Image forming apparatus

Abstract

To appropriately control an image forming operation according to the temperature of a recording sheet even when a sheet temperature detection means is omitted.SOLUTION: The image forming apparatus includes a sheet storage part for storing a recording sheet S, an image forming part 1 for forming an image on the recording sheet fed from the sheet storage part, and a control part 300 for controlling an image forming operation according to the temperature of the recording sheet. The image forming apparatus includes the temperature detector 301,302 that detects at least one of the temperature outside the apparatus and the temperature inside the apparatus, and the information acquisition unit that acquires at least one of the latest operation time information indicating the time when the latest image forming operation is performed, the number-of-fed-sheets information indicating the number of recording sheets fed from the sheet storage unit within a predetermined immediately preceding period, and the sheet size information indicating the size of the recording sheet stored in the sheet storage unit.SELECTED DRAWING: Figure 9

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus. [Background technology]

[0002] Conventionally, an image forming apparatus is known that includes a sheet storage section that stores recording sheets, an image forming section that forms an image on the recording sheets fed from the sheet storage section, and a control section that controls the image forming operation in accordance with the temperature of the recording sheets.

[0003] For example, Patent Document 1 discloses an image forming device that, when the temperature of a fed recording sheet is equal to or higher than a predetermined value, controls to shorten the sheet interval (the interval between successively conveyed recording sheets) and delay the timing of changing the sheet interval (the time from when an increase in edge temperature is detected until the sheet interval is changed).In this image forming device, in order to reduce costs by omitting a sheet temperature detection means that directly detects the temperature of the recording sheet, the temperature of the recording sheet is indirectly determined from the detection result of an existing environmental temperature detection means that detects the installation environmental temperature of the image forming device (temperature outside the device or temperature inside the device), and the above control is performed. Summary of the Invention [Problem to be solved by the invention]

[0004] However, conventional image forming devices that omit a sheet temperature detection means for directly detecting the temperature of the recording sheet have the problem that they are unable to properly control the image forming operation in accordance with the temperature of the recording sheet. [Means for solving the problem]

[0005] In order to solve the above-mentioned problems, the present invention provides an image forming apparatus comprising a sheet storage section that stores recording sheets, an image forming section that forms an image on a recording sheet fed from the sheet storage section, and a control section that controls the image forming operation in accordance with the temperature of the recording sheet, and the image forming apparatus has a temperature detection section that detects at least one of the temperature outside the machine and the temperature inside the machine, and an information acquisition section that acquires at least one of the following information: most recent operation time information indicating the time when the most recent image forming operation was performed, fed sheet number information indicating the number of recording sheets fed from the sheet storage section within a specified immediately previous period, and sheet size information indicating the size of the recording sheets stored in the sheet storage section, and the control section controls the image forming operation based on the detected temperature detected by the temperature detection section and the at least one piece of information acquired by the information acquisition section. [Effects of the Invention]

[0006] According to the present invention, even if a sheet temperature detection unit that directly detects the temperature of the recording sheet is omitted, it is possible to appropriately control the image forming operation in accordance with the temperature of the recording sheet. [Brief explanation of the drawings]

[0007] [Figure 1] 1 is a cross-sectional view showing an example of an image forming apparatus according to an embodiment of the present invention; [Figure 2] FIG. 2 is a schematic diagram illustrating the configuration of a fixing device in the image forming apparatus. [Figure 3] FIG. 3 is a plan view showing a movable light blocking plate in the fixing device. [Figure 4] 5A and 5B are schematic diagrams for explaining a temperature rise in a non-sheet passing area. [Figure 5] 10 is a graph showing a temperature rise in a non-paper passing area depending on the temperature of a recording sheet. [Figure 6] 10 is a graph illustrating temperature transitions in a paper passing area and a paper non-passing area under conventional control. [Figure 7] (a) is a graph showing the paper interval time required for heat dissipation, and (b) is a graph showing the timing for changing the paper interval time. [Figure 8]6 is a graph showing temperature transitions in a paper passing area and a paper non-passing area in the present embodiment. [Figure 9] FIG. 2 is a control block diagram of the main parts of the image forming apparatus according to the embodiment. [Figure 10] 4 is a flowchart showing an example of a control flow in the present embodiment. [Figure 11] 10 is a flowchart showing another example of the control flow in the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0008] An embodiment in which the present invention is applied to a color printer, which is an electrophotographic image forming apparatus, will be described below. Although the present embodiment is an example of a tandem intermediate transfer color printer, the present invention may be applied to any image forming apparatus that controls the image forming operation in accordance with the temperature of the recording sheet. Therefore, the present invention may be applied to an image forming apparatus other than an electrophotographic type (such as an inkjet type), or may be an image forming apparatus other than a printer, such as a copying machine or a facsimile machine.

[0009] The image forming apparatus 100 of this embodiment employs a tandem structure in which photoreceptor drums 20Y, 20C, 20M, and 20Bk are arranged side by side as latent image carriers capable of forming color-separated images of yellow, cyan, magenta, and black. Each of the photoreceptor drums 20Y, 20C, 20M, and 20Bk is disposed opposite an intermediate transfer belt 11, which serves as an intermediate transfer body and is an endless belt movable in the direction of arrow A1 in the figure. The toner images (visible images) formed on each of the photoreceptor drums 20Y, 20C, 20M, and 20Bk are superimposed and transferred (primary transfer) onto the intermediate transfer belt 11 through a primary transfer process. The image on the intermediate transfer belt 11 is then transferred to a recording sheet S through a secondary transfer process.

[0010] Various devices are arranged around each photosensitive drum to perform image formation processing in accordance with the rotation of the photosensitive drum. Taking the photosensitive drum 20Bk, which forms a black image, as an example, a charging device 30Bk, a developing device 40Bk, a primary transfer roller 12Bk, and a cleaning device 50Bk are arranged along the rotation direction of the photosensitive drum 20Bk. An optical writing device 8 is used to write a latent image onto the photosensitive drum 20Bk after the charging device 30Bk charges the photosensitive drum 20Bk.

