JPS58179815A - Optical scanner - Google Patents

Abstract

PURPOSE:To eliminate the error of a focusing position, by projecting the optical beam from a laser light source to a light deflecting means through the first lens for spreading the optical beam and the second lens for condensing the optical beam. CONSTITUTION:A condenser lens system 2 consists of two lenses 21 and 22, and the lens 21 functions to spread the beam, and the lens 22 functions to focus the beam onto a photosensitive drum 4. A lens driving means 7 is provided for moving the lens 21 in the direction of the optical axis in relation to the scanning position of a light spot on the photoreceptor, and a signal related to the scanning position of the light spot is inputted from a counter 61 to this means 7. The timing signal from a detecting means 80 of the scanning position of the optical beam is applied to a timing controlling circuit 8 to control rotating operations of a deflecting means 3 and the photosensitive drum 4 through a driving motor 30 and a driving motor 40.

Description

[Detailed Description of the Invention] [Technical field to which the invention pertains] The present invention relates to an optical scanning device that is effective for use in devices that record or display signals, pictures, etc. using optical signals. . More specifically, the present invention deflects a light beam from a light source by a light deflecting means such as a galvanometer or a polygon mirror, and horizontally scans a light spot on the surface of a photoreceptor such as a photoreceptor drum. Part 4 relates to optical scanning devices.

[Description of prior art]

FIG. 1 is a block diagram of main parts of an optical scanning device used in a conventionally known laser printer. This device projects a light beam from a laser light source 1, such as a semiconductor laser, through a focusing lens 2 onto a polygon -5, projects reflected light from here onto a photosensitive drum 4, and creates a laser beam spot. is horizontally scanned (main scan) on the photosensitive drum 4. Here, the laser light source 1 is controlled on and off by the drive circuit 5 according to the image information to be recorded. As the photosensitive drum 4 rotates in a direction perpendicular to the horizontal scanning direction (this is called sub-scanning), an electrostatic potential corresponding to the ms information is formed by a collection of dots on the photosensitive drum 4. Although it is not shown in the diagram, the hidden process is the current process,
A recorded image can be obtained on recording paper through a transfer process and a fixing process.

By the way, in the optical scanning device having such a configuration, the focusing lens 2 focuses the laser beam spot so that the laser beam spot is focused, for example, at the center point Pc of the photosensitive drum (so that the spot diameter is minimized). In this case, the imaging position is broken 11AI! along with the scanning of the laser beam. Move like p,
There is a drawback that the image formation position is shifted near both ends of the photosensitive drum 4, and the degree of resolution is reduced.

In order to eliminate this drawback, an optical system such as an imaging lens may be installed between the polygon holder 3 and the photosensitive drum 4, but such an optical system such as this lens is expensive. Also,
The disadvantage is that the configuration is complicated.

[Object of the present invention]

The present invention aims to eliminate these drawbacks of conventional devices and provide an optical scanning device that can reduce the diameter of a light spot with a simple configuration, eliminate errors in imaging position, and perform optical scanning. .

[Summary of the invention]

The device according to the present invention uses IJ! for expanding a light beam from a laser light source. One feature is that the light beam is made to pass through the first lens and the second lens for forming an image on the photoreceptor. Also, the first
and the second lens in the optical axis direction (the direction in which the focal position changes) in relation to the scanning position of the light spot on the photoreceptor! This is another feature.

[Explanation of Examples]

FIG. 2 is a block diagram showing an example of a device according to the present invention. Here, a case will be exemplified in which a laser beam from a laser light source 1 is irradiated onto the optical deflection means 5 via a lens system 2, is deflected by ξ, and a light spot is horizontally scanned on the surface (photosensitive surface) of the photosensitive drum 40. . In the figure, 5 is a drive circuit for the laser light source 1, which controls the laser light source 1 on and off depending on the image information to be recorded. 6 is a buffer memory, in which the information to be recorded is stored in dots. For example, one raster or one sheet is stored sequentially. 61 is a counter that specifies the read address of the buffer memory 6; 42 is a clock oscillator whose output is applied to the counter 61;

2 is a condensing lens system, here two lenses 21°22
The lens 21 serves to spread the beam, and the lens 22 serves to narrow the beam so that it is focused on the photosensitive drum 4. 7 is a lens moving means for moving the lens 21 in the direction of its optical axis in relation to the scanning position of the light spot on the photoreceptor;
A signal related to the scanning position of the light spot is input from the Reference numeral 8 denotes a timing control circuit to which a timing signal from the light beam scanning position detection means 80 is applied, and is connected to the deflection means 3 via the drive motor sO and the drive motor 40.
The rotational operation of the photosensitive drum 4 is controlled.

FIG. 3 is a sectional view showing an example of the lens system 2 and lens moving means 7 in the apparatus shown in FIG.

The lens moving means 7 here uses electromagnetic force, and includes a ring-shaped coil A/720 movably held by a flexure 75 between a ring-shaped magnet C and a ring-shaped coil A/720.
(force coil) 74 is installed, and the lens 21 is attached to this coil 74.

