Method for Driving a Pump Device

Abstract

During switchover from a suctioning step to a discharging step, a mixing pump (1) carries out a correcting step for displacing a displacing member (17) in the direction for reducing an internal volume of a pump chamber (2); and during switchover from the discharging step to the suctioning step, the pump carries out a correcting step for displacing a displacing member (17) in the direction for increasing the internal volume of the pump chamber (2). In the correcting step, intake ports (30a, 30b), and discharging ports (40a, 40b) of the pump chamber (2) are closed, and the displacing member (17) undergoes displacement for increasing or reducing the internal volume of the pump chamber (2) in a hermetic state. Instability caused by backlash of the displacing member (17) drive system can be eliminated, and a pressure difference between the pump chamber (2) interior and the fluid intake end or the fluid discharge end can be eliminated. It is therefore possible to eliminate or reduce variability in the amount of fluid intake or amount of fluid discharge when switching between the suctioning step and the discharging step.

Description

TECHNICAL FIELD

The present invention relates to a method for driving a pump device such as a diaphragm pump, which suctions fluid form its intake port and discharges fluid from its discharge port by casing displacement of a displacing member defining a part of a pump chamber.

BACKGROUND ART

One mixing pump device known in the art for mixing a plurality of fluids in prescribed proportions is an apparatus designed to suction a plurality of fluids into a single pump chamber, mix them in the pump chamber to form a mixed fluid, then discharge the mixed fluid from the pump chamber. Patent Citation 1 discloses a mixing pump device in a high-performance liquid chromatography device, for suctioning in and mixing several types of solvents with a plunger pump, and discharging the mixed fluid obtained thereby to the column.

The mixing pump device disclosed therein is designed to transmit rotation of a stepping motor to the plunger via a cam mechanism, increasing or decreasing the internal volume of the pump chamber. In the fluid suctioning step, during expansion of the pump chamber, valves positioned on each of two inflow passages communicating with the pump chamber are opened in sequence, and the fluids are suctioned via the inflow passages into the pump chamber where they are mixed. Subsequently, a discharge process is carried out, constricting the pump chamber and discharging the mixed liquid.

[Patent Citation 1] JP 3117623 B

However, with a mixing pump device of this design, during switchover from the discharging step to the suctioning step, a pressure differential may arise between the internal pressure of the pump chamber, and the pressure on the inflow passages currently partitioned off by the valves. Where such a pressure differential exists, if a valve that was closed is then opened, there will be a temporary backflow of fluid, the intake of the two types of fluid drawn into the pump chamber via the inflow passages will change, and their mixture ratio will fluctuate.

In the case of diaphragm pumps, a “non-responsive zone,” in which pump chamber volume is unchanged despite deformation, is observed at the outset of deformation by the diaphragm. Consequently, with a mixing pump device that employs a diaphragm pump, during switchover from the discharging step to the suctioning step or switchover from the suctioning step to the discharging step, a delay will occur in the change in the internal volume of the pump chamber. In addition, there will be variation in the fluid intake to the pump chamber and in the fluid discharge from the pump chamber.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a method for driving a pump device able to eliminate instability of the fluid intake operation and fluid discharge operation during switching between the discharging step and the suctioning step.

In order to solve the aforementioned problem, the method for driving a pump device of the present invention comprises a suctioning step for suctioning a fluid into a pump chamber from an intake port by inducing displacement of a displacing member that defines part of an inside peripheral surface of the pump chamber in the direction of increasing internal volume of the pump chamber, with the discharge port of the pump chamber closed and the intake port open; a discharging step for discharging the fluid from the pump chamber by inducing displacement of the displacing member in the direction of decreasing internal volume of the pump chamber, with the discharge port open and the intake port closed; and a correcting step for inducing displacement of the displacing member with both the intake port and the discharge port of the pump chamber closed. The steps are carried out in the order of suctioning, correcting, and discharging; or in the order of discharging, correcting, and suctioning.

With the method of the present invention, a correcting step is executed subsequent to completion of the discharging step, followed thereafter by switchover to the suctioning step. Alternatively, a correcting step is executed subsequent to completion of the suctioning step, followed thereafter by switchover to the discharging step. In the correcting step, since the displacing member undergoes displacement while the intake port and the discharge port are closed, an increase or decrease in the internal volume of the pump chamber occurs in a hermetic state, and the internal pressure of the pump chamber changes in association therewith. Consequently, through appropriate setting of the direction of displacement and the displacement level of the displacing member, it is possible to eliminate the difference between the internal pressure of the pump chamber and the pressure on the fluid discharge end of the discharge port. In the case of a diaphragm pump, since displacement of the diaphragm can be brought about by changing the internal pressure of the pump chamber, in the subsequent suctioning step or discharging step, it will be possible to change the internal volume of the pump chamber with accurate response to displacement of the diaphragm. It is accordingly possible to eliminate or reduce the extent of variation in the fluid intake or fluid discharge during switchover between the suctioning step and the discharging step.

Here, where the suctioning step and the discharging step are performed alternately, the correcting step will preferably be carried out both during switchover from the suctioning step to the discharging step, and during switchover from the discharging step to the suctioning step.

In the correcting step executed between the suctioning step and the discharging step, it is possible for example to induce displacing movement of the displacing member in the direction for reducing the internal volume of the pump chamber; and in the correcting step executed between the discharging step and the suctioning step, conversely, to induce displacement of the displacing member in the direction for increasing the internal volume of the pump chamber.

In order to eliminate the pressure differential inside and outside the pump chamber at initiation of the discharging step, in the correcting step executed between the suctioning step and the discharging step, displacement of the displacing member is induced so as to eliminate the difference between the internal pressure of the pump chamber and the pressure on the fluid discharge flow passage communicating with the discharge port. In order to eliminate the pressure differential inside and outside the pump chamber at initiation of the suctioning step, in the correcting step executed between the discharging step and the suctioning step, displacement of the displacing member is induced so as to eliminate the difference between the internal pressure of the pump chamber and the pressure on the fluid intake flow passage communicating with the intake port.

In this case, during the correcting step executed between the suctioning step and the discharging step, the difference between the internal pressure of the pump chamber and the pressure on the fluid discharge flow passage communicating with the discharge port can be monitored, and displacement of the displacing member induced on the basis of the results of the monitoring. Similarly, during the correcting step executed between the discharging step and the suctioning step, the difference between the internal pressure of the pump chamber and the pressure on the fluid intake flow passage communicating with the intake port can be monitored, and displacement of the displacing member induced on the basis of the results of the monitoring.

Rather than performing closed loop control for monitoring the pressure, it is possible to carry out open loop control whereby during the correcting step, displacement of the displacing member is induced in accordance with a predetermined condition.

Next, in the event that a plurality of fluids of different type are to be taken in and mixed, a plurality of the intake ports may be formed in the pump chamber; and during the suctioning step, an intake operation involving sequentially opening the closed plurality of intake ports and taking in fluid is performed repeatedly, forming a mixed fluid in which the different types of fluids are mixed in predetermined proportions.

In this case, in preferred practice, before the fluid with the smallest mixture proportion is delivered into the pump chamber, at least some fluid having a larger mixture proportion than that fluid will be delivered into the pump chamber. By having fluids with large intake levels so delivered over several cycles, the fluids can be thoroughly mixed within the pump chamber.

Next, where fluids delivered into the pump chamber are to be distributed to different points, a plurality of the discharge ports may be formed in the pump chamber; and during the discharging step, the closed plurality of discharge ports may be opened sequentially and the fluid discharged.

The actuating method of the present invention is effective when implemented in a pump device constituted with a diaphragm pump in which the displacing member is a diaphragm. By inducing displacement of the diaphragm in the correcting step executed prior to initiation of the suctioning step or prior to initiation of the discharging step, the internal volume of the pump chamber can be increased or decreased with accurate response to displacement of the diaphragm during the suctioning step or the discharging step, whereby the fluid intake operation and the fluid discharge operation can be carried out properly.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a conceptual diagram showing the basic configuration of a mixing pump device embodying the present invention;

FIG. 2A and FIG. 2B are respectively a timing chart depicting operation of the mixing pump device shown in FIG. 1, and a descriptive diagram depicting the relationship of the position of the piston to resolution;

FIGS. 3A to 3D are descriptive diagrams relating to deformation of a diaphragm;

FIG. 4 is a conceptual diagram showing the basic configuration of a mixing pump device embodying the present invention;

FIG. 5A and FIG. 5B are respectively a perspective view of a mixing pump device embodying the present invention, and a descriptive diagram showing the flow passages thereof in plan view;

FIG. 6 is an exploded perspective view of the mixing pump device of FIG. 5, viewed from diagonally above;

FIG. 7 is a descriptive diagram showing in cross section the configuration of the mixing pump device of FIG. 5A;

FIG. 8 is an exploded perspective view of the mixing pump device of FIG. 5A, shown divided on the vertical;

FIG. 9A and FIG. 9B are respectively a descriptive diagram of the pump chamber in a state of expanded internal volume, and the pump chamber in a state of contracted internal volume, in the mixing pump device of FIG. 8;

FIGS. 10A to 10C are respectively a perspective view, a plan view, and a sectional view of a rotor employing the rotating body of the pump mechanism shown in FIG. 8;

FIGS. 11A to 11C are respectively a perspective view, a plan view, and a sectional view of a moving body employing the rotating body of the pump mechanism shown in FIG. 8;

FIG. 12 is a descriptive diagram of the principal parts of a valve used for the active valves 5, 6 of the mixing pump device embodying the invention, shown cut along the axis and viewed from diagonally above; and

FIG. 13 is a descriptive diagram of the lines of magnetic force of the valve shown in FIG. 12.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention will be described hereinbelow with reference to the accompanying drawings.

FIG. 1 is a conceptual diagram showing the basic configuration of a mixing pump device embodying the present invention. As illustrated in FIG. 1, the mixing pump device 1 has a pump chamber 2. In the pump chamber 2 there are formed a plurality (two, in this example) of intake ports 30a, 30b; and a plurality (two, in this example) of discharge ports 40a, 40b. The intake ports 30a, 30b communicate respectively with inflow passages 3a, 3b; and the discharge ports 40a, 40b communicate respectively with outflow passages 4a, 4b. The pump device main unit 7 is made up of the pump chamber 2, the intake ports 30a, 30b, the discharge ports 40a, 40b, the inflow passages 3a, 3b, and the outflow passages 4a, 4b.

Inflow-side active valves 5a, 5b for individually opening and closing the intake ports 30a, 30b are disposed in these ports. Outflow-side active valves 6a, 6b for individually opening and closing the discharge ports 40a, 40b are disposed in these ports. These inflow-side active valves 5a, 5b and outflow-side active valves 6a, 6b are opened and closed by means of a control unit 18.

A portion of the inside peripheral surface of the pump chamber 2 is defined by a displacing member 17 such as a piston or diaphragm. The displacing member 17 is displaceable in the outward and inward direction of the pump chamber; in the present example, the displacing member 17 undergoes displacement by means of a drive unit 105 equipped with a stepping motor 12. The pump drive mechanism 13 is composed of this displacing member 17 and drive unit 105. When the stepping motor 12 of the drive unit 105 turns in one direction, the displacing member 17 is displaced in the direction A of increasing internal volume of the pump chamber 2; and when the stepping motor 12 turns in the opposite direction, the displacing member 17 is displaced in the direction B of decreasing internal volume of the pump chamber 2.

During the suctioning step of the mixing pump device 1 of this design, for example, with one inflow-side active valve 5a open, and with the other inflow-side active valve 5b and the outflow-side active valves 6a, 6b closed by the control unit 18, the displacing member 17 undergoes displacement towards direction A by means of the drive unit 105, thereby suctioning a fluid LB into the pump chamber 2 from the inflow passage 3b via the intake port 30b. Next, by switching the open/closed states of the inflow-side active valves 5a, 5b and displacing the displacing member 17 further towards direction A, another fluid LA is suctioned into the pump chamber 2 from the inflow passage 3a via the intake port 30a. The fluids. LA, LB are mixed within the pump chamber 2.

During the discharging step of the mixing pump device, for example, with one outflow-side active valve 6a open, and with the other outflow-side active valve 6b and the inflow-side active valves 5a, 5b closed by the control unit 18, the displacing member 17 undergoes displacement towards direction B via the drive unit 105, thereby discharging the mixed fluid from the pump chamber 2 into the outflow passage 4a via the discharge portion 40a. By switching the open/closed states of the outflow-side active valves 6a, 6b and displacing the displacing member 17 further towards direction B, the mixed fluid can be discharged to the outflow passage 4b from the other discharge port 40b.

In this mixing pump device 1, a correcting step, discussed below, is executed in the interval between the suctioning step and the discharging step.

FIGS. 2A and 2B are respectively a timing chart depicting operation of the mixing pump device shown in FIG. 1, and a descriptive diagram depicting the relationship of the position of the displacing member to resolution. The operation of the mixing pump device 1 will be described in detail with reference to FIG. 2A. In the description hereinbelow, the proportion of inflow (mixture proportion) of the first fluid LA and the second fluid LB taken in via the two inflow passages 3a, 3b is assumed to be 1:5.

In FIG. 2A, the uppermost level shows the intake operation and discharge operation by the pump drive mechanism 13; the intake operation by the pump drive mechanism 13 is accomplished, for example, by clockwise rotation of the stepping motor 12 displacing the displacing member 17 in the direction A of increasing the internal volume of the pump chamber 2 (see FIG. 1). The discharge operation by the pump drive mechanism 13 is accomplished, for example, by counterclockwise rotation of the stepping motor 12 displacing the displacing member 17 in the direction B of decreasing the internal volume of the pump chamber 2 (see FIG. 1). The pump drive mechanism 13 is halted via suspending the power supply to the stepping motor 12.

The inflow-side active valves 5a, 5b and the outflow-side active valves 6a, 6b all assume the open state once a positive pulse has been input, switching to the closed state at the point in time that a negative pulse is input. Once a negative pulse has been input, the valves assume the closed state once a positive pulse has been input, switching to the open state at the point in time that a negative pulse is input.

In FIG. 2A, first, at time t1, power to the stepping motor 12 is suspended, and the pump drive mechanism 13 comes to a stop. At time t1, all of the active valves 5a, 5b, 6a, 6b are in the closed state.

In this state, at time t1, of the two inflow-side active valves 5a, 5b, only the inflow-side active valve 5b located in the inflow passage 3b which corresponds to the liquid LB is switched to the open state. Next, at time t2, power is supplied to the stepping motor 12, and the stepping motor 12 rotates clockwise displacing the displacing member 17 in the direction A of increasing the internal volume of the pump chamber 2. As a result, the liquid LB flows into the pump chamber 2 from the inflow passage 3b. At time t3 following input of a 125-step pulse to the stepping motor 12, power to the stepping motor 12 is suspended, and the displacing member 17 comes to a halt as well. At the same time, the inflow-side active valve 5b is switched from the open state to the closed state. As a result, the flow of the liquid LB into the pump chamber 2 from the inlet passage 3b halts. According to this intake operation, one-half of the total inflow amount of the liquid LB is drawn into the pump chamber 2.

Next, at time t4, only the inflow-side active valve 5a is switched to the open state; and at time t5 power is supplied to the stepping motor 12, and the stepping motor 12 rotates in the same direction (clockwise) displacing the displacing member 17 in the same direction (the direction A of increasing the internal volume of the pump chamber 2). As a result, the liquid LA flows into the pump chamber 2 from the inflow passage 3a. Then, at time t6 following input of a 50-step pulse to the stepping motor 12, power to the stepping motor 12 is suspended, and the displacing member 17 comes to a halt as well. At the same time, the inflow-side active valve 5a is switched from the open state to the closed state. As a result, the flow of the liquid LA into the pump chamber 2 from the inlet passage 3a halts. According to this intake operation, the total inflow amount of the liquid LA is drawn into the pump chamber 2.

Next, at time t7, the inflow-side active valve 5b only is again switched to the open state, and at time t8 power is supplied to the stepping motor 12, whereupon the stepping motor 12 rotates in the same direction (clockwise). The displacing member 17 is thereby displaced further in the same direction (the direction of increasing the internal volume of the pump chamber 2), and the fluid LB flows into the pump chamber 2 from the inlet passage 3b. Then, at time t9 following input of a 125-step pulse to the stepping motor 12, power to the stepping motor 12 is suspended, and the displacing member 17 comes to a halt as well. At the same time, the inflow-side active valve 5b is switched from the open state to the closed state. As a result, the flow of the liquid LB into the pump chamber 2 from the inlet passage 3b halts. According to this intake operation, the remaining one-half of the total inflow amount of the liquid LB is drawn into the pump chamber 2.

After completion of the suctioning step in the above manner, during time t10 and time t11, the correcting step is executed, followed by switchover to the discharging step. The correcting step will be discussed later; first, a description of the discharging step starting at time t11 shall be provided.

At time t11, of the two outflow-side active valves 6a, 6b, only the outflow-side active valve 6a is switched to the open state; at time t12, power is supplied to the stepping motor 12, and the stepping motor 12 rotates in the opposite direction (counterclockwise direction). The displacing member 17 is thereby displaced in the direction B of decreasing the internal volume of the pump chamber 2, and the mixed liquid in the pump chamber 2 is discharged into the outflow passage 4a. Then, at time t13 following input of a 150-step pulse to the stepping motor 12, power to the stepping motor 12 is suspended, and the displacing member 17 comes to a halt as well. At the same time, the outflow-side active valve 6a is switched from the open state to the closed state. As a result, the mixed liquid is discharged from the outflow passage 4a, in an amount equivalent to one-half the liquid that has flowed into the pump chamber 2. Subsequently, during time t17 and time t18, the correcting step is executed, and the operation concludes.

Next, at time t14, of the two outflow-side active valves 6a, 6b, only the outflow-side active valve 6b is switched to the open state; at time t15, power is supplied to the stepping motor 12, and the stepping motor 12 rotates in the same direction (counterclockwise direction), displacing the displacing member 17 further in the direction B of decreasing the internal volume of the pump chamber 2, and discharging the mixed liquid in the pump chamber 2 into the outflow passage 4b. Then, at time t16 following input of a 150-step pulse to the stepping motor 12, power to the stepping motor 12 is suspended, and the displacing member 17 comes to a halt. At the same time, the outflow-side active valve 6b is switched from the open state to the closed state. As a result, the mixed liquid is discharged from the outflow passage 4b, in an amount equivalent to one-half the liquid that has flowed into the pump chamber 2. Subsequently, during time t17 and time t18, the correcting step is executed, and the operation concludes.

The correcting step which is performed during the interval of time t10 to t11 and during the interval of time t17 to t18 will now be described. At points in time of switchover of the direction of displacement of the displacing member 17, specifically, at top dead center during switchover from the suctioning step to the discharging step, and at bottom dead center during switchover from the discharging step to the suctioning step, there is a tendency for resolution of positioning to be low, as shown in FIG. 2B. In the case where a gear mechanism is used as the drive unit 105 for example, this tendency could be caused by backlash. The displacing member 17 is also susceptible to delayed response to operation and slipping out of position at top dead center and bottom dead center.

Particularly where a diaphragm is employed as the displacing member 17, delayed response to displacement tends to occur at top dead center and bottom dead center, where the direction of displacement of the diaphragm changes. Also, the shape of the diaphragm is susceptible to a pressure difference between the internal pressure of the pump chamber 2 and atmospheric pressure. This point shall be discussed with reference to FIGS. 3A to 3D.

Where, for example, the internal pressure of the pump chamber 2 is equal to atmospheric pressure as illustrated in FIG. 3A, the diaphragm 170 will not experience any unintended displacement due to a pressure difference. Where the internal pressure of the pump chamber 2 is greater than atmospheric pressure as illustrated in FIG. 3B, the diaphragm 170 becomes distended due to the pressure difference. Conversely, where the internal pressure of the pump chamber 2 is lower than atmospheric pressure as illustrated in FIG. 3C, the diaphragm 170 becomes constricted by the equivalent of the pressure difference.

Consequently, when the pump chamber 2 is at negative pressure upon completion of the suctioning step at time t9, the diaphragm will tend to assume the condition depicted in FIG. 3C. Or, when the pump chamber 2 is at positive pressure upon completion of the discharging step at time t16, the diaphragm will tend to assume the condition depicted in FIG. 3B. Thus, if in the condition depicted in FIG. 3C, the outflow-side active valve 6a is opened at time t11 and the pump chamber 2 now communicates with the outflow passage 4a to the outflow port 40a end thereof with respect to the valve 6a, there is a risk that the mixed fluid in the outflow passage 4a on the outflow port 40a end thereof will backflow into the pump chamber 2 due to the differential head. If such a condition occurs, the discharged amount of the mixed liquid will be less than the intended amount. If in the condition depicted in FIG. 3B, the inflow-side active valve 5b is opened at time t1 and the pump chamber 2 now communicates with the inflow passage 3b to the outflow inflow port 30b end thereof with respect to the valve 5b, the mixed liquid in the pump chamber 2 will backflow from the inflow passage 3b, and the inflowing amount of the second liquid LB will be less than the intended amount.

Meanwhile, even in instances where the pump chamber 2 is at a pressure equal to atmospheric pressure upon completion of the suctioning step at time t9 or upon completion of the discharging step at time t16, a problem such as is described hereunder may occur where the outflow passages 4a, 4b are situated above and the inflow passages 3a, 3b are situated below as depicted in FIG. 3D. First, upon completion of the intake at time t9, since the pressure of the pump chamber 2 equals the pressure to the outside of the inflow-side active valve 5b, when the outflow-side active valve 6a is opened at time t11 and the pump chamber 2 communicates with the outflow port 40a end of the outflow passage 4a, there is a risk that the fluid mixed at the outflow port 40b via the valve 6a of the outflow passage 4a will flow back into the pump chamber 2 due to the differential head. If such a condition occurs, the diaphragm 170 will become distended prior to actuation of the diaphragm 170, and the discharged amount of the mixed liquid will be less than the intended amount. Also, even where the pump chamber 2 is at a pressure equal to atmospheric pressure upon completion of the discharging step at time t16, after completion of the discharging step at time t16, since the pressure of the pump chamber 2 equals the pressure to the outside of the outflow-side active valve 6b, when during the second intake cycle the inflow-side active valve 5b is opened at time t1 and the pump chamber now communicates with the inflow port 30b end of the inflow passage 3b, there is a risk that the mixed liquid will backflow through the inflow passage 3b. If such a condition occurs, the diaphragm 170 will become indented prior to actuation of the diaphragm 170, and the inflow amount of the liquid LB will be less than the intended amount.

In order to avoid such adverse effects, a correcting step for the purpose of correcting the position of the displacing member 17 is executed during switchover from the suctioning step to the discharging step, and during switchover from the discharging step to the suctioning step. During switchover from the suctioning step to the discharging step, the displacing member 17 undergoes displacement to a slight extent in the direction for reducing the internal volume of the pump chamber 2, whereas during switchover from the discharging step to the suctioning step the displacing member 17 undergoes displacement to a slight extent in the direction for increasing the internal volume of the pump chamber 2.

Turning now to a more detailed description, as shown in FIG. 2A, during time t10 to time t11 after completion of intake and prior to initiating discharge, power is supplied to the stepping motor 12, which rotates in the counterclockwise direction, displacing the displacing member 17 in the direction of decreasing the internal volume of the pump chamber 2. Conversely, during time t17 to time t18 after completion of discharge and prior to initiating intake, power is supplied to the stepping motor 12 which rotates in the clockwise direction, displacing the displacing member 17 in the direction of increasing the internal volume of the pump chamber 2.

In this correcting step, the valves 5a, 5b, 6a, 6b and the displacing member 17 can be actuated under control by the control unit 18, in accordance with preestablished conditions.

It is also possible to employ a method wherein during changeover from intake to discharge, and during changeover from discharge to intake, the pressure difference between locations to either side of the valves 5b, 6a that switch from the open state to the closed state is monitored either directly or indirectly; and during the correcting step, based on the monitoring results, the displacing member 17 is displaced in the direction eliminating the pressure difference.

Direct monitoring of the pressure difference between locations to either side of the valves 5b, 6a may be accomplished by positioning pressure sensors in the pump chamber 2, at a location in the inflow passage 3b to the outside of the valve 5b, and at a location in the outflow passage 4a to the outside of the valve 6a, and detecting pressure difference on the basis of detection results of these pressure sensors. Indirect monitoring of the pressure difference between locations to either side of the valves 5b, 6a may be accomplished by measuring the height location of the outflow port 40a of the outflow passage 4a, and monitoring the level of the second liquid LB shown in FIG. 3D.

In the mixing pump device 1 discussed above, when the stepping motor 12 turns in a first direction the displacing member 17 undergoes displacement in the direction for increasing the internal volume of the pump chamber 2, and when the stepping motor 12 turns in the opposite direction, the displacing member 17 undergoes displacement in the direction for reducing the internal volume of the pump chamber 2. Consequently, irrespective of the position of the displacing member 17, during the interval that the stepping motor 12 is turning in the first direction, a plurality of fluids can be suctioned into the pump chamber 2 in prescribed proportions simply by closing the active valves 6a, 6b positioned on the outflow passages 4a, 4b, and sequentially opening and closing the active valves 5a, 5b positioned on the inflow passages 3a, 3b. Then, during the interval that the stepping motor 12 is turning in the opposite direction, the mixed fluid can be discharged from the pump chamber 2 simply by closing the active valves 5a, 5b positioned on the inflow passages 3a, 3b, and opening one or both of the active valves 6a, 6b positioned on the outflow passages 4a, 4b. Thus, unlike a mechanism which transmits rotation of the stepping motor 12 to the displacing member 17 via a cam mechanism, there is no need to monitor cam position with a photointerrupter or the like. It is therefore possible to simplify the design of the mixing pump device 1, and make it smaller and less expensive.

It is a simple matter to modify the extent of displacement stroke of the displacing member 17 by varying the signal pattern presented to the stepping motor 12. A resultant advantage is that the extent of displacement stroke of the displacing member 17 can be set appropriately depending on the type of liquids being used.

The control unit 18 controls opening and closing of the active valves 5a, 5b, 6a, 6b in such a way that, of the first liquid LA and the second liquid LB which inflow from the inflow passages 3a, 3b, a portion of the second liquid LB having the larger mixture proportion flows into the pump chamber 2 prior to suctioning in the first liquid LA having the smaller mixture proportion. It is therefore possible to prevent the first liquid LA from becoming unevenly distributed in a corner of the pump chamber 2, e.g. in proximity to the active valve 5a, so as to achieve thorough mixing of the first liquid LA and the second liquid LB. In particular, more thorough mixing of the first liquid LA and the second liquid LB can be achieved because an amount equivalent to one-half of the total amount of the second liquid LB having the larger mixture proportion is suctioned into the pump chamber 2, then the first liquid LA having the smaller mixture proportion is suctioned into the pump chamber 2, and finally the remaining one-half of the second liquid LB is suctioned into the pump chamber 2.

The correcting step is executed during the interval from time t10 to time t11, and during the interval from time t17 to time t18. Even where the displacing member 17 has reached top dead center or bottom dead center, it will return from the top dead center or bottom dead center and perform intake or discharge. Accuracy of the intake amount and discharge amount is accordingly high. Particularly where the displacing member 17 is a diaphragm, during switchover from the discharging step to the suctioning step, or during switchover from the suctioning step to the discharging step, there is a tendency for displacement to occur in a non-responsive condition in which the internal volume of the pump chamber does not change despite deformation of the diaphragm, and for there to be variation in the intake amount and discharge amount. By interposing the correcting step, such variability can be eliminated.

Furthermore, where a diaphragm is employed as the displacing member 17, a pressure differential between the internal pressure of the pump chamber 2 and atmospheric pressure can produce unwanted deformation of the diaphragm. Since intake and discharge are carried out after correcting such deformation by executing the correcting step, accuracy of the intake amount and discharge amount is high.

[Specific Configuration Example of the Mixing Pump Device]

Next, a specific configuration example of a mixing pump device embodying the present invention will be described.

First, the basic design of the mixing pump device to be discussed hereinbelow shall be described with reference to FIG. 4 in order to reduce the level of complexity. Since the basic design of the mixing pump device of the present example is the same as that of the mixing pump 1 depicted in FIG. 1, corresponding parts have been assigned identical symbols in the drawing.

As shown in FIG. 4, the pump device main unit 7 of the mixing pump device 1A of the present example has a pump chamber 2, two inflow passages 3a, 3b communicating with the pump chamber 2, and six outflow passages 4a through 4f communicating with the pump chamber 2. The two inflow passages 3a, 3b and the six outflow passages 4a through 4f communicate mutually independently with the pump chamber 2. Inflow-side active valves 5a, 5b are positioned respectively on the two inflow passages 3a, 3b. Outflow-side active valves 6a through 6f are positioned respectively on the six outflow passages 4a through 4f.

The pump drive mechanism 13 has a diaphragm 170 that defines a portion of the inside peripheral surface of the pump chamber 2; a drive unit 105 equipped with a stepping motor 12 for displacing this diaphragm 170; and a control unit 18 for controlling opening and closing of the inflow-side active valves 5a, 5b and the outflow-side active valves 6a through 6f.

Next, FIG. 5A and FIG. 5B are respectively a perspective view and a plan view of the mixing pump device 1A. FIG. 6 is an exploded perspective view thereof; and

FIG. 7 is a descriptive diagram showing the configuration thereof in cross section.

Reference to these drawings is made in the description provided hereunder. The mixing pump device 1A has pipes defining intake ports 30a, 30b and discharge ports 40a through 40f connected to one face 71 of the pump device main unit 7 which is in the shape of a box. The pump device main unit 7 has a stacked structure composed, in order, of a circuit board 74 for the pump drive mechanism 13 and the active valves 5a, 5b, 6a through 6f; a bottom plate 75; a base plate 76; a flow passage formation plate 77 having formed thereon flow passages of channel shape to be described later; a sealing sheet 78 for sealing off the upper sides of the flow passages via covering the upper face of the flow passage formation plate; and an upper plate 79 to which the aforementioned pipes are connected.

Holes 137, 67a through 67h providing installation spaces for the pump drive mechanism 13 and for the active valves 5a, 5b, and 6a through 6f are formed in the base plate 76. A round through-hole 21 constituting the pump chamber 2 is formed at a central location in the flow passage formation plate 77; and around this through-hole 21, on the lower face of the flow passage formation plate 77, are formed recesses (not shown) constituting the valve chambers of the active valves 5a, 5b, 6a through 6f Eight channels 41a through 41h extend radially out from the through-hole 21. Additional channels 42a, 42b . . . , etc. are formed in proximity to the channels 41a through 41h of the flow passage formation plate 77.

The inflow passages 3a, 3b and the outflow passages 4a through 4f are formed by the eight channels 41a through 41h. Specifically, when the base plate 76, the flow passage formation plate 77, and the sealing sheet 78 are stacked, the inflow passages 3a, 3b and the outflow passages 4a through 4f are formed by the channels 41a through 41f, 42a, 42b . . . ; and the inflow-side active valves 5a, 5b and the outflow-side active valves 6a through 6f are positioned in the individual inflow passages 3a, 3b and outflow passages 4a through 4f.

Since the active valves 5a, 5b, 6a through 6f are positioned in a plane around the pump chamber 2, the flow passages in the individual inflow passages 3a, 3b and the outflow passages 4a through 4f are short, and the mixing pump device 1A can have a thin profile. Additionally, since variation in the amount discharged from the outflow passages 4a through 4f can be minimized, fluids can be discharged accurately in the proper amounts. Moreover, the length of the flow passage from the pump chamber 2 to the outflow-side active valves 6a through 6f is the same in each of the plurality of outflow passages 4a through 4f. Thus, outflow amounts via the outflow passages 4a through 4f can be controlled with high accuracy. Furthermore, since the inflow ports 30a, 30b and the outflow ports 40a through 40f open onto the same surface 71 of the pump device main unit 7, external connection of the mixing pump device 1A is a simple matter. Moreover, since the pump device main unit 7 is furnished with a flow passage formation plate 77 having inflow passages 3a, 3b and outflow passages 4a through 4f formed in the shape of a channel on one face thereof, and with a sealing sheet 78 that is positioned juxtaposed against this one face, a multitude of flow passages can be formed in a compact pump device main unit 7, and the mixing pump device 1A can be manufactured efficiently as well.

Furthermore, the two inflow passages 3a, 3b and the six outflow passages 4a through 4f have mutually identical design; and the inflow-side active valves 5a, 5b and the outflow-side active valves 6a through 6f have mutually identical design. Consequently, any of the inflow passages 3a, 3b and the outflow passages 4a through 4f can be utilized as the inflow passages 3a, 3b or the outflow passages 4a through 4f. Consequently, [the mixing pump device] is not limited to two types of liquid, but can be used to mix and discharge three or more types of liquid.

(Detailed Design of the Pump Drive Mechanism)

The pump drive mechanism 13 which is incorporated into the mixing pump device 1A will be described with reference to FIGS. 8 to 11. FIG. 8 is an exploded perspective view of the mixing pump device 1A, shown divided on the vertical. FIG. 9A and FIG. 9B are [respectively] a descriptive diagram of the pump chamber in the expanded state, and the pump chamber in the contracted state. FIGS. 10A to 10C are respectively a perspective view, a plan view, and a sectional view of a rotor employing the rotating body of the pump mechanism shown in FIG. 8. FIGS. 11A to 11C are respectively a perspective view, a plan view, and a sectional view of a moving body employing the rotating body of the pump mechanism shown in FIG. 8.

As shown in FIGS. 8 and 9A, the pump drive mechanism 13 is furnished generally with a diaphragm 170 that functions as the displacing member for taking in and discharging liquid by expanding and contracting the pump chamber 2 communicating with the inflow passages 3a, 3b and the outflow passages 4a through 4f; and a drive unit 105 for driving the diaphragm 170.

The drive unit 105 is furnished with an annular stator 120; a rotating body 103 disposed coaxially to the inside of this stator 120; a moving body 160 disposed coaxially to the inside of this rotating body 103; and a conversion mechanism 140 for converting rotation of the rotating body 103 to motion of the moving body 160 in the axial direction. The drive unit 105 is installed between the bottom plate 75 and the base plate 76, within a space formed in the base plate 76.

The stator 120 has a structure including a two-level stack of units each composed of a coil 121 wound around a bobbin 123, and a pair of yokes 125 positioned so as to cover the coil. In the each of two units in the upper and lower levels, the pole teeth which project in the axial direction from the inside peripheral edges of the pair of yokes 125 are arrayed in alternating fashion in the circumferential direction.

As shown in FIGS. 8, 9 and 10A through 10C, the rotating body 103 has a cup-shaped member 130 open at the top, and an annular rotor magnet 150 attached to the outside peripheral face of a cylindrical-shaped rotating body 103 drum portion 131 of the cup-shaped member 130. In the center of the floor 133 of the cup-shaped member 130 there is formed a recess 135 recessed upwardly in the axial direction; on the bottom plate 75 there is formed a bearing portion 751 adapted to receive a ball 118 that is positioned within the recess 135. An annular shoulder portion 766 is formed on the inside rim of the upper edge of the base plate 76. At the upper end portion of the cup-shaped member 130, an annular shoulder portion which faces towards the annular shoulder portion 766 on the base plate 76 is formed by the upper edge of the drum portion 131 and an annular flange 134. The annular space defined by these annular shoulder portions accommodates a bearing 180 which is composed of an annular retainer 181 and ball bearings 182 held at locations spaced apart in the circumferential direction by the retainer 181. In this way, the rotating body 103 is supported rotatably about the axis on the pump device main unit 7.

The outside peripheral face of the rotor magnet 150 faces towards the pole teeth which are lined up in the circumferential direction along the inside peripheral face of the stator 120. On the outside peripheral face of the rotor magnet 150, S poles and N poles are lined up in alternating fashion in the circumferential direction, with the stator 120 and the cup-shaped member 130 constituting the stepping motor.

As shown in FIGS. 8, 9, and 11A through 11C, the moving body 160 has a floor 161, a cylindrical portion 163 projecting out in the axial direction from the center of the floor 161, and a drum portion 165 of cylindrical shape formed so as to surround this cylindrical portion 163; a male thread 167 is formed on the outside periphery of the drum portion 165.

In order to constitute the conversion mechanism 140 for bringing about reciprocating movement of the moving body 160 in the axial direction by means of rotation of the rotating body 103, as shown in FIGS. 8, 9, 10A through 10C, and 11A through 11C, a female thread 137 is formed at four locations spaced apart in the circumferential direction, on the inside peripheral face of the drum portion 165 of the cup-shaped member 130. The male thread 167, which engages with the female thread 137 and constitutes a power transmission mechanism 141, is formed on the outside peripheral face of the drum portion 165 of the moving body 160. Consequently, the moving body 160 is supported to the inside of the cup-shaped member 130, with the moving body 160 positioned to the inside of the cup-shaped member 130 so that the male thread 167 meshes with the female thread 137.

On the floor 161 of the moving body 160 there are formed through-holes constituting six slots 169 along the circumferential direction; meanwhile, six projections 769 extend from the base plate 76, with the lower ends of the projections 769 fitting into the slots 169 and constituting a co-rotation preventing mechanism 149. Specifically, during rotation of the cup-shaped member 130, the moving body 160 is prevented from rotating by the co-rotation preventing mechanism 149 composed of the projections 769 and the slots 169; therefore, rotation of the cup-shaped member 130 will be transmitted to the moving body 160 via the power transmission mechanism 141 composed of the female thread 137 and the male thread 167 of the moving body 160, as a result of which the moving body 161 undergoes linear movement to one side or the other in the axial direction, depending on the direction of rotation of the rotating body 103.

(Configuration of Displacing Member)

Referring back to FIGS. 8 and 9A, the diaphragm 170 is linked directly to the moving body 160. The diaphragm 170, which is cup-shaped, has a floor 171; a drum portion 173 of cylindrical shape rising up in the axial direction from the outside peripheral edge of the floor 171; and a flange portion 175 spreading towards the outside periphery from the upper end of this drum portion 173. The diaphragm, with the center portion of the floor 171 thereof covering the cylindrical portion 163 of the moving body 160, is secured in place from above and below by a fastening screw 178 and a cap 179. The outside peripheral edge of the flange portion 175 of the diaphragm 170 is constituted by a thick section, which is adapted to ensure liquid-tightness, and also functions as a positioning section. The thick section is secured in place between the base plate 76 and the flow passage formation plate 77, around the through-hole 21 of the flow passage formation plate 77. In this way, the diaphragm 170 defines the lower face of the pump chamber 2, and assures liquid-tightness between the base plate 76 and the flow passage formation plate 77 around the pump chamber 2.

The drum portion 173 of the diaphragm 170 doubles back in a U shaped cross section, with the doubled back portion 172 thereof changing shape depending on the position of the moving body 160. The doubled back portion 172 having a U shaped cross section of the diaphragm 170 is positioned within a space of annular shape defined between a first wall face 168 composed of the outside peripheral face of the cylindrical portion 163 of the moving body, and a second wall face 768 composed of the inside peripheral faces of the projections 769 extended from the base plate 76. Consequently, with the diaphragm in any of the states shown in FIG. 9A or 9B, or during the process of moving between the states shown in these drawings, the doubled back portion 172 of diaphragm 170, while remaining retained within the annular space, undergoes deformation so as to expand or roll up along the first wall face 168 and the second wall face 768.

As shown in FIGS. 8, 9A, and 10A through 10C, a single groove 136 is formed on the floor 133 of the cup-shaped member 130 over an angular range of 270° in the circumferential direction, while a projection 166 is formed facing downward from the bottom face of the moving body 160. Here, the moving body 160 does not rotate about the axis but does move in the axial direction, while the rotating body 103 does rotate about the axis but does not move in the axial direction. Consequently, the projection 166 and the groove 136 function as a stopper for regulating the stop position of the rotating body 103 and the moving body 160. Specifically, the groove 136 changes in depth in the circumferential direction; as the moving body 160 moves downward in the axial direction the projection 166 will engage within the groove 136, and upon rotation of the rotating body 103, the edge of the groove 136 will come into abutment with the projection 166. As a result, the rotating body 103 will be prevented from rotating, thus regulating the stop position of the rotating body 103 and the moving body 160, i.e. the position of maximum expansion of the internal volume of the diaphragm 170.

(Operation of the Pump Drive Mechanism)

In the pump drive mechanism 13 of such a design, when power is supplied to the coil 121 of the stator 120, the cup-shaped member 130 rotates, and this rotation is transmitted to the moving body 160 via the conversion mechanism 140. Consequently, the moving body 160 undergoes linear reciprocating motion in the axial direction. As a result, the diaphragm 170 deforms in association with the motion of the moving body 160, causing the pump chamber 2 to expand or contract, whereby the inflow of liquid from the inflow passages 3a, 3b and the discharging of liquid to the outflow passages 4a through 4f take place in the pump chamber 2. During this time, the doubled back portion 172 of diaphragm 170, while remaining retained within the annular space, undergoes deformation so as to expand or roll up along the first wall face 168 and the second wall face 768, so no unnecessary sliding motion occurs. Moreover, even if the diaphragm 170 is subjected to pressure from the fluid in the pump chamber 2, the diaphragm is restricted both inside and out within the annular space, and thus will not deform. Furthermore, the lower position of the moving body 160 is restricted by the stopper composed of the groove 136 of the cup-shaped member 130 and the projection 166 of the moving body 160. Thus, the diaphragm 170 undergoes displacement with high accuracy, in association with the rotation of the cup-shaped member 130. In the drive unit 105, when the stepping motor rotates in one direction, the diaphragm 170 is displaced the direction of increasing the internal volume of the pump chamber 2; and when the stepping motor rotates in the other direction, the diaphragm 170 is displaced the direction of decreasing the internal volume of the pump chamber 2.

As discussed above, in the pump drive mechanism 13, rotation of the rotating body 103 by the stepping motor mechanism is transmitted to the moving body 160 via the conversion mechanism 140 which utilizes the power transmission mechanism 141 composed of the male thread 167 and the female thread 137, causing the moving body 160 to which the diaphragm 170 is fastened to undergo reciprocating linear motion. Thus, power is transmitted from the drive unit 105 to the diaphragm 170 by the minimum number of components needed to do so, whereby the pump drive mechanism 13 can be made smaller, thinner, and less expensive. Moreover, by giving the male thread 167 and the female thread 137 in the power transmission mechanism 141a smaller lead angle, or by increasing the number of pole teeth of the stator on the drive end, it is possible for the moving body 160 to be advanced in very small increments. Consequently, the volume of the pump chamber 2 can be finely controlled, so metered discharge can be carried out with high accuracy.

Furthermore, the doubled back portion 172 of diaphragm 170, while remaining retained within the annular space, undergoes deformation so as to expand or roll up along the first wall face 168 and the second wall face 768, so no unnecessary sliding motion occurs. Consequently, no unnecessary load is produced, and the diaphragm 170 will have a longer life. Moreover, even if the diaphragm 170 is subjected to pressure from the fluid in the pump chamber 2, it will not deform. Therefore, the pump drive mechanism 13 can carry out metered discharge with high accuracy, and reliability is high as well.

Moreover, since the rotating body 103 is rotatably supported about the axis on the pump device main unit 7 via the ball bearings 182, sliding loss is minimal, and the rotating body 103 is held stably in the axial direction, stabilizing the thrust in the axial direction. It is therefore possible to make the drive unit 105 smaller, improve durability, and improve discharging ability.

While threads were employed for the power transmission mechanism 141 of the conversion mechanism 140, it is also possible to employ a cam mechanism instead. Furthermore, while a cup-shaped diaphragm has been used, a diaphragm of some other shape, or a piston equipped with an O-ring, can be used instead.

The numbers of intake ports and discharge ports may be different from those described hereinabove. Furthermore, while the sealing sheet 78 for sealing off the upper face and the upper plate 79 to which the pipes are connected are formed by separate components, an arrangement that dispensed with the pipes of the upper plate 79 and provides only outflow holes to the sealing sheet 78, for connection via seal members would also be possible.

(Configuration of Active Valves)

FIGS. 12 and 13 are, respectively, a descriptive diagram of the principal parts of a valve used for the active valves 5a, 5b and the active valves 6a through 6f of the mixing pump device 1A, shown cut along the axis and viewed from diagonally above; and a descriptive diagram of the lines of magnetic force thereof.

As shown in the drawings, the active valves 5a, 5b (hereinafter denoted as active valves 5) and the active valves 6a through 6f (hereinafter denoted as active valves 6) are provided with a linear actuator 201 positioned in the holes 57, 67a through 67h of the base plate 76; this linear actuator 201 has a stationary body 203 having a cylindrical shape, and a moveable body 205 having a round rod shape positioned inside the stationary body 203. The stationary body 203 has a coil 233 wound in annular configuration onto a bobbin 231; and a stationary body yoke 235 running around both sides of the coil in the axial direction from the outside peripheral face of the coil 233, with one distal edge 236a and the other distal edge 236b thereof facing in the axial direction across a slit 237, to the inside peripheral side of the coil 233. The movable body 205 has a first movable body yoke 251 having a disk shape, and a pair of magnets 253a, 253b stacked on either side of the first movable body yoke 251 in the axial direction. For the pair of magnets 253a, 253b it is possible to use Nd—Fe—B or Sm—Co rare earth magnets, or resin magnets. In the movable body 205, a second movable body yoke 255a, 255b is stacked on each of the pair of magnets 253a, 253b, on the end face thereof on the opposite side from the first movable body yoke 251.

The pair of magnets 253a, 253b are each magnetized in the axial direction, and oriented with the same pole facing the direction of the first movable body yoke 251. Here, the pair of magnets 253a, 253b are described as oriented with the N pole of each facing the direction of the first movable body yoke 251, and the S pole of each facing towards the outside in the axial direction; however, the direction of magnetization could be reversed.

The outside peripheral face of the first movable body yoke 251 protrudes out beyond the outside peripheral faces of the pair of magnets 253a, 253b. Likewise, the outside peripheral faces of the second movable body yokes 255a, 255b protrude out beyond the outside peripheral faces of the pair of magnets 253a, 253b.

Recesses are formed in each axial end of the first movable body yoke 251, and the pair of magnets 253a, 253b are fitted respectively into these recesses and secured there with adhesive or the like. It is acceptable to employ any arrangement in which the first movable body yoke 251, the pair of magnets 253a, 253b, and the second movable body yokes 255a, 255b are fastened through unification by an adhesive, press-fitting, or a combination of these.

Bearing plates 271a, 271b (bearing members) are fastened in openings at either axial end of the stationary body 203, and spindles 257a, 257b which project out to either side in the axial direction from the second movable body yokes 255a, 255b are each slidably inserted into holes in the bearing plates 271a, 271b. In this way, the movable body 205 is supported on the stationary body 203 so as to be capable of reciprocating motion in the axial direction. In this state, the movable body 205 faces the inside peripheral face of the stationary body 203 across a prescribed gap, with the distal edges 236a, 236b of the stationary body yoke 235 facing one another in the axial direction within the gap between the outside peripheral face first movable body yoke 251 and the inside peripheral face of the coil 233. A gap is maintained between the moveable body 205 and the stationary body yoke 235 as well. It is acceptable to employ any arrangement in which the second movable body yokes 255a, 255b and the spindles 257a, 257b are fastened through unification by an adhesive, press-fitting, or a combination of these.

In the linear actuator 201 of the design described above, for the period that electrical current, on the right side when facing the drawing, is flowing through the coil 233 towards the viewer from the far side and, on the left side facing the drawing, is flowing away from the viewer and towards the far side, the lines of magnetic force will be as depicted in FIG. 13. Accordingly, the moveable body 5 is first subjected to thrust and moves in the axial direction due to Lorentz force, as indicated by arrow A. On the other hand, when the direction of current through the coil 233 reverses, the moveable body 205 will descend along the axial direction as indicated by arrow B.

In the linear actuator 201, the moveable body 205 is propelled by magnetic force, and a frustoconically shaped coil spring 291 is positioned as an urging member between the bearing plate 271a and the second movable body yoke 255a, on one side in the axial direction. Consequently, the moveable body 205 descends while deforming the compression spring; and as the moveable body 205 moves at high speed when ascending, assisted by the shape recovery force of the compression spring.

In the linear actuator 201 designed in this manner, the center portion of a diaphragm valve 260 positioned in the valve chamber 270 (recess 68a through 68h) is connected to the end of one of the spindles 257b. An annular thick section 261 providing liquid-tightness and a positioning function is formed on the outside periphery of the diaphragm 260; the outside peripheral section of the diaphragm 260 including this annular thick section 261 is held between the base plate 76 and the flow passage formation plate 77, ensuring liquid-tightness.

The displacing member is not limited to a diaphragm 260, it being possible to employ a bellows valve or some other valve instead. An arrangement in which the spindles 257a, 257b and the displacing member are separate components connected together, or an arrangement in which the spindles 257a, 257b and the displacing member are formed integrally, is acceptable.

As discussed above, the pair of magnets 253a, 253b in the moveable body 205 are oriented with identical poles facing one another, producing magnetic repulsive force, but since the first movable body yoke 251 is positioned between the magnets 253a, 253b, the pair of magnets 253a, 253b can be secured oriented with identical poles facing one another.

