JPH11249349A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure the accurate toner adhesive amount of a toner mark and to excellently control toner concn. by providing a surface state detection means for detecting the surface state of a reference pattern transfer position. SOLUTION: When a transfer belt 58 is driven to be rotated, first surface measurement is performed, and the measured value of a surface measuring sensor 305 obtained by the first measurement and a clock timer measuring time being the measuring time at such a time are stored in a RAM 303. Based on each stored information in the RAM 303, a CPU 302 controls so that the toner mark may be formed on the peripheral surface of a photoreceptor drum 51 and transfered to a specified position on the belt 58. The toner concn. of the toner mark transferred to the belt 58 is measured by a toner concn. sensor 306. The toner adhesive amount is calculated every time the toner mark passes a detecting position by the sensor 306 by driving and turning the belt 58, and image density is automatically controlled based on the calculated result.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an improvement in an automatic image density control (AIDC) technique.

[0002]

2. Description of the Related Art Generally, in an image forming apparatus that reproduces a document image using toner, it is important to form an image on a recording sheet with a toner density that is faithful to the document density. For this reason, a toner mark is formed at a position on the peripheral surface of the photosensitive drum that is outside the original image forming area, the amount of toner attached to the mark is measured by a sensor, and the density of the toner image is determined based on the measured value. AIDC (Auto Image Density Control) for automatically correcting to ideal density is performed. In this AIDC, a transfer surface of a transfer belt or a transfer drum predicts a density state of a toner image formed on a recording sheet on a transfer surface of a transfer belt or a transfer drum as a measurement surface of a sensor for measuring a toner adhesion amount of a toner mark. It is considered that the correction result can be easily reflected. For example, in an image forming apparatus having a transfer belt and a photosensitive drum, a toner mark is directly transferred from the photosensitive drum to the surface of the transfer belt in Japanese Patent Application Laid-Open No. 63-14349. The technology which measures AIDC and performs AIDC is disclosed.

Generally, the transfer drum is formed of a soft dielectric resin film such as polycarbonate on the peripheral surface, and the transfer belt is formed of the same material or a flexible material such as synthetic rubber or synthetic fiber. For this reason, they have the property of being easily scratched, and if a toner mark is formed on the surface, the measured value of the amount of toner adhered to each toner mark varies depending on the presence or absence of the scratch and the degree of the scratch. To solve this, for example, the background of the photoreceptor drum or the background of the transfer belt surface is measured as a reference density,
AIDC technology (for example, Japanese Patent Application Laid-Open No. 4-1) discloses a method of forming a toner mark on the surface to be measured, subtracting the background measurement value from the measured toner adhesion amount, and correcting the toner adhesion amount to an accurate value.
46449, JP-A-63-14349).

[0004]

However, in the case of detection on a transfer belt or a transfer drum, the state of the bare surface differs greatly, for example, between the position where the paper is always placed and the position where it is not, and the difference in output when the test pattern is detected. Appears. When the detection position is on the surface of the photoreceptor drum, it is not necessary to consider the background detection position because the bare surface state changes relatively uniformly. When the pattern output created at another position is corrected using the background density at the position, there is a possibility that an image due to incorrect correction may be formed as a result.

The present invention has been made in view of such a problem, and an object of the present invention is to provide an image forming apparatus based on a toner mark transferred from a photosensitive drum to a transfer belt or a transfer drum.
An object of the present invention is to provide an image forming apparatus that can accurately measure the amount of toner adhering to a toner mark and perform good toner density control even when performing IDC.

[0006]

In order to solve the above-mentioned problems, the present invention is to develop a transfer belt or a transfer belt after visualizing a latent image of a reference pattern formed on an electrostatic latent image carrier by applying toner with developing means. In an image forming apparatus for transferring an image to a transfer drum and automatically adjusting the image density by detecting the density of the reference pattern after the transfer, the reference pattern on the rotating transfer belt or the transfer drum before the reference pattern is transferred. The image processing apparatus further includes a background state detection unit that detects a background state at a pattern transfer position, and automatically adjusts an image density using the reference pattern density detection value and the background state detection value.

