JP2000272167A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain an image with less density variation by a method wherein a temperature difference between light sources of LD array is lowered and the thermal crosstalk is reduced. SOLUTION: A video signal processing section 22 sequentially switches light sources for emitting lights in order to obtain a synchronous detecting signal (in order to allow a synchronous detecting sensor 11 to generate the synchronous detecting signal). That is, the channels are switched in the order of the channel 1, channel 2, channel 3, channel 4, channel 1, channel 2.... In order to execute emission of the light from the changed light source, a light emission signal for the channel is outputted to a corresponding PM section to allow the light source to output the light and the synchronous detecting sensor 11 to generate the synchronous detecting signal at each time of the switching. At that time, the emission power of the changed light source is varied corresponding to the arranged position of the light source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention includes optical scanning means (optical scanning optical system) using a laser diode (hereinafter abbreviated as "LD") array in which a plurality of light emitting sources are arranged on one chip. And various image forming apparatuses such as printers, digital copiers and facsimile machines.

[0002]

2. Description of the Related Art An optical scanning optical system of an image forming apparatus as described above is individually modulated (ON / O) at substantially the same position in the main scanning direction and at a predetermined distance in the sub-scanning direction which is the rotation direction of the photosensitive member.
FF) A plurality of controllable light-emitting sources (LD) have an LD array arranged on one chip, and a laser beam from each light-emitting source is rotated by a polygon mirror (hereinafter also referred to as a “polygon mirror”). The main scanning is performed on the photosensitive member surface with a positional difference in the sub-scanning direction on the photosensitive member surface.

[0003]

By the way, as an LD array, the distance between each light emitting source is generally as small as several tens of microns to several tens of microns. However, when each light emitting source is individually modulated, the There is a thermal difference between each light source,
The so-called thermal crosstalk occurs in which the influence of the modulation of the light emitting sources affects the adjacent light emitting sources as a change in the amount of light. Therefore, in an image forming apparatus provided with an optical scanning optical system using an LD array, this thermal crosstalk appears in an image as uneven density.

Conventionally, as shown in FIG. 8, for example, as shown in FIG. 8, a synchronization detection signal (a signal for defining a writing start position in the main scanning direction), and a synchronization detection signal generating means is provided outside the main scanning writing area with respect to the photosensitive member surface The light-emitting source that emits light to obtain a laser beam and outputs it by detecting the laser beam is a specific one light-emitting source (in this example, emits light by a light-emitting signal of one channel (ch)). Since the light emission time of only the light emitting source is increased, a temperature difference from other light emitting sources is easily generated.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and in an image forming apparatus having an optical scanning optical system using an LD array, a temperature difference between light emitting sources of the LD array is reduced. To reduce thermal crosstalk and obtain an image with less density unevenness.

[0006]

In order to achieve the above object, the present invention has an LD array in which a plurality of light emitting sources are arranged on one chip, and rotates a laser beam from each light emitting source. An optical scanning means for periodically deflecting by a polygon mirror and for main-scanning the photoconductor surface with a positional difference in the sub-scanning direction on the photoconductor surface to be sub-scanned, and a laser beam outside the main scanning writing area for the photoconductor surface. A synchronous detection signal generating means for generating and outputting a synchronous detection signal for detecting and defining a write start position in the main scanning direction; and generating a synchronous detection signal in the synchronous detection signal generating means. In order to perform this, light emitting source switching means for sequentially switching the light emitting sources that emit light is provided.

Further, it is desirable to provide a light emission power changing means for changing the light emission power of the light source switched (selected) by the light source switching means in accordance with the arrangement position of the light sources. Further, it is preferable to provide a failure detection unit that detects a failure of each light emitting source of the LD array based on the synchronization detection signal output from the synchronization detection signal generation unit.

In the image forming apparatus according to the present invention, all the light emission sources of the LD array are sequentially switched by emitting light sources for emitting light in order to obtain a synchronization detection signal (to cause the synchronization detection signal generating means to generate the synchronization detection signal). Since the light sources are made to emit light evenly, the temperature difference between the light emitting sources is reduced, and the thermal crosstalk is reduced. Therefore, an image with less density unevenness can be obtained.

Further, the light emission power of the switched light source is changed according to the arrangement position of the light source (for example, L
When three or more light emitting sources are arranged on one chip of the D array, the light emitting power of the light emitting sources at both ends is made larger than the light emitting power of the inner light emitting source. (For example, the temperature difference between the light-emitting sources at both ends and the light-emitting source inside) is further reduced, and thermal crosstalk is reduced. Therefore, an image with less density unevenness can be obtained.

