JP2003145837A - Imaging apparatus and semiconductor laser drive circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reproduce the reproducibility and halftoning of the microdots of an electrostatic latent image at a high resolution through a convenient low cost arrangement. SOLUTION: The imaging apparatus 1 comprises a laser diode 201 outputting a laser beam for exposure. In the semiconductor laser drive circuit 210 for controlling the laser output of the laser diode 201, an overshoot circuit part 220 is connected in series to the ground side of the laser diode 201. When the inductance of an inductance component 221 in the overshoot circuit part 220 is altered, an overshoot occurs at the rising part of optical output from the laser diode 201 and a photosensitive drum 30 is overexposed resulting in formation of a sufficient electrostatic latent image.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital image forming apparatus and a semiconductor laser driving circuit, and more particularly to an electrophotographic image forming apparatus and a semiconductor laser driving circuit.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic system (for example, a copying machine, a printer, a fax machine, etc.), the surface of a photoconductor is uniformly charged in the dark, and then exposure using a laser beam is performed. By exposing the photoconductor with the device, a desired electrostatic latent image is formed on the charged photoconductor surface,
By supplying toner to the electrostatic latent image, the electrostatic latent image is visualized to form an image. Then, the image visualized with the toner is transferred to a recording medium and fixed to perform printing, and the untransferred toner is removed by a cleaning unit or the like.

The image forming apparatus having such a structure is
In recent years, there has been a strong demand for higher speed, higher image quality, and higher resolution. However, at a high resolution of 1200 dpi or higher, and when the electrophotographic process speed is high, the resolution is remarkably reduced due to phenomena such as so-called image blurring and latent image deletion, and good image quality is obtained. There was a problem that it would be difficult.

Therefore, in order to improve the reproducibility of minute dots, it is necessary to hold the electrostatic latent image, that is, to prevent the flow of the electrostatic latent image. Since the flow of the electrostatic latent image is greatly influenced by the emission rising characteristic of the laser, the electrostatic latent image is strongly retained by overexposing the photoconductor with the laser light.

However, if the photosensitive member is overexposed, the gradation of the halftone image is lost and the image quality tends to be poor in contrast. Therefore, the emission intensity of the laser for obtaining the image quality with excellent reproducibility of the fine dots and the emission intensity of the laser for obtaining the image quality with excellent gradation are required to be different. That is, an exposure apparatus capable of controlling the output of these two or more types of emission intensity is required.

Further, in a high-speed and high-resolution image forming apparatus, the noise level of unnecessary radiation and the like becomes large and various noise countermeasures are required. In particular, the signal line that transmits image information and converts it into an optical output is EMI (Select).
It is necessary to take measures against the romantic interference.

As an example of the prior art for obtaining such high resolution image quality, Japanese Patent Laid-Open No. 9-114206 discloses an image forming apparatus and an image forming method. In the image forming apparatus and the image forming method disclosed in this publication, the output control wave generating means generates a waveform having a sharp peak within the writing time of each pixel, and controls the emitted light of the laser light with this waveform to perform exposure. Concentrating energy.
This makes it possible to prevent interference between pixels and improve the reproducibility of thin lines without changing the beam diameter of the laser light.

An example of another prior art for obtaining high resolution image quality is disclosed as an image forming apparatus in Japanese Patent Laid-Open No. 2000-127498. In the image forming apparatus disclosed in this publication, the surface of the photoconductor is charged to a potential VH1 higher than the potential VH at which the toner does not adhere, and the semiconductor laser causes background exposure of intensity 1 with the photoconductor surface potential being VH. Intensity and an exposure intensity of intensity 2 which is higher than intensity 1 and which, when continuously exposed, lowers the surface potential of the photoreceptor to a potential lower than the surface potential VL suitable for toner adhesion. .

Further, the exposure with the intensity 1 and the exposure with the intensity 2, and the exposure OFF state are combined and given, and thereby the surface potential of the image portion is set to VL, and the contrast is controlled so as to increase, so that software or Correct the image information sent by hardware.

With such a configuration, the image forming apparatus disclosed in this publication does not modulate the intensity of the laser beam in multiple stages, does not reduce the beam diameter, and does not generate ripples for exposure. After that, the contrast is increased and the rounding of the gradation is improved so that the reproducibility and gradation of minute dots can be obtained. Therefore, in the image forming apparatus disclosed in this publication, when the laser beam is pulse-width modulated for gradation reproduction, the laser light is not accurately reproduced in the highlight portion and the dark portion due to the Gaussian distribution. Can be prevented.

[0011]

However, the conventional image forming apparatus and image forming method (Japanese Patent Laid-Open No. 9-11420).
No. 6) was not for obtaining image quality at a high resolution of 1200 dpi or higher. Furthermore, this conventional image forming apparatus and image forming method require an output control wave generating means for generating a waveform having a sharp peak within the writing time of each pixel, and thus require complicated control.

Further, another conventional image forming apparatus (Japanese Laid-Open Patent Publication No.
No. 00-127498) discloses a background exposure intensity of intensity 1 where the surface potential of the photoconductor is VH by laser light, and a surface which is stronger than the intensity 1 and is suitable for toner adhesion to the surface potential of the photoconductor when continuously exposed. A mechanism for giving an excessive intensity 2 for reducing the potential to a potential lower than the potential VL, a mechanism for generating an exposure intensity of the intensity 2 and a pulse for turning off the exposure are required, which is complicated in terms of software and hardware. I had no choice. Furthermore, if noise countermeasures such as unnecessary radiation, especially EMI countermeasures, are applied to the signal line that transmits image information, the voltage waveform becomes dull, the dots of the obtained image cannot be reproduced sufficiently, and only low quality images are obtained. There wasn't.

