U.S. patent application number 10/359470 was filed with the patent office on 2004-08-05 for measuring laser light transmissivity in a to-be-welded region of a work piece.
Invention is credited to Kwan, Kin-Ming, Laurer, Jonathan H., Rodgers, Audrey D., Shadwick, David T..
Application Number | 20040150688 10/359470 |
Document ID | / |
Family ID | 32771349 |
Filed Date | 2004-08-05 |
United States Patent
Application |
20040150688 |
Kind Code |
A1 |
Kwan, Kin-Ming ; et
al. |
August 5, 2004 |
Measuring laser light transmissivity in a to-be-welded region of a
work piece
Abstract
Methods for measuring laser light transmissivity of a specific
position in a work piece prior to the work piece undergoing laser
welding at the specific position with a laser beam having a
specific welding wavelength. To obtain a baseline measurement
reading, a laser light source projects a laser beam at the welding
wavelength directly into a detector. Thereafter, the work piece
becomes suspended between the laser light source and detector
whereby an output of the detector now corresponds to a work piece
measurement reading. Differences between the two readings reveal
whether the work piece will yield a satisfactory weld at the
specific position when later welded by a laser beam at the welding
wavelength. Preferred work pieces include inkjet printhead lids and
bodies.
Inventors: |
Kwan, Kin-Ming; (Lexington,
KY) ; Laurer, Jonathan H.; (Lexington, KY) ;
Shadwick, David T.; (Versailles, KY) ; Rodgers,
Audrey D.; (Lawrenceburg, KY) |
Correspondence
Address: |
JACQUELINE M. DASPIT
LEXMARK INTERNATIONAL, INC.
740 WEST NEW CIRCLE ROAD, DEPT. 865A/ 082-1
LEXINGTON
KY
40550
US
|
Family ID: |
32771349 |
Appl. No.: |
10/359470 |
Filed: |
January 30, 2003 |
Current U.S.
Class: |
347/19 ;
219/121.64; 347/47 |
Current CPC
Class: |
B29C 66/24244 20130101;
B23K 26/032 20130101; B23K 26/034 20130101; B29C 66/71 20130101;
B29K 2025/00 20130101; B29C 65/1687 20130101; B23K 31/12 20130101;
B29C 66/61 20130101; B41J 2/1634 20130101; B29C 65/1622 20130101;
B29C 65/1619 20130101; B29C 66/1222 20130101; B29C 66/71 20130101;
B23K 31/125 20130101; B29C 65/1635 20130101; B29C 66/53461
20130101; B29C 66/71 20130101; B41J 2/16 20130101; G01N 21/359
20130101; B23K 26/32 20130101; B29C 65/1674 20130101; B23K 2103/50
20180801; G01N 21/3563 20130101; B29C 65/1606 20130101; B29C
65/1616 20130101; B23K 26/22 20130101; B29C 66/95 20130101; B29L
2031/767 20130101; B29C 66/1224 20130101; B29K 2025/06 20130101;
B29C 65/1654 20130101; B29C 66/21 20130101; B29C 66/73921 20130101;
B29K 2071/12 20130101 |
Class at
Publication: |
347/019 ;
219/121.64; 347/047 |
International
Class: |
B41J 029/393; B23K
026/20; B41J 002/14 |
Claims
What is claimed is:
1. A method for measuring laser light transmissivity, comprising:
introducing a work piece that is to undergo laser welding at a
specific laser wavelength at a work piece position between a laser
light source and a detector; passing a laser beam at said
wavelength from said laser light source through said work piece in
a vicinity of said work piece position and into said detector to
obtain a work piece measurement reading; based upon said reading,
assessing whether said work piece will satisfactorily undergo laser
welding at said work piece position at said wavelength.
2. The method of claim 1, further including stepwise controlling
movement of said work piece between said laser light source and
said detector through a plurality of positions.
3. The method of claim 1, further including projecting said laser
beam at said wavelength from said laser light source into said
detector without passing through said work piece to obtain a
baseline measurement reading.
4. The method of claim 3, further including determining a
difference between said baseline measurement reading and said work
piece measurement reading.
5. The method of claim 1, wherein said introducing further includes
suspending said work piece in a substantially bottomless tray.
6. The method of claim 1, further including laser welding said work
piece to an ink-jet printhead body at said work piece position.
7. A method for measuring laser light transmissivity in a work
piece, comprising: providing a work piece that undergoes laser
welding at a specific laser wavelength at a work piece position;
providing a laser light source and a detector; projecting a laser
beam at said wavelength from said laser light source into said
detector to obtain a baseline measurement reading; thereafter,
suspending said work piece between said laser light source and said
detector; projecting said laser beam at said wavelength from said
laser light source through said work piece in a vicinity of said
work piece position and into said detector to obtain a work piece
measurement reading; determining a difference between said work
piece measurement reading and said baseline measurement reading;
and based upon said determining a difference, identifying whether
said work piece will satisfactorily undergo laser welding at said
work piece position at said wavelength.
8. The method of claim 7, wherein said suspending further includes
framing said work piece in a substantially bottomless tray such
that, in a direct line between said laser light source and said
detector, no portion of said tray crosses said line.
9. The method of claim 7, further including stopping said
projecting said laser beam and indexing said work piece.
10. The method of claim 7, further including projecting said laser
beam at said wavelength from said laser light source through said
work piece in a vicinity of a second work piece position and into
said detector to obtain a second work piece measurement
reading.
11. The method of claim 10, further including determining a
difference between said second work piece measurement reading and
said baseline measurement reading.
12. The method of claim 11, based upon said determining a
difference between said second work piece measurement reading and
said baseline measurement reading, identifying whether said work
piece will satisfactorily undergo laser welding at said second work
piece position at said wavelength.
13. The method of claim 7, further including laser welding said
work piece to an ink-jet printhead body at said work piece
position.
14. A method for measuring laser light transmissivity of a work
piece, comprising: providing a work piece that undergoes laser
welding at a specific laser wavelength at a plurality of work piece
positions; fixing a position of a laser light source and a detector
relative to one another; suspending said work piece at a home
position, said suspending including framing said work piece in a
substantially bottomless tray such that, in a direct line between
said laser light source and said detector, no portion of said tray
crosses said line; with said work piece at said home position,
projecting a laser beam at said wavelength from said laser light
source into said detector to obtain a baseline measurement reading;
moving said work piece from said home position to a first of said
plurality of work piece positions, said work piece at said first of
said plurality of work piece positions crossing said direct line;
thereafter, projecting said laser beam at said wavelength from said
laser light source through said work piece at said first of said
plurality of work piece positions and into said detector to obtain
a first work piece measurement reading; indexing said tray;
projecting said laser beam at said wavelength from said laser light
source through said work piece at a second of said plurality of
work piece positions and into said detector to obtain a second work
piece measurement reading; determining a difference between each of
said first and second work piece measurement readings and said
baseline measurement reading; and based upon said determining a
difference, identifying whether said work piece will satisfactorily
undergo laser welding at said first and second work piece positions
at said wavelength.
15. The method of claim 14, further including laser welding said
work piece to an ink-jet printhead body at said first and second
work piece positions.
16. The method of claim 14, wherein said indexing further includes
stepping said tray in a pattern substantially paralleling a
periphery of said work piece.
17. The method of claim 14, wherein said suspending further
includes laying a surface of said work piece onto a ledge of said
substantially bottomless tray.
18. An inkjet printhead, comprising: an inkjet printhead body; and
an inkjet printhead lid having at least one work piece position
thereof measured for laser light transmissivity at a specific laser
wavelength laser welded to said ink-jet printhead body at said at
least one work piece position.
19. The inkjet printhead of claim 18, wherein said inkjet printhead
lid further includes a plurality of work piece positions measured
for laser light transmissivity at said wavelength arranged in a
pattern substantially paralleling a periphery of said work
piece.
20. The inkjet printhead of claim 19, wherein said pattern is
substantially rectangular.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to measuring light
transmissivity of a work piece. In particular, it relates to
measuring laser light transmissivity of a specific position in a
work piece prior to the work piece undergoing laser welding at that
specific position. Even more particularly, it relates to assessing
whether the work piece will yield a satisfactory weld at the
specific location when welded by a laser beam irradiated at a
specific welding wavelength. Work pieces may comprise inkjet
printhead lids and bodies.
BACKGROUND OF THE INVENTION
[0002] The art of measuring light transmissivity in a work piece is
relatively well known. In general, light from a source passes from
a front side of the work piece to the backside where a detector
collects it. The difference between the light irradiated towards
the work piece and the light that actually passes through the work
piece, as collected by the detector, corresponds to the work piece
transmissivity.
[0003] Problems arise, however, because the light source, often a
white light source, illuminates the front of the work piece with
multiple wavelengths while the detector only collects light at its
tuned wavelength. This can unnecessarily limit measurement of
multiple wavelengths to incorporating multiple detectors.
