U.S. patent application number 10/024788 was filed with the patent office on 2003-04-10 for automatic filter changer for use on surface mounter inspection camera.
This patent application is currently assigned to KONINKLIJKE PHILIPS ELECTRONICS N.V.. Invention is credited to Swab, Michael Thomas.
Application Number | 20030068078 10/024788 |
Document ID | / |
Family ID | 25517762 |
Filed Date | 2003-04-10 |
United States Patent
Application |
20030068078 |
Kind Code |
A1 |
Swab, Michael Thomas |
April 10, 2003 |
Automatic filter changer for use on surface mounter inspection
camera
Abstract
A printed circuit board assembly machine inspects circuit boards
and parts to be mounted on those circuit boards prior to assembly.
This assembly machine may visualize and recognize physical features
of the circuit boards and parts as part of this inspection. A
filter may be deployed while visualizing certain types of circuit
boards or parts to remove characteristic defects found in images of
those types of parts. When several types of circuit boards or parts
inspected by the assembly machine exhibit different characteristic
visualization problems, the assembly machine may deploy a different
filter for each type of circuit board or part.
Inventors: |
Swab, Michael Thomas;
(Acworth, GA) |
Correspondence
Address: |
Philips Electronics North America Corporation
Corporate Patent Counsel
580 White Plains Road
Tarrytown
NY
10591
US
|
Assignee: |
KONINKLIJKE PHILIPS ELECTRONICS
N.V.
|
Family ID: |
25517762 |
Appl. No.: |
10/024788 |
Filed: |
December 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10024788 |
Dec 19, 2001 |
|
|
|
09970960 |
Oct 4, 2001 |
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Current U.S.
Class: |
382/145 ;
250/225; 250/559.45 |
Current CPC
Class: |
G01N 21/956 20130101;
G01N 21/21 20130101 |
Class at
Publication: |
382/145 ;
250/559.45; 250/225 |
International
Class: |
G06T 007/00; G01N
021/88; G02F 001/01; G06K 009/00 |
Claims
What is claimed is:
1. In an automated printed circuit board assembly machine, a method
for visualizing an item having physical features on a background,
comprising the steps of: illuminating the item with electromagnetic
radiation, including the physical features and the background,
using an illumination source; forming an image of electromagnetic
radiation reflected from the item, said image containing a
characteristic defect depending on the type of item; and
automatically filtering said reflected electromagnetic radiation to
remove said characteristic defects from said image, whereby in said
filtered image said characteristic defect is reduced and an
improved contrast between the physical features and the background
is produced.
2. The method as claimed in claim 1, further comprising recognizing
the physical features in the filtered image.
3. The method as claimed in claim 1, wherein said electromagnetic
radiation is light and said filtered image is formed by a
camera.
4. The method as claimed in claim 2, wherein said electromagnetic
radiation is light, said filtered image is formed by a camera of a
computer vision system, and said recognizing is performed by said
computer vision system.
5. The method as claimed in claim 1, wherein the item is a printed
circuit board.
6. The method as claimed in claim 2, wherein the item is a printed
circuit board.
7. The method as claimed in claim 1, wherein the item is a part to
be mounted on a printed circuit board.
8. The method as claimed in claim 2, wherein the item is a part to
be mounted on a printed circuit board.
9. In an automated printed circuit board assembly machine, an
apparatus for visualizing an item having physical features on a
background, comprising: one or more sources for illuminating the
item with electromagnetic radiation; an image forming device for
forming an image of electromagnetic radiation reflected from the
item, said image having a characteristic defect depending on the
type of item; a filter; and an actuator positioning said filter,
such that said image is formed of electromagnetic radiation passing
through the filter, whereby said filter reduces said characteristic
defect in said filtered image and an improved contrast between the
physical features and the background is produced.
10. The apparatus as claimed in claim 9, further comprising a
computer vision system for recognizing the physical features in the
filtered image.
11. The apparatus as claimed in claim 9, wherein said
electromagnetic radiation is light and said image forming device is
a camera.
12. The apparatus as claimed in claim 10, wherein said
electromagnetic radiation is light and said image forming device is
a camera of said computer vision system.
13. The apparatus as claimed in claim 9, wherein the item is a
printed circuit board.
14. The apparatus as claimed in claim 10, wherein the item is a
printed circuit board.
15. The apparatus as claimed in claim 9, wherein the item is a part
to be mounted on a printed circuit board.
