U.S. patent number RE34,197 [Application Number 07/725,651] was granted by the patent office on 1993-03-16 for computer controller viscous material deposition apparatus.
Invention is credited to Harold J. Engel.
United States Patent |
RE34,197 |
Engel |
March 16, 1993 |
Computer controller viscous material deposition apparatus
Abstract
A device for uniform and discretely controlled deposition of
small quantities of viscous material at each of a succession of
locations on a surface according to a digital X-Y-Z program. A
particular application is for deposition of a viscous solder flux
or slurry of very small solder particles in such a flux material,
through a small (needle) orifice. A pumping valve is driven,
typically by pneumatic pressure, during the brief dwell time of the
needle at each programmed X, Y location, on an electronic circuit
board or the like. A mechanical contact member is provided for
automatically optimizing the needle orifice height (Z dimension)
over each programmed location irrespective of irregularities or
curvature of the plane of the circuit board. In an optional
embodiment spaced needle orifices provide contemporaneous
deposition of the viscous material.
Inventors: |
Engel; Harold J. (Northridge,
CA) |
Family
ID: |
26757020 |
Appl.
No.: |
07/725,651 |
Filed: |
July 3, 1991 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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75571 |
Jul 20, 1987 |
|
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Reissue of: |
303077 |
Jan 30, 1989 |
04941428 |
Jul 17, 1990 |
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Current U.S.
Class: |
118/680;
346/140.1; 118/401; 118/697; 118/708 |
Current CPC
Class: |
H05K
3/3485 (20200801); B05C 5/02 (20130101); B05C
11/1034 (20130101); H05K 2203/0126 (20130101); H05K
2203/1509 (20130101) |
Current International
Class: |
B05C
5/02 (20060101); B05C 11/10 (20060101); H05K
3/34 (20060101); B05C 005/02 () |
Field of
Search: |
;118/401,411,680,681,696,697,708 ;346/14R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Chiesa; Richard L.
Attorney, Agent or Firm: Smegal, Jr.; Thomas F. Mondry; Mark
B.
Parent Case Text
This is a continuation of co-pending application Ser. No.
07/075,571 filed on July 20, 1987, now abandoned.
Claims
I claim:
1. Apparatus for successive deposition of viscous fluid quantities
on a planar surface at each of a corresponding succession of X Y
coordinate locations on said surface, said apparatus
comprising:
a positionable carriage and a plurality of hollow needle elements
mounted on said carriage, each of said needle elements having an
orifice directed to deposit said viscous fluid onto said surface
from corresponding points of optimum Z axis clearance with respect
to said surface, said plural hollow needle elements extending
substantially mutually parallel and normal to said surface, said
needle elements further being mounted to be rotatable in a plane
parallel to said planar surface;
first means for successively positioning said carriage and
therefore said needle elements for a corresponding dwell time in a
succession of X, Y.[., Z.]. positions with respect to said surface,
said first means also including means for rotating said needle
elements .[.for discretely determining the pattern of the
corresponding plural depositions of said fluid on said surface.].
.Iadd.to a desired orientation .Iaddend.during each of said dwell
times.
2. Apparatus according to claim 1 in which said plural needles are
arranged to rotate as a unit about a center of rotation.
3. Apparatus set forth in claim 1 in which said first means
comprises a digitally controlled programmed positioning device.
4. Apparatus according to claim 1 further comprising second means
for effecting optimum location of said orifices in the Z coordinate
with respect to said surface, said second means being in the form
of a hollow sleeve contact member through which said needle
elements pass, said hollow sleeve extending beyond said needle
member orifices by an amount substantially equal to said Z optimum
axis clearance between said orifice and said surface when said
sleeve is in contact with said surface.
5. Apparatus according to claim 4 further comprising a Z axis
contact force sensor mounted on said carriage and arranged to
detect the force of said sleeve contacting against said surface for
modifying a programmed Z axis position control provided by said
first means to compensate for variations along said surface
.[.discretely driving each of said dwell times.]..
