JP2009251395A - Image forming apparatus and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce paper supplying error in a situation when time for retrying the paper supplying can be secured in such situation as when a through put is suppressed. <P>SOLUTION: The image forming apparatus includes: an image forming means for forming an image on recording paper; a paper supplying means for supplying the recording paper to a transporting path going through to the image forming means; a retrying processing means; and a control means. The retrying processing means, for example, performs retrying of paper supplying to the paper supplying means when the recording paper has not reached a prescribed position in the transporting path within the reference time which is determined beforehand. Furthermore, the control means makes a retrying function in the retrying processing means effective when a starting condition for an image formation applied to the recording paper is the starting condition in which the retrying time which is necessary for the retrying of the paper supplying can be secured. At the same time, the control means makes the retrying function ineffective when the starting condition for the image formation applied to the recording paper is not the starting condition in which the retrying time can be secured. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention generally relates to an image forming apparatus, and more particularly to a recording paper feed retry.

  Generally, an image forming apparatus has a jam detection function. The jam detection function determines that a paper feed jam has occurred when a sheet is not conveyed within a predetermined time from a paper feed start position to a sheet detection position provided downstream of the conveyance path. On the other hand, as a relief means when a sheet is not conveyed within a predetermined time, there is a paper feed retry operation. As a result, the occurrence of paper jam is reduced.

According to Japanese Patent Laid-Open No. 2004-228561, setting means for setting the number of paper feed retries for each sheet type is disclosed. Patent Document 2 discloses a setting unit that can arbitrarily set the number of retries. Japanese Patent Laid-Open No. 2004-228628 discloses a time required for a paper feed retry by starting paper feeding for only the first sheet of a job before starting the formation of a toner image on an image carrier. An invention to ensure is also disclosed.
JP 2003-306251 A JP 11-334935 A

  By the way, as a technique for increasing the number of images formed per unit time (throughput), there is a technique of fixing the formation intervals of a plurality of toner images on an image carrier at a predetermined time interval. There is also a method of starting the formation of a toner image on the image carrier prior to the start of sheet feeding. In particular, in these methods, it is normal that there is no time delay for performing a paper feed retry when the paper feeding fails. If the time for performing paper feeding retry is forcibly secured, the toner image formation interval is uniformly increased for each sheet, and the throughput is likely to decrease. Note that the apparatuses described in Patent Documents 1 and 2 are basically based on the assumption that a paper feed retry is executed. Therefore, the throughput of these apparatuses is lower than that of an apparatus that is premised on not performing a paper feed retry (an apparatus that has no time delay for paper feed retry).

  On the other hand, even in an image forming apparatus that does not have a time delay for paper feed retry during normal printing, there may be a situation in which a sufficient time delay for performing paper feed retry can be secured. Such a situation is a situation where the throughput is temporarily suppressed for some reason, such as a situation where throughput down control is performed to prevent overheating in the fixing unit. However, in the related art, when a paper feed jam occurs in a state where throughput is temporarily suppressed, the image forming apparatus is stopped without executing a paper feed retry.

  Therefore, an object of the present invention is to solve at least one of such problems and other problems. For example, an object of the present invention is to reduce paper feed mistakes in a situation where a paper feed retry time can be secured, such as a situation where throughput is suppressed. Other issues can be understood throughout the specification.

  The image forming apparatus of the present invention includes an image forming unit that forms an image on a recording sheet, a sheet feeding unit that feeds the recording sheet to a conveyance path leading to the image forming unit, a retry processing unit, and a control unit. For example, if the recording paper has not arrived at a predetermined position on the transport path within a predetermined reference time, the retry processing unit causes the paper feeding unit to perform paper feeding retry. The control means validates the retry function in the retry processing means if the image formation start condition is a start condition that can ensure a retry time required for paper feed retry. On the other hand, the control unit invalidates the retry function unless the image formation start condition is a start condition capable of securing a retry time.

  According to the present invention, it is possible to reduce paper feed mistakes in a situation where a paper feed retry time can be secured, such as a situation where throughput is suppressed.

  An embodiment of the present invention is shown below. The individual embodiments described below will help to understand various concepts, such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

[Embodiment 1]
FIG. 1 is a schematic cross-sectional view of a laser printer according to an embodiment. The laser printer 100 is an example of an image forming apparatus. Note that the image forming apparatus of the present invention may be realized as a printing apparatus, a copying machine, a multifunction machine, or a facsimile. The image forming method may be, for example, an electrophotographic method, an electrostatic recording method, a magnetic recording method, an ink jet method, a sublimation method, or an offset printing method.

  The laser printer 100 forms a color visible image on a sheet using an electrophotographic process. As is well known, the electrophotographic process has a charging step, an exposure step, a development step, a transfer step, and a fixing step. An electrostatic latent image is formed on an image carrier such as a photosensitive drum by the charging process and the exposure process. In the development process, the electrostatic latent image is developed to form a visible image. In the transfer step, the visible images of the respective colors are superimposed and transferred to form a color visible image, and the color visible image is transferred to the sheet. In the fixing step, the color visible image on the sheet S is fixed. Incidentally, the sheet may be called a recording paper, a recording material, a recording medium, a paper, a transfer material, or a transfer paper.

  The image forming unit includes a plurality of stations corresponding to different development colors. The image forming unit is an example of an image forming unit that forms an image on recording paper. Each station includes a photosensitive drum 5, an injection charger 7 as a primary charging unit, a developing unit 8, and a toner cartridge 11. The image forming unit includes an intermediate transfer body 12, a paper feeding unit 1, a transfer unit including a secondary transfer roller 9, and a fixing unit 13. In the exposure process, the scanner unit 10 irradiates the photosensitive drum 5 with light corresponding to the image signal, thereby forming an electrostatic latent image.

  The injection charger 7 for charging the photosensitive drum includes a sleeve 27. The four developing sections 8 that perform development of yellow (Y), magenta (M), cyan (C), and black (K) each include a sleeve 28.

  The sheets S are stacked on the sheet feeding cassette 2 of the sheet feeding unit 1, and are sent one by one to the conveyance path by the sheet feeding roller 39. The paper feed unit 1 is an example of a paper feed unit that feeds recording paper to a conveyance path that leads to an image forming unit. The registration sensor 19 detects that the sheet S has arrived at a predetermined position on the conveyance path (eg, in the vicinity of the registration roller 3). The registration sensor 19 is a sheet sensor that outputs a signal indicating that the sheet is detected from the arrival of the leading edge of the sheet until the trailing edge comes out.

  When the registration sensor 19 detects the leading edge of the sheet S, the conveyance of the sheet S is temporarily stopped. Note that a timer measures the time from when the sheet S is fed from the sheet feeding port of the sheet feeding unit 1 until it arrives at a predetermined position. The paper feed port may refer to the entire paper feed cassette, but here refers to the outlet of the paper feed cassette 2 (the entrance of the conveyance path). If the registration sensor 19 cannot detect the arrival of the leading edge of the sheet S before the timer finishes measuring a predetermined time, it is determined that a jam has occurred. In the present embodiment, if a retry time necessary for paper feed retry can be secured, the retry is executed. On the other hand, if the retry time cannot be secured, the image forming operation is stopped.

  A visible image on each photosensitive drum 5 is primarily transferred to the intermediate transfer body 12 by a primary transfer bias applied to the primary transfer roller 4. Further, the color visible image on the intermediate transfer body 12 is secondarily transferred onto the sheet S by the secondary transfer roller 9.

  The fixing unit 13 is an example of a fixing unit that fixes an unfixed toner image on a recording sheet. The fixing unit 13 is a device that fixes the color visible image on the sheet S while conveying the sheet S. The fixing unit 13 includes a fixing roller 14 that heats the sheet S and a pressure roller 15 that presses the sheet S against the fixing roller 14. The fixing roller 14 and the pressure roller 15 are formed in a hollow shape, and heaters 16 and 17 are incorporated therein. That is, the sheet S holding the color visible image is conveyed by the fixing roller 14 and the pressure roller 15, and the toner is fixed on the surface by applying heat and pressure. The sheet S after fixing the visible image is discharged to the paper discharge unit.

  Note that the sheet discharge sensor 20, the pre-fixing sensor 37, and the double-sided conveyance sensor 38 are also provided in the middle of the conveyance path, and the sheet conveyance status is managed based on these detection results.

(Image formation interval suppression control (throughput down control))
FIG. 2 is a schematic cross-sectional view of the fixing roller for explaining an excessive temperature rise suppression mechanism of the fixing unit. In this embodiment, in order to suppress an excessive temperature rise in the fixing unit 13, image formation interval control (hereinafter, throughput reduction control) is employed.

  Inside the fixing roller 14, a main thermistor 201 for detecting the temperature of the central portion and a sub thermistor 202 for detecting the temperature of the end portion are provided. When the sheet S passes through the fixing roller 14, the heater 16 performs heating control while feeding back the detected temperature of the main thermistor 201.

  Here, when a sheet having a width narrower than the width L in the longitudinal direction of the fixing roller 14 is used, the sheet passes through the central portion of the fixing roller 14 but does not pass through the vicinity of the end portion. This is because a centering mechanism for allowing the center line of the sheet S to pass through the central portion of the fixing roller 14 is provided in the conveyance path.

  However, since the heater 16 is controlled to be heated based on the temperature detected by the central thermistor 201, the temperature at the end of the fixing roller 14 may extremely increase. In order to prevent such extreme end-part overheating, the engine control unit performs throughput down control.

  The throughput reduction control is a control for reducing the number of sheets passing through the fixing unit 13 per unit time by gradually increasing the image formation time interval (image formation interval) in accordance with the detected temperature of the sub-thermistor 202. . By this control, temperature control bias when the sheet passes is suppressed.

  FIG. 3 is an example of a table showing a correspondence relationship between the detection temperature of the sub-thermistor, the throughput down level, and the throughput down offset time. For example, the offset time applied when changing from the first throughput (eg, level 0) to the second throughput (eg, level 1) smaller than the first throughput is +1000 milliseconds. The offset time when shifting from level 3 to level 4 is +10000 milliseconds.

  The engine control unit 403 applies the detected temperature of the sub-thermistor 202 to the table, and determines the corresponding throughput down level and throughput down offset time. The throughput down offset time is an extended time for extending the image forming interval. The engine control unit adds the determined throughput down offset time to the normal image formation interval.

(Printer system configuration)
FIG. 4 is a block diagram of the printer control mechanism. The laser printer 100 receives a print job from the host computer 400 by the controller unit 401. The controller unit 401 transmits the received print job data to the CPU 405 via the video interface unit 404 of the engine control unit 403. The engine control unit 403 includes an image processing GA 406, a fixing control unit 408, a sheet conveyance unit 409, a drive control unit 410, a throughput reduction control unit 411, and a paper feed retry control unit 412. The engine control unit 403 includes a memory 407 for storing various data. GA is an abbreviation for gate array.

  The image processing GA 406 executes image processing such as image data expansion. The fixing control unit 408 adjusts the fixing temperature based on the temperature detected by the main thermistor 201 and the sub-thermistor 202. The sheet conveying unit 409 is an example of a sheet feeding unit, and includes a stepping motor and a solenoid that drive various rollers for conveying the sheet. A drive control unit 410 controls a motor of the sheet conveying unit 409 and the like. The throughput down control unit 411 can switch between the first throughput and the second throughput based on the temperature detected by the sub-thermistor 202. The first throughput corresponds to the best throughput, for example. For example, the second throughput is lower than the first throughput in order to protect the fixing unit 13.

  For example, the sheet feed retry control unit 412 determines whether or not the sheet has arrived at a predetermined position on the conveyance path within a predetermined reference time. Whether or not the sheet has arrived at a predetermined position is determined according to the detection result of the registration sensor 19. If the sheet has not arrived at the predetermined position, the paper feed retry control unit 412 causes the sheet conveyance unit to execute a paper feed retry through the drive control unit 410. Accordingly, the drive control unit 410 is an example of a retry processing unit that causes the paper feeding unit to perform a paper feed retry if the recording paper does not arrive at a predetermined position on the transport path within a predetermined reference time.

  Further, the paper feed retry control unit 412 determines whether or not the image formation start condition applied to the sheet is a start condition that can secure a retry time necessary for paper feed retry. If the start condition is not sufficient to ensure the retry time, the paper feed retry control unit 412 disables the retry function in the sheet conveying unit. On the other hand, if the start condition can ensure the retry time, the paper feed retry control unit 412 validates the retry function in the sheet conveying unit. In this way, the paper feed retry control unit 412 validates the retry function in the retry processing means if the image formation start condition applied to the recording paper is a start condition that can secure the retry time required for paper feed retry. It is an example of the control means to do. The paper feed retry control unit 412 is also an example of a control unit that invalidates the retry function unless the image formation start condition applied to the recording paper is a start condition that can ensure a retry time.

  FIG. 5 is a diagram showing interface signals between the engine control unit 403 and the controller unit 401. In FIG. 5, a serial command transmission signal line 503 is a signal line for transmitting commands and commands from the controller unit 401 to the engine control unit 403 by serial communication. The serial status transmission signal line 504 is a signal line for transmitting status data from the engine control unit 403 to the controller unit 401 by serial communication in response to a command.