Further, by detecting a failure of each light emitting source of the LD array based on the synchronization detection signal output from the synchronization detection signal generating means, if any of the light emitting sources of the LD array fails, Failure of each light emitting source of the LD array can be accurately detected with a simple configuration, and the failed light emitting source can be specified.

[0011]

Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a perspective view illustrating a configuration example of a mechanism of an optical scanning optical system (multi-beam writing device) of the image forming apparatus according to the embodiment of the present invention.

In this optical scanning optical system, reference numeral 1 denotes an LD array, and the photosensitive drum 7 is located at substantially the same position in the main scanning direction.
A plurality of light-emitting sources (LDs) that can be individually modulated and separated by a predetermined distance in the sub-scanning direction, which is the rotation direction of, are arranged on one chip. From each light source of this LD array,
A laser beam modulated according to image data is emitted (emitted). The plurality of laser beams are shaped into laser beams having a narrow cross section of a predetermined shape by the collimator lens 2, the aperture 8, and the cylindrical lens 3, and are irradiated to the polygon mirror 4.

That is, the plurality of laser beams are:
The collimated lens 2 converts the beam into a parallel light beam, and then an extra laser beam is cut by an aperture 8 having a slit corresponding to the size of a writing dot (scan density). Each parallel light beam shaped by the aperture 8 is collected by the cylindrical lens 3 so that each laser beam for writing an image in the main scanning direction has a predetermined size on the surface (photosensitive surface) of the photosensitive drum 7. The light is irradiated to the polygon mirror 4.

Reference numeral 4 denotes a polygon mirror, which is continuously rotating at a predetermined rotation speed, so that the laser beam impinging on the polygon mirror 4 is directed to a reflection mirror 9 where it is reflected (deflected) by the main scanning direction ( It is repeatedly moved and scanned in X) (axial direction of the photosensitive drum 7). At this time, the laser beam reflected by the polygon mirror 4 is converted by a pair of Fθ lenses 5 from equiangular motion to uniform motion, and is subjected to surface tilt correction by a surface tilt correction lens 6, and then is reflected by a reflection mirror 9. The angle is changed, and an image is formed on the surface of the photosensitive drum 7 in a spot shape with a predetermined beam diameter.

Since the LD array 1 has a plurality of light emitting sources, a plurality of light sources having a pitch (positional difference) in the sub-scanning direction (rotation direction of the photosensitive drum 7) Y on the surface of the photosensitive drum 7. The laser beam irradiation trajectory of the book is drawn.

FIG. 3 is an enlarged perspective view of the LD array 1 of FIG. In the heterodyne junction surface 1A of the LD array 1,
A plurality of light emitting sources are arranged. Here, assuming that two light-emitting sources are arranged for convenience of illustration, the laser beams emitted from the two light-emitting sources are B1 and B2 as illustrated. The optical scanning optical system according to this embodiment includes the LD array 1 having four light emitting sources, but instead includes an LD array having two, three, or five or more light emitting sources. You may do so.

In FIG. 2, the laser beam immediately before the main scanning on the photosensitive drum 7 is a laser beam path on the main scanning starting point side outside the main scanning writing area (outside the predetermined main scanning width) with respect to the surface of the photosensitive drum 7. Since the laser beam passes through a synchronization detection sensor (synchronization detection signal generation means) 11 via a synchronization mirror 10 provided in the device, the synchronization detection sensor 11 detects the laser beam and generates and outputs a synchronization detection signal.

FIG. 4 shows the relationship between the four laser beams B1, B2, B3, and B4 and the synchronization detection sensor 11 immediately before scanning on the photosensitive drum 7. Note that the synchronization detection sensor 1
1 is an optical sensor (here, a photodiode) that detects a laser beam outside the main scanning writing area on the surface of the photosensitive drum 7 and outputs a laser beam detection signal.
The writing start position in the main scanning direction is defined according to the laser beam detection signal (positioning in the main scanning direction is performed).
And a synchronization detection signal generator for generating and outputting a synchronization detection signal.

FIG. 1 is a block diagram showing an example of the configuration of a write control unit of an image forming apparatus provided with this optical scanning optical system.
The write control unit 20 includes an LVDS unit 21, a video signal processing unit (video control unit) 22, a PLL IC 23, PM units 24a, 24b, 24c, 24d, and an LD drive circuit (LD
D) 25a, 25b, 25c, 25d, an APC control unit 26, and the like.

[0020] LVDS (Low Voltage Differential Sig)
The naling) unit 21 is a high-speed transmission circuit using a small-amplitude differential signal (clock), and synchronizes an 8-bit video signal (image data) from a controller (not shown) with the clock to the video signal processing unit 22. High-speed transmission.

