JP2002079705A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus which automatically, simply and highly accurately adjusts the quantity of light of a laser light source for imaging by forming electrostatic latent images to a photoreceptor. SOLUTION: At an APC circuit 20, in a sampling mode in which a synchronous detection signal XDETP is low and an S/H signal control circuit outputs a low S/H signal, a control circuit 25 selectively turns on switches SW1 and SW2, thereby charging one of capacitors C1 and C2 by a constant current source 26 for charging via a switch circuit 28. In a hold mode in which the synchronous detection signal XDETP is high and the S/H signal control circuit outputs a high S/H signal, the control circuit 25 turns off the switches SW1 and SW2, whereby a potential of the capacitors C1 and C2 is inputted to an error amplifier 29. The error amplifier 29 amplifies an error of an input voltage V3 from a reference voltage Vref3, increasing/decreasing a collector current of a transistor Tr1 to hold the quantity of an LD 3 to be a constant value. When the quantity of light is changed in the sampling mode, the S/H signal control circuit outputs the high S/H signal to bring about the hold mode to appropriately prevent the LD3 from emitting light extraordinarily.

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 for automatically adjusting a light amount of a laser light source for forming an electrostatic latent image on a photosensitive member to form an image.

[0002]

2. Description of the Related Art Image forming apparatuses such as digital copiers, digital printers, and digital facsimile machines include:
Because high-quality images can be recorded at high speed,
2. Description of the Related Art An electrophotographic image forming apparatus that forms an image using a laser beam emitted from a laser light source such as a semiconductor laser has become widespread.

In an electrophotographic image forming apparatus using such a laser light source, it is necessary to keep the output of the laser light source constant in order to improve the image quality. The output of the laser light source is kept constant using a power control (automatic light output control) circuit.

That is, in the case of a laser light source such as a semiconductor laser, its light output characteristics are sensitive to changes in the ambient temperature. Changes the light output. In order to keep the fluctuation of the light output constant, a monitor diode for monitoring the light output of the laser light source is incorporated in the package of the laser light source, and the drive current of the laser light source is controlled based on the detection result of the monitor diode. An APC circuit has been used as a drive circuit of a semiconductor laser having a feedback mechanism for maintaining a constant optical output (Japanese Patent Application Laid-Open No. Hei 8-
88429, JP-A-5-226751, etc.).

In an electrophotographic image forming apparatus, a laser light source is turned on / off in accordance with image data. In such an image forming apparatus, the lighting time of the laser light source is irregular. Therefore, in general,
Turn on the laser light source for a certain time outside the image area,
It is carried out.

[0006]

However, in an image forming apparatus, particularly in an image forming apparatus capable of switching the pixel density, the light amount of the laser light source is switched in order to change the linear velocity according to the pixel density. However, when the light amount is switched, if the APC circuit enters a sample mode in which the light amount of the laser light source is sampled, the voltage for adjusting the light amount of the APC circuit becomes unstable, and the laser light source such as a semiconductor laser becomes excessive. It emits light, the laser light source deteriorates,
It was not possible to perform appropriate light amount adjustment, and there was a possibility that an image would be deteriorated.

Therefore, according to the first aspect of the present invention, the light quantity of the laser light emitted from the laser light source is detected by the light quantity monitoring element, and the automatic light quantity adjustment of the laser light source is performed based on the detection result of the light quantity monitoring element. At the same time, when the emission light amount of the laser light source is switched using a plurality of light amount setting resistors, when the emission light amount is switched, the automatic light amount adjustment is set to a hold mode for holding the light amount of the laser light source, so that the automatic light amount adjustment circuit It is an object of the present invention to provide an image forming apparatus capable of preventing a light amount adjustment voltage value from becoming unstable, preventing a laser light source from being over-emitted and being deteriorated, and improving the image quality of a formed image. I have.

According to a second aspect of the present invention, the amount of light emitted from the laser light source is switched in accordance with the pixel density of an image to be formed, so that the amount of light is switched in accordance with the pixel density to form a higher quality image. It is an object of the present invention to provide an image forming apparatus capable of performing the operation.

