Patent Publication Number: US-8113612-B2

Title: Ink delivery system

Description:
BACKGROUND 
     Conventional ink-jet printers utilize a carriage that carries one or more ink-jet printheads in a scanning motion that is perpendicular to the direction of the printer paper path. The printheads scan the page while ejecting ink droplets to form the desired image. In a page-wide-array printer, a page-wide-array (“PWA”) printhead spans an entire pagewidth (e.g., 8.5 inches) and has many more ink nozzles than the scanning-type printheads. The PWA printhead is fixed on a print bar that is typically oriented orthogonally to the paper path. The page moves relative to the fixed PWA printhead as the printhead prints one or more lines at a time of the desired image. 
     Ink-jet printers often include stationary ink reservoirs connected to the printheads through tubes. These printers are generally called “off-axis” printers, as the external reservoirs are typically known as “off-axis” ink reservoirs. Many off-axis printers have pressurized ink supplies that enable higher flow rates of supply ink to the printheads. A supply may be pressurized by an external source such as an air pump, or it may be a self-pressurized supply that contains a propellant and remains pressurized at all times. In either case the pressure source is used to pressurize the supply&#39;s ink. 
     Pressurized ink supplies provide significant advantages in transferring ink from the supplies to the printheads in required time limits. However, challenges remain with respect to regulating the pressure and the ink associated with pressurized ink supplies. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present embodiments will now be described, by way of example, with reference to the accompanying drawings, in which: 
         FIG. 1  shows an example of an ink supply system according to an embodiment; 
         FIG. 2A  shows an example of an ink supply according to an embodiment; 
         FIG. 2B  shows an example of a self-pressurized ink supply according to an embodiment; 
         FIG. 3A  shows an example of an ink valve in an ink supply system according to an embodiment; 
         FIG. 3B  shows an example of an ink valve with a switch in an ink supply system according to an embodiment; 
         FIG. 3C  shows an example of an ink valve with another switch in an ink supply system according to an embodiment; 
         FIG. 4  shows another example of an ink supply system including a pressure switch according to an embodiment; 
         FIG. 5  shows another example of an ink supply system having self-pressurized ink supplies according to an embodiment; 
         FIG. 6  shows a flowchart of a method of regulating an ink supply system according to an embodiment; 
         FIG. 7  shows a flowchart of another method of regulating an ink supply system according to an embodiment; 
         FIG. 8  shows a flowchart of another method of regulating an ink supply system according to an embodiment; 
         FIG. 9  shows a flowchart of another method of regulating an ink supply system according to an embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     Overview of Problem and Solution 
     As noted above, there are challenges that remain in regulating the pressure and ink in pressurized ink supplies. One issue inherent to pressurized ink supply systems is the back pressure (a negative pressure) exerted by the ink container on the ink that occurs when the air pressure applied as the motive force is removed and the driving side of the system is allowed to return to atmospheric pressure. Although pressurized ink supply systems regulate upstream ink pressure to the printheads (pens), the regulators do not work in reverse. When a negative pressure is applied, a regulator can open completely, applying a high back pressure condition to the pen orifices. The back pressure can result in air being pulled into the ink orifices, filling the pen firing chambers and causing a “de-prime” condition. De-prime can, depending on other systems that are designed to maintain nozzle health, cause complete failure of the pen. The effect of back pressure is even more apparent when the ink container nears depletion. Therefore, regulating system pressure and determining when a low ink or an out of ink condition occurs have been challenging problems to solve with pressurized ink supply systems. 
     Various solutions to these problems have been developed. For example, there have been a number of different devices and techniques employed for determining when an ink container is low on ink or is out of ink. Optical sensors, air-ink sensors, capacitance sensors, mechanical sensors, and drop counting are among these devices and techniques. These solutions have disadvantages, however, such as the need for complex algorithms, additional complex electronics, and extensive characterization experiments to adequately predict low on ink and out of ink behavior in the ink supply. 
     In regulating the pressure source, prior pressurized ink supply systems have utilized expensive pressure transducers. For example, these systems often utilize high quality pressure transducers to monitor and control an air pump, and they frequently contain separate transducers to monitor the difference between the ink pressure and the system pressure. Some pressurized supplies contain smaller, less expensive pressure transducers to directly measure the difference between the system air pressure and ink pressure. However, ink compatibility issues have plagued these systems and have lead to additional problems. 
     Other systems have moved the ink pressure transducers off of the supply and into the printer. These systems have the same disadvantages listed above. In general, pressure transducer based systems are expensive and burden the consumer with a higher cost for the print mechanism or ink supplies or both. 
     Embodiments of the present disclosure overcome disadvantages associated with the use of various complex sensors and expensive pressure transducers like those noted above. In one embodiment, for example, an ink delivery system includes a plurality of ink supplies, an air pressure source to generate ink pressure for each ink supply, and an ink valve associated with each ink supply. Each ink valve is configured to prevent a reverse flow of ink from a pen to the associated ink supply, and each ink valve includes a switch configured to provide an open signal when the ink valve is open. In this embodiment the ink delivery system also includes a controller configured to determine a normal ink condition, an out of ink condition or a system pressure problem based on receiving the open signals from the switches. The controller regulates the pressure source based on its determination of a normal ink condition, an out of ink condition or a system pressure problem. 
     In another embodiment, an ink delivery system includes a plurality of ink supplies, an air pressure source, an ink valve associated with each ink supply, and a controller as noted above. The ink delivery system in this embodiment also includes a system pressure switch configured to close when system air pressure from the air pressure source reaches a threshold. In this embodiment the controller is further configured to determine a low ink condition in an ink supply when a corresponding ink valve opens after the system pressure switch closes. 
     In still another embodiment an ink delivery system includes a plurality of ink supplies, an air pressure source, an ink valve associated with each ink supply, and a controller as noted above. In this embodiment, the ink supplies are self-pressurized supplies. The ink delivery system in this embodiment also includes first stage regulators associated with each pressurized ink supply in order to regulate the ink pressure from a propellant pressure to an ink system pressure. 
     In another embodiment, a method of regulating ink supply pressure in an ink delivery system includes initiating an air pressure source, monitoring ink valve switches to determine a system pressure problem, a normal ink condition, and an out of ink condition, and then regulating the air pressure source based on which problem or condition is determined. 
     In another embodiment, a method of regulating ink supply pressure in an ink delivery system includes initiating an air pressure source, monitoring ink valve switches and a system pressure switch to determine a system pressure problem, a normal ink condition, an out of ink condition or a low ink condition, and then regulating the air pressure source based on which problem or condition is determined. 
     In another embodiment, a method of regulating ink supply pressure in an ink delivery system having self-pressurized supplies includes engaging first stage regulators, monitoring ink valve switches and the first stage regulators to determine a system pressure problem, a normal ink condition and an out of ink condition and then regulating the air pressure source through controlling the first stage regulators according to which problem or condition is determined. 
     First Illustrative Embodiment 
       FIG. 1  shows an example of an ink delivery system  100  according to an embodiment of the present disclosure. Ink delivery system  100  may operate, for example, in a conventional ink-jet printer, a page-wide-array printer, or the like. The system  100  includes an air pressure source (e.g., air pump)  102  with a motor feedback signal mechanism  104 . The air pressure source  102  is coupled to, and provides air pressure to, a plurality of ink supplies  106  via air tubing  108 . In  FIG. 1  there are four ink supplies  106  illustrated; a black ink supply  106 A, a magenta ink supply  106 B, a yellow ink supply  106 C, and a cyan ink supply  106 D. Although four ink supplies  106  are illustrated, the illustration is made by way of example only, and it is to be understood that different ink delivery systems may employ a greater or lesser number of ink supplies. 
     Different embodiments of the ink supplies  106  of  FIG. 1  will now be discussed briefly with reference to  FIGS. 2A and 2B . As shown in  FIG. 2A , an ink supply  106  includes a rigid outer container or housing in the form of a canister  200 . Each canister  200  contains an internal flexible container in the form of an ink bladder  202  that contains a quantity of ink. Each canister  200  includes an air input port  204  coupled to air tubing  108  to receive pressurized air from air pressure source  102 . Each canister also includes an ink output port  206  to which the internal ink bladder  202  is connected such that ink can flow out of the ink bladder and into the ink tubing  110  as pressure within the canister increases within the interstitial volume  208  between the canister  200  and the bladder  202 . 
     In  FIG. 2B , an alternate form of an ink supply  106  is illustrated. In  FIG. 2B , the alternate ink supply is a self-pressurized supply  210  that contains a propellant and remains pressurized continuously. This self-pressurized supply  210  is appropriate for use in an alternate embodiment of an ink supply system such as that discussed below with reference to  FIG. 5 . The self-pressurized ink supply  210  is not coupled to an air pressure source  102  through air tubing  108 . It therefore does not include an air input port  204 . Rather, self-pressurized ink supply  210  contains a propellant  212  arranged within the interstitial volume  208  between the canister  200  and the bladder  202 . The propellant  212  maintains pressure on the bladder  202 . A suitable propellant  212  is a compressed gas such as compressed nitrogen. The compressed gas gives a stable pressure over a wide temperature range. 
     Referring again to  FIG. 1 , coupled between each ink supply  106  and one or more printer pens (printheads)  116  via ink tubing  110 , is an ink valve  112  (ink valves  112 A- 112 D). Each ink valve  112  is configured to prevent a reverse flow of ink from a pen (printhead)  116  to its associated or corresponding ink supply  106 . For example, ink valve  112 A prevents a reverse flow of ink from a pen (printhead)  116  to ink supply  106 A. A reverse flow of ink can occur when the ink bladder  202  is almost empty and the interstitial volume  208  between the canister  200  and the ink bladder  202  is depressurized. In this circumstance the depressurized bladder  202  will move from a collapsed state to a free state which can pull ink from the pens  116  back into the supplies  106 . This is an example of a reverse flow of ink that the ink valve  112  can prevent. 
       FIG. 3A  illustrates an embodiment of an ink valve  112 . Ink valve  112  includes ink inlet port  300  (a non-sealed port) and ink outlet port  302  (a sealed port) to allow ink to flow in and out of valve  112 . Ink from a pressurized ink supply  106  flows in the non-sealed port into valve chamber  304  and out the sealed port. A diaphragm  306  includes a bump or other sealing feature  308  to seal outlet port  302  when valve  112  is closed. An elastic object such as a spring  310  is used to push seal  306  against outlet port  302  to close valve  112 . The non-ink containing side of valve  112  is open to the atmosphere via vent hole  312 , and stops  314  relieve tension in diaphragm  306 . 
     When an ink supply  106  is pressurized, the ink in valve chamber  304  is also pressurized because the open inlet port  300  of valve  112  is connected to the pressurized ink supply line  110 . This pressure forces diaphragm  306  to move, and seal  308  moves off or away from outlet port  302 , opening valve  112 . The ink then flows freely through valve  112 . 
     In the embodiment of the ink delivery system  100  illustrated in  FIG. 1 , each ink valve  112  is configured with an ink valve switch  114  (switches  114 A- 114 D). Switch  114  is configured to trigger (e.g., close) when ink pressure moves diaphragm  306  and breaks the seal  308  away from outlet port  302 , opening valve  112 . When switch  114  triggers (e.g., closes), it provides an “open signal” indicating that ink valve  112  has opened. Switch  114  can be configured as various types of switches, and is not limited by the embodiments described herein. For example, switch  114  may be configured as an opto-sensor switch, a contact switch or a hall effect switch. 
       FIGS. 3B and 3C  illustrate ink valves  112  with two different exemplary embodiments of a switch  114 . In  FIG. 3B , ink valve  112  includes an opto-sensor switch  316  that is triggered (e.g., it closes) when it senses, via a diaphragm flag  318 , enough movement of diaphragm  306  to open valve  112 . The diaphragm flag  318  is coupled to diaphragm  306  such that when ink pressure forces diaphragm  306  to move, breaking the seal  308  away from outlet port  302  and opening valve  112 , the opto-sensor switch  316  is triggered (e.g., the switch  316  closes). Opto-sensor switch  316  senses movement of the diaphragm  306  through corresponding movement of the diaphragm flag  318 . 
     Referring to  FIG. 3C , ink valve  112  includes a contact switch  320  that is triggered (e.g., it closes) when it senses, via diaphragm flag  318 , enough movement of diaphragm  306  to open valve  112 . The diaphragm flag  318  is coupled to diaphragm  306  such that when ink pressure forces diaphragm  306  to move, breaking the seal  308  away from outlet port  302  and opening valve  112 , the contact switch  320  is triggered (e.g., the switch  320  closes). Contact switch  320  senses movement of the diaphragm  306  through corresponding movement of the diaphragm flag  318 . 
     Referring again to  FIG. 1 , a controller  118  is configured to regulate the air pressure source (e.g., air pump)  102 . Controller  118  includes a processor (CPU)  120  and memory  122 . Processor  120  is a hardware device for executing software that can be stored in memory  122 . Processor  120  can be any custom-made or commercially available processor, including a central processing unit (CPU), an auxiliary processor among several processors associated with ink delivery system  100  within a printer, or a semiconductor-based microprocessor (in the form of a microchip). When the ink delivery system  100  is in operation, the processor  120  is configured to execute software stored within memory  122 , to communicate data to and from the memory  122 , and to generally control operations of the ink delivery system  100 . 
     Memory  122  can include any one or combination of volatile memory elements (e.g., random access memory (RAM, such as dynamic RAM or DRAM, static RAM or SRAM, etc.)) and nonvolatile memory elements (e.g., read-only memory (ROM), drives, discs, etc.). Memory  122  may contain data files and various software application programs, each of which typically comprises an ordered listing of executable instructions for implementing logical functions. In the illustrated example, the software in memory  122  includes pressure regulation algorithm  124  configured to execute on processor  120  and cause controller  118  to regulate air pump  102 . 
     The controller  118 , through execution of algorithm  124  on processor  120 , regulates air pump  102  in part based on the “open signals” it receives from switches  114 . Based on the open signals, controller  118  determines different conditions and/or problems that may exist within ink delivery system  100  and regulates air pump  102  accordingly. For example, during the execution of algorithm  124 , controller  118  initiates air pump  102  and then monitors the ink valve switches  114  for open signals. If it receives open signals from all of switches  114  prior to a preset time period elapsing from the initiation of the pump  102 , it determines that a normal ink condition exists. The controller  118  then waits for a second time period and stops the pump. If the controller  118  receives open signals from less than all of switches  114  prior to the preset time period elapsing from initiation of the pump  102 , it determines that one or more ink supplies is out of ink and stops the pump to inform the user. If the controller  118  receives no open signals from switches  114  prior to the preset time period elapsing from initiation of the pump  102 , it determines that a system pressure problem exists and it stops the pump and informs the user. The operation of the controller  118  regarding algorithm  124  is discussed in greater detail below with respect to embodiments of methods for regulating the ink supply pressure. 
     Second Illustrative Embodiment 
       FIG. 4  shows another example of an ink delivery system  100  according to an embodiment of the present disclosure. The system  100  is similar to the embodiment discussed with reference to  FIG. 1 , except that it additionally includes a pressure switch  400  and a different algorithm  402  stored in memory  122 . Pressure switch  400  provides a trigger (e.g., closes) when air pressure in air tubing  108  reaches a preset system air pressure threshold. Use of the pressure switch enables controller  118  to make an additional determination regarding a low ink condition in an ink supply  106 . That is, based on the open signals from ink valve switches  114  and an additional trigger from pressure switch  400 , controller  118  can determine a normal ink condition, an out of ink condition, a low ink condition and a system pressure problem existing within ink delivery system  100 , and regulate air pump  102  accordingly. 
     The basis for determining a low ink condition in a supply  106  is that the corresponding valve  112  does not open until after a higher threshold system air pressure is reached (i.e., triggering the pressure switch  400 ). That is, in a supply  106  that has low ink, a higher system air pressure is needed to generate enough ink pressure to open the corresponding valve  112 . When determining a low ink condition, the execution of algorithm  402  on processor  120  causes controller  118  to initiate air pump  102 , and then to monitor the ink valve switches  114  for open signals, and the pressure switch  400  for a trigger. If, prior to the preset time period elapsing from initiation of the pump  102 , the controller  118  receives an open signal from switches  114  but one or more of the switches does not open until after the pressure switch  400  is triggered, then the controller determines which switches  114  opened-after the pressure switch  400  triggered and notifies the user that the ink supplies  106  corresponding to those switches  114  have a low ink condition. The operation of the controller  118  regarding algorithm  402  is discussed in greater detail below with respect to embodiments of methods for regulating the ink supply pressure. 
     Third Illustrative Embodiment 
       FIG. 5  shows another example of an ink delivery system  100  according to an embodiment of the present disclosure. The system  100  is similar to the embodiment discussed with reference to  FIG. 1 , except that the ink supplies are self-pressurized supplies  210  ( 210 A- 210 D) such as those discussed above with respect to  FIG. 2B . In addition, the system  100  of  FIG. 5  includes first stage regulators  500  ( 500 A- 500 D) located between each of the self-pressurized supplies  210  and their corresponding ink valves  112 . The first stage regulators  500  are used to reduce the ink pressure from propellant pressure (i.e., the pressure from the propellant  212  within the self-pressurized supplies  210 ) to an ink system pressure. The regulators  500  can engage and disengage in order to isolate the self-pressurized supplies  210  from the system  100 . 
