JPH0441176A - Micropolishing method - Google Patents

Abstract

PURPOSE:To uniformly bore the whole face of a work trace even in the case of a work diameter being enlarged, to form a smooth recessed face like work trace without a projective residual part being left at the center of the work trace and to increase the efficiency in polishing with the work diameter being enlarged, by periodically changing the phase difference in the XY direction, in the case of a polishing part being subjected to a micromotion. CONSTITUTION:A polishing part 26 is subjected to a micromotion in the XY direction parallel to a polishing face by actuators 24X, 24Y composed of electrostrictive elements in the state of a polishing material being held between the polishing part 26 of the polishing tool tip and a work W. Moreover, the work W is polished with the phase difference in the X direction micromotion and Y direction micromotion being changed periodically. Consequently, the work W shows a smooth recessed face shape at its whole face, with the work trace H obtainable of uniform and good polishing over the motion range whole body of the polishing part 26 having no projective residual part at all.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a micro-polishing method, and more specifically, in the field of manufacturing lenses, optical elements, etc., it is a method for polishing a micro-polishing area in order to perform ultra-high precision processing. Precise polishing Aspherical lenses and X-ray optical elements used in various electronic and optical devices are manufactured by polishing, but the shape accuracy of the product is extremely high precision of 0.01 μm or less. There is a need for a processing method that can perform such ultra-high precision polishing processing. For this purpose, a polishing method that can precisely polish only a minute area of the polished surface is required.

Conventionally, polishing processing, lapping processing, etc. have been adopted as high-precision polishing methods, but the above-mentioned 0, 0
Ultra-high precision machining of 1 μm or less was completely impossible, so
In recent years, a magnetic polishing method that uses a magnetic polishing fluid as an abrasive has been attracting attention as a method that can perform processing with higher precision. Here, the term "magnetic polishing fluid" refers to a magnetic fluid alone or a magnetic fluid in which fine particles of abrasive material are suspended and dispersed.

In the magnetic polishing method, a magnetic polishing fluid is supplied and a magnetic field is applied between a polishing part at the tip of a polishing tool and a workpiece to be polished. Then, the magnetic polishing fluid is held between the polishing section and the material to be polished while applying pressure to the polishing surface of the material to be polished by magnetic action.

In this state, when the polishing tool is rotated at high speed, the magnetic polishing fluid is dragged by the rotation of the polishing tool and is rotated at high speed, thereby polishing the material to be polished. At this time, by varying the direction and strength of the applied magnetic field, the force applied to the polishing surface by the magnetic polishing fluid can be varied and the movement of the magnetic polishing fluid can be controlled to improve polishing performance. is also being carried out. Specific examples of this magnetic polishing method are disclosed in, for example, Japanese Patent Application Laid-open No. 1-118466, Japanese Patent Application Laid-open No. 61-244457, and Japanese Patent Publication No. 16623/1989.

According to this magnetic polishing method, the magnetic holding force allows the abrasive to act intensively on a minute area of the polishing surface, making it possible to achieve higher precision polishing compared to conventional polishing methods. There are advantages.

However, even with this magnetic polishing method, it has not been possible to sufficiently cope with ultra-high precision machining of 0.01 μm or less.

That is, in this method, the magnetic polishing fluid is rotated at high speed by the high speed rotation of the polishing tool, so the finish of the polished surface is directly affected by the rotational state of the polishing tool. However, as the rotation of the polishing tool is prone to fluctuations in rotational speed and shaft deviation, this method results in fluctuations in the polishing amount, local polishing bias, and fluctuations in the polishing area in the finished polished surface. There was a problem that it would end up happening. Mechanical operating mechanisms such as rotating mechanisms require sufficient space to allow each member to move smoothly, and it is unavoidable that there will be some wobble in the movement of the polishing unit. There was also the problem that unevenness and fluctuations occurred in the finish of the polished surface. In short, it has been impossible to completely prevent these problems as long as the polishing section is rotated at high speed.

In the conventional high-speed rotation magnetic polishing method, the pressure force for pressing the magnetic polishing fluid against the polishing surface is not generated by the rotation of the polishing tool itself, but by the application of magnetism as described above. If the magnetic strength is not strong enough, sufficient polishing force will not be generated, and if the magnetic strength changes, the amount of polishing will change. Therefore, this high-speed rotational magnetic polishing method requires a large-scale magnetism generating means such as an electromagnet, and also has the problem of requiring strict control of the magnetic force. Furthermore, since the material to be polished itself must constitute a part of the magnetic circuit for obtaining this pressing force, there is a restriction that the material to be polished must be a magnetic conductor, that is, a magnetic material. However, even if the material to be polished is a non-magnetic material, a magnetic circuit can be constructed through the non-magnetic material as long as it is thin. However, even in this case,
Since the pressing force of the magnetic polishing fluid on the polishing surface changes due to slight variations in the thickness or magnetic properties of the material to be polished, there has been a problem in that it is difficult to control the amount of polishing, polishing accuracy, etc. In addition,
The above-mentioned lenses, optical elements, etc. are non-magnetic and have considerable thickness, so the high-speed rotational magnetic polishing method described above cannot be applied to them.

Therefore, we have solved the problems of the conventional high-speed rotation magnetic polishing method mentioned above, and it is possible to process with higher precision. In order to provide a micro-polishing method that can be successfully applied to the polishing surface, the inventors first moved the polishing section in the XY directions parallel to the polishing surface and in the We have developed a micro-polishing method and a micro-polishing tool that make micro-movements in the Z direction and transmit the micro-movements of the polishing part to a magnetic polishing fluid to polish the polished surface of the workpiece.

This new micro-polishing method and micro-polishing tool using an actuator consisting of an electrostrictive element does not require high-speed rotation of the chamber, and also allows the workpiece to be polished to hold and pressurize the magnetic polishing fluid. Since there is no need to make it a part of the magnetic circuit for the purpose, the problems of the conventional high-speed rotation micro-polishing method described above can be completely solved.

In other words, in the micropolishing method using this new drive method,
The electrostrictive element forces the magnetic polishing fluid onto the workpiece and causes the polishing section to move minutely along the polishing surface, thereby polishing the workpiece. In other words, a minute movement is applied to the polishing part by an XY-direction actuator or a Z-direction actuator that uses an electrostrictive element, so that the magnetic polishing fluid is caused to make a minute movement in the horizontal or vertical direction with respect to the polishing surface of the material to be polished. ,
The magnetic polishing fluid is made to perform a minute polishing movement along the polishing surface by making a minute movement in the horizontal direction with respect to the polishing surface, and to obtain a pressing force against the polishing surface by making a minute movement in the vertical direction to the polishing surface. .

In this way, the micro-polishing method using this novel drive method does not require rotation of the polishing section, and as a result, there are no variations in polishing or uneven surface roughness due to uneven rotation, shaft runout, or the like.

An actuator using an electrostrictive element has no mechanical sliding parts or operating mechanisms, and is driven extremely accurately according to an applied voltage, so that the movement of the magnetic polishing fluid is also stable.

In this respect as well, variations and unevenness in polishing are prevented. The movement of the magnetic polishing fluid in the X and Y directions by the actuator is much smaller than conventional rotational movement, so it is possible to finely polish the material to be polished and achieve ultra-high precision mirror finishing with extremely low surface roughness. possible.

In addition, in the micro-polishing method using this new drive method, the pressure force for pressing the magnetic polishing fluid onto the material to be polished is applied by a Z-direction actuator using an electrostrictive element, so the magnetic circuit connecting from the polishing part of the polishing tool to the material to be polished is As a result, even if the material to be polished is non-magnetic, it can be polished without any problem, and regardless of the difference in magnetic properties due to the material and thickness of the material to be polished, the actuator can be Since the pressure applied to the material to be polished can be set and controlled using only the applied voltage, polishing efficiency and polishing accuracy are not affected by the material or shape of the material to be polished. As the material to be polished, in addition to magnetic materials such as steel that can be polished by conventional high-speed rotational magnetic polishing methods, non-magnetic materials such as glass and ceramics that cannot be polished by conventional high-speed rotational magnetic polishing methods can also be used. The non-abrasive material can be used in a wide variety of shapes, from thin to thick, and the polished surface can be flat, spherical, or free-form.

According to the micro magnetic polishing method using this new driving method,
As mentioned above, the minute movement of the polishing part is an extremely small movement obtained by applying a voltage to the electrostrictive element, so the magnetic polishing fluid can only affect the material to be polished in an extremely small area around the polishing part. can be polished with high precision, and the surface of the material to be polished can be polished finely and uniformly. Compared to conventional high-speed rotation polishing methods, the polishing process is much more uniform, making it possible to perform ultra-high-precision mirror finishing, making ultra-high-precision polishing with a shape accuracy of 0.01 μm or less easier and more reliable. It can be achieved.

Note that the micropolishing method and micropolishing tool using this novel driving method can also be used in a method that does not use a magnetic polishing fluid as an abrasive.

[Problems to be Solved by the Invention] However, subsequent research has revealed that this new micro-polishing method and micro-polishing tool have the following new problems.

In other words, in the micro-polishing method using this new drive method, if you try to expand the range of motion of the polishing part to increase the machining diameter for the purpose of improving machining efficiency, the shape of the machining marks will collapse and it will not be possible to obtain a good machining mark. No concave machining marks were obtained,
There is a problem in that unevenness occurs on the machined surface, making it impossible to obtain a smooth finished surface.

The reason why such a problem occurs is considered to be as follows.

In the micro-polishing method, the polishing section periodically moves in an arcuate shape based on its support point by the periodically varying acting force of the actuator in the x and y directions, and the movement trajectory of the polishing section is Machining marks are formed along. FIG. 6 schematically shows the movement locus T of such a polishing part and the cross-sectional shape of a machining mark H' formed on the material W to be polished. Since the movement of the polishing part is determined by the excitation frequency applied to the actuators in the X and Y directions,
X-direction component X = Asinωt and Y-direction component Y-Asin
(ωt+90°), and draws a circular arc with radius A (To increase the machining diameter, increase the amplitude of the excitation frequency applied to the XY direction actuator, and increase the radius A of the motion trajectory T. do it.

However, the workpiece W to be polished due to the movement of the polishing part is carved into a spherical shape centered on the position of the polishing part at that time, so the machining mark H' is within the radius A. An annular groove is formed along the circumference. In other words, since the polishing part does not pass through the center part of the machining mark H',
An unprocessed portion Q remains in the center of the bottom surface of the processing mark H in a convex shape. When the radius A is small, the convex remaining portion Q is also small and inconspicuous, but as the machining diameter of the machining mark H becomes larger, the convex remaining portion Q becomes more conspicuous, which may adversely affect polishing accuracy. Become.

Therefore, even if the machining diameter is increased, no convex residual part remains at the bottom of the machining mark, and a smooth concave machining mark is formed, resulting in a smooth and well-polished surface. The purpose of this study is to provide a micropolishing method using a driving method.

[Means to solve the problem]

The main structure of the micro-polishing method according to the present invention for solving the above problems is as follows.The polishing part is held in the state where the polishing material is held between the polishing part at the tip of the polishing tool and the workpiece to be polished. The workpiece is polished by making small movements in the XY force directions parallel to the polishing surface using an actuator consisting of an electrostrictive element, and by periodically changing the phase difference between the small movements in the X direction and the small movements in the Y direction. do.

In this invention, the polishing tool is supported by a suitable support member and the polishing part at the tip is moved along the material to be polished, as in the case of the conventional high-speed rotation magnetic polishing method.
As this supporting means and moving means, means used in various machine tools and the like are employed.

The polishing tool moves its polishing part in a direction horizontal to the polishing surface, that is, in the XY force direction, by a micro-driving means described later, depending on the shape and purpose of the material to be polished, and also moves the polishing part in the XY force direction as necessary. Make a small movement in the vertical direction, that is, in the Z direction.

Furthermore, if you make it perform actions such as tilting the axis,
It is possible to polish complex curved surfaces.

The material to be polished is processed to have properties corresponding to the surface properties of the polished portion. This polishing part can be composed of a Sn plating layer, a polyurethane layer, or the like. The shape of the polishing part may be flat, but if it is made spherical, the corners of the polishing part can easily be prevented from coming into contact with the polishing surface.

When the polishing part is made of polyurethane, the
When the amplitude of the micromovement in the Y force direction is made larger than the pore diameter of the polyurethane, partial polishing due to polishing breakage does not occur, and machining marks of a desired shape can be easily obtained.

The spherical polishing section is preferably composed of a sphere that is movably held at the tip of the polishing tool. This is because this transfer prevents uneven wear of the polishing part. The sphere may be held mechanically, like the sphere of a bearing mechanism, or may be held magnetically. Alternatively, it may be held by the viscosity of the abrasive.

The abrasive used in this invention is not limited to so-called magnetic polishing fluids, but non-magnetic polishing fluids can also be used.

