JP2001125321A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device in which paper reversal transport is smoothly performed by reliably preventing the occurrence of paper transporting trouble due to paper jamming(jam) on the paper sheets reversal transporting route. SOLUTION: This image forming device performs, after one side printing process by an image forming part 10, both side printing process by transporting the leading end Pa of recording paper sheet P from a main transporting route 16 onto the paper sheet reversal transporting route 17 and introducing the trailing end Pb of the recording paper sheet P on this paper sheet reversal transporting route 17 into a sub-transporting route 28 by means of switch controlling of the switching gate 21. The paper sheet reversal transporting route 17 is provided with a starting end part side bending transport part 17A being bent from the trailing end 16a of the main transporting route 16 and trailing end part side straight line transporting part 17B extending toward a paper discharge port 20 side in a straight line state. By providing a gate sensor 27 for detecting both front and rear end parts in the traveling direction of the recording paper sheet passing through a switching position of the switching gate 21 on the starting end part side bending transport part 17A, the image forming device is controlled so as to start reversing operation the recording paper sheet P in a section for the leading end Pa of the recording paper sheet P to reach the paper discharging port 20 on the terminal end side straight line transporting part 17B side and during the period for the trailing end Pb of the recording paper sheet P to run through the starting end part side bending transporting part 17A.

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 having a double-sided printing function, and more particularly, to an image forming apparatus having a sheet reversing and conveying mechanism.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as a copying machine or a printer, an image forming section (printing section) is disclosed in, for example, JP-A-5-131696 or JP-A-10-171177. ), The transfer paper as a recording medium after printing on one side (hereinafter, referred to as recording paper) is turned upside down in a paper reversing conveyance path, and is again conveyed to the image forming unit, so that the recording paper is on both sides. Has been proposed that has a configuration in which continuous printing processing is performed on the image data.

As shown in FIG. 11, for example, as shown in FIG. 11, a sheet reversing and conveying mechanism in a conventional image forming apparatus uses a sheet which also serves as a sheet discharging conveying path from a fixing device a in an image forming process via a main conveying path b. The leading end Pa side of the recording paper P after the single-sided printing process is conveyed onto the reverse conveying path c, and is controlled to be temporarily stoppable.
By closing the main transport path b by switching the opening and closing operations in the direction and the β direction, the recording paper P is switched back toward the sub-transport path e and is reversely transported.

[0004] A sheet reversing conveyance path c is a starting end side curved conveyance section c1 which is curved in a substantially arc shape from the end of the main conveyance path b.
Paper having a form of a trailing end side linear transport section c2 extending linearly toward the paper discharge port E side, and switching the traveling direction of the recording paper P and reversing the way along the trailing end side linear transport section c2. By arranging the transport roller f, the recording paper P on the paper reversal transport path c is reversely introduced into the sub-transport path e by the switching control based on the reverse rotation of the paper transport roller f.

[0005]

However, in the sheet reversing conveyance mechanism in the image forming apparatus having the conventional structure as described above, the sheet reversing conveyance path c has a substantially circular arc shape that is continuous from the end of the main conveyance path b. As shown in FIG. 12, since there is a form of the start end side curved conveyance section c1 of the curved range R and the end section side straight conveyance section c2 of the linear range S at least up to the position where the paper conveyance roller f is arranged, When the recording sheet P after the single-sided printing process from the fixing device a in the image forming process is conveyed from the main conveyance path b to the sheet reversing conveyance path c and stopped, the stop position of the rear end Pb of the recording sheet P ( If the reversal start position) is set within the linear range S of the terminal-side linear transport section c2, for example, as shown in FIG. 12A, recording from the main transport path b to the sheet reverse transport path c is performed. When transporting paper P, after recording paper P Pb is the result completely through the bending range R of the starting end side curved conveying section c1.

For this reason, at the time of double-sided printing, the recording paper P is made to reversely travel from the paper reversing transport path c toward the sub-transport path e, and the rear end of the recording paper P is moved straight to the end-side linear transport section c2. When re-introducing from the range S to the curved range R of the start end side curved conveyance section c1, as shown in FIG.
Rear end Pb collides with a boundary wall surface H between the start end side curved transfer section c1 and the end section side straight transfer section c2.

As a result, when the thin recording paper P is used, the rear end Pb of the recording paper P is bent at the collision portion, as shown in FIG. Paper jam (jam) occurs on the sheet c, and a sheet conveyance failure is likely to occur.

[0008] Further, the occurrence of a paper conveyance failure due to such a paper jam (jam) is caused by the conveyance of the paper conveyance roller f even when the reversal start position of the rear end of the recording paper P is properly set. If the force decreases due to aging or adhesion of paper dust, the paper transport roller f
It is difficult to completely avoid slippage due to slippage between the sheet transport time and the sheet transport position.

Further, the recording paper P after the single-sided printing process from the fixing device a to the paper reversing conveyance path c in the image forming process.
13A, 13B, 13C, at the time of transportation of
When a jam occurs while the recording sheet P is receiving a conveying force from the pair of fixing rollers a1 and a2 and the sheet conveying roller f, the reversing operation of the recording sheet P by the reverse rotation of the sheet conveying roller f during the occurrence of the jam. Is performed, the jam condition tends to fall into a very serious condition.

By the way, it is conceivable to detect the passage of the leading end of the recording sheet P to the sheet conveying roller f when the recording sheet P is reversely conveyed, thereby timing the reverse running of the recording sheet P. Recording paper P
The time at which the trailing end Pb separates from the fixing roller pair a1, a2 differs depending on the paper size, and the switching timing of the switching gate d becomes longer, so that the amount of deviation between the paper transporting time and the paper transporting position is reduced. The sheet is likely to be large, and a sheet conveyance failure due to a paper jam (jam) on the sheet reversing conveyance path c is likely to occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is possible to reliably prevent the occurrence of a sheet conveyance failure due to a paper jam (jam) on a sheet reversal conveyance path and to smoothly perform the sheet reversal conveyance. It is an object of the present invention to provide an image forming apparatus capable of performing such operations.

[0012]

According to a first aspect of the present invention, a printing process is performed on one side of recording paper fed from a paper feed cassette onto a main transport path. An image forming unit for applying, a start-end-side curved conveyance section curved in a substantially arc shape from the end of the main conveyance path, and an end-portion-side linear conveyance section extending linearly toward the paper discharge port side; It is possible to switch between a forward and reverse rotation direction for switching the running direction of the recording paper by reversing the running direction of the recording paper, which is disposed along the paper reversing conveyance path where the recording paper after the printing process from the forming means is conveyed and discharged, and which is arranged along the paper reversing conveyance path. A paper transport roller, a paper transport roller control means for controlling the rotation direction of the paper transport roller, and a sub-transport path through which recording paper on the sheet reversal transport path is introduced by reverse rotation control of the paper transport roller. The sheet counter on the sub-transport path side A switching gate disposed at the start end side of the transport path and switched to open and close so as to introduce recording paper into the sub-transport path; and the image forming device passing the switching position of the switching gate on the way to the sheet reversing transport path. An image forming apparatus provided with a sheet reversing and conveying mechanism having a double-sided printing processing function, comprising a sheet end detecting means for detecting both end positions in the running direction of the recording sheet after the printing processing from the means, Is in a section until the leading end of the recording sheet reaches the sheet discharge port on the end portion side linear conveyance portion side of the sheet reversing conveyance path, and the trailing end of the recording sheet travels on the start end side curved conveyance portion. During the period, the rotation direction of the paper transport roller is switched to start the reversing operation of the recording paper.

According to a second aspect of the present invention, in the first aspect of the present invention, the control means records the sheet transport roller by reverse rotation control after confirming a closed state of the main transport path by the switching gate. The reversing operation of the sheet is started.

According to a third aspect of the present invention, in the first or second aspect of the present invention, the control means confirms the open / close state of the main transport path by the switching gate, and closes the main transport path. To start the reversing operation of the recording paper, and stop the reversing operation of the recording paper in the open state of the main transport path.

According to a fourth aspect of the present invention, in the first, second or third aspect of the present invention, the control means checks whether the main transport path is opened or closed by the switching gate and determines whether the switching gate is open or closed. The open / close state of the main transport path is switched and controlled.

The invention according to claim 5 is the invention according to claims 1, 2, and
In the invention described in 3 or 4, the control means stops the reversing operation of the recording paper in a state where the main transport path is opened by the switching gate, and at the same time, stops the main rotation drive system of the apparatus main body. It is characterized by the following.

The invention according to claim 6 is the invention according to claims 1, 2, and
In the invention described in 3, 4, or 5, the control means controls switching of the paper transport roller in a reverse rotation direction after the return of the main transport path from an open state to a closed state by the switching gate, The reversing operation of the recording paper is started.

[0018]

FIG. 1 is a block diagram showing an embodiment of the present invention.
1 will be described in detail with reference to the drawings shown in FIGS. 1 to 10. FIG. 1 schematically shows the entire configuration of an image forming apparatus according to the present invention, and reference numeral 1 denotes an apparatus main body (body).

On the upper surface of the apparatus main body 1, there is provided a document placing table 2 made of transparent glass on which a document (not shown) is placed. On the upper surface of the document placing table 2, a document pressing cover 3 is openable and closable. And a scanner unit 4 as a document reading unit is disposed below the scanner unit.

The scanner unit 4 includes a first scanning unit 5 and a second scanning unit 6 which are arranged below the document table 2 and reciprocate in parallel, an optical lens body 7, a photoelectric conversion element (CCD). 8 and a document image reading unit.

The first scanning unit 5 includes an exposure lamp 5A
A reflector 5B for exposing the light from the exposure lamp 5A to the surface of the original image, and a first light guide for guiding a reflected light image from the original which is exposed and reflected via the reflector 5B toward a predetermined direction. And a mirror 5C, which is controlled to reciprocate in parallel at a predetermined scanning speed while maintaining a constant distance with respect to the lower surface of the document table 2.

The second scanning unit 6 includes a second mirror 6A for guiding the reflected light image from the document guided by the first mirror 5C of the first scanning unit 5 further in a predetermined direction. It has a third mirror 6B, and is controlled to reciprocate in parallel with the first scanning unit 5 while maintaining a constant speed relationship.

The optical lens body 7 includes a second scanning unit 6
Is arranged on the optical path of the reflected light of the original image guided by the third mirror 6B, and the light image is formed on the photoelectric conversion element 8.
Reads the optical image of the original image formed by the optical lens body 7, performs image processing on the original image data, and photoelectrically converts the read image into an electric signal, so that the image data is input to the image data input unit of the laser scanning unit (LSU) 9. It is to be transferred.

The laser scanning unit 9
A laser beam is irradiated on the surface of a photosensitive drum 11 constituting an image forming unit (image forming process) 10 in accordance with image data of a document image-processed by the photoelectric conversion element 8, so that the photosensitive drum An electrostatic latent image of a document image is written and formed on the reference numeral 11.

The photosensitive drum 11 is driven to rotate in the direction of an arrow, and a main charger is provided around the photosensitive drum 11 for charging the surface of the photosensitive drum 11 to a predetermined potential for forming image data into an electrostatic latent image. A developing device 13 which develops the electrostatic latent image formed by the charging of the main charger 12 with toner to form a visualized image; and a toner of a document image visualized by the developing device 13 A transfer charger 14 for transferring an image onto a recording sheet P fed from a sheet feed cassette 23 to be described later via a sheet feed path, and residual toner remaining on the photosensitive drum 11 after transfer by the transfer charger 14 Cleaning devices 15 for cleaning are arranged, respectively.

Each of the devices constituting the image forming section 10 includes a developing device 13, a transfer charger 14, a cleaning device 15, and a main charger 12 in the order from the laser irradiation point L to the photosensitive drum 11 in the rotational direction. The main charger 12 has a cleaning device 15
A static eliminator (not shown) that eliminates the charge on the surface of the photoconductor drum 11 after the cleaning is performed.

The recording paper P after the transfer of the toner image by the transfer charger 14 is separated from the photosensitive drum 11 and is conveyed to the main conveyance path 16.
The fixing device 30 conveys the unfixed toner image transferred to the recording sheet P by being conveyed to a nip portion between the heat roller 31 and the pressure roller 32 of the recording sheet P. P is conveyed on a sheet reversal conveyance path 17 which also serves as a sheet discharge conveyance path.

This sheet reversing transport path 17 is
At the start end side of the substantially arc-shaped curved range R that is continuous from the end 16a of the first end portion, and at the end portion side linear transfer portion 17B that extends linearly toward the paper discharge port 20 to the paper discharge tray 22, which will be described later. As shown in FIG. 2, as shown in FIG. 2, the end-portion-side linear transfer section 17 which continues from the boundary wall H on the end side of the start-end-side curved transfer section 17A while leaving a linear range S.
In the middle of B, a paper transport roller 18 that is controlled to rotate forward and reverse is provided.

The paper transport roller 18 is driven by the forward rotation of the leading edge P of the fixed recording paper P from the main transport path 16.
a is guided onto the sheet reversing conveyance path 17, and is conveyed toward the paper discharge roller 19 side of the paper discharge port 20 at the time of single-sided printing, and is conveyed from the main conveyance path 16 at the time of double-sided printing. The recording sheet P is temporarily stopped by chucking and holding the rear end Pb of the recording sheet P, and reversely controlled so as to guide the recording sheet P to the later-described sub-transport path 28 through the switching gate 21 by the reverse rotation control. Thus, the running direction of the recording paper P is switched and reversed.

The recording paper P conveyed on the paper reversing conveyance path 17 is rotated by the paper conveyance roller 18 and the paper discharge roller 19 as it is in normal one-sided printing, and is discharged from the paper discharge port 20 to the scanner unit 4. The paper is discharged onto a paper discharge tray 22 installed in the lower space.

On the other hand, on the inner bottom side of the apparatus main body 1, a replaceable paper feed cassette 23 in which recording paper P is loaded and stored for each predetermined paper size is arranged. Is provided with a half-moon-shaped pickup roller 24. The pickup roller 24 picks up the recording sheets P stacked and accommodated in the sheet feeding cassette 23 one by one from the uppermost layer, and feeds the sheet P to the sheet feeding path 25. Is transported to the upstream side of the registration roller 26.

The registration roller 26 temporarily holds the leading end Pa of the recording sheet P fed from the sheet feeding cassette 23 to the image forming section 10 via the main transport path 16 while maintaining the sheet feeding timing. By transporting, the recording paper P
Is transferred to one side of the document.

As shown in FIG. 2, a fixing device 30 is disposed downstream of the image forming section 10. The fixing device 30 has a heat roller 31 and a pressure roller 32. The recording paper P on which the unfixed toner image has been transferred is passed through the nip portion between the rollers 31 and 32 and is fixed, thereby performing printing processing on one side of the recording paper P.

At this time, when the recording paper P passes through the fixing device 30, the leading end Pa of the recording paper P, which is to adhere to the heat roller 31, is peeled off by the scraper 33 and is reversed through the switching gate 21. The paper is conveyed toward the conveyance path 17 side.

The switching gate 21 is, as shown in FIG.
In the initial state, the recording paper P is rotated in the α direction, the end 16a of the main transport path 16 is kept closed, and when the recording paper P is transported from the main transport path 16, as shown in FIG. By rotating the leading edge Pa of the sheet P in the β direction against the urging force of a spring (not shown), the trailing edge P of the recording sheet P
Until b passes, the end 16a of the main transport path 16 is made openable, and after passing the rear end Pb of the recording sheet P, the gate is rotated in the α direction by the weight of the gate and the urging force of a spring (not shown). It automatically returns to the standby position in the initial state as shown in FIG. 3 and closes the end 16a side of the main transport path 16.

During double-sided printing, the switching gate 21 returns to the initial standby position after the trailing edge Pb of the recording paper P has passed, as shown in FIG. The transported recording paper P is switched back by the reverse rotation control of the paper transport roller 18, and FIG.
As shown in (b), the guide is guided to the sub-transport path 28 and the sub-transport rollers 2
At 9, the recording paper P is again conveyed to the upstream side of the registration roller 26, so that printing on the other side of the recording paper P is performed.

At this time, the recording sheet P conveyed on the sheet reversing conveyance path 17 after passing through the front end (gate end) 21a of the switching gate 21 has the front end Pa immediately before the reversal conveyance, and the front end Pa is moved to the terminal side linear conveyance section. The paper discharge port 2 of the paper discharge roller 19 on the 17B side
In the section before reaching zero, the rear end Pb is
As shown in (a), the paper is held by the paper conveyance roller 18 so as to stop before the boundary wall surface H during the period of traveling in the arc-shaped curved range R of the start end side curved conveyance section 17A. .

Further, the leading and trailing edges P of the recording paper P
The opening and closing operation of the switching gate 21 due to the passage of a and Pb
Detected by the gate sensor 27, this gate sensor 27
Is a sheet edge detection sensor 27A provided on the sheet inlet 17a side of the sheet reversing conveyance path 17, and a tip 21a of the switching gate 21.
And a sensor shutter 27B provided coaxially on its side, and ON / OF of the sheet end detection sensor 27A by the sensor shutter 27B in accordance with the opening / closing operation of the switching gate 21.
F constitutes a paper end detecting means for detecting the opening / closing state of the switching gate 21 and the passing state of the leading and trailing ends Pa and Pb of the recording sheet P at the same time.

FIG. 6 shows a system control mechanism of a sheet conveying system in the image forming apparatus according to the present invention. The control unit 40 includes a timer 41, an input interface 42, and an R interface.
An OM 43, a RAM 44, an output interface 45, and a CPU 46 are provided. According to the ON / OFF opening / closing signal from the gate sensor 27 and input information such as desired printing conditions from the operation panel 50, the driving circuit 51 52, thereby controlling the main motor (M) for rotating the heat roller 31 of the fixing device 30.
Motor 53 and a duplex motor (D motor) 54 for rotating the paper transport roller 18 forward and reverse.

That is, the gate sensor 27 constituting the paper edge detecting means is in the standby state in the initial state of the switching gate 21 as shown in FIG.
When the sensor shutter 27B is fitted in the
It is set to output an OFF signal to the control unit 40 while maintaining the FF state, and as shown in FIG. 4, the leading end Pa of the recording paper P from the main conveyance path 16 passes in the β direction when passing. When the sensor shutter 27B separates from the inside of the sheet edge detection sensor 27A by the rotation to
The control section 40 is set to output an ON signal, and detection of the leading edge Pa of the recording paper P and detection of the presence of the recording paper P are performed.

On the other hand, in the state where the sensor shutter 27B is fitted into the paper end detection sensor 27A due to the rotation return of the switching gate 21 in the α direction after passing the rear end Pb of the recording paper P, the OFF state is returned again. Becomes OFF to the control unit 40
A signal is set to be output, and the trailing edge Pb of the recording paper P is detected and the passage of the signal is confirmed. With this, the control unit 40 can detect the open / closed state of the switching gate 21.

In the gate sensor 27, the type of signal transmitted to the control unit 40 is changed after the OFF state or the ON state lasts for 30 ms or more. Even if the gate sensor 27 in the ON state is turned on,
When returning to the F state, the control section 40 continues to output the OFF signal.

At this time, the gate sensor 27
If the signal does not return to the OFF state even after 0 ms, the signal output to the control unit 40 is switched to the ON signal.

Similarly, when the gate sensor 27 in the ON state is
Even if the FF state is reached, if the state returns to the ON state within 30 ms, the ON signal is continuously output to the control unit 40,
If the gate sensor 27 does not return to the ON state after 30 msec, the signal output to the control unit 40 is switched to the OFF signal.

Next, the printing (copying) operation of the image forming apparatus according to the present invention will be described with reference to the flowchart shown in FIG. In a model equipped with a processing device, a document is placed on a document tray and desired printing conditions are set on the operation panel 50.

In this case, the printing conditions include, for example, the paper size of the recording paper P, selection of a printing mode of either double-sided printing or single-sided printing, printing density, the number of printed sheets, and the like.

When the copying operation is started by a start button (not shown) on the operation panel 50,
The recording papers (sheets) P stacked and stored in the paper feed cassette 23 are picked up one by one from the uppermost layer by the rotation control of the pickup roller 24, conveyed to the paper feed path 25, and the registration rollers 26 are controlled. The sheet is taken out so as to temporarily hold the recording paper P (Step 1: hereinafter, this is abbreviated as S1).

In this state, the control unit 40 operates the operation panel 5
The print mode of one-sided mode or two-sided mode is determined based on the print condition of 0 (S2). If the one-sided mode is selected as the print mode, the scanner unit 4 and the image forming unit 10 are controlled. A one-sided printing process is performed (S3).

When the duplex mode is selected as the print mode, the scanner unit 4, the image forming unit 10, and the sheet reversing and transporting mechanisms 17, 18, 21, 27, 28, and 29 are controlled to perform the duplex printing described later. Processing (S4), and the recording paper P after such single-sided printing processing or double-sided printing processing is performed.
Is discharged onto the discharge tray 22 via the discharge port 20 by the sheet transport roller 18 and the discharge roller 19 (S5).

Next, the control unit 40 determines from the printing conditions whether or not there is the next print, that is, whether or not to make a continuous copy (S6). Is S1
When the copying is not performed, the process ends (ends).

FIG. 8 is a flowchart showing a flow of the operation in the double-sided printing process in S4 when the double-sided mode is selected as the printing mode in S2. The control unit 40 controls the scanner unit 4 to store the image information (image data) on the front and back sides of the document in the RAM 4.
4 (S11).

After storing the image information on both sides of the original in the RAM 44, the control unit 40 controls the laser scanning unit (LSU) 9 to read the image information on the back side of the original from the RAM 44 to the image forming unit 10, The electrostatic latent image corresponding to the image information is transferred to the photosensitive drum 11 of the image forming unit 10.
The toner image is developed by the developing device 13, the toner image is transferred to one side of the recording paper P by the transfer charger 14, and the unfixed toner is fixed on the recording paper P by the fixing device 30. Thus, the image information on the back side of the document is printed on one side of the recording paper P (S12).

Next, the control unit 40 controls the gate sensor 2
7, controlling the driving circuits 51 and 52, respectively,
By driving a main motor (M motor) 53 for rotating the 0 heat roller 31 and a duplex motor (D motor) 54 for rotating the paper transport roller 18, the recording paper P after one-side printing is placed on the paper reverse transport path 17. The recording paper P conveyed and conveyed on the paper reversing conveyance path 17
Is switched back and introduced into the sub-transport path 28, thereby performing the reversing process of the recording paper P (S1).
3) Then, the sheet is fed again to the registration roller 26 (S14).

Then, the control section 40 reads out the image information on the front side of the document stored in the RAM 44 to the image forming section 10 and prints the image information on the front side of the document on the other side of the recording paper P in the same manner as in S12. Thereafter (S15), the process returns to S5 shown in FIG.

By the way, as shown in the flowchart of FIG. 9, the control section 40 monitors the ON / OFF state of the gate sensor 27 in the reversing process of the recording paper P in S13, and performs the process after the single-sided printing in S12. It is determined whether or not the rear end Pb of the recording paper P has passed the switching position of the switching gate 21 (S21), and the gate sensor 27 in the OFF state is turned ON by the passage of the leading end Pa of the recording paper P. When the state is changed from the OFF state to the OFF state, it is determined that the rear end Pb of the recording paper P has passed the switching position of the switching gate 21, and the OFF signal is transmitted to the control unit 40. , As shown in FIG.
The rotation is automatically returned in the α direction by the urging force of a spring (not shown) (S22).

The control unit 40 turns off the gate sensor 27.
When a signal is received, a clock (not shown) is controlled to
With the reception start time of the FF signal as an initial value, measurement of the rotation time of the paper transport roller 18, that is, the rotation time of the D motor 54 that rotates the paper transport roller 18 is started (S2).
3).

When the measurement of the rotation time of the D motor 54 is started, the ON state / OFF state of the gate sensor 27 is monitored (S24), and the gate sensor 27 is kept OFF without being turned ON again. Then, it is determined whether or not the rotation time of the D motor 54 has elapsed 100 ms (S25).

When the rotation time of the D motor 54 has passed 100 ms, the control unit 40 controls the drive circuit 52 to rotate the D motor 54 in the reverse direction (S26), and FIG.
As shown in (b), the recording paper P after one-side printing on the paper reversing conveyance path 17 is switched back by the reverse rotation of the paper conveyance roller 18 so that the recording paper P is conveyed to the sub conveyance path 28 side and introduced. It returns to S14.

If the rear end Pb of the recording sheet P is caught by the switching gate 21 due to a malfunction of the gate sensor 27 or an abnormal conveyance of the recording sheet P on the sheet reversing conveyance path 17, the recording is performed. Since part of the paper P remains at the switching position of the switching gate 21, the gate sensor 27 is turned on.

At the time of such an abnormality, the control unit 40
Detects the ON state of the gate sensor 27 in S24, and the ON state indicates that the rotation time of the D motor 54 is
It is determined whether or not m seconds have elapsed (S27).

The rotation time of the D motor 54 is 170
If m seconds have elapsed, it is determined that a jam or the like of the recording paper P has occurred, and the control unit 40 stops the copying (printing) operation and executes the heat of the fixing device 30 to perform the jam processing. The driving of the main roller (M roller) 53 for rotating the roller 31 and the driving of the D motor 54 are stopped (S28), and the process ends.

In S27, while the rotation time of the D motor 54 is within 170 msec, the ON / OFF state of the gate sensor 27 similar to S21 is monitored.
It is determined whether the rear end Pb of the recording paper P has passed the switching position of the switching gate 21 (S29).

The rotation time of the D motor 54 is 170
Within m seconds, the ON state gate sensor 27 is turned off again.
When the state is reached, that is, when the switching gate 21 is automatically rotated in the α direction by the urging force of a spring (not shown) (S30), the rear end Pb of the recording paper P passes through the switching position of the switching gate 21. It is determined that it has been performed, and the OFF signal is transmitted to the control unit 40 after 30 ms has elapsed.

When the control unit 40 receives such an OFF signal of the gate sensor 27, the D motor 54 is rotated in the reverse direction (S26). Is switched back, and is conveyed and introduced to the sub-conveying path 28 side.
Return to 4.

FIG. 10A is a timing chart of the normal processing from S21 to S26 in the flow of the reversing process of the recording paper P shown in FIG.
Rotates the recording paper P after one-sided printing on the main transport path 16.
Is transported to the start-end-side curved transport section 17A of the sheet reversing transport path 17 by the switching gate 2 at the leading end Pa of the recording paper P.
2 is rotated in the β direction so as to open the paper inlet side of the start-end-side curved conveyance section 17A, as indicated by a dotted line in FIG. Maintain the ON state until Pb passes, and switch gate 2
1 is detected as open.

From the ON state of the gate sensor 27, 30 ms have elapsed from the time TA when the switching gate 21 is closed, that is, the time TA until the rear end Pb of the recording paper P passes the switching position of the switching gate 21. Time T
B, the gate sensor 27 outputs an ON signal to the control unit 40, and after a lapse of time TB, the gate sensor 27 outputs the OFF signal to the control unit 40.
In this case, since the state of the switching gate 21 does not change at this time, the D motor 54 is rotated in reverse at time TC 100 ms after the time of outputting the OFF signal to the control unit 40. Thus, the conveyance reversal of the recording paper P is started.

That is, the time TA until the rear end Pb of the recording paper P passes the switching position of the switching gate 21 is:
This is the time until the recording sheet P passes through the leading end (gate end) 21a of the switching gate 21, that is, the time immediately after the trailing end Pb of the recording sheet P has come off from the turning radius of the switching gate 21. The position of the rear end Pb is shown in FIG.
As shown in FIG.
R1 of the recording paper P at time TB
Is a point R2.

At time TC 100 ms after the output of the OFF signal to the control unit 40, the switching gate 21 returns to the rotation state, that is, the switching gate 21 rotates in the α direction, and This is the time until the switching gate 21 confirms whether or not the end 16a of the recording paper 16 is in the closed state. The position of the rear end Pb of the recording paper P at this time is shown in FIG.
As shown in FIG.
Is a point R3 in the recording paper P
Is the stop position of the rear end Pb, and the reversal start position during the paper reversal process.

Thus, during the sheet reversing process, the trailing end Pb of the recording sheet P is moved to the bending range R of the starting end side curved conveying portion 17A.
, The rear end Pb of the recording paper P on the boundary wall H with the end-side linear transport portion 17B as before.
Will not collide.

FIG. 10 (b) shows a timing chart at the time of abnormal processing in S24 to S27, S29 and S30 in the flow of the reversing process of the recording paper P shown in FIG.

That is, after 70 ms from the time TA when the switching gate 21 is closed, the switching gate 21 is rotated in the β direction for some reason, and is again opened, and the gate sensor 27 is turned on. At the time T
A time TB after 30 ms from A, that is, 70 ms after the OFF signal of the gate sensor 27 is output to the control unit 40, the ON signal of the gate sensor 27 is output to the control unit 40. It is found that the recording paper P remains at the switching position 21.

30 ms after the ON signal of the gate sensor 27 is output to the control unit 40, that is, one time from the time TB.
After 50 msec from the time TC after the lapse of 00 msec, the switching gate 21 is again closed, and the gate sensor 27
Is turned off, the control unit 40 outputs the OFF signal of the gate sensor 27 to the control unit 40 after 30 ms has elapsed, and at time TE 200 ms after time TB, the control unit 4 outputs the signal.
In the case of 0, the reverse of the transport of the recording paper P is started by reversing the D motor 54.

At this time, as shown in FIG. 2, when the recording sheet P is normally conveyed to the sheet reversing conveyance path 17, the rear end Pb of the recording sheet P is moved to the start end side curved conveying section 17A as shown in FIG. The position of the trailing end Pb of the recording sheet P at this time TE is near the end of the curving range R, and the position of the trailing end Pb in the curving range R is the point R4 within the curving range R. This is the stop position of Pb, and the reversal start position during the paper reversal process.

FIG. 10C shows the flow of the reversing process of the recording sheet P shown in FIG. 9 from S24 to S27 and S28.
5 shows a timing chart at the time of jam clearance in FIG.
After m seconds, the switching gate 21 becomes β
The gate sensor 27 is turned on again in the opening direction, the gate sensor 27 is turned on again, and a time TB after 30 ms from the time TA, that is, an OFF signal of the gate sensor 27 is output to the control unit 40. 70 ms after the time, the control unit 4
Since the ON signal of the gate sensor 27 is output to 0,
It is found that the recording paper P is sandwiched between the switching gates 21.

Thereafter, since the open state of the switching gate 21 does not change by 170 msec after the time TB, the control unit 40 determines that a paper jam has occurred in the paper reversal conveyance path 17 due to a paper jam. Then, the M motor 53 and the D motor 54 are stopped 30 ms later, that is, at a time TE 200 ms after the time TB.

That is, the image forming apparatus according to the present invention
When performing double-sided printing, when the trailing end Pb of the recording paper P after single-sided printing conveyed on the sheet reversing conveyance path 17 is located at a point within the curving range R of the starting end side curving conveying section 17A, The reverse rotation of the transport roller 18 causes the recording paper P to be switched back so as to run in the reverse direction and to reverse the transport, so that the recording paper P is recorded on the boundary wall surface H with the second terminal end side linear transport section 17B as before. The trailing edge Pb of the paper P does not collide, thereby avoiding the occurrence of jams due to paper jam in the paper reversing conveyance path 17 during reverse running even when a thin and weak recording paper P is used. It becomes possible.

Further, the control unit 40 controls the O
The N / OFF state is constantly monitored, and the opening / closing state of the switching gate 21 is set to be appropriately changed according to the ON / OFF state, and the timing of closing the switching gate 21 is shifted, and the recording paper P is switched. Even when the switching gate 21 is sandwiched between the gates 21, the switching gate 21 can be controlled so as to return to the open state, so that the occurrence of a jam is reliably prevented.

Further, the control unit 40 is, for example, 200 m
The recording paper P is switched over a predetermined time of 2 seconds.
When the sheet remains at the sheet detection position corresponding to the switching position of No. 1, it is determined that a jam has occurred on the sheet reversing conveyance path 17, and the M motor 53 and the D motor 54 are controlled to stop. Therefore, it is possible to minimize the occurrence of jam.

It should be noted that the present invention is not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the spirit of the present invention.

[0080]

As is apparent from the above description, the first aspect of the present invention relates to an image forming apparatus for performing printing on one side of a recording sheet fed from a sheet feeding cassette onto a main transport path. Means, a start-end-side curved conveyance section curved in a substantially arc shape from the end of the main conveyance path, and an end-portion-side linear conveyance section extending linearly toward the paper discharge port side. A paper reversal transport path on which the recording paper after the printing process is transported and discharged is disposed on the way of the paper reversal transport path,
A paper transport roller capable of switching between forward and reverse rotation directions for switching and reversing a traveling direction of the recording paper, a paper transport roller control means for controlling a rotation direction of the paper transport roller, and a reverse rotation control of the paper transport roller. A sub-conveying path on which a recording sheet is introduced on the sheet reversing conveying path and a start / end side of the sheet reversing conveying path on the sub-conveying path side are switched to open and close so as to introduce recording paper into the sub-conveying path. A double-sided sheet comprising: a switching gate; and sheet edge detecting means for detecting both end positions in the traveling direction of the recording sheet after printing from the image forming means passing through the switching position of the switching gate on the way of the sheet reversing conveyance path. In the image forming apparatus provided with a sheet reversing transport mechanism having a print processing function, the control unit may control the recording sheet to reach a discharge port on a terminal side linear transport unit side of the sheet reversing transport path. During the section until the leading end of the recording sheet reaches, and during the period when the trailing end of the recording sheet travels on the start end side curved conveying section, the rotation direction of the sheet conveying roller is switched to reverse the recording sheet. The operation is started, and when the recording paper conveyed on the paper reversing conveyance path is reversed and conveyed, the reversing operation is performed in a state where the rear end of the recording paper follows the form of the start end side curved conveyance section. This can prevent the rear end of the recording sheet from colliding with the boundary wall surface with the terminal-side linear conveyance unit as in the related art. Even when the sheet is used, it is possible to avoid the occurrence of a jam (a sheet conveyance failure) due to a paper jam in the sheet reversing conveyance path, and it is possible to perform both-side printing smoothly and reliably.

Further, during the section until the leading edge of the recording paper reaches the paper discharge port on the side of the linear transport section on the terminal end side of the sheet reversing transport path, the trailing edge of the recording paper is moved by the curved transport section on the starting end side. Since the reversing process of the recording paper is performed during the traveling period, the reversal section of the recording paper can be shortened, so that the paper transport distance can be shortened, and thereby the double-sided printing speed is improved. be able to.

According to a second aspect of the present invention, the control means starts the reversing operation of the recording paper by reversely controlling the paper transport roller after confirming the closed state of the main transport path by the switching gate. Characterized by this,
Since the reversal section of the recording paper can be shortened, the paper conveyance distance can be shortened, and the double-sided printing speed can be improved.

According to a third aspect of the present invention, the control means checks the open / close state of the main transport path by the switching gate, and starts the reversing operation of the recording paper in the closed state of the main transport path. The reversing operation of the recording paper is stopped when the main transport path is open, so that when the jam occurs, the reversing operation is stopped, so that the adverse effect caused by the occurrence of the jam (paper conveyance failure) is prevented. Can be minimized.

According to a fourth aspect of the present invention, the control means checks the open / closed state of the main transport path by the switching gate and controls the open / closed state of the main transport path by the switch gate. Even if the rear end of the recording sheet is restricted at the switching position of the switching gate and a jam occurs, the restriction of the recording sheet can be easily released by switching the open / close state of the main transport path. Therefore, the adverse effect caused by the occurrence of the jam can be minimized, whereby the double-sided printing process can be continued without interruption.

According to a fifth aspect of the present invention, the control means stops the reversing operation of the recording sheet in a state where the main transport path is opened by the switching gate, and simultaneously stops the main rotation drive system of the apparatus main body. For example, if a jam occurs on the sheet reversing conveyance path during the execution of a plurality of continuous image forming operations, the driving of the main drive system is also stopped along with the stop of the sheet reversing operation. To become
It is possible to prevent a plurality of recording sheets from being conveyed on the sheet reversing conveyance path, thereby minimizing the adverse effect caused by the occurrence of a jam.

According to a sixth aspect of the present invention, the control means controls the switching of the paper transport roller in the reverse rotation direction after the return of the main transport path from the open state to the closed state by the switching gate. Characterized in that the reversing operation of the recording sheet is started, and even if the rear end of the recording sheet is restrained at the switching position of the switching gate and a jam occurs, the rotation direction of the sheet conveying roller is switched, thereby Since the restraint on the recording paper can be easily released, the adverse effect due to the occurrence of the jam can be minimized, so that the double-sided printing process can be continued without interruption.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram schematically showing an overall configuration of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing a sheet reversal conveyance portion in an enlarged manner.

FIG. 3 is an explanatory diagram showing an enlarged main part of a sheet edge detection state when the switching gate is closed.

FIG. 4 is an explanatory diagram showing an enlarged main part of a sheet edge detection state when the switching gate is opened.

5 (a) and 5 (b) are diagrams illustrating a state in which the recording sheet is reversed to a sheet reversing conveyance path after single-sided printing during the double-sided printing process. FIG.
FIG. 3 is an explanatory diagram showing a sheet reversal conveyance state of a recording sheet.

FIG. 6 is a block diagram of a control unit of the fuselage.

FIG. 7 is a flowchart showing a printing (copying) operation.

FIG. 8 is a flowchart showing a flow of an operation in a double-sided printing process.

FIG. 9 is a flowchart showing a recording sheet reversing operation.

10 (a) and 10 (b) are timing charts in the flow of the sheet reversing process, FIG. 10 (a) is a timing chart in a normal process, FIG. 10 (b) is a timing chart in an abnormal process, and FIG. 10 (c) is a jam process. It is a timing chart of time.

FIG. 11 is an explanatory diagram showing, in an enlarged manner, a sheet reversal conveyance portion during double-sided printing in a conventional image forming apparatus.

12 (a) and 12 (b) are diagrams showing a sheet reversal conveyance state in a conventional image forming apparatus, wherein FIG. 11 (a) is an explanatory view showing a conveyance state of a recording sheet to a sheet reversal conveyance path, and FIG. FIG. 12C is an explanatory view showing a collision state of the trailing end of the recording sheet on the sheet reversal conveyance path, and FIG. 12C is an explanatory view showing a jam occurrence state of the rear end of the recording sheet on the sheet reversal conveyance path.

13A and 13B are diagrams illustrating a sheet conveyance state in the conventional image forming apparatus, and FIG. 13A is an explanatory diagram illustrating a state in which a recording sheet is conveyed from a main conveyance path to a sheet reversal conveyance path, and FIG.
FIG. 13C is an explanatory diagram illustrating a state in which the leading edge of the recording sheet is conveyed to the sheet reversing conveyance path by the sheet conveying roller, and FIG. 13C is an explanatory diagram illustrating a state in which a jam occurs due to the fixing roller at the rear end of the recording sheet.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Apparatus main body 10 Image forming part 11 Photoreceptor drum 12 Main charging device 13 Developing device 14 Transfer charger 15 Cleaning device 16 Main conveyance path 16a Termination 17 Paper reversal conveyance path 17A Start end side curved conveyance section 17B Termination side linear conveyance section 18 Paper transport roller 19 Discharge roller 20 Discharge port 21 Switching gate 21a Tip (gate end) 22 Discharge tray 23 Paper feed cassette 24 Pickup roller 25 Paper feed transport path 26 Registration roller 27 Paper end detection means (gate open / close detection sensor) 28 Sub-Conveyance Path 30 Fixing Device 31 Heat Roller 32 Pressure Roller 40 Control Unit 41 Timer 42 Input Interface 43 ROM 44 RAM 45 Output Interface 46 CPU 50 Operation Panel 51 Drive Circuit 52 Drive Circuit 53 Main Motor (M Motor) 5 4 Duplex motor (D motor) H Boundary wall surface P Recording paper Pa Front end Pb Rear end R Curved range S Linear range

Continued on the front page (72) Inventor Hidetoshi Kaneko 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (reference) 2H028 BA06 BA09 BA16 BB02 2H072 CB01 3F053 EA02 EB04 3F100 AA02 BA13 CA12

Claims (6)

[Claims] An image forming means for performing a printing process on one side of a recording sheet fed from a sheet feeding cassette onto a main transport path; and a start-end-side curved transport curved in a substantially arc shape from the end of the main transport path. And a sheet reversing conveyance path, which comprises a trailing end side linear conveyance section extending linearly toward the paper ejection port side, and on which the recording paper after the printing process from the image forming means is conveyed and discharged, and the paper A sheet transport roller disposed in the reverse transport path and capable of switching between forward and reverse rotation directions for switching and reversing the traveling direction of the recording sheet; control means for controlling the rotation direction of the sheet transport roller; A sub-conveyance path into which recording paper on the paper reversal conveyance path is introduced by reverse rotation control; and a sub-transportation path disposed at a start end side of the sheet reversal conveyance path to introduce recording paper into the sub-conveyance path. Switch to open / close control And a sheet edge detecting means for detecting both end positions in the running direction of the recording sheet after the printing process from the image forming means passing through a switching position of the switching gate on the way of the sheet reversing conveyance path. In the image forming apparatus provided with a sheet reversing and conveying mechanism having a print processing function, the control unit may control that the leading end of the recording sheet reaches the discharge port on the side of the linear conveying unit at the end of the sheet reversing and conveying path. And during a period in which the trailing edge of the recording sheet travels along the start-end side curved transport section, the rotation direction of the sheet transport roller is switched to start the reversing operation of the recording sheet. An image forming apparatus comprising: 2. The control device according to claim 1, wherein after confirming the closed state of the main transport path by the switching gate, the sheet transport roller starts reverse operation of the recording paper by reverse rotation control. 2. The image forming apparatus according to 1. 3. The control means confirms the open / close state of the main transport path by the switching gate, starts a reversing operation of the recording paper in the closed state of the main transport path, and starts the reversal operation of the recording paper in the open state of the main transport path. 3. The image forming apparatus according to claim 1, wherein the reversing operation of the recording sheet is stopped. 4. The apparatus according to claim 1, wherein said control means checks the open / closed state of said main transport path by said switching gate, and switches and controls the open / closed state of said main transport path by said switch gate. 4. The image forming apparatus according to 1, 2, or 3. 5. The apparatus according to claim 1, wherein the control means stops the reversing operation of the recording paper in a state where the main transport path is opened by the switching gate, and at the same time, stops a main rotation drive system of the apparatus main body. The image forming apparatus according to claim 1, 2, 3, or 4, wherein 6. The control means controls switching of the paper transport roller in the reverse rotation direction after the return of the main transport path from the open state to the closed state by the switching gate, thereby performing a reversal operation of the recording paper. 6. The image forming apparatus according to claim 1, wherein the image forming apparatus is started.