Patent Publication Number: US-2022227153-A1

Title: Production method of a modeled object

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Divisional application of U.S. application Ser. No. 15/889,832, filed Feb. 6, 2018, which is based upon and claims the benefit of priority from Japanese Patent Application No. 2017-060040, filed Mar. 24, 2017, the entire contents of all of which are incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an expansion device, a three-dimensional image forming system, a method of expanding a thermally expandable sheet, and a computer readable storage medium. 
     2. Description of the Related Art 
     A technique for forming a three-dimensional image is known. For example, JP S64-28660 A and JP 2001-150812 A disclose methods of forming a three-dimensional image using a thermally expandable sheet. Specifically, in the methods disclosed in JP S64-28660 A and JP 2001-150812 A, a pattern is formed on a back surface of a thermally expandable sheet with a material having excellent light absorption characteristics, and the formed pattern is heated by being irradiated with light. As a result, the portion of the thermally expandable sheet on which the pattern is formed expands and swells to form a three-dimensional image. 
     A thermally expandable sheet may be deformed by heat when being expanded by heat. When the thermally expandable sheet is deformed, a three-dimensional image formed thereon is also distorted. Therefore, it becomes difficult to obtain a desired three-dimensional image. As a result, it is required to expand the thermally expandable sheet while suppressing deformation of the sheet. 
     The present invention is intended to solve the above problems, and an object of the present invention is to provide an expansion device capable of expanding a thermally expandable sheet while suppressing the deformation of the sheet, a three-dimensional image forming system, a method of expanding a thermally expandable sheet, and a program. 
     SUMMARY OF THE INVENTION 
     An expansion device, including: an installation unit in which a thermally expandable sheet is disposed; an irradiation unit configured to irradiate the thermally expandable sheet placed on the installation unit with light; and a control unit configured to perform processes described below, wherein after an expansion process to expand the thermally expandable sheet by irradiating the thermally expandable sheet placed on the installation unit with light by the irradiation unit, a cooling process to cool the thermally expandable sheet by a predetermined cooling unit while maintaining the state in which the thermally expandable sheet is placed on the installation unit. 
     An expansion method for a thermally expandable sheet, which is performed by an expansion device, the method including the steps of: expanding the thermally expandable sheet by causing the irradiation unit to emit light while moving the irradiation unit along a front or back surface of the thermally expandable sheet; and cooling the inside of the expansion device after the expanding step has been performed. 
     A non-transitory computer-readable recording medium storing a program executable by a computer for causing a computer controlling an expansion device to realize the following functions: moving the irradiation unit configured to emit light along a front or back surface of a thermally expandable sheet; cooling the inside of the expansion device; and performing a cooling process to cool the inside of the expansion device after the expansion process to expand the thermally expandable sheet has been performed by causing the irradiation unit to emit light while moving the irradiation unit. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view of a thermally expandable sheet according to a first embodiment of the present invention; 
         FIG. 2  is a view illustrating a back surface of the thermally expandable sheet illustrated in  FIG. 1 ; 
         FIG. 3  is a diagram indicating a schematic configuration of a three-dimensional image forming system according to the first embodiment; 
         FIG. 4  is a block diagram indicating a configuration of a terminal device according to the first embodiment; 
         FIG. 5  is a perspective view illustrating a configuration of a printing device according to the first embodiment; 
         FIG. 6  is a cross-sectional view illustrating a configuration of an expansion device according to the first embodiment; 
         FIG. 7  is a view illustrating a thermally expandable sheet disposed on a tray according to the first embodiment; 
         FIG. 8  is a block diagram indicating a configuration of a control board of the expansion device according to the first embodiment; 
         FIG. 9  is a view illustrating a state in which the expansion device performs an expansion process in the first embodiment; 
         FIG. 10  is a view illustrating a state in which the expansion device performs a cooling process in the first embodiment; 
         FIG. 11  is a flowchart indicating a flow of a three-dimensional image forming process according to the first embodiment; 
         FIGS. 12A to 12E  are views gradually illustrating formation of a three-dimensional image on the thermally expandable sheet illustrated in  FIG. 1 ; 
         FIG. 13  is a flowchart indicating a flow of the processes performed by the expansion device according to the first embodiment; 
         FIG. 14  is a flowchart indicating a flow of processes performed by an expansion device according to a second embodiment the present invention; 
         FIG. 15  is a view illustrating a state in which the expansion device performs a drying process in the second embodiment; 
         FIG. 16  is a view illustrating a state in which the expansion device performs a ventilation process in the second embodiment; 
         FIGS. 17A to 17D  are views illustrating thermally expandable sheets disposed on a tray by being pressed on two facing sides in a variation of the present invention; and 
         FIGS. 18A to 18C  are views illustrating thermally expandable sheets disposed on a tray by being pressed at least two facing corners in the variation of the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     An embodiment of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same or corresponding portions are denoted by the same reference numerals. 
     First Embodiment 
     &lt;Thermally Expandable Sheet  100 &gt; 
       FIG. 1  illustrates a configuration of a thermally expandable sheet  100  for forming a three-dimensional image by a three-dimensional image forming system  1  according to the first embodiment. The thermally expandable sheet  100  is a medium on which a three-dimensional image is formed by expansion of a preselected portion. The three-dimensional image is a three-dimensional image formed by expanding a part of a two-dimensional sheet in the direction perpendicular to the sheet. 
     In addition, a “three-dimensional image” refers to as a molded object, and the molded object widely includes a general shape, such as a simple shape, a geometric shape, and characters. Furthermore, the molded object also includes an ornament formed as a result of decoration. The ornament refers to the sense of beauty through visual and/or tactile sense. “Three-dimensional image formation” includes not only forming the molded object but also decoration (ornament). 
     As illustrated in  FIG. 1 , the thermally expandable sheet  100  includes a base material  101 , a thermally expandable layer  102 , and an ink receiving layer  103  in this order. Note that  FIG. 1  illustrates a cross section of the thermally expandable sheet  100  before a three-dimensional image is formed, that is, in a state where none of the parts are expanded. 
     The base material  101  is a sheet-like medium as a base of the thermally expandable sheet  100 . The base material  101  is a support that supports the thermally expandable layer  102  and the ink receiving layer  103  and plays a role of maintaining the intensity of the thermally expandable sheet  100 . As the base material  101 , for example, a general printing paper can be used. Alternatively, the material of the base material  101  may be a synthetic paper, a cloth such as canvas, and a plastic film such as polypropylene, polyethylene terephthalate (PET), and polybutylene terephthalate (PBT) and is not particularly limited. 
     The thermally expandable layer  102  is laminated on the upper side of the base material  101  and expands when being heated to a temperature equal to or higher than a specified temperature. The thermally expandable layer  102  includes a binder and a thermally expandable agent dispersed in the binder. The binder is a thermoplastic resin such as a vinyl acetate type polymer, and an acryl type polymer. The thermally expandable agent is a thermally expandable microcapsule (micropowder) having a particle size of about 5 to 50 μm and containing a low boiling point vaporizing substance such as propane and butane in the outer shell of the thermoplastic resin. When the thermally expandable agent is heated to a temperature of, for example, 80 to 120° C., the contained substance is vaporized, and foams and distends due to a pressure of the substance. In this way, the thermally expandable layer  102  expands according to the amount of absorbed heat. The thermally expandable agent is also referred to as a foaming agent. 
