JPH04311914A - Scanning optical system - Google Patents

Abstract

PURPOSE:To obtain a scanning optical system which has a constant scanning pitch in all scanning areas during beam scanning on a scanned plane to allow high precision beam scanning. CONSTITUTION:In a scanning optical system that beam is modulated by external signals from a beam source means 2, deflected by a scanning means with a rotary multiplane mirror 4 via a converging means 3, and then guided onto a scanned plane via an imaging means 5 for beam scanning, part of beam entered into the scanned plane is detected by scanning position detecting means 6a-6c and part of the optical elements of the converging means 3 or the imaging means 5 is driven and controlled by using output signals from the scanning position detecting means 6a-6c to adjust the shift of a beam scanning position on the scanned plane.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a scanning optical system that optically scans a surface to be scanned, such as a photoreceptor drum surface, using a light beam modulated from a laser light source, for example, through an optical deflector having a plurality of deflection surfaces. Regarding the device, in particular, it is possible to satisfactorily compensate for variations in the scanning position of the light beam when optically scanning the scanned surface due to manufacturing errors in each deflection surface of the optical deflector, vibrations of the motor as a driving means, etc., and to achieve high precision. The present invention relates to a scanning optical device suitable for, for example, a laser beam printer (LBP) that enables scanning.

0002

2. Description of the Related Art Conventionally, in a scanning optical device such as a laser beam printer, a light beam from a laser light source is optically modulated in accordance with an image signal.

The optically modulated light beam is then periodically deflected by an optical deflector such as a rotating polygon mirror and focused into a spot on the surface of a photosensitive recording medium by an imaging optical system such as an f-theta lens. , images are recorded by optical scanning.

FIGS. 8A and 8B are main part configuration diagrams of a main scanning section and a sub-scanning section when a conventional scanning optical device is applied to a laser beam printer.

In the figure, when forming a desired image, a laser driver 91 is driven by an electric signal (emission signal) from a control section 90.
For example, a solid-state laser element 9 which is a laser light source connected to 1
2 is made to blink (ON, OFF) by the light emission signal. The light beam from the solid-state laser element 92 is made into a parallel light beam by a collimator lens 93a, focused in the sub-scanning direction by a cylindrical lens 93b, and the light beam is focused on a deflection surface 94a of an optical deflector 94. . After being reflected and deflected by the deflection surface 94a, the lens 95a,
The light is guided onto the surface of the photoreceptor drum 99, which is the surface to be scanned, through an imaging optical system 95 having an f-.theta.

By rotating the optical deflector 94 at a constant speed in the direction of arrow A, the light is scanned at a constant speed on the surface of the photosensitive drum 99.

At this time, before optically scanning the surface of the photoreceptor drum 99, a portion of the light beam reflected by the deflection surface of the optical deflector 94 is used to control the timing of the scanning start position on the surface of the photoreceptor drum 99. is guided to a synchronous detector 97. The control section 90 drives and controls the laser driver 91 based on the signal from the synchronization detector 97. The laser driver 91 blinks (ON, OFF) the solid-state laser element 92 based on the image signal.
) to reproduce the bright and dark parts of the image on the surface of the photoreceptor drum 99. This records image information.

At this time, in the sub-scanning section, the deflection surface 9
4a and the photosensitive drum surface 99 are in a conjugate relationship,
The angle error of the deflection surface 94a, that is, the inclination of the deflection surface 94a in the sub-scanning direction is corrected. As a result, the photosensitive drum surface 99
The same position on the top can be optically scanned.

[0009]

Generally, the deflection surface of an optical deflector in a scanning optical device is made of a flat surface. When the optical deflector is rotated to perform optical scanning, the position of the deflecting surface 94a in the optical axis direction differs between the central scanning area and the peripheral scanning area on the photosensitive drum surface 99, as shown in FIG. For example, as shown in FIG. 9, the deflection surface 94a approaches the cylindrical lens 93b during peripheral scanning, and the deflection surface 94a approaches the cylindrical lens 93b during center scanning.
moves away. As a result, if the light beam is imaged on the deflection surface 94a during peripheral scanning, then when scanning the center, the light beam forms an image on the deflection surface 94a.
The image will be formed at a position away from 4a.

For this reason, as shown in FIG. 10, the apparent focal point of the light beam is displaced from the deflection surface 94a to a different position during center scanning, as shown in FIG. 10(B).

Incidentally, FIG. 10(A) shows the peripheral scanning, in which the light beam is focused on the deflection surface 94a, and at this time the inclination of the deflection surface 94a has been corrected.

As a result, even if the optical system is configured as described above and the tilting of the deflecting surface is corrected, the tilting cannot be completely corrected over the entire scanning area.

[0013] In this way, in conventional scanning optical devices, if there is an angular error in the deflection surface, the inclination is corrected in a certain scanning area, but the pitch of the scanning line becomes uneven in other scanning areas, resulting in a decrease in the quality of the output image. There was a problem with this. Such a reduction in image quality cannot be tolerated in devices that require high-quality images, and has become a major problem.

[0014] The present invention corrects the deterioration in image quality in the scanning area where the tilt correction by the optical system is insufficient by driving some optical elements, and enables good optical scanning in the entire scanning area, resulting in high quality. The purpose of the present invention is to provide a scanning optical device that can obtain images with a wide range of images.

[0015]

[Means for Solving the Problems] The scanning optical device of the present invention deflects a light beam optically modulated by an external signal from a light source means through a condensing means by a scanning means having a rotating polygon mirror, and then In a scanning optical device that guides light onto a surface to be scanned via an imaging means to perform light scanning, a part of the light beam incident on the surface to be scanned is detected by a scanning position detection means, and a part of the light beam incident on the surface to be scanned is detected by a scanning position detection means. It is characterized in that the output signal is used to drive and control some optical elements of the condensing means or the imaging means to adjust the scanning position shift of the light beam on the surface to be scanned. .

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIGS. 1A and 1B are schematic diagrams of main scanning sections and sub-scanning sections of a first embodiment of the present invention.

In the figure, reference numeral 1 denotes a laser driver, which drives and controls the laser light source 2 in accordance with an electric signal (emission signal) from a control section 10. The laser light source 2 is made of, for example, a solid-state laser element, is connected to the laser driver 1, and blinks (ON, OFF) a light beam in response to a light emission signal from the laser driver 1. A collimator lens 3a converts the light beam emitted from the laser light source 2 into a substantially parallel beam. A cylindrical lens 3b focuses a light beam in the sub-scanning direction and forms an image on the deflection surface 4a of the optical deflector 4. The collimator lens 3a and the cylindrical lens 3b constitute a condensing means 3. The optical deflector 4 has a plurality of deflection surfaces, and is made of, for example, a rotating polygon mirror, and is rotated in the direction of arrow A by a driving means (not shown) such as a motor.

5 is an imaging optical system (imaging means) having f-θ characteristics, which includes a spherical lens 5a and a toric lens 5b.
A light beam based on image information reflected and deflected by a light deflector 4 is imaged on the surface of a photoreceptor drum 9 via a parallel plane glass 8, which will be described later.

Reference numeral 7 denotes a synchronization detector, which detects the light beam reflected by each deflection surface in order to control the timing of the scanning start position on the surface of the photoreceptor drum 9 before optically scanning the surface of the photoreceptor drum 9. Some of them have been detected. The signal obtained by the synchronization detector 7 is used to control the timing of the scanning start position for recording an image on the surface of the photosensitive drum 9.

8 is a parallel plane glass, and driving means 11
It can be rotated by. When rotated, the parallel plane glass 8 deflects and emits the light beam from the imaging optical system 5 and guides it onto the surface of the photosensitive drum 9 . Reference numeral 12 denotes an optical path switching mirror, which is rotatable about a fulcrum 12a in front of the photosensitive drum 9.

Reference numeral 6 denotes a scanning position detecting means, which detects the position of the light beam incident on the photosensitive drum 9 via the optical path switching mirror 12. In the figure, three sensors 6a and 6b are used.
, 6c. Reference numeral 13 denotes an arithmetic circuit which determines the incident position of the light beam on the surface of the photosensitive drum 9 based on the signal from the scanning position detection means 6.

In this embodiment, around the photosensitive drum 9, there are a developing device (not shown), a primary and transfer charger, a fixing device,
A cleaner or the like is provided, and the latent image formed on the surface of the photosensitive drum 9 is visualized by a known electrophotographic process and transferred to a transfer material.

In this embodiment, a light beam from a laser light source 2, which is optically modulated by a light emission signal from a laser driver 1, is converted into a parallel beam by a collimator lens 3a. Then, the light is focused in the sub-scanning direction by the cylindrical lens 3b, and is made incident on the deflection surface 4a of the optical deflector 4 in the form of a parallel light beam in the main-scanning direction. By rotating the optical deflector 4, the light beam reflected and deflected by the deflection surface 4a is focused by the imaging optical system 5, and is imaged on the surface of the photoreceptor drum 9 via the parallel plane glass 8 for optical scanning. ing. At this time, before optical scanning, an optical path switching mirror 12 is placed in the optical path in advance to reflect the light beam from the imaging optical system 5 and make it enter the scanning position detection means 6. Then, based on the signal from the scanning position detection means 6, the arithmetic circuit 13 detects an error in the incident position of the light beam on the photoreceptor drum 9, that is, an error in the incident position of the light beam (due to insufficient correction of the surface tilt of the deflection surface, etc.) (Depending on factors such as overall assembly error.) Based on the result at this time, the driving means 11 is driven and controlled, and the driving means 11 rotates the parallel plane glass 8 to correct errors in the light beam incident on the surface of the photosensitive drum 9. .

FIG. 2 is a block diagram of main parts showing the operation of this embodiment.

Based on the signals from the three sensors 6a, 6b, and 6c constituting the scanning position detection means 6, the arithmetic circuit 1
3, the incident position on the surface of the photoreceptor drum 9 accompanying the optical scanning of the light beam is determined.

The driving means 11 rotates the parallel plane glass 8 based on the signal from the arithmetic circuit 13, and adjusts the deflection position (deviation amount Δ) of the light beam emitted from the parallel plane glass 8 as shown in FIGS. 3 and 4. are being adjusted. Further, the driving means 11 stores the calculation result from the calculation circuit 13 in the memory 14, and detects the scanning position of the light beam not every time, but periodically.

When the scanning position of the light beam is not detected, the parallel plane glass 8 is rotated based on the signal from the synchronous detector 7, for example, using the data stored in the memory 14, and the light beam is detected. is adjusting the deflection state of.

In this embodiment, the scanning position detecting means 6
The case is shown in which the scanning position is detected at each point by using three sensors 6a, 6b, and 6c, but three or more sensors may be used, or a continuous line sensor or image sensor may be used. Alternatively, the scanning position in the main scanning direction may be continuously detected.

FIG. 3 is an explanatory diagram showing the optical path of a light beam passing through the parallel plane glass 8. As shown in FIG. As shown in the figure, a light beam 31a incident on the parallel plane glass 8 at an angle θ is emitted with its optical path shifted due to refraction. The amount of deviation Δ at this time is given by the thickness of the parallel plane glass 8 being d and the refractive index of the material being n.

[0030]

[Math 1] becomes.

In this embodiment, as shown in FIG. 4, the position of the emitted light beam is displaced by rotating the parallel plane glass 8 to change the incident angle θ of the light beam 31a.

This adjusts the position of incidence of the light beam onto the surface of the photosensitive drum 9.

FIGS. 5(A) and 5(B) are main part schematic diagrams of a main scanning section and a sub-scanning section of a second embodiment of the present invention.

In this embodiment, the error in the incident position of the light beam on the surface of the photosensitive drum 9 is corrected by moving the cylindrical lens 3b instead of the parallel plane glass in the direction perpendicular to the optical axis (sub-scanning direction) by the driving means 11. This differs from the first embodiment in that the correction is performed by adjusting the angle, and the other configurations are the same.

FIG. 6 is a schematic view of the main parts when the optical path in the sub-scanning section is expanded when the cylindrical lens 3b is displaced in the direction perpendicular to the optical axis (sub-scanning direction) in FIG. 5(A). .

As shown in FIG. 6, when the cylindrical lens 3b is moved by a certain amount in a direction orthogonal to the optical axis, the light beam is displaced by the same amount in the sub-scanning direction on the deflection surface 4a.

Therefore, if the imaging magnification in the sub-scanning section of the imaging optical system 5 is M, the amount of deviation X of the scanning position on the surface of the photosensitive drum 9 can be obtained by moving the cylindrical lens 3b by X/M. Can be corrected.

In this embodiment, the cylindrical lens 3
Since the amount of movement b is generally small, it is sufficient to support high-speed scanning.

FIG. 7 is a schematic diagram of the main parts of a third embodiment of the present invention when the optical path in the sub-scanning section is developed.

In this embodiment, the error in the incident position of the light beam on the surface of the photoreceptor drum 9 is corrected by using the driving means 11 to move the collimator lens 3a instead of the parallel plane glass in the direction perpendicular to the optical axis (sub-scanning direction). The difference from the first embodiment is that the correction is performed by moving, and the other configurations are the same.

As shown in FIG. 7, the collimator lens 3a
When the deflection surface 4a is moved by e in the direction perpendicular to the optical axis, the deflection surface 4a
The amount of deviation Δ of the light beam above is given by f3a, the focal length of collimator lens 3a, and f3b, the focal length of cylindrical lens 3b.

[0042]

[Math. 2] If the imaging magnification of the imaging optical system 5 is M, the amount of deviation X of the scanning position on the surface of the photosensitive drum 9 is

[0043]

[Math. 3] From this, the movement amount e of the collimator lens 3a is

[0044]

[Math 4] becomes.

In this embodiment, the collimator lens 3a is moved in a direction perpendicular to the optical axis by the driving means 11 based on a signal from the arithmetic circuit 13 in accordance with the optical scanning, thereby reducing the deviation of the scanning position of the optical beam. (error) is corrected.

[0046]

According to the present invention, as described above, the scanning position detecting means detects the incident position of the light beam modulated and emitted from the light source means onto the photoreceptor drum surface, and the arithmetic circuit detects the incident position of the light beam modulated and emitted from the light source means. The optical scanning pitch can be made constant by obtaining correction data and driving and adjusting part of the optical system using the driving means to correct errors in the incident position of the light beam, making it easy to create high-quality images. The resulting scanning optical device can be achieved.

[Brief explanation of drawings]

FIG. 1: Schematic diagram of main parts of Embodiment 1 of the present invention

[Fig. 2] Main part block diagram of Embodiment 1 of the present invention

[Figure 3] Explanatory diagram of a portion of Figure 1

[Fig. 4] Explanatory diagram of a part of Fig. 1

[Fig. 5] Schematic diagram of main parts of Embodiment 2 of the present invention

[Fig. 6] Explanatory diagram when the optical path in the sub-scanning cross section of Fig. 5 is expanded.

FIG. 7 is a schematic diagram of main parts in the sub-scanning cross section of Embodiment 3 of the present invention.

[Fig. 8] Schematic diagram of main parts of a conventional scanning optical device

[Figure 9] Figure 8
An explanatory diagram of a part of

[Fig. 10] Explanatory diagram of a part of Fig. 8

[Explanation of symbols]

1 Laser driver 2 Laser light source 3. Light collecting means 3a Collimator lens 3b Cylindrical lens 4. Optical deflector 5 Imaging optical system 5a Spherical lens 5b Toric lens 6 Scanning position detection means 7 Synchronization detector 8 Parallel plane glass 9 Photoreceptor drum 10 Control section 11 Driving means 12 Optical path switching mirror 13 Arithmetic circuit

Claims (1)

[Claims] 1. A light beam modulated by an external signal from a light source means is deflected by a scanning means having a rotating polygon mirror through a condensing means, and then guided onto a surface to be scanned through an imaging means. In a scanning optical device that performs optical scanning, a part of the light beam incident on the surface to be scanned is detected by a scanning position detection means, and an output signal from the scanning position detection means is used to detect a part of the light beam incident on the surface to be scanned. What is claimed is: 1. A scanning optical device, characterized in that a deviation in the scanning position of the light beam on the surface to be scanned is adjusted by driving and controlling some optical elements of the image means.