JP2838976B2 - Laser scanning device for image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for an electrophotographic printer, and more particularly to a laser scanning apparatus used in an exposing device for forming an electrostatic latent image on the surface of a photoreceptor.

[0002]

2. Description of the Related Art Conventionally, it has been desired that this type of image forming apparatus forms an image that faithfully reproduces given image data. For example, JP-A-3-279974 discloses that
A technique has been disclosed that enables finely controlled high-quality images to be formed by changing two or more types of light emission intensity within the time of a light emission pulse width of a semiconductor laser used as a light source of a laser scanning device. ing.

[0003]

The laser scanning device of this conventional image forming apparatus uses only one of a plurality of types of light emission intensities due to variations in the light emission intensity between the image forming apparatuses of the semiconductor laser and the printing environment. The emission intensity control is performed to absorb the influence of the characteristic fluctuation. However, for other types of emission intensities, since such control is not performed and a fixed value is obtained, image data cannot be faithfully reproduced due to a difference in device or printing environment. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming apparatus for forming a finely controlled high-quality image by changing two or more kinds of light emission intensities within the light emission pulse width of a semiconductor laser. Laser scanning of an image forming device that can faithfully reproduce image data by implementing light emission intensity control that absorbs variations in light emission intensity between semiconductor laser image forming devices and fluctuations in light emitting characteristics due to printing environment, etc. It is to provide a device.

[0005]

According to the present invention, there is provided a laser scanning device of an image forming apparatus for forming an image on a record carrier by a laser beam emitted from a semiconductor laser which emits light in response to an image signal. A light emitting circuit unit that emits light, and a laser driving voltage generating unit that generates a plurality of laser driving voltages having different levels supplied to the light emitting circuit unit;
A determining unit that determines a level of a laser driving voltage from the laser driving voltage generating unit to the light emitting circuit unit; a detecting unit that detects a laser light amount from the semiconductor laser to generate a light amount detecting signal; A control unit that compares the level of the laser drive voltage generated by the laser drive voltage generation unit until the image signal reaches the reference value. After period
When switching from the white print state to the black print state,
From the beginning of the black printing section, apply a higher laser drive voltage than usual.
A pulse to be selected is output, and the white printing period of the image signal is
If it is shorter than a certain set time, it will be lower for a certain time than usual
A laser scanning device for an image forming apparatus characterized by selecting a laser driving voltage is obtained.

The deciding section forcibly switches the level of the laser driving voltage from the laser driving voltage generating section during the adjustment of the laser driving voltage level by the control section, and controls the laser in accordance with the image signal while the image signal is supplied. Switches the level of the drive voltage.

The switching of the level of the laser drive voltage during the supply of the image signal is executed, for example, according to the length of the white printing section of the image signal.

According to the present invention, there is further provided a laser scanning device of an image forming apparatus for forming an image on a record carrier by a laser beam emitted from a semiconductor laser which emits light in accordance with an image signal.
A light emitting circuit for driving a semiconductor laser to emit light, a plurality of laser driving voltage generators supplied to the light emitting circuit to generate laser driving voltages of different levels, and from the laser driving voltage generator to the light emitting circuit A switching unit for switching the output of the laser, a pulse generation unit for generating a pulse for controlling the switching of the switching unit, a detection unit for detecting the amount of laser light from the semiconductor laser and generating a light amount detection signal, and a laser drive voltage for the light amount detection signal. A control unit that adjusts the level of the laser drive voltage from the laser drive voltage generation unit selected by the switching unit until the reference value is reached, and the pulse generation unit Is before
The image signal is changed from white printing state to black printing state for a certain period or more.
When switching to, from the beginning of the black printing section,
Switching the pulse to select a higher laser drive voltage
A set time during which there is a white printing period of the image signal
If shorter, lower the laser drive power for a certain period of time.
A pulse for selecting a pressure is output to the switching unit, thereby providing a laser scanning device of the image forming apparatus.

[0009]

Next, embodiments of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a circuit diagram showing an embodiment of the present invention. 1, a laser scanning device 1 includes a laser diode light emitting circuit unit 2 having a laser light source and a driving circuit,
A laser drive voltage switching unit 3 for switching between the first laser drive voltage (1) from the laser drive voltage generator 4 and the second laser drive voltage (2) from the second laser drive voltage generator 4, and a controller 6 and a laser diode light amount detection unit 7
And a pulse generator 8. This image forming apparatus includes:
The amount of light obtained by the laser drive voltage from the laser drive voltage switching unit 3 is used as an image signal or the output light of the laser diode light emitting circuit unit 2 that causes the laser diode to emit light in accordance with the image data and the forced light emission signal. An electrostatic latent image is formed on a body (not shown).

The laser drive voltage switching unit 3 is, for example,
The first laser drive voltage (1) for setting the laser light quantity to a standard value and the second laser drive voltage (2) for increasing the laser light quantity from the standard value are set by a forced selection signal from the control unit 6. And a pulse from the pulse generator 8 determined by the image data and outputs the selected laser drive voltage to the laser diode light emitting circuit 2.

The first laser drive voltage generator 4 and the second laser drive voltage generator 5 are provided with a first laser drive voltage (1) and a second laser drive voltage (2) according to a signal from the controller 6.
Is output to the laser drive voltage switching unit 3.

The laser diode light amount detecting section 7 converts the light amount input from the laser diode light emitting section 2 into a voltage,
It outputs to the control unit 6 as a light amount detection voltage.

Next, the operation of the circuit of FIG. 1 will be described with reference to the waveform diagram of FIG. At the time of adjusting the laser drive voltage, the control section 6 forcibly causes the laser diode to emit light by the forced light emission signal (A). At this time, the control unit 6
Outputs a signal for determining the level of the laser drive voltage to the first laser drive voltage generator 4, and the first laser drive voltage generator 4 outputs the first laser corresponding to the signal given to the controller 6. The driving voltage (1) is output to the laser driving voltage switching unit 3.

On the other hand, at the time of adjusting the laser drive voltage, the pulse generator 8 forcibly changes the first laser drive voltage (1) regardless of the presence or absence of an image by the forced selection signal (B) from the controller 6. Generate a pulse (D) to select
The laser driving voltage switching unit 3 uses the pulse to
The driving voltage (1) is output to the laser diode light emitting circuit 2. At that time, the light amount of the laser diode emitted by the laser diode light emitting circuit unit 2 is detected by the laser diode light amount detection unit 7. The laser diode light amount detection unit 7 converts the received light amount into a voltage and outputs the voltage to the control unit 6 as a light amount detection voltage (E). The control unit 6 compares the light amount detection voltage with an internal first reference value. At this time, if the first reference value does not match the light amount detection voltage (E), the control section 6 outputs a signal for changing the laser drive voltage level to the first laser drive voltage generation section 4, and outputs the changed first laser drive voltage level.
The laser drive voltage (1) is changed to the first laser drive voltage generator 4
Is supplied to the laser diode light emitting circuit unit 2 via the laser drive voltage switching unit 3. The amount of laser light from the laser diode light emitting circuit 2 is detected by the laser diode light emitting circuit 7, and the light amount detection voltage (E) is controlled by the controller 6.
, The light amount detection voltage is again compared with a first reference value inside the control unit 6. This processing is performed until the light amount detection voltage (E) matches the first reference value, and if they match, the adjustment and setting of the first laser drive voltage (1) are completed. In FIG. 2, a transient phenomenon is observed in the light amount detection voltage (E) because the control unit 6 performs the PID control.

After the adjustment of the first laser drive voltage (1) is completed,
The control of the control unit 6 shifts to adjustment of the second laser drive voltage (2). The controller 6 outputs a signal for determining a laser drive voltage to the second laser drive voltage generator 5 while the laser diode is forcibly emitted by the forced light emission signal (A). As a result, the second laser drive voltage generator 5 generates the second laser drive voltage (2) according to the signal given by the controller 6.
Is output to the laser drive voltage switching unit 3. On the other hand, the pulse generator 8 generates a pulse (D) for forcibly selecting the second laser drive voltage (2) regardless of the presence or absence of image data by the laser drive voltage according to the forced selection signal (B) from the controller 6. The laser driving voltage switching unit 3 outputs the second laser driving voltage (2) to the laser diode light emitting circuit unit 2. At this time, the light amount of the laser diode emitted by the laser diode light emitting circuit unit 2 is detected by the laser diode light amount detection unit 7, and the light amount detection voltage (E) converted into a voltage is supplied to the control unit 6,
The light amount detection voltage is compared with a second reference value inside the control unit 6. At this time, if the second reference value does not match the light amount detection voltage (E), the controller 6 outputs a signal for changing the laser drive voltage level to the second laser drive voltage generator 5,
The changed second laser drive voltage (2) is output from the second laser drive voltage generator 5 to the laser diode light emitting circuit 2. Light amount detection voltage (E) corresponding to the light amount of the laser diode emitted by the laser diode light emitting circuit unit 2
Is supplied from the laser diode light amount detection unit 7 to the control unit 6, and the light amount detection voltage is compared again with a second reference value inside the control unit 6. This processing is performed by comparing the light amount detection voltage and the control unit 6
The process is performed until the internal reference value matches.
The adjustment and setting of the laser drive voltage (2) are completed.

