JPH04366977A - Image forming method - Google Patents

Abstract

PURPOSE:To obtain an image forming method which does not require the control of a driving for semiconductive laser current by setting laser beam transmissivity so that a variable amount of in the intensity of the layer beam on an object is within the permitted range. CONSTITUTION:The laser beam from the semiconductive laser 3 as a light source is deflected for scanning by a polygon mirror 4, travels via an ftheta lens 5, and is reflected by reflecting mirrors 6 so as to turn to a photosensitive body 2. An electrostatic latent image formed on the photosensitive body 2 by the laser beam is reversely developed, and an image is formed on a copy sheet by a well-known process. Also, it is preferable that a dipping means provided on a halfway in an optical path from the semiconductive laser 3 to the object. Also the laser beam transmissivity from the semiconductive laser 3 to the object is set to that the variable amount in the intensity of the laser beam on the object is in the permitted range.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method using a semiconductor laser, and more particularly to a laser optical system installed in a digital copying machine, a laser beam printer, etc.

0002

2. Description of the Related Art Hitherto, semiconductor lasers have generally been used as light sources for digital copying machines, laser beam printers, and the like.

FIG. 1 shows the relationship among the drive current I, oscillation intensity P, and environmental temperature T of such a semiconductor laser. As is clear from FIG. 1, the semiconductor laser is very sensitive to temperature T, and the oscillation start current Ith increases as the environmental temperature T rises. In general, the temperature dependence of the oscillation starting current Ith can be expressed as Ith∝expT/T0 T0: Characteristic temperature (value unique to semiconductor lasers), and the smaller the characteristic temperature T0, which is a value unique to semiconductor lasers, the greater the temperature dependence. Become.

[0004] Furthermore, the drive current given to the semiconductor laser is
It can be seen that when the environmental temperature T is constant at 0, the fluctuation width of the oscillation intensity P becomes ΔP when the environmental temperature T changes within the range of T1 to T3.

Striped semiconductor lasers, which are most commonly used as light sources for digital copying machines and laser beam printers, have a small characteristic temperature T0 and a large temperature dependence, so the fluctuation width ΔP of the oscillation intensity P is within the allowable range of the image forming process. If the range is exceeded, the dot diameter representing one pixel on the image will vary, resulting in significant image deterioration.

For this reason, an automatic power control circuit (hereinafter referred to as an APC circuit) has been added to control the driving current I of the semiconductor laser so that the oscillation intensity P is constant.

[0007]

However, in a device using such an APC circuit, in order to detect the oscillation intensity P, the
The semiconductor laser must be forced to emit light regardless of image formation, which shortens the life of the semiconductor laser. Furthermore, since the photoreceptor is irradiated with the forcibly emitted laser beam, the irradiated area undergoes development unrelated to image formation, and developer is wasted. Furthermore, the automatic power control circuit itself is also a factor in increasing the cost of the device.

On the other hand, in addition to the above-mentioned striped semiconductor laser, there are various types of semiconductor lasers, including quantum well semiconductor lasers, which have a large characteristic temperature T0 and a relatively small temperature dependence. be. However, because the differential efficiency η (the slope of the straight line in the laser oscillation region) is large, the fluctuation width ΔP of the oscillation intensity exceeds the allowable range of the image forming process, similar to the striped semiconductor laser described above.
It was extremely difficult to use it with a laser beam printer or the like.

The present invention has been made in view of the above problems, and focuses on the characteristics of semiconductor lasers to suppress the fluctuation range of the oscillation intensity due to temperature of the semiconductor laser to within the allowable range of the image forming process. An object of the present invention is to achieve an image forming method that does not require controlling the driving current of a semiconductor laser.

0010

[Means for Solving the Problems] In order to solve these problems, the present invention deflects and scans a laser beam modulated based on an image signal and emitted from a semiconductor laser using a deflection means, and scans the laser beam onto an irradiated object. In an image forming method in which an image is formed by irradiation, the laser beam transmittance from a semiconductor laser to an object to be irradiated is set so that the amount of variation in laser beam intensity on the object to be irradiated is within an allowable range. shall be.

[0011]

[Operation] If the set intensity of the laser beam to be irradiated to the irradiated object is PP, and the variation in the intensity of the laser beam that maintains a good image is ±A%, then the laser beam that the irradiated object can tolerate is The fluctuation range ΔPP of the set strength is ΔPP=
PP・2A/100=PP・A/50.

