JP3139926B2 - Image forming apparatus and semiconductor laser controller - 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, and more particularly, to an image forming apparatus such as a laser printer, a digital copying machine, and a facsimile.

[0002]

2. Description of the Related Art In image forming apparatuses such as laser printers and digital copiers, semiconductor lasers are most often used as recording light sources. In general, a semiconductor laser has a problem that a threshold current changes due to a change in temperature, which causes a change in laser beam intensity. For this reason, it is said that laser light intensity must be stabilized so that the laser light intensity does not fluctuate even when a temperature change occurs.

[0003] Further, as a multi-level modulation method of a semiconductor laser for the purpose of improving the image quality of halftones or line drawings (also referred to as smoothing), there are a pulse width modulation method and a pulse intensity modulation method, and furthermore, a pulse width modulation method. A system using pulse intensity modulation has been proposed.

A technique for stabilizing laser light intensity and a technique for modulating laser intensity are disclosed in Japanese Patent Application Laid-Open No. 4-366657 "Laser Driving Apparatus". In the laser light intensity stabilization method of the laser drive circuit, the light intensity of the semiconductor laser is detected outside the recording area, and the light intensity stabilization operation of the semiconductor laser is executed based on the detected detection signal. That is, the laser drive current is corrected based on the detection signal, the corrected laser drive current is held, and the semiconductor laser emits light based on the held laser drive current to record an image.

In order to reproduce halftones, the laser intensity modulation method of this laser drive circuit has a laser light intensity stabilization circuit and a laser drive circuit corresponding to the number of intensity modulations, respectively. A circuit configuration for selectively driving the laser drive circuit based on a signal is employed.

[0006]

In such a conventional laser light intensity stabilizing method, the laser drive current is fixed during recording, and therefore, the droop characteristic (thermal characteristic) of the laser is fixed.
As a result, the laser beam output during recording changes while being noticed, which causes a problem that the density of the recorded image fluctuates. Particularly, in the case of a halftone image, there is a problem that a minute change in the laser beam output during recording greatly affects a change in image density.

In reproducing halftones, the pulse width modulation method has a problem that the time resolution increases with an increase in recording speed, and circuit means for generating a modulation signal becomes complicated. Furthermore, if the pulse intensity modulation method is adopted to reduce the time resolution, the laser light intensity stabilizing circuit and the laser drive circuit are provided in correspondence with the intensity modulation numbers. However, there is a problem that the circuit scale becomes complicated.

The present invention has been made in view of the above circumstances, and stabilizes the light intensity of a semiconductor laser during recording with high accuracy, thereby stabilizing the image density and obtaining a high-quality image. It is an object to provide an image forming apparatus.

Further, the present invention provides a method for recording without increasing the circuit scale or complicating the pulse width modulation, the pulse intensity modulation, and the method using both the pulse width modulation and the pulse intensity modulation. It is an object of the present invention to provide an image forming apparatus which stabilizes the light intensity of a semiconductor laser with high accuracy, thereby stabilizing the image density, and obtaining a high quality image.

[0010]

According to the present invention, an image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting the light intensity of the semiconductor laser and generating a detection current, An optical system that scans the image carrier with the laser beam to form an image on the image carrier, converts an input image signal into a voltage that is an analog amount, and controls the voltage using a current mirror circuit. Control current signal generating means for converting the current into a current signal, and the semiconductor so that a detection signal from the light intensity detecting means and a control current signal generated by the control current signal generating means always have a constant ratio. An image forming apparatus comprising: a driving current control unit that controls a driving current of a laser.

Further, according to the present invention, an image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting a light intensity of the semiconductor laser and generating a detection current, and An optical system that scans the image carrier to form an image on the image carrier, converts an input image signal into a voltage that is an analog amount, and uses a current mirror circuit to convert the voltage into a control current signal. Control current signal generating means for converting to a current; control current signal switching means for switching the control current signal; and a detection signal from the light intensity detection means and the switched control current signal always having a constant ratio. And a drive current control means for controlling the drive current of the semiconductor laser.

Further, according to the present invention, an image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting a light intensity of the semiconductor laser and generating a detection current, and An optical system that scans the image carrier to form an image on the image carrier, and a constant current circuit corresponding to an input image signal from a plurality of constant current circuits is selected, and an output of the constant current circuit is selected. After the voltage is converted, the current is input to a current mirror circuit, the current mirror circuit converts the voltage into a current that is a control current signal, a control current signal generation unit, a detection signal from the light intensity detection unit, and the control current signal. And a drive current control means for controlling a drive current of the semiconductor laser so that the control current signal generated by the generation means always has a constant ratio. It is subjected.

Still further, according to the present invention, an image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting the light intensity of the semiconductor laser and generating a detection current, and the laser beam An optical system for scanning the image carrier to form an image on the image carrier, and a constant current circuit corresponding to an input image signal from a plurality of constant current circuits, and an output of the constant current circuit. After voltage conversion, the current is input to a current mirror circuit, control current signal generating means for converting the voltage into a current that is a control current signal by the current mirror circuit, control current signal switching means for switching the control current signal, Driving for controlling the driving current of the semiconductor laser so that the detection signal from the light intensity detecting means and the switched control current signal always have a constant ratio. Image forming apparatus is provided which is characterized by comprising a flow control means. Still further, according to the invention, a semiconductor laser that generates a laser beam in accordance with an input signal, a light intensity detection unit that detects a light intensity of the semiconductor laser and generates a detection current, and Control current signal generating means for converting a signal into a voltage which is an analog quantity, and converting the voltage into a current which is a control current using a current mirror circuit; a detection signal from the light intensity detecting means; A drive current control means for controlling a drive current of the semiconductor laser so that a control current signal generated by the means always has a constant ratio.

