U.S. patent application number 09/324166 was filed with the patent office on 2001-12-13 for printed circuit board testing apparatus.
Invention is credited to KAKU, KAZUHIKO, NISHIKAWA, HIDEO.
Application Number | 20010050572 09/324166 |
Document ID | / |
Family ID | 15555156 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050572 |
Kind Code |
A1 |
NISHIKAWA, HIDEO ; et
al. |
December 13, 2001 |
PRINTED CIRCUIT BOARD TESTING APPARATUS
Abstract
A printed circuit board testing apparatus includes a first
measuring system for determining a relative position between a
circuit board carrying table and a test head with respect to two
dimensions and angular direction, a second measuring system for
determining a relative position between the table and a circuit
board carried by the table with respect to two dimensions and
angular direction, and a drive system for bringing the table and
test head into a first relative positional relationship for the
testing of circuit board in accordance with the relative positions
determined by the first and second measuring system.
Inventors: |
NISHIKAWA, HIDEO; (KYOTO-FU,
JP) ; KAKU, KAZUHIKO; (ISHIKAWA-KEN, JP) |
Correspondence
Address: |
SMITH PATENT OFFICE
1901 PENNSYLVANIA AVE N W
SUITE 200
WASHINGTON
DC
20006
|
Family ID: |
15555156 |
Appl. No.: |
09/324166 |
Filed: |
June 2, 1999 |
Current U.S.
Class: |
324/750.18 |
Current CPC
Class: |
G01R 31/2887
20130101 |
Class at
Publication: |
324/761 |
International
Class: |
G01R 031/02 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 2, 1998 |
JP |
10-153108(PAT) |
Claims
What is claimed is:
1. A printed circuit board testing apparatus for testing
conductivity between particular points on a circuit pattern of a
printed circuit board with at least a pair of probes, the apparatus
comprising: a table for carrying the circuit board to be tested; a
test head provided with the probes; a first measuring system for
determining a relative position between the table and the test head
with respect to two dimensions and angular direction; a second
measuring system for determining a relative position between the
table and the circuit board carried by the table with respect to
two dimensions and angular direction; and a drive system for
bringing the table and test head into a first relative positional
relationship for the testing of circuit board in accordance with
the relative positions determined by the first and second measuring
system.
2. A printed circuit board testing apparatus according to claim 1,
wherein the first measuring system includes a position control
system for bringing the table and test head into a second relative
positional relationship, and the test head has two marks fixedly
formed thereon, and a measuring mechanism for determining the
positions of the two marks relative to a particular point of the
table with the table and test head being at the second relative
positional relationship.
3. A printed circuit board testing apparatus according to claim 2,
wherein the drive system includes a table transport mechanism for
transporting the table in a first direction; and the first
measuring system includes a coordinate system defining means for
defining a coordinate system having a first axis extending in the
first direction, and a second axis extending in a second direction
perpendicular to the first direction, with the positions of the two
marks being identified with respect to the coordinate system.
4. A printed circuit board testing apparatus according to claim 1
wherein the drive system includes: a table transport system for
transporting the table in a first direction; a test head driving
system for driving the test head in the first direction, in a
second direction perpendicular to the first direction and in
angular direction; and a drive controller for controlling the
amount of drive of the table and test head in accordance with the
relative positions determined by the first and second measuring
system.
5. A printed circuit board testing apparatus according to claim 4,
wherein the first measuring system includes a second drive control
mechanism for bringing the table and test head into a third
relative positional relationship wherein a particular point on the
table coincide with one of the two marks on the test head, and into
a fourth relative positional relationship wherein the particular
point on the table coincide with the other of the two marks on the
test head, with the positions of the two marks being determined as
a function of relative movement of the table and test head from the
second to third and fourth relative positional relationship.
6. A printed circuit board testing apparatus according to claim 5,
wherein the first measuring system includes a third mark formed on
the table and a first camera connected with the mechanism for
driving the test head in the second direction and arranged for
taking the picture of the third mark.
7. A printed circuit board testing apparatus according to claim 6
wherein the first measuring system further include a second camera
integrally moveable with the table and arranged to take the
pictures of the two marks on the test head.
8. A printed circuit board testing apparatus according to claim 4,
further comprising an adjusting mechanism for controlling the test
head driving system to adjust the positional relationship of the
test head with the table such that the test head is in parallel
with the table.
9. A printed circuit board testing apparatus according to claim 8
wherein the adjusting mechanism includes means for adjusting the
position of the test head relative to the table with respect to the
first second and angular directions such that the coordinates of
the two marks on the test head in the first direction are equal to
each other.
10. A printed circuit board testing apparatus according to claim 4,
wherein the drive controller includes means for adjusting the
amount of drive in accordance with the relative position determined
by the second measuring system.
11. A printed circuit board testing apparatus according to claim 4,
further comprising a second test head driving mechanism to drive
the test head to an operating position where the probes are
electrically coupled with the circuit pattern.
12. A printed circuit board testing apparatus according to claim
11, further comprising a confirming means for confirming relative
position between the printed circuit board and the test head with
the circuit board being at a tested position while the test head
being at the operating position.
13. A printed circuit board testing apparatus according to claim
11, wherein the test head is provided with more than two contact
probes fixedly arranged on the test head to correspond to the
circuit pattern of the circuit board, with the probes being in
contact with the circuit pattern at the operating position of the
test head.
14. A printed circuit board testing apparatus according to claim 1,
wherein the first measuring system includes a position control
system for bringing the table and test head into a second relative
positional relationship, and the test head is provided with a pair
of probes and probe drive mechanism to drive the probes to bring
them into contact with required points on the circuit pattern of
the circuit board to be tested, and a measuring mechanism for
determining the positions of the probes relative to a particular
point of the table with the table and the test head being at the
second relative positional relationship and the probes being at
initial positions.
15. A method for adjusting the relative position of a circuit board
to be tested and a test head of a circuit board testing apparatus,
the circuit board being formed with a circuit pattern and carried
by a table which is moveable between an initial position where the
circuit board is set on the table and a test position where the
circuit board is tested, and the test head being provided with a
plurality of probes to be electrically connected with particular
points of the circuit pattern and detect conductivity therebetween,
the method comprising the steps of: determining a relative
positional relationship between the table and test head with
respect to two dimensions and angular direction; determining a
relative positional relationship between the table and the circuit
board; causing relative movement between the table and the test
head; and controlling the amount of the relative movement in
accordance with the relative positional relationships between the
table and test head and between the table and the circuit
board.