As described above, the first laser drive voltage (1)
And a light amount detection voltage (E) obtained by converting the light amount of the laser diode according to the second laser drive voltage (2) to a voltage, and the first laser drive voltage (1) and the second laser drive voltage (2), respectively. First and second inside the control unit 6
By performing the process of making the laser diode coincide with the reference value, it is possible to absorb the influence of the variation in the light emission characteristics between the devices of the laser diode and the fluctuation of the light emission characteristics due to the printing environment and the like.

At the time of printing, when the image data (C) is switched from OFF (white printing) to ON (black printing) for a certain period or more, the second laser drive voltage (2) is changed from the beginning of the ON section. The pulse generator 8 outputs a pulse (D) to be selected to the laser drive voltage switching unit 3, which selects the laser drive voltage 2 and outputs it to the laser diode light emitting circuit unit 2 to output the laser diode. The light amount is a value increased from the standard value. After a lapse of a predetermined time, the pulse generator 8 outputs a pulse (D) for switching from the second laser drive voltage (2) to the first laser drive voltage (1) to the laser drive voltage switching unit 3, and the laser drive voltage switching unit 3
Outputs the first laser drive voltage (1) to the laser diode light emitting circuit section 2 and sets it to a standard value that does not increase the light amount of the laser diode. However, if the OFF (white printing) section during printing is shorter than a set time, the pulse generator 8 outputs a pulse (D) for selecting the laser drive voltage 1 to the laser drive voltage switching section 3 and the laser drive is performed. The voltage switching unit 3 outputs the first laser drive voltage (1) to the laser diode light emitting circuit unit 2, and sets the light amount of the laser diode to a standard value. Based on this logic, a laser drive voltage is output from the laser drive voltage switching unit 3 to the laser diode light emitting circuit unit 2, and the laser diode emits light with a corresponding light amount.

The laser diode light emitting circuit 2 is configured to stop emitting the image data (C) during the white printing period, and emit the light by the laser driving voltage from the laser driving voltage switching unit 3 only during the black printing period. Have been.

Next, as a second embodiment, a laser scanning device having three laser drive voltages will be described with reference to FIG.

In the second embodiment, image formation is performed by a laser diode light emitting circuit section 14 which causes a laser diode to emit light in accordance with image data and a forced light emission signal with a light amount obtained by a laser drive voltage from a laser drive voltage switching section 13. I do.

The laser drive voltage switching unit 13 includes, for example, a first laser drive voltage (21) for setting the laser light amount to a standard value and a second laser drive voltage (21) for increasing the laser light amount.
A laser drive voltage (22) and a third laser drive voltage (23) for reducing the amount of laser light are selected by a pulse from the pulse generator 12 determined by a forced selection signal from the controller 6 and image data, and the selected laser is selected. The driving voltage is output to the laser diode light emitting circuit section 14.

The first laser drive voltage generator 10, the second laser drive voltage generator 11, and the third laser drive voltage generator 16 provide a first laser drive voltage (in accordance with a signal from the controller 9). 21) The second laser drive voltage (22) and the third laser drive voltage (23) are output to the laser drive voltage switching unit 13.

The laser diode light quantity detecting section 15 converts the light quantity inputted from the laser diode light emitting circuit section 14 into a voltage, and outputs the voltage to the control section 9 as a light quantity detecting voltage.

The adjustment of each laser drive voltage in this embodiment is performed in the same manner as in the first embodiment. The switching of the laser drive voltage in the present embodiment is normally in the state of the first laser drive voltage (21), and
The selection of 2) is performed for a certain period when the image signal is turned on after a certain OFF (white printing) period, and the light amount is increased. Next, when the OFF (white printing) period is shorter than a certain set time, the third laser drive voltage (23) is selected for a certain time,
Decrease light intensity.

The invention of claim 1 is not limited to the above embodiment. In the embodiment of FIGS. 1 and 3, there are a plurality of laser drive voltage generators,
13 selects any one of the outputs, one laser drive voltage generator generates a plurality of levels of laser drive voltages, and the laser drive voltage is determined by the output of the determiner when adjusting the laser drive voltage. May be switched. In this case, the determination unit is a pulse generation unit, and the output pulse is supplied to the laser drive voltage generation unit, where each level is determined.

