Image forming apparatus

Abstract

To obtain an image forming apparatus that maintains an appropriate fixing temperature even when the inter-sheet time is reduced in continuous printing.SOLUTION: A controller 41 derives a correction value of a heater control temperature on the basis of the increment of the inter-sheet time of print sheets and a heater lighting time in continuous printing, and (b) corrects a predetermined reference value with the correction value within a range not exceeding an upper limit value of the correction value to derive a heater control temperature. In that case, the controller 41 sets the above-mentioned upper limit value on the basis of the increment of the inter-sheet time and the heater lighting time. When the inter-sheet time of print sheets is reduced, the controller reduces the value of the heater lighting time.SELECTED DRAWING: Figure 2

Description

Technical Field

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

Background Art

[0002] When a certain image forming apparatus controls the heater of a fixing device, while making the sum of the passing time of a recording medium (print sheet) and the inter-sheet time an integral multiple of the control cycle of the heater, it changes the heater lighting duty at the entry timing of the recording medium into the fixing device (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Normally, in order to maintain a constant fixing temperature (such as the fixing belt temperature), the heater control temperature is decreased with time. At that time, the heater control temperature is derived by subtracting a correction value from a reference value of the heater control temperature, and the correction value is changed with time.

[0005] Also, since the fixing device does not nip the print sheet between sheets, the fixing belt temperature tends to rise. The inter-sheet time may change due to changes in the print sheet size or the paper feed cassette in continuous printing. At that time, when the inter-sheet time decreases, the fixing temperature may decrease.

[0006] The present invention has been made in view of the above problems, and an object thereof is to obtain an image forming apparatus that maintains an appropriate fixing temperature even when the inter-sheet time decreases in continuous printing.

Means for Solving the Problems

[0007] The image forming apparatus according to the present invention includes a fixing device that fixes a toner image on a print sheet by a heating and pressing method using a fixing heater, and a controller that controls energization to the fixing heater so as to achieve a heater control temperature. Then, the controller: (a) derives a correction value of the heater control temperature based on an increase amount of the inter-sheet time of the print sheet in continuous printing; (b) derives the heater control temperature by correcting a predetermined reference value with the correction value within a range not exceeding an upper limit value of the correction value; (c) sets the upper limit value based on the increase amount of the inter-sheet time and the heater lighting time; and (d) when the inter-sheet time of the print sheet decreases, decreases the value of the heater lighting time. Here, the heater lighting time is a value indicating the cumulative time of the energization time of the fixing heater from the start of the continuous printing.

Advantages of the Invention

[0008] According to the present invention, an image forming apparatus can be obtained that maintains an appropriate fixing temperature even when the inter-sheet time decreases in continuous printing.

[0009] The above or other objects, features, and advantages of the present invention will become more apparent from the following detailed description together with the accompanying drawings.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0012] Embodiment 1.

[0013] FIG. 1 is a side view showing a part of the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is an apparatus having an electrophotographic printing function such as a printer, a facsimile apparatus, a copier, a multifunction machine, or the like.

[0014] The image forming apparatus of this embodiment has a tandem type color developing device. This color developing device has photosensitive drums 1a to 1d, exposure devices 2a to 2d, and developing units 3a to 3d. The photosensitive drums 1a to 1d are photosensitive bodies of four colors: cyan, magenta, yellow, and black.

[0015] The exposure devices 2a to 2d are devices that form an electrostatic latent image by irradiating laser light while scanning the photosensitive drums 1a to 1d. The laser light is scanned in a direction (main scanning direction) perpendicular to the rotation direction (sub-scanning direction) of the photosensitive drums 1a to 1d. The exposure devices 2a to 2d have a laser scanning unit including a laser diode that is a light source of the laser light and optical elements (such as lenses, mirrors, polygon mirrors) that guide the laser light to the photosensitive drums 1a to 1d.

[0016] Furthermore, around the photosensitive drums 1a to 1d, a charger such as a scorotron, a cleaning device, a discharger, and the like are arranged. The cleaning device removes residual toner on the photosensitive drums 1a to 1d after primary transfer, and the discharger discharges the photosensitive drums 1a to 1d after primary transfer.

[0017] The developing units 3a to 3d each have a toner cartridge filled with toner of four colors: cyan, magenta, yellow, and black, and a developing device that attaches the toner conveyed from the toner hopper in the toner cartridge to the photoreceptor drums 1a to 1d, and attaches the toner to the electrostatic latent image on the photoreceptor drums 1a to 1d to form a toner image.

[0018] Magenta development is performed by the photoreceptor drum 1a, the exposure device 2a, and the developing unit 3a. Cyan development is performed by the photoreceptor drum 1b, the exposure device 2b, and the developing unit 3b. Yellow development is performed by the photoreceptor drum 1c, the exposure device 2c, and the developing unit 3c. Black development is performed by the photoreceptor drum 1d, the exposure device 2d, and the developing unit 3d.

[0019] The intermediate transfer belt 4 is an annular image carrier (intermediate transfer body) that contacts the photoreceptor drums 1a to 1d and is primarily transferred with the toner images on the photoreceptor drums 1a to 1d. The intermediate transfer belt 4 is stretched over the driving roller 5 and circulates in the direction from the contact position with the photoreceptor drum 1d to the contact position with the photoreceptor drum 1a by the driving force from the driving roller 5.

[0020] The transfer roller 6 contacts the print sheet conveyed as described later with the intermediate transfer belt 4 and secondarily transfers the toner image on the intermediate transfer belt 4 to the print sheet. The print sheet onto which the toner image has been transferred is conveyed to the fixing device 9, and the toner image is fixed to the print sheet.

[0021] The fixing device 9 incorporates a fixing heater 9a (see Fig. 2), and the fixing heater 9a fixes the toner image on the printed sheet by a heat and pressure method. Specifically, the fixing device 9 fixes the toner image on the printed sheet onto which the toner image corresponding to the printed image has been transferred by a heat and pressure method. The fixing heater 9a is a heater of a resistance heating element, such as a ceramic heater or a planar heater. For example, the fixing heater 9a is disposed inside an internal structure that supports a fixing belt, a fixing film, etc., or inside a fixing roller. That is, the fixing heater 9a heats a specific part (fixing belt, fixing film, fixing roller, etc.) by resistance heating.

[0022] The roller 7 has a cleaning brush, and the cleaning brush is brought into contact with the intermediate transfer belt 4 to remove the toner remaining on the intermediate transfer belt 4 after the transfer of the toner image to the printed sheet or after calibration.

[0023] The sensor 8 irradiates the intermediate transfer belt 4 with a light beam and detects the reflected light from the surface of the intermediate transfer belt 4 or the toner pattern on its surface. For example, when calibrating the toner gradation or toner density, the sensor 8 irradiates a predetermined area of the intermediate transfer belt 4 (the area where the toner patch for calibration is transferred) with a light beam, detects the reflected light of the light beam, and outputs an electrical signal corresponding to the amount of light.

[0024] Furthermore, the image forming apparatus according to this embodiment includes a plurality of paper feed cassettes 11, 12. The paper feed cassettes 11, 12 accommodate the printed sheets 31, 32, and the lift plates 21, 24 push up the printed sheets 31, 32 upward to abut against the pickup rollers 22, 25. The printed sheets 31, 32 placed on the paper feed cassettes 11, 12 are picked up one by one from above by the pickup rollers 22, 25 and fed to the paper feed rollers 23, 26. The paper feed rollers 23, 26 are rollers that convey the printed sheets 31, 32 fed from the paper feed cassettes 11, 12 by the pickup rollers 22, 25 one by one onto the conveyance path.

[0025] The conveying roller 27 is a conveying roller on the common conveying path for the printed sheets 31 and 32 conveyed from the paper feed cassettes 11 and 12.

[0026] The registration roller 28 temporarily stops the conveyed printed sheet and conveys the printed sheet to the transfer position by the intermediate transfer belt 4 and the transfer roller 6 at the secondary paper feed timing. The secondary paper feed timing is specified by the controller 41 described later so that the toner image on the intermediate transfer belt 4 is transferred to the specified position on the printed sheet. The registration sensor 29 is installed near the registration roller 28 and is a sensor that optically detects that the printed sheet has reached the registration roller 28 (that is, the secondary paper feed position).

[0027] FIG. 2 is a block diagram showing a part of the electrical configuration of the image forming apparatus according to the embodiment of the present invention. As shown in FIG. 2, this image forming apparatus includes a controller 41, a printing apparatus 42, an operation panel 43, and a communication apparatus 44.

[0028] The controller 41 includes a computer, an ASIC (Application Specific Integrated Circuit), etc., realizes various processing units by software and / or hardware, monitors and controls internal devices such as the printing apparatus 42, and performs various data processes.

