Print head and image forming apparatus

Abstract

The present invention provides a print head and image forming apparatus that can prevent step formation in printed images while reducing the number of drive circuits and inrush current. [Solution] The print head 12a includes a plurality of light-emitting elements 41 that expose a photoreceptor, a signal output unit 51 that outputs drive signals with different phases, and a drive unit 52 that causes each of the plurality of light-emitting elements 41 to emit light individually based on these drive signals. The plurality of light-emitting elements 41 divide the array of light-emitting elements arranged in the main scanning direction into n light-emitting element groups G, and are driven by the drive signal such that a phase difference T1 occurs in the light emission timing for each light-emitting element group G. The light-emitting element groups G are arranged such that there is a step difference Ydiff between groups in the sub-scanning direction for each light-emitting element group.

Description

Technical Field

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[0001] The present disclosure relates to a print head having a plurality of light emitting elements and an image forming apparatus.

Background Art

[0002] Conventionally, an electrophotographic image forming apparatus that forms an electrostatic latent image on a photoreceptor using laser light or the like and forms an image on paper through steps of developing, transferring, and fixing this electrostatic latent image has been widely used. In recent years, in an exposure apparatus that exposes a photoreceptor, a print head of a linear light source in which point light sources such as light emitting elements are linearly arranged may be used. In such a print head, there may be provided light emitting elements equivalent to tens of thousands of pixels.

[0003] In a print head, in order to cause all light emitting elements to emit light simultaneously, the same number of DA converter circuits as the light emitting elements are required, increasing the number of parts. Further, when attempting to simultaneously perform emission control (lighting and extinguishing) on tens of thousands of light emitting elements, there are problems such as the need to drive a large amount of wiring capacitance and bonding capacitance and an increase in inrush current.

[0004] Patent Document 1 discloses a print head that divides a light emitting element group into a plurality of light emitting element groups and performs emission control for each light emitting element group, thereby reducing the drive circuit and reducing the inrush current.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] The print head described in Patent Document 1 divides the group of light-emitting elements into multiple groups of light-emitting elements along the main scanning direction, and the light emission control is performed with a time delay for each group of light-emitting elements. In this case, the photoreceptor drum continues to rotate, and as a result, steps in the pixel rows occur in the electrostatic latent image (and printed image) on the photoreceptor drum in the areas between the groups of light-emitting elements. Such steps are particularly noticeable as vertical lines in the halftone areas, degrading the quality of the printed image.

[0007] This disclosure has been made in view of the above-mentioned problems, and aims to provide a print head and image forming apparatus that can prevent steps in printed images while reducing the number of drive circuits and inrush current. [Means for solving the problem]

[0008] To solve the above problems, the print head of the present disclosure comprises a plurality of light-emitting elements that expose a photoreceptor, a signal output unit that outputs drive signals with different phases, and a drive unit that causes each of the plurality of light-emitting elements to emit light individually based on the drive signals, wherein the plurality of light-emitting elements are characterized in that a row of light-emitting elements arranged in the main scanning direction is divided into n light-emitting element groups, and each of the light-emitting element groups is driven by the drive signals such that there is a phase difference in the light emission timing, and each of the light-emitting element groups is arranged such that there is a step difference between groups in the sub-scanning direction.

[0009] Furthermore, the print head may have multiple light-emitting elements formed from organic EL diodes that constitute the pixels of the organic EL panel.

[0010] Furthermore, the image forming apparatus of this disclosure is an image forming apparatus having the print head described above, characterized in that, when the step difference between groups is Ydiff, the phase difference is T1, and the surface velocity of the photoreceptor exposed to the print head is V, the condition Ydiff = V × T1 is satisfied.

[0011] Furthermore, the image forming apparatus described above can be configured such that the surface velocity V is variable, and when the surface velocity V changes, the signal output unit changes the phase difference T1 to control the system so that the condition Ydiff = V × T1 is satisfied. [Effects of the Invention]

[0012] The print head and image forming apparatus of this disclosure have the effect of eliminating pixel row steps in the printed image by having the timing difference of light emission for each light-emitting element group and the step difference between groups cancel each other out. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view of an image forming apparatus according to an embodiment of the present disclosure. [Figure 2] This is a schematic diagram of an image forming apparatus according to an embodiment of the present disclosure. [Figure 3] This is a plan view showing an example of the arrangement of light-emitting elements in a print head. [Figure 4] This is a schematic diagram showing an example of a print head circuit block. [Figure 5] This is a timing chart showing an example of printhead light emission control. [Figure 6] This is an explanatory diagram showing the relationship between the light-emitting element group and the pixel arrangement of the electrostatic latent image formed by the exposure of the light-emitting element group in a conventional print head configuration. [Figure 7] This is an explanatory diagram showing the relationship between the light-emitting element group and the pixel arrangement of the electrostatic latent image formed by exposure of the light-emitting element group in the print head of the embodiment of the present disclosure. [Modes for carrying out the invention]

[0014] [First Embodiment] Embodiments of this disclosure will be described in detail below with reference to the drawings. Figure 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment of this disclosure.

[0015] The image forming apparatus 100 is a multifunctional device having a copy function, a scanner function, a facsimile function, and a printer function, and transmits the image of a document read by the image reading device 130 to the outside, or forms the image of a document read by the image reading device 130 or an image received from the outside in color or monochrome on a recording medium such as paper.

[0016] Above the image reading device 130, a document conveying device 110 that is supported so as to be openable and closable is provided. The document conveying device 110 conveys one or a plurality of documents one by one in order. The image reading device 130 reads the document placed on the document placement table 130a by scanning the scanning optical system 130b, or reads the document conveyed by the document conveying device 110 to generate image data.

[0017] The image forming apparatus 100 is provided with a fixing device 1, a developing device 2, a photosensitive drum 3 (an example of a photoreceptor), a drum cleaning device 4, a charger 5, an intermediate transfer belt device 7, a secondary transfer device 11, an exposure device 12, a paper feeding unit 18, and the like.

[0018] In the image forming apparatus 100, image data corresponding to a color image using each color of black (K), cyan (C), magenta (M), and yellow (Y), or a monochrome image using a single color (for example, black) is handled. The image forming apparatus 100 is provided with four developing devices 2, photosensitive drums 3, drum cleaning devices 4, and chargers 5 for forming four types of toner images, and each is associated with black, cyan, magenta, and yellow, respectively, to constitute four image stations Pa, Pb, Pc, and Pd.

[0019] The charger 5 uniformly charges the surface of the photosensitive drum 3 to a predetermined potential. The exposure device 12 has a print head 12a facing the surface of the photosensitive drum 3, and exposes the surface of the photosensitive drum 3 to form an electrostatic latent image. The developing device 2 develops the electrostatic latent image on the surface of the photosensitive drum 3 to form a toner image on the surface of the photosensitive drum 3. The drum cleaning device 4 removes and collects the residual toner on the surface of the photosensitive drum 3. By the above-described series of operations, toner images of each color are formed on the surface of each photosensitive drum 3. Note that the distance between the photosensitive drum 3 and the print head 12a may be appropriately set according to the resolution of the electrostatic latent image and the light amount of the print head 12a. Details of the print head 12a will be described later.

[0020] The intermediate transfer belt device 7 includes an intermediate transfer roller 6, an endless intermediate transfer belt 71, an intermediate transfer driving roller 72, an intermediate transfer driven roller 73, and a cleaning device 9. Four intermediate transfer rollers 6 corresponding to each color are provided inside the intermediate transfer belt 71 so as to form four types of toner images corresponding to each color. The intermediate transfer roller 6 transfers the toner images of each color formed on the surface of the photosensitive drum 3 to the circumferentially moving intermediate transfer belt 71.

[0021] The intermediate transfer belt 71 is stretched between the intermediate transfer driving roller 72 and the intermediate transfer driven roller 73. In the image forming apparatus 100, the toner images of each color formed on the surface of each photosensitive drum 3 are sequentially transferred and overlapped to form a color toner image on the surface of the intermediate transfer belt 71. The cleaning device 9 removes and collects the waste toner remaining on the surface of the intermediate transfer belt 71 without being transferred to the paper.

[0022] The secondary transfer device 11 sandwiches and conveys the paper conveyed through the paper conveyance path 21 at the transfer nip portion TN between the secondary transfer roller 11a and the intermediate transfer belt 71. When the paper passes through the transfer nip portion TN, the toner image on the surface of the intermediate transfer belt 71 is transferred and the paper is conveyed to the fixing device 1.

[0023] The fixing device 1 includes a fixing belt 31 and a pressure roller 32 that rotate around an axis. The fixing device 1 inserts the paper on which the toner image has been transferred into the nip portion N between the fixing belt 31 and the pressure roller 32, heats and pressurizes it, and fixes the toner image to the paper. Although not shown in Figure 1, the fixing device 1 may have components other than the fixing belt 31 and the pressure roller 32.

[0024] The paper feeding unit 18 is equipped with a paper feeding cassette for loading recording media (paper) used for image formation and is located below the exposure unit 12. The paper is pulled out of the paper feeding unit 18 by the pickup roller 16 and transported to the paper transport path 21. The paper transported to the paper transport path 21 passes through the secondary transfer unit 11 and the fixing unit 1, and is then discharged to the output tray 19 by the discharge roller 17.

[0025] The paper transport path 21 is equipped with a transport roller 13, a registration roller 14, and an ejection roller 17. The transport roller 13 facilitates the transport of the paper. The registration roller 14 transports the paper at a speed equal to the process speed at which the image is formed on the paper. This registration roller 14 is located between the paper feed unit 18 and the secondary transfer device 11 and adjusts the timing of the paper transport so that the toner image is transferred to the paper by the secondary transfer device 11. For example, the registration roller 14 holds the paper transported from the paper feed unit 18 and waits (stops temporarily), then starts transporting the paper at a constant speed in synchronization with the secondary transfer device 11.

[0026] When image formation is to be performed on the back side of the paper as well as the front side, the paper transport direction is changed by the discharge roller 17 and the paper is transported to the inversion transport path 22. In the inversion transport path 22, the paper is guided to the registration roller 14 with its front and back sides reversed by the inversion transport roller 15. The image forming apparatus 100 forms an image on the back side of the paper guided to the registration roller 14 in the same way as the front side and discharges it to the output tray 19.

[0027] Figure 2 is a schematic diagram of the image forming apparatus 100. Note that Figure 2 shows only a part of the image forming apparatus 100, and other components not shown in Figure 2 may be included as appropriate.

[0028] The print head 12a has a plurality of light-emitting elements 41 that expose the photosensitive drum 3 to form dots on the drum surface. The light-emitting elements 41 are, for example, organic light-emitting diodes (OLEDs) or LEDs. That is, when the light-emitting elements 41 are formed from organic light-emitting diodes, the print head 12a is provided as an organic light-emitting panel in which pixels are composed of organic light-emitting diodes. The signal output unit 51 outputs a plurality of drive signals with different phases. The drive unit 52 is, for example, a drive circuit that causes each of the plurality of light-emitting elements 41 to emit light individually based on the drive signals. The image forming apparatus 100 may be equipped with a control unit that controls the operation of each part.

[0029] In the exposure apparatus 12, four print heads 12a are provided, each facing one of the four photoreceptor drums 3. Note that the exposure apparatus 12 may be provided independently for each photoreceptor drum 3, and it is sufficient that a print head 12a is provided corresponding to each of the four photoreceptor drums 3. Since the four print heads 12a have substantially the same configuration, the following explanation will use one print head 12a as an example. Although not shown in the diagram, an optical component such as a lens may be placed between the photoreceptor drum 3 and the print head 12a, so that the light emitted from the light-emitting element 41 forms an image on the surface of the photoreceptor drum 3. Furthermore, a spacer or the like may be provided to maintain a certain distance between the photoreceptor drum 3 and the print head 12a.

[0030] In the image forming apparatus 100, the axial direction of the photoreceptor drum 3 along its rotation axis is parallel to the width direction of the paper on which the image is formed, and the photoreceptor drum 3 is configured to rotate around the axis of the rotation axis. The print head 12a is a rectangular flat plate, with its longitudinal direction (main scanning direction X) corresponding to the axial direction of the photoreceptor drum 3, and its short direction (sub-scanning direction Y) corresponding to the rotation direction of the photoreceptor drum 3.

[0031] Figure 3 is a plan view showing an example of the arrangement of light-emitting elements 41 in the print head 12a in this embodiment. Note that the print head 12a in Figure 3 shows an example of arrangement when the light-emitting elements 41 are arranged in a single stage. However, the print head 12a is not limited to a single-stage arrangement, and may have multiple rows of light-emitting elements arranged in multiple stages along the sub-scanning direction Y (multi-stage arrangement). In a multi-stage print head 12a, multiple light-emitting elements 41 can be exposed in the same pixel area in the electrostatic latent image formed on the photoreceptor drum 3, thereby increasing the exposure amount. For this reason, a multi-stage arrangement of light-emitting elements 41 is suitable for a print head 12a using an OLED, which has a smaller light emission amount compared to semiconductor lasers or LEDs.

[0032] As shown in Figure 3, the print head 12a has a row of light-emitting elements 41 arranged along the main scanning direction. In the main scanning direction X, the width M of the light-emitting elements 41 is smaller than the pitch Ph between the light-emitting elements 41 due to the separation of the light-emitting elements 41 themselves and the clearance of the wiring. For example, if the resolution of the image forming apparatus 100 is 1200 dpi, the width M is 19 μm and the pitch Ph is 21 μm.

[0033] The array of light-emitting elements in the print head 12a is divided into multiple (e.g., n) light-emitting element groups G1 to Gn (collectively referred to as light-emitting element group G if not distinguished). Each light-emitting element group G contains a predetermined number of light-emitting elements arranged consecutively, and the number of light-emitting elements 41 included in each light-emitting element group G is the same (e.g., m elements). Furthermore, all light-emitting elements 41 included in the same light-emitting element group G are positioned at the same location in the sub-scanning direction Y. On the other hand, the arrangement positions of different light-emitting element groups G are offset in the sub-scanning direction Y. In this embodiment, the arrangement positions of light-emitting element groups G1 to Gn are shifted downstream in the sub-scanning direction Y. As a result, in two adjacent light-emitting element groups G in the main scanning direction X, an inter-group step difference Ydiff occurs in the sub-scanning direction Y. The inter-group step difference Ydiff is set to be the same size between any two light-emitting element groups G. Furthermore, the inter-group step difference Ydiff satisfies the condition Ydiff ≤ Pv / n. Here, Pv is the pitch of one pixel in the resolution of the sub-scanning direction Y.

[0034] In the print head 12a, the light emission timing is staggered for each light-emitting element group G. Specifically, the light-emitting elements are emitted in the order of G1 to Gn (in other words, in the order of the light-emitting element group G located on the upstream side in the sub-scanning direction Y). By controlling the light emission for each light-emitting element group G in the print head 12a, the inrush current can be reduced compared to when all light-emitting elements 41 are emitted simultaneously.

[0035] Furthermore, in the print head 12a, a step difference Ydiff is provided between different light-emitting element groups G in the sub-scanning direction. As a result, although the details will be described later, the timing difference of light emission for each light-emitting element group G and the step difference Ydiff cancel each other out, making it possible to form a step-free image (eliminate the step) in the electrostatic latent image on the photoreceptor drum 3 and in the printed image.

[0036] Figure 4 is a schematic diagram showing an example of the circuit block of the print head 12a. Note that the circuit block in Figure 4 shows an example corresponding to a single-stage arrangement of light-emitting elements, and the light-emitting element arrangement is divided into n light-emitting element groups G1, G2, ... Gn.

[0037] As shown in Figure 4, the print head 12a includes a D / A conversion circuit 511, a sampling-hold timing generation circuit 512, and a light emission timing generation circuit 513 as the signal output unit 51 in Figure 2. Horizontal synchronization signals and image data are input to the signal output unit 51 from the image processing controller of the image forming apparatus 100.

[0038] Furthermore, the print head 12a has a DRV circuit 521 and a switch 522 as the drive unit 52 in Figure 2. The same number of DRV circuits 521 and switches 522 as there are light-emitting elements 41, with one DRV circuit 521 and one switch 522 connected in series to each light-emitting element 41. The DRV circuit 521 is positioned on the input side of the light emission level signal to the light-emitting element 41 (i.e., between the D / A conversion circuit 511 and the light-emitting element 41). In the example in Figure 4, the switch 522 is positioned on the output side of the light emission level signal to the light-emitting element 41, but the position of the switch 522 may be on the input side of the light emission level signal to the light-emitting element 41. The DRV circuit 521 is composed of, for example, a thin-film transistor and a capacitor.

[0039] There are as many D / A conversion circuits 511 as there are "total number of light-emitting elements 41 ÷ number of light-emitting element groups (n elements)". In other words, there are as many D / A conversion circuits 511 as there are light-emitting elements 41 included in one light-emitting element group G (for example, m elements). As a result, the signal output unit 51 can simultaneously output the same number of light emission level signals as the D / A conversion circuits 511.

[0040] The sampling-hold timing generation circuit 512 outputs sample-hold signals corresponding to each of the light-emitting element groups G, for a number of signals equal to the number of light-emitting element groups (n). Here, the sample-hold signals corresponding to each of the light-emitting element groups G1, G2, ... Gn are referred to as sample-hold signals SH1, SH2, ... SHn (or simply sample-hold signals SH if not distinguished). The sample-hold signals SH are input to the DRV circuits 521 corresponding to each of the light-emitting element groups G. The sample-hold signals SH are part of the drive signals for the light-emitting elements 41.

[0041] The light emission timing generation circuit 513 outputs light emission control signals for each of the light-emitting element groups G, corresponding to the number of light-emitting element groups (n elements). Here, the light emission control signals corresponding to each of the light-emitting element groups G1, G2, ... Gn are referred to as light emission control signals LC1, LC2, ... LCn (or simply light emission control signals LC if not distinguished). The light emission control signals LC are input to the switches 522 corresponding to each of the light-emitting element groups G. The light emission control signals LC are part of the drive signals for the light-emitting element 41.

[0042] Figure 5 is a timing chart showing an example of light emission control for print head 12a. In the light emission control shown in Figure 4, control is performed for one row of light-emitting elements triggered by a horizontal synchronization signal. The horizontal synchronization signal is defined as the line period Thsyn(s). The line period Thsyn is set to be longer than the product of the phase difference T1(s), which will be described later, and the number of light-emitting element groups G (n elements) (Thsyn > T1 × n).

[0043] In Figure 4, the light emission level signals are output by the D / A conversion circuit 511, which converts the image data (digital signal) input to the signal output unit 51 into an analog signal. The light emission level signals are output sequentially as follows: (light emission level signal for light-emitting element group G1), (light emission level signal for light-emitting element group G2), ..., (light emission level signal for light-emitting element group Gn). In addition, the (light emission level signal for light-emitting element group G) corresponds to the number of light-emitting elements 41 (m elements) included in one light-emitting element group G, and m signals are output synchronously from m D / A conversion circuits 511.

[0044] The sample-and-hold signal SH becomes "L" level when the light emission intensity of the light-emitting element 41 connected to the DRV circuit 521 is changed. When the sample-and-hold signal SH becomes "L" level, the voltage of the light emission level signal at that time is held in the DRV circuit 521 (the voltage is held in the capacitor included in the DRV circuit 521). For example, the sample-and-hold signal SH1 becomes "L" level while the light emission level signal is (the light emission level signal of light-emitting element group G1), causing the DRV circuit 521 connected to the light-emitting element 41 of light-emitting element group G1 to hold the voltage of the light emission level signal. While the sample-and-hold signal SH is "H" level, the holding voltage of the DRV circuit 521 remains unchanged. In other words, in the DRV circuit 521 to which a sample-and-hold signal SH at "H" level is input, the holding voltage does not change even if the voltage of the light emission level signal changes.

[0045] The light emission control signal LC controls the ON / OFF state of switch 522. In this embodiment, switch 522 is ON when the light emission control signal LC is at the "H" level. A current corresponding to the holding voltage of the DRV circuit 521 flows through the light-emitting element 41 while switch 522 connected to the element is ON. As a result, for example, the light-emitting element 41 of light-emitting element group G1 lights up (emits light) when the light emission control signal LC is at the "H" level. The light emission control signal LC is at the "L" level while the holding voltage of the DRV circuit 521 is being rewritten in the corresponding light-emitting element group G1, and becomes at the "H" level after the rewriting of the holding voltage is completed. Here, the phase difference T1 is the phase difference between the light emission control signals LC corresponding to two adjacent light-emitting element groups G. The light emission time Ton(s) is the light emission time of the light-emitting element 41 in one light-emitting element group G.

[0046] As described above, in the light emission control of the print head 12a, a predetermined group of light-emitting elements G is selected by the sample-and-hold signal SH and the light emission control signal LC, and the light emission intensity of the light-emitting elements 41 is determined by the light emission level signal. Furthermore, the light emission intensity can be maintained by the DRV circuit 521.

[0047] Next, we will explain the conditions for forming a seamless image as an electrostatic latent image and a printed image on the photoreceptor drum 3 in the print head 12a that performs the light emission control described above.

[0048] First, let's assume that the photoreceptor drum 3 is rotating at a surface velocity V (μm / sec) in the sub-scanning direction Y. In this case, the product of the line period Thsyn and the surface velocity V (Thsyn × V) is equal to the pixel pitch Pv of the resolution in the sub-scanning direction Y (Thsyn × V = Pv). Also, as already mentioned, (Thsyn > T1 × n).

[0049] Here, we consider the case where an electrostatic latent image is formed on the photoreceptor drum 3 by light emission control according to the timing chart in Figure 5, in a print head with a conventional configuration, that is, a print head that does not have inter-group step differences Ydiff between light-emitting element groups G.

[0050] Figure 6 is an explanatory diagram showing the relationship between the light-emitting element groups G1 and G2 and the pixel arrangement of the electrostatic latent image formed by exposure of the light-emitting element groups G1 and G2 in a conventional print head configuration.

[0051] There is a phase difference T1 between the light-emitting element group G1 and the light-emitting element group G2 in terms of their light emission timing. During this phase difference T1, the photoreceptor drum undergoes a rotation of V × T1 (μm) in terms of surface distance. Therefore, in the electrostatic latent image formed on the photoreceptor drum, a step of V × T1 (μm) is created between pixel group P1 formed by the exposure of light-emitting element group G1 and pixel group P2 formed by the exposure of light-emitting element group G2. Similarly, a step of V × T1 (μm) is created between any two adjacent pixel groups P.

[0052] In contrast, in the print head 12a of this embodiment, a step difference Ydiff is formed between the light-emitting element groups G. Figure 7 is an explanatory diagram showing the relationship between the light-emitting element groups G1 and G2 and the pixel arrangement of the electrostatic latent image formed by exposure of the light-emitting element groups G1 and G2 in the print head of this embodiment. As shown in Figure 7, by setting the print head 12a so that Ydiff = V × T1, the step difference can be eliminated in all pixel groups P included in the same pixel row in the electrostatic latent image on the photoreceptor drum 3.

[0053] Furthermore, since the print head 12a, which uses OLEDs or micro-LEDs as light-emitting elements 41, is manufactured using photolithography, similar to the manufacturing processes for semiconductors and liquid crystal panels, not only are manufacturing errors that are perceptible to humans not generated at all, but it is also possible to adjust the placement of the light-emitting elements 41 in sub-micron units. For this reason, the print head 12a can achieve the aforementioned elimination of steps with high precision.

[0054] [Second Embodiment] The surface velocity V of the photoreceptor drum 3 may be variable. In this embodiment, when the surface velocity V of the photoreceptor drum 3 changes, the signal output unit 51 changes the phase difference T1 accordingly to control (V × T1) to remain constant. That is, by keeping (V × T1) constant, the condition Ydiff = V × T1 can be satisfied even when the surface velocity V of the photoreceptor drum 3 changes, and the step difference of the pixel group P in the electrostatic latent image on the photoreceptor drum 3 can be eliminated.

[0055] As is clear from Figure 5, the phase difference T1 can be changed by adjusting the light emission control signal LC. When adjusting the light emission control signal LC, it is also necessary to adjust other signals (horizontal synchronization signal, light emission level signal, sampling hold signal), but all of these adjustments can be controlled at the signal output unit 51.

[0056] The embodiments disclosed herein are illustrative in all respects and are not intended to be restrictive. Therefore, the technical scope of this disclosure is not to be interpreted solely by the embodiments described above, but rather by the claims. [Explanation of symbols]

[0057] 100 Image forming apparatus 12. Exposure apparatus 12a printhead 3. Photoconductor drum 41 Light-emitting element 51 Signal output section 511 D / A Conversion Circuit 512 Sampling-Hold Timing Generation Circuit 513 Light emission timing generation circuit 52 Drive unit 521 DRV circuit 522 Switch G1~Gn light-emitting element group SH1~SHn Sample-and-Hold Signals (Part of the Drive Signals) LC1~LCn Light emission control signals (part of the drive signal)

Claims

1. Multiple light-emitting elements that expose a photoreceptor, A signal output section that outputs drive signals with different phases, The system includes a drive unit that causes each of the plurality of light-emitting elements to light up individually based on the drive signal, The plurality of light-emitting elements are divided into n groups, and each of the light-emitting elements is driven by the drive signal such that a phase difference occurs in the light emission timing for each of the light-emitting elements. The print head is characterized in that the light-emitting groups are arranged such that each group has a step difference between them in the sub-scanning direction.

2. A print head according to claim 1, A print head characterized in that the plurality of light-emitting elements are formed by organic EL diodes that constitute the pixels of an organic EL panel.

3. An image forming apparatus having a print head as described in claim 1, When the step difference between the groups is Ydiff, the phase difference is T1, and the surface velocity of the photoreceptor exposed to the print head is V, An image forming apparatus characterized by satisfying the condition Ydiff = V × T1.

4. An image forming apparatus according to claim 3, The surface velocity V is variable, An image forming apparatus characterized in that, when the surface velocity V changes, the signal output unit changes the phase difference T1 so that the condition Ydiff = V × T1 is satisfied.

Images