JPH06334871A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a high definition picture with a minimum memory capacity by changing a compression rate of a memory in response to the mode in the image forming device having the memory when a double side image is formed. CONSTITUTION:Picture data are color-converted by a color converter 301 and when it is coded by a brightness coder 302 and a chromaticity coder 303, a compression rate of the picture data at double sided image forming is increased more than that at one side image forming. Then coded data for at least one side are compressed able to be stored in a picture memory 300 at one side image forming, and coded data for at least double sides are compressed able to be stored in the memory 300 at double sided image forming. When the stored data are decoded by a brightness decoder and a chromaticity decoder, the data are expanded corresponding to the compression rate and color-converted by a color converter to form an image on a recording medium.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, for example, an image forming apparatus having an image memory and capable of forming a full-color image by an electrophotographic system or an electrostatic recording system.

[0002]

2. Description of the Related Art A plurality of photosensitive drums (electrophotographic photosensitive bodies) which are image bearing members are provided, images of different colors are formed on the respective photosensitive drums, and the images are transferred onto a single transfer material. Therefore, an image forming apparatus capable of forming a multicolor image is widely known. (For example, JP-A-59-62879).

In such an image forming apparatus, process cartridges having a charging device, a developing device, a transfer charging device, and a cleaning device are provided around the photosensitive drum by the number of colors of the necessary developer (toner), and each process cartridge is provided. A toner image of each color formed on the photosensitive drum is sequentially transferred onto one transfer material to form a multicolor image. On the other hand, in such an image forming apparatus, it is desired to realize both sides of an image formed on a transfer material, particularly, an automatic double-sided method.

For example, with reference to FIG. 2, an automatic double-sided image forming method in such an image forming apparatus will be described with reference to an apparatus using this image forming apparatus for a conventionally proposed intermediate tray system. FIG. 2 shows a cross section of an image forming apparatus capable of forming four full-color images using magenta, cyan, yellow, and black toners.

In FIG. 2, a detailed description of the electrophotographic image forming process will be omitted because it is already obvious except for a special part. FIG. 2 is a diagram illustrating a double-sided image forming method using such an image forming apparatus in a conventionally proposed intermediate tray system. In FIG. 2, the second sheet feeding roller release solenoid is turned on at the same time when the image formation start signal is turned on, and the second tray of the intermediate tray 101 is turned on.
The paper feed roller (re-feed roller) 102 rises in preparation for forming a double-sided image. After that, image leading edge signal (ITOP)
After a certain period of time from the occurrence of, the sheet conveying path deflecting plate solenoid is turned on and the sheet deflecting plate 103 operates to form a sheet conveying path for double-sided formation. At the same time, the paper stopper plate solenoid in the intermediate tray unit 101 is turned on, and the paper stopper plate in the intermediate tray is operated.

At the same time, the second conveying section drive solenoid SL6 (not shown) is turned on, and the second conveying section, that is, the roller pair 106, starts driving. On the other hand, the paper feed cassette 9a-
The movement of the transfer material P loaded in 9c is as follows:
At the same time when the image formation start signal is turned on, the first paper feed roller solenoid is turned on, and the feeding operation of the transfer material P in the cassette is started. The transfer material P fed from the inside of the cassette is conveyed by the conveying roller 52, and the first registration roller pair 5
With the tip of the transfer material P abutting on 8, a predetermined loop is formed and temporarily stopped.

After that, when an image leading edge signal (ITOP) is generated, the driving of the first registration roller 58 is started, and by this driving, the transfer material P is attracted to a predetermined position on the conveying means 8 for image formation. -Transported. The image forming apparatus shown in FIG. 2 has four photosensitive drums (electrophotographic photosensitive pairs) 1 (specifically, 1a to 1d) as image carriers, which are independently described. 1 is provided with a laser scanning system 2 (specifically, 2a to 2d), and around each photosensitive drum 1, a one-time charger 3 (specifically, a surface of the photosensitive drum 1 is charged in advance). Is 3a-3
d), a developing device 4 (specifically 4a to 4d) having toners of magenta, cyan, yellow, and black, and transfer charging for transferring the toner image on each photosensitive drum 1 to a transfer material P as a transfer medium. Vessel 5 (specifically 5a-5
d), a cleaning device 6 (specifically, 6a to 6d) for removing the residual toner on each photosensitive drum 1 is provided.

Below the four photosensitive drums 1 and the like, the photosensitive drums 1 and the transfer charger 5 are rotatively moved in the directions of the arrows in FIG.
A conveying unit 8 configured by an endless upper conveying belt or the like for sequentially conveying the transfer material P is disposed between the sheet feeding cassettes 9 (9a to 9a) for holding the transfer material P on the sheet feeding side of the conveying unit 8.
d), and a fixing means 11 for fixing the toner images transferred from the paper feed cassette 9 onto the transfer material P in an overlapping manner.
Also, a discharging unit for discharging the transfer material P after the fixing process is provided.

In FIG. 2, the first station (the photosensitive drum 1a with the suffix a) is arranged in the order in which the transfer material P advances.
Image forming station), a magenta image at the second station (image forming station for subscript b), a cyan image at third station (image forming station for subscript c), and a fourth station (image forming station for subscript d). ), Black images are formed respectively.

That is, in the first station, the photosensitive drum 1a uniformly charged by the one-time charger 3a is exposed to image light based on magenta image information through the laser scanning system 2a, and the photosensitive drum 1a is electrostatically charged. When the latent image is formed, the electrostatic latent image is directed toward the developing device 4a as the photosensitive drum 1a rotates, and magenta toner is supplied by the developing device 4a to be visualized as a toner image. .

Then, the toner image is directed toward the transfer charger 5a, and is transferred onto the transfer material P on the conveying means 8 by the transfer charger 5a. After the transfer, the photosensitive drum 1a is prepared for the next image formation after the residual toner is cleaned by the cleaning device 6.
Similarly, in the second, third, and fourth stations, the toner images of cyan, yellow, and black are transferred and superposed on the transfer material P.

The transfer material P, which is fixed on the conveying means 8 by suction means or the like, is fixed between the photosensitive drum 1 and the transfer charger 5 in the first, second, third, and fourth stations in this state. The toner images of four colors are transferred while passing through. Then, the transferred transfer material P is sent from the conveying means 8 to the fixing means 11, and the fixing means 11 melt-mixes and fixes the toner image to finish the image formation on the first surface. First
When the fixing operation for the first surface is completed, the transfer material P is conveyed to the double-sided path by the above-described first sheet deflection plate 103 and is then conveyed to the conveyance rollers 106 and 107.

When the transfer material P passes through the paper reversal detection sensor Q21 provided in the switch pack section (paper reversal section) 114, the reverse drive solenoid is turned on and the forward / reverse roller 107 is rotated in reverse. As a result, the transfer material P is switched back, and the second transport unit 210 (transport rollers 108 to 1
10). Deflection plates 112 and 113 for each paper size change the conveyance path of the transfer material P conveyed to the intermediate tray 101 by driving the paper deflection solenoid according to the size of the transfer material P.

When the first transfer material P is conveyed into the intermediate tray, the second paper feed roller release solenoid is temporarily turned off, and the rotating second paper feed roller 102 is transferred to the transfer material P. Move it down. As a result, the transferred transfer material P is abutted against the paper stopper plate 105 so that the tray paper sensor Q19 can reliably detect the copy paper. Through the series of operations, the transfer material on which the image formation on the first surface is completed is sequentially stacked on the intermediate tray 101,
Ready for image formation on the second side.

When the final transfer material having the image formed on the first side is stored in the intermediate tray, each solenoid is turned off.
To be done. In this state, the second paper feed roller 102 is lowered onto the transfer material stacked in the tray. In this state, when the second surface image forming start signal is transmitted, the image forming operation for the second surface is started. That is, the second
The conveyance section drive solenoid is turned on, and the second paper feed roller 10
2 rotates to re-feed one transfer material P in the tray from the top. When the first transfer material starts to be fed, that is, when it is started to be conveyed by the conveyance roller 55, the second paper feed roller moves up.

When the feeding of the first transfer material is completed, the rotating second feeding roller is lowered at a predetermined timing to feed the next transfer material (second sheet). The second paper feed roller 102 repeats this vertical movement. The re-fed transfer material is conveyed by the conveyance rollers 55 and 52, the leading end hits the first register roller pair 58, forms a predetermined loop, and is temporarily stopped, and then when the image is formed on the first surface. Similarly, at a predetermined timing, it is fixed and conveyed on the conveying means 8 and passes through the first to fourth stations,
After the second surface image is formed, the fixing of the second surface image is completed.

On the other hand, when the image formation on the second side is started, the above-mentioned sheet deflection plate solenoid is turned off. Therefore, the image forming on the second side is completed and the transfer material which has been fixed is discharged. It is guided to the rollers and discharged / loaded onto the paper discharge tray via the paper discharge means 12. After discharging the final transfer material, the series of operations is completed.

[0018]

However, in order to realize double-sided image formation in the above-mentioned conventional apparatus for forming a multicolor image using a plurality of colors, there are the following drawbacks. First, there is the problem of image curl. That is, in the case of a multicolor image forming apparatus, due to its characteristics, the transfer material warps (hereinafter referred to as “curl”). That is, when an unfixed toner image on a transfer material is heat-fixed by a fixing device including a pair of heat rollers, when the image is discharged and cooled, there is a difference between the shrinkage ratio of the transfer material and the shrinkage ratio of the toner. As a result, they appear as curls of the transfer material. (Usually, the image surface is curled.) That is, in a color image forming apparatus that forms an image of a plurality of colors, the amount of toner used is larger than that in the case of black and white due to its characteristics, and all density Image is assumed. In particular, when images are formed on both sides of the transfer material, the image on the first side is fixed by the fixing device and then the image on the second side is formed. This causes the problem of curling of the material. Therefore, according to the conventional double-sided method with the intermediate tray method,
It becomes difficult to handle the transfer material at the time of re-feeding, and a curling forcing means, a curling forcing means and the like are newly required.

The second problem is the influence of the release material on re-feeding. This is because a releasing agent (silicon oil, etc.) is applied on the roller in order to improve the releasing property between the fixing roller and the transfer material, especially when the color image is fixed by the electrophotographic method. This is a problem that arises. That is, since silicon oil as a release agent remains on the transfer material after fixing, when re-feeding this image, a failure such as a separation error or a paper feed error occurs. Is.

The third problem is the deterioration of the image surface due to the rubbing of the image surface during re-feeding, roller marks, and the like. In particular, for a high-density image such as a color image, the re-feeding roller rubs the image surface formed on the first surface with the pick-up roller, so that roller marks are left on the image. However, when the image quality is deteriorated and the image quality is deteriorated, problems are likely to occur.

A fourth problem is that, in the conventional intermediate tray system, the transfer material is temporarily loaded in the transfer material transport path for refeeding. Since the intermediate tray portion is required, a large space is required, and there are disadvantages that the size of the apparatus is increased and the cost is increased.

[0022]

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above problems and provide an image forming apparatus capable of stably forming double-sided images on all images. Then, for example, the following configuration is provided as one means for achieving the object. That is, an image processing means for compression-encoding and decompressing image data and a storage means for storing the compression-encoded data in the image processing means are provided, and a recording material is recorded on the recording material according to the encoded image data. An image recording unit for forming an image is provided, and the image processing unit increases the compression / expansion rate of the image data at the time of double-sided image formation as compared with the case of single-sided image formation.

For example, the image processing means can change the compression / expansion rate for compression encoding and expansion decoding depending on the recording material size, or the image recording means forms a full-color image on the recording material. For example, the image processing unit further compresses at least one side of the encoded data so that it can be stored in the storage unit when the one-sided image is formed, and compresses at least both sides of the encoded data that can be stored in the storage unit when the two-sided image is formed. Then, the image recording means continuously conveys the recording material even during double-sided image formation, and continuously records the images of the two surfaces stored in the storage means on the recording material.

[0024]

With the above construction, by changing the compression ratio of the memory in accordance with the mode when forming images on both sides,
High-definition images can be provided with the minimum memory capacity. Also,
By storing the coded data of the first side and the coded data of the second side for two sides in the storage unit and continuously conveying the recording material, after the first side image formation is completed. The double-sided image can be formed automatically and at high speed without loading and storing the recording material in the intermediate portion for forming the image on the second side.

As a result, it is possible to solve the problems such as the curl of the transfer material, the influence of the fixing mold material, the rubbing of the image at the time of re-feeding, the large space, the cost up, etc. it can. In particular, an image forming apparatus having a plurality of image forming stations arranged side by side and sequentially transferring images of a plurality of colors to form a multi-color image is usually used effectively from a characteristic of having a memory because of its characteristics. Moreover, it is possible to realize the formation of a multicolor double-sided image by compensating for the conventional defects.

[0026]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment according to the present invention will be described in detail below with reference to the drawings. FIG. 1 is a side sectional view of an image forming apparatus according to an embodiment of the present invention. In FIG. 1, for example, image forming media (photosensitive drums) 1a, 1b, 1c, 1d corresponding to magenta, cyan, yellow, and black, for example.
And the developing devices 4a, 4b, 4c and 4d and the cleaner 6a,
The image forming station 6b, 6c, 6d and the like are combined for each color.

An image writing device such as a laser optical system L is used for these image forming stations.
Is provided. The transfer material P, which is a recording medium, is housed in the cassettes 9a to 9c. The cassettes 9a to 9c are configured so that they can be pulled out toward the front side in the figure. For example, paper replenishment and a jam treatment at the time of jamming in the cassette can be performed by pulling out the cassette toward the front side of the apparatus. .

The double-sided image forming operation of the apparatus of the present embodiment having the above construction will be described below by taking the case of feeding from the transfer material in the upper cassette 9a as an example. In this embodiment,
Two or more double-sided images (10
The operation of the apparatus when creating a sheet will be described. At the same time when the image forming start signal is turned on, the first paper feed roller solenoid is turned on, and the transfer material P is sent out from the cassette 9a one by one by the pick-up roller 59 in the paper feeding device, and then the transfer rollers 52 and 55, and then the registration rollers. 58
After being timed at, the sheet is placed on the belt conveyor 8 and conveyed in the direction of the arrow A, and by the known image transfer process, the first to fourth image forming stations juxtaposed in one row, Images are sequentially transferred to form a multicolor image.

On the other hand, at the same time when the image forming start signal is turned on, the image of the document A placed on the document image reading device (hereinafter referred to as a reader) is changed to magenta, cyan, yellow, by an optical reading sensor such as CCD. The black color components are separated, read into the image memory, and temporarily stored. The image information of the document A stored in the memory is obtained at each timing when the transfer material P passes through the magenta, cyan, yellow, and black stations.
It is written on each color photosensitive drum by a laser optical system L as an image writing device so as to be superposedly transferred onto a transfer material.

By such an operation, the multicolor image of the original A, that is, the transfer material P on which the image on the first side is superposed and transferred is sent from the belt conveying section 8 to the fixing device 11,
The heat roller is fixed by the fixing device 11. Simultaneously with or after these operations, the image of the document B is similarly read by the reader, read into the memory, and stored.

As a result, in the image memory in the apparatus,
It has image information for two sides of the original A and the original B. When the fixing operation for the first side (original A image) is completed, the transfer material P is transferred by the above-described first sheet deflection plate 103.
The sheet is conveyed to the double-sided path and is conveyed to the conveying rollers 106 and 107. The transfer material P is a switch back part (paper reversal part) 1
When the paper reverse detection sensor Q21 provided in 14 is passed, the reverse drive solenoid SL5 is turned on, and the forward / reverse roller 107 is rotated in reverse. As a result, the transfer material P is switched back and inverted, and the transfer roller 2 of the double-sided transfer path 210
01-208.

Among the transport rollers 201 to 208, 20
Each of the roller pairs 1, 203, 205 and 207 is provided with a drive contacting / separating means such as a clutch capable of turning the drive ON / OFF, and can be driven independently. Each of these roller pairs is similar to the registration roller 58 in the transfer material P.
It has a structure capable of being stopped by abutting the tip end of the, and forming a predetermined loop. Further, with respect to these roller pairs, the roller pairs 202, 204, 206 and 208 are rollers for carrying the transfer material,
202 is 201, 204 is 203, and 206 is 205
, 208 are driven in the same manner as 207, and are configured to perform the same operation.

Of these conveying rollers, the above-mentioned distance between the rollers of the roller pair 201, 203, 205, 207, for example, the distance between 201 and 203 (sheet passing distance) can be used in the apparatus. Among the transfer materials, the length is longer than the length of the maximum size paper in the transport direction. The first transfer material P1 has the double-sided conveyance path 2 after the switching back.
10 is sequentially conveyed by the conveying rollers 201 to 208, the leading end abuts on the first registration roller pair 58, and a predetermined loop is formed to temporarily stop. In this state, each roller of the transport roller pair 208, 58 is stopped.

The second transfer material P2 is conveyed back through the double-sided conveyance path 210 after the transfer back, and is successively conveyed by the conveyance rollers 201 to 20.
The sheet is conveyed by means of 6, and the leading end abuts on the roller pair 207, forms a predetermined loop, and is temporarily stopped. In this state, the conveying roller pairs 207, 206 and 2
The driving of the rollers 08 and 58 is stopped. The third transfer material P3 has the double-sided conveyance path 2 after the switching back.
10 is sequentially conveyed by the conveying rollers 201 to 204, and the leading end abuts on the roller pair 205 to form a predetermined loop and temporarily stop. In this state,
Conveying roller pairs 205, 204 and 206 to 208, 58
The drive of each roller is stopped.

The transfer material P5 of the fourth sheet is conveyed back through the double-sided conveyance path 210 in sequence after being switched back.
The sheet is conveyed by means of 2, and the leading end hits the roller pair 203, forming a predetermined loop and temporarily stopping. In this state, the conveying roller pair 203, 202 and 2
The driving of the rollers 04 to 208 and 58 is stopped.

The transfer material P5 of the fifth sheet is conveyed by the conveying roller 107 through the double-sided conveying path 210 after the switching back, and the leading end hits the roller pair 201 to form a predetermined loop and temporarily stop. There is. In this state, the conveying roller pairs 201 and 107 and 202 to 20
The drive of each of the rollers 8, 58 is stopped. In this state, the transfer materials P1 to P5 from the first sheet to the fifth sheet, on which the image formation on the first surface (original A image) is completed, are respectively the transport rollers 58, 207, 205, 203, 201.
With the tip of each of them in contact with the
The image forming apparatus is waiting for the formation of the image of the first side (original B image).

The fifth transfer material P5 is a roller pair 201.
When the second surface (original B image) formation start signal is transmitted from the stopped state, the image forming operation of the second surface (original B image) is started. That is, the image information of the original document B stored in the above-described memory is transferred onto the transfer material at each timing when the transfer agents P1 to P5 pass through the magenta, cyan, yellow, and black stations. As described above, data is written on the photosensitive drum of each color by the laser optical system L as an image writing device.

The first transfer material P1 is formed by the registration roller pair 58 being driven at a predetermined timing.
It is fixed and conveyed to a predetermined position on the conveying means 8. When the trailing edge of the first transfer material P1 has finished passing through the registration roller pair 58, the drive of the registration roller pair 58 is cut off again,
Prepare for the next transfer material. The transfer material P1 fixed on the conveying unit 8 passes through the first to fourth stations, forms an image on the second surface (original B image) by the electrophotographic process, and then transfers the image on the second surface. Finish fixing.

The transfer materials P2 to P5 for the second and subsequent sheets are the first
After a certain time has passed since the transfer material P1 for the first sheet was started,
When the driving of the pair of conveying rollers 107, 201 to 208 is started, the first pair of rollers is advanced in the conveying path and stopped.
The leading end hits the pair of registration rollers 58, and a predetermined loop is formed to temporarily stop. In this state, the rollers of the conveying roller pairs 107, 201 to 208, 58 are stopped.

In this state, the registration roller pair 58
However, by being driven again at a predetermined timing, it is fixed and conveyed to a predetermined position on the conveying means 8.
When the trailing edge of the second transfer material P2 has finished passing through the registration roller pair 58, the registration roller pair 58 is again stopped from driving, and the next transfer material is prepared. 3rd to 5th
For the transfer materials P3 to P5 up to the first sheet, as in the case of the second transfer material P2, after the fixed period of time from the start of the first transfer material, the leading ends of the pair of registration rollers 58 are stopped. After stopping butting, the transport means 8 is almost continuously
It is fixed and conveyed to a predetermined upper position, and the second side (original B image) is transferred and transferred.

On the other hand, when the image formation of the second side (original B image) is started, the above-mentioned first and second sheet deflector solenoids are turned off, and the image formation of the second side (original B image) is completed. Then, the transfer materials P1 to P5 that have been fixed are guided to the paper discharge rollers, and discharged and stacked on the paper discharge tray via the paper discharge means 12. Next, the double-sided image forming method for the sixth and subsequent sheets will be described.

When the image formation on the second side (original B image) of the transfer materials P1 to P5 is completed, the images on the first side (original A image) of the sixth to tenth sheets are next. Perform the forming operation. When the trailing edge of the fifth transfer material P5 sent for forming the image on the second side (original B image) has finished passing through the registration roller pair 58, the registration roller pair 5
8 is stopped. Then, the transfer materials P6 to P10 are sent out one by one from the cassette 9a by the pick-up roller 59 in the paper feeding device, and the leading end portions are abutted against the registration rollers 58 via the transfer rollers 52 and 53, and after the loop formation, Similar to the case of the first to fifth transfer materials P1 to P5, after the timing is adjusted, the transfer material P1 to P5 is placed on the belt transfer unit 8 and is transferred in the direction of arrow A, and a known image transfer process is performed. And the first to the fourth arranged side by side in the one row
By the image forming station, images are sequentially transferred based on the first side (original A image) stored in the memory, and a multicolor image of the first side (original A image) is formed again. .

When the fixing operation for the first side (original A image) is completed, the transfer material P is conveyed to the double-sided path by the above-mentioned first sheet deflecting plate 103, and the conveying rollers 106, 107.
Sent to. When the transfer material P passes through the paper reversal detection sensor Q21 provided in the switch back section (paper reversal section) 114, the reverse rotation drive solenoid is turned on and the forward / reverse rotation roller 107 is rotated in the reverse direction. As a result, the transfer material P is switched back, and the transfer rollers 201 to 2 of the double-sided transfer path 210 are transferred.
It is sent to 08.

The transfer material P6 of the sixth sheet is transferred back and forth through the double-sided transfer path 210 to the transfer rollers 201 to 20 sequentially.
The sheet is conveyed by means of 8, and the leading end abuts against the first pair of registration rollers 58, forms a predetermined loop, and temporarily stops. In this state, each roller of the transport roller pair 208, 58 is stopped. The seventh transfer material P7 is
After the switch back, the double-sided transport path 210 is sequentially transported by the transport rollers 201 to 206, the leading end hits the roller pair 207, and a predetermined loop is formed to temporarily stop. In this state, the conveying roller pair 207,
The driving of the rollers 206, 208, and 58 is stopped.

The transfer material P8 of the eighth sheet is sequentially transferred through the double-sided transfer path 210 after transfer back.
The sheet is conveyed by means of No. 4 and its tip hits the roller pair 205, forming a predetermined loop and temporarily stopped. In this state, the conveying roller pair 205, 204 and 2
The driving of the rollers of 06 to 208 and 58 is stopped.

The transfer material P9 of the ninth sheet is sequentially transferred through the double-sided transfer path 210 after being switched back.
The sheet is conveyed by means of 2, and the leading end hits the roller pair 203, forming a predetermined loop and temporarily stopping. In this state, the conveying roller pair 203, 202 and 2
Each roller drive of 04 to 208 and 58 is stopped.

After the switching back, the tenth transfer material P10 is conveyed by the conveying roller 107 through the double-sided conveying path 210, the leading end abuts on the roller pair 201, forms a predetermined loop, and is temporarily stopped. There is. In this state, the conveyance rollers 6 pairs 201, 107, and 202-
The driving of the rollers 208 and 58 is stopped. In this state, the transfer materials P6 to P1 from the sixth sheet to the tenth sheet on which the image formation on the first side (original A image) is completed.
0 is the transport rollers 58, 207, 205, 20 respectively.
It is stopped in a state in which the respective tip ends are abutted against 3, 201, and stands by in preparation for image formation of the second side (image of original B).

The tenth transfer material P10 is the roller pair 20.
When the image formation start signal for the second side (original B image) is transmitted from the state in which the front end is abutted against No. 1 and is stopped,
The image forming operation of the second surface (original B image) is started. That is, the image information of the document B stored in the memory described above is transferred onto the transfer material P6 to P10 on the transfer material at each timing when the transfer materials P6 to P10 pass through the magenta, cyan, yellow, and black stations. As described above, data is written on the photosensitive drum of each color by the laser optical system L as an image writing device.

The sixth transfer material P6 is formed by the registration roller pair 58 being driven at a predetermined timing.
It is fixed and conveyed to a predetermined position on the conveying means 8. When the trailing edge of the sixth transfer material P6 has finished passing through the registration roller pair 58, the registration roller pair 58 is turned off again,
Prepare for the next transfer material. The transfer material P6 fixed on the conveying means 8 passes through the first to fourth stations, forms a second surface (original B image) image by an electrophotographic process, and then fixes the second surface image. To finish.

For the transfer materials P7 to P10 for the seventh and subsequent sheets, the drive of the conveying roller pair 107, 201 to 208 is started after a predetermined time has elapsed since the transfer material P6 for the sixth sheet was started. Then, it advances in the conveyance path, the leading end hits the stopped first registration roller pair 58, forms a predetermined loop, and temporarily stops. In this state,
Each roller of the conveying roller pairs 107, 201 to 208, 58 is stopped.

In this state, the registration roller pair 58
Is driven again at a predetermined timing,
It is fixed and conveyed to a predetermined position on the conveying means 8. When the trailing edge of the seventh transfer material P7 has finished passing through the registration roller pair 58, the registration roller pair 58 is again cut off,
Prepare for the next transfer material. For the eighth to tenth transfer materials P8 to P10, like the seventh transfer material P7, the resists stopped after a predetermined time from the start of the first transfer material. After each tip is abutted against the roller pair 58 and stopped, it is fixed and conveyed to a predetermined position on the conveying means 8 almost continuously, and the second surface (image of original B).
Are overlaid and transferred.

On the other hand, when the image formation on the second side (original B image) is started, the above-mentioned sheet deflection plate solenoid is turned off.
Then, the transfer materials P1 to P5 on which the image formation on the second side (original B image) is completed and the fixing is completed are guided to the paper discharge roller,
It is discharged and stacked on the discharge tray via the discharge means 12. After that, in the case of the eleventh sheet or more, a plurality of automatic double-sided image formations can be performed by repeating the same operation.

The operation described above is summarized as follows. P1 to P5: First surface image formation ↓ P1 to P5: Second surface image formation ↓ P6 to P10: First surface image formation ↓ P6 to P10: Second surface image formation ↓ Repeatedly thereafter, the above memories are compared. Since the image data is expensive, the read image data is actually sent to the compression unit, where it is subjected to predetermined compression processing, encoded, and then stored in the memory to save the memory capacity. Then, the compression-encoded data read from the memory is sent to the decompression unit, where it is decompressed and decoded to be actually subjected to image formation processing.

The image data compression / decompression unit of this embodiment will be described below. FIG. 4 shows an encoder unit 357 that performs color conversion processing and compression encoding of input R, G, B image data.
5 shows the detailed configuration of the decoder unit 359 that performs the color conversion processing by decompressing and decoding the image data compressed and encoded by the encoder unit 357. 4 and 5, 300 is an image memory for storing encoded data 308, 301 and 306 are color converters, 302 is a lightness encoder, 303 is a chromaticity encoder, 304 is a lightness decoder, and 305.
Indicate chromaticity decoders, respectively. The image memory 300 according to the present embodiment has A3 size image data × 1/4.
The memory capacity is (compression) × 4 (color) = (one sheet of A3).

In the present embodiment having the above-described structure, for example, when the image data shown in FIG. 3 is sent to the color converter 301, the thick frame hatched portion (shown by A in FIG. 3) at the time of single-sided image formation. Block) processing. In FIG. 3, one square corresponds to one pixel, and each one pixel includes 8 bits of R, G, and B color data. Using this as a processing unit, data of 16 pixels of 1 block is 4 pixels × 4 lines is used as the color converter 301.
To convert L ^* a ^* b ^* . Then, the data of 16 pixels × 3 colors × 8 bits = 384 bits is converted into the brightness encoder 30.
2 and the chromaticity encoder 303 compresses it to (1/4) to obtain 96-bit data. The compression coded data 308 is stored in the image memory 300.

The encoded data 309 read from the image memory 300 is sent to the brightness decoder 304 and the chromaticity decoder 305 of the decoder unit 359 shown in FIG. 5, where it is expanded four times and the original 384-bit data. Return to. Then, in the color converter 306, L ^* a ^* b ^{* is} converted again into R, G, B data or Y, M, C (and K if necessary) data (24-bit data in the case of YMCK). .

When forming a single-sided image, a desired image can be formed by the above processing, but generally, when a double-sided image is to be formed at one time, a memory capacity twice as large as that of the single-sided image is required. Therefore, even with the image memory 300 of this embodiment, if the size is A4 or smaller, the above-mentioned 1/4
The memory capacity is sufficient at the image compression rate of. However, A4
If a double-sided image is to be formed at a time when the image size is larger, the memory capacity becomes insufficient with the above-mentioned compression rate of (1/4). Therefore, in this embodiment, A4
Larger (up to A3) double-sided image formation,
Image compression of (1/8) is performed. That is, the brightness encoder 30
2 and the 384-bit image data input to the chromaticity encoder 303 is not compressed to the normal 96-bit data, but is halved to 48-bit data.

