JP3304629B2 - Photodetector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of writing image data on a photoreceptor using a plurality of laser beams, which is used particularly in color recording in an image forming apparatus such as a printer, a copying machine and a facsimile. To form an image.

[0002]

2. Description of the Related Art With respect to 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 by a plurality of laser beams corresponding to respective colors is known. . In this type of recording apparatus, 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 detecting device for obtaining a write synchronization timing between a plurality of laser beams has been developed.

An outline of a digital printer synchronization detection device will be described with reference to FIGS. The write control controller (ASIC) 1 outputs image data (digital signal) to be recorded to an LD (laser diode) driver 2 in synchronization with the write timing. A series of controls by the write control controller (ASIC) 1 are instructed by the CPU. The LD drive unit 2 performs D / A conversion of the image data (digital signal) from the write control control unit 1 and drives the LD 3 with current. The LD 3 emits a laser beam 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 distal end in the rotation direction of the mirror surface 7 is reflected by the synchronous reflecting mirror 8 and is used for a PD (photodetector / synchronous detector)
(Light receiving element) 4. The reflected light after the front end of the mirror surface 7 in the rotation direction is reflected by the folding mirror 9, passes through a dustproof filter (not shown), and is irradiated on a photoconductor (not shown) to form a latent image. Contribute. The synchronization detector 5 outputs a synchronization signal for writing in the main scanning direction based on the detection signal of the laser beam incident on the PD 4 for synchronization detection. The synchronizing signal is input to the writing control control unit 1 to control writing timing of image data to be recorded (synchronous control).

There are various means for obtaining a synchronization signal.
As shown in the figure, a light receiving element configuration in which two synchronization detecting PD-1 and PD-2 are arranged in the scanning direction of laser light is adopted.
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 in the case of the example shown in FIG.
The synchronization signal is obtained at the timing when the output from D-2 becomes equal. According to the above method, as is apparent from the solid line and the dotted line in FIG. 4, there is almost no shift in the timing of the generation of the synchronization signal due to the intensity of the laser beam. Therefore, the above method is a synchronization detecting means effective for power modulation type laser writing in which an image is formed using the intensity of laser light. In particular, in the case of color recording, the emission characteristics of laser light are varied for each color in accordance with the requirements from the respective color recording agents, which is a typical application example of the power modulation method.

[0005]

However, even in the above-mentioned synchronous 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 very complicated work was required. In view of the above, the present invention has been made in view of the above problems, and provides an image forming apparatus having a simple structure of a polygon mirror surface, which has a simple structure in which a synchronous detection unit and a plurality of PDs are used. It is.

[0006]

According to a first aspect of the present invention, there is provided an image recording apparatus for performing recording using a plurality of laser beams, wherein the image recording apparatus corresponds to an allowable range of laser beam fluctuation due to 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 disposed downstream of the first light receiving element in the main scanning direction of the laser light and corresponding to a detectable range of laser light fluctuation due to surface tilt. And a second light receiving element having a length perpendicular to the main scanning direction of the laser beam.

According to a second aspect of the present invention, there is provided an image recording apparatus for performing recording using a plurality of laser beams, wherein the length perpendicular to the main scanning direction of the laser beam corresponding to the permissible range of the laser beam variation due to surface tilt. And a first light receiving element having a length perpendicular to the laser light main scanning direction, which is arranged downstream of the first light receiving element with respect to the laser light main scanning direction and corresponds to a detectable range of laser light fluctuation due to surface tilt. A first light receiving portion having the first light receiving portion, the first light receiving portion extending from the first light receiving portion in the upstream direction of the main scanning of the laser beam with the first light receiving element interposed therebetween, and an end face arranged in line with the first light receiving element. A second light receiving section
And a light receiving element.

[0008]

According to the first aspect of the present invention, the synchronization detecting means and the plurality of Ps
Since a trouble detecting means having a simple structure that also serves as D can be realized, it is possible to provide a light detecting device that can detect the trouble very easily without providing a special detecting device dedicated to the trouble.

According to the second aspect of the present invention, since the trouble detecting means can be realized with a simple structure in which both the synchronous detecting means and the plurality of PDs are used, it is not necessary to provide a special detecting device dedicated to the trouble.
It is possible to provide a light detection device that can detect a surface tilt very easily.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below. In the pulse power modulation method (PM method) of laser light, the amount of light emission is controlled by the amount of current input to an 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). The light emission amount of the LD is controlled based on the ratio of the recording image data to the maximum value of the image data, based on the current amount determined based on the set current amount. 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 light emission amount characteristics for image data are set differently according to the toner characteristics for each color, control is performed so that the light emission amount differs between different colors even with the same output image data (digital signal). Is done. The characteristics of the light emission amount for the above image data cannot be changed within one main scanning line.

As shown in FIG. 3, two PDs for synchronization detection
A description will be given below of an example in which a light-receiving element configuration in which PD-1 and PD-2 are arranged in the scanning direction of laser light is employed, and writing is performed by a plurality of laser lights using LD-1 and LD-2. P
D-1 and PD-2 correspond to the PD4 for synchronization detection in FIG. LD-1 and LD-2 laser light is PD
In the state where light is incident on -1 and 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. Are output (two LDs). However, the laser beam of LD-2 is distorted by the PD-
1, a state where light does not enter PD-2 (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 so as to differ between the colors in accordance with the toner characteristics for each color.
It is not easy to distinguish whether the output is two LDs or one minute. That is, in the light receiving element configuration of FIG.
It cannot be distinguished whether or not the laser beam D-2 is incident on PD-1 and PD-2 (the normal state shown in FIG. 3).

