Abstract:
A system for intermittently refilling the cartridge reservoir in an ink jet printer from an off-board ink supply tests the ink flow path prior to initiating a refill operation. Air at a pressure greater than the ink feed pressure is applied to the ink flow path to check the integrity of the system. After venting the system to the atmosphere, a slow leak check is made by closing the system, pressurizing it at the feed pressure, turning off the pressure source and, after a short interval, checking the pressure to see if the feed pressure is being maintained. If the integrity check or the slow leak test should fail, the refill operation is aborted and an indicator is set to alert an operator that intervention is required. During the interval the system is being raised from atmospheric to feed pressure, the air displacement is measured and saved as an indication of whether the amount of ink in the off-board supply exceeds a given level. As ink is being transferred into the reservoir, the ink level in the reservoir is monitored. When the ink level does not rise, or rises too slowly, the saved air displacement is used to determine whether to abort the refill operation and indicate a system problem, or set an indicator to signal that the off-board ink supply is exhausted. A controller measures the air displacement by measuring the time, or counting the number of pump strokes, required to raise the system pressure from atmospheric to feed pressure.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method and apparatus for refilling disposable ink cartridges of ink jet printheads from ink reservoirs located off-board the printhead carriages. The pressure in ink lines connecting the off board reservoirs to the cartridges is monitored prior to and during a refill operation so that refilling is prohibited or stopped if an ink line is open to atmospheric pressure. 
     BACKGROUND OF THE INVENTION 
     To reduce printhead carriage mass so as to obtain high carriage accelerations and velocities, ink jet printers are provided with ink reservoirs located off-board the carriages, ink in these reservoirs being used to replenish ink drawn from the printhead cartridge reservoirs during printing. The refill may take place continuously or intermittently. For continuous refilling, the off-board reservoirs may be connected via hoses to the printhead cartridges as shown for example in U.S. Pat. No. 5,369,429. For intermittent refilling as shown in U.S. Pat. Nos. 5,136,305, 4,967,207 and 4,968,998, the printheads are moved to a refill station where the printhead cartridges are refilled with ink from the off-board reservoirs. 
     Ink leakage is a particular concern in network printers using the intermittent type refill system. Such printers are frequently left running unattended for extended periods of time and, generally speaking, have larger off-board ink reservoirs. Therefore, the potential for catastrophic ink spillage exists if a leak should occur during a period when the printer is running unattended. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a refill system for intermittently refilling a cartridge reservoir of an ink jet printer from an off-board ink supply, the system providing checks for catastrophic and slow leaks prior to initiating each refill operation. 
     Another object of the invention is to provide a refill system for intermittently refilling the cartridge reservoir of an ink jet printer from an off-board ink supply via an ink flow path, the refill system being characterized in that the ink flow path is monitored for leaks both before and during each refill operation. 
     A further object of the invention is to provide a refill system for intermittently refilling the cartridge reservoir of an ink jet printer from an off-board ink supply via an ink flow path, the system being characterized in that, after each refill operation, ink is purged from the ink flow path and the path is vented to the atmosphere. 
     According to the invention, a refill system for intermittently refilling the cartridge reservoir of an ink jet printer from an off-board ink supply comprises an ink flow path connected to the ink supply for dispensing ink into the cartridge reservoir; a pressure detector; an air pump; a pressure control valve for selectively connecting the ink flow path and the ink supply to the air pump; a controller responsive to the pressure detector for controlling the pump and the pressure control valve to apply air at a test pressure from the pump to the ink flow path to check for leaks in the ink flow path, and apply air at an ink feed pressure from the pump to the ink supply to feed ink from the ink supply through the ink flow path to the cartridge reservoir. A dispensing valve blocks the ink flow path during the interval the test pressure is being applied and vents the ink flow path to the atmosphere after a refill operation is completed. The control valve is a multiport valve having positions for connecting the ink flow path to the atmosphere or to the pump, and positions for applying atmospheric pressure or pressure from the pump to the off-board ink supply. 
     In accordance with one aspect of the invention, the air displacement required to raise the pressure in the ink flow path from atmospheric pressure to the ink flow pressure is measured and utilized as an indication of the volume of ink in the off-board ink supply prior to initiating an ink transfer. 