When a driving current is applied to the coil 74 via the lead wire 75, the coil 74 is in the direct current magnetic field of the magnets 71 and 72, so it generates an electromagnetic force, and the lens 21 responds to the magnitude of the driving current I. can be moved in the optical axis direction (arrow C direction). As a result, the distance between the laser light source 1 and the lens 21 can be dynamically changed. FIG. 4 shows the apparatus shown in FIG. Light deflection means 3. 4 is a plan view showing an example of arrangement of photosensitive drums 4. FIG.

In the lens system 2, each lens 21, 22 and the laser light source 1 are arranged so that the lens 21 is at a distance from the laser light source 1 to a point (
When the lens 21 is located at the center of the magnets 71 and 72) K, the imaging spot position on the photosensitive drum 4 is indicated by the solid line e1.
As shown in the figure, a point P on the photosensitive drum 4 moves in accordance with the deflection angle (deflection angle) K of the light beam.

It is arranged so that the image is formed near P2 (the spot diameter is the minimum). Therefore, in this state, the image formation position is shifted in the center Pc, both ends p, and p4 of the photosensitive drum 4. In the apparatus according to the present invention, the lens moving means 7 is A current I is applied to the coil 74, which changes as shown in FIG.
I try to let it flow.

As a result, the lens 21 receives a driving current in the optical axis direction! It moves by a small distance Δ corresponding to I'm trying to make it look like it's above. Note that the light deflection means S and the photosensitive drum 4
For example, when the distance r from
By moving the photosensitive drum 4 by 5 mm, the imaging spot can be constantly scanned on the photosensitive drum 4.

Further, in the apparatus according to the present invention, the lens system 2 is connected to the first lens 21 . It is composed of a second lens 22, and the lens 21 of I81 serves to widen the light beam, and the lens 22 serves to narrow it down, thereby increasing the spot diameter of the light beam entering the light deflection means sK. 1 by narrowing down the spot diameter on the photosensitive drum 4 to a small size. I'm trying to do it for the sake of it. That is, in general, when a prismatic rotating polygon mirror with the number of faces N is used as the light deflecting means S and a laser beam having a spot diameter is incident on the mirror, the number of resolution points Nr is expressed by the following equation.

However, λ is the wavelength of the laser beam. By increasing the spot diameter of the light beam incident on the rotating polygon mirror using the first lens 21, the number of resolution points Nr can be increased and the resolution can be improved. It's loud.

FIG. 6 is a cross-sectional view showing another example of the structure of the lens system 2. In this example, two lenses 2 are used as the lens 21.
In this case, each lens 21m, 21b is dynamically moved by Δb in a direction perpendicular to the optical axis of the laser beam in relation to the scanning position of the spot. This allows the focal length to be changed. Also,
Lenses 21m and 21b K are used as a means of moving the lenses.
Using the piezoelectric elements 76 and 77 to couple, the piezoelectric elements 76 and 7
Using the compression and expansion of 7, the lenses 21m and 21b are adjusted to Δ
I am trying to move only b.

In the above embodiment, a rotating polygon mirror is used as the light deflection means 3, but instead of this, a light deflection means using a galvanometer or an electro-optical element may be used. . Furthermore, although the light spot is shown as scanning on a photosensitive drum, it may be scanning on photosensitive paper or a display screen. Further, although the lens 21 of '@1 is moved by an amount here, the second lens 22 or the light source 1 may be moved.

[Effects of the present invention]

As explained above, according to the present invention, with a simple configuration,
It is possible to realize an optical scanning device in which the diameter of the optical spot can be narrowed to a small size and optical scanning can always be carried out without shifting the imaging position regardless of the scanning position of the optical spot.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of main parts of a conventionally known optical scanning device, FIG. 2 is a block diagram showing an example of the device according to the present invention, and FIG. 5 is an example of the lens system and lens moving means of the device shown in FIG. FIG. 4 is a plan view showing an example of the arrangement of the main parts of the device, and FIG. The diagram shown in FIG. 6 is a structural sectional view showing another example of the structure of the lens system. 1...v-f light R,'...lens system, 21...th lens, 22...second lens, S...light deflection means,
4... Photosensitive drum, 7... Lens moving means, 71.
72... Magnet, 73... Flexure, 74... Coil. Atsushi 3 Figure 4 Tail Figure 5

Claims (5)

[Claims] (1) An optical scanning device in which a light beam from a laser light source is deflected by a light deflecting means to scan a light spot on the surface of a photoreceptor, characterized in that the light beam from the laser light source is emitted as a light beam. Sui optical scanning device 0 (2) At least one of the first lens and the second lens is moved in relation to the scanning position of the light spot on the photoreceptor, so that a light spot of a uniform size is directed onto the photoreceptor. An optical scanning device according to claim 1, which is adapted to perform scanning. (3) A claim that uses a force fill supported by 7-rexia in a DC magnetic field as a means for moving the lens, and uses the electromagnetic force generated in this force coil to move the lens. The optical scanning device according to item 2. (4) The optical scanning device according to claim 2, which uses a piezoelectric element as a means for moving the lens. (5) The optical scanning device according to claim 2, wherein a laterally shifted variable focus lens is used as the lens, and the lens is moved in a direction perpendicular to the optical axis of the laser beam.