JPH06316107A - Driving device for semiconductor laser - Google Patents

Abstract

PURPOSE:To prevent the change of the density of an output image even when the characteristics of various parts change in a semiconductor laser driving device modulating a laser beam corresponding to a multi-gradation image signal. CONSTITUTION:In a semiconductor laser driving device driving a semiconductor laser 3 by the sum of the current from a first current source 33 for issuing the use min. beam output of the laser and the current from a second current source 34 corresponding to a multi-gradation image signal, a means 19 detecting the error from the required value of output image density at a time when an image signal value is set to a certain specific value is provided. By this error, the gain of a D/A converter 45 converting an image signal to an analogue value in order to control the current of the second current source 34 is controlled. By this constitution, even when the characteristics of respective parts change by a temp. change or a secular change, a laser driving current is corrected so that the density of an output image becomes required density and, therefore, excellent image quality can be kept.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser driving device for changing the optical output of a semiconductor laser according to multi-tone image signals.

[0002]

2. Description of the Related Art A semiconductor laser driving device for changing the optical output of a semiconductor laser according to a multi-gradation image signal is mounted, for example, in a laser printer. FIG. 7 shows a conventional laser printer. In FIG. 7, 1 is an image signal processing circuit, 2 is a semiconductor laser driving device, 3 is a semiconductor laser, 4
Is a lens, 5 is a laser beam, 6 is a polygon mirror, 7
Is a polygon mirror drive unit, 8 is a lens, 9 is a mirror, 1
Reference numeral 0 is a charger, 11 is a developing device, 12 is a static eliminator, 13 is a sheet, 14 is a transfer charger, 15 is a photoconductor drum, 16 is a cleaning device, and 17 is an erase lamp.

The semiconductor laser drive device 2 controls the drive current of the semiconductor laser 3 by the image signal from the image signal processing circuit 1. Laser beam 5 emitted from semiconductor laser 3
Is reflected by the polygon mirror 6 through the lens 4. Since the polygon mirror 6 is rotated at a constant speed by the polygon mirror drive unit 7, the reflection angle of the laser beam 5 is continuously changed and scanning is performed. The laser beam 5 passing through the lens 8 and the mirror 9 irradiates the photoconductor drum 15.

Although the photosensitive drum 15 is rotated in the direction of the arrow, it is first uniformly charged by the charger 10. By being irradiated with the laser beam 5, the potential of the irradiated portion changes and a latent image is drawn. The latent image is developed with toner attached by the developing device 11. The static eliminator 12 is
Prior to the transfer of the toner image, the charge is removed so that the potential becomes easy to transfer. The transfer charger 14 transfers the toner image onto the sheet 13. The cleaning device 16 removes the toner remaining on the surface of the photosensitive drum 15 even after the transfer. The erase lamp 17 removes the remaining charges.

The minimum light output to be used for irradiation of the photosensitive drum is set within the laser emission region of the laser characteristics of the semiconductor laser, and the semiconductor laser driving device 2 outputs a light output higher than that according to the image signal. Control the laser drive current. Since the characteristics of the semiconductor laser change depending on the temperature, the laser drive current is sometimes reset so that the intended optical output can be obtained.

Prior art documents relating to a semiconductor laser driving device include, for example, Japanese Patent Laid-Open Nos. 57-4780, 62-116071, 63-229468, and 3-234075. There is a bulletin, etc.

[0007]

[Problems to be Solved by the Invention]

(Problem) However, in the above-mentioned conventional semiconductor laser driving device, it is necessary to control the laser driving current so as to compensate for changes in performance and characteristics in various parts of equipment in which the semiconductor laser driving device is mounted. I can not do it, so
There has been a problem that the output image density changes unexpectedly.

(Explanation of Problems) When the semiconductor laser driving device is installed in a laser printer, for example, the charging characteristics of the photosensitive drum change due to temperature, light fatigue, etc., and the performance in processes such as development and transfer is improved. By changing
Before long, the output image density may be different from the desired one. FIG. 3 shows such a change in output image density. The horizontal axis is the image signal, and the vertical axis is the output image density. 53 is a concentration characteristic curve when outputting a desired concentration, and 54 and 55 are concentration characteristic curves when a concentration different from the desired concentration is output due to a change in characteristics or the like. Is. That is, when the image signal value is S, the density K should be output, but K _{1 and} K ₂ having different densities are output.

In the conventional semiconductor laser drive device, the laser drive current is not controlled in consideration of the above change. Therefore, the output image density may be different from the expected one and the image quality may be deteriorated. In order to solve the above problems, the present invention compensates for the influence of the characteristic change of various parts of the equipment in which the semiconductor laser driving device is mounted.
It is an object to control the laser drive current.

[0010]

In order to solve the above problems, according to the present invention, there is provided a first current source, the current value of which is set so as to independently output a minimum light output for use in a laser emission region.
A semiconductor comprising: a second current source whose current value is controlled by a multi-gradation image signal; and means for supplying a semiconductor laser with the sum of the currents of the first current source and the second current source. In the laser driving device, a detection means for detecting an error from an expected value of an output image density when the second current source is controlled by a specific image signal value, and a minimum floor when setting the first current source. A gate circuit that outputs a value of an image signal that obtains a tone and allows the image signal to pass as it is after setting, a DA converter whose gain is adjusted by the error, and an image signal through the gate circuit and the DA converter. And means for supplying to the second current source.

Instead of the output image density, the toner image density or latent image potential on the photosensitive drum can be used.

[0012]

[Operation] Semiconductor laser drive for driving a semiconductor laser with a sum of a current from a first current source for producing a minimum usable light output and a current from a second current source according to a multi-gradation image signal The apparatus is provided with means for detecting an error from an expected value of the output image density when the image signal value is set to a specific value. Then, the error controls the gain of the DA converter that converts the image signal into an analog value in order to control the current of the second current source. As a result, the laser exposure amount is corrected by correcting the laser drive current so that the output image density becomes the desired density even if the characteristics of some part change due to temperature or aging. It becomes possible to maintain good image quality.

[0013]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 2 is a diagram showing a first example of a laser printer using the semiconductor laser driving device of the present invention. Reference numerals correspond to those in FIG. 7, 19 is a differential amplifier, and 20 is a densitometer. In this example, the density of the output image after being transferred to the paper 13 is detected by the densitometer 20, and an error from the initial value is detected, or the density of the toner image which is the previous stage of the output image is detected, The error from the desired value is detected. The differential amplifier 19 obtains and amplifies the error between the detection signal and the desired value. The desired value is given to the differential amplifier 19 in advance.

Here, the desired value means a normal value before the characteristic changes, and in the case of FIG. 3, the image signal value S
At that time, the expected value is K. After the characteristic changes as shown by the characteristic curve 54, K ₁ is detected by the densitometer 20, so the error A is detected and amplified by the differential amplifier 19 and sent to the semiconductor laser drive device 2 as a disturbance detection signal. To be

The semiconductor laser driving device 2 takes into consideration the disturbance detection signal as described below with reference to FIG. 1 in addition to the multi-gradation image signal from the image signal processing circuit 1. Since the drive current of No. 3 is controlled, the output image density is maintained at the desired density, and deterioration of image quality is prevented.

FIG. 1 is a diagram showing a semiconductor laser driving device of the present invention. Reference numerals correspond to those of FIG. 6, 19-1 is a differential amplifier, 30 is a monitoring photodiode, 31 is a resistor, 32 is a switching circuit, 33 and 34 are current sources,
35 is a clock generator, 36 is an input terminal, 37 is an optical output setting unit, 38 is an AD converter (analog / digital converter), 39 is a controller, 40 is a DA converter (digital / analog converter), 41, 42 and 43 are input terminals, 44 is a gate circuit, 45 is a DA converter, 46 is voltage holding means, and 47 is an OR circuit.

