An automatic dross removal apparatus is disclosed for removing dross from the surface of a solder bath in an automated electric component handling system. A rotatable wiper blade is positioned adjacent the solder bath which skims the dross off of the surface prior to the dipping of a robot conveyed component into the bath. An electronic control circuit causes a motor to rotate the wiper arm one full rotational cycle each time a pulse is received from a robot controller as a component approaches the solder bath

Webb, Winston S.

English

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NASA
National Aeronautics and
Space Administration
Washington, D.C.
20546
Reply to Attn of:
NASA Case No. _- z_'_O/9-/
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The invention disclosed in this document resulted from research in
aeronautical and space activities performed under programs of the
National Aeronautics and Space Administration. The invention is
4" available for licensing in
-- o owned by NASA and is, therefore,
C¢,,,
o accordance with the NASA Patent Licensing Regulation (14 Code of
Federal Regulation 1245.2).
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To storage commercial utilization of NASA-owned inventions, it is
NASA policy to grant licenses to commercial concerns. Although
NASA encourage nonexclusive licensing to promote competition and
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necessary incentive to the licensee to achieve early practical
application of the invention.
Address inquires
invention to
and all applications for license
Off_0e of P_t_n_ _ounsel LCUol)
for this
Approved NASA forms for application for nonexclusive or exclusive
license are available from the above address.
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TECHNICAL ABSTRACT
NASA Case MFS-28406-I
SOLDER DROSS REMOVAL APPARATUS
The present invention relates to an
automatic solder dross removal apparatus for
removing dross and burnt flux from a static
solder pot in an automated electronic component
preparation system. The apparatus serves to
skim the surface of a solder bath each time an
electronic component is to be dipped therein by
a robot arm, and thereby ensures that a clean
solder surface will be presented to each
component.
The solder dross removal apparatus i0
includes a rotatable shaft and arm assembly 12
having a wiper blade 14 attached thereto. The
apparatus i0 is attached to the side of an
electric heater solder pot 20 and includes a
circular cam wheel 24 which guides the arm as it
rotates on a teflon slide bearing 26. As the
arm rotates, the wiper blade 14 skims across
the top surface of a solder bath 22 and moves
any dross and burnt flux to one side. To
control the rotation of the shaft and arm
assembly 12, an electric gear motor 32 is
attached thereto which is operated by signals
from a motor control circuit 34. The motor
control circuit 34 includes and OR gate 52 that
has its output connected to a transistor switch
50 which is placed in the ground line for the
motor 32. The OR gate 52 has two inputs, a
first input from a robot controller 44 and a
second input from a switch 38 that is attached
to a cam wheel support arm 25. Power is
"I0
supplied to the electric motor 32 whenever a
pulse is provided by the robot controller 44
which occurs in response to the approach of a
component to be dipped into the solder bath 22
by a robot arm. The shaft and arm assembly 12
continues to rotate the wiper blade 14 one full
turn until the switch 38 is closed and power to
the motor 32 is disconnected.
The novelty of the invention lies in the
provision of a means to automatically ensure
that a clean solder surface will be presented
each time a component is dipped into a static
solder bath in an automated electronic componeht
handling system.
Inventor:
Employer:
Date Filed:
Serial Number:
Winston S. Wehb
Honeywell Space and Strategic
Avionics
May 16, 1990
07/524,110
/ \
NASA Case No. MFS-28406-1
1
Description
Solder Dross Removal Apparatus
Oriqin of the Invention
The invention described herein was made
5 by an employee of the United States Government
and may be manufactured and used by or for the
Government for Government purposes without the
payment of any royalties thereon or therefore.
Technical Field
i0 The present invention relates in general
to a solder dross removal apparatus for
removing dross and burnt flux from a static
solder pot in an automated electronic
component preparation system.
15 Backqro_nd Art
In automated electronic component
preparation systems, the components are
typically assembled to printed wiring boards
or modules after having their leads tinned in
20 a molten solder bath. Wave soldering machines
have been used for this purpose and employ a
solder bath that is agitated so that the
solder rises in waves against the component
leads as the components are conveyed above the
25 bath. A difficulty with these types of
soldering machines is that the waves are
unsteady and hard to control which makes
positioning of the components relative to the
soldering machine difficult. The use of a
30 static solder pot remedies this problem,
however, a top layer of dross and burnt flux
which adversely affects the quality of the
solder process quickly builds up if the solder
is not agitated.
35
PATENT
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Disclosure of _nvention
It is therefore the object of the present
invention to provide an apparatus for removing
dross from a static solder pot in an automated
electronic component preparation system.
This and other objects of the invention are
achieved through provision of an automatic
dross removing apparatus which includes a
rotatable wiper blade that skims across the
top surface of a solder bath in a pot and
moves the dross to one side so that a clean
solder surface is provided each time a
component is dipped into the bath by a robot
arm. The wiper is rotated by a motor that is
intermittently driven in response to control
signals from a robot controller so that the
wiper sweeps the dross just before the robot
arm dips a component into the solder bath. In
this manner, the cleanest possible solder
surface will be provided for each component
