Print medium drying unit, printer, and print medium temperature estimation method

Abstract

An infrared sensor 56(1) is disposed so as to be tilted toward a Dw1 side (first side) in the width direction Dw with respect to the surface Ma of a print medium M. Therefore, temperatures in a relatively wide range of the surface Ma of the print medium M can be detected by the infrared sensor 56(1). Moreover, an infrared sensor 56(2) is disposed so as to be tilted toward a Dw2 side in the width direction Dw with respect to the surface Ma of the print medium M. Therefore, temperatures in a relatively wide range of the surface Ma of the print medium M can be detected by the infrared sensor 56(2).

Description

Print medium drying unit, printing apparatus, and print medium temperature estimation method

[0001] The present invention relates to a technology for estimating the temperature of a print medium.

[0002] Patent Document 1 discloses a drying apparatus that dries ink ejected onto a medium. This drying apparatus includes a heater that heats the medium, and controls the heater based on the temperature of the medium detected by a sensor.

[0003] Japanese Unexamined Patent Application Publication No. 2015-168089

[0004] Incidentally, in recent years, the types of print media have diversified, and print media having a large width may be used in some cases. For this reason, there has been a demand for a technology capable of detecting temperature over a wide range in the width direction of the print medium. However, the detection range in which a temperature sensor can detect temperature is limited to a predetermined angular range centered on the temperature detection unit.

[0005] Accordingly, it is conceivable to place the temperature sensor sufficiently far from the print medium so that the wide print medium is included in the detection range of the temperature sensor. However, it is difficult to secure a large gap between the temperature sensor and the print medium in an apparatus including many components. Alternatively, it is conceivable to arrange a plurality of temperature sensors facing the print medium from a short distance in the width direction, and detect the temperature of the print medium with each temperature sensor. However, providing a plurality of temperature sensors causes an increase in cost.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to obtain the temperature of a wide print medium with a small number of temperature sensors arranged close to the print medium.

[0007] The printing apparatus according to the present invention comprises a transport unit for transporting a printing medium having a predetermined width in the width direction, a heater unit for heating and drying the printing medium, a temperature detection unit for detecting the temperature of the printing medium, and a heater control unit for controlling the heater unit based on the temperature detected by the temperature detection unit. The temperature detection unit includes a first infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward the first side in the width direction with respect to the surface of the printing medium, and a second infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward the second side opposite to the first side in the width direction with respect to the surface of the printing medium. The first infrared sensor detects infrared radiation emitted from each of M1 (M1 is an integer of 2 or more) first detection areas that overlap and are arranged in the width direction on the surface of the printing medium, and the first detection area The heater control unit outputs first temperature data indicating the temperature of the printing medium for each of the M1 first detection areas, the second infrared sensor detects infrared radiation emitted from each of the M2 (M2 is an integer greater than or equal to 2) second detection areas that overlap and are arranged in the width direction on the surface of the printing medium, and outputs second temperature data indicating the temperature of each of the M2 second detection areas, and the heater control unit estimates the temperature of the printing medium based on the first temperature data output by the first infrared sensor for at least N1 (N1 is an integer greater than or equal to 1 and less than M1) first detection areas counted from the first side out of the M1 first detection areas, and the second temperature data output by the second infrared sensor for at least N2 (N2 is an integer greater than or equal to 1 and less than M2) second detection areas counted from the second side out of the M2 second detection areas.

[0008] The printing medium temperature estimation method according to the present invention is a printing medium temperature estimation method using a printing medium temperature estimation unit comprising: a transport unit for transporting a printing medium having a predetermined width in the width direction; a temperature detection unit for detecting the temperature of the printing medium; and a temperature estimation unit for estimating the temperature of the printing medium based on the temperature detected by the temperature detection unit, wherein the temperature detection unit comprises: a first infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward a first side in the width direction with respect to the surface of the printing medium; and a second infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward a second side opposite to the first side in the width direction with respect to the surface of the printing medium, wherein the first infrared sensor detects infrared radiation emitted from each of M1 (M1 is an integer of 2 or more) first detection areas arranged in the width direction on the surface of the printing medium and outputs first temperature data indicating the temperature of the first detection area for each of the M1 first detection areas, The second infrared sensor detects infrared radiation emitted from each of M2 second detection areas (where M2 is an integer greater than or equal to 2) arranged in the width direction on the surface of the printing medium, and outputs second temperature data indicating the temperature of each of the M2 second detection areas. The temperature estimation unit estimates the temperature of the printing medium based on first temperature data output by the first infrared sensor for at least N1 first detection areas (where N1 is an integer greater than or equal to 1 and less than M1) counted from the first side out of M1 first detection areas, and second temperature data output by the second infrared sensor for at least N2 second detection areas (where N2 is an integer greater than or equal to 1 and less than M2) counted from the second side out of M2 second detection areas.

[0009] The printing apparatus according to the present invention comprises a dispensing unit for dispensing ink onto a printing medium and the above-mentioned printing medium drying unit for drying the printing medium.

[0010] In the present invention (printing medium drying unit, printing apparatus, and printing medium temperature estimation method) configured as described above, two infrared sensors (first and second infrared sensors) are used to estimate the temperature of the printing medium. The first infrared sensor detects infrared radiation emitted from M1 first detection areas arranged in the width direction of the printing medium and outputs first temperature data indicating the temperature of each of the M1 first detection areas. The second infrared sensor detects infrared radiation emitted from M2 second detection areas arranged in the width direction of the printing medium and outputs second temperature data indicating the temperature of each of the M2 second detection areas.

[0011] The first infrared sensor is positioned at a first angle in the width direction relative to the surface of the printing medium. Compared to the case where the first infrared sensor is positioned perpendicular to the printing medium (i.e., the first infrared sensor is positioned directly facing the printing medium without tilting), tilting the first infrared sensor allows each first detection area on the surface of the printing medium to be expanded in the width direction. Therefore, the temperature of a relatively wide area on the surface of the printing medium can be detected by the first infrared sensor. The second infrared sensor is positioned at a second angle in the width direction relative to the surface of the printing medium. Compared to the case where the second infrared sensor is positioned perpendicular to the printing medium (i.e., the second infrared sensor is positioned directly facing the printing medium without tilting), tilting the second infrared sensor allows each second detection area on the surface of the printing medium to be expanded in the width direction. Therefore, the temperature of a relatively wide area on the surface of the printing medium can be detected by the second infrared sensor.

[0012] Furthermore, the widthwise spread of the first detection area becomes more pronounced the further it is from the first infrared sensor. Consequently, the further the first detection area is from the first infrared sensor towards the second side, the more distorted its shape becomes. The reliability of the first temperature data obtained for such a distorted first detection area is low. In other words, the temperature data calculated for the first detection area on the first side has higher reliability. Similarly, the widthwise spread of the second detection area becomes more pronounced the further the second detection area is from the second infrared sensor. Consequently, the further the second detection area is from the second infrared sensor towards the first side, the more distorted its shape becomes. Consequently, the reliability of the second temperature data obtained for such a distorted second detection area is low. In other words, the temperature data calculated for the second detection area on the second side has higher reliability. In contrast, the temperature of the printing medium is estimated based on first temperature data output by the first infrared sensor for at least N1 first detection areas counting from the first side, and second temperature data output by the second infrared sensor for at least N2 second detection areas counting from the second side. In other words, the temperature of the printing medium can be estimated based on relatively reliable first and second temperature data.

[0013] In this way, the first and second infrared sensors are positioned diagonally to ensure a wide range in which each infrared sensor can detect temperature, and the temperature of the printing medium is estimated based on the first and second temperature data, which have relatively high reliability. As a result, it is possible to determine the temperature of a wide printing medium using a small number of infrared sensors positioned close to the printing medium.

[0014] Alternatively, the printing medium drying unit may be configured such that M1 is an integer greater than N1, M2 is an integer greater than N2, and the heater control unit estimates the temperature of the printing medium by executing a normal temperature estimation mode. In the normal temperature estimation mode, the heater control unit uses the first temperature data output by the first infrared sensor for N1 first detection areas to estimate the temperature of the printing medium, while not using the first temperature data output by the first infrared sensor for first detection areas other than the N1 first detection areas. Furthermore, the printing medium drying unit may be configured such that the second temperature data output by the second infrared sensor for N2 second detection areas is used to estimate the temperature of the printing medium, while not using the second temperature data output by the second infrared sensor for second detection areas other than the N2 second detection areas. In such a configuration, it is possible to suppress the influence of unreliable first and second temperature data on the estimation of the printing medium's temperature.