[0014]

According to the image forming apparatus of the present invention, an input image signal is converted into a voltage which is an analog quantity, and the voltage is converted into a current which is a control current signal by using a current mirror circuit. By controlling the drive current of the semiconductor laser so that the current signal and the detection signal from the light output detection means for detecting the light intensity of the output of the semiconductor laser are always constant, the junction capacitance of the light intensity detection means is affected. Without
High-precision pulse intensity modulation becomes possible, whereby image density is stabilized and a high-quality halftone image is obtained.

Further, according to the image forming apparatus of the present invention, the input image signal is converted into a voltage which is an analog quantity, and the voltage is converted into a current which is a control current signal by using a current mirror circuit. The control current signal is switched by the control current signal switching means in synchronization with the input pulse width modulation signal. The switching control current signal is fed back with a detection signal from a light intensity detection unit that detects the light intensity of the semiconductor laser and generates a detection current, so that the ratio of the control current signal to the detection signal is always constant. By controlling the drive current of the semiconductor laser so as to be constant, it is possible to use a high-precision pulse width modulation and pulse intensity modulation combined method without being affected by the junction capacitance of the light intensity detection means. The density can be stabilized, and a high-quality halftone image and line drawing can be obtained.

Further, according to the image forming apparatus of the present invention, 2
A control current signal for generating a control current signal for modulating the light intensity of a semiconductor laser composed of a plurality of constant current circuits and a current mirror circuit when only a low gradation such as a gradation or a gradation is required. The generating means selects a constant current circuit according to the image signal, converts the output of the constant current circuit into a voltage, inputs the voltage to a current mirror circuit, and converts the voltage into a current as a control current signal by the current mirror circuit. I do. Then, the control current signal is fed back with a detection signal from a light intensity detection unit that detects the light intensity of the semiconductor laser and generates a detection current, so that the ratio between the control current signal and the detection signal is always constant. By controlling the driving current of the semiconductor laser so that the pulse width modulation can be performed with high accuracy without being affected by the junction capacitance of the light intensity detecting means, the image density can be stabilized, and high image quality can be achieved. A halftone image and line drawing can be obtained.

Furthermore, according to the image forming apparatus of the present invention, when only low gradations such as two gradations and four gradations are required, a semiconductor laser comprising a plurality of constant current circuits and a current mirror circuit In the control current signal generating means for generating a control current signal for modulating the light intensity of the light, a constant current circuit corresponding to the image signal is selected, the output of the constant current circuit is converted into a voltage, and then input to the current mirror circuit. The current mirror circuit converts the voltage into a current that is a control current signal. The control current signal is switched by the control current signal switching means in synchronization with the input pulse width modulation signal. The switching control current signal is fed back with a detection signal from a light intensity detection unit that detects the light intensity of the semiconductor laser and generates a detection current, so that the ratio of the control current signal to the detection signal is always constant. By controlling the drive current of the semiconductor laser to be constant, without being affected by the junction capacitance of the light intensity detection means,
It is possible to use a combination of high-precision pulse width modulation and pulse intensity modulation, thereby stabilizing the image density and obtaining high-quality halftone images and line drawings.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 2 schematically shows a sectional view of a full-color recording apparatus as an image forming apparatus according to the present invention. In FIG. 2, reference numeral 901 denotes a photosensitive drum as an image carrier on which an electrostatic latent image is formed, and is rotated in a counterclockwise direction. A charger 902 for charging the photosensitive drum 901 and a photosensitive drum 9 are provided around the photosensitive drum 901.
Developing units 90 for developing the first and second developing devices 01 with different developers, respectively.
9, a second developing device 910, a third developing device 911, a fourth developing device 912, a transfer drum 915 supporting a transfer material onto which an image developed by the photosensitive drum 901 is transferred, and a photosensitive drum 901 Pre-cleaning static eliminator 913 that removes the charged electric charge before cleaning, the photosensitive drum 90
1 is disposed.

A polygon mirror 907 for deflecting and scanning a laser beam from the semiconductor laser 3 as shown in FIG. 3 and a polygon motor for rotating the polygon mirror 907 (see FIG. 3) are provided between the charger 902 and the first developing unit 909. (Not shown), an Fθ lens 955 for forming an image of the deflected laser beam on the photosensitive drum 901 and mirrors 905 and 90 for reflecting the laser beam toward the photosensitive drum 901
4 is provided.

Developing units 909, 910, 911, 912
Is a photosensitive drum 9 made of four different toners.
For example, the first developing device 909 has magenta, and the second developing device 910 has
Cyan, third developer 911 contains yellow toner, and fourth developer 912 contains black toner as developer, and supplies them to the photosensitive drum 901.

The photosensitive drum 901 whose surface is uniformly charged by the charger 902 is scanned and exposed by a laser beam modulated by an image signal by an exposure unit 903 to form an electrostatic latent image. This electrostatic latent image is developed by developing units 909, 910, 911, 91 corresponding to the image signals.
2 is developed by the transfer drum 91
5 is sequentially transferred to a transfer material electrostatically attracted to the transfer member 5 by a transfer charger 917. The untransferred toner on the photosensitive drum 901 is removed by the pre-cleaning charge remover 913 and then removed by the photosensitive member cleaning 914.

On the other hand, paper as a transfer material is stored in a cassette 9
The sheet is sent out from the feed roller 23 by a feed roller 924, and is temporarily aligned by a registration roller 925. Then, the transfer material is sent by a registration roller 925 toward a suction roller 926 and a suction charger 916 provided at a position corresponding to a suction position of the transfer drum 915, and is electrostatically transferred onto the transfer drum 915 by the suction charger 916. Is adsorbed. After that, the color toner on the photosensitive drum 901 is transferred by the transfer charger 917 provided at the position facing the photosensitive drum 901 as described above. In the case of multicolor printing, the above-described development process and transfer process are repeated up to four times. Then, the transfer material is separated from the transfer drum 915 by the separation unit 927, and the conveyance belts 928, 929, the fixing unit 930
Is discharged to the tray 931 via the.

FIG. 3 is a block diagram of a semiconductor laser control circuit incorporated in the image forming apparatus according to one embodiment of the present invention. In FIG. 3, the semiconductor laser 3 is current-driven by the drive current control means 2, and a laser beam output from the semiconductor laser 3 is collimated by a collimator lens 953 and irradiated on a polygon mirror 907.
The polygon mirror 907 transmits the laser beam to the fθ lens 9
The scanning is performed on a photosensitive drum 901 as an image carrier via 55, driven by a polygon motor (not shown), and rotated at a high speed in the direction of the arrow.

The light intensity detecting means 4 receives the laser beam output from the semiconductor laser 3 and detects the light intensity of the laser beam, and outputs a current Im proportional to the detected light intensity of the laser beam. The output current Im of the light intensity detection means 4 is input to a drive current control means 2 for controlling the drive current of the semiconductor laser 3, and the other input of the drive current control means 2 receives an image signal D to control the control current. The output of the control current signal generating means 1a (1b) for generating the signal Ic is input. In the drive current control means 2, automatic light intensity control (Auto Power Control) is executed, and the light output of the semiconductor laser 3 is stabilized.

In the semiconductor laser control circuit shown in FIG. 3, an image signal is input to control current signal generating means 1a (1b), which will be described later in detail with reference to FIG. 1, and is converted into a current corresponding to the image signal. This current is output as a control current signal Ic, and this control current signal Ic is input to the drive current control means 2. Further, the drive current of the semiconductor laser 3 is controlled by the drive current control means 2, the light output of the semiconductor laser 3 is received by the light intensity detection means 4, and the detection signal Im is input to the drive current generation means 2. In the drive current control means 2, the drive current of the semiconductor laser 3 is controlled so that the control current signal Ic and the detection signal Im always have a constant ratio. Since the intensity of the optical output of the semiconductor laser 3 is proportional to the detection signal Im, the detection signal Im can be operated by controlling the drive current. That is, when the light intensity of the laser beam output from the semiconductor laser 3 fluctuates, the amount of the fluctuation is detected by the light intensity detection means 4 and is input to the drive current control means 2 as its output current Im. At this time, according to the difference current between the control current signal Ic and the output current Im of the light intensity detection means 4,
An error e occurs in the output of the drive current control means 2. The drive current of the drive current control means 2 is controlled so that the error e becomes zero. That is, the drive current of the drive current control means 2 is controlled so that the light intensity fluctuation of the semiconductor laser 3 is compensated.

The control current signal generating means for controlling the semiconductor laser will be described in detail with reference to FIG. In the circuit diagram shown in FIG. 1, reference numeral 101 denotes a digital / digital converter for converting a digital signal into a voltage value or a current value which is an analog signal.
An analog converter (hereinafter referred to as D / A) outputs a voltage in FIG. The current mirror circuit 102
Two transistors TR11 and TR12 having the same characteristics and two resistance elements R1 having the same characteristics and the same resistance value.
The control current signal generating means 1a includes the D / A 101 and the current mirror circuit 102. The current mirror circuit 102 includes a resistor R1
3. It is connected to the drive current control means 2 via the diode D1. LD3 is equivalent to the semiconductor laser 3, and PD4 is a photodiode corresponding to the light intensity detecting means 4.

In the circuit shown in FIG.
/ A101, and converted into a voltage corresponding to the image signal by the D / A101. The converted voltage is applied to the collector terminal and the base terminal of the transistor TR11 and the base terminal of the transistor TR12. At the emitter terminal of the transistor R11, there appears a voltage Ve obtained by subtracting the voltage drop between the base and the emitter of the transistor R11 from the voltage output from the D / A 101. Since the transistors TR11 and TR12 have the same characteristics as described above, the voltage V is also applied to the emitter terminal of the transistor TR12.
e appears. Therefore, the same amount of current flows through the resistance elements R11 and R12. Since the current flowing into the base terminal of the transistor is very small, the amount of current flowing into the collector terminal and the amount of current flowing out from the emitter terminal are considered to be equal, and the current flowing through the resistance element R12 becomes the above-described control current signal Ic. The direction in which the control current signal Ic flows is the direction in which the current flows from the drive current control means 2 to the collector terminal of the transistor TR12 of the current mirror circuit 102 via the diode D1 and the resistor R13. As described above, the image signal, which is a digital signal, can be converted into the control current signal Ic of the drive current control means 2, and the pulse intensity modulation of the semiconductor laser 3 can be easily realized.

