Image forming device

Abstract

To perform pre-exposure with the high reliability at a low cost.SOLUTION: An image formation apparatus comprises: a photoreceptor drum 105 which rotates; an electrification roller 107 which electrifies the photoreceptor drum 105; a laser scanner 102 which forms a latent image by irradiating the photoreceptor drum 105 electrified by the electrification roller with emitted light to perform exposure; a development roller 104 which develops the latent image with toner; a transfer roller 106 which transfers the toner image that is developed and formed by the development roller 104 to a recording material; and a pre-exposure device 108 which exposes the surface of the photoreceptor drum 105 after transferring the toner image to the recording material before the electrification roller 107 electrifies the photoreceptor drum. The pre-exposure device 108 includes a substrate which is arranged in the vicinity of one end in the longitudinal direction of the photoreceptor drum 105 and on which an LED 1 and an LED 2 with the narrower directional characteristics than that of the LED 1 are mounted.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an image forming apparatus such as an electrophotographic laser printer. [Background technology]

[0002] Today, light-emitting diodes (hereinafter referred to as LEDs) are widely used as compact, inexpensive light sources, not only for display purposes but also for lighting and functional components in many products. LEDs are used, for example, in fluorescent-type lighting, backlights for liquid crystal displays, lighting for illuminating documents in image reading devices such as scanners, and static elimination lamps (hereinafter referred to as pre-exposure devices) in image forming devices. A pre-exposure device is a device that irradiates light onto a photosensitive drum in the image forming section of an image forming device, such as a laser printer, after a toner image formed on the surface of the photosensitive drum is transferred to a recording material. This pre-exposure device reduces the surface potential of the photosensitive drum and uniforms the distribution of the surface potential. For example, Patent Document 1 discloses an example of a method for irradiating light onto a photosensitive drum in a pre-exposure device. Patent Document 1 proposes a configuration in which light emitted by an LED is projected from one end of a light guide arranged parallel to the longitudinal direction of the photosensitive drum. The projected light is reflected by grooves in the light guide, thereby uniformly irradiating the photosensitive drum along the longitudinal direction. Furthermore, for example, Patent Document 2 discloses a configuration in which, instead of providing a light guide, LEDs are provided on each end side of the photosensitive drum in the longitudinal direction, and the light emitted by the LEDs is irradiated onto the photosensitive drum. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2012-163601 [Patent Document 2] Japanese Patent Application Laid-Open No. 2010-160185 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the pre-exposure device of Patent Document 1 mentioned above is equipped with a light guide, which is an expensive component. Furthermore, Patent Document 2 mentioned above requires LEDs to be placed on both longitudinal ends of the photosensitive drum. This requires a circuit board on which each LED is mounted, and a signal cable, which is a bundle of wires that supplies signals and power voltage to drive the LEDs, is required between the LEDs and the control unit that controls the LEDs. Furthermore, of the two signal cables connecting the control unit and the two circuit boards, at least one signal cable is long. This increases costs and also increases the work time in the assembly process.

[0005] Furthermore, conventional pre-exposure devices lack diagnostic capabilities for the LED light source, making it impossible to detect a malfunction. Even if the pre-exposure device malfunctions and the LED does not emit light, preventing the photosensitive drum from receiving light, printing is still possible, making it difficult for users of image forming devices to notice an LED malfunction. However, if the pre-exposure device malfunctions and the photosensitive drum is not discharged, a phenomenon known as "fog" occurs, in which the image formed on the photosensitive drum one revolution before is faintly overlapped with the image formed on the next revolution. As a result, when printing a print that requires high image quality, such as a photograph, the image degradation becomes clearly noticeable.

[0006] The present invention has been made under these circumstances, and has as its object to perform pre-exposure at low cost and with high reliability. [Means for solving the problem]

[0007] In order to solve the above-mentioned problems, the present invention has the following configuration.

[0008] (1) An image forming apparatus comprising: a rotating photosensitive member; a charging means for charging the photosensitive member; an exposure means for irradiating the photosensitive member charged by the charging means with light emitted thereto to expose the photosensitive member and form a latent image; a developing means for developing the latent image with toner; a transfer means for transferring the toner image developed and formed by the developing means to a recording material; and a pre-exposure means for exposing the surface of the photosensitive member after the toner image has been transferred to the recording material and before the surface of the photosensitive member is charged by the charging means, wherein the pre-exposure means has a substrate on which a first light-emitting element and a second light-emitting element having a narrower directional characteristic than the first light-emitting element are mounted, the first light-emitting element being arranged near one end of the longitudinal direction of the photosensitive member. [Effects of the Invention]

[0010] According to the present invention, pre-exposure can be performed at low cost and with high reliability. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a cross-sectional view showing the configuration of an image forming apparatus according to first and second embodiments; [Figure 2] FIG. 1 is a diagram illustrating the configuration of a pre-exposure device according to a first embodiment. [Figure 3] FIG. 1 is a diagram illustrating the directional characteristics of an LED according to the first embodiment. [Figure 4] Table and graph showing the experimental results of Example 1 [Figure 5] FIG. 10 is a diagram illustrating the configuration of a pre-exposure device according to a second embodiment. [Figure 6] FIG. 10 is a diagram illustrating the connection between the pre-exposure device and the control unit in the second embodiment. [Figure 7] FIG. 10 is a diagram illustrating the operation of the control unit according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. [Example]

[0013] [Configuration of image forming device] FIG. 1 is a cross-sectional view illustrating the configuration of a monochrome laser printer 100 (hereinafter referred to as printer 100), which is an image forming apparatus to which the first embodiment is applied. In FIG. 1, an image forming unit that forms an image on a recording material includes a photosensitive drum 105, which is a photosensitive member, and a charging roller 107, which is a charging means that charges the photosensitive drum 105 to a uniform potential. The image forming unit also includes a laser scanner 102, which is an exposure means that irradiates the surface of the photosensitive drum 105 with laser light 113 to form an electrostatic latent image. The image forming unit also includes a developing roller 104, which is a developing means that develops the electrostatic latent image formed on the photosensitive drum 105 with magnetic toner contained in a toner tank 103 to form a toner image. A pre-exposure device 108 is also provided downstream of a transfer roller 106 in the rotation direction of the photosensitive drum 105 and upstream of the charging roller 107 to expose the surface of the photosensitive drum 105 (referred to as pre-exposure) to light, thereby uniforming the surface potential of the photosensitive drum 105. The control unit 120 controls the image forming unit and the like so that the printer 100 performs an image forming operation.

[0014] The paper feed unit 101 feeds the stored recording material to a conveying path 112, and the fed recording material passes through the conveying path 112 and is conveyed to a transfer roller 106. The transfer roller 106, which is a transfer means, transfers the toner image formed on the photosensitive drum 105 onto the recording material. The fixing device 114 is a device that fixes the toner image transferred onto the recording material onto the recording material, and has a fixing roller 109 that heats the toner image, and a pressure roller 110 that comes into contact with the fixing roller 109 and applies pressure to the recording material as it passes. The recording material that has passed through the fixing device is discharged to and stacked on a discharge unit 111.

[0015] [Image formation operation] Next, the image forming operation of the printer 100 will be described. When the control unit 120 of the printer 100 receives a print job from an external device (not shown) such as a personal computer, it drives each roller within the device to form an image and starts the operation of the laser scanner 102. A charging voltage, which is a negative high voltage, is applied to the charging roller 107 from a power supply device (not shown). The charging roller 107 contacts the photosensitive drum 105, which rotates in the direction of the arrow in the figure (clockwise), and charges the surface of the photosensitive drum 105 to a uniform voltage. The laser scanner 102 emits a laser beam 113 in accordance with image data included in the print job. The laser beam 113 emitted from the laser scanner 102 is irradiated onto the photosensitive drum 105, and the charge in the portion of the photosensitive drum 105 irradiated with the laser beam 113 disappears, forming an electrostatic latent image. The developing roller 104 has a magnet inside, and when a negative high voltage developing voltage is applied from a power supply (not shown), the magnetic force attracts the magnetic toner in the toner tank 103. Then, the developing roller 104 uses electrostatic force to move the toner to the electrostatic latent image formed on the photosensitive drum 105, forming a toner image.

[0016] Meanwhile, in response to an instruction from the control unit 120, a recording material fed from the paper feed unit 101 passes through a conveying path 112 and is conveyed to a nip formed by the contact of a transfer roller 106 and a photosensitive drum 105. A positive high voltage transfer voltage is applied to the transfer roller 106 from a power supply (not shown), and the toner image formed on the photosensitive drum 105 is transferred to the recording material. The recording material with the transferred toner image is then conveyed to a fixing device 114 and conveyed to a fixing nip formed by the contact of a fixing roller 109 and a pressure roller 110. In the fixing nip, the toner image is heated to several hundred degrees by the fixing roller 109 and pressed by the pressure roller 110, thereby fixing the unfixed toner image to the recording material. The recording material with the fixed toner image is then discharged to a discharge unit 111 and stacked. After the toner image has been transferred to the recording material, the surface potential of the photosensitive drum 105 is uneven due to the image. Therefore, the pre-exposure device 108 uniformly neutralizes the surface potential of the photosensitive drum 105 to approximately 0 V by irradiating the surface of the photosensitive drum 105 with light emitted by an LED, which is a light source (not shown). This prevents the image formed on the photosensitive drum 105 and transferred to the recording material from affecting the next image to be formed. The monochrome laser printer 100 then executes the print job while repeating the image formation operation described above.

[0017] [Configuration of pre-exposure device] Next, the pre-exposure device 108 of this embodiment will be described. FIG. 2 is a schematic diagram illustrating the configuration of the pre-exposure device 108 of this embodiment. As shown in FIG. 2, the pre-exposure device 108 of this embodiment has two light-emitting elements (LEDs) mounted on a single board, and is different from the pre-exposure device of the conventional example described above in that it is configured with a single board. Furthermore, in the pre-exposure device of the conventional example described above, light emitted from the LEDs of the pre-exposure device is irradiated onto the photosensitive drum via a light guide. In contrast, the pre-exposure device 108 of this embodiment is configured so that light emitted from the two LEDs is directly irradiated onto the photosensitive drum 105 without passing through a light guide. Therefore, as shown in FIG. 2, the pre-exposure device 108 is positioned vertically above one longitudinal end of the photosensitive drum 105, tilted toward the photosensitive drum 105 so that the light emitted by the LEDs irradiates the entire longitudinal surface of the photosensitive drum 105. The two LEDs, LED1 and LED2, mounted on the circuit board are arranged vertically (vertically in the drawing) side by side, with LED1 positioned on the lower side and LED2 positioned on the upper side. Also, in FIG. 2, the ranges reached by the light emitted by LED1 and LED2 are indicated by dashed lines, and the ranges reached by the light emitted by LED1 and LED2 are different. As shown in FIG. 2, the light emitted by LED1 (first light-emitting element) is irradiated from the end of the photosensitive drum 105 on the side where the pre-exposure device 108 is disposed to near the center in the longitudinal direction. Meanwhile, the light emitted by LED2 (second light-emitting element) is irradiated from near the center of the photosensitive drum 105 on the side opposite the end where the pre-exposure device 108 is disposed to the end on the side opposite the end where the pre-exposure device 108 is disposed.

[0018] [Directional characteristics of LED] As described above, LED1 and LED2 in this embodiment have different directional characteristics. Figure 3 shows directional characteristic diagrams illustrating the directional characteristics of LED1 and LED2, with Figure 3(a) showing the directional characteristic diagram for LED1 and Figure 3(b) showing the directional characteristic diagram for LED2. The directional characteristic diagram in Figure 3 represents the spread of light emitted by the LEDs in terms of relative brightness (relative luminous intensity) per angle, with the directional characteristic of each LED depicted as a graph on a semicircular diagram. In the directional characteristic diagram, the numbers 0, 10, ..., and 90 on the circumference of the semicircle indicate the angle (unit: degrees) of the light emitted by the LED, and the numbers 0, 50, and 100 on the straight line representing the diameter of the semicircle indicate the relative luminous intensity (unit: %). The directional characteristic diagram shows how the brightness decreases relative to the angle of the light emitted by the LED, with the brightness at the brightest part (angle) being 100% relative luminous intensity. As shown in FIG. 3, LED1 has wide directivity (wide-angle directivity), while LED2 has narrow (sharp) directivity (narrow-angle directivity). That is, the light emitted by LED1 can illuminate a wide area close to the board on which LED1 is mounted, but cannot illuminate a distant point. On the other hand, the light emitted by LED2 can illuminate a narrow area far from the board on which LED2 is mounted, but cannot illuminate a wide area close to the board. Therefore, by mounting two LEDs, LED1 and LED2, with different directivity characteristics on the same board, LED1 can irradiate light from the end of the photosensitive drum 105 on the side where the pre-exposure device 108 is located to near the center in the longitudinal direction. On the other hand, LED2 can irradiate light from near the center of the photosensitive drum 105 on the side opposite the end where the pre-exposure device 108 is located. As a result, the photosensitive drum 105 can be neutralized by the light emitted by the two LEDs, LED1 and LED2, on the photosensitive drum 105.

[0019] [Eliminating static electricity from the photosensitive drum using a pre-exposure device] Figure 4 shows a table (top of Figure 4) that shows the results of measurements using a light intensity meter to measure the detected power (emission intensity) of light emitted by LED1 and LED2 using the pre-exposure device 108 configured as shown in Figure 2, and a graph (bottom of Figure 4) created based on the data shown in the table. The table at the top of Figure 4 shows, from top to bottom, the distance from the LEDs (unit: mm), the detected power of LED1 (unit: mW), the detected power of LED2 (unit: mW), and the combined value of the detected power of LED1 and LED2 (unit: mW). The table shows the measurement results of the detected power of LED1, the detected power of LED2, and the combined value of the detected power of LED1 and LED2 at distances from the LEDs in 10 mm increments from 10 mm to 150 mm.

[0020] The graph shown at the bottom of Figure 4 was created based on the distances and detected power (emission intensity) of LED1 and LED2 shown in the table at the top. In the graph of Figure 4, the horizontal axis represents the distance from the LED (unit: mm), and the vertical axis represents the detected power (unit: mW). The dotted line represents the detected power of LED1, which has a wide beam angle, and the dashed line represents the detected power of LED2, which has a narrow beam angle. The solid line represents the combined detected power of LED1 and LED2 at each distance.

[0021] As shown in FIG. 4, the detected power of light emitted by LED1 is highest at a position 60 mm from the center of the photosensitive drum 105 in the longitudinal direction, and the detected power of light emitted by LED2 is highest at a position 120 mm from the photosensitive drum in the longitudinal direction. The solid line graph showing the combined detected power of light emitted by LED1 and LED2 appears wavy, but it can be seen that light with a detected power (emission intensity) of 20 mW or more is always irradiated up to a position 140 mm from the light source (LED). Since the pre-exposure device 108 can discharge residual charge on the photosensitive drum 105 as long as it emits light with an emission intensity of a certain value (e.g., 20 mW) or more, the wavy appearance of the graph showing the detected power of light is not a problem. As shown in FIG. 4, there are positions where the detected power of each of LED1 and LED2 alone falls below 20 mW. For example, the detected power of LED1 is below 20 mW at positions 10 mm to 40 mm and 90 mm to 150 mm. Similarly, the detected power of LED2 is below 20 mW at positions from 10 mm to 100 mm, 140 mm, and 150 mm. However, by arranging two LEDs, LED1 and LED2, with different directivity angles in a vertical direction (vertical direction), it is possible to irradiate light with a detected power that does not fall below 20 mW from one end of the photosensitive drum 105 to the other in the longitudinal direction. As described above, in this embodiment, by using only one board on which the LEDs are mounted and eliminating the need for a light guide, costs are reduced, and the use of a single board also reduces the work time in the assembly process. Furthermore, by using a single board, the possibility of failure is reduced compared to a case where two boards are used, and reliability is improved.

[0022] As described above, according to this embodiment, pre-exposure can be performed at low cost and with high reliability. [Example]

[0023] In the second embodiment, a diagnostic method for diagnosing whether or not the LED used in the pre-exposure device has failed will be described.

[0024] [Configuration of pre-exposure device] FIG. 5 is a schematic diagram showing the positional relationship of the pre-exposure device, photosensitive drum 105, and charging roller 107 used in this embodiment. LED1 and LED2 in FIG. 5 are LEDs in the pre-exposure device, mounted on substrates located near each longitudinal end of the photosensitive drum 105. The pre-exposure device of this embodiment, as in Patent Document 2 (FIG. 2), irradiates pre-exposure light from both longitudinal ends of the photosensitive drum 105 without a light guide. Specifically, LED1 irradiates the left half of the photosensitive drum 105 in the longitudinal direction, and LED2 irradiates the right half of the photosensitive drum 105 in the longitudinal direction, thereby eliminating charge on the photosensitive drum 105. This embodiment will be described using a pre-exposure device in which LEDs are located at both longitudinal ends of the photosensitive drum 105.

[0025] The LED (light-emitting diode), which is the light source for the pre-exposure device, is a semiconductor element with an exposed PN junction. When current is passed between the cathode and anode terminals of the LED, the PN junction emits light, radiating light to the outside. Solar cells are similar to LEDs in that their PN junctions are exposed to the outside, and when external light is shone on the light-emitting part of an LED (PN junction), current flows between the anode and cathode terminals of the LED, generating a voltage. Naturally, LEDs are designed so that the PN junction emits light efficiently when current is passed through them, so the electromotive force generated is small compared to solar cells. However, depending on the intensity of the light shining on the LED's light-emitting part and the output impedance, it is possible to generate a voltage of several volts (V).

[0026] [Pre-exposure device diagnosis] The two LEDs of the pre-exposure device of this embodiment are arranged facing each other on both longitudinal ends of the photosensitive drum 105, as shown in FIG. 5. When used as a pre-exposure device, the two LEDs are turned on and light is irradiated onto the photosensitive drum 105, thereby eliminating static electricity from the photosensitive drum 105. Taking advantage of the aforementioned characteristic that an electromotive force is generated when light is irradiated onto the LEDs, it is possible to diagnose whether or not an LED is faulty by turning on one LED and irradiating the other LED with light from one LED and determining whether or not an electromotive force is generated. The function of diagnosing whether or not an LED is faulty will be described below.

[0027] The LEDs of the pre-exposure device are controlled by a CPU 121 (central control unit) (see FIG. 6), which is the control means of the control unit 120 shown in FIG. 1. The CPU 121 has two modes: a pre-exposure mode in which the pre-exposure device is used to neutralize the photosensitive drum 105, and a diagnostic mode in which the LEDs of the pre-exposure device are diagnosed for malfunction. In the pre-exposure mode, the CPU 121 controls the lighting of two LEDs, LED1 and LED2. In the diagnostic mode, when LED1 is lit, the CPU 121 uses LED2 as a light-receiving element to measure the electromotive force generated in LED2. Since LED2 is positioned opposite LED1, an electromotive force is generated when LED2 is operating normally in response to the light emitted by LED1. For example, if LED1 is malfunctioning and not lit, no light is emitted and no electromotive force is generated in LED2. Therefore, if LED2 is operating normally, a malfunction of LED1 can be detected. Similarly, when LED2 is lit, the CPU 121 uses LED1 as a light-receiving element to measure the electromotive force generated in LED1. When LED1 is operating normally in response to the light emitted by LED2, an electromotive force is generated. For example, if LED2 is faulty and does not light up, no light is emitted and no electromotive force is generated in LED1. Therefore, if LED1 is normal, it is possible to detect a fault in LED2.

[0028] [Controller configuration] FIG. 6 shows the connection relationship between the CPU 121 and the two LEDs, LED1 and LED2. The anode terminal of LED1 is connected to I / O port 1 of the CPU 121 via a resistor, and the cathode terminal is connected to ground (grounded). On the other hand, the anode terminal of LED2 is connected to I / O port 2 of the CPU 121 via a resistor, and the cathode terminal is connected to ground (grounded). As shown in FIG. 6, LED1 and LED2 are connected to different I / O ports 1 and 2 (input / output ports) of the CPU 121, respectively. Furthermore, I / O ports 1 and 2 to which LED1 and LED2 are connected need to detect the electromotive voltages output by LED1 and LED2 in order to diagnose whether or not the LEDs are faulty. Therefore, I / O ports 1 and 2 to which LED1 and LED2 are connected need to have an A / D conversion (analog-to-digital conversion) function (conversion unit) that converts analog input voltage signals into digital values. When LED1 and LED2 are used as pre-exposure devices, the CPU 121 switches I / O ports 1 and 2, to which LED1 and LED2 are connected, to use them as output ports. For example, when LED1 and LED2 are turned on, high-level signals are output from I / O ports 1 and 2, and when LED1 and LED2 are turned off, low-level signals are output from I / O ports 1 and 2.

[0029] [Control of diagnostic functions] Next, the control operation of the CPU 121 when executing the diagnostic function will be described. FIG. 7(a) is a diagram illustrating the control when diagnosing whether or not LED1 is faulty. When diagnosing whether or not LED1 is faulty, the CPU 121 switches I / O port 1, to which LED1 is connected, to use it as an output port, and switches I / O port 2, to which LED2 is connected, to use it as an input port with an A / D conversion function. To light up LED1, the CPU 121 outputs a high-level signal from the I / O port 1 to which LED1 is connected. When a high-level signal is input to the anode terminal of LED1, LED1 becomes conductive and emits light. On the other hand, when LED1 emits light, light emitted by LED1 enters LED2, causing it to become conductive. This causes current to flow through the resistor connected to the anode terminal of LED2, and a voltage signal is input to the I / O port 2 to which LED2 is connected. The CPU 121 then determines whether or not the electromotive force generated in LED2 is equal to or greater than a predetermined value, based on the digital value obtained by A / D converting the input voltage signal. If the electromotive voltage is equal to or greater than a predetermined value, the CPU 121 determines that LED1 is lit and in a normal state. On the other hand, if LED1 is faulty and not lit, the light emitted by LED1 is not incident on LED2, and therefore no electromotive voltage is generated in LED2. Therefore, if the electromotive voltage is less than a predetermined value, the CPU 121 determines that LED1 is not lit and in a faulty state. Note that the above-mentioned predetermined value depends on the configuration of the pre-exposure device, and may be determined based on the results of actual experiments.

[0030] Furthermore, if the output voltage of LED2 is sufficiently high, such as several volts, it is not necessary to use an I / O port with A / D conversion functionality; an I / O port without A / D conversion functionality may be used. The reason for using an I / O port with A / D conversion functionality in this embodiment is as follows: Because LEDs are not inherently light-receiving elements, their output voltages are likely to be low, and the threshold level at the I / O port through which the signal is input, i.e., the threshold for signal input from TTL, CMOS, or the like, may not be recognized as a high level. On the other hand, an I / O port with A / D conversion functionality allows the threshold to be freely set, making it possible to set a threshold that matches the configuration of the pre-exposure device.

[0031] FIG. 7(b) is a diagram illustrating the control when diagnosing whether or not LED2 has failed. When diagnosing whether or not LED2 has failed, CPU 121 uses I / O port 2, to which LED2 is connected, as an output port, and uses I / O port 1, to which LED1 is connected, as an input port with an A / D conversion function. The control of CPU 121 when diagnosing whether or not LED2 has failed is the same as that shown in FIG. 7(a) above, and therefore will not be described here. By diagnosing LED1 and LED2 based on FIGS. 7(a) and 7(b) above when not performing a printing operation, CPU 121 can check whether or not the LEDs of the pre-exposure device have failed, thereby improving the reliability of the pre-exposure device.

[0032] As described above, according to this embodiment, pre-exposure can be performed at low cost and with high reliability. [Explanation of symbols]

[0033] 102 Laser scanner 104 Developing roller 105 Photosensitive drum 106 Transfer roller 107 Charging roller 108 Pre-exposure device LED1, LED2 Light Emitting Diodes

Claims

1. A rotating photoreceptor; a charging means for charging the photosensitive member; an exposure unit that irradiates the photosensitive member charged by the charging unit with emitted light to expose the photosensitive member and form a latent image thereon; a developing means for developing the latent image with toner; a transfer means for transferring the toner image developed by the developing means onto a recording material; a pre-exposure means for exposing the surface of the photoconductor after the toner image has been transferred to the recording material, the surface of the photoconductor before the charging means charges the surface; Equipped with An image forming apparatus characterized in that the pre-exposure means has a substrate on which a first light-emitting element and a second light-emitting element having a narrower directional characteristic than the first light-emitting element are mounted, the first light-emitting element being arranged near one end of the longitudinal direction of the photosensitive body.

2. the first light-emitting element exposes the surface of the photosensitive member from one end side of the photosensitive member on which the substrate is disposed toward the center of the photosensitive member in the longitudinal direction; 2. The image forming apparatus according to claim 1, wherein the second light emitting element exposes the surface of the photosensitive member from near the center of the photosensitive member in the longitudinal direction toward the other end of the photosensitive member.

3. a control means for controlling the pre-exposure means, 3. The image forming apparatus according to claim 2, wherein the control means controls the first light-emitting element and the second light-emitting element to emit light and expose the surface of the photosensitive member.

4. The image forming apparatus according to claim 3, characterized in that the control means controls the first light-emitting element or the second light-emitting element to emit light, detects an electromotive voltage generated when the second light-emitting element receives the light emitted by the first light-emitting element, or detects an electromotive voltage generated when the first light-emitting element receives the light emitted by the second light-emitting element, and determines whether or not the first light-emitting element or the second light-emitting element is faulty based on the detected electromotive voltage.

5. 5. The image forming apparatus according to claim 4, wherein the control means has input / output ports to which the first light-emitting element and the second light-emitting element are respectively connected, and switches the input / output ports to output ports when the first light-emitting element and the second light-emitting element are caused to emit light, and switches the input / output ports to input ports having a conversion unit that converts the electromotive voltage into a digital value when the electromotive voltage is input from the first light-emitting element and the second light-emitting element.

6. 6. The image forming apparatus according to claim 1, wherein the first light-emitting element and the second light-emitting element are light-emitting diodes.

Images