Patent Publication Number: US-11383528-B2

Title: Liquid discharge apparatus

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-195038, filed on Oct. 28, 2019, in the Japan Patent Office and Japanese Patent Application No. 2020-154804, filed on Sep. 15, 2020, in the Japan Patent Office, the entire disclosures of which are hereby incorporated by reference herein. 
     BACKGROUND 
     Technical Field 
     Aspects of the present disclosure relate to a liquid discharge apparatus. 
     Related Art 
     Various apparatuses control a preheating operation during a printing operation. For example, an image forming apparatus may be used as a plurality of image recording apparatuses such as a copier, a facsimile, and a printer. 
     The image forming apparatus includes a temperature detector and a controller of a heating element, a device to change a preheating temperature of the heating element, and a counter to count a number of image formation for each of the above-described functions in a predetermined time. 
     The image forming apparatus controls the preheating temperature of the heating element according to a counting result of the counter. Further, the controller of the heating element of the image forming apparatus has two states of a power saving state and a standby state. The controller of the heating element controls to switch between the two states of the power saving state and the standby state based on the counting result of the counter. 
     SUMMARY 
     In an aspect of this disclosure, a liquid discharge apparatus includes a heater configured to heat a medium, a detector configured to detect a temperature of the heater, a conveyor configured to convey the medium during a printing operation, and circuitry configured to control the heater to heat the medium with a first output during a preheating operation before the printing operation, control the heater to heat the medium with a second output that is equal to or higher than the first output when the temperature of the heater reaches a predetermined threshold value to complete the preheating operation, and control the conveyor to start conveying the medium to start the printing operation. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The aforementioned and other aspects, features, and advantages of the present disclosure will be better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  are schematic perspective view of an inkjet recording apparatus according to an embodiment of the present disclosure; 
         FIG. 2  is a schematic plan view of a carriage scanner of the inkjet recording apparatus of  FIG. 1 ; 
         FIG. 3  is a cross-sectional side view of the inkjet recording apparatus including a dryer illustrated in  FIG. 1 ; 
         FIG. 4  is a block diagram illustrating a functional configuration of the inkjet recording apparatus according to the embodiment of the present disclosure; and 
         FIG. 5  is a graph illustrating a preheating operation performed in the inkjet recording apparatus according to the embodiment of the present disclosure. 
     
    
    
