JP2727572B2 - Optical scanning device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates to an optical scanning device, and more particularly, to an optical scanning device that optically scans a scanning surface, which is a recording medium surface, with a laser beam through an optical deflector such as a rotary polygon mirror. For example, a laser beam printer (LB) having an electrophotographic process for recording and reading
The present invention relates to an optical scanning device suitable for devices such as P).

2. Description of the Related Art Conventionally, in an optical scanning device such as a laser beam printer (LBP), an image is read or read by optically scanning a recording medium surface using a laser beam.

Generally, in many LBPs and the like, a laser beam from a laser oscillator is converted into a parallel beam by a collimator lens and is incident on a reflection surface of an optical deflector which is a rotating polygon mirror. The laser beam reflected by the reflection surface of the optical deflector is condensed by a scanning lens or the like having F-θ characteristics, reflected by a mirror, and then guided on a surface to be scanned, which is a drum-state light body. .

The optical deflector is rotated by a motor or the like to optically scan the surface to be scanned.

In this apparatus, the light intensity at the scanning end is lower than that at the center due to the angular characteristics of the transmittance of the scanning lens, and for example, an angle dependency of the light intensity called shading as shown in FIG. 6 occurs.

Conventionally, such shading correction stores the shading correction data in a memory in the optical scanning device, synchronizes with a signal detected by a scanning position detection unit in the optical scanning device, and based on the shading correction data, For example, a uniform light intensity distribution has been obtained on the surface to be scanned by controlling the injection current of the laser light source.

However, this method requires many electric circuits such as a memory and an arithmetic circuit, and the whole apparatus tends to be complicated.

(Problems to be Solved by the Invention) The present invention uses a laser beam as a scanning beam, and is one of optical elements arranged in an optical path between an optical deflector and a surface to be scanned.
An optical scanning device with a simple configuration that can perform optical scanning with a uniform amount of light over the entire surface to be scanned by appropriately setting the polarization characteristics of the mirror and the transmission member according to the polarization state of the incident laser beam. The purpose is to provide.

(Means for Solving the Problems) A linearly polarized laser beam is guided to an optical deflector by a light guide, and the laser beam deflected by the optical deflector is scanned via a scanning lens and an optical member. When light is guided upward and optically scanned, a laser beam corresponding to the optical axis of the scanning lens is incident on the optical member in a state where the deflection direction is polarized in the P polarization direction. When the reflection or transmission characteristics X _P and X _{S of the} P-polarized light and the S-polarized light are set such that X _P <X _S, and when the light is incident on the optical member while being polarized in the S-polarized direction, X _P > such that X _S is that which constitutes the reflection or transmission characteristics of the optical Faculty member.

(Embodiment) FIG. 1 is a schematic view of a main part of an embodiment when the present invention is applied to an LBP.

In FIG. 1, reference numeral 1 denotes a laser oscillator such as a semiconductor laser, and 2 denotes a collimator lens. The laser beam from the laser oscillator 1 is a parallel beam. Reference numeral 3 denotes a cylindrical lens having a refractive power in a direction (sub-scanning direction 7b) perpendicular to a scanning direction on a surface to be described later.

Reference numeral 4 denotes an optical deflector comprising a rotating polygon mirror, which rotates at a constant speed in the direction of arrow 4a. Reference numeral 5 denotes a scanning lens having f-θ characteristics, and reference numeral 6 denotes a mirror. The polarization reflection characteristics of P-polarized light and S-polarized light are set according to the polarization state of the incident laser beam as described later.

 Reference numeral 7 denotes a surface to be scanned such as the drum-shaped photoconductor 8.

In this embodiment, as the light deflector 4 rotates, the scanning surface 7
The optical scanning is performed in the direction of arrow 7a between the scanning directions 1 to -1.

In this embodiment, the laser beam is incident on the mirror 6 so as to be in the P-polarized state only when the polarization direction of the laser beam is on the axis of the scanning lens 5. In many cases, the polarization direction is determined by restrictions such as the spot shape of the laser beam on the surface 7 to be scanned.

On the other hand, when the laser deflector 4 sequentially scans the scanned surface 7 from the axis of the scanning lens 5 to the off-axis by the laser deflector 4, the polarization direction of the laser beam deviates from the P-polarized light.
This increases as the scanning angle increases, and the ratio of the S-polarized light component increases.

FIG. 2 is a configuration diagram showing a state in which the laser beam is incident on the mirror 6 at this time.

In the figure, a plane including the x-axis and the y-axis is a plane including the main scanning direction. It is assumed that the scanning light beam travels from the point A to the origin O at an angle α with the x-axis (the same direction as the on-axis light beam). At this time, the polarization direction of the laser beam is a direction parallel to the z-axis indicated by the arrow b. The plane including the mirror 6 is arranged at an angle φ with respect to the x-axis as shown by oblique lines in FIG. The plane including the P-polarized light component is a plane including the normal line of the mirror 6 and points A and O. The equation of the plane HA is expressed as xy / tan α + tan φz = 0 using the symbols shown in FIG. If the normal vector of the plane HA is A, then A = (1, −1 / tan α, tan φ) (2).

On the other hand, a plane HB including the traveling direction (AO) of the laser beam and the vibration direction indicated by the arrow b is xy / tan α = 0 (3). Similarly, if the normal vector is B, B = (1, −1 / tanα, 0). To find the ratio of S-polarized component, use the plane HA and plane
It is necessary to find the SIN component of the angle θ formed by HB. For this reason, when calculating the inner product of the vectors A and B, Becomes In general, the angle φ is often set to 45 degrees. Becomes

FIG. 3 shows the ratio of S-polarized light when the scanning angle α is changed.

As can be seen from the figure, as the scanning angle α increases, the ratio of the S-polarized light component increases. Since the reflectivity R of the mirror is the synthesis of the reflectivity R _S of the reflectance R _P and S-polarized component of the P-polarized component, the value variable θ described above as a function Is represented by From the equation (4), the reflectance R is R = _RP = _RS when R _P = _RS , but when R _P ≠ _RS , the reflectance R is a value combined with the equation (4).

In this embodiment, by utilizing the relationship at this time,
The values of the reflectances R _P and R _S are controlled according to the film forming conditions at the time of forming the mirror, so that R _P <R _S and the combined reflectance R is increased with the increase of the scanning angle α. I have.

Thus, shading on the surface to be scanned is corrected.

For example, if the scanning angle α is 30 degrees at the maximum, θ = 26.6 degrees. Now, assuming that R _P = 60% and R _S = 90%, the reflectance R = 66% from equation (4).

By using this method, the edge light amount on the surface to be scanned is corrected by about 10% as shown in FIG.

FIG. 5 is a schematic diagram of another embodiment when the present invention is applied to an LBP.

In the present embodiment, a laser beam from a semiconductor laser 12 is converted into a parallel beam by a collimator lens 13, condensed in a one-dimensional direction by a cylindrical lens 14, and guided to an optical deflector 11 composed of a rotating polygon mirror. Then, the laser beam deflected by the optical deflector 11 is condensed by a scanning lens 15 having f-θ characteristics, reflected by a mirror 16, and then passed through a dustproof glass 17 to a scanning surface 18 formed of a drum-state light body. It is incident on the top.

Optical scanning on the scanned surface 18 is performed by rotating the optical deflector in the same manner as in the embodiment shown in FIG.

The dustproof glass 17 is provided to prevent toner, paper dust, and the like from a developing device or the like from entering the scanning optical system unit. The dustproof glass is provided with an antireflection film for preventing reflected light.

In this embodiment, when this antireflection film is applied, the P-polarized light component and the S-polarized light component are reflected in the same manner as the reflection characteristics of the folding mirror 6 shown in FIG.
By controlling the transmittances T _P and T _S of the polarized light components, that is, the transmission characteristics are high in the peripheral portion and low in the central portion so that the light amount distribution is uniform on the surface to be scanned.

In the embodiment shown in FIG. 1, when the polarization state of the laser beam corresponding to the axis of the scanning lens 5 is incident on the mirror 6 in the S polarization state, the reflectance R of the P polarization component and the S polarization component is obtained. _{If P} and R _S are set so that R _P > R _S , optical scanning can be performed with a uniform light amount distribution over the entire surface to be scanned, as described above.

(Effects of the Invention) According to the present invention, the laser injection current is controlled by appropriately setting the reflection or transmission polarization characteristics of the optical member disposed in the optical path between the optical deflector and the surface to be scanned as described above. Thus, it is possible to achieve an optical scanning device having a simple configuration capable of performing optical scanning with a uniform light amount distribution over the entire surface to be scanned without using an electrically complicated circuit.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an embodiment when the present invention is applied to an LBP, FIG. 2 is an explanatory view showing a relationship between a laser beam and a mirror, and FIG. FIG. 4 is an explanatory diagram showing the relationship, FIG. 4 is an explanatory diagram showing the relationship between the reflectance and the scanning angle,
FIG. 5 is a schematic diagram of a main part of another embodiment of the present invention, and FIG. 6 is an explanatory diagram showing a relationship between a scanning angle on a surface to be scanned and shading. In the figure, 1 and 12 are laser oscillators, 2 and 13 are collimator lenses, 3 and 14 are cylindrical lenses, 4 and 11 are optical deflectors, 5 and 15 are scanning lenses, 6, 16 are mirrors, and 17 is dustproof glass. , 8, and 18 are drum-shaped photosensitive members, and 7 is a surface to be scanned.

Claims (1)

(57) [Claims] A linearly polarized laser beam is guided by a light guide to an optical deflector, and the laser beam deflected by the optical deflector is guided onto a surface to be scanned via a scanning lens and an optical member. In the optical scanning device for optically scanning the optical member, when the laser beam corresponding to the optical axis of the scanning lens is incident on the optical member with the polarization direction polarized in the P polarization direction, the P-polarized light of the optical member reflection or transmission characteristics of the S-polarized light X _P, X _S is
<Made to be X _S, X _P in case of incident in the state of polarized in S-polarization direction to the optical Faculty member Conversely> X _P constituting the reflection or transmission characteristics of the optical faculty member such that X _S An optical scanning device, comprising: