JP2003341131A - Imaging apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an imaging apparatus which can adjust a plotting timing of laser beams precisely by a small number of parts. <P>SOLUTION: The imaging apparatus has laser equipment 1K and 1Y corresponding to each photoreceptor. The laser equipment 1K and 1Y are arranged so that respective optical axes including a normal of a deflection face become symmetric to each other via a plane orthogonal to a rotational axis direction of a polygon mirror. Each laser equipment also has a light emitting element and an optical sensor. In other words, the optical sensor of the laser equipment 1Y can detect laser beams emitted from the laser equipment 1K. A scanning start timing can be controlled on the basis of a detection timing of the laser beam. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image. More specifically, the present invention relates to an image forming apparatus having a print head that optically scans using a laser beam.

[0002]

2. Description of the Related Art Conventionally, a print head of an image forming apparatus forms an electrostatic latent image by scanning a laser beam on a photosensitive member using a polygon mirror. Further, the scanning start timing of the laser beam is determined by a scanning start signal (hereinafter referred to as "SOS signal"). As shown in the conceptual diagram of FIG. 9, this SOS signal indicates the light reception timing of the laser beam detected by the scanning start timing detection sensor (hereinafter referred to as “SOS sensor”) arranged near the start end of the scanning region. It is output to the base.

Further, on the photosensitive member, due to uneven rotation of the polygon mirror or accuracy error of the deflecting surface of the polygon mirror,
A position shift in the main scanning direction as shown in FIG. 10 may occur. Such misalignment causes considerable image deterioration at the position where the image is written (hereinafter referred to as “EOI”). In order to correct this image deterioration, the position of the beginning of writing the image (hereinafter referred to as “SOI”) and the EOI
Has been proposed, and a drawing timing is adjusted based on the detected content (Patent Publication No. 26).
No. 15668). With such a print head,
As shown in the conceptual diagram of No. 1, in addition to the SOS sensor, a scanning end timing detection sensor (hereinafter referred to as “EOS sensor”) is provided near the end of the scanning area of the photoconductor.

[0004]

However, the above-mentioned conventional image forming apparatus has the following problems.
That is, in order to detect the light receiving timing of each laser beam on the photoconductor, the SOS sensor or E for each photoconductor is detected.
OS sensor required. Then, the SOS sensor and the EOS sensor must be arranged near the photoconductor. Therefore, the arrangement of devices inside the image forming apparatus becomes complicated.

The present invention has been made to solve the problems of the above-described conventional image forming apparatus. That is, an object of the invention is to provide an image forming apparatus capable of adjusting the drawing timing of a laser beam with a small number of parts and with high accuracy.

[0006]

An image forming apparatus, which has been made for the purpose of solving this problem, is an image forming apparatus which forms an image by scanning a plurality of light beams, and has a plurality of deflecting surfaces and is rotatable. With a built-in optical deflector and optical sensor
It has a light source and a second light source with a built-in optical sensor. The first light source and the second light source each have a plane whose optical axis includes the normal line of the deflection surface and is orthogonal to the rotation axis direction of the optical deflector. It is arranged so as to be symmetrical with respect to each other, and the drawing timing is controlled based on the timing at which the optical sensor of one light source receives the light beam emitted from the other light source.

In this image forming apparatus, the first light source and the second light source are arranged so that their optical axes are symmetrical with respect to a plane that includes the normal line of the deflection surface and is orthogonal to the rotation axis direction of the optical deflector. is doing. Therefore, there is a moment when the light beam emitted from one light source is deflected by the optical deflector and is incident on the other light source. In addition, each light source has an optical sensor. Therefore, each light source can detect the incidence of the light beam emitted from the other light source by its own optical sensor. Then, the scanning timing of the laser beam can be controlled based on the detection timing of the light beam.
Therefore, it is not necessary to provide a component for detecting various timings. Therefore, the scanning timing of the laser beam can be adjusted with a small number of parts.

Further, in this image forming apparatus, the drawing start timing can be controlled based on the timing at which one optical sensor receives the light beam. That is, the signal output from the optical sensor at the light receiving timing can be the SOS signal. Therefore, it is not necessary to provide the SOS sensor.

Further, in this image forming apparatus, a signal output when one optical sensor receives a light beam can be used as a signal indicating the drawing end timing. That is, the signal output from the optical sensor at the light receiving timing can be the EOS signal. Therefore, E
There is no need to provide an OS sensor.

