JPH10170844A - Light beam output controller - Google Patents

Abstract

PROBLEM TO BE SOLVED: To almost equalize the power of (n) lines of light beams on a photoreceptor surface only by inputting only one set value of target output of a light beam to the light beam controller of an image forming device having a beams scanning system using the (n) lines of light beams. SOLUTION: This light beam output controller is equipped with optical detecting means 14 and 15, which detect light output of light beams, a command setting means 10, which sets the command of light output, and control means 16 and 17, which compare the output signals from the optical detecting means 14 and 15 with a reference signal Vref outputted and controls the light output intensity of the light beams according to the comparison output for the (n) lines of light beams respectively. The command setting means 10 is equipped with a setting-changeable reference signal correction value setting means 14 for each of the 2nd and succeeding light beam and uses a reference signal V'ref generated by operating the 1st reference signal with a reference signal correction value corresponding to each light beam as the reference signal for the 2nd and succeeding light beams.

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 such as a laser beam printer, a digital copier, a facsimile, etc., and more particularly to an image forming apparatus using a multi-beam scanning optical system having a plurality of semiconductor lasers. The present invention relates to a light beam output control device of a forming apparatus.

[0002]

2. Description of the Related Art In an apparatus for forming an image by using a semiconductor laser, for example, a semiconductor laser beam printer, a light beam from a semiconductor laser (hereinafter, referred to as a light beam) modulated by an image signal.
(Laser beam) is radiated onto the photoreceptor via a polygon mirror, an imaging lens, etc., and scans the photoreceptor to form an image. In a conventional semiconductor laser beam printer, an image is formed using a single light source. Therefore, when high speed is required in such a printer, it is necessary to further increase the rotation speed of the polygon motor for rotating the polygon mirror or the frequency of the image signal. However, there is a limit to increasing the rotation speed of the polygon motor and the frequency of the image signal, and the processing cannot always be performed at a desired processing speed.

Therefore, a multi-laser beam printer having a plurality of semiconductor laser light sources has been proposed. In this multi-laser beam method, since recording is performed by scanning a plurality of laser beams, the amount of information that can be recorded simultaneously increases, and the number of rotations of the polygon motor and the frequency of the image signal can be reduced, thereby achieving stable operation. Images can be processed at high speed. An apparatus for forming an image by scanning a plurality of laser beams is disclosed in JP-B-63-4243.
There is a recording device and the like described in Japanese Patent Publication No. 2 (JP-A) No. 2 (1994).

[0004]

[Problems to be Solved by the Invention] JP-B-63-4243
In the case of the recording apparatus described in Japanese Patent Laid-Open Publication No. 2000-209, the embodiment is a multi-laser light source having two laser light sources, in which the light output from each laser light source is controlled in order for one reference signal. However, in general, in a semiconductor laser array in which a plurality of semiconductor lasers are mounted on one chip, the number of light receiving elements is often one, and the optical output of each laser cannot be controlled in real time. Is difficult to achieve accurate light output control due to the influence of the laser light emitting part (due to light leakage, heat generation, etc.), it is difficult to suppress the variation of the interval between the light emitting parts, As shown in FIG. 4, a multi-beam scanning optical system configured by using a plurality of independent optical systems with a single laser diode has a problem in that Superior advantage If there is a.

The configuration of the multi-beam scanning optical system shown in FIG. 4 will be briefly described. Reference numerals 100 and 101 in the figure denote semiconductor lasers each having a single laser light source. Laser beams emitted from each of the semiconductor lasers 100 and 101 are collimated by collimating lenses 200 and 201, respectively. The two laser beams are combined as a scanning beam having a predetermined pitch. These laser beams are deflected and scanned by the rotation of the polygon mirror 400, condensed by the imaging lens 500, and fθ
After the correction, the beam is exposed and scanned as two beams on the drum-shaped photoconductor 600 or the like.

In general, the interval between two laser beams that scan the photoconductor 600 must be about the resolution of an output image. However, for reasons such as the package size of the semiconductor lasers 100 and 101, reference numerals in the figure are used. A beam combining prism (not limited to a prism) as shown by 300 is always required. Here, the beam powers of the two laser beams that scan on the photoconductor 600 need to be substantially the same, but when the laser beams are combined using an optical element such as the prism 300, the respective optical paths of Since the light transmission efficiency is different, it is necessary to set the light output of the two semiconductor lasers 100 and 101 to different target values in consideration of the light transmission efficiency. This means that two semiconductor lasers 100,
This is because if the light output of the laser beam 101 is set to the same target value, a difference occurs in the beam power of the two laser beams on the photoconductor due to a difference in light transmission efficiency.