16. A method according to claim 15, wherein the step of determining
the relative position between the table and the test head includes
the steps of: locating the table at an origin determining position
relative to the test head; and determining positions of two points
on the test head relative to the table at the origin determining
position.
17. A method according to claim 16, wherein the step of determining
positions of two points includes the step of determining the
positions of the two points with regard to two dimensional
coordinate system associated with the table at the origin
determining position.
18. A method according to claim 17, wherein the step of determining
the positions of the two points includes the steps of: causing
relative movement between the table and test head to bring them
from the origin determining relative position to a first
identifying position where one of the two points on the test head
coincided with a particular point on the table, and to a second
identifying position where the other of the two points on the test
head coincided with a particular point on the table; and
determining the positions of the two points in accordance with the
amount of relative movement of the table and test head between the
origin determining to the first and second identifying relative
positions.
Description
[0001] This application is based on patent application No.
10-153108 filed in Japan, the contents of which is hereby
incorporated by reference.
BACKGROUND OF THE INVENTION
[0002] This invention relates to a printed circuit board testing
apparatus for testing open circuit and current leakage or
conductivity of a circuit pattern formed on a printed circuit
board.
[0003] A circuit board testing apparatus is disclosed, for example,
in Japanese Unexamined Patent Publication No. (Hei) 5-73149 and
Japanese Unexamined Patent Publication (Hei) 6-118115. In such
circuit board testing apparatus, a circuit pattern on a circuit
board is tested by the process of loading the circuit board on a
transfer table, moving the transfer table to a position under a
test head, and then lowering the test head to the transfer table to
thereby allow contacts, such as checker pins or probe pins,
attached on the test head to come into contact with specified
positions of the circuit pattern formed on the circuit board. When
the circuit board is placed at a designed position on the transfer
table, and the transfer table is moved to the target position below
the test head, the contacts provided on the test head come into the
designed positional relationship with the circuit pattern of the
circuit board, thereby assuring correct testing. However, it has
been practically difficult to place a circuit board at the designed
position on the transfer table.
[0004] The conventional circuit board testing apparatus is provided
with a camera to pick up an image of a positioning mark provided on
a circuit board to confirm correct setting of the circuit board on
the transfer table. Specifically, the amount of displacement of the
circuit board with respect to the transfer table is calculated
based on thus-obtained mark image. In accordance with the
calculated amount of displacement, the relative position of the
test head and the transfer table is adjusted to compensate the
displacement.
[0005] However, it is necessary to establish a correct positional
relationship in advance between the transfer table carrying a
circuit board and the test head provided with contacts. In the
conventional circuit board testing apparatus, the try and error
operation must be performed to determine the position of the camera
until the positioning mark provided on the circuit board to
coincide with the optical axis of the camera, and render the
contacts of the test head to come into correct positional
relationship with the circuit pattern on the circuit board.
[0006] Also, there has been proposed a circuit board testing
apparatus which is provided with a test head having the so-called
flying probes or movable contacts which move from one to another
position of a circuit pattern in accordance with predetermined
program to inspect a plurality of electrically conductive paths on
the circuit board with a pair of the probes or contacts. The
provision of movable contacts enables different types of circuit
board to be tested by the same test head. However, in such type of
testing apparatus, the number of contacts are limited. Accordingly,
each of the contacts must come into contact with the circuit board
an increased number of times, consequently the tip of each contact
wears off in a shorter time. This requires frequent replacement of
contacts or probes. At each replacement, it is necessary to adjust
the positional relationship to ensure correct matching of the tip
of a replaced contact with the specified position of the circuit
pattern.
[0007] Further, recent circuit boards are formed with more
complicated circuit pattern. Accordingly, more precise positional
control is required for the contact or probe to meet or come into
contact with the specified position of the circuit pattern.
[0008] With the conventional circuit board testing apparatus, the
adjustment of positional relationship between the contacts on
probes and a circuit board to be tested is performed manually by
the operator. Accordingly, the more the circuit pattern is
complicated, the more the load for the operator is, consequently
lowering the operation efficiency for circuit board testing.
Further, the troublesome adjustment of the positional relationship
between the test head and the circuit board carrier or transfer
table must be performed each time a test head is replaced with
another because each test head has its own dimensional
characteristic. Furthermore, even during the testing operation by
the use of the same test head, it has been necessary to adjust the
position of the positioning mark image pick-up camera at a
specified interval. This is because the relative position between
the camera (or the test head) and the transfer table changes with
repeated testing operations, possibly lowering the accuracy of the
test. Accordingly, the operator is required to carry out the
troublesome adjustment of the positional relationship or the camera
position frequently, thus resulting in tremendous load for the
operator.
SUMMARY OF THE INVENTION
[0009] It is an object of the present invention to provide a
circuit board testing apparatus and method which are free from the
problems residing in the prior art.
[0010] It is another object of the present invention to provide a
circuit board testing apparatus that enables precise positioning of
a circuit board relative to test probes or contacts.
[0011] It is further object of the present invention to provide a
circuit board testing apparatus which can be easily operated but
ensures precise control of the relative positions of the test head
and a circuit board to be tested.
[0012] It is another object of the present invention to provide a
circuit board testing apparatus which automatically determines and
adjusts relative position of a circuit board to be tested and a
test head or test probes carried thereon.
[0013] It is still further object of the present invention to
provide a method of automatically determining and adjusting
relative position of a circuit board to be tested and a test head
or test probes carried thereon.
[0014] In one aspect of the present invention, a printed circuit
board testing apparatus includes a first measuring system for
determining a relative position between a circuit board carrying
table and a test head with respect to two dimensions and angular
direction, a second measuring system for determining a relative
position between the table and a circuit board carried by the table
with respect to two dimensions and angular direction, and a drive
system for bringing the table and test head into a first relative
positional relationship for the testing of circuit board in
accordance with the relative positions determined by the first and
second measuring system.
[0015] In another aspect of the present invention, a method for
adjusting the relative position of a circuit board to be tested and
a test head, includes determining a relative positional
relationship between a circuit board carrying table and a test head
with respect to two dimensions and angular direction; determining a
relative positional relationship between the table and the circuit
board carried by the table. The table and the test head are moved
in accordance with the determined relative positional
relationships.
