JPS62166374A - Original document density detecting method for copying machine - Google Patents

Abstract

PURPOSE:To arrange a photosensor in the vicinity of a halogen lamp and to detect original document density accurately by making the quantity of light of the halogen lamp slightly less when the density of the original document is detected. CONSTITUTION:When the density of the original document is detected by prescanning, the halogen lamp 1 is turned on with a voltage which is as low as possible, and then a temperature rise is suppressed and this is advantageous to the life as well. Consequently, the temperature rise is suppressed even during continuous use, the photosensor 6 can be arranged in the vicinity of the halogen lamp 1, and the original density is detected more accurately. In this case, the photocurrent output of the photosensor 6 decreases owing to low-voltage lighting and this is disadvantageous to the S/N, but this is dealt with by setting the circuit constant of an amplifier 8.

Description

Detailed Description of the Invention Technical Field The present invention relates to an automatic double image density control mechanism (which detects the density of a document and automatically sets and controls double image forming conditions to obtain optimal double images).
The present invention relates to a document density detection method in a copying machine equipped with an AE mechanism.

BACKGROUND ART Conventionally, as a method for detecting the density of an original, there is a method that uses a light source dedicated to detecting the density of the original, which is separate from a light source for exposing the original. However, in this method, it is necessary to select a light source for detection whose emission wavelength is similar to the emission wavelength of an exposure light source, and the mechanism for scanning the document becomes complicated, resulting in high cost.

There is also a device in which the exposure light source is a halogen lamp, and the density of the document is detected by lighting the halogen lamp at an amount of light close to that required for actually forming a latent image. However, since the halogen lamp is turned on at near rated power even when detecting the density of the document, there are disadvantages such as a rise in temperature and restrictions on the arrangement of the optical sensor.

Purpose The present invention has been made in view of the above points, and makes it possible to dispose an optical sensor near the halogen lamp by suppressing the heat generation of the halogen lamp and reducing the temperature rise during document density detection. An object of the present invention is to provide a method for detecting document density in a copying machine.

Structure In order to achieve the above object, the present invention illuminates the original with a light source prior to the copying process, detects the density of the original based on the light reflected from the original, and automatically sets both image forming conditions to perform the copying operation. The copying machine is characterized in that a halogen lamp is used as an original exposure light source, and the amount of light from the halogen lamp during document density detection is controlled to be less than the amount of exposure light necessary for actually forming a latent image.

Hereinafter, one embodiment of the present invention will be described based on the drawings. First, an example of a part of an illumination optical system and an original density detection section of a copying machine using a halogen lamp l as an original exposure light source will be explained with reference to FIG. An original 3 is set on a movable contact glass 2.

This original 3 is subjected to slit exposure by condensing light from a halogen lamp 1 by a reflecting plate 4. and,
From this document 3, the reflected light is reflected from the lens of the first mirror 5 or less,
An electrostatic latent image is formed on the photoreceptor by a mirror system, and is subjected to a series of copying steps such as development and transfer.

However, such a copying machine has an A that detects the density of the original and automatically sets the conditions for forming both images so that the optimum images are obtained.
It is equipped with an E mechanism.

For this reason, an optical sensor 6 is provided facing the original 3 on the contact glass 2 to detect the density of the original. Here, in this optical sensor 6, the halogen lamp 1 is also used for detection, and a slit 4a is formed in a part of the reflector plate 4 for irradiating a small amount of detection light from the halogen lamp 1. has been done. And the optical sensor
6 is placed inside a light-shielding tube 7 to avoid stray light and the like.

The original density signal (minor current) detected by this optical sensor 6 is converted into current and voltage by an amplifier 8, amplified, and inputted to an A/D converter in a main control unit 9 equipped with a CPU. It is configured. Further, a lamp regulator 10 is connected to the main control section 9 in order to variably control both image forming conditions, for example, the light amount of the halogen lamp 1, according to document density information and the like. 11 is a cooling fan.