[0015] Furthermore, the printing medium drying unit may be configured to include an abnormality detection unit that detects abnormalities in the temperature detection unit, and when the abnormality detection unit detects an abnormality in the first infrared sensor, the heater control unit executes a first abnormal temperature estimation mode, and when the abnormality detection unit detects an abnormality in the second infrared sensor, it executes a second abnormal temperature estimation mode, and in the first abnormal temperature estimation mode, the heater control unit uses all of the second temperature data output by the second infrared sensor for each of the M2 second detection areas to estimate the temperature of the printing medium, and does not use the first temperature data output by the first infrared sensor to estimate the temperature of the printing medium, and in the second abnormal temperature estimation mode, the heater control unit uses all of the first temperature data output by the first infrared sensor for each of the M1 first detection areas to estimate the temperature of the printing medium, and does not use the second temperature data output by the second infrared sensor to estimate the temperature of the printing medium.

[0016] Furthermore, the printing media drying unit may be configured such that the abnormality detection unit detects an abnormality in the first infrared sensor if any of the first temperature data output for each of the M1 first detection areas falls outside a predetermined first normal range, and detects an abnormality in the second infrared sensor if any of the second temperature data output for each of the M2 second detection areas falls outside a predetermined second normal range. This allows for appropriate detection of abnormalities in the first and second infrared sensors.

[0017] Furthermore, the heater control unit may be configured to store a storage unit that stores a first correction table showing a first correction amount for correcting the first temperature data corresponding to each of the M1 first detection areas, and a second correction table showing a second correction amount for correcting the second temperature data corresponding to each of the M2 second detection areas. The heater control unit estimates the temperature of the first target detection area, which is the target of temperature estimation among the M1 first detection areas, by correcting the first temperature data output for the first target detection area with a first correction amount corresponding to the first target detection area, and estimates the temperature of the second target detection area, which is the target of temperature estimation among the M2 second detection areas, by correcting the second temperature data output for the second target detection area with a second correction amount corresponding to the second target detection area. In such a configuration, the first and second temperature data can be appropriately corrected in response to the distortion of the shape of the first and second detection areas due to the diagonal arrangement of the first and second infrared sensors. As a result, the temperature of the printing medium can be accurately estimated.

[0018] Furthermore, the printing medium drying unit may be configured to include a light-shielding section, wherein the transport section transports the printing medium in a transport direction perpendicular to the width direction, and the light-shielding section has a light-shielding member positioned on at least one side of the transport direction of an infrared passage range through which infrared rays emitted from M1 first detection ranges and incident on the first infrared sensor pass, and infrared rays emitted from M2 second detection ranges and incident on the second infrared sensor pass, and the light-shielding member prevents infrared rays from entering the first and second infrared sensors from outside the infrared passage range in the transport direction. In such a configuration, stray light can be prevented from entering the first and second infrared sensors.

[0019] As described above, according to the present invention, it is possible to determine the temperature of a wide printing medium using a small number of temperature sensors placed in close proximity to the printing medium.

[0020] A schematic diagram showing an example of a printing apparatus according to the present invention. A schematic diagram showing the configuration of the heater. A schematic diagram showing the configuration of the infrared sensor. A block diagram showing the electrical configuration of the drying section. A schematic diagram showing the positional relationship between the infrared sensor located on one side in the width direction of the two infrared sensors of the temperature detection section and the printing medium. A schematic diagram showing the positional relationship between the infrared sensor located on the other side in the width direction of the two infrared sensors of the temperature detection section and the printing medium. A schematic diagram showing the positional relationship between the two infrared sensors of the temperature detection section and the printing medium. A flowchart showing a first example of temperature estimation performed by the control unit. A diagram showing an example of a correction table used in the temperature estimation of Figure 5. A diagram showing an example of a correction table used in the temperature estimation of Figure 5. A schematic diagram showing the relationship between the detection area of ​​the infrared sensor and the heating area of ​​the lamp. A schematic diagram showing a method for estimating the temperature of the heating area from the estimated temperature of the detection area. A flowchart showing a second example of temperature estimation performed by the control unit. A schematic diagram showing an example of a light-shielding section that can be placed relative to the temperature detection section. A flowchart showing the temperature estimation according to this modified example, performed by the control unit 591. Figure showing Table 1. Figure showing Table 2. Figure showing Table 3. Figure showing Table 4. Figure showing Table 5. Figure showing Table 6. Figure showing Table 7. Figure showing Table 8.

[0021] Figure 1 is a schematic diagram showing an example of a printing apparatus according to the present invention. In this figure, the horizontal direction X, the horizontal direction Y perpendicular to the X direction, and the vertical direction Z are shown. The X1 and X2 sides of the X direction are also shown. Here, the X1 and X2 sides face opposite each other.

[0022] The printing apparatus 1 comprises a printing apparatus body 2, a dispensing unit 11 for dispensing a printing medium M into the printing apparatus body 2, and a winding unit 12 for winding the printing medium M from the printing apparatus body 2. The dispensing unit 11 has a dispensing roller 111, and the winding unit 12 has a winding roller 121. The printing apparatus body 2 is positioned between the dispensing unit 11 and the winding unit 12 in the X direction. The printing apparatus body 2 prints an image on the printing medium M, which is conveyed roll-to-roll from the dispensing roller 111 to the winding roller 121. The printing medium M is made of, for example, paper or film.

[0023] The printing apparatus body 2 includes a transport unit 3 that transports the printing medium M by a plurality of rollers R in the transport direction Dc from the unwinding roller 111 toward the winding roller 121. Furthermore, the printing apparatus body 2 includes a printing unit 4 that prints an image on the printing medium M transported by the transport unit 3, and a drying unit 5 that dries the printing medium M transported by the transport unit 3. The drying unit 5 is located downstream of the printing unit 4 in the transport direction Dc of the printing medium M and dries the printing medium M on which the image has been printed by the printing unit 4.

[0024] The transport unit 3 has a loading unit 31 that transports the printing medium M fed out by the loading roller 111 of the loading unit 11. The loading unit 31 transports the medium upward in the Z direction. The transport unit 3 also has a printing transport unit 32 that transports the printing medium M that has been transported upward in the Z direction by the transport of the loading unit 31. The printing transport unit 32 transports the printing medium M toward the X1 side toward the drying unit 5. The roller R of the printing transport unit 32 transports the printing medium M while in contact with the back surface Mb of the printing medium M. The printing unit 4 has a plurality of print heads 41 arranged along the printing medium M that is transported in the transport direction Dc by the printing transport unit 32. The plurality of print heads 41 eject ink of different colors onto the surface Ma (the side opposite the back surface Mb) of the printing medium M using an inkjet method. In this way, a color image is printed on the surface Ma of the printing medium M.

[0025] The transport unit 3 has a drying transport unit 33 that transports the printing medium M within the drying unit 5. The drying transport unit 33 has a pre-stage drying transport unit 331 that transports the printing medium M that has been brought into the drying unit 5 from the printing transport unit 32. The pre-stage drying transport unit 331 transports the printing medium M so as to descend as it moves toward the X1 side. The drying transport unit 33 has an intermediate drying transport unit 332 that transports the printing medium M that has been transported toward the X1 side by the pre-stage drying transport unit 331. The intermediate drying transport unit 332 transports the printing medium M toward the downward side in the Z direction. The drying transport unit 33 has an intermediate transport unit 333 that transports the printing medium M that has been transported toward the downward side by the intermediate drying transport unit 332. The intermediate transport unit 333 transports the printing medium M toward the X2 side. The drying transport unit 33 has a final stage drying transport unit 334 that transports the printing medium M that has been transported toward the X2 side by the intermediate transport unit 333. The subsequent drying and conveying unit 334 conveys the printing medium M upward in the Z direction. The drying and conveying unit 33 has a final conveying unit 335 that unloads the printing medium M that has been conveyed upward by the subsequent drying and conveying unit 334. The final conveying unit 335 conveys the printing medium M to the X1 side, then to the X2 side, and then conveys the printing medium M downward in the Z direction.

[0026] Thus, within the drying section 5, the pre-stage drying and conveying section 331, the middle stage drying and conveying section 332, the intermediate conveying section 333, the post-stage drying and conveying section 334, and the final stage conveying section 335 are arranged in order in the conveying direction Dc of the printing medium M. The pre-stage drying and conveying section 331, the middle stage drying and conveying section 332, the intermediate conveying section 333, and the post-stage drying and conveying section 334 support the printing medium M with rollers R that contact the back surface Mb of the printing medium M, and do not have rollers R that contact the front surface Ma. In contrast, the final stage conveying section 335 supports the printing medium M with rollers R that contact the back surface Mb and rollers R that contact the front surface Ma.

[0027] The transport unit 3 has an unloading unit 34 that unloads the printing medium M unloaded from the drying unit 5 by the final transport unit 335 toward the winding unit 12. The unloading unit 34 transports the printing medium M toward X1. The printing medium M that has been transported toward X1 by the unloading unit 34 is wound up by the winding roller 121 of the winding unit 12.

[0028] Furthermore, the printing apparatus 1 includes a cooling unit 13 and an inspection unit 14 positioned between the drying unit 5 and the winding unit 12 in the discharge path (in other words, the discharge unit 34) of the printing medium M from the drying unit 5 to the winding unit 12. The cooling unit 13 cools the image printed on the surface Ma of the printing medium M being transported by the discharge unit 34. The inspection unit 14 inspects the image printed on the surface Ma of the printing medium M being transported by the discharge unit 34 on the downstream side of the transport direction Dc of the printing medium M.

[0029] The drying unit 5 has a plurality (four) of heaters 51A, 51B, 51C, and 51D that heat the surface Ma of the printing medium M conveyed by the drying conveying unit 33. Heaters 51A and 51B are arranged along the printing medium M conveyed by the preceding drying conveying unit 331 and face the surface Ma of the printing medium M. Heater 51C faces the surface Ma of the printing medium M conveyed by the intermediate drying conveying unit 332. Heater 51D faces the surface Ma of the printing medium M conveyed by the subsequent drying conveying unit 334.

[0030] Furthermore, the drying unit 5 has a plurality of temperature sensing units 55A, 55B, 55C, and 55D, each corresponding to a plurality of heaters 51A, 51B, 51C, and 51D. The temperature sensing units 55A, 55B, 55C, and 55D each detect infrared radiation emitted from the surface Ma of the printing medium M downstream of the corresponding heater 51A, 51B, 51C, and 51D in the transport direction Dc of the printing medium M. In other words, the temperature sensing units 55A, 55B, 55C, and 55D each detect infrared radiation emitted from the surface Ma of the printing medium M that has passed through the corresponding heaters 51A, 51B, 51C, and 51D. In this way, the temperature sensing units 55A, 55B, 55C, and 55D each detect the temperature of the surface Ma of the printing medium M heated by the corresponding heaters 51A, 51B, 51C, and 51D.

[0031] Figure 2A is a schematic diagram showing the configuration of the heater. In this figure, the Dw1 side and Dw2 side of the width direction Dw are shown. Here, the Dw1 side and Dw2 side face opposite directions. Heaters 51A to 51D all have a common configuration, so in Figure 2A they are not distinguished and are shown as heater 51. In this figure, the transport direction Dc of the printing medium M by the transport unit 3, the width direction Dw of the printing medium M, and the normal direction Dn of the printing medium M are shown. The width direction Dw is the horizontal direction corresponding to the Y direction and is perpendicular to the transport direction Dc. The normal direction Dn is the direction of the normal perpendicular to the surface Ma of the printing medium M and is perpendicular to the transport direction Dc and the width direction Dw. As shown in Figure 2A, the length of the width direction Dw of the printing medium M is the paper width W11.

[0032] As shown in Figure 2A, the heater 51 has a plurality (9) of lamps 511 arranged at a predetermined pitch in the width direction Dw. Each lamp 511 faces the surface Ma of the printing medium M from the direction normal to the surface Ma, and applies thermal energy to the surface Ma by irradiating it with light. In this way, the surface Ma of the printing medium M is heated.

[0033] As described above, a temperature detection unit 55 is located downstream of the heater 51 in the transport direction Dc. Since the temperature detection units 55A to 55D all have a common configuration, they are not distinguished and are shown as the temperature detection unit 55 in Figure 2A. The temperature detection unit 55 detects the temperature of the surface Ma of the printing medium M heated by the heater 51. This temperature detection unit 55 has two infrared sensors 56(1) and 56(2). From a viewpoint in the normal direction Dn perpendicular to the surface Ma of the printing medium M, the infrared sensors 56(1) and 56(2) are located on both sides of the width direction Dw of the printing medium M, with infrared sensor 56(1) located on the Dw1 side of the printing medium M and infrared sensor 56(2) located on the Dw2 side of the printing medium M. More specifically, the infrared sensor 56(1) is positioned outside the Dw1 side edge M1 of the printing medium M (on the Dw1 side), and the infrared sensor 56(2) is positioned outside the Dw2 side edge M2 of the printing medium M (on the Dw2 side). In this way, the infrared sensors 56(1) and 56(2) are positioned outside the projection of the printing medium M in the normal direction Dn perpendicular to the surface Ma of the printing medium M.

[0034] Figure 2B is a schematic diagram showing the configuration of an infrared sensor. Note that the two infrared sensors 56(1) and 56(2) have the same configuration, and are therefore not distinguished in Figure 2B and are simply referred to as infrared sensor 56. The infrared sensor 56 is a line-type thermopile sensor and is arranged parallel to the width direction Dw. The infrared sensor 56 has a sensor substrate 561 provided parallel to the width direction Dw. This sensor substrate 561 has a plurality (8) of infrared detection elements E arranged at a predetermined pitch in the width direction Dw. Each infrared detection element E outputs temperature data Te indicating the temperature corresponding to the infrared light it receives. The sensor substrate 561 outputs the temperature data Te output by the infrared detection elements E. The temperature data Te is, for example, the value of the current or voltage output by the infrared detection elements E. The infrared sensor 56 also has a lens 562 (for example, a Fresnel lens) facing the sensor substrate 561 and a frame 563 that supports the lens 562 relative to the sensor substrate 561. The lens 562 focuses infrared light emitted from the surface Ma of the printing medium M onto the infrared detection element E. The optical axis Do of the lens 562 extends perpendicular to the width direction Dw. Furthermore, the length of the width direction Dw of each infrared sensor 56 is the sensor width W12. The sensor width W12 is smaller than the paper width W11 of the printing medium M.

[0035] Figure 3 is a block diagram showing the electrical configuration of the drying unit. As shown in Figure 3, the temperature sensing unit 55 has two infrared sensors 56. The temperature data Te output by infrared sensor 56(1) is shown as temperature data Te1, and the temperature data Te output by infrared sensor 56(2) is shown as temperature data Te2. The drying unit 5 also has a heater drive unit 52 that drives the heaters 51. The heater drive unit 52 is provided for each of the multiple heaters 51. The heater drive unit 52 supplies current individually to each of the multiple (9) lamps 511 of the corresponding heater 51, and the lamps 511 release thermal energy corresponding to the current supplied from the heater drive unit 52 to heat the surface Ma of the printing medium M.

[0036] Furthermore, the drying unit 5 includes a control unit 591 and a storage unit 592. The control unit 591 is a processor such as a CPU (Central Processing Unit), and the storage unit 592 is a storage device such as an HDD (Hard Disk Drive) or SSD (Solid State Drive). The control unit 591 estimates the temperature of the surface Ma of the printing medium M based on temperature data Te1 and Te2, thereby determining the estimated temperature Tm of the surface Ma. The control unit 591 then provides feedback control to the current supplied by the heater drive unit 52 to the lamp 511 so that the estimated temperature Tm approaches the target temperature Tt. The storage unit 592 also stores correction tables B1 and B2, which the control unit 591 uses to estimate the estimated temperature Tm. Correction table B1 is used to determine the estimated temperature Tm based on temperature data Te1, and correction table B2 is used to determine the estimated temperature Tm based on temperature data Te2.

[0037] Figure 4A schematically shows the positional relationship between the infrared sensor, which is located on one side in the width direction of the two infrared sensors in the temperature detection unit, and the printing medium. The infrared sensor 56(1) faces the surface Ma of the printing medium M from the Dw1 side of the printing medium M, and the optical axis direction Do of the infrared sensor 56(1) is tilted towards Dw1 with respect to the surface Ma of the printing medium M (in other words, the normal direction Dn). That is, the infrared sensor 56(1) faces the surface Ma of the printing medium M from the optical axis direction Do, which is tilted towards Dw1 with respect to the surface Ma of the printing medium M. Note that the state in which the optical axis direction Do is not parallel to the normal direction Dn (in other words, intersecting state) is expressed as the optical axis direction Do being tilted towards the normal direction Dn, and the state in which the optical axis direction Do is parallel to the normal direction Dn is expressed as the optical axis direction Do not being tilted towards the normal direction Dn.

[0038] Here, each of the eight infrared detection elements E shown in Figure 2B has a field of view F1 to F8 with a predetermined angle θ. In Figure 4A, the fields of view F of each of the eight infrared detection elements E are shown as fields of view F1 to F8 in order from the Dw1 side. When fields of view F1 to F8 are not specifically distinguished, they are simply referred to as field of view F. The field of view F of the infrared detection element E spreads symmetrically with respect to a central axis that passes through the center of the infrared detection element E and is parallel to the optical axis direction Do. In other words, the field of view F of the infrared detection element E has a rectangle in a cross-section perpendicular to the optical axis direction Do, and the size of this rectangle increases as you move away from the infrared detection element E in the optical axis direction Do.

[0039] The infrared detection element E receives infrared radiation emitted from an area of ​​the surface Ma of the printing medium M that overlaps with the field of view F of the infrared detection element E (i.e., detection area Aa), and outputs temperature data Te1 indicating the temperature of the detection area Aa. In Figure 4A, the detection areas Aa for each of the eight infrared detection elements E are shown as detection areas Aa1 to Aa8 in order from the Dw1 side. When detection areas Aa1 to Aa8 are not specifically distinguished, they are simply referred to as detection area Aa. Since the optical axis direction Do is tilted towards Dw1 with respect to the surface Ma of the printing medium M, detection areas Aa located on the Dw2 side have a larger area and have a wider width in both the width direction Dw and the transport direction Dc. In other words, detection areas Aa that are further away from the infrared sensor 56(1) in the width direction Dw have a more distorted shape. To put it another way, among the detection areas Aa1 to Aa8 of the infrared sensor 56(1), the detection area Aa on the Dw1 side has a more appropriate shape.

[0040] Figure 4B schematically shows the positional relationship between the infrared sensor located on the other side in the width direction of the two infrared sensors in the temperature detection unit and the printing medium. The infrared sensor 56(2) faces the surface Ma of the printing medium M from the Dw2 side of the printing medium M, and the optical axis direction Do of the infrared sensor 56(2) is tilted towards the Dw2 side with respect to the surface Ma of the printing medium M (in other words, the normal direction Dn). That is, the infrared sensor 56(2) faces the surface Ma of the printing medium M from the optical axis direction Do which is tilted towards the Dw2 side with respect to the surface Ma of the printing medium M.

[0041] Furthermore, in Figure 4B, the fields of view F of each of the eight infrared detection elements E of the infrared sensor 56(2) are shown as fields of view F1 to F8 in order from the Dw2 side. Similar to the infrared sensor 56(1), the fields of view F of the infrared detection elements E of the infrared sensor 56(2) spread symmetrically with respect to a central axis parallel to the optical axis direction Do, passing through the center of the infrared detection elements E.

[0042] The infrared detection element E receives infrared radiation emitted from an area of ​​the surface Ma of the printing medium M that overlaps with the field of view F of the infrared detection element E (i.e., detection area Ab), and outputs temperature data Te2 indicating the temperature of the detection area Ab. In Figure 4B, the detection areas Ab for each of the eight infrared detection elements E are shown as detection areas Ab1 to Ab8 in order from the Dw2 side. When detection areas Ab1 to Ab8 are not specifically distinguished, they are simply referred to as detection area Ab. Because the optical axis direction Do is tilted towards Dw2 with respect to the surface Ma of the printing medium M, detection areas Ab located on the Dw1 side have a larger area and have a wider width in both the width direction Dw and the transport direction Dc. In other words, detection areas Ab that are further away from the infrared sensor 56(2) in the width direction Dw have a more distorted shape. To put it another way, among the detection areas Ab1 to Ab8 of the infrared sensor 56(2), detection areas Ab on the Dw2 side have a more appropriate shape.

[0043] Figure 4C schematically shows the positional relationship between the two infrared sensors in the temperature detection unit and the printing medium. In the example shown in this figure, the surface Ma of the printing medium M is broadly divided into a region Ma1 biased towards the Dw1 side and a region Ma2 biased towards the Dw2 side. Regions Ma1 and Ma2 are adjacent without gaps in the width direction Dw.

[0044] In region Ma1, detection areas Aa1 to Aa6 of the infrared sensor 56(1) overlap the fields of view F7 to F8 of the infrared sensor 56(2). As described above, for the infrared sensor 56(1), the detection area Aa on the Dw1 side has a shape with less distortion, whereas for the infrared sensor 56(2), the detection area Ab on the Dw1 side has a shape with greater distortion. Therefore, for estimating the temperature of region Ma1, the control unit 591 uses temperature data Te1 detected by the infrared sensor 56(1) for detection areas Aa1 to Aa6, while not using temperature data Te2 detected by the infrared sensor 56(2) for detection areas Ab7 to Ab8.

[0045] In region Ma2, detection areas Ab1 to Ab6 of the infrared sensor 56(2) overlap the fields of view F7 to F8 of the infrared sensor 56(1). As described above, for the infrared sensor 56(2), the detection area Ab on the Dw2 side has a shape with less distortion, whereas for the infrared sensor 56(1), the detection area Aa on the Dw2 side has a shape with greater distortion. Therefore, for estimating the temperature of region Ma2, the control unit 591 uses temperature data Te2 detected by the infrared sensor 56(2) for detection areas Ab1 to Ab6, while not using temperature data Te1 detected by the infrared sensor 56(1) for detection areas Aa7 to Aa8.

[0046] FIG. 5 is a flowchart showing a first example of temperature estimation executed by the control unit, and FIGS. 6A and 6B are diagrams showing an example of a correction table used in the temperature estimation of FIG. 5. In particular, the correction table B1 in FIG. 6A is used to correct temperature data Te1 acquired by the infrared sensor 56(1), and the correction table B2 is used to correct temperature data Te2 acquired by the infrared sensor 56(2). The correction table B1 shows a plurality of correction coefficients Ca1 to Ca8 respectively associated with the plurality of detection areas Aa1 to Aa8. The correction table B2 shows a plurality of correction coefficients Cb1 to Cb8 respectively associated with the plurality of detection areas Ab1 to Ab8.

[0047] In step S101, the control unit 591 acquires temperature data Te1 from the infrared sensor 56(1) or temperature data Te2 from the infrared sensor 56(2). Then, the control unit 591 determines whether to use the temperature data Te1 or Te2 acquired in step S101 (step S102).

[0048] When the temperature data Te1 is acquired, it is determined whether or not the temperature data Te1 has been acquired for the detection areas Aa7 to Aa8 of the infrared sensor 56(1). When the temperature data Te1 is acquired for the detection areas Aa7 to Aa8, the control unit 591 determines not to use the temperature data Te1 ("NO" in step S102), and returns to step S101. On the other hand, when the temperature data Te1 is acquired for the detection areas Aa1 to Aa6, the control unit 591 determines to use the temperature data Te1 ("YES" in step S102), and proceeds to step S103.

[0049] When the temperature data Te2 is acquired, it is determined whether or not the temperature data Te2 has been acquired for the detection areas Ab7 to Ab8 of the infrared sensor 56(2). When the temperature data Te2 is acquired for the detection areas Ab7 to Ab8, the control unit 591 determines not to use the temperature data Te2 ("NO" in step S102), and returns to step S101. On the other hand, when the temperature data Te2 is acquired for the detection areas Ab1 to Ab6, the control unit 591 determines to use the temperature data Te2 ("YES" in step S102), and proceeds to step S103.

[0050] In step S103, the control unit 591 reads out the correction coefficient associated with the detection area for which the temperature data Te1 or Te2 was acquired in step S101, the coefficient being associated via the correction table B1 or B2. Then, the control unit 591 estimates a value obtained by multiplying the temperature indicated by the temperature data Te1 or Te2 by the correction coefficient as the temperature of the corresponding detection area (estimated temperature Tm) (step S104).

[0051] For example, if temperature data Te1 indicating the temperature of detection area Aa2 is acquired, the control unit 591 reads the correction coefficient Ca2 associated with detection area Aa2 from the correction table B1 (step S103). Then, the control unit 591 calculates the temperature obtained by multiplying the temperature indicated by temperature data Te1 by the correction coefficient Ca2 as the estimated temperature Tm of detection area Aa2 (step S104). If temperature data Te2 is acquired, the temperature of each of the multiple detection areas Ab is similarly estimated using the correction table B2.

[0052] By performing the temperature estimation shown in Figure 5, the estimated temperature Tm for each detection area Aa1 to Aa6 on the surface Ma of the printing medium M is calculated, and the estimated temperature Tm for each detection area Ab1 to Ab6 on the surface Ma of the printing medium M is also calculated. In this way, the temperature of the surface Ma of the printing medium M is estimated based on the temperature data Te1 acquired by the infrared sensor 56(1) and the temperature data Te2 acquired by the infrared sensor 56(2). In particular, the temperature distribution in the width direction Dw can be obtained. Based on this, the control unit 591 controls each lamp 511 of the heater 51 based on the temperature distribution on the surface Ma of the printing medium M.

[0053] Figure 7A schematically shows the relationship between the detection area of ​​the infrared sensor and the heating area of ​​the lamp, and Figure 7B schematically shows the method for estimating the temperature of the heating area from the estimated temperature of the detection area. Multiple lamps 511 face each of the multiple heating areas H1 to H9. In other words, each of the multiple lamps 511 heats the opposite heating areas H1 to H9. The control unit 591 estimates the temperatures of the heating areas H1 to H9 based on the detection areas Aa and Ab that overlap with each of the heating areas H1 to H9. For example, in heating area H1, detection areas Aa1 and Aa2 overlap. Therefore, the control unit 591 estimates the temperature of heating area H1 based on the estimated temperatures Tm of detection areas Aa1 and Aa2, respectively.

[0054] The method for estimating the temperature when multiple detection areas A1 and A2 overlap in a single heating area H is described in detail below. When multiple detection areas A1 and A2 overlap in a heating area H, the temperature of heating area H can be estimated as shown in Figure 7B. In the width direction Dw, detection area A1 overlaps with heating area H by a width w1, and detection area A2 overlaps with heating area H by a width w2. Here, the sum of widths w1 and w2 corresponds to the width Wh of heating area H. Assuming that the estimated temperature Tm1 is obtained for detection area A1 and the estimated temperature Tm2 is obtained for detection area A2, the estimated temperature Tmh of heating area H is given by the following equation: Tmh = Tm1 × w1 / (w1 + w2) + Tm2 × w2 / (w1 + w2). In other words, the weighted average of the estimated temperatures Tm of each detection area A, weighted according to the overlap width between detection area A and heating area H, is estimated as the temperature of heating area H. This method can also be applied when three or more detection areas A overlap in a single heating area H. In other words, let's generalize and explain the case where n detection areas A(1), A(2), ... A(n) overlap in a single heating area H. First, the ratio (w(k) / Wh) of the width w(k) over which the k-th detection area A(k) (where k is an integer between 1 and n) overlaps with heating area H is calculated. Then, the apportioned temperature (= Tm × w(k) / Wh) is calculated by multiplying the estimated temperature Tm(k) obtained for detection area A(k) by this ratio (i.e., the weighting coefficient). This apportioned temperature is calculated for each of the n detection areas A(1), A(2), ... A(n), and the sum of these is obtained as the estimated temperature Tmh of heating area H.

[0055] As described above, two infrared sensors 56(1) and 56(2) (first and second infrared sensors) are used to estimate the temperature of the printing medium M. Infrared sensor 56(1) (first infrared sensor) detects infrared radiation emitted from eight (M1) detection areas Aa1 to Aa8 (first detection areas) arranged in the width direction Dw of the printing medium M, and outputs temperature data Te1 (first temperature data) indicating the temperature of each of the eight detection areas Aa1 to Aa8. Infrared sensor 56(2) (second infrared sensor) detects infrared radiation emitted from eight (M2) detection areas Ab1 to Ab8 (second detection areas) arranged in the width direction Dw of the printing medium M, and outputs temperature data Te2 (second temperature data) indicating the temperature of each of the eight detection areas Ab1 to Ab8.

[0056] The infrared sensor 56(1) is positioned at an angle to the Dw1 side (first side) in the width direction Dw relative to the surface Ma of the printing medium M. Compared to the case where the infrared sensor 56(1) is facing the printing medium M from the normal direction Dn perpendicular to the printing medium M (i.e., when the infrared sensor 56(1) is facing the printing medium M without being tilted), tilting the infrared sensor 56(1) allows the detection areas Aa1 to Aa8 on the surface Ma of the printing medium M to be expanded in the width direction Dw. Therefore, the infrared sensor 56(1) can detect the temperature over a relatively wide area of ​​the surface Ma of the printing medium M. The infrared sensor 56(2) is positioned at an angle to the Dw2 side in the width direction Dw relative to the surface Ma of the printing medium M. Compared to the case where the infrared sensor 56(2) is positioned facing the printing medium M from a normal direction Dn perpendicular to the printing medium M (i.e., when the infrared sensor 56(2) is facing the printing medium M without tilting), tilting the infrared sensor 56(2) allows the detection areas Ab1 to Ab8 on the surface Ma of the printing medium M to be expanded in the width direction Dw. Therefore, the temperature of a relatively wide range of the surface Ma of the printing medium M can be detected by the infrared sensor 56(2).

[0057] Furthermore, the spread of detection areas Aa1 to Aa8 in the width direction Dw becomes more pronounced the further the detection area Aa is from the infrared sensor 56(1). Therefore, detection areas Aa that are further from the infrared sensor 56(1) towards Dw2 have a distorted shape. The reliability of temperature data Te1 obtained for detection areas Aa with such distorted shapes is low. In other words, the temperature data Te1 calculated for detection areas Aa on the Dw1 side has higher reliability. Similarly, the spread of detection areas Ab1 to Ab8 in the width direction Dw becomes more pronounced the further the detection area Ab is from the infrared sensor 56(2). Therefore, detection areas Ab that are further from the infrared sensor 56(2) towards Dw1 have a distorted shape. The reliability of temperature data Te2 obtained for detection areas Ab with such distorted shapes is low. In other words, the temperature data Te2 calculated for detection areas Ab on the Dw2 side has higher reliability. In response to this, the temperature of the printing medium M is estimated based on temperature data Te1 output by the infrared sensor 56(1) for at least six (N1) detection areas Aa1 to Aa6 counted from the Dw1 side, and temperature data Te2 output by the infrared sensor 56(2) for at least six (N2) detection areas Ab1 to Ab6 counted from the Dw2 side. In other words, the temperature of the printing medium M can be estimated based on relatively reliable temperature data Te1 and temperature data Te2.

[0058] In this way, the infrared sensors 56(1) and 56(2) are arranged diagonally to ensure a wide range in which each infrared sensor 56(1) and 56(2) can detect temperature, and the temperature of the printing medium M is estimated based on relatively reliable temperature data Te1 and Te2. As a result, it is possible to determine the temperature of a wide printing medium M using a small number of infrared sensors 56(1) and 56(2) placed in close proximity to the printing medium M.