[0016] According to an embodiment of the present invention, the
circuit board carrying table is movable in a first direction as
identified by Y direction, by for example in the embodiment. The
drive system first transports the table to a predetermined position
relative to the test head. The first measuring system determines
the positions of two points on the test head relative to a
particular point of the table at the second relative positional
relationship. The drive system drives the test head in the Y
direction, in a second direction perpendicular to the Y direction
and referred to as X direction by for example in the embodiment,
and in angular direction. An adjusting mechanism controls a test
head driving mechanism to adjust the positional relationship of the
test head with the table such that the test head is in parallel
with the table.
[0017] In an embodiment, the relative position between the
particular point on the table and the two points on the test head
may be identified by coordinates in a coordinate system with x and
y axes extending in the X and Y directions with its origin being
coincident with the particular point on the table. The test head
driving mechanism adjusts the position of the test head in
accordance with the x and y coordinates of the two points on the
test head such that the y coordinates of the two points become
equal to each other. Then, the table is returned back to an initial
or preparatory position where a circuit board to be tested is
mounted. The table carrying the circuit board is transported to a
testing position in accordance with the y coordinates of the two
points of the test head at the adjusted position. The test head may
be driven in X direction in accordance with the x coordinates. The
data determined by the second measuring system are used to correct
or compensate the amount of movement of the table and the test
head.
[0018] In the embodiment of the present invention, the first
measuring system includes a mechanism to bring the table and the
test head into a first, second and third relative positional
relationship. The positions of the two points on the test head are
determined as a function of relative movement of the table and the
test head from the first, second, and third relative positional
relationships. The first, second and third relative positional
relationships may be determined by target marks fixed on them and
image taking device such as camera.
[0019] These and other objects, features and advantages of the
present invention will become more apparent upon a reading of the
following detailed description and accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] FIG. 1 is a schematic side view of a circuit board testing
apparatus as a first embodiment of the present invention;
[0021] FIG. 2 is a schematic top plan view of the circuit board
testing apparatus shown in FIG. 1;
[0022] FIG. 3 is a diagram showing a main construction of the
circuit board testing apparatus;
[0023] FIG. 4 is a perspective view showing an operation of the
circuit board testing apparatus;
[0024] FIG. 5 is a sectional view showing a configuration of an
auxiliary camera provided in the circuit board testing
apparatus;
[0025] FIG. 6 is a flowchart showing a main operation of the
circuit board testing apparatus;
[0026] FIG. 7 is a flowchart showing the process of adjusting the
positional relationship, carried out in the circuit board testing
apparatus;
[0027] FIG. 8 is a perspective view showing another operation of
the circuit board testing apparatus;
[0028] FIG. 9 is a diagram showing a positional relationship
between a test head and a transfer table in the circuit board
testing apparatus;
[0029] FIG. 10 is a perspective view showing another operation of
the circuit board testing apparatus;
[0030] FIG. 11 is a flowchart showing the process of confirming and
readjusting the alignment carried out in the circuit board testing
apparatus;
[0031] FIG. 12 is a diagram showing a main construction of a
circuit board testing apparatus as a second embodiment of the
present invention;
[0032] FIG. 13 is a perspective view showing an operation of the
circuit board testing apparatus of the second embodiment;
[0033] FIG. 14 is a flowchart showing a main operation of the
circuit board testing apparatus of the second embodiment;
[0034] FIG. 15 is a flowchart showing the process of adjusting the
positional relationship carried out in the circuit board testing
apparatus of the second embodiment;
[0035] FIG. 16 is a perspective view showing another operation of
the circuit board testing apparatus of the second embodiment;
and
[0036] FIG. 17 is a diagram showing a positional relationship
between a test head and a transfer table in the circuit board
testing apparatus of the second embodiment.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION
[0037] FIG. 1 shows a schematic side view of a circuit board
testing apparatus according to the first embodiment of the present
invention, and FIG. 2 is a schematic top plan view of the same
circuit board testing apparatus. In order to clarify directions of
movement and relative positions of the parts of the apparatus in
drawings, X, Y and Z axes of rectangular coordinates are shown.
[0038] The circuit board testing apparatus includes a door 11
provided on the front (-Y side) of a main body 1 of the apparatus.
The door 11 is opened to place a printed circuit board 2 to be
tested in an initial position 3 provided in a middle of a forward
chamber of the apparatus. The printed circuit board to be tested
may be a bare printed circuit board on which an electric circuit
pattern is printed but circuit elements such as IC chip,
capacitors, resistors have not been mounted. Further, on the rear
(+Y side) of the initial position 3 is provided a test section 4
where the circuit board 2 is tested or inspected. The signals
representative of conductivity between points on the circuit
pattern of the circuit board 2 is picked up or detected to evaluate
the circuit board 2 to accept or deny. The tested circuit board 2
is returned to the initial position 3 where the tested board is in
turn taken out through the front opening by the operator.
[0039] In this embodiment, circuit boards 2 are manually placed in
and taken out by the operator. However, automatic placement and
withdrawal of circuit boards may be available with a circuit board
transfer mechanism having a supply unit and a removing unit
arranged on both sides of the initial position or along the
X-direction. The supply unit receives circuit boards to be tested
from an external device, and then places the circuit boards in the
initial position 3. The removing unit takes out tested circuit
boards from the initial position 3, and transfers it to the
external device.
[0040] A transfer table 5 is provided to transfer a circuit board
2. The transfer table 5 is reciprocatively moved in Y-directions
between the initial position 3 and the test section 4 by a transfer
table drive mechanism 6. The transfer table drive mechanism 6
includes two guide rails 61 and 61 extending in the Y direction and
spaced from each other in the X-direction. The transfer table 5 is
slidable on those guide rails 61 and 61. In parallel with the guide
rails 61 and 61, a ball screw 62 is disposed. One end (-Y side) of
the ball screw 62 is rotatably supported on the main body 1 of the
apparatus by way of a bearing. The other end (+Y side) is connected
to a drive shaft 64 of a motor 63, whereby the ball screw 62 is
rotated by the motor 63. Also, the ball screw 62 threads through a
bracket 65 fixedly attached on the transfer table 5. The ball screw
62 and the bracket 65 are mechanically associated with each other
such that when the motor 63 is permitted to drive in response to a
command from a controller to be described later, the transfer table
5 is moved in the Y direction, that is, to the initial position 3
or to the test section 4. The movement of the transfer table 5
corresponds to the rotation of the motor 63. Details of the
transfer table 5 will be described later.
[0041] The test section 4 includes an upper tester unit 4U disposed
on an upper side (+Z side) of the transfer table drive mechanism 6
for testing a circuit pattern formed on a top of a circuit board 2
and a lower tester unit 4D disposed on a lower side (-Z side) of
the transfer table drive mechanism 6 for testing a circuit pattern
formed on an underside of the circuit board 2. Both tester units 4U
and 4D have the same configuration and are symmetrically disposed
with respect to the travel path of the transfer table 5. Therefore,
the configuration of the upper tester unit 4U will be only
described. The same numerals are given to the corresponding parts
of the lower tester unit 4D and its description is not made here
for the simplicity of description. It is to be noted that the
following description can apply to the lower tester unit 4D.
[0042] The upper tester unit 4U includes a test head 41 carrying a
plurality of contacts 42. The contacts 42 project from the test
head 41, and their respective tips face the transfer table 5 at a
test position. After being positioned relative to the circuit board
2 on the transfer table 5 as described later, the contacts are
brought into contact with the circuit pattern on the circuit board
2 by a test head drive mechanism 43 which is controlled by the
controller.
[0043] Referring to FIG. 3, the test head drive mechanism 43 is
provided with an X-head drive section 43X for moving the test head
41 in the X direction with respect to the main body 1, a Y-head
drive section 43Y connected with the X-head drive section 43X for
moving the test head 41 in the Y direction, a .theta.-head drive
section 43.theta. connected with the Y-head drive section 43Y for
turning the test head 41 about the Z-axis, and a Z-head drive
section 43Z connected with .theta.-head drive section 43.theta. for
moving the test head 41 in the Z direction, whereby the test head
41 is positioned relative to the transfer table 5, and the contacts
42 are moved to and away from the circuit pattern formed on the
circuit board 2.
[0044] Further, a main camera 44 is mechanically connected to the
X-head drive section 43X so as to move in the X direction
integrally with the test head 41.
[0045] On the test head 41 is provided, as shown FIG. 3, a
confirmation camera 45 for confirming relative position of the
circuit board 2 and the test head 4. The confirmation camera 45
picks up an image of a board positioning mark provided on the
circuit board 2 placed on the transfer table 5 through a through
hole 46 formed on the test head 41. Indicated at 47A and 47B are
head positioning marks which are arranged in the X-direction
symmetrically on the right and left of a designed center of the
test head 41. The head positioning marks face the transfer table 5
at its test position.
[0046] Next will be described a configuration of the transfer table
5 with reference to FIGS. 4 and 5. The transfer table 5 includes,
as shown in FIG. 4, a circuit board holder section 51 for retaining
a circuit board 2 and an auxiliary camera carrier section 52
protruding in the +Y-direction from the circuit board holder
section 51. The circuit board holder section 51 is provided with
three retainer pins 53. A circuit board 2 is pushed against the
three retainer pins 53 by a biasing member (not shown), thereby
being firmly retained on the holder section 51 of the transfer
table 5.
[0047] Further, the circuit board holder section 51 of the transfer
table 5 is formed with an opening 54 in a specified area thereof.
The opening 54 is adapted for allowing contacts or probes 42 of the
lower tester unit 4D to come into contact with a circuit pattern
formed on the underside of the circuit board 2 represented by the
phantom lines.
[0048] The auxiliary camera carrier section 52 is provided with
auxiliary cameras 55 and 56. These cameras are arranged side by
side in the X direction. The auxiliary camera 55 is adapted for
picking up an image of the head positioning marks 47A and 47B (but,
only 47A is shown in FIG. 4) provided on the test head 41 of the
upper tester unit 4U. The auxiliary camera 56 is adapted for
picking up an image of the head positioning marks 47A and 47B
provided on the test head 41 of the lower tester unit 4D. The
auxiliary cameras 55 and 56 have the same configuration as each
other. Accordingly, only a configuration of the auxiliary camera 55
will be described here. The same description apply to the
configuration of the other auxiliary camera 56.
[0049] Referring to FIG. 5, the auxiliary camera 55 mainly includes
an illumination member 551, a prism 553, a barrel 554, a lens 555,
and a charge-coupled device (CCD) 556.
[0050] The illumination member 551 is provided on a top surface 52a
of the auxiliary camera carrier section 52 to illuminate the upper
tester unit 4U. The illumination member 551 is composed of an outer
metal cylinder 551a and an inner light diffuser 551b. The inside
wall of the metal cylinder 551a is light reflective. The light
diffuser 551b also has a cylindrical shape but made of light
diffusing or transparent material such as acrylic plastic or glass.
Light from a light source 551c provided in the auxiliary camera
carrier section 52 is introduced to the light diffuser through a
light guide 551d such as a glass fiber. The light is diffused in
the diffuser 551b, and emitted from the upper end of the diffuser
551b in a ring shape to illuminate the head positioning mark 47A or
47B. The center of the illumination member 551 coincides with the
optical axis of the auxiliary camera 55.
[0051] The prism 553 is held by a prism holder 552 provided inside
the auxiliary camera carrier section 52, and serves to introduce
light rays L reflected from the upper tester unit 4U through the
illumination member 551 to the lens 555. The lens 555 focuses the
light rays L onto the CCD 556.
[0052] Further, a table positioning mark 57 is provided on the
bottom surface of the recess formed in the top surface 52a of the
auxiliary camera carrier section 52 of the transfer table 5. The
table positioning mark 57 is spaced a predetermined distance from
the illumination member 551 of the auxiliary camera 55.
[0053] The auxiliary camera 55 has a field of view about twice
larger in a diameter than the head positioning marks 47A and 47B.
The transfer table 5 and the test head 41 are relatively moved to a
position where the head positioning mark 47A or 47B comes into the
field of view of the auxiliary camera 55 in accordance with
positional data stored in the controller 71. Thereafter, the
auxiliary camera 55 is activated to pick up an image of the head
positioning mark 47A or 47B at a predetermined interval until the
center of the head positioning mark 47A or 47B is detected to
coincide with the center of the illumination member 551 or the
optical axis of the auxiliary camera 55.
[0054] The main camera 44 is composed of an object lens and a CCD
to take a picture. The field of view of the main camera 44 is
rectangular each side of which is about twice as large as the
diameter of the target mark 57. Accordingly, capturing of an image
of the table positioning mark 57 is executed in a similar way.
