Image forming apparatus

Abstract

To obtain an image forming apparatus that can appropriately generate a sub-scan synchronization signal even when the exposure control unit that controls the exposure of the photoreceptor drum and the drive control unit that generates a sub-scan reference signal used when generating a sub-scan synchronization signal are operating asynchronously. [Solution] The drive control unit generates a sub-scan reference signal VSYNCref. The exposure control unit generates a sub-scan synchronization signal VSYNC synchronized with the main scan reference signal (BD signal) corresponding to the edges of the sub-scan reference signal VSYNCref, and controls the exposure apparatus to cause the exposure apparatus to form an electrostatic latent image corresponding to the image signal synchronized with the sub-scan synchronization signal VSYNC. The drive control unit then generates the sub-scan reference signal VSYNCref with a waveform having at least one additional edge within a predetermined period from the aforementioned edges.

Description

Technical Field

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

Background Art

[0002] A certain electrophotographic image forming apparatus generates (a) a main scanning reference signal corresponding to an exposure scanning period for a photoreceptor, (b) generates a sub-scanning synchronization signal corresponding to the main scanning reference signal, and (c) determines the position of an image formed on the photoreceptor based on the sub-scanning synchronization signal (see, for example, Patent Document 1).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] FIG. 7 is a diagram for explaining the generation of a sub-scanning synchronization signal synchronized with a main scanning reference signal based on a sub-scanning reference signal. In an image forming apparatus as described above, when an exposure control unit that controls the exposure of a photoreceptor drum and a drive control unit that generates a sub-scanning reference signal used when generating a sub-scanning synchronization signal operate asynchronously, for example, as shown in FIG. 7, a sub-scanning reference signal VSYNCref output by the drive control unit is input to the exposure control unit. When the exposure control unit detects an edge of the sub-scanning reference signal VSYNCref, it generates a sub-scanning synchronization signal VSYNC synchronized with the first main scanning reference signal (BD signal) after the detection of the edge, and resets the edge detection state of the sub-scanning reference signal VSYNCref for the next edge detection.

[0005] Figure 8 illustrates a case where the sub-scan synchronization signal is not generated properly. However, since the drive control unit operates asynchronously with the exposure control unit, if the exposure control unit resets the edge detection state in synchronization with the main scan reference signal (BD signal) before detecting the edge of the sub-scan reference signal VSYNCref, as shown in Figure 8, the edge of the sub-scan reference signal VSYNCref may not be detected properly. In other words, if edge detection by the exposure control unit is performed repeatedly with a periodic TD, and the BD signal arrives before the TD has elapsed from the timing of the edge in the sub-scan reference signal VSYNCref, the edge of the sub-scan reference signal VSYNCref may not be detected. And if the edge of the sub-scan reference signal VSYNCref is not detected, the sub-scan synchronization signal VSYNC will not be generated, as shown in Figure 8.

[0006] The present invention has been made in view of the above problems, and aims to provide an image forming apparatus that appropriately generates a sub-scanning synchronization signal even when the exposure control unit that controls the exposure of the photoreceptor drum and the drive control unit that generates a sub-scanning reference signal used when generating a sub-scanning synchronization signal are operating asynchronously. [Means for solving the problem]

[0007] The image forming apparatus according to the present invention comprises: an exposure apparatus that scans light on a photoreceptor drum and exposes the photoreceptor drum to form an electrostatic latent image; a drive control unit that generates a sub-scan reference signal; and an exposure control unit that generates a sub-scan synchronization signal synchronized with a main scan reference signal corresponding to the edge of the sub-scan reference signal, and controls the exposure apparatus to cause the exposure apparatus to form an electrostatic latent image corresponding to an image signal synchronized with the sub-scan synchronization signal. The drive control unit generates the sub-scan reference signal with a waveform having at least one additional edge within a predetermined period from the edge. [Effects of the Invention]

[0008] According to the present invention, an image forming apparatus is obtained that can appropriately generate a sub-scan synchronization signal even when the exposure control unit that controls the exposure of the photoreceptor drum and the drive control unit that generates a sub-scan reference signal used when generating a sub-scan synchronization signal are operating asynchronously.

