Image forming device

Abstract

To provide an image forming apparatus that, when winding of a sheet around a heating roller occurs, can promptly stop conveyance of the sheet and can prevent erroneous detection of the occurrence of winding.SOLUTION: An image forming apparatus 1 is an apparatus that forms an image on a sheet S while conveying the sheet S, and the image forming apparatus comprises: a fuser 8 having a heating roller 81 that heats the sheet S; a temperature sensor 85 for measuring the temperature of the heating roller 81; and a control unit 100. The control unit 100 acquires a measured temperature measured by the temperature sensor 85 for every predetermined sampling time. The controls unit 100 calculates, for every sampling time, the amount of reduction in the measured temperature during a unit time longer than the sampling time, and when the calculated temperature reduction amount is larger than a predetermined threshold, stops the conveyance of the sheet S.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an image forming apparatus that forms an image on a sheet while conveying the sheet. [Background technology]

[0002] Conventionally, there is known an image forming apparatus that includes a fixing unit having a heating roller, a temperature sensor that detects the temperature of the heating roller, and a control unit (Patent Document 1). In this technology, the control unit is configured to calculate a temperature gradient value of the temperature change of the heating roller based on the detection result of the temperature of the heating roller by the temperature sensor, and to determine whether or not a sheet is wrapped around the heating roller based on the temperature gradient value and the elapsed time of the temperature gradient value measured by a timer. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2008-191182 A Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the sheet wraps around the heating roller and the wrapping continues over time, it is desirable to be able to stop the conveyance of the sheet as soon as wrapping occurs. However, since the temperature detected by the temperature sensor may suddenly fluctuate significantly due to disturbances, etc., there is a possibility that the occurrence of wrapping may be erroneously detected if it is determined that the temperature of the heating roller has dropped significantly due to such fluctuations.

[0005] Therefore, an object of the present invention is to provide an image forming device that can quickly stop sheet transport when the sheet wraps around the heating roller, and that can suppress erroneous detection of the occurrence of wrapping. [Means for solving the problem]

[0006] An image forming apparatus for achieving the above-mentioned object is an image forming apparatus that forms an image on a sheet while transporting the sheet, and is equipped with a fixing unit having a heating roller that heats the sheet, a temperature sensor for measuring the temperature of the heating roller, and a control unit. The control unit acquires the temperature measured by the temperature sensor at each predetermined sampling time. In addition, the control unit calculates, for each sampling time, an amount of temperature drop in the measured temperature during a unit time longer than the sampling time, and stops conveying the sheet when the calculated amount of temperature drop is greater than a predetermined threshold value.

[0007] According to this configuration, the temperature drop amount of the measured temperature measured by the temperature sensor is calculated for each sampling time, and the sheet transport is stopped when the calculated temperature drop amount is greater than a threshold value, so that the sheet transport can be stopped quickly when the sheet wraps around the heating roller. Furthermore, by calculating the temperature drop amount not during the sampling time but during a unit time longer than the sampling time, the calculated temperature drop amount is less susceptible to the influence of sudden temperature fluctuations, and it is possible to suppress erroneous detection that the sheet has wrapped around the heating roller.

[0008] In the image forming apparatus described above, the control section may be configured to stop heating of the sheet by the heat roller when the amount of temperature decrease is greater than a threshold value.

[0009] According to this, when the conveyance of the sheet is stopped, it is possible to prevent the sheet wrapped around the heating roller from being overheated.

[0010] In the image forming apparatus described above, the temperature sensor may be configured not to be in contact with the heating roller.

[0011] According to this, the temperature sensor can be disposed in the range of the heating roller in the width direction of the sheet where the sheet comes into contact with the heating roller, so that wrapping of the sheet around the heating roller can be detected with high accuracy.

[0012] In the image forming apparatus described above, the control unit may be configured to notify the user that a sheet has jammed in the fixing unit when the amount of temperature drop becomes greater than a threshold value and sheet transport is stopped.

[0013] This makes it possible to inform the user that the cause of the stop of the sheet transport is the fixing unit.

[0014] The image forming apparatus may include an internal temperature sensor that measures an internal temperature of the image forming apparatus, and the control unit may set the threshold value in accordance with the internal temperature.

[0015] In the image forming apparatus described above, the control unit may be configured to set the threshold value to a smaller value when the internal temperature is higher than a predetermined temperature than when the internal temperature is equal to or lower than the predetermined temperature.

