JP2824259B2 - Double-sided printing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a double-sided printing apparatus provided with a double-sided unit.

[Conventional technology]

In the double-sided printing apparatus as described above, after printing the front side (one side) of the paper in the main body, the paper is once sent to the double-sided unit, turned over, and re-fed to the main body to be backed (the other side). Is printed, and then the next sheet is fed to perform the same process as described above.

Further, as a double-sided printing apparatus other than the above, for example, an intermediate tray capable of storing a plurality of sheets in a double-sided unit is provided, and after printing the surfaces of a large number of sheets collectively in the main body, the sheets are sequentially printed. There is a printer in which a sheet is sent to an intermediate tray for stacking, and thereafter, the sheet is sequentially fed one by one from the intermediate tray to the main body to perform back-side printing.

[Problems to be solved by the invention]

By the way, in such a conventional double-sided printing apparatus, in the former, the time required for reversal for printing the back side is long, so that the number of prints per unit time is very small.

In the latter case, information for the back side of the page order information necessary for printing must be held in the buffer until the back side printing is started, and a large-capacity buffer is required.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to improve print processing performance without increasing costs.

[Means for solving the problem]

In order to achieve the above object, the present invention provides a paper storage portion capable of storing paper, a printing means for printing on paper fed from the paper storage portion, and a paper printed on one or both surfaces by the means. Discharging means for discharging paper outside the machine, reversing means for reversing a sheet printed on one side by the printing means, a first transport path from a paper storage section to the printing means, A second transport path from the means to the paper discharge means, and a third transport path branched from the middle of the second transport path and passing through the reversing means to a junction with the first transport path. A third conveyance path having N sheet holding positions capable of holding at least 2 or more N (arbitrary integer) sheets, and N + 1 sheets from the sheet storage unit via the first conveyance path. Paper to the printing means It is sequentially printed on one side of each sheet of conveying the sheet of N sheets printed on one surface thereof to the third transport path through the transport path of the forward soon 2 N
After performing the operation of holding the sheets at the respective sheet holding positions, the (N + 1) th sheet printed on one side is moved to the third sheet.
And transporting the first sheet from the third transport path to the printing unit via the first transport path. And the paper is conveyed to the paper discharging means via the second conveying path and discharged out of the apparatus in parallel. To feed one sheet of paper to the printing means and print it on one side of the sheet, and transport the sheet printed on one side thereof to the third transport path via the second transport path. An operation of holding the sheet at any one of the sheet holding positions, and re-feeding one sheet of paper from the third conveyance path via the first conveyance path to the printing means to print on the other side;
Provided is a double-sided printing apparatus provided with a control means for alternately performing a parallel operation of an operation of conveying a sheet to a sheet discharging unit via a second conveying path and discharging the sheet to the outside of the apparatus.

Further, the control means includes means for detecting the length of the paper fed from the paper storage unit, and determining whether the length of the paper exceeds a predetermined value by the means. And means for varying the number of sheets to be held in the third transport path depending on whether or not exceeds a predetermined value.

In the double-sided printing apparatus configured as described above, when performing single-sided printing, sheets are fed one by one from the sheet storage unit to the printing unit via the first transport path, and one side of each sheet ( On the front side). Then, the sheet printed on one side is conveyed to the sheet discharging means via the second conveying path and discharged outside the apparatus.

On the other hand, when performing double-sided printing, N + 1 sheets are sequentially fed from the sheet storage unit to the printing unit via the first transport path, and are sequentially printed on one side of each sheet. The N sheets printed on the surface are sequentially conveyed to the third conveyance path via the second conveyance path and held at the N sheet holding positions.

Then, the (N + 1) th sheet printed on one side is transported to the third transport path and held at any of the N paper holding positions, and the first transport is performed from the third transport path. The operation of re-feeding the first sheet to the printing unit via the path and printing it on the other side, and conveying the sheet to the sheet discharging unit via the second conveying path and discharging the sheet to the outside of the apparatus are performed in parallel. And do it.

Thereafter, an operation of feeding one sheet of paper from the paper storage unit via the first transport path to the printing means and printing it on one side thereof, and transferring the sheet printed on the one side thereof to the second side.
The sheet is conveyed to the third conveyance path via the first conveyance path and is held at any of the N sheet holding positions, and one sheet of paper is printed from the third conveyance path via the first conveyance path Means to re-feed and print on the other side,
And the parallel operation of the operation of transporting the paper to the paper discharging means through the transport path and discharging the paper to the outside of the apparatus is performed alternately.