[0029] The controller 41 receives a print request from a host device (not shown) using, for example, the communication device 44, and in accordance with the received print request, executes image processing (such as color conversion, color correction, halftoning, etc.) on the page images specified for each page by the print request, and controls the printing device 42 to execute a print job. Specifically, the controller 41 controls a drive source (not shown) that drives a conveyance roller or the like, a bias application circuit that applies a developing bias and a primary transfer bias, exposure devices 2a to 2d, and the fixing temperature of the fixing device 9 (for example, the temperature of the fixing heater 9a) to execute the formation of an electrostatic latent image, the development, transfer, and fixing of a toner image, and the paper feeding and discharging.

[0030] Also, the printing device 42 is an internal device that prints a document image with a mechanical configuration as shown in FIG. 1.

[0031] The operation panel 43 includes an input device 43a such as a touch panel and hard keys that receive user operations, and a display device 43b such as a liquid crystal display that displays an operation screen for the user. The communication device 44 is a wired or wireless network interface, a modem, a peripheral device interface, etc., and performs data communication with a host device (not shown) or the like.

[0032] Furthermore, the controller 41 performs energization control of the fixing heater 9a so that the heater control temperature is achieved. Specifically, the controller 41 derives a correction value tc of the heater control temperature based on (a) an increase amount DT (an increase amount from a reference value obtained from the line speed, sheet size, etc.) of the inter-sheet time of the print sheets in continuous printing, and (b) derives the heater control temperature by correcting a predetermined reference value with the correction value tc within a range not exceeding the upper limit value tcl of the correction value tc. At that time, the controller 41 sets the upper limit value tcl based on (c) the increase amount DT of the inter-sheet time and the heater lighting time TF. Note that in continuous printing, the inter-sheet time changes due to changes in the print sheet size or the paper feed cassette.

[0033] Further, when the inter-sheet time of the print sheet decreases, the controller 41 decreases the value of the heater lighting time TF. Here, the heater lighting time TF is a value indicating the cumulative time of the energization time of the fixing heater from the start of continuous printing, and is used for specifying the above-mentioned upper limit value.

[0034] In Embodiment 1, when the inter-sheet time of the print sheet decreases, the controller 41 resets the value of the heater lighting time TF to zero.

[0035] FIG. 3 is a diagram for explaining the correction value of the heater control temperature. As shown in FIG. 3, for example, the controller 41 derives a correction value tc based on the increase amount DT of the inter-sheet time according to a calculation formula, a table, etc., and subtracts the correction value tc from the reference value to derive the heater control temperature. Note that FIG. 3 shows the case where the line speed is 40 PPM and the values when the print sheet is A4.

[0036] FIG. 4 is a diagram for explaining the upper limit value of the correction value of the heater control temperature. As shown in FIG. 4, for example, the controller 41 sets an upper limit value tcl based on the increase amount DT of the inter-sheet time and the heater lighting time TF according to a calculation formula, a table, etc. As shown in FIG. 4, the larger the increase amount DT of the inter-sheet time, the higher the above-mentioned upper limit value tcl is set, and the larger the value of the heater lighting time TF, the higher the above-mentioned upper limit value tcl is set.

[0037] Next, the operation of the above image forming apparatus will be described. FIG. 5 is a flowchart for explaining the control of the fixing device in the image forming apparatus shown in FIGS. 1 and 2.

[0038] When a continuous printing job is started, the controller 41 performs energization control of the fixing heater 9a, and monitors whether or not an inter-sheet is detected (step S1) and whether or not the job has ended (step S2).

[0039] When an inter-sheet gap is detected, the controller 41 sets the current inter-sheet time Time1 to the inter-sheet time Time2 indicating the previous inter-sheet time (step S3), identifies the current inter-sheet time, and updates the inter-sheet time Time1 (step S4).

[0040] Next, the controller 41 determines whether the inter-sheet time has decreased (i.e., whether Time1 < Time2) (step S5).

[0041] When the inter-sheet time has decreased (i.e., when Time1 < Time2), the controller 41 resets the value of the heater lighting time (step S6), and does not reset the value of the heater lighting time otherwise.

[0042] Then, as shown in FIG. 3 for example, the controller 41 derives a correction value tc according to the increase amount DT (= Time1 - reference value) of the inter-sheet time Time1, and as shown in FIG. 4 for example, derives an upper limit value tcl based on the increase amount DT of the inter-sheet time and the current heater lighting time. When the correction value tc exceeds the upper limit value tcl, the correction value tc is changed to the upper limit value tcl (step S7).

[0043] Thereafter, the controller 41 updates the control temperature of the fixing heater 9a at a predetermined timing (step S8). For example, this predetermined timing is (a) when the nip of the fixing device 9 with respect to the trailing edge of the first printed sheet is released after the heater lighting time exceeds a predetermined value, (b) when the next printed sheet is conveyed to a position that is a predetermined time (here, 100 milliseconds) before the nip start time of the fixing device 9 after the heater lighting time exceeds a predetermined value (note that this time point is detected by a sheet sensor installed in the conveyance path), (c) at job reception, (d) when the discharge after printing of the previous printed sheet is completed, etc.

[0044] Thereafter, it returns to step S1, and the controller 41 continues the above monitoring until the job ends.

[0045] As described above, according to the first embodiment, the controller 41 derives a correction value tc of the heater control temperature based on an increase amount DT of the inter-sheet time of the print sheet in continuous printing, and (b) corrects a predetermined reference value with the correction value tc within a range not exceeding an upper limit value tcl of the correction value tc to derive the heater control temperature. At this time, the controller 41 sets the above upper limit value tcl based on the increase amount DT of the inter-sheet time and the heater lighting time TF. Further, when the inter-sheet time of the print sheet decreases, the controller 41 decreases the value of the heater lighting time TF.

[0046] Thereby, since the upper limit value for the correction value of the heater control temperature is set, an appropriate fixing temperature is maintained even when the inter-sheet time decreases in continuous printing.

[0047] Second Embodiment.

[0048] In the second embodiment, when the inter-sheet time of the print sheet decreases, the controller 41 resets the value of the heater lighting time TF to a value corresponding to the decrease amount of the inter-sheet time.

[0049] For example, when the decrease amount (Time2 - Time1) of the inter-sheet time is 2 seconds or more, the value of the heater lighting time TF is reset to zero. When the decrease amount of the inter-sheet time is 1 second or more and less than 2 seconds, the value of the heater lighting time TF is reset to 1 / 3 of the current value of the heater lighting time TF. When the decrease amount of the inter-sheet time is 0 second or more and less than 1 second, the value of the heater lighting time TF is reset to 2 / 3 of the current value of the heater lighting time.

[0050] Note that since other configurations and operations of the image forming apparatus according to the second embodiment are the same as those of the first embodiment, the description thereof is omitted.

[0051] It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing the intended advantages. That is, it is intended that such changes and modifications be included within the scope of the claims.

[0052] For example, although the image forming apparatus according to the above embodiment is an image forming apparatus using an indirect transfer method, it may also be an image forming apparatus using a direct transfer method.

Industrial Applicability

[0053] The present invention is applicable to, for example, an electrophotographic image forming apparatus.

Explanation of Reference Numerals

[0054] 9 Fixer 9a Fixing heater 41 Controller

Claims

1. A fixing device that fixes a toner image on a print sheet by a heating and pressing method using a fixing heater, and a controller that controls energization to the fixing heater so as to achieve a heater control temperature, wherein the controller: (a) derives a correction value for the heater control temperature based on an increase in the inter-sheet time of the print sheet and the heater lighting time in continuous printing; (b) derives the heater control temperature by correcting a predetermined reference value with the correction value within a range not exceeding the upper limit value of the correction value; (c) sets the upper limit value based on the increase in the inter-sheet time and the heater lighting time; and (d) when the inter-sheet time of the print sheet decreases, decreases the value of the heater lighting time, wherein the heater lighting time is a value indicating the cumulative time of the energization time of the fixing heater from the start of the continuous printing, and an image forming apparatus characterized by the above.

2. wherein the upper limit value is set higher as the increase in the inter-sheet time becomes longer, and the upper limit value is set higher as the value of the heater lighting time becomes larger, and an image forming apparatus according to Claim 1, characterized by the above.

3. and an image forming apparatus according to Claim 1, wherein the controller resets the value of the heater lighting time to zero when the inter-sheet time of the print sheet decreases.

4. and an image forming apparatus according to Claim 1, wherein the controller resets the value of the heater lighting time to a value corresponding to the decrease amount of the inter-sheet time when the inter-sheet time of the print sheet decreases.

Images