JP2018010051A - Image forming apparatus and light intensity adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To achieve a reduction in intensity of a laser beam with a simple and inexpensive configuration without using a special detection circuit.SOLUTION: An image forming apparatus compares the time for outputting a BD signal and the intensity of a received BD signal with predetermined prescribed time and prescribed intensity, and determines whether the intensity of light is reduced from a result of the comparison. When determining that the intensity of light is reduced, the image forming apparatus controls the intensity of light on a surface of a photoreceptor to be a target value by adjusting the intensity of a laser beam.SELECTED DRAWING: Figure 4

Description

  The present invention relates to an image forming apparatus and a light amount adjusting method, and more particularly, to an image forming apparatus that forms an image on a recording medium according to, for example, an electrophotographic method, and a laser light amount adjusting method.

  In an image forming apparatus that forms an image in accordance with an electrophotographic method, the optical power of a semiconductor laser irradiated to the surface of a photoconductor through a scanning optical system such as an fθ lens and a polygon mirror is compared with that in the initial stage of manufacturing the apparatus for the following reason. May decrease. In other words, if the apparatus continues to be used, toner or the like scattered on any glass surface forming the scanning optical system adheres and accumulates as dust, which reduces the amount of light obtained on the surface of the photoreceptor. . As a result, a desired density cannot be obtained in the formed image.

  Conventionally, in order to cope with such a decrease in the amount of light, when the amount of light obtained on the surface of the photoconductor decreases, the amount of light incident on the BD sensor also decreases, and the image from the amount of light incident on the BD sensor is reduced. A decrease in density is detected. Specifically, the BD sensor is provided with a means capable of variably setting the minimum incident light amount, and the set value is compared with the incident light amount. When the incident light amount falls below the set light amount, the light amount is reduced, that is, the image density is reduced. To do. Then, when it is determined that the image density is lowered, the output of the BD sensor is cut off, it is assumed that a failure has occurred, and the user is notified of this (for example, see Patent Document 1).

JP 2004-354704 A

  However, in the above-described conventional example, a means capable of variably setting the minimum incident light quantity must be provided in the BD sensor, which increases the circuit scale of the apparatus and increases the production cost of the apparatus. In addition, although the semiconductor laser and its drive circuit are not actually failed, it is regarded as a failure and image formation becomes impossible.

  The present invention has been made in view of the above-described conventional example, and an image forming apparatus capable of appropriately correcting the light amount of the light projection unit and performing good image formation with an inexpensive and simple configuration, and the light amount adjustment thereof It aims to provide a method.

  In order to achieve the above object, the image forming apparatus of the present invention has the following configuration.

  That is, the light projection means for projecting light onto the photosensitive member to form an image, the detection means for detecting the time when the output value of the light projection means is a predetermined value or more, and the light based on the result of the detection means And a light amount adjusting means for adjusting the light amount of the projection means.

  Therefore, according to the present invention, there is an effect that good image formation can be performed by appropriately correcting the light amount of the light projection unit with an inexpensive and simple configuration.

1 is a perspective view showing a schematic configuration of an image forming apparatus that forms an image on a recording medium in accordance with an electrophotographic system that is a representative embodiment of the present invention. It is a figure which shows the input / output of a BD sensor. FIG. 2 is a block diagram illustrating a control configuration of the image forming apparatus illustrated in FIG. 1. 3 is a flowchart illustrating light amount adjustment control processing of the image forming apparatus illustrated in FIG. 1.

  Hereinafter, preferred embodiments of the present invention will be described more specifically and in detail with reference to the accompanying drawings.

  In this specification, “sheet (or recording medium)” refers not only to recording paper and printing paper for forming images used in general image forming apparatuses, but also to cloth, plastic film (OHP). , Including a transportable medium such as a metal plate, wood, and leather.

・ Outline of image forming apparatus (Fig. 1)
FIG. 1 is a perspective view showing a schematic configuration of an image forming apparatus (LBP) that forms an image on a recording medium in accordance with an electrophotographic system as a typical embodiment of the present invention. In particular, FIG. 1 illustrates a configuration of a scanning optical unit 9 that scans a light beam onto the photosensitive drum 8 of the image forming apparatus.

