JPS6068317A - Optical scanner of laser beam printer - Google Patents

Abstract

PURPOSE:To control the diameter of a spot image on an image carrier and obtain a print of good quality corresponding to the kind of an original image by providing a control means which varies the diameter of a parallel laser beam projected upon a deflecting means. CONSTITUTION:A divergent laser beam from a semiconductor laser 1 is passed through a collimator 2 to obtain a parallel laser beam L, which is projected. The beam is passed through a rotary polygon mirror 3 and lens 4 to form a fine spot image on the image carrier 5. A controller 6 is put in operation to drive a stepping motor 7 and a zoom ring 2a is rotated associatively to vary and control the focal length of the collimator 2. Thus, the spot image has a diameter suitable for the kind of the original image and an image of good quality is printed.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an optical scanning device for a laser beam printer.

Generally, the optimum value of the diameter of a spot image formed on an image carrier of a laser beam printer differs depending on the type of original image. For example, in images such as document images that are composed of large characters and symbols in two colors, white or black, there is a lot of so-called solid black, and the larger the diameter of the spot image formed on the image carrier, the more solid black. A good image with high density can be obtained. On the other hand, in printers such as laser beam printers that record original images with herb tones like photographs using dots, one pixel is constructed from a matrix such as 4X4 or 8X8, and several dots are Dither processing is required to express gradation. In the case of this dither processing, the smaller the diameter of the spot image formed by the optical system, the greater the effect of the dither processing, and a higher quality image can be obtained.

However, in the conventional optical scanning device of a laser beam printer, as shown in FIG. 1, the focal length of the collimator 2' for converting the diverging laser beam emitted from the semiconductor laser 1 into a parallel laser beam L is fixed. Tame 2nd
As shown in the figure, the diameter of the beam emitted from the collimator 2/ was fixed. Therefore, since the diameter of the spot image formed on the image carrier is also fixed, there is a drawback that it is impossible to obtain a high-quality image with a suitable spot diameter corresponding to the type of original image.

The present invention has been proposed in order to eliminate the above-mentioned drawbacks, and is a laser that can form high-quality print images by adjusting and controlling the spot diameter formed on an image carrier according to the type of original image. An object of the present invention is to provide an optical scanning device for a beam printer.

As described above, since the diameter of a suitable spot image differs depending on the type of document image, it is sufficient to adjust and control the diameter of the spot image in accordance with the document image. The diameter of this spot image is d1 The focal length of the optical system that forms the image on the image carrier is fl The diameter of the laser beam incident on this imaging optical system is D The wavelength of the laser beam is 2 A relational expression is established: do. As is clear from equation (1), controlling the laser beam diameter will control the spot image diameter d. The present invention is based on this knowledge and includes means for controlling the diameter d of the spot image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on embodiments with reference to the drawings. FIGS. 3(a) and 3(b) are schematic configuration diagrams of an embodiment of the present invention. The semiconductor laser 1 is a light source that emits a diverging laser beam, and is modulated and controlled by a video signal input from a video signal control circuit (not shown). The collimator 2 converts the diverging laser beam from the semiconductor laser I into a parallel laser beam L, and is capable of varying its focal length. The collimator 2 is equipped with a zoom ring 2a for varying its focal length. The F number of the collimator 2 is determined to be the optimum value based on the divergence angle of the semiconductor laser 1, taking energy efficiency into consideration. The collimator 2 changes the focal length by moving a part of the optical system (not shown), and by moving this optical system, the focal length can be changed without changing the F number and the parallelism of the parallel laser beam L. let By rotating a zoom ring 2a disposed around the outer periphery of the collimator 2, the optical system moves and the focal length changes. If the focal length of the collimator is f, and the diameter of the emitted laser beam L is D, then F = flD (2). As is clear from equation (2), by changing the focal length f, the diameter of the emitted laser beam also changes. Fig. 4(a) shows a state in which the zoom ring 2a is rotated and adjusted so that the focal length f of the collimator 2 is the longest, and the output beam diameter becomes the maximum Dmax, and conversely, Fig. 4(b)
) indicates a state in which the diameter of the emitted beam is the minimum Dmin. Since the focal length f of the collimator 2 can be changed continuously, the diameter of the output beam can also be changed continuously from the maximum diameter Dmax to the minimum diameter Dmin.