before it is dipped into the solder bath.
Brief Description of Drawinqs
The foregoing and additional objects,
features and advantages of the present
invention will become apparent from the
following detailed description thereof, taken
in conjunction with the accompanying drawings
in which:
FIG. 1 is a side view of a preferred
embodiment of the present invention, showing
a solder pot in cross section;
FIG. 2 is a top view of a preferred
embodiment of the present invention;
FIG. 3 is a schematic circuit diagram of
a motor control circuit for a preferred
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3
embodiment of the present invention; and,
FIG. 4 is a timing diagram for the
circuit of FIG. 3.
Best Mode _0r Ca_ryinq out _he _Dventio_
Turning now to a more detailed
consideration of the present invention, a
solder dross removal apparatus is illustrated
in FIG. 1 generally at i0 which includes a
rotatable shaft and arm assembly 12 having a
wiper blade 14 attached to a free end 16
thereof. The apparatus i0 is attached by
means of a support bracket 18 to the side of
an electric solder heater pot 20 which
contains a molten solder bath 22 for use in
tinning the leads of electrical components.
A circular cam wheel 24 is attached to the
support bracket 18 by means of a plurality of
support arms 25 which guides the arm 12 as it
rotates on a teflon slide bearing 26. As
illustrated in FIG. i, the cam wheel 24 is
disposed at an inclined angle relative to the
surface of the solder bath 22 so that as the
arm 12 rotates, the wiper blade 14 will be
dipped into the solder bath 22 and then raised
above the bath so that it will clear the edge
of the pot 20. This action causes the wiper
blade 14 to skim the top surface of the solder
bath 22 and form a clean area of solder 28 as
illustrated by the dash lines in FIG. 2. The
dross and burnt flux that is removed from the
clean area 28 is moved to one side of the
solder pot 20 as illustrated generally at 30.
Preferably, the arm assembly is positioned so
that the wiper blade 14 skims the top
approximately 0.150 microns of the solder bath
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4
22.
To control the intermittent rotation of
the shaft and arm assembly 12, an electric
gear motor 32 of conventional design is
attached thereto which is operated by signals
from a motor control circuit 34 that is
electrically connected to the motor 32 via a
line 36. The motor 32 rotates the shaft and
arm assembly 12 so that the wiper blade 14
travels at a suitable speed, such as
approximately 3.5 inches per second. A
mechanically actuated electrical switch 38 is
attached to the cam wheel assembly 24 in such
a position that the arm assembly 12 will
contact it and cause switch 38 to close as the
arm contacts switch 38. The switch 38 is
electrically connected via a line 40 to the
motor control circuit 34, which in turn is
connected via a line 42 to a robot controller
44.
The schematic for the motor control
circuit 34 is illustrated in FIG. 3 and
essentially comprises a transistor switch 50
that is placed in a ground line 51 for the
motor 32 and is controlled by the output of an
OR gate 52 connected to a base 53 of the
transistor switch 50. The OR gate 52 has two
inputs, a first input from the robot
controller 44 which generates a pulse in
response to the approach of a component to be
dipped in the solder bath 22 on a robot arm,
and a second input from ground through the
switch 38. A five volt DC source is connected
through a pair of pull-up resistors 54 to the
inputs of the OR gate 52. In this manner,
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whenever either the switch 38 is open
circuited or a pulse is generated by the robot
controller 44, the output of the OR gate 52
will be high so that the transistor switch 50
will complete the circuit to the motor 32 and
the motor 32 will be actuated to thereby
rotate the shaft and arm assembly 12.
The timing diagram for the motor control
circuit 34 is illustrated in FIG. 4. As the
robot arm approaches the solder bath with a
component to be dipped therein, a short pulse
of approximately i00 milliseconds appears on
the input from the robot controller 44 and the
OR gate 52 generates a high output so that the
motor 32 is actuated and rotates the arm
assembly 12. As this happens, the switch 38
will open so that the output of the OR gate
52 will remain high and the arm assembly 12
will continue to rotate through one full
rotation cycle until the arm closes the switch
38 once again and the motor 32 stops. This
cycle repeats each time a pulse is sent by the
robot controller 44 to the OR gate 52.
In the above manner, the present
invention provides an apparatus for sweeping
dross off the surface of a molten solder bath
that is automatically operated in response to
a trigger pulse each time a component to be
dipped into the solder bath approaches the
bath on a robot arm. The invention thereby
enables the use of a static solder pot which
ensures accurate positioning of the solder
bath relative to the components to be dipped
therein and eliminates dross build up problems
that are normally associated with such static
6solder pots.
Although the invention has been disclosed
in terms of a preferred embodiment, it should
be understood that numerous modifications and
variations could be made thereto without
departing from the true spirit and scope
thereof as defined by the following claims.
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q
Abstract
An automatic dross removal apparatus (i0)
is disclosed for removing dross from the surface
of a solder bath (22) in an automated electric
component handling system. A rotatable wiper
blade (14) is positioned adjacent the solder
bath (22) which skims the dross off of the
surface prior to the dipping of a robot conveyed
component into the bath. An electronic control
circuit (34) causes a motor (32) to rotate the
wiper arm (14) one full rotational cycle each
time a pulse is received from a robot controller
(44) as a component approaches the solder bath
(22).
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I ROTATIONCYCLE I
FIG.4


Solder dross removal apparatus

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