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

[0010] [Figure 1] Figure 1 is a side view showing the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. [Figure 2] Figure 2 shows an example of the configuration of the exposure apparatus 2 and its surroundings in Figure 1. [Figure 3] Figure 3 is a block diagram showing the electrical configuration of the image forming apparatus shown in Figures 1 and 2. [Figure 4] Figure 4 is a block diagram showing the configuration of the exposure control unit 32 in Figure 3. [Figure 5] Figure 5 shows an example of the sub-scan reference signal VSYNCref and the main scan reference signal (BD signal). [Figure 6] Figure 6 is a timing chart illustrating the operation of the drive control unit 31 and the exposure control unit 32. [Figure 7] Figure 7 illustrates the generation of a sub-scan synchronization signal synchronized with the main scan reference signal, based on a sub-scan reference signal. [Figure 8] Figure 8 illustrates the case where the sub-scan synchronization signal is not generated properly. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described below with reference to the figures.

[0012] FIG. 1 is a side view showing the mechanical internal configuration of an image forming apparatus according to an embodiment of the present invention. The image forming apparatus shown in FIG. 1 is a device having an electrophotographic printing function, such as a printer, a facsimile apparatus, a copying machine, a multifunction peripheral, etc. Further, the image forming apparatus shown in FIG. 1 is a monochrome and direct transfer type image forming apparatus.

[0013] The image forming apparatus shown in FIG. 1 includes a photosensitive drum 1, an exposure device 2, a developing device 3, a conveyance belt 4, a driving roller 5, a transfer roller 6, and a fixing device 7.

[0014] The exposure device 2 exposes the photosensitive drum 1 while scanning light on the photosensitive drum 1 to form an electrostatic latent image.

[0015] The developing device 3 is equipped with a toner container filled with toner, and attaches the toner supplied from the toner container to the electrostatic latent image on the photosensitive drum 1.

[0016] The conveyance belt 4 rotates by the driving force from the driving roller 5, and conveys the print sheet to the photosensitive drum 1 and between the photosensitive drum 1 and the transfer roller 6. The transfer roller 6 brings the conveyed print sheet into contact with the photosensitive drum 1, and transfers the toner image on the photosensitive drum 1 to the print sheet. The print sheet with the transferred toner image is conveyed to the fixing device 7, and the toner image is fixed to the print sheet.

[0017] FIG. 2 is a diagram showing an example of the configuration of the exposure device 2 and its periphery in FIG. 1. The exposure device 2 shown in FIG. 2 includes a light source 21, a collimator lens 22a, a correction lens 22b, a polygon mirror 23, a motor 23a for rotating the polygon mirror 23, a BD sensor 24, etc.

[0018] In FIG. 2, the light source 21 emits laser light. The light source 21 is, for example, a laser diode. The collimator lens 22a is a lens that converts the laser light emitted from the light source 21 into parallel light. The correction lens 22b is a lens for making the moving speed of the irradiation position of the laser light constant.

[0019] Also, the polygon mirror 23 has an axis perpendicular to the axis of the photosensitive drum 1, the cross-section perpendicular to its axis is polygonal, and its side surface is a mirror. The polygon mirror 23 rotates about its axis and scans the laser light emitted from the light source 21 along its axial direction (main scanning direction) on the photosensitive drum 1.

[0020] Also, the BD sensor 24 is a sensor that receives the laser light scanned by the polygon mirror 23 at a predetermined position and generates a main scanning reference signal (a signal indicating the reference timing in the main scanning direction). The BD sensor 24 is arranged at a predetermined position on the line where the laser light is scanned, and generates a main scanning reference signal (BD signal) by receiving the scanned laser light at the predetermined position.

[0021] Here, the main scanning reference signal is a signal that is at a low level when the laser light spot passes over the BD sensor 24 and is at a high level during other periods. Therefore, the main scanning reference signal has a period corresponding to the rotational speed of the polygon mirror 23 and the like.