Therefore, by generating an overshoot at the rising portion of the optical output of the semiconductor laser,
A technique capable of forming a sufficient electrostatic latent image even at a high resolution of 00 dpi or more can be considered. However, in a laser diode generally used in a printer, a copying machine, etc., as shown in FIG. 14, the anode side of the laser diode 901 (LD901) and the cathode side of the photodiode 902 (PD902) are normally connected. In this state, it is enclosed in one package 903.

When the inductance L for generating the overshoot is connected to the anode side of the LD 901, the inductance L is also connected to the cathode side of the PD 902. Therefore, APC (Au
PD90 in to Power Control)
Due to the occurrence of overshoot distortion in the output of No. 1 (mainly the current output), there is a possibility that the power control of the LD 901 takes time and the power cannot be controlled as designed. And P
If the output distortion of D902 is too large, in the worst case,
The LD901 was even destroyed during APC.

The present invention has been made in view of the above circumstances, and shows the reproducibility and gradation of minute dots of an electrostatic latent image when the resolution is increased or the electrophotographic process speed is increased. Of an image forming apparatus that can be reproduced at a low cost with a simple configuration, can prevent the occurrence of overshoot distortion in the PD output in the APC, and can prevent noise such as unnecessary radiation (especially EMI measures). For the purpose of provision.

[0016]

To achieve this object, an image forming apparatus according to claim 1 of the present invention turns on a semiconductor laser based on image information and outputs a laser beam from the semiconductor laser. An image forming apparatus having an exposing unit for scanning and exposing the photosensitive member to form an electrostatic latent image by the exposing unit, turning on a semiconductor laser based on image information, and exposing the photosensitive member at a normal light intensity. The light intensity control circuit unit for scanning and exposing the upper portion and the overshoot circuit unit for increasing the light intensity at the rising portion of the light output of the semiconductor laser lighted by the light intensity control circuit unit are provided. Part has an inductance component that sets the component value of the inductance, and this inductance component is commonly connected to the photodiode among the terminals of the semiconductor laser. It was connected to each other in the stomach not terminal.

When the image forming apparatus has such a configuration,
The light intensity control circuit section causes the semiconductor laser to output a laser beam with normal light intensity, and the overshoot circuit section,
An overshoot can be generated at the rising portion of the optical output of the laser beam.

Therefore, even when the resolution is increased or the electrophotographic process speed is increased, the electrostatic latent image on the photosensitive drum can be sufficiently formed. Therefore, the reproducibility and gradation of the minute dots of the electrostatic latent image can be enhanced, and thus it becomes possible to prevent image blurring and latent image deletion due to insufficient formation of the electrostatic latent image.

Furthermore, since the light intensity overshoot that overexposes the photosensitive member to strongly hold the electrostatic latent image can be generated simply by giving a pulse of a steep rising edge, the output control wave in the conventional image forming apparatus is generated. It is possible to provide an image forming apparatus that can realize high image quality with excellent reproducibility of minute dots without using a generating unit or a mechanism for generating excess intensity and having a low cost and a simple configuration.

In addition, by connecting the inductance component to a terminal of the semiconductor laser which is not commonly connected to the photodiode (that is, the anode of the terminals of the semiconductor laser is connected to the photodiode). Then, by connecting an inductance component to one cathode, and by connecting an inductance component to one anode if the cathode is connected to a photodiode), distortion of overshoot to PD output in APC Can be prevented.

Generally, the laser diode LD and the photodiode PD are usually the anode of the LD and the photodiode P, respectively.
Since the cathode of D is connected and enclosed in one package, when the inductance L is connected to the anode side of LD, the inductance L is connected to the cathode side of PD.

Therefore, due to factors such as distortion such as overshoot occurring in the PD output during APC, L
There is a possibility that the power control of D takes a long time, the power cannot be controlled as designed, and further, in the worst case, because the PD output is distorted too much, the LD is destroyed during APC. There was a possibility. Therefore, by connecting the inductance L to the cathode side terminal of the LD (that is, the side not connected to the PD), the inductance L acts only on the LD,
Since it does not affect the PD output, P at APC
It is possible to prevent problems such as distortion of the D output such as overshoot.

In the image forming apparatus according to the second aspect, the inductance component is connected to the ground side terminal of the semiconductor laser. With this configuration of the image forming apparatus, when the package including the semiconductor laser (laser diode LD) and the photodiode PD is provided in the image forming apparatus, the side where the LD and PD are connected is the power source side. On the other hand, since the side where the LD and the PD are not connected is the ground side, the inductance component connected to the ground side of the LD is not connected to the PD. Therefore, since the inductance component acts only on the LD and does not affect the output of the PD, it is possible to prevent a problem such as distortion of the PD output during APC such as overshoot.

Further, in the image forming apparatus according to the third aspect, the overshoot generated at the rising portion of the light output by the overshoot circuit portion accounts for 60% of the light output irradiation time for forming one pixel. The configuration takes up more time. With such a configuration of the image forming apparatus, even when the resolution is increased or the electrophotographic process speed is increased, the photosensitive drum is overexposed to sufficiently form the electrostatic latent image. be able to.

In particular, when light is emitted in a time shorter than one pixel in the conventional case, the overshoot irradiation time is O
Although it was not possible to follow the signal for controlling N / OFF, and the optical waveform was disturbed to obtain a high-quality image, the image forming apparatus of the present invention does not disrupt the optical waveform. An electrostatic latent image can be formed sufficiently to obtain a high quality image.

Further, in the image forming apparatus according to the fourth aspect, the overshoot is preferably about 100% of the irradiation time.
It is configured to converge at. When the image forming apparatus is configured as described above, the electrostatic latent image is sufficiently formed by overexposing the photosensitive drum even when the resolution is increased or the electrophotographic process speed is increased. You can

Further, in the image forming apparatus according to the fifth aspect of the present invention, the maximum value of the light intensity in the overshoot is 1.2 times or more and 5 times or less of the normal light intensity. With such a configuration of the image forming apparatus, the photosensitive drum can be overexposed and a sufficient electrostatic latent image can be formed even at high resolution.

Further, in the image forming apparatus according to the sixth aspect of the present invention, the maximum value of the light intensity in the overshoot is preferably 1.2 times or more and not more than 2 times the normal light intensity. . When the image forming apparatus has such a configuration, the electrostatic latent image can be sufficiently formed by overexposing the photosensitive drum even at high resolution.

An image forming apparatus according to a seventh aspect of the present invention has speed acquisition means for acquiring the electrophotographic process speed, and the light intensity control circuit section is based on the electrophotographic process speed acquired by the speed acquisition means. The configuration is such that the normal light intensity is changed. When the image forming apparatus has such a configuration, the light intensity control circuit section can control the normal light intensity based on the electrophotographic process speed. Therefore, the light intensity of the laser output in which the overshoot has occurred is controlled to be shifted to the normal light intensity based on the electrophotographic process speed in the light intensity control circuit section.

Further, the image forming apparatus according to the present invention has environmental information acquisition means for acquiring environmental information such as temperature and humidity, and the light intensity control circuit section has the environmental information acquired by the environmental information acquisition means. Based on the above, it is configured to change the normal light intensity. When the image forming apparatus has such a configuration,
The light intensity control circuit unit can control the normal light intensity based on the environmental information. Therefore, the light intensity of the laser output where the overshoot has occurred is
It is controlled to shift to normal light intensity based on environmental information.

In the image forming apparatus according to the ninth aspect, the semiconductor laser is composed of a semiconductor laser capable of emitting a plurality of laser beams. With such a configuration of the image forming apparatus, the present invention can be applied to, for example, an image forming apparatus using a multi-beam laser diode as a semiconductor laser to achieve reproducibility and gradation of fine dots at high resolution. It is possible to reproduce and acquire a high quality image.

An image forming apparatus according to a tenth aspect of the invention is
The inductance component is a noise countermeasure component. When the image forming apparatus has such a configuration, by increasing the inductance component of the inductance component that constitutes the overshoot circuit unit, not only the reproducibility of minute dots and the reproducibility of gradation are achieved, but also unnecessary radiation, etc. It is possible to take noise countermeasures, especially EMI countermeasures.

This is because when the inductance value of the inductance component is increased, an overshoot is generated at the rising portion of the optical output of the laser beam, a sufficient electrostatic latent image can be formed, and the inductance value is increased. This is because the effect of the EMI countermeasure becomes larger.

A semiconductor laser drive circuit according to claim 11 is a semiconductor laser drive circuit for driving and controlling a semiconductor laser for scanning and exposing on a photosensitive member, wherein the optical output of the semiconductor laser is at a normal light intensity. It has a light intensity control circuit section for outputting and an overshoot circuit section for generating an overshoot at the rising portion of the light output of the semiconductor laser, and this overshoot circuit section has an inductance component for setting the component value of the inductance. Then, the inductance component is connected to a terminal of the semiconductor laser which is not commonly connected to the photodiode.

If the semiconductor laser drive circuit is constructed as described above, since the inductance component is connected to the semiconductor laser, an overshoot can be generated at the rising portion of the optical output of the laser beam. As a result, since the photosensitive drum is overexposed, the reproducibility and gradation of the minute dots of the electrostatic latent image can be reproduced when the resolution is increased or the electrophotographic process speed is increased.

Further, by connecting the inductance component to a terminal of the semiconductor laser which is not commonly connected to the photodiode, it is possible to avoid the inconvenience caused when the inductance component is connected to the power source side. That is, conventionally, by connecting an inductance component to the power source side of the packaged LD and PD connected on the power source side, overshoot distortion occurs in the PD output, and it takes time to control the power of the LD. However, in the image forming apparatus having the semiconductor laser drive circuit of the present invention,
Since the inductance component is connected to the ground side of the semiconductor laser, distortion of overshoot does not occur in the PD output, and the inconvenience associated with this occurrence can be eliminated.

In the semiconductor laser drive circuit according to the twelfth aspect, the inductance component is connected to the ground side terminal of the semiconductor laser. When the semiconductor laser drive circuit has such a structure, when the package in which the semiconductor laser (laser diode LD) and the photodiode PD are enclosed is provided in the image forming apparatus, the LD and the P are usually provided.
The side connected to D is the power supply side, while LD and PD
Since the side not connected to is the ground side, L
The inductance component connected to the ground side of D is not connected to PD. Therefore, since the action of the inductance component does not adversely affect the output of the PD, it is possible to prevent a problem such as distortion of the PD output during APC such as overshoot.

Further, in the semiconductor laser drive circuit according to the thirteenth aspect, the light intensity control circuit section is configured to change the light intensity during normal exposure based on the electrophotographic program speed acquired by the speed acquisition means. . When the semiconductor laser drive circuit has such a configuration, the light intensity control circuit section can control the normal light intensity based on the electrophotographic process speed. Therefore, the light intensity of the laser output in which the overshoot has occurred is controlled to be shifted to the normal light intensity based on the electrophotographic process speed in the light intensity control circuit section.