Specifically, the transfer table 5 is moved to a position in the
Y-direction and the test head drive mechanism 43X is moved in
Y-direction such that the table positioning mark 57 comes into the
field of view of the main camera 44 in accordance with positional
data stored in the controller 71. At this state, the image pick-up
operation of the main camera is continued until the center of the
table positioning mark 57 is detected to coincide with the optical
axis of the main camera 44.
[0055] Now description will be made about an electric circuit
arrangement of the circuit board testing apparatus with reference
back to FIG. 3. The circuit board testing apparatus is provided
with a CPU, a ROM, a RAM, a motor driver, and the controller 71.
The controller 71 controls the entire operations of the apparatus
in accordance with a program pre-stored in the ROM. The apparatus
is further provided with an image processor 72 for processing image
signals obtained by the cameras 44, 45, 55, and 56 disposed in the
specified positions of the apparatus and outputting processed
signals to the controller 71.
[0056] The controller 71 controls the transfer table drive
mechanism 6 and the test head drive mechanism 43 based on signals
from the image processor 72 to render the contacts 42 of the upper
and lower tester units 4U and 4D to come into contact with the
specified points of the circuit pattern formed on the circuit board
2 on the transfer table 5.
[0057] Further, the controller 71 is electrically connected to a
tester controller 73. Upon completion of the contact of the
contacts 42 with the circuit pattern as mentioned above, a test
start command is given to the tester controller 73 from the
controller 71. The tester controller 73 permits the scanner 74 to
electrically connect a signal source such as a constant voltage
source with the contacts 42 alternatively or selectively to send a
test signal to each of the contacts 42, thereby initiating testing.
The signal applied to one end of an electric path of the circuit
pattern is picked-up at the other end of the electric path, and it
is determined whether the picked-up signal is at an acceptable
level or not. In this way, all the electric paths are tested one by
one, and the results of the determinations are accumulated to
finally determine whether the circuit board is acceptable or not.
With the testing completed, test results are given to the
controller 71 through the tester controller 73. An operation panel
75 is electrically connected to the controller 71 to enable the
operator to input instruction or set parameters to the controller
71.
[0058] Next will be described operations of the circuit board
testing apparatus.
[0059] FIG. 6 is a flowchart showing a main operation of the
circuit board testing apparatus. The operator places or sets a
circuit board 2 on the transfer table 5 stayed in the initial
position 3, and gives a test command through the operation panel
75. The controller 71 outputs various commands to relevant sections
of the apparatus to perform the automatic circuit board testing in
accordance with the flowchart shown in FIG. 6. The upper tester
unit 4U and the lower tester unit 4D both perform testing in the
same operation sequence. Accordingly, the operation of the upper
tester unit 4U will be described while description of the lower
tester unit 4D is omitted.
[0060] Upon receiving a test command, the controller 71 first
judges as to whether or not a new test head 41 is set (Step S1) on
the apparatus. If it is judged to be "NO" in Step S1, the flow
proceeds to Step S3 without executing adjustment of the positional
relationship between the test head 4U and the transfer table 5, the
circuit board testing is initiated based on the previously obtained
positional relationship between the transfer table 5 and the test
head 41, since the data of positional relationship has been already
stored in the controller 71. On the other hand, if it is judged to
be "YES" in Step S1, the adjustment of the positional relationship
is executed in Step S2.
[0061] FIG. 7 is a flowchart showing the process of adjusting the
positional relationship between the test head 4U and the transfer
table 5. In adjustment of the positional relationship, the transfer
table drive mechanism 6 and the X-head drive section 43X are
controlled based on image signals obtained by the main camera 44 so
that the table positioning mark 57 comes onto the optical axis OA1
of the main camera 44 (Step S20). Specifically, the transfer table
5 is moved for a distance of MY1 in the Y-direction from the
initial position represented by the broken lines in FIG. 4 while
the test head 41 carrying the main camera 44 is moved for a
distance of MX.sub.1 in the X-direction from the initial position.
In this state, a hypothetical reference coordinate system is
defined (Step S21), with its origin O being coincident with the
designed center 5C of the transfer table 5.
[0062] Subsequently, as shown in FIG. 8, the transfer table drive
mechanism 6 and the X-head drive section 43X are driven based on
image signals obtained by the auxiliary camera 55 so that the head
positioning mark (left) 47A comes onto the optical axis OA.sub.2 of
the auxiliary camera 55 (Step S22). In other words, the transfer
table 5 is moved in the Y-direction and the test head 41 is moved
in the X-direction until the optical axis OA.sub.2 coincides with
the head positioning mark 47A. At this state, coordinates
(X.sub.A0, Y.sub.A0) of the head positioning mark 47A with respect
to the reference coordinate system is determined by the amount of
movement of the transfer table 5 and the test head 41 (Step
S23).
[0063] Subsequently, coordinates of the head positioning mark 47B
in the reference coordinate system is determined in the same manner
as Steps S22 and S23. Specifically, the transfer table drive
mechanism 6 and the X-head drive section 43X are controlled based
on image signals obtained by the auxiliary camera 55 so that the
head positioning mark (right) 47B comes onto the optical axis OA2
of the auxiliary camera 55 (Step S24). In other words, the transfer
table 5 is moved in the Y-direction and the test head 41 is moved
in the X-direction until the optical axis OA.sub.2 coincides with
the head positioning mark 47B. At this state, coordinates
(X.sub.B0, Y.sub.B0) of the head positioning mark 47B with respect
to the reference coordinate system is determined by the amount of
movement of the transfer table 5 and the test head 41 (Step
S25).
[0064] Next, the Y-head drive section 43Y and the .theta.-head
drive section 43.theta. are activated until the two head
positioning marks 47A and 47B have the same coordinate with respect
to the Y-coordinate (Step S26). Thereafter, respective coordinates
of the head positioning marks 47A and 47B with respect to the
reference coordinate system are calculated as follows (Step
S27):
[0065] Coordinates of the head positioning mark 47A (X.sub.A1,
Y.sub.A1)
[0066] Coordinates of the head positioning mark 47B (X.sub.B1,
Y.sub.B1)
[0067] It is judged in Step S28 whether test head 41 is corrected
in the Y-direction and the .theta.-directions. If it is judged that
the correction is not completed, the flow returns to Step S22 to
perform the operations of Steps S22 to S27. On the other hand, if
it is judged that the correction is completed, coordinates
(X.sub.41C, Y.sub.41C) of a center 41C of the test head 41 are
calculated (Step S29). The center 41C of the test head 41 is shown
in FIG. 9. The coordinates (X.sub.41C, Y.sub.41C) of the center 41C
can be expressed as follows:
X.sub.41C=(X.sub.A1+X.sub.B1)/2
Y.sub.41C=Y.sub.A1=Y.sub.B1
[0068] These coordinates are stored in the memory (not shown) of
the controller 71 until the test head 41 is replaced with another
test head.
[0069] After the adjustment of the positional relationship of the
test head and the transfer table is completed (Step S2), a circuit
board 2 to be tested is placed or set on the circuit board holder
section 51 of the transfer table 5 (Step S3). In this embodiment, a
circuit board 2 to be tested is placed on the circuit board holder
section 51 by the operator. As described above, however, a circuit
board 2 may be automatically placed on the circuit board holder
section 5 by an automatic placement device.
[0070] Next, coordinates of the circuit board positioning marks 2A
and 2B provided on the circuit board 2 are calculated with respect
to the reference coordinate system (Step S4). Specifically, as
shown in FIG. 10, the transfer table drive mechanism 6 and the
X-head drive section 43X are actuated to drive the transfer table 5
and the test head 41 based on image signals from the main camera 44
until the board positioning mark 2A on the circuit board 2 comes
onto the optical axis OA1 of the main camera 44. In other words,
the transfer table 5 is moved in Y-direction and the test head 41
carrying the main camera 44 is moved in the X direction until the
board positioning mark 2A coincides with the optical axis OA.sub.1.
At this state, coordinates (X.sub.2A, Y.sub.2A) of the board
positioning mark 2A are calculated in accordance with the amount of
movement of the transfer table 5 and the test head 41 from the
original position where the designed center 5C coincides with the
origin O of the reference coordinate system.
[0071] Similarly, the transfer table drive mechanism 6 and the
X-head drive section 43X are actuated to drive the transfer table 5
and the test head 41 based on image signals from the main camera 44
until the board positioning mark 2B on the circuit board 2 comes
onto the optical axis OA.sub.1 of the main camera 44. In other
words, the transfer table 5 is moved in Y-direction and the test
head 41 carrying the main camera 44 is moved in the X direction
until the board positioning mark 2B coincides with the optical axis
OA.sub.1. At this state, coordinates (X.sub.2B, Y.sub.2B) of the
board positioning mark 2B are calculated in accordance with the
amount of movement of the transfer table 5 and the test head 41
from the original position.
[0072] In Step S5, thereafter, displacements .DELTA.X.sub.2,
.DELTA.Y.sub.2, and .DELTA..theta..sub.2 of the placed circuit
board 2 from the designed center 51C (0, -Y.sub.51C) in X-, Y-, and
.theta.-directions are calculated based on the above-calculated
coordinates (X.sub.2A, Y.sub.2A) and (X.sub.2B, Y.sub.2B) of the
board positioning marks 2A and 2B as follows:
.DELTA.X.sub.2={(X.sub.2A-X.sub.2A0)+(X.sub.2B-X.sub.2B0)}/2
.DELTA.Y.sub.2={(Y.sub.2A-Y.sub.2A0)+(Y.sub.2B-Y.sub.2B0)}/2
.DELTA..theta..sub.2=tan.sup.-1.times.(Y.sub.2A-Y.sub.2B)/(X.sub.2A-X.sub.-
2B)-tan.sup.-1.times.(Y.sub.2A0-Y.sub.2B0)/(X.sub.2A0-X.sub.2B0)
[0073] wherein X.sub.2A0 and Y.sub.2A0 denote designed coordinates
of the board positioning mark 2A, and X.sub.2B0 and Y.sub.2B0
denote designed coordinates of the board positioning mark 2B. These
designed coordinates are stored in the controller 71 in
advance.
[0074] Subsequently, amounts (.DELTA.X, .DELTA.Y, .DELTA..theta.)
of movement of the test head 41 for the compensation for the
displacement of the circuit board 2 are calculated as follows:
.DELTA.X=.DELTA.X.sub.41C-.DELTA.X.sub.2
.DELTA.Y=-.DELTA.Y.sub.2
.DELTA..theta.=-.DELTA..theta..sub.2
[0075] In Step 6, the test head 41 is moved by the test head drive
mechanism 43 by the calculated amounts for the compensation
(.DELTA.X, .DELTA.Y, .DELTA..theta.) to thereby adjust the position
of the test head 41 with respect to the circuit board 2. At the
same time, the transfer table 5 is moved for the distance
(Y.sub.41C+Y.sub.51C) in the Y-direction by the transfer table
drive mechanism 6. In this way, the transfer table 5 is set at the
exact position below the test head 41. Accordingly, the contacts 42
carried by the test head 41 will come into contact with specified
positions of the circuit pattern formed on the circuit board 2 at
high accuracy.
[0076] The test head 41 is moved to the circuit board 2 by the
Z-head drive section 43Z, thereby rendering the contacts 42 of the
test head 41 to come into contact with the circuit pattern of the
circuit board 2 (Step S7), and testing is performed with the
scanner 74 (Step S8).
[0077] However, there may be a likelihood that the circuit board 2
shifts when the contacts 42 come into contact with the circuit
pattern of the circuit board 2, consequently causing an error in
the testing. In this embodiment, for this reason, the matching
between the contacts and the circuit pattern is judged, and
position correction is conducted if an undesired shift is judged to
occur, and another testing is performed (Step S9).
[0078] More specifically, as shown in FIG. 11, an image of the
board positioning mark 2A of the circuit board 2 on the transfer
table 5 is first picked up by the confirmation camera 45 through
the through hole 46. A displacement of the board positioning mark
2A from a specified position (e.g., a center) of the through hole
46 is calculated based image signals obtained by the confirmation
camera 45 (Step S91). It is judged in Step S92 whether a calculated
amount of displacement is in an allowable range. If the calculated
displacement is in the allowable range (YES in Step S92), the flow
proceeds to Step S10 of the main routine shown in FIG. 6 with no
further testing positional check being done. On the other hand, if
the calculated amount of displacement is out of the allowable range
(NO in Step S92), positional correction is carried out to render
the displacement between the through hole 46 and the board
positioning mark 2A come into the allowable range (Step S93). When
the positional correction is carried out, the test head 41 is
lifted up. After the correction is completed, the Z-head drive
section 43Z is controlled to move the test head 41 so that the
contacts 42 of the test head 41 come into contact with the circuit
pattern of the circuit board 2, and testing is performed again
using the scanner 74 (Step S94).