  The reference vertical synchronization signal line 505 is a signal line for transmitting a reference vertical synchronization signal (/ TOP signal) from the engine control unit 403 to the controller unit 401. The Y horizontal synchronization signal line 506 is a signal line for transmitting a yellow horizontal synchronization signal from the engine control unit 403 to the controller unit 401. The M horizontal synchronizing signal line 507, the C horizontal synchronizing signal line 508, and the K horizontal synchronizing signal line 509 are for transmitting horizontal synchronizing signals of magenta, cyan, and black from the engine control unit 403 to the controller unit 401, respectively.

  The Y image data signal line 510 is a signal line for transmitting a yellow image data signal from the controller unit 401 to the engine control unit 403. The M image data signal line 511, the C image data signal line 512, and the K image data signal line 513 are signal lines for transmitting magenta, cyan, and black image data signals from the controller unit 401 to the engine control unit 403.

  The controller unit 401 receives image information and a print command from the host computer 400, analyzes the received image information, and converts it into bit data. Further, the controller unit 401 sends a print reservation command, a print start command, and a video signal for each sheet to the engine control unit 403 via the video interface unit 404.

  The controller unit 401 transmits a print reservation command according to a print command from the host computer 400 to the engine control unit 403. Further, the controller unit 401 transmits a print start command to the engine control unit 403 at a timing when the engine control unit 403 is ready to print.

  The engine control unit 403 prepares for execution according to the order of reception of print reservation commands, and waits for a print start command from the controller unit 401. When the engine control unit 403 receives the print start command, the engine control unit 403 outputs to the controller unit 401 a / TOP signal that is a reference timing for the output of the video signal, and starts a printing operation according to the print reservation command.

  FIG. 6 is a timing chart showing a time difference between the reference vertical synchronizing signal and the image data signal of each color during the printing operation according to the first embodiment. The transmission timing of each color image data transmitted from the controller unit 401 to the engine control unit 403 when executing image formation will be described below with reference to FIG.

  In FIG. 6, T1 indicates the time difference between the reference vertical synchronizing signal and the yellow image data. That is, T1 corresponds to the time difference between the time when the controller unit 401 receives the reference vertical synchronization signal from the engine control unit 403 and the time when the yellow image data is transmitted to the engine control unit 403.

  Similarly, T2 indicates the time difference between the reference vertical synchronization signal and the magenta image data. T3 indicates a time difference between the reference vertical synchronizing signal and the cyan image data. T4 indicates the time difference between the reference vertical synchronizing signal and the black image data. The controller unit 401 corresponds to a time difference from when the reference vertical synchronization signal is received from the engine control unit 403 to when each color image data is transmitted to the engine control unit 403.

  When the controller unit 401 receives a print start command from the host computer 400, the controller unit 401 selects an image print mode and transmits a print start command to the engine control unit 403 via the serial command transmission signal line 503. . When the engine control unit 403 receives the print start command, the engine control unit 403 starts the print operation and notifies the controller unit 401 that the print operation is started via the serial status transmission signal line 504. When the printing operation is started, the drive control unit 410 starts driving the photosensitive drum driving motor that rotates the photosensitive drum 5, the intermediate transfer belt driving motor that rotates the intermediate transfer body 12, and each scanner unit 10. .

  Next, when image formation is ready for each color, the engine control unit 403 outputs a reference vertical synchronization signal (hereinafter referred to as a / TOP signal) via the reference vertical synchronization signal line 505. The controller unit 401 applies the Y image data signal line 510 to the Y image data signal line 510 when the time difference T1 stored in advance in the memory has elapsed from the falling edge of the reference vertical synchronization signal (/ TOP signal) via the reference vertical synchronization signal line 505. Outputs yellow image data. The image data is a signal for turning on / off a laser beam provided in the scanner unit. The yellow scanner unit 10 emits a laser beam based on the image data input from the controller unit 401 to form an electrostatic latent image on the photosensitive drum 5.

  The yellow developing unit 8 visualizes the electrostatic latent image formed on the photosensitive drum 5 with toner. The visible image on the photosensitive drum 5 is primarily transferred to the intermediate transfer body 12 by the primary transfer unit 4 disposed at the lowest point of the photosensitive drum 5. A visible image of yellow toner transferred to the intermediate transfer body 12 passes through the lowest point of the magenta photosensitive drum 5. The magenta image data is output to the M image data signal line 511 so that the visible image of the magenta toner comes to the lowest point of the magenta photosensitive drum 5 in accordance with the passage timing. Note that the output timing of the magenta image data is the timing when the time difference T2 has elapsed from the fall of the reference vertical synchronization signal.

  Similarly, the output timing of cyan image data is the timing at which the time difference T3 has elapsed since the fall of the reference vertical synchronization signal. Further, the output timing of the black image data is the timing at which the time difference T4 has elapsed since the fall of the reference vertical synchronization signal.

(Normal printing / TOP interval calculation method)
Next, a method for calculating the time interval (image formation interval) from the disclosure time of image formation on the preceding recording paper to the disclosure time of image formation on the subsequent recording paper will be described. The image formation interval corresponds to the transmission interval (/ TOP interval) of two adjacent reference vertical synchronization signals (/ TOP signals).

  When the engine control unit 403 receives the N-th print reservation command from the controller unit 401, the engine control unit 403 stores the reserved page sub-scanning direction size (that is, the sheet conveyance direction size) L_paper_size [N] in the memory 407.

  The registration sensor 19 includes a flag that rotates when the leading edge of the sheet comes into contact therewith. In order to return to the original position after the flag is rotated, a certain return time is required. Also, a removal time for removing flag chattering is required. In consideration of these, the minimum sheet distance L_gap_min necessary for reliably detecting the trailing edge of the preceding sheet and the leading edge of the succeeding sheet is determined in advance. If a paper distance shorter than the minimum paper distance L_gap_min is set, it becomes impossible to distinguish between the preceding sheet and the subsequent sheet (separation).

  In normal continuous printing, the time interval T_top_interval [N] from transmission of the / TOP signal for the Nth sheet to transmission of the / TOP signal for the (N + 1) th sheet is the rotational speed (circumferential speed) of the intermediate transfer body 12. It can be calculated using V_process.

T_top_interval [N] = (L_paper_size [N] + L_gap_min) / V_process (1)
(/ TOP interval calculation method when throughput is reduced)
A method of calculating the / TOP interval when the throughput down control is performed will be described. The engine control unit 403 refers to the table based on the throughput down level at the time when the N-th / TOP signal is transmitted. Thereby, the throughput down offset T_down_offset [N], which is the addition time of the / TOP interval, is determined. Using this, when the throughput down control is performed, the / TOP interval T_top_interval [N] from the Nth / TOP signal transmission to the (N + 1) th / TOP signal transmission is obtained from Equation (2). Calculated.

T_top_interval [N] = (L_paper_size [N] + L_gap_min) / V_process + T_down_offset [N] (2)
As described above, the / TOP interval is calculated from the sum of the conveyance time obtained by dividing the distance from the leading edge to the trailing edge in the conveyance direction of the recording paper by the conveyance speed and the throughput down offset time. This calculation may be handled by, for example, a paper feed retry control unit. In this case, the paper feed retry control unit functions as a calculation unit.

  FIG. 7 is a diagram illustrating the relationship between the image formation start timing, the sheet feeding start timing, and the re-conveyance start timing. T_gap_min in FIG. 7 is a time corresponding to the minimum sheet distance L_gap_min. Here, in order to improve the throughput, it is assumed that no paper feed retry is executed. Incidentally, when the paper feeding fails (when a jam is detected), the image forming operation is stopped.

  The color visible image formed on the intermediate transfer body 12 reaches the secondary transfer position after a predetermined time from the output of the / TOP signal. On the other hand, the engine control unit 403 starts the sheet S feeding operation after a predetermined time T_pick with reference to the output time of the / TOP signal corresponding to the color visible image formed on the intermediate transfer body 12. When there are a plurality of paper feed ports (paper feed cassettes), T_pick has a different value for each paper feed port. This is because the distance from each paper feed opening to the secondary transfer position is different.

  The conveyance time from the start of the sheet feeding operation until the sheet S arrives at the registration sensor 19 depends on the variation in the position of the sheet S in the sheet feeding cassette 2 and the path difference in the conveyance path. An error with respect to the design value occurs for each sheet. Therefore, the engine control unit 403 temporarily stops the sheet S at the detection position of the registration sensor 19 (hereinafter also referred to as a refeed standby position) and makes it wait.

  Thereafter, the engine control unit at the same speed as the transport speed of the intermediate transfer body 12 after a predetermined time T_refed, based on the output time point of the / TOP signal corresponding to the color visible image formed on the intermediate transfer body 12, The conveyance of the sheet S is resumed. This is called re-conveyance. As a result, the leading edge of the color visible image on the intermediate transfer body 12 and the leading edge of the sheet S that has been conveyed again coincide with each other at the secondary transfer position.

(Explanation of jam detection)
If the sheet feeding unit 1 fails to pick up a sheet or a sheet jam occurs in the conveyance, the leading edge of the sheet S reaches the detection position of the registration sensor 19 within a predetermined time T_jamwin from the feeding start time. There may not be. In this case, since the leading edge of the color visible image on the intermediate transfer body 12 and the leading edge of the sheet S conveyed again do not coincide with each other at the secondary transfer position, the engine control unit 403 performs a printing operation assuming that a jam has occurred. To stop.

  Here, the predetermined time T_jamwin is obtained by estimating in advance a maximum time such as a variation in the stacking position of the sheets S in the sheet feeding cassette 2, a sheet slip in the conveyance process to the registration sensor 19, and a path difference in the conveyance path. Is set. The predetermined time T_jamwin is used as a reference time necessary for conveying the sheet from the paper feed port of the paper feed cassette 2 to the detection position of the registration sensor 19. Hereinafter, T_jamwin is referred to as a paper feed completion reference time.

(Time constraints to ensure print productivity)
Even when the leading edge of the sheet S has not reached the detection position of the registration sensor 19 within a predetermined time T_jamwin after the start of paper feeding, the pickup may be successful by retrying the paper feeding operation. Therefore, the paper feed operation retry control (hereinafter also referred to as paper feed retry control) for the purpose of reducing the probability of jam occurrence will be described.

  FIG. 8 is a diagram for explaining an example of successful pickup by retrying the paper feeding operation. At time tA, the first paper feeding operation is started. If the leading edge of the sheet has not reached the registration sensor 19 by the time tB when the predetermined time T_jamwin has elapsed from the time tA, the paper feed retry control is executed. That is, the paper feed retry is started at time tB. If the sheet has not reached the registration sensor 19 by the time tC when the predetermined time T_jamwin has further passed from the time tB, the CPU 405 of the engine control unit 403 recognizes that a jam has occurred. If the sheet reaches the registration sensor 19 within a predetermined time T_jamwin from time tB, the paper feed retry control is successful. Therefore, when the retry is successful, the engine control unit continues the subsequent printing operation.

  When such a paper feed retry is performed, at least two paper feed completion reference times are required between the first paper feed start timing (time tA) and the re-transport start timing (time tD). .

  On the other hand, the distance between two continuous sheets entering the detection position of the registration sensor 19 needs to be set to be not less than the minimum distance L_gap_min.

  FIG. 9 is a diagram illustrating the relationship between the image formation start timing, the sheet feeding start timing, and the re-conveyance start timing. In FIG. 9, paper feed retry control is applied to all sheets. On the other hand, FIG. 7 is based on the assumption that no paper feed retry is performed. Therefore, when FIG. 7 and FIG. 9 are compared, it is necessary to widen the / TOP interval. This leads to a decrease in print productivity.

  FIG. 10 is a diagram illustrating an example of a paper feed retry according to related technology. As described above, there are time restrictions in performing the paper feed retry. Therefore, in this related technique, the paper feed retry control can be performed only for the first sheet of a print job (only the first sheet takes a long time from the start of feeding to the start of refeeding). That is, the paper feed retry is not executed for the second and subsequent sheets. In FIG. 10, the / TOP interval is set based on such a premise. As a result, print productivity is ensured to some extent.

  As described above, in order to execute the paper feed retry control during continuous printing, it is necessary to widen the / TOP interval, but this reduces the productivity of printing. Therefore, in the related techniques described in FIG. 7 and FIG. 10, priority is given to improving print productivity by not executing the paper feed retry control during continuous printing.

  Incidentally, the laser printer 100 may perform throughput down control, for example, in order to suppress excessive temperature rise of the fixing unit 13. If the addition time of the / TOP interval that accompanies the throughput down control is longer than the addition time of the / TOP interval that accompanies the paper feed retry control, it is possible to execute the paper feed retry control without incurring unnecessarily low print productivity. Become. That is, even during continuous printing, there is a possibility that a time during which the paper feed retry control can be executed without forcibly securing the retry time may occur.

  Therefore, in the first embodiment, a paper feed retry control unit 412 that performs the paper feed retry as long as it determines whether or not there is a time restriction in performing the paper feed retry and does not affect print productivity will be described.

  FIG. 11 is a diagram illustrating a relationship between the sheet feeding start timing and the re-conveyance start timing according to the embodiment. The horizontal axis indicates time. The vertical axis indicates the distance from the paper feed port along the transport path.

  As described with reference to FIG. 8, when a paper feed retry is performed, at least two paper feed completion reference times must be ensured between the initial paper feed start timing and the re-transport start timing. This is defined as a paper feed retry required time T_retry_margin. Note that the paper feed retry required time T_retry_margin is abbreviated as a retry time. In FIG. 11, T_paper_out indicates the time required from the start of refeeding until the trailing edge of the sheet S passes through the sheet feed port.

  Here, for convenience of explanation, it is assumed that throughput down control is performed during continuous printing and the / TOP interval for the (N + 1) th sheet and the (N + 2) th sheet is widened. A method for determining whether or not the sheet feeding retry control can be executed for the (N + 2) th sheet will be described.

  First, with reference to the / TOP signal transmission timing for the (N + 1) th sheet, the time required until the trailing edge of this sheet passes through the sheet feeding port (time tA) can be expressed by the following equation.

T_referenced + T_paperout (3)
In FIG. 11, T_gap_min is a time corresponding to the minimum inter-paper distance L_gap_min described with respect to the expression (1). Therefore, T_gap_min is calculated by Expression (4).

T_gap_min = L_gap_min / V_process (4)
V_process is a sheet conveyance speed. Here, in order to secure the minimum distance L_gap_min between the (N + 1) th sheet and the (N + 2) th sheet, the feeding of the (N + 2) th sheet may be started after time tB.

  Next, when a paper feed retry is performed on the (N + 2) th sheet, the first paper feed start timing (time tC) is calculated. Note that the time from the (N + 1) th / TOP signal transmission timing to the time tc is T_pre_pick [N + 1], and is calculated based on Equation (5).

T_pre_pick [N + 1] = T_top_interval [N + 1] + T_reeded−T_retry_margin (5)
Therefore, when the sheet feeding retry operation is performed on the (N + 2) th sheet, as shown in FIG. 11, the time tC may arrive after the time tB. Note that time tB is the timing when the minimum sheet interval time T_gap_min has elapsed since the trailing edge of the (N + 1) th sheet has passed through the sheet feeding port. The time tC is the paper supply start timing for the (N + 2) th sheet. Therefore, the condition for determining whether or not to perform the paper feed retry control for the (N + 2) th sheet can be expressed by the following expression from Expression (3) and Expression (5).

T_referenced + T_paperout + T_gap_min <T_top_interval [N + 1] + T_rerefed−T_retry_margin (6)
When formula (6) is rearranged using formula (2) and formula (4), formula (7) is obtained.

(L_paper_size [N + 1]) / V_process + T_down_offset [N + 1] −T_retry_margin−T_paperout> 0 Equation (7)
In other words, if the conditional expression (7) is satisfied during continuous printing, the execution time of the paper feed retry can be secured. For example, the offset time of the / TOP interval that is added to suppress overheating of the fixing unit 13 is longer than the offset time of the / TOP interval that is caused by performing the N + 2 sheet feeding retry. Therefore, if Expression (7) is established, it can be said that even if the paper feed retry is executed, there is no influence on the print productivity. In this way, the paper feed retry control unit calculates the sum of the paper feed time and the retry time required from the start of the retry operation until the trailing edge of the recording paper passes through the paper feed port of the paper feed means from the / TOP interval. It functions as a calculation means for calculating a difference by subtraction. The paper feed retry control unit functions as a comparison unit that compares the calculated difference with a threshold value (eg, zero).

  FIG. 12 is a flowchart illustrating an example of paper feed retry control according to the embodiment. In step S100, the paper feed retry control unit 412 of the engine control unit 403 determines whether throughput down control is being executed during continuous printing. For example, the paper feed retry control unit 412 inquires the throughput down control unit 411 whether or not the throughput is down. The paper feed retry control unit 412 determines whether or not the throughput down control is being executed based on the response content to the inquiry. If the throughput down control is being executed, the process proceeds to step S101.

  In step S101, the paper feed retry control unit 412 acquires the throughput down offset time T_down_offset [N + 1] from the above-described table.

  On the other hand, if the throughput down control is being executed, the process proceeds to step S102. In step S102, the paper feed retry control unit 412 substitutes zero for the throughput down offset time T_down_offset [N + 1]. If the initial value of the throughput down offset time T_down_offset [N + 1] is zero, step S102 may be omitted.

  In step S103, the paper feed retry control unit 412 calculates / TOP interval T_top_interval [N + 1]. For example, the / TOP interval T_top_interval [N + 1] is calculated by adding the throughput down offset time T_down_offset [N + 1] to the normal / TOP interval. As described above, the paper feed retry control unit 412 is an example of a determination unit that determines a time interval in conjunction with the throughput applied to the image forming unit.

  In step S104, the paper feed retry control unit 412 determines based on the / TOP interval whether the retry time can be secured without reducing the throughput. Therefore, the paper feed retry control unit 412 determines whether or not the retry time can be secured according to the time interval from the disclosure time of image formation on the preceding recording paper to the disclosure time of image formation on the subsequent recording paper. It is an example of the determination means to determine. For example, the paper feed retry control unit 412 determines, based on T_top_interval [N + 1], whether or not the paper feed retry execution possibility determination condition of Expression (6) or Expression (7) is satisfied. If the paper feed retry can be executed, the paper feed retry control unit 412 switches the paper feed retry function from invalid to valid, and proceeds to step S105. The throughput down offset time is an example of an image formation start condition applied to the recording paper.

  In step S105, the paper feed retry control unit 412 calculates a paper feed start timing T_pre_pick [N + 1] of the (N + 2) th sheet. This calculation is executed using, for example, Expression (5).

  In step S106, the paper feed retry control unit 412 monitors the elapsed time from the (N + 1) th / TOP signal transmission timing with a timer, and determines whether or not the elapsed time matches T_pre_pick [N + 1]. When T_pre_pick [N + 1] has elapsed from the N + 1-th / TOP signal transmission timing, the process proceeds to step S107.

  In step S107, the paper feed retry control unit 412 transmits a command to the drive control unit 410 to start feeding the N + 2th sheet. Upon receiving this command, the drive control unit 410 rotates the stepping motor of the sheet conveying unit 409.

  In step S108, the paper feed retry control unit 412 monitors the elapsed time from the (N + 1) th sheet / TOP signal transmission timing, and determines whether or not the elapsed time has reached T_top_interval [N + 1]. When T_top_interval [N + 1] has elapsed, the process proceeds to step S109.

  In step S <b> 109, the paper feed retry control unit 412 transmits a / TOP signal for the (N + 2) th sheet to the controller unit 401. If the CPU 405 or the paper feed retry control unit 412 detects a jam between steps S105 and S108, the drive control unit 410 retry the paper feed.

  On the other hand, in S104, if the paper feed retry execution determination condition is not satisfied (if the retry time cannot be secured without reducing the throughput), the paper feed retry control unit 412 disables the retry function. Then, the process proceeds to step S110. As a result, the sheet feeding retry is not applied to the (N + 2) th sheet. Therefore, when a jam occurs, the image forming operation is stopped.

  In step S110, the paper feed retry control unit 412 monitors the elapsed time from the / TOP signal transmission timing for the (N + 1) th sheet with a timer, and determines whether the elapsed time has reached T_top_interval [N + 1]. To do. When T_top_interval [N + 1] has elapsed, the process proceeds to step S109. In step S <b> 109, the paper feed retry control unit 412 transmits a / TOP signal for the (N + 2) th sheet to the controller unit 401.

  As described above, in the first embodiment, if the image formation start condition applied to the recording sheet is a start condition that can secure the retry time required for the retry of the sheet feeding operation, the retry function in the retry processing unit is performed. Valid. On the other hand, if the start condition of image formation is not a start condition that can ensure a retry time, the retry function is disabled. More specifically, the presence / absence of a paper feed retry time constraint is determined in consideration of the offset time of the / TOP interval by throughput down control. As a result, paper feed retry is executed as long as print productivity is not affected. Therefore, it is possible to execute a paper feed retry without causing unnecessary reduction in print productivity.

  In this embodiment, a retry time (T_retry_margin) can be secured according to the time interval (T_top_interval [N + 1]) from the disclosure time of image formation on the preceding recording paper to the disclosure time of image formation on the subsequent recording paper. It is determined whether or not. In particular, in this embodiment, the time interval (T_top_interval [N + 1]) is determined in conjunction with the throughput applied to the image forming unit (S100 to S103). Therefore, when the throughput decreases for some reason, the paper feed retry function becomes effective. This is because when the throughput is lowered, the distance between sheets (interval between sheets) is extended, and it becomes easy to secure the retry time.

  In the present embodiment, for convenience of explanation, it has been described that a paper feed retry is allowed only once. For this reason, the paper feed retry required time T_retry_margin coincides with the paper feed completion reference time (2 × T_jamwin) for two times. However, this premise is merely an example. The time required for paper feed retry according to the present invention can be set in accordance with the allowable number of paper feed retries.

[Embodiment 2]
In the first embodiment, the engine control unit determines whether the retry time can be secured (whether there is a time constraint) based on the offset time of the / TOP interval generated by the throughput down control. In the second embodiment, a further application example of the present invention will be described. That is, in the second embodiment, it is determined whether or not the retry time can be secured (whether or not there is a time constraint) in consideration of the addition time of the / TOP interval depending on the command from the controller unit 401. As a result, the paper feed retry function is effective as long as print productivity is not affected.

  Normally, the controller unit 401 receives image information and a print command from the host computer 400, analyzes the image information and converts it into a video signal, and then transmits a print start command and a video signal to the engine control unit 403. The engine control unit 403 monitors whether or not the print reservation command and the print start command for the (N + 1) th sheet are received within a predetermined time T_best from the / TOP signal output timing for the Nth sheet. When these commands are received within T_best, the engine control unit 403 performs image formation and paper feeding so as to achieve the fastest print productivity in the image forming unit. The video interface unit 404 of the engine control unit 403 is an example of a receiving unit that receives a command related to an image formation start condition.

  FIG. 13A is an exemplary timing chart related to image formation. The engine control unit 403 starts image formation by outputting a / TOP signal for the (N + 1) th sheet. If a print start command for the (N + 2) th sheet has not been received when a predetermined time T_timeout has elapsed since the start of image formation, the engine control unit 403 performs post-rotation to end printing. Upon receiving a print start command for the (N + 2) th sheet after starting the post-rotation, the engine control unit 403 executes the pre-rotation after the end of the post-rotation. The pre-rotation is a rotation operation for preparing image formation. When the preparation for image formation is completed, the engine control unit 403 performs printing on the (N + 2) th sheet.

  As described above, the engine control unit 403 may not receive the print start command for the (N + 2) th sheet within the predetermined time T_timeout. This is because, for example, the controller unit 401 takes time to analyze image information and convert it to bit data. In this case, since the post-rotation is once executed before printing all the pages requested from the host computer 400, the time performance until the job is completed is greatly lowered. As a method for avoiding such post-rotation, a method for transmitting a command for postponing the start timing of post-rotation from the controller unit 401 to the engine control unit 403 can be considered. By delaying the start timing of the post-rotation, the / TOP interval is temporarily extended.

  FIG. 13B is another exemplary timing chart related to image formation. When the controller unit 401 determines that the print start command for the (N + 2) th sheet cannot be transmitted within the predetermined time T_timeout, the controller unit 401 transmits to the engine control unit 403 a postponement command for postponing the timing of starting the post-rotation by T_delay. Upon receiving the postponement command, the engine control unit 403 starts printing the N + 2th sheet without starting the post-rotation until a predetermined time T_timeout has elapsed from the / + 1 signal of the (N + 1) th sheet and further, the postponement time T_delay has elapsed. Wait for command. If the print start command for the (N + 2) th sheet is received before the postponement time T_delay elapses, the engine control unit 403 outputs the / TOP signal for the (N + 2) th sheet when a predetermined time T_timeout + T_delay has elapsed from the / TOP signal. Thereby, printing of the (N + 2) th sheet is started.

  Note that by delaying the start timing of the post-rotation, the / TOP interval is temporarily extended. That is, the engine control unit 403 is an example of an extension unit that extends the / TOP interval according to a command. An example of the command is a command for postponing post-rotation in the image forming means, but it goes without saying that the present invention can be applied to any command that changes the image forming start condition.

  As described above, by using the postponement command (“post-rotation postponement command”), it is possible to prevent a decrease in time performance until the job is completed. Note that the postponement time T_delay may not be a fixed value. For example, the controller unit 401 may set the postponement time to an arbitrary time according to a command system defined separately.

  FIG. 14 is a flowchart illustrating an example of paper feed retry control according to the embodiment. Note that the same reference numerals are assigned to steps common to FIG. 12 to simplify the description.

  In step S <b> 200, the paper feed retry control unit 412 determines whether a post-rotation postponement command has been received from the controller unit 401. If received, the process proceeds to step S201.

  In step S201, the paper feed retry control unit 412 calculates an addition time to be added to the / TOP interval. First, the paper feed retry control unit 412 acquires the postponement time T_delay. The postponement time T_delay is read from the memory 407 or notified from the controller unit 401, for example. It is assumed that T_timeout is also stored in the memory 407 in advance.

