U.S. patent application number 10/595172 was filed with the patent office on 2007-01-04 for free curved surface precision machining tool.
Invention is credited to Takashi Matsuzawa, Hitoshi Omori, Hidenori Yamaki.
Application Number | 20070004318 10/595172 |
Document ID | / |
Family ID | 34372877 |
Filed Date | 2007-01-04 |
United States Patent
Application |
20070004318 |
Kind Code |
A1 |
Omori; Hitoshi ; et
al. |
January 4, 2007 |
Free curved surface precision machining tool
Abstract
A free curved surface precision machining tool for
precision-machining a surface to be machined with the lower end in
contact therewith by rotation around an axis x. It includes a
drum-shaped tool having a rotation axis x orthogonal to the axis z
and rotationally driven around the rotation axis x. This
drum-shaped tool has a convex machining surface in the form of an
arcuate rotary body obtained by rotating an arc of a radius r with
the center at the intersection O between the axis z and the
rotation axis x around the rotation axis x. The convex machining
surface contacts the surface to be machined to precision-machine
the latter, while the convex machining surface is rotated around
the orthogonal axis x so as to disperse the machining position of
the convex machining surface.
Inventors: |
Omori; Hitoshi; (Saitama,
JP) ; Yamaki; Hidenori; (Saitama, JP) ;
Matsuzawa; Takashi; (Saitama, JP) |
Correspondence
Address: |
GRIFFIN BUTLER WHISENHUNT & SZIPL LLP;SUITE PH-1
2300 NINTH STREET SOUTH
ARLINGTON
VA
222042396
US
|
Family ID: |
34372877 |
Appl. No.: |
10/595172 |
Filed: |
September 16, 2004 |
PCT Filed: |
September 16, 2004 |
PCT NO: |
PCT/JP04/13512 |
371 Date: |
March 17, 2006 |
Current U.S.
Class: |
451/8 ;
451/56 |
Current CPC
Class: |
B24B 41/04 20130101;
B23C 5/1009 20130101; B23C 3/16 20130101 |
Class at
Publication: |
451/008 ;
451/056 |
International
Class: |
B24B 49/00 20060101
B24B049/00; B24B 1/00 20060101 B24B001/00 |
Foreign Application Data
Date |
Code |
Application Number |
Sep 19, 2003 |
JP |
327645/2003 |
Claims
1. A free curved surface precision machining tool for
precision-machining a surface to be machined with the lower end in
contact therewith by rotation around an axis z, comprising a
drum-shaped tool having an orthogonal axis x orthogonal to the axis
z and rotationally driven around the orthogonal axis x, wherein the
drum-shaped tool has a convex machining surface in the form of an
arcuate rotary body obtained by rotating an arc of a radius r with
the center at the intersection O between the axis z and the
orthogonal axis x around the orthogonal axis x, whereby the convex
machining surface contacts the surface to be machined to
precision-machine the latter, while the convex machining surface is
rotated around the orthogonal axis x so as to disperse the
machining position of the convex machining surface.
2. The free curved surface precision machining tool according to
claim 1, wherein the radius r is set smaller than the maximum
radius R of the convex machining surface from the orthogonal axis
x, whereby the position control of a machining trajectory is
performed at the center O of rotation of the arc.
3. The free curved surface precision machining tool according to
claim 1, wherein the radius r is set larger than the maximum radius
R of the convex machining surface from the orthogonal axis x,
whereby the position control of a machining trajectory is performed
at the center A of the lowest arc.
4. The free curved surface precision machining tool according to
claim 1, wherein the convex machining surface of the drum-shaped
tool is made of a grindstone or a cutter.
5. The free curved surface precision machining tool according to
claim 4, wherein the grindstone includes a metal in its bonding
material.
6. The free curved surface precision machining tool according to
claim 1, further comprising a non-machining section for protecting
the end of the convex machining surface without direct involvement
in machining, the non-machining section being adjacent to the
convex machining surface of the drum-shaped tool.
7. The free curved surface precision machining tool according to
claim 6, wherein the non-machining section is made of material
wearing out more easily than a grindstone bonding material so as
not to damage the surface to be machined and includes a conductive
material in its material.
8. The free curved surface precision machining tool according to
claim 1, further comprising an impeller disposed on both sides or
one side of the drum-shaped tool and a flow channel for emitting a
jet of fluid to the impeller in the rotative direction, wherein the
drum-shaped tool is rotationally driven around the orthogonal axis
x.
9. The free curved surface precision machining tool according to
claim 1, further comprising a belt in contact with the outer
peripheral surface of the drum-shaped tool and a pulley for holding
the belt between the pulley and the drum-shaped tool, wherein the
drum-shaped tool is rotationally driven around the orthogonal axis
x by rotation of the belt.
10. The free curved surface precision machining tool according to
claim 9, wherein the belt has a polishing surface on the side in
contact with the outer peripheral surface so as to correct the
convex machining surface of the drum-shaped tool as soon as the
drum-shaped tool begins to be rotationally driven.
11. The free curved surface precision machining tool according to
claim 6, further comprising a pulley in contact with the outer
peripheral surface of the non-machining section and a belt for
rotationally driving the pulley, wherein the drum-shaped tool is
rotationally driven around the orthogonal axis x by rotation of the
pulley.
12. The free curved surface precision machining tool according to
claim 1, further comprising a driven gear disposed on both sides or
one side of the drum-shaped tool and a main driving gear for
driving the driven gear, wherein the main driving gear is
belt-driven so as to rotationally drive the drum-shaped tool around
the orthogonal axis x.
13. The free curved surface precision machining tool according to
claim 1, further comprising correction means for correcting the
convex machining surface of the drum-shaped tool.
14. The free curved surface precision machining tool according to
claim 13, wherein the correction means is formed of grindstone,
electrolysis, or discharge means or combined means thereof.
15. The free curved surface precision machining tool according to
claim 12, wherein the correction means functions simultaneously
with the machining of material to be machined.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to a free curved surface
precision machining tool for precision-machining a free curved
surface (more specifically, for precision-removing the free curved
surface with grinding or cutting), having a convex machining
section in the form of an arcuate rotary body at the lower end.
[0003] 2. Description of the Related Art
[0004] Referring to FIG. 1, there is typically shown machining
(removal machining) of a free curved surface with a conventional
free curved surface machining tool. The conventional free curved
surface machining tool 1 is, for example, a ball nose grindstone or
a ball end mill, which has a spherical machining surface at the
lower end and is configured to rotate around the axis z. A free
curved surface 2 is a part of, for example, a molding die, an
aspherical lens, or the like. With high-speed rotation around the
axis z, the free curved surface machining tool 1 machines the free
curved surface 2 while relatively moving the lower end along the
free curved surface 2. A free curved surface of a die, an
aspherical lens, or the like can be freely formed with repetition
of the machining using the machining tool 1.
[0005] Moreover, there has already been disclosed a free curved
surface machining tool wherein the circumferential speed of the
axis does not reach zero (0) in Patent Document 1.
[0006] The "free curved surface machining tool" in Patent Document
1 is a tool for machining a surface to be machined with the lower
end in contact therewith by rotation around an axis z, including a
spherical tool having at least a spherical machining section on the
lower side thereof and a support bearing for supporting the
spherical tool on a rotation axis a, which is different from the
axis z and passes through the center of the spherical surface.
[Patent Document 1]
[0007] Japanese Patent Laid-Open No. H10-156729
[0008] The free curved surface machining tool 1 shown in FIG. 1
rotates around the axis z and therefore the circumferential speed
of the machining surface is zero (0) at the position of the axis
(radius 0), by which the axis (radius 0) is the dead center of
machining. Moreover, the radius of rotation significantly depends
upon the position of the machining surface, and thus the
circumferential speed and the rotation load largely fluctuate,
which leads to a problem that the precision machining
(high-precision and high-quality machining) cannot be performed. In
addition, the free curved surface machining tool 1 has a problem
that there is a need to maintain sharpness and an accurate
spherical surface of the tool machining surface on a constant basis
in order to achieve the machining function and precision.
[0009] Accordingly, it has conventionally been necessary to prepare
a multi-axis NC machining apparatus having four or five axes
wherein the axis z of the free curved surface machining tool 1 can
be arbitrarily inclined during machining and a program creation
therefor. This kind of program creation, however, is complicated
and difficult, and further the increase in the number of axes
requires an advanced technique in manufacturing the machining
apparatus. This leads to a problem that the multi-axis NC machining
apparatus having four or more axes capable of precision machining
becomes expensive and poor in versatility.
[0010] The following gives more detailed description of the above
problems in cases where precision machining is performed.
[0011] Referring to FIGS. 2A to 2D, there are shown illustrations
of machining portions, which are enlarged in some measure so as to
be easy to understand. If the depth of the cut c (the depth of
machining) is deep (FIG. 2A), the contact surface e is wide
independently of the magnitude of feed d (a moving distance of the
tool) unless the feed direction y (a direction of movement of the
tool) is the vertical direction, and thus the main machining
portion is far from the axis z. In this case, the roughness
(concavity and convexity) of the surface to be machined is large (a
plane roughness is large), but it does not become a problem since
rough machining is mainly aimed for.
[0012] If the depth of the cut c is shallow (FIG. 2B), in other
words, in precision machining, the contact surface e is narrow, and
as the main machining portion comes close to the axis z, the
roughness of the surface to be machined becomes small. In this
case, however, the above matters in question such as the precision
machining (high-precision and high-quality machining) and the need
for maintaining the sharpness and the accurate spherical surface of
the tool machining surface are coming to the fore.
[0013] Moreover, as well as the narrow contact surface e, the
peripheral speed and the required driving torque undergo drastic
changes according to the magnitude of the distance of the contact
surface e from the axis (radius of rotation), thereby causing
problems of irregularity in the roughness of the surface to be
machined, a chatter mark (caused by vibration), or a decrease in
machining accuracy.
[0014] On the other hand, the narrowing of the contact surface e
causes a local convergence of the contact position or frequency of
the machining tool according to the feature of the free curved
surface to be machined, which results in a local convergence of
portions where the machining function (the sharpness) declines and
of deformations caused by contact friction, by which the
deformations are reverse-transferred to the surface to be machined
or the surface is damaged. These are magnified by the
interaction.
[0015] In the NC grinding, it is essential to generate a new
surface and to maintain an accurate spherical surface in the
grinding section at all times in order to maintain the machining
function and precision machining.
[0016] Referring to FIG. 3, there is shown an illustration of a
deformation in a spherical grindstone and correction thereof, which
is enlarged so as to be easy to understand. The deformation occurs
more easily as the contact frequency is higher and it is farther
from the axis, and once the deformation begins to occur, a reverse
transfer occurs and thereby the deformation is accelerated.
Therefore, if so, rapid correction is required. It is necessary to
fair the shape until there is nothing left of the deformation by
removal machining from the radius m of an old spherical surface to
the radius n of a new spherical surface. It is, however, generally
hard to correct the deformation in a situation where the
deformation from the spherical surface is significant.
[0017] Therefore, there is a need to control a contact wear
position and a contact frequency by inclining the axis z in such a
way that the contact frequency of the grinding section is uniform
over the entire surface thereof to reduce the need for the
correction. Unless the axis z can be inclined arbitrarily, however,
the grinding section is continuously and systematically corrected
by using a setting value previously incorporated into the program,
by which a large part of the spherical machining section is removed
wastefully.
[0018] Moreover, the correction of the spherical machining section
of the spherical tool is made by decreasing the radius, in other
words, by changing the curvature, and therefore there is a need for
precision removal machining with an NC machining apparatus.
[0019] Referring to FIG. 2C and FIG. 2D, there are shown cross
sections perpendicular to a machining trajectory. It is necessary
to minimize or remove a cusp amount h by decreasing a pick feed g
or increasing the spherical radius of the machining tool. The
spherical radius of the machining tool, however, need be equal to
or larger than the curvature of the minimum negative (concave)
curved surface in the free curved surface in order to prevent a
damage to the machined curved surface, which may be caused by a
tool interference. Therefore, it leads to a problem that there is
no other choice but to select a measure to shift the pick feed g by
a half pitch or decrease it, though the machining time thereby
increases.
[0020] Moreover, while the accuracy of machining position can be
improved by decreasing the spherical radius of the machining tool,
it leads to a problem that the machining time increases as
described above.
SUMMARY OF THE INVENTION
[0021] The present invention has been provided to resolve the above
various problems. Specifically, it is an object of the present
invention to provide a free curved surface precision machining tool
capable of efficiently precision-machining a free curved surface
using a versatile 3-axis NC machining apparatus, by dispersing the
moving trajectory of the contact surface of a tool machining
section and achieving a constant moving speed and driving torque so
as to maintain the sharpness of the tool machining section, to
achieve uniform wear and a self-correction function thereof, and to
decrease the wearing speed, whereby the accuracy of form of the
tool machining section can be maintained continuously.
[0022] According to the present invention, there is provided a free
curved surface precision machining tool for precision-machining a
surface to be machined with the lower end in contact therewith by
rotation around an axis z, including a drum-shaped tool having a
rotation axis x orthogonal to the axis z and rotationally driven
around the rotation axis x, the drum-shaped tool having a convex
machining surface in the form of an arcuate rotary body obtained by
rotating an arc of a radius r with the center at the intersection O
between the axis z and the rotation axis x around the rotation axis
x, whereby the convex machining surface contacts the surface to be
machined to precision-machine the latter, while the convex
machining surface is rotated around the orthogonal axis x so as to
disperse the machining position of the convex machining
surface.
[0023] According to a preferred embodiment of the present
invention, the radius r is set smaller than the maximum radius R of
the convex machining surface from the rotation axis x, whereby the
position control of a machining trajectory is performed at the
center O of rotation of the arc.
[0024] According to another preferred embodiment of the present
invention, the radius r is set larger than the maximum radius R of
the convex machining surface from the rotation axis x, whereby the
position control of a machining trajectory is performed at the
center A of the lowest arc.
[0025] The convex machining surface of the drum-shaped tool is made
of a grindstone or a cutter. The grindstone includes a metal in its
bonding material. Moreover, the free curved surface precision
machining tool has a non-machining section for protecting the end
of the convex machining surface without direct involvement in
machining, the non-machining section being adjacent to the convex
machining surface of the drum-shaped tool. The non-machining
section is made of material wearing out more easily than the
grindstone bonding material so as not to damage the surface to be
machined and includes a conductive material in its material.
[0026] According to a preferred embodiment of the present
invention, the free curved surface precision machining tool further
includes an impeller disposed on both sides or one side of the
drum-shaped tool and a flow channel for emitting a jet of fluid to
the impeller in the rotative direction, wherein the drum-shaped
tool is rotationally driven around the orthogonal axis x.
[0027] According to still another preferred embodiment of the
present invention, the free curved surface precision machining tool
further includes a belt in contact with the outer peripheral
surface of the drum-shaped tool and a pulley for holding the belt
between the pulley and the drum-shaped tool, wherein the
drum-shaped tool is rotationally driven around the orthogonal axis
x by rotation of the belt.
[0028] The belt has a polishing surface on the side in contact with
the outer peripheral surface so as to correct the convex machining
surface of the drum-shaped tool as soon as the drum-shaped tool
begins to be rotationally driven.
[0029] According to further another preferred embodiment, the free
curved surface precision machining tool includes a pulley in
contact with the outer peripheral surface of the non-machining
section and a belt for rotationally driving the pulley, wherein the
drum-shaped tool is rotationally driven around the orthogonal axis
x by rotation of the pulley.
[0030] According to still another preferred embodiment, the free
curved surface precision machining tool includes a driven gear
disposed on both sides or one side of the drum-shaped tool and a
main driving gear for driving the driven gear, wherein the main
driving gear is belt-driven so as to rotationally drive the
drum-shaped tool around the orthogonal axis x.
[0031] Moreover, the free curved surface precision machining tool
includes correction means for correcting the convex machining
surface of the drum-shaped tool. The correction means is formed of
grindstone, electrolysis, or discharge means or combined means
thereof. The correction means functions simultaneously with the
machining of material to be machined.
[0032] According to the above configuration of the present
invention, the free curved surface precision machining tool
precision-machines a surface to be machined with the convex
machining surface in contact therewith by rotation around the axis
z and the convex machining surface is rotated around the orthogonal
axis x so as to disperse the machining position of the convex
machining surface. Therefore, the free curved surface precision
machining tool is capable of efficiently precision-machining a free
curved surface using a versatile 3-axis NC machining apparatus by
dispersing the moving trajectory of the contact surface of the tool
machining section and achieving a constant moving speed and driving
torque so as to maintain the sharpness of the tool machining
section, to achieve uniform wear and a self-correction function
thereof, and to decrease the wearing speed, whereby the accuracy of
form of the tool machining section can be maintained
continuously.
[0033] The above and other objects and advantageous features of the
invention will be apparent from the following description taken in
connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0034] FIG. 1 is a schematic diagram of a conventional free curved
surface machining tool;
[0035] FIGS. 2A to 2D are schematic diagrams of conventional
machining modes;
[0036] FIG. 3 is a diagram showing a wear mode of the conventional
tool;
[0037] FIG. 4 is a diagram showing a first embodiment of a free
curved surface precision machining tool according to the present
invention;
[0038] FIG. 5 is a diagram showing a second embodiment of the
present invention;
[0039] FIG. 6 is a diagram showing a third embodiment of the
present invention;
[0040] FIG. 7 is a diagram showing a fourth embodiment of the
present invention;
[0041] FIGS. 8A and 8B are diagrams for explaining an operation of
the present invention;
[0042] FIGS. 9A and 9B are other diagrams for explaining an
operation of the present invention;
[0043] FIG. 10 is a diagram showing a fifth embodiment of the
present invention;
[0044] FIG. 11 is a diagram showing a profile of roughness of a
surface machined by the free curved surface precision machining
tool of the present invention; and
[0045] FIG. 12 is a macrophotograph of the surface machined by the
free curved surface precision machining tool of the present
invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0046] Preferred embodiments of the present invention will be
described hereinafter with reference to the accompanying drawings.
The same reference numerals have been used for similar parts in
respective diagrams, with duplicate description omitted.
[0047] Referring to FIG. 4, there is shown a diagram illustrating a
first embodiment of a free curved surface precision machining tool
according to the present invention. The free curved surface
precision machining tool 10 of the present invention is configured
to machine a surface to be machined 2 (see FIGS. 1 and 2) with the
lower end in contact therewith by rotation around an axis z of a
tool body 11. While the following embodiment will be described in a
situation where the surface to be machined 2 is located below the
free curved surface precision machining tool 10 and is machined at
the lower end of the free curved surface precision machining tool
10. However the present invention is not limited thereto, but can
be applied directly to an embodiment in which the surface is
machined at the horizontal end or upper end of the free curved
surface precision machining tool 10 by using it in a horizontal or
inverted position.
[0048] The free curved surface precision machining tool 10 of the
present invention includes a drum-shaped tool 12. The drum-shaped
tool 12 is rotatably supported by a support bearing 14 around the
orthogonal axis x, which is orthogonal to the vertical axis z in
this diagram, and the bearing 14 is supported by a support shaft
12a of the drum-shaped tool 12.
[0049] Moreover, the drum-shaped tool 12 has a convex machining
surface 13 for machining a surface to be machined with being in
contact therewith. The convex machining surface 13 has a form of an
arcuate rotary body obtained by rotating an arc of a radius r with
the center at the intersection O between the axis z and the
rotation axis x around the rotation axis x.
[0050] The convex machining section 13a of the drum-shaped tool 12
is a conductive grindstone including a metal in its bonding
material in this embodiment, so as to machine the surface to be
machined efficiently by being in contact therewith. The convex
machining section 13a may be a cutter instead of the
grindstone.
[0051] Moreover, in this embodiment, the free curved surface
precision machining tool 10 according to the present invention
includes an impeller 15 disposed on both sides (or one side) of the
drum-shaped tool 12 and a via hole 11a for emitting a jet of fluid
3 to the impeller 15 in the rotative direction, so that the
drum-shaped tool 12 is rotationally driven around the orthogonal
axis x. Although the fluid is preferably conductive grinding fluid
in this embodiment, it may be other fluids or compressed air.
[0052] In FIG. 4 described above, the impeller 15 is disposed on
both sides or one side of the drum-shaped tool 12 and a jet of the
fluid 3 is emitted to the impeller 15 in the rotative direction, so
that the drum-shaped tool 12 is driven at high speed around the
orthogonal axis x. This configuration minimizes the radius of
rotation around the axis z of the tool and is free from restriction
caused by interference between the material to be machined and the
machining tool, thereby achieving a high degree of freedom of the
machining trajectory. Therefore, the use of the versatile 3-axis NC
machining apparatus can be secured.
[0053] Moreover, the free curved surface precision machining tool
10 of the present invention further includes correction means for
correcting the convex machining surface 13 of the drum-shaped tool
12. In this embodiment, the correction means is formed of an
electrode 21 spaced from the convex machining surface 13, which is
a conductive grindstone, and a voltage application unit 22 for
applying a pulse voltage to the convex machining surface 13 and the
electrode 21. In this diagram, reference numeral 24 is an
insulation material.
[0054] With this configuration, it is possible to grind the surface
to be machined by using the convex machining surface 13 while
correcting the surface of the conductive grindstone (the convex
machining surface 13) by electrolytic dressing. It should be noted,
however, that the correction means of the present invention is not
limited to the formation, but can be grindstone, electrolytic, or
discharge means or combined means thereof. By the grindstone,
electrolytic, discharge or other correction means, preferably the
convex machining section 13 in the form of an arcuate rotary body
can be corrected during machining of the material to be machined,
whereby the precision machining can be continued for a long
time.
[0055] Referring to FIG. 5, there is shown a diagram illustrating a
second embodiment of the free curved surface precision machining
tool according to the present invention. In this diagram, the free
curved surface precision machining tool 10 of the present invention
includes a non-machining section 13b adjacent to the convex
machining surface 13 of the drum-shaped tool 12. The non-machining
section 13b has a function of protecting the end of the convex
machining surface 13 and is made of a material wearing out more
easily than the grindstone bonding material so as not to damage the
surface to be machined, regardless of whether it is directly
machined. Alternatively, the non-machining section 13b may include
a conductive material in its material, so as to apply a voltage for
electrolytic dressing from the surface to be machined (not shown)
to the convex machining surface 13 via the non-machining section
13b.
[0056] Since the drum-shaped tool 12 rotates around the axis z, it
receives machining resistance sideways. Accordingly, if the tool
machining section is thin-walled, there is a need for rigidity
reinforcement. Therefore, in FIG. 5, there is provided the
non-machining section 13b, which is made of the material easily
wearing out so as not to damage the bonding material not directly
involved in machining and the surface to be machined. The
non-machining section 13b preferably includes a conductive material
in its material. The drum-shaped tool 12 having the above structure
not only prevents an occurrence of vibration, but also further
improves precision of the free curved surface precision
machining.
[0057] Moreover, in this embodiment, the free curved surface
precision machining tool 10 of the present invention includes a
driven gear 16 disposed on both sides (or one side) of the
drum-shaped tool 12 and a main driving gear 16a for driving the
driven gear 16. The main driving gear 16a is rotatably supported by
a support shaft 17b and a bearing 17c in this embodiment and
directly engages with the driven gear 16. Furthermore, the main
driving gear 16a is rotationally driven by a belt 18 provided
within the tool body 11.
[0058] With this configuration, the drum-shaped tool 12 can be
rotationally driven around the orthogonal axis x by rotationally
driving the main driving gear 16a by using the belt 18. Other
respects of the configuration are the same as those in FIG. 4.
[0059] In FIG. 5, the gear 16 is disposed in both sides or one side
of the drum-shaped tool 12 and the opposite driving gear 16a is
engaged therewith, so that the drum-shaped tool 12 is powerfully
and reliably driven around the orthogonal axis x. This
configuration minimizes the radius of rotation around the axis z of
the tool and is free from restriction caused by interference
between the material to be machined and the machining tool, thereby
achieving a high degree of freedom of the machining trajectory.
Therefore, the use of the versatile 3-axis NC machining apparatus
can be secured.
[0060] Referring to FIG. 6, there is shown a diagram of a third
embodiment of the free curved surface precision machining tool
according to the present invention. In this diagram, the free
curved surface precision machining tool 10 of the present invention
includes a belt 18 in contact with the outer peripheral surface of
the drum-shaped tool 12 and a pulley 19 for holding the belt 18
between the pulley 19 and the drum-shaped tool 12. The belt 18 is
rotationally driven with being passed through the tool body 11 and
the drum-shaped tool 12 is rotationally driven around the
orthogonal axis x by rotation of the belt. In this diagram,
reference numerals 19b and 19c designate a pulley shaft and a
bearing, respectively.
[0061] In FIG. 6, the belt 18 and the outer peripheral surface of
the pulley 19 are brought into contact with the outer peripheral
surface of the drum-shaped tool 12 so as to drive the drum-shaped
tool 12 around the orthogonal axis x smoothly. This configuration
minimizes the radius of rotation around the axis z of the tool and
is free from restriction caused by interference between the
material to be machined and the machining tool, thereby achieving a
high degree of freedom of the machining trajectory. Therefore, the
use of the versatile 3-axis NC machining apparatus can be
secured.
[0062] Moreover, in this embodiment, the belt 18 has a polishing
surface on the side in contact with the outer peripheral surface so
as to correct the convex machining surface of the drum-shaped tool
simultaneously with the rotational driving. Other respects of the
configuration are the same as those in FIG. 4.
[0063] Referring to FIG. 7, there is shown a diagram of a fourth
embodiment of the free curved surface precision machining tool
according to the present invention. In this embodiment, the free
curved surface precision machining tool includes a non-machining
section 13b adjacent to the convex machining surface 13 of the
drum-shaped tool 12 similarly to the second embodiment and includes
a belt 18 and a pulley 19 similarly to the third embodiment. Other
respects of the configuration are the same as those in FIG. 4.
[0064] With the above configuration, the free curved surface
precision machining tool can precision-machine a surface to be
machined with the convex machining surface 13 in contact therewith
by rotation around the axis z and can disperse the machining
position of the convex machining surface 13 by rotating the convex
machining surface 13 around the orthogonal axis x.
[0065] In FIG. 7, it is also possible to rotationally drive the
drum-shaped tool 12 around the orthogonal axis x by rotation of the
pulley 19 by bringing the pulley 19 in contact with the outer
peripheral surface of the non-machining section 13b and
rotationally driving the pulley 19 by the belt 18. The pulley 19 is
preferably pressed against the non-machining section 13b by means
of biasing means (spring or the like), which is not shown, so as to
maintain the frictional force therebetween.
[0066] With this configuration, the pulley 19 does not directly
contact the convex machining surface 13, thereby reducing wear of
the pulley 19.
[0067] Referring to FIGS. 8A and 8B, there are shown diagrams for
explaining operations of the present invention, showing side views
of the drum-shaped tool 12. FIG. 8A shows an illustration in which
the radius r of the arc is smaller than the radius R of the most
outer circumference of the arcuate rotary body. A spherical
machining surface U has a hemispherical machining range D, whose
center is located at the intersection between the axis z and the
orthogonal axis x of the drum-shaped tool 12 and at the center O of
rotation of the arc. Therefore, the position control of the
machining trajectory can be performed at the center O of rotation
of the arc.
[0068] Referring to FIG. 8B, there is shown an illustration in
which the radius r of the arc is larger than the radius R of the
most outer circumference of the arcuate rotary body. In this case,
the spherical machining surface U has a spherical crown machining
range D, whose center is located at the center A of the radius r of
the lowest arc on the axis z, at which the position control of the
machining trajectory can be performed.
[0069] Meanwhile, the radius r of the arc may be set identical with
the maximum radius R of the convex machining surface from the
rotation axis x. If this is the case, the center O of rotation of
the arc is coincident with the center A of the radius of the lowest
arc and therefore the position control of the machining trajectory
can be performed at the same center.
[0070] According to the above configuration of the present
invention, the free curved surface precision machining tool 10
rotates the drum-shaped tool 12 located on the lower side thereof
around the axis z so as to obtain the spherical machining surface U
at the lower end and adds the rotation around the orthogonal axis x
so as to obtain a winding moving trajectory of a contact surface e
of the convex machining section 13 in the form of the arcuate
rotary body.
[0071] Referring to FIG. 9A and FIG. 9B, there are shown other
diagrams for explaining operations of the present invention,
typically showing the winding conditions. FIG. 9A shows a situation
in which a rotation speed j around the orthogonal axis x is
substantially equal to a rotation speed k around the axis z. FIG.
