JP2012123268A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce first print-out time while suppressing a positional shift of an image.SOLUTION: A CPU 102 determines initial time (TS) by subtracting, from transition time (T0;Tf) taken by image forming means to undergo transition from its start to a stable state, first conveyance time (TB;TC) corresponding to a length of a margin provided in a head portion of a recording medium along a conveyance direction and second conveyance time (TA) that has elapsed from timing of starting paper feed by paper feeding means to timing of detecting the recording medium by detecting means. Furthermore, the CPU 102 controls the paper feeding means so that the paper feeding means may start the paper feed at timing when the initial time (TS) has elapsed from timing of the start of the image forming means.

Description

  The present invention relates to an image forming apparatus that forms an image on a recording medium.

  In an image forming apparatus of an electrophotographic system or an electrostatic recording system, a toner image is formed on an image carrier in advance, and then the image is transferred to a conveyed recording medium. In particular, the image forming apparatus stably obtains a good image by starting the paper feeding and conveyance after the preparation operation of the image forming means such as the exposure device and the fixing device is completed. For example, the feeding of the recording medium is started at the timing when the rotation speed of the scanner motor provided in the exposure apparatus reaches the target value and the temperature of the fixing device reaches the target temperature.

  The image forming apparatus can both form a good image and have a short first printout time (FPOT), which is the time from when an image formation is instructed until the recording medium on which the image is formed is output. Is required. As described above, in order to form a good image, it is necessary to wait until the preparation operation of the exposure device and the fixing device is completed, so this waiting time is a limitation of FPOT.

  According to Patent Document 1, in order to shorten the FPOT, formation of a latent image is started simultaneously with the completion of preparation of the exposure apparatus, and a toner image corresponding to the latent image reaches the transfer roller and at the same time, the leading edge of the recording medium reaches the transfer roller. Thus, a configuration for controlling the paper feed timing is disclosed. In Patent Document 2, the recording medium is fed at a timing when the rotational speed of the scanner motor reaches a target value lower than the final target value, and at the same time the rotational speed of the scanner motor reaches the final target value, A configuration is disclosed in which the paper feed timing is controlled so as to reach the transfer roller.

JP-A-6-64219 JP 2003-280488 A

  However, Patent Documents 1 and 2 do not consider the margin that exists at the leading edge of the image to be printed. For this reason, the engine control unit that controls the image forming engine outputs a TOP signal simultaneously with the completion of preparation of the exposure apparatus, and the image data generation unit transmits the raster image data (margin data) of the margin when receiving the TOP signal. In other words, although preparation for image formation is complete, in practice, an image is formed after the blank portion is formed on the recording medium. This means that there is a possibility that the FPOT can be further shortened by the time for forming the blank portion.

  As one proposal, a method for shortening the FPOT by outputting the TOP signal forward by the amount of the blank formed on the paper can be considered. However, in this proposal, the TOP signal is output before the scanner converges to the target rotational speed. For this reason, in the mechanism that determines the image position based on the number of times the scanner scanning signal (BD signal) is output after the TOP signal output timing, the TOP signal is output during a period in which the BD signal cycle is unstable. As a result, the position of the output image is also out of order. In general, in order to match the leading edge of the recording medium and the image forming position, a TOP signal is output after the position of the recording medium is detected by a sensor. Therefore, when the output timing of the TOP signal is advanced by the amount corresponding to the margin, the TOP signal is output before the position of the recording medium is detected by the sensor, depending on the length of the advance time according to the amount of the margin. For this reason, it is directly affected by the conveyance variation that occurs when paper is fed, and the output position of the actual image may be shifted.

  Therefore, an object of the present invention is to shorten the first printout time while preventing the image position from shifting.

  The image forming apparatus includes a sheet feeding unit that feeds a recording medium to a conveyance path, a detection unit that detects the recording medium in the conveyance path, a signal output unit, an image data output unit, an image formation unit, a determination unit, and a feeding unit. A paper control means is provided. The signal output means outputs a signal indicating the start of image writing. The image data output means outputs the image data when a signal indicating the start of image writing is input. The image forming unit forms an image corresponding to the image data output by the image data output unit. The determining unit determines the length of the blank portion formed at the head of the recording medium in the transport direction from the transition time (T0; Tf) from when the image forming unit is activated until the image forming unit transitions to a stable state. The initial time is obtained by subtracting the corresponding first transport time (TB; TC) and the second transport time (TA) from the timing when the paper feeding means starts feeding to the timing when the detecting means detects the recording medium. (TS) is determined. The sheet feeding control unit controls the sheet feeding unit so that the sheet feeding unit starts feeding at the timing when the initial time (TS) has elapsed from the timing when the image forming unit is activated.

  According to the present invention, it is possible to shorten the first printout time while preventing the shift of the image position.

1 is a diagram illustrating a configuration of an image forming system according to Embodiment 1. FIG. 1 is a diagram illustrating a basic configuration of an image forming apparatus according to Embodiment 1. FIG. FIG. 3 is a diagram illustrating a control operation of a controller during image formation in Embodiment 1. FIG. 5 is a diagram illustrating raster image data and actual image data start positions in the first embodiment. 3 is a diagram illustrating a control operation of the image forming apparatus during image formation in Embodiment 1. FIG. FIG. 6 is a diagram illustrating sheet feeding control during image formation according to the first exemplary embodiment. FIG. 6 is a diagram illustrating image formation timing executed when paper feed control is performed in the first exemplary embodiment. FIG. 3 is a diagram illustrating various distances in the first embodiment. FIG. 3 is a diagram illustrating image forming processing according to the first exemplary embodiment. 10 is a diagram illustrating sheet feeding control during image formation in Embodiment 2. FIG. FIG. 10 is a diagram illustrating image formation timing executed when sheet feeding control is performed in the second embodiment.

[Example 1]
The image forming apparatus according to the first embodiment will be described with reference to FIGS. In FIG. 1, an image forming apparatus 100 receives job data for forming an image from a host computer 101, which is an example of an external device, and forms an image on a recording medium. The image forming apparatus 100 may be any of a printing apparatus, a printer, a copier, a multifunction machine, and a facsimile. The recording medium may also be called a recording material, paper, sheet, transfer material, or transfer paper. The job data includes image data and a print command. The host computer 101 may be a personal computer, a personal digital assistant (PDA), a digital camera, or the like.

  The image forming apparatus 100 includes a print controller 120 and an image forming engine 130. The print controller 120 functions as an image data generation unit and includes various units. The CPU 102 is a control unit that comprehensively controls the entire print controller 120. The CPU 102 executes, for example, processing for expanding image data (PDL data or the like) into raster image data, processing for converting a print command into a print reservation / print instruction command, margin deletion, margin length measurement, and the like. . Raster image data is a kind of image data. The communication control circuit 103 receives image data and a print command transmitted from the host computer 101, and transmits information indicating the printing status to the host computer 101. The RAM 104 is a kind of storage device, and temporarily stores programs, raster image data, and the like. The RAM 104 may be a storage device such as a hard disk drive or a solid state drive. The video interface control circuit 105 transmits raster image data, margin data indicating the length of the margin, and a print reservation / print instruction command to the image forming engine 130. Further, the video interface control circuit 105 receives a TOP signal, a BD signal, and a status signal indicating the state of the image forming engine from the image forming engine 130. The TOP signal is a signal for instructing start of output of raster image data. The BD signal is a signal that is output once every time the light beam operated by the rotary polygon mirror scans one line on the image carrier. When the CPU 102 receives image data and a print command from the host computer 101, the CPU 102 converts the image data into raster image data, analyzes the print command, and generates a print reservation command that matches the configuration of the image forming engine 130. Then, the CPU 102 sends a print reservation command, a print start command for instructing printing start, margin data indicating the length of the margin, and raster image data to the image forming engine 130 via the video interface control circuit 105. The video interface control circuit 105 functions as image data output means for outputting image data when a signal indicating the start of image writing is input.

  The image forming engine 130 functions as an image forming unit that forms an image corresponding to the image data output by the image data output unit. The CPU 106 is a control unit that comprehensively controls the entire image forming engine 130. The high voltage control circuit 107 is a circuit that controls application of a high voltage (high voltage) necessary for image formation. The charging roller 108 is applied with a charging bias controlled by the high voltage control circuit 107, and uniformly charges the circumferential surface of the photosensitive drum 206 shown in FIG. The developing device 109 is a developing unit that develops the latent image to form a developer image, and develops the electrostatic latent image formed on the peripheral surface of the photosensitive drum 206 as a toner image with the developer (toner). The developing device 109 includes a developing roller 208 to which a developing bias controlled by the high voltage control circuit 107 is applied. The transfer roller 110 is a transfer unit that transfers the developer image to a recording medium, and is a contact transfer member that transfers the toner image developed by the developing device 109 to a predetermined recording medium. A transfer bias controlled by the high voltage control circuit 107 is applied to the transfer roller 110. The high voltage control circuit 107 receives the PWM signal indicating the applied voltage level designated by the CPU 106 and the CLK signal for controlling the frequency of the applied voltage, and applies voltages to the charging roller 108, the developing device 109, and the transfer roller 110, respectively. To do. The fixing control circuit 111 controls a fixing device including a fixing roller 212 and a pressure roller 213. The fixing roller 212 and the pressure roller 213 are an example of a fixing unit that heats a developer image and fixes it on a recording medium. The fixing control circuit 111 detects the temperature of the fixing device by the thermistor 112 and controls the value of the current supplied to the heater so that the temperature of the fixing device becomes the target temperature. The TOP sensor 113 is an example of a detection unit that detects a recording medium in the conveyance path. The TOP sensor 113 detects the recording medium conveyed through the conveyance path 200 and detects the recording medium while the recording medium is being detected. The detection signal which shows that is output. The DC brushless motor 114 is a motor that drives a roller related to image formation such as the photosensitive drum 206. The DC brushless motor 115 is a motor that drives the fixing roller 212 and the pressure roller 213. The scanner motor 117 is a motor that rotates a rotary polygon mirror such as a polygon mirror. The rotation speed sensor 121 is a sensor that detects the rotation speed of the scanner motor 117. The laser diode 118 is a light source that irradiates the polygon mirror with a light beam. The scanner control circuit 116 is a circuit that controls the scanner motor 117 and the laser diode 118 so that a latent image corresponding to raster image data is formed on the photosensitive drum 206. The scanner control circuit 116 receives the scanner motor drive signal output from the CPU 106, activates the scanner motor 117, and controls the scanner motor 117 so that the rotational speed detected by the rotational speed sensor 121 becomes the target value. . Further, the scanner control circuit 116 controls the laser diode 118 according to the laser on / off signal output from the CPU 106. The scanner control circuit 116 transmits a SPEED signal indicating the rotation speed of the scanner motor 117 monitored by the rotation speed sensor 121 to the CPU 106. The video interface control circuit 119 receives raster image data, margin data, a print reservation command, and a print instruction command from the print controller 120. The video interface control circuit 119 transfers the raster image data to the scanner control circuit 116. Further, the video interface control circuit 119 transfers margin data, a print reservation command, and a print instruction command to the CPU 106. When the video interface control circuit 119 receives a TOP signal output instruction from the CPU 106, the video interface control circuit 119 outputs a TOP signal to the print controller 120. The video interface control circuit 119 is an example of a signal output unit that outputs a signal indicating the start of image writing. The video interface control circuit 119 outputs a status signal indicating the state of the image forming engine 130 to the print controller 120 by the BD signal described above. The CPU 106 prepares for image formation according to a print reservation command and waits for a print start command. When the print start command is received, the CPU 106 starts printing according to the reserved print contents. The CPU 106 outputs a TOP signal for starting the raster image data output to the print controller 120 at a predetermined timing.

  As shown in FIG. 2, in the image forming apparatus 100, a recording medium (hereinafter referred to as a recording medium) housed in a recording medium cassette 202 is fed to the conveyance path 200 by a paper feed roller 203. The paper supply roller 203 functions as a paper supply unit that supplies a recording medium to the conveyance path. The driving roller 204 is a roller that further conveys the recording medium fed to the conveyance path 200. In the transport path 200, a TOP sensor 113 is provided downstream of the drive roller 204 in the transport direction. The cartridge 209 includes a photosensitive drum 206, a charging roller 108, and a developing roller 208. The transfer roller 110 is pressed against the photosensitive drum 206 with a predetermined pressure to form a nip portion as a transfer portion. The paper feed roller 203, the photosensitive drum 206, the charging roller 108, the developing roller 208, and the transfer roller 110 are driven by a DC brushless motor 114. The optical unit 211 is exposure means for forming a latent image on an image carrier, and includes a polygon mirror driven by a scanner motor 117 and a laser diode 118. The beam light output from the optical unit 211 scans the surface of the uniformly charged photosensitive drum 206, whereby a latent image is formed. The latent image is developed into a toner image by the developing roller 208 and transferred to a recording medium by the transfer roller 110. Further, the toner image is fixed on the recording medium by the fixing roller 212 and the pressure roller 213 and is discharged out of the apparatus via a paper discharge path.

<Processing of Print Controller 120>
An image forming process executed when the print controller 120 receives a print instruction from the host computer 101 will be described using the flowchart shown in FIG. It is assumed that a program executed by the CPU 102 is stored in a ROM (not shown).

  FIG. 4 shows an example of the start positions of raster image data and actual image data stored in the RAM 104 of the print controller 120. Here, it is assumed that data corresponding to one scan (one line) of the laser is 64-bit data. Also, 1 shown in FIG. 4 means that there is image data whose density is not zero, and 0 means that there is no image data (density is zero). Therefore, the margin data is generally 0.

  In step S <b> 301, the CPU 102 analyzes the print instruction received from the host computer 101 through the communication control circuit 103 and generates a print reservation command corresponding to the print instruction. Then, the CPU 102 transmits a print reservation command to the image forming engine 130 through the video interface control circuit 105. In step S <b> 302, the CPU 102 expands image data received from the host computer 101 into raster image data and stores the raster image data in the RAM 104.

  In S303, the CPU 102 analyzes the raster image data stored in the RAM 104 and detects the start position of the actual image data. For example, the CPU 102 analyzes raster image data line by line in order from the address at the leading edge of the recording medium toward the trailing edge of the recording medium, and detects an address of image data that is not a margin. According to FIG. 4, the CPU 102 starts a search from 0x0000, which is the address of the leading end of the recording medium, and finds image data that is not a blank for the first time at 0x0021. Since the head address of the line including the address where the image data that is not the margin is found is 0x0020, the CPU 102 specifies the actual image data start position as 0x0020.

  In S304, the CPU 102 obtains a margin data amount from the actual image data start position. For example, the CPU 102 obtains the data amount from the difference between the address of the leading edge of the recording medium and the actual image data start position, and calculates the distance (margin data amount) from the leading edge of the recording medium to the leading edge of the image based on this and the scanning speed of the scanner motor 117 To do. According to FIG. 4, since the actual image data start position is 0x0020, the CPU 102 recognizes that the start address of the margin data is 0x0000 and the end address of the margin data is 0x001F. From the start address and end address of the margin data, the CPU 102 also recognizes that the four lines from 0x0000 to 0x001F are the margin data.

  In step S <b> 305, the CPU 102 deletes the margin data from the leading edge (0x0000) to the trailing edge (0x001F) of the raster image data stored in the RAM 104. As a result, the arrangement of data in the RAM 104 is changed so that raster image data can be output from data at the actual image data start position. As described above, the CPU 102 functions as an image data generation unit that expands the image forming job data received from the external device and generates image data that is the remaining raster image excluding the blank portion.

  In step S <b> 306, the CPU 102 transmits a print instruction command and blank data amount to the image forming engine 130 through the video interface control circuit 105. The CPU 102 confirms in advance that the image forming engine 130 is ready to form an image through the video interface control circuit 105, and then transmits a print start command and a margin data amount. In the example shown in FIG. 4, the CPU 102 calculates the margin length [mm] on the recording medium corresponding to four lines as the margin data amount d4.

d4 = n × w
Here, n is the number of lines corresponding to the margin, and w is the width per line. As described above, the CPU 102 functions as a determination unit that determines the length (d4) of the blank portion in the conveyance direction from the image forming job data.

  In step S <b> 307, the CPU 102 determines whether a TOP signal output from the image forming engine 130 has been detected. When the TOP signal is detected, the process proceeds to S308, and the CPU 102 transmits the raster image data from which the margin data is deleted to the image forming engine 130.

<Processing of Image Forming Engine 130>
An image forming process executed by the CPU 106 in accordance with a program stored in a ROM (not shown) when the image forming engine 130 forms an image on a recording medium will be described with reference to FIG. Here, the image forming processing shown in FIG. 5 is started by the CPU 106 when a print instruction command is received from the print controller 120.

  In step S <b> 501, the CPU 106 receives the amount of blank data transmitted from the print controller 120 through the video interface control circuit 119. In step S <b> 502, the CPU 106 instructs the scanner control circuit 116 to start the scanner motor 117. Further, the CPU 106 controls the rotation speed of the scanner motor 117 so that the light beam can be irradiated to an accurate position on the peripheral surface (image forming surface) of the photosensitive drum 206 through the scanner control circuit 116.

  In S503, the CPU 106 activates the DC brushless motor 114 and the DC brushless motor 115. In step S <b> 504, the CPU 106 instructs the fixing control circuit 111 to start heating the heater provided in the fixing roller 212. The fixing control circuit 111 heats the fixing roller 212 by applying a voltage to a heater provided inside the fixing roller 212. In step S <b> 505, the CPU 106 instructs the high voltage control circuit 107 to start applying predetermined voltages to the charging roller 108, the developing roller 208, and the transfer roller 110. In response to this instruction, the high voltage control circuit 107 applies a charging voltage to the charging roller 108, applies a developing voltage to the developing roller 208, and applies a transfer voltage to the transfer roller 110.

  In step S <b> 506, the CPU 106 performs paper feed processing in synchronization with the timing of writing an actual image determined based on the amount of blank data, the state of the rotation speed of the scanner motor 117, and the conveyance time of the recording medium by the DC brushless motor 114. For example, the CPU 102 determines the timing for writing the actual image in accordance with the timing at which the rotation speed of the scanner motor 117 is stabilized at the target rotation speed. Since the head margin data is deleted from the raster image data, the CPU 106 advances the paper feeding timing in accordance with the margin data amount. Details of paper feed control will be described later.

  In step S <b> 507, the CPU 106 instructs the scanner control circuit 116 to expose the photosensitive drum 206 uniformly charged by the charging roller 108 according to the raster image data. The scanner control circuit 116 exposes the photosensitive drum 206 according to the raster image data received through the video interface control circuit 119 to form an electrostatic latent image. The electrostatic latent image is developed into a toner image by toner supplied from the developing roller 208. The developed toner image moves to a transfer position as the photosensitive drum 206 rotates, and is transferred onto the recording medium by the transfer roller 110. The recording medium on which the unfixed toner image is placed is conveyed toward the fixing device, and the toner image is fixed by the fixing roller 212 and the pressure roller 213.

  In step S <b> 508, the CPU 106 determines whether the next print instruction has been received through the video interface control circuit 119. When the next print instruction is received, the process returns to S506, and the CPU 106 continues image formation. On the other hand, if the next print instruction has not been received, the process advances to step S509.

  In step S <b> 509, the CPU 106 stops the actuator and stops the voltage applied to the charging roller 108, the developing roller 208, and the transfer roller 110. The actuator is the optical unit 211, the DC brushless motor 114, the DC brushless motor 115, the fixing roller 212, the photosensitive drum 206, or the like described above.

<Feed control>
The flow of paper feed control executed in S506 will be described in detail with reference to FIGS. In S601, the CPU 106 acquires, from the RAM 104 or the ROM, the time T0 from when the scanner motor 117 is started until the rotation speed reaches the target rotation speed and stabilizes. The RAM 104 and the ROM function as a storage unit that stores the transition time (T0). This time T0 may be acquired by experiment at the time of factory shipment, or may be calculated by simulation. Alternatively, at the timing when an image is not formed, the CPU 106 sets a time T0 from when the scanner motor 117 is activated until the rotation speed measured by the rotation speed sensor 121 reaches the target rotation speed and stabilizes, as an internal timer. You may measure using. Alternatively, the CPU 106 measures the rotational speed Rx by the rotational speed sensor 121 at an arbitrary timing after the scanner motor 117 is activated, and measures the time Tx from the activation of the scanner motor 117 to the measured timing. Further, the CPU 106 may calculate the scanner activation time T0 by substituting the target rotation speed Rt, the rotation speed Rx, and the time Tx into the function. An example of this function is:
T0 = (Tx / Rx) × Rt
Thus, the scanner activation time T0 is a transition time from the activation of the exposure unit to the transition of the exposure unit to a stable state.

  In step S <b> 602, the CPU 106 acquires a time TA from the start of paper feeding until the leading edge of the recording medium reaches the TOP sensor 113. The time TA may be acquired by experiment at the time of factory shipment, or may be calculated by simulation. It is assumed that the time TA is stored in advance in the RAM 104 or a ROM (not shown). Therefore, the RAM 104 and the ROM function as a storage unit that stores the second transport time (TA) obtained in advance by experiments or simulations.

  In step S <b> 603, the CPU 106 acquires a time TB from when the leading edge of the recording medium reaches the TOP sensor 113 until the image starts to be drawn on the photosensitive drum 206. A method for calculating the time TB will be described with reference to FIG.

  According to FIG. 8, the distance from the TOP sensor 113 to the transfer roller 110 is d1. Further, the distance until the toner image drawn on the photosensitive drum 206 reaches the transfer roller 110 is d2. According to FIG. 8, a line connecting the contact point between the photosensitive drum 206 and the developing roller 208 from the center point of the cross section of the photosensitive drum 206 is defined as a line La. Further, a line connecting the contact point between the photosensitive drum 206 and the transfer roller 110 from the center point of the photosensitive drum 206 is defined as a line Lb. If the angle formed by the line La and the line Lb is θ [degrees], the CPU 106 calculates the distance d by the following equation.

d2 = 2πrθ / 360
Further, a distance that the recording medium travels in the transport direction from when the toner passes through the TOP sensor 113 until the developing roller 208 starts to draw a toner image on the photosensitive drum 206 is defined as d3. CPU 106 calculates distance d3 by the following equation. It is assumed that the distance d1 and the distance d2 are stored in advance in the RAM 104 or the ROM. The distance d3 itself may be stored in advance in the RAM 104 or ROM.

d3 = d1-d2 (d1> d2)
The CPU 106 acquires the time TB from the distance d3 read from the RAM 104 or the ROM and the blank data amount acquired from the video interface control circuit 119. For example, the CPU 106 calculates the time TB using the following formula.

TB = (d3 + d4) / v
= (D1-d2 + d4) / v
Here, v is the recording medium conveyance speed [mm / sec], and d4 is the margin data amount [mm]. The reason why the margin data amount d4 is added is to advance the feeding timing in accordance with the margin. That is, when the margin portion on the recording medium passes through the transfer position, the scanner motor 117 may not be stable yet, but the scanner motor 117 is stable at the timing when the margin portion passes the transfer position. is doing. As a result, the accuracy of the image forming position can be maintained while shortening the first printout time. As described above, the CPU 106 adds the length (d4) in the conveyance direction of the blank portion to the difference distance (d3) obtained by subtracting the distance (d2) from the distance (d1). It functions as a means for calculating. Here, the distance (d1) is the distance from the detection position where the detection means in the transport path detects the recording medium to the center of the nip formed by the image carrier and the transfer means. The distance (d2) is a distance on the circumferential surface of the image carrier, and is a distance from the development position where the developing means applies developer to the image carrier to the center of the nip portion. Further, the CPU 106 functions as means for calculating the first transport time (TB) by dividing the sum by the transport speed (v) of the recording medium. Further, the CPU 106 functions as means for calculating the first transport time (TB) from the length of the blank portion in the transport direction and the recording medium transport speed (v) in the transport path.

  In step S <b> 604, the CPU 106 obtains a time TS from the start of the scanner motor 117 to the start of paper feeding from the scanner start time T <b> 0, time TA, and time TB. The time TS can be calculated by the following equation as shown in FIG.

TS = T0-(TA + TB)
As described above, the CPU 106 functions as a determination unit that determines the initial time (TS) by subtracting the first transport time (TB) and the second transport time (TA) from the transition time (T0). Here, the transition time (T0) is a transition time from the start of the image forming unit to the transition of the image forming unit to a stable state. The first transport time (TB) is a transport time corresponding to the length in the transport direction of the blank portion formed at the head of the recording medium in the transport direction. The second transport time (TA) is a second transport time from the timing when the sheet feeding unit starts feeding to the timing when the detecting unit detects the recording medium. The CPU 106 functions as a determination unit that reads and uses the second transport time (TA) and the transition time (T0) from the storage unit when determining the initial time (TS).

  In step S <b> 605, the CPU 106 measures whether or not the time TS has elapsed since the scanner motor 117 was activated, and determines whether or not the measured elapsed time has exceeded the time TS. Note that the CPU 106 may determine whether the elapsed time has reached the time TS. When the measured elapsed time exceeds the time TS, the process proceeds to S606, and the CPU 106 drives the paper feed roller 203. Thereby, the recording medium can be fed from the recording medium cassette 202 to the conveyance path. The CPU 106 drives the paper feed roller 203 by the DC brushless motor 114 by connecting a clutch (not shown) that connects the DC brushless motor 114 and the paper feed roller 203. As described above, the CPU 106 functions as a paper feed control unit that controls the paper feed unit so that the paper feed unit starts feeding at the timing when the initial time (TS) has elapsed from the timing when the image forming unit is activated.

<Image formation processing>
The flow of the image forming process executed in S507 will be described with reference to FIG. In step S901, the CPU 106 determines whether the TOP sensor 113 has detected the leading edge of the recording medium. When the TOP sensor 113 detects the leading edge of the recording medium, the process proceeds to S902.

  In step S902, the CPU 106 determines whether the elapsed time from the timing when the TOP sensor 113 detects the leading edge of the recording medium has exceeded the time TB. The CPU 106 measures the elapsed time using an internal timer or counter. When the elapsed time exceeds the time TB, the process proceeds to S903.

  In step S <b> 903, the CPU 106 outputs a TOP signal to the print controller 120 through the video interface control circuit 119. As described above, the CPU 106 and the video interface control circuit 119 function as signal output means for outputting a signal indicating the start of image writing at the timing when the first conveying time (TB) has elapsed from the timing at which the detection means detects the recording medium. To do. Upon receiving the TOP signal, the print controller 120 transmits raster image data from which the margin data has been deleted to the image forming engine 130.

  In step S <b> 904, the CPU 106 turns on the laser diode 118 based on the raster image data received through the video interface control circuit 119 and controls the optical unit 211 to form a latent image on the photosensitive drum 206.

  In step S <b> 905, the CPU 106 controls the developing device 109 to develop the latent image on the photosensitive drum 206 into a toner image using a developer (toner). In step S <b> 906, the CPU 106 rotates the photosensitive drum 206, transfers the transfer voltage to the transfer roller 110, and transports the recording medium so that the toner image developed on the photosensitive drum 206 is transferred onto the recording medium by the transfer roller 110. Control. In S907, the CPU 106 executes rotation control of the fixing roller 212 and temperature control of a heater provided therein so as to fix the toner image transferred onto the recording medium.

  In this way, the FPOT can be shortened by feeding and conveying the scanner motor so as to write the actual image in accordance with the stable timing at the target rotation speed. Further, since the TOP signal is output after the front end of the recording medium is detected by the sensor, an image can be formed at an accurate position on the recording medium.

  As described above, according to the first embodiment, it is possible to advance the feeding timing in accordance with the length of the blank portion formed on the recording medium in the conveyance direction. As a result, the first printout time can be reduced. Can be shortened. In the first embodiment, since the TOP sensor 113 detects the leading edge of the recording medium and outputs a TOP signal indicating the start of image writing, an image can be formed at an accurate position on the recording medium. Therefore, in the first embodiment, it is possible to reduce the first printout time while preventing the image position from shifting.

[Example 2]
The first embodiment is an invention in which a recording medium is fed and conveyed so that an actual image is written at a timing when the scanner motor 117 is stabilized at a target rotational speed. However, depending on the performance of the scanner motor 117 and the fixing device, the starting time of the fixing device may be later than the starting time of the scanner motor 117. In that case, the activation time of the fixing device limits the FPOT. Therefore, in the third embodiment, the FPOT is shortened by performing conveyance control so that the fixing device fixes the actual image on the recording medium at the timing when the temperature of the fixing device reaches the target temperature. In the second embodiment, items common to the first embodiment are omitted for the sake of brevity. That is, only the portion of paper feed control executed in S506 of FIG. 5 is different only in the first embodiment and the second embodiment, and this portion will be mainly described.

<Feed control>
The flow of paper feed control according to the second embodiment will be described in detail with reference to FIGS. In S <b> 1001 of FIG. 10, the CPU 106 obtains a time Tf from when the heater of the fixing device is activated to start heating the fixing roller 212 until the temperature of the fixing roller 212 reaches the target temperature. The CPU 102 uses the thermistor 112 to measure the temperature (Cx) of the fixing unit when an image formation is instructed. Therefore, the thermistor 112 functions as a measurement unit. The time Tf varies depending on the initial temperature Cx of the fixing roller 212 when heating by the heater is started. Therefore, the CPU 106 measures the intermediate temperature C1 of the fixing roller 212 at an arbitrary first timing after starting the heater, and the intermediate temperature C2 of the fixing roller 212 at another second timing. That is, after the fixing unit is activated, the CPU 102 measures the first temperature (C1) of the fixing unit at the first timing and the second temperature (C2) of the fixing unit at the second timing. Measure. Further, the CPU 106 measures an elapsed time T1 from the timing when the midway temperature C1 is measured to the timing when the midway temperature C2 is measured by an internal timer or counter. Further, the CPU 106 obtains a time (fixing activation time Tf) until the temperature of the fixing roller 212 reaches the target temperature Ct from the initial temperature Cx based on the elapsed time T1 and the intermediate temperatures C1 and C2.

Tf = (Ct−Cx) × β
β = T1 / (C2-C1)
Here, the fixing activation time Tf is a transition time from the activation of the fixing unit to the transition of the fixing unit to a stable state. Β is a temperature increase coefficient. The CPU 102 divides the elapsed time (T1) from the first timing to the second timing by the difference between the second temperature (C2) and the first temperature (C1), thereby obtaining the temperature increase coefficient (β). It functions as a means for calculating. As described above, the CPU 102 multiplies the difference between the target temperature (Ct) preset in the fixing unit and the temperature (Cx) measured by the measuring unit by the temperature increase coefficient (β) obtained in advance. By this, it functions as a means for calculating the transition time (Tf).

  In S1002, the time (time TA) from the start of paper feeding until the leading edge of the recording medium reaches the TOP sensor 113 is acquired. In this embodiment, it is assumed that the time TA is stored in advance in a ROM (not shown).

  In step S <b> 1003, the CPU 106 acquires a conveyance time TC from when the leading edge of the recording medium reaches the TOP sensor 113 until the leading edge of the unfixed toner image transferred onto the recording medium reaches the fixing roller 212. For example, the CPU 106 obtains the transport time TC from the distance d5 from the TOP sensor 113 to the fixing roller 212 and the blank data amount d4 acquired through the video interface control circuit 119. In the second embodiment, it is assumed that the distance d5 from the TOP sensor 113 to the fixing roller 212 is stored in advance in the RAM 104 or the ROM.

TC = (d5 + d4) / v
Here, v is the recording medium conveyance speed [mm / sec], and d4 is the margin data amount [mm]. As described above, the CPU 106 adds the length (d4) of the blank portion in the conveyance direction to the distance (d5) from the detection position where the detection unit in the conveyance path detects the recording medium to the nip portion of the fixing unit. Function as a means for calculating the sum. Further, the CPU 102 also functions as means for calculating the first transport time (TC) by dividing the sum by the transport speed (v) of the recording medium. Here, the margin data amount d4 is added in order to advance the paper feed timing in accordance with the margin. When the margin portion on the recording medium passes through the nip portion (fixing position) formed by the fixing roller and the pressure roller, the temperature of the fixing roller 212 may not yet reach the target temperature. . However, at the timing when the blank portion passes the fixing position, the temperature of the fixing roller 212 reaches the target temperature. The margin data amount d4 is added by advancing the paper feed timing in accordance with the margin, thereby reducing the first printout time and maintaining the accuracy of the image formation position.

  In step S <b> 1004, the CPU 106 obtains a time TS from the timing at which the heater of the fixing device is activated to the timing at which paper feeding is started, using the fixing device activation time Tf, the time TA, and the time TC.

TS = Tf− (TA + TC)
In step S <b> 1005, the CPU 106 determines whether the elapsed time from the timing when the fixing device is activated has exceeded the time TS. The elapsed time can be measured by an internal timer or a counter. When the elapsed time exceeds the time TS, the process proceeds to S1006. In step S1006, the CPU 106 controls the DC brushless motor 114 and the above-described clutch so as to drive the paper feed roller 203.

  As described above, according to the second embodiment, it is possible to advance the feeding timing in accordance with the length of the blank portion formed on the recording medium in the conveyance direction. As a result, the first printout time can be reduced. Can be shortened. In the first embodiment, since the TOP sensor 113 detects the leading edge of the recording medium and outputs a TOP signal indicating the start of image writing, an image can be formed at an accurate position on the recording medium. Therefore, in the first embodiment, it is possible to reduce the first printout time while preventing the image position from shifting.

Claims (9)

A paper feeding means for feeding a recording medium;
Detecting means for detecting the recording medium;
A signal output means for outputting a signal indicating the start of image writing;
When a signal indicating the start of image writing is input, image data output means for outputting image data;
Image forming means for forming an image corresponding to the image data output by the image data output means;
From the transition time (T0; Tf) from when the image forming unit is activated to when the image forming unit transitions to a stable state, the length in the transport direction of the blank portion formed at the head of the recording medium in the transport direction Is subtracted from the first transport time (TB; TC) corresponding to the second transport time (TA) from the timing when the paper feeding unit starts feeding to the timing when the detecting unit detects the recording medium. Determining means for determining the initial time (TS) in
An image forming apparatus comprising: a control unit that starts paper feeding by the paper feeding unit at a timing when the initial time (TS) has elapsed from a timing at which the image forming unit is activated. The image forming unit includes:
An image carrier;
Exposure means for forming a latent image on the image carrier;
Developing means for developing the latent image to form a developer image;
Transfer means for transferring the developer image to a recording medium;
Fixing means for heating and fixing the developer image to a recording medium,
The transition time (T0) is a transition time from the start of the exposure unit to the transition of the exposure unit to a stable state,
The signal output means outputs a signal indicating the start of image writing at a timing when the first conveying time (TB; TC) has elapsed from the timing at which the detecting means detects the recording medium. The image forming apparatus described in 1. The determining means includes
From the distance (d1) from the detection position where the detection means in the transport path detects the recording medium to the center of the nip formed by the image carrier and the transfer means, the distance on the circumferential surface of the image carrier. The margin portion with respect to the difference distance (d3) obtained by subtracting the distance (d2) from the development position where the developing means applies the developer to the image carrier to the center of the nip portion. Means for adding the length (d4) in the transport direction to calculate an output value;
The image forming apparatus according to claim 2, further comprising: a unit that calculates the first transport time (TB) by dividing the output value by the transport speed (v) of the recording medium. A storage means for storing the second transfer time (TA) and the transition time (T0);
The determination unit reads out and uses the second transport time (TA) and the transition time (T0) from the storage unit when determining the initial time (TS). 4. The image forming apparatus according to any one of items 3. The image data output means includes
Image data generating means for developing the image forming job data received from the external device and generating the image data which is the remaining raster image excluding the margin part;
Discriminating means for discriminating the length (d4) in the conveyance direction of the margin from the image forming job data;
The image forming apparatus further includes:
2. The apparatus according to claim 1, further comprising means for calculating the first transport time (TB) from a length (d4) in the transport direction of the blank portion and a transport speed (v) of the recording medium in the transport path. 5. The image forming apparatus according to any one of items 4 to 4. The image forming unit includes:
An image carrier;
Exposure means for forming a latent image on the image carrier;
Developing means for developing the latent image to form a developer image;
Transfer means for transferring the developer image to a recording medium;
Fixing means for heating and fixing the developer image to a recording medium,
The image forming apparatus according to claim 1, wherein the transition time (Tf) is a transition time from when the fixing unit is activated to when the fixing unit shifts to a stable state. The determining means includes
An output value is obtained by adding the length (d4) of the margin in the conveyance direction to the distance (d5) from the detection position where the detection unit detects the recording medium in the conveyance path to the nip portion of the fixing unit. Means for calculating
The image forming apparatus according to claim 6, further comprising: a unit that calculates the first transport time (TC) by dividing the output value by the transport speed (v) of the recording medium. A measuring unit for measuring a temperature (Cx) of the fixing unit when image formation is instructed;
The determining means includes
By multiplying the difference between the target temperature (Ct) preset in the fixing unit and the temperature (Cx) measured by the measuring unit by a temperature increase coefficient (β) determined in advance, 8. The image forming apparatus according to claim 6, further comprising means for calculating a transition time (Tf). After the fixing unit is activated, the measuring unit measures the first temperature (C1) of the fixing unit at the first timing and the second temperature (C2) of the fixing unit at the second timing. Measure and
The determining means divides an elapsed time (T1) from the first timing to the second timing by a difference between the second temperature (C2) and the first temperature (C1), The image forming apparatus according to claim 8, wherein a temperature increase coefficient (β) is calculated.

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