JPS63232932A - Polishing method and device therefor - Google Patents

Abstract

PURPOSE:To enable removal of a ripple produced during polishing of an optical element, by a method wherein a ring beltform polishing tool is scanned in a swung state over a workpiece, and the scanning range of the tool is controlled by a position detecting means as a relative speed therebetween is suppressed within a given value. CONSTITUTION:By means of a control device 39, a motor 26 rotates a work support body 14 and a workpiece 12, a motor 30 rotates a polishing tool 28, a motor 34 exerts scanning movement on a column 32, and the polishing tool 28 is swung by a crank mechanism, rotated by a swing motor, and a swing arm. A position detecting means 37 detects the position in a scanning direction of the polishing tool 28 to the workpiece 12 to feed a signal to a control device 39, and a control device 37 controls the scanning range of the polishing tool 28 by means of the feed signal. In which case, the workpiece 12 is rotated at (a) rpm and the polishing tool 28 is rotated at (b) rpm. A given magnitude of swing movement is exerted in a direction C on the polishing tool 28, further, scanning movement in a distance from a position (d) to a position (e) is exerted on the polishing tool 28, a ripple on the surface of a lens and the like can be removed with high efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION (Field of Industrial Application) The present invention relates to a polishing method and apparatus, and more particularly to a polishing method and apparatus suitable for high-precision polishing of optical elements.

[Conventional technology]

Conventionally, in order to finish the surface of optical elements such as lenses, prisms, or reflective mirrors with extremely high precision, a method has been used in which the surface, which has been polished to a certain degree, is partially corrected and polished using a small-diameter polishing pad. It is being

FIG. 5 is a schematic perspective view showing a specific example of such correction polishing. In the figure, the object to be polished 12 is a disk-shaped optical glass parallel plate, and its lower surface is bonded and fixed to a workpiece support 14. The work support 14 is rotatably supported by a work rotation shaft 25, and the object to be polished I2 is fixed to the work support 14 so as to be rotationally symmetrical about the work rotation shaft 25. The upper surface of the object to be polished 12 is mirror-polished in advance by pre-processing. However, it is assumed that the illustrated ring zone Y has a convex shape due to this pre-processing. In the correction polishing, a polishing pad 16 having a diameter smaller than that of the object 12 to be polished is used. The polishing pad 16 is bonded and fixedly supported on the lower surface of the tool support 18, and one end of the rod 20 is abutted against the center of the upper surface of the tool support 18. The rod 20 is swingable in the radial direction of the object to be polished 12 with an appropriate width as shown by arrow A. A polishing liquid is supplied between the polishing object 12 and the polishing pad 16 through a nozzle 22 . While supplying the polishing liquid from the nozzle 22 to the upper surface of the workpiece 12,
Corrective polishing of the object to be polished 12 is performed by rotating the tool support 18 in the direction of arrow B and simultaneously rotating the tool support 18 in the direction of arrow C and swinging it in the direction of the arrow.

[Problem that the invention seeks to solve]

When the object to be polished has an axially symmetrical shape, the polishing process is usually performed while rotating the object around the axis. However, when the object is large, there are four small convex parts concentrically centered around the center of rotation. May occur alternately. (Hereinafter, the state in which these concentric minute convex portions and four portions occur alternately is called a ripple.) - The purpose of the conventional polishing method described above is to remove large concentric undulations, so it is Even if an attempt is made to remove the above-mentioned ripples, the object to be polished is removed, but the ripples remain as they are, which is a drawback.

SUMMARY OF THE INVENTION An object of the present invention is to provide a polishing method and a polishing apparatus for removing ripples from an object to be polished during polishing of an optical element.

(Means for Solving the Problems) The polishing method of the present invention includes performing a scanning motion in a separately determined direction while swinging a polishing tool formed in an annular shape in a predetermined direction on the workpiece to be polished. In addition, the velocity component in the rotational direction of the object to be polished in the configuration of the relative velocity caused by the mutual movement between the object to be polished and the polishing tool is set so as not to exceed a predetermined value. The device includes a feeding means for swinging the polishing tool in a predetermined direction and scanning in a separately determined direction, and a position detection means with respect to the scanning direction, and a control device that can control the scanning range of the polishing tool based on a signal from the position detection means. It is equipped with

(Operation) We have examined in detail the motion conditions of the tool and the conditions of the tool necessary to remove minute ripples.

