JPH082674Y2 - Image density control device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to an image density control device used in an image forming apparatus such as a copying machine, and more particularly, to optical density information of an original placed on a platen. The present invention relates to an improvement in an image density control device which is controlled to detect the image density and controls the image density based on the detected information.

[Prior Art] Conventionally, an image density control device of this type is disclosed in Japanese Patent Laid-Open No. 54-88.
The ones disclosed in Japanese Patent Nos. 118 and 60-79372 are known.
These are image density control devices used in copying machines, in which the density of the original is continuously detected by an optical density sensor along the scanning direction of the original, and the detection signal is integrated and smoothed. The original image density is controlled by adjusting the light source voltage of the optical system, the developing bias of the developing device, etc. based on the comparison value of the smoothed density data and the reference data.

[Problems to be Solved by the Invention] In a copying machine or the like, since the size of the document placed on the platen varies, when the document is the maximum size, it is detected by the density sensor. It can be said that the entire amount of light emitted from the original is from the original, but for small-sized originals, part of the amount of light detected by the density sensor is not from the original surface, but from the platen cover surface, for example. Therefore, even if the light amount detected by the density sensor is the same, if the image density is uniformly controlled based on this, the problem that the image density control becomes inaccurate depending on the document size. Occurs.

[Means for Solving Problems] The present invention has been made in view of the above problems, and an image in which the image density control can be accurately performed without being affected by the document size. A concentration control device is provided.

That is, this invention, as shown in FIG. 1, is a density detecting means 1 for optically detecting the density level of a document placed on a platen over the entire width dimension of the maximum size document.
And a document size detecting means 2 for detecting the size of the document.
And a density correction unit 4 for correcting the density information detected by the density detection unit 1 based on the document size detected by the document size detection unit.

In such technical means, the concentration detecting means 1
As long as the light reflected from the original is optically detected, it may be appropriately selected, and its installation location may be provided in the vicinity of the exposure scanning system unit. You may make it provide in the middle part. Particularly, in the latter case, it is necessary to dispose it at a position deviated from the optical path portion forming the original image from the viewpoint of maintaining good original image quality. Further, the timing of detecting the document density may be simultaneously performed during the exposure scanning or may be performed before the exposure scanning.

As for the original size detecting means 2, if the size of the original placed on the platen can be detected, a sensor for size detection is provided in the exposure scanning system unit, or a size detection sensor is provided on the platen cover side. The design may be changed as appropriate, such as by providing a sensor. The former type has a wider range of application than the latter type in that it can detect the document size without being affected by the opening and closing of the platen cover. Since it is often used after closing, the latter type does not matter.

Further, regarding the concrete calculation method of the density calculation means 3 for calculating the density information based on the detection result from the density detection means 1, it is possible to obtain the density information corresponding to the density level of the document. You can set it appropriately if you like,
Further, the correction amount of the density correction means 4 is also appropriately set within a range that can correspond to the density information from the substantial original area.

Furthermore, as the control means 5 for controlling the image density,
Any control parameter corresponding to the finally determined density information may be appropriately selected as long as it gives the image density adjusting means 6.

The parameters of the image density adjusting means 6 include the light amount of the light source of the exposure scanning system, the developing bias of the developing device, the charging voltage of the pre-charging device for pre-charging the latent image carrier, and the like.

[Operation] According to the technical means as described above, the concentration detecting means 1
Detects the density level of the document placed on the platen optically over the entire width dimension of the maximum size document, while
The document size detecting means 2 detects the size of the target document.

At this time, if the size of the target document is the maximum document size, it can be said that all the density information detected by the density detecting means 1 is for the document, but the size of the target document is other than the maximum document size. In this case, the density information detected by the density detecting means 1 includes information (platen cover) other than some originals.

Therefore, in the present invention, the density correction unit 4 corrects the density information detected by the density detection unit 1 based on the document size to obtain the true density information from the document.

Thereafter, the density information corrected by the density correcting means 4 is sent to the control means 5 as density control information, and the control means 5 controls the image density adjusting means 6 based on the given density control information.

Hereinafter, the present invention will be described in detail based on an embodiment shown in the accompanying drawings.

FIG. 2 shows an image density control device used in a copying machine to which the present invention is applied.

In the figure, 11 is a platen for placing a document 12, 13 is a scanner for exposing and scanning the surface of the document 12, 14 is an exposure light source stored in the scanner 13, and 15 is a reflection from the surface of the document 12. An optical system consisting of a plurality of mirrors 17 for focusing light on the surface of the photosensitive drum 16 and an imaging lens 18, 19 a pre-charger for precharging the surface of the photosensitive drum 16 before exposure, and 20 formed on the photosensitive drum 16. The developing device for developing the latent image corresponding to the formed original 12 with toner, 21 is a transfer device for transferring the toner image on the photosensitive drum 16 to the recording sheet (not shown) side, and 22 is the fixing of the transferred image on the recording sheet. It is a fixing device.

In this embodiment, an optical path regulating plate 26 having, for example, two through holes 25 is disposed on the optical path rear side of the imaging lens 18, as shown in FIGS. On the non-imaging lens 18 side of the regulation plate 26, a concentration sensor 30 (corresponding to the concentration detecting means 1) formed of a light receiving element such as a phototransistor is provided at a position outside the through hole 25 region.
Is provided. That is, the density sensor 30 detects leak light from the optical path of the optical system so as not to block the original image during exposure scanning. Reference numeral 31 is a reference reflector for giving the density information as a reference to the density sensor 30.

Further, in this embodiment, a platen cover 40 for opening and closing the platen 11 is provided, and a cover switch 42 composed of a limit switch or the like is provided in the machine body 41 portion corresponding to one side of the platen cover 40. The cover switch 42 contacts the platen cover 40 and is turned on to detect the closed state of the platen cover 40. The platen cover 42 has a document size sensor for detecting the size of the document 12, as shown in FIG.
Four 50's (specifically indicated by 50a to 50d) are arranged in an appropriate positional relationship. More specifically, as shown in FIG. 4, the original size sensor 50 has a housing 51 in which a light emitting element 52 such as a photodiode and a light receiving element 53 such as a phototransistor are housed.
If the original 12 is located in the irradiation light path from 52, the original 12
The reflected light from the light enters the light receiving element 53 side, while the light emitting element
When the original 12 does not exist in the irradiation light path portion from 52, the irradiation light from the light emitting element 52 is directly transmitted to the platen 11 side and the light is not incident on the light receiving element 53 side. In FIG. 4, reference numeral 54 is a light receiving element 52 and a light receiving element 53.
It is a harness for energizing to. As for the positional relationship between the four original size sensors 50, for example, as shown in FIG. 5, the four original size sensors 50a to 50d with respect to the occupied area of the original P1 of the maximum size (for example, JIS standard A3 version). Are placed appropriately, and manuscript P of intermediate size (for example, JIS standard A4 version)
Two document size sensors 50a and 50 for two occupied areas
Manuscript P3 with minimum size (for example, JIS standard B5 version) with d placed
If the original size sensor 50
The originals 12a to 50d are arranged, and the originals 12 are based on the combination of outputs from the original size sensors 50.
The size of is determined.

Further, the signals from the density sensor 30, the cover switch 42, and the document size sensors 50 are input to the control unit 70 via the input interface 60. The control unit 70 includes a CPU 71 that controls a series of processes, a RAM 72 that exchanges data in the process of the CPU 71, and the CPU 71.
ROM73 that stores a program that shows a series of processing procedures
In the ROM 73, as shown in FIG. 6, a program for calculating and correcting the density information detected during the exposure scanning and creating the image density control information is provided together with a series of copying operation programs. Pre-stored,
The CPU 71 executes the program based on the data given through the input interface 60, and outputs the light quantity control device 81 of the exposure light source 14 through the output interface 80 and other various devices necessary for the copying operation (FIG. Control signals are sent to each (not shown) to control them. In this embodiment, the control unit 70 simultaneously comprises the density calculation means 3, the density correction means 4 and the control means 5 of the present invention.

Next, the operation of the image density control apparatus according to this embodiment will be described with a focus on the flowchart shown in FIG.

First, after placing a document 12 of a predetermined size on the platen 11, when the platen cover 40 closes the platen 11 surface and a copy switch (not shown) is turned on, the control unit 70 causes the scanner 13
To start exposure scanning (step ST1). Thereafter, the control unit 70 AD-converts the output of the density sensor 30 and then samples the data every predetermined time Xms and fetches data (step ST2). Then, the control unit 70 calculates the density calculation data M according to the output from the density sensor 30 (step ST3).

Further, after confirming that the cover switch 42 is in the ON state, the control unit 70 determines that the target document size determined based on the information from each document size sensor 50 is the reference document size (the maximum size in this embodiment). Original size JIS standard A3
It is determined whether or not it matches the version (step ST
Four). If the target original size is A3, the control unit 70 sets the density calculation data M as the density control data C as it is (step ST5), whereas the target original size is other than A3. In some cases, the control unit
A reference numeral 70 designates the reference document size to correct the density calculation data M by the following calculation formula (Y) to obtain the density control data C (step ST6).

C = k × M (Y) However, k is a density correction coefficient and indicates the width dimension of the maximum size original document / the width dimension of the target original document.

Thereafter, the control unit 70 controls the light amount adjusting device 81 of the exposure light source 14 based on the density control data C determined as described above.
The target light source voltage V1 to be applied is calculated from the following arithmetic expression (Z) and the light quantity adjusting device 81 is controlled (step ST7).

V1 = (C0 / C) × V0 (Z) where C0 is the density sensor 30 against the white ground of the original 12.
Density calculation data based on the output, V0 indicates the current light source voltage.

After that, the control unit 70 controls the specified sampling number N
Each operation step (ST1 to ST7)
This is repeated to control the light amount adjusting device 81 at appropriate intervals during the exposure scanning (step ST8).

In such a control process, since the density control data C is set based on the density information corresponding to the substantial original area, the original density is accurately grasped without being affected by the original size. Therefore, the image density control can be accurately performed correspondingly.

In the above embodiment, the document density is detected during the exposure scanning, but the invention is not limited to this.
For example, a pre-exposure scanning process may be provided, the document density is detected during this pre-exposure scanning, and the density control data based on this may be set. As a concrete means for this, for example, the flow chart of the control unit 70 may be changed to that shown in FIG. That is, the control unit 70 first starts the pre-exposure scanning, and then, the predetermined number N of times for every predetermined time Xms.
The output of the concentration sensor 30 is sampled and captured only once (steps ST1 and ST2), the concentration calculation data Mi is calculated from the captured sampling data, and the average value thereof is calculated.
Calculate Ma (step ST3). Then, the control unit 70
After determining whether or not the target document size matches the reference document size (step ST4), the same calculation as that in the embodiment is performed to set the density control data C (steps ST5, S5).
T6), the target light source voltage V1 to be applied to the exposure light source 14 at the time of exposure scanning is obtained by the same calculation as in the embodiment, and the light quantity adjusting device 81 is controlled by this (step ST
7).

[Advantages of the Invention] As described above, according to the image density control device of the present invention, the density detecting means for optically detecting the density level of the original document over the entire width dimension of the maximum size original document is used. In controlling the image density, since the fluctuation of the document density due to the difference of the document size is effectively corrected, the image density can be controlled more accurately without being affected by the difference of the document size. it can.

Further, according to this invention, the density information to be detected by the density detecting means does not have to be only for the original area placed on the platen, and the maximum original size area (in the case of a small size original, Since an average density level within an area outside the original area (including the platen cover surface) is sufficient, for example, as shown in Japanese Patent Laid-Open No. 59-42551, the density detecting means of the density detecting means It is not necessary to add a circuit or mechanism for making the detection region variable, and the structure of the concentration detecting means can be simplified accordingly.

Further, according to the present invention, as the calculation processing by the density calculation means, for example, it is sufficient to average a certain number of density detection data groups sampled at a predetermined timing. As shown in the figure, dummy processing is performed to remove unnecessary density signals detected by the light-receiving element array, and the original density stored in RAM is compared with predetermined reference black level values and reference white level values. It is possible to simplify the calculation processing of the density detection data without requiring complicated processing such as obtaining the maximum density and the minimum density.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a basic structure of an image density control device according to the present invention, FIG. 2 is an explanatory view showing an embodiment in which the image density control device of the present invention is applied to a copying machine, and FIG. II in Fig. 2 showing an example of the position of the density sensor used in the example
FIG. 4 is an explanatory view showing details of an original size sensor used in the embodiment, FIG. 5 is an explanatory view showing an arrangement example of the original size sensor used in the embodiment, and FIG. FIG. 7 is an explanatory diagram showing the operation steps of the control unit used in the embodiment, and FIG. 7 is a flowchart showing a modification of the operation steps of the control unit. [Explanation of Codes] (1) ... Density detecting means (2) ... Document size detecting means (3) ... Density calculating means (4) ... Density correcting means (5) ... Control means (6) ... Image density adjusting means (11) )… Platen (12)… Original (14)… Light source for exposure (30)… Density sensor (50)… Original size sensor (70)… Control section

Claims (1)

[Scope of utility model registration request] 1. A density detecting means for optically detecting a density level of an original placed on a platen over the entire width dimension of a maximum size original, and an original size detecting means for detecting the size of the original. An image density control apparatus comprising: a density correction unit that corrects the density information detected by the density detection unit based on the document size detected by the document size detection unit.