JP2002120398A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a sensor for detecting a timing of scanning of a light beam to stably operate irrespective of fluctuation of a light quantity of an incident light. SOLUTION: This image recorder has an SOS sensor 54 that detects a scanning start timing of the light beam of which the amplification factor can be switched corresponding to an amplification factor switching signal Vg. A peak value Vp of an output voltage Va from an amplifier 64A that is varied corresponding to the light quantity of the light incident on the SOS sensor 54 is detected by a peak hold circuit 72. The peak value Vp, i.e., a signal value after being amplified and threshold levels Ref1, Ref2 are compared with each other to generate an amplification factor switching signal Vg based on the compared result and then the amplification factor of the SOS sensor 54 is switched to an optimum one. When the amplification factor is already set to an upper limit or a lower limit of the available amplification factor and then the switching to the suitable one is not executed, it is judged that an error occurs and an error signal is outputted.

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 that forms an image by scanning a light beam and irradiating a photosensitive member.

[0002]

2. Description of the Related Art An image forming apparatus, such as a laser printer or an electrophotographic copying machine, for recording an image by scanning a light beam on a photoreceptor by an optical scanning device has become widespread. In an optical scanning device, generally, a light beam modulated based on image data output from a light source such as a semiconductor laser is made incident on a reflecting surface of a rotating polygon mirror rotating at a predetermined speed via a collimator lens or the like. Due to the rotation of the rotary polygon mirror, the incident angle of the light beam is deflected while continuously changing, and the light beam scans on the photoconductor to form an electrostatic latent image on the photoconductor. .

In such an image forming apparatus, a sensor for detecting a scanning timing, such as an SOS (Start of Scan) sensor, is provided outside the image recording area, and indicates a scanning timing output from the sensor. The signal is used as a synchronization signal to control the image writing position in the main scanning direction. A sensor that detects the scanning timing detects a scanning light beam with a photodetector, and uses a logical level signal obtained by comparing the detected light beam amount with a predetermined threshold level as a signal indicating the scanning timing. Output.

The photodetection circuit used conventionally has a circuit configuration for converting a photocurrent of a photodiode or the like into a voltage. Therefore, the light quantity of the light beam incident on the photodetector changes depending on the light quantity setting at the time of writing an image. Then, the rising / falling characteristics of the output waveform of the photodetector change. Due to this change, the rise / fall timing at the time of comparison with the predetermined threshold level at the subsequent stage changes. That is,
Since the generation timing of the synchronizing signal is shifted according to the incident light amount of the light beam incident on the photodetector, there is a problem that the image writing timing in the main scanning direction changes and the output image is distorted.

In general, the amount of light incident on a photodetector changes according to the setting of the amount of light beam when recording an image on a photoreceptor. Further, the setting range of the light amount of the light beam is determined by the sensitivity characteristics of the photoconductor. In particular, in the case of a multi-color image forming apparatus for forming a color image, in addition to the reproducibility of halftone, the color of the photoconductor caused by the different electrical characteristics of the toner for each color such as yellow, magenta, cyan, and black It is necessary to set the light amount of the light beam in consideration of the sensitivity variation for each. That is, in the multicolor image forming apparatus, in order to obtain good image quality irrespective of the change in the sensitivity of the photoconductor, it is required that the light beam setting range of the light beam be wider than that of the image forming apparatus that forms a single color image.

For this reason, Japanese Patent Application Laid-Open No. 63-267908 discloses a method of controlling a threshold level to be compared with an output of a photodetector circuit when generating a synchronizing signal, according to a light quantity setting signal for setting a light quantity of a light beam. Thus, a technique is disclosed in which even when the light amount of a light beam incident on a photodetector decreases, the rising / falling timing of a synchronization signal is compensated to prevent a variation in image writing timing in the main scanning direction. .

Japanese Patent Application Laid-Open No. 6-286217 discloses that when an output of a photodetector is amplified and compared with a predetermined threshold level to obtain a synchronization signal, the output of the photodetector before amplification is peaked. By holding the peak voltage in the hold circuit and controlling the amplification factor based on the difference between the peak voltage and the threshold level, even if the light amount of the light beam incident on the photodetector changes, the rising / falling of the synchronization signal is obtained. There is disclosed a technique for compensating timing and preventing fluctuation in image writing timing in the main scanning direction.

[0008]

However, according to the technique described in Japanese Patent Application Laid-Open No. 63-267908, when the threshold level is lowered, noise from the outside or the like may cause noise.
There has been a problem that a synchronizing signal output defect occurs. For example, as shown in FIG.
When the threshold level at 0 V is set to half of 1.0 V, and the incident light amount to the photodetector becomes 1/5,
As shown in FIG. 16, the output level becomes 0.4 V and the threshold level becomes 0.2 V. At this time, since the noise level due to external noise mixing is about 200 mV, the difference between the noise level and the threshold level disappears, and a synchronizing signal output defect due to the noise mixing occurs.

On the other hand, according to the technique described in Japanese Patent Application Laid-Open No. 6-286217, when an output signal obtained by amplifying the output voltage of the photodetector is abnormal due to poor amplification rate control, the rising of the synchronous position signal is performed. / There has been a problem that the fall timing cannot be compensated and the image writing timing in the main scanning direction changes. Also, no error detection due to poor amplification rate control has been performed.

An object of the present invention is to provide an image forming apparatus capable of stably operating a sensor for detecting a scanning timing of a light beam irrespective of a variation in the amount of incident light. The purpose is to:

[0011]

According to an aspect of the present invention, there is provided an image forming apparatus for forming an image by scanning a light beam and irradiating a photosensitive member with the light beam. Scanning is provided at a position where a light beam is incident, and has a function of amplifying a signal corresponding to an incident light amount to detect a scanning timing of the light beam and changing an amplification factor of a signal according to the incident light amount. A timing detection unit, a timing control unit that controls an image writing timing in synchronization with the scanning timing detected by the scanning timing detection unit, and a function of changing the amplification factor of the scanning timing detection unit, Gain change control means for changing the gain based on an amplified signal obtained by amplifying a signal corresponding to the amount of incident light in the scanning timing detecting means. It is characterized in Rukoto.

According to the first aspect of the present invention, in the image forming apparatus, the timing control unit detects the scanning timing of the light beam by the scanning timing detection unit, and the timing control unit synchronizes with the detected scanning timing. To control the image writing timing (image writing position). This scanning timing detection means,
It has a function of changing the amplification factor when amplifying a signal corresponding to the incident light beam stepwise or continuously, that is, a function of changing the detection sensitivity, and the amplification factor change control means changes this amplification factor. The amplification factor is changed based on a signal (amplified signal) obtained by amplifying a signal corresponding to the incident light amount.

As described above, since the amplification factor can be changed to the optimum one in accordance with the amplified signal which changes in accordance with the incident light amount, the scanning timing detecting means can be operated stably even if the incident light amount changes. Can be. That is, stable operation can be performed in a wider light amount range than in the related art. In addition, by changing the amplification factor using the amplification signal, the operation of the scanning timing detection unit becomes unstable due to poor amplification factor control, and there is no fear of malfunction of the image forming apparatus such as a shift in image writing timing. .

[0014] As described in claim 2,
It is preferable that the apparatus further comprises a light quantity setting means for setting the light quantity of the light beam, and an amplification factor initial value setting means for setting an initial value of the amplification factor based on the light quantity set by the light quantity setting means.

According to a third aspect of the present invention, the amplification factor change control unit includes an amplification unit that amplifies a signal corresponding to the incident light amount in the scanning timing detection unit. It is preferable that a comparison unit that compares the signal with a predetermined threshold level is provided, and the amplification factor is changed based on a comparison result by the comparison unit.

At this time, as set forth in claim 4, the comparing means determines the level of the amplified signal before the operation of the scanning timing detecting means becomes unstable when the incident light amount is small; When the incident light amount is large, the scanning timing detection unit compares the amplified signal with two threshold levels each corresponding to a level of the amplified signal before the operation becomes unstable, and the amplification factor change control unit includes: The amplification factor may be changed when the amplified signal is out of a predetermined range determined by the two threshold levels. Specifically, as described in claim 5,
The amplification factor change control unit may decrease the amplification factor when the amplification signal is larger than the predetermined range. As described in claim 6, the amplification factor change control means may increase the amplification factor when the amplified signal is smaller than the predetermined range.

Further, the amplification factor change control means, as described in claim 7, makes it impossible to change the amplification factor based on the amplified signal, when the amplification factor reaches an upper limit or a lower limit that can be changed. In such a case, an error may be determined.

The scanning timing detecting means is provided along the scanning direction of the light beam and includes two light detecting means for detecting the amount of incident light. Amplifying means for amplifying the output signals of the two light detecting means, a clamping means for clamping a signal obtained by amplifying the output signal of one light quantity detecting means by the amplifying means to a predetermined level, a signal clamped by the clamping means, Scanning timing signal generating means for comparing an output signal from the other light quantity detecting means with a signal amplified by the amplifying means, converting the comparison result into a logical level and generating a signal indicating the scanning timing. It is good to do so.

[0019]

Next, an example of an embodiment according to the present invention will be described in detail with reference to the drawings.

(Overall Configuration) FIG. 1 shows an image forming apparatus 10.
Is schematically shown. As shown in FIG. 1, the image forming apparatus 10 is covered with a casing 12. An image forming unit 14 is provided in the casing 12. The image forming unit 14 mainly rotates a cylindrical photoconductor 16 that rotates at a constant speed in the direction of arrow A shown in FIG. 1 and directs a light beam toward the photoconductor 16 based on desired image data (see arrow B). And an optical scanning device 18 (detailed later) for irradiating while scanning.

A charger 20 is provided near the peripheral surface of the photoconductor 16. The charger 20 charges the photoconductor 16 uniformly. Photoconductor 16 uniformly charged by charger 20
Is rotated in the direction of arrow A, so that the optical scanning device 1
The light beam from 8 is applied. Thereby, the photosensitive member 1
6, a latent image is formed on the peripheral surface.

Further, on the downstream side in the rotation direction of the photoconductor 16 from the irradiation position of the light beam by the optical scanning device 18,
A developing unit 22, a transfer charger 24, and a cleaner 26 are provided. The developing device 22 supplies the toner and
The latent image formed on the peripheral surface of the photosensitive member 16 is developed to form a toner image on the peripheral surface of the photoconductor 16. This toner image is transferred from the recording paper tray 28 to the recording paper 30 guided between the photosensitive member 16 and the transfer charging member 24 by the transfer charging member 24, and remains on the peripheral surface of the photosensitive member 16 after the transfer. The remaining toner is removed by the cleaner 26. The recording paper 30 to which the toner image has been transferred is conveyed to a fixing device 32 and subjected to a fixing process, and then discharged to a discharge tray 34.

The image forming apparatus 10 has a main control unit 36. The main control unit 36 controls an image forming operation (printing operation) in the image forming unit 14.

(Detailed Configuration of Optical Scanning Device) Next, the schematic configuration of the optical scanning device 18 will be described with reference to FIGS.

The optical scanning device 18 includes a semiconductor laser 40 as a light source, and a polygon mirror 42 that reflects a light beam output from the semiconductor laser 40 and irradiates the photosensitive member 16 with a light beam.

The semiconductor laser 40 includes a laser driving circuit 44
It is connected to the. The laser drive circuit 44 controls the output light amount of the semiconductor laser 40 based on a light amount setting signal from the outside (the main control unit 36), and controls ON / OFF of the lighting of the semiconductor laser 40 based on an image signal.
The semiconductor laser 40 outputs a light beam based on image data at a predetermined intensity under the control of the laser drive circuit 44.

The light beam output from the semiconductor laser 40 is made substantially collimated by a collimator lens 45, focused in a sub-scanning direction by a cylindrical lens 46, and made incident on a polygon mirror 42.

The polygon mirror 42 is formed in a regular polygonal shape (a regular hexagon in this embodiment) having a plurality of reflecting surfaces 42A on the side surfaces, and the incident light beam converges on the reflecting surface 42A. It has become. The polygon mirror 42 is axially mounted on a motor 48, and is rotated at a predetermined number of rotations (a predetermined speed) in the direction of arrow C by driving the motor 48. By this rotation, each reflection surface 4
The angle of incidence of the light beam on 2A changes continuously and is deflected. Thereby, the axial direction of the photoconductor 16 (see arrow D,
The light beam is irradiated on the photoconductor 16 by scanning in the “main scanning direction”.

In the traveling direction of the light beam reflected by the polygon mirror 42, the first lens 50A and the second lens 5
FB lens 50 and a cylindrical lens 51 are provided. Polygon mirror 4
The light beam reflected by the optical scanning device 18 passes through the fθ lens 50 and the cylindrical lens 51,
And irradiates the photoconductor 16. At this time, f
The scanning speed when irradiating the photoconductor 16 with the light beam is made uniform by the θ lens 50, the beam is focused in the main scanning direction, and the beam is focused in the sub-scanning direction by the cylindrical lens 51. Connect the imaging points.

In the optical scanning device 18, a mirror 52 is disposed downstream of the fθ lens 50 in the traveling direction of the light beam and outside the image forming area on the upstream side in the scanning direction of the light beam. An SOS sensor 54 (to be described in detail later) including a photodiode or the like is disposed at a position substantially equivalent to the photoconductor 16 with respect to the mirror 52 in the direction in which the mirror 52 reflects the light beam.

Each time the photosensitive member 16 is scanned in the axial direction of the SOS sensor 54, a light beam outside the image forming area on the upstream side in the scanning direction is guided by the mirror 52.
That is, the SOS sensor 54 detects the timing at which the optical scanning device 18 starts scanning the photoconductor 16 for each scan, and outputs the result as an SOS signal. This SO
The S sensor 54 corresponds to the scanning timing detecting means of the present invention.

The SOS signal is input to the main control unit 36. The main control unit 36 outputs an image signal to the laser drive circuit 44 in synchronization with the SOS signal, so that the laser drive circuit 4
4 starts lighting based on the image data of the semiconductor laser 40, and controls the writing position of the image. That is, the main control unit 36 corresponds to the timing control means.

(Detailed Configuration of SOS Sensor) Next, SOS
The detailed configuration of the sensor 54 will be described.

As shown in FIG. 4, the SOS sensor 54 includes
Two photodiodes (hereinafter, “PD”) 60A and 60B are arranged as light detecting means with the light receiving surfaces arranged in the main scanning direction with the light receiving surface facing the light beam incident direction. PD
Each of 60A and 60B outputs a photocurrent according to the amount of incident light.

