JPH09212061A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To satisfactorily pass paper with no decrease in processing speed even when switching picture-element density, in an image forming device which carries out the switching of the picture-element density by the alteration of the linear velocity of an image carrier. SOLUTION: The device switches picture-element density for an image to be formed, by switching a linear velocity at which the image carrier is driven in a subscanning direction and a speed at which the writing means writes onto the image carrier in a main-scanning direction. In this case, the device is equipped with a control means 1201 which exerts control so that the carrying speed of a timing carrying-means, which sends and carries recording paper to a transfer part with transfer timing, is switched according to the switching of the picture-element density and so that the carrying speed of at least one of recording-paper carrying means other than the timing carrying-means is made constant irrespective of the switching of the picture-element density.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image recording apparatus for forming an image based on image data, and more particularly to an image forming apparatus capable of changing a conveyance speed in a process related to image formation.

[0002]

2. Description of the Related Art Generally, in an electrophotographic image forming apparatus, an electric signal (image signal) corresponding to the density of image information (original image) of an original is converted into an electric signal (laser light) and the like. It is used to form an electrostatic latent image on the photoconductor drum.

Then, the electrostatic latent image is developed into a toner image and then transferred to a recording paper, and the toner image on the recording paper is heated and fused and fixed by a heater of a fixing device. In such an image forming apparatus, it has been proposed to switch the pixel density of an image to be formed. When such pixel density switching is performed, the linear velocity at which the image carrier (photoreceptor drum or the like) is driven in the sub-scanning direction (rotational speed in the case of the photoreceptor drum) and the image carrier of the writing means are selected. It is realized by switching the writing speed in the main scanning direction.

[0004]

In the image forming apparatus for switching the pixel densities as described above, the conveying speed other than the steps related to the image formation (latent image formation on the photosensitive drum, development, transfer, fixing) No consideration was given. That is, when the pixel density is switched in the image forming apparatus, what is considered is the influence of the transportability in the steps of sheet feeding (from the sheet feeding cassette to the registration roller (timing conveying means)) and sheet discharging (after fixing). Was not done.

Therefore, if the transport speed of each part is switched according to the switching of the pixel density, the appropriate values of various transport conditions such as the pressure of various rollers for transport and the separation pressure of the recording paper will change. It becomes difficult to control such that such an appropriate value is maintained. Further, if various conveying conditions such as pressure of various rollers for conveying and separation pressure of recording paper cannot be maintained at appropriate values, jamming may occur.

Further, when images are formed on both sides of the recording paper, the recording paper is temporarily stored in the sub-conveyance path (reversal conveyance section or circulation conveyance section), but in this case as well. The problem occurs.

Further, a sorter (post-processing means) as a sorting device is provided after fixing, but similar problems occur in control by the sorter. In addition, if there is a difference in the conveyance speed between the fixing device and the sorter, there is a possibility that a trace of pulling by the conveyance roller or a shift in the transfer of the image may occur.

Therefore, it is an object of the present invention to provide an image forming apparatus having a paper passing property even when the pixel density is switched in the image forming apparatus which switches the pixel density by changing the linear velocity of the image carrier. That is.

[0009]

That is, the present invention which constitutes means for solving the problems is as described in the following (1) to (5).

(1) The first invention comprises an image carrier on which a latent image is formed and a writing means for forming a latent image on the image carrier, and the image carrier is driven in the sub-scanning direction. An image forming apparatus for switching the pixel density of an image to be formed by switching the linear velocity and the writing speed of the writing unit to the image carrier in the main scanning direction. Transfer the toner image onto the recording paper. Transfer the recording paper to the transfer unit at the transfer timing in accordance with the transfer timing and transfer it. The transfer speed of the timing transfer means is switched according to the pixel density switching, and the recording paper other than the timing transfer means is transferred. The image forming apparatus is provided with a control unit that controls at least one of the conveyance speeds to be constant regardless of the pixel density switching.

According to the invention of this image forming apparatus, the conveying speed of the timing conveying means for feeding and conveying the recording paper from the image carrier to the transfer portion for transferring the toner image onto the recording paper at the transfer timing is switched to the pixel density. The recording speed is controlled according to the pressure of various rollers for conveyance and recording by controlling at least one conveyance speed of the conveyance means other than the timing conveyance means to be constant regardless of the pixel density switching. Since various conveying conditions such as the paper separating pressure are kept within the proper range, recording paper jams will not occur. Therefore, it is possible to provide an image forming apparatus having good paper passing property.

(2) In a second aspect based on the first aspect, the transporting means is controlled so that the transporting speed is constant regardless of the switching of the pixel density, and the transporting means transfers the recording paper having one side recorded thereon. At least one of a circulation type conveyance section for re-feeding the sheet to the sheet feeding section, or a paper feed conveyance section for feeding the recording paper stored in the recording paper storage section to the timing conveyance means. Is.

In the invention of this image forming apparatus, the transport speed of the timing transport means for feeding and transporting the recording paper at the transfer timing to transfer the toner image from the image carrier to the recording paper is switched to the pixel density. Switching according to the above, a circulation type transport unit for re-feeding the one-side recorded recording paper to the transfer unit, or a paper feed for feeding the recording paper stored in the recording paper storage unit to the timing transportation unit By controlling the transport unit to be constant regardless of the switching of the pixel density, various transport conditions such as the pressure of various rollers for feeding and transporting the recording paper and the separation pressure of the recording paper can be kept within appropriate ranges. Therefore, a recording paper jam or the like does not occur when the paper is fed. Therefore, it is possible to provide an image forming apparatus having good paper passing property.

(3) A third invention is the above-mentioned first or second invention.
In the invention, the transport speed of the transport means is controlled so that the transport speed is constant regardless of the pixel density switching, and the transport speed is adjusted to the highest linear speed of the image carriers switched by the pixel density switching. It is characterized by a high transport speed.

In the invention of this image forming apparatus, the conveyance speed of the timing conveying means for feeding and conveying the recording paper from the image carrier to the transfer portion for transferring the toner image onto the recording paper at the transfer timing is switched to the pixel density. Switching according to the above, a circulation type transport unit for re-feeding the one-side recorded recording paper to the transfer unit, or a paper feed for feeding the recording paper stored in the recording paper storage unit to the timing transportation unit Regardless of the pixel density switching, the transport unit is controlled to be constant at a transport speed that matches the highest linear velocity of the image carriers that is switched by the pixel density switching, so that the feeding transport is performed. Since various transport conditions such as the pressure of various rollers and the separation pressure of the recording paper are kept within the proper range, recording paper jam etc. may occur during paper feeding. Processing speed is also fast with the Kunar. Therefore, it is possible to provide the image forming apparatus which has good paper-passing property and does not decrease the processing speed.

(4) A fourth invention is a writing means for forming a latent image on an image carrier, and a transfer means for transferring a toner image formed by developing the latent image on the image carrier to a recording paper. A fixing means for fixing the toner image transferred onto the recording paper by the transfer means, a post-processing means for receiving the recording paper on which the toner image is fixed by the fixing means and performing a sorting operation, and a post-processing means. A post-processing conveyance control means for controlling the conveyance of the recording paper inside, and a linear velocity at which the image carrier is driven in the sub-scanning direction, and the writing means writes the image carrier in the main scanning direction. An image forming apparatus for switching the pixel density of an image to be formed by switching the speed and the image density of the recording paper from the transfer by the transfer means to the fixing by the fixing means. Transport speed changed When the, the post transport control means is an image forming apparatus and controlling so that the transport speed in said post-processing means to the equivalent speed and conveying speed in the fixing unit.

In the invention of this image forming apparatus, the post-processing conveyance is performed when the conveyance speed of the recording paper from the transfer by the transfer means to the fixing by the fixing means is changed in accordance with the pixel density switching. The control unit controls the conveyance speed in the post-processing unit to be a speed equivalent to the conveyance speed in the fixing unit, and thereby various conveyance conditions such as pressure of various rollers for conveyance and separation pressure of recording paper. Is kept within an appropriate range, recording paper jams may occur,
Eliminates scratches and image transfer deviations due to differences in transport speed. Therefore, it is possible to provide an image forming apparatus which has good paper-passing properties and also has good images.

(5) In a fifth aspect based on the fourth aspect, the post-treatment conveyance control means conveys at least the recording speed of the recording paper by the fixing means at a conveyance speed in the post-treatment means. The interval is controlled so as to be the same speed as the conveying speed in the fixing means.

In the invention of this image forming apparatus, the post-processing conveyance is performed when the conveyance speed of the recording paper from the transfer by the transfer means to the fixing by the fixing means is changed in accordance with the switching of the pixel density. The control means controls the conveying speed in the post-processing means to be a speed equal to the conveying speed in the fixing means at least while the recording paper is being nipped and conveyed by the fixing means, so that the speed between the both is increased. It is possible to prevent the occurrence of pulling marks and transfer deviation of images due to the difference in transport speed, and to prevent the occurrence of recording paper jams and the like. Further, it becomes possible to control the conveying speed in the post-processing means at a high speed at the time when the nipping and conveying of the fixing means is released, and it is possible to provide an image forming apparatus having a good paper passing property.

[0020]

Embodiments of the present invention will be described below with reference to the drawings. Regarding the image forming apparatus of the present embodiment, the mechanical configuration will be described first, the electrical configuration will be described next, and then the operation will be described.

<Mechanical Structure> FIG. 2 is a structural diagram showing the mechanical structure of the image forming apparatus. First, the mechanical structure of the image forming apparatus will be described with reference to FIG. Note that a black-and-white digital copying machine will be described as an example of the image forming apparatus.

In FIG. 2, the black-and-white digital copying machine comprises an image reading section A, an image processing section B, an image storage section C, an image forming section D and a post-processing section E, and the image reading section A has an ADF ( Equipped with an automatic document feeder.

In the image reading section A, a document 121 is placed on a document table glass 122 and illuminated by a halogen light source 123 provided on a left extension of an optical frame 126 which moves on a slide rail (not shown). . And
A mirror 127 that moves together with the halogen light source 123 at a speed V, and a pair of mirrors 124 provided on an optical mount 126 that moves at a speed half that of the mirror 127.
125 and platen glass (original platen glass) 12
The reflected light from the original 121 on the second sheet 2 is guided to the lens reading unit 128. The lens reading unit 128 includes an imaging lens 129 and a CCD line sensor 130. The image corresponding to the image on the original 121 reflected by the mirrors 124, 125, 127 is converged by the image forming lens 129, and the CCD line sensor 130.
An image is formed on the light receiving surface of, and the optical image on the line is photoelectrically converted into an electric signal by the CCD line sensor 130.

An image signal in the lateral direction (main scanning direction) of the original 121 is output in response to a CCD reading clock pulse, and the original 121 is scanned in the longitudinal direction (sub-scanning direction) by movement of the optical mount 126 or the like. An image signal for one page is output. In this way, the image signal of the original image read by the image reading unit A by scanning the optical frame or the like, that is, the image data, is subjected to density conversion, filter processing, scaling processing, γ correction in an image processing unit B described later. After being subjected to various image processing such as
It is output to the image forming unit D. The image forming unit D forms an image on a recording sheet according to the input image data by a laser printer using an electrophotographic technique.

That is, in the image forming section D, a laser beam generated by a semiconductor laser (not shown) is modulated based on the image signal. The laser beam is reflected by the polygon mirror 142 rotated by the drive motor 141, passed through an unillustrated fθ lens, reflected by the reflection mirror 143, scanned on the surface of the photosensitive drum 151, and uniformly charged. An electrostatic latent image is formed on the photoconductor drum 151.

Further, a charging device 152 for uniformly charging the photosensitive drum 151, a developing device 153, and a transfer electrode 1
57, a separation electrode 158, a cleaning device 159, and a fixing device 160 are provided, and the electrostatic latent image formed on the photoconductor drum 151 is developed by the developing device 153 to become a toner image. Is transferred onto a recording paper and fixed by a fixing device 160 to obtain a copy image of the original.

The recording paper 1 has cassettes 221 ...
The recording paper 1 is stocked in 224, and the recording paper 1 is taken out by the belt-equipped paper feed rollers 225 to 228 from the cassettes 221 to 224 of the corresponding paper feed means in accordance with the instruction of the recording paper size, and the registration rollers 229 are the photoconductors of the image forming means. The image is formed as described above by being fed to the drum 151.

In the single-sided copy mode in which the image is formed on one side of the recording paper, the switching guide 230 is switched so as to move straight, and the recording paper on which the image is formed on one side is discharged to the outside of the copying machine to be sorted. The post-processing section E having the above-mentioned section sorts and the like.

In the composite copy mode in which an image is formed twice on the same side of one side of the recording paper, the recording paper with the image formed on one side is switched to the side of the route for circulating and conveying in the copying machine. The guide 230 guides the changeover guide 230 to a circulation path from the changeover guide 246 to the registration roller 229 via the changeover guide 246 and the rectilinear section 245. And the recording paper is
It is conveyed by a plurality of conveyance rollers 232 driven by a conveyance motor (not shown) and reaches the switching guide 246. The switching guide 246 is switched to the position shown by the broken line in the figure and connected to the straight-ahead portion 245. The recording paper sent to the straight advance section 245 goes straight without inverting the front and back and is sent straight from the left side to the right side of the circulation type conveyance path, and further fed upward by the conveyance roller and the guide, and the registration roller 2
He is hit by 29 and is blocked.

In the case of the double-sided copy mode in which images are formed on both sides of the recording paper, the recording paper with the image formed on one side is switched to the side of the conveying path through the circulation type conveying path in the copying machine. Switching guide 230
To the registration roller 229 through the switching guide 246 and the reversing unit 235. Then, the recording paper is transported by a plurality of transport rollers 232 driven by a transport motor (not shown), reaches the reversing unit 235 via the switching guide 246, and passes near the sensor 240 provided in the reversing unit 235. When the sensor 240 detects the end of the recording paper, the switching guide 234 switches from the position of the broken line in the drawing to the position of the solid line, and the recording paper is rotationally fed from left to right in FIG. 2 until that time. The reversing roller 236 that has been rotating reversely rotates the recording paper to the U-shaped conveyance guide 2
Send to 44.

As a result, the fed recording paper is temporarily stopped and sent out in the opposite direction (from right to left in FIG. 2). The recording paper sent to the U-shaped transport guide 244 changes its direction and is sent out in the original feeding direction (from the left side to the right side in FIG. 2), but the front and back sides are reversed at that time. .

After that, the recording paper is fed from the left to the right along the circulation type conveyance path, and then further fed upward, and hits the registration roller 229 and is blocked. The sensors 241 and 24 are provided in the middle of the circulation type conveyance path from the reversing unit 235 to the outlet of the sheet feeding roller 225 of the cassette 221.
3, 247 are arranged, the recording paper is detected by a single sensor, and the presence or the position of the recording paper is detected from the detection information of the plurality of sensors, or the length of the recording paper, the conveyance speed of the recording paper, the recording speed, The paper transportation time, the recording paper transportation interval, and the like are required.

When the positions of the recording paper and the image on the back surface formed on the photosensitive drum 151 have become optimum, the registration rollers 229 start feeding the recording paper, and the second image formation is performed. The toner image is fixed by the fixing device 160, and is discharged to the post-processing unit E through the switching guide 230 that is switched to the straight-moving side, and the double-sided recording is completed.

In the black-and-white digital copying machine according to the present embodiment, the image reading section A is provided with a circulation type automatic document feeder ADF which automatically conveys a read document on the platen glass 122. When the automatic document feeder ADF driven by a motor (not shown) sets a plurality of read originals on the original setting table 182, the pages of the originals are turned by the first reversing unit 190 to be turned in order. In addition to automatically transporting the document to the predetermined position on the platen glass, the read document is removed from the platen glass 122 and discharged onto the document discharge tray 199.

Further, as described above, the ADF sequentially sends out and reads one-sided originals having image information on one side of the originals, and also takes out one double-sided original and sends it to the platen glass 122 to send the one-sided image. When the reading is completed, the original is moved in the opposite direction, the direction is changed by the second reversing unit 191, the original is turned over and sent to a predetermined position of the platen glass 122 to read the image information on the back surface of the original.

Furthermore, in the double-sided document mode, the ADF directly feeds the document after the reading is completed to the document discharge tray 19
9 is fed to the third reversing unit 192 instead of being ejected onto the document 9 so that the front and back of the document are reversed and the document setting table 182
Accumulated on top. When the first document reading is completed, the stack of documents is switched by a switching plate 19 which rotates about a fulcrum 195 as an axis.
When 6 moves from the lower side (the position of the broken line in the drawing) to the upper side (the position of the solid line in the drawing), the feeding of the first original is started again and the reading of the second original is started.

In order to automatically convey the original document as described above,
The ADF includes a paper feed roller 184 for feeding the originals on the original set table 182 one by one, an intermediate conveyance roller 185,
A driving roller 188 and a driven roller 187, and a conveyor belt 189 wound around the driving roller 188 and the driven roller 187 are provided, and a discharge roller 193 and a guide plate are provided for changing the feeding direction or reversing the original. The first inverting unit 190, the second inverting unit 191, and the third inverting unit 192 are provided.

FIG. 3 is a block diagram showing an example of a sorter as the post-processing section E. In FIG. 3, a bin-type sorter will be described as an example, but in the present embodiment, it is also possible to use another type of sorter (for example, a shift tray sorter).

