JPS6115120A - Laser printer - Google Patents

Abstract

PURPOSE:To reduce a non-linear error, and to adjust a spot interval with high accuracy by synthesizing optically plural optical beams whose wavelength is different from each other by using a dichroic mirror, and adjusting the beam spot interval by changing an angle of the mirror. CONSTITUTION:Optical beams B1, B2 whose wavelength is different from each other from laser light sources 11, 12 are made incident on a dichroic mirror 9, and synthesized optically to one beam by making the optical axis approach optionally by the mirror 9. Subsequently, this synthesized light is reflected by a polygon mirror 6 and projected to a photosensitive drum 8, but in that case, a beam spot interval is adjusted by driving an actuator 11 and changing an angle of the mirror 9. Accordingly, since the dichroic mirror 9 is used, the optical axis can be made to approach optionally, and a non-linear error can be reduced. Also, since the interval can be adjusted by only changing the angle of the mirror 9, the spot interval can be adjusted with a high accuracy.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention horizontally scans a light beam spot emitted from a laser light source on a photoreceptor to form an image to be recorded in dots (
This relates to a laser printer that displays and records information using a set of pixels (pixels).

[Conventional technology]

Conventionally, such laser printers generally scan the photoconductor with a single light beam, but in order to increase the recording speed, multiple laser printers scan multiple light beams simultaneously. Beam-type laser printers have also been put into practical use.

FIG. 3 is a block diagram showing an example of a conventional multi-beam laser printer. The laser printer shown in the figure is configured to scan four light beams at once. That is, a light beam emitted from a laser light source 1 such as a He-Ne laser is transmitted through mirrors 2I to 2. and beam splitter 3. ~3. The beam is divided into four beams with equal brightness by the focusing lens 4. ~44 via modulator 5
．． ~54. Weird 11 5. ~5. is for controlling the on/off of the light beam according to the image information to be recorded.The light beam that has passed through the modulators 5 to 54 is reflected by the polygon mirror 6, and is directed to the photosensitive drum 8 via the optical path adjustment section 7. The laser beam is projected and horizontally scans (main scan) the photosensitive drum 8 as a laser beam spot. The photosensitive drum 8 rotates in a direction perpendicular to the horizontal scanning direction of the laser beam spot (this is called sub-scanning), and the photosensitive drum 8 rotates in a direction perpendicular to the horizontal scanning direction of the laser beam spot. A latent image is formed by a collection of dots. Although not shown, this electrostatic latent image is obtained as a recorded image on recording paper through a development process and a transfer process.

Here, the interval between the laser beam spots obtained on the photosensitive drum 8 is determined according to the resolution of the image, and the distance between the laser beam spots obtained on the photosensitive drum 8 is determined according to the resolution of the image. .about.54 is positioned such that the laser beam spots are aligned at predetermined intervals and perpendicularly to the main scanning direction.

(Problems to be Solved by the Invention) However, in order to accurately project a plurality of light beams having different optical axes as shown in the figure onto the photosensitive drum 8, the modulator 5. ~5. High precision is required for positioning. Further, even if it is attempted to perform these positional adjustments by mechanical processing, very high processing accuracy is required as in the above case.

Furthermore, if there is a difference in the angle of incidence of each light beam on the polygon mirror 6, the scanning line of the laser beam spot projected onto the photosensitive drum 8 will not be uniformly straight;
This results in non-linear errors.

The illustrated device has a long optical path length to reduce the difference in the angle of incidence between light beams and reduce non-linear errors. In this case, the transformer 5. ~5. There is a limit to miniaturization, etc., and it becomes impossible to bring each light beam close to each other and reduce non-linear errors.

The present invention eliminates the drawbacks of the conventional device as described above, and even when the optical path length is shortened, the nonlinear error of the scanning line does not become large, and multiple laser beam spots can be arranged at regular intervals. The object of this invention is to realize a laser printer capable of scanning with a simple configuration.

(Means for Solving the Problems) The laser printer of the present invention combines a plurality of light beams of different wavelengths emitted from independent laser light sources using a light combining element such as a dichroic mirror,
The optical axis of each light beam is made to be close to the distance between the laser beam spots projected onto the photosensitive drum, and then the light beams are made incident on the polygon mirror.

Further, in the laser printer of the present invention, the interval between the laser beam spots can be arbitrarily adjusted by changing the angle of the dichroic mirror.

(Function) In this way, when multiple light beams are combined using a light combining element such as a dichroic mirror, the optical axes of the respective light beams are brought close to the same distance between the laser beam spots on the photosensitive drum. It is possible to reduce the non-linear error in the scanning line.
Since the interval between laser beam spots can be adjusted simply by changing the angle of the dichroic mirror, high image accuracy can be maintained with a simple mechanism.

〔Example〕

FIG. 1 is a configuration diagram showing an embodiment of a laser printer of the present invention. In the figure, the same parts as in FIG. 3 of liJ are designated by the same reference numerals. 1. , 1. 9 is a dichroic mirror, and a light beam B1 having a wavelength λ1 emitted from the laser light source 1 is passed through a focusing lens 4. After being focused to a desired beam diameter, the beam enters the dichroic mirror 9. On the other hand, a light beam B2 having a wavelength λ2 emitted from the laser light source 18 is transmitted through a focusing lens 4. After being focused to a desired beam diameter, the beam enters the dichroic mirror 9. Here, the dichroic mirror 9 is made by alternately depositing a non-absorbing material with a high refractive index and a material with a low refractive index on a glass substrate, and by selecting appropriate film thickness and number of layers, light interference can be prevented. second in action
It is possible to provide transmission characteristics as shown in the figure. Therefore, if the wavelengths λ1 and λ2 of the two light beams Bl and B2 are selected for the transmission region and non-transmission region as shown in the figure, the light beam B1 will pass through the dichroic mirror 9.
However, the light beam B2 passes through the dichroic mirror 9.
Dichroic mirror 9
two light beams B1. B2 can be synthesized, and their leading axes can be arbitrarily approached. Furthermore, when the dichroic mirror 9 is used to combine the light beams Bl and B2 in this way, the light beam Bl.

