Abstract:
An ink jet recorder includes an ink jet head having nozzles, through which ink can be ejected. The recorder also includes an apparatus for purging the head. The apparatus includes a cap for covering the nozzles. The apparatus also includes a suction pump for sucking ink from the head through the cap covering the nozzles. The apparatus further includes a memory, a temperature sensor and a controller. The memory stores the purge interval at which the pump should suck ink. The sensor measures ambient temperature. If the measured temperature is abnormal, the controller replaces the stored purge interval with shorter interval. In this case, the apparatus purges the head at the shorter interval. This keeps the ejection of ink in good condition regardless of ambient temperature.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an apparatus for purging the ink jet head and an ink jet recorder including the ink jet head. In particular, the invention relates to an ink jet head purging apparatus which can suitably change the suction time interval depending on ambient temperature variations, and an ink jet recorder including the ink jet head. 
     2. Description of Related Art 
     A conventional ink jet printer includes a print head having a number of nozzles for ejecting ink to print a sheet of paper. While the head is used, air bubbles may be produced in it, and ink may stick to the nozzle walls, resulting in defective ejection of ink. If the printer is not used for a long time, the nozzles may clog with thick ink, resulting in defective ejection of ink. Defective ejection of ink results in defective print. In this case, the nozzles are purged to recover good ejection of ink. The purging includes capping the head with a suction cap, and sucking ink out of the capped head by a pump developing negative pressure. Normally, the nozzles are purged at regular interval of time, which may be five days. 
     Because the ink ejected from the print head is a viscous liquid, however, its state may change at abnormal temperature. Therefore, at abnormal temperature, if the nozzles are not purged frequently, the ejection of ink from nozzles may become defective. If the purging time interval is short on the assumption that the temperature may be abnormal, the purges at normal temperature are too frequent. This accelerates the ink consumption of the printer, because the purging involves suction of ink. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing problem, it is an object of the invention to provide an ink jet head purging apparatus which can change the suction time interval depending on ambient temperature variations. It is another object to provide an ink jet recorder including such a purging apparatus. 
     In accordance with a first aspect of the invention, an apparatus is provided for purging an ink jet head having nozzles, through which ink can be ejected. The apparatus includes a cap for covering the nozzles. The apparatus also includes a suction pump for sucking ink from the nozzles through the cap covering the nozzles. A memory stores the regular interval at which the pump should suck ink from the nozzles. A temperature sensor measures ambient temperature. Depending on the measured temperature, a suction interval change device can change the stored interval. A controller can operate the pump at the stored interval. 
     If the ambient temperature measured by the temperature sensor reaches either a low or a high temperature which may cause defective ejection of ink, the suction interval change device changes the suction or purge interval stored in the memory. The changed interval may be shorter than the set interval. The controller causes the suction pump to suck ink at the changed interval. Therefore, the apparatus can purge the ink jet head at suitable interval depending on the temperature history around the head. Consequently, the ejection of ink from the head can be kept in good condition at any temperature. 
     The purging apparatus may include a counter counting how many times the temperature measured by the temperature sensor is out of a predetermined range of temperature, which may be between 10 and 35 centigrade. If the temperature has been out of the range more than a predetermined number of times, which may be 24 times, the controller may cause the suction pump to suck ink. The reason for this is that it is enough to purge the ink jet head only if the ambient temperature keeps abnormal for a predetermined period. This prevents the head from being purged too often and ink from being wasted. 
     The purging apparatus may include a timer for clocking the elapsed time after the preceding purge. 
     The purging apparatus may include a reset device for initializing the stored purge interval after the suction pump sucks ink. For instance, if the suction interval change device has shortened the stored interval from five days to three days, the reset device replaces the shortened interval with five days again. Consequently, after the ink jet head is purged, it is purged at the same interval to keep its ejection of ink in good condition unless the ambient temperature becomes abnormal. After the pump sucks ink, the reset device may reset at least one of the counter and the timer. 
     The temperature sensor may be a temperature detecting circuit including a thermister. 
     The controller may be an exclusive purge controller fitted in the purging apparatus. Otherwise, the controller may be a minicomputer connected to the apparatus. The controller may also function as the suction interval change device. 
