Image forming device

Abstract

This image forming device forms a toner image onto a recording material, and comprises a rotating photoreceptor and an exposure unit which has a plurality of exposure heads arranged side-by-side in the direction of rotation of the photoreceptor and which can form an electrostatic latent image by irradiating the surface of the photoreceptor with light to thereby expose the photoreceptor. The exposure heads have a plurality of light-emitting elements that are arrayed along the rotational axis direction of the photoreceptor and that emit light with which to irradiate the surface of the photoreceptor. The exposure unit exposes the photoreceptor in one of the following modes: a first lighting mode in which all of the plurality of exposure heads are lighted to expose the photoreceptor (NO in S13, S18); and a second lighting mode (YES in S13, S16, S19) in which a subset of the plurality of exposure heads is lighted to expose the photoreceptor.

Description

Image forming device

[0001] The present invention relates to an image forming apparatus using an electrophotographic method, such as a printer, a copying machine, a facsimile machine, or a multifunction machine.

[0002] An electrophotographic image forming apparatus includes an exposure unit that exposes the surface of a rotating photosensitive drum to light to form an electrostatic latent image on the surface of the photosensitive drum. A conventional apparatus has been proposed in which an exposure head, in which a plurality of light-emitting elements such as LEDs or organic ELs are arranged in the direction of the rotation axis of the photosensitive drum (main scanning direction), is arranged in the direction of rotation of the photosensitive drum (sub-scanning direction) (see Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2004-325872

[0004] In an image forming apparatus, the rotation speed of a photoconductor may be changed depending on, for example, the basis weight of a recording material. In such a case, in order to form an electrostatic latent image on the photoconductor with an appropriate amount of light, it is necessary to adjust the amount of light irradiated from the exposure head according to the changed rotation speed of the photoconductor. However, in the past, it was difficult to adjust the amount of light irradiated from multiple exposure heads arranged in the rotation direction of the photoconductor.

[0005] The present invention has been made in consideration of the above problems, and aims to provide an image forming device that is configured to expose a photosensitive member using multiple exposure heads arranged in the rotational direction of the photosensitive member, and that can adjust the amount of light irradiated from the multiple exposure heads to form an electrostatic latent image on the photosensitive member with an appropriate amount of light.

[0006] An image forming apparatus according to one embodiment of the present invention is an image forming apparatus that forms a toner image on a recording material, and comprises: a rotating photosensitive member; and an exposure unit having a plurality of exposure heads arranged in a line in the rotation direction of the photosensitive member, and capable of exposing the photosensitive member by irradiating light onto the surface of the photosensitive member to form an electrostatic latent image; the exposure heads are arranged along the rotation axis direction of the photosensitive member and have a plurality of light-emitting elements that emit light to irradiate the surface of the photosensitive member; and the exposure unit exposes the photosensitive member in either a first lighting mode in which all of the plurality of exposure heads are lit to expose the photosensitive member, or a second lighting mode in which some of the plurality of exposure heads are lit to expose the photosensitive member.

[0007] According to the present invention, in a configuration in which a photosensitive body can be exposed by multiple exposure heads arranged in a row in the rotation direction of the photosensitive body, the amount of light irradiated from the multiple exposure heads can be adjusted to form an electrostatic latent image on the photosensitive body with an appropriate amount of light.

[0008] 1 is a schematic diagram showing an image forming apparatus of the present embodiment; FIG. 1 is a perspective view showing the arrangement of a photosensitive drum and an exposure head; FIG. 2 is a schematic view showing the arrangement of a photosensitive drum and an exposure head; FIG. 3 is a view showing a surface of a printed circuit board on which light-emitting elements are not mounted; FIG. 4 is a view showing a surface of a printed circuit board on which light-emitting elements are mounted; FIG. 5 is a view showing a boundary portion between light-emitting element array chips; FIG. 6 is a control block diagram showing a control system of an exposure device in a first embodiment; FIG. 7 is a flowchart showing an image forming process in the first embodiment; FIG. 8 is a flowchart showing a lighting mode setting process in the first embodiment; FIG. 9 is a control block diagram showing a control system of an exposure device in a second embodiment; FIG. 10 is a flowchart showing a lighting mode setting process in the second embodiment; FIG. 11 is a flowchart showing a lighting mode setting process in the third embodiment; FIG. 12 is a control block diagram showing a control system of an exposure device in a fourth embodiment; FIG. 13 is a flowchart showing an image forming process in the fourth embodiment; FIG. 14 is a flowchart showing a lighting mode setting process in the fourth embodiment.

[0009] [First Embodiment] <Image Forming Apparatus> This embodiment will now be described. First, the configuration of the image forming apparatus of this embodiment will be described with reference to Fig. 1. As shown in Fig. 1, the image forming apparatus 1 of this embodiment includes a scanner unit 100, an image creating unit 103, a fixing unit 104, a supply / conveyance unit 105, an operation unit 114, and a control unit 401 that controls these. The scanner unit 100 shines light onto a document placed on a document table to optically read an image on the document, and converts the read image into an electrical signal to create image data.

[0010] In this embodiment, the image forming unit 103 has four image forming stations that perform a series of electrophotographic processes (charging, exposing, developing, and transferring) described below. The four image forming stations form toner images of each color, cyan (C), magenta (M), yellow (Y), and black (K), in that order from the right in FIG. 1. In the image forming unit 103, a full-color image can be formed on the recording material by sequentially starting image forming at the magenta, yellow, and black image forming stations after a predetermined time has elapsed since the start of image forming at the cyan image forming station.

[0011] Each imaging station has a photosensitive drum 102 as a photosensitive member, a charger 107, an exposure unit 106, and a developing unit 108. In the imaging station for each color, the surface of the photosensitive drum 102, which is rotated, is first uniformly charged by the charger 107. Then, the exposure unit 106 forms an electrostatic latent image on the surface of the charged photosensitive drum 102. The exposure unit 106 can form an electrostatic latent image on the surface of the photosensitive drum 102 by focusing light emitted from a light-emitting element, which will be described later, on the surface of the photosensitive drum 102 in accordance with image data.

