JP2002211032A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an imaging apparatus which can automatically control a quantity of light of a semiconductor laser appropriately by a simple constitution. SOLUTION: The imaging apparatus for imaging latent images to a photoreceptor by scanning a laser light automatically controls the quantity of light of the semiconductor laser (LD1) by sampling a monitor current by a light quantity-detecting element (PD) set to the vicinity of the semiconductor laser as a charging potential of a hold capacitor. A rise time of the potential of the hold capacitor at the sampling time and discharge characteristics of the hold capacitor at a hold mode time are detected by detecting a voltage V4 by an A/D converter (10), so that a capacity of the hold capacitor is selected from C1 and C2, and a control time for the automatic light quantity control is selected from APCTIME1 and APCTIME2. The imaging apparatus features the other two claims.

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 for forming an image by scanning a laser beam with a polygon scanner to charge a photosensitive member.

[0002]

2. Description of the Related Art As a prior art of the present invention, Japanese Patent Laid-Open No.
No. 88429. This publication discloses a technique for performing APC (Automatic Light Amount Control) using a photodiode (hereinafter, referred to as PD) current incorporated in a package of a semiconductor laser (eg, a laser diode, hereinafter, referred to as LD). LD optical output characteristics are sensitive to ambient temperature and self-heating, so LD optical output (light intensity)
Is constantly detected as the value of the PD current, and control is performed so as to keep the optical output constant. Note that, here, the PD current is charged and discharged via a resistor, and the PD current is measured by measuring the time during which the voltage across the capacitor is equal to or higher than a predetermined value with a clock having a predetermined frequency. I have. As described above, a method of performing APC using a PD current is already known.

[0003]

However, in the method of performing APC by performing charging and discharging of a capacitor as disclosed in Japanese Patent Application Laid-Open No. 8-88429, the capacity of the capacitor and the APC time are not considered. If the value is not appropriate, there is a problem that the LD light amount does not increase to an appropriate value and the LD light amount decreases with time. An object of the present invention is to solve the problems of the prior art as described above and to have a simple configuration.
An object of the present invention is to provide an image forming apparatus capable of increasing an LD light amount to an appropriate value and performing appropriate LD light amount control.

[0004]

According to a first aspect of the present invention, there is provided an image forming apparatus for forming a latent image on a photosensitive member by scanning a laser beam. In an image forming apparatus which performs automatic light amount control of the semiconductor laser by sampling a monitor current obtained by a light amount detection element provided near a laser as a charged potential of a hosed capacitor, a rise time of a hold capacitor potential at the time of sampling and // Hold in hold mode
The discharge characteristics of the hold capacitor are detected to select the hold capacitor capacity.

According to a second aspect of the present invention, there is provided an image forming apparatus for forming a latent image on a photosensitive member by scanning with a laser beam, the monitor comprising a light amount detecting element provided near a semiconductor laser. In an image forming apparatus which performs automatic light intensity control of the semiconductor laser by sampling a current as a charge potential of a hold capacitor, a rise time of a hold capacitor potential at the time of sampling and / or a hold time of a hold mode. The discharge characteristic of the capacitor is detected, and the automatic light control time or the hold capacitor capacity and the automatic light control time are selected. Also,
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the light amount is switched according to the pixel density.

[0006]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 shows a configuration diagram of an LD scanning optical system. As shown, the laser diode (L
D) 1, an LD control unit 2 for controlling the LD 1, a collimating lens 3, a polygon scanner 4, an fθ lens 5, a photoconductor 6, a synchronization detecting element 7, etc., and the LD light emitted from the LD 1 is a collimating lens. 3, the light becomes parallel light, is scanned by the polygon scanner 4, passes through the fθ lens 5,
A latent image is formed by exposing the photoconductor 6 to light. Further, a synchronization detection element (for example, a photo sensor) 7 provided at an end portion in the main scanning direction (line direction) detects a laser beam that has been scanned outside the latent image forming area, and thereby a start position (for example, each scanning). A synchronization detection signal for aligning the left end of the line) is generated.

FIG. 2 shows a circuit configuration of the synchronization detection signal generator. When the synchronous detection element 7 receives the LD light, a current I flows, and a voltage V1 is generated at the input 1 of the comparator 8. When V1 becomes larger than Vref, a pulse output (synchronization detection signal XDETP) is generated at the output of the comparator 8.

FIG. 4 shows a synchronization detection signal (XDETP). The cycle is the same as one line cycle T2. That is, a signal having the width T1 is generated once for each line.