16. The apparatus as claimed in claim 10, wherein the item is a
part to be mounted on a printed circuit board.
17. The apparatus as claimed in claim 16, further comprising a
manipulator for positioning the part on a circuit board or card
with recognized physical features of the part in registration with
contact pads of the board or card.
18. A circuit board or card on which is surface mounted a part that
has been recognized in accordance 18 with the method of claim 8,
such surface mounting being with recognized physical features of
the part in registration with contact pads of the board or card.
Description
[0001] This application is a continuation-in-part of prior
co-pending application U.S. Ser. No. 09/970,960, filed Oct. 4,
2001.
TECHNICAL FIELD OF THE INVENTION
[0002] The invention relates to visualization of printed circuit
boards and parts presenting characteristic visualization problems.
The invention is particularly, but not exclusively, useful for
recognizing by computer vision physical features of any of several
types of printed circuit boards or electronic parts, where each
type of board or part presents a different characteristic
visualization problem.
BACKGROUND OF THE INVENTION
[0003] Automated printed circuit board assembly equipment, such as
the Automated Component Mounter from Assemblon, utilize computer
vision systems to inspect and accurately place printed circuit
boards and parts to be mounted on those boards. The inspection of
these items typically requires visualizing an item, recognizing the
physical features of the item and analyzing the physical
characteristics of the physical features.
[0004] An empty printed circuit board or card is typically picked
out of a storage location and computer vision equipment, including
a camera and frontal lighting, is employed by the assembly machine
to inspect the physical features on the board. Certain of these
physical features are called fiducials, which are provided to
precisely register the parts that will be installed on the board.
Other such physical features on the circuit board are solder paste
contact pads. If the inspected board is not rejected, the assembly
machine then places it into position to receive parts for
mounting.
[0005] Each part to be mounted is then picked out of a storage
location and computer vision equipment, again including a camera
and frontal lighting, is employed by the assembly machine to
inspect the part. If the part is not rejected, the assembly machine
then steers the placement of the part with proper registration to
its mounting position on the board or card.
[0006] Characteristic problems can arise, however, when the
computer vision system attempts to inspect certain types of circuit
boards, cards or parts. Some boards or cards are made of a light
colored ceramic material and have gold or silver fiducials or
solder paste contact pads. These colors do not provide sufficient
visual contrast for current computer vision systems to reliably
recognize the fiducials or contact pads.
[0007] A similar problem is encountered with parts that have silver
or gold metallic contacts on a white or light colored ceramic
background, preventing the contacts from being reliably
recognized.
[0008] Other parts have contacts of one color on a background of
another color, which colors, when imaged by a monochrome camera,
lack sufficient contrast to permit reliable recognition of the
contacts.
[0009] Another characteristic problem encountered with certain
types of parts is glare from the contacts and the background, again
preventing reliable recognition of the contacts.
[0010] Yet another problem arises because the charge coupled device
(CCD) cameras typically used in computer vision systems are
extremely sensitive to infrared. As a result, images of parts that
are especially reflective in the infrared spectrum are washed out
and difficult to recognize reliably.
[0011] The predecessor of the present application teaches an
inventive technique for recognizing the physical features of parts
having metallic contacts on a light colored background. However, a
printed circuit board assembly machine often must handle, in turn,
a mixture of circuit boards and parts, each exhibiting a different
one or more of the recognition problems described above. Currently,
there are no techniques in use in printed circuit board assembly
machines that overcome the variety of recognition problems thereby
encountered.
SUMMARY OF THE INVENTION
[0012] In a printed circuit board assembly machine handling several
types of circuit boards and parts, aspects of the invention may be
found in a method and apparatus in which a filter is automatically
deployed when inspecting circuit boards and parts of a certain
type. The filter corrects characteristic problems encountered when
visualizing the physical features of items of that type.
[0013] The contrast in a image between silver fiducials and a light
colored printed circuit board, or between silver contacts and a
light colored part, may be improved by linearly polarizing the
illumination of the circuit board and imaging the board or part
through a linear polarizing filter oriented in a different
direction than the illumination filter.
[0014] The contrast between contacts of one color and a background
of another color in an image of a part may be improved by imaging
the part through a color filter.
[0015] The glare in an image of a circuit board or part may be
reduced by imaging the board or part through a circular polarizing
filter.
[0016] The effect of reflected infrared radiation on a CCD camera
may be reduced in an image of a circuit board or part by imaging
the board or part through a filter rejecting infrared.