The inventor of the present invention has made a tremendous effort to obtain PD-
1, PD-2 was formed into the shape shown in FIG. 8 to invent a light detecting device which serves both as a synchronous detecting means and a polygon mirror surface tilt detecting means. That is, the length L1 perpendicular to the laser beam main scanning direction D of PD-1 (first light receiving element)
Is set to a permissible range of variation due to surface tilt of the polygon mirror surface of the laser light. The PD-2 (second light receiving element) is arranged downstream of the PD-1 in the main scanning direction of the laser beam, and sets a length L2 perpendicular to the main scanning direction D of the laser beam to the polygon mirror surface of the laser beam. A “light-receiving unit a” 10 (first light-receiving unit) set in a range in which fluctuation due to surface tilt can be detected;
From the “light receiving portion a” 11 (second light receiving portion), which extends in the main scanning upstream direction of the laser beam with the PD-1 interposed therebetween and whose end surface is aligned with the PD-1. Become.

The output of the photodetector of FIG. 8 is as follows. If the laser beams of LD-1 and LD-2 are within the permissible range of the change due to the inclination of the polygon mirror surface, PD
-1 and normally incident on 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. (See FIG. 5) If both the laser beams of LD-1 and LD-2 are out of the permissible range of the change due to the tilt of the polygon mirror surface,
Since no laser light is incident on PD-1, the detection output of PD-1 becomes zero. In the case of the B path in FIG. 8 in which one of the laser beams LD-1 and LD-2 does not enter the PD-1 due to surface tilt, the detection outputs of the PD-1 and PD-2 rise at the same time. (See FIG. 9) In the case of the path A in FIG. 8 in which one of the laser beams of the LD-1 and LD-2 does not enter the PD-1 due to the surface tilt, an output larger than that detected by the PD-1 is obtained. It is detected by PD-2 with a delay of a predetermined time difference t. (See FIG. 10.) In detail, the output detected by PD-1 is the output corresponding to LD-1, and the output detected by PD-2 is L
This is an output corresponding to the sum of D-2. In the above case, in particular, in the case of the output of FIG. 9, the detection output timing of PD-1 and PD-2 is measured, and in the case of the output of FIG. 10, the detection output level of PD-1 and PD-2 is measured. By doing so, it is determined that the writing system is abnormal due to trouble, and a user is warned by an abnormality display device or the like (not shown).

If it is determined in the output state as shown in FIG. 10 that the writing system is abnormal due to surface tilt, the PD-2 is disposed downstream of the PD-1 in the main scanning direction of the laser beam, and is arranged in the main scanning direction of the laser beam. The length L2 perpendicular to D may be constituted only by the “light receiving portion a” 10 set in a detectable range of the fluctuation of the laser beam due to the surface inclination of the polygon mirror surface. Further, in FIG. 8, the “light receiving portion b” 11 (second light receiving portion) is connected to PD-1.
Are arranged in two parts, but if the range in which the fluctuation of the laser beam can be detected due to surface tilt is small (L2 can be short), the "light receiving portion b" 11 (second light receiving portion) )
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 light detection device of the present invention is also effective in the case where 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 which combines the synchronous detecting means and the plurality of PDs can be realized, the trouble detecting means is specially used. It is possible to provide a photodetection device that can very easily detect a fall without providing the detection device.

According to the second aspect of the present invention, the trouble detecting means can be realized with a simple structure in which both the synchronous detecting means and the plurality of PDs are used. It is possible to provide a light detection device capable of easily detecting a surface tilt.

[0017]

[Brief description of the drawings]

FIG. 1 is a control block diagram of a conventional synchronous detection device of a 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 diagram of a conventional synchronous detection light receiving element, and shows a state in which laser light is normally incident on the light receiving element.

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

FIG. 5 is a diagram illustrating an output of a light receiving element when 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. 3;

FIG. 7 is a diagram showing a light receiving element output in a state where laser light is not normally incident on the light receiving element of FIG. 6;

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

FIG. 9 shows a photodetector of FIG.
FIG. 4 is a diagram illustrating the output of the light receiving element when the laser beam enters the first laser beam and the other laser beam scans the B path.

FIG. 10 shows a photodetector shown in FIG.
FIG. 9 is a diagram illustrating a light-receiving element output when the laser beam is incident on −1 and the other laser beam scans the A path.

[Explanation of symbols]

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

Claims (2)

(57) [Claims] An image recording apparatus for performing recording using a plurality of laser beams, wherein a first length having a length perpendicular to a laser beam main scanning direction corresponding to a permissible range of laser beam fluctuation due to surface tilt.
A second light-receiving element disposed downstream of the first light-receiving element with respect to the first light-receiving element and having a length perpendicular to the laser light main-scanning direction corresponding to a detectable range of laser light fluctuation due to surface tilt. A light detection device comprising a light receiving element. 2. An image recording apparatus for performing recording by using a plurality of laser beams, wherein a first length having a length perpendicular to a main scanning direction of a laser beam corresponding to a permissible range of laser beam fluctuation due to surface tilt.
And a first light-receiving element disposed downstream of the first light-receiving element in the main scanning direction of the laser light and having a length perpendicular to the main scanning direction of the laser light corresponding to a detectable range of the fluctuation of the laser light due to surface tilt. A light receiving section, extending from the first light receiving section in the upstream direction of the main scanning of the laser beam with the first light receiving element interposed therebetween;
A second light receiving element having an end face aligned with the first light receiving element and a second light receiving section arranged in line with the first light receiving element.