U.S. patent number 3,736,426 [Application Number 05/230,673] was granted by the patent office on 1973-05-29 for methods of and apparatus for inspecting crystals.
This patent grant is currently assigned to Western Electric Company, Incorporated. Invention is credited to Albin R. Anderson, Robert P. Grenier, Peter R. Perri.
United States Patent |
3,736,426 |
Anderson , et al. |
May 29, 1973 |
METHODS OF AND APPARATUS FOR INSPECTING CRYSTALS
Abstract
In order to determine the angular orientation of atomic planes
in a crystal relative to a reference surface thereof, the crystal
is inspected by an X-ray defraction technique in which a pair of
X-ray beams are sequentially passed through the crystal from
opposite directions while the crystal is rotated through a small
arc and monitored for Bragg angle reflections. The two angles at
which reflections occur are then averaged to determine an average
Bragg angle of reflection. This technique compensates for the
situation in which the atomic planes of the crystal are completely
oblique to the reference surface by cancelling component vectors of
reflection introduced by the complete obliqueness.
Inventors: |
Anderson; Albin R. (Lowell,
MA), Grenier; Robert P. (Newburyport, MA), Perri; Peter
R. (Atkinson, NH) |
Assignee: |
Western Electric Company,
Incorporated (New York, NY)
|
Family
ID: |
22866137 |
Appl.
No.: |
05/230,673 |
Filed: |
March 1, 1972 |
Current U.S.
Class: |
378/73; 209/589;
378/81 |
Current CPC
Class: |
G01N
23/207 (20130101) |
Current International
Class: |
G01N
23/207 (20060101); G01N 23/20 (20060101); G01n
023/20 (); H01j 037/20 () |
Field of
Search: |
;250/51.5
;209/111.5 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Lawrence; James W.
Assistant Examiner: Anderson; B. C.
Claims
What is claimed is:
1. In a method of measuring the axial orientation of atomic planes
in a crystal relative to a reference surface of the crystal where
the atomic planes may be completely oblique relative to the
reference surface, comprising the steps of:
rotating the crystal about an axis thereof through an arc,
passing radiant energy through a reference surface of the crystal
while the crystal is being rotated,
determining the angle of rotation at which radiant energy is
reflected through the reference surface of the crystal from the
atomic planes,
storing the determined angle,
passing radiant energy through a surface of the crystal opposite
the reference surface,
determining the angle of rotation at which radiant energy is
reflected through the opposite surface from the atomic planes,
and
averaging the angle at which radiant energy is reflected through
the opposite surface with the stored angle to compensate for
inaccuracies introduced into the measurements because of the
complete obliqueness.
2. The method of claim 1 wherein the radiation employed is
X-radiation.
3. In a method of determining the axial orientation of atomic
planes in a crystal wherein the crystal is rotated through a sector
intersected by an X-ray beam which is, in turn, monitored for
reflections through one surface of the crystal from the atomic
planes to determine the angle at which reflections occur, the
improvement comprising the steps of:
again rotating the crystal,
impinging an additional X-ray beam through another surface of the
crystal,
monitoring the X-ray beam for reflections from the atomic planes
through the other surface to determine the angle at which the
reflections occur, and
averaging the angles at which reflections occur through both the
surfaces to determine the axial orientation of the atomic planes in
the crystal.
4. In an apparatus for determining the angle of orientation of
atomic planes in a crystal relative to a reference surface of the
crystal,
means for sequentially focusing oppositely directed X-ray beams for
passage into the crystal,
means for angularly displacing the crystal relative to the X-ray
beams,
means for detecting Bragg angle X-ray reflections from the
crystal,
means for determining the angular positions of the rystal at which
Bragg angle reflections occur from the crystal, and
means for averaging the angular positions at which Bragg angle
reflections occur to determine the angle of orientation of the
atomic planes in the crystal relative to the reference surface of
the crystal.
5. The apparatus of claim 4 further including means responsive to
said averaging means for directing the crystal to a selected
location after the average angular position has been computed.
6. An apparatus for determining the angle of orientation of atomic
planes relative to an axis of a reference surface of a crystal
comprising:
means for passing sequentially a pair of X-ray beams through the
crystal from generally opposite directions,
means for oscillating the crystal about the axis while the X-ray
beams are impinging thereon,
means for detecting Bragg angle reflections from the crystal while
the crystal is oscillating,
means for determining when the reflections reach a predetermined
level of intensity,
means for computing the mean of the angles at which reflections
occur from the crystal after the reflections reach a predetermined
level of intensity, and
means for averaging the mean angles after the angles are computed
to determine the angle which the atomic planes make with the
reference surface of the crystal.
7. The apparatus of claim 6 further including means for rejecting
the crystal if the Bragg angle reflections do not reach the
predetermined level of intensity.
Description
FIELD OF THE INVENTION
The present invention relates generally to the manufacture of
piezoelectric quartz crystal elements, and more particularly to
automatic apparatus adapted to measure the axial orientation of
crystal blanks and to sort the blanks according to the orientation
measurements.
BACKGROUND OF THE INVENTION
Using piezoelectric quartz crystals in electronic systems is well
known. A piezoelectric crystal undergoes a change in dimension or
form proportional to an applied electrical potential. Conversely,
the crystal generates a surface charge when subjected to stress.
The crystal is said to be a piezoelectric resonator when the
mechanical resonances of the crystal itself are used to control
frequency response.
Crystal blanks for piezoelectric units are cut from quartz stones.
When the crystal blank is excited, the resulting modes of motion
and the properties of those modes depend markedly on how the
surfaces of the cut crystal blanks are oriented relative to the
bases of the uncut stones. The angle at which a crystal blank is
cut with reference to the natural crystal axis of the uncut stone
determines the temperature coefficient of the frequency of the
crystal unit. Obviously, to preclude or minimize departures from an
assigned frequency as a result of temperature variations, it is
essential that this coefficient be as close as possible to
zero.
A rectangular uncut quartz stone has a Z or optic axis extending in
a longitudinal direction, an X axis extending through one of the
apexes of the stone and a Y axis extending normal to both the Z and
X axes. The stone is cut along what is generally referred to as the
Z'-X plane and the angle defined by the Z axis and the resulting
crystal face or the Z--Z' angle is especially significant as
regards to the temperature coefficient. For AT cuts, the crystal
blank is rotated about the X axis and cut along a plane that makes
an angle with the Z axis of approximately 35.12.degree..There are
of course many other useful crystal cuts involving different
angles. This angle can be cut for any particular nominal frequency
so that the unit will be stable throughout an extended temperature
range, running for example from -55.degree. to +90.degree. C.
The Z--Z' crystal angle is highly critical. It is the current
practice to cut the Z--Z' angle with diamond saws but the state of
this art is not such that it is presently possible to control the
angle with sufficient precision so as to produce all blanks within
the desired angular specification. On the other hand, the Z--Z'
angle can be chosen for any nominal frequency so that the
temperature coefficient of frequency is close to zero.
Consequently, given broad production requirements for blanks
covering the entire frequency spectrum, no blank need be rejected.
But since the blanks so cut are different, they must first be
individually measured by X-ray diffraction techniques and then
sorted into angular increments preparatory to final processing.
Blanks from the proper incremental class will thereafter be
selected for the fabrication of a group of crystals having a
predetermined frequency.
In existing X-ray diffraction techniques for determining the angle
between the face of a crystal and its atomic plane, an X-ray beam
is directed at the face of the crystal while the crystal is rotated
on a goniometer turntable. At solely one specific angle between the
atomic plane of the crystal and the X-ray beam there will be X-ray
reflection. This angle is known as the Bragg angle. A detector is
positioned to intercept the reflected beam as the face of the
crystal lies against a reference surface. The angular position of
the crystal can then be determined electronically when the detector
receives a reflection, thereby establishing the Bragg angle.
PRIOR ART AND TECHNICAL CONSIDERATIONS
In one prior art procedure, the X-ray measurement is carried out
manually by peaking a signal output meter for maximum reflection
and then reading a vernier position indicator mechanically coupled
to the turntable to fix the crystal angle. This procedure is of
course time-consuming and requires that the turntable be swung
slowly in either direction until the peak position is found and the
turntable movement arrested to enable a vernier reading to be
taken. Thereupon the blank is removed from the turntable and placed
into an appropriate grouping. Because of the skill entailed in
making the X-ray measurements and the manual operations called upon
both in determining the peak position of the cyrstal blanks and in
sorting the blanks, this method does not lend itself to large scale
mechanized production. In addition, the manual technique does not
ensure the degree of accuracy necessary in current transmission
equipment.
In order to increase accuracy and production, automated X-ray
equipment has been introduced in which there is provided means for
automatically feeding crystal wafer blanks, one at a time, with the
X-axis oriented to a Z-axis determining position. At the Z-axis
determining position, the crystal wafer blanks are held by a vacuum
after being secured in a reference position to a rotating spindle
of the X-ray machine which is automatically rotated through a
predetermined angle. During this rotation, a shaft encoder provides
an output signal indicating the degree of rotation of the spindle
in digital form while X-rays are impinged on the crystal. When
Bragg angle reflections from the crystal planes occur, the
reflections are detected by a radiation detector, the electrical
output of which is amplified and fed to a peak sensing circuit. At
the peak of the sensed reflected X-rays, the peak sensing circuit
produces a pulse which is digitally encoded by the shaft encoder,
thus indicating digitally the angle of rotation at which the
maximum peak occurs. This digital signal from the shaft encoder is
used to operate logic circuitry which, in turn, controls a tree
type sorter to sort the wafer blanks into one of a large number of
bins in accordance with the determined angle of the Z-axis.
These prior art procedures while usually determining the angular
orientation of most crystal planes with adequate accuracy, do not
however take into account and compensate for crystal planes which
might be skewed in relation to the reference surface of the
crystal. In otherwords, crystals in which the crystal planes make
angles with both the Z' and X axes of the reference surface of the
crystal. Accordingly, a method of and apparatus for discovering and
compensating for skewed crystal planes is needed.
SUMMARY OF THE INVENTION
It is therefore an object of this invention to provide new and
improved methods of and apparatus for more accurately determining
the angle that the crystal planes of a crystal make with a
reference surface of the crystal.
An additional object of this invention is to provide methods of and
apparatus for compensating for component vectors introduced into
measurements of crystal plane angles due to skewed orientations of
the crystal planes relative to a reference surface.
With these and other objects in view, the present invention
contemplates supporting a crystal to be measured on a goniometer
spindle for oscillation about the X-axis of the crystal while
sequentially directing a first X-ray beam through a reference
surface of the crystal while the crystal oscillates in a small arc
and then directing a second X-ray beam through a surface opposite
the reference surface while the spindle again oscillates in a small
arc. First and second X-ray detectors are positioned adjacent the
reference surface and opposite surface, respectively, to detect the
angles of rotation at which Bragg angle reflections occur. These
angles are then averaged by electronic circuitry to obtain the
correct angle that the crystal planes of the crystal make with the
reference surface.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is an enlarged isometric view of a quartz crystal of the
type inspected by the instant invention schematically showing one
atomic plane of many within the crystal skewed relative to a
reference surface of the crystal and showing X-ray beams impinging
upon and being reflected from top and bottom sides of the atomic
plane;
FIG. 2 is a view taken along line 2--2 of FIG. 1 showing the angles
that a reflected X-ray beam makes with the top surface of the
atomic plane and with the reference surface of the crystal;
FIG. 3 is a view similar to FIG. 2, however, the quartz crystal has
been rotated slightly in the clockwise direction and an X-ray beam
is shown reflecting from the bottom surface of the atomic
plane;
FIG. 4 is an isometric view, schematically arranged, of an X-ray
machine and sorting device which may be used to practice the
instant invention;
FIG. 5 is a block diagram of a circuit which may be used to control
the X-ray machine and sorting device of FIG. 2; and
FIG. 6 is a graph plotting the intensity of two X-ray reflections
from a crystal as function of the angle of incidence of X-ray beams
with the crystal.
DETAILED DESCRIPTION
Referring now to FIGS. 1-3, a rectangular quartz crystal,
designated generally by the numeral 10, is shown with a single
atomic plane 11 disposed therein which, for purposes of
illustration, is indicative of all the atomic planes in the crystal
each of which is parallel to the illustrated plane 11. In FIG. 1,
the atomic plane 11 is shown skewed in relation to a top reference
surface 12 of the crystal 10 forming angles .tau. in the Z'-Y plane
and .beta. in the X-Y plane. For purposes of illustration, the
extent of obliqueness of the plane 11 relative to the reference
surface 12 is exaggerated. Ordinarily, the angle between the atomic
plane 11 and reference surface 12 is approximately 3.degree.. It
should be noted that FIG. 1 depicts a situation where the plane 11
is completely oblique in relation to the surface 12. In other
words, the plane 11 makes angles with both the Z' and X axes of the
surface 12. The purpose of the instant invention is to accurately
determine the angle .tau..
In FIG. 2 an X-ray beam 14 contained in the Z'-Y plane is shown
passing through the reference surface 12 and forming an angle
.gamma. with the atomic plane 11. Assuming .gamma. is the Bragg
angle, a reflection will occur from the atomic plane 11 at an angle
.gamma.'. .gamma.' differs from .gamma. because upon being
reflected, the beam 14 moves out of the Z'-Y plane due to an
angular component .omega. introduced into the reflection because of
an angle .beta. that the atomic plane 11 makes with the reference
surface 12 in the Z'-Y plane. The component .omega. may make the
angle .gamma.' slightly greater as is the case illustrated or
slightly less as would be the case if the angle .beta. opened in
the opposite direction.
The X-ray beam 14 also makes an incidence angle .theta. and
reflection angle .theta.' with the reference surface 12. The
reflection angle .theta.' differs from the angle of incidence
.theta. for two reasons. First of all .theta.' is larger than
.theta. due to the angle .tau. that the atomic plane 11 makes with
the reference surface 12 or the Z' axis of the crystal 10.
Secondly, .theta.' is affected by the angular component in the same
way as .gamma.' is affected in that the angle of the atomic plane
12 causes the X-ray beam 14 to bend out of its incidence plane
thereby slightly increasing the size of .theta.' over what it would
be if .beta. were zero.
Determining the angle .theta.' enables one to determine the angle
.tau. because the Bragg angle for the quartz crystals is known to
be 13.degree. 20'. By simply substracting 13.degree. 20' from the
angle .theta.' the angle .tau. is obtained. Generally the angle
.theta.' will be approximately 16.degree. 20' in which case .tau.
will be 3.degree. 00'. However, it can be readily seen that any
error in .theta.' will result in an error in computing the angle
.tau.. If the angle .beta. is not zero then there will be an error
in the angle .theta.' because of the angular component .omega.. The
prior art methods of and apparatus for determining the angle
.theta.' do not compensate for the component .omega.. Consequently,
whenever an angle exists, the prior art techniques result in an
inaccurate determination of the angle .tau..
The present invention compensates for the component .omega. by
passing an additional oppositely directed X-ray beam 16 through a
surface 17 which is opposite the reference surface 12. As seen in
FIG. 3, the beam 16 reflects from the bottom of the atomic plane 11
upon impinging on the atomic plane at an angle equal to the Bragg
angle of reflection .gamma.. Due to the angle .beta., the beam 16
will form an angle .gamma." upon being reflected from the bottom of
plane 11. .gamma." is different from .gamma. for the same reason
that the angle .gamma.' formed by beam 14 is different from .gamma.
upon being reflected from the top of plane 11. The reason of course
being that an angular component .omega.' is introduced into the
angle of reflection .gamma.". However, .omega.' is opposite in sign
to .omega. and will decrease the size of .gamma." by the same
amount that .omega. increases the size of .gamma.'. Accordingly, an
angle .theta." between the reflected beam 16 and the reference
surface 12 will be decreased by an equivalent amount. Now if
.theta." is measured and then averaged with .theta.', then .omega.'
and .omega. will cancel one another out giving an accurate
determination of .tau. once the Bragg angle .gamma. which is a
known value is subtracted from the average of .theta." and
.theta.'.
Referring now to FIG. 4 where there is shown an X-ray machine and
sorter for practicing the principles of the invention, the quartz
crystal 10 is supported by three nozzles 20 of a vacuum chuck 21
for rotary movement about the X-axis of the crystal. The crystal 10
is initially stored with a plurality of other crystals within a
rotary magazine 23. As the magazine 23 indexes in the
counterclockwise direction, a carriage 26 which reciprocates on a
pair of guide rods 27 engages one of the crystals 10 with a pair of
push rods 24 and advances the crystal onto an aligning platform 28
which is spring-supported. The aligning platform 28 has a slot 29
in the top thereof which closely approximates the configuration of
the crystals 10 to ensure that each crystal is identically aligned
with the nozzles 20. After receiving one of the crystals 10, the
aligning platform 28 is advanced upwardly by a vertical transport
31, which spring supports the aligning platform, to engage the
crystal with the vacuum nozzles 20. The vertical transport then
lowers away from the crystal 10 leaving the crystal supported by
the nozzles 20 and ready for sequential inspection by the X-ray
beams 14 and 16 as described in FIG. 1.
The X-ray beam 14 is generated by a first X-ray gun 32 positioned
above and to the left of the crystal 10 to direct beam 14 at an
angle of approximately 10.degree. 19' to the Z' axis of the crystal
while the X-ray beam 16 is generated by a gun 33 positioned below
and to the right of the crystal to direct beam 16 at an identical
angle. Associated with the pair of guns 32 and 33 are a pair of
Geiger Mueller X-ray detector tubes 34 and 36, respectively, which
sequentially feed signals into a test set designated generally by
the numeral 37 when an X-ray reflection is detected by either tube.
Circuitry (not shown) is provided to energize the X-ray gun 32
while the crystal oscillates through an arc of about 10 minutes.
The gun 32 is then de-energized and the gun 33 energized while the
crystal 10 again oscillates through an arc of about 10 minutes.
The test set 37 also receives signals from a displacement
transducer 38 indicative of the angular position of the crystal 10
at which X-ray reflections are occurring. The angular orientation
of the crystal 10 is achieved by oscillating a spindle 39 of a
goniometer 40 to vary the angular position of the vacuum chuck 21
which is secured to one end of the spindle.
The spindle 39 is mounted within a bearing raceway 41 and is
oscillated by an arm 42 which is rigidly secured to the spindle.
The arm 42 has a follower 43 at one end thereof which is held in
engagement with a cam 44 by a spring 45. The cam 44 is mounted on a
shaft 46 which is rotated in one direction by a motor 47. In the
preferred embodiment, the cam 44 has a double-lobed profile so that
the follower 43 rises and falls twice for each revolution of the
shaft 46. While the follower 43 is being lifted by an advancing
high profile of the cam 44, the arm 42 pivots in a counterclockwise
direction rotating the spindle 39 in a counterclockwise direction
within the raceway 41. While the follower 43 is lowering on a low
profile portion of the cam 44, the arm 42 pivots in the clockwise
direction rotating the spindle 39 in a clockwise direction within
the raceway 41. While the spindle 39 is thus oscillating, the
raceway 41 is being constantly rotated in one direction by a
sprocket 48 which is driven by the shaft 46 with a belt 49. This
insures that the various parts of the raceway 41 wear evenly as the
spindle 39 oscillates to change the angular orientation of the
crystal 10.
The left end of the arm 42 engages a plunger 51 located within the
transducer 38 and reciprocates the plunger against an upward bias
of a spring (not shown). The position of the plunger 51 is
calibrated to be indicative of the angular displacement of the
spindle 39 and is thereby indicative of the angular displacement of
the crystal 10. As described hereinafter, the signals from tubes 36
are coordinated with the signals from transducer 38 and averaged to
accurately disclose the orientation of atomic planes 11 with
respect to the reference surface 12 of the crystal 10 by observing
Bragg angle reflections.
After each crystal 10 is scanned by the X-ray beams 14 and 16 and
analized by the test set 37, it is directed into a tree sorter,
designated generally by the numeral 55. The tree sorter 55 has a
plurality of sorting gates 56 each of which is connected to a
separate bin (not shown) by chutes 57. Each sorting gate 56 is
assigned a value corresponding to an angular orientation of atomic
planes 11 in the crystal 10. When the test set 37 determines that
angular orientation, only the sorting gate 56 corresponding thereto
will be opened.
Since the transport 31 is positioned beneath the nozzles 20, the
tree sorter 55 must be set back from the nozzles. Consequently, a
directing gate 58 must be hinged to the tree sorter 55 to swing
beneath the nozzles 20 and the crystal 10 prior to releasing the
crystal in order to channel the crystal into the sorter.
The elements of the test set 37 are more fully disclosed in the
block diagram of FIG. 5 where the crystal 10 is shown being
monitored by the detector tubes 34 and 36. Connected to the
detectors 34 and 36 are converters 61 and 62, respectively, which
convert pulses from the tubes 34 and 36 into signal pulses suitable
for pulse rate counting. The converters 61 and 62 are both
connected to a solid state switch 63 which determines whether the
X-ray gun 32 is generating the beam 14 and a signal from detector
34 is being applied to a pulse rate counter 64 or whether the X-ray
gun 33 is generating the beam 16 and a signal from the detector 36
is being applied to the pulse rate counter.
The setting of the solid state switch 63 is determined by a cam
operated mechanical switch 66 which is closed during only half a
revolution of the shaft 46 by a single lobed cam 67 (FIG. 4)
mounted on the shaft 46 (FIG. 4). When the switch 66 is closed, the
switch 63 transmits pulses from the converter 61 to the pulse rate
counter 64 and when the switch 66 is open, the switch 63 transmits
pulses from the converter 62 to the pulse rate counter. Since the
cam 67 (FIG. 4) is single lobed and the cam 44 (FIG. 4) double
lobed, the arm 42 will undergo two oscillations for each condition
of the switch 63. The crystal 10 which is oscillated by the arm 42
via the spindle 39 is therefore rotated both clockwise and
counterclockwise each time it is scanned by one of the X-ray beams
14 or 16.
The pulse rate counter 64 applies a digital signal indicative of
pulses per millisecond to a programmable digital comparitor 69
which is programmed to relay signals from the pulse rate counter to
an arithmetic unit 70 when instructed to do so by presets 71 and
72. The presets 71 and 72 are operated selectively by a solid state
switch 73 which is controlled by the cam operated mechanical switch
66. When the switch 66 is closed, signals from converter 61 and
preset 71 are applied simultaneously to the comparitor 69. When the
switch 66 is open, signals from the converter 62 and preset 72 are
applied to the comparitor 69.
Referring now to FIG. 6 where pulse rates generated by the X-ray
beams 14 and 16 are plotted against angular displacement to form
curves 74 and 76, it is seen that the pulse rates rapidly increase
as the crystal 10 approaches a critical angle at which reflectivity
is a maximum and then rapidly decline. The presets 71 and 72 are
set at a pulse rate intensity of about seventy per cent of the
maximum pulse rate intensity expected to occur at the critical
angle. Since signals from the detectors 34 and 36 are different due
to their different orientations relative to the crystal 10, the
presets 71 and 72 will of course be set at different values which
is why two presets are used. If the pulse rate intensity of either
signal does not reach the preset value, then an output signal from
the digital comparitor 69 instructs the X-ray machine of FIG. 2 to
reject the crystal 10 under consideration, whereupon the vacuum
chuck 21 (FIG. 4) releases the crystal and it is directed by the
sorting tree 55 (FIG. 4) into a reject bin (not shown).
Referring now to FIG. 5, if the intensity of the signal from the
pulse rate counter 64 exceeds the preset value being impressed on
the digital comparitor 69 by either preset 71 or 72, then the
comparitor instructs the arithmetic unit 70 to accept angular
displacement readings from the displacement transducer 38 for as
long as the pulse rate counter continues to exceed the preset
value. The arithmetic unit 70 then computes mean values represented
by vertical lines 78 and 79 (FIG. 4) of the angular displacement
readings. If the mean value of the angular displacement is
determined while detector 34 is generating pulses as represented by
the line 78, then the mean value is temporarily stored. However, if
the mean value of the angular displacement is determined while
detector 36 is generating pulses as represented by line 79, then
the mean value is averaged with the stored mean value 78 to compute
a final mean value, represented by the line 80. The final mean
value 80 is a very accurate determination of the angular
displacement at which Bragg reflections occur in individual
crystals 10. As mentioned earlier in the discussion of FIG. 1, when
the angles of reflection of the X-ray beams 14 and 16 are averaged,
the angular components .omega. and .omega.' caused by oblique or
skewed orientation of the atomic planes 11 cancel one another
out.
A signal indicative of the true angle of reflection is then
transmitted by the arithmetic unit 70 to the X-ray machine of FIG.
4 to open the proper gate 56 in the tree sorter 55. After the
proper sorting gate 56 is opened, the directing gate 58 is opened
and the vacuum released on the nozzles 20 to drop the crystal 10
onto the directing gate whereupon the crystal is directed into the
chute and thereafter into the proper bin. In this manner, crystals
10 having identical or approximately identical axial orientations
of their respective atomic planes 11 relative to their reference
surfaces 12 in the Z' direction, are separated from an assortment
of crystals having various axial orientations.
* * * * *