JP3754720B2 - Image forming apparatus - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to an image forming apparatus that forms and records image information such as characters on a sheet-like recording material (hereinafter referred to as a sheet material), and more particularly to an image forming apparatus that controls the image formation by obtaining the timing of the trailing edge of the sheet material. About.
[0002]
[Prior art]
Conventionally, in this type of image forming apparatus such as a laser beam printer or a digital copying apparatus, the sheet material trailing edge timing calculating means for obtaining the timing of the sheet material trailing edge in various image forming controls is constant regardless of the conditions of the sheet material. Is being processed.
[0003]
For example, even if there are multiple conveyance paths and the conditions of the sheet material are different for each conveyance path, the same processing may be performed, or the conditions may be different for each sheet material even in the same conveyance path. The same processing is performed.
[0004]
Conventionally, the sheet material trailing edge timing calculating means as described above includes a sheet material sensor that is arranged on the conveyance path and detects the presence of the sheet material by contacting the sheet material, and an output signal of the sheet material sensor Is detected as the timing at which the trailing edge of the sheet material passes the sensor position at the timing when the sheet material is changed from the presence of the sheet material, and the timing corresponding to the trailing edge of the sheet material in each image formation control is obtained based on this timing. However, the reading of the signal from the sheet material sensor is constant regardless of the sheet material conditions.
[0005]
[Problems to be solved by the invention]
However, since the sheet material trailing edge timing calculation means of the conventional image forming apparatus as described above performs all the same processing without considering the sheet material conditions, the timing of the sheet material trailing edge depends on the conditions. May be misdetected.
[0006]
In particular, when the above timing is obtained using a sheet material sensor that detects the presence of the sheet material by contacting a part of the sheet material that is installed on the conveyance path, the method of changing the signal from the sheet material sensor is Although it differs depending on the conveyance mode of the sheet material, when the same trailing edge detection process is performed, there are cases where accurate trailing edge detection cannot be performed.
[0007]
Further, even in the case of a sheet material having information on the size in advance, performing the trailing edge detection process by the sheet material sensor similar to the sheet material having an undefined size is an error caused by fluttering of the sensor output due to the looseness of the sheet material. The risk of detection is violated and wasteful processing is performed.
[0008]
The present invention solves the problems of the prior art as described above, performs an optimum rear end detection process according to the conditions of the sheet material, and can minimize the possibility of erroneous detection. The object is to provide a device.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention includes a sheet material storage unit that stores a sheet material of a standard size, Based on image signal Form an image on the sheet material for An image forming means, and a sheet material conveying path for conveying the sheet material fed from the sheet material accommodating means to the image forming means, A first conveying unit configured to convey the sheet material in the sheet material conveying path; and provided downstream of the first conveying unit in the conveying direction of the sheet material, and before conveying the sheet material to the image forming unit A second conveying means for adjusting the conveying operation of the sheet material; A sensor that is provided in the sheet material conveyance path and detects the presence or absence of the sheet material; When the sheet material fed from the sheet material storage unit is conveyed to the image forming unit by the first conveyance unit and the second conveyance unit, the sheet material is formed from a state in which a loop is formed in the sheet material. Control means for controlling the operation of the first transport means and the second transport means so as to eliminate the loop while transporting the material, and the sheet material storage means. Based on the size of the sheet material, After the loop of the sheet material is eliminated Of the sheet material by the sensor. Trailing edge Calculating means for calculating the timing for starting detection; The control means includes The sensor starts detecting the trailing edge of the sheet material from the timing calculated by the calculation means, and the sensor Result of the trailing edge detection of the sheet material by And controlling to prohibit image formation by the image forming means.
[0011]
In addition, the calculation unit may calculate the timing based on a maximum size of the sheet material that can be conveyed.
[0012]
Further, the calculation unit may calculate the timing based on a minimum size of the sheet material that can be conveyed.
[0014]
In addition, Accommodates irregularly sized sheet material Non-standard size sheet material Containing means; and Irregular size For transporting the sheet material fed from the sheet material storing means to the image forming means; A third conveying means, The control means includes the Irregular size When the sheet material is fed from the sheet material storing means, detection of the trailing edge of the sheet material is started by the sensor from the timing when the sheet material is fed. And controlling to prohibit image formation by the image forming means based on the result of the trailing edge detection of the sheet material by the sensor. It is characterized by be able to .
[0016]
[Action]
From the above configuration, according to the present invention, the rear end of the sheet material is erroneously detected. Do By minimizing the possibility, the timing of the trailing edge of the sheet material can be accurately obtained, and the image mask processing at the trailing edge of the sheet material can be accurately performed.
[0020]
【Example】
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0021]
(First embodiment)
1 to 8 show a first embodiment of the present invention. FIG. 1 shows a functional configuration of a control system of an image forming apparatus according to the present embodiment, and FIG. 2 shows a cross-sectional structure of a laser beam printer as an example of an image forming apparatus according to the present invention. First, the mechanical configuration of FIG. 2 will be described.
[0022]
As shown in FIG. 2, the laser beam printer 1 has a cassette 23 for storing recording paper (sheet material) S, a pickup roller 24 for picking up the recording paper from the cassette 23, and further picked up recording paper. A paper feed roller 25 is provided. A conveyance roller 26 that conveys the fed recording paper to a registration roller 32 (described later) is disposed downstream of the paper supply roller 25.
[0023]
On the other hand, the laser beam printer 1 has a multi-paper tray (hereinafter referred to as MPT) 28 capable of manually feeding another non-standard paper, and MPT paper feeding for feeding recording paper from the MPT 28. An MPT lifter 29 for pressing the recording paper set on the roller 30 and the MPT 28 against the MPT paper supply roller 30 is provided.
[0024]
The recording paper conveyance path 27 from the cassette 23 and the conveyance path 31 from the MPT 28 merge at a merge point C and reach a registration roller 32 described later. A registration roller 32 that synchronously conveys the recording sheet S is disposed downstream of the junction C, and a sheet sensor 17 is disposed immediately before the registration roller 32. The paper sensor 17 detects the presence of paper at the position by a movable light shielding plate that shields the photo interrupter by contact of the paper. An image forming unit 33 that forms an image with a laser beam from the laser scanner unit 34 is disposed downstream of the registration roller 32. Further, a fixing unit 35 is disposed downstream of the image forming unit 33, and sheet discharge transport rollers 36, 37, 38, 39 are disposed downstream of the fixing unit 35, up to the sheet discharge tray 40. Transport recording paper.
[0025]
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), ROM (Read Only Memory), RAM (Random Access Memory), a gate element, etc., and the main part of control is realized by software written in the ROM. Yes. However, in FIG. 1, the inside of the main control unit 2 is represented by a functional configuration. The main control unit 2 is connected to the external device 3 via the external interface 22.
[0026]
The functions of the main control unit 2 are as follows: rear end mask timing calculation means 4, sensor reading means 6, sensor confirmation timer 7, external device communication means 9, paper conveyance information storage means 8, paper conveyance control means 10, print control timer 15, And image forming control means 16. With these functions, the main control unit 2 causes the cassette 23, the pickup roller 24, the paper feed roller 25, the transport roller 26, and the cassette paper feed mechanism 18 composed of these drive mechanisms, the MPT 28, the MPT lifter 29, and the MPT feed. MPT paper feed mechanism 19 composed of paper rollers 30 and their drive mechanisms, resist roller mechanism 20 composed of resist rollers 32 and their drive mechanisms, laser scanner section 34, fixing device 35, high voltage unit (not shown), etc. Each of the image forming mechanisms 21 is controlled.
[0027]
The trailing edge mask timing calculation means 4 has a trailing edge detection management means 5 and manages trailing edge detection processing (1) indicated by 50A and trailing edge detection processing (2) indicated by 50B. The paper transport control unit 10 includes a paper transport management unit 11, a cassette paper feed control unit 12, an MPT paper feed control unit 13, and a print transport control unit 14.
[0028]
Next, the function of each part will be described. The trailing edge mask timing calculating means 4 is a timing T at which the trailing edge of the paper passes the position of the paper sensor 17 based on information from the paper sensor 17 received via the sensor reading means 6. ₀ Ask for. Subsequently, this timing T ₀ To T corresponding to the trailing edge of the recording paper at the laser irradiation position of the image forming unit 33. _e This timing T _e Then, an image mask is instructed to the image formation control means 16. The sensor reading means 6 and the rear end mask timing calculation means 4 will be described in detail later.
[0029]
The external device communication unit 9 controls communication with the external device 3 via the interface 22, and stores paper conveyance information in the paper conveyance information storage unit 8 when receiving an instruction regarding paper conveyance from the external device 3.
[0030]
The sheet conveyance control means 10 conveys the sheet by controlling the driving of the cassette sheet feeding mechanism 18, the MPT sheet feeding mechanism 19, the registration roller mechanism 20, and the rollers 24 to 26, 30, 32 described above.
[0031]
The paper transport management means 11 manages the operations of the cassette paper feed control means 12, the MPT paper feed control means 13, and the print transport control means 14 based on the transport information stored in the paper transport information storage means 8, and is discharged from the paper feed. Controls overall paper transport to the paper. The cassette paper feed control means 12 controls the cassette paper feed mechanism 18 in accordance with instructions from the paper transport management means 11 and transports the recording paper S stored in the cassette 23 to the registration rollers 32. The MPT paper feed control means 13 controls the MPT paper feed mechanism 19 in accordance with the instruction from the paper transport management means 11 and transports the recording paper set in the MPT 28 to the registration rollers 32. The print transport control unit 14 sends the recording paper transported to the registration rollers 32 to the image forming unit 33 and the fixing device 35 in accordance with an instruction from the paper transport management unit 11 and discharges the recording paper to the paper discharge tray 40.
[0032]
The paper transport information storage unit 8 stores various information related to paper transport. The image formation control unit 16 controls the image forming mechanism 21 in synchronization with the conveyance of the recording sheet by the sheet conveyance control unit 10 based on the information stored in the sheet conveyance information storage unit 8, and is sent from the external device 3. An image corresponding to the incoming image signal is formed on the recording paper.
[0033]
The print control timer 15 manages the reference timing t for print control by the paper transport control means 10, the image formation control means 16, and the trailing edge mask timing calculation means 4.
[0034]
Upon receiving a print request from the external device 3, the paper transport management unit 11 transports the recording paper S to the registration rollers 32 by the cassette paper feed control unit 12 or the MPT paper feed control unit 13, and then the external device 3. The print control timer 15 is started by using the vertical synchronization signal from as a trigger, and the print conveyance control means 14 is activated. Thereafter, the image formation control means 16 performs a printing operation in accordance 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 vertical synchronization signal, and prints an image at a predetermined position on the paper. Since these controls are publicly known, details are omitted.
[0035]
Here, the image formation control means 16 has a timing T corresponding to the trailing edge of the recording paper at the laser irradiation position of the image forming section 33 that receives the laser light from the laser scanner section 34. _e Thus, the image signal from the external device 3 is masked to forcibly prohibit image writing. _e Is obtained by the trailing edge mask timing calculation means 4 as follows.
[0036]
The position of the trailing edge of the sheet at a certain point in the printing control is indefinite. This is because in the case of paper feeding from the MPT 28, it is impossible to predict what size paper will be fed. For this reason, the timing T at which the trailing edge of the sheet passes through the sheet sensor 17. ₀ Timing T _e Seeking.
[0037]
FIG. 3 is a flowchart showing the control procedure of the sensor reading means 6 of FIG. Note that S in S001 to S006 represents a step.
[0038]
First, in step S001, the process waits until a rear end detection start instruction is output from the rear end mask timing calculation unit 4. If an instruction to start rear end detection is issued, the process proceeds to S002. In S002, the process waits until the signal from the sheet sensor 17 changes from the presence of the sheet to the absence of the sheet. If the sheet is not present, the process proceeds to S003, and the sensor confirmation timer 7 for confirming the sensor signal is started. In step S004, the process waits until a predetermined time elapses. After a predetermined time, the signal from the paper sensor 17 is confirmed again in step S005. If the signal from the paper sensor 17 is present, the process returns to S002. This is a process for avoiding erroneous detection due to noise or flapping of the light shielding plate.
[0039]
If the signal from the paper sensor 17 is out of paper, the process proceeds from S005 to S006, and the rear end detection management means 5 is informed as the rear end detection is confirmed.
[0040]
For example, when the signal from the paper sensor 17 changes as shown in FIG. 4A, the process proceeds from S002 to S003 and S004 at the timing of the arrow a in the figure. Then, the signal is read and confirmed again at the timing of the arrow b after the confirmation time has passed (S005), and confirmed in S006.
[0041]
On the other hand, when the change is made as shown in FIG. 4B, the process proceeds from S002 to S003 and S004 at the timing of the arrow c, but the sheet sensor 17 indicates that there is a sheet at the timing of the arrow d after the confirmation time has elapsed. Therefore, the process returns from S005 to S002 again. As a result, the trailing edge of the sheet can be accurately detected.
[0042]
By the way, since the recording paper and the image signal from the external device 3 are synchronized by the registration roller 32 as described above, it is necessary to make the front end of the paper constant at the registration roller position before printing conveyance. Therefore, the cassette paper feed control means 12 and the MPT paper feed control means 13 feed the recording paper longer than the transport distance to the registration roller 32 during paper feeding so that the recording paper is pressed against the registration roller 32. ing. For this reason, when the paper feeding is completed, the recording paper can be slack as shown in FIGS. Hereinafter, this slack is called a loop. Then, after the predetermined loop is formed and the paper feeding is completed, as described above, the registration roller 32 is driven in accordance with the vertical synchronization signal from the external device 3 to start the print conveyance.
[0043]
Here, in the case of paper feeding from the MPT 28, the MPT lifter 29 is lowered immediately after the start of the driving of the registration roller 32 to release the paper from the MPT paper feeding roller 30, so that the loop is eliminated during printing conveyance (FIG. 5 (b) during printing conveyance).
[0044]
On the other hand, in the case of paper feeding from the cassette 23, the conveyance roller 26 is driven together with the driving of the registration roller 32 so that the conveyance roller 26 does not pull the paper being conveyed. For this reason, the paper is fed while being looped for a while after the start of printing conveyance ((a) during printing conveyance 1 in FIG. 5), and the loop is canceled after the trailing edge of the sheet leaves the conveyance roller 26 (FIG. 5). (B) During printing conveyance 2).
[0045]
FIG. 6 shows the state of signals from the paper sensor 17 after the start of print conveyance in the case of cassette paper feed and in the case of MPT paper feed.
[0046]
As shown in FIG. 6A, in the case of paper fed from the cassette 23, the rear end of the paper leaves the transport roller 26 until the state shown in FIG. Is Le Since the loop is formed, the signal of the paper sensor 17 becomes very unstable.
[0047]
As described above, the sensor reading means 6 has a confirmation time for preventing erroneous detection. This confirmation time is for noise and small chattering at the rear end of the paper as described above. FIG. If the paper sensor 17 flutters due to the loop of the recording paper as shown, there is a possibility that the rear end of the paper is erroneously detected.
[0048]
On the other hand, in the case of paper feeding from the cassette 23, the paper size is known in advance.
[0049]
Therefore, in the present invention, the trailing edge mask timing calculation means 4 is provided with the trailing edge detection management means 5, and the trailing edge detection management means 5 allows the information of the sheet sensor 17 described above when the sheet feeding port is MPT 28. The rear end detection process (1) based on is selected and executed, and if the paper feed port is the cassette 23, the rear end detection process (2) based on a known paper size is selected and executed. The rear end detection method is switched.
[0050]
The flowchart of FIG. 7 shows the control procedure of the trailing edge detection management means 5 of this embodiment.
[0051]
First, it waits until a vertical synchronizing signal comes from the external device 3 in S101. If the vertical synchronizing signal is input, the process proceeds to S102, and the information on the paper feed port of the recording sheet printed at that time is taken out from the sheet conveyance information storage means 8, and the process proceeds to S103.
[0052]
In step S103, the trailing edge detection process is selected from the information on the sheet feeding port that has been taken out. Here, if the recording paper being printed is fed from the cassette 23, the process proceeds to S104 and the trailing edge detection process (2) is selected. If not (if it is MPT28), the process proceeds to S105. Select edge detection process (1).
[0053]
Next, the process proceeds to S106, and the timing T at which the trailing edge of the sheet passes the position of the sheet sensor 17 obtained by the respective methods in S104 and S105. ₀ To T corresponding to the trailing edge of the recording paper at the laser irradiation position of the image forming unit 33. _e Is calculated. This T _e Is T ₀ After a certain time (determined from the relationship between the paper sensor 17 position, laser irradiation position, and transfer position).
[0054]
In step S107, the value t of the print control timer 15 is set to T. _e In step S108, the image forming control unit 16 is instructed to mask an image.
[0055]
The flowchart of FIG. 8 shows the processing procedure of the rear end detection process (1). In the trailing edge detection process {circle around (1)}, the trailing edge detection is started immediately after the start of printing conveyance. First, in S201, the sensor reading means 6 is instructed to start detection of the sensor position rear end passage timing, and in S202, the process waits until the sensor position rear end passage is confirmed. If the sensor position rear end passage is determined by the procedure shown in steps S001 to S006 of FIG. 3 in S202, the process proceeds to S203 and the sensor position rear end passage timing T is reached. ₀ Ask for. This timing T ₀ Is a timing that goes back from the timing at which the sensor position rear end passage confirmation is received from the sensor reading means 6 by the aforementioned sensor confirmation time in FIG.
[0056]
On the other hand, in the trailing edge detection process {circle around (2)}, the time T predicted that the trailing edge of the sheet will pass the position of the sheet sensor 17 from the sheet size information of the cassette 23 set in the sheet conveyance information storage means 8. ₀ Is calculated. This is calculated by the following equation (1).
[0057]
[Expression 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 at the trailing edge of the sheet is fed regardless of whether the paper is fed from the MPT 28 whose paper size is indefinite or from the cassette 23 where the sensor signal is unstable. Mask processing can be performed accurately.
[0058]
(Second embodiment)
In the first embodiment of the present invention described above, in the case of paper feeding from the cassette 23, the timing of the trailing edge of the sheet is obtained from the known sheet size. It is also possible to avoid the erroneous detection due to the fluttering of the sensor, and to detect the trailing edge based on the information from the paper sensor 17 only in the vicinity of the timing predicted to come to the position 17. This will be described below as a second embodiment of the present invention.
[0059]
The configuration of the laser beam printer of this embodiment is the same as that of the first embodiment shown in FIGS. 1 and 2, and the operation of each part is the same except for the rear end detection process (2).
[0060]
As shown in FIG. 6A, in the case of paper feeding from the cassette 23, the signal from the paper sensor 17 fluctuates until the trailing edge of the paper leaves the conveying roller 26 and the loop is eliminated. Therefore, in the trailing edge detection process (2) of this embodiment, the detection of the trailing edge of the sheet is started immediately before the timing at which it is considered that the trailing edge of the sheet comes to the position of the sheet sensor 17 from the known sheet size.
[0061]
The flowchart of FIG. 9 shows the control procedure of the rear end detection process (2) in this embodiment.
[0062]
First, in step S <b> 301, the value T of the print control timer 15 is a timing T immediately before the trailing edge of the paper being printed comes to the position of the paper sensor 17. _ns Is calculated by the following equation (2).
[0063]
[Expression 2]
T _ns = (L _p -L _sr ) / V _t -M (2)
L _p : Paper length
L _sr : Distance between paper sensor 17 and registration roller 32
V _t : Paper transport speed
m: Margin considering transport error
L above _p Is obtained from the paper size information stored in the paper conveyance information storage means 8.
[0064]
In step S302, the value t of the print control timer 15 is set to T. _ns Wait until
[0065]
Subsequent processes S303 to S305 are the same as the flowchart in FIG. 8 and S201 to S203 of the rear end detection process (1) of the first embodiment.
[0066]
As described above, in the second embodiment, when paper is fed from the cassette 23, the reading of the paper sensor information is limited to the vicinity of the timing at which the trailing edge of the paper comes to the paper sensor 17, and the paper sensor 17 Since the sheet trailing edge detection process is performed based on the output, the timing of the sheet trailing edge can be obtained more accurately.
[0067]
(Third embodiment)
In the above-described second embodiment of the present invention, in the case of paper feeding from the cassette 23, the paper trailing edge detection is performed only from the known paper size to the vicinity where the paper trailing edge reaches the paper size 17. However, if the wrong size paper is set in the cassette 23, the image mask processing cannot be performed accurately, and various adverse effects may be caused on each part of the image forming mechanism.
[0068]
Therefore, as a third embodiment of the present invention, in the trailing edge detection process (2) in the case of paper feeding from the cassette 23, it is considered that the predicted trailing edge of the maximum size sheet is separated from the conveying roller 26 and the loop is eliminated. The reading of the paper sensor 17 is performed only at the timing after the recording timing.
[0069]
The configuration of the laser beam printer of this embodiment is the same as that of the first embodiment shown in FIGS. 1 and 2, and the operation of each part is the same except for the rear end detection process (2).
[0070]
The flowchart of FIG. 10 shows the control procedure of the rear end detection process {circle around (2)} in this embodiment.
[0071]
First, in step S401, the timing T at which the loop of the sheet having the maximum value t in the print control timer 15 is considered to be eliminated. _nr Wait until T _nr Is a value obtained in advance by calculation as in the following equation (3).
[0072]
[Equation 3]
T _nr = (L _pmax -L _ft ) / V _t ... (3)
L _pmax : Maximum paper length
L _fr : Distance between the conveyance roller 26 and the registration roller 32
V _t : Paper transport speed
S402 to S404 are the same as the flowchart in FIG. 8 and S201 to S203 of the rear end detection process (1) of the first embodiment.
[0073]
As described above, in the third embodiment, the sheet trailing edge detection process when the sheet is fed from the cassette 32 is performed, and the sheet sensor information is read after the timing when the loop of the predicted maximum size sheet is eliminated. Since the determination is made based on the output of the sheet sensor 17, the timing of the trailing edge of the sheet can be obtained correctly even if a wrong size sheet is set in the cassette 23.
[0074]
(Fourth embodiment)
In the third embodiment of the present invention described above, it is limited to the timing after which the maximum size paper loop predicted in the trailing edge detection process {circle around (2)} in the case of feeding from the cassette 23 is considered to be eliminated. The paper sensor 17 is read, but when the difference between the maximum length of the maximum paper that can be transported and the minimum length of the paper is smaller than the distance between the transport roller 26 and the paper sensor 17, the trailing edge of the minimum size paper It is also possible to read the paper sensor 17 after the timing at which the paper sensor 17 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 paper feed port.
[0075]
The structure of the laser beam printer of this embodiment is the same as that of FIG. 1 of the first embodiment, but the control configuration is partially different from that of FIG. 1 of the first embodiment as shown in FIG. That is, in FIG. 11, the trailing edge mask timing calculation means 4 has only one trailing edge detection process indicated by 50.
[0076]
The flowchart of FIG. 12 shows the control procedure of the trailing edge mask timing calculation means 4 of this embodiment.
[0077]
First, it waits until a vertical synchronizing signal comes from the external device 3 in S501. If the vertical synchronization signal is input, the process proceeds to S502, and the trailing edge detection process is started. Details of the trailing edge detection processing in S502 will be described later.
[0078]
Thereafter, in S503, the timing T at which the trailing edge of the sheet passes the position of the sheet sensor 17 obtained in S502. ₀ To T corresponding to the trailing edge of the recording paper at the laser irradiation position of the image forming unit 33. _e In step S504, the value t of the print control timer 15 is T _e Wait until _e In step S505, the image forming control unit 16 is instructed to set an image mask.
[0079]
The flowchart of FIG. 13 shows the details of the control procedure of the rear end detection process of S502 of FIG. 12 in the present embodiment.
[0080]
Basically, it is almost the same as the flowchart (FIG. 10) of the trailing edge detection process (2) of the third embodiment, but the waiting time at S601 is that the trailing edge of the minimum size sheet is at the position of the sheet sensor 17. It is the timing that is expected to come. Timing T at which the trailing edge of the minimum size paper is considered to be at the position of the paper sensor 17 _s Is a value obtained in advance by calculation as in the following equation (4).
[0081]
[Expression 4]
T _s = (L _pmin -L _sr ) / V _t -M (4)
L _pmin : Minimum paper length
L _sr : Distance between paper sensor 17 and registration roller 32
V _t : Paper transport speed
m: Margin considering transport error
Subsequent processes S602 to S604 are the same as S402 to S404 in FIG.
[0082]
As described above, in the fourth embodiment, the reading of the sheet sensor information is limited to the timing after the timing when the trailing edge of the minimum size sheet comes to the position of the sheet sensor 17, so erroneous detection of the trailing edge of the sheet is detected. In addition, when the difference between the maximum paper length and the minimum paper length that can be transported is smaller than the distance between the transport roller 26 and the paper sensor 17, Control can be simplified because it can be handled by edge detection processing.
[0083]
【The invention's effect】
As described above, according to the present invention, the sheet material trailing edge detection process corresponding to the conditions of the sheet material is performed, so the sheet material trailing edge is erroneously detected. Do In addition to minimizing the possibility, it is possible to accurately obtain the timing of the trailing edge of the sheet material in printing control and to accurately perform the image mask processing of the trailing edge of the sheet material.
[Brief description of the 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 the sensor reading means 6 of FIG.
4 is a timing chart for explaining the signal of the paper sensor 17 and the operation of the sensor reading means 6 in FIG.
FIG. 5 is an operation mode diagram showing a paper conveyance state of the laser beam printer 1 of FIG. 2;
FIG. 6 is a waveform diagram showing a comparison of signal characteristics of the paper sensor 17 in the case of cassette paper feeding and MPT paper feeding.
FIG. 7 is a flowchart showing the control procedure of the trailing edge detection management means 5 in the first embodiment of the present invention.
FIG. 8 is a flowchart showing a control procedure of rear end detection processing {circle around (1)} of the first embodiment of the present invention.
FIG. 9 is a flowchart showing a control procedure of rear end detection processing {circle around (2)} of the second embodiment of the present invention.
FIG. 10 is a flowchart showing a control procedure of rear end detection processing {circle around (2)} 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 the control procedure of the trailing edge mask timing calculation means 4 of the fourth embodiment of the present invention.
FIG. 13 is a flowchart showing a control procedure of rear end detection processing according to the fourth embodiment of the present invention.
[Explanation of symbols]
1 Laser beam printer
2 Main control unit
3 External equipment
4 Rear end mask timing calculation means
5 Rear end detection management means
6 Sensor reading means
7 Sensor confirmation timer
8 Paper transport information storage means
10 Paper transport control means
11 Paper transport management means
12 Cassette paper feed control means
13 MPT paper feed control means
14 Print transport control means
15 Print control timer
16 Image formation control means
17 Paper sensor
23 cassette
24 Pickup roller
25 Paper feed roller
26 Conveying 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 section
34 Laser scanner

Claims (4)

Sheet material storage means for storing a standard size sheet material;
Image forming means for forming an image on the sheet material based on an image signal ;
A sheet material conveyance path for conveying the sheet material fed from the sheet material accommodation unit to the image forming unit;
First conveying means for conveying the sheet material in the sheet material conveying path;
A second conveying unit that is provided on the downstream side of the first conveying unit in the conveying direction of the sheet material and adjusts the conveying operation of the sheet material before conveying the sheet material to the image forming unit;
A sensor that is provided in the sheet material conveyance path and detects the presence or absence of the sheet material;
When the sheet material fed from the sheet material storage unit is conveyed to the image forming unit by the first conveyance unit and the second conveyance unit, the sheet material is formed from a state in which a loop is formed in the sheet material. Control means for controlling the operation of the first conveying means and the second conveying means so as to eliminate the loop while conveying the material;
Based on the size of the sheet material accommodated in the sheet material accommodation means, calculating means for calculating the timing of starting the trailing edge detection of the sheet material by the sensor after the loop of the sheet material is eliminated ,
And the control means starts detection of the trailing edge of the sheet material by the sensor from the timing calculated by the calculating means, and based on the result of detection of the trailing edge of the sheet material by the sensor An image forming apparatus that controls to prohibit image formation by an image forming unit. The image forming apparatus according to claim 1 , wherein the calculation unit calculates the timing based on a maximum size of the sheet material that can be conveyed. The image forming apparatus according to claim 1 , wherein the calculation unit calculates the timing based on a minimum size of the sheet material that can be conveyed. Further, an irregular size sheet material accommodating means for accommodating an irregular size sheet material ,
A third conveying means for conveying the sheet material fed from the irregular size sheet material accommodating means to the image forming means ,
Wherein, when said feeding of the sheet material from the irregular size sheet accommodating means starts detection of the trailing end of the sheet by the sensor from the timing to start sheet feeding of the sheet material 2. The image forming apparatus according to claim 1 , wherein control is performed so as to prohibit image formation by the image forming unit based on a result of detection of a trailing edge of the sheet material by the sensor .

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