Drying apparatus, fixing apparatus, drying and fixing apparatus

Abstract

In a configuration where the belt is heated using multiple heaters, it is not possible to control the amount of heat in the center and at the ends. [Solution] A drying apparatus (4000) for drying ink discharged onto a sheet, comprising: a rotating endless first belt (30·40); a first heater (110a) and a second heater (110b) arranged inside the first belt, non-contacting the first belt and along the width direction of the first belt intersecting the rotation direction of the first belt, and heating the first belt by radiating heat, wherein the first heater and the second heater are characterized in that, in the longitudinal direction intersecting the transport direction of the recording material, the amount of heat generated per unit length at the ends is greater than the amount of heat generated at the center, and the difference in the amount of heat generated at the center and ends of the first heater is different from the difference in the amount of heat generated at the center and ends of the second heater.

Description

Technical Field

[0001] The present invention relates to a drying device and a fixing device.

Background Art

[0002] In an inkjet recording type image forming apparatus, after drying a recording medium to which ink has been applied to evaporate moisture, a method of applying heat and pressure to fix an image is known. Conventionally, heat roller fixing, in which a recording medium is passed between a heating roller and a pressure roller, has been used as a fixing method for fixing ink on a recording medium by applying heat and pressure.

[0003] In recent years, with the increase in speed and productivity of image forming apparatuses, a fixing system using a pair of heating belts instead of rollers has become known, which enables a longer nip distance. In this method, an on-demand drying and fixing method in which the belt is directly heated by a heater is used to quickly heat the recording medium that has entered the nip. The on-demand drying and fixing method has good thermal efficiency and a high heating speed, but on the other hand, since the time to reach a temperature at which belt deformation occurs when abnormal heating occurs is also short, it is necessary to detect abnormal heating with good responsiveness.

[0004] In Patent Document 1, a drying device that fixes an image on a sheet by heating and drying the sheet and the image has been conventionally known, which includes a plurality of halogen heaters.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Unlike conventional heat roller heat storage methods, the on-demand drying and fixing system has a configuration in which multiple HOD units (direct heating of the belt's underside with halogen heaters) are provided for both the upper and lower belts.

[0007] Characteristics of the on-demand drying and fixing method include a relatively low target temperature for belt temperature control and a long fixing heating nip width.

[0008] Therefore, in the on-demand drying and fixing method, the long length of the edges causes heat to be dissipated outside the material. Consequently, multiple heaters are required, but if there are multiple heaters that generate heat uniformly, it becomes impossible to control the amount of heat in the center and edges, for example, during warm-up when the internal temperature is low, or during continuous paper feeding when the internal temperature rises. [Means for solving the problem]

[0009] A drying apparatus for drying ink discharged onto a sheet by an image forming unit that discharges ink to form an image on the sheet, wherein the sheet is heated to dry the ink discharged onto the sheet, comprising: a rotating endless first belt; a rotating endless second belt that forms a nip portion for gripping and conveying the sheet between itself and the first belt; and a first heater and a second heater arranged inside the first belt, non-contacting the first belt and along the width direction of the first belt intersecting the rotation direction of the first belt, and heating the first belt by radiating heat, wherein the first heater and the second heater are characterized in that, in the longitudinal direction intersecting the conveying direction of the recording material, the amount of heat generated per unit length at the ends is greater than the amount of heat generated at the center, and the difference in the amount of heat generated at the center and ends of the first heater is different from the difference in the amount of heat generated at the center and ends of the second heater. [Effects of the Invention]

[0010] By arranging two or more heaters with different heat distributions, where the heat distribution ratio is higher at the ends than in the center along the length, temperature sag at the ends along the length is eliminated. Furthermore, stable in-plane control of the fixing belt temperature is possible in all states: when warm-up is complete, between sheets of paper (standby), and during paper feeding. [Brief explanation of the drawing]

[0011] [Figure 1] Schematic diagram of the image forming system of this embodiment [Figure 2] Overall configuration diagram of the drying and fixing apparatus [Figure 3] Detailed configuration diagram of the drying and fixing apparatus in Example 1. (a) is a front cross-sectional view showing the heating section and the air blowing section, and (b) is a detailed shape diagram of the reflector section. [Figure 4] Hard block diagram of the drying and fixing apparatus in Example 1 [Figure 5] Flowchart of the drying and fixing apparatus in Example 1 [Figure 6] Diagram showing the configuration of the temperature sensor in the drying and fixing device. [Figure 7] This is an overall configuration diagram of the upper fixing belt system 10 of the fixing system in the inkjet recording device in the embodiment. [Figure 8] This diagram shows the configuration of the heater. [Figure 9] This diagram illustrates the power ratio of the heater in the present invention. [Figure 10] This is a conventional example illustrating the changes in detected temperature from the temperature sensor at the center of the belt and the temperature sensor at the end of the belt in Example 2. [Figure 11] This is an example illustrating the changes in detected temperatures from the temperature sensor at the center of the belt and the temperature sensor at the end of the belt in Example 2. [Figure 12] Detailed configuration diagram of the drying and fixing apparatus in Example 1. (a) is a partial perspective view, and (b) is a side cross-sectional view. [Modes for carrying out the invention]

[0012] Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

Example

[0013] <Figure 1> Schematic of the image forming system This embodiment will be described with reference to FIG. 1. First, the schematic configuration of the image forming system of this embodiment will be described with reference to FIG. 1.

[0014] [Image forming system] The inkjet recording system 100 of this embodiment uses an inkjet recording method in which ink is ejected to form an image on a sheet, and is a so-called sheet-fed inkjet recording apparatus that forms an ink image on a sheet using two liquids, a reaction liquid and ink. The sheet S may be any recording material that can receive ink, such as ordinary paper, thick paper, a plastic film for an overhead projector, a special-shaped sheet such as an envelope or index paper, and cloth.

[0015] As shown in FIG. 1, the inkjet recording system 100 of this embodiment is an example of an image forming apparatus, and includes a feeding module 1000, a printing module 2000, and a drying module 3000. Further, the inkjet recording system 100 includes a fixing module 4000, a cooling module 5000, a reversing module 6000, and a stacking module 7000. The sheet S supplied from the feeding module 1000 is subjected to various processes when being conveyed along the conveyance path within each module, and is finally discharged to the stacking module 7000.

[0016] Note that from the feeding module 1000 to the stacking module 7000, each may have a separate housing, and those housings may be connected to constitute the inkjet recording system 100. Alternatively, the feeding module 1000, the printing module 2000, the drying module 3000, the fixing module 4000, the cooling module 5000, the reversing module 6000, and the stacking module 7000 may be arranged in one housing.

[0017] The feeding module 1000 has storage compartments 1100a, 1100b, and 1100c for storing sheets S, and storage compartments 1100a to 1100c are provided so as to be retractable to the front side of the device for storing sheets S. Sheets S are fed one by one in each storage compartment 1100a to 1100c by a separation belt and a transport roller and transported to the print module 2000. Note that the storage compartments 1100a to 1100c are not limited to three, but may be one, two, or four or more.

[0018] An example of an image forming unit, the print module 2000, includes a pre-image registration correction unit (not shown), a print belt unit 2200, and a recording unit 2300, and forms an image by ejecting ink onto a sheet S. The sheet S, transported from the supply module 1000, has its tilt and position corrected by the pre-image registration correction unit and is transported to the print belt unit 2200. With respect to the transport path, the recording unit 2300 is positioned opposite the print belt unit 2200. The recording unit 2300 is an inkjet recording unit that forms an image by ejecting ink onto the transported sheet S from above using a recording head. Multiple recording heads that eject ink are arranged along the transport direction. In this embodiment, in addition to the four colors Y (yellow), M (magenta), C (cyan), and Bk (black), there are a total of five line-type recording heads corresponding to the reaction liquid. The sheet S is transported by suction on the print belt unit 2200, ensuring clearance with the recording head.

[0019] The number of ink colors and recording heads are not limited to the five mentioned above. The inkjet method can employ methods using heating elements, piezoelectric elements, electrostatic elements, MEMS (Micro Electro Mechanical Systems) elements, etc. Each color of ink is supplied to the recording head from an ink tank (not shown) via an ink tube. The ink contains, based on the total mass of the ink, resin components in an amount of "0.1% to 20.0% by mass," water, water-soluble organic solvents, colorants, waxes, additives, etc.

[0020] The sheet S, on which an image has been formed by the recording unit 2300, is transported by the print belt unit 2200 and detected by an inline scanner (not shown) located downstream of the recording unit 2300 in the transport direction of the sheet S. Here, any misalignment or color density of the image formed on the sheet S is detected, and based on this misalignment and color density, corrections are made to the image and density formed on the sheet S.

[0021] The drying module 3000 is an example of a drying apparatus that dries a sheet S on which an image has been formed by ejecting ink by blowing hot air onto the sheet S. The drying module 3000 has a decoupling section 3200, a drying belt unit 3300, and a hot air blowing unit 3400. The drying module 3000 reduces the liquid content of the ink and reaction solution applied to the sheet S in order to improve the ink fixation to the sheet S by the subsequent fixing module 4000. The image-formed sheet S is transported to the decoupling section 3200 located within the drying module 3000. In the decoupling section 3200, the wind pressure from the wind blown from above generates a frictional force between the sheet S and the endless belt, causing the sheet S to be gripped and transported by the belt. In this way, the sheet S placed on the belt is gripped and transported by frictional force, preventing the sheet S from shifting as it is transported between the print belt unit 2200 and the decoupling section 3200. The sheet S, transported from the decoupling unit 3200, is carried by suction on the drying belt unit 3300, and hot air is blown onto the sheet S from the hot air blowing unit 3400 located above the belt to dry the ink and reaction liquid applied to the sheet S.

[0022] In this way, the drying module 3000 heats the ink and reaction solution applied to the sheet S, promoting the evaporation of moisture, which suppresses the occurrence of so-called cockling, where the paper stretches locally and wrinkles due to the absorption of ink by the ink-coated areas of the sheet S. As for the heater that heats the air, heating by electric heating wires or infrared heaters is preferable from the standpoint of safety and energy efficiency. In addition to the method of applying hot air, the drying method may also be configured by combining a method of irradiating the surface of the sheet S with electromagnetic waves (such as ultraviolet or infrared rays) or a conduction heat transfer method by contact with a heating element.

[0023] The fixing module 4000 is an example of a drying and fixing device and includes a fixing belt unit 4100. Here, it is referred to as fixing, but since the ink is fixed to the paper by drying it with heat and pressure, it is sometimes simply called a drying device. The fixing belt unit 4100 fixes the ink to the sheet S on which the image has been formed, which has been conveyed from the drying module 3000, by passing it between a heated upper belt unit and a lower belt unit.

[0024] The cooling module 5000 has multiple cooling units 5001, which cool the high-temperature sheet S transported from the fixing module 4000. The cooling units 5001, for example, draw outside air into the cooling box with a fan to increase the pressure inside the cooling box, and then blow air out from the cooling box through nozzles under pressure onto the sheet S to cool the sheet S. The cooling units 5001 are arranged on both sides of the transport path of the sheet S, and both sides of the sheet S are cooled.

[0025] The cooling module 5000 is provided with a transport path switching unit 5002. The transport path switching unit 5002 switches the transport path of the sheet S depending on whether the sheet S is being transported to the inversion module 6000 or to the double-sided transport path for double-sided printing in which images are formed on both sides of the sheet S.

[0026] The inversion module 6000 has an inversion unit 6400. The inversion unit 6400 inverts the front and back sides of the conveyed sheet S, changing the orientation of the sheet S when it is discharged to the loading module 7000. The loading module 7000 has a top tray 7200 and a loading unit 7500, and loads the sheet S conveyed from the inversion module 6000.

[0027] During double-sided printing, the sheet S is transported by the transport path switching unit 5002 to the transport path below the cooling module 5000. The sheet S then passes through the double-sided transport path of the fuser module 4000, drying module 3000, print module 2000, and feed module 1000, and is returned to the print module 2000. The double-sided transport unit of the fuser module 4000 is provided with a reversal unit 4200 that reverses the front and back sides of the sheet S. Once returned to the print module 2000, an image is formed on the other side where no image has been formed, and the sheet S is discharged from the drying module 3000 through the reversal module 6000 to the loading module 7000.

[0028] <Figure 2> Explanation of the entire anchoring belt system Figure 2 is a schematic diagram showing the fixing module 4000. A fixing belt unit 4100 is provided at the top of the fixing module 4000. The fixing belt unit 4100 has a substantially linear sheet transport path 1 for receiving the sheet S discharged from the drying module 3000, fixing it, and then transferring the sheet S to the cooling module 5000.

[0029] The anchoring belt unit 4100 has an upper anchoring belt system 10 and a lower anchoring belt system 20. The upper anchoring belt system 10 is positioned vertically above the lower anchoring belt system 20. The upper anchoring belt system 10 has an upper belt 30, which is an example of an anchoring belt and a conveying belt (first conveying belt), and a plurality of tension rollers. That is, the upper anchoring belt system 10 is an example of a belt unit (first belt unit) and has a detachable upper belt 30 for conveying the sheet S. The lower anchoring belt system 20 is an example of a second belt unit and has a lower belt 40, a plurality of tension rollers, and a pad 423. The pad 423 is positioned to form a nip portion N with the upper belt 30 via the lower belt 40.

[0030] The sheet S is held and transported by a nip between the upper fixing belt system 10 and the lower fixing belt system 20. The pressure at the nip is determined by the tension and thickness of the upper belt 30 and the curvature of the pad 423. If the pressure at the nip is too high, the ink from the sheet S may adhere to the upper fixing belt system 10, and the ink may peel off the sheet S. Therefore, the pressure is preferably 1 Pa to 2000 Pa, and more preferably 1 Pa to 200 Pa.

[0031] If the curvature of the pad 423 increases, the difference in the transport path between the front and back of the sheet S increases, which may cause friction between the sheet S and the belt. If the curvature of the pad 423 increases, there is a risk that the sheet S itself will retain its curved shape and curl, so it is desirable that the radius of curvature of the pad 423 be 50 mm or more. Furthermore, from the standpoint of manufacturing precision, it is desirable that the radius of curvature of the pad 423 be 100,000 mm or less. Due to these constraints, in this embodiment, the tension of the upper belt 30 is set to 200 N, the thickness to 0.3 mm, the curvature of the pad 423 to 30,000 mm, and the nip pressure to be approximately 16 Pa.

[0032] By adopting this configuration, uniform pressure can be applied even to wide nips. This allows sufficient heat transfer to the sheet S by increasing the contact time between the sheet S and the upper fixing belt system 10, even when the temperature of the upper fixing belt system 10 is set to the melting point of wax or the boiling point of water. However, if the nip continues to form after sufficient heat has been transferred, the ink may adhere to the upper belt 30 and peel off the sheet S, or the upper belt 30 and the sheet S may rub against each other, causing the image to become distorted. Therefore, excessively long contact times are undesirable. For this reason, the time it takes for the leading edge of the sheet S to enter the nip entrance and exit the nip exit is preferably 0.5s to 4s. In this embodiment, a pad 423 with a length of 900mm in the sheet transport direction is used, the sheet S is transported at 700mm / s, and the time required for the leading edge of the sheet S to enter the nip entrance and exit the nip exit is set to approximately 1.3s. Furthermore, since moisture is necessary for the ink to penetrate into the sheet S, it is preferable that the upper belt 30 and lower belt 40 be made of a material that does not allow moisture to pass through them, so that when the sheet becomes hot, moisture evaporated from the surface of the sheet S does not escape through the upper belt 30 or lower belt 40 that they come into contact with. In this embodiment, the upper belt 30 and lower belt 40 are made of a belt material with a thickness of approximately 0.4 mm, with a PTFE coating on the surface of a glass fiber base material, taking into consideration heat resistance, sliding properties, airtightness, and durability.

[0033] Furthermore, of the multiple tension rollers provided in the upper anchoring belt system 10 and the lower anchoring belt system 20, one roller in each is a drive roller 450 and a drive roller 460 for driving the upper belt 30 and the lower belt 40. The drive rollers 450 and 460 are rotationally driven by the frictional force between the roller surface and the inner surface of the belt, by rotating their respective drive motors (not shown). In addition, rotation detection sensors 410 and 420 are disposed on the shafts (not shown) that constitute the driven rollers 430 and 440, which rotate in response to the rotation of the upper belt 30 and the lower belt 40. The rotation detection sensors 410 and 420 are elements composed of magnets whose magnetic force switches in the direction of rotation of the driven rollers. By detecting the change in the N and S poles caused by the rotation of the driven rollers using a Hall sensor (not shown), it is possible to detect that the upper belt 30 and the lower belt 40 are rotating reliably. In this embodiment, the rotation detection sensor is a magnetic element, but a transmissive sensor or the like may be used, which detects changes in light blocking and light transmission using a physical flag with an edge in the direction of rotation of the driven roller.