[0012] Here, if the transmittance of the optical system until the laser beam oscillated from the semiconductor laser reaches the irradiated object is X%, then the range of variation in the oscillation intensity of the semiconductor laser that is allowed by the entire image forming process is ΔPA is as follows: ΔPA=ΔPP・100/X=PP・2A/X. Next, the temperature T of the semiconductor laser actually used is
The fluctuation width ΔP of the oscillation intensity from 1 to T3 is determined. Temperature T
The intermediate temperature between 1 and T3 is T2, the driving current of the semiconductor laser required to irradiate the irradiated object with intensity PP under this temperature T2 environment is I0, and the differential efficiency of the semiconductor laser at temperature T2 is η. shall be. Here, since the differential efficiency of the semiconductor laser with respect to each temperature is considered to be almost the same, the fluctuation range ΔP of the oscillation intensity from the above temperature T1 to T3 is ΔP
It can be approximated as =ΔI·η. Therefore, it is sufficient that the variation range ΔP of the semiconductor laser oscillation intensity from temperature T1 to T3 is equal to or less than the variation range ΔPA of the semiconductor laser oscillation intensity allowed by the image forming process obtained previously, that is, ΔP≦ΔPA. In other words, if the formula ΔI·η≦2APP/X holds true, a good image can be maintained even if the oscillation intensity of the semiconductor laser varies depending on the temperature.

Here, ΔI·η is a unique value determined by the characteristics of the semiconductor laser, and PP, A are unique values determined by the characteristics of the image forming process. On the contrary,
The transmittance X of the optical system meter can be adjusted relatively easily by inserting a filter or the like into the optical path or by coating a reflective surface such as a mirror.

Therefore, the transmittance X of the optical system is adjusted so that X≦2APP/ΔI·η (1).

[0015]

Embodiment FIG. 2 is a sectional view of an image forming section to which the present invention is applied. In the figure, reference numeral 2 denotes a print head, and a laser beam from a semiconductor laser 3 serving as a light source is deflected and scanned by a polygon mirror 4, passed through an fθ lens 5, and reflected by a reflection mirror 6 so as to be directed toward the photoreceptor 2. The electrostatic latent image formed on the photoreceptor 2 by the laser beam is reversely developed, and an image is formed on copy paper (not shown) by a well-known image forming process.

Specific conditions for such an image forming section are shown below.

Characteristics of photoreceptor Photoreceptor Laminated organic photoreceptor Film thickness of photosensitive layer 19.0 μm Relative dielectric constant 3.77 Scanning data Pixel density 300 DPI (number of pixels per inch) Scanning time 0.6566 μs/pixel beam shape Width in the main scanning direction: 60 μm Width in the sub-scanning direction: 85 μm Development conditions: Development bias: 250 V Charging conditions: Charging potential: 610 V In the above-described image forming process, in order to obtain the preferred line width of 1 dot (108 μm), the photoreceptor is irradiated. The set intensity PP of the laser beam needs to be 200 μW. Therefore, if the variation in line width allowed for a good image is ±5 μm, the variation in the laser beam irradiated onto the photoreceptor must be suppressed to ±10%.

FIG. 3 shows the configuration of a double quantum well semiconductor laser used in the example, and from the bottom, n
-GaAs base, n-AlGaAs, active layer (GaAs
), convex p-AlGaAs, and p-Ga on the convex part.
It has a laminated structure of As and polyimide on both sides of the convex portion. The arrow portion indicated by a corresponds to the horizontal axis of the graph in FIG. FIG. 4 is a graph showing the distribution of the Al content near the active layer, with the vertical axis representing the Al content and the horizontal axis representing the position of the active layer indicated by a in FIG. , a large concave low distribution portion and two further small concave low distribution portions.

FIG. 5 is a graph showing the relationship between the environmental temperature T and the differential efficiency η of the double quantum well semiconductor laser shown in FIGS. 3 and 4, and FIG. 6 is a graph showing the relationship between the environmental temperature T and the oscillation starting current Ith. It is a graph showing a relationship.

Assuming that the environmental temperature range in which the semiconductor laser is used is 10° C. to 50° C., the differential efficiency η at the intermediate temperature of 30° C. is 0.9 from FIG. 5, and ΔI is 3.0° C. from FIG.
It is 8mA. Substituting these values into equation (1) reveals that the transmittance X of the optical system should be 1.17% or less. Here, since the transmittance of commonly used optical systems is about 5%, it is necessary to provide a filter or the like in the optical path in order to reduce the transmittance X to 1.17% or less.

