JPH08137144A - Image forming device - Google Patents

Abstract

PURPOSE: To excellently detect toner density of color toner with simple structure. CONSTITUTION: The electrostatic latent image of a multi-level test pattern is formed on a photoreceptor 8, and the toner density of the test pattern developed with the color toner is optically detected. Based on the maximum value and the minimum value of the detected result, the detected result of the high density part of the test pattern is read, whereby the toner density is excellently detected while keeping an irradiating angle or a light receiving angle in optical detection for the test pattern fixed as it is.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus used in color copying machines, color printers, color facsimiles and the like.

[0002]

2. Description of the Related Art A conventional color printer forms a color image by sequentially transferring color toner consisting of yellow toner, magenta toner, and cyan toner onto printing paper by electrophotography. There is also a color printer that forms a color image by using black toner together with such color toner.

However, in such a color printer,
The print density and gradation of a specific color toner may be deteriorated due to a change with time of the photosensitive drum. in this case,
Since the color balance of the color image to be printed out is also deteriorated, the print quality is extremely deteriorated.

Therefore, in a conventional digital color copying machine or the like, a multi-tone test pattern is individually formed with each color toner and black toner, and these test patterns are illuminated and read by a sensor unit.
The print densities of the color toner and the black toner are individually corrected based on the detection result.

However, the black toner absorbs the incident light in the entire spectrum, but the color toner reflects the incident light in a specific spectrum, so that the reading characteristics of the sensor unit are different between the black toner and the color toner.

In order to solve such a problem, Japanese Unexamined Patent Publication No.
In the color copying machine disclosed in Japanese Patent No. 249787, a black toner test pattern is read by a sensor unit having both an irradiation angle and a light receiving angle of 45 degrees, and a color toner is read by a sensor having an irradiation angle of 45 degrees and a light receiving angle of 0 degree. Read the test pattern of.

[0007]

The above-mentioned color copying machine satisfactorily detects the print densities of the color toner and the black toner by the two types of sensor units.

However, in this case, since it is necessary to have two kinds of sensor units and to use them properly, the structure is complicated and miniaturization and productivity are hindered.

[0009]

According to the first aspect of the present invention,
An electrostatic latent image of the printed image is formed on the photoconductor by the exposure device, the electrostatic latent image is developed with color toner by the developing device, the developed color toner is transferred to the printing paper, and the transferred color is transferred. An image forming apparatus in which toner is fixed on a printing paper by a fixing device is provided with pattern forming means for forming an electrostatic latent image of a preset multi-tone test pattern on the photoconductor, and a test developed with color toner is performed. A density detecting means for optically detecting the toner density of the pattern is provided, and a density reading means for reading the detection result of the high density portion of the test pattern based on the maximum value and the minimum value of the detection result of the density detecting means is provided. It was

According to a second aspect of the invention, in the first aspect of the invention, the concentration detecting means has a low pass filter.

According to a third aspect of the present invention, in the first aspect of the present invention, the test pattern is an image in which the density continuously changes.

According to a fourth aspect of the present invention, in the first aspect of the present invention, the photosensitive member is an endless photosensitive belt which is stretched in a freely circulating manner, and a belt which supports the photosensitive belt at a position where density detecting means face each other. A support mechanism was provided.

According to a fifth aspect of the present invention, in the first aspect of the present invention, the density reading means reads the detection result of the density detecting means at a plurality of points and approximates it with a curve. Read the detection result of the density part.

According to a sixth aspect of the present invention, in the first aspect of the present invention, the density reading means reads the detection result of the density detecting means at a plurality of points and approximates the curve, and the initial value of this curve is set as the maximum value. Read and read the peak at which this curve reverses from falling to rising as the minimum value.

According to a seventh aspect of the invention, in the first aspect of the invention, a bias setting means for setting the developing bias of the developing device based on the detection result of the high density portion of the test pattern read by the density reading means is provided. Setting the developing bias by the bias setting means, forming the test pattern by the pattern forming means, developing the test pattern by the developing device, and detecting the density until the detection result of the high density portion of the test pattern falls within a preset allowable range. An operation control means for repeating the density detection by the means and the result reading by the density reading means is provided.