The magnetic polishing fluid has properties as a so-called magnetic fluid and functions as an abrasive, and can be the same as those used in normal magnetic polishing methods. - The magnetic fluid used for boat fishing is made by dispersing fine magnetic powder particles such as Fe20a with a particle size of about 10 nm J22 or less in water or oil in a colloidal manner. A magnetic fluid made of such magnetic powder particles can be used as is, as long as it has abrasive properties for the material to be polished. Specific examples of magnetic abrasive particles include α-Fel 04 (red iron) and the like. Alternatively, ordinary abrasive particles without magnetism may be suspended and dispersed in a magnetic fluid made of magnetic particles without abrasive properties. In this case, the abrasive powder particles are Al2
ot, 5in2, etc. are used, and particles with a particle size of about 1100 nm or less are preferably used.

When using a magnetic polishing fluid as an abrasive, in order to magnetically hold the magnetic polishing fluid between the polishing part at the tip of the polishing tool and the material to be polished, for example, the magnetic polishing fluid must be placed close to the polishing part at the tip of the polishing tool. If a magnetic circuit is configured by providing a yoke, the magnetic polishing fluid can be easily held near the polishing section by its magnetic action.

The actuator that makes minute movements of the polishing part uses an electrostrictive element, also called a piezo element, which expands and contracts by applying a voltage. By connecting the polishing section to this actuator and applying a periodically varying voltage to the actuator, the polishing section can be moved minutely. The frequency of the minute movement of the actuator changes depending on the frequency of the applied voltage, and the amplitude of the minute movement of the actuator changes depending on the magnitude of the applied voltage. This minute movement of the abrasive part is transmitted to the abrasive material, the abrasive material performs the same minute movement as the abrasive part, and the material to be polished is polished by this minute movement of the abrasive material.

The X-direction actuator makes a small movement of the polishing part in the X direction, which is horizontal to the polishing surface, and the X-direction actuator makes a small movement of the polishing part in the Y direction, which is horizontal to the polishing surface and perpendicular to the above-mentioned X direction. The material to be polished is polished by making small movements in a direction parallel to the polishing surface of the material to be polished. The movement of the polishing section by the XX direction actuator can be made to have an arbitrary shear surge movement by controlling the phase of the movement in the X direction and the Y direction. By periodically changing the phase difference between the motions in the
Continuously and periodically changing shapes such as straight lines and ellipses, etc.
More complex serge figures can be drawn. The above phase difference may be created by moving at a constant phase in either the X direction or the Y direction and changing only the other phase, or by changing the phase in both the X and Y directions. Good too. In order to add a phase difference to the movement of the polishing section in the XY force directions, it is sufficient to add a phase difference to the signals applied to the XX direction actuators. For this purpose, a variable phase signal generator capable of changing the phase of the applied signal may be connected to the drive circuit of the XX direction actuator.

The X-direction actuator moves the polishing part in a direction perpendicular to the polishing surface, moves the abrasive so that it collides with the workpiece from the perpendicular direction, and applies pressure to the workpiece. Therefore, the pressing force applied to the material to be polished can be controlled by the magnitude of the voltage applied to the X-direction actuator. Moreover, the abrasive material is sequentially supplied to the polishing surface by the pumping effect caused by the minute movement of the X-direction actuator.

The XX-direction actuator and the X-direction actuator are wired to apply voltage in each direction separately. The drive wiring that applies voltage to each actuator is connected to a drive amplifier, function generator, etc. These drive circuits or drive mechanisms are A structure similar to that of an actuator using an element can be adopted.

It is preferable that the X-direction actuator, the X-direction actuator, and the X-direction actuator are constructed using stacked electrostrictive elements. If a laminated type is used, minute movements in the X direction, Y direction, or X direction can be made by expansion and contraction. A stacked electrostrictive element expands and contracts by applying a voltage to both ends thereof. If such a laminated electrostrictive element is used, a large displacement can be obtained, and the displacement of minute movements in the XY force directions does not vary depending on the magnitude of external force.

The XX-direction actuator and the X-direction actuator usually do not directly drive the polishing section, but instead drive the polishing section by applying micro-drives in the horizontal or vertical direction to a polishing shaft whose tip is the polishing section. do.