The contents are described below.

The test piece used in this study was a quartz glass lens with an outer diameter of 170 mm and a radius of curvature of 490 mm.
This causes a ripple of 4. Also, the outside diameter of the tool is 2
0+nm, and the contact surface is 20mm in diameter for tool A.
The entire surface has a concave surface equal to the curvature of the workpiece.

(Hereinafter, B and C also have similar concave contact areas). Tool B has an outer diameter of 20 mm and an inner diameter of 10 mm, and tool C has an outer diameter of 20 mm and an inner diameter of 15 mm. The contact surfaces are all flat. It was created by The polishing device shown in Figure 1 was used for the study.

■I of! The study was carried out on a section of 60 mm to 80+ nm from the center of the object to be polished, respectively. Further, the velocity component ratios in Table 1 are average values at a distance of 70 mm above the object to be polished. Consideration 1.
is an example of the conventional example, study 2. In consideration 3., when the three elements of the main polishing motion, namely rotation of the object to be polished, rotation of the tool, and rocking of the tool, are made approximately equal. is the rotation rate of the polished object 1
This is an example where it is 0% or less. At this time, tool B was used. Note that scanning is based on consideration 1. 〜3, which is a common condition for I
60mm to 80m above the object to be polished at a speed of IIIm/min
The scan was performed over an interval of m.

Consideration 1. Although the removal amount is large, the ripple remains and the removal does not progress.

Consideration 2. In this case, the ripples are removed to some extent, but the amount of removal itself is small, so it takes a very long time to remove the ripples.

Consideration 3. So, the ripple removal has progressed.

The following can be derived from this study. In other words, the ratio of rotation of the object to be polished in the composition of the relative speed is preferably low. At this time, among other factors, tool scanning is an element for continuously removing ripples over a wide area on the workpiece, so tool scanning does not account for a high proportion of the relative speed configuration. do not have. Additionally, a crank mechanism is usually used to swing the tool, as shown in Figure 1.
Vibrations are likely to occur from the crank portion, and the number of times the crankshaft can be oscillated per unit time cannot be increased due to restrictions on the weight of the oscillating parts and the load on the crank mechanism. The swing stroke cannot be too long due to the size and load of the crank mechanism. Therefore, it becomes difficult for the swing of the tool to occupy an extremely high proportion in the configuration of the relative speed when the absolute value of the relative speed becomes large to a certain extent. The rotation of the tool has a large degree of freedom and can account for a large proportion of the relative speed. It can account for 87% even at relatively high relative speeds such as .

M-type Hobeho I Study 3. The difference in ripple removal ability of tools A, B, and C was examined under the following conditions. At this time, the loads applied to the blood tl' 1 area were made equal to each other. As a result, the ripple removal ability of tools B and C was good, and tool A
ability was low.

Moreover, among tools B and C, tool C was better. The difference between tools A, B, and C can be considered to be a difference in stability during movement of the tools on the workpiece. In other words, if a tool with poor stability is used, the tool will hit the valley of the ripple during polishing, especially during rocking, and the polishing will be in a state contrary to the intention of selectively removing the sopple peak. It is considered to be.

From the above, it is assumed that the tool has a ring shape.3.
In other words, what is necessary to remove ripples is to satisfy both of the following conditions: the relative velocity in the normal direction of the ripple should be the main one, and the relative velocity component in the tangential direction of the ripple should be reduced as much as possible. Understood. Further, it is preferable that the outer diameter of the contact surface of the tool is at least twice the ripple.

Note that the polishing device swings the polishing tool in a predetermined direction while making a scanning motion in another direction, detects the scanning direction by a position detection means, and receives a signal from the position detection means by a control device to control the polishing tool. control the scanning range. If it is kept below a predetermined value, the polishing efficiency will be further improved.

[16 Examples] Next, examples of the present invention will be described with reference to the drawings.

