Patent Publication Number: US-7717537-B2

Title: Liquid ejection apparatus and liquid maintenance method

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a liquid ejection apparatus and a liquid maintenance method, and more particularly, to a liquid ejection apparatus which ejects liquid toward a prescribed medium and a liquid maintenance method which maintains the state of the liquid. 
   2. Description of the Related Art 
   There is a liquid ejection apparatus which ejects dispersion liquid in which dispersed micro-particles are suspended. Examples of material of the micro-particles include, for instance, pigment, high-polymer resin, metal, glass, or oxide or compound of these. Generally, the micro-particles tend to aggregate and settle with the passage of time. When the liquid in which the micro-particles have aggregated and settled is ejected, then there is deterioration of quality in the ejection results, namely, density non-uniformities or distortions, poor color reproduction, non-uniform density of the micro-particles, and the like. Therefore, technology for maintaining the state of the dispersion liquid has been proposed. 
   For example, Japanese Patent Application Publication No. 2004-167698 discloses a liquid ejection apparatus in which a liquid ejection head having a projection on the bottom is supported on a carriage, which moves reciprocally in a main scanning direction, and a cam is provided to press the projection of the liquid ejection head to move the liquid ejection head in a substantially perpendicular direction (a vertical direction) with respect to the carriage so that the liquid ejection head to perform a swinging motion in the substantially perpendicular direction (the vertical direction) and the liquid inside a liquid chamber (ink cartridge) held on the liquid ejection head is agitated in such a manner that a settled state of the contents in the liquid is eliminated. 
   Japanese Patent Application Publication No. 2004-216809 discloses technology in which, when nozzles of an inkjet head oppose a recording medium (i.e., in a printing state), a free surface of the ink (the liquid-atmosphere interface, which is also commonly called “meniscus”) in the nozzle that is not to eject the ink is caused to vibrate to an extent in which the ink is not ejected, while the ink is ejected and discarded through the nozzles when not printing. 
   Japanese Patent Application Publication No. 2003-72104 discloses technology in which a manifold guiding ejection material (e.g., ink) to a nozzle of a liquid ejection head is provided with a piezoelectric element for agitating the ejection material inside the manifold. By continuously agitating the ejection material inside the manifold by means of the piezoelectric element, the ejection material immediately prior to ejection is maintained in a state of stable dispersion of micro-particles. 
   However, in some cases, it is difficult to achieve efficient agitation of liquid in which dispersed micro-particles are suspended. 
   In particular, in a liquid ejection apparatus having a liquid ejection head in which the liquid ejection face is situated in a bottommost position, nozzle blockages are liable to occur due to sedimented micro-particles in the nozzles. In the case of a so-called shuttle head structure in which the liquid ejection head performs a reciprocal back and forth movement, the liquid inside the liquid ejection head is agitated by the reciprocal motion of the liquid ejection head, but in the case of a line head structure where the liquid ejection head does not perform reciprocal movement, the liquid is not agitated usually. 
   As described above, technology has been proposed for carrying out various maintenance operations, such as the vertical swinging of the liquid ejection head, the slight vibration of the free surface of the ink in the nozzle, the discarding of the ink, and the like; however, these operations are difficult to apply in practice, since they are not efficient because of long waiting times, increased costs, and so on. 
   For example, in Japanese Patent Application Publication No. 2004-167698, the liquid ejection head is caused to swing in the substantially vertical direction by means of the cam pressing the projection arranged on the bottom of the liquid ejection head; however, the liquid ejection head performs no reciprocal back and forth movement. The liquid having the aggregated and settled micro-particles in the liquid cartridge is thus agitated only by the displacement of the liquid ejection head in the substantially perpendicular direction, and hence the agitation performance is low and a long time is required until the liquid is agitated to a satisfactory extent. 
   In Japanese Patent Application Publication No. 2004-216809, since valuable liquid is ejected and discarded when the apparatus is not in printing, there is a problem in that costs increase. 
   In Japanese Patent Application Publication No. 2003-72104, since the dispersed state of the micro-particles is maintained by continuously agitating the liquid by means of the piezoelectric element, then it is not effective unless the piezoelectric element continuously carries out the agitating operation even while the apparatus is not operating, and it results in high power consumption and increased costs. 
   Furthermore, if a structure is adopted in which a common liquid chamber is arranged at a position higher than pressure chambers and the base of the common liquid chamber is connected to the pressure chambers through liquid supply channels, then the high-density liquid nearby the base of the common liquid chamber in which the micro-particles have settled is supplied to the pressure chambers, and hence there is a progressive density change (from thick to thin) in the liquid as being consumed by ejection. Consequently, quality deterioration occurs in the ejection results. 
   SUMMARY OF THE INVENTION 
   The present invention has been contrived in view of the foregoing circumstances, an object thereof being to provide a liquid ejection apparatus and a liquid maintenance method whereby it is possible to prevent deterioration of the quality of liquid as a result of aggregation and/or settling of micro-particles in the liquid, and to eject liquid in a stable fashion. 
   In order to attain the aforementioned object, the present invention is directed to a liquid ejection apparatus, comprising: a liquid ejection head which has nozzles ejecting liquid in a downward-facing state and pressure chambers connected to the nozzles; a turning device which turns the liquid ejection head to switch the nozzles of the liquid ejection head between the downward-facing state and an upward-facing state; and a sealing device which seals the nozzles when the nozzles of the liquid ejection head are in the upward-facing state. 
   According to the present invention, since the liquid ejection head is switched between the state where the nozzles are orientated in the downward direction and the state where the nozzles are orientated in the upward direction, by turning the liquid ejection head, and since the nozzles are sealed when the nozzles are in the upward-orientated state, then the micro-particles dispersed in the liquid do not aggregate and settle toward the free surface of the liquid in the nozzles, and therefore, blockages of the nozzles are prevented and the liquid can be ejected in a stable fashion. 
   Preferably, the turning device turns the liquid ejection head to make the liquid ejection head swing to agitate the liquid inside the liquid ejection head. 
   According to this aspect of the present invention, since the liquid ejection head is caused to swing and the liquid inside the liquid ejection head is agitated by turning the liquid ejection head, then the micro-particles that have aggregated and settled can be redispersed more readily in the liquid than in a case where the aggregated and settled micro-particles are displaced in the vertical direction only, and therefore density non-uniformities are eliminated and it is possible to eject the liquid of uniform density. 
   Preferably, the liquid ejection apparatus further comprises a vibrating device which vibrates the liquid in the pressure chambers slightly to an extent which does not cause the liquid to be ejected from the nozzles, during the turning device making the liquid ejection head swing. 
   According to this aspect of the present invention, the micro-particles that have aggregated and settled are broken up by the slight vibration of the liquid, and greater effect of agitation is obtained by the slight vibration. 
   In order to attain the aforementioned object, the present invention is also directed to a liquid maintenance method for maintaining a state of liquid inside a liquid ejection head which has nozzles ejecting the liquid and pressure chambers connected to the nozzles, the method comprising the step of: agitating the liquid inside the liquid ejection head by making the liquid ejection head swing by turning the liquid ejection head. 