According to a third aspect of the present invention, a capacitor for holding a drive current for driving a laser light source is charged and discharged based on the detection result of the light amount monitoring element, and the laser light source is charged and discharged based on the amount of charge held by the capacitor. By performing automatic light intensity adjustment, the size of the automatic light intensity adjustment circuit is reduced, the number of components is reduced, the automatic light intensity adjustment of the laser light source is performed with high accuracy with a simple configuration, It is an object of the present invention to provide an image forming apparatus capable of forming a high quality image.

According to a fourth aspect of the present invention, there is provided a capacitor which is charged and discharged based on the detection result of the light amount monitoring element and automatically adjusts the light amount of the laser light source based on the held charge amount.
According to the cycle of the synchronization detection signal output by the synchronization detection means,
By charging and discharging, the size of the automatic light amount adjustment circuit is reduced, the number of components is reduced, the automatic light amount adjustment of the laser light source is performed with higher accuracy with a simple configuration, and the cost is less, the density fluctuation is less, and It is an object of the present invention to provide an image forming apparatus capable of forming a high quality image.

[0011]

An image forming apparatus according to the first aspect of the present invention scans a laser beam modulated by image data from a laser light source onto a latent image carrier and places the laser beam on the latent image carrier. When forming an electrostatic latent image and developing the electrostatic latent image on the latent image carrier with a developer to form an image, the amount of laser light emitted from the laser light source is detected by a light amount monitoring element, An image forming apparatus that performs automatic light amount adjustment of the laser light source based on a detection result of the light amount monitoring element, and that switches an output light amount of the laser light source using a plurality of light amount setting resistors. At the time of switching, the above object is achieved by setting the automatic light amount adjustment to a hold mode for holding the light amount of the laser light source.

According to the above configuration, the light amount of the laser light emitted from the laser light source is detected by the light amount monitoring element, and the automatic light amount adjustment of the laser light source is performed based on the detection result of the light amount monitoring element. When switching the output light amount of the laser light source using the light amount setting resistor, the automatic light amount adjustment is performed in the hold mode for holding the light amount of the laser light source when the output light amount is switched. Can be prevented from becoming unstable, the laser light source can be prevented from being over-emitted and deteriorated, and the image quality of the formed image can be improved.

In this case, for example, the image forming apparatus may switch the amount of light emitted from the laser light source according to the pixel density of the image to be formed.

According to the above configuration, the amount of light emitted from the laser light source is switched in accordance with the pixel density of the image to be formed. Therefore, the amount of light is switched in accordance with the pixel density, and a higher quality image can be formed. it can.

Further, for example, the image forming apparatus charges and discharges a capacitor for holding a driving current for driving the laser light source based on a detection result of the light amount monitoring element, The automatic light amount adjustment of the laser light source may be performed based on the charge amount held by the capacitor.

According to the above configuration, the capacitor for holding the drive current for driving the laser light source is charged and discharged based on the detection result of the light amount monitoring element, and the automatic light amount of the laser light source is determined based on the charge amount held by the capacitor. Since the adjustment is performed, the size of the automatic light amount adjustment circuit can be reduced, the number of parts can be reduced, the automatic light amount adjustment of the laser light source can be performed with high accuracy with a simple configuration, and the density fluctuation can be performed at low cost. It is possible to perform high-quality image formation with a small amount.

Further, for example, in the image forming apparatus, the image forming apparatus may be provided on a scanning line of a laser beam from the laser light source to the latent image carrier, and the latent image of the latent image carrier may be provided. Synchronization detecting means for receiving the laser beam scanned and arranged at a position deviating from the formation area and outputting a synchronization detection signal is provided, and according to a cycle of the synchronization detection signal output from the synchronization detection means, The charge and discharge of the capacitor may be performed.

According to the above configuration, the capacitor that is charged and discharged based on the detection result of the light amount monitoring element and that automatically adjusts the light amount of the laser light source based on the amount of electric charge held is connected to the synchronization detection signal output from the synchronization detection means. Since the charge and discharge are performed in accordance with the cycle, the automatic light amount adjustment circuit can be downsized, the number of components can be reduced, and the automatic light amount adjustment of the laser light source can be performed with higher accuracy with a simple configuration. Thus, it is possible to form an image of lower quality with less density fluctuation and higher quality.

[0019]

Preferred embodiments of the present invention will be described below in detail with reference to the accompanying drawings. It should be noted that the embodiments described below are preferred embodiments of the present invention, and therefore, various technically preferable limitations are added. However, the scope of the present invention is not limited to the following description. The embodiments are not limited to these embodiments unless otherwise specified.

FIGS. 1 to 5 show an embodiment of an image forming apparatus according to the present invention. FIG. 1 shows an image forming apparatus 1 to which an embodiment of the image forming apparatus according to the present invention is applied. FIG. 2 is a schematic configuration diagram of a main part of a scanning optical system.

In FIG. 1, an image forming apparatus 1 includes an LD
(Laser diode) LD 3 as a laser light source attached to substrate 2, collimating lens 4, polygon scanner 5, fθ lens 6, photoconductor 7, and synchronization detecting element unit 8
Etc. are provided.

The LD 3 emits a divergent laser beam, and the collimating lens 4 converts the divergent laser beam emitted from the LD 3 into a parallel laser beam and irradiates it to a polygon scanner 5.

The polygon scanner 5 is driven to rotate at a high speed at an angular velocity corresponding to the image density of the image forming apparatus 1, deflects the laser light incident from the polygon scanner 5 in the main scanning direction and reflects the laser light on the fθ lens 6.

Lens 6 forms an image of the laser beam reflected and deflected by polygon scanner 5 on photosensitive member (latent image carrier) 7 and at a position on the scanning line of the laser beam which is outside the image forming area. Also, the light is irradiated on the synchronization detecting element portion 8 disposed in the vicinity of the photoconductor 7. The photoreceptor 7 is rotated and uniformly charged by a charging unit (not shown), and then is irradiated with the laser light to form an electrostatic latent image. Developer) to form a toner image. Image forming apparatus 1
The image is formed by transferring the toner image on the photoreceptor 7 to recording paper and fixing the toner image on the recording paper by a fixing unit. Then, after cleaning the photoreceptor 7 to which the toner image has been transferred, the charging unit uniformly charges the photoreceptor 7, and performs image formation again.

The synchronization detecting element (synchronization detecting means) 8
As shown in FIG. 2, the device includes a synchronization detecting element 10 such as a photodiode, a resistor R1, a comparator 11, and the like, and the laser light is incident on the synchronization detecting element 10. When a laser beam is incident on the synchronization detection element 10, a current Id flows through the synchronization detection element 10 and the resistor R1, and the comparator 1
The voltage Vd is input to the input terminal 1. Comparator 11
Outputs a synchronization detection signal XDETP which is a pulse output when the input voltage Vd becomes higher than the comparison voltage Vrefa.
As shown in FIG. 3, the synchronization detection signal XDETP is a signal that is output once during the width T1 and becomes low during the width T1 in one line cycle T2.

The image forming apparatus 1 includes an APC circuit 20 shown in FIG. 4, and the APC circuit 20 includes a PD (photodiode) 21, a switch circuit 22, and a variable resistor VR.
1, VR2, comparator 23, switch circuit 24, control circuit 25, switches SW1, SW2, constant current source 26 for charging, constant current source 27 for discharging, switch circuit 2
8, capacitors C1 and C2, an error amplifier 29, a transistor Tr1, a resistor R2, and the like.
The S / H signal control circuit 30 shown in FIG.

The PD (light quantity monitoring element) 21 is incorporated in the package of the LD 3, and the monitor current Im flows when the laser light emitted from the LD 3 enters.
This PD 21 is connected to the switch circuit 22 and to the input of the comparator 23. The switch circuit 22 includes a switch SW21 and a switch SW2.
2 and a switch SW2 according to the switching signal IN1.
1 and switch SW22 are selectively connected to PD21.
In the switch circuit 22, a variable resistor VR1 for setting the light quantity of the LD3 is connected to the switch SW21, and a variable resistor V1 for setting the light quantity of the LD3 is connected to the switch SW22.
R2 is connected. When the switching signal IN1 is low, the switch circuit 22 turns on the switch SW21, turns off the switch SW22, connects the PD 21 to the variable resistor VR1 via the switch SW21, and sets the switching signal IN to high. ), The switch SW21 is turned off, the switch SW22 is turned on, and the PD 21 is connected to the variable resistor VR2 via the switch SW22.

As described later, the image forming apparatus 1 changes the switching signal IN1 from high to low when switching the light amount.
Alternatively, by changing from low to high, the variable resistor VR1 and the variable resistor VR2 connected to the PD 21 are switched,
The light amount is switched. Therefore, the variable resistor VR1
The variable resistor VR2 functions as a light amount setting resistor.

Then, the monitor current Im of the PD1 is switched to a line flowing through the variable resistor VR1 and a line flowing through the variable resistor VR2 by the switching signal IN1.
When connected to the variable resistor VR1 by the switch circuit 22, the potential of the input voltage V1 of the comparator 23 becomes V1
= Im * VR1, and when the switch circuit 22 connects the variable resistor VR2, the potential of the input voltage V1 of the comparator 23 becomes V1 = Im * VR2.

The reference voltage Vref1 and the reference voltage Vref2 are selectively inputted to the comparison input of the comparator 23 via the switch circuit 24, and the switch circuit 24
2, the input reference voltage Vref1 and the input reference voltage Vref2
Is selectively switched, and is output to the comparison input of the comparator 23 as the reference voltage Vrefb. The comparator 23
When the input voltage V1 is smaller than the reference voltage Vrefb,
The comparison output V2 of High is applied to the control circuit 2
5, when the input voltage V1 is higher than the reference voltage Vrefb, a low comparison output V2 is output to the control circuit 25.

The control circuit 25 receives the comparison output V2 from the comparator 23,
The H signal is input, and the output of the control circuit 25 is connected to the switches SW1 and SW2.
The control circuit 25 switches between a sampling mode and a hold mode according to the S / H signal. The S / H signal is low (Low), in the sampling mode, and high (H).
i) in hold mode. That is, when the S / H signal is low, the control circuit 25 enters a sampling mode in which the switch SW1 and the switch SW2 are selectively closed according to the high / low state of the comparison output V2 from the comparator 23. Is in the hold mode in which both the switches SW1 and SW2 are open. In the sampling mode, when the S / H signal is low and the input voltage V1 of the comparator 23 is equal to the reference voltage V
When the comparison output V2 of the comparator 23 is high, the switch SW2 is turned off, and the switch SW1 is turned off.
Is turned on, the input voltage V of the comparator 23 is higher than the reference voltage Vrefb, and the comparison output V2
Is low, switch SW1 is turned off and switch S1 is turned off.
Turn on W2.

The switches SW1 and SW2 are connected in series between a constant current source for charging 26 and a constant current source 27 for discharging, and a switch circuit 28 is connected between the switches SW1 and SW2. And is connected to the input terminal of the error amplifier 29.

The switch circuit 28 further has a capacitor C1 and a capacitor C2 connected to its switch terminals, and the switch circuit 28 operates in response to a switching signal IN3.
Between the switch SW1 and the switch SW2 and the error amplifier 2
9 is selectively connected to the capacitor C1 or the capacitor C2.

That is, when the control circuit 25 is in the hold mode in which both the switches SW1 and SW2 are open, the voltage (output voltage) charged in the capacitor C1 or the capacitor C2 selected by the switching signal IN3. Is connected to the error amplifier 29 through the switch circuit 28.
Is input as an input voltage V3.

As described above, the input voltage V3 is input to the input terminal of the error amplifier 29, and the reference voltage Vref3 is input to the reference input terminal of the error amplifier 29, and the potential of the input voltage V3 is changed to the reference voltage Vref3. The error is amplified to increase or decrease the collector current of the transistor Tr1. An LD3 is connected to the collector of the transistor Tr1, and the drive current (LD current) of the LD3 increases and decreases as the collector current of the transistor Tr1 increases and decreases.
Is adjusted and held at the set value.

That is, the APC circuit 20 increases the LD current when the light amount of the LD 3 is smaller than the set light amount, and decreases the LD current when the light amount of the LD 3 is larger than the set light amount.

When the capacitance values of the capacitors C1 and C2 are large, the input voltage V3 of the error amplifier 29 is
Is held constant for a long time, and when the capacitance values of the capacitors C1 and C2 are small, the error amplifier 2
The input voltage V3 at 9 is held constant for a short period of time. However, as the APC circuit 20, when the capacitance values of the capacitors C1 and C2 are small, the error amplifier 2
There is an advantage that the time required for the potential of the input voltage V3 of No. 9 to be charged to the set value is short. For example, when the capacitor C1 is 1 uF and the capacitor C2 is 0.1 uF,
When the synchronization detection signal XDETP is used as the sample signal of the control circuit 25, the capacitor C1 is selected when the period of the synchronization detection signal XDETP is long, and the capacitor C2 is selected when the period of the synchronization detection signal XDETP is short. It is preferable to do so.

As described above, when the capacitance value of the capacitor C1 is large and the capacitance value of the capacitor C2 is small, when the switching circuit 28 selects the capacitor C2 with the switching signal IN3, the set light amount is reached in a short time. However, when the capacitor C1 is selected, the time required to hold the light amount is long, but the time required to hold the light amount at a constant time is long.

As described above, when the S / H signal is low and in the sampling mode, the control circuit 25 sets the input voltage V1 of the comparator 23 to the reference voltage Vrefb.
When the comparison output V2 of the comparator 23 is high, the switch SW2 is turned off, the switch SW1 is turned on, and the capacitor C is switched by the charging constant current source 26 through the switch SW1 according to the selection of the switch circuit 28.
1 or the capacitor C2, and the input voltage V of the error amplifier 29 is increased.
1 is higher than the reference voltage Vrefb and the comparison output V2 of the comparator 23 is low, the switch SW1 is turned off,
Turn on switch SW2, and through switch SW2,
In accordance with the selection of the switch circuit 28, the electric charge of the capacitor C1 or the capacitor C2 is discharged, and the error amplifier 29
Is lowered by the PD 21 by lowering the input voltage V3 of the
Based on the detection result of the light amount of D3, the capacitor C1 or the capacitor C2 is charged by sampling a charge amount corresponding to the light amount of the LD3. A voltage corresponding to the charge amount sampled and charged in the capacitor C1 or the capacitor C2 is supplied to the error amplifier 29 in the sampling mode.
Is output as an input voltage V3 to the input terminal of, and the light amount is automatically adjusted.

The APC circuit 20 of the image forming apparatus 1
Is, as described above, the S / H signal control circuit 30 shown in FIG.
The S / H signal control circuit 30 includes an edge change detection circuit 31, a one-shot pulse generation circuit 32, and an OR circuit 33, as shown in FIG.

The switching signal IN1 is input to the edge change detecting circuit 31, and the edge change detecting circuit 31 changes the edge of the switching signal IN1 which changes from high (High) to low (Low) or from low to high. And outputs the detection result to the one-shot pulse generation circuit 32.

The one-shot pulse generation circuit 32 outputs a one-shot pulse to the OR circuit 33 when the edge change detection circuit 31 detects an edge change of the switching signal IN1. The one-shot pulse generation circuit 32 can appropriately change the generation timing of the generated one-shot pulse.

The OR circuit 33 further receives the synchronization detection signal XDETP. The OR circuit 33 outputs an OR output of the synchronization detection signal XDETP and the one-shot pulse generated by the one-shot pulse generation circuit 32. The signal is output to the control circuit 25 as an S / H signal.

Normally, when the synchronization detection signal XDETP is low, the S / H signal becomes low and the control circuit 2
5 is the sampling mode, and the APC circuit 20
Performs light amount adjustment. At this time, when the switching signal IN1 changes from high to low or from low to high, the edge change of the switching signal IN1 is detected by the edge change detection circuit 31, and the one-shot pulse generation circuit 32 changes to high for a certain period of time. Output a one-shot pulse
Since the / H signal becomes high, the APC circuit 20 is in the hold mode, and the light amount is held.

Next, the operation of the present embodiment will be described. In the image forming apparatus 1 of the present embodiment, when the light amount is switched in the sampling mode, the variable resistors VR1 and VR2 become unstable in the hold mode, thereby preventing the LD3 from emitting excessive light.

That is, as shown in FIG. 1, the image forming apparatus 1 converts the divergent laser light emitted from the LD 3 into parallel laser light with the collimating lens 3 and irradiates the parallel laser light with the polygon scanner 5. 5 deflects light in the main scanning direction and irradiates it on the photoreceptor 7 with the fθ lens 6 to form an image. The synchronization adjustment in the main scanning direction is performed based on the synchronization detection signal XDETP output by the control unit 8.

The image forming apparatus 1 includes the APC circuit 20 shown in FIG. 2, and the sampling mode in which the synchronization detection signal XDETP goes low and the S / H signal control circuit 30 outputs a low S / H signal. Then, the light amount of the LD3 is sampled by the PD21 incorporated in the package of the LD3, and the input voltage V1 generated by the variable resistor VR1 or the variable resistor VR2 set according to the image resolution (pixel density) at that time is obtained. The comparator 23 compares with the reference voltage Vref1 selected from the reference voltage Vref1 or the reference voltage Vref2 according to the variable resistors VR1 and VR2,
Depending on whether the input voltage V1 is greater than the reference voltage Vrefb,
The control circuit 25 includes the switch SW1 and the switch SW
2 is selectively turned on. When the switch SW1 or the switch SW2 is selectively turned on, the synchronization detection signal XDE
The capacitor C1 or the capacitor C2 selected by the switch circuit 28 is charged or discharged according to the length of the cycle of TP, and the potential of the capacitor C1 or the capacitor C2 rises or falls. The potential is input to the input terminal of the error amplifier 29 as the input voltage V3.

During image formation, in the hold mode in which the synchronization detection signal XDETP goes high and the S / H signal control circuit 30 outputs a high S / H signal, the control circuit 25
Turns off both switch SW1 and switch SW2,
The potential of the capacitor C1 or C2 selected by the switch circuit 28 is held constant for a time corresponding to the capacitance value of the capacitor C1 or C2, and is input to the input terminal of the error amplifier 29 as the input voltage V3.

The error amplifier 29 amplifies the potential of the input voltage V3 with the reference voltage Vref3 by error amplification, and
By increasing or decreasing the collector current of the transistor 1 and increasing or decreasing the collector current of the transistor Tr1, the drive current (LD current) of the LD3 increases or decreases, and the light amount of the LD3 is maintained at a constant value.

When the pixel density is switched, for example, when switching is performed between 600 dpi and 1200 dpi), at 1200 dpi, the rotation speed of the polygon motor for driving the polygon scanner 5 is increased, and the video clock frequency is increased. And the linear velocity is 600dp
It may be に す る of i. In such a case, L
The light amount of D3 is 600 dpi when the resolution is 1200 dpi.
In the case of に な る.

Therefore, the variable resistor VR1 and the variable resistor VR2 are switched to adjust the light amount of the LD3. For example, the variable resistor VR1 is 1KΩ and the variable resistor VR2 is 2KΩ.
If it is KΩ, the variable resistor VR1 is selected at 600 dpi, and the variable resistor VR is selected at 1200 dpi.
When the switching signal IN1 is controlled so as to select R2,
The APC circuit 20 determines that the input voltage V1 of the comparator 23 is equal to the reference voltage Vrefb (input voltage V1 = reference voltage Vreb).
fb), the light amount of the LD 3 at 1200 dpi is の of the light amount of the LD 3 at 600 dpi.

The value of the monitor current Im of the PD 21 incorporated in the package of the LD 3 varies greatly depending on the LD 3. Therefore, the monitor current Im of the PD 21
Is small, it is necessary to increase the values of the variable resistors VR1 and VR2, but the variable resistors VR1 and VR2
Is too large, the monitor current Im of the PD 21
Is large, the setting accuracy of the light amount of the LD 3 is deteriorated.

However, the APC circuit 20 of the present embodiment
Then, the reference voltage Vrefb is changed by the switch circuit 24 to the reference voltage Vrefb.
ref1 and the reference voltage Vref2. The reference voltage Vrefb is changed in accordance with the magnitude of the monitor current Im of the PD 21. The switching operation of the switch circuit 24 is controlled by the switching signal IN2. By switching between Vref1 and reference voltage Vref2, the above problem can be addressed.

For example, assuming that the reference voltage Vref1 is 1 V and the reference voltage Vref2 is 2 V, when the monitor current Im of the PD 21 is small, the switch circuit 24 uses the reference voltage Vref1.
When the monitor current Im is large, the reference voltage Vref2 is selected by the switch circuit 24. Even when the monitor current Im is small, the reference voltage Vref1 having a small value is selected as the reference voltage Vrefb. VR
1. It is not necessary to make VR2 too large.
Can be accurately set.

When the pixel density is switched,
As described above, the light amount of the LD 3 is switched.
In the C circuit 20, when this light amount is switched in the sampling mode, the values of the variable resistors VR1 and VR2 become unstable, and the LD3 may emit excessive light.

However, the image forming apparatus 1 of the present embodiment
When the S / H signal control circuit 30 shown in FIG. 5 switches the amount of light, the APC circuit 20 sets the APC circuit 20 to the hold mode to prevent the LD 3 from emitting excessive light.

That is, when the synchronization detection signal XDETP goes low, the S / H signal control circuit 30 outputs a low S / H signal from the OR circuit 33 to the control circuit 25 to set the sampling mode. When switching the light amount, as described above, the switching signal IN1 switches from high to low or from low to high.

When the switching signal IN1 changes from high to low or from low to high, the switching signal IN1 changes.
Is detected by the edge change detection circuit 31 and the one-shot pulse generation circuit 32 is set to high (Hig) for a predetermined time.
h), and the S / H signal goes high.
1 and the switch SW2 are both turned off to enter the hold mode, and the light amount of the LD 3 is held.

Therefore, when the light amount is switched, the values of the variable resistors VR1 and VR2 become unstable, so that it is possible to appropriately prevent the LD3 from emitting excessive light, and to improve the image quality. Deterioration of LD3 can be prevented.

As described above, in the image forming apparatus 1 of the present embodiment, the PD 21 detects the amount of laser light emitted from the LD 3 serving as a laser light source, and based on the detection result of the PD 21, the automatic light amount of the LD 3 When performing the adjustment and switching the output light amount of the LD3 using the plurality of variable resistors VR1 and VR2, the automatic light amount adjustment is set to the hold mode for holding the light amount of the LD3 when the output light amount is switched.

Accordingly, it is possible to prevent the values of the variable resistors VR1 and VR2 of the APC circuit 20 from becoming unstable, to prevent the LD3 from being over-emitted and deteriorated, and to prevent deterioration of the formed image. Quality can be improved.

Further, the image forming apparatus 1 of the present embodiment
The output light amount of the LD 3 is switched according to the pixel density of the image to be formed.

Therefore, it is possible to form an even higher quality image by switching the light amount according to the pixel density.

Further, the image forming apparatus 1 of the present embodiment
Performs charging / discharging of the capacitors C1 and C2 holding the drive current for driving the LD3 based on the detection result of the PD21, and performs automatic light amount adjustment of the LD3 based on the amount of charge held by the capacitors C1 and C2. .

Therefore, the APC circuit 20 can be reduced in size, the number of components can be reduced, the automatic light amount adjustment of the LD 3 can be performed with high accuracy with a simple configuration, and the density can be reduced at low cost. High quality image formation can be performed.

The image forming apparatus 1 according to the present embodiment
The capacitors C1 and C2 that are charged / discharged based on the detection result of the PD 21 and that automatically adjusts the light amount of the LD 3 based on the held charge amount are changed according to the cycle of the synchronization detection signal XDETP output from the synchronization detection element unit 8. Charging and discharging.

Therefore, the APC circuit 20 can be reduced in size, the number of parts can be reduced, the automatic light amount adjustment of the LD 3 can be performed with higher accuracy with a simple structure, and the density fluctuation can be reduced at low cost. It is possible to perform image formation with less and higher quality.

Although the invention made by the inventor has been specifically described based on the preferred embodiments, the invention is not limited to the above-described embodiment, and various modifications can be made without departing from the gist of the invention. It goes without saying that it is possible.

