JP3578935B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is directed to, for example, a method in which a transfer material such as a sheet is supported and conveyed by a transfer conveyance belt abutting in a predetermined positional relationship with a transfer unit surface of a rotationally driven image carrier such as a photosensitive drum. The present invention relates to an image forming apparatus that transfers and reproduces a toner image formed thereon on a transfer material, and more specifically, controls a positional relationship when an image carrier stops to stop with a predetermined positional relationship. Further, the present invention relates to an image forming apparatus capable of performing subsequent image formation with high accuracy.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there is a color image forming apparatus in which a color image is transferred to a recording unit as YMCK image data, and the color image of each color is sequentially superimposed and reproduced as a color image by a transfer unit for each color.
In such a color image forming apparatus, there is a problem that a color image cannot be faithfully reproduced unless images of the respective colors are accurately superimposed at each transfer unit. This is a major development challenge.
[0003]
In an image forming apparatus having an infinite number of components, there is a small variation in the component accuracy of each component, and a variation occurs in each image forming device due to the assembling accuracy when assembling these components.
Therefore, conventionally, a pattern adjustment of each color is performed by forming a pattern image of each color on a trial basis, confirming the positional relationship between the pattern images of each color, and adjusting the image formation position for each image forming unit of each color ( Registered Patent No. 2642351).
[0004]
However, even if the above-described registration adjustment is performed, the "color shift" due to the "shift of the image writing start position" can be corrected, but the periodic drive of a drive system such as a drive gear for driving the photosensitive drum can be corrected. It was not possible to correct color misregistration caused by irregular speed fluctuations of the photosensitive drum caused by unevenness.
In other words, in such an image forming apparatus, there has conventionally been a problem of drive unevenness that periodically occurs in each recording unit of an image. When the images recorded with the color materials are sequentially superimposed and reproduced as a color image, there is a problem that a color shift occurs and a faithful color image cannot be reproduced.
[0005]
Therefore, in the conventional color image forming apparatus, when the image formed on the photosensitive drum in each recording unit is transferred in the transfer unit, the condition of the drive unevenness that periodically occurs is the same. It has been considered that the relationship between the distance (time) from the image writing position to the transfer position to the photosensitive drum and the drive fluctuation period of the drive mechanism is N times as large as the relationship (Japanese Patent Publication No. Hei 7-31446). Gazette, Japanese Patent Publication No. 8-14731, etc.).
[0006]
FIG. 9 shows a configuration around a transfer belt that conveys each image forming unit and a transfer material that transfers an image formed by each image forming unit of a conventional color image forming apparatus employing the above-described method.
In FIG. 9, photosensitive drums 322a, 322b, 322c, and 322d constituting black, cyan, magenta, and yellow recording units in order from the right. The images of the respective colors formed by the photosensitive drums 322 a to 322 d are transferred to a transfer material (not shown) supported and transported by the transfer and transport belt 316 as the transfer and transport belt 316 moves. At the transfer portion A where the conveyance belt is close to the transfer belt, the transfer is performed in a superimposed order from black ink.
Here, the photosensitive drums 322a to 322d are connected to each other so that their driving is connected and start rotating at the same time. Each photosensitive drum is mounted such that its rotational drive unevenness is in the same phase. I have.
[0007]
As a specific example, a drive gear (not shown) to which a drive shaft (not shown) of each of the photoconductor drums 322a to 322d is fitted is set to a certain reference (for example, a key type as shown in FIG. Holes) are all aligned in the same direction. Thus, at the same time, each photosensitive drum always rotates with the same driving unevenness.
Therefore, each distance L ′ between the transfer portions of each photoconductor drum is defined as the diameter of the photoconductor drum as d.
L ′ = Nπd (N is an integer)
In the transfer process of the image at each transfer portion A of the four photosensitive drums 322a to 322d arranged in parallel as viewed in FIG. The images formed of the color materials of the respective colors are sequentially superimposed in a cycle, and as a result, a color shift caused by driving unevenness is eliminated.
[0008]
[Problems to be solved by the invention]
However, in the above-described conventional configuration, the distance relationship between the recording units arranged in parallel must be arranged in accordance with the periodic drive fluctuation. When the distance between the recording units is determined in this way, even if the integer N is set to 1, a distance corresponding to the peripheral length of the photosensitive drum is necessarily required. As a result, the size of the image forming apparatus itself becomes large, so that not only can the size of the image forming apparatus desired by the user not be reduced, but also it takes a long time to assemble each part, or each part has a high precision. Is required and the production cost increases.
[0009]
On the other hand, in a device that detects a color shift of each component color image or a rotational position shift of each of the photosensitive drums 322a to 322d and constantly corrects the phase of each printing unit, the photosensitive unit of each printing unit always responds to the generated shift. The speed of the body drum is controlled and the phase is constantly adjusted. In this case, the phase adjustment control is performed even for a minute phase shift of each photosensitive drum that does not significantly affect the color shift of an image. In order to match the phase of the photosensitive drum, rubbing occurs between the photosensitive drum and the recording medium or the transfer carrier, causing damage to the photosensitive drum, greatly affecting the life of the photosensitive drum, and significantly shortening the life cycle. There was a problem.
[0010]
SUMMARY OF THE INVENTION The present invention has been made to solve the above-described problem, and has been made in response to a periodic drive fluctuation in each of the recording units arranged in parallel (perpendicular to the flow direction of the transfer conveyance belt) as in the related art. Provided is an image forming apparatus which can be faithfully reproduced as one color image, and which can be reduced in size even if an image carrier having the same diameter is used and the installation area in an office environment is minimized. The purpose is to do.
