JPH01227121A - Image forming optical device - Google Patents

Abstract

PURPOSE:To impart the identical illuminance to all dots in one character on a photosensitive plane by setting the pupil of a 2nd lens system at the size which allows luminous fluxes out of two or more lenses in a lens array to make incident and arranging the pupil of a 1st lens system near the forward focal plane of the 2nd lens system. CONSTITUTION:The title device has two lens systems: the 1st lens system is a fine lens array 3 wherein plural lenses are arrayed one- or two-dimensionally, and the 2nd lens system is a projecting lens 4 arranged behind the 1st lens system. The size of the pupil of the projecting lens 4 is the one which allows luminous fluxes coming out of two or more lenses in the fine lens array 3 to make incident. The fine lens array 3 is arranged near the forward focal plane of the projecting lens 4. Consequently, the inclination angles alpha1 and alpha2 of the main beams of the luminous fluxes involved in image formation between points Q1 and Q2 can be made equal to uniformize illuminance at each point. Thus, the photosensitive amount of any dot in any character can be made equal.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to an imaging optical device, and particularly to an imaging optical device that is capable of switching patterns of letters, numbers, etc. arranged in large numbers spatially and forming images at the same image position. The present invention relates to an imaging optical device.

[Conventional technology]

Traditionally, printing devices such as printers and typewriters have
Types such as thermal printers and dot matrix printers that print characters as a collection of printing points arranged in a matrix (called dot matrix type), and types such as daisy-wheel printers that print character patterns prepared for each character as typefaces. (called the daisy-wheel type).

Since the dot matrix type expresses characters as a series of dots arranged with a fixed pinch, there are problems such as diagonal lines appearing like steps when printed characters are enlarged.

Daisy-wheel type printers do not have the problems described above with dot matrix type printers because each character is prepared as a printed character, but normal daisy-wheel type printers do not mechanically strike the ink ribbon. Noise during printing is a problem because it is printed on paper.

In addition, in recent years, laser printers, LED printers, liquid crystal printers, etc. have been developed, and by making the 0N10FF spacing of the scan beam finer in laser printers, the pitch of LED arrays and liquid crystal shunter arrays in LED printers and liquid crystal printers has been made finer. Therefore, there is an approach to printing high-definition characters by increasing the number of dots corresponding to one character, although it is basically a dot matrix type. However, these printers have many disadvantages in terms of manufacturing and cost, such as requiring a highly accurate optical system and having a low manufacturing yield for LED arrays and liquid crystal shutter arrays.

In order to eliminate such problems associated with conventional printers, typewriters, etc., a structure such as that disclosed in Japanese Patent Application No. 62-267843, for example, can be considered in which a lens array and a projection lens are combined. The apparatus described in Japanese Patent Application No. 62-267843 is shown in FIG. This is done by lighting up a specific LED in the LE [l array (11) to illuminate the corresponding character in the character pattern array (2), and then transmitting this image to the corresponding character in the microlens array (3). An image is formed on a photosensitive surface (5) using a microlens and a projection lens (4).

[Problem that the invention seeks to solve]

With the configuration described above, it is possible to achieve high-quality printing comparable to the conventional daisy-wheel type with low noise and an hour wheel configuration.

However, in the configuration shown in Fig. 2, the principal ray of the image formed by the microlenses in the periphery is tilted with respect to the optical axis of the projection lens (4), so the photosensitive surface (5) is not perpendicular to the optical axis. When placed, the light beam hits the photosensitive surface at an angle. Generally, when illuminating a certain surface, the illuminance of that surface decreases according to the cosine of the inclination angle of the light ray. Therefore, if the emission intensity of each light source is constant, There is a problem in that the brightness per unit area of the image formed by the lens and the image formed by the microlens located at a distant position are equal, and the conditions for exposure to light become non-uniform.

In order to solve this problem of uneven light intensity, for example, as shown in Japanese Patent Application No. 62-323484, the lens diameter of each microlens in the microlens array is set to a different value depending on the position where the lens is placed. One approach is to make the illuminance on the photosensitive surface constant by setting .

Although it is possible to make the illuminance on the photosensitive surface constant between individual characters using this method, inconsistency in illuminance also occurs depending on the location within one character.

That is, as shown in Figure 3, the inclination angle (01 and 02 in the figure) of the principal ray of the light beam incident on the image plane generally differs depending on the position within one character. Points P1 and P2 at different positions within the character have different illuminances on the image plane.

[Means for solving problems]

The imaging optical system consists of a microlens array as a lens system and a second lens system placed behind this lens array, and the size of the entrance pupil of the second lens system is determined by adjusting the size of the entrance pupil of the second lens system. The size is such that the light flux emitted from at least two lenses can enter, and the pupil position of the second lens system is set to the second lens system.
Placed near the front focal plane of the lens system.

[Effect]

All points within one character have the same illuminance on the photosensitive surface.

〔Example〕

FIG. 1 is a schematic diagram showing an embodiment of the present invention.

The configuration is the same as in FIG. 2 or 3 except that the first lens system, the microlens array (3), is arranged near the front focal plane of the projection lens (4).

By defining the positional relationship between the microlens array (3) and the projection lens (4) in this way, for example, point Q in the figure can be
1 and the inclination angle α1 of the chief ray of the light beam related to the imaging of Q2. α
It is possible to make 2 equal.

That is, at any point on the object (one character), the inclination angles of the principal rays of the light beams involved in the image formation can all be made equal, and the illuminance at each point can be made uniform.

〔Effect of the invention〕

As described above, according to the present invention, the conventional problem of non-uniformity in the amount of exposure depending on the location within one character is solved, and the amount of exposure at any point in an arbitrary character pattern is made equal. By specifying the positional relationship between the two lens systems, high-quality printing with uniform quality is possible. .

[Brief explanation of the drawing]

FIG. 1 is a side sectional view showing an embodiment of the present invention, FIG. 2 is a perspective view showing a conventional device, and FIG. 3 is a side sectional view of the device shown in FIG. 1...Light source array, 2...Character pattern array, 3
... Microlens array, 4... Projection lens, 5...
・Photosensitive surface. Figure 1 Da 1 = Be 2 Figure 2

Claims (1)

[Claims] It has two sets of lens systems, the first lens system is a row of minute lenses arranged one-dimensionally or two-dimensionally, and the second
The lens system is arranged behind the first lens system, and the size of the entrance pupil of the second lens system is large enough to allow light beams emitted from at least two lenses of the first lens system to enter. An imaging optical device characterized in that the pupil position of the first lens system is arranged near the front focal plane of the second lens system.