JPH0882756A - Photodetector - Google Patents

Abstract

PURPOSE: To provide a plane tilt detection means simple in the structure to be used for a synchronism detection means and plural PDs(photodetectors). CONSTITUTION: In an image recorder using plural laser beams, this detector is constituted of a first photodetector PD-1 having a vertical length L1 in the main scan direction of the laser beam corresponding to a laser beam fluctuation tolerance by plane tilt and a second photodetector PD-2 arranged on the downstream for the first photodetector PD-1 in the main scan direction of the laser beam and having the vertical length L2 in the main scan direction of the laser beam corresponding to a laser beam fluctuation detectable range by the plane tilt.

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 such as a printer, a copying machine, a facsimile, etc., and is used for writing image data on a photosensitive member by using a plurality of laser beams, which is used particularly for color recording. And a device for forming an image.

[0002]

2. Description of the Related Art Regarding a writing system for writing image data using a plurality of laser beams, a full-color image forming apparatus for recording image data of a plurality of colors with a plurality of laser beams corresponding to respective colors is known. . In the recording apparatus of this type, it is necessary to align writing start positions in the main scanning line direction by writing with a plurality of laser beams. For this reason, a synchronization detection device has been developed for obtaining a write synchronization timing between a plurality of laser beams.

An example of a synchronization detecting device of a digital printer will be described with reference to FIGS. The write control controller (ASIC) 1 outputs the image data (digital signal) to be recorded to the LD (laser diode) driver 2 at the write timing. A series of controls by the write control controller (ASIC) 1 is instructed by the CPU. The LD drive section 2 D / A converts the image data (digital signal) from the write control control section 1 and drives the LD 3 with current. The LD 3 emits laser light according to the drive current. The laser light is reflected by the mirror surface 7 of the polygon mirror 6 rotating at high speed. Of the reflected laser light, the light reflected at the tip of the mirror surface 7 in the rotation direction is reflected by the synchronous reflection mirror 8 and is used for synchronous detection PD (photodetector / photodetector).
It is incident on the light receiving element) 4. Further, the reflected light after the tip of the mirror surface 7 in the rotating direction is reflected by the folding mirror 9, passes through a dust filter (not shown), and is irradiated onto a photoconductor (not shown) to form a latent image. Contribute. The synchronization detection section 5 outputs a synchronization signal for writing in the main scanning direction based on the detection signal of the laser light incident on the PD 4 for synchronization detection. The synchronization signal is input to the write control controller 1 to control the write timing of image data to be recorded (synchronization control).

Although there are various means for obtaining the synchronization signal, FIG.
As shown in FIG. 2, a light receiving element configuration in which two synchronous detection PD-1 and PD-2 are arranged in the scanning direction of the laser light is adopted, and P
A synchronization signal is obtained by comparing the outputs from D-1 and PD-2. Comparing the outputs from PD-1 and PD-2 means that PD-1 and P-2 in the case of the example shown in FIG.
The synchronization signal is obtained at the timing when the outputs from D-2 become equal. According to the above method, as shown by the solid line and the dotted line in FIG. 4, the deviation of the synchronization signal generation timing due to the intensity of the laser light hardly occurs. Therefore, the above method is a synchronization detection means effective for laser writing of the power modulation system which forms an image by utilizing the intensity of laser light. Particularly in the case of color recording, the emission amount characteristic of the laser light is made different for each color in response to the request from each color recording material, which is a typical application example of the power modulation method.

[0005]

However, even in the above synchronization detecting means, in order to detect the surface tilt of the polygon mirror surface, the formed image is directly measured or the reflected light from the mirror surface is measured. There was only a detection method, and it required very complicated work. Therefore, the present invention has been made in view of the above-mentioned problems, and provides an image forming apparatus having a polygon mirror surface trouble detecting means of a simple structure that also serves as a synchronization detecting means and a plurality of PDs. Is.

[0006]

In order to achieve the above object, the invention described in claim 1 is an image recording apparatus for recording by using a plurality of laser beams, and corresponds to a laser beam fluctuation allowable range due to a surface tilt. A first light receiving element having a length perpendicular to the main scanning direction of the laser light, and a first light receiving element arranged downstream of the first light receiving element in the main scanning direction of the laser light and corresponding to a laser light fluctuation detectable range due to surface tilt. The second light receiving element has a length perpendicular to the laser beam main scanning direction.

