Abstract:
The present invention appropriately determines a point of time when a pressurization member such as a pump roller starts squeezing an elastic tube, that is, a point of time when a tube pump starts to generate pressure. The present invention thereby provides a pressure generating apparatus that can stably generate pressure without increasing costs, a printing apparatus including this pressure generating apparatus, and a method for controlling this printing apparatus. To achieve this, a tube pump is provided that operates after a pump roller acting as a pressurization member has come in pressure contact with a tube, to allow the pump roller to squeeze the tube to generate pressure therein. Then, after the pump roller has moved a predetermined amount to come in pressure contact with the tube, movement of the pump roller is stopped. Subsequently, a valve lever is allowed to perform a closing operation and the pump roller is then moved again. When a cap for introducing negative pressure from the tube pump is shut off from atmosphere due to the closing operation of the valve lever, negative pressure from the tube pump can be introduced.

Description:
This application is based on Japanese Patent Application No. 11-236292 (1999) filed Aug. 24, 1999, the content of which is incorporated hereinto by reference. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a pressure generating apparatus comprising a tube pump for squeezing an elastic tube to generate pressure therein, a printing apparatus including this pressure generating apparatus, and a method for controlling this printing apparatus. 
     The present invention is applicable to general printing apparatuses, apparatuses such as copying machines, facsimile machines having a communication system, and word processors having a printing section, as well as industrial printing apparatuses combined with various processing apparatuses in a compound manner. 
     2. Description of the Related Art 
     Printing apparatuses include those having functions of printers, copying machines, facsimile machines, or the like, or those used as output equipment for compound electronic equipment including a computer or a word processor or for work stations. These printing apparatuses are configured to images on printing media such as paper or thin plastic sheets. 
     Of these printing apparatuses, an ink jet type (ink jet printing apparatuses) carries out printing by ejecting ink onto a printing medium from a printing head acting as printing means. This ink jet printing apparatus has the advantages of allowing the printing head to be compactified easily, being able to print high-definition images at a high speed, being able to print images on plain paper without any special processing, and requiring reduced running costs. In addition, since this ink jet printing apparatus is based on the non-impact type, it makes reduced noise and can easily print color images using a large number of color inks. Alternatively, line type ink jet printing apparatuses using a line type printing head with a large number of nozzles arranged in a sheet width direction of printing paper can carry out printing at a higher speed. 
     In particular, ink jet type printing means (printing head) for using thermal energy to eject ink can be manufactured using a semiconductor fabrication process such as etching, deposition, or sputtering. Such printing means can further be compactified because liquid paths (nozzles) can be densely arranged therein by forming thermoelectric converters, electrodes, liquid path walls, roofs, or the like on a substrate. 
     The ink jet printing apparatus print an image on a printing medium by ejecting ink from the nozzles in response to electric signals. Entry of air into a nozzle or an increase in ink viscosity due to drying may preclude the nozzle from ejecting an ink droplet in response to electric signal. To recover the nozzle which cannot eject the ink properly, ink that does not contribute to image printing can be sucked and ejected from a tip of the nozzle (suction recovery). For this suction recovery means, a tube pump is often used as means for generating a negative pressure for sucking the ink. This tube pump generates a negative force inside a pump tube by rotating a pump roller in pressure contact with the pump tube, that is, squeezing the pump. 
     The suction recovery means comprises, for example, a cap that can cap the printing head and that has a suction port and an air communication port formed therein, the suction port being connected to a tube pump and the air communication port being connected to a valve rubber that is opened and closed by a valve lever. The cap and the tube pump are driven correlatively depending on a rotating direction of a PG motor, as shown, for example, by (a), (b), and (c) in FIG.  25 . Additionally, the valve lever is driven depending on a rotating direction of a printing medium ejection roller rotated by an LF motor, as shown, for example, by (d) and (e) in FIG.  25 . 
     First, the ejection roller is reversely driven for reverse rotation to cause the valve lever to open the valve rubber, and the PG motor subsequently rotates forward to bring the cap into abutment with a surface of the printing head which has the ink ejection port formed therein, to cap the printing head. At this point, the tube pump is forwardly driven for normal rotation due to the forward rotation (normal rotation) of the PG motor. The forward driving of the tube pump, however, prevents the pump roller from coming in pressure contact with the pump tube, so that the tube pump generates no negative force. Subsequently, the ejection roller is forwardly driven for normal rotation to cause the valve lever to close the valve rubber. Then, the PG motor rotates reversely to reversely drive the tube pump. When the tube pump is reversely driven for reverse rotation, the pump roller rotates in pressure contact with the pump tube to squeeze it to generate a negative force. This negative pressure is introduced into the cap through the suction port. Then, the cap caps the printing head and the air communication port is closed by the valve rubber, so that the negative pressure introduced into the cap causes ink of increased viscosity which is no longer suitable for printing as well as bubbles to be forcibly sucked and ejected from the ink ejection port of the printing head. 
     Subsequently, the ejection roller is reversely driven for reverse rotation to cause the valve lever to open the valve rubber. Then, the air communication port in the cap is opened to set the interior of the cap at atmospheric pressure. As a result, the ink is prevented from being sucked or ejected from the ink ejection port, while the ink inside the cap and the pump tube is sucked and ejected from an ink eject end of the pump tube (this operation is hereafter referred to as “idle suction”). Subsequently, the PG motor is stopped, and the ejection roller is forwardly driven for normal rotation to separate the cap from the ink ejection port forming surface of the printing head to release the capping to cause the valve lever to close the valve rubber. Then, the series of suction recovery operations are completed. 
     The pressure generating apparatus in the conventional suction recovery means described above, however, has the following problems: 
     (1) In FIG. 25, reference t 0  denotes a rotation start time when the pump roller of the tube pump starts rotating and reference t 1  denotes a pressure generation time when the pump roller comes in complete pressure contact with the pump tube to start generating pressure. The amount of rotation made by the PG motor between a rotation start time P 0  and the pressure generation time t 1  varies depending on the position of the pump roller at the point of rotation start time t 0 , that is, deviations in the initial positions of the pump roller. Consequently, pressure generated by the tube pump is unstable. 
     (2) The unstable pressure from the tube pump significantly varies the amount of ink sucked during the suction recovery operation. 
     (3) If detection means is provided to detect the initial position of the pump roller to take action based on results of the detection, the inclusion of the detection means increases costs for the entire apparatus. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to stably generate pressure by appropriately determining a point of time when a pressurization member such as a pump roller starts squeezing an elastic tube, that is, a point of time when a tube pump starts to generate pressure. It is another object of the present invention to provide a pressure generating apparatus that does not increase costs, a printing apparatus including this pressure generating apparatus, and a method for controlling this printing apparatus. 
     In the first aspect of the present invention, there is provided a pressure generating apparatus including a tube pump for, when a pressurization member is moved in a predetermined direction, squeezing the tube with the pressurization member coming into pressure contact with an elastic tube, thereby generating in the tube a pressure to be introduced into a pressure introduction section, the apparatus comprising: 
     switching means for switching to a state where the pressure from the tube pump can or cannot be introduced into the pressure introduction section; and 
     control means for allowing the switching means to switch to the state where the pressure from the tube pump can be introduced into the pressure introduction section after the pressurization member has moved a predetermined amount in the predetermined direction. 
     In the second aspect of the present invention, there is provided a printing apparatus that can print an image on a printing medium using a printing head capable of ejecting inks and that includes recovery means for effecting pressure on the printing head to eject ink that does not contribute to printing, from the printing head, the apparatus comprising: 
     the pressure generating means as claimed in claim 1 as a supply source of the pressure that is introduced into the recovery means. 
     In the third aspect of the present invention, there is provided a method for controlling a printing apparatus that can print an image on a printing medium using a printing head capable of ejecting ink and that includes recovery means for effecting pressure to the printing head to eject ink that do not contribute to printing, from the printing head, wherein: 
     a tube pump is provided as a supply source of pressure that is introduced into the recovery means, 
     when a pressurization member is moved in a predetermined direction, the tube pump squeezes the tube with the pressurization member coming into pressure contact with an elastic tube, thereby generating in the tube a pressure to be introduced into the recovery means, 
     after the pressurization member has moved a predetermined amount in the predetermined direction, a state is switched to one where the pressure from the tube pump can be introduced into the recovery means, from another where the pressure from the tube pump cannot be introduced into the recovery means. 
     The present invention comprises a tube pump including a pressurization member such as a pump roller that comes in pressure contact with an elastic tube and then squeezes it to generate pressure therein, wherein after the pressurization member has moved a predetermined amount, switching means switches to a state where the pressure from the tube pump can be introduced into a pressure introduction section. This allows adequate determination of a point of time when the pressurization member starts to squeeze the tube, that is, a point of time when the tube pump starts to generate pressure. As a result, the tube pump stably generates pressure, and an appropriate pressure can be introduced into the pressure introduction section such as a cap for a printing head of a printing apparatus to reliably provide an intended function such as ink suction recovery. 
     In addition, when the switching means switches to the state where the pressure from the tube pump can be introduced into the pressure introduction section, the movement of the pressurization member is temporarily stopped. Accordingly, after the operation of the switching means, the tube pump can be redriven to generate a stable pressure irrespective of variations in the amount of time required for the switching means to operate. 
     Additionally, a stable pressure can be generated without detection means for detecting the position of the pressurization member such as the pump roller. Accordingly, the absence of the detection means serves to reduce the costs of the apparatus. 