The video signal processing section 22 includes an LVDS section 21
Is converted into video signals of channels (ch) 1, 2, 3, and 4, which are video signals for four channels, and the input timing of the synchronization detection signal from the synchronization detection sensor 11 is set as a reference timing, and the PLL is used. Channel 1 is synchronized with the pixel clock (write clock) from IC 23
The video signals of 2, 3, and 4 are respectively transmitted to the PM circuits 24a and 2a.
4b, 24c and 24d.

PLL (Phase Locked Loop) IC 23
Generates a pixel clock in synchronization with a PLL reference clock from a controller (not shown) using the input timing of a synchronization detection signal sent from the synchronization detection sensor 11 via the video signal processing unit 22 as a reference timing. Output to the unit 22.

The PM section (pulse width modulation circuit) 24a performs pulse width modulation based on the video signal of channel 1 from the video signal processing section 22, generates a modulation signal of channel 1, and outputs it to the LD drive circuit 25a. I do. PM part 2
4b performs pulse width modulation based on the video signal of channel 2 from the video signal processing unit 22, generates a modulated signal of channel 2, and outputs the modulated signal to the LD drive circuit 25b.

The PM section 24c performs pulse width modulation on the basis of the channel 3 video signal from the video signal processing section 22, generates a channel 3 modulation signal, and outputs it to the LD drive circuit 25c. The PM unit 24d performs pulse width modulation based on the video signal of channel 4 from the video signal processing unit 22, generates a modulated signal of channel 4, and outputs the modulated signal to the LD drive circuit 25d.

The LD drive circuit 25a modulates (ON / OFF) the light emission source of the channel 1 of the LD array 1 in accordance with the modulation signal of the channel 1 from the PM section 24a, and generates a corresponding laser beam. LD drive circuit 25b
Controls the modulation of the light source of channel 2 of the LD array 1 according to the modulation signal of channel 2 from the PM unit 24b,
Generate a corresponding laser beam.

The LD drive circuit 25c modulates and controls the light emission source of the channel 3 of the LD array 1 according to the modulation signal of the channel 3 from the PM section 24c, and generates a corresponding laser beam. The LD drive circuit 25d controls the modulation of the light emission source of the channel 4 of the LD array 1 according to the modulation signal of the channel 4 from the PM unit 24d, and generates a corresponding laser beam.

APC control unit (Automatic Power Control
l) Reference numeral 26 denotes a circuit for controlling the amount of light of each light emitting source (LD) of the LD array 1 to be constant, and an output signal (PD signal) of an optical sensor (PD = Photo Detector) (not shown) built in the LD array 1. ) Is sequentially fed back to the LD drive circuit that drives the sequentially switched light-emitting sources (light-emitting sources that emit light for causing the synchronization detection sensor 11 to generate a synchronization detection signal), thereby sequentially correcting the light amount of each light-emitting source. . In addition, since the LD has a large fluctuation in the light quantity with respect to the temperature fluctuation, it is necessary to correct the light quantity to keep the light quantity constant.

When the laser beam immediately before scanning the photosensitive drum 7 enters the detection area, the synchronization detection sensor 11 detects the laser beam and generates and outputs a low-level "L" synchronization detection signal. When the laser beam leaves the detection area and goes to the main scanning writing area (effective scanning area), the synchronization detection signal is returned to the high level “H” (the output of the synchronization detection signal DP is stopped).

FIG. 5 is a block diagram showing a configuration example of a main part (part relating to the third aspect of the present invention) in the video signal processing unit 22. The video signal processing unit 22 includes the timing control unit 3
1 and a synchronization detection error detection unit 32.

The timing control section 31 sets the input timing of the synchronization detection signal sent from the synchronization detection sensor 11 via the synchronization detection error detection section 32 as a reference timing,
The video signals of channels 1, 2, 3, and 4 are output to PM circuits 24a, 24b, 24c, and 24d, respectively, in synchronization with the pixel clock (write clock) from LLIC 23.

The synchronization detection error detection section 32 detects a synchronization detection error of each channel based on the synchronization detection signal output from the synchronization detection sensor 11, and this processing will be described in detail later.

Here, a normal image forming operation in the image forming apparatus of this embodiment will be briefly described. When an image formation start is instructed, a controller (not shown) of the image forming apparatus rotates a polygon motor (not shown) to rotate the polygon mirror 4 at a predetermined rotation speed, and sends a video signal to the write control unit 20. Send out.