     The ink receiving layer  103  is a layer laminated on the upper side of the thermally expandable layer  102  to absorb and receive the ink. The ink receiving layer  103  receives a printing ink used in an ink jet-type printer, a printing toner used in a laser-type printer, a ball pen or fountain pen ink, pencil graphite, and the like. The ink receiving layer  103  is formed of a suitable material for fixing these on a surface. As the material of the ink receiving layer  103 , for example, a general-purpose material used for an ink jet paper can be used. 
       FIG. 2  illustrates the back surface of the thermally expandable sheet  100 . The back surface of the thermally expandable sheet  100  is the surface of the thermally expandable sheet  100  on the side of the base material  101  and corresponds to the back surface of the base material  101 . On the other hand, the front surface of the thermally expandable sheet  100  is the surface of the thermally expandable sheet  100  on the ink receiving layer  103  side and corresponds to the front surface of the ink receiving layer  103 . 
     As illustrated in  FIG. 2 , a plurality of barcodes B is attached on the back surface of the thermally expandable sheet  100  along an edge of the back surface. The barcode B is an identifier for identifying the thermally expandable sheet  100  and is information indicating that the thermally expandable sheet  100  is a dedicated sheet for forming a three-dimensional image. The barcode B is read by the expansion device  50  of the three-dimensional image forming system  1  to be described later and is an identifier for determining whether or not to use the thermally expandable sheet  100  in the expansion device  50 . 
     &lt;Three-Dimensional Image Forming System  1 &gt; 
     Next, with reference to  FIG. 3 , a three-dimensional image forming system  1  for forming a three-dimensional image (three-dimensional object or modeled object) on the thermally expandable sheet  100  will be described. As illustrated in  FIG. 3 , the three-dimensional image forming system (molding system)  1  includes a terminal device  30 , a printing device  40 , and an expansion device  50 . 
     The terminal device  30  is an information processing device such as a personal computer, a smartphone, and a tablet and is a control unit that controls the printing device  40  and the expansion device  50 . As illustrated in  FIG. 4 , the terminal device  30  includes a control unit  31 , a storage unit  32 , an operation unit  33 , a display unit  34 , a recording medium driving unit  35 , and a communication unit  36 . These units are connected by a bus for transmitting signals. 
     The control unit  31  includes a central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM). In the control unit  31 , the CPU reads a control program stored in the ROM and controls the entire operation of the terminal device  30  while using the RAM as a work memory. 
     The storage unit  32  is a nonvolatile memory such as a flash memory or a hard disc and stores a program or data to be performed by the control unit  31 . More specifically, the storage unit  32  stores color image data, front surface foaming data, and back surface foaming data printed by the printing device  40 . 
     The operation unit  33  includes input devices such as a keyboard, a mouse, a button, a touch pad, and a touch panel and accepts an operation from a user. By operating the operation unit  33 , a user can input an operation of editing color image data, front surface foaming data, and back surface foaming data and an operation on the printing device  40  or the expansion device  50 . 
     The display unit  34  includes a display device such as a liquid crystal display and an organic electro luminescence (EL) display and a display driving circuit for displaying an image on the display device. For example, the display unit  34  displays color image data, front surface foaming data, and back surface foaming data. Further, the display unit  34  displays information indicating the current state of the printing device  40  or the expansion device  50  as necessary. 
     The recording medium driving unit  35  reads a program or data recorded on a portable recording medium. The portable recording medium is a compact disc (CD)-ROM, a digital versatile disc (DVD)-ROM, a flash memory provided with a universal serial bus (USB) standard connector, or the like. For example, the recording medium driving unit  35  reads and acquires color image data, front surface foaming data, and back surface foaming data from a portable recording medium. 
     The communication unit  36  has an interface for communicating with an external device including the printing device  40  and the expansion device  50 . The terminal device  30  is connected to the printing device  40  and the expansion device  50  via a wired line such as a flexible cable and a wired local area network (LAN), or a wireless line such as a wireless LAN and Bluetooth (registered trademark). Under the control of the control unit  31 , the communication unit  36  communicates with the printing device  40  and the expansion device  50  according to at least one of the communication standards. 
     &lt;Printing Device  40 &gt; 
     The printing device  40  is a printing unit that prints an image on a front or back surface of the thermally expandable sheet  100 . The printing device  40  is an ink jet printer that prints an image by a method of forming ink droplets and directly spraying it onto a printing medium. 
       FIG. 5  illustrates a detailed configuration of the printing device  40 . As illustrated in  FIG. 5 , the printing device  40  is provided with a carriage  41  capable of reciprocating in a main scanning direction D 2  (X direction) orthogonal to a sub scanning direction D 1  (Y direction) in which the thermally expandable sheet  100  is conveyed. 
     On the carriage  41 , a print head  42  that performs printing and ink cartridges  43  ( 43   k ,  43   c ,  43   m , and  43   y ) that store ink are attached. Color inks of black K, cyan C, magenta M, and yellow Y are contained in the ink cartridges  43   k ,  43   c ,  43   m , and  43   y , respectively. Each color ink is ejected from the corresponding nozzle of the print head  42 . 
     The carriage  41  is slidably supported on a guide rail  44  and is sandwiched by a drive belt  45 . When the drive belt  45  is driven by rotation of a motor  45   m , the carriage  41  moves in the main scanning direction D 2  together with the print head  42  and the ink cartridge  43 . 
     At the bottom of a frame  47 , a platen  48  is provided at a position facing the print head  42 . The platen  48  extends in the main scanning direction D 2  and constitutes a part of a conveying path of the thermally expandable sheet  100 . A paper feed roller pair  49   a  (a lower roller is not illustrated) and a paper discharge roller pair  49   b  (a lower roller is not illustrated) are provided in the conveying path of the thermally expandable sheet  100 . The paper feed roller pair  49   a  and the paper discharge roller pair  49   b  convey the thermally expandable sheet  100  supported by the platen  48  in the sub scanning direction D 1 . 
     The printing device  40  is connected to the terminal device  30  via a flexible communication cable  46 . The terminal device  30  controls the print head  42 , the motor  45   m , the paper feed roller pair  49   a , and the paper discharge roller pair  49   b  via the flexible communication cable  46 . More specifically, the terminal device  30  causes the paper feed roller pair  49   a  and the paper discharge roller pair  49   b  to convey the thermally expandable sheet  100 . Further, the terminal device  30  rotates the motor  45   m  to move the carriage  41  and conveys the print head  42  to an appropriate position in the main scanning direction D 2 . 
     The printing device  40  acquires image data from the terminal device  30  and performs printing based on the acquired image data. More specifically, the printing device  40  acquires color image data, front surface foaming data, and back surface foaming data as image data. The color image data is data indicating a color image to be printed on a front surface of the thermally expandable sheet  100 . The printing device  40  ejects cyan C, magenta M, and yellow Y inks to the print head  42  toward the thermally expandable sheet  100  to print a color image. 
