JPH08314214A - Image forming device - Google Patents

Abstract

PURPOSE: To suppress the possibility of an erroneous detection of a sheet material to irreducible minimum, in a device provided with a means for calculating the timing of the tailing edge of the sheet material, at the time of forming an image. CONSTITUTION: A tail edge detecting and controlling means 5 executes selective driving for tail edge detection processing 50A for calculating the timing of the tail edge of a form, based on the size of the form fed from a cassette paper feeding mechanism 18 for feeding a known regular size form, in it and tail edge detection processing 50B for calculating the timing of the tail edge of the form, based on a sensor signal from a paper sensor 27 detecting the tail edge of the form during feeding, in the paper fed from an MPT paper feeding mechanism 19 for feeding an unknown irregular size form, in accordance with a difference in a paper feeding port, so that the timing of the tail edge of the form is calculated. Thus, image mask processing on the tail edge of the sheet material is accurately executed even from the MPT having an irregular size sheet material and a cassette unstable in the sensor signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming and recording image information such as characters on a sheet-shaped recording material (hereinafter referred to as a sheet material), and more particularly to forming an image by determining the timing of the trailing edge of the sheet material. The present invention relates to an image forming apparatus that controls the above.

[0002]

2. Description of the Related Art Conventionally, in this type of image forming apparatus such as a laser beam printer or a digital copying machine, a sheet material trailing edge timing calculating means for obtaining a timing of the sheet material trailing edge in various image forming controls has a sheet material. Certain processing is performed regardless of conditions.

For example, the same processing may be performed even if there are a plurality of transport paths and the conditions of the sheet material differ for each transport path, or the conditions may differ for each sheet material even on the same transport path. Even in this case, the same processing is performed.

Further, conventionally, the sheet material rear end timing calculating means as described above is provided with a sheet material sensor which is arranged on the conveying path and detects the presence of the sheet material when the sheet material comes into contact with the sheet material sensor. Output signal is detected as the timing when the rear edge of the sheet passes the sensor position at the timing when there is no sheet material from when there is a sheet material, and the timing corresponding to the rear edge of the sheet material in each image forming control is based on this timing. However, the method of reading the signal of the sheet material sensor is constant regardless of the conditions of the sheet material.

[0005]

However, in the sheet material trailing edge timing calculating means of the conventional image forming apparatus as described above, the same processing is performed without considering the conditions of the sheet material. Depending on the conditions, the timing of the trailing edge of the sheet material may be erroneously detected.

In particular, when the above-mentioned timing is obtained by using a sheet material sensor which is installed on the conveying path and detects the presence of the sheet material when a part of the sheet material comes into contact with the sheet material, the signal from the sheet material sensor changes. The method depends on the form of conveyance of the sheet material, but if the same trailing edge detection processing is performed, accurate trailing edge detection may not be possible.

Further, even in the case of a sheet material having size information in advance, performing the trailing edge detection processing by the sheet material sensor similar to the sheet material of an indefinite size causes the sensor output to flutter due to the looseness of the sheet material. There is a risk of erroneous detection due to, and unnecessary processing is performed.

The present invention solves the problems of the prior art as described above, and performs the optimum trailing edge detection processing according to the conditions of the sheet material so as to minimize the possibility of erroneous detection. It is an object of the present invention to provide the image forming apparatus.

[0009]

In order to achieve the above object, the present invention is an image forming apparatus having a trailing edge timing calculating means for calculating the timing of the trailing edge of a sheet material when an image is formed on the sheet material. In the above, the trailing edge timing calculation means feeds a sheet material of a known standard size.
For the sheet material fed from the sheet feeding means, the first trailing edge detection processing means for calculating the timing of the trailing edge of the sheet material based on the set known size, and the unknown size unknown For the sheet material fed from the second sheet feeding means for feeding the standard sheet material, the sheet material rearward based on the sensor signal from the sensor detecting the rear end of the sheet material being fed. And a second trailing edge detection processing means for calculating the timing of the edge.

According to another aspect of the present invention, in an image forming apparatus having a trailing edge timing calculating means for calculating a timing of a trailing edge of a sheet material when an image is formed on the sheet material, It has a sensor that detects the rear end,
The sheet material of a known standard size is fed loosely in the vicinity of the sensor until the sheet material conveying means on the conveying path is completely separated, and the trailing edge timing calculating means causes the sheet material to move to the sheet material conveying means. A characteristic is that the sensor signal from the sensor is read from a timing at which the slack of the sheet material is predicted to be sufficiently eliminated and the timing of the rear end of the sheet material is calculated based on the read sensor signal. To do.

In still another embodiment of the present invention, the trailing edge timing calculating means previously obtains a timing T _{1 at} which the trailing edge of the maximum transportable sheet material leaves the sheet material transporting means. It is possible to read the sensor signal from the sensor after the timing T ₁ .

In still another form of the present invention, the trailing edge timing calculating means previously obtains a timing T _{2 at} which a trailing edge of a sheet material having a minimum size that can be conveyed reaches the sensor. The sensor signal from the sensor may be read shortly before the timing T ₂ .

As still another form of the present invention, the sensor is a contact type sensor arranged on a conveying path and a signal output is inverted when a part of the sheet material is touched, and the rear end timing calculation is performed. The means may be characterized in that the timing of the signal of the sensor changing from the presence of the sheet material to the absence of the sheet material determines the timing when the rear end of the sheet material passes the position of the detection sensor.

In still another form of the present invention, the sensor feeds a first conveyance path for feeding a known standard size sheet material and an unknown size irregular sheet material. It can be characterized in that it is arranged on a third conveyance path where the second conveyance path joins.

Further, according to the present invention, in the image forming apparatus having the trailing edge timing calculating means for calculating the timing of the trailing edge of the sheet material when the image is formed on the sheet material, the trailing edge of the sheet material being fed is determined. A first conveyance for feeding a sheet material of a known standard size, which is a contact type sensor having a sensor for detecting, and the output of the signal is inverted when a part of the sheet material is touched. The trailing edge timing calculation means is arranged on a third conveyance path where the path and a second conveyance path for feeding an unfixed size sheet material of unknown size merge, and the trailing edge timing calculation means is the smallest size sheet material that can be conveyed. The timing T _{2 at} which the trailing edge of the sheet is predicted to reach the sensor is obtained in advance, and the sensor signal is read from the sensor slightly before the timing T ₂ regardless of the conveying path along which the sheet material is fed. Do , At the timing when the signal of the sensor changes from the presence of the sheet material to the absence thereof, it is determined that the rear end of the sheet material passes the position of the detection sensor,
The timing of the rear end of the sheet material can be calculated.

[0016]

In the first aspect of the present invention, the sheet material fed from the first sheet feeding means for feeding the sheet material of the known standard size is based on the set known size. The timing of the trailing edge of the sheet material is calculated, and for the sheet material fed from the second sheet feeding unit that feeds an irregular size sheet material of unknown size, The timing of the trailing edge of the sheet material is calculated based on the sensor signal from the sensor that detects the edge. As a result, the timing of the trailing edge of the sheet material can be accurately obtained even when the sheet is fed from the MPT of which the size of the sheet material is indefinite or when the sheet is fed from the cassette in which the sensor signal is unstable. The image mask processing at the edge can be performed accurately.

According to the second aspect of the present invention, the reading range of the sensor signal from the sensor for detecting the sheet material with respect to the sheet material fed from the sheet feeding means for feeding the standard size sheet material of the known size. When the trailing edge of the sheet material reaches the position of the sensor, the timing is estimated to be near the timing predicted from the known size, and the timing of the trailing edge of the sheet material is calculated based on the sensor signal read in this limitation. As a result, erroneous detection due to the flap of the sensor can be avoided, and the timing of the trailing edge of the sheet material can be obtained more accurately.

In the third embodiment of the present invention, the timing T _{1 at} which the trailing edge of the maximum size sheet material that can be conveyed leaves the sheet material conveying means is obtained in advance, and after this timing T ₁ , the sensor signal from the sensor is sent. Read. As a result, the timing of the trailing edge of the sheet material can be accurately obtained even if the sheet material of the wrong size is set in the cassette.

According to the fourth aspect of the present invention, the timing T _{2 at} which the trailing edge of the sheet material of the smallest size that can be conveyed reaches the sensor is obtained in advance, and the sheet is fed to the conveying path where the sheet material is fed. Irrespective of that, the sensor signal is read from a little before the timing T ₂ . As a result, erroneous detection of the trailing edge of the sheet material can be avoided, and control can be simplified because the same processing procedure can be used regardless of the conditions of the sheet material.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

(First Embodiment) FIGS. 1 to 8 show a first embodiment of the present invention. FIG. 1 shows a functional configuration of a control system of the image forming apparatus of this embodiment, and FIG. 2 shows a sectional structure of a laser beam printer as an example of the image forming apparatus embodying the present invention. First, the mechanical configuration of FIG. 2 will be described.

As shown in FIG. 2, the laser beam printer 1 has a cassette 23 for accommodating the recording paper (sheet material) S, a pickup roller 24 for picking up the recording paper from the cassette 23, and further picked up. A paper feed roller 25 for feeding the recording paper is provided.
A transport roller 26 that transports the fed recording paper to a registration roller 32, which will be described later, is disposed downstream of the paper feed roller 25.

On the other hand, the laser beam printer 1 has another
M has a multi-paper tray (hereinafter referred to as MPT) 28 that can manually feed atypical sheets of paper.
An MPT paper feed roller 30 for feeding the recording paper from the PT 28 and an MPT lifter 29 for pressing the recording paper set on the MPT 28 against the MPT paper feed roller 30 are provided.

The recording paper transport path 27 from the cassette 23 and the M
It merges with the transport path 31 from the PT 28 at a merge point C and reaches a registration roller 32 described later. A registration roller 32 that synchronously conveys the recording paper S is arranged downstream of the confluence C, and a paper sensor 17 is arranged immediately before the registration roller 32. The paper sensor 17 detects the presence of the paper at the relevant position by the movable light-shielding plate blocking the photo interrupter by the contact of the paper. An image forming unit 33 that forms an image by the laser light from the laser scanner unit 34 is disposed downstream of the registration roller 32. Further, this image forming unit 33
A fixing device 35 is disposed downstream of the fixing device 35, and paper discharge conveying rollers 36, 37, 38, 39 are arranged downstream of the fixing device 35, and the recording paper is conveyed to a paper discharge tray 40.

Next, the control system of FIG. 1 will be described. The laser beam printer 1 has a main control unit 2 that controls the whole. The main control unit 2 is composed of a CPU (central processing unit), a ROM (read only memory), a RAM (random access memory), a gate element, etc., and a main part of control is realized by software written in the ROM. There is. However, in FIG. 1, the inside of the main control unit 2 is represented by a functional configuration. The main controller 2 is connected to the external device 3 via the external interface 22.

The functions of the main control unit 2 are as follows: trailing edge mask timing calculation unit 4, sensor reading unit 6, sensor confirmation timer 7, external device communication unit 9, sheet conveyance information storage unit 8,
The sheet transport control unit 10, the print control timer 15, and the image forming control unit 16 are included. With these functions, the main controller 2 causes the cassette paper feed mechanism 18, which includes the cassette 23, the pickup roller 24, the paper feed roller 25, the transport roller 26, and their drive mechanism,
Further, the MPT 28, the MPT lifter 29, the MPT sheet feeding roller 30, and the MPT sheet feeding mechanism 19 including the driving mechanism thereof, the registration roller 32 and the registration roller mechanism 20 including the driving mechanism, and the laser scanner unit 34. The image forming mechanism 21 including a fixing device 35 and a high-voltage unit (not shown) is controlled.

The trailing edge mask timing calculation means 4 has a trailing edge detection management means 5 and manages the trailing edge detection processing indicated by 50A and the trailing edge detection processing indicated by 50B. The paper conveyance control means 10 is composed of a paper conveyance management means 11, a cassette paper feed control means 12, an MPT paper feed control means 13, and a print conveyance control means 14.

Next, the function of each unit will be described. The trailing edge mask timing calculation means 4 is a sensor reading means 6
Timing T at which the trailing edge of the sheet passes the position of the sheet sensor 17 based on the information from the sheet sensor 17 received via
_Ask for ₀ . Subsequently, from this timing T ₀ , a timing T _e corresponding to the trailing edge of the recording paper at the laser irradiation position of the image forming unit 33 is obtained, and the image mask is instructed to the image forming control means 16 at this timing T _e . The sensor reading means 6 and the trailing edge mask timing calculation means 4 will be described in detail later.

The external device communication means 9 controls communication with the external device 3 via the interface 22,
When the sheet conveyance information is received from the sheet conveyance information, the sheet conveyance information storage unit 8 stores the sheet conveyance information.

The paper transport control means 10 includes a cassette paper feed mechanism 18, an MPT paper feed mechanism 19, a registration roller mechanism 20,
Further, the drive of each of the rollers 24 to 26, 30, 32 described above is controlled to convey the paper.

The paper feed management means 11 manages the operations of the cassette paper feed control means 12, the MPT paper feed control means 13 and the print feed control means 14 based on the paper feed information stored in the paper feed information storage means 8 and feeds the paper. Controls the entire paper transport from paper to paper discharge. The cassette paper feed control unit 12 controls the cassette paper feed mechanism 18 according to the instruction of the paper feed management unit 11 to feed the recording paper S stored in the cassette 23 to the registration rollers 32. MPT paper feed control means 13
In accordance with the instruction of the paper conveyance management means 11, the MPT paper feed mechanism 19 is controlled to convey the recording paper set in the MPT 28 to the registration rollers 32. The print conveyance control means 14 follows the instructions of the paper conveyance management means 11 and the registration rollers 3
The recording paper that has been conveyed up to 2 is attached to the image forming unit 33 and the fixing device 35.
And is discharged to the paper discharge tray 40.

The paper transport information storage means 8 stores various information relating to paper transport. The image forming control means 16 controls the image forming mechanism 21 in synchronization with the conveyance of the recording paper by the paper conveyance control means 10, based on the information stored in the paper conveyance information storage means 8, and is sent from the external device 3. An image corresponding to the incoming image signal is formed on the recording paper.

The print control timer 15 is the paper conveyance control means 1.
0, the image formation control unit 16, and the reference timing t of the print control by the trailing edge mask timing calculation unit 4 are managed.

Upon receipt of a print request from the external device 3, the above-mentioned sheet conveyance management means 11 receives the cassette paper feed control means 1.
2, or the recording paper S by the MPT paper feed control means 13
After the sheet is conveyed to the registration roller 32, the print control timer 15 is started by the vertical synchronizing signal from the external device 3 as a trigger, and the print conveying control means 14 is started. After that, the image forming control means 16 performs a printing operation in synchronization with the print control timer 15, and the trailing edge mask timing calculation means 4 also starts control. The external device 3 outputs an image signal at a predetermined timing from the above-mentioned vertical synchronization signal to print an image at a predetermined position on the paper. Since these controls are publicly known, their details are omitted.

Now, the image forming control means 16 is _operated by the external device 3 at the timing T _e corresponding to the trailing edge of the recording paper at the laser irradiation position of the image forming section 33 which receives the laser beam from the laser scanner section 34. The image signal from is masked to forcibly prohibit the writing of the image. The timing T _e is obtained by the trailing edge mask timing calculation means 4 as follows.

The position of the trailing edge of the paper at a certain point in printing control is indefinite. This is because it is impossible to predict what size of paper will be fed when the paper is fed from the MPT 28. Therefore, the timing T _e is calculated based on the timing T ₀ when the trailing edge of the sheet passes the sheet sensor 17.

FIG. 3 is a flow chart showing the control procedure of the sensor reading means 6 shown in FIG. Note that S001 to S00
S in 6 represents a step.

First, in S001, the process waits until the trailing edge mask timing calculation means 4 outputs an instruction to start trailing edge detection. When the instruction to start the trailing edge detection is issued, the process proceeds to S002. S0
In 02, the process waits until the signal from the paper sensor 17 changes from the presence of paper to the absence of paper. When the paper is exhausted, the process proceeds to S003.
The sensor confirmation timer 7 for confirming the sensor signal is started. Then, in S004, the process waits until a predetermined time elapses, and after a predetermined time, the signal from the paper sensor 17 is confirmed again in S005. If the signal from the paper sensor 17 is present, the flow returns to S002. This is a process for avoiding erroneous detection due to noise, flapping of the light shielding plate, or the like.

If the signal from the paper sensor 17 indicates that there is no paper, the flow advances from S005 to S006 to notify the trailing edge detection management means 5 that the trailing edge detection is confirmed.

For example, the signal from the paper sensor 17 is shown in FIG.
In the case of a change as shown in (a), the process proceeds from S002 to S003 and S004 at the timing of arrow a in the figure. Then, the signal is read again at the timing of the arrow b after the confirmation time has passed, and the signal is confirmed (S005).
Confirm with.

On the other hand, when there is a change as shown in FIG. 4 (b), the above S002 to S0 are performed at the timing of arrow c.
03, the process proceeds to S004, but since the paper sensor 17 is out of paper at the timing of arrow d after the confirmation time has elapsed, the process returns from S005 to S002 again. As a result, the trailing edge of the paper can be detected accurately.

By the way, as described above, since the recording paper and the image signal from the external device 3 are synchronized by the registration roller 32, it is necessary to align the leading edge of the paper at the registration roller position uniformly before the printing conveyance. . Therefore, the cassette paper feed control means 12 and the MPT paper feed control means 13 feed the recording paper more than the conveying distance to the registration roller 32 at the time of paper feeding so that the recording paper is pressed against the registration roller 32. ing. For this reason, when the feeding is completed, the recording sheet is loosened as shown in FIGS. 5 (a) and 5 (b). Hereinafter, this slack is called a loop. Then, after a predetermined loop is formed and the paper feeding is completed, the registration roller 32 is driven in accordance with the vertical synchronizing signal from the external device 3 to start the print conveyance as described above.

Here, in the case of paper feeding from the MPT 28,
Immediately after the registration roller 32 starts driving, the MPT lifter 2
By lowering 9 to free the paper from the MPT paper feed roller 30, the loop is not in print conveyance ((b) print conveyance in FIG. 5).

On the other hand, when the paper is fed from the cassette 23,
In order to prevent the carrying roller 26 from pulling the paper being printed and carried, the carrying roller 26 is driven together with the registration roller 32. For this reason, the paper is sent in a loop for a while after the start of the print conveyance ((a) in FIG. 5).
During print conveyance 1), the loop is eliminated after the trailing edge of the paper leaves the conveyance roller 26 ((b) print conveyance 2 in FIG. 5).

FIG. 6 shows the signal state of the paper sensor 17 after the start of print conveyance in the case of cassette paper feeding and in the case of MPT paper feeding.

As shown in FIG. 6A, the cassette 23
If the paper is fed from, the trailing edge of the paper is
The signal from the paper sensor 17 becomes very unstable because the loop is formed until the state such as 2 in FIG.

As described above, the sensor reading means 6 has a confirmation time for preventing erroneous detection, but this confirmation time is due to noise and the small chattering at the trailing edge of the paper as described above. When the paper sensor 17 flaps due to a loop of recording paper as shown in a),
The trailing edge of the paper may be erroneously detected.

On the other hand, when the paper is fed from the cassette 23, the size of the paper is known in advance.

Therefore, in the present invention, the trailing edge mask timing calculating means 4 is provided with the trailing edge detection managing means 5, and the trailing edge detection managing means 5 allows the above-mentioned sheet sensor when the sheet feeding port is the MPT 28. The rear end detection processing based on the information of 17 is selected and executed, and when the paper feed port is the cassette 23, the rear end detection processing based on the known paper size is selected and executed. The detection method is switched.

The flow chart of FIG. 7 shows the control procedure of the trailing edge detection management means 5 of this embodiment.

First, in S101, the process waits until a vertical synchronizing signal comes from the external device 3. If the vertical sync signal is input, S
In step 102, the information of the paper feed port of the recording paper which is being printed at that time is taken out from the paper carrying information storage means 8 and S1 is executed.
Go to 03.

In S103, the trailing edge detection process is selected from the information of the taken out paper feed port. If the recording paper being printed is fed from the cassette 23, the process proceeds to S104 to select the trailing edge detection process, and if not (MPT
(If 28), the process proceeds to S105 to select the trailing edge detection process.

Next, the process proceeds to S106, S104 and S10.
In step 5, the timing T _e corresponding to the trailing edge of the recording paper at the laser irradiation position of the image forming unit 33 is calculated from the timing T _{0 when the} trailing edge of the paper passes the position of the paper sensor 17 obtained by each method. This T _e is obtained after a certain time from T ₀ (determined from the relationship between the position of the paper sensor 17, the laser irradiation position, and the transfer position).

Subsequently, after waiting until the value t of the print control timer 15 reaches T _e in S107, the image forming control means 16 is instructed to perform image masking in S108.

The flowchart of FIG. 8 shows the processing procedure of the trailing edge detection processing. In the trailing edge detection process, the trailing edge detection is started immediately after the start of print conveyance. First, in step S201, the sensor reading unit 6 is instructed to start detection of the sensor position rear end passage timing, and in step S202, the process waits until the sensor position rear end passage is confirmed. In S202, steps S001 to S in FIG.
If the sensor position rear end passage is confirmed by the procedure shown in 006, the process proceeds to S203, and the sensor position rear end passage timing T ₀
Ask for. This timing T ₀ is a timing that is traced back by the sensor confirmation time described above in FIG. 3 from the timing when the sensor position rear end passage confirmation is received from the sensor reading means 6.

On the other hand, in the trailing edge detection process, the time T ₀ predicted when the trailing edge of the sheet passes the position of the sheet sensor 17 is calculated from the sheet size information of the cassette 23 set in the sheet transport information storage means 8. . This is calculated by the following equation (1).

[0057]

[Equation 1] T ₀ = (L _p −L _sr ) / V _t (1) L _p : Paper length L _sr : Distance between paper sensor 17 and registration roller 32 V _t : Paper transport speed As described above, According to the first embodiment, the image mask processing at the trailing edge of the sheet is accurately performed even when the sheet is fed from the MPT 28 having an indefinite sheet size or the sheet fed from the cassette 23 in which the sensor signal is unstable. It can be carried out.

(Second Embodiment) In the above-described first embodiment of the present invention, when the paper is fed from the cassette 23, the timing of the trailing edge of the paper is obtained from the known paper size. The reading range of the paper sensor 17
Only near the timing that is predicted to come to
Avoid erroneous detection due to the fluttering of the above sensor,
It is also possible to detect the trailing edge based on the information from the paper sensor 17. This will be described below as a second embodiment of the present invention.

The configuration of the laser beam printer of this embodiment is the same as that of FIGS. 1 and 2 of the first embodiment, and the operation of each part is also the same except for the trailing edge detection processing.

As shown in FIG. 6A, in the case of sheet feeding from the cassette 23, the signal from the sheet sensor 17 flickers until the trailing edge of the sheet leaves the conveying roller 26 and the loop is eliminated. . Therefore, in the trailing edge detection process of this embodiment, the trailing edge of the sheet is detected immediately before the timing when the trailing edge of the sheet is considered to come to the position of the sheet sensor 17 from the known sheet size.

The flowchart of FIG. 9 shows the control procedure of the trailing edge detection process in this embodiment.

First, in step S301, the timing t _ns immediately before the value t of the print control timer 15 reaches the position of the paper sensor 17 at the rear end of the paper being printed is calculated by the following equation (2).

[0063]

[Number 2] _{T ns = (L p -L sr} ) / V t -m ... (2) L p: sheet length L _sr: distance between the sheet sensor 17 and the registration roller 32 V _t: sheet conveying speed m: conveying Margin in consideration of error amount The above L _p is obtained from the paper size information stored in the paper transport information storage means 8.

Next, in step S302, the process waits until the value t of the print control timer 15 reaches T _ns .

The subsequent processes S303 to S305 are the first
FIG. 8 is a flowchart of the trailing edge detection process of the embodiment of FIG.
The same as 01 to S203.

As described above, in the second embodiment, when the paper is fed from the cassette 23, the reading of the paper sensor information is limited to the vicinity of the timing when the trailing edge of the paper comes to the paper sensor 17, and then the paper is fed. Since the trailing edge of the sheet is detected based on the output of the sensor 17, the timing of the trailing edge of the sheet can be obtained more accurately.

(Third Embodiment) In the above-described second embodiment of the present invention, when the paper is fed from the cassette 23, the known paper size is limited to the vicinity where the trailing edge of the paper comes to the paper size 17. However, if the wrong size of paper is set in the cassette 23, the image mask process cannot be performed accurately and various adverse effects may occur on each part of the image forming mechanism. May affect.

Therefore, as a third embodiment of the present invention, in the trailing edge detection processing when the sheet is fed from the cassette 23, it is considered that the trailing edge of the predicted maximum size sheet is separated from the transport roller 26 and the loop is eliminated. The paper sensor 17 is read only after the predetermined timing.

The configuration of the laser beam printer of this embodiment is the same as that of FIGS. 1 and 2 of the first embodiment, and the operation of each part is also the same except for the trailing edge detection processing.

The flowchart of FIG. 10 shows the control procedure of the trailing edge detection processing in this embodiment.

First, in step S401, the process waits until the value t of the print control timer 15 reaches the timing T _nr at which the loop of the maximum size sheet is considered to be resolved. T _nr is a value calculated and calculated in advance by the following equation (3).

[0072]

[ _Formula 3] T _nr = (L _pmax −L _ft ) / V _t (3) L _pmax : maximum size sheet length L _fr : distance between the transport roller 26 and the registration roller 32 V _t : sheet transport speed S402 to S404 is the same as the flowchart of the trailing edge detection process of the first embodiment shown in FIG. 8 and S201 to S203.

As described above, in the third embodiment, the paper trailing edge detection process when the paper is fed from the cassette 32 is performed after the timing when the loop of the predicted maximum size paper is eliminated. After limiting the loading of
Since it is performed based on the output of the sheet sensor 17, the timing of the trailing edge of the sheet can be correctly obtained even if the wrong size sheet is set in the cassette 23.

(Fourth Embodiment) In the above-described third embodiment of the present invention, it is considered that the loop of the maximum size paper predicted in the trailing edge detection processing when the paper is fed from the cassette 23 is eliminated. The sheet sensor 17 is read only after the timing, but when the difference between the maximum and minimum sheet lengths that can be conveyed is smaller than the distance between the conveyance roller 26 and the sheet sensor 17. It is also possible to read the paper sensor 17 after the timing when the trailing edge of the minimum size paper is considered to come to the position of the paper sensor 17. In this case, it is not necessary to switch the trailing edge detection process, and the sheet trailing edge timing can be obtained by the same trailing edge detection process regardless of which sheet feeding port.

The structure of the laser beam printer of this embodiment is the same as that of the first embodiment shown in FIG. 1, but the control configuration is partially different from that of the first embodiment shown in FIG. That is, the trailing edge mask timing calculation means 4 in FIG.
Has only one trailing edge detection process indicated by 50.

The flowchart of FIG. 12 shows the control procedure of the trailing edge mask timing calculation means 4 of this embodiment.

First, in S501, the process waits until a vertical synchronizing signal comes from the external device 3. If the vertical sync signal is input, S
In step 502, the trailing edge detection process is started. Details of the trailing edge detection process of S502 will be described later.

Thereafter, in step S503, the timing T at which the trailing edge of the sheet passes the position of the sheet sensor 17 obtained in step S502.
₀ determine the timing T _e corresponding to the rear end of the recording sheet in the laser irradiation position of the image forming unit 33, and waits until the value t of the print control timer 15 is T _e at S504, T _e
If so, the image formation control means 16 is instructed to perform image masking in step S505.

The details of the control procedure of the trailing edge detection process of S502 of FIG. 12 in this embodiment are shown in the flowchart of FIG.

Basically, it is almost the same as the flowchart (FIG. 10) of the trailing edge detection processing of the third embodiment, but S6
The waiting time at 01 is the timing at which the trailing edge of the minimum size sheet is considered to come to the position of the sheet sensor 17. The timing T _{s at} which the trailing edge of the smallest size sheet is supposed to come to the position of the sheet sensor 17 is a value calculated and calculated in advance by the following equation (4).

[0081]

[ _Formula 4] T _s = (L _pmin −L _sr ) / V _t −m (4) L _pmin : Minimum size paper length L _sr : Distance between paper sensor 17 and registration roller 32 V _t : Paper transport speed m: Margin considering the transport error amount The subsequent processes S602 to S604 are S402 in FIG.
Is the same as S404.

As described above, in the fourth embodiment, the reading of the sheet sensor information is limited to the timing after the trailing edge of the smallest size sheet reaches the position of the sheet sensor 17, so that the trailing edge of the sheet is detected. It is possible to avoid erroneous detection, and in particular, when the difference between the lengths of the maximum sheet and the minimum sheet that can be conveyed is smaller than the distance between the conveyance roller 26 and the sheet sensor 17, regardless of which sheet feeding port. Since the same paper trailing edge detection processing can be used, control can be simplified.

[0083]

As described above, according to the present invention,
Since the sheet trailing edge detection processing is performed according to the conditions of the sheet material, the risk of false detection of the trailing edge of the sheet material is minimized, and efficient processing that does not waste the sheet material trailing edge in print control. The edge timing can be accurately determined.

More specifically, as the first embodiment of the present invention, the trailing edge detection process based on the known sheet size is selected when the sheet feed port is a cassette, and the trailing edge detection process based on the information from the sheet sensor is selected in the case of MPT. By selecting the processing, it is possible to accurately perform the image mask processing at the trailing edge of the paper, whether the paper is fed from the MPT of which the paper size is indeterminate or the paper of the cassette in which the sensor signal is unstable. it can.

As a second aspect of the present invention, in the case of paper feeding from a cassette, the reading range of the paper sensor is limited to the vicinity of the timing when the trailing edge of the paper is predicted to be the position of the paper sensor, and then the paper sensor. By performing the paper detection process based on the output of the above, it is possible to avoid the erroneous detection due to the fluttering of the paper sensor and to accurately obtain the timing of the rear end of the paper.

As a third aspect of the present invention, the paper trailing edge detection processing when the paper is fed from the cassette is performed by reading the paper sensor information after the timing when the predicted maximum size paper loop is resolved. By limiting and performing based on the output of the paper sensor, the timing of the trailing edge of the paper can be accurately obtained even if the wrong size of paper is set in the cassette.

Further, as a fourth mode of the present invention, the reading of the paper sensor information is limited to the timing after the trailing edge of the smallest size sheet reaches the position of the sheet sensor, thereby avoiding the erroneous detection of the trailing edge of the sheet. In addition, if the difference between the maximum and minimum paper lengths that can be transported is smaller than the distance between the transport roller and the paper sensor, the same paper trailing edge detection process will be performed regardless of which paper feed port. It can be dealt with and control can be simplified.

[Brief description of drawings]

FIG. 1 is a block diagram showing a functional configuration of a control system according to a first embodiment of the present invention.

FIG. 2 is a longitudinal sectional view showing a schematic structure of a laser beam printer embodying the present invention.

FIG. 3 is a flowchart showing a control procedure of a sensor reading unit 6 in FIG.

FIG. 4 is a timing chart for explaining the signals of the paper sensor 17 and the operation of the sensor reading means 6 in FIG.

5 is an operation mode diagram showing a sheet conveyance state of the laser beam printer 1 of FIG.

FIG. 6 is a waveform diagram showing a comparison of signal characteristics of the paper sensor 17 in case of cassette feeding and in case of MPT feeding.

FIG. 7 is a flowchart showing a control procedure of the trailing edge detection management means 5 according to the first embodiment of the present invention.

FIG. 8 is a flowchart showing a control procedure of trailing edge detection processing according to the first embodiment of this invention.

FIG. 9 is a flowchart showing a control procedure of trailing edge detection processing according to the second embodiment of the present invention.

FIG. 10 is a flowchart showing a control procedure of a trailing edge detection process of the third embodiment of the present invention.

FIG. 11 is a block diagram showing a functional configuration of a control system according to a fourth embodiment of the present invention.

FIG. 12 is a flowchart showing a control procedure of a trailing edge mask timing calculation means 4 according to a fourth embodiment of the present invention.

FIG. 13 is a flowchart showing a control procedure of a trailing edge detection process of the fourth embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Laser beam printer 2 Main control unit 3 External device 4 Rear end mask timing calculation unit 5 Rear end detection management unit 6 Sensor reading unit 7 Sensor confirmation timer 8 Paper conveyance information storage unit 10 Paper conveyance control unit 11 Paper conveyance management unit 12 Cassette Paper feed control means 13 MPT paper feed control means 14 print transport control means 15 print control timer 16 image forming control means 17 paper sensor 23 cassette 24 pickup roller 25 feed roller 26 transport roller 27 recording paper transport path 28 MPT (multi paper tray) ) 29 MPT lifter 30 MPT paper feed roller 31 transport path 32 registration roller 33 image forming unit 34 laser scanner unit

Claims (8)

[Claims] 1. An image forming apparatus having a trailing edge timing calculating means for calculating a timing of a trailing edge of the sheet material when forming an image on the sheet material, wherein the trailing edge timing calculating means is a sheet of a known standard size. First trailing edge detection processing means for calculating the timing of the trailing edge of the sheet material based on the known size that has been set for the sheet material fed from the first paper feeding means And a sensor signal from a sensor that detects the trailing edge of the sheet material that is being fed to the sheet material that is fed from the second sheet feeding unit that feeds an irregular size sheet material of unknown size. An image forming apparatus including: a second trailing edge detection processing unit that calculates the timing of the trailing edge of the sheet material based on the sheet material. 2. An image forming apparatus having a trailing edge timing calculating means for calculating the timing of the trailing edge of the sheet material when forming an image on the sheet material, wherein the trailing edge timing calculating means is a standard size sheet of known size. For the sheet material fed from the sheet feeding means for feeding the material, the reading range of the sensor signal from the sensor that detects the trailing edge of the sheet material being fed is within the range where the trailing edge of the sheet material is the sensor. The image forming apparatus is characterized in that the timing of the trailing edge of the sheet material is calculated based on the sensor signal from the sensor when the position is reached, and the timing is estimated to be near the timing predicted from the known size. 3. An image forming apparatus having a trailing edge timing calculating means for calculating the timing of the trailing edge of the sheet material when an image is formed on the sheet material, and a sensor for detecting the trailing edge of the sheet material being fed. The sheet material having a known standard size is fed loosely in the vicinity of the sensor until the sheet material conveying means on the conveying path is completely separated from the sheet material, and the trailing edge timing calculating means uses the sheet material as the sheet material. A sensor signal is read from the sensor at a timing at which it is predicted that the slack of the sheet material will be sufficiently eliminated by leaving the conveying means, and the timing of the rear end of the sheet material is calculated based on the read sensor signal. An image forming apparatus characterized by. 4. The trailing edge timing calculating means obtains in advance a timing T _{1 at} which the trailing edge of the sheet material of the maximum size that can be conveyed leaves the sheet material conveying means, and after the timing T ₁ , the sensor outputs the timing T _1. The image forming apparatus according to claim 3, which reads the sensor signal of. 5. The trailing edge timing calculating means previously obtains a timing T _{2 at} which the trailing edge of a sheet material having a minimum size that can be conveyed reaches the sensor, and starts from slightly before the timing T _2. The image forming apparatus according to claim 3, wherein a sensor signal is read from the sensor. 6. The sensor is a contact-type sensor which is arranged on a conveying path and whose signal output is inverted when a part of the sheet material is touched, and the trailing edge timing calculation means outputs a signal from the sensor to the sheet. 6. The image forming apparatus according to claim 1, wherein it is determined that the timing when the trailing edge of the sheet material passes the position of the detection sensor is changed at the timing when the material is changed to the absence. 7. The sensor has a first conveyance path for feeding a sheet material of a known standard size and a second conveyance path for feeding an irregular sheet material of an unknown size. The image forming apparatus according to any one of claims 1 to 6, wherein the image forming apparatus is arranged on the third conveying path. 8. An image forming apparatus having a trailing edge timing calculating means for calculating the timing of the trailing edge of the sheet material when forming an image on the sheet material, wherein a sensor for detecting the trailing edge of the sheet material being fed is provided. The sensor is a contact type sensor in which the output of the signal is inverted when a part of the sheet material is touched. The sensor has a first conveyance path and a size for feeding a sheet material of a known standard size. The trailing edge timing calculation means is arranged on a third conveyance path that joins with a second conveyance path for feeding an unknown irregular-shaped sheet material, The timing T ₂ predicted to reach the sensor is obtained in advance, and the sensor signal from the sensor is read from a short time before the timing T ₂ regardless of the conveying path along which the sheet material is fed. Sensor An image characterized by calculating the timing of the rear end of the sheet material by judging that the rear edge of the sheet material has passed the position of the detection sensor at the timing when the signal changes from the presence of the sheet material to the absence of the sheet material Forming equipment.