[0027]

As described above, in the image forming apparatus according to the present invention, in the plurality of laser drive voltage generators, all the laser drive voltage generators, or the lasers which generate a plurality of levels of laser drive voltages are provided. The drive voltage generation circuit controls the laser diode to determine the laser drive voltage by performing control to absorb the variation in the light emission characteristics between the devices of the laser diode and the fluctuation of the light emission characteristics due to the printing environment, etc. Irrespective of the difference, given image data can be faithfully formed.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing a configuration of a first embodiment of the present invention.

FIG. 2 is a waveform chart showing the operation of the embodiment of FIG.

FIG. 3 is a circuit diagram showing a configuration of a second embodiment of the present invention.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 laser scanning device 2 laser diode light emitting circuit section 3 laser drive voltage switching section 4 first laser drive voltage generation section 5 second laser drive voltage generation section 6 control section 7 laser diode light quantity detection section 8 pulse generation section 9 control section DESCRIPTION OF SYMBOLS 10 1st laser drive voltage generation part 11 2nd laser drive voltage generation part 13 laser drive voltage switching part 14 laser diode light emission circuit part 15 laser diode light quantity detection part 16 3rd laser drive voltage generation part

Claims (6)

(57) [Claims] 1. A laser scanning device of an image forming apparatus for forming an image on a record carrier by a laser beam emitted from a semiconductor laser that emits light in response to an image signal, comprising: a light emitting circuit unit that drives the semiconductor laser to emit light;
A laser drive voltage generator that generates a plurality of laser drive voltages having different levels supplied to the light emitting circuit, and a determiner that determines the level of the laser drive voltage from the laser drive voltage generator to the light emitting circuit. A detection unit that detects a laser light amount from the semiconductor laser and generates a light amount detection signal, compares the light amount detection signal with a reference value corresponding to each level of the laser drive voltage, and until the reference value is reached. A control unit that adjusts the level of the laser drive voltage generated by the laser drive voltage generation unit, the determination unit, when the image signal is switched from a white print state to a black print state for a certain period or more, From the beginning of the black printing section, a pulse for selecting a laser drive voltage higher than usual is output, and if the white printing period of the image signal is shorter than a certain set time, a certain time, usually A laser scanning device for an image forming apparatus, wherein a lower laser drive voltage is selected. Wherein said determining unit, in level adjustment of the laser drive voltage by the control unit, each level of the laser drive voltage to claim 1, wherein sequentially switching that after reaching the reference value A laser scanning device for the described image forming apparatus. 3. The laser drive voltage generator includes a plurality of laser drive voltage generators, each of which generates a laser drive voltage having a different level.
3. The laser scanning device according to claim 2 , wherein the determination unit switches to one of the outputs of the plurality of laser drive voltage generation circuits. Wherein said determining unit includes a switching unit that selects to switch to one of among outputs of the plurality of laser drive voltage generating circuit, and a pulse generator for generating a switching control pulse to the switching unit A laser scanning device for an image forming apparatus according to claim 3 . 5. A laser scanning device of an image forming apparatus for forming an image on a record carrier by a laser beam emitted from a semiconductor laser that emits light in response to an image signal, comprising: a light emitting circuit unit that drives the semiconductor laser to emit light;
A plurality of laser drive voltage generators that are supplied to the light emitting circuit unit and generate laser drive voltages having different levels, a switching unit that switches output from the laser drive voltage generator to the light emitting circuit unit, and the switching unit A pulse generator for generating a pulse for controlling the switching of the laser, a detector for detecting a laser light amount from the semiconductor laser and generating a light amount detection signal, and a reference corresponding to each level of the laser drive voltage for the light amount detection signal. A control unit that adjusts the level of the laser drive voltage from the laser drive voltage generation unit selected by the switching unit until the pulse reaches the reference value. When the signal switches from the white print state to the black print state for a certain period or more, a laser drive voltage higher than normal is selected from the beginning of the black print section And outputting a pulse for selecting a laser driving voltage lower than normal to the switching unit for a predetermined time if the white printing period of the image signal is shorter than a certain set time. Scanning device of an image forming apparatus. Wherein said pulse generator during level adjustment of the laser drive voltage by the control unit, generates a forcibly switched pulse output of the laser drive voltage generating unit to the switching unit, the image signal 6. The laser scanning device of the image forming apparatus according to claim 5 , wherein a pulse for switching an output of the laser drive voltage generation circuit is generated in accordance with the image signal while being supplied.