[0017] More specifically, an aspect of the invention may be found
in the following method for visualizing an item having physical
features on a background. The item is illuminated with
electromagnetic radiation, using an illumination source. An image
is formed of the electromagnetic radiation reflected from the item,
which image has characteristic defects depending on the type of
item being visualized. The reflected electromagnetic radiation is
automatically filtered to remove the characteristic defects from
the image, thereby improving the contrast between the physical
features and the background in the filtered image.
[0018] The physical features of the circuit board or part may be
recognized in the filtered image for the purpose of inspection.
[0019] Further aspect of the invention may be found in an apparatus
for visualizing an item having physical features on a background.
One or more sources illuminate the item with electromagnetic
radiation. An image forming device forms an image of
electromagnetic radiation reflected from the item, which image has
a characteristic defect depending on the type of item being
visualized. An actuator positions a filter such that the image is
formed of electromagnetic radiation passing through the filter,
thereby removing the characteristic defect from the image and
improving the contrast between the physical features and the
background in the image.
[0020] In one exemplary embodiment of the invention the filter is
moved linearly into position.
[0021] In another exemplary embodiment of the invention several
available filters are mounted on a wheel and rotated into
position.
[0022] Another aspect of the invention may be found in a circuit
board or card on which is surface mounted a part that has been
recognized in accordance with the method. Through use of the
method, recognized physical features of the mounted part are placed
in registration with contact pads of the board or card.
BRIEF DESCRIPTION OF THE DRAWINGS
[0023] Other aspects of the invention will become apparent upon
perusal of the following detailed description when taken in
conjunction with the appended drawing, wherein:
[0024] FIG. 1 is a schematic elevational cross-section view of
visualization, recognition and placement apparatus in accordance
with the invention;
[0025] FIG. 2 is a top view of illumination and reption parts of
FIG. 1, as viewed from the lines 2-2;
[0026] FIG. 3 is a cross-section view of visualization,
recognition, placement and linear filter deployment apparatus in
accordance with the invention, with the filter retracted;
[0027] FIG. 4 is a cross-section view with the filter deployed;
[0028] FIG. 5 is a cross-section view of another embodiment of the
invention, showing a rotational filter deployment apparatus;
and
[0029] FIG. 6 is a top view of the rotational filter deployment
apparatus of FIG. 5.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0030] Referring to FIG. 1 of the drawing, an embodiment of the
present invention for visualization of parts having metallic
objects against a dielectric or nonmetallic poorly contrasting
background, is explained in conjunction with a conventional
computer vision system 10 recognizing a usually two dimensional
Ball Grid Array (BGA) 12 of small high melt solder balls 14 carried
by a ceramic dielectric substrate 16.
[0031] BGA 12 is held by a gripper or manipulator 18 of a pick and
place machine (not shown) over an upwardly looking camera 20 of
computer vision system 10. The camera 20 forms and provides an
electronic image to computer vision system 10, which system
utilizes the electronic image to recognize and inspect the solder
balls 14 of the BGA 12, as to existence, size and spacing. If the
BGA 12 passes inspection, the vision system 10 steers the
translation and placement of BGA 12 by manipulator 18 on a circuit
board or card 22, with the recognized solder balls 14 of the BGA in
registration with contact pads 24 of the board or card 22.
[0032] As is conventional, prior to placement of the BGA 12 and
other surface mount components on the circuit board or card 22 the
contact pads 24 are coated with a eutectic solder paste, and after
the placement of the BGA 12 and other surface mount components on
circuit board or card 22, heat is applied to card with placed BGA
and other components to fuse the solder paste into fillets (not
shown) firmly surface mounting the BGA to the circuit board or
card.
[0033] In the poorest contrast situation when the solder balls 14
are silver colored and the substrate 16 is white or light colored,
the light box 26 is used to provide generally upwardly and inwardly
directed polarized illumination I of BGA 12, in conjunction with a
polarization filter 28 in front of the lens 30 of camera 20, in
order to allow for proper visualization by camera 20, and proper
recognition by vision system 10 of solder balls 14.
[0034] As shown in FIG. 2, a preferred embodiment of light box 26
has a central aperture 32 through which camera 20 looks upward via
polarization filter 28, and four upwardly and outwardly inclined
trapezoidal faces 34, 36, 38, 40 of a frusto-pyramid, each face
forming a separate source of polarized light. The faces 34, 36, 38,
and 40 comprise polarization filters 40, 42, 44, and 46 over
respective milk glass diffuser panels 50, over LED arrays 52.
