JPS63142961A - Laser beam printer - Google Patents

Abstract

PURPOSE:To reproduce an image with resulting high resolution and high accuracy even when an error exists in the focal distance of an image forming lens, by correcting the error in the focal distance of the image forming lens by adjusting the rotating speed of a rotary polygon mirror and a photosensitive drum. CONSTITUTION:The frequency demultiplication factor of a variable frequency demultiplier is adjusted corresponding to the error in the focal distance (f) of an Ftheta lens. In other words, the angular velocity omegas=fs/ns of the polygon mirror and the angular velocity m=fs/KDnd are adjusted by the frequency demultiplication factor. Therefore, even when the error exists in the focal distance (f) of the Ftheta lens 5, it is possible to image form the image with resulting the high resolution and high accuracy on the photosensitive drum by adjusting the angular velocity of the polygon mirror 3 and the photosensitive drum 6 by adjusting the frequency demultiplication factor of a variable frequency oscillator 18.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a laser beam printer, and in particular, a laser beam printer that deflects a laser beam with a rotating polygon mirror and scans a spot image on a photosensitive drum through an imaging lens. The present invention relates to a laser beam printer suitable for exposure.

[Conventional technology]

Laser beam printers generally use a method of reproducing images by scanning a laser spot on a photosensitive drum, and this method allows high-speed, high-resolution images to be reproduced.

As a method of scanning a laser spot on a photosensitive drum, there are many known methods that use a combination of a single-rotation pot mirror and an Fθ lens (imaging lens). For example, the one described in Japanese Utility Model Publication No. 52-28666 is known. However, the above publication does not give consideration to manufacturing errors of the Fθ lens.

[Problem that the invention seeks to solve]

In order to obtain a clear image by scanning a laser spot, it is necessary to scan a spot with an appropriate imaging diameter at an appropriate scanning pitch. That is, with respect to pitch irregularities, it is possible to obtain pitch accuracy to a level that does not pose any practical problem by correcting as described above.

On the other hand, the appropriate spot is basically determined by the focal length of the Fθ lens and the imaging spot diameter determined by the diameter of the incident beam, but in reality, the focal length F of the Fθ lens depends on the manufacturing of the lens and barrel. There is an error of about ±1%. Therefore, a normal lens has a focusing function using means such as a screw in the lens barrel as a holder, and this adjusts the distance between the lens and the drum that is the imaging surface.
Optimal imaging can be obtained.

However, when an image is formed using the conventional method, there is a problem in that the image size, that is, Q=F·θ, also changes as the focal length moves. Conversely, if emphasis is placed on the dimensions of the reproduced image, a problem arises in that the resolution changes.

The present invention has been made in view of the above-mentioned conventional problems, and its purpose is to correct the error in the focal length of an imaging lens,
An object of the present invention is to provide a laser beam printer that can obtain high-resolution images.

[Means for solving problems]

In order to achieve the above object, the present invention includes an image signal generator that generates a 1-pixel signal, a laser beam generator that converts the 9-pixel signal into a laser beam, a coupling lens that converts the laser beam into a laser beam, A rotating polygon mirror that deflects the laser beam from the coupling lens at a constant angular velocity, a photosensitive drum that rotates about a rotation axis parallel to the scanning direction of the laser beam deflected by the rotating polygon mirror, and the rotating polygon mirror. an imaging lens that forms a spot image of the deflected laser beam on the photosensitive drum; and a first lens that adjusts the rotational speed of the photosensitive drum in conjunction with changes in the frequency of a reference clock output from a single variable frequency oscillator. The laser beam printer includes a rotation speed adjuster for adjusting the rotation speed of the rotating polygon mirror and a second rotation speed adjuster for adjusting the rotation speed of the rotating polygon mirror.

[Effect]

If there is an error in the focal length of the imaging lens.

The rotational speed of the photosensitive drum and the rotational speed of the rotating polygon mirror are adjusted according to this error to correct the error in the focal length of the imaging lens. That is, since the size of the image changes depending on the scanning width and scanning speed, the size of the image formed on the photosensitive drum can be modified by adjusting the rotational speeds of the single-rotation polygon mirror and the photosensitive drum, respectively. .

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 shows the configuration of a preferred embodiment of the present invention. In FIG. 1, the one-image signal generator 14 outputs a pixel signal in synchronization with a clock signal from a video clock oscillator 15, and this pixel signal is supplied to the semiconductor laser 1. The semiconductor laser] functions as a laser light generator, converts one pixel signal into laser light, and irradiates the imaging lens 2 with the converted laser light. The imaging lens 2 converts the laser light into a laser beam, and irradiates the converted laser beam onto a polygon mirror 3 serving as a rotating polygon mirror. The polygon mirror 3 is rotated by the scanner mode 4 and deflects the laser beam from the imaging lens at a constant angular velocity ωS, and the deflected laser beam is passed through the Fθ lens 5 as the imaging lens.
The light is irradiated onto the photosensitive drum 6 through the .

That is, the laser beam scans the photosensitive drum 6 by rotating the polygon mirror 3, and forms a minute spot image on the surface of the photosensitive drum 6.

This spot diameter is determined by the focal length f of the Fθ lens 5 and the beam diameter di of the laser beam incident on the Fθ lens 5. This relationship is shown in FIG. FIG. 2 shows variations in the diameter of the imaged spot on the surface of the photosensitive drum 6 when the focal length of the Fθ lens 5 is shifted by Δf from the reference focal length fo. Do indicates the minimum spot diameter at fo.

D indicates the spot diameter when Δf (%) fo is shifted.

The photosensitive drum 6 is supported by a drum shaft 7, and the driving force of the drum drive mode 11 is transmitted by a pinion 9. The signal is transmitted to the drum shaft 7 via the drum gear 8. The photosensitive drum 6 is rotated at a rotational speed ωD by the driving force of the drum drive mode 11.

Further, the laser beam from the Fθ lens 5 is irradiated onto a small mirror 12, and the laser beam scanned onto the small mirror 12 is transmitted to an image signal generator 14 via a beam detector 13.
It is supplied as a trigger signal. That is, the pixel signal output from the one-image signal generator 14 uses the signal from the beam detector as a trigger, so that the image writing position is kept constant without being affected by the division accuracy of the polygon mirror 3.

Scanner mode 4. A reference clock pulse from a variable frequency oscillator 16 is supplied to each drum drive mode 11 via a scanner motor drive circuit 17 and a drive circuit 18 . This variable frequency oscillator 16 has a crystal oscillator and a variable frequency divider, and outputs a reference clock obtained by dividing the reference frequency. The frequency division ratio of this variable frequency divider is adjusted according to the error in the focal length f of the Fθ lens. That is, the angular velocity ωs=fs/ns of the polygon mirror and the angular velocity ωo=fs/KDnd of the photosensitive drum 6 are adjusted by the frequency division ratio. Therefore, even if there is an error in the focal length f of the FO lens 5, the frequency division ratio of the variable frequency generator 16 can be adjusted to adjust the angular velocity of the polygon mirror 3 and the photosensitive drum 6, thereby creating a high-frequency image on the photosensitive drum 6. It is possible to form high-resolution and high-precision images.

〔Effect of the invention〕

As explained above, according to the present invention, since the rotational speed of the rotating polygon mirror and the photosensitive drum is adjusted to correct the error in the focal length of the imaging lens, there is an error in the focal length of the imaging lens. It is possible to reproduce high-resolution and high-precision images even when

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a characteristic diagram of an imaging lens. 1... Semiconductor radar, 2... Imaging lens, 3...
Polygon mirror, 5... Fθ lens, 6... Photosensitive drum, 14... Image signal generator, 16... Variable frequency oscillator. Also 1 Figure also 20

Claims (1)

[Claims] 1. An image signal generator that emits a pixel signal, a laser beam generator that converts the pixel signal into a laser beam, a coupling lens that converts the laser beam into a laser beam, and a laser beam from the coupling lens at a constant angular velocity. A rotating polygon mirror that deflects the
A photosensitive drum that rotates around a rotation axis parallel to the scanning direction of the laser beam deflected by the rotating polygon mirror, and an image forming system for forming a spot image of the laser beam deflected by the rotating polygon mirror on the photosensitive drum. a lens, a first rotational speed regulator that adjusts the rotational speed of the photosensitive drum in conjunction with frequency changes of a reference clock output from a single variable frequency oscillator, and a second rotational speed regulator that adjusts the rotational speed of the rotating polygon mirror. A laser beam printer comprising: a rotation speed regulator; and a rotation speed regulator.