Apparatus for and method of supplying liquid

A liquid supply apparatus includes a reservoir for storing a liquid therein, a supply path for supplying the liquid from the reservoir to a liquid consuming apparatus, a pump for feeding the liquid from the reservoir to the supply path, and a controller for outputting a driving signal to the pump to control the supply of the liquid. The controller acquires a target feed volume of the liquid from the pump to gradually change a feed volume of the liquid from the pump from a current feed volume to the target feed volume, based on a request signal from the liquid consuming apparatus serving as a destination to which the liquid is supplied. This suppresses an abrupt change in pressure in the liquid consuming apparatus serving as the destination to which the liquid is supplied.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an apparatus for and a method of supplying a liquid.

2. Description of the Background Art

A liquid supply apparatus for supplying a liquid through a liquid feed pipe has been hitherto known. A known example of the liquid supply apparatus includes an ink supply apparatus in which ink is supplied from an ink cartridge through a liquid feed tube to a head tank for supplying ink directly to an ink ejection head.

An inkjet recording apparatus including a conventional ink supply apparatus is disclosed, for example, in Japanese Patent Application Laid-Open No. 2011-189701. The inkjet recording apparatus disclosed in Japanese Patent Application Laid-Open No. 2011-189701 includes droplet ejection heads for ejecting ink, head tanks for supplying ink directly to the droplet ejection heads, ink cartridges for adding and supplying ink to the head tanks, and supply tubes for supplying ink from the ink cartridges to the head tanks (in paragraphs 0015 and 0031).

In such an inkjet recording apparatus, the ejection of appropriate amounts of ink droplets from the droplet ejection heads necessitates the adjustment of the pressure of ink in nozzles of the droplet ejection heads to within an appropriate range. The droplet ejection heads, on the other hand, are susceptible to the internal pressure in the head tanks (in paragraph 0003).

In such an ink supply apparatus for supplying ink from the ink cartridges to the head tanks, an abrupt change in ink supply volume causes an abrupt change in internal pressure in the head tanks. As a result, appropriate amounts of ink droplets cannot be ejected from the droplet ejection heads.

In particular, there are cases where a high-power pump is used for supply of ink in a large-scale inkjet printing machine which consumes a large amount of ink. Thus, large vibrations occur in some cases when the pump is turned on or off or when the output of the pump is changed. This results in apprehension that an abrupt change in internal pressure in the droplet ejection heads or the head tanks occurs to influence printing quality.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention to provide an apparatus for and a method of supplying a liquid which are capable of suppressing an abrupt change in pressure in a destination to which the liquid is supplied.

A first aspect of the present invention is intended for a liquid supply apparatus for supplying a liquid to at least one liquid consuming apparatus. The liquid supply apparatus comprises: a reservoir for storing a liquid therein; a supply path for supplying the liquid from the reservoir to the liquid consuming apparatus; a pump for feeding the liquid from the reservoir to the supply path; and a controller for outputting a driving signal to the pump to control the supply of the liquid, the controller acquiring a target feed volume of the liquid from the pump to gradually change a feed volume of the liquid from the pump from a current feed volume to the target feed volume, based on a request signal from the liquid consuming apparatus.

According to the first aspect of the present invention, the liquid supply apparatus is capable of suppressing an abrupt change in pressure in the liquid consuming apparatus serving as the destination to which the liquid is supplied.

A second aspect of the present invention is intended for a method of supplying a liquid to a liquid consuming apparatus. The method comprising the steps of: a) providing a request signal from the liquid consuming apparatus to a controller which controls a pump for feeding a liquid stored in a reservoir to the liquid consuming apparatus; b) providing a target feed volume of the liquid from the pump, to the controller, based on the request signal; and c) outputting a driving signal from the controller to the pump, the driving signal gradually changing a feed volume of the liquid from the pump from a current feed volume to the target feed volume.

According to the second aspect of the present invention, the method is capable of suppressing an abrupt change in pressure in the liquid consuming apparatus which is a destination to which the liquid is supplied.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

1. Liquid Supply Apparatus According to One Preferred Embodiment

<1-1. Configuration of Liquid Supply Apparatus>

FIG. 1is a diagram showing a configuration of a liquid supply apparatus1according to one preferred embodiment of the present invention.FIG. 2is a block diagram showing a main control mechanism in the liquid supply apparatus1. The liquid supply apparatus1is an apparatus for supplying ink from at least one ink tank8to at least one printer9that is an inkjet printing machine. The “liquid” which the liquid supply apparatus1according to the present preferred embodiment supplies is ink.

In the liquid supply apparatus1according to the present preferred embodiment, ink is supplied from two ink tanks8which are more specifically referred to as a first ink tank81and a second ink tank82. In the liquid supply apparatus1according to the present preferred embodiment, ink is supplied to two printers9which are more specifically referred to as a first printer91and a second printer92. In the present preferred embodiment, the at least one ink tank8serves as a “supply tank” and the at least one printer9serves as a “liquid consuming apparatus”. The number of ink tanks8may be one or greater than two. Likewise, the number of printers9may be one or greater than two.

The liquid supply apparatus1includes a counting tank21, an intermediate tank22, a filter23, a deaeration module24, a suction pump31, and a supply pump32. As shown inFIG. 1, the aforementioned components21,22,23,24,31and32are connected through pipes41to43. The counting tank21, the intermediate tank22, the deaeration module24, the suction pump31and the supply pump32are controlled by a controller10.

The counting tank21is a container which measures the volume of ink supply from the at least one ink tank8to the intermediate tank22to thereby manage the feed volume of ink. The counting tank21includes a low liquid level sensor211and a high liquid level sensor212both of which sense the liquid level of ink stored in the counting tank21. The low liquid level sensor211senses whether the liquid level of ink in the counting tank21is higher than a predetermined first vertical position or not. The first vertical position is a position higher than an ink discharge port210provided in the counting tank21. The high liquid level sensor212senses whether the liquid level of ink in the counting tank21is higher than a predetermined second vertical position or not. The second vertical position is a position higher than the first vertical position. In other words, the high liquid level sensor212is provided at a position higher than that of the low liquid level sensor211. The measurement of the volume of ink in the counting tank21will be described later.

The intermediate tank22is a container for temporarily storing therein ink that is a liquid. In the present preferred embodiment, the intermediate tank22serves as a “reservoir”. The intermediate tank22includes a first sensor221and a second sensor222both of which sense the liquid level of ink stored in the intermediate tank22. The first sensor221is provided at a position higher than that of an ink discharge port220provided in the intermediate tank22. The second sensor222is provided at a position higher than that of the first sensor221. Preferably, there is a greater difference in height between the first sensor221and the second sensor222.

The filter23is a filter for removing foreign matter from ink passing through the pipe43.

The deaeration module24is a container for removing dissolved gases from ink. The deaeration module24includes, for example, a vacuum pump for exhausting gases from the interior of the deaeration module24. The deaeration module24may have other structures capable of removing dissolved gases from ink. When the ink in the at least one ink tank8is deaerated ink, the deaeration module24may be dispensed with.

The suction pump31is a pump for sucking ink from the at least one ink tank8to supply the ink to the counting tank21. The suction pump31is interposed in the pipe41which connects the at least one ink tank8and the counting tank21for communication therebetween. In the present preferred embodiment, the suction pump31serves as a “first feeding part” for feeding ink from the at least one ink tank8to the counting tank21.

The supply pump32is a pump for sucking ink from the intermediate tank22to supply the ink through the deaeration module24to the at least one printer9. The supply pump32is interposed in the pipe43which connects the intermediate tank22and the at least one printer9for communication therebetween. In the present preferred embodiment, the supply pump32serves as a “pump” for feeding ink from the intermediate tank22to the pipe43.

The pipe41connects the at least one ink tank8and the counting tank21for communication therebetween. In the present preferred embodiment, two ink tanks, i.e. the first ink tank81and the second ink tank82, are used as the at least one ink tank8, as mentioned above. Accordingly, the pipe41includes a pipe410which connects to the counting tank21and in which the suction pump31is interposed, a pipe411which connects the pipe410and the first ink tank81to each other, and a pipe412which connects the pipe410and the second ink tank82to each other. Suction valves51and52that are on-off valves are provided in the pipes411and412, respectively.

The pipe42connects the counting tank21and the intermediate tank22for communication therebetween. An end of the pipe42which is closer to the counting tank21is connected to the discharge port210of the counting tank21. A discharge valve53that is an on-off valve is provided in the pipe42. In the present preferred embodiment, the discharge valve53serves as a “second feeding part” for feeding ink from the counting tank21to the intermediate tank22.

The pipe43connects the intermediate tank22and the at least one printer9for communication therebetween. An end of the pipe43which is closer to the intermediate tank22is the discharge port220of the intermediate tank22. In the present preferred embodiment, two printers, i.e. the first printer91and the second printer92, are used as the at least one printer9, as mentioned above. Accordingly, the pipe43includes a pipe430which connects to the intermediate tank22, a pipe431which connects the pipe430and the first printer91to each other, and a pipe432which connects the pipe430and the second printer92to each other.

The supply pump32, a supply valve54, the filter23and the deaeration module24are provided in the pipe430in the order named as seen from the intermediate tank22.

In the present preferred embodiment, the pipe43serves as a “supply path” for supplying ink from the intermediate tank22to the at least one printer9. Specifically, the pipe430and the pipe431serve as a supply path from the intermediate tank22to the first printer91, and the pipe430and the pipe432serve as a supply path from the intermediate tank22to the second printer92.

As shown inFIGS. 1 and 2, the first printer91includes a first printer controller910, a first head tank911for supplying ink directly to an ink ejection head, and a first printer valve912for making and breaking a connection between the first head tank911and the liquid supply apparatus1. The pipe431is connected for communication with the first head tank911through the first printer valve912. The first printer controller910controls the first printer valve912.

Likewise, the second printer92includes a second printer controller920, a second head tank921for supplying ink directly to an ink ejection head, and a second printer valve922for making and breaking a connection between the second head tank921and the liquid supply apparatus1. The pipe432is connected for communication with the second head tank921through the second printer valve922. The second printer controller920controls the second printer valve922.

As shown inFIG. 2, the controller10receives sensing signals from the low liquid level sensor211and the high liquid level sensor212of the counting tank21and from the first sensor221and the second sensor222of the intermediate tank22. The controller10also receives ink supply request signals from the first printer controller910and the second printer controller920. Specifically, the first printer controller910and the second printer controller920send connection making signals to the first printer valve912and the second printer valve922respectively, and at the same time send the request signals to the controller10. The first printer controller910and the second printer controller920send connection breaking signals to the first printer valve912and the second printer valve922respectively, and at the same time stop the request signals to the controller10.

The controller10is electrically connected to the suction pump31, the supply pump32, the suction valves51and52, the discharge valve53and the supply valve54. The controller10controls the operations of opening and closing the suction pump31, the supply pump32, the suction valves51and52, the discharge valve53and the supply valve54in accordance with user's manipulations, various input signals or previously set programs.

The controller10is formed by, for example, a computer including a computation processor such as a CPU, and a memory. As shown inFIG. 2, the controller10includes a storage area11for storing a correspondence table111to be described later therein.

With the aforementioned configuration, the liquid supply apparatus1supplies ink from the at least one ink tank8to the at least one printer9. The brief description of the operation of the liquid supply apparatus1is as follows.

First, the suction pump31is driven to supply ink from the at least one ink tank8through the pipe41to the counting tank21. The ink temporarily stored in the counting tank21is discharged through the pipe42and the discharge valve53to the intermediate tank22. The ink stored in the intermediate tank22is fed into the pipe43by the supply pump32in accordance with the request signal from the at least one printer9. The ink fed by the supply pump32passes through the pipe43and then through the supply valve54to the filter23, which in turn removes foreign matter from the ink. Then, the ink reaches the deaeration module24, which in turn removes dissolved gases from the ink. Finally, the ink is supplied to the at least one printer9.

The details of a configuration for suppressing an abrupt change in pressure in the at least one printer9which is a destination to which ink is supplied in such a liquid supply apparatus1will be described later.

Next, the measurement of the volume of ink in the counting tank21will be described.FIG. 3is a flow diagram showing an example of a procedure for measurement of the volume of ink in the counting tank21.

In the present preferred embodiment, 18 liters of ink is stored in each ink tank8before use. The counting tank21has an ink capacity of 100 milliliters from the first vertical position to the second vertical position. The ink capacity of the counting tank21from the first vertical position to the second vertical position shall be referred to simply as the ink capacity of the counting tank21hereinafter. It should be noted that the ink capacity of each ink tank8and the ink capacity of the counting tank21are not limited to the aforementioned values. The operation of the counting tank21and its adjacent components is described below.

As mentioned above, the counting tank21includes the low liquid level sensor211and the high liquid level sensor212which sense the liquid level of ink stored in the counting tank21.

At the start of the operation of the liquid supply apparatus1, the controller10initially checks a count N (in Step S101). The count N is treated as a variable in the computation process in the controller10. The count N is zero when a new ink tank8is to be used. When the ink tank8used during the preceding operation is to be continuously used without change, the count N has the same value as that obtained at the completion of the preceding operation. For convenience of description, it is assumed that the ink tank8to be used in this case is the first ink tank81. At this time, the suction pump31is unoperated, and the discharge valve53is closed. Also, the suction valve51which controls the communication between the first ink tank81to be used and the suction pump31is open, and the suction valve52which controls the communication between the second ink tank82not to be used and the suction pump31is closed.

Next, the controller10opens the discharge valve53to discharge the ink remaining in the counting tank21to the intermediate tank22(in Step S102). Then, the controller10judges whether the liquid level of ink in the counting tank21is higher than the aforementioned first vertical position or not, based on the sensing signal sent from the low liquid level sensor211(in Step S103). When the liquid level of ink in the counting tank21is higher than the first vertical position, the discharge of ink is continued, and the procedure returns to Step S103.

When the liquid level of ink in the counting tank21becomes lower than the first vertical position in Step S103, the controller10closes the discharge valve53(in Step S104). This stops the discharge of ink from the counting tank21to the intermediate tank22.

Then, the controller10increases the value of the count N by one. That is, the controller10increments the count N (in Step S105). Then, the controller10judges whether the count N is less than a predetermined value or not (in Step S106). The predetermined value is a value determined by the ink capacity of the ink tank8to be used and the ink capacity of the counting tank21. The predetermined value is less than the quotient of the ink capacity of the ink tank8divided by the ink capacity of the counting tank21, and is preferably a greater value. In the present preferred embodiment, the predetermined value may be set to 178, for example, because the ink capacity of the ink tank8is 18 liters and the ink capacity of the counting tank21is 100 milliliters.

When the count N is not less than the predetermined value in Step S106, the procedure proceeds to Step S111in which the ink tank8is changed. In the present preferred embodiment, the suction valve51is closed and the suction valve52is opened, whereby the ink tank8to be used is changed from the first ink tank81to the second ink tank82. The change of the ink tank8may be done either manually or automatically by the controller10. After the controller10automatically changes the ink tank8, the count N may be reset to zero and the procedure may return to Step S106.

On the other hand, when the count N is less than the predetermined value in Step S106, the suction pump31is brought into operation (in Step S107). This causes the supply of ink from the ink tank8to the counting tank21.

Subsequently, the controller10judges whether the liquid level of ink in the counting tank21is higher than the aforementioned second vertical position or not, based on the sensing signal sent from the high liquid level sensor212(in Step S108). When the liquid level of ink in the counting tank21is not higher than the second vertical position, the supply of ink is continued, and the procedure returns to Step S108.

When it is judged in Step S108that the liquid level of ink in the counting tank21reaches the second vertical position, the suction pump31is stopped (in Step S109). This stops the supply of ink from the ink tank8to the counting tank21.

Thereafter, the discharge valve53is opened to start the discharge of ink (in Step S110). Then, the procedure returns to Step S103.

Steps S104to S107in which the suction pump31is brought into operation and the discharge valve53is closed after the liquid level of ink in the counting tank21becomes lower than the first vertical position shall be collectively referred to as a first process. Steps S109to S110in which the suction pump31is stopped and the discharge valve53is opened after the liquid level of ink in the counting tank21reaches the second vertical position shall be collectively referred to as a second process. The controller10repeats the first process and the second process to measure the number of repetitions by incrementing the count N in Step S105. Then, the controller10estimates the volume of ink supplied from the ink tank8to the intermediate tank22, based on the count N, thereby to estimate the volume of ink remaining in the ink tank8being used. As a result, before the volume of ink remaining in the ink tank8becomes zero, the change to another ink tank8is done to prevent a situation such that ink can no longer be supplied to the counting tank21. Also, the entry of air into the pipe41is suppressed.

While the liquid level of ink in the intermediate tank22is higher than the second sensor222in Steps S102and S110, the opening of the discharge valve53may be temporarily stopped.

<1-3. Operation of Supply Pump>

Next, the operation of the supply pump32will be described.FIG. 4is a graph showing an example of a relationship between the request signals from the two printers9and the feed volume of the liquid from the supply pump32(the feed volume of the liquid per unit time; the same shall apply hereinafter).FIG. 5is a flow diagram showing a procedure for operation of the supply pump32in response to the request signals from the two printers9. The abscissa ofFIG. 4represents time which is common to upper, middle and lower parts ofFIG. 4. The upper part ofFIG. 4represents a request signal91P from the first printer91; the middle part thereof represents a request signal92P from the second printer92; and the lower part thereof represents the feed volume W of the liquid from the supply pump32.

In the present preferred embodiment, assuming that the maximum feed volume of the liquid from the supply pump32is 100%, the supply pump32supplies ink in a feed volume W of 50% to the first printer91, and supplies ink in a feed volume W of 50% to the second printer92.

At time T0in the example ofFIG. 4, the request signal91P and the request signal92P are OFF, and the operation starts when the supply pump32is in a stopped state. Thereafter, the request signal91P is turned ON at time T1, and the signal92P is subsequently turned ON at time T2. Then, the request signal91P is turned OFF at time T3, and the request signal92P is turned OFF at time T4. Changes in the feed volume W of the liquid from the supply pump32in this operation will be described with reference toFIG. 5.

First, the request signal91P is turned ON at the time T1. In other words, the controller10receives the request signal91P (in Step S301).

Next, the controller10acquires the target feed volume Wg of the liquid from the supply pump32, based on the received request signal91P (in Step S302). In the present preferred embodiment, the target feed volume Wg of the liquid which is 50% is acquired because the feed volume W of the liquid to the first printer91is 50% of the maximum feed volume.

Then, the controller10sends a driving signal S to the supply pump32, based on the acquired target feed volume Wg (in Step S303). Subsequently, the supply pump32operates, based on the received driving signal S (in Step S304). Specifically, the supply pump32feeds the liquid in accordance with the output of the driving signal S. In response to the driving signal S, the supply pump32gradually changes the feed volume W from a current feed volume Wn of 0% to a target feed volume Wg of 50%. In the example ofFIG. 4, the feed volume W gradually increases from the time T1at which the request signal91P is received, and reaches a target feed volume Wg of 50% after a lapse of time t. A procedure during the output of the driving signal S in Step S303will be described later.

Likewise, when the request signal92P is turned ON at the time T2, the controller10acquires a target feed volume Wg of 100%. The feed volume W of the liquid from the supply pump32gradually changes from 50% to 100%. Next, when the request signal91P is turned OFF at the time T3, the controller10acquires a target feed volume Wg of 50%. The feed volume W of the liquid from the supply pump32gradually changes from 100% to 50%. When the request signal92P is turned OFF at the time T4, the controller10acquires a target feed volume Wg of 0%. The feed volume W of the liquid from the supply pump32gradually changes from 50% to 0%.

Gradually changing the feed volume W of the liquid from the supply pump32in this manner suppresses an abrupt change in pressure in the printers9which is a destination to which ink is supplied.

Next, the driving signal S sent from the controller10to the supply pump32will be described.FIG. 6is a graph showing waveforms of the driving signal S during changes in output.FIG. 7shows the correspondence table111between the output number of the driving signal S and a duty ratio.FIG. 8is a flow diagram showing a procedure in the controller10during the output of the driving signal S.

In the present preferred embodiment, the operation of the supply pump32is under PWM (pulse width modulation) control. Specifically, the driving signal S sent from the controller10to the supply pump32is in the form of a rectangular pulse wave whose high state voltage is constant. The pulse wave has a constant frequency and a pulse width with a variable duty ratio D. Thus, the output of the driving signal S in the present preferred embodiment is the duty ratio D of the pulse width.

The feed volume W of the liquid from the supply pump32depends on the driving signal S inputted thereto. In other words, the feed volume W of the liquid from the supply pump32varies in corresponding relation to the duty ratio D of the driving signal S. In the present preferred embodiment, the feed volume W of the liquid from the supply pump32and the duty ratio D of the driving signal S are in the following corresponding relation: D=0% for W=0%; D=50% for W=50%; and D=100% for W=100%.

FIG. 6shows an example of the driving signal S in the case where the driving signal S is gradually changed from an initial output to a target output. The abscissa ofFIG. 6represents time. The driving signal S shown inFIG. 6is that obtained in the case where the duty ratio D is changed from 0% to 50%, from 50% to 100%, from 100% to 50%, and from 50% to 0% in top-to-bottom order. In the example ofFIG. 6, the duty ratio D of the driving signal S changes stepwise from the initial output to the target output in steps of 10%.

FIG. 7shows the correspondence table111between the output number M of the driving signal and the duty ratio D. The values of the output number M, and the values of the duty ratio D, an OFF time interval and an ON time interval corresponding to the output number M are listed in the correspondence table111. In the present preferred embodiment, the driving signal S has a period of 10 ms, the sum of the OFF time interval and the ON time interval per period is 10 ms. A procedure using the correspondence table111during the output of the driving signal S will be described below with reference toFIG. 8.

At the start of driving of the liquid supply apparatus1, the supply pump32is not driven, so that the feed volume W of the liquid from the supply pump32is 0%. At this time, the controller10does not send the driving signal S, so that the duty ratio D of the driving signal S is 0%. When the liquid supply apparatus1is driven, the controller10sets a current output number Mn and a target output number Mg to zero in corresponding relation to a duty ratio D of 0% (in Step S501). At this time, the output of the driving signal S is OFF.

Next, the controller10acquires the target output number Mg corresponding to a target duty ratio, based on the target feed volume Wg of the liquid from the supply pump32acquired in Step S302described above (in Step S502).

Then, the controller10judges whether the current output number Mn coincides with the target output number Mg or not (in Step S503). When the current output number Mn coincides with the target output number Mg, the procedure proceeds to Step S507.

When the current output number Mn does not coincide with the target output number Mg, the controller10judges whether the current output number Mn is less than the target output number Mg or not (in Step S504). When the current output number Mn is less than the target output number Mg, the value of the current output number Mn is increased by one. That is, the current output number Mn is incremented (in Step S505). Then, the procedure proceeds to Step S507. On the other hand, when the current output number Mn is greater than the target output number Mg, the value of the current output number Mn is decreased by one. That is, the current output number Mn is decremented (in Step S506). Then, the procedure proceeds to Step S507.

In Step S507, the controller10references the correspondence table111stored in the storage area11to acquire the OFF and ON time intervals corresponding to the current output number Mn.

Subsequently, the controller10judges whether the acquired OFF time interval is zero or not (in Step S508). When the acquired OFF time interval is zero, the procedure proceeds to Step S511. When the acquired OFF time interval is not zero, the controller10turns OFF the output of the driving signal S (in Step S509), and waits for the acquired OFF time interval (in Step S510).

Then, the controller10judges whether the acquired ON time interval is zero or not (in Step S511). When the acquired ON time interval is zero, the procedure returns to Step S502. When the acquired ON time interval is not zero, the controller10turns ON the output of the driving signal S (in Step S512), and waits for the acquired ON time interval (in Step S513). Then, the procedure returns to Step S502.

Using the aforementioned procedure, the controller10changes the driving signal S in the form of a pulse wave while acquiring the duty ratio D by reference to the correspondence table111. Specifically, the controller10acquires the target duty ratio and the target output number Mg corresponding to the target feed volume Wg, based on the request signal from the at least one printer9to change the duty ratio D of the driving signal S stepwise from the current duty ratio to the target duty ratio. In the present preferred embodiment, the duty ratio D of the driving signal S changes stepwise in steps of 10%, as shown inFIG. 6. This gradually changes the feed volume W of the liquid from the supply pump32. As a result, an abrupt change in pressure in the at least one printer9which is a destination to which ink is supplied is suppressed.

In the aforementioned example, the duty ratio D of the driving signal S is changed for each period of a pulse. The present invention, however, is not limited to this. The duty ratio D of the driving signal S may be changed for each group of periods. This changes the feed volume W of the liquid from the supply pump32more slowly to further suppress an abrupt change in pressure in the at least one printer9which is a destination to which ink is supplied.

While the one preferred embodiment according to the present invention has been described hereinabove, the present invention is not limited to the aforementioned preferred embodiment.

In the aforementioned preferred embodiment, the required feed volume of the liquid from the supply pump32to the first printer91is 50%, and the required feed volume of the liquid from the supply pump32to the second printer92is 50%. The present invention, however, is not limited to this. When the at least one printer9includes a plurality of printers9, the required feed volumes different from each other may be set for the respective printers9. In this case, the maximum value of the target feed volume of the liquid from the supply pump32is the sum of the required feed volumes of the liquid to the respective printers9. Also, the target feed volume is the sum of the required feed volumes of the liquid to the respective printers9outputting the request signals. This achieves the supply of ink in appropriate volumes to the respective printers9.

The required feed volumes of the liquid to the printers9may correspond to the lengths of the supply paths to the printers9, respectively. For example, when the total length of the pipes430and431serving as the supply path to the first printer91is shorter than the total length of the pipes430and432serving as the supply path to the second printer92, the required feed volume of the liquid to the first printer91may be less than the required feed volume of the liquid to the second printer92.

The controller10may vary the feed volume of the liquid from the suction pump31, based on the request signals from the printers9. For example, the controller10may control the suction pump31so that the greater the number of printers9outputting the request signals or the target feed volume is, the greater the feed volume of the liquid from the suction pump31is. This allows the volume of ink in the intermediate tank22to be maintained at an appropriate volume.

In the aforementioned preferred embodiment, the duty ratio D of the driving signal S is changed in steps of 10%. The present invention, however, is not limited to this. The duty ratio D may be changed in steps of 5%, 1% or less than 1%. Similarly, the number of steps of the duty ratio D of the driving signal S for one printer9is five in the aforementioned preferred embodiment. The present invention, however, is not limited to this. The number of steps of the duty ratio D for one printer9may be less than or more than five. Also, when the at least one printer9includes a plurality of printers9, the number of steps of the duty ratio D may be set for each of the printers9.

In the aforementioned preferred embodiment, the driving signal S has a period of 10 ms, i.e. a frequency of 0.1 kHz. The present invention, however, is not limited to this. The driving signal S may have a frequency of 1 kHz, for example. An appropriate frequency may be used as the frequency of the driving signal S, as required, in accordance with the output from the liquid supply apparatus1and the like.

In the aforementioned preferred embodiment, the controller10uses the PWM control to control the operation of the supply pump32. The present invention, however, is not limited to this. The controller10may control the operation of the supply pump32by changing the driving voltage stepwise, in place of the PWM control. The PWM control is, however, preferable in being able to change the output while maintaining a rated voltage suitable for the driving of the supply pump32.

The configurations of the details of the liquid supply apparatus may differ from those shown in the figures of the present invention. The components described in the aforementioned preferred embodiment and in the various modifications may be consistently combined together, as appropriate.

The liquid supply apparatus according to the present invention is not limited to an ink supply apparatus for a printer, but may be, for example, an apparatus for supplying a treatment liquid to an apparatus (a liquid consuming apparatus) which applies the treatment liquid to surfaces of a semiconductor substrate and a substrate for a flat panel display device.