Further, in the image forming apparatus of the present invention, it is preferable that the light amount adjustment of the first light source and the second light source is performed based on the output value of the optical sensor of each light source. By adjusting the light amount, the drive current of the light source can be controlled. That is, the optical sensor built in each light source can output a signal for adjusting the scanning timing and a signal for controlling the current. As a result, it is not necessary to separately provide devices for controlling these. In the case of a monochrome image, only the light amount adjustment of one light source may be performed.

Further, in this image forming apparatus, during the first sampling period, the first light source emits a predetermined amount of light to hold the drive current value at that time, and the first sampling period. Second current control means for holding the drive current value at that time by causing the second light source to emit a predetermined amount of light during a second sampling period that does not overlap with the first light source and the second light source. To the first current control means and the second current control means, and drawing means for drawing on the respective image signals while being driven by the drive current values held by the respective first and second current control means. The timing at which the light sensor of the light source that does not emit light detects the light beam during the period or the second sampling period may be used as the reference for the drawing timing control.

This image forming apparatus causes the light source to emit light during the sampling period corresponding to each light source and holds the drive current value when the detected light amount reaches a predetermined value. The sampling periods do not overlap. That is, the second light source does not emit light during the sampling period of the first light source. On the other hand, the first light source does not emit light during the sampling period of the second light source. Therefore, the detected light quantity is not affected by the light source of the other party. Further, during the hold period, drawing is performed on each image signal while driving with each drive current value controlled during the sampling period. As a result, a latent image can be formed with a stable light amount. Further, the timing at which the optical sensor of the light source that does not emit light detects a light beam during the first sampling period or the second sampling period is used as a reference for drawing timing control. Accordingly, the drawing timing control and the drive current control can be performed by the pair of optical sensors. Therefore, it is possible to adjust the scanning timing and control the drive current with a small number of parts.
The sampling period is a period for controlling the drive current value of the light source. The hold period is a period in which the light source emits light for drawing according to the held current value.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the image forming apparatus according to the present invention will be described below with reference to the drawings. In this embodiment, the present invention is applied to a tandem type color printer.

[First Embodiment] A color printer according to the first embodiment includes laser devices 1K and 1K as shown in the configuration diagram of FIG.
C, 1M, 1Y, collimator lens 2, polygon mirror 3, fθ lens 4, reflection mirrors 5K, 5C, 5
M, 5Y and photoconductors 7K, 7C, 7M, 7Y. Then, laser beams LK, LC, LM, and LY are emitted from the laser devices 1K, 1C, 1M, and 1Y, respectively. In addition, laser beams LK, LC, LM, LY
Are irradiated onto the photoconductors 7K, 7C, 7M and 7Y, respectively. Note that, in FIG. 1, the collimator lens 2 and each laser device are actually present at positions substantially overlapping with the fθ lens 4 and the like. However, in order to make it easier to see, they are drawn with the actual position shifted downward in the figure.

As shown in the conceptual diagram of FIG. 2, the laser device 1K includes a light emitting element EK and an optical sensor PDK arranged on the back surface of the light emitting element EK. Therefore, the laser device 1K can detect the amount of light when the light emitting element EK is emitting light. In addition, the light emitting element E
If light from another laser device enters when K is not emitting light, that fact can be detected. The other laser devices also include a light emitting element and an optical sensor, like the laser device 1K.

Further, in the laser device 1K and the laser device 1Y, as shown in the conceptual diagram of FIG. 3, the angle of incidence on the deflection surface of the polygon mirror 3 includes the normal line A of the deflection surface and the rotation axis of the polygon mirror 3 It is arranged so as to be symmetrical with respect to a plane orthogonal to the B direction. The laser device 1C and the laser device 1M are also arranged so as to have the same positional relationship as the laser device 1K and the laser device 1Y.

Next, the operation of the color printer of this embodiment will be described. First, laser devices 1K, 1C, 1M, 1
The four divergent lights emitted from the Y light emitting element are converted into four parallel laser beams LK and L by the collimator lens 2.
C, LM, LY. Each laser beam is applied to the polygon mirror 3 and is deflected by the polygon mirror 3. Each deflected laser beam is irradiated onto each photoconductor through the fθ lens 4 and each reflection mirror.

Further, each photoconductor is rotationally driven in synchronization with the scanning of the corresponding laser beam. As a result, exposure corresponding to the image data of each color is performed, and an electrostatic latent image is formed on each photoconductor. Then, toner is attached to the electrostatic latent image, and the toner image is transferred to the recording paper.

Next, the control of the scanning start timing of the laser beam will be described with reference to the conceptual diagram of FIG. The conceptual diagram of FIG. 4 is a diagram viewed from above in FIG. In FIG. 4, the polygon mirror 3 rotates counterclockwise. Therefore, on the photoconductor 7K, the irradiation position of the laser beam LK moves from left to right in FIG. In addition, in FIG. 4, laser device 1K
Are actually present at positions substantially overlapping with the laser device 1Y. However, here, the laser device 1
K is shifted from the actual position to the left in the figure.

The control of the scanning start timing of the laser beam is based on the time when the laser device 1Y detects the laser beam LK emitted from the laser device 1K. The timing at which the laser device 1Y receives the laser beam LK is, as shown in the conceptual diagram of FIG. 5, the laser beam LK emitted from the laser device 1K with respect to the deflection surface of the polygon mirror 3 in the X direction in FIG. It is when it is incident vertically. At this light reception timing, the SOS signal is output by the optical sensor PDY. Then, the scanning start timing is controlled by the SOS signal. Then, the laser beam LK is irradiated onto the photoconductor 7K in accordance with the scanning start timing. That is, the scanning start timing is controlled by receiving the laser beam LK from the laser device 1Y before irradiating the scanning area on the photoconductor 7K.

The color printer of this embodiment controls the current of each laser device. In this control, the light amount of each laser device is detected for a certain period, and the current value is set based on the detected light amount. The light quantity of the laser device is obtained based on the signal output from the optical sensor built in the laser device.

Next, the control of the laser devices 1K and 1Y will be described with reference to the timing chart of FIG. The EK forced light emission signal and the EY forced light emission signal in FIG. 6 are signals for forcing the light emitting elements EK and EY to emit light, respectively. In addition, the term “compulsively” here means that the light emitting element emits light regardless of the image signal.

First, during the sampling period TY, the light emitting element E
Y is forcibly emitted by the EY forced emission signal. During this time, the light emitting element EK does not emit light. Then, during this period, the drive current of the light emitting element EY is adjusted so that the amount of light detected by the optical sensor PDY becomes a predetermined value. Then, the current value when the detected light amount reaches a predetermined value is held. By this,
The current value of the laser device 1Y is set. This period for setting the current value is the "sample period". When the sample period TY ends, the light emitting element EY is turned off.
Next, during the sample period TK, the light emitting element EK is forcibly made to emit light by the EK forced light emission signal. During this period, the light emitting element EY does not emit light. And during this time, the optical sensor PDK
The drive current of the light emitting element EK is adjusted so that the detected light amount of is a predetermined value. Then, the current value when the detected light amount reaches the predetermined value is held separately from the current value held for the light emitting element EY. As a result, the laser device 1
The current value of K is set. Note that the sampling period TY and the sampling period TK do not overlap. This is because if both are made to emit light at the same time, detection of the amount of light will be affected.

Further, during the sampling period TK, there is a moment when the laser beam LK of the laser device 1K enters the laser device 1Y as shown in FIG. The output of the photosensor PDY at this time is the SOS signal. Based on this SOS signal, the drawing start timing SOI of the laser devices 1K and 1Y
Is determined. After the drawing start timing SOI, the laser devices 1K and 1Y are driven by the current value held for each, and blink according to each image data. Drawing is thus performed. The period in which the laser devices 1K and 1Y follow the current value held is the "hold period".

It is preferable that the interval between the output timing of the SOS signal and the drawing start timing SOI is short. This is because the shorter the distance is, the shorter the distance between the laser device and the photoconductor can be, so that the color printer itself can be made compact.

A sampling period including the timing at which the SOS signal is output (the sampling period TK in this embodiment)
Is preferably longer than the other sample periods (the sample period TY in this embodiment). This is because the SOS signal can be reliably output even if the rotation speed of the polygon mirror 3 has some unevenness by lengthening the sample period.

The above current control is performed by the LD drive circuit 10 shown in the block diagram of FIG. LD drive circuit 10
Is a sample and hold circuit 11 and a current control circuit 12
And a switching circuit 13. The current control circuit 12 controls the current value. sample&
The hold circuit 11 causes the current control circuit 12 to set the current value during the sampling period to hold the current value, and holds the held current value during the hold period.
It is what you instruct 2. The switching circuit 13 blinks the light emission of the light emitting element according to the input image data. The LD drive circuit 10 is provided for each laser device.

When forming a monochrome image with the color printer of this embodiment, only one light emitting element emits light. For example, when forming an electrostatic latent image on the photoconductor 7K, only the light emitting element EK is caused to emit light. The light amount of the light emitting element EK is detected by the output signal of the photo sensor PDK. Further, the SOS signal is output by the photosensor PDY.

As described in detail above, the color printer of this embodiment is provided with the laser devices 1K and 1K corresponding to the respective photoconductors.
It has C, 1M and 1Y. And the laser device 1Y
Are arranged at positions where the laser beam LK emitted from the laser device 1K can be received while the polygon mirror 3 is rotating. In addition, each laser device is provided with a light sensor along with a light emitting element. Therefore, the laser beam LK can be detected by the optical sensor PDY of the laser device 1Y. The signal output from the optical sensor PDY upon detection is used as the SOS signal. Furthermore, based on this SOS signal,
The scanning start timing of the laser beam is controlled. As a result, the SOS for the laser devices 1K and 1Y
There is no need to provide a sensor. Furthermore, the laser device 1C,
The same applies to 1M. Therefore, an image forming apparatus capable of adjusting the scanning start timing of the laser beam with a small number of parts is realized.

Further, the color printer of the present embodiment detects the light quantity of the laser device based on the output signal of the optical sensor built in the laser device. And
The sample period for detecting the light amount is set to a time when the sample period TK of the light emitting element EK and the sample period TY of the light emitting element EY do not overlap each other. That is,
It is assumed that the light emitting element EY does not emit light during the sampling period of the light emitting element EK. On the other hand, during the sampling period of the light emitting element EY, the light emitting element EK does not emit light.
Therefore, the detected light amount is not affected by the light emitting element of the other party. Therefore, stable latent image formation can be performed.

[Second Mode] The color printer of the second mode is different from the color printer of the first mode in that it is equipped with an SOS sensor 6K as shown in the conceptual diagram of FIG. Further, in FIG. 8, the polygon mirror 3 rotates clockwise, which is the reverse of the first embodiment. Therefore, on the photoconductor 7K,
The irradiation position of the laser beam LK moves from right to left in FIG. It should be noted that an SOS sensor is provided near the other photoconductors as well as the photoconductor 7K.

Further, the laser device 1K and the laser device 1
Y has a light emitting element and an optical sensor as in the first embodiment. Further, the laser device 1K and the laser device 1Y have a plane in which the angle of incidence on the deflection surface of the polygon mirror 3 includes the normal line of the deflection surface and is orthogonal to the rotation axis direction of the polygon mirror 3 as in the first embodiment. They are arranged so as to be symmetrical with respect to each other.

Next, the adjustment of the scanning timing of the laser beam will be described with reference to the conceptual diagram of FIG. The laser printer of this embodiment differs from the first embodiment (see FIG. 4) in the rotation direction of the polygon mirror 3. The adjustment of the scanning timing of the laser beam is based on the time when the SOS sensor 6K detects the laser beam LK emitted from the laser device 1K and the time when the laser device 1Y detects it. First, SO
The SOS signal is output by the SOS sensor 6K at the light receiving timing of the S sensor 6K. After that, the photoconductor 7K is irradiated with the laser beam LK. After that, a scanning end signal (hereinafter referred to as an “EOS signal”) is output by the optical sensor PDY at the light receiving timing of the laser device 1Y.
The rotation speed and the clock speed of the polygon mirror 3 are adjusted based on the SOS signal and the EOS signal.

As described in detail above, the color printer of this embodiment includes the SOS sensor 6K. And
The laser device 1Y is arranged at a position where the laser beam LK emitted from the laser device 1K can be received while the polygon mirror 3 is rotating. For this reason,
The laser beam LK can be detected by the optical sensor PDY of the laser device 1Y. The signal output from the optical sensor PDY upon detection is used as an EOS signal. Further, the scanning timing of the laser beam is controlled based on the EOS signal and the SOS signal output from the SOS sensor 6K. As a result, it is not necessary to provide an EOS sensor for the laser devices 1K and 1Y. The same applies to the laser devices 1C and 1M. Therefore, an image forming apparatus has been realized in which the drawing timing of the laser beam can be adjusted with a small number of parts.

The present embodiment is merely an example and does not limit the present invention. Therefore, naturally, the present invention can be variously improved and modified without departing from the gist thereof. For example, the color printer of the present embodiment is a tandem type, but the color printer is not limited to this. That is, a plurality of laser beams may be irradiated onto one photoconductor to write a plurality of lines in one scan.

Further, the laser device 1K and the laser device 1Y of this embodiment are arranged at the same position in the left-right direction of the polygon mirror 3 in FIG. 3, but the invention is not limited to this. That is, the laser device 1K and the laser device 1
It suffices that the respective optical axes of Y are arranged symmetrically with respect to a plane that includes the normal line A of the deflecting surface and that is orthogonal to the rotation axis B direction of the polygon mirror 3. Therefore, the laser device 1K and the laser device 1Y may be arranged at appropriate positions by using a reflection mirror or the like.

Further, in the color printer of the present embodiment, the scanning start timing is controlled based on the SOS signal during the subsequent sampling period, but the present invention is not limited to this. That is, the scan start timing may be controlled based on the SOS signal output during the previous sample period. For example, in FIG.
If the optical sensor PDK receives the laser beam LY during the sampling period TY of the
The scanning start timing may be controlled based on the S signal. However, since the distance between the laser device and the photosensitive member is increased, it is possible to make the color printer itself more compact by outputting the SOS signal during the subsequent sampling period.

[0038]

As is apparent from the above description, according to the present invention, there is provided an image forming apparatus capable of adjusting the drawing timing of a laser beam with a small number of parts and with high accuracy.

[Brief description of drawings]

FIG. 1 is a diagram showing a device configuration of an image forming apparatus according to an embodiment.

FIG. 2 is a conceptual diagram showing an internal configuration of a laser device according to an embodiment.

FIG. 3 is a conceptual diagram showing a cross section in a rotation axis direction including a rotation axis of the polygon mirror in the first embodiment.

FIG. 4 is an optical system (S of the image forming apparatus according to the first embodiment;
It is a conceptual diagram which shows (without OS sensor).

FIG. 5 is a conceptual diagram showing a deflecting surface of a polygon mirror in the first embodiment.

FIG. 6 is a timing chart showing the emission timing of the laser devices 1K and 1Y and the detection timing of the SOS signal.

FIG. 7 is a block diagram showing a drive circuit of a laser device according to an embodiment.

FIG. 8 is an optical system (E of the image forming apparatus according to the second embodiment.
It is a conceptual diagram which shows (without OS sensor).

FIG. 9 is an optical system (S of the image forming apparatus according to the related art.
It is a conceptual diagram showing (with OS sensor).

FIG. 10 is a diagram showing a positional deviation of a laser beam due to uneven rotation of a polygon motor.

FIG. 11 is a conceptual diagram showing an optical system (with an EOS sensor) of an image forming apparatus in a conventional form.

[Explanation of symbols]

1K laser device 3 polygon mirror 5K reflective mirror 6K SOS sensor 7K photoconductor 10 LD drive circuit 11 Switching circuit 12 Current control circuit 13 sample circuit

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Yoshikazu Watanabe             2-3-13 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka             Toki Building Minolta Co., Ltd. (72) Inventor Naruyuki Tanaka             2-3-13 Azuchi-cho, Chuo-ku, Osaka-shi, Osaka             Toki Building Minolta Co., Ltd. F-term (reference) 2C362 AA00 AA11 BA04 BA70                 2H045 BA22 BA34 CA88 CA89 CA98                       CB42                 5C072 AA03 BA04 BA19 HA02 HA06                       HA13 HB04 HB08 HB11 QA14                       UA18

Claims (5)

[Claims] 1. An image forming apparatus for scanning a plurality of light beams to form an image, an optical deflector having a plurality of deflecting surfaces and rotating, a first light source having a built-in optical sensor, and a built-in optical sensor. And a second light source, wherein the optical axes of the first light source and the second light source are symmetrical with respect to a plane that includes a normal line of the deflection surface and is orthogonal to the rotation axis direction of the optical deflector. An image forming apparatus which is arranged in such a manner that the drawing timing is controlled based on the timing at which the optical sensor of one light source receives the light beam emitted from the other light source. 2. The image forming apparatus according to claim 1, wherein the drawing start timing is controlled based on the timing at which one of the optical sensors receives a light beam. 3. The image forming apparatus according to claim 1, wherein a signal output when one of the optical sensors receives a light beam is used as a signal indicating a drawing end timing. apparatus. 4. Any one of claims 1 to 3
The image forming apparatus according to the third aspect, wherein the light amounts of the first light source and the second light source are adjusted based on the output values of the optical sensors of the respective light sources. 5. The image forming apparatus according to claim 4, wherein the first light source emits a predetermined amount of light during a first sampling period to hold a drive current value at that time.
Current control means, second current control means for causing the second light source to emit a predetermined amount of light during a second sampling period that does not overlap with the first sampling period, and holding a drive current value at that time; In addition, the first light source and the second light source are driven by the first current control means and the second current control means at the drive current values held respectively, and drawing is performed according to each image signal. And a drawing means for performing the drawing means, wherein the drawing means uses the timing at which the optical sensor of the light source which is not emitting light detects the light beam during the first sampling period or the second sampling period as a reference for the drawing timing control. An image forming apparatus comprising: