JPH04331911A - Optical scanning device - Google Patents

Abstract

PURPOSE:To correct a light output with high accuracy, to emit invariably constant laser light from a laser light source, and to enable high-performance image formation by adjusting the light emission timing of a light source means. CONSTITUTION:The laser output of a laser diode 1 is detected by a photodiode 12, whose output signal is sent out to a laser driver 11, which supplies a driving current to the laser light source 1 according to the input signal so that laser output becomes constant. The laser light source 1 is turned on firstly for the detection of the laser output, and the laser light is emitted even in the opposite direction from the direction of the laser diode 12 at this time. Therefore, when the laser light irradiating the side of a scanning optical system is made incident on the laser light source side again as return light, the quantity of light detected by the photodiode 12 apparently increases. Consequently, the detection timing of the laser output can optionally be set in an area where the return light is made incident again except in an image write area.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical scanning device, and more particularly, to an optical scanning device, in which an image bearing surface such as a photoreceptor or an electrostatic recording medium is optically scanned with a light beam modulated by an image signal. The present invention relates to an optical scanning device that is suitable for devices such as laser beam printers, color laser beam printers, and multicolor laser beam printers that use an electrophotographic process.

0002

2. Description of the Related Art Conventionally, in optical scanning devices such as laser beam printers, image information is written by optically scanning the surface of an image carrier with a light beam modulated.

FIG. 9 is a schematic diagram of the main parts of a conventional optical scanning device. In FIG. 9, a light beam emitted from a light source unit 1 such as a semiconductor laser is made into a parallel light beam by a collimator lens 2, and is focused by a cylindrical lens 3 having refractive power only in the sub-scanning direction, and a deflector 4 consisting of a rotating polygon mirror or the like. deflection reflecting surface 4
It is made linearly incident on a. The collimator lens 2 and the cylindrical lens 3 constitute an imaging optical system.

The light beam reflected and deflected by the deflection/reflection surface 4a is reflected and deflected by a lens 7a having a negative refractive power made of a spherical surface constituting the scanning lens 7, and a lens 7b having a toric surface having different refractive powers in two orthogonal directions. The light is guided onto the surface to be scanned 9 to form a spot. The deflector 4 is rotated by the motor 5 about the rotating shaft 13 in the direction of the arrow 6, thereby optically scanning the deflection scanning surface on the surface to be scanned 9 in the direction of the arrow 10.

Generally, the amount of emitted light (output light) of a semiconductor laser as a light source varies greatly depending on the ambient temperature. For this reason, in many cases, a temperature correction circuit is used to adjust the temperature.

FIG. 3 shows the PI (optical output-forward current) characteristic of the relationship between the optical output P and the injection current I of a semiconductor laser, using the ambient temperature as a parameter. As shown in the figure, the P-I characteristic exhibits a characteristic in which the current value I, which is determined depending on the ambient temperature, is a boundary value and rises rapidly. In other words, the P-I characteristic moves in parallel in the I-axis direction depending on the temperature.

[0007] As described above, the optical output of a semiconductor laser varies greatly depending on changes in ambient temperature, and this results in disturbance (noise) to image information. To compensate for this,
Conventionally, as a first method, as shown in FIG. 4, a temperature correction element 41 was attached to the laser tube to adjust the temperature of the laser tube to a constant value.

As a second method, as shown in FIG. 5, an optical output compensation circuit is used to adjust the ambient temperature to a constant value. In FIG. 5, the optical output level of the semiconductor laser 51 is detected by the photodiode 52, and the APC section 53 detects the optical output level of the semiconductor laser 51.
The laser driving current is changed so that the optical output level of the semiconductor laser 51 is kept constant.

[0009]

[Problems to be Solved by the Invention] In the method of using a temperature correction element, a Peltier element or the like is usually used as the temperature correction element. There are problems in that it is expensive and cannot be easily used. On the other hand, the method using the optical output compensation circuit shown in FIG. 5 has a problem in that highly accurate adjustment is difficult.

That is, in a device such as a copying machine that changes the gradation of an image, the optical output fluctuation must be 2 to 3% or less. However, in Figure 5, if disturbance light such as return light from a rotating polygon mirror enters the feedback photodiode, the feedback in the APC section will not work with high precision, resulting in a variation in optical output of 2 to 3% or more. There was a problem.

[0011] Furthermore, as a means of reducing the influence of the disturbance light at this time, the S/N ratio with respect to the disturbance light can be improved by increasing the level of the amount of light detected by the photodiode.

