Pumps – Motor driven – Electric or magnetic motor
Reexamination Certificate
2001-07-09
2003-05-20
Freay, Charles G. (Department: 3746)
Pumps
Motor driven
Electric or magnetic motor
C417S206000, C417S416000, C417S469000, C417S505000, C417S509000
Reexamination Certificate
active
06565333
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a fluid discharge apparatus, and a fluid discharge method, which are capable of feeding fluid at a minute flow rate with high accuracy in fields such as consumer products, information-processing equipment, equipment for factory automation, and production machines.
With employment of the present invention, a fluid discharge apparatus and a fluid discharge method can be provided which are capable of discharging intermittently or continuously various types of fluid in a constant amount, such as adhesives, solder paste, fluorescent substances, grease, paints, hotmelt, chemicals, and foods. The method and apparatus can also be used in production processes for such fields as electronic components and household electric appliances.
Liquid discharging apparatus (dispensers) have been conventionally used in various fields, and techniques for controlling discharge of a minute amount of fluid material with high accuracy and stability have been demanded with needs for miniaturization and increased recording density of electronic components in recent years.
There is also a great demand for a fluid discharging method for applying fluorescent substances uniformly to display surfaces of a CRT (Cathode Ray Tube) and a PDP (Plasma Display Panel), for example.
In the field of surface mounting technology (SMT), for example, requests of dispensers with regard to trends of speed-up, miniaturization, densification, quality improvement, and automation of mounting are summarized as follows.
(i) increase in accuracy in an amount of application
(ii) reduction in discharging time
(iii) minimization in an amount of application in one operation
(iv) diameter reduction in and miniaturization of a dispenser body
(v) equipment with multi-nozzles.
As liquid discharging apparatus, conventionally, such dispensers employing an air pulse system as shown in
FIG. 21
have been widely used, and this technique is presented, for example, in “Jidoka-gijutsu (Mechanical automation)”, vol. 25, No. 7, '93. A dispenser of this system applies a constant amount of air supplied from a source of a constant pressure into a vessel (cylinder)
150
in pulsed manner, and discharges from a nozzle
151
a certain amount of liquid corresponding to a pressure increase in the cylinder
150
.
On the other hand, micropumps employing piezoelectric elements have been developed for a purpose of discharging fluid at a minute flow fate. For example, the following is presented in “Cho-onpa TECHNO (ultrasonic TECHNO)”, the June issue, '59.
FIG. 22
is a figure of a principle of such a micropump, and
FIG. 23
illustrates its concrete structure., Upon application of a voltage to a laminated piezoelectric actuator
200
, the actuator undergoes a mechanical elongation, which is magnified by action of a displacement magnifying mechanism
201
. Then, a diaphragm
203
is pushed upwardly in
FIG. 22
via a thrust-up rod
202
, and capacity of a pump chamber
204
therefore decreases. At this time, a check valve
206
in a suction opening
205
closes, and a check valve
208
in a discharge opening
207
opens and fluid in the pump chamber
204
is discharged. Upon a reduction in the applied voltage, subsequently, the mechanical elongation decreases with the reduction in the voltage. The diaphragm
203
is then pulled back downwardly by a coiled spring
209
(by returning action) and capacity of the pump chamber
204
increases and pressure in the pump chamber
204
turns negative. The negative pressure opens the check valve
206
in the suction opening and the pump chamber
204
is filled with fluid. At this time, the check valve
208
in the discharge opening remains closed. The coiled spring
209
has an important role of applying a mechanical pre-load to the laminated piezoelectric actuator
200
via the displacement magnifying mechanism
201
, in addition to the action of pulling back the diaphragm
203
. After that, the above operations are repeated.
It is thought that a miniature pump having a minute flow rate with excellent accuracy with respect to flow rate can be obtained with the above configuration using a piezoelectric actuator.
Among the above-mentioned prior art, dispensers of air pulse systems had the following issues.
(1) variation in discharge amount resulting from pulsation of discharge pressure
(2) variation in discharge amount resulting from a water head difference
(3) change in discharge amount resulting from a change in viscosity of liquid.
The shorter cycle time (tact) and discharge time are, the more remarkable the phenomenon of the above-mentioned first issue. Therefore, there have been made such contrivances as provision of a stabilizer circuit for equalizing heights of air pulses.
The above-mentioned second issue occurs for the following reason. Capacity of a cavity
152
in the cylinder varies with a residual quantity H of the liquid, and therefore, a degree of a change in pressure in the cavity
152
caused by discharge of a given amount of high-pressure air varies enormously with the quantity H. As a consequential issue, a decrease in a residual quantity of the liquid reduces an amount of application, e.g., by fifty to sixty percent as compared with a maximum amount. Therefore, remedies that have been adopted include detection of the residual quantity H of the liquid during each discharge operation, and subsequent adjustment of a pulse duration in order to make a discharge amount uniform.
The above-mentioned third issue occurs in a case that viscosity of a material, for example, containing a large quantity of solvent changes with time. As an example of remedies which have been adopted for this issue, a tendency of viscosity change with respect to a time axis is previously programmed into a computer and, for example, pulse length is adjusted so that influence of viscosity change may be corrected.
Any of the remedies for the above-mentioned issues has not served as a fundamental solution, because these remedies complicate a control system including a computer, and have difficulty in accommodating irregular changes in environmental conditions (e.g., temperature).
The following is a predicted issue in adaptation of an above-mentioned piezo-pump, using the laminated piezoelectric actuator shown in
FIGS. 22 and 23
, to high-speed intermittent application of high viscosity fluid employed in such fields as surface mounting.
In the field of surface mounting, a dispenser which is capable of applying, e.g., not more than 0.1 mg of adhesive (having a viscosity in the range of one hundred thousand to one million CPS) instantaneously within 0.1 sec. has been demanded in recent years. It is therefore presumed that such a dispenser requires a high hydrostatic pressure in the pump chamber
204
, and high responsibility of the suction valve
206
and the discharge valve
208
communicating with the pump chamber
204
. For a pump equipped with a passive discharge valve and a passive suction valve, however, it is extremely difficult to intermittently discharge rheological fluid, having extremely poor fluidity and high viscosity, with high accuracy in flow rate and at a high speed.
In order to eliminate the above-mentioned defects of an air pulse system, a piezo system employing a laminated piezoelectric actuator and the like, and a pump for a minute flow rate that will be described below, has been already proposed by the inventor(in Japanese Unexamined Patent Publication No. 10-128217).
Suction action or discharge action of this pump is obtained by applying relative linear motion and relative rotational motion between a piston and a cylinder by virtue of independent actuators, and electrically and synchronously controlling operation of the actuators.
In
FIG. 24
, reference numeral
301
denotes a first actuator composed of a laminated piezoelectric element. Numeral
302
denotes a piston driven by the first actuator
301
, and the piston corresponds to a direct-acting part of a pump. Between the piston
302
and a lower housing
303
is formed a pump chamber
304
, o
Solak Timothy P.
Wenderoth , Lind & Ponack, L.L.P.
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