JP4214724B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrophotographic image forming technique such as a printer, a copying machine, and a facsimile machine.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus, a developing unit configured to be able to switch the arrangement positions of a plurality of developing units each containing toner of different colors is provided, and one developing unit of the plurality of developing units is provided. It is known that an electrostatic latent image on a photoreceptor is developed at a development position facing the photoreceptor, and the toner image is primarily transferred to an intermediate transfer medium. In this image forming apparatus, a color toner image is formed by superimposing a plurality of color toner images on an intermediate transfer medium by switching the development unit arranged at the development position and repeating development with each color toner and primary transfer. The color toner image is secondarily transferred from the intermediate transfer medium to the transfer paper at the secondary transfer position to obtain a color image.
[0003]
In recent years, there has been a demand for space saving when installing an image forming apparatus. A transfer paper storage unit is disposed below the apparatus body, and an intermediate transfer medium is disposed above the transfer paper storage unit. Many structures are used to transport transfer paper along a transfer paper transport path extending substantially vertically from the container toward the secondary transfer position on the intermediate transfer medium, and further downsizing the device Therefore, the transfer paper conveyance path is made as short as possible.
[0004]
In many cases, a so-called universal cassette capable of selectively storing transfer sheets of a plurality of sizes is employed as a transfer sheet storage unit for storing transfer sheets. The transfer paper storage unit is provided with a transfer paper sensor for detecting the presence or absence of transfer paper. In order to be able to detect the presence or absence of transfer paper of the minimum size that can be stored, the transfer paper sensor The arrangement position is limited. For example, in order to be able to detect B5-size transfer paper stored in the direction in which the paper feed direction is the short side, the transfer paper sensor is disposed at a position less than 182 mm from the leading end of the transfer paper storage unit in the paper feed direction. Must.
[0005]
[Problems to be solved by the invention]
In such a small image forming apparatus, when a transfer sheet having a size larger than the minimum size (for example, A3) that can be stored in the transfer sheet storage unit is stored, when continuous printing is performed on a plurality of transfer sheets, It is impossible to detect the presence or absence of the next transfer sheet unless the trailing edge of the A3 size transfer sheet has passed through the transfer sheet sensor.
[0006]
In particular, the distance from the transfer sheet sensor to the secondary transfer position along the transfer sheet conveyance path is a dimension in the sheet feeding direction of a size that can be accommodated in the transfer sheet accommodating portion (for example, 420 mm if the long side is A3 size). When the image is formed on the transfer paper of the size, the transfer paper is transferred when the leading edge of the transfer paper reaches the secondary transfer position. Since the trailing edge of the sheet does not pass through the transfer sheet sensor, the presence or absence of the next transfer sheet cannot be accurately determined.
[0007]
On the other hand, as described above, there is a limit to moving the transfer paper sensor arrangement position away from the secondary transfer position in consideration of detection of a small-size transfer paper. Therefore, when performing continuous printing on a plurality of transfer sheets, it may be possible to individually set the next transfer sheet presence / absence determination timing according to the transfer sheet size. This is not preferable.
[0008]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of accurately determining whether or not there is a next transfer sheet at a certain timing.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, there is provided an exposure unit that forms an electrostatic latent image on a photoreceptor and a plurality of development units arranged selectively at predetermined development positions. A developing unit for developing the toner of the developing unit disposed at the developing position by attaching the toner to the electrostatic latent image, and a toner image that is primarily transferred from the photosensitive member at a predetermined primary transfer position. The intermediate transfer medium transported to a predetermined secondary transfer position, a transfer paper storage unit capable of selectively storing transfer papers of a plurality of sizes, and a detection signal corresponding to the presence or absence of the transfer paper in the transfer paper storage unit are output. Transfer sheet detecting means, a transfer paper determining means for taking in the detection signal output from the transfer paper detecting means, and determining the presence or absence of transfer paper in the transfer paper containing portion based on the taken-in detection signal, and the transfer paper Paper storage Disposed in the developing position in the order and the transfer sheet conveying path for guiding the transfer paper to the secondary transfer position, the first developing unit defined a different color the plurality of developing units which toner is accommodated in each advance to final development unit And a toner image developed by each of the plurality of developing units is superimposed on the intermediate transfer medium, and the superimposed color toner image is secondarily applied to the transfer paper at the secondary transfer position. Secondary transfer control means for performing transfer control, and D1 is a distance from the transfer paper detection means to the secondary transfer position along the transfer paper transport path, along the surface of the photoconductor. The distance from the development position to the primary transfer position is D2, and the front of the intermediate transfer medium in the toner image transport direction from the primary transfer position to the front. When the distance up to the secondary transfer position and D3, D1> (D2 + D3 ) is set to, the transfer paper judging means, incorporating said detection signal in synchronism with the developing operation completion of the final developing unit It is characterized by.
[0010]
According to this configuration, the toner image formed by developing the electrostatic latent image on the photoreceptor at the development position is primarily transferred to the intermediate transfer medium at the primary transfer position, and is conveyed to the secondary transfer position. When the secondary transfer position is subjected to secondary transfer onto the transfer sheet guided to the secondary transfer position along the transfer sheet conveyance path as it is, the development of the toner image is completed after the transfer sheet is completed. The end is located at a distance (D2 + D3) from the secondary transfer position along the transfer sheet conveyance path toward the transfer sheet detecting unit. Accordingly, since D1> (D2 + D3) is set, the trailing edge of the transfer paper has already passed through the transfer sheet detecting means, so that at the end of the development or at the subsequent development unit switching time, Therefore, it is possible to reliably determine the presence or absence of the transfer paper.
[0011]
As a result, the detection signal from the transfer paper detection means is captured in synchronization with the end of the development operation of the final development unit, and the presence or absence of the transfer paper in the transfer paper storage unit is determined based on the acquired detection signal, thereby transferring the transfer paper. Regardless of the paper size, the presence / absence of the transfer paper is reliably determined at a fixed timing, and the control configuration can be simplified.
[0012]
Note that “capturing a detection signal in synchronization with the switching timing” is not limited to “capturing a detection signal at the same time as the switching operation”, but relates to, for example, “development unit switching such as the end of the developing operation”. This includes the case of “capturing the detection signal simultaneously with the operation”. The plurality of developing units may store different color toners.
[0014]
In addition , a plurality of developing units containing different color toners are sequentially arranged at a developing position from a predetermined first developing unit to a final developing unit, and the respective toner images are superimposed on the intermediate transfer medium. Since the superimposed color toner image is secondarily transferred to the transfer paper at the secondary transfer position, when the development operation of the final development unit is completed, it is continuously transferred to the transfer paper as it is at the secondary transfer position. It will be. Therefore, since the trailing edge of the transfer paper has already passed through the transfer paper detecting means, the detection signal is taken in synchronization with the end of the developing operation of the final developing unit, so that the presence / absence of the next transfer paper is accurately determined. This makes it possible to make a reliable determination. In addition, since the presence or absence of transfer paper is determined before the next developing operation is started, it is possible to reliably avoid a situation in which toner is wasted.
[0015]
When the transfer paper determining means determines that there is transfer paper, the drive control means places the first developing unit at the development position, and when the transfer paper determining means determines that there is no transfer paper. The developing means may be disposed at a preset standby position (claim 2 ).
[0016]
According to this configuration, when the transfer paper determination unit determines that there is transfer paper, the first developing unit is disposed at the development position, and when it is determined that there is no transfer paper, the development unit is set at a preset standby position. Therefore, it is possible to detect the presence or absence of transfer paper in the transfer paper storage unit by taking in a detection signal output from the transfer paper detection means in synchronization with the end of the development operation by the final development unit. The operation is determined efficiently.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
First, the configuration of a printer that is an embodiment of an image forming apparatus according to the present invention will be described with reference to FIGS. 1 is a diagram showing an internal configuration of the printer, FIG. 2 is a schematic diagram of a rotary developing unit, FIG. 3 is a development view of an intermediate transfer belt, FIG. 4 is a schematic diagram for explaining dimensions between respective parts of the printer, and FIG. FIG. 2 is a block diagram showing an electrical configuration of the printer.
[0018]
This printer forms a full color image by superposing four color toners of yellow (Y), magenta (M), cyan (C), and black (K), or uses only black (K) toner, for example. A monochrome image is formed. In this printer, when a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 causes each part of the engine unit 1 to respond to the control signal from the main control unit 100. And an image corresponding to the image signal is printed out on the transfer paper 4 conveyed from the paper feed cassette 3 provided in the lower part of the apparatus main body 2.
[0019]
The engine unit 1 includes a photosensitive unit 10, a rotary developing unit 20, an intermediate transfer unit 30, a fixing unit 40, and an exposure unit 50 in addition to the paper feed cassette 3. It is arranged. The photoconductor unit 10 includes a photoconductor 11, a charging unit 12, and a cleaning unit 13. The rotary developing unit 20 includes a yellow developing unit 2Y containing yellow toner, a magenta developing unit 2M containing magenta toner, and a cyan toner. Are provided. The intermediate transfer unit 30 includes an intermediate transfer belt 31, a vertical synchronization sensor 32, a belt cleaner 33, a secondary transfer roller 35, a photosensitive roller, and the like. A body drive motor 36 is provided. The seven units 10, 2Y, 2C, 2M, 2K, 30, 40 are configured to be detachable from the apparatus main body 2, respectively.
[0020]
The photoconductor 11 of the photoconductor unit 10 is moved in the direction of the arrow 5 by the photoconductor drive motor 36 in a state where the seven units 10, 2Y, 2C, 2M, 2K, 30, 40 are mounted on the apparatus main body 2. The rotating member is in contact with the intermediate transfer belt 31, and the contact position (primary transfer position) is set in the primary transfer unit 14. Around the photoreceptor 11, a charging unit 12, a rotary developing unit 20, and a cleaning unit 13 are arranged along the rotation direction 5.
[0021]
The charging unit 12 includes a wire electrode to which a predetermined high voltage is applied, and uniformly charges the outer peripheral surface of the photoconductor 11 by, for example, corona discharge, and has a function as a charging unit. The cleaning unit 13 is disposed immediately upstream of the charging unit 12 in the rotation direction 5 of the photoconductor 11 and downstream of the primary transfer unit 14, and the primary image of the toner image from the photoconductor 11 to the intermediate transfer belt 31 is disposed. The toner remaining on the outer peripheral surface of the photoconductor 11 after the transfer is scraped off by a cleaning blade to clean the surface of the photoconductor 11.
[0022]
The exposure unit 50 includes, for example, a laser light source 51 made of a semiconductor laser, a polygon mirror 52 that reflects the laser light from the laser light source 51, a polygon motor 53 that rotationally drives the polygon mirror 52, and a laser light reflected by the polygon mirror 52. Lens section 54, a plurality of reflecting mirrors 55, a horizontal synchronization sensor 56, and the like. The laser beam 57 reflected by the polygon mirror 52 and emitted through the lens unit 54 and the reflection mirror 55 is scanned in the main scanning direction (direction perpendicular to the paper surface of FIG. 1) on the surface of the photoreceptor 11. Then, an electrostatic latent image corresponding to the image signal is formed on the surface of the photoreceptor 11. At this time, the horizontal synchronization sensor 56 obtains a synchronization signal in the main scanning direction, that is, a horizontal synchronization signal.
[0023]
The polygon motor 53 rotates the polygon mirror 52 at a high speed at a preset rotation speed, for example, 30,000 rpm (rotation / minute). The polygon motor 53 has a configuration capable of high-speed rotation with an oil bearing, for example, and starts driving. When the rotation speed reaches the set rotation speed, a ready signal is sent to the CPU 111. The exposure unit 50 corresponds to exposure means.
[0024]
The rotary developing unit 20 has a holding frame 22 fixed to a rotation shaft 21 at the center thereof, and the holding frame 22 holds the four color developing units 2Y, 2C, 2M, and 2K in a detachable manner. The developing units 2Y, 2C, 2M, and 2K have developing rollers 23Y, 23C, 23M, and 23K, respectively, and the developing rollers 23Y, 23C, 23M, and 23K are disposed at a developing position 15 that faces the photoconductor 11. In this state, each color toner adheres to the electrostatic latent image on the photoreceptor 11 and development is performed.
[0025]
A side plate 24 is disposed in the apparatus main body 2 on the near side perpendicular to the paper surface of FIG. 1 of the rotary developing unit 20 as indicated by a broken line in FIG. 2, and the side plate 24 has an outlet 241 drilled at an appropriate position. It has. In FIG. 2, for convenience of explanation, the side plate 24 is shown in a circular shape, but is not limited thereto, and may have another shape, for example, a shape that covers the entire side surface of the apparatus main body 2.
[0026]
Each of the developing units 2Y, 2C, 2M, 2K and the holding frame 22 are provided with guide rails (not shown) that engage with each other in parallel with the rotation shaft 21, and each of the developing units 2Y, 2C, 2M, 2K. Can be pulled out through the outlet 241 in the direction of the rotating shaft 21 of the holding frame 22. Further, the new developing unit can be attached to the holding frame 22 by pushing it in the direction of the rotating shaft 21 of the holding frame 22 through the outlet 241.
[0027]
Here, for example, as shown in FIG. 2C, only when one of the developing units (here, the developing unit 2K) is arranged at the taking-out position, the developing unit is taken out through the take-out port 241, and a new one is taken out after taking out. A development unit can be installed. While the developing unit is disposed at a position other than the take-out position, the side plate 24 prevents the development unit from being taken out. When all the developing units 2Y, 2C, 2M, and 2K are attached to the holding frame 22, the developing units 2Y, 2C, 2M, and 2K are arranged radially about the rotation shaft 21.
[0028]
A developing system driving motor 81 is connected to the rotary shaft 21 via a rotary clutch 82. In the present embodiment, the developing system driving motor 81 is formed of a stepping motor, for example, and is connected to the developing rollers 23Y, 23C, 23M, and 23K in addition to the rotating shaft 21. When the rotary clutch 82 is turned on and the development system drive motor 81 is driven forward, the holding frame 22 rotates and the arrangement positions of the four development units 2Y, 2C, 2M, and 2K move. On the other hand, when one developing unit is disposed at the developing position 15 and the rotary clutch 82 is turned off and the developing system driving motor 81 is driven in reverse, the developing rollers 23Y, 23C, 23M, and 23K rotate. 1 and 2, in this embodiment, for example, the holding frame 22 rotates clockwise, and the developing rollers 23Y, 23C, 23M, and 23K rotate counterclockwise.
[0029]
Further, a position sensor 25 for detecting a standby position (home position) of the holding frame 22 (rotary developing unit 20) is provided on one end side of the rotating shaft 21 (for example, the front side in FIG. 2). . The position sensor 25 includes, for example, a detection disc 251 fixed to one end of the rotating shaft 21 and a photo interrupter 252 in which a light emitting unit (for example, an LED) and a light receiving unit (for example, a photodiode) are arranged to face each other. The detection disc 251 is arranged so that the peripheral edge of the detection disc 251 rotates in the gap between the light emitting portion and the light receiving portion of the photo interrupter 252.
[0030]
With this configuration, when the slit formed in the peripheral edge of the detection disc 251 passes through the gap of the photo interrupter 252, the output signal from the photo interrupter 252 is switched between a low level and a high level. Then, after driving for a predetermined number of driving pulses set in advance from the change in the output signal level, the developing system driving motor 81 is stopped, and the rotary developing unit 20 is stopped at the standby position. When rotating from the standby position, the position of the holding frame 22 is determined based on the number of drive pulses of the development system drive motor 81 from the time when the output signal level of the position sensor 25 changes. FIG. 1 shows a state in which the black developing unit 2K is arranged at the developing position 15, FIG. 2A shows a state in which the holding frame 22 is arranged in the standby position, and FIG. 1B shows a state in which the yellow developing unit 2Y is in the developing position. (C) shows a state where the black developing unit 2K is arranged at the take-out position.
[0031]
The configuration of the position sensor 25 is not limited to this, and a reflective optical sensor may be used instead of the photo interrupter. Further, for example, a feature portion such as a protrusion may be formed on a part of the outer peripheral edge of the holding frame 22, and the standby position may be detected by detecting this feature portion. In this case, there is no need to provide the detection disk 251 on the rotating shaft 21, the axial size can be reduced, and this is advantageous in reducing the size of the apparatus.
[0032]
Further, unit-side connectors 26Y, 26C, 26M, and 26K are fixed to one end side surfaces of the developing units 2Y, 2C, 2M, and 2K, respectively, and a body-side connector 27 is movably disposed on the apparatus main body 2. When the holding frame 22 (rotary developing unit 20) is arranged at the developing position 15, the unit fixed to the developing unit one downstream in the rotation direction of the holding frame 22 of the developing unit at the developing position 15 The side connector (for example, as shown in FIG. 2B, when the yellow developing unit 2Y is at the developing position 15, the unit side connector 26K fixed to the black developing unit 2K on the downstream side thereof) is the main body side connector. It is comprised so that it may be arrange | positioned in 27 opposing positions.
[0033]
The unit-side connectors 26Y, 26C, 26M, and 26K incorporate nonvolatile memories 83Y, 83C, 83M, and 83K (FIG. 5), respectively. The nonvolatile memories 83Y, 83C, 83M, and 83K are for storing various data related to the developing units 2Y, 2C, 2M, and 2K, and are respectively terminal electrodes (not shown) of the unit side connectors 26Y, 26C, 26M, and 26K. Is omitted). As the nonvolatile memory, an EEPROM such as a flash memory, a ferroelectric memory (Ferroelectric RAM), or the like can be employed.
[0034]
The connector drive motor 28 moves the main body side connector 27 in the contact / separation direction with respect to the rotary developing unit 20, and is a unit side connector (in FIG. 2B), the unit side connector disposed opposite to the main body side connector 27. 26K), the main body connector 27 is moved between the fitting position and the separating position.
[0035]
At the fitting position, the terminal electrode of the unit side connector 26K and the terminal electrode of the main body side connector 27 are electrically connected, whereby the nonvolatile memory built in the unit side connector and the CPU 111 are connected to both connectors. Is connected to the CPU 111 and transfers data to and from the CPU 111, thereby detecting mounting of the developing unit, detection of a new product, life management, and the like.
[0036]
The apparatus main body 2 has a front cover that covers the engine unit 1 including the units 10, 2Y, 2C, 2M, 2K, 30, and 40. When the user or the like replaces the developing unit, Work is performed with the front cover open, but normal printing operations are performed with the front cover closed.
[0037]
A developing bias in which an AC component is superimposed on a DC component or a DC component is applied to the developing roller by the developing bias generation circuit 118, and the toner of the color from the developing unit disposed at the developing position 15 facing the photoreceptor 11. Is attached to the electrostatic latent image on the surface of the photoconductor 11 and developed.
[0038]
The rotary developing unit 20 (developing units 2Y, 2C, 2M, 2K) corresponds to the developing means, and the holding frame 22 corresponds to the unit holding unit. Further, the developing system driving motor 81 and the rotary clutch 82 have a function as unit driving means.
[0039]
The intermediate transfer belt 31 of the intermediate transfer unit 30 is stretched over a tension roller 31A, a driving roller 31B, a tension roller 31C, and a driven roller 31D, and corresponds to an intermediate transfer medium. The tension roller 31 </ b> A is for reliably bringing the intermediate transfer belt 31 into contact with the photoconductor 11. The driving roller 31B is rotationally driven together with the photosensitive member 11 by the photosensitive member driving motor 36.
[0040]
As shown in FIG. 3, the intermediate transfer belt 31 is an endless belt formed by joining substantially rectangular sheet bodies at a seam 71. In FIG. 3, an arrow 72 indicates the rotational drive direction (toner image transport direction), and an arrow 73 indicates the rotational axis direction.
[0041]
The intermediate transfer belt 31 has a protrusion 74 provided on one end side (upper side in FIG. 3) in the rotation axis direction 73, and also has a transfer prohibition area 75 and a transfer permission area 76. The transfer prohibition area 75 is set from one end to the other end in the rotation axis direction 73 within a predetermined size range on both sides of the joint 71. The transfer permission area 76 is an area other than the transfer prohibition area 75 and is set to a rectangular area excluding one end portion and the other end portion in the rotation axis direction 73, and the toner image is primary in the transfer permission area 76. Transcribed.
[0042]
As shown in FIG. 3A, an A3 size toner image 77 having a long side direction in the rotational drive direction 72 can be transferred to the transfer permission area 76. Further, as shown in FIG. 3B, the transfer permission area 76 is divided into two sub areas 76A and 76B, and is A4 size or less which is the short side direction in the rotation driving direction 72 in one rotation of the intermediate transfer belt 31. For example, two A4, A5, and B5 toner images can be transferred. In FIG. 3B, an A4 size toner image 78 is shown.
[0043]
For example, a roller-like bias applying member (not shown) is in contact with the intermediate transfer belt 31, and a predetermined primary transfer bias is applied to the bias applying member. The toner image on the photoreceptor 11 is primarily transferred to the intermediate transfer belt 31 by the primary transfer bias.
[0044]
The vertical synchronization sensor 32 includes, for example, a photo interrupter having a light emitting unit (for example, an LED) and a light receiving unit (for example, a photodiode) disposed to face each other, and is disposed on one end side in the rotational axis direction 73 of the rotating intermediate transfer belt 31. The detection signal is output by detecting the passage of the protrusion 74. The detection signal output from the vertical synchronization sensor 32 is used as a vertical synchronization signal serving as a reference for image formation control by the engine control unit 110. The vertical synchronization sensor 32 is disposed in the vicinity of the driven roller 31D, thereby reducing the influence of bending and shaking of the intermediate transfer belt 31 so that the protrusion 74 can be detected stably.
[0045]
The belt cleaner 33 is arranged so that the contact state (solid line in FIG. 1) and the separation state (broken line in FIG. 1) and the separation state (broken line in FIG. 1) can be switched by the cleaner connecting / disconnecting clutch. In this state, the residual toner on the intermediate transfer belt 31 is scraped off. The contact and separation of the belt cleaner 33 are performed with respect to the transfer prohibited area 75 of the intermediate transfer belt 31.
[0046]
The secondary transfer roller 35 is switched between a contact state (solid line in FIG. 1) and a separation state (broken line in FIG. 1) with the intermediate transfer belt 31 by the secondary transfer roller separation / contact clutch. A predetermined secondary transfer bias is applied to the secondary transfer roller 35 in contact with the intermediate transfer belt 31, and the toner image on the intermediate transfer belt 31 is transferred to the transfer paper 4 while the transfer paper 4 is conveyed. For the next transfer, the contact position (secondary transfer position) is set in the secondary transfer portion 37.
[0047]
The fixing unit 40 includes a heating roller 41 and a pressure roller 42, and the toner on the transfer paper 4 is heated and melted and fixed to the transfer paper 4 while the transfer paper 4 is conveyed by the rollers 41 and 42. It functions as a fixing unit.
[0048]
The paper feed cassette 3 is configured as a so-called universal cassette that can selectively accommodate transfer papers of A3, B4, A4, and B5 sizes. The A3 and B4 size transfer papers are fed in the paper feed direction (FIG. 1). The A4 and B5 size transfer paper can be accommodated in either the long side or the short side.
[0049]
A transfer paper sensor 90 for detecting the presence or absence of the transfer paper 4 is disposed inside the paper feed cassette 3. The transfer paper sensor 90 includes a rotatable turning piece and a photo interrupter that detects the turning piece. For example, when the turning piece is in a position rotated by the transfer paper 4 on which the turning pieces are stacked. (Indicated by a solid line in FIG. 1) is an on signal, and when there is no transfer paper 4 and the rotating piece is at a position lowered by its own weight (indicated by a broken line in FIG. 1), a detection signal that is an off signal is It is sent to the control unit 110. The transfer paper sensor 90 is disposed at a position where the B5-size transfer paper can be detected (position less than 182 mm from the end of the paper feed cassette 3).
[0050]
A paper feed roller 61 is disposed at the front end (right end in FIG. 1) of the paper feed cassette 3. A feed roller pair 62 and a gate roller pair 63 are disposed above the paper feed roller 61. A conveyance roller pair 64 and a discharge roller pair 65 are disposed with the next transfer unit 37 and the fixing unit 40 interposed therebetween.