[0034] The upper fixing belt system 10 and the lower fixing belt system 20 are each equipped with heating units 117, 127, 137 and 147, 157, each having multiple heaters. The heating units 117, 127, and 137 of the upper fixing belt system 10 are located inside the upper fixing belt system 10 and above the nip N, heating the upper belt 30 from the inside. By directly heating the nip N, heat can be efficiently transferred to the sheet S. The heating units 117, 127, and 137 control the temperature by controlling the power input based on the value detected by a temperature sensor 310 that detects the surface temperature of the upper belt 30, thereby maintaining the temperature of the upper belt 30 at a predetermined temperature.

[0035] The heating units 147 and 157 of the lower anchoring belt system 20 are located inside the lower anchoring belt system 20 and heat the lower surface of the lower belt 40 from the inside. The lower surface is the surface on which the lower belt 40 is suspended in a nearly horizontal direction. The lower anchoring belt system 20 is provided with a pad 423, which prevents direct heating of the nip N. Therefore, by placing the heating units on the lower surface, the lower belt 40 is efficiently heated directly. The heating units 147 and 157 control the power input based on the value detected by a temperature sensor 320 that detects the surface temperature of the lower belt 40, thereby maintaining the temperature of the lower belt 40 at a predetermined temperature.

[0036] Furthermore, the rotation detection sensors 410 and 420 are set to stop heating by the heating units 117, 127, 137 and 147, 157 when they detect that the belt has stopped rotating. This prevents localized heating from occurring when the upper belt 30 and lower belt 40 are heated while stopped.

[0037] <Figure 3> Detailed explanation of the heating and air blowing sections Next, we will provide a detailed explanation of the heating and blowing sections using Figures 3 and 12.

[0038] Figure 3(a) is a front cross-sectional view showing the heating and blowing sections, Figure 3(b) is a detailed shape diagram of the reflector section, Figure 12(a) is a partial perspective view, and Figure 12(b) is a side cross-sectional view.

[0039] Regarding the heating sections 117, 127, 137, 147, and 157 provided in the upper fixing belt system 10 and the lower fixing belt system 20, respectively, there are many common items among them. Therefore, the explanation of the common parts and the heating section as a whole will be limited to heating section 117 only. Parts that span multiple heating sections will be explained separately.

[0040] "Common parts and heating unit only" The heater 110 consists of two heaters 110a and 110b with different maximum powers, and its ends are supported by support means (not shown). In this embodiment, the heater 110 is a halogen heater, and 110a is a heater that can be supplied with higher power than 110b. The heater 110 is positioned inside the belt, not in contact with the belt, and further positioned along the width direction of the belt, intersecting the direction of rotation of the belt. The heater 110 is covered by a reflector 115, which heats the belt portion directly below the heater 110. The reflector 115 is made of, for example, a mirror-finished aluminum material, and concentrates the light generated from the heater 110 onto the belt portion by reflecting it.

[0041] Furthermore, the reflector 115, which acts as a reflector, has a shape that includes part of a parabola. The reflector 115 is a parabola with the reflector vertex 115 as its vertex. The parabolic shape formed from the reflector vertex 115 in the direction of the belt 30 extends to the end point of the reflector parabola 115c, and then extends almost vertically toward the belt 30 to form the reflector straight section 115b. Note that due to manufacturing constraints of the parts, it may be approximated by a polygonal shape consisting of multiple line segments. It is preferable to make the reflector straight section 115b as short as possible (it may even be zero), but it is provided in order to secure space for the temperature sensor 210, which will be described later.

[0042] Heaters 110a and 110b are positioned with respect to the focus 115d of the parabola guided by the reflector vertex 115 and the reflector parabola endpoint 115c, as follows: Both heaters are positioned closer to the belt 30 than the reflector focus 115d, and have a height difference in the vertical direction with respect to the front cross-sectional direction. Furthermore, heater 110a, which is available for operation and has higher power, is positioned on the lower side.

[0043] By positioning the heater 110 closer to the belt 30 than the reflector focal point 115d, it is possible to reduce the proportion of light generated from the heater that is reflected by the reflector 115, thereby increasing heating efficiency. On the other hand, if the heater is placed too close to the belt 30, heating efficiency can be increased, but the intensity distribution of the light irradiated onto the belt 30 becomes more uneven.

[0044] Furthermore, by arranging the two heaters 110a and 110b with a difference in height in the vertical direction, it is possible to create a difference in the bias of the light distribution when each heater is lit individually. Therefore, it is possible to suppress the localized concentration of light distribution in one place when both heaters are lit simultaneously.

[0045] The temperature sensor 210 is a safety sensor that detects the temperature of the belt area heated by the heater 110 and checks whether the temperature exceeds 200°C. The temperature sensor 210 is a non-contact IR sensor that detects temperature by detecting infrared energy. Because the temperature sensor 210 needs to directly detect the temperature of the belt area heated by the heater 110, it is placed near the outside of the reflector 115. This 200°C temperature is set to prevent the belt from deforming, and is not limited to this temperature as it is determined according to the belt material. Normally, when the upper belt 30 is rotating and temperature control is in place, the temperature sensor 210 maintains a temperature of approximately 130°C or lower and does not detect temperatures above 200°C. On the other hand, if the rotation detection sensor 420 malfunctions and the upper belt 30 stops rotating, the area around the detection position of the temperature sensor 210 will continue to be heated locally and become hot. By placing the temperature sensor 210, even in the event of a malfunction, the highest point on the uppermost belt 30 can be directly detected. This allows the device to be stopped before the belt is damaged due to deformation or other reasons, resulting in a safer fixing system.