9B shows a situation in which the rotation speed j around the
orthogonal axis x is greater than the rotation speed k around the
axis z.
[0072] There is a difference between an arbitrary time and its
subsequent time. It is caused by a difference in rotation angle
speed and it disperses the moving trajectory of the contact surface
e. Moreover, the fluctuation of the moving speed of the contact
surface e is reduced by the combination of the perpendicular speed
components. This function allows the convex machining section 13 in
the form of an arcuate rotary body to maintain the sharpness, to
wear uniformly, and to achieve the self correction function, as
well as lowering the wearing speed, thereby successfully
maintaining and sustaining the accuracy of form of the convex
machining section 13 in the form of arcuate rotary body. Therefore,
the free curved surface precision machining tool can
precision-machine a free curved surface efficiently by using a
versatile 3-axis NC machining apparatus.
[0073] Referring to FIG. 10, there is shown a diagram of a fifth
embodiment of the free curved surface precision machining tool
according to the present invention. In this embodiment, the free
curved surface precision machining tool 10 of the present invention
includes a driven gear 16 disposed on both sides (or one side) of a
drum-shaped tool 12 and a main driving gear 16a for driving the
driven gear 16. The main driving gear 16a is rotationally driven by
a belt 18 disposed within a tool body 11. In addition, an
intermediate gear 16b, which is rotationally supported by a bearing
17d, between the main driving gear 16a and the driven gear 16.
[0074] With this configuration, the main driving gear 16a can be
rotationally driven by the belt 18, by which the drum-shaped tool
12 can be rotationally driven around the orthogonal axis x via the
intermediate gear 16b.
[0075] In addition, a chain can be used instead of the belt in this
embodiment. In this diagram, an electrode 21 is placed in the
intermediate gear 16b. Other respects of the configuration are the
same as those in FIG. 4 and FIG. 5.
[0076] According to this embodiment, the following additional
effects can be achieved: [0077] (1) Since the belt is not seated on
the intermediate gear 16b, the center distance from the driven gear
can be decreased. More specifically, the external diameter of the
gear can be adjusted to within the outline of the cross section of
the tool body. [0078] (2) The diameter of the intermediate gear can
be smaller than the external diameter of the driven gear, thereby
enabling a reduced transmission, which is advantageous in the
aspects of teeth strength, wear, and efficiency. [0079] (3) The
degree of freedom in setting a rotation speed of the tool can be
increased by a combination of the number of teeth of the
intermediate gear. Moreover, with one or two intermediate gears,
whether the drum-shaped tool 12 should rotate to the left or right
is determined and then a couple of force generated by gyroscopic
precession can be used to offset a pressing force against the tool.
[0080] (4) The electrode 21 can be placed in the intermediate gear.
[0081] (5) The degree of freedom in the shape of cross section of
the belt increases. It is also possible to use a chain.
First Embodiment
[0082] Referring to FIG. 11, there is shown a diagram of a profile
of roughness of a surface machined by the free curved surface
precision machining tool according to the present invention.
Referring to FIG. 12, there is shown a macrophotograph of the
machined surface.
[0083] The work is made of steel for a molding die (stainless steel
HRC 42) and the grindstone is a cast iron bond CBN#4000 grindstone
(20 mm in diameter and 8 mm in thickness). The work was machined
under the machining conditions listed in Table 1: a spindle
rotation speed of 1500 rpm, a feed speed of 100 mm/min, a pitch of
0.1 mm, and a depth of the cut of 10 .mu.m/pass. TABLE-US-00001
TABLE 1 Machining condotions spindle rotation speed 1500 rpm feed
speed 100 mm/min pich 0.1 mm cut depth 10 .mu.m/pass
[0084] The surface roughness after the machining is 0.0188 .mu.mRa
or 0.1392 .mu.mRy as shown in Table 2. From this result, it has
therefore been confirmed that an excellent mirror surface can be
obtained by using the #4000 grindstone in the free curved surface
precision machining tool of the present invention. TABLE-US-00002
TABLE 2 Surface roughness before machining after machining
Ra(.mu.m) 0.648 0.0188 .mu.m Ry(.mu.m) 3.298 0.1392 .mu.m
[0085] It is understood that the present invention is not limited
to the above embodiments, but various changes may be made without
departing from the gist of the invention.
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