As D in the above equation (1) changes, the diameter d of the spot image on the image carrier 5 also changes continuously as shown in FIGS. 5(a) to 5h).

This zoom ring 2a meshes with a gear 7a fixed to the rotating shaft of the stepping motor. This stepping motor 7 is connected to a control device 6.

The method of this control device 6 is not particularly limited, such as a button control method. By operating this control device 6, the rotation of the stepping motor 7 is controlled, and the zoom ring 2 is further controlled.
By interlockingly controlling the rotation of a, the focal length of the collimator 2 is variably controlled. The laser beam L converted into a parallel beam by the collimator 2 is irradiated onto the rotating polygon mirror 3. The rotating polygon mirror 8 is for deflecting the laser beam L. Laser beam L reflected by this rotating polygon mirror 8
is imaged by the imaging optical system 4 on the image carrier 5 as a spot image. The image carrier 5 is exposed to the laser beam L
This is a photoreceptor that converts the light amount distribution into a potential distribution.

Next, the operation will be explained. First, the known operation will be described. A diverging laser beam is emitted from the semiconductor laser 1 under modulation control by a video signal control circuit (not shown). This diverging laser beam is converted into a parallel laser beam L by a collimator 2 and is emitted. This parallel laser beam L
is incident on the rotating polygon mirror 3, reflected and deflected. Further, the parallel laser beam L forms a minute spot image on the image carrier 5 via the imaging lens 4. The image carrier 5 is exposed to light by this spot image and recorded and printed on paper (not shown).

Here, the focal length f of the collimator 2 is controlled to change by operating the control device 6 to rotate the stepping motor 7 and rotate the zoom ring 2a in conjunction.

By controlling the change in the focal length f of the collimator 2, a spot image having a diameter d suitable for the type of original image can be obtained, thereby making it possible to print a high-quality image. Figure 3(a)
, Fig. 4(a) and Fig. 5(b) show that the diameter d of the spot image is the minimum, and Fig. 3(b), Fig. 4(b), and Fig. 5(c) show that the diameter of the spot image is the minimum. The case where d is maximum is shown.

As explained above, the present invention provides a control means for changing the diameter of the parallel laser beam irradiated to the deflection means in the optical scanning device of the laser beam printer, thereby controlling the diameter of the spot image on the image carrier, thereby controlling the diameter of the spot image on the image carrier. The effect is that high-quality printing can be performed depending on the type of paper.

[Brief explanation of the drawing]

Fig. 1 is a configuration diagram of an optical scanning device of a conventional laser beam printer, Fig. 2 is a state diagram showing a case where the laser beam radius is constant, and Figs. 8(a) and (b) are an embodiment of the present invention. 4 (a) (t)) are state diagrams of the laser beam emitted from the collimator, and Fig. 5 (a) (b) (
c) is a state diagram of a spot image formed on the image carrier of the embodiment shown in FIGS. 8(a) and 8(b). ■... Semiconductor laser, 2... Collimator, 2a.
... Collimator ring, 8... Rotating polygon mirror, 4...
Imaging lens, 5... image carrier, 6... control device,
7...Stepping motor, L...Laser beam. Patent applicant: Canon Corporation (a) (b) Figure 4 (a) Figure 5

Claims (1)

[Scope of Claims] A light source that emits a diverging laser beam modulated by a video signal, a light flux converting means that converts the diverging laser beam emitted from the light source into a parallel laser beam, and a light flux converting means that converts the divergent laser beam emitted from the light source into a parallel laser beam. A laser comprising a deflecting means for deflecting a laser beam, an imaging optical system for forming an image of the laser beam from the deflecting means, and an image carrier on which the laser beam is imaged by the imaging optical system. An optical scanning device for a laser beam printer, characterized in that the optical scanning device for a laser beam printer is provided with beam diameter control means for controlling the diameter of the parallel laser beam incident on the deflection means.