JP4044377B2 - Exposure method and apparatus in image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exposure method and apparatus for forming a latent image on a photosensitive member in an image forming apparatus used for a copying machine, a printer, a facsimile, a composite machine thereof, and the like, and in particular, a light emitting diode (hereinafter abbreviated as LED). The present invention relates to an exposure method and apparatus in an image forming apparatus in which an exposure apparatus using LED heads arranged in the axial direction is configured to prevent a decrease in the amount of light caused by an increase in LED temperature.
[0002]
[Prior art]
Recently, image forming apparatuses used for copiers, printers, facsimiles, and multifunctional machines thereof have been required to be downsized and reduced in price due to the demand for personalization, and used conventional laser diodes and polygon mirrors. Instead of an exposure apparatus, a head in which LEDs are arranged in an array has been used. In other words, an exposure apparatus using an LED head is smaller than an exposure apparatus using a laser diode and a polygon mirror, and does not require expensive precision moving parts such as a polygon mirror and a polygon motor, and a complicated control circuit. This is because it can be configured easily and inexpensively.
[0003]
However, the exposure apparatus using this LED head has a problem that the temperature inside the image forming apparatus rises due to continuous printing or the like, and when the LED temperature rises, the light quantity decreases, resulting in density reduction and density unevenness. . Therefore, conventionally, anticipating a decrease in the amount of light with respect to an increase in the temperature of the LED head, the light output and development characteristics are set higher from the beginning to cope with the decrease in the amount of light. In addition, when the number of continuous prints increases, the development bias is automatically controlled to prevent density reduction.
[0004]
Further, Japanese Patent Laid-Open No. 3-229283 discloses a detector for detecting the amount of light emitted from a laser semiconductor constituting an exposure apparatus in order to correct the phenomenon that the image density becomes lighter or darker due to the change of developer over time. An image forming apparatus is shown in which the output is connected to an operational amplifier, and the reference voltage of the operational amplifier is changed according to the number of copies to change the amount of emitted light. Japanese Patent Laid-Open No. 2001-80115 discloses that the toner charge amount distribution is relatively broad after installation of the image forming apparatus and after toner replenishment. In order to prevent the occurrence of uneven stripes on the surface, the laser power of the exposure apparatus is increased in the initial stage of use, the latent image bright potential VL is brought close to the limit of the residual potential of the drum, and the ripple is reduced to reduce the fog. An image forming apparatus for preventing the above is shown.
[0005]
[Problems to be solved by the invention]
However, the conventional method of setting the light output and development characteristics higher has the disadvantage that the initial image density is naturally high, the half image and the resolution pattern are easily crushed, and the image is not clear. Setting to a higher value makes it easier to cover with less merge with fog. There is also a method of storing changes in the light output of the LED due to temperature changes and measuring the temperature around the LED head with a sensor so that an optimum light output can be obtained, but in order to measure the ambient temperature of the LED head This apparatus must be provided in the image forming apparatus, the main body becomes large in order to secure the space, and a peripheral driver device or the like is required, which is expensive. In addition, the method of adjusting the developing bias according to the number of continuous prints is complicated and the cost is inevitably increased.
[0006]
An apparatus disclosed in Japanese Patent Application Laid-Open No. 3-229283 is for correcting a phenomenon in which an image density becomes thin or dark due to a change with time of a developer. It is not intended to prevent a decrease in the amount of light, but requires a detector and an operational amplifier for the amount of light emitted from the laser semiconductor, and must naturally be expensive. Furthermore, the apparatus disclosed in Japanese Patent Application Laid-Open No. 2001-80115 is also for preventing unevenness caused by the toner charge amount distribution in the initial stage of use after installation of the image forming apparatus and after toner replenishment. It is not intended to prevent a decrease in the amount of light due to an increase in LED temperature due to continuous printing.
[0007]
In view of the above circumstances, the present invention provides an image forming apparatus using an LED head as an exposure apparatus, and a stable light output can be obtained from the LED head with a simple and inexpensive configuration even when the temperature inside the apparatus increases due to continuous printing or the like. It is an object to provide an exposure method and apparatus in the image forming apparatus as described above.
[0008]
[Means for Solving the Problems]
In order to solve the above problems, claim 1 of the present invention is a method invention,
Using an exposure device composed of a light emitting diode head in which a plurality of light emitting diodes (LEDs) are arranged in the axial direction, an image is exposed to a charged photosensitive member to form a latent image and developed, and a toner image formed is developed. In the exposure method in the image forming apparatus, after the image is transferred to the recording medium selected by the paper selection control means, the heater is heat-fixed by the fixing device whose pulse is controlled .
Based on the ratio of the actually counted number of printed sheets BP to the number of consecutive printed sheets AP within a predetermined time (BP / AP), the type of printing is determined as continuous printing or intermittent printing, and the printing type and the paper selection are selected. Based on the combination with the recording medium size selected by the control means,
Set a set value for the number of prints to increase the amount of exposure by the light emitting diode,
When the actually counted number of printed sheets becomes equal to or greater than the set value within a predetermined time, the amount of light emitted by the light emitting diode is increased to cope with a decrease in the amount of light emitted due to a temperature rise of the light emitting diode.
[0009]
The claim 2 apparatus an invention for carrying out the method invention,
An exposure apparatus that includes a light emitting diode head in which a plurality of light emitting diodes (LEDs) are arranged in the axial direction, exposes an image to a photosensitive member charged by the light emitting diode head, and forms a latent image, and is formed on the photosensitive member. A developing unit for developing the latent image formed to form a toner image, a transfer body for transferring the formed toner image to a recording medium selected by a paper selection control means, and a pulse control of the heater for the toner image. In an image forming apparatus comprising a heat fixing device that fixes heat while
Means for counting the number of prints of the image forming apparatus, and exposure control means for controlling the amount of exposure by the light emitting diode to be increased,
The exposure control means discriminates a print type of continuous printing or intermittent printing based on a ratio of an actual counted number of printed sheets BP to a continuous number of printed sheets AP within a predetermined time (BP / AP). Based on the combination of the print type and the recording medium size selectively conveyed from the paper feed cassette,
Set a set value for the number of prints to increase the amount of exposure by the light emitting diode,
Control means for increasing an exposure amount by the light emitting diode when the actually counted number of printed sheets becomes equal to or more than the set value within a predetermined time .
[0010]
In this way, by counting the number of prints within a predetermined time and increasing the exposure amount of the light emitting diode when printing of a predetermined number or more is performed, it is possible to cope with the temperature rise of the LED head with a simple and inexpensive configuration. As in the conventional method, the light output and development characteristics are set high, so that the half image and the resolution pattern are easily crushed, the image is not sharp, and the fog is not increased. Even when printing is performed, a stable light output can be obtained from the LED head. Further, since a temperature change measuring instrument or the like is not required, a driver or space is not required, and the image forming apparatus main body can be configured to be small and inexpensive.
[0011]
[0012]
In this way, the predetermined number of prints for increasing the exposure amount is set to a different value corresponding to the size (size) of the recording medium to be printed, so that the light amount can be accurately adjusted in response to the temperature rise of the LED. be able to.
[0013]
Further, according to the present invention, the print type of the continuous print or the intermittent print is discriminated based on the ratio of the actually counted print number BP to the continuous print number AP (BP / AP) within a predetermined time. And
[0014]
As will be described later, in continuous printing and intermittent printing, the LED head temperature rises faster in intermittent printing, so the amount of exposure is increased depending on whether printing is performed continuously or intermittently. By varying the predetermined number of prints, the light amount can be adjusted more accurately.
[0015]
[0016]
In this way, as in the case where the number of prints is counted in the number of times the heater of the fixing device is turned on, image formation with a simple and low-cost configuration and stable light output from the LED head can be obtained even when continuous printing is performed. it is possible to provide the equipment.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. This is just an example.
[0018]
FIG. 1 is a schematic configuration diagram when the present invention is applied to a color image forming apparatus as an example, FIG. 2 is a diagram showing a relationship between a light emitting diode array and a photosensitive drum used in the present invention, and FIG. FIG. 4 is a graph showing the relationship between the temperature of the light emitting diode and the light emission output, and FIG. 5 is a graph showing that the rate of increase in the temperature of the light emitting diode varies depending on the size of the recording medium to be printed. FIG. 6 is a graph for explaining the temperature rise of the light emitting diode due to the number of times the heater of the fixing device is turned on, and FIG. 7 is a graph showing the difference in the temperature rise of the light emitting diode due to the distance from other heat sources. .
[0019]
In the figure, reference numeral 1 denotes a photosensitive drum composed of amorphous silicon (abbreviated as a-Si), an organic photosensitive drum (OPC), and the like. Reference numeral 2 denotes an exposure apparatus using a light emitting diode (LED), which is shown in FIG. As described above, LEDs are arranged in the axial direction in the vicinity of the photosensitive drum 1 to constitute a light emitting diode head. 3 is a charger for the photosensitive drum 1, and 4 to 7 are developing devices including toner containers for each color of yellow (Y) 4, magenta (M) 5, cyan (C) 6, and black (K) 7, for example. 8 is a cleaning device for the photosensitive drum 1, 9 is an intermediate transfer member for transferring a toner image formed on the photosensitive drum 1, 10 is a cleaning device for the intermediate transfer member 9, 11 is a fixing device, and 12 is a fixing device. Secondary transfer means, 13 is a control device of the image forming apparatus, 14 is an exposure control circuit, 15 is a print number counter, 16 is a drive circuit for the photoreceptor 1, 17 is a control circuit for the fixing device 11, and 18 is paper (recording medium) ) Selection control circuit. In the following description, a color image forming apparatus that superimposes each color toner image using the intermediate transfer member 9 and transfers it to a recording medium will be described as an example. However, a development process in which a photosensitive drum is provided for each color is described. It is obvious that the present invention can be applied not only to a tandem color image forming apparatus arranged around the intermediate transfer member, but also to a monochrome image forming apparatus as well as a color image forming apparatus.
[0020]
As described above, when the LED is continuously printed on the exposure device 2 of the image forming apparatus, the temperature of the LED increases according to the number of prints as shown in FIG. That is, FIG. 3 is a graph showing the relationship between the number of prints when printing is performed using an A4 size recording medium and the temperature rise of the LED head in the exposure apparatus 2, in which the horizontal axis represents the number of prints and the vertical axis represents the number of prints. This is the temperature of the LED head. In the case of continuous printing, ◆ indicates measurement data when the driving motor for the photosensitive drum 1 is intermittently printed such that the driving motor stops for 2 seconds and repeats re-driving, for example. As apparent from FIG. 3, the temperature of the LED rises from about 23 ° C. to about 50 ° C. with about 2000 sheets in the case of continuous printing and about 1000 sheets in the intermittent printing.
[0021]
When the temperature of the LED rises in this way, the light emission output of the LED decreases as shown in FIG. That is, in FIG. 4, the horizontal axis is the LED head temperature (° C.), and the vertical axis is the light emission output (μW). As is apparent from FIG. 4, the LED head temperature is from about 23 ° C. to about 50 ° C. When it rises, it turns out that the light emission output has fallen by 10% or more.
[0022]
Further, the LED temperature rise rate by the continuous printing also varies depending on the size (size) of the recording medium to be printed. That is, FIG. 5 is a graph showing the relationship between the number of prints and the temperature rise of the LED head when printing using an A5 size recording medium. In FIG. 5, the horizontal axis is the number of prints and the vertical axis is the same as FIG. The temperature of the LED head, ♦ indicates the case of continuous printing, and x indicates the case of intermittent printing. As is apparent from the graph of FIG. 5, the temperature of intermittent printing tends to rise earlier than that of continuous printing, as in the graph of FIG. 3, but in the case of FIG. Then, when about 1500 sheets were printed, the temperature of the LED head rose to near 50 ° C. Compared with the case of A4 size in Fig. 3, about 2000 sheets were required to reach the same 50 ° C. The temperature is rising fairly quickly. This is also the case with intermittent printing, and although not as remarkable as continuous printing, the temperature rises somewhat earlier. That is, it can be seen that the temperature rise is faster in the case of printing in the small size of A5 than in the A4 size.
[0023]
Further, as shown in FIG. 6, the temperature of the LED also rises when the heater of the fixing device 11 in the image forming apparatus is turned on. That is, in FIG. 6, the horizontal axis indicates the number of times the heater of the fixing device 11 is turned on. For example, when the fixing device control circuit 17 performs pulse control of the heater of the fixing device 11, the horizontal axis indicates the number of ON times. Shows the temperature. Further, ■ indicates a case of continuous printing, and ◆ indicates a case of intermittent printing. As can be seen from FIG. 6, the temperature of the LED reaches approximately 50 ° C. when the heater of the fixing device 11 is turned on around 1000 times. . The number of times the heater of the fixing device is turned on is almost proportional to the number of prints.
[0024]
The LED of the exposure device 2 is provided in contact with the photosensitive drum 1 in the axial direction of the photosensitive drum 1 as shown in FIG. 2, and for this reason, for example, the photosensitive drum 1 is provided on one side of the photosensitive drum 1. When there is a heat source such as a drive motor, the temperature of the LED closer to the heat source changes higher. This is shown in the graph of FIG. 7, which is printed using an A4 size recording medium as in FIG. 3, and shows the number of prints and the temperature rise at different positions in the axial direction of the LED head. In the graph showing the relationship, the horizontal axis in the figure is the number of prints, and the vertical axis is the temperature of the LED head. The line plotted with ■ is closer to a heat source such as a motor for driving the photosensitive drum, ◆ is the opposite, and x is the middle. As is apparent from FIG. 7, the temperature of the LED closer to the heat source tends to be higher than that farther from the heat source, and is influenced by the temperature of the heat source.
[0025]
In the present invention therefore, the number of prints, the size (size) of the print recording medium, continuous, depending on mode such intermittent printing, which has to be able to adjust the exposure amount by changing the LED light-emitting strobe time Hereinafter, the present invention will be described in detail.
[0026]
First, an outline of the operation of the color image forming apparatus shown in FIG. 1 will be briefly described. Now, when image data to be printed is sent to the control device 13, the control device 13 first retracts the cleaning means 10 and the secondary transfer means 12 for the intermediate transfer member 9 by a retracting device (not shown), and the photosensitive member. The drum 1 is charged by the charger 3 while being driven by the photosensitive member driving circuit 16. Then, when image data is sent to the exposure control circuit 14 and an image corresponding to each color is exposed from the exposure device 2, a latent image is formed in the exposed portion (exposure portion). A toner image is formed when developed with a developing device of the color. This toner image is transferred to the intermediate transfer member 9 side by the primary transfer bias applied between the photosensitive drum 1 and the intermediate transfer member 9 at the nip portion where the photosensitive drum 1 and the intermediate transfer member 9 are in contact with each other. Thus, all other color toner images are primarily transferred to the intermediate transfer member 9. When the toner images of all colors are transferred to the intermediate transfer member 9, the cleaning unit 10 and the secondary transfer unit 12 for the intermediate transfer member 9 are brought into contact with the intermediate transfer member 9 with a retracting device (not shown), and A recording medium is selected from a paper feeding cassette (not shown) by the paper selection control circuit 18 and conveyed, and sent to the nip portion between the intermediate transfer member 9 and the secondary transfer means 12. When a transfer bias is applied to the secondary transfer means 12, the toner image on the intermediate transfer member 9 is secondarily transferred to the recording medium. Therefore, the heater of the fixing device 11 is heated in advance by the fixing device control circuit 17. Then, the recording medium is conveyed to the fixing device 11 and heated and pressurized to fix the toner image on the recording medium and eject it.
[0027]
In the image forming apparatus configured as described above, the print number counter 15 counts the number of prints by counting the signal each time the control device 13 sends a print signal (image data) to the exposure control circuit 14. Based on the number of prints, the size of the recording medium to be printed, the print mode such as continuous / intermittent print, and the like, the exposure control circuit 14 sets the predetermined number of sheets within a predetermined time as shown in FIGS. When the above printing is performed, it is determined that the temperature of the LED head has increased, the exposure amount of the light emitting diode is increased, and a decrease in the amount of emitted light due to the temperature increase of the light emitting diode is dealt with.
[0028]
The temperature of the LED head for increasing the exposure amount is set to 40 ° C., for example, and when continuously printing using an A4 size recording medium, the exposure amount is obtained when about 1200 to 1300 sheets are printed from the graph of FIG. Increase. Various methods such as a method of increasing the current supplied to the LED for light emission and a method of adjusting by the strobe time are possible as the method of increasing the exposure amount, but the method of adjusting by the strobe time is the simplest. Efficiency is good. Then, when printing is not performed for a certain time or longer, the increased exposure amount is returned to the original state because the temperature of the LED head is lowered.
[0029]
This is the same in the case of intermittent printing in the graph of FIG. 3. In this case, since the temperature rises faster than in the case of continuous printing, the exposure amount is increased when about 600 to 700 sheets are printed. The determination of the intermittent printing or the continuous printing is, for example, that the driving state of the driving motor for the photosensitive drum 1 is obtained from the photosensitive member driving circuit 16 via the control device 13, and the driving motor is stopped for 2 seconds and re-driven. As described above, when the driving is intermittently repeated, it is determined as intermittent printing. Actually, for example, it is assumed that intermittent printing is performed when the number of prints is 1/5 or more and 3/5 or less of continuous time in 10 minutes.
[0030]
The same applies to printing using an A5 size recording medium as shown in FIG. 5. In this case, the temperature rise of the LED head is faster than in the case of A4 size shown in FIG. In the case of 900 to 1000 sheets and intermittent printing, about 600 sheets reach 40 ° C. Therefore the exposure control circuit 14, based on the magnitude of the signal recording medium sent to the sheet selection control circuit 18 from the control unit 13 determines the size of the paper used for printing (size), the size ( Size) and the number of prints corresponding to the above-described continuous / intermittent printing, the LED head temperature is judged to have increased, and the exposure amount of the LED head is increased.
[0031]
The same applies not only to the number of prints but also to the temperature rise of the LED head due to the number of times the heater of the fixing device 11 is turned on as shown in FIG. For example, when the fixing device control circuit 17 controls the heater temperature by controlling the heater temperature by the fixing device control circuit 17, the heater of the fixing device 11 sends a pulse when fixing the toner image on the recording medium. In this graph, the number of pulses, that is, the number of times the heater is turned on, is plotted as the number of times of lighting, and the relationship with the temperature of the LED head is plotted. The temperature has reached 40 ° C. For this reason, the exposure control circuit 14 determines that the temperature of the LED head has increased when the number of times the heater of the fixing device 11 has been turned on within a predetermined time, and increases the exposure amount of the light emitting diode. Addresses a decrease in the amount of light emitted due to temperature rise.
[0032]
When there is a heat source such as a driving motor for the photosensitive drum 1 on one side of the photosensitive drum 1, the exposure control circuit 14 takes into account the temperature rise of the LED head due to the heat source as shown in FIG. The amount of light is increased by the number of prints corresponding to the distance from the heat source in the LED. That is, in the example of FIG. 7, the number of printed sheets is about 1100 for the LED closer to the heat source, and about 1300 to 1400 for the LED far from the heat source. When the value is reached, the light quantity of the LED may be increased as described above.
[0033]
When performing continuous printing in this way, the recording medium size, continuous printing, intermittent printing, the number of times the heater of the fixing device 11 is turned on, the distance from the heat source of each LED in the LED head, and the like are taken into account for a predetermined time. By increasing the light quantity of the LED according to the number of prints in the printer, the half image and resolution pattern are easily crushed by setting the light output and development characteristics higher as in the conventional method, and the image is not sharp. In addition, since fog does not increase, a stable light output can be obtained from the LED head even when continuous printing is performed with a simple and inexpensive configuration. Further, since a temperature change measuring instrument or the like is not required, a driver or space is not required, and the image forming apparatus main body can be configured to be small and inexpensive.
[0034]
【The invention's effect】
According to如rather present invention described above, it counts the number of prints in a predetermined time period, the LED head with a simple, inexpensive configuration of increasing the exposure amount of the light emitting diode when a predetermined number or more prints were made By dealing with the temperature rise, the half-image and resolution pattern are not easily lost by setting the light output and development characteristics higher as in the conventional method, and the image is not lost, and the fog increases. Therefore, a stable light output can be obtained from the LED head even when continuous printing is performed. Further, since a temperature change measuring instrument or the like is not required, a driver or space is not required, and the image forming apparatus main body can be configured to be small and inexpensive.
[0035]
According to or present invention, a predetermined number of prints to increase the exposure amount, that is corresponding to the size of the print recording medium to a different value, more accurate light amount adjustment in response to the temperature rise of the LED Can do.
[0036]
According to the element present invention, a predetermined number of prints to increase the amount of exposure, by varying between when intermittently performing the case of performing printing in succession, it is possible to perform more accurate light amount adjustment.
[0037]
And instead of the number of prints may count the number of lighting times of the fuser heater, by the number of lighting times of the heater within a predetermined time to increase the exposure amount of the light emitting diode when a predetermined number of times or more, printing Similarly to the case of counting the number, simple, inexpensive structure, it is possible to provide an image forming equipment which is adapted stable light output from the LED head even when continuous printing is obtained.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram when the present invention is applied to a color image forming apparatus as an example.
FIG. 2 is a diagram showing a relationship between a light-emitting diode array used in the present invention and a photosensitive drum.
FIG. 3 is a graph showing the relationship between the number of printed sheets and the temperature of a light emitting diode (LED head).
FIG. 4 is a graph showing the relationship between the temperature of a light emitting diode and the light emission output.
FIG. 5 is a graph for explaining that the rate of increase in the temperature of a light emitting diode varies depending on the size of a recording medium to be printed.
FIG. 6 is a graph showing a temperature rise of a light emitting diode according to the number of times a heater of a fixing device is turned on.
FIG. 7 is a graph showing a difference in temperature rise of a light emitting diode according to a distance from another heat source.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Exposure apparatus 3 Charger 4 Yellow (Y) developing apparatus 5 Magenta (M) developing apparatus 6 Cyan (C) developing apparatus 7 Black (K) developing apparatus 8 Cleaning apparatus 9 Intermediate transfer body 10 Cleaning apparatus 11 Fixing 12 Secondary transfer means

Claims (2)

Using an exposure device composed of a light emitting diode head in which a plurality of light emitting diodes (LEDs) are arranged in the axial direction, an image is exposed to a charged photosensitive member to form a latent image and developed, and a toner image formed is developed. In the exposure method in the image forming apparatus in which the image is transferred to the recording medium selected by the paper selection control means and then heat-fixed by a fixing device in which the heater is pulse-controlled .
Based on the ratio of the actually counted number of printed sheets BP to the number of consecutive printed sheets AP within a predetermined time (BP / AP), the type of printing is determined as continuous printing or intermittent printing, and the printing type and the paper selection are selected. Based on the combination with the recording medium size selected by the control means, set a set value of the number of prints to increase the amount of exposure by the light emitting diode,
When the actual counted number of printed sheets becomes equal to or greater than the set value within a predetermined time, the exposure amount by the light emitting diode is increased to cope with a decrease in the amount of light emitted due to a temperature rise of the light emitting diode. An exposure method in a forming apparatus. An exposure apparatus that includes a light emitting diode head in which a plurality of light emitting diodes (LEDs) are arranged in the axial direction, exposes an image to a photosensitive member charged by the light emitting diode head, and forms a latent image, and is formed on the photosensitive member. A developing unit for developing the latent image formed to form a toner image, a transfer body for transferring the formed toner image to a recording medium selected by a paper selection control means, and a pulse control of the heater for the toner image. In an image forming apparatus comprising a heat fixing device that fixes heat while
Means for counting the number of prints of the image forming apparatus, and exposure control means for controlling the amount of exposure by the light emitting diode to be increased,
The exposure control means discriminates a print type of continuous printing or intermittent printing based on a ratio of an actual counted number of printed sheets BP to a continuous number of printed sheets AP within a predetermined time (BP / AP). Based on the combination of the print type and the recording medium size selected by the paper selection control means,
Set a set value for the number of prints to increase the amount of exposure by the light emitting diode,
An image forming apparatus, comprising: control means for increasing an exposure amount by the light emitting diode when the actually counted number of printed sheets becomes equal to or more than the set value within a predetermined time.

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