JP2009006561A - Image formation device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image formation device, in which a formed image is not affected by correcting a light-intensity change to be constant even if the light intensity of a laser diode 7 is changed due to the influence of a continuous printing, operating environment and temperature in device. <P>SOLUTION: The image formation device having the laser diode 7 and a photosensitive body is equipped with a light-intensity detection part 8a for detecting the light intensity of a laser beam emitted by the laser diode 7, a memory unit 8c for memorizing a reference voltage output from the light-intensity detection part 8a, a comparison part for outputting a correction signal to correct the light intensity of the laser diode 7 such that the output voltage of the light-intensity detection part 8a becomes equal to the reference voltage when the both voltages are different in comparing the voltage output from the light-intensity detection part 8a with the reference voltage memorized by the memory unit 8c, and a light-intensity correction part 8d which corrects the light intensity of the laser diode 7 according to the correction signal output from the comparison part. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, or a multifunction machine that performs image formation by scanning and exposing the surface of a photoreceptor.

  Conventionally, in image forming apparatuses such as printers, copiers, and multifunction machines, when an image is formed, after the photosensitive drum is charged to a predetermined potential, the exposure device scans the photosensitive drum based on the image data. Exposure to form an electrostatic latent image, supply toner to the electrostatic latent image, develop the toner image, transfer the toner image to various sheets such as copy paper, and fix the toner image; Some perform image formation (electrophotographic method).

  When a photosensitive drum is scanned and exposed to form an electrostatic latent image, a laser diode may be employed as a light source. The laser diode is turned on and off in accordance with the image data of the image to be formed. The laser light emitted from the laser diode is guided to the photosensitive drum by a polygon mirror, a polygon motor, an fθ lens, etc., and scanning and exposure of the photosensitive drum are performed.

  However, in the laser diode, when the temperature changes, the threshold current (current value at which the output of the laser diode increases rapidly), the oscillation wavelength of the laser light, and the light amount (light output) change. That is, the characteristics of the laser diode change with temperature. Accordingly, depending on the environmental temperature and the temperature inside the apparatus, there are cases where the photosensitive drum is scanned and exposed by laser light which is not optimal, which affects the formed image, for example, the density of the image.

  For example, regarding the temperature rise, the temperature of the laser diode rises due to heat generation of the laser diode itself, heat radiation of a polygon motor that rotates a polygon mirror that deflects laser light, or the like. In particular, when image formation is performed continuously, the temperature of the laser diode rises. Furthermore, in recent years, due to demands for higher processing speed and higher image quality (improved image resolution) of image forming apparatuses, laser diodes have been increased in output and polygon motors have also been rotated at higher speeds, so that the temperature of the laser diodes has been further increased. In this situation, it is easy to change, and it is difficult to maintain the optimal light quantity for scanning / exposure.

Japanese Patent Application Laid-Open No. 2004-228688 describes a configuration for making the amount of emitted laser light constant corresponding to the change in characteristics of the laser diode due to this temperature. In Patent Document 1, for example, in an image forming apparatus that develops an electrostatic latent image obtained by irradiating a charged photoreceptor with laser beam light modulated from a laser light source with toner and obtains an image, the laser light source Supply means for supplying current, detection means for detecting the amount of light output from the laser light source, and light intensity output from the laser light source corresponding to the detection result of the detection means forms an electrostatic latent image. An image forming apparatus including a control unit that controls a current value supplied by a supply unit so as to be stabilized at a predetermined level obtained is disclosed. (See Patent Document 1: Claim 2, FIG. 3, etc.).
JP-A-7-89130

  In Patent Document 1, the amount of laser diode light is monitored using a photodiode, and as a result, the threshold current is set so that the laser diode drive current becomes a predetermined value (see Patent Document 1: Paragraph 0028). . However, after all, the invention described in Patent Document 1 merely sets the threshold current and sets the laser diode driving current to a predetermined value. There is a problem that it is not possible to completely cope with changes in wavelength and light quantity. Patent Document 1 does not specifically show how to determine the laser diode drive current.

  The present invention has been made in view of the above-mentioned problems of the prior art, and corrects the change in the light amount even if the light amount changes due to the temperature characteristics of the laser diode such as continuous printing, use environment, and internal temperature. An object of the present invention is to provide an image forming apparatus that does not affect the formed image by making the light quantity constant.

  In order to solve the above problems, an invention according to claim 1 is an image forming apparatus including a laser diode and a photoconductor, wherein the laser diode turns on / off emission of laser light in accordance with image data of an image to be formed. A laser emitted from the laser diode in an image forming apparatus that is turned off and deflects the emitted laser light by an optical system member and irradiates the photosensitive member to form an electrostatic latent image on the photosensitive member. A light amount detection unit that detects a light amount of light and outputs the detected light amount as a voltage, a storage unit that stores a reference voltage of a voltage output by the light amount detection unit, a voltage output by the light amount detection unit, and the storage When the reference voltage stored in the light quantity detection unit is different from the reference voltage stored in the light quantity detection unit, the output voltage of the light quantity detection unit matches the reference voltage. A comparing section for outputting a correction signal for correcting the light amount of The diode, in accordance with the correction signal the comparison unit outputs, was to have a light amount correcting unit for correcting a light amount of said laser diode.

  According to this configuration, since the light amount of the laser diode is corrected so that the output voltage of the light amount detection unit matches the reference voltage as a reference, the laser is always used regardless of the characteristics (for example, temperature change) of the laser diode. The light quantity of the diode can be made constant. That is, the amount of current flowing through the laser diode that is affected by temperature changes is not used as a reference. Therefore, it is possible to provide an image forming apparatus in which there is no fluctuation in the amount of laser light for exposing the photosensitive drum, for example, there is no underexposure and the quality of the formed image is constant.

  According to a second aspect of the present invention, in the first aspect of the invention, the light amount detection unit includes a photoelectric conversion unit that outputs received laser light as a current, and a current that amplifies the current output from the photoelectric conversion unit. An amplification unit and a current-voltage conversion unit that converts the current output from the current amplification unit into a voltage output are included.

  According to this configuration, the light amount detection unit is configured to have a configuration of a photoelectric conversion unit and a current-voltage conversion unit, and can easily convert the light amount of the laser diode into a voltage. Therefore, the light quantity can be clearly compared with the voltage as a reference. In addition, this invention shows an example of suitable embodiment.

  According to a third aspect of the present invention, in the second aspect of the present invention, the photoelectric conversion unit is disposed so as to receive a laser beam irradiated outside an electrostatic latent image forming region of the photoconductor, The light quantity detection unit outputs a horizontal synchronization signal for synchronizing the irradiation of the laser beam to the photoconductor based on the output of the photoelectric conversion unit.

  According to this configuration, since the photoelectric conversion unit is not provided in the vicinity of the laser diode, the photoelectric conversion unit can be hardly affected by the heat generated by the laser diode, and the amount of light can be detected more accurately. The light quantity detection unit detects the light quantity of the laser diode, adjusts the timing of laser light irradiation to the photosensitive member, and performs horizontal synchronization to start writing at the same position in the circumferential direction of the photosensitive member. Also outputs signals. That is, the light amount detection unit can be provided with functions as a light amount detection unit and a horizontal synchronization signal output unit, and cost and space can be reduced compared to the case where both functions are provided separately.

  The invention according to claim 4 is the invention according to claim 2 or 3, wherein the photoelectric conversion unit is a photodiode, and the current-voltage conversion unit is configured by a resistor.

  According to this structure, since the member which comprises a light quantity detection part is cheap, it can achieve cost reduction. Further, the configuration of the light quantity detection unit itself can be simplified, the life and reliability of the light quantity detection unit can be improved, and the light quantity of the laser diode can be accurately detected over a long period of time.

  The invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the light amount correction unit corrects the light amount of the laser diode by changing a bias current flowing through the laser diode. It was.

  According to this configuration, the current for driving the laser diode is corrected by increasing / decreasing the bias current previously supplied to the laser diode in order to shorten the time until the laser diode oscillates. Therefore, the light amount of the laser diode can be made constant in response to changes in the light amount of the laser light and the oscillation wavelength depending on the temperature.

  The invention according to claim 6 is the invention according to any one of claims 1 to 5, wherein a temperature detection unit for detecting the temperature in the device is provided in the device, and the comparison unit is When the temperature detection unit detects a temperature change equal to or greater than a predetermined value, the output voltage of the light amount detection unit is compared with a reference voltage and a correction signal is output.

  According to this configuration, the light amount can be corrected only when the temperature changes by a predetermined value or more and the light amount of the laser diode is considered to vary greatly, and the light amount can be corrected efficiently. For example, the time for correcting the light amount can be reduced.

  As described above, according to the present invention, even if the light quantity of the laser diode changes due to the characteristics of the laser diode such as a temperature change, the light quantity of the laser diode can always be made constant, and the quality of the formed image An image forming apparatus with high image quality can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. 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.

  First, the present invention can be applied to various image forming apparatuses. As an example, a case where the present invention is applied to a color-compatible printer 1 among image forming apparatuses will be described with reference to FIG. FIG. 1 is a schematic front sectional view showing a schematic structure of a printer 1 according to an embodiment of the present invention.

  The printer 1 according to the present embodiment receives image data of an image to be formed from an external computer 100 connected via a network, a cable, and the like, and forms an image on a sheet S such as copy paper. As shown in FIG. 1, the printer 1 includes an intermediate transfer unit 2, an image forming unit 3, a fixing unit 4, a sheet supply unit 5, a sheet conveyance path 6, and the like in a box-shaped apparatus body. Is provided.

  The intermediate transfer unit 2 and the image forming unit 3 are in contact with each other and are provided in a central portion inside the apparatus main body. The image forming unit 3 includes four image forming units 31 to form toner images of a plurality of colors. Details of the intermediate transfer unit 2 and the image forming unit 3 will be described later.

  The fixing unit 4 performs fixing processing on the toner image formed by the image forming unit 3 and then transferred to the sheet S by the intermediate transfer unit 2. The fixing unit 4 includes a heating roller 41 provided with a heating element therein, and a pressure roller 42 that presses against the heating roller 41. Then, the sheet S on which the toner image is transferred enters the nip between the heating roller 41 and the pressure roller 42 through the sheet conveyance path 6 and is pressed and heated to fix the toner image. The sheet S after the completion of processing is discharged to the discharge tray 61.

  The sheet supply unit 5 is provided at the lowermost part of the printer 1 and includes a cassette 51, a mounting plate 52, a pickup roller 53, and the like. The cassette 51 is detachable from the printer 1 and has a box shape with an upper surface opened. The placement plate 52 is disposed inside the cassette 51, and stacks various sheets S such as printer paper, label paper, OHP sheets, and cardboard, and makes the uppermost sheet S contact the pickup roller 53. The pickup roller 53 sends out the sheets S one by one to the sheet conveyance path 6 during image formation.

  The sheet conveyance path 6 is a path through which the sheet S is conveyed from the sheet supply unit 5 through the intermediate transfer unit 2 and the fixing unit 4 to the discharge tray 61. A guide and a pair of conveyance rollers 62 are appropriately provided in the sheet conveyance path 6.

  Next, the intermediate transfer unit 2 and the image forming unit 3 will be described in detail with reference to FIG. FIG. 2 is an enlarged front schematic cross-sectional view of the intermediate transfer unit 2 and the image forming unit 3 of the printer 1 according to the embodiment of the present invention.

  The image forming unit 3 includes four image forming units 31K, 31Y, 31C, and 31M. Here, the image forming unit 31K forms black, the image forming unit 31Y forms yellow, the image forming unit 31C forms cyan, and the image forming unit 31M forms magenta. Each of the image forming units 31K, 31Y, 31C, and 31M has almost the same configuration although the color of the toner to be used is different. Therefore, the characters K, Y, C, and M are used unless otherwise described below. Is omitted.

  Each image forming unit 31 includes a photosensitive drum 32 (corresponding to a photosensitive member), a charging device 33, an exposure device 34, a developing device 35, a cleaning device 36, and the like. The photosensitive drum 32 is rotated counterclockwise by a driving mechanism (not shown) including a motor, a gear, and the like. When forming a toner image, first, the charging device 33 provided below the photosensitive drum 32 charges the peripheral surface of the photosensitive drum 32 to a predetermined potential.

  Next, the exposure device 34 further below the charging device 33 irradiates the charged photosensitive drum 32 with a laser beam (illustrated by a broken line) corresponding to each color based on the input image data, and the photosensitive member. The surface of the drum 32 is scanned and exposed to form an electrostatic latent image. Details of the exposure device 34 will be described later.

  The developing device 35 supplies toner to the electrostatic latent image, and the electrostatic latent image on the photosensitive drum 32 is developed with the toner. Each image forming unit 31 has a different toner color supplied from the developing device 35. In this embodiment, four colors of black, yellow, cyan, and magenta are used. The cleaning device 36 performs cleaning by removing the toner remaining on the peripheral surface of the photosensitive drum 32 after the primary transfer.

  Next, the intermediate transfer unit 2 will be described.

  The intermediate transfer unit 2 includes a driving roller 21, a driven roller 22, a primary transfer roller 23, an intermediate transfer belt 24, a secondary transfer roller 25, and the like.

  The drive roller 21 is connected to a drive mechanism (not shown) including a motor, a gear, and the like, and is driven to rotate at a predetermined speed. The intermediate transfer belt 24 is stretched around the drive roller 21, the driven roller 22, and the primary transfer roller 23, and the intermediate transfer belt 24 circulates when the drive roller 21 rotates (in FIG. 2, the intermediate transfer belt 24 rotates clockwise). ).

  Further, a total of four primary transfer rollers 23 are provided and abut on the respective photosensitive drums 32 via the intermediate transfer belt 24. Further, in order to primarily transfer the toner image formed on the photosensitive drum 32 to the intermediate transfer belt 24, a predetermined voltage is applied to the primary transfer roller 23 at a predetermined timing.

  The specific primary transfer sequence is the start position of the primary transfer on the intermediate transfer belt 24, the transfer of the magenta toner image on the photosensitive drum 32 of the image forming unit 31M is started, and then the same as the magenta. A cyan toner image by the image forming unit 31C is overlaid at the start position of the primary transfer, and thereafter a yellow toner image by the image forming unit 31Y and a black toner image by the image forming unit 31K are overlaid in the same manner. As a result, a full-color toner image is superimposed on the surface of the intermediate transfer belt 24.

  The secondary transfer roller 25 is in contact with the drive roller 21 via the intermediate transfer belt 24, and a predetermined voltage is applied at a timing when the toner image formed to overlap the nip and the conveyed sheet S overlap. The toner image on the intermediate transfer belt 24 is secondarily transferred to the sheet S. The sheet S to which the toner image is transferred is sent to the fixing unit 4 where the toner image is fixed. The intermediate transfer belt 24 after the secondary transfer is cleaned by removing residual toner and the like by a belt cleaning device 26 that contacts the driven roller 22 via the intermediate transfer belt 24.

  Next, the details of the exposure apparatus 34 according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a schematic cross-sectional view for explaining the configuration of the exposure apparatus 34 according to the embodiment of the present invention.

  Note that the printer 1 according to the embodiment of the present invention is color-compatible and includes four photosensitive drums 32. However, scanning and exposure performed on each photosensitive drum 32 are the same, and FIG. For convenience, scanning and exposure of one photosensitive drum 32 will be shown and described.

  The exposure apparatus 34 of the present embodiment is configured as a unit that performs scanning and exposure using laser light. Specifically, the exposure device 34 includes a laser diode 7, a polygon mirror 71, a polygon motor 72, and an fθ lens 73. The laser diode 7 is turned on / off to emit laser light in accordance with pixels of image data to be formed. In other words, turning on and off is repeated according to the image data. The laser light from the laser diode 7 is emitted toward the polygon mirror 71.

  The polygon mirror 71 has a plurality of plane reflecting surfaces on the peripheral surface and is formed in a polygonal column shape (in this embodiment, a hexagonal column). The polygon mirror 71 has a mirror-finished surface. The polygon mirror 71 is rotated by a polygon motor 72, and the rotation position of the polygon mirror 71 moves the irradiation position of the laser light along the axial direction of the photosensitive drum 32 (the moving direction is indicated by a solid arrow). Here, the peripheral surface of the photosensitive drum 32 is charged to a constant potential, but the charge is erased in the portion irradiated with the laser beam.

  In order to make the movement of the laser beam irradiation position on the photosensitive drum 32 constant, an fθ lens 73 is provided. The fθ lens 73 corrects the difference in optical path length and corrects the scanning speed of the laser light to be constant. In the present embodiment, two fθ lenses 73 are provided.

  In FIG. 3, the area where the electrostatic latent image is formed on the photosensitive drum 32 does not use up the entire length of the photosensitive drum 32 as shown by the broken line, and is slightly at both ends of the photosensitive drum 32. An area where no electrostatic latent image is formed is provided.

  A mirror 74 is disposed in the vicinity of the photosensitive drum 32, and the laser beam reflected by the mirror 74 is received by a photodiode 75 (corresponding to a photoelectric conversion unit). As described above, the photodiode 75 is disposed closer to the photosensitive drum 32 than the laser diode 7 and is disposed so as to receive the laser light irradiated outside the electrostatic latent image forming area of the photosensitive drum 32. . The current generated by the incidence of light on the photodiode 75 is converted into a voltage in order to detect the amount of light of the laser diode 7 and is also synchronized horizontally to synchronize the irradiation of the laser light in the circumferential direction of the photosensitive member. Used for signal output (details will be described later).

  Therefore, the incident angle and the incident position of the laser beam on the polygon mirror 71 are adjusted so that the light emitted from the laser diode 7 is incident on the photodiode 75. In other words, the laser light is also irradiated outside the electrostatic latent image forming area of the photosensitive drum 32, and the photodiode 75 receives the laser light irradiated outside the electrostatic latent image forming area.

  In this way, the photosensitive drum 32 is rotated and the scanning exposure is repeated while the horizontal synchronization is performed and the scanning / exposure start positions on the circumferential surface of the photosensitive drum 32 are made to coincide with each other. An electrostatic latent image is also formed sequentially in the direction, and a two-dimensional electrostatic latent image is formed on the peripheral surface of the photosensitive drum 32. When the developing device 35 supplies toner to the electrostatic latent image, the electrostatic latent image is developed as a toner image.

  Since the printer 1 according to this embodiment is color-compatible, the exposure device 34 can include four sets of laser diodes 7, fθ lenses 73, mirrors 74, and photodiodes 75 for forming toner images of the respective colors. . On the other hand, one polygon mirror 71 and one polygon motor 72 are provided in the exposure device 34, and four laser beams are adjusted by adjusting the incident angle and incident position of the laser light emitted from each laser diode 7 to the polygon mirror 71. The photoconductor drum 32 is scanned and exposed.

  Further, a temperature sensor 76 (corresponding to a temperature detection unit, for example, a thermistor) is provided in the vicinity of the laser diode 7 according to the present embodiment. This is for detecting the temperature of the exposure device 34 and the laser diode 7.

  Further, the laser diode 7 according to the embodiment of the present invention is controlled so that the amount of light is constant even if the laser diode 7 itself or the ambient temperature in the exposure device 34 changes. Therefore, the point that the characteristics of the laser diode change with temperature will be described with reference to FIG.

  FIG. 4 is a diagram showing an example of a change in characteristics due to temperature of a laser diode, (a) is a graph showing an example of a correlation between threshold current and temperature, and (b) is a graph showing a correlation between oscillation wavelength and temperature. It is a graph which shows an example.

  As shown in FIG. 4A, as the temperature of the laser diode rises, the threshold current Ith of the laser diode also increases (for example, it is about 22 to 23 mA at 10 ° C., whereas 60 ° C. Then, it exceeds 30 mA.) If the current flowing through the laser diode does not exceed the threshold current Ith, the inversion distributed carrier density does not exceed the value necessary for causing laser oscillation, and stimulated emission does not occur, so that almost no laser light is emitted. Therefore, if the temperature of the laser diode rises, it is necessary to increase the current flowing through the laser diode in order to emit laser light. On the other hand, even if the temperature falls, the light quantity of the laser diode may be too strong unless the current flowing through the laser diode is changed.

  Next, referring to FIG. 4B, the wavelength Lp of the laser light emitted from the laser diode becomes longer as the temperature of the laser diode increases (for example, about 780 nm at 10 ° C., whereas At 60 ° C., it is about 793 nm). This is said to be partly due to a decrease in the energy of the emitted photons because the band gap becomes narrower due to the influence of heat as the temperature increases. In general, the shorter the wavelength, the higher the energy of the photon, so if the wavelength increases due to temperature rise, the light output may decrease and the amount of light may decrease (for example, from red to infrared). .

  Thus, when the temperature of the laser diode changes, not only the threshold current but also the portion depending on the type of the laser diode is large, but the wavelength and light quantity also change. In particular, due to recent demands for higher definition and higher processing speed of image forming apparatuses, laser diodes with higher output have been adopted, and the rotational speed of polygon motors has been increased. Then, although the exposure apparatus 34 is usually provided with a heat exhaust mechanism (for example, a cooling fan), the light quantity of the laser diode is kept constant by the self-heating of the laser diode and the increase of the heat released from the polygon motor. Is a difficult situation. If the light amount of the laser diode is not constant, unevenness will occur in exposure, and adverse effects will occur such as density unevenness in the formed image.

  On the other hand, according to the present invention, even if the temperature in the laser diode 7 or the printer 1 changes, the light quantity of the laser diode 7 is made constant and the quality of the formed image is improved.

  Therefore, a configuration for keeping the light amount of the laser diode 7 according to the embodiment of the present invention constant will be described below with reference to FIGS. FIG. 5 is a block diagram showing an example of the configuration of the printer 1 according to the embodiment of the present invention. FIG. 6 is a circuit diagram showing an example of a configuration for making the light quantity of the laser diode 7 according to the embodiment of the present invention constant.

  As a configuration for making the light amount of the laser diode 7 constant, the printer 1 according to this embodiment includes a light amount detection unit 8a, a comparison circuit 8b (corresponding to a comparison unit), a storage unit 8c, a light amount correction unit 8d, and the like. The outline of each component will be described.

  As shown in FIG. 5, the printer 1 according to the embodiment of the present invention includes a light amount detection unit 8 a as a configuration for detecting the light amount of the laser diode 7. The light amount detection unit 8a includes a photodiode 75 (corresponding to a photoelectric conversion unit), a resistor 81 (corresponding to a current-voltage conversion unit), and the like, detects the light amount of the laser diode 7, and outputs the light amount as a voltage. Further, a Schmitt trigger 82 for outputting a horizontal synchronizing signal for scanning / exposure to the photosensitive drum 32 is also provided.

  The comparison circuit 8b is a part that compares the output voltage of the light amount detection unit 8a with the reference voltage stored in the storage unit 8c. As a result of the comparison calculation, a voltage for controlling the light amount of the laser diode 7 is output to the light amount correction unit 8d as a correction signal for correcting the light amount of the laser diode 7. Further, a temperature sensor 76 is connected to the comparison circuit 8b, and the temperature sensor 76 functions as a switch for allowing the comparison circuit 8b to perform a comparison calculation only when a certain temperature change occurs.

  The light quantity correction unit 8d is a part that receives the signal for correcting the light quantity of the laser diode 7 from the comparison circuit 8b and controls the light quantity of the laser diode 7 of the exposure device 34. By this light amount control, the light amount of the laser diode 7 of the exposure device 34 is maintained in an appropriate range.

  In addition, the printer 1 according to the embodiment of the present invention includes a control unit 9 on a substrate that is appropriately provided inside the printer 1 in order to control each component such as the image forming unit 3 and the intermediate transfer unit 2. The control unit 9 includes a CPU 91 and a memory 92, and the CPU 91 functions as a central processing unit. The memory 92 is a storage device and includes a ROM and a RAM. For example, a program for controlling the printer 1 and control data are stored in the ROM. The RAM is used for the CPU 91 to control the printer 1 in order to temporarily develop a control program and data and to store image data transmitted from the external computer 100.

  Then, the control unit 9 also controls the exposure device 34, and controls turning on / off of the laser diode 7 with a digital signal in accordance with image data to be formed (see FIG. 6). That is, for each dot of the image data, the turning on / off of the laser diode 7 is controlled to form an electrostatic latent image of the image data. Then, the rotational speed of the polygon motor 72 is controlled, and the basic scanning / exposure control of the photosensitive drum 32 is performed.

  Next, the configuration for correcting the light amount of the laser diode 7 will be described in detail with reference to FIG.

  First, the light quantity detection unit 8a includes a photodiode 75, a resistor 81 (corresponding to a current-voltage conversion unit), a Schmitt trigger 82, a current amplifier 83 (corresponding to a current amplification unit), and the like.

  The photodiode 75 is a photodiode 75 provided in the exposure device 34 for receiving laser light outside the electrostatic latent image forming area of the photosensitive drum 32 (see FIG. 3). Specifically, the photodiode 75 receives the laser beam irradiated outside the electrostatic latent image forming area of the photosensitive drum 32 by the reflection of the mirror 74. The current generated when the photodiode 75 receives the laser beam is input to the current amplifier 83 and amplified. Note that a power source 84 for driving the current amplifier 83 is connected to the current amplifier 83.

  Here, the current output from the photodiode 75 varies depending on the light amount emitted by the laser diode 7, that is, the light amount received by the photodiode 75. Therefore, if the light amount of the laser diode 7 is large, the output current of the photodiode 75 is large. However, if the light quantity of the laser diode 7 is small, the output current of the photodiode 75 is small.

  The output current of the photodiode 75, that is, the current amplified by the current amplifier 83 is connected to the comparison circuit 8b. The output current of the photodiode 75 finally appears as a voltage due to the resistor 81 connected between the current amplifier 83 and the comparison circuit 8b. Thereby, the output of the photodiode 75 is converted into a voltage. Then, this voltage is input to the comparison circuit 8b. With these configurations, the light amount detection unit 8a detects the light amount of the laser light emitted from the laser diode 7 and outputs the detected light amount as a voltage.

  On the other hand, the connection line between the current amplifier 83 and the comparison circuit 8 b is branched, and the output of the current amplifier 83 is also connected to one terminal of the Schmitt trigger 82. In other words, the output of the current amplifier 83 is connected to the comparison circuit 8 b and branched to be connected to one terminal of the Schmitt trigger 82. Then, as shown in FIG. 6, a voltage that has been subjected to current-voltage conversion by the resistor 81 appears at one terminal of the Schmitt trigger 82. A power supply 85 for comparison is connected to the other terminal of the Schmitt trigger 82.

  Here, the Schmitt trigger 82 is an element having two threshold voltages, high and low, and the input voltage is an element whose state changes depending on whether the input becomes higher or lower from this range. The Schmitt trigger 82 is generally reversed in input and logic. Specifically, first, if the input voltage is lower than the upper threshold voltage, the output becomes High. When the input voltage reaches the upper side, the output changes to Low. In this state, even if the input voltage falls below the upper threshold voltage, the output remains low if the input voltage is higher than the lower side. Thereafter, when the input voltage falls below the lower threshold voltage, the output becomes High. That is, the Schmitt trigger 82 has hysteresis with respect to fluctuations in the input voltage, and the output does not become unstable even if noise is slightly superimposed on the input voltage.

  In short, since the current output from the photodiode 75 changes greatly when the photodiode 75 receives the laser beam from the laser diode 7, the Schmitt trigger 82 is used when the photodiode 75 receives the laser beam, and When the laser beam is not received, the output is switched abruptly and the laser beam received by the photodiode 75 can be detected. Therefore, the output signal of the Schmitt trigger 82 can be used as a horizontal synchronization signal for synchronizing the irradiation of the laser beam to the photosensitive drum 32.

  The voltage obtained by current-voltage conversion of the current output from the photodiode 75 is input to the comparison circuit 8b. The comparison circuit 8b is a circuit for comparing a voltage obtained by converting the output of the photodiode 75 with a reference voltage. The comparison circuit 8b may be constituted by an element such as a comparator, or the CPU 91 of the control unit 9 may be used as long as a comparison operation can be performed.

  Here, the reference voltage is a voltage value input to the comparison circuit 8b when the output current of the photodiode 75 when the light amount of the laser diode 7 is appropriate is subjected to current-voltage conversion by the resistor 81. Further, the value of the reference voltage does not need to be one fixed value, and may have a certain range. The reference voltage value is stored in the storage unit 8c connected to the comparison circuit 8b. When the CPU 91 is used for the comparison circuit 8b, the storage unit 8c may be configured by a ROM and stored digitally, or may be configured as an analog circuit that outputs a reference voltage.

  For example, as the reference voltage, a voltage value obtained by current-voltage conversion of the output current of the photodiode 75 in a room temperature environment at the time of product inspection at the time of factory shipment of the printer 1 by the resistor 81 is adopted, and the storage unit 8c. Can be memorized. In addition, a constant voltage value may be stored in the storage unit 8c in consideration of variations in characteristics of the photodiode 75 and the like.

  Then, the comparison circuit 8b outputs a correction signal to the comparator 86 of the light amount correction unit 8d based on the result of the comparison calculation. In other words, the correction signal is input to one terminal of the comparator 86.

  For example, the correction signal sets a reference voltage setting value output from the comparison circuit 8b when the light amount is not changed, and when the light amount is increased, the correction signal voltage value is raised above the setting value. When reducing the amount of light, the voltage value of the correction signal can be made lower than the set value. As will be described later, this correction signal is finally input to the analog controller 87, and the analog controller 87 changes the bias current of the laser diode 7 according to the voltage value of the correction signal, thereby increasing or decreasing the light amount of the laser diode 7. Do.

  The light amount correction unit 8d that corrects the light amount of the laser diode 7 in accordance with the correction signal from the comparison circuit 8b includes an analog controller 87, a comparator 86, a current amount adjustment resistor 88, and the like.

  As described above, the correction signal is input to one terminal of the comparator 86, but the variable resistor 89, the second photodiode 77, the digital controller 78, and the laser diode 7 are sequentially input to the other terminal of the comparator 86. The analog controller 87 is connected after the current amount adjusting resistor 88 is connected in this order. That is, a loop-like circuit is formed.

  First, the digital controller 78 controls ON / OFF of the voltage applied to the laser diode 7 based on the image data transmitted from the control unit 9. That is, based on the image data, when irradiating the photosensitive drum 32 with laser light, a constant voltage is applied to the laser diode 7. When not irradiating the photosensitive drum 32 with laser light, voltage application is turned off. In other words, the turning on / off of the laser diode 7 is controlled.

  Then, an analog controller 87 is connected after a current amount adjusting resistor 88 is connected in a direction in which a current flows through the laser diode 7 by a voltage applied by the digital controller 78. The analog controller 87 controls a bias current that is supplied to the laser diode 7 in advance.

  Here, the bias current is a current that is supplied to the laser diode in advance in order to increase the light emission reactivity of the laser diode. When the laser diode exceeds the threshold current, the output of the laser beam suddenly increases, and even if a current is passed in a range not exceeding the threshold current, the laser diode hardly emits laser light. Therefore, in this embodiment, a bias current equal to or lower than the threshold current is passed through the laser diode 7. The analog controller 87 controls the amount of this bias current.

  A signal for controlling the amount of bias current is output from the comparison circuit 8b. That is, the analog controller 87 increases or decreases the amount of the bias current according to the voltage value of the correction signal from the comparison circuit 8b. Specifically, the correction signal output from the comparison circuit 8 b is input to the terminal of the comparator 86. A capacitor C1 is connected between the comparison circuit 8b and the comparator 86, and this capacitor C1 holds the output voltage of the comparison circuit 8b. A capacitor C2 is also provided to hold the potential of the analog controller 87.

  On the other hand, a second photodiode 77 is connected to the other terminal of the comparator 86 via a variable resistor 89. The second photodiode 77 and the laser diode 7 constitute a laser diode portion 7a as one unit (= configured as one semiconductor element). Then, the reflection of light is repeated in the laser diode 7, but the second photodiode 77 detects that the energy of the light generated by the laser diode 7 exceeds a certain value, and at this time, the laser beam is not emitted. Radiated. Although the laser diode portion 7a itself has a function of making the light quantity constant, the characteristics of the second photodiode 77 also change depending on the temperature. Perform the correction.

  Thus, the correction signal as the voltage from the comparison circuit 8b is input to one of the terminals of the comparator 86, and the voltage generated by the light reception of the second photodiode 77 is input to the other. Thus, the voltage of the correction signal is adjusted to prevent a large fluctuation in the current flowing through the laser diode 7. Then, the calculation result (output) of the comparator 86 is input to the analog controller 87, and the amount of current flowing through the laser diode 7 is determined by this correction signal.

  With these configurations, even if the temperature of the laser diode 7 changes, the amount of light of the laser diode 7 becomes substantially constant. For example, when the light amount changes due to the temperature rise, and the light amount increases, the photodiode 75 detects the increase in the light amount. The detection result is input to the comparison circuit 8b, and the comparison circuit 8b calculates the increased amount of light based on the reference voltage. Then, the comparison circuit 8b outputs a correction signal corresponding to the increased light amount (for example, the correction signal is output with a voltage smaller than the set value). The analog controller 87 receives the correction signal and reduces the bias current flowing through the laser diode 7. Then, the light amount correction of the laser diode 7 is performed. On the other hand, for example, when the amount of light decreases due to a decrease in the temperature of the laser diode 7, for example, the comparison circuit 8b outputs, for example, a correction signal at a voltage larger than the set value, and receives this. The analog controller 87 increases the bias current of the laser diode 7 to increase the light amount of the laser diode 7 and perform correction.

  Note that if the light amount of the laser diode 7 is corrected too frequently, the image forming processing speed and the image quality may be affected. Therefore, the temperature sensor 76 detects a temperature change of a predetermined value or more. Only in this case, the comparison circuit 8b may receive the output of the photodiode 75 and correct the light amount of the laser diode 7. Therefore, the temperature sensor 76 is connected to the comparison circuit 8b.

  Here, the predetermined value can be determined, for example, in the range of 1 to 6 ° C, more specifically in the range of 3 to 5 ° C. This is because if the temperature changes by about 3 to 5 ° C., the change in the light amount of the laser diode 7 often affects the image quality. If the laser diode 7 used in the printer 1 is not easily affected by temperature changes, the predetermined value range may be 5 to 10 ° C. If it is easily affected by temperature changes, The range of the predetermined value may be 1 to 3 ° C. In summary, the predetermined value can be appropriately set between about 1 to 10 ° C.

  In this way, according to the above-described embodiment of the present invention, the light amount of the laser diode 7 is corrected so that the output voltage of the light amount detector 8a (photodiode 75, resistor 81, etc.) matches the reference voltage as a reference. Therefore, the light quantity of the laser diode 7 can always be made constant regardless of the characteristics (for example, temperature change) of the laser diode 7. Accordingly, it is possible to provide an image forming apparatus (printer 1) in which there is no fluctuation in the amount of laser light for exposing the photosensitive drum 32, for example, there is no underexposure and the quality of the formed image is constant.

  The light quantity detection unit 8a is configured to have a configuration of a photoelectric conversion unit (photodiode 75) and a current-voltage conversion unit (resistor 81), and can easily convert the light quantity of the laser diode 7 into a voltage. Therefore, the light quantity can be clearly compared with the voltage as a reference.

  Further, since the photoelectric conversion unit is not provided in the vicinity of the laser diode 7, the photoelectric conversion unit can be hardly affected by the heat generated by the laser diode 7, and the amount of light can be detected more accurately. The light amount detection unit 8a detects the light amount of the laser diode 7 and adjusts the irradiation timing of the laser light to the photosensitive drum 32 so that writing is started at the same position in the circumferential direction of the photosensitive drum 32. It also outputs a horizontal sync signal for That is, the light amount detection unit 8a can be provided with the functions of the light amount detection unit 8a and the horizontal synchronization signal output unit (Schmitt trigger 82), and the cost and space saving can be reduced compared to the case where both functions are provided separately. Can be planned.

  Further, since the members constituting the light amount detection unit 8a are inexpensive, the cost can be reduced, and the configuration of the light amount detection unit 8a itself can be simplified. The life and reliability of the light amount detection unit 8a can be simplified. Therefore, the light quantity of the laser diode 7 can be accurately detected over a long period of time.

  Further, in order to shorten the time until the laser diode 7 oscillates, the light amount of the laser diode 7 can be reduced by increasing / decreasing the bias current flowing in the laser diode 7 in advance by the light amount correction unit 8d (analog controller 87 or the like). Since the current for driving and correcting the laser diode 7 is varied without being constant, the light amount of the laser diode 7 is made constant in response to changes in the light amount and oscillation wavelength of the laser diode 7 depending on the temperature. be able to.

  Further, the light amount can be corrected only when the temperature changes by a predetermined value or more and it is considered that the light amount of the laser diode 7 has a large fluctuation, and the light amount can be corrected efficiently. For example, the time for correcting the light amount can be reduced.

  Hereinafter, another embodiment will be described. In the above-described embodiment, the tandem color printer 1 has been described. However, the printer 1 can also be applied to an image forming apparatus such as a rotary color printer, and further applied to an image forming apparatus such as a monochrome printer. Is possible.

  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 copying machine, a multifunction machine, and a printer.

1 is a schematic front sectional view showing a schematic structure of a printer according to an embodiment of the present invention. FIG. 2 is an enlarged front schematic cross-sectional view of an intermediate transfer unit and an image forming unit of a printer according to an embodiment of the present invention. 1 is a schematic cross-sectional view for explaining a configuration of an exposure apparatus according to an embodiment of the present invention. It is a figure which shows an example of the change of the characteristic by the temperature of a laser diode, (a) is a graph which shows an example of the correlation of threshold current and temperature, (b) is a graph which shows an example of the correlation of an oscillation wavelength and temperature. It is. 1 is a block diagram illustrating an example of a configuration of a printer according to an embodiment of the present invention. It is a circuit diagram which shows an example of the structure for making constant the light quantity of the laser diode which concerns on embodiment of this invention.

Explanation of symbols

1 Printer (image forming device)
32 Photosensitive drum (photosensitive member)
7 Laser diode 71 Polygon mirror (optical system member)
73 fθ lens (optical system member)
75 photodiode (a part of the light amount detection unit 8a, photoelectric conversion unit)
76 Temperature sensor (temperature detector)
8a Light quantity detection unit 8b Comparison circuit (comparison unit)
8c Storage unit 8d Light amount correction unit 81 Resistance (a part of the light amount detection unit 8a, current-voltage conversion unit)
82 Schmitt trigger 83 Current amplifier (a part of the light intensity detector 8a, current amplifier)
87 Analog controller (part of the light quantity correction unit 8d)

Claims (6)

A laser diode and a photoconductor, wherein the laser diode emits laser light on / off in accordance with image data of an image to be formed, and deflects the emitted laser light by an optical system member. In an image forming apparatus for forming an image by forming an electrostatic latent image on the photoconductor,
A light amount detector that detects the amount of laser light emitted by the laser diode and outputs the detected amount of light as a voltage;
A storage unit for storing a reference voltage of the voltage output by the light amount detection unit;
The voltage output from the light quantity detection unit is compared with the reference voltage stored in the storage unit. If the voltage output from the light quantity detection unit is different from the reference voltage, the output voltage of the light quantity detection unit matches the reference voltage. A comparator for outputting a correction signal for correcting the amount of light of the laser diode,
An image forming apparatus, comprising: a light amount correction unit that corrects a light amount of the laser diode in accordance with a correction signal output from the comparison unit.   The light quantity detection unit converts a received laser beam as a current, a photoelectric conversion unit, a current amplification unit that amplifies the current output from the photoelectric conversion unit, and converts the current output from the current amplification unit into a voltage output The image forming apparatus according to claim 1, further comprising a current-voltage conversion unit configured to perform conversion. The photoelectric conversion unit is arranged to receive laser light irradiated outside the electrostatic latent image forming region of the photoconductor,
The image forming apparatus according to claim 2, wherein the light amount detection unit also outputs a horizontal synchronization signal for synchronizing irradiation of the laser beam to the photoconductor based on an output of the photoelectric conversion unit.   The image forming apparatus according to claim 2, wherein the photoelectric conversion unit is a photodiode, and the current-voltage conversion unit is configured by a resistor.   5. The image forming apparatus according to claim 1, wherein the light amount correction unit corrects a light amount of the laser diode by changing a bias current flowing through the laser diode. Inside the device, there is a temperature detector for detecting the temperature in the device,
The comparison unit compares the output voltage of the light amount detection unit with a reference voltage and outputs a correction signal when the temperature detection unit detects a temperature change of a predetermined value or more. The image forming apparatus according to any one of the above.

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