FIG. 3 is a block diagram of the post-processing section E (sorter) connected to the image forming apparatus D. This sorter includes a base section E10, a down transport section E20, an up transport section E30, and
It is composed of a bin moving unit E40.

The base portion E10 includes casters E11, connecting means E12 for connecting the main body of the image forming apparatus E1, and a conveyor belt E1.
3, a driving roller E141, a driven roller E142, a conveying roller E14 composed of a tension roller E143, pressing rollers E15A, E15R, E15C, E15D, a guide plate E19, a driving means (described later), and the like are incorporated and fixed on the floor.

Further, in the base part (intermediate transfer part) E10,
The stay member E16 is fixed in the direction orthogonal to the paper surface of FIG. The rack gear RG is provided on the upper surface side of the stay member E16.
Has been fixed. On the other hand, rollers E17A and E17B for moving the housing are pivotally supported in the housing of a bin moving unit E40, which will be described later, and the rollers E17A and E17B are mounted on the base E.
It slides on a rail (not shown) 10 and moves the casing of the bin moving unit E40 in the direction orthogonal to the plane of the drawing.

A drive motor M1 is installed in the housing of the bin moving section E40, and drives and rotates the pinion gear PG via gears G1 and G2. Since the pinion gear PG meshes with the rack gear RG fixed to the stay member E16, the drive rotation of the motor M1 moves the casing of the bin moving unit E40 in the direction orthogonal to the plane of the drawing. Incidentally, E18 is a rotatable roller provided coaxially with the pinion gear PG, and the roller E18 rolls on and guides the stay member E16.

The down conveyance section E20 is the main body of the image forming apparatus D.
And a transport belt E22 for receiving the discharged recording paper S by the guide plate of the receiving port E21, transporting it downward, and feeding it to the transport belt E13 in the base portion E10. The roller E23 and the pressing roller E28 are included.

The conveyor belt E22 is stretched between the lower drive roller E231 and the upper driven roller E232, the intermediate rollers E233 and E234 are fixed inward, and the tension roller E235 is outward. It is stretched. Further, the pressing roller E28 can press and separate the conveying belt E22 from the pressing rollers E22A and E28.
B and E28C, and a roller E28D that presses the outer periphery of the drive roller E231 via the conveyor belt E22, and presses the conveyor belt E22 to rotate to convey the recording paper S.

Further, a paper discharge roller E24 for discharging the preceding recording paper in the image forming apparatus main body D and an intermediate tray E25 are provided when the paper is branched from this conveyance path and a jam occurs in the ADF and the sorter.

The intermediate tray E25 also stores special recording paper SE1 in addition to the jammed paper storage described above. The special recording paper SE1 is a recording paper of a normal size or smaller (for example, B
E6 size, postcard size, E5. E5 × E8 inch size recording paper) or recording paper that is unsuitable for passing through the sorter transport path (eg OHP film, label paper, thin recording paper, etc.)
These recording sheets SE1 are recorded on the down conveyance section E2 in response to a command (such as loading a special cassette) on the image forming apparatus main body side.
In the pressing roller E28C of 0, the guide plate E2 is separated from the conveyor belt E22 and branched by the branching unit.
9, the sheet is discharged onto the intermediate tray E25 via a sheet discharge roller E24 composed of a driving roller E241 and a driven roller E242 which rotate in pressure contact with each other.

The recording paper SE2 which requires sorting, grouping and stapling goes straight through the branch point, and the conveyor belt E
It is carried out by being sandwiched by the pressure roller E28D and the pressing roller E28D, enters the base portion (intermediate transport portion) E10, and is fed onto the transport belt E13 along the guide plate E19.

The conveyor belt E13 has a driving roller E1.
41, driven roller E142, tension roller E143
Is wound, and slides on the support plate E144. In addition, pressure rollers E13A and E1 are provided on the upper surface of the conveyor belt E13.
3B, E13C, and E13D are pressed against each other so that they can be driven to rotate, hold the recording sheet SE2, and move up the transport section E30.
Send to

The upstream conveying section E30 includes rollers E32, E33 rotatably fixed to the upper and lower portions of the support frame.
A plurality of endless conveyor belts are stretched around.
Inside the transport belt E31, a plurality of rollers E34 corresponding to an insertion port, which will be described later, are rotatably contacted. On the outside of the conveyor belt E31 facing the roller E34,
The plurality of transport rollers E35 are rotated and driven to rotate.

Further, branch guides E36 are located at the entrances of the bins between the transport rollers E35 and swing. These branch guides E36 are rotatably supported by a shaft E37 installed on the support frame, and the shaft E3
It is swung by a lever and a solenoid (not shown) provided at the shaft end of 7. Therefore, by rotating the branch guide E36 in the clockwise direction, the lower end claw portion of the branch guide E36 is made to intersect the recording paper conveying path constituted by the conveying belt E31 and the conveying roller E35, and the recording paper is vertically upwardly moved. Blocking the belief in, the branch guide E36 prepares the recording paper acceptance posture. When the recording sheet SE2 is conveyed to the recording sheet SE2, the recording sheet SE2 is deflected at a right angle along the inner curved surface of the branch guide E36 and is received in the bin E41.

That is, the recording paper SE2, which has been carried in at high speed to the ascending transport section E30 of the sorter, is lifted by being sandwiched between the transport belt E31 and the transport roller E35, and is actuated by a solenoid (not shown) to diverge in the clockwise direction. E36
The sheet is deflected to the right by (the E2 step from the bottom in the figure), passes above the upright stopper wall E41S of the bin, rises along the inclined surface of the bin E41, and the recording sheet S
After the rear end of E2 passes above the stopper E41S, the recording paper SE2 turns from rising to lowering, and the recording paper S slides down on the surface of the bin E41 by its own weight, and the rear end of the recording paper SE2 is stopped by the stopper wall. Stop at E41S.

At this time, the recording paper SE2 having curling
Even if the rear end of the bottle E4 is lifted, the lifting is prevented by the claw portion E41B provided on the top of the bottle E41.
The sheets are accommodated in the sheet No. 1 and contact the stopper wall E41 by its own weight to align the sheets.

A deep bottom type non-sort tray E49 is fixedly provided on the uppermost side of the plurality of bins (E20-stage sort bins in FIG. 3) E41. The non-sort tray E4
Reference numeral 9 denotes a tray for accommodating the image-formed recording paper SE3 that does not require sorting, and is capable of accumulating a large amount of recording paper E100 to E300. Designation and cancellation of collation (sorting) and sorting (grouping) are selected and instructed by a key on the operation panel on the image forming apparatus main body side.

On the other hand, a sorter equipped with a stapler device is
Since the bin E41 inserts the recording paper SE2 to be loaded into the stapler device, the entire bin E41 is moved forward and backward by the motor M1 in accordance with the size of the recording paper together with the bin moving part E40, and is further swung about the fixed support shaft E43. Be moved.

Next, the electrical configuration and operation of the image forming apparatus constructed as above will be described below. <Electrical Configuration> FIG. 1 is a block diagram showing the electrical configuration of the image forming apparatus according to the present embodiment. Note that, here, an image forming apparatus that can also form an image by receiving image data from an external device such as a computer (PC) will be described as an example.

In FIG. 1, an external device 1000 is an external device such as a computer that supplies image data to the image forming apparatus 1100 of this embodiment. The image forming apparatus 1100 is mechanically configured as shown in FIGS. 2 and 3, and is electrically configured as described below.

The main CPU 1101 is the image forming apparatus 11
00 to control the whole, and the operation unit 110
The operation of the image forming apparatus is controlled in response to various instructions from 2 and instructions from various sensors, power switches, etc. not shown.

The printer unit 1200 is the image forming apparatus 110.
This block is a block that operates particularly as a printer in 0, and includes a sub CPU 1201 and various control circuits.

That is, 1202 is an image pickup device switching means for switching the pixel density when reading the CCD line sensor 130, 1203 is a charging grid voltage control circuit of the charger 152, 1204 is the rotation speed of the drive motor 141 of the polygon mirror 142. Polygon mirror control circuit to control,
Reference numeral 1205 is a photoconductor rotation speed control circuit that controls the rotation speed of a motor that drives the photoconductor drum 151, 1206 is a development sleeve rotation speed control circuit that controls the rotation speed of the development sleeve 153A, and 1207 is an adjustment prism by a motor or a solenoid. Is a laser spot interval changing means for changing the position of the laser spot B in the sub-scanning direction by changing the position of the laser spot B on the photosensitive drum 151 in the sub-scanning direction.

Reference numeral 1208 denotes an image forming conveyance speed control circuit for controlling the conveyance speed of the recording paper at the time of image formation (registration roller 229 to fixing device 160) according to the switching of the pixel density, and 1209 denotes a post-processing section E (sorter). ) Is a sorter transport speed control circuit for controlling the transport speed of the recording paper according to the pixel density switching.

From the external device 1000 to the main CPU 110
When the signal of the selected pixel density is input to 1, the main CPU 1101 issues a pixel density switching command to the sub CPU 1
Give to 201. Note that here, the pixel density switching is set to 4
The description will be continued by taking the case of using 00 dpi and 600 dpi as an example.

Sub-C receiving this pixel density switching command
The PU 1201 sends a switching signal for switching the reading density, the grid voltage and the laser spot interval according to the selected pixel density to the image sensor switching unit 1202, the charging grid voltage control circuit 1203 and the laser spot interval changing unit 1207, and the laser spot interval. Pixel density A =
63.5 μm at 400 dpi, pixel density B = 600 dpi
In the case of, the switching signal is switched to 42.3 μm, and the switching signal for switching to the rotation speed corresponding to the selected pixel density is sent to the polygon mirror control circuit 1204, the photoconductor rotation speed control circuit 1205 and the developing sleeve rotation speed control circuit 1206. The peripheral speed of the photosensitive drum 151, the polygon mirror 14
2, the number of revolutions, the grid voltage of the charger 152, and the number of revolutions of the developing sleeve 153A are changed to values corresponding to the selected pixel density as shown in FIG. It is held constant both at (600 dpi) and at pixel density B (400 dpi), and the developer is also conveyed in an amount suitable for the pixel density.

Further, in response to the change of the peripheral speed of the photosensitive drum 151, the image forming transfer speed control circuit 1208 relating to the image formation related thereto adjusts the transfer speed of the recording paper to the peripheral speed of the photosensitive drum 151. To control. In addition, the sorter transport speed control circuit 1209 controls the transport speed of the post-processing unit E at the receiving portion of the recording paper after fixing to match the transport speed of the fixing device 160.

<Mechanical Structure + Roller Control> FIG. 5 is an explanatory diagram showing a main part of a structure for controlling the conveyance of the recording paper in the image forming apparatus of the present embodiment.

In FIG. 5, the recording paper 1 accommodated in the cassette 221 of the paper feed unit 2 surrounded by the broken line is frictionally driven by the paper feed roller 225 to register roller 229.
Then, the recording paper 1 is stopped by the registration roller 229 which is fed to the stationary state.

When the positional relationship between the toner image formed on the photosensitive surface of the photosensitive drum 151 of the image forming means 4 surrounded by the broken line and the recording paper 1 to be fed becomes appropriate, the sub CPU
Feed motor 4 according to a registration signal output from 1201
The registration roller 229 is rotated by driving 33, and the recording paper 1 is sent to the image forming means 4.

The toner image transferred onto the first surface of the recording paper 1 is fixed by the fixing device 160 and an image is formed on the first surface. In the case of one-sided copying (single-sided printing), the recording paper is conveyed as it is to a sorter which constitutes the post-processing section E. On the other hand, in the case of double-sided copying (double-sided printing), the recording paper 1 is guided to the circulation path by the switching guide 230, is transported by the transporting roller 232 driven by the transporting motor 454, and reaches the switching guide 246. When the switching guide 246 is set at the position indicated by the broken line in the figure, the switching guide 246 is guided to the reversing unit 235.

In the reversing unit 235, when the sensor 240 detects the trailing edge of the recording paper, the switching guide 234 is switched from the position of the broken line to the position of the solid line, and in the direction shown by the solid line (reverse direction). The reversing roller 236 rotates, the recording paper is turned upside down by the U-shaped conveyance guide 244, and is fed rightward in the drawing.

After the reversing unit 235 of the circulation type conveyance path,
A plurality of photo sensors 241 as recording paper detection sensors,
243 and 247 are arranged and used for measuring the position and speed of the recording paper on which the image is formed on the first surface, the distance between the recording paper and the paper feeding means 2, and the time interval at which the recording paper is conveyed. To be done.

Then, the recording sheet conveyed through the circulation type conveying path is applied to the stationary registration roller 229 with the first surface on which the image is formed facing down and stopped. Here, a latent image is formed on the photosensitive drum 151 by the image data recorded on the second surface of the recording paper, and then the toner image developed by a developing device (not shown) and the recording paper 1 to be fed.
When the positional relationship between and becomes appropriate, the feeding motor 433 is driven, and the registration roller 229 sends the recording paper 1 to the image forming unit 4, and an image is formed on the second surface of the recording paper 1. After that, the recording paper 1 is sent to the discharge path switched by the switching guide 230 and discharged to the post-processing section E.

Then, the post-processing section E has a conveyance motor 444.
The whole is driven by the (motor M1), and the recording paper is conveyed by the conveying rollers E28, E142, E141, E32 and stacked on the discharge tray of each bin.

<Conveyance Control When Pixel Density is Switched> Next, the operation of the conveyance control when the pixel density is switched will be described. When the pixel density switching is switched from 400 dpi to 600 dpi by a command from the external device 1000, the sub CP that has received the command from the main CPU 1101.
U1201 gives each part an instruction according to the switching of the pixel density.

As a result, the photoconductor rotation speed control circuit 120
By controlling from 5, the peripheral speed of the photoconductor drum 151 is 2
It decreases from 80 mm / sec to 125 mm / sec. This is the square of the ratio of the switched pixel densities (that is, the main scanning direction (4
(00/600) × sub-scanning direction (400/600)).

Along with this, the conveyance speed of the recording paper is also reduced to 125 mm / sec by the control from the image forming conveyance speed control circuit 1208. By the way, the paper feed roller 225
Feeds the recording paper to the registration roller 229 while keeping 280 mm / sec so as not to change the paper feeding performance. By not changing the paper feed speed of the paper feed roller 225 in this manner, it is not necessary to change various transport conditions such as the pressure of the roller and the separation pressure of the recording paper, and there is no fear of jamming.

Here, the paper feed speed was controlled so as to be constant at the conveying speed of 280 mm / sec for the image formation of 400 dpi, but even if the speed is other than this, the paper feed speed is fixed in consideration of the roller pressure and the like. It is also possible to make the speed constant. However, when the transport speed changes in accordance with the switching of the pixel density, it is preferable from the viewpoint of efficiency that the paper feed speed is kept constant at the highest transport speed.

The registration roller 229 is driven at an appropriate transfer timing in consideration of the change of the peripheral speed of the photosensitive drum 151, and conveys the transfer paper toward the transfer section.
At this time, the feeding motor 433 that drives the registration roller 229 sends a signal for switching the pixel density to the sub CPU 1201.
It has received more, and the transport speed is 125 mm / sec. This conveying speed is maintained at 125 mm / sec up to the fixing device 160, and in the case of single-sided printing, the recording paper is conveyed as it is to the sorter which constitutes the post-processing section E. On the other hand, in the case of double-sided copying (double-sided printing), the recording paper 1 is guided to the circulation path by the switching guide 230, is transported by the transporting roller 232 driven by the transporting motor 454, and reaches the switching guide 246. When the switching guide 246 is set at the position indicated by the broken line in the figure, the switching guide 246 is guided to the reversing unit 235.

The conveyance motor 454 in this circulation path conveys at a conveyance speed of 280 mm / sec. Consider that the conveyance performance is not changed even if the conveyance speed is changed in the image forming section by switching the pixel density. 280 mm / sec. By thus not changing the conveyance speed of the conveyance motor 454 in the circulation path, it is not necessary to change various conveyance conditions such as the pressure of the roller and the separation pressure of the recording paper, and there is no fear of jamming.

Here, the paper feed speed is controlled so as to be constant at the conveying speed of 280 mm / sec for the image formation of 400 dpi, but even if the speed is other than this, a constant paper feed in consideration of the roller pressure and the like. It is also possible to make the speed constant. However, when the transport speed changes in accordance with the switching of the pixel density, it is preferable from the viewpoint of efficiency that the paper feed speed is kept constant at the highest transport speed.

The transport speed in the circulation path is 280 mm / sec,
Since the fixing speed of the fixing device 160 is 125 mm / sec, the rollers on the circulation path side are in a slipping state until the recording paper is released from the nip of the fixing rollers. Therefore, the fixing device 1
When the recording paper is released from 60, the transport speed is 280 mm
/ Sec. Then, in this circulation path, it is conveyed at a section of 280 mm / sec up to the above-mentioned registration roller 229. After that, the registration roller 229 is driven at a predetermined timing to similarly transfer and fix the second surface.

Here, with reference to FIG. 6, the sub CPU 12 will be described with respect to the part relating to the main part of the paper feeding and feeding of the present embodiment.
The relationship between 01 and each part around it will be described. Sub CPU
A ROM 1201 stores a control program
A RAM 1211 that stores 1210 and control data is connected. Then, from the sub CPU 1201,
A driving signal for driving the sheet feeding motor 422 to the sheet feeding unit 2, a registration driving signal for driving the sheet feeding motor 433 that rotationally drives the registration roller 229, and a conveying roller 232 of the circulation type conveying path. Conveyor motor 4 for driving
54, drive signals for 54, and transport rollers E28, E142, E141, E32 of the post-processing unit E (sorter) of recording paper.
The drive signals of the sorter transport motors 444 for driving the motors are output. A control circuit and a drive circuit are arranged between the sub CPU 1201 and each motor as needed.

Further, PS240, PS241, PS24
3, PS 247 are respective recording paper detection sensors, and the sub CPU 1201 outputs the result of detection of the presence or absence of recording paper in each section.
To tell.

PS 250 is a recording paper detection sensor provided at the rear of the fixing device 160, and the recording paper is the fixing device 1.
It is detected whether or not 60 has been passed. Based on this detection result, the sub CPU 1201 controls the conveyance in the post-processing section E.

<Conveyance Control in Post-Processing> Next, end of fixing-
The procedure of paper discharge to post-processing will be described with reference to the block diagram of FIG. 5 and the flowchart of FIG. 7.

As shown in FIG. 5, the recording sheet detection sensor PS250 and the sorter section conveying motor 444 for driving each section of the post-processing section E are related to the sheet discharge after fixing, and are instructed by the sub CPU 1201. PS25 after fixing
The conveyance of the recording paper is controlled by the detection state of 0.

Specifically, the sub CPU 1201 controls the operation of the post-processing section E according to a subroutine (flowchart in FIG. 7) called from the main program.
This program and subroutine are stored in the ROM 1210.
Is stored in

First, the rise of PS250 is determined (S1 in FIG. 7). As a result, it can be detected that the recording paper is ejected from the fixing device 160 and is conveyed to the receiving port E21 of the post-processing unit E.

When this state is detected, the pixel density is 600 dp
The RAM 12 is used to determine whether the image formation of i is being carried.
11 a predetermined state flag is checked to make a judgment (FIG. 7).
S2).

When the image formation of 600 dpi is not conveyed, the conveyance speed of the receiving section of the post-processing section E is set to 28.
It is controlled to 0 mm / sec (S3 in FIG. 7). On the other hand, when the image formation of 600 dpi is being carried, the post-processing unit E
Control the transport speed of the receiving part of 125mm / sec (Fig. 7S
4). That is, the sub CPU 1201 gives a drive signal for carrying out such transport control to the sorter transport motor 444.

By controlling in this way, when the recording paper is conveyed from the fixing device 160 to the post-processing portion E, the conveying speed of the receiving portion coincides with the conveying speed of the fixing device. It is possible to deliver without force. Therefore, there is no possibility that the image on the recording paper will be scratched by the transport roller or the image will be displaced.

Next, the fall of PS250 is determined (S5 in FIG. 7). This fall of PS250 is due to the fixing device 1
This means that the fixing roller 60 is released from the nip conveyance. At this point, since the recording paper can be controlled at the unique conveying speed of the post-processing section E, the conveying speed in the post-processing section E is controlled to 800 mm / sec (S6 in FIG. 7). That is, the sub CPU 1201 gives a drive signal for carrying out such transport control to the sorter transport motor 444.

In the example shown here, the sorter transport motor 444 is used to transport and drive everything in the post-processing section E, but different motors are used for the receiving section of the post-processing section E and for the subsequent sections. It is also possible to drive it by transport. In that case, in order to realize the above operation, the sub CPU 1201
Supplies a drive signal corresponding to each motor.

As described above, at least the recording paper is the fixing device 1.
While the sheet is being nipped and conveyed by 60, the conveying speed of the post-processing section E is controlled to be the same as the conveying speed in the fixing device, so that appropriate values of various conveying conditions such as pressures of various rollers for conveying can be obtained. Therefore, the recording paper jam, the defective image, etc. do not occur. Further, when the recording paper is released from the nipping and conveying of the fixing device 160, the recording paper is conveyed at a higher speed than the conveying speed of the fixing device 160, so that it is possible to provide a high-speed image forming apparatus with good paper passing property.

In each of the above embodiments, two types of pixel density switching, 400 dpi and 600 dpi, are exemplified, but other pixel densities may be used, and more types may be used. It is also possible to switch the pixel density.

Although the control means using the main CPU and the sub CPU has been described as an example, the control means is not limited to this type as long as the above-mentioned conveyance control can be performed.

[0095]

As described above, according to the present invention, the following effects can be obtained. (1) In the invention of the first image forming apparatus, the timing of feeding the recording paper from the image carrier to the transfer portion for transferring the toner image onto the recording paper and transferring the recording paper at the transfer timing is the pixel density. The pressure of various rollers for transportation is controlled by switching according to the switching and controlling at least one transportation speed of the transportation means for transporting the recording paper other than the timing transportation means to be constant regardless of the pixel density switching. Since various conveying conditions such as the recording paper separation pressure and the recording paper are kept within the proper range, the recording paper jam does not occur. Therefore, it is possible to provide an image forming apparatus having good paper passing property.

(2) In the invention of the second image forming apparatus, the transport speed of the timing transport means for feeding and transporting the recording paper at the transfer timing to the transfer portion for transferring the toner image from the image carrier to the recording paper. According to the switching of the pixel density, and a recirculation type conveyance unit for re-feeding the one-side recorded recording sheet to the transfer section, or the recording sheet stored in the recording sheet storage section is fed to the timing conveying means. By controlling the paper feeding / conveying unit so as to be constant regardless of the pixel density switching, various feeding conditions such as the pressure of various rollers for feeding and feeding the paper and the separation pressure of the recording paper are set to appropriate values. Since it is kept within the range, recording paper jam or the like does not occur at the time of feeding. Therefore, it is possible to provide an image forming apparatus having good paper passing property.

(3) In the invention of the third image forming apparatus, the transport speed of the timing transport means for feeding and transporting the recording paper from the image carrier to the transfer portion for transferring the toner image onto the recording paper at the transfer timing. According to the switching of the pixel density, and a recirculation type conveyance unit for re-feeding the one-side recorded recording sheet to the transfer section, or the recording sheet stored in the recording sheet storage section is fed to the timing conveying means. By controlling the paper feeding / conveying unit for this purpose, the feeding speed is controlled to be constant at a feeding speed that matches the fastest linear velocity of the image carriers switched by the pixel density switching, regardless of the pixel density switching. Since various transport conditions such as the pressure of various rollers for feeding and feeding the paper and the separation pressure of the recording paper are kept within the proper range, recording paper jams etc. may occur during feeding. That processing speed is also fast with the disappears. Therefore, it is possible to provide the image forming apparatus which has good paper-passing property and does not decrease the processing speed.

(4) In the invention of the fourth image forming apparatus, when the conveyance speed of the recording paper from the transfer by the transfer means to the fixing by the fixing means is changed in accordance with the switching of the pixel density. The post-processing conveyance control means controls the conveyance speed in the post-processing means to be the same as the conveyance speed in the fixing means, so that the pressure of various rollers for conveyance and the separation pressure of the recording paper are controlled. Since various transport conditions such as the above are kept within an appropriate value range, recording paper jams, etc., pull marks and image transfer deviation due to the difference in transport speed are eliminated. Therefore, it is possible to provide an image forming apparatus which has good paper-passing properties and also has good images.

(5) In the invention of the fifth image forming apparatus, when the conveying speed of the recording paper from the transfer by the transfer means to the fixing by the fixing means is changed in accordance with the pixel density switching. The post-processing conveyance control means controls the conveyance speed in the post-processing means to be equal to the conveyance speed in the fixing means at least while the recording paper is nipped and conveyed by the fixing means. With this, it is possible to prevent the occurrence of a tensile mark and an image transfer shift due to the difference in the transport speed between the two, and it is possible to prevent a recording paper jam or the like from occurring. Further, it becomes possible to control the conveying speed in the post-processing means at a high speed at the time when the nipping and conveying of the fixing means is released, and it is possible to provide an image forming apparatus having a good paper passing property.

[Brief description of drawings]

FIG. 1 is a functional block diagram illustrating an electrical configuration of an image forming apparatus according to an embodiment of the present invention;

FIG. 2 is a configuration diagram illustrating a mechanical configuration of a main part of an image forming apparatus according to an example of an embodiment of the present invention.

FIG. 3 is a configuration diagram showing a mechanical configuration of a main part of a post-processing device used in the image forming apparatus according to the exemplary embodiment of the present invention.

FIG. 4 is an explanatory diagram illustrating a state of each unit that is switched according to a pixel density switching.

FIG. 5 is a configuration diagram showing a conveyance state of a main part of the image forming apparatus according to the example of the embodiment of the present invention.

FIG. 6 is a functional block diagram illustrating an electrical configuration regarding conveyance control of the image forming apparatus according to the example of the embodiment of the present invention.

FIG. 7 is a flowchart illustrating a processing procedure relating to conveyance control of the image forming apparatus according to the example of the embodiment of the present invention.

[Explanation of symbols]

 1000 External device 1100 Image forming apparatus 1101 Main CPU 1102 Operation unit 1200 Printer unit 1201 Sub CPU 1202 Image sensor switching unit 1203 Charging grid voltage control circuit 1204 Polygon mirror control circuit 1205 Photoconductor rotation speed control circuit 1206 Development sleeve rotation speed control circuit 1207 Laser spot interval changing means

Claims (5)

[Claims] 1. An image carrier on which a latent image is formed, and a writing unit for forming a latent image on the image carrier, the linear velocity at which the image carrier is driven in the sub-scanning direction, An image forming apparatus for switching a pixel density of an image to be formed by switching a writing speed of a writing unit to the image carrier in the main scanning direction, wherein a toner image is transferred from the image carrier to a recording sheet. At least one of the transporting means for transporting the recording paper other than the timing transporting means, by switching the transporting speed of the timing transporting means for feeding and transporting the recording paper to the transfer section An image forming apparatus comprising a control means for controlling the speed to be constant regardless of the switching of the pixel density. 2. The conveying means, which is controlled so that the conveying speed is constant regardless of the switching of the pixel density, is a circulation type conveying section for re-feeding the recording sheet on which one side has been recorded to the transfer section, or recording. The image forming apparatus according to claim 1, wherein the image forming apparatus is at least one of a paper feed / conveyance unit for feeding the recording paper stored in the paper storage unit to the timing conveyance unit. 3. The carrying speed of the carrying means, which is controlled so that the carrying speed is constant irrespective of the switching of the pixel density, is the fastest linear speed of the linear velocities of the image carrier switched by the switching of the pixel density. The image forming apparatus according to claim 1, wherein the image forming apparatus has a combined conveyance speed. 4. A writing unit for forming a latent image on an image carrier, a transfer unit for transferring a toner image formed by developing the latent image on the image carrier to a recording paper, and a recording unit for recording by the transfer unit. A fixing unit that fixes the toner image transferred onto the paper, a post-processing unit that receives the recording paper on which the toner image is fixed by the fixing unit and performs sorting work, and a conveyance of the recording paper in the post-processing unit. And a post-processing conveyance control means for controlling the image carrier, by switching the linear speed at which the image carrier is driven in the sub-scanning direction and the writing speed of the writing device in the main scanning direction on the image carrier, An image forming apparatus for switching the pixel density of an image to be formed, wherein the conveyance speed of the recording paper from the transfer by the transfer unit to the fixing by the fixing unit is changed in accordance with the pixel density switching. After the above The image forming apparatus is characterized in that the processing / conveying control means controls the conveying speed in the post-processing means to be equal to the conveying speed in the fixing means. 5. The post-processing conveyance control means has a conveyance speed in the post-processing means which is at least equivalent to a conveyance speed in the fixing means while the recording paper is being nipped and conveyed by the fixing means. The image forming apparatus according to claim 4, wherein the image forming apparatus is controlled as follows.