U.S. patent number 3,579,922 [Application Number 04/766,735] was granted by the patent office on 1971-05-25 for apparatus for abrading articles.
This patent grant is currently assigned to Western Electric Company, Incorporated. Invention is credited to Nicholas J. Mandonas, Paul A. Ryll.
United States Patent |
3,579,922 |
Mandonas , et al. |
May 25, 1971 |
APPARATUS FOR ABRADING ARTICLES
Abstract
Apparatus for fine lapping of thin piezoelectric crystals to a
desired resonant frequency characteristic includes a number of
holders urging and lapping the crystals against a vibrating,
relatively movable lapping plate bearing very fine abrasive
particles. Probes are successively pivoted into engagement with
selected holders, one at a time, during lapping to sample the
instant resonant frequency of each of the vibrating crystals by
coupling the crystals successively into a test circuit. While
lapping of the other crystals continues, a crystal which has
attained the desired frequency characteristic may be withdrawn with
its holder and replaced by another holder and crystal.
Inventors: |
Mandonas; Nicholas J. (Medford,
MA), Ryll; Paul A. (Haverhill, MA) |
Assignee: |
Western Electric Company,
Incorporated (New York, NY)
|
Family
ID: |
25077360 |
Appl.
No.: |
04/766,735 |
Filed: |
October 11, 1968 |
Current U.S.
Class: |
451/9; 451/163;
451/41 |
Current CPC
Class: |
B24B
49/00 (20130101); B24B 37/013 (20130101); B24B
37/04 (20130101); B24B 35/00 (20130101); B24B
49/04 (20130101) |
Current International
Class: |
B24B
37/04 (20060101); B24B 35/00 (20060101); B24B
49/02 (20060101); B24B 49/00 (20060101); B24B
49/04 (20060101); B24b 049/04 () |
Field of
Search: |
;51/165,165.20,165.21,57,58,129,131,283 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Swingle; Lester M.
Claims
We claim:
1. In apparatus for abrading an article having a vibration response
characteristic which is determined by the thickness of the article
to alter the vibration response characteristic to a predetermined
value:
an abrading member mounted for movement upon vibration thereof;
article holder means for urging the article against said abrading
member so that the thickness of the article will be decreased and
the vibration response characteristic of the article will be
altered upon movement of the abrading member;
means for vibrating said abrading member to abrade the article and
vary the vibration response characteristic; and
means responsive to vibration during the abrading for indicating
the attainment by the article of the predetermined value of the
vibration response characteristic.
2. In apparatus for lapping a piezoelectric crystal:
a fixed holder for the crystal;
a relatively movable lapping member positioned to contact the
crystal on said holder;
means for moving said lapping member with respect to the holder
during said contact to reduce the thickness of the held crystal,
said means comprising means for vibrating the lapping member to
excite the crystal; and
circuit means, completable through the held crystal and rendered
effective when completed upon excitation of the crystal with
movement of said lapping member, for measuring the instant resonant
frequency of the excited crystal.
3. In apparatus for lapping piezoelectric crystals:
a first fixed holder for a first crystal;
a relatively movable lapping member positioned to contact the first
crystal on said holder;
means for moving said lapping member with respect to the holder
during said contact to reduce the thickness of the first
crystal;
at least one additional relatively fixed crystal holder located
adjacent said movable lapping member in position to lap another
crystal between the additional crystal holder and the relatively
movable lapping member;
means for removably mounting each of said holders in the fixed
position thereof such that at least one of the crystal holders may
be removed during movement of said lapping member; and
circuit means completable through each held crystal and rendered
effective during movement of said lapping member for measuring the
instant resonant frequency of each crystal through which the
circuit means is completed.
4. In apparatus for lapping crystals, as set forth in claim 3:
said crystal holders each being composed of an electrically
conductive material;
said holder-mounting means being composed of a dielectric material
so as to electrically isolate the crystal holders from each other;
and
said circuit means including an electrical conductive probe mounted
for engaging one of said crystal holders to measure the frequency
of a crystal held thereby during lapping.
5. In apparatus for lapping piezoelectric crystals to vary the
resonant frequency of the crystals:
a plurality of holders for the crystals;
a lapping plate mounted for movement;
means removably mounting each of said holders fixed with respect to
said lapping plate and positioned to urge the crystals held by the
holders against the lapping plate for lapping the crystals upon
movement of the lapping plate;
means for vibrating and moving said lapping plate to excite and lap
the crystals; and
means operated during the vibration and movement of said lapping
plate for measuring the instant resonant frequency of a crystal
being lapped.
6. In apparatus for lapping piezoelectric crystals to adjust the
crystals to a predetermined resonant frequency value:
a fixed plate having a pair of opposite faces and having a
plurality of apertures extending through the fixed plate between
said faces;
a lapping plate having a lapping surface and mounted for movement
with the lapping surface maintained adjacent one of said faces of
the fixed plate;
individual holder means removably positionable in said apertures of
the fixed plate for releasably holding a crystal and urging the
crystal against said lapping surface of the lapping plate to be
lapped upon movement of the lapping plate;
means for moving the lapping plate to lap the held crystals;
and
means selectively monitoring the instant resonant frequency of the
held crystals during continued lapping for indicating that a held
crystal has attained the predetermined value.
7. In apparatus for lapping piezoelectric crystals, as set forth in
claim 6, said lapping plate moving means comprising:
means for vibrating the lapping plate during movement to excite the
held crystals.
Description
BACKGROUND OF THE INVENTION
This invention relates to apparatus for abrading one or more
articles and, more particularly, to apparatus for the fine lapping
of thin piezoelectric crystals to adjust the crystals precisely to
a predetermined resonant frequency characteristic.
In the production of piezoelectric crystals, for example, thin
quartz crystals to be used in electronic systems for frequency
control, the crystals are ground lapped or polished to impart a
desired resonant frequency characteristic to each finished crystal.
It is generally required that the frequency which is obtained for
each crystal so produced be within extremely close tolerances.
Thus, a final, precision lapping operation on the crystals is most
critical.
In order that an inordinate amount of time and effort not be
expended in lapping piezoelectric crystals to value, it is
desirable that a number of crystals be lapped simultaneously.
However, in utilizing certain prior-art apparatus for lapping
plural crystals simultaneously, it is necessary that lapping be
periodically interrupted so that the individual crystals may each
be tested for instant resonant frequency. Continued lapping cannot
occur during the testing of the crystals. Thus, a series of
intermittent lapping operations, followed by intermittent testing
operations, is required. A crystal attaining the desired frequency
value is removed from the apparatus after a testing operation and
prior to a subsequent lapping operation. Those crystals which have
not attained the desired frequency characteristic, on the other
hand, must be lapped further. Such continued lapping cannot occur,
however, during the intermittent testing operations or the crystal
removal operations. It is clear from the foregoing that it would be
desirable to provide methods and apparatus for fine lapping of
piezoelectric crystals such that crystal lapping may be
accomplished more efficiently, allowing lapping to occur during a
greater percentage of the time during which the apparatus is
utilized.
SUMMARY OF THE INVENTION
An object of the invention resides in new and improved apparatus
for abrading one or more articles, such as in the fine lapping of
piezoelectric crystals to adjust the crystals precisely to a
desired resonant frequency characteristic within close
tolerances.
The invention contemplates the use of a number of electrically
conductive crystal holders each urging one or more thin
piezoelectric crystals against a lapping plate. A fixed housing
retains the crystal holders in nest positions, from which each
holder may be individually removed. The lapping plate is vibrated
and is moved relatively to the crystal holders by a substantially
noise-free, vibration-induced driving arrangement which will not
interfere with crystal frequency measurement during lapping. Very
fine abrasive particles on the lapping plate lap the crystals to
alter their resonant frequency characteristics. The contemplated
apparatus may be utilized to provide a final lapping step in a
series of one or more abrading operations so as to impart a desired
resonant frequency characteristic, within close tolerances, to the
crystals.
A number of spring-loaded electrical probes are each individually
engageable with a different crystal holder during the lapping
operation. Engagement of a probe with a crystal holder couples the
holder and its crystal or crystals into a test circuit which
includes testing apparatus for measuring the instant resonant
frequency of the held crystal or crystals. Such testing may occur
with the lapping operation continuing, the engagement of a probe
with a selected fixed crystal holder providing a precise indication
of the instant resonant frequency of the held crystal or crystals
being lapped between the selected crystal holder and the vibrating
lapping plate. The vibration of the plate constitutes a complex
vibration with components of multiple frequencies, including the
resonant frequency of the crystal at any instant. Thus, the crystal
is excited and voltage spike may be observed at the resonant
frequency. This effect is utilized in measuring the resonant
frequency characteristic at the particular instant.
Testing and lapping may occur simultaneously until a first crystal
attains its desired frequency value. Sampling of the first crystal
by the testing apparatus will indicate that the first crystal
should now be withdrawn from lapping contact with the lapping
plate. The apparatus is so constructed that the crystal holder
which holds the first crystal may be removed manually from the
fixed housing while movement of the lapping plate continues and
while the other crystal holders urge other crystals against the
lapping plate. As a result, the lapping of the other crystals is
not interrupted by the removal of the first crystal and its holder.
Likewise, the replacement of the holder with a new crystal to be
lapped does not interfere with the continued lapping of the crystal
held in other crystal holders. Thus, the structure of the apparatus
permits its use in a most efficient manner to perform a new and
improved method as follows: a plurality of crystals are lapped
continuously and simultaneously until one crystal attains a desired
frequency value, which value is indicated by testing during
lapping. The lapping of only the crystal attaining the desired
frequency value is terminated, so that such crystal may be replaced
by a new crystal, while the lapping of other crystals which have
not yet attained the desired value in continued. As a result, at
any given instant during the operation of the apparatus, a number
of crystals are simultaneously undergoing lapping.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a plan view of crystal-lapping apparatus constructed in
accordance with the principles of the invention, showing a probe
positioned to sample, with the aid of a test set, the instant
resonant frequency of a selected crystal or group of crystals which
are urged against a moving lapping plate by an associated one of
several crystal holders each urging crystals against the lapping
plate; and
FIG. 2 is an enlarged fragmentary side view, partly in section,
illustrating the selected crystal holder urging the crystals
against the moving lapping plate and showing a fixed plate mounting
the crystal holder for removal therefrom and withdrawal of the
crystals from the moving lapping plate when the test set indicates
that a predetermined resonant frequency characteristic has been
attained for the crystals.
DETAILED DESCRIPTION
Referring to FIGS. 1 and 2 of the drawing, an apparatus for lapping
articles such as thin quartz crystals 11 or other piezoelectric
crystals includes an annular lapping plate 12 positioned between an
annular upper plate or housing 13 and a base plate 14. The lapping
plate 12 is positioned beneath the upper plate 13 with a pair of
annular shoulders 16 and 17 of the lapping plate located below a
pair of radially extending flange sections 18 and 19, respectively,
of the upper plate. A flat bottom surface of the lapping plate 12
rests on a flat upper bearing surface of the base plate 14. The
annular upper plate 13 is fixed against either horizontal or rotary
movement by conventional mechanisms, e.g., keys, splines or studs,
securing an outer edge of the upper plate to a fixed rim 21. The
annular lapping plate 12 is not so constrained, but is free to move
circumferentially beneath the fixed upper plate 13. The baseplate
14, in similar manner to the upper plate 13, is fixed against
movement on a supporting frame 22.
A conventional vibration-inducing mechanism 23 is coupled to the
supporting frame 22 for the baseplate 14. The vibrator 23 is
effective to impart force components such that the freely movable
lapping plate 12 will be caused to move circumferentially, at a
relatively slow speed, in either a clockwise or counterclockwise
direction between the fixed, annular upper plate 13 and the fixed
baseplate 14 when the vibrator is energized. Alternatively, the
lapping plate 12 may be oscillated about an intermediate position.
An annular bottom ridge portion 24 below the annular shoulders 18
and 19 of the upper plate 13 extends downwardly between the
shoulders 16 and 17 of the lapping plate 12 so as to allow only
rotary circumferential movement of the lapping plate upon
energization of the vibrator 23. The upper plate 13 is constructed
of relatively lightweight dielectric material in order that (1) no
substantial frictional drag force will interfere with rotary
movement of the lapping plate 12 and (2) electrical isolation will
be provided by the lapping plate 12.
A groove 26 extends into a top surface of the fixed upper plate 13
and runs circumferentially thereabout. A number of spaced
cylindrical apertures or bores 27 are arranged along the groove 26
and extend vertically through the upper plate 13 between the top
and bottom surface thereof. Each of the apertures 27 in the fixed
upper plate 13 constitutes a nest for housing a cylindrically
shaped crystal holder 28 therein. Each crystal holder 28 is
constructed of electrically conductive material and may
individually be manually placed into or removed from its respective
aperture 27. The operator need only grasp that portion of the outer
cylindrical surface of the crystal holder 28 which normally extends
vertically within the groove 26 to insert or remove the holder.
Each crystal holder 28 includes one or more appropriately shaped,
shallow recesses 29 (three shown in FIG. 1) for each holding a
crystal 11 therein. The crystals may be held in place in the
recesses 29 by an adhesive or by other suitable means, e.g.,
mechanical fastening mechanisms or vacuum. Each crystal extends
slightly outwardly from a recess 29. Thus, an exposed surface of
the crystal will contact a raised annular lapping surface 31 of the
lapping plate 12 when the associated crystal holder 28 is nested in
its aperture 27 with the crystal facing downwardly, as shown in
FIG. 1. Very fine abrasive particles 32, e.g., silicon carbide or
aluminum oxide, may be placed onto the lapping surface 31 of the
lapping plate through one or more of the apertures 27 when the
associated crystal holder or holders 28 are removed. As a result,
upon energization of the vibrator 23 to impart circumferential,
rotary or oscillatory movement to the lapping plate 12, the
surfaces of the crystals 11 which are in contact with the raised
lapping surface 31 will be finely lapped by the abrasive particles
32. The abrasive particles may be suspended in any suitable carrier
fluid, e.g., oil. The crystals will be continuously urged against
the abrasive particles 32 on the lapping surface 31, as lapping
continues, by the weight of the removable crystal holders 28.
As stated previously, the fixed upper plate 13 is composed of a
dielectric material, e.g., a lightweight plastic. Thus, the crystal
holders 28, which are made of an electrically conductive material,
will be electrically isolated from each other when nested in the
apertures 27. The lapping plate 12, the baseplate 14, and the
abrasive particles 32 are all formed of electrically conductive
materials. A number of electrically conductive probes 33 are
pivotally mounted on a support member 34, which is composed of a
dielectric material. The support member 34 may, alternatively, be
integral with the upper plate 13. Each probe 33 is attached to a
lever 35 and is associated with a different aperture 27 in the
upper plate 13. When a lever 35 is pivoted, the attached probe is
moved into engagement with a crystal holder 28 positioned in the
associated aperture. The probe and lever are preferably lightly
spring loaded in order to maintain such engagement once the probe
is pivoted. The spring loading obviates any necessity for frequent
position adjustments for the probe as the lapping of a held crystal
or crystals 11 results in downward movement of the crystal holder
28. The engagement of a pivoted probe with a crystal holder will
complete an electrical circuit from a test set 40 through a wire or
other conductor 36, the pivoted probe 33, the engaged crystal
holder 38, one or more crystals residing in one or more recesses 29
in the engaged crystal holder, the lapping plate 12 and the
abrasive particles 32 thereon, the baseplate 14 and a wire or other
conductor 37. The conductors 36 and 37 may be separately arrayed
wires or may be conductive elements within a single coaxial
cable.