Video signal processing section 22 of write control section 20
Are respectively based on the video signals sent from the controller via the LVDS unit 21 to each of the PM units 24a, 24b, 2
4c, 24d and LD drive circuits 25a, 25b, 25
By modulating and driving each light emitting source of the LD array 1 via c and 25d, an image (electrostatic latent image) is generated on the surface (precharged surface) of the photosensitive drum 7.

Thereafter, the image formed on the surface of the photosensitive drum 7 is developed with a toner from a developing device (not shown) into a visible image, and is transferred onto a sheet fed from a sheet feeding unit (not shown). After the image is transferred by the apparatus and further fixed by a fixing device (not shown), the sheet on which the image is fixed is discharged outside the apparatus.

Next, the control of the video signal processing section 22 according to the first aspect of the present invention will be described with reference to FIG. The video signal processing unit 22 that performs this control is
It functions as the light emitting source switching means of the first aspect. FIG.
Are transmitted from the video signal processing unit 22 to the PM units 24a, 24b,
Each channel (c
3 is a timing chart showing an example of a relationship between a light emission signal (video signal) of h) and a synchronization detection signal input from the synchronization detection sensor 11 to the video signal processing unit 22.

The video signal processing unit 22 sequentially switches the light emitting sources for emitting light in order to obtain a synchronization detection signal (to cause the synchronization detection sensor 11 to generate a synchronization detection signal). In this example, channel 1 → channel 2 → channel 3
Switch to a light emitting source for obtaining a synchronization detection signal in the order of → channel 4 → channel 1 → channel 2 ... Then, in order to emit light from the light emitting source switched each time, the light emitting signal of that channel is output to the corresponding PM unit, and the light emitting source is caused to emit light by the corresponding LD drive circuit, and is synchronized with the synchronization detection sensor 11. Generate a detection signal.

Next, control by the video signal processing unit 22 according to the second aspect of the present invention will be described with reference to FIG. The video signal processing unit 22 that performs this control is
The function as the light emission source switching means and the light emission power changing means of the second aspect is achieved. FIG. 7 shows that the video signal processor 22
Another relationship between the light emission signal (video signal) of each channel (ch) input to each of the M units 24a, 24b, 24c, and 24d and the synchronization detection signal input from the synchronization detection sensor 11 to the video signal processing unit 22. 6 is a timing chart showing an example.

The video signal processing section 22 performs the
The light emitting sources for emitting light are sequentially switched to obtain a synchronization detection signal. Then, in order to emit light from the light emitting source switched each time, the light emitting signal of that channel is output to the corresponding PM unit, and the light emitting source is caused to emit light by the corresponding LD drive circuit, and is synchronized with the synchronization detection sensor 11. Generate a detection signal. At this time, the light emission power of the switched light source is changed according to the arrangement position of the light source.

That is, when the light source is switched to the light source of channel 1 or 4 located outside the LD array 1,
The emission signal output to the corresponding PM unit is changed so that the emission source emits light at the emission power value A. Also, LD
When the light source is switched to the light source of channel 2 or 3 located inside the array 1, the light source has the light emission power value A
The light emission signal to be output to the corresponding PM unit is changed so that light is emitted with a smaller light emission power value B.

The reason for performing such a change processing is as follows.
Comparing the light-emitting sources at both ends (channels 1 and 4) and the light-emitting sources at the inner side (channels 2 and 3) of the array 1, the inner light-emitting source absorbs the heat generated by the light-emitting sources at both ends and becomes higher in temperature. This is because it has characteristics. Emission power values A and B
Is set to a value, which is obtained in advance by simulation or experiment or the like, so as to reduce the temperature difference between the light emitting sources of the respective channels.

Next, control by the video signal processing unit 22 according to the third aspect of the present invention will be described. The video signal processing unit 22 performs the following control in addition to the control similar to the control according to the first or second aspect of the present invention.

That is, if the light emitting source that has emitted light to obtain a synchronization detection signal normally emits a laser beam (its emission timing is shown in FIG. 6 or FIG. 7), the laser beam is emitted from the synchronization detection sensor. 11, the synchronization detection signal is input to the synchronization detection error detection unit 32. Therefore, the synchronization detection error detection unit 32 does not detect the synchronization detection error of the corresponding channel, and outputs the error detection signal of that channel. There is no output to a controller not shown.

However, if the light emitting source that has emitted light to obtain the synchronization detection signal fails for some reason and does not emit light, the synchronization detection sensor 11 does not output the synchronization detection signal. If no synchronization detection signal is input, the synchronization detection error detection unit 32 detects a synchronization detection error (failure of the light emitting source) of the corresponding channel, and outputs an error detection signal of that channel to the controller.