Additionally, typical commercial transmissivity measurement devices
lack sufficient irradiation power to penetrate work pieces and
project light to backside detectors when the work pieces embody
other than visibly clear compositions. Traditional visibly clear
compositions include glass, quartz, polycarbonate, polystyrene, and
the like. They usually also lack sufficient power to project light
through work pieces, such as high impact polystyrene and polyester
having typically low transmissivity characteristics.
[0004] Accordingly, the arts for measuring light transmissivity
desire solutions for overcoming the aforementioned and other
problems.
[0005] Numerous reasons exist for understanding light
transmissivity in a work piece. For example, consider instances
when two work pieces undergo laser welding. As background, first
and second work pieces become welded to one another by way of a
fixed or sweeping irradiated beam of laser light. As is known, the
beam passes through the first work piece, which is transparent to
laser light, where it gets absorbed by the second work piece, which
is laser light absorbent. As the beam irradiates, the weld
interface heats-up which causes the adjoining surfaces of the work
pieces to melt. Upon cooling, the two work pieces meld together as
one.
[0006] Yet, if the first work piece prevents sufficient amounts of
laser light from reaching the weld interface, poor welding
(underweld) results. Further, if the first work piece absorbs too
much energy, the first work piece may overheat and/or suffer
material degradation potentially causing poor weld appearance or
unsatisfactory welds. Numerous parameters contribute to the
absorption and transmission characteristics of a work piece
including, but not limited to, laser wavelength, incident angle of
the laser beam during welding, surface roughness of the work piece,
temperature of the work pieces, thickness/dimensions of the work
piece, composition of the work piece and, in instance when work
pieces comprise plastics, additives such as flame retardants,
plasticizers, fillers and colorants.
[0007] When the material properties and laser properties become
fixed in a given system, however, the transmission rate of the
laser through a work piece follows the well known Beer-Lambert Law,
specifically: I/Io=e.sup.(-sx); where Io is the intensity of the
light source incident on the work piece, I is the intensity of the
light after passing through the work piece, x is the thickness of
the work piece, and s is the total extinction coefficient which, in
turn, is the work piece light scattering coefficient plus the work
piece light absorption coefficient. Accordingly, the transmissivity
of the work piece constitutes an important variable (underscored by
the ratio I/I.sub.o) in light transmission rates.
[0008] As such, those skilled in the laser welding arts will
appreciate that having an ability to assess, predict or otherwise
identify a laser light transmissivity characteristic of a work
piece before the piece undergoes welding will likely significantly
decrease failure weld-rates in to-be-welded work pieces.
[0009] Accordingly, a need exists in the laser welding arts for
efficaciously predicting and identifying laser light transmissivity
in to-be-welded regions of a work piece.
[0010] Regarding the technology of inkjet printing, it too is
relatively well known. In general, an image is produced by emitting
ink drops from an inkjet printhead at precise moments such that
they impact a print medium, such as a sheet of paper, at a desired
location. The printhead is supported by a movable print carriage
within a device, such as an inkjet printer, and is caused to
reciprocate relative to an advancing print medium and emit ink
drops at such times pursuant to commands of a microprocessor or
other controller. The timing of the ink drop emissions corresponds
to a pattern of pixels of the image being printed. Other than
printers, familiar devices incorporating ink-jet technology include
fax machines, all-in-ones, photo printers, and graphics plotters,
to name a few.
[0011] A conventional thermal inkjet printhead includes access to a
local or remote supply of color or mono ink, a heater chip, a
nozzle or orifice plate attached to the heater chip, and an
input/output connector, such as a tape automated bond (TAB)
circuit, for electrically connecting the heater chip to the printer
during use. The heater chip, in turn, typically includes a
plurality of thin film resistors or heaters fabricated by
deposition, masking and etching techniques on a substrate such as
silicon.
[0012] To print or emit a single drop of ink, an individual heater
is uniquely addressed with a small amount of current to rapidly
heat a small volume of ink. This causes the ink to vaporize in a
local ink chamber (between the heater and nozzle plate) and be
ejected through and projected by the nozzle plate towards the print
medium.
[0013] During manufacturing of the printheads, a printhead body
gets stuffed with a back pressure device, such as a foam insert,
and saturated with mono or color ink. A lid welds to the body via
ultrasonic vibration. This, however, sometimes causes cracks in the
heater chip, introduces and entrains air bubbles in the ink and
compromises overall integrity.
[0014] Even further, as demands for higher resolution and increased
printing speed continue, heater chips become engineered with more
complex and denser heater configurations which raises printhead
costs. Simultaneously, the heater chips become smaller and flimsier
to save silicon costs. Thus, as printheads evolve, a need exists to
control overall costs and to reliably and consistently manufacture
a printhead without causing cracking of the ever valuable heater
chip.