   Preferably, in the agitating step, the liquid inside the pressure chambers is vibrated slightly to an extent which does not cause the liquid to be ejected from the nozzles, during swinging the liquid ejection head. 
   In order to attain the aforementioned object, the present invention is also directed to a liquid maintenance method for maintaining a state of liquid inside a liquid ejection head which has nozzles ejecting the liquid when the nozzles are in a downward-facing state, and pressure chambers connected to the nozzles, the method comprising the steps of: switching the nozzles of the liquid ejection head between the downward-facing state and an upward-facing state by turning the liquid ejection head; and sealing the nozzles when the nozzles of the liquid ejection head are in the upward-facing state. 
   According to the present invention, deterioration of liquid quality due to aggregation or settling of micro-particles in the liquid is prevented, and stable ejection of liquid is achieved. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The nature of this invention, as well as other objects and advantages thereof, will be explained in the following with reference to the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures and wherein: 
       FIG. 1  is a plan view perspective diagram showing an approximate view of the general structure of a liquid ejection head according to an embodiment of the present invention; 
       FIG. 2  is a cross-sectional diagram along line  2 - 2  in  FIG. 1 ; 
       FIG. 3  is a plan view perspective diagram showing the general structure of a liquid ejection head according to a further embodiment of the present invention; 
       FIG. 4  is a cross-sectional diagram along line  4 - 4  in  FIG. 3 ; 
       FIG. 5  is a diagram showing the general functional composition of an image forming apparatus according to an embodiment of the present invention; 
       FIG. 6  is a plan diagram showing the principal part of an image forming system of the image forming apparatus; 
       FIG. 7  is a schematic drawing showing the principal part of a liquid flow system of the image forming apparatus; 
       FIG. 8  is a block diagram showing the general composition of the image forming apparatus; 
       FIG. 9  is an oblique diagram showing a maintenance mechanism of the image forming apparatus; 
       FIG. 10  is a cross-sectional diagram showing a liquid receptacle of the image forming apparatus; 
       FIG. 11  is a flowchart showing a maintenance sequence that is carried out before image formation in the image forming apparatus; 
       FIG. 12  is a flowchart showing a maintenance sequence that is carried out after image formation in the image forming apparatus; 
       FIG. 13  is a flowchart showing the details of adjustment of a position of a free surface of the liquid; 
       FIGS. 14A to 14C  are side view diagrams showing the aspects of an upward-facing swinging motion of the liquid ejection head; 
       FIGS. 15A to 15C  are side view diagrams showing the aspects of a downward-facing swinging motion of the liquid ejection head; and 
       FIG. 16  is a schematic drawing used to describe slight vibration of the diaphragm. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Liquid Ejection Head 
     FIG. 1  is a plan diagram showing the general structure of a liquid ejection head according to an embodiment of the present invention, giving a perspective view of the left-hand half in the diagram. 
   The liquid ejection head  50   a  shown in  FIG. 1  is a so-called full line head, having a structure in which a plurality of liquid ejection ports or nozzles  51 , which eject liquid toward an ejection receiving medium or a recording medium  116 , are arranged through a length corresponding to a width Wm of the recording medium  116  in a main scanning direction indicated by arrow M in  FIG. 1  perpendicular to a sub-scanning direction indicated by arrow S in  FIG. 1 , which is a conveyance direction of the recording medium  116 . 
   More specifically, the liquid ejection head  50   a  has a composition in which a plurality of pressure chamber units  54 , each having the nozzle  51 , a pressure chamber  52  connected to the nozzle  51 , and an opening section serving as a liquid supply port  53  to supply the liquid to the pressure chamber  52 , are arranged two-dimensionally along two directions, namely, the main scanning direction, and an oblique direction forming a prescribed acute angle θ (where 0°&lt;θ&lt;90°) with respect to the main scanning direction. In  FIG. 1 , in order to simplify the drawing, some of the pressure chamber units  54  are omitted from the drawing. 
   More specifically, by arranging the nozzles  51  at a uniform pitch of d in the direction forming the acute angle of θ with respect to the main scanning direction, it is possible to treat the nozzles  51  as being equivalent to an arrangement of nozzles at a prescribed pitch (d×cos θ) in a straight line in the main scanning direction. According to this nozzle arrangement, for example, it is possible to achieve a composition substantially equivalent to a high-density nozzle arrangement reaching 4800 nozzles per inch in the main scanning direction. In other words, the effective nozzle pitch (projected nozzle pitch) obtained by projecting the nozzles to a straight line aligned with the lengthwise direction of the liquid ejection head  50   a  (the main scanning direction) can be reduced, and high image resolution can be achieved. 
   A common liquid chamber  55  (also called a “common flow channel”) supplying the liquid or ink to the pressure chambers  52  includes a main channel  551  and distributary channels  552  branching from the main channel  551 . An opening formed at an end of the main channel  551  serves as a liquid inlet port  553 , through which the ink is introduced into the common liquid chamber  55  from the outside of the liquid ejection head  50   a  (more specifically, from a sub-tank  61  described later with reference to  FIG. 7 ). The distributary channels  552  are connected to the pressure chambers  52  through the liquid supply ports  53  thereof. 
   In the present embodiment, the common liquid chamber  55  including the main channel  551  and the distributary channels  552  is formed by etching a metal plate (more specifically, a common liquid chamber forming plate  506  described later with reference to  FIG. 2 ), and the rigidity of the common liquid chamber  55  is ensured. 
     FIG. 2  shows a cross-sectional view along line  2 - 2  in  FIG. 1 . As shown in  FIG. 2 , the liquid ejection head  50   a  has a laminated structure of a plurality of plates including a nozzle forming plate  501 , a pressure chamber forming plate  502 , a diaphragm  503 , actuator protection plates  504  and  505 , the common liquid chamber forming plate  506 , and a sealing plate  507 . 
   The nozzles  51  ejecting the liquid are formed in a two-dimensional matrix fashion in the nozzle forming plate  501 . 
   The pressure chambers  52  connected to the nozzles  51  are formed in the pressure chamber forming plate  502  bonded on the nozzle forming plate  501 . 
   The diaphragm  503 , on which actuators  58  are arranged, is bonded on the pressure chamber forming plate  502 , and constitutes one face (a vibrating face) of each pressure chamber  52 . 
   Each actuator  58  has a laminated structure of the diaphragm  503 , a piezoelectric body  580  for generating pressure, and an individual electrode  57 , such that the piezoelectric body  580  is arranged between the diaphragm  503  and the individual electrode  57 . The piezoelectric body  580  is made of piezoelectric material such as PZT (lead zirconate titanate), and the diaphragm  503  and the individual electrode  57  are made of conductive material. 
   The actuators  58  are arranged on the diaphragm  503  at positions corresponding to the pressure chambers  52 , and each actuator  58  functions as a pressure generating device causing the pressure inside the pressure chamber  52  to change by changing the volume of the pressure chamber  52 . 
   The diaphragm  503  is grounded, and constitutes a common electrode for the actuators  58 . The other electrodes for the actuators  58  are the individual electrodes  57 , from which electrical wires (drive wires) for driving the actuators  58  extend. 
   The liquid supply ports  53  shown in  FIG. 1  are formed in the diaphragm  503 . 
   The actuator protection plates  504  and  505  are bonded on the diaphragm  503 , and protect the whole actuators  58  while preventing any obstruction of the operation of the actuators  58  by creating spaces  581  around the actuators  58 . 
   The common liquid chamber forming plate  506  is bonded on the actuator protection plate  505  on the side reverse to the side where the actuator protection plate  504 , the diaphragm  503 , and the pressure chamber forming plate  502  are arranged. The common liquid chamber  55  supplying the liquid to the pressure chambers  52  is formed in the common liquid chamber forming plate  506 . 
   The sealing plate  507  constituting a ceiling of the common liquid chamber  55  is arranged on the common liquid chamber forming plate  506 . The space between the actuator protection plate  505  and the sealing plate  507  constitutes the common liquid chamber  55 , in which the liquid or ink is filled. 
   When viewed with the nozzles  51  positioned below the pressure chambers  52 , the common liquid chamber  55  is arranged over the pressure chambers  52  and is connected to the pressure chambers  52  through liquid supply flow channels  531  extending from connecting ports  530 , which are opening sections formed in the base of the common liquid chamber  55 , passing through the actuator protection plates  504  and  505 , to the liquid supply ports  53  formed in the diaphragm  503 . In other words, the ink inside the common liquid chamber  55  flows directly to the pressure chambers  52  situated under the common liquid chamber  55  through the liquid supply flow channels  531 , and good refilling characteristics are hence achieved in the supply of ink to the pressure chambers  52 . Moreover, since the common liquid chamber  55  is disposed above the diaphragm  503 , then the length of nozzle flow channels  511  from the pressure chambers  52  to the nozzles  51  is short, and it becomes possible to eject ink of high viscosity (for example, approximately 20 cP to 50 cP). 
   There are no particular restrictions on arrangement of the drive wires for the actuators  58 . For example, it is possible to arrange the drive wires to pass through the common liquid chamber forming plate  506  in the vertical direction inside partitions defining the liquid chamber  55 . In this case, it is possible to arrange the pressure chambers  52  and the nozzles  51  at higher density compared with a case where the drive wires are arranged in the horizontal direction. It is also possible to arrange the drive wires on the actuator protection plate  505  in the horizontal direction. 
   When a drive signal is supplied to the individual electrode  57  of the actuator  58  through the drive wire, the piezoelectric body  580  of the actuator  58  is displaced, and the volume of the pressure chamber  52  is changed through the diaphragm  503 . Accordingly, the liquid in the pressure chamber  52  is ejected from the nozzle  51  connected to the pressure chamber  52 . 
     FIG. 3  is a plan diagram showing the general structure of a liquid ejection head  50   b  according to another embodiment of the present invention, giving a perspective view of the left-hand half in the diagram.  FIG. 4  shows a cross-sectional diagram along line  4 - 4  in  FIG. 3 . 
   In the liquid ejection head  50   b  shown in  FIGS. 3 and 4 , the constituent elements that are the same as elements of the liquid ejection head  50   a  shown in  FIGS. 1 and 2  are denoted with the same reference numerals, and description thereof is omitted here. 
   In the present embodiment, the common liquid chamber  55  is formed in the common liquid chamber forming plate  506  as a flow channel that occupies a single space covering all of the pressure chambers  52 , rather than having the structure composed of the main channel and the distributary channels. It is thereby possible to increase the size of the common liquid chamber  55  and to reduce the flow channel resistance inside the common liquid chamber  55 , and hence the present embodiment is suitable for the ejection of high-viscosity liquid. 
   In implementing the present invention, the arrangement structure of the nozzles  51 , and the like, is not limited in particular to the embodiment shown in  FIG. 1  or  3 . For example, it is also possible to compose a full line liquid ejection head by adopting a staggered arrangement of a plurality of short liquid ejection head blocks each comprising a plurality of nozzles  51  arranged two-dimensionally, thus achieving a long head by joining these liquid ejection head blocks together. 
   General Composition of Image Forming Apparatus 
     FIG. 5  is a schematic drawing showing a general view of an image forming apparatus  110  according to an embodiment of the present invention. The image forming apparatus  110  comprises a plurality of the liquid ejection heads  50   a  shown in  FIGS. 1 and 2 , or the liquid ejection heads  50   b  shown in  FIGS. 3 and 4 , and these heads are denoted in  FIG. 5  with reference numerals “ 112 ” appended with letters indicating the colors of ink ejected (K: black, C: cyan, M: magenta, and Y: yellow). 
   More specifically, the image forming apparatus  110  comprises: a liquid ejection unit  112  having the liquid ejection heads  112 K,  112 C,  112 M and  112 Y for respective ink colors; an ink storing and loading unit  114 , which stores the inks to be supplied to the liquid ejection heads  112 K,  112 C,  112 M and  112 Y; a paper supply unit  118 , which supplies a recording medium  116 , such as paper; a decurling unit  120 , which removes curl in the recording medium  116 ; a belt conveyance unit  122 , which is disposed facing the nozzle face of the liquid ejection unit  112  and conveys the recording medium  116  while keeping the recording medium  116  flat; a print determination unit  124 , which reads the ejection result (liquid droplet deposition state) produced by the liquid ejection unit  112 ; and a paper output unit  126 , which outputs printed recording medium to the exterior. 
   By depositing liquids (inks) containing coloring agents (also referred to as coloring material) on the recording medium  116  from the liquid ejection heads  112 K,  112 C,  112 M and  112 Y, an image is formed on the recording medium  116 . 
   The ink contains an insoluble or slightly water-soluble coloring material dispersed in water, and examples of the coloring material include, for instance, a dispersive dye, a metal complex dye, a pigment, or the like. Examples of dispersing agents for the coloring material in the ink dispersion, it is possible to use a so-called dispersant, surfactant, a resin, or the like. Examples of the dispersant or surfactant include anionic or nonionic materials, and examples of the resin dispersant include styrene or derivatives, vinylnaphthalene or derivatives, acrylic acid or derivatives, and the like. Desirably, the resin dispersant is alkali-soluble resin, which can be dissolved in an aqueous solution containing a basic material. The pigment may be an organic pigment or an inorganic pigment, but it is not limited to these. Pigment-based inks have excellent resistance to light and water; however, they tend to sediment more readily than dye-based inks. 
   In  FIG. 5 , a supply of rolled paper (continuous paper) is displayed as one embodiment of the paper supply unit  118 , but it is also possible to use a supply unit which supplies cut paper that has been cut previously into sheets. In a case where rolled paper is used, a cutter  128  is provided. The recording medium  116  delivered from the paper supply unit  118  generally retains curl. In order to remove this curl, heat is applied to the recording medium  116  in the decurling unit  120  by a heating drum  130  in the direction opposite to the direction of the curl. After decurling in the decurling unit  24 , the cut recording medium  116  is delivered to the belt conveyance unit  122 . 
