JP2810689B2 - Document density detector - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a document density detecting device, and more particularly, to a document density detecting device of an image forming apparatus such as a copying machine, a printer, and a facsimile.

[Prior art] In a copying machine or the like, reflected light when an original is exposed is detected by an optical sensor, and the density of the original is determined based on the photoelectrically converted value, and image forming conditions such as a developing bias voltage and the like are determined. Adjustment has conventionally been performed.

Such document density detection is good if the amount of exposure light is constant, but if the amount of exposure light changes, the document density cannot be detected accurately. In order to solve this problem, a reference pattern is provided, and the determination is made using a comparison value between the background density of the reference pattern and the output of the sensor regarding the background density of the document.

In an image forming apparatus such as a copying machine, a control method can determine an exposure position by an exposure light source using a pulse signal using an encoder or the like. Can detect the original density and detect the density of the original.
Some control devices have no means for distinguishing whether the exposure light source is exposing a reference pattern or a document. In such an apparatus, the density cannot be determined by detecting the reference pattern and the reflected light of the document by one exposure scan of the exposure light source.

[Problems to be solved by the invention]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned conventional problems and to provide a document density detecting device capable of detecting a relative density from a reference pattern and the density of a document even in a control method in which an exposure position cannot be recognized.

[Means for solving the problem]

The present invention solves the above problem by providing a reference pattern and a discriminating pattern provided before and after the reference pattern in the exposure scanning direction by the document exposing device, and changing the output of the sensor in the discriminating pattern during exposure to the reference pattern and the document. The problem was solved by a document density detecting device characterized in that

[Action]

According to the present invention, the exposure light source exposes the discrimination pattern, the reference pattern, the discrimination pattern, and the document in this order by one exposure scan, and detects the reflected light by the optical sensor.

The detection output of the sensor increases when shifting from the discrimination pattern to the reference pattern and when shifting from the discrimination pattern to the document. By setting a threshold value for identifying the difference between the detection output of the discrimination pattern, the reference pattern, and the document, it is possible to identify that the discrimination pattern has shifted to the reference pattern or the document when the threshold value is exceeded. Further, when shifting from the reference pattern to the discrimination pattern, the detection output of the sensor decreases. At this time, if a threshold value indicating the boundary between the reference pattern and the discrimination pattern is set, it can be understood that the transition from the reference pattern to the discrimination pattern occurs when the threshold value is exceeded. It is possible to identify whether the data is the data of the reference pattern or the data of the document at the points exceeding the respective threshold values, and detect the relative density of the background of the document with respect to the background of the reference pattern from both data, and control the density of the image forming apparatus. Can be performed accurately.

〔Example〕

 The details of the present invention will be described based on an embodiment shown in the drawings.

1 and 2, a document 2 is placed on a contact glass 1 and exposed from below by an exposure light source.
The position of the document 2 is determined by the document leading edge presser 3. A reference pattern 4 is provided outside the document area and outside the contact glass 1 in the figure. A first distinction pattern 5 is provided at the front of the reference pattern 4 and a second distinction pattern 6 is provided at the rear of the reference pattern 4 in the exposure scanning direction by the exposure light source. The second discriminating pattern 6 extends just over the entire length of the area between the reference pattern and the document. As an example, the distinction patterns 5 and 6 can be black patterns.

At the time of exposing the reference pattern 4 and the document 2 by the exposure light source, the discrimination patterns 5 and 6, the reference pattern 4 and the light reflected from the document are formed into an imaging lens The reflected light from the third mirror 9 is detected by a reflected light amount sensor (hereinafter referred to as an AE sensor) 11.

The light incident on the imaging lens 10 is incident on an image carrier, for example, a photosensitive drum, and is exposed to light to form an electrostatic latent image. The electrostatic latent image is developed by a developer, and the toner image is detected by an optical sensor as toner adhesion amount detection means (referred to as a P sensor), and the discrimination pattern, the reference pattern, the original, and the toner adhesion amount, that is, the toner density are detected. Is done.