Further, the electrostatic latent image carrier is a photosensitive drum, and the background state detecting means sets the circumferential length of the drum from the drum surface position where the latent image of the reference pattern is formed to the transfer position to L. In this case, the transfer belt or the transfer position on the transfer belt surface may be arranged at a position equal to or more than L upstream from the transfer position. Further, the background state detecting means can also be used as a density detecting means for detecting the density of the transferred reference pattern.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS <Description of Configuration> A digital copying machine according to an embodiment of the present invention will be described below. As shown in a front sectional view (FIG. 1) showing a main structure of the copying machine, the copying machine is roughly divided into an image reader section 10 and a printer section 20, and the printer section 20 is further provided with a control section 30, a writing optical system. The system 40 includes an image forming unit 50, a paper feeding unit 60, a fixing unit 70, and the like.

The image reader section 10 is composed of a platen glass 2 arranged in the horizontal direction of the drawing, a CCD scanner unit 5 having a CCD scanner 4 and an exposure lamp 3, and the like. By moving the scanner unit 5 in parallel with the glass plane, data of the document image placed on the platen glass 2 is read by the CCD scanner 4.

The controller 30 is connected to the CCD scanner 4 and stores therein an image memory (not shown) for storing the read original image data, a known shading correction for the original image data, and a UCR-BP. And an image correction circuit (not shown) for performing image processing such as gamma correction,
An AIDC circuit 301 that performs AIDC based on measurement signals from a background measurement sensor 305, a toner density measurement sensor 306, and the like disposed near the transfer belt 58 described below is provided.

The writing optical system 40 includes a semiconductor laser 4
1. A polygon mirror 42, which is composed of a polygon mirror 42, a scanning lens 43, an fθ lens 44, and the like, modulates the laser light of the semiconductor laser 41 using image data on which image processing has been performed by the control unit 30, and is driven to rotate. The laser light is reflected by the mirror surface of FIG. 1, and the peripheral surface of the photosensitive drum 51 can be scanned after passing through the scanning lens 43, the fθ lens 44, and the like using the dashed line in the drawing as the laser light path.

[0012] The image forming unit 50 includes a photosensitive drum 51 which is rotated in the X _B direction in the center of the copier housing portion
And a drum cleaner 52, a charging device 53, a developing device 54, which are disposed clockwise from the lower left in the drawing in the vicinity of the peripheral surface.
Configuration such as a transfer unit 55, in yet directly below the photosensitive drum 51, the driving roller 57, is stretched to the driven roller 56, configuration such as a transfer belt 58 which is driven to rotate in the X _A direction in synchronism with the photosensitive drum 51 And a belt cleaner 59 having a flexible blade for cleaning the surface of the transfer belt 58 is disposed near the surface of the transfer belt 58 that runs on the driving roller 57. These configurations mainly perform the following operations.

That is, the peripheral surface of the photosensitive drum 51 cleaned by the drum cleaner 52 is uniformly charged by the charger 53 and irradiated with a laser beam to form an electrostatic latent image of a document image. A toner image is formed by a developing unit 54 on the recording sheet S conveyed on a transfer belt 58 cleaned by a belt cleaner 59, and the toner image on the peripheral surface of the photosensitive drum 51 is generated by an electric field generated by the transfer unit 55. Is formed. In the present embodiment, the AIDC toner mark is written at a predetermined position on the peripheral surface of the photosensitive drum 51 by the writing optical system 40 in the same manner as the original image.

The recording paper S is fed from a paper feed cassette 61 provided on the side of the copier housing by a feed roller 62 in a paper feed unit 60 on the upstream side in the transport direction of the transfer belt 58, and is fed by a separating roller 63. Each of them is sent from the upstream side of the transfer belt 58 on the outward path.
Recording sheet S after transfer, the fixing unit 70 in the forward path downstream side of the transfer belt 58, is pressed against the peripheral surface of one another are each Y _A or Y _B direction rotation driven fixing roller 71,
72, the toner image is heat-fixed, and is discharged onto a discharge tray 80 downstream of the fixing unit 70.

The developing device 54 includes a toner tank 452 containing toner and a developing sleeve 451 arranged close to the peripheral surface of the photosensitive drum 51. A bias power supply 540 is connected to the developing sleeve 451, and a predetermined bias voltage (developing bias voltage Vb) is applied to the developing sleeve 451, and an amount of toner corresponding to the voltage value is applied to the circumference of the photosensitive drum 51. The density of the toner image transferred to the recording sheet from the photosensitive drum 51 is controlled by being attached to the surface.

The toner adhesion amount R1 at a certain position where the toner is transferred from the photosensitive drum 51 onto the transfer belt 58,
Regarding the toner adhesion amount Rp as a control target on the transfer belt 58 (or on the recording sheet), generally, Mp / M1
= Rp / R1 holds. In this embodiment, utilizing this, the developing bias voltage Vb is changed to form a toner mark of a predetermined toner concentration on the transfer belt 58 from the photosensitive drum 51, and AIDC is performed. . In addition, a method of adjusting the maximum output of the semiconductor laser 41 to change the Vi level can be adopted.

On the other hand, on the outward path of the transfer belt 58, a light emitting diode is used as a light emitting element 306A as shown in FIG.
A reflection type photosensor having a phototransistor as a light receiving element 306B is disposed downstream of the photosensitive drum 51 as a toner density measuring sensor 306. Similarly, a background measurement sensor 305 including a light emitting element 305A and a light receiving element 305B is used as a transfer belt 58 are located near the lowermost downstream of the return route. The background measurement sensor 305 detects the background density of the surface of the transfer belt 58, and the toner density measurement sensor 306 detects the density of the toner mark transferred to the detection position of the background measurement sensor 305. These background measurement sensors 305
The toner concentration measurement sensor 306 is controlled by the CPU 302 so as to obtain a detection value as a periodic pulse signal, and the rotation speed V ₁ (m / sec) of the transfer belt 58 and the background measurement sensor 305 and the toner concentration measurement sensor 306 are controlled. The pulse signal period is controlled so that the detection interval X ₁ V ₁ (m / pulse) on the transfer belt 58, which is expressed by the product of the pulse detection period X ₁ (sec / pulse), is always constant. Be activated.

Next, the configuration of the AIDC circuit 301 will be specifically described. As shown in FIG. 1, the circuit mainly includes a CPU 302, a RAM 303, a ROM 304, and the like.
302. The CPU 302 uses a clock timer and a flag register provided inside to
Based on the program stored in the OM 304, the control flow related to the AIDC process and the copy process shown in FIGS. 3 and 4 is executed. The control is generally as follows.

When the user makes a copy selection, the CPU 302 first executes the transfer belt 5 prior to copy processing.
8 is rotated (runs idle), and the background measurement sensor 305 moves the background in a predetermined area of the transfer belt 58 at a constant interval X ₁ V _1.
The number of measurements (corresponding to the number of pulses) is counted while detecting each time with a synchronization pulse. Subsequently, the CPU 302 calculates the rotation distance n of the transfer belt 58 from the start of the measurement count based on the value of the detection interval X ₁ V ₁ on the transfer belt 58 and the count of the number of measurements (measurement count n). × X ₁ V ₁
(M), and further utilizing the clock timer time information at the start of the count, the transfer belt 5 used for detection.
8 where the background area is located on the transfer belt 58 being driven to rotate.

Further, the CPU 302 determines that the length L of the toner mark along the longitudinal direction of the transfer belt 58 is L = j.
An integer j that satisfies × X ₁ V ₁ is set as the upper limit value of the measurement count number n. When the measurement count number n reaches the upper limit value j, the counting operation is reset and the operation is repeated from 1 again. The CPU 302 also counts the number of repeats as a count repeat number C separately from the measurement count number n. The number of count repeats C is
It is equivalent to the number of toner marks formed on the top,
C = C _max is set as the upper limit. This is a numerical value set as a value equal to or less than the number of toner marks that can be formed on the transfer belt 58.

In this embodiment, the background detection value detected while performing two types of counting is referred to as V
_{(c, n)} (C; count repeat number 1 to C _max , n; measured count number 1 to j). For example, V
_{(5, 8)} represents the background detection value detected when the count number C is the fifth and the count number n is the eighth. CPU
Reference numeral 302 denotes a count operation as described above, where two background measurement values V _{(c, n-1)} continuous in one count repeat number C,
The measurement is continuously performed only when V _{(c, n)} satisfies the following equation ₍₁₎ , and the obtained background measurement values are sequentially stored in the RAM 303. If the formula 1 is not satisfied, the current count repeat number C and the measured count number n are reset, and all background measurement values belonging to the count repeat number C stored up to that point are cleared.

(Equation ₁₎ | V _{(c, n)} -V _{(c, n-1)} | <Vs In other words, the CPU 302 obtains the obtained ground measurement value V _{(c, n).}
And whether the difference between the immediately preceding background measurement value V _{(c, n-1)} and the difference target value Vs is smaller than the difference target value Vs is determined. Only when this is true, the next background measurement value V ₍ The same counting operation is continuously performed for _{c, n + 1)} . When the measurement count number n reaches the upper limit value j, the CPU 302 determines that all the background measurement values V belonging to the count repeat number C
The average value of _{(c, n)} (average background measurement value Vc) is calculated and stored in RAM 303 together with clock timer time information Tc indicating the background measurement time when measurement count n = 1.

In the present embodiment, when the difference between successive background measurement values is larger than the difference target value, that is, when the background measurement value changes suddenly to a certain degree or more, severe damage to the background measurement point is made. Is formed, and formation of a toner mark in this area is avoided. In other words, the toner mark is formed only when the scratch on the surface of the transfer belt is less than a certain level.

Here, in the front view of the transfer belt viewed from the Z direction in FIG. 2, a rectangular spot shaded partially in a detection spot array P extending from the background measurement sensor 305 and parallel to the belt rotation direction. The area indicates an area where the CPU 302 has determined that the output of the toner mark can be corrected. This rectangle corresponds to the size and shape of the toner mark actually formed in the present embodiment.
In the rectangular area, the detection spot interval X ₁ V ₁
The length of the j detection spot rows arranged in the column corresponds to the length L of the toner mark along the belt rotation direction. In FIG. 2, toner mark formation positions are displayed for three positions where the repeat count number C of the detection area where a toner mark can be formed is (C = C, C + 1, C + 2). Further, the continuous background measurement values V _{(C + 3,1)} and V _{(C + 3,2)} close to the background measurement sensor 305 are measured and counted at the repeat count C = C + 3 in the state shown in FIG. The detection position of the measured value obtained by counting the number n is shown.

The CPU 302 stores the average background measurement value Vc corresponding to each count repeat number C and the background measurement time information of the measurement count number n = 1 in the RAM 303 until the count repeat number C reaches the upper limit value _Cmax. I do.
Subsequently, the CPU 302 stores the RAM stored as described above.
The following AIDC copy processing is executed based on each information in 303. Specifically, first, at the timing when the leading end of the measurement position on the transfer belt 58 where the measurement count number n = 1 of each average background detection value Vc reaches the transfer position of the photosensitive drum 51 by the rotation drive of the transfer belt 58. At the same time, a toner mark is formed on the peripheral surface of the photosensitive drum 51 and is transferred to a predetermined position on the transfer belt 58. In this case, the timing at which the toner mark is formed on the photosensitive drum 51 is determined based on the toner mark forming position and the transfer belt 5
Assuming that the circumferential length up to the transfer position to the position 8 is L, this corresponds to the case where the leading end reaches a position L upstream from the transfer position. Note that the CPU 302 performs R
The shape data of the toner mark stored in the OM 304 is sequentially read.

The toner density of the toner mark transferred onto the transfer belt 58 is measured by a toner density sensor 306, and the CPU 302 grasps the toner density as a measured toner density Mc corresponding to each count repeat number C on a one-to-one basis. You. The toner adhesion amount Rc is calculated for each toner mark each time the toner mark passes the detection position of the toner density sensor 306 by the rotation driving of the transfer belt 58, and based on the calculation result, the AIDC copy for the original image is performed. Processing is performed continuously. In the AIDC copy process, the CPU 302 adjusts the amount of toner adhered on the photosensitive drum 51 based on a program in the ROM 304.

The toner mark used for the AIDC copy process is erased by the belt cleaner 59. Further, the toner adhesion amount Rc value used for the density adjustment of the document image is also sequentially erased from the RAM 303. <Description of Operation> According to the above-described configuration, when commercial power is supplied to the copier by the user and the copier is started, first, the clock timer in the CPU 302 is started in the main routine of FIG. Internal fixing unit 7
Initial settings such as a temperature rise of 0 are made (S100). After the initial setting S100, the main routine goes through AIDC preprocessing S200 and AIDC copy processing S300, and waits for the clock timer to end (S400) and returns.

When the user selects copy start after starting the copying machine, the CPU 302 executes AIDC copy processing S
Prior to 300, AIDC pretreatment, ie, transfer belt 5
8 to execute the background measurement process (S200) of FIG.
The process proceeds to a subroutine of IDC pre-processing S200. In S201 of the subroutine, the CPU 302
It is determined whether or not the preprocessing end flag is set in a predetermined flag register in CPU 302. Where AID
The C pre-processing end flag indicates that the AIDC pre-processing S 200
Prior to the IDC process S300, the process is used by the CPU 302 to determine whether or not the process has been completely completed, and is erased when the main power of the copying machine is turned off. Therefore, in this case immediately after the startup, the CPU 302 confirms that the flag is not set.

Next, in S202, the CPU 302
It is determined whether or not the IDC pre-processing start flag is set in the CPU 302. The AIDC pre-processing start flag is
The background measurement processing of the transfer belt 58 is started, and the first
This indicates that the th background measurement has been made. Here, since the background measurement has not been started yet, the flag is set in S203 (AIDC pre-processing start flag ←
1) The transfer belt 58 is driven to rotate, and the count operation for the count repeat number C and the measured count number n is started (n ← 1, C ← C + 1). Then, the first background measurement is performed, and the measurement value V _{(c, 1)} obtained by the background measurement sensor 305 (n = 1 and C = 1 in this case ₎ is obtained.
V _(1,1) ) and the clock timer measurement time Tc, which is the measurement time at this time, are stored in the RAM 303. C
Thereafter, the processing of the PU 302 is returned to the main routine. It is to be noted that the count repeat number C and the measured count number n are naturally kept in a reset state before the start of the counting.

The processing shifts to the subroutine again, and S
If the CPU 302 confirms that the AIDC pre-processing start flag has been set at 202, then the CPU 3
02 advances the process to S204, delays the measurement by the detection interval X ₁ V ₁ (m / pulse) on the transfer belt 58 from the first background measurement time by using the clock timer, and performs the second background measurement. Take the measurement timing. When the timings are aligned, the CPU 302 updates the measurement count number n in step S205 (n ← n + 1), and measures the measured value V _{( c, 2) based} on the background measurement (in this case, C = 1 and n = 2, V _{(1, 2)} ), and this is stored in the RAM 303.