6. Apparatus for successive deposition of a viscous fluid quantity
at each of a plurality of X-Y coordinate positions on a surface,
said apparatus comprising: a carriage carrying at least one hollow
needle element having an orifice at a first end thereof facing said
surface;
first means for effecting relative motion between said carriage and
said surface in the X-Y plane, thereby positioning said needle
element for a dwell time at each of a sequence of said X-Y
positions;
a pressurized reservoir of said viscous fluid and means covering
said quantity of fluid to emit from said needle orifice onto said
surface during each of said dwell times;
second means for establishing the Z axis clearance of said orifice
with respect to said surface comprising a rigid contact member
affixed to said carriage and said at least one needle member, said
second means extending downward beyond said needle member orifice
by an amount substantially equal to a programmed optimum Z axis
clearance between said orifice and said surface when said contact
member is in contact with said surface; and
third means for controlling the Z axis positioning of said rigid
contact member and said needle member as a unit, said third means
including Z axis actuation means and means for sensing the force of
said rigid contact member against said surface to produce a control
signal and apply said signal to said Z axis actuation means to
establish the force of said rigid member against said surface
during each of said dwell times.
7. Apparatus according to claim 6 in which said rigid contact
member is a hollow sleeve and said at least one needle member
passes through the hollow interior thereof.
8. Apparatus according to claim 7 in which a single one of said
needle members is employed, said hollow sleeve is of substantially
circular cross-section and said needle member and said hollow
sleeve are substantially concentric.
9. Apparatus according to claim 7 in which said at least one hollow
needle element comprises a plurality of needle elements extending
mutually parallel through said hollow sleeve.
10. Apparatus set forth in claim 6 further defined in that said at
least one needle element is rotatable mounted within said carriage,
said at least one hollow needle element comprises a plurality of
said hollow needle elements mounted to be rotated as a unit in a
plane parallel to the plane said surface; and
fourth means comprising a servomechanism responsive to a discrete
programmed rotation control signal from said first means to rotate
said plural needle elements as a unit in said plane parallel to
said surface during each successive one of said dwell times, said
rotation being programmed to occur at a time other than when said
second means is in contact with said surface; and
means within said first means for generating said discrete rotation
control signal corresponding to each of said dwell times.
Description
BACKGROUND OF THE INVENTION
(1) Field Of The Invention
The invention relates generally to devices and systems for discrete
computer controlled small-quantity deposition of viscous a material
at a succession of X Y locations on a surface. More specifically,
the invention relates to such devices with additional apparatus for
discrete control of the height of the dispensing needle orifice (or
orifices) over the surface irrespective of surface height
variations, and for discrete orientation of multiple needle
orifices in the plane of the surface at each X Y location.
(2) Description of The Prior Art
In the prior art, systems of the general computer positioning type
are known and have been used to deposit small quantities of viscous
material such as solder flux, a slurry of such flux with solder
particles or a solder masking material according to a computer
directed program successively positioning a needle orifice over
each preselected location on a surface such as an electronic
printed circuit board. Two particularly pertinent devices and
systems are disclosed in U.S. Pat. Nos. 4,584,964 and 4,572,103.
Both of these patents have the same inventorship and ownership as
this application and the inventive subject matter described
herein.
U.S. Pat. No. 4,584,964 describes a system of the computer
controlled type which employs a controlled valve for passing a
predetermined quantity of the viscous material to be deposited at
each discrete location on the surface over which its needle orifice
is successively positioned. That disclosure particularly includes
novel means for drawback (anti-drip) from the needle orifice.
However, it does not address the problem of vertical needle orifice
positioning over a less than completely regular and planar surface.
The needle orifice height (Z coordinate) is uniformly programmed to
a valve which is only optimum if the surface is flat and extremely
smooth. Since devices of this type deposit very small quantities at
each discrete location, optimization of Z coordinate is important
and cannot be programmed along with the successive X and Y
coordinates, because each circuit board or other surface is likely
to contain its own unique variation, warp or distortions.
In the device of U.S. Pat. No. 4,572,103 the deposition of the
viscous material is via a pumping valve (force piston thrusting
within a cylinder). This configuration is better adapted to the
handling of solder particle slurry materials than is the controlled
valve version of U.S. Pat. No. 4,584,964 because of the relatively
large effective pressure applied to the needle by the force piston.