[0011] The photosensitive drums 20Y, 20C, 20M, and 20Bk are arranged in this order from the upstream side in the A1 direction. The photosensitive drums 20Y, 20C, 20M, and 20Bk are provided in imaging units 1Y, 1C, 1M, and 1Bk for forming yellow, cyan, magenta, and black images, respectively. An optical writing device 8 is disposed below these four imaging units 1Y, 1C, 1M, and 1Bk.

[0012] The optical writing device 8 is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a folding mirror, and a rotating polygonal mirror as a deflection means. The optical writing device 8 emits writing light Lb corresponding to each color to each of the photoconductor drums 20Y, 20C, 20M, and 20Bk, forming electrostatic latent images on the photoconductor drums 20Y, 20C, 20M, and 20Bk. For convenience, the writing light Lb in FIG. 1 is labeled only for the black image forming unit 1Bk, but the same applies to the other imaging units 1Y, 1C, and 1M.

[0013] In the superimposed transfer onto the intermediate transfer belt 11, as the intermediate transfer belt 11 moves in the A1 direction, the toner images of each color formed on each of the photosensitive drums 20Y, 20C, 20M, and 20Bk are transferred and superimposed onto the same position on the intermediate transfer belt 11. At this time, a voltage is applied to primary transfer rollers 12Y, 12C, 12M, and 12Bk disposed opposite each of the photosensitive drums 20Y, 20C, 20M, and 20Bk across the intermediate transfer belt 11.

[0014] The image forming apparatus 100 is provided with a transfer unit 10 which is disposed above and facing the photosensitive drums 20Y, 20C, 20M, and 20Bk and which includes an intermediate transfer belt 11 and primary transfer rollers 12Y, 12C, 12M, and 12Bk. The image forming apparatus 100 also includes a secondary transfer roller 5 which is disposed facing the intermediate transfer belt 11 and serves as a secondary transfer member which rotates in conjunction with the intermediate transfer belt 11. The image forming apparatus 100 also includes a cleaning device 13 which is disposed facing the intermediate transfer belt 11 and which cleans the surface of the intermediate transfer belt 11.

[0015] The image forming apparatus 100 also includes a sheet feeding device including a paper feed tray 61 as a sheet storage unit that holds recording sheets S that are transported toward between the photosensitive drums 20Y, 20C, 20M, and 20Bk and the intermediate transfer belt 11. The recording sheets S fed from the paper feed tray 61 are fed by the registration roller pair 4 toward the transfer unit between each of the photosensitive drums 20Y, 20C, 20M, and 20Bk and the intermediate transfer belt 11 at predetermined timings that match the timings of the formation of toner images by the imaging units 1Y, 1C, 1M, and 1Bk.

[0016] The image forming apparatus 100 is also provided with a fixing device 200 as a fixing section for fixing the toner image onto the recording sheet S onto which the toner image has been transferred. The recording sheet S onto which the toner image has been fixed by the fixing device 200 is disposed above the main body of the image forming apparatus 100, and is discharged to the outside of the main body of the image forming apparatus 100 by a paper discharge roller 7, and is stacked on a paper discharge tray 17. Note that toner bottles 9Y, 9C, 9M, and 9Bk filled with toner of each color, yellow, cyan, magenta, and black, are disposed below the paper discharge tray 17.

[0017] In addition to the intermediate transfer belt 11 and primary transfer rollers 12Y, 12C, 12M, and 12Bk, the transfer unit 10 also has a drive roller 72 and a driven roller 73 around which the intermediate transfer belt 11 is wound. The driven roller 73 also functions as a means for applying tension to the intermediate transfer belt 11, and for this purpose, a biasing means such as a spring is provided on the driven roller 73. The transfer unit 10, primary transfer rollers 12Y, 12C, 12M, and 12Bk, secondary transfer roller 5, and cleaning device 13 constitute a transfer device 71.

[0018] The sheet feeding device is disposed at the bottom of the main body of the image forming apparatus 100, and has a feeding roller 3 that comes into contact with the upper surface of the uppermost recording sheet S among the recording sheets stacked on the paper feed tray 61. When the feeding roller 3 is driven to rotate counterclockwise, the uppermost recording sheet S is fed toward the pair of registration rollers 4.

[0019] The cleaning device 13 provided in the transfer device 71 has a cleaning brush and a cleaning blade disposed so as to face and contact the intermediate transfer belt 11. The cleaning brush and the cleaning blade scrape off and remove foreign matter such as residual toner on the intermediate transfer belt 11, thereby cleaning the intermediate transfer belt 11. The cleaning device 13 also has a discharge means for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

[0020] FIG. 2 is a cross-sectional view showing the main part of the fixing device 200 according to this embodiment. Fixing device 200 of this embodiment has pressure roller 203 as a pressure member and fixing belt 201 as a fixing member, and fixing belt 201 is directly heated from the inner peripheral side by heat source 202 such as a halogen heater as heating means. On the inner peripheral surface side of fixing belt 201, nip forming member 206 is provided, which is pressed against pressure roller 203, which faces fixing belt 201 across fixing belt 201, to form a nip. Nip forming member 206 slides directly (or indirectly via a sliding sheet) against the inner surface of fixing belt 201. In FIG. 2, nip portion N has a flat shape, but it may have a concave shape or other shapes.

[0021] The fixing belt 201 can be a metal belt made of nickel, SUS, or an endless belt (or film) made of a resin material such as polyimide. The belt surface preferably has a release layer, such as a PFA or PTFE layer, to prevent toner from adhering. An elastic layer, such as a silicone rubber layer, may be placed between the belt substrate and the release layer. Without an elastic layer, the thermal capacity is reduced, but when an unfixed image is crushed and fixed, minute irregularities on the belt surface are transferred to the image, resulting in a problem of citrus peel-like uneven gloss (citrus peel image) remaining in solid areas of the image. To improve this, a silicone rubber layer of 100 μm or more is recommended. The deformation of the silicone rubber layer absorbs the minute irregularities, improving the citrus peel image.

[0022] Inside fixing belt 201, stay 207 is provided as a support member for supporting nip forming member 206. This prevents bending of nip forming member 206 when pressure is applied by pressure roller 203, ensuring a uniform nip width in the axial direction. Stay 207 is held and fixed at both ends by holding members 208 (flanges) for positioning. A reflecting member 209 is provided between heat source 202 and stay 207. Reflecting member 209 prevents unnecessary energy consumption caused by heating of stay 207 by radiant heat from heat source 202. Instead of providing reflecting member 209, the same effect can be achieved by insulating or mirror-finishing the surface of stay 207.

[0023] The heat source 202 may be a halogen heater, an induction heater, a resistance heating element, a carbon heater, or the like. Reference numeral 210 denotes a movable light shielding plate. The heat source 202 generates heat under output control by a power supply unit disposed in the main body of the image forming apparatus 100. The output control is performed based on the detection result of the surface temperature of the fixing belt 201 by a fixing temperature sensor 220 (see FIG. 9). By controlling the output of the heat source 202 in this way, the temperature (fixing temperature) of the fixing belt 201 can be maintained at a desired temperature.

[0024] The pressure roller 203 is configured with a core metal 205 coated with an elastic rubber layer 204, and a release layer (PFA or PTFE layer) is provided on the surface to provide releasability. The pressure roller 203 rotates by receiving a driving force from a drive source such as a motor provided in the image forming apparatus via a gear. The pressure roller 203 is pressed against the fixing belt 201 by a spring or the like, and the elastic rubber layer 204 is compressed and deformed to provide a predetermined nip width. The pressure roller 203 may be a hollow roller or may include a heating source such as a halogen heater. The elastic rubber layer 204 may be solid rubber, but if the pressure roller 203 does not have an internal heater, sponge rubber may be used. Sponge rubber is preferable because it provides higher thermal insulation and is less likely to lose heat from the fixing belt 201.

[0025] The fixing belt 201 rotates together (is driven by) the pressure roller 203. In this embodiment, the pressure roller 203 is rotated by a drive source, and the driving force is transmitted to the fixing belt 201 at the nip portion N, causing the fixing belt 201 to rotate. The fixing belt 201 rotates while being sandwiched at the nip portion N, and is guided by holding members 208 at both ends outside the nip portion and runs.

[0026] FIG. 3 is a plan view showing the movable light blocking plate 210, and FIG. 4 is a schematic diagram for explaining the temperature rise in the non-paper passing area (hereinafter also referred to as "edge temperature rise"). The movable light-shielding plate 210 used in the fixing device 200 of this embodiment has a shape with an opening (non-light-shielding portion) corresponding to the sheet size, as shown in Figure 3, and by blocking the heat from the heater with the light-shielding portion (light-shielding plate), it prevents temperature rise in non-paper passing areas.

[0027] As can be seen from FIG. 2, the movable light shielding plate 210 is configured to have an arc-shaped cross section that follows the inner circumferential surface of the fixing belt 201, and is movable in the circumferential direction of the fixing belt 201 as needed. In this embodiment, there is a direct heating area where the heat source 202 directly faces the fixing belt 201 and heats it, and a non-direct heating area where a reflecting member 209 or the like is interposed. When heat shielding is required, the movable light shielding plate 210 is disposed in a shielding position on the direct heating area side (the state shown in FIG. 2). On the other hand, when heat shielding is not required, the movable light shielding plate 210 is moved to a retracted position on the non-direct heating area side. Furthermore, since the movable light shielding plate 210 must be heat resistant, it is preferable to use a metal material such as aluminum, iron, or stainless steel, or ceramic as its material.

[0028] The fixing device 200 shown in FIG. 2 is configured with two heat sources 202, and each heat source 202 is composed of a central heater 202A and an edge heater 202B, as shown in FIG. 4. The central heater 202A has a heat generating region in the center in the sheet width direction (the direction perpendicular to the sheet conveying direction), and the edge heater 202B has heat generating regions on both outer sides in the sheet width direction. Since the fixing device 200 of this embodiment uses the center as the sheet conveyance reference, only the central heater 202A is used when passing a sheet of a predetermined size (letter portrait size in this case) or less, and both the central heater 202A and the edge heater 202B are used when passing a sheet wider than the predetermined size.

[0029] In the fixing device 200 of this embodiment, when postcard-sized paper, which is narrower than the width of the heating area of ​​the center heater 202A, is passed through, a temperature rise in the non-paper passing area can occur even when only the center heater 202A is used. Because postcard-sized paper is frequently used, a temperature rise in the non-paper passing area can result in a decrease in productivity. Therefore, in this embodiment, a measure to prevent a temperature rise in the non-paper passing area is taken using the movable light shielding plate 210 to prevent a decrease in productivity due to a temperature rise in the non-paper passing area. Similarly, when B4-sized paper, which is narrower than the combined heating area of ​​the center heater 202A and the edge heater 202B, is passed through, the paper is frequently used, so a measure to prevent a temperature rise in the non-paper passing area is taken using the movable light shielding plate 210 to prevent a decrease in productivity due to a temperature rise in the non-paper passing area.

[0030] However, when A5 paper is fed lengthwise in the fixing device 200 having the above configuration, a temperature rise occurs in the non-paper-passing area, as shown in the "longitudinal temperature distribution" in Fig. 4. As shown in Fig. 5, the temperature rise in this non-paper-passing area is significantly higher than the temperature transition in the paper-passing area, and over time exceeds the upper limit of the usable temperature of the fixing belt 201, etc. In particular, when the temperature of the fed recording sheet is low, the fixing set temperature (target temperature) rises, and the temperature rise in the non-paper-passing area transitions to rise more steeply and higher, as shown in the graph in Fig. 5.

[0031] Therefore, even when the temperature of the recording sheet being fed is low, it is necessary to increase the sheet interval (paper interval time) and reduce the number of sheets passed per unit time so that the temperature of the non-sheet passing area does not exceed the upper limit of the usable temperature of the fixing belt 201, etc. However, in this case, as shown in Figure 6, when the temperature of the recording sheet is not low (standard environment, high temperature environment), the temperature of the non-sheet passing area becomes excessively lower than the upper limit of the usable temperature of the fixing belt 201, etc. In other words, when the temperature of the recording sheet is not low (standard environment, high temperature environment in Figure 5), it would actually be possible to increase the number of sheets passed per unit time by making the sheet interval (paper interval time) shorter, which results in a decrease in productivity.

[0032] Therefore, in this embodiment, as shown in the graph of Fig. 7(a), control is performed to change the required sheet interval (sheet interval time) (sheet interval between sequentially conveyed recording sheets) depending on the temperature of the recording sheets being fed. Note that in this embodiment, control is also performed to change the time from when an increase in edge temperature is detected until the sheet interval time is changed (sheet interval time change timing), as shown in the graph of Fig. 7(b).

[0033] Fig. 7(a) is a graph showing the sheet interval time required for heat dissipation, with the horizontal axis representing sheet temperature and the vertical axis representing sheet interval time. Fig. 7(b) is a graph showing the timing for changing the sheet interval time, with the horizontal axis representing sheet temperature and the vertical axis representing the time from when an edge temperature rise is detected until the sheet interval time is changed.

[0034] FIG. 8 is a graph showing temperature transitions in the paper passing area and non-paper passing area in this embodiment. In this embodiment, by controlling the sheet interval time and the timing of changing the sheet interval time according to the temperature of the recording sheet, it is possible to obtain the temperature transition in the non-sheet passing area as shown in the graph of FIG. 8, regardless of the temperature of the recording sheet. Specifically, after the start of sheet passing, the temperature in the non-sheet passing area becomes higher than in the sheet passing area, but after a certain time, the temperature in the non-sheet passing area remains constant regardless of the temperature of the recording sheet, and remains close to the upper limit of the usable temperature. As a result, regardless of the temperature of the recording sheet, productivity can be improved without exceeding the upper limit of the usable temperature of the fixing belt 201, etc.

[0035] The control for changing the sheet interval time in accordance with the temperature of the recording sheet will be described. In this embodiment, the sheet interval (sheet interval time) between sequentially conveyed recording sheets is controlled to change from a predetermined sheet interval time (predetermined time) depending on the temperature of the recording sheets. The predetermined sheet interval time (predetermined time) here refers to a reference sheet interval time, so any point in FIG. 7A may be used. When the recording sheet temperature corresponding to this reference time is low, the sheet interval time is controlled to be longer than the predetermined time, and when the recording sheet temperature is high, the sheet interval time is controlled to be shorter than the predetermined time. For example, if the reference recording sheet temperature is 23°C and the sheet interval time (predetermined time) corresponding to that reference temperature is 2 seconds, the sheet interval time is controlled to be 3 seconds when the recording sheet temperature is 10°C, and 1 second when the recording sheet temperature is 32°C. The values ​​shown here are examples and are specific to the fixing device, so they must be set appropriately.

[0036] Next, a control for changing the timing for changing the sheet interval time in accordance with the temperature of the recording sheet will be described. In this embodiment, a predetermined timing for changing the paper interval time (predetermined timing) is controlled based on the temperature of the recording sheet. The predetermined timing for changing the paper interval time (predetermined timing) here refers to a reference timing for changing the paper interval time, and therefore any point in FIG. 7B may be used for the timing. If the recording sheet temperature is lower than the reference timing, the timing for changing the paper interval time is set earlier than the predetermined timing. If the recording sheet temperature is higher than the reference timing, the timing for changing the paper interval time is set later than the predetermined timing. For example, if the reference recording sheet temperature is 23°C and the timing for changing the paper interval time for that reference temperature is 10 seconds, the timing for changing the paper interval time is set to 0 seconds when the recording sheet temperature is 10°C, and set to 15 seconds when the recording sheet temperature is 32°C. The values ​​shown here are examples and are specific to the fixing device, so they must be set appropriately.

[0037] As in this embodiment, by changing (controlling) the paper interval time according to the temperature of the recording sheet and by changing (controlling) the timing of the paper interval change, it is possible to keep the edge temperature rise below a specified value while ensuring the necessary amount of heat dissipation time, thereby improving energy savings in a variety of environments and maximizing productivity.

[0038] Here, when controlling the sheet interval (sheet interval time) between sequentially conveyed recording sheets or the timing of changing the sheet interval time in accordance with the temperature of the recording sheets, it is necessary to acquire the temperature of the recording sheets. One method for directly acquiring the temperature of the recording sheets is to provide a temperature sensor in the paper feed tray 61 that detects the temperature of the recording sheets contained in the paper feed tray 61, and acquire the temperature of the recording sheets from the detection result of the temperature sensor. However, this method requires providing a temperature sensor in the paper feed tray 61, which increases costs.

[0039] Therefore, in order to reduce costs, a method is required in which the temperature of the recording sheet is indirectly obtained by not installing a temperature sensor in the paper feed tray 61 but by using existing components (sensors, etc.) installed in the image forming device for purposes other than controlling the change of the paper interval time or the timing of changing the paper interval time.

[0040] Some conventional image forming apparatuses acquire the temperature of recording sheets from a temperature sensor (such as an environmental temperature sensor) that detects the temperature outside the image forming apparatus, assuming that the temperature of recording sheets stored in the paper feed tray 61 is the same as the temperature outside the image forming apparatus. If the paper feed tray 61 is left unused for a long period of time without image formation, the temperature of the recording sheets will be the same as the temperature outside the apparatus. Therefore, conventional image forming apparatuses can appropriately control the sheet interval time or the timing for changing the sheet interval time. However, when image formation is performed, the temperature of the recording sheets stored in the paper feed tray 61 will fluctuate from the temperature outside the apparatus due to various factors. Therefore, conventional image forming apparatuses, which assume that the temperature outside the apparatus is the same as the temperature of the recording sheets, cannot appropriately control image formation in accordance with the temperature of the recording sheets.

[0041] More specifically, when an image forming operation is performed, the various components within the image forming apparatus operate and generate heat, causing an increase in the temperature inside the apparatus. This increase in the temperature inside the apparatus warms the recording sheets contained in the paper feed tray 61, causing the temperature of the recording sheets to increase. The extent to which the temperature of the recording sheets in the paper feed tray 61 increases due to the increase in the temperature inside the apparatus caused by the image forming operation can be determined from a correlation with the temperature detected by a temperature detection unit that detects at least one of the temperature outside the apparatus and the temperature inside the apparatus. However, even if the extent to which the temperature of the recording sheets in the paper feed tray 61 increases due to the increase in the temperature inside the apparatus caused by the image forming operation can be determined, the temperature of the recording sheets during the image forming operation cannot be determined accurately unless the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation is properly determined. Therefore, it is not possible to properly control the paper interval time or the timing to change the paper interval time based solely on the temperature outside the apparatus.

[0042] Therefore, in this embodiment, in addition to the detection results of the temperature outside the machine and the temperature inside the machine, other information for determining the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation is also obtained from the existing components, and the paper interval time and the timing of changing the paper interval time are controlled. Specifically, as the other information, at least one of the following information is used: most recent operation time information indicating when the most recent image forming operation was performed, fed sheet number information indicating the number of recording sheets fed from the paper feed tray 61 within a predetermined immediately previous period, and sheet size information indicating the size of the recording sheets stored in the paper feed tray 61.

[0043] The temperature of the recording sheet in the paper feed tray 61 at the start of an image forming operation decreases the longer the elapsed time (i.e., the time left unused) since the most recent image forming operation was performed. To explain why, immediately after the most recent image forming operation is performed, the temperature inside the machine rises due to the heat generated by each component during the most recent image forming operation, warming the recording sheet in the paper feed tray 61 and raising the temperature of the recording sheet. However, after the most recent image forming operation is completed, the components stop operating and no longer generate heat, so the inside of the machine gradually cools down and the temperature inside the machine drops, and the recording sheet in the paper feed tray 61 also gradually cools down and the temperature of the recording sheet drops. After a sufficiently long time has passed, the temperature of the recording sheet in the paper feed tray 61 drops to approximately the same as the detected temperature outside the machine or the detected temperature inside the machine.

[0044] In this way, a correlation is found between the time elapsed since the most recent image forming operation was performed (idle time) and the temperature of the recording sheet in the paper feed tray 61 at the start of the image forming operation. Therefore, by acquiring the most recent operation information (print history) including the most recent operation time information indicating the time when the most recent image forming operation was performed, it is possible to confirm whether or not a sufficient amount of time has passed for the temperature to drop to approximately the same as the detected temperature outside or inside the machine, and if a sufficient amount of time has passed, the temperature of the recording sheet in the paper feed tray 61 can be properly determined from the detected temperature outside or inside the machine.

[0045] In particular, when the detected temperature inside the machine is used, the temperature inside the machine at the time after the most recent image forming operation is completed can be determined, and from this temperature inside the machine, it is possible to estimate the temperature of the recording sheets in the paper feed tray 61 at the time after the most recent image forming operation is completed. In this case, even before the above-mentioned sufficient time has passed, it is possible to appropriately determine the temperature of the recording sheets in the paper feed tray 61 at the time when the image forming operation starts, from the correlation between the time elapsed since the most recent image forming operation was performed (leave time) and the temperature change of the recording sheets in the paper feed tray 61 at the time when the image forming operation starts.

[0046] Furthermore, if the most recent operation information includes information such as the image formation operation time or the number of images formed in the most recent image forming operation, it is possible to more appropriately determine the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation. In other words, the temperature inside the apparatus at the end of the most recent image forming operation affects the temperature of the recording sheets in the paper feed tray 61 at that end, and in turn affects the temperature of the recording sheets in the paper feed tray 61 at the start of the subsequent image forming operation. Therefore, by using information such as the image formation operation time or the number of images formed in the most recent image forming operation, it is possible to more appropriately determine the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation. The most recent operation time information can be obtained by a timer unit or the like provided in the control device 300.

[0047] Furthermore, the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation increases as the number of recording sheets fed from the paper feed tray 61 increases within a predetermined immediately preceding period. To explain this, when the topmost recording sheet is fed from a stack of recording sheets stored in the paper feed tray 61, the topmost recording sheet slides against the next recording sheet in contact with it, and the frictional heat caused by this sliding warms the recording sheets remaining in the paper feed tray 61. The more recording sheets are fed from the paper feed tray 61, the more frequently frictional heat is generated by sliding during feeding, and the temperature of the recording sheets in the paper feed tray 61 increases. Therefore, the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation increases as the number of recording sheets fed from the paper feed tray 61 increases within the immediately preceding period.

[0048] As described above, a correlation is observed between the number of recording sheets fed from the paper feed tray 61 within a predetermined immediately preceding period and the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation. Therefore, by obtaining fed sheet number information indicating the number of recording sheets fed from the paper feed tray 61 within a predetermined immediately preceding period, it is possible to properly grasp the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation. The fed sheet number information can be obtained by a fed sheet number counting unit provided in the control device 300, for example.

[0049] Furthermore, the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation decreases as the size of the recording sheets stored in the paper feed tray 61 increases. This is because the larger the size of the recording sheets stored in the paper feed tray 61, the larger the surface area of ​​the recording sheets, which makes it easier for them to dissipate heat, and therefore the temperature of the recording sheets in the paper feed tray 61 decreases more easily. As such, a correlation is observed between the size of the recording sheets stored in the paper feed tray 61 and the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation. Therefore, by obtaining sheet size information indicating the size of the recording sheets stored in the paper feed tray 61, it is possible to accurately determine the temperature of the recording sheets in the paper feed tray 61 at the start of the image forming operation. Note that the sheet size information can be obtained from sheet size information input by the user to the operation unit of the image forming apparatus 100, the detection results of position sensors of paper regulation units such as the side fences and end fences of the paper feed tray 61, etc.

[0050] FIG. 9 is a control block diagram relating to the main parts of the image forming apparatus according to this embodiment. The image forming apparatus 100 of this embodiment includes a control device 300 serving as a control unit. The control device 300 includes a central processing unit (CPU), random access memory (RAM), read-only memory (ROM), and flash memory. The ROM stores a control program for controlling each component of the image forming apparatus. Based on the control program, the control device 300 controls the operation of each component within the image forming apparatus and exchanges information and data with each component. The control device 300 is electrically connected to imaging units 1Y, 1C, 1M, and 1Bk for Y, C, M, and Bk, a write control unit 311, a fixing device 200, a transfer unit 10, an image information input unit 310, an ambient temperature sensor 301, and an internal temperature sensor 302.

[0051] The image information input unit 310 receives image information sent from an external personal computer or scanner and sends it to the control device 300 and the writing control unit 311. The writing control unit 311 controls the driving of the optical writing device 8 based on the received image information, thereby performing optical writing processing on the photosensitive drums 20Y, 20C, 20M, and 20Bk of each color. The control device 300 also controls the output of the heating source 202 of the fixing device 200 based on the detection result of the surface temperature of the fixing belt 201 by the fixing temperature sensor 220. This maintains the temperature of the fixing belt 201 (fixing temperature) at a desired temperature.

[0052] In this embodiment, the control device 300 acquires the environmental temperature from an environmental temperature sensor 301, which serves as a temperature detection unit that detects the environmental temperature (temperature outside the device). The environmental temperature sensor 301 may be any sensor that can detect the temperature outside the image forming device 100, and may be placed, for example, in a location within the image forming device 100 that is less susceptible to an increase in the temperature inside the device due to the image formation operation.

[0053] Furthermore, the control device 300 acquires the internal temperature from an internal temperature sensor 302, which serves as a temperature detection unit that detects the internal temperature. The internal temperature sensor 302 is an existing temperature sensor that detects the temperature inside the image forming device 100, and is a temperature sensor used for control different from the control of the paper interval time and the timing of changing the paper interval time executed by the control device 300 (for example, control of the toner concentration of the developer in the developing device 40, optical writing control in the write control unit 311, etc.).

[0054] In this embodiment, the control device 300 controls the sheet interval time and the timing of changing the sheet interval time as control of the image forming operation according to the temperature of the recording sheets in the paper feed tray 61. More specifically, the control device 300 acquires the detection results of the environmental temperature sensor 301 and the internal temperature sensor 302, as well as all of the above-mentioned information, such as the most recent operation time information, the number of fed sheets information, and the sheet size information. The control device 300 then estimates the temperature of the recording sheets in the paper feed tray 61 from this acquired information, and controls the sheet interval time and the timing of changing the sheet interval time according to the estimated temperature of the recording sheets.

[0055] Any means can be used to detect the temperature rise in the non-paper passing area as long as it can properly detect the temperature. For example, when detecting the temperature rise in the non-paper passing area using a temperature sensor, the method is to detect the temperature rise in the non-paper passing area using an edge temperature sensor (see Figure 9) installed in or near the area heated by the heat source and in the non-paper passing area. The temperature sensor used can be a widely used contact temperature sensor or non-contact temperature sensor.

[0056] Although the present embodiment is an example in which all of this information is used to control the sheet interval time and the timing of changing the sheet interval time, the control device 300 may also control the sheet interval time and the timing of changing the sheet interval time using at least one of the detection results of the environmental temperature sensor 301 and the internal temperature sensor 302, and at least one of the above-mentioned most recent operation time information, information on the number of fed sheets, and sheet size information. However, in order to estimate the temperature of the recording sheets in the paper feed tray 61 with higher accuracy, it is preferable to use all of the detection results of the environmental temperature sensor 301 and the internal temperature sensor 302, and the above-mentioned most recent operation time information, information on the number of fed sheets, and sheet size information.

[0057] As described above, the control device 300 of this embodiment controls the change of the specified time (specified inter-sheet time) in accordance with the temperature of the recording sheet, for example, based on the data shown in the graph in Fig. 7(a). Furthermore, as described above, the control device 300 of this embodiment controls the change of the specified timing (timing for changing the specified inter-sheet time) in accordance with the temperature of the recording sheet, for example, based on the data shown in the graph in Fig. 7(b). In carrying out these controls, the temperature of the recording sheet is estimated from the detection results of the environmental temperature sensor 301 and the internal temperature sensor 302, as well as all of the information described above, including the most recent operation time information, the number of fed sheets information, and the sheet size information.

[0058] As a specific example, the control device 300 estimates a higher temperature for the recording sheet as the detection results of the environmental temperature sensor 301 and the internal temperature sensor 302 are higher. Data on the temperature transition of the recording sheet according to the detection results of the environmental temperature sensor 301 and the internal temperature sensor 302 is obtained in advance through tests and simulations and is stored in the storage device of the control device 300.

[0059] Furthermore, based on the most recent operation time information, the shorter the time that has elapsed since the most recent image forming operation was performed, the higher the estimated temperature of the recording sheet is. Data on the temperature transition of the recording sheet according to the time that has elapsed since the most recent image forming operation was performed is obtained in advance through tests and simulations and stored in the storage device of the control device 300.

[0060] Similarly, based on the information on the number of fed sheets, the control device 300 estimates a higher temperature for the recording sheets as the number of recording sheets fed from the paper feed tray 61 within a predetermined immediately preceding period increases. Data on the temperature transition of the recording sheets according to the number of recording sheets fed from the paper feed tray 61 within a predetermined immediately preceding period is obtained in advance through tests and simulations and stored in the storage device of the control device 300.

[0061] Furthermore, based on the sheet size information, the control device 300 estimates a higher temperature for smaller sizes of recording sheets stored in the paper feed tray 61. Data on the temperature transition of recording sheets according to the size of recording sheets stored in the paper feed tray 61 is obtained in advance through tests and simulations and is stored in the storage device of the control device 300.

[0062] FIG. 10 is a flowchart showing an example of a control flow of this embodiment. In this embodiment, when the control device 300 receives a print instruction (S1), it first acquires the detection results of the environmental temperature sensor 301 and the in-machine temperature sensor 302 (S2). The control device 300 also acquires all of the above-mentioned information, such as the most recent operation time information, the number of fed sheets, and the sheet size information (S3 to S5). The control device 300 then calculates an estimated temperature of the recording sheet from the acquired detection results of the environmental temperature sensor 301 and the in-machine temperature sensor 302, and all of the above-mentioned information, such as the most recent operation time information, the number of fed sheets, and the sheet size information, in accordance with the data stored in the storage device (S6).

[0063] Thereafter, the control device 300 performs control to change the sheet interval time and the timing of changing the sheet interval time according to the calculated estimated temperature of the recording sheet (S7). Specifically, when the calculated estimated temperature of the recording sheet is equal to or higher than a predetermined value, the control device 300 controls to shorten the sheet interval time (sheet interval) compared to when the estimated temperature is below the predetermined value. Furthermore, when the calculated estimated temperature of the recording sheet is equal to or higher than a predetermined value, the control device 300 controls to advance the timing of changing the sheet interval time compared to when the estimated temperature is below the predetermined value.

[0064] In this embodiment, there are cases where new recording sheets are placed in the paper feed tray 61. For example, this occurs when the paper feed tray 61 runs out of recording sheets and new recording sheets are added to the paper feed tray 61. In such cases, the temperature of the new recording sheets is unknown, and for a while after the new recording sheets are placed in the paper feed tray 61, there is a risk that there will be a large difference between the temperature of the new recording sheets and the temperature outside the apparatus (ambient temperature) or inside the apparatus, making it difficult to estimate the temperature of the recording sheets with high accuracy.

[0065] 11, when new recording sheets are added to the paper feed tray 61, the control device 300 may refrain from estimating the temperature of the recording sheets based on the detection results of the environmental temperature sensor 301 and the internal temperature sensor 302, as well as all of the information, such as the most recent operation time information, the number of sheets fed, and the sheet size information, until a predetermined time has elapsed since the new recording sheets were added (No in S10). Specifically, in the control device 300 of this embodiment, the sheet interval time is set to a fixed value at a specified time, and the timing for changing the sheet interval time is also set to a fixed value at a specified timing (S11). This makes it possible to prevent inappropriate control from being performed due to a large error between the estimated temperature of the recording sheets and the actual temperature.

[0066] The above description is merely an example, and each of the following aspects provides unique effects. [First aspect] The first aspect is an image forming device 100 comprising a sheet storage section (e.g., a paper feed tray 61) for storing recording sheets S, an image forming section (e.g., an imaging unit 1) for forming an image on a recording sheet fed from the sheet storage section, and a control section (e.g., a control device 300) for controlling the image forming operation in accordance with the temperature of the recording sheet, and further comprising a temperature detection section (e.g., an environmental temperature sensor 301, an internal temperature sensor 302) for detecting at least one of the temperature outside the device and the temperature inside the device, and an information acquisition section (e.g., the control device 300) for acquiring at least one of the following information: most recent operation time information indicating the time when the most recent image forming operation was performed; fed sheet number information indicating the number of recording sheets fed from the sheet storage section within a specified immediately preceding period; and sheet size information indicating the size of the recording sheets stored in the sheet storage section, and the control section is characterized in that it controls the image forming operation based on the detected temperature detected by the temperature detection section and the at least one piece of information acquired by the information acquisition section. Conventional image forming apparatuses that omit a sheet temperature detection unit that directly detects the temperature of a recording sheet are based on the assumption that the temperature of the recording sheet stored in the sheet storage unit is the same as the installation environment temperature (external or internal temperature of the apparatus) of the image forming apparatus. Indeed, if the apparatus is left unused for a long period of time without image formation, the temperature of the recording sheet stored in the sheet storage unit will become the same as the installation environment temperature (external or internal temperature of the apparatus). However, once image formation is performed, the temperature of the recording sheet stored in the sheet storage unit will fluctuate from the external or internal temperature of the apparatus due to various factors. Therefore, conventional image forming apparatuses that are based on the assumption that the installation environment temperature (external or internal temperature of the apparatus) is the same as the temperature of the recording sheet cannot properly control the image formation operation in accordance with the temperature of the recording sheet. Specifically, when an image formation operation is performed, the various components within the image forming apparatus operate and generate heat, causing an increase in the temperature inside the apparatus. This increase in the temperature inside the apparatus warms the recording sheets stored in the sheet storage unit, causing the temperature of the recording sheets to also increase. The extent of the temperature increase of the recording sheets due to the increase in the temperature inside the apparatus due to the image formation operation can be calculated based on the correlation with the temperature detected by a temperature detection unit that detects at least one of the temperature outside the apparatus and the temperature inside the apparatus. However, even if the extent of the temperature increase of the recording sheets due to the increase in the temperature inside the apparatus due to the image formation operation can be calculated, the temperature of the recording sheets during the image formation operation cannot be properly determined unless the temperature of the recording sheets at the time the image formation operation starts is known. Therefore, it is not possible to properly control the image formation operation in accordance with the temperature of the recording sheets based solely on the temperature detected by a temperature detection unit that detects at least one of the temperature outside the apparatus and the temperature inside the apparatus. According to the inventor's research, the temperature of the recording sheet at the time when an image forming operation starts becomes lower the longer the time that has passed since the most recent image forming operation was performed, and after a sufficiently long time has passed, the temperature becomes the same as the temperature detected by the temperature detection unit that detects at least one of the temperature outside the machine and the temperature inside the machine. Therefore, by acquiring the most recent operation time information that indicates the time when the most recent image forming operation was performed, it is possible to appropriately grasp the temperature of the recording sheet at the time when an image forming operation starts. Furthermore, the temperature of the recording sheet at the time when the image forming operation starts increases as the number of recording sheets fed from the sheet storage unit increases within a predetermined period of time. Therefore, by acquiring information on the number of fed sheets, which indicates the number of recording sheets fed from the sheet storage unit within a predetermined period of time, it is possible to properly grasp the temperature of the recording sheet at the time when the image forming operation starts. Furthermore, the temperature of the recording sheet at the start of the image formation operation will be lower as the size of the recording sheet stored in the sheet storage unit increases, as the surface area of ​​the recording sheet increases and heat dissipates more easily. Therefore, by acquiring sheet size information indicating the size of the recording sheet stored in the sheet storage unit, it is possible to properly determine the temperature of the recording sheet at the start of the image formation operation. In this aspect, at least one of the most recent operation time information, the number of sheets fed, and the sheet size information is acquired by the information acquisition unit, and the image forming operation is controlled using the acquired information in addition to the temperature detected by the temperature detection unit. This allows the temperature of the recording sheet at the time the image forming operation is started to be accurately determined from the acquired information. Furthermore, based on the temperature rise of the recording sheet due to the image forming operation, which is determined from the temperature detected by the temperature detection unit that detects at least one of the temperature outside the machine and the temperature inside the machine, the temperature of the recording sheet during the image forming operation can be estimated with high accuracy from the temperature of the recording sheet at the time the image forming operation is started. Therefore, according to this aspect, it is possible to appropriately control the image forming operation according to the temperature of the recording sheet, even if a sheet temperature detection unit that directly detects the temperature of the recording sheet is omitted.

[0067] [Second mode] The second aspect is characterized in that the first aspect has a fixing section (e.g., fixing device 200) that fixes the image formed by the image forming section to the recording sheet at a fixing nip N between a fixing member (e.g., fixing belt 201) heated by a heating means (e.g., heat source 202) and a pressure member (e.g., pressure roller 203), and the control section controls the sheet interval (e.g., paper interval time) between recording sheets that are sequentially transported to the fixing section as part of the control of the image forming operation. This makes it possible to improve productivity without exceeding the upper limit of the usable temperature of the fixing device, regardless of the temperature of the recording sheet.

[0068] [Third aspect] A third aspect is characterized in that, in the second aspect, the control unit shortens the sheet interval when the estimated temperature of the recording sheet estimated based on the detected temperature and the at least one piece of information is equal to or higher than a predetermined value, compared to when the estimated temperature is less than the predetermined value. This makes it possible to improve productivity without exceeding the upper limit of the usable temperature of the fixing device, regardless of the temperature of the recording sheet.

[0069] [Fourth aspect] A fourth aspect is characterized in that, in any of the first to third aspects, the control unit does not execute control of the image forming operation based on the detected temperature and the at least one piece of information until a predetermined period has elapsed since a new recording sheet was stored in the sheet storage unit. This makes it possible to prevent inappropriate control from being performed due to a large error between the estimated temperature and the actual temperature of the recording sheet. [Explanation of symbols]

[0070] 1: Imaging unit 3: Feed roller 4: Registration roller pair 5: Secondary transfer roller 7: Paper ejection roller 8: Optical writing device 9: Toner bottle 10: Transcription unit 11: Intermediate transfer belt 12: Primary transfer roller 13: Cleaning device 17: Paper output tray 20: Photosensitive drum 30: Charging device 40: Developing device 50: Cleaning device 61: Paper tray 71: Transfer device 100: Image forming device 200: Fixing device 201: Fixing belt 202:Heating source 202A: Central heater 202B: Edge heater 203: Pressure roller 204: Elastic rubber layer 205: Core 206: Nip forming member 207: Stay 208: Retaining member 209: Reflective material 210: Movable light shielding plate 300: Control device 301: Environmental temperature sensor 302: Internal temperature sensor 310: Image information input unit 311: Write control unit [Prior art documents] [Patent documents]

[0071] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-187692

Claims

1. a sheet storage section for storing recording sheets; an image forming unit that forms an image on a recording sheet fed from the sheet storage unit; a control unit that controls an image forming operation in accordance with the temperature of the recording sheet, a temperature detection unit that detects at least one of an external temperature and an internal temperature; an information acquisition unit that acquires at least one of most recent operation time information indicating the time when the most recent image forming operation was performed, fed sheet number information indicating the number of recording sheets fed from the sheet storage unit within a predetermined immediately preceding period, and sheet size information indicating the size of the recording sheets stored in the sheet storage unit, The image forming apparatus is characterized in that the control unit controls the image forming operation based on the detected temperature detected by the temperature detection unit and the at least one piece of information acquired by the information acquisition unit.

2. 2. The image forming apparatus according to claim 1, a fixing unit that fixes the image formed by the image forming unit onto the recording sheet at a fixing nip between a fixing member heated by a heating means and a pressure member; The image forming apparatus is characterized in that the control unit controls the intervals between recording sheets sequentially conveyed to the fixing unit as part of the control of the image forming operation.

3. 3. The image forming apparatus according to claim 2, The image forming apparatus is characterized in that the control unit shortens the sheet interval when the estimated temperature of the recording sheet estimated based on the detected temperature and at least one piece of information is above a predetermined value compared to when the estimated temperature is below the predetermined value.

4. 4. The image forming apparatus according to claim 1, An image forming apparatus characterized in that the control unit does not execute control of the image forming operation based on the detected temperature and at least one piece of information until a predetermined period has elapsed since a new recording sheet was stored in the sheet storage unit.

Images