[0016] According to this, when the temperature inside the machine is high, the temperature of the heating roller is difficult to decrease even if the sheet wraps around the heating roller, so by reducing the threshold value, it is possible to detect the decrease in the temperature of the heating roller early. As a result, even when the temperature inside the machine is high, it is possible to detect the occurrence of the sheet wrapping around the heating roller early.

[0017] In the image forming apparatus described above, the control section can be configured to execute a plurality of print modes in which the sheet transport speed differs, and to set the unit time in accordance with the transport speed.

[0018] In the image forming apparatus described above, the control section may be configured to set the unit time to be longer when the transport speed is slower than a predetermined speed than when the transport speed is equal to or faster than the predetermined speed.

[0019] According to this, when the conveying speed is slow, the temperature of the heating roller decreases gradually when the sheet wraps around the heating roller, so that the temperature drop can be detected more reliably by calculating the temperature drop amount by lengthening the unit time. This makes it possible to more reliably detect the occurrence of the sheet wrapping around the heating roller even when the conveying speed is slow.

[0020] In the above-mentioned image forming apparatus, the fixing unit can be configured to have an endless belt that transports a sheet between itself and a heating roller, a first elastic body that sandwiches the endless belt between itself and the heating roller, and a second elastic body that sandwiches the endless belt between itself and the heating roller, the second elastic body being positioned downstream of the first elastic body in the sheet transport direction.

[0021] In the image forming apparatus described above, the heat roller may have an elastic layer on its outer periphery, the elastic layer being harder than the first elastic body and softer than the second elastic body.

[0022] According to this, since the second elastic body can be caused to bite into the elastic layer of the heating roller via the endless belt, the sheet can be peeled off from the heating roller by changing the orientation of the sheet between the heating roller and the second elastic body, thereby making it possible to prevent the sheet from wrapping around the heating roller. Effect of the Invention

[0023] According to the present invention, when the sheet wraps around the heating roller, the transport of the sheet can be stopped quickly, and erroneous determination that the wrap has occurred can be suppressed. [Brief description of the drawings]

[0024] [Figure 1] 1 is a diagram showing a configuration of an image forming apparatus according to an embodiment; [Diagram 2] FIG. 2 is a diagram illustrating a configuration of a fixing unit. [Diagram 3]4 is a timing chart showing an example of temperatures measured by a temperature sensor. [Figure 4] 10 is a flowchart showing an example of an operation of a control unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0025] Hereinafter, an embodiment of the invention will be described in detail with reference to the drawings as appropriate. 1, the image forming apparatus 1 is an apparatus that forms an image on a sheet S while conveying the sheet S. The image forming apparatus 1 is a color printer capable of forming color images, and includes a sheet supply unit 3, an image forming unit 4, a post-registration sensor 22, an internal temperature sensor 23, and a control unit 100 within a housing 2. The housing 2 has a discharge tray 21 on the top surface.

[0026] The sheet supply unit 3 has a function of supplying sheets S to the image forming unit 4. The sheet supply unit 3 includes a supply tray 31 capable of accommodating a plurality of sheets S, and a sheet supply mechanism 32. The sheet supply mechanism 32 includes a pickup roller 33, a separation roller 34, a separation pad 35, a conveying roller 36, and a registration roller 37.

[0027] The sheet supply unit 3 sends out the sheets S in the supply tray 31 using a pickup roller 33, separates the sheets S one by one using a separation roller 34 and a separation pad 35, and conveys the sheets S toward a registration roller 37 using a conveyance roller 36. Thereafter, the sheet supply unit 3 aligns the position of the leading edge of the sheet S using the registration roller 37 to correct skew of the sheet S, and supplies the sheet S to the image forming unit 4.

[0028] The image forming section 4 has a function of forming an image on a sheet S. The image forming section 4 includes an exposure unit 5, a photosensitive drum 61, a charger 62, a developing cartridge 63, a transfer unit 7, and a fixing unit 8. The image forming section 4 includes four photosensitive drums 61, four chargers 62, and four developing cartridges 63.

[0029] The exposure unit 5 has a plurality of light sources, a polygon mirror, a lens, a reflecting mirror, etc. (not shown). The exposure unit 5 emits a light beam (see dashed line) based on image data to expose the surface of the photosensitive drum 61, thereby forming an electrostatic latent image on the surface of the photosensitive drum 61.

[0030] The photosensitive drum 61 is a member in which a photosensitive layer is formed on the outer periphery of a cylindrical drum main body having electrical conductivity. The four photosensitive drums 61 are arranged side by side in the conveying direction of the sheet S. The charger 62 has a function of charging the surface of the photosensitive drum 61. The charger 62 has a charging wire, a grid electrode, and the like. Each of the developing cartridges 63 has a developing roller 64 capable of carrying toner. The developing cartridges 63 contain yellow, magenta, cyan, or black toner.

[0031] The transfer unit 7 has a drive roller 71, a driven roller 72, a conveyor belt 73, and four transfer rollers 74. The conveyor belt 73 is an endless belt, and is stretched between the drive roller 71 and the driven roller 72. The transfer rollers 74 are disposed inside the conveyor belt 73 so as to sandwich the conveyor belt 73 between themselves and the corresponding photosensitive drums 61.

[0032] The fixing device 8 has a function of fixing a toner image onto the sheet S. The fixing device 8 has a heating roller 81, a pressure unit 82, a first heater 83, a second heater 84, and a temperature sensor 85. The heating roller 81 is a roller that heats the sheet S. The pressure unit 82 is disposed so as to sandwich the sheet S between itself and the heating roller 81, and has a function of applying pressure to the sheet S between itself and the heating roller 81. The heaters 83 and 84 are disposed inside the heating roller 81. The heaters 83 and 84 are, for example, halogen heaters, and generate heat when energized to heat the heating roller 81. The fixing device 8 will be described in detail later.

[0033] In the image forming unit 4, the surface of the photosensitive drum 61 is charged by the charger 62, and then exposed by the exposure unit 5. As a result, an electrostatic latent image based on image data is formed on the surface of the photosensitive drum 61. Next, the image forming unit 4 supplies toner from the developing roller 64 to the electrostatic latent image formed on the photosensitive drum 61. As a result, a toner image is formed on the photosensitive drum 61.

[0034] Next, the image forming unit 4 transfers the toner image formed on the photosensitive drum 61 onto the sheet S by passing the sheet S supplied from the sheet supply unit 3 between the photosensitive drum 61 and the transfer roller 74 while conveying the sheet S by the conveyor belt 73. As a result, the toner image is formed on the sheet S.

[0035] Thereafter, the image forming unit 4 fixes the toner image onto the sheet S by conveying the sheet S on which the toner image has been formed between the heating roller 81 and the pressure unit 82. This forms an image on the sheet S. The sheet S on which the image has been formed is conveyed by conveying rollers 91 and 92, and is discharged onto the discharge tray 21 by a discharge roller 93.

[0036] The post-registration sensor 22 has a function of detecting the sheet S supplied from the sheet supply unit 3 toward the image forming unit 4. The post-registration sensor 22 is disposed downstream of the registration rollers 37 in the transport direction of the sheet S. More specifically, the post-registration sensor 22 is disposed between the registration rollers 37 and the photosensitive drum 61 disposed most upstream in the transport direction of the sheet S.

[0037] The post-registration sensor 22 may be, for example, a sensor consisting of a lever that rotates when the sheet S comes into contact with it, and an optical sensor that detects the position of the lever. The post-registration sensor 22 outputs a detection signal to the control unit 100 when it detects the sheet S, and outputs a non-detection signal to the control unit 100 when it does not detect the sheet S. It does not matter which of the detection signal and the non-detection signal has a higher voltage.

[0038] The in-machine temperature sensor 23 is a sensor that measures the temperature inside the image forming apparatus 1, more specifically, the in-machine temperature that is the temperature inside the housing 2, and is disposed at an appropriate position inside the housing 2. For example, a thermistor can be used as the in-machine temperature sensor 23. The in-machine temperature sensor 23 outputs the measurement result (in-machine temperature TM) to the control unit 100.

[0039] Next, the fixing unit 8 will be described in detail. 2, the heating roller 81 has a base tube 81A made of metal and an elastic layer 81B formed on the outer periphery of the base tube 81A. In other words, the heating roller 81 has the elastic layer 81B on the outer periphery. The elastic layer 81B is made of rubber such as silicone rubber and has elasticity. The heating roller 81 is rotatably supported by a frame (not shown) of the fixing unit 8, and rotates when a rotational driving force is input.

[0040] The pressure unit 82 includes an endless belt 181, a first elastic body 182, a second elastic body 183, a support member 184, and belt guides 185 and 186. The endless belt 181 is a belt that conveys the sheet S by nipping it between itself and the heating roller 81, and is made of metal or the like.

[0041] The first elastic body 182 and the second elastic body 183 are members that sandwich the endless belt 181 between the heating roller 81 and the first elastic body 182 and the second elastic body 183. The first elastic body 182 and the second elastic body 183 are made of rubber such as silicone rubber, for example, like the elastic layer 81B of the heating roller 81, and have elasticity. The first elastic body 182 is softer than the elastic layer 81B, and the second elastic body 183 is harder than the elastic layer 81B. In other words, the elastic layer 81B of the heating roller 81 is harder than the first elastic body 182 and softer than the second elastic body 183.

[0042] The first elastic body 182 and the second elastic body 183 are arranged side by side in the transport direction of the sheet S. More specifically, the second elastic body 183 is arranged downstream of the first elastic body 182 in the transport direction of the sheet S.

[0043] The support member 184 is a member that supports the elastic bodies 182, 183. The first elastic body 182 is fixed to a first support plate 182A, and is supported by the support member 184 via the first support plate 182A. The second elastic body 183 is fixed to a second support plate 183A, and is supported by the support member 184 via the second support plate 183A.

[0044] The belt guides 185 and 186 are members that rotatably guide the endless belt 181. The endless belt 181 is rotated in accordance with the heating roller 81 as the heating roller 81 is driven to rotate.

[0045] The temperature sensor 85 is a sensor for measuring the temperature of the heating roller 81. More specifically, the heating roller 81 has a central region including a central portion in the width direction of the sheet S, which is a direction perpendicular to the conveying direction of the sheet S, and the temperature sensor 85 measures the temperature of the central region of the heating roller 81. The temperature sensor 85 is disposed outside the heating roller 81 at a position facing the central region of the heating roller 81 in the width direction of the sheet S.

[0046] Furthermore, the heating roller 81 has a contact area that comes into contact with the sheet S of the minimum size when the sheet S has a width direction size that is the minimum size that can be conveyed by the image forming unit 4 and the temperature sensor 85 detects the temperature of the contact area of ​​the heating roller 81. The contact area is an area including the central area in the width direction of the sheet S.

[0047] The temperature sensor 85 is not in contact with the heating roller 81. In other words, the temperature sensor 85 measures the temperature of the heating roller 81 without contacting the heating roller 81. More specifically, the temperature sensor 85 is disposed at a distance from the heating roller 81. For example, a non-contact thermistor can be used as the temperature sensor 85. The temperature sensor 85 outputs the measurement result (measured temperature TH) to the control unit 100.

[0048] The control unit 100 (see FIG. 1) includes a CPU, RAM, ROM, input / output circuits, etc., and performs various types of arithmetic processing based on programs and data stored in the ROM or the like, thereby executing control.

[0049] 3, the control unit 100 acquires the measured temperature TH measured by the temperature sensor 85 at every predetermined sampling time ts. In detail, the control unit 100 acquires the measured temperature TH at every sampling time ts after the image forming apparatus 1 is powered on. The sampling time ts is, for example, several tens of milliseconds.

[0050] During printing to form an image on the sheet S, if the sheet S (see the imaginary line in FIG. 2) wraps around the heating roller 81, the sheet S gets between the heating roller 81 and the temperature sensor 85, causing a sudden drop in the measured temperature TH measured by the temperature sensor 85. Therefore, the control unit 100 calculates a temperature drop amount TD of the measured temperature TH during a predetermined unit time tc for each sampling time ts, and stops conveying the sheet S when the calculated temperature drop amount TD is greater than a predetermined threshold value TDth that has been set in advance.

[0051] Specifically, the control unit 100 calculates the temperature drop amount TD during a predetermined unit time tc for each sampling time ts during printing. Here, the unit time tc is longer than the sampling time ts, for example, several hundred milliseconds to several seconds. The temperature drop amount TD can be calculated, for example, by integrating a value ΔTH obtained by subtracting the current value of the measured temperature TH from the previous value of the measured temperature TH over the unit time tc, and dividing the integrated value ΣΔTH by the unit time tc. Alternatively, the temperature drop amount TD may be calculated by subtracting the measured temperature TH acquired this time from the measured temperature TH unit time tc ago, and dividing the result by the unit time tc.

[0052] The period during printing may be, for example, the period from when the control unit 100 receives a print job including a command to start printing and image data and starts supplying the sheet S, and a predetermined time tp has elapsed since the sheet S supplied from the sheet supply unit 3 toward the image forming unit 4 is detected by the post-registration sensor 22, until the sheet S on which the image has been formed is discharged outside the housing 2. The predetermined time tp may be set, for example, to the period from when the leading edge of the sheet S supplied from the sheet supply unit 3 is detected by the post-registration sensor 22 until it reaches the nip portion between the heating roller 81 and the pressure unit 82.

[0053] In addition, when printing is performed continuously on multiple sheets S, the period during printing can be, for example, from the time when a predetermined time tp has elapsed after the first sheet S supplied from the sheet supply unit 3 to the image forming unit 4 is detected by the post-registration sensor 22 to the time when the last sheet S is discharged outside the housing 2.

[0054] The control unit 100 calculates the temperature drop amount TD for each sampling time ts, and determines whether the temperature drop amount TD is greater than a threshold value TDth. If the temperature drop amount TD is greater than the threshold value TDth as a result of the determination, the control unit 100 stops conveying the sheet S. In detail, if the temperature drop amount TD is greater than the threshold value TDth, the control unit 100 stops the conveying of the sheet S by stopping the rotation of the rollers of the sheet supply unit 3, the photosensitive drum 61, the drive roller 71 of the transfer unit 7, the heating roller 81 of the fixing device 8, and the like.

[0055] Furthermore, when the temperature drop amount TD is greater than the threshold value TDth, the control unit 100 stops heating of the sheet S by the heating roller 81. In detail, the control unit 100 stops heating of the sheet S by the heating roller 81 by stopping the supply of electricity to the heaters 83, 84 to stop the heating of the heating roller 81 by the heaters 83, 84.

[0056] Furthermore, when the temperature drop amount TD becomes larger than the threshold value TDth and the conveyance of the sheet S is stopped, the control unit 100 notifies that a sheet jam has occurred in the fixing unit 8. The control unit 100 notifies that a sheet jam has occurred in the fixing unit 8, for example, by emitting a warning sound from a speaker provided in the housing 2 and displaying the warning on a screen provided in the housing 2.

[0057] The method of notification is not limited to this. For example, the control unit 100 may notify that a sheet jam has occurred in the fixing unit 8 by issuing a sound from a speaker. The control unit 100 may also notify that a sheet jam has occurred in the fixing unit 8 by turning on or blinking a dedicated lamp provided in the housing 2.

[0058] Furthermore, in this embodiment, the control unit 100 sets the threshold value TDth according to the in-machine temperature TM acquired from the in-machine temperature sensor 23. In particular, when the in-machine temperature TM is higher than a predetermined temperature TMth, the control unit 100 sets the threshold value TDth to a value whose absolute value is smaller than that when the in-machine temperature TM is equal to or lower than the predetermined temperature TMth. Specifically, when the in-machine temperature TM is equal to or lower than the predetermined temperature TMth, the control unit 100 sets the threshold value TDth to a first threshold value TDthN, and when the in-machine temperature TM is higher than the predetermined temperature TMth, the control unit 100 sets the threshold value TDth to a second threshold value TDthS whose absolute value is smaller than that of the first threshold value TDthN.

[0059] Furthermore, in this embodiment, the control unit 100 can execute a plurality of printing modes with different conveying speeds of the sheet S. Specifically, the control unit 100 can execute a full-speed mode, which is a printing mode for forming an image on plain paper or the like as the sheet S, and a half-speed mode, which is a printing mode for forming an image on an envelope, thick paper or the like as the sheet S. The conveying speed of the sheet S in the half-speed mode is slower than the conveying speed of the sheet S in the full-speed mode. Specifically, the conveying speed of the sheet S in the half-speed mode is approximately half the conveying speed of the sheet S in the full-speed mode.

[0060] The control unit 100 sets the unit time tc according to the conveying speed of the sheet S. In detail, when the conveying speed of the sheet S is slower than a predetermined speed, the control unit 100 sets the unit time tc to a time longer than when the conveying speed of the sheet S is equal to or higher than the predetermined speed. More specifically, in the half-speed mode, the control unit 100 sets the unit time tc to a time longer than in the full-speed mode. Specifically, in the full-speed mode, the control unit 100 sets the unit time tc to a first unit time tcN, and in the half-speed mode, the control unit 100 sets the unit time tc to a second unit time tcL longer than the first unit time tcN. The second unit time tcL is, for example, twice the first unit time tcN.

[0061] Next, an example of the operation of the control unit 100 will be described with reference to the flowchart of FIG. After the image forming apparatus 1 is powered on, the control unit 100 repeatedly executes the process shown in FIG. 4 at every sampling time ts (predetermined control cycle).

[0062] 4, the control unit 100 determines whether printing is in progress (S110). If printing is not in progress (S110, No), the control unit 100 acquires the measured temperature TH measured by the temperature sensor 85 (S111) and ends this processing. If printing is in progress (S110, Yes), the control unit 100 acquires the measured temperature TH and the internal temperature TM (S120).

[0063] The control unit 100 also determines whether the print mode is the half-speed mode (S121). If the print mode is not the half-speed mode (S121, No), that is, if the print mode is the full-speed mode, the control unit 100 sets the unit time tc to the first unit time tcN (S122) and proceeds to the process of step S130. If the print mode is the half-speed mode in step S121 (Yes), the control unit 100 sets the unit time tc to a second unit time tcL longer than the first unit time tcN (S123) and proceeds to the process of step S130.

[0064] In step S130, the control unit 100 calculates the temperature drop amount TD. For example, the control unit 100 calculates the temperature drop amount TD by integrating a value ΔTH obtained by subtracting the current value of the measured temperature TH from the previous value of the measured temperature TH over a unit time tc, and dividing the integrated value ΣΔTH by the set unit time tc.

[0065] The control unit 100 also determines whether the internal temperature TM is higher than a predetermined temperature TMth (S131). If the internal temperature TM is equal to or lower than the predetermined temperature TMth (S131, No), the control unit 100 sets the threshold TDth to a first threshold TDthN (S132) and proceeds to the process of step S140. If the internal temperature TM is higher than the predetermined temperature TMth in step S131 (Yes), the control unit 100 sets the threshold TDth to a second threshold TDthS smaller than the first threshold TDthN (S133) and proceeds to the process of step S140.

[0066] In step S140, the control unit 100 determines whether the temperature drop amount TD is greater than a set threshold value TDth. If the temperature drop amount TD is equal to or smaller than the threshold value TDth (S140, No), the control unit 100 ends the current process.

[0067] In step S140, if the temperature drop amount TD is greater than the threshold value TDth (Yes), the control unit 100 stops the rotation of the heating roller 81 and the like to stop the conveyance of the sheet S (S151). The control unit 100 also stops the supply of electricity to the heaters 83 and 84 to stop the heating of the sheet S by the heating roller 81 (S152). Thereafter, the control unit 100 notifies that an error has occurred, specifically, that a sheet jam has occurred in the fixing unit 8 (S153), and temporarily ends the process shown in FIG.

[0068] When the user removes the sheet S that is jammed in the fixing unit 8 (the sheet S wrapped around the heating roller 81), the control unit 100 repeats the process shown in FIG. 4 again at every sampling time ts.

[0069] According to the present embodiment described above, the temperature drop amount TD of the measured temperature TH measured by the temperature sensor 85 is calculated for each sampling time ts, and the conveyance of the sheet S is stopped when the calculated temperature drop amount TD is greater than the threshold value TDth, so that the conveyance of the sheet S can be stopped promptly when the sheet S wraps around the heating roller 81. Furthermore, by calculating the temperature drop amount TD not during the sampling time ts but during a unit time tc longer than the sampling time ts, the calculated temperature drop amount TD is less susceptible to the influence of sudden temperature fluctuations, and therefore it is possible to suppress erroneous detection that the sheet S has wrapped around the heating roller 81.

[0070] In addition, when the temperature drop amount TD is greater than the threshold value TDth, the heating of the sheet S by the heating roller 81 is stopped, so that the sheet S wrapped around the heating roller 81 can be prevented from being overheated when the conveyance of the sheet S is stopped.

[0071] In addition, since the temperature sensor 85 is not in contact with the heating roller 81, the temperature sensor 85 can be disposed in a range (range of the contact area) of the heating roller 81 that contacts the sheet S in the width direction of the sheet S. This makes it possible to accurately detect the wrapping of the sheet S around the heating roller 81.

[0072] Furthermore, when the temperature drop amount TD becomes larger than the threshold value TDth and the conveyance of the sheet S is stopped, a notification is issued that a sheet has jammed in the fixing unit 8, so that the user can be informed that the cause of the stop of the conveyance of the sheet S is the fixing unit 8. This makes it easier for the user to take subsequent measures, thereby improving the usability of the image forming apparatus 1.

[0073] Furthermore, when the in-machine temperature TM is high, the temperature of the heating roller 81 is difficult to decrease even if the sheet S wraps around the heating roller 81, so by reducing the threshold value TDth (absolute value) in this case, it is possible to detect early that the temperature of the heating roller 81 is decreasing. This makes it possible to detect early that the sheet S has wrapped around the heating roller 81 even when the in-machine temperature TM is high.

[0074] Furthermore, when the conveying speed of the sheet S is slow, such as when the print mode is the half-speed mode, the temperature of the heating roller 81 decreases slowly when the sheet S wraps around the heating roller 81, so that the temperature decrease TD can be calculated by lengthening the unit time tc, thereby making it possible to more reliably detect the decrease in temperature of the heating roller 81. This makes it possible to more reliably detect the occurrence of the wrapping of the sheet S around the heating roller 81, even when the conveying speed of the sheet S is slow.

[0075] Furthermore, by configuring the elastic layer 81B of the heating roller 81 to be softer than the second elastic body 183 disposed downstream, the second elastic body 183 can be caused to bite into the elastic layer 81B of the heating roller 81 via the endless belt 181. This allows the orientation of the sheet S to be changed between the heating roller 81 and the second elastic body 183, and the sheet S can be peeled off from the heating roller 81, thereby preventing the sheet S from wrapping around the heating roller 81.

[0076] Although the embodiment has been described above, the present invention is not limited to the above embodiment, and can be modified as appropriate as exemplified below.

[0077] For example, in the above embodiment, the conveyance of the sheet S and the heating of the sheet S by the heating roller 81 are stopped when a state in which the temperature drop amount TD is greater than the threshold value TDth occurs once, but the present invention is not limited to this, and the conveyance of the sheet S may be stopped when a state in which the temperature drop amount TD is greater than the threshold value TDth occurs multiple times in succession. For example, the conveyance of the sheet S may be stopped when a state in which the temperature drop amount TD is greater than the threshold value TDth occurs two times in succession, or the conveyance of the sheet S may be stopped when a state in which the temperature drop amount TD is greater than the threshold value TDth occurs two or more times in succession.

[0078] In the above embodiment, when the temperature drop amount TD is greater than the threshold value TDth, the heating of the sheet S by the heating roller 81 is stopped, but the present invention is not limited to this, and the heating of the sheet S by the heating roller 81 may not be completely stopped. For example, when the temperature drop amount TD is greater than the threshold value TDth, such as in a ready mode waiting for input of a print job, the output of the heaters 83, 84 may be made smaller than in a print mode in which an image is formed on the sheet S (before the sheet S wraps around the heating roller 81).

[0079] In the above embodiment, the fixing unit 8 includes the temperature sensor 85, but the present invention is not limited to this. For example, the temperature sensor may be provided separately from the fixing unit.

[0080] In addition, in the above embodiment, two types of printing modes, full speed mode and half speed mode, which have different conveying speeds of the sheet S, can be executed, but this is not limited to this. For example, three or more types of printing modes with different sheet conveying speeds may be executed. In this case, the unit time may be changed for each printing mode. For example, the unit time may be set to a longer time as the sheet conveying speed is slower. Furthermore, the image forming apparatus may be configured not to execute multiple printing modes with different conveying speeds of the sheet S. In this case, the unit time may not be changed.

[0081] In the above embodiment, the threshold value TDth is set to the first threshold value TDthN or the second threshold value TDthS according to the internal temperature TM, but is not limited thereto. For example, the threshold value may be set to a smaller value from among three or more preset values ​​as the internal temperature increases. Also, the threshold value may be configured not to be changed, and in this case, the internal temperature sensor may not be provided.

[0082] In the above embodiment, the temperature drop amount TD is calculated by integrating the value ΔTH obtained by subtracting the current value of the measured temperature TH from the previous value over the unit time tc, and dividing the integrated value ΣΔTH by the unit time tc, or by subtracting the measured temperature TH acquired this time from the measured temperature TH measured a unit time tc ago, and dividing the result by the unit time tc. However, the present invention is not limited to this. For example, the integrated value ΣΔTH may be used as the temperature drop amount TD, or the temperature drop amount TD may be used by subtracting the measured temperature TH acquired this time from the measured temperature TH measured a unit time tc ago.

[0083] In the above embodiment, the heating roller 81 has an elastic layer 81B on its outer periphery, but this is not limiting. For example, the heating roller may have a configuration that does not include an elastic layer on its outer periphery.

[0084] In addition, in the above embodiment, the first elastic body 182 and the second elastic body 183 have different hardnesses, but this is not limited to this, and for example, the first elastic body and the second elastic body may have the same hardness.

[0085] In the above embodiment, the fixing device 8 is provided with the pressure unit 82 having the endless belt 181 and the elastic bodies 182 and 183, but the present invention is not limited to this. For example, the fixing device may be provided with a pressure roller having a core and an elastic layer formed on the outer periphery of the core, instead of the pressure unit 82 of the above embodiment.

[0086] In the above embodiment, when the temperature drop amount TD becomes larger than the threshold value TDth and the conveyance of the sheet S is stopped, it is determined that a sheet jam has occurred in the fixing unit 8, and a message to that effect is issued, but this is not limiting. For example, it may be possible to simply issue a message to the effect that a sheet jam has occurred inside the device, without determining that a sheet jam has occurred in the fixing unit.

[0087] In the above embodiment, a color printer is used as an example of the image forming apparatus, but the present invention is not limited to this and may be, for example, a monochrome printer capable of forming only monochrome images. Also, the image forming apparatus is not limited to a printer and may be, for example, a copier or a multifunction machine.

[0088] Furthermore, the elements described in the above embodiment and modified examples may be implemented in any combination. [Explanation of symbols]

[0089] 1. Image forming device 8 Fixing unit 81 Heating roller 85 Temperature Sensor 100 Control section S Seat

Claims

1. An image forming apparatus that forms an image on a sheet while conveying the sheet, a fixing unit having a heating roller for heating the sheet; a temperature sensor for measuring the temperature of the heating roller; A control unit, The control unit, when conveying a sheet to the fixing unit for printing, performs the following at each predetermined sampling time: A process of acquiring a measured temperature measured by the temperature sensor; a process of calculating a temperature drop amount of the measured temperature during a unit time from a plurality of measured temperatures including the currently acquired measured temperature and a measured temperature acquired a unit time earlier than the sampling time, and stopping conveyance of the sheet when the calculated temperature drop amount is greater than a predetermined threshold value; The fixing device includes: an endless belt for transporting a sheet between the heating roller and the endless belt; a first elastic body that sandwiches the endless belt between the first elastic body and the heating roller; a second elastic body that sandwiches the endless belt between the heating roller and the second elastic body, the second elastic body being disposed downstream of the first elastic body in a sheet conveying direction, The heating roller has an elastic layer on its outer periphery, The image forming apparatus according to claim 1, wherein the elastic layer is harder than the first elastic body and softer than the second elastic body.

2. 2 . The image forming apparatus according to claim 1 , wherein the control unit stops heating the sheet by the heat roller when the amount of the temperature decrease is greater than the threshold value.

3. 3. The image forming apparatus according to claim 1, wherein the temperature sensor is not in contact with the heating roller.

4. 4. The image forming apparatus according to claim 1, wherein the control unit notifies the user that a sheet has jammed in the fixing unit when the amount of temperature drop becomes greater than the threshold value and sheet transport is stopped.

5. An internal temperature sensor is provided for measuring an internal temperature of the image forming apparatus, 5. The image forming apparatus according to claim 1, wherein the control unit sets the threshold value in accordance with the internal temperature of the image forming apparatus.

6. 6. The image forming apparatus according to claim 5, wherein when the internal temperature is higher than a predetermined temperature, the control unit sets the threshold value to a value smaller than that when the internal temperature is equal to or lower than the predetermined temperature.

7. The control unit is Multiple print modes with different sheet transport speeds can be performed.

7. The image forming apparatus according to claim 1, wherein the unit time is set in accordance with the transport speed.

8. 8. The image forming apparatus according to claim 7, wherein the control unit, when the transport speed is slower than a predetermined speed, sets the unit time to a longer time than when the transport speed is equal to or faster than the predetermined speed.

9. 9. The image forming apparatus according to claim 1, wherein the control unit stops conveying the sheet when the amount of temperature decrease calculated for each sampling time is greater than the threshold value for a plurality of consecutive times.

Images