JP2003110189A - Semiconductor laser controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a structure capable of preventing the formation of an electrostatic latent image due to offset light emission in an non-image area and substrate contamination due to the attachment of toner, in an image forming apparatus. SOLUTION: A means 34 is provided which sets an offset level control signal for determining an offset current at the time of offset light emission of a semiconductor laser PD to a desired value according to the characteristics, types, individual differences or the like of a semiconductor laser.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser printer,
The present invention relates to a semiconductor laser control device for driving and controlling a semiconductor laser used as a light source in an image forming apparatus to which an electrophotographic process is applied, such as a digital copying machine, and an image forming apparatus to which the semiconductor laser control device is applied.

[0002]

2. Description of the Related Art FIG. 1 shows a schematic structure of an example of a general image forming apparatus utilizing an electrophotographic process.

In FIG. 1, when the polygon mirror 16 rotates, the laser beam output from the semiconductor laser unit 15 is deflected and scanned by the polygon mirror 16.
The surface of the photoconductor 19 is exposed through the fθ lens 17 to form an electrostatic latent image thereon. This semiconductor laser unit 15
Controls the light emission time of the semiconductor laser through the laser drive circuit 12 according to the image data generated by the image processing unit 11 and the image modulation signal whose phase is set by the phase synchronization circuit 14, thereby causing the photoconductor to emit light as described above. 19 controls the electrostatic latent image formed on the surface. The phase synchronization circuit 14 applies the modulation signal generated by the clock generation circuit 13 to the polygon mirror 1 as described above.
The phase is set in synchronism with the detection signal generated by the photodetector 18 which detects the laser light from the semiconductor laser which is deflected and scanned by 6.

Since the semiconductor laser used here is extremely small and can directly modulate the laser light generated by the drive current at high speed, it has been widely used as a light source for laser printers in recent years. However, since the relationship between the drive current of the semiconductor laser and the light output changes significantly depending on the ambient temperature, this point needs to be solved when the light intensity of the semiconductor laser is set to a desired value. In order to solve this problem and make full use of the advantages of the above-mentioned laser diode, various APC (Automatic Power Control)
l) A circuit is proposed. As an example of this APC circuit,
There is one disclosed in JP-A-11-298079.

Generally, there are the following three methods applied to the APC circuit.

The light output of the semiconductor laser is monitored by the light receiving element, and the signal is proportional to the monitor current proportional to the light output signal generated in the light receiving element and the light emission level signal is always made to be equal by the optical / electrical negative feedback loop. A method in which the forward current of the semiconductor laser is controlled, and thus the optical output of the semiconductor laser is controlled to a desired value.

The light output of the semiconductor laser is monitored by the light receiving element, and the light output level signal and the signal proportional to the monitor current proportional to the light output are equalized within the power setting time by the optical / electrical negative feedback loop. The forward current of the semiconductor laser is controlled by the sample hold circuit to hold the semiconductor laser forward term current set within the power setting time outside the power setting time, and the optical output is set to a desired value. A method in which a semiconductor laser is turned on and offset light is emitted by a modulation signal by modulating it based on a modulation signal.

The optical output of the semiconductor laser is desired by measuring the temperature of the semiconductor laser and controlling the forward current of the semiconductor laser by the measured temperature signal or by controlling the temperature of the semiconductor laser to be constant. Method to control the value of.

Of the above methods, the method for obtaining a desired value as the optical output of the semiconductor laser is desirable.
It may be difficult to realize the method depending on the limit of the response speed of the light receiving element and the operation speed of the element forming the optical / electrical negative feedback loop.

Further, in the method (1), the problems as in the method described above do not occur, and the high speed modulation of the semiconductor laser becomes possible. However, in this method, since the optical output of the semiconductor laser is not always controlled, there is a problem that the optical output easily changes due to disturbance or the like. Further, the droop characteristic of the semiconductor laser may be considered as the disturbance, which may cause an error of several% in the optical output. As a method that improves these points, there is a method disclosed in Japanese Patent Application Laid-Open No. 2-205086.

[0011]

In this method, when controlling the offset level of the semiconductor laser, one method for monitoring the offset light emission state of the laser is to connect the emitter terminal of the laser driving transistor to a resistor and connect the transistor to the transistor. The flowing current is converted into current-voltage, and the voltage signal is fed back to the laser control circuit. However, the threshold current of the laser may vary depending on conditions such as the type and individual difference. As a result, when driven by a certain offset current, the offset level may vary depending on the above conditions.

Further, in the case of performing modulation by ON light emission at a certain level and offset light emission of a steady value, the larger the difference between the offset current value and the threshold current at the time of offset light emission, the more the modulation characteristics tend to deteriorate. However, there is a possibility that the modulation characteristics may differ due to the fluctuation of the threshold current. Therefore, in order to perform highly accurate control of variations due to individual differences during light output modulation that performs modulation by switching between the offset light emission state and the ON light emission state, the offset level can be set to a desired value. Is desirable.

Further, since the forward current-light output characteristics of the semiconductor laser fluctuate particularly in the LD region due to temperature fluctuation, the ON emission level is changed according to the temperature fluctuation in order to perform modulation with a constant light amount. Although control is widely performed, it is general to control the offset level with a certain steady value as the forward current.

In an image forming apparatus that switches between two types of states, offset light emission and on light emission level, which differ from each other in accordance with an on light emission level modulation signal of a semiconductor laser, a non-image area is formed during offset light emission and an image area is formed during on light emission. This makes it possible to form an image based on the modulated signal. However, in the image forming apparatus having the above-described configuration, when the light emission amount exceeds a certain light amount at the offset level, a minute charge is accumulated on the photoconductor due to the light output, and a slight amount of toner adheres to the image forming device to cause background stain. There was a problem that it could be the cause.

To solve this problem, it is usually desirable to make the offset level lower than the sensitivity of the photoconductor, and therefore the offset current that determines the offset level is set to a value sufficiently smaller than the threshold current of the laser. Is desirable. On the other hand, as the operation of the semiconductor laser, when the modulation is performed between the ON emission level and the offset level, when the offset level becomes a value as large as the threshold current, the modulation characteristics including the light rising characteristic are good. Tends to be.

Further, in a semiconductor laser used as a light source in an image forming apparatus such as a laser printer or a digital copying machine in recent years, it is desired to reduce the beam spot diameter by the laser beam as the image density becomes higher. As a means, there is an increasing need for short wavelength semiconductor lasers.

As the wavelength of the semiconductor laser becomes shorter, the threshold current tends to increase. For example, when the current is set to control the offset level in the same manner as the conventional one, the threshold level is turned on. There was a tendency that the amount of current change until reaching the light emission level became large.

Since the threshold current tends to increase as the wavelength of the laser becomes shorter, the amount of current change becomes large when the offset current is set in the same manner as the conventional one, resulting in high speed. The problem is that the modulation characteristic is degraded.

Therefore, the present invention provides a semiconductor laser control device which provides a method of stably and accurately outputting light output control even when a semiconductor laser having a short wavelength or a semiconductor laser having a large individual difference is used. The purpose is to provide.

[0020]

In order to solve the problems of the threshold current and the optical output characteristics, which are caused by variations due to individual differences of semiconductor lasers and shortening of wavelength in the semiconductor laser control device described above, the present invention provides an offset method. By providing means for setting the level control signal to a desired value, and controlling the offset level to a desired value in accordance with the threshold current and offset emission characteristics of the semiconductor laser to be controlled,
This makes it possible to stabilize the light output and perform highly accurate control.

As means for that purpose, for example, a current source,
The configuration is such that a plurality of offset level control signals can be arbitrarily switched using a voltage source or the like, and such a configuration is intended to stabilize or highly accurately control the light output.

Further, the above problem is solved by adopting a structure in which a plurality of signal levels can be selected as the offset level control signal.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Next, embodiments of the present invention will be described.

In the embodiment of the present invention, similarly to the structure shown in FIG. 1, the semiconductor laser 15 as the light source is modulated and driven based on the image modulation signal, and the laser light from the semiconductor laser 15 is rotationally driven. A desired electrostatic latent image is formed on the surface of the photoconductor 19 by exposing the photoconductor 19 at a predetermined timing based on a synchronization signal detected by the synchronization detection sensor 18 while deflecting and scanning the photoconductor 19 by scanning means such as a polygon mirror 16. And a semiconductor laser control device applied therefor.

First, as a comparison, the configuration of a conventional semiconductor laser control device is shown in FIG.

In the configuration shown in the figure, a monitor signal (monitor current) proportional to the optical output of the semiconductor laser LD and a light receiving element PD for monitoring a part of the optical output of the semiconductor laser when the semiconductor laser is turned on, The on-emission level control means 31 for controlling the forward current of the semiconductor laser by the on-emission level control signal and the semiconductor laser LD are connected to the collector of the drive transistor Q1 for driving the semiconductor laser LD, and the forward current of the semiconductor laser is connected to the base. A signal is supplied, a resistor RLD is connected between the emitter and ground, and the semiconductor laser L is set so that the emitter potential during offset emission of the semiconductor laser LD becomes equal to the offset level signal Vb0.
A first optical / electrical negative feedback loop 36 composed of a first error amplification section 32 for controlling the forward current of D, and a current for switching the forward current of ON emission and offset emission of the semiconductor laser LD by a modulation signal. When the modulation signal is '0', the forward current for offset light emission is L
It is a configuration in which control is performed so as to flow to D.

Here, the offset level signal Vb0 has a certain constant value, and control is performed so that Vb0 and the emitter potential at the time of offset light emission become equal, so that the offset current is always maintained at a constant value determined by Vb0.

Next, FIG. 3 shows the configuration of a semiconductor laser control device according to the first embodiment of the present invention.

In this embodiment, the semiconductor laser LD, the ON emission level setting means 31 for setting the ON emission current during ON emission of the semiconductor laser, and the first control for controlling the offset current during offset emission of the semiconductor laser LD. The first control means is a semiconductor laser L.
The semiconductor laser LD is connected to the collector of the drive transistor Q1 for driving D, the forward current signal of the semiconductor laser is supplied to the base, the resistor RLD is connected between the emitter and ground, and the emitter of the semiconductor laser LD at the time of offset light emission. It is composed of a first optical / electrical negative feedback loop composed of a first error amplification section 32 which controls the forward current of the semiconductor laser LD so that the potential becomes equal to the offset level control signal Vb, and 36.

In this embodiment, a current drive unit 33 (changeover switch) for switching the forward current of ON emission of the semiconductor laser LD and offset emission by a modulation signal is provided, and means for setting the offset level control signal Vb to a desired value. Three
By having 4 (a signal generation circuit for generating a predetermined voltage signal Vb), it becomes possible to set a desired offset emission current of the semiconductor laser LD by arbitrarily setting the offset level control signal Vb, and the characteristics of the semiconductor laser LD It is possible to set the offset level to a desired value according to the type, individual difference, and the like.

Next, the configuration of the second embodiment of the present invention is shown in FIG.
Shown in.

In this embodiment, the semiconductor laser LD, the ON emission level setting means 31 for setting the ON emission current during ON emission of the semiconductor laser, and the first control for controlling the offset current during offset emission of the semiconductor laser LD. Means 3
6, a first timing generation circuit 35 for generating a signal indicating the control timing of the first control means by the logical product of the modulation signal for driving the semiconductor laser LD to light up and the delay signal obtained by delaying the modulation signal. ing.

In this way, the delay circuit 37 and the AND circuit 38
By using and, the hold control timing for the first hold means (hold capacitor C1) for holding the offset level value of the optical output obtained from the error amplification unit output 32 is controlled by the bottom control for a fixed period during which the modulation signal is continuous. Only when they are in the same state, the switch 39 is closed to charge the capacitor C1 to control the first holding means, and the offset level control of the optical output is performed to obtain the offset level control signal. The value is set to. In this way, the desired offset current can be set based on the control signal.

According to this structure, the offset current can be set without being affected by the response speed of the detection circuit of the offset current of the semiconductor laser LD, and means for setting the offset level control signal to a desired value is provided. As a result, it is possible to set a desired offset current based on the offset level control signal, and it is possible to set the offset level to a desired value according to the characteristics, types and individual differences of the semiconductor laser. Next, the configuration of the third embodiment of the present invention is shown in FIG.

In the configuration shown in the figure, the first control means for controlling the offset current of the semiconductor laser LD during the offset light emission and the second control means for controlling the on light emission current of the semiconductor laser LD during the on light emission. Further, the monitor signal proportional to the optical output at the time of ON emission of the semiconductor laser obtained from the semiconductor laser LD and the light receiving element PD for monitoring a part of the optical output of the semiconductor laser is equal to the ON emission level control signal. As described above, an optical / electrical negative feedback loop including the error amplification unit 42 for controlling the forward current of the semiconductor laser is provided.

In the embodiment shown in FIG. 5, the light receiving element PD for monitoring the optical output of the semiconductor laser LD is converted into a voltage by the monitor resistor RPD, and the terminal voltage thereof is converted into the first error amplifier 42.
Is input to the first error amplifier 42, and the terminal voltage is compared with the ON emission level control signal. Here, when the light emission command signal to the transistor Q1 connected to the semiconductor laser LD is'H ', the switch SW1 is closed by the signal obtained by inverting the modulation signal by the inverter 43, and the changeover switch 33 is switched upward, The hold capacitor C1 of No. 1 is charged with the control voltage, and the voltage across the terminals of the semiconductor laser LD is controlled by the output thereof to control the optical output of the semiconductor laser LD to a desired value. When the light emission command signal is'L ',
The switch SW1 is opened and the changeover switch 33 is opened.
Changes downward, and the first hold capacitor C1
Holds its control value. Also, the light emission command signal is
In the case of L ', the same switch SW2 is used depending on the modulation signal.
Is closed, and the voltage across the resistor RLD for detecting the current flowing through the semiconductor laser LD is input to the second error amplifier 32. As a result, the second hold capacitor C2 is adjusted so that the current becomes a predetermined offset current. Is controlled via.

Thus, the terminal voltage of the first hold capacitor C1 is set when the light emission command signal is "H", and the second hold capacitor C is set when the light emission command signal is "L".
The voltage of 2 is applied between the terminals of the semiconductor laser LD. As a result, when the emission command signal is'H ', the semiconductor laser L
When the emission level of D is controlled to a predetermined ON emission level and the emission command signal is'L ', the semiconductor laser LD
The bias current is controlled so that Here, the first error amplifier 42 and the first hold capacitor C
1 configures a first control hold circuit, and the second error amplifier 32 and the second hold capacitor C2 configure a second control hold circuit.

With such a configuration, both the ON emission level and the offset level of the semiconductor laser LD can be controlled at the timing of the modulation signal.

The configuration of the fourth embodiment of the present invention is shown in FIG.

In the configuration shown in the figure, the first control means for controlling the offset current when the semiconductor laser LD emits the offset light and the second control means for controlling the ON emission current when the semiconductor laser LD emits the ON light. And laser diode LD
A first timing generation means 35 for generating a signal indicating the control timing of the first control means by a logical product of a modulation signal for turning on and a delay signal obtained by delaying the modulation signal, and a modulation signal for turning on the semiconductor laser LD. And the second control means 4 by the logical sum of the delayed signal obtained by delaying the modulated signal
The second timing generation unit 44 generates a signal indicating the control timing of 1.

In the embodiment shown in FIG. 6, the light receiving element PD for monitoring the light output of the semiconductor laser LD is converted into a voltage by the monitor resistor RPD, and the terminal voltage thereof is converted into the first error amplifier 42.
Is input to the first error amplifier 42, and the terminal voltage is compared with the ON emission level control signal. Here, when the light emission command signal to the transistor Q1 connected to the semiconductor laser LD is'H ', the above (refer to the description of the third embodiment).
As described above, the first hold capacitor C1 is charged with the control voltage, and the output voltage of the semiconductor laser LD is controlled to control the optical output of the semiconductor laser LD to a desired value. Also, when the light emission command signal is'L ', the first hold capacitor C1 operates to hold the control value as described above. Further, when the light emission command signal is'L ', the terminal voltage of the resistor RLD for detecting the current flowing through the semiconductor laser LD is input to the second error amplifier 32 as described above. Is controlled via the second hold capacitor C2 so that the voltage becomes a predetermined offset current.

Thus, the terminal voltage of the first hold capacitor C1 is set when the light emission command signal is "H", and the second hold capacitor C is set when the light emission command signal is "L".
The voltage of 2 is applied between the terminals of the semiconductor laser LD. As a result, when the emission command signal is'H ', the semiconductor laser L
When the emission level of D is controlled to a predetermined ON emission level and the emission command signal is'L ', the semiconductor laser LD
The bias current is controlled so that Here, the first error amplifier 42 and the first hold capacitor C
1 configures a first control hold circuit, and the second error amplifier 32 and the second hold capacitor C2 configure a second control hold circuit. Further, in this embodiment, the first and second error amplifying sections 42 and 32 are combined by the combination of the delay circuit 37 and the logical product circuit 38 and the combination of the delay circuit 37 and the negative logical product circuit 43.
The two-system hold circuit, that is, the peak and bottom that respectively hold the ON emission level value and the offset level value of the optical output obtained from the output of, perform automatic control only when the modulation signal remains in the same state for a certain period of time. Controlled at various timings. As a result, in the image forming apparatus or the like, the forward current of the semiconductor laser is controlled during the control period in which the ON emission or the offset emission is continuously performed for a certain period regardless of the image region and the non-image region. The ON emission current can be controlled without being affected by the response speed of the detection circuit of the ON emission current of the semiconductor laser LD.
Further, by further having means for setting the offset level control signal for performing the offset level control of the light output to a desired value, it becomes possible to set a desired offset current based on the control signal.

Next, FIG. 7 shows the structure of a semiconductor laser control apparatus according to the fifth embodiment of the present invention.

The semiconductor laser control apparatus according to the embodiment shown in the figure has a structure in which the offset level control signal for controlling the offset level of the optical output can be changed to a desired value.

In the prior art shown in FIG. 2, since the offset level signal Vb0 has a constant value, for example, when different semiconductor lasers are controlled using the same circuit, the optical output at a certain offset current value determined by the offset level signal is obtained. Control is performed as an offset level, but if one laser has the same current value and a different amount of offset light emission compared to the other, the offset level will be different, and depending on the laser, scumming may occur during offset light emission. . Therefore, as shown in FIG. 7, by providing means (changeover switch) 34 that can change the offset level to a desired value, it becomes possible to set the offset current to a desired value for each laser. Further, the offset level determined by setting the offset current to a desired value can also be controlled to a desired value.

FIG. 8 shows an embodiment of the semiconductor laser control device according to the sixth embodiment.

In the semiconductor laser control device according to the embodiment shown in FIG. 5, the offset level control signal for controlling the offset level of the optical output can be switched between two values.
3 (changeover switch) is provided.

The offset level control signal is the offset level control signal 1 (Vb1) and the offset level control signal 2 (Vb
It is possible to switch to either of two types of 2), and by providing a switching means 53 that switches so as to input one of the signals to the offset level control means 32, for example, an IC
The offset level control signals 1 and 2 having different levels are set for each, and the switching means 53 selects the offset level control signal with which the optical output close to the desired offset level can be obtained depending on the characteristics, type, and individual difference of the laser to be controlled. With such a configuration, it is possible to select an offset light emission amount close to a desired value.

Next, FIG. 9 shows the structure of the semiconductor laser control apparatus according to the seventh embodiment.

The semiconductor laser control apparatus according to the embodiment of the figure is provided with means 53 (changeover switch) capable of switching the value of the offset level control signal for controlling the offset level of the optical output to two kinds of signal level values, and Each of the signal level values to be switched has a configuration that can be changed to a desired value.

In this configuration, the offset level control signal can be switched between two types, that is, the offset level control signal 1 (Vb1) and the offset level control signal 2 (Vb2), and each signal level can be made variable. Either one of the signals is input to the offset level control means 32. For example, by setting the offset level control signals 1 and 2 having different levels for each IC to desired values, and further controlling the characteristics, type, and individual difference of the laser to be controlled, an offset level control signal that provides an optical output close to the desired offset level can be obtained. By selecting by the switching means 53, it is possible to select the offset light emission amount of a desired value from two types.

Next, FIG. 10 shows the configuration of a semiconductor laser control device according to the eighth embodiment of the present invention.

In this configuration, the memory 55 for storing the offset level control signal for performing the offset level control is provided, and a desired value is read out by giving a memory setting signal to the memory 55. That is, with this configuration, when a plurality of offset level control signal values are stored in the memory 55 in advance and the stored data is read from the memory 55, the data is read according to the signal level value of the memory setting signal to be given and the desired offset is obtained. By performing the level control, the offset level can be arbitrarily selected from a plurality of levels without using a switching unit or the like.

Next, FIG. 11 shows the configuration of a semiconductor laser control device according to the ninth embodiment.

In this structure, the variable resistor Rb is provided as a means for variably setting the offset level control signal to a desired value. That is, a constant voltage source Vb and a variable resistor R
It is possible to set the offset control signal level Vb obtained from the terminal of the variable resistance to a desired value by providing b and changing the resistance value of the variable resistance Rb. It is possible to reduce the influence of the light emitting characteristics. Also, for example, when the semiconductor laser control circuit unit is integrated into an IC, the variable resistance unit is provided on a substrate outside the IC, and the variable resistance value is changed to a desired value according to the characteristics of the semiconductor laser mounted on the substrate. By doing so, it becomes possible to easily change the offset level according to the type of LD and individual difference.

Next, FIG. 12 shows the configuration of a semiconductor laser control device according to the tenth embodiment of the present invention.

Here, the offset level control means 36 for controlling the offset level value and the ON emission level control means 31 for controlling the ON emission level value are incorporated in a single IC, and the offset level control signal is used as an input signal. It is configured to input. By thus forming the control circuit into an IC and inputting the offset level control signal from the external terminal of the IC, it becomes possible to variably control the offset level control signal from outside the IC. This can be easily dealt with by changing the level of the control signal.

FIG. 13 shows the structure of the semiconductor laser control device according to the eleventh embodiment of the present invention.

Here, the photoelectric negative feedback loop for controlling the offset level value and the ON emission level control means 31 for controlling the ON emission level value are incorporated in a single IC, and the offset level control signal is The input signal from the outside of the IC is converted by the signal converter 61 and supplied. In such a configuration, the control circuit
The control signal can be variably controlled over time by turning it into an IC and inputting an input signal from the external terminal of the IC, converting the input signal to a signal that includes signal amplification and level shifting, and supplying an offset level control signal. This makes it possible to easily cope with, for example, changes in the optical output characteristics of the laser over time. Further, since the input signal is converted by the signal converter 61, the level of the input signal may remain high even if the offset level control signal becomes small, for example, in a laser having a very small monitor current, and the signal conversion is performed. As a result, a desired offset level control signal can be obtained, and highly accurate control can be performed.

Next, FIG. 14 shows the structure of a semiconductor laser control device according to the twelfth embodiment of the present invention.

Here, a rotating polyhedron (polygon mirror 1) that rotates the light emitted from the semiconductor laser LD in a fixed direction.
6, FIG. 1), a system for periodically scanning in the same direction is provided with a means 53 (switching switch) for switching the signal level of the offset level control signal inside and outside the effective scanning range forming the image area. FIG. 1 shows the effective scanning range. In the image forming apparatus configured as shown in FIG. 1, a semiconductor laser 15 as a light source is modulated and driven based on an image modulation signal, and light from the semiconductor laser 15 is scanned by a polygon mirror or the like with respect to a photoconductor 19 which is rotationally driven. While deflecting and scanning by the means 16, the electrostatic latent image is formed by exposing at a predetermined timing based on the synchronization signal detected by the synchronization detection sensor 18. In this embodiment, the semiconductor laser 1 deflected and scanned by the polygon mirror 16 is used.
The light of No. 5 passes on the photoconductor 19 and the synchronization detection sensor 18 arranged in the long axis direction of the photoconductor 19, but the image data of the image data is actually printed on the photoconductor 19 during the scanning period corresponding to the scanning range. When the period for forming the electrostatic latent image is the effective scanning period, the offset level control signal is switched between the effective scanning period corresponding to the effective scanning range on the photoconductor 19 and the period corresponding to the outside of the effective scanning range. There is.

For example, by setting a certain offset level control signal 1 within the effective scanning period (a period corresponding to the effective scanning range), and switching to an offset level control signal 2 having a smaller value than the offset level control signal 1 outside the effective scanning period. , Originally it is not necessary to form an image,
A slight electrostatic latent image is formed by the offset light emission, and it is possible to prevent the occurrence of background stains due to toner adhesion due to the resulting charges, and at the same time, it is possible to reduce deterioration of the photoconductor 19. . Further, by setting the offset level control signal level to a desired higher value within the effective scanning period than outside the effective scanning period, the offset light emission amount and the modulation characteristic can be optimized.

FIG. 15 shows the structure of the semiconductor laser control device according to the thirteenth embodiment of the present invention.

Here, a plurality of reference voltage sources 71, 72
And switching means 53 (switching switch) for switching the electrical connection state between these voltage sources 71 and 72. With this configuration, a desired offset level signal can be selected from a plurality of offset level control signals. For example, the output signals of the reference voltage sources 71 and 72 are the offset level control signals and the offset level control signals 1 (Vb
1), the offset level control signal 2 (Vb2) is composed of two types of switchable signals, and by providing switching means 53 for switching to input one of the signals to the offset level control circuit 32, for example, an IC The offset level control signals 1 and 2 having different levels are set for each of them, and the switching means 53 selects the offset level control signal that gives an optical output close to a desired offset level depending on the type of laser to be controlled and individual differences. This makes it possible to select an offset light emission amount close to a desired value.

FIG. 16 shows the structure of the semiconductor laser control device according to the fourteenth embodiment of the present invention.

Here, a current source 75 and a plurality of resistors R1, R2, R are used as a means for varying the offset level control signal.
3 and 3 are provided. Specifically, three resistors R1, R2, R3 are connected in series to a certain constant current source 75, and the output voltage is output from the R1-R2 terminal and the R2-R3 terminal from the connection between the resistors. The bird
A switching means 53 (switching switch) for switching these output terminals is provided. When the current of the constant current source 75 is I and the values of the resistors R1, R2, and R3 are R, the signal level output to each terminal is obtained by the following equation. R1-R2 terminal output = I × 2R R2-R3 terminal output = I × R Therefore, the switching means 53 for switching between the above two types of signal levels
By providing the offset level control signals 1 and 2 having different levels for each IC, for example, an offset level control signal for obtaining an optical output close to a desired offset level depending on the type of laser to be controlled and individual difference is provided. By selecting by the switching means 53, it is possible to select an offset light emission amount close to a desired value.

FIG. 17 shows the arrangement of the semiconductor laser control apparatus according to the 15th embodiment.

Here, a switching means 82 is provided which converts a constant current obtained from the current sources 83 and 84 into an offset level control signal by the IV converter 81 and switches the electrical connection state between the current sources 83 and 84. As a result, a desired offset level control signal can be selected from the plurality of offset level control signals. For example, reference current sources 83, 84
A switching means 82 for switching so that either one of the two types of signals of the current source 1 (I1) and the current source (I2) as the output signal of the above is input to the IV (current-voltage) converter 81. As a result, the values of the current sources 83 and 84 and the offset level control signals Vb1 and Vb2 obtained by the IV converter 81 can be switched. As a result, for example, the offset level control signals 1 and 2 having different levels are set for each IC, and the offset level control signal that provides the optical output close to the desired offset level is switched depending on the characteristics, type, and individual difference of the laser to be controlled. By selecting by means, it becomes possible to select an offset light emission amount close to a desired value.

Next, FIG. 18 shows the structure of a semiconductor laser controller according to the sixteenth embodiment of the present invention.

Here, in the case where the semiconductor laser control circuit unit is formed as an IC, a plurality of voltage sources 91, 92, 9 are used.
Switching means 95 (switching switch) for switching the electrical connection state with any one of 3, 94 or current sources, and desired electrical wiring between the voltage sources or current sources 91, 92, 93, 94 and the switching means 95. By providing the means for cutting the pattern, it becomes possible to obtain a desired signal among the plurality of ON light emission level control signal set values. Specifically, in FIG. 18, four reference voltage sources 1 to 4 (91, 9
2,93,94) of the reference voltage sources 2,3 (92,9)
3) and the electrical connection pattern between the switching means 95 are selected and cut in advance, so that the reference voltage source 1
By switching (91) and the reference voltage source 4 (94), the offset level control signals 1 and 2 are obtained, and as a result, it becomes possible to select from a plurality of narrowed offset level control signals.

In this case, for example, the reference voltage sources 91, 94
The offset level control signal as an output signal of the offset level control signal 1 (Vb1) and the offset level control signal 2 (Vb4) are composed of two kinds of switchable signals, and one of the signals is used as the offset level control circuit 32. By configuring the switching means 95 for switching to input to, the offset level control signals 1 and 2 having different levels are set for each IC, and the offset level is close to the desired offset level depending on the type of laser to be controlled and individual difference. By selecting the offset level control signal for obtaining the light output by the switching means, it becomes possible to select the offset light emission amount close to a desired value.

As described above, by adopting the structure in which the selection can be made in two steps, that is, the pattern cutting and the changeover switch, a wide range of options can be selected with a simple structure.

Next, FIG. 19 shows the structure of a semiconductor laser control apparatus according to the seventeenth embodiment of the present invention.

Here, the timing for switching the signal level of the offset level control signal is generated from the phase synchronization detection signal.

For example, as shown in FIG. 1, a semiconductor laser 15 as a light source is modulated and driven based on an image modulation signal, and light from the semiconductor laser 15 is rotationally driven.
In the image forming apparatus for forming an electrostatic latent image by exposing the light beam 9 at a predetermined timing based on a synchronization signal detected by the synchronization detection sensor 18 while deflecting and scanning the scanning means 16 such as a polygon mirror. In accordance with the phase synchronization detection signal obtained by the synchronization detection sensor 18, the light from the semiconductor laser 15 deflected and scanned by the polygon mirror 16 passes over the photoconductor 19 and the synchronization detection sensor 18 arranged in the long axis direction of the photoconductor 19. If the period during which the electrostatic latent image of the image data is actually formed on the photoconductor 19 is the effective scanning period (the period corresponding to the effective scanning range) among the passing periods, it is within the effective scanning range on the photoconductor 19. A signal indicating the timing of switching the offset level control signal between the period corresponding to the above and the period corresponding to the outside of the range. Configuration to be obtained by the timing circuit for generating a clock signal.

The signal indicating this timing is generated by starting the counting operation by the clock signal at the timing of the phase synchronization detection signal which is repeatedly detected at a constant cycle when the laser beam is deflected and scanned, and the effective scanning on the photosensitive member is performed. The timing corresponding to the period is defined by the count number, and when the count number is reached, the effective scanning period detection signal is output,
By this, the offset level control signal is switched. As a result, for example, a certain offset level control signal 1 is set within the effective scanning period and is switched to an offset level control signal 2 having a smaller value than the offset level control signal 1 outside the effective scanning period. Therefore, a timing signal generated from the phase synchronization detection signal It is possible to accurately define the inside and outside of the effective scanning period based on the above. As a result, although it is not necessary to form an image originally, a slight electrostatic latent image is formed due to offset light emission, and as a result, it occurs. It is possible to more reliably prevent the occurrence of background stain due to the adhesion of toner due to the electric charge, and at the same time, to reduce the deterioration of the photoconductor. Further, by setting the offset level control signal level to a desired higher value within the effective scanning period than outside the effective scanning period, the offset light emission amount and the modulation characteristic can be optimized.

The semiconductor laser control device of any of the first to seventeenth embodiments can be applied to the image forming apparatus as shown in FIG. 1, for example (specifically, it can be applied to the laser drive circuit 12 thereof). Each of the image forming apparatuses applied as described above can be an embodiment of the present invention and are included in the scope of the present invention.

[0078]

As described above, according to the present invention, by providing the means for setting the offset level control signal for controlling the offset level to a desired value, it is possible to respond to the type of semiconductor laser and individual differences. , The offset current and the offset level can be set to desired values. Further, by providing a means for setting the offset level to a desired value for each LD, it is possible to prevent the formation of an electrostatic latent image due to offset light emission in the non-image area of the image forming apparatus and the occurrence of background stain due to toner adhesion. Becomes possible,
Moreover, by reducing the offset level, it is possible to reduce energy consumption and extend the life of the photoconductor. Further, by setting the offset current controlled by the offset level to a desired value, the modulation characteristics of the semiconductor laser can be improved and stabilized.

[Brief description of drawings]

FIG. 1 is a block diagram showing a schematic configuration of an image forming apparatus to which a semiconductor laser control device of the present invention can be applied.

FIG. 2 is a circuit diagram showing a configuration of a conventional semiconductor laser control device.

FIG. 3 is a circuit diagram showing a configuration of a semiconductor laser control device according to a first embodiment of the present invention.

FIG. 4 is a circuit diagram showing a configuration of a semiconductor laser control device according to a second embodiment of the present invention.

FIG. 5 is a circuit diagram showing a configuration of a semiconductor laser control device according to a third embodiment of the present invention.

FIG. 6 is a circuit diagram showing a configuration of a semiconductor laser control device according to a fourth embodiment of the present invention.

FIG. 7 is a circuit diagram showing a configuration of a semiconductor laser control device according to a fifth embodiment of the present invention.

FIG. 8 is a circuit diagram showing a configuration of a semiconductor laser control device according to a sixth embodiment of the present invention.