[0069]

According to the image forming apparatus of the present invention, the light amount of the laser light emitted from the laser light source is detected by the light amount monitoring element, and the laser light source is detected based on the detection result of the light amount monitoring element. Automatic light intensity adjustment of
When switching the emission light amount of the laser light source using a plurality of light amount setting resistors, when switching the emission light amount, the automatic light amount adjustment is performed in a hold mode for holding the light amount of the laser light source. It is possible to prevent the voltage value from becoming unstable, prevent the laser light source from being over-emitted and deteriorated, and improve the image quality of the formed image.

According to the image forming apparatus of the second aspect of the present invention, the emission light amount of the laser light source is switched according to the pixel density of the image to be formed. High quality image formation can be performed.

According to the image forming apparatus of the present invention, the capacitor for holding the drive current for driving the laser light source is charged / discharged based on the detection result of the light amount monitoring element, and the charge amount held by the capacitor Since the automatic light amount adjustment of the laser light source is performed based on, the size of the automatic light amount adjustment circuit can be reduced, and the number of parts can be reduced.
With a simple configuration, automatic light amount adjustment of the laser light source can be performed with high precision, and inexpensive, with little density fluctuation, and high quality image formation can be performed.

According to the image forming apparatus of the present invention, charging and discharging are performed based on the detection result of the light amount monitoring element.
The capacitor for automatically adjusting the light amount of the laser light source based on the amount of charge held is charged and discharged in accordance with the cycle of the synchronization detection signal output from the synchronization detection means, so that the automatic light amount adjustment circuit can be downsized. In addition, the number of parts can be reduced, the automatic light amount adjustment of the laser light source can be performed with higher accuracy with a simple configuration, and a higher quality image can be formed at low cost with less density fluctuation.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of a main part of a scanning optical system of an image forming apparatus to which an embodiment of the image forming apparatus of the present invention is applied.

FIG. 2 is a detailed circuit configuration diagram of a synchronization detection element unit in FIG. 1;

FIG. 3 is a waveform diagram of a synchronization detection signal output from a current detection unit in FIG. 2;

FIG. 4 is a circuit diagram of an APC circuit of the image forming apparatus of FIG. 1;

FIG. 5 is a circuit configuration diagram of an S / H signal control circuit incorporated in the APC circuit of FIG. 4;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 2 LD board 3 LD 4 Collimating lens 5 Polygon scanner 6 fθ lens 7 Photoreceptor 8 Synchronous detection element unit 10 Synchronous detection element 11 Comparator 20 APC circuit 21 PD 22 Switch circuit 23 Comparator 24 Switch circuit 25 Control circuit 26 Charging Constant current source 27 constant current source for discharge 28 switch circuit 29 error amplifier 30 S / H signal control circuit 31 edge change detection circuit 32 one-shot pulse generation circuit 33 OR circuit R1 resistor R2 resistor VR1, VR2 variable resistor SW1, SW2 Switch C1, C2 Capacitor Tr1 Transistor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04N 1/29

Claims (4)

[Claims] A laser beam modulated by image data is scanned from a laser light source onto a latent image carrier to form an electrostatic latent image on the latent image carrier, and an electrostatic latent image is formed on the latent image carrier. When developing the latent image with a developer to form an image, the light amount of the laser light emitted from the laser light source is detected by a light amount monitoring element, and the automatic light amount of the laser light source is detected based on the detection result of the light amount monitoring element. An image forming apparatus that performs adjustment and switches the emission light amount of the laser light source by using a plurality of light amount setting resistors, wherein the automatic light amount adjustment holds the light amount of the laser light source when the emission light amount is switched. An image forming apparatus, wherein a hold mode is set. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus switches the amount of light emitted from the laser light source according to a pixel density of the image to be formed. 3. The image forming apparatus charges and discharges a capacitor holding a drive current for driving the laser light source based on a detection result of the light amount monitoring element, and performs charging / discharging of the capacitor based on an amount of charge held by the capacitor. 3. The automatic light amount adjustment of a laser light source.
The image forming apparatus as described in the above. 4. The image forming apparatus is arranged and scanned on a scanning line of a laser beam from the laser light source to the latent image carrier and away from a latent image forming area of the latent image carrier. Synchronization detection means for receiving the laser light and outputting a synchronization detection signal, and charging and discharging the capacitor in accordance with the cycle of the synchronization detection signal output from the synchronization detection means. The image forming apparatus according to claim 3.