The semiconductor laser 3 has a current I of a current source 33.
A current that is the sum of ₁ and the current I ₂ of the current source 34 is passed through the switching circuit 32. Switching circuit 32
Is turned on / off by a clock (video clock) generated in synchronization with the horizontal scanning start position signal from the input terminal 36. The current I ₁ is controlled by the DA converter 40, and the input D ₁ to the DA converter 40 is the controller 39.
Given more. The current I ₂ is controlled by the DA converter 45, and the input to the DA converter 45 is the signal D ₂ from the gate circuit 44.

The gate circuit 44 is controlled by the controller 39 and has two states. For example, when the control signal is "0", the minimum value 0 is output, and when the control signal is "1", the image signal from the input terminal 41 is passed as it is. The image signal is shown in FIG.
From the image signal processing circuit 1. DA converter 4
The gain of No. 5 is adjusted by the disturbance detection signal. By this adjustment, the disturbance (characteristic change in various parts) is corrected.

The AD converter 38 digitizes the optical output monitor voltage V _m and the optical output set value V ₁ which are analog values, and sends them to the controller 39. The monitor voltage V _m is a voltage generated across the resistor 31. Since the resistor 31 is connected in series to the monitor photodiode 30 that causes a current corresponding to the received laser beam to flow, a voltage corresponding to the laser beam appears at both ends thereof. The light output set value V ₁ will be described with reference to FIG.

FIG. 4 is a diagram showing the characteristics of the semiconductor laser. The horizontal axis represents the laser drive current, and the vertical axis represents the optical output detection voltage (monitor voltage V _m ). Laser characteristic curve 50 (T
₁ ) is when the temperature is T ₁ , and laser characteristic curve 5
0 (T ₂ ) is when the temperature is T ₂ which is higher than T ₁ . The laser characteristic curve is composed of the spontaneous emission region L ₁ and the laser emission region L ₂ , and the inflection point C is the boundary. The laser light is light generated in the laser emission region L ₂ .

As the optical output corresponding to the minimum value of the multi-gradation image signal, the minimum usable optical output P ₁ is determined. The light output detection voltage when the minimum light output P _{1 is} used is V ₁ . Therefore,
When the image signal changes, the light output changes in the laser emission region L ₂ that is equal to or more than the minimum use light output P ₁ and the light output detection voltage is V
_It changes while taking a value of ₁ or more.

[0022] (Configuration of the current I ₁₎ laser driving current of FIG. 1, when the image signal is a minimum value of (0), using minimum light output P ₁
It must be controlled so that First, the gate circuit 44 is set to output 0 by the control signal from the controller 39, and the current I of the current source 34 is
₂ is set to 0. This corresponds to the state when the image signal has the minimum value (0).

In this state, the input from the controller 39 to the DA converter 40 is increased so that the monitor voltage V _m becomes equal to V ₁ . The controller 39 determines whether or not they are equal. When they become equal, the current I ₁ of the current source 33 is fixed. As a result, the current I ₁ is set. As shown in FIG. 4, when the temperature changes and the characteristics change, the value of I ₁ also changes.

(Adjustment of gain) After setting the current I ₁ ,
The gain of the DA converter 45 is adjusted as follows. First, a control signal from the controller 39 sets the state of the gate circuit 44 to a state in which the image signal passes.
Then, a certain specific image signal value (for example, the value S in FIG. 3)
Enter. The output image density at that time is detected by the densitometer 20, and the detection signal is input to the input terminal 42 of the differential amplifier 19.
To enter.

The other input terminal 43 of the differential amplifier 19-1
In, a desired value K of the density of the output image corresponding to the image signal value S is input in advance. Then, the error from the expected value K is output as a disturbance detection signal to the output of the differential amplifier 19, and is held in the voltage holding means 46. The gain of the DA converter 45 is adjusted by this disturbance detection signal.

FIG. 5 is a diagram showing how the current I ₂ changes due to the gain adjustment of the DA converter 45. Horizontal axis is D
It is the input of the A converter 45, and the vertical axis is the current I of the current source 34.
_{Is 2} . When the gain is increased like the curve 51, DA
The output of the converter 45 increases and the current I ₂ of the current source 34 also increases. In the opposite case, it is reduced. Voltage holding means 46
The reason for providing is that the gain is kept fixed until a certain print job is completed. Since the laser characteristics change depending on the temperature, the setting of the current I ₁ and the adjustment of the gain are performed at regular intervals or every time a predetermined operation is completed.

