JPS58151171A - Laser printer - Google Patents

Abstract

PURPOSE:To obtain a sharp picture, by controlling the lighting time of a semiconductor laser in the range of a time corresponding to one dot and correcting elliptic spot shape of a light beam. CONSTITUTION:A laser beam irradiated from a semicondutor laser 1 is deflected at an optical deflection means 2 and scanned on a photosensitive drum 3 horizontally. The drum 3 rotates with a driving motor 30 in a direction orthogonal to the scanning direction of the laser beam while taking the timing the scanning position of the laser beam, and electrostatic latent image corresponding to the input data is formed on the drum 3 in the set of dots. This latent image (not shown) is obtained on a recording paper as a recorded picture via the development and transfer processes.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a laser printer using a semiconductor laser as a light source. More specifically, the present invention is a laser printer in which a light beam from a laser light source is horizontally scanned on a photoreceptor, and an image to be recorded is displayed and recorded as a set of dots, and the spot of the light beam is This invention relates to a laser printer that corrects defects in pattern images due to shape and provides clear images.

When a semiconductor laser is used as a light source in a laser printer, it is possible to make the device smaller, more functional, more reliable, lower in power, and lower in price. Here, the shorter the wavelength of the semiconductor laser used as the light source, the better. The reason for this is that the shorter the wavelength, the greater the diffraction limit of light, making it easier to narrow down the spot to a smaller spot diameter, making it easier to design lenses.Furthermore, there are many types of photoreceptors for electrophotographic recording. It will come out. Currently, various companies are researching various structures for semiconductor lasers.

Although these have been put into practical use, the ones available as visible semiconductor lasers have a wavelength of about 780 nm.

FIG. 1 is a perspective view showing an example of a semiconductor laser. This semiconductor laser shows a double heterojunction structure semiconductor laser made by proton irradiation. l g
A GaAeAs layer 11 is epitaxially grown on a GmAg substrate 10, and a thin active layer 13 is formed between mWi and a p-type cladding layer 12. In this active layer 13, current-injected carriers (electron-hole pairs) undergo radiative recrystallization, and a laser beam is emitted.

In a semiconductor laser having such a structure, the shape of the beam is elliptical, not circular, as shown in the figure, regardless of whether it is in the near field or in the far field. Normally, the beam radiation angle (spread polygon) of a semiconductor laser is expressed as a full width at half maximum, and the ratio of the direction θ11 parallel to the junction and the direction θ perpendicular to the junction is 1.
:2~1+2.5.

For semiconductor lasers used in laser printers, it is desirable that the beam shape be circular (circular spot). However, as mentioned above, the ones currently available in A/B are those with elliptical spots, and the line widths of forging and horizontal tightening are different. Problems such as dripping occur.

Here, the present invention aims to provide a laser printer that uses a light beam having an elliptical shape, corrects this, and provides a clear image.

The apparatus according to the present invention is characterized in that the intensity distribution of the scanning spot is corrected by controlling the lighting time of the semiconductor laser within the time range corresponding to one dot.

FIG. 2 is a diagram showing the main part configuration of an example of a laser printer according to the present invention. Here, an example is shown in which the light beam from the semiconductor laser 1 is projected onto the surface (photosensitive surface) of the photosensitive drum 30 via the optical deflection means 2. In the figure, 4 is the light source drive of the semiconductor laser 1. A circuit controls the semiconductor laser 1 on and off depending on the image information to be recorded. 5 is a buffer memory in which the information to be recorded is a set of dots, for example one raster or one image. It is stored as soon as the application is distributed. 50 is the buffer memory 5
The clock oscillator 6 designating the 0 start address is a clock oscillator whose output is applied to the color/receiver 50.

7 is a line width correction circuit to which a clock signal from the clock oscillator 6 is applied. This line width correction circuit 7 uses, for example, a known Norms width signal generation circuit,
The pulse width of the signal outputted from this circuit is configured to be settable by a setting circuit 71. 8 is a timing control circuit which receives the clock signal from the clock oscillator 6 and the timing 1 from the light beam scanning position detection means 80;
No. 6 is applied to control the rotational operation of the optical deflection means 2 and the photosensitive drum 50 via the driving motor 20 and the drive motor 30. The laser beam thus generated is deflected by the optical deflection means 2 and horizontally scanned onto the photosensitive drum 3.

