JPS63198043A - Light quantity detector for copying machine - Google Patents

Abstract

PURPOSE:To obtain a correct exposure quantity even against an original whose concentration is greatly different partially, by installing an interference filter for reflecting infrared rays into an optical path of a reflected light from an original, and also, allowing a visible light to transmit, at a prescribed angle to an optical axis, and also, providing a photodetector for detecting a reflected light from the interference filter. CONSTITUTION:A reflected light from an original 2 illuminated by a light source 1 is led to a photosensitive body 3 by a lens 4. In an optical path of the lens 4, an interference filter 10 for reflecting infrared rays, and also, allowing a visible light to transmit is installed at an angle of 45 deg. against the optical axis, and also, a photodetector 6 for detecting a reflected light from the interference filter is provided. In such a way, the center of a detection range of the photodetector 6 coincides with the center of a visual field of the lens, therefore, a correct exposure quantity is obtained even against an original whose concentration is greatly different partially.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to a light amount detection device for automatic exposure adjustment in a copying machine.

2. Description of the Related Art Conventionally, this type of light amount detection device has a reflector 5 provided near a lens 4 that guides reflected light from a document 2 illuminated by a light source 1 to a photoreceptor 3, as shown in FIG. , and a light receiving element 6 that detects the reflected light from the reflecting mirror 5, and the power supplied to the light source 1 is controlled according to the output of the light receiving element 6 to obtain an appropriate amount of exposure.

In FIG. 2, 7 is a reflecting mirror for condensing light from the light source 1, 8 is a glass plate on which the original 2 is placed, and 9 is an infrared cut filter.

However, in such a conventional light amount detection device, the center 2a of the detection range of the light receiving element 6 and the center 2b of the field of view of the lens 4 (i.e., a point on the optical axis) are Therefore, if the density of the original 2 is partially thick (different), the actual exposure amount (the amount of light guided to the photosensitive drum 3 through the lens 4) and the detected light amount may differ, making it impossible to obtain an appropriate exposure amount. There was a problem.

The present invention has been made to solve these problems, and provides a light amount detection device for a copying machine that can obtain an appropriate amount of exposure even for originals whose densities differ greatly in parts.

Means for Solving the Problem In order to solve this problem, the light amount detection device of the copying machine of the present invention has an infrared ray An interference filter that reflects visible light and transmits visible light is installed at a predetermined angle with respect to the optical axis, and a light receiving element that detects the reflected light from the interference filter is provided.

Effect: With this configuration, the center of the detection range of the light-receiving element coincides with the center of the field of view of the lens, so that an appropriate amount of exposure can be obtained even for originals whose densities differ greatly from part to part.

Embodiment FIG. 1 is a sectional view of an exposure system of a copying machine provided with a light amount detection device according to an embodiment of the present invention. In FIG. 1, reflected light from a document 2 illuminated by a light source 1 is guided by a lens 4 to a photoreceptor 3-.

In the optical path of the lens 4, an interference filter 10 that reflects infrared rays and transmits visible light is installed at an angle of 45° to the optical axis, and a light receiving element 6 that detects the reflected light from the interference filter. This is provided.

In this embodiment, as the interference filter 10, a Z
A multilayer coating of nS/Na5AePH is used. Such an interference filter has a characteristic that the transmitted wavelength and the reflected wavelength shift depending on the incident angle, and it is necessary to use it at a predetermined incident angle depending on the thickness of the coating layer.

The angle of incidence of the interference filter can be set arbitrarily depending on the thickness of the coating layer, but if it exceeds 60°, the angle of incidence
It was found that variations in the thickness of the coating layer greatly affected the wavelength characteristics of transmission and reflection, making it impractical for practical use. Furthermore, if the incident angle is made small, the light receiving element 6 that detects the reflected light approaches the optical axis of the lens 4 and blocks the optical path, so for practical purposes, the angle of incidence is 10" or more. Therefore, the interference filter's light The angle of incidence with respect to the axis is 10° to 60°
A range of 50° is preferred.

A silicon photodiode having maximum sensitivity at a wavelength of 1u11 is used as the light receiving element 6, and the reflected light at the interference filter 10 also reaches its maximum at a wavelength of around 1us+, so that sufficient detection sensitivity is obtained.

In addition, in FIG. 1, 7 indicates a reflecting mirror for condensing the light from the light source 1.

With the above-described configuration, the light amount detection device according to the embodiment of the present invention can detect originals with partially large densities because the center 2a° of the detection range of the light-receiving element 6 coincides with the center 2b of the field of view of the lens 4. An appropriate amount of path light can also be obtained.

As described in detail, 'According to the present invention, a lens system that guides reflected light from an original illuminated by a light source to a photoreceptor enters the optical path of a lens system that reflects infrared rays and transmits visible light. By installing the interference filter at a predetermined angle with respect to the optical axis and by providing a light receiving element to detect the reflected light from the interference filter, the density is partially thick (even for different originals). An appropriate amount of exposure can be obtained.Furthermore, since the interference filter reflects infrared rays and transmits visible light, it can also function as a conventional infrared cut filter, and can be used separately from an infrared cut filter. There is no need to provide one. This simplifies the structure and reduces costs.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of an exposure system of a copying machine equipped with a light amount detection device according to an embodiment of the present invention, and FIG. 2 is a sectional view of an exposure system of a copying machine equipped with a conventional light amount detection device. 1...Light source, 2...Document, 3...
...photoreceptor, 4...lens, 6...light receiving element, 10...interference filter. Name of agent: Patent attorney Toshio Nakao and 1 other person 1-5 circles
Wolf 10--Lens G--Eating and dying F 10--Thousand filters Fig. 2

Claims (1)

[Claims] An interference filter that reflects infrared rays and transmits visible light is installed at a predetermined angle with respect to the optical axis in the optical path of a lens system that guides reflected light from a document illuminated by a light source to a photoreceptor. . A light amount detection device for a copying machine, comprising a light receiving element for detecting reflected light from the interference filter.