U.S. patent application number 12/580934 was filed with the patent office on 2011-04-07 for method and apparatus for polishing a curved edge.
This patent application is currently assigned to APPLE INC.. Invention is credited to Thomas Johannessen, Simon Lancaster.
Application Number | 20110081839 12/580934 |
Document ID | / |
Family ID | 43823538 |
Filed Date | 2011-04-07 |
United States Patent
Application |
20110081839 |
Kind Code |
A1 |
Lancaster; Simon ; et
al. |
April 7, 2011 |
METHOD AND APPARATUS FOR POLISHING A CURVED EDGE
Abstract
A method and an apparatus for polishing a curved edge of a
molded part. A surface of the curved edge is abraded by contacting
a polishing surface of a first polishing wheel to the curved edge
repeatedly in a first direction concurrent with a rotational
spinning direction of the first polishing wheel. The abraded
surface of the curved edge is polished by contacting a polishing
surface of a second polishing wheel to the curved edge in the first
direction and in a second direction opposite to the first
direction. The polishing surfaces of the first and second polishing
wheels are shaped to conform to a portion of the surface of the
curved edge of the molded part. The polishing wheel is maintained
at a constant rotational speed by a controller when contacting the
curved edge. The polished surface of the curved edge is visually
smoothly uniform in reflective appearance.
Inventors: |
Lancaster; Simon;
(Gloucester, CA) ; Johannessen; Thomas;
(Fjerdingby, NO) |
Assignee: |
APPLE INC.
Cupertino
CA
|
Family ID: |
43823538 |
Appl. No.: |
12/580934 |
Filed: |
October 16, 2009 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61249200 |
Oct 6, 2009 |
|
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Current U.S.
Class: |
451/57 ;
451/231 |
Current CPC
Class: |
B24B 9/00 20130101; B24B
29/02 20130101; B24B 19/26 20130101 |
Class at
Publication: |
451/57 ;
451/231 |
International
Class: |
B24B 9/20 20060101
B24B009/20; B24B 1/00 20060101 B24B001/00 |
Claims
1. A method for polishing a curved edge of a molded part, the
method comprising: abrading a first surface of the curved edge of
the molded part by contacting a first polishing surface on a first
polishing wheel to the first surface of the curved edge of the
molded part repeatedly in a first direction concurrent with a
rotational spinning direction of the first polishing wheel, the
first polishing surface shaped to substantially conform to a
portion of the first surface of the curved edge of the molded part;
and polishing the abraded first surface of the curved edge of the
molded part by contacting a second polishing surface on a second
polishing wheel to the abraded first surface of the curved edge of
the molded part, alternating contact in the first direction and in
a second direction opposite to the first direction, the second
polishing surface shaped to substantially conform to the portion of
the first surface of the curved edge of the molded part.
2. The method of claim 1 further comprising: abrading a second
surface of the curved edge of the molded part by contacting a third
polishing surface on the first polishing wheel to the second
surface of the curved edge of the molded part repeatedly in the
first direction concurrent with the rotational spinning direction
of the first polishing wheel, the third polishing surface shaped to
substantially conform to a portion of the second surface of the
curved edge of the molded part; and polishing the abraded second
surface of the curved edge of the molded part by contacting a
fourth polishing surface on the second polishing wheel to the
abraded second surface of the curved edge of the molded part,
alternating contact in the first direction and in the second
direction opposite to the first direction, the fourth polishing
surface shaped to substantially conform to the portion of the
second surface of the curved edge of the molded part.
3. The method of claim 1 wherein the molded part is formed from an
injection molded thermoplastic.
4. The method of claim 1 wherein the first surface of the curved
edge of the molded part comprises a parting line surface
defect.
5. The method of claim 4 wherein the parting line surface defect
comprises a step having a displacement greater than 10 microns
perpendicular to the first surface of the curved edge of the molded
part.
6. The method of claim 5 wherein the first direction of abrading is
into a face of the parting line surface defect.
7. The method of claim 1 further comprising: maintaining the first
polishing wheel at a constant rotational speed when in contact with
the first surface of the curved edge of the molded part.
8. The method of claim 7 wherein the maintaining comprises varying
a position of the first polishing wheel with respect to the first
surface of the curved edge of the molded part while abrading or
polishing.
9. The method of claim 1 wherein the polished first surface of the
curved edge of the molded part is visually smoothly uniform in
reflective appearance.