Further, in the semiconductor laser drive circuit according to the fourteenth aspect, the light intensity control circuit section is configured to change the light intensity at the time of normal exposure based on the environmental information acquired by the environmental information acquisition means. If the semiconductor laser driving circuit has such a configuration, the light intensity control circuit section can control the normal light intensity based on the environmental information. Therefore, the light intensity of the laser output in which the overshoot has occurred is controlled to shift to the normal light intensity based on the environmental information in the light intensity control circuit section.

According to a fifteenth aspect of the present invention, in the semiconductor laser drive circuit, the semiconductor laser is a semiconductor laser that emits a plurality of laser beams. With such a configuration of the semiconductor laser drive circuit, even when the semiconductor laser drive circuit is provided in an image forming apparatus using, for example, a multi-beam laser diode as a semiconductor laser, reproducibility and gradation of fine dots at high resolution and the like are obtained. It is possible to reproduce the sex and acquire a high quality image.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. First, an embodiment of an image forming apparatus and a semiconductor laser driving circuit of the present invention will be described with reference to FIG. FIG. 1 is a schematic diagram showing the configuration of the image forming apparatus of this embodiment.

As shown in FIG. 1, the image forming apparatus 1 includes a charger 10, a laser scanner 20, and a photosensitive drum 30.
And a developing device 40, a transfer roller 50, and a fixing device 60. Here, the charging device 10 uniformly charges the surface of the photoconductor drum 30, which is an image carrier.

The laser scanner 20 (exposure means) emits a laser beam based on the image data that has been subjected to various image processing after reading the original with the scanner or receiving print data from a personal computer (PC) or the like. The charged photosensitive drum 30 is irradiated. As a result, the surface of the photoconductor drum 30 is exposed and an electrostatic latent image is formed. As shown in FIG. 2, the laser scanner 20 includes a laser diode 201, a collimator lens 202, and
A cylindrical lens 203, a plane mirror 204a,
204b, rotating polygon mirror 205, fθ lens 206
a, 206b, a reflection mirror 207, and a mirror 208
And a photodetector 209 and a semiconductor laser drive circuit 210.

The laser diode 201 (LD 201, semiconductor laser) is a light source that outputs a laser beam, is connected to the semiconductor laser drive circuit 210, and is controlled so that the laser beam is emitted based on image information. The collimator lens 202 converts the laser beam emitted from the LD 201 from a diffused ray into a parallel ray. The laser beam converted into parallel rays by the collimator lens 202 passes through the cylindrical lens 203 and the plane mirrors 204a and 204b, and the rotary polygon mirror 2
It is incident on 05. The plane mirrors 204a, 204
b can be omitted.

The rotary polygon mirror 205 (polygon mirror) is
It is formed in a regular polygonal shape having a plurality of reflecting surfaces on its side surface, and the incident laser beam is focused on this reflecting surface. The laser beam reflected by the rotating polygon mirror 205 is fθ lenses 206a and 206b.
Of light, is bent by the reflection mirror 207, and is irradiated onto the photoconductor drum 30.

Of the traveling direction of the laser beam reflected by the rotary polygon mirror 205, the mirror 2 is located on the upstream side in the main scanning direction.
08 are arranged. A photodetector 209 is arranged in the direction in which the laser beam is reflected by the mirror 208. In the mirror 208 and the photo detector 209, the irradiation start timing (SOS: S) from the laser scanner 20 to the photosensitive drum 30 for each line.
start of scan) is detected.

As shown in FIG. 3, the semiconductor laser drive circuit 210 has a light intensity control circuit section 211, an overshoot circuit section 220, a snubber circuit section 230, and a photodiode 240 (PD240). . The light intensity control circuit unit 211, as shown in FIG.
The switching unit 213, the S / H unit 214, the comparator 215, and the load resistor RL216.

The current source 212 has a bias current source (not shown) and a switching current source (not shown), and a bias current of a predetermined current value flows through the LD 201 by the bias current source. The bias current is set to be less than the threshold current necessary for the LD 201 to output coherent light.

The switching current source receives a set voltage from the outside and supplies a switching current corresponding to a desired output intensity to the LD 201. The current value of the switching current is set to exceed the threshold current required for the LD 201 to output coherent light, depending on the sum of the switching current and the bias current. That is, the switching unit 21
The lighting of the LD 201 is controlled by switching whether or not a switching current is passed to the LD 201 side by 3.

The switching unit 213 outputs the LD based on the Video signal (image signal based on image data).
ON / OFF control of the laser beam output from 201 is performed. The S / H unit 214 (Sample / Hold circuit) changes the switching current set in the current source 212 based on the output of the comparator 215, and generates the switching current such that the monitor voltage matches the reference voltage. .

Further, the S / H section 214 is provided with an LD while the sample signal is being input from the external terminal.
Lighting control of 201 is performed. Then, the S / H unit 214
The result of the lighting (optical output) control is held while the sample signal is not input, that is, while the hold (Hold) signal is input.

The positive terminal side of the comparator 215 has P
The monitor voltage output from D240 and converted into current-voltage is input. Further, the negative terminal side of the comparator 215 inputs a predetermined reference voltage from the reference voltage terminal. Then, the comparator 215 compares the monitor voltage with the reference voltage, and sends the result as an output signal from the output terminal side to the S / H unit 214. The load resistance RL216 is LD2
01 is connected in parallel, and a current flows when the output of the laser beam is OFF.

Photodiode 240 (PD240)
Outputs a current corresponding to the output light amount of the LD 201.
This current is converted into a monitor voltage by a current-voltage converter (not shown) and input to the positive terminal side of the comparator 215. As shown in FIG. 14, the PD 240 and the LD 201 are generally connected to the anode of the LD 201 and the cathode of the PD 240, and are enclosed in one package.

The overshoot circuit section 220 includes an inductance component 221 for setting the component value of the inductance.
And is connected to the ground side A of the LD 201. By connecting the inductance component 221 to the LD 201 in series, the switching unit 213 is connected to Vid.
When the laser beam is ON / OFF controlled based on the eo signal, an overshoot is formed at the rising portion of the optical waveform. Then, this inductance component 221
The magnitude of overshoot can be controlled by changing the constant of.

Here, the inductance component 221 is L
It is also conceivable to connect to the power source side B of D201. However, since the LD 201 is generally connected to the PD 240 on the anode side (the power source side B in FIG. 14) and enclosed in a package, the LD 201 is not included in the LD 201.
When connected to the anode side (power source side B) of 201, PD2
The inductance component 221 is also connected to the cathode side (power source side B) of 40.

In this case, the APC (Auto power)
Due to distortion such as overshoot occurring in the output (mainly current output) of the PD 240 during control, there are problems such as time-consuming power control of the LD 201 and inability to control the power as designed. Become. Furthermore, if the output distortion of PD240 is too large, in the worst case, LD2 will be
01 may be destroyed.

Therefore, the inductance component 221 is LD
When connected to the cathode side of 201 (ground side A in FIG. 14, in other words, of the terminals of the LD201, which is not commonly connected to the PD240), this inductance component 221 acts only on the LD201. PD
Since the output of 240 is not affected, the above-mentioned problems do not occur. The terminal to which the inductance component 221 is connected is not limited to the ground side A of the LD 201, and may be, for example, the terminal of the LD 201 and the LD 201.
It may be a terminal in which the PD 240 and the PD 240 are not connected.

The LD 201 and PD 240 are shown in FIG.
In FIG. 4, the anode side of the LD 201 and the cathode side of the PD 240 are connected, but the connection is not limited to this and there are connection examples as shown in FIGS. 4A and 4B, for example. In these connection examples as well, when the inductance component 221 is connected to the power source side B of the LD 201, the above-mentioned problem (for example, power control failure of the LD 201) occurs, but on the other hand, its inductance If the component 221 is connected to the ground side A of the LD 201, the problem is solved.

The snubber circuit section 230 is composed of a resistor R231 and a capacitor C232 connected in series, and is turned on.
Shapes the optical waveform of a laser beam controlled to be turned off.
Therefore, when the inductance component 221 is not connected to the LD 201, the optical waveform of the laser beam controlled by the snubber circuit unit 230 has a waveform as shown in FIG. 5A, that is, there is no overshoot at the rising portion. It becomes a waveform.

On the other hand, the inductance component 2 is added to the LD 201.
When 21 is connected, the snubber circuit unit 2
The magnitude of the overshoot can be changed by changing the constants of the resistor R231 and the capacitor C232 included in 30. The optical waveform of the laser beam when the overshoot occurs has a waveform as shown in FIG.

Furthermore, the snubber circuit section 230 is
1 and the inductance component 221 are connected in parallel to the series connection. However, the snubber circuit unit 230
In FIG. 3, the LD 201 and the inductance component 2 are shown.
21 connected in parallel to the series connection of 21
The connection of the LD 201 and the inductance component 221 is not limited to the series connection.
It is also possible to connect only one in parallel.

Further, although the snubber circuit section 230 is constituted by the series connection of the resistor R231 and the capacitor C232 in the same drawing, the snubber circuit section 230 is not limited to these series connections, and for example, the resistor R231 and the capacitor C232 are connected. It can also be configured by parallel connection with C232.

In this case, the resistor R231 is connected in parallel to the series connection of the LD 201 and the inductance component 221, and the capacitor C232 is connected in parallel to this circuit. In addition, the LD 201 and the inductance component 22
The LD 201 is not limited to the serial connection with the LD 201.
The resistor R231 may be connected in parallel only to this, and the capacitor C232 may be connected in parallel to this circuit.

An overshoot may be formed at the rising portion of the optical waveform due to the resistance component, electrostatic capacitance component, inductance component, etc. of the LD 201 itself. In this case, these resistance component, capacitance component,
The values of the inductance component 221, the resistor R231, and the capacitor C232 are set in consideration of the values of the inductance component and the like.

The photoconductor drum 30 (photoconductor) is a cylindrical photoconductor that rotates at a constant speed in a fixed direction. The photoconductor drum 30 is uniformly charged by the charger 10 and then rotated at a constant speed in a fixed direction to be irradiated with a laser beam to be exposed. As a result, a latent image is formed on the photoconductor drum 30.

Specifically, in the exposed portion, a positive charge is generated from the photosensitive layer of the photosensitive drum 30, and a latent image having a constant potential (for example, -150V) is formed. . The latent image potential of a constant voltage mentioned here is a convergence potential when the entire surface is exposed by the scanning exposure device 11, that is, when the entire image area is scanned.

The developing device 40 (developing means) faces the peripheral surface of the photosensitive drum 30 and supplies toner to the photosensitive drum 30. The transfer roller 50 (transfer means) transfers the electrostatic latent image visualized on the photoconductor drum 30 onto the recording paper.
The fixing device 60 (fixing means) heats and pressurizes the sheet on which the toner image has been transferred to melt and fix the toner. As a result, the toner image transferred onto the recording paper is fixed.

Next, the operation of the image forming apparatus of this embodiment will be described with reference to FIG. First, the photoconductor drum 30, which is an image bearing member, is uniformly charged by the charger 10, and is further exposed by the laser scanner 20, which is an exposing unit, to form an electrostatic latent image.