FIG. 4 is a conceptual diagram of the drive current control means 2,
FIG. 5 shows an example of a block diagram of the drive current control means 2. In the circuit shown in FIG. 4, the control current signal Ic generated from the input image signal is input to the drive current control means 2 as a modulation signal, and is input to the control amplifier 201 via the resistance element Ri. . Control amplifier 20
1 comprises an operational amplifier 202 and a correction amplifier 203. The output of the control amplification unit 201 is
Is connected to the semiconductor laser (LD) 3 via the. This configuration can be equivalently regarded as a simple inverting amplifier. The detection signal Im, which is a feedback signal, includes a correction amplifier 203 that corrects a delay in a control loop and a deterioration in phase margin caused by a narrow band characteristic of the light intensity detection unit 4, a resistance element Rc, and a capacitance element Cc. Compensation circuit 205 configured
Is compensated for.

Next, a specific correction operation will be described with reference to FIGS. The input modulation signal is converted into a voltage signal by an IV conversion circuit 206 that converts a current into a voltage, and is input to an inverting input of an operational amplifier 202 inside the control amplification unit 201 via a resistance element Ri. Also,
The non-inverting input of the operational amplifier 202 has a reference voltage ref2
Is input via the resistance element Ri. When the modulation signal is not input, the potentials of the inverting input and the non-inverting input of the operational amplifier 202 are equal, and the amount of current flowing into the drive unit 204 is set to zero. Therefore, no drive current flows through the semiconductor laser (LD) 3. Therefore, the detection signal Im is not output from the light intensity detection means (PD) 4.

When the modulation signal is input, the operational amplifier 2
02, the potential of the inverting amplifying unit becomes lower than the non-inverting input unit of 02, the control amplifying unit 201 adjusts the current value so as to increase the potential of the inverting amplifying unit, and supplies the current to the gain adjusting unit GC1 Becomes The gain adjustment current signal LGA1 input from the outside is obtained by converting an electric current to a voltage into an I-V
The voltage is converted into a voltage value by the conversion circuit 207, and the gain of the current supplied to the gain adjustment unit GC1 is adjusted by the voltage. The adjusted current is input to the drive unit 204 and output as a drive current for the semiconductor laser (LD) 3.

The driving current of the semiconductor laser (LD) 3 is roughly set by the resistor R20. In the circuit shown in FIG. 5, the output from the light intensity detecting means 4a incorporated in the element of the semiconductor laser 3 is input to a pre-monitor detecting circuit 212 used for monitoring during adjustment, and the light intensity detecting means 4b connected to the outside is used. Is input to the inverting input part of the operational amplifier 201, but the output from the light intensity detecting means 4a built in the element of the semiconductor laser 3 is output to the operational amplifier 20.
Needless to say, the input can be made to the inverting input unit 1. However, in that case, the pre-monitor detection circuit 212 and the light intensity detection means 4a are not connected. The light intensity detecting means 4a built in the semiconductor laser element detects the back beam of the semiconductor laser, and the light intensity detecting means 4b provided outside the semiconductor laser element detects the front beam of the semiconductor laser. .

By the detection signal Im output from the light intensity detecting means 4b, the potential of the inverting input section of the operational amplifying section 202 is changed in a higher direction, and is controlled so as to have the same potential as the non-inverting input section. When the potential of the inverting input section is about to exceed the potential of the non-inverting input section, the current flowing to the gain adjusting section GC1 is reduced so that the detection signal Im becomes smaller, and the potential of the inverting amplifier section is reduced. The current limiting unit 208 is a circuit that sets the maximum drive current of the semiconductor laser (LD) 3 in combination with the resistance element R21.
D) It functions as a protection circuit for preventing 3 from being destroyed. The abnormality detection unit 209 detects whether the closed loop feedback is normally applied or not, and whether the drive current by the current limiting unit 208 is limited or not.
It has the function of notifying as ST2. Power monitoring unit 2
Reference numeral 10 denotes a portion for detecting whether the power supply voltage is normally applied. The power save unit 211 is provided for the semiconductor laser 3
In the case where it is not necessary to limit the power consumption of the driving current control unit 2, a function other than the reference voltage generation unit (not shown) and the abnormality detection 208 is cut off in order to minimize the power consumption.

Next, another embodiment of the present invention of the control current signal generating means for controlling the semiconductor laser incorporated in the image forming apparatus will be described with reference to FIGS. FIG. 6 shows another electric circuit diagram of the control current signal generating means incorporated in the image forming apparatus of the present invention. In the circuit shown in FIG. 6, the D / A 101 has the same characteristics as the two transistors TR11 and TR12 having the same characteristics and has the same resistance value.
Current mirror 1 including two resistance elements R11 and R12
02, and a resistance element R13 connected to the drive current control means 2 described above.
To control ON / OFF of the diode D1 and the control current signal Ic generated by the control current signal generating means 1a, the buffer IC1, the transistor TR13, and the resistance element R
The control current signal switching means 5 comprises the control current signal switching means 5. LD3 is the semiconductor laser 3, PD4
Indicates the light intensity detecting means 4.

An image signal (IM) for modulating the intensity of the laser beam is input to the D / A 101, and is converted into a voltage corresponding to the image signal by the D / A 101. The converted voltage is applied to the collector and base terminals of the transistor TR11 and the base terminal of the transistor TR12. D / A1 is connected to the emitter terminal of the transistor R11.
A voltage Ve is obtained by subtracting the voltage drop between the base and the emitter of the transistor R11 from the voltage output from 01. Further, as described above, the transistors TR11, TR1
2 has the same characteristics, the voltage Ve also appears at the emitter terminal of the transistor TR12. Therefore, the resistance elements R11,
12, the same amount of current flows. Since the current flowing into the base terminal of the transistor is very small, the amount of current flowing into the collector terminal and the amount of current flowing out from the emitter terminal are considered to be equal, and the current flowing through the resistance element R12 becomes the above-described control current signal Ic. Control current signal Ic
Flows from the drive current control means 2 to the diode D
1 and the current flows into the collector terminal of the transistor TR12 of the current mirror circuit 102 via the resistance element 13. Here, the image signal for turning on / off the control current signal Ic input to the buffer IC1 can be used for performing pulse width modulation, and is shown as an image signal (W). When the image signal (W) shown in FIG. 7B is at the "L" level (0 V), the output of the buffer IC1 is also at the "L" level, and the potential of the base terminal of the transistor TR13 is at the "L" level. TR13 is OF
In the F state, the emitter potential of the transistor TR13 becomes lower than the potential of the modulation signal input terminal of the drive current control means 2, and the control current signal Ic shown in FIG. FIG. 7 (b)
When the image signal (W) is "H" (+ 5V), the output of the buffer IC1 becomes "H" level, the transistor TR13 is turned on, and the emitter potential at this time is determined by the output voltage of the buffer IC1. Transistor TR1
3 is a value obtained by subtracting the voltage drop between the base and the emitter, but since it is set to be higher than the potential of the modulation signal input terminal of the drive current control means 2, the diode D
1 causes the control current Ic to be reduced by the transistor TR.
2 does not flow to the collector terminal. Therefore, the buffer IC1
The output waveform of FIG. 7 is changed to the waveform shown in FIG.
A modulation signal as shown in (c) is supplied to the semiconductor laser 3. In such a circuit, if necessary, a buffer IC
By using an inverter for 1, the polarity of the image signal (W) and the polarity of the transistor TR13 can be inverted.

FIGS. 7A, 7B, and 7C show an example of the combined use of the pulse intensity modulation and the pulse width modulation using the above operation. In the waveform diagram shown in FIG. ,
For convenience of explanation, the control current signal Ic for intensity modulation shown in FIG. 7A is set to eight gradations, and the image signal (W) for pulse width modulation shown in FIG. It is set, but by increasing the number of gradations and the number of steps as necessary, more multi-valued gradations can be realized.

As described above, a circuit that can be simply configured as shown in FIG. 6 can realize a combined system of pulse intensity modulation and pulse width modulation as shown in FIG. Also, by always fixing the image signal (W) to the “L” level, pulse intensity modulation can be performed only by the control current signal Ic. In addition, the control current signal Ic is fixed to a constant level, and only the image signal (W) is used. It goes without saying that pulse width modulation is possible.

FIG. 8 is an electric circuit diagram showing still another example of the control current signal generating means incorporated in the image forming apparatus of the present invention. Reference numeral 103 denotes a constant current circuit unit including a plurality of constant current circuits, and the number of constant current circuits corresponding to the number of pulse intensity modulations is provided. (In FIG. 8, the constant current circuits are denoted by reference numerals i1, i2,..., Ix.) The current mirror circuit 102 has the same characteristic 2
With the same characteristics as the two transistors TR11 and TR12, and
The control current signal generating means 1b is composed of two constant resistance circuit groups 103 and a current mirror circuit 102, which are composed of two resistance elements R11 and R12 having the same resistance value.
The current mirror circuit 102 is connected to the above-described drive current control means 2 via a resistance element R13 and a diode D1. LD3 indicates the semiconductor laser 3, and PD4 indicates the light intensity detecting means 4.

In the circuit shown in FIG. 8, one of the constant current circuits i1, i2,... Ix in the constant current circuit group 103 is selected according to the input image signal. Here, the operation of the selected constant current circuit will be described as a constant current circuit i1. The resistance element R1 is controlled by the constant current circuit i1.
5 is determined, which results in the transistor T
The base potentials of R11 and R12 and the potential of the collector terminal of transistor TR11 are determined.

The emitter current of the transistor TR11 is determined by the connected resistance element R11. As described above, the transistors TR11 and TR12 are
Since the resistance elements R11 and R12 have the same characteristic and the same resistance value, the transistor TR
The emitter current of the transistor 12 becomes equal to the emitter current of the transistor TR11. Since the current flowing into the base terminal of the transistor is very small, the amount of current flowing into the collector terminal and the amount of current flowing out from the emitter terminal are considered to be equal, and the current flowing through the resistance element R12 becomes the above-described control current signal Ic. The direction in which the control current signal Ic flows is the direction in which the current flows from the drive current control means 2 to the collector terminal of the transistor TR12 of the current mirror circuit 102 via the diode D1 and the resistor R13. As described above, the image signal, which is a digital signal, can be converted into the control current signal Ic of the drive current control means 2, and the pulse intensity modulation of the semiconductor laser 3 can be easily realized.

When the number of pulse intensity modulations is small, the cost of the constant current circuit group 103 in the configuration shown in FIG. 8 can be lower than the cost of the D / A 101 in the configuration shown in FIG. When the number of pulse intensity modulations is small, it may be better to adopt the configuration shown in FIG.