     In accordance with a second aspect of the invention, an ink jet recorder is provided. The recorder includes an ink jet head having nozzles, through which ink can be ejected. The recorder also includes an apparatus for purging the head. The apparatus includes a cap for covering the nozzles. The apparatus also includes a suction pump for sucking ink from the nozzles through the cap covering the nozzles. A memory stores the regular interval at which the pump should suck ink from the nozzles. A temperature sensor measures ambient temperature. Depending on the measured temperature, a suction interval change device can change the stored interval. A controller can operate the pump at the stored interval. 
     Depending on ambient temperature, the purge interval of the purging apparatus (recovery mechanism) of the recorder are controlled. Therefore, regardless of ambient temperature variation, the ejection of ink from the ink jet head can be kept in good condition. 
     The purging apparatus of the recorder may purge the ink jet head provided that a signal for recording is input to the recorder. Otherwise, whether a signal for recording is input to the recorder or not, the apparatus may be forced to purge the head at the interval stored in the memory. 
     The recorder may include a timer for clocking the elapsed time after the preceding suction. When a signal for recording is input to the recorder, the controller compares the elapsed time clocked by the timer with the stored interval. As a result of the comparison, if the clocked time is longer than the stored interval, the controller causes the suction pump to suck ink. 
     The temperature sensor of the recorder may be a temperature detecting circuit including a thermister. 
     The controller of the recorder may be an exclusive purge controller fitted in the purging apparatus of the recorder. Otherwise, the controller may be a printer control circuit in the recorder, which may be an ink jet printer. Otherwise, the controller may be a minicomputer connected to the apparatus or the recorder. The controller may also function as the suction interval change device. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A preferred embodiment of the invention will be described with reference to the accompanying drawings, in which: 
     FIG. 1 is a perspective view of a piece of multifunctional peripheral equipment embodying the invention; 
     FIG. 2 is a perspective view of the ink jet printer mounted in this equipment; 
     FIG. 3 is a block diagram of the electric system of this equipment; 
     FIG. 4 is a flow chart of the purge interval change process executed in the printer unit of this equipment; 
     FIG. 5 is a flow chart of the purge process executed in this printer unit. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     With reference to FIGS. 1 and 2, a piece of multifunctional peripheral equipment  1  embodying the invention functions as a fax machine, a scanner, a copier, a video printer and another printer. The equipment  1  is fitted with an ink jet printer  26  for multicolored print. The printer  26  is a serial printer, which includes a print head unit  65 . The unit  65  is mounted on a carriage  66 , which can move in the direction A and the opposite direction. 
     As shown in FIG. 1, the equipment  1  includes a body  2  in the form of a box. A control panel  3  is mounted on the top of a front portion of the body  2 . The panel  3  has numeric buttons  3   a , a start button  3   b  and other buttons or keys, which can be pushed for various operations. By manipulating some of the buttons, it is possible to set the present time as stated later. The panel  3  has a liquid crystal display  6  formed near its rear, which shows the setting of the equipment  1 , an operation message or the like, as the occasion demands. While the equipment  1  is standing by, the display  6  shows the present time. 
     The equipment  1  also includes an original inlet  4  formed in the rear of the display  6  and an original outlet  9  formed under or below the control panel  3 . Fax or copying originals can be stacked in the inlet  4 , from which they can be fed into the equipment body  2 . The originals can be scanned in the equipment  1 , and then be discharged into the outlet  9 , where they can be stacked. 
     The equipment  1  further includes a cassette holder  5  formed in the rear of the original inlet  4  and a sheet outlet  10  formed under the original outlet  9 . The holder  5  can hold a sheet cassette (not shown), in which recording sheets are stacked. A recording sheet P can be fed from the cassette, and then be printed by the printer  26 . The printed sheet P can be discharged through the outlet  10 . 
     Adjacently on the left (right in FIG. 1) of and below the sheet outlet  10 , a video signal input terminal  7  is provided, which can be connected with a video camera. The image data output in the form of video signals from the camera can be sent into the equipment  1 , and then be printed by the printer  26 . 
     The printer  26  includes a frame  63 , by which a horizontal platen roller  61  is supported rotatably to feed a recording sheet P perpendicularly to it. The roller  61  is parallel with a guide rod  62 , which is fixed to the frame  63 . The carriage  66  is supported slidably on the rod  62 , and can be moved along it by a timing belt  70 , which extends between a driving pulley  68  and a driven pulley  69 . The driving pulley  68  can be rotated by a carriage motor  67 , which is supported by the frame  63  near the left (right in FIG. 2) end of the frame. 
     The print head unit  65  includes four print heads, and holds ink tanks  65   a ,  65   b ,  65   c  and  65   d . The tanks  65   a - 65   d  are filled with black, cyan, magenta and yellow inks, respectively, and each connected to one of the heads. Each of the heads has a number of nozzles, through which ink can be ejected. The tanks  65   a - 65   d  can be fitted to and removed from the unit  65  individually. When one or some of the tanks  65   a - 65   d  are short of ink, only it or they can be replaced. 
     The print head unit  65  is fitted with a thermister  29   a  near the print heads. The thermister  29   a  is part of a temperature detecting circuit  29  (FIG.  3 ). The thermister  29   a  converts the temperature around the print heads into a value of electric resistance, and outputs the value to the circuit  29 . Near the right (left in FIG. 2) end of the frame  63 , a recovery mechanism (an apparatus for purging the print heads)  71  is mounted on the frame  63  to recover normal ejection of ink. 
     The mechanism  71  includes a suction cap  72 , which can cap all the print heads at a time to close all their nozzles. Fixed to the back of the cap  72  is one end of a bar  73  for moving the cap  72  toward and away from the print head unit  65 . A lever  74  includes a cylindrical or circular portion in slidable contact with the other end of the bar  73 . When the lever  74  moves in the direction B from its position shown in FIG. 2, the cap  72  moves forward with the bar  73 . After the carriage  66  moves to its position shown with two-dot chain lines in FIG. 2, the movement of the lever  74  in the direction B causes the cap  72  to cap the heads of the unit  65 . The lever  74  can be moved in the direction B and the opposite direction by a cam  76 , which can be turned by a motor  75 . 
     The recovery mechanism  71  includes a suction pump (not shown) for suction through a suction tube  77 , which is connected to the suction cap  72 . The pump can be driven by the cam  76 . With the cap  72  capping the print heads, the pump operation sucks ink out of the nozzles of the heads to recover normal ejection of ink. Herein, a series of suction (recovery) actions for recovery of ink ejection is referred to as purging or purges. 
     With reference to FIG. 3, the equipment  1  includes a facsimile unit FU and a printer unit PU, which are interconnected through an interface  30 . 
     The fax unit FU includes a CPU  11 , a ROM  12 , a RAM  13 , an EEPROM  14 , a network control unit (NCU)  15 , a modem  16 , an encoder  17 , a decoder  18 , a scanner  19 , the control panel  3 , the LCD  6 , the video signal input terminal  7 , an original sensor  8 , a timing circuit  28  and the temperature detecting circuit  29 . These components are interconnected through a facsimile control circuit  20 . 
     On the basis of signals transmitted and received through the NCU  15 , the CPU  11  controls the components connected to the fax controller  20 , and implements fax operation etc. 
     The ROM  12  stores the control programs to be executed by the equipment  1 . The stored programs cannot be altered. The RAM  13  can store data, which can be altered. 
     The EEPROM  14  is a nonvolatile memory. The data stored in this memory can be altered, and is retained even after the power switch of the equipment  1  is turned off. The EEPROM  14  includes a purge time memory  14   a , a purge interval memory  14   b , a high temperature counter  14   c  and a low temperature counter  14   d.    
     The purge time memory  14   a  stores the time (including the date) at which the preceding purge was carried out. Just after the nozzles are purged, the present time clocked by the timer  28  is written in the memory  14   a.    
     The purge interval memory  14   b  stores the regular interval at which the nozzles should be purged. For normal temperature between 10 and 35 centigrade around the print head unit  65 , this memory  14   b  stores an initial value of five days as the purge interval. For abnormal temperature below 10 centigrade or above 35 centigrade around the print heads, the memory  14   b  stores a value of three days as the interval. Just after the nozzles are purged, the memory  14   b  is reset for the initial value of five days. Thereafter, if the temperature around the heads is and keeps abnormal, the content of the memory  14   b  is changed to three days. Once this content is changed to three days, it is not reset for the initial value of five days, even if the temperature returns to normal, until the nozzles are purged next. 
     The purge interval and the abnormal temperatures might be determined suitably depending on ink type etc., and might not be limited to the foregoing values and ranges. 
     The high temperature counter  14   c  stores the frequency of detection of abnormal temperature above 35 centigrade. The temperature detector  29  detects the temperature around the print heads, every time a process for changing the purge interval (FIG. 4) is carried out in the printer unit PU. If the detector  29  detects a temperature above 35 centigrade, the count of this counter  14   c  increments by one. If this count exceeds twenty-four (24), the value of the purge interval memory  14   b  is changed from five days to three days. This shortens the purge interval. Just after the nozzles are purged, the count of the counter  14   c  is cleared. 
     The low temperature counter  14   d  stores the frequency of detection of abnormal temperature below 10 centigrade. If a temperature below 10 centigrade is detected in the purge interval change process (FIG.  4 ), the count of this counter  14   d  increments by one. If this count exceeds twenty-four (24), the value of the purge interval memory  14   b  is changed from five days to three days. This shortens the purge interval. Just after the nozzles are purged, the count of the counter  14   d  is cleared as zero (0). 
     The NCU  15  is connected through a telephone line  52  to another fax machine  51 . The NCU  15  can send a dial signal to the line  52 , and respond to a call signal from this line. 
     The modem  16  can modulate and demodulate image data. The modulated data is transmitted through the NCU  15  to the fax machine  51 . The modem  16  can transmit and receive procedural signals for transmission control. 
     The scanner  19  scans an original fed from the original inlet  4  into the equipment  1 . The encoder  17  encodes the image data from the scanner  19  etc. to compress them. The decoder  18  decodes the facsimile data received by the equipment  1  and other coded data. The original sensor  8  determines if an original is placed in the original inlet  4 . 
     The timer  28  clocks the present time, and includes a battery  28   a  to keep clocking the time even after the power switch of the equipment  1  is turned off. The timer  28  can be initialized through the control panel  3 . While the equipment  1  is standing by, the present time clocked by the timer  28  is output to the LCD  6 , which then functions as a clock display. Just after the nozzles are purged, the present time is read out from the timer  28  by the printer unit PU, and written in the purge time memory  14   a.    
     The temperature detector  29  detects the temperature around the print heads. As stated already, the thermister  29   a  of the detector  29  converts the temperature into a value of electric resistance. On the basis of this value, the detector  29  outputs the temperature as digital data. 
     The printer unit PU includes a CPU  21 , a ROM  22 , a RAM  23 , an interface  24  for a personal computer, a character generator  25  and the printer  26 . These components are interconnected through a printer control circuit  27 . 
     The ROM  22  stores the program of the purge interval change process (FIG. 4) and the program of a purge process (FIG.  5 ), which can be carried out in the printer unit PU. The ROM  22  also stores the control programs to be executed by the CPU  21 . The RAM  23  includes work memories, which can be referred to and updated when the CPU  21  executes programs. The RAM  23  also includes a print memory for storing print data. 
     The interface  24  for a personal computer may be a Centronics (parallel) interface. The interface  24  is connected through a cable  54  to a personal computer  53  as the central unit of the recovery apparatus. The equipment  1  can transmit data to and receive data from the computer  53  through the cable  54 . The character generator  25  stores print characters and other vector fonts. In the main process of the printer unit PU, the purge interval change process is carried out regularly once an hour. This changing process can change the value of the purge interval memory  14   b , depending on the temperature around the print heads. 
     With reference to FIG. 4, the purge interval change process includes reading out the temperature measured by the temperature detector  29  (S 1 ). This reading step is carried out when the power switch of the equipment  1  is turned on, or when one hour has passed after the preceding interval changing process. 
     If this temperature is above 35 centigrade (S 2 : yes), the count of the high temperature counter  14   c  increments by one (S 3 ). 
     If the count of the high temperature counter  14   c  exceeds twenty-four (24) (S 4 : yes), it may be considered that the temperature was above 35 centigrade substantially for at least 24 hours. Then, the value of the purge interval memory  14   b  is changed from the initial value of five days to three days (S 8 ). This makes the purge interval shorter than normal by two days. Then, the process ends. 
     If the count of the high temperature counter  14   c  is 24 or less (S 4 : no), the process ends without changing the value of the purge interval memory  14   b . In this case, the purge interval is not changed to avoid too frequent purges, because it is considered that temporary abnormality of temperature does not affect the ejection of ink substantially. 
     If the temperature is below 10 centigrade (S 2 : no, S 5 : yes), the count of the low temperature counter  14   d  increments by one (S 6 ). If the count of the low temperature counter  14   d  exceeds 24 (S 7 : yes), it may be considered that the temperature was below 10 centigrade substantially for at least 24 hours. Then, the value of the purge interval memory  14   b  is changed from the initial value of five days to three days (S 8 ). Then, the process ends. If the count of the low temperature counter  14   d  is 24 or less (S 7 : no), the process ends without changing the value of the purge interval memory  14   b.    
     If the temperature ranges between 10 and 35 centigrade (S 2 : no, S 5 : no), it is normal. Then, the process ends without changing the value of the purge interval memory  14   b  and the counts of the counters  14   c  and  14   d.    
     The purge process is carried out in the printer unit PU before a printing process is carried out. The printing process is carried out when the equipment  1  prints data received by fax, data input from the computer  53 , or the like. 
     With reference to FIG. 5, the purge process includes calculating the elapsed time which has passed after the preceding purge (S 11 ). The elapsed time is calculated from the present time read out from the timer  28  and the time read out from the purge time memory  14   a . As already stated, this memory  14   a  stores the time at which the preceding purge was carried out. The calculated time is compared with the value of the purge interval memory  14   b , (S 12 ). 
     As a result of the comparison, if the elapsed time is equal to or shorter than the time stored in the purge interval memory  14   b  (S 12 : no), it is judged that ink can be ejected normally. Then, the purge process ends without purging the print heads. After this process ends, the printing process is carried out. Because ink can be ejected in good condition, no defective print occurs. 
     If the elapsed time is longer than the time stored in the purge interval memory  14   b  (S 12 : yes), ink may be ejected defectively. Then, the recovery mechanism  71  is operated to purge the nozzles (S 13 ). 
     After the nozzles are purged, the present time is read out from the timer  28  and written in the purge time memory  14   a  (S 14 ). Next, the counts of the counters  14   c  and  14   d  are cleared (S 15 ). Further, the purge interval memory  14   b  is reset for the initial value of five days (S 16 ). Thereafter, the purge process end. 
     After this process ends, the printing process is carried out. Because the purge process has restored the ejection of ink to normal, no defective print occurs. 
     As stated above, the purge interval is changed suitably depending on the temperature around the print heads. It is therefore possible to purge the nozzles at a suitable time. This prevents the nozzles from being purged at too long interval, which may cause defective print. This also prevents the nozzles from being purged at too short interval, which accelerates the consumption of ink. 
     As also stated, the suction cap  72  (FIG. 2) can close all the nozzles of the print heads at a time. It is therefore possible to purge all the nozzles at a time. It is considered that, if a long time has passed after the preceding purge, the nozzles are clogged substantially equally. By purging the nozzles at a time, it is possible to carry out the purge process before the printing process efficiently in a short time. 
     The invention has been explained hereinbefore with reference to the preferred embodiment, but is not limited to it. Obviously, various improvements and/or modifications may be made without departing from the spirit of the invention. 
     As stated already, the suction cap  72  can cap the print heads at a time for suction for them all at a time. Otherwise, the heads might be capped individually. 
     As also stated, the purge time memory  14   a  stores the time at which the preceding purge was carried out, and the purge interval memory  14   b  stores the purge interval. The elapsed time is calculated from the present time clocked by the timer  28  and the time stored in the purge time memory  14   a . If the elapsed time is longer than the time stored in the purge interval memory  14   b , the nozzles are purged. 
     Another purge process embodying the invention includes storing the initial value of five days in the purge interval memory  14   b  after purging the nozzles. In accordance with the timing of the timer  28 , the stored value is decreased. When this value is decreased to zero, it is inhibited from decreasing further, and the nozzles are purged. In this case, if the abnormal temperature below 10 centigrade or above 35 centigrade is detected 24 times, two days are subtracted from the value of the purge interval memory  14   b . If the result of the subtraction is a minus, it is replaced with zero.