U.S. patent application number 16/512762 was filed with the patent office on 2021-01-21 for ultrasonic sub-aperture polishing of an optical element.
The applicant listed for this patent is Facebook Technologies, LLC. Invention is credited to Alexander Sohn.
Application Number | 20210016409 16/512762 |
Document ID | / |
Family ID | 1000004212544 |
Filed Date | 2021-01-21 |
United States Patent
Application |
20210016409 |
Kind Code |
A1 |
Sohn; Alexander |
January 21, 2021 |
ULTRASONIC SUB-APERTURE POLISHING OF AN OPTICAL ELEMENT
Abstract
Aspects of an ultrasonic polishing system include an ultrasonic
actuator and a polishing arm. The ultrasonic actuator is configured
to generate ultrasonic vibrations and the polishing arm is coupled
to the ultrasonic actuator. The polishing arm includes a horn and a
polishing ball. The horn has a proximal end and a distal end. The
proximal end is coupled to receive the ultrasonic vibrations and
the horn is configured to propagate the ultrasonic vibrations from
the proximal end to a distal end. The polishing ball is attached to
the distal end of the horn, where the polishing ball vibrates in
response to the ultrasonic vibrations for polishing a surface of an
optical element. The polishing ball is configured to provide a
polishing area on the surface of the optical element that is
smaller than an aperture of the optical element.
Inventors: |
Sohn; Alexander; (Seattle,
WA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Facebook Technologies, LLC |
Menlo Park |
CA |
US |
|
|
Family ID: |
1000004212544 |
Appl. No.: |
16/512762 |
Filed: |
July 16, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B24B 13/01 20130101;
B24B 1/04 20130101 |
International
Class: |
B24B 13/01 20060101
B24B013/01; B24B 1/04 20060101 B24B001/04 |
Claims
1. An ultrasonic polishing system for polishing an optical element,
the system comprising: an ultrasonic actuator configured to
generate ultrasonic vibrations; and a polishing arm coupled to the
ultrasonic actuator, wherein the polishing arm includes: a horn
having a proximal end coupled to receive the ultrasonic vibrations,
wherein the horn is configured to propagate the ultrasonic
vibrations from the proximal end to a distal end of the horn; and a
polishing ball attached to the distal end of the horn, wherein the
polishing ball is configured to vibrate in response to the
ultrasonic vibrations for polishing a surface of the optical
element, and wherein the polishing ball is configured to provide a
polishing area on the surface of the optical element that is
smaller than an aperture of the optical element.
2. The ultrasonic polishing system of claim 1, wherein the aperture
of the optical element is 3 millimeters or smaller.
3. The ultrasonic polishing system of claim 1, wherein the
polishing area has a diameter of 10 micrometers or smaller.
4. The ultrasonic polishing system of claim 1, wherein the
polishing ball has a spherical shape.
5. The ultrasonic polishing system of claim 1, wherein the
polishing ball comprises sapphire.
6. The ultrasonic polishing system of claim 1, wherein the
polishing arm has a natural frequency that matches a frequency of
the ultrasonic vibrations.
7. The ultrasonic polishing system of claim 1, wherein a frequency
of the ultrasonic vibrations is greater than 20 kHz.
8. The ultrasonic polishing system of claim 1, wherein a frequency
of the ultrasonic vibrations is between 20 kHz and 40 kHz.
9. The ultrasonic polishing system of claim 1, further comprising:
a computer numerical control (CNC) positioner coupled to the
polishing arm to vary a position of the polishing ball relative to
the surface of the optical element.
10. The ultrasonic polishing system of claim 9, further comprising:
a computing device that includes: at least one processor; and at
least one memory coupled to the at least one processor, the at
least one memory having instructions stored therein, which when
executed by the at least one processor, direct the computing device
to: generate one or more control signals to direct the CNC
positioner to vary the position of the polishing ball relative to
the surface of the optical element.
11. The ultrasonic polishing system of claim 10, wherein the
instructions to generate the one or more control signals to direct
the CNC positioner to vary the position of the polishing ball
comprise instructions to direct the polishing ball along a
polishing path on the surface of the optical element.
