JPH0447829B2 - - Google Patents

Description

[Detailed Description of the Invention] Technical Field The present invention relates to laser light output control, and in particular to a laser that can be controlled to correct sensitivity dependence of a photoreceptor due to fluctuations in laser oscillation wavelength by controlling laser light output. This invention relates to a light control device.

Prior Art Conventionally, semiconductor laser elements have been widely used as light sources in fields such as optical communications. In such cases, so-called auto power is used to maintain the optical output of the semiconductor laser at a constant power.
Control (hereinafter referred to as APC) is often adopted.

FIG. 1 explains this method. The optical output of the semiconductor laser emitted from the semiconductor laser element 1 is received by the photodetector 2, amplified by the amplifier 3, and then fed back to the laser drive circuit 4. The output of the photodetector 2 is controlled to be constant. This method is widely used as a method for correcting changes in the optical output of a semiconductor laser device due to changes in environmental temperature, deterioration of the device, and the like.

However, when a semiconductor laser element is used for image recording or the like, the wavelength dependence of the sensitivity of the photoreceptor used in the image receiving section poses a major problem. Normal He−Ne
In devices using a short wavelength laser such as a laser, the spectral sensitivity of the photoreceptor near the laser wavelength is often flat, making it possible to employ the conventional APC method.

On the other hand, semiconductor lasers have a wavelength of around 800 nm and He-
Compared to Ne lasers, it is in the near-infrared region, so it has lower sensitivity with commonly used photoreceptors. For this reason, when a semiconductor laser is used in such an image recording device, the photoreceptor is often sensitized. However, even with sensitization, it is not possible to flatten the spectral sensitivity even in the semiconductor laser wavelength range due to image quality stability, photoreceptor durability, etc., and the relative spectral sensitivity characteristic shown in curve a in Figure 2. Similarly, sensitivity has dependence on wavelength.

Therefore, it is necessary to control the amount of light according to the wavelength of the semiconductor laser element used, and if wavelength fluctuations occur during the operation of the semiconductor laser, good images cannot be obtained with the conventional APC method.

Next, referring to Fig. 3, an example of a change in laser oscillation wavelength due to a change in the operating ambient temperature is given. A semiconductor laser has a temperature coefficient of wavelength of 0.25 nm to 0.3 nm, and for example, a temperature change of 30°C causes a temperature coefficient of up to 9 nm. A wavelength change occurs. For this reason, there is a drawback that the higher the wavelength dependence of the sensitivity of the photoreceptor, the worse the obtained image becomes.

Purpose The present invention was made in view of the above-mentioned drawbacks of the prior art, and its purpose is to improve the sensitivity of a photoconductor having spectral sensitivity characteristics even when the oscillation wavelength of a laser, which is a light source, changes. The object of the present invention is to provide a laser light control device that can relatively correct or control the light output by controlling the light output.

Another object of the present invention is to prevent substantial fluctuations in laser light output due to variations in characteristics, deterioration of characteristics, and changes in the operating environment of a laser element and its peripheral circuit elements, and to prevent laser oscillation from a photoreceptor having spectral sensitivity characteristics. It is an object of the present invention to provide a laser light control device which is capable of correcting or controlling relative fluctuations in laser light output due to wavelength fluctuations by controlling the laser light output, and which has a simple configuration and is inexpensive.

Another object of the present invention is to use a laser light detection means made of the same photosensitive material as the photoreceptor serving as an image receiving part so that the sensitivity of the photoreceptor corresponds to changes due to laser oscillation wavelength fluctuations and changes over time, and also to changes in the operating environment. It is an object of the present invention to provide a laser light control device that can always perform highly stable image exposure control on an image receiving section by obtaining such an output from a light detection means.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described in detail below with reference to the drawings.

Figure 1 is a block diagram showing the principle of conventional technology that maintains the optical output of a semiconductor laser at a constant power, and Figure 2 shows the relationship between the laser light wavelength and relative spectral sensitivity of a single photoreceptor used in laser beam printers, etc. FIG. FIG. 3 is a graph showing the relationship between the operating ambient temperature and the laser oscillation wavelength of one semiconductor laser element, which was referred to in the above-mentioned prior art section.

FIG. 4 is an explanatory diagram showing a scanning optical system between a light projecting section and an image receiving section of an electrophotographic laser beam printer equipped with a laser beam control device according to an embodiment of the present invention. In the figure, laser light output emitted from a semiconductor laser element 5 passes through a collimator lens 6, is reflected by a scanner polygon mirror 7, and is focused onto the surface of a photosensitive drum 9 by an Fθ lens 8. Here, the scanner polygon mirror 7 rotates in the direction of arrow 15 and repeatedly scans the laser beam in the direction of arrow 11 on the photosensitive drum. At the same time, since the photosensitive drum 9 is rotating at a constant speed in the direction of the arrow 16, if the video signal modulates the laser beam into brightness and darkness, an exposed image can be formed on the circumferential surface of the photosensitive drum 9 by the laser beam.