FIG. 9 is an electric circuit diagram showing still another example of the control current signal generating means incorporated in the image forming apparatus of the present invention. FIG. 9 shows a constant current circuit group 103,
Two transistors TR11 and TR12 having the same characteristic and two resistance elements TR1 having the same characteristic and the same resistance value.
1 and 12 and a resistance element R1 connected to the drive current control means 2 described above.
3. To control ON / OFF of the control current signal Ic generated by the diode D1 and the control current signal generation unit 1b, the control current signal switching unit 5 includes a buffer IC1, a transistor TR13, and a resistance element R14. Have been. LD3 is the semiconductor laser 3,
PD4 indicates the light intensity detecting means 4.

One of the constant current circuits in the constant current circuit group 103 is selected according to the input image signal. Here, the circuit operation will be described with the selected constant current circuit as a constant current circuit i1. The resistance element R15 is set by the constant current circuit i1.
Is determined, and as a result, the transistor TR
The base potentials of the transistors 11 and 12 and the potential of the collector terminal of the transistor TR11 are determined. Therefore, the transistor TR1
The emitter current of 1 is determined by the connected resistance element R11.

As described above, the transistor TR1
1, 12 have the same characteristics, and furthermore, the resistance elements R11, 1
2 have the same characteristics and the same resistance, the emitter current of the transistor TR12 is
11 is equal to the emitter current. Since the current flowing into the base terminal of the transistor is very small, the amount of current flowing into the collector terminal and the amount of current flowing out from the emitter terminal are considered to be equal, and the current flowing through the resistance element R12 becomes the above-described control current signal Ic. The direction in which the control current signal Ic flows is the direction in which the current flows from the drive current control means 2 to the collector terminal of the transistor TR12 of the current mirror circuit 102 via the diode D1 and the resistor R13. Here, the control current signal I input to the buffer IC 1
The image signal for turning ON / OFF c can be used for performing pulse width modulation, and is therefore referred to as an image signal (W). When the image signal (W) is at the “L” level (0 V), the output of the buffer IC 1 is also at the “L” level, the potential of the base terminal of the transistor TR13 is at the “L” level, and the transistor TR13 is turned off. , The emitter potential of the transistor TR13 becomes lower than the potential of the modulation signal input terminal of the drive current control means 2, and the control current signal Ic flows into the current mirror circuit 102. When the image signal (W) is at "H" (+5 V), the output of the buffer IC1 is at "H" level, the transistor TR13 is in the ON state, and the emitter potential at this time is determined based on the output voltage of the buffer IC1. TR1
3 is a value obtained by subtracting the voltage drop between the base and the emitter, but since it is set to be higher than the potential of the modulation signal input terminal of the drive current control means 2, the diode D
Due to the rectification of 1, the control current signal Ic does not flow. Further, if necessary, the polarity of the image signal (W) and the polarity of the transistor TR13 can be inverted by using an inverter for the buffer IC1.

As described above, a combination of pulse intensity modulation and pulse width modulation can be realized with a circuit having a simple configuration as shown in FIG. Also, by always fixing the image signal (W) to the “L” level, pulse intensity modulation can be performed only by the control current signal Ic. In addition, the control current signal Ic is fixed to a constant level, and only the image signal (W) is used. It goes without saying that pulse width modulation is possible.

When the number of pulse intensity modulations is small, the cost of the constant current circuit group 103 in the configuration shown in FIG. 9 can be made lower than the cost of the D / A 101 in the configuration shown in FIG. When the number of pulse intensity modulations is small, it may be better to adopt the configuration shown in FIG.

FIG. 10 shows an example of a circuit in which a control current signal generator is constituted by a plurality of switching circuits, and FIG.
An example of a modulated signal that can be generated by the circuit configuration shown in FIG. 10 is shown.

The switching circuit SWC1 includes a transistor TR31 and a diode D31, and resistance elements R311 and R311.
312. This switching circuit is provided in parallel with the switching circuits SWC2, 3,. Here, only the switching circuit SWC1 is described in detail, and the switching circuit S
Although detailed circuits after WC2 are omitted, the configuration is the same as that of the switching circuit SWC1.

When the clock CLK31 shown in FIG. 11A is "H" (+ 5V), the transistor TR31 is turned on.
At this time, the emitter potential of the transistor TR31 changes from + 5V to the base potential of the transistor TR31.
This is a value obtained by subtracting the voltage drop between the emitters. Since this value is set to be higher than the potential of the modulation signal input terminal of the drive current control means 2, the diode D31
Rectifies, the current i31 does not flow. When the clock CLK31 is at the "L" level (0 V), the transistor TR13 is turned off, the emitter potential of the transistor TR13 becomes lower than the potential of the modulation signal input terminal of the drive current control means 2, and the current i3
1 flows into the switching circuit SWC1. At this time, a value obtained by dividing the voltage of the cathode terminal of the diode D31 by the resistance value obtained by adding and combining the resistance values of the resistance elements R311 and R312 is the amount of current flowing into the switching circuit SWC1.

Similarly, the clock CLK32 is applied to the switching circuit SWC2 and the clock C is applied to the switching circuit SWx.
When LK3x is input at the timings shown in FIGS. 11B and 11C, the modulation signal flowing out of the drive current control means 2 is the sum of the currents flowing into the respective switching circuits (= i
31 + i32 + i3x), a step-like current waveform is obtained as in the modulation signal shown in FIG.

FIGS. 12 and 13 show the relationship between the exposure energy and the surface potential on the photosensitive drum 901 when the light output of the semiconductor laser 3 is exposed on the photosensitive drum 901. As shown in FIG. 13, the latent image waveform formed on the photosensitive drum 901 becomes dull with respect to the exposure energy shown in FIG. When exposure is performed with a waveform in which a pulse is applied to an edge portion as shown in FIG. 13, an edge enhancement effect is obtained as shown in FIG. 13, and a latent image waveform with sharper edges is obtained as compared with FIG. Therefore, the fact that the stepped modulated signal waveform shown in FIG. 11 can be obtained with the simple configuration shown in FIG. 10 is effective for improving reproducibility.

[0051]

As described above, according to the present invention,
An input image signal can be converted into a control current signal for pulse intensity modulation by a simple circuit composed of a D / A and a current mirror circuit, and this control current signal is used as a modulation signal for controlling the drive current control means. A drive current for the semiconductor laser is generated to drive the semiconductor laser. Also, a detection signal corresponding to the output light of the semiconductor laser obtained by the light intensity detection means is negatively fed back to the drive current control means so that the ratio between the detection signal and the control current signal always becomes a constant value. ,
The stable pulse intensity modulation of the semiconductor laser becomes possible.
As a result, the image density can be stabilized, and a multi-tone image capable of reproducing high-quality halftones can be obtained. Also, the present invention
By using pulse intensity modulation, the temporal resolution of the control signal can be set lower than in pulse width modulation, which is suitable for improving the recording speed.

Further, according to the present invention, the input image signal can be converted into a control current signal for pulse intensity modulation by a simple circuit composed of a D / A and a current mirror circuit. By controlling with a pulse width modulation signal corresponding to an image signal using a switching circuit, it is possible to generate a modulation signal for controlling a drive current control means for pulse intensity modulation synchronized with the timing of the pulse width modulation signal, and A drive current for the laser is generated to drive the semiconductor laser. Further, by negatively feeding back the detection signal corresponding to the output light of the semiconductor laser obtained by the light intensity detection means to the drive current control means so that the ratio between the detection signal and the control current signal always becomes a constant value, A stable modulation scheme using both pulse intensity modulation and pulse width modulation of a semiconductor laser is made possible. This makes it possible to stabilize the image density, reproduce the microscopic halftone which is an advantage of the pulse intensity modulation, and obtain a high-quality multi-tone image having the stability of the pulse width modulation. Further, in the same circuit configuration, by fixing the pulse width modulation signal to an effective level, pulse intensity modulation by a pulse intensity modulation signal becomes possible, and by fixing the pulse intensity modulation signal at a constant level, the pulse width is fixed. Pulse width modulation by the modulation signal becomes possible.

Further, according to the present invention, the input image signal is converted into a control current signal for pulse intensity modulation by a simple circuit including a constant current circuit and a current mirror circuit of a number corresponding to the required number of gradations. The control current signal can be converted and used as a modulation signal for controlling the drive current control means to generate a drive current for the semiconductor laser and drive the semiconductor laser. Further, by negatively feeding back the detection signal corresponding to the output light of the semiconductor laser obtained by the light intensity detection means to the drive current control means so that the ratio between the detection signal and the control current signal always becomes a constant value, The stable pulse intensity modulation of the semiconductor laser becomes possible. Thereby, especially when only low gradations are required, a multi-gradation image capable of stabilizing the image density with a low-cost circuit and reproducing high-quality halftones can be obtained.

Further, according to the present invention, the input image signal is converted into a control current signal for pulse intensity modulation by a simple circuit composed of a constant current circuit and a current mirror circuit of a number corresponding to the required number of gradations. By controlling the control current signal with a pulse width modulation signal corresponding to an image signal using a switching circuit, the drive current control means for pulse intensity modulation synchronized with the timing of the pulse width modulation signal can be converted. A modulation signal for controlling can be generated, a drive current for the semiconductor laser is generated, and the semiconductor laser is driven. Further, by negatively feeding back the detection signal corresponding to the output light of the semiconductor laser obtained by the light intensity detection means to the drive current control means so that the ratio between the detection signal and the control current signal always becomes a constant value, A stable modulation scheme using both pulse intensity modulation and pulse width modulation of a semiconductor laser is made possible. This makes it possible to stabilize the image density with an inexpensive circuit, especially when only low gradations are required, to reproduce the microscopic halftone which is an advantage of pulse intensity modulation, and to stabilize pulse width modulation. A multi-tone image with high quality and high quality can be obtained. Further, in the same circuit configuration, by fixing the pulse width modulation signal to an effective level, pulse intensity modulation by a pulse intensity modulation signal becomes possible, and by fixing the pulse intensity modulation signal at a constant level, the pulse width is fixed. Pulse width modulation by the modulation signal becomes possible.

[Brief description of the drawings]

FIG. 1 is an electric circuit of a control current signal generating means for controlling a semiconductor laser incorporated in an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view schematically showing an image forming apparatus in which the control current signal generation circuit of FIG. 1 is incorporated.

FIG. 3 is a schematic block diagram illustrating a basic configuration of an image forming apparatus in which the control current signal generation circuit of FIG. 1 is incorporated.

FIG. 4 is a block diagram for explaining a basic concept of a drive current control unit shown in FIG.

FIG. 5 is a block diagram of a drive current control unit shown in FIG.

FIG. 6 is an electric circuit of a control current signal generating means for controlling a semiconductor laser incorporated in an image forming apparatus according to another embodiment of the present invention.

FIG. 7 is an explanatory diagram of a control signal generated by the circuit shown in FIG.

FIG. 8 is an electric circuit of a control current signal generating means for controlling a semiconductor laser incorporated in an image forming apparatus according to still another embodiment of the present invention.

FIG. 9 is an electric circuit of a control current signal generating means for controlling a semiconductor laser incorporated in an image forming apparatus according to still another embodiment of the present invention.

FIG. 10 is an electric circuit diagram of a control current signal generation unit for controlling the semiconductor laser incorporated in the image forming apparatus using the drive current control unit shown in FIG.

FIG. 11 is an explanatory diagram for explaining an operation of the circuit in FIG. 10;

FIG. 12 is an explanatory diagram for explaining a relationship between a position on a photosensitive drum and exposure energy thereof.

FIG. 13 is an explanatory diagram for explaining a relationship between a position on a photosensitive drum and a surface potential thereof.

[Explanation of symbols]

 1a, 1b: control current signal generation means 101: D / A 102: current mirror circuit 103: constant current circuit group 2: drive current control means 3: semiconductor lasers 4, 4a, 4b: light intensity detection means 5: control current signal Switching means 201: control amplifier 202: operational amplifier 203: compensation amplifier 204: drive unit 205: correction circuit 206, 207: current-voltage converter (IV converter) 208: current limiter 209: abnormality detector 210 ... Power monitoring 211 Power saving section 212 Pre-monitor detection section 901 Photoconductor drum 902 Charger 903 Exposure section 904, 905 Mirror 907 Polygon mirror 909-912 Developing device 913 Cleaner before cleaning 914 Photosensitive Body cleaner 915: transfer drum 916: adsorption charger 917: transfer charger 92 ... cassette 924 ... feeding roller 925 ... registration rollers 926 ... suction roller 927 ... separating portion 928 and 929 ... conveyor belt 930 ... fixing portion 931 ... tray 953 ... collimator lens 955 ... f [theta] lens.

────────────────────────────────────────────────── ─── Continued on the front page Examiner Masaaki Sudo (56) References JP-A-2-175266 (JP, A) JP-A-5-129702 (JP, A) (58) Fields investigated (Int. Cl. ⁷⁾ , DB name) B41J 2/44 H04N 1/113 H01S 3/102

Claims (9)

(57) [Claims] An image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting a light intensity of the semiconductor laser and generating a detection current, and scanning the image carrier with the laser beam An optical system for forming an image on the image carrier, and converting the input image signal into a voltage which is an analog quantity,
A control current signal generating unit that converts the voltage into a current that is a control current signal using a current mirror circuit; and a detection signal from the light intensity detection unit and a control current signal generated by the control current signal generation unit. An image forming apparatus comprising: a driving current control unit that controls a driving current of the semiconductor laser so as to always maintain a constant ratio. 2. An image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting a light intensity of the semiconductor laser and generating a detection current, and scanning the image carrier with the laser beam. An optical system for forming an image on the image carrier, and converting the input image signal into a voltage which is an analog quantity,
A control current signal generating unit that converts the voltage into a current that is a control current signal using a current mirror circuit; a control current signal switching unit that switches the control current signal; a detection signal from the light intensity detection unit; An image forming apparatus comprising: a drive current control unit that controls a drive current of the semiconductor laser so that the switched control current signal always has a constant ratio. 3. An image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting a light intensity of the semiconductor laser and generating a detection current, and scanning the image carrier with the laser beam. An optical system that forms an image on the image carrier by selecting a constant current circuit corresponding to an input image signal from among a plurality of constant current circuits, and converts the output of the constant current circuit into a voltage. A control current signal generating means for inputting the voltage to a mirror circuit and converting the voltage into a current which is a control current signal by the current mirror circuit; a detection signal from the light intensity detecting means and the control current signal generating means An image forming apparatus comprising: a driving current control unit that controls a driving current of the semiconductor laser so that a control current signal always has a constant ratio. 4. An image carrier, a semiconductor laser for generating a laser beam, light intensity detecting means for detecting a light intensity of the semiconductor laser to generate a detection current, and scanning the image carrier with the laser beam. An optical system that forms an image on the image carrier by selecting a constant current circuit corresponding to an input image signal from among a plurality of constant current circuits, and converts the output of the constant current circuit into a voltage. A control current signal generating unit that inputs the current to the mirror circuit and converts the voltage into a current that is a control current signal by the current mirror circuit; a control current signal switching unit that switches the control current signal; and the light intensity detection unit. And a drive current control means for controlling the drive current of the semiconductor laser so that the detection signal and the switched control current signal always have a constant ratio. Image forming apparatus, characterized in that the. 5. The image forming apparatus according to claim 1, wherein said light intensity detecting means detects a back beam generated from behind said semiconductor laser. 6. The image forming apparatus according to claim 1, wherein said light intensity detecting means detects a front beam generated from a front surface of said semiconductor laser. 7. A pulse width modulation signal generated by modulating an image signal to an external signal input to said control current signal switching means is used.
The image forming apparatus according to any one of the above. 8. An image according to claim 2, wherein a binarized modulation signal generated by modulating an image signal to an external signal input to said control current signal switching means is used. Forming equipment. 9. A semiconductor laser for generating a laser beam in accordance with an input signal, light intensity detecting means for detecting a light intensity of the semiconductor laser and generating a detection current, and converting the input signal into an analog signal. A control current signal generating unit that converts the voltage into a certain voltage and converts the voltage into a current that is a control current using a current mirror circuit; a detection signal from the light intensity detecting unit; and a control current signal generating unit. And a drive current control means for controlling a drive current of the semiconductor laser so that a control current signal always has a constant ratio.