JP2004102104A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device for preventing the occurrence of image defects without impairing its usability by reducing overshooting of fixing roller temperature. <P>SOLUTION: Print temperature control of a fixing device is stopped before the fixation of a final page is completed to quit heating operation or start post-rotation temperature control. If an LBP engine is unable to recognize the number of pages constituting image data, it is judged whether the operation is performed according to whether data are available in the imaging start timing of a 1st developing station. When the number of pages of a job can be recognized, the timing of the operation is predetermined by being calculated back to from fixation end timing according to the number of pages. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic apparatus and an electrostatic recording apparatus.
[0002]
[Prior art]
Image forming apparatuses such as copiers and printers use recording materials (transfer material sheets, electrofax sheets, electrostatic recording paper, OHP sheets) by appropriate image forming process means such as electrophotographic processes, electrostatic recording processes, and magnetic recording processes. An unfixed image (toner image) of the target image information formed and carried on a printing paper or a format paper by a transfer method or a direct method by an image heating device (hereinafter, referred to as a fixing device). In general, a method of fixing by heat and pressure as a permanently fixed image is used.
[0003]
The toner image formed on the recording material is melted by a heat source of a fixing device, and is fixed as a permanent image on the recording material by applying pressure.
[0004]
Particularly, in a color image forming apparatus, since an appropriate gloss is required for an image after fixing, it is common to use a heat roller type fixing apparatus to which a larger pressing force can be applied.
[0005]
However, in the heat roller method, the heat capacity of the fixing device is larger than in other fixing methods, for example, a method using a thin fixing film as a heating member.
[0006]
When the heat capacity of the fixing device is increased, the response (response) of the surface temperature of the fixing roller to a heating operation by a heat source such as a halogen heater is reduced.
[0007]
In the heat roller fixing method, ON / OFF control of the heater is performed so that the temperature of the fixing roller surface maintains a desired fixing temperature.
[0008]
When continuous printing is performed, the lighting time of the heater becomes unnecessarily long for the above-described reason, and the temperature of the fixing roller excessively increases (overshoots) after printing is completed.
[0009]
[Problems to be solved by the invention]
1) This has caused the following problems. That is, if the fixing operation is performed in a state where the temperature of the fixing roller is excessively increased, the toner to be fixed to the recording material is offset to the surface of the fixing roller, and adheres to the recording material sent to the fixing device thereafter, and becomes dirty. Image problem (hot offset).
[0010]
2) In order to avoid the above problem, when the surface temperature of the fixing roller is equal to or higher than a predetermined temperature, it is possible to inhibit the printing operation and wait until the temperature decreases. However, since the heat capacity is large, a waiting time of several minutes may be required, which is not preferable in terms of usability.
[0011]
Accordingly, it is an object of the present invention to provide an image forming apparatus which avoids the above two problems 1) and 2) and enables both good images and usability.
[0012]
[Means for Solving the Problems]
The present invention is an image forming apparatus having the following configuration.
[0013]
[1]: a fixing roller and a pressing member rotatably disposed, and a heat source for heating the fixing roller, the fixing roller and the pressing member being pressed against each other to form a fixing nip, An image heating device for heating and fixing the fixing roller to a predetermined fixing temperature, and passing a recording material carrying the toner image through the fixing nip to fix the toner image on the recording material by heat and pressure. In the forming device,
At a predetermined timing before the recording material of the last page of the print job passes through the fixing nip, the heating operation of the heat source in the image heating device is stopped, or the temperature control is started so that the fixing roller temperature becomes lower than the predetermined fixing temperature. An image forming apparatus having a fixing mode.
[0014]
[2]: A plurality of image carriers arranged in parallel with the first color, the second color,..., An image forming mechanism for forming and carrying a toner image on a recording material, and rotatably disposed. An image heating device that presses the fixed fixing roller and the pressing member together to form a fixing nip, passes a recording material carrying a toner image through the fixing nip, and heat-presses the toner image onto the recording material. In the image forming apparatus,
When the image formation of the next page of the first color is not started even after a predetermined time has elapsed after the completion of the image formation on the image carrier of the first color, the heating operation of the heat source in the image heating device is stopped or fixed. An image forming apparatus having a fixing mode for starting temperature control so that a roller temperature becomes lower than the predetermined fixing temperature.
[0015]
[3] The image forming apparatus according to [1] or [2], wherein the predetermined timing or the predetermined time is different depending on at least one condition of a size or a type of a recording material during image formation.
[0016]
[4]: The method according to any one of [1] to [3], wherein the predetermined timing or the predetermined time differs depending on the temperature of the fixing roller at the time when the predetermined timing or the predetermined time has elapsed. Image forming apparatus.
[0017]
[5] The image forming apparatus according to any one of [1] to [4], wherein the predetermined timing or the predetermined time differs depending on an environmental temperature in which the image forming apparatus is installed.
[0018]
[6] The image forming apparatus according to any one of [1] to [5], wherein the predetermined timing or the predetermined time differs depending on the number of prints.
[0019]
[7]: The predetermined timing or predetermined time is:
▲ 1 ▼. At least one condition of the size or type of recording material during image formation
▲ 2 ▼. Fixing roller temperature at a given time or at a given time
(3). Environmental temperature at which the image forming device is installed
▲ 4 ▼. Number of prints
The image forming apparatus according to [1] or [2], wherein the image forming apparatus differs depending on a combination of a plurality of conditions described in at least two or more of them.
[0020]
<Operation>
(1) Fixing after printing is completed by stopping the heating of the fixing device heat source before the end of the fixing operation of the last page of the print job, or by starting the temperature control so that the fixing roller temperature becomes lower than the predetermined fixing temperature. Temperature overshoot can be reduced.
[0021]
(2) The timing of stopping the heating of the fixing device heat source or starting the temperature control so that the fixing roller temperature becomes lower than the predetermined fixing temperature is based on the image forming operation in the first color developing station. In addition, overshoot can be effectively reduced even in an image forming apparatus that cannot recognize the number of pages constituting a print job.
[0022]
(3) By determining the timing with reference to the temperature of the fixing roller, it is possible to surely secure a good image and reduce overshoot.
[0023]
(4) By making the timing variable according to the recording material used, the number of prints, and the environment, overshoot can be effectively reduced without impairing the optimal fixing conditions.
[0024]
(5) By reducing the overshoot by using one or more of the methods (1) to (4), it is possible to simultaneously prevent image defects and improve usability by shortening the print standby time.
[0025]
(6) More specifically, before the fixing of the last page is completed, the print temperature control of the image heating apparatus is stopped and the heating operation is stopped, or the process shifts to post-rotation temperature control. If the LBP engine cannot recognize the number of pages making up the image data, it is determined whether to execute the above operation based on the presence or absence of data at the image forming start timing in the first developing station. When the number of pages of the job can be recognized, the timing of the above operation is determined in advance by calculating backward from the fixing end timing based on the number of pages.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
[Example 1]
(1) Example of image forming apparatus
FIG. 2 is a schematic configuration diagram of an example of the image forming apparatus according to the present embodiment. The image forming apparatus of this embodiment is a color laser printer using an electrophotographic process, a tandem type, and an intermediate transfer belt type, and corresponds to an A3-size recording material (hereinafter, referred to as a transfer material).
[0027]
Reference numerals Y, M, C, and Bk denote four electrophotographic image forming units, each of which forms a yellow, magenta, cyan, and black toner image.
[0028]
Reference numeral 6 denotes an intermediate transfer belt, which is an intermediate transfer member, and is suspended between three rollers of a driving roller 6a, a secondary transfer opposing roller 6b, and a turn roller (tension roller) 6c. The four image forming units Y, M, C, and Bk are arranged in a line at a predetermined interval from the left side to the right side in the drawing above the horizontal intermediate transfer belt portion between the tension roller 6c and the driving roller 6a. It is arranged.
[0029]
The intermediate transfer belt 6 is rotationally driven at a predetermined process speed in the clockwise direction of the arrow d2 by the drive roller 6a being rotationally driven by a drive system (not shown).
[0030]
In each of the image forming units Y, M, C, and Bk, photosensitive drums 1a to 1d as image carriers are provided. Around the photosensitive drums, primary charging rollers 2a to 2d, laser scanners 3a to 3d, developing units 4a to 4d, and cleaning devices 5a to 5d are installed, respectively. Each of the developing devices 4a to 4d contains a yellow toner, a magenta toner, a cyan toner, and a black toner, respectively.
[0031]
Primary transfer rollers 7a to 7d are disposed on the lower surfaces of the photosensitive drums 1a to 1d of the image forming units Y, M, C, and Bk via an intermediate transfer belt 6 in pressure contact with the photosensitive drums 1a to 1d, respectively. And the intermediate transfer belt 6 to form primary transfer nips Ta to Td.
[0032]
Reference numeral 11 denotes a secondary transfer roller, which is disposed in such a manner that the intermediate transfer belt 6 is sandwiched and pressed against the secondary transfer opposing roller 6b, and the secondary transfer roller 6b is disposed between the intermediate transfer belt 6 and the secondary transfer opposing roller 11. The next transfer nip Te is formed.
[0033]
Reference numeral 8 denotes a fixing device as a heating device for heating and fixing an image on the transfer material, and is disposed at a position downstream of the secondary transfer nip Te in the transfer material transport direction.
[0034]
When an image forming operation start signal (print start signal) is issued, the photosensitive drums 1a to 1d of the image forming units Y, M, C, and Bk move counterclockwise as indicated by arrow d1, and the intermediate transfer belt 6 moves as indicated by arrow d2. It is rotated clockwise at a predetermined process speed. In the present embodiment, the photosensitive drums 1a to 1d and the intermediate transfer belt 6 are driven to rotate at the same peripheral speed, and 120 [mm / sec] in the normal mode for printing plain paper, and 60 [mm / sec] in the special paper mode such as gloss paper or OHT. It is driven at [mm / sec]. The throughput of the image forming apparatus according to the present embodiment is 22 ppm in the normal mode and 11 ppm in the special paper mode (both in the case of LETTER transverse feeding).
[0035]
In this embodiment, the photosensitive drums 1a to 1d are uniformly charged to a predetermined negative potential by the primary charging rollers 2a to 2d, respectively. The laser scanners 3a to 3d of the image forming units Y, M, C, and Bk output laser beams modulated in accordance with the color-separated digital image signals of the full-color image information, and output the laser beams via the image-forming exposure optical system. The uniformly exposed surfaces of the photosensitive drums 1a to 1d are scanned and exposed. As a result, a color separation image pattern of a full-color image (first color component = yellow, second color component = magenta, third color component = cyan, fourth color component) in each of the photosensitive drums 11a to 11d. An electrostatic latent image corresponding to each image pattern (color component = black) is formed.
[0036]
The image forming apparatus of this embodiment is connected to a plurality of host computers via a network, a control unit (controller) receives image data of a print job transmitted from these hosts, and sequentially transmits image data of the plurality of jobs. This is developed into laser lighting signals of the laser scanners 3a to 3d corresponding to each color.
[0037]
The electrostatic latent image on each of the photosensitive drums 1a to 1d reaches a portion facing the developing units 4a to 4d by rotation of the photosensitive drum, and toner charged to the same polarity (in this example, negative polarity) is supplied to the electrostatic latent images to be observed. Imaged. That is, a yellow toner image, a magenta toner image, a cyan toner image, and a black toner image, which are color separation image patterns of a full-color image, are formed on the respective photosensitive drums 1a to 1d.
[0038]
Then, the yellow toner image, the magenta toner image, the cyan toner image, and the black toner image on each of the photosensitive drums 11a to 11d are sequentially placed on the intermediate transfer belt 17 as an intermediate transfer body at each of the primary transfer nip portions Ta to Td. A full-color toner image is synthesized by superimposition transfer.
[0039]
In each of the primary transfer nip portions Ta to Td formed by the intermediate transfer belt 6 and the photosensitive drums 1a to 1d, power is applied to the primary transfer rollers 7a to 7d that are in contact with the back surface of the intermediate transfer belt 6 from the power sources S1 to S4. The toner image is primarily transferred from each of the photosensitive drums 1a to 1d to the intermediate transfer belt 6 by the positive primary transfer bias having the polarity opposite to that of the toner.
[0040]
At the stage when the intermediate transfer belt 6 has passed the primary transfer nip portion Td with the photosensitive drum 1d of the last image forming portion Bk, a full-color toner image is superimposed and formed on the intermediate transfer belt 17 and is carried thereon. Is completed.
[0041]
On the other hand, the surfaces of the photosensitive drums 1a to 1d after the primary transfer of the toner image to the intermediate transfer belt 6 have been cleaned by the cleaning devices 5a to 5d, respectively, and are ready for the next image forming step.
[0042]
Then, one transfer material P is fed from a paper supply unit (not shown) in synchronization with the timing when the leading end of the full-color toner image on the intermediate transfer belt 6 reaches the secondary transfer nip Te, and is synchronized. Is inserted into the secondary transfer nip Te. At this time, a positive secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 11 from the power supply S5, and the full-color toner image is collectively and secondarily transferred from the intermediate transfer belt 6 to the transfer material P.
[0043]
The transfer material P, on which the unfixed full-color toner image has been placed and has passed through the secondary transfer nip area, reaches the fixing device 8, and the unfixed full-color toner image is nipped (fixed) between the fixing roller 9 and the pressure roller 10. Is fixed by heat and pressure.
[0044]
The surface of the intermediate transfer belt 6 on which the full-color toner image has been secondarily transferred onto the transfer material P at a time is cleaned by removing a transfer residual toner by a belt cleaning device (not shown), and is repeatedly provided for image formation.
[0045]
The monochrome image forming mode is executed when only the image forming unit Bk that forms a black toner image among the four image forming units Y, M, C, and Bk performs an image forming operation.
[0046]
(2) Fixing device 8
FIG. 3 is a schematic cross-sectional view of the fixing device 8 in the present embodiment. The fixing device 8 in the present embodiment is a heat roller type fixing device.
[0047]
Reference numeral 9 denotes a fixing roller (heat roller) as a fixing member, and 10 denotes a pressing roller as a pressing member. The two rollers 9 and 10 are arranged in parallel and pressed against each other to form a fixing nip portion N having a predetermined width. _F Is formed. In this embodiment, the outer diameter of the fixing roller 9 is R = 50φ, and the outer diameter of the pressure roller 10 is 45φ.
[0048]
The fixing roller 9 has a three-layer structure including a core bar 9a, an elastic layer 9b, and a release layer 9c. A hollow metal roller made of aluminum is used for the metal core 9a, and a halogen heater (hereinafter, referred to as a fixing heater) 9d as a heat source is inserted and disposed inside the hollow metal roller. Silicone rubber is used as the elastic layer 9b on the aluminum core 9a, and a PFA tube is coated on the outermost layer as the release layer 9c.
[0049]
On the other hand, the pressure roller 10 also has an elastic layer 10b of silicone rubber on an aluminum core 10a and a PFA release layer 10c on the outermost layer, similarly to the fixing roller 9.
[0050]
In order to obtain a moderately high gloss fixed image, in the fixing device 8 of this embodiment, the pressure roller 10 is ⁵ [N / m ² ]. When the elastic layers 9b and 10b are crushed by the above pressing force, the fixing nip N _F Is formed. In this embodiment, N _F = 10 [mm].
[0051]
The fixing roller 9 is driven by a fixing drive motor (not shown), and the pressing roller 10 _F The fixing roller 9 rotates following the rotation of the fixing roller 9 due to the frictional force.
[0052]
In addition, power is supplied from the power supply circuit unit 101 to the fixing heater 9d in the fixing roller 9, and the fixing roller 9 is heated by the heat generated by the fixing heater 9d. The temperature of the outer peripheral surface of the fixing roller 9 is detected by a temperature control thermistor 13 as temperature detecting means, and the temperature detection information is input to a controller (control circuit unit) 100. The controller 100 controls the entire image forming sequence of the image forming apparatus. The controller 100 sends the halogen heater 9 d in the fixing roller 9 from the power supply circuit 101 based on the outer peripheral surface temperature information of the fixing roller 9 input from the temperature control thermistor 13 so that the fixing roller surface temperature is maintained at a predetermined fixing temperature. Is controlled.
[0053]
Then, while the fixing roller 9 is driven to rotate and the pressure roller 10 is driven to rotate accordingly, and the fixing roller 9 is heated to a predetermined fixing temperature, the unfixed toner image t is formed. The material P is guided by the fixing entrance guide 12 and the fixing nip N _F Is transferred to the fixing nip N _F Is conveyed. During the nipping and conveying process, the transfer material P is heated by the heat of the fixing roller 9 and the fixing nip N _F , The unfixed toner image t is heat and pressure fixed on the surface of the transfer material P.
[0054]
Fixing nip N _F Is discharged from the fixing roller 9 and discharged and conveyed.
[0055]
(3) Overshoot of fixing roller temperature
FIG. 4 shows the surface temperature of the fixing roller and the state of energization to the fixing heater when an A4 size transfer material is printed at a throughput of 20 sheets per minute on a general heat roller type fixing device.
[0056]
Here, when printing on plain paper, the lighting of the fixing heater is controlled so that the surface temperature of the fixing roller is maintained at Tf = 170 ° C.
[0057]
As shown in FIG. 4, when the paper is started to be transferred and the transfer material loses heat and the temperature of the fixing roller drops to the fixing temperature Tf, power is supplied to the fixing heater.
[0058]
When the fixing roller temperature recovers to the fixing temperature Tf, the power supply to the fixing heater is stopped.
[0059]
By repeating this operation, the temperature of the fixing roller is maintained within a certain temperature range around the fixing temperature Tf.
[0060]
Here, attention is paid to the fixing roller temperature after the printing is completed and the rotation of the fixing roller is completed.
[0061]
In FIG. 4, it can be confirmed that the temperature of the fixing roller after printing is rapidly increased (overshoot).
[0062]
This is a phenomenon that occurs because the heat capacity of the fixing device is large and the thermal responsiveness is not good, as described above, and an excessive amount of heat more than actually required is supplied to maintain the fixing roller temperature during printing in a steady state. Because it is.
[0063]
For this reason, if there is no transfer material for removing heat, the temperature of the fixing roller rises (overshoot) due to the excess heat, and the heat roller type fixing device has a heat capacity compared to a film type fixing device due to its configuration. Is disadvantageous in terms of
[0064]
Problems caused by the occurrence of the above-described overshoot will be described below.
[0065]
FIG. 5 shows the fixing roller temperature and the problems that occur in each temperature range.
[0066]
In order to obtain a good image, fixing must be performed in a temperature range of TL to TH.
[0067]
When the temperature of the fixing roller falls below the TL, the fixing force of the toner to the transfer material is reduced and the toner is easily peeled off (defective fixing), or the toner adheres to the fixing roller and stains the next page (cold offset). ).
[0068]
On the other hand, if the temperature of the fixing roller rises to TH or more, the toner adheres to the fixing roller and stains the next page (hot offset) as in the case of low temperature, or the elastic layer of the roller breaks at a higher temperature. And the life is extremely shortened due to accelerated deterioration.
[0069]
As described above, when the above-described overshoot occurs and Tmax in FIG. 4 rises to TH or more, hot offset occurs.
[0070]
To prevent this, there is a method in which when the temperature of the fixing roller is equal to or higher than TH, even if a print job is received, the printing operation is not started until the temperature drops to a temperature lower than TH.
[0071]
However, since the heat capacity of the fixing device is large, it may take several minutes for the temperature to decrease, which is a problem from the viewpoint of usability.
[0072]
(4) Solution to the above problem
Therefore, in the image forming apparatus of the present invention, in order to reduce the overshoot of the fixing roller temperature and prevent image defects and improve usability, in a situation where overshoot is likely to occur such as continuous printing, the fixing operation of the last page is performed. The power supply to the heater is stopped before completion.
[0073]
The operation sequence in the fixing device of the present embodiment will be described below while comparing the operation sequence in a general heat roller fixing device as a comparative example.
[0074]
FIG. 1 compares the fixing roller temperature and the fixing heater lighting control of Example 1 and Comparative Example 1 during continuous printing.
[0075]
FIG. 1 shows a portion where the fixing roller temperature overshoots when printing is completed from the latter half of printing. The fixing device of the comparative example has the same configuration as that of the first embodiment, and the timing of starting printing is completely equivalent.
[0076]
As shown in FIG. 5, Tf indicates the temperature of the temperature of the fixing roller, and TH and TL indicate the upper and lower limit temperatures of a region where good fixing properties can be obtained.
[0077]
When the temperature of the fixing roller is equal to or higher than TH, hot offset occurs, and when the temperature is equal to or lower than TL, fixing defects occur.
[0078]
During printing, the relationship of TL <fixing roller temperature <TH holds, but after printing, the overshoot occurs and the fixing roller temperature reaches the hot offset area.
[0079]
Therefore, the printing operation of the next job is not started unless the temperature of the fixing roller drops to TH.
[0080]
FIG. 6 shows the relationship between the overshoot temperature and the print inhibition time (standby time).
[0081]
The origin of the horizontal axis is the upper limit temperature TH at which good fixability can be ensured, and shows the case where overshoots after printing have reached temperatures Ta and Tb = 2 (Ta−TH), respectively.
[0082]
The standby times required for the fixing roller temperature to cool to TH in order to prevent hot offset are Wa and Wb, respectively.
[0083]
As can be seen from FIG. 6, Wb> 2Wa, indicating that the standby time increases exponentially as the overshoot increases.
[0084]
Therefore, if the overshoot can be reduced even a little, the standby time can be greatly reduced, and usability is improved.
[0085]
Returning to FIG. 1 again, an overshoot of Comparative Example 1 and Example 1 will be compared.
[0086]
In Comparative Example 1, the power supply to the heater 9d was turned off at time t0 before the end of printing, but the overshoot after the end of printing reached Tref in the hot offset area.
[0087]
On the other hand, in this embodiment, the timing for stopping the energization to the fixing heater 9d is t1 earlier than in Comparative Example 1, and the overshoot temperature Tmax reaches the hot offset region, but is kept lower than Tref in Comparative Example 1. .
[0088]
In the image forming apparatus of this embodiment, the fixing temperature Tf is 170 ° C., and the upper and lower limit temperatures of a temperature region in which good fixing properties can be secured are TH = 190 ° C. and TL = 155 ° C.
[0089]
In FIG. 1, the overshoot of Comparative Example 1 was Tref = 210 ° C., and the overshoot temperature of Example 1 was Tmax = 195 ° C.
[0090]
At this time, the time required for the fixing roller temperature to decrease to TH is 4 minutes in Comparative Example 1 and 20 seconds in Example 1.
[0091]
Therefore, the waiting time from the reception of the next job instruction to the start of printing is reduced to 1/12.
[0092]
Here, the timing of stopping the power supply to the fixing heater 9d will be described.
[0093]
1) Turn-off timing of heater in comparative example 1
Since the normal print sequence is followed until the fixing operation is completed, the heater 9d is turned on until the fixing roller temperature reaches the fixing temperature Tf in FIG.
[0094]
2) Heater extinguishing timing in the first embodiment
In the first embodiment, the last page is the fixing nip N _F From the moment of exit from 10 sec. It is determined beforehand whether the fixing heater 9d is forcibly turned off.
[0095]
In the first embodiment, the controller 100 of the image forming apparatus sequentially recognizes the number of jobs received from the host and the number of pages of each job, and can provide the information to the image forming unit of the apparatus.
[0096]
If the controller 100 of the image forming apparatus has not received a job command from the host computer at the above time, the fixing heater 9d is forcibly turned off.
[0097]
However, in order to avoid that the fixing heater 9d does not turn on at the time of printing, this determination is started for 10 seconds from the start of printing. After the passage of time.
[0098]
In the following examples, 10 sec. The state after the lapse has been described.
[0099]
FIG. 8 shows that the final page has a fixing nip N at different timings. _F Shows a state in which an overshoot occurs when the fixing operation is completed after passing through.
[0100]
The fixing end state {circle around (1)} is such that the last page is fixed to the fixing nip N at the moment when the fixing roller temperature ripple during printing drops from the top to the temperature Tf at which the fixing heater 9d is turned on. _F Is shown.
[0101]
The fixing end state {circle around (2)} is such that the final page is fixed to the fixing nip N at the moment when the fixing roller temperature ripple during printing rises from the lowest point to the temperature Tf at which the fixing heater 9d is turned off. _F Shows a state in which it has been completely removed.
[0102]
The overshoot temperature after completion of the fixing is the lowest T = T in the fixing completed state (1). _os (Min) = 195 ° C., the highest T = T in the fixing completed state (2) _os (Max) = 210 ° C.
[0103]
As shown in FIG. 7, the temperature ripple period during printing in the fixing device of the first embodiment is 60 sec. It is.
[0104]
As can be seen from FIG. 8, since the heater 9d is already in the light-off state at the heater forcible light-off timing in the fixing end state {circle around (1)}, there is no influence on the subsequent temperature transition.
[0105]
On the other hand, in the fixing end state (2) in which the overshoot temperature is maximum, the heater is turned off earlier than the timing at which the heater is turned off, so that the temperature rise can be slowed down.
[0106]
As shown in FIG. _os (Max) = T from 210 ° C. _os (Rd) = 195 ° C.
[0107]
Thereby, the maximum waiting time until the next job can be started can be reduced from W (Comparative Example 1) = 4 minutes to W (Example 1) = 20 seconds.
[0108]
Here, a possible problem when the fixing heater 9d is forcibly turned off at the timing of the first embodiment will be described.
[0109]
a. Evil 1
In the first embodiment, forcibly turning off the heater is performed earlier than the timing for turning off the heater in the first comparative example. Therefore, the fixing roller temperature may be lower than that in the first comparative example.
[0110]
If the temperature drop after the forcible extinguishing of the heater is within the fixing property assurance area, a good fixed image substantially equal to that of Comparative Example 1 can be obtained.
[0111]
Here, it will be described at what timing when the forced heater extinguishing is performed, the temperature decrease until the end of fixing becomes the largest.
[0112]
FIG. 10 shows a transition of the fixing roller temperature when the heater is forcibly turned off at two different timings A and B.
[0113]
FIG. 10A shows a timing at which the fixing roller temperature ripple drops from the top to the fixing temperature Tf, and FIG. 10B shows a timing at which the fixing roller temperature ripple drops to the lowest point.
[0114]
The timing A is the timing when the heater has been turned off for the longest time in the print job, and the timing B is the timing when the temperature has dropped the most.
[0115]
The timings A and B are most disadvantageous in terms of the lighting state of the heater 9d and the temperature of the fixing roller with respect to the temperature drop when the heater is forcibly turned off.
[0116]
When the lights are forcibly turned off at the respective timings of A and B, 10 sec. The subsequent fixing roller temperatures are TD-A and TD-B.
[0117]
T = TD-A, TD-B: Fixing Nip N _F Since this temperature is within the fixing property assurance area (TL <fixing roller temperature T <TH), a good fixed image can be secured.
[0118]
b. Evil 2
Next, fixing is completed for 10 sec. It is assumed that the controller determines that the job being executed is the last job, forcibly turns off the heater, and then receives a new job instruction.
[0119]
In the image forming apparatus according to the present exemplary embodiment, when different print jobs are sequentially executed, when a transfer material corresponding to the same print mode is specified in two jobs, the print operation is continuously performed without interrupting the two jobs. And execute the job.
[0120]
Therefore, when a print job is received at the above timing, when the transfer material of the second job starts the fixing operation, the temperature of the fixing roller may be lower than usual.
[0121]
As described in the problem 1, even if the temperature is lowered, a good image can be secured if the minimum temperature is within the fixing property guarantee area.
[0122]
After the heater is forcibly turned off in the first job, the last page of the first job is the fixing nip N _F 10 sec. In between, consider at what timing it is most disadvantageous to receive the next job.
[0123]
Assume the following case (the last page is the fixing nip N _F Is referred to as the end of the fixing operation).
[0124]
・ First print job: Print 25 LETTER size images in normal mode
-Second print job: print 10 LETTER size images in normal mode
-Second print job reception: 8 sec. When the fixing operation ends in the first job. Previous
Here, in the image forming apparatus of the first embodiment, the time required from the reception of a job to the end of image data development by the controller is 2 seconds. It is.
[0125]
The image forming section starts the printing operation immediately after the completion of the image development, and the transfer material is fixed to the fixing nip N. _F Takes 6 sec. And the transfer material is fixed to the fixing nip N after receiving the job command. _F Is 8 sec. It becomes.
[0126]
Therefore, in the above assumption, the image forming apparatus determines that the first job and the second job can be executed consecutively, and upon receiving the second print job, cancels the forced heater extinguishing and returns to the print temperature control.
[0127]
If the reception of the second print job is delayed more than the above assumption, an interval longer than a specified sheet interval is formed between the two print jobs, which is advantageous against a temperature drop.
[0128]
Conversely, if the reception of the second print job is earlier than the above-mentioned assumption, the time for forcibly turning off the heater 9d becomes shorter, which is also advantageous for the temperature drop.
[0129]
For these reasons, the fixing operation is completed in the first job for 8 sec. Receiving the second job before is most disadvantageous for temperature drop.
[0130]
Also, considering the fixing roller temperature state at this time, the most disadvantageous for the temperature drop is the most disadvantageous for the temperature drop when the second job is received two seconds after point B in FIG. .
[0131]
FIG. 11 illustrates the case of the worst condition considering the above.
[0132]
The broken line P indicates the end of fixing of the first job for 10 sec. It shows the fixing roller temperature when a new job is not received after the heater 9d is forcibly turned off before.
[0133]
Solid line Q indicates the end of fixing of the first job 10 sec. After forcibly turning off the heater 9d before, 2 sec. This is the temperature of the fixing roller when the second job is received after that.
[0134]
In the fixing roller temperature transition Q, the temperature continues to decrease after the heater is forcibly turned off. However, when the second job is received, the temperature returns to the print temperature control, and the fixing roller temperature starts increasing again.
[0135]
However, since the heater lighting starts at a temperature lower than the lowest point of the temperature ripple of the first job, the fixing roller temperature in the second job drops to TD-min = 157 ° C. in the drawing.
[0136]
Here, comparing TD-min and the lower limit temperature TL = 155 ° C. of the fixing property assurance area, TD-min> TL, so that good fixing property can be ensured even if the temperature decreases.
[0137]
As described above, even if a job is received under the worst condition with respect to the temperature drop, since the maximum temperature drop during printing is within the fixability assurance area, the timing of the next print job , It is possible to guarantee good fixability.
[0138]
In the above description, the LETTER size plain paper is described, and the timing for forcibly turning off the heater 9d is optimally set according to the type of each transfer material and the print mode.
[0139]
Further, the timing for forcibly turning off the heater may not be fixed, but may be varied with reference to the fixing roller temperature or the environmental temperature.
[0140]
Here, the heater is forcibly turned off, but the same effect can be obtained by setting the temperature control temperature to an appropriate low temperature, for example, about 100 ° C.
[0141]
As described above, in the first embodiment, it is possible to improve the usability by reducing the overshoot of the fixing roller temperature, securing a good fixed image without generating hot offset, and shortening the standby time. .
[0142]
[Example 2]
In the second embodiment as well, the heater is forcibly turned off before the end of the fixing operation. However, in the first embodiment, the heater is turned off only before the time counted from the end of the fixing operation, whereas in the second embodiment, the image forming operation for each page is performed. , The heater 9d is forcibly turned off.
[0143]
In the first embodiment, since the scheduled time of the end of the fixing operation is used as a reference for the timing of forcibly turning off the heater, the image forming apparatus must recognize the number of prints.
[0144]
In the present embodiment, unlike the first embodiment, means for reducing overshoot in an image forming apparatus in which the number of prints cannot be recognized will be described.
[0145]
The configuration of the image forming apparatus of this embodiment is the same as that of the first embodiment, and the conditions such as the temperature setting of the fixing device are the same as those of the first embodiment unless otherwise specified.
[0146]
The transfer material conveyance speed of the image forming apparatus is the same as that of the first embodiment, and is 120 [mm / sec] for plain paper.
[0147]
As described in the first embodiment, the image forming apparatus of the present embodiment has a configuration in which individual photosensitive drums are provided for each color and these are arranged in parallel.
[0148]
Yellow (Y), magenta (M), cyan (C), and black (Bk) are arranged in this order from the upstream in the rotation direction of the intermediate transfer belt, and the respective color images are sequentially overlapped and transferred to the intermediate transfer belt. After that, the color image is transferred to the transfer material at once.
[0149]
In the second embodiment, the image forming operation of the Y station is used as a reference for the timing for forcibly turning off the heater 9d of the fixing device 8.
[0150]
Here, FIG. 12 schematically shows the configuration of the image forming apparatus of the present embodiment described above.
[0151]
A path length from the photosensitive drum and the intermediate transfer belt contact portion X to the fixing nip exit Y at the Y station is indicated by L [mm].
[0152]
The transfer material of the intermediate transfer belt 6 is 120 mm / sec. The toner image transferred to the intermediate transfer belt at the Y station is transferred to the transfer material, and the fixing nip N _F Is required to reach TR = L / 120 [sec. ].
[0153]
In this embodiment, since L = 750 mm, TR = 6.3 sec. It becomes.
[0154]
Further, since the throughput is 22 ppm in the LETTER size lateral feed as in the first embodiment, the time corresponding to the interval between the sheets is about 0.9 sec. It becomes.
[0155]
Since the engine of the image forming apparatus cannot know the number of prints of the print job, it determines whether or not to end the print operation for each print operation.
[0156]
FIG. 13 shows the operations of the Y station, the intermediate transfer belt, and the fixing device at the time of judging the end of the printing operation in parallel in chronological order.
[0157]
In FIG. 13, page P1 is the last page of the print job, and P2 is a virtual page shown for easy understanding of timing.
[0158]
In the second embodiment, whether or not image development has been started is checked twice for each page.
[0159]
The first check timing is indicated by CP1 in FIG.
[0160]
CP1 is 0.2 sec. From the time T1 when the primary transfer at the Y station is completed (the primary transfer position is determined to be the time when the rear end position of the transfer material on the page P1 passes). Later.
[0161]
If image data starts to be developed by this point, continuous printing can be continued while maintaining the specified throughput.
[0162]
Even if image data development has not been performed at the time of CP1, it is not determined that printing has been completed at this time, and when the transfer material has the LETTER size, 0.8 sec. The printing operation is continued until CP2.
[0163]
1.0 sec. After the primary transfer of P1 is completed at the Y station. If the image data is not developed in CP2, the end of the print is determined.
[0164]
In this case, the throughput is reduced because the specified sheet interval cannot be maintained, but the productivity can be higher than when the stop and start operations are performed by performing the image data development at timings CP1 and CP2.
[0165]
It is conceivable that the time from CP1 to CP2 is set longer than in this example in order to further increase the productivity. However, if the print standby state is prolonged, the rotation time of each unit increases and the life of the apparatus is shortened.
[0166]
Therefore, it is appropriate to set the timing of CP2 to the level of this embodiment.
[0167]
In the second embodiment, if it is determined at this point that the printing is to be ended, the fixing heater 9d is forcibly turned off at the same time as the end of the image forming unit.
[0168]
Last page is fixing nip N _F Calculated from the time of passing through TR-1.0 = 5.3 sec. Before that, the heater is forcibly turned off.
[0169]
This makes it possible to reduce the Tmax in FIG. 8 from 210 ° C. to 203 ° C., and reduce the waiting time from 4 minutes to 1 minute.
[0170]
The time from the forcible turning off of the heater 9d to the completion of the fixing operation of the last page is 10 sec. 5.3 sec. Therefore, the temperature decrease after the heater is turned off is less than that in the first embodiment, and a good fixed image is guaranteed.
[0171]
In the above description, plain paper of LETTER size is described, and the timing of CP2 is optimally set according to the type of each transfer material and the print mode.
[0172]
Further, the same effect can be obtained by setting the temperature control temperature to an appropriate low temperature, for example, about 100 ° C., instead of forcibly turning off the heater.
[0173]
As described above, in the second embodiment, in the image forming apparatus that does not recognize the number of prints included in the print job and determines the end of printing for each sheet, the overshoot of the fixing roller temperature is reduced to prevent image defects. Meanwhile, the usability was improved by reducing the standby time.
[0174]
[Example 3]
The configuration of the image forming apparatus of the present embodiment is the same as that of the first embodiment.
[0175]
The transfer material conveyance speed of the image forming apparatus is also the same as that of the first embodiment, and is 120 [mm / sec] for plain paper and 60 [mm / sec] of 1/2 speed for special paper such as OHT or gloss film.
[0176]
In the third embodiment, in consideration of the heat storage when the fixing operation is continuously performed, the timing of forcibly turning off the heater is made variable according to the number of prints.
[0177]
In the third embodiment, as in the first embodiment, the controller of the image forming apparatus sequentially recognizes the number of jobs received from the host and the number of pages of each job, and can provide such information to the image forming unit of the apparatus. it can.
[0178]
FIG. 14 shows how the overshoot of the fixing roller temperature changes according to the number of prints when the transfer material of the LETTER size is continuously printed.
[0179]
The origin of the vertical axis is the fixing temperature Tf, and the upper limit temperature TH at which good fixing properties can be guaranteed is also shown.
[0180]
As can be seen from the figure, the change in the overshoot temperature according to the number of prints is relatively large up to about 20 when the number of prints is relatively small, and thereafter the overshoot temperature does not change much even when the number of prints increases, and is almost saturated. (Saturation temperature T _SAT ).
[0181]
This is because, as the number of prints increases, the total lighting time of the heater 9d increases and heat is stored in the fixing device, and the heat storage amount is saturated, and the heat input and the heat release amount of the heater 9d reach a steady state and exceed. This is because the shoot temperature is saturated.
[0182]
Here, if the number of prints is up to seven, the overshoot temperature is equal to or lower than TH, and it can be seen that hot offset does not occur even if printing is newly started here.
[0183]
Therefore, in this case, it is not necessary to forcibly turn off the heater 9d before the fixing is completed as in the first embodiment. However, when the number of prints increases, the method of the first embodiment needs to be used.
[0184]
In consideration of the above, in the present embodiment, execution / non-execution of the forced heater extinguishing performed in the first embodiment is switched according to the number of prints.
[0185]
From FIG. 14, the heater 9d is not forcibly turned off until the number of prints is seven, and the print temperature is adjusted until the fixing of the last page is completed.
[0186]
When the number of prints is eight or more, the heater 9d is forcibly turned off in the same manner as in the first embodiment.
[0187]
By forcibly turning off the heater in accordance with the number of sheets in this manner, it is possible to avoid a large decrease in the temperature of the fixing roller when printing a small number of sheets having a small heat storage amount, and to provide more stable image quality than in the first embodiment.
[0188]
Further, in the area where the heater is forcibly turned off, the same effect as that of the first embodiment can be obtained.
[0189]
In the third embodiment, for the sake of simplicity, only the execution / non-execution of the forced heater extinguishment is switched. However, the timing of the forced extinguishing is made variable stepwise according to the overshoot temperature at each number of prints. It is also possible.
[0190]
In the above description, the LETTER size plain paper is described, and the number of sheets for switching the execution / non-execution of the forced heater extinguishing is set optimally according to the type of each transfer material and the print mode. It is.
[0191]
Further, the number of sheets for switching the execution / non-execution of the forced heater extinguishing may not be fixed, but may be varied with reference to the fixing roller temperature or the environmental temperature.
[0192]
Here, the heater is forcibly turned off, but the same effect can be obtained by setting the temperature control temperature to an appropriate low temperature, for example, about 100 ° C.
[0193]
As described above, in the third embodiment, as in the first embodiment, it is possible to reduce the overshoot of the fixing roller temperature, secure a good fixed image, shorten the standby time, and improve the usability. It has become possible to obtain a more stable image than 1.
[0194]
【The invention's effect】
As described above, in the present invention, the overheating of the fixing roller temperature is reduced by stopping the heating by the heater or lowering the temperature adjustment temperature before the completion of the fixing, thereby realizing the improvement of the usability by preventing the image defect and shortening the print waiting time. did it.
[Brief description of the drawings]
FIG. 1 is a diagram showing how overshoot is reduced in a first embodiment.
FIG. 2 is a cross-sectional model diagram of the color laser printer according to the first embodiment.
FIG. 3 is a schematic cross-sectional view of a fixing device.
FIG. 4 is a diagram showing a state of occurrence of overshoot.
FIG. 5 is a diagram showing a problem that occurs in each temperature region.
FIG. 6 is a diagram showing a relationship between an overshoot temperature and a standby time.
FIG. 7 is a diagram illustrating a ripple cycle of a fixing temperature during printing.
FIG. 8 is a diagram showing a change in overshoot temperature depending on a fixing end timing.
FIG. 9 is a diagram showing a state in which overshoot is reduced by forcibly turning off a heater.
FIG. 10 is a diagram showing a temperature drop with respect to different heater forced OFF timings.
FIG. 11 is a diagram showing a temperature transition when a print job is received after the heater is forcibly turned off.
FIG. 12 shows a fixing nip N from a primary transfer position of a first color. _F Diagram showing the route to
FIG. 13 is a diagram showing the timing of forcibly turning off the heater in the second embodiment.
FIG. 14 is a diagram showing the relationship between the number of prints and the overshoot temperature.
[Explanation of symbols]
Photosensitive drum 1a, 1b, 1c, 1d
Charging roller 2a, 2b, 2c, 2d
Laser scanner 3a, 3b, 3c, 3d
Developing device 4a, 4b, 4c, 4d
Cleaning device 5a, 5b, 5c, 5d
Intermediate transfer belt ・ ・ ・ 6
Secondary transfer roller 11
Primary transfer bias voltage source S1, S2, S3, S4
Secondary transfer bias voltage source S5
Fixing entrance guide ・ ・ ・ 12

Claims (7)

A fixing roller and a pressure member rotatably disposed, and a heat source for heating the fixing roller, the fixing roller and the pressure member are pressed against each other to form a fixing nip, and the heat source is heated. An image forming apparatus having an image heating device that heats and fixes a toner image to a recording material by passing a recording material carrying a toner image through the fixing nip while controlling the temperature of the fixing roller to a predetermined fixing temperature,
At a predetermined timing before the recording material of the last page of the print job passes through the fixing nip, the heating operation of the heat source in the image heating device is stopped, or the temperature control is started so that the fixing roller temperature becomes lower than the predetermined fixing temperature. An image forming apparatus having a fixing mode. An image forming mechanism for forming and carrying a toner image on a recording material, and a fixing roller having a plurality of image carriers arranged in parallel with the first color, the second color,... An image forming apparatus having an image heating device for forming a fixing nip by pressing a pressure member against each other, forming a fixing nip, passing a recording material carrying a toner image through the fixing nip, and thermally fixing the toner image on the recording material. ,
When the image formation of the next page of the first color is not started even after a predetermined time has elapsed after the completion of the image formation on the image carrier of the first color, the heating operation of the heat source in the image heating device is stopped or fixed. An image forming apparatus having a fixing mode for starting temperature control so that a roller temperature becomes lower than the predetermined fixing temperature. The image forming apparatus according to claim 1, wherein the predetermined timing or the predetermined time is different depending on at least one condition of a size or a type of a recording material during image formation. 4. The image forming apparatus according to claim 1, wherein the predetermined timing or the predetermined time differs depending on a temperature of the fixing roller at a time when the predetermined timing or the predetermined time has elapsed. 5. . The image forming apparatus according to claim 1, wherein the predetermined timing or the predetermined time differs depending on an environmental temperature in which the image forming apparatus is installed. The image forming apparatus according to claim 1, wherein the predetermined timing or the predetermined time differs depending on the number of prints. The predetermined timing or predetermined time,
▲ 1 ▼. At least one condition of the size or type of the recording material during image formation (2). Fixing roller temperature at the time when a predetermined timing or a predetermined time has elapsed {3}. Environmental temperature at which the image forming apparatus is installed {4}. The image forming apparatus according to claim 1, wherein the image forming apparatus is different depending on a combination of a plurality of conditions described in at least two or more of the number of prints.

Images