10. An apparatus for polishing a curved edge of a molded part, the
apparatus comprising: a first polishing wheel comprising a first
polishing surface shaped to substantially conform to a portion of a
first surface of the curved edge of the molded part; a second
polishing wheel comprising a second polishing surface shaped to
substantially conform to the portion of the first surface of the
curved edge of the molded part; a first positioning assembly
configured to contact the first polishing surface of the first
polishing wheel to the first surface of the curved edge of the
molded part repeatedly in a first direction concurrent with a
rotational spinning direction of the first polishing wheel to
abrade the first surface of the curved edge of the molded part to a
first smoothness; and a second positioning assembly configured to
contact the second polishing surface of the second polishing wheel
to the first surface of the curved edge of the molded part
alternately in the first direction and in a second direction
opposite to the first direction to polish the abraded first surface
of the curved edge of the molded part to a second smoothness.
11. The apparatus of claim 10 further comprising: the first
polishing wheel further comprises a third polishing surface shaped
to substantially conform to a portion of a second surface of the
curved edge of the molded part; the second polishing wheel further
comprises a fourth polishing surface shaped to substantially
conform to the portion of the second surface of the curved edge of
the molded part; the first positioning assembly further configured
to contact the third polishing surface to the second surface of the
curved edge of the molded part repeatedly in the first direction
concurrent with the rotational spinning direction of the first
polishing wheel to abrade the second surface of the curved edge of
the molded part to the first smoothness; and the second positioning
assembly further configured to contact the fourth polishing surface
to the second surface of the curved edge of the molded part
alternately in the first direction and in the second direction
opposite to the first direction to polish the second surface of the
curved edge of the molded part to the second smoothness.
12. The apparatus of claim 10 wherein the molded part is formed
from an injection molded thermoplastic.
13. The apparatus of claim 10 wherein the unpolished first surface
of the curved edge of the molded part comprises a parting line
surface defect.
14. The apparatus of claim 13 wherein the parting line surface
defect comprises a step having a displacement greater than 10
microns perpendicular to the first surface of the curved edge of
the molded part.
15. The apparatus of claim 14 wherein the first direction of
abrading is into a face of the parting line surface defect.
16. The apparatus of claim 10 further comprising a controller to
maintain a constant rotational speed of the first polishing wheel
when in contact with the first surface of the curved edge of the
molded part.
17. The apparatus of claim 10 wherein the second smoothness is
visually smoothly uniform in reflective appearance.
18. A computer readable medium for storing computer program code
executed by a processor for controlling a computer aided
manufacturing operation for polishing a curved edge of a molded
part, the computer readable medium comprising: computer program
code for abrading a first surface of the curved edge of the molded
part by contacting a first polishing surface on a first polishing
wheel to the first surface of the curved edge of the molded part
repeatedly in a first direction concurrent with a rotational
spinning direction of the first polishing wheel, the first
polishing surface shaped to substantially conform to a portion of
the first surface of the curved edge of the molded part; and
computer program code for polishing the abraded first surface of
the curved edge of the molded part by contacting a second polishing
surface on a second polishing wheel to the abraded first surface of
the curved edge of the molded part, alternating contact in the
first direction and in a second direction opposite to the first
direction, the second polishing surface shaped to substantially
conform to the portion of the first surface of the curved edge of
the molded part.
19. The computer readable medium of claim 18 further comprising:
computer program code for abrading a second surface of the curved
edge of the molded part by contacting a third polishing surface on
the first polishing wheel to the second surface of the curved edge
of the molded part repeatedly in the first direction concurrent
with the rotational spinning direction of the first polishing
wheel, the third polishing surface shaped to substantially conform
to a portion of the second surface of the curved edge of the molded
part; and computer program code for polishing the abraded second
surface of the curved edge of the molded part by contacting a
fourth polishing surface on the second polishing wheel to the
abraded second surface of the curved edge of the molded part,
alternating contact in the first direction and in the second
direction opposite to the first direction, the fourth polishing
surface shaped to substantially conform to the portion of the
second surface of the curved edge of the molded part.
20. The computer readable medium of claim 18 further comprising:
computer program code for maintaining the first polishing wheel at
a constant rotational speed when in contact with the first surface
of the curved edge of the molded part.