In the above-described example, the output image density of the paper 13 is detected, but the densitometer 20 is arranged at the next stage of the developing device 11 so that the density of the toner image is detected and the density is corrected. You may

FIG. 6 is a diagram showing a second example of a laser printer using the semiconductor laser driving device of the present invention. Reference numerals correspond to those in FIG. 2, and 18 is a surface electrometer. The surface electrometer 18 is used for the laser beam 5 on the photosensitive drum 15.
The surface potential of the part irradiated with the light is detected. The latent image potential, which is the previous stage of the toner image, is detected and the error from the desired value of the latent image potential is used as the disturbance detection signal. The processing of the signal is the same as that of the first example, and therefore its explanation is omitted.

[0029]

As described above, according to the semiconductor laser driving apparatus of the present invention, a DA for detecting an error from an expected value of the output image density or an element affecting it, and converting the image signal into an analog value. Since the gain of the converter is controlled by the above error, the laser drive current is corrected so that the output image density becomes the desired density even if the characteristics of each part change due to temperature or aging, and good image quality is achieved. Can be maintained.

[Brief description of drawings]

FIG. 1 is a diagram showing a semiconductor laser driving device of the present invention.

FIG. 2 is a diagram showing a first example of a laser printer using the semiconductor laser driving device of the present invention.

FIG. 3 is a diagram showing changes in output image density.

FIG. 4 is a diagram showing characteristics of a semiconductor laser.

FIG. 5 is a diagram showing how the current I ₂ changes according to the gain adjustment of the DA converter 45.

FIG. 6 is a diagram showing a second example of a laser printer using the semiconductor laser driving device of the present invention.

FIG. 7 is a laser printer using a conventional semiconductor laser driving device.

[Explanation of symbols]

1 ... Image signal processing circuit, 2 ... Semiconductor laser driving device, 3
... semiconductor laser, 4 ... lens, 5 ... laser beam, 6 ...
Polygon mirror, 7 ... Polygon mirror driving unit, 8 ... Lens, 9 ... Mirror, 10 ... Charging device, 11 ... Developing device, 12 ...
Static eliminator, 13 ... Paper, 14 ... Transfer charger, 15 ... Photosensitive drum, 16 ... Cleaning device, 17 ... Erase lamp, 18 ... Surface potential meter, 19 ... Differential amplification section, 20 ... Density meter, 30 ... Photodiode for monitor, 31 ... Resistor,
32 ... Switching circuit, 33, 34 ... Current source, 35 ...
Clock generator, 36 ... Input terminal, 37 ... Optical output setting section, 38 ... AD converter, 39 ... Controller, 40 ... D
A converter, 41, 42, 43 ... Input terminal, 44 ... Gate circuit, 45 ... DA converter, 46 ... Voltage holding means, 47 ...
OR circuit

Claims (3)

[Claims] 1. A first current source, the current value of which is independently set so as to produce a minimum light output for use in a laser emission region, and a second current whose current value is controlled by a multi-gradation image signal. A semiconductor laser driving device comprising a source and a means for supplying a semiconductor laser with a sum of the currents of the first current source and the second current source, wherein the second current source is controlled by a specific image signal value. When the first current source is set, a detection unit that detects an error from an expected value of the output image density is output, and when the first current source is set, the value of the image signal that obtains the minimum gradation is output, and after the setting, the image signal is directly It further comprises a gate circuit for passing the signal, a DA converter whose gain is adjusted by the error, and means for supplying an image signal to the second current source via the gate circuit and the DA converter. Semiconductor laser drive device. 2. The semiconductor laser driving device according to claim 1, wherein the toner image density on the photosensitive drum is used instead of the output image density. 3. The semiconductor laser driving device according to claim 1, wherein the latent image potential on the photosensitive drum is used instead of the output image density.