SUMMARY OF THE INVENTION
[0015] The above-mentioned and other problems become solved by
applying the principles and teachings associated with the
hereinafter described measurement of laser light transmissivity in
a to-be-welded region of a work piece.
[0016] In one embodiment, the invention teaches methods for
measuring laser light transmissivity of a specific position in a
work piece prior to the work piece undergoing laser welding at the
specific position with a laser beam having a specific welding
wavelength. As a first step, the invention teaches obtaining a
baseline measurement reading between a laser light source and a
detector by projecting a laser beam, at the to-be-welded welding
wavelength, directly into the detector. The work piece becomes
suspended between the laser light source and detector such that the
laser beam at the welding wavelength passes through the work piece
in the vicinity of the specific to-be-welded position and into the
detector. An output of the detector corresponds to a work piece
measurement reading. Differences between the two readings reveal
whether the work piece will yield a satisfactory weld at the
specific position when later welded by a laser beam at the welding
wavelength. The invention also contemplates filters, mirrors,
collimators, lenses and the like in the optical path between the
light source and the detector.
[0017] In another aspect of the invention, a substantially
bottomless tray suspends work pieces between the laser light source
and the detector such that when the work piece becomes indexed to a
new position, the tray never interferes with the beam of laser
light. An X-Y motion table in combination with a stepper motor
preferably provides the impetus for indexing.
[0018] In still another aspect, indexing motion and laser light
transmissivity readings occur in patterns substantially paralleling
a periphery of the work piece.
[0019] Inkjet printhead lids and bodies, laser welded together at
specific positions having undergone laser light transmissivity
measurements at specific welding wavelengths, and printers
containing the printheads are also disclosed.
[0020] These and other embodiments, aspects, advantages, and
features of the present invention will be set forth in the
description which follows, and in part will become apparent to
those of ordinary skill in the art by reference to the following
description of the invention and referenced drawings or by practice
of the invention. The aspects, advantages, and features of the
invention are realized and attained by means of the
instrumentalities, procedures, and combinations particularly
pointed out in the appended claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] FIG. 1 is a diagrammatic view in accordance with the
teachings of the present invention of an apparatus for measuring
laser light transmissivity in a to-be-welded region of a work
piece;
[0022] FIG. 2A is a diagrammatic view in accordance with the
teachings of the present invention of a tray for suspending a work
piece between a laser light source and a detector for use with the
apparatus of FIG. 1;
[0023] FIG. 2B is a cross-section view in accordance with the
teachings of the present invention of the to-be-welded work piece
of FIG. 2A after being placed in the tray;
[0024] FIG. 2C is a planar view in accordance with the teachings of
the present invention of the to-be-welded work piece held in the
tray of FIG. 2B having pluralities of laser light transmissivity
measurement positions indicated;
[0025] FIG. 3 is a diagrammatic view in accordance with the
teachings of the present invention of laser light projected through
a work piece and collected by a detector for use with the apparatus
of FIG. 1;
[0026] FIG. 4 is a graph in accordance with the teachings of the
present invention of measured laser light transmissivity of a work
piece plotted against discrete measurement positions;
[0027] FIG. 5 is a perspective view in accordance with the
teachings of the present invention of an inkjet printhead with a
laser light transmissivity measured inkjet lid laser welded to an
inkjet body; and
[0028] FIG. 6 is a perspective view in accordance with the
teachings of the present invention of an inkjet printer for housing
an inkjet printhead with a laser light transmissivity measured
inkjet lid laser welded to an inkjet body.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0029] In the following detailed description of the preferred
embodiments, reference is made to the accompanying drawings that
form a part hereof, and in which is shown by way of illustration,
specific embodiments in which the inventions may be practiced.
These embodiments are described in sufficient detail to enable
those skilled in the art to practice the invention, and it is to be
understood that other embodiments may be utilized and that process
or other changes may be made without departing from the scope of
the present invention. As a matter of convention herein, direction
arrows and lines in-between serve to show interconnections between
devices. The following detailed description is, therefore, not to
be taken in a limiting sense, and the scope of the present
invention is defined only by the appended claims and their
equivalents. In accordance with the present invention, we
hereinafter describe measurement of laser light transmissivity in a
to-be-welded region of a work piece.