These can be combined without losing the power of B2, and a highly efficient device can be realized.

The light beams 81 and B2 combined in this way are reflected by the polygon mirror 6, and then passed through the imaging lens or f
The image is projected onto the photosensitive drum 8 via the θ lens 10. At this time, the optical axes of the two light beams Bl and B2 combined by the dichroic mirror 9 are close to each other to the extent of the desired laser beam spot spacing, and the laser beam spots are aligned perpendicularly to the main scanning direction. . Further, the interval between two laser beam spots obtained on the photosensitive drum 8 can be controlled by the angle of the dichroic mirror 9.

11 is an actuator, such as a galvanometer, for adjusting the angle of the dichroic mirror 9;
A spot position detector 12 is arranged in a part of the scanning range of the laser beam spot and detects the interval between the laser beam spots, and a reference numeral 13 drives the actuator 11 according to the output of the spot position detector 12 to detect the distance between the laser beam spots. A servo circuit that maintains the spacing at a desired value. The spot position detector 12 is composed of, for example, a COD line sensor or a photodiode array, and detects the interval between two laser beam spots at all times or at any time, such as during startup.

Therefore, if the support state of the dichroic mirror 9 changes due to changes in ambient temperature or changes over time, and the reflection angle changes slightly, the interval between the laser beam spots will change, directly affecting the image quality. However, by detecting the interval between the laser beam spots with the spot position detector 12 and adjusting the angle of the dichroic mirror 9 via the servo circuit 13 and the actuator 11,
The interval between laser beam spots can always be maintained constant.

In addition, in the above description, the case where two light beams are combined by a dichroic mirror was illustrated, but the number of light beams to be combined is not limited to two. Furthermore, the arrangement of the laser beam spots projected onto the photosensitive drum 2 is not limited to arranging them perpendicularly to the main scanning direction, but any arrangement can be selected as long as the positional relationship is constant. In this case, the state of the arrangement of the laser beam spots can be monitored by a spot position detector, and the laser light source can be controlled based on this. Furthermore, although a dichroic mirror was shown as an example of a light combining element that combines light beams, this is not limited to dichroic mirrors; it reflects or transmits an incident light beam depending on its wavelength, and combines multiple light beams into a light beam. Any light combining element may be used as long as it combines light beams in one direction with adjacent axes.

〔Effect of the invention〕

As explained above, in the laser printer of the present invention, a plurality of light beams of different wavelengths emitted from independent laser light sources are combined using a light combining element such as a dichroic mirror, and the optical axis of each light beam is The laser beam spot projected on the photosensitive drum is made to be close to the distance between the laser beam spots and then incident on the polygon mirror, so it is possible to reduce non-linear errors in the scanning line and also to adjust the angle of the dichroic mirror. The spacing between the laser beam spots can be adjusted by simply changing the distance between the laser beam spots, and even if the optical path length is shortened, the non-linear error of the scanning line will not increase. A laser printer capable of scanning can be realized with a simple configuration.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the laser printer of the present invention, Fig. 2 is a characteristic diagram showing the transmission characteristics of a dichroic mirror used in the laser printer of the invention, and Fig. 3 is a conventional multi-beam type laser printer. 1 is a configuration diagram showing an example of a laser printer of FIG. 1.1. ．． 1. ...Laser light source, 2. ~2. ...Mirror, 3, ~3. ...beam splitter, 4. ~44
...Focusing lens 5...5...Modulator, 6...
Polygon mirror, 7... Optical path adjustment unit, 8... Photosensitive drum, 9... Dichroic mirror, 10... Imaging lens, 11... Actuator, 12... Spot position detector, 13... ...Servo circuit.

Claims (2)

[Claims] (1) A laser printer that simultaneously scans a photoconductor with multiple light beams includes multiple laser light sources that emit multiple light beams with different wavelengths, and an incoming light beam that is reflected or reflected depending on the wavelength. It includes a light combining element that transmits and combines a plurality of light beams into a unidirectional light beam with close optical axes, and a polygon mirror that reflects the light beam combined by the light combining element and projects it onto a photoreceptor,
A laser printer characterized in that the interval between laser beam spots obtained on the photoreceptor is adjusted by changing the angle of the photosynthesis element. (2) In a laser printer that simultaneously scans a photoreceptor with multiple light beams, there are multiple laser light sources that emit multiple light beams with different wavelengths, and the incoming light beam is reflected or reflected depending on the wavelength. a light combining element that transmits and combines a plurality of light beams into a unidirectional light beam with close optical axes; a polygon mirror that reflects the light beam combined by the light combining element and projects it onto a photoreceptor; an actuator that adjusts the angle; a spot position detector that is arranged in a part of the scanning range of the light beam that scans the photoreceptor and detects the interval between laser beam spots obtained on the photoreceptor; and this spot position detection. a servo circuit that adjusts the angle of the photosynthesis element via the actuator so as to maintain a constant interval between laser beam spots in response to the output of the laser printer.