Reference numeral 10 denotes a laser light detection element, which is arranged on an extension of the laser beam scanning line at one end in the axial direction of the photosensitive drum. In this way, the laser light detection element 10 receives a predetermined laser light detection beam at the beginning of each scanning line under substantially the same environmental conditions as the photosensitive drum 9. Therefore, there is an advantage that a laser light detection output that corresponds to the actual environment in which the photosensitive drum is placed can be obtained.

Alternatively, especially when the light source is a semiconductor laser element, the laser light detection element 10 may be placed close to the semiconductor laser element 5 so that the laser light detection element exclusively receives one of the laser beams emitted at the same time.
Therefore, the semiconductor laser element 5, the laser light detection element 10, and the laser light detection control section 17 are arranged in one place.
It may also be arranged in a compact manner.

Sensitized CdS-based photoconductors have extremely high photoconductive sensitivity and are currently widely used as photosensitive materials for photosensitive drums. According to the present invention, by forming the laser light detection element with the same photosensitive material, it has the same spectral sensitivity characteristics as the photosensitive drum, and is also resistant to changes in the operating environment or to changes over time. It becomes possible to configure a laser light detection means that changes the light receiving ability almost equally. Another specific example of such a combination is an amorphous silicon drum and an amorphous silicon sensor.

In addition, for photosensitive drums made of different photosensitive materials, we focus on the spectral sensitivity characteristics of the photosensitive materials and add a laser light detection element that has almost the same spectral sensitivity characteristics to, for example, a CdS-based photoconductor. It may also be formed by changing the amount of impurities.

FIG. 5 is a circuit diagram showing a laser beam control device according to an embodiment of the present invention. In the figure, 18 is a video signal that modulates the laser light into brightness and darkness. If this embodiment is used in a laser beam printer, the video signal may be a digital signal corresponding to a dot pattern. Reference numeral 14 denotes a laser drive circuit which turns on/off the laser drive currents of leads 20 and 21 based on the video signal of lead 19.

FIG. 6 is a circuit diagram explaining the operating principle of this laser drive circuit 14, and shows a well-known differential amplification circuit. In the figure, transistors Q1 and Q2 are connected to the inverted video signal inverted by the inverter 22.
It forms a differential body that makes a discrimination based on whether or not a threshold value determined by R7 and R8 is exceeded. In addition, transistor Q3 works together with resistor R6 to form a constant current source,
The amplification degree of the actuating pair is controlled by making the current value variable by a laser light output control signal inputted through the lead 23. The video signal of lead 19 is
If it is HI, the transistor Q1 is cut off, current flows to the transistor Q21, and the potential difference of the resistor R5 is applied to the semiconductor laser element 5 via the leads 20 and 21.
Laser oscillation is activated by supplying a pumping current to. At this time, if a high potential is applied to the base of the transistor Q3, the laser light output increases, and if a low potential is applied, the laser light output decreases. Also, the video signal of lead 19 is LO.
If so, current flows through transistor Q1, transistor Q2 is cut off, and semiconductor laser device 5 is deenergized.

Reference numeral 10 denotes a laser light detection element, which is made of a photosensitive material having substantially the same spectral sensitivity characteristics as at least the photoreceptor of the image receiving section, as described above. A photocurrent I flows through the laser light detection element 10 by receiving the laser light from the semiconductor laser element 5, but this photocurrent I is subject to at least variations in the characteristics of the laser element 5 and its peripheral circuit elements. This depends on substantial fluctuations in the laser light output due to deterioration and changes in the operating environment, and on its own spectral sensitivity characteristics, which are approximately the same as those of the image receiving part photoreceptor due to fluctuations in the laser oscillation wavelength.

Reference numeral 11 denotes an operational amplifier which works together with a resistor R2 to constitute a photocurrent-voltage conversion circuit. Further, the resistor R1 is an offset compensation resistor. When the photocurrent I increases, a large negative potential is output to the lead 24, and when the photocurrent I decreases, a small negative potential is output.

Reference numeral 12 denotes a sample and hold circuit, which stores the negative potential output to lead 24 in an internal capacitor using the sample signal from lead 25, amplifies this value with a high input impedance amplifier, and outputs the negative potential output to lead 23.
Outputs a laser light output control signal to.

A timing circuit 13 is composed of a plurality of one-shot circuits. Its operation is such that when the laser light detection element 10 receives the laser light output from the semiconductor laser element 5 at the beginning of each scanning line of the laser beam, the rising edge of the photocurrent I is converted into a negative potential falling edge by the operational amplifier 11 and is read. 24. When this fall exceeds a predetermined threshold value, the first one-shot circuit of timing circuit 13 is triggered. The time constant of this first one-shot circuit times out when the laser light detection element 10 sufficiently receives the laser light output from the semiconductor laser element 5 and the photocurrent I and the negative potential of the lead 24 are sufficiently stabilized. triggers the second one-shot circuit. The second one-shot circuit outputs a pulse signal of a predetermined width to the lead 25. This pulse signal has a pulse width sufficient to store a new negative potential in the capacitor of the sampling and holding circuit 12.