     The controller  118  also executes a different algorithm  502  on processor  120 , and thereby regulates pressure from self-pressurized supplies  210  in part based on the “open signals” it receives from switches  114  and further based on regulator feedback signals from regulators  500 . Based on the open signals, controller  118  determines different conditions and/or problems that may exist within ink delivery system  100  and controls regulators  500  accordingly. When algorithm  502  is initiated, controller  118  engages the first stage regulators  500  and then monitors the ink valve switches  114  for open signals. If the controller  118  does not receive an open signal from any of the switches  114  prior to a preset time period elapsing from engaging the regulators  500 , it determines there is a system pressure problem due to an error in regulators  500  and/or all of the supplies  210  are out of ink, and it disengages the regulators  500  and informs the user of an error. If the controller  118  receives an open signal from all of switches  114  prior to a preset time period elapsing from engaging the regulators  500 , it determines that a normal ink condition exists and that the system is operating at adequate pressure. If the controller  118  receives open signals from at least one but not all of switches  114  prior to a preset time period elapsing from engaging the regulators  500 , it checks the regulator feedback signals to determine if there is a problem regulating pressure from any of the ink supplies  210 . If there is a problem, the controller  118  disengages the regulators  500  and informs the user of an out of ink condition in the ink supply  210  whose regulator  500  had the error. The operation of the controller  118  regarding algorithm  502  is discussed in greater detail below with respect to embodiments of methods for regulating the ink supply pressure. 
     Fourth Illustrative Embodiment 
       FIG. 6  shows a flowchart of a method  600  of regulating an ink supply system  100  according to an embodiment. Method  600  is associated with the ink delivery system  100  of  FIG. 1  and the execution of algorithm  124  on processor  120  to manage the controller  118  in regulating the ink supply system  100 , as discussed briefly above. Method  600 , through the execution of algorithm  124  on processor  120 , operates to determine a normal ink condition, an out of ink condition, or a system pressure problem in ink supply system  100  and to regulate the system accordingly. References made to ink delivery system  100  in the following description of method  600  therefore refer to the  FIG. 1  embodiment of ink delivery system  100 . 
     Referring to  FIG. 6 , method  600  begins at block  602  when the air pressure source (e.g., air pump)  102  is turned on, for example by controller  118  executing a firmware command when a host printer receives a print job. At the same time, as shown at block  604 , a timer is started to keep track of an elapsed time T 1 . At decision block  606 , controller  118  determines whether the elapsed time T 1  has exceeded a preset time limit before an ink valve  112  has opened. The preset time limit is typically determined based on the torque of the air pump motor  102  and the current protection mechanisms in the pump motor  102  that limit the amount of time the pump can run on a continuous basis. 
     In making its determination at decision block  606 , the controller  118  monitors a plurality of ink valve switches  114  within respective ink valves  112  and receives an “open signal” from a switch  114  when the switch senses the opening of its respective ink valve  112 . The “open signal” is typically indicated by a closure of the switch  114 , but may also be indicated by an opening of the switch  144 , depending on the switch configuration. At block  606 , if controller  118  determines that the elapsed time T 1  has exceeded the preset limit before even one ink valve opens, then the air pump  102  is stopped, as shown at block  608 . The user is then informed of a system pressure error at block  610 . A system pressure error indicates a system pressure problem that may be caused by a leak in a hose (e.g., air tubing  108 ) or by a hose that has become unattached and is open, etc. After the user is informed of the system pressure error, the method  600  ends at block  612 . 
     Referring again to decision block  606 , if controller  118  determines that the elapsed time T 1  has not exceeded the preset limit before even one ink valve opens, then the controller  118  checks all the ink valve switches  114  for “open signals” to determine if all the ink valves  112  are open, as shown at decision block  614 . If all the ink valves  112  are open then the controller  118  determines that a normal ink condition exists within system  100 , and it waits an additional period of time T 2  and stops the air pump  102 , as shown at blocks  616  and  618 , respectively. The controller  118  then performs a loop between decision block  620  and decision block  622 , continually checking to see if all the ink valves  112  are still open while also checking for a printer interrupt. If all the ink valves  112  remain open at block  620  and the controller  118  receives a printer interrupt at block  622 , then the method ends at block  624 . In this situation, the print job has probably been completed, causing the printer interrupt, or there may be another reason for the printer interrupt. 
     Referring again to decision blocks  620  and  622 , if all the ink valves  112  do not remain open at block  620  (i.e., if one or more ink valves close during printing), then the controller  118  resets the timer T 1  and restarts the air pump  102 , at blocks  626  and  602 , respectively. 
     Referring again to decision block  614 , if all the ink valves  112  are not open, then the controller  118  checks the air pump motor load through the air pump motor feedback signal mechanism  104 , as shown at decision block  628 . The motor feedback signal may originate from a motor encoder, a back EMF measurement, a measurement of the air pump motor&#39;s current, or a measurement of the pulse width modulation (PWM) delivered to the motor by the printer&#39;s electronics. In any case, the motor feedback signal enables the controller  118  to determine if the air pump motor is experiencing a load which would indicate a higher system pressure. If the motor is experiencing a substantial load, the controller  188  determines that the system  100  is operating at or above the desired pressure, so the air pump  102  is turned off, as shown at block  630 . In this case, the controller  118  determines there is an out of ink condition in one or more ink supplies  106 . At block  632 , the controller  118  evaluates the ink valve switches  114  to determine which valves  112  are closed. The controller  118  concludes that the ink supplies  106  associated with closed ink valves  112  are empty supplies. Thus, at block  634 , the controller  118  informs the user of an out of ink condition with respect to the ink supply or supplies  106  associated with whichever ink valves  112  are closed. The method  600  then ends at block  624 . 
     Referring again to decision block  628 , if the air pump motor is not experiencing a high load, then the controller  118  checks for printer interrupts at decision block  636 . If there is no printer interrupt at block  636 , then the controller  118  begins the method  600  again at decision block  606 . If there is a printer interrupt at block  636 , then the method  600  ends at block  624 . 
     Fifth Illustrative Embodiment 
       FIG. 7  shows a flowchart of a method  700  of regulating an ink supply system  100  according to an embodiment. Method  700  is associated with the ink delivery system  100  of  FIG. 4  and the execution of algorithm  402  on processor  120  to manage the controller  118  in regulating the ink supply system  100 , as discussed briefly above. Method  700 , through the execution of algorithm  402  on processor  120 , operates to determine a normal ink condition, an out of ink condition, a low ink condition and a system pressure problem existing within ink delivery system  100 , and to regulate air pump  102  accordingly. References made to ink delivery system  100  in the following description of method  700  therefore refer to the  FIG. 4  embodiment of ink delivery system  100 . 
     Referring to  FIG. 7 , method  700  begins at block  702  when the air pressure source (e.g., air pump)  102  is turned on, for example by controller  118  executing a firmware command when a host printer receives a print job. At the same time, as shown at block  704 , a timer is started to keep track of an elapsed time T 1 . At decision block  706 , controller  118  determines whether the elapsed time T 1  has exceeded a preset time limit before an ink valve  112  has opened. The preset time limit is typically determined based on the torque of the air pump motor  102  and the current protection mechanisms in the pump motor  102  that limit the amount of time the pump can run on a continuous basis. 
     In making its determination at decision block  706 , the controller  118  monitors a plurality of ink valve switches  114  within respective ink valves  112  and receives an “open signal” from a switch  114  when the switch senses the opening of its respective ink valve  112 . The “open signal” is typically indicated by a closure of the switch  114 , but may also be indicated by an opening of the switch  144 , depending on the switch configuration. At block  706 , if controller  118  determines that the elapsed time T 1  has exceeded the preset limit before even one ink valve opens, then the air pump  102  is stopped, as shown at block  708 . The user is then informed of a system pressure error at block  710 . A system pressure error indicates a system pressure problem that may be caused by a leak in a hose (e.g., air tubing  108 ) or by a hose that has become unattached and is open, etc. After the user is informed of the system pressure error, the method  700  ends at block  712 . 
     Referring again to decision block  706 , if controller  118  determines that the elapsed time T 1  has not exceeded the preset limit before even one ink valve opens, then the controller  118  checks all the ink valve switches  114  for “open signals” to determine if all the ink valves  112  are open, as shown at decision block  714 . If all the ink valves  112  are open then the controller  118  determines that a normal ink condition exists within system  100 , and it waits an additional period of time T 2  and stops the air pump  102 , as shown at blocks  716  and  718 , respectively. The controller  118  then performs a loop between decision block  720  and decision block  722 , continually checking to see if all the ink valves  112  are still open while also checking for a printer interrupt. If all the ink valves  112  remain open at block  720  and the controller  118  receives a printer interrupt at block  722 , then the method ends at block  724 . In this situation, the print job has probably been completed, causing the printer interrupt, or there may be another reason for the printer interrupt. 
     Referring again to decision blocks  720  and  722 , if all the ink valves  112  do not remain open at block  720  (i.e., if one or more ink valves close during printing), then the controller  118  resets the timer T 1  and restarts the air pump  102 , at blocks  726  and  702 , respectively. 
     Referring again to decision block  714 , if all the ink valves  112  are not open, then the controller  118  determines which ink valves  112  are closed at block  728 . At decision block  730 , the controller  118  then checks to see if the pressure switch  400  has been triggered. Pressure switch  400  provides a trigger (e.g., closes) when air pressure in air tubing  108  reaches a preset system air pressure threshold. If the pressure switch  400  has not been triggered, then the controller  118  continues the method at decision block  706 , as discussed above. If the pressure switch  400  has been triggered, however, then the controller  118  checks if all the ink valves  112  are open at decision block  732 . If all ink valves are open, the controller  118  concludes there is a low ink condition in the ink supply or supplies  106  associated with the ink valve or valves  112  determined at block  728  to have been closed. The controller  118  then informs the user of the low ink condition at block  734  and the method  700  continues at block  716  as discussed above. 
     Referring again to decision block  732 , if all the ink valves  112  are not open, then the controller  118  checks the air pump motor load through the air pump motor feedback signal mechanism  104 , as shown at decision block  736 . The motor feedback signal may originate from a motor encoder, a back EMF measurement, a measurement of the air pump motor&#39;s current, or a measurement of the pulse width modulation (PWM) delivered to the motor by the printer&#39;s electronics. In any case, the motor feedback signal enables the controller  118  to determine if the air pump motor is experiencing a load which would indicate a higher system pressure. If the motor is experiencing a substantial load, the controller  188  determines that the system  100  is operating at or above the desired pressure, so the air pump  102  is turned off, as shown at block  738 . In this case, the controller  118  determines there is an out of ink condition in one or more ink supplies  106 . At block  740 , the controller  118  evaluates the ink valve switches  114  to determine which valves  112  are closed. The controller  118  concludes that the ink supplies  106  associated with closed ink valves  112  are empty supplies. Thus, at block  742 , the controller  118  informs the user of an out of ink condition with respect to the ink supply or supplies  106  associated with whichever ink valves  112  are closed. The method  700  then ends at block  724 . 
     Referring again to decision block  736 , if the air pump motor is not experiencing a high load, then the controller  118  checks for printer interrupts at decision block  744 . If there is no printer interrupt at block  744 , then the controller  118  begins the method  700  again at decision block  706 . If there is a printer interrupt at block  744 , then the method  700  ends at block  724 . 
     Sixth Illustrative Embodiment 
       FIG. 8  shows a flowchart of a method  800  of regulating an ink supply system  100  according to an embodiment. Method  800  is associated with the ink delivery system  100  of  FIG. 5  and the execution of algorithm  502  on processor  120  to manage the controller  118  in regulating the ink supply system  100 , as discussed briefly above. Method  800 , through the execution of algorithm  502  on processor  120 , operates to determine a normal ink condition, an out of ink condition and a system pressure problem due to regulator error, existing within self-pressurized ink supplies  210  of ink delivery system  100 , and to regulate air pressure accordingly through control of first stage regulators  500 . References made to ink delivery system  100  in the following description of method  800  therefore refer to the  FIG. 5  embodiment of ink delivery system  100 . 
     Referring to  FIG. 8 , method  800  begins at block  802  when the first stage regulators  500  are engaged, for example by controller  118  executing a firmware command when a host printer receives a print job. At the same time, as shown at block  804 , a timer is started to keep track of an elapsed time T 1 . At decision block  806 , controller  118  determines whether the elapsed time T 1  has exceeded a preset time limit before an ink valve  112  has opened. 