  In step S203, the paper feed retry control unit 412 calculates the / TOP interval T_top_interval [N + 1] in consideration of the postponement time T_delay. The / TOP interval T_top_interval [N + 1] calculates the / TOP interval T_top_interval [N + 1] from the N-th / TOP signal transmission timing to the (N + 1) -th / TOP signal transmission. This calculation is calculated using, for example, the equation (8).

T_top_interval [N + 1] = (L_paper_size [N + 1] + L_gap_min) / V_process + T_timeout + T_delay
... Formula (8)
Here, symbols other than T_timeout and T_delay are as already described with respect to the equation (1).

  By the way, if the post-rotation postponement command is not received from the controller unit 401 in step S200, post-rotation postponement is not necessary, and the process proceeds to step S202. In step S202, the paper feed retry control unit 412 sets the addition time to zero. That is, T_timeout + T_delay = 0. If the initial value of the addition time is zero, step S202 may be omitted.

  In step S <b> 204, the paper feed retry control unit 412 determines whether or not the conditions for determining whether or not to perform paper feed retry control are satisfied. If the condition for determining whether or not to execute the paper feed retry control is satisfied, the paper feed retry control unit 412 enables the retry function. On the other hand, if the condition for determining whether or not to perform the paper feed retry control is not satisfied, the paper feed retry control unit 412 disables the retry function. The conditions for determining whether or not to perform paper feed retry control according to the second embodiment are as follows.

  Here, it is assumed that a post-rotation postponement command is transmitted during continuous printing, and the / TOP interval between the (N + 1) th sheet and the (N + 2) th sheet increases. If the time secured by the increase in the / TOP interval is longer than the time required for the retry, the retry function is enabled. On the other hand, if the time ensured by the expansion of the / TOP interval is less than the time required for the retry, the retry function is invalidated.

  As described with reference to FIG. 11, when the paper feed retry is enabled for the (N + 2) th sheet, the time tC may arrive after the time tB. Therefore, the condition for determining whether or not to perform the paper feed retry control is the same as that in Expression (6).

When formula (6) is rearranged using formula (8) and formula (4), formula (9) is obtained.
(L_paper_size [N + 1]) / V_process + T_timeout + T_delay−T_retry_margin−T_paperout> 0 Equation (9)
In other words, if the conditional expression (9) is satisfied, it can be said that there is no influence on the print productivity even if the paper feed retry is executed. The processes after step S204 (S105 to S110) are as already described.

  As described above, in the second embodiment, the / TOP interval is extended according to the command related to the image formation start condition. If the retry can be executed within the extended time, the retry function is set to be valid, and if the retry cannot be executed within the extended time, the retry function is set to be invalid. As a result, the paper feed retry control can be executed without causing an unnecessarily lower print productivity.

[Embodiment 3]
In the second embodiment, the method of determining whether or not to execute the paper feed retry in consideration of the addition time (extension time) of the / TOP interval depending on the command has been described. In the third embodiment, as a specific example of the present invention, a method for determining whether or not to perform paper feed retry in consideration of the / TOP interval corresponding to the image forming mode (printing mode) will be described.

  As already described with respect to equation (1), the / TOP interval during normal printing is calculated from the size of the page in the sub-scanning direction and the inter-paper distance. On the other hand, the print mode of the page reserved by the controller unit 401 may be a mode in which the image quality of the output paper should be prioritized over the print productivity. Examples of the image quality priority mode include a gloss mode and an OHT (overhead transparency sheet) mode. Since the inter-paper distance in the image quality priority mode is set larger than the inter-paper distance in the normal mode, the / TOP interval is also increased.

  FIG. 15A is a diagram illustrating the timing at which the sheet passes through the fixing unit in the normal mode. FIG. 15B is a diagram illustrating the timing at which the sheet passes through the fixing unit in the image quality priority mode. 15A and 15B also show the fixing temperature in the fixing unit 13.

  For example, it is assumed that the heat capacity of the sheet passing through the fixing unit 13 is relatively large. As shown in FIG. 15A, when a plurality of sheets are continuously conveyed with the distance between the sheets kept at a minimum, heat cannot be sufficiently stored in the non-sheet passing section depending on the heating ability of the fixing unit 13. . For this reason, the fixing temperature gradually decreases with time, and a sufficient amount of heat cannot be applied to the sheet. In general, if a sufficient amount of heat cannot be applied to a toner image transferred onto a sheet, problems such as insufficient gloss (glossiness) on the sheet and defective images occur.

  For this reason, in a mode for printing on a sheet such as gloss paper or gloss film where sufficient gloss is desired, the non-sheet passing section is intentionally set large as shown in FIG. 15B. As a result, the fixing temperature is sufficiently maintained. As described above, the engine control unit 403 may change the inter-paper distance according to the image forming mode. Such control is referred to as “inter-sheet offset control”.

  In the present embodiment, it is determined whether or not the retry time can be ensured when the / TOP interval is changed by executing the inter-sheet offset control according to the image forming mode. As a result of changing the / TOP interval, if the retry time can be secured, the paper feed retry function is set to be valid. If the retry time cannot be secured, the paper feed retry function is disabled.

  FIG. 16 is a flowchart illustrating an example of paper feed retry control according to the embodiment. Note that the same reference numerals are assigned to the steps common to FIGS. 12 and 14 to simplify the description.

  In step S <b> 300, the paper feed retry control unit 412 determines whether the image forming mode designated by the controller unit 401 is an image forming mode that requires the inter-paper offset control. For example, the memory 407 stores a table indicating whether or not the paper gap offset control is required for each of a plurality of image forming modes, and the paper feed retry control unit 412 refers to this table. Make a decision. If the paper gap offset control is necessary, the process proceeds to step S301.

  In step S301, the paper feed retry control unit 412 determines the inter-paper addition distance L_gap_offset. The inter-paper addition distance L_gap_offset is an addition value for the minimum inter-paper distance. The inter-paper addition distance L_gap_offset may be stored in advance in the memory 407 for each image forming mode, or may be calculated based on some arithmetic expression. The inter-paper addition distance L_gap_offset may be determined experimentally or by theoretical analysis. Thereafter, the process proceeds to step S303.

  By the way, if it is determined in step S200 that the paper gap offset control is not necessary, the process proceeds to step S302. In step S302, the paper feed retry control unit 412 sets the inter-paper addition distance to zero. That is, L_gap_offset = 0. If the initial value of L_gap_offset is zero, step S302 may be skipped. Thereafter, the process proceeds to step S303.

  In step S303, the paper feed retry control unit 412 calculates the / TOP interval T_top_interval [N + 1] in consideration of the inter-paper addition distance L_gap_offset. / TOP interval T_top_interval [N + 1] can be calculated using, for example, the following equation.

