JP2000221749A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the occurrence of color smear due to the unevenness of rotation caused independently of each of plural image carriers in an image forming device by which an image is formed by superimposing and transferring images formed on plural image carriers. SOLUTION: In this image forming device, image patterns 50C to 50K that are image patterns where a multiple number of specified line segments are installed at equivalent time intervals on the plural image carriers and where only one line segment among the plural line segments included in one cycle of an image pattern corresponding to one rotation of the image carrier is different in characteristic from the other line segments are each formed. Then, the unevenness in the rotation generated in the plural image carries are detected based on the detected result from an optical sensor unit 28 for each image pattern formed above. Next, the rotation of each image carrier is controlled so that phases of unevenness in rotation generated in each of the multiple number of image carriers is made equivalent based on the detected unevenness in rotation.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image forming apparatus for forming an image by multiply transferring images formed on a plurality of image carriers, respectively.

[0002]

2. Description of the Related Art In recent years, various types of full-color image forming apparatuses have been developed. One of the methods for forming a full-color image which is currently becoming mainstream is a method called a tandem method. In a tandem-type image forming apparatus, an image to be formed is generally represented by cyan (C), magenta (M), yellow (Y), and black (K) reproduction colors (hereinafter, each reproduction color is represented by C , M, Y, and K, and portions corresponding to the respective reproduced colors are C,
It is represented by adding the subscripts of M, Y, and K. ), A toner image is formed on a plurality of image carriers provided for each of the reproduced colors, and then these are multiply transferred to form a full-color image. Therefore, if the transfer position shifts between the toner images formed in the respective colors, even if it is a shift of several pixels, the color shift will occur, and the image quality will be extremely deteriorated. The biggest issue is how to reduce it.

Therefore, in a tandem type image forming apparatus, conventionally, a pattern of each color formed in a predetermined shape by an image forming unit corresponding to each color on a transfer material conveying belt (hereinafter, simply referred to as “conveying belt”). It is formed at a predetermined position, and this is detected by an optical sensor or the like, thereby estimating the amount of position shift that occurs, and changing the image forming position on each of the image carriers according to the estimated result. The so-called registration correction for correcting the displacement is performed.

[0004]

However, in the above-described registration correction, the cause of the positional shift is uneven rotation caused by eccentricity of the drive shaft of each photosensitive drum generally used as an image carrier. In some cases, there is a problem that appropriate correction may not be performed. Less than,
A case where the displacement due to the rotation unevenness cannot be properly corrected will be specifically described with reference to the drawings. FIG. 9 is a diagram for describing the occurrence of positional deviation when independent rotation unevenness occurs on the K photoconductor drum and the Y photoconductor drum in the conventional tandem image forming apparatus. is there.

FIG. 1A shows the effect of uneven rotation occurring on the K photosensitive drum. FIG.
In the graph, the graph (KG) represents the rotation speed fluctuation of the photosensitive drum due to the rotation unevenness occurring on the K photosensitive drum. (KI) is the shape of a resist correction pattern formed on the surface of the K photoconductor drum by a laser diode (hereinafter abbreviated as “LD”) for exposing the K photoconductor drum, and This represents the formation timing. As shown in the figure, in this example, as the registration correction pattern, a line segment of the same shape having a predetermined length in the main scanning direction and the sub-scanning direction (hereinafter, the length in the main scanning direction is referred to as “length”) , The length in the sub-scanning direction is referred to as “width”) at regular time intervals.

On the other hand, (K-II) shows a line which is actually formed as an electrostatic latent image (toner image after development) on the surface of the photosensitive drum due to uneven rotation of the K photosensitive drum. This indicates that a deviation occurs at the minute position. That is, if there is no rotation unevenness, the position represented by the narrower line segment in FIG.
As in the case of I), the electrostatic latent images should be formed at regular intervals. However, the positions where the electrostatic latent images are actually formed are not regular intervals but are represented by thicker line segments. This means that each line segment image is formed at the set position.

The reason why such a deviation of the image forming position occurs is as follows. That is, in the graph of (KG) in the same figure, in the portion where the rotation speed V is higher than the predetermined speed, the interval between the line segments is wider than the predetermined interval, while the rotation speed V is lower. In a portion where the speed is lower than the predetermined speed, the interval between the line segments becomes narrower than the predetermined interval. In addition, since the speed fluctuation due to the eccentricity of the rotating shaft appears periodically as one cycle of the photosensitive drum in principle, at a predetermined position in the one cycle, an ideal image forming position and an ideal image forming position are determined. (The positions indicated by BP1 to BP3 in the figure).

[0008] Regarding these, the same can be said for FIG. 1B showing the same phenomenon that occurs in the Y photosensitive drum. Here, by the conventional registration correction, the timing of Ka in the graphs of FIGS. (A) and (K-G) (the same as the timing of Yb in the graphs of FIGS. (B) and (Y-G), hereinafter referred to as this timing) In the "correction timing"), the K and Y image forming positions on the photosensitive drum surface were corrected so that no deviation occurred between the image forming positions of the formed K and Y registration marks. Then, although the positional deviation at the correction timing is certainly eliminated, the positional deviation amount increases as the distance from the correction timing increases. FIG.
FIG. 4 is a diagram showing an increase in the amount of displacement.

As shown in FIG. 1, the rotation speed of the K photoconductor drum gradually decreases after the correction timing, so that the interval of the line segment to be formed gradually increases. Become. On the other hand, since the rotation speed of the Y photoconductor drum gradually increases after the correction timing, the interval of the line segment for Y gradually narrows. As described above, the relative positional deviation amount between the colors gradually increases after the correction timing elapses due to the rotation unevenness that occurs independently on the K and Y photoconductor drums. In such a case, it is not possible to appropriately prevent color misregistration by conventional resist correction.

The present invention has been made in view of the above problems, and can prevent the occurrence of color misregistration caused by rotational unevenness which can occur independently on a plurality of image carriers. It is an object to provide an image forming apparatus.

[0011]

In order to solve the above problems, an image forming apparatus according to the present invention comprises a plurality of image carriers,
An image forming apparatus that forms an image on said plurality of image carriers by image writing means and forms an image by multiple transfer of the images, wherein the image writing apparatus is controlled to control the plurality of image carriers. On the body, pattern forming means for respectively forming a predetermined image pattern, pattern detecting means for detecting the image pattern formed by the pattern forming means, respectively, based on the result of detection by the pattern detecting means, Rotation unevenness detecting means for respectively obtaining information on rotation unevenness occurring on each of the plurality of image carriers; and rotation unevenness occurring on each of the plurality of image carriers based on the information obtained by the rotation unevenness detecting means. Control means for controlling the rotation of each image carrier so that the phases of the predetermined image patterns are equal. An image pattern formed by arranging a plurality of predetermined line segments at equal time intervals, wherein one of a plurality of line segments included in one cycle of the image pattern corresponding to one rotation of the image carrier; Only, so that it can be distinguished from other line segments from the result of detection by the pattern detection means,
It is characterized in that it is an image pattern in which predetermined attributes are different.

With this configuration, even when rotation unevenness occurs independently on a plurality of image carriers, the phases of the rotation unevenness can be made equal. Therefore, in the multiple transfer of the toner images formed on the surfaces of the plurality of image carriers, the shift of the image forming position due to the rotation unevenness does not become apparent as the color shift, so that the occurrence of the color shift can be prevented. . Here, as one specific method for making the attribute of the one line segment different from that of the other line segment, there is a method of making the length in the sub-scanning direction different from that of the other line segment. Other methods are also conceivable as long as the attribute can be distinguished by.

The image forming apparatus further includes transfer means for transferring the image patterns respectively formed on the plurality of image carriers to a predetermined transfer member, and the pattern detection means transfers the image pattern to the transfer member. The detected image pattern may be detected. With this configuration, even when the rotation of the rollers for driving the conveyor belt is uneven,
The occurrence of color misregistration can be prevented in response to the speed fluctuation including the above.

[0014] As a specific method of adjusting the phase, for example, the rotation unevenness detecting means obtains a time interval at which a plurality of line segments included in the image pattern are sequentially detected by the pattern detecting means. A non-uniformity information acquisition unit, and a phase information acquisition unit that acquires a difference between a timing at which the time interval acquired by the rotation unevenness information acquisition unit is a maximum or a minimum and a timing at which the one line segment is detected. The control unit includes: a rotation unit that rotates the image carriers based on a difference between the timings detected by the phase information acquisition unit so that phases of the rotation unevenness generated in the plurality of image carriers are equal. More specifically, the control unit may control the plurality of images based on a difference between the timings detected by the phase information acquisition unit. The rotation start timing of each image carrier can be controlled so that the phases of the rotation unevenness occurring on the respective bodies become equal, but not only the control of the rotation start timing but also the adjustment of the phase while driving the rotation. Is also possible.

[0015] In addition to the above, the control means may further reduce rotation unevenness occurring in each of the image carriers based on the time interval acquired by the rotation unevenness information acquiring section. It is preferable to control the rotation of each image carrier. By doing so, the size of the rotation unevenness itself that should be matched in phase can be reduced, so that the occurrence of color shift can be further suppressed.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, as one application example of the present invention,
An embodiment of the present invention in a case where the present invention is applied to a tandem digital full-color copying machine (hereinafter, simply referred to as a "copying machine") will be described with reference to the drawings. (1) Configuration of Copying Machine FIG. 1 is a front view of a copying machine according to the present embodiment. As shown in FIG. 1, the copying machine according to the present embodiment includes a paper feed cassette 11 which is set at the bottom of a housing 10 so as to be freely inserted and removed.
The conveyor belt 1 extends horizontally in the lower space of the housing up to the paper discharge tray 13 attached to the left side wall 12 of the housing in an outwardly protruding posture.
A plurality (four in the illustrated example) of image forming units 30C, 30M, 30Y, and 30K are arranged in a row above the transport belt 14 along the longitudinal direction of the transport belt, and recording is performed by the transport belt 14. The toner image of each color component is transferred onto the recording sheet S by the image forming units 30C to 30K while the sheet S is being conveyed, and a color image is formed by superimposing the colors.

An image reader 15 is provided on the upper part of the housing 10.
The image data of the document image optically read here is subjected to required image processing by the control unit 300, and is decomposed into C, M, Y, and K color components. The laser diodes 41C to 41K of the optical units 40C to 40K disposed above the image units 30C to 30K are optically modulated based on the respective color component signals. The light-modulated laser light is scanned in the main scanning direction by the polygon mirrors 42C to 42K while the image forming unit 30C of the corresponding color component.
~ 30K.

Each of the image forming units 30C to 30K has a photosensitive charger 31C to 31K as a center, a charging charger, a developing unit, and the like arranged around the photosensitive drums 31C to 31K.
Is a unit structure for forming an image by an electrophotographic method, in which the electrostatic latent image formed by the exposure is visualized as a toner image by a developing device while exposing the photosensitive drums 31C to 31K rotating in the direction of. is there. Each image forming unit 30
The developing devices of C to 30K supply the developer containing the toners of C, M, Y, and K to the photosensitive drums 31C to 31K, respectively, corresponding to the light modulation color components of the optical units 40C to 40K.

Transfer chargers 17C to 17K are disposed directly below the photosensitive drums of the respective image forming units 30C to 30K via the conveyor belt 14, and are provided with photosensitive drums 31C to 31K.
Of the toner image formed on the surface of the conveyor belt 14
The image is transferred onto the recording sheet S conveyed above. The transport belt 14 includes a driving roller 18, a driven roller 1,
When the drive roller 18 is rotated in the direction of arrow b by a motor (not shown), the transport belt 14 travels in the direction of arrow c. At this time, the traveling speed of the conveyor belt 14 and the peripheral speed of the photosensitive drum during image formation (hereinafter, referred to as “process speed”)
Is controlled so that the rotation speed of the motor is controlled. Further, the tension roller 20 is pulled in the direction of arrow d by a tension spring (not shown), whereby the tension of the transport belt 14 is kept constant.

On the upstream side of each of the photosensitive drums 31C to 31K, there is a corresponding one of the registration sensors 32C to 32C.
32K are provided.
By 32K, the leading end of the recording sheet S conveyed on the conveyor belt 14 is detected. Each resist sensor 32C ~
32K is an exposure position on the corresponding photosensitive drum 31C to 31K, which is a distance along a recording sheet conveyance path from a position detected by the registration sensor 32C to 32K to a toner image transfer position of the corresponding photosensitive drum 31C to 31K. It is installed so that it is longer than the distance measured in the direction in which the photosensitive drum rotates in the circumferential direction of the photosensitive drum from the transfer position to the transfer position.

The photosensitive drums 31C to 31K are driven to rotate by individually provided stepping motors 33C to 33K (see FIG. 4). However, the type of the motor is not limited to the stepping motor. An optical sensor unit 28 is installed at the most downstream in the transport direction of the recording sheet S, and a toner pattern (hereinafter simply referred to as a “pattern”) formed on the transport belt 14 for registration correction in the present embodiment. ") Is detected. In the present embodiment, a transparent resin material such as polyethylene terephthalate (PET) is used as the transport belt 14, and as the optical sensor unit 28, an LED is used for a light emitting unit, and a photodiode (hereinafter, referred to as a light receiving unit). , “PD”) are used. However, when a material having low transparency is used as the transport belt 14, a reflective sensor may be used.

A fixing device 2 is provided at the most downstream in the recording sheet transport direction.
After the toner image transferred onto the recording sheet S is fixed by heating, the recording sheet S is discharged to the paper discharge tray 13. In addition, the optical units 40C to 40K,
The control unit 300 controls the formation of the toner images by the image forming units 30C to 30K, the rotation driving of the photosensitive drums 31C to 31K, and the like. The configuration and processing contents of the control unit 300 will be described later in detail.

(2) Configuration of Control Unit 300 Next, the configuration of the control unit 300 will be described based on the functional block diagram of FIG. As shown in FIG.
Image processing control unit 310 and pattern generation control unit 320
A print data control unit 330, a main body control unit 340,
The control unit 310 includes a pattern detection control unit 350 and a drive control unit 360. Each of the control units 310 to 360 stores a control program, various initial data, and the like, centered on a CPU.
An OM, a RAM for temporarily storing control variables, and the like are connected and configured.

The image processing control section 310 further includes an image memory section 311, a rotation unevenness information obtaining section 312, and a phase information obtaining section 313. The R, G, and B image data obtained by the image reader 15 is transferred to an image processing controller 31.
After being input to 0 and undergoing A / D conversion and shading correction, it is converted into density data of C, M, Y, and K as reproduction colors. These density data are further subjected to known data processing for improving image quality such as edge enhancement processing and smoothing processing, and then stored in the image memory unit 311 for each reproduced color.

The print data control unit 330 controls the driving of the optical units 40C to 40K based on the print data output from the image processing control unit 310, emits a laser beam, and exposes the photosensitive drums 31C to 31K. Scan. On the other hand, the pattern generation control unit 320 generates print data of a predetermined toner pattern used for detecting rotation unevenness of each photoconductor drum, and sends the print data to the image processing control unit 310 at a predetermined timing. In the present embodiment, a shape pattern composed of a plurality of line segments printed at equal intervals in time (hereinafter, this toner pattern is simply referred to as “pattern”) is used as the toner pattern. FIG. 3 specifically shows an example of the pattern shape. As shown in the figure, each color pattern 50K to 50C has a predetermined length in the main scanning direction and the sub-scanning direction (hereinafter, the length in the main scanning direction is “length”, and the length in the sub-scanning direction). The width is referred to as “width”), and is formed at equal intervals in time. Here, “equal intervals in time” means that the photosensitive units 31C to 31K are formed by the optical units 40C to 40K when forming the line segments constituting the pattern.
Although it is necessary to expose the surface and form an electrostatic latent image for each line segment, this means that the intervals between exposure timings corresponding to each line segment by the optical units 40C to 40K are uniform. is there. That is, the photosensitive drums 31C-3C
This is because, when the rotation unevenness occurs at 1K, even if the exposure is performed at a uniform interval timing, the intervals between the line segments formed on the photosensitive drum surface are not equal.

In FIG. 3, PK corresponds to one rotation cycle of the photosensitive drum, and dK represents the interval between the respective line segments. This pattern shape will be described in more detail below with reference to the enlarged view of FIG. As shown in the figure, in the pattern in the present embodiment, one of the line segments constituting the pattern has a different width from the other line segments. The line segments having different widths are hereinafter referred to as “reference lines”, and the other line segments are referred to as “normal lines”. The interval PK between the left end position of the reference line of each color pattern and the left end position of the last normal line is equal to one rotation period of the photosensitive drum, and the left end position of the reference line and the left end of the adjacent normal line The distance dK from the position is set equal to the distance between the left end positions of the adjacent normal lines. Hereinafter, this dK is simply referred to as an “interval” between the line segments.

In the present embodiment, the first line segment in each color pattern is used as a reference line. However, if only one reference line is formed within one rotation period PK of the photosensitive drum, Regardless of the position of the reference line, the position of the reference line in each color need not necessarily be the same. There is no particular limitation on the size of the distance dK between the adjacent reference lines or the normal lines.
Also, it is appropriate to secure about 0.5 mm as the width that can be detected by a CCD or the like that can be used in place of the PD even in the narrowest case. Therefore, in the case of 400 dpi (dot per inch), a width of 7 to 8 dots is secured on both sides of the center position of the normal line in the sub-scanning direction.

On the other hand, how much difference is provided between the width of the reference line and the width of the normal line depends on the specifications of the copying machine, specifically, the size of the rotation unevenness that can occur, and the like. Need to adjust. Due to the occurrence of rotation unevenness, it is considered that a slight error may occur in the value detected as the width of the reference line and the normal line, and the reference line is detected to be narrower than the original width, and the normal line is detected to be smaller than the original width. This is because it is necessary to provide a difference that does not cause confusion between the two even if they are widely detected.

Further, the length of the entire pattern for each color in the sub-scanning direction is not limited to one cycle of the photosensitive drum, but is equivalent to several cycles (that is, PK equal to N as an integer).
* N) may be formed. As described above, the processing content regarding the detection of the rotation unevenness and the phase detection of the rotation unevenness using the pattern including the reference line will be described later. When receiving an instruction to detect rotation unevenness from the main body control unit 340, the pattern generation control unit 320 reads the print data of the pattern from the internal ROM, and sends it to the print data control unit 330 via the image processing control unit 310. send.
The print data control unit 330, based on the print data,
Optical units 40C to 40K and image forming units 30C to 30
By controlling K, a pattern of each color is formed on the conveyor belt 14 at a predetermined timing.

The pattern detection control section 350 controls the ON / OFF operation of the optical sensor unit 28, and performs A / D conversion by sampling a pattern detection signal from the optical sensor unit 28 at regular intervals. The A / D conversion in the present embodiment is a so-called binarization process, which is a process of converting a detection signal of the optical sensor unit 28 into a rectangular wave using a predetermined threshold. The pattern detection control unit 350 associates this sampling value (the result of the binarization process) with the detection timing and
1 sequentially. Hereinafter, the rectangular wave formed by this sampling value is referred to as “sampling rectangular wave”.

The sampling rectangular wave is turned on at a timing when a line segment forming the pattern is detected, and turned off at a timing when the line segment forming the pattern is not detected. In the present embodiment, the rising edge of the sampling rectangular wave is used as information relating to the detection timing of each line segment forming the pattern (hereinafter, referred to as “detection timing information”). The interval between them is defined as information on the width of each line segment (hereinafter, referred to as “width information”). The pattern detection control unit 350 acquires the detection timing information and the width information, and transmits the information to the image processing control unit 310.

The rotation unevenness information acquisition section 312 of the image processing control section 310 outputs information (hereinafter, referred to as “rotation unevenness”) representing rotation unevenness occurring in each of the photosensitive drums 31C to 31K based on the detection timing information. Information ”) is calculated. Here, the “rotation unevenness information” specifically refers to a timing interval of each rising edge corresponding to an adjacent line segment in the detection timing information. That is, as described above, since the line segments constituting the pattern are formed at equal intervals in time, the interval of the timing of the rising edge is always uniform (or within a certain range) unless rotation unevenness occurs. It should be. Therefore, rotation unevenness can be detected from the change in the interval. The calculated rotation unevenness information is sent to the phase information acquisition unit 313 in association with the detection timing of the rising edge itself. Hereinafter, the description of “rotational unevenness information” includes the detection timing of the rising edge itself.

The phase information acquisition unit 313, based on the rotation unevenness information, obtains information on the phase of the rotation unevenness occurring independently on the photosensitive drums 31C to 31K of the respective colors (hereinafter referred to as "phase information"). calculate. Here, the “phase information” refers to the interval between the timing at which the interval between the rising edges in the rotation unevenness information becomes widest due to the rotation unevenness and the reference line detection timing in the sampling rectangular wave. Say. Therefore, when the rotation unevenness does not occur and the intervals between the rising edges are all within a predetermined range, it is not necessary to calculate the phase information.

Based on the above definition of the phase information, the phase information can be calculated, for example, by the following method. That is, the interval between the rising edges included in the rotation unevenness information is sequentially compared with the edge interval (ideal edge interval) when rotation unevenness is not generated,
The difference is calculated. An ideal edge interval can be calculated in advance from an interval of exposure timing and a system speed to form line segments constituting a pattern, and stored in a memory in the image processing control unit 310. Then, from the calculated difference and the timing of each rising edge included in the rotation unevenness information, the timing at which the interval between the rising edges is widest can be easily obtained.

On the other hand, in the present embodiment, since the width of the reference line is different from the width of the normal line, the position of the rising edge of the reference line can be easily determined based on the width information sent from the pattern detection control unit 350. It is possible to identify. Therefore, the difference between the timing of the rising edge corresponding to the reference line and the timing at which the interval between the rising edges is the widest can be calculated as the phase information. The calculated phase information is sent to the drive control section 360 via the main body control section 340.

The drive controller 360 controls the photosensitive drums 31C to 31K based on the transmitted phase information so that the phases of the rotation unevenness generated on the respective photosensitive drums become equal. , Photosensitive drums 31C-3
The rotation of the stepping motors 33C to 33K that drive 1K is controlled. Here, the rotation unevenness information is also sent to the drive control unit 360, and based on the rotation unevenness information, the stepping motors 33C to 33C to reduce the rotation unevenness occurring in each of the photosensitive drums 31C to 31K. It is also possible to control the rotation drive of 33K.

Next, the drive control unit 3 in the present embodiment
The configuration of 60 will be described. FIG. 5 shows a drive control unit 3 which mainly performs drive control of the stepping motors 33C to 33K.
FIG. 3 is a functional block diagram showing a configuration of a second embodiment. As shown in the figure, the drive control section 360 includes a pulse generation section 52C to 52K,
3C to 53K, registration sensors 32C to 32K, RAM
58 and ROM 59 are connected to each other.
U51 controls according to the program stored in ROM59.

The pulse generators 52C to 52K, etc.
In the case where it is not necessary to distinguish each color of C, M, Y, and K having the same configuration for each color, for simplicity, for example, the “pulse generation unit 52” It is sometimes described as follows. Pulse generator 5
2 generates a clock pulse having a cycle corresponding to the frequency specified by the CPU 51. By changing the period of the clock pulse, the rotation speed of the stepping motor 33 is variably controlled. Therefore, by changing the period of the clock pulse based on the rotation unevenness information, the rotation control can be performed so as to reduce the rotation unevenness of the stepping motor 33 as described above. This control is a known technique. Therefore, detailed description here is omitted.

On the other hand, by controlling the number of clock pulses to be generated by the pulse generator 52, the positioning of the stepping motor 33 can be controlled. Further, by controlling the transmission start timing of the clock pulse, it is also possible to control the rotation start timing of the stepping motor 33. Driver unit 5
Numeral 3 controls the drive of the stepping motor 33 at a rotation speed according to the frequency of the clock pulse by an excitation phase switching method according to an excitation mode switching signal input from the CPU 51. Here, the excitation mode switching signal is a signal for instructing the excitation phase control unit 54 of one of the four-phase excitation and the four- and five-phase excitation modes, and is distinguished between High and Low. Is done. A High signal is output when instructing 4-phase excitation, and a Low signal is output when instructing 4-5 phase excitation.

The driver unit 53 includes an excitation phase control unit 5
4. Power amplification unit 55, current detection unit 56, and voltage control unit 5
7. The excitation phase control unit 54 generates a drive pulse signal by dividing the clock pulse at a division ratio according to the excitation mode switching signal, and distributes the drive pulse signal to each excitation phase of the stepping motor 33. That is, the stepping motor 33 is rotated by one step for each pulse of the drive pulse signal. In addition, the excitation phase control unit 54 includes a CPU
In accordance with the start / stop signal from 51, a power amplifying section 55 for starting / stopping the distribution of the drive pulse signal amplifies the drive pulse signal to supply a drive current to the excitation coil, and a current detection section 56 detects the drive current. The current value is detected and the voltage control unit 5
Numeral 7 controls the voltage applied to the exciting coil in accordance with the detected value, and each of them is constituted by a known circuit.

Here, the stepping motor 33 is driven by a full-step drive in which the step angle becomes the basic step angle according to the four-phase excitation method, and the step angle becomes the basic step angle according to the 4-5 phase excitation method. Although the half-step driving is performed by half, in the present embodiment, the driving is performed in full steps of four-phase excitation. The copying machine according to the present embodiment is characterized in that the rotation of the stepping motor 33 is controlled so that the phases of the rotation unevenness generated independently on the photosensitive drums 31C to 31K are matched. However, as a specific phase matching method, the following method can be considered. This will be described with reference to FIG.

FIG. 7K shows a K photosensitive drum 31K, and FIG. 7Y shows a Y photosensitive drum 31Y. In the figure, Ks and Ys are K and Y photosensitive drums 3
It is assumed that 1K and 31Y represent formation positions of reference lines that can be obtained from the width information. The formation position of the reference line on the surface of the photosensitive drum can be recognized by sending the timing of forming an electrostatic latent image on the pattern to the drive control unit 360.

On the other hand, the drive control section 360 receives the phase information from the phase information acquisition section 313. As described above, this phase information represents a difference in timing between the position of the reference line and the peak position of the rotation unevenness (the position where the actual rotation speed becomes the highest due to the rotation unevenness). In addition, if the system speed and the radius RK and RY of each photosensitive drum can be obtained, the position (Kp and Yp) on the photosensitive drum surface corresponding to the peak position of the rotation unevenness and the position of the reference line (Ks and Ys) ), That is, θ ₁ and θ ₂ can be calculated. Since the system speed and the radius of the photosensitive drum are predetermined, these values are stored in the ROM 5.
9, the calculation of the above θ ₁ and θ ₂ is easy.

Once the above angle is obtained, it can be easily converted to the number of steps of the stepping motors 33K and 33Y. That is, according to the following (Equation 1), the angle θ between the formation position Ks of the reference line on the K photosensitive drum 31K and the position Kp corresponding to the peak of the rotation unevenness.
₁ can be calculated step number N ₁ of the stepping motor 33K corresponding to the (°). Here, θ (°) means the step angle of the stepping motor 33K.

[0045]

(Equation 1)

On the other hand, according to the following (Equation ₂ ), the stepping corresponding to the angle θ ₂ (°) between the formation position Ys of the reference line on the Y photosensitive drum 31Y and the position Yp corresponding to the peak of the rotation unevenness. it is possible to calculate the number of steps N ₂ of the motor 33Y.

[0047]

(Equation 2)

Since the difference ΔN between the number of steps is calculated by the following (Equation 3), the driving of the stepping motors 33K and 33Y is started by shifting the timing by a time corresponding to the number of steps ΔN. The phases of the rotation unevenness occurring on the two-color photosensitive drums 31K and 31Y can be matched.

[0049]

(Equation 3)

In addition to the method of shifting the driving start timing, for example, before the actual driving of each stepping motor 33 is started, the rotation unevenness of each of the photosensitive drums 31C to 31K is determined based on the phase information. May be temporarily stopped in a state where all the positions corresponding to the peaks are matched at a predetermined position (for example, the top position), and then the driving of the stepping motor 33 may be started at the same timing. However, it is also possible to perform the phase matching by controlling the rotation speed while driving each of the stepping motors 33C to 33K.

(3) Processing Contents of Control Unit 300 Next, processing contents of the control unit 300 will be described. FIG.
5 is a flowchart illustrating an operation of a print control process of the copying machine according to the present embodiment. When the power of the apparatus is turned on (S100), first, the heater of the fixing device 26 is energized (fixing ON), and the initial values of the voltage value of the charging grid voltage of the charging charger, the voltage value of the developing bias of the developing device, and the like. The value is set in the main body control unit 340 and the image forming unit 30 is set.
C to 30K are set to the standby state (S200).

Further, it is determined whether or not the warm-up is completed (S300). In the present embodiment, the fixing device 2
When the temperature of the fixing roller of the fixing device 26 reaches a predetermined fixing temperature based on the output value from the temperature detection sensor (thermistor) provided in 6, it is determined that the warm-up is completed. When the warm-up is completed (S300: Ye
s), an operation of detecting rotation unevenness of the photosensitive drums 31C to 31K is performed (S400). Hereinafter, detailed processing contents in the rotation unevenness detection operation will be described.

FIG. 8 is a flowchart showing the details of the rotation unevenness detecting operation. This rotation unevenness detection operation
Programmed to run as needed,
In particular, it is executed when the power of the copier is turned on or after a predetermined number of copies are made. First, the switch of the optical sensor unit 28 is turned on by the pattern detection control unit 350 (S401). Next, preprocessing for calibrating the sensor output is performed (S402). Specifically, this pre-processing is performed based on the output value (0
Level, maximum level), but detailed description here is omitted.

When the preprocessing is completed, a pattern forming process for forming a pattern of each color on the transport belt 14 is performed (S403). In the pattern creation processing, first, process conditions, that is, a charging grid voltage value, a developing bias voltage value, and the like are set in the main body control unit 340. These process conditions are obtained in advance and stored in the ROM so that the image density becomes an appropriate value for each color.

Subsequently, R in the pattern generation control unit 320
The print data of each color pattern stored in the OM is read out, set as image data to be formed in an internal line memory, and the operation of each unit of the image forming unit is started.
That is, under the control of the main body control unit 340, the photosensitive drums 31C to 31K and the transport belt 14 are rotationally driven,
Image forming units 30C to 3 for starting operation of the developing device
0K and the operation of the transport system are started.

Next, based on the set pattern print data, the photosensitive units 31C to 31K are exposed at predetermined timings by the optical units 40C to 40K to write an electrostatic latent image of the pattern on each photosensitive drum. These are transferred onto the conveyor belt 14 by the image forming units 30C to 30K. The timing of pattern exposure is sent to the drive control unit 360 as described above.

In the present embodiment, the photosensitive drum 3
Of the line segments constituting the pattern corresponding to one rotation cycle of 1C to 31K, it is necessary to form a pattern by changing one of the line segments as a reference line and changing the width. The print data including the line may be stored in the ROM, or the print data may be the same for all the line segments, and the control may be performed such that only the width of the reference line is changed at the time of setting in the line memory. it can.

Upon completion of the pattern creation processing, the flow shifts to pattern sampling processing (S404). In this process, the LED of the light emitting unit of the optical sensor unit 28 emits light, and the detection signal of the PD, which is the light receiving unit, is sampled at a predetermined timing to detect the toner concentration on the transport belt 14. The sampled detection signal is stored in the RAM 351 after the above-described binarization processing.

Subsequently, the flow shifts to the processing for acquiring the detection timing information and the width information (S405). In this step,
From the information stored in the RAM 351, the detection timing information and the width information for each reference line and each normal line of each pattern are obtained. When the detection timing information and the width information are obtained, the rotation unevenness information is obtained from the information (S406). Since the acquisition of the rotation unevenness information has been described in detail above, the description is omitted here.

Next, position information of the reference line is obtained (S4).
07). As described above, in the present embodiment, since the width information is completely different between the reference line and the normal line, the identification is easy. Next, the peak position of the rotation unevenness is obtained from the rotation unevenness information by the method already described in detail (S408). Note that various methods may be considered as a method for acquiring the peak position of the rotation unevenness, in addition to the method described above, and some examples thereof will be described later as modified examples.

Next, the phase information is obtained from the position of the reference line and the rotational unevenness peak position (S409). Since the detailed description of the phase information has already been completed, the description here is omitted. When the rotation unevenness detection operation as described above is completed, returning to the flowchart of FIG.
A phase correction operation is performed (S500). The phase correction operation includes, as described above, the stepping motors 33C-3C.
Processing such as setting to shift the 3K drive start timing or moving the rotation unevenness peak positions of the respective photosensitive drums 31C to 31K to predetermined positions and stopping the processing is performed.

After the phase correction operation is performed, the stepping motors 33C to 33K are driven in a state where the phases of the rotation unevenness generated are in phase with each other, but as described above, based on the rotation unevenness information. By controlling the cycle of the drive pulse for each stepping motor,
By performing the rotation control so as to reduce the rotation unevenness, the color shift can be further suppressed.

As described above, when the rotation unevenness detection and phase correction operations are completed, various control operations such as an AIDC (automatic image density control) operation and a registration correction operation are executed (S600). In the AIDC operation, a reference patch is formed on each photosensitive drum, the toner density of the reference patch is detected by a reflection-type photoelectric sensor (AIDC sensor) (not shown), and the image density is optimized based on the detection result. This is a known control for changing image forming conditions such as the charging grid voltage value and the developing bias voltage value. Also, the resist correction operation is a known technique, and a description thereof will be omitted.

When the above control process is completed, it is determined whether or not the copy start key on the operation panel (not shown) has been turned on (S700). If it is on, a print operation is executed (S700). S800). The printing operation is continued until the output of the designated output number is completed (S90).
0: Yes), when printing is completed, the process returns to the control flow of the entire copying machine (not shown).

<Modifications> Although the embodiments of the present invention have been described above, it is needless to say that the contents of the present invention are not limited to the specific examples described in the above embodiments. The following modified example can be considered. (1) In the above embodiment, the pattern is transferred onto the conveyor belt 14 and the pattern is detected by the single optical sensor unit 28. However, the pattern is not transferred and formed on the surfaces of the photosensitive drums 31C to 31K. The detection may be performed in a state where it is performed. In that case, for example, for example, a reflection type optical sensor unit is provided for each photosensitive drum, and a pattern formed on the surface of the photosensitive drum is detected by each optical sensor unit. Even in such a case, since the angle between the reference line and the peak position of the rotation unevenness can be obtained for each photosensitive drum, phase correction can be performed. However,
It is conceivable that the method described in the above embodiment has a greater practical effect in many cases. Once the image is transferred onto the transport belt 14, the transfer belt 14
This is because the correction including the rotation unevenness occurring in the drive system can be performed.

(2) Also, in this embodiment, when acquiring the rotation unevenness information, the interval between the rising edges of the sampling rectangular wave is acquired. Because the pattern is formed so that the distance between the left ends of the lines is uniform at dK, if the pattern is formed such that the distance between the right ends of the reference line and the normal line is uniform, The interval between the falling edges of the sampling rectangular wave may be used as the rotation unevenness information.

(3) Further, in the present embodiment, when acquiring the phase information, the peak position of the rotation unevenness is simply set to the position where the interval between the rising edges is the widest. However, the present invention is not limited to this. Alternatively, the position may be the position with the smallest interval. Here, the more accurately the rotational unevenness peak position is determined, the greater the effect of preventing color misregistration. However, various methods for improving the accuracy of obtaining the rotational unevenness peak position can be considered.
Specifically, it is also conceivable to estimate which timing in the rectangle where the peak of the rotation unevenness exists is closer to the actual rotation unevenness peak while also referring to the rotation unevenness information other than the peak position. Can be

(4) In order to improve the accuracy of obtaining the peak position of the rotation unevenness, the output signal of the optical sensor unit 28 is not binarized as in the present embodiment, but is multi-step A / A. It is also effective to obtain a curved output instead of a rectangular wave by performing the D conversion. Also in this case, in addition to the method of determining the timing with the largest output as the peak of the rotation unevenness, the rotation unevenness peak position is determined by determining the center of gravity of the curve formed by the sampling output and determining the center of gravity as the peak position. Various methods can be considered for the determination. However, when these methods are used, it is necessary to change the pattern formation method and form the pattern so that the distance between the center positions of the reference line and the normal line is uniform at dK.

[0069]

As described above, according to the image forming apparatus of the present invention, a predetermined image pattern formed on each of a plurality of image carriers is detected by an optical sensor or the like, and the detection result is obtained. Based on the information about the rotation unevenness that has occurred in each of the plurality of image carriers obtained based on the information, the rotation of each image carrier is controlled so that the phase of the rotation unevenness becomes equal. Therefore, there is an effect that it is possible to prevent the occurrence of color misregistration at the time of multi-transfer of the image formed on the image.

Further, if the rotation of each image carrier is controlled so as to reduce the rotation unevenness occurring in each image carrier, there is an effect that the color shift can be further suppressed. .

[Brief description of the drawings]

FIG. 1 is a front view of a copying machine according to an embodiment of the present invention.

FIG. 2 is a functional block diagram showing a configuration of a control unit 300 according to one embodiment of the present invention.

FIG. 3 is a diagram illustrating an example of a pattern formed on a conveyor belt 14;

FIG. 4 is an enlarged view showing a detailed shape of a pattern.

FIG. 5 shows a drive control unit 36 according to an embodiment of the present invention.
FIG. 2 is a functional block diagram showing a configuration of No. 0.

FIG. 6 is a diagram for explaining a specific method of phase matching.

FIG. 7 is a flowchart illustrating a control operation of print control.

8 is a flowchart showing the details of a rotation unevenness detection operation in the flowchart of FIG. 7;

FIG. 9 is a diagram for explaining a problem of the conventional position shift correction.

FIG. 10 is a diagram for explaining a problem of the conventional misalignment correction.

[Explanation of symbols]

 14 Conveyor belt 15 Image reader unit 18 Drive roller 28 Optical sensor unit 30C-30K Image forming unit 31C-31K Photoconductor drum 32C-32K Registration sensor 33C-33K Stepping motor 40C-40K Optical unit 50C-50K Pattern 52C-52K Pulse generation Unit 53C to 53K Driver unit 54C to 54K Excitation phase control unit 55C to 55K Power amplification unit 56C to 56K Current detection unit 57C to 57K Voltage control unit 300 Control unit 310 Image processing control unit 311 Image memory unit 312 Rotation unevenness information acquisition unit 313 Phase information acquisition section 320 Pattern generation control section 330 Print data control section 340 Main body control section 350 Pattern detection control section 351 RAM 360 Drive control section

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takahiro Tsujimoto 2-3-1-13 Azuchicho, Chuo-ku, Osaka-shi, Osaka Inside Osaka International Building Minolta Co., Ltd. (72) Inventor Hideki Matsuura Azuchi, Chuo-ku, Osaka-shi, Osaka 2-13-3, Osaka International Building Minolta Co., Ltd. F-term (reference) 2H027 DA38 EB04 EC03 EC06 EC20 ED02 ED06 EE02 EE03 EE04 EE07 EF09 2H030 AA01 AB02 AD05 AD12 AD17 BB02 BB16 BB23 BB44 BB56

Claims (6)

[Claims] 1. An image forming apparatus comprising: a plurality of image carriers; forming an image on the plurality of image carriers by an image writing unit; and multiplex-transferring the images to form an image. A pattern forming unit that controls an image writing unit to form a predetermined image pattern on each of the plurality of image carriers; a pattern detection unit that detects an image pattern formed by the pattern forming unit; On the basis of the result of the detection by the pattern detection means, rotation unevenness detection means to obtain information on the rotation unevenness respectively occurring in the plurality of image carriers, based on the information obtained by the rotation unevenness detection means,
Control means for controlling the rotation of each image carrier so that the phases of the rotation unevenness occurring in each of the plurality of image carriers are equal, wherein the predetermined image pattern is equal to a predetermined line segment. A plurality of image patterns arranged at a time interval, wherein only one of the plurality of line segments included in one cycle of the image pattern corresponding to one rotation of the image carrier is detected by the pattern detection unit; An image forming apparatus characterized in that the image pattern is an image pattern in which a predetermined attribute is changed so that the line pattern can be distinguished from another line segment based on a result of detection by the image pattern. 2. The image pattern according to claim 1, wherein the length of the one line segment is different from that of the other line segment in the sub-scanning direction.
An image forming apparatus according to claim 1. 3. The image forming apparatus further includes a transfer unit that transfers an image pattern formed on each of the plurality of image carriers to a predetermined transfer body, and the pattern detection unit transfers the image pattern to the transfer body. The image forming apparatus according to claim 1, wherein the detected image pattern is detected. 4. The rotation unevenness detecting unit, wherein the rotation unevenness detecting unit obtains a time interval at which a plurality of line segments included in the image pattern are sequentially detected by the pattern detecting unit; A phase information acquisition unit that acquires a difference between a timing at which the time interval acquired by the unit is maximum or minimum and a timing at which the one line segment is detected, wherein the control unit acquires the phase information. The rotation of each image carrier is controlled based on a difference in timing detected by the unit such that phases of rotation unevenness generated in the plurality of image carriers become equal. 4. The image forming apparatus according to any one of claims 1 to 3, 5. The image processing apparatus according to claim 1, wherein the control unit is configured to control each of the plurality of image carriers based on a timing difference detected by the phase information acquisition unit so that phases of rotation unevenness generated in the plurality of image carriers are equal. The image forming apparatus according to claim 4, wherein timing of starting rotation of the body is controlled. 6. The image forming apparatus according to claim 1, wherein the control unit is further configured to reduce rotation unevenness occurring in each of the image carriers based on the time interval acquired by the rotation unevenness information acquiring unit. The image forming apparatus according to claim 4, wherein rotation of the image forming apparatus is controlled.