FIG. 9 is a circuit diagram showing a configuration of a semiconductor laser control device according to a seventh embodiment of the present invention.

FIG. 10 is a circuit diagram showing a configuration of a semiconductor laser control device according to an eighth embodiment of the present invention.

FIG. 11 is a circuit diagram showing a configuration of a semiconductor laser control device according to a ninth embodiment of the present invention.

FIG. 12 is a circuit diagram showing a configuration of a semiconductor laser control device according to a tenth embodiment of the present invention.

FIG. 13 is a circuit diagram showing a configuration of a semiconductor laser control device according to an eleventh embodiment of the present invention.

FIG. 14 is a circuit diagram showing a configuration of a semiconductor laser control device according to a twelfth embodiment of the present invention.

FIG. 15 is a circuit diagram showing a configuration of a semiconductor laser control device according to a thirteenth embodiment of the present invention.

FIG. 16 is a circuit diagram showing a configuration of a semiconductor laser control device according to a fourteenth embodiment of the present invention.

FIG. 17 is a circuit diagram showing a configuration of a semiconductor laser control device according to a fifteenth embodiment of the present invention.

FIG. 18 is a circuit diagram showing a configuration of a semiconductor laser control device according to a sixteenth embodiment of the present invention.

FIG. 19 is a circuit diagram showing the structure of a semiconductor laser control device according to a seventeenth embodiment of the present invention.

[Explanation of symbols]

15 semiconductor laser unit 18 photodetector 31 ON emission level control means 32 differential amplifier 33 changeover switch 34 offset level control signal generating means 37 delay circuit 38 AND circuit 39 changeover switch 41 changeover switch 42 differential amplifier 43 negative OR circuit 51, 52 Offset level signal generating means 51 ', 52' Variable offset level signal generating means 53 Changeover switch 55 Memory LD Semiconductor laser PD Photodetector

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C362 AA03 AA54 AA56 AA61 DA28                 2H076 AB05 AB12 AB22 AB32 AB34                       DA04 DA11 DA17                 5F073 AB27 AB29 BA07 EA15 GA12                       GA18 GA24 GA38

Claims (8)

[Claims] 1. In an image forming apparatus for forming an image by scanning a light beam from a semiconductor laser on a photosensitive member and scanning the image, an offset level control signal for determining an offset current at the time of offset light emission of the semiconductor laser is provided. A semiconductor laser control device comprising means for setting a desired value according to the characteristics, types, individual differences, etc. of the semiconductor laser. 2. In an image forming apparatus for forming and scanning a light beam from a semiconductor laser on a photosensitive member to record an image, a control timing for controlling an offset current at the time of offset emission of the semiconductor laser is set to the semiconductor. A timing generation circuit for generating a logical product of a modulation signal for driving a laser and a delay signal obtained by delaying the modulation signal, and an offset level control signal for determining the offset current, the characteristics, types and individual differences of the semiconductor laser. And a means for setting a desired value according to the above. 3. An image forming apparatus for forming an image by scanning an image of a light beam from a semiconductor laser on a photoconductor and scanning the image on the photoconductor, and a first control means for controlling an offset current of the semiconductor laser during offset light emission. A second control means for controlling an on-light emission current of the semiconductor laser during on-light emission, and an offset level control signal for determining the offset current, which is desired according to characteristics, types, individual differences, etc. of the semiconductor laser. And a means for setting a value. 4. In an image forming apparatus for forming an image by scanning a light beam from a semiconductor laser on a photoconductor and scanning the image, a control timing for controlling an offset current at the time of offset emission of the semiconductor laser is set to the semiconductor. A first timing generating means for generating a logical product of a modulation signal for turning on a laser and a delay signal obtained by delaying the modulation signal; and a control timing for controlling an ON light emission current at the time of ON light emission of the semiconductor laser, Second timing generation means for generating a logical sum of a modulation signal for driving a semiconductor laser and the delayed signal obtained by delaying the modulation signal; and an offset level control signal for determining the offset current, the characteristics of the semiconductor laser. And a means for setting a desired value according to the type, individual difference and the like. 5. The device according to claim 1, further comprising a unit capable of variably setting an offset level control signal for performing an offset level control of optical output to a desired value. Semiconductor laser controller. 6. The apparatus according to claim 1, further comprising means for switching the value of the offset level control signal for performing the offset level control of the optical output to a predetermined plurality of types of signal level values. The semiconductor laser control device described. 7. A means for switching the value of the offset level control signal for controlling the offset level of the optical output to a plurality of types of signal level values, and a means for variably setting each of the signal level values to be switched to a desired value. The semiconductor laser control device according to claim 1, wherein the semiconductor laser control device comprises: 8. A memory for storing information for setting an offset level control signal for performing offset level control, wherein a desired signal is output by giving a setting signal to the memory and outputting information according to the signal. The semiconductor laser control device according to claim 1, wherein the semiconductor laser control device is configured to obtain an offset level control signal.