That pressure does not affect the apparatus "upstream" from the
force piston cylinder.
Systems of the prior art, including those described in the
referenced U.S. patents find their greatest application in
production set-ups where a number of circuit board units of the
same configuration are being prepared for solder application by
flow soldering or other known techniques. The computerized flux or
slurry deposition is very rapidly accomplished. The economics of
manufacture of such circuit boards demands that costs be minimized
and that fabrication be performed by relatively low skill operators
and automatic equipment.
The aforemention U.S. patents discuss other prior art extant in
this general art, such as U.S. Pat. Nos. 3,731,648 and 3,785,898
which show the general type of computerized X, Y and Z axis
positioning which is an element of the combination of this
invention as well as of the systems of U.S. Pat. Nos. 4,584,964 and
4,572,103 discussed hereinbefore.
None of the known systems of the type described provides a solution
to the problem of circuit board warp and surface Z axis
perturbations. Moreover, since the deposition of a single bead or
cone of viscous material at a time is contemplated by the known
apparatus, there is room for improvement and corresponding
production time reduction.
The invention herein described deals in unique ways with both the
circuit board variations and need for increased speed of operation
in accordance with unique advancements in this art which will be
described as this specification proceeds.
SUMMARY OF THE INVENTION
In consideration of the state of the prior art as aforesaid, it may
be said to have been the general object of the invention to provide
Z axis position modification to account for circuit board warp or
surface variations in a system of the character described, and also
to provide means for contemporaneous deposition at more than one
location and to provide programmed rotational orientation of the
plural needle elements effecting said contemporaneous depositions
in a plane generally parallel to the plane of the said circuit
board. The Z axis in this sense is usually vertical, but this is
not necessarily true.
The disclosures of U.S. Pat. Nos. 4,584,964 and 4,572,103 (having
common ownership vis-a-vis this application) are hereby
incorporated by reference into this disclosure to provide
understanding of other details not herein repeated and to provide a
fuller understanding of the utility of the invention.
Basically, the invention includes two major aspects. One aspect
relates to the modification of the Z axis control of the needle
element carriage to account for curvature and surface variations on
a circuit board to which the flux, slurry or solder masking
material is being applied. A mechanical contact member is arranged
to contact the board surface as a finder to establish the optimum
needle orifice clearance at the board surface for each X Y position
of the carriage mounting the needle or needles. The Z axis fixed
programming for each dwell time over a corresponding X Y position
on the board at which a fluid deposition is to occur is
theoretically constant over the board surface provided the board is
perfectly flat and there are no surface variations. However, in
practice, this is never completely true, and one board of a series
may have different variations vis-a-vis other boards to be
processed. Relatively minor variations are important because the
optimum elevation (Z axis clearance) of the needle orifice or
orifices may be as little as 0.010 inches.
To achieve modification of the Z axis programmed positioning to
provide optimum Z axis clearance irrespective of the aforementioned
variations of board characteristics, the preprogrammed Z axis
clearance may be overstated, i.e. may call for too small a
clearance value. A mechanical contact member affixed to the needle
element carriage contacts the board surface at optimum clearance
and a contact force sensor generates a signal supplied to the X, Y,
Z programmer to adjust the Z axis clearance to a value resulting in
minimal contact force of the contact member against the board. The
preferred form of this mechanical member is that of a hollow tube
through which the needle or needles extend with their orifice ends
recessed from the tube extremity by the aforementioned optimum Z
axis clearance. Thus the Z axis clearance is adjusted from the
pre-programmed value at each X Y location.
Another important aspect of the invention relates to the plural
needle (usually two needles) configuration whereby two (or more)
depositions are applied contemporaneously. This arrangement affords
a reduction in the time for processing of a circuit board where
inherent circuit board symmetry permits. In view of the quest for
production efficiency, circuit boards may be designed such that a
number of solder points are located in close spaced relationship
either along the X axis or the Y axis of the board or at some angle
in between. Still further, the solder points for certain components
may be about a small circular pattern. Accordingly, the invention
provides rotation of the needle pair to accomodate those situations
to deposit the flux or slurry corresponding thereto.