     The above and other objects, effects, features, and advantages of the present invention will become more apparent from the following description of embodiments thereof taken in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view showing an external construction of an ink jet printer as one embodiment of the present invention; 
     FIG. 2 is a perspective view showing the printer of FIG. 1 with an enclosure member removed; 
     FIG. 3 is a side view of FIG. 2; 
     FIG. 4 is a front view showing a feed roller and an LF gear cover shown in FIG. 2; 
     FIG. 5 is a perspective view showing pinch rollers and others shown in FIG. 2; 
     FIG. 6 is a perspective view showing an assembled print head cartridge used in the printer of one embodiment of the present invention; 
     FIG. 7 is an exploded perspective view showing the print head cartridge of FIG. 6; 
     FIG. 8 is an exploded perspective view of the print head of FIG. 7 as seen from diagonally below; 
     FIG. 9 is a perspective view showing the front side of a carriage used in the embodiment of the invention; 
     FIG. 10 is a perspective view showing the back side of the carriage of FIG. 9; 
     FIG. 11 is a perspective view showing one side of an ejection performance recovery unit in the embodiment of the invention; 
     FIG. 12 is a perspective view showing the other side of the ejection performance recovery unit of FIG. 11; 
     FIGS. 13A and 13B are perspective views showing a construction of a scanner cartridge upside down which can be mounted in the printer of one embodiment of the present invention instead of the print head cartridge of FIG. 6; 
     FIG. 14 is a perspective view showing a storage case in the embodiment of the invention; 
     FIG. 15 is a block diagram schematically showing the overall configuration of an electric circuitry of the printer according to one embodiment of the present invention; 
     FIG. 16 is a diagram showing the relation between FIGS. 16A and 16B, FIGS. 16A and 16B being block diagrams representing an example inner configuration of a main printed circuit board (PCB) in the electric circuitry of FIG. 15; 
     FIG. 17 is a diagram showing the relation between FIGS. 17A and 17B, FIGS. 17A and 17B being block diagrams representing an example inner configuration of an application specific integrated circuit (ASIC) in the main PCB of FIGS. 16A and 16B; 
     FIG. 18 is a flow chart showing an example of operation of the printer as one embodiment of the present invention; 
     FIG. 19 is a view showing the internal configuration of a tube pump and which is useful for explaining the characteristic configuration of a first embodiment of the present invention; 
     FIG. 20 is a view showing the internal configuration of the tube pump in FIG. 19 in a different operational state; 
     FIG. 21 is a perspective view showing an integral part of a printing apparatus including the tube pump in FIG. 19; 
     FIG. 22 is a perspective view showing an integral part of the printing apparatus including the tube pump in FIG. 19 in a different operational state; 
     FIG. 23 is a timing chart useful for explaining the operation of the tube pump in FIG. 19; 
     FIG. 24 is a timing chart useful for explaining the operation of the tube pump according to a second embodiment of the present invention; and 
     FIG. 25 is a timing chart useful for explaining the operation of a conventional tube pump. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiments of the printing apparatus according to the present invention will be described by referring to the accompanying drawings. 
     In this specification, a word “print” (or “record”) refers to not only forming significant information, such as characters and figures, but also forming images, designs or patterns on printing medium and processing media, whether the information is significant or insignificant or whether it is visible so as to be perceived by humans. 
     The word “print medium” or “print sheet” include not only paper used in common printing apparatus, but cloth, plastic films, metal plates, glass, ceramics, wood, leather or any other material that can receive ink. This word will be also referred to “paper”. 
     Further, the word “ink” (or “liquid”) should be interpreted in its wide sense as with the word “print” and refers to liquid that is applied to the printing medium to form images, designs or patterns, process the printing medium or process ink (for example, coagulate or make insoluble a colorant in the ink applied to the printing medium). 
     In the following description we take up as an example a printing apparatus using an ink jet printing system. 
     I. Fundamental Construction 
     By referring to FIGS. 1 to  18  a fundamental construction of a printer will be described. 
     I.1 Apparatus Body 
     FIGS. 1 and 2 show an outline construction of a printer using an ink jet printing system. In FIG. 1, a housing of a printer body M 1000  of this embodiment has an enclosure member, including a lower case M 1001 , an upper case M 1002 , an access cover M 1003  and a discharge tray M 1004 , and a chassis M 3019  (see FIG. 2) accommodated in the enclosure member. 
     The chassis M 3019  is made of a plurality of plate-like metal members with a predetermined rigidity to form a skeleton of the printing apparatus and holds various printing operation mechanisms described later. 
     The lower case M 1001  forms roughly a lower half of the housing of the printer body M 1000  and the upper case M 1002  forms roughly an upper half of the printer body M 1000 . These upper and lower cases, when combined, form a hollow structure having an accommodation space therein to accommodate various mechanisms described later. The printer body M 1000  has an opening in its top portion and front portion. 
     The discharge tray M 1004  has one end portion thereof rotatably supported on the lower case M 1001 . The discharge tray M 1004 , when rotated, opens or closes an opening formed in the front portion of the lower case M 1001 . When the print operation is to be performed, the discharge tray M 1004  is rotated forwardly to open the opening so that printed sheets can be discharged and successively stacked. The discharge tray M 1004  accommodates two auxiliary trays M 1004   a , M 1004   b . These auxiliary trays can be drawn out forwardly as required to expand or reduce the paper support area in three steps. 
     The access cover M 1003  has one end portion thereof rotatably supported on the upper case M 1002  and opens or closes an opening formed in the upper surface of the upper case M 1002 . By opening the access cover M 1003 , a print head cartridge H 1000  or an ink tank H 1900  installed in the body can be replaced. When the access cover M 1003  is opened or closed, a projection formed at the back of the access cover, not shown here, pivots a cover open/close lever. Detecting the pivotal position of the lever as by a micro-switch and so on can determine whether the access cover is open or closed. 
     At the upper rear surface of the upper case M 1002  a power key E 0018 , a resume key E 0019  and an LED E 0020  are provided. When the power key E 0018  is pressed, the LED E 0020  lights up indicating to an operator that the apparatus is ready to print. The LED E 0020  has a variety of display functions, such as alerting the operator to printer troubles as by changing its blinking intervals and color. Further, a buzzer E 0021  (FIG. 15) may be sounded. When the trouble is eliminated, the resume key E 0019  is pressed to resume the printing. 
     I.2 Printing Operation Mechanism 
     Next, a printing operation mechanism installed and held in the printer body M 1000  according to this embodiment will be explained. 
     The printing operation mechanism in this embodiment comprises: an automatic sheet feed unit M 3022  to automatically feed a print sheet into the printer body; a sheet transport unit M 3029  to guide the print sheets, fed one at a time from the automatic sheet feed unit, to a predetermined print position and to guide the print sheet from the print position to a discharge unit M 3030 ; a print unit M 4000  to perform a desired printing on the print sheet carried to the print position; and an ejection performance recovery unit M 5000  to recover the ink ejection performance of the print unit M 4000 . 
     Next, the construction of each mechanism will be explained. 
     I.2.1 Automatic Sheet Feed Unit 
     By referring to FIGS. 2 and 3 the automatic sheet feed unit M 3022  will be described. 
     The automatic sheet feed unit M 3022  in this embodiment horizontally feeds one of print sheets stacked at an angle of about 30-60 degrees to the horizontal plane, so that the sheet is discharged out of a sheet feed port not shown into the printer body while being kept in an almost horizontal attitude. 
     The automatic sheet feed unit M 3022  includes feed rollers M 3026 , sheet guides M 3024   a , M 3024   b , a pressure plate M 3025 , an ASF base M 3023 , sheet separators M 3027 , and separation claws not shown. The ASF base M 3023  forms a housing of the automatic sheet feed unit M 3022  and is provided at the back of the printer body. On the front side of the ASF the pressure plate M 3025  supporting the print sheets is mounted at an angle of about 30-60 degrees to the horizontal plane and a pair of sheet guides M 3024   a , M 3024   b  that guide the ends of the print sheets project forwardly. One of the sheet guides M 3024   b  is movable in the sheet width direction to conform to the horizontal size (width) of the sheets. 
     Rotatably supported on the left and right sides of the ASF base M 3023  is a drive shaft M 3026   a  that is connected through a gear not shown to a PG motor and which has rigidly secured thereto a plurality of feed rollers M 3026  semicircular in cross section. 
     The print sheets stacked on the pressure plate M 3025  are fed by the feed rollers M 3026  that are driven by the PG motor E 0003  (FIG.  15 ). The stacked sheets are separated one by one from the top of the stack by the sheet separators M 3027  and the separation claws and forwarded to the paper transport unit M 3029 . The lower end of the pressure plate M 3025  is resiliently supported by a pressure plate spring M 3028  interposed between the pressure plate M 3025  and the ASF base M 3023 , so that the contact force between the feed rollers and the sheet can be kept constant regardless of the number of sheets stacked. 
     In a transport path from the automatic sheet feed unit M 3022  to the paper transport unit M 3029 , a PE lever M 3020  urged clockwise in FIG. 3 by a PE lever spring M 3021  is pivotally mounted on a chassis M 3019  which is secured to the printer body M 1000  and formed of a metal plate member with a predetermined rigidity. When the print sheet separated and fed from the automatic sheet feed unit M 3022  moves along the path and its front end abuts against one end of the PE lever and pivots it, a PE sensor not shown senses the rotation of the PE lever M 3020 , detecting that the print sheet has entered into the transport path. 
     After the entrance into the transport path of the print sheet has been detected, the print sheet is transported a predetermined distance downstream by the feed rollers M 3026 . That is, the print sheet is fed until its front end contacts a nip portion formed by an LF roller M 3001 , which is at rest and provided in the paper transport unit described later, and pinch rollers M 3014  and the print sheet deflects about 3 mm in loop, at which time the sheet is stopped. 
     I.2.2 Paper Transport Unit 
     The paper transport unit M 3029  has an LF roller M 3001 , pinch rollers M 3014  and a platen M 2001 . The LF roller M 3001  is secured to a drive shaft rotatably supported on the chassis M 3019  and, as shown in FIG. 4, has attached to one end thereof an LF gear cover M 3002  that protects both an LF gear M 3003  secured to the drive shaft M 3001   a  and a small gear M 3012   a  (see FIG. 2) of an LF intermediate gear M 3012  in mesh with the LF gear M 3003 . The LF intermediate gear M 3012  is interlocked with a drive gear of a drive shaft of an LF motor E 0002  described later and is driven by the driving force of the motor. 
     The pinch rollers M 3014  are rotatably mounted at the front end of pinch roller holders M 3015  which is pivotally supported on the chassis M 3019 . The pinch rollers M 3014  are pressed against the LF roller M 3001  by spiral spring-like pinch roller springs M 3016  that bias the pinch roller holders M 3015 . As a result, the pinch rollers M 3014  rotate following the rotation of the LF roller M 3001  to feed forwardly the print sheet, which was at rest in a looped state as described above, by gripping it between the pinch rollers M 3014  and the LF roller M 3001 . 