As shown in FIG. 5, the PDs 60A and 60B have current / voltage converters (I / V) 62A and 62B, respectively.
, Are connected to amplifiers 64A and 64B as amplifying means. The photocurrents output from the PDs 60A and 60B are voltage-converted by the current / voltage converters 62A and 62B, respectively, and then input to the amplifiers 64A and 64B, respectively, where they are amplified at a predetermined amplification factor.

The amplification factors of the amplifiers 64A and 64B can be switched in a plurality of stages, and are switched by an amplification factor switching signal Vg from an amplification factor switching signal generation circuit 66 as an amplification factor change control means. In the present embodiment, it is possible to switch between two stages of a high amplification factor (3 times) and a low amplification factor (1 time).

The signal Va amplified and output by the amplifier 64A is applied to a clamp circuit 68 as a clamp means.
After being clamped to a predetermined level (clamp level) Vc, it is inputted to the comparator 70. On the other hand, the signal V amplified and output by the amplifier 64B is output.
b is input to the comparator 70 as it is. The comparator 70 compares the signal Vac from the clamp circuit 68 with the signal Vb from the amplifier 64B, and outputs a logic level signal based on the comparison result as an SOS signal. That is, the comparator 70 corresponds to a scanning timing signal generation unit.

More specifically, the signal V from the clamp circuit 68
The level of the logical level signal is switched at the cross point between ac and the signal Vb from the amplifier 64B. When the signal Vac becomes lower than the signal Vb, the output voltage of the comparator 70 becomes H level. When the potential becomes high, the output voltage of the comparator 70 becomes L level. That is, the position of the scanning light beam is
When moving from A to the PD 60B, an SOS signal which is a rising edge is generated.

The amplifier 64A is also connected to the peak hold circuit 72, and the signal Va amplified and output by the amplifier 64A is also input to the peak hold circuit 72. The peak hold circuit 72 includes an amplifier 64
A peak value of the signal Va output from A is detected, and a signal Vp indicating the detected peak value is output.

The peak hold circuit 72 is connected to comparators 74 and 76 as comparing means. The comparators 74 and 76 receive signals Ref1 and Ref of predetermined threshold levels from outside (the main control unit 36).
2 are input.

The comparators 74 and 76 are respectively provided with predetermined threshold levels Ref1 and Ref2 and a peak hold circuit 72.
(A signal indicating the peak value of the signal Va output from the amplifier 64A, hereinafter referred to as “peak value”) Vp, and outputs a logic level signal based on the comparison result. Specifically, the comparator 74,
When the threshold levels Ref1 and Ref2 are higher than the peak value Vp, the output voltage at the L level and the peak value V
When it is smaller than p, it becomes H level.

The output signals of the comparators 74 and 76 are input to an amplification factor switching signal generation circuit 66. In the amplification factor switching signal generation circuit 66, the output signals of the comparators 74 and 76, that is, the comparison result between the predetermined threshold levels Ref1 and Ref2 and the peak value Vp, and the amplification factor of the currently set amplifiers 64A and 64B (high / Low), the amplification factor switching signal Vg is generated. This amplification factor switching signal Vg
Is input to the amplifiers 64A and 64B, and as described above,
The amplifiers 64A and 64B switch the gain based on the gain switching signal Vg.

That is, the sensitivity of the SOS sensor 54 is increased by switching the amplification factors of the amplifiers 64A and 64B to a high amplification factor by the amplification factor switching signal Vg.
The sensitivity of the SOS sensor 54 can be reduced by switching the amplification factors of A and 64B to low amplification factors. Thus, even if the light amount of the light beam incident on the SOS sensor 54 changes, the SOS signal can be stably generated. In the following, the amplifier 64
The gain of A and 64B is referred to as the gain of the SOS sensor 54.

Here, the clamp level Vc and the threshold levels Ref1 and Ref2 of the SOS sensor 54 will be described in detail.

The clamp level Vc needs to be set to a level higher than a predicted noise level of external noise caused by disturbance light or the like. Also, the threshold level Re
f1 and Ref2 need to be set so as to correspond to the output signal level of the amplifier 64A before the SOS sensor 54 becomes unstable when the incident light amount is small or the incident light amount is large. .

More specifically, the threshold level Ref1 is equal to PD6
0A and 60B, the signal Vac output from the clamp circuit 68 and the amplifier 64B
Is set to a level at which a cross point with the signal Vb output from the controller can be stably obtained. Also, the threshold level Ref2
Is due to external noise caused by disturbance light or the like even when the amount of light incident on the PDs 60A and 60B is large.
Signal Vac output from clamp circuit 68 and amplifier 6
The level is set to a level before the level at which a cross point with the signal Vb output from 4B is no longer generated, that is, a level at which a cross point can be stably obtained regardless of external noise.

More specifically, in the present embodiment, when the maximum light quantity incident on the PDs 60A and 60B of the SOS sensor 54 is 1 and the amplifiers 64A and 64B have a low amplification factor, the signals Va output from the respective amplifiers 64A and 64B. , Vb have a voltage amplitude of 2 V and a noise level of 200 mV. For this reason, the clamp level Vc is preset to 300 mV which has a margin for the noise level.

In this case, if the amount of incident light on the PDs 60A and 60B is reduced, there is no margin when the amount of incident light is 1/4. That is, when the signals Va and Vb become 500 mv, the clamp circuit 6 inputted to the comparator 70
The cross point between the signal Vac from the amplifier 8 and the signal Vb from the amplifier 64B may become unstable due to the influence of external noise (see FIG. 6). For this reason, the threshold level Ref1 is set to 6 which is the level before falling into unstable operation.
It is set to 00 mV in advance.

When the amount of incident light is reduced to 1/4 and there is no margin, the amplifiers 64A and 64B are changed from 1 times the low amplification rate to 3 times the high amplification rate, so that the signal V is increased.
The amplitudes of a and Vb can be set to 1.5 V (see FIG. 7). In other words, the conventional S type in which the amplification factor is not switched
The light amount range in which the OS sensor can operate stably is up to 1/4. However, by switching the setting of the amplification factor by three times using an SOS sensor of the amplification factor switching type, it can be further reduced to one third, that is, 1/12 in total. It can be used up to the light amount (see FIG. 8).

When a high amplification factor is set, a noise level due to external noise is also amplified at a high amplification factor. Therefore, when disturbance light enters the PD 60A or PD 60B, the clamp circuit is input to the comparator 70. A cross point may be formed between the signal Vac from 68 and the signal Vb from the amplifier 64B. For this reason, the threshold level Ref2 is set in advance to a level of 1.9 V at which a cross point is not formed by external noise.

(Operation) Next, the operation of the present embodiment will be described. First, the operation of the SOS sensor will be described.

Each time the light beam is scanned, the light beam outside the image forming area on the upstream side of the scanning is incident on the SOS sensor 54 while scanning, and is received by the PDs 60A and 60B. The PDs 60A and 60B output a photocurrent corresponding to the amount of the received light beam.
After voltage conversion by the voltage converters 62A and 62B,
The signals are input to the amplifiers 64A and 64B, and are amplified at a predetermined amplification rate (high amplification rate / low amplification rate) set by the amplification rate switching signal Vg from the amplification rate switching signal generation circuit 66.

The output signal Va amplified and output by the amplifier 64A is clamped to a predetermined crank level Vc by the clamp circuit 68, and is input to the comparator 70 as an output signal Vac. Comparator 7
At 0, the output signal Vac is compared with the signal Vb amplified and output by the amplifier 64B, the output signal level is switched at these cross points, and output as the SOS signal.

Next, the amplification factor switching control processing of the SOS sensor 54 executed by the amplification factor switching signal generation circuit 66 will be described.

The amplification factor switching signal generation circuit 66 uses the comparators 74 and 76 to compare the peak value Vp of the signal Va output from the amplifier 64A detected by the peak hold circuit 72 with the threshold levels Ref1 and Ref2. The signals shown in FIG. The amplification factor switching signal generation circuit 66 generates an amplification factor switching signal Vg based on the signals from the comparators 74 and 76 and the amplification factor of the currently set SOS sensor 54.
The amplification factor of the S sensor 54 is switched and controlled.

[0056]

[Table 1]

FIG. 9 shows a flowchart of a process executed by the amplification factor switching signal generation circuit 66 to perform control as shown in Table 1. Note that the amplification factor switching signal generation circuit 66 performs the process of FIG.
This is performed at the start of printing of a job or one page, every scanning of a light beam, and the like. 10 to 13 show SOS.
The input signal (signal Va) of the comparator 70 of the sensor 54
c, Vb) and the waveform of the output signal (SOS signal).

In the gain switching signal generating circuit 66, as shown in FIG. 9, first, the state of the gain switching signal is checked.
If the amplification factor of the SOS sensor 54 is set to a high amplification factor, the process proceeds from step 100 to step 102. In the present embodiment, the amplification factors of the amplifiers 64A and 64B are set to a high amplification factor in the initial state (that is, the initial value of the amplification factor is high).

In step 102, it is checked whether the peak value Vp is larger than the threshold level Ref1 based on the signal input from the comparator 74.
At 4, it is checked whether the peak value Vp is smaller than the threshold level Ref2 based on the signal input from the comparator 76.

If the relationship of Ref1 <Vp <Ref2 is satisfied, a positive determination is made in steps 102 and 104, and the routine proceeds to step 106. In step 106, as shown in FIG. 10, it is determined that an appropriate amplification factor for stably obtaining a cross point is set, and the amplification factor switching signal V
The process is terminated without changing g, that is, without changing the amplification factor of the SOS sensor 54 while maintaining the high amplification factor (state 2 in Table 1).

When the relationship of Vp <Ref1 holds,
A negative determination is made in step 102 and the routine proceeds to step 108. In step 108, as shown in FIG. 11, some trouble (failure of the semiconductor laser 40, misalignment of the optical system, etc.) occurs in the image forming apparatus 10, and the amount of light incident on the SOS sensor 54 is too small and the high amplification rate is high. However, it is not possible to obtain a stable cross point
It determines that A has failed and outputs an error signal to the main control unit 36. The main control unit 36 receives this error signal and performs error processing such as notifying the user of an error (state 3 in Table 1).

When the relationship of Vp> Ref2 holds,
A negative determination is made in step 104 and the routine proceeds to step 110. In step 110, as shown in FIG.
It is determined that the amplification factor is too high with respect to the amount of light incident on the sensor 54 and that a cross point may be generated due to external noise, that is, it is determined that an SOS signal other than the normal one is generated, and the amplification factor switching signal Vg And the amplification factor of the SOS sensor 54 is changed from a high amplification factor to a low amplification factor (Table 1).
State 1). By lowering the amplification factor in this way, the waveforms of the input signals (signals Vac and Vb) of the comparator 70 become as shown in FIG. 13, and it is possible to prevent the occurrence of cross points due to external noise and obtain an appropriate SOS signal. Can be.

On the other hand, if the amplification factor of the SOS sensor 54 is set to a low amplification factor, the process proceeds from step 100 to step 112. In step 112, as in step 102, it is determined whether the peak value Vp is greater than the threshold level Ref1 based on the signal input from the comparator 74. In step 114, the comparator 76 is executed, as in step 104. It is confirmed whether or not the peak value Vp is smaller than the threshold level Ref2 based on the signal input from.

If the relationship of Ref1 <Vp <Ref2 is satisfied, a positive determination is made in steps 112 and 114, and the routine proceeds to step 116. In step 116, as shown in FIG. 13, it is determined that an appropriate amplification factor for stably obtaining a cross point is set, and the amplification factor switching signal V
The processing is terminated without changing g, that is, without changing the amplification factor of the SOS sensor 54 and keeping the low amplification factor (state 5 in Table 1).

When the relationship of Vp <Ref1 holds,
A negative determination is made in step 112, and the process proceeds to step 118. In step 118, as shown in FIG. 11, the amplification factor is low with respect to the amount of light incident on the SOS sensor 54, the margin of the clamp level with respect to the noise level is lost, and a stable cross point cannot be obtained.
When it is determined that the output timing of the S signal is not stable, the gain switching signal Vg is changed, and the gain of the SOS sensor 54 is changed from a low gain to a high gain (state 6 in Table 1). By increasing the amplification factor in this manner, the waveforms of the input signals (signals Vac and Vb) of the comparator 70 become as shown in FIG. 10, and it is possible to stably obtain a cross point, and obtain an appropriate SOS signal. be able to.

When the relationship of Vp> Ref2 holds,
A negative determination is made in step 114, and the process proceeds to step 108. In step 108, as shown in FIG. 12, some trouble occurs in the image forming apparatus 10, and the amount of light incident on the SOS sensor 54 is too large to stably obtain a cross point even at a low amplification factor, or the amplifier 64A And outputs an error signal to the main control unit 36. The main control unit 36
Upon receiving the error signal, error processing such as notifying the user of an error is performed (state 4 in Table 1).

As described above, in the first embodiment, the SO
An amplifier 64 that changes according to the amount of light incident on the S sensor 54
The gain of the SOS sensor 54 (specifically, the amplifiers 64A and 64B) is switched according to the peak value Vp of the output voltage Va from A, that is, according to the amplified signal.

Thus, even if the amount of light incident on the SOS sensor 54 changes, the amplification factor of the SOS sensor 54 can be switched to the optimum amplification factor in accordance with the amplified signal that changes with the change. Therefore, an SOS signal can be stably obtained in a wide light amount range.

Further, by performing the switching control of the amplification factor using the amplified signal, it is possible to prevent a malfunction of the image forming apparatus 10 due to a poor amplification control. In addition, the gain is already the upper limit or lower limit of the switchable gain, and by setting an error when the gain cannot be switched to an appropriate gain, an error due to a gain control failure that could not be detected conventionally can be detected. It is possible to perform error processing such as notifying a control failure.

In the above description, the case where the initial value of the amplification factor of the SOS sensor 54 is previously set to a high amplification factor has been described as an example, but the present invention is not limited to this.

[Second Embodiment] Next, as a second embodiment, an initial value of the amplification factor of the SOS sensor 54 is set based on a light quantity setting signal for setting the output light quantity of the semiconductor laser 40. The case will be described. Note that the configuration of the image forming apparatus is the same as that of the first embodiment, and a description thereof will not be repeated.

FIG. 14 shows an initial value setting process of the amplification factor of the SOS sensor 54. Note that this initial value setting process is automatically executed at a predetermined timing (such as when the set light amount is changed by the light amount setting signal).

In the initial value setting process, as shown in FIG. 14, first, at step 150, it is checked whether or not the light amount setting signal is equal to or higher than the reference level. Specifically, similarly to the first embodiment, the variable range of the light amount setting signal is set to 0.
The reference level is set to 0.6 V, which is the same value as the threshold level Ref1 when the maximum of the incident light amount range of the photodetector is 2 V when the amplification factor is set to 2 V and the low amplification factor is set.

If the light amount setting signal is equal to or higher than the reference level (0.6 V), the process proceeds to step 152, where the peak value of the signal Va output from the amplifier 64A is not amplified, that is, even at a low amplification factor (1 time). When it is determined that Vp becomes larger than the threshold level Ref1, the initial gain switching signal, that is, the initial value of the gain of the SOS sensor 54 is set to a low gain.

On the other hand, when the light quantity setting signal is equal to the reference level (0.6
If it is less than V), the process proceeds to step 154, and unless amplification is performed, it is determined that the peak value Vp of the signal Va output from the amplifier 64A cannot exceed the threshold level Ref1, and the initial amplification factor switching signal, that is, SOS sensor 5
The initial value of the amplification factor of No. 4 is set to a high amplification factor.

After setting the initial value of the amplification factor of the SOS sensor 54 in this way, switching control of the amplification factor is performed in the same manner as in the first embodiment (see FIG. 9).

As described above, in the second embodiment, by setting the initial value of the amplification factor in accordance with the light quantity setting signal, the SOS sensor 54 is operated at an appropriate amplification factor from the beginning, and a stable SOS sensor is obtained. A signal can be obtained. In addition, for example, the SOS is affected by dust in the optical scanning device 18 or the like.
Even if an abnormality occurs in the setting of the amplification factor based on the light intensity setting signal, for example, when the incident light intensity on the sensor 54 is different from the light intensity corresponding to the light intensity setting signal, the amplification factor switching control (see FIG. 9) automatically performs the setting. It is possible to switch to an appropriate amplification factor.

In the first and second embodiments,
Although the case where the amplification factor of the SOS sensor 54 is controlled to be switched between two stages of a low amplification factor and a high amplification factor has been described as an example, the present invention is not limited to this. Alternatively, it may be changed continuously according to the amplified signal.

In the first and second embodiments,
The amplified signal (peak value Vp) is divided into two threshold levels Re.
Although the case where the amplification factor is switched in comparison with f1 and Ref2 has been described, one threshold level may be compared. In this case, although the control becomes rough, the circuit configuration can be simplified, and the switching of the amplification factor and the error determination can be performed in the same manner as described above.

In the first and second embodiments,
Although the two PDs 60 </ b> A and 60 </ b> B are provided as the light detecting means, and the outputs of the PDs 60 </ b> A and 60 </ b> B are compared and the SOS sensor 54 that generates the SOS signal is described as an example, the present invention is not limited to this. It is essential to change the amplification factor of the SOS sensor according to the amplified signal, and the present invention is applicable as long as it has a function of changing the amplification factor. For example,
By applying the present invention to an SOS sensor that obtains an SOS signal by comparing the output of the light detection unit with a predetermined reference voltage, and setting the amplification factor optimally,
Even if the difference in the amount of light incident on the light amount detecting means is large, the S
An OS signal can be obtained.

In the first and second embodiments,
The case where the SOS sensor is used to detect the scanning timing has been described as an example, but the present invention is not limited to this. For example, an EO that detects the scanning end timing is used.
An S (End of Scan) sensor may be used.

In the first and second embodiments,
Although the image forming apparatus for forming a monochromatic image has been described as an example, the present invention is not limited to this, and is applicable to an image forming apparatus for forming a color image. Further, the case where an image is formed by one light beam has been described as an example, but the present invention is not limited to this. For example, a divided scanning method in which one main scan is divided by a plurality of light beams. The present invention is also applicable to an image forming apparatus.

[0083]

As described above, the present invention has an excellent effect that the sensor for detecting the scanning timing of the light beam can be operated stably irrespective of the fluctuation of the incident light amount.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a detailed configuration diagram of an optical scanning device.

FIG. 3 is a block diagram illustrating an optical system of the optical scanning device.

FIG. 4 is a top view on the light incident side of the SOS sensor.

FIG. 5 is a circuit diagram showing a detailed configuration of the SOS sensor.

FIG. 6 shows an input signal (A) input to a comparator of an SOS sensor and an output signal (B) from the comparator when the incident light amount is 1/4 and a low amplification factor (1 time) is set. FIG.

FIG. 7 is a diagram showing an input signal (A) input to a comparator of the SOS sensor and an output signal (B) from the comparator when the amplification factor is switched to a high amplification factor (3 times) from FIG. 6; is there.

FIG. 8 is a diagram showing an operable light amount range of the SOS sensor (amplification ratio switching type) of the present embodiment and a conventional SOS sensor (amplification ratio switching is not performed).