However, the normal photodiode is shown in FIG.
It is installed on the side opposite to the emission side of the laser light source as shown in
It is configured to detect weak light from the light emitting end face and the reflecting end face of the chip.

For this reason, there is a problem in that increasing the light intensity level of the photodiode lowers the laser emission efficiency on the emission side.

In the present invention, when detecting the light output with a photodiode in order to adjust the light output from the light source, the return reflected light from the rotating polygon mirror, which is the strongest amount of disturbance light, is incident on the photodiode. By specifying the lighting timing to prevent the laser from burning, we perform highly accurate optical output correction (APC) to ensure that the laser light source always emits a constant laser light.
The purpose of the present invention is to provide an optical scanning device capable of high-performance image formation.

[0015]

[Means for Solving the Problems] In the optical scanning device of the present invention, a light beam modulated by an image signal from a light source means is deflected by a deflector via an imaging optical system, and then is deflected by a deflector via a scanning lens. In an optical scanning device configured to conduct light scanning by guiding light onto a scanning surface, a light detection means for detecting light output from the light source means is provided, and an output signal from the light detection means is used to detect the light source. When controlling the light output from the light source means, by adjusting the light emission timing of the light source means, the light flux emitted from the light source means during the operation of the light detection means is reflected by the deflector and returned to the light detection means. It is characterized by the fact that it prevents it from entering.

In particular, the present invention is characterized in that the light detecting means is arranged on the opposite side of the light emitting opening with respect to the light emitting chip of the light source means.

[0017]

Embodiment FIG. 1 is a schematic diagram of a main part of Embodiment 1 of the present invention. In FIG. 1, a diverging light beam emitted from a light source unit 1 (for example, a semiconductor laser, etc.) is converted into a parallel light beam by a collimator lens 2, and enters a cylindrical lens 3 having refractive power only in the sub-scanning direction. The light is condensed into a line by the cylindrical lens 3, and is incident as a linear light beam onto the deflection reflection surface 4a of the deflector 4, which is a rotating polygon mirror. Here, the collimator lens 2 and the cylindrical lens 3 constitute an imaging optical system.

The light beam incident on the deflection/reflection surface 4a is reflected and deflected by the deflection/reflection surface 4a, and then passes through the scanning lens 7 having f-θ characteristics.
incident on . The scanning lens 7 includes a lens 7a having a negative refractive power and a lens 7b having a toric surface having different refractive powers in the main scanning direction and the sub-scanning direction. The light beam 14 incident on the scanning lens 7 is condensed to form a light spot on a surface to be scanned 9 such as a photosensitive drum. Then, the deflector 4 is connected to the rotating shaft 13.
By rotating the scanned surface 9 in the direction of the arrow 6 about the axis
The light is scanned as shown by an arrow 10 on the main scanning plane.

In this embodiment, the laser output from the laser light source (laser diode) 1 is detected by a photodiode 12 as a light detection means, and the output signal is outputted to the laser driver 11. The laser driver 11 applies a driving current to the laser light source 1 based on the input signal so that the laser output (laser light amount) is constant.

FIG. 2 is an explanatory diagram showing the lighting timing of the laser light source 1 in this embodiment. FIG. 2A shows the lighting timing of the laser light source 1 when writing an image on the surface of the photosensitive drum 9. First, the laser light source 1 emits light at time A1 for BD signal detection. Next, after a certain period of time has elapsed since the BD signal, the laser light source 1 is pulse-lit within time A2 according to the image information. Time A2 is the lighting timing within one scanning time, and this is sequentially repeated.

FIG. 2B shows the timing at which the laser light incident on the deflection reflecting surface 4a of the deflector 4 is reflected and enters the photodiode 12 for detecting laser output as returned light.

FIG. 2C shows the lighting timing of the laser light source 1 for detecting the laser output. Here, the lighting process of the laser light source will be explained within the time it takes to scan one main scan line.

First, the laser diode 1 is turned on at time D1 to detect the laser output. At this time, the laser drive current is set to a constant value. Here, the laser output is detected by the photodiode 12 and output to the APC circuit via the laser driver 11. In the APC circuit, it is determined from the relationship between the laser drive current and the detected laser output what current value is required as the laser drive current in order to obtain the amount of light (laser light) required when scanning the photoreceptor 9. Calculate whether

Next, the laser diode 1 is turned on at time A1 to obtain a BD signal for detecting the image writing timing. This is usually called a BD signal. When the BD signal is detected, the laser diode 1 is pulse-lit at time A2 in accordance with the image information after a certain period of time has elapsed. Here, currents determined within the APC circuit are supplied as drive currents for the BD signal and image signal. In other words, a constant amount of stable optical output can always be obtained as the BD signal and the image signal. Now main scan 1
Line scanning ends.

In this lighting process, the laser light source is first turned on to detect the laser output, but at this time, of course, the laser light is also irradiated in the opposite direction to the photodiode 12, that is, in the direction of the scanning optical system. Therefore, when the laser light irradiated to the scanning optical system side returns to the laser light source side and enters again as light, the amount of light detected by the photodiode increases apparently.

As a result, the current value set by the APC circuit is undesirably lower than the desired current value. Therefore, in this embodiment, the laser output detection timing is set to a region where the return light from the scanning optical system such as a rotating polygon mirror re-enters the laser light source side, as shown in FIG. 3(C), that is, other than time B1. ing.

Further, the detection timing of the laser output can be arbitrarily set in a region where the returning light does not enter again and in a region other than the image writing region.

In this embodiment, if the image is detected at a timing much earlier than the image writing timing A2 in FIG. 2(A),
Since the environmental conditions of the laser light source at the time of detection and the environmental conditions of the laser light source at the time of writing may be different, detection is performed in a timing region as close to the writing timing as possible.

Although this embodiment shows the case where the laser output is detected by the photodiode for each scan, in an optical scanning device such as a copying machine, the detection is performed only once every time one page is copied. You can also do it. In this case, due to environmental fluctuations of the laser light source at the leading edge and trailing edge of the copy,
Although it is conceivable that the laser output may change, the feedback time from the photodiode to the laser drive current becomes longer, so the circuit etc. of the feedback section can be manufactured at low cost.

FIGS. 7 and 8 are explanatory diagrams of embodiments 2 and 3 showing the lighting timing of the laser light source according to the present invention. The meaning of the time in the figure is the same as that shown in FIG.

In the second embodiment shown in FIG. 7, the total lighting time of the laser light source during one line scanning is shortened by using the lighting timing of the laser light source for both APC photodiode detection and BD detection.

In Embodiment 3 shown in FIG. 8, the lighting timing of the laser light source is changed to lower the drive current when detecting the APC photodiode, that is, the emitted laser output is reduced, and the S/N ratio is adjusted by the output from the photodiode. By lowering this to a level that does not cause any deterioration, we aim to improve the lighting life of the laser light source.

[0033]

According to the present invention, when detecting the light output with a photodiode in order to adjust the light output from the light source, as mentioned above, the return from the rotating polygon mirror, which is the strongest amount of disturbance light, is detected. The lighting timing is specified to prevent reflected light from entering the photodiode, and this enables highly accurate optical output correction (APC) to ensure that a constant laser beam is always emitted from the laser light source, enabling high-performance image formation. It is possible to achieve an optical scanning device with the following characteristics.

[Brief explanation of drawings]

[Figure 1] Schematic diagram of main parts of Example 1 of the present invention

[Figure 2]
An explanatory diagram of the lighting timing of the laser light source in Example 1 of FIG.

[Figure 3] Explanatory diagram showing the current-light output characteristics of a semiconductor laser

[Figure 4] Schematic diagram of a conventional semiconductor laser

[Figure 5]
An explanatory diagram of the optical output correction circuit in Example 1 of FIG.

[Figure 6] Schematic diagram of a conventional semiconductor laser

[Figure 7]
An explanatory diagram of the lighting timing of the laser light source according to the second embodiment of the present invention

[Fig. 8] An explanatory diagram of the lighting timing of the laser light source in Embodiment 3 of the present invention

[Figure 9] Schematic diagram of the main parts of a conventional optical scanning device

[Explanation of symbols]

1 Light source section (semiconductor laser) 2 Collimator lens 3 Cylindrical lens 4 Deflector 5 Motor 7 Scanning lens 9 Scanned surface 11 Laser driver 12 Photo detection means

Claims (2)

[Claims] 1. A light beam modulated by an image signal from a light source means is deflected by a deflector through an imaging optical system, and then guided onto a surface to be scanned through a scanning lens for optical scanning. In the optical scanning device according to the present invention, a light detection means for detecting the light output from the light source means is provided, and when the light output from the light source means is controlled using the output signal from the light detection means, the light source By adjusting the light emission timing of the means, the light beam emitted from the light source means during the operation of the light detecting means is prevented from being reflected by the deflector and returning to the light detecting means. Optical scanning device. 2. The optical scanning device according to claim 1, wherein the light detecting means is disposed on a side opposite to a light exit opening with respect to the light emitting chip of the light source means.