FIG. 1(a) is a longitudinal sectional view of one embodiment of the polishing apparatus of the present invention, and FIG. 1(b) is a view taken along the line II in FIG. 1(a).

In addition, Fig. 2(a) is a perspective view of the polishing tool, Fig. 2(6)
is a cross-sectional view of the polishing tool installed.

The object to be polished 12 is a disc-shaped optical glass plane, and its lower surface is adhesively fixed to a workpiece support 14 . The workpiece support 14 is the machine frame; the workpiece rotating shaft 25 supported on the machine frame 0 is the machine frame l.
It is connected to be rotated via a gear body 27 from a drive motor 26 which is fixed to O.

The polishing tool 28 is rotatably supported on the head 31a of the arm 31,
Head 31. It is connected to a tool rotating shaft 29 that is connected to a motor 30 fixed to a. The arm 31 is rotatably connected to the feed column 2 via a pin 33 and a metal fitting 33a, and is swingably attached to the metal fitting 33a by a vertical pin 42. Arm 31
One end of a swinging arm 41 is separately attached to the head 31a, and the other end of the swinging arm 41 is attached to the outer periphery of a crank mechanism 40 provided at the top of the feed column 32 with a pin 40a. It is driven by a motor (not shown) directly connected to the lower side of the shaft of 40. Feed column 32
is slidably fitted to a slide guide 36 fixed to the machine frame IO, and includes a feed motor 34 fixed to the machine frame IO, and a feed screw 35 connected to this motor 34 and supported on the machine frame IO.
, and a nut (not shown) fixed to the feed column 32 into which the feed screw 35 is screwed into the arrow A in FIG. 1(b).
sent in the direction. Feed position detection unit 3 such as optical or magnetic linear scale or inductosin
7 is fixed to the slide guide 36 and the feed column 32. A polishing liquid supply nozzle 2 is provided in the space above the object to be polished 12.
2, and a housing 38 is fixed to the machine frame IO around the outer periphery of the object to be polished 12 and the work support 14 to prevent and collect the supplied polishing liquid from scattering. The control device 39 controls the motors 26, 30 . Signals are input from the feed motor 34 and a swinging motor position detection unit 37 (not shown) to give the polishing tool 28 a swinging motion, a scanning motion, and a rotational motion, and to control the scanning range of the polishing tool 28.

As shown in FIG. 2(a), the polishing tool has two notches 28a in its cylindrical body that are driven by drive pins 29a inserted perpendicularly to the axis of rotation of the tool 29, and a lower end. A ring-shaped polishing tool 28b is fixed to. In this embodiment, pitch is used as the material for the polishing tool 28, but it may also be made of foamed polyurethane material.

Next, the operation of the apparatus of this embodiment will be explained. First of all,
The object to be polished 12 is adhesively fixed onto the work support 14 and fitted onto the rotating shaft 25 . Next, the arm 31 is set so that the tool rotation shaft 29 is perpendicular to the object to be polished 12, and the polishing tool 28 is attached to the tip of the tool rotation shaft 29. Next, polishing liquid is supplied from the polishing liquid supply nozzle 22 . Subsequently, the control device 39 applies rotation to the motors 26, 30, 34 and a swing motor (not shown). motor 26
rotates the workpiece support 14 and the object to be polished 12, the motor 30 rotates the polishing tool 28, the motor 34 provides a scanning motion to the feed column 32, and the polishing tool 28 is driven by a crank mechanism rotated by an oscillating motor. 40 and a swinging arch 41. The position detection means 37 detects the position of the polishing tool 28 in the scanning direction with respect to the object to be polished 12 and sends a signal to the control device 39, and the control device 37 controls the scanning range of the polishing tool 28 based on the sent signal.

FIGS. 3(a) and 3(b) are diagrams showing the cross-sectional shape and the shape of the correction words of the object I2 to be polished before correction, which is to be corrected by the polishing apparatus of the present invention. There are ripples with pitch p and depth h on the surface.

FIG. 4 shows the direction of the relative movement of the polishing tool 28 with respect to the object 12, in which the object 12 rotates by ARPM, and the polishing tool 28 rotates by BRPM.