According to an eighth aspect of the invention, in the invention of the seventh aspect, detection of a high density portion of a test pattern read by the density reading means even when the number of repetitions of the operation control means reaches a preset prescribed number of times. When the result does not fall within the preset allowable range, the information notifying means for notifying and outputting the notification information indicating that the developing bias is not set is provided.

The color toner referred to in the present invention is a general term for toner forming a color image, such as yellow toner, magenta toner, and cyan toner, and does not include black toner.

[0018]

According to the present invention, when the pattern forming means forms an electrostatic latent image of a preset multi-tone test pattern on the photoconductor, the test pattern is developed with color toner by the developing device. The toner density of the developed test pattern is optically detected by the density detecting means,
Based on the maximum value and the minimum value of this detection result, the density reading means reads the detection result of the high density portion of the test pattern.
Although the detection result of the test pattern by the density detecting means changes depending on the incident angle, the light receiving angle, etc., the relationship between the maximum value and the minimum value and the detection result of the high density portion does not change. Is determined.

According to the second aspect of the invention, the noise of the detection result is removed by the low-pass filter included in the density detecting means.

According to the third aspect of the present invention, since the test pattern is an image in which the density continuously changes, the detection result of the density detecting means also becomes a continuously changing curve, and the toner density can be determined with high accuracy.

According to the fourth aspect of the invention, since the belt support mechanism supports the endless photosensitive belt stretched in a circulating manner at the position where the density detecting means faces each other, the density detecting means detects the test pattern with high accuracy. To do.

According to a fifth aspect of the present invention, the density reading means is
The detection result of the high density part of the test pattern is read as the peak of this curve by reading the detection result of the density detection means at multiple points and approximating it with a curve, so the detection result of the high density part of the test pattern can be read easily and accurately. To be

According to a sixth aspect of the present invention, the density reading means is
The detection result of the density detection means is read at multiple points and approximated by a curve, the initial value of this curve is read as the maximum value, and the peak at which this curve reverses from decrease to increase is read as the minimum value. The maximum and minimum values of can be read easily and accurately.

According to a seventh aspect of the present invention, the developing bias is set by the bias setting means, the test pattern is formed by the pattern forming means, and the developing is performed until the detection result of the high density portion of the test pattern reaches a preset allowable range. Since the operation control means repeats the development of the test pattern by the container, the density detection by the density detection means, and the result reading by the density reading means, the print density can be adjusted easily and accurately.

According to the present invention, the detection result of the high density portion of the test pattern read by the density reading means can be set within a predetermined permissible range even if the number of repetitions of the operation control means reaches a preset specified number of times. If the developing bias cannot be set, the information notifying unit outputs the notification information indicating that the developing bias has not been set. Therefore, when the developing bias cannot be set, this is notified to the user.

[0026]

An embodiment of the present invention will be described below with reference to the drawings. Note that the directions such as front and rear and up and down in this embodiment are shown for convenience in order to simplify the description,
This does not limit the actual installation or use direction of the device.

First, as shown in FIG. 1, in the color printer 1 which is the image forming apparatus of the present embodiment, a paper feed cassette 3 is mounted on the bottom of the apparatus main body 2, and the upper portion of the rear surface of the apparatus main body 2 is mounted. The paper ejection tray 4 is attached. Inside the main body 2 of the apparatus, a paper transport path 5 that communicates from the paper feed cassette 3 to the paper discharge tray 4 is formed, and an electrophotographic mechanism 6 is provided on the paper transport path 5. .

The structure of the electrophotographic mechanism 6 will be described in detail below.

First, a laser scanner 7 is arranged on the paper feed cassette 3, and an endless photosensitive belt 8 as a photosensitive member is arranged on a scanning optical path extending from a front end portion of the laser scanner 7 to an upper portion. . This photosensitive belt 8
Is stretched around a pair of rotating rollers 9 and 10 in a freely circulating manner, and the laser scanner 7 faces the photosensitive belt 8 on the peripheral surface of one rotating roller 9. Further, the rotating roller 9 is attached to the photosensitive belt 8.
On the peripheral surface of the toner cleaner 11, the static elimination lamp 1
2. The charging roller 13 is arranged to face each other, and the developing unit 14 is arranged to face the portion stretched linearly by the rotating rollers 9 and 10.