[0079] This increases the testing accuracy because of the fact that
even if any displacement between the test head 41 and the circuit
board 2 occurs due to the contact of the contacts on the circuit
pattern, the displacement is properly corrected to set the circuit
board 2 and the test head 41 in the corrected positional
relationship for testing.
[0080] Upon completion of the circuit board test, a test result is
displayed, and the tested circuit board 2 is returned to the
initial position 3. Subsequently, it is judged whether there is
another circuit board to be tested (Step S10). If there is judged
to be another circuit board 2 (YES in Step S10), the flow returns
to Step S1 to repeat the series of operations. On the other hand,
if there is judged to be no circuit board to be test (NO in Step
S10), the flow ends.
[0081] Next, a circuit board testing apparatus according to a
second embodiment of the present invention will be described with
reference to FIGS. 12 to 17. In the circuit board testing apparatus
of the second embodiment, parts or elements which are given the
same reference characters as the first circuit board testing
apparatus have like function, and description of them is thus
omitted.
[0082] The circuit board testing apparatus of the first embodiment
is adapted for the use of a test head having fixed contacts or
probes arranged to be exclusively applicable for a particular type
of circuit board. The circuit board testing apparatus of the second
embodiment is mounted with a test head having the so-called flying
probes or movable contacts. The circuit board testing apparatus of
the second embodiment is preferable for testing a variety of types
of circuit boards, wherein circuit boards of the same circuit
pattern is small in number.
[0083] The circuit board testing apparatus of the second embodiment
includes, similarly to the first embodiment, an upper tester unit
104U for testing a circuit pattern formed on a top of a circuit
board 2 and a lower tester unit 104D for testing a circuit pattern
formed on an underside of the circuit board 2. The tester units
104U and 104D both have the same configuration and are
symmetrically disposed with the travel path of the transfer table
5.
[0084] The upper tester unit 104U includes a test head 141 provided
with a pair of contacts 142A and 142B. The contacts 142A and 142B
extend toward the transfer table 5, and are moved by contact
drivers 145A and 145B, respectively. After being positioned
relative to the circuit board 2 on the transfer table 5 as
described later, the contacts 142A and 142B are brought into
contact with predetermined points on the circuit pattern of the
circuit board 2 by a test head drive mechanism 143 and the contact
drivers 145A and 145B under the control of the controller.
[0085] The test head drive mechanism 143 includes an X-head drive
section 143X, a Y-head drive section 143Y, a .theta.-head drive
section 143.theta., and a Z-head drive section 143Z. Those sections
have functions similar to the corresponding sections of the test
head drive mechanism 43 of the first embodiment to thereby moving
the test head 141 relative to the transfer table 5.
[0086] The contact driver 145A (145B) is attached to the test head
141, and provided with a mechanism for moving the contact 142A
(142B) in the X-, Y-, and Z-directions. The contact drivers 145A
and 145B are controlled by a tester controller 73 to move the
contact 142A and 142B in lateral directions, and move them to and
away from the circuit pattern formed on the circuit board 2.
[0087] Also, a main camera 44 is mechanically connected to the
X-head drive section 143X so as to move in the X direction
integrally with the test head 41. Further, a match confirmation
camera 45 is provided on the test head 141.
[0088] The transfer table 5 has a similar construction to the
circuit board testing apparatus of the first embodiment. However,
auxiliary camera 55 (56) is adapted for picking up an image of a
tip of the contacts 142A and 142B of the test head 141 of the
tester unit 104U (104D).
[0089] An electrical configuration of the circuit board testing
apparatus of the second embodiment is similar to that of the first
embodiment. However, this apparatus is not provided with a scanner
for selectively supplying a test signal to each one of a plurality
of contacts. Test results are given to the controller 171 through
the tester controller 73.
[0090] Next will be described operations of the circuit board
testing apparatus of the second embodiment with reference to FIGS.
14 and 15. Upon receiving a test command, the controller 171 judges
as to whether or not new contacts 142A and 142B or a new test head
141 has been set (Step S101). If no replacement is executed ("NO"
in Step S101), the flow proceeds to Steps S103 to S110 where the
same operations are executed as the first embodiment. Accordingly,
detailed description of those operations is to be omitted.
[0091] On the other hand, if it is judged to be "YES" in Step S101,
the adjustment of the positional relationship is executed in Step
S102. The adjustment of the positional relationship is basically
similar to that of the first embodiment as shown in FIG. 15.
[0092] The transfer table drive mechanism 6 and the X-head drive
section 143X are driven based on image signals obtained by the main
camera 44 so that the table positioning mark 57 comes onto the
optical axis OA.sub.1 of the main camera 44 (Step S120). At this
state, a hypothetical reference coordinate system is defined with
its origin O being coincident with the designed center 5C of the
transfer table 5 (Step S121).
[0093] The transfer table drive mechanism 6 and the X-head drive
section 143X are driven based on image signals obtained by the
auxiliary camera 55 so that the tip of the contact 142A attached on
the test head 141 comes onto the optical axis OA.sub.2 of the
auxiliary camera 55 (Step S122). In this time, the contact 142A is
held at an initial position pre-defined on the test head 141.
Coordinates (X.sub.A10, Y.sub.A10) of the contact 142A with respect
to the reference coordinate system is determined by the amount of
movement of the transfer table 5 and the test head 141 (Step
S123).
[0094] Coordinates of the contact 142B in the reference coordinate
system is determined in the same manner as Steps S122 and S123.
Specifically, the transfer table drive mechanism 6 and the X-head
drive section 143X are driven based on image signals obtained by
the auxiliary camera 55 so that the tip of the contact 142B comes
onto the optical axis OA.sub.2 of the auxiliary camera 55 (Step
S124). In this time, the contact 142B is held at an initial
position pre-defined on the test head 141. Coordinates (X.sub.B10,
Y.sub.B10) of the contact 142B with respect to the reference
coordinate system is determined by the amount of movement of the
transfer table 5 and the test head 141 (Step S125).