  As shown in FIG. 1, the semiconductor laser 107 constituting the laser beam scanning optical system is optically modulated in accordance with an image signal input from a laser driving circuit 130. The laser beam emitted from the semiconductor laser 107 passes through the collimator lens 134 and is deflected by the polygon mirror (rotating polygon mirror) 133. The deflected laser beam is imaged by the fθ lens 132 and irradiated onto the photosensitive drum (photosensitive member) 8. The beam is sequentially scanned on the photosensitive drum 8 at a constant speed and at a predetermined timing in the main scanning direction shown in the drawing, and the sub-scanning direction perpendicular to the main scanning direction. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 8 whose surface is uniformly charged. In particular, the semiconductor laser 107, the polygon mirror (rotating polygonal mirror) 133, the fθ lens 132, and the like of the scanning optical unit 9 may be collectively referred to as light projection means.

  This electrostatic latent image is developed with toner (not shown), transferred to a recording medium such as a recording sheet fed in the sub-scanning direction, and further heat-fixed to generate a recorded image. Further, a part of the laser beam is reflected by the reflection mirror 131 provided at a position upstream of the scanning start position outside the image forming area in the main scanning direction, and is incident on the BD sensor 121 that detects the laser beam. A BD synchronization signal for determining the main scanning timing is generated.

  Further, the BD synchronization signal is input to an image processing unit (not shown), and is synchronized with an image clock for image scanning to perform timing control for starting image formation. Then, the image signal input to the image processing unit is output to the laser driving circuit 130 according to the image clock at the timing when the image writing start is controlled, and laser deflection scanning is executed through the above-described path.

  Here, if variation occurs in each scan in the timing control for starting image recording, distortion appears in the dot pattern that forms the image, making it impossible to form a high-quality image. For this reason, as described above, timing control for starting image formation is performed based on the BD synchronization signal. As a result, dot pattern distortion does not occur for each scanning line. Further, information on photodiodes arranged in the vicinity of the laser in the semiconductor laser 107 is detected, and APC (Automatic Power Control) control is performed based on this information so that the emission power of the semiconductor laser becomes a standard light amount.

  Now, the feedback control that makes the light emission amount of the laser constant by APC is a control that makes it possible to obtain a predetermined standard light emission power on the surface of the element chip of the semiconductor laser, and is required for high-quality image formation. Is the light emission power obtained on the surface of the photosensitive drum 8. However, the APC control alone does not necessarily guarantee against the deterioration over time of the light emission power on the surface of the photosensitive drum 8.

  As is clear from FIG. 1, a scanning optical system such as a collimator lens 134, a polygon mirror 133, an fθ lens 132, and a reflection mirror 131 exists in the light path from the semiconductor laser 107 to the photosensitive drum 8. The standard power of the APC-controlled semiconductor laser 107 is controlled so that the optical power on the semiconductor laser chip surface is constant by the monitor signal of the photodiode near the semiconductor laser.

  The laser beam emitted from the semiconductor laser 107 is shaped by the collimator lens 134 and converted into a parallel beam, then reflected by the rotating polygon mirror 133 and deflected and scanned. The laser beam that has been deflected and scanned passes through the fθ lens 132 and forms an image on the surface of the rotating photosensitive drum 8 as indicated by the arrow in FIG. 8 parallel to the rotation axis direction). Thereby, a scanning line is formed and the photosensitive drum 8 is exposed.

  Further, as shown in FIG. 1, a reflection mirror 131 is provided at a position where the laser beam at the position upstream of the scanning start position S of the scanning line on the photosensitive drum 8 is incident on the upstream side in the main scanning direction. The laser light incident on the reflection mirror 131 is incident on the BD sensor 121. The BD sensor 121 detects that a laser beam has entered, and outputs a BD signal corresponding thereto. Based on the output from the BD sensor 121, the laser beam scanning start timing is determined.

  Further, after the laser beam scans the photosensitive drum 8 and before the photosensitive drum 8 is scanned next, information on the photodiodes arranged in the vicinity of the laser in the semiconductor laser 107 is detected, and the output of the semiconductor laser is detected from this information. APC control is performed so that the power becomes the standard light amount.

  In the image formation, the scanning optical unit 9 uses a laser at a light emission level (intensity) that allows toner to adhere to an image formable area (effective area of the photosensitive drum 8) on the surface of the photosensitive drum 8 based on image data. Emits light.

  FIG. 2 is a diagram showing the relationship between the amount of light incident on the BD sensor and the BD signal output from the BD sensor.

  As shown in FIG. 2, the output time of the BD signal changes according to the amount of light incident on the BD sensor 121. The smaller the amount of light incident on the BD sensor 121, the shorter the time for exceeding the threshold, so the output time of the BD signal is also shortened. In this embodiment, the output time of the BD signal in the initial stage of the assembly of the image forming apparatus is stored in a non-volatile memory (described later), and when the output time of the detected BD signal becomes shorter than that in the initial stage of the apparatus assembly, the photosensitive drum Judge that the amount of light on the surface has decreased. Further, when the light amount is reduced, the light amount correction value is calculated depending on how much the time has changed from the output time of the BD signal at the initial assembly of the image forming apparatus.

  FIG. 3 is a block diagram showing a control configuration of the image forming apparatus shown in FIG.

  As shown in FIG. 3, the semiconductor laser 107 with a built-in photodiode is driven by the laser driver 12 to receive laser light and execute APC control.

  The control unit 19 includes a CPU 27, a memory 28, a timing signal generator 25, and an image signal generator 26, and the CPU 27 reads out and executes a program stored in the memory 28, so that the timing signal generator 25 operations are controlled. In addition, the memory 28 is configured by a non-volatile memory such as a ROM or RAM that stores programs for controlling various operations of the image forming apparatus, for example, an EEPROM. The RAM is used as a work area for executing various processes executed by the CPU 27 and a storage area for temporarily storing data such as variables and setting information. The nonvolatile memory of the memory 28 stores the output time of the BD signal at the initial assembly of the image forming apparatus. Then, the CPU 27 compares this with the output time of the detected BD signal to calculate the light amount correction value.

  The timing signal generator 25 executes APC control and generates a control signal indicating an image forming area. The timing signal generator 25 inputs the control signal to the laser driver 12 and inputs the rotation control signal to the motor driver 15. The motor driver 15 drives the polygon motor 13 to rotate the polygon mirror 133 based on the rotation control signal. Further, based on the light quantity correction value calculated by the CPU 27, the light quantity reference voltage (PWM) is varied to control the light quantity on the surface of the photosensitive drum 8 to be a target value.

  The image signal generator 26 uses the image data input from the external device as an image signal, and inputs it to the laser driver 12 in the image forming area according to the main scanning timing and the sub-scanning timing generated by the timing signal generator 25 based on the BD signal. To do. The laser driver 12 modulates the drive current set by the APC control with an image signal and outputs it to the semiconductor laser 107. As a result, the semiconductor laser 107 outputs laser light having a lighting time corresponding to the gradation represented by the image data.

  FIG. 4 is a flowchart showing light amount adjustment control processing executed by the image forming apparatus shown in FIG.

  First, in step S1, the polygon motor 13 is rotated by a command from the control unit 19. Next, in step S2, it is checked whether or not the polygon motor 13 has reached a steady rotational speed at which an image can be formed. If it is determined that the rotation speed of the polygon motor 13 has not reached the steady rotation speed, the process waits in step S2 until the rotation speed reaches the steady rotation speed. On the other hand, when it is determined that the rotation speed of the polygon motor 13 has reached the steady rotation speed, the process proceeds to step S3, the semiconductor laser 107 is turned on, and APC emission is started.