As described above, in the case of performing double-sided printing, since the N sheets printed on one side by the printing means are held at the respective sheet holding positions on the third conveyance path, the efficiency of conveyance control is increased. The print processing capacity can be increased as compared with the case where the print sheet is conveyed to the printing means without being held in the third conveyance path, and the printed sheet is discharged outside the machine regardless of the single-sided print or double-sided print. Since the sheet passes through only the second transport path, the time required for sheet discharge can be minimized.
Therefore, the number of prints per unit time greatly increases.

Further, the length (size) of the paper fed from the paper storage unit is detected, and it is determined whether or not the length of the paper exceeds a predetermined value. If the number of sheets to be held in the third conveyance path is made different between the case and the case where the number of sheets is not exceeded, printing can be performed at a maximum speed according to the sheet size within a printable range.

〔Example〕

Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings.

2 and 3 are an external perspective view of a laser printer according to an embodiment of the present invention and a cross-sectional view schematically showing an internal mechanism thereof.

This laser printer comprises a main body 1 and a table 2, and the main body 1 is provided with two upper and lower paper feed trays (cassettes) 3 and 4 capable of storing 250 sheets of cut paper, respectively. A paper stacker 6 and a second paper discharge stacker 7 are provided in a two-tiered manner, and a third paper discharge stacker 8 is provided at a rear portion of the paper discharge port 9.
3 in such a manner as to be openable and closable in the direction of arrow A in FIG.

In the main body 1, a photosensitive drum 10, a charging unit 11, an optical writing unit 12, a developing unit 13, a transfer unit 14, a fixing unit 15, and a pair of registration rollers 16, A paper transport section including a transport roller pair 17, a lower transport roller pair 18, and a number of other transport rollers and a paper guide plate, a main motor 19 for rotating and driving the respective rollers, and a charging section 11 and a transfer section 14. A power supply unit 20 for applying a voltage and a registration sensor 21 are provided.

Further, a substrate of a printer controller 50 for controlling the laser printer and an engine driver 60 for controlling a sequence operation of the printer engine are mounted above the main body 1.

The table 2 is equipped with a large-capacity paper tray (LCIT) 5 that can hold 1000 sheets of cut paper.
31 and a reversing sheet feeding unit 32, a sheet course changing claw (hereinafter referred to as a “fork gate”) 33, a pair of conveying rollers 34, 35, 36,
A double-sided unit (DPX) 30 including a double-sided entrance sensor 37, a double-sided exit sensor 38, a double-sided drive motor (hereinafter referred to as "DPX motor") 39, and the like is provided.

Further, inside the table 2, a pair of paper feed rollers 40 for the large-volume paper feed tray 5 and the duplex unit 30, and a table exit sensor 41
And a sheet feed drive motor (hereinafter referred to as “LCIT motor”) 42.

Although not shown, a mechanism for raising and lowering the stored paper and a motor for driving the same are provided in the large-volume paper feed tray 5.

Further, as shown in FIG. 3, the laser printer has a transport path (first transport path) from the large-volume paper feed tray 5 to the pair of registration rollers 16 (part of the printing unit).
A conveyance path (second conveyance path) from the fixing unit 15 (part of the printing means) to the second discharge stacker 7 and a branch from the middle of the conveyance path, passing through the double-sided unit 30 (reversing means). The transport route (the third route) up to the position where it merges with the first transport route
Transport path).

On the other hand, an operation panel 45 is provided on the upper part of the printer main body 1 in FIG.
6, 47 and an emulation card (hereinafter referred to as "IC card") 48 are detachably mounted.

On the operation panel 45, various switches for the operator to instruct including a switch for setting the mode of single-sided printing or double-sided printing, an LCD display for displaying various items in character strings, and a plurality of displays. For L
Equipped with ED.

Each of the font cartridges 46 and 47 has a built-in RAM or ROM storing font data of a different character type.

Also, by inserting the IC card 48 into the laser printer main body 1, an emulation function according to the type of host can be exhibited, and the IC card 48 can be operated in the same manner as various existing printers such as a dot print and a data wheel printer. it can.

Next, the operation of the laser printer will be briefly described with reference to FIG.