[0012] In this embodiment, the exposure unit 106 serving as an exposure section has two exposure heads (106a and 106b, 106c and 106d, 106e and 106f, and 106g and 106h). The two exposure heads (106a and 106b, 106c and 106d, 106e and 106f, and 106g and 106h) are arranged side by side in the direction of rotation of the photosensitive drum 102 (see FIG. 2A, which will be described later).

[0013] In each imaging station, by staggering the light emission timing of a pair of exposure heads (106a to 106h), the same location on the photosensitive drum 102 can be multiplexed and exposed in accordance with the same image data. For example, for the photosensitive drum 102 used to form a black toner image, the first exposure head 106a, located upstream in the rotation direction of the photosensitive drum 102, first exposes the surface of the photosensitive drum 102. Thereafter, the second exposure head 106b, located downstream in the rotation direction of the photosensitive drum 102, can expose the same location on the photosensitive drum 102 as that exposed by the exposure head 106a. In the configuration shown in FIG. 1, the photosensitive drum 102 is rotated clockwise by a motor (not shown).

[0014] The developing device 108 uses a developer containing toner to develop the electrostatic latent image formed on the photosensitive drum 102 into a toner image. The toner image on the photosensitive drum 102 is transferred onto a recording material (sheet) conveyed by a sheet conveying belt 111.

[0015] In the supply / conveyance section 105, a recording material is supplied from a pre-designated supply unit among the internal supply units 109a and 109b, the external supply unit 109c, and the manual supply unit 109d. The supplied recording material is conveyed to the registration rollers 110. The registration rollers 110 convey the recording material onto the sheet conveyance belt 111 at the timing when the toner image formed in the image forming section 103 is transferred to the recording material.

[0016] With respect to the conveyance direction of the recording material by the sheet conveying belt 111, an optical sensor 113 is disposed downstream of the sheet conveying belt 111. The optical sensor 113 detects the position of a test image formed on the sheet conveying belt 111, for example, to measure the amount of misalignment of the toner images formed by each image forming station. The obtained amount of misalignment is sent to the control unit 401, and the control unit 401 performs positional misalignment correction control to correct the image position of each color based on the amount of misalignment. By performing this positional misalignment correction control, a full-color toner image without color misalignment is formed on the recording material.

[0017] The recording material onto which the toner image has been transferred is conveyed to fixing unit 104. Fixing unit 104 has, for example, a pair of rollers that contact each other and a heat source such as a halogen heater that heats the rollers, and applies heat and pressure to the recording material onto which the toner image has been transferred, thereby fixing the toner image to the recording material. The recording material onto which the toner image has been fixed is discharged outside the main body of image forming apparatus 1 by discharge rollers 112.

[0018] The operation unit 114 is a touch panel input device having a display unit such as a liquid crystal display and a detection unit that detects touches on the display unit. A user can touch the operation unit 114 to input information such as the number of sheets of recording material on which images are to be formed, the size of the recording material (e.g., A3, B4, postcard), and the basis weight of the recording material stored in the supply units (109a to 109d) (e.g., cardboard or plain paper).

[0019] <Exposure Unit> Next, the exposure unit 106 will be described using Figures 2A and 2B. Note that the exposure units 106 in each imaging station may all have the same configuration, and therefore the following description will be given using the exposure unit 106 in the black imaging station as an example. Note that the number of exposure heads (106a, 106b) is not limited to two, and three or more may be arranged side by side in the rotation direction of the photosensitive drum 102.

[0020] As shown in FIG. 2A , the exposure unit 106 has two exposure heads (106 a, 106 b). In this embodiment, the first exposure head 106 a is disposed upstream in the direction of rotation of the photosensitive drum 102, and the second exposure head 106 b is disposed downstream in the direction of rotation of the photosensitive drum 102. Each exposure head (106 a, 106 b) is configured so that, in the direction of rotation of the photosensitive drum 102 (the direction of arrow Q), the downstream second exposure head 106 b can irradiate light onto the exposure area of ​​the photosensitive drum 102 exposed by the upstream first exposure head 106 a, thereby overlapping the exposed area. The exposure unit 106 and the photosensitive drum 102 are each attached to the main body of the image forming apparatus 1 by attachment members (not shown). Since the exposure heads 106 a and 106 b are identical, only the exposure head 106 a is shown in FIG. 2B , and the description will be given using the exposure head 106 a as an example.

[0021] 2B , the exposure head 106a is composed of a light-emitting element group 201, a printed circuit board 202 on which the light-emitting element group 201 is mounted, a rod lens array 203, and a housing 204 on which the rod lens array 203 and the printed circuit board 202 are attached. The light-emitting element group 201 is made up of a plurality of light-emitting element array chips having light-emitting elements such as LEDs and organic ELs. When assembling the image forming apparatus 1, the exposure head 106a is subjected to a focus adjustment operation to adjust the spot at the light-condensing position on the photosensitive drum surface to a predetermined size, and an adjustment of the light amount on the photosensitive drum surface.

[0022] Here, the exposure head 106a is positioned so that the distance between the photosensitive drum 102 and the rod lens array 203 and the distance between the rod lens array 203 and the light emitting element group 201 are predetermined intervals at which light (light beams) emitted from the light emitting element group 201 are imaged on the photosensitive drum 102. Therefore, in the focus adjustment operation, the attachment position of the rod lens array 203 is adjusted so that the distance between the rod lens array 203 and the light emitting element group 201 is a desired value. In the light intensity adjustment operation, each light emitting element is made to emit light individually and sequentially, and the drive current of each light emitting element is adjusted so that the light focused on the surface of the photosensitive drum 102 via the rod lens array 203 has a predetermined light intensity.

[0023] <Printed Circuit Board> Next, the configuration of the printed circuit board 202 on which the light-emitting element groups 201 are arranged will be described with reference to Figures 3A to 3C. Figure 3A shows the surface of the printed circuit board 202 opposite to the surface on which the light-emitting element groups 201 are mounted (referred to as the light-emitting element non-mounting surface). Figure 3B shows the surface of the printed circuit board 202 on which the light-emitting element groups 201 are mounted (referred to as the light-emitting element mounting surface). The printed circuit board 202 is a board on which components can be mounted on both the light-emitting element non-mounting surface shown in Figure 3A and the light-emitting element mounting surface shown in Figure 3B.

[0024] 3A, a connector 305 for electrically connecting the printed circuit board 202 to a control unit 401 is mounted on the surface of the printed circuit board 202 on which no light-emitting elements are mounted. The printed circuit board 202 is connected via the connector 305 to a signal line for receiving control signals for controlling the printed circuit board 202 from the control unit 401, and is also connected to a power supply line for supplying power for driving each light-emitting element array chip. Each light-emitting element array chip mounted on the printed circuit board 202 is driven upon receiving a control signal from the control unit 401 via the connector 305.

[0025] As shown in FIG. 3B , a light-emitting element group 201 is mounted on the light-emitting element mounting surface of the printed circuit board 202. The light-emitting element group 201 has a plurality of light-emitting element array chips (400-1 to 400-m) arranged in a staggered pattern in the longitudinal direction (main scanning direction). These light-emitting element array chips (400-1 to 400-m) are arranged in two staggered rows, and each row is arranged on the printed circuit board 202 along the longitudinal direction (the rotation direction of the photosensitive drum 102). In this way, in the exposure head 106a, odd-numbered light-emitting element array chips and even-numbered light-emitting element array chips are arranged alternately in the rotation direction of the photosensitive drum 102, as viewed from one end of the rotation axis of the photosensitive drum 102 in the rotation axis direction.

[0026] The light-emitting element array chips (400-1 to 400-m) have a plurality of light-emitting elements 602 arranged in the longitudinal direction at a predetermined resolution pitch. In this embodiment, the pitch between adjacent light-emitting elements 602 in the longitudinal direction is set to a pitch (approximately 21.16 μm) corresponding to a resolution of "1200 dpi." The light-emitting element group 201 has a plurality of light-emitting element array chips (400-1 to 400-m) arranged in the longitudinal direction, which enables image formation corresponding to an image width of the longitudinal length of the photosensitive drum 102 (for example, approximately 313 mm).

[0027] As shown in FIG. 3C , even at the boundary between the light-emitting element array chips (e.g., 400-2 and 400-3), the longitudinal pitch between one light-emitting element 602 and the other light-emitting element 602 is the pitch (approximately 21.16 μm) of a resolution of 1200 dpi. Furthermore, with respect to the rotation direction of the photosensitive drum 102, the two rows of light-emitting element array chips (400-2, 400-3) are arranged so that the distance (S in the figure) between their respective light-emitting points is approximately 105 μm (equivalent to five pixels at 1200 dpi). Furthermore, with respect to the longitudinal direction, the two rows of light-emitting element array chips (400-2, 400-3) are arranged so that the distance (L in the figure) between their respective light-emitting points is approximately 21.16 μm (equivalent to one pixel at 1200 dpi). Note that, in the present invention, the distances S and L between the light-emitting element array chips are not limited to the above values.

[0028] <Control Block> Next, the control system of the exposure unit 106 in the first embodiment will be described with reference to Fig. 4. Fig. 4 is a control block diagram showing the control system of the exposure unit 106 in the first embodiment. Note that, to make the explanation easier to understand, the control system of the black exposure unit 106 will be described as an example.

[0029] The control unit 401 is connected to the scanner unit 100, the image creating unit 103, the fixing unit 104, the supply / conveying unit 105, and the operation unit 114 (see FIG. 1 ), and controls each of these units to operate the image forming apparatus 1. When controlling the image creating unit 103, the control unit 401 controls the exposure unit 106 so as to form a desired electrostatic latent image on the photosensitive drum 102.

[0030] 4, the control unit 401 has an image data generation unit 403, an image data distribution unit 406, a CPU (Central Processing Unit) 405, and multiple image processing chips (407-1, 407-2). The CPU 405 is electrically connected to the image data generation unit 403, the image data distribution unit 406, the image processing chips (407-1, 407-2), a communication IF 413, and the printed circuit boards (202-1, 202-2) via a communication signal line 412. The CPU 405 is connected to the printed circuit board 202-1 of the exposure head 106a and the printed circuit board 202-2 of the exposure head 106b, so that control signals are transmitted from the control unit 401 to the printed circuit boards (202-1, 202-2).

[0031] The control unit 401 receives image data from the scanner unit 100 or an external device (e.g., a personal computer) (not shown) connected to the image forming apparatus 1. The image data generation unit 403 performs dithering processing on the received image data at a resolution instructed by the CPU 405, and generates image data for print output (referred to as print data for distinction). The CPU 405 instructs the image data generation unit 403 to perform dithering processing at a resolution of "2400 dpi" in the rotation direction (sub-scanning direction) of the photosensitive drum 102 and "1200 dpi" in the direction of the rotation axis of the photosensitive drum 102 (main scanning direction), for example.

[0032] The image data distribution unit 406 performs a data distribution operation to distribute the print data generated by the image data generation unit 403 to the image processing chips (407-1, 407-2) based on the lighting mode of the exposure unit 106 determined by the CPU 405 as described below. Upon receiving the print data distributed from the image data distribution unit 406, the image processing chips (407-1, 407-2) generate drive signals for driving the light-emitting element array chips (400-1, 400-2, 400-3, ... 400-m) and transmit the drive signals to the light-emitting element array chips (400-1 to 400-m).

[0033] The image processing chips (407-1, 407-2) have a chip data conversion unit 410 and a synchronization signal generation unit 409. The synchronization signal generation unit 409 generates a line synchronization signal at a generation cycle instructed by the CPU 405 and transmits the generated line synchronization signal to the chip data conversion unit 410. The chip data conversion unit 410 divides one line of printing data for each light-emitting element array chip (400-1 to 400-m), synchronizes it with the line synchronization signal generated by the synchronization signal generation unit 409, and transmits it to the printed circuit boards (202-1, 202-2). Specifically, the chip data conversion unit 410 transmits the line synchronization signal lsync, the clock signal clk, and the divided printing data "data_i" (i = 0 to m) to the printed circuit boards (202-1, 202-2).

[0034] The light-emitting element array chips (400-1 to 400-m) on the printed circuit boards (202-1, 202-2) control the light emission on / off of the light-emitting elements 602 based on the line synchronization signal "lsync", the clock signal "clk", and the print data "data_i" transmitted from the chip data conversion unit 410. As a result, in the exposure heads (106a, 106b), the plurality of light-emitting elements 602 are turned on / off appropriately according to the image data.

[0035] In this embodiment, in order to have the image data distribution unit 406 perform a data distribution operation, the CPU 405 executes a "lighting mode setting process" that determines the lighting mode of the exposure unit 106. As will be described in detail later, the CPU 405 determines, as the lighting mode of the exposure unit 106, either a first lighting mode in which all of the two exposure heads (106a, 106b) are turned on, or a second lighting mode in which one (part) of the two exposure heads (106a, 106b) is turned on. The "lighting mode setting process" executed by the CPU 405 will be described later (see FIG. 5B). In the exposure heads (106a, 106b) to be turned on, the control unit 401 appropriately turns on / off the light emitting elements 602 according to the image data as described above.

[0036] Each of the printed circuit boards (202-1, 202-2) has a temperature detection unit 411 capable of detecting the temperature of the printed circuit board (202-1, 202-2) as the temperature of each exposure head, and these temperature detection units 411 are connected to the CPU 405 via a communication signal line 412.

[0037] <Operation Mode> The control unit 401 can rotate the photosensitive drum 102 in either operation mode: a normal mode at a first speed, or a low-speed mode at a second speed slower than the first speed. In the electrophotographic image forming apparatus 1, the speed at which the recording material is conveyed by the sheet conveying belt 111 may be changed to improve the fixation of toner to the recording material, and the rotation speed of the photosensitive drum 102 is changed in accordance with such a change in the recording material conveying speed. In particular, high-speed machines for commercial printing can accommodate a wider range of basis weights by being equipped with a low-speed mode.

[0038] When forming an image on a recording material with a large basis weight, the rotation speed of the photosensitive drum 120 is reduced in accordance with the reduction in the conveyance speed of the recording material (low-speed mode). However, when the rotation speed of the photosensitive drum 120 is reduced, the exposure time of the photosensitive drum 120 by the exposure device 160 becomes longer. If the photosensitive drum 120 is exposed to light with the same amount of light as in normal mode, the accumulated amount of light may become excessive, resulting in excessive toner deposition during development. Therefore, the amount of light from the exposure device 160 must be adjusted depending on whether the mode is normal or low-speed. In this embodiment, the amount of light from the exposure device 160 is adjusted by turning on both of the multiple exposure heads (106a, 106b) in normal mode and turning on only one of the multiple exposure heads (106a, 106b) in low-speed mode.

[0039] <Lighting Mode Setting Process> The "lighting mode setting process" of this embodiment will be described using Figures 5A and 5B while also referring to Figures 1 and 4. Note that, for ease of understanding, the process related to the black exposure unit 106 will be described as an example, but the control unit 401 also simultaneously performs similar processes in parallel for the exposure units 106 of the other colors.

[0040] FIG. 5A is a flowchart showing the "image forming process" in the first embodiment. As shown in FIG. 5A, the control unit 401 receives an image forming job from the operation unit 114 (S1). Upon receiving the image forming job, the control unit 401 executes an "illumination mode setting process" to determine an illumination mode (S2). After completing the "illumination mode setting process," the control unit 401 starts forming an image on a recording material (S3). During image formation, the control unit 401 turns on one or both of the exposure heads (106a, 106b) of the exposure unit 106 in accordance with the determined illumination mode, thereby forming an electrostatic latent image on the photosensitive drum 120. That is, the control unit 401 can selectively execute a first illumination mode or a second illumination mode.

[0041] FIG. 5B is a flowchart showing the "lighting mode setting process" in the first embodiment. As described above, the lighting mode is determined after receiving an image formation job and before starting image formation on the recording material. As shown in FIG. 5B, the control unit 401 acquires information regarding the basis weight of the recording material (referred to as basis weight information) input by the user through operation of the operation unit 114 (S11). Based on the acquired basis weight information, the control unit 401 determines the operating mode for the recording material conveyance speed to be either the "normal mode" or the "low-speed mode" described above (S12). If the basis weight of the recording material is less than a predetermined value (threshold value), the control unit 401 determines that the recording material is plain paper and selects the "normal mode." On the other hand, if the basis weight of the recording material is equal to or greater than the predetermined value, the control unit 401 determines that the recording material is thick paper and selects the "low-speed mode."

[0042] Once the control unit 401 has determined the operating mode, it determines whether the operating mode is "low speed mode" or "normal mode" (S13). If the operating mode is "normal mode" (NO in S13), the control unit 401 sets the lighting mode information (sel) to "data 3" (S18) and proceeds to the processing of step S17. On the other hand, if the operating mode is "low speed mode" (YES in S13), the control unit 401 acquires temperature information from the temperature detection units 411 of each of the printed circuit boards (202-1, 202-2) (S14). Here, the temperature information acquired from the temperature detection unit 411 of the printed circuit board 202-1 is referred to as "tmp0," and the temperature information acquired from the temperature detection unit 411 of the printed circuit board 202-2 is referred to as "tmp1."

[0043] The control unit 401 compares the acquired temperature information "tmp0" and temperature information "tmp1" to determine which is larger (S15). If the temperature information "tmp0" is lower than the temperature information "tmp1", that is, if the temperature of printed circuit board 202-1 is lower than the temperature of printed circuit board 202-2 (YES in S15), the control unit 401 sets the lighting mode information (sel) to "data 1" (S16) and proceeds to the processing of step S17. If the temperature information "tmp1" is equal to or lower than the temperature information "tmp0", that is, if the temperature of printed circuit board 202-2 is equal to or lower than the temperature of printed circuit board 202-1 (NO in S15), the control unit 401 sets the lighting mode information (sel) to "data 2" (S19) and proceeds to the processing of step S17.

[0044] The control unit 401 sets the set lighting mode information (sel) in the image data distribution unit 406 (S17). If the lighting mode information (sel) is "data 3," the image data distribution unit 406 distributes print data to both image processing chips 407-1 and 407-2. If the lighting mode information (sel) is "data 1," the image data distribution unit 406 distributes print data only to image processing chip 407-1. If the lighting mode information (sel) is "data 2," the image data distribution unit 406 distributes print data only to image processing chip 407-2. As a result, in normal mode, both of the two exposure heads (106a, 106b) are lit, and in low-speed mode, the exposure head with the lower temperature of the printed circuit boards (202-1, 202-2) is lit. After the control unit 401 has finished setting the lighting mode information (sel) to the image data distribution unit 406, the "lighting mode setting process" ends.

[0045] As described above, in this embodiment, one or both of the exposure heads (106a, 106b) are turned on to form an electrostatic latent image on the photosensitive drum 120. In normal mode, both of the two exposure heads (106a, 106b) are turned on (first lighting mode), and in low-speed mode, one of the two exposure heads (106a, 106b) is turned on (second lighting mode). According to the present invention, in a configuration in which the photosensitive drum 120 can be exposed by multiple exposure heads (106a, 106b) arranged in the rotation direction of the photosensitive drum 120, an electrostatic latent image can be formed on the photosensitive drum 120 with an appropriate amount of light.

[0046] Furthermore, in this embodiment, during the second lighting mode, only the exposure head with the lower temperature of the printed circuit boards (202-1, 202-2) of the two exposure heads (106a, 106b) is turned on. That is, the exposure head with the higher temperature of the printed circuit boards (202-1, 202-2) is not turned on and is not used for exposure. Compared to the exposure head with a lower temperature, the exposure head with a higher temperature is more susceptible to thermal expansion of the printed circuit boards (202-1, 202-2) and rod lens array 203 due to heat generated by the light emission of the light-emitting elements 602, which in turn causes an electrostatic latent image to be improperly formed, resulting in image defects. In light of this, in this embodiment, by turning on only the exposure head with a lower temperature, it is possible to form an electrostatic latent image on the photosensitive drum 120 with an appropriate amount of light while suppressing the occurrence of image defects caused by an increase in the temperature of the exposure head.

[0047] Furthermore, in this embodiment, the image processing chips (407-1, 407-2) that generate drive signals for each light-emitting element array chip (400-1, 400-2, 400-3, ... 400-m) can have a simpler configuration than conventional chips, thereby reducing costs. That is, when both exposure heads are turned on, adjusting the light intensity requires a wide adjustment range for each exposure head (e.g., 40% to 110%). To adjust the light intensity, for example, a D / A conversion circuit can be used to control the current supplied to the light-emitting element 602, or a PWM signal can be used to control the light-emitting time of the light-emitting element 602. However, image processing chips (407-1, 407-2) that provide a wide adjustment range while maintaining sufficient adjustment resolution have complex signal circuit structures and are expensive. In contrast, in this embodiment, because one of the exposure heads is not turned on in low-speed mode, the adjustment range for the lit exposure head does not need to be as wide (e.g., 90% to 110%). Therefore, the image processing chips (407-1, 407-2) can have a simple configuration.

[0048] Second Embodiment Next, a second embodiment will be described. Fig. 6 is a control block diagram showing the control system of the exposure unit 106 in the second embodiment. As can be understood by comparing Fig. 6 with Fig. 4, the control system of the exposure unit 106 in the second embodiment differs from the control system of the exposure unit 106 in the first embodiment described above in that the control unit 401 has a counting unit 450, and the printed circuit boards (202-1, 202-2) have a head information storage unit 414 instead of the temperature detection unit 411. Note that in the second embodiment, components similar to those in the first embodiment described above are assigned the same reference numerals, and descriptions thereof will be simplified or omitted.

[0049] 6, the CPU 405 is electrically connected to the image data generation unit 403, the image data distribution unit 406, the image processing chips (407-1, 407-2), the communication IF 413, the count unit 450, and the printed circuit boards (202-1, 202-2) via a communication signal line 412. In addition, the head information storage unit 414 of the printed circuit boards (202-1, 202-2) is connected to the CPU 405 via the communication signal line 412.

[0050] The counting unit 450 counts the number of times each exposure head (106a, 106b) has been used (number of uses) as information regarding the lighting time of each exposure head (106a, 106b). The counting unit 450 counts the number of uses for the exposure heads (106a, 106b) that are turned on according to the operation mode each time an image formation job is acquired. The counting unit 450 counts the number of image formation jobs in which an electrostatic latent image is formed using the exposure head 106a, and stores this as the number of uses in the head information storage unit 414 of the printed circuit board 202-1. The counting unit 450 also counts the number of image formation jobs in which an electrostatic latent image is formed using the exposure head 106b, and stores this as the number of uses in the head information storage unit 414 of the printed circuit board 202-2. In this way, the head information storage unit 414 stores the number of uses for each exposure head (106a, 106b) counted by the counting unit 450.

[0051] Next, the "lighting mode setting process" in the second embodiment will be described using FIG. 7 with reference to FIG. 6 . FIG. 7 is a flowchart showing the lighting mode setting process in the second embodiment. In the second embodiment, as in the first embodiment, both exposure heads (106a, 106b) are turned on in normal mode, and only one of the exposure heads (106a, 106b) is turned on in low-speed mode. However, in low-speed mode, the exposure head (106a, 106b) that has been used less frequently is turned on as appropriate. Note that in the "lighting mode setting process" in the second embodiment described below, processes similar to the "lighting mode setting process" in the first embodiment described above (see FIG. 5B) are assigned the same step numbers, and their descriptions will be simplified or omitted.

[0052] As shown in FIG. 7, the control unit 401 acquires basis weight information (S11) and determines the operating mode as either the normal mode or the low-speed mode based on the acquired basis weight information (S12). If the operating mode is the "normal mode" (NO in S13), the control unit 401 sets the lighting mode information (sel) to "data 3" (S18). In this case, the counting unit 450 adds "1" to the usage count "cnt0" in the head information storage unit 414 of the printed circuit board 202-1, and also adds "1" to the usage count "cnt1" in the head information storage unit 414 of the printed circuit board 202-2. On the other hand, if the operating mode is the "low-speed mode" (YES in S13), the control unit 401 acquires the usage count from the head information storage unit 414 of each printed circuit board (202-1, 202-2) (S21).

[0053] The control unit 401 compares the acquired usage counts "cnt0" and "cnt1" to determine which is larger (S22). If the usage count "cnt0" is smaller than the usage count "cnt1," that is, if the number of image formation jobs in which electrostatic latent images were formed using the exposure head 106a is smaller than the number of image formation jobs in which electrostatic latent images were formed using the exposure head 106b (YES in S22), the control unit 401 sets the lighting mode information (sel) to "data 1" (S23). In this case, the counting unit 450 adds "1" to the usage count "cnt0" in the head information storage unit 414 of the printed circuit board 202-1 (S24).

[0054] On the other hand, if the number of uses "cnt1" is equal to or less than the number of uses "cnt0", that is, if the number of image formation jobs in which electrostatic latent images were formed using the exposure head 106b is equal to or less than the number of image formation jobs in which electrostatic latent images were formed using the exposure head 106a (NO in S22), the control unit 401 sets the lighting mode information (sel) to "data 2" (S25). In this case, the counting unit 450 adds "1" to the number of uses "cnt1" in the head information storage unit 414 of the printed circuit board 202-2 (S26).

[0055] The control unit 401 sets the set lighting mode information (sel) in the image data distribution unit 406 (S17). If the lighting mode information (sel) is "data 3," the image data distribution unit 406 distributes print data to both image processing chips 407-1 and 407-2. If the lighting mode information (sel) is "data 1," the image data distribution unit 406 distributes print data only to image processing chip 407-1. If the lighting mode information (sel) is "data 2," the image data distribution unit 406 distributes print data only to image processing chip 407-2. As a result, in normal mode, both of the two exposure heads (106a, 106b) are lit, and in low-speed mode, the exposure head that has been used less frequently is lit. After the control unit 401 has finished setting the lighting mode information (sel) in the image data distribution unit 406, the "lighting mode setting process" ends.

[0056] As described above, the second embodiment also has the advantage that, in a configuration in which the photosensitive drum 120 can be exposed by multiple exposure heads (106a, 106b) arranged in the rotational direction of the photosensitive drum 120, an electrostatic latent image can be formed on the photosensitive drum 120 with an appropriate amount of light. Furthermore, in the second embodiment, the exposure head that has been used less frequently is turned on in the second lighting mode. This makes it possible to suppress bias in the cumulative light emission time among the multiple exposure heads (106a, 106b), thereby achieving a longer life for the exposure heads.

[0057] [Third Embodiment] Next, a third embodiment will be described. Fig. 8 is a flowchart showing a lighting mode setting process in the third embodiment. Note that, in the "lighting mode setting process" in the third embodiment described below, processes similar to the "lighting mode setting process" in the first embodiment described above (see Fig. 5B) are assigned the same step numbers, and descriptions thereof will be simplified or omitted.

[0058] In the third embodiment, the counting unit 450 counts the number of sheets of recording material on which an electrostatic latent image is formed using each exposure head (106a, 106b) as information regarding the lighting time of each exposure head (106a, 106b). The counting unit 450 counts the number of sheets of recording material for the exposure heads (106a, 106b) that are turned on according to the operating mode each time an image formation job is acquired. The counting unit 450 counts the number of sheets of recording material on which an electrostatic latent image is formed using the exposure head 106a, and stores the cumulative number in the head information storage unit 414 of the printed circuit board 202-1. The counting unit 450 also counts the number of sheets of recording material on which an electrostatic latent image is formed using the exposure head 106b, and stores the cumulative number in the head information storage unit 414 of the printed circuit board 202-2.

[0059] As shown in FIG. 8, the control unit 401 acquires basis weight information (S11) and determines the operating mode as either the normal mode or the low-speed mode based on the acquired basis weight information (S12). If the control unit 401 is in the "normal mode" (NO in S13), it sets the lighting mode information (sel) to "data 3" (S18). In this case, the counting unit 450 adds the counted number of sheets of recording material to the cumulative number "cnt0" in the head information storage unit 414 of the printed circuit board 202-1 to update it, and also adds the counted number of sheets of recording material to the cumulative number "cnt1" in the head information storage unit 414 of the printed circuit board 202-2 to update it. On the other hand, if the operating mode is the "low-speed mode" (YES in S13), the control unit 401 acquires the cumulative number of sheets from the head information storage unit 414 of each printed circuit board (202-1, 202-2) (S31). Here, the cumulative number acquired from the head information storage unit 414 of the printed circuit board 202-1 is "cnt0", and the cumulative number acquired from the head information storage unit 414 of the printed circuit board 202-2 is "cnt1".

[0060] The control unit 401 compares the acquired cumulative sheet count "cnt0" with the cumulative sheet count "cnt1" to determine which is larger (S32). If the cumulative sheet count "cnt0" is smaller than the cumulative sheet count "cnt1," that is, if the cumulative number of sheets of recording material on which electrostatic latent images are formed using the exposure head 106a is smaller than the cumulative number of sheets of recording material on which electrostatic latent images are formed using the exposure head 106b (YES in S32), the control unit 401 sets the lighting mode information (sel) to "Data 1" (S33). In this case, the counting unit 450 updates the cumulative sheet count "cnt0" in the head information storage unit 414 of the printed circuit board 202-1 by adding the number of counted sheets of recording material (S34). On the other hand, if the cumulative number "cnt1" is equal to or less than the cumulative number "cnt0," that is, if the cumulative number of recording materials on which electrostatic latent images are formed using exposure head 106b is equal to or less than the cumulative number of recording materials on which electrostatic latent images are formed using exposure head 106a (NO in S32), the control unit 401 sets the lighting mode information (sel) to "data 2" (S35). In this case, the counting unit 450 adds the number of counted recording materials to the cumulative number "cnt1" in the head information storage unit 414 of the printed circuit board 202-2 to update it (S36).

[0061] The control unit 401 sets the set lighting mode information (sel) in the image data distribution unit 406 (S17). If the lighting mode information (sel) is "Data 3," the image data distribution unit 406 distributes print data to both image processing chips 407-1 and 407-2. If the lighting mode information (sel) is "Data 1," the image data distribution unit 406 distributes print data only to image processing chip 407-1. If the lighting mode information (sel) is "Data 2," the image data distribution unit 406 distributes print data only to image processing chip 407-2. As a result, in normal mode, both of the two exposure heads (106a, 106b) are lit, and in low-speed mode, the exposure head (106a, 106b) that has printed the fewer cumulative sheets of recording material on which electrostatic latent images are formed is lit. After setting the lighting mode information (sel) in the image data distribution unit 406, the control unit 401 terminates the "lighting mode setting process."

[0062] As described above, the third embodiment also has the advantage of being able to form an electrostatic latent image on the photosensitive drum 120 with an appropriate amount of light when the photosensitive drum 120 can be exposed by multiple exposure heads (106a, 106b) arranged in the rotational direction of the photosensitive drum 120. Furthermore, in the third embodiment, the exposure head that has formed an electrostatic latent image on a smaller cumulative number of sheets of recording material in the second lighting mode is turned on. This makes it possible to suppress bias in the cumulative light emission time among the multiple exposure heads (106a, 106b), thereby achieving a longer life for the exposure heads. Compared to the second embodiment, the third embodiment makes it possible to suppress bias in the cumulative light emission time among the multiple exposure heads (106a, 106b) and achieve equalization with higher accuracy.

[0063] [Fourth Embodiment] Next, a fourth embodiment will be described. Figure 9 is a control block diagram showing the control system of the exposure unit 106 in the fourth embodiment. As can be understood by comparing Figure 9 with Figure 6, the control system of the exposure unit 106 in the fourth embodiment differs from the control system of the exposure unit 106 in the second embodiment in that the image processing chips (407-1, 407-2) have an image data counting unit 415, and the control unit 401 does not have a counting unit 450. Note that in the fourth embodiment, the same components as those in the second embodiment described above are assigned the same reference numerals, and their description will be simplified or omitted.

[0064] In the fourth embodiment, the image data counting unit 415 counts the number of pixels formed by each exposure head (106a, 106b) as information regarding the lighting time of each exposure head (106a, 106b). As shown in FIG. 9, the image data counting unit 415 is provided between the image data distribution unit 406 and the chip data conversion unit 410. The image data counting unit 415 counts the sum of the data values ​​of the printing data distributed by the image data distribution unit 406 each time an image formation job is acquired. The sum of the data values ​​of the printing data for one image formation job represents the number of pixels formed on the photosensitive drum 120 during one image formation job.

[0065] The sum of the data values ​​counted by the image data counting unit 415 is transmitted to the CPU 405 via the communication signal line 412. The CPU 405 stores a cumulative value (referred to as a cumulative data count value) obtained by adding the sum of the data values ​​up to the previous image formation job and the sum of the data values ​​in the current image formation job in the head information storage unit 414. That is, the CPU 405 calculates the sum of the cumulative data count value acquired from the head information storage unit 414 of the printed circuit board 202-1 and the sum of the data values ​​in one image formation job acquired from the image data counting unit 415 of the image processing chip 407-1, and stores this as a cumulative data count value in the head information storage unit 414 of the printed circuit board 201-1. Similarly, the CPU 405 calculates the sum of the cumulative data count value acquired from the head information storage unit 414 of the printed circuit board 202-2 and the total sum of the data values ​​in one image formation job acquired from the image data count unit 415 of the image processing chip 407-1, and stores this as the cumulative data count value in the head information storage unit 414 of the printed circuit board 202-2. In this way, the cumulative number of pixels is stored in the head information storage unit 414.

[0066] Next, the "lighting mode setting process" in the fourth embodiment will be described using Figures 10A and 10B while also referring to Figure 9. Figure 10A is a flowchart showing the "image formation process" in the fourth embodiment. Figure 10B is a flowchart showing the "lighting mode setting process" in the fourth embodiment. Note that, in the "image formation process" and "lighting mode setting process" in the fourth embodiment described below, processes similar to the "image formation process" and "lighting mode setting process" in the first embodiment described above (see Figures 5A and 5B) are assigned the same step numbers, and their descriptions will be simplified or omitted.

[0067] As shown in FIG. 10A , the control unit 401 receives a command to start an image formation job from the operation unit 114 (S1). Upon receiving the command, the control unit 401 executes a lighting mode setting process to determine a lighting mode (S2). After the lighting mode setting process is completed, the control unit 401 starts forming an image on the recording material (S3). At this time, the control unit 401 forms an electrostatic latent image on the photosensitive drum 120 using one or both of the exposure heads (106a, 106b) of the exposure unit 106 in accordance with the determined lighting mode. After the image formation process, the control unit 401 updates the cumulative data count values ​​stored in the head information storage units 414 of the printed circuit boards (202-1, 202-2) in accordance with the operation mode (S4).

[0068] 10B, the control unit 401 acquires basis weight information (S11) and determines the operating mode as either the normal mode or the low-speed mode based on the acquired basis weight information (S12). If the operating mode is the "normal mode" (NO in S13), the control unit 401 sets the lighting mode information (sel) to "data 3" (S18). On the other hand, if the operating mode is the "low-speed mode" (YES in S13), the control unit 401 acquires the cumulative data count value from the head information storage unit 414 of each printed circuit board (202-1, 202-2) (S41). Here, the cumulative data count value acquired from the head information storage unit 414 of printed circuit board 202-1 is set to "pcnt0," and the cumulative data count value acquired from the head information storage unit 414 of printed circuit board 202-2 is set to "pcnt1."

[0069] The control unit 401 compares the acquired cumulative data count value "pcnt0" with the cumulative data count value "pcnt1" to determine which is larger (S42). If the cumulative data count value "pcnt0" is smaller than the cumulative data count value "pcnt1," that is, if the number of pixels on which an electrostatic latent image is formed using exposure head 106a is smaller than the number of pixels on which an electrostatic latent image is formed using exposure head 106b (YES in S42), the control unit 401 sets the lighting mode information (sel) to "Data 1" (S43). On the other hand, if the cumulative data count value "pcnt1" is equal to or smaller than the cumulative data count value "pcnt0," that is, if the number of pixels on which an electrostatic latent image is formed using exposure head 106b is smaller than the number of pixels on which an electrostatic latent image is formed using exposure head 106a (NO in S42), the control unit 401 sets the lighting mode information (sel) to "Data 2" (S44).

[0070] The control unit 401 sets the set lighting mode information (sel) in the image data distribution unit 406 (S17). If the lighting mode information (sel) is "data 3," the image data distribution unit 406 distributes print data to both image processing chips 407-1 and 407-2. If the lighting mode information (sel) is "data 1," the image data distribution unit 406 distributes print data only to image processing chip 407-1. If the lighting mode information (sel) is "data 2," the image data distribution unit 406 distributes print data only to image processing chip 407-2. As a result, in normal mode, both of the two exposure heads (106a, 106b) are lit, and in low-speed mode, the exposure head (106a, 106b) that forms the fewer pixels of an electrostatic latent image is lit. After setting the lighting mode information (sel) in the image data distribution unit 406, the control unit 401 ends the "lighting mode setting process."

[0071] As described above, the fourth embodiment also has the advantage of being able to form an electrostatic latent image on the photosensitive drum 120 with an appropriate amount of light when the photosensitive drum 120 can be exposed by multiple exposure heads (106a, 106b) arranged in the rotational direction of the photosensitive drum 120. Furthermore, in the fourth embodiment, the exposure head that forms the electrostatic latent image with fewer pixels is turned on in the second lighting mode. This makes it possible to suppress bias in the cumulative light emission time among the multiple exposure heads (106a, 106b), thereby achieving a longer life for the exposure heads. In the fourth embodiment, it is possible to suppress bias in the cumulative light emission time among the multiple exposure heads (106a, 106b) and achieve equalization with greater accuracy than in the second and third embodiments.

[0072] Other Embodiments In the above-described embodiment, the printer has two operating modes, a "normal mode" and a "low-speed mode." However, the printer may have three or more operating modes. For example, if the printer has three operating modes, a "normal mode," a "low-speed mode," and a "high-speed mode" faster than the normal mode, the control unit 401 may determine the operating mode by comparing the basis weight of the recording material with two different predetermined values ​​(threshold values). In this case, it is preferable to have three exposure heads. The photosensitive drum 120 may be exposed by turning on all three exposure heads in the "high-speed mode," turning on two exposure heads in the "normal mode," and turning on one exposure head in the "low-speed mode." Furthermore, when turning on one or two exposure heads, it is preferable to turn on one or two of the three exposure heads in order of the shortest cumulative lighting time based on information about the lighting time of each exposure head.

[0073] In the above-described embodiment, the image forming apparatus 1 is a direct transfer type in which a toner image is directly transferred from the photosensitive drum 102 that rotates while carrying the toner image to a recording material, but the present invention is not limited to this. The above-described embodiment can also be applied to an image forming apparatus of an intermediate transfer type in which a toner image is primarily transferred from the photosensitive drum of each color to an intermediate transfer body, and then the toner image is secondarily transferred from the intermediate transfer body to a recording material.

[0074] The image forming apparatus can be used in electrophotographic image forming apparatuses such as printers, copiers, facsimiles, and multifunction machines, and is particularly suitable for use in those equipped with an exposure unit having multiple exposure heads. The present invention is not limited to the above-described embodiment, and various changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, in order to clarify the scope of the present invention, the following claims are appended.

[0075] 1...image forming apparatus, 102...photosensitive member (photosensitive drum), 106...exposure section (exposure device), 106a to 106h...exposure heads, 400-1 to 400-m...light emitting element array chips, 401...control section, 411...temperature detection section, 415...counting section (image data counting section), 450...counting section

Claims

1. An image forming device that forms a toner image on a recording material, comprising: a rotating photosensitive member; and an exposure unit having a plurality of exposure heads arranged in a row in the rotation direction of the photosensitive member, and capable of exposing the photosensitive member by irradiating light onto the surface of the photosensitive member to form an electrostatic latent image, wherein the exposure heads are arranged along the rotation axis direction of the photosensitive member and have a plurality of light-emitting elements that emit light to irradiate the surface of the photosensitive member, and the exposure unit exposes the photosensitive member in either a first lighting mode in which all of the plurality of exposure heads are lit to expose the photosensitive member, or a second lighting mode in which some of the plurality of exposure heads are lit to expose the photosensitive member.

2. The image forming apparatus according to claim 1, wherein the plurality of exposure heads are arranged so that, in the rotation direction, the downstream exposure head can irradiate light onto the exposure area of ​​the photosensitive member exposed by the upstream exposure head, thereby overlapping the exposure area.

3. An image forming apparatus as described in claim 1, further comprising a control unit that controls the exposure unit, wherein the control unit controls the exposure unit to the first lighting mode when the photosensitive body rotates at a first speed, and controls the exposure unit to the second lighting mode when the photosensitive body rotates at a second speed slower than the first speed.

4. The image forming apparatus according to claim 3, further comprising a temperature detection unit for detecting the temperature of each exposure head, and wherein the control unit turns on the exposure head with the lowest temperature among the plurality of exposure heads in the second lighting mode.

5. The image forming apparatus according to claim 3, wherein the control unit, in the second lighting mode, turns on the exposure head with the shortest cumulative lighting time among the plurality of exposure heads based on information regarding the lighting time of each exposure head.

6. An image forming apparatus according to claim 5, further comprising a counting unit for counting the number of times each exposure head has been used by lighting up the exposure head, and wherein the control unit lights up the exposure head that has been used least frequently among the plurality of exposure heads in the second lighting mode.

7. An image forming apparatus according to claim 5, further comprising a counting unit for counting the number of sheets of recording material on which an electrostatic latent image has been formed using each exposure head, and wherein the control unit, in the second lighting mode, lights up an exposure head among the plurality of exposure heads that has formed the smallest cumulative number of sheets of recording material.

8. The image forming apparatus according to claim 5, further comprising a counting unit for counting the number of pixels formed by each exposure head, and wherein the control unit, in the second lighting mode, lights up an exposure head of the plurality of exposure heads that has the smallest number of pixels.

Images