According to a second aspect of the invention, in an image recording apparatus for recording using a plurality of laser beams, a length perpendicular to the laser beam main scanning direction corresponding to a laser beam fluctuation allowable range due to surface tilt. And a first light-receiving element having a vertical line in the laser light main-scanning direction, which is disposed downstream of the first light-receiving element in the laser-light main-scanning direction and corresponds to a laser-light fluctuation detection range due to surface tilt. A first light-receiving portion that is provided, and a first light-receiving portion, the first light-receiving element, the first light-receiving element, the first light-receiving element, the first light-receiving element, the first light-receiving element, the first light-receiving element, the first light-receiving element, the first light-receiving element, and the first light-receiving element that extend in the upstream direction of the main scanning direction of the laser beam. Second having a second light receiving section
The light receiving element of

[0008]

According to the invention of claim 1, the synchronization detecting means and the plurality of P's are provided.
Since the trouble detection means having a simple structure that also serves as D can be realized, it is possible to provide a light detection device that can very easily detect a trouble without providing a detection device dedicated to the trouble.

According to the second aspect of the invention as well, since the trouble detecting means having a simple structure which also serves as the synchronization detecting means and the plurality of PDs can be realized, it is possible to provide a detecting device dedicated to the trouble.
It is possible to provide a light detection device that can detect a tumble easily.

[0010]

The present invention will be described in detail below. The pulse power modulation method (PM method) of laser light controls the amount of emitted light according to the amount of current input to the LD. Usually, the maximum light amount of the LD is determined by the set current amount input to the LD corresponding to the maximum value of the image data (digital signal). Then, the light emission amount of the LD is controlled by a current amount determined based on the ratio of the recorded image data to the maximum value of the image data, with the set current amount as a reference. Therefore, the characteristic of the light emission amount with respect to the image data (digital signal) is determined by the set current amount input to the LD corresponding to the maximum value of the image data. In color recording, if the characteristics of the light emission amount for image data are set differently according to the toner characteristics for each color, the light emission amount is controlled to be different between different colors even for the same output image data (digital signal). To be done. It is impossible to change the characteristics of the light emission amount with respect to the image data within one main scanning line.

As shown in FIG. 3, two PDs for synchronization detection-
A case will be described below as an example where a light receiving element configuration in which 1 and PD-2 are arranged in the scanning direction of laser light is adopted and writing is performed by a plurality of laser lights by LD-1 and LD-2. P
D-1 and PD-2 correspond to the PD 4 for synchronization detection of FIG. Laser light of LD-1 and LD-2 is PD
In the state of being incident on -1, PD-2 (normal state shown in FIG. 3), the outputs of PD-1 and PD-2 are the laser light outputs of LD-1 and LD-2, as shown in FIG. Is an output corresponding to the sum of (2 LDs). However, the laser light of the LD-2 is PD- due to the tilt of the polygon mirror surface.
1, PD-2 is not incident (abnormal state shown in FIG. 6)
Then, the outputs of PD-1 and PD-2 are as shown in FIG.
The output corresponds to the laser light output of LD-1 (one LD). On the other hand, as described above, in the color recording, the light emission amount (laser light output) is controlled to be different between the colors according to the toner characteristics for each color.
It is not easy to distinguish whether the output of the LD is two minutes or one minute. That is, in the light receiving element configuration of FIG.
It cannot be distinguished whether or not the laser beam of D-2 is in the state of being incident on PD-1 and PD-2 (normal state shown in FIG. 3).

Therefore, as a result of earnest efforts, the inventor has found that PD-
1 and PD-2 having the shape shown in FIG. 8 has invented a photodetection device which also serves as a synchronization detection means and a surface tilt detection means for the polygon mirror surface. That is, the length L1 of the PD-1 (first light receiving element) perpendicular to the laser light main scanning direction D
Is set to a permissible variation range of the laser beam due to the surface tilt of the polygon mirror surface. The PD-2 (second light receiving element) is arranged downstream of the PD-1 in the laser beam main scanning direction, and has a length L2 perpendicular to the laser beam main scanning direction D on the polygon mirror surface of the laser beam. A “light-receiving part a” 10 (first light-receiving part) set in a variation detectable range due to surface tilt,
From the “light receiving portion a” 11 (second light receiving portion) that extends in the laser light main scanning upstream direction across the PD-1 from the “light receiving portion a”, and the end face is aligned with the PD-1. Become.