  In step S4, the process waits until the BD signal is detected. If it is determined that the BD signal is detected, the process proceeds to step S5, and the output time of the BD signal is measured. In step S6, the measured output time of the BD signal is compared with the specified time (reference time) of the BD signal in which the surface of the photosensitive drum 8 stored in advance in the above-described nonvolatile memory becomes the target light amount.

  If it is determined that the measured output time of the BD signal is equal to or shorter than the specified time, the process proceeds to step S7, and the CPU 27 corrects the amount of light from the difference between the specified time and the measured output time of the BD signal by the CPU 27. Calculate the value. Further, in step S8, the light quantity reference voltage (PWM) output from the timing signal generator 25 is varied based on the calculated light quantity correction value so that the light quantity on the surface of the photosensitive drum 8 becomes the target value. Make adjustments. When the light amount adjustment is completed, image formation is executed in step S9. On the other hand, if the output time of the measured BD signal is exceeded, the process proceeds to step S9 without executing light amount correction, and image formation is executed.

  Therefore, according to the embodiment described above, it is possible to detect whether or not a light amount reduction has occurred on the surface of the photosensitive drum based on the output time of the BD signal. Thus, in this embodiment, unlike the conventional example, the amount of light on the surface of the photosensitive drum can be reduced and corrected to an appropriate amount of light without requiring a special circuit configuration.

  In the embodiment described above, it is configured to detect whether or not a light amount reduction has occurred on the surface of the photosensitive drum based on the output time of the BD signal, but the present invention is not limited to this. For example, when the amount of light on the surface of the photosensitive drum is larger than expected, the present invention can also be applied to the case where adjustment is made so that the amount of light is reduced to a target value.

  As described above, in this image forming apparatus, without using a special circuit, a photoconductor generated by adhesion of toner or the like to any glass surface such as a rotating polyhedron or an fθ lens forming a scanning optical system. It is possible to detect a decrease in the amount of light obtained on the surface. A good image can be formed by adjusting the power of the semiconductor laser so that the amount of light on the surface of the photosensitive member becomes a predetermined amount of light.

  Furthermore, in the above-described embodiments, a single-function image forming apparatus (printer apparatus) has been described as an example, but the present invention is not limited thereto. The present invention can be applied to, for example, a copier system in which an image reading apparatus (scanner apparatus), an image forming apparatus (LBP), and an ADF apparatus are integrated, or a combined system in which a facsimile function is added to the copier system. good.

8 Photosensitive drum, 12 Laser driver, 13 Polygon motor,
15 motor driver, 19 control unit, 107 semiconductor laser, 121 BD sensor,
133 Polygon mirror

Claims (6)

A light projection means for projecting light onto the photoreceptor to form an image;
Detecting means for detecting a time when the output value of the light projecting means is a predetermined value or more;
An image forming apparatus comprising: a light amount adjusting unit that adjusts a light amount of the light projecting unit based on a result of the detecting unit. A storage means for storing a reference time of a time detected by the detection means when the light projection means projects a predetermined amount of light;
The light amount adjustment means compares the reference time with the time detected by the detection means. If the time is longer than the reference time, the light amount of the light projection means is made smaller than the predetermined light amount, and the time 2. The image forming apparatus according to claim 1, wherein when the time is shorter than the reference time, the light amount of the light projection unit is adjusted to be larger than the predetermined light amount.   The image forming apparatus according to claim 1, wherein the light amount adjusting unit adjusts a light amount of the light projecting unit by changing a light amount reference voltage.   The image forming apparatus according to claim 1, wherein the detection unit detects an output time of a BD sensor that generates a BD signal. A rotating polyhedron that reflects the light of the light projecting means and rotates so that the reflected light scans over the photoreceptor;
A motor for rotating the rotating polyhedron,
The image forming apparatus according to claim 4, wherein the detection unit detects an output time of the BD sensor after the motor reaches a steady rotational speed. A light amount adjusting method for a light projecting unit in an image forming apparatus having a light projecting unit for projecting light onto a photoconductor to form an image,
A detection step of detecting a time when the output value of the light projection means is a predetermined value or more;
A light amount adjustment step of adjusting a light amount of the light projection unit based on a detection result in the detection step.

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