   The belt conveyance unit  122  has a configuration in which an endless belt  133  is set around rollers  131  and  132  so that the portion of the endless belt  33  facing at least the nozzle face of the liquid ejection unit  112  and the sensor face of the ejection determination unit  124  forms a horizontal plane. The belt  133  has a width that is greater than the width of the recording medium  116 , and a plurality of suction apertures are formed on the belt surface. A suction chamber  134  is disposed in a position facing the sensor surface of the ejection determination unit  124  and the nozzle surface of the liquid ejection unit  112  on the interior side of the belt  133 , which is set around the rollers  131  and  132 , as shown in  FIG. 5 ; and this suction chamber  134  provides suction with a fan  135  to generate a negative pressure, thereby holding the recording medium  116  onto the belt  133  by suction. The belt  133  is driven in the clockwise direction in  FIG. 5  by the motive force of a motor (not shown) being transmitted to at least one of the rollers  131  and  132 , which the belt  133  is set around, and the recording medium  116  held on the belt  133  is conveyed from left to right in  FIG. 5 . Since ink adheres to the belt  133  when a marginless print or the like is formed, a belt cleaning unit  136  is disposed in a predetermined position on the exterior side of the belt  133 . A heating fan  140  is provided on the upstream side of the liquid ejection unit  112  in the paper conveyance path formed by the belt conveyance unit  122 . This heating fan  140  blows heated air onto the recording medium  116  before printing, and thereby heats up the recording medium  116 . Heating the recording medium  116  immediately before printing has the effect of making the ink dry more readily after landing on the paper. 
     FIG. 6  is a principal plan diagram showing the liquid ejection unit  112  of the image forming apparatus  110 , and the peripheral region of the liquid ejection unit  112 . 
   In  FIG. 6 , the liquid ejection heads  112 K,  112 C,  112 M and  112 Y constituting the liquid ejection unit  112  are arranged following a direction perpendicular to the medium conveyance direction (sub-scanning direction) (in other words, they are arranged in the main scanning direction), and they are full line heads having the nozzles (ejection ports) arranged through a length exceeding at least one edge of the maximum-size recording medium  116  that can be used in the image forming apparatus  110 . 
   The liquid ejection heads  112 K,  112 C,  112 M and  112 Y corresponding to the respective ink colors are disposed in the order, black (K), cyan (C), magenta (M) and yellow (Y), from the upstream side (left-hand side in  FIG. 6 ), following the direction of conveyance of the recording medium  116  (the sub-scanning direction). A color image can be formed on the recording medium  116  by ejecting the inks including coloring material from the print heads  112 K,  112 C,  112 M and  112 Y, respectively, toward the recording medium  116  while conveying the recording medium  116 . 
   The liquid ejection unit  112 , in which the full-line heads are thus provided for the respective ink colors, can record an image over the entire surface of the recording medium  116  by moving the recording medium  116  and the liquid ejection unit  112  relatively to each other in the medium conveyance direction (sub-scanning direction) just once (in other words, by means of a single sub-scanning action). Higher-speed printing is thereby made possible and productivity can be improved in comparison with a shuttle type head which moves reciprocally back and forth in the main scanning direction. 
   The terms “main scanning direction” and “sub-scanning direction” are used in the following senses. In a full-line head comprising rows of nozzles that have a length corresponding to the entire width of the recording medium, “main scanning” is defined as printing one line (a line formed of a row of dots, or a line formed of a plurality of rows of dots) in the breadthways direction of the recording medium (the direction perpendicular to the conveyance direction of the recording medium) by driving the nozzles in one of the following ways: (1) simultaneously driving all the nozzles; (2) sequentially driving the nozzles from one side toward the other; and (3) dividing the nozzles into blocks and sequentially driving the nozzle from one side toward the other in each of the blocks. The direction indicated by one line recorded by a main scanning action (the lengthwise direction of the band-shaped region thus recorded) is called the “main scanning direction”. 
   On the other hand, sub-scanning is defined as printing the line (a line constituted by a single dot array or a line constituted by a plurality of dot arrays) formed by the main scanning described above repeatedly by moving the full line head and recording medium relative to each other as described above. The direction in which this sub-scanning is performed is known as the sub-scanning direction. Consequently, the recording medium conveyance direction is the sub-scanning direction, and the direction perpendicular to the sub-scanning direction is the main scanning direction. 
   Although a configuration with the four standard colors, K, C, M and Y, is described in the present embodiment, the combinations of the ink colors and the number of colors are not limited to those of the present embodiment, and light and/or dark inks can be added as required. For example, a configuration is possible in which liquid ejection heads for ejecting light-colored inks such as light cyan and light magenta are added. 
   As shown in  FIG. 5 , the ink storing and loading unit  114  has ink tanks for storing the inks of the colors corresponding to the liquid ejection heads  112 K,  112 C,  112 M and  112 Y, and the ink tanks are connected to the liquid ejection heads  112 K,  112 C,  112 M and  112 Y through channels (not shown). 
   The ejection determination unit  124  has an image sensor (line sensor, or the like) for capturing an image of the ejection result of the liquid ejection unit  112 , and functions as a device to check for ejection defects such as blockages of the nozzles in the liquid ejection unit  12  on the basis of the image read in by the image sensor. 
   A post-drying unit  142  is provided at a downstream stage from the ejection determination unit  124 . The post-drying unit  142  is a device for drying the printed image surface, and it may comprise a heating fan, for example. A heating and pressurizing unit  144  is provided at a stage following the post-drying unit  142 . The heating and pressurizing unit  144  is a device which serves to control the luster of the image surface, and it applies pressure and heat to the image surface by means of pressure rollers  145  having prescribed surface undulations. Accordingly, an undulating form is transferred to the image surface. 
   The printed object generated in this manner is output via the paper output unit  126 . In the image forming apparatus  110 , a sorting device (not shown) is provided for switching the outputting pathway in order to sort the printed matter with the target print and the printed matter with the test print, and to send them to output units  126 A and  126 B, respectively. If the main image and the test print are formed simultaneously in a parallel fashion, on a large piece of printing paper, then the portion corresponding to the test print is cut off by means of the cutter (second cutter)  140 . The cutter  140  is disposed immediately in front of the paper output section  126 , and serves to cut and separate the main image from the test print portion, in cases where a test image is printed onto the white margin of the image. Moreover, although omitted from the drawing, a sorter for collating and stacking the images according to job orders is provided in the paper output section  126 A corresponding to the main images. 
     FIG. 7  is a schematic diagram showing the composition of a liquid supply system in the image forming apparatus  110 . In  FIG. 7 , the reference numeral  50  denotes the liquid ejection head. 
   The main tank  60  is a source of the liquid to be supplied to the liquid ejection head  50 , and corresponds to the ink storing and loading unit  114  in  FIG. 5 . The liquid in of the main tank  60  is supplied to the sub-tank  61  by means of a liquid supply pump  62 . The internal pressure of the liquid ejection head  50  is adjusted to a negative pressure, by means of the positional relationship between the free surface of the liquid in the sub-tank  61  and the nozzle surface  510  of the liquid ejection head  50 . A liquid supply channel  615  linking the sub-tank  61  with the liquid ejection head  50  passes along a turning axis  40  of the liquid ejection head  50  and is connected to the common liquid chamber  55  in the liquid ejection head  50  (and more specifically, to the liquid inlet port  553  shown in  FIGS. 1 and 3 ). 
   A liquid receptacle  64  is formed in a recessed shape, and receives liquid ejected by dummy ejection from the nozzles  51  of the liquid ejection head  50  in a state where the liquid receptacle  64  is in tight contact with the nozzle surface  510  of the liquid ejection head  50  or opposes the nozzle surface  510  of the liquid ejection head  50 . When a liquid suction pump  67  is driven in the state where the liquid receptacle  64  is in tight contact with the nozzle surface  510  of the liquid ejection head  50 , the liquid inside the liquid ejection head  50  is suctioned from the nozzles  51  of the liquid ejection head  50 , toward the liquid receptacle  64 . The liquid received in the liquid receptacle  64  due to the dummy ejection and the suctioning is sent to a collection tank  68  via the liquid suction pump  67 . 
     FIG. 8  is a block diagram showing the functional composition of the image forming apparatus  110 . As shown in  FIG. 8 , the image forming apparatus  110  comprises: the liquid ejection unit  112 , a communication interface  210 , a system controller  212 , memories  214  and  252 , a conveyance unit  220 , a head turning unit  242 , a head vertical movement unit  244 , an actuator drive unit  246 , a liquid flow unit  248 , a head controller  250 , and a liquid receptacle movement unit  264 . 
   The liquid ejection unit  112  is constituted by the plurality of liquid ejection heads  50 , which respectively eject inks of the colors of black (K), cyan (C), magenta (M) and yellow (Y). 
   The communication interface  210  is an image data input device for receiving image data transmitted by a host computer  300 . For the communication interface  210 , a wired or wireless interface, such as a USB (Universal Serial Bus), IEEE 1394, or the like, can be used. The image data acquired by the image forming apparatus  110  via the communication interface  210  is stored temporarily in a first memory  214  for storing image data. 
   The system controller  212  is constituted by a microcomputer and peripheral circuits thereof, and the like, and it forms a main control device which controls the whole of the image forming apparatus  110  in accordance with a prescribed program. More specifically, the system controller  212  controls units of the communication interface  210 , the conveyance unit  220 , the head controller  250 , and the like. 
   The conveyance unit  220  comprises a conveyance motor and driver circuit for same, and it conveys the recording medium  116  by using the rollers  131  and  132  and the belt  133  shown in  FIG. 5 . In other words, by means of the conveyance unit  220 , the liquid ejection heads  50  and the recording medium  116  move relatively to each other. 
   The head turning unit  242  serves to turn the liquid ejection head  50  about its axis of turning. The mechanism (turning mechanism) of the head turning unit  242  is described in detail later. 
   The head vertical movement unit  244  moves the liquid ejection head  50  in a direction perpendicular to the conveyance surface of the recording medium  116 . The mechanism (vertical movement mechanism) of the head vertical movement unit  244  is described in detail later. 
   The actuator drive unit  246  supplies drive signals to the actuators  48  of the liquid ejection head  50 . 
   The liquid flow unit  248  is constituted by the main tank  60 , the sub-tank  61 , the liquid supply pump  62 , the liquid suction pump  67 , the collection tank  68 , the channel for guiding the ink from the main tank  60  to the liquid ejection head  50 , and the channel for guiding the ink from the liquid receptacle  64  to the collection tank  68 , which are described above with reference to  FIG. 7 . 
   The liquid receptacle movement unit  264  moves the liquid receptacle  64  in the medium conveyance direction (the sub-scanning direction). The mechanism of the liquid receptacle movement unit  264  is described in detail later. 
   The head controller  250  is constituted by a microcomputer and peripheral circuits thereof, and the like, and it forms a control device which controls the liquid ejection heads  50  and peripheral units in accordance with a prescribed program. 
   The head controller  250  generates data (dot data), which is required when forming dots on a recording medium  116  by ejecting liquid toward the recording medium  116  from the liquid ejection heads  50  on the basis of the image data input to the image forming apparatus  110 . More specifically, the head controller  250  is a control unit that functions as an image processing device carrying out various image treatment processes, corrections, and the like, in order to generate dot data from the image data stored in the first memory  214 , in accordance with the control of the system controller  212 , and the head controller  250  supplies the dot data thus generated to the actuator drive unit  246 . When the dot data is supplied to the actuator drive unit  246 , drive signals are output to the actuators  58  of the liquid ejection heads  50  from the actuator drive unit  246  according to the dot data, and liquid is ejected from the nozzles  51  of the liquid ejection heads  50  toward the recording medium  116 . 
   Furthermore, the head controller  250  carries out various maintenance operations in order to maintain the state of the liquid inside the liquid ejection heads  50 . More specifically, the head controller  250  implements operations for: turning the liquid ejection heads  50  by means of the head turning unit  242 , vertically moving the liquid ejection heads  50  by means of the head vertical movement unit  244 , causing slight vibration of the diaphragms  503  of the liquid ejection heads  50  by means of the actuator drive unit  246 , performing dummy ejection (purging) from the nozzles  51  of the liquid ejection heads  50  by using the actuator drive unit  246  and the liquid flow unit  248 , suctioning the liquid inside the liquid ejection heads  50  by using the liquid flow unit  248 , and sealing the nozzles  51  of the liquid ejection heads  50  by using the head vertical movement unit  244 . The details of these maintenance operations are described further later. 
   In  FIG. 8 , the second memory  252  is depicted as being appended to the head controller  250 ; however, it can be combined with the first memory  214 . Also possible is a mode in which the head controller  250  and the system controller  212  are integrated to form a single micro-processor. 
   Maintenance Mechanism 
   The agitation of the liquid in the liquid ejection head  50  is performed by, firstly, swinging the liquid ejection head  50 , and, secondly, slightly vibrating the liquid inside the liquid ejection head  50  by means of the actuators  58  of the liquid ejection head  50 . 
   Hereinafter, the turning mechanism and the vertical movement mechanism used in the swinging of the liquid ejection head  50 , and peripheral parts to the liquid ejection head  50 , such as the liquid receptacle  64 , are described in detail. 
     FIG. 9  is an oblique diagram showing the liquid ejection head  50  and the peripheral area of same. 
   In  FIG. 9 , the liquid ejection head  50  is tunable on the turning axis  40  of the liquid ejection head  50  as denoted by a double-headed arrow T, and the liquid ejection head  50  is also vertically movable in the direction perpendicular to the conveyance surface  16  for the recording medium  116 , as denoted by a double-headed arrow V. 
   The turning axis  40  is attached to the liquid ejection head  50  in the longitudinal direction of the liquid ejection head  50 . In other words, the turning axis  40  forming the center of turning of the liquid ejection head  50  is disposed in a plane parallel with the conveyance surface  16  for the recording medium  116 , following the main scanning direction, which is perpendicular to the medium conveyance direction denoted by an arrow S in  FIG. 9 . 
   The turning axis  40  of the liquid ejection head  50  is rotatably held by brackets  41  having ball bearings. In other words, the liquid ejection head  50  is rotatably held by the brackets  41  through the turning axis  40 . A ball screw  42  and a guide shaft  43  arranged in a direction perpendicular to the conveyance surface  16  are installed on each bracket  41 . In other words, the liquid ejection head  50  is supported movably in the vertical direction by means of the brackets  41 . First motors  46  function as vertical movement drive units which move the liquid ejection head  50  by a prescribed distance in the direction perpendicular to the conveyance surface  16 , by rotating the ball screws  42 , which are connected respectively to the shafts of the first motors  46  through couplings (not shown). 
   In other words, the vertical movement mechanism vertically moving the liquid ejection head  50  is constituted by the brackets  41 , the ball screws  42 , the guide shafts  43  and the first motors  46 . 
   A first gear wheel  44  is attached to the turning axis  40  of the liquid ejection head  50 , and a second gear wheel  45  engages with the first gear wheel  44  and transmits the turning movement of the shaft of a second motor  47  to the first gear wheel  44  at a prescribed gear ratio. The second motor  47  functions as the turning drive unit, which turns the liquid ejection head  50  by a prescribed amount of turning, by rotating the two gear wheels  44  and  45  at the prescribed gear ratio. 
   In other words, the turning mechanism turning the liquid ejection head  50  is constituted by the brackets  41 , the two gear wheels  44  and  45 , and the second motor  47 . 
   In the vertical movement mechanism described above, when the ball screws  42  are rotated by the first motors  46 , then the brackets  41  move by a prescribed distance in the direction perpendicular to the conveyance surface  16 , while being guided by the guide shafts  43 , and consequently, the liquid ejection head  50  also moves in the direction perpendicular to the conveyance surface  16 , in conjunction with these brackets  41 . 
   In the turning mechanism described above, when the first gear wheel  44  attached to the turning axis  40  of the liquid ejection head  50  and the second gear wheel  45  coupled to the shaft of the second motor  47  are in an engaged state, and the two gear wheels  44  and  45  are rotated by driving the second motor  47 , then the liquid ejection head  50  turns on the turning axis  40  of the liquid ejection head  50 . In other words, the liquid ejection head  50  turns in a plane perpendicular to the conveyance surface  16 , while the turning axis  40  is in the plane parallel to the conveyance surface  16  for the recording medium  116 . 
   The turning mechanism is able to turn the liquid ejection head  50  by a prescribed, limited angle (for example, 45° or 90°). 
   The modes of controlling the amount of movement of the liquid ejection head  50  in the vertical direction and the amount of turning movement of the liquid ejection head  50  include a mode in which the movements are controlled on the basis of the number of pulses of the drive signals supplied to the motors  46  and  47 , a mode in which sensors are provided and the movements are performed and halted by monitoring with the sensors, and a mode in which the positions are controlled by means of encoders. 
   A cap  63  is disposed at the end of the range of vertical movement of the liquid ejection head  50 , on the opposite side to the conveyance surface  16 , and the cap  63  seals the nozzles  51  of the liquid ejection head  50  when the nozzles  51  of the liquid ejection head  50  are facing vertically upward. 
   In other words, by turning the liquid ejection head  50  through a half turn by means of the turning mechanism when the nozzles  51  of the liquid ejection head  50  are facing downward, the nozzles  51  of the liquid ejection head  50  are set to an upward facing state (in other words, a state where the nozzle surface  510  opposes the cap  63 ), whereupon the nozzles  51  are sealed by pressing the liquid ejection head  50  against the cap  63  by means of the vertical movement mechanism. By turning the liquid ejection head  50  through the half turn and sealing the nozzles  51  by means of the cap  63  in this way, it is possible to prevent the micro-particles dispersed in the liquid inside the liquid ejection head  50  from aggregating and settling in the nozzles  51 , as well as preventing evaporation of the liquid from the nozzles  51 . 
   The liquid receptacle  64  is provided movably in parallel with the conveyance surface  16 , in the medium conveyance direction S. More specifically, during suctioning or dummy ejection, after separating the nozzle surface  510  of the liquid ejection head  50  from the conveyance surface  16  by means of the vertical movement mechanism, the liquid receptacle  64  is moved in parallel with the conveyance surface  16 , in the medium conveyance direction S, and is inserted in between the liquid ejection head  50  and the conveyance surface  16 . In other words, by means of the parallel movement of the liquid receptacle  64 , the liquid ejection head  50  is moved relatively in parallel to a position opposing the liquid receptacle  64 . In the case of suctioning, the liquid ejection head  50  is then moved downward in the vertical direction by the vertical movement mechanism, and thereby the liquid ejection head  50  is engaged with the liquid receptacle  64 , whereupon suctioning is carried out using the liquid receptacle  64 . In the case of dummy ejection, there are a mode in which the liquid ejection head  50  is moved downward in the vertical direction, and a mode in which the liquid ejection head  50  is not moved. 
   The liquid receptacle  64  has a wiper  66  movable in the direction perpendicular to the medium conveyance direction S (namely, in the main scanning direction) in such a manner that the wiper  66  wipes over the nozzle surface  510  of the liquid ejection head  50 . 
     FIG. 10  is a cross-sectional diagram of the liquid receptacle  64  taken along the medium conveyance direction S. As shown in  FIG. 10 , the liquid receptacle  64  has rollers  642 , which are provided on the adjacent side to the conveyance surface  16  and make point contacts with the recording medium  116 , so as to prevent the recording medium  116  from floating up from the conveyance surface  16 . On the upstream side of these rollers  642  in terms of the medium conveyance direction S, a slant  644  is provided for guiding the recording medium  116  in between the liquid receptacle  64  and the conveyance surface  16 . Thereby, it is possible to convey the recording medium  116  stably. 
   In the present embodiment, since the liquid ejection head  50  can be separated from the conveyance surface  16  for the recording medium  116  in the vertical direction by means of the ball screws  42 , then by retracting the liquid ejection head  50  by means of the ball screws  42  prior to turning the liquid ejection head  50 , it is possible to avoid contact between the liquid ejection head  50  and the conveyance surface  16 , even if there is little clearance between the conveyance surface  16  and the nozzle surface  510  of the liquid ejection head  50 . Moreover, since the ball screws  42  are used, then it is possible accurately to maintain a uniform distance between the nozzle surface  510  of the liquid ejection head  50  and the recording medium  116 , and furthermore, it is also possible to adjust the pressing force when the liquid ejection head  50  is pressed against the cap  63 . 
   It is also possible to use a link or a cam, instead of the ball screws  42 , in order to achieve vertical movement of the liquid ejection head  50 . 
   Maintenance Operation 
     FIG. 11  is a flowchart showing an embodiment of a maintenance sequence that is carried out prior to image formation. 
   Before carrying out the maintenance sequence in  FIG. 11 , the image forming apparatus  110  is in a power off state or a standby state awaiting a print instruction, the nozzles  51  of the liquid ejection head  50  are orientated vertically upward and sealed with the cap  63  for preventing drying, and the liquid receptacle  64  is arranged between the liquid ejection head  50  and the conveyance surface  16 . In this state, when the power of the image forming apparatus  110  is switched on and a print instruction is input to the image forming apparatus  110 , then the maintenance sequence shown in  FIG. 11  starts. 
   Firstly, the liquid ejection head  50  is separated from the cap  63  by moving the liquid ejection head  50  vertically downward (S 2 ). 
   Then, the positions of the free surfaces of the liquid in the nozzles  51  of the liquid ejection head  50  are adjusted in accordance with the vertical movement distance of the liquid ejection head  50  (S 4 ). If there is no change in the positions of the free surfaces of the liquid in the nozzles  51  due to the vertical movement of the liquid ejection head  50 , then this adjustment is not necessary. The adjustment of the positions of the free surfaces of the liquid in the nozzles  51  is described in detail hereinafter. 
   Next, a slight vibration of the diaphragm  503  is started by driving the actuators  58  of the liquid ejection head  50  (S 6 ), and the liquid ejection head  50  is turned by the turning mechanism on the turning axis  40  of the liquid ejection head  50  in the plane perpendicular to the conveyance surface  16 , symmetrically on either side of the upward direction perpendicular to the conveyance surface  16  within a prescribed angular range, thereby causing the liquid ejection head  50  to perform a swinging motion (S 8 ). 
   The swinging motion of the liquid ejection head  50  is described below in further detail with reference to  FIGS. 14A to 14C . When the liquid ejection head  50  is turned through 45° in the counter-clockwise direction from a state shown in  FIG. 14A  where the normal to the nozzle surface  510  of the liquid ejection head  50  is orientated in the upward vertical direction, then as shown in  FIG. 14B , the normal to the nozzle surface  510  becomes inclined at −45° with respect to the upward vertical direction. The direction of turning is reversed in this state, and the liquid ejection head  50  is turned through 90° in the clockwise direction, then as shown in  FIG. 14C , the normal to the nozzle surface  510  of the liquid ejection head  50  becomes inclined at 45° with respect to the upward vertical direction. The direction of turning is reversed again in this state, and the liquid ejection head  50  is turned through 45° in the counter-clockwise direction, then the liquid ejection head  50  returns to the state shown in  FIG. 14A . This sequence of turning operations is repeated a prescribed number of times. In other words, the swinging motion is performed by turning the liquid ejection head  50  to a maximum angle of inclination θg (here, 45°) shown in  FIG. 14A  by observing the normal to the nozzle surface  510 . 
   The maximum angle of inclination θg of the nozzle surface  510  of the liquid ejection head  50  with respect to the direction perpendicular to the conveyance surface  16  is 45° in the above-described case, but the maximum angle of inclination θg is not limited to 45° and may be less than 45°. 
   The slight vibration of the diaphragm  503  is carried out under a condition (condition A) where the actuators  58  of the liquid ejection head  50  are applied with the drive voltage that does not cause the liquid to be ejected from the nozzles  51  when the nozzles  51  are in the upward orientated state or the obliquely upward orientated state during the swinging of the liquid ejection head  50  and that has drive frequencies of the slight vibration changing with time from a prescribed low frequency to a prescribed high frequency. In other words, the drive waveform that does not cause the liquid to be ejected from the nozzles  51  at the maximum angle of inclination θg in the swinging motion is applied to the actuators  58 , and furthermore, the frequency of the drive waveform (drive frequency) is swept through the prescribed range. By performing the slight vibration of the diaphragm  503  in this way, sediment  92  on the diaphragm  503  shown in  FIG. 16  is broken up, and furthermore, the micro-particles in a high-density region  93  in the vicinity of the diaphragm  503  are redispersed. 
   After performing the swinging motion of the liquid ejection head  50  a prescribed number of times, the slight vibration of the diaphragm  503  is halted (S 10 ). 
   Thereupon, the liquid ejection head  50  is turned through half a turn by the turning mechanism and set in such a manner that the nozzles  51  are facing vertically downward (S 12 ), whereupon a slight vibration of the diaphragm  503  is started by driving the actuators  58  of the liquid ejection head  50  (S 14 ), and the liquid ejection head  50  is turned by the turning mechanism on the turning axis  40  of the liquid ejection head  50  in the plane perpendicular to the conveyance surface  16 , symmetrically on either side of the downward direction perpendicular to the conveyance surface  16  within a prescribed angular range, thereby causing the liquid ejection head  50  to perform a swinging motion (S 16 ). 
   The swinging motion of the liquid ejection head  50  is described below in further detail with reference to  FIGS. 15A to 15C . When the liquid ejection head  50  is turned through 45° in the counter-clockwise direction from a state shown in  FIG. 15A  where the normal to the nozzle surface  510  of the liquid ejection head  50  is orientated in the downward vertical direction, then as shown in  FIG. 15B , the normal to the nozzle surface  510  becomes inclined at −45° with respect to the upward vertical direction. The direction of turning is reversed in this state, and the liquid ejection head  50  is turned through 90° in the clockwise direction, then as shown in  FIG. 15C , the normal to the nozzle surface  510  of the liquid ejection head  50  becomes inclined at 45° with respect to the downward vertical direction. The direction of turning is reversed again in this state, and the liquid ejection head  50  is turned through 45° in the counter-clockwise direction, then the liquid ejection head  50  returns to the state shown in  FIG. 15A . This sequence of turning operations is repeated a prescribed number of times. In other words, the swinging motion is performed by turning the liquid ejection head  50  to a maximum angle of inclination θg (here, 45°) shown in  FIG. 15A  by observing the normal to the nozzle surface  510 . 
   The slight vibration of the diaphragm  503  is carried out under a condition (condition B) where the actuators  58  of the liquid ejection head  50  are applied with the drive voltage that does not cause the liquid to be ejected from the nozzles  51  when the nozzles  51  are in the downward orientated state or the obliquely downward orientated state during the swinging of the liquid ejection head  50  and that has a constant drive frequency of the slight vibration. In other words, by means of the falling motion of the micro-particles due to gravity, and the slight vibration applied, the liquid is agitated and the micro-particles become further redispersed in the liquid. 
   After performing the swinging motion of the liquid ejection head  50  a prescribed number of times, the slight vibration of the diaphragm  503  is halted (S 18 ). 
   Thereupon, the liquid ejection head  50  is moved vertically downward toward the liquid receptacle  64  by means of the vertical movement mechanism, and the liquid ejection head  50  is placed in tight contact with the liquid receptacle  64  (S 22 ). 
   The positions of the free surfaces of the liquid in the nozzles  51  of the liquid ejection head  50  are adjusted in accordance with the vertical movement distance of the liquid ejection head  50  (S 4 ). If there is no change in the positions of the free surfaces of the liquid in the nozzles  51  due to the vertical movement of the liquid ejection head  50 , then this adjustment is not necessary. 
   In the state in which the nozzles  51  of the liquid ejection head  50  are facing downward and the liquid ejection head  50  is tightly in contact with the liquid receptacle  64 , suctioning by means of the liquid suction pump  67  (S 26 ), purging by driving the actuators  58  of the liquid ejection head  50  (S 28 ), and wiping of the nozzle surface  50  using the wiper  66  (S 30 ) are carried out, and it is then judged whether this sequence of maintenance operations (S 26 , S 28 , S 30 ) has been completed a prescribed number of times (S 32 ). 
   After carrying out the sequence of maintenance operations (S 26 , S 28 , S 30 ) the prescribed number of times, the liquid receptacle  64  is retracted (S 34 ), and the liquid ejection head  50  is moved vertically by means of the vertical movement mechanism, in such a manner that a prescribed clearance is formed between the nozzle surface  510  of the liquid ejection head  50  and the conveyance surface  16  (S 36 ). 
   After completing the above-described operations (S 2  to S 36 ), the recording medium  116  is conveyed, and an image is formed on the recording medium  116  by ejecting ink toward the recording medium  116  from the nozzles  51  of the liquid ejection head  50 , on the basis of image data. 
     FIG. 12  is a flowchart showing an embodiment of a maintenance sequence that is carried out after the image formation. 
   Prior to the maintenance sequence shown in  FIG. 12 , in the image forming apparatus  110 , the nozzles  51  of the liquid ejection head  50  are positioned facing vertically downward, and the liquid receptacle  64  is set in the retracted position. 
   Firstly, the liquid ejection head  50  is separated from the conveyance surface  16  by moving the liquid ejection head  50  vertically upward by means of the vertical movement mechanism (S 52 ). 
   Then, the positions of the free surfaces of the liquid in the nozzles  51  of the liquid ejection head  50  are adjusted in accordance with the vertical movement distance of the liquid ejection head  50  (S 54 ). If there is no change in the positions of the free surfaces of the liquid in the nozzles  51  due to the vertical movement of the liquid ejection head  50 , then this adjustment is not necessary. The adjustment of the positions of the free surfaces of the liquid in the nozzles  51  is described in detail hereinafter. 
   Thereupon, the liquid receptacle  64  is introduced between the liquid ejection head  50  and the conveyance surface  16  (S 56 ), and the nozzle surface  510  of the liquid ejection head  50  is wiped by means of the wiper  66  (S 58 ). 
   Then, the liquid ejection head  50  is turned through a half turn by the turning mechanism, thereby setting the nozzles  51  to face in the upward vertical direction, and the liquid ejection head  50  is then moved vertically upward by the vertical movement mechanism (S 62 ). 
   The positions of the free surfaces of the liquid in the nozzles  51  of the liquid ejection head  50  are then adjusted in accordance with the vertical movement distance of the liquid ejection head  50  (S 64 ). More specifically, the adjustment is performed so that the free surface  91  of the liquid is positioned inside the nozzle  51  as shown in  FIG. 16 . If there is no change in the positions of the free surfaces of the liquid in the nozzles  51  due to the vertical movement of the liquid ejection head  50 , then this adjustment is not necessary. 
   Thereupon, the liquid ejection head  50  is pressed against the cap  63  by means of the vertical movement mechanism, and the nozzles  51  of the liquid ejection head  50  are sealed by the cap  63  (S 66 ). 
   In this way, the nozzle surface  510  of the liquid ejection head  50  is set to face upward and is sealed by the cap  63 . Hence, even if aggregation and settling of the micro-particles in the liquid occur, it merely results in the sediment  92  settling on the diaphragm  503  and/or the high-density region  93  arising in the vicinity of the diaphragm  503 , as shown in  FIG. 16 . Consequently, it is possible to prevent blockage of the nozzle  51 , which is liable to occur in the related art due to the sediment settling toward the free surface  91  of the liquid in the nozzle  51 . 
     FIG. 13  is a flowchart showing the details of the position adjustment operation for the free surfaces of the liquid in the nozzles  51  using the vertical movement of the liquid ejection head  50  (steps S 4  and S 24  in  FIG. 11 , and steps S 54  and S 64  in  FIG. 12 ). 
   The position of the free surface of the liquid (the liquid-atmosphere interface, which is also commonly called “meniscus”) in the liquid ejection head  50  is governed by the internal pressure of the liquid ejection head  50 . The internal pressure of the liquid ejection head  50  is adjusted by varying the height differential between the free surface of the liquid in the sub-tank  61  shown in  FIG. 7  and the nozzle surface  510  of the liquid ejection head  50 . In general, apart from during liquid ejection, the internal pressure of the liquid ejection head  50  is set to a pressure slightly lower than the atmospheric pressure (this lower pressure is commonly called the “negative pressure”). 
   In the composition where the liquid supply pump  62  is provided between the main tank  60  and the sub-tank  61  as shown in  FIG. 7 , desirably, the position of the free surface of the liquid is adjusted finely by using the liquid supply pump  62 . It is also possible to adjust the positions of the free surfaces of the liquid in the nozzles  51  by vertically moving the sub-tank  61 . 
   The positions of the free surfaces of the liquid in the nozzles  51  are adjusted by driving the liquid supply pump  62  (or vertically moving the sub-tank  61 ), only in cases where the positions of the free surfaces of the liquid in the nozzles  51  change due to the variation of the internal pressure caused by the change of the height differential between the nozzle surface  510  of the liquid ejection head  50  and the free surface of the liquid in the sub-tank  61  according to the distance of vertical movement of the liquid ejection head  50  (S 402 ). Time is measured by a timer (not shown), and it is judged whether or not a prescribed time period has elapsed (S 404 ). If the prescribed time period has elapsed, then the driving of the liquid supply pump  62  (or the vertical movement of the sub-tank  61 ) is halted. 
   The liquid maintenance operations described above with reference to  FIGS. 11 ,  12  and  13  are carried out under the control of the head controller  250  shown in  FIG. 8 , in accordance with a program. 
   The slight vibration of the diaphragm  503  is carried out during the swinging of the liquid ejection head  50  in the above-described embodiments, and moreover, during a long period without performing printing, it is also preferable to carry out the slight vibration of the diaphragm  503  on the basis of time management, under the condition (the condition A) where the drive frequency is swept through a range as described above, without implementing a swinging motion of the liquid ejection head  50  by driving turning, and while the liquid ejection head  50  remains sealed by the cap  63 . 
   The common liquid chamber  55  is situated on the opposite side of the actuators  58  from the pressure chambers  52  in the above-described embodiments as shown in  FIGS. 1 to 4 , but the present invention may also be applied to a composition where the common liquid chamber is situated on the same side of the actuators as the pressure chambers, as long as the direction of liquid ejection is a downward direction. 
   The liquid ejected from the liquid ejection head  50  is ink in the above-described embodiments, but the present invention may also be applied to a conductive liquid ejected toward a substrate when forming conductive wires on the substrate, or a liquid ejected toward an optical material during manufacture of a color filter, or the like. 
   It should be understood, however, that there is no intention to limit the invention to the specific forms disclosed, but on the contrary, the invention is to cover all modifications, alternate constructions and equivalents falling within the spirit and scope of the invention as expressed in the appended claims.