With the above configuration, the laser light output control signal of the lead 23 is based on the laser light detection output detected at the beginning of each scanning line of the laser beam, and is based on the substantial fluctuation of the laser light output and the laser oscillation wavelength as described above. In order to correct relative fluctuations in the laser light output as seen from the light receiving section caused by fluctuations, the laser light output control signal value is corrected to a new one for each scanning cycle, and as a result, a new laser light output control signal value is displayed on the photosensitive drum 9, which is the image receiving section. The laser light output is controlled so that a stable exposure image is always obtained.

In the description of the embodiments described above, a case has been described in which the laser light detection element 10 is arranged on the extension of the scanning line of the photosensitive drum 9. Alternatively, for example, by arranging a laser light detection element to detect the laser light emitted behind the semiconductor laser element, it is possible to always receive and detect the laser light modulated by the video signal. Therefore, a configuration may be adopted in which the laser light output can be finely controlled.

Effects As described above, according to the present invention, substantial fluctuations in laser light output due to variations in characteristics of the laser element and its peripheral circuits, deterioration of characteristics, and changes in the operating environment can be avoided, and the image receiving section having spectral sensitivity characteristics can be prevented. It has become possible to correct or control relative fluctuations in laser light output due to fluctuations in laser oscillation wavelength when viewed from the photoreceptor by controlling the laser light output. In particular, if the laser light detection means is constructed from a single laser light detection element having at least the same spectral sensitivity characteristics as the photoreceptor serving as the image receiving section, the laser light control device according to the present invention can be constructed extremely simply and at low cost. can be provided.

Further, according to the present invention, it is possible to control the light output of the laser as described above by using the laser light detection means made of the same photosensitive material as the photoreceptor serving as the image receiving section. Therefore, the laser light detection means not only has the same spectral sensitivity characteristics as the photoreceptor serving as the image receiving section, but also has a spectral sensitivity characteristic that is consistent with the aging of the image receiving characteristics of the photoreceptor and also with changes in the operating environment. This makes it possible to detect laser light in accordance with the actual environment in which it is placed. Conversely, this has the effect of greatly relaxing restrictions on the selection of a laser element as a light emitting source. That is, according to the laser light detection means according to the present invention, it is possible to always obtain a laser light detection output that has characteristics equivalent to those of the image receiving section and is in accordance with the actual environment.
The optimum laser light output control signal can always be easily obtained even for different types of laser light sources.

Therefore, in an image recording apparatus or the like equipped with a laser light control device according to the present invention, the sensitivity of the photoreceptor may be shifted during manufacturing, over time, or under conditions where the sensitivity of the photoreceptor shifts due to fluctuations in the laser oscillation wavelength. For example, a stable recorded image can always be obtained on the output recording paper.

[Brief explanation of the drawing]

Figure 1 is a block diagram showing the principle of conventional technology that maintains the optical output of a semiconductor laser at a constant power, Figure 2 is a graph showing the relationship between the laser light wavelength of one photoreceptor and the relative spectral sensitivity, and Figure 3 is a graph showing the relationship between the laser light wavelength of one photoreceptor and the relative spectral sensitivity. A graph showing the relationship between the operating ambient temperature of a semiconductor laser element and the laser oscillation wavelength. Figure 4 is an explanatory diagram showing the scanning optical system between the light projecting part and the image receiving part of an electrophotographic laser beam printer. FIG. 6 is a circuit configuration diagram showing a laser light control device according to an embodiment of the invention, and FIG. 6 is a circuit diagram explaining the operating principle of the laser drive circuit. 5... Semiconductor laser element, 6... Collimator lens, 7... Scanner polygon mirror, 8...
Fθ lens, 9... Photosensitive drum, 10... Laser light detection element, 11... Operational amplifier, 12... Sample hold circuit, 13... Timing circuit, 1
4... Laser drive circuit, 17... Laser light detection control section, 18... Video signal.

Claims (1)

[Scope of Claims] 1. Laser light detection means made of a photosensitive material having a spectral sensitivity characteristic substantially equal to that of a photoreceptor that receives an image signal from a laser light source, and the laser light detection means detects laser light from the laser light source. A laser light control device comprising a laser light output control means for controlling the laser light output of the laser light source based on the output. 2. Laser light detection means made of the same photosensitive material as the photoreceptor that receives the image signal from the laser light source;
A laser light control device characterized in that the laser light detection means comprises a laser light output control means for controlling the laser light output of the laser light source based on the output of the laser light detected by the laser light source.