[0095] The Y-head drive section 143Y and the .theta.-head drive
section 143.theta. are driven so that the two contacts 142A and
142B have the same coordinate with respect to the Y-coordinate
(Step S126). Respective coordinates of the contacts 142A and 142B
with respect to the reference coordinate system are calculated as
follows (Step S127):
[0096] Coordinates of the contact 142A (X.sub.A11, Y.sub.A11)
[0097] Coordinates of the contact 142B (X.sub.B11, Y.sub.B11)
[0098] In Step S128, it is judged whether test head 141 is
corrected in the Y-direction and the .theta.-directions. If the
correction is judged not to be completed, the flow returns to Step
S122 to perform the operations of Steps S122 to S127. On the other
hand, if the correction is judged to be completed, coordinates
(X.sub.141C, Y.sub.141C) of a center 141C of the test head 141 are
calculated (Step S129). The center 141C of the test head 141 is
shown in FIG. 17. The coordinates (X.sub.141C, Y.sub.141C) of the
center 141C can be expressed as follows:
X.sub.141C=(X.sub.A11+X.sub.B11)/2
Y.sub.141C=Y.sub.A11=Y.sub.B11
[0099] These coordinates are stored in the memory of the controller
171 until the test head 141 or the contacts 142A, 142B are replaced
with another test head or contacts. After the adjustment of the
positional relationship between the transfer table 5 and the test
head 141, the flow returns to Step S102 of the main flow, and
executes the operations of Steps S103 to S110.
[0100] In the second embodiment described above, both upper and
lower test heads 145A and 145B are of the type having a pair of
flying contacts or moving probes, but one of the test heads 145A or
145B, preferably the lower test head 145B may be of the type
provided with fixed contacts.
[0101] As described above, in the foregoing embodiments, the
auxiliary cameras 55 and 56 are mounted on the transfer table 5, An
image of the table positioning mark 57 provided on the transfer
table 5 is picked up by the main camera 44 to define the reference
coordinate system. An image of the head positioning marks 47A and
47B (or tips of the contacts 142A and 142B) of the test head 41 is
picked up by the auxiliary cameras 55 to determine a relative
position between the transfer table 5 and the test head 41 (141)
with respect to two dimensions and angular direction. The
positional relationship between the test head 41 (141) and the
transfer table 5 is adjusted based on the relative position thus
determined.
[0102] Further, a displacement of the circuit board 2 from its
standard position on the transfer table 5 is calculated based on an
image signal of the board positioning marks 2A and 2B obtained by
the main camera 44, and correction based on the calculated amount
of displacement is added to the amount of drive of the table
transport mechanism and the test head drive mechanism 43 (143).
Therefore, this eliminates the try and error adjustment by the
operator which is required in the conventional apparatus, and
enables automatic testing of circuit board, thus reducing the work
load on the operator.
[0103] Further, since the circuit pattern of the circuit board 2
and the contacts are made to come into contact with each other
under thus corrected positional relationship, the contacts
correctly come into contact with specified positions or points of
the circuit pattern of the circuit board 2, thus ensuring accurate
circuit board testing.
[0104] In the foregoing embodiments, the main camera 44 is
mechanically connected with the X-head drive section 43X (143X),
and thus movable in the X-direction. However, it may be appreciated
to provide a drive mechanism for exclusive use to drive the main
camera 44 in the X-direction, so that the main camera 44 is movable
independently of the test head 41 (141).
[0105] In this case, the reference coordinate system is associated
with the stationary part of the apparatus, such as the frame or
bracket of the apparatus. Thus, coordinate system may be referred
to as an absolute coordinate system. The absolute coordinate system
defines the coordinates of the head positioning marks 47A and 47B
(or tips of the contacts 142A and 142B), as well as the coordinates
of the board positioning marks.
[0106] Furthermore, instead of allowing the main camera 44 to move
in the X-direction, it may be appreciated to make the transfer
table 5 movable in the X-direction.
[0107] In the foregoing embodiments, the test head 41 is adjusted
in two dimensions, i.e., X- and Y-directions and angular direction,
after the coordinates XA.sub.0, YA.sub.0, XB.sub.0, YB.sub.0 of the
head positioning marks 47A and 47B are determined such that the
Y-coordinates of the marks are equal to each other. Then, the
coordinates XA.sub.1, YA.sub.1, XB.sub.1, YB.sub.1 of the head
positioning marks 47A and 47B are determined with the test head
having been adjusted to determine a target relative position.
However, the relative position of the table 5 and the test head 41
may be adjusted collectively or accumulatively when the table 5
carrying a circuit board to be tested is brought into a test
position.
[0108] In the foregoing embodiments, furthermore, the adjustment of
the positional relationship is carried out only when a test head 41
(141) or the contacts 142A, 142B are newly set. However, there is a
likelihood that the optical axis of the main camera 44 shifts with
lapse of time during repeated test operation by the same test head.
Accordingly, it would be appreciated to adjust the positional
relationship before testing every circuit board or a specified
number of circuit boards, thereby increasing the testing
accuracy.
[0109] Further, in the foregoing embodiments, description has been
made on with reference to the circuit board testing apparatus which
executes testing for both surfaces of a circuit board at the same
time. However, the present invention is not limited to such
apparatus, but applicable to a circuit board testing apparatus
which executes testing for one surface of a circuit board each
time.
[0110] Still further, in the foregoing embodiments, the relative
position between the table 5 and the test head 41 (141) is
identified by a combination of a camera and a fixed mark. However,
other means for the identification is available, such as a
combination of a narrow light beam and a two dimensional position
sensor. Also, the present invention is applicable to various types
of test heads.
[0111] In the foregoing embodiments, all the contacts or proves are
fixed on the head and are brought into contact with the circuit
pattern, the pair of flying probes 142A and 142B are brought into
contact with various points on the circuit pattern. The present
invention is applicable to the type wherein a set of fixed contacts
are to be brought into contact with particular points of the
circuit pattern while a single or a plurality of electrode
confronts the circuit pattern with a gap such that the electrode or
electrodes are electrically coupled with the circuit pattern though
which rapidly changing electric signals may pass or detected. The
signal may change its voltage or electric current in sin wave form,
pulse wave form or in the form of turning on or off of an electric
voltage or current. The electric coupling may be of capacitance or
induction coupling.
[0112] As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
foregoing embodiment is therefore illustrative and not restrictive,
since the scope of the invention is defined by the appended claims
rather than by the description preceding them, and all changes that
fall within metes and bounds of the claims, or equivalence of such
meets and bounds are therefore intended to embraced by the
claims.
* * * * *