As mentioned above, the pressure applied by the abrasive to the material to be polished is
It is determined by the pressure applied by the X-direction actuator, and when magnetic holding force is used in combination, it is also affected by this holding force. However, this pressing force decreases as processing progresses. Therefore, it is preferable to detect the value of the pressurizing load applied to the material to be polished and feed this back to the control of the two-way actuator to control the pressurizing force. As the load detection means for detecting the applied load value, pressure sensors similar to those built into various ordinary mechanical devices can be used as long as they can detect the vertical load applied to the material to be polished. . For example, if polishing is performed with the material to be polished placed on a load cell, the magnitude of the pressurized load applied to the material to be polished can be detected by the load cell and extracted as an electrical signal.

The pressurized load value detected by the load detection means is converted into an electric signal to control the drive of the actuator. Specifically, the detection signal is processed by an appropriate electric circuit and input to a drive circuit that applies voltage to the actuator, where the preset pressure load value and the detected pressure load value are compared. to increase or decrease the voltage applied to the X-direction actuator. In other words, the pressure applied by the X-direction actuator is subjected to feedbank control. This feedback control can, for example, always keep the pressure applied by the X-direction actuator at a predetermined level, or keep it large at the beginning of the machining process (rough polishing), moderate in the middle (medium polishing), and small at the end (finishing). polishing).

Note that even in the case of this multi-step polishing, it is preferable to control the pressing force in each step to be constant.

In this way, when the pressing force in the X direction is held constant, if vibration is controlled to be added to the pressing force by the X direction actuator, the pumping action of this vibration will sequentially supply the abrasive to the polishing surface. Moreover, a phenomenon in which they are gradually eliminated begins to occur.

The set value of the pressing force is appropriately determined according to conditions such as the material of the workpiece to be polished and the polishing accuracy.

When using magnetic polishing fluid as the polishing material, the polishing shaft is
The polishing shaft is made of a magnetic material because it serves as a central yoke as part of the magnetic circuit for maintaining the magnetism. The opposing yoke facing this is arranged with a gap forming a magnetic gap between it and the polishing portion at the tip of the central yoke. For example, a central yoke having a circular cross section is surrounded by annular opposing yokes at intervals. By doing so, the magnetic polishing fluid can be well maintained around the polishing portion of the central yoke. Note that a bar-shaped or plate-shaped opposing yoke may be arranged side by side with the central yoke. Since the opposing yoke also constitutes a part of the magnetic circuit, it goes without saying that it is made of a magnetic material. It is preferable that the distal end portion of the opposing yoke, which faces the central yoke, has a tapered shape so that the magnetic field can be concentrated at the distal end portion of the opposing yoke.

A magnetic circuit is constructed by connecting the central yoke and the opposing yoke with magnetism generating means. Although either a permanent magnet or an electromagnet can be used as the magnetism generating means, in this invention, since there is no need to change the direction or magnitude of the magnetic field, a permanent magnet is preferable because it has a simpler structure. As the permanent magnet, a magnet made of SmC0 magnet or the like can be used.

[For production]

When moving the polishing part minutely in the X and Y directions,
The phase difference in the Y direction determines the drawn Lissajous figure, that is, the motion trajectory. Therefore, if the motion is made in the same phase in both the X and Y directions as in the conventional method, the locus of motion will only draw a constant circular arc, so the abrasive part will not pass through the center of the locus of motion at all, and sufficient polishing action will be achieved. This results in a portion that cannot be covered, and a convex residual portion at the center of the machining mark.

On the other hand, when the phase difference between the X and Y directions is changed periodically, the locus of motion becomes an arc at one point, a straight line at another point, an ellipse at another point, and so on. The shape will change. In other words, the polishing section moves so as to reliably pass through the entire range of motion. As a result, the material to be polished receives a uniform and good polishing action over the entire range of motion of the polishing part, and the resulting machining marks have a smooth concave shape on the entire surface without any remaining convex parts. [Example] Next, an example of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows a polishing tool which is the main part of a polishing apparatus used to carry out the micropolishing method according to the present invention. This polishing tool 1 has a main body 10 that is a polishing device main body (not shown).
is supported and fixed by a support shaft 11. This support shaft 11 can move freely in the horizontal and vertical directions, and can also be tilted at any angle.

The operating mechanism of the support shaft 11 is similar to that of a machining shaft or the like in a normal machine tool.

At the center of the bottom surface of the tool body 10 is a vertical barrel 2.
A direction actuator 20 is provided, and from its lower end, via a connection part 21 having a ball-to-corner connection action,
A block 22 is suspended. Here, the sphere-to-corner connection action means that the block 22 can freely move minutely with respect to the X-direction actuator 20 in the Reliably blocks minute movements of the direction actuator 20 in the X direction 2
It refers to the connecting action that is transmitted to 2.

The X-direction actuator 20 is connected to the structural part of the tool body 10 via a restriction fitting 80, which is an XYX-direction movement restriction means, at a portion immediately above the connection portion 21. Second
The figure shows the detailed structure of the regulating fitting 80. The regulating fitting 80 includes a central portion 83 that is sandwiched and attached between the X-direction actuator 20 and the connecting portion 21;
3, and a rod-shaped regulation support part 81.82 extending in the XYX direction from the tool body part 1.
Fixed to 0. A constriction part 84 is formed in the middle of the restriction support part 81, 82 in the length direction, and the restriction support part 81, 82 can be bent and deformed at the constriction part 84. Therefore, although the X-direction actuator 20 cannot move in the axial direction of the regulation support part 81.82, that is, in the XYX direction, it can expand and contract in the bending direction of the constriction part 84 of the regulation support part 81.82, that is, in the X direction. be.

Next, a central yoke 23 serving as a polishing shaft is integrally connected to the lower end of the block 22 and hangs down therefrom. In Figure 2,
The block 22 and the central yoke 23 are threadedly connected.

At the top of the block 22, the tip of an X-direction actuator 24x is connected in contact with the side surface in the X direction that is horizontal in the figure, and the side surface in the Y direction that is horizontal in the figure and perpendicular to the X direction (
The tip of the Y-direction actuator 24y is abutted and connected to the opposite side surface in FIG. In this embodiment, the X-direction actuator 20, the X-direction actuator 24x, and the Y-direction actuator 24y are all formed by stacking a large number of thin episodic elements, and are activated in the X direction (the axial direction of the central yoke 23) by applying a voltage. , expands and contracts in the X and Y directions, presses the abrasive material against the material to be polished with minute movements in the X direction, and
The abrasive material can be freely moved within the polishing surface of the material to be polished by a combination of minute movements in the direction and the Y direction.

As the specifications of the XYz direction actuator, those shown in Table 1 below can be used.

Table 1 The tip of the central yoke 23 is gradually tapered and has a spherical tip surface. This spherical portion is the polishing portion 26. This polishing part 26 may be made of a Sn plating layer or the like, but when it is made of a polyurethane layer, the magnetic polishing fluid M impregnated and retained in this polyurethane layer polishes the polishing surface of the material W to be polished. be.

In this embodiment, as shown in detail in FIG.
6 consists of a sphere 25 held movably at the tip of a central yoke 23, the surface of which is finished with a Sn plating layer. In this embodiment, the sphere 25 is held at the tip of the central yoke 23 by the viscosity of the magnetic polishing fluid M. However, such a sphere is
It may be held mechanically by being fitted inside the tip of the holder, or it may be held by magnetic force.

Drive wiring 50 for each actuator 20, 24x, 24y
is a drive amplifier 5 consisting of a 3CH piezo driver amplifier.
1 is electrically connected to. The specific specifications of the 3CH piezo driver amplifier are, for example, 350V, 100V,
mA, 30kHz. A signal generator 52 for the Z direction and a variable phase two-output signal generator 53 for the XY directions are connected to the drive amplifier 51. These signal generators 52
53 to each actuator 2 via the drive amplifier 51.
A voltage having a predetermined frequency is applied to actuators 20, 24x, and 24y to control the driving of each actuator 20, 24x, and 24y.

A cylindrical body 30 made of a non-magnetic material is provided on the lower surface of the tool body 10.
is attached. An opening 31 is formed in the middle portion of the cylindrical body 30 (the right side surface portion in FIG. 1), into which the actuators 24x, 24y, drive wiring 50 of each actuator, etc. are inserted. A connecting body 32 made of a ring-shaped magnetic material is screwed and connected to the lower part of the cylindrical portion 30 . A portion of the inner peripheral portion of the connecting body 32 extends to a position close to the outer peripheral surface of the central yoke 23. The connecting body 32 has a fluid supply path 33 penetrating from the outer circumferential side to the inner circumferential lower surface.
A fluid supply pipe 34 is connected to the outer peripheral end of the fluid supply path 33. When the magnetic polishing fluid is supplied to the fluid supply pipe 34, the magnetic polishing fluid is supplied to the fluid supply path 3.
3 to the vicinity of the outer periphery of the tip of the central yoke 23. A permanent magnet 40 made of a ring-shaped S m -Co magnet is attached to the lower end of the connecting body 32 . The strength of the magnetic force of the permanent magnet 40 is, for example, about 5 Gauss.

At the lower end of the permanent magnet 40 is an opposing yoke 35 made of a magnetic material.
is installed. The opposing yoke 35 narrows in a conical shape toward the lower end, and has a tapered inner circumferential portion at the tip, and a certain gap is left between this inner circumferential tip and the tip of the central yoke 23. They are placed opposite each other. As a result, a magnetic circuit is formed from the permanent magnet 40, through the connecting body 32, the central yoke 23, and from the opposing yoke 35 back to the permanent magnet 40.
5, a donut-shaped magnetic gap is formed.

A load cell 60 serving as a load detection means is installed below the central yoke 23 and the opposing yoke 35, and the workpiece W to be polished is polished while being placed on the load cell 60. The detection output of the load cell 60 is inputted to the drive amplifier 51 via the controller 61, so that the pressing force applied from the Z-direction actuator 20 to the workpiece W to be polished is subjected to under-fee hack control. .

A vibration application signal is also input to the drive amplifier 51 from the FC generator 70 in order to apply vibration to the pressing force of the Z-direction actuator 20 .

The magnetic micropolishing method of the present invention, which is carried out using a polishing apparatus having such a structure, will be specifically described below.

The polishing tool 1 is placed on the workpiece W with the workpiece W placed on the load cell 60. Fluid supply pipe 34
When the magnetic polishing fluid M is supplied to the tip of the central yoke 23 from the central yoke 23, the magnetic polishing fluid M is magnetically held near the magnetic gap between the central yoke 23 and the opposing yoke 35. In this state, as schematically shown in FIG. 3, the magnetic polishing fluid M is held covering the lower surface of the tip of the central yoke 23, so that the magnetic polishing fluid M is held by the magnetic action. It is pressed against the surface of the material W.

Next, when a periodic voltage is applied to the Z-direction actuator 20, the Z-direction actuator 20 causes minute expansion and contraction movements in a direction perpendicular to the polishing surface of the material W to be polished (vertical direction as seen in FIG. 1). Accordingly, the polished portion 26, which is the tip of the central yoke 23, moves in the vertical direction (in the direction of the straight arrow) as seen in FIG.
A minute movement is made to press the magnetic polishing fluid M against the surface (polishing surface) of the workpiece W to be polished. Further, a periodic voltage is also applied to the XY direction actuators 24x and 24y,
The block 22, to which the tips of the XY direction actuators 24x and 24y are abutted, swings in the horizontal direction (left and right directions as seen in the figure). As a result, the polishing portion 26 forms a ball-to-corner connecting portion 2.
1 as the center, as shown by the arc-shaped arrow in FIG. This oscillation becomes a minute movement in the horizontal direction (XY force direction) with respect to the surface (polishing surface) of the material to be polished W.
The small movement in the Y force direction and the small movement in the X direction are transmitted to the magnetic polishing fluid M, and the magnetic polishing fluid M polishes the surface (polishing surface) of the material to be polished W. The magnetic polishing fluid M performs a polishing action by pressurizing the workpiece W only in the vicinity of the portion sandwiched between the tip of the central yoke 23 and the workpiece W. A machining mark H having a shape and size corresponding to the range of motion of the polishing portion 26 of the yoke 23 is formed.

At this time, the X-direction actuator 20 is connected to the X-Y-direction actuators 24x, 24y via the ball-to-even connecting portion 21.
are connected, so the XY direction actuator 24x,
24y can be freely performed, and at the same time, the pressing force of the X-direction actuator 20 is reliably transmitted to the polishing section 26.

In addition, the X-Y direction actuator 20 can be
Since movement in the force direction is restricted, the connecting portion 21 or the X-direction actuator 20, which serves as a fulcrum of movement for the XY-direction actuators 24x, 24y, will not move due to the movement of the XY-direction actuators 24x, 24y. . As a result, the polishing section 26 can be made to perform a predetermined movement accurately, and polishing accuracy is improved.

Then, during the polishing process as described above, the phase difference of the minute movements in the XY force directions is periodically changed. When the movement of the polishing section 26 in a plane is divided into XY coordinate components, it can be expressed by the following formula.

X = A sinωt - (1) Y = A
sin ((1) t + δ) - (2) where A is the amplitude, ω is the frequency, t is the time, and δ is the change in phase, and the value of δ can be increased or decreased periodically. As a result, the phase difference between the X direction and the Y direction changes periodically. That is, in this case, while vibrating at a constant frequency in the X direction, the phase in the Y direction is increased or decreased to change the phase difference.

FIG. 4 schematically shows a movement trajectory T-1 of the polishing section 26 that changes depending on the value of δ. For example, δ−0°
Now, draw a linear trajectory passing through the origin of the XY coordinates,
At 0° and δ<90°, an elliptical trajectory is drawn, and δ=90
At °, it draws an arc-shaped trajectory. If δ exceeds 90°,
The slope of a straight line or ellipse is reversed. That is, during the first cycle in which δ gradually increases from Oo to 360 degrees, that is, returns to the original state, the motion trajectory T of the polishing section 26 must pass through a circular range with the radius of the amplitude A. become. As a result, as shown in FIG. 5, the machining marks H on the polished material W are
The entire bottom surface of radius A including the center is dug uniformly.

As described above, the movement of the polishing section 26 can be changed continuously into a straight line, an ellipse, or an arc, or it can be moved at a constant rate by periodically changing the phase difference between the movements in the X direction and the Y direction. Any other crimp motion other than the one described above may be performed as long as the motion can be made to pass through the entire range of motion.

While performing such a polishing action, the entire polishing tool 1 is moved horizontally or three-dimensionally according to a predetermined polishing surface shape, and when the machining marks 11 have been spread over the entire polishing surface of the material to be polished W, Desired polished surfaces such as flat, spherical, or free-form surfaces can be obtained freely.

During this time, in the load cell 60 on which the workpiece W is placed, the pressure applied by the polishing section 26 of the polishing tool 1 to the workpiece W through the magnetic polishing fluid M is detected as a pressure load value. The pressure load signal is fed back to the drive amplifier 51 via the controller 61. Therefore, for example, if the pressure applied to the material W to be polished exceeds a specified value,
The driving amplifier 51 is controlled to reduce the applied force by lowering the voltage applied to the X-direction actuator 20, etc.
Conversely, if the pressure applied to the material to be polished W becomes less than a specified value, the drive amplifier 51 increases the voltage applied to the X-direction actuator 20, thereby increasing the pressure. On the other hand, in the process of machining one machining mark,
Since the pressurizing force tends to decrease over time,
The load cell 60 also detects this tendency and feeds back the detection result to the drive amplifier 51, thereby ensuring that the pressing force is always constant. In addition, the signal generator 52 for the Z direction is configured such that in the process of machining one machining mark, the pressing force is large at the beginning, the pressing force is medium in the middle period, and the pressing force is small at the final stage. A control signal is issued to the drive amplifier 51. Meanwhile, the FG generator 70
A vibration imparting signal for imparting vibration to the pressing force of the Z-direction actuator 20 is continuously emitted to the drive amplifier 51.

〔Effect of the invention〕

As described above, by periodically changing the phase difference in the x and y directions when making minute movements of the polishing part, the entire surface of the machining mark can be dug uniformly even if the machining diameter is increased. Therefore, no convex residual portion remains at the center of the machining mark, and a smooth concave machining mark is formed. Therefore, the efficiency of polishing can be increased by increasing the machining diameter, and at the same time, the polishing accuracy can be further improved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of a polishing tool which is the main part of the polishing device used to carry out the micro-polishing method according to the present invention, Fig. 2 is an exploded perspective view of the actuator portion, and Fig. 3 is an explanatory diagram of the polishing action of the present invention. , Fig. 4 is an explanatory diagram showing the locus of movement of the polishing part, Fig. 5 is a schematic cross-sectional view of the formed machining marks, and Fig. 6 shows the cross-sectional shape of the machining marks and the locus of movement of the polishing part by the conventional method. It is an explanatory diagram. ■... Polishing tool 24x... X direction actuator 24y... Y direction actuator 26... Polishing section 53... Variable phase 2 output signal generator H... Machining mark M... Magnetic polishing fluid T...Trajectory of motion W...Name of agent for polished material Patent attorney Shigetaka Awano (1 person)Figure 1Figure 4Figure 5Figure 6

Claims (1)

[Claims] 1. With the abrasive material held between the polishing part at the tip of the polishing tool and the workpiece to be polished, the polishing part is minutely moved in the XY directions parallel to the polishing surface by an actuator consisting of an electrostrictive element, and A micropolishing method that polishes a material to be polished by periodically changing the phase difference between the micromovement and the Y-direction micromovement.