The developing unit 14 includes four developing units 1.
It is a unit in which 5 to 18 are integrated, and is rotatably supported. Yellow toner, magenta toner, cyan toner, and black toner are individually stored in the container 19 of each of the developing units 15 to 18, and when the developing unit 14 rotates, one developing roller of each of the developing units 15 to 18 is stored. 20 selectively opposes the photosensitive belt 8. Further, as shown in FIGS. 2 and 3, the photosensitive belt 8 is linearly stretched by the rotating rollers 9 and 10,
A backup plate 21, which is a belt supporting mechanism, is arranged above the position facing the developing unit 14, and a reflection type photo sensor 22 is provided at the center of the position where the photosensitive belt 8 is supported by the backup plate 21. It is arranged opposite from the outside.

Further, as shown in FIGS. 1 and 2, a transfer belt 23 is in contact with the photosensitive belt 8 on the peripheral surface of the rotating roller 10.
3 is also stretched in a circulating manner by a pair of rotating rollers 24 and 25 and a single supporting roller 26. At the position where the support roller 26 and the rotation roller 25 are stretched in a straight line, the transfer belt 23 is moved to the rotation roller 10
Is in contact with the photosensitive belt 8 located on the peripheral surface.
A cleaning blade 28 of a toner cleaner 27 is arranged to face the transfer belt 23 on the peripheral surface of one of the rotary rollers 25 so as to be freely contactable and separable, and a transfer roller 29 is pressed against the transfer belt 23. The sheet conveying path 5 passes through a gap between the transfer roller 29 and the transfer belt 23, and a fixing device 30 is arranged at a position communicating with the sheet discharge tray 4 from this position. As shown in FIGS. 2 and 4, six white position marks 31 to 36 are formed at equal intervals on the left side edge portion of the outer peripheral surface of the transfer belt 23, and these position marks 31 to 36 are formed. A reflection type photo interrupter 37 is arranged at a position opposed to.

As shown in FIG. 5, the photo interrupter 37 includes a CPU (Central Processing Unit).
A position discriminating circuit 40 composed of 38 and an OR gate 39 is connected, and a drive circuit 41 of the laser scanner 7 is connected to the position discriminating circuit 40.

Further, as shown in FIG. 6, a detection drive circuit 42 is connected to the photosensor 22, and the detection drive circuit 42 and the photosensor 22 connect the photodetector 22 to a density detector. 43 is provided. The structure of the density detector 43 will be described in detail below. First, the photo sensor 22 includes one LED (Light Emitting Diode).
de) 44 and one phototransistor 45, and a resistor 46 is connected to the phototransistor 45. This resistor 46 and the phototransistor 45
A low-pass filter 47 is connected between and, and this low-pass filter 47 has an A / DC (Analog / Digita).
A CPU 49 is connected via a converter 48. This CPU 49 has a D / AC (Digital / Analog Con
The drive transistor 51 is connected via the vertor) 50, and the drive transistor 51 is connected to the LED 44 of the photo sensor 22.

The color printer 1 of this embodiment is
For example, the CPU 38 controls the drive circuit 41 according to the preset storage data to drive the laser scanner 7, thereby causing the electrostatic latent image of the multi-tone test pattern 52 preset on the photosensitive belt 8. A pattern forming means (not shown) for forming an image is provided. As shown in FIG. 7B, the test pattern 52 is an image in which the density continuously changes in the sub-scanning direction, and low density portions are formed at both ends and a high density portion is formed in the center.

The electrostatic latent image of the test pattern 52 formed on the photosensitive belt 8 in this way is developed by the developing units 15 to 18 of the developing unit 14 into yellow toner, magenta toner and cyan toner which are color toners. To selectively develop. Since the toner density of the test pattern 52 thus developed is optically detected by the density detecting section 43, the detection result of the high density section of the test pattern 52 is detected based on the maximum value and the minimum value of the detection result. A density reading unit (not shown) for reading the is provided.

More specifically, as shown in FIG. 7A, the light intensity of the laser scanner 7 that exposes the electrostatic latent image of the test pattern 52 is the test pattern 52.
7 is set so as to change linearly from "0" at both ends to the maximum "Max" in the center. The amount of color toner adhered when the test pattern 52 is developed by the developing devices 15 to 18 is shown in FIG. As shown in (c), the test pattern 52 has a smooth curve with "0" at both ends and a maximum "Mmax" at the center. However, the detection result when such a test pattern 52 is read by the density detecting section 43 becomes a curve having three polarization points as shown in FIG. 8A. That is, the low density portions at both ends of the test pattern 52 show the maximum value "Vsg", but the predetermined position near the center shows the minimum value "Vp", and the high density portion in the center of the test pattern 52 shows the minimum value "Vsg". Value higher than Vp "Vmax"
Indicates.

