JPH02251835A - Image input device - Google Patents

Abstract

PURPOSE:To obtain uniform bias light by employing an image forming lens itself as a means guiding bias light to an image sensor. CONSTITUTION:Light beams coming out of a light source irradiate an original surface 1. Out of light beams reflected thereon, the light beam 8 made incident on a rod lens 4A within a certain range of an lens opening angle proceeds meanderingly in the lens 4A in the form of a sine curve, instead of being reflected on the lateral periphery, is light-condensed, and is made incident on the image sensor 5. On the other hand, the light beam 9 made incident on the lens 4A beyond the lens opening angle after being reflected on the original surface comes into the lateral side of the lens 4A, where it is totally reflected, and this total reflection repeats. After the light beam 9 proceeds in the lens 4A, it comes out of the lens 4A. Light beams made incident on the lens at any angle beyond the lens opening angle come out in random directions from the lens end because of the total reflection, and irradiate the image sensor 5 with uniform illuminance. The totally reflected light 9 turns into bias light to raise sensor sensitivity.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image input device, and more particularly to an improvement in an optical system for uniformly applying bias light when an image sensor reads a document.

[Conventional technology]

In an image input device using a contact image sensor such as a facsimile, the sensitivity of the sensor becomes extremely poor when the amount of light is small.

To compensate for this, we increase the overall light intensity by covering the original image light intensity with uniform light, and use it at a brightness that provides good sensor sensitivity.

Unlike the photosensitive drum of a copying machine, a sensor treats it as an electrical signal, so by applying a bias, it is possible to remove light signals other than the image light amount.

In order to input a good image, the key is to uniformly apply light that is not involved in image formation (hereinafter referred to as bias light) to the sensor.
No. 60 proposes a configuration in which a light reflecting plate is provided near the original document almost parallel to the original surface, a window is provided on the outer periphery of the imaging optical system, and the light reflected by the reflecting plate is used as the aforementioned bias light. ing.

Furthermore, Japanese Patent Application Laid-Open No. 178658/1983 proposes a configuration in which a light guiding means for guiding light from a light source directly to an image sensor is attached in addition to the imaging optical system.

[Problem that the invention seeks to solve]

In the configuration disclosed in Japanese Patent Application Laid-Open No. 63-182960, it is difficult to maintain a constant gap between the imaging optical system and the surrounding frame, and there is a problem that the bias light does not uniformly strike the document surface. Additionally, since there is a gap, there is also the problem that paper dust from feeding the document can adhere to the sensor.

On the other hand, in the configuration of JP-A-63-178658, since the side leakage light of the light source lamp is used as the bias light, it is difficult to keep the illuminance of the document constant and also keep the bias light constant. There is a problem.

Furthermore, in any of the above configurations, it is necessary to provide a reflecting mirror or some kind of light guide, which increases the production cost and has the disadvantage that it becomes difficult to miniaturize the image input device.

[Means for solving problems]

A gradient index rod lens is used as an imaging optical system disposed between the document surface and the image sensor, and the side peripheral surface of this rod lens is made smooth. In other words, in the conventional gradient index rod lens array used in the optical system of copying machines, flare light that does not contribute to image formation passes through the rod lens and hits the document surface, reducing the contrast of the image. In order to prevent this phenomenon, the peripheral surface of the rod lens side is roughened, but it is sufficient to simply maintain the smooth state of the glass rod surface of the lens base without performing this surface roughening treatment. Furthermore, a low refractive index coating layer may be provided on the lens side peripheral surface.

[For production]

According to the above configuration, among the reflected light from the document surface, the reflected light within the aperture angle of the lens travels in a sine curve shape without hitting the inner peripheral surface of the lens, and then forms an image on the image sensor. The light that enters the lens beyond the aperture angle hits the inner peripheral surface of the lens, and since this surface is a smooth surface, it is totally reflected, and after traveling through the lens by repeating this total reflection, it exits the lens. incident on the image sensor.

In other words, the latter totally reflected light enters the entire image sensor with uniform illuminance because the light at various incident angles entering the lens from the document surface is not focused and exits from the lens in random directions. It acts as bias light to increase the sensitivity of the image sensor mentioned above.

〔Example〕

The present invention will be described in detail below based on embodiments shown in the drawings.

FIG. 1 is a cross-sectional view showing one embodiment of the present invention, in which 1 is a document surface, 2 is a platen, and 3 is an LE as a light source.
D, 4 is a rod lens array, and 5 is an image sensor. The gap between the rod lens array 4 and the housing 6 is filled with a filler 7 such as adhesive or sponge to block light and seal it, thereby preventing dust from adhering to the surface of the image sensor 5. As shown in FIGS. 2 and 3, the rod lens array 4 is a rod lens 4A having a refractive index distribution in which the refractive index in the cross section is maximum on the central axis and gradually decreases parapolitically in the radial direction toward the outer circumference. A large number of these are arranged with their central axes parallel to each other, the periphery is held by a holding plate 4B and a spacer member 4C, and the gap is filled with a light-absorbing adhesive 4D to form a structure in which they are joined and integrated. ing.

The side circumferential surface of each rod lens 4A is a fire polished surface (smooth surface) after thermoforming of the glass rod of the lens base without roughening treatment such as chemical etching.
Assemble it into lens array 4 as it is.

In the apparatus shown in FIG. 1, the light emitted from the light source 3 illuminates the document surface 1, and as shown in FIG. The light ray 8 meandering through the lens 4A in a sine curve shape without being reflected by the side peripheral surface, is condensed, and enters the image sensor 5. That is, the image of the document surface is formed on the image sensor 5 and read.

On the other hand, after being reflected on the document surface, the light ray 9 that enters the rod lens 4A outside the lens aperture angle reaches the side peripheral surface of the lens 4A, where it is totally reflected, and this total reflection is repeated until it enters the lens 4A. After traveling, the light is emitted from the lens 4A.

In this way, light rays that deviate from the lens aperture angle and enter the lens from all angles are emitted from the lens end face in random directions by total internal reflection, and illuminate the image sensor 5 with uniform illuminance.

In other words, the totally reflected light 9 acts as bias light for increasing sensor sensitivity.

FIG. 5 shows another structural example of the rod lens 4A used in the present invention.

In this example, a coating layer 10 made of a low refractive index resin or glass is provided on the side peripheral surface of the bare rod lens 4A,
The total reflection efficiency of bias light on the lens side peripheral surface is further increased.

Rod lens 4 provided with such a low refractive index coating layer 10
A large number of lenses A are arranged and bonded together to form the lens array 4 shown in FIG.

〔Effect of the invention〕

According to the present invention, since the imaging lens itself is used as a bias guiding light means for the image sensor, there is no need to change the structure of the device or add any parts, and the device can be manufactured at low cost and the entire device can be sufficiently constructed. Can be made smaller.

In addition, since it utilizes total internal reflection on the inner peripheral surface of the lens,
Uniform bias light can be obtained.

Furthermore, since the area around the image sensor can be completely sealed, there is no dust adhering to the sensor, and stable performance can be maintained over a long period of time.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing an embodiment of the present invention, FIGS. 2 and 3 are cross-sectional views and perspective views showing a gradient index lens array used in the present invention, and FIG. 4 is an operation of the present invention. FIG. 5 is a cross-sectional view showing another example of the rod lens used in the present invention. ■...Document surface 3...Light source LED4.
...Rod lens array 4A...Gradient index rod lens 5...Image sensor 6...Housing 7...
Light-shielding filler 8...Imaging light 9...Bias light 10...Low refractive index coating layer Fig. 1 Fig. 2/-4 Fig. 3 Fig. 4

Claims (1)

[Claims] Between the document surface illuminated by a light source and the image sensor,
A gradient index rod lens is arranged to form an original image on an image sensor, and the rod lens side peripheral surface is made a smooth surface to direct light that does not contribute to image formation from the original surface to the lens. An image input device characterized by being guided by total reflection on a peripheral surface and used as bias light to an image sensor.