[0046] Although the reflector 115 has been subjected to the mirror finish and other treatments described above to increase its reflection efficiency, some of the light irradiated by the heater 110 is absorbed by the reflector 115 itself, causing the temperature of the reflector 115 to rise. If this embodiment is not implemented, the temperature of the reflector 115 will eventually rise to about 300°C. On the other hand, the surrounding atmosphere is also heated by the high temperature of the reflector 115, and the temperature of the temperature sensor 210 placed near the reflector 115 may also rise to about 200°C. The temperature sensor 210 has a heat resistance temperature of about 110°C, and there is a risk that problems may occur such as the temperature sensor 210 placed near the reflector 115 not being able to detect the temperature accurately. In this embodiment, the following measures are taken to suppress the temperature rise of the temperature sensor 210.

[0047] (Countermeasure 1) In this embodiment, the temperature sensor 210 is positioned on the side of the reflector 115 that is closer to the heater 110b. Since the power input to the heater 110b is lower than that of the heater 110a, the partial temperature rise of the reflector 115 is suppressed, and therefore the temperature rise of the temperature sensor 210 can be suppressed.

[0048] (Countermeasure 2) On the outer side of the reflector 115 in the front cross-sectional direction, a flow path 116a is formed by the flow path member 116, including the outer wall of the device, and the reflector 115 itself. A flow path inlet (unit) 116c is connected to the front side of the flow path 116a. The flow path inlet (unit) 116c is connected to a flow path inlet (frame) 116b provided on the frame 35, and further connected to the fan 1500. A flow path outlet 116d is provided at the back side of the flow path 116a, allowing the air that has passed through the flow path 116a to be exhausted to the upper fixing belt system 10. At least a portion of the temperature sensor 210 is enclosed and positioned inside the flow path 116a. The flow path member 116 may be composed of multiple members, and a part of the reflector 126 of an adjacent heating section 127 may also perform that function.

[0049] Fan 1500 draws in air and blows it in the direction of arrow 1500a, forming an airflow in the passage 116a. The formed airflow cools the temperature sensor 210.

[0050] The temperature sensor 210, which detects the temperature of the belt heated by the heater 110, is located between the reflectors 115 and 125 and is positioned close to the fan 1500 with respect to the center 2200 in the belt width direction. The area detected by the temperature sensor is represented by 211.

[0051] "The part that spans multiple heating elements" We will only describe the portion that spans multiple adjacent heating sections.

[0052] As in this embodiment, when multiple heating elements are arranged side by side, the temperature sensor receives heat from adjacent reflectors, causing its temperature to rise. Therefore, the following countermeasures are implemented.

[0053] (Countermeasure 3) The heating sections 147 and 157 are two heating sections attached to the lower belt fixing system 20. The temperature sensor 240 provided in heating section 147 and the temperature sensor 250 provided in heating section 157 are both located between the reflectors 145 and 155. Furthermore, the temperature sensors 240 and 250 are located on the side of the reflectors 145 and 155 that is close to the heaters 140b and 150b. At least a portion of both the temperature sensors 240 and 250 are embedded within the flow path of the flow path 146a.

[0054] With the arrangement in this embodiment, two temperature sensors 240 and 250 can be placed within a single flow path 146a, making it possible to efficiently cool the temperature sensors with fewer fans.

[0055] Furthermore, heating units 117, 127, and 137 are three heating units attached to the upper belt fixing system 10. The temperature sensor 210 provided in heating unit 117 and the temperature sensor 220 provided in heating unit 127 are both positioned between the reflectors 115 and 125. In addition, the temperature sensors 210 and 220 are positioned on the side of the reflectors 115 and 125 that is close to the heaters 110b and 120b. At least a portion of both the temperature sensors 210 and 220 are embedded and positioned inside the flow path of the flow path 116a.

[0056] On the other hand, the temperature sensor 230 provided in the heating section 137 is positioned between the reflectors 125 and 135. The temperature sensor 230 is positioned on the side of the reflector 135 that is close to the heater 130b, and at least a part of the temperature sensor 230 is contained within the flow path of the flow path 117a. However, the heater 120a (high power side) is the one that offers the shortest distance between the temperature sensor 230 and the adjacent heater 120 of the heating section 127.

[0057] When three or more heating units are installed side by side, it is not possible to position all temperature sensors close to the low-power heaters. However, the heaters in heating units 127 and 137 that are closest to the temperature sensor 230 are not both high-power heaters 120a and 130a.

[0058] <Figure 4> Block diagram of the anchoring belt system Figure 4 is a hard block diagram of the upper fixing belt system 10 of the fixing system in Example 1. The upper fixing belt system 10 consists of a CPU 1100, a Relay 1200, FETs 111, 121, 131, over-temperature detection HW 211, 221, 231, heaters 110, 120, 130, temperature sensors 210, 220, 230, and temperature sensor 310.