Subsequently, the CPU 302 calculates the background measurement value V _{(c, n)} (here, V _(1,2) ) just stored and the previously stored background measurement value V _{(c, n-1). )} (V _(1,1) here)
It is determined whether or not the difference with the difference is equal to or greater than the difference target value Vs (S
206). At this time, if the difference is equal to or greater than the difference target value Vs, the CPU 302 determines the clock timer time information Tc regarding the current count repeat number C stored in the RAM 303 and the count repeat number C
All background measurements _{V (c, 1) ~V (} c, n) to the corresponding clearing, and resets the measured count number n (n ← 0) to (S2
07). Accordingly, in a region where the difference between two consecutive background measurement values rapidly changes to be equal to or greater than the difference target value Vs, storage of the information is avoided.

FIG. 6 shows the background measurement sensor 30.
FIG. 5 is a diagram showing the background measurement signal of No. 5 in voltage, and showing the relationship between the measurement signal of this sensor and the position of the transfer belt from which the signal was obtained over the circumference of the transfer belt. As the figure shows,
The measurement value (voltage value) of the background measurement sensor 305 always changes in magnitude regardless of the position of the transfer belt 58.
The degree of this change is expressed as Vs when the difference target value Vs experimentally set for the difference between the background measurement values is used as a scale.
Transfer belt areas 601 to 607 having a smaller change amount;
It is divided into regions 608 to 612 in which the amount of change is larger than Vs. Of these, regions 608 to 6 where the amount of change is larger than Vs
Reference numeral 12 corresponds to a region where the difference between two successive background measurement values rapidly changes to be equal to or greater than the difference target value Vs. That is, S20
The processing of the CPU 302 at step 7 is to prevent the toner mark from being formed on the areas 608 to 612 where the change amount is larger than the difference target value Vs.

On the other hand, if it is determined in S206 that the difference is smaller than the difference target value Vs, the process proceeds to S208. Here, the CPU 302 determines whether or not the measurement count number n has reached the upper limit value j or more. If it is determined that the measurement count number n has not reached the upper limit value j or more, the control flow returns to the main routine again. This (S206 → S208)
→ Return to the main routine) is repeated until the measured count number n reaches the upper limit value j. During this time, in S206, the difference between the background measurement values is the difference target value V
If it is determined that the number is equal to or longer than s, all the information corresponding to the count repeat number C is cleared or reset (S207).

When the CPU 302 determines in step S208 that the measured count number n has reached the upper limit value j, the control flow proceeds to step S209, where the CPU 302 determines the average background measured value Vc (in this case, V ₁ ) is calculated and stored in the RAM 303. Then, in exchange for this storage processing, the CPU 302 determines the background measurement value Vc used for calculating the average background measurement value Vc.
_{(c, 1) to} V _{(c, n)} are cleared from the RAM 303, the measurement count number n is reset (n ← 0), and the count repeat number C is updated (C ← C + 1). That is, at this point, R
In the AM 303, the average background measurement value Vc and the clock timer time information Tc of the background measurement value V _{(c, 1)} used for calculating the average background measurement value Vc are stored in association with each other. .

Next, in S210, the CPU 302 determines whether or not the count repeat number C has reached the upper limit value _Cmax . Here, if it is determined that the count repeat number C has not reached _Cmax , the CPU 302 returns the control flow to the main routine as it is, but if it is determined that the count repeat number C has reached _Cmax , C
The PU 302 sets an AIDC pre-processing end flag internally (AIDC pre-processing end flag ← 1), and ends the AIDC pre-processing (S211). Thereafter, the control flow is S2
When the CPU 302 determines that the AIDC pre-processing end flag has been set in 01, the routine immediately returns to the main routine.

Subsequently, the CPU 302 advances the control flow to AIDC copy processing S300, and executes subroutine S3 in FIG.
01, where it is determined whether the AIDC preprocessing end flag is set inside the CPU 302 or not. At the stage when the AIDC pre-processing S200 has been completed, the flag has already been set, so that the CPU 302
Advances the flow to S302, and then determines whether the copier is currently in the middle of a copy process. Here, the copy processing is to form an electrostatic latent image on the photosensitive drum 51,
This shows a series of processes for forming a toner image and transferring the toner image onto a recording sheet. Therefore, since the copy processing has not been performed yet at this time, the CPU 302 proceeds to S30.
In step 3, the operation of the copy process is started.

Then, the CPU 302 next determines the circumferential length L from the scanning position on the circumferential surface of the photosensitive drum 51 from the writing optical system 40 to the transfer position at which transfer to the recording sheet is performed.
On the other hand, at the position on the transfer belt 58 which is upstream of the transfer position by the same distance as the distance L from the transfer position in the recording sheet conveying direction, the background measurement value V _(C It is determined whether or not the belt positions obtained _{in (1)} and ₍₂₎ match using the clock timer time information Tc of the skin average measurement value Vc stored in the RAM 303 (S304). This determination is for forming an electrostatic latent image of the toner mark on the photosensitive drum 51 in accordance with the transfer position of the toner mark. Above ground measurement value V _{(C, 1)}
If the obtained belt position is not at the L position, the CPU 302 advances the processing to S305.

In step S305, the CPU 302
It is determined whether information on the toner adhesion amount Rc is stored in 303. At this time, if it is determined that the information of the toner adhesion amount Rc is not stored, the CPU 302 proceeds to the next S
In step 306, a normal copy process, that is, a copy process in which no AIDC copy process is performed and a toner mark is not created is performed. On the other hand, if it is determined in step S305 that the information of the toner adhesion amount Rc is stored, the CPU 302 advances the process to step S311, where the AIDC copy process is performed while forming a toner mark based on the information of the toner adhesion amount Rc. Execute However, in this case, since the information of the Rc has not been stored in the RAM 303 yet, this S311
Does not shift to the control flow.

After executing the predetermined copy processing in S306 or S311, the CPU 302 next determines whether or not the toner adhesion amount of the toner mark is detected by the toner adhesion amount measurement sensor 306 (S307). If not detected, the control flow returns to the main routine. On the other hand, if it is determined that the detection has been made, the toner adhesion amount Rc information is stored in the RAM 303 (S312), and then the control flow returns to the main routine.

Next, the CPU 302 changes the control flow to S301.
→ proceed to S302 → S304, where the measurement count number n
= 1, the belt position where the background measurement value V _{(C, 1)} was obtained is L
If it is determined that the position coincides with the position, the process advances to step S308 to determine whether the AIDC copy start flag is set in the CPU 302. Here, the AIDC copy has not been started yet, and thus the flag is not set.
Stand in U302 (AIDC copy start flag ←
1) Perform normal copy processing and toner mark formation (S)
309).

After the AIDC copy start flag is once set, if it is determined in S304 that the leading end of the average background measurement value is located at the L position on the transfer belt 58, the CPU 302 executes a control flow. To S304
The process proceeds from S308 to S311 to perform AIDC copy processing and toner mark formation. That is, after the AIDC copy start flag is set, the RAM is selected in the AIDC pre-processing and RAM unless the main power of the copying machine is turned off.
Toner marks are sequentially formed at the detection positions of the average background measurement values Vc stored in the memory 303, whereby the AIDC copy process is performed for the entire number of times of copying specified by the user.

Although the toner shape is rectangular in the present embodiment, the present invention is not limited to this shape, but may be changed in size or by forming a mark of a shape conventionally used. Is also good. Also, the area where the toner mark is formed may be a linear area parallel to the belt width direction at the recording sheet conveyance interval as well as the area near the transfer belt width direction.

Further, an example in which a reflection type photosensor is used as the background measurement sensor and the toner adhesion amount detection sensor has been described, but a transmission type photosensor or an infrared sensor may be used instead. However, when a transmission type photosensor is used, naturally, the detection target member (transfer belt or transfer drum) must be basically made of a transparent material.

Further, in the present embodiment, an example has been described in which the background density of the transfer belt is measured before the copy processing is performed.
The background measurement processing may be performed during the copy processing, and a toner mark may be formed in this area to detect the toner adhesion amount. Further, in the present embodiment, an example has been described in which formation of a toner mark is avoided in an area where the background density changes abruptly. , The information of the toner adhesion amount may be invalidated.