It will be realized that more than two needles could be employed
within the sleeve contact member if, for example, a number of
points about a relatively tight circle were extant.
The details of structure and systems for effecting the
aforementioned major aspects, and other aspects which will be
evident as this specification proceeds, will be explained
hereinafter.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a partially cut-away view of the basic apparatus
according to the invention;
FIG. 2 is a sectioned view of a dual needle arrangement within a
hollow sleeve board contact member;
FIG. 3 is a bottom view of the structure of FIG. 2 with the dual
needle orifices oriented in a first mode;
FIG. 4 is a bottom view of the FIG. 2 structure with the dual
needle orifices orthogonally oriented vis-a-vis the showing of FIG.
3; and
FIG. 5 is a schematic block diagram of the control system according
to the invention.
DETAILED DESCRIPTION
Referring to FIG. 1, the viscous fluid dispensing structure is
shown in partial cut-away form. This structure 10 is referred to
herein as the dispenser head or carriage for convenience. It is
carried and positioned by a digitally controlled programmed X, Y, Z
electro-mechanical locator (plotter) such as shown and described in
U.S. Pat. No. 4,584,964, the disclosure of which has been
incorporated herein by reference.
The structural parts 11 and 11a support a pump 12, an air (electric
or hydraulic) piston actuator 13, and a syringe 14. An optional
syringe brace 15 is shown affixed to the structural member 11.
Structural parts in turn are attached to the positionable member of
the aforementioned electro-mechanical locator such that the needle
and mechanical contact member assembly is successively positioned
directly above each location at which a deposit of flux or slurry
is required.
Looking ahead to FIG. 5, this schematic block diagram will be
explained and related with FIG. 1, 3 and 4 for clarity. Within the
control system of FIG. 5, a conventional compressed air supply 37
provides moderately pressurized air (5 to 10 psi, for example).
This basic air supply is available in steady form via lead 38
through electro-pneumatic controller unit 42 and thence via lead 35
through dispenser positioning unit 43 and thence into the syringe
14 (FIG. 1) at port 18. The steady air pressure thereat urges an
O-ring sealed free piston (not shown in FIG. 1) downward within the
body of syringe 14 against the fluid supply therein. Thus syringe
14 operates as a pressurized reservoir.
The viscous fluid within syringe 14 is continually urged down into
passage 20 and thence into the pre-dispense chamber 25. Lock
fitting 19 joins the body of syringe 14 to the passage 20 within
structural block 11.
The viscous fluid thus driven into the pre-dispense chamber 25 does
not significantly travel down the bore 26a in bushing 26 because of
its viscosity and the relatively low air pressure into port 18. The
downward stroke of rod piston 22 pushes the fluid ahead of itself
through bore 26a. The maximum downward travel of piston 22 may, for
example, be down to the top of the plenum chamber 27. The chamber
27 is shown as it would be for a two needle dispensing
configuration. However, for the single needle plenum chamber 27
could be much smaller, or could be merely an extension of bore 26a
as will be appreciated from FIG. 1.
The rod piston 22 is guided accurately by bushings 23 and 24 so
that it slides smoothly into bore 26a. The air operated piston
connected within air piston actuator 13 to adjustment screw 21 at
upper extension 13a receives only the relatively low air supply
pressure, but because of the ratio of the reaction piston diameter
within air piston actuator 13 to the very small diameter of rod
piston 22, the effective pressure applied to the viscous fluid
within bore 26a is high, on the order of 5,000 to 10,000 psi, for
example. The air piston actuator 13 may have a pancake type piston
arrangement according to a known form.
Although the air cylinder (piston actuator) 13 is assumed to be
pneumatically operated, it will be obvious to those of skill in
this art that it could be of an appropriately configured hydraulic
or electric solenoid type thrust actuator.
The apparatus of FIG. 1 is all within the dispenser head (carriage)
10, some air and electrical lines are fed through intermediate
units because of mechanical considerations between moving and
stationary elements. An example of this is the air pulse on air
inlet 35 defining the dwell time at each location on the board
surface. This pulse comes from the stationary electropneumatic
controller 42 (which is essentially a solenoid operated air switch)
and the steady air supply 37.
