JP3523976B2 - Image forming device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic system such as an optical printer such as a laser printer which prints (forms) an image on a transfer paper through each process of charging, exposing, transferring and fixing, a copying machine, a facsimile machine and the like. Image forming apparatus.

[0002]

2. Description of the Related Art As an image forming apparatus as described above, after performing surface printing for printing an image on one surface of a transfer paper through each process of charging, exposing, transferring and fixing, the above-mentioned respective processes are performed again. After that, there is also one that can perform back surface printing for printing an image on the other surface of the transfer paper.

By the way, since the moisture content and the resistance value of the transfer paper are changed by the front surface printing, if the back surface printing is performed under the same transfer condition (transfer current or transfer voltage) as that of the front surface printing, Depending on the state of the transfer paper, it may cause image unevenness such as toner scattering.

Therefore, as disclosed in, for example, Japanese Patent Application Laid-Open No. 2-273771, an image forming apparatus has been proposed in which a transfer bias (transfer voltage) is changed when printing on the back surface. However, since the transfer bias is changed to a predetermined value, the above problem cannot be reliably prevented. This is because the moisture content and the resistance value of the transfer paper change depending on the elapsed time after the completion of the surface printing.

Therefore, an image forming apparatus (for example, see Japanese Patent Laid-Open No. 2-264987) in which the transfer current is changed according to the type and characteristics of the transfer material (transfer paper) when performing the back surface printing, and the back surface printing An image forming apparatus in which the transfer condition (transfer current) is changed according to the temperature and humidity inside the machine (see, for example, JP-A-7-199679).
Is also proposed.

[0006]

However, in the image forming apparatus as described above, means (sensor, sensor, etc.) for detecting the type and characteristics of the transfer paper, the temperature and humidity inside the machine, and the like.
Since it is necessary to provide a circuit, etc., the cost is increased accordingly. The present invention has been made in view of the above problems, and an object of the present invention is to make it possible to appropriately change transfer conditions when performing back surface printing, with almost no increase in cost.

[0007]

In order to achieve the above-mentioned object, the present invention, as shown in the functional block diagram of FIG. 1, applies a process of charging, exposing, transferring and fixing to one surface of a transfer paper. Transfer conditions that change transfer conditions such as transfer voltage or transfer current when performing back side printing to print an image on the other side of the transfer paper through the above-mentioned processes after performing front side printing to print an image. In the image forming apparatus including the changing unit A, the time monitoring unit B that monitors the time from the start or end of the front surface printing to the start of the back surface printing.
The transfer condition changing means A is provided with a means for changing the transfer condition according to the time monitored by the time monitoring means B.

Further, it is desirable that the transfer condition changing means A is provided with a means for changing the transfer condition according to the type of transfer paper used. Further, it is preferable to provide a transfer condition changeability selection unit C for selecting whether or not the transfer condition is changed by the transfer condition changing unit A.

In the image forming apparatus of the present invention, the time monitoring means B of FIG. 1 monitors the time from the start or end of the front surface printing to the start of the back surface printing, and the transfer condition changing means A detects the time (transfer). Since the transfer conditions are changed according to the water content of the paper and the resistance value (property value), it is possible to prevent image unevenness such as toner scattering and maintain proper image quality. In addition, since the function of the time monitoring unit B may be provided to the CPU or the like with the built-in timer provided in the control unit of the image forming apparatus, the cost is hardly increased.

Further, if the transfer conditions are changed (adjusted) according to the type of transfer paper used by the transfer condition changing means A, image unevenness can be prevented more effectively. Further, by providing the transfer condition changeability selection unit C for selecting whether or not the transfer condition is changed by the transfer condition changing unit A, the user is allowed to perform the back side printing under the transfer condition according to the purpose of use, and the desired printing is performed. The result can be obtained.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be specifically described below with reference to the drawings. FIG. 2 is a diagram showing a schematic configuration of a mechanical portion of a laser printer which is an embodiment of the present invention.

This laser printer is mainly composed of a laser printer main body 1 and an optional table 2, and the laser printer main body 1 is detachably provided with two upper and lower two paper feed cassettes 3 and 4 and is provided with a first upper tray. The first and second sheet discharge stackers 6 and 7 are provided in a two-tiered manner, and the third sheet discharge stacker 8 is provided at the rear part so as to be openable and closable with respect to the sheet discharge port 9.

Further, in the laser printer main body 1, a photosensitive drum 10, a charging charger 11, a laser writing device 12, a developing device 13, a transfer charger 14, which constitute an image forming portion of an engine unit (printer engine) described later,
A fixing device 15; a paper feed unit including two upper and lower paper feed rollers 16 and 17, a registration roller pair 19, and the like; and a paper ejection conveyance unit 20 including a large number of conveyance rollers and a paper guide plate.
A power supply unit 21, a controller (board) 50, an engine driver (board) 60, a registration sensor 24, and eight position sensors 31 to 38 are provided.

On the other hand, the table 2 is a double-sided sheet comprising a large-volume sheet-feeding tray 5 and a sheet-feeding roller 18 included in the above-mentioned sheet-feeding section, a plurality of conveying rollers constituting a double-sided machine (double-sided unit), and a paper guide plate. Reversing unit 25 and reversal paper feeding unit 26 for printing (double-sided printing), and five position sensors 39
To 43 are provided.

When a paper feed command is sent from the controller 50, the engine driver 60 causes the paper feed rollers 16, 17,
18 is driven to start feeding from a selected one of the upper paper feeding cassette 3, the lower paper feeding cassette 4, and the large-volume paper feeding tray 5 to feed the transfer paper, and then transfer the transfer paper. When the leading edge of the paper is detected by the registration sensor 24,
The pair of rollers is temporarily stopped while being held by the registration roller pair 19.

When the video data for one page or more is created, a print command is sent from the controller 50, whereby the engine driver 60 starts the print sequence. At this time, the photosensitive drum 10 rotates in the direction of the arrow, and the surface charged by the charging charger 11 is main-scanned in the drum axis direction by the laser beam modulated by the laser writing device 12 according to the video data. Irradiate and expose to form a latent image.

The latent image is developed with toner from the developing device 13, and the registration roller pair 19 is developed at a predetermined timing.
The image is transferred by the transfer charger 14 onto the transfer paper fed by. The transferred transfer paper is used as the photosensitive drum 1.
It is peeled from 0 and conveyed to the fixing device 15 to be heated for fixing, and the transfer paper which has been fixed and heated is delivered to the paper discharge section. At that time, either the first paper output stacker 6 or the second paper output stacker 7 located at the upper part of the printer via the paper output transport part 20 as the paper output part, or the third paper output stacker 8 located at the rear part of the printer. The paper is ejected to the selected paper ejection stacker.

Normally, either the first paper output stacker 6 or the second paper output stacker 7 is selected, but in a special case such as when using an easily curled paper such as an envelope or a postcard, the first paper output stacker 6 or the second paper output stacker 7 is selected. 3 The paper discharge stacker 8 is selected. However, when the sheet discharge port 9 is closed and the sheet cannot be discharged, the third sheet discharge stacker 8 cannot be selected.

By the way, when the double-sided printing mode is selected, the transfer paper having the image printed on one side (front side) by front-side printing is sent to the reversing section 25 for double-sided printing, and then the conveying direction is reversed. The sheet is conveyed to the reversal sheet feeding unit 26, and is temporarily held there. And the video data is 1
If more than one page has been created, the transfer paper is fed at a predetermined timing, the back surface is printed with an image based on the video data, and then the paper is ejected to one of the paper ejection stackers.

FIG. 3 is a block diagram showing the control system of this laser printer. This laser printer includes a controller 50, an engine unit 90, an operation panel 80, a font cartridge 81, an option 8
It is composed of two.

The controller 50 controls the interface with the host machine 83, the control mode set at that time, and the control code from the host machine 83.
The engine driver 60 in the engine unit 90 by converting the print data from the host machine 83 into video data
It is a general term for the control and processing units that output to, and includes the following units.

That is, host interface (hereinafter "interface" is abbreviated as "I / F") 51, engine I / F 52, panel I / F 53, and central processing unit 54 (hereinafter "controller CP").
U ”), program ROM 55, font ROM
56, a RAM 57, and an optional RAM 58.

The host I / F 51 is an interface circuit for transmitting and receiving various control commands and data to and from the host machine 83, and selects various serial interfaces or parallel interfaces according to the connected host machine. . The engine I / F 52 controls transmission / reception of data such as instruction commands and status information with the engine unit 90. The panel I / F 53 transmits display control data with the operation panel 80 and receives each key information.

The controller CPU 54 is a general-purpose 16- or 32-bit central processing unit and has a program ROM.
It controls the overall control of the entire controller 50 according to a control program stored in 55. Program ROM55
Is a control program for controlling data processing in the controller 50 and peripheral modules by the controller CPU 54, and the font ROM 56 is a read-only memory that stores various fonts used for printing.

The RAM 57 is a random access memory, which is a work memory used when the controller CPU 54 processes data, a buffer for managing the data from the host machine 83 in page units and temporarily storing the data, and a temporary storage in the buffer. The converted data is converted into an actual print pattern and used as a bit map memory for storing as video data.

The option RAM 58 is a non-volatile memory that stores and holds internal data even when the power is turned off, and mode information set by the operation panel 80 (selected print format, font, emulation, paper feed port). , Paper exit, resolution, transfer conditions, ID (paper number), host interface, etc.)
It also stores service information (error information, operation information, etc.).

The operation panel 80 has a display section for displaying various information such as the printer status, and an operation section for setting the operation mode and font of the printer. The font cartridge 81 has a built-in RAM or ROM that stores optional font data. By inserting this into a slot provided on the outer surface of the printer, printing can be performed using the font data. it can.

The host machine 83 is a host device such as an office computer, a personal computer, a word processor, a data processing device or an image processing device, and is used to print an image of document information or the like created here on a transfer paper. The corresponding print data and control code are sent to the printer.

The engine unit 90 drives the dip switch 73, the laser writing device 12 shown in FIG. 2, the photosensitive drum 10, each process device (including the transfer charger 14) around the device, each roller, and the rollers. Sequence equipments (sensors / switches 72, motor 7)
4, a clutch 75) and the like, and a mechanical section configured by a transfer paper transport section and the like, and an engine driver 60 that is a control section (including a high-voltage power supply 76 that connects the transfer charger 14). Driver 6
0 controls the sequence operation of each process device of the mechanical section and the transfer sheet conveying section and the video modulation signal to the laser writing device 12 by the command and the video data from the controller 50 to perform printing, monitor the status of the printer, etc. Do.

The engine driver 60 is a controller I
/ F61, each interface circuit of option I / F62, CPU63 (hereinafter referred to as "engine CPU"),
Interrupt control circuits 64, 65, ROM 66, flash RO
M67, RAM68, EEPROM69, input port 7
0 and an output port 71.

The controller I / F 61 controls transmission / reception of data such as instruction commands and status information to / from the controller 50. The option I / F 62 is connected to an option 82 such as a large-volume paper feed tray, a double-sided machine, and a sorter, and controls the transmission and reception of data such as command commands and status information with the option 82. Here, Option I
The / F 62 is connected to the large-volume paper feed tray 5 and the table 2 including a double-sided machine.

The engine CPU 63 is a general-purpose 16 or 3
It is a 2-bit central processing unit and controls the overall control of the engine driver 60 according to a control program stored in the ROM 66 or the flash ROM 67. The interrupt control circuits 64 and 65 are circuits that control each interrupt state for the engine CPU 63.

The ROM 66 is a read-only memory that stores a control program for controlling data processing in the engine driver 60 and peripheral modules by the engine CPU 63. Flash ROM 67
Is a readable / writable memory that can store control programs other than the resident control programs stored in the ROM 66.

The RAM 68 is a memory having a function as a buffer register. The EEPROM 69 is a readable / writable non-volatile memory that records a maintenance cycle. The input port 70 is the registration sensor 2
4, position sensors 31 to 43, sensor switches 72 such as a synchronization detection sensor of the laser writing device 12, dip switches 73, and the like.

The output port 71 sends a control signal to the power supply unit 21 including the high-voltage power supply 76 and sequence equipment such as the motor 74 and the clutch 75 for rotating the photosensitive drum 10 and each roller shown in FIG. It is what is output. It should be noted that each of the above-mentioned units includes the transfer condition changing means A, the time monitoring means B, and the transfer condition change availability selection means C shown in FIG.
Function as.

FIG. 4 is a flow chart showing the main routine by the controller CPU 54 and engine CPU 63 of FIG. This routine starts when the power is turned on, first performs initial settings (system initialization) such as setting of each port and checking of RAM, and then repeats the control shown in (1) to (5) below.

(1) Engine status check task This is a process for checking the status of the engine unit 90. For example, the status of sensor input, presence / absence of a paper feed port, presence / absence of transfer paper, presence / absence of maintenance request, presence / absence of error, etc. Is checked, and if there is a state change, it is recognized by means such as turning the flag on and off (holding the state in RAM).

(2) Engine-controller interface task Interface control of commands and signals between the controller 50 and engine unit 90 (paper feed command, print command, resolution setting command, paper feed port setting command, paper ejection port setting) Receive instructions, etc.). (3) Engine-Option Interface Task Separately from the engine unit 90, interface control is performed between the option 82 having a dedicated control CPU and the engine unit 90.

(4) Print control task Check the internal state of the engine unit 90 such as maintenance request and error request, paper feed timing (paper feed timing), on / off timing of clutch, solenoid, charger, etc. Controls sequence devices in the printer. (5) Queue control task Controls a queue described later.

FIG. 5 is a flow chart showing a routine of interrupt processing by the engine CPU 63 of FIG.
This routine starts every predetermined time set in advance, judges the presence or absence of an interrupt check by a signal from the interrupt control circuit 64 or 65, and if there is no interrupt check, it remains as it is, and if there is, it executes each processing. After performing each interrupt process for time monitoring and control, the process returns to the main routine of FIG.

FIG. 6 is a diagram showing a configuration example of a queue in this laser printer, and FIG. 7 is a diagram showing an example in which the stored contents of the queue are different. In this example, it is assumed that there are 16 queues of 1 byte (byte) × 5 = 5 bytes. In this case, the RAM area (for example, R in FIG. 3)
AM68) is at least 1 byte x 5 x 16 = 30
It takes a bite. The queue is an area (management area) for managing predetermined mode data for each page to be printed from the start of paper feeding to the completion of paper ejection.

The engine driver 60 is the controller 5
When a paper feed print command is received from 0 (for convenience of description, the paper feed command and the print command are collectively referred to as a paper feed print command), the paper feed port for one page and the paper ejection port for one page are received. , Resolution, and ID (transfer paper number) are fetched (set) as data (mode data) at the 1st, 2nd, 3rd, and 5th bytes of the queue, respectively. For example, when a paper feed printer command is received from the controller 50 three times (three pages), the mode data of each page is set to the first, second, third, and fifth bytes of each queue.

It should be noted that, although the paper feed port, the paper ejection port, and the resolution set in each byte of the queue, the paper feed specified by the previous paper feed print command is received until immediately before the paper feed print command is received. Since the mouth, the paper ejection port, and the resolution are set in the queue, the controller 50 causes the engine driver 60 to change the paper feed port, the paper ejection port, and the resolution for each page.
To each of the following commands (1) to (3), for example. Thereby, the engine driver 60
As shown in (a) to (c) of FIG. 7, desired mode data can be set in each of the first three queues.

(1) Paper feed port 1 (upper paper feed cassette 3) setting command, paper discharge port 2 (second paper discharge stacker 7)
Setting command, resolution 600 dpi setting command, paper feed print command (2) paper feed port 3 (assuming large-volume paper feed tray 5) setting command,
Paper discharge port 1 (first paper discharge stacker 6) setting command, resolution 400 dpi setting command, paper feed print command (3) paper feed port 2 (lower paper feed cassette 4) setting command,
Paper ejection port 2 setting command, resolution 300 dpi setting command, paper feed print command

Further, when setting the above-mentioned mode data at the 1st, 2nd, 3rd and 5th bytes of each queue, the normal transfer conditions (transfer current or transfer voltage) are shown at the 4th byte as shown in FIG. A transfer mode (normal transfer mode “0”) for turning on the transfer charger 14 (making the transfer charger 14 perform the transfer output) is set.

Thereafter, printing is started and the transfer charger 1
When the timing to make the transfer output to 4 is reached, check the transfer mode of the 4th byte of the cue of the page,
Any one of the following (1) to (3) is performed. When the back side printing is started, the transfer mode of the 4th byte of the queue of the page is switched to the special transfer mode 1 or 2 as necessary, which will be described later in detail.

(1) As shown in Table 1, 4 of the above queues
The transfer mode of the byte is the normal transfer mode (the mode that instructs the transfer output by the normal transfer current (transfer voltage))
If it is "0", the transfer output port buffers TCHG1 and TCHG2 in the output port 71 connected to the high-voltage power supply 76 are turned on (ON) and off (OFF), respectively, and the transfer charger 14 is made to perform transfer output.

(2) The transfer mode is the special transfer mode 1
If the mode is a mode for instructing the transfer output by the special transfer current (transfer voltage) 1, the transfer output port buffer TCHG
Transfer charger 14 with 1 and 2 turned off and on respectively
To perform the transfer output. (3) If the transfer mode is the special transfer mode 2 (mode for instructing the transfer output by the special transfer current (transfer voltage) 2), both the transfer output port buffers TCHG1 and TCHG2 are turned on and transferred to the transfer charger 14. Cause output.

[0049]

[Table 1]

On the other hand, when the transfer paper on which the image is printed is ejected, the queue in which the mode data of the page is set at that time is released. When mode data is set in 16 queues, whether or not mode data can be set in the first queue depends on whether or not the transfer paper corresponding to the mode data set in the first queue is ejected. decide. If the transfer paper is not ejected,
The 17th mode data cannot be accepted.

FIG. 8 is a flow chart showing an example of processing according to the present invention in the print control task shown in FIG. This routine starts when back side printing is started. First, the type of transfer paper to be fed next is checked. If it is P1 (for example, plain paper), the time T0 is 5 minutes and the time T1 is 5 minutes in step 2. If it is 10 minutes and P2 (for example, recycled paper), the time T0 is set to 15 minutes and the time T1 is set to 30 minutes in step 3.

After that, in step 4, the queue (Que) that manages the page on which the back side printing is started is checked, and in step 5, the paper feed port set in the first byte is the paper feed port 4 (table). It is determined whether or not it is a double-sided machine of No. 2), and it is not the paper feed port 4 (in this case, 4 of the above queue).
When the transfer on timing (the timing at which the transfer charger 14 performs the transfer output) is reached in step 13, the transfer mode of the byte is the normal transfer mode), and the transfer mode of the 4th byte of the queue is confirmed in step 14 Then, the transfer output port buffers TCHG1 and TCHG2 are turned on and off, respectively, and the transfer charger 14 is made to perform the transfer output.

If the first byte of the queue is the sheet feed port 4, the time counted by the check counter (monitoring counter) (not shown) in step 6 (count value)
Check Ct. Note that, for example, by the interrupt processing shown in FIG. 5, the check counter starts time measurement when front surface printing starts or ends for each page, stops when back surface printing starts, and clears when back surface printing ends.

When the time Ct measured by the check counter is less than T0 (5 minutes or 15 minutes), the transfer mode of the 4th byte of the queue is switched to the special transfer mode 1 in step 7, and the transfer is performed in step 8. When the on timing is reached, the transfer mode of the 4th byte of the queue is confirmed in step 9 and the transfer output port buffer TCHG
Transfer charger 14 with 1 and 2 turned off and on respectively
To perform the transfer output.

The time Ct measured by the check counter is T
If 0 or more and less than T1 (10 minutes or 30 minutes), the transfer mode of the fourth byte of the queue is switched to the special transfer mode 2 in step 10, and when the transfer on timing is reached in step 11, step 12 In the above queue 4
After confirming the transfer mode of the byte, the transfer output port buffers TCHG1 and TCHG2 are both turned on to cause the transfer charger 14 to perform the transfer output.

The time Ct measured by the check counter is T
In the case of 1 or more, the transfer mode of the 4th byte of the queue is kept as the normal transfer mode, and when the transfer ON timing is reached in step 13, the transfer mode of the 4th byte of the queue is confirmed in step 14, The transfer output port buffers TCHG1 and TCHG2 are turned on and off, respectively, and the transfer charger 14 is made to perform the transfer output.

Next, a specific processing example according to the present invention by the controller 50 and the engine driver 60 when the laser printer performs double-sided printing will be described. However, description of processes other than transfer is omitted. When the controller 50 receives the print data of the first page from the host machine 83, it performs the following processing. It is assumed that print data for 5 pages is sequentially sent from the host machine 83.

That is, a data expansion process for expanding the print data into a print pattern (video data) is started, and at the same time, the engine driver 60 is issued with a paper feed port 1 setting command, a paper discharge port (double-sided machine) 4 setting command, and a resolution. A 600 dpi setting command is sequentially transmitted, and when the data expansion process for the first page is completed, a print start command is transmitted to the engine driver 60 (video data is also transmitted at this time).

The engine driver 60 is the controller 5
When a paper feed port 1 setting command, a paper discharge port (double-sided machine) 4 setting command, and a resolution 600 dpi setting command are received from 0, as shown in FIG. 9A, each byte of the head (first block) queue Paper feed port 1, paper ejection port (double-sided machine) 4,
Resolution 600 dpi, normal transfer mode (“0”), ID
When 1 is set and the print start command is received from the controller 50, the front side printing of the first page is started.

Since the second byte of the first block queue is the sheet discharge port 4, when the front side printing of the first page is started (it may be the end point), the back side of the second page is printed. A check counter for determining the transfer mode is started. Then, when the transfer on timing is reached, the transfer mode of the 4th byte of the queue of the 1st block is confirmed, and the transfer output port buffer TCHG1, 2 in the output port 71 connected to the high voltage power supply 76 is turned on. , Is turned off to cause the transfer charger 14 to perform transfer output.

After completing the data expansion processing for the first page, the controller 50 starts the data expansion processing for the second page, and also instructs the engine driver 60 to set the paper feed port 4 setting command, the paper discharge port 1 setting command, and A resolution 600 dpi setting command is sequentially transmitted, and when the data expansion process for the second page is completed, a print start command is transmitted to the engine driver 60.

The engine driver 60 is the controller 5
When receiving a paper feed port 4 setting command, a paper discharge port 1 setting command, and a resolution of 600 dpi setting command from 0, each of the bytes of the queue of the second block has a paper feeding port 4, a paper discharging port 1, a resolution of 600 dpi, and a normal transfer. Mode (“0”), ID1
(Back side) is set, and when the print start command is received from the controller 50, the back side printing of the second page is started.

Since the 1st byte paper feed port of the queue of the 2nd block is the paper feed port 4, the time measured by the check counter is confirmed when the back side printing of the 2nd page is started. Switches the transfer mode for the 4th byte of the queue. Here, the time measured by the check counter is set to less than 5 minutes (or 15 minutes), and the transfer mode of the 4th byte of the queue of the 2nd block is set to the special transfer mode 1 (“1” as shown in FIG. 9B). ).

When the transfer on timing is reached, the transfer mode of the 4th byte of the queue of the 2nd block is confirmed, and the transfer output port buffer TCHG1, 2 in the output port 71 connected to the high-voltage power supply 76 is confirmed. Are turned off and on respectively, and the transfer charger 14 is made to perform transfer output.

After completing the data development processing for the second page, the controller 50 starts the data development processing for the third page, and at the same time, instructs the engine driver 60 to set the paper feed port 1 setting command, the paper discharge port 4 setting command, and A resolution setting instruction of 400 dpi is sequentially transmitted, and when the data expansion processing for the third page is completed, a print start instruction is transmitted to the engine driver 60.

The engine driver 60 is the controller 5
When a paper feed port 1 setting command, a paper discharge port 4 setting command, and a resolution of 400 dpi setting command are received from 0, the paper feeding port 1 is set to each byte of the queue of the third block as shown in FIG. The discharge port 4, the resolution of 400 dpi, the normal transfer mode (“0”), and the ID2 are set, and when the print start command is received from the controller 50, the front surface printing of the third page is started.

Since the second byte paper ejection port of the third block queue is the paper ejection port 4, the transfer mode for the back side printing of the fourth page is determined when the front side printing of the third page is started. Start the check counter of. When the transfer on timing is reached, the transfer mode of the 4th byte of the queue of the 3rd block is confirmed, and the transfer output port buffers TCHG1 and TCHG2 of the output port 71 connected to the high voltage power supply 76 are turned on. , Is turned off to cause the transfer charger 14 to perform transfer output.

After completing the data expansion processing for the third page, the controller 50 starts the data expansion processing for the fourth page, and at the same time, instructs the engine driver 60 to set the paper feed port 4 setting command, the paper discharge port 1 setting command, and A resolution setting instruction of 400 dpi is sequentially transmitted, and when the data expansion processing of the fourth page is completed, a print start instruction is transmitted to the engine driver 60.

The engine driver 60 is the controller 5
When the paper feed port 4 setting command, the paper discharge port 1 setting command, and the resolution 400 dpi setting command are received from 0, the paper feeding port 4, the paper discharging port 1, the resolution 400 dpi, and the normal transfer are respectively transferred to the bytes of the queue of the fourth block. Mode (“0”), ID2
(Back side) is set, and when the print start command is received from the controller 50, the back side printing of the fourth page is started.

Since the 1st byte paper feed port of the 4th block queue is the paper feed port 4, the time measured by the check counter is confirmed when the back side printing of the 4th page is started. Switches the transfer mode for the 4th byte of the queue. Here, the time measured by the check counter is 5 minutes (or 15 minutes) or more and 10 minutes (or 30 minutes).
9 min.) And the transfer mode of the 4th byte of the queue of the 4th block is set to the special transfer mode 2 as shown in (d) of FIG.
Switch to (“2”).

When the transfer on timing is reached, the transfer mode of the 4th byte of the queue of the 4th block is confirmed, and the transfer output port buffer TCHG 1, 2 in the output port 71 connected to the high voltage power supply 76 is confirmed. Is turned on to cause the transfer charger 14 to perform transfer output.

The controller 50 starts the data expansion process for the fifth page after completing the data expansion process for the fourth page, and sends the engine driver 60 a paper feed port 1 setting command, a paper discharge port 2 setting command, and A resolution setting command of 300 dpi is sequentially transmitted, and when the data expansion processing for the fifth page is completed, a print start command is transmitted to the engine driver 60.

The engine driver 60 is the controller 5
When a paper feed port 1 setting command, a paper discharge port 2 setting command, and a resolution 300 dpi setting command are received from 0, (e) of FIG.
As shown in FIG. 5, a paper feed port 1, a paper ejection port 2, a resolution of 300 dpi, a normal transfer mode (“0”), and ID3 are set in each byte of the queue of the fifth block, and the controller 50
When the print start command is received from, the front side printing of the fifth page is started.

Since the second byte ejection port of the fifth block queue is not the ejection port 4, the check counter is not started even when the front side printing of the fifth page is started.
When the transfer on timing is reached, the transfer mode of the 4th byte of the queue of the 5th block is confirmed, and the transfer output port buffers TCHG1 and TCHG2 in the output port 71 connected to the high voltage power supply 76 are turned on. , Is turned off to cause the transfer charger 14 to perform transfer output.

As described above, in the laser printer of this embodiment, the time from the start or end of the front surface printing to the start of the back surface printing is monitored, and the transfer condition is changed according to the time (however, it is used. Since it is adjusted according to the type of transfer paper), image unevenness such as toner scattering can be effectively prevented and proper image quality can be maintained. Moreover,
Since the engine CPU 63 with a built-in timer provided in the engine driver 60 is provided with the function as the time monitoring means, the cost is hardly increased.

It should be noted that between step 5 and step 6 in FIG. 8, the determination in step 20 in FIG. 11, that is, whether or not the mode using the special transfer mode is set (whether or not the transfer condition is changed). It is possible to change the transfer mode of the 4th byte of the corresponding queue to the special transfer mode 1 or 2 only when the mode is set. In this case, the DIP switch 73 is used to determine whether or not to set the special transfer mode.
(Or the operation panel 80). Therefore, the user can perform the back surface printing under the transfer condition according to the purpose of use and obtain a desired print result.

The embodiments in which the present invention is applied to a laser printer have been described above, but the present invention is not limited to this, and other optical printers such as LED printers and liquid crystal shutter printers, as well as copying machines, facsimile machines, etc. Can be applied to various electrophotographic image forming apparatuses.

[0078]

As described above, according to the image forming apparatus of the present invention, it is possible to appropriately change the transfer condition when printing on the back surface with almost no increase in cost.

[Brief description of drawings]

FIG. 1 is a functional block diagram showing a basic configuration of the present invention.

FIG. 2 is a diagram showing a schematic configuration of a mechanical portion of a laser printer which is an embodiment of the present invention.

FIG. 3 is a block diagram showing a control system of the laser printer shown in FIG.

4 is a controller CPU 54 and an engine C of FIG.
It is a flowchart which shows the main routine by PU63.

FIG. 5 is a flowchart showing a routine of interrupt processing by the engine CPU 63.

6 is a diagram showing a configuration example of a queue in the engine driver 60 shown in FIG.

7A and 7B are diagrams showing different examples of stored contents of the queue of FIG.

8 is a flowchart showing an example of processing according to the present invention in the print control task shown in FIG.

9 is a diagram showing an example of stored contents of respective queues of a first block to a fourth block during double-sided printing in the engine driver 60 shown in FIG.

FIG. 10 is a diagram showing an example of stored contents of the respective queues of the fifth block and the sixth block.

11 is a flowchart showing another example of the process according to the present invention in the print control task shown in FIG.

[Explanation of symbols]

1: Laser printer body 2: Table (double-sided machine) 3: Upper paper feed cassette 4: Lower paper feed cassette 5: Mass paper feed tray 6: First paper output stacker 7: Second output stacker 8: Third output stacker 14: Transfer charger 50: Controller 54: Controller CPU 60: Engine driver 63: Engine CPU 68: RAM 71: Output port 73: Dip switch 76: High-voltage power supply 90: Engine unit

Claims (3)

(57) [Claims] 1. An image is printed on the other surface of the transfer paper after performing surface printing by printing an image on one surface of the transfer paper through each process of charging, exposure, transfer, and fixing. In the image forming apparatus including a transfer condition changing unit that changes the transfer condition such as the transfer voltage or the transfer current when performing the back side printing, the back side printing is started from the time when the front side printing is started or finished. An image forming apparatus comprising: a time monitoring unit for monitoring the time until the transfer condition changing unit has a unit for changing the transfer condition according to the time monitored by the time monitoring unit. 2. The image forming apparatus according to claim 1, wherein the transfer condition changing unit has a unit that changes the transfer condition according to the type of transfer paper used. 3. The image forming apparatus according to claim 1, further comprising means for selecting whether or not the transfer condition is changed by the transfer condition changing means.