[0022] Figure 3 is a block diagram showing the electrical configuration of the image forming apparatus shown in Figures 1 and 2. For example, as shown in Figure 3, the image forming apparatus comprises a drive control unit 31, an exposure control unit 32, and an image generation unit 33. The drive control unit 31, the exposure control unit 32, and the image generation unit 33 are implemented as independent internal devices and operate asynchronously with respect to each other. The drive control unit 31, the exposure control unit 32, and the image generation unit 33 each include a processor (a computer including a CPU (Central Processing Unit) etc.) or an ASIC (Application Specific Integrated Circuit), and perform predetermined control and data processing with their respective processors and ASICs.

[0023] The drive control unit 31 executes the print job by controlling the exposure control unit 32 and the print sheet transport device (not shown), etc. The drive control unit 31 also generates a sub-scan reference signal VSYNCref and outputs it to the exposure control unit 32. The sub-scan reference signal VSYNCref indicates the starting position (starting drawing timing) of the page image to be printed.

[0024] The exposure control unit 32 receives the BD signal from the exposure apparatus 2 and supplies an image signal to the exposure apparatus 2 in synchronization with the BD signal. The exposure apparatus 2 forms an electrostatic latent image corresponding to the image signal on the photoreceptor drum 1. The exposure control unit 32 also generates a sub-scan synchronization signal VSYNC and a main scan synchronization signal HSYNC to be supplied to the image generation unit 33 in synchronization with the BD signal.

[0025] Specifically, the exposure control unit 32 generates a sub-scan synchronization signal VSYNC synchronized with the main scan reference signal (BD signal) in accordance with the edge (in this case, the rising edge) of the sub-scan reference signal VSYNCref, and controls the exposure apparatus 2 to form an electrostatic latent image corresponding to the image signal (for one page) synchronized with the sub-scan synchronization signal VSYNC.

[0026] Here, the edge of the sub-scan reference signal VSYNCref, which indicates the starting position (starting timing) in the sub-scan direction, is defined as the rising edge; however, it may be defined as the falling edge instead.

[0027] In particular, the drive control unit 31 generates a sub-scan reference signal VSYNCref with a waveform having at least one additional edge within a predetermined period from the aforementioned edge.

[0028] Here, this predetermined period is set to be less than a time that is shorter than the period TD mentioned above from the period of the main scan reference signal (BD signal), and is preferably less than or equal to half the period of the main scan reference signal. Also, the time between the edge and the additional edge mentioned above is set to be longer than the period TD mentioned above.

[0029] Figure 4 is a block diagram showing the configuration of the exposure control unit 32 in Figure 3. For example, as shown in Figure 4, the exposure control unit 32 includes a processor 41 that performs the control and signal processing described above, and an edge detection flag 42.

[0030] The edge detection flag 42 indicates the edge detection status for the sub-scan reference signal VSYNCref. Here, the sub-scan reference signal VSYNCref is an interrupt signal, and when an edge is sensed and an edge is detected, the value of the edge detection flag 42 changes from low to high. The edge detection flag 42 is reset by the main scan reference signal (BD signal). The edge detection flag 42 is also reset by the reverse edge of the sub-scan reference signal VSYNCref (here, the falling edge). In this reset, the value of the edge detection flag 42 is set low by the BD signal (pulse).

[0031] The processor 41 detects the aforementioned edge or additional edge by referring to the edge detection flag 42. The processor 41 operates with a clock of a predetermined period (the period TD mentioned above), and edge detection by the processor 41 is subject to a delay due to this clock period.

[0032] Furthermore, the exposure control unit 32 may adjust the image position in the sub-scan direction in accordance with the number of edges of the sub-scan reference signal VSYNCref detected in one cycle of the main scan reference signal (BD signal). In this case, when only one of the two edges (the edge mentioned above and the additional edge) is detected, the edge of the sub-scan synchronization signal VSYNC is delayed by one cycle (i.e., one line) of the BD signal, and the position of the image to be drawn is shifted by one line in the sub-scan direction by that amount.

[0033] Furthermore, the image generation unit 33 identifies the beginning of the page image to be printed using the sub-scan synchronization signal VSYNC, and in synchronization with the main scan synchronization signal HSYNC, generates line images of each line of the page image to be printed, and outputs them sequentially as image signals to the exposure control unit 32.

[0034] Next, the operation of the image forming apparatus described above will be explained.

[0035] Figure 5 shows an example of the sub-scan reference signal VSYNCref and the main scan reference signal (BD signal).

[0036] For example, as shown in Figure 5, the drive control unit 31 generates a sub-scan reference signal VSYNCref as a rectangular wave with a predetermined period and outputs it to the exposure control unit 32. The exposure apparatus 2 emits light from the light source 21 in response to the image signal and rotates the polygon mirror 23 to scan the spot position of that light on the photoreceptor drum 1. The exposure apparatus 2 also lights up the light source 21 when the spot position passes the BD sensor 24. As a result, a pulse-like BD signal is generated with each scan in the main scanning direction, as shown in Figure 5.

[0037] Figure 6 is a timing chart illustrating the operation of the drive control unit 31 and the exposure control unit 32. Figure 6 is an enlarged view of the rising edge portion of the sub-scan reference signal VSYNCref in Figure 5. Although not shown in Figure 5, in reality, the sub-scan reference signal VSYNCref has additional edges in addition to the leading edge, as shown in Figure 6, for example.

[0038] When such a sub-scan reference signal VSYNCref is input to the edge detection flag 42, the output value VSYNC_r of the edge detection flag 42 becomes high, and when a BD signal is detected, the output value VSYNC_r of the edge detection flag 42 returns to a low level. The processor 41 then checks the output value VSYNC_r of the edge detection flag 42 at predetermined cycle TDs, and if the output value VSYNC_r of the edge detection flag 42 is high, it determines that an edge has been detected.

[0039] Here, if the time from the first edge of the sub-scan reference signal VSYNCref to the BD signal is short and less than the predetermined period TD mentioned above, the edge detection flag 42 is reset by the BD signal. As a result, the first edge may not be detected by the processor 41, for example, as shown in Figure 6. Even in that case, the additional edge is detected by the processor 41 because it is far enough away from the BD signal. Therefore, in this case, the processor 41 generates the sub-scan synchronization signal VSYNC in synchronization with the first BD signal after the detection of the additional edge (pattern #1).

[0040] Furthermore, if two edges (i.e., the initial edge and an additional edge) are detected in one cycle of the BD signal, the processor 41 generates a sub-scan synchronization signal VSYNC in synchronization with the first BD signal after those two detections (pattern #2).

[0041] If a BD signal is detected between the leading edge and the additional edge, the processor 41 generates a sub-scan synchronization signal VSYNC synchronized with the first BD signal after the detection of the leading edge (i.e., the first edge), and ignores the detection of the additional edge (i.e., the second edge) (Pattern #3). In this case, since the additional edge is detected in the period following the period of the BD signal in which the leading edge was detected, if an edge is detected in two consecutive periods of the BD signal, the edge in the second period (the additional edge) is ignored.

[0042] Here, when the exposure control unit 32 adjusts the image position in the sub-scan direction in accordance with the number of edges of the sub-scan reference signal VSYNCref detected in one cycle of the main scan reference signal (BD signal), for pattern #1, the sub-scan synchronization signal VSYNC is generated with a one-cycle delay from the BD signal immediately following the leading edge, so the image position is adjusted by one line in the sub-scan direction as described above. For pattern #2, the sub-scan synchronization signal VSYNC is generated with the first BD signal after the leading edge, so no adjustment is performed in the sub-scan direction. Pattern #3 is excluded from this adjustment, and the sub-scan synchronization signal VSYNC is generated with the first BD signal after the leading edge, so no adjustment is performed in the sub-scan direction, similar to pattern #2.

[0043] In this manner, the exposure control unit 32 generates a sub-scan synchronization signal VSYNC and supplies it to the image generation unit 33, and also supplies a main scan synchronization signal HSYNC based on the BD signal to the image generation unit 33. The image generation unit 33 then outputs line image signals to the exposure control unit 32 in sequence, synchronized with these synchronization signals VSYNC and HSYNC.

[0044] The exposure control unit 32 supplies the image signal of the line image to the exposure device 2 in synchronization with the BD signal or the main scan synchronization signal HSYNC. The exposure device 2 lights up the light source 21 in response to the image signal and forms an electrostatic latent image corresponding to the image signal on the photoreceptor drum 1, one line at a time. The developing device 3 then deposits toner onto the electrostatic latent image to form a toner image. The toner image is transferred to a print sheet and fixed by the fuser 7.

[0045] As described above, according to the above embodiment, the drive control unit 31 generates a sub-scan reference signal VSYNCref. The exposure control unit 32 generates a sub-scan synchronization signal VSYNC synchronized with the main scan reference signal (BD signal) corresponding to the edge of the sub-scan reference signal VSYNCref, and controls the exposure apparatus 2 to cause the exposure apparatus 2 to form an electrostatic latent image corresponding to the image signal synchronized with the sub-scan synchronization signal VSYNC. The drive control unit 31 then generates the sub-scan reference signal VSYNCref with a waveform having at least one additional edge within a predetermined period from the aforementioned edge.

[0046] As a result, even if the exposure control unit 32 and the drive control unit 31 that generates the sub-scanning reference signal VSYNCref are operating asynchronously, the sub-scanning synchronization signal VSYNC is generated appropriately.

[0047] Furthermore, various changes and modifications to the embodiments described above will be obvious to those skilled in the art. Such changes and modifications may be made without deviating from the spirit and scope of the subject matter and without diminishing the intended advantages. In other words, such changes and modifications are intended to be included in the claims.

[0048] For example, in the above embodiment, the image forming apparatus is a monochrome image forming apparatus, but it may also be a color image forming apparatus. In the case of a color image forming apparatus, the above-mentioned print engine (photoreceptor drum, exposure device, developing device, etc.) is provided for each of the multiple toner colors (e.g., cyan, magenta, yellow, and black). Also, in the above embodiment, the image forming apparatus is a direct transfer type image forming apparatus, but it may also be an indirect transfer type image forming apparatus. In the case of an indirect transfer type image forming apparatus, the toner image on the photoreceptor drum is first transferred to an intermediate transfer body, and then secondarily transferred from the intermediate transfer body to a print sheet.

[0049] Furthermore, in the above embodiment, the drive control unit 31 generates the sub-scan reference signal VSYNCref with a waveform having one additional edge within a predetermined period from the aforementioned edge, but the sub-scan reference signal VSYNCref may be generated with a waveform having multiple additional edges within a predetermined period from the aforementioned edge. [Industrial applicability]

[0050] The present invention can be applied, for example, to an electrophotographic image forming apparatus. [Explanation of symbols]

[0051] 1. Photoconductor drum 2. Exposure apparatus 31 Drive control unit 32 Exposure Control Unit 42 Edge detection flags

Claims

1. An exposure apparatus that scans light over a photosensitive drum and exposes the photosensitive drum to form an electrostatic latent image, A drive control unit that generates a sub-scan reference signal, The system includes an exposure control unit that generates a sub-scan synchronization signal synchronized with the main scan reference signal in accordance with the edge of the sub-scan reference signal, and controls the exposure apparatus to cause the exposure apparatus to form an electrostatic latent image corresponding to the image signal synchronized with the sub-scan synchronization signal, The drive control unit generates the sub-scan reference signal with a waveform having at least one additional edge within a predetermined period from the edge. An image forming apparatus characterized by the following.

2. The exposure control unit includes an edge detection flag indicating the edge detection status for the sub-scan reference signal, and detects the edge or the additional edge by referring to the edge detection flag. The edge detection flag is reset by the main scan reference signal. The image forming apparatus according to claim 1, characterized by the following:

3. The image forming apparatus according to claim 1, characterized in that the drive control unit generates the sub-scan reference signal with a waveform having a plurality of additional edges within the predetermined period from the edge.

4. The image forming apparatus according to claim 1, characterized in that the exposure control unit adjusts the image position in the sub-scan direction in accordance with the number of edges of the sub-scan reference signal detected in one cycle of the main scan reference signal.

5. The image forming apparatus according to any one of claims 1 to 4, characterized in that the predetermined period is less than or equal to half the period of the main scanning reference signal.

Images