This is a characteristic peculiar to the color toner, and in the case of the black toner, the toner density is directly proportional to the reading result. In other words, the black toner absorbs the incident light in the entire spectrum, but the color toner reflects the incident light in a specific spectrum, so that the reflected light decreases as the density increases in the low density portion, but the reflected light at a constant density. Shows a peak, and the reflected light increases in the high density area. The curve shape of the detection result is the test pattern 52.
Since it changes depending on the irradiation angle of the LED 44 of the photosensor 22 and the light receiving angle of the phototransistor 45, it is not possible to simply read the detection result of the density detection unit 43 for the high density portion at the center of the test pattern 52 as the toner density. Can not. It is an object of the present invention to satisfactorily read the toner density of such a color toner, and the black toner is read in the same manner as in the prior art, and will not be described in this embodiment.

First, as shown in FIG. 8B, the density reading means reads the detection result of the density detecting section 43 at a plurality of points and approximates it with a curve by the method of least squares. The value "Vsg" is read, the peak at which this curve reverses from decrease to increase is read as the minimum value "Vp", and the detection result "Vmax" of the high density portion of the test pattern 52 is read as the peak of this curve. Further, as shown in FIG. 8C, the highest value “Vsg” and the lowest value “Vp” read in this way are normalized to “1” and “0” to obtain the test pattern. The detection result “a” of the high-density portion 52 is read as a ratio.

Further, bias setting means for individually setting the developing bias of the developing devices 15 to 18 is provided based on the detection result "a" of the high density portion of the test pattern 52 read by the density reading means in this way. Has been.
The developing bias of the developing devices 15 to 18 is a voltage applied to the developing roller 20, which changes the toner density during development.

Then, the developing bias is set by the bias setting means, the test pattern 52 is formed by the pattern forming means, the test pattern 52 is developed by the developing devices 15 to 18, and the density detecting section 43 is used. The density detection of the test pattern 52 by the test pattern 52 and the result reading by the density reading unit are performed by the test pattern 52.
There is provided an operation control means (not shown) that repeats until the detection result "a" of the high density portion of No. 2 becomes within the preset allowable range "as ± Δa".

“As” is a preset reference value, and “Δa” is a preset allowable value. To set the developing bias by the bias setting means, the difference between the detection result "a" and the reference value "as" is multiplied by a coefficient, and the calculation result is subtracted from the current developing bias to obtain the next developing bias. Executed by.

Further, even if the number of repetitions of the operation control means reaches the preset specified number "4", the detection result "a" of the high density portion of the test pattern 52 read by the density reading means is within the allowable range. If "as ± Δa" does not occur, information notifying means (not shown) is provided for notifying and outputting notification information indicating that the developing bias has not been set by displaying a message on the display.

In such a configuration, first, the processing operation when the color printer 1 of this embodiment prints out a color image will be described below.

The developing unit 14 is positioned at a predetermined angle, and the developing device 15 containing the yellow toner is arranged to face the photosensitive belt 8. In this state, since the electrostatic latent image of the yellow image is exposed on the circulating photosensitive belt 8 by the laser scanner 7, the electrostatic latent image on the photosensitive belt 8 is developed by the developing device 15 with yellow toner and circulates on the transfer belt 23.
Are sequentially transferred to. At this time, the transfer belt 23 is not cleaned by the toner cleaner 27, but the photosensitive belt 8 is cleaned by the toner cleaner 11.

Next, the developing unit 14 is rotated by 90 degrees so that the developing device 16 containing the magenta toner is arranged opposite to the photosensitive belt 8. In this state, the laser scanner 7 circulates the photosensitive belt 8 to circulate the magenta image. Since the electrostatic latent image is exposed, the electrostatic latent image on the photosensitive belt 8 is developed by the developing device 16 with magenta toner and circulates on the transfer belt 23.
Are sequentially transferred to.