As a method of controlling the light output of the laser beam, for example, the light output of the laser beam emitted from the rear of the semiconductor laser is detected by the light detecting means, and the output signal from the light detecting means is compared with the target value by the comparing means. There is a method in which the output intensity of the semiconductor laser is controlled by the control means in accordance with the comparison output from the comparison means. In this case, as described above, there is a problem that a value serving as a target value of the optical output must be set separately for each semiconductor laser.

On the other hand, a laser beam printer generally adopts an image stabilization method of detecting conditions of an image forming process and changing and setting a beam power based on the detection result. If the above-described two-beam multi-beam scanning optical system is applied to this image forming system, as described above, the target value of the light output of each of the two semiconductor lasers must be independently set and controlled. If each target value is reset every time the power is changed and set, the control becomes very complicated. In addition, this is not limited to two beams, and is more difficult in a multi-beam scanning optical system having more laser beams. For example, in a case where n laser beams are provided, the number of n laser beams is increased. Each target value must be set, and the control becomes very complicated and complicated.

The present invention has been made in view of the above circumstances, and in order to solve the above-described problem, a multi-beam scanning optical system using n (n is a natural number of 2 or more) light beams is provided. An object of the present invention is to provide a light beam output control device capable of inputting one set value of a target output of a light beam so that the beam powers of the n light beams can be made substantially the same on the photosensitive member surface. .

[0010]

In order to achieve the above object, the present invention provides a method of scanning a latent image by scanning an image carrier made of a photosensitive member with light beams from n light sources (n is a natural number of 2 or more). An image is formed, the latent image is visualized with a developer, and the visible image is transferred and fixed to a transfer material to obtain an image. Light detection means for detecting an output, target value setting means for setting a target value of light output, and comparison means for comparing an output signal from the light detection means with a reference signal output from the target value setting means. And a control unit for controlling the intensity of the light output of the light beam according to the comparison output from the comparison unit, for each of the n light beams. The target value setting means includes, for each light beam, a reference signal correction value setting means variably set for the second and subsequent light beams. 1
A configuration is used in which a reference signal correction value corresponding to each light beam is calculated as the reference signal of the light beam.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described in detail based on illustrated embodiments. FIG. 1 is a diagram showing an embodiment of the present invention, and is a block diagram showing an example of the configuration of a multi-beam scanning optical system and a light beam output control device of a laser beam printer. This configuration example uses two semiconductor lasers 1 and 2.

In FIG. 1, light beams (hereinafter, laser beams) emitted from first and second semiconductor lasers 1 and 2 are shown.
Are collimated by first and second collimating lenses 3 and 4, respectively, are combined by a beam combining element (for example, a prism) 5, and then are incident on an optical scanning device 6 composed of a rotating polygon mirror at a predetermined beam interval. The beam is deflected and scanned. Then, an image is formed on a charged surface of a drum-shaped photoconductor 8 as an image carrier by an imaging lens 7 such as an fθ lens. While the imaged spot is modulated according to the image signal, it repeatedly moves in the main scanning direction indicated by the arrow x in the figure according to the rotation of the optical scanning device 7, and at the same time, the photoconductor 8 rotates and performs sub-scanning. Thereby, an electrostatic latent image is formed on the photoconductor 8. The electrostatic latent image on the photoreceptor 8 is visualized with a developer by a developing unit (not shown), and the visible image is transferred to a transfer material such as transfer paper by a transferring unit (not shown). The image on the transfer material is fixed by the fixing unit.

In FIG. 1, reference numeral 9 denotes a photodetector for synchronization detection. This photodetector 9 is provided outside the image data writing area in the axial direction of the photoconductor 8, and The deflection-scanned laser beams are sequentially detected, and a synchronization signal (a line synchronization signal LSYN) of each laser beam is detected.
C). Further, the signal processing circuit 11 applies a signal to the first and second laser driving circuits 12 and 13 based on the image signal (image data), and generates the synchronization signal L
The first and second semiconductor lasers 1 and 2 are modulated so as to expose from a predetermined position on the photoconductor 8 in synchronization with SYNC.

By the way, unless the beam powers of the two laser beams for exposing and scanning the photosensitive member 8 are controlled to be substantially equal, an image will be uneven. The intensity of the light output of the first and second semiconductor lasers 1 and 2 is controlled by first and second control circuits (output control circuits) 16 and 17, respectively, but there is a difference between the optical paths of the two laser beams. (Mainly due to the beam combining element (for example, prism) 5),
In order to make the beam powers of the two laser beams substantially equal, each light output needs to be controlled to a target value in consideration of a difference in light transmission efficiency caused by an optical path difference.

As a method of controlling the light output of the laser beam, the rear side (not necessarily the rear side) of each of the first and second semiconductor lasers 1 and 2 corresponds to each of the semiconductor lasers 1 and 2.
And photodetectors 14 and 15 for detecting the optical output of the laser beam emitted to the laser beam (for example, providing a photodiode in a semiconductor laser package), and setting a target value for the optical output of the laser beam. From the means 10, the first
When the reference signal Vref corresponding to the target value of the optical output of the semiconductor laser 1 is supplied to the first control circuit 16, the photodetector 14
Output of the laser beam and the reference signal V
ref is compared with comparison means in the first control circuit 16,
The first control circuit 16 instructs the laser drive circuit 12 of an error between the detected value and the target value, and controls the intensity of the light output from the semiconductor laser 1 to be constant. Therefore, in this case, the photodetector 1
The power is controlled so that the detected value from No. 4 substantially matches the target value (reference signal Vref). The configuration of the control circuit 16 and the specific control operation of the light output will be described later.

On the other hand, when the light output from the second semiconductor laser 2 is controlled using the same reference signal Vref as the first semiconductor laser 1 as the target value, the difference in the optical path (mainly due to the beam combining element (for example, prism) 5). Do), for example, 1 /
Since the power is controlled to be different by α times (the difference between the transmission efficiencies of the first and second optical paths is 1 / α times), the target value setting means of the second semiconductor laser 2 uses A reference signal correction value setting means 18 for correcting the reference signal Vref from the setting means 10 is provided, and the reference signal Vre is multiplied by a coefficient α preset by the reference signal correction value setting means 18.
f is corrected, and V′ref = Vref · α is set as a new target value (a reference signal of the optical output of the second semiconductor laser). That is, V′ref is used as a reference signal corresponding to the new target value, and the second control circuit 17 uses the photodetector 15
Comparing the laser power detected by V'ref with V'ref,
By instructing the laser drive circuit 1 of the error and controlling the intensity of the light output from the second semiconductor laser 2 to be constant,
The beam power of the second laser beam on the photoreceptor 9 can be made substantially equal to the beam power of the first laser beam.

As a specific example of the reference signal correction value setting means 218, assuming that the difference in light transmission efficiency due to the optical path difference between the first and second laser beams is 1 / α times, the target of the first laser power is The target value of the second laser power with respect to the value Vref may be V'ref = Vref · α, so that a general multiplication circuit may be employed. If the value α is measured once at the time of adjustment at the factory and set, it can be set to a constant value unless the optical component is replaced.

As shown in FIG. 3, when the optical outputs of the first and second semiconductor lasers 1 and 2 are controlled at the same target value Vref, the beam power P on the photoconductor 8 becomes equal to the first laser beam. A power difference of ΔP occurs between the laser beam and the second laser beam. Therefore, as described above, by setting V′ref = Vref · α as the target value of the second semiconductor laser 2, the beam powers of the first and second laser beams on the photoconductor 8 are matched. be able to. Further, the target value V of the optical output of the first semiconductor laser 1 is changed by changing the setting of the image forming condition or the like.
When the ref is changed, the reference signal correction value setting means 21
8 is increased by α times the second semiconductor laser 2
(V′ref = Vref · α), the beam powers of the two laser beams on the photoreceptor 8 can always be matched.

Next, first and second control circuits (output control circuits) 16, 1 for controlling the optical output of each of the semiconductor lasers 1, 2
7 shows an example of the specific configuration and the optical output control operation. However, the configuration and the optical output control operation of the first and second control circuits 16 and 17 are exactly the same, and the input control target value is Since they are only different, the following description is common. FIG. 2 is a block diagram showing a configuration example of the control circuit.