By one exposure scan, for example, detection data as shown in FIG. 3 is obtained. FIG. 3A shows the detection output by the toner adhesion amount detecting means, and FIG. 3B shows the detection output of the reflected light amount sensor 11. FIGS. 3 (a) and 3 (b) show the reference pattern and the position of the document side by side so as to correspond to each other, so that they can be easily understood.

In FIG. 3 (b), TH1 indicates a threshold value when shifting from the discrimination pattern, TH2 indicates a threshold value when shifting from the reference pattern to the discrimination pattern, and TH2 is lower than TH1 to facilitate discrimination from TH1. It has been set.

The control at the time of detecting the document density is performed according to a flow as shown in FIG.

In FIG. 4, whether AE strobe is present, that is, AE
Check whether there is a signal for instructing reading by the sensor 11. If YES, the detection value of the reference pattern and the discrimination pattern of the memory by the AE sensor 11 (hereinafter abbreviated as AEP) and the detection value of the document by the AE sensor 11 (hereinafter abbreviated as AEO) are cleared to zero.

Next, it is checked whether the output value AD of the detection value of the AE sensor 11 by the AD converter is larger than the threshold value TH1. Check if it is bigger than AEP, and if so, save the AD to AEP. That is,
Save the peak value of the AE sensor detection value of the reference pattern. Thereafter, it is checked whether AD is smaller than the threshold value TH2. If AEP <AD, check if AD <TH2. Thus, the transition from the reference pattern to the discrimination pattern is checked.

When AD <TH2, the pattern shifts to the discrimination pattern. Then, it is checked whether AD ≧ TH1 and whether it has shifted to the original document.

If AD ≧ TH1, it is determined that the document has been transferred, and AEO <AD is checked. If YES, the AD is saved in AEO. That is, the peak value of the detection value of the AE sensor of the document portion is saved.
Thereafter, it is checked whether or not a predetermined time, for example, 150 ms, has elapsed.

The detection value of the AE sensor 11 clearly distinguishes the detection of the reference pattern portion and the document portion as described above, so the relative density is calculated from the detection amount of the image carrier corresponding to the reference pattern portion and the document portion by the P sensor. can do.

The reference pattern and the toner density of the original document can be detected by the reference pattern detected by the AE sensor and the amount of reflected light from the original document. It can also be detected by the potential of the electrostatic latent image on the carrier.

〔effect〕

According to the present invention, even in an image forming apparatus having a control device that cannot recognize the position of an exposure light source, a reference pattern and a document can be easily distinguished based on an analog output value from a sensor. This makes it possible to accurately detect the relative density of a document.

[Brief description of the drawings]

FIG. 1 is a perspective view of an example of an exposure optical device of an image forming apparatus utilizing the present invention, FIG.
FIG. 3A shows an example of a change in the output of the P sensor. FIG. 3B shows an example of a change in the output of the AE sensor.
The figure is a control flowchart. 1 ... contact glass, 2 ... document 3 ... document top edge press, 4 ... reference pattern 5, 6 ... discrimination pattern

Continuation of the front page (56) References JP-A-58-85448 (JP, A) JP-A-57-23972 (JP, A) JP-A-53-103736 (JP, A) JP-A-61-35060 (JP) , A) JP-A-59-93463 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G03G 15/04 111-120 G03G 15/00 303 G03G 21/00 370-502 G01N 21/47 G03B 27/72-27/80

Claims (1)

(57) [Claims] An original density detecting apparatus detects an original and a reference pattern provided outside the original area by an optical sensor and detects the density based on a density ratio between the original and the reference pattern. It has a distinction pattern provided before and after the reference pattern in the direction,
A document density detecting device for distinguishing between a reference pattern and a document based on a change in output of a sensor in a discrimination pattern at the time of exposure.