[0011]
Furthermore, the timing shift between the start and stop of the driving of the image carrier such as the photosensitive drum and the contact portion of the transfer conveyance belt contacting the transfer portion of the image carrier is performed, and the phase matching control is performed. Provided is an image forming apparatus capable of minimizing deterioration of the image carrier and the surface of the transfer carrier due to wear of the image carrier and the transfer carrier, and reproducing a faithful image all around the image carrier. The purpose is to:
[0012]
[Means for Solving the Problems]
The present invention has the following configuration to achieve the above object.
First gist of the present invention A plurality of image carriers, a driving unit that rotationally drives the image carriers, a detection unit that detects a rotation state of each image carrier when the image carriers are rotating, and the detection unit Control means for controlling the driving means based on the detection signal of the phase adjustment means for stopping the image carrier at a preset rotation phase state, wherein the detection signal of the detection means is provided at a predetermined timing. On the other hand, if there is a deviation exceeding the preset tolerance, I An image forming apparatus, wherein the phase adjusting means is not executed when the deviation does not exceed the allowable value.
[0013]
Second summary of the present invention If the detection signal of the detection means does not exceed a predetermined allowable value with respect to a predetermined timing, the rotation of all the image carriers is stopped simultaneously without executing the phase adjustment means. Characterized by First summary An image forming apparatus according to any one of the preceding claims.
[0014]
Third summary of the present invention Is characterized in that, when simultaneously stopping a plurality of image carriers, all the image carriers are stopped based on a detection signal of a predetermined image carrier. Second summary An image forming apparatus according to any one of the preceding claims.
[0015]
Fourth Summary of the Invention Is that the allowable value serving as a criterion for judging the execution of the phase adjustment stop control is provided separately from the phase adjustment unit amount for presetting the stop position of each image carrier, and is smaller than the phase adjustment unit amount. Characterized by First summary An image forming apparatus according to any one of the preceding claims.
[0016]
Fifth summary of the present invention Wherein the allowable value serving as a criterion for determining execution of the phase adjustment stop control can be changed. First summary An image forming apparatus according to any one of the preceding claims.
[0017]
First summary According to the above, only when the rotational phase of any one of the plurality of image carriers deviates from the predetermined rotational phase state, the rotational phase state between the image carriers is reset to the preset rotational phase state. The stop position of the image carrier is controlled by performing phase matching control so as to be set, but if any of the image carriers has a rotation phase smaller than a predetermined shift, the phase matching means is not executed.
[0018]
Therefore, the phase adjustment control is performed only when the magnitude of the rotational phase state deviation exceeds the allowable value, regardless of the large number of copies, the long-time operation of the device, and other environmental changes or troubles. If the value does not exceed the allowable value, the phase adjustment control is not performed, so that the phase control is always performed, the image carrier is wasted after a predetermined number of copies, after a predetermined time of operation, or after a predetermined environmental change or trouble occurs. Rotational operation for performing appropriate phase alignment control and the accompanying rubbing and abrasion of the image carrier can be prevented as much as possible, which not only extends the life of the image carrier but also saves energy.
[0019]
Second summary According to the above, when the rotational phase relationship between a plurality of image carriers is within a predetermined range, the phase matching control for resetting the rotational phase state between the image carriers to a preset rotational phase state is performed. Without stopping, all the image carriers are simply stopped at the same time. That is, even if the rotational phase state of the plurality of image carriers does not completely match the preset state, if the color misregistration is less than a preset allowable value that is not conspicuous, the phase adjustment stop control is not performed. The stop position does not need to be stopped at a preset stop position. If the stop is performed at any point, the shift of the rotational phase state of all the image carriers remains within the allowable range.
[0020]
Therefore, even after a large amount of copying, long-time operation of the apparatus, changes in the surrounding environmental conditions, or occurrence of minor trouble, if the deviation from the preset rotation phase state between the image carriers is within the allowable value range. Since all the image carriers are stopped at the same time irrespective of the set stop position of each image carrier without performing the phase adjustment control at all, all the image carrier rotation operations are the same and contact with the image carrier Rubbing with the transfer carrier is reduced, and mutual abrasion is reduced.
Further, as compared with the conventional apparatus that always performs the phase adjustment control, useless rotation of the image carrier can be prevented as much as possible, and not only can the rotation time of the image carrier be shortened, but also the life of the image carrier can be prolonged. It is also very useful for energy saving.
[0021]
Third summary According to the method, all the image carriers can be stopped by the same operation using the control program for any one image carrier serving as a reference, so that the rotation phase state between the image carriers before the stop is changed. All the image carriers can be stopped while maintaining them. Therefore, since it is not necessary to perform different control for each image carrier, not only the control is simplified, but also unnecessary rotation operation of the image carrier can be prevented as much as possible in comparison with a conventional apparatus that always performs phase adjustment control. Not only can the rotation time of the image carrier be shortened and the life of the image carrier can be prolonged, but it is also very useful for saving energy.
[0022]
Fourth summary According to the above, a phase shift which is a reference for determining whether or not to execute the phase adjustment control separately from the unit amount of the phase adjustment for setting the stop position of each image carrier for setting the rotational phase state of the image carrier. By separately setting the allowable value of the amount, the allowable value of the phase shift amount can be changed when the occurrence of the color shift is conspicuous, and by making the allowable value of the phase shift unit smaller than the unit amount of the phase adjustment (preferably １ ／ or less). It is possible to prevent a large shift in the rotational phase state, and it is possible to set the phase matching control according to the state of the apparatus.
[0023]
Fifth summary According to the above, the allowable value for judging whether or not to execute the phase matching control can be changed, so that the allowable value is set when the color shift is conspicuous at the set allowable value. By making the change, the criterion for judging the phase shift can be made strict, and the occurrence of the color shift can be prevented.
In addition, the allowable value can be increased in a range where the occurrence of color shift is not conspicuous, the criterion for determining the phase shift can be lowered, the phase adjustment control of the image holder can be reduced as much as possible, and the useless rotation operation of the image carrier Can be prevented.
[0024]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
One embodiment of the present invention will be described below with reference to FIGS.
FIG. 1 is a schematic front sectional view showing a configuration of a digital color copying machine 1 which is an image forming apparatus according to an embodiment of the present invention. A document table 111 and an operation panel (not shown) are provided on the upper surface of the copying machine main body 1, and an image reading unit 110 and an image forming unit 210 are provided inside the copying machine main body 1. A reversing automatic document feeder (RADF; Reversing Automatic Document Feeder) 112 is mounted on the upper surface of the platen 111 so as to be openable and closable with respect to the platen 111 and has a predetermined positional relationship with the surface of the platen 111. Have been.
[0025]
The automatic double-sided document feeder 112 first conveys the document such that one side of the document faces the image reading unit 110 at a predetermined position on the document table 111, and after the image reading on one side is completed, the other side. The document is inverted and transported toward the document table 111 such that the surface of the document faces the image reading unit 110 at a predetermined position on the document table 111. Then, after the two-sided image reading for one document has been completed, the double-sided automatic document feeder 112 discharges the document and performs a double-sided conveyance operation for the next document.
The above-described document transport and reverse operation are controlled in relation to the operation of the entire copying machine 1.
[0026]
The image reading section 110 is arranged below the document table 111 for reading an image of a document conveyed onto the document table 111 by the automatic duplex document feeder 112.
The image reading unit 110 has document scanning bodies 113 and 114 that reciprocate in parallel along the lower surface of the document table 111, an optical lens 115, and a CCD line sensor 116 that is a photoelectric conversion element.
[0027]
The document scanning bodies 113 and 114 include a first scanning unit 113 and a second scanning unit 114. The first scanning unit 114 has an exposure lamp for exposing the surface of the original image, and a first mirror for deflecting a reflected light image from the original in a predetermined direction. It reciprocates in parallel at a predetermined scanning speed while maintaining the distance. The second scanning unit 114 has second and third mirrors for further deflecting the reflected light image from the document deflected by the first mirror of the first scanning unit 113 in a predetermined direction. It reciprocates in parallel with one scanning unit 113 while maintaining a constant speed relationship.
[0028]
The optical lens 115 reduces the reflected light image from the document deflected by the third mirror of the second scanning unit, and forms the reduced light image at a predetermined position on the CCD line sensor 116.
[0029]
The CCD line sensor 116 photoelectrically converts the formed light image in order and outputs it as an electric signal. The CCD line sensor 116 is a three-line color CCD capable of reading a black-and-white image or a color image and outputting line data separated into R (red), G (green), and B (blue) color components. is there. The document image information converted into an electric signal by the CCD line sensor 116 is further transferred to an image processing unit (not shown) to perform predetermined image data processing.
[0030]
Next, the configuration of the image forming unit 210 and the configuration of each unit related to the image forming unit 210 will be described.
Below the image forming unit 210, paper (for example, a recording medium such as paper, OHP paper) P stacked and stored in the paper tray TR is separated one by one and supplied to the image forming unit 210. A paper mechanism 211 is provided. Then, the sheets P separated and supplied one by one are conveyed to the image forming unit 210 at a controlled timing by a pair of registration rollers 212 disposed in front of the image forming unit 210. Further, the sheet P on which an image is formed on one side is re-supplied and conveyed to the image forming unit 210 in synchronization with the image formation of the image forming unit 210.
[0031]
Below the image forming unit 210, a transfer and transport belt mechanism 213 is disposed. The transfer transport belt mechanism 213 transports the paper P by electrostatically attracting the paper P to a transfer transport belt 216 stretched so as to extend substantially parallel between the drive roller 214 and the driven roller 215. Further, a pattern image detection unit 300 that detects a test pattern formed on the transfer / transport belt 216 is provided near the lower side of the rotation orbit of the transfer / transport belt 216.
[0032]
Further, a fixing device 217 for fixing the toner image transferred and formed on the paper P on the paper P is disposed near the drive roller 214 on the downstream side of the transfer and transport belt mechanism 213 in the paper transport path. . The sheet P having passed through the nip between the pair of fixing rollers of the fixing device 217 passes through a conveyance direction switching gate 218, and is discharged by a discharge roller 219 onto a discharge tray 220 attached to the outer wall of the copying machine body 1. Is discharged.
[0033]
The switching gate 218 selectively switches the conveyance path of the sheet P after fixing between a path for discharging the sheet P to the copying machine main body 1 and a path for re-supplying the sheet P to the image forming unit 210. Things. The sheet P whose transport direction has been switched again toward the image forming unit 210 by the switching gate 218 is turned upside down via the switchback transport path 221, and is again supplied to the image forming unit 210.
[0034]
In addition, above the transfer conveyance belt 216 in the image forming section 210, the first image formation station Pa, the second image formation station Pb, the third image formation station Pc, and the proximity of the transfer conveyance belt 216. A fourth image forming station Pd is provided in order from the upstream side of the sheet transport path.
[0035]
The transfer conveyance belt 216 is frictionally driven by the drive roller 214 in the direction indicated by the arrow Z in FIG. 1 to grip the sheet P fed through the sheet feeding mechanism 211 as described above, and transfer the sheet P to the image forming station Pa. To Pd.
Each of the image stations Pa to Pd has substantially the same configuration. Each of the image stations Pa, Pb, Pc, and Pd includes a photosensitive drum 222a, 222b, 222c, and 222d that is driven to rotate in the direction of arrow F shown in FIG.
[0036]
Around the photosensitive drums 222a to 222d, chargers 223a, 223b, 223c, 223d for uniformly charging the photosensitive drums 222a to 222d, respectively, and electrostatic latents formed on the photosensitive drums 222a to 222d. Developing devices 224a, 224b, 224c, 224d for developing the respective images; transfer dischargers 225a, 225b, 225c, 225d for transferring the developed toner images on the photosensitive drums 222a to 222d to the paper P; Cleaning devices 226a, 226b, 226e, and 226d for removing toner remaining on the drums 222a to 222d are sequentially arranged along the rotation direction of the photosensitive drums 222a to 222d.
[0037]
Laser beam scanner units 227a, 227b, 227c, and 227d are provided above the photosensitive drums 222a to 222d, respectively. Each of the laser beam scanner units 227a to 227d includes a semiconductor laser device (not shown) for emitting dot light modulated according to image data, and a polygon mirror (not shown) for deflecting a laser beam from the semiconductor laser device in the main scanning direction. Deflecting device) 240, an fθ lens 241 and mirrors 242 and 243 for forming an image of the laser beam deflected by the polygon mirror 240 on the surfaces of the photosensitive drums 222a to 222d.
[0038]
A pixel signal corresponding to the black component image of the color original image is supplied to the laser beam scanner 227a, a pixel signal corresponding to the cyan component image of the color original image is provided to the laser beam scanner 227b, and the color original image is provided to the laser beam scanner 227c. , And a pixel signal corresponding to the yellow component image of the color document image is input to the laser beam scanner 227d.
[0039]
Thus, an electrostatic latent image corresponding to the color-converted document image information is formed on each of the photosensitive drums 222a to 222d. The developing device 227a contains black toner, the developing device 227b contains cyan toner, the developing device 227c contains magenta toner, and the developing device 227d contains yellow toner. The electrostatic latent images on the photoconductive drums 222a to 222d are developed with the toners of these colors. As a result, the document image information color-converted by the image forming unit 210 is reproduced as a toner image of each color.
[0040]
Further, a paper suction (brush) charger 228 is provided between the first image forming station Pa and the paper feed mechanism 211, and the suction charger 228 charges the surface of the transfer conveyance belt 216. The sheet P supplied from the sheet feeding mechanism 211 is conveyed without shifting between the first image forming station Pa and the fourth image forming station Pd in a state where the sheet P is securely attracted onto the transfer conveying belt 216.
[0041]
On the other hand, between the fourth image station Pd and the fixing device 217, a cathode (not shown) is provided almost directly above the drive roller 214. An AC current is applied to the static eliminator to separate the sheet P electrostatically attracted to the transport belt 216 from the transfer transport belt 216.
[0042]
In the digital color copier having the above configuration, cut sheet-shaped paper is used as the paper P. When the sheet P is sent out from the sheet cassette and supplied into the guide of the sheet feeding path of the sheet feeding mechanism 211, the leading end of the sheet P is detected by a sensor (not shown). Is temporarily stopped by the pair of registration rollers 212 based on the detection signal output from the printer.
Then, the paper P is sent onto the transfer / conveying belt 216 rotating in the direction of arrow Z in FIG. 1 at the timing of each of the image stations Pa to Pd. At this time, as described above, the transfer conveyance belt 216 is given a predetermined charge by the suction charger 228, so that the paper P is stably conveyed and supplied while passing through the image stations Pa to Pd. .
[0043]
In each of the image stations Pa to Pd, a toner image of each color is formed, and is superposed on the support surface of the paper P conveyed by being electrostatically attracted by the transfer / conveyance belt 216. When the transfer of the image by the fourth image station Pd is completed, the sheet P is sequentially separated from the transfer conveyance belt 216 by the negative discharger from the leading end thereof, and is guided to the fixing device 217. Finally, the paper P on which the toner image has been fixed is discharged onto a paper discharge tray 220 from a paper discharge port (not shown). In the above description, the laser beam is scanned and exposed by the laser beam scanner units 227a to 227d, thereby performing optical writing on the photosensitive member.
[0044]
Note that a writing optical system (LED head) including a light emitting diode array and an imaging lens array may be used instead of the laser beam scanner unit. The LED head is smaller in size than the laser beam scanner unit, and has no moving parts and is silent. Therefore, it can be suitably used in an image forming apparatus such as a tandem type digital color copying machine which requires a plurality of optical writing units.
[0045]
Next, the rotation phase control of each photosensitive drum, which is a characteristic part of the present embodiment, will be described.
In the digital color copying machine of the present embodiment, as shown in FIG. 2, unlike the conventional image forming apparatus shown in FIG. 9, the four photosensitive drums 222a to 222d of the respective image forming stations Pa to Pd are provided. Rotation of the photoconductive drum (if the phases are the same, common to each photoconductive drum), the phase is shifted by a predetermined amount (in the image, the expansion / contraction phase of each color component image matches) Driven. More specifically, since the photoconductor drums start rotating at the same time and stop rotating at the same time, the stop positions (rotation start positions) are shifted and stopped. In the future, each photoconductor drum will be rotated with its phase shifted so that the expansion and contraction of each color component image on the image will match, but the rotation phase state of each photoconductor drum will be changed. The description will be made with the description that the state is the predetermined state.