     The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. 
     DETAILED DESCRIPTION 
     In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this patent specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have the same function, operate in a similar manner, and achieve similar results. 
     Although the embodiments are described with technical limitations with reference to the attached drawings, such description is not intended to limit the scope of the disclosure and all of the components or elements described in the embodiments of this disclosure are not necessarily indispensable. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. 
     Hereinafter, a liquid discharge apparatus according to an embodiment of the present disclosure is described with reference to the accompanying drawings. The liquid discharge apparatus according to an embodiment of the present disclosure has following features in a serial type inkjet recording apparatus using an infrared heater. That is, the liquid discharge apparatus controls to enter the preheating operation of the infrared heater before the printing operation is started when a print job is input to the liquid discharge apparatus. 
     Therefore, the liquid discharge apparatus can satisfy dry quality of image at a print start portion of a recording medium. Further, the liquid discharge apparatus controls the preheating operation so that the preheating temperature of the preheating operation is lower than a heating temperature during an actual printing operation. Thus, the preheating operation at the preheating temperature does not actually damage the recording medium. 
     Therefore, the liquid discharge apparatus can prevent damage on the recording medium such as deformation and melting of the recording medium due to the preheating operation. The liquid discharge apparatus thus controls the preheating operation to determine completion of the preheating operation at timing when an internal temperature of the infrared heater becomes equal to or higher than a predetermined threshold value. Then, the liquid discharge apparatus shifts from the preheating operation to the printing operation. 
     The above features of the embodiments of the present disclosure are described below in detail with reference to the following drawings. 
       FIG. 1  are schematic perspective view of the inkjet recording apparatus  100  serving as the liquid discharge apparatus according to the embodiment of the present disclosure.  FIG. 2  is a schematic plan view of a carriage scanner of the inkjet recording apparatus  100  of  FIG. 1 . As illustrated in  FIGS. 1 and 2 , the inkjet recording apparatus  100  includes a guide rod  1  and a sub-guide rail  2  bridged between both side plates of the inkjet recording apparatus  100 . The inkjet recording apparatus  100  includes a carriage  5  held by the guide rod  1  and the sub-guide rail  2 . 
     The carriage  5  is reciprocally movable in a main-scanning direction indicated by arrow “A.” The carriage  5  is connected to a timing belt  11  wound around a drive pulley  7  and a pressure pulley  10  (see  FIG. 2 ). The inkjet recording apparatus  100  includes a main-scanning motor  9  to move the timing belt  11  via the drive pulley  7  to reciprocally move the carriage  5  in the-main scanning direction A. 
     The pressure pulley  10  applies a tension to the timing belt  11  so that the carriage  5  can be driven without sagging. A “home position” indicated by a line “P” is set above a maintenance mechanism  26 , for example. The home position is also simply referred to as “HP.” 
     The recording medium  150  is intermittently conveyed in a sub-scanning direction indicated by arrow “B” below a scanning area of the carriage  5  in which the carriage  5  reciprocally moves. 
     The sub-scanning direction B is also referred to as a “conveyance direction” of the recording medium  150 . The inkjet recording apparatus  100  includes recording heads  6  ( 6   k ,  6   c ,  6   m , and  6   y ) mounted on the carriage  5 . The recording heads  6  ( 6   k  to  6   y ) discharge ink as liquid droplets onto the recording medium  150  to form a predetermined image on the recording medium  150  on a platen  16 . Hereinafter, the recording heads  6   k ,  6   c ,  6   m , and  6   y  are simply referred to as the “heads  6 .” 
     Each of the heads  6  includes a plurality of nozzles to discharge ink from the plurality of nozzles. The recording medium  150 , on which the image is formed, is dried by a dryer  17  that faces an ejection guide  32  (see  FIG. 3 ). The dryer  17  includes a drying heater. The inkjet recording apparatus  100  includes a cartridge  60  and the maintenance mechanism  26 . The cartridge  60  (see  FIG. 1 ) supplies the ink to the heads  6  (see  FIG. 3 ). 