T_top_interval [N + 1] = (L_paper_size [N + 1] + L_gap_min + L_gap_offset) / V_process (10)
In step S304, the paper feed retry control unit 412 determines whether a condition for determining whether or not to perform paper feed retry control is satisfied. If the condition for determining whether or not to execute the paper feed retry control is satisfied, the paper feed retry control unit 412 enables the retry function. Thereafter, the process proceeds to step S105. On the other hand, if the condition for determining whether or not to perform the paper feed retry control is not satisfied, the paper feed retry control unit 412 disables the retry function. Then, it progresses to step S110. The conditions for determining whether or not to perform paper feed retry control according to the third embodiment are as follows.

  As described with reference to FIG. 11, in order to be able to execute the paper feed retry on the (N + 2) th sheet, the time tC should arrive after the time tB. Therefore, the condition for determining whether or not to perform the paper feed retry control for the (N + 2) th sheet can be expressed by Expression (6). Therefore, when Expression (6) is rearranged using Expression (10) and Expression (4), Expression (11) is obtained.

(L_paper_size [N + 1] + L_gap_offset) / V_process−T_retry_margin−T_paperout> 0 Expression (11)
In other words, if the expression (11) is satisfied, it can be said that there is no influence on the print productivity by executing the paper feed retry.

  As described above, the third embodiment focuses on the fact that the engine control unit 403 changes the / TOP interval according to the image forming mode. Therefore, the paper feed retry control unit 412 is an example of a changing unit that changes the time interval according to the image forming mode. Then, the paper feed retry control unit 412 determines whether the retry time can be secured based on the / TOP interval changed according to the image forming mode. If the image forming mode is such that a retry time can be secured without affecting print productivity, the paper feed retry function is enabled.

  Note that the paper feed retry control unit 412 may determine the / TOP interval according to the adjustment time required for adjusting the temperature of the fixing unit 13 that is different for each image forming mode. This is because, as described above, the length of the non-sheet passing section is determined by the sheet type (heat capacity), and the image forming mode can be determined by the sheet type. In this case, the paper feed retry control unit 412 functions as a determination unit that determines the time interval according to the adjustment time required for adjusting the temperature of the fixing unit, which is changed based on the image forming mode.

  As described above, according to the first to third embodiments, a paper feed error in a situation where a paper feed retry time can be secured, such as a situation where throughput is suppressed, is reduced. Since the paper feed retry is interposed only in a situation where the retry time can be secured without affecting the print productivity, there is no need to forcibly or uniformly increase the / TOP interval.

1 is a schematic cross-sectional view of a laser printer according to an embodiment. FIG. 3 is a schematic cross-sectional view of a fixing roller for explaining an excessive temperature rise suppression mechanism of a fixing unit. It is an example of the table which showed the correspondence of the detection temperature of a sub thermistor, a throughput down level, and a throughput down offset time. It is a block diagram of the control mechanism of a printer. It is a figure which shows the interface signal of the engine control part 403 and the controller part 401. 6 is a timing chart showing a time difference between a reference vertical synchronization signal and an image data signal of each color during a printing operation according to the first embodiment. FIG. 6 is a diagram illustrating a relationship between an image formation start timing, a sheet feeding start timing, and a re-conveyance start timing. FIG. 10 is a diagram for explaining an example of successful pickup by retrying a paper feeding operation. FIG. 6 is a diagram illustrating a relationship between an image formation start timing, a sheet feeding start timing, and a re-conveyance start timing. It is a figure which shows an example of the paper feed retry which concerns on related technology. 6 is a diagram illustrating a relationship between sheet feeding start timing and re-conveyance start timing according to the embodiment. FIG. 6 is a flowchart illustrating an example of paper feed retry control according to the embodiment. 3 is an exemplary timing chart related to image formation. 6 is another exemplary timing chart related to image formation. 6 is a flowchart illustrating an example of paper feed retry control according to the embodiment. FIG. 6 is a diagram illustrating timing when a sheet passes through a fixing unit in a normal mode. FIG. 6 is a diagram illustrating timing at which a sheet passes through a fixing unit in an image quality priority mode. 6 is a flowchart illustrating an example of paper feed retry control according to the embodiment.

Claims (9)

An image forming apparatus,
Image forming means for forming an image on recording paper;
A paper feeding means for feeding recording paper to a conveyance path leading to the image forming means;
Retry processing means for causing the paper feed means to perform a paper feed retry if the recording paper does not arrive at a predetermined position in the transport path within a predetermined reference time;
If the image formation start condition is a start condition that can ensure the retry time required for the paper feed retry, the retry function in the retry processing unit is validated, and the image formation start condition is the start condition that can ensure the retry time. Otherwise, the image forming apparatus includes control means for invalidating the retry function. The control means includes
And determining means for determining whether or not the retry time can be secured according to a time interval from a disclosure time of image formation on the preceding recording paper to a disclosure time of image formation on the subsequent recording paper. The image forming apparatus according to claim 1. The control means includes
The image forming apparatus according to claim 2, further comprising a determining unit that determines a time interval in conjunction with a throughput applied to the image forming unit. The determination means includes
This is applied when the conveyance time obtained by dividing the distance from the leading edge to the trailing edge in the conveyance direction of the recording paper by the conveyance speed and when the first throughput is changed to a second throughput smaller than the first throughput. From the sum of the offset time,
A calculating means for calculating a difference by subtracting a sum of a paper feeding time required from the start of the paper feeding retry until the trailing edge of the recording paper passes through the paper feeding port of the paper feeding means and the retry time;
The image forming apparatus according to claim 2, further comprising a comparison unit that compares the difference with a threshold value. Receiving means for receiving a command related to the image forming start condition;
Extending means for extending the time interval in response to the command,
The image forming apparatus according to claim 2, wherein the determination unit determines whether or not the retry time can be secured according to the extended time interval.   The image forming apparatus according to claim 5, wherein the command is a command for postponing post-rotation in the image forming unit.   The image forming apparatus according to claim 2, further comprising a changing unit that changes the time interval according to an image forming mode. The image forming means includes a fixing means for fixing an unfixed toner image on a recording paper,
8. The change unit includes a determination unit that determines the time interval according to an adjustment time required for adjusting the temperature of the fixing unit, which is changed based on the image forming mode. The image forming apparatus described in 1. Image forming means for forming an image on recording paper;
A paper feeding means for feeding recording paper to a conveyance path leading to the image forming means;
If the recording paper does not arrive at a predetermined position in the transport path within a predetermined reference time, the image forming apparatus includes a retry processing unit that causes the paper feeding unit to perform a paper feeding retry. And
If the image formation start condition is a start condition that can secure a retry time required for the paper feed retry, a step of enabling a retry function in the retry processing unit;
And a step of invalidating the retry function if the start condition of the image formation is not a start condition capable of securing the retry time.

Images