By inputting an error detection signal for each channel, the controller can identify which of the light emitting sources of the LD array 1 is out of order, and the content thereof is displayed on the display panel on the operation unit. The information can be displayed to the operator or printed on a sheet so that the operator can be notified. Therefore, the controller and the synchronization detection error detection unit 32 function as a failure detection unit of the third aspect.

[0045]

As described above, according to the image forming apparatus of the present invention, the light emitting sources that emit light are sequentially switched to obtain a synchronization detection signal, and all the light emitting sources of the LD array emit light uniformly. By doing so, it is possible to reduce the temperature difference between the respective light emitting sources and reduce the thermal crosstalk. Therefore, an image with less density unevenness can be obtained.

Further, according to the second aspect of the present invention, the temperature difference between the light emitting sources can be further reduced by changing the light emitting power of the switched light emitting sources according to the arrangement position of the light emitting sources. Thermal crosstalk can be reduced. Therefore, an image with less density unevenness can be obtained.

Further, according to the third aspect of the present invention, L based on the synchronization detection signal output from the synchronization detection signal generating means.
By detecting the failure of each light source in the D array, the LD
When a failure occurs in any of the light emitting sources of the array, the failure of each of the light emitting sources of the LD array can be accurately detected with a simple configuration, and the failed light emitting source can be specified.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration example of a writing control unit of an image forming apparatus including the optical scanning optical system illustrated in FIG.

FIG. 2 is a perspective view illustrating a configuration example of a mechanical unit of an optical scanning optical system (multi-beam writing device) of the image forming apparatus according to an embodiment of the present invention.

FIG. 3 is an enlarged perspective view of the LD array 1 of FIG.

FIG. 4 is a diagram showing a relationship between four laser beams B1, B2, B3, and B4 immediately before scanning on the photosensitive drum 7 in FIG.

FIG. 5 is a block diagram showing a configuration example of a main part in a video signal processing unit 22 of FIG. 1;

FIG. 6 shows a video signal processing unit 22 to a PM unit 24 shown in FIG.
FIG. 4 is a timing chart showing an example of a relationship between light emission signals of each channel (ch) input to a, 24b, 24c, and 24d and a synchronization detection signal input from the synchronization detection sensor 11 to the video signal processing unit 22.

FIG. 7 shows a video signal processing unit 22 to a PM unit 24 shown in FIG.
FIG. 9 is a timing chart showing another example of the relationship between the light emission signals of the respective channels input to a, 24b, 24c, and 24d and the synchronization detection signals input from the synchronization detection sensor 11 to the video signal processing unit 22, respectively.

FIG. 8 illustrates an example of a relationship between a light emission signal of each channel input to each PM unit from a video signal processing unit and a synchronization detection signal input to a video signal processing unit from a synchronization detection sensor in a conventional image forming apparatus. It is a timing diagram shown.

[Explanation of symbols]

 1: LD array 4: Polygon mirror 7: Photoconductor drum 11: Synchronous detection sensor 20: Write control unit 21: LVDS unit 22: Video signal processing unit 23: PLL ICs 24a, 24b, 24c, 24d: PM unit 25a, 25b, 25c, 25d: LD drive circuit 26: APC control unit 31: Timing control unit 32: Synchronization detection error detection unit

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 2C362 AA16 AA60 AA74 BA56 BA60 BA67 BA69 BB33 EA04 2H027 DA07 EA11 ED04 ED07 EF09 EK09 GB08 2H045 AA01 BA23 CA88 CA98 DA41 5C072 AA03 CA06 CA09 CA12 CA15 CA17 HA02 H 9A001 JJ35 KK16 LL05

Claims (3)

[Claims] A laser diode array having a plurality of light-emitting sources arranged on a single chip, and a laser beam from each light-emitting source is periodically deflected by a rotary polygon mirror, and is subjected to sub-scanning. An optical scanning means for main-scanning the surface of the photoconductor with a positional difference in the sub-scanning direction, and a laser beam outside the main-scanning writing area with respect to the surface of the photoconductor is detected to define a writing start position in the main scanning direction. And a synchronization detection signal generating means for generating and outputting a synchronization detection signal for performing the synchronization detection signal, wherein a light emission source for emitting light is sequentially switched to cause the synchronization detection signal generation means to generate the synchronization detection signal. An image forming apparatus comprising a light emitting source switching unit. 2. The image forming apparatus according to claim 1, wherein
An image forming apparatus comprising: a light emitting power changing unit that changes a light emitting power of a light emitting source switched by the light emitting source switching unit according to an arrangement position of the light emitting source. 3. The image forming apparatus according to claim 1, wherein a failure of each light emitting source of the laser diode array is detected based on a synchronization detection signal output from the synchronization detection signal generating unit. An image forming apparatus comprising: