39 are arranged symmetrically around the rotating shaft (FIG. 3, 34). This arrangement may cause ultrasonic vibration to the annular elastic body 37 in such mode as to vibrate symmetrically around the rotating shaft (FIG. 3, 34) (for instance, the ultrasonic vibration indicated in FIG. 6 by the long dashed double-short dashed line).

When the annular elastic body 37 vibrates in the mode indicated in FIG. 6 by the long dashed double-short dashed line, the elastic body 37 does not vibrate in the area connected to the connection sections 43. Therefore, the ultrasonic vibration generated by the ultrasonic vibrators 39 hardly escapes to the connection plate via the connection sections 43, and hence most of the ultrasonic vibration is transmitted to the grind stone 38 via the annular elastic body 37. This means that the grind accuracy is further increased.

The adjustment of the frequency of ultrasonic vibration (for instance, free oscillation to oscillate in the mode indicated in FIG. 6 by the long dashed double-short dashed line) produced in the annular elastic body can be performed by the steps of calculating the natural frequency of the grinding tool and adjusting the shape of the connection plate 42, connection means 45, annular elastic body 37, or grind stone 38.

In the space sections 44 of the connection means 45, such material as hardly transmitting the ultrasonic vibration generated in the annular elastic body 37 to the connection plate 42 (e.g., material having an acoustic impedance greatly differing from that of the material (such as metal) of the annular elastic body, for instance, silicone rubber) can be filled.

FIG. 10 is a front view showing another embodiment of a grinding tool to be used in the grinding machine of the invention, and FIG. 11 is a perspective exploded view of the grinding tool 100 of FIG. 10. The grinding tool 100 shown in FIGS. 10 and 11 have a structure which is essentially the same as that of the grinding tool 40 of FIG. 4, except that the connection sections 43 of the connection means 45 is beforehand fixed to the annular elastic body 37, and that the connection sections 43 are fixed to the connection plate 42 by screwing bolts into the screw holes 62a.

If the frequency of ultrasonic vibration generated by each ultrasonic vibrator 39 of the grinding tool 100 is adjusted, it is possible to produce the ultrasonic vibration (free vibration differing the free vibration explained with reference to FIG. 6, named perpendicular to plane bending vibration) in such mode as shown by the long dashed double-short dashed line and the dashed dotted line which is shown in FIG. 10. The ultrasonic vibration showing the mode shown in FIG. 10 as the long dashed double-short dashed line subsequently shows a mode opposite to the long dashed double-short dashed line (shown in FIG. 10) with reference to the dashed dotted line after a half-period of the vibration period.

When the annular elastic body 37 vibrates in the mode indicated in FIG. 10 by the long dashed double-short dashed line, the elastic body 37 does not vibrate in the area connected to the connection sections 43. Therefore, the ultrasonic vibration generated by the ultrasonic vibrators 39 hardly escapes to the connection plate via the connection sections 43, and hence most of the ultrasonic vibration is transmitted to the grind stone 38 via the annular elastic body 37. This means that the grind accuracy is further increased.

In addition, if the frequency of the ultrasonic vibration generated by each ultrasonic vibrator 39 of the grinding tool 100 is adjusted, the annular elastic body 37 can vibrate in the manner as shown in FIG. 6 by the long dashed double-short dashed line.

FIG. 12 is a perspective view illustrating a further embodiment of a grinding tool to be used in the grinding machine of the invention. The structure of the grinding tool 120 of FIG. 12 is that of the grinding tool 40 of FIG. 4 except that the connection plate 42 and the connection sections 43 are both made of elastic material (which is the same as the metallic material used for the annular elastic body 37), and the connection plate 42, connection sections 43 and annular elastic body 37 are all molded in one unit.

If the connection plate 42, connection sections 43 and annular elastic body 37 are all molded in one unit, the grinding tool 120 can be readily manufactured, for instance, by drilling a metal disc in the axial direction, forming plural through-holes which serve as the space sections 44 of the connection means 45 in the radial direction, and fixing the ultrasonic vibrators 39 and the grind stone 38. The grind stone 38 can be composed of circularly arranged pieces of grind stones 38a.

The grinding tool 120 is fixed to the base portion of the rotating shaft (FIG. 3, 34) via a mounting disc (not shown). The connection plate 42 has a screw hole 62b which is used for connecting the mounting disc and the grinding tool 120 by a bolt.

In addition, if the frequency of the ultrasonic vibration generated by each ultrasonic vibrator 39 of the grinding tool 120 is adjusted, the annular elastic body 37 can vibrate in the manner as shown in FIGS. 6 and 10 by the long dashed double-short dashed line. In FIG. 12, the vibration of the annular elastic body 37 of the grinding tool 120 generated in the manner as in the grinding tool 100 of FIG. 10 is shown by the dashed dotted line and the long dashed double-short dashed line.

FIG. 13 is a perspective view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention. The grinding tool 130 of FIG. 13 has the same structure as that of the grinding too. 120 of FIG. 12 except that the ultrasonic vibrators 39 are attached to the outer side surface of the annular elastic body 37 in the position below the space sections 44 of the connection means 45. Thus, the ultrasonic vibrators 39 can be arranged on the outer side surface (or inner side surface) of the annular elastic body 37 in the position below the space sections 44 of the connection means 45.

If the ultrasonic vibrators are arranged on the outer side surface (or inner side surface) of the annular elastic body, the ultrasonic vibrators preferably have the following structure.

FIG. 14 and FIG. 15 are respectively a front view and a top view of the ultrasonic vibrator 39 attached to the grinding tool 130 of FIG. 13.

The ultrasonic vibrator 39 shown in FIGS. 14 and 15 is composed of a piezoelectric element 39e curved along the periphery of the annular elastic body 37, a pair of electrodes 39a, 39a arranged on its upper surface in such manner that a upper portion of the piezoelectric element is sandwiched by the electrodes in the thickness direction, and a pair of electrodes 39b, 39b arranged on its lower surface in such manner that a lower portion of the piezoelectric element is sandwiched by the electrodes. The upper portion of the piezoelectric element sandwiched by the electrodes 39a, 39a is polarized in the direction from the front side to the back side of the figure, while the lower portion of the piezoelectric elements sandwiched by the electrodes 39b, 39b is polarized in the direction from the back side to the front side of the figure. A portion of the piezoelectric element neither sandwiched by the electrodes 39a, 39a nor sandwiched by the electrodes 39b, 39b is not polarized (not functions as ultrasonic vibrator).

When an a.c. voltage is supplied to the ultrasonic vibrator 39 under such condition that one of the combination of the electrode 39a and electrode 39b placed on the front side (electrode placed on the outer side of the vibrator) and the combination of the electrode 39a and electrode 39b placed on the back side (electrode placed on the inner side of the vibrator) serves as a positive electrode and another serves as a negative electrode, the ultrasonic vibrator 39 can generate ultrasonic vibration shown in FIG. 14 by the long dashed double-short dashed line with reference to the dashed dotted line. The ultrasonic vibration vibrates as shown in FIG. 12 by the long dashed double-short dashed line, and then vibrates symmetrically with reference to the dashed dotted line.

If the a.c. voltage is supplied to each of the ultrasonic vibrators 39 of the grinding tool 130 under such condition that adjacently arranged ultrasonic vibrators 39 receive a.c. voltage of opposite phases (for instance, the combination of electrodes placed on the outer surface of one vibrator serves as positive electrodes, while the combination of electrodes placed on the outer surface of another vibrator serves as negative electrodes), the annular elastic body 37 vibrates in the mode shown in FIG. 13 by the long dashed double-short dashed line.

FIG. 16 is a front view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention, FIG. 17 is a top view of the grinding tool of FIG. 16, and FIG. 18 is a sectional view of the grinding tool taken along the line IV-IV shown in FIG. 17.

The grinding tool 160 of FIG. 16 has the same structure as that of the grinding tool 130 of FIG. 13 except that each of the connection plate 42 and the annular elastic body 37 has an octagonal periphery.

If the annular elastic body 37 is formed to have a polygonal (particularly, a regular polygonal which facilitates stable rotation of the annular elastic body) outer or inner periphery, easily manufacturable flat vibrators can be arranged on the outer or inner flat side surfaces of the annular elastic body 37 below the space sections 44 of the connection means 45. There are no specific limitations with respect to the shapes of the outer and inner peripheries of the connection plate 42. However, manufacture of the grinding tool 160 is facilitated if the peripheries of the connection plate are the same as those of the annular elastic body 37.

Further, as is illustrated in FIG. 17, when the a.c. voltages are applied to the ultrasonic vibrators 39 under such condition that a.c. voltages having phase difference of 90° are applied to adjacently arranged vibrators 39, the annular elastic body vibrates in the manner as is shown in FIG. 13 by the long dashed double-short dashed line and the ultrasonic vibration travels (travelling wave of ultrasonic vibration) along the periphery of the annular elastic body 37. If the travelling wave of ultrasonic vibration is applied to the annular grind stone 38 (each grind stone piece 38a), the grind stone pieces 38a not only vibrate vertically but also vibrate horizontally (in the periphery direction of the annular elastic body), whereby the grinding procedure is accelerated.

The application of the a.c. voltages having phase difference of 90° to the ultrasonic vibrators can be performed by attaching another rotary transformer to the rotating shaft 34 of the grinding machine 30 of FIG. 3 in addition to the rotary transformer 41, electrically connecting the former rotary transformer to a power source other than the power source 65, and supplying an a.c. voltage of sin wave to a set of ultrasonic vibrators 39 from one power source and rotary transformer, while supplying an a.c. voltage of cos wave to other set of ultrasonic vibrators 39 from another power source and rotary transformer.

In FIG. 17, a set of “sin” and an allow means that the ultrasonic vibrator indicated by the set receives an a.c. voltage of sin wave at the outer positive electrode and at the inner negative electrode, while a set of “-sin” and allow means that the ultrasonic vibrator indicated by the set receives the same a.c. voltage of sin wave at the outer negative electrode and at the inner positive electrode.

Alternatively, the rotary transformer 41 shown in FIG. 3 can be manufactured to have double channels (for instance, two sets of coils arranged facing each other are attached to the power supply unit and power receiving unit of the rotary transformer so that the a.c. voltages can be transmitted independently of each other by the two coils), and the a.c. voltage of sin wave is supplied to one set of ultrasonic vibrators through in one channel, while the a.c. voltage of cos wave is supplied to another set of ultrasonic vibrators through another channel.

FIG. 19 is a perspective view illustrating a still further embodiment of a grinding tool to be used in the grinding machine of the invention, and FIG. 20 is a sectional view of the grinding tool 190 taken along the line V-V shown in FIG. 19.

The grinding tool 190 shown in FIG. 19 have a structure which is essentially the same as that of the grinding tool 40 of FIG. 4, except that the outer periphery of the connection plate 42 is connected to the inner periphery of the annular elastic body 37 by a connection means 45 composed of alternately formed connection sections 43 and space sections 44, and that the ultrasonic vibrators are placed on the top surface of the annular elastic body 39 in the position adjacent to the space sections 44 of the connection means.

Even in the grinding machine of the invention having the grinding tool 190, the ultrasonic vibrations generated by the ultrasonic vibrators 39 placed on the predetermined positions hardly escape to the rotating shaft (FIG. 3, 34) via the connection sections 43 (and the connection plate 42), because the portions between the adjacently arranged connection sections 43 easily vibrate as compared with the portions connected to the connection sections 43, and hence most of the ultrasonic vibrations are transmitted to the grind stones 38. Therefore, the grinding machine having the grinding tool 190 according to the invention (shown in FIG. 19) can grind the object at high accuracy.

In addition, if frequency of the ultrasonic vibration generated by each ultrasonic vibrator 39 is adjusted, a ultrasonic vibration vibrating in the manner indicated in FIGS. 6 and 10 by the long dashed double-short dashed line. In FIG. 19, the ultrasonic vibration produced in the annular elastic body 37 of the grinding tool 190 in the manner as described for the grinding tool 100 of FIG. 10 is illustrated by the dashed dotted line and long dashed double-short dashed line.

The grinding tool 190 of FIG. 19 comprises an elastic connection plate 42 and elastic connection sections 43 which are molded together with the annular elastic body 37 to give a united structure. The grinding tool 190 of FIG. 19 is advantageous in that the space sections 44 of the connection means 45 can be easily formed.

The ultrasonic vibrators 39 of the grinding tool 190 of FIG. 19 can have the following structure.

FIG. 21 and FIG. 22, respectively are a top view and a front view of a ultrasonic vibrator 39 to be attached to the grinding tool 190 of FIG. 19.

The ultrasonic vibrators 39 shown in FIGS. 21 and 22 are composed of an annular piezoelectric element 39e and four pairs of electrodes (a pair of electrodes 39a, 39a, a pair of electrodes 39b, 39b, a pair of electrodes 39c, 39c, and a pair of electrodes 39d, 39d) which sandwick the element 39 in the thickness direction. The piezoelectric element sandwiched by the pair of electrodes 39a, 39a and the pair of electrodes 39c, 39c is polarized in the direction from the front side to the back side, while the piezoelectric element sandwiched by the pair of electrodes 39b, 39b and as the pair of electrodes 39d, 39d is polarized in the direction from the back side to the front side. The piezoelectric element in the areas not sandwiched by the four pairs of electrodes are not polarized (not active as ultrasonic vibrator).

When the ultrasonic vibrators 39 are supplied with a.c. voltages under such condition that the electrodes 39a, 39b, 39c, 39d on the front side (in FIG. 21) are made positive electrodes and the electrodes 39a, 39b, 39c, 39d on the back side are made negative electrodes, the annular elastic body 37 shows a ultrasonic vibration indicated in FIG. 19 by the long dashed double-short dashed line.

FIG. 23 is a front view illustrating a still further embodiment of a grinding tool used in the grinding machine of the invention, and FIG. 24 is a sectional view of the grinding tool taken along the line VI-VI shown in FIG. 23.

The grinding tool 230 shown in FIGS. 23 and 24 has the same structure as that of the grinding tool 190 of FIG. 9 except that ultrasonic vibrators 39 are placed not only on the inner side surfaces of the annular elastic body 37 which face the space sections 44 of the connection means 45 but also the outer side surfaces opposite to the inner side surface. Thus, the ultrasonic vibrators can be attached to the side surfaces. Each ultrasonic vibrator 39 may have a structure shown in FIGS. 14 and 15.

FIG. 25 is a top view illustrating a still further embodiment of a grinding tool used in the grinding machine of the invention. The grinding tool 250 of FIG. 25 has the same structure as that of the grinding tool 230 of FIG. 23 except that the annular elastic body 37 has an octagonal outer periphery (and octagonal inner periphery) and that the ultrasonic vibrators 39 are placed on the annular elastic body 37 on the outer side surfaces opposite to the inner side surfaces facing the space sections 44 of the connection means 45.

FIG. 26 is a perspective view illustrating a still further embodiment of a grinding tool used in the grinding machine of the invention.

The grinding tool 260 of FIG. 26 has the same structure as that of the grinding tool 230 of FIG. 23 except that ultrasonic vibrators 39 are placed on the annular elastic body 37 on the outer side surfaces opposite to the inner side surface facing the space sections 44 of the connection means 45 and that the outer side surfaces of the annular elastic body has through-holes 44a extending to the space sections 44 in the position above the ultrasonic vibrators 39.

If these through-holes 44a are formed, the through-holes 44a function as the space sections 44 of the connection means 45 and the connection sections 43a formed between the adjacently formed through-holes 44a, 44a function as the connection sections 43 of the connection means 45. Therefore, the ultrasonic vibration generated by each ultrasonic vibrator 39 hardly escapes to the area above the through-hole 44a. Hence, the grinding machine having the grinding tool 260 of FIG. 26 according to the invention can grind the object with high accuracy.

In the present specification, the structure in which ultrasonic vibrators are placed on the top surface, inner side surface or outer side surface of the annular elastic body embraces the structure in which the ultrasonic vibrators are placed within the through-holes (e.g., through-holes 44a of the annular elastic body 37 as shown in FIG. 26) or grooves. For instance, in the grinding tool 260 of FIG. 26, each ultrasonic vibrator 39 is described to be placed on the outer side surface of the annular elastic body 37 which is opposite to the inner side surface facing the space section 44 of the connection means 45. The outer side surface includes the inner side surface of the through-hole 44a formed in the outer side surface. Thus, in FIG. 26, each ultrasonic vibrator 39 can be placed in the inner surface of the through-hole 44a.

Claims

1. A grinding machine comprising a support table on which an object to be ground is supported and fixed, a vertically movable rotating shaft arranged above the support table, a drive device for vertically moving the rotating shaft, a drive device for rotating the rotating shaft, an elastic body fixed to a base section of the rotating shaft, an annular grind stone provided to a bottom of the elastic body, ultrasonic vibrators arranged on the elastic body, and a transmission unit for transmitting electric energy to the ultrasonic vibrators, wherein the elastic body is an annular elastic body, a connection plate having connection means comprising alternately formed connection sections and space sections on a bottom surface thereof is provided between the annular elastic body and the base section of the rotating shaft under the condition that the connection sections are bonded to a top surface of the annular elastic body, and the ultrasonic vibrators are placed on the top surface of the annular elastic body in an area facing the space sections or on an inner or outer side surface of the annular elastic body in a area adjacent to the area facing the space sections, orthe elastic body is an annular elastic body, a connection plate having connection means comprising alternately formed connection sections and space sections on an outer side surface thereof is provided between the annular elastic body and the base section of the rotating shaft under the condition that the connection sections are bonded to an inner side surface of the annular elastic body, and the ultrasonic vibrators are placed on the inner side surface of the annular elastic body in an area facing the space sections or on a top surface or an outer side surface of the annular elastic body in a area adjacent to the area facing the space sections.

2. The grinding machine of claim 1, in which the connection plate and connection sections are made of elastic material.

3. The grinding machine of claim 1, in which the connection plate and connection sections are made of elastic material, and the connection plate, connection sections and annular elastic body are formed as a single unit.

4. The grinding machine of claim 1, in which a ratio of a length of the connection section and a length of the space section is in the range of 1:1 to 1:20, the length being determined along a periphery of the connection plate.

5. The grinding machine of claim 1, in which the transmission unit for transmitting electric energy to the ultrasonic vibrators is a rotary transformer.

6. The grinding machine of claim 1, in which the connection sections are arranged symmetrically around the rotating shaft and the space sections of the connection means are arranged symmetrically around the rotating shaft.

7. The grinding machine of claim 1, in which the ultrasonic vibrators are arranged symmetrically around the rotating shaft.

8. The grinding machine of claim 1, in which the support table is rotatable, and the rotatable support table is equipped with a drive unit driving the support table.