In this configuration, the original density detection operation is performed by prescanning the contact glass 2 prior to the actual copying process.

Here, there is a method in which such pre-scanning is not performed, but in real time, that is, the original is exposed with the actual original exposure light amount, the density is detected, and it is immediately fed back to the developing bias control.

However, in the case of this real-time processing method, the density of the original is detected and the conditions for forming both images are set and controlled immediately.
When controlling the amount of exposure light from the lamp, a time delay occurs due to the process structure, and this instability appears on both images. Therefore, the control is limited to the developing bias voltage of both image forming conditions. In this regard, according to the pre-scanning detection method as in this embodiment, either or both of the light amount control of the halogen lamp 1 and the development bias voltage control can be adopted as a control target in automatic double image density adjustment. In general, controlling the amount of light from a lamp is better than controlling the developing bias voltage in terms of both images, and
It also becomes possible to correct the background over a wide range.

By the way, halogen lamp 1 for detecting the original density
The light irradiated on the original by
This is advantageous for a device that detects minute photocurrents such as the one described above because it has a large S/N ratio.

However, when considering an actual copying machine, the heat generated by the halogen lamp 1 increases, and the optical sensor 6, which is sensitive to heat, cannot be disposed near the halogen lamp 1. This is not limited to halogen lamps 1, but generally for tungsten lamp light sources, the total luminous flux ratio (light amount) changes exponentially with respect to the lighting voltage ratio (= lighting voltage / rated voltage) as shown in Figure 2. However, it can be seen that the lower the lamp is lit at a lower voltage, the more the temperature rise can be suppressed in terms of the amount of heat generated by the lamp, which is indicated by the power ratio. Therefore, in this embodiment, when detecting the density of the document, the halogen lamp 1 is turned on with an amount of light that is smaller than the amount of exposure light necessary for actually forming a latent image. In addition, considering the life span of the halogen lamp 1, the halogen lamp 1 is often turned on at a voltage of around 70% of the rated voltage during actual latent image formation, and is turned on at a lower voltage than this when detecting the density of the original. It is something that makes you

In this way, when detecting the document density by pre-scanning, by lighting the halogen lamp 1 at as low a voltage as possible, temperature rise can be suppressed to a low level, which is advantageous in terms of service life. As a result, temperature rise is reduced even during continuous use, and the optical sensor 6 can be disposed near the halogen lamp 1, making it possible to more accurately detect the document density. However, due to low voltage lighting, the photocurrent output of the optical sensor 6 decreases, which is disadvantageous in terms of S/N ratio, but this can be countered by setting the circuit constants of the amplifier 8.

There are continuous variable methods and stepwise variable methods for changing the lamp exposure light amount when manually correcting density.
In either method, when detecting the density of the original, the halogen lamp 1 is turned on at a specified light amount (voltage) set by these methods, so that detection can always be performed under the same conditions.

Effects As described above, the present invention reduces the light intensity of the halogen lamp when detecting the original density, so the temperature rise due to heat generated by the halogen lamp can be suppressed to a low level. Therefore, the optical sensor can be disposed near the halogen lamp. The density of the document can be detected accurately.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a schematic side view, and FIG. 2 is a lighting voltage ratio-total luminous flux ratio and power ratio characteristic diagram. 1...Halogen lamp, 3...Amount of manuscript request person
Riko Co., Ltd. -, %, l figure, ¥5Z figure, 0 month electric loaf ratio -

Claims (1)

[Claims] In a copying machine that illuminates an original with a light source prior to the copying process, detects the density of the original using light reflected from the original, and automatically sets both image forming conditions to perform the copying operation, the original exposing light source is a halogen lamp, A method for detecting document density in a copying machine, characterized in that the amount of light from this halogen lamp during document density detection is controlled to be less than the amount of exposure light necessary for actually forming a latent image.