     The maintenance mechanism  26  performs a maintenance operation on the heads  6  mounted on the carriage  5 . The inkjet recording apparatus  100  includes a main-scanning encoder sensor  13  in the carriage  5 . Hereinafter, the main-scanning encoder sensor  13  is simply referred to as an “encoder sensor  13 .” 
     The encoder sensor  13  sequentially reads an encoder sheet  14  bridged between the both side plates. The inkjet recording apparatus  100  thus drives the carriage  5  between two side plates while detecting a position of the carriage  5  in the main-scanning direction A. 
     Further, the inkjet recording apparatus  100  includes a medium detection sensor  20  attached to the carriage  5 . The medium detection sensor  20  is, for example, a reflection type sensor. The medium detection sensor  20  includes a light emitting diode (LED) to emits light on the recording medium  150  and detects a reflected light reflected from the recording medium  150  to detect presence or absence of an object (recording medium  150 ) that faces the medium detection sensor  20 . 
     The inkjet recording apparatus  100  according to the embodiment of the present disclosure recognizes an exterior area of the platen  16  (area outside a right end  16   a  of the platen  16 , for example), an upper area of the platen  16 , and an upper area of the recording medium  150  (area between a left end  150   a  and a right end  150   b  of the recording medium  150 ) according to a value of the reflected light. The “exterior area of the platen  16 ” is an area immediately below the carriage  5  and is also referred to as a “platen outer area.” The upper area of the platen  16  is also referred to as a “platen upper area.” The upper area of the recording medium  150  is also referred to as a “medium upper area.” 
       FIG. 3  is a cross-sectional side view of the inkjet recording apparatus  100  including the dryer  17  illustrated in  FIG. 1 . A left side of the inkjet recording apparatus  100  in  FIG. 3  corresponds to a front side of the inkjet recording apparatus  100  as illustrated in  FIG. 1 . The recording medium  150  is conveyed from a right side to the left side in the conveyance direction of the recording medium  150  as indicated by arrow “D”. Hereinafter, the conveyance direction of the recording medium  150  is simply referred to as a “conveyance direction D.” 
     Further, the conveyance direction D is identical with the “sub-scanning direction B” in  FIG. 1 . The inkjet recording apparatus  100  includes four heaters, a preheater  17 - 1 , a print heater  17 - 2 , a post heater  17 - 3 , and an infrared heater  17 - 4  in an order from the right side (upstream side) to the left side (downstream side) in the conveyance direction D on a conveyance path of the recording medium  150 . 
     The preheater  17 - 1  is also referred to as a “first heater”. The infrared heater  17 - 4  is also referred to as a “second heater.” The preheater  17 - 1  contacts the recording medium  150  to heat the recording medium  150 . The infrared heater  7 - 4  heats the recording medium  150  without contacting the recording medium  150  (in a non-contact manner). 
     The preheater  17 - 1  heats the recording medium  150  at a preheating area upstream of a printing area in the conveyance direction D before the recording medium  150  is conveyed to the printing area at which the recording medium  150  faces the head  6 . The preheater  17 - 1  heats the recording medium  150  from a back side (lower side) of the recording medium  150  conveyed in the conveyance direction D to the preheating area. The preheater  17 - 1  gradually heats the recording medium  150  from a downstream side of the recording medium according to a conveyance of the recording medium  150  in the conveyance direction D. 
     Thus, the ink discharged from the heads  6  and landed onto the recording medium  150  easily evaporates by heat applied on the recording medium  150  by the preheater  17 - 1  (preheating operation). The print heater  17 - 2  heats the recording medium  150  onto which an image is formed by the ink (liquid droplets) discharged from the heads  6 . The print heater  17 - 2  heats the ink on the recording medium  150  to evaporate water content in the ink so that a dried ink surface forms a film (ink set) on the recording medium  150 . 
     The ink surface is film-formed to form a membrane on the ink surface. The print heater  17 - 2  heats and dries the ink to extent so that the ink does not adhered to a hand even when the ink is touched with the hand. The film-forming of the ink is also referred to as an “ink set” because a spread and a size of ink droplets (dots) are determined at the time of film-forming. 
