Patent Publication Number: US-2007120932-A1

Title: Droplet ejection apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
      This application is based upon and claims the benefit of priority from prior Japanese Patent Application Nos. 2005-344648 filed on Nov. 29, 2005, and 2006-256167 filed on Sep. 21, 2006, the entire contents of which are incorporated herein by reference.  
     BACKGROUND  
      The present invention relates to a droplet ejection apparatus.  
      Typically, a display such as a liquid crystal display or an electroluminescence display includes a substrate that displays an image. The substrate has an identification code (for example, a two-dimensional code) representing product information including the name of the manufacturer and the product number, for purposes of quality control and production control. The identification code is formed by a plurality of dots arranged in such a manner as to form a prescribed pattern. As a method for forming one such identification code, JP-A-11-77340 discloses a laser sputtering method and JP-A-2003-127537 discloses a waterjet method. In the laser sputtering method, dots are formed by films provided through sputtering by radiating laser beams onto a metal foil. In the waterjet method, dots are marked on a substrate by ejecting water containing abrasive onto the substrate.  
      However, in the laser sputtering method, the interval between the metal foil and the substrate must be adjusted to several or several tens of micrometers in order to form each dot in a desired size. Thus, the substrate and the metal foil thus must have extremely flat surfaces and adjustment of the interval between the substrate and the metal foil must be carried out with accuracy on the order of micrometer. This limits application of the method to a restricted range of substrates, and use of the method is limited. In the waterjet method, the substrate may be contaminated by water, dust, and the abrasive that are splashed onto the substrate when the dots are marked on the substrate.  
      In order to solve these problems, an inkjet method has been focused on as an alternative method for forming the identification code. In the inkjet method, dots are formed on a substrate by ejecting droplets of liquid containing metal particles from an ejection head onto the substrate through nozzles. The droplets are then dried to mark the dots on the substrate. The method thus can be applied to a relatively wide range of substrates. Further, the method prevents contamination of the substrate caused by formation of the identification code.  
      In the inkjet method, the droplets quickly spread wet on the surface of the substrate in correspondence with the condition of the surface of the substrate or surface tension produced by the droplets after having been received by the substrate. Therefore, if the time necessary for drying the droplets exceeds a certain extent (for example, 100 milliseconds), the droplets excessively spread on the surface of the substrate and flow beyond the desired dot formation areas.  
      This problem is solved by radiating laser beams onto the droplets on the substrate, thus instantly solidifying the droplets. However, in this case, elements evaporated from the droplets may adhere to optical systems that radiate the laser beams, contaminating the optical systems. Therefore, a droplet ejection apparatus having a laser head that radiates laser beams must include a suction device that removes the evaporated elements. Specifically, the suction device draws and removes the floating evaporated elements from the vicinity of the laser head.  
      Generally, such techniques using a suction device for drawing floating evaporated elements from the vicinity of a droplet ejection head have been proposed. In this manner, excessive flowing of droplets is suppressed or mist generation in the vicinity of the droplet ejection head is avoided.  
      For example, as described in JP-A-2003-136689, a droplet ejection apparatus having a fan or a vacuum suction device has been proposed. After having been received by an ejection target, droplets are exposed to an air flow produced by the fan or the vacuum suction device, thus promoting drying of the droplets. Alternatively, as has been described in JP-A-2005-22194, a droplet ejection apparatus may include a suction device formed in a zone above a droplet ejection head. The suction device draws and removes volatile matter floating and remaining in the vicinity of the bottom surface of the droplet ejection head, together with the air. Further, JP-A-2003-145737 describes a droplet ejection apparatus that draws elements evaporated from the droplets through ultraviolet radiation. Such suction is performed at opposing sides of a printing sheet or a position downstream from an ultraviolet radiation area in a transport direction of the printing sheet.  
      The techniques described in JP-A-2003-136689 and JP-A-2005-22194 aim to prevent excessive spreading of droplets or mist generation. Therefore, the evaporated elements are removed from the vicinity of the droplets received by an ejection target or a droplet ejection head. However, the relationship between the flow path of the removed evaporated elements and the locations of the optical systems are not considered. Further, the apparatus described in JP-A-2003-145737 has optical systems including an electromagnetic radiant ray transmissible board and a reflective board. The electromagnetic radiant ray transmissible board guides ultraviolet rays from an ultraviolet lamp to the exterior. The reflective board reflects the ultraviolet rays and radiates the ultraviolet rays onto the droplets. Therefore, the technique is aimed to protect the optical systems. However, since the evaporated elements released at a position immediately below an electromagnetic radiation device are drawn from the opposing sides of the printing sheet or a at the position downstream from the radiation area, the evaporated elements that are not yet drawn pass immediately below the electromagnetic radiation device. Some of the elements thus adhere to and contaminate the optical systems.  
      Accordingly, the above-described typical droplet ejection apparatuses cannot prevent a droplet ejection head or optical systems that radiate laser beams from being contaminated by elements evaporated from droplets through laser radiation.  
     SUMMARY  
      Accordingly, it is an objective of the present invention to provide a droplet ejection apparatus that stabilizes optical characteristics of laser beams radiated onto droplets of liquid.  
      In accordance with a first aspect of the present invention, a droplet ejection apparatus including a droplet ejection head, a laser radiation device, and a suction device is provided. The droplet ejection head ejects a droplet of a liquid onto a target. The laser radiation device radiates a laser beam onto an area on the target opposed to the droplet ejection head. The suction device is arranged between the laser radiation device and a radiating position on the target at which the laser beam is radiated, and draws an element that has evaporated from the droplet.  
      In accordance with another aspect of the present invention, a droplet ejection apparatus including a head unit and a movement device is provided. The head unit includes a droplet ejection head, a laser radiation device, and a suction port. The droplet ejection head ejects a droplet of a liquid onto a target. The laser radiation device radiates a laser beam onto an area on the target opposed to the droplet ejection head. The suction port is arranged between the droplet ejection head and the laser radiation device, and draws an element that has evaporated from the droplet through radiation of the laser beam. The movement device moves the head unit above the target in such a manner that the droplet ejection head precedes the suction port and the suction port precedes the laser radiation device.  
      Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       FIG. 1  is a plan view showing a droplet ejection apparatus;  
       FIG. 1A  is an enlarged view showing the portion indicated by circle  1 A of  FIG. 1 ;  
       FIG. 2  is a perspective view schematically showing a droplet ejection apparatus according to one embodiment of the present invention;  
       FIG. 3  is a plan view schematically showing the droplet ejection apparatus of  FIG. 2 ;  
       FIG. 5  is a view showing a droplet ejection head;  
       FIG. 6  is a view for explaining a head unit; and  
       FIG. 7  is a block diagram representing the electric configuration of the droplet ejection apparatus. 
    
    
     DESCRIPTION OF EXEMPLARY EMBODIMENTS  
      A first embodiment of the present invention will now be described with reference to FIGS.  1  to  7 . A liquid crystal display  1  having an identification code  10  formed by a droplet ejection apparatus  20  of the present invention will first be explained.  
      As shown in  FIG. 1 , a rectangular display portion  3  in which liquid crystal molecules are sealed is formed substantially at the center of one side surface (a surface  2   a ) of a transparent substrate  2 . A scanning line driver circuit  4  and a data line driver circuit  5  are provided outside the display portion  3 . In correspondence with a scanning signal generated by the scanning line driver circuit  4  and a data signal produced by the data line driver circuit  5 , the liquid crystal display  1  adjusts orientation of the liquid crystal molecules in the display portion  3 . Area light emitted by a non-illustrated illumination device is modulated depending on the orientation of the liquid crystal molecules. Through such modulation, the liquid crystal display  1  displays a desired image on the display portion  3 .  
      A code area S, which is a square each side of which is approximately one millimeter, is formed in the left corner of the surface  2   a.  The code area S is virtually divided into a plurality of cells C that form a matrix of 16 rows by 16 columns. A plurality of dots D, each of which is a mark, are formed in selected ones of the data cells C and thus define the identification code  10  of the liquid crystal display  1 . In the first embodiment, the center of each of the data cells C in which the dots D are provided will be referred to as an “ejection target position P”. The length of each side of the data cell C will be referred to as the “cell width W”.  
      Each of the dots D is a mark and has a semispherical shape. The outer diameter of each dot D is equal to the length of each side of the data cell C (the “cell width W”). The outer diameter of each dot D is equal to the length of each side of each data cell C (the cell width W). Each dot D has a semispherical shape. A droplet Fb of liquid F (see  FIG. 5 ) containing metal particles (for example, nickel or manganese particles) dispersed in dispersion medium is ejected onto each of the data cells C and received by the data cell C. Each of the dots D is formed by drying and baking the droplet Fb that has been received by each data cell C. Drying and baking of the droplet Fb in the data cell C is achieved by radiating a laser beam B (see  FIG. 5 ) onto the droplet Fb.  
      The dots D formed in the selected data cells C are arranged in a certain pattern, in accordance of which the identification code  10  reproduces the product number and the lot number of the liquid crystal display  1 . In the first embodiment, throughout FIGS.  1  to  5 , the longitudinal direction of the transparent substrate  2  will be referred to as direction X and a direction perpendicular to direction X on a plane parallel with the substrate  2  will be referred to as direction Y. A direction perpendicular to directions X and Y will be referred to as direction Z. Particularly, the directions indicated by the arrows in the drawings will be referred to as direction +X, direction +Y, or direction +Z. The directions opposite to these directions will be referred to direction −X, direction −Y, or direction −Z.  
      Next, the droplet ejection apparatus  20  for forming the identification code  10  will be described with reference to  FIG. 2 . In the illustrated embodiment, the identification codes  10  are formed at separate positions in correspondence with the transparent substrates  2  on the mother substrate  2 M, which is a mother material of the multiple transparent substrates  2 . The mother substrate  2 M is a target onto which the droplets are ejected by the droplet ejection apparatus  20 .  
      As shown in  FIG. 2 , the droplet ejection apparatus  20  has a base  21 , which has a substantially parallelepiped shape. A substrate stocker  22 , which receives multiple mother substrates  2 M, is arranged at one side (in direction X) of the base  21 . The substrate stocker  22  moves in an up-and-down direction as viewed in  FIG. 2  (in direction +Z or direction−Z). This allows each of the mother substrates  2 M to be retrieved from the substrate stocker  22 , transported to the base  21 , and returned to a corresponding slot of the substrate stocker  22 .  
      A running device  23 , which extends in direction Y, is arranged on an upper surface  21   a  of the base  21  and at a position close to the substrate stocker  22 . A running motor MS (see  FIG. 7 ) is provided in the running device  23 . The running device  23  operates a transport device  24 , which is operably connected to the output shaft of the running motor MS, to run in direction Y. The transport device  24  is a horizontal articulated robot that has a transport arm  24   a.  The transport arm  24   a  draws and holds a backside  2 Mb of each mother substrate  2 M. A transport motor MT (see  FIG. 7 ) is arranged in the transport device  24 . The transport arm  24   a  is operably connected to the output shaft of the transport motor MT. The transport device  24  extends and contracts or pivots the transport arm  24   a  on the X-Y plane and raises or lowers the transport arm  24   a.    
      A pair of mounting tables  25 R,  25 L are formed on the upper surface  21   a  of the base  21  at opposing sides in direction Y. The corresponding one of the mother substrates  2 M is mounted on each of the mounting tables  25 R,  25 L with a surface  2 Ma of the mother substrate  2 M facing upward. Each mounting table  25 R,  25 L defines a space (a recess  25   a ) with respect to the backside  2 Mb of the mother substrate  2 M. The transport arm  24   a  can be received in and removed from the recess  25   a.  By moving upward or downward in the recess  25   a,  the transport arm  24   a  raises the mother substrate  2 M from the mounting table  25 R,  25 L or places the mother substrate  2 M on the mounting table  25 R,  25 L.  
      In response to prescribed control signals input to the running motor MS and the transport motor MT, the running device  23  and the transport device  24  retrieve the corresponding one of the mother substrates  2 M from the substrate stocker  22  and place the mother substrate  2 M on the corresponding one of the mounting tables  25 R,  25 L. Also, the running device  23  and the transport device  24  re-collect the mother substrates  2 M by returning each mother substrate  2 M from the mounting table  25 R,  25 L to a predetermined slot of the substrate stocker  22 .  
      In the first embodiment, referring to  FIG. 3 , a code area S is defined on each of the mother substrates  2 M mounted on the mounting tables  25 R,  25 L. In each mother substrate  2 M, the rows of the code areas S are defined as the first row of the code areas S 1 , the second row of the code areas S 2 , the third row of the code areas S 3 , the fourth row of the code areas S 4 , and the fifth row of the code areas S 5  sequentially in direction −X, or from the uppermost row to the lowermost row as viewed in  FIG. 3 .  
      As shown in  FIG. 2 , a multi-joint robot (hereinafter, referred to as a SCARA robot)  26 , which functions as a movement mechanism, is arranged between the two mounting tables  25 R,  25 L and on the upper surface  21   a  of the base  21 . The SCARA robot  26  has a main shaft  27  that is fixed to the upper surface  21   a  of the base  21  and extends upward (in direction +Z).  
      A first arm  28   a  is provided at the upper end of the main shaft  27 . The proximal end of the first arm  28   a  is connected to the output shaft of a first motor M 1  (see  FIG. 7 ), which is provided in the main shaft  27 . The first arm  28   a  pivots on a horizontal plane, or about a pivotal axis extending in direction Z. A second motor M 2  (see  FIG. 7 ) is provided at the distal end of the first arm  28   a.  The proximal end of a second arm  28   b  is connected to the output shaft of the second motor M 2 . This allows the second arm  28   b  to pivot on a horizontal plane, or about an axis extending in direction Z.  
      A third motor M 3  (see  FIG. 7 ) is arranged at the proximal end of the second arm  28   b.  A pillar-like third arm  28   c  is connected to the output shaft of the third motor M 3  and thus pivots about a pivotal axis extending in direction Z. A head unit  30  is provided at the lower end of the third arm  28   c.    
      The head unit  30  has a casing  31  having a box-like shape. A droplet ejection head (hereinafter, referred to simply as an ejection head)  32  and a suction port  33 , which forms a suction device, are provided below the casing  31 . A laser head  34 , or a laser radiation device, is arranged at one side surface of the casing  31 .  
      If the first, second, and third motors M 1 , M 2 , M 3  receive prescribed control signals, the SCARA robot  26  pivots the corresponding first, second, and third arms  28   a,    28   b,    28   c,  thereby moving the head unit  30  in a predetermined area defined on the upper surface  21   a.    
      Specifically, as shown in  FIG. 3 , the SCARA robot  26  generates a “target path R” in accordance with the position coordinates of the code areas S (the ejection target positions P) and operates the head unit  30  to perform scanning along the target path R. That is, as indicated by the arrows corresponding to the mounting table  25 L of  FIG. 3 , the SCARA robot  26  pivots a first arm  28   a,  a second arm  28   b,  and a third arm  28   c  in such a manner as to deploy the head unit  30  (the distal end of the third arm  28   c ) at the “start point SP” in the first row of the code areas S 1 . In the drawing, the start point SP corresponds to the right end of the first row of the code areas S 1 . In this state, the laser head  34 , the suction port  33 , and the ejection head  32  are aligned in the head unit  30  in this order in direction +Y.  
      With the head unit  30  arranged at the start point SP, the SCARA robot  26  moves the head unit  30  in direction +Y. In other words, the SCARA robot  26  operates the head unit  30  in such a manner that the ejection head  32  precedes the suction port  33  and the suction port  33  precedes the laser head  34 . When the head unit  30  reaches the end point in the first row of the code areas S 1 , the SCARA robot  26  pivots the first, second, and third arms  28   a,    28   b,    28   c,  thus rotating the head unit  30  counterclockwise at 180 degrees outside the mother substrate  2 M and sending the head unit  30  to the start point in the second row of the code areas S 2  (the left end as viewed in  FIG. 3 ). In this state, in the head unit  30 , the laser head  34 , the suction port  33 , and the ejection head  32  are aligned in this order in direction −Y.  
      When the head unit  30  is deployed at the start point in the second row of the code areas S 2 , the SCARA robot  26  pivots the first, second, and third arms  28   a,    28   b,    28   c  in such a manner as to move the head unit  30  in direction −Y. In other words, as in the case of scanning in the first row of the code areas S 1 , the SCARA robot  26  operates the head unit  30  in such a manner that the ejection head  32  precedes the suction port  33  and the suction port  33  precedes the laser head  34 . Afterwards, in the same manner as has been described, the SCARA robot  26  operates the head unit  30  to scan the third, fourth, and fifth rows of the code areas S 3 , S 4 , S 5  in this order in direction Y, until the head unit  30  reaches the end point EP of the fifth row of the code areas S 5 .  
      Accordingly, while moving the head unit  30  along the “target path R” having a zigzag shape, the SCARA robot  26  operates in such a manner that the suction port  33  constantly precedes the laser head  34 . In the illustrated embodiment, the scanning direction of the head unit  30  is defined as the “scanning direction RA”.  
       FIGS. 4 and 5  are views each showing the head unit  30 , and  FIG. 6  is a plan view schematically showing the head unit  30  as viewed from the side corresponding to the mother substrate  2 M.  
      As shown in  FIG. 4 , the casing  31  has a liquid tank  35  that retains liquid F (see  FIG. 5 ). The droplet ejection head  32  is arranged below the casing  31 . The liquid F is supplied from the liquid tank  35  to the ejection head  32 .  
      As shown in  FIG. 5 , a nozzle plate  36  is provided at the lower surface of the ejection head  32 . A plurality of circular bores (nozzles N) are defined in the lower surface (a nozzle surface  36   a ) of the nozzle plate  36 , extending in a normal direction of the mother substrate  2 M (direction Z) through the nozzle plate  36 . As shown in  FIG. 6 , the nozzles N are aligned in a direction perpendicular to the scanning direction RA of the head unit  30 . The pitch of the nozzles N is equal to the cell width W. In the illustrated embodiment, the positions on the mother substrate  2 M opposed to the nozzles N will be referred to as the droplet receiving positions PF.  
      As illustrated in  FIG. 5 , the ejection head  32  has cavities  37  that are defined above the nozzles N and communicate with the liquid tank  35 . Each of the cavities  37  supplies the liquid F from the liquid tank  35  to the corresponding one of the nozzles N. An oscillation plate  38  is bonded with the upper sides of the walls defining each cavity  37 . The oscillation plates  38  each oscillate in the up-and-down direction in such a manner as to increase and decrease the volume of the corresponding one of the cavities  37 . A plurality of piezoelectric elements PZ are arranged on the oscillation plates  38  in correspondence with the nozzles N. When the droplet receiving positions PF coincide with the ejection target positions P and in response to a prescribed drive signal (drive voltage COM 1 : see  FIG. 7 ) input to each of the piezoelectric elements PZ, the piezoelectric element PZ contracts and extends in the up-and-down direction, oscillating the associated oscillation plate  38 . Specifically, through contraction and extension of each piezoelectric element PZ, the interface (the meniscus) of the liquid F in the corresponding nozzle N oscillates in the up-and-down direction. In this manner, a droplet Fb the weight of which corresponds to the drive voltage COM 1  is ejected from the nozzle N. The ejected droplet Fb travels in the space (the traveling zone FS) between the nozzle plate  36  and the mother substrate  2 M in direction −Z, reaching the corresponding droplet receiving position PF, or ejection target position P. The droplet Fb then spreads wet on the surface  2 Ma and the outer diameter of the droplet Fb becomes equal to the cell width W.  
      In the illustrated embodiment, the time from when ejection of the droplets Fb starts to when the outer diameter of each droplet Fb becomes equal to the cell width W will be referred to as the “radiation standby time”. Movement of the head unit  30  during the “radiation standby time” covers the distance (the radiation standby distance Lw) double the cell width W.  
      As shown in  FIG. 4 , the suction port  33  has a box-like shape and has a lower opening. The suction port  33  communicates with a suction tube  39  extending in the casing  31 . The suction tube  39  passes through the interiors of the third arm  28   c,  the second arm  28   b,  the first arm  28   a,  and the main shaft  27  and is connected to a suction pump  40  (see  FIGS. 2 and 3 ) in the base  21 . In other words, the suction port  33  communicates with the suction pump  40  through the suction tube  39 .  
      In response to a suction start signal input to the suction pump  40 , the suction pump  40  starts suction. The gas in the space between the suction port  33  and the mother substrate  2 M is thus drawn from the suction port  33  to the suction pump  40  through the suction tube  39 . The gap between the ejection head  32  and the mother substrate  2 M is relatively narrow. Thus, in the zone between the ejection head  32  and the mother substrate  2 M, or the traveling zone FS, the flow resistance of the gas becomes great with respect to that in the area around the traveling zone FS. Therefore, when the gas is drawn from the suction port  33 , the gas forward from the suction port  33  in the scanning direction RA reaches the suction port  33  while avoiding the area in which the flow resistance is great, or the traveling zone FS. Accordingly, in suction of the gas by the suction pump  40 , the flow of the gas in the traveling zone FS is suppressed, stabilizing the traveling direction of the droplets Fb ejected by the ejection head  32 .  
      As shown in  FIG. 4 , a plurality of lasers, which are a plurality of semiconductor lasers LD in this embodiment, are arranged in the laser head  34  in correspondence with the nozzles N and aligned in the alignment direction of the nozzles N. In response to a drive signal (drive voltage COM 2 : see  FIG. 7 ) input to the semiconductor lasers LD, the semiconductor lasers LD each radiate a laser beam B downward in direction Z. The laser beam B falls in the wavelength range corresponding to the absorption wavelength of the droplets Fb. A reflective mirror M as an optical system is provided at the lower end of the laser head  34  and immediately below the array of the semiconductor lasers LD in correspondence with the array of the semiconductor lasers LD. The reflective mirror M extends along the alignment direction of the nozzles N. The reflective mirror M totally reflects the laser beams B radiated by the semiconductor lasers LD and sends the laser beams B in a diagonally downward direction with respect to the scanning direction RA of the head unit  30 . That is, the laser beam B radiated by each semiconductor laser LD is guided to the position on the mother substrate  2 M forward from the position on the mother substrate  2 M immediately below the semiconductor laser LD in the scanning direction RA of the head unit  30 .  
      Referring to  FIG. 5 , in the illustrated embodiment, the position at which the surface  2 Ma of the mother substrate  2 M crosses the optical axis of each laser beam B proceeding diagonally downward is defined as a radiating position PT. The distance between the radiating position PT and the corresponding droplet receiving position PF is set to the radiation standby distance Lw. In other words, by the time the radiation standby time elapses since reception of a droplet Fb at the ejection target position P, the radiating position PT reaches the droplet Fb that has reached the ejection target position P.  
      Each semiconductor laser LD receives the drive voltage COM 2  to radiate the laser beam B when the corresponding radiating position PT coincides with the ejection target position P. The laser beam B is totally reflected by the reflective mirror M and irradiates the droplet Fb at the corresponding radiating position PT. The laser beam B thus evaporates the solvent or the dispersion medium from the droplet Fb as evaporated elements Ev and bakes the metal particles of the droplet Fb. In this manner, a dot D having an outer diameter equal to the cell width W of each data cell C is formed at the ejection target position P.  
      With reference to  FIG. 6 , the evaporated elements Ev float in the vicinity of the radiating positions PT between the nozzles N and the reflective mirror M, as viewed in a normal direction of the mother substrate  2 M. The floating evaporated elements Ev are drawn through the suction port  33 , which is rearward from the nozzles N in the scanning direction RA, in the direction opposite to the scanning direction RA. That is, the evaporated elements Ev are drawn in the direction opposite to the movement direction of the nozzles N in such a manner as to separate the evaporated elements Ev from the nozzles N. The suction port  33  is located forward from the reflective mirror M in the scanning direction RA. Therefore, the floating evaporated elements Ev are drawn through the suction port  33  at positions forward from the reflective mirror M (the laser head  34 ) in the movement direction of the reflective mirror M (the laser head  34 ). This prevents the reflective mirror M from being exposed to the evaporated elements Ev.  
      Accordingly, adhesion of the evaporated elements Ev to the nozzles N and the reflective mirror M is avoided. This ensures stable ejection of the droplets Fb by the ejection head  32  and stabilizes optical characteristics of the optical systems that provide the laser beams B. The laser beams B are thus effectively radiated onto a desired point at a desired intensity.  
      The electric configuration of the droplet ejection apparatus  20 , the structure of which has been described so far, will hereafter be explained with reference to  FIG. 7 .  
      As shown in  FIG. 7 , the droplet ejection apparatus  20  has a controller  51  including a CPU, a ROM, and a RAM. In accordance with the current position of the distal end of the third arm  28   c  (the ejection head  32 ) and different control programs, the controller  51  operates the running device  23 , the transport device  24 , and the SCARA robot  26  while actuating the ejection head  32  and the laser head  34 .  
      An input device  52  having manipulation switches such as a start switch and a stop switch is connected to the controller  51 . Through the input device  52 , information regarding the identification code  10  is input to the controller  51  as a prescribed form of imaging data Ia. The controller  51  generates bit map data BMD by processing the imaging data Ia provided by the input device  52 . In accordance with the bit map data BMD, the controller  51  generates the position coordinates (instruction coordinates Tp) of each of the ejection target positions P. The position coordinates (the instruction coordinates Tp) are provided in correspondence with an orthogonal coordinate system. Further, the controller  51  subjects the imaging data Ia to a process different from the process for the bit map data BMD, thus generating the drive voltage COM 1  for the piezoelectric elements PZ and the drive voltage COM 2  for the semiconductor lasers LD.  
      The controller  51  has a memory  51 A that stores data such as the bit map data BMD and a program for forming the identification code  10 .  
      The bit map data BMD indicates whether to eject the droplets Fb onto the areas provided by virtually dividing an imaging plane defined on the orthogonal coordinate system (the surface  2 Ma of the mother substrate  2 M). In other words, the bit map data BMD is used for instructing whether to actuate the piezoelectric elements PZ in accordance with the value of each bit (0or 1). The bit map data BMD is thus used for instructing whether to eject the droplets Fb from the nozzles N when the ejection head  32  scans the first to fifth rows of the code areas S 1  to S 5 .  
      The controller  51  serially transfers the ejection control signals SI produced by synchronizing the bit map data BMD with a prescribed clock signal to the ejection head driver circuit  56 .  
      The controller  51  has an interpolation operation section  51 B. The interpolation operation section  51 B performs an interpolation process (for example, linear or circular interpolation) on a space between each adjacent pair of the instruction coordinates Tp at prescribed interpolation cycles. The interpolation operation section  51 B thus calculates the position coordinates (the interpolation coordinates) of each of interpolation points that form the target path R. The interpolation operation section  51 B calculates information (path information TaI) including the instruction coordinates Tp and the interpolation coordinates and outputs the path information TaI to an inverse operation section  51 C.  
      The inverse operation section  51 C sequentially calculates pivotal angles and other parameters of the motors M 1 , M 2 , M 3  in accordance with the path information TaI, which has been output from the interpolation operation section  51 B, in such a manner that the position of the distal end of the third arm  28   c  sequentially coincides with the instruction coordinates Tp and the interpolation coordinates. In other words, the inverse operation section  51 C sequentially calculates information (arm pivot information θI) that can provide the posture of the SCARA robot  26  that allows the suction port  33  to precede the laser head  34  in the scanning direction RA when the head unit  30  moves along the target path R. The inverse operation section  51 C outputs the calculated arm pivot information θI to the SCARA robot driver circuit  55 .  
      A running device driver circuit  53  is connected to the controller  51 . The running device driver circuit  53  is connected to the running motor MS and a running motor rotation detector MSE. In response to a control signal from the controller  51 , the running device driver circuit  53  operates to rotate the running motor MS in a forward direction or a reverse direction. The controller  51  also calculates the movement direction and the movement amount of the transport device  24  in correspondence with a detection signal generated by the running motor rotation detector MSE.  
      A transport device driver circuit  54  is connected to the controller  51 . The transport device driver circuit  54  is connected to the transport motor MT and a transport motor rotation detector MTE. In response to a control signal from the controller  51 , the transport device driver circuit  54  operates to rotate the transport motor MT in a forward direction or a reverse direction. Further, the controller  51  calculates the movement direction and the movement amount of the transport arm  24   a  in correspondence with a detection signal received from the transport motor rotation detector MTE.  
      A SCARA robot driver circuit  55  is connected to the controller  51 . The SCARA robot driver circuit  55  is connected to the first motor M 1 , the second motor M 2 , and the third motor M 3 . In response to inputting of the arm pivot information θI from the controller  51 , the SCARA robot driver circuit  55  operates to rotate the first, second, and third motors M 1 , M 2 , M 3  in a forward direction or a reverse direction. The SCARA robot driver circuit  55  is connected also to a first motor rotation detector M 1 E, a second motor rotation detector M 2 E, and a third motor rotation detector M 3 E. In correspondence with detection signals provided by the first, second, and third motor rotation detectors M 1 E, M 2 E, M 3 E, the SCARA robot driver circuit  55  computes the movement direction and the movement amount of the distal end of the third arm  28   c  (the ejection head  32 ).  
      The controller  51  moves the head unit  30  in a zigzag manner along the target path R through the SCARA robot driver circuit  55 . The controller  51  outputs different control signals in correspondence with the calculation result (the current position of the ejection head  32 ) obtained by the SCARA robot driver circuit  55 .  
      Specifically, the controller  51  generates a signal that instructs activation of the suction pump  40  (a start signal TP 1 ) and sends the signal to a suction pump driver circuit  58  in correspondence with the timing at which scanning by the head unit  30  starts, or the ejection head  32  is located at the start point SP.  
      Further, the controller  51  generates a signal (an ejection timing signal LP) that instructs ejection of the droplets Fb and sends the signal to an ejection head driver circuit  56  in correspondence with the timing at which the ejection head  32  is (the droplet receiving positions PF are) located in the corresponding code area S (at the corresponding ejection target positions P).  
      Further, the controller  51  generates a signal (a stop signal TP 2 ) that instructs deactivation of the suction pump  40  and provides the signal to the suction pump driver circuit  58  in correspondence with the timing at which scanning of the head unit  30  ends, or the ejection head  32  is located at the end point EP.  
      The ejection head driver circuit  56  is connected to the controller  51 . The controller  51  sends the ejection timing signal LP to the ejection head driver circuit  56  and supplies the drive voltage COM 1  to the ejection head driver circuit  56  synchronously with the ejection timing signal LP. The controller  51  also serially transfers the ejection control signals SI to the ejection head driver circuit  56 . The ejection head driver circuit  56  converts the ejection control signals SI in the serial forms to parallel signals in such a manner that the parallel ejection control signals SI correspond to the piezoelectric elements PZ.  
      After receiving the ejection timing signal LP from the controller  51 , the ejection head driver circuit  56  supplies the drive voltage COM 1  to those of the piezoelectric elements PZ that are selected in accordance with the parallel ejection control signals SI, which have been converted from the serial forms. Further, in response to the ejection timing signal LP input from the controller  51 , the ejection head driver circuit  56  outputs the parallel ejection control signal SI to a laser head driver circuit  57 .  
      The laser head driver circuit  57  is connected to the controller  51 . The controller  51  supplies the drive voltage COM 2  to the laser head driver circuit  57  synchronously with the ejection timing signal LP. After having received the ejection control signals SI from the ejection head driver circuit  56 , the laser head driver circuit  57  stands by for a predetermined time, or the radiation standby time. The laser head driver circuit  57  then supplies the drive voltage COM 2  to the semiconductor lasers LD corresponding to the ejection control signals SI.  
      When the ejection control signals SI are received by the laser head driver circuit  57 , the controller  51  instructs the laser head driver circuit  57  to stand by for the radiation standby time and operates the head unit  30  to scan for the radiation standby time. After the radiation standby time, or when the radiating positions PT coincide with the corresponding droplet receiving target positions P, the controller  51  operates the laser head driver circuit  57  to radiate the laser beams B from the laser head  34  onto the droplets at the droplet receiving target positions P.  
      The suction pump driver circuit  58  is connected to the controller  51 . The controller  51  outputs a corresponding control signal (the start signal TP 1  or the end signal TP 2 ) to the suction pump driver circuit  58 . The suction pump driver circuit  58  is connected to the suction pump  40 . In response to the start signal TP 1  from the controller  51 , the suction pump driver circuit  58  starts suction by the suction pump  40 . In response to the end signal TP 2  from the controller  51 , the suction pump driver circuit  58  stops the suction by the suction pump  40 . While moving the head unit  30  along the target path R, the controller  51  activates the suction pump  40  to continuously perform suction through the suction port  33 .  
      A procedure for forming the identification codes  10  using the droplet ejection apparatus  20  will hereafter be explained.  
      First, the imaging data Ia is input to the controller  51  by manipulating the input device  52 . The controller  51  then drives the running device  23  and the transport device  24  to retrieve the corresponding mother substrate  2 M from the substrate stocker  22  and place the mother substrate  2 M on the mounting table  25 R (or the mounting table  25 L). Further, by processing the imaging data Ia sent from the input device  52 , the controller  51  generates the bit map data BMD and the instruction coordinates Tp. The controller  51  then stores the bit map data BMD and the instruction coordinates Tp in the memory  51 A.  
      Further, the controller  51  operates the SCARA robot driver circuit  55  to move the distal end of the third arm  28   c  to the start point SP. Meanwhile, the controller  51  sequentially calculates the interpolation coordinates between each group of the instruction coordinates Tp and the subsequent instruction coordinates Tp, with the start point SP of the first row of the code areas S 1  as a start point. The controller  51  outputs path information TaI consisting of the interpolation coordinates and the instruction coordinates Tp to the inverse operation section  51 C. The inverse operation section  51 C sequentially generates the arm pivot information ΘI corresponding to the interpolation coordinates and the instruction coordinates Tp.  
      When the distal end of the third arm  28   c  (the ejection head  32 ) is arranged at the start point SP, the controller  51  sends the start signal TP 1  to the suction pump driver circuit  58  in such a manner as to start suction by the suction pump  40  through the suction port  33 .  
      When the ejection head  32  is located at the start point SP, the controller  51  sequentially provides the arm pivot information θI to the SCARA robot driver circuit  55  through the inverse operation section  51 C. This causes the head unit  30  to start scanning. Specifically, while maintaining the position of the suction port  33  between the laser head  34  and the droplet ejection head  32 , the controller  51  starts scanning of the head unit  30  along the target path R from the start point SP.  
      In correspondence with the calculation results obtained by the SCARA robot driver circuit  55 , the controller  51  determines whether the droplet receiving positions PF have reached the foremost ones of the ejection target positions P in the first row of the code areas S 1 . The foremost ones of the ejection target positions P correspond to the rightmost column of the data cells C in the rightmost code area S of the first row of the code areas S 1 , as viewed in  FIG. 3 . Also, the controller  51  provides the ejection control signals SI and the drive voltage COM 1  to the ejection head driver circuit  56  and the drive voltage COM 2  to the laser head driver circuit  57 .  
      When the droplet receiving positions PF coincide with the foremost ones of the ejection target positions P in the first row of the code areas S 1 , the controller  51  outputs the ejection timing signal LP to the ejection head driver circuit  56  and supplies the drive voltage COM 1  to those of the piezoelectric elements PZ that are selected in accordance with the ejection control signals SI. In response to such supply of the drive voltage COM 1 , those of the nozzles N that are selected in accordance with the ejection control signals SI simultaneously eject the droplets Fb. The ejected droplets Fb travel in the traveling zone FS and reach the surface  2 Ma of the mother substrate  2 M.  
      Specifically, since the gas flow in the traveling zone FS is suppressed, the droplets Fb reach the corresponding ejection target positions P without becoming offset from the traveling path. After having reached the corresponding ejection target position P, each droplet Fb spreads wet in the corresponding data cell C in such a manner that the outer diameter of the droplet Fb becomes equal to the cell width W after the radiation standby time has elapsed since the start of ejection.  
      Further, the controller  51  sends the parallel ejection control signals SI, which have been converted from the serial forms, to the laser head driver circuit  57  through the ejection head driver circuit  56 . After the radiation standby time has elapsed since the start of ejection, or when the radiating positions PT coincide with the corresponding ejection target positions P, the controller  51  supplies the drive voltage COM 2  to those of the semiconductor lasers LD that are selected in accordance with the ejection control signals SI. In response to such supply of the drive voltage COM 2 , the selected semiconductor lasers LD simultaneously radiate the laser beams B. The laser beams B are then totally reflected by the reflective mirror M and thus radiate the droplets Fb that are located at the corresponding radiating positions PT, or ejection target positions P, and have the outer diameter equal to the cell width W. This causes evaporation (drying) of the solvent or the dispersion medium from the droplets Fb and baking of the metal particles in the droplets Fb. As a result, each of the droplets Fb is fixed to the surface  2 Ma as a dot D having the outer diameter equal to the cell width W. In this manner, the dots D are provided in correspondence with the cell width W.  
      Specifically, the evaporated elements Fv floating in the vicinity of the radiating positions PT are drawn by the suction port  33 , which is rearward from the nozzles N but forward from the reflective mirror M in the scanning direction RA. The evaporated elements Ev are thus removed from the space between the nozzles N (the ejection head  32 ) and the reflective mirror M (the laser head  34 ) without reaching the nozzles N (the ejection head  32 ) and the reflective mirror M (the laser head  34 ).  
      Afterwards, the controller  51  operates to move the head unit  30  along the target path R in the same manner as has been described, with the suction port  33  maintained at a position between the laser head  34  and the droplet ejection head  32  in the scanning direction RA. Each time the droplet receiving positions PF coincide with the ejection target positions P, the controller  51  operates the selected nozzles N to eject the droplets Fb. When the outer diameter of each droplet Fb becomes equal to the cell width W, the controller  51  operates to radiate the laser beams B onto the droplets Fb. In this manner, the dots D are provided in each of the code areas S on the mother substrate  2 M in such a manner as to form a prescribed pattern, while preventing the nozzles N (the ejection head  32 ) and the reflective mirror M (the laser head  34 ) from being contaminated by the evaporated elements Ev.  
      When the head unit  30  reaches the end point EP after having completed formation of the dots D on the mother substrate  2 M, the controller  51  outputs the suction end signal TP 2  to the suction pump driver circuit  58 , thus stopping suction by the suction pump  40  through the suction port  33 . The controller  51  then operates the running device  23  and the transport device  24  to transport the mother substrate  2 M on which the dots D have been formed to the substrate stocker  22 , ending formation of the identification codes  10  on the mother substrate  2 M.  
      The illustrated embodiment has the following advantages.  
      (1) The suction port  33 , which draws the evaporated elements Fv, is arranged forward from the laser head  34  (the reflective mirror M) in the scanning direction RA. Therefore, the evaporated elements Ev released from the droplets Fv through radiation of the laser beams B are drawn through the suction port  33  at a position forward from the laser head  34  (the reflective mirror M) in the scanning direction RA. This prevents the evaporated elements Ev from adhering to the laser head  34  (the reflective mirror M). Contamination of the reflective mirror M by the evaporated elements Ev is thus avoided, stabilizing the optical characteristics of the reflective mirror M. This improves controllability for shaping the dots D formed by the droplets Fb.  
      (2) The suction port  33  is arranged between the laser head  34  (the reflective mirror M) and the radiating positions PT. Therefore, compared to the case in which the suction port  33  is located forward from the radiating positions PT in the scanning direction RA, the evaporated elements Ev proceeding toward the reflective mirror M are reliably removed before reaching the reflective mirror M. This further stabilizes the optical characteristics of the reflective mirror M.  
      (3) The radiating positions PT of the laser beams B are set at the positions opposed to the ejection head  32 . The suction port  33  is located between the ejection head  32  and the laser head  34 . The evaporated elements Fv proceeding toward the ejection head  32  (the nozzles N) are thus reliably drawn through the suction port  33 , preventing contamination of the ejection head  32  (the nozzles N) by the evaporated elements Ev. This stabilizes ejection of droplets.  
      (4) The flow resistance of the gas moving from the mother substrate  2 M to the suction port  33  is increased in the traveling zone FS. This suppresses flow of the gas in the traveling zone FS when the evaporated elements Ev are drawn through the suction port  33 . The traveling direction of the droplets Fb ejected from the ejection head  32  is thus stabilized.  
      (5) In the movement of the head unit  30  in the scanning direction RA, the droplets Fb that have received the laser beams B reach the positions opposed to the laser head  34  after the positions opposed to the suction port  33 . In other words, after having been irradiated with the laser beams B, the droplets Fb reliably reach the positions immediately below the suction port  33  before the positions immediately below the laser head  34 . The evaporated elements Ev are thus reliably removed by suction through the suction port  33  before reaching the laser head  34  (the reflective mirror M). This allows the suction port  33  and the laser head  34  to move above the mother substrate  2 M without varying the optical characteristics of the reflective mirror M. The productivity for forming the identification codes  10  is thus enhanced.  
      (6) When the head unit  30  moves in the scanning direction RA, the evaporated elements Ev from the droplets Fb that have received the laser beams B are drawn through the suction port  33 , which is located rearward from the ejection head  32 . That is, the evaporated elements EV from the droplets Fb are drawn in the direction opposite to the movement direction of the nozzles N. The evaporated elements Fv are thus further quickly separated from the nozzles N. In this manner, contamination of the nozzles N by the evaporated elements Ev is further reliably avoided, stabilizing ejection of droplets.  
      The illustrated embodiment may be modified in the following forms.  
      In the illustrated embodiment, the ejection head  32 , the suction port  33 , and the laser head  34  move relative to the mother substrate  2 M. However, for example, the ejection head  32 , the suction port  33 , and the laser head  34  may be fixed and the mother substrate  2 M (specifically, the mounting table  25 L,  25 R on which the mother substrate  2 M is mounted) may be moved relative to the ejection head  32 , the suction port  33 , and the laser head  34 .  
      The ejection head  32 , the suction port  33 , and the laser head  34  do not necessarily have to be formed as a single head unit but may be provided independently from one another as long as the ejection head  32 , the suction port  33 , and the laser head  34  are each movable relative to the mother substrate  2 M or the mother substrate  2 M is movable relative to the ejection head  32 , the suction port  33 , and the laser head  34 .  
      In the illustrated embodiment, the suction port  33  is provided between the laser head  34  and the radiating positions PT. However, the suction port  33  may be arranged, for example, immediately above the radiating positions PT.  
      In the illustrated embodiment, the movement device (the movement mechanism) is embodied as the SCARA robot  26 . However, the movement device may be a mounting table that carries and moves the mother substrate  2 M relative to the laser head  34  or a carriage that carries and moves the laser head  34  relative to the mother substrate  2 M. That is, the movement device may be embodied in any suitable forms, as long as relative movement between the suction port  33  and the mother substrate  2 M or the laser head  34  and the mother substrate  2 M occurs.  
      In the illustrated embodiment, the droplets Fb are dried and baked by the laser beams B. However, the droplets Fb may be caused to flow in a desired direction by energy produced by the radiated laser beams B. Alternatively, the droplets Fb may be fixed by radiating the laser beams B onto only the periphery of the droplets Fb. That is, any suitable method may be employed, as long as marks formed by the droplets Fb are provided through radiation of the laser beams B.  
      Although each of the dots D has the semispherical shape in the illustrated embodiment, oval dots or linear marks may be provided according to the present invention.  
      In the illustrated embodiment, the ejected droplets Fb form the dots D that define each of the identification codes  10 . However, the droplets Fb may form, for example, different types of thin films, metal wirings, or color filters of various types of displays such as the liquid crystal display  1  or a field effect type device (an FED or an SED). The field effect type device has a flat electron release element that emits light from a fluorescent substance. That is, the droplet ejection apparatus is applicable to any suitable uses, as long as marks are formed by the ejected droplets Fb.  
      In the illustrated embodiment, the target onto which the droplets Fb are ejected is embodied as the mother substrate  2 M. However, the target may be a silicone substrate, a flexible substrate, or a metal substrate. In other words, as long as marks are formed by the ejected droplets Fb, any suitable targets may be selected.