[0059] The CPU 1100 controls the heaters 110, 120, and 130 by driving the FETs 111, 121, and 131 with ON / OFF control. The temperature sensors 210, 220, and 230 are connected to the over-temperature detection hardware 211, 221, and 231, which use hardware circuits to detect when the temperature exceeds 200°C. This 200°C temperature is set to prevent belt deformation and is not limited to the temperature determined by the belt material. If any of the over-temperature detection hardware 211, 221, or 231 detects a temperature of 200°C or higher, it stops controlling the corresponding FET 111, 121, or 131. When the temperature of the temperature sensor 210 is detected by the over-temperature detection hardware 211, the control of FET 111 is stopped, but the over-temperature detection hardware 211 does not stop the control of the other FETs 121 and 131 via hardware circuits. The CPU 1100 detects the interrupt signal from the over-temperature detection hardware 211 and stops FETs 121 and 131 via software. In this patent, the FETs are stopped by the CPU, but they may also be stopped by hardware circuits.

[0060] <Figure 5> Flowchart of the anchoring belt system Figure 5 is a flowchart of the upper fixing belt system 10 of the fixing system in Example 1. Under normal circumstances, all steps in the flowchart are performed by the CPU 1100. When fixing control is started, the process proceeds to S101.

[0061] In S101, the CPU1100 controls the drive motor for the upper belt 30, causing the upper belt 30 to rotate. The CPU1100 also turns on the RELAY1200.

[0062] In S102, the CPU 1100 uses the rotation detection sensor 510 to determine whether the upper belt 30 is rotating. If the CPU 1100 determines that the upper belt 30 is rotating, it proceeds to S103; otherwise, it proceeds to S105.

[0063] In S103, the CPU 1100 controls the temperatures of heaters 110, 120, and 130 based on the temperature values ​​read from the temperature sensor 310. The CPU 1100 controls the temperatures of heaters 110, 120, and 130 by controlling the FETs 111, 121, and 131 with a PWM control signal duty cycle.

[0064] In S104, if the temperature values ​​read by the CPU 1100 from temperature sensors 210, 220, and 230 are higher than the threshold temperature of 200°C, the process proceeds to S105. In S104, if the temperature values ​​read by the CPU 1100 from temperature sensors 210, 220, and 230 are lower than the threshold temperature of 200°C, the process proceeds to S102.

[0065] In S105, CPU1100 stops heaters 110, 120, and 130 by turning off FETs 111, 121, and 131.

[0066] <Figure 6> Configuration of the temperature sensor Figure 6 illustrates the configuration of the temperature sensor 210. Figure 6(a) is an outline view of the temperature sensor 210. Figures 6(b) and 6(c) illustrate the field of view of the temperature sensor 210. Package 3801 is a package with a sensor module built inside, mounted on the substrate 3800, and has a detection window 3802 at the top. The temperature sensor 210 absorbs infrared radiation emitted from the object to be measured through the detection window 3802 and converts the absorbed infrared energy into an electrical signal, thereby enabling non-contact temperature detection. The temperature sensor 210 can also output the results detected by the sensor module 3801 from the connector 3806. In this embodiment, the package 3801 that actually detects the temperature is located at the very edge of the substrate among the components mounted on the substrate 3800. Figure 6(b) schematically represents the field of view of the temperature sensor 210. The detection window 3802 not only allows infrared radiation to pass into the package 3801 but also acts as a lens. In other words, the temperature sensor 210 has a constant field of view 3804 and detects the temperature of the object to be measured 3803 within the field of view 3804 without contact. Figure 6(c) is a diagram illustrating the definition of the field of view 3804. The temperature measurement accuracy is defined as 100% when the object to be measured 3803 is located on the center line 3805 of the field of view 3804. Next, the object to be measured 3803 is moved away from the center line 3805 without changing the distance to the temperature sensor 210. The angle θ formed between the object to be measured 3803 and the center line 3805 when the temperature measurement accuracy decreases to 50% due to the movement is defined as the field of view 3804. Note that the value of 50% in this embodiment is merely an example and is not limited to 50%.

[0067] <Figure 7> Example of temperature sensor placement Figure 7 shows an example of the arrangement of temperature sensors 210, 220, and 230. Figure 7(a) shows the arrangement of the belt 30, heaters 110, 120, 130, and temperature sensors 210, 220, and 230 when viewed from above the upper fixing belt system 10. Temperature sensors 210, 220, and 230 are positioned to detect the temperature directly below heaters 110, 120, and 130, respectively.

[0068] Figure 7(b) shows the positional relationship between the belt 30 and the temperature sensor 210 when viewed from the upstream side to the downstream side of the sheet conveying system. The temperature sensor 210, positioned outside the end of the belt 30, is positioned to detect the belt end region 2501 at an angle. The temperature sensor 210 is positioned so that the heater 110 does not enter the detection region 2101 in order to directly observe the heating region directly below the heater 110. As a result, the downward angle of the temperature sensor 210 relative to the belt 30 becomes larger. When the downward angle of the temperature sensor 210 becomes larger, a wider belt area is included in the detection region 2101. Therefore, it is necessary to use a temperature sensor 210 with a narrower detection region 2101, or to take into account that a wide range of belt temperatures is being detected and to provide a margin for overheating detection.

[0069] Figure 7(c) shows the relationship between heating time and belt temperature at various positions on the belt when the belt is continuously heated by the heater. The horizontal axis represents time, and the vertical axis represents belt temperature. Graph 2201 shows the temperature rise at the end position 2102 directly below the heater 110. Graph 2202 shows the temperature rise at the central position 2103 directly below the heater 110. The difference in the slope of the temperature rise between graphs 2201 and 2202 is due to the difference in heater light distribution. In this embodiment, the temperature sensor 210 detects the temperature of the region 2102 with the highest temperature rise rate. Therefore, the limit temperature 2006 of the belt 30 and the over-temperature detection threshold temperature 2204 are the same temperature. Note that the relationship between the limit temperature and the over-temperature detection threshold temperature in this embodiment is merely an example and is not limited to this. For example, it is possible to set the over-temperature detection threshold temperature 2204 with a safety margin, lower than the limit temperature 2206.

[0070] <Figure 8> Heater configuration Figure 8 is a diagram illustrating the light distribution of heaters 110, 120, and 130.

[0071] Figure 8(a) shows the relative positions of the heater 110 and the belt 30 as viewed from the upstream to the downstream side in the sheet conveying direction, and a graph showing the heating intensity at a position in the belt width direction. The belt width direction is the direction perpendicular to the sheet conveying direction and is shown as the x-axis in the figure. The sheet conveying direction is shown as the y-axis, and the height direction as the z-axis. In the following explanation, the x, y, and z axes all represent the same direction. In this embodiment, the heating area of ​​the belt is 400 mm wide, and the central area 2502 is 260 mm inward. That is, the end area 2501 is a 70 mm area in the direction furthest from both ends of the central area 2502. By distributing the heater 110 so that the heating intensity is higher in the belt end areas 2501 and 2503 than in the central area 2502, uneven heating in the belt width direction is suppressed.

[0072] Figure 8(b) shows the relationship between heating time and belt temperature when the belt is continuously heated by a heater. The horizontal axis represents time, and the vertical axis represents belt temperature. Graph 2504 shows the temperature rise in the belt end regions 2501 and 2503, and graph 2505 shows the temperature rise in the belt center region 2502. Because the heating intensity is higher in the belt end regions 2501 and 2503 than in the belt center region 2502, the temperature rise in graph 2504 is steeper. The dashed line 2506 shown in the figure represents the limit temperature set to prevent belt deformation, and this temperature is determined according to the belt material. It is necessary to set an over-temperature detection threshold so that the belt does not exceed the limit temperature 2506.

[0073] <Figure 9> Heat output distribution of the heater Figure 9 shows the relationship between the heat generated in the longitudinal direction of the two heaters 110a and 110b that constitute the heater 110 in this embodiment.

[0074] As mentioned above, two or more types of heaters are provided in the heating section 117. Among these, the relationship between at least two types of heaters is defined, specifically the relationship between the heat generated in the longitudinal central region and the longitudinal end region.

[0075] Specifically, when the amount of heat generated per unit length in the central region of the heating elements of heaters 110a and 110b is defined as Mid1 and Mid2, respectively, and the amount of heat generated per unit length in the end regions of the heating elements is defined as Ext1 and Ext2, the power is determined such that the following relationship holds. Ext2 / Mid2 > Ext1 / Mid1 > 1 In other words, the difference in heat output between the center and the edges of heater 110a is different from the difference in heat output between the center and the edges of heater 110b, and the difference in heat output between the center and the edges of heater 110b is larger than the difference in heat output between the center and the edges of heater 110a. Note that the two heaters 110a and 110b are heaters in which the heat output distribution is symmetrical with respect to the center of the heating element.

[0076] In this embodiment, the values ​​for heat generation per unit length and power were set according to the values ​​in Table 1 below.

[0077] [Table 1]

[0078] Table 1 shows the amount of heat generated per unit length when the lengths of both ends are the same, as shown in Figure 9. In this embodiment 1, as explained in Figures 3 and 12, fans 1500, 1501, and 1502 are used to blow air to cool the thermistor. In other words, the blower blows air in the front-back direction perpendicular to the belt's conveying direction. If we call the side with the fan Ext11, it can be seen that air at ambient temperature is blown onto the Ext11 side, while air heated by the reflector passes through the Ext12 side, which does not have a fan. In other words, although the fan does not directly cool the belt, the ambient temperature is Ext12 > Ext11.

[0079] Therefore, the heat generation at the end can be set to 100% for Ext11, and lower for Ext12 but higher for Mid. Preferably, a heat generation of 95% is considered.

[0080] In addition to the method of controlling by calorific value, it may be configured such that the lengths of the ends indicating a high calorific value are different at both ends. That is, it may be configured such that the length of Ext12 < the length of Ext11. In the example of FIG. 9, both ends were 70 mm each. Therefore, in consideration of cooling by the fan, for example, it is conceivable to set Ext2 to 68 mm and Ext1 to 72 mm.

[0081] In the first embodiment, the power control is implemented in the same manner as in Reference 1 as before. That is, the heaters 110a and 110b are power-controlled synchronously.

[0082] Next, the effects of the configuration in the first embodiment will be described.

[0083] When there is a limit to the maximum power of a single heater and it is necessary to operate beyond that maximum power, it becomes necessary to use multiple heaters. In that case, in order to avoid the phenomenon of local concentration of the condensing distribution to one place as described above, a difference is made in the arrangement and power relationship of the multiple heaters.

[0084] For a heater with a large power, there is a limit to the maximum calorific value per unit length. When it is desired to increase the calorific value at the longitudinal end, it is possible to operate while suppressing the maximum calorific value by increasing the calorific value at the end from a heater with a small power, and the condensing distribution to one place can also be improved.

[0085] In the case of this embodiment, the maximum calorific value per unit length at the end could be suppressed to 6.5 [W / mm] for the heater 110a and 4.5 [W / mm] for the heater 110b.

[0086] If this ratio is to be achieved with two heaters of the same duty cycle, it is possible with a relationship of 51% in the center and 100% at the ends. However, in this case, the maximum heat output at the end of heater 110a becomes large at 7.3 [W / mm], causing the slope of graph 2504 to move in the direction of increasing slope. As a safety device, a rapid rise in temperature is undesirable. In this embodiment 1, the power control of the two heaters is synchronized by the values ​​of the same temperature control sensors 310 and 320, so if the total heat output is the same, the temperature rise during normal operation will be equivalent. On the other hand, considering the safety margin when detecting a rise in temperature during an abnormality, it is better to have a smaller maximum heat output. In other words, it is advantageous for the end duty cycle of the heater with higher power to be smaller than the end duty cycle of the heater with lower power.

[0087] In other words, because the areas 2110, 2111, and 2112 detected by sensors 210, 220, and 230 are located at the edges where heat generation is high, any abnormalities can be detected relatively early. This is because the temperature rise when an abnormality occurs is steeper at the edges where heat generation is high compared to the central area where heat generation is low, so detecting the edges allows for relatively early detection. [Examples]

[0088] The configuration of the image forming system, the heater configuration, etc., are the same as in Example 1, so a description will be omitted.

[0089] By controlling the lighting during the warm-up of the drying and fixing device using the following procedure, it is possible to eliminate the large temperature difference between the longitudinal center and the edges until printing begins, without changing the required warm-up time.

[0090] Figure 10 shows the changes in the belt center temperature detected by sensor 310 and the belt end temperature detected by sensor 311 from the initial startup, as presented as a conventional example (Example 1). Sensor 311 is an end temperature sensor (not shown) placed on the same circumference as sensor 310, 160 mm in the longitudinal direction, to check the temperature of the longitudinal end region of the belt. Until 80s, when the temperature detected by sensor 310 reaches the temperature control target temperature of 105°C, heating is performed at 100% power, so the end temperature remains high. After that, the power is reduced to supply heat in a way that compensates for the amount of heat dissipated to the surroundings. Therefore, in this example, at 160s, the end temperature is lower than the center temperature. This is because, when no paper is passing through, the amount of heat escaping from the longitudinal end is relatively greater than the amount of heat escaping from the center, and as the amount of heat added decreases, the end temperature becomes insufficient.

[0091] In this case, once the target temperature for temperature control at 80s is reached, the drop in edge temperature can be mitigated by heating with heaters that have a higher power ratio at the edges to maintain temperature control. Figure 11 shows the same control as Figure 10 up to the point where the target temperature for temperature control at 80s is reached, but when the power is reduced after 80s, heat is supplied using only heater 110b. By adding more heat to the edges than to the center, the balance of heat between the center and the edges is maintained, and the belt before printing can be kept with a uniform heat distribution.

[0092] Table 2 below summarizes the relationship between the heater lighting conditions based on these control explanations.

[0093] [Table 2]

[0094] Here, temperature control (synchronous) is a control system in which the ON / OFF timing of heaters 110a and 110b is synchronized. The ON / OFF control of the heaters is performed by the CPU 1100, which acts as the control unit, by controlling the power supply to each heater. The ON / OFF timing is controlled so that the heater turns OFF when the temperature detected by the temperature sensor reaches the target temperature and turns ON when it falls below the target temperature. Alternatively, temperature control can be controlled in which heaters 110a and 110b are turned ON / OFF independently without timing synchronization. The optimal ON / OFF timing is adopted based on the temperature detected by the temperature sensors at the center and ends of the belt.

[0095] Furthermore, in Example 2, the temperature control from 80s onwards is performed by turning only heater 110b ON / OFF based on the temperature detected by sensor 310. During the warm-up from room temperature from 0 to 80s, heater 110a is used in conjunction to increase the total heat in the center and because heat is needed in the center. Once warm-up is complete, only heater 110b is used to maintain the temperature for the reasons of the aforementioned heat supply balance.

Claims

1. A drying apparatus that heats a sheet on which an image has been formed by an image forming unit that ejects ink to form an image on the sheet, in order to dry the ink ejected onto the sheet, A rotating, endless first belt, A nip portion is formed between the first belt and the rotating endless second belt for gripping and conveying the sheet, The first belt has a first heater and a second heater that are positioned inside the first belt, non-contact with the first belt, and along the width direction of the first belt intersecting the rotation direction of the first belt, and heat the first belt by radiating heat. The first heater and the second heater are such that, in the longitudinal direction intersecting the transport direction of the recording material, the amount of heat generated per unit length at the ends is greater than the amount of heat generated in the center. The difference in heat output between the center and the edges of the first heater is different from the difference in heat output between the center and the edges of the second heater. A drying apparatus characterized by the following features.

2. The first heater and the second heater are heaters whose heat output distribution is symmetrical with respect to the center of the heating element. The drying apparatus according to feature 1.

3. The drying apparatus according to claim 1, wherein the first belt has a reflector on the inside of the first belt that reflects light generated from a heater and focuses the light onto the first belt, and the first heater and the second heater are arranged inside the reflector.

4. The system includes one or more first temperature sensors that detect the surface temperature of the belt in the area irradiated by the first heater, The detection area of ​​the first temperature sensor detects the surface temperature of the area irradiated by the end of the first heater. The drying apparatus according to feature 1.

5. The first heater and the second heater are halogen heaters. The drying apparatus according to feature 1.

6. The amount of heat generated in the central part of the first heater per unit length does not include zero. The drying apparatus according to feature 1.

7. A control unit that controls the supply of power to the first heater and the second heater, The system includes one or more second temperature sensors that detect the surface temperature of the belt in a range different from the range irradiated by the first heater and the second heater in the rotational direction of the belt. The control unit controls the supply of power to the first heater and the second heater, respectively, based at least on the output of the second temperature sensor. The drying apparatus according to feature 1.

8. The power supply to the first heater and the second heater in the control unit is controlled synchronously based on the output of the second temperature sensor. The drying apparatus according to feature 7.

9. The first temperature sensor is a non-contact IR sensor that detects temperature by detecting infrared energy. The drying apparatus according to feature 4.

Images