     On the other hand, the front surface foaming data is data indicating a portion to be foamed and expanded on the front surface of the thermally expandable sheet  100 . The back surface foaming data is data indicating a portion to be foamed and expanded on the back surface of the thermally expandable sheet  100 . The printing device  40  ejects black K ink containing carbon black toward the thermally expandable sheet  100  to print a grayscale image (grayscale pattern) by black color on the print head  42 . The black ink containing carbon black is an example of a material that converts an electromagnetic wave into heat (for example, an electromagnetic wave thermal conversion material such as carbon), that is, a material that converts light into heat. 
     &lt;Expansion Device  50 &gt; 
     The expansion device  50  is an expansion unit which irradiates a front or back surface of the thermally expandable sheet  100  with light (electromagnetic waves) to heat a grayscale image printed on the front or back surface of the thermally expandable sheet  100  and expand a portion of the thermally expandable sheet  100  on which the grayscale image is printed. 
       FIG. 6  schematically illustrates a configuration of the expansion device  50 . In  FIG. 6 , the X direction corresponds to the width direction of the expansion device  50 , the Y direction corresponds to the longitudinal direction of the expansion device  50 , and the Z direction corresponds to the vertical direction. The X direction, the Y direction, and the Z direction are orthogonal to each other. As illustrated in  FIG. 6 , the expansion device  50  includes a housing  51 , an insertion portion  52 , a tray  53 , a ventilation unit  54 , a conveyance motor  55 , a conveyance rail  56 , an irradiation unit  60 , a cooling unit  64 , a barcode reader  65 , a power supply board  69 , and a control board  70 . 
     The insertion portion  52  is provided with an openable and closable door and is a mechanism for inserting the thermally expandable sheet  100 , which is a target for forming a three-dimensional image, into the housing  51 . A user opens the insertion portion  52 , slides the tray  53 , and pulls out the tray  53  to the near side, and then disposes the thermally expandable sheet  100  on the tray  53  with its front or back surface facing upward. At this time, a user disposes the thermally expandable sheet  100  on the tray  53  such that the end portion of the thermally expandable sheet  100  to which the barcode B is attached is positioned on the far side. Then, when the tray  53  on which the thermally expandable sheet  100  is disposed is returned to the inside of the housing  51 , and the insertion portion  52  is closed, the thermally expandable sheet  100  is disposed at a position which can be irradiated with light by the irradiation unit  60 . 
     The tray  53  is a mechanism for disposing the thermally expandable sheet  100  at an appropriate position in the housing  51 . The tray  53  functions as an installation unit (installation portion) on which the thermally expandable sheet  100  is disposed.  FIG. 7  illustrates the tray  53  on which the thermally expandable sheet  100  is disposed, as viewed from above (Z direction). As illustrated in  FIG. 7 , the tray  53  is provided with a rectangular frame-like fixing member  57  and fixed by pressing edges of the four sides of the disposed thermally expandable sheet  100  from above by the fixing member  57 . In addition, the tray  53  is provided with a sensor for detecting the thermally expandable sheet  100 , detects whether or not the thermally expandable sheet  100  is disposed, and detects the size of the thermally expandable sheet  100  when the thermally expandable sheet  100  is disposed. 
     The ventilation unit  54  is provided at an end portion on the far side in the expansion device  50  and functions as a ventilation unit for ventilating the inside of the expansion device  50 . The ventilation unit  54  includes at least one exhaust fan and ventilates the inside of the housing  51  by discharging the air inside the housing  51  to the outside. The air in the housing  51  is supplied from the outside by the cooling unit  64  and discharged to the outside by the ventilation unit  54 . The ventilation unit  54  circulates the air inside the housing  51  by discharging the air supplied from the outside by the cooling unit  64  to the outside. 
     The conveyance motor  55  is, for example, a stepping motor that operates in synchronization with pulse electric power and functions as a movement unit that moves the irradiation unit  60  along the front or back surface of the thermally expandable sheet  100 . In the inside of the housing  51 , a conveyance rail  56  is provided in the Y direction, that is, in a direction parallel to the front or back surface of the thermally expandable sheet  100 . The irradiation unit  60  is attached to the conveyance rail  56  so as to be movable along the conveyance rail  56 . The irradiation unit  60  reciprocates along the conveyance rail  56  while keeping a constant distance from the thermally expandable sheet  100  by using a driving force resulting from the rotation of the conveyance motor  55  as a power source. 
     More specifically, the irradiation unit  60  reciprocates between a first position P 1  corresponding to the end portion on the far side of the thermally expandable sheet  100  and a second position P 2  corresponding to the end portion on the near side of the thermally expandable sheet  100 . The first position P 1  is an initial position (home position) of the irradiation unit  60 . The irradiation unit  60  stands by at the first position P 1  when the expansion device  50  is not operating. 
     The first position P 1  is a position on the side opposite to the side where the insertion portion  52  is provided in the housing  51 , and the second position P 2  is a position on the side where the insertion portion  52  is provided in the housing  51 . In other words, the first position P 1  is positioned farther from the end portion of the expansion device  50  on the side where the thermally expandable sheet  100  is inserted than the second position P 2 . Since the initial position of the irradiation unit  60  is provided on the side opposite to the insertion portion  52  in the housing  51 , when a user inserts the thermally expandable sheet  100  into the housing  51 , the user does not touch the irradiation unit  60 . Therefore, a user can dispose the thermally expandable sheet  100  smoothly. 
     The irradiation unit  60  is a mechanism for emitting light. The irradiation unit  60  functions as an irradiation unit (irradiation unit) for irradiating the thermally expandable sheet  100  disposed on the tray  53  with light. As illustrated in  FIG. 6 , the irradiation unit  60  includes a lamp heater  61 , a reflecting plate  62 , a temperature sensor  63 , a cooling unit  64 , and a barcode reader  65 . 
     The lamp heater  61  is provided with, for example, a halogen lamp, and irradiates the thermally expandable sheet  100  with light in a near infrared region (wavelength is 750 to 1400 nm), a visible light region (wavelength is 380 to 750 nm), or a mid-infrared region (wavelength is 1400 to 4000 nm). When the thermally expandable sheet  100  on which a grayscale image is printed by black ink containing carbon black is irradiated with light, the light is more efficiently converted into heat in the portion where the grayscale image is printed than the portion where the grayscale image is not printed. Therefore, the portion of the thermally expandable sheet  100  on which the grayscale image is printed is mainly heated and expands when a thermally expandable agent reaches the temperature at which expansion starts. 
     The reflecting plate  62  is disposed so as to cover the upper side of the lamp heater  61  and is a mechanism that reflects the light emitted from the lamp heater  61  toward the thermally expandable sheet  100 . The temperature sensor  63  is a thermocouple, a thermistor, or the like and functions as a measuring unit that measures a temperature of the reflecting plate  62 . 
