JPH06312531A - Semiconductor-laser driving apparatus - Google Patents

Abstract

PURPOSE:To maintain excellent picture quality even if the characteristics of elements affecting on the picture quality are changed in a semiconductor-laser driving apparatus, which modulates laser light in response to picture signals in many gradations. CONSTITUTION:In a semiconductor-laser driving apparatus, which controls a laser driving signal in response to picture signals in many gradations, a detected disturbance signal and the picture signal are synthesized in a DA converter 45 so that the picture signal is located at the upper-bit side and the detected disturbance signal is located at the lower-bit side. The detected disturbance signal is the signal, which is obtained by detecting the error from the expected state of an element affecting on picture quality (e.g. the surface potential of the drum of a photosensitive body and the density of a toner). The laser driving current of a semiconductor laser diode 3 is controlled by the synthesized signal. Then, the detected disturbance signal finely adjusts the intensity of the laser light when the laser light is modulated by the picture signal, and the error of the element affecting the picture quality is compensated. Therefore, the excellent picture quality can be maintained.

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. 3 shows a conventional laser printer. In FIG. 3, 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.

In the laser emission region of the laser characteristics of the semiconductor laser, the minimum light output and the maximum light output to be used for irradiating the photosensitive drum are set, and the semiconductor laser driving device 2 determines the light output between them. The laser drive current is controlled so as to output in accordance with the image signal. Since the characteristics of the semiconductor laser change depending on the temperature, the laser drive current is sometimes reset depending on whether the expected optical output is produced.

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 other parts of equipment in which the semiconductor laser driving device is mounted. There was a problem that I could not do it.

(Explanation of Problems) When the semiconductor laser driving device is mounted on a laser printer, for example, the charging characteristic of the photosensitive drum changes due to temperature, light fatigue and the like. Figure 6
Shows the charging characteristics of the photosensitive drum. The horizontal axis represents the image signal value (thus, it may be considered as light output), the vertical axis represents the surface potential of the photosensitive drum 15, 53 is the initial characteristic curve, and 54 is the value after the change due to light fatigue or the like. It is a characteristic curve. The potential of the portion not irradiated with the laser light is the charger 10.
Is the potential V _H charged by. As the image signal value becomes large and the light output becomes large, the surface potential of the irradiated portion decreases.

When the image signal value is D _a , the initial surface potential is V _a , but the surface potential after the characteristic of the photoconductor is changed becomes V _a1 . A is an error between the two, but if such an error occurs with respect to the same image signal value D _a , the degree of toner adhesion differs when developing the same, and the gradation is different from what was planned. It will be different. In the conventional semiconductor laser drive device, the laser drive current is not controlled in consideration of the above change. Therefore, the image quality may be deteriorated. SUMMARY OF THE INVENTION In order to solve the above problems, it is an object of the present invention to control a laser drive current so as to compensate for an influence of a characteristic change of other parts of a device equipped with a semiconductor laser drive device. Is.

[00010]

In order to solve the above-mentioned problems, the present invention sets a minimum value and a maximum value of a laser driving current, and controls the laser driving current according to an image signal of multiple gradations between them. As a result, in the semiconductor laser driving device that modulates the intensity of the laser light within the predetermined range of the laser emission region, from the intended state of the factors that affect the image quality (for example, the surface potential of the photosensitive drum and the density of the toner image). The disturbance detection signal and the image signal, which are signals in which the error is detected, are synthesized by a synthesizing means for synthesizing the image signal so that the image signal is at the upper bit side and the disturbance detection signal is at the lower bit side, and the signal synthesized by the synthesizing means And means for controlling the laser drive current.

As the synthesizing means, a DA converter whose gain is adjusted when setting the laser drive current is used, and an image signal is directly input to the upper bit side of the input to the DA converter, On the bit side, when setting the minimum and maximum values of the laser drive current, the gate circuit that outputs the intermediate value of the range of values that the disturbance detection signal can take, and otherwise passes the disturbance detection signal The output from can be input.

[00012]

[Operation] In a semiconductor laser drive device that controls a laser drive current according to a multi-gradation image signal, a disturbance detection signal that is a signal that detects an error from an expected state of an element that affects image quality The image signal is combined so that the image signal is on the upper bit side and the disturbance detection signal is on the lower bit side, and the laser drive current is controlled by this combined signal. Then, when the laser light is modulated by the image signal,
The disturbance detection signal finely adjusts the intensity of the laser light to compensate for an error from an expected value of an element that affects image quality. Therefore, it is possible to maintain good image quality.

[00013]

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. 3, 18 is a surface electrometer, and 19 is a differential amplifier. The surface electrometer 18 detects the surface potential of the portion irradiated with the laser beam 5, and the differential amplifier 19 amplifies the difference between the detection signal and the desired value. The desired value is given to the differential amplifier 19 in advance. The desired value is a normal value before the characteristic changes, and in FIG. 6, the desired value when the image signal value D _a is V _a . Characteristic is characteristic curve 5
After changing to 4, the error A is amplified by the differential amplifier 19 because V _a1 is detected by the surface electrometer 18. The amplified signal of the error A is sent to the semiconductor laser driving device 2. This error amplified signal will be referred to as "disturbance detection signal" for convenience.

The semiconductor laser drive device 2 controls the drive current of the semiconductor laser 3 in consideration of the disturbance detection signal as well as the multi-gradation image signal from the image signal processing circuit 1. By doing so, even if the characteristics of the photoconductor are changed, the surface potential of the photoconductor drum 15 is set to the initial normal value. That is, the disturbance detection signal is used as a fine adjustment signal for compensating for the characteristic change.

FIG. 1 is a diagram showing a semiconductor laser driving device of the present invention. Reference numerals correspond to those of FIG. 2, 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, and 37 is an optical output setting unit. , 38 is AD
Converter, 39 is controller, 40 is DA converter, 4
Reference numerals 1 and 42 are input terminals, 43 is an AD converter, 44 is a gate circuit, and 45 is a DA converter.

In the semiconductor laser 3, the sum of the current I ₁ of the current source 33 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 a combined value in which the image signal D ₂ from the input terminal 41 is the upper bit and the signal D ₃ from the gate circuit 44 is the lower bit. It is D ₂ + D ₃ . The image signal D ₂ is from the image signal processing circuit 1 of FIG.

The gate circuit 44 is controlled by the controller 39 and has two states. For example, when the control signal is "0", an intermediate value (assuming that the gate circuit 44 is a 4-bit circuit, "1000") is output, and when the control signal is "1", The state is such that the signal from the AD converter 43 is allowed to pass as it is. The input of the AD converter 43 is the disturbance detection signal (the signal from the differential amplification section 19 in FIG. 2). The DA converter 45 is
The gain is adjusted by the gain adjustment signal from the controller 39. The gain adjustment is performed in order to respond to the temperature change of the laser characteristics. The adjustment method will be described in detail later.

The AD converter 38 digitizes the optical output monitor voltage V _m and the optical output set values V ₁ and V ₂ , which are analog values, and sends them to the controller 39. Monitor voltage V
_m is a voltage generated across the resistor 31. Resistance 31
Are connected in series to the monitor photodiode 30 which supplies a current according to the received laser light, so that a voltage corresponding to the laser light is generated at both ends thereof. Light output set value V
₁ , V ₂ 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 the laser characteristic curve 50 (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 .

The minimum useable light output P ₁ is determined as the light output corresponding to the minimum value of the multi-gradation image signal, and the use maximum light output P ₂ is determined as the light output corresponding to the maximum value of the image signal. The optical output detection voltage at the minimum use optical output P ₁ is V ₁ , and the optical output detection voltage at the maximum use optical output P ₂ is V ₂
Is. Therefore, when the image signal changes, the light output changes in the range of the minimum use optical output P ₁ and the maximum use optical output P ₂ ,
The light output detection voltage changes between V ₁ and V ₂ .

Laser drive current (I ₁ + I ₂ ) of FIG.
Must be controlled so that when the image signal D ₂ has the minimum value (0), the minimum light output P ₁ is used, which is as follows. First, the image signal D _{2 is set} to 0, a control signal is sent from the controller 39 to the gate circuit 44, and the signal D ₃ is set to an intermediate value (“1000” in the case of 4 bits). Therefore, the current source 34 becomes a minute current according to D ₃ . The reason why D ₃ is set to an intermediate value is that the disturbance detection signal may be positive or negative, so that there is room for vertical fluctuation. In this state, the input from the controller 39 to the DA converter 40 is increased to make the monitor voltage V _m 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. The laser drive current at this time is I _V1 in FIG.

After setting as described above, the image signal D ₂ is set to the maximum value (“1111 1111” in the case of 8 bits), and D
The gain of the A converter 45 is adjusted. Signal D ₃ remains held at an intermediate value. DA converter 45 when gain is increased
Output becomes large and the current I ₂ of the current source 34 also increases.
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 DA converter 45
Is input, and the vertical axis is the current I ₂ of the current source 34. The gain is changed, and when the monitor voltage V _m becomes equal to V ₂ , the gain is fixed. Thereby, the gain is set. The laser drive current at this time is I in FIG.
It is _V2 . Since the laser characteristic changes depending on the temperature, the setting of the current I _{1 and} the setting of the gain are performed at regular intervals or every time a predetermined operation is completed.

