JPS62237418A - Light quantity control device - Google Patents

Abstract

PURPOSE:To equalize the light quantity of each scanning line by providing a nonvolatile memory element for storing an emitted light quantity data of a light source which is varied in accordance with each specular surface of a rotary polyhedral mirror, and a current control means for controlling a driving current impressed to the light source, based on the emitted light quantity data. CONSTITUTION:When a photosensitive drum has executed the previous rotation (preparatory rotation) or a position of the photosensitive drum for scanning a scanning light has rotated to a transfer position, if a paper exists in the middle position of the paper and the paper, a laser chip 1a is lighted, and the light quantity at that time is photodetected by a photosensor 1b and inputted to a CPU 3 through an amplifier 5 and an A/D converter 6. The CPU 3 controls a driving current of a laser driving circuit so that an output value of the photosensor 1b becomes a value which has been determined in advance. A laser light emission for obtaining an optimum laser driving current from an APC data of this time is executed in a position of the photosensitive drum which is not transferred to the paper. In a PROM 2, this APC data is stored in advance, and controlled so as to become a prescribed scanning light quantity irrespective of the surface of a polygon mirror and a scanning position.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a light amount control device that controls the light amount of a scanning optical device.

[Conventional technology]

Conventional laser beam printers are equipped with a synchronization detector that detects the position of a scanning beam from a scanning optical device, and controls the timing at which image signals are written.

As a general method, a bin photodiode is provided at a scan position on the scan start side slightly away from the image area,
The writing timing of the image signal is controlled from a signal (beam detect signal (hereinafter referred to as BD double signal)) obtained by cutting out the rising part of the output signal obtained by detecting the passage of the scanning light at a constant slice level.

However, according to this method, if the reflectance of each surface of the rotating polygon mirror is different, the intersection of the BD double signal rising waveform and the slice level changes in the time axis direction, resulting in image jitter. It appears as. At the same time, the density of each scanning line changes, resulting in a striped pattern, especially in halftone images. Factors that change the reflectance of such a polygon mirror include a diffraction phenomenon caused by the cutting lines of the metal polygon mirror and coating unevenness on the mirror surface. It is known that the reflectance of a polygon mirror and the diffracted light due to cutting lines do not change over time, and once corrected, there is no need to change it.

[Problem that the invention seeks to solve]

In recent years, high-quality images produced by laser beam printers have been attracting attention, and it is clear that there will be a demand for even higher-definition image prints and color prints in the future. When used for such printing purposes, the image quality must not be degraded due to diffracted light or reflectance. However, with the current technology, it is difficult to keep the reflectance constant or eliminate the rough edges at low cost, and there is a strong desire to solve these problems.

In addition, the conventional light amount control is +73
Arc (auto power control) is based on a photosensor housed in the package of the semiconductor laser that is the light source, and its main purpose is to compensate for changes in light intensity due to temperature changes and deterioration of the laser chip. It is not possible to correct variations in light amount due to the influence of mirrors.

This invention was made to solve the above problems, and by measuring the amount of scanning light corresponding to each surface of the polygon mirror in advance and correcting the amount of scanning light based on that data, each scanning line is An object of the present invention is to obtain a light amount control device that can make the amount of light uniform.

[Means for solving problems]

The light amount control device according to the present invention includes a non-volatile memory element that stores data on the amount of light emitted from a light source that is changed in accordance with each mirror surface of a rotating polyhedral mirror, and a light amount control device based on the amount of light emitted from the light source written in the non-volatile memory element. The light source is provided with current control means for controlling the drive current applied to the light source.

[Effect]

In this invention, the current control means reads light emission amount data corresponding to each mirror surface of the rotating polygon mirror from the nonvolatile memory and controls the drive current applied to the light source.

〔Example〕

FIG. 1 is a block diagram illustrating the configuration of a light amount control device showing an embodiment of the present invention. Reference numeral 1 denotes a semiconductor laser, which is composed of a laser chip la and a photosensor 1b. Reference numeral 2 denotes a FROM, which serves as a nonvolatile memory element, and stores data on the amount of light emitted as shown in FIG. 3 to be applied to the semiconductor laser 1, which serves as a light source. Note that the data writing operation to FROM2 will be described later. 3 is a CPU that reads digital light emission data stored in the FROM 2 in synchronization with a tack pulse signal 9 that is output once every rotation of the polygon mirror 11, which will be described later, and sends the digital light amount data to the D/A converter 4. In addition to transmitting the light amount data, the light amount output from the photosensor 1b is transmitted to the A/D via the amplifier 5.
The drive current applied to the semiconductor laser 1 is controlled based on the light amount data converted by the converter 6, and light amount data is calculated to keep the amount of light emitted from the laser chip 1a constant. 7
is a laser drive circuit that applies a drive current to the laser chip 1a of the semiconductor laser 1 based on analog light amount data inputted via the low-pass filter 8.

Next, the operation shown in FIG. 1 will be explained.

First, when the photosensitive drum (not shown) is pre-rotated (preparatory rotation) or the photosensitive drum position scanned by the scanning light is rotated to the transfer position, when the paper is at an intermediate position between the paper sheets, so-called between the paper sheets, the laser chip 1a is turned on, the amount of light at that time is received by the photosensor 1b, and the amplifier 5 and A/
The signal is input to the CPU 3 via the D converter 6. The CPU 3 controls the drive current of the laser drive circuit so that the output value of the photosensor 1b becomes a predetermined value.

The light amount data at this time is called APC data, and is set in advance according to the sensitivity of the photosensitive drum. This AP
To obtain the optimum laser drive current from the C data, laser emission is performed at a position on the photosensitive drum that is not transferred to the paper, and the method is to gradually increase the laser drive current from zero in a very short period of time until the output value of the photo sensor 1b increases. The laser drive current when it matches the APC data is stored in the internal memory of the CPU 3. The relationship between the light emission output of the laser chip 1a and the driving current at this time is thought to vary by about 0.1 to 0.8 mW/mA depending on the temperature, lifespan, and variations in characteristics of the laser, so it is necessary to perform this at regular intervals. be.

On the other hand, although there are variations in the output characteristics of the photosensor 1b, there are few changes due to temperature or lifetime, and if only the characteristics are corrected with a simple circuit, compatibility can be fully guaranteed. Here, the above-mentioned APC refers to automatic power control, which means that the amount of light emitted by the laser is automatically controlled so that it is always constant. This APC data is stored in 210M2, and the amount of scanning light is controlled to be constant regardless of the surface of the polygon mirror or the scanning position.

FIG. 2 is a configuration diagram for explaining the data writing operation to 210M2 shown in FIG. 1, and the same parts as in FIG. 1 are given the same reference numerals.

In this figure, reference numeral 11 denotes a polygon mirror, which is rotated at a constant speed in the direction of arrow a by a scanner motor (not shown). 1
2a to 12c are scanning beam enlargement projection lenses provided at focal positions of the scanning optical system;
The images are projected onto the surfaces of the CD sensors 13a to 13c. 1
4 is an fθ lens, and 15 is a light source, which is composed of a semiconductor laser 1, a collimator lens (not shown), and the like. 1
61±A/D converter, 17 is a CPU.

First, it is assumed that a scanner motor (not shown) is rotating in the direction of arrow a, and that a beam passing through the CCD sensor 13a first, counting from the tack pulse signal 9 from the scanner motor, is on the first surface 11a of the polygon mirror 11. The beam passing through the 0-order CCD sensor 13b, which is light intensity data on the scanning start side, is defined as light intensity data at the center of the first surface 11a of the polygon mirror 11, and the beam passing through the CCD sensor 13c is defined as the first surface 11a of the polygon mirror 11. This is the light amount data at the end of scanning. In this way, the light amount data for the remaining second surface 11b to sixth surface 11f of the polygon mirror 11 is detected in the same manner as described above. These light amount data are sequentially A/D
It is converted into a digital signal by the converter 16 and sent to the CPU 1.
7, where it is processed and temporarily stored in the internal memory of the CPU 17. Note that these light amount data samplings may be performed a plurality of times and averaged in order to reduce data errors. Next, the light amount data corresponding to each mirror surface of the polygon mirror 11 held in the CPU 17 is written into the PROM 2 as a series of light amount data.