     The rotation center of the pinch rollers M 3014  is offset about 2 mm downstream of the rotation center of the LF roller M 3001  in the direction of transport. Hence, the print sheet fed by the LF roller M 3001  and the pinch rollers M 3014  advances toward lower right in FIG. 3 along a print sheet support surface M 2001   a  (FIG.  5 ). 
     A predetermined time after the feeding operation by the feed rollers M 3026  of the automatic sheet feed unit M 3022  has stopped, the paper transport unit constructed as described above starts the LF motor E 0002 . The driving force of the LF motor E 0002  is transmitted via the LF intermediate gear M 3012  and the LF gear M 3003  to the LF roller M 3001 . As the LF roller M 3001  rotates, the print sheet whose front end is in contact with the nip portion between the LF roller M 3001  and the pinch rollers M 3014  is carried to the print start position on the platen M 2001 . 
     At this time, the feed rollers M 3026  resume rotating simultaneously with the LF roller M 3001 , so that the print sheet is transported downstream by the cooperation of the feed rollers M 3026  and the LF roller M 3001  for a predetermined period of time. A print head cartridge H 1000  described later moves, mounted on a carriage M 4001 , along a carriage shaft M 4012  secured at its ends to the chassis M 3019 , the carriage M 4001  being adapted to reciprocate in a direction (scan direction) perpendicular to the direction in which the print sheet is fed. As it travels in the scan direction, the print head cartridge H 1000  ejects ink, according to an image information, onto the print sheet held at the print start position to form an image. 
     After the image has been printed, the LF roller M 3001  is rotated to feed the print sheet a predetermined distance at a time, which may correspond to one line height of, for example, 5.42 mm, followed by the carriage M 4001  performing the main scan along the carriage shaft M 4012 . This process is repeated to complete an entire image on the print sheet placed on the platen M 2001 . 
     The carriage shaft M 4012  has its one end mounted on an adjust plate (not shown) through an adjust lever  2015  and the other end mounted on another adjust plate M 2012  through a carriage shaft cam M 2011 . The carriage shaft M 4012  is biased by a carriage shaft spring M 2014 . The adjust plate M 2012  and the other adjust plate not shown are secured to the chassis M 3019  so that the distance between the ejecting face of the print head cartridge H 1000  and the print sheet support surface M 2001   a  of the platen M 2001  can be adjusted to be an appropriate value. 
     Further, the adjust lever  2015  can be selectively set at one of two stop positions, an upper end position shown in FIG. 1 and a lower end position not shown. When the adjust lever  2015  is moved to the lower end position, the carriage M 4001  is retracted about 0.6 mm from the platen M 2001 . Hence, if the print sheet is thick, as when an envelope is printed, the adjust lever  2015  is moved to the lower end position before the sheet feeding operation by the automatic sheet feed unit M 3022  is started. 
     When the adjust lever  2015  is located at the lower end position, this state is detected by the GAP sensor E 0008  (see FIG.  14 ). Therefore, when the print sheet begins to be fed by the automatic sheet feed unit M 3022 , it is checked whether the position setting of the adjust lever  2015  is appropriate or not. When an inappropriate state is detected, a warning is issued by displaying a message or activating a buzzer to prevent the printing operation from being executed in an inappropriate condition. 
     I.3 Discharge Unit 
     Next, the discharge unit M 3030  will be described by referring to FIGS. 2 and 3. 
     As shown in FIG. 3, the discharge unit M 3030  has a discharge roller  2003 ; a discharge gear M 3013  mounted on the discharge roller  2003  to transmit the driving force of the LF motor E 0002  through the LF intermediate gear M 3012  to the discharge roller  2003 ; a first spur M 2004  rotated by the rotation of the discharge roller  2003  to grip the print sheet between it and the discharge roller  2003  to feed the sheet, and a discharge tray M 1004  to aid in the discharge of the print sheet. The first spur M 2004  is pressed against the discharge roller  2003  by a biasing force of a spur spring M 2009  attached to a first spur holder M 2006  mounted on a spur stay M 2007 . 
     The print sheet carried to the discharge unit M 3030  is subjected to the transport force from the discharge roller  2003  and the first spur M 2004 . The rotation center of the first spur M 2004  is offset about 2 mm upstream, in the transport direction, of the rotation center of the discharge roller  2003 . Hence, the print sheet moved by the discharge roller  2003  and the first spur M 2004  comes into light contact with the print sheet support surface M 2001   a  of the platen M 2001  with no gap between them and is therefore transported properly and smoothly. 
     The speed of the print sheet carried by the discharge roller  2003  and the first spur M 2004  is almost equal to the speed of the sheet fed by the LF roller M 3001  and the pinch roller M 3014 . To effectively prevent the print sheet from becoming slack, the speed at which the sheet is moved by the discharge roller  2003  and the first spur M 2004  is set slightly higher. 
     Further, a second spur M 2005  accommodated in a second spur holder M 2008  is held on a part of the spur stay M 2007  downstream of the first spur M 2004  to prevent the print sheet from coming into a frictional, sliding contact with the spur stay M 2007 . 
     When the printing of an image on the print sheet is finished and the rear end of the print sheet comes off from between the LF roller M 3001  and the pinch roller M 3014 , the print sheet is moved only by the discharge roller  2003  and the first spur M 2004  until it is completely discharged. 
     I.4 Print Unit 
     Here, the print unit M 4000  will be described. The print unit M 4000  comprises a carriage M 4001  movably supported on a carriage shaft M 4021  and a print head cartridge H 1000  removably mounted on the carriage M 4001 . 
     I.4.1 Print Head Cartridge 
     First, the print head cartridge used in the print unit will be described with reference to FIGS. 6 to  8 . 
     The print head cartridge H 1000  in this embodiment, as shown in FIG. 3, has an ink tank H 1900  containing inks and a print head H 1001  for ejecting ink supplied from the ink tank H 1900  out through nozzles according to print information. The print head H 1001  is of a so-called cartridge type in which it is removably mounted to the carriage M 4001  described later. 
     The ink tank for this print head cartridge H 1000  consists of separate ink tanks H 1900  of, for example, black, light cyan, light magenta, cyan, magenta and yellow to enable color printing with as high an image quality as photograph. As shown in FIG. 4, these individual ink tanks are removably mounted to the print head H 1001 . 
     Then, the print head H 1001 , as shown in the perspective view of FIG. 5, comprises a print element substrate H 1100 , a first plate H 1200 , an electric wiring board H 1300 , a second plate H 1400 , a tank holder H 1500 , a flow passage forming member H 1600 , a filter H 1700  and a seal rubber H 1800 . 
     The print element silicon substrate H 1100  has formed in one of its surfaces, by the film deposition technology, a plurality of print elements to produce energy for ejecting ink and electric wires, such as aluminum, for supplying electricity to individual print elements. A plurality of ink passages and a plurality of nozzles H 1100 T, both corresponding to the print elements, are also formed by the photolithography technology. In the back of the print element substrate H 1100 , there are formed ink supply ports for supplying ink to the plurality of ink passages. The print element substrate H 1100  is securely bonded to the first plate H 1200  which is formed with ink supply ports H 1201  for supplying ink to the print element substrate H 1100 . The first plate H 1200  is securely bonded with the second plate H 1400  having an opening. The second plate H 1400  holds the electric wiring board H 1300  to electrically connect the electric wiring board H 1300  with the print element substrate H 1100 . The electric wiring board H 1300  is to apply electric signals for ejecting ink to the print element substrate H 1100 , and has electric wires associated with the print element substrate H 1100  and external signal input terminals H 1301  situated at electric wires&#39; ends for receiving electric signals from the printer body. The external signal input terminals H 1301  are positioned and fixed at the back of a tank holder H 1500  described later. 
     The tank holder H 1500  that removably holds the ink tank H 1900  is securely attached, as by ultrasonic fusing, with the flow passage forming member H 1600  to form an ink passage H 1501  from the ink tank H 1900  to the first plate H 1200 . At the ink tank side end of the ink passage H 1501  that engages with the ink tank H 1900 , a filter H 1700  is provided to prevent external dust from entering. A seal rubber H 1800  is provided at a portion where the filter H 1700  engages the ink tank H 1900 , to prevent evaporation of the ink from the engagement portion. 
     As described above, the tank holder unit, which includes the tank holder H 1500 , the flow passage forming member H 1600 , the filter H 1700  and the seal rubber H 1800 , and the print element unit, which includes the print element substrate H 1100 , the first plate H 1200 , the electric wiring board H 1300  and the second plate H 1400 , are combined as by adhesives to form the print head H 1001 . 
     I.4.2 Carriage 
     Next, by referring to FIGS. 2,  9  and  10 , the carriage M 4001  carrying the print head cartridge H 1000  will be explained. 
     As shown in FIG. 2, the carriage M 4001  has a carriage cover M 4002  for guiding the print head H 1001  to a predetermined mounting position on the carriage M 4001 , and a head set lever M 4007  that engages and presses against the tank holder H 1500  of the print head H 1001  to set the print head H 1001  at a predetermined mounting position. 
     That is, the head set lever M 4007  is provided at the upper part of the carriage M 4001  so as to be pivotable about a head set lever shaft M 4008 . There is a spring-loaded head set plate (not shown) at an engagement portion where the carriage M 4001  engages the print head H 1001 . With the spring force, the head set lever M 4007  presses against the print head H 1001  to mount it on the carriage M 4001 . 
     At another engagement portion of the carriage M 4001  with the print head H 1001 , there is provided a contact flexible printed cable (simply referred to as a contact FPC hereinafter) E 0011  whose contact unit E 0011   a  electrically contacts a contact portion (external signal input terminals) H 1301  provided in the print head H 1001  to transfer various information for printing and supply electricity to the print head H 1001 . 
     An elastic member such as rubber not shown is provided between a contact unit E 0011   a  of a contact FPC E 0011  and the carriage M 4001 . The elastic force of the elastic member and the pressing force of the head set lever spring combine to ensure a reliable contact between the contact unit E 0011   a  and the carriage M 4001 . The contact FPC E 0011  is drawn to the sides of the carriage M 4001  and, as shown in FIGS. 9 and 10, has its end portions securely held to the sides of the carriage M 4001  by a pair of FPC retainers M 4003 , M 4006 . The contact FPC E 0011  is connected to a carriage printed circuit board E 0013  mounted on the back of the carriage M 4001  (see FIG.  10 ). 
     As shown in FIG. 10, the carriage printed circuit board E 0013  is electrically connected through a carriage flexible flat cable (carriage FFC) E 0012  to a main printed circuit board E 0014  mounted on the chassis M 3019  (see FIG.  15 ), which will be described later. Further, as shown in FIG. 10, at a joint portion between one end of the carriage FFC E 0012  and the carriage printed circuit board E 0013  a pair of retainer members, flexible flat cable retainers (FCC retainers) M 4015 , M 4016 , are provided to fixedly secure the carriage FFC E 0012  to the carriage printed circuit board E 0013  (see FIG.  15 ). Also installed at the joint portion is a ferrite core M 4017  that shields electromagnetic radiations emitted from the carriage FFC E 0012  and others. 
     The other end of the carriage FFC E 0012  is fixed to the chassis M 3019  (FIG. 2) by an FFC retainer M 4028  (FIG. 2) and then drawn out to the rear side of the chassis M 3019  through a hole not shown in the chassis M 3019  and connected to the main printed circuit board E 0014  (FIG.  15 ). 
     As shown in FIG. 10, the carriage printed circuit board E 0013  has an encoder sensor E 0004 , which detects information from an encoder scale E 0005  extending parallel to the carriage shaft M 4012  between the both sides of the chassis M 3019  to detect the position and scan speed of the carriage M 4001 . In this embodiment, the encoder sensor E 0004  is of an optical transmission type. The encoder scale E 0005  is a resin film, such as polyester film, which is printed, by the photographic plate making technique, alternately at a predetermined pitch with light shielding portions for shielding detection light emitted from the encoder sensor and light transmitting portions for transmitting the detection light. 
     Therefore, the position of the carriage M 4001  moving along the carriage shaft M 4012  can be detected at any time by first putting the carriage M 4001  against one side plate of the chassis M 3019  provided at an end of the scanning track of the carriage M 4001 , taking this position as a reference position, and counting the number of patterns formed on the encoder scale E 0005  by the encoder sensor E 0004  as the carriage M 4001  performs scanning. 
     The carriage M 4001  is guided for scan operation along the carriage shaft M 4012  and the carriage rail M 4013  extending between the both sides of the chassis M 3019 . At bearing portions for the carriage shaft M 4012 , the carriage M 4001  has integrally formed therewith as by an insert molding a pair of carriage shaft bearings M 4029  made of a sintered metal impregnated with lubricant such as oil. Further, at a portion engaging with the carriage rail M 4013 , the carriage M 4001  has a carriage slider (CR slider) M 4014  made of resin with excellent sliding performance and wear resistance. Along with the carriage shaft bearings M 4029 , the CR slider M 4014  enables a smooth scanning motion of the carriage M 4001 . 
     The carriage M 4001  is secured to a carriage belt M 4018  that extends almost parallel to the carriage shaft between an idler pulley M 4020  (FIG. 2) and a carriage motor pulley M 4024  (FIG.  2 ). The carriage motor E 0001  (FIG. 14) drives the carriage motor pulley M 4024  to move the carriage belt M 4018  in the forward or backward direction and thereby scan the carriage M 4001  along the carriage shaft M 4012 . The carriage motor pulley M 4024  is held at a fixed position by the chassis, whereas the idler pulley M 4020  together with a pulley holder M 4021  is held movable relative to the chassis M 3019 . Because the idler pulley M 4020  is urged away from the carriage motor pulley M 4024  by a spring, the carriage belt M 4018  wound around the both pulleys M 4020  and M 4024  is given an appropriate tension at all times and thus kept in good state with no slack. 
     At the connecting portion between the carriage belt M 4018  and the carriage M 4001  is provided a carriage belt holder M 4019  that ensures a secure holding of the carriage M 4001  to the belt. 
     On the spur stay M 2007  in the scanning track of the carriage M 4001  an ink empty sensor E 0006  (FIG. 2) is exposed facing an ink tank H 1900  to measure the remaining amount of ink contained in the ink tank H 1900  of the print head cartridge H 1000  mounted on the carriage M 4001 . The ink empty sensor E 0006  is held by an ink empty sensor holder M 4026  and accommodated in an ink empty sensor cover M 4027  having a metal plate to shield noise from outside, thus preventing erroneous operations of the sensor. 
     I.5 Ejection Performance Recovery Unit 
     Next, by referring to FIGS. 11 and 12, an ejection performance recovery unit that recovers the ejection performance of the print head cartridge H 1000  will be described. 
     The ejection performance recovery unit  5000  in this embodiment can be mounted to and dismounted from the printer body M 1000 . The ejection performance recovery unit M 5000  has a cleaning means to remove foreign matters adhering to a print element substrate H 1100  of the print head H 1001  and a recovery means to reinstate the normal condition of the ink path from the ink tank H 1900  to the print element substrate H 1100  of the print head H 1001  (flow path from the portions H 1501  to H 1400  via H 1600 ). 
     In FIGS. 11 and 12, denoted E 0003  is a PG motor which drives a cap M 5001  to be described later, a pump M 5100 , wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  and the automatic sheet feedunit M 3022 . The driving force is extracted from both sides of the motor shaft of the PG motor E 0003 . The driving force extracted from one side is transmitted to the pump M 5100  or the automatic sheet feed unit M 3022  through a drive path switching means described later. The driving force extracted from the other side is transmitted to the cap M 5001  and the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  through a one-way clutch M 5041  that engages when the PG motor E 0003  rotates only in a particular direction (this rotation direction is referred to as a forward direction and the opposite direction as a reverse direction). Hence, when the PG motor E 0003  is rotating in the reverse direction, the one-way clutch M 5041  disengages blocking the driving force from being transmitted, so that the cap M 5001  and the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  are not operated. 
     The cap M 5001  is made of an elastic member such as rubber and mounted on a cap lever M 5004  that can be pivoted about its axis. The cap M 5001  is moved in the direction of arrow A (FIG. 12) through the one-way clutch M 5041 , a cap drive transmission gear train M 5110 , a cap cam and the cap lever M 5004  so that it can be brought into and out of contact with the print element substrate H 1100  of the print head H 1001 . In the cap M 5001  there is provided an absorbing member M 5002  which is arranged to oppose the print element substrate H 1100  with a predetermined gap therebetween during a capping operation. 
     The absorbing member M 5002  disposed in this way can accept ink drawn out from the print head cartridge H 1000  during the suction operation. Further, the ink in the cap M 5001  can be discharged out into a used ink absorbing member completely by an evacuation operation described later. The cap M 5001  is connected with two tubes, a cap tube M 5009  and a valve tube M 5010 . The cap tube M 5009  is connected to a pump tube M 5019  of a pump M 5100  described later and the valve tube M 5010  to a valve rubber M 5036  described later. 
     The wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  are made of elastic members such as rubber and are erected on a blade holder M 5013  so that their edges project upward. The blade holder M 5013  has a lead screw M 5031  inserted therethrough with a projection not shown of the blade holder M 5013  movably engaging in a groove formed in the lead screw M 5031 . As the lead screw M 5031  rotates, the blade holder M 5013  moves back and forth along the lead screw M 5031  in the direction of arrow B 1  or B 2  (FIG.  12 ), causing the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  to wipe clean the print element substrate H 1100  of the print head cartridge H 1000 . The lead screw M 5031  is connected to one side of the PG motor E 0003  through the one-way clutch M 5041  and a wiper drive transmission gear train M 5120 . 
     Designated M 5100  is a pump that produces a pressure by pressing a roller (not shown) against and moving it along the pump tube M 5019 . This pump is connected to the other side of the PG motor E 0003  via a drive path switching means and the pump drive transmission gear train M 5130 . The drive path switching means switches the driving force transmission path between the automatic sheet feed unit M 3022  and the pump M 5100 . Although details are not provided, the pump M 5100  has a mechanism to release the pressing force with which the roller (not shown) is pressed against the pump tube M 5019  to squeeze it. When the PG motor E 0003  rotates in the forward direction, the mechanism releases the pressing force from the roller, leaving the tube intact. When the PG motor E 0003  rotates in the reverse direction, the mechanism applies the pressing force to the roller to squeeze the tube. One end of the pump tube M 5019  is connected to the cap M 5001  through the cap tube M 5009 . 
     The drive path switching means has a pendulum arm M 5026  and a selector lever M 5043 . The pendulum arm M 5026  is pivotable about a shaft M 5026   a  in the direction of arrow C 1  or C 2  (FIG. 11) depending on the rotation direction of the PG motor E 0003 . The selector lever M 5043  is switched according to the position of the carriage M 4001 . That is, when the carriage moves M 4001  to a position over the ejection performance recovery unit M 5000 , a part of the selector lever M 5043  is contacted by a part of the carriage M 4001  and moved in the direction of arrow D 1  or D 2  (FIG. 11) depending on the position of the carriage M 4001 , with the result that a lock hole M 5026   b  of the pendulum arm M 5026  and a lock pin M 5043   a  of the selector lever M 5043  engage. 
     The valve rubber M 5036  is connected with one end of the valve tube M 5010  the other end of which is connected to the cap M 5001 . A valve lever M 5038  is connected to the discharge roller  2003  (FIG. 5) through a valve cam M 5035 , a valve clutch M 5048  and a valve drive transmission gear train M 5140 . As the discharge roller  2003  rotates, the valve lever M 5038  is pivoted about a shaft M 5038   a  in the direction of arrow E 1  or E 2  to come into or out of contact with the valve rubber M 5036 . When the valve lever M 5038  is in contact with the valve rubber M 5036 , the valve is closed. When the lever is parted, the valve is open. 
     Denoted E 0010  is a PG sensor that detects the position of the cap M 5001 . 
     Next, the operations of the ejection performance recovery unit M 5000  of the above construction will be explained. 
     First, let us explain about the driving operation of the automatic sheet feed unit M 3022 . 
     When, with the carriage M 4001  at the retracted position where it does not contact the selector lever M 5043 , the PG motor E 0003  rotates in the reverse direction, the pendulum arm M 5026  is pivoted in the direction of arrow C 1  (FIG. 11) through a pendulum drive transmission gear train M 5150 , causing a selector output gear M 5027  mounted on the pendulum arm M 5026  to mesh with an ASF gear M 5064  at one end of an ASF drive transmission gear train M 5160 . When in this state the PG motor E 0003  continues to rotate in the reverse direction, the automatic sheet feed unit M 3022  is driven by the PG motor through the ASF drive transmission gear train M 5160 . At this time, the driving force is not transmitted to the cap M 5001  and the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  because the one-way clutch M 5041  is disengaged. Thus, the wiper blades are not operated. 
     Next, the suction operation of the pump M 5100  will be described. 
     When, with the carriage M 4001  at the retracted position where it does not contact the selector lever M 5043 , the PG motor E 0003  rotates in the forward direction, the pendulum arm M 5026  is pivoted in the direction of arrow C 2  through the pendulum drive transmission gear train M 5150 , causing the selector output gear M 5027  mounted on the pendulum arm M 5026  to mesh with a pump gear M 5053  at one end of the pump drive transmission gear train M 5130 . 
     Then, when the carriage M 4001  moves to the capping position (a carriage position where the print element substrate H 1100  of the print head cartridge H 1000  faces the cap M 5001 ), a part of the carriage M 4001  abuts against a part of the selector lever M 5043 , which is then moved in the direction of D 1 , causing the lock pin M 5043   a  of the selector lever M 5043  to fit into the lock hole M 5026   b  of the pendulum arm M 5026 . As a result, the pendulum arm M 5026  is locked connected to the pump side. 
     Here, the discharge roller  2003  is driven in the reverse direction and the valve lever M 5038  is rotated in the direction of arrow E 1 , opening the valve rubber M 5036 . In this open state, the PG motor E 0003  rotates in the forward direction to drive the cap M 5001  and the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  to perform the capping operation (an operation whereby the cap M 5001  hermetically contacts and covers the print element substrate H 1100  of the print head H 1001 ). At this time, the pump M 5100  is operated but the pressing force of a roller (not shown) against the pump tube M 5019  is released, so that the pump tube M 5019  is not worked and no pressure is generated. 
     When the discharge roller  2003  is driven in the forward direction and the valve lever M 5038  is pivoted in the direction of arrow E 2  (FIG.  12 ), the valve rubber M 5036  is closed. At this time, the PG motor E 0003  rotates in the reverse direction to squeeze the pump tube M 5019  by the pressing force of the roller to apply a negative pressure to the print element substrate H 1100  of the print head cartridge H 1000  through the cap tube M 5009  and the cap M 5001 , forcibly drawing out ink and foams not suited for printing from the nozzles in the print element substrate H 1100 . 
     After this, the PG motor E 0003  rotates in the reverse direction and at the same time the discharge roller  2003  is driven in the reverse direction to pivot the valve lever M 5038  in the direction of arrow E 1  (FIG.  12 ). Now the valve rubber M 5036  is open. As a result, the pressure in the pump tube M 5019 , the cap tube M 5009  and the cap M 5001  is equal to an atmospheric pressure, stopping the forced suction of the ink nozzles in the print element substrate H 1100  of the print head cartridge H 1000 . At the same time, the ink contained in the pump tube M 5019 , the cap tube M 5009  and the cap M 5001  is drawn out from the other end of the pump tube M 5019  into the used ink absorbing member (not shown). This operation is referred to as an evacuation. Then, the PG motor E 0003  is stopped, the discharge roller  2003  is driven in the forward direction and the valve lever M 5038  is pivoted in the direction of arrow E 2  (FIG.  12 ), closing the valve rubber M 5036 . Now the suction operation is finished. 
     Next, the wiping operation will be explained. 
     During the wiping operation, the PG motor E 0003  is first rotated in the forward direction to move the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  to the wiping start position (a position where the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  are upstream of the print head cartridge H 1000  in the printing operation, with the cap M 5001  separated from the print head cartridge H 1000 ). Next, the carriage M 4001  moves to a wiping position where the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  face the print element substrate H 1100 . At this time, the carriage M 4001  is not in contact with the selector lever M 5043  and the pendulum arm M 5026  is not in the locked state. 
     Then, the PG motor E 0003  rotates in the forward direction to move the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2  in the direction of arrow B 1  (FIG. 12) wiping clean the print element substrate H 1100  of the print head cartridge H 1000 . Further, a wiper blade cleaning means (not shown) provided downstream of the print element substrate H 1100  of the print head cartridge H 1000  in the direction of the printing operation clears the wiper blades of the adhering ink. At this time, the cap M 5001  is kept in the separated state. 
     When the wiper blades reach the wiping end position (a downstream end position in the printing operation), the PG motor is stopped and the carriage M 4001  is moved to the wiping standby position out of the wiping operation range of the wiper blades M 5011 , M 5012 - 1 , M 5012 - 2 . Then, the PG motor E 0003  is rotated in the forward direction to move the wiper blades to the wiping end position. At this time, too, the cap M 5001  is maintained in the separated state. Now, the wiping operation is finished. 
     Next, the preliminary ejection will be explained. 
     Performing the suction operation and the wiping operation on a print head that uses a plurality of inks may cause a problem of ink mixing. 
     For example, during the suction operation, ink drawn out from the nozzles may get into nozzles of other color inks and, during the wiping operation, inks of various colors adhering to the circumferences of the nozzles may be pushed into nozzles of different color inks by the wipers. When the next printing is started, the initial part of the printed image may be discolored (or exhibit mixed colors), degrading the printed image. 
     To prevent the color mixing, the ink that may have mixed with other color inks is ejected out immediately before printing. This is called a preliminary ejection. In this embodiment, as shown in FIG. 11, a preliminary ejection port M 5045  is arranged near the cap M 5001 . Immediately before printing, the print element substrate H 1100  of the print head is moved to a position opposing the preliminary ejection port M 5045  where it is subjected to the preliminary ejection operation. 
     The preliminary ejection port M 5045  has a preliminary ejection absorbing member M 5046  and a preliminary ejection cover M 5047 . The preliminary ejection absorbing member M 5046  communicates with the used ink absorbing member not shown. 
     I.6 Scanner 
     The printer of this embodiment can mount a scanner in the carriage M 4001  in place of the print head cartridge H 1000  and be used as a reading device. 
     The scanner moves together with the carriage M 4001  in the main scan direction, and reads an image on a document fed instead of the printing medium as the scanner moves in the main scan direction. Alternating the scanner reading operation in the main scan direction and the document feed in the sub-scan direction enables one page of document image information to be read. 
     FIGS. 13A and 13B show the scanner M 6000  upside down to explain about its outline construction. 
     As shown in the figure, a scanner holder M 6001  is shaped like a box and contains an optical system and a processing circuit necessary for reading. A reading lens M 6006  is provided at a portion that faces the surface of a document when the scanner M 6000  is mounted on the carriage M 4001 . The lens M 6006  focuses light reflected from the document surface onto a reading unit inside the scanner to read the document image. An illumination lens M 6005  has a light source not shown inside the scanner. The light emitted from the light source is radiated onto the document through the lens M 6005 . 
     The scanner cover M 6003  secured to the bottom of the scanner holder M 6001  shields the interior of the scanner holder M 6001  from light. Louver-like grip portions are provided at the sides to improve the ease with which the scanner can be mounted to and dismounted from the carriage M 4001 . The external shape of the scanner holder M 6001  is almost similar to that of the print head H 1001 , and the scanner can be mounted to or dismounted from the carriage M 4001  in a manner similar to that of the print head H 1001 . 
     The scanner holder M 6001  accommodates a substrate having a reading circuit, and a scanner contact PCB M 6004  connected to this substrate is exposed outside. When the scanner M 6000  is mounted on the carriage M 4001 , the scanner contact PCB M 6004  contacts the contact FPC E 0011  of the carriage M 4001  to electrically connect the substrate to a control system on the printer body side through the carriage M 4001 . 
     I.7 Storage Box 
     FIG. 14 shows a storage box M 6100  for storing the print head H 1001 . 
     The storage box M 6100  comprises a storage box base M 6101  having an opening at its top, a storage box cover M 6102  pivotally mounted on the storage box base M 6101  to open and close the opening, a storage box cap M 6103  secured to the bottom of the storage box base M 6101 , and a leaf spring-like storage box spring M 6104  secured to the inner top portion of the storage box cover M 6102 . 
     When the print head is to be stored in the storage box of the above construction, the print head is inserted into the storage box base M 6101  so that the nozzle portion faces the storage box cap and then the storage box cover M 6102  is closed to engage a locking portion of the storage box base M 6101  with the storage box cover M 6102  to keep the storage box cover M 6102  in a closed state. Because the storage box spring M 6104  in this closed state applies a pressing force to the print head H 1001 , the nozzle portion of the print head H 1001  is hermetically covered by the storage box cap M 6103 . Therefore, this storage box can protect the print head nozzles against dust and ink evaporation and therefore maintain the print head in good condition for a long period of time. 
     The storage box M 6100  for storing the print head H 1001  can also be used for storing the scanner M 6000 . It is noted, however, that because the storage box cap M 6103  that protects the nozzle portion of the print head H 1001  is smeared with ink, it is strongly suggested that to prevent the ink from adhering to the scanner, the scanner be stored so that the scanner surface on which the scanner reading lens M 6006  and the scanner illumination lens M 6005  are arranged is directed away from the storage box cap M 6103 . 
     I.8 Example Configuration of Printer Electric Circuit 
     Next, an electric circuit configuration in this embodiment of the invention will be explained. 
     FIG. 15 schematically shows the overall configuration of the electric circuit in this embodiment. 
     The electric circuit in this embodiment comprises mainly a carriage substrate (CRPCB) E 0013 , a main PCB (printed circuit board) E 0014  and a power supply unit E 0015 . 
     The power supply unit E 0015  is connected to the main PCB E 0014  to supply a variety of drive power. 
     The carriage substrate E 0013  is a printed circuit board unit mounted on the carriage M 4001  (FIG. 2) and functions as an interface for transferring signals to and from the print head through the contact FPC E 0011 . In addition, based on a pulse signal output from an encoder sensor E 0004  as the carriage M 4001  moves, the carriage substrate E 0013  detects a change in the positional relation between an encoder scale E 0005  and the encoder sensor E 0004  and sends its output signal to the main PCB E 0014  through a flexible flat cable (CRFFC) E 0012 . 
     Further, the main PCB E 0014  is a printed circuit board unit that controls the operation of various parts of the ink jet printing apparatus in this embodiment, and has I/O ports for a paper end sensor (PE sensor) E 0007 , an automatic sheet feeder (ASF) sensor E 0009 , a cover sensor E 0022 , a parallel interface (parallel I/F) E 0016 , a serial interface (Serial I/F) E 0017 , a resume key E 0019 , an LED E 0020 , a power key E 0018  and a buzzer E 0021 . The main PCB E 0014  is connected to and controls a motor (CR motor) E 0001  that constitutes a drive source for moving the carriage M 4001  in the main scan direction; a motor (LF motor) E 0002  that constitutes a drive source for transporting the printing medium; and a motor (PG motor) E 0003  that performs the functions of recovering the ejection performance of the print head and feeding the printing medium. The main PCB E 0014  also has connection interfaces with an ink empty sensor E 0006 , a gap sensor E 0008 , a PG sensor E 0010 , the CRFFC E 0012  and the power supply unit E 0015 . 
     FIG. 16 is a diagram showing the relation between FIGS. 16A and 16B, and FIGS. 16A and 16B are block diagrams showing an inner configuration of the main PCB E 0014 . 
     Reference number E 1001  represents a CPU, which has a clock generator (CG) E 1002  connected to an oscillation circuit E 1005  to generate a system clock based on an output signal E 1019  of the oscillation circuit E 1005 . The CPU E 1001  is connected to an ASIC (application specific integrated circuit) and a ROM E 1004  through a control bus E 1014 . According to a program stored in the ROM E 1004 , the CPU E 1001  controls the ASIC E 1006 , checks the status of an input signal E 1017  from the power key, an input signal E 1016  from the resume key, a cover detection signal E 1042  and a head detection signal (HSENS) E 1013 , drives the buzzer E 0021  according to a buzzer signal (BUZ) E 1018 , and checks the status of an ink empty detection signal (INKS) E 1011  connected to a built-in A/D converter E 1003  and of a temperature detection signal (TH) E 1012  from a thermistor. The CPU E 1001  also performs various other logic operations and makes conditional decisions to control the operation of the ink jet printing apparatus. 
     The head detection signal E 1013  is a head mount detection signal entered from the print head cartridge H 1000  through the flexible flat cable E 0012 , the carriage substrate E 0013  and the contact FPC E 0011 . The ink empty detection signal E 1011  is an analog signal output from the ink empty sensor E 0006 . The temperature detection signal E 1012  is an analog signal from the thermistor (not shown) provided on the carriage substrate E 0013 . 
     Designated E 1008  is a CR motor driver that uses a motor power supply (VM) E 1040  to generate a CR motor drive signal E 1037  according to a CR motor control signal E 1036  from the ASIC E 1006  to drive the CR motor E 0001 . E 1009  designates an LF/PG motor driver which uses the motor power supply E 1040  to generate an LF motor drive signal E 1035  according to a pulse motor control signal (PM control signal) E 1033  from the ASIC E 1006  to drive the LF motor. The LF/PG motor driver E 1009  also generates a PG motor drive signal E 1034  to drive the PG motor. 
     Designated E 1010  is a power supply control circuit which controls the supply of electricity to respective sensors with light emitting elements according to a power supply control signal E 1024  from the ASIC E 1006 . The parallel I/F E 0016  transfers a parallel I/F signal E 1030  from the ASIC E 1006  to a parallel I/F cable E 1031  connected to external circuits and also transfers a signal of the parallel I/F cable E 1031  to the ASIC E 1006 . The serial I/F E 0017  transfers a serial I/F signal E 1028  from the ASIC E 1006  to a serial I/F cable E 1029  connected to external circuits, and also transfers a signal from the serial I/F cable E 1029  to the ASIC E 1006 . 
     The power supply unit E 0015  provides a head power signal (VH) E 1039 , a motor power signal (VM) E 1040  and a logic power signal (VDD) E 1041 . A head power ON signal (VHON) E 1022  and a motor power ON signal (VMON) E 1023  are sent from the ASIC E 1006  to the power supply unit E 0015  to perform the ON/OFF control of the head power signal E 1039  and the motor power signal E 1040 . The logic power signal (VDD) E 1041  supplied from the power supply unit E 0015  is voltage-converted as required and given to various parts inside or outside the main PCB E 0014 . 
     The head power signal E 1039  is smoothed by a circuit of the main PCB E 0014  and then sent out to the flexible flat cable E 0011  to be used for driving the print head cartridge H 1000 . E 1007  denotes a reset circuit which detects a reduction in the logic power signal E 1041  and sends a reset signal (RESET) to the CPU E 1001  and the ASIC E 1006  to initialize them. 
     The ASIC E 1006  is a single-chip semiconductor integrated circuit and is controlled by the CPU E 1001  through the control bus E 1014  to output the CR motor control signal E 1036 , the PM control signal E 1033 , the power supply control signal E 1024 , the head power ON signal E 1022  and the motor power ON signal E 1023 . It also transfers signals to and from the parallel interface E 0016  and the serial interface E 0017 . In addition, the ASIC E 1006  detects the status of a PE detection signal (PES) E 1025  from the PE sensor E 0007 , an ASF detection signal (ASFS) E 1026  from the ASF sensor E 0009 , a gap detection signal (GAPS) E 1027  from the GAP sensor E 0008  for detecting a gap between the print head and the printing medium, and a PG detection signal (PGS) E 1032  from the PG sensor E 0010 , and sends data representing the statuses of these signals to the CPU E 1001  through the control bus E 1014 . Based on the data received, the CPU E 1001  controls the operation of an LED drive signal E 1038  to turn on or off the LED E 0020 . 
     Further, the ASIC E 1006  checks the status of an encoder signal (ENC) E 1020 , generates a timing signal, interfaces with the print head cartridge H 1000  and controls the print operation by a head control signal E 1021 . The encoder signal (ENC) E 1020  is an output signal of the CR encoder sensor E 0004  received through the flexible flat cable E 0012 . The head control signal E 1021  is sent to the print head H 1001  through the flexible flat cable E 0012 , carriage substrate E 0013  and contact FPC E 0011 . 
     FIG. 17 is a diagram showing the relation between FIGS. 17A and 17B, and FIGS. 17A and 17B are block diagrams showing an example internal configuration of the ASIC E 1006 . 
     In these figures, only the flow of data, such as print data and motor control data, associated with the control of the head and various mechanical components is shown between each block, and control signals and clock associated with the read/write operation of the registers incorporated in each block and control signals associated with the DMA control are omitted to simplify the drawing. 
     In the figures, reference number E 2002  represents a PLL controller which, based on a clock signal (CLK) E 2031  and a PLL control signal (PLLON) E 2033  output from the CPU E 1001  shown in FIG. 16A, generates a clock (not shown) to be supplied to the most part of the ASIC E 1006 . 
     Denoted E 2001  is a CPU interface (CPU I/F) E 2001 , which controls the read/write operation of register in each block, supplies a clock to some blocks and accepts an interrupt signal (none of these operations are shown) according to a reset signal E 1015 , a software reset signal (PDWN) E 2032  and a clock signal (CLK) E 2031  output from the CPU E 1001 , and control signals from the control bus E 1014 . The CPU I/F E 2001  then outputs an interrupt signal (INT) E 2034  to the CPU E 1001  to inform it of the occurrence of an interrupt within the ASIC E 1006 . 
     E 2005  denotes a DRAM which has various areas for storing print data, such as a reception buffer E 2010 , a work buffer E 2011 , a print buffer E 2014  and a development data buffer E 2016 . The DRAM E 2005  also has a motor control buffer E 2023  for motor control and, as buffers used instead of the above print data buffers during the scanner operation mode, a scanner input buffer E 2024 , a scanner data buffer E 2026  and an output buffer E 2028 . 
     The DRAM E 2005  is also used as a work area by the CPU E 1001  for its own operation. Designated E 2004  is a DRAM control unit E 2004  which performs read/write operations on the DRAM E 2005  by switching between the DRAM access from the CPU E 1001  through the control bus and the DRAM access from a DMA control unit E 2003  described later. 
     The DMA control unit E 2003  accepts request signals (not shown) from various blocks and outputs address signals and control signals (not shown) and, in the case of write operation, write data E 2038 , E 2041 , E 2044 , E 2053 , E 2055 , E 2057  etc. to the DRAM control unit to make DRAM accesses. In the case of read operation, the DMA control unit E 2003  transfers the read data E 2040 , E 2043 , E 2045 , E 2051 , E 2054 , E 2056 , E 2058 , E 2059  from the DRAM control unit E 2004  to the requesting blocks. 
     Denoted E 2006  is an IEEE 1284 I/F which functions as a bi-directional communication interface with external host devices, not shown, through the parallel I/F E 0016  and is controlled by the CPU E 1001  via CPU I/F E 2001 . During the printing operation, the IEEE 1284 I/F E 2006  transfers the receive data (PIF receive data E 2036 ) from the parallel I/F E 0016  to a reception control unit E 2008  by the DMA processing. During the scanner reading operation, the 1284 I/F E 2006  sends the data (1284 transmit data (RDPIF) E 2059 ) stored in the output buffer E 2028  in the DRAM E 2005  to the parallel I/F E 0016  by the DMA processing. 
     Designated E 2007  is a universal serial bus (USB) I/F which offers a bi-directional communication interface with external host devices, not shown, through the serial I/F E 0017  and is controlled by the CPU E 1001  through the CPU I/F E 2001 . During the printing operation, the universal serial bus (USB) I/F E 2007  transfers received data (USB receive data E 2037 ) from the serial I/F E 0017  to the reception control unit E 2008  by the DMA processing. During the scanner reading, the universal serial bus (USB) I/F E 2007  sends data (USB transmit data (RDUSB) E 2058 ) stored in the output buffer E 2028  in the DRAM E 2005  to the serial I/F E 0017  by the DMA processing. The reception control unit E 2008  writes data (WDIF E 2038 ) received from the 1284 I/F E 2006  or universal serial bus (USB) I/F E 2007 , whichever is selected, into a reception buffer write address managed by a reception buffer control unit E 2039 . Designated E 2009  is a compression/decompression DMA controller which is controlled by the CPU E 1001  through the CPU I/F E 2001  to read received data (raster data) stored in a reception buffer E 2010  from a reception buffer read address managed by the reception buffer control unit E 2039 , compress or decompress the data (RDWK) E 2040  according to a specified mode, and write the data as a print code string (WDWK) E 2041  into the work buffer area. 
     Designated E 2013  is a print buffer transfer DMA controller which is controlled by the CPU E 1001  through the CPU I/F E 2001  to read print codes (RDWP) E 2043  on the work buffer E 2011  and rearrange the print codes onto addresses on the print buffer E 2014  that match the sequence of data transfer to the print head cartridge H 1000  before transferring the codes (WDWP E 2044 ). Reference number E 2012  denotes a work area DMA controller which is controlled by the CPU E 1001  through the CPU I/F E 2001  to repetitively write specified work fill data (WDWF) E 2042  into the area of the work buffer whose data transfer by the print buffer transfer DMA controller E 2013  has been completed. 
     Designated E 2015  is a print data development DMA controller E 2015 , which is controlled by the CPU E 1001  through the CPU I/F E 2001 . Triggered by a data development timing signal E 2050  from a head control unit E 2018 , the print data development DMA controller E 2015  reads the print code that was rearranged and written into the print buffer and the development data written into the development data buffer E 2016  and writes developed print data (RDHDG) E 2045  into the column buffer E 2017  as column buffer write data (WDHDG) E 2047 . The column buffer E 2017  is an SRAM that temporarily stores the transfer data (developed print data) to be sent to the print head cartridge H 1000 , and is shared and managed by both the print data development DMA CONTROLLER and the head control unit through a handshake signal (not shown). 
     Designated E 2018  is a head control unit E 2018  which is controlled by the CPU E 1001  through the CPU I/F E 2001  to interface with the print head cartridge H 1000  or the scanner-through the head control signal. It also outputs a data development timing signal E 2050  to the print data development DMA controller according to a head drive timing signal E 2049  from the encoder signal processing unit E 2019 . 
     During the printing operation, the head control unit E 2018 , when it receives the head drive timing signal E 2049 , reads developed print data (RDHD) E 2048  from the column buffer and outputs the data to the print head cartridge H 1000  as the head control signal E 1021 . 
     In the scanner reading mode, the head control unit E 2018  DMA-transfers the input data (WDHD) E 2053  received as the head control signal E 1021  to the scanner input buffer E 2024  on the DRAM E 2005 . Designated E 2025  is a scanner data processing DMA controller E 2025  which is controlled by the CPU E 1001  through the CPU I/F E 2001  to read input buffer read data (RDAV) E 2054  stored in the scanner input buffer E 2024  and writes the averaged data (WDAV) E 2055  into the scanner data buffer E 2026  on the DRAM E 2005 . 
     Designated E 2027  is a scanner data compression DMA controller which is controlled by the CPU E 1001  through the CPU I/F E 2001  to read processed data (RDYC) E 2056  on the scanner data buffer E 2026 , perform data compression, and write the compressed data (WDYC) E 2057  into the output buffer E 2028  for transfer. 
     Designated E 2019  is an encoder signal processing unit which, when it receives an encoder signal (ENC), outputs the head drive timing signal E 2049  according to a mode determined by the CPU E 1001 . The encoder signal processing unit E 2019  also stores in a register information on the position and speed of the carriage M 4001  obtained from the encoder signal E 1020  and presents it to the CPU E 1001 . Based on this information, the CPU E 1001  determines various parameters for the CR motor E 0001 . Designated E 2020  is a CR motor control unit which is controlled by the CPU E 1001  through the CPU I/F E 2001  to output the CR motor control signal E 1036 . 
     Denoted E 2022  is a sensor signal processing unit which receives detection signals E 1032 , E 1025 , E 1026  and E 1027  output from the PG sensor E 0010 , the PE sensor E 0007 , the ASF sensor E 0009  and the gap sensor E 0008 , respectively, and transfers these sensor information to the CPU E 1001  according to the mode determined by the CPU E 1001 . The sensor signal processing unit E 2022  also outputs a sensor detection signal E 2052  to a DMA controller E 2021  for controlling LF/PG motor. 
     The DMA controller E 2021  for controlling LF/PG motor is controlled by the CPU E 1001  through the CPU I/F E 2001  to read a pulse motor drive table (RDPM) E 2051  from the motor control buffer E 2023  on the DRAM E 2005  and output a pulse motor control signal E 1033 . Depending on the operation mode, the controller outputs the pulse motor control signal E 1033  upon reception of the sensor detection signal as a control trigger. 
     Designated E 2030  is an LED control unit which is controlled by the CPU E 1001  through the CPU I/F E 2001  to output an LED drive signal E 1038 . Further, designated E 2029  is a port control unit which is controlled by the CPU E 1001  through the CPU I/F E 2001  to output the head power ON signal E 1022 , the motor power ON signal E 1023  and the power supply control signal E 1024 . 
     I.9 Operation of Printer 
     Next, the operation of the ink jet printing apparatus in this embodiment of the invention with the above configuration will be explained by referring to the flow chart of FIG.  18 . 
     When the printer body M 1000  is connected to an AC power supply, a first initialization is performed at step S 1 . In this initialization process, the electric circuit system including the ROM and RAM in the apparatus is checked to confirm that the apparatus is electrically operable. 
     Next, step S 2  checks if the power key E 0018  on the upper case M 1002  of the printer body M 1000  is turned on. When it is decided that the power key E 0018  is pressed, the processing moves to the next step S 3  where a second initialization is performed. 
     In this second initialization, a check is made of various drive mechanisms and the print head of this apparatus. That is, when various motors are initialized and head information is read, it is checked whether the apparatus is normally operable. 
     Next, steps S 4  waits for an event. That is, this step monitors a demand event from the external I/F, a panel key event from the user operation and an internal control event and, when any of these events occurs, executes the corresponding processing. 
     When, for example, step S 4  receives a print command event from the external I/F, the processing moves to step S 5 . When a power key event from the user operation occurs at step S 4 , the processing moves to step S 10 . If another event occurs, the processing moves to step S 11 . 
     Step S 5  analyzes the print command from the external I/F, checks a specified paper kind, paper size, print quality, paper feeding method and others, and stores data representing the check result into the DRAM E 2005  of the apparatus before proceeding to step S 6 . 
     Next, step S 6  starts feeding the paper according to the paper feeding method specified by the step S 5  until the paper is situated at the print start position. The processing moves to step S 7 . 
     At step S 7  the printing operation is performed. In this printing operation, the print data sent from the external I/F is stored temporarily in the print buffer. Then, the CR motor E 0001  is started to move the carriage M 4001  in the main-scanning direction. At the same time, the print data stored in the print buffer E 2014  is transferred to the print head H 1001  to print one line. When one line of the print data has been printed, the LF motor E 0002  is driven to rotate the LF roller M 3001  to transport the paper in the sub-scanning direction. After this, the above operation is executed repetitively until one page of the print data from the external I/F is completely printed, at which time the processing moves to step S 8 . 
     At step S 8 , the LF motor E 0002  is driven to rotate the paper discharge roller M 2003  to feed the paper until it is decided that the paper is completely fed out of the apparatus, at which time the paper is completely discharged onto the paper discharge tray M 1004 . 
     Next at step S 9 , it is checked whether all the pages that need to be printed have been printed and if there are pages that remain to be printed, the processing returns to step S 5  and the steps S 5  to S 9  are repeated. When all the pages that need to be printed have been printed, the print operation is ended and the processing moves to step S 4  waiting for the next event. 
     Step S 10  performs the printing termination processing to stop the operation of the apparatus. That is, to turn off various motors and print head, this step renders the apparatus ready to be cut off from power supply and then turns off power, before moving to step S 4  waiting for the next event. 
     Step S 11  performs other event processing. For example, this step performs processing corresponding to the ejection performance recovery command from various panel keys or external I/F and the ejection performance recovery event that occurs internally. After the recovery processing is finished, the printer operation moves to step S 4  waiting for the next event. 
     II. Characteristic Configuration 
     Next, an embodiment of a characteristic configuration of the present invention in a printer having a “basic configuration” such as that described above will be described with reference to the drawings. 
     First Embodiment 
     FIGS. 19 to  23  are views useful for explaining a pressure generating apparatus according to a first embodiment of the present invention. The pressure generating apparatus according to this example include a pump (hereafter referred to as a “tube pump”) M 5100 . 
     In the tube pump M 5100 , reference numeral M 5019  denotes an elastic pump tube and reference numeral M 5022  denotes a pump tube guide. The pump tube guide M 5022  has a semicylindrical inner wall extending over 180° or more around a pump center shaft M 5076 , and pump tube M 5019  disposed along the inner wall. Reference numeral M 5021  denotes a pump roller guide rotatably supported on the pump center shaft M 5076 . Two pump roller holders M 5020  are held on the pump roller guide M 5021  so as to be rotated by a rotating shaft  5020   a  and to have an angular phase difference of 180° around the pump center shaft M 5076 . In FIGS. 19 and 20 shows only the rotating shaft M 5020   a  for one of the pump roller holder M 5020 . Each pump roller holder M 5020  has a movement groove M 5020   b  for rotatably and movably guiding a pump roller M 5018 . The pump roller M 5018  comes in pressure contact with the pump tube M 5019  to squeeze it to generate pressure therein. A pump roller pressure contact spring M 5025  that brings the pump roller M 5018  into pressure contact with the pump tube M 5019  is provided between each pump roller holder M 5020  and the pump roller guide M 5021 . Reference numeral M 5018   a  denotes a shaft of the pump roller M 5018 , and reference numeral M 5023  denotes a pump tube joint. 
     The pump roller M 5018  is brought into pressure contact with the pump tube M 5019  and has the pressure contact released depending on a rotating direction of the pump roller guide M 5021 . 
     That is, when the pump roller guide M 5021  is rotated in an arrow F 1  direction as shown in FIG. 19, the pump roller M 5018  is moved, at a position opposed to a roller damper M 5016 , through the movement groove M 5020   b  in an arrow G 1  direction due to an urging force effected by the roller damper M 5016 . Thus, the distance between the pump roller  5018  and the pump center shaft M 5076  becomes relatively large, so that the pump roller  5018  is brought into pressure contact with the pump tube M 5019 . Then, the pump roller guide M 5021  rotates in the arrow F 1  direction while the pressure contact between the pump roller M 5018  and the pump tube M 5019  remains. Consequently, the pump tube M 5019  is squeezed between the pump tube guide M 5022  and the pump roller M 5018  to generate pressure inside the pump tube M 5019 . 
