JP2000284555A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve efficiency in a recording operation and also ensure image stability by disposing a detection means, which detects an image, onto a tertiary image carrier (secondary transfer roller) on which an image is secondarily transferred from a secondary image carrier (intermediate transfer belt). SOLUTION: This device comprises image forming parts 40C-40K arranged from the side of an intermediate transfer belt cleaner 105 and along the carrying side for a recording sheet S, and a secondary transfer roller 104 for secondarily transferring toner images on an intermediate transfer belt 103 to the recording sheet S. The images formed on the intermediate transfer belt 103 are secondarily transferred to the recording sheet S in the position of the secondary transfer member. Here, on the periphery of the secondary transfer roller 104, misalignment detectors RS1 and RS2 for the detection of the misalignment of the image transferred to the surface of the roller are disposed in a straight line in the direction of main scanning (direction orthogonal to the direction of carrying). They detect amounts of displacement of criss-cross register marks of respective colors transferred from the intermediate transfer belt 103 to the vicinity of both axial ends of the surface of the secondary transfer roller 104.

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 for forming an image on a transfer material such as paper in a color copying machine, a color printer, or the like, and detects an image recording position and density for controlling image formation. It is about.

[0002]

2. Description of the Related Art In recent years, with the spread of personal computers, the number of color recording documents has increased with the spread of personal computers, and color copiers and color printers have been demanded. In a so-called tandem type color image forming apparatus in which a plurality of photoconductors are arranged in parallel, an unfixed toner image of each color according to image information formed on the photoconductor is directly transferred to a recording sheet. For this reason, there has been a problem that image disturbance and color misregistration are likely to occur in a color image formed on the recording paper due to many factors such as the thickness and surface characteristics of the recording paper, and the transport characteristics to the photosensitive member.

Therefore, the color misregistration of a plurality of photoconductors is corrected,
In order to keep the density of each color at an appropriate level, a registration sensor and an AIDC (Auto Image Density Control) sensor are used, and correction control of image recording is performed based on the sensor output. Further, in a configuration in which a recording sheet is transported by a belt, a sheet feeding unit, an image forming unit, and a fixing unit are arranged in parallel with respect to a sheet passing path, and the size of the apparatus is increased.

A system using an intermediate transfer member (belt or the like) is known as a means for solving such an increase in the size of the apparatus. In this method, an unfixed toner image of each color is temporarily transferred to an intermediate transfer member by multiple transfer, and then the unfixed toner image is transferred to recording paper. In this method, since the paper feeding unit and the fixing unit are not arranged in parallel with the image forming unit, it is easy to reduce the size of the apparatus. In this intermediate transfer type color machine, a toner image pattern is recorded on an intermediate transfer belt, and the above pattern is read by a sensor or the like in order to stabilize the image and maintain a highly accurate multiplex image. The image recording control is performed based on this.

[0005]

However, in the above-described recording control in the intermediate transfer type image forming apparatus, since the pattern on the intermediate transfer belt is read by the sensor, if the belt fluctuates, the accuracy of the sensor output becomes low. become worse. Further, if the sensor is to be arranged on the photosensitive member side on the circumference of the intermediate transfer belt, the intermediate transfer belt must be enlarged by the arrangement of the sensor, and the apparatus becomes large.

When a sensor is arranged on the non-photosensitive member side,
Because of the intermediate transfer method, the secondary transfer roller must be separated from the intermediate transfer belt so that the pattern recorded for the test does not transfer onto the secondary transfer roller before reaching the sensor reading unit. Therefore, the impact noise when the secondary transfer roller is re-pressed to the intermediate transfer belt affects the image being recorded, and the image recording cannot be performed during the pressure contact or separation, which reduces the efficiency of the recording operation. Or

Further, the magnification of the image transferred to the paper depends on the nip portion of the secondary transfer portion, which also has the highest pressure. For this reason, the amount of biting of the pair of rollers in the secondary transfer changes due to an error in mounting the transfer roller or the like, a difference in manufacturing, or the like, resulting in a magnification shift or the like. Therefore, if the pattern is detected on the intermediate transfer belt, the magnification on the paper cannot be detected. Therefore, after actually recording, it is necessary for a serviceman, a user, or the like to perform magnification correction or the like based on the image.

