JP2002090671A - Light beam scanner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multi-beam scanner which can accurately detect the positions of individual beams, even when the light quantity of the beams made incident on a single optical sensor are mutually different and generate an accurate horizontal synchronizing signal which have no shift in the scanning or the writing position. SOLUTION: The signals of a plurality of light beams, detected by an optical sensor 21, are compared with at least two reference voltages, and obtained output signals are selectively used to obtain one horizontal synchronizing signal which has no shift in the interval of detection time of the horizontal synchronizing signal between the preceding and following light beams.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a light beam scanning device for forming an image using a plurality of light beams, and more particularly, to a light beam scanning device capable of accurately detecting the position of each light beam. About.

[0002]

2. Description of the Related Art In recent years, an image forming apparatus using a light beam, such as a laser printer, a copying machine, and a facsimile machine, has been rapidly improving image quality and resolution.
To cope with this, for example, Japanese Patent Laid-Open No. 10-1610
Japanese Patent Application Laid-Open No. 49-49493 discloses a technology that enables APC (Automatic Power Control) of a plurality of light beams by using only one light receiving unit. Each technique is disclosed in which an error due to a delay time between a plurality of beams is eliminated by adjusting a distance between the beams to reduce jitter.

FIG. 2 is a diagram showing a horizontal synchronizing signal generator, that is, a horizontal synchronizing signal generating circuit in a conventional image forming apparatus. Optical sensor 21, comparator 22, and resistors 23, 24
The comparator 22 compares the reference voltage Va set by the resistors 23 and 24 with the output of the optical sensor, thereby outputting a horizontal synchronizing signal. That is, when the optical sensor 21 receives the laser light, it photoelectrically converts the light and generates a pulsed light detection signal. This light detection signal is input to the non-inverting terminal of the comparator 22 while the resistor 2
3 and the reference voltage set by the resistor 24
2 is input to the inverting terminal. This voltage comparison type comparator 2
2 outputs a horizontal synchronizing signal. As described above, the conventional image forming apparatus adjusts the light amount before detecting the horizontal synchronization signal, emits light with the adjusted light emission amount when the horizontal synchronization signal is detected, and compares the light detection with one reference voltage. Detection is being performed.

[0004]

However, when an image is formed using a plurality of light beams, in the above-described conventional example, the position of the light beam cannot be detected correctly, and the position on the surface to be scanned cannot be detected. A temporal shift has occurred in the writing start position, causing image deterioration. There were various factors, such as:

First, there is a difference in the amount of light incident on the optical sensor due to a change in the amount of laser emission. Ideally, the amount of laser emission is rectangular from the start of laser emission to the end of emission, but the actual amount of emission is called overshoot or droop characteristic of light that occurs at the start of laser emission, as shown in FIG. It is not constant due to light quantity fluctuation (a phenomenon that changes with time). Variations in laser elements also affect the amount of laser emission. Due to such a variation in the amount of laser light emission, if the time from the start of laser light emission to the incidence on the optical sensor is different, such as ta, tb, and tc, even if the light amount setting of a plurality of lasers is the same, In some cases, the amount of light incident on the sensor differs as Vsa, Vsb, and Vsc, and the position of the light beam cannot be correctly detected.

The difference in the amount of light incident on the optical sensor due to the difference in the angle of the polygon is also a factor. When scanning with a plurality of lasers shifted in the main scanning direction on the surface to be scanned, if the position of the light beam is detected by the same optical sensor, the angle of the polygon differs depending on the light beam. A difference occurs in the optical path and the state of reflection of the light, and the amount of light incident on the optical sensor changes. In particular, the first light beam and the second light beam
There is a case where a difference in the light amount tends to occur between the light beam after the light beam and the light beam after the light beam.

[0007] Differences in response characteristics of the sensor, which occur when a plurality of light beams having different wavelengths and characteristics are used, have also become obstacles to correct position detection of the light beams. FIG. 3 is a diagram showing a detection position shift that occurs when a light beam having a light amount difference is detected with one reference voltage. Light beams having different light amount settings enter a slit for position detection, and the position is determined. An example of the output of the optical sensor when the light is turned off after detection is shown. Since the output of the optical sensor differs in proportion to the amount of incident light, if the detection of the position of the light beam is performed with one reference voltage, the position of detection of the light beam is changed to position B according to the magnitude of the amount of light.
a and Bb, and the time interval T
A shift of z is generated. Such a shift of the light beam detection position occurs not only between light beams having different light amounts but also between light beams having different laser wavelengths. Such a shift in the light beam detection position causes a shift in the timing of detecting the horizontal synchronizing signal among the plurality of light beams, which leads to a shift in the writing start position on the surface to be scanned, thereby causing image deterioration. .

FIG. 4 is a diagram showing a shift in light beam detection time that occurs when two light beams A and B having different amounts of light, wavelengths, and the like enter the optical sensor. After the detection of the horizontal synchronizing signal BD-A by the preceding light beam A and the detection of the horizontal synchronizing signal BD-B by the succeeding light beam B, the time interval Ta should originally be generated. The following light beam B may be detected by the optical sensor prior to the original timing due to a difference in the wavelength characteristic of the sensor or the like. Then, the time interval between the horizontal synchronizing signal BD-A by the preceding light beam A and the horizontal synchronizing signal BD-B by the following light beam B becomes a time interval Ta 'different from the original time interval. In other words, the detection timing of the horizontal synchronizing signal is shifted by | Ta−Ta ′ |. The deviation of the detection timing of the horizontal synchronizing signal causes a deviation of the writing start position on the scanned surface, which is a factor of causing image deterioration.

The present invention has been made in view of such a problem, and an object thereof is to provide a case where the light amount of a light beam incident on a single optical sensor is different among a plurality of light beams. Another object of the present invention is to provide a light beam scanning device which accurately detects the position of each light beam and generates an accurate horizontal synchronizing signal without any deviation in the scanning and writing positions.

[0010]

According to a first aspect of the present invention, there is provided an apparatus for rotating a polygonal surface by using light beams from a plurality of laser light sources having light emission driving means and light amount adjustment means. In a light beam scanning device for scanning a rotating photosensitive body via a mirror, one optical sensor having at least two or more reference voltages for each of the plurality of laser light sources and detecting a scanning start position of each of the light beams And a horizontal synchronizing signal generating means for comparing the signal of each of the light beams detected by the optical sensor with the reference voltage and outputting the same as a horizontal synchronizing signal.

The invention according to claim 2 is characterized in that the horizontal synchronizing signal generating means includes reference voltage switching means for switching the reference voltage for each of the laser light sources.

The invention according to claim 3 is characterized in that the horizontal synchronizing signal generating means includes reference voltage control means for controlling the reference voltage for each of the laser light sources.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing a basic configuration of a multiple-beam scanning device of the present invention and a control block thereof. The semiconductor laser 7 has two light emitting sources,
Based on the light emission signal, a light beam modulated according to the image signal is emitted from a laser drive circuit (not shown) of the laser drive unit 11. The light beam emitted from the semiconductor laser 7 is
The light is collimated by a collimator lens (not shown), passes through a cylindrical lens 8, and enters the rotary polygon mirror 1.
The semiconductor laser 7 reflected by the rotating polygon mirror 1 is deflected by the rotation of the rotating polygon mirror 1 whose driving speed is controlled by a motor drive circuit (not shown) of the motor drive control unit 10 and is deflected.
The light passes through the fθ lens 3 composed of one or a plurality of lenses, is reflected by the reflection mirror 5, is irradiated on the photoreceptor 6, and performs main scanning.

A multiple scanning control device (hereinafter, referred to as a "controller") 12 for controlling these components includes a timer (not shown) and a read-only memory (hereinafter, referred to as a "ROM") storing a control program of the present embodiment. ), A microcomputer (hereinafter referred to as “MPU”) 13 including a random access memory (hereinafter referred to as “RAM”: not shown), a nonvolatile memory (not shown), and various input / output control devices (see FIG. (Not shown).

The light beam emitted from the semiconductor laser 7 is shifted by a predetermined distance in the sub-scanning direction of the photoconductor 6. Further, the light beam is set so as to be incident on the rotary polygon mirror 1 in a state shifted by the angle θ, so that the spot of the light beam on the surface to be scanned of the photoconductor 6 is separated by fθ = ΔA in the main scanning direction. Will be shifted. At the starting side of the semiconductor laser 7 in the main scanning direction, a photodetector 4 using a photodetector as a light receiving element is provided. Two light beams reflected by the rotary polygon mirror 1 are used for scanning in the main scanning direction. Prior to this, the light detecting element 4 sequentially detects the signals and outputs them as timing signals indicating the reference positions of the two spots. With this signal, the writing positions of the two spots in the main scanning direction are synchronized.

Although the semiconductor laser 7 in this embodiment has two laser emission sources for emitting two light beams, two or more laser emission sources for emitting two or more light beams are provided. A source may be provided.

FIG. 5 is a diagram showing a first embodiment of a horizontal synchronizing signal generation circuit in the multiple beam scanning device shown in FIG. In the first embodiment, a comparator 51 and resistors 52 and 53 are added to the conventional horizontal synchronizing signal generating circuit shown in FIG. 2, and two types of reference voltages are provided for each of two laser light emitting sources. . Here, the resistors 52 and 53 generate a reference voltage Vb that satisfies Vb ≠ Va. The reference voltage Vb is determined by the light amount ratio or output ratio of the light beam A and the light beam B incident on the optical sensor. It is assumed that the voltages are set to the same ratio.

FIG. 6 is a diagram showing output signals in the first embodiment of the horizontal synchronizing signal generation circuit shown in FIG. Two output signals BDa and BDb are obtained from the light beam A and the light beam B by two kinds of reference voltages of the horizontal synchronizing signal generation circuit of the first embodiment. When these two signals are selectively used in a method as shown in FIG.
It is possible to obtain one horizontal synchronizing signal in which the detection time interval of the horizontal synchronizing signal between the preceding light beam and the following light beam is the original timing Ta. As described above, even when the detection position in the optical sensor differs with only one reference voltage due to a difference in light amount or wavelength characteristics, two output signals output using two types of reference voltages are selectively used. As a result, it is possible to obtain one horizontal synchronization signal without a temporal shift in the write start position of the preceding light beam and the following light beam on the surface to be scanned, and it is possible to generate a high quality image. Become.

FIG. 7 shows a first embodiment of the horizontal synchronizing signal generating circuit shown in FIG. 6 with a BD selecting circuit added as means for selecting a horizontal synchronizing signal. This BD selection circuit selects a signal portion required for obtaining a horizontal synchronization signal from BDb of two output signals BDa using two types of reference voltages, and generates a BD selection signal for synthesizing one horizontal synchronization signal. It includes AND circuits 71 and 72, an inverter 73, and an OR circuit 74. By using this BD selection signal, after the light sensor of the light beam A is output and before the light beam B is incident on the light sensor, the signal level can be switched to selectively synthesize the output signals BDa and BDb. It is possible to generate an accurate horizontal synchronization signal BD at the detection position as shown by.

The BD selection signal is a B signal as shown in FIG.
A retriggerable multivibrator and a counter circuit, such that the level is switched after a predetermined time triggered by the light sensor output by the light beam A and reset by the light sensor output by the light beam B, as well as by the D selection circuit; It can also be generated by a circuit.

FIG. 9 is a diagram showing a second embodiment of the horizontal synchronizing signal generation circuit. In this embodiment, a reference voltage switching circuit including a resistor 91 and a transistor 92 is added to the conventional horizontal synchronization signal generation circuit shown in FIG. That is, in FIG. 9, the voltage input to the (−) terminal of the comparator 22 is switched between when the reference voltage switching signal is on and when it is off. By switching the reference voltage signal from on to off at a timing after the light sensor output of the light beam A and before the light beam B is incident, the reference voltage switching signal generated from this reference voltage switching circuit is A signal can be output with a reference voltage according to the properties of the beam A and the light beam B. As a result, it is possible to generate an accurate horizontal synchronizing signal BD at the detection position, as shown in FIG. 8, in which the detection time interval between the preceding light beam and the following light beam is the original timing Ta.