12. The ultrasonic polishing system of claim 11, wherein the
instructions to direct the polishing ball along the polishing path
comprise instructions to vary at least one of: (a) a load applied
to the polishing arm, or (b) a velocity of the polishing ball along
the polishing path, to adjust an amount of material removed from
the surface of the optical element at one or more positions along
the polishing path.
13. The ultrasonic polishing system of claim 11, further
comprising: an interferometer disposed to obtain one or more
surface measurements of the optical element, wherein the at least
one memory further comprises instructions to direct the computing
device to generate a surface error map of the optical element based
on the surface measurements, and wherein the instructions to vary
the load or velocity are responsive to the surface error map.
14. The ultrasonic polishing system of claim 1, wherein the
ultrasonic actuator comprises a magnetostrictive actuator and
wherein the polishing ball is configured to vibrate along an
elliptical stroke path on the surface of the optical element in
response to the ultrasonic vibrations generated by the
magnetostrictive actuator.
15. The ultrasonic polishing system of claim 1, wherein the
ultrasonic actuator comprises a piezoelectric actuator and wherein
the polishing ball is configured to vibrate along a linear stroke
path on the surface of the optical element in response to the
ultrasonic vibrations generated by the piezoelectric actuator.
16. A method of ultrasonic sub-aperture polishing of an optical
element, the method comprising: enabling an ultrasonic actuator to
generate ultrasonic vibrations; and generating one or more control
signals to direct a computer numerical control (CNC) positioner to
vary a position of a polishing arm relative to a surface of the
optical element, wherein the polishing arm includes: a horn having
a proximal end coupled to receive the ultrasonic vibrations
generated by the ultrasonic actuator, wherein the horn is
configured to propagate the ultrasonic vibrations from the proximal
end to a distal end of the horn; and a polishing ball attached to
the distal end of the horn, wherein the polishing ball is
configured to vibrate in response to the ultrasonic vibrations for
polishing the surface of the optical element, and wherein the
polishing ball is configured to provide a polishing area on the
surface of the optical element that is smaller than an aperture of
the optical element.
17. The method of claim 16, wherein varying the position of the
polishing ball comprises directing the polishing ball along a
polishing path on the surface of the optical element, the method
further comprising: generating one or more additional control
signals to direct the CNC positioner to vary at least one of: (a) a
load applied to the polishing arm, or (b) a velocity of the
polishing ball along the polishing path, to adjust an amount of
material removed from the surface of the optical element at one or
more positions along the polishing path.
18. The method of claim 17, further comprising: receiving one or
more surface measurements of the optical element; and generating a
surface error map of the optical element based on the surface
measurements, wherein varying the load or velocity is responsive to
the surface error map.
19. An optical element polished by a method comprising: enabling an
ultrasonic actuator to generate ultrasonic vibrations; and
generating one or more control signals to direct a computer
numerical control (CNC) positioner to vary a position of a
polishing arm relative to a surface of the optical element, wherein
the polishing arm includes: a horn having a proximal end coupled to
receive the ultrasonic vibrations generated by the ultrasonic
actuator, wherein the horn is configured to propagate the
ultrasonic vibrations from the proximal end to a distal end of the
horn; and a polishing ball attached to the distal end of the horn,
wherein the polishing ball is configured to vibrate in response to
the ultrasonic vibrations for polishing the surface of the optical
element, and wherein the polishing ball is configured to provide a
polishing area on the surface of the optical element that is
smaller than an aperture of the optical element.
20. The optical element polishing by the method of claim 19, the
method further comprising: receiving one or more surface
measurements of the optical element; generating a surface error map
of the optical element based on the surface measurements;
generating one or more additional control signals in response to
the surface error map to direct the CNC positioner to vary at least
one of: (a) a load applied to the polishing arm, or (b) a velocity
of the polishing ball along a polishing path, to adjust an amount
of material removed from the surface of the optical element at one
or more positions of the polishing arm along the polishing path.
Description
FIELD OF DISCLOSURE
[0001] Aspects of the present disclosure relate generally to
sub-aperture polishing of optical elements, and in particular but
not exclusively, relate to ultrasonic sub-aperture polishing of
optical elements.
BACKGROUND
[0002] A head mounted display (HMD) is a display device, typically
worn on the head of a user. HMDs may be used in a variety of
applications, such as gaming, aviation, engineering, medicine,
entertainment and so on to provide artificial reality content to a
user. Artificial reality is a form of reality that has been
adjusted in some manner before presentation to the user, which may
include, e.g., virtual reality (VR), augmented reality (AR), mixed
reality (MR), hybrid reality, or some combination and/or derivative
thereof.
[0003] The accuracy of the various optical elements included in the
HMD, such as lenses, polarizers, waveplates, etc. may be dependent
on the particular application. For example, some HMDs may
incorporate an eye-tracking system that includes an integrated
camera to track a user's eye movements. Thus, as the requirements
and accuracy for the eye-tracking system increases, the accuracy
required in the manufacturing of the various optical elements used
by the eye-tracking system also increases.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] Non-limiting and non-exhaustive aspects of the present
disclosure are described with reference to the following figures,
wherein like reference numerals refer to like parts throughout the
various views unless otherwise specified.
[0005] FIG. 1 illustrates a head mounted display (HMD), in
accordance with aspects of the present disclosure.
[0006] FIG. 2 illustrates an example ultrasonic polishing system,
in accordance with aspects of the present disclosure.
[0007] FIG. 3 illustrates another example ultrasonic polishing
system, in accordance with aspects of the present disclosure.
[0008] FIG. 4 illustrates a polishing path of a polishing ball, in
accordance with aspects of the present disclosure.
[0009] FIGS. 5A-5C illustrate various stroke paths, contact areas,
and corresponding polishing areas of a polishing ball, in
accordance with aspects of the present disclosure.
[0010] FIG. 6 illustrates an example computing device for use with
an ultrasonic polishing system, in accordance with aspects of the
present disclosure.
[0011] FIG. 7 is a flow chart that illustrates an example process
for ultrasonic sub-aperture polishing of an optical element, in
accordance with aspects of the present disclosure.
DETAILED DESCRIPTION
[0012] Various aspects and embodiments are disclosed in the
following description and related drawings to show specific
examples relating to the ultrasonic sub-aperture polishing of an
optical element. Alternate aspects and embodiments will be apparent
to those skilled in the pertinent art upon reading this disclosure
and may be constructed and practiced without departing from the
scope or spirit of the disclosure. Additionally, well-known
elements will not be described in detail or may be omitted so as to
not obscure the relevant details of the aspects and embodiments
disclosed herein.
[0013] FIG. 1 illustrates an HMD 100, in accordance with aspects of
the present disclosure. The illustrated example of HMD 100 is shown
as including a viewing structure 140, a top securing structure 141,
a side securing structure 142, a rear securing structure 143, and a
front rigid body 144. In some examples, the HMD 100 is configured
to be worn on a head of a user of the HMD 100, where the top
securing structure 141, side securing structure 142, and/or rear
securing structure 143 may include a fabric strap including elastic
as well as one or more rigid structures (e.g., plastic) for
securing the HMD 100 to the head of the user. HMD 100 may also
optionally include one or more earpieces 120 for delivering audio
to the ear(s) of the user of the HMD 100.
[0014] The illustrated example of HMD 100 also includes an
interface membrane 118 for contacting a face of the user of the HMD
100, where the interface membrane 118 functions to block out at
least some ambient light from reaching to the eyes of the user of
the HMD 100.
[0015] Example HMD 100 may also include a chassis for supporting
hardware of the viewing structure 140 of HMD 100 (chassis and
hardware not explicitly illustrated in FIG. 1). The hardware of
viewing structure 140 may include any of processing logic, wired
and/or wireless data interface for sending and receiving data,
graphic processors, and one or more memories for storing data and
computer-executable instructions. In one example, viewing structure
140 may be configured to receive wired power and/or may be
configured to be powered by one or more batteries. In addition,
viewing structure 140 may be configured to receive wired and/or
wireless data including video data.
[0016] Viewing structure 140 may include a display system having
one or more electronic displays for directing light to the eye(s)
of a user of HMD 100. The display system may include one or more of
an LCD, an organic light emitting diode (OLED) display, or
micro-LED display for emitting light (e.g., content, images, video,
etc.) to a user of HMD 100.
[0017] In some examples, a sensor 145 may be included in viewing
structure 140. In some aspects, the sensor 145 is a camera for
capturing image(s) of an eye of a user of HMD 100 for eye-tracking
operations. In other aspects, the sensor 145 is a Simultaneous
Localization and Mapping (SLAM) sensor, such as an optical sensor,
rangefinder, LiDAR sensor, sonar sensor, etc., for mapping the user
and/or environment surrounding the HMD 100.
[0018] In some aspects, the sensor 145 may include one or more
small-diameter optical elements, such as a lens, a polarizer, a
waveguide, reflector, a waveplate, etc. In some aspects, a
"small-diameter" optical element refers to an optical element
having a diameter (e.g., aperture) that is 3 millimeters or less.
As mentioned above, as the requirements and accuracy for the
various systems (e.g., eye-tracking system or SLAM system) of an
HMD increases, so too does the accuracy required in the
manufacturing of the various small-diameter optical elements.
[0019] The manufacture of a conventional optical element typically
begins with the generation of the optical element's rough shape by
diamond turning, grinding a blank or by forming the optical element
in a mold. Subsequently, the optical element or its mold may be
polished to its final form to achieve the desired shape and/or
surface finish. In one example, polishing may be employed to remove
"high spots" on the optical surface. Conventional polishing
approaches involve utilizing a rotating pad or spinning wheel that
is applied to the optical surface. However, for small-diameter
optical elements (e.g., lenses with an aperture less than 3 mm) it
is difficult to achieve the desired accuracy using a rotating pad
or spinning wheel.
[0020] Accordingly, aspects of the present disclosure are directed
to the sub-aperture polishing of optical surfaces, such as the
surfaces of molds used to form the various optical elements, and/or
the surfaces of the optical elements themselves. In some aspects, a
high-frequency (e.g., ultrasonic (>20 kHz)) actuator is utilized
for sub-aperture polishing of various optical elements. For
example, as will be described below, a high-frequency actuator may
be configured to vibrate a polishing arm that includes a polishing
ball attached to an end of a horn. The polishing of an optical
element, according to aspects described herein, may provide a
polishing area that is less than 10 microns in diameter.
[0021] FIG. 2 illustrates an ultrasonic polishing system, in
accordance with aspects of the present disclosure. The illustrated
example of ultrasonic polishing system 200 is shown as including a
housing 202, an ultrasonic actuator 204, and a polishing arm 206.
The example polishing arm 206 is shown as including a horn 208 and
a polishing ball 210. FIG. 2 also illustrates optical elements 212A
and 212B. As shown in FIG. 2, optical element 212A is illustrated
as a lens having an optical surface 205A and an aperture 213A,
whereas optical element 212B is illustrated as a mold having a
surface 205B and an aperture 213B.
[0022] Ultrasonic actuator 204 is shown as being included in the
housing 202 and is configured to generate ultrasonic vibrations. In
one example, a frequency of the ultrasonic vibrations is greater
than 20 kHz. In another example, the frequency of the ultrasonic
vibrations is in the range of 20 kHz to 40 kHz. In some
implementations, the ultrasonic actuator 204 includes a
magnetostrictive actuator. The magnetostrictive actuator may
include a ferromagnetic material that generates the ultrasonic
vibrations responsive to a magnetic field applied to the
ferromagnetic materials. In another implementation, the ultrasonic
actuator 204 includes a piezoelectric actuator. The piezoelectric
actuator may include a solid material (e.g., crystal, ceramic,
etc.) that generates the ultrasonic vibrations in response to an
electrical field applied to the solid material.
[0023] As shown in FIG. 2, the polishing arm is coupled to the
housing to receive the ultrasonic vibrations generated by the
ultrasonic actuator 204. In particular, a proximal end 207 of the
horn 208 is coupled to the ultrasonic actuator 204 to receive the
ultrasonic vibrations. In operation, the horn 208 is configured to
propagate the ultrasonic vibrations from the proximal end 207 to a
distal end 209 of the horn 208. In some examples, horn 208 may be
made from a metal, such as a stainless-steel alloy. Furthermore,
although FIG. 2 illustrates horn 208 as having a curved shape, in
other implementations, horn 208 may have a variety of shapes, such
as a straight shape, or a shape with multiple curves.
[0024] Attached to the distal end 209 of the horn 208, is a
polishing ball 210. In some examples, polishing ball 210 is
attached to the distal end 209 of the horn 208 by way of a glue,
epoxy, or other adhesive. In some examples, polishing ball 210 is
soldered to the distal end 209. In yet another example, polishing
ball 210 may include a threaded cavity for securing it to the
distal end 209.
[0025] Polishing ball 210 may be made from a variety of materials
such as sapphire, ceramics or polymers. As shown in FIG. 2, the
polishing ball 210 may have a spherical shape. In some examples,
the polishing ball 210 may have a diameter that is 3 millimeters or
smaller. In one embodiment, the polishing ball 210 has a diameter
in the range of 0.5 millimeters to 3 millimeters.
[0026] In operation, the polishing ball 210 is configured to
vibrate in response to the ultrasonic vibrations. As shown in FIG.
2, the polishing ball 210 is configured to provide lateral
vibrations 211 (i.e., along the x-y plane) responsive to the
ultrasonic vibrations propagated to the distal end 209 of the horn
208. In some examples, polishing arm 206, including the horn 208
and the polishing ball 210, has a natural frequency that matches
the frequency of the ultrasonic vibrations generated by the
ultrasonic actuator 204. In some embodiments, a combined mass of
the horn 208 and polishing ball 210 is configured to provide a
natural frequency of the polishing arm 206 that matches the
frequency of the ultrasonic vibrations. In other examples, a
frequency of the ultrasonic vibrations generated by the ultrasonic
actuator 204 is tuned to match the natural frequency of the
polishing arm 206.
[0027] As will be described in more detail below with reference to
FIGS. 4 and 5, the polishing ball 210 is configured to provide a
polishing area on a surface of an optical element that is smaller
than an aperture of the optical element, itself. For example, as
mentioned above, optical element 212A is shown in FIG. 2 as a lens
having an aperture 213A. Thus, the polishing ball 210 may be
applied to the surface 205A to provide a polishing area that is
smaller than the aperture 213A. In some examples, the optical
element 212A may be glass or polymer. By way of another example,
the optical element 212B is shown in FIG. 2 as a mold used for
forming various small-diameter optics, such as a lens. The optical
element 212B is shown as including an aperture (i.e., diameter)
213B. Thus, the polishing ball 210 may be applied to the surface
205B to provide a polishing area that is smaller than aperture
213B. In some examples, the apertures 213A/213B are 3 millimeters
or smaller and the polishing area provided by the polishing ball
210 has a diameter that is 10 micrometers or smaller.
[0028] FIG. 3 illustrates an ultrasonic polishing system 300, in
accordance with aspects of the present disclosure. The illustrated
example of ultrasonic polishing system 300 is shown as including a
computer numerical control (CNC) positioner 302, an ultrasonic
actuator 304, a polishing arm 306, a computing device 314, and an
interferometer 316. The polishing arm 306 is shown as including a
horn 308 and a polishing ball 310. Also shown in FIG. 3 is an
optical element 312.
[0029] Ultrasonic actuator 304, polishing arm 306, horn 308, and
polishing ball 310 are configured similarly to corresponding
components 204, 206, 208, and 210, described above with reference
to FIG. 2. As shown in FIG. 3, ultrasonic actuator 304 and
polishing arm 306 may be attached to, or incorporated into, a CNC
positioner 302 to vary a position of the polishing ball 310
relative to a surface 311 of the optical element 312.
[0030] In one aspect, CNC positioner 302 is a motorized
maneuverable platform that is controlled by one or more control
signals 315 generated by a computing device 314. In some examples,
CNC positioner 302 is a CNC mill that is configured to move the
polishing arm 306 and/or the optical element 312 to various
locations and/or depths. In some embodiments, CNC positioner 302
may include one or more direct-drive stepper motors or servo motors
in order to provide highly accurate movements of the polishing arm
306, and thus polishing ball 310, along multiple axes (e.g., X, Y,
and Z axes).
[0031] In some aspects, the computing device 314 is configured to
generate the control signals 315 to direct the CNC positioner 302
to vary the position of the polishing ball 310 and/or optical
element 312, to direct the polishing ball 310 along a polishing
path on the surface 311 of the optical element 312. By way of
example, FIG. 4 illustrates a top view of a polishing path 404 of
polishing ball 310 along surface 311 of optical element 312, in
accordance with aspects of the present disclosure. In some aspects,
the CNC positioner 302 is configured to direct the polishing ball
310 along the polishing path 404 to polish the entirety of surface
311 in a contiguous manner Thus, FIG. 4 illustrates the polishing
path 404 as having a spiral pattern. However, various other
patterns such as raster or quasi-random meander for polishing path
404 may be utilized for polishing the surface 311.
[0032] FIG. 4 illustrates various positions (e.g., position 406A
and position 406B) of the polishing ball 310 as the CNC positioner
302 directs the polishing ball 310 along the polishing path 404. As
mentioned above, the polishing ball 310 may laterally vibrate in
response to the ultrasonic vibrations generated by the ultrasonic
actuator. Thus, in operation the polishing ball 310 may vibrate on
a stroke path 408 (e.g., due to the lateral vibrations) as the
polishing ball is directed along the polishing path 404. When at
position 406A, the polishing ball 310 may vibrate along the stroke
path 408 to provide a polishing area 410A. As mentioned above, the
polishing area 410A may have a diameter that is 10 micrometers or
less.
[0033] In some examples, the CNC positioner 302 may be directed, by
the computing device 314, to vary one or more parameters as the
polishing ball 310 is directed along the polishing path 404 to
adjust an amount of material removed from the surface 311 at one or
more positions. In one aspect, the CNC positioner 302 may adjust a
velocity with which the polishing ball 310 is directed along the
polishing path 404. By way of example, the CNC positioner 302 may
move the polishing ball 310 at a first velocity 412A as the
polishing ball 310 passes through position 406A. However, the
velocity may be adjusted to a second velocity 412B as the polishing
ball 310 passes through position 406B. In one example, the CNC
positioner 302 may decrease the velocity of the polishing ball 310
to increase the amount of time that the polishing ball 310 remains
over an area of the surface 311 to increase the amount of material
that is removed from the surface 311.
[0034] Returning now to FIG. 3, the CNC positioner 302 may also be
configured to vary a load 322 that is applied by the polishing ball
310 to the surface 311. In some aspects, the load 322 is a downward
mechanical force applied by the CNC positioner 302 to the polishing
arm 306. In some examples, the CNC positioner 302 may adjust the
load 322, responsive to control signals 315, to adjust a size of
the polishing area (e.g., polishing area 410A and/or 410B of FIG.
4). In one aspect, the CNC positioner 302 may increase the load 322
to increase the size of the polishing area provided by the
polishing ball 310. In another aspect, the CNC positioner 302 may
increase the load 322 at one or more positions along the polishing
path to increase the amount of material removed from the surface
311.
[0035] As discussed above, the computing device 314 is configured
to generate the control signals 315 to direct the CNC positioner
302 to vary the position of the polishing ball 310 along a
polishing path (e.g., polishing path 404 of FIG. 4). In addition,
the computing device 314 may be configured to vary one or more
parameters (e.g., velocity and/or load) of the CNC positioner 302
to adjust the amount of material that is removed by the polishing
ball 310 at various positions along the polishing path 404. In some
examples, the computing device 314 is configured to vary the one or
more parameters based on a surface error map of the optical element
312. In one aspect, a surface error map is a representation of the
current surface 311 of the optical element 312 and may identify one
or more high spots and/or low spots on the surface 311. In another
aspect, the surface error map may identify one or more locations on
the surface 311 that deviate from a desired shape of the optical
element 312.
[0036] Thus, in some examples, the ultrasonic polishing system 300
may include an interferometer 316 that is disposed to obtain one or
more surface measurements (i.e., measurements 317) of the optical
element 312. In one aspect, interferometer 316 is configured to
measure small displacements, refractive index changes, and/or
surface irregularities of the optical element 312. By way of
example, interferometer 316 may generate a single source of light
318 at various locations of the optical element 312. The single
source of light 318 may be split into two beams that travel in
different optical paths, which are then combined to produce
interference. The interference may then be analyzed to generate the
measurements 317. In response to receiving the measurements 317,
the computing device 314 may generate a surface error map, which it
then uses to generate the removal map. In some aspects, the one or
more control signals 315 are generated by the computing device 314
based on the removal map.
[0037] As mentioned above, as the polishing ball (e.g., polishing
ball 310 of FIG. 3) is directed along a polishing path the
polishing ball may also follow a stroke path (e.g., due to the
lateral vibrations). Thus, FIGS. 5A-5C illustrate various stroke
paths (e.g., stroke paths 504A, 504B, and 504C), contact areas
(e.g., contact area 502), and corresponding polishing areas (e.g.,
polishing areas 506A, 506B, and 506C) of a polishing ball, in
accordance with aspects of the present disclosure.
[0038] FIG. 5A illustrates an example contact area 502. In some
aspects, the contact area 502 represents the area of contact
between the polishing ball and the surface of the optical element.
The size of the contact area 502 may be dependent on a variety of
factors, such as the load applied to the polishing ball, the
diameter of the polishing ball, and the material properties of the
polishing ball and/or of the optical element, itself. In operation,
the polishing ball may vibrate in response to the ultrasonic
vibrations to provide a stroke path 504A which results in an
effective polishing area 506A. The polishing area 506A may have a
diameter that is less than 10 micrometers.
[0039] As shown in FIG. 5A, the stroke path 504A is a linear stroke
path that provides movement of the polishing ball along the Y-axis
in response to the ultrasonic vibrations. In one example, a linear
stroke path is provided in response to ultrasonic vibrations
generated by a piezoelectric actuator that may be included in the
ultrasonic actuator (e.g., ultrasonic actuator 304 of FIG. 3).
[0040] FIG. 5B illustrates a stroke path 504B that is another
linear stroke path, but one that provides movement of the polishing
ball along the X-axis. As shown, movement of the polishing ball
along the stroke path 504B provides an effective polishing area
506B. Similar to the stroke path 504A, discussed above, the stroke
path 504B of FIG. 5B may be generated in response to ultrasonic
vibrations generated by a piezoelectric actuator.
[0041] FIG. 5C illustrates an example elliptical stroke path 504C.
As shown in FIG. 5C, the elliptical stroke path 504C provides for
elliptical movement of the polishing ball on the X-Y plane to
provide an effective polishing area 506C. In one example, the
elliptical stroke path 504C is provided in response to ultrasonic
vibrations generated by a magnetostrictive actuator that may be
included in the ultrasonic actuator (e.g., ultrasonic actuator 304
of FIG. 3).
[0042] FIG. 6 illustrates an example computing device 602 for use
with an ultrasonic polishing system, in accordance with aspects of
the present disclosure. The illustrated example of computing device
602 is shown as including a communication interface 604, one or
more processors 606, hardware 608, and a memory 610. Computing
device 602 is one possible implementation of computing device 314
of FIG. 3.
[0043] The communication interface 604 may include wireless and/or
wired communication components that enable the computing device 602
to transmit data to and receive data from other devices, such as
the CNC positioner 302 of FIG. 3. The hardware 608 may include
additional hardware interface, data communication, or data storage
hardware. For example, the hardware interfaces may include a data
output device (e.g., electronic display, audio speakers), and one
or more data input devices.
[0044] The memory 610 may be implemented using computer-readable
media, such as computer storage media. In some aspects,
computer-readable media may include volatile and/or non-volatile,
removable and/or non-removable media implemented in any method or
technology for storage of information such as computer-readable
instructions, data structures, program modules, or other data.
Computer-readable media includes, but is not limited to, RAM, ROM,
EEPROM, flash memory or other memory technology, CD-ROM, digital
versatile disks (DVD), high-definition multimedia/data storage
disks, or other optical storage, magnetic cassettes, magnetic tape,
magnetic disk storage or other magnetic storage devices, or any
other non-transmission medium that can be used to store information
for access by a computing device.
[0045] The processors 606 and the memory 610 of the computing
device 602 may implement a surface error map and removal module 612
and a CNC control module 614. The surface error map and removal
module 612 and the CNC control module 614 may include routines,
program instructions, objects, and/or data structures that perform
particular tasks or implement particular abstract data types. The
memory 610 may also include a data store (not shown) that is used
by the surface error map and removal module 612 and/or CNC control
module 614.
[0046] The surface error map and removal module 612 may be
configured to generate a surface error map and a removal map of the
optical element (e.g., optical element 312 of FIG. 3). In one
example, the surface error map and removal module 612 may generate
the surface error map in response to one or more measurements
obtained from an interferometer (e.g., measurements 317 generated
by interferometer 316 of FIG. 3). In other examples, the surface
error map and removal module 612 may generate the surface error map
based on one or more other optical metrology techniques, such as
direct surface profiling (e.g., by way of a profilometer).
[0047] The CNC control module 614 is configured to generate one or
more control signals (e.g., control signals 315 of FIG. 3) to
direct a CNC positioner (e.g., CNC positioner 302 of FIG. 3) to
vary a position of a polishing arm (e.g., polishing arm 306)
relative to a surface of an optical element (e.g., surface 311 of
optical element 312). In some examples, the CNC control module 614
is configured to generate the control signals based on the removal
map generated by the surface error map and removal module 612. For
example, the removal map may identify one or more areas on the
surface 311 of the optical element 312 that are high areas, or
areas at which additional material needs to be removed. Thus, the
CNC control module 614 may generate the control signals to vary the
load and/or velocity of the polishing ball as it is directed along
the polishing path to increase the amount of material that is
removed from the surface of the optical element when the polishing
ball is at a position corresponding to the identified high areas of
the optical element.
[0048] FIG. 7 is a flow chart that illustrates an example process
700 for ultrasonic sub-aperture polishing of an optical element, in
accordance with aspects of the present disclosure. Process 700 is
one example process that may be performed by computing device 314
of FIG. 3 and/or computing device 602 of FIG. 6.
[0049] In a process block 702, the ultrasonic actuator (e.g.,
ultrasonic actuator 304) is enabled to generate ultrasonic
vibrations. In one aspect, the CNC control module 614 may enable
the ultrasonic actuator by generating one or more control signals
315 via communication interface 604. Next, in a process block 704,
the CNC control module 614 generates one or more of the control
signals (e.g., control signals 315) to vary a position of the
polishing arm (e.g., polishing arm 306 of FIG. 3) to vary a
position of the polishing arm relative to a surface of the optical
element.
[0050] As mentioned above, in some example, the CNC control module
614 may generate the control signals to vary a parameter, such as
load and/or velocity of the polishing arm based on a surface error
map of the optical element. Thus, process 700 may further include
the surface error map and removal module 612 receiving one or more
surface measurements (e.g., measurements 317 of FIG. 3) and
generating the surface error map of the optical element based on
the surface measurements. The CNC control module 614 may then
generate one or more additional control signals to vary the load
and/or velocity at various positions of the polishing ball along
the optical path to adjust and amount of material that is removed
from the surface of the optical element.
[0051] Embodiments of the invention may include or be implemented
in conjunction with the manufacture of an artificial reality
system. Artificial reality is a form of reality that has been
adjusted in some manner before presentation to a user, which may
include, e.g., a virtual reality (VR), an augmented reality (AR), a
mixed reality (MR), a hybrid reality, or some combination and/or
derivatives thereof. Artificial reality content may include
completely generated content or generated content combined with
captured (e.g., real-world) content. The artificial reality content
may include video, audio, haptic feedback, or some combination
thereof, and any of which may be presented in a single channel or
in multiple channels (such as stereo video that produces a
three-dimensional effect to the viewer). Additionally, in some
embodiments, artificial reality may also be associated with
applications, products, accessories, services, or some combination
thereof, that are used to, e.g., create content in an artificial
reality and/or are otherwise used in (e.g., perform activities in)
an artificial reality. The artificial reality system that provides
the artificial reality content may be implemented on various
platforms, including a head-mounted display (HMD) connected to a
host computer system, a standalone HMD, a mobile device or
computing system, or any other hardware platform capable of
providing artificial reality content to one or more viewers.
[0052] The above description of illustrated embodiments of the
invention, including what is described in the Abstract, is not
intended to be exhaustive or to limit the invention to the precise
forms disclosed. While specific embodiments of, and examples for,
the invention are described herein for illustrative purposes,
various modifications are possible within the scope of the
invention, as those skilled in the relevant art will recognize.
[0053] These modifications can be made to the invention in light of
the above detailed description. The terms used in the following
claims should not be construed to limit the invention to the
specific embodiments disclosed in the specification. Rather, the
scope of the invention is to be determined entirely by the
following claims, which are to be construed in accordance with
established doctrines of claim interpretation.
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