21. The computer readable medium of claim 20 wherein the
maintaining comprises varying a position of the first polishing
wheel with respect to the first surface of the curved edge of the
molded part while abrading or polishing.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This U.S. patent application Ser. No. ______ (APL1P607)
entitled "METHOD AND APPARATUS FOR POLISHING A CURVED EDGE" by
Lancaster et al. takes priority under 35 U.S.C. 119(e) to U.S.
Provisional Patent Application Ser. No. 61/249,200 entitled
"COMPLEX GEOGRAPHICAL EDGE POLISHING" by Johannessen filed Oct. 6,
2009 and incorporated by reference in its entirety.
[0002] This U.S. patent application is also related to and
incorporates by reference in their entireties for all purposes the
following co-pending patent applications filed concurrently
herewith: [0003] (i) U.S. patent application Ser. No. ______
(APL1P602) entitled "PORTABLE COMPUTER DISPLAY HOUSING" by Bergeron
et al.; [0004] (ii) U.S. patent application Ser. No. ______
(APL1P603) entitled "PORTABLE COMPUTER ELECTRICAL GROUNDING AND
AUDIO SYSTEM ARCHITECTURES" by Thomason et al.; [0005] (iii) U.S.
patent application Ser. No. ______ (APL1P604) entitled "PORTABLE
COMPUTER HOUSING" by Casebolt et al.; [0006] (iv) U.S. patent
application Ser. No. ______ (APL1P601) entitled "COMPUTER HOUSING"
by Raff et al.; [0007] (v) U.S. patent application Ser. No. ______
(APL1P608) entitled "SELF FIXTURING ASSEMBLY TECHNIQUES" by
Thompson et al.; [0008] (vi) U.S. patent application Ser. No.
______ (APL1P593X1) entitled "BATTERY" by Coish et al. that is a
continuation in part of U.S. patent application Ser. No. 12/549,570
filed Aug. 28, 2009; [0009] (vii) U.S. patent application Ser. No.
______ (APL1P612) entitled "PORTABLE COMPUTER DISPLAY HOUSING" by
Bergeron et al.; and [0010] (viii) U.S. patent application Ser. No.
______ (APL1P613) entitled "COMPUTER HOUSING" by Raff et al.
TECHNICAL FIELD
[0011] The present invention relates generally to the polishing of
a three dimensional curved edge of an object. More particularly, a
method and an apparatus are described for polishing the edge of an
injection molded part, formed using a thermoplastic compound, to a
visually smooth and consistent reflective appearance.
BACKGROUND OF THE INVENTION
[0012] The proliferation of high volume manufactured, portable
electronic devices has encouraged innovation in both functional and
aesthetic design practices for enclosures that encase such devices.
Manufactured devices can include a casing that provides an
ergonomic shape and aesthetically pleasing visual appearance
desirable to the user of the device. Surfaces of casings molded
from thermoplastic compounds can be shaped and polished to a highly
reflective finish; however, the polished reflective surface can
reveal minor variations in the final surface geometry. Molded
casings can include complex geometric shapes that are difficult to
finish to a uniform surface appearance. Prior art techniques can
result in a tactilely smooth finish with an undesirable variation
in visual reflective appearance. Thus there exists a need for a
method and an apparatus for polishing a three dimensional curved
edge of an object resulting in a visually smooth and consistent
reflective appearance.
SUMMARY OF THE DESCRIBED EMBODIMENTS
[0013] A method for polishing a three dimensional curved edge of a
molded part is disclosed. The method can be carried out by at least
abrading a surface of the curved edge of the molded part by
contacting a polishing surface on a first polishing wheel to the
unpolished surface of the curved edge of the molded part. The
abrading can occur repeatedly in a first direction concurrent with
a rotational spinning direction of the first polishing wheel. The
polishing surface on the first polishing wheel can be shaped to
substantially conform to a portion of the surface of the curved
edge of the molded part. The abraded surface of the curved edge of
the molded part can subsequently be polished by contacting a
polishing surface on a second polishing wheel to the abraded
surface. The polishing can be accomplished by alternating contact
in the first direction and in a second direction opposite to the
first direction. The polishing surface on the second polishing
wheel can also be shaped to substantially conform to the portion of
the surface of the curved edge of the molded part.