[0046]
In FIG. 2, similarly to FIG. 9, in order to correct a phase shift in each photosensitive drum, a predetermined positional relationship (a position where periodic driving unevenness is a certain condition) with respect to the shaft driven to rotate is used. (Relationship), taking into account that the photoconductor drums are attached in such a manner, the respective photoconductor drums are shifted by a predetermined angle (the difference between the circumference of the photoconductor drum and the distance between transfer portions of adjacent photoconductors). The state of stopping is shown with reference to a key-shaped hole (or projection) ha of the drive gear attached to the shaft.
[0047]
Now, with reference to the black photosensitive drum 222a, the phase of the adjacent cyan photosensitive drum 222b is advanced by about 60 degrees. Similarly, the phase of the magenta photosensitive drum 222c is advanced by 120 degrees, and the phase of the yellow photosensitive drum 222d is advanced by 180 degrees.
In this way, by shifting the phase of the drive unevenness in each photoconductor drum, the distance between the transfer units A-A corresponding to the respective image forming stations Pa to Pd is reduced by the amount corresponding to the phase shift. Even if the transfer material is reduced, the drive unevenness between the photosensitive drums can be the same for the transfer material passing through the transfer unit A. In addition, by shifting in the opposite direction, the distance between A and A can be made longer than the circumference of the photosensitive drum.
[0048]
As described above, if the diameter of the photosensitive drum is d by advancing the cycle of drive unevenness between adjacent photosensitive drums by 60 degrees, L corresponding to the distance between the transfer portions A-A is:
L = circumferential length πd of the photosensitive drum × ((360−60) degrees / 360 degrees)
It becomes.
[0049]
Here, for convenience of explanation, the distance between the transfer units A-A is set based on the phase shift in each photosensitive drum, but actually, the distance L between the transfer units A-A is determined. Then, based on this, the phase shift of each photosensitive drum may be set. For example, when a photosensitive drum having a drum diameter of 40 mm is used and the distance L between the transfer units A-A is set to 105 mm, the stop position between the adjacent photosensitive drums is set as described above for each drive. The unevenness is set so that the phase is shifted by about 60 degrees.
[0050]
Here, the manner in which images of the respective photosensitive drums are superimposed without color shift due to driving unevenness will be described with reference to FIG.
Now, it is assumed that four photosensitive drums are rotating in a state as shown in FIG. The image written at the timing of (1) at the position of “G” of the black photosensitive drum 222a (the reference of drive unevenness is indicated by line a for clarity) is the timing of (4) (at the position of the photosensitive drum 222a). After the time required for 180 ° rotation has elapsed), the image is transferred onto the transfer / conveying belt 216, and is superimposed on the image on the cyan photosensitive drum 222b at the timing (9). Here, an image has already been formed on the cyan photosensitive drum 222b by the laser beam at the timing (6). FIG. 3A shows the position of the line a of the cyan photosensitive drum 222b at the timings (1) to (6). As is clear from the figure, the line a at the timing (9) is located at the same position as the black photosensitive drum 222a at the timing (4). Therefore, the driving unevenness of the superposed images is the same, and there is no color shift due to the influence of the driving unevenness.
[0051]
Similarly, the image formed on the magenta photosensitive drum 222c is superimposed at the timing (14). Here, an image has already been formed on the magenta photosensitive drum 222c at the timing (11). FIG. 3B shows the position of the line a of the magenta photosensitive drum 222c at the timings (1) to (11). As is clear from the figure, the line a at the timing (11) is located at the same position as the black and cyan photosensitive drums at the timings (1) and (6). Therefore, the superimposed images have the same driving unevenness, and there is no color shift due to the influence of the driving unevenness.
[0052]
Similarly, the image formed on the yellow photosensitive drum 222d is superimposed at the timing (19). Accordingly, an image has already been formed on the yellow photosensitive drum 222d at the timing of (16). FIG. 3C shows the position of the line a of the yellow photosensitive drum 222d at the timings (1) to (16). As is clear from the figure, the line a at the timing (16) is located at the same position as the black and cyan photosensitive drums at the timings (1), (6) and (11). Therefore, the superimposed images have the same driving unevenness, and there is no color shift due to the influence of the driving unevenness. The rotational driving of the four photosensitive drums 222a to 222d is controlled by the control unit CON shown in FIG. 4 based on the reference mark Q that can specify the driving unevenness of each photosensitive drum.
[0053]
Hereinafter, the rotation drive control (phase matching control) of the photosensitive drum will be described with reference to FIGS.
As shown in FIG. 4, a key-shaped mark (convex portion) ha is provided in a hole of the drive gears G1 to G4 for transmitting a rotational drive force to the photosensitive drums 222a to 222d in the digital color copying machine of the present embodiment. The pins provided on the shafts engage with the protrusions ha, so that any of the shafts connected to the drive mechanism having the same configuration is rotationally driven with a constant periodic drive unevenness characteristic. .
Since the image carrier (photosensitive drum) is also supported in a predetermined positional relationship with respect to the shaft that is rotationally driven, the periodic drive unevenness in each photosensitive drum is reduced. , All become almost identical.
[0054]
Further, as shown in FIG. 4, the reference marks Q attached to the drive gears G1 to G4 are detected by detection sensors S1 to S4 including optical sensors and the like, respectively.
Each of the sensors S1 to S4 is attached at the same position from each transfer portion A. The sensor output is sent to the control unit CON, and based on this, the control unit CON controls the motors M that independently drive the respective photosensitive drums.
Although the sensors S1 to S4 detect the reference marks Q attached to the drive gears G1 to G4 and control the stop position of the photosensitive drum, the sensors S1 to S4 may be used in another sequence. Is used as a reference for correcting the conditions for forming an image formed on each photosensitive drum by detecting the reference mark Q. (For details, see JP-A-6-51551)
[0055]
The control unit CON includes a first control unit that controls an image forming process on the photosensitive drum based on a detection result (signal) from each sensor based on a different sequence, and the stop position of each photosensitive drum is in a predetermined positional relationship. And a second control means for controlling so as to reliably stop at each stop position so that each control sequence is automatically performed when a predetermined condition and a predetermined timing (timing) are reached.
[0056]
FIG. 5 shows a timing chart of the outputs of the sensors S1 to S4 when the photosensitive drum is stopped. The pattern Q is detected and turned on sequentially from the sensor S4 of the photosensitive drum 222d located on the downstream side, and the sensor Sl of the photosensitive drum 222a located on the most upstream side is turned on last.
The time when the pattern Q shown in FIG. 4 reaches the transfer portion A (in this case, the time for rotating about 90 degrees) after the last sensor S1 is turned on is defined as a margin time and a margin angle. The photosensitive drum 222a is stopped.
In the photosensitive drums 222b to 222d other than the reference photosensitive drum 222a, the correction amount is detected from the detection results of the sensors S2 to S4 and the detection result of the sensor S1, and the correction amount is added to the extra time. Later, when that time has elapsed, the operation is stopped.
[0057]
For example, when the photosensitive drum 222b for cyan is considered, there is a shift of 60 degrees between the photosensitive drum 222b and the reference photosensitive drum 222a. Therefore, the correction amount of the photosensitive drum 222b is calculated from the timing when the sensor S1 is turned on and the timing when the sensor S2 is turned on. In this case, if the interval is 61 degrees and is advanced by 1 degree, it is necessary to return it once. Therefore, the correction amount is set to −1, this is added to 90 degrees of the extra time, and the extra time is 89 After the sensor S1 is turned on and the margin time for 89 degrees has elapsed, the operation is stopped.
[0058]
If the above-mentioned margin time is not set, if the correction amount is positive, the photosensitive drum 222b may be further rotated and stopped by that much, but if it is negative, the photosensitive drum 222b has already passed the stop position. In order to stop at the correct position, it is necessary to make one more rotation. If this is done, the surface of the transfer conveyance belt 216 and the surface of the photosensitive drum will be damaged by contact. While suppressing, it is possible to stop in a state where an ideal image can be recorded in a short time, and the subsequent image recording can be smoothly performed.
[0059]
A stepping motor is most suitable as a motor for individually driving the photosensitive drums.
[0060]
Further, no matter how precisely the dimension between the transfer sections A-A is set, if the mounting position of the photosensitive drum is shifted and there is an error of only 100 μm in the dimension, 600 dpi (diameter of one dot: 43 μm) In the image forming apparatus for high-density recording such as (approximately), a large color shift appears. Therefore, it is desirable to additionally provide a means for adjusting the stop position of each photosensitive drum regardless of the drive unevenness of the photosensitive drum. Similarly, an error is likely to occur in the mounting position of the above-described sensors S1 to S4. Therefore, it is desirable that the configuration be such that such an error can be corrected.
[0061]
Specifically, any configuration may be used as long as the above-mentioned margin time (margin angle) can be adjusted for each photosensitive drum. That is, in the above description, the allowance time is set to 90 degrees for all four photosensitive drums. However, the allowance time is corrected in advance in accordance with the sensor mounting error and the dimensional error between the transfer units, and the corrected allowance is used. It is only necessary to newly add (subtract) the correction amount at the time of stop to the time.
[0062]
Further, since it is difficult to correct these errors in advance, a method of adjusting a stop position of each photoconductor automatically or manually by outputting a specific test image in an adjustment process after assembly is completed. Good.
[0063]
Next, a method for adjusting the stop positions of the photosensitive drums 222a to 222d by manual setting will be described with reference to FIGS. The apparatus is changed to an adjustment mode (simulation mode) by operating a plurality of predetermined keys from an operation panel (not shown), and the touched display screen TP on the operation panel shifts the stop position of each photosensitive drum and the set phase state. Screens (FIGS. 6 and 7) for displaying the limit values (permissible values) of the above, and setting and changing those values and the like are performed. Here, the limit value (permissible value) is the limit (permissible) phase shift amount (angle) serving as a criterion for determining whether to execute or not to perform the rotation drive control (phase adjustment stop position control) of the photosensitive drum described above. Or the number of driving steps of the driving means).
[0064]
First, the photosensitive drum position setting screen 300 is displayed, and the cursor 306 is moved up and down with the selection keys 301 and 302 to determine the limit value or the recording color (the stop position of the photosensitive drum for forming an image of the described color). (Indicated by color name display).
[0065]
The set value of the stop position of the photosensitive drum is coded, and a desired value is input using a numeric key (not shown) on the operation panel.
That is, the stop position of the photosensitive drum is [1] is 60 degrees, [2] is 120 degrees, [3] is 180 degrees, [4] is 240 degrees, and [5] is relative to the reference photosensitive drum. By inputting [1] to [5] to the setting window 305, the stop position of the photosensitive drum of each color except the reference color is input and set.
[0066]
In the present embodiment, the reference color is black, and the photosensitive drum 222a for forming a black component image does not input the stop position, and the photosensitive drum 222a for the black component always stops at the predetermined position. However, the stop position of the photosensitive drum 222a for the black component may be settable, or may be automatically set according to conditions.
[0067]
Further, in the present embodiment, the unit for adjusting the phase shift of the photosensitive drum is set to 60 degrees. However, the present invention is not limited to this, and a value such as 30 degrees or 90 degrees may be used, but preferably 90 degrees or less.
The set value at the time of input setting is determined by pressing the OK key 303 after inputting the numerical value of the numeric keys or by operating the selection keys 301 and 302 as it is.
[0068]
To set a limit value (allowable value) as a criterion for determining whether or not to execute the phase adjustment stop position control of the photosensitive drum, select the uppermost LIMIT by operating the select keys 301 and 302, and operate The value can be set by setting the value of the setting window 305 to one of [1] to [3] using the numeric keys on the panel. Here, [1] is set to 10 degrees, [2] is set to 20 degrees, and [3] is set to 30 degrees, which is set to a value smaller than the position (phase) adjustment unit amount of each photoconductor drum 60 degrees. Is a value equal to or less than 1/2 of the position (phase) adjustment unit amount. In the present embodiment, the limit value (allowable value) is represented by an angle, but may be the number of drive steps of the drive means.
The setting of the limit value (allowable value) is determined by the same operation as the setting of the stop position of the photosensitive drum.
[0069]
The EXECUT key 304 is a key for executing a sample output of a test image in the set phase state of each photoconductor drum, so that the adjustment result can be viewed immediately after setting, and if there is a problem, the setting can be reset immediately. I can do it.
[0070]
In the present embodiment, the case where the phase adjustment unit amount is fixed to 60 degrees has been described. However, by changing the unit amount, it is possible to select and perform a rough phase setting or a fine phase setting. In this case, the limit value (permissible value) of the phase shift is also automatically determined in accordance with the selection of the phase adjustment unit amount, and the value is smaller than the phase adjustment unit amount, preferably １ ／ or less of the phase adjustment unit amount. It is good to set to the value of.
[0071]
Next, the stop control of the photosensitive drum when the phase shift amount of the photosensitive drum according to the present invention is equal to or larger than the limit value (allowable value) will be described with reference to the flowchart of FIG.
When the formation of each color component image for color printing on the paper is completed (step (hereinafter abbreviated as "ST") 1), a reference mark Q attached to the surface of each photosensitive drum is detected by an optical sensor or the like. Each is detected by Sl to S4 (ST2).
Based on the detection signals of the detection sensors S1 to S4, a phase corresponding to a preset stop position relationship with respect to the photosensitive drum 222a forming a black component image based on the rotational phase state of all the photosensitive drums is checked. When the limit value (allowable value) is set to, for example, 30 degrees with respect to the set shift amount, it is determined whether or not it is within a range of ± 30 degrees (ST3). If any of the determination results for the remaining photosensitive drums 222b to 222d excluding the reference photosensitive drum 222a has a phase shift of 30 degrees or more of the limit value (allowable value), the shift from the set value is performed. The above-described phase adjustment stop control for controlling the stop timing is executed so that there is no stop, and all the photosensitive drums 222a to 222d are stopped at preset stop positions (ST4).
[0072]
If the result of the phase shift determination for the remaining photosensitive drums 222b to 222d excluding the reference photosensitive drum 222a is less than the limit value (allowable value) of 30 degrees, the phase shift stop control is performed as a range in which the color shift is not conspicuous. Without executing, all the photosensitive drums 222a to 222d are simultaneously stopped by driving control of the stepping motor which is the driving means at the stop timing based on the detection signal of the reference photosensitive drum 222a detection sensor S1 (ST5). . At this time, the rotational phase state of all the photosensitive drums is shifted from a phase state corresponding to a preset stop state within a limit value (allowable value). The stop position of the photosensitive drum 222a may or may not be a preset stop position.
As a matter of course, the reference photoconductor drum may not be the photoconductor drum 222a for forming a black component image, and the number of photoconductor drums may be two, three, or more than four instead of four.
[0073]
As described above, when the detection signals of the detection sensors S2 to S4 deviate by more than the limit value (permissible value), the phase adjustment control of the photosensitive drum is executed. If the value does not exceed the value, the phase adjustment control of the photoconductor drum is not executed, and the other photoconductor drums 222b to 222d are stopped simultaneously with the stop of the rotation of the photoconductor drum 222a as a reference, so that the phase control is always performed. After a predetermined number of copies, after a predetermined time of operation, after a predetermined environmental change or trouble, etc., rotation operation for performing unnecessary phase alignment control of the image carrier, and accompanying rubbing wear of the image carrier can be minimized. This not only extends the life of the image carrier, but also saves energy.
[0074]
In addition, the rotation phase of the other photosensitive drum is stopped by the same operation using the control program for any one of the photosensitive drums as a reference, so that the rotational phase state between the photosensitive drums before the stop is maintained. By stopping all the photosensitive drums while keeping the same, it is not necessary to perform different control for each of the photosensitive drums. Useless rotation of the body drum can be prevented as much as possible. If the deviation is within the allowable value, the stop position of the photoconductor drum is not limited, and the photoconductor drum may be stopped in any rotational state, so that unnecessary rotation operation of the photoconductor drum can be prevented as much as possible.
[0075]
In addition, by providing an allowable value separately from the unit amount of the phase adjustment for setting the stop position of the photoconductor drum, the allowable value can be changed when the occurrence of color shift is conspicuous, and is smaller than the unit amount of the phase adjustment. By doing so (preferably 以下 or less), it is possible to prevent a large shift in the rotational phase state, and it is possible to set phase matching control according to the state of the apparatus.
[0076]
In addition, the allowable value for judging whether or not to execute the phase matching control can be changed. When the state where the color shift is conspicuous with the set allowable value occurs, the allowable value is changed by changing the allowable value. Can be made strict, and the occurrence of color misregistration can be prevented.
In addition, the allowable value can be increased in a range where the occurrence of color misregistration is inconspicuous, the criterion for judging the phase misregistration can be reduced, the phase adjustment control of the photosensitive drum can be reduced as much as possible, and unnecessary rotation of the photosensitive drum Can be prevented.
[0077]
In addition, when the allowable value is automatically set based on the preset phase adjustment unit amount for the stop position of each photoconductor drum, it is not necessary to reset the allowable position each time, It is possible to prevent troubles such as the allowable position being larger than the phase adjustment unit amount.
[0078]
【The invention's effect】
As explained above, First summary According to the above, phase adjustment control is performed only when the magnitude of the rotation phase state deviation exceeds the allowable value despite the large number of copies, long-time operation of the device, and other environmental changes or troubles. If the value does not exceed the allowable value, the phase adjustment control is not performed.Therefore, phase control is always performed, after copying a predetermined number of sheets, after running for a predetermined time, or after a predetermined environmental change or trouble occurs, the The rotation operation for performing unnecessary phase alignment control and the accompanying rubbing and abrasion of the image carrier can be prevented as much as possible, so that not only the life of the image carrier can be extended but also energy can be saved.
[0079]
Second summary According to this, even after a large amount of copying, long-time operation of the apparatus, changes in the surrounding environmental conditions, or occurrence of a minor trouble, the deviation of the image carriers from the preset rotational phase state is within an allowable value range. If any, perform phase adjustment control at all Lasso Instead, all the image carriers are stopped at the same time irrespective of the set stop position of each image carrier, so that all the image carrier rotation operations are the same and the transfer carrier that is in contact with the image carrier is And the mutual abrasion is reduced.
Further, as compared with the conventional apparatus that always performs the phase adjustment control, useless rotation of the image carrier can be prevented as much as possible, and not only can the rotation time of the image carrier be shortened, but also the life of the image carrier can be prolonged. It is also very useful for energy saving.
[0080]
Third summary According to this method, different controls need not be performed for each of the image carriers, so that not only the control is simplified, but also the useless rotation of the image carrier is minimized as compared with a conventional apparatus that always performs phase adjustment control. This not only prevents the rotation time of the image carrier and shortens the life of the image carrier, but also greatly saves energy.
[0081]
Fourth summary According to the above, when the occurrence of the color shift is conspicuous, the allowable value of the phase shift amount can be changed, and by making it smaller than the phase adjustment unit amount (preferably 位相 or less), the shift of the rotational phase state can be reduced. A large deviation can be prevented, and the phase matching control can be set according to the status of the apparatus.
[0082]
Fifth summary According to the above, when a state where the color shift is conspicuous with the set allowable value occurs, the allowable value can be changed, so that the criterion of the phase shift can be strict, and the color shift occurrence trouble can be prevented. Can be prevented.
In addition, the allowable value can be increased in a range where the occurrence of color shift is not conspicuous, the criterion for determining the phase shift can be lowered, the phase adjustment control of the image holder can be reduced as much as possible, and the useless rotation operation of the image carrier Can be prevented.
[Brief description of the drawings]
FIG. 1 is an operational explanatory view showing a side cross section of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is an operational explanatory view of a plurality of photosensitive drums arranged in parallel according to an embodiment of the present invention in a phase matching state.
FIG. 3 is an operational explanatory diagram illustrating an overlapping state of images on a plurality of photosensitive drums according to the embodiment of the present invention.
FIG. 4 is an explanatory diagram of phase control of a plurality of arranged photosensitive drums according to the embodiment of the present invention.
FIG. 5 is a time chart of an output signal of a sensor for detecting a shift angle of a plurality of photosensitive drums according to the embodiment of the present invention.
FIG. 6 is an explanatory diagram of an operation panel of the image forming apparatus according to the embodiment of the present invention.
FIG. 7 is an explanatory diagram of an operation panel of the image forming apparatus according to the embodiment of the present invention.
FIG. 8 is a flowchart for determining whether to perform phase control of the photosensitive drum according to the embodiment of the present invention.
FIG. 9 is an operational explanatory diagram of a conventional plurality of photosensitive drums arranged in parallel in a phase matching state.
[Explanation of symbols]
1 Image forming apparatus
216 Transfer belt
222a-222d photosensitive drum
M motor
Q fiducial mark
CON control unit
G1-G4 drive gear
S1 to S4 sensor

Claims (5)

A plurality of image carriers,
Driving means for driving the image carrier to rotate,
Detection means for detecting the rotation state of each image carrier when the image carrier is rotating,
By controlling the driving unit based on the detection signal of the detection unit, the image carrier has a phase matching unit to stop the image carrier in a preset rotation phase state,
When the detection signal of the detecting means is generated an allowable value or more shift preset for a given timing running means was I the phase case, when the deviation does not exceed the permissible value the phase Without performing the matching means ,
The permissible value serving as a criterion for determining the execution of the phase adjustment stop control is provided separately from a phase adjustment unit amount for presetting a stop position of each image carrier, and is smaller than the phase adjustment unit amount. Image forming apparatus. If the detection signal of the detection unit does not exceed a predetermined allowable value with respect to a predetermined timing, the rotation of all the image carriers is stopped at the same time without executing the phase adjustment unit. The image forming apparatus according to claim 1, wherein: 3. The image forming apparatus according to claim 2, wherein when stopping a plurality of image carriers at the same time, all the image carriers are stopped based on a detection signal of a predetermined image carrier. 2. The image forming apparatus according to claim 1 , wherein the allowable value is equal to or less than 1/2 of the phase adjustment unit amount . The image forming apparatus according to claim 1, wherein the allowable value serving as a criterion for determining execution of the phase adjustment stop control is changeable.

Images