FIG. 3 shows a block diagram of the control system of the present invention. Hereinafter, FIG. 3 will be described. P in LD package
The monitor current Im of D is switched by the IN1 signal and flows through a line connected to VR1 or a line connected to VR2. VR1 and VR2 are variable resistors for setting the amount of light. When connected to VR1, the potential of V2 becomes V2 = Im * VR
1 and connected to VR2, the potential of V2 becomes V2 = Im
* VR2.

Reference potentials Vref1, Vref of comparator 8
ref2 is switched by IN2 acting on SW2. By switching Vref1 and Vref2, LD
The amount of light can be switched. When V2 is smaller than V1, V3 becomes HIGH, SW4 is turned on, current is supplied to the capacitor C1 or C2, and the potential of V4 rises. When V2 is larger than V1, V3 becomes LO
It becomes W, SW5 is turned on, the electric charge of the capacitor C1 or C2 is discharged, and the potential of V4 falls.

Further, C1 and C2 are switched by the IN3 signal acting on SW3, and the control circuit is controlled by S /
Sampling and hold are switched by the H signal. When the S / H signal is LOW, HIGH and LO of V3
Either SW4 or SW5 is closed in response to W, but when the S / H signal is HIGH, both SW4 and SW5 are open and the potential of V4 is held (S / H).
Is sampling at L, hold mode at H). The potential of V4 is error-amplified with respect to the reference potential Vref3, so that the collector current of Tr1 increases and decreases.
The current increases or decreases, and the light amount of the LD is maintained at the set value. LD
When the light amount is smaller than the set light amount, the LD current increases and L
When the D light quantity is larger than the set light quantity, the LD current decreases.

A bias current IB flows through LD1 from a bias current source. The value of the bias current IB can be changed by changing the value of the fixed resistor R2. By flowing the bias current IB, the speed of LD modulation can be increased. XDATA is video data
When XDATA is LOW, LD1
(Collector current of tr1) + IB flows. XDATA
Is H, the current of the LD is only IB and only emits offset light.

When the APC is performed, the current of the LD is the sum of the collector current ISW of tr1 and the bias current IB. When the APC signal (S / H signal) is L, it is in the sampling mode, and when it is H, it is in the hold mode. The synchronization detection signal can be used as an APC signal. That is, APC can be performed in the sampling mode when the synchronization detection signal is L, and in the hold mode when the synchronization detection signal is H. The APC signal can be created in another configuration, and the APC signal can be selected.

If the value of the hold capacitor is too large,
Since it takes time to charge the capacitor in the sample mode, the potential of V4 does not rise to an appropriate value.
The amount of light does not increase to an appropriate amount. The present invention is an invention for preventing this.

In the present invention, in order to prevent this, V4
And the potential is detected by the A / D converter 10 as CP.
Send to U as digital data. The potential V4a of V4 is measured at a predetermined timing, and V4 after a predetermined time elapses with a timer.
Is measured, and the state of charge is determined from the difference. If the value of the hold capacitor is too large, it takes time to charge the capacitor.
4a does not reach the set potential. When V4b-V4a falls below the set potential, the hold capacitor is switched to C2 by switching the IN3 signal. Similarly,
When the potential of V4b-V4a is equal to or higher than the set potential, IN3
By switching the signal, the hold capacitor becomes C
Switch to 1.

C1 is larger than C2. When it takes time to raise the potential of V4, C2 having a small capacitance is selected, so that the LD light amount reaches an appropriate value quickly in the sample mode. If it does not take long time for the potential of V4 to rise, C1 having a large capacity is selected, so that a decrease in the amount of light in the hold mode can be reduced (because the capacity of the capacitor is large,
The discharge of the capacitor in the hold mode can be made slower).

In the hold mode, the potential V4a of V4 is measured. The potential V4 of V4 after a lapse of a predetermined time by a timer
b is measured, and when V4a-V4b is larger than the set potential, the amount of discharge of the hold capacitor at the time of holding is large, so that IN4 is set to L and the automatic light amount control time APCtim
e2 is selected. When V4a-V4b is smaller than the set potential, the discharge amount of the hold capacitor at the time of hold is small.
Select PCtime1.

The sampling time of APCtime2 is
It is set longer than the sampling time of APCtime1 (see FIG. 7). If the discharge amount of the hold capacitor is large, the hold capacitor potential does not rise to a required potential at the time of sampling unless the sampling time is set long, so that the current value of the LD does not increase to the required value. The light quantity may not increase to the required value.
Therefore, when V4a-V4b is larger than the set potential, the discharge amount of the hold capacitor at the time of holding is large. Therefore, IN4 is set to L, APCtime2 is selected, and when V4a-V4b is smaller than the set potential, ,
Since the discharge amount of the hold capacitor during holding is small,
NPC is set to H and APCtime1 is selected.
By making the APC time (sampling time + hold time) of time2 shorter than the APC time (sampling time + hold time) of APCtime1, the AP
The control to properly perform the C control is performed.