     The print heater  17 - 2  is the most important heater to form an image on the recording medium  150 . The post heater  17 - 3  further heats the recording medium  150  at a post-heating area downstream of the print area in the conveyance direction D to evaporate the water content and solvent in the ink to dry the ink. The infrared heater  17 - 4  faces a front surface (upper surface) of the recording medium  150 . The infrared heater  17 - 4  heats an ink surface from an interior of the ink by far infrared rays (IR). Thus, the infrared heater  17 - 4  causes a polymerization reaction in resin in the ink by the far infrared rays (IR) to cure the ink. 
     The preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  respectively include thermistors  17 - 1   a ,  17 - 2   a , and  17 - 3   a  serving as temperature sensors (detectors) to respectively measure temperatures of conveyance surfaces of the preheating area, the print area, and the post-heating area of the conveyance path heated by the preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3 . The inkjet recording apparatus  100  controls the preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  according to a measurement results of the thermistors  17 - 1   a ,  17 - 2   a , and  17 - 3   a  (temperature sensors) to control the temperature the conveyance surface of the preheating area, the print area, and the post-heating area in the conveyance path. 
     The thermistors  17 - 1   a ,  17 - 2   a , and  17 - 3   a  are used as the temperature sensors (detectors) and are attached to the back side of a conveyance surface of the conveyance path. Further, the preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  respectively includes thermostats  17 - 1   b ,  17 - 2   b , and  17 - 3   b . The thermostats  17 - 1   b ,  17 - 2   b , and  17 - 3   b  also serves as the detector in the embodiments of the present disclosure. 
     Thus, the thermostats  17 - 1   b ,  17 - 2   b , and  17 - 3   b  are turned off when each of the preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  becomes out of control and cause an abnormal temperature rises. The preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  and the thermostats  17 - 1   b ,  17 - 2   b , and  17 - 3   b  are electrically serially connected. When a power to the thermostat  17 - 1   b ,  17 - 2   b , and  17 - 3   b  is cut off, the power supply to the preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  is also cut off to ensure the safety. 
     The infrared heater  17 - 4  includes at least one or more (two in  FIG. 3 ) infrared heater  17 - 4   a , a thermopile  17 - 4   b , a thermistor  17 - 4   c , a thermostat  17 - 4   d , a curing fan  17 - 4   e , and a reflection plate  17 - 4   f . The infrared heater  17 - 4   a  is a heat source. The thermopile  17 - 4   b  is a non-contact temperature sensor that measures the surface temperature of the recording medium  150 . 
     The thermistor  17 - 4   c  measures a temperature of the reflection plate  17 - 4   f  to measure a temperature inside the infrared heater  17 - 4 . The thermostat  17 - 4   d  disconnects an electrical connection from the power source to the infrared heater  17 - 4  during abnormal heating to secure safety of the infrared heater  17 - 4 . The curing fan  17 - 4   e  generates an air flow to control an increase in humidity near the recording medium  150  to accelerate drying of the ink on the recording medium  150 . 
     The curing fan  17 - 4   e  further blows air to the infrared heater  17 - 4  to control overheating of the infrared heater  17 - 4 . The reflection plate  17 - 4   f  reflects infrared rays emitted from the infrared heater  17 - 4   a  toward the recording medium  150  to accelerate heating of the recording medium  150 . The infrared heater  17 - 4  includes a thermopile  17 - 4   b  to control temperature of the infrared heater  17 - 4 . The thermopile  17 - 4   b  is a non-contact temperature sensor. The thermopile  17 - 4   b  measures temperature at a front surface (upper surface) of the recording medium  150 . 
     The inkjet recording apparatus  100  controls an output of the infrared heater  17 - 4   a  so that the surface temperature of the recording medium  150  becomes a desired temperature. The thermistor  17 - 4   c , as a second temperature sensor, is mounted on a reflection plate  17 - 4   f . The thermistor  17 - 4   c  measures a temperature of the reflection plate  17 - 4   f . The thermistor  17 - 4   c  monitors whether the temperature in the infrared heater  17 - 4  abnormally increases and determines whether the preheating operation is completed. 
       FIG. 4  is a block diagram illustrating a functional configuration of the inkjet recording apparatus  100  according to the embodiment of the present disclosure. As illustrated in  FIG. 4 , the inkjet recording apparatus  100  includes a controller  400  (circuitry) to perform various controls in the inkjet recording apparatus  100  according to the embodiments of the present disclosure. 
     For example, the controller  400  includes a central processing unit (CPU)  401 , a field-programmable gate array (FPGA)  402 , and a motor driver  403 . The CPU  401 , the FPGA  402 , and the motor driver  403  performs various controls performed by the inkjet recording apparatus  100  such as a CPU control, a memory control, an ink discharge control, a sensor control, and a motor control. 
     Further, as illustrated in  FIGS. 1 and 2 , the inkjet recording apparatus  100  includes the main-scanning motor  9 , the carriage  5  driven by the main-scanning motor  9 , the heads  6  (recording heads) mounted on the carriage  5 , and the encoder sensor  13 , and the medium detection sensor  20 . 
     The encoder sensor  13  is also referred to as a “main-scanning encoder sensor.” The inkjet recording apparatus  100  includes a sub-scanning motor  404  and a conveyor  405  to be driven by the sub-scanning motor  404 . The conveyor  405  includes a sub-scanning encoder sensor  4051  and a conveyance roller  4052 . The sub-scanning encoder sensor  4051  detects a conveyance amount of the recording medium  150  in the sub-scanning direction B (conveyance direction D). The conveyance roller  4052  conveys the recording medium  150  in the sub-scanning direction B (conveyance direction D). 
     Further, the inkjet recording apparatus  100  includes various mechanisms to be provided to an ordinary recording apparatus. Examples of the various mechanisms include a winding device including a winding motor, a winding roller, and a winding encoder sensor, a feeding device including a feed motor, and a feed roller, and a feed encoder sensor, for example. The dryer  17  includes the preheater  17 - 1 , the print heater  17 - 2 , the post heater  17 - 3 , and the infrared heater  17 - 4 . The dryer  17  includes “M” number of the preheaters  17 - 1  in which the preheater  17 - 1  is divided into M number in the sub-scanning direction B. 
     The dryer  17  includes “N” number of the print heaters  17 - 2  in which the print heater  17 - 2  is divided into N number in the main-scanning direction A. The dryer  17  includes “K” number of the post heaters  17 - 3  in which the post heater  17 - 3  is divided into K number in the main-scanning direction A and the sub-scanning direction B. The dryer  17  includes “L” number of the infrared heaters  17 - 4  in which the infrared heater  17 - 4  is divided into L number in the main-scanning direction A. The number of the infrared heater  17 - 4  may be one (L=1). 
     Further, the dryer  17  includes the temperature sensors to measure the temperatures of the preheaters  17 - 1 , the print heaters  17 - 2 , the post heaters  17 - 3 , and the infrared heaters  17 - 4  divided into various number of M, N, L, and L, respectively. For example, the preheater  17 - 1  includes the thermistor  17 - 1   a  serving as the temperature sensor. The print heater  17 - 2  includes the thermistor  17 - 2   a  as the temperature sensor. The post heater  17 - 3  includes the thermistor  17 - 3   a  as the temperature sensor. 
     Further, the infrared heater  17 - 4  includes a thermistor  17 - 4   c  as the temperature sensor (second temperature sensor) and a thermopile  17 - 4   b  as the non-contact temperature sensor. The controller  400  controls each of an output of the preheater  17 - 1 , the print heater  17 - 2 , the post heater  17 - 3 , and the infrared heater  17 - 4  so that each of the preheater  17 - 1 , the print heater  17 - 2 , the post heater  17 - 3 , and the infrared heater  17 - 4  to reach a target temperature based on values of the above-described temperature sensors (the thermistors  17 - 1   a ,  17 - 2   a , and  17 - 3   a , the thermopile  17 - 4   b , and the thermistor  17 - 4   c ). 
       FIG. 5  is a graph illustrating a preheating operation performed in the inkjet recording apparatus  100  according to the embodiment of the present disclosure. As illustrated in  FIG. 5 , each of the preheater  17 - 1 , the print heater  17 - 2 , the post heater  17 - 3 , and the infrared heater  17 - 4  starts the preheating operation when the controller  400  determines that a print job is input to the controller  400 . When the preheating operation is completed, the controller  400  starts conveyance of the recording medium  150  and the print operation. 
     The preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  are heaters that heats the recording medium  150  by a heat transferred from the back side (lower side in  FIG. 3 ) of the recording medium  150  via a guide plate  18 . The controller  400  completes the preheating operation when the temperature of each portions (the preheating area, the print area, and the post heating area) of the guide plate  18  monitored by each thermistor  17 - 1   a ,  17 - 2   a , and  17 - 3   a , the thermopile  17 - 4   b , and the thermistor  17 - 4   c  reaches the target temperature. 
     The infrared heater  17 - 4  is not in direct contact with the recording medium  150 . Thus, the controller  400  measures the surface temperature of the recording medium  150  with the thermopile  17 - 4   b  as the non-contact temperature sensor and monitors the surface temperature of the recording medium  150 . The infrared heater  17 - 4   a  provided in the infrared heater  17 - 4  has a good temperature response to the recording medium  150 . 
     Thus, the temperature of the recording medium  150  rises quickly even if the infrared heater  17 - 4   a  is not sufficiently warmed in a state in which the recording medium  150  is stopped. Therefore, if the controller  400  starts the printing operation because the surface temperature of the recording medium  150  reaches the target temperature, heat quantity of the infrared heater  17 - 4   a  cannot follow (reach) the target temperature when the recording medium  150  starts moving because the infrared heater  17 - 4   a  is not sufficiently warmed. Thus, it becomes difficult for the dryer  17  to maintain the temperature of the recording medium  150   
     From the above, it is not sufficient to measure only the surface temperature of the recording medium  150  by the thermopile  17 - 4   b  as a condition for completion of the preheating operation of the infrared heater  17 - 4 . Therefore, the controller  400  measures the temperature of the thermistor  17 - 4   c  as the condition for completion of the preheating operation of the infrared heater  17 - 4 . The thermistor  17 - 4   c  is the second temperature sensor that monitors the temperature of the reflection plate  17 - 4   f  in the infrared heater  17 - 4 . 
     Thus, if the infrared heater  17 - 4   a  is sufficiently heated, the controller  400  can determine that the temperature of the thermistor  17 - 4   c  in the vicinity of the infrared heater  17 - 4   a  also exceeds a predetermined threshold value. Thus, the controller  400  appropriately sets the threshold value to satisfy the condition for completion of the preheating operation. 
     The preheating operation of the infrared heater  17 - 4  is described below with reference to  FIG. 5 . The controller  400  turns on the infrared heater  17 - 4   a  when the controller determines that the print job has been input to the controller  400 . When the infrared heater  17 - 4   a  is turned on, the temperature of the surface of the recording medium  150  increases. The controller  400  controls the infrared heater  17 - 4   a  so that the detected temperature  501  of the thermopile  17 - 4   b  becomes a control temperature B ° C. during the preheating operation. The “control temperature during the preheating operation” is also referred to as a “control temperature during preheating (B ° C.).” 
     When the controller  400  determines that the temperature of the thermopile  17 - 4   b  has reached the control temperature during preheating (B ° C.), the detected temperature  502  of the thermistor  17 - 4   c  is lower than a preheating target temperature “T” and is in a state of gradually increasing. The preheating target temperature T is the predetermined threshold value as described above. The controller  400  continues the preheating operation while keeping the thermopile  17 - 4   b  at the control temperature during preheating (B ° C.) until the temperature of the thermistor  17 - 4   c  reaches the preheating target temperature T. Then, the controller  400  determines that the preheating operation is completed at timing “t” when the detected temperature  502  of the thermistor  17 - 4   c  exceeds the preheating target temperature T. 
     At the timing t, the controller  400  starts (enters) the printing operation P and conveys the recording medium when the detected temperature  502  of the thermistor  17 - 4   c  reaches the predetermined threshold value (preheating target temperature T) so that the controller  400  can determine that the preheating operation of the preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  have already been completed. The controller  400  controls the thermopile  17 - 4   b  so that the detected temperature  501  of the thermopile  17 - 4   b  becomes the control temperature (A ° C.) during the printing operation. The “control temperature during the printing operation” is also referred to as a “control temperature during printing (A ° C.).” 
     The control temperature during printing (A ° C.) is equal to or higher than the control temperature during preheating (A≥B). The control temperature during printing (A ° C.) is a temperature in which a predetermined difference temperature “d” is added to the control temperature during preheating (B ° C.). The controller  400  controls to maintain the temperature of the thermopile  17 - 4   b  to be the control temperature during preheating (B ° C.) until completion of the preheating operation and also after completion of the preheating when the controller  400  determines that the preheating operation of the preheater  17 - 1 , the print heater  17 - 2 , and the post heater  17 - 3  have not been completed. 
     The controller  400  sets the temperature of the thermopile  17 - 4   b  to the control temperature during printing (A ° C.) as the temperature needed to dry the ink on the recording medium  150 . Since the control temperature during printing (A ° C.) has to be a high temperature to a degree, the control temperature during printing (A ° C.) is a temperature at which the recording medium  150  may be damaged or burnt. 
     However, if the recording medium  150  is conveyed, time taken for application of the control temperature during printing (A ° C.) on the recording medium  150  is limited. Thus, the recording medium  150  is not damaged by the control temperature during printing (A ° C.). Therefore, if the recording medium  150  is stopped (not conveyed) while the control temperature during printing (A ° C.) is applied to the recording medium  150 , excessive heat quantity may be applied to the recording medium  150 . Thus, a risk of damaging the recording medium  150  such as deformation or burnt of the recording medium  150  may occur. 
     Therefore, the controller  400  sets the temperature of the thermopile  17 - 4   b  to be the control temperature during printing (B ° C.) that does not damage the recording medium  150  even when the recording medium  150  is stopped (not conveyed). The controller  400  according to the embodiment of the present disclosure controls a temperature difference between the control temperature during printing (A ° C.) and the control temperature during preheating (B ° C.) to become the difference temperature d. 
     When the controller  400  determines that the recording medium  150  is not damaged (or the damage is less than a predetermined reference value) even when the recording medium  150  is stopped at the control temperature during printing (A ° C.), the controller  400  may set the control temperature during printing (A ° C.) and the control temperature during preheating (B ° C.) to the same temperature (d=0 and A=B). 
     The values of the control temperature during printing (A ° C.) and the control temperature during preheating (B ° C.) are different for each recording medium  150 , for example, for each type of recording medium  150 . For example, when the inkjet recording apparatus  100  prints on the recording medium  150  having different permeability, the controller  400  sets the temperature of the thermopile  17 - 4   b  to temperature higher than the control temperature during printing (A ° C.) because the recording medium  150  having low permeability needs more energy to be dried than the recording medium  150  having higher permeability. 
     The controller  400  changes the control temperature during preheating (B ° C.) according to a heat-resistant temperature of the recording medium  150 . Thus, the controller  400  changes the temperature difference “d” between the control temperature during printing (A ° C.) and the control temperature during preheating (B ° C.) according to the types of the recording medium  150 . 
     Therefore, the controller  400  stores a unique value of the control temperature during printing (A ° C.) and the control temperature during preheating (B ° C.) for each recording medium  150  in a storage medium such as a memory. Further, the controller  400  calls the above unique values from the storage medium such as the memory and executes the above-described control process. 
     For example, the controller  400  sets different values for the control temperature during printing (A ° C.) and the control temperature during preheating (B ° C.) for each type of the recording medium  150  made of polyvinyl chloride (PVC) and the recording medium  150  made of polyethylene terephthalate (PET) as illustrated in Table 1 below. 
     
       
         
           
               
               
               
               
             
               
                 TABLE 1 
               
               
                   
               
               
                 TYPES OF 
                 CONTROL 
                 CONTROL 
                 DETECTED 
               
               
                 RECORDING 
                 TEMPERATURE 
                 TEMPERATURE 
                 TEMPERATURE 
               
               
                 MEDIUM 
                 “A” 
                 “B” 
                 502 
               
               
                   
               
             
            
               
                   
               
            
           
           
               
               
               
               
            
               
                 PVC 
                 90 
                 70 
                 50 
               
               
                 PET 
                 70 
                 60 
                 50 
               
               
                   
               
            
           
         
       
     
     In Table 1, the detected temperature  502  is a fixed value. However, the value of the detected temperature  502  may differ according to a difference in a position at which the control temperature during preheating (B ° C.) and the detected temperature  502  of the thermistor  17 - 4   c  are measured and design layout. In such a case, the controller  400  may set the value of the detected temperature  502  of the thermistor  17 - 4   c  within a range of approximately 50 to 100% with respect to the control temperature during preheating (B ° C.). 
     As illustrated in  FIG. 5 , the controller  400  may output a control signal  503  to stop operating (turns OFF) the curing fan  17 - 4   e  until the controller  400  determines that the preheating operation is completed to accelerate the preheating operation of the infrared heater  17 - 4 . When the controller  400  determines that the preheating operation is completed, the controller  400  may output a control signal  504  to start operating (turning ON) the curing fan  17 - 4   e . The controller  400  stops the curing fan  17 - 4   e  to prevent the infrared heater  17 - 4   a  and the reflection plate  17 - 4   f  from cooling and to quickly complete the preheating operation. Further, the controller  400  operates the curing fan  17 - 4   e  after completion of the preheating operation to prevent an interior of the infrared heater  17 - 4  from overheating. 
     Further, the inkjet recording apparatus  100  may include an operation panel  15  or a communication unit  19  so that the controller  400  can receive an operation related to the preheating operation such as a setting of preheating time from the user via the operation panel  15  or the communication unit  19 . The communication unit  19  of the inkjet recording apparatus  100  is communicable with an operation terminal such as a smartphone via wireless communication. Thus, the operation panel  15  or the communication unit  19  receives the operation related to the preheating operation. 
     The controller  400  may execute the preheating operation of the inkjet recording apparatus  100  according to the operation received from the operation panel  15  or from the communication unit  19  via the wireless communication when the controller  400  determines that the operation is received from the operation panel  15  or the communication unit  19 . The controller  400  performs such controls to set, change and delete the time of preheating operation by intention of the user. 
     Thus, the controller  400  can obtain balance between dry quality according to individual requirements of each user and damage to the recording medium  150 . Further, the controller  400  may control a heating process of the recording medium  150  based on the control temperature during preheating (B ° C.) and the control temperature during printing (A ° C.) received from the user via the operation panel  15  according to the type of the recording medium  150  when the inkjet recording apparatus  100  includes the above-described operation panel. 
     The controller  400  thus can set above-described values according to a request from each user. 
     The inkjet recording apparatus  100  according to the embodiment of the present disclosure includes a serial-type inkjet printer for industrial use. The inkjet recording apparatus  100  performs dry control of media and ink. The inkjet recording apparatus  100  heats the recording medium  150  by a heater such as the infrared heater  17 - 4 . The heater such as the infrared heater  17 - 4  heats the recording medium  150  with a first output such as the control temperature during preheating (B ° C.) before a start of the printing operation. 
     When the temperature of the heater (infrared heater  17 - 4 , for example) reaches a predetermined threshold value (preheating target temperature T, for example), the controller  400  controls the heaters (infrared heater  17 - 4 , for example) with a second output such as the control temperature during printing (A ° C.) that is higher than the first output such as the control temperature during preheating (B ° C.). 
     The inkjet recording apparatus  100  includes a controller such as the controller  400  including the CPU  401 , the FPGA  402 , and the motor driver  403 , for example, to start conveyance of the recording medium  150  by the conveyor  405 , for example. Thus, the controller  400  of the inkjet recording apparatus  100  can control the preheating operation while avoiding damage to the recording medium  150  and improving the image quality. Specifically, the controller  400  can soften a sudden temperature change on the recording medium  150 , reduce deformation and cockling of the recording medium  150 , and reduce an occurrence of jam. 
     The heater includes the infrared heater  17 - 4   a , a first temperature sensor (thermopile  17 - 4   b , for example) that detects a surface temperature of the recording medium  150 , and a second temperature sensor (thermistor  17 - 4   c , for example) that detects an inner temperature of the infrared heater  17 - 4 . The controller  400  continuously output the first output until the first temperature sensor (thermopile  17 - 4   b , for example) detects the first temperature that is the control temperature during preheating (B ° C.). 
     When the second temperature sensor (thermistor  17 - 4   c ) detects that the inner temperature of the infrared heater  17 - 4  becomes (reaches) the predetermined threshold value (preheating target temperature T), the controller  400  changes the output of the infrared heater  17 - 4  from the first output (B ° C.) to the second output (A ° C.). Therefore, the serial-type inkjet recording apparatus  100  using the heater to dry the ink on the recording medium  150  can satisfy dry quality even for the image at the print start portion on the recording medium  150  and prevent defects such as medium deformation and melting. 
     Further, the controller  400  performs a heating with the first output and a heating with the second output according to the type of the recording medium  150 . Thus, the controller  400  sets the unique value according to the type of each recording medium  150  to ensure the dry quality regardless of the type of the recording medium  150  used and avoid the damage to the recording medium  150 . 
     Further, the heater (infrared heater  17 - 4 , for example) includes a fan (curing fan  17 - 4   e , for example) to control the heating process of the heaters. The controller  400  stops the fan (curing fan  17 - 4   e ) until the temperature of the heater (infrared heater  17 - 4 ) reaches the predetermined threshold value (preheating target temperature T). The controller  400  then operates the fan (curing fan  17 - 4   e ) after the temperature of the heater (infrared heater  17 - 4 ) reaches a predetermined threshold value (preheating target temperature T). 
     Therefore, the inkjet recording apparatus  100  can prevent cooling of a portion, at which the infrared heater  17 - 4  and the second temperature sensor (thermistor  17 - 4   c ) are disposed, and quickly complete the preheating operation. 
     Each of the functions of the described embodiments may be implemented by one or more processing circuits or circuitry. Processing circuitry includes a programmed processor, as a processor includes circuitry. A processing circuit also includes devices such as an application specific integrated circuit (ASIC), digital signal processor (DSP), field programmable gate array (FPGA), and conventional circuit components arranged to perform the recited functions. For example, the controller  400  (circuitry) as described above may be implemented by one or more processing circuits or circuitry. 
     Numerous additional modifications and variations are possible in light of the above teachings. It is therefore to be understood that, within the scope of the above teachings, the present disclosure may be practiced otherwise than as specifically described herein. With some embodiments having thus been described, it is obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the scope of the present disclosure and appended claims, and all such modifications are intended to be included within the scope of the present disclosure and appended claims.