[0059] Furthermore, the storage unit 592 stores a correction table B1 (first correction table) that shows correction coefficients Ca1 to Ca8 (first correction amounts) for correcting temperature data Te1 corresponding to each of the eight detection areas Aa1 to Aa8, and a correction table B2 (second correction table) that shows correction coefficients Cb1 to Cb8 (second correction amounts) for correcting temperature data Te2 corresponding to each of the eight detection areas Ab1 to Ab8. The control unit 591 (heater control unit) then estimates the temperature of the target detection area that is the subject of temperature estimation among the eight detection areas Aa1 to Aa8 as follows. That is, it estimates the temperature by correcting the temperature data Te1 output for the target detection area with the correction coefficient corresponding to the target detection area (temperature estimation in Figure 5). Similarly, the control unit 591 estimates the temperature of the target detection area that is the subject of temperature estimation among the eight detection areas Ab1 to Ab8 as follows. In other words, the temperature data Te2 output for the target detection area is estimated by correcting it with a correction coefficient corresponding to the target detection area (temperature estimation in Figure 5). With this configuration, the temperature data Te1 and Te2 can be appropriately corrected according to the distortion of the shape of the detection areas Aa1 to Aa8 and Ab1 to Ab8 caused by the diagonal arrangement of the infrared sensors 56(1) and 56(2). As a result, the temperature of the printing medium M can be accurately estimated.

[0060] Figure 8 is a flowchart showing a second example of temperature estimation performed by the control unit. In this second example of temperature estimation, the control unit 591 determines whether an abnormality has occurred in at least one of the infrared sensors 56(1) and 56(2) (step S201). Specifically, the control unit 591 compares the output values ​​(temperature data Te1, Te2) of the infrared detection element E with the abnormality determination range. The control unit 591 then determines whether there is an abnormal element among the multiple infrared detection elements E of each of the infrared sensors 56(1) and 56(2) that shows an output value outside the abnormality determination range. If an abnormal element exists, it is determined that one of the infrared sensors 56(1) and 56(2), including the abnormal element, is abnormal. The abnormality determination range is set in advance between an allowable lower limit and an allowable upper limit greater than the allowable lower limit, and is stored, for example, in the storage unit 592.

[0061] If both infrared sensors 56(1) and 56(2) are determined to be normal (NO in step S201), the control unit 591 executes the normal temperature estimation mode (step S202). In this normal temperature estimation mode, the temperature of the printing medium M is estimated according to the first example of temperature estimation shown in Figure 5 above.

[0062] If either infrared sensor 56(1) or 56(2) is determined to be abnormal (YES in step S201), the control unit 591 executes the abnormal temperature estimation mode (step S203). For example, if infrared sensor 56(1) is determined to be abnormal, the control unit 591 estimates the surface temperature Ma of the printing medium M using only the normal infrared sensor 56(2) out of infrared sensors 56(1) and 56(2). In particular, the temperature data Te2 acquired for each of the detection areas Ab1 to Ab8 of infrared sensor 56(2) is used. That is, the estimated temperature Tm for each of the detection areas Ab1 to Ab8 is calculated based on the temperature data Te2 and correction coefficients Cb1 to Cb8 for each of the detection areas Ab1 to Ab8.

[0063] In this manner, the control unit 591 (heater control unit) estimates the temperature of the printing medium M by executing the normal temperature estimation mode (step S202). In this normal temperature estimation mode, the control unit 591 uses the temperature data Te1 (first temperature data) output by the infrared sensor 56(1) for six (N1) detection areas Aa1 to Aa6 (first detection areas) to estimate the temperature of the printing medium M, while not using the temperature data Te1 output by the infrared sensor 56(1) for detection areas Aa7 to Aa8 other than the six detection areas Aa1 to Aa6 to estimate the temperature of the printing medium M. Similarly, the control unit 591 uses the temperature data Te2 (second temperature data) output by the infrared sensor 56(2) for six (N2) detection areas Ab1 to Ab6 (second detection areas) to estimate the temperature of the printing medium M, while not using the temperature data Te2 output by the infrared sensor 56(2) for detection areas Ab7 to Ab8 other than the six detection areas Ab1 to Ab6 to estimate the temperature of the printing medium M. In this configuration, it is possible to suppress the influence of unreliable temperature data Te1 and Te2 on the estimation of the temperature of the printing medium M.

[0064] Furthermore, the control unit 591 (anomaly detection unit) detects an anomaly in the temperature detection unit 55 (step S201). When the control unit 591 detects an anomaly in the infrared sensor 56(1), it executes an anomaly temperature estimation mode (first anomaly temperature estimation mode) that uses only the infrared sensor 56(2) and not the infrared sensor 56(1) (step S203). Furthermore, when the control unit 591 detects an anomaly in the infrared sensor 56(2), it executes an anomaly temperature estimation mode (second anomaly temperature estimation mode) that uses only the infrared sensor 56(1) and not the infrared sensor 56(2) (step S203). In the former abnormal temperature estimation mode (first abnormal temperature estimation mode), the control unit 591 uses all of the temperature data Te2 output by the infrared sensor 56(2) for each of the eight (M2) detection areas Ab1 to Ab8 to estimate the temperature of the printing medium M, but does not use the temperature data Te1 output by the infrared sensor 56(1) to estimate the temperature of the printing medium M. In the latter abnormal temperature estimation mode (second abnormal temperature estimation mode), the control unit 591 uses all of the temperature data Te1 output by the infrared sensor 56(1) for each of the eight (M1) detection areas Aa1 to Aa8 to estimate the temperature of the printing medium M, but does not use the temperature data Te2 output by the infrared sensor 56(2) to estimate the temperature of the printing medium M. In this configuration, even if an abnormality occurs in either the infrared sensor 56(1) or 56(2), the estimation of the temperature of the printing medium M can be continued.

[0065] Furthermore, the control unit 591 detects that an abnormality has occurred in the infrared sensor 56(1) if, among the temperature data Te1 output for each of the eight (M1) detection areas Aa1 to Aa8, there is any temperature data Te1 that falls outside a predetermined abnormality judgment range (first normal range). Similarly, if, among the temperature data Te2 output for each of the eight (M2) detection areas Ab1 to Ab8, there is any temperature data Te2 that falls outside a predetermined abnormality judgment range (second normal range), the control unit 591 detects that an abnormality has occurred in the infrared sensor 56(2). This allows for the appropriate detection of abnormalities in the infrared sensors 56(1) and 56(2).

[0066] Figure 9 is a schematic diagram showing an example of a light-shielding section that can be positioned relative to the temperature detection section. The light-shielding section 6 has a light-shielding plate 61 that blocks the passage of infrared rays. In the example of Figure 9, a pair of light-shielding plates 61 are provided spaced apart in the transport direction Dc. As shown in Figure 9, infrared rays emitted from the surface Ma of the printing medium M pass through the infrared-passing range P and are focused onto the infrared detection element E of the infrared sensor 56. Of the pair of light-shielding plates 61, one light-shielding plate 61 (upstream side in the transport direction Dc) is positioned upstream of the infrared-passing range P in the transport direction Dc, and the other light-shielding plate 61 (downstream side in the transport direction Dc) is positioned downstream of the infrared-passing range P in the transport direction Dc. These light-shielding plates 61 prevent infrared rays from entering the infrared sensors 56(1) and 56(2) of the temperature detection section 55 from outside the infrared-passing range P in the transport direction Dc. Furthermore, the infrared sensor 56 does not necessarily need to have light-shielding plates 61 on both sides of the infrared transmission range P; it may have a light-shielding plate 61 on only one side of the infrared transmission range P.

[0067] Thus, the light-shielding section 6 has a light-shielding plate 61 (light-shielding member) positioned on at least one side of the transport direction Dc of the infrared passage range P, through which infrared rays emitted from eight (M1) detection areas Aa1 to Aa8 and incident on the infrared sensor 56(1) pass, and through which infrared rays emitted from eight (M2) detection areas Ab1 to Ab8 and incident on the infrared sensor 56(2) pass. The light-shielding plate 61 prevents infrared rays from entering the infrared sensors 56(1) and 56(2) from outside the infrared passage range P in the transport direction Dc. With this configuration, it is possible to suppress stray light from entering the infrared sensors 56(1) and 56(2).

[0068] Incidentally, it is not necessary to provide the light-shielding section 6 for all of the temperature detection sections 55A to 55D. Therefore, the light-shielding section 6 may be provided only for, for example, the temperature detection section 55B and the temperature detection section 55D.

[0069] (Modified Version) In the embodiment described above, the surface temperature Tm of the printing medium M was estimated by applying the temperature data Te1 output by the infrared sensor 56(1) to the correction table B1, and the temperature data Te2 output by the infrared sensor 56(2) to the correction table B2. However, it is also possible to estimate the surface temperature Tm of the printing medium M without using correction tables B1 and B2. This will be described in detail in the modified version below.

[0070] Figure 10 is a flowchart showing the temperature estimation process performed by the control unit 591 in this modified example. For simplicity, the number of lamps 511 provided by the heater 51 is assumed to be 1. Figures 11A-11H show Tables 1-8.

[0071] In step S301, the control unit 591 acquires temperature data Te1 from infrared sensor 56(1) and temperature data Te2 from infrared sensor 56(2). Assume that the temperature data Te1 output by infrared sensor 56(1) includes multiple temperature data Te11 to Te18 indicating the temperatures of multiple detection areas Aa1 to Aa8 (see Table 1). Assume that the temperature data Te2 output by infrared sensor 56(2) includes multiple temperature data Te21 to Te28 indicating the temperatures of multiple detection areas Ab1 to Ab8 (see Table 2). In step S301, the control unit 591 acquires the above temperature data Te11 to Te18 and Te21 to Te28.

[0072] Then, the control unit 591 converts the temperature data Te1 and Te2 acquired in step S301 into radiant energy data Ee1 and Ee2. More specifically, it converts each of the multiple temperature data Te11 to Te18 and temperature data Te21 to Te28, which represent the temperatures of the multiple detection areas Aa1 to Aa8 and Ab1 to Ab8, into radiant energy data Ee11 to Ee18 and Ee21 to Ee28, which represent the amount of radiant energy irradiated to the multiple detection areas Aa1 to Aa8 and Ab1 to Ab8. According to Boltzmann's law, radiant energy is proportional to the fourth power of temperature, so this conversion is performed, for example, using the following equation 1.

[0073]

[0074] Next, the control unit 591 corrects the radiant energy data Ee1 and Ee2 considering the reliability of the corresponding detection area (step S303). As described above using Figure 2B, the infrared sensor 56 is equipped with a plurality of infrared detection elements E, and the reliability of the temperature data Te output by each infrared detection element E changes depending on the distance from the infrared detection element E to the detection areas Aa and Ab that the infrared detection element E reads. More specifically, the reliability of the temperature data Te output by the infrared detection element E is inversely proportional to the square of the distance from the infrared detection element E to the detection areas Aa and Ab that the infrared detection element E reads. Therefore, for example, the radiant energy data Ee11 is corrected based on the following equation 2.

[0075]

[0076] As a result of the correction process in step S303, the radiant energy data Ee1 in Table 3 is corrected as shown in Table 5. Similarly, the radiant energy data Ee2 in Table 4 is corrected as shown in Table 6.

[0077] Next, the control unit 591 corrects the radiant energy data (Ee1)' and (Ee2)' taking into account the variation in the amount of light received in the corresponding detection area (step S304). This variation is corrected, for example, with respect to the radiant energy data (Ee11)' based on the following equation 3.

[0078]

[0079] As a result of the correction process in step S304, the radiant energy data Ee1 in Table 5 is corrected as shown in Table 7. Similarly, the radiant energy data Ee2 in Table 6 is corrected as shown in Table 8.

[0080] Next, the control unit 591 calculates the sum of the radiant energy amounts SU1 received by all the infrared detection elements E of the infrared sensor 56(1) (step S305). More specifically, the sum of the radiant energy data (Ee1)'' obtained by processing the temperature data Te1 for each detection area acquired in step S301 in the correction process in steps S303 and S304 is calculated based on the following equation 4.

[0081]

[0082] Next, the control unit 591 calculates the sum of the radiant energy amounts SU2 received by all the infrared detection elements E of the infrared sensor 56(2) (step S306). More specifically, the sum of the radiant energy data (Ee2)'' obtained by processing the temperature data Te2 for each detection area acquired in step S301 in the correction process in steps S303 and S304 is calculated based on the following equation 5.

[0083]

[0084] Next, the control unit 591 calculates the total amount of radiant energy SU3 received by the temperature detection unit 56 based on the following equation 6 (step S307).

[0085]

[0086] Finally, the control unit 591 converts the sum of the radiant energy amounts SU3 received by the temperature detection unit 56 into temperature data based on the following equation 7.

[0087]

[0088] In the embodiments described above, the width direction Dw corresponds to an example of the "width direction" of the present invention, the printing medium M corresponds to an example of the "printing medium" of the present invention, the transport unit 3 corresponds to an example of the "transport unit" of the present invention, the heater 51 corresponds to an example of the "heater unit" of the present invention, the temperature detection unit 55 corresponds to an example of the "temperature detection unit" of the present invention, the control unit 591 corresponds to an example of the "heater control unit" of the present invention, the Dw1 side corresponds to an example of the "first side" of the present invention, the infrared sensor 56(1) corresponds to an example of the "first infrared sensor" of the present invention, the Dw2 side corresponds to an example of the "second side" of the present invention, the infrared sensor 56(2) corresponds to an example of the "second infrared sensor" of the present invention, each of the detection areas Aa1 to Aa8 corresponds to an example of the "first detection area" of the present invention, the temperature data Te1 corresponds to an example of the "first temperature data" of the present invention, and each of the detection areas Ab1 to Ab8 corresponds to an example of the "second detection area" of the present invention. In this case, the drying unit 5 and the drying transport unit 33 correspond to an example of the "printing media drying unit" of the present invention, the control unit 591 corresponds to an example of the "abnormality detection unit" of the present invention, each of the correction coefficients Ca1 to Ca8 corresponds to an example of the "first correction amount" of the present invention, the correction table B1 corresponds to an example of the "first correction table" of the present invention, the correction coefficients Cb1 to Cb8 correspond to an example of the "second correction amount" of the present invention, the correction table B2 corresponds to an example of the "second correction table" of the present invention, the storage unit 592 corresponds to an example of the "storage unit" of the present invention, the light-shielding unit 6 corresponds to an example of the "light-shielding unit" of the present invention, the light-shielding plate 61 corresponds to an example of the "light-shielding member" of the present invention, the printing unit 4 corresponds to an example of the "discharge unit" of the present invention, and the printing device 1 corresponds to an example of the "printing device" of the present invention.

[0089] It should be noted that the present invention is not limited to the embodiments described above, and various modifications can be made without departing from the spirit of the invention. For example, the number of lamps 511 provided in the heater 51 is not limited to the above example, and may be as few as one.

[0090] Furthermore, the number of infrared detection elements E provided by each of the infrared sensors 56(1) and 56(2) is not limited to the above examples. In other words, the specific example of M1 is not limited to the above 8, and the specific example of M2 is not limited to the above 8. Also, the specific example of N1 is not limited to the above 6, and the specific example of N2 is not limited to the above 6. Moreover, the number of infrared detection elements E provided by infrared sensor 56(1) (M1) and the number of infrared detection elements E provided by infrared sensor 56(2) (M2) may be different.

[0091] Furthermore, in the above example, the detection area Aa6 of infrared sensor 56(1) and the detection area Ab6 of infrared sensor 56(2) are adjacent without any gaps (Figure 4C). However, they may overlap, for example. In that case, the temperature of the overlapping portion may be estimated by the average of the estimated temperature Tm of detection area Aa6 and the estimated temperature Tm of detection area Ab6.

[0092] Furthermore, the dimensional relationship between the detection areas Aa1 to Aa8 and the printing medium M in the width direction Dw, and the dimensional relationship between the detection areas Ab1 to Ab8 and the printing medium M can be changed as appropriate. For example, the area where the detection areas Aa1 to Aa8 are located may be configured to include the entire area of ​​the printing medium M, and the area where the detection areas Ab1 to Ab8 are located may be configured to include the entire area of ​​the printing medium M.