Similarly, since a cyan image and a black image are transferred to the transfer belt 23 to form a color image on the transfer belt 23, the color image is fed from the paper feeding cassette 3. Then, the print sheet is transferred to another print sheet, the print sheet is fixed by the fixing device 30, and then the print sheet is discharged to the sheet discharge tray 4, whereby the print output of the color image is completed.

As described above, one transfer belt 23
In order to superimpose four single-color images, it is necessary to control the operation timing of the laser scanner 7 in correspondence with the circulating position. The six position marks 31 to 36 of the circulating transfer belt 23 are detected by the photo interrupter 37,
The position determination circuit 40 manages the circulating position of the transfer belt 23 according to the detected number, so that the laser scanner 7
The start timing of the exposure operation is controlled. That is, when the photo interrupter 37 detects a specific one of the position marks 31 to 36, the position determination circuit 40 causes the laser scanner 7 to move.
However, the operation permission signal is masked when the other position marks 31 to 36 are detected.

More specifically, the photo interrupter 37
Since the output signal of is input to the INP terminal of CPU38,
Inside the CPU 38, the position marks 31 to 36 are provided.
It becomes the clock signal of the down counter that counts.
In the CPU 38, as shown in FIG. 9, the position marks 31 to 31 are generated in accordance with the output signal of the photo interrupter 37.
The presence or absence of detection of 36 is determined (step S1), and when the detection is determined, the down counter is initialized to "5" (step S2). At this time, the operation permission signal of the laser scanner 7 is generated (step S3), but if the detected position marks 31 to 36 are not one specific one for starting the operation of the laser scanner 7, the operation permission signal is masked. It

In this way, the CPU 38 inverts the operation enable signal ENB from "L" to "H" according to the count value of the down counter, so that the operation enable signal and the output signal of the photo interrupter 37 are logically operated by the OR gate 39. , Is output to the drive circuit 41 of the laser scanner 7 as a start signal.

Next, the CPU 38 judges whether or not the one printing plate is finished (step S4), and this judgment is executed based on the count value of the down counter by the interrupt process. In this interrupt processing, as shown in FIG. 10, the count value of the down counter is decremented (step T1) every time the position marks 31 to 36 are detected (step T1).
2).

As shown in FIG. 9, when it is judged that one printing plate is finished, it is judged whether all printing plates are finished (step S).
5) If it is determined to be completed, the processing operation is completed, and if it is not determined to be completed, it is determined whether or not the down counter is "0" (step S6). This step is repeated until the down counter reaches "0", and when the down counter reaches "0", the initial state is restored.

As described above, the color printer 1 controls the timing of the laser scanner 7 to form a color image on the transfer belt 23 and transfer it to the printing paper. However, if the transfer densities of the color toners individually change due to changes with time of the photosensitive belt 8, the color balance changes, and the print quality of the color image deteriorates. In order to prevent such a situation, the color printer 1 of this embodiment detects the toner densities of each of the color toners and the black toner when the main body power supply (not shown) is turned on, and the developing device 15 is detected according to the detection result. By setting the developing bias of ~ 18 to the initial value, the print quality of the color image is maintained good.

In the initial setting of the color printer 1, the output intensity of the LED 44 of the photo sensor 22 is first set. LED of this photo sensor 22
The output adjustment processing operation 44 will be described below with reference to FIG.

First, the photosensitive belt 8 is circulated (step E1), and the LED 44 of the photo sensor 22 is turned on (step E2). When the phototransistor 45 of the photosensor 22 outputs a current in this state, a corresponding voltage is generated by the resistor 46, so that this analog voltage is filtered by the low-pass filter 47 and then A /
It is converted into a digital value "VAD" by the DC 48 (step E3).

The CPU 49 compares the digital value "VAD" with the preset reference value "Vsg" (step E).
4) If “VAD> Vsg + ΔV”, reduce the output level of D / AC 50 (step E5), and set “VAD <Vsg
In the case of −ΔV ”, the output level of the D / AC 50 is increased (step E6). When the processing operation described above is repeated and“ Vsg−ΔV ≦ VAD ≦ Vsg + ΔV ”is satisfied, D / AC
The output level of the AC 50 is fixed and the output adjustment of the photo sensor 22 is completed. Note that “ΔV” is a preset allowable value.

Then, as described above, the photo sensor 2
When the output adjustment of No. 2 is completed, the initial setting of the developing bias of the developing devices 15 to 18 is started. This processing operation is shown in FIG.
It will be described below based on.

First, the developing device 1 containing the yellow toner.
5 is arranged to face the photosensitive belt 8, the developing bias of the developing device 15 is defaulted, and the default processing counter is reset to "0" (step P1). Next, the pattern forming means drives and controls the laser scanner 7 to form an electrostatic latent image of a preset multi-tone test pattern 52 on the circulating photosensitive belt 8, and the electrostatic latent image is developed. It is developed with the yellow toner supplied from the container 15 according to the developing bias.

At this time, as shown in FIG. 7A, the light intensity of the laser scanner 7 linearly changes from "0" at both ends of the test pattern 52 to the maximum "Max" at the center.
As shown in FIG. 7C, the adhesion amount of the yellow toner after developing the test pattern 52 is a smooth curve with "0" at both ends and maximum "Mmax" at the center. As shown in FIG. 7B, the both ends in the sub-scanning direction are the low density portion and the center is the high density portion.

Then, when such a test pattern 52 is optically detected by the photosensor 22 in accordance with the circulation of the photosensitive belt 8 (step P2), the initialization processing counter is incremented. As shown in FIG. 8A, the result “Vmax” of the high density portion at the center of the test pattern 52 detected by the photosensor 22 is the maximum value “V” at both ends.
It is lower than sg ”and higher than the lowest value“ Vp ”near the center.

Therefore, as shown in FIG. 8B, the density reading means reads the detection result of the density detecting unit 43 at a plurality of points and approximates it with a curve by the method of least squares. The initial value of this curve is the maximum value. It is read as "Vsg", and the peak at which this curve reverses from decrease to rise is read as the minimum value "Vp". As shown in FIG.
g "and the minimum value" Vp "are normalized to" 1 "and" 0 ". Since the detection result of the high density portion of the test pattern 52 is read as the peak of this curve, this detection result" a "
Is calculated from the ratio as a = (Vmax-Vp) / (Vsg-Vp) (step P3).

Next, the count value of the initially set processing counter is compared with "4" (step P4), and when the count value reaches "4", the information notifying means indicates that the developing bias has not been set. Is displayed on the screen (step P5).

When the count value is smaller than "4", the detection result "a" of the high density portion of the test pattern 52 is obtained.
And the preset reference value "as" are compared, and "a>as"
In the case of + Δa ”, the developing bias of the developing device 15 is lowered (step P6), and in the case of“ a <as−Δa ”, the developing bias of the developing device 15 is raised (step P7).
The development bias is set by multiplying the difference between the detection result “a” and the reference value “as” by a coefficient and subtracting this calculation result from the current development bias to obtain the next development bias. To be done.

When "as-.DELTA.a.ltoreq.a.ltoreq.as + .DELTA.a", the developing bias is fixed and the initial setting is completed. However, when the process proceeds to steps P6 and P7, the operation control is performed. The processing operation is repeated from step P2 by the means. For this reason, the processing operation is repeated until the detection result “a” of the high density portion of the test pattern 52 reaches the preset allowable range “as ± Δa”, and thus the print density of the yellow toner is set to the preset reference value. The density will be initialized.

Therefore, by performing the above-described processing operation on the magenta toner and the cyan toner as well, the color printer 1 is initially set to the color balance in the reference state, so that the color image is always printed in good condition. be able to.

Although the processing operation for initializing the developing bias is repeated as described above, when the number of repetitions reaches "4", the information notifying means displays a message indicating that the developing bias has not been set on the display ( Step P5). In this case, since the color printer 1 is in a state in which the toner density cannot be corrected by adjusting the developing bias, the user who confirms the message performs maintenance work such as replacement of the photosensitive belt 8.

In the color printer 1 of the present embodiment, the backup plate 21 supports the photosensitive belt 8 stretched in a circulating manner at the position where the photo sensor 22 faces it.
The photo sensor 22 can detect the test pattern 52 well. It should be noted that the present invention is not limited to the above embodiment, and when the photoconductor is a high-rigidity photoconductor drum, the photosensor 22 can detect the test pattern 52 well without the need for the backup plate 21. it can.

Further, since the low-pass filter 47 is provided between the photo sensor 22 and the A / DC 48 in the density detecting section 43, noise is removed from the detection result of the photo sensor 22 and the accuracy is improved. There is.

Moreover, the test pattern 52 is shown in FIG.
As shown in FIG. 8B, since the image is composed of images whose density changes continuously, as shown in FIG. 8A, the detection result of the density detection unit 43 also becomes a curve that changes continuously, and minute noise is generated. Since it is possible to ignore the polarization point and pay attention to the polarization point, it is possible to determine the toner density with high accuracy.

Further, the detection result of the density detecting section 43 is read at a plurality of points and approximated by a curve, the initial value of this curve is read as the maximum value "Vsg", and a peak at which this curve reverses from decrease to increase is found. Since the minimum value "Vp" is read and the detection result "Vmax" of the high density portion is read as the peak of this curve, the maximum value "Vsg" and the minimum value "Vp" of the test pattern 52 and the detection result of the high density portion are read. "Vmax" can be read easily and accurately.

Then, the density reading means sets the maximum value "Vsg".
By normalizing the minimum value "Vp" to "1" and "0", the detection result "Vmax" of the high density portion is read as the ratio "a". The toner concentration can be satisfactorily detected by the single photo sensor 22 having fixed corners.

Moreover, the operation control means repeats the initial setting processing operation until the detection result "a" of the high density portion of the test pattern 52 reaches the preset allowable range "a ± Δa". Since the print density of the toner is automatically adjusted, the color printer 1 can always print out a color image well.

Further, if the detection result "a" does not fall within the allowable range "a ± Δa" even when the number of repetitions of the operation control means reaches the preset specified number "4", the information notifying means performs development. Since the notification information indicating that the bias has not been set is output as a message displayed on the display, when the developing bias cannot be set, this is notified to the user, and the user can perform appropriate measures such as parts replacement.

[0073]

According to the present invention, the toner of the test pattern developed with color toner is provided with the pattern forming means for forming the electrostatic latent image of the preset multi-tone test pattern on the photoconductor. By providing the density detecting means for optically detecting the density and providing the density reading means for reading the detection result of the high density part of the test pattern based on the maximum value and the minimum value of the detection result of the density detecting means, Even if the irradiation angle and the light receiving angle of the density reading unit with respect to the test pattern are fixed to one, the toner density of the color toner can be detected satisfactorily, so that the toner density can be satisfactorily detected with a simple structure. be able to.

According to the second aspect of the present invention, since the density detecting means has the low-pass filter, noise in the toner density detection result is removed, so that the toner density detection accuracy can be improved.

According to the third aspect of the present invention, since the test pattern is an image in which the density continuously changes, the detection result of the density detecting means also becomes a curve that continuously changes. Can be improved.

According to a fourth aspect of the present invention, a belt supporting mechanism for supporting the photosensitive belt at a position where the density detecting means faces each other is provided, so that the photosensitive member is an endless photosensitive belt which is stretched in a freely circulating manner. However, the density detecting means can detect the test pattern satisfactorily, and the toner density detection accuracy can be improved.

According to the invention of claim 5, the density reading means is
By reading the detection result of the density detection means at multiple points and approximating it with a curve, and by reading the detection result of the high density portion of the test pattern as the peak of this curve, the detection result of the high density portion of the test pattern can be easily and accurately obtained. Since it is read, it is possible to improve the toner density detection accuracy.

According to the invention of claim 6, the density reading means is
By reading the detection result of the density detection means at multiple points and approximating it with a curve, reading the initial value of this curve as the maximum value, and reading the peak at which this curve reverses from rising to rising as the minimum value, the maximum of the test pattern Since the value and the minimum value can be easily and accurately read, the toner density detection accuracy can be improved.

According to a seventh aspect of the invention, there is provided bias setting means for setting the developing bias of the developing device based on the detection result of the high density portion of the test pattern read by the density reading means, and the high density portion of the test pattern is detected. Until the detection result falls within the preset allowable range, the developing bias is set by the bias setting means, the test pattern is formed by the pattern forming means, the test pattern is developed by the developing device, the density is detected by the density detecting means, and the result is obtained by the density reading means. Since the print density of the color toner is automatically adjusted by providing the operation control means for repeating the reading, the color image can always be printed out favorably.