In order to set the transmittance of the optical system lower than before, it is necessary to increase the oscillation intensity of the semiconductor laser. Therefore, it is desirable to use a semiconductor laser with high differential efficiency so that a large emission intensity can be obtained even if the drive current I0 is small.

In this embodiment, the transmittance X of the optical system is reduced by providing a reflective film with a reflectance of 77% on the emission surface of the semiconductor laser 3. Specifically, the transmittance X was set to 1.15% by coating Al2O3 with a thickness of 1200 Å as the first layer of the reflective film and Si with a thickness of 596 Å as the second layer.

Adjustment of the optical system configured as described above is as follows:
Assuming that the environmental temperature range is 10°C to 50°C, the test is carried out at 30°C, which is in the middle. That is, when the environmental temperature T is 30°C, the driving current I0 is set so that the intensity of the laser beam passing through the optical system set as described above is 200 μW, and the semiconductor laser is to emit light.

In such an image forming method, even without using an APC circuit, it is possible to always obtain a good image because fluctuations in the emission intensity of the laser beam due to temperature changes are within the permissible range of the image forming process. can.

[0025] Although specific numerical values are listed as conditions in the examples, the present invention is not limited to such conditions. In addition, although a reflective film is provided on the emission surface of the semiconductor laser in the description, it may be provided anywhere in the optical path of the optical system. For example, in FIG. 6 or the fθ lens 5 that focuses or corrects the laser beam may be provided with a reflective film. Further, as the polygon mirror 4 for deflecting the laser beam, a mirror made of opaque plastic whose surface is only smoothed (without a reflective film) may be used.

[0026]

[Effect of the invention] As is clear from the description of the embodiments above,
By using the image forming method of the present invention, the APC circuit of the semiconductor laser that has been commonly used can be omitted, leading to cost reduction. Also, A
By eliminating the PC circuit, it is no longer necessary to force the semiconductor laser to emit light for each scan line or page, regardless of the image formation being performed, in order to detect the oscillation intensity, thereby extending the life of the semiconductor laser. be able to. Furthermore, since there is no need to forcibly emit a laser beam to detect the emission intensity, the photoreceptor is not irradiated with the beam, resulting in an effect that developer can be saved.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between drive current, emission intensity, and environmental temperature in a semiconductor laser.

FIG. 2 is a cross-sectional view of the configuration of an image forming section.

FIG. 3 is a perspective view of the configuration of a double electron well semiconductor laser.

FIG. 4 is a structural diagram of the vicinity of the active layer of a double electron well semiconductor laser.

FIG. 5 is a graph showing the relationship between the differential efficiency of a double electron well semiconductor laser and the environmental temperature.

FIG. 6 is a graph showing the relationship between the emission starting current of a double electron well semiconductor laser and the environmental temperature.

[Explanation of symbols]

Claims (6)

[Claims] Claims: 1. An image forming method in which a laser beam modulated based on an image signal and emitted from a semiconductor laser is deflected and scanned by a deflection means, and irradiated onto an object to be irradiated to form an image. An image forming method characterized by setting the laser beam transmittance up to the irradiation object so that the amount of variation in laser beam intensity on the irradiation object falls within a permissible range. 2. In the image forming method according to claim 1, the laser beam transmittance is X%, and X is expressed by the following formula: X≦2APP/
An image forming method characterized by satisfying ΔI·η. However, A: Laser beam intensity variation rate allowed by the photoreceptor PP: Set intensity Δ of the laser beam irradiated to the irradiated object
I: Difference in the oscillation start current of the semiconductor laser corresponding to the allowable temperature change width η: Differential efficiency of the semiconductor laser 3. The image forming method according to claim 1, wherein a light attenuation means is provided in the optical path from the semiconductor laser to the object to be irradiated to set the transmittance. 4. The image forming method according to claim 1, wherein a light attenuation means is provided on the laser beam exit surface of the semiconductor laser to set the transmittance. 5. The image forming method according to claim 1, further comprising a reflecting means for reflecting the laser beam and guiding it onto the object to be irradiated;
An image forming method in which transmittance is set by providing a light reduction means on the reflective surface. 6. The image forming method according to claim 1, further comprising a lens member for focusing or correcting the laser beam, and a light attenuation means provided on the surface of the lens member to set transmittance.