[0008] Further, there has been known a method in which an image density on an intermediate transfer belt before transfer to a sheet is detected by a sensor to control the image density (see Japanese Patent Application Laid-Open No. 10-20579). Has the following problems: (1) Since an image before being transferred to a sheet is detected, there is a difference from an image actually transferred to a sheet. This is because there is a speed difference between the secondary transfer to the sheet and the intermediate transfer belt, a speed fluctuation, and a transfer deviation.
Therefore, it is preferable to detect an image closer to the final image. (2) Even when the secondary transfer roller has a greater dominant force with respect to the paper transport at the secondary transfer position (the secondary transfer roller grips the belt strongly against the paper / the secondary transfer roller (E.g., high speed), the same behavior as the above (1) occurs. (3) When the intermediate transfer member is formed by a belt, the detection accuracy of the sensor may deteriorate due to the fluttering of the belt. For this reason,
It may be necessary to prepare a plurality of sensors to cancel fluttering or the like.

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned problems, and to save the space and to secure the impact of the pressure contact of the member such as the secondary transfer roller while ensuring the efficiency of the image recording operation and the stability of the image. It is an object of the present invention to provide an image forming apparatus capable of achieving appropriate density control and proper registration correction without causing image noise and image magnification deviation due to image formation.

[0010]

In order to achieve the above object, a first aspect of the present invention is directed to a method for driving a plurality of rotating images while carrying an image.
A primary image carrier, a secondary image carrier that rotates while being in contact with the first image carrier, and a primary transfer that transfers an image carried by the first image carrier to a secondary image carrier A member that rotates while contacting with the secondary image carrier and conveys a recording medium;
A secondary image carrier, a secondary transfer member for transferring the image transferred to the secondary image carrier to the tertiary image carrier or a recording medium, and detecting the image transferred to the tertiary image carrier An image forming apparatus provided with a detecting unit.

In the above arrangement, the images on the plurality of primary image carriers are transferred onto the secondary image carrier by the primary transfer member, and the images on the secondary image carrier are further transferred to the secondary transfer member. Is transferred onto the tertiary image carrier. The tertiary image carrier conveys the recording medium carrying the final image at its transfer position, and moves at the same speed as the recording medium. Therefore, the image on the tertiary image carrier is equivalent to the image transferred to the recording medium. The detecting means detects such an image on the tertiary image carrier. Since the image is detected in this manner, it is not necessary to perform the pressing and separating operations of the secondary transfer member as in the related art, and it is possible to secure the efficiency of the recording operation, reduce the impact noise, reduce the cost by eliminating the separating mechanism, Space saving. The information about the image on the tertiary image carrier detected by the detection means is used for performing registration correction, density correction, and the like.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the secondary image bearing member and the tertiary image bearing member are pressed against each other, and the tertiary image bearing member at the contact position therebetween. The amount of deformation of the secondary image carrier is larger than the amount of deformation.

[0013] In this configuration, the secondary image carrier is 3
The hardness of the secondary image carrier is large, and the amount of deformation of the tertiary image carrier at the secondary transfer position is small. If the amount of deformation is reversed, the position of the tertiary image carrier (axial position in the case of a roller) and the position of the secondary image carrier (axial position in which the belt is run in the case of a belt) during product assembly If it varies, the distance from the axis to the secondary transfer position changes, so that the deformation amount and the peripheral speed of the tertiary image carrier at the secondary transfer position vary,
As a result, the paper transport speed at the secondary transfer position varies. Also, when the ladder chart of C, M, Y, and K is transferred onto the tertiary image carrier and detected by the detecting means, the pitch of the ladder chart varies from product to product and is calibrated. Control is required, or control for converting the pitch of the ladder chart detected by the detecting means into the pitch of the ladder chart actually transferred to the recording medium at the secondary transfer position is required.

On the other hand, according to the second aspect of the present invention, since the deformation (change in diameter) of the tertiary image carrier is reduced, the conveyance speed of the recording medium does not vary. Further, since the difference between the diameter of the tertiary image carrier at the secondary transfer position and the diameter at the detection position by the detection means is small, it is possible to omit the control for calibration and conversion.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, the secondary image bearing member and the tertiary image bearing member are pressed against each other, and the secondary image bearing member is located at the contact position therebetween. And a signal correction control circuit for correcting the detection signal from the detecting means in accordance with the amount of deformation of the tertiary image carrier. In this configuration, as described above, it is necessary to convert the data to the data actually transferred to the recording medium at the secondary transfer position, and the signal correction control circuit has the function. That is,
The detection means detects a color misregistration pattern such as a ladder chart, and the signal correction control circuit calculates a color misregistration amount due to a difference in magnification of each color or a misregistration of a recording start position from the detected relative position error of each color. The color misregistration is corrected by correcting the pixel address position of, or by correcting the transport speed of the recording medium.