The output of the photodetector of FIG. 8 is as follows. If the laser light of LD-1 and LD-2 is within the permissible range of change due to the tilt of the polygon mirror surface, PD
Since it normally enters -1, PD-2, an output having the same magnitude as that detected by PD-1 is also detected by PD-2 with a delay of a predetermined time difference t. (Refer to FIG. 5) When both of the laser lights of LD-1 and LD-2 are out of the allowable range of change due to the tilt of the polygon mirror surface,
Since the laser light is not incident on PD-1, the detection output of PD-1 becomes 0. In the case of the path B shown in FIG. 8 in which one of the laser lights of LD-1 and LD-2 does not enter PD-1 due to the surface tilt, the detection outputs of PD-1 and PD-2 rise at the same time. (Refer to FIG. 9) In the case of the route A in FIG. 8 in which one of the laser beams of LD-1 and LD-2 is not incident on PD-1 due to the tilt, a larger output than that detected by PD-1 is generated. It is detected by PD-2 with a delay of a predetermined time difference t. (See FIG. 10) In detail, what is detected by PD-1 is the output corresponding to LD-1, and what is detected by PD-2 is L-1 by LD-1.
It is the output corresponding to the addition of D-2. In the above case, the detection output timings of PD-1 and PD-2 are measured in the case of the output of FIG. 9, and the detection output levels of PD-1 and PD-2 are measured in the case of the output of FIG. By doing so, it is determined that the writing system is abnormal due to a trouble, and the user is warned by an abnormality display device or the like (not shown).

If it is judged that the writing system is abnormal due to a surface tilt in the output state as shown in FIG. 10, the PD-2 is arranged downstream of the PD-1 in the laser light main scanning direction, and the PD-2 is arranged in the laser light main scanning direction. The length L2 perpendicular to D may be configured only by the "light receiving portion a" 10 set in the detectable range of the fluctuation of the laser light due to the tilt of the polygon mirror surface. Further, in FIG. 8, the “light receiving portion b” 11 (second light receiving portion) is referred to as PD-1.
Although they are arranged in two parts sandwiching, when the variation detectable range due to the surface tilt of the laser light is sufficient (when L2 may be short), “light receiving part b” 11 (second light receiving part) )
May be only one of the two parts. Further, in the above embodiment, the case where two laser beams are used has been described, but the photodetector of the present invention is also effective when two or more laser beams are used.

[0015]

As described above, according to the first aspect of the present invention, since the trouble detecting means having a simple structure in which the synchronization detecting means and the plurality of PDs are combined can be realized, the trouble detecting means is specially used. It is possible to provide an optical detection device that can detect a face tilt very easily without providing the detection device.

According to the second aspect of the present invention as well, since the trouble detecting means having a simple structure that also serves as the synchronization detecting means and a plurality of PDs can be realized, it is extremely useful even if a detecting device dedicated to the trouble is not provided. Thus, it is possible to provide a light detection device that can easily detect a tilt.

[0017]

[Brief description of drawings]

FIG. 1 is a control block diagram of a synchronization detection device of a conventional digital printer.

FIG. 2 is a schematic diagram of an optical system of a synchronization detection device of a conventional digital printer.

FIG. 3 is a schematic view of a conventional light receiving element for synchronization detection, showing a state where laser light is normally incident on the light receiving element.

FIG. 4 is a diagram showing an output of the light receiving element of FIG. 3 and a synchronization signal.

FIG. 5 is a diagram showing a light receiving element output in a state where laser light is normally incident on the light receiving element.

FIG. 6 shows a state where laser light is not normally incident on the light receiving element of FIG.

7 is a diagram showing an output of the light receiving element when laser light is not normally incident on the light receiving element of FIG.

FIG. 8 is a configuration diagram of a light detection device of the present invention.

9 is a photodetector of FIG. 8, one of the laser beams PD-
It is a figure which shows the light receiving element output in case 1 enters into 1 and the other laser beam scans B path | route.

10 is a photodetector of FIG. 8, one of the laser beams is PD
It is a figure which shows the light receiving element output in case -1 is made incident and the other laser beam scans the A path.

[Explanation of symbols]

 10. First light receiving unit 11. Second light receiving section

Claims (2)

[Claims] 1. An image recording apparatus for recording by using a plurality of laser beams, wherein a first length having a length perpendicular to a laser beam main scanning direction corresponds to a laser beam fluctuation allowable range due to surface tilt.
And a second light receiving element which is disposed downstream of the first light receiving element in the laser light main scanning direction and has a length perpendicular to the laser light main scanning direction corresponding to a laser light fluctuation detectable range due to surface tilt. A photodetector comprising a light receiving element. 2. An image recording apparatus for recording by using a plurality of laser beams, the first having a length perpendicular to a laser beam main scanning direction corresponding to a laser beam fluctuation allowable range due to surface tilt.
And a first light receiving element which is arranged downstream of the first light receiving element in the laser beam main scanning direction and has a length perpendicular to the laser beam main scanning direction corresponding to a laser beam fluctuation detectable range due to surface tilt. A light-receiving portion and a first light-receiving portion, and the first light-receiving element sandwiched between the light-receiving portion and the first light-receiving portion.
A photodetector comprising: a second light-receiving element having an end face and a second light-receiving portion arranged in alignment with the first light-receiving element.