JP2001341349A - Semiconductor laser control device of electro photographic apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a semiconductor laser control device of a electro photographic apparatus capable of improving a falling responsiveness of the semiconductor laser. SOLUTION: A value of a bias current always flowing in the semiconductor laser is forced to be lowered in a range not greater than one dot time for forming a minimum dot in synchronism with an OFF timing of print data for controlling the emission of the semiconductor laser.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor laser control device of an electrophotographic apparatus for controlling a bias current value which always flows through a semiconductor laser in synchronization with print data for controlling light emission of the semiconductor laser.

[0002]

2. Description of the Related Art Conventionally, as a method of controlling a semiconductor laser in an electrophotographic recording apparatus, a constant bias current is constantly supplied to the semiconductor laser to improve the high-speed response of the semiconductor laser and to control the temperature by the light emission of the semiconductor laser itself. It was trying to suppress the rise. This bias current is usually set to a current value that does not cause a potential drop of the photoconductor due to light emission of the semiconductor laser.

However, if the bias current is set near the threshold current of the semiconductor laser, the characteristics of the semiconductor laser fluctuate due to changes in the ambient temperature and deterioration of the semiconductor laser, and the semiconductor laser emits light. As a result, there is a possibility that the potential of the photoreceptor drops in the blank print area and the image is developed. For this reason, it is necessary to control a bias current and a modulation current in response to a change in characteristics due to a change in ambient temperature or deterioration of a semiconductor laser element.

As one example of this semiconductor laser control method,
Japanese Patent Application Laid-Open No. 8-139869 discloses that the current supplied to a semiconductor laser is increased stepwise, and the current value of the semiconductor laser up to the second stage after the light intensity exceeds a reference value and the light intensity thereof are increased. A method is disclosed in which a threshold current and a light emission efficiency are calculated from a proportional relationship between a current and a light emission amount using a value, and a bias current and a modulation current are controlled based on the calculation result.

[0005]

The above-mentioned control method is an effective means for the rising response of the semiconductor laser. However, the semiconductor laser is turned off by setting the bias current near the threshold current of the semiconductor laser. In this case, the fall response of the semiconductor laser is deteriorated.
This is because when the drive current flowing through the semiconductor laser attempts to return to the preset bias current value, the drive current becomes lower than the threshold current of the semiconductor laser due to the influence of the internal impedance of the semiconductor laser. This is because it takes time. That is, the semiconductor laser is turned off.
When the bias current value is set as low as possible, the fall response of the semiconductor laser can be improved.

An object of the present invention is to provide a semiconductor laser control device for an electrophotographic apparatus in which the fall response of a semiconductor laser is improved. Another object of the present invention is to reduce the power consumption in order to set the bias current low depending on the conditions, and to prevent the life of the semiconductor laser from deteriorating.

[0007]

The object of the present invention is to provide a photoconductor,
A charger for charging the photoreceptor, an exposure optical unit for scanning and exposing the charged photoreceptor with a laser beam, a laser control device for controlling the amount of light emitted from the semiconductor laser, and a developing device for developing the scan-exposed image area In a semiconductor laser control device of an electrophotographic apparatus having a copying machine and a transfer device for transferring a developed image to a recording material, a bias current value which always flows through the semiconductor laser is used to control a light emission of the semiconductor laser. 1 that forms the smallest dot in synchronization with
This is achieved by forcibly lowering the bias current value within the range of the dot time or less.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor laser control device according to one embodiment of the present invention will be described below. First, the configuration and operation principle of a recording apparatus according to an embodiment of the present invention will be described with reference to FIG. As shown in FIG.
1, a charger 202, an exposure optical unit 203 equipped with a semiconductor laser controller, a developing machine 204, and a transfer unit 20.
5, a cleaner 206 and an eraser 207 are arranged. The photoconductor 201 is uniformly charged by the charger 202, and the exposure optical unit 203 scans and exposes the photoconductor 201 based on the print data 211 sent from the host 210. Next, the toner charged by the developing device 204 is developed into an image area, and then the toner is
Transfer onto 9 The toner remaining on the photoconductor 201 is removed by the cleaner 206, and the charge is uniformly removed by the eraser 207.
Return to initial charging. On the other hand, the toner transferred on the sheet 209 is fixed on the sheet 209 by the fixing device 208. The above is the description of the configuration and operation principle of the recording apparatus according to one embodiment of the present invention.

Next, an exposure optical section 2 according to an embodiment of the present invention.
The configuration and operating principle of the device 03 will be described with reference to FIG. As shown in FIG. 3, the exposure optical unit 203 includes a semiconductor laser control device 301, a semiconductor laser 302, and a rotating polygon mirror 30.
3. It is composed of a beam detector 304.

The semiconductor laser controller 301 controls the semiconductor laser 302 based on the print data 211 to generate an appropriate driving current I.
Flow D. The semiconductor laser 302 emits light based on the drive current ID, and the laser beam is deflected by the rotary polygon mirror 303 to scan and expose the photoconductor 201. At this time, the laser beam immediately before writing is guided to the beam detector 304 in order to align the writing position, and a detection signal BDT for aligning the writing position is obtained. The semiconductor laser 30
A current IP proportional to the amount of emitted light flows from the photodetector for measuring the amount of emitted light contained in the semiconductor laser controller 301 to the semiconductor laser controller 301. The above is the description of the configuration and operation principle of the exposure optical unit 203 according to one embodiment of the present invention.

Next, the configuration and operation principle of the semiconductor laser control device 301 according to one embodiment of the present invention will be described with reference to FIG. As shown in FIG. 1, the semiconductor laser control device 3
01 is a sample and hold circuit 101, a switching current circuit 102 for modulation current, and a constant current circuit 10 for bias current.
3, delay element 104, inversion element 105, AND element 10
6, a transistor 107, and a resistor 108.

The semiconductor laser 302 generally has a drive current I
Even if D is constant, the amount of emitted light fluctuates due to ambient temperature and deterioration of the element. Therefore, the light emission amount of the semiconductor laser 302 is measured by the photodetector PD built in the semiconductor laser 302, and the current IP proportional to the light emission amount at that time is sampled by the sample hold circuit 101. The sample hold circuit 101 compares the light emission target value P with the actual light emission amount, and controls the modulation current ISW output from the modulation current switching current circuit 102 to increase if the light emission light amount is smaller than the target value. Is performed, and if the light emission amount is larger than the target value, control is performed so as to reduce the modulation current ISW.
By performing such control, the semiconductor laser 302
Can be emitted with a stable light emission amount in accordance with the print data 211. Further, a constant current circuit 1 for bias current
Numeral 03 denotes a constant current generating circuit for constantly flowing a bias current IB to the semiconductor laser 302.

Next, the bias current forcible OFF function according to one embodiment of the present invention will be described. Bias current forced O
The FF function includes a delay element 104, an inversion element 105, an AND element 106, a transistor 107, and a resistor 108. This function forcibly reduces the bias current IB constantly flowing to the semiconductor laser 302 in synchronization with the fall of the print data 211, and an operation timing chart is shown in FIG. The print data 211 sent from the host 210 is input to the delay element 104 and the inversion element 105, and the print data 2
11 is delayed within the range of one dot time or less for forming the minimum dot, and inverted by the inverting element 105.
A forced OFF signal is created by the ND element and input to the transistor 107. Transistor 107 is forced off
In accordance with the signal, the bias current IB constantly flowing through the semiconductor laser 302 is drawn into the transistor side and is forcibly reduced. At this time, the current value IOFF drawn by the transistor 107 can be set by the resistance value of the resistor 108.

Next, the effect when the bias current is forcibly turned off will be described with reference to FIGS. As a general semiconductor laser control method, a constant bias current IB is constantly supplied to the semiconductor laser in order to improve the high-speed response of the semiconductor laser and to suppress a rise in temperature due to light emission of the semiconductor laser itself. This bias current IB is usually
Since the current value is set so as not to cause a potential drop of the photoconductor due to the light emission of the semiconductor laser, the current value is set to be equal to or less than the threshold current Ith of the semiconductor laser and in the vicinity thereof. But,
The bias current IB is changed to the threshold current Ith of the semiconductor laser.
By setting it near, the time for the drive current to reach the threshold current Ith of the semiconductor laser is shortened, and the rising response of the semiconductor laser is improved, but the semiconductor laser when the semiconductor laser is turned off as shown in FIG. The fall responsiveness of is deteriorated. This is because when the drive current flowing through the semiconductor laser attempts to return to the preset bias current value, the drive current becomes lower than the threshold current of the semiconductor laser due to the influence of the internal impedance of the semiconductor laser. This is because it takes time. That is, when the bias current value is set as low as possible when the semiconductor laser is turned off, the fall response of the semiconductor laser can be improved. Therefore, the fall response of the semiconductor laser can be improved by forcibly reducing the bias current IB flowing to the semiconductor laser in synchronization with the OFF timing of the print data. The above is the description of the embodiment of the present invention.

In this embodiment, a delay element, an inversion element, an AND element, a transistor, and a resistor are used to reduce the bias current, but the present invention is not limited to this. For example, there is no problem even if the bias current is reduced by directly controlling the constant current circuit for flowing the bias current.
In this case, it is sufficiently possible to use a constant current circuit that can control the current within one dot time for forming the minimum dot.

In this embodiment, the bias current is normally set to a fixed value, and the bias current is forcibly reduced in synchronization with the OFF timing of the print data. However, the present invention is not limited to this. The present invention, if the bias current value when the semiconductor laser is turned off can be set lower than the bias current value when the semiconductor laser emits light,
The bias current need not be fixed.

[0017]

According to the present invention, the fall response of the semiconductor laser can be improved by controlling the bias current in synchronization with the print data for controlling the light emission of the semiconductor laser. Further, since the bias current is reduced depending on the conditions, power consumption can be reduced, and the life of the semiconductor laser can be prevented from being shortened.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a semiconductor laser control device according to one embodiment of the present invention.

FIG. 2 is a configuration diagram of a recording apparatus according to an embodiment of the present invention.

FIG. 3 is a configuration diagram of an exposure optical unit including the semiconductor laser control device of FIG. 1;

FIG. 4 is an operation timing chart according to an embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a relationship between a driving current of a semiconductor laser and an amount of emitted light.

FIG. 6 is an explanatory diagram showing an effect according to one embodiment of the present invention.

[Explanation of symbols]

101: sample and hold circuit, 102: switching current circuit for modulation current, 103: constant current circuit for bias current, 104: delay element, 105: inversion element, 106: A
ND element, 107: transistor, 108: resistor, 2
01: photoreceptor, 202: charger, 203: exposure optical unit,
204: developing machine, 205: transfer unit, 206: cleaner, 207: eraser, 208: fixing unit, 209: paper, 210: host, 211: print data, 301: semiconductor laser control device, 302: semiconductor laser, 303 ...
Rotating polygon mirror, 304 ... laser beam detector.

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2C362 AA03 AA61 AA75 2H076 AB05 AB12 DA17 DA19 DA42 5C074 AA15 AA17 BB03 BB26 CC26 DD08 EE06 GG02 GG12 5F073 AB21 BA09 FA02 GA03 GA12 GA24 GA25 GA38

Claims (1)

[Claims] A photoconductor, a charger for charging the photoconductor,
An exposure optical unit that scans and exposes the charged photoreceptor with laser light, a laser controller that controls the amount of light emitted by the semiconductor laser, a developing machine that develops the scan-exposed image area, and a recording of the developed image. In a semiconductor laser control device of an electrophotographic apparatus having a transfer device for transferring an image onto an object, a minimum dot is formed by synchronizing a bias current value always flowing through the semiconductor laser with an OFF timing of print data for controlling light emission of the semiconductor laser. A semiconductor laser control device for an electrophotographic apparatus, wherein the bias current value is forcibly made lower than the bias current value in a range of a dot time or less.