According to a fourth aspect of the present invention, in the image forming apparatus of the first aspect, the tertiary image carrier is a roller, the detecting means is an optical sensor, the radius of the roller is r, and the detection spot of the optical sensor is When the diameter is s, these relations are set to r−√ (r ＾ 2 ＾ × s ＾ 2) <0.2. In this configuration, even if the detection is dependent on the distance between the central portion of the sensor and the end portion of the sensor, the reading error falls within the allowable range, and the image can be detected with high accuracy.

According to a fifth aspect of the present invention, in the image forming apparatus according to the first aspect, the detecting means includes an AI for measuring an image density.
It also serves as a DC sensor and a registration sensor for measuring the deviation of the image recording position from the reference position. As a result, one type of sensor can perform a plurality of functions, and space is saved.

According to a sixth aspect of the present invention, in the image forming apparatus according to the first aspect, the transfer electric field output when the image on the secondary image carrier is secondarily transferred is transferred to a recording medium when the image is transferred to a recording medium. The value is different from that at the time of transfer to the carrier. In this configuration, when the image on the secondary image carrier is secondarily transferred, there is a case where the recording medium (paper or the like) is present and a case where the recording medium is not present.
If the transfer electric field output voltage is the same due to the resistance component of the recording medium, the transfer current greatly changes, which is not preferable. However, this point is solved by reducing the transfer electric field output when transferring to the tertiary image carrier. You.

According to a seventh aspect of the present invention, in the image forming apparatus of the first aspect, the surface roughness of the tertiary image carrier is set to Rmax3.
2 (μm) or less. Thereby, the accuracy of image detection can be appropriately maintained.

According to an eighth aspect of the present invention, in the image forming apparatus of the first aspect, the primary image carrier is a photosensitive member, the secondary image carrier is an intermediate transfer belt, and the primary transfer member is a transfer roller. The tertiary image carrier and the secondary transfer member also serve as a secondary transfer roller, and control the formation of a latent image on the photosensitive member based on a detection signal from a detection unit. In this configuration, the secondary transfer roller also functions as the tertiary image carrier and the secondary transfer member, so that the configuration can be simplified and the space can be saved.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An image forming apparatus according to an embodiment of the present invention will be described below with reference to a tandem type color digital copying machine (hereinafter, simply referred to as "copying machine"). Figure 1
Indicates the configuration of the entire copying machine. The copying machine includes an image reader unit 10 for reading a document image, and a printer unit 20 for printing the read image on a recording sheet S (recording medium) and reproducing it. Image reader unit 10
Is a known device that reads an image of a document placed on a document glass plate (not shown) by moving a scanner. The document image is composed of red (R), green (G), and blue (B). After being separated into three colors, a CCD image sensor (not shown)
(Referred to as a D sensor), thereby obtaining R, G, and B image data of the document.

The image data for each color component obtained by the image reader section 10 undergoes various data processing in the control section 30 and further undergoes cyan (C), magenta (M), yellow (Y), and black (K ) (Hereinafter, cyan, magenta, yellow, and black reproduced colors are represented as C, M, Y, and K, and the numbers of the components related to each reproduced color are represented by C , M, Y, and K are added as subscripts).

The image data is stored in the image memory 33 in the control unit 30 for each reproduced color, and after undergoing necessary image correction for positional deviation correction, performs one scan in synchronization with the supply of the recording sheet S. It is read out line by line, and the exposure scanning unit 70
C, 70M, 70Y, and 70K are driving signals for the light emitting diodes. The printer unit 20 forms an image by an electrophotographic method. An intermediate transfer belt 103 (secondary image carrier) is stretched between rollers 101 and 102, and faces the intermediate transfer belt 103. Each of C, M, Y, and K colors arranged at predetermined intervals from the intermediate transfer belt cleaner 105 side (hereinafter, referred to as an upstream side) to a recording sheet S transport side (hereinafter, referred to as a downstream side). Image forming units 40C to 40K and a secondary transfer roller 10 for secondary transferring the toner image on the intermediate transfer belt 103 to the recording sheet S
4 (a secondary transfer member and a tertiary image carrier);
An intermediate transfer belt cleaner 105 for removing residual toner on the intermediate transfer belt 103;
And a known fixing unit 80 disposed on the downstream side.

Each of the image forming units 40C to 40K includes a transfer roller 45 for transferring the toner image on each of the photosensitive drums 41C to 41K (primary image carrier) to the intermediate transfer belt 103.
C to 45K (primary transfer member) and exposure scanning units 70C to 7C
0K and image processing units 60C to 60K. The exposure scanning units 70C to 70K are provided with the control unit 30.
A light emitting diode or a semiconductor laser that emits light in response to a drive signal output from the device. Image processing unit 60
C to 60K are photosensitive drums 41C to 41K and charging chargers 42C to 42C arranged around the photosensitive drums 41C to 41K.
42K, developing units 43C to 43K, and cleaners 44C to
44K or the like.

The paper supply unit 50 is provided with a recording sheet S (recording medium,
Paper cassette 51 for storing paper or paper)
And a paper feed roller 52 for feeding out the recording sheet S from the paper feed cassette 51, and a registration roller 53 for setting the timing for feeding out the recording sheet S to the intermediate transfer belt 103. A sheet detection sensor SE1 for detecting the leading edge of the sheet S is provided.

The leading end of the recording sheet S is a registration roller 53
Is detected by the sheet detection sensor SE1, the control unit 30 receives the detection signal and takes a timing to transmit a leading end registration roller signal to a driving unit (not shown) of the registration roller 53. The sheet feeding by the registration rollers 53 is started, and the recording sheet S is sent toward the intermediate transfer belt 103.

The light emitting diodes of the exposure scanning units 70C to 70K receive the drive signal from the control unit 30 and emit light, respectively, and this light exposes and scans the surfaces of the photosensitive drums 41C to 41K, respectively. Photoconductor drums 41C to 41
Before receiving the exposure, K is cleaned by removing residual toner on the surface with cleaners 44C to 44K, further irradiating an eraser lamp (not shown), and then uniformly charged by charging chargers 42C to 42K. When the light-emitting diode is exposed to light with the uniformly charged state, an electrostatic latent image is formed on the surfaces of the photosensitive drums 41C to 41K.

Each electrostatic latent image is developed by a developing unit 43 of each color.
C to 43K, thereby developing the photosensitive drum 4
C, M, Y, and K toner images are formed on the surfaces 1C to 41K, a voltage is applied to the transfer rollers 45C to 45K, and the toner images on the respective photosensitive drums are sequentially transferred onto the intermediate transfer belt 103. Go. At this time, the image forming operation of each color is executed with a timing shifted from the upstream side to the downstream side so that the toner image is transferred to the same position on the intermediate transfer belt 103 being conveyed in a superimposed manner. The image formed on the intermediate transfer belt 103 is transported to the position of the secondary transfer member, where the secondary transfer is performed on the recording sheet S.

Recording sheet S on which toner images of each color have been transferred
Is transported to the fixing unit 80 and is pressurized with high heat so that the toner particles on the surface of the recording sheet S are fused and fixed to the surface of the recording sheet S, and then discharged onto the paper discharge tray 81.

Next, the secondary transfer section will be described. On the periphery of the secondary transfer roller 104, two displacement detectors RS1 and RS2 (detection means) for detecting the displacement of the image transferred on the roller are provided in the main scanning direction (perpendicular to the transport direction). (The direction in which the secondary transfer roller 103 is moved) from the intermediate transfer belt 103 to the secondary transfer roller 1.
The positional deviation amounts of the cross registration marks 111C and 111M (FIG. 2) of each color transferred near the both ends in the axial direction on the reference numeral 04 are detected. The secondary transfer roller 104 is provided with a cleaning device 106,
The cleaning device 106 includes a cleaning blade for scraping the toner on the secondary transfer roller 104 and a box unit for storing the scraped toner.

FIG. 2 shows the configuration of the displacement detector RS1. As shown in the figure, the displacement detector RS1 is composed of a convex lens 120 and a CCD sensor 121. CCD
The CCD pixels 122 of the sensor 121 are arranged in the main scanning direction, and the images of the center points (cross points) of the registration marks 111C and 111M (pattern) transferred onto the secondary transfer roller 104 are collected by the convex lens 120. The light is emitted and detected by a predetermined CCD pixel 122. Which C
Since the position of the center point of the registration mark in the main scanning direction can be known from the detection of the CD pixel 122, the control unit 30 determines the main point of the registration mark from the difference between the positions of the center points of the registration marks 111C and 111M. The amount of displacement in the scanning direction is obtained. Since the CCD sensor 121 can also detect the image density, the detector RS1
Also serves as a DC (image density) sensor. Since the other displacement detectors RS2 have the same configuration, the description is omitted.

In this embodiment, the detectors RS1, RS
2, the CCD sensor 121 is shown. However, as another example, a reflection type sensor or the like that can identify the image density and color based on the intensity of reflected light such as a CTD (color toner density) sensor may be used. Good.

Next, referring to FIG. 3 and FIG.
1 and RS2 will be described. Detectors RS1, R
S2, as shown in FIGS. 3A and 3B, when the radius of the secondary transfer roller 104 is r, and the detection spot diameter of the detector (optical sensor) is s, these relations are expressed by the following equation. Like

## EQU1 ## r-＾ (r ＾ 2-1 / 4 × s ＾ 2) <0.2

That is, in this way, the difference between the focal lengths of the sensor center portion and the sensor end portion is always within 0.2 mm, so that the distance dependency of detection between the sensor center portion and the sensor end portion is reduced. Even if there is, the reading error of the sensor always falls within the allowable value and the pattern can be read with high accuracy, based on the sensitivity characteristics of the sensor shown in FIG.

Next, the secondary transfer density control will be described. To transfer the image density and the resist pattern on the intermediate transfer belt 103 onto the secondary transfer roller 104,
The voltage value applied to the secondary transfer roller 104 is set from +500 V to +3 KV by constant current and constant voltage control.

FIG. 5 shows a configuration for setting the secondary transfer application voltage. A CPU 121 for setting a secondary transfer application voltage is provided. When the power is turned on, the CPU 121 sets the switch circuit 122 to a constant current source while the secondary transfer roller 104 is in pressure contact with the secondary transfer belt 103. Switching to the 123 side, a constant current of, for example, 6 μA is generated from the constant current source 123. At that time, the voltage generated in the constant current source 123 is detected by the voltage detection circuit 124, and the detected voltage Vre
f is given to the CPU 121. The CPU 121 holds the detected voltage Vref, and when starting a printing operation, measures an absolute humidity by using an environment sensor (not shown), and compares the absolute humidity with the held detected voltage Vref.
And an optimum transfer voltage is selected based on
2 is switched to the constant voltage source 125 side to output a predetermined transfer voltage from the constant voltage source 125, and the transfer voltage is
04.

With the above-described secondary transfer application voltage setting, the transfer electric field output when the image on the intermediate transfer belt 103 (secondary image carrier) is secondarily transferred is transferred to the recording sheet S and to the secondary transfer. The value is different when the image is transferred to the roller 104. That is, when the image on the secondary image carrier is transferred to the secondary transfer roller 104 at the time of the secondary transfer, the transfer electric field output voltage is transferred to the recording sheet S because there is no resistance component of the recording sheet S. If this is the case, a large transfer current results. Therefore, when transferring to the secondary transfer roller 104, the transfer electric field output is reduced so that an appropriate transfer current is obtained.

Next, the influence of the deformation of the roller contact at the secondary transfer portion on the transfer will be described. Now, the intermediate transfer belt 103 (secondary image carrier) and the secondary transfer roller 10
4 (tertiary image carrier) and 2 at their contact position.
From the deformation amount of the next transfer roller 104, the intermediate transfer belt 10
If the deformation amount of No. 3 (involving the roller 101) is larger, the change in the diameter of the secondary transfer roller 104 is reduced, so that the paper conveyance speed does not vary. The diameter of the secondary transfer roller 104 at the secondary transfer position and the sensor RS
Because the difference from the diameter at the detection position by RS1 and RS2 is small,
Calibration and conversion control can be omitted.

On the contrary, if the deformation amount of the secondary transfer roller 104 is larger than the deformation amount of the second intermediate transfer belt 103 at the secondary transfer contact position, the shaft of the secondary transfer roller Position and Intermediate Transfer Belt 10
When the axial position of the third roller 101 varies, 2
Since the distance to the next transfer position changes, the amount of deformation and the peripheral speed of the secondary transfer roller 104 at the secondary transfer position fluctuate, and the paper transport speed at the secondary transfer position varies. Also, on the secondary transfer roller 104, C, M, Y,
Even when a ladder chart (registration mark) of K is transferred and detected by a sensor, the pitch of the ladder chart varies from product to product, and control for calibrating the pitch is required. Is required to be converted to the pitch of the ladder chart actually transferred to the sheet at the secondary transfer position.

In the case described above, the correction control of the detection data (color shift data) when the secondary transfer roller 104 is elastically deformed will be described with reference to FIGS. In FIG. 6, if the secondary transfer roller 104 is not driven, the transport force in the secondary transfer is insufficient, and the paper cannot be transported accurately. In addition, when the secondary transfer is driven, the peripheral speed at the secondary transfer nip becomes slower by the radius of the bite amount. Therefore, it is necessary to detect the bite amount of the secondary transfer and correct the roller speed by the radius. There is. Therefore, a bite amount detection mode (see the flowchart in FIG. 9) is provided to detect and correct the bite amount of the roller. The device includes a signal correction control circuit that corrects the detection signal from the sensor according to the bite amount (deformation amount). In the bite amount detection mode, the drive of the secondary transfer, which is normally transmitted from the outside and is independently driven, is separated using a clutch or the like. Then, the secondary transfer roller 104 is driven by the intermediate transfer belt 103.

The function of the signal correction control circuit is as follows.
0 (FIG. 1) or the like. here,
The relationship between bite amount detection, color shift detection, and color shift correction will be described. In the color misregistration correction control, as described above, the color misregistration detection pattern including the ladder chart and the cross pattern is secondarily transferred, and is transferred to the position misalignment detectors RS1 and RS.
Detect at 2. Then, based on the relative position error of each pattern of cyan (C), magenta (M), yellow (Y) and black (K), the overall magnification difference in the main scanning direction and sub-scanning direction of each color, and the deviation / The amount of color misregistration such as the pixel position periodic fluctuation due to skew / pixel position deviation at a specific position / transport speed fluctuation is calculated, and based on the result, C, M, and C on the image memory 33 (FIG. 1) are calculated. Y, K
, And correction of the transport speed of the recording medium. As a result, color shift correction can be performed.

In performing such color misregistration correction control, misregistration detection is performed for a recording start misalignment in the sub-scanning direction, a magnification difference in the sub-scanning direction, a pixel misalignment at a specific position in the sub-scanning direction, and the like. The values detected by the devices RS1 and RS2 indicate that when the amount of bite on the secondary transfer roller varies,
fluctuate. Therefore, by accurately detecting the bite amount and performing correction in consideration of the bite amount to the color shift detection value, accurate color shift detection data can be obtained and color shift can be reduced.

The following describes the bite amount detection mode described above. In the same mode, the secondary transfer roller 1
As for the pattern transferred on 04, as shown in FIG. 6, an image formed at a pitch of P on intermediate transfer belt 103 is transferred at the same pitch. When the secondary transfer roller 104 passes through the nip portion, the pitch interval extends to P1 because the secondary transfer roller 104 is an elastic body. The image formed on the intermediate transfer belt 103 is transferred at the nip at a speed of R1 × ω (where R1 is the radius of the radius R of the secondary transfer roller 104 at the nip, and ω is the angular velocity). However, at the location where the pattern is detected by the sensor, since the speed is R × ω, the pitch interval P1 is as follows.

P1 = P × (R × ω) / (R1 × ω) = P × R / R1

Now, assuming that the bite amount of the secondary transfer roller 104 is K, since K = R−R1, R1 = R−R
K, and the secondary transfer roller 104 itself also has a tolerance in diameter. If the deviation of the diameter due to the tolerance is ΔR, the pitch interval P1 is as follows.

P1 = P × (R + ΔR) / (R1 + ΔR)

Here, as an embodiment, R = 12 (mm)
Then, the image elongation magnification R / R1 becomes as shown in FIG. 7 due to the diameter tolerance and the amount of the secondary transfer bite. Further, the relationship between the diameter of the secondary transfer roller and the magnification of image elongation at each bite amount is as shown in FIG.

The diameter tolerance of the actual secondary transfer is ± 0.06, and there is almost no difference due to the diameter tolerance of the secondary transfer. Therefore, for example, when a pitch pattern of 1 mm is formed on the belt, the pitch pattern is set to 1.
When it is detected that the pitch is 025 mm, it can be determined that the secondary transfer is 0.3 mm deep (marked in FIG. 7). Therefore, when carrying out the transport speed correction, 2
Assuming that the next transfer roller 104 is rotating at ω0, when the bite amount is K, the corrected rotation ω1 is changed to ω1 = R
/ R1ω0.

FIG. 10 shows a correction value detection pattern. The arrow is the transport direction. This pattern may be created with one of the four colors of the normal EP process, but in this example, the pattern was created with cyan since the surface color of the secondary transfer roller 104 is black.

Another embodiment will be described with reference to FIG. The pattern formed on the intermediate transfer belt 103 is held between the intermediate transfer belt 103 and the secondary transfer roller 104 at the entrance of the nip. At the entrance of the nip, the radius of the secondary transfer roller 104 is the same as that of the sensor reading unit, so that the radius is always constant irrespective of the amount of bite in the secondary transfer. Nevertheless, the reason why the image magnification is shifted due to the nip bite amount is that the transfer to the secondary transfer roller 104 at the place where the nip thickness is the strongest is dominant, and dominates at other places within the nip. It is considered that the reason is that slippage occurs between the intermediate transfer belt 103 and the secondary transfer roller 104. Therefore, even if the pitch interval of the pattern is not shifted, the pitch line width is widened (narrowed) depending on the bite amount.

Therefore, by detecting the B / W ratio of the line width (the ratio of the base portion to the image portion), that is, the density, by the sensor, the bite amount of the secondary transfer can be detected. That is, when the bite amount is, for example, 0.4 mm, the image density is high, and when the bite amount is 0.2 mm, the image density is low. FIG. 12 shows the relationship between the amount of secondary penetration and the pattern density.

The S of the detection signal by the displacement detector
In order to increase / N, it is desirable to employ an appropriate sensor according to the surface state (mirror surface, black, rough surface, etc.) of the secondary transfer roller 104. Hereinafter, the use of the CTD sensor as the position shift detector will be described. CTD
The sensor can simultaneously detect the specularly reflected light P wave and the irregularly reflected light S wave. A general reflection sensor can detect only regular reflection light. FIG. 13 shows the output characteristics of the P, S, and P-S waves by the CTD sensor with respect to the toner concentration. Since the irregular reflection component is included in the regular reflection light, an error occurs in a measured value such as a toner density and a position depending on a base material and a type of the detected object. By using the CTD sensor, the P wave and the S wave are detected, and by calculating the PS wave, it is possible to extract only an accurate specular reflection component.

It should be noted that the present invention is not limited to the configuration of each of the above embodiments, but can be variously modified. For example, in the embodiment of FIG. 1, a tertiary image carrier (secondary transfer) Although the roller 104) and the secondary transfer member are formed of the same member, they may be formed of different members.
Although two detectors RS1 and RS2 are arranged in a direction orthogonal to the transport direction, one detector may be used. In the case of two rollers as in the present embodiment, it can be determined from both detection outputs whether the axial direction of the roller is appropriate or whether the image has a skew deviation at both ends in the direction orthogonal to the transport direction, and corrects image formation. It is possible to do.

It is desirable that the surface roughness of the secondary transfer roller 104 be Rmax 3.2 (μm) or less from the viewpoint of image detection accuracy. Also, the secondary transfer roller 10
Reference numeral 4 denotes a soft roller (a core bar coated with conductive rubber), and a roller 101 is a combination of a hard roller (a core bar grounded through high resistance). The roller 101 is a combination of a hard roller (a metal core coated with conductive rubber), the secondary transfer roller 104 and the roller 101 are soft rollers, and the rubber hardness is different. Various forms can be adopted, such as one in which the transfer roller 104 and the roller 101 are soft rollers and the rubber layer thickness is different, and those in which the secondary transfer roller 104 and the roller 101 are soft rollers and the number of rubber foam cells and the diameter are different.

[0053]

As described above, according to the present invention, the image is
By arranging detection means for detecting an image on a tertiary image carrier (secondary transfer roller) to which secondary transfer is performed from a next image carrier (intermediate transfer belt), it is possible to perform image detection as in the related art. There is no need to separate the tertiary image carrier from the secondary image carrier, so that image noise due to the impact of the secondary transfer pressure contact can be reduced, and there is no time for the pressure contact and separation, thereby improving the efficiency of the recording operation. Thus, the stability of the image can be ensured. Further, since the detecting means is not disposed on the circumference of the secondary image carrier (intermediate transfer belt), the space of the apparatus can be saved. In particular, in the tandem process of the intermediate transfer system, the effect of stabilizing an image is remarkably obtained while saving space and increasing efficiency.

[Brief description of the drawings]

FIG. 1 is a sectional view of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a detector used in the apparatus.

3A is a detailed configuration diagram of the detector, and FIG. 3B is an enlarged view thereof.

FIG. 4 is a sensitivity characteristic diagram of a detector.

FIG. 5 is a circuit configuration diagram for controlling secondary transfer constant current and constant voltage.

FIG. 6 is an explanatory diagram of a secondary transfer roller unit according to one embodiment.

FIG. 7 is a diagram illustrating an image expansion magnification in the embodiment of FIG. 6;

FIG. 8 is a diagram showing a relationship between a secondary transfer diameter and a bite amount in the embodiment of FIG. 6;

FIG. 9 is a flowchart of a pattern pitch correction process based on bite amount detection in the embodiment of FIG. 6;

FIG. 10 is a diagram showing a correction value detection pattern.

FIG. 11 is an explanatory diagram of a secondary transfer roller unit according to still another embodiment.

FIG. 12 is a diagram illustrating a relationship between a secondary transfer bite amount and a pattern density.

FIG. 13 is a characteristic diagram of the CTD sensor.

[Explanation of symbols]

41C, 41M, 41Y, 41K Photoconductor drum (primary image carrier) 45C, 45M, 45Y, 45K Transfer roller (primary transfer member) 103 Intermediate transfer belt (secondary image carrier) 104 Secondary transfer roller (3 Secondary image carrier, secondary transfer member) RS1, RS2 misalignment detector (detection means) S recording sheet (recording medium)

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2H027 DA09 DA20 DE02 DE07 DE10 EA18 EA20 EB04 EC04 EC06 EC09 EC11 EC12 ED03 ED24 EE03 FD08 2H030 AA01 AB02 AD16 AD19 BB02 BB23 BB42 BB46 BB54 BB56

Claims (8)

[Claims] 1. A plurality of primary image carriers that rotate while carrying an image, a secondary image carrier that rotates while being in contact with the first image carrier, and a carrier of the first image carrier A primary transfer member that transfers an image to be transferred to a secondary image carrier, a tertiary image carrier that rotates while contacting with the secondary image carrier, and conveys a recording medium; An image forming apparatus comprising: a secondary transfer member that transfers a transferred image to the tertiary image carrier or a recording medium; and a detection unit that detects the image transferred to the tertiary image carrier. apparatus. 2. The secondary image bearing member and the tertiary image bearing member are pressed against each other, and the secondary image bearing member and the tertiary image bearing member are in contact with each other.
2. The image forming apparatus according to claim 1, wherein the deformation amount of the secondary image carrier is larger than the deformation amount of the secondary image carrier. 3. The secondary image carrier and the tertiary image carrier are pressed against each other, and the secondary image carrier and
A signal correction control circuit for correcting the detection signal of the detection means in accordance with the deformation amount of the tertiary image carrier, wherein the deformation amount of the tertiary image carrier is larger than the deformation amount of the secondary image carrier. The image forming apparatus according to claim 1, further comprising: 4. When the tertiary image carrier is a roller, and the detecting means is an optical sensor, and the radius of the roller is r, and the detection spot diameter of the optical sensor is s, these relations are determined. 2. The image forming apparatus according to claim 1, wherein r-√ (r ＾ 2−1 / 4 × s ＾ 2) <0.2. 5. The image forming apparatus according to claim 1, wherein said detecting means measures an image density.
2. The image forming apparatus according to claim 1, wherein the image forming apparatus also serves as an IDC sensor and a registration sensor for measuring a deviation of an image recording position from a reference position. 6. A transfer electric field output at the time of secondary transfer of the image on the secondary image carrier, and a transfer electric field output at the time of transfer to a recording medium.
2. The image forming apparatus according to claim 1, wherein the value is different from when the image is transferred to the next image carrier. 7. The surface roughness of the tertiary image carrier is defined as Rmax
2. The image forming apparatus according to claim 1, wherein the thickness is 3.2 (μm) or less. 8. The primary image carrier is a photoreceptor, the secondary image carrier is an intermediate transfer belt, the primary transfer member is a transfer roller, the tertiary image carrier and the secondary image carrier are
2. The image forming apparatus according to claim 1, wherein a secondary transfer roller also serves as a secondary transfer member, and controls formation of a latent image on the photosensitive member based on a detection signal from the detection unit.