[0051]
The feed roller 61, the feed roller pair 62, the gate roller pair 63, the secondary transfer roller 35, the heating roller 41 of the fixing unit 40, the transport roller pair 64, and the discharge roller pair 65 are respectively the same through a driving force transmission mechanism. It is connected to a conveyance system drive motor 84. The conveyance system drive motor 84 outputs a ready signal when it reaches a predetermined rotational speed. The feed roller 61 is turned on by the feed clutch 85, the feed roller pair 62 is turned on by a feed clutch (not shown), and the gate roller pair 63 is turned on by the gate clutch 86. Is transmitted and driven to rotate. Then, the transfer paper 4 is discharged to a paper discharge unit 6 provided on the upper part of the apparatus main body 2 by a discharge roller pair 64.
[0052]
The position at which the paper feed roller 61 is disposed in the paper feed cassette 3 is set to the paper feed position 91, and the transfer paper transport path 7 (in FIG. A pair of feed rollers 62 and a pair of gate rollers 63 are arranged in this order from the bottom on the transfer paper conveyance path 7.
[0053]
Here, with reference to FIG. 4, the dimension between each part of this printer is demonstrated. FIG. 4A is a schematic diagram for explaining the dimension between each part of the transfer paper conveyance path 7, and FIG. 4B is a diagram illustrating the development position 15 and the primary position in the rotation direction 5 of the photoconductor 11 along the surface of the photoconductor 11. FIG. 4C is a schematic diagram illustrating the distance between the primary transfer unit 14 and the secondary transfer unit 37 in the rotational driving direction 72 along the intermediate transfer belt 31. is there. In FIG. 4, for convenience of explanation, the transfer paper conveyance path 7, the surface of the photoconductor 11, and the intermediate transfer belt 31 are respectively represented by straight lines.
[0054]
As shown in FIG. 4A, the distance between the transfer paper sensor 90 and the feed roller pair 62 is L1, the distance between the feed roller pair 62 and the gate roller pair 63 is L2, and the gate roller pair 63 to the secondary transfer unit 37. In this embodiment, for example, if the distance is L3,
L1 = 74.5 mm,
L2 = 12.8 mm,
L3 = 66.3mm
Respectively. Accordingly, the distance D1 between the transfer paper sensor 90 and the secondary transfer unit 37 is:
D1 = L1 + L2 + L3 = 263.6 mm
It becomes. Since the dimensions of the long sides of the A4, B4, and A3 sizes are 297, 364, and 420 mm, respectively, the A4 accommodated in the secondary transfer unit 37 in the paper feed cassette 3 in the direction in which the paper feed direction is the long side. , B4, and A3 size transfer paper 4, when the secondary transfer is started, the rear end of the transfer paper 4 has not yet passed through the transfer paper sensor 90.
[0055]
Further, as shown in FIG. 4B, the distance between the developing position 15 and the primary transfer portion 14 in the rotation direction 5 of the photoconductor 11 along the surface of the photoconductor 11 is D2, and FIG. As shown, when the distance from the primary transfer unit 14 to the secondary transfer unit 37 in the rotational drive direction 72 on the intermediate transfer belt 31 is D3,
D2 = 42.9 mm,
D3 = 114mm
Is set to
[0056]
Accordingly, since the secondary transfer is performed in the secondary transfer unit 37 following the primary transfer of the last color in the primary transfer unit 14, after the development of the last color is completed, The end faces downward from the secondary transfer unit 37 along the transfer paper transport path 7,
D2 + D3 = 156.9mm
In the position.
[0057]
Here, since D1> (D2 + D3), at that time, the rear end of the transfer paper 4 reliably passes through the transfer paper sensor 90 regardless of the size of the transfer paper 4. Therefore, by setting D1> (D2 + D3), it is possible to accurately determine the presence or absence of the next transfer sheet 4 at the end of the development of the last color regardless of the size of the transfer sheet 4 accommodated in the paper feed cassette 3. Is possible.
[0058]
The feed roller pair 62, the gate roller pair 63, the transport roller pair 64, the discharge roller pair 65, the transport system drive motor 84, the paper feed clutch 85, the feed clutch, the gate clutch 86, and the like constitute the transfer paper transport unit 60. The paper feed cassette 3 corresponds to a transfer paper storage unit, and the transfer paper sensor 90 corresponds to a transfer paper detection unit.
[0059]
In FIG. 5, the operation display panel 8 is disposed at an appropriate position on the upper surface of the apparatus main body 2 and includes a plurality of operation keys and a display unit made up of, for example, a liquid crystal display. The main control unit 100 includes a CPU 101, an interface 102 that exchanges control signals with an external device, and an image memory 103 that stores an image signal given through the interface 102. When the CPU 101 receives a print command signal including an image signal from an external device via the interface 102, the CPU 101 converts the job data into a format suitable for an operation instruction of the engine unit 1 and sends the job data to the engine control unit 110.
[0060]
The engine control unit 110 includes a CPU 111, a ROM 112, a RAM 113, and the like. The ROM 112 stores a control program for the CPU 111 and the like. The RAM 113 temporarily stores the control data of the engine unit 1 and the calculation result by the CPU 111, and the CPU 111 stores data related to the image signal sent from the external device via the CPU 101 in the RAM 113.
[0061]
For example, the CPU 111 receives a vertical synchronization signal Vsync from the vertical synchronization sensor 32 as an input signal from the engine unit 1, receives a horizontal synchronization signal Hsync from the horizontal synchronization sensor 56, and receives detection signals from the position sensor 25 and the transfer paper sensor 90. . The CPU 111 controls the operation of each unit of the engine unit 1 based on these input signals and the control program.
[0062]
That is, the CPU 111 sends a control signal to the motor drive circuit 114 that drives the photoconductor drive motor 36 to rotate the photoconductor 11 and the intermediate transfer belt 31 in synchronization. Further, the CPU 111 sends a control signal to a separation / engagement clutch drive circuit (not shown) that drives each of the separation / contact clutches, and controls separation and contact of the belt cleaner 33 and the secondary transfer roller 35 with respect to the intermediate transfer belt 31. . In addition, the CPU 111 receives the operation contents for the operation keys of the operation display panel 8 and controls the display contents of the display unit.
[0063]
The CPU 111 sends a control signal to the motor drive circuit 115 that drives the conveyance system drive motor 84 to control the conveyance of the transfer paper 4 from the paper feed cassette 3 to the paper discharge unit 6. The paper 4 is conveyed at the same speed as the peripheral speed of the intermediate transfer belt 31. Further, the CPU 111 sends a control signal to the clutch drive circuit 116 that drives the paper feed clutch 85, and controls the feeding of the transfer paper 4 from the paper feed cassette 3 to the transfer paper transport path 7. In addition, the CPU 111 sends a control signal to the clutch drive circuit 117 that drives the gate clutch 86, and in synchronization with the primary transfer toner image on the intermediate transfer belt 31, the gate roller pair 63 toward the secondary transfer unit 37. The secondary feeding of the transfer paper 4 is performed.
[0064]
The CPU 111 sends a control signal to the development bias generation circuit 118 to control the application of the development bias. Further, the CPU 111 sends a control signal to the motor drive circuit 119 that drives the connector drive motor 28 to control the fitting and separation between the unit side connectors 26Y, 26C, 26M, and 26K and the main body side connector 27. Further, the CPU 111 counts the number of written pixels of the electrostatic latent image using a control signal sent to the laser light source 51, calculates the amount of toner used for each color based on the number of pixels, and stores the non-volatile memories 83Y, 83C, By writing data relating to the amount of toner used to 83M and 83K and reading the stored contents of the non-volatile memories 83Y, 83C, 83M and 83K, it is possible to detect the newness of the installed development units 2Y, 2C, 2M and 2K and Make a decision.
[0065]
In addition, the CPU 111 sends a control signal to the motor drive circuit 120 that drives the developing system drive motor 81 and also sends a control signal to the clutch drive circuit 121 that drives the rotary clutch 82, so that the holding frame 22 and the developing roller The rotational drive of 23Y, 23C, 23M, and 23K is controlled.
[0066]
Here, the CPU 111 arranges the rotary developing unit 20 (holding frame 22) at the standby position when the printing operation is not performed. When a plurality of color print command signals are input to the CPU 111 from the external device via the CPU 101 of the main control unit 100, the holding frame 22 at the standby position is rotated and the developing units 2Y, 2C, 2M, 2K are rotated. A color toner image is formed at the developing position 15 in this order. That is, from the standby position, the holding clutch 22 is rotated by turning on the rotary clutch 82 and the forward drive of the developing system driving motor 81 to place the developing unit 2Y at the developing position 15, and the rotary clutch 82 is turned off and the developing is performed. The developing roller 23Y is rotated by the reverse drive of the system driving motor 81. When the development by the developing unit 2Y is completed, the developing roller 23Y starts decelerating. When the decelerating is completed, the holding frame 22 is rotated by turning on the rotary clutch 82 and driving the developing system driving motor 81 in the normal direction. 2C is arranged at the development position 15. Then, each color is sequentially developed, and when the development by the developing unit 2K is completed, the developing roller 23K starts decelerating. When the decelerating is completed, the holding frame 22 is rotated.
[0067]
At this time, in synchronization with the start of deceleration of the developing roller 23K, the detection signal of the transfer sheet sensor 90 is taken in and the presence or absence of the transfer sheet 4 in the sheet feeding cassette 3 is determined. When it is determined that there is transfer paper, the holding frame 22 is rotated to place the developing unit 2Y at the developing position 15, and an exposure operation using the next image signal is started. Then, in synchronization with the formation of the primary transfer toner image on the intermediate transfer belt 31, the paper feed clutch 85 is turned on at a predetermined timing to start feeding the transfer paper 4 from the paper feed cassette 3.
[0068]
On the other hand, if it is determined that there is no transfer paper, the holding frame 22 is rotated and placed at the standby position, and a signal indicating the absence of transfer paper is sent to the external device via the CPU 100 without performing an exposure operation.
[0069]
The CPU 111 corresponds to transfer sheet determination means and drive control means, the development unit 2Y corresponds to the first development unit, and the development unit 2K corresponds to the final development unit. Note that the ROM 112 and the RAM 113 may employ a nonvolatile memory such as an EEPROM or another memory.
[0070]
Next, the operation of this printer will be described. When a print command signal including an image signal is given to the main control unit 100 from an external device such as a host computer, the engine control unit 110 starts operation of each unit of the engine unit 1 in response to the control signal from the main control unit 100. To do. Here, it is assumed that a print command signal for printing a plurality of color images is given.
[0071]
At this time, if the size of the transfer paper 4 loaded in the paper feed cassette 3 does not match the size instructed by the print command signal, a message prompting the user to replace the paper feed cassette is displayed on the operation display panel 8. To do. In FIG. 1, the printer is provided with one paper feed cassette 3, but the printer is not limited to this, and may be provided with a plurality of paper feed cassettes.
[0072]
The size of the transfer paper 4 loaded on the paper feed cassette 3 matches the size indicated by the print command signal (or the size indicated by the print command signal among the plurality of paper feed cassettes). First, the transport system driving motor 84 is turned on. Subsequently, when a ready signal is output from the conveyance system driving motor 84, the driving of the photosensitive member driving motor 36 is started, the intermediate transfer belt 31 is driven at a predetermined peripheral speed S1, and the vertical synchronizing signal Vsync is cycled. And the polygon motor 53 starts to be driven. When the ready signal is output from the polygon motor 53, the next vertical synchronization signal Vsync is effectively received, the surface of the photoconductor 11 is uniformly charged by the charging unit 12, and the surface of the photoconductor 11 is exposed to light. An electrostatic latent image corresponding to the image signal is formed by the laser light 57 from the unit 50, and the electrostatic latent image is developed by the rotary developing unit 20 to form a toner image. The toner image is transferred to the primary transfer unit. 14, primary transfer is performed on the intermediate transfer belt 31.
[0073]
That is, the vertical synchronization signal Vsync is output for each round of the intermediate transfer belt 31, and the image request signal Vreq is output after a predetermined time from the output time of each vertical synchronization signal Vsync. The formation of the corresponding electrostatic latent image is started and the developing bias is turned on. By this time, the rotary developing unit 20 (unit holding unit 22) is rotated from the standby position, and the developing unit 2Y is arranged at the developing position 15.
[0074]
The developing unit of the rotary developing unit 20 is switched every time the vertical synchronization signal Vsync is output, and toner images of each color are formed on the photoconductor 11 and sequentially transferred to the intermediate transfer belt 31 sequentially. During this time, the secondary transfer roller 35 is separated from the intermediate transfer belt 31, so that the toner images of the respective colors are superimposed on the intermediate transfer belt 31.
[0075]
The developing bias is turned off after a predetermined time predetermined by the transfer paper size from the output time of each vertical synchronizing signal Vsync, and the developing rollers 23Y, 23C, 23M, and 23K start decelerating in synchronization with this turning off. The rotary developing unit 20 starts rotating in synchronization with the end of deceleration, and the next developing unit is arranged at the developing position 15. As a result, the toner images Y, C, M, and K are superimposed on the transfer permission area 76 of the intermediate transfer belt 31.
[0076]
On the other hand, the uppermost transfer sheet 4 in the bundle of transfer sheets loaded in the sheet feed cassette 3 is taken out by the sheet feed roller 61 and conveyed at a predetermined speed by the feed roller pair 62, and the leading end of the transfer sheet 4 is the gate roller pair. The feed roller pair 62 stops after a predetermined time after reaching 63. As a result, the transfer paper 4 is held in a bent state as shown in FIG. 1, so that the leading end of the transfer paper 4 is securely nipped between the rollers of the gate row pair 63 over the entire width direction by the bending force. The Then, the gate clutch 86 is turned on in synchronization with the toner image on the intermediate transfer belt 31, and the transfer paper 4 is secondarily fed from the gate roller pair 63 toward the secondary transfer unit 37.
[0077]
Then, after a predetermined time from the output time of the vertical synchronization signal Vsync, the secondary transfer roller separating clutch is turned on, the secondary transfer roller 35 comes into contact with the intermediate transfer belt 31, and then the secondary transfer after a predetermined time. Application of the secondary transfer bias to the roller 35 is turned on. As a result, the color toner image in which the toner images Y, C, M, and K that are primarily transferred to the transfer permission area 76 of the intermediate transfer belt 31 are superimposed is secondarily transferred to the transfer paper 4.
[0078]
The gate clutch 86 is turned off after the transfer paper 4 is carried out, and the secondary transfer bias is turned off after an application time set in advance according to the size of the transfer paper 4. After the application of the secondary transfer bias is turned off, the secondary transfer roller separating clutch is turned on, and the secondary transfer roller 35 is separated from the intermediate transfer belt 31. In the fixing unit 40, the toner image is fixed to the transfer paper 4 while the transfer paper 4 is conveyed. The transfer paper 4 is further transported by the transport roller pair 64 and discharged to the paper discharge unit 6 by the discharge roller pair 65.
[0079]
Next, when the development of the last color by the developing unit 2K is completed, the detection signal of the transfer sheet sensor 90 is taken in at the time when the developing roller 23K starts to decelerate (when the developing bias is turned off), and the transfer sheet in the sheet feeding cassette 3 is captured. The presence or absence of 4 is determined.
[0080]
Here, if it is determined that there is transfer paper, the rotary developing unit 20 rotates and the developing unit 2Y is arranged at the developing position 15. Subsequently, the same operation is performed in synchronization with the vertical synchronization signal Vsync, and the second image is transferred to the transfer paper 4.
[0081]
On the other hand, when it is determined that there is no transfer paper, the rotary developing unit 20 (holding frame 22) is arranged at the standby position by the rotation of the rotary developing unit 20. In addition, a signal indicating that there is no transfer paper is sent to the external device via the CPU 101, and the printing operation is stopped. After a predetermined time elapses, the photosensitive member driving motor 36 decelerates and stops, and the transfer paper 4 is stopped. Wait for replenishment.
[0082]
As described above, according to the present embodiment, the distance from the transfer sheet sensor 90 to the secondary transfer unit 37 along the transfer sheet conveyance path 7 is D1, and from the developing position 15 along the surface of the photoconductor 11. If the distance to the primary transfer position 14 is D2, and the distance from the primary transfer portion 14 to the secondary transfer portion 37 in the toner image transport direction along the surface of the intermediate transfer belt 31 is D3, Since D1> (D2 + D3) is set, the trailing edge of the transfer sheet 4 has surely passed the transfer sheet sensor 90 when the primary transfer of the development unit 2K (final development unit) is completed. Therefore, it is possible to accurately determine the presence or absence of the next transfer sheet 4.
[0083]
Further, according to the present embodiment, the detection signal of the transfer paper sensor 90 is captured in synchronization with the deceleration start time of the developing roller 23K of the developing unit 2K (final developing unit), so that it is always at a constant timing. The presence / absence of the transfer paper 4 can be determined, whereby the configuration of the control program can be simplified.
[0084]
Further, according to the present embodiment, when it is determined that there is transfer paper in the state where the developing unit 2K is disposed at the developing position 15, the rotary developing unit 20 (holding frame 22) is rotated to develop the developing roller 23Y (developing unit). 2Y) is arranged at the developing position 15, and when it is determined that there is no transfer paper, the rotary developing unit 20 (holding frame 22) is rotated and arranged at the standby position, and the developing unit 2K (final developing unit) By capturing the detection signal of the transfer paper sensor 90 in synchronization with the deceleration start time of the developing roller 23K, the movement control of the rotary developing unit 20 can be performed efficiently.
[0085]
The present invention is not limited to the above embodiment, and various modifications can be made to the above without departing from the spirit thereof. For example, in the above embodiment, the holding frame 22 is rotated. In the above description, the development unit 2Y, 2C, 2M, and 2K is provided with the rotary development unit 20 that selectively places the development unit 15 at the development position 15. However, the present invention is not limited to this. For example, the development units for each color are arranged side by side at a position away from the photosensitive belt, and the arrangement position of the development roller of each development unit is sequentially switched to the development position that contacts the photosensitive belt, thereby obtaining a color image. A thing (for example, refer Unexamined-Japanese-Patent No. 8-76542) may be used. In this case, the detection signal of the transfer sheet sensor 90 may be captured in synchronization with the switching timing from the final development unit (K toner in the above publication) to the first development unit (C toner in the above publication). . The above-described embodiment including the rotary developing unit 20 is more advantageous in terms of downsizing the apparatus main body 2.
[0086]
In the above-described embodiment, the detection signal of the transfer paper sensor 90 is captured in synchronization with the development end time of the development unit 2K (final development unit) in color image formation. Also in the formation, the detection signal of the transfer paper sensor 90 may be captured in synchronization with the development end time of the development unit 2K. As a result, the presence / absence of the transfer paper 4 in the paper feed cassette 3 can be accurately determined as in the above embodiment.
[0087]
In the above embodiment, the intermediate transfer belt 31 having the seam 71 is used as the image carrier. However, the present invention is not limited to this, and a seamless intermediate transfer belt or intermediate transfer drum may be used.
[0088]
In the above embodiment, a printer that prints an image supplied from an external device such as a host computer on transfer paper is described. However, the present invention is not limited to this, and includes a copying machine, a facsimile machine, and the like. The present invention can be applied to a general electrophotographic image forming apparatus.
[0089]
【The invention's effect】
As described above, according to the first aspect of the present invention, the distance from the transfer sheet detection means to the secondary transfer position along the transfer sheet conveyance path is D1, and the distance from the development position along the surface of the photosensitive member is D1. If the distance to the primary transfer position is D2, and the distance from the primary transfer position to the secondary transfer position in the toner image transport direction along the surface of the intermediate transfer medium is D3, D1> (D2 + D3 ), The detection signal from the transfer paper detection means is taken in synchronization with the end of the developing operation of the final development unit, and the presence or absence of the transfer paper in the transfer paper storage unit is determined based on the acquired detection signal. Therefore, it is possible to accurately determine the presence / absence of the transfer sheet at a fixed timing, thereby simplifying the control configuration.
[0090]
Further, arranged in development position in order from the first developing unit to which the toner of each Re their Re different colors predetermined plural developing units housed to the final development unit, which is developed by each of the plurality of developing units toner The images are superimposed on each other on the intermediate transfer medium, and the superimposed color toner images are secondarily transferred to the transfer paper at the secondary transfer position, and a detection signal is generated in synchronization with the end of the developing operation of the final developing unit. Therefore, when the developing operation of the final developing unit is completed, the image is continuously transferred to the transfer paper as it is at the secondary transfer position, and the transfer paper detecting means has already been placed at the rear end of the transfer paper. Since the detection signal is received in synchronization with the end of the developing operation of the final developing unit, the presence / absence of the next transfer sheet is detected. Do determination can be reliably performed. In addition, since the presence or absence of the transfer paper is determined before the next developing operation is started, it is possible to reliably avoid a situation in which the toner is wasted.
[0091]
According to the second aspect of the present invention, when the transfer paper determining means determines that there is transfer paper, the first developing unit is disposed at the development position, and when the transfer paper determining means determines that there is no transfer paper, Since the developing means is arranged at a preset standby position, the detection signal output from the transfer paper detecting means is taken in synchronization with the end of the developing operation by the final developing unit, and the transfer paper in the transfer paper storage unit is loaded. By determining the presence or absence, the operation of the next developing means can be determined efficiently.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an internal configuration of a printer which is an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is a schematic diagram of a rotary developing unit.
FIGS. 3A and 3B are development views of the intermediate transfer belt. FIGS.
FIGS. 4A, 4B, and 4C are schematic views for explaining dimensions between respective parts of the printer.
FIG. 5 is a block diagram illustrating an electrical configuration of the printer.
[Explanation of symbols]
2 Device body 3 Paper feed cassette (transfer paper container)
4 Transfer paper 7 Transfer paper transport path 11 Photoconductor 14 Primary transfer portion (primary transfer position)
20 Rotary development section (development means)
21 Rotating shaft 22 Holding frame (unit holding part)
2Y, 2C, 2M, 2K Development unit 2Y First development unit 2K Final development unit 31 Intermediate transfer belt (intermediate transfer medium)
37 Secondary transfer section (secondary transfer position)
50 exposure unit (exposure means)
61 Feed roller 63 Registration roller pair 81 Development system drive motor 82 Rotary clutch 90 Transfer paper sensor (transfer paper detection means)
110 Engine control unit 111 CPU (transfer sheet determination means, drive control means, secondary transfer control means)

Claims (2)

Exposure means for forming an electrostatic latent image on the photoreceptor;
Development means for selectively switching the arrangement positions of the plurality of development units to a predetermined development position, and developing the toner by attaching the toner of the development unit arranged at the development position to the electrostatic latent image;
An intermediate transfer medium that carries a toner image that is primarily transferred from the photoreceptor at a predetermined primary transfer position and that conveys the toner image to a predetermined secondary transfer position;
A transfer paper storage section capable of selectively storing a plurality of sizes of transfer paper;
Transfer paper detection means for outputting a detection signal according to the presence or absence of transfer paper in the transfer paper storage unit;
Transfer paper determination means for capturing the detection signal output from the transfer paper detection means, and determining the presence or absence of transfer paper in the transfer paper storage unit based on the captured detection signal;
A transfer paper transport path for guiding the transfer paper from the transfer paper container to the secondary transfer position ;
Drive control means for sequentially arranging the plurality of developing units each containing toner of different colors from the first developing unit to the final developing unit in a predetermined position;
Control is performed to superimpose toner images developed by each of the plurality of developing units on the intermediate transfer medium, and secondarily transfer the superimposed color toner images onto the transfer paper at the secondary transfer position 2 Next transfer control means ,
A distance from the transfer sheet detection unit to the secondary transfer position along the transfer sheet conveyance path is defined as D1, and a distance from the development position to the primary transfer position along the surface of the photoreceptor. Is set to D1, and the distance from the primary transfer position to the secondary transfer position in the toner image transport direction along the surface of the intermediate transfer medium is set to D3, D1> (D2 + D3) is set. ,
The image forming apparatus according to claim 1, wherein the transfer sheet determination unit captures the detection signal in synchronization with the end of the developing operation of the final developing unit . The drive control means arranges the first developing unit at the development position when the transfer paper determining means determines that there is transfer paper, and when the transfer paper determining means determines that there is no transfer paper, 2. The image forming apparatus according to claim 1 , wherein the developing unit is disposed at a preset standby position.

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