This electrostatic latent image is developed by the developing device 4 as a developing means.
The image is visualized by 0 and is transferred onto the recording paper by a transfer roller 50 which is a transfer unit. Then, the toner image transferred onto the recording paper is fixed by a fixing device 60 which is a fixing unit.

Next, the state of the electrostatic latent image formed on the photosensitive drum will be described with reference to FIG. When the resolution is low or the electrophotographic process speed is slow, a sufficient electrostatic latent image is formed as indicated by A in FIG.

However, when the resolution becomes higher or the electrophotographic speed becomes faster, the electrostatic latent image is not sufficiently formed as shown by B and C in FIG. Therefore, when the emission intensity of the laser beam is set to a waveform as shown in FIG. 5B, that is, a waveform in which an overshoot is generated at the rising portion of the optical waveform, the photoconductor is overexposed. As a result, an insufficient electrostatic latent image such as B and C in FIG. 6 was formed, but a sufficient electrostatic latent image such as A in FIG. 6 is formed.

At this time, the overshoot at the rising portion of the optical waveform may be 50% or more, preferably about 100%, when forming one pixel.
The light intensity is 1.2 times or more the light intensity during normal exposure, and
It is desirable to be 5 times or less, preferably 1.2 times or more, and 2 times or less.

Next, the operation of the semiconductor laser drive circuit in the laser scanner will be described with reference to FIG.
When a current corresponding to a desired output intensity is sent by the set voltage in the current source 212, the switching unit 21
It is switching-controlled by 3 and is supplied to the LD 201 or the load resistor RL216. This switching unit 213
The control of the supply current is performed based on the Video signal (image signal based on the image data), and the laser beam output from the laser diode LD201 is turned on.
/ OFF is controlled.

When a current is supplied to the LD 201, each time the LD 201 outputs a laser beam, the overshoot circuit unit 220 causes the rising portion of the optical output of the laser beam as shown in FIG. 5B. Overshoot occurs. This overshoot
The size is determined by the constant of the inductance component 221 included in the overshoot circuit unit 220, the constants of the resistor R231 and the capacitor C232 included in the snubber circuit unit 230, and the like. When no current is supplied to the LD 201, that is, when the output of the laser beam is OFF, the supplied current is supplied to the load resistance RL.

The laser beam optically output from the LD 201 is received by the PD 240. Based on the amount of the received laser beam, the PD 240 outputs a current (received current). The output received light current is the current −
The voltage is converted into a monitor voltage by a voltage converter (not shown) and input to the positive terminal side of the comparator 215.

In the comparator 215, the reference voltage received at the minus terminal side is compared with the monitor voltage received at the plus terminal side, and the result is sent as an output signal from the output terminal side to the S / H section 214. In the S / H unit 214, the switching current set by the current source 212 is changed based on the output signal from the comparator 215, and the switching current is generated so that the monitor voltage matches the reference voltage.

Further, in the S / H section 214, the lighting control of the LD 201 is performed while the sample signal is being input from the external terminal. Further, in the S / H unit 214, while the sample signal is not input,
That is, the result of the lighting (light output) control is held while the hold (Hold) signal is input.

Next, the control of the output intensity of the laser beam by changing the set voltage will be described with reference to FIG.
The output intensity of the laser beam from the laser diode LD201 can be changed based on the electrophotographic process speed.

The electrophotographic process speed is acquired by speed acquisition means (not shown). The speed acquisition means stores the electrophotographic process speed information in a recording device such as a non-volatile memory in advance, reads the electrophotographic process speed information when the power is turned on, and determines the process speed (set voltage) of the recording device. To do. This determined set voltage is
It is supplied to the current source 212. This supply controls the output intensity of the laser diode LD.

The recording device may be provided on the engine substrate or the control substrate because it is sufficient to read the stored electrophotographic process speed information when the power is turned on. Further, it may be provided on another substrate or unit (for example, HDD or CF card).

Further, the output intensity of the laser beam from the laser diode LD201 can be changed based on the environmental information. The environmental information includes information about temperature and humidity. Then, this environmental information is acquired by an environmental information acquisition unit (not shown).

The environmental information acquisition means is means for detecting the temperature and humidity of the environment in which the image forming apparatus 1 is installed as environmental information, and is composed of a temperature / humidity sensor unit. The temperature / humidity sensor unit is provided with a thermistor for temperature detection and a humidity sensor for humidity detection.

In this environment information acquisition means, the set voltage is changed based on the environment information acquired by the thermistor for temperature detection and the humidity sensor for humidity detection,
It is supplied to the current source 212. This supply controls the output intensity of the laser diode LD. The thermistor for temperature detection and the humidity sensor for humidity detection may be directly mounted on a substrate such as an engine substrate instead of the temperature / humidity sensor unit.

Next, the inductance component of the LD driving means in the laser scanner will be described with reference to FIG. In the present embodiment, the overshoot circuit section 220 is composed of the inductance component 221.

The inductance component 221 is a pure inductance electronic component (for example, a single coil).
But not limited to components that include inductance components,
For example, parts such as beads and impeders used for EMI countermeasures (EMI countermeasure components, noise countermeasure components) can also be used. By using this EMI countermeasure component as the inductance component 221, not only the overshoot of the rising portion of the optical waveform of the laser diode can be controlled but also noise such as EMI can be performed at the same time.

7 to 10 show examples of optical waveforms of the laser beam when beads, which are one of the EMI countermeasure components, are used for the inductance component 221. 7 and 8 show
9 and 10 show optical waveforms when beads having an impedance of 60 Ω at 100 MHz are used.
Shows the optical waveforms when beads having an impedance of 120Ω at 100 MHz were used.