[0014] In a second embodiment, a method for polishing at least two
surfaces of a three dimensional curved edge of a molded part is
disclosed. The method can include abrading a first surface and a
second surface of the curved edge using at least two different
polishing surfaces on a first polishing wheel. Each polishing
surface on the first polishing wheel can be shaped to substantially
conform to a corresponding portion of the surface of the curved
edge of the molded part. The abrading can be carried out by
contacting the polishing surfaces of the first polishing wheel with
the surfaces of the curved edge of the molded part repeatedly in a
direction concurrent with a rotational spinning direction of the
first polishing wheel. The method can also include polishing the
first and second surfaces using different polishing surfaces on a
second polishing wheel. Each polishing surface on the second
polishing wheel can be shaped to substantially conform to a
corresponding portion of the surface of the curved edge of the
molded part. The polishing can be carried out by contacting the
polishing surfaces of the second polishing wheel to the abraded
surface, alternately in the first direction and in a second
direction opposite to the first direction. In an embodiment, molded
parts can be formed from an injection molded thermoplastic
compound. The surface of the three dimensional curved edge of the
molded part to be polished can include a parting line surface
defect. The parting line surface defect can have a vertical
displacement greater than 10 microns approximately perpendicular to
the surface of the curved edge of the molded part.
In an embodiment, the polishing wheel can be maintained at a
constant rotational speed by a controller when contacting the
surface of the curved edge of the molded part. The polished surface
of the curved edge of the molded part can be visually smoothly
uniform in reflective appearance.
[0015] In another embodiment an apparatus for polishing a three
dimensional curved edge of a molded part is described. The
apparatus can include two polishing wheels, and two positioning
assemblies to contact surfaces of the two polishing wheels to a
surface of the curved edge of the molded part. Each polishing wheel
can include a polishing surface shaped to substantially conform to
a portion of the surface of the curved edge of the molded part. The
first positioning assembly can be configured to contact the
polishing surface of the first polishing wheel to the surface of
the curved edge of the molded part repeatedly in a first direction
concurrent with a rotational spinning direction of the first
polishing wheel, thereby abrading the surface of the curved edge of
the molded part to a first smoothness. The second positioning
assembly can be configured to contact the polishing surface of the
second polishing wheel to the abraded surface of the curved edge of
the molded part alternating in the first direction and a second
direction opposite to the first direction, thereby polishing the
abraded surface of the curved edge of the molded part to a second
smoothness.
[0016] In another embodiment, each polishing wheel of an apparatus
for polishing a curved edge of a molded part can include a second
polishing surface shaped to substantially conform to a second
portion of the surface of the curved edge of the molded part. The
first positioning assembly can be configured to contact the second
polishing surface of the first polishing wheel to abrade the second
portion of the surface of the curved edge of the molded part
repeatedly in the first direction concurrent with the rotational
spinning direction of the first polishing wheel, thereby abrading
the second portion of the surface of the curved edge of the molded
part to a first smoothness. The second positioning assembly can be
configured to contact the second polishing surface of the second
polishing wheel to the abraded second surface of the curved edge of
the molded part alternating in the first direction and a second
direction opposite to the first direction, thereby polishing the
abraded second surface of the curved edge of the molded part to a
second smoothness.
[0017] In yet another embodiment, a computer readable medium for
storing program code executed by a processor for controlling a
computer aided manufacturing operation for polishing a three
dimensional curved edge of a molded part is disclosed. The computer
program code can control abrading and polishing a surface of the
curved edge of the molded part. Abrading can be accomplished by
contacting a polishing surface of a first polishing wheel to the
curved edge of the molded part repeatedly in a first direction
concurrent with a rotational spinning direction of the first
polishing wheel. The polishing surface of the first polishing wheel
can be shaped to substantially conform to a portion of the surface
of the curved edge of the molded part. Polishing can be
accomplished by contacting a polishing surface of a second
polishing wheel to the abraded surface of the curved edge of the
molded part, alternately in the first direction and in a second
direction opposite to the first direction. The polishing surface of
the second polishing wheel can also be shaped to substantially
conform to the portion of the surface of the curved edge of the
molded part.
[0018] In a further embodiment, the computer program code for
controlling the computer aided manufacturing operation for
polishing at least two surfaces of the three dimensional curved
edge of the molded part is disclosed. The computer program code can
control abrading and polishing the at least two surfaces using
different surfaces on different polishing wheels. The computer
program code can direct a first polishing wheel to abrade at least
two different surfaces shaped to conform to two different portions
of the surface of the curved edge of the molded part. The computer
program code can also control a second polishing wheel to polish
the at least two different surfaces shaped to conform to the two
different portions of the surface of the curved edge of the molded
part.