The test set 40 includes a precision frequency selector or tuner 41
and a highly sensitive voltmeter 42. When one of the probes 33 is
engaged with a crystal holder 28, the test set 40 will sample the
instant resonant frequency of one or more crystals 11 being lapped
by the lapping plate 12 beneath the holder. If more than one
crystal is held by the holder 28, each crystal will provide an
individual frequency indication through use of the test set 40. The
test set will indicate that a sampled crystal 11 is close to or has
attained the desired resonant frequency and, in the latter case,
that lapping of the sample crystal should be ceased.
It should be noted that the vibrator 23 performs simultaneously
several functions. Thus, the vibrator will induce a slow rotary or
oscillatory movement of the lapping plate 12 to lap the crystals
11. At the same time, the use of the vibrator 23, rather than an
induction motor, to drive the lapping plate 12 will eliminate a
potential source of stray frequency noise. Such noise would
interfere with the precision frequency measurement required in
ascertaining the instant resonant frequency characteristic in a
selected crystal 11 undergoing lapping. Additionally, the vibrator
will excite the selected crystal 11 at its instant resonant
frequency, the vibrator causing the lapping plate 12 to vibrate
with components of vibration at multiple frequencies including a
component corresponding to the resonant frequency of the crystal at
any given instant during lapping. Thus, the vibrated crystal 11
will generate a voltage signal at its instant resonant frequency.
The frequency of this signal will change continuously, but slowly,
as the selected crystal is lapped to decrease its thickness.
Manipulation of the frequency selector or tuner 41 until a
relatively large voltage spike is observed on the meter 42 will
indicate that the instant resonant frequency of the crystal 11
being tested has been located by the tuner 41. The instant resonant
frequency value may then be read directly from the tuner.
In the operation of the apparatus of FIGS. 1 and 2, it is assumed
that all of the crystal holders 28 are initially withdrawn from the
apertures 27 in the fixed, annual upper plate 13. Very fine
abrasive particles 32 may, thus, be introduced onto the raised
lapping surface 31 of the lapping plate 12 through one or more of
the open apertures 27.
Crystals 11 are now inserted into the recesses 29 in the crystal
holders 28, to be retained therein during a fine lapping operation,
with an exposed surface of each crystal extending outwardly from
its recess 29. Next, the crystal holders 28 are inverted and are
inserted manually one into each aperture 27 in the fixed upper
plate 13. The inversion of the crystal holders results in the
exposed surfaces of the held crystals 11 being placed into contact
with the abrasive particles 32 on the raised lapping surface
31.
The vibrator 23 is now energized by the operator closing a switch
(not shown) in a line to a power source. Vibration is imparted to
the supporting frame 22, the baseplate 14, the lapping plate 12 and
the crystals 11 in the holders 28. The vibration induces a slow
rotary or oscillatory movement of the lapping plate 12
circumferentially of the annual upper plate 13. The vibrating
crystals 11 are, thus, lapped on the surfaces thereof which extend
outwardly from the holders 28 and contact the abrasive particles 32
on the lapping surface 31. The weight of the crystal holders 28
urges the crystals into continuous contact with the abrasive
particles during lapping. The crystal holders 28, while constrained
by the walls of the aperture 27 against movement circumferentially
of the fixed plate 13, are free to rotate about their own axes in
the apertures 27 so that the crystals 11 held by each holder may be
more evenly lapped. A convex or domed tip or nose 43 of each probe
33 is positioned to extend when pivoted, into a similarly shaped
cavity 44 in each associated crystal holder 28. The domed tips 43
act as pintles to permit continued crystal holder rotation during
testing engagement between a probe and a crystal holder.
As lapping continues, the instant resonant frequencies of the
various vibrating crystals 11 being lapped are sampled
successively. Thus, a first probe 33 is pivoted into engagement
with its associated crystal holder 28 (FIG. 2) and the instant
resonant frequencies of the held crystal or crystals are measured.
Such measurement occurs as the frequency selector or tuner 41 is
adjusted until a surge of high voltage is observed on the meter 42.