The syringe 14 is shown with a cap 17 having radially inwardly
extending projections 17a over a fraction of the circumference of
cap 17 to engage outwardly extending projection 14a over a portion
of the upper lip of the body of syringe 14 in the familiar
twist-cap configuration. Obviously, a threaded engagement or other
form of attachment within the knowledge of persons of skill in this
art could be used as well. Port previously identified, receives the
low but steady air pressure from air line 35a (see FIG. 5).
Disengagement of cap 17 facilitates reloading of syringe 14 with
fluid after the free piston within has been withdrawn vertically.
To facilitate this, a threaded bore (not shown) axially part way
through the upper end of this piston may be provided for inserting
a threaded dowel therein as an extracting tool. Referring now to
FIG. 2, a much enlarged view upward as indicated on FIG. 1 is
shown. It is to be understood that, although a dual needle
arrangement is depicted in FIG. 2, 3 and 4 and assumed in FIG. 1
and 5, a single needle configuration could be employed if
appropriate. In that alternative, the hollow sleeve mechanical
contact member 16 and the single needle may be coaxial. In the
single needle form, the retaining screw 28 can be drawn in tightly,
since the cup 16a, which is integral with the hollow sleeve
mechanical contact member 16, need not be rotatable within the bore
12a in the structural body 12 as it is required to be in the dual
needle version.
Reverting to the description of the dual needle embodiment, it will
be noted that FIG. 2 depicts two needles 46 and 47 fed from the
plenum 27. The guide bushing 26 is a separate part but is press
fitted into cup 16a. This is a convenience of manufacture to permit
machining the plenum 27 before guide bushing 26 is fitted into cup
16a. A shoulder of cup 16a will be seen to be axially engaged by
the head of screw 28, but with enough axial looseness to permit
rotation, of up to 90 degrees, of the entire assembly of hollow
sleeve contact member 16 and cup 16a. Rotation is effected by an
axial throw air cylinder 29, shown in FIG. 1, 3 and 4, but not FIG.
2. Such an arrangement is fast acting and capable of effecting the
positioning of needles 46 and 47 between that of FIG. 3 and FIG. 4
or at any required orientation therebetween. FIG. 3 depicts an
extension of connecting rod 30 and FIG. 4 shows the retraction of
connecting rod 30 consistent with the corresponding orientations of
needles 46 and 47. The connections of rod 30 via a conventional pin
31, linkage 30a, and pin 32 to control ring 48 (which is affixed to
hollow sleeve 16) will be obvious.
Referring now to FIG. 5, the description thereof continues with
functional comments included.
Basically the X-Y-Z programmer 34 and dispensing positioning unit
43 may be identical to those recognized to be prior art-per se, and
as indentified in U.S. Pat. No. 4,584,964 which has been
incorporated into this disclosure by reference. The compressed air
supply 37 is provided to the dispensing head (carriage) 10 via lead
35a at port 18 of the syringe 14 of FIG. 1 and via lead 38 to
electro-pneumatic controller 42 which in turn is controlled from
programmer 34 via lead 39 to open and transmit an air pulse during
the dwell time of dispenser head (carriage) 10 at each location to
which the latter is programmed. This air pulse via lead 35 effects
the viscous fluid deposition at the aforementioned location as
hereinbefore described. Each such location is identified within
programmer 34 as to orientation of the needles and is controlled
via lead 33 after each fluid deposition (during dispensing head
slew to the next X-Y location) to operate the orientation servo 44
for any required change of needle pair angular orientation. This
function is readily added to the programmed data stored in
programmer 34. The dashed lead 44a represents the mechanical
linkages described with respect to the operation of cylinder
29.
The lead 36 conveys programmed commands for X-Y positioning and
lead 49 represents Z axis positioning commands as modified for the
optimized Z axis needle positioning. This function provides the Z
axis position modification previously said to be required because
of curvature and surface irregularities of circuit boards to be
processed by the apparatus of the invention. Mechanical linkage 36a
represents all X-Y-Z positioning commands to dispensing head 10 as
modified in respect to the Z axis.