     In accordance with a further aspect of the invention, an ink level sensor is provided in the cartridge reservoir for sensing the level of ink therein. During a refill operation the controller monitors the ink level sensor to determine if the ink level is continuously rising. If the ink level is not continuously rising, the refill operation is terminated and an indicator is set. In an alternative embodiment, one of two indicators may be set depending on the saved indication of the volume of ink in the off-board ink supply prior to initiating the ink transfer. 
    
    
     Other objects and advantages of the invention will become obvious upon consideration of the following description and the accompanying drawings. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 schematically illustrates an ink supply system according to the invention; 
     FIG. 2 is a sectional view of a pressure sensor suitable for use in the ink supply system; 
     FIG. 3 is a block diagram illustrating electrical connections between components of the ink supply system; 
     FIGS. 4A-4D illustrate four positions of a control valve used to control pressure in the system; and, 
     FIGS. 5A and 5B illustrate a dispensing valve in a dispensing position (FIG. 5A) and a venting position (FIG.  5 B). 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     FIG. 1 illustrates an ink supply system  10  for replenishing the ink supply in a single, preferably foam-filled, ink reservoir  12  of a printhead cartridge  14 . The cartridge  14  is conventional and is mounted in a conventional manner on a printhead carriage  16  slidable back and forth on a support shaft  17  so that the cartridge may be moved back and forth during printing or moved to a refill station (not shown) when the supply of ink in reservoir  12  must be replenished. 
     Ink supply system  10  comprises a pump or pressure source  18 , an off-board ink reservoir  20 , a pressure control valve  22 , a dispensing valve  24  and a pressure sensor  26 . Pressure source  18  may, for example, comprise a pump or bellows  28  and an electric drive motor  30  for alternately expanding and contracting the bellows, but other pressure sources may be used provided they may be controlled as subsequently described to vary the pressure in an air line  32  connected to the chamber  29  of the bellows. 
     The off-board reservoir  20  may also be of conventional design but preferably comprises an air-tight rigid hollow shell  34  having therein a bladder or sac  36  filled with ink. The shell is provided with first and second openings  38 , 40  which are sealed by elastic barriers that are pierceable by hollow needles (not shown). One needle connects with an air line  42  and the other needle connects with an ink flow path, comprising lines  44  and  64 , through a check valve  45 . When cartridge reservoir  12  requires refilling, a positive pressure is applied via line  42  to the interior region of shell  34  between the shell and bladder  36  so that ink is forced out of the bladder through check valve  45  and through the ink flow path  44 , 64 . 
     The control valve  22  is preferably a multi-port ball valve having input ports  50  and  52  vented to atmosphere, an input port  54  connected to the air line  32 , and first and second output ports  56  and  58 . Output port  56  is connected via the air line  42  to the region between the shell  34  and bladder  36 . Output port  58  is connected via an air/ink line  60  to a T-connector  62  having arms connecting the ink output line  44  of the ink reservoir  20  to an ink line  64  which conveys ink from the reservoir to an input port  70  of dispensing valve  24 . Because the greatest exposure to ink loss is through lines  44 ,  60  and  62  in the region near T-connector  62 , the sections of these lines which are below the top of reservoir  20  are strengthened to increase leak resistance. 
     Valve  22  has a handle  48  that is driven or stepped between four positions by electro mechanical or other drive means so as to connect the input ports of the valve to its output ports via two air passages  55 ,  57  in ball  59 . The connections may be made in any one of four configurations as shown in FIGS. 4A-4D. Handle  48  is biased so that when it is not driven, valve  22  returns to the state shown in FIG.  4 D. By way of example only, handle  48  may be driven by a spring biased rotary stepper motor. 
     Valve  24  is a ball valve having a handle  74  that is driven or stepped between two positions (FIGS. 5A and 5B) by electro-mechanical or other drive means so as to selectively connect one of the valve input ports  68  or  70  to the output port  72  via one of two passages  69 , 71  in ball  73 . Input port  68  is vented to atmosphere and input port  70  is connected to the reservoir  20  via ink lines  64  and  44 . The ink line dispensing segment  46  is connected to the output port  72 . Handle  74  is biased so that when the handle is not driven, the dispensing line  46  is connected to atmosphere via passage  69  and input port  68  as shown in (FIG.  5 B). 