FIG. 9 is a flowchart illustrating an amplification factor switching control process for switching the amplification factor of the SOS sensor.

FIG. 10: SO in the case where an appropriate amplification factor is set
An input signal (A) input to the comparator of the S sensor,
FIG. 4 is a diagram illustrating an output signal (B) from the comparator.

FIG. 11 shows a case where an appropriate amplification factor is not set.
FIG. 3 is a diagram illustrating an input signal (A) input to a comparator of an OS sensor and an output signal (B) from the comparator.

FIG. 12 shows a case where an appropriate amplification factor is not set.
FIG. 3 is a diagram illustrating an input signal (A) input to a comparator of an OS sensor and an output signal (B) from the comparator.

FIG. 13 shows SO in a case where an appropriate amplification factor is set.
An input signal (A) input to the comparator of the S sensor,
FIG. 4 is a diagram illustrating an output signal (B) from the comparator.

FIG. 14 is a flowchart showing an initial value setting process for setting an initial value of the amplification factor of the SOS sensor.

FIG. 15 is a diagram showing input signals and output signals of a conventional SOS sensor.

FIG. 16 shows a conventional SOS when the amount of incident light is reduced.
It is a figure showing an input signal and an output signal of a sensor.

[Explanation of symbols]

 Reference Signs List 10 image forming apparatus 16 photoreceptor 18 optical scanning device 36 main control unit 40 semiconductor laser 42 polygon mirror 44 laser drive circuit 54 SOS sensor 60A, 60B photodiode 62A, 62B current / voltage converter 64A, 64B amplifier 66 amplification rate switching signal Generation circuit 68 Clamp circuit 70 Comparator 72 Peak hold circuit 74 Comparator 76 Comparator

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) H04N 1/23 103 F term (reference) 2C362 AA54 BB30 BB32 BB37 2H045 CA88 CA98 DA41 2H076 AB05 AB12 AB32 AB34 DA04 DA22 5C072 AA03 BA13 HA02 HA13 HB04 HB08 HB11 HB13 UA05 XA01 XA05 5C074 AA15 BB02 BB03 CC26 DD08 DD11 DD15 EE02 EE06 GG19 HH02

Claims (8)

[Claims] 1. An image forming apparatus for forming an image by scanning a light beam and irradiating a photoreceptor, wherein the image forming apparatus is arranged at a position where the light beam is incident, and amplifies a signal corresponding to an incident light amount to amplify the signal. A scanning timing detecting unit having a function of detecting a scanning timing of the light beam and changing an amplification factor of a signal according to the amount of incident light; and synchronizing an image with the scanning timing detected by the scanning timing detecting unit. Timing control means for controlling the write timing of the signal; anda gain change control means for changing the gain based on an amplified signal obtained by amplifying a signal corresponding to the incident light amount in the scanning timing detecting means. Image forming apparatus. 2. A light quantity setting means for setting a light quantity of the light beam; and an amplification factor initial value setting means for setting an initial value of the amplification factor based on the light quantity set by the light quantity setting means. Item 2. The image forming apparatus according to Item 1. 3. The gain change control unit includes a comparison unit that compares an amplified signal obtained by amplifying a signal corresponding to the amount of incident light in the scanning timing detection unit with a predetermined threshold level. The image forming apparatus according to claim 1, wherein the amplification factor is changed based on a result. 4. The apparatus according to claim 1, wherein the comparing unit detects the level of the amplified signal before the operation of the scanning timing detecting unit becomes unstable when the amount of incident light is small, and detects the scanning timing when the amount of incident light is large. The means compares the amplified signal with two threshold levels each corresponding to the level of the amplified signal before the operation becomes unstable, and the amplification factor change control means determines that the amplified signal is determined by the two threshold levels. The image forming apparatus according to claim 3, wherein the amplification factor is changed when the gain is out of a predetermined range. 5. The image forming apparatus according to claim 4, wherein the amplification factor change control unit reduces the amplification factor when the amplification signal is larger than the predetermined range. 6. The image forming apparatus according to claim 4, wherein the amplification factor change control unit increases the amplification factor when the amplification signal is smaller than the predetermined range. 7. The amplification factor change control unit determines that an error has occurred when the amplification factor has reached a changeable upper or lower limit and the amplification factor cannot be changed based on the amplified signal. The image forming apparatus according to any one of claims 1 to 6, wherein: 8. The scanning timing detecting means is arranged along a scanning direction of the light beam, two light detecting means for detecting an incident light amount, and amplifying output signals of the two light detecting means, respectively. Amplifying means, a clamp means for clamping a signal obtained by amplifying an output signal of one light quantity detecting means by the amplifying means to a predetermined level, a signal clamped by the clamp means, and an output signal from the other light quantity detecting means. A scanning timing signal generating unit that compares the signal amplified by the amplifying unit, converts the comparison result into a logical level, and generates a signal indicating the scanning timing. 8. The image forming apparatus according to claim 7.