[0093] Furthermore, the above-mentioned correction tables B1 and B2 can be experimentally determined, for example, as follows. That is, the temperature of the printing medium M that has passed through the heater 51 is measured by a plurality of temperature sensors (reference temperature sensors) that are directly facing the printing medium M. In parallel with the measurement by the reference temperature sensors, the temperature of the printing medium M is measured by two infrared sensors 56(1) and 56(2) that are positioned diagonally on both sides of the printing medium M. Then, correction coefficients Ca1 to Ca8 and Cb1 to Cb2 are calculated from the relationship between the temperature measured by the reference temperature sensors and the temperatures measured by the infrared sensors 56(1) and 56(2). Finally, correction tables B1 and B2 showing the correspondence between the detection areas Aa1 to Aa8 and Ab1 to Ab8 and the correction coefficients Ca1 to Ca8 and Cb1 to Cb2 are created and stored in the storage unit 592.

[0094] Furthermore, the present invention is also applicable when one infrared sensor 56(1) is positioned at an angle to one side of the transport direction Dc of the printing medium M, and the other infrared sensor 56(2) is positioned at an angle to the other side of the transport direction Dc of the printing medium M.

[0095] The present invention is applicable to all techniques for estimating the temperature of printing media.

[0096] 1…Printing device 3…Conveying unit 33…Drying conveying unit 4…Printing unit 5…Drying unit 51…Heater 55…Temperature detection unit 56(1)…Infrared sensor 56(2)…Infrared sensor 591…Control unit 592…Storage unit 6…Light shielding unit 61…Light shielding plate Aa1 to Aa8…Detection area Ab1 to Ab8…Detection area B1…Correction table B2…Correction table Dw…Width direction M…Printing medium Te1…Temperature data Te2…Temperature data

Claims

1. The apparatus comprises: a transport unit for transporting a printing medium having a predetermined width in the width direction; a heater unit for heating and drying the printing medium; a temperature detection unit for detecting the temperature of the printing medium; and a heater control unit for controlling the heater unit based on the temperature detected by the temperature detection unit, wherein the temperature detection unit includes: a first infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward a first side in the width direction with respect to the surface of the printing medium; and a second infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward a second side opposite to the first side in the width direction with respect to the surface of the printing medium, wherein the first infrared sensor detects infrared radiation emitted from each of M1 (M1 is an integer of 2 or more) first detection areas that overlap and are arranged in the width direction on the surface of the printing medium, and outputs first temperature data indicating the temperature of each of the M1 first detection areas. The printing medium drying unit detects infrared radiation emitted from each of M2 (M2 is an integer of 2 or more) second detection areas that overlap and are arranged in the width direction on the surface of the printing medium, and outputs second temperature data indicating the temperature of each of the M2 second detection areas. The heater control unit estimates the temperature of the printing medium based on the first temperature data output by the first infrared sensor for at least N1 (N1 is an integer of 1 or more and less than M1) first detection areas out of the M1 first detection areas, counted from the first side, and the second temperature data output by the second infrared sensor for at least N2 (N2 is an integer of 1 or more and less than M2) second detection areas out of the M2 second detection areas, counted from the second side.

2. The printing medium drying unit according to claim 1, wherein M1 is an integer greater than N1, M2 is an integer greater than N2, the heater control unit estimates the temperature of the printing medium by executing a normal temperature estimation mode, and in the normal temperature estimation mode, the heater control unit uses the first temperature data output by the first infrared sensor for the N1 first detection areas to estimate the temperature of the printing medium, while not using the first temperature data output by the first infrared sensor for the first detection areas other than the N1 first detection areas to estimate the temperature of the printing medium, and uses the second temperature data output by the second infrared sensor for the N2 second detection areas to estimate the temperature of the printing medium, while not using the second temperature data output by the second infrared sensor for the second detection areas other than the N2 second detection areas to estimate the temperature of the printing medium.

3. A printing medium drying unit according to claim 1 or 2, further comprising an abnormality detection unit for detecting an abnormality in the temperature detection unit, wherein the heater control unit executes a first abnormal temperature estimation mode when the abnormality detection unit detects an abnormality in the first infrared sensor, and executes a second abnormal temperature estimation mode when the abnormality detection unit detects an abnormality in the second infrared sensor, wherein in the first abnormal temperature estimation mode, the heater control unit uses all of the second temperature data output by the second infrared sensor for each of the M2 second detection areas to estimate the temperature of the printing medium, and does not use the first temperature data output by the first infrared sensor to estimate the temperature of the printing medium, wherein in the second abnormal temperature estimation mode, the heater control unit uses all of the first temperature data output by the first infrared sensor for each of the M1 first detection areas to estimate the temperature of the printing medium, and does not use the second temperature data output by the second infrared sensor to estimate the temperature of the printing medium.

4. The printing media drying unit according to claim 3, wherein the abnormality detection unit detects that an abnormality has occurred in the first infrared sensor if, among the first temperature data output for each of the M1 first detection areas, there is a first temperature data that falls outside a predetermined first normal range, and detects that an abnormality has occurred in the second infrared sensor if, among the second temperature data output for each of the M2 second detection areas, there is a second temperature data that falls outside a predetermined second normal range.

5. The printing media drying unit according to claim 1, further comprising a storage unit that stores a first correction table showing a first correction amount for correcting the first temperature data corresponding to each of the M1 first detection areas, and a second correction table showing a second correction amount for correcting the second temperature data corresponding to each of the M2 second detection areas, wherein the heater control unit estimates the temperature of the first target detection area that is the subject of temperature estimation among the M1 first detection areas by correcting the first temperature data output for the first target detection area with the first correction amount corresponding to the first target detection area, and estimates the temperature of the second target detection area that is the subject of temperature estimation among the M2 second detection areas by correcting the second temperature data output for the second target detection area with the second correction amount corresponding to the second target detection area.

6. The printing medium drying unit according to claim 1, further comprising a light-shielding section, wherein the transport section transports the printing medium in a transport direction perpendicular to the width direction, and the light-shielding section has a light-shielding member positioned on at least one side of the transport direction of an infrared passage range through which infrared rays emitted from the M1 first detection ranges and incident on the first infrared sensor pass, and infrared rays emitted from the M2 second detection ranges and incident on the second infrared sensor pass, and the light-shielding member prevents infrared rays from entering the first infrared sensor and the second infrared sensor from outside the infrared passage range in the transport direction.

7. A printing apparatus comprising an ejection unit for ejecting ink onto a printing medium, and a printing medium drying unit according to any one of claims 1 to 6 for drying the printing medium.

8. A method for estimating the temperature of a printing medium using a printing medium temperature estimation unit comprising: a transport unit for transporting a printing medium having a predetermined width in the width direction; a temperature detection unit for detecting the temperature of the printing medium; and a temperature estimation unit for estimating the temperature of the printing medium based on the temperature detected by the temperature detection unit, wherein the temperature detection unit includes: a first infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward a first side in the width direction with respect to the surface of the printing medium; and a second infrared sensor for detecting infrared radiation emitted from the surface of the printing medium facing the printing medium from a direction inclined toward a second side opposite to the first side in the width direction with respect to the surface of the printing medium; the first infrared sensor detects infrared radiation emitted from each of M1 (M1 is an integer of 2 or more) first detection areas arranged in the width direction on the surface of the printing medium, and outputs first temperature data indicating the temperature of the first detection area for each of the M1 first detection areas. A printing medium temperature estimation method comprising: the second infrared sensor detects infrared radiation emitted from each of M2 second detection areas (where M2 is an integer of 2 or more) arranged in the width direction on the surface of the printing medium, and outputs second temperature data indicating the temperature of each of the M2 second detection areas; and the temperature estimation unit estimates the temperature of the printing medium based on the first temperature data output by the first infrared sensor for at least N1 first detection areas (where N1 is an integer of 1 or more and less than M1) counted from the first side among the M1 first detection areas, and the second temperature data output by the second infrared sensor for at least N2 second detection areas (where N2 is an integer of 1 or more and less than M2) counted from the second side among the M2 second detection areas.

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