The surge of voltage indicates that the frequency to which the
selector 41 has been adjusted corresponds to the instant resonant
frequency of one of the crystals 11 being lapped beneath the
engaged crystal holder 28. The frequencies of any other crystals 11
held by the engaged crystal holder may be similarly identified. A
precise, sequential monitoring of the individual crystal
frequencies is possible due both to (1) a relative absence of stray
frequency noise through the use of the vibrator 23 rather than an
induction motor in driving the lapping plate 12 and (2) the
relatively slow rate of change of the resonant frequency
characteristic in the crystals undergoing precision lapping at slow
speed using very fine abrasive particles.
The first probe 33 is next pivoted out of engagement with its
crystal holder and a second probe 33 is pivoted to sample the
instant resonant frequency of the crystal or crystals held by a
second holder 28. All of the crystals are tested successively in
similar manner an their instant resonant frequencies are noted.
The crystal 11 having a tested resonant frequency characteristic
closest to a desired final value is now sampled once again. Other
crystals having approximately equal frequencies may also be
retested. The crystal 11 closest in frequency to the desired value
is monitored continually until the desired value is attained. The
crystal holder 28 retaining this crystal is now grasped by the
operator and is lifted from its aperture 27 in the fixed upper
plate 13 to remove the crystal from contact with the lapping plate
12. A spare crystal holder (not shown) with one or more crystals
retained therein may be inserted immediately into the empty
aperture 27 to replace the removed crystal holder 28. If more than
one crystal 11 is retained in the removed crystal holder,
sequential testing of the individual crystals in the removed holder
will indicate which of the crystals has attained the desired
resonant frequency value. Movement of the lapping plate 12,
meanwhile, continues. Thus, lapping of other crystals is not
interrupted.
A second crystal 11, now closest in frequency to the desired value,
is identified and sampled. The procedure outlined above in
connection with the first crystal is repeated for the second
crystal. Meanwhile, the first crystal may be removed from its
recess 29 in the crystal holder 28 and a new crystal inserted into
the recess 29. The first crystal holder 28 may be set aside as a
spare, while monitoring of the second crystal continues.
Similar operations may follow, in order to lap any number of
crystals 11 to the desired resonant frequency characteristic. Any
number or all of the crystal holders 28 may be nested in the
apertures 27 at any given time. Movement of the lapping plate 12
may be continued so long as further lapping of any crystal is
required. The number of apertures 27 is preferably not overly large
and the speed of movement of the lapping plate 12, which carries
the very fine abrasive particles 32, is relatively slow. Thus,
neither the number of crystals to be monitored nor the rate of
change of crystal frequencies makes individual sampling and removal
of crystals during the lapping operation too difficult for the
operator to accomplish.
Briefly, reviewing the method of the invention, articles, such as
piezoelectric crystals, are abraded by urging the articles against
a lapping plate or other abrasive surface while moving the abrading
surface with respect to the articles, for example by vibrating the
abrading surface. A characteristic of a selected article, which
characteristic, such as resonant frequency, is altered by abrasion,
is measured simultaneously with the abrading steps. When the
characteristic value attains a predetermined level, the article is
removed from contact with the abrading surface while abrasion of at
least one other article continues. This method of abrading may be
performed using the exemplary apparatus of FIGS. 1 and 2, or with
any other apparatus for abrading articles, suitably modified to
whatever extent may be necessary to allow individual testing of
articles undergoing abrasion.
It is to be understood that the above-described method and
apparatus are simply illustrative of one embodiment of the
invention. Another embodiment of the apparatus might utilize only a
single probe, the single probe being mounted to be moved into
engagement successively with each of the crystal holders 28 in the
apertures 27, e.g., by movement of the probe along a trackway on
the rim 21. Certain embodiments might use other known frequency
measuring circuits in place of the exemplary test set 40. Likewise,
plural test sets may be used to measure the instant resonant
frequencies of plural crystals simultaneously. Additional
embodiments might be provided for lapping, polishing, grinding or
otherwise abrading other types of articles to any given thickness
tolerance or smoothness, for example, in order to alter any
measurable characteristic of the article or articles. Many other
modifications may be made without departing from the invention.
* * * * *