In FIG. 2, first, a control circuit 16 (1) is provided from a main body side controller (not shown) of a laser beam printer or the like.
The timing signal T ₁ of the order to start the output control operation 7) is input, the output signal JK flip-flop 26 is cleared to allow the counting operation of the up-down counter 27 by the L level. The output signal of the comparator 22 as the comparing means is latched by the D flip-flop 23 by the clock signal from the oscillator 28, and the output signal of the D flip-flop 23 is added to the up / down counter 27 as a counting mode signal. And D flip-flop 2
At 4, it is latched by the clock signal from the oscillator 28. The non-inverted output of the D flip-flop 23 and the inverted output of the D flip-flop 24 are input to a NOR circuit 25,
The JK flip-flop 26 is set by the output signal of the NOR circuit 25.

An output proportional to the light output of the laser beam detected by the light receiving element (photodiode or the like) 14a of the photodetector 14 (15) and amplified by the amplifier 14b is output by the comparator 22 to target value setting means (reference signal). The signal is compared with the reference signal Vref (V'ref) from the correction value setting means), and a high-level or low-level signal is output from the comparator 22 according to the comparison result. For example, when the output of the comparator 22 is at a high level (that is, the optical output of the semiconductor laser 1 (2) is larger than the reference signal Vref (V'ref)), the timing signal T
_When the count operation of the up / down counter 27 is permitted by ₁ , the up / down counter 27 operates as a down counter by the high level output of the D flip-flop 23. Then, the output of the up / down counter 27 is converted into an analog output by the digital / analog converter 29, and the drive current from the laser drive circuit 12 (13) to the semiconductor laser 1 (2) changes according to the output. Therefore, in this case, the drive current of the semiconductor laser 1 decreases,
The output voltage from the amplifier 14b of the photodetector 14 (15) decreases. Then, when the output of the comparator 22 is inverted from the high level to the low level, the output of the D flip-flop 23 goes low, the output of the NOR circuit 15 goes high, and the JK flip-flop 26 is set and up-down. The counting operation of the counter 27 is prohibited.

On the other hand, when the output of the comparator 22 is low (that is, the optical output of the semiconductor laser 1 (2) is the reference signal Vref).
In the case of (smaller than V'ref), when the count operation of the up / down counter 27 is permitted by the timing signal T ₁ , the up / down counter 27 operates as an up counter by the low level output of the D flip-flop 23. Then, the output of the up / down counter 27 is converted into an analog output by the digital / analog converter 29, and the current from the laser drive circuit 12 (13) to the semiconductor laser 1 (2) changes according to the output. Therefore, in this case, the drive current of the semiconductor laser 1 (2) increases, and the output voltage from the amplifier 14b of the photodetector 14 (15) increases. Then, when the output of the comparator 22 is inverted from a low level to a high level, the output of the D flip-flop 23 goes high. Thus, the up / down counter 27 operates as a down counter. At this time, the output of the NOR circuit 25 remains low, the JK flip-flop 26 is not reset, and the up / down counter 27
, The counting operation is still permitted. That is, when the light output of the semiconductor laser 1 (2) increases and exceeds the reference signal Vref (V'ref), the up / down counter 27 does not inhibit the count operation, and the light output of the semiconductor laser 1 (2) is reduced. The count operation is prohibited only when the voltage decreases and exceeds the reference voltage Vref (V'ref). Therefore, the holding current of the semiconductor laser 1 (2) is always constant.

Contrary to the above example, when the light output of the semiconductor laser 1 (2) decreases and exceeds the reference signal Vref (V'ref), the up / down counter 27 does not disable the count operation. Alternatively, the semiconductor laser 1 (2) may be set so that the count operation is prohibited when the optical output of the semiconductor laser 1 (2) increases and exceeds the reference signal Vref (V'ref).
Is always kept constant.

That is, a portion surrounded by a frame 21 in FIG. 2 detects a transition of the output from the comparator 22,
This corresponds to an edge detection circuit that permits or inhibits the counting operation of the up / down counter 27. Then, as described above, the optical output from the semiconductor laser 1 (2) is adjusted so that the output voltage from the amplifier 14b of the photodetector 14 (15) becomes a constant value with reference to the reference signal Vref (V'ref). Control (light output is always kept at a constant value).

The configuration of the control circuit and an example of the control operation have been described above. However, the configuration of the control circuit is not limited to FIG. 2 and various configurations are conceivable. For example, the control circuits 16 and 17 shown in FIG. 1 can be configured by an analog circuit including a comparator and a sample and hold circuit. That is, the laser beams emitted from the semiconductor lasers 1 and 2 are received by the photodetectors 14 and 15, and the detection signals are sent to the reference signal Vre by comparators in the control circuits 16 and 17.
f, V′ref, and an error signal is output as the comparison result. A sample and hold circuit as control means in the control circuits 16 and 17 holds the error signal from the comparator and outputs it to the laser drive circuits 12 and 13. The laser drive circuit 26 increases or decreases a current value applied to the semiconductor lasers 1 and 2 in accordance with a signal from the sample and hold circuit to make the light intensity constant.

As described above, the multi-beam scanning optical system and the light beam output control device of the laser beam printer using two semiconductor lasers have been described as the embodiments of the present invention, but three or more n semiconductor lasers are used. A multi-beam scanning optical system can be implemented in the same manner. In that case, a photodetector, a control circuit, and a laser drive circuit are provided for each semiconductor laser, and the second laser is used as target value setting means. For the laser beams subsequent to the first laser beam, a reference signal correction value setting means variably set is provided for each beam, and the reference signal Vref of the first laser beam is used as a reference signal for the second and subsequent laser beams. The reference signals V′ref, V ″ ref,... Obtained by calculating the reference signal correction values α, β,. Thus, the beam powers of the n laser beams on the photoconductor can always be kept the same.

[0027]

As described above, according to the present invention,
In a multi-beam scanning optical system provided with n (n is a natural number of 2 or more) semiconductor lasers, light transmission by a difference in optical paths through which n light beams pass only by giving a target value Vref of one light output. Since the difference in efficiency can be corrected by the reference signal correction setting unit, the light output can be appropriately controlled by each control unit, and the beam power of each laser beam on the photoconductor can be controlled to be substantially the same. The laser power can be easily set and changed during process control, density control, or when changing the printer output speed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an embodiment of the present invention, and is a block diagram illustrating an example of a configuration of a multi-beam scanning optical system and a light beam output control device of a laser beam printer.

FIG. 2 is a block diagram showing an example of a configuration of a control circuit of the light beam output control device shown in FIG.

FIG. 3 is a diagram illustrating a relationship between a beam power on a photoconductor and a control target value of a light output.

FIG. 4 is a diagram showing an example of a configuration of a conventional multi-beam scanning optical system.

[Explanation of symbols]

 1, 2: semiconductor laser 3, 4: collimating lens 5: beam combining element (for example, prism) 6: optical scanning device (rotating polygon mirror, etc.) 7: imaging lens (fθ lens, etc.) 8: photoconductor (image carrier) 9: photodetector for synchronization detection 10: target value setting means 11: signal processing circuit 12, 13: laser drive circuit 14, 15: photodetector for laser power detection 16, 17: control circuit 18: reference signal Correction value setting means 22: Comparator

Continued on the front page (51) Int.Cl. ⁶ Identification code FI H04N 1/113 H04N 1/04 104A

Claims (1)

[Claims] 1. A latent image is formed by scanning an image carrier made of a photosensitive member with light beams from n light sources (n is a natural number of 2 or more), and the latent image is formed into a visible image with a developer. A light beam output control device of an image forming apparatus for obtaining an image by transferring and fixing the visible image to a transfer material, wherein: a light detection means for detecting a light output of each light beam; and a target value of the light output. Target value setting means to be set; comparison means for comparing an output signal from the light detection means with a reference signal output from the target value setting means; and a light beam of the light beam according to a comparison output from the comparison means. Control means for controlling the intensity of the light output are provided for each of the n light beams,
The target value setting means includes: for the second and subsequent light beams,
A variable reference signal correction value setting means is provided for each light beam, and reference signal correction corresponding to each light beam is used as a reference signal of the first light beam as a reference signal of the second and subsequent light beams. A light beam output control device using a value calculated.