JP2009255313A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform a one-line skip simply at low cost by without causing the complication of a circuit due to the installation of a new circuit etc. when forming an image at a half speed. <P>SOLUTION: An image formation device capable of forming an image at two kinds of speeds which are a usual image forming speed and a half speed is equipped with a control part 8, a photosensitive material drum 41, an exposure system equipped with a laser light source and a spinning reflector, an image data formation part 9, a detecting element 75 for receiving a laser beam and issuing a detection signal, and a sample signal generation part 97 which generates a sample signal SPN for making the laser light source emit light forcibly by a counter 98 at a predetermined interval T2. When forming an image at a half speed, the photosensitive material drum 41 revolves at a half speed to make the reflective rotor of the exposure device revolve at the same speed as a usual time, so that the counter 98 extends the predetermined interval T2 until issuing the sample signal SPN by a scan period of one line of the laser beam. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copier, or a multi-function machine that forms an image by scanning and exposing the surface of a photoreceptor with a laser beam.

  Conventionally, in an image forming apparatus such as an electrophotographic printer, a copying machine, or a multifunction machine, for example, an image can be formed at a half speed (half speed) with respect to a normal image forming speed. There is something with variable. Currently, there is a competition for high-speed printing. However, in high-speed printing, for example, the toner supply time to the electrostatic latent image on the photosensitive drum is shortened, and the toner image transferred to the sheet is heated and applied. The time in each process of image formation is shortened, for example, the fixing time in the fixing device that performs pressure is shortened. Therefore, for example, if image formation is performed at half speed, sufficient time is given in each process, and image quality is improved. In addition, since postcards and cardboards require more time to heat than plain papers, image formation may be performed consciously at half speed when printing on cardboards and the like, and sufficient heating may be performed by the fixing device. Considering these points, half-speed image formation is performed.

  In some electrophotographic image forming apparatuses, an exposure apparatus forms an electrostatic latent image by scanning and exposing a photosensitive drum charged to a predetermined potential by laser light based on image data. In this type of exposure apparatus, for example, when an image is formed at half speed, the rotation speed of the polygon motor that rotates the polygon mirror is halved while the sheet conveyance speed is halved, and the laser light scanning cycle is 2 There are some which perform image formation at half speed by doubling.

  However, in this method, the irradiation time of the laser beam per pixel is doubled, and the irradiation energy amount of the laser beam per unit area of the photosensitive drum is increased as compared with the normal image formation. As a result, the formed electrostatic latent image is different from the normal image formation, and various parameters (for example, the charging potential of the photosensitive drum, the supply amount of toner, various bias values, etc.) need to be adjusted. . Therefore, for each image forming speed, it is necessary to adjust values while developing various parameters at the time of development, and complicated controls and mechanisms for changing the various parameters are required during operation of the apparatus. Therefore, in order to avoid preparing all the parameters for each process for each image forming speed, the scanning of the laser beam is delayed by one line (one period) at the time of half-speed image formation, or (one line is skipped). ), The laser power is reduced.

  For example, in the image forming apparatus described in Patent Document 1, the exposure control unit outputs a laser beam in accordance with an image signal, and the laser beam is a two-beam method and exposes up to two dots in one scan in the main scanning direction. If the transfer speed is half, switch to the 1-beam method. By switching to the one-beam method, the image forming apparatus described in Patent Document 1 achieves one line skip (or laser power reduction) (see Patent Document 1: Paragraph 0014).

The image forming apparatus described in Patent Document 2 prohibits the read / write operation of the sub-scanning delay memory for each line during half-speed control, so that a DRAM control signal output from a control pulse generation unit in the DRAM controller. When -FREEZE = "L", it is made inactive. In short, the image data read operation is stopped for each line by the DRAM control signal, and one line skip is realized (see Patent Document 2: paragraphs 0036, 0039, etc.).
JP 2004-317806 A JP 2000-015869 A

  First, in order to reduce the laser power to an appropriate power at the time of image formation at half speed, a circuit and a program for controlling the energy supply to the laser light source (for example, a laser diode) are separately required. There is a problem that costs increase. If the current amount is simply halved, the laser power is not halved. Therefore, there are cases where delicate energy supply control is required, and the circuit is complicated and expensive.

  Further, in the invention described in Patent Document 1 of the two-beam method, it is considered that one line skip can be realized by switching to the one-beam method, but this cannot be realized without two laser light sources per color. That is, two or more laser light sources per color are essential, and there is a problem that the manufacturing cost of the exposure apparatus increases. Further, if the switching to the one-beam system is frequently performed, there is a difference in the life of the laser light source, and there may be a problem that the quality of the formed image is lowered due to the difference in deterioration of the laser light source. Although Patent Document 1 does not describe a scanning control method and configuration when switching to the one-beam method, there are cases where the circuit becomes complicated and the manufacturing costs of the exposure apparatus and the image forming apparatus increase.

  In the method of prohibiting reading of image data from the memory described in Patent Document 2, one line is surely skipped. However, as described in Patent Document 2, in order to handle image data, other circuits and the like are used. When combined, there arises a problem that the circuit configuration becomes considerably complicated. This complication of the circuit configuration has a problem that it may lead to a circuit design error, a manufacturing cost and an increase in failure rate. In addition, for example, it is necessary to verify whether the DRAM control signal is generated at an appropriate timing in the designed complicated circuit, and the verification work becomes complicated.

  The present invention has been made in view of the above-described problems of the prior art. At least in an image forming apparatus in which the image forming speed is variable between normal and half speed, a new circuit is provided at the time of image formation at half speed. It is an object of the present invention to easily skip one line at a low cost without incurring circuit complexity due to provision or the like.

  In order to solve the above-mentioned problems, the invention according to claim 1 is an image forming apparatus capable of forming an image at at least two speeds of a normal image forming speed and a half speed of a normal image forming speed. A control unit for controlling, a photosensitive drum that is driven to rotate, a laser light source, and a rotary reflector; the laser beam is deflected by the rotary reflector to move the irradiation position of the laser beam; An exposure device that scans and exposes the photosensitive drum by turning off and turning on the laser light source, an image data generation unit that outputs image data to the exposure device, and a laser beam of the laser light source in the exposure device A detection unit that emits a detection signal when receiving the laser beam to detect the scanning position of the laser beam by being incident, and the laser light source is strong for the detection unit to receive the laser beam. A sample signal generation unit that generates a sample signal, which is a signal for causing light emission, at predetermined intervals by counting by a counter, and the laser light source is configured to detect the detection signal of the detection unit for synchronization of scanning of each line. After a lapse of a predetermined time from the occurrence of the occurrence, light emission for scanning / exposure of the photosensitive drum is started in accordance with the image data, and from the generation of the sample signal until the detection unit issues the detection signal When the image is formed at half speed, the photosensitive drum rotates at half the normal speed, the reflection rotator of the exposure apparatus rotates at the same speed as normal, and the counter The predetermined interval until the sample signal is emitted is extended by the scanning period of one line of laser light.

  According to this configuration, when the image is formed at half speed, the rotation speed of the reflecting rotator is the same as that during normal image formation, and the irradiation period of the laser beam is not changed. It doesn't change even at half-speed. Therefore, it is not necessary to adjust / set parameters for each process in image formation for each image formation speed. Further, one line skip is realized by extending the predetermined interval until the sample signal is generated by the scanning cycle time of one line of laser light. That is, the counter of the sample signal generator is configured to be able to count up to about twice that during normal image formation, and one line skip is realized by simply switching the operation of the counter according to the image forming speed. In order to double the count number of the counter, it is only necessary to increase it by about one digit in terms of bits.

  Therefore, unlike the conventional case, a complicated circuit configuration such as providing two laser light sources for each color and prohibiting reading / writing to the memory for each line by newly installing a circuit is not required, and the manufacturing cost is low. Thus, one line can be easily skipped. In addition, according to the present invention, it is only necessary to switch the counting operation of the counter for skipping one line, which eliminates the need for complicated circuit design and verification of the operation of the designed circuit, thereby reducing development costs. The

  According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, a clock generation circuit for generating a clock signal is provided, and the counter counts the clock signal of the clock generation circuit. The control unit switches and controls the count number of the counter between normal time and half speed.

  This configuration is a preferred example of the present invention, and the counter counts the clock signal, and the control unit switches the count number of the counter at the normal time and the half speed, so that the normal time and the half time can be easily changed. Scanning / exposure to each photosensitive drum at high speed is realized.

  According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the image data generation unit is provided with an image data output counter for measuring the predetermined time, and the detection is performed. The detection signal is input to the counter and the image data output counter, and the counter and the image data output counter are reset by the detection signal.

  According to this configuration, the laser light source receives the detection signal output from the image data output counter and starts scanning / exposure of the photosensitive drum after a predetermined time elapses. When forced light emission occurs after the interval, the detection signal is used in common for the reset signals of both counters, so that the timing start timing of the predetermined time and the predetermined interval can be matched. Accordingly, the laser light source can be operated by reliably distinguishing the exposure of the photosensitive drum from the forced light emission based on the coincidence of the timing start timing. Further, since the reset signal is shared, the circuit configuration can be simplified, and the manufacturing cost of the image forming apparatus can be reduced.

  According to a fourth aspect of the present invention, in the image forming apparatus according to the third aspect, the image data output counter counts the clock signal generated by the clock generation circuit to measure time. .

  According to this configuration, since the counter for image data output and the clock signal counted by the counter are shared, the clock generation circuit can be shared, and the time measurement at a predetermined time and a predetermined interval can be accurately performed based on the same clock signal. It can be carried out. Therefore, the circuit configuration can be simplified, and the manufacturing cost of the image forming apparatus can be reduced.

  According to a fifth aspect of the present invention, in the image forming apparatus according to any one of the first to fourth aspects, the detection unit is provided outside an exposure range of the photosensitive drum, and the reflection rotator is rotated by a polygon motor. The number of laser light sources is one for each color.

  According to this configuration, it is possible to realize image formation by skipping one line at half speed regardless of the two-beam method as in the prior art. Therefore, only one laser light source is required for each color, and the exposure apparatus and image Members required for the forming apparatus can be reduced. Accordingly, the manufacturing costs of the exposure apparatus and the image forming apparatus can be reduced.

  As described above, according to the present invention, in an image forming apparatus capable of forming an image at a normal image forming speed and at a half speed, a counter for generating a sample signal without greatly changing various parameters in image forming. By simply changing the time measured depending on the number, it is possible to skip one line in scanning and exposure of the photosensitive drum at half speed.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. Here, the present invention can be applied to various image forming apparatuses. The case where the present invention is applied to the printer 1 will be described as an example. However, each element such as configuration and arrangement described in this embodiment does not limit the scope of the invention and is merely an illustrative example.

(Outline of image forming apparatus)
First, a schematic configuration of the printer 1 according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic front sectional view showing an example of a printer 1 according to an embodiment of the present invention.

  The printer 1 in the present embodiment receives image data of an image to be formed from a user terminal 100 (for example, a personal computer, see FIG. 3) connected by a network, a cable, and the like, and forms an image on a sheet such as printer paper ( Print). As shown in FIG. 1, the printer 1 includes a sheet supply unit 2, a sheet conveyance path 3, an image forming unit 4, and a fixing unit 5. An operation panel 6 for the user to operate and set the printer 1 is provided, for example, at the upper front of the apparatus (shown by a broken line in FIG. 1).