FIG. 10 is a diagram showing a third embodiment of the horizontal synchronizing signal generation circuit. In this embodiment, the reference voltage switching circuit in the horizontal synchronizing signal generation circuit of the second embodiment is replaced with a reference voltage control circuit. The reference voltage control circuit includes, for example, a D / A converter, and outputs a reference voltage previously controlled for the preceding optical sensor to the comparator 22 based on a signal from a control device such as the MPU 13 in the controller 12. Thus, as in the second embodiment, the voltage input to the (-) terminal of the comparator 22 is switched between when the preceding light beam is received and when the following light beam is received. This reference voltage is MPU
It is determined by the output ratio of the optical sensor input to the 12 A / D ports. The reference voltage control circuit converts the reference voltage input to the comparator 22 into a reference voltage for the preceding light beam A at a timing after the light sensor output of the light beam A and before the light beam B is incident. By switching from Va to the reference voltage Vb for the succeeding light beam B, the light beam B is detected by the optical sensor at the original timing. As a result, it is possible to generate an accurate horizontal synchronizing signal BD at the detection position, as shown in FIG. 8, in which the detection time interval between the preceding light beam and the following light beam is the original timing Ta.

[0023]

As described above, according to the present invention, the light for scanning the rotary photosensitive member via the rotary polygon mirror by the light beams from the plurality of laser light sources provided with the light emission driving means and the light quantity adjusting means. In the beam scanning device, each of the plurality of laser light sources has at least two or more reference voltages, and one optical sensor for detecting a scanning start position of each of the light beams, and each of the optical sensors detected by the optical sensor. By including a horizontal synchronization signal generating means for comparing the signal of the light beam with the reference voltage and outputting it as a horizontal synchronization signal,
Even if the amount of light beam incident on a single optical sensor is different between multiple light beams, the position of each light beam is accurately detected, and a precise horizontal synchronization signal with no deviation in the scanning and writing positions Can be provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing a basic configuration of the present invention and a control block thereof.

FIG. 2 is a diagram illustrating a conventional example of a horizontal synchronization signal generation unit in a conventional image forming apparatus.

FIG. 3 is a diagram illustrating a deviation of a detection position when detecting a plurality of beams having a light amount difference with one reference voltage.

FIG. 4 is an example showing deviation of detection positions when detecting a plurality of beams having different amounts of light, wavelengths, and the like.

FIG. 5 is a diagram showing a first embodiment of a horizontal synchronization signal generation circuit.

FIG. 6 is a diagram showing output signals in the first embodiment of the horizontal synchronizing signal generation circuit.

FIG. 7 is a diagram showing an embodiment obtained by improving the first embodiment of the horizontal synchronizing signal generation circuit.

8 is a diagram showing output signals in the horizontal synchronization signal generation circuit of FIG.

FIG. 9 is a diagram showing a second embodiment of the horizontal synchronizing signal generation circuit.

FIG. 10 is a diagram showing a third embodiment of the horizontal synchronizing signal generation circuit.

FIG. 11 is a diagram showing a change in a light emission amount of a laser.

[Explanation of symbols]

 Reference Signs List 1 rotating polygon mirror 2 motor 3 fθ lens 4 photodetector 5 reflecting mirror 6 photoconductor 7 semiconductor laser 8 cylindrical lens 10 motor drive control unit 11 laser drive unit 12 control device 13 microcomputer 21 optical sensor 22, 51 comparator 23, 24, 52, 53, 91 resistor 92 transistor

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C362 AA54 BA69 BB32 2H045 AA01 BA02 BA22 BA24 CA63 CA88 CB42 5C072 AA03 BA04 HA02 HA06 HA13 HB08 HB11 HB13 HB15 XA01 XA05 5C074 AA10 BB03 BB26 CC22 CC26EE02 DD04

Claims (3)

[Claims] 1. A light beam scanning device which scans a rotating photosensitive member via a rotating polygon mirror with light beams from a plurality of laser light sources provided with a light emission driving means and a light amount adjusting means,
Each of the plurality of laser light sources has at least two or more reference voltages, one optical sensor for detecting a scanning start position of each of the light beams, and a signal of each of the light beams detected by the light sensor. A light beam scanning device comprising: a horizontal synchronizing signal generating unit that outputs a horizontal synchronizing signal as compared with the reference voltage. 2. The light beam scanning device according to claim 1, wherein said horizontal synchronizing signal generating means includes a reference voltage switching means for switching said reference voltage for each of said laser light sources. 3. The light beam scanning device according to claim 1, wherein said horizontal synchronizing signal generating means includes reference voltage control means for controlling said reference voltage for each of said laser light sources.