     In making its determination at decision block  806 , the controller  118  monitors a plurality of ink valve switches  114  within respective ink valves  112  and receives an “open signal” from a switch  114  when the switch senses the opening of its respective ink valve  112 . The “open signal” is typically indicated by a closure of the switch  114 , but may also be indicated by an opening of the switch  144 , depending on the switch configuration. At block  806 , if controller  118  determines that the elapsed time T 1  has exceeded the preset limit before even one ink valve opens, then the regulators  500  are disengaged, as shown at block  808 . The user is then informed of a system pressure error at block  810 . A system pressure error indicates a system pressure problem that may be caused by a leak in a hose (e.g., air tubing  108 ), by a hose that has become unattached and is open, or by a regulator  500  malfunction. After the user is informed of the system pressure error, the method  800  ends at block  812 . 
     Referring again to decision block  806 , if controller  118  determines that the elapsed time T 1  has not exceeded the preset limit before even one ink valve opens, then the controller  118  checks all the ink valve switches  114  for “open signals” to determine if all the ink valves  112  are open, as shown at decision block  814 . If all the ink valves  112  are open then the controller  118  determines that a normal ink condition exists within system  100 , and it checks for a printer interrupt at block  816 . If the controller  118  receives a printer interrupt at block  816 , then the method ends at block  818 . In this situation, a printer interrupt likely indicates the print job has been completed, or there may be another reason for the printer interrupt. If there is no printer interrupt at block  816 , the controller  118  resets the timer T 1  at block  820  and begins the method  800  again at block  804 . 
     Referring again to decision block  814 , if all the ink valves  112  are not open, then the controller  118  determines if there is a regulator  500  error at decision block  822 . If there is no regulator error, the controller  118  begins the method  800  again at decision block  806 . If there is a regulator error, however, the controller  118  disengages the regulators  500  as shown at block  824 , and determines which ink valves  112  are closed at block  826 . At block  828 , the controller then informs the user that there is an out of ink condition with respect to those self-pressurized ink supplies  210  associated with those ink valves  112  determined to be closed at block  826 . The method  800  then ends at block  812 . 
     Seventh Illustrative Embodiment 
       FIG. 9  shows a flowchart of a general method  900  of regulating an ink supply system  100  according to an embodiment. Method  900  generally encompasses methods  600 ,  700  and  800  discussed above and is therefore generally associated with the ink delivery systems  100  of  FIGS. 1 ,  4  and  5 , and the execution of algorithms  124 ,  402  and  502  on processor  120  to manage the controller  118  in regulating the ink supply system  100 . Method  900 , through the execution of algorithms  124 ,  402  and  502  on processor  120 , operates to determine a normal ink condition, an out of ink condition, a low ink condition and a system pressure problem existing within ink supplies  106  and  210  of ink delivery system  100 , and to regulate air pressure accordingly. References made to ink delivery system  100  in the following description of method  900  therefore may refer to any of the embodiments of the ink delivery systems  100  illustrated in  FIGS. 1 ,  4  and  5 . 
     Referring to  FIG. 9 , method  900  begins at block  902  with initiating an air pressure source. As shown at block  902 , initiating an air pressure source can include any starting of an air pressure source already discussed above with respect to the methods of  FIGS. 6-8 , such as, starting an air pump or engaging first stage regulators. Method  900  continues at block  904  with monitoring ink valve switches to determine one of a system pressure problem, a normal ink condition, an out of ink condition or a low ink condition. Monitoring may include any of the various steps already noted above with respect to the methods of  FIGS. 6-8 , such as, starting a timer upon initiation of the air pressure source, comparing a preset time limit with a time T 1  elapsed since start of timer, determining that T 1  exceeds the preset time limit without having received an open signal from an ink valve switch, concluding that the system pressure problem exists, receiving an open signal from an ink valve switch prior to T 1  exceeding the preset time limit, determining from receiving additional open signals that all ink valves are open, concluding that the normal ink condition exists, determining from receiving additional open signals from fewer than all ink valve switches that at least one ink valve is not open, concluding that the out of ink condition exists, identifying a closed ink valve based on an absence of an open signal, determining that a system pressure switch has closed, determining from receiving open signals from all of the ink valve switches, that all ink valves are open, concluding that the low ink condition exists with respect to an ink supply associated with the previously closed ink valve. 
     Method  900  continues at block  906  with regulating the air pressure source based on the determination. Regulating may include any of the various steps already noted above with respect to the methods of  FIGS. 6-8 , such as, stopping the air pressure source, informing a user of the system pressure problem, stopping the air pressure source after an additional time T 2 , checking a motor load on the air pressure source, stopping the air pressure source when the motor load exceeds an upper limit, identifying closed ink valves based on an absence of open signals, informing a user of the low ink condition.