The photosensitive drum 5 is rotated by a drive motor 30 in a direction perpendicular to the scanning direction of the laser beam while adjusting the scanning position and timing of the laser beam, and an electrostatic latent image corresponding to input data is formed on the photosensitive drum s. is formed by a collection of dots. Although this electrostatic latent image is not shown, the current salary process,
After the transfer process 1, a recorded image is obtained on recording paper.

FIG. 5 0) shows the shape of a scanning spot on the photosensitive drum S, which corresponds to one dot and dot. In the apparatus according to the present invention, the lighting time (writing time) tα of the semiconductor laser 1 is corrected in accordance with the correction signal from the line width correction circuit 7 with respect to the spora) l16x in the scanning direction (in the direction of the arrow). By doing so, this is controlled so that it becomes e satsu e ``too'' dK as shown in FIG. 3(a). Note that here, t is the length of one dot, and α
is the pulse width of the signal from the line width correction circuit 7.

In this way, the lighting time of the semiconductor laser 1 is controlled within the time range corresponding to one dot, and
By adjusting this lighting time to an optimal value, the light intensity distribution due to the scanning spot on the photosensitive drum 5 becomes rectangular, with overlapping dots and dots, as shown in Fig. 5 (←). This eliminates the occurrence of scratches, etc., and allows a clear image to be obtained.

FIG. 4 is an operational waveform diagram for explaining the operation in the block diagram of FIG. 2. FIG. - Fig. 4 (A) is a waveform diagram of the clock signal from the clock oscillator 6], and Fig. 4 (←) shows an example of the writing signal output from the buffer memory 5. Here, exposure is "1°1. Non-exposure is represented by the signal II Q 11. In FIG. 4e, the line width correction circuit 7
The O correction signal pW is output from Ruru. The pulse width α of the correction signal pw of and 9 is adjusted by the setting means 71. The light source drive circuit 4 receives a write signal from the buffer memory 5,
A correction signal pi is inputted, and the semiconductor laser 1 is driven and its lighting time tα is controlled according to both signals. Fig. 4) shows a signal waveform for driving the semiconductor laser 1 from the light source driving circuit 4, and by adjusting the pulse width α of the correction signal pw, the lighting time tα can be adjusted within the time range T corresponding to one dot. The line width can be changed to the optimum value.

In the above embodiment, it is assumed that the pulse width a of the correction signal PW is manually set to the optimum value, but the line width of the image formed on the photosensitive drum 3 is detected. For example, an image quality sensor may be provided close to the photosensitive drum δ, and the pulse width α of the correction signal pw may be automatically adjusted in accordance with a signal related to the line width from the image quality sensor.

In addition, in FIG. 2, a clock period correction circuit is coupled to the clock 6, and the period T of this clock signal is dynamically controlled according to the deflection angle of the laser beam (corresponding to the scanning position of the scanning spot). The write period of data corresponding to one dot and the lighting time may be changed little by little within one scan. As a result, it is possible to obtain a very clear image on the photosensitive drum 3 with no scanning distortion and constant line width at the scanning center and at the edges.

As described above, according to the present invention, it is possible to realize a laser printer that can produce clear images even though it uses an inexpensive semiconductor laser.

[Brief explanation of drawings]

FIG. 91 is a perspective view showing an example of a semiconductor laser; FIG. 2 is a block diagram showing an example of a device according to the present invention;
Figure 5 0) is an explanatory diagram showing the shape of the scanning spot, #E'
Figure ←) is a diagram showing the light intensity distribution, and Figure 4 is an operation waveform diagram for explaining the operation of Figures 2 and 3. DESCRIPTION OF SYMBOLS 1... Semiconductor laser, 2... Light deflection means, S...
Photosensitive drum, 4...Light source drive circuit, 5...Buffer memory, 6...Black and red generation circuit, 7...Line width correction circuit〇th/+th vJ 1st (a) 41st

Claims (1)

[Claims] (Re) A laser printer that uses a semiconductor laser and horizontally scans a light beam from the semiconductor laser on a photoreceptor to display a recorded full-color image as a set of dots, A laser printer (2) characterized in that the lighting time of the semiconductor laser is controlled within a time range corresponding to one dot, and the intensity distribution of the scanning spot by the light beam is corrected. 2.) A laser printer according to claim 1, wherein the lighting time of the semiconductor laser is dynamically controlled according to the deflection angle of the laser beam.