JP2016016523A - Image formation device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To use a laser diode, with an image plane light quantity error eliminated under a condition of good droop characteristic.SOLUTION: An image formation device includes a maximum light quantity control means which controls so that a light quantity emitted from a light source becomes a maximum light quantity of the light source, and an on-off control which, in a state in which the light quantity emitted from the light source by the maximum light quantity control means is controlled to be the maximum light quantity, repeatedly controls at a predetermined cycle an on-time and an off-time of a light beam emitted from the light source.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus.

  In an LD (Laser Diode) element used for an electrophotographic writing method, a technique for changing the amount of light according to the density of an image using APC (Automatic Power Control) control is already known. Here, APC control refers to control in which set power is always supplied stably.

  Patent Document 1 discloses a detection reference image obtained by developing a detection reference latent image formed on an image carrier for the purpose of controlling a vertical / horizontal line width ratio without causing an increase in cost. The image forming condition setting means for setting the image forming condition, and the writing control means for controlling the exposure energy of the laser writing system by pulse width modulation according to the image forming condition, the writing control means is the image forming condition setting means. An image forming apparatus is disclosed in which the duty of PWM (Pulse Width Modulation) control is changed according to the set value.

  PWM (Pulse Width Modulation) is one of the methods for controlling power using a semiconductor, and controls output power by repeatedly turning on and off. Specifically, it refers to a power control method in which a constant period of ON and OFF of a pulse train is made from a constant voltage input and the ON time width is changed.

  However, the conventional LD control method that changes the amount of light according to the density of the image has a problem that the divergence angle changes depending on the amount of light due to the characteristics of the LD, thereby causing an image plane light amount error. It was. In addition, there is a problem that the droop characteristic is deteriorated when the light is used at a low light quantity. Here, the droop characteristics will be described briefly. In an image forming apparatus that scans a photoreceptor with LD light modulated in accordance with image data to form an image, the development conditions of the electrophotographic process change depending on the operating temperature and humidity environment of the apparatus and deterioration of the photoreceptor. The required light amount on the photoconductor also changes. Therefore, it is necessary to adjust to the optimal light quantity. In addition, the semiconductor laser has a droop characteristic, which causes image degradation in a low output region.

  The droop characteristic is one of the thermal characteristics of a semiconductor laser, and refers to a phenomenon in which the amount of light gradually decreases due to heat generated during light emission. If the droop is large, an image density difference occurs between the vicinity of the start of printing in the main scanning direction, which is a direction orthogonal to the moving direction of the recording medium, and the other portions, and the image quality deteriorates. In general, the lower the light emission amount (LD light emission amount) of the semiconductor laser, the larger the droop, and the higher the LD light emission amount, the smaller the droop.

  In the invention described in Patent Document 1, the duty of PWM control is changed to control the exposure energy. However, in this control, it is defined that the light amount is controlled to be constant at the maximum light amount. Therefore, the problem that the light quantity error of the image plane occurs and the droop characteristic is deteriorated when using with a low light quantity has not been solved.

  Therefore, the present invention has been made in view of the above-mentioned problems of the prior art, and the light amount is set to a constant amount as the maximum light amount to be used. An object of the present invention is to provide an image forming apparatus capable of using the LD in a state where the droop characteristic is in a favorable condition.

  In order to solve the above-described problems, an image forming apparatus according to the present invention includes a maximum light amount control unit that controls a light amount emitted from a light source to be a maximum light amount of the light source, and a light amount emitted from the light source by the maximum light amount control unit. ON / OFF control means for repeatedly controlling the ON time and OFF time of the light beam emitted from the light source at a predetermined cycle in a state where the light amount is controlled to be the maximum light amount.

  According to the present invention, it is possible to obtain an image forming apparatus that can eliminate the light quantity error on the image surface and can use the LD in a state where the droop characteristic is in a favorable condition.

FIG. 3 is a diagram illustrating a configuration of an image writing unit for a photoconductor of the image forming apparatus according to the present embodiment. FIG. 5 is a block diagram illustrating processing for generating a write signal in the image forming apparatus according to the present embodiment. It is a figure explaining the divergence angle which arises by changing the light quantity of the image forming apparatus which concerns on this embodiment. (A) Exposure amount control method of conventional image forming apparatus, (b) Exposure amount control method by PWM control of image forming apparatus according to Embodiment 1, and (c) Image formation according to Embodiment 2. It is a figure explaining the control method of the exposure amount by PWM control of an apparatus. (A) In the conventional image forming apparatus, when the LD is used with a high light amount and a long lighting time, and (b) In the image forming apparatus according to this embodiment, the LD is used with a high light amount and a short lighting time. It is a figure explaining.

  The image forming apparatus according to the present embodiment includes a light source that is controlled to be turned on according to image data, a lighting control unit that controls lighting of the light source, and a light beam emitted from the light source in a direction orthogonal to the moving direction of the recording medium. And a deflection unit that deflects in the main scanning direction. A latent image is formed by emitting a light beam on the rotating or moving image carrier, and the latent image is visualized by a toner developing unit. Then, the visualized image is transferred onto a recording medium conveyed by a rotating or moving transfer unit, or transferred to a rotating or moving transfer unit, and the image transferred to the transferring unit is transferred to the recording medium. An image is formed depending on whether or not.

  Then, when changing the exposure amount, the lighting control unit always controls the light amount of the laser diode to a constant value so as to be the maximum light amount of the light source to be used. When the exposure amount is lowered, the exposure is adjusted by PWM (Pulse Width Modulation) control. Accordingly, an image forming apparatus capable of reducing the light amount error on the image plane and using the LD in a state where the droop characteristic is in a favorable condition is provided.

  In short, the present invention is characterized in that the LD is used in a state where the light amount error of the image plane caused by the change in the light amount of the LD is reduced and the droop characteristic is in a favorable condition.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol is attached | subjected to the part which is the same or it corresponds, The duplication description is simplified thru | or abbreviate | omitted suitably.

  First, the configuration of the image writing unit for the photoreceptor of the image forming apparatus according to the embodiment will be described with reference to FIG. FIG. 1 is a diagram illustrating a configuration of an image writing unit for a photoconductor of the image forming apparatus according to the present embodiment.

  In FIG. 1, an image writing unit 10 for a photoconductor of an image forming apparatus includes a laser diode (LD) 1, an aperture 2, a polygon mirror 3, and an fθ lens 4. The aperture 2 converges a light beam emitted from a laser diode (LD) 1 as a light source onto the polygon mirror 3. The image writing unit 10 includes folding mirrors 5, 6, 7, a synchronization detection sensor 8, and a photoreceptor 9. A light beam emitted from a laser diode (LD) 1 that is a light emitting element is scanned by a polygon mirror 3, and an image is formed on a photoreceptor 9 through an fθ lens 4 and folding mirrors 5, 6, and 7.

  Next, a processing flow for generating a write signal in the image forming apparatus according to the present embodiment will be described. FIG. 2 is a block diagram illustrating processing for generating a write signal in the image forming apparatus according to the present embodiment.

  In FIG. 2, the image write control unit 23 that generates a write signal includes a speed conversion line memory 231, various pattern generation units 232, a write γ conversion unit 233, an LD modulation and various clock generation unit 234, and the like. It is equipped with. The image writing control unit 23 includes a continuous lighting detection unit 235, an LUT (lookup table) 236, and a bias current generation unit 237. Further, the image writing control unit 23 includes an image area control and various timing control unit 238, and various setting registers and a polygon motor control unit 239.

  The image writing control unit 23 includes an image data input I / F (Interface) 240, a command I / F 241, an LD modulation I / F 242, a synchronization detection I / F 243, and a polygon motor I / F 244. The image writing control unit 23 inputs data or signals from the outside or outputs data or signals to the outside by using these I / Fs.

  The image writing control unit 23 composed of such components stores the image data input through the image data input I / F 240 in the speed conversion line memory 231 and is acquired through the continuous lighting detection unit 235. The lighting time for each scanning line is read into the LUT 236. Note that the LUT is a table in which a certain calculation result is stored in advance, whereby the processing speed can be increased and the burden on the system can be reduced.

  The various pattern generation unit 232 generates and outputs various patterns from the image data stored in the speed conversion line memory 231. The writing γ conversion unit 233 performs writing γ conversion on the various patterns generated by the various pattern generation unit 232. Here, the γ conversion refers to color conversion that converts input color information into output color information. The PWM control in the present embodiment is executed in the writing γ conversion unit 233.

  Next, a light amount error generated by changing a specific light amount of the image forming apparatus according to the present embodiment will be described. FIG. 3 is a diagram for explaining a divergence angle generated by changing the light amount of the image forming apparatus according to the present embodiment.

  As the light amount of the light beam emitted from the laser diode (LD) 1 is increased, the divergence angle irradiated to the aperture 2 for converging the light beam increases from θ to θ ′ as shown in FIG. Then, a coupling that is a ratio between the output (the amount of light emitted from the light source) emitted from the laser diode (LD) 1 that is the light source and the amount of light after passing through the aperture 2 (the amount of light incident on the synchronization detection sensor 8). Efficiency decreases.

  Here, the coupling efficiency will be described. Coupling efficiency refers to the ratio of the amount of light incident on the photodetector to the amount of light emitted from the light source in the optical system. A reduction in coupling efficiency causes an image plane light amount error. In the prior art, there has been a problem that the amount of light beam emitted from the laser diode (LD) 1 changes.

  That is, in the conventional technique, the control is performed on the assumption that the coupling efficiency is constant. However, the laser diode (LD) 1 has a characteristic that the divergence angle changes depending on the amount of light. Therefore, when the divergence angle changes, the coupling efficiency changes, and the linearity between the light amount of the laser diode (LD) 1 and the image surface light amount is lost. As a result, there is a problem in that an image plane light amount error that causes an error with respect to the target light amount occurs.

  On the other hand, in the present embodiment, as will be described later, by setting the light amount of the laser diode (LD) 1 to be a constant maximum light amount, the target light amount and the image surface light amount can be obtained without changing the coupling efficiency. This error is eliminated.

  Next, a conventional exposure amount control method of the image forming apparatus and an exposure amount control method by PWM control of the image forming apparatus according to the present embodiment will be described. 4A shows the exposure amount control method of the conventional image forming apparatus, FIG. 4B shows the exposure amount control method by PWM control of the image forming apparatus according to the first embodiment, and FIG. 4C shows the second embodiment. It is a figure explaining the control method of the exposure amount by PWM control of the image forming apparatus concerning.

  As shown in FIG. 4A, in the conventional image forming apparatus, the light amount of the laser diode (LD) 1 fluctuates within the range of the maximum light amount. Therefore, when the light amount is decreased, the above-described coupling efficiency is changed (decreased), and an image plane light amount error is generated due to the change in the light amount, which causes a drop in droop characteristics.

  On the other hand, as shown in FIGS. 4B and 4C, in the image forming apparatus according to the first embodiment or the second embodiment, the maximum light amount is maintained and the cycle is always constant. The amount of light is controlled. That is, when the exposure amount is lowered, the light amount is adjusted by executing PWM control in the writing γ conversion unit 233 in the image writing control unit 23 described above. Specifically, the light amount on time and off time are repeatedly controlled at a predetermined cycle. If the integrated value of light quantity (area of light quantity) is equal, the image density (exposure energy) becomes the same value. Therefore, since the light amount is adjusted by PWM control while the maximum light amount is maintained, the coupling efficiency can be maintained constant, and the droop characteristic is prevented from deteriorating.

  Next, a case where the LD is used with a high light amount and a long lighting time in the conventional image forming apparatus and a case where the LD is used with a high light amount and a short lighting time in the image forming apparatus according to the present embodiment will be described. 5A shows a case where an LD is used with a high light quantity and a long lighting time in a conventional image forming apparatus, and FIG. 5B shows a case where an LD is used with a high light quantity and a short lighting time in the image forming apparatus according to the present embodiment. It is a figure explaining the case where it uses.

  As shown in FIG. 5A, the conventional image forming apparatus has a characteristic that the amount of light decreases with time. When the amount of light decreases, the coupling efficiency also decreases, and the droop characteristic also deteriorates. On the other hand, as shown in FIG. 5B, in the image forming apparatus according to the present embodiment, PWM control is performed so that the light quantity is not decreased over time while maintaining the maximum light quantity. Further, since the lighting time of the laser diode (LD) 1 is reduced by PWM control, a droop characteristic reduction effect can be expected as a result.

  As described above, the laser diode (LD) 1 has a characteristic that the divergence angle changes depending on the amount of light, and this causes a light amount error on the image plane. In the present embodiment, the lighting control unit performs control so that the maximum light amount using the light amount of the laser diode (LD) 1 is always constant, and when lowering the exposure amount, adjustment is performed only by PWM control. As a result, the divergence angle of the LD can always be controlled to be constant.

  As described above, the laser diode (LD) has a characteristic that the droop characteristic also deteriorates when the amount of light is reduced. In this embodiment, the lighting control unit controls the maximum light amount using the light amount of the laser diode (LD) 1 to be always constant, and the lighting time is shorter than that of the conventional image forming apparatus. Reduction effect can be expected. Accordingly, it is possible to reduce the light quantity error on the image plane and to use the laser diode (LD) under the condition that the droop characteristic is good.

  According to the present invention, the light amount is set to a constant amount as the maximum light amount to be used, while the exposure amount is changed by PWM control to eliminate the image surface light amount error and to set the LD in a state where the droop characteristic is in a favorable condition. An image forming apparatus that can be used is obtained.

  The present invention has been described above by the preferred embodiments of the present invention. While the invention has been described with reference to specific embodiments thereof, various modifications and changes can be made to these embodiments without departing from the broader spirit and scope of the invention as defined in the claims. is there.

1, 25 LD (laser diode)
DESCRIPTION OF SYMBOLS 2 Aperture 3 Polygon mirror 4 f (theta) lens 5, 6, 7 Folding mirror 8 Synchronization detection sensor 9 Photoconductor 10 Image writing part 21 Image processing ASIC (Application Specific Integrated Circuit) or controller 22 CPU (Central Processing Unit)
23 Image Write Control Unit 24 Laser Drive Unit 26 Synchronization Detection Unit 27 Polygon Motor Driver 28 Polygon Motor 231 Speed Conversion Line Memory 232 Various Pattern Generation Units 233 Write γ Conversion Unit 234 LD Modulation and Various Clock Generation Units 235 Continuous Lighting Detection Part 236 LUT
237 Bias current generation unit 238 Image area control and various timing control units 239 Various setting registers and polygon motor control unit 240 Image data input I / F
241 Command I / F
242 LD modulation I / F
243 Synchronization detection I / F
244 Polygon motor I / F

JP 2000-052590 A

Claims (5)

Maximum light quantity control means for controlling the light quantity emitted from the light source to be the maximum light quantity of the light source;
On / off control means for repeatedly controlling the on time and off time of the light beam emitted from the light source at a predetermined cycle in a state where the light quantity emitted from the light source is controlled to be the maximum light quantity by the maximum light quantity control means. ,
An image forming apparatus comprising:   A coupling efficiency, which includes an aperture for converging a light beam emitted from the light source, is a ratio between a light amount of the light beam irradiated onto the aperture from the light source and a light amount of the light beam after passing through the aperture, The image forming apparatus according to claim 1, wherein the image forming apparatus is constant.   The image forming apparatus according to claim 2, wherein a divergence angle of the light beam emitted from the light source to the aperture is constant.   The image forming apparatus according to claim 1, further comprising a table that stores an on-time of a light beam emitted from the light source.   5. The image forming apparatus according to claim 1, wherein the on / off control unit performs PWM (Pulse Width Modulation) control. 6.

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