Although an example in which a transfer belt is used in this embodiment has been described, the present invention is not limited to this, and may be applied to a case where a transfer drum is used. The present invention may be applied not only when a transfer belt or a transfer drum is used as a recording paper transporting body but also when these are used as a transfer intermediate. Further, when the number of toner marks to be formed (that is, the number of count repeats C = C _max ) is set to be small, it is not necessary to make the transfer belt make one round to search for an area suitable for forming toner marks. The background measurement process may be stopped when the transfer area of the number of toner marks is determined.

Further, in this embodiment, an example has been described in which the background measurement sensor and the toner adhesion amount measurement sensor are separately arranged, but these may be shared by one sensor.
However, in this case, it is necessary to provide the sensor downstream of the transfer position of the photosensitive drum and upstream of the belt cleaner, so that the background of the transfer belt or the transfer drum must be measured before performing the copy processing.

Further, in this embodiment, an example using a monochrome copying machine has been described, but the present invention is not limited to this, and may be applied to a color copying machine. In particular, for a tandem type color copying machine in which a plurality of photosensitive drums are arranged in series on a transfer belt, even if a toner adhesion amount measurement sensor is provided for each color, one sensor can measure the toner adhesion amount of all colors. It may be.

[0048]

As is apparent from the above, according to the present invention, the latent image of the reference pattern formed on the electrostatic latent image carrier is visualized by attaching toner with developing means and then transferred to a transfer belt or a transfer drum. In an image forming apparatus that automatically adjusts the image density by detecting the density of the reference pattern after transfer,
Before the transfer of the reference pattern, a background state detecting means for detecting a background state of the reference pattern transfer position on the rotating transfer belt or the transfer drum is provided, using the reference pattern density detection value and the background state detection value. , The image density is automatically adjusted.
Is performed, the amount of toner mark attached is detected according to the background level of the transferred position, and an appropriate AI
There is an effect that DC can be performed.

[Brief description of the drawings]

FIG. 1 is a front sectional view showing a main configuration of a digital copying machine as an application example of the present invention.

FIG. 2 is a front view of the transfer belt viewed from a Z direction.

FIG. 3 is a main routine of a CPU 302;

FIG. 4 is a subroutine of AIDC preprocessing.

FIG. 5 is a subroutine of AIDC copy processing.

FIG. 6 is a diagram illustrating a detection result of a background measurement sensor of the transfer belt.

[Explanation of symbols]

 Reference Signs List 51 photoconductor drum 59 belt cleaner 54 developing device 301 AIDC circuit 302 CPU 303 RAM 304 ROM 305 background measurement sensor 306 toner adhesion amount measurement sensor 540 power supply for bias 541 development sleeve

Claims (3)

[Claims] 1. A latent image of a reference pattern formed on an electrostatic latent image carrier is visualized by attaching toner with developing means,
In an image forming apparatus for transferring an image onto a transfer belt or a transfer drum and automatically adjusting the image density by detecting the density of the reference pattern after the transfer, the transfer belt or the transfer drum being rotated before the transfer of the reference pattern Image forming means for detecting a background state at the reference pattern transfer position, wherein the image density is automatically adjusted using the reference pattern density detection value and the background state detection value. apparatus. 2. The image forming apparatus according to claim 1, wherein the electrostatic latent image carrier is a photosensitive drum, and the background state detecting means sets a drum circumferential length from a drum surface position where a latent image of a reference pattern is formed to a transfer position to L. 2. The image forming apparatus according to claim 1, wherein in the case where the transfer is performed, the transfer belt or the transfer belt on the transfer belt surface is arranged at a position upstream of or equal to L from the transfer position. 3. The image forming apparatus according to claim 1, wherein said background state detecting means is also used as density detecting means for detecting the density of the transferred reference pattern.