  The sheet supply unit 2 is provided at the bottom of the printer 1 and mainly includes two cassettes 21 for stacking and storing sheets. The cassette 21 is provided with a sheet feeding roller 22, and the uppermost sheet among the sheets to be placed contacts the sheet feeding roller 22. The sheet feed roller 22 is rotated by receiving a drive from a sheet feed motor 2M (see FIG. 3) during image formation, and the sheet is fed into the sheet conveyance path 3.

  The sheet conveyance path 3 is a path for conveying sheets inside the apparatus from the cassette 21 to the discharge tray 31 on the upper surface of the printer 1. In the sheet conveyance path 3, a guide plate (not shown) for guiding the sheet conveyance direction, a registration roller pair 32 that is driven to rotate by receiving a drive from a conveyance motor 3M (see FIG. 3), and a plurality of rollers are appropriately provided. A conveyance roller pair 33 is provided. When the sheet arrives, the registration roller pair 32 does not rotate but bends the sheet to correct skew, and rotates the toner image according to the transfer timing of the toner image to the sheet to supply the sheet to the image forming unit 4. . The conveyance roller pair 33 conveys the sheet.

  The image forming unit 4 is provided almost in the center of the apparatus, and includes a photosensitive drum 41, a charging device 42, a laser unit 43 (corresponding to an exposure device), a developing device 44, a transfer roller 45, a cleaning device 46, and the like. The photosensitive drum 41 has a photosensitive layer (for example, an α-Si layer or an organic photosensitive layer) on the surface, extends in a direction perpendicular to the paper surface of FIG. 1, and includes a main motor 4M (see FIG. 3), a gear (not shown). 1 is rotated clockwise in FIG. When forming a toner image, first, the charging device 42 provided obliquely to the upper right of the photosensitive drum 41 charges the surface of the photosensitive drum 41 to a predetermined potential.

  Next, in FIG. 1, the laser unit 43 on the right side of the photosensitive drum 41 irradiates the circumferential surface of the photosensitive drum 41 with laser light (shown by a broken line) based on the input image data, and the photosensitive drum 41. The surface is scanned and exposed to form an electrostatic latent image. Details of the laser unit 43 will be described later.

  The developing device 44 supplies toner to the electrostatic latent image formed by scanning / exposure by the laser unit 43. Thereby, the electrostatic latent image is developed. The transfer roller 45 is rotatably supported and is pressed against the photosensitive drum 41 on the left side of the photosensitive drum 41 in FIG. When a sheet conveyed in time with the toner image enters the nip (transfer nip) between the transfer roller 45 and the photosensitive drum 41, a predetermined voltage is applied to the transfer roller 45, and the sheet is conveyed. The toner image is transferred to the sheet. The cleaning device 46 performs cleaning by removing toner remaining on the peripheral surface of the photosensitive drum 41 after the primary transfer.

  The fixing unit 5 performs a fixing process on the toner image transferred to the sheet. The fixing unit 5 includes, for example, a heating roller 51 provided with a heating element inside, and a pressure roller 52 pressed against the heating roller 51. The heating roller 51 and the pressure roller 52 are rotatably supported, and the driving force of the fixing motor 5M (see FIG. 3) is transmitted to either or both of the heating roller 51 and the pressure roller 52. And the pressure roller 52 rotates. When the sheet onto which the toner image has been transferred and conveyed enters a nip between the heating roller 51 and the pressure roller 52 (hereinafter referred to as “fixing nip”), the sheet is conveyed while being pressed and heated, The toner image is fixed. The processed sheet is discharged to the discharge tray 31.

  On the operation panel 6, a liquid crystal display unit 61 for displaying the state of the apparatus, an operation menu, and the like and various keys 62 for setting / input are arranged. The user can set the operation of the printer 1 while confirming the display on the liquid crystal display unit 61. According to the present invention, by pressing the key 62 on the operation panel 6, the user can instruct to perform image formation at half speed compared to normal image formation.

(Configuration of laser unit 43)
Next, based on FIG.1 and FIG.2, the structure of the laser unit 43 which concerns on embodiment of this invention is demonstrated. FIG. 2 is a schematic diagram showing an example of the configuration of the laser unit 43 according to the embodiment of the present invention.

  As shown in FIG. 1, the laser unit 43 (corresponding to an exposure apparatus) has a housing 43a for dust prevention and the like, and the semiconductor laser device 7 (corresponding to a laser light source) as shown in FIG. For example, a laser diode), a lens 71, a polygon motor 72, a polygon mirror 73 (corresponding to a rotating reflector), an fθ lens 74, a detection unit 75, and the like are provided.

  One semiconductor laser device 7 is provided for each color for scanning and exposure of the photosensitive drum 41 (that is, one in the present embodiment), and is turned on / off in correspondence with each pixel of image data of an image to be formed. Then, the photosensitive drum 41 is scanned and exposed. Although the details will be described later, in the present invention, the semiconductor laser device 7 receives the generation of the phase detection signal PDN of the detection unit 75 to synchronize the scanning of each line, and after the elapse of the predetermined time T1, Light emission for scanning / exposure of the photosensitive drum 41 is started in accordance with the data, and forced light emission is performed from the generation of the sample signal SPN until the detection unit 75 issues the phase detection signal PDN (see FIG. 5).

  The lens 71 adjusts the optical path of the laser light emitted from the semiconductor laser device 7. The polygon motor 72 rotates the polygon mirror 73. The polygon mirror 73 has a plurality of plane reflection surfaces, is formed in a polygonal column shape (in this embodiment, a hexagonal column), and is mirror-finished for reflection of laser light. If the polygon mirror 73 is rotated by the polygon motor 72 while irradiating the laser beam toward the polygon mirror 73 (an example of the rotation direction is indicated by a white arrow), the laser light from the semiconductor laser device 7 is deflected. As shown by the solid line arrow in FIG. 2, the irradiation position of the laser beam moves. A photosensitive drum 41 is disposed at the laser beam irradiation destination.

  In this manner, scanning and exposure of laser light for one line is performed in the main scanning direction (axial direction) of the photosensitive drum 41, and further, the photosensitive drum 41 rotates and scanning and exposure are repeated in line units. As a result, an electrostatic latent image is also formed in the sub-scanning direction (sheet conveying direction). That is, the laser unit 43 of the present embodiment includes the semiconductor laser device 7 and the polygon mirror 73, deflects the laser light with a rotating reflector to move the irradiation position of the laser light, and adjusts the laser light according to the image data. The photosensitive drum 41 is scanned and exposed by turning on and off 7. One or a plurality of fθ lenses 74 are provided (only one is shown in FIG. 2), and the difference in the optical path length from the polygon mirror 73 to the photosensitive drum 41 is corrected, and the scanning speed of the laser light becomes constant. Correct as follows.

  In addition, the detection unit 75 is provided outside the range in which the laser beam can be irradiated and outside the scanning / exposure range of the photosensitive drum 41. That is, the laser unit 43 is provided with a detection unit 75 that emits a detection signal when the laser beam is received in order to detect the scanning position of the laser beam when the laser beam of the semiconductor laser device 7 is incident thereon. The detection unit 75 is configured using a photodiode or a phototransistor, and generates a current (voltage) upon incidence of laser light. The time point when the laser beam irradiates the detection unit 75 can be confirmed by a signal generated by the detection unit 75.

  The signal of the detection unit 75 can be used as the phase detection signal PDN in the scanning period of the laser beam, and the phase detection signal PDN is used to synchronize the start and end points of scanning / exposure of each line (details). Will be described later). The installation position of the detection unit 75 is shown as the front side in the axial direction of the photoconductive drum 41 in FIG. 2, but it may be located in the back side in the axial direction of the photoconductive drum 41 or reflected by a mirror (not shown). The laser beam may be incident on the detection unit 75. That is, the detection unit 75 only needs to be able to detect the scanning cycle outside the scanning / exposure range of the photosensitive drum 41, and can freely determine the installation position.

(Hardware configuration of printer 1)
Next, an example of the hardware configuration of the printer 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a block diagram illustrating an example of a hardware configuration of the printer 1 according to the embodiment of the present invention.

  The printer 1 of this embodiment is provided with a control unit 8 having a CPU 81 and a storage unit 82 for controlling the operation of the printer 1. The CPU 81 is a central processing unit, and controls and calculates each unit of the printer 1 based on a control program and control data stored in the storage unit 82 and developed. The storage unit 82 includes a storage device such as a ROM, a RAM, an HDD, or a flash ROM, and stores a control program, control data, setting data, image data, and the like.

  The control unit 8 includes a sheet supply unit 2, a sheet conveyance path 3, an image forming unit 4, a fixing unit 5, an operation panel 6, a paper feed motor 2M, a conveyance motor 3M, a main motor 4M, a fixing motor 5M, an I / I The control unit 8 is connected to the F unit 83 (interface unit), the image data generation unit 9 and the like, and receives the outputs of sensors (not shown) provided in the respective units, and the control unit 8 controls the operations of these units.

  Here, the I / F unit 83 is provided with a connector or the like for connecting the user terminal 100 to the printer 1 through various networks, cables, and the like. Through this I / F unit 83, an image formation instruction from the user terminal 100, image data of an image to be formed, and setting data for printing are input to the control unit 8. In the present invention, when the user terminal 100 is used to set image formation at half speed with respect to normal image formation using the driver utility software of the printer 1 installed in the user terminal 100, the I / F The image forming instruction at half speed is input to the control unit 8 via the unit 83.

  The image data generation unit 9 performs image processing on the image data transmitted from the user terminal 100 and the image data stored in the storage unit 82 to generate and output image data to be transmitted to the laser unit 43. The semiconductor laser device 7 of the laser unit 43 turns on / off in response to the output from the image data generation unit 9. Specifically, the image data generation unit 9 is an image processing circuit unit configured by an ASIC (Application Specific Integrated Circuit), an IC chip, or the like that is an integrated circuit in which a plurality of functional circuits are integrated into a single circuit dedicated to image processing. 90, a CPU 91 that performs operations related to image processing, operation control of the image data generation unit 9, communication control with the control unit 8, and the like, and a work / storage area for developing image data and performing image processing A memory 92 (eg, RAM) is provided. The image data generation unit 9 can perform various image processing such as density change processing and enlargement / reduction processing. However, it is assumed that a known image processing technique can be applied, and a detailed detailed description of the image processing is omitted. .

  Here, the printer 1 of the present embodiment is capable of performing image formation at least at two speeds of a normal image forming speed and a half speed (half speed) with respect to the normal image forming speed. The control in that case will be described.

  In view of the fact that the time required for image formation at half speed has been reduced by increasing the printing speed in recent years, the printing speed has been intentionally halved to allow sufficient time for each process. It is intended to improve the quality of the formed image. In addition, since thick sheets such as thick paper and postcards are difficult to warm up, in the printing of thick sheets, the fixing unit 5 is sufficiently heated so that the image forming speed may be reduced to half speed.

  At the time of image formation at half speed, the printer 1 according to the present embodiment reduces the rotational speed of the photosensitive drum 41, the transfer roller 45, the heating roller 51 of the fixing unit 5, and the pressure roller 52 to 1/2 that of normal image formation. And As a result, the peripheral speed of the photosensitive drum 41 and the like is halved. Accordingly, the sheet conveyance speed entering the transfer nip or the fixing nip is halved, and a sufficient time can be taken in each process of image formation such as development, transfer, and fixing. The reduction in the rotation speed of the photosensitive drum 41, the heating roller 51, and the pressure roller 52 during image formation at half speed controls the rotation speed (rotation speed) of the main motor 4M and the fixing motor 5M by the CPU 81 of the control unit 8. Is realized.

  If the rotational speeds of the photosensitive drum 41, the heating roller 51, etc. are halved, but the rotational speeds of the paper feed motor 2M and the conveyance motor 3M remain the same, the subsequent sheet catches up with the preceding sheet. In some cases, jamming (clogging) may occur due to a difference in sheet conveyance speed. Therefore, when an image is formed at half speed, the control unit 8 also reduces the rotation speed of the paper feed motor 2M and the conveyance motor 3M to 1/2. Is possible to control.

  In the printer 1 according to the present embodiment, a sheet feeding motor 2M, a conveyance motor 3M, a main motor 4M, and a fixing motor 5M and four types of motors related to sheet conveyance are provided. For example, the sheet feeding roller 22 and the conveying roller pair 33 may be rotated by the same motor by connecting the electromagnetic clutch, and as a matter of course, each member that supplies and conveys the sheet with only one motor is used. It may be rotated. Moreover, you may make it provide a motor other than four types.

  When the image is formed at half speed, the polygon motor 72 is rotated at the same speed as that during normal image formation for scanning / exposure of the photosensitive drum 41. It is delayed by one cycle at the time of formation. That is, at the time of image formation at half speed, the scanning of each line is started after waiting for the scanning time (cycle) for one line, and the photosensitive member is skipped without performing the scanning / exposure operation for one cycle. The drum 41 is scanned and exposed (hereinafter referred to as “one line skip”). As a result, even when the rotational speed of the photosensitive drum 41 is halved, an electrostatic latent image having the same size as that during normal image formation is formed. In summary, at the time of image formation at half speed, the photosensitive drum 41 rotates at about half the normal speed, and the polygon mirror 73 of the laser unit 43 is rotated at the same speed as normal, and a counter 98 described later. The one line skip is realized by extending the predetermined interval T2 until the sample signal SPN is generated by the scanning period of one line of the laser light.

  In this scanning / exposure by skipping one line, the irradiation energy of the laser beam applied to the photosensitive drum 41 is theoretically the same as that during normal image formation. Therefore, it is not necessary to change parameters such as the charging potential of the photosensitive drum 41 by the charging device 42, the transfer bias, and the developing bias in the developing device 44 during normal image formation. That is, it is not necessary to adjust and set each parameter for each image forming speed, and it is not necessary to shorten the development period and to perform complicated control for each image forming speed.

(Hardware configuration in 1 line skip)
Next, based on FIG. 4, an example of a configuration for realizing one line skip in the printer 1 according to the embodiment of the present invention will be described. FIG. 4 is a block diagram showing an example of the configuration of one line skip in the printer 1 according to the embodiment of the present invention. Each configuration for skipping one line (video data output unit 93, sample signal generation unit 97, etc.) is basically provided in a part of the image processing circuit unit 90 of the image data generation unit 9. Although described, it is not always necessary to provide the image processing circuit unit 90, and the installation position and location are not particularly limited. Also, white arrows in FIG. 4 indicate the flow of image data, and solid arrows indicate the flow of signals.

  As shown in FIG. 4, the image processing circuit unit 90 of the image data generation unit 9 includes a video data output unit 93 and a sample signal generation unit 97. First, the video data output unit 93 is provided with a line buffer 94, a shift register 95, and an image data output counter 96 for measuring a predetermined time T1.

  The line buffer 94 can receive image data after completion of image processing from the memory 92 in units of lines in the main scanning direction, and can accumulate image data for a plurality of lines. The line buffer 94 outputs image data to the shift register 95 in units of one line or a plurality of lines in the main scanning direction. The shift register 95 is a video that instructs the semiconductor laser device 7 of the laser unit 43 to turn on and off one bit (one pixel) at a time in synchronization with the clock signal CLK generated by the clock generation circuit 200. The data signal VDA is output. When the semiconductor laser device 7 receives this video data signal VDA and turns it on and off, an electrostatic latent image corresponding to the image data is formed. The clock generation circuit 200 may be provided inside the image processing circuit unit 90 or inside or outside the image data generation unit 9, and there is no restriction on the installation location, and the clock signal CLK is generated. I just need it.

  The image data output counter 96 is a circuit that counts the clock signal CLK generated by the clock generation circuit 200 to measure time. The image data output counter 96 receives a laser beam phase detection signal PDN (corresponding to a detection signal) output by the detection unit 75 upon receiving the laser beam, and is reset by the phase detection signal PDN for a predetermined time. The clock signal CLK corresponding to T1 is counted. The clock count corresponding to the predetermined time T1 is determined by the time from the detection of the phase detection signal PDN to the start of scanning / exposure and the clock frequency.

  The image data output counter 96 instructs the shift register 95 to start outputting the video data signal VDA to the semiconductor laser device 7 when counting the clock signal CLK corresponding to the predetermined time T1. An output start signal VS is output. By the operation of the image data output counter 96, the output start time of the video data signal VDA is adjusted for each line, and the start / end positions of scanning / exposure on the lines in each main scanning direction coincide.

  On the other hand, the sample signal generator 97 is provided with a counter 98 and a sample signal register 99. The sample signal SPN is a signal for forcibly causing the semiconductor laser device 7 to emit light so that the detection unit 75 can receive laser light. That is, the detection unit 75 is provided so as to detect the irradiation of the laser beam outside the scanning / exposure range of the photosensitive drum 41 and within the movable range of the laser beam. In order to receive light, the semiconductor laser device 7 is forcibly set at a time when the detection unit 75 can receive light before or after the output of the video data signal VDA of each line (determined by the installation position of the detection unit 75). It is necessary to emit light.