     The cooling unit  64  is provided above the reflecting plate  62  and functions as a cooling unit for cooling the inside of the expansion device  50 . The cooling unit  64  includes at least one air supply fan and cools the irradiation unit  60  by sending air from the outside of the expansion device  50  to the irradiation unit  60 . More specifically, the cooling unit  64  sucks air outside the expansion device  50  from the air supply port provided on the upper side of the cooling unit  64  and sends the sucked air to the irradiation unit  60 . The air sucked by the cooling unit  64  is supplied to the reflecting plate  62 , and the reflecting plate  62  is air-cooled. Further, the air sucked by the cooling unit  64  is supplied to the inside of the expansion device  50  through the irradiation unit  60 , and each unit in the housing  51  including the thermally expandable sheet  100  disposed on the tray  53  is cooled. 
     The barcode reader  65  functions as a reading unit for reading the barcode B attached to the back surface of the thermally expandable sheet  100 . When the thermally expandable sheet  100  is inserted into the expansion device  50  with its front surface facing upward, the barcode reader  65  reads the barcode B attached to the back surface of the thermally expandable sheet  100  via a reflector (not illustrated). The reflector is disposed at the end portion on the far side of the tray  53  and is a reflecting mirror for enabling the barcode reader  65  to read the barcode B from the opposite side. On the other hand, when the thermally expandable sheet  100  is inserted into the expansion device  50  with the back surface facing upward, the barcode reader  65  directly reads the barcode B attached to the back surface of the thermally expandable sheet  100  without using the reflector. 
     The expansion device  50  determines whether or not a medium disposed on the tray  53  can be used in the expansion device  50 , depending on whether or not the barcode B can be read by the barcode reader  65 . If a medium that is not a dedicated sheet for forming a three-dimensional image is inserted into the expansion device  50 , the expansion device  50  may not operate properly. Therefore, when the barcode reader  65  cannot read the barcode B, the expansion device  50  does not start a light irradiation process by the irradiation unit  60 . As a result, malfunction of the expansion device  50  is reduced. 
     The power supply board  69  includes a power supply integrated circuit (IC) and the like and generates necessary power and supplies the power to each portion in the expansion device  50 . For example, the ventilation unit  54 , the conveyance motor  55 , the lamp heater  61 , and the cooling unit  64  operate by obtaining power from the power supply board  69 . 
     The control board  70  is provided on a board disposed under the housing  51  and controls operation of each unit of the expansion device  50 . As illustrated in  FIG. 8 , the control board  70  includes a control unit  71 , a storage unit  72 , a clocking unit  73 , and a communication unit  74 . 
     The control unit  71  includes a CPU, a ROM, and a RAM and is connected to each unit of the expansion device  50  via a system bus that is a transmission path for transferring commands and data. The CPU is, for example, a microprocessor and is a central processing unit that performs various processes and operations. In the control unit  71 , the CPU reads the control program stored in the ROM and controls the entire operation of the expansion device  50  while using the RAM as a work memory. 
     The storage unit  72  is a nonvolatile memory such as a flash memory or a hard disc. The storage unit  72  stores programs or data performed by the control unit  71  and data generated or acquired by the control unit  71  performing various processes. The clocking unit  73  includes a clocking device such as a real time clock (RTC) and clocks even while the power of the expansion device  50  is off. 
     The communication unit  74  has an interface for communicating with the terminal device  30 . Under the control of the control unit  71 , the communication unit  74  performs wired or wireless communication with the terminal device  30 . For example, the communication unit  74  acquires, from the terminal device  30 , a command to start a light irradiation process input from a user in the terminal device  30 . Further, the communication unit  74  transmits information indicating the current state of the expansion device  50  to the terminal device  30 . 
     The control unit  71  functions as a control unit that controls operations of the ventilation unit  54 , the conveyance motor  55 , the irradiation unit  60 , and the cooling unit  64 . More specifically, the control unit  71  performs an expansion process for expanding the thermally expandable sheet  100  and a cooling process for cooling the inside of the expansion device  50 . The following will be described in order. 
     &lt;Expansion Process&gt; 
     The control unit  71  performs a process of expanding the thermally expandable sheet  100  by irradiating the thermally expandable sheet  100  disposed on the tray  53  with light by the irradiation unit  60 . Specifically, the control unit  71  moves the irradiation unit  60  by the conveyance motor  55  while causing the irradiation unit  60  to emit light such that the thermally expandable sheet  100  is heated to or above a specified temperature to expand the thermally expandable sheet  100 . 
       FIG. 9  illustrates how the expansion device  50  performs the expansion process. In the expansion process, the control unit  71  supplies a power supply voltage to the irradiation unit  60  to light the lamp heater  61 . At this time, the control unit  71  adjusts the power supply voltage to be supplied to the irradiation unit  60  and causes the irradiation unit  60  to emit light with a predetermined intensity. Then, the control unit  71  moves the irradiation unit  60  from the first position P 1  toward the second position P 2  at a predetermined speed by driving the conveyance motor  55  in the state in which the irradiation unit  60  is emitting light. In the expansion process, the ventilation unit  54  and the cooling unit  64  are not driven. 
     When light is emitted by the irradiation unit  60 , a portion of the thermally expandable sheet  100  on which a grayscale image including carbon black is printed generates heat and expands when being heated to a specified temperature. The specified temperature is a temperature at which the thermally expandable agent included in the thermally expandable layer  102  starts to expand and is, for example, a temperature of about 80° C. to 120° C. The predetermined intensity and speed are preset such that the thermally expandable sheet  100  can be heated to a temperature equal to or higher than the specified temperature. 
     For example, the higher the intensity of the light emitted by the irradiation unit  60  is, the more the thermally expandable sheet  100  receives light and therefore the thermally expandable sheet  100  is further heated. Further, as the movement speed of the irradiation unit  60  is reduced, the irradiation time becomes long, and the thermally expandable sheet  100  is further heated. Therefore, by adjusting at least one of the intensity of the light emitted by the irradiation unit  60  and the movement speed of the irradiation unit  60 , the amount of heat applied to each portion of the thermally expandable sheet  100  can be adjusted. 
     The predetermined intensity and the predetermined speed are set to values that can apply a sufficient amount of heat to the thermally expandable sheet  100  in consideration of such a relationship. The control unit  71  moves the irradiation unit  60  emitting light with a predetermined intensity at a predetermined speed to heat a portion of the thermally expandable sheet  100  on which a grayscale image is printed to a temperature equal to or higher than a specified temperature. As a result, the thermally expandable sheet  100  expands to a height corresponding to the density of black in the grayscale image. 
     &lt;Cooling Process&gt; 
     After performing the expansion process, the control unit  71  performs a cooling process to cool the thermally expandable sheet  100  by the cooling unit  64  while maintaining a state where the thermally expandable sheet  100  is disposed on the tray  53 . 
     Due to the expansion process, the inside of the housing  51  including the thermally expandable sheet  100  contains a lot of heat. When the thermally expandable sheet  100  contains heat, its shape may be distorted and deformed in some cases. For example, the thermally expandable sheet  100  may be warped, that is, arched due to a difference in thermal characteristics of a plurality of layers included in the thermally expandable sheet  100 . In order to suppress the warpage of the thermally expandable sheet  100 , the control unit  71  cools the inside of the housing  51  and the thermally expandable sheet  100  by driving the cooling unit  64  after the expansion process has been performed. 
       FIG. 10  illustrates how the expansion device  50  performs the cooling process. Immediately after the expansion process, the irradiation unit  60  has reached the second position P 2  which is positioned on the near side of the expansion device  50 . In the cooling process, the control unit  71  causes the cooling unit  64  to cool the inside of the expansion device  50  while moving the irradiation unit  60  by the conveyance motor  55 . More specifically, the control unit  71  stops supplying a power supply voltage to the irradiation unit  60  and turns off the lamp heater  61 . Then, the control unit  71  supplies air outside the housing  51  into the housing  51  by driving the cooling unit  64 . The control unit  71  moves the irradiation unit  60  from the second position P 2  toward the first position P 1  by driving the conveyance motor  55  while being cooled by the cooling unit  64 . 
     At this time, the control unit  71  drives the ventilation unit  54  to discharge the air in the housing  51  to the outside. As the cooling unit  64  and the ventilation unit  54  are driven in this manner, as illustrated in  FIG. 10 , the air supplied from the outside by the cooling unit  64  flows to the far side of the expansion device  50  and discharged from the ventilation unit  54 . 
     Since the cooling unit  64  is attached to the irradiation unit  60 , it moves together with the irradiation unit  60 . Therefore, by driving the cooling unit  64  while moving the irradiation unit  60 , it is possible to widely supply the air outside the housing  51  into the housing  51  and to evenly cool the whole of the thermally expandable sheet  100 . In this manner, the control unit  71  cools the thermally expandable sheet  100  after the expansion process has been performed, while moving the cooling unit  64  and in a state where edge portions of the four sides of the sheet are fixed to the tray  53 . As a result, it is suppressed that the thermally expandable sheet  100  is warped after being removed from the tray  53 . 
     &lt;Three-Dimensional Image Forming Process&gt; 
     The flow of a three-dimensional image forming process performed in the three-dimensional image forming system  1  configured as described above will be described with reference to the flowchart indicated in  FIG. 11  and the cross sectional views of the thermally expandable sheet  100  illustrated in  FIGS. 12A to 12E . 
     First, a user prepares the thermally expandable sheet  100  before the three-dimensional image is formed and specifies color image data, front surface foaming data, and back surface foaming data via the operation unit  33  of the terminal device  30 . Then, the thermally expandable sheet  100  is inserted into the printing device  40  with its front surface facing upward. The printing device  40  prints a light-to-heat conversion layer  104  on the front surface of the inserted thermally expandable sheet  100  (step S 1 ). The light-to-heat conversion layer  104  is a layer formed of a material that converts light into heat, specifically, black ink containing carbon black. The printing device  40  ejects black ink containing carbon black on the surface of the thermally expandable sheet  100  according to the specified front surface foaming data. As a result, as illustrated in  FIG. 12A , the light-to-heat conversion layer  104  is formed on the ink receiving layer  103 . 
     Secondly, a user inserts the thermally expandable sheet  100  on which the light-to-heat conversion layer  104  is printed into the expansion device  50  with its front surface facing upward. The expansion device  50  irradiates the front surface of the inserted thermally expandable sheet  100  with light by the irradiation unit  60  (step S 2 ). The light-to-heat conversion layer  104  printed on the front surface of the thermally expandable sheet  100  generates heat by absorbing the emitted light. As a result, as illustrated in  FIG. 12B , a portion of the thermally expandable sheet  100  on which the light-to-heat conversion layer  104  is printed swells and expands. 
     Thirdly, a user inserts the thermally expandable sheet  100  of which front surface has been heated and expanded, into the printing device  40  with its front surface facing upward. The printing device  40  prints a color ink layer  105  on the front surface of the inserted thermally expandable sheet  100  (step S 3 ). Specifically, the printing device  40  ejects inks of cyan C, magenta M, and yellow Y onto the surface of the thermally expandable sheet  100  according to the specified color image data. As a result, as illustrated in  FIG. 12C , the color ink layer  105  is formed on the ink receiving layer  103  and the light-to-heat conversion layer  104 . 
     In the case of printing an image of black or gray color in the color ink layer  105 , the printing device  40  forms the color ink layer  105  by mixing colors of inks of three colors of cyan C, magenta M, and yellow Y, or by further using a black ink that does not contain carbon black. This prevents the portion on which the color ink layer  105  is formed from being heated in the expansion device  50 . 
     Fourthly, a user turns over the thermally expandable sheet  100  on which the color ink layer  105  is printed and inserts the thermally expandable sheet  100  into the expansion device  50  with its back surface facing upward. The expansion device  50  heats the thermally expandable sheet  100  from the back surface by irradiating the back surface of the inserted thermally expandable sheet  100  with light by the irradiation unit  60 . As a result, the expansion device  50  volatilizes solvent contained in the color ink layer  105  to dry the color ink layer  105  (step S 4 ). By drying the color ink layer  105 , the thermally expandable sheet  100  can be easily expanded in a later step. 
     Fifthly, a user inserts the thermally expandable sheet  100  on which the color ink layer  105  is printed into the printing device  40  with its back surface facing upward. The printing device  40  prints the light-to-heat conversion layer  106  on the back surface of the inserted thermally expandable sheet  100  (step S 5 ). As with the light-to-heat conversion layer  104  printed on the front surface of the thermally expandable sheet  100 , the light-to-heat conversion layer  106  is a layer formed of a material that converts light into heat, specifically, black ink containing carbon black. The printing device  40  ejects black ink containing carbon black onto the back surface of the thermally expandable sheet  100  according to the specified back surface foaming data. As a result, as indicated in  FIG. 12D , the light-to-heat conversion layer  106  is formed on the back surface of the base material  101 . 
     Sixthly, a user inserts the thermally expandable sheet  100  on which the light-to-heat conversion layer  106  is printed into the expansion device  50  with its back surface facing upward. The expansion device  50  irradiates the back surface of the inserted thermally expandable sheet  100  with light by the irradiation unit  60  (step S 6 ). The light-to-heat conversion layer  106  printed on the back surface of the thermally expandable sheet  100  generates heat by absorbing the emitted light. As a result, as illustrated in  FIG. 12E , the portion of the thermally expandable sheet  100  on which the light-to-heat conversion layer  106  is printed swells and expands. 
     In  FIGS. 12A to 12E , for clarification, the light-to-heat conversion layer  104  and the color ink layer  105  are formed on the ink receiving layer  103 . However, more precisely, the color ink and the black ink are absorbed inside the ink receiving layer  103 , and therefore the light-to-heat conversion layer  104  and the color ink layer  105  are formed in the ink receiving layer  103 . 
     As described above, a portion of the thermally expandable sheet  100  on which the light-to-heat conversion layers  104  and  106  are formed expands, and a color three-dimensional image is formed on the thermally expandable sheet  100 . Since the light-to-heat conversion layers  104  and  106  are heated as its density increases, the light-heat converting layers  104  and  106  further expand. Therefore, three-dimensional images of various shapes can be obtained by adjusting the density of the light-to-heat conversion layers  104  and  106  according to the target height. 
     Either one of the process of heating the thermally expandable sheet  100  from the front surface and the process of heating from the back surface may be omitted. For example, when only the front surface of the thermally expandable sheet  100  is heated and expanded, steps S 5  and S 6  in  FIG. 11  are omitted. On the other hand, in the case where only the back surface of the thermally expandable sheet  100  is heated and expanded, steps S 1  and S 2  in  FIG. 11  are omitted. Further, printing of the color image in step S 3  may be performed after the process of heating the thermally expandable sheet  100  from the back surface in step S 6 . 
     Further, when forming a monochrome three-dimensional image, the printing device  40  may print a monochrome image instead of a color image in step S 3 . In this case, a layer of black ink is formed on the ink receiving layer  103  and the light-to-heat conversion layer  104  instead of the color ink layer  105 . 
     Next, with reference to the flowchart indicated in  FIG. 13 , the details of the process performed by the expansion device  50  in steps S 2  and S 6  will be described. 
     In step S 2 , a user places the thermally expandable sheet  100  on the tray  53  with its front surface facing upward and inserts the sheet into the expansion device  50 . In step S 6 , a user places the thermally expandable sheet  100  on the tray  53  with its back surface facing upward and inserts the sheet into the expansion device  50 . Thereafter, a user operates the operation unit  33  of the terminal device  30  and inputs a command to expand the thermally expandable sheet  100 . When the control unit  71  of the expansion device  50  receives the command input from the user from the terminal device  30  in this way, the control unit  71  starts the process indicated in  FIG. 13 . 
     When the process is started, the control unit  71  determines whether or not the thermally expandable sheet  100  is properly disposed (step S 11 ). More specifically, the control unit  71  determines whether or not the thermally expandable sheet  100  is disposed at a proper position on the tray  53  via a sensor provided in the tray  53 . 
     When the thermally expandable sheet  100  is not disposed properly (step S 11 ; NO), the control unit  71  stops the process in step S 11 . At this time, by issuing a warning, the control unit  71  notifies a user that the thermally expandable sheet  100  is not properly disposed and requests the user to properly dispose the thermally expandable sheet  100 . 
     If the thermally expandable sheet  100  is disposed properly (step S 11 ; YES), the control unit  71  determines whether or not the barcode B attached to the back surface of the thermally expandable sheet  100  can be read via the barcode reader  65  (step S 12 ). The barcode B is an identifier for determining whether or not to use the thermally expandable sheet  100  and is provided at the end portion on the far side of the thermally expandable sheet  100  disposed on the tray  53 . 
     When it is not possible to read the barcode B attached to the thermally expandable sheet  100  (step S 12 ; NO), the control unit  71  returns the process to step S 11 . At this time, the control unit  71  notifies a user that the thermally expandable sheet  100  cannot be used and requests the user to replace the thermally expandable sheet  100  with an appropriate sheet. 
     When the barcode B can be read (step S 12 ; YES), the control unit  71  performs preheating (step S 13 ). The preheating is a process of preliminarily heating the irradiation unit  60  before the expansion device  50  starts a main operation. More specifically, the control unit  71  turns on the lamp heater  61 , heats the irradiation unit  60  to a predetermined temperature, and then drives the cooling unit  64  to cool the irradiation unit  60 . 
     When the preheating is performed, the control unit  71  performs an expansion process (step S 14 ). More specifically, the control unit  71  turns on the lamp heater  61  and causes the irradiation unit  60  to emit light with predetermined intensity. Then, as illustrated in  FIG. 9 , the control unit  71  drives the conveyance motor  55  to move the irradiation unit  60  emitting the light with the predetermined intensity from the first position P 1  toward the second position P 2  at a predetermined speed. As a result, the control unit  71  heats a portion of the thermally expandable sheet  100  on which a grayscale image is printed to a temperature equal to or higher than a specified temperature to expand the thermally expandable sheet  100 . Step S 14  is an example of the expansion step. 
     After performing the expansion process, the control unit  71  performs the cooling process (step S 15 ). More specifically, the control unit  71  turns off the lamp heater  61 , causes the irradiation unit  60  to stop emitting light, and drives the cooling unit  64 . Then, as indicated in  FIG. 10 , the control unit  71  drives the conveyance motor  55  while cooling by the cooling unit  64  to move the irradiation unit  60  from the second position P 2  toward the first position P 1 . As a result, the control unit  71  cools the thermally expandable sheet  100  heated in the expansion process and suppresses warpage of the thermally expandable sheet  100 . Step S 15  is an example of the cooling step. 
     As described above, the expansion device  50  according to the first embodiment expands the thermally expandable sheet  100  by causing the irradiation unit  60  to emit light while moving the irradiation unit  60  along the thermally expandable sheet  100 . After the expansion process of the thermally expandable sheet  100  is performed, the cooling process is performed in the expansion device  50 . By performing the cooling process after the expansion process, since the thermally expandable sheet  100  heated in the expansion process can be cooled, it is possible to suppress warpage and deformation of the thermally expandable sheet  100 . 
     In particular, the expansion device  50  according to the first embodiment heats the thermally expandable sheet  100  by moving the irradiation unit  60 , not by moving the thermally expandable sheet  100 . Therefore, it is possible to cool the thermally expandable sheet  100  by a simple method of emitting light while moving the irradiation unit  60  after the expansion process. 
     Further, the expansion device  50  according to the first embodiment performs the expansion process when the irradiation unit  60  is moved from the first position P 1  toward the second position P 2  and performs the cooling process when the irradiation unit  60  is moved from the second position P 2  toward the first position P 1 . As described above, since the expansion device  50  performs the expansion process and the cooling process while the irradiation unit  60  reciprocates once between the first position P 1  and the second position P 2 , the expansion device  50  can efficiently performs the expansion process and the cooling process. 
     Second Embodiment 
     Next, a second embodiment of the present invention will be described. In the second embodiment, description of the same configuration as that of the first embodiment will be omitted. 
     In the first embodiment, the expansion device  50  has performed the expansion process for expanding the thermally expandable sheet  100  and the cooling process for cooling the inside of the expansion device  50 . In contrast, in the second embodiment, in addition to the expansion process and the cooling process, the expansion device  50  performs a drying process for drying the thermally expandable sheet  100  and a ventilation process for ventilating the inside of the expansion device  50 . 
       FIG. 14  indicates a flow of the processes performed by the expansion device  50  according to the second embodiment. Similarly to  FIG. 13 , the processes indicated in  FIG. 14  are started upon receipt of a command to expand the thermally expandable sheet  100  from a user via a terminal device  30  in a state in which the thermally expandable sheet  100  is inserted into the expansion device  50  with its front or back surface facing upward. Since the processes in steps S 21  to S 23  in  FIG. 14  are the same as the processes in steps S 11  to S 13  in  FIG. 13 , the description thereof will be omitted. 
     &lt;Drying Process&gt; 
     When preheating is performed in step S 23 , the control unit  71  performs a drying process (step S 24 ). In the drying process, a control unit  71  causes an irradiation unit  60  to emit light while moving the irradiation unit  60  by a conveyance motor  55  such that the thermally expandable sheet  100  is maintained at a temperature lower than the specified temperature to dry the thermally expandable sheet  100 . Step S 24  is an example of a drying step. 
     The thermally expandable sheet  100  may contain moisture, for example, when the ink applied in the printing device  40  is not sufficiently dried, or due to factors such as surrounding environment. When the thermally expandable sheet  100  contains a large amount of moisture, the thermally expandable sheet  100  is not heated to a temperature needed to expand the thermally expandable sheet  100 , and it becomes difficult to expand the thermally expandable sheet  100  to a desired height. To suppress such a situation and to expand the thermally expandable sheet  100  with high accuracy, the expansion device  50  performs the drying process of the thermally expandable sheet  100  before performing the expansion process of the thermally expandable sheet  100 . 
       FIG. 15  illustrates how the expansion device  50  performs the drying process. In the drying process, the control unit  71  supplies a power supply voltage to the irradiation unit  60  to turn on a lamp heater  61 . At this time, the control unit  71  causes the irradiation unit  60  to emit light with the first intensity by adjusting a power supply voltage to be supplied to the irradiation unit  60 . Then, the control unit  71  moves the irradiation unit  60  from the first position P 1  toward the second position P 2  at the first speed by driving the conveyance motor  55  in the state in which the irradiation unit  60  is emitting light. In the drying process, a ventilation unit  54  and a cooling unit  64  are not driven. 
     When light is emitted by the irradiation unit  60 , a portion of the thermally expandable sheet  100  on which a grayscale image including carbon black is printed generates heat. In the drying process, the control unit  71  dries the thermally expandable sheet  100  without expanding the sheet. Therefore, the first intensity and the first speed are preset such that the thermally expandable sheet  100  can be maintained below a specified temperature at which a thermally expandable agent starts to expand, in other words, such that the thermally expandable sheet  100  is not heated to a temperature equal to or higher than a specified temperature. 
     For example, the higher the intensity of the light emitted by the irradiation unit  60  is, the more the thermally expandable sheet  100  receives a large amount of light, and therefore the thermally expandable sheet  100  is further heated. Further, as the movement speed of the irradiation unit  60  is reduced, the irradiation time becomes long, and the thermally expandable sheet  100  is further heated. Therefore, by adjusting at least one of the intensity of the light emitted by the irradiation unit  60  and the movement speed of the irradiation unit  60 , the amount of heat applied to each portion of the thermally expandable sheet  100  can be adjusted. 
     In consideration of such a relationship, the first intensity and the first speed are set to values that can apply to the thermally expandable sheet  100  an amount of heat that does not expand the sheet. The control unit  71  maintains the thermally expandable sheet  100  at a temperature lower than the specified temperature by moving the irradiation unit  60  emitting light with the first intensity at the first speed. As a result, moisture contained in the thermally expandable sheet  100  is evaporated and dried. 
     &lt;Ventilation Process&gt; 
     After performing the drying process, the control unit  71  performs a ventilation process (step S 25 ). In the ventilation process, the control unit  71  causes the ventilation unit  54  to ventilate the inside of the expansion device  50  while moving the irradiation unit  60  by the conveyance motor  55 . Step S 25  is an example of a ventilation step. 
     By the drying process, the air in the housing  51  contains moisture evaporated from the thermally expandable sheet  100 . To remove moisture in the housing  51 , the control unit  71  ventilates the inside of the housing  51  by driving the ventilation unit  54  after performing the drying process. 
       FIG. 16  indicates how the expansion device  50  performs the ventilation process. In the ventilation process, the ventilation unit  54  ventilates the inside of the expansion device  50  by sending the air inside the expansion device  50  in the direction in which the irradiation unit  60  moves in a return path after the irradiation unit  60  moves along the thermally expandable sheet  100  in the drying process and discharging the air outside the expansion device  50 . More specifically, immediately after the drying process, the irradiation unit  60  reaches the second position P 2  which is the near side of the expansion device  50 . In the ventilation process, the control unit  71  stops supplying the power supply voltage to the irradiation unit  60  and turns off the lamp heater  61 . Then, the control unit  71  drives the ventilation unit  54  to exhaust the air inside the housing  51  to the outside. The control unit  71  moves the irradiation unit  60  from the second position P 2  toward the first position P 1  by driving the conveyance motor  55  in a state in which the ventilation unit  54  is ventilating. 
     In the drying process, since the irradiation unit  60  moves from the first position P 1  toward the second position P 2 , moisture evaporated from the thermally expandable sheet  100  is contained more in the farther side than the irradiation unit  60 . Since the ventilation unit  54  is disposed at an end portion on the far side of the expansion device  50 , it is possible to efficiently remove moisture contained on the farther side than the irradiation unit  60 . In particular, by moving the irradiation unit  60  from the near side to the far side, it is possible to send the air inside the housing  51  toward the far side, such that the air from the ventilation unit  54  disposed at the end portion on the far side can be efficiently ventilated. 
     &lt;Expansion Process&gt; 
     After performing the ventilation process, the control unit  71  performs an expansion process (step S 26 ). The expansion process in the second embodiment is the same as the expansion process in the first embodiment. Step S 26  is an example of an expansion step. 
     More specifically, the control unit  71  turns on the lamp heater  61  and causes the irradiation unit  60  to emit light with the second intensity. Then, as illustrated in  FIG. 9 , the control unit  71  drives the conveyance motor  55  to move the irradiation unit  60  emitting light with the second intensity from the first position P 1  toward the second position P 2  at a second speed. As a result, the control unit  71  heats a portion of the thermally expandable sheet  100  on which a grayscale image is printed to a temperature equal to or higher than a specified temperature to expand the thermally expandable sheet  100 . 
     Here, since the thermally expandable sheet  100  is irradiated with a greater amount of light than in the drying process, the second intensity is set to a value higher than the first intensity in the drying process. As an example, the second intensity is set to the intensity about two to three times the first intensity. Further, the second intensity is set to a value higher than the first intensity, or alternatively, the second speed is set to a value lower than the first speed in the drying process. As an example, the second speed is set to a speed of about half to one third of the first speed. Since the second speed is set to a value lower than the first speed, the moving time of the irradiation unit  60  is longer than that in the drying process. Therefore, it is possible to irradiate the thermally expandable sheet  100  with more light. 
     &lt;Cooling Process&gt; 
     After performing the expansion process, the control unit  71  performs the cooling process (step S 27 ). The cooling process in the second embodiment is the same as the cooling process in the first embodiment. Step S 27  is an example of a cooling step. 
     More specifically, the control unit  71  turns off the lamp heater  61 , causes the irradiation unit  60  to stop emitting light, and drives the cooling unit  64 . Then, as illustrated in  FIG. 10 , the control unit  71  drives the conveyance motor  55  while cooling by the cooling unit  64  to move the irradiation unit  60  from the second position P 2  toward the first position P 1 . As a result, the control unit  71  cools the thermally expandable sheet  100  heated in the expansion process and suppresses warpage of the thermally expandable sheet  100 . 
     As described above, the expansion device  50  according to the second embodiment performs the drying process and the ventilation process before performing the expansion process of the thermally expandable sheet  100 . By performing the drying process before the expansion process, it is possible to prevent the thermally expandable sheet  100  from being difficult to heat in the expansion process. Therefore, the thermally expandable sheet  100  can be expanded with high accuracy. Further, by performing the ventilation process after the drying process, moisture evaporated from the thermally expandable sheet  100  by the drying process can be removed from the inside of the expansion device  50 . 
     In addition, the expansion device  50  according to the second embodiment performs the drying process when the irradiation unit  60  is moved from the first position P 1  toward the second position P 2 , performs the ventilation process when the irradiation unit  60  is moved from the second position P 2  toward the first position P 1 , performs the expansion process when the irradiation unit  60  is moved from the first position P 1  toward the second position P 2 , and performs the cooling process when the irradiation unit  60  is moved from the second position P 2  toward the first position P 1 . As described above, the expansion device  50  performs the drying process, the ventilation process, the expansion process, and the cooling process while the irradiation unit  60  reciprocates twice between the first position P 1  and the second position P 2 . Therefore, these four processes can be efficiently performed. 
     (Variation) 
     Although the embodiments of the present invention have been described above, the above-described embodiments are merely an example, and the application range of the present invention is not limited thereto. That is, the embodiments of the present invention can be applied in various ways, and all embodiments fall within the scope of the present invention. 
     For example, in the above embodiment, the control unit  71  performs each of the drying process, the ventilation process, the expansion process, and the cooling process when the irradiation unit  60  is moved from the first position P 1  toward the second position P 2  or when the irradiation unit  60  is moved from the second position P 2  toward the first position P 1 . However, in the present invention, the control unit  71  is not limited to performing these processes only in an outward path or a return path, and if necessary, to perform each process, the irradiation unit  60  may be reciprocated once or a plurality of times between the first position P 1  and the second position P 2 . 
     Further, the number of times or order of performing the drying process, the ventilation process, the expansion process, and the cooling process is not limited to those described in the above embodiments. For example, the control unit  71  may perform the ventilation process after the expansion process, or omit the drying process or the ventilation process. 
     In the above embodiments, the control unit  71  performs the cooling process when the irradiation unit  60  is returned from the second position P 2  to the first position P 1  by the conveyance motor  55 . However, in the present invention, as long as the control unit  71  can cool the inside of the expansion device  50  including the thermally expandable sheet  100  after the expansion process, the control unit  71  may perform the cooling process when the irradiation unit  60  is not moving. 
     In the above-described embodiments, the cooling unit  64  is attached to the irradiation unit  60  and moved together with the irradiation unit  60 . However, in the present invention, the cooling unit  64  may be provided at a position other than the irradiation unit  60  as long as it can cool the inside of the expansion device  50  including the thermally expandable sheet  100 . Further, in the above-described embodiments, the ventilation unit  54  is provided at the end portion on the far side of the expansion device  50 . However, in the present invention, the ventilation unit  54  may be provided in other position as long as it can ventilate the inside of the expansion device  50 . 
     In the above-described embodiment, the initial position (home position) of the irradiation unit  60  has been on the far side of the expansion device  50 . However, the initial position of the irradiation unit  60  may be on the near side of the expansion device  50 . When the initial position of the irradiation unit  60  is on the near side of the expansion device  50 , it can be explained in the same way as in the above embodiment by reversing the positional relationship between the first position P 1  and the second position P 2 . 
     In the above-described embodiment, as illustrated in  FIG. 7 , the tray  53  is disposed so as to press the four sides of the thermally expandable sheet  100  by the fixing member  57 . However, in the present invention, as long as the thermally expandable sheet  100  can be fixed, it is not necessary for all of the four sides to be pressed down by the tray  53 . For example, as indicated in  FIGS. 17A and 17B , the tray  53  may be disposed so as to press two opposed sides by two rod-shaped fixing members  57 . Alternatively, as illustrated in  FIGS. 17C and 17D , the tray  53  may be provided so as to press two opposing sides by two point-like fixing members  57 . As described above, the tray  53  may be disposed to press at least two sides facing each other out of the four sides of the thermally expandable sheet  100 . 
     Further, as illustrated in  FIG. 18A , the tray  53  may be disposed to press the four corners of the thermally expandable sheet  100  with four point-like fixing members  57 . Alternatively, as indicated in  FIGS. 18B and 18C , the tray  53  may be disposed to press two corners facing each other out of four corners of the thermally expandable sheet  100  by the two point-like fixing members  57 . The two corners facing each other are two corners connected by a diagonal line in the rectangular thermally expandable sheet  100 . In this manner, the tray  53  may be disposed to press at least two corners facing each other out of the four corners of the thermally expandable sheet  100 . 
     In the above-described embodiments, the thermally expandable sheet  100  includes the base material  101 , the thermally expandable layer  102 , and the ink receiving layer  103 . However, in the present invention, the configuration of the thermally expandable sheet  100  is not limited thereto. For example, the thermally expandable sheet  100  may not include the ink receiving layer  103 . Alternatively, the thermally expandable sheet  100  may be provided with a layer of any other material between the base material  101  and the thermally expandable layer  102  or between the thermally expandable layer  102  and the ink receiving layer  103 . 
     In the above-described embodiments, the terminal device  30 , the printing device  40 , and the expansion device  50  are independent devices. However, in the present invention, at least two of the terminal device  30 , the printing device  40 , and the expansion device  50  may be integrated. 
     The printing method of the printing device  40  is not limited to an ink jet method. For example, the printing device  40  is a laser-type printer, and an image may be printed with a toner and a developer. In addition, the light-to-heat conversion layers  104  and  106  may be formed of a material other than black ink containing carbon black as long as it is a material that easily converts light into heat. In this case, the light-to-heat conversion layers  104  and  106  may be formed by a unit other than the printing device  40 . 
     In the above-described embodiment, the control unit  71  of the expansion device  50  includes a CPU and performs a drying process for drying the thermally expandable sheet  100 , a ventilation process for ventilating the inside of the expansion device  50 , an expansion process for expanding the thermally expandable sheet  100 , and a cooling process for cooling the inside of the expansion device  50 . However, in the expansion device  50  according to the present invention, the control unit  71  may include dedicated hardware such as an application specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or various control circuits, instead of CPU, and the dedicated hardware may perform each of the drying process, the ventilation process, the expansion process, and the cooling process. In this case, each process may be performed by individual hardware, or all the processes may be performed by single hardware. In addition, some of the processes may be performed by dedicated hardware, and others may be performed by software or firmware. 
     Note that, in addition to providing the expansion device with the configuration for realizing the functions according to the present invention, each functional configuration by the expansion device  50  exemplified in the above-described embodiments can be realized in a computer controlling the expansion device by applying a program. That is, a program for realizing each functional configuration by the expansion device  50  exemplified in the above embodiments can be applied such that a CPU or the like for controlling an existing information processing device or the like can execute the program. 
     A method of applying such a program is arbitrary. The program can be stored in a computer readable recording medium such as a flexible disc, a compact disc (CD)-ROM, a digital versatile disc (DVD)-ROM, or a memory card. Furthermore, the program may be superimposed on a carrier wave and applied via a communication medium such as the Internet. For example, a program may be distributed by posing on a bulletin board (BBS: Bulletin Board System) on a communication network. Then, the above-described processes may be performed by starting up this program and executing it under the control of an operation system (OS) as with other application programs. 
     The preferable embodiments according to the present invention have been described above. However, the present invention is not limited to the specific embodiment, and the invention described in Claims and a scope equivalent thereto are included in the present invention.