     On the other hand, when the pump roller guide M 5021  is rotated in an arrow F 2  direction as shown in FIG. 20, the pump roller M 5018  moves through the movement groove M 5020   b  in the arrow G 2  direction due to a frictional force effected between the pump roller M 5018  and the pump tube M 5019 . The distance between the pump roller  5018  and the pump center shaft M 5076  becomes relatively small, so that the pressure contact between the pump roller M 5018  and the pump tube M 5019  is released. Then, the pump roller guide M 5021  rotates in the arrow F 2  direction while the pressure contact between the pump roller M 5018  and the pump tube M 5019  is released. As a result, the pump tube M 5019  is prevented from being squeezed between the pump tube guide M 5022  and the pump roller M 5018 , and no pressure is generated inside the pump tube M 5019 . 
     As described above, the tube pump M 5100  is connected to the other side of a PG motor E 0003  via a drive switching means and a pump drive transmission gear train M 5130 . The drive switching means switches a transmission path for a driving force for the tube pump M 5100  and the automatic feed means M 3022 . In addition, the pump tube M 5019  has one end connected to the cap M 5001  via the cap tube M 5009  as shown in FIGS. 21 and 22. The cap M 5001  has a suction port M 5001   a  and an air communication port M 5001   b  formed therein. The suction port M 5001   a  has the cap tube M 5009  connected thereto and the valve tube M 5010  connected to the air communication port  5001   b . Additionally, reference numeral M 5003  denotes a cap holder, reference numeral M 5024  denotes pump gear, and reference numeral M 5067  denotes a valve lever spring. As described above, when the valve lever M 5038  rotatively moves in the arrow E 1  or E 2  direction, the valve rubber M 5036  is opened or closed, respectively, to in turn open or close the valve tube M 5010  connected to the air communication port M 5001   b  of the cap M 5001 . 
     Next, characteristic operations of the tube pump M 5100  will be described (see FIG.  23 ). 
     The cap M 5001  and the tube pump M 5100  are driven correlatively depending on a rotating direction of the PG motor E 0003 , as shown by (a), (b), and (c) in FIG.  25 . Additionally, the valve lever M 5038  is driven depending on a rotating direction of the ejection rollers M 2003  rotated by the LF motor E 0002 , as shown by (d) and (e) in FIG.  23 . 
     That is, first, the ejection rollers M 2003  are reversely driven for reverse rotation to cause the valve lever M 5038  to open the valve rubber M 5036 . The PG motor E 0003  subsequently rotates forward for normal rotation to bring the cap M 5001  into abutment with a surface of the printing head H 1001  which has the ink ejection port formed therein, to cap the printing head H 1001 . At this point, the tube pump M 5100  is driven in an arrow F 2  direction (normal rotation), as shown in FIG. 20, due to the normal rotation of the PG motor E 0003 . The forward driving of the tube pump M 5100 , however, prevents the pump roller M 5018  from coming in pressure contact with the pump tube  5019 , so that the tube pump M 5100  generates no pressure. 
     Subsequently, between points of time ta and tb, the PG motor E 0003  is reversely rotated to reversely drive the tube pump M 5100  in the arrow F 1  direction at least by 180°. Accordingly, the pump roller M 5018  passes through the position opposed to the roller damper M 5016 . Consequently, an active force from the roller damper M 5016  causes the pump roller M 5018  to move along the movement groove M 5020   b  of the pump roller holder M 5020  in an arrow G 1  direction and into pressure contact with the pump tube M 5019  (this state is hereafter referred to as a “pressure contact state”). Once the pump roller M 5018  has been moved to the pressure contact position in this manner, the PG motor E 0003  is stopped at a point of time tb. Since the valve rubber M 5046  is open between the points of time ta and tb, no pressure is generated in the cap M 5001  and no negative pressure acts on the printing element substrate H 1100  of the printing head H 1001 . 
     Subsequently, the ejection rollers M 2003  are forwardly driven for normal rotation to cause the valve lever M 5038  to close the valve rubber M 5046 . Then, at a point of time tc, the PG motor E 0003  is reversely rotated again to reversely drive the tube pump M 5100  in the arrow F 1  direction. Consequently, the pump roller M 5018  rotates in the arrow F 1  direction while in pressure contact with the pump tube M 5019 , thereby squeezing the pump tube M 5019  to generate pressure therein. As a result, a negative pressure is introduced into the cap M 5001  through the cap tube M 5009  and acts on the printing element substrate H 1100  of the printing head H 1001 . Therefore, ink of increased viscosity which are no longer suitable for printing as well as bubbles is forcibly sucked and ejected from the ink ejection port of the printing head. 
     Subsequently, the ejection rollers M 2003  are reversely driven to cause the valve lever M 5038  to open the valve rubber M 5046 . Then, the air communication port M 5001   b  in the cap M 5001  is opened to set the interior of the cap M 5001  at atmospheric pressure. As a result, ink is prevented from being sucked or ejected from the ink ejection port of the printing head H 1001 . At the same time, ink inside the cap M 5001 , cap tube M 5009 , and pump tube M 5019  is sucked and ejected from the other end of the pump tube M 5019  into a waste ink absorbent (this operation is hereafter referred to as “idle suction”). 
     Subsequently, the PG motor E 0003  is stopped, and the ejection rollers M 2003  are forwardly driven for normal rotation. Thus, the cap M 5001  is separated from the ink ejection port forming surface of the printing head H 1001  to release the capping to cause, and the valve lever M 5038  close the valve rubber M 5046 . In this case, the PG motor E 0003  stops after a small amount of normal rotation. Accordingly, the tube pump M 5100  moves through the movement groove M 5020   b  in an arrow G 2  direction and is thus prevented from coming in pressure contact with the pump tube M 5019  (this state is hereafter referred to as a “non-pressure contact state). Then, the series of suction recovery operations are completed. 
     As described above, in this example, the tube pump M 5100  is driven between the points of time ta and tb to bring the pump roller M 5018  into pressure contact with the pump tube M 5019 . Subsequently, the valve lever M 5038  closes the valve rubber M 5036 , and at the point of time tc, the tube pump M 5100  is driven again. The reason why the tube pump M 5100  is driven according to two steps is shown below. 
     The active force from the roller damper M 5016  is required to move the pump roller M 5018  along the movement groove M 5020   b  of the pump roller holder M 5020  from a position where it is not in pressure contact with the pump tube M 5019  (this position is hereafter referred to as a “non-contact pressure position”) to the contact pressure position. In addition, the amount of rotation required for the tube pump M 5100  to move the pump roller M 5018  to the pressure contact position is varied by about 180° depending on the initial position of the pump roller M 5018 . Additionally, since this example omits the detection means for detecting the position of the pump roller M 5018 , the amount of rotation of the tube pump M 5100  cannot be controlled depending on the initial position of the pump roller M 5018 . It is then assumed that the tube pump M 5100  is simply driven in the arrow F 1  direction after the valve rubber M 5036  has been closed as in the above described conventional example in FIG.  25 . In this case, the amount of rotation of the tube pump M 5100  from the start of its rotation until it starts to squeeze the pump tube M 5019  after the pump roller M 5018  has moved to the contact pressure position, that is, the amount of rotation of the tube pump M 5100  from a point of time when the driving is started until a point of time when pressure is generated. Accordingly, under such an assumption, the amount of pressure generated when the tube pump is rotated by a predetermined amount, is significantly varied, and thus the amount of ink sucked and ejected is significantly varied. 
     On the contrary, in this embodiment, at the point of time tc when the tube pump M 5100  is redriven, the pump roller M 5018  is already in pressure contact with the pump tube M 5019 . Consequently, the tube pump M 5100  can squeeze the pump tube M 5019  to generate pressure therein at the point of time tc. That is, the period of time when pressure is generated by the tube pump M 5100  can be accurately determined. The valve rubber M 5036  is also closed before the redriving time tc. Thus, this embodiment is not affected by variations in the operation time of the valve rubber M 5036  from the start of movement of the valve lever M 5038  and valve rubber M 5036  until the valve rubber M 5036  is completely closed. That is, the period of time when pressure is generated by the tube pump M 5100  is set without being affected by variations in the operation time of the valve rubber M 5038  resulting from mechanical factors. 
     Furthermore, once the pump roller M 5018  has rotated in the arrow F 1  direction by a fixed amount after the redriving time tc, the ejection rollers M 2003  are reversely rotated to open the valve rubber M 5036 . Consequently, the amount of negative pressure generated by the tube pump M 5100  or the amount of ink sucked and ejected can be adequately determined and variations in these amounts can be minimized, regardless of the initial position of the pump roller M 5018 . 
     Second Embodiment 
     FIG. 24 is a timing chart useful for explaining the operation of the pump tube M 5100  in a pressure generating apparatus according to a second embodiment of the present invention. 
     If the amount of time required for the opening and closing operations of the valve lever M 5038  and valve rubber M 5036  is too short to affect the total amount of time required for the tube pump M 5100  to generate pressure, the tube pump M 5100  need not be driven according to two steps as shown in FIG.  24 . That is, when the valve lever M 5038  closes the valve rubber M 5036 , the driving of the tube pump M 5100  need not be stopped. Accordingly, a negative pressure can be generated depending on the period of time when the valve rubber  5036  is closed. As a result, effects similar to those of the above described first embodiment can be obtained, and the period of time when the tube pump M 5100  is driven can also be reduced. 
     OTHER EMBODIMENTS 
     The pressure generating apparatus according to the present invention is widely applicable as printing apparatuses and pressure supply sources for various apparatuses using pressure. In addition, the means for switching to the state where pressure from the tube pump can or cannot be introduced into the pressure introduction section such as the cap may be configured in various manners. For example, an opening and closing valve may be interposed in a pressure introduction path between the tube pump and the pressure introduction section such as the cap. Alternatively, the pressure introduction section may introduce a positive pressure from the tube pump. 
     The present invention can be effectively used in an aspect where thermal energy generated by a thermoelectric converter is used to cause film boiling in the liquid to generate bubbles therein. 
     The present invention has been described in detail with respect to various embodiments, and it will now be apparent from the foregoing to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and it is the intention, therefore, in the appended claims to cover all such changes and modifications as fall within the true spirit of the invention.