  For example, the counter 98 counts a predetermined interval T2 until the sample signal SPN is generated. Specifically, after the phase detection signal PDN is input to the counter 98 and reset by the phase detection signal PDN, the counter 98 generates the clock signal CLK generated by the clock generation circuit 200 for a time corresponding to, for example, a predetermined interval T2. Count minutes. Note that the clock count corresponding to the predetermined interval T2 is determined by the time from the detection of the phase detection signal PDN to the start of forced light emission and the clock frequency. That is, the counter 98 measures time by counting the clock signal CLK of the clock generation circuit 200.

  For example, when the counter 98 counts the clock signal CLK corresponding to the predetermined interval T2, the counter 98 outputs the sample signal output start signal SS to the sample signal register 99. The sample signal register 99 stores a sample signal SPN (in other words, video data for lighting the semiconductor laser device 7). The sample signal register 99 receives the sample signal output start signal SS and receives the sample signal output signal SS. A sample signal SPN is issued toward In other words, the sample signal generator 97 generates the sample signal SPN, which is a signal for forcibly emitting the semiconductor laser device 7 so that the detector 75 receives the laser light, at a predetermined interval T2 by counting by the counter 98. .

  Further, in the counter 98 of the present embodiment, the count number (time) until the sample signal output start signal SS is issued can be switched to at least two stages. The count switching signal CS can be output from the CPU 81 of the control unit 8, the CPU 91 of the image data generation unit 9, or the like. The counter 98 receives this switching signal CS and switches the count number. That is, the control unit 8 switches and controls the count number of the counter 98 between the normal time and the half speed. For example, the CPU 81 and the counter 98 may be connected, and the CPU 81 may switch the count number of the counter 98. Alternatively, the CPU 91 may switch the count number of the counter 98 upon receiving a switching instruction from the CPU 81 of the control unit 8.

  Specifically, the counter 98 counts the number of clocks corresponding to the predetermined interval T2 during normal image formation, and in addition to the predetermined interval T2 during half-speed image formation, the laser beam during normal image formation. The counting is performed by adding the time corresponding to the scanning period T3 of one line. As described above, since the video data signal VDA is output after a predetermined time T1 after the generation of the phase detection signal PDN of the detection unit 75, the phase detection signal PDN is generated during image formation at half speed. If the predetermined interval T2 until the sample signal SPN is transmitted is extended by the time corresponding to the scanning period T3 for one line of laser light, one line skip is realized. That is, skipping one line can be realized simply by changing the clock count number in the counter 98.

(Signal generation timing for one line)
Next, with reference to FIG. 5, signal generation timings during normal image formation and half-speed image formation of the printer 1 according to the embodiment of the present invention will be described. FIG. 5 is a timing chart for explaining an example of various signal generation timings of the printer 1 according to the embodiment of the present invention.

  First, normal image formation will be described. In FIG. 5, the upper three timing charts show timing charts of the video data signal VDA, the sample signal SPN, and the phase detection signal PDN during normal image formation. The sample signal SPN and the phase detection signal PDN are negative logic (hereinafter the same).

  As shown in FIG. 5, during normal image formation, the video data signal VDA (first stage in FIG. 5) is a predetermined time from the detection of “Low” of the phase detection signal PDN (= laser light is incident on the detector 75). The output is started after the elapse of T1. Note that the video data signal VDA is indicated by vertical line shading because the semiconductor laser device 7 is repeatedly turned on and off by image data. The sample signal SPN (second stage in FIG. 5) is output after a predetermined interval T2 from the detection of “Low” of the phase detection signal PDN (High → Low). The sample signal SPN is output until “Low” of the phase detection signal PDN is detected, and when “Low” of the phase detection signal PDN is detected, the sample signal SPN is stopped (Low → High). Therefore, the semiconductor laser device 7 repeats the forced light emission by the sample signal SPN and the output of the video data signal VDA. Note that the writing start timing of the first line of the image data in the main scanning direction continues, for example, the forced light emission state of the semiconductor laser device 7, the rotational speed of the polygon motor 72 is stabilized, and the detection cycle of the phase detection signal PDN is constant. It may be determined with reference to the point of time and the sheet conveyance timing.

  Next, a description will be given of image formation at half speed based on FIG. In FIG. 5, the timing chart at the time of image formation at half speed is the fourth and lower stages. FIG. 5 shows a timing chart at the time of image formation at half speed of the video data signal VDA, the sample signal SPN, and the phase detection signal PDN in order from the fourth stage.

  As shown in FIG. 5, the video data signal VDA (fourth stage in FIG. 5) is also output after a predetermined time T1 has elapsed from the detection of “Low” of the phase detection signal PDN even during image formation at half speed. Is started. At the time of image formation at half speed, the sample signal SPN (fifth stage in FIG. 5) is detected by scanning period T3 corresponding to one line of laser light at a predetermined interval T2 from the detection of “Low” of the phase detection signal PDN. Is output after the time (T3 + T2 in FIG. 5) has elapsed (High → Low).

  The sample signal SPN is output until “Low” of the phase detection signal PDN is detected, and when the “Low” of the phase detection signal PDN is detected, the output of the sample signal SPN stops (Low → High). Is the same as in normal image formation. In this manner, the semiconductor laser device 7 is not lit at all for the scanning period T3 for one line, and the non-lighting for the scanning period T3 is realized only by switching the count number of the counter 98.