When the above-mentioned setting is completed and an actual image signal is input, a control signal is sent from the controller 39 to the gate circuit 44 so that an intermediate value is not output, but an AD converter 43 outputs. The digitized disturbance detection signal D ₃ is passed. In this state, D
The input of the A converter 45 is such that the disturbance detection signal D ₃ is the lower bit and the image signal D ₂ is the upper bit. If D ₃ is 4 bits and D ₂ is 8 bits, the total is 1.
It becomes a 2-bit input, and the current source 34 is controlled by this value. Since the disturbance detection signal D ₃ occupies the lower bit, it acts to finely adjust the current of the current source 34. By this fine adjustment, the error A in FIG. 6 is compensated, and the desired image quality can be obtained even if the characteristics of the photoconductor are changed due to light fatigue or the like.

FIG. 7 is a diagram showing a second example of a laser printer using the semiconductor laser driving device of the present invention.
This example is an example of compensating the potential when the photoconductor drum 15 is uniformly charged by the charger 10 when the potential has changed from the desired potential. Surface electrometer 1
2 is different from the example of FIG. 2 only in that the surface 8 is arranged so as to detect the surface before the irradiation of the laser beam 5, and detailed description thereof will be omitted.

FIG. 8 is a diagram showing a third example of a laser printer using the semiconductor laser driving device of the present invention.
The reference numeral corresponds to that of FIG. 2, 20 is a polygonal surface number detector, and 21 is a reflectance correction value generator. This example is an example of compensating for the difference in reflectance between the mirror surfaces of the polygon mirror 6. The reflectance of the mirror surface is not uniform, and it is usually slightly different depending on the degree of contamination. Therefore, in this example, the difference in reflectance is investigated in advance, and when actually used, the output of the laser light is changed according to the difference in reflectance, and when the image signals of the same value have the same intensity of reflected light. So that

FIG. 9 is a view of the polygon mirror 6 used in the example of FIG. 8 as seen from above, in which 6-1 is a reference plane mark and M1 to M6 are mirror planes. The polygon surface number detector 20 detects the position of the mirror surface M1 by reading the reference surface mark 6-1 and detects the position of another mirror surface from the rotation angle and the like. The reflectance correction value for each mirror surface is written in advance in the reflectance correction value generation unit 21, and the reflectance correction value corresponding to each mirror surface is obtained according to the detection number of the polygon surface number detector 20. Is output.
This is sent to the semiconductor laser driving device 2 as a disturbance detection signal.

FIG. 10 is a diagram showing a fourth example of a laser printer using the semiconductor laser driving device of the present invention. Reference numerals correspond to those in FIG. 2, and 22 is a densitometer.
In this example, as the disturbance detection signal, an error of the density of the toner image from the desired state is used, or an error of the density of the image after being transferred to the sheet 13 from the desired state is used.

[00028]

As described above, according to the semiconductor laser driving apparatus of the present invention, when the laser light is modulated by the multi-gradation image signal, the disturbance detection signal finely adjusts the intensity of the laser light to obtain the image quality. Since the change in the characteristics of the part that affects the image quality is compensated, it is possible to maintain a good image quality.

[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 laser printer using a conventional semiconductor laser driving device.

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 charging characteristics of a photosensitive drum.

FIG. 7 is a diagram showing a second example of a laser printer using the semiconductor laser driving device of the present invention.

FIG. 8 is a diagram showing a third example of a laser printer using the semiconductor laser driving device of the present invention.

9 is a polygon mirror used in the example of FIG.

FIG. 10 is a diagram showing a fourth example of a laser printer using the semiconductor laser driving device of the present invention.

[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 electrometer, 19 ... Differential amplification section, 20 ... Polygon surface number detector , 21 ... Reflectance correction value generator, 22
... densitometer, 30 ... monitor photodiode, 31 ... resistor, 32 ... switching circuit, 33, 34 ... current source, 3
5 ... Clock generator, 36 ... Input terminal, 37 ... Optical output setting section, 38 ... AD converter, 39 ... Controller, 40 ...
DA converter, 41, 42 ... Input terminal, 43 ... AD converter, 44 ... Gate circuit, 45 ... DA converter

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhiko Nishizawa 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. The intensity of laser light within a predetermined range of a laser emission region is set by setting a minimum value and a maximum value of a laser drive current and controlling the laser drive current in accordance with a multi-gradation image signal during that period. In a semiconductor laser driving device that modulates, the disturbance detection signal and the image signal, which are signals that have detected an error from an intended state of an element that affects image quality, A semiconductor laser driving device comprising: a synthesizing unit for synthesizing so as to be on a lower bit side, and a unit for controlling a laser driving current by a signal synthesized by the synthesizing unit. 2. A DA converter whose gain is adjusted when setting a laser drive current is used as the synthesizing means.
The image signal is directly input to the upper bit side of the input to the converter, and the lower bit side is the middle of the range of values that the disturbance detection signal can take when setting the minimum and maximum values of the laser drive current. 2. The semiconductor laser drive device according to claim 1, wherein an output from a gate circuit that outputs a value and otherwise passes a disturbance detection signal is input. 3. The semiconductor laser driving device according to claim 1, wherein an error signal from a desired value of the surface potential of the photosensitive drum is used as the disturbance detection signal.