When the print sequence is started by the engine driver 60, paper feeding is started from a selected one of the paper feed trays 3 and 4 or the large-volume paper feed tray 5 at a predetermined timing, and the resist sensor 21 detects the paper. As a result, the sheet is temporarily stopped while the leading end of the sheet is held between the registration roller pair 16.

On the other hand, the photosensitive drum 10 rotates in the direction indicated by the arrow in FIG.
The surface charged by the charging unit 11 is irradiated with a laser beam modulated by the optical writing unit 12 in accordance with the video data while main scanning is performed in the drum axis direction, and an electrostatic latent image is formed. Form.

The latent image is developed by toner from the developing unit 13 and is transferred by a transfer unit 14 to a sheet fed by a pair of registration rollers 16 at a predetermined timing.

The transferred paper is peeled off from the photosensitive drum 10 and transported to the fixing unit 15 for fixing and heating. Further, the paper heated and fixed, that is, the print paper, is transported by the upper transport roller pair 17 and many other rollers. And discharge it to the paper discharge section.

At this time, the sheet is discharged to a selected one of the first discharge stacker 6 or the second discharge stacker 7 located at the upper part of the printer or the third discharge stacker 8 located at the rear part of the printer. Is done.

Usually, the first discharge stacker 6 and the second discharge stacker 7 are used.
Is selected. In a special case such as when using easily curlable paper such as an envelope or a postcard, the third discharge stacker 8 is selected.

However, when the discharge port 9 is closed and the discharge is not possible, the third discharge stacker 8 cannot be selected.

By the way, when the double-sided print mode is set, the sheet printed on one side is changed in the conveyance path and the lower conveyance roller pair 18 is used to set the double-sided unit 30 in the table 2.
Send to

Then, the sheet sent into the duplex unit 30 is sent to the reversing unit 31 by the transport roller pair 34, and stopped by the trailing edge of the sheet passing through the duplex sensor 37.

The transport roller pair 34 is driven by a DPX motor 39 via a number of gears (not shown), and rotates forward or backward by driving the DPX motor 39.

Next, the forked sheet 33 is switched by a solenoid (not shown) and the transport roller pair 34 is rotated in the reverse direction (the DPX motor 39 at this time is in the normal rotation state) to reverse the transport direction of the sheet stopped in the reversing unit 31. To the reversing paper feeding unit 32.

Then, the sheet sent to the reversing sheet feeding section 32 is conveyed from the middle by the conveying roller pair 35, and the sheet is sandwiched by the conveying roller pair 36 by detecting the sheet by the both-side exit sensor 38. To stop and wait.

The two transport roller pairs 35 and 36 are driven by a DPX motor 39 via a number of gears and a one-way clutch (or an electromagnetic clutch) (not shown), and only when the DPX motor 39 rotates forward. The power is transmitted to rotate the sheet in the sheet feeding direction.

Next, the sheet waiting in the reversing sheet feeding unit 32 is transported at a predetermined timing by the pair of transport rollers 35 and 36, and the table exit sensor 41 detects the sheet. The paper is conveyed by the pair of paper feed rollers 40 driven by the printer and sent to the printer main body 1 to be fed again.

Then, printing is performed on the back surface (the other surface) of the paper in the same manner as described above, and thereafter, the paper is discharged to one of the paper discharge trays.

FIG. 4 and FIG. 5 are block diagrams showing the configuration of the control unit of the laser printer.

The printer controller 50 includes a microcomputer (hereinafter referred to as a “CPU”) 51 and a ROM for storing fixed data.
52, a RAM 53 for storing temporary data, an I / O 54 for controlling data input / output, and an internal interface (I / F) 55
And are connected to each other by a data bus, an address bus or the like.

The I / O 54 is also connected to the above-described operation panel 45 and a host machine 80 such as a computer, a workstation, or a word processor.

The main parts of the above parts will be described in detail.
Reference numeral 1 denotes a general-purpose 16-bit or 32-bit microcomputer including a CPU, a ROM, a RAM, an I / O, and the like, which controls the entire printer controller.

The CPU 51 also transfers video data created on a video buffer in a RAM 53, which will be described later, to an internal interface.
Output to the engine driver 60 via 55.

Further, the CPU 51 also functions as a means for changing the number of simultaneously usable paper holding positions among a plurality of paper holding positions to be described later according to the length of paper to be printed. When the paper size information specified in step (1) is input, a sequence control command corresponding to the input is output to the engine driver 60 via the internal interface 55.

The ROM 52 is a read-only memory and stores various programs for controlling the CPU 51, resident fonts, and the like.

The RAM 53 is a large-capacity random access memory, and is mainly used for the following purposes.

(A) Input buffer (b) Page buffer (c) Video buffer (d) System memory (e) Font file Note that these buffers and files require a RAM area other than the one used for system software in advance by a necessary amount. To use. In this case, if the memory capacity is insufficient, a message to that effect is displayed and the function is abandoned.

In that case, it is necessary to erase some data and return it to a usable state. That is, a dynamic management system is employed in which the entire memory area is not fixedly allocated and used, but is secured and used as needed.

Here, the function of each buffer and file will be described.

[Input buffer]

When data such as character codes, control codes, and commands are sent from the host machine 80 via the I / O 54, the input buffer temporarily holds the data, and the printer software stores the data. Data is sequentially extracted and processed.

[Page buffer]

The data sent from the host is added with information such as a source address where the data is actually stored, a destination address for designating where to create the video data in the video buffer, and a size. Create page data in the page buffer.

[Video buffer]

In the video buffer, video data is created using page data of a page buffer and font data of a font file described later.

In this video buffer, for example, when printing on a relatively small-sized sheet, a small amount of RAM area is used per page unit, so that video data for many pages is created together.

Conversely, when printing on a relatively large paper size or printing an image, use RAM per page unit.
Since the used capacity of the area becomes considerably large, it may not be possible to create even one page, rather than collectively create several pages of video data.

Therefore, in such a case, a partial bit map method in which one page of video data is divided and partially created is adopted. Note that a general method for creating video data in page units is called a full bit map method.

[Font file]

All fonts are treated as files, and serve as source data when video data is expanded in a video buffer. Accordingly, a list indicating addresses at which usable fonts are stored and a list indicating addresses of respective characters in each font are provided in the form of a table.

The font file can be loaded from the ROM 52 or the font cartridges 46, 47 shown in FIG. 2 or designated by the host machine 8 by designating the font to be used.
Downloaded from 0 and stored as a file.

The engine driver 60 includes a sequence control unit 61 composed of a CPU, a ROM 62 storing programs, data, and the like required by the control unit 61, and a RAM storing temporary data.
63 and an I / O 64 for storing data input / output, and are connected to each other by a data bus, an address bus and the like.

The I / O 64 is connected to the internal interface 55 of the printer controller 50, inputs video data and commands from the printer controller 50, and outputs a status signal to the printer controller 50.

Also, the I / O 64 is a third component of the printer engine 65.
The optical writing unit 12, the main motor 19 for driving the photosensitive drum 10 and the like, a sequence device group 66 such as a solenoid, and sensors 67 such as various sensors and switches including the resist sensor 21 are also connected.

The sequence control unit 61 receives the video data and commands from the print controller 50,
It controls the sequence device group 66 of 65, outputs a video signal necessary for image writing to the optical writing unit 12, inputs signals indicating the state of each engine unit from the sensors 67, performs processing, etc. A status signal such as information or an error status such as a paper end or an error message is output to the printer controller 50.

The sequence control unit 61 exchanges information with the table CPU 70 shown in FIG. 5 via the I / O 64 by a serial communication method, and the sequence control unit 61 receives a sequence control command from the printer controller 50. Then, a control command is sent to the table CPU 70.

5, the table CPU 70 is a one-chip microcomputer, and when the screen print mode is designated, the screen entrance sensor 37, the double-side exit sensor 38 and the table exit sensor 41 in the table 2 shown in FIG.
The DPX motor 39, the LCIT motor 42, and the fork gate 33 that drive the rollers based on the detection signals from the
The DPX solenoid 71 that drives the printer is controlled via a driver (not shown), and paper is transported in various transport modes according to the number of paper retaining positions (the number of papers retained in the transport path of the duplex unit 30) described later. To be transported.

The table CPU 70 receives an instruction signal from the operation panel 45 and detection signals from a plurality of sensors (other sensors) (not shown) in the large-volume sheet feeding tray 5 shown in FIG. And the like to control the drive of a lift motor (other motor) not shown.

Further, the table CPU 70 inputs and processes signals indicating the state of each unit in the table 2 and the large-volume paper feed tray 5 from each of the above sensors, and processes necessary information and error conditions as status signals in the engine driver 60. The data is sent to the printer controller 50 via the I / O 64.

Next, the operation of this embodiment will be described with reference to FIGS.

First, the paper holding position will be described with reference to FIG. The thick lines shown in FIG. 1 indicate paper.

On the paper transport path in the duplex unit 30, (b)
Indicates a state in which the sheet is held in the reverse sheet feeding unit 32,
(B) shows a state in which the paper is held in two places, the reversing paper feeding unit 32 and the reversing unit 31, respectively. The former holds only one sheet with one side printed, and the latter prints one side. In a state where two sheets of the sheets are held, the next sheet is fed, and one side thereof is printed.

Therefore, the position where the paper is held,
31 and the reversing sheet feeding unit 32 are at the sheet holding position.

In the present invention, if the memory capacity used for the video buffer in the RAM 53 shown in FIG.
Double-sided printing is performed using the two paper holding positions shown in FIG.

However, if the length of the sheet held in the reversing sheet feeding section 32 exceeds a predetermined value, that is, the rear end of the sheet is held between the pair of conveying rollers 34 as shown in FIG. When the second sheet is fed into the reversing unit 31, the sheet being held is also pushed back by the pair of transport rollers 34, so that the memory capacity is sufficient to avoid this. Also, double-sided printing is performed using only one sheet holding position.

The mode for duplex printing without holding the paper is MODE1, the mode for holding the paper at one holding position and the mode for duplex printing is MODE2, and the paper is held at two holding positions. The mode when performing double-sided printing is MODE3.

In these three modes, the order of pages for reading and printing video data from the video buffer on the RAM 53 and the sequence of printing on the front and back sides of a sheet are different from each other.

Therefore, the sheets are numbered # 1, # 2, # 3,... In the order of paper feeding, and the print pages on the front and back sides are shown in the printing order in each mode as follows.

[MODE 1] (a) First page print (table of # 1) ← paper feed (b) Second page print (back of # 1) (c) Third page print (table of # 2) ← paper feed ( d) 4th page print (back of # 2) Same as below [MODE2] (a) 1st page print (# 1 table) ← paper feed (b) 3rd page print (# 2 table) ← Paper feed (c) 2nd page print (back of # 1) (d) 5th page print (front of # 3) ← paper feed (e) 4th page print (back of # 2) (f) 7th page Print (Table # 4) ← Feed (g) 6th page print (Back of # 3) Same as below [MODE3] (a) Print 1st page (Table # 1) ← Feed (b) Third page print (table of # 2) ← paper feed (c) Fifth page print (table of # 3) ← paper feed (d) Second page print (back of # 1) (e) seventh (F) 4th page print (back of # 2) (g) 9th page print (table of # 5) ← paper feed (h) 6th page print (# 3) Back) Same as below. The printing process in each mode is shown in Figs.
8 and FIG. 8, each of these figures schematically shows the transport path of the paper used for duplex printing.
The positions of odd-numbered sheets are indicated by thick solid lines, and the positions of even-numbered sheets are indicated by thick broken lines.

In FIG. 6, steps 1 corresponding to those in FIG. 3 are denoted by the same reference numerals, but in other figures, only steps 1 are denoted by the same reference numerals.

In addition, in each of the printing process diagrams, the time required for the paper to travel from one side of the paper transport path, which is shown in a substantially square shape to the next side, to represent the flow of time is taken as one step, and the steps are numbered and arranged in order. is there.

First, the printing process of MODE1 will be described with reference to steps 1 to 7 in FIG.

Any of the paper feed trays may be selected. In this example, the upper paper feed tray 3 attached to the printer body is selected. The process is started (Step 1), and the first page is printed on the front surface (Step 2).

The paper # 1 is conveyed with the course changed to the two-sided unit 30 side (step 3), sent to the reversing unit 31 of the two-sided unit 30 (step 4), and the conveyance direction is reversed without being held there and reversed. The paper is sent to the paper feeding unit 32 (Step 5).

Then, without holding the sheet, the sheet # 1 is again fed from the large-volume sheet feeding tray 5 to the transfer position through the common sheet feeding path (step 6), and the second page is printed on the back surface. (Step 7) The sheet # 1 on which double-sided printing has been completed is sent to the selected discharge stacker.

Similarly, the second and subsequent sheets are sequentially printed on the front surface and the back surface in page order and sent out.

Next, the printing process of MODE2 will be described with reference to steps 1 to 10 in FIG.

Next, in the example in which the lower paper feed tray 4 is selected as the paper feed tray, paper feeding is started from the lower paper feed tray 4 (Step 1), and the first page is printed on the front surface of the paper # 1 (Step 1). Step 2).

The sheet # 1 is conveyed with the course changed to the double-sided unit 30 side (step 3), sent to the reversing unit 31 of the double-sided unit, and subsequently, the feeding of the second sheet # 2 is started (step 4). .

Then, the reversing section 31 sends out the sheet # 1 to the reversing sheet feeding section 32 without holding the sheet # 1 and holds it there, and prints the third page on the surface of the second sheet # 2 (step 5).

The paper # 2 is conveyed while changing its course to the double-sided unit 30 side, and the first paper # 1 held in the reversing paper feeding unit 32 is again fed to the transfer position at a predetermined timing (step S1). 6).

Next, the second sheet # 2 is placed in the reversing section of the screen unit 30.
At the same time, the second page is printed on the back side of the sheet # 1, and the feeding of the third sheet # 3 is started (step 7). Then, the first sheet # 1 on which double-sided printing has been completed is sent to the selected discharge stacker.

Then, in the same manner as described above, the reversing unit 31 executes the second sheet # 2
Is sent to the reversing sheet feeding unit 32 without being held, and is held there, and the fifth page is printed on the front surface of the third sheet # 3 (step 8).

After that, in the same manner as described above, 2
The second sheet # 2 is fed again to the transfer position at a predetermined timing, and the third sheet # 3 is conveyed to the double-sided unit 30 with the course changed (step 9).

The third sheet # 3 is placed in the reversing unit 31 of the duplex unit 30.
And the fourth page is printed on the back side of the second sheet # 2, and then the feeding of the fourth sheet # 4 is started (step 10). Then, the second sheet # 2 on which double-sided printing has been completed is sent to the selected discharge stacker.

Thereafter, similarly, printing on the back side of the sheet printed on the front side and printing on the front side of a new sheet are alternately performed.

Next, the printing process of MODE3 will be described with reference to steps 1 to 13 in FIG.

Next, in the example in which the large-volume paper feed tray 5 is selected as the paper-supply tray, paper supply of the first sheet # 1 is started from the large-volume paper supply tray 5 (Step 1), and the first page is printed on the front surface thereof. Print (Step 2).

The sheet # 1 is conveyed with the course changed to the double-sided unit 30 side, and then the feeding of the second sheet # 2 is started (step 3).

Next, the first sheet # 1 is turned over by the reversing unit of the duplex unit 30.
And the third page is printed on the front side of the second sheet # 2 (step 4).

Then, the first sheet # 1 is sent out to the reversing sheet feeding unit 32 without being held in the reversing unit 31, where the first sheet # 1 is held.
The path of the second sheet # 2 is changed to the double-sided unit 30 and conveyed, and then the feeding of the third sheet # 3 is started (step 5).

Then, while the first sheet # 1 is held in the reversing sheet feeding unit 32, the second sheet # 2 is reverted to the reversing unit of the duplex unit 30.
Then, it is sent to 31 and held, and the fifth page is printed on the front side of the third sheet # 3 (step 6).

The paper # 3 is conveyed while changing its course to the double-sided unit 30 side, and the first and second papers # 1 and # 2 held in the reversing paper feeding unit 32 and the reversing unit 31, respectively, are At the predetermined timing, the conveyance is restarted at the same time, and the first sheet # 1 is again fed to the transfer position through the sheet feeding path to the transfer position, and the second sheet # 2 is fed to the reversing sheet feeding section 32 and held there (step). 7).

Then, while the second sheet # 2 is held in the reversing sheet feeding unit 32, the third sheet # 3 is sent to the reversing unit 31 of the duplex unit 30 to be held, and the first sheet # 3 is also held. Paper #
The second page is printed on the back side of No. 1 and then feeding of the fourth sheet # 4 is started (Step 8). Then, the first sheet # 1 on which double-sided printing has been completed is sent to the selected discharge stacker.

Next, the seventh page is printed on the surface of the fourth sheet # 4, and the second and third sheets # 2 held in the reversing sheet feeding unit 32 and the reversing unit 31, respectively, as described above. , #
3 is simultaneously conveyed again at a predetermined timing, the second sheet # 2 is again fed to the transfer position through the sheet feeding path, and the third sheet # 3 is fed to the reversing sheet feeding unit 32 and held. (Step 9).

Next, while the third sheet # 3 is held in the reversing sheet feeding unit 32, the fourth sheet # 4 is transported with the course changed to the double-sided unit 30 side, and the second sheet # 2 is conveyed. Then, the fourth page is printed on the back side, and the feeding of the fifth sheet # 5 is started (step 10). Then, the second sheet # 2, for which double-sided printing has been completed, is sent to the selected discharge stacker.

Further, while the third sheet # 3 is held in the reversing sheet feeding section 32, the fourth sheet # 4 is fed to the reversing section of the duplex unit 30.
Then, it is sent to 31 and held, and the ninth page is printed on the front side of the fifth sheet # 5 (step 11).

Next, the paper # 5 is re-routed to the screen unit 30 and conveyed, and the third and fourth papers # 3 and # 4 held in the reversing paper feeding unit 32 and the reversing unit 31, respectively, are removed. The conveyance is restarted at the same time at a predetermined timing, and the third sheet # 3 is again moved to the transfer position through the sheet feeding path and the fourth sheet # 3
4 is fed to the reversing paper feeding section 32 (step 12).

After that, while the fourth sheet # 4 is held in the reversing sheet feeding section 32, the fifth sheet # 5 is fed to the reversing section of the duplex unit 30.
31 and hold it, and print the sixth page on the back side of the third sheet # 3.
Paper feed is started (step 13). Then, the paper # 3 for which double-sided printing has been completed is sent to the selected discharge stacker.

Thereafter, similarly, printing on the front side of a new sheet and printing on the back side of the sheet two sheets before are performed alternately.

By the way, the printing speed in each of the three double-sided printing modes can be generally known from the number of steps per unit number of sheets.

Therefore, a brief summary of the execution procedure when duplex printing is performed on five sheets in each mode is as shown in FIGS. 11 to 13.

Therefore, comparing the number of steps in each mode from the above three figures, the printing speed in each mode is as follows: MODE1 <MODE2 <MODE3 MODE2 is 1.5 times or more of MODE1, and MODE3 is 2 times of MODE1. Print speed more than doubled.

Therefore, when performing large-volume double-sided printing, use MODE
3 should just be selected.

However, in order to execute double-sided printing in MODE3, a sufficient memory capacity is required to create at least 5 pages of video data. Therefore, it can be used only when the memory capacity is sufficient for the paper size.

MODE1 is effective when the available memory capacity is small, but the printing speed is considerably reduced. MODE2 is between the two.

Here, first, when a memory having a sufficient capacity to cope with the case where the maximum size of paper and the image density per page is considerably high is used, when double-sided printing is specified, The mode is determined by the flow chart.

That is, first check the size of the paper to be used,
If X ≧ Y, MODE3 is determined.

Note that X is such a length that the rear end of the sheet held in the reversing sheet feeding section 32 does not reach the reversing section 31, as shown in FIG. The length of the paper.

If X <Y, MODE2 is determined, and double-sided printing is executed in the determined mode.

Therefore, normally, the double-sided printing is executed in MODE3 by holding the sheet in two places, the reversing unit 31 and the reversing sheet feeding unit 32 shown in FIG.

If the length of the sheet held in the reversing sheet feeding section 32 in the transport direction exceeds a predetermined value, that is, the rear end of the sheet reaches the reversing section 31 as shown in FIG. In such a case, switch from MODE3 to MODE2 and feed the paper
And the double-sided printing is executed while being held at only one location.

Next, when a large memory capacity cannot be secured, the printer controller 50 shown in FIG. 4 dynamically manages the memory in the controller as described above.
The available free area can always be determined, and when the paper size to be used is determined, it is possible to determine how many pages of memory are available.When double-sided printing is specified, the flow chart in FIG. 10 is displayed. Therefore, the mode is determined.

That is, first, the memory capacity and the size of the paper to be used are checked.

If X.gtoreq.Y and the memory capacity is equal to or more than five pages, MODE3 is determined.

Further, if X <Y and the memory capacity is less than 5 pages, 3
If it is more than pages, it is decided to MODE2, and if less than 3 pages, it is 1
If it is equal to or more than a page, the mode is determined to be the full bit map mode of MODE1, and if less than one page, it is determined to be the partial bit map mode of MODE1. Then, double-sided printing is performed in the determined mode.

Therefore, according to the above-described manner, the mode for duplex printing can always be determined to be the optimal mode according to the conditions at that time, and the printing speed can be increased as much as possible.

For example, even when the memory capacity is small, when using small-size paper, MODE3 can be selected to perform high-speed double-sided printing.