[0030] With reference to FIG. 1, an apparatus for measuring light
transmissivity is shown generally as 10. The apparatus includes a
computing system environment 12 having, at one end thereof,
bi-directional communication with a laser diode power controller 14
and a laser diode temperature controller 16. In a preferred
embodiment, the power controller embodies a Thorlabs Inc., LDC2000
2A laser diode controller while the temperature controller embodies
a Thorlabs Inc., TEC2000 TEC controller. The computing system
environment embodies a general or specific purpose computer with
attendant processors, memory, monitors, input devices, network
connections, peripheral devices, application programs, connections
to intranets and internets and the like.
[0031] At the other end, the computing system environment
bi-directionally couples with a laser light source structure 20, a
motion table 22 and a detector structure 24. In more detail, the
laser light source structure 20 includes a laser mount 26, a laser
diode 28 and collimating and focusing optics 30. In a preferred
embodiment, the laser mount includes a Thorlabs Inc., TCLDM3 TEC LD
mount while the diode includes a 1200 mW, TO-3 package from
Coherent Laser Diode, S-81-1200C-100-Q. The collimating and
focusing optics comprise one or some of Thorlabs Inc.'s: C230TM-B,
600-1500 nm Moderate NA Optics; C260TM-B 600-1500 nm 0.15 NA AR
coating; E09 RMS Microscope Objective Adapter Extension Tube;
Optics Adapter S1TM09; CP02 Threaded Cage Plate; SM1A3 Microscope
Objective to SM1 Adapter; ER4 0876-001 REV B, Extension Rod 4 inch
(.times.4); and SM1RR Retaining Ring. In other embodiments, the
laser diode represents an 810 nm wavelength aluminum gallium
arsenide (AlGaAs) semiconductor laser having a laser power of about
1000 mW. Still other embodiments include, but are not limited to,
other types of continuous wave lasers with similar power
intensities such as semiconductor lasers based on Indium Gallium
Arsenide (InGaAs) with wavelengths of 940-990 nm and Aluminum
Gallium Indium Phosphide (AlGaInP) with wavelengths of 630-680 nm,
solid state lasers such as lamp pumped Neodymium-doped Yttrium
Aluminum Garnet (Nd:YAG) with a wavelength of 1064 nm and diode
pumped Neodymium-doped Yttrium Aluminum Garnet (Nd:YAG) with a
wavelength of 1064 nm or solid-state, gas, excimer, dye, ruby or
semiconductor lasers or argon fluoride, krypton fluoride, nitrogen,
argon (blue or green), helium neon (blue or green), rhodamine 6G
dye (tunable), CrAlO.sub.3, NIR or carbon dioxide (FIR) laser types
or other. The laser diodes of the laser light structure may
additionally have labels of class I, I.A, II, IIIA, IIIB, or IV as
those are well understood in the art.
[0032] The motion table 22 has an elevation arm 32 that allows
insertion of a work piece 50 into an optical path (dashed straight
line between laser and detector structures) at a position above the
laser light source structure. An offset arm 34 of the motion table
provides lateral control with motion controlled in a region away
(action arrow A) from the optical path. A microcontroller 36 and
stepper motor 38 provide the electrical and mechanical impetus to
the motion table preferably from instructions originating in the
computing system environment. In one embodiment, the motion table
22 has X-Y positioning. In other embodiments, the motion table has
X-Y-Z motion, theta motion, angular motion, linear motion or
combinations of some or all of the foregoing.
[0033] The detector structure 24 includes a photodetector 40 and an
optional filter 42. In one embodiment, the photodetector is a
Thorlabs Inc., DET 110 350-1100 nm Photodetector while the filter
is an NE20A D-2.0 Mounted Absorptive Natural Density Filter.
[0034] A support frame 44a, 44b extending from a base 46 provides a
platform upon which the laser light source structure 20, the motion
table 22 and detector structure 24 commonly connect. In this
manner, the frame maintains a common reference point and distances
and angles between all structures are known or can be measured. In
a preferred embodiment, the frame fixes the laser light source and
detector structures relative to one another.
[0035] The apparatus 10 may additionally include various
mechanical/electrical interlocks (not shown) between any or all of
the foregoing structures to meet or exceed federal safety
requirements. In one embodiment, the base 46, the frame 44 and all
structures connected thereto reside within a light safe enclosure
(not shown) according to ANSI standard Z136.1, for example. Other
apparatus structures include suitable power sources (not shown) to
power some or all of the foregoing.
[0036] During use, the apparatus 10 works to emanate and project a
laser beam(s) along the optical path from the laser light source
structure 20 to a front side 52 of the work piece. In turn, the
laser beam(s) passes, or not, through the work piece 50 to a
backside 54 and into the detector. Signals output from the detector
become transferred to the computing system environment where a
user/software analyzes them for light transmissivity
characteristics of the work piece.
[0037] More specifically, and as a preliminary matter, the work
piece 50 is loaded in the tray 70 at a home position, which is
around 200 mm away from the laser light source structure 20 and the
detector structure 24. A safety door of the light safe enclosure
shuts and the apparatus obtains a baseline measurement reading by
originating and projecting a laser beam along the optical path in a
direct line from the light source structure to the detector
structure without passing the laser beam through the work
piece.
[0038] Thereafter, the work piece 50 is inserted into the optical
path by movement from the home position to a starting position
between the laser light source and detector structures by the X-Y
motion table. The laser beam projects toward/through the work piece
and light collected from the backside 54 by the detector
corresponds to a work piece measurement reading. This process
repeats, as described in greater detail below, such that
pluralities of work piece measurement readings are obtained.
Differences between the baseline measurement and the work piece
measurement readings reveal the laser light transmissivity of the
work piece. In a preferred embodiment, voltage outputs of the
detector structure 24 have a mathematical relationship in terms of
transmitted light T(t) such that T(t)=Y(t)/X; where Y is the
detected intensity at time t and X is the baseline measurement
reading. A mean transmissivity value can be calculated by summing
the above equation for the duration of a given time interval.
[0039] As an example, consider a baseline measurement reading
having some trivial output of about 10 volts. Next consider a first
work piece measurement reading of about 7 volts. In percentages,
the laser light transmissivity of the work piece at that work piece
position is about 70%. Then, as additional work piece measurement
readings are taken, preferably at other work piece positions,
information about the work piece transmissivity is obtained and can
be graphed as shown representatively in FIG. 4.
[0040] As readily identifiable in the graph, laser light
transmissivity preferably stays within a zone B between 50 and 100
percent, for example. Yet, at measurement positions 1000 and 4000,
laser light transmissivity drops to much lower percentage levels.
Over time, and from knowledge learned by testing and identifying
acceptable laser welds of work pieces, users can set some minimum
acceptable level, such as dashed line 60, that readily identifies
whether the work piece under test in apparatus 10 will yield
satisfactory weld results. Users will set their own criteria for
distinguishing satisfactory welds from unsatisfactory ones. The
criteria may include, but are not limited to, how many aberrations
such as those found at positions 1000/4000 a weld can withstand or
how high a laser light transmissivity percentage on average, total,
or other will yield an acceptable result. For thorough disclosure,
the representative readings taken at work piece measurement
positions 1000 and 4000 were found in one actual reduction to
practice to correspond to impurities, such as carbon or steel, in
the composition of the work piece in instances when the work piece
comprised a plastic formed in an injection molding chamber.
[0041] It should be appreciated, however, that testing the work
piece in apparatus 10 (FIG. 1) for transmissivity characteristics
is performed at a laser wavelength corresponding substantially to
the specific laser wavelength used during laser welding. Even more
preferably, testing of the work pieces in apparatus 10 occurs with
the same exact laser light source structure 20 used during
subsequent laser welding operations of the work piece. In this
manner, users can even more accurately predict and identify a
direct correlation between transmissivity and satisfactory
welds.
[0042] To physically introduce the work piece between the laser
light source and detector structures, the offset arm 34 having the
work piece 50 therewith rotates or otherwise moves into the optical
path. With reference to FIGS. 2A and 2B, a preferred structure for
holding the work piece at a terminal end of the offset arm includes
a tray 70.
[0043] As shown, the tray 70 has a plurality of walls 72(a-d) that
form a frame around a periphery 56 of the work piece 50. A
perimeter distance of an interior 74 of the walls is slightly
larger than the perimeter distance of the periphery 56. In this
manner, a user may easily insert the work piece into the tray and
the tray will maintain the work piece in a fixed position relative
thereto. Near a bottom 75(a-d) of the walls, a ledge 76(a-d) juts
out slightly such that when the work piece is inserted into the
tray, the front side 52 surface of the work piece rests in contact
on a top surface 80(a-d) thereof. In one embodiment, the ledge juts
out a distance d of about {fraction (5/1000)}.sup.th of an
inch.
[0044] Those skilled in the art should observe that despite a
slight ledge, the tray otherwise has a substantially bottomless
quality. In this manner, when the laser light source structure 20
(FIG. 1) projects laser beams of light towards, and perhaps through
the work piece, the substantially bottomless tray 70 suspends the
work piece between the laser light source and detector structures
such that nearly the entirety of the front side 52 surface of the
work piece receives direct laser light without any interference
from the tray. Preferably, in a direct line (e.g., optical path,
dashed line, FIG. 1) between the laser light source structure 20
and the detector structure 24, no portion of the tray ever crosses
the line.
