JP2009199030A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of performing fixing processing in accordance with a temperature state (cooled state or warmed state) of a press roller. <P>SOLUTION: The image forming apparatus is provided with a thermistor 38 detecting surface temperature of the press roller 33 coming into contact with a fixing roller 28. The falling rate of the surface temperature of the press roller 33 is calculated on the basis of a detection signal from the thermistor 38. When the calculated falling rate is judged not to be equal to or under a set value, heating control of the fixing roller is performed to control to warm the press roller by rotating the fixing roller for a prescribed time without starting paper feeding when the temperature thereof rises to pickup temperature. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a facsimile machine, and a printer.

  In the above-described image forming apparatus, an electrostatic latent image is formed on the surface of the photosensitive drum and visualized with toner, the formed toner image is transferred to a sheet to form an image, and the toner transferred to the sheet The toner image is fixed on the sheet in the fixing device. In the fixing device, a sheet is carried into a nip portion with a press roller while rotating a heated fixing roller, and a fixing operation is performed by thermally fusing toner.

  In such a fixing device, the surface temperature of the fixing roller is constantly detected, and when the surface temperature falls below a predetermined temperature, heating of the fixing roller is started, and when the surface temperature reaches the predetermined temperature, the heating control is performed so as to stop the heating. The surface temperature of the fixing roller is maintained at a predetermined temperature. When such heating control is performed, it is necessary to consider the surface temperature of the press roller because the press roller pressed against the fixing roller takes heat from the fixing roller.

For example, Patent Document 1 describes that a temperature sensor is provided in the vicinity of the press roller to detect the temperature, and the control temperature of the fixing roller is changed according to the detected temperature.
JP 2003-098898 A

  In Patent Document 1, attention is paid only to the temperature in the vicinity of the press roller, and the influence of the internal temperature of the press roller is not taken into consideration. For example, when the inside of the press roller is cold, only the surface is heated by the fixing roller, and once the temperature rises, the temperature immediately decreases. In this case, if the temperature control of the fixing roller is performed only with the temperature at the time of the rise, sufficient fixing processing cannot be performed.

  In particular, when the entire press roller is cooled in an environment where the room temperature is lowered, it takes time to warm the inside of the press roller. For this reason, if the fixing control is performed only at the temperature near the press roller, it is inevitable that the fixing property deteriorates.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of performing a satisfactory fixing process in accordance with the temperature state (cooled state or warmed state) of a press roller.

  An image forming apparatus according to the present invention fixes an image forming unit that forms an electrostatic latent image on the surface of a photosensitive drum, develops the electrostatic latent image, and transfers the toner image onto a sheet, and fixes the sheet on which the toner image is transferred. A fixing unit configured to fix a toner image by being sandwiched between a roller and a press roller and heated and pressed; a temperature detection unit configured to detect a surface temperature of the press roller; and the press based on a detection signal from the temperature detection unit. A calculation unit that calculates a reduction rate of the surface temperature of the roller, and a conveyance control unit that adjusts the sheet feeding timing while rotating the fixing roller based on the calculated reduction rate. And a determination unit configured to determine whether or not the calculated decrease rate is equal to or greater than a predetermined value, and the conveyance control unit rotates the fixing roller for a predetermined time when the determination unit determines that the calculated decrease rate is equal to or greater than the predetermined value. It is characterized in that it is controlled to feed after being fed.

  By having the configuration as described above, the surface temperature of the press roller is detected, and the feeding timing is adjusted while rotating the fixing roller based on the rate of decrease in the surface temperature, so it is good according to the temperature state of the press roller Fixing process can be performed.

  In a state where the entire press roller is cooled, the surface temperature of the contact portion with the fixing roller once increases, but the surface temperature rapidly decreases. Similarly, when the press roller is warm, even if the surface temperature rises due to the contact with the fixing roller, the subsequent temperature drop becomes gradual. Therefore, if the reduction rate calculated based on the detected surface temperature of the press roller is used, the fixing process according to the temperature state of the press roller can be performed.

  Therefore, when the rate of decrease is large, adjustment may be made so as to delay the paper feed timing in order to take time to warm the press roller while rotating the fixing roller. Alternatively, the time until the paper feed timing may be set in advance according to the reduction rate, and the paper feed timing may be determined according to the calculated reduction rate.

  In this way, since the fixing process is always performed in a state where the press roller is warm, it is possible to realize a good fixing property from the first sheet fed.

  Further, if it is determined that the rate of decrease in the surface temperature of the press roller is equal to or greater than a predetermined value and the fixing roller is rotated for a predetermined time and then controlled to be fed, a satisfactory fixing process can be performed reliably. .

  Hereinafter, embodiments according to the present invention will be described in detail. The embodiments described below are preferable specific examples for carrying out the present invention, and thus various technical limitations are made. However, the present invention is particularly limited in the following description. Unless otherwise specified, the present invention is not limited to these forms.

  FIG. 1 is a schematic view of an entire image forming apparatus according to an embodiment of the present invention. A document reading unit 1 that conveys a document and reads the document is disposed at an upper part of the image forming apparatus, and a recording unit 2 that records an image, a sheet transport unit 3 that transports a sheet on which an image is recorded, and a paper feeding unit 4 is arranged.

  The document reading unit 1 includes a cover unit 10 having a document feeder (ADF) therein and a reading body unit 12 having a scanner 11. On the upper surface of the reading main body 12, a platen glass 13 is disposed at a portion for reading the conveyed document, and a placement bed 14 made of a transparent glass material is disposed at a portion for placing and reading the document or book. Yes. When reading a transported document, the scanner 11 is stopped at a position facing the platen glass 13 to perform a reading operation. When reading a document placed on the mounting bed 14, the scanner 11 reads a document or the like. Are scanned to perform a reading operation.

  A document retainer 15 is attached to the surface of the cover portion 10 facing the placement bed 14, and a document tray 16 on which a plurality of documents are placed is provided above the document retainer 15. A document placed on the document tray 16 is carried into the ADF by a pickup roller 17 and a separation roller 18, conveyed to a reading position facing the platen glass 13 by a feed roller 19, read by a scan 11, and read by a discharge roller 20. It is discharged to the document discharge tray 21.

  In the recording unit 2, a developer 22, a charging brush 23, a photosensitive drum 24, a transfer roller 25, an exposure head 26, and a memory removal brush 27 are used as an image forming unit in order to record on the sheet conveyed by the sheet conveying unit 3. And a fixing roller 28 and a press roller 33 as a fixing unit. First, the surface of the photosensitive drum 24 is uniformly charged by the charging brush 23, and the electrostatic latent image is formed by exposing the charged surface of the photosensitive drum 24 according to the image recording signal by the exposure head 26. . Next, the toner in the developing device 22 is transferred to the electrostatic latent image formed on the photosensitive drum 24 by the supply roller and the developing roller to be visualized, and formed on the surface of the photosensitive drum 24 by the transfer roller 25. Transfer the toner image onto the paper. The transferred toner image is heated and pressed by the fixing roller 28 and fixed on the paper.

  In this way, a series of processes such as charging on the photoreceptor, exposure, development, transfer to paper and fixing are performed, and an image is formed on the paper. The toner remaining on the surface of the photosensitive drum 24 after the transfer is weakened in adhesion by a memory removal brush (ERS brush) 27 and dispersed on the surface of the photosensitive drum 10. The residual toner is collected on the developing roller of the developing device 22.

  A plurality of sheets are stacked and set in the sheet feeding cassette 5 in the sheet feeding unit 4, and are fed one by one by the sheet feeding roller 29 to the sheet conveying unit 3. The fed paper is conveyed by the feed roller 30 and is sandwiched between the feed rollers 31 and 32. Then, the sheet is conveyed to the recording unit 2 by the feed roller 31 to form an image, and the sheet subjected to the image forming process is sandwiched between the fixing roller 28 and the press roller 33 to perform the fixing process, and then the sheet discharge roller 34 and It is carried out to the paper discharge tray 36 by the press roller 35.

  FIG. 2 is a schematic sectional view of a fixing unit in which a fixing mechanism including the fixing roller 28 and a paper discharge mechanism including the paper discharge roller 34 are unitized. In the fixing unit, a fixing roller 28 and a paper discharge roller 34 are attached to the unit frame U1. A press roller 33 is provided on the lower frame U <b> 2 so as to face the fixing roller 28, and a press roller 35 is attached so as to face the paper discharge roller 34. The lower frame U2 is assembled by being fixed to the lower part of the unit frame U1.

  The thermistor 37 for detecting the surface temperature is in contact with the surface of the fixing roller 28. The thermistor 37 is attached to the unit frame U1 and is urged toward the fixing roller 28. The thermistor 37 may be set at any position as long as the sheet conveyed to the surface of the fixing roller 28 is in contact with the surface. The surface of the press roller 33 is in contact with a thermistor 38 that detects the surface temperature. The thermistor 38 is attached to the unit frame U2 and is urged toward the press roller 33. The contact position of the thermistor 38 with the press roller 33 is set on the upstream side in the rotation direction of the press roller 33 in the vicinity of the nip position with the fixing roller 28.

  FIG. 3 is a schematic diagram illustrating a circuit configuration in the recording unit 2. The recording control unit 40 that controls the entire recording operation includes an image formation control unit 40a, a fixing control unit 40b, a calculation unit 40c, a determination unit 40d, and a conveyance control unit 40e.

  The image formation control unit 40a transmits a control signal to a charging voltage application circuit 41 that applies a charging voltage to the charging brush 23, and a development voltage application circuit 42 that applies a development voltage and a supply voltage to the development roller and the supply roller of the developing device 22. Thus, voltage control of each member is performed. Further, a control signal is transmitted to a distributed voltage application circuit 43 that applies a distributed voltage to the memory removal brush 27 and a transfer voltage application circuit 44 that applies a transfer voltage to the transfer roller 25 to control the voltage of each member. Further, exposure control of the LED head 26 is performed based on the image signal, and an electrostatic latent image is formed on the surface of the photosensitive drum 24 that is uniformly charged by the charging brush 23.

  The fixing control unit 40b performs fixing control by transmitting an on / off control signal to a heater drive circuit 46 that is driven by energizing a heater built in the fixing roller 28. At that time, a detection signal relating to the surface temperature of the fixing roller 28 from the temperature detection circuit 47 provided with the thermistor 37 is received and fixing control is performed.

FIG. 4 is a graph showing the transition of the surface temperature of the fixing roller regarding the heating control of the fixing roller by energization of the heater. The vertical axis represents the surface temperature (T), and the horizontal axis represents time (t). The surface temperature of the fixing roller is T _{0 when the} apparatus is not energized with the power off. When the power is turned on at time t ₀ , the heater is energized and heating control is started.

When the heating control is started, the fixing roller is heated and the surface temperature rises. When the set temperature (standby temperature) T ₁ in the standby state of the apparatus is reached at time t ₁ , the energization of the heater is controlled to be kept at the standby temperature T ₁ . Therefore, the surface temperature of the fixing roller will be the temperature change at a predetermined amplitude about the standby temperature T _1.

When a recording start signal is input at time t ₂ in the standby state of the apparatus, heating control by continuous energization of the heater is started, and the surface temperature of the fixing roller is increased again. When the driving start temperature T ₂ is reached at time t ₃ , the driving of the main motor is started and the rotation driving of the fixing roller is started. Further, when the surface temperature rises and reaches the pick-up temperature T ₃ at time t ₄ , the pick-up roller is driven to rotate to start the paper feeding operation.

Furthermore the surface temperature rises from the pickup temperature T _3, and reaches the fixing temperature T ₄ to time t _5, on-off controlling energization of the heater to maintain a fixing temperature T _4. Therefore, the surface temperature of the fixing roller changes with a predetermined amplitude around the fixing temperature T ₄ .

  A temperature detection circuit 48 including a thermistor 38 as a temperature detection unit detects the surface temperature of the press roller 33. The detection start timing of the surface temperature may be performed at the timing of stopping the rotation of the press roller 33 after the end of the recording operation job. Since the contact position of the thermistor 38 is set on the upstream side in the rotation direction with respect to the nip position with the fixing roller 28, the surface temperature is detected when time elapses after contacting the fixing roller 28 and being heated. The Therefore, the surface temperature of the press roller 33 is cooled, and the surface temperature can be detected in a state that is easily affected by the temperature state of the entire press roller 33.

  Based on the surface temperature detection data of the press roller 33 transmitted from the temperature detection circuit 48, the calculation unit 40c obtains the amount of decrease in the temperature during a predetermined time and calculates the rate of decrease in the surface temperature per unit time. Is calculated.

  Generally, the surface temperature of the press roller 33 changes so that the temperature greatly decreases from the initial high temperature state and gradually decreases. When the entire press roller 33 is cooled, the initial temperature drop is large, and when the press roller 33 is warm, the initial temperature drop is moderate.

  Therefore, the determination unit 40d determines whether data such as the maximum value of the decrease rate per unit time or the average value of the decrease rate per short time within a predetermined time from the start of detection is equal to or less than a set value, and the temperature of the press roller 33 The state can be accurately determined.

  The conveyance control unit 40e transmits a control signal to the main motor (RX) 45 to perform rotation drive control. The main motor 45 rotationally drives the pickup roller 29, the feed roller 31, the photosensitive drum 24, the supply roller and the developing roller of the developing device 22, the transfer roller 25, and the fixing roller 28 based on a control signal from the recording control unit 40. Let

  Then, the conveyance control unit 40e adjusts the sheet feeding timing by controlling the pickup roller 29 while rotating the fixing roller 28 based on the rate of decrease in the surface temperature of the press roller 33 calculated by the calculation unit 40c. The rotation control of the pickup roller 29 is performed by turning on and off the clutch 50 that contacts and separates the drive of the main motor 45.

  FIG. 5 is a processing flow for performing control based on the temperature decrease rate of the surface temperature of the press roller. First, it is checked whether the job processing relating to the recording operation has been completed (S100). If the job processing has been completed, detection of the surface temperature of the press roller 33 by the thermistor 38 is started (S101). Then, the surface temperature of the press roller 33 is continuously detected for a predetermined period after the start of detection, and the temperature decrease rate is calculated every predetermined time (S102).

  Next, the maximum decrease rate is extracted from the calculated decrease rates, and a preset registered value is compared with the maximum decrease rate to determine whether or not it is equal to or less than the set value (S103). When the maximum decrease rate is not less than the set value, the temperature state of the press roller is cold because the temperature decrease is large. In this case, when a recording signal is input (S104), the heater of the fixing roller is heated (S105), and it is detected that the surface temperature of the fixing roller has reached the pickup temperature (S106). The fixing roller is rotationally driven without starting (S107).

  In this case, if the clutch 50 is switched off and the main motor 45 is controlled to rotate, the fixing roller 28 can be controlled to rotate without rotating the pickup roller 29. As the fixing roller rotates, the press roller 33 also rotates, so that the surface of the press roller 33 is warmed by the fixing roller 28. Then, it is checked whether or not the fixing roller 28 has been rotated for a predetermined time (S108). After a predetermined time has elapsed, the clutch 50 is turned on and the pickup roller 29 is rotationally driven to start a paper feeding operation (S109). Then, an image forming process is performed on the fed paper (S110).

  In such a state where the press roller is cooled, the fixing roller is heated by rotating the fixing roller for a predetermined time before starting the paper feeding operation, so that the fixing roller is deprived of heat by the press roller and the fixing performance is deteriorated. Can be prevented.

  In step S103, when the maximum decrease rate is equal to or less than the set value, the temperature state of the press roller is warm because the temperature decrease is small. Therefore, when a recording signal is input (S111), the heater of the fixing roller is heated (S112) as usual. When it is detected that the surface temperature of the fixing roller has reached the pickup temperature (S113), a paper feeding operation is started (S109) and an image forming process is performed (S110).

  In a state where the press roller is warmed, the fixing roller is less likely to be deprived of heat by the press roller, so that the sheet feeding operation is started immediately after reaching the pickup temperature.

  In the processing flow described above, the determination is made using the maximum reduction rate in step S103, but the determination may be made using the average value of the reduction rates. In addition, the time until the paper feed timing is set in advance corresponding to the maximum reduction rate or the average value of the reduction rates without performing the determination process, and the time until the paper feed timing is read out in step S108. You may make it decide.

  In addition, after the apparatus is turned on and when the apparatus starts the recording operation from the sleep state, the process proceeds from step S101 to step S104 without checking the temperature decrease of the press roller in step S103, and the fixing roller is controlled to rotate for a predetermined time. The post-feeding operation may be started.

1 is a schematic view of an entire image forming apparatus including an embodiment according to the present invention. It is a schematic sectional drawing regarding a fixing unit. It is a whole block diagram regarding the embodiment concerning the present invention. 6 is a graph showing a transition of the surface temperature of the fixing roller with respect to heating control of the fixing roller. It is a processing flow which controls based on the temperature fall rate of the surface temperature of a press roller.

Explanation of symbols

1 Document Reading Unit 2 Recording Unit 3 Paper Conveying Unit 4 Paper Feeding Unit
28 Fixing roller
33 Press roller
34 Paper discharge roller
35 Press roller
37 Thermistor
38 Thermistor

Claims (2)

  An image forming unit that forms an electrostatic latent image on the surface of the photosensitive drum, develops the electrostatic latent image, and transfers the toner image to the paper, and heats the paper on which the toner image has been transferred by the fixing roller and the press roller. And a fixing unit that fixes the toner image by applying pressure, a temperature detection unit that detects the surface temperature of the press roller, and a rate of decrease in the surface temperature of the press roller based on a detection signal from the temperature detection unit. An image forming apparatus comprising: a calculating unit configured to adjust the sheet feeding timing while rotating the fixing roller based on the calculated decrease rate.   A determination unit configured to determine whether or not the calculated decrease rate is equal to or greater than a predetermined value; and the conveyance control unit rotates the fixing roller for a predetermined time when the determination unit determines that the calculated decrease rate is equal to or greater than the predetermined value. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled so as to be fed later.

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