FIGS. 5 and 6 show the operation flow of this embodiment. When the S / H signal is H, both SW4 and SW5 are open, and the potential of V4 is held by C1 or C2. When the control circuit is in the hold mode, the input voltage V4 of the error amplifier is held by the capacitor C1 or C2. (SW4 and SW5 are both open.) When the capacitance value of the capacitor is large, the potential of V4 is held constant for a long time, and when the capacitance value is small,
The potential of V4 is held constant for a short time. However, when the capacitance value is small, there is an advantage that the time required for the potential of V4 to be charged to the set value is short. Depending on the pixel density, for example, a method of halving the linear velocity and halving the LD light amount may be performed. In such a case, SW1 is switched by the IN1 signal in accordance with the pixel density to set the light amount. VR1 and VR2 may be switched.

If the value of VR1 is twice as large as the value of VR2, for example, if the LD light quantity at a pixel density of 1200 dpi is reduced to half that at a pixel density of 600 dpi, 1200d
At pi, the IN1 signal is set to H, and the LD light amount setting V
If VR2 is selected for R, the amount of LD light becomes １ ／. By switching the IN2 signal, Vref1,
By switching 2, the LD light amount can also be switched. If Vref1 is set to の of Vref2, and if Vref1 is selected, the LD light amount is reduced to Vre1.
The amount of light can be reduced to half when f2 is selected.

[0021]

As described above, according to the present invention,
According to the first aspect of the present invention, when the light amount of the semiconductor laser is sampled as the charged potential of the hosed capacitor to perform the automatic light amount control of the semiconductor laser, the rise time of the hold capacitor potential at the time of sampling, and / or Since the discharge characteristics of the hold capacitor in the hold mode are detected and the capacitance of the hold capacitor is selected in accordance with the detection, the light quantity of the semiconductor laser is not detected small, and therefore the semiconductor laser is not detected. A decrease in the amount of laser light is prevented, and a high-quality image can be obtained.

According to the second aspect of the present invention, when performing automatic light amount control of the semiconductor laser by sampling the light amount of the semiconductor laser as the charge potential of the hold capacitor, the rise time of the hold capacitor potential at the time of sampling. And / or the discharge characteristic of the hold capacitor in the hold mode is detected, and the automatic light control time or the hold capacitor capacity and the automatic light control time are selected. The same effect as described above, or a higher effect can be obtained. According to the third aspect of the present invention, in the first aspect or the second aspect,
In the image forming apparatus described above, since the light amount is switched according to the pixel density, a high-quality image can be obtained even if the pixel density differs.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a main part of an image forming apparatus showing an embodiment of the present invention.

FIG. 2 is a circuit diagram of a main part of an image forming apparatus control system showing an embodiment of the present invention.

FIG. 3 is a block diagram of a main part of an image forming apparatus control system according to an embodiment of the present invention.

FIG. 4 is a timing chart of a main part of the image forming apparatus showing one embodiment of the present invention.

FIG. 5 is an operation flowchart of the main part of the image forming apparatus showing one embodiment of the present invention.

FIG. 6 is another operation flowchart of the main part of the image forming apparatus showing one embodiment of the present invention.

FIG. 7 is another timing chart of the main part of the image forming apparatus showing one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Semiconductor laser 4 Polygon scanner 6 Photoconductor 7 Synchronous detection element 8 Comparator 10 A / D converter

Claims (3)

[Claims] 1. An image forming apparatus for forming a latent image on a photosensitive member by scanning a laser beam, wherein a monitor current detected by a light amount detecting element provided near a semiconductor laser is charged to a charged potential of a hosed capacitor. In the image forming apparatus which performs automatic light amount control of the semiconductor laser by sampling as above, the rise time of the hold capacitor potential at the time of sampling and / or the discharge characteristic of the hold capacitor during the hold mode are detected. An image forming apparatus wherein the hold capacitor capacity is selected. 2. An image forming apparatus for forming a latent image on a photosensitive member by scanning a laser beam, wherein a monitor current detected by a light amount detecting element provided near a semiconductor laser is used as a charge potential of a hold capacitor. In an image forming apparatus for performing automatic light amount control of the semiconductor laser by sampling, a rise time of a hold capacitor potential at the time of sampling and / or a discharge characteristic of the hold capacitor at a hold mode are detected. Automatic light control time or
An image forming apparatus configured to select a capacitor and an automatic light amount control time. 3. The image forming apparatus according to claim 1, wherein a light amount is switched according to a pixel density.