[0045] The tray 70 can affix to the offset arm at any variety of
positions, such as outside 73 of wall 72a, by adhesives, clamps,
fasteners or other or by integral formation therewith.
[0046] As depicted, the work piece 50 has a thickness t less than a
height h of the walls so that it nests within the tray. Those
skilled in the art will appreciate, however, that the work piece
may have other thicknesses that extend beyond or exist
substantially parallel to a top 82(a-d) of the walls and this
invention embraces all varieties.
[0047] To have even greater usefulness, the positions, in which
transmissivity measurements are taken, should correspond directly
to the positions that will later become laser welded. With
reference to FIG. 2C, a plurality of such later-welded work piece
positions are shown generally as a plurality of discrete dots (with
two labeled 90-1 and 90-4) arranged in a substantially rectangular
pattern (although only shown on three sides of the work piece 50
with a dashed line arrow C indicating continuation of the pattern)
substantially paralleling a periphery 56 of the work piece. Thus,
when users take measurements they do so at the positions indicated
by the pattern.
[0048] The invention, however, should not be considered so narrowly
to preclude other patterns of work piece positions. Thus, the
invention contemplates other patterns and user need generally
dictates them. For example, the invention finds equal utility with
round, triangular, square, linear, spotted and random or other
patterns or patterns of continual lines of positions instead of
discrete positions or combinations thereof.
[0049] In one actual embodiment, the invention found utility with
about 12,000 work piece positions in a substantially rectangular
pattern with about 1/2 of {fraction (1/1000)}.sup.th of an inch
between positions. The measurements occurred at the work piece
positions in the following manner: i) introduce and suspend the
work piece in the tray at a home position away from the optical
path; ii) project a laser beam directly from the light source to
the detector structure; iii) obtain a baseline measurement reading;
(iv) energize stepping motor to stepwise control movement of the
tray and work piece to the starting position between the light
source and detector structures directly in the optical path; v)
obtain a work piece measurement reading by passing the laser beam
(which is continuous on, but not necessarily required to be) from
the light source structure into the work piece and
observing/recording the output of the detector structure; (vi)
energize the stepping motor to stepwise control movement of the
tray; (vii) index the tray 70 and work piece 50 such that the next
work piece position is in the optical path; (viii) repeat steps
(v)-(viii) until an entirety of the work piece is measured; ix)
stop the laser beam from projecting; and x) return tray 70 and work
piece to the home position by indexing the stepping motor. The work
piece embodied a substantially rectangular solid plastic
composition of Noryl Brand TN 300 having a thickness of about 2 mm
and a length and width of about 50 mm and 25 mm, respectively.
[0050] With reference to FIG. 3, the invention presents a more
detailed illustration of a preferred optical path for use in the
apparatus 10 of FIG. 1. In particular, laser diode 28 in
combination with a collimating lens 100 and focusing lens 102
projects a laser beam 104 from the laser light source structure
towards a front side 52 of the work piece 50. The detector
structure collects transmitted laser light 106 from a back side 54
of the work piece with assistance from a converging lens 108,
filter 42 and photodetector 40. In other embodiments, the optical
path optionally includes additional lenses, filters collimators or
other optical elements, such as mirrors, fiber optic strands,
scanning structures or the like.
[0051] Finally, since the invention herein contemplates the work
piece as an ink-jet printhead lid or body, the remaining
description relates to specific work piece compositions and their
arrangement as part of a laser welded printhead lid/body.
[0052] With reference to FIG. 5, a printhead of the present
invention is shown generally as 101. The printhead 101 has a
housing 121 formed of a body 161 and a lid 160 laser welded
together by a laser beam at a welding laser wavelength at a
specific work piece position at a time after the lid has its work
piece position measured for laser light transmissivity at the
specified welding laser wavelength. In one preferred embodiment,
the lid comprises a laser transparent material having a composition
of polyphenylene ether plus polystyrene while the body comprises a
laser absorbing material also having a composition of polyphenylene
ether plus polystyrene. Although shown generally as a rectangular
solid, the housing shape varies and depends upon the external
device that carries or contains the printhead. The housing has at
least one compartment, internal thereto, for holding an initial or
refillable supply of ink and a structure, such as a foam insert,
lung or other, for maintaining appropriate backpressure in the
inkjet printhead during use. In one embodiment, the internal
compartment includes three chambers for containing three supplies
of ink, especially cyan, magenta and yellow ink. In other
embodiments, the compartment may contain black ink, photo-ink
and/or plurals of cyan, magenta or yellow ink. It will be
appreciated that fluid connections (not shown) may exist to connect
the compartment(s) to a remote source of ink.