[0019] In an embodiment, the computer program code can maintain the
polishing wheels at a constant rotational speed when in contact
with the surfaces of the curved edge of the molded part. The
computer program code can also vary the position of the polishing
wheels with respect to the surfaces of the curved edge of the
molded part while abrading or polishing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] The invention and the advantages thereof may best be
understood by reference to the following description taken in
conjunction with the accompanying drawings.
[0021] FIG. 1A illustrates a top view of a portable computing
device including a molded thermoplastic casing.
[0022] FIG. 1B illustrates a front view of the portable computing
device of FIG. 1A.
[0023] FIG. 2 illustrates a cross section of the molded
thermoplastic casing of FIG. 1B including a shaped geometric
edge.
[0024] FIG. 3A illustrates a cross section of a polishing wheel
with surfaces that conform to the cross section of the molded
thermoplastic casing of FIG. 2.
[0025] FIG. 3B illustrates a magnified view of a surface defect on
the shaped geometric edge of the thermoplastic casing of FIG.
2.
[0026] FIG. 3C illustrates a top view of the polishing wheel and
two directions of movement of the polishing wheel relative to the
surface defect on the shaped geometric edge of the thermoplastic
casing of FIG. 2.
[0027] FIG. 3D illustrates a representative embodiment of a
polishing wheel including two surfaces and a representative
embodiment of a molded thermoplastic casing including a shaped
geometric edge.
[0028] FIG. 3E illustrates the polishing wheel and the
thermoplastic casing of FIG. 3D with one of the surfaces of the
polishing wheel in contact with the thermoplastic casing.
[0029] FIG. 4A illustrates three front and side views of the
surface of the shaped geometric edge of the thermoplastic casing of
FIG. 2 with different polishing results.
[0030] FIG. 4B illustrates a surface defect on an edge of an
unpolished thermoplastic casing and a second thermoplastic casing
including a polished edge with a surface defect removed.
[0031] FIG. 4C illustrates two thermoplastic casings including
polished edges using two different polishing methods.
DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS
[0032] The present invention relates generally to the polishing of
a three dimensional curved edge of a molded object. More
particularly, a method and an apparatus are described for polishing
the edge of an object, formed using an injection molded
thermoplastic compound, to a visually smooth and consistent
reflective appearance.
[0033] In the following description, numerous specific details are
set forth to provide a thorough understanding of the present
invention. It will be apparent, however, to one skilled in the art
that the present invention may be practiced without some or all of
these specific details. In other instances, well known process
steps have not been described in detail in order to avoid
unnecessarily obscuring the present invention.
[0034] High volume manufactured portable electronics devices can
include injection molded thermoplastic parts with various
geometrically shaped surfaces. Thermoplastic compounds can provide
a lightweight moldable material that exhibits desirable properties,
such as strength, heat resistance and structural flexibility well
suited for casings of portable electronic devices. A representative
thermoplastic compound can include PC/ABS (polycarbonate
acrylonitrile butadience styrene) polymer, although other
thermoplastic compounds can be used. Both the tactile and visual
appearance of a portable electronics device can enhance the
desirability of the device to the consumer. A cosmetic outer layer
formed from a thermoplastic blend can be polished to a desired
reflective appearance while retaining an aesthetically pleasing
shape. In some embodiments, a continuously smooth shape having a
uniformly visually smooth appearance can be desired.
[0035] Prior to post-process finishing, injection molded
thermoplastic parts can include surface defects, e.g. parting
lines, at seams where individual sections of a mold, in which the
thermoplastic molded part is formed, come apart. Parting lines can
occur for numerous reasons, e.g. because the edges of two
individual sections of the mold cannot perfectly align or because
the surface of the mold can become slightly damaged or wear over
time during repeated use in high volume manufacturing. The molding
process can also require high pressure injection of a thermoplastic
compound which can cause slight deviations in the positions of the
mold sections. It is desirable to post-process finish the surface
of molded thermoplastic parts so that the parting lines cannot be
detected tactilely or visually.
[0036] FIG. 1A illustrates a top view of a portable electronics
device 101 including markings of several possible parting lines 102
on a molded thermoplastic top casing of the portable electronics
device 101. FIG. 1B illustrates a front view of the portable
electronics device 101 of FIG. 1A including a molded thermoplastic
top casing 105, a molded thermoplastic center casing 103 and a base
106. The top casing 105 and the center casing 103 can be formed
separately in two different injection molds, each with differently
located parting lines in general, even though a parting line 107 of
the center casing 103 aligns with the parting line 102 of the top
casing 105 as illustrated in FIG. 1B. Each of the parting lines of
the center casing 103 can be removed by appropriate polishing. The
three-dimensional edge 104 of the center casing can have a specific
complex geometric shape that provides an aesthetically pleasing
appearance for the portable electronics device 101. FIG. 2
illustrates a cross section 203 of the center casing 103 (along the
dashed line and viewed in the direction A in FIG. 1A) including a
complex shaped edge 206 (cross section of edge 104 of FIG. 1B). The
complex shaped edge 206 can include three distinct regions, a
corner region 205 where the side meets the top, an upper region 202
of the side and a lower region 204 of the side. The three different
regions 202, 204 and 205 can be finished using one or more
different polishing methods. In particular, the corner region 205
can be finished to produce an unsharpened rounded edge using a
conventional technique. Such techniques are well known to those
skilled in the art. The upper region 202 and the lower region 204
of the complex shaped edge can be finished to achieve a tactilely
and visually uniformly smooth reflective surface using a new
polishing method as described herein.
[0037] Conventional polishing techniques applied to a thermoplastic
molded part that includes a complex three-dimensional geometric
shape, such as edge 104 of the center casing 103 of FIG. 1B, can
result in a visually non-uniform surface, even when the polished
surface provides a smooth tactile finish. Highly reflective, glossy
polished surfaces can reveal even minute irregularities in surface
finish. A visually uniformly smooth, reflective polished surface
can be achieved using two stages of polishing, each using different
directional movements of one or more polishing wheels. It has been
found that shaping the surface of the polishing wheel to mirror the
shape of the edge can improve the final resulting surface
appearance.
[0038] FIG. 3A illustrates a cross section of a polishing wheel 306
having an edge with two abrasive surfaces 302 and 303 that are
shaped to match to portions of the complex three dimensional edge
104 of the center casing 103 of FIG. 1B. An end cross section 301
of the three dimensional edge 104 (i.e. an end portion of the cross
section edge 206 of FIG. 2) can include a convex upper region 202
and a convex lower region 204. The concave surface 302 of the
polishing wheel 306 can match to the convex upper region 202 of the
edge 301, while the concave surface 303 of the polishing wheel 306
can match to the convex lower region 204 of the edge 301. Depending
on the geometry of a complex three-dimensional edge, a surface can
be polished using one or more surfaces of a polishing wheel, where
each surface can polish a different region of an edge. Lower
curvature edges can use one polishing surface of the polishing
wheel 306, while higher curvature edges can use two or more
polishing surfaces of the polishing wheel 306.
[0039] In a representative embodiment, the polishing wheel 306 can
be turned in a rotational direction 305 along a longitudinal axis
of the edge 301 that it polishes. To align each of the surfaces of
the edge 301 of the center casing 103 to a surface of the polishing
wheel 306, either the polishing wheel 306 or the center casing 103
can be positioned appropriately in an assembly fixture. In an
embodiment, the center casing 103 can be fixed on a stand, while
the polishing wheel 306 can be moved along one or more axes in
three dimensions and tilted at an angle to align a surface of the
polishing wheel 306 to a portion of an edge of the center casing
103. The position and rotational velocity of the polishing wheel
306 can be controlled by a computer to maintain a desired position
and consistent speed when contacting a surface of the center casing
103.
[0040] Both the upper region 202 and the lower region 204 of the
center casing 103, formed of an injection molded thermoplastic
compound, can contain surface defects along boundaries where
separate portions of a mold in which the center casing 103 can be
formed come apart. As shown in FIG. 3B, a surface defect 308 can
include a change in vertical displacement approximately
perpendicular to the surface edge. A surface defect can be at least
10 microns high and typically can be approximately 20 microns high.
This relatively small displacement can be visible as a discrete
line surface defect 308 across the edge of the molded center casing
103 as shown by a side view 401 in FIG. 4A. To remove the discrete
line surface defect 308 from the edge of the molded center casing
103, a two stage polishing method can be used, a first abrading
stage to eliminate the vertical displacement and a second polishing
stage to remove any residual visible variation in surface
reflectance along the edge of the center casing 103. Surface
defects up to approximately 30 microns high can be removed using
the two stage polishing method described herein.
