JP2006154400A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an low-cost image forming apparatus that reduces generation of jitter. <P>SOLUTION: The copying machine 1 for forming images by using a laser beam includes: a polygon motor 335 for changing the direction of a polygon mirror 332 used for determining the position of the laser beam in a main scanning direction, the laser beam being emitted to a photoreceptor drum 31; a polygon motor clock generating section 61 for generating a clock signal used to control the polygon motor 335; a main motor 70 for rotating the photoreceptor drum 31; and a frequency dividing section 621 for receiving a PD signal from a laser scanner unit 33 for each one line and generating, based on the PD signal, a clock signal used for controlling the main motor 70, the PD signal being used for indicating the reference timing of starting one line scanning, and the laser scanner unit 33 being used for writing images onto the photoreceptor drum 31 by the laser beam. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including a laser scanner unit that writes an image on a photosensitive drum with a laser.

  In a conventional image forming apparatus such as a copying machine, a main motor clock that determines the rotation speed of a main motor that rotates and drives a photosensitive drum, and a polygon mirror that controls the position of a laser that irradiates the photosensitive drum. The polygon motor clock that determines the rotational speed of the polygon motor that changes the direction and the motor clock that controls the drive of the image reading unit that reads the image are each for realizing the theoretically determined rotational speed. Frequency clocks are used, and each clock is generated independently.

  However, when independently generated clocks are used, interference occurs due to subtle differences in the frequency of each clock, and image jitter occurs. In addition, it is expensive to generate clocks independently using different vibrators. Further, when generating a clock using an inexpensive CPU (ie, a low processing frequency) CPU (central processing unit), it is difficult to generate a highly accurate clock.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an inexpensive image forming apparatus that can reduce the occurrence of jitter.

  An image forming apparatus according to claim 1 is an image forming apparatus that forms an image using a laser, and a mirror driving unit that changes a direction of a polygon mirror that determines a position in a main scanning direction of a laser irradiated on a photosensitive drum. One line scanning from a polygon clock generating means for generating a clock signal for controlling the mirror driving means, a drum driving means for rotating the photosensitive drum, and a laser scanner unit for writing an image on the photosensitive drum by a laser. Clock signal generating means for receiving a PD signal indicating the reference timing for start for each line and generating a clock signal for controlling the drum driving means based on the PD signal is provided.

  According to this configuration, based on the clock signal generated by the polygon clock generating means, the PD signal based on the laser irradiation whose position is controlled by the mirror driving means is received by the clock generating means. Based on this PD signal, A clock signal for controlling the drum driving unit is generated by the clock generating unit, and the rotational position of the photosensitive drum is controlled by the drum driving unit based on the clock signal.

  An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, wherein a determination unit that determines a resolution for writing an image, and correspondence between the PD signal and the clock signal corresponding to the resolution A storage unit for storing the relationship; and an acquisition unit for acquiring the correspondence from the storage unit according to the resolution determined by the determination unit, wherein the clock generation unit is acquired by the acquisition unit. The PD signal is converted into the clock signal using the correspondence relationship.

  According to this configuration, the correspondence between the PD signal and the clock signal corresponding to the writing resolution determined by the determination unit is acquired from the storage unit by the acquisition unit, and the clock generation unit uses the correspondence to acquire the PD. The signal is converted into a clock signal.

  An image forming apparatus according to a third aspect is the image forming apparatus according to the first or second aspect, comprising: an image reading unit that reads an image; a reading drive unit that drives the image reading unit; and the laser scanner unit. The laser scanner unit further includes a reading clock generating unit that receives the PD signal and generates a clock signal for controlling the reading driving unit based on the PD signal, and the laser scanner unit is configured to display an image of the image reading unit. The image is written directly in conjunction with the reading.

  According to this configuration, in an image forming apparatus including a laser scanner unit that writes an image directly in conjunction with image reading by the image reading unit, a PD signal based on laser irradiation whose position is controlled by the mirror driving unit is generated as a reading clock. Based on this PD signal, a clock signal for controlling the reading driving means is generated by the reading clock generating means, and the reading position of the image by the image reading means is determined by the reading driving means based on this clock signal. Be controlled.

  According to the first aspect of the present invention, even when the laser irradiation scanning speed fluctuates, the rotational speed of the photosensitive drum (that is, the moving speed in the sub-scanning direction) changes accordingly. Since the scanning lines in forming the image on the body drum are more regularly spaced, the occurrence of jitter with respect to the formed image is reduced. In addition, since a plurality of clocks can be generated based on one clock generation mechanism, component costs can be suppressed, and an image forming apparatus can be provided at low cost.

  According to the second aspect of the present invention, the clock signal corresponding to the resolution is generated according to the writing resolution.

  According to the third aspect of the present invention, even when the laser irradiation scanning speed fluctuates, the moving speed of the image reading position changes accordingly, and the image reading position and writing position are more Since it matches exactly, the occurrence of jitter to the image to be formed is reduced. In addition, since a plurality of clocks can be generated based on one clock generation mechanism, component costs can be suppressed, and an image forming apparatus can be provided at low cost.

  Embodiments according to the present invention will be described below with reference to the drawings. FIG. 1 is a side view schematically showing a mechanical configuration of a copying machine as an example of an image forming apparatus according to an embodiment of the present invention. As shown in FIG. 1, the copying machine 1 includes a sheet feeding mechanism 10 disposed at the bottom of a box-shaped copying machine main body 2, a sheet transport mechanism 20 disposed above the sheet feeding mechanism 10, The image forming mechanism 30 disposed above the sheet conveying mechanism 20, the fixing device 40 disposed on the discharge side of the image forming mechanism 30, and above the image forming mechanism 30 and the fixing device 40. The image reading device 50 and the laser scanner unit 33 are provided, and a control device 60 that controls the operation of the entire copying machine is provided.

  The paper feed mechanism 10 includes a paper feed cassette 11 that stores a bundle of stacked transfer papers P1 and a paper feed roller 12 that is provided above the outlet of the paper feed cassette 11 and has an arcuate outer peripheral portion. When the paper feeding roller 12 is rotated in a predetermined direction, the arc-shaped outer peripheral portion comes into contact with the uppermost transfer paper P1, and the transfer paper P1 is sent to the right side in FIG.

  The paper transport mechanism 20 has a transport roller pair 22 for transporting the transfer paper P1 supplied from the paper feed mechanism 10 to the left side in FIG. 1 and the leading end in the width direction of the transported transfer paper P1, and will be described later. The registration roller pair 23 for timing the start of toner image transfer in accordance with the rotation of the photosensitive drum 31 and the transfer sheet P1 from the registration roller pair 23 to the transfer position where the photosensitive drum 31 and the transfer device 35 face each other. The toner image is fixed by the transfer guide 27 for accurately transporting, the transport guide 24 for transporting the transfer paper P1 on which the toner image is transferred to the fixing device 40, and the fixing device 40 to form an image. And a discharge roller pair 25 for discharging the transfer sheet onto the discharge tray 26. Each roller of the paper transport mechanism 20 rotates using the main motor 70 (see FIG. 2) as a drive source.

  The image forming mechanism 30 forms a predetermined toner image on the transfer paper P1 by an electrophotographic process. The image forming mechanism 30 is rotatably supported by a photosensitive drum 31 having a photoconductive material applied to the surface of the drum. The surface of the photosensitive drum 31 is selectively exposed corresponding to the image on the original paper P2 and the charging device 32 for applying a predetermined potential to the surface of the photosensitive drum 31 (charging the predetermined charge uniformly). As a result, a laser scanner unit 33 for forming an electrostatic latent image on the surface of the photosensitive drum, and a toner selectively attached to the surface of the photosensitive drum 31, thereby forming a static image formed on the surface of the photosensitive drum. A developing device 34 that develops the electrostatic latent image and a transfer device 35 that transfers the developed toner image on the photosensitive drum 31 onto the surface of the transfer paper are configured.

  The charging device 32 is provided on the upstream side in the rotation direction of the photosensitive drum 31 with respect to an exposure position to be described later so as to face the surface of the photosensitive drum 31 with a predetermined distance therebetween. A wire for generating a corona discharge and a grid to which a predetermined voltage (for example, +850 V) is applied are provided, and a predetermined potential is applied to the surface of the photosensitive drum 31 by the wire and the grid.

  The laser scanner unit 33 includes a laser oscillator 331, a polygon mirror 332 that is a rotating polyhedron for reflecting the laser beam output from the laser oscillator 331, and distortion of the laser beam reflected by the polygon mirror 332. An fθ lens 334 and a mirror 333 for re-reflecting the light reflected by the polygon mirror 332 to the exposure position of the photosensitive drum 31 are provided. The laser oscillator 331 outputs a laser beam based on the image data of the original read by the image reading device 50. The polygon mirror 332 is rotated at a constant speed in a predetermined direction by driving by a polygon motor 335 (see FIG. 2), and the angle of the mirror surface that reflects the laser beam output from the laser oscillator 331 changes every moment. The laser beam is scanned in the width direction of the photosensitive drum 31.

  The laser scanner unit 33 generates a PD (Photo Detect) signal indicating the timing at which scanning with the laser beam comes to the head of each main scanning row based on the operation of the polygon mirror 332, and sends it to the main motor clock generation unit 62. Send.

  The photoconductor drum 31 is obtained by applying a film of a photoconductive material such as an organic photoconductor (OPC) material on an outer peripheral surface of a drum such as aluminum, and the charging device 32 in an unexposed state. Therefore, a positive charge is charged so that the surface potential becomes constant (for example, +800 V). In this state, when the surface of the photosensitive drum 31 is selectively exposed by the laser scanner unit 33, the potential of the exposed portion decreases due to the photoelectric effect of the photoconductive material applied to the surface. That is, an electrostatic latent image is formed on the surface of the photosensitive drum 31.

  The developing device 34 is provided on the downstream side in the rotation direction of the photosensitive drum 31 with respect to the exposure position so as to face the surface of the photosensitive drum 31 with a predetermined distance, and holds a predetermined amount of toner. At the same time, the toner is charged to a positive charge, for example. When the electrostatic latent image portion formed on the surface of the photosensitive drum 31 approaches the developing device 34, toner adheres to the surface of the photosensitive drum 31 from the developing device 34, and thereby the toner on the surface of the photosensitive drum 31. An image will be formed.

  The transfer device 35 faces the surface of the photosensitive drum 31 with a predetermined distance so that a gap is generated even when the transfer paper P1 is conveyed between the photosensitive drum 31 and the transfer device 35. By supplying a transfer current having a polarity opposite to the surface potential of the photosensitive drum 31, the toner is attached to the transfer paper P 1 interposed between the photosensitive drum 31 and the transfer device 35. ing. This adhesion causes the toner image on the surface of the photosensitive drum 31 to be transferred to the transfer paper P1.

  The fixing device 40 heats and presses the transfer paper P1 onto which the toner image has been transferred by the image forming mechanism 30 with a heating roller 41 and a pressure roller 42 to fix the toner image on the transfer paper P1. It is.

  The image reading device 50 includes a contact glass 51 that also serves as a document table, an exposure lamp 52 that illuminates the original surface of the original paper P2 placed on the contact glass 51, and an image of the original paper P2 that is the subject. An imaging lens 57 for forming an image on a photoelectric conversion element 56 such as a line sensor, and mirrors 53, 54, 55 for refracting and reflecting the optical axis of the imaging lens 57 connecting the document sheet P 2 and the photoelectric conversion element 56; In order to scan the original paper P2 on the contact glass 51 from the left end to the right end in FIG. A scanning mechanism (motor) 59 (see FIG. 2) for moving the inside is provided.

  FIG. 2 is a block diagram illustrating a functional configuration of a clock generation mechanism that generates a clock for determining the rotation speeds of the polygon motor 335, the main motor 70, and the scanning mechanism unit (motor) 59 in the copying machine 1. The clock generation mechanism includes a laser scanner unit 33, an image reading device 50, and a control unit 60.

  The control unit 60 includes a CPU (Central Processing Unit), a ROM (Read Only Memory) that stores a program that operates on the CPU, and a RAM (Random Access Memory) that provides a storage area such as a work area used by the program. Consists of The control unit 60 includes a polygon motor clock generation unit 61, a main motor clock generation unit 62, a read clock generation unit 65, a frequency division ratio storage unit 63, and a writing resolution acquisition unit 64.

  The polygon motor clock generation unit 61 generates a clock signal (polygon motor clock) for controlling the polygon motor 335 (that is, determining the rotation speed of the polygon motor). The polygon motor clock generation unit 61 generates a polygon motor clock from the operation clock of the control unit 60 and inputs it to the polygon motor 335.

  The frequency division ratio storage unit 63 stores a frequency division ratio used when the main motor clock generation unit 62 generates a main motor clock from the PD signal received from the laser scanner unit 33, and is a ROM, for example. The main motor clock is a clock signal for controlling the main motor (that is, determining the rotation speed of the main motor). The frequency division ratio storage unit 63 stores, for example, frequency division ratios corresponding to a plurality of types of writing resolutions. Here, the frequency division ratio is the ratio of the number of pulses of the main motor clock to the number of pulses of the PD signal. At this time, the number of teeth of a gear (for rotating the photosensitive drum 31) provided in the photosensitive drum 31 that is rotated by the main motor 70 becomes an integer (that is, the rotation of the photosensitive drum 31 is exactly the same). The above division ratio is given so that it stops between the gear teeth.

  The writing resolution acquisition unit 64 acquires information about which one of a plurality of predetermined writing resolutions is selected. The writing resolution acquisition unit 64 determines the writing resolution based on, for example, a user instruction input from the operation unit. The writing resolution acquisition unit 64 instructs the main motor clock generation unit 62 on the determined writing resolution.

  The main motor clock generation unit 62 generates a main motor clock from the PD signal received from the laser scanner unit 33. The main motor clock generation unit 62 includes a frequency division unit 621 and a frequency division ratio acquisition unit 622.

  The frequency division ratio acquisition unit 622 acquires the currently selected writing resolution from the writing resolution acquisition unit 64 and reads the frequency division ratio corresponding to this writing resolution from the frequency division ratio storage unit 63. The frequency dividing unit 621 acquires the frequency dividing ratio from the frequency dividing ratio acquiring unit 622, divides the PD signal received from the laser scanner unit 33 by this frequency dividing ratio, and generates a new clock signal (main motor clock). It is generated and transmitted to the main motor 70. The frequency divider 621 includes a frequency divider, for example.

  The reading clock generation unit 65 generates a clock for the scanning mechanism 59 of the image reading apparatus 50 from the PD signal received from the laser scanner unit 33. The read clock generation unit 65 includes a frequency division unit 651.

  The frequency divider 651 generates a new clock signal (scanning mechanism clock) by dividing the PD signal received from the laser scanner unit 33 by a predetermined frequency dividing ratio, and transmits the clock signal to the scanning mechanism 59. It is. The frequency divider 651 includes a frequency divider, for example.

  The laser scanner unit 33 operates in conjunction with the image reading device 50, and an image is formed by the laser scanner unit 33 in direct association with image reading of the image reading device 50.

  Next, the processing flow of the clock generation mechanism will be described. FIG. 3 is a flowchart showing a processing flow of the clock generation mechanism.

  In step S <b> 1, the writing resolution acquisition unit 64 acquires the writing resolution selected by the user using an operation unit (not shown), for example, and transmits the writing resolution to the frequency division ratio acquisition unit 622. In step S <b> 2, the frequency division ratio acquisition unit 622 acquires the frequency division ratio corresponding to the writing resolution received from the writing resolution acquisition unit 64 from the frequency division ratio storage unit 63. In step S <b> 3, the polygon motor clock generation unit 61 starts generating and outputting a polygon motor clock and starts driving the polygon motor 335.

  In step S4, the frequency divider 621 checks whether or not a PD signal has been received from the laser scanner unit 33 (NO in step S4). If received (YES in step S4), step S5 Proceed to In step S <b> 5, the frequency dividing unit 621 acquires the frequency dividing ratio from the frequency dividing ratio acquiring unit 622, generates a main motor clock at this frequency dividing ratio, and outputs the main motor clock to the main motor 70. In step S <b> 6, the frequency dividing unit 651 generates a reading clock with a preset frequency dividing ratio and outputs it to the scanning mechanism unit 59.

  As described above, in the present embodiment, based on the PD signal received from the laser scanner unit including the polygon motor driven based on the clock generated by the polygon motor clock generation unit 61, the main motor clock generation unit 62 A clock for driving a main motor 70 that rotates rollers such as the photosensitive drum 31 is generated. Further, based on the PD signal, the reading clock generation unit 65 generates a clock for driving the motor of the scanning mechanism unit 59 that controls the reading scanning position of the image reading apparatus 50. For this reason, even when the scanning speed of the laser irradiation varies, the rotational speed of the photosensitive drum changes accordingly, and the occurrence of jitter for the image to be formed is reduced. In addition, even when the laser irradiation scanning speed fluctuates, the moving speed of the image reading position changes accordingly, and the generation of jitter for the image to be formed is reduced. In addition, since a plurality of clocks can be generated based on one clock generation mechanism, component costs can be suppressed, and an image forming apparatus can be provided at low cost.

  In addition, this invention is not limited to the thing of the said embodiment, The aspect described below can be employ | adopted. In the present embodiment, the image forming apparatus has been described by taking an example of a so-called analog type copying machine in which the image formation of the laser scanner unit 33 is directly linked to the image reading of the image reading apparatus 50, but the present invention is not limited thereto. The image forming apparatus to be implemented includes an image forming apparatus in which the image formation of the laser scanner unit 33 is not interlocked with the image reading of the image reading apparatus 50 (that is, a digital type in which image data is temporarily stored in a memory or the like) An image forming apparatus that does not include the image reading apparatus 50 may be used. In this case, it is not necessary to provide the read clock generation unit 65 in the clock generation mechanism.

  In the present embodiment, the read clock generation unit 65 divides the frequency by a predetermined division ratio. However, as in the case of the main motor clock generation unit 62, the read clock generation unit 65 uses a plurality of division ratios (for example, One corresponding to the reading resolution of the image may be selected. Further, a mechanism for determining the reading resolution, for example, a reading resolution acquisition unit similar to the writing resolution acquisition unit 64 may be provided.

  The clock conversion need not necessarily be a frequency division, and a frequency divider is not necessarily used as a mechanism for converting (generating) the clock.

1 is a side view showing a mechanical configuration of an image forming apparatus according to an embodiment of the present invention. It is a block diagram which shows the function structure of the clock generation mechanism in one Embodiment of this invention. It is a flowchart which shows the flow of a process of the clock generation mechanism in one Embodiment of this invention.

Explanation of symbols

1 Copying machine (image forming device)
31 Photosensitive drum 33 Laser scanner unit 332 Polygon mirror 335 Polygon motor (mirror drive means)
50 Image reading device (image reading means)
59 Scanning mechanism (reading drive means)
621 Frequency divider (clock generation means)
622 frequency division ratio acquisition unit (acquisition means)
61 Polygon motor clock generator (polygon clock generator)
63 Dividing ratio storage unit (storage means)
64 Writing resolution acquisition unit (determination means)
651 frequency divider (read clock generation means)
70 Main motor (drum drive means)

Claims (3)

In an image forming apparatus that forms an image using a laser,
Mirror driving means for changing the direction of the polygon mirror for determining the position of the laser in the main scanning direction with which the photosensitive drum is irradiated;
A polygon clock generating means for generating a clock signal for controlling the mirror driving means;
Drum driving means for rotating the photosensitive drum;
In order to control the drum driving means on the basis of the PD signal indicating the reference timing for starting scanning of one line for each line from the laser scanner unit for writing an image on the photosensitive drum by the laser. An image forming apparatus comprising: clock generation means for generating a clock signal of Determining means for determining a resolution for writing an image;
Storage means for storing a correspondence relationship between the PD signal and the clock signal corresponding to the resolution;
An acquisition unit for acquiring the correspondence relationship from the storage unit according to the resolution determined by the determination unit;
The image forming apparatus according to claim 1, wherein the clock generation unit converts the PD signal into the clock signal by using the correspondence acquired by the acquisition unit. Image reading means for reading an image;
A reading drive means for driving the image reading means;
Read clock generation means for receiving the PD signal from the laser scanner unit and generating a clock signal for controlling the read drive means based on the PD signal;
The image forming apparatus according to claim 1, wherein the laser scanner unit writes an image in direct association with reading of an image by the image reading unit.

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