[0053] A portion 191 of a tape automated bond (TAB) circuit 201
adheres to one surface 181 of the housing while another portion 211
adheres to another surface 221. As shown, the two surfaces 181, 221
exist perpendicularly to one another about an edge 231.
[0054] The TAB circuit 201 has a plurality of input/output (I/O)
connectors 241 fabricated thereon for electrically connecting a
heater chip 251 to an external device, such as a printer, fax
machine, copier, photo-printer, plotter, all-in-one, etc., during
use. Pluralities of electrical conductors 261 exist on the TAB
circuit 201 to electrically connect and short the I/O connectors
241 to the bond pads 281 of the heater chip 251 and various
manufacturing techniques are known for facilitating such
connections. It will be appreciated that while eight I/O connectors
241, eight electrical conductors 261 and eight bond pads 281 are
shown, any number are embraced herein. It is also to be appreciated
that such number of connectors, conductors and bond pads may not be
equal to one another.
[0055] The heater chip 251 contains at least one ink via 321 that
fluidly connects to a supply of ink internal to the housing. During
printhead manufacturing, the heater chip 251 preferably attaches to
the housing with any of a variety of adhesives, epoxies, etc. well
known in the art. As shown, the heater chip contains two columns of
heaters on either side of via 321. For simplicity in this crowded
figure, dots depict the heaters in the columns. It will be
appreciated that the heaters of the heater chip preferably become
formed as a series of thin film layers made via growth, deposition,
masking, photolithography and/or etching or other processing steps.
A nozzle plate with pluralities of nozzle holes, not shown, adheres
over the heater chip such that the nozzle holes align with the
heaters.
[0056] With reference to FIG. 6, an external device, in the form of
an inkjet printer, for containing the printhead 101 is shown
generally as 401. The printer 401 includes a carriage 421 having a
plurality of slots 441 for containing one or more printheads. The
carriage 421 is caused to reciprocate (via an output 591 of a
controller 571) along a shaft 481 above a print zone 461 by a
motive force supplied to a drive belt 501 as is well known in the
art. The reciprocation of the carriage 421 is performed relative to
a print medium, such as a sheet of paper 521, that is advanced in
the printer 401 along a paper path from an input tray 541, through
the print zone 461, to an output tray 561.
[0057] In the print zone, the carriage 421 reciprocates in the
Reciprocating Direction generally perpendicularly to the paper
Advance Direction as shown by the arrows. Ink drops from the
printheads (FIG. 5) are caused to be ejected from the heater chip
at such times pursuant to commands of a printer microprocessor or
other controller 571. The timing of the ink drop emissions
corresponds to a pattern of pixels of the image being printed.
Often times, such patterns are generated in devices electrically
connected to the controller (via Ext. input) that are external to
the printer such as a computer, a scanner, a camera, a visual
display unit, a personal data assistant, or other.
[0058] To print or emit a single drop of ink, the heaters (the dots
of FIG. 5) are uniquely addressed with a small amount of current to
rapidly heat a small volume of ink. This causes the ink to vaporize
in a local ink chamber and be ejected through, and projected by, a
nozzle plate towards the print medium.
[0059] A control panel 581 having user selection interface 601 may
also provide input 621 to the controller 571 to enable additional
printer capabilities and robustness.
[0060] As described herein, the term inkjet printhead may in
addition to thermal technology include piezoelectric technology, or
other, and may embody a side-shooter structure instead of the
head-shooter structure shown. Finally, since the to-be-welded work
piece described above may embody an inkjet printhead lid and/or
body and since laser welding imparts essentially no vibratory
motion in the work pieces, unlike ultrasonic welding, less cracking
of the heater chip occurs and less air becomes entrained in the ink
during printhead manufacturing.
[0061] The foregoing description is presented for purposes of
illustration and description of the various aspects of the
invention. The descriptions are not intended to be exhaustive or to
limit the invention to the precise form disclosed. The embodiments
described above were chosen to provide the best illustration of the
principles of the invention and its practical application to
thereby enable one of ordinary skill in the art to utilize the
invention in various embodiments and with various modifications as
are suited to the particular use contemplated. All such
modifications and variations are within the scope of the invention
as determined by the appended claims when interpreted in accordance
with the breadth to which they are fairly, legally and equitably
entitled.
* * * * *