An alternative Z axis positioning concept involves a simple spring,
(not illustrated). For example, a coil spring coaxially arranged
externally over the hollow sleeve 16 could be employed to limit the
force of the end of the sleeve 16 againsts the circuit board if the
dispenser positioning unit 43 (FIG. 5) were arranged to apply only
a limited predetermined maximum Z axis downward force. The reaction
of this spring could then equal that Z axis force during the dwell
time while sleeve 16 and this spring contact the circuit board.
Such an arrangement is not, however, as accurate and definitive of
Z axis positioning as contemplated in the hereinbefore
description.
It will be realized that the more or less standard Z axis
pre-programmed positioning could be eliminated and reliance placed
on Z axis positioning of the end of sleeve 16 as a result of Z axis
force sensing by sensor 45 (FIG. 5) to establish the contact force
without modification of a pre-programmed Z axis signal during each
dwell time. The three axis pre-programmed positioner is, however, a
standard prior art device per se, as identified hereinbefore and
modification of the Z axis pre-programmed positioning is,
therefore, a desirable design option with the addition of force
sensor 45, as described. In that way maximum use of existing
electronic assemblies is possible.
Block 45 depicts a compressive force sensor which is preferably
associated with the Z axis drive within unit 43. That Z axis drive
is conventional as set forth in U.S. Pat. No. 4,584,964 and
otherwise in the technical literature. Block 45 may include a force
sensor (such as a strain gauge or piezoelectric element or other
known force sensor) through which the Z axis positioning is
accomplished.
As previously indicated, the programmed unmodified Z axis position
for each location may be intentionally overemphasized (such as
would position the needle or needles too close to the board
surface). The Z axis force sensor 45 is mechanically connected as
aforesaid, linkage 40 representing this connection.
The force sensor 45 responds to the reaction force generated as the
sleeve 16 touches the board surface, generating a modification
signal on lead 41 which overrides the Z axis pre-programmed Z axis
signal to effect a minimal contact pressure of sleeve 16 against
the board surface. Thus the Z axis net control function operates to
insure optimum needle orifice clearance 50 which is built into the
needle assembly (see FIG. 2). The Z axis clearance is normally
empirically determined to an optimum value. The factors affecting
this optimum Z axis clearance include quality of each deposition,
fluid viscosity and other factors well known in this art.
The control of a contact or touching force is a well known
technique in the robotics art and the detail instrumentation is
readily accomplished by the skilled practitioner. The touch force
sensing technique is considered to be the preferred form. However,
it could also be replaced by a clearance detector, (photoelectric
or otherwise). The inventive concept broadly presumes that any
instrumentation locating the hollow sleeve 16 bottom end lightly
against the circuit board suffices.
Various modifications will suggest themselves to those of skill in
this art. Just one such modification could be the substitution of a
non-tubular mechanical contact member in lieu of sleeve 16. An
important consideration, however, is that the point or points of
touch on the circuit board surface be close to the needle orifice
or orifices in the horizontal plane for optimum sensing of
irregularities. The coaxial nature of hollow sleeve 16 containing
the needle or needles 46 and 47 is particularly effective in that
respect.
Referring back to FIGS. 3 and 4, it will be realized that, if
desired, one of the two needles 46 and 47 could in fact be located
at the center of rotation of the needle assembly which includes the
elements attached to cup 16a within body 12 (FIG. 2).
It will be noted from FIG. 3 and 4 that slots 16b and 16c, a short
distance up from the lower end of tube 16 are provided, preferably
to a point just above the orifices of needles 46 and 47, to provide
pressure relief for the rapid deposition of the viscous
material.
Another variation is readily possible in the apparatus for
establishing the needle horizontal place positions, i.e. that shown
if FIG. 3 and 4. Such variation would be within ordinary mechanical
skill.
Other variations within the spirit of the inventions are of course
possible once the inventive concepts are appreciated. Accordingly,
it is not intended that the invention be limited other than by the
claims hereinafter. The drawings and this description are intended
to be typical and illustrative only.
* * * * *