Next, the light amount control operation according to the present invention will be explained with reference to FIG.

FIG. 3 is a timing chart for explaining the light amount control operation according to the present invention, and the same parts as in FIG. 1 are given the same reference numerals.

In this figure, 21 is the effective scanning time on each surface of the polygon mirror 11, 22 is the BD multiplied signal 23, which is an image signal, and the BD signal 22 is also output after a certain delay. 24
is a laser light intensity signal read out from 210M2 from the first surface 11a to the sixth surface 11f of the polygon mirror 11 (consisting of the six-sided mirror shown in FIG. 2), for each surface from the scanning start side, the center, and the scanning end. It consists of a total of 18 pieces of light amount data, three on each side. Note that the relationship between the first surface physically defined on each surface of the polygon mirror 11 and the tack signal is determined when the polygon mirror 11 is attached to the scanner motor.

When the tack pulse signal 9 is sent to the CPU 3, the laser light amount signal 2 is sent in synchronization with the rise of the tack pulse signal 9.
4 is 18 light amount data DI from 210M2
8 is read out one data at a time at equal intervals within a certain period of time. At this time, the BD signal 22 from the BD sensor (not shown)
is sent to the CPU 3, and in synchronization with this BD signal 22, the image signal 23 and the read light amount data D1-018 are processed to obtain the optimal laser drive current, and the current value is
Stored in the internal memory (RAM) of PU3. These operations are performed between sheets or during preparation rotation, and during printing, the CP
The values of the 18 laser drive currents stored in the memory of U3 are repeatedly converted at fixed time intervals in synchronization with the tack pulse signal 9, as described above. In this way, the light amount data D1 to DI corresponding to each scanning surface of each polygon mirror 1 is
By storing 8 in the FROM 2, the laser output changes accordingly, and as a result, the amount of light on the photosensitive drum surface becomes constant.

Note that the tack pulse signal 9 does not need to be output from the scanner motor; for example, the configuration may be such that the signal is obtained from the polygon mirror 11. Furthermore, in the above embodiment, since the polygon mirror 11 is composed of six mirror surfaces, the number of samplings for the light amount data is 18, but the number of samplings is not limited to 18, and the number of samplings can be increased. It goes without saying that the amount of emitted light can be precisely controlled to a constant value by The mechanical accuracy of the optical scanning system can be improved by providing a non-volatile memory element that stores the amount of light and a current control means that controls the drive current applied to the light source based on the light emission data written in the non-volatile memory element. This has the excellent advantage that the amount of light in each scanning line scanned from each surface of the rotating polygon mirror can be made uniform without causing any problems, and that high-quality images can be formed at low cost.

[Brief explanation of drawings]

FIG. 1 is a block diagram illustrating the configuration of a light amount control device showing an embodiment of the present invention, and FIG.
FIG. 3 is a configuration diagram for explaining the data writing operation to M, and a timing chart for explaining the light amount control operation according to the present invention. In the figure, 1 is a semiconductor laser, 2 is a t*F ROM, 3 is a CPU, 4 is a D/A converter, 5 is an amplifier, 6 is an A/D converter, 7 is a laser drive circuit, 80 is a pass filter, 9 is the tack pulse signal. Figure 2 Figure 3

Claims (2)

[Claims] (1) A scanning optical device comprising a light source, a rotating polygonal mirror, and an imaging lens, including a nonvolatile memory element that stores data on the amount of light emitted from the light source that is changed in accordance with each mirror surface of the rotating polygonal mirror; 1. A light amount control device comprising: current control means for controlling a drive current applied to the light source based on the light emission amount data written in a digital memory element. (2) Light intensity control according to claim (1), characterized in that the nonvolatile memory element stores emitted light intensity data that changes stepwise corresponding to each mirror surface of the rotating polygonal mirror. Device.