Method for driving a pump device

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.

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.

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.

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.