In addition, when the printed sheet is ejected outside the machine regardless of the single-sided printing or double-sided printing, the sheet is ejected from the fixing unit 15 in FIG. 3 to the first ejection stacker 6 and the second ejection stacker 7. Alternatively, since only the transport path to the third discharge stacker 8 is passed (not through the transport path on the double-sided stacker 30 side), the time required for paper discharge can be minimized.

Therefore, the number of prints per unit time greatly increases.

In this embodiment, two paper holding positions in the duplex unit 30 have been described as a plurality of paper holding positions. However, if the entire length of the paper transport path in the apparatus is long, many paper holding paths are required. Double-sided printing can be performed in the mode in which the holding position is provided, and high-speed double-sided printing close to the continuous printing speed in the single-sided printing mode can be performed.

Although the embodiment in which the present invention is applied to a laser printer as a two-sided printing apparatus has been described in detail, the present invention is not limited to this. The present invention can also be applied to an image forming apparatus.

〔The invention's effect〕

As described above, according to the present invention, the double-sided print processing capability can be improved without increasing the cost.

Further, double-sided printing can be executed at the maximum speed according to the paper size.

[Brief description of the drawings]

FIG. 1 is an explanatory view of a paper holding position, FIG. 2 is an external perspective view of a laser printer according to an embodiment of the present invention, FIG. 3 is a schematic cross-sectional view schematically showing an internal mechanism of the laser printer, and FIG. FIG. 5 also shows the printer controller and the engine driver. FIG. 5 is a block diagram showing the table CPU and its input / output unit. FIG.
FIG. 7 is an explanatory view of a printing process using MODE2, FIG. 8 is an explanatory diagram of a printing process using MODE3, and FIG. FIG. 10 is a flowchart of a mode determination process when double-sided printing is designated, FIG. 10 is a flowchart of a mode determination process when double-sided printing is designated when the memory capacity of the video buffer according to this embodiment is limited, and FIGS. FIG. 4 is a diagram for explaining the effect of the present invention according to this embodiment. 1 Laser printer body 2 Table 30 Double-sided unit 31 Reversing unit 32 Reversing paper feeding unit 50 Printer controller 51 CPU (microcomputer) 60 Engine driver 61 ... Sequence control unit 65 ... Printer engine 70 ... Table CPU

Claims (2)

(57) [Claims] 1. A paper storage unit capable of storing paper, printing means for printing on paper fed from the paper storage unit, and discharging paper printed on one or both sides by the means to the outside of the machine. Sheet discharging means, a reversing means for reversing the sheet printed on one side by the printing means, and a first means from the sheet storage section to the printing means.
, A second conveying path from the printing unit to the paper discharging unit, and a branch from the middle of the second conveying path, passing through the reversing unit and merging with the first conveying path. A third transport path to a position, wherein the third transport path has N sheet holding positions capable of holding at least two or more N (arbitrary integer) sheets, and And N + 1 sheets are sequentially fed to the printing means via the first transport path from the unit, and are sequentially printed on one side of each sheet, and the N sheets printed on one side are After performing the operation of sequentially transporting the sheet to the third transport path via the second transport path and holding the N sheets at the N sheet storage positions, the (N + 1) th sheet printed on one surface is removed. The sheet is conveyed to the third conveyance path and the N sheet holding positions And re-feeding the first sheet of paper from the third transport path via the first transport path to the printing means and printing on the other side, The operation of transporting the sheet to the paper discharging means via the second transport path and discharging the paper to the outside of the apparatus is performed in parallel. Thereafter, one sheet of paper is printed from the paper storage section via the first transport path. Means for feeding paper to the means and printing on one surface thereof, and transporting the paper printed on one surface thereof to the third transport path via the second transport path and the N sheets of paper. An operation of holding at one of the holding positions, and re-feeding one sheet of paper from the third conveyance path to the printing means via the first conveyance path, and printing the sheet on the other side; And transported to the paper discharging means via the transport path 2 Sided printing apparatus characterized in that a control means for performing a parallel operation of the operation to the paper alternately. 2. The control device according to claim 1, wherein the control unit detects a length of the sheet fed from the sheet storage unit, and the unit determines whether the length of the sheet exceeds a predetermined value. 2. The double-sided printing apparatus according to claim 1, further comprising: means for changing the number of sheets to be held in the third transport path when the length of the sheet exceeds a predetermined value.