Also, since the pair of magnets 253a, 253b in the moveable body 205[are oriented] with identical poles facing the first movable body yoke 251, strong magnetic flux is generated in the radial direction from the first movable body yoke 251. Accordingly, where the peripheral faces of the first movable body yoke 251 and the coil 233 are juxtaposed, the moveable body 205 can be imparted with strong thrust.

Since the magnets 253a, 253b need only be magnetized in the axial direction, in contrast to the case where the magnets 253a, 253b are magnetized in the radial direction, magnetization is a simple matter even where the magnets are small, which is suitable for mass production purposes.

Moreover, since the outside peripheral face of the first movable body yoke 251 protrudes out beyond the outside peripheral faces of the pair of magnets 253a, 253b, the magnetic attracting force acting in the axial direction and the perpendicular direction on the moveable body 205 can be minimized, even if the stationary body yoke 235 is provided. Similarly, since the outside peripheral faces of the second movable body yokes 255a, 255b protrude out beyond the outside peripheral faces of the pair of magnets 253a, 253b, the magnetic attracting force acting in the axial direction and the perpendicular direction on the moveable body 205 can be minimized, even when the stationary body yoke 235 is provided. The assembly operation is facilitated and the moveable body resists tilting, which are advantages obtained as a result.

Since the magnets 253a, 253b are positioned at the outside periphery side in the coil 33, the magnets 253a, 253b can be smaller, and the active valves 5, 6 may be designed less expensively, as compared to when the magnets 253a, 253b are positioned outwardly from the coil 233. Also, since the coil 233 is positioned to the outside, the magnetic path can be closed with the stationary yoke only.

Furthermore, in the stationary body 203, since the bearing plates 271a, 271b for supporting the spindles 257a, 257b so as to be moveable in the axial direction are held in openings that open in the axial direction, there is no need for separate bearing members. An additional advantage is that since the bearing plates 271a, 271b can be secured on the basis of the stationary body 203, the spindles 257a, 257b will not tilt.

[Applications of the Mixing Pump Device]

The mixing pump device embodying the present invention can be used, for example, for a direct methanol fuel cell (hereinafter DMFC) that takes protons directly from methanol in order to generate electricity. This kind of DMFC has a generating unit having a electromotive portion (cell), and a liquid feed pump for pumping a methanol aqueous solution. The cell is composed of an anode (fuel electrode) having an anode collector and an anode catalyst layer; a cathode (air electrode) having a cathode collector and a cathode catalyst layer; and an electrolyte membrane positioned between the anode and the cathode. The methanol aqueous solution is delivered to the anode by the liquid feed pump, while air is delivered to the cathode by an air pump or blower.

Accordingly, by employing the mixing pump device embodying the present invention as the liquid feed pump, it is possible to appropriately mix methanol with water, methanol with a methanol aqueous solution, a methanol aqueous solution with methanol, or a methanol aqueous solution with another methanol aqueous solution, and to supply the cell with a methanol aqueous solution of adjusted methanol concentration. At the anode of the cell, which is the electromotive portion of the DMFC, methanol oxidation activity is low, with associated voltage loss. Voltage loss occurs at the cathode as well. Thus, the output drawn from a single cell is very low, so the DMFC employs a plurality of cells in order to generate a prescribed output. In such instances as well, the mixing pump device 1A embodying the present invention can be used to deliver methanol aqueous solution of adjusted methanol concentration to each cell.

Applications of the mixing pump device embodying the present invention are not limited to fuel cells. The mixing pump device can be used as a pump for blending a plurality of chemical solutions in order to blend a compound chemical. It can also be used as a refrigerator icemaker pump, for discharging from outflow paths sherbets of different color and flavor for each icemaker block.

OTHER EMBODIMENTS

While the preceding embodiment focused on the example of using a diaphragm 170 as the displacing member 17, the invention can instead be embodied in a mixing pump device of a type using a plunger as the displacing member. Also, while the preceding embodiment was an example designed with a plurality of outflow passages, the invention can instead be embodied in a mixing pump device having a single outflow passage.

In the preceding embodiment, the invention was embodied in a mixing pump device, but the invention can also be embodiment in a metering pump for discharging a single type of liquid.

Claims

1. A method for driving a pump device, comprising:

a suctioning step for suctioning a fluid into a pump chamber from an intake port by inducing displacement of a displacing member that defines part of an inside peripheral surface of the pump chamber in the direction of increasing internal volume of the pump chamber, with the discharge port of the pump chamber closed and the intake port open;

a discharging step for discharging the fluid from the pump chamber by inducing displacement of the displacing member in the direction of decreasing internal volume of the pump chamber, with the discharge port open and the intake port closed; and

a correcting step for inducing displacement of the displacing member with both the intake port and the discharge port of the pump chamber closed;

wherein the steps are carried out in the order of suctioning, correcting, and discharging; or in the order of discharging, correcting, and suctioning.

2. The method for driving a pump device of claim 1 wherein the suctioning and discharging steps are performed alternatingly, with the correcting step therebetween.

3. The method for driving a pump device of claim 1 wherein

the displacing member is subjected to a displacing movement in the direction for reducing the internal volume of the pump chamber in the correcting step executed between the suctioning and discharging steps; and

the displacing member is subjected to a displacing movement in the direction for increasing the internal volume of the pump chamber in the correcting step executed between the discharging and suctioning steps.

4. The method for driving a pump device of claim 1 wherein

the displacing member is subjected to a displacing movement so as to eliminate the difference between an internal pressure of the pump chamber and a pressure on the fluid discharge flow passage communicating with the discharge port in the correcting step executed between the suctioning and discharging steps; and

the displacing member is subjected to a displacing movement so as to eliminate the difference between the internal pressure of the pump chamber and the pressure on the fluid intake flow passage communicating with the intake port in the correcting step executed between the discharging and suctioning steps.

5. The method for driving a pump device of claim 4 wherein

the difference between the internal pressure of the pump chamber and the pressure in the fluid discharge flow passage communicating with the discharge port is monitored, and the displacing member is displaced on the basis of the results of the monitoring in the correcting step executed between the suctioning and discharging steps; and

the difference between the internal pressure of the pump chamber and the pressure on the fluid intake flow passage communicating with the intake port is monitored, and the displacing member is displaced on the basis of the results of the monitoring in the correcting step executed between the discharging and suctioning steps.

6. The method for driving a pump device of claim 4 wherein

during the correcting step, the displacing member is displaced in accordance with a predetermined condition.

7. The method for driving a pump device of claim 1 wherein

a plurality of the intake ports are formed in the pump chamber; and

during the suctioning step, a suctioning operation involving sequentially opening the closed plurality of intake ports and drawing in fluid is performed repeatedly, forming a mixed fluid in which the different types of fluids are mixed in predetermined proportions.

8. The method for driving a pump device of claim 7 wherein

before the fluid with the smallest mixture ratio is taken into the pump chamber, at least some fluid having a larger mixture proportion than the aforementioned fluid is taken into the pump chamber.

9. The method for driving a pump device of claim 1 wherein

a plurality of the discharge ports are formed in the pump chamber; and

the closed plurality of discharge ports are opened sequentially and the fluid is discharged during the discharging step.

10. The method for driving a pump device of claim 1 wherein

the displacing member is a diaphragm.