The polishing tool 28 is given a swinging motion of a predetermined magnitude in the direction C, and furthermore, the polishing tool 28 is given a scanning motion of a length from position d to e. Here, an example of machining conditions will be given based on the surface discussion. The object to be polished 12 has an outer diameter of 170 mm.
, a convex lens made of quartz glass with a pole radius of 490 mm. The polishing tool 28 is made of pitch material and has an outer diameter of 20 mm.
An unbroken ring zone with an inner diameter of 17 mm and 5 mm, the rotation speed of the workpiece is a = 2 rpm, and the rotation speed of the polishing tool is b =
200 rpm, oscillation at 100 cycles/min, stroke c = 1001111, scanning position d = 401
11[11,e = 70mm, scanning speed = 1mm/
min, and the polishing liquid was 6 weight percent cerium oxide. Under these processing conditions, when a material with ripples with pitch p = 5 to 7 mm and unevenness difference h = 0.1- was polished twice, the ripple depth was reduced to h = 0.06-.
When polishing was performed three more times for a total of five times, h=0.03p, which was an almost satisfactory result.

Table 2 shows a comparison with the conventional method.

Note that slits may be provided at predetermined intervals in the annular zone of the polishing tool.

(Effects of the Invention) As explained above, the present invention involves making a polishing tool whose contact surface has an annular shape swing motion in a predetermined direction on the workpiece to be polished and scanning motion in a separately determined direction. A polishing method in which the velocity component of the relative speed of the polishing tool and the object to be polished is suppressed to a predetermined value or less, and a polishing method using this method, which gives swinging motion and scanning motion to the polishing tool, and scans the polishing tool by using a position detection means. Polishing equipment equipped with a control device that can control the range,
This has the effect that ripples on the surface of optical elements such as lenses can be removed with high efficiency.

[Brief explanation of the drawing]

FIG. 1(a) is a longitudinal cross-sectional view of one embodiment of the polishing apparatus of the present invention, FIG. 1(b) is a view taken along the line II in FIG. 1(a), and FIG. 2(a) is a polishing device. A perspective view of the tool, FIG. 2(b) is a cross-sectional view of the polishing tool in its installed state, and FIGS. 3(a) and (b) are cross-sectional views showing the shape of the object to be polished before and after modification, respectively. FIG. 4 is a top view showing the relative movement of the polishing tool with respect to the object to be polished, and FIG. 5 is a perspective view showing an example of a conventional polishing method. 10......Machine frame, 12-...
...-Object to be polished, 14... Work support, 22-... Polishing liquid supply nozzle, 26.3
0.34...Motor, 27...
...Gear body, 28-... Polishing tool,
29--... Tool rotation axis, 31--
---Arm, 32...Feed column, 33.42--Bin, 35...
...Feed screw, 36-----Slide guide, 37...Position detection unit, 38
-... Housing, 39-...
...Control device, 40...Crank mechanism,
41---------... Swinging arm.

Claims (1)

[Scope of Claims] 1. A polishing method in which a rotatable polishing tool whose effective contact surface with the polished object is formed in an annular shape is pressed against the rotatable polished object to polish the polished object, A polishing method characterized in that the polishing tool is moved in a scanning motion in a separately determined direction while swinging the polishing tool in a predetermined direction on the object to be polished. 2. The polishing method according to claim 1, wherein a velocity component generated by rotation of the object to be polished in a configuration of relative velocity caused by mutual movement between the object to be polished and the polishing tool does not exceed a predetermined value. 3. A polishing tool whose effective contact surface with the object to be polished is formed in a ring shape, a drive means for rotating the polishing tool, a drive means for rotating the object to be polished, and a drive means for rotating the polishing tool in a predetermined direction. A polishing apparatus having a drive means for swinging the polishing tool in a predetermined direction, and a feeding means for scanning in a separately determined direction while swinging the polishing tool in a predetermined direction, and a position detection means with respect to the scanning direction, the position detection means A polishing apparatus comprising a control device that can control the scanning range of the polishing tool based on a signal.