According to the present invention, the detection result of the high-density portion of the test pattern read by the density reading means is set in a permissible range set in advance even if the number of times of repetition of the operation control means reaches a preset specified number of times. In the case where the toner density cannot be corrected by adjusting the developing bias, the user can be informed of this by notifying the output of the notification information indicating that the developing bias has not been set. it can.

[Brief description of drawings]

FIG. 1 is a vertical cross-sectional side view showing a color printer which is an embodiment of an image forming apparatus of the present invention.

FIG. 2 is a vertical sectional side view showing a peripheral portion of a photosensitive belt and a transfer belt.

FIG. 3 is a perspective view showing a peripheral portion of a photosensitive belt.

FIG. 4 is a perspective view showing a peripheral portion of a transfer belt.

FIG. 5 is a block diagram showing a position determination circuit.

FIG. 6 is a block diagram showing a density detecting unit which is a density detecting unit.

7A is a characteristic diagram showing emission intensity of a laser scanner that exposes a test pattern, FIG. 7B is a front view showing a developed test pattern, and FIG. 7C is a characteristic showing toner adhesion amount of the test pattern. It is a figure.

8A is a characteristic diagram showing a detection result of a test pattern by a density detection unit, FIG. 8B is a characteristic diagram showing a detection result approximated to a curve by a density reading unit, and FIG. 8C is a maximum value and a minimum value. FIG. 6 is a characteristic diagram showing a detection result in which a value is normalized to “1” and “0”.

FIG. 9 is a flowchart showing timing control of image printing.

FIG. 10 is a flowchart showing an interrupt process.

FIG. 11 is a flowchart showing output adjustment of LEDs of a photo sensor.

FIG. 12 is a flowchart showing the initial setting of the developing bias of the developing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Image forming apparatus 7 Exposure device 8 Photosensitive member, photosensitive belt 15-18 Developing device 21 Belt support mechanism 43 Density detecting means 47 Low-pass filter 52 Test pattern

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Kenji Shinohara 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Co., Ltd. (72) Inventor Yutaka Shio 10-3 Kitamura, Tottori-shi, Tottori Ricoh Micro Electronics Co., Ltd. Within

Claims (8)

[Claims] 1. An electrostatic latent image of a printed image is formed on a photoconductor by an exposure device, the electrostatic latent image is developed with color toner by a developing device, and the developed color toner is transferred to a printing paper, In the image forming apparatus for fixing the transferred color toner on the printing paper by the fixing device, pattern forming means for forming an electrostatic latent image of a preset multi-tone test pattern on the photoconductor is provided, and the color toner A density detecting means for optically detecting the toner density of the test pattern developed by is provided, and the detection result of the high density portion of the test pattern is read based on the maximum value and the minimum value of the detection result of the density detecting means. An image forming apparatus comprising a density reading unit. 2. The image forming apparatus according to claim 1, wherein the density detecting means has a low-pass filter. 3. The image forming apparatus according to claim 1, wherein the test pattern comprises an image whose density continuously changes. 4. A photosensitive member is an endless photosensitive belt which is stretched in a circulating manner, and a belt supporting mechanism for supporting the photosensitive belt at a position facing a density detecting means is provided. Image forming device. 5. The density reading means reads the detection result of the density detecting means at a plurality of points and approximates the curve, and reads the detection result of the high density portion of the test pattern as a peak of the curve. 1. The image forming apparatus according to 1. 6. The density reading means reads the detection result of the density detecting means at a plurality of points and approximates it with a curve, reads the initial value of this curve as the maximum value, and minimizes the peak at which this curve reverses from decrease to increase. The image forming apparatus according to claim 1, wherein the image is read as a value. 7. A bias setting means for setting the developing bias of the developing device based on the detection result of the high density portion of the test pattern read by the density reading means is provided, and the detection result of the high density portion of the test pattern is preset. The developing bias is set by the bias setting unit, the test pattern is formed by the pattern forming unit, the test pattern is developed by the developing unit, the density is detected by the density detecting unit, and the result is read by the density reading unit until the allowable range is reached. The image forming apparatus according to claim 1, further comprising an operation control unit that repeats. 8. The developing bias when the detection result of the high density portion of the test pattern read by the density reading means does not fall within a preset allowable range even when the number of repetitions of the operation control means reaches a preset specified number. 8. The image forming apparatus according to claim 7, further comprising an information notifying unit that notifies and outputs notification information indicating that the setting has not been made.