JPH03253357A - Image recorder - Google Patents

Abstract

PURPOSE:To prevent irregularity in image density from occurring by a method wherein control operation is performed by turning on a light source containing a scan period within an image forming area prior to recording operation of an image and besides, after starting recording operation of the image, control is performed by turning on the light source in a scan period outside the inmage forming area within a scan area. CONSTITUTION:In closing a power source of a laser beam printer and in last time rotation, a PRL signal for forced lighting of lasers is made True irrespective of synchronization with an image, and a laser diode 30 is continuously lighted. At the same time an up down counter 37 becomes under a counting state since the PRL signal is True. A photodiode 31 detects outgoing light of a laser diode 30, and feeds that back to a comparator 35 via an amplifier 34. The comparator 35 compares output voltage of the amplifier 34 with standard voltage to be generated with a standard voltage generator 36. When timing between paper to start of exposure of the image on the second page comes after ending exposure of the image on the first page, a NMBL signal between paper to be combinedly used for a laser forced lighting signal and a start signal of a counter 37 outside the image area is made True.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an image recording apparatus that performs automatic optical output control (APC).

[Conventional technology]

Conventionally, in image recording devices using semiconductor lasers, light-emitting diodes, etc. used in printers, copying machines, etc., the light intensity output of the semiconductor lasers, light-emitting diodes, etc. changes depending on temperature and time. Changes in line width of characters, etc. and deterioration of image quality occur. Therefore,
In order to prevent such deterioration in image quality, image recording apparatuses have been put into practical use that control the light intensity output of semiconductor lasers, light emitting diodes, etc. to be kept constant.

FIG. 7 shows an example of an automatic light output control (APC) circuit of an image exposure apparatus 3 using a semiconductor laser. 30 is a laser diode, 31 is a photodiode, and 32 is the amount of current for causing the laser diode 30 to emit light. 33 is a switching circuit thereof. The switching circuit 33 determines whether or not to cause the current determined by the constant current circuit 32 to flow to the laser diode 30 side based on an external image signal.

Further, the photodiode 31 is connected to an amplifier 34,
A comparator 35 compares the output voltage of the amplifier 34 with the output voltage of a reference voltage generator 36 . The output of the comparator 35 is connected to the constant current circuit 32.

A comparator 35 outputs a signal from the photodiode 31 corresponding to the optical output of the laser diode 30 and the reference voltage generator 36.
The comparison result with the output voltage of the laser diode 30 is fed back to the constant current circuit 32 to control the light output intensity of the laser diode 30 to be constant.

FIG. 342 shows an example of a laser beam printer using such an image exposure device 3.

The photosensitive drum 1 rotates in the direction of the arrow, and a latent image is formed on the photosensitive drum 1 by irradiating a laser beam with a zero image exposure device 3 that is uniformly negatively charged by a charging roller 2 to which a high voltage is applied ( image exposure), the latent image is visualized by negatively charged toner in the developing device 4. The visualized toner image is transferred onto a transfer material P by a transfer roller 5 and then fixed by a fixing device 6. The residual toner on the photosensitive drum 1 is removed by a cleaning device 7.

The image exposure device 3 performs APC during a period called a pre-rotation prior to exposure of the first page and between sheets. During the APC period, the emitted light of the semiconductor laser 30 in the image exposure device 3 passes over the photosensitive drum 1. Since the scanning is being performed, a latent image is formed on the photosensitive drum 1 during the APC period, and when the latent image is developed by the developing device 4, unnecessary toner adheres to the photosensitive drum 1. As a result, problems such as toner stains on the transfer roller 5 occur. The dirt on the transfer roller 5 causes dirt on the back side of the transfer material P. Furthermore, if a transfer bias is applied when this latent image passes through a transfer site, a memory is generated in the photosensitive drum 1 corresponding to the latent image. This memory appears as uneven charging potential during the next charging, and when developed, fog occurs on the image.

Therefore, unblanking APC has been proposed in which APC exposure is performed only outside the image area on the sides of the image.

FIG. 8 shows an unblanking APC circuit diagram.

30 is a laser diode, 31 is a photodiode,
32 is a constant current circuit that controls the amount of current for causing the laser diode 30 to emit light, and 33 is a switching circuit thereof.

The switching circuit 33 determines whether or not to cause the current determined by the constant current circuit 32 to flow to the laser diode 30 side based on an external image signal.

The UNBL signal is a horizontal synchronization signal (referred to as BD) required for synchronization in the main scanning direction in order to synchronize images in a laser beam printer that has a laser scanning optical system.
This is a laser forced lighting signal to generate a signal.

When the BD is turned on by the UNBL signal, the current determined by the constant current circuit 32 is applied to the switching circuit 3.
3 to the laser diode 30.

At the same time, the up/down counter 37 enters a counting state because the UNBL signal is true.

A photodiode 31 that detects the optical output intensity of the laser diode 30 feeds back a detected voltage to a comparator 35 via an amplifier 34. A comparator 35 compares this voltage with a reference voltage generated by a reference voltage generator 36.

If the output voltage of the amplifier 34 has not reached the reference voltage, the output of the comparator 35 instructs to count up, and the up/down counter 37 counts up the D/A converter 38 and outputs a constant current through the buffer 39. Circuit 32 increases the current flowing through laser diode 30.

When the diode 30 emits light in the above operation, the UNBL signal has a BD period, becomes True only in the area outside the photoreceptor, and APC exposure is performed only in the area outside the photoreceptor.

If the output voltage of the amplifier 34 is higher than the reference voltage,
The output of the comparator 35 has a logic opposite to that in the above case, causing the counter 37 to count down and the current to the laser diode 30 to decrease.

In this way, if the CLK period of the up/down counter 37 is longer than the response time of the feedback circuit, in unblanking APC, it is possible to correct the current of the laser diode 30 with the least significant bit for each scanning line. .

[Problem that the invention is trying to solve]

However, the above conventional example has the following two drawbacks.

1) In unblanking APC, APC cannot be performed until the scanning mechanism of the laser scanning optical system is in a steady state, and the amount of change in current to the laser diode 30 is minute every BD cycle. For this reason, when the amount of correction of the current to the laser diode 30 is large, such as when the laser beam printer is turned on, or when the laser beam printer is left unused for a long period of time after the power is turned on, the amount of correction of the current to the laser diode 30 is large. It is necessary to input a large number of % security signals to obtain the desired result, which takes a long time, which increases the wait time and first print time of the laser beam printer.

2) Images with solid black or almost uniform density (for example, main scan 1
When the laser diode 30 is driven at a constant current within the page for images with repeated line printing, one-line pauses, or almost uniform halftone images using a pulse width modulation driving method for the image signal, the laser diode 30 Since the light output intensity of the laser diode 30 changes continuously, unevenness on the image is hardly noticeable.
The light output intensity changes discontinuously before and after the scanning in which the current correction has occurred, and a sudden change appears in the image density, resulting in visually extremely noticeable unevenness.

An object of the present invention is to provide an image recording apparatus that solves the above-mentioned technical problems and can improve the quality of images to be recorded without prolonging the waiting time or the like during image recording.

(Means and effects for solving the problems) According to the present invention, an image carrier is scanned with a light beam from a light source, and the light beam is modulated in an image forming area within the scanning area of the light beam. An image recording device for recording an image, comprising a detection means for detecting a light output intensity of the light source, and a detection means for adjusting the light output intensity from the light source to a target light output intensity based on the detection by the detection means. The control means performs a control operation by turning on a light source including a scanning period in the image forming area prior to an image recording operation, and the image recording operation starts. By controlling the light source by turning on the light source during the scanning period within the scanning area and outside the image forming area after the printing has been completed, toner stains on the transfer and cleaning section and fog due to the memory of the photoreceptor are not caused, and The wait time and first print time are short, and image density unevenness is prevented.

[First Embodiment] FIG. 1 is a block diagram showing the configuration of an automatic light output control circuit in an image recording apparatus according to a first embodiment of the present invention.

30 is a laser diode, 31 is a photodiode,
32 is a constant current circuit that controls the amount of current for causing the laser diode 30 to emit light, and 33 is a switching circuit thereof.

The switching circuit 33 determines whether or not to cause the current determined by the constant current circuit 32 to flow to the laser diode 30 side based on an external image signal.

When the laser beam printer, which is the image recording device of the present invention, is powered on or rotates before rotation, the PRL signal, which is a signal for forcing the laser to turn on regardless of image synchronization, is set to True, and the laser diode 30 is turned on continuously. .

At the same time, the up/down counter 37 indicates that the PRL signal is true.
e, it enters a counting state.

A photodiode 31 detects the light emitted from the laser diode 30 and sends it to a comparator 35 via an amplifier 34.
Give feedback. Comparator 35 compares the output voltage of amplifier 34 with a reference voltage generated by reference voltage generator 36 . When the output voltage of the amplifier 34 has not reached the reference voltage, the output of the comparator 35 is output to the up/down counter 37.
The output value to the D/A converter 38 is counted up. The output of the D/A converter 38 is given to the constant current circuit 32 via the buffer 39, thereby increasing the current flowing through the laser diode 30.

When the output voltage of the amplifier 34 reaches the reference voltage,
The PRL signal is set to false, and the counter 37 is placed in a hold state. At this time, the laser diode 30 is driven at a constant current using the held current value to perform image exposure for the first page.

When the image exposure of the first page is finished and the paper interval timing is reached until the start of image exposure of the second page, the paper interval UNBL signal which serves as the laser forced lighting signal and the start signal of the counter 37 is set to True outside the image area.

Photodiode 31 detects the optical output intensity of laser diode 30 and feeds the detected voltage back to comparator 35 via amplifier 34 .

Comparator 35 is based on the output voltage of amplifier 34! ! It is compared with a reference voltage generated by the voltage generator 36.

If the output voltage of the amplifier 34 does not reach the reference voltage,
The output of the comparator 35 instructs to count up, and the up/down counter 37 counts up the output value to the D/A converter 38.

The output of the D/A converter 38 is given to the constant current circuit 32 via the buffer 39, thereby increasing the current flowing through the laser diode 30.

When the output voltage of the amplifier 34 is higher than the reference voltage,
The output of the comparator 35 has a logic opposite to that in the above case, causing the counter 37 to count down and the current to the laser diode 30 to decrease.

In this way, if the CLK period of the up/down counter 37 is longer than the response time of the feedback circuit, in unblanking APC, the current of the laser diode 30 is corrected using the least significant bit for each scanning line.

When the correction of the optical output intensity is completed, the inter-paper UNBL signal is fa
lse, the counter 37 is placed in a hold state, and the laser diode 30 is driven at a constant current using the held current value to perform image exposure for the second page.

The paper interval unblanking APC is performed for the paper interval after the second page in the same way as the paper interval between the first page and the second page.
Corrects fluctuations in light output intensity due to temperature rise of the laser during continuous use.

Specifically, an example in which the image exposure apparatus shown in FIG. 1 is used as the image exposure apparatus 3 of a laser beam printer as shown in FIG. 2 will be described.

In Fig. 2, when the forward rotation operation is started, the A of φ30
Photosensitive drum 1 with OPC photosensitive material coated on J2 cylinder
is rotated at a process speed of 47 mm/see, and negatively charged to 600 V by the charging roller 2. As this charging roller 2, a conductive elastic body is used.

During the pre-rotation operation, the image exposure device 3 continuously lights up the AP.
Since the light from the laser diode 30 scans the photosensitive drum 1, a latent image is formed on the photosensitive drum 1. When the latent image is developed by the negatively charged toner of the developing device 4, the photosensitive drum Unnecessary toner adheres to the transfer roller 1, resulting in staining of the transfer roller 5.However, during the previous rotation, the problem c can be easily solved in the following points compared to the paper spacing.

Toner stains on the transfer roller 5 will not adhere to the back surface of the transfer material if a polar (negative) bias is applied to the transfer roller 5 so that the toner on the transfer roller 5 is transferred to the photosensitive drum 1. When using continuous lighting APC between sheets C
If an attempt is made to transfer the toner adhering to the photosensitive drum 1, the throughput will be extremely reduced. If the toner is not transferred to the photosensitive drum 1, the toner will appear as a stain on the back side of the next transfer material. On the other hand, when performing continuous lighting APC during the pre-rotation, the throughput will not deteriorate even if the toner attached to the transfer roller 5 is transferred to the photosensitive drum 1, and the surface of the transfer roller 5 can be sufficiently cleaned. I can do it.

An operation time chart in such a case is shown in FIG.

Alternatively, the operation may be performed as shown in FIG. In this case, for the latent image formed by the continuous lighting APC,
If a positive transfer bias is applied when the developing bias is turned off and the image passes through the transfer site without being developed, a memory is generated on the photoreceptor corresponding to the latent image.

If the transfer bias is set negative to prevent memory from occurring, when the developing bias is turned off for the latent image formed by continuous lighting AP and C, the developing bias is off and the non-exposed area of the photosensitive drum 1 has the opposite polarity. Since the toner charged to a positive polarity is attached, this toner is transferred onto the transfer roller 5. Attempts to clean this toner between sheets will result in a reduction in throughput, but during the pre-rotation, a positive bias is applied to the toner adhering portion on the transfer roller 5 with a tie ring facing the photosensitive drum 1. By doing so, the transfer roller 5 can be cleaned during the period W1.

Note that in the example described above, the photosensitive drum 1 is
However, charging was not started at the start of the previous rotation, and continuous lighting APC was performed on the uncharged part of the photosensitive drum 1, and A
Charging may be started after the PC is finished, and in this case, the above-mentioned problem does not occur, and the pre-rotation time increases by about 0.3 m5ec at most, which poses no problem.

From the above, continuous lighting APC during pre-rotation can be executed without any problem.

When the drive current of the laser diode 30 to obtain the target light output intensity is held by the continuous lighting APC during pre-rotation, the image exposure device 3 applies a 300 dpi light to the charged surface.
An image-modulated laser beam is projected onto the area, and the potential at that area is attenuated to form an electrostatic latent image.

When this electrostatic charge ms arrives at the developing portion of the developing device 4 facing the photosensitive drum 1, negatively charged toner is supplied from the developing device 4 and adheres to the latent image portion to form a toner image 6
During the image exposure period, the laser diode 30 is driven with a constant current, so that sudden density unevenness does not occur during development.

When the photosensitive drum 1 further rotates and the toner image reaches a transfer site that is a pressure nip between the photosensitive drum 1 and a transfer roller 5 with a diameter of 20 mm that is in pressure contact with the photosensitive drum 1, the transfer material P
is conveyed to the transfer site, and at the same time, a positive transfer bias is applied to the transfer roller 5, and the toner image on the photosensitive drum 1 is transferred to the transfer material.

Thereafter, the transfer material P is separated from the photosensitive drum 1, and the toner image is fixed onto the transfer material P by a fixing device 6. On the other hand, the toner remaining on the photosensitive drum i is removed by a cleaner 7, and the photosensitive drum 1 is The image forming process will begin.

The transfer roller 5 is generally made of chloroprene rubber, N
By dispersing carbon, etc. in BR, urethane rubber, silicone rubber, EPDM, etc., the volume resistance can be increased to 105~10''Ωe.
m, hardness adjusted to 20 to 30° (Asker-C hardness), or use polyvinylidene fluoride, polyester thermoplastic elastomer, polyolefin thermoplastic elastomer, or urethane thermoplastic elastomer on the surface of this roller. Plastic elastomer Polystyrene thermoplastic elastomer Polyamide thermoplastic elastomer Fluorine thermoplastic elastomer, ethylene-vinyl acetate thermoplastic elastomer Polyvinyl chloride thermoplastic elastomer is coated with a two-layer structure, and this elastomer is coated with carbon. Mixing conductive fillers such as black, metal phase, or semiconductive fillers such as titanium compounds, nickel compounds, silicon compounds, etc.
Alternatively, the resistance of the elastomer can be adjusted by changing the structure of the polymer itself, increasing the volume resistance of the elastomer layer to 1011~
It shall be adjusted to 1015 Ωcm.

The image exposure device 3 will be described in further detail.

! In Figure @1, a 5 mW laser diode 30 and a photodiode 31 are integrated into a laser unit with a φ9 package, and the reference voltage generator 36 is configured by dividing the circuit supply voltage Vcc by a variable resistor. Note that a 12-bit D/A converter was used as 38.

Since the far field pattern of light emission from the laser diode 30 varies among individual laser diodes 30, the efficiency of transmitting the divergent light of the laser diode 30 in the optical system of the image exposure device 3 through the collimator lens that converts it into parallel light varies. As a result, in order to obtain a desired amount of light on the surface of the photosensitive drum, the light output intensity on the surface of the laser diode 30 chip varied from about 1.5 to 4.0 mW depending on the individual laser diodes.

Continuous lighting AP like this example as APC during pre-rotation
If unblanking APC is used instead of C, it will take a maximum of 1.5 seconds or more to reach the target light output, but continuous lighting APC during pre-rotation as in the present invention
By using this, it was possible to complete the process within 250m5ec at maximum.

The unblanking APC1f light between the sheets is approximately 1.8m5
The unblanking APC between 0 sheets, which was performed for a period of about 150 μsec for each BD cycle of ec, could be completed in one to several main scanning lines.

According to this embodiment of the present invention, it is possible to provide an image recording apparatus having an image exposure apparatus that performs unblanking APC, has a short wait time and first print time, and does not cause sharp density unevenness within a page.

Next, as another embodiment of the present invention, an image exposure apparatus 3 having an automatic light output control mechanism similar to that shown in the embodiment described above will be described.
In a laser beam printer using a laser beam printer, a case will be described in which staining of the transfer roller 3 is prevented and transfer roller 3 is cleaned by applying a bias having the same polarity as the toner to the transfer roller 3 between sheets.

The laser beam printer is similar to that shown in FIG.

! FIG. 45 shows a sequence diagram of this embodiment. This will be explained based on FIG.

The photosensitive drum 1 is rotated by the main motor or the like at a process speed of 47 mm/see, and the printer is put into a pre-rotation operation which is the kth preparatory rotation for printing. Continuous lighting APC is performed during the pre-rotation, and the light output intensity of the laser diode 30 is set as a target value. When the continuous lighting APC is finished, the charging roller 2 is applied with a DC bias of 600V for 400H.
z.

A charging bias superimposed with an AC bias of 150Vp-p is applied to charge the photosensitive drum 1 to -600V.Next, a DC bias of -450V and a DC bias of 1800Hz, TaOOV is applied to the developer carrier of the developing device 4 having negatively charged toner.
A pp alternating current bias was superimposed. Apply developing bias. +1 to the transfer roller 5 similar to that shown in the first embodiment.
．． Apply a positive transfer bias of 5 kV.

When printing of the first page is started, the laser diode 30 is driven at a constant current value determined during the previous rotation to perform image exposure. The surface potential of the exposed photosensitive drum 1 is attenuated to -150V, developed with toner in a developing device 4, and transferred onto a transfer material P by a transfer roller 5.

When the printing of the first page is completed and there is a paper interval, the image exposure device 3 performs unblanking APC similar to that shown in the first embodiment, and corrects the light output intensity of the laser diode 30.

On the other hand, a negative transfer bias of -2 kV is applied to the transfer roller 5 between sheets. At this time, the surface of the photosensitive drum 1 is -60
Since the transfer roller 5 is uniformly charged to 0V, the negatively charged toner adhering to the surface of the transfer roller 5 is transferred from the surface of the transfer roller 5 to the surface of the photosensitive drum 1, and the surface of the transfer roller 5 is cleaned. Since unblanking APC is performed between papers,
The transfer roller 5 scrapes off the developing toner on the photosensitive drum 1 when continuous lighting APC is performed between sheets, and the surface of the transfer roller 5 is not soiled. Also, the surface potential of the photosensitive drum 1 during cleaning of the transfer roller between sheets. Since the surface of the transfer roller 5 is -like, the surface of the transfer roller 5 can be uniformly turned.

The larger the potential difference between the negative transfer bias and the surface potential of the photosensitive drum 1, the higher the cleaning effect on the surface of the transfer roller 5, but it must be at a level that does not cause dielectric breakdown of the photosensitive member. According to the paper, dielectric breakdown of the photoreceptor occurred when the negative transfer bias was set to -4kV, so
The negative transfer bias is preferably −3.5 kV or less.

When printing the second page, unblanking A
The laser diode 30 is driven with a constant current value determined by the PC to perform image exposure. At this time, a negative transfer bias is applied.

When printing of the second page is completed, the laser beam printer enters post-rotation, turns off the charging bias, developing bias, and positive transfer bias and stops.

According to this embodiment, the effects of shortening the first print time shown in the above-mentioned embodiments and preventing sudden unevenness in image shading are achieved, and since the transfer roller 5 is prevented from becoming dirty, the transfer material This prevents toner stains on the back of the P. Further, since the transfer roller 5 is cleaned between sheets, the cleaning time of the transfer roller 5 during the forward rotation and the backward rotation can be shortened. As a result, it is possible to shorten the time for the front rotation and the back rotation, thereby shortening the printing time.In addition, it is possible to reduce the abrasion of the photoconductor, especially in the cleaning section, caused by the rotation of the photoconductor drum 1. It also has the effect of prolonging the lifespan of the body.

[Second Embodiment] In this embodiment, the size of the transfer material in the image scanning width direction is detected and the light emitting time during sheet unblanking APC is switched.

This embodiment will be explained with reference to FIG.

Reference numeral 1 indicates a photoreceptor, reference numeral 30 indicates a semiconductor laser light source,
80 is a collimator lens, 81 is a polygon mirror for scanning the laser beam, 82 is an imaging lens for focusing the laser beam to a predetermined beam diameter, and 83 is for making a part of the laser beam incident on the laser beam detector 84 The reflecting mirror 85 indicates the position where a signal for controlling the image signal is sent to the image signal control circuit, and S (shaded area) is the area swept by the laser beam.

Prior to image recording, the image recording apparatus of this embodiment detects the size of the transfer material in the image scanning width direction using a paper feed cassette capable of recognizing the size of the transfer material, a transfer material width detection sensor, or the like.

During pre-rotation prior to image recording of the first page, continuous lighting APC is performed, the laser diode 30 is driven with a constant current, and one-page one-color image exposure is performed.

Between the first and second pages, APC is applied at a position corresponding to the image area of the transfer material according to the detected size of the transfer material.
is performed to correct the drive current of the laser diode 30.

For example, in the case of the transfer material size of 86 in figure 's6,
APC is performed in an area shown by 7, and in the case of a transfer material size of 88, APC is performed in an area shown by 89.

As a result, in the case of a small-sized transfer material, by increasing the correction amount of the light output intensity of the laser diode 30 in one light emission of the paper-to-paper unblanking APC, the number of light emission scans in the paper-to-paper unblanking APC can be reduced. can be reduced.

In addition, in the case of small-sized transfer materials, memory of the photosensitive drum 1 occurs due to the application of transfer bias to the paper unblanking APC exposure section, but since it is outside the area of the transfer material, it does not appear in the image and is a problem. do not have.

Contamination of the transfer roller 5 when the exposed area is developed is not a problem in actual purchase because the number of scans of the paper-to-sheet APC is small in this embodiment, but it is preferable that the transfer roller 5 transfers the toner to the photosensitive drum 1. Apply a bias to
It is preferable to remove the toner on the surface of the transfer roller 5 by mechanically rubbing the surface of the transfer roller 5 or the like.

〔Effect of the invention〕

As explained above, according to the present invention, the control means operates during the image non-output period, operates continuously including the image forming area of the image carrier when operating prior to image recording, and operates continuously including the image forming area of the image carrier during other operations. By operating without including any area, toner stains on the transfer section and cleaning section and fog due to memory on the photoreceptor are not caused, and the wait time and first print time are short, and image density unevenness is prevented. The effect is that it can be done.

[Brief explanation of drawings]

Figure 1 is a block diagram showing the configuration of an automatic light output control circuit in an image recording apparatus according to the first embodiment of the present invention, Figure 2 is a sectional view of the image recording apparatus, and Figures 3 to 5 are FIG. 6 is a diagram for explaining the operation in the second embodiment, and FIGS. 7 and 8 are the configurations of conventional automatic light output control circuits. FIG. 3... Image exposure device 30... Laser diode 31... Photodiode 2... Constant current circuit 3... Switching circuit 5... Comparator 6... Reference voltage generation circuit 7... Up/down counter 8... D/A converter No. 7 VCQ Vself C Bow S Figure

Claims (1)

[Scope of Claims] An image recording apparatus that scans an image carrier with a light beam from a light source and records an image by modulating the light beam in an image forming area within the scanning area of the light beam, comprising: a detection means for detecting the light output intensity of the light source; and a control means for controlling the light output intensity from the light source to a target light output intensity based on the detection by the detection means; The means performs a control operation by turning on a light source including a scanning period within the image forming area prior to the image recording operation, and performs a control operation within the scanning area after the image recording operation is started. An image recording apparatus characterized in that a control operation is performed by turning on a light source during a scanning period outside an image forming area.