[0041] As illustrated by FIG. 3C, the polishing wheel 306 can be
turned in a rotational direction 305 about a central rotational
axis 304 and moved longitudinally in two directions 309 and 310
along regions 202 or 204 of the edge 206 of the molded part when
polishing their surfaces. For clarity, FIG. 3C is shown as a
two-dimensional cross section of a three-dimensional surface with
the polishing wheel moving along one axis. It should be understood
that the polishing wheel 306 also can be positioned along the two
other axes perpendicular to the directions 309/310 shown, as well
as tilted as needed to match a surface of the polishing wheel 306
to the edge 104. The three-dimensional edge 104 may be curved, and
the polishing wheel 306 may be positioned to follow along the
three-dimensional edge 104 when polishing.
[0042] We will describe polishing the upper region 202 of the edge
cross section 301; however the same method described can apply to
polishing the lower region 204. In the first abrading stage of
polishing the upper region 202, the surface defect 308 can be
reduced in height by contacting the rotationally spinning polishing
wheel 306 along the direction 309 that points into the face of the
surface defect 308. The rotating polishing wheel 306 can contact
the upper region 202 at a portion of the surface 311 below the
surface defect 308 and traverse longitudinally along the edge into
the face of the surface defect 308 and then along a portion of the
surface 312 above the surface defect 308. Contacting the surface
repeatedly can abrade the surface defect 308 to remove the change
in vertical displacement thereby producing an even surface.
[0043] The rotating polishing wheel can be moved laterally to sever
contact with the portion of the surface 312 and reoriented to start
the wheel at the portion of the surface 311 below the surface
defect 308 for each successive pass during the first abrading stage
of polishing. By removing the surface defect 308 uni-directionally
during the first abrading stage of polishing rather than
bi-directionally, as can be used conventionally, the surface of the
edge can be polished in the second stage to achieve a desired
visually uniformly smooth appearance. In the second polishing stage
of polishing, the rotating polishing wheel 306 can contact the
surface of the edge bi-directionally in both the first direction
309 and a second direction 310 longitudinally along the edge. In
some embodiments a second rotating polishing wheel can be used have
a finer abrasive surface than the coarser abrasive surface of the
first rotating polishing wheel 306 used to abrade the surface
defect. The second polishing wheel can be similarly shaped to match
geometrically to the portion of the edge to which it would contact.
The first polishing wheel 306 can be used to produce a first
smoothness on the surface, while the second polishing wheel can be
used to produce a second finer smoothness on the surface. The
surface having a first smoothness can be tactilely smooth but
visually non-uniform, while the second surface having a finer
smoothness can be additionally visually uniformly smooth in
appearance.
[0044] FIG. 3D illustrates a representative embodiment of a
polishing wheel 314 including a concave surface 315 that conforms
to the convex shape of a portion of the surface of the complex
geometric edge 316 on a representative embodiment of a
thermoplastic casing 313 for a portable computing device. FIG. 3E
illustrates the concave surface 315 of the polishing wheel 314
contacting the portion of the surface of the complex geometric edge
316 of the thermoplastic casing 313. The polishing wheel 314 can
move laterally along the edge 316 when abrading or polishing the
surface of the edge 316 of the thermoplastic casing 313. The
polishing wheel 314 of FIG. 3D can correspond to an embodiment of
the polishing wheel 306 of FIG. 3A including the concave surface
315 corresponding to an embodiment of the convex surface 302.
Similarly the complex geometric edge 316 of the thermoplastic
casing 313 can correspond to an embodiment of the portion of the
surface 202 that conforms to the surface of the polishing
wheel.
[0045] FIG. 4A illustrates two different surface appearances that
can result when polishing a complex geometrically shaped edge to
remove a surface defect 308. A uniform surface appearance 405 with
no visible variations can result when using the method described
above. A non-uniform surface appearance 403 can result when using a
polishing method that abrades the surface bi-directionally during
the first stage rather than uni-directionally as described herein,
even when followed by a bi-directional polishing during the second
stage. By abrading the surface defect 308 in one direction only
during the first stage of polishing, the resulting polished surface
edge can change height approximately linearly with a uniform
surface appearance 405, while abrading the surface bi-directionally
can result in a polished surface edge having a "dip" resulting in a
visually non-uniform appearance 403.
[0046] FIG. 4B illustrates the surface defect 308 on a surface edge
of a first thermoplastic casing 406 which can be visible before
polishing and can be visually uniformly smooth after polishing as
shown by the surface 405 on the second thermoplastic casing 407.
FIG. 4C illustrates a third thermoplastic casing 408 with a surface
of a geometric edge abraded and polished bi-directionally resulting
in a visually non-uniform surface 403. While the visually
non-uniform surface 403 on the thermoplastic casing 408 may be
tactilely smooth, the non-uniform surface 403 reflects light
irregularly. Using the method described herein instead to abrade
the surface uni-directionally followed by polishing the surface
bi-directionally, the surface defect 308 of a fourth thermoplastic
casing 409 is completely removed providing a visually uniformly
smooth surface 405 as illustrated in FIG. 4C.
[0047] One embodiment of the polishing method described herein can
use two different polishing wheels to remove a surface defect on a
complex geometric shaped edge, one polishing wheel to abrade the
surface and a second polishing wheel to polish the surface. The
polishing wheels can include multiple surfaces, each shaped to
conform to a different portion of the surface of the complex
geometric shaped edge to be polished. The use of two polishing
wheels in the embodiment is not intended to limit the invention.
The number of polishing wheels and the number of surfaces on each
polishing wheel can vary based on the size of the defect and the
complex geometric shape of the edge to be polished. More complex
geometric shaped edges can use one or more surfaces on one or more
wheels. In some embodiments a single polishing wheel can be used,
such as when the surface defect is less than 15 microns in
height.
[0048] In high volume manufacturing it is also desired to provide
consistency between multiple parts even as the polishing surfaces
302 and 303 of the polishing wheel 306 can change with repeated use
(and the unpolished edges of different molded parts can vary as
well). The polishing wheel can be connected to a controller that
measures the rotational velocity (in terms of revolutions per
minute, or RPM) of the polishing wheel and maintains the rotational
velocity within a specified range when contacting the surface of
the molded part by controlling the exact position of the rotational
axis 304 of the polishing wheel in three dimensions with respect to
the molded part. The angular tilt of the polishing wheel can also
be controlled. By controlling the polishing to use a constant
rotational velocity even as the abrasive surfaces of the polishing
wheel change shape can provide consistency in the resulting surface
appearance of the polished molded part.
[0049] It should be noted that RPM can be set according to material
type. For example, for example, blends of poly-carbonate (PC) and
acrylonitrile butadiene styrene (ABS), or PC/ABS, has a lower
melting point than PC alone and thus RPM should be reduced to lower
the chance of overheating and damaging the unit. Otherwise a
cooling system can be used such as a cooled holding fixture or air
conditioning.
[0050] The various aspects, embodiments, implementations or
features of the described embodiments can be used separately or in
any combination. Various aspects of the described embodiments can
be implemented by software, hardware or a combination of hardware
and software. The described embodiments can also be embodied as
computer readable code on a computer readable medium for
controlling manufacturing operations or as computer readable code
on a computer readable medium for controlling a manufacturing line
used to fabricate thermoplastic molded parts. The computer readable
medium is any data storage device that can store data which can
thereafter be read by a computer system. Examples of the computer
readable medium include read-only memory, random-access memory,
CD-ROMs, DVDs, magnetic tape, optical data storage devices, and
carrier waves. The computer readable medium can also be distributed
over network-coupled computer systems so that the computer readable
code is stored and executed in a distributed fashion.
[0051] The foregoing description, for purposes of explanation, used
specific nomenclature to provide a thorough understanding of the
invention. However, it will be apparent to one skilled in the art
that the specific details are not required in order to practice the
invention. Thus, the foregoing descriptions of specific embodiments
of the present invention are presented for purposes of illustration
and description. They are not intended to be exhaustive or to limit
the invention to the precise forms disclosed. It will be apparent
to one of ordinary skill in the art that many modifications and
variations are possible in view of the above teachings.
[0052] The embodiments were chosen and described in order to best
explain the principles of the invention and its practical
applications, to thereby enable others skilled in the art to best
utilize the invention and various embodiments with various
modifications as are suited to the particular use contemplated. It
is intended that the scope of the invention be defined by the
following claims and their equivalents.
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