     Pressure sensor  26  is provided to sense the pressure in air line  32 . As illustrated in FIG. 2, the pressure sensor  26  is a low-cost digital sensor including a flexible membrane  76  which divides the interior of a housing  78  into first and second chambers  80  and  82 . Chamber  80  connects with air line  32  via an opening  84  so that air pressure in line  32  acts against the membrane  76 . A flexible electrical contact  86  is disposed within chamber  82  and connected at one end in cantilever fashion to an electrical terminal  88 . The contact  86  engages the flexible membrane  76  so that as the pressure in line  32  varies the pressure in chamber  80  to move the membrane, the free end surface  90  of the contact wipes across a plurality of arcuately disposed stationary electrical contacts  92 , 94  held within a non-conductive stationary frame  96 . 
     Membrane  76  is capable of moving contact  86  so that the contact end surface  90  may move over a range from below contact  92  to above contact  94 . Pressure sensor  26 , in combination with a microprocessor controller  100  (FIG. 3) monitors line  32  for three different pressures or, more accurately, three different pressure ranges. The first pressure is atmospheric pressure. When the pressure in line  32  and chamber  80  is at atmospheric pressure the surface  90  is below contact  92  so that there is no electrical connection through the sensor. 
     The second pressure range, referred to herein as the ‘low’ or ink feed pressure is on the order of 5 to 10 inches of water. The low pressure, when admitted to the reservoir  20  via valve  22  and line  42 , is adequate to force ink at the desired rate from reservoir  20  to the cartridge  14  via valve  24 . When the pressure in line  32  is in the ‘low’ pressure range, contact surface  90  ranges in position (moving counterclockwise) from just engaging the lower edge of contact  92  to a position just engaging the lower edge of contact  94 . 
     The third pressure range, referred to herein as the ‘high’ or test pressure range, is on the order of two to three times the low pressure and is used to check the system for leaks. A pressure of this magnitude causes membrane  76  to move contact  86  counterclockwise from the low to the high pressure range. While in the ‘high’ pressure range, contact surface  90  ranges in position (moving counterclockwise from the ‘low’ position) from no longer engaging the upper edge of contact  92  to a position no longer engaging the upper edge of contact  94 . 
     At pressures above the range of the high pressure, contact end surface  90  moves above contact  94  so that there is no electrical connection through the sensor. 
     The arcuate length of surface  90  is greater than the arcuate distance of frame  96  between contacts  92  and  94  so that the surface  90  may bridge or simultaneously engage both contacts. The purpose of this bridging is to allow the controller  100  to distinguish between, on one hand, a pressure between the high and low pressures, and on the other hand, atmospheric pressure or a pressure higher than the high pressure. Without bridging, all three conditions would result in the same output signal from the sensor. 
     By providing the contact bridging, only atmospheric pressure and a pressure higher than the high pressure result in the same output indication from the sensor, and the controller can determine which is the correct pressure by considering the previous pressure indication. Each time the controller  100  determines a pressure, it saves an indication of the pressure, and by comparing a previous indication with a current indication the controller can determine if the correct pressure is atmospheric or higher than the high pressure. For example, if the controller samples the sensor by applying a signal to terminal  88 , and no output signal is produced at either contact  92  or  94 , the pressure may be either atmospheric or higher than the high pressure. The previous saved indication is examined and if it indicated a high pressure then the current pressure must be higher than the high pressure, but if the saved indication indicated a low pressure then the current pressure must be atmospheric pressure. 
     The printhead cartridge  14  has therein an ink level sensor  98 . Sensor  98  may be a variable sensor having a capacitance which varies according to the level of ink in the foam-filled ink reservoir  12 . The controller  100  (FIG. 3) samples the sensor  98  on the order of every 100 ms and includes an analog-to-digital. converter  101  for digitizing the feedback signal from the sensor. The controller compares the digitized value with two reference values to determine when the reservoir  12  is ‘empty’, that is, when the ink level is so low that the reservoir should be refilled, or full. As subsequently explained, the feedback signal from sensor  98  is also monitored during intervals when ink should be flowing into the reservoir  12  and serves as a way for detecting when the off-board reservoir  20  is empty. Preferably, the sensor  98  is connected to controller  100  via contacts on a conventional flex circuit  99  so that the sensor feedback signal is lost if the cartridge  14  is removed from the carrier  16 . This permits detection of the removal of the cartridge during a refill operation so that ink loss may be minimized by terminating the refill operation as later described. 
     As shown in FIG. 3, the cartridge ink level sensor  98 , pressure sensor  26 , the drive motors for valves  22  and  24 , and bellows drive motor  30  are connected to the controller  100 . The controller may be the microprocessor which controls operation of the printer and is of conventional design. Periodically, the controller samples the level sensor  98  in the printhead cartridge  14  and when the sensor indicates that the cartridge requires refilling, the controller controls a carriage drive mechanism  102  which moves carriage  16  and the cartridge to a refill station (not shown), slides open a sliding cover  15  on the cartridge, and establishes a connection between the dispensing line  46  and the reservoir  12 , after which the controller initiates a refill operation. The drive mechanism and refill station are not shown but they may take any one of many forms known in the art. The cartridge, for example, may have an ink input opening closed by a valve as shown in the patents mentioned above, so that the sliding cover is not required. 
     A refill operation is initiated when controller  100  determines that the reservoir  12  is empty and the cartridge  14  is positioned at the refill station. Prior to initiation of a refill operation the system is in an initial or reset state wherein bellows drive motor  30  is off, the valve  22  is in the position shown in FIG. 4D so that line  42  is connected to the ambient atmosphere via passage  57  and the valve port  52 , and dispensing valve  24  is in the position shown in FIG. 5B so that the dispensing line  46  is connected to ambient atmosphere via passage  69  and valve port  68 . There is no ink in any of the lines or connections  32 ,  42 ,  44 ,  46 ,  60  and  64 , except for possibly a small amount of ink in the region of the T-connection  62 . The refill operation is carried out in five phases. 
     Phase I. 
     In phase I, the integrity of the system is checked to determine if there are any leaks in the ink lines  44  and  64  or their connections, or if there is no off-board supply of ink connected to the system. The controller  100  sets valve  22  to the position shown in FIG. 4B so that communication is established between line  32  and lines  60 ,  44  and  64 . Next, the controller energizes motor  30  for a fixed interval of time or for a fixed number of strokes. Since valve  24  is still in the position shown in FIG. 5B, the downstream end of line  64  is blocked by the valve so that operation of bellows  28  builds up the pressure in lines  32 ,  60 ,  44  and  64 . The check valve  45  prevents air from entering bladder  36  during this time. 
     The motor  30  is energized for an interval of time T 1 , or for a fixed number of strokes of bellows  28  sufficient to raise the pressure in the lines to the high pressure. It is possible that the high pressure may be achieved even though there is a slow leak in the system. Therefore, after the interval T 1  has elapsed, the controller waits for a second interval T 2 . At the end of interval T 2  the controller samples the output of pressure sensor  26  to determine if the high pressure is still being maintained in the lines. 
     The intervals T 1  and T 2  will vary depending on such factors as bellows volume and stroke length and the internal volume of the portion of the system being tested. 
     If the high pressure is not maintained until the end of interval T 2 , there must be a leak in the system. The controller  100  terminates the refill operation and sets a visual or audible indicator  104  (FIG. 3) to signal that service intervention is required. On the other hand, if the system is still at the high pressure the controller advances to phase II of the refill operation. 
     Phase II. 
     This phase releases the high pressure used to test the integrity of the ink lines and their connections. The phase is initiated when the controller sets valve  22  to the position shown in FIG.  4 A. This connects lines  60 ,  44  and  64  to atmosphere through passage  55  and valve port  55  thus releasing the high pressure in these lines. At the same time, air under the high pressure is trapped in line  32 . 
     Next the controller moves valve  22  to the position shown in FIG. 4C thereby connecting the interior of shell  34  to line  32  via line  42  and passage  55  in the valve. This releases the air under high pressure trapped in line  32 . Because the free air volume of shell  34  is much greater than the volume of line  32 , the pressure in line  32  drops to some value which is insignificantly above atmospheric pressure. 
     Phase III. 
     This phase tests the ability of the system to maintain the low pressure level necessary for causing the feeding of ink from reservoir  20  to the dispensing line  46 . Controller  100  energizes pump drive motor  30  and begins monitoring the pressure by sampling pressure sensor  26 . The pump motor is energized for an interval of time T 3  or until the sensor indicates that the low pressure has been reached, whichever comes first. The air displacement (pump motor on time or number of pump strokes) required to reach the low pressure level is saved in a memory in controller  100  as an indication of the ink level in the off-board reservoir  20 . If the minimum air displacement is required, the reservoir  20  is full but if the maximum air displacement is required the reservoir is empty or almost empty. A value somewhere between the maximum and minimum can be used to infer, by interpolation, the current ink level or capacity of the reservoir  20 . 
     The controller  100  repetitively samples sensor  26  while the pump motor is energized. If the pressure in line  32  reaches the desired pressure within the interval T 3  then a check is made for a slow leak in the air line  42  and its connections. The energizing of the pump motor and the sampling of the pressure sensor are terminated either when the pressure in line  32  reaches the low pressure or when the interval T 3  has elapsed. Then, after an interval T 4  the pressure sensor is again sampled. If the line  32  is still at the low pressure, it means that there is no leak and phase IV of the refill operation is initiated. 
     If, at the end of interval T 4 , the pressure in line  32  has dropped below the low level, it means that there is a leak in line  42  or its connections. The indicator  104  is energized to signal that operator intervention is required and the refill operation is aborted by jumping to Phase V described below. 
     If the pressure in line  32  never reaches the low pressure during the interval T 3 , it probably means that reservoir  20  is not installed. The refill operation is aborted by jumping to Phase V and an indicator is energized to signal the operator. This indicator may be the indicator  104  but preferably it is a different indicator  106  so the operator may immediately discern the problem. 
     Phase IV. 
     The actual refill or transfer of ink from off-board reservoir  20  to printhead cartridge reservoir  12  takes place during phase IV. Dispensing valve  24  is set to the position shown in FIG. 5A so that the dispensing line  46  communicates with ink line  64  through passage  71  and valve port  70 . Control valve  22  was set to the position shown in FIG. 4C during phase III and is still in that position so as soon as valve  24  is set, the low pressure in lines  32  and  42  and in shell  34  forces ink from bladder  36  so that it flows through lines  44  and  64 , valve  24  and line  46  to the cartridge reservoir  12 . 
     As the ink flows from the bladder, the pressure in lines  32  and  42  and shell  34  gradually drops. The controller  100  periodically samples the pressure sensor  26  during phase IV and, when the sensor produces an indication that the pressure has dropped below the low pressure, the controller energizes pump motor  30  to bring the system back to the low pressure level. Referring to FIG. 2, the pump is energized when contact surface  90  moves below contact  92  and the energizing continues until the contact surface  90  has been moved counterclockwise to bridge between contact  92  and the lower edge of contact  94 . 
     The refill operation continues for a fixed interval of time T 5  or until the level sensor  98  indicates to the controller  100  that the cartridge reservoir  12  is full. 
     The interval T 5  is the time it should take to refill an empty cartridge if the refill system is operating normally and there is no leakage or blockage of the ink flow path. 
     During the interval T 5  the controller  100  repetitively samples the level sensor  98  which should indicate rising levels of ink in cartridge reservoir  12  if ink is flowing from the off-board reservoir  20  into the cartridge reservoir. If the sampling of sensor  98  does not indicate a rising ink level in reservoir  12  and if the air displacement required to bring the system to the low pressure during Phase III exceeded a threshold value (indicating a low level of ink in reservoir  20 ) the controller sets indicator  106  to signal an operator that the off-board reservoir  20  is empty. In this case printing may be continued until the ink in cartridge reservoir  12  is exhausted. On the other hand, if the sampling of level sensor  98  does not indicate a rising ink level in reservoir  12  but the air displacement required to bring the system to the low pressure during Phase III did not exceed the threshold value (indicating an adequate level of ink in reservoir  20 ) indicator  104  is turned on to signal that operator intervention or a service call is required. 
     As previously stated, the pump  18  is intermittently actuated during Phase  4  to bring the system pressure back to the low level. During the entire Phase  4  the time between pump actuations and the time (or number of actuations) required to return the system to the low pressure level are closely monitored by controller  100 . If pressure is lost too soon or if it takes too long to bring the system back to the low pressure level, the ink is flowing at an unusually high rate. This indicates a leak. Indicator  104  is actuated to signal that operator intervention is required, Phase IV is terminated and Phase V is initiated. 
     On the other hand, if the pressure drops too slowly the ink is flowing at too slow a rate. This indicates a blockage. Again, indicator  104  is actuated, Phase IV is terminated and Phase V is initiated. 
     Phase V. 
     Phase V is carried out after a successful refill operation or when the refill operation is aborted. During Phase V the system is depressurized and the lines are purged of ink. Control valve  22  is permitted to return to the position shown in FIG. 4D so that the pressure in reservoir  20  and line  42  is relieved by venting to the atmosphere through outlet  52 . Valve  22  is then set to the position shown in FIG. 4B so that line  32  communicates with line  60  through passage  57 . Pump  18  is energized for a fixed interval of time sufficient to drive ink in lines  60  and  64  through dispensing valve  24 , fill tube  46  and into the cartridge reservoir  12 . Pump  18  is then stopped and control valve  22  is returned to the position shown in FIG. 4A thereby relieving the pressure in lines  44 ,  46 ,  60  and  64  and valve  24 . Finally, dispensing valve  24  is permitted to return to the position shown in FIG. 5B so that line  46  is open to the atmosphere through port  68  and ink in the fill tube drains into the cartridge reservoir. 
     A small volume of ink remains in line  44  until the next refill operation. This volume may be adjusted or selected by proper selection of the length and/or diameter of line  44 . An adequate volume must exist such that the ink remains in a fluid state after air trapped in lines  60  and  64  becomes saturated with water vapor from the ink trapped in line  44 . If the ink volume in line  44  is at least 1% of the air volume in lines  60  and  64 , less than 1% of the water in the trapped ink will be lost as water vapor. 
     The invention may be adapted for use in color printers having three ink supplies  20  for refilling each of three printhead cartridge reservoirs  12  with inks of different colors. The cartridge reservoirs may be contained within a single cartridge or each reservoir may be in a different cartridge. If more than one printhead cartridge is used, the apparatus described above may be duplicated for each cartridge, or another multiport valve, similar to control valve  22 , may be provided between the pressure detector  26  and the existing control valve  22 , allowing use of a single pump and pressure detector for all cartridges. 
     If plural reservoirs are provided in a single cartridge, the control valve  22  must have an additional output for each reservoir and the dispensing valve  24  must have an additional output for each cartridge reservoir. 
     From the foregoing description it is evident that the ink supply system of the present invention provides many advantages over the prior art. Prior to each cartridge refill operation the system is checked for leaks using air rather than ink, thus reducing ink loss if there is a leak in the system. Because the system is tested at high pressure relative to its operating pressure, potential causes of ink leakage may be detected before actual ink loss occurs. In the event of a leak the source of the leak may be determined with air by turning the system on one or more times while examining lines, connections, etc. This avoids the necessity of repeating an earlier failing condition with its attendant loss of ink. 
     If electrical power is lost during a refill operation, the system automatically returns to the initial state. The bias on the handle of valve  22  returns the valve to the position shown in FIG. 4D so that the pressure in reservoir  20  and line  42  is relieved, and the bias on the handle of valve  24  returns this valve to the position shown in FIG. 5B so that dispensing line  46  is vented to the atmosphere to permit any ink therein to drain into cartridge reservoir  12 . 
     Although some ink may be lost if an ink line should break or fall off while ink is being pumped, the pumping operation is aborted within a small fraction of a second, thereby reducing ink loss, and the system is returned to its initial state. The pumping operation is also aborted to reduce ink loss if the printhead cartridge  14  is removed during a refill operation. 
     Finally, the ink supply system monitors the presence of the off-board reservoir and the presence of an adequate supply of ink therein, and informs an operator when the reservoir requires attention.