In this way, by changing the compression ratio of the image data at the time of single-sided image formation and at the time of double-sided image formation,
Even if the image size is larger than the A4 size, it is possible to form images on both sides with the image memory capacity of this embodiment.
It should be noted that when the image compression rate is doubled on one side for both sides, there is some deterioration in terms of high definition of the image as compared with one side, but in reality, the deterioration is slight.
Also, while single-sided images are often high-definition images such as photographs, double-sided images are often used for so-called office documents,
Even if the compression ratio is changed, the problem on the image is small. It should be noted that the above description has been given only for the compression / expansion portion of the image, but since other configurations are known, detailed description thereof will be omitted.

As described above, according to the present embodiment, the recording material can be continuously conveyed by changing the compression ratio of the memory according to the mode when forming images on both sides. The double-sided image can be formed automatically and at high speed without loading and storing the recording material after the surface image formation on the intermediate portion for forming the image on the second surface. This allows
It is possible to solve the problems of the conventional intermediate tray system, such as curling of the transfer material, the influence of the fixing mold material, the rubbing of the image at the time of re-feeding, the large space, and the cost up.

In particular, in an image forming apparatus in which a plurality of image forming stations are juxtaposed and images of a plurality of colors are sequentially transferred in succession to form a multicolor image, the characteristic of having a memory is usually effective due to its characteristics. It is possible to realize the formation of a multicolor double-sided image by utilizing it and compensating for the conventional defects.

[0061]

Other Embodiments In the above-described embodiments, the image compression rate is changed according to the paper size during double-sided image formation. However, the present invention is not limited to the above example, and the size of the original document is not limited to this. The compression rate may be changed depending on the contents of the sheath image data. For example, when the document size is A3 size, one side is a black and white document, and the other side is a full color document, A3 size image data is 4 colors (full color side) +
Divide into 5 colors of 1 color (black and white surface) and compress the image by 1/5
By so doing, it is possible to form images on both sides, and it is possible to form high-definition images that are almost inferior to the image compression rate of 1/4 only on one side.

As described above, the image of the first surface and
By storing the images on the second side for two sides in the above-mentioned image memory and continuously conveying the transfer material,
The double-sided image can be formed automatically and at high speed without loading and storing the transfer material after the completion of the first-side image formation on the intermediate portion for forming the second-side image. The present invention may be applied to a system including a plurality of devices or an apparatus including one device.

It goes without saying that the present invention can also be applied to the case where it is achieved by supplying a program to a system or an apparatus.

[0064]

As described above, according to the present invention, in an image forming apparatus having a memory, when a double-sided image is formed, the compression rate of the memory is changed according to the mode, so that the memory capacity can be minimized. A fine image can be provided.

[Brief description of drawings]

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

FIG. 2 is a schematic sectional view of an image forming apparatus according to a conventional example.

FIG. 3 is a diagram illustrating a compression method according to an embodiment similar to the present invention.

FIG. 4 is a diagram showing a detailed configuration of an encoder unit of the present embodiment.

FIG. 5 is a diagram showing a detailed configuration of a decoder unit according to the present embodiment.

[Explanation of symbols]

 1 Photosensitive Drum 4 Developing Device 8 Conveying Belt 9 Cassette 11 Fixing Device 58 Registration Roller 101 Intermediate Tray 114 Switch Back Section 210 Double-sided Conveying Path 357 Encoder 359 Decoder 300 Image Memory 302, 306 Color Converter 302 Brightness Encoder 303 Chromaticity Encoder 304 Brightness Decoder 305 Chromaticity Decoder

Claims (4)

[Claims] 1. An image processing means for compression-encoding and decompressing image data, and a storage means for storing the compression-encoded data in the image processing means, according to the encoded image data. An image forming apparatus, comprising: an image recording unit that forms an image on a recording material, wherein the image processing unit increases a compression / expansion rate of the image data when forming a double-sided image as compared to when forming a single-sided image. 2. The image forming apparatus according to claim 1, wherein the image processing means can change a compression / expansion rate for compression encoding and expansion decoding according to the recording material size. 3. The image forming apparatus according to claim 1, wherein the image recording means forms a full-color image on the recording material. 4. The image processing means compresses coded data for at least one side so that it can be stored in the storage means during single-sided image formation, and compresses so that at least coded data for both sides can be stored in the storage means during double-sided image formation. The image recording means continuously conveys the recording material even during double-sided image formation, and continuously records the images for two surfaces stored in the storage means onto the recording material. The image forming apparatus according to claim 1.