  Here, specific numerical values will be given for explanation. For example, during normal image formation, the scanning period T3 for one line of laser light is 300 μs, the output time of the video data signal VDA in one line is 200 μs, and the predetermined interval T2 counted by the counter 98 is 250 μs. To do. Therefore, after detecting “Low” of the phase detection signal PDN, the output of the sample signal SPN becomes “Low” after 250 μs (after the predetermined interval T2). Since the scanning cycle T3 for one line of the laser light is 300 μs, “Low” of the phase detection signal PDN is detected again 300 μs after detecting “Low” of the previous phase detection signal PDN. . As a result, the same operation is repeated for each line in the main scanning direction.

  Next, at the time of image formation at half speed, for example, the scanning cycle T3 for one line of laser light is set to 300 μs, which is the same as the normal time (because the rotation speed of the polygon motor 72 is not changed). Assume that the VDA output time is 200 μs. The time counted by the counter 98 is defined as a predetermined interval T2 + scanning cycle T3 for one line of laser light. That is, the count time is switched to 250 μs (predetermined interval T2) +300 μs (scanning period T3) = 550 μs according to an instruction from the control unit 8.

  With regard to the hardware configuration in the switching of the counter 98, if configured as in the present embodiment, the number of bits that can be counted by the counter 98 is increased by about 1 bit to the configuration at the time of normal image formation (for example, (10 bits to 11 bits), the count number is doubled, and one line skip at half speed is realized. Therefore, the circuit configuration of one line can be greatly simplified. The number of bits (number of digits) that the counter 98 should count at the time of image formation at half speed is determined by the clock frequency of the clock generation circuit 200, the predetermined interval T2, and the period of one line. For example, when four-bit counters are connected and used, if there are three 4-bit counters, it is possible to count either 10 bits or 11 bits, and it may be unnecessary to add the counters themselves.

Note that the number of digits by which the counter 98 increases the number of bits that can be counted with respect to the number of counts during normal image formation is not limited to 1 bit, and may be 2 bits or 3 bits, and may be 1 bit or more. If the number of bits is increased by 2 bits, the countable number is quadrupled, and if the sheet conveyance speed is ¼, image formation at ¼ speed can be realized. Further, if the number of bits is increased by 3 bits, the countable number becomes 8 times, and if the sheet conveyance speed is made 1/8, image formation at 1/8 times speed can be realized. That is, if n bits (n is an integer) is increased, the sheet conveyance speed is set to 1 / n.
Image formation at 1/2 ⁿ times speed becomes possible.

  Next, an example of a control flow in image formation of the printer 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 6 is a flowchart illustrating an example of control at the time of image formation of the printer 1 according to the embodiment of the present invention. In this description, in order to simplify the description, the image forming speed of the printer 1 is two types, that is, a normal image forming speed and a half speed thereof, and a case where only one sheet is printed will be described. When printing a plurality of sheets, the flow may be repeated.

  First, the start is when an image formation instruction is given to the printer 1. For example, when image data or setting data for printing is transmitted from the user terminal 100 to the I / F unit 83 of the printer 1, it can be determined that an image formation instruction has been issued.

  Next, the control unit 8 determines that the print setting data transmitted from the driver application software installed in the user terminal 100 does not include data instructing printing at half speed, or the sheet to be printed is thick paper Therefore, the necessity of image formation at half speed is checked (step # 1). Also, it is checked whether or not an input indicating that image formation should be performed at half speed from the operation panel 6 is performed (step # 2). If a sheet thickness detection sensor (not shown) is provided in the cassette 21 or the sheet conveyance path 3, the control unit 8 may confirm the sheet thickness.

  Then, the control unit 8 confirms from step # 1 and step # 2 whether printing should be performed at a normal image forming speed (not half-speed image formation) (step # 3). When printing at a normal image forming speed (Yes in step # 3), the control unit 8 sets the time measured by the counter 98 of the sample signal SPN generation unit to a predetermined interval T2 (step # 4). Then, the control unit 8 sets and drives the rotation speed of each motor related to sheet conveyance, such as the conveyance motor 3M, the main motor 4M, and the fixing motor 5M, as a normal speed, thereby forming an image with the sheet conveyance speed as a normal speed. Perform (Step # 5 → End).

  On the other hand, when printing is performed at the half-speed image forming speed (No in step # 3), the control unit 8 sets the time measured by the counter 98 of the sample signal SPN generation unit to a scanning interval T3 corresponding to a predetermined interval T2 + one line of laser light. (Step # 6). Then, the control unit 8 sets and drives the rotation speed of each motor related to sheet conveyance, such as the main motor 4M, the fixing motor 5M, and the conveyance motor 3M, as half of normal image formation, so that the sheet conveyance speed is set to normal. The image is formed at half the speed (step # 7 → end).

  As described above, according to the configuration of the present invention, when the image is formed at half speed, the rotation speed of the polygon mirror 73 (reflection rotator) is set to the same speed as that during normal image formation, and the laser light irradiation cycle is changed. Therefore, the irradiation energy to the photosensitive drum 41 does not change at normal time or at half speed. Therefore, it is not necessary to adjust / set parameters for each process in image formation for each image formation speed. Further, one line skip is realized by extending the predetermined interval T2 until the sample signal SPN is generated by the time of the scanning period T3 of one line of laser light. That is, the counter 98 of the sample signal generation unit 97 is configured to be able to count up to about twice that during normal image formation, and by skipping the operation of the counter 98 according to the image forming speed, one line can be skipped. The In order to double the count number of the counter 98, it is only necessary to increase it by about one digit in terms of bits.

  Therefore, unlike the prior art, there is no need for a complicated circuit configuration in which two semiconductor laser devices 7 (laser light sources) are provided for each color and reading / writing to the memory is prohibited for each line due to the establishment of a new circuit or the like. Thus, one line can be easily skipped at a low manufacturing cost. Further, according to the present invention, it is only necessary to switch the counting operation of the counter 98 for skipping one line, which eliminates the need for complicated circuit design and verification of the operation of the designed circuit, thereby reducing development costs. Is done.

  Further, the counter 98 counts the clock signal CLK, and the control unit 8 switches the count number of the counter 98 at the normal time and the half speed, so that the respective photosensitive members at the normal time and the half speed can be easily obtained. Appropriate scanning / exposure to the drum 41 is realized. The laser light source receives the output of the phase detection signal PDN (detection signal) from the image data output counter 96 and starts scanning / exposure of the photosensitive drum 41 after a predetermined time T1 has passed. When the signal output is forcibly emitted after a predetermined interval T2, the detection signal is used in common for the reset signal of both counters 98, so that the timing start timings of the predetermined time T1 and the predetermined interval T2 can be matched. . Therefore, it is possible to operate the laser light source by reliably distinguishing the exposure of the photosensitive drum 41 from the forced light emission based on the coincidence of the timing start timing. Further, since the reset signal is shared, the circuit configuration can be simplified, and the manufacturing cost of the image forming apparatus can be reduced.

  Further, since the clock signal CLK counted by the image data output counter 96 and the counter 98 is shared, the clock generation circuit 200 can be shared, and the time of the predetermined time T1 and the predetermined interval T2 can be accurately measured. . Therefore, the circuit configuration can be simplified, and the manufacturing cost of the image forming apparatus can be reduced. In addition, since it is possible to realize image formation by skipping one line at half speed regardless of the two-beam method as in the prior art, only one laser light source is required for each color, which is necessary for the exposure apparatus and the image forming apparatus. Members can be reduced. Accordingly, the manufacturing costs of the exposure apparatus and the image forming apparatus can be reduced.

  Hereinafter, another embodiment will be described. In the above-described embodiment, the case of the monochrome printer 1 has been described. However, for example, the tandem-type printer 1 compatible with tandem color printing having a plurality of photosensitive drums 41, charging devices 42, and developing devices 44 corresponding to the toner colors. The present invention can also be applied to an image forming apparatus such as a printer. When the exposure apparatus in the color image forming apparatus is the laser unit 43, a plurality of semiconductor laser devices 7 are usually provided for the toner color, and a sample signal generator 97 is provided for each of the semiconductor laser devices 7. If the number of bits that can be counted by each counter 98 is increased by about 1 bit, one line can be skipped at half speed.

  Moreover, although the embodiment of the present invention has been described, the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention can be used for an image forming apparatus such as a printer, a copying machine, or a multifunction machine that performs scanning / exposure with a laser beam.

1 is a schematic front cross-sectional view illustrating an example of a printer according to an embodiment. It is the schematic which shows an example of a structure of the laser unit which concerns on embodiment. FIG. 3 is a block diagram illustrating an example of a hardware configuration of a printer according to an embodiment. 3 is a block diagram illustrating an example of a configuration of one line skip in the printer according to the embodiment. FIG. 5 is a timing chart for explaining an example of various signal generation timings of the printer according to the embodiment. 6 is a flowchart illustrating an example of image formation control of the printer according to the embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer (image forming apparatus) 41 Photosensitive drum 43 Laser unit (exposure apparatus) 7 Semiconductor laser apparatus (laser light source)
72 polygon motor 73 polygon mirror (rotary reflector)
75 Detection unit 8 Control unit 9 Image data generation unit 96 Image data output counter 97 Sample signal generation unit 98 Counter 200 Clock generation circuit PDN Phase detection signal (detection signal)
SPN sample signal CLK clock signal T1 predetermined time T2 predetermined interval T3 1 line scanning cycle

Claims (5)

At least in an image forming apparatus capable of forming an image at two speeds, a normal image forming speed and a half speed of a normal image forming speed,
A control unit for controlling the operation of the device;
A rotating photosensitive drum,
A laser light source and a rotary reflector are provided, the laser light is deflected by the rotary reflector to move the irradiation position of the laser light, and the laser light source is turned on and off according to image data to scan the photosensitive drum. An exposure apparatus that performs exposure;
An image data generation unit for outputting image data to the exposure apparatus;
A detection unit that emits a detection signal when laser light is received in order to detect a scanning position of the laser light when the laser light of the laser light source is incident in the exposure apparatus;
A sample signal generator for generating a sample signal, which is a signal for forcibly causing the laser light source to emit light, in order to receive the laser beam, at a predetermined interval by counting by a counter;
The laser light source starts light emission for scanning / exposure of the photosensitive drum in accordance with image data after a lapse of a predetermined time from the generation of the detection signal of the detection unit for synchronization of scanning of each line. In addition, forced emission is performed until the detection unit emits the detection signal from the generation of the sample signal,
When forming images at half speed,
The photosensitive drum rotates at half the normal speed,
The reflection rotator of the exposure apparatus is rotated at the same speed as normal,
2. The image forming apparatus according to claim 1, wherein the counter extends the predetermined interval until the sample signal is generated by a scanning period of one line of laser light. A clock generation circuit for generating a clock signal is provided;
The counter measures time by counting the clock signal of the clock generation circuit,
The image forming apparatus according to claim 1, wherein the control unit switches and controls a count number of the counter between a normal time and a half speed. The image data generation unit is provided with an image data output counter for measuring the predetermined time,
The detection signal of the detection unit is input to the counter and the image data output counter,
The image forming apparatus according to claim 1, wherein the counter and the image data output counter are reset by the detection signal.   The image forming apparatus according to claim 3, wherein the image data output counter counts the clock signal generated by the clock generation circuit to measure time. The detection unit is provided outside the exposure range of the photosensitive drum,
The reflection rotator is a polygon mirror rotated by a polygon motor,
The image forming apparatus according to claim 1, wherein the number of the laser light sources is one for each color.

Images