[0035] With the direction of linear polarization passed by
polarization filter 28 taken as 0.degree., polarization filters 40
and 44 are oriented to pass linear polarization directed at
90.degree. and polarization filters 42 and 46 are oriented to pass
linear polarization directed at 180.degree.. The result is that the
downwardly directed component of light from the four sources
reflected from the solder balls 14 has a polarization at
90.degree., which is, or is nearly, orthogonal with the
polarization direction that would be passed by polarization filter
28. Therefore no light reflected by solder balls 14 reach the lens
30 of camera 20.
[0036] On the other hand, the downwardly directed component of
light reflected from the white or light colored substrate 16 is
substantially uniformly distributed in polarization and a
substantial amount of light reflected downward from the substrate
16 passes through polarization filter 28 and reaches the lens 30 of
camera 20. As a result, in the electronic image formed by camera
20, the solder balls 14 appear substantially black and the
substrate 16 appears substantially white, providing good contrast
for reliable recognition of solder balls 14. This contrast
producing effect is thought to be due to a preservation of
polarization in reflection of electromagnetic radiation from shiny
metal objects versus a the smearing of polarization in reflection
of electromagnetic radiation from dielectric objects.
[0037] A printed circuit board assembly machine will inspect parts
of different types during the assembly of a single circuit board.
If some of the parts being inspected have a light colored
substrate, while others have a black substrate, an additional
problem arises. Because the effect of the linear polarizing filter
28 is to cause the solder balls 14 appear substantially black in
the electronic image formed by camera 20, the solder balls may not
be easily recognized on parts having a black substrate, when viewed
through such a filter. In this situation, it is desirable to deploy
the filter 28 in front of the lens 30 of camera 20 when visualizing
parts with a white substrate, and retract the filter when
visualizing parts with a black substrate.
[0038] A similar problem arises when the circuit board assembly
machine handles printed circuit boards or cards. Some circuit
boards are manufactured with a fiberglass substrate, which is
typically green in color. Such a substrate provides good contrast
with the silver or gold colored fiducials used to register the
parts installed on the circuit board. However, other circuit boards
or cards handled by the same assembly machine may have a white, or
other light colored, ceramic substrate, which provides poor
contrast with the metallic fiducials. The technique described above
for deploying a filter when appropriate to achieve reliable
recognition of solder balls on parts having either light colored or
dark colored substrates can also be used to reliably recognize
metallic fiducials on either light colored or dark colored printed
circuit boards and cards.
[0039] The control system of a circuit board assembly machine
typically utilizes a specification file for each type of item
(printed circuit board, card or part) it handles. This file
contains information on the characteristics of each type of item.
Information from that file, such as the number and location of
physical features (fiducials and contact pads on boards and cards,
or contacts on parts), is provided to the computer vision system
for the inspection process. In an assembly machine employing the
techniques of the invention, the specification file would also
contain information indicating whether a filter should be used when
inspecting an item of that type and, for the embodiment shown in
FIG. 5, specifying which type of filter is to be used.
[0040] Referring now to FIG. 3 of the drawing, an embodiment of the
invention employing a linear filter deployment apparatus 60 is
shown with the filter retracted. A filter 61 is attached by linkage
64 to linear actuator 65. When energized by the circuit board
assembly machine control system, the linear actuator 65 will adopt
the configuration shown, with the filter retracted from the optical
axis of the camera 20. When de-energized by the control system, the
linear actuator 65 will adopt the configuration shown in FIG. 4 of
the drawing, with the linkage extended and the filter 61 deployed
in front of the lens 30 of camera 20.
[0041] For some types of linear actuators, the action of the
actuator 65 will be the opposite of that described above: when the
actuator 65 is energized, the filter 61 will be deployed and when
the actuator 65 is de-energized, the filter 61 will be retracted.
While the above description discusses the use of a linear actuator
to deploy filter 61, it should be understood that a solenoid could
also be employed in an embodiment of the invention.
[0042] Filter 61 in FIGS. 3 and 4 could be the linear polarization
filter 28 shown in FIG. 1, employed in combination with linearly
polarized illumination, as described above, to correct the
visualization problem associated with metallic physical features on
a light colored background. Or, filter 61 could be one of several
other types of filter chosen to correct other characteristic
problems, as will now be described. These other types of filters
can be used to equal effectiveness with polarized or non-polarized
illumination.
[0043] If the item being visualized has, for example, red physical
features on a green background, filter 61 could be chosen to be a
red color filter. Such a filter would pass the red light reflecting
from the red physical features while blocking the green light
reflecting from the background, causing the physical features to
appear substantially white and the background to appear
substantially black in the image from a monochrome camera.
[0044] If camera 20 employs a charge coupled device (CCD) to form
the electronic image, items that are especially reflective in the
infrared spectrum may present a different characteristic
visualization problem. Because a CCD is very sensitive to radiation
in the infrared spectrum, the electronic image of such an item may
be washed out, with both the physical features and the background
of the item appearing as light gray objects in the image,
preventing the computer vision system from being able to recognize
the physical features on the item. For this type of item, filter 61
could be chosen to be an infrared filter, which blocks infrared
radiation and passes visible light. Blocking the infrared radiation
would allow the CCD to form an electronic image only from the
visible light reflected from the item, resulting in better contrast
between the physical features and background of the item in the
filtered image.
[0045] If glare is characteristically encountered when visualizing
certain items, the image produced by camera 20 will again be washed
out. In these situations, filter 61 could be chosen to be a
circular polarizing filter. Such a filter restricts the rotation
component of the illumination reflected from the item, thereby
reducing glare from the item and allowing correct recognition of
the physical features on the item.
[0046] While the preceding discussion has described recognizing
contacts on electronic parts or fiducials and contact pads on
printed circuit boards and cards, it should be understood that the
physical features being recognized on other items may not be
contacts or fiducials. For example, when a lens is to be mounted
over a light emitting diode, the lens will be inspected for
mounting features that allow it to be attached to the circuit board
or card. Similarly, a circuit board or card may be inspected for
the presence and accurate placement of thermoset adhesive glue
dots, which serve to mount parts that are not soldered to the
board.
[0047] If the items being handled by a circuit board assembly
machine each exhibit a different characteristic problem, then one
of several different filters must be deployed, depending on the
item being inspected, to allow reliable recognition of the physical
features of that item. An embodiment of the invention allowing one
of several filters to be deployed is illustrated in FIG. 5 of the
drawing. A rotational filter deployment apparatus 70 is shown,
which is a filter wheel 75 mounted on the shaft of stepper motor
76. Also visible in FIG. 5 are filters 61 and 63 mounted on the
filter wheel 75 in registration with apertures 72 and 74. In
response to signals from the assembly machine control system,
stepper motor 76 will rotate to a specified position, thereby
deploying the appropriate filter for the part being visualized.
[0048] The rotational filter deployment apparatus 70 is shown in
more detail in FIG. 6. Filter wheel 75 can be seen to have, in this
embodiment of the invention, four apertures 71, 72, 73, and 74.
Apertures 72, 73, and 74 are covered by filters 61, 62, and 63,
respectively, while aperture 71 is not covered with a filter. The
hub of filter wheel 75 is mounted to the shaft of stepper motor 76.
Lens 30 is seen through aperture 74.
[0049] While motor 76 is described above as a stepper motor, it
should be understood that servo motors could also be used in an
embodiment of the invention to position filter wheel 75 in response
to signals from the assembly machine control system.
[0050] While FIGS. 3, 4 and 5 show embodiments of the invention
being used for visualization of a BGA package, it should be
appreciated that the techniques of the invention can be used to
improve visualization of other types of packages and of printed
circuit boards and cards.
[0051] While the embodiments discussed above show only a single
filter deployment apparatus in use, it should be understood that,
in yet another embodiment of the invention, multiple filters could
be deployed together by multiple filter deployment apparatuses, to
improve visualization of items that present multiple characteristic
problems.
[0052] It should now be appreciated that the objects of the
invention have been satisfied. While the invention has been
described in particular detail, it should also be appreciated that
numerous modifications are possible within the intended spirit and
scope of the invention. In interpreting the appended claims it
should be understood that:
[0053] a) the word "comprising" does not exclude the presence of
other elements or steps than those listed in a claim;
[0054] b) the word "a" or "an" preceding an element does not
exclude the presence of a plurality of such elements.
[0055] c) any reference signs in the claims do not limit their
scope; and
[0056] d) several "means" may be represented by the same item of
hardware or software implemented structure or function.
* * * * *