Further, FIGS. 7 and 9 show the optical waveform of the laser beam during the time when about two pixels are formed, and FIGS. 8 and 10 show the optical waveform of the laser beam during the time when about 1/2 pixel is formed. Waveforms are shown respectively. As shown in FIGS. 7 and 9, in the semiconductor laser drive circuit 210 that outputs an optical waveform, when the impedance value of the EMI countermeasure component is increased, the overshoot at the rising portion is increased, which is effective for overexposure. Moreover, the greater the impedance, the greater the effect of the EMI countermeasure, which is effective.

However, as shown in FIGS. 8 and 10, in the semiconductor laser drive circuit 210 that outputs an optical waveform,
If the impedance value of the EMI countermeasure component is made too large, the light emission in the time shorter than one pixel causes the O
N / OFF cannot be followed and the optical waveform is destroyed.

If the light waveform is broken during light emission in a time shorter than one pixel, the light emission in the so-called smoothing process is broken and a high quality image cannot be obtained. Therefore, it is desirable to control the overshoot so that the overshoot is reproduced without being distorted even when the light is turned on for a time shorter than the time for forming one pixel.

As a preferred example, the overshoot is controlled so that the maximum value is 1.2 times or more and not more than 2 times the light intensity at the time of normal exposure for almost 100% of the time for forming one pixel. Good to do. Further, as another preferable example, the overshoot is performed so that the light converges in 50% or more of the time for forming one pixel and the maximum value is 1.2 times or more and 5 times or less of the normal light intensity. May be controlled.

By the way, in the present embodiment, the radio wave countermeasure components (beads, impeders, etc.) used as the inductance components of the overshoot circuit section 220 cause a high frequency loss by passing a signal through a magnetic material such as ferrite, thereby causing noise. It is a part that suppresses

This radio wave countermeasure component has its constant determined by the impedance Z at a specific frequency (for example, 100 MHz). The impedance Z has a resistance component R and an inductance component X, and the constant of the countermeasure component is changed. Then, not only the impedance Z but also its resistance component R
Then, the inductance component X changes and the magnitude of the overshoot changes.

For overshoot, these Z, R, X
Since the frequency characteristic of 1 contributes greatly, the overshoot cannot be increased only by increasing the constant of the radio wave countermeasure component. For example, even if the impedance Z at the frequency of 100 MHz is the same, the overshoot is small in the part where the difference between the impedance Z on the low frequency side and the high frequency side is small, and the overshoot is large for the part where the difference is large.

Further, for example, Z, R and X are 100 MH
If the characteristic has a peak at a frequency higher than z, the overshoot becomes larger. It is considered that the peak frequency in the Z, R, and X frequency characteristics differs depending on the characteristics of the printed board (material, pattern length, etc.), the type of laser diode, the frequency at which the laser is actually turned on / off, and the like.

As an actual example, the countermeasure component having the characteristics shown in FIG.
The overshoot is larger in the countermeasure component having the characteristics shown in. However, in the component having the characteristics of FIG. 13, the overshoot can be made larger than that of FIG. 12, but the laser emission of about 1/2 dot (about 10 ns) smaller than the dot (about 20 ns) forming one pixel The problem that the waveform is broken occurs.

This means that the peak value of X is large, Z,
It is considered that this is because the peak frequency of R is lower than that in FIG. Therefore, the characteristic of the countermeasure component cannot be uniquely determined, and it is necessary to select the optimum characteristic according to the ON / OFF frequency of the laser and the like.

The effect as a countermeasure against radio waves increases in the order of FIG. 11, FIG. 12, and FIG. 13, and the parts having the characteristics of FIG. 13 are the most effective, but this is also the case if the model of the image forming apparatus changes. It may be completely ineffective. In addition, in the present invention, a so-called multi-beam laser diode that emits a plurality of laser beams may be used for the LD 201, and may be applied to an image forming apparatus that forms a color image.

[0098]

As described above, according to the present invention, in an electrophotographic image forming apparatus, an inductance component is connected to a semiconductor laser to generate an overshoot at the rising portion of the optical output of a laser beam. Due to
Even when the resolution is increased or the electrophotographic process speed is increased, the reproducibility and gradation of the fine dots can be reproduced at low cost.

By connecting the inductance component to the ground side of the semiconductor laser, that is, to the terminal side of the terminals of the semiconductor laser that is not commonly connected to the photodiode, the overshoot to the PD output in the APC is prevented. The occurrence of distortion can be prevented. Furthermore, by using an EMI component as an inductance component that causes overshoot, it is possible to simultaneously take measures against unwanted radiation and the like.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a main configuration of an image forming apparatus of the present invention.

FIG. 2 is a schematic diagram showing an internal configuration of a laser scanner in the image forming apparatus of the present invention.

FIG. 3 is an electric circuit diagram showing an internal configuration of a semiconductor laser drive circuit in the image forming apparatus of the present invention.

FIG. 4 is an electric circuit diagram showing a circuit configuration in a package that encloses a laser diode and a photodiode.

FIG. 5 is a graph showing the exposure intensity of each light output before and after overshoot is generated.

FIG. 6 is a schematic diagram showing a formation state of an electrostatic latent image on a photosensitive drum based on resolution, electrophotographic process speed, or the like.

FIG. 7 is a graph (100) showing the emission intensity of the optical output when an EMI countermeasure component is used as the overshoot circuit unit.
It is an optical waveform of a laser beam at the time of forming about 2 pixels when a bead having an impedance of 60 Ω at MHz is used.

FIG. 8 is a graph (100) showing the emission intensity of the optical output when an EMI countermeasure component is used as the overshoot circuit unit.
It is an optical waveform of a laser beam during the time when about 1/2 pixel is formed when a bead having an impedance of 60 Ω at MHz is used.

FIG. 9 is a graph (100) showing the emission intensity of the optical output when an EMI countermeasure component is used as the overshoot circuit unit.
It is an optical waveform of a laser beam at the time of forming about 2 pixels when a bead having an impedance of 120Ω at MHz is used.

FIG. 10 is a graph (10) showing the emission intensity of the optical output when an EMI countermeasure component is used as the overshoot circuit unit.
It is an optical waveform of a laser beam at the time when about 1/2 pixel is formed when a bead having an impedance of 0Ω at 0 MHz is used.

FIG. 11 is a graph showing frequency characteristics of an impedance component Z, an inductance component X and a resistance component R in an EMI countermeasure component (impedance Z on the low frequency side and the high frequency side).
If the difference is small).

FIG. 12 is a graph showing frequency characteristics of an impedance component Z, an inductance component X and a resistance component R in an EMI countermeasure component (impedance Z on a low frequency side and a high frequency side).
If the difference is medium).

FIG. 13 is a graph showing frequency characteristics of an impedance component Z, an inductance component X and a resistance component R in an EMI countermeasure component (impedance Z on the low frequency side and the high frequency side).
If the difference is large).

FIG. 14 is an electric circuit diagram showing a circuit configuration in a package enclosing a laser diode and a photodiode.

[Explanation of symbols]

1 Image forming device 10 Charger 20 laser scanner 201 Laser diode (LD) 202 collimator lens 203 Cylindrical lens 204 plane mirror 205 rotating polygon mirror 206 fθ lens 207 reflective mirror 208 mirror 209 Photo Detector 210 Semiconductor laser drive circuit 211 Light intensity control circuit 212 current source 213 Switching unit 214 S / H section 215 Comparator 216 Load resistance RL 220 Overshoot circuit 221 Inductance parts 230 snubber circuit 231 Resistance R 232 Capacitor C 240 Photodiode (PD) 30 photoconductor drum 40 developer 50 transfer roller 60 fixer 901 Laser diode (LD) 902 Photodiode (PD) 903 package

Continued front page    F-term (reference) 2C362 AA03 AA13 AA52 AA55 AA61                       AA63                 5F073 AB27 AB29 BA07 EA17 EA27                       FA02 GA04 GA12 GA18 GA19                       GA25

Claims (15)

[Claims] 1. An image forming apparatus having an exposing means for turning on a semiconductor laser on the basis of image information, and scanning and exposing a photosensitive member with a laser beam outputted from the semiconductor laser to form an electrostatic latent image. In the device, the exposure unit turns on the semiconductor laser based on the image information,
A light intensity control circuit unit that scans and exposes the photosensitive member with a normal light intensity, and an overshoot circuit that increases the light intensity at the rising portion of the light output of the semiconductor laser that is turned on by the light intensity control circuit unit. The overshoot circuit section has an inductance component for setting a component value of the inductance, and the inductance component is a terminal of the terminals of the semiconductor laser that is not commonly connected to the photodiode. An image forming apparatus connected to the. 2. The image forming apparatus according to claim 1, wherein the inductance component is connected to a ground side terminal of the semiconductor laser. 3. The overshoot generated at the rising portion of the optical output by the overshoot circuit unit,
Of the irradiation time of the light output for forming one pixel,
6. Occupying more than 60% of the time.
Or the image forming apparatus according to 2. 4. The image forming apparatus according to claim 1, wherein the overshoot converges preferably at about 100% of the irradiation time. 5. The maximum value of the light intensity in the overshoot is 1.2 times or more and 5 times or less of the normal light intensity.
The image forming apparatus according to 3 or 4. 6. The maximum value of the light intensity in the overshoot is preferably 1.2 times or more and not more than 2 times the normal light intensity. The image forming apparatus according to any one of 1. 7. A speed acquisition means for acquiring an electrophotographic process speed is provided, wherein the light intensity control circuit section determines the normal light intensity based on the electrophotographic process speed acquired by the speed acquisition means. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed. 8. An environmental information acquisition unit for acquiring environmental information such as temperature and humidity, wherein the light intensity control circuit unit is configured to perform the normal operation based on the environmental information acquired by the environmental information acquisition unit. The image forming apparatus according to claim 1, wherein the light intensity is changed. 9. The image forming apparatus according to claim 1, wherein the semiconductor laser is a semiconductor laser capable of emitting a plurality of laser beams. 10. The image forming apparatus according to claim 1, wherein the inductance component is a noise countermeasure component. 11. A semiconductor laser drive circuit for driving and controlling a semiconductor laser for scanning and exposing on a photoconductor, comprising: a light intensity control circuit section for outputting a light output of the semiconductor laser at a normal light intensity; An overshoot circuit section for generating an overshoot at the rising portion of the optical output of the semiconductor laser; the overshoot circuit section has an inductance component for setting the component value of the inductance; A semiconductor laser drive circuit characterized in that the semiconductor laser drive circuit is connected to one of the terminals of the laser which is not commonly connected to the photodiode. 12. The semiconductor laser drive circuit according to claim 11, wherein the inductance component is connected to a ground side terminal of the semiconductor laser. 13. The light intensity control circuit unit changes the light intensity during the normal exposure based on the electrophotographic program speed acquired by the speed acquisition unit. Semiconductor laser drive circuit. 14. The light intensity control circuit unit changes the light intensity during the normal exposure based on the environment information acquired by the environment information acquisition means.
13. The semiconductor laser drive circuit described in 1 or 12. 15. The semiconductor laser driving circuit according to claim 11, wherein the semiconductor laser is a semiconductor laser that emits a plurality of laser beams.