Fluid discharge device and fluid discharge method

Details Fluid discharge device and fluid discharge method Fluid discharge device and fluid discharge method

2001-03-07

2003-05-06

Freay, Charles G. (Department: 3746)

Pumps

Condition responsive control of pump drive motor

By control of electric or magnetic drive motor

C222S333000, C239S537000, C239S584000, C239S585500

Reexamination Certificate

active

06558127

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a fluid discharge device for discharging and feeding in a specified amount a variety of liquids such as conductive paste, adhesive, solder cream, grease, paint, hot melt, chemicals, and foods, or for uniformly coating a fluorescent material or the like onto the display surface of CRT, PDP, or the like with high accuracy, in production processes in the fields of electronic components, household electric appliances, and so on.
The fluid discharge device (dispenser) has conventionally been used in a variety of fields. In response to recent years' needs for smaller size and higher recording density of electronic components, there has arisen a demand for a technique that allows an infinitesimal quantity of fluid material to be fed stably with high accuracy.
Otherwise, there is also a great demand for a fluid discharge method for uniformly coating a fluorescent substance on the display surface of CRT, PDP, or the like.
Taking the field of surface mount technology (SMT) as an example, the issues of the dispenser are summarized as follows in line with the trend towards higher mounting speed, miniaturization, higher density, higher quality, and automatization:
(1) Higher accuracy of coating quantity;
(2) Reduction in discharge time
(3) Smaller coating quantity per dot
Conventionally, a dispenser of an air pulse system as shown in
FIG. 17
is widely used as a fluid discharge device. The technique is introduced in, for example, “AUTOMATED ENGINEERING, '93, Vol. 25, No. 7.”
The dispenser of this system applies in pulses a specified amount of air supplied from a constant pressure source to the inside of a container (cylinder)
150
to discharge a specified amount of liquid corresponding to a rise in pressure inside the cylinder
150
from a nozzle
151
.
For the purpose of feeding a fluid at an infinitesimal flow rate, a micro pump utilizing a piezoelectric element has been developed. For example, “SUPERSONIC TECHNO, June Issue, '59” introduces the contents as follows.
FIG. 18
shows a principle diagram, while
FIG. 19
shows its concrete structure. When a voltage is applied to a laminate piezoelectric actuator
200
, a mechanical extension occurs, and this extension is increased by the action of a displacement magnifying mechanism
201
. Further, a diaphragm
203
is pushed upward in the figure via a thrust rod
202
, and the capacity of a pump chamber
204
is reduced. In this stage, a check valve
206
of an inlet
205
is closed, and a check valve
208
of an outlet
207
is opened, discharging the fluid located inside the pump chamber
204
. Next, when the application voltage is decreased, the mechanical extension decreases with decreasing voltage. The diaphragm
203
is pulled back downward by a coil spring
209
(restoring action), by which the internal capacity of the pump chamber
204
is increased to provide a negative pressure in the pump chamber
204
. Due to this negative pressure, the inlet check valve
206
is opened to fill the pump chamber
204
with the fluid. In this stage, the outlet check valve
208
is closed. The coil spring
209
plays the important role of applying a mechanical pre-load to the laminate piezoelectric actuator
200
via the displacement magnifying mechanism
201
in addition to the action of pulling back the diaphragm
203
. The above operations will subsequently be repeated.
This constitution employing the piezoelectric actuator could make it possible to realize a small-size, infinitesimal-flow-rate pump having excellent flow rate accuracy.
Out of the aforementioned prior art examples, the dispenser of the air pulse system has had the following issues.
(1) Variations in discharge rate due to discharge pressure pulsations
(2) Variations in discharge rate due to water head differences
(3) Changes in discharge rate due to liquid viscosity changes
The phenomenon of the issue (1) appears more noticeably as the cycle time becomes shorter and the discharge time is shorter. Accordingly, it has been practiced to take measures such as providing a stabilizer circuit for uniforming the air pulse height.
The issue (2) is ascribed to the reason that the capacity of an air gap portion
152
in the cylinder differs depending on a remaining liquid quantity H, and the degree of pressure change inside the air gap portion
152
is largely changed by the quantity H when a specified amount of high-pressure air is supplied. There has been an issue that the coating quantity decreases by, for example, about 50 to 60% as compared with the maximum value if the remaining liquid quantity is lowered. Accordingly, it has been practiced to take measures such as detecting the remaining liquid quantity H every occasion of discharge and adjusting the time duration of the pulse so that the discharge rate becomes uniform.
The issue (3) occurs, for example, when a material containing a large amount of solvent has changed in viscosity with a lapse of time. As a countermeasure against the issue, there has been taken a measure of preparatorily programming the tendency of the viscosity change on the time base in a computer and adjusting, for example, the pulse width so as to correct the influence of the viscosity change.
Any of the countermeasures against the issues has led to a complicated control system including the computer and has difficulties in coping with irregular changes in environment conditions (temperature and the like). Thus, the countermeasures have not been drastic proposals for solution.
Furthermore, when a piezo-pump employing the aforementioned laminate piezoelectric actuator shown in
FIGS. 18 and 19
is used for high-speed intermittent coating of a high-viscosity fluid for use in the field of surface mount technology or the like, or when it is necessary to abruptly stop the outflow after a continuous coating, the following issues are predicted.
In the field of surface mount technology, recently, there has been a desire for, for example, a dispenser that instantaneously coats not more than 0.1 mg of an adhesive (viscosity: 100,000—several 1,000,000's CPS) within a time of not longer than 0.1 second. Therefore, it is predicted that there is a need for generating a high fluid pressure in the pump chamber
204
, and that the inlet valve
206
and the discharge valve
208
communicating with the pump chamber
204
are required to have a high response characteristic. However, in this pump accompanied by the passive discharge valve and inlet valve, it is extremely difficult to intermittently discharge a poor-fluidity, high-viscosity rheology fluid with high flow-rate accuracy at high speed.
For coating of an infinitesimal flow rate of high-viscosity fluid, thread-groove type dispensers, which are viscosity pumps, have already been developed into practical use. The thread-groove type dispensers allow preferable results to be obtained in continuous coating by virtue of their permitting a choice of pump characteristics that less depend on nozzle resistance, but are not good at intermittent coating in terms of the characters of the viscosity pumps. Accordingly, the thread-groove type dispensers have conventionally been provided in a constitution that:
(1) an electromagnetic clutch is provided between a motor and a main shaft of a pump, and this electromagnetic clutch is interlocked or opened at the time of discharge-ON or -OFF; or
(2) a DC servomotor is used for rapid rotation start or rapid stop.
However, in either case, since the response characteristic is determined by the time constant of the mechanical system, there have been restrictions on high-speed intermittent operation. Also, because of not a few indeterminate factors of rotation characteristics of the main shaft at transient responses (rotation starts and stops), there have been difficulties in strictly controlling the flow rate and limitations in coating accuracy.
In order to solve the aforementioned defects of the air pulse system, the piezo-system employing a laminate piezoelectric actuator, or the thread-groove type pump, the presen

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