JP2007187833A - Image forming apparatus and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve on-demand performance of an image forming apparatus by shortening a warmup period. <P>SOLUTION: A warmup operation is executed in a first warmup mode or a second warmup mode. In the first warmup mode, a fixing unit is set to the state in which the fixing unit is allowed to perform a fixing operation provided that the fixing roll is heated to first temperature Tb by a main heater and the length of time that the fixing roll is rotated by a drive motor has elapsed a first time ta. In a second warmup mode, the fixing unit is set to the state in which the fixing unit is allowed to perform the fixing operation provided that the fixing roll is heated to second temperature Tc by the main heater and the length of time that the fixing roll is rotated by the drive motor has elapsed the second time tb. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus including a fixing device that fixes a toner image formed using, for example, an electrophotographic method onto a recording material.

  In an image forming apparatus such as a copying machine or a printer using an electrophotographic method, generally, a surface of a photosensitive drum rotating at a constant speed is uniformly charged by a charger, and then a laser controlled based on image information. Light is scanned and exposed to form an electrostatic latent image. The electrostatic latent image formed on the photosensitive drum is developed by a developing device, and the developed toner image is electrostatically transferred onto the recording paper. Then, the toner image is fixed on the recording paper by the fixing device, and a print image is formed.

  As a fixing device used in such an image forming apparatus, a configuration called a two-roll system has been widely used. This two-roll type fixing device includes a fixing roll formed by laminating a heat-resistant release layer on the surface of a cylindrical core bar in which a heat source (for example, a halogen heater) is disposed, and a core. A pressure roll formed by laminating a heat-resistant elastic layer and a release layer made of a heat-resistant resin film on gold is configured to be in pressure contact with each other. Then, the recording paper carrying the unfixed toner image is passed through a pressure contact area (fixing nip portion) between the fixing roll and the pressure roll, and the unfixed toner image is heated and pressed to thereby form a toner. The image is fixed.

  In such a fixing device, a warm-up operation is performed when the power of the image forming apparatus is turned on. The warm-up operation is an operation for mainly setting the fixing roll to a predetermined temperature (fixing temperature) suitable for fixing prior to the image forming operation. A predetermined time (warm-up time) is required for the fixing roll to be heated to the fixing temperature. Therefore, the user cannot perform an image forming operation immediately after turning on the power of the image forming apparatus. Therefore, in order to improve the on-demand property of the image forming apparatus, it is inevitable to shorten the warm-up time. Here, as a technique for shortening the warm-up time in the fixing device, for example, there is a technique for reducing the heat capacity of the fixing roll by forming a thin thickness of the fixing roll (see, for example, Patent Document 1).

JP-A-9-244448 (page 3-4)

By the way, in the warm-up operation, it is necessary to heat the pressure roll to a certain temperature simultaneously with the fixing roll. Therefore, by including a process of rotating the fixing roll and the pressure roll during the warm-up operation, the heat of the fixing roll is conducted to the pressure roll to heat the pressure roll.
However, when the warm-up operation is completed and the fixing device is set to the standby state, the rotation of the fixing roll and the heating roll is normally stopped from the viewpoint of saving energy and suppressing noise. Therefore, in the standby state, the heat conduction from the fixing roll to the pressure roll is extremely reduced, so that the temperature of the pressure roll gradually decreases. In particular, when printing is started in a state where the temperature of the pressure roll is lowered to a predetermined temperature or less, the amount of heat taken away from the fixing roll to the pressure roll is increased, and fixing defects are likely to occur. Therefore, even if the temperature of the pressure roll decreases at the stage of transition to the standby state, the rotation time of the fixing roll and the pressure roll in the warm-up operation is suppressed in order to prevent the pressure roll from decreasing to a predetermined temperature or lower. Must be set sufficiently long. Therefore, the conventional fixing device has a certain limit for shortening the warm-up time.

  In particular, in a configuration in which the fixing roll is formed thin to reduce the heat capacity of the fixing roll, the heat of the fixing roll is easily conducted to the pressure roll. Therefore, in order to suppress the occurrence of fixing failure, it is necessary to heat the pressure roll sufficiently for the warm-up operation. As a result, the effect of shortening the warm-up time due to the low heat capacity of the fixing roll could not be sufficiently enhanced.

  The present invention has been made to solve the technical problems as described above, and an object thereof is to shorten the warm-up time.

  For this purpose, an image forming apparatus according to the present invention heats a toner image forming unit that forms a toner image on a recording material, a fixing roll, a pressure member disposed in pressure contact with the fixing roll, and the fixing roll. A fixing unit that fixes the toner image formed by the toner image forming unit on the recording material, a driving unit that rotationally drives the fixing roll and the pressure member, and a warm-up operation and a fixing operation of the fixing unit. A control unit that controls the fixing unit on the condition that the fixing roll is heated to the first temperature by the heating member and that the rotational driving time by the driving unit has passed the first time. The first warm-up mode in which the fixing operation is enabled, the fixing roll is heated to the second temperature by the heating member, and the rotation driving time by the driving unit has passed the second time. As a condition By one of the second warm-up mode for setting a section in a state capable of fixing operation, it is characterized by performing the warm-up operation of the fixing unit.

Here, when the toner image forming instruction is given to the toner image forming unit before the first time has elapsed, the control unit executes the fixing operation continuously in the first warm-up mode. Can be a feature. Further, the control unit performs a warm-up operation in the second warm-up mode when a toner image formation instruction is not given to the toner image forming unit before the first time has elapsed. You can also.
Further, the control unit is configured to supply toner to the toner image forming unit when the apparatus is turned on, or when the power saving mode in which the power supplied to the heating member is set lower than that during the fixing operation is released. The warm-up operation can be performed in any of cases where an image formation instruction is issued.

In addition, the control unit adjusts the first temperature and the first temperature so that the temperature of the fixing roll reaches the lower limit value of the temperature at which the toner image can be fixed in accordance with the time when the recording material reaches the fixing unit. It is also possible to set a time of 1.
Furthermore, the power supply voltage detection part which detects the voltage of the commercial power supply which supplies electric power inside an apparatus is further provided, and a control part is based on the voltage value of the commercial power supply detected by the power supply voltage detection part, 1st temperature, One or more of the second temperature, the first time, and the second time may be set.

  Further, the present invention is regarded as an image forming method, and the image forming method according to the present invention is configured to rotate a toner image formed on a recording material, a rotatable fixing roll, and a rotatable pressurizing press disposed on the fixing roll. An image forming method for forming a toner image on a recording material by performing a fixing process using a fixing device including a member and a heating member for heating the fixing roll, wherein the temperature of the fixing roll is a first temperature. Toner image forming operation when the rotation time of the fixing roll and the pressure member has passed the first time and the toner image forming instruction is given before the first time has passed. Is started, and when the temperature of the fixing roll reaches the first temperature and the rotation time of the fixing roll and the pressure member has passed the first time, there is no instruction to form a toner image. The second temperature of the fixing roll is higher than the first temperature. The fixing device is shifted to a standby state on condition that the temperature has been reached and a second time that is longer than the first time has elapsed since the rotation time of the fixing roll and the pressure member has elapsed. .

  Here, the first temperature may be a temperature lower than a lower limit value of a temperature at which the toner image can be fixed. The second temperature may be higher than a lower limit value of a temperature at which the toner image can be fixed. Furthermore, the first time and the second time can be characterized in that they are longer than the time required to heat the pressure member to a predetermined temperature or higher.

  According to the present invention, since the warm-up time can be shortened, the on-demand property of the image forming apparatus can be improved.

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus to which the exemplary embodiment is applied. An image forming apparatus 1 shown in FIG. 1 includes, as a toner image forming unit, a charging roll 11 that charges a photosensitive drum 10 around a photosensitive drum 10 as a toner image carrier that rotates in the direction of arrow A, and a photosensitive drum. A laser exposure device 12 for writing an electrostatic latent image on the photosensitive drum 10 (in the drawing, an exposure beam is indicated by a symbol Bm), a developing device 13 for visualizing the electrostatic latent image on the photosensitive drum 10 with toner, a photosensitive device There are disposed electrophotographic devices such as a transfer roll 14 for transferring a toner image formed on the body drum 10 onto a sheet P as a recording material, and a drum cleaner 15 for removing residual toner on the photoreceptor drum 10. . Further, a fixing device (fixing unit, fixing device) 60 that fixes an unfixed toner image transferred onto the paper P, an image processing unit 30 that performs predetermined image processing on input image data, and each device (each unit). A control unit 40 for controlling the operation is provided.

  Next, a basic image forming process of the image forming apparatus 1 according to the present embodiment will be described. In the image forming apparatus 1 as shown in FIG. 1, image data output from an image reading device (IIT) not shown, a personal computer (PC) not shown, or the like is input to the image processing unit 30. The image processing unit 30 performs predetermined image processing such as various image editing such as shading correction, position shift correction, gamma correction, frame deletion editing, and movement editing on the input image data. Then, the image data subjected to the image processing is output to the laser exposure device 12.

The laser exposure device 12 irradiates the photosensitive drum 10 with an exposure beam Bm emitted from, for example, a semiconductor laser, according to the image data input from the image processing unit 30. In the photosensitive drum 10, the surface is uniformly charged to a predetermined charging potential (for example, −550 V) by the charging roll 11, and then the surface is scanned and exposed by the laser exposure device 12 to form an electrostatic latent image. The
The formed electrostatic latent image is reversely developed with negatively charged toner by the developing device 13. That is, for example, a direct current from a power source (not shown) is applied to a developer carrying member (developing sleeve) 13a carrying a developer prepared by a polymerization method and having a toner having a shape factor SF1 of 100 to 140 mixed with a carrier made of magnetic particles. A developing bias composed of a voltage or a developing bias in which an AC voltage is superimposed on a DC voltage is applied to form a developing electric field between the photosensitive drum 10 and the developing bias. As a result, the toner on the developing sleeve 13a is transferred to the image portion (exposure portion) of the electrostatic latent image, and the electrostatic latent image is visualized as a toner image.

  The toner image formed on the photoconductor drum 10 is then conveyed to the transfer nip C where the photoconductor drum 10 and the transfer roll 14 abut. Then, in the paper transport system, the pickup roll 51 rotates in accordance with the timing at which the toner image is transported to the transfer nip C, and the paper P of a predetermined size is supplied from the paper tray 50. The paper P supplied by the pickup roll 51 is transported by the transport roll 52 and reaches the registration roll 53. In the registration roll 53, the paper P is temporarily stopped, and the registration roll 53 rotates in accordance with the movement timing of the photosensitive drum 10 carrying the toner image. Thereby, the position of the paper P and the position of the toner image are aligned, and the paper P is guided to the inlet chute 54 and sent out to the transfer nip C.

In the transfer nip portion C, the transfer roll 14 is disposed in pressure contact with the photosensitive drum 10. Further, for example, a constant current-controlled current is applied to the transfer roll 14 so that a transfer bias having a polarity (plus polarity) opposite to the toner charging polarity (minus polarity) is stably applied from a transfer power source (not shown). Is supplied. As a result, a charge having a polarity opposite to the toner charging polarity on the photosensitive drum 10 is applied from the transfer roll 14 to the paper P.
Then, the sheet P conveyed at the same timing is conveyed to the transfer nip C and is sandwiched between the photosensitive drum 10 and the transfer roll 14. At that time, a transfer bias is applied from the transfer roll 14, whereby the unfixed toner image carried on the photosensitive drum 10 is electrostatically transferred onto the paper P.

Thereafter, the sheet P on which the toner image has been electrostatically transferred is peeled from the photosensitive drum 10 by the electrostatic attraction force from the transfer roll 14 and the stiffness of the sheet P. Then, it is guided by the conveyance guide 55 and the fixing inlet guide 80 and is sent to the fixing device 60 provided on the downstream side of the transfer roll 14 in the conveyance direction of the paper P.
The unfixed toner image on the paper P conveyed to the fixing device 60 is fixed on the paper P by being subjected to fixing processing by heat and pressure in the fixing device 60. Then, the paper P on which the fixed image is formed is conveyed to a paper discharge mounting portion 58 provided in the discharge portion of the image forming apparatus 1, and a series of image forming operations is completed.

Next, the configuration of the fixing device 60 will be described.
FIG. 2 is a cross-sectional view showing the configuration of the fixing device 60. As shown in FIG. 2, the fixing device 60 rotatably supports a fixing roll 61 as an example of a heating member, and includes a first casing 65 disposed so as to cover a partial region of the fixing roll 61. A second casing 66 that rotatably supports a pressure roll 62 as an example of a pressure member is connected to form a unit. At that time, the pressure roll 62 is pressed against the fixing roll 61 by a pressing means (not shown) made of a coil spring or the like, and a fixing nip portion N through which the paper P passes is formed.

The fixing roll 61 includes a cylindrical core 611 and a release layer 612 covered on the surface side of the core 611. The core 611 is formed of a thin roll made of, for example, iron and having an outer diameter of, for example, 25 mm and a thickness of, for example, 0.1 to 0.6 mm. As described above, the fixing roll 61 of the present embodiment is thin and has a small heat capacity, so that the warm-up time for raising the fixing roll 61 to a temperature suitable for fixing can be shortened as much as possible. It becomes.
For the release layer 612, for example, a heat-resistant resin such as a silicone resin or a fluororesin is used, but a fluororesin is suitable from the viewpoint of the release property to the toner and the wear resistance. As the fluororesin, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), tetrafluoroethylene-hexafluoropropylene copolymer (FEP) and the like can be used. The film thickness of the release layer 612 is, for example, 5-100 μm.

In addition, as an example of a heating member, two halogen heaters having different light distribution characteristics, that is, a main heater 67 and a sub-heater 68 are disposed inside the fixing roll 61 to heat the fixing roll 61. At this time, the temperature sensor 69 is disposed in contact with the surface of the fixing roll 61, and the control unit 40 of the image forming apparatus 1 turns on the main heater 67 and the sub heater 68 based on the temperature measurement value by the temperature sensor 69. Control (energization). The surface temperature of the fixing roll 61 is adjusted to maintain a predetermined set temperature (for example, 175 ° C.). Further, a thermostat 70 is provided in the vicinity of the fixing roll 61 inside the first housing 65, and the thermostat 70 prevents a failure due to overheating of the fixing roll 61.
The temperature sensor 69 is disposed in the vicinity of the main heater 67 in the circumferential direction of the fixing roll 61 in order to accurately detect the temperature of the surface of the fixing roll 61 during the warm-up operation.

Here, FIG. 3 is a diagram showing the light distribution characteristics of the main heater 67 and the sub heater 68. 3A shows the light distribution characteristic of the main heater 67, and FIG. 3B shows the light distribution characteristic of the sub heater 68. Here, the light distribution characteristic refers to a heat amount distribution in the axial direction when the main heater 67 and the sub heater 68 are energized.
As shown in FIG. 3A, the main heater 67 is light-distributed so as to heat substantially the entire area of the maximum width sheet passing region in the axial direction of the fixing roll 61. On the other hand, as shown in FIG. 3B, the sub heater 68 is distributed so as to mainly heat a central region (minimum width sheet passing region) narrower than the main heater 67 in the axial direction of the fixing roll 61. Yes. In other words, in the central region of the fixing roll 61 in the axial direction, the regions heated by the main heater 67 and the sub heater 68 overlap. The light distribution characteristic of the sub-heater 68 is constant along the axial direction of the fixing roll 61, but the light distribution characteristic of the main heater 67 is set to be larger at both ends than at the center. This is because when the main heater 67 is turned on for a long time, heat is stored in the central portion of the main heater 67 in the axial direction, and heat of the main heater 67 is dissipated in both end regions located outside the central portion. This is to prevent the temperature distribution from becoming uneven.
Note that the fixing device 60 of the present embodiment employs a so-called center resist system in which the minimum width sheet passing area exists in the center of the maximum width sheet passing area. Further, the temperature sensor 69 is provided at a substantially central portion of the minimum width sheet passing area of the fixing roll 61.

In the fixing device 60 of the present embodiment, the sub heater 68 is a heater used when fixing A4SEF (A4 short edge feed), and the heat generation area length of the sub heater 68 in the axial direction of the fixing roll 61 is A4 size. The length of the short edge is substantially the same. In the sub-heater 68, when fixing the A4SEF and B5SEF sheets (small size sheets), energization ON / OFF control is performed so that the temperature of the fixing area of the small size sheets is maintained at a predetermined fixing temperature. .
On the other hand, the main heater 67 is a heater used when fixing A4LEF (A4 long edge feed), and the heat generation area length of the main heater 67 in the axial direction of the fixing roll 61 is substantially equal to the length of the A4 size long edge. The same. In the main heater 67, when fixing A4LEF, A3SEF (A3 short edge feed), B4SEF, and B5LEF sheets (large size sheets), the temperature of the fixing area of the large size sheets is maintained at a predetermined fixing temperature. Energization ON / OFF control is performed.

  Next, the pressure roll 62 includes, for example, a cylindrical shaft 621, a heat-resistant elastic body layer 622 provided around the shaft 621, and a release layer 623 that covers the surface of the heat-resistant elastic body layer 622. ing. The shaft 621 is made of, for example, iron or aluminum and may be hollow. The heat-resistant elastic layer 622 is a heat-resistant material having a hardness of, for example, 45 ° (Asker C), and is formed of, for example, silicon sponge or silicon rubber. The heat-resistant elastic layer 622 has a thickness of 6 mm, for example, and is formed so as to obtain a substantially constant nip width when the pressure roll 62 is pressed against the fixing roll 61. The thickness of the heat resistant elastic body layer 622 is preferably in the range of 6 to 8 mm. The release layer 623 is made of, for example, PFA having release properties and abrasion resistance with respect to the toner. Moreover, the film thickness of the release layer 623 is preferably in the range of 30 to 100 μm, for example.

  Further, a conveyance path for conveying the paper P is formed in the upstream direction and the downstream direction across the fixing nip portion N formed by the fixing roll 61 and the pressure roll 62, and the paper P is moved upward from below. It is conveyed to. A paper feed port formed on the upstream side of the fixing nip N is provided with a fixing inlet guide 80 made of, for example, a plate-like metal that constitutes a paper transport system. Discharge guides 90 and 91 constituting a sheet transport system are disposed at a discharge port formed on the downstream side of the fixing nip N, respectively. The paper discharge guides 90 and 91 are formed of a plurality of ribs, and are provided on the first housing 65 side and the second housing 66 side, respectively. The paper P is configured to pass between the paper discharge guide 90 and the paper discharge guide 91.

  Further, in the first casing 65 in the vicinity of the downstream side of the fixing nip portion N, a plurality of peeling claws 92 as peeling members are arranged in the axial direction of the fixing roll 61 (paper width direction). The peeling claw 92 is urged toward the fixing roll 61 with a weak force that does not damage the surface of the fixing roll 61, and the tip of the fixing roll 61 comes into pressure contact with the surface of the fixing roll 61 and is wound around the fixing roll 61. It is configured to peel off the paper to be removed.

Subsequently, when the main switch of the image forming apparatus 1 is turned on, when the power saving mode is canceled during the power saving mode, or during the power saving mode or in the standby state, the print start button is pressed from the operation panel (not shown). An operation (warm-up operation) for heating the fixing roll 61 until it reaches a predetermined temperature (fixing temperature) suitable for fixing, performed by the fixing device 60 of the present embodiment, will be described. Here, in the power saving mode, although the main switch of the image forming apparatus 1 is turned on, the image forming operation is not performed, so that the main heater 67 and / or the sub heater 68 in the fixing roll 61 is energized. A state (mode) in which power consumption is reduced by stopping or reducing the amount of current.
FIG. 4 is a flowchart illustrating a processing procedure during a warm-up operation performed by the control unit 40 when the main switch of the image forming apparatus 1 is turned on. Hereinafter, the warm-up operation will be described in order according to FIG.
In the fixing device 60 of the present embodiment, during the warm-up operation, only the main heater 67 is energized, and only the main heater 67 generates heat (emits light). As described above, the main heater 67 is light-distributed so as to heat substantially the entire width of the sheet passing area in the axial direction of the fixing roll 61, so that it is uniform over the axial direction of the fixing roll 61. This is because it is appropriate to heat only the main heater 67 for heating.

In the warm-up operation, first, the main switch of the image forming apparatus 1 is turned on, so that the main heater 67 in the fixing roll 61 is turned on, and the temperature of the fixing roll 61 is controlled to the control temperature (second temperature) Tc. The heater control to be controlled is started (S1). Here, a drive motor (not shown) as an example of a drive unit that drives the fixing roll 61 and the pressure roll 62 is turned off, and the fixing roll 61 is maintained in a stopped state for a while. This is because when the main heater 67 is turned on and the drive motor is also turned on to rotate the fixing roll 61, the heat of the fixing roll 61 heated by the radiant heat from the main heater 67 is transmitted to the pressure roll 62 side. Therefore, the heating efficiency for the fixing roll 61 is decreased.
After the main heater 67 is turned on, the control unit 40 turns on the drive motor when the detection value of the temperature sensor 69 reaches the rotation start temperature Ta (S2). Then, rotation of the fixing roll 61 and the pressure roll 62 is started (S3). Here, the fixing roll 61 and the pressure roll 62 are rotated in order to reduce temperature unevenness in the circumferential direction of the fixing roll 61 and to conduct heat from the fixing roll 61 to the pressure roll 62. This is for heating 62.

Furthermore, when the detected value of the temperature sensor 69 reaches the rotation start temperature Ta (S2), the control unit 40 measures the elapsed time from the time when the rotation start temperature Ta is reached (S2). Timer count) is started (S4). Subsequently, it is determined whether or not the timer count has passed a predetermined first time ta (S5). Furthermore, the control unit 40 determines whether or not the detection value of the temperature sensor 69 has reached the first temperature Tb (S6). Then, when the first time ta has passed and the temperature of the fixing roll 61 has reached the first temperature Tb, for example, a print start configured on the operation panel (not shown) of the image forming apparatus 1 is started. It is determined whether or not there has been a print instruction due to the button being pressed (S7).
If there is a print instruction in step 7, the image forming apparatus 1 starts conveying a predetermined size of paper P from the paper tray 50 based on a control signal from the control unit 40 (S8), and An image forming operation is executed.

Here, temperature control and drive control related to the fixing roll 61 and the pressure roll 62 when there is a print instruction in step 7 will be described. FIG. 5 is a diagram showing changes over time in the temperatures of the fixing roll 61 and the pressure roll 62 when a printing instruction is given in step 7, and FIG. 5B is a diagram of the main heater 67 in that case. FIG. 4 is a timing chart showing ON / OFF control and a timing chart showing ON / OFF control of a drive motor (not shown) that drives the fixing roll 61 and the pressure roll 62 to rotate. In FIG. 5A, the solid line indicates the change over time of the temperature of the fixing roll 61, and the broken line indicates the change over time of the temperature of the pressure roll 62. 5A and 5B, the time axes are the same.
As shown in FIG. 5, in the fixing device 60 of the present embodiment, the first temperature Tb at which it is determined whether or not the temperature has reached in step 6 is the lower limit at which the toner image on the paper P can be fixed. It is set to a temperature lower than the temperature (the lowest temperature that can be fixed). Further, the first time ta for determining whether or not the time has elapsed in Step 5 is a time sufficient for reducing the temperature unevenness in the circumferential direction of the fixing roll 61, and the pressure roll 62 is sufficient. This is a sufficient time for heating.

By the way, the lowest fixable temperature is the lower limit temperature at which the toner image can be fixed as described above, but the control temperature Tc that is the control target during the warm-up operation is higher than the lowest fixable temperature. It is set. This is mainly due to the following reasons.
That is, when the warm-up operation is completed and the image forming apparatus 1 shifts to the standby state, the drive motor is stopped from the viewpoint of energy saving and noise reduction, and therefore the fixing roll 61 to the pressure roll 62. There is almost no heat transfer to the. Therefore, normally, the temperature of the pressure roll 62 heated by the warm-up operation gradually decreases. When the image forming operation is started in this state, the amount of heat taken away from the fixing roll 61 by the pressure roll 62 increases because the temperature of the pressure roll 62 has decreased. As a result, the amount of heat supplied from the main heater 67 and the sub-heater 68 temporarily temporarily becomes insufficient until the pressure roll 62 is sufficiently heated again at the start of the image forming operation. Is likely to occur.
Further, the commercial power input to the image forming apparatus 1 usually has a fluctuation range of about 10%. For this reason, the amount of heat generated by the main heater 67 also varies. Further, the heat capacity varies due to individual differences of members constituting the fixing device 60. For this reason, it is necessary to set a margin for the fixable temperature.

  Therefore, the control temperature Tc is set to a temperature higher than the lowest fixable temperature. Thereby, it is possible to set a sufficient fixable temperature when the warm-up operation is completed. Further, as will be described in detail later (see FIG. 6), the pressure roll 62 can be sufficiently heated and the entire fixing device 60 can be heated. As a result, even when in the standby state, it is possible to suppress the temperature of the pressure roll 62 from dropping below a predetermined temperature, and even when the image forming operation is started from the standby state, the occurrence of fixing failure is prevented. It becomes possible to suppress it reliably.

  On the other hand, the pressure roll 62 is sufficiently heated at the time when the first time ta at which the rotation operation in the warm-up operation is performed. That is, as shown by the broken line in FIG. 5A, when the temperature of the pressure roll 62 is set to the image forming operation by passing the first time ta, the pressure roll 62 becomes the fixing roll. The temperature can be raised to a temperature that does not increase the amount of heat deprived from 61 (necessary temperature of the pressure roll). Thereby, at the time when the first time ta has passed, even if the image forming operation is performed immediately, the amount of heat taken away from the fixing roll 61 to the pressure roll 62 does not increase. Therefore, if the first time ta has passed and the temperature of the fixing roll 61 is heated to the lowest fixable temperature, even if the image forming operation is performed, the temperature of the fixing roll 61 is set to the lowest fixable temperature. It is possible to keep it.

That is, when the image forming operation is performed simultaneously with the completion of the warm-up operation, it is assumed that the image forming operation is started from the standby state because the pressure roll 62 is heated to a temperature higher than the pressure roll required temperature. It is not necessary to raise the temperature of the fixing roll 61 to the control temperature Tc. Therefore, when the first time ta has passed and the temperature of the fixing roll 61 has risen to the first temperature Tb close to the lowest fixable temperature, fixing is performed while reliably suppressing the occurrence of fixing failure. Processing can be performed.
Therefore, in the image forming apparatus 1 according to the present embodiment, when the print instruction has already been made when both the arrival of the first temperature Tb and the passage of the first time ta are satisfied, the image is displayed. It is set so that the forming operation can be executed (first warm-up mode). Thereby, it is not necessary to wait until the fixing roll 61 reaches the control temperature Tc, and the warm-up time can be shortened.

Here, the first time ta in which it is determined whether or not the time has elapsed in step 5 and the first temperature Tb in which it is determined whether or not the time has reached in step 6 indicate that the paper P is the fixing device 60. Each time can be set so that the time when the temperature of the fixing roller 61 reaches the time when the temperature of the fixing roller 61 reaches or exceeds the lowest fixable temperature.
One specific example is shown. For example, after the rotation of the fixing roll 61 and the pressure roll 62 is started in Step 3, the fixing roll 61 is used until the temperature of the fixing roll 61 reaches the first temperature Tb (first time ta). A temperature increase rate ΔT (deg / sec) indicating how many times the temperature of 61 has increased per unit time is obtained. In this case, the temperature increase rate ΔT can be expressed as the following equation (1).
ΔT = (Tb−Ta) / ta (1)

Even after the temperature of the fixing roll 61 reaches the first temperature Tb, the paper P is fed from the paper tray 50 and reaches the fixing device 60 on the assumption that the temperature rise continues at the same temperature increase rate ΔT. If the first time ta and the first temperature Tb are set so that the following expression (2) is satisfied when the time to do is t1, the temperature of the fixing roll 61 is equal to or higher than the lowest fixable temperature. The conveyance of the sheet P of a predetermined size from the sheet tray 50 can be started in accordance with the time point when the sheet reaches the position. In Formula (2), the lowest fixable temperature is represented as Tmin.
Tmin−Tb = t1 × ΔT
= T1 * (Tb-Ta) / ta (2)
In this way, for example, by setting the first temperature Tb lower than the minimum fixable temperature Tmin that satisfies the expression (2) and the first time ta, the transport time of the paper P can be effectively used, and the warm temperature can be increased. It becomes possible to further promote shortening of uptime.

  Further, in the image forming apparatus 1 of the present embodiment, when the image forming operation is started, it is a condition that both the arrival of the first temperature Tb and the passage of the first time ta are satisfied. As a result, the temperature unevenness in the circumferential direction of the fixing roll 61 caused by the fact that the first time ta has not elapsed even when the first temperature Tb is reached is insufficient, or the pressure roll 62 It can suppress that temperature is a state below a pressure roll required temperature. Further, the end region in the axial direction of the fixing roll 61 can be sufficiently heated. Accordingly, even when the image forming operation is started from the standby state, it is possible to suppress the occurrence of fixing failure.

In addition, it is possible to suppress the occurrence of fixing failure caused by not reaching the first temperature Tb even when the first time ta has elapsed. For example, the amount of heat generated by the main heater 67 used during the warm-up operation has a characteristic that increases or decreases due to voltage fluctuations of the commercial power supply supplied to the image forming apparatus 1. In general, when a heater that outputs a heating value of W1 (W) at a voltage V1 (V) is used, when the voltage of the commercial power supply changes to V2 (V), the following equation (3) As shown, the heating value W2 (W) increases or decreases. That is,
W2 = (V2 / V1) ^1.54 × W1 (3)
Specifically, when the main heater 67 that outputs a calorific value of 1000 (W) at 100 (V) is used, when the voltage of the commercial power supply is reduced to 90 (V) by 10%, (3) From the formula
(90/100) ^1.54 × 1000≈850 (W)
Thus, the amount of heat generated by the main heater 67 varies by 15%.
Therefore, there is a possibility that a situation in which the first temperature Tb has not been reached even if the first time ta has elapsed, and in this case, even if the first time ta has elapsed, the first time ta has elapsed. If the temperature Tb has not been reached, the start of the image forming operation is not permitted, thereby suppressing the occurrence of fixing failure.

In addition, in the fixing device 60 of the present embodiment, a power supply voltage detection unit (not shown) that detects a voltage supplied from a commercial power supply is provided in the image forming apparatus 1 and is detected by the power supply voltage detection unit. Based on the obtained voltage value, the control unit 40 can also be configured to set a combination of the first time ta and the first temperature Tb with the shortest warm-up time.
In this case, as shown in the above equation (2), the time when the paper P reaches the fixing device 60 coincides with the time when the temperature of the fixing roll 61 reaches or exceeds the lowest fixable temperature. Thus, a combination of the first time ta and the first temperature Tb can also be set.

  Next, a case where there is no print instruction in step 7 will be described. As shown in FIG. 4, when there is no print instruction in step 7, the control unit 40 determines whether or not the timer count has passed a predetermined second time tb (S9). Further, the control unit 40 determines whether or not the detection value of the temperature sensor 69 has reached the control temperature Tc (S10). Then, when the second time tb has elapsed and the temperature of the fixing roll 61 has reached the control temperature Tc, the drive motor is stopped and a transition is made to a standby state (S11) (second warm-up) mode).

Here, temperature control and drive control related to the fixing roll 61 and the pressure roll 62 when there is no print instruction in Step 7 will be described. FIG. 6A is a diagram showing a change over time in the temperature of the fixing roll 61 and the pressure roll 62 when there is no print instruction in step 7, and FIG. 6B is a diagram showing the main heater 67 in that case. FIG. 4 is a timing chart showing ON / OFF control and a timing chart showing ON / OFF control of a drive motor (not shown) that drives the fixing roll 61 and the pressure roll 62 to rotate. In FIG. 6A, the solid line indicates the change over time of the temperature of the fixing roll 61, and the broken line indicates the change over time of the temperature of the pressure roll 62. Moreover, in FIG. 6 (a), (b), each time-axis is the same.
As shown in FIG. 6, the control temperature Tc at which it is determined whether or not it has been reached in step 10 is higher than the lower limit temperature (the lowest fixable temperature) at which the toner image on the paper P can be fixed. Is set. In addition, the second time tb in which it is determined whether or not the time has passed in step 9 is set to be longer than the first time ta set in step 5.

When the warm-up operation is completed and the image forming apparatus 1 shifts to the standby state, the drive motor is stopped from the viewpoints of energy saving and noise reduction, so that the fixing roll 61 to the pressure roll 62 is stopped. There is almost no heat transfer. Therefore, when shifting to the standby state, normally, the temperature of the pressure roll 62 heated by the warm-up operation gradually decreases as shown by the broken line in FIG. And when predetermined time (for example, several seconds later) passes since the time of shifting to a standby state, the temperature of the pressure roll 62 shows the minimum value. When the image forming operation is started in a state where the temperature of the pressure roll 62 shows the minimum value, the amount of heat taken from the fixing roll 61 to the pressure roll 62 increases. In particular, when the fixing roll 61 is formed thin and has a small heat capacity, the temperature drop of the fixing roll 61 becomes large. As a result, the amount of heat supplied from the main heater 67 and the sub-heater 68 is temporarily insufficient until the pressure roll 62 is sufficiently heated again, and a fixing defect tends to occur in the image at the start of the image forming operation.
Note that after the temperature of the pressure roll 62 shows the minimum value, the entire fixing device 60 is heated, so that the temperature of the pressure roll 62 also starts to rise. Therefore, fixing failure is most likely to occur when a predetermined time elapses from the time when the standby state is entered.

Therefore, in the fixing device 60 of the present embodiment, the pressure roll 62 can be sufficiently heated by setting the second time tb to be longer than the first time ta. Accordingly, even when the temperature of the pressure roll 62 shows the minimum value when the standby state is entered, the pressure roll 62 is moved from the fixing roll 61 when the image forming operation is performed at the minimum value. It is possible to set the temperature so that the amount of heat taken away does not increase (the pressure roll required temperature) or higher.
In addition, by setting the second time tb to be longer than the first time ta, the entire fixing device 60 can be sufficiently heated. Accordingly, since the entire fixing device 60 is sufficiently heated in the standby state, the temperature of the pressure roll 62 is promoted to rise after the temperature of the pressure roll 62 shows the minimum value. Is also possible.
In this way, by setting the second time tb to a time longer than the first time ta, it is possible to suppress the temperature of the pressure roll 62 from dropping below the required temperature of the pressure roll, and waiting. Even when the image forming operation is started from the state, it is possible to reliably suppress the occurrence of fixing failure.

  Further, in the image forming apparatus 1 of the present embodiment, when shifting to the standby state, both the arrival of the control temperature Tc and the elapse of the second time tb are satisfied. Thereby, even if the control temperature Tc is reached, the second time tb has not elapsed, or even if the first time ta has elapsed, the first temperature Tb has not been reached. It becomes possible to suppress that the temperature of the pressure roll 62 falls below the pressure roll required temperature.

In this case, the amount of heat generated by the main heater 67 increases or decreases due to voltage fluctuations of the commercial power supply supplied to the image forming apparatus 1, so that the voltage supplied from the commercial power supply to the image forming apparatus 1 is the same as described above. A power supply voltage detection unit (not shown) for detection is provided, and based on the voltage value detected by the power supply voltage detection unit, the control unit 40 determines that the temperature of the pressure roll 62 is equal to or lower than the pressure required for the pressure roll. It is also possible to set the combination of the second time tb and the control temperature Tc so as to suppress the decrease.
Even if the second time tb is set longer, in this case, since the image forming operation is not performed continuously to the warm-up operation, the warm-up time is not hindered.

  Further, in the image forming apparatus 1 according to the present embodiment, when both the arrival of the first temperature Tb and the elapse of the first time ta are satisfied, if no print instruction is given, The warm-up operation is continued until both the arrival of the control temperature Tc and the passage of the second time tb are satisfied. Therefore, even when the user performs the operation of the print start button with a delay, the energization to the main heater 67 and the rotation drive of the drive motor can be continued to shift to the image forming operation. As a result, since the restart of the main heater 67 and the drive motor is reduced, it is possible to obtain a failure reduction effect and a life extension effect by reducing the load on the circuit system and the drive system.

In the image forming apparatus 1 according to the present embodiment, as a start condition for the warm-up operation, when the main switch of the image forming apparatus 1 is turned on, when the power saving mode is canceled during the power saving mode, or when the power saving mode is released. It is assumed that the print start button is pressed from the operation panel (not shown) during the mode or in the standby state. In addition to such a case, the user may perform an operation on the image forming apparatus 1 during the power saving mode or in the standby state, for example, when an operation for opening the document table of the image scanner or an operation for inserting and removing the paper tray 50 is performed. The warm-up operation can be started when any operation is performed.
Furthermore, it is also possible to configure so that a warm-up operation start condition can be selected from the above-described conditions, for example, according to a user designation.

As described above, in the fixing device 60 of the present embodiment, when the image forming operation is performed continuously with the warm-up operation, the first temperature Tb is reached and the elapse of the first time ta. The image forming operation is set to start on condition that both are satisfied. On the other hand, when the image forming operation is not performed continuously after the warm-up operation, setting is made so as to shift to the standby state on condition that both the arrival of the control temperature Tc and the passage of the second time tb are satisfied. is doing.
Accordingly, it is possible to shorten the warm-up time while suppressing the occurrence of fixing failure. In addition, even when the image forming operation is started from the standby state, it is possible to reliably suppress the occurrence of fixing failure.

1 is a schematic configuration diagram showing an image forming apparatus of the present invention. FIG. 3 is a cross-sectional view illustrating a configuration of a fixing device. It is the figure which showed the light distribution characteristic of the main heater and a subheater. It is the flowchart which showed the process sequence at the time of warm-up operation | movement. (A) is a figure which showed the time-dependent change of the temperature of a fixing roll and a pressure roll when there is a printing instruction | indication in step 7, (b) is a timing chart which shows ON / OFF control of a main heater, FIG. 4 is a timing chart showing ON / OFF control of a drive motor that rotationally drives a fixing roll and a pressure roll. (A) is a figure which showed the time-dependent change of the temperature of a fixing roll and a pressure roll when there is no printing instruction | indication in step 7, (b) is a timing chart which shows ON / OFF control of a main heater, FIG. 4 is a timing chart showing ON / OFF control of a drive motor that rotationally drives a fixing roll and a pressure roll.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Image forming apparatus, 10 ... Photosensitive drum, 11 ... Charging roll, 12 ... Laser exposure device, 13 ... Developing device, 14 ... Transfer roll, 15 ... Drum cleaner, 40 ... Control part, 60 ... Fixing device, 61 ... Fixing roll, 62 ... Pressure roll, 65 ... First housing, 66 ... Second housing, 67 ... Main heater, 68 ... Sub heater, 69 ... Temperature sensor, 70 ... Thermostat, 80 ... Fixing inlet guide, 90, 91 ... paper discharge guide, 92 ... peeling nail

Claims (10)

A toner image forming unit for forming a toner image on the recording material;
A fixing unit that includes a fixing roll, a pressure member disposed in pressure contact with the fixing roll, and a heating member that heats the fixing roll, and fixes the toner image formed by the toner image forming unit to the recording material;
A drive unit that rotationally drives the fixing roll and the pressure member;
A controller for controlling a warm-up operation and a fixing operation of the fixing unit;
The control unit can perform the fixing operation of the fixing unit on the condition that the fixing roller is heated to the first temperature by the heating member and the rotation driving time by the driving unit has passed the first time. On the condition that the fixing roller is heated to the second temperature by the heating member and the rotation driving time by the driving unit has passed the second time. An image forming apparatus, wherein a warm-up operation of the fixing unit is executed in any one of a second warm-up mode in which the fixing unit is set in a state where a fixing operation is possible.   The control unit executes a fixing operation in succession to the first warm-up mode when a toner image forming instruction is given to the toner image forming unit before the first time elapses. The image forming apparatus according to claim 1.   The control unit executes a warm-up operation in the second warm-up mode when a toner image formation instruction is not given to the toner image forming unit before the first time elapses. The image forming apparatus according to claim 1.   The control unit is configured to turn on the power of the apparatus, or to release the power saving mode in which the power supplied to the heating member is set lower than that during the fixing operation, or to the toner image forming unit. The image forming apparatus according to claim 1, wherein the warm-up operation is performed in any case where a toner image formation instruction is issued.   The control unit adjusts the first temperature and the first temperature so that the temperature of the fixing roll reaches a lower limit value of the temperature at which the toner image can be fixed in accordance with the time when the recording material reaches the fixing unit. The image forming apparatus according to claim 1, wherein the first time is set. It further includes a power supply voltage detector that detects the voltage of a commercial power supply that supplies power to the inside of the device,
The control unit is configured to select any one of the first temperature, the second temperature, the first time, and the second time based on the voltage value of the commercial power supply detected by the power supply voltage detection unit. The image forming apparatus according to claim 1, wherein one or more of these are set. The toner image formed on the recording material includes a rotatable fixing roll, a rotatable pressure member disposed in pressure contact with the fixing roll, and a heating member that heats the fixing roll. An image forming method for forming a toner image on a recording material by performing a fixing process with a fixing device,
The toner is heated until the temperature of the fixing roll reaches the first temperature, the rotation time of the fixing roll and the pressure member passes the first time, and the first time passes. When there is an image formation instruction, a toner image forming operation is started,
When the temperature of the fixing roll reaches the first temperature and there is no instruction to form a toner image when the rotation time of the fixing roll and the pressure member has passed the first time. The second time when the temperature of the fixing roll reaches a second temperature higher than the first temperature and the rotation time of the fixing roll and the pressure member is longer than the first time. The image forming method is characterized in that the fixing device is shifted to a standby state on condition that the process has passed.   The image forming method according to claim 7, wherein the first temperature is lower than a lower limit value of a temperature at which the toner image can be fixed.   The image forming method according to claim 7, wherein the second temperature is higher than a lower limit value of a temperature at which the toner image can be fixed.   8. The image forming method according to claim 7, wherein the first time and the second time are longer than a time required for heating the pressure member to a predetermined temperature or higher.

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