JP2010211039A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of stably performing read register correction, even if the operation load is in a high-load state. <P>SOLUTION: A period Tx till paper 31 is detected by a paper-detecting sensor 40, after an image is detected by an image detection sensor 35 is measured by a division period Tcap, obtained by dividing a reference signal by predetermined frequency dividing ratio, the measured counted value is corrected with a predetermined value of Pd_SOFT; and a switching instruction of conveyance speed of the paper 31 from first speed V1 to second speed V2 is performed, when a period for the corrected counted value passes by a period of the reference signal after the paper 31 is detected by the paper-detecting sensor 40. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus.

  As a technique relating to lead registration correction that accurately matches the arrival timing of a recording medium such as paper to a transfer position and the arrival timing of an image developed with a developer such as toner, Japanese Patent Application Laid-Open No. H10-228667 detects a conveyed image. Describes technology for measuring the period from detection of an image by an image detection sensor to detection of the recording medium by a medium detection sensor, and controlling the conveyance speed of the recording medium according to the length Has been.

  Since Patent Document 1 performs read registration correction by software control, it uses a lot of processing time of an arithmetic device such as a CPU.

JP 2000-238931 A

  An object of the present invention is to provide an image forming apparatus capable of performing lead registration correction stably even when a calculation load is high.

  An image forming apparatus according to a first aspect of the present invention includes an image conveying unit that conveys an image developed by a developer to a transfer position to a recording medium at a predetermined speed, and an image conveyance path that is closer than the transfer position. Can be switched between two stages: an image detecting means for detecting the image to be conveyed, and a first speed when transferring the image and a second speed faster than the first speed. The recording medium is conveyed at the second speed in synchronization with the image conveyance by the image conveying means, and when the switching instruction is received, the conveyance speed is switched to the first speed to transfer the recording medium. A recording medium transporting means for transporting to a position; and a medium for detecting the transported recording medium provided upstream of the transfer position of the recording medium and closer to the transfer position than the image detecting means. Detection And a period from when the image is detected by the image detection means to when the recording medium is detected by the paper passage detection means by dividing a reference signal having a predetermined period by a predetermined division ratio. A measuring means for measuring at a circumferential period; a correcting means for correcting a count value measured by the measuring means with a predetermined correction value; and a recording medium detected by the medium detecting means, and the period of the reference signal Switching instruction means for instructing the recording medium conveying means to switch when a period corresponding to the count value corrected by the correcting means has elapsed.

  According to a second aspect of the present invention, in the first aspect of the present invention, the correction value is changed when the conveyance speed is switched from the second speed to the first speed when a switching instruction is received. It is determined in consideration of the period and speed change distance.

  The invention according to claim 3 is the invention according to claim 1 or 2, wherein the period of the reference signal is Tm, the first speed is V1, and the second speed is V2. The frequency dividing period is a period shown in the following formula (A).

また、請求項４に記載の発明は、請求項３記載の発明において、前記画像検知手段から前記転写位置までの距離をＬ０とし、前記画像搬送手段により画像を搬送する予め定められた速度をＶ０とし、前記第１速度Ｖ１から前記第２速度Ｖ２への速度変更期間をＴｄとし、前記第１速度Ｖ１から前記第２速度Ｖ２への速度変更距離をＬｄとした場合、前記補正値を以下の（Ｂ）式に示す値としている。

According to a fourth aspect of the present invention, in the third aspect of the present invention, the distance from the image detecting means to the transfer position is L0, and a predetermined speed at which the image is conveyed by the image conveying means is V0. When the speed change period from the first speed V1 to the second speed V2 is Td and the speed change distance from the first speed V1 to the second speed V2 is Ld, the correction value is The value shown in the equation (B) is used.

さらに、請求項５に記載の発明は、請求項１〜請求項４の何れか１項記載の発明において、前記計数値及び前記補正値は、予め定めた小数点以下桁数の値とし、前記補正手段は、前記計数値を前記補正値で補正した値に対して０．５を加算して小数点以下を切り捨てる補正を行なう。

Furthermore, the invention according to claim 5 is the invention according to any one of claims 1 to 4, wherein the count value and the correction value are values of a predetermined number of decimal places, and the correction is performed. The means performs a correction by adding 0.5 to the value obtained by correcting the count value with the correction value and truncating the decimal part.

  According to the first aspect of the invention, there is an excellent effect that the lead registration correction can be performed stably even when the calculation load is in a high load state.

  According to the second aspect of the present invention, there is an excellent effect that the lead registration correction can be performed with high accuracy.

  Further, according to the third aspect of the invention, there is an excellent effect that the timing of the switching instruction can be directly counted.

  Moreover, according to the invention of Claim 4, it has the outstanding effect that a correction value can be made into a fixed value.

  Furthermore, according to the fifth aspect of the present invention, there is an excellent effect that the error of lead registration correction can be reduced.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment. It is a figure which shows schematic structure inside the apparatus main body which concerns on embodiment. It is a figure which shows the positional relationship of the image detection sensor which concerns on embodiment, a paper detection sensor, an image, and a paper. FIG. 6 is an explanatory diagram focusing on the sheet conveyance path side according to the embodiment. It is a figure which shows the structure of the conveyance control part which concerns on 1st Embodiment. It is a figure which shows the relationship between the frequency division period Tcap and the number of clocks which concern on 1st Embodiment. It is a figure which shows an example of the result at the time of performing a lead registration correction | amendment by software control. It is a figure which shows the structure of the conveyance control part which concerns on 2nd Embodiment. It is a figure which shows the relationship between the frequency division period Tcap and the number of clocks concerning 2nd Embodiment.

  DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. Hereinafter, a case where the present invention is applied to an image forming apparatus having a copy function and a print (print) function will be described.

[First Embodiment]
FIG. 1 shows a schematic configuration of an image forming apparatus 10 according to the present embodiment.

  As shown in the figure, the image forming apparatus 10 reads an image from a document placed at a reading position, acquires image data indicating the image, and acquires image data acquired by the scanner 11 or externally. The apparatus main body 12 that performs image forming processing using various image data such as the image data and the like, and a touch panel display (hereinafter referred to as “transparent type touch panel”) that displays an operation menu, a message, and the like and is integrally provided on the surface. 14) and a discharge tray 39 for holding a sheet 31 (see also FIG. 2) as a recording medium on which an image is formed and discharged from the apparatus main body 12.

  Note that in the image forming apparatus 10 according to the present embodiment, a pressure-sensitive touch panel is used as the touch panel, and image formation is performed when the user touches the display surface of the display 14 with a fingertip (touch operation). Various operations can be instructed to the apparatus 10.

  Next, a schematic configuration inside the apparatus main body 12 will be described with reference to FIG.

  As shown in the figure, the apparatus main body 12 according to the present embodiment includes an image forming engine unit 15 that performs an image forming process on a paper 31 by an electrophotographic method, and a paper supply that stores the paper 31 before image formation. A paper tray 30.

  The image forming engine unit 15 according to the present embodiment is of a full color type and includes four image forming units 20Y, 20M, 20C, and 20K. These image forming units 20 are arranged at predetermined intervals along the longitudinal direction of the intermediate transfer belt 18. The intermediate transfer belt 18 is stretched around a plurality of winding rollers 19 and has an endless belt shape that is conveyed in the direction of arrow E in FIG. 2 at a predetermined speed.

  The image forming unit 20Y corresponds to yellow (Y), the image forming unit 20M corresponds to magenta (M), the image forming unit 20C corresponds to cyan (C), and the image forming unit 20K corresponds to black (K). An image of each corresponding color is formed. In FIG. 2, an alphabet (Y / M / C / K) indicating a color corresponding to the end of the code is given, but in the following, this alphabet at the end of the code is omitted unless the color is particularly distinguished. I will explain.

  The image forming unit 20 is provided with a cylindrical photosensitive drum 22 that is rotationally driven at a predetermined rotational speed in the direction of arrow F in FIG. Further, a charger 24 for uniformly charging the surface of the photosensitive drum 22 is disposed around each photosensitive drum 22. Charging of the photosensitive drum 22 by the charger 24 is the first stage of a series of image forming processes. Further, a light beam based on a desired image is irradiated in the axial direction of the photosensitive drum 22 uniformly charged by the charger 24 on the downstream side of the charger 24 along the rotation direction of each photosensitive drum 22. An optical scanning device 26 for forming an electrostatic latent image is disposed on the photosensitive drum 22.

  Further, there are colors around the photosensitive drums 22 that are respectively responsible for the electrostatic latent images formed on the photosensitive drums 22 on the downstream side of the optical scanning device 26 along the rotation direction of the photosensitive drums 22. A developing unit 28 is provided that develops the toner of (yellow / magenta / cyan / black) to form an image of each color. A contact point with the intermediate transfer belt 18 is located downstream of the developing device 28, and a first transfer device 29 is disposed so as to sandwich the intermediate transfer belt 18 with the photosensitive drum 22. Yes. The first transfer device 29 has a role of transferring an image on the photosensitive drum 22 to the intermediate transfer belt 18 by applying a predetermined voltage.

  Images of different colors formed on the respective photosensitive drums 22 are respectively transferred to the intermediate transfer belt 18 so as to overlap (in the same area) on the belt surface of the intermediate transfer belt 18. As a result, a full-color image is formed on the intermediate transfer belt 18.

  A second transfer unit 34 including a pair of rollers 34A and 34B is disposed downstream of the transfer position of the image on the intermediate transfer belt 18 from the photosensitive drum 22 in the conveyance direction (the direction of arrow E in FIG. 2). Has been.

  Further, an image detection sensor 35 for detecting the conveyed image is provided on the upstream side of the intermediate transfer belt 18 from the second transfer unit 34. When the image detection sensor 35 detects the conveyed image, the image detection sensor 35 outputs a high-level image detection signal.

  The image forming apparatus 10 includes a paper feed tray 30 at the bottom. The paper feed tray 30 stores sheets 31 in a stacked state. A pickup roll 32 is in contact with the leading end of the paper 31 stored in the paper feed tray 30 in the conveyance direction. The paper 31 is separated from the paper feed tray 30 one by one by the pickup roll 32 and paper unwinding means (not shown). Paper is fed downstream in the transport direction. A conveyance roller 33 and a registration roller 37 are arranged on the downstream side of the pickup roll 32 in the conveyance direction, and the sheet 31 is conveyed to the second transfer unit 34 above by the conveyance force from the conveyance roller 33 and the registration roller 37. The

  A paper detection sensor 40 that detects the paper 31 is provided in the conveyance path of the paper 31 upstream of the second transfer unit 34 and closer to the transfer position than the image detection sensor 35. When the paper detection sensor 40 detects the paper 31 being conveyed, it outputs a high level paper detection signal.

  The sheet 31 conveyed by the conveying roller 33 and the registration roller 37 is sandwiched between the rollers 34A and 34B in the second transfer unit 34, and the sheet is transferred from the intermediate transfer belt 18 by this nipping and conveying. The image is transferred to 31.

  The sheet 31 on which the image has been transferred is conveyed to a nip portion between each of the rollers 36A and 36B of the fixing unit 36 including a pressure roller 36A and a heating roller 36B that are arranged to face each other, and is subjected to heat fixing. As a result, the image is fixed on the paper 31 and a desired image is formed on the paper 31. The sheet 31 on which the image is formed is discharged to a discharge tray 39 by a pair of discharge rollers 38 disposed on the downstream side of the fixing device 36 in the sheet conveyance direction.

  In the image forming apparatus 10 according to the present embodiment, the conveyance speed of the paper 31 from the paper feed tray 30 to the discharge tray 39 is determined by the conveyance control unit 50 (see FIG. 5) by the pickup roll 32, the conveyance roller 33, By controlling the rotation speed of a motor (not shown) that drives the registration roller 37, the second transfer device 34, the fixing device 36, and the paper discharge roller 38, the discharge speed of the paper 31 to the discharge tray 39 can be changed. .

  In the present embodiment, the intermediate transfer belt 18 is rotationally driven at a predetermined speed. On the other hand, in the present embodiment, by controlling the rotation speed of the registration roller 37, the conveyance speed of the paper 31 is switched between two stages of a first speed when transferring an image and a second speed that is faster than the first speed. The conveyance speed of the paper 31 is switched according to the period from when the image on the intermediate transfer belt 18 is detected by the image detection sensor 35 to when the paper 31 conveyed on the conveyance path is detected by the paper detection sensor 40. By adjusting the switching tying, lead registration correction is performed to match the arrival timing of the paper 31 to the transfer position with the arrival timing of the image. The first speed is determined so that the speed difference from the conveyance speed of the intermediate transfer belt 18 is within a specified range (for example, 10%) in order to stably transfer the image.

  Next, read registration correction according to the present embodiment will be described with reference to FIGS.

  As shown in FIG. 3, the distance from the image detection sensor 35 to the transfer position 34C by the second transfer device 34 is L0, and the conveyance speed of the intermediate transfer belt 18 is V0. In this case, the arrival time T0 until the image detected by the image detection sensor 35 reaches the transfer position 34C is obtained from the following equation (1).

Arrival time T0 = L0 / V0 (1)
On the other hand, when paying attention to the conveyance path side of the paper 31, as shown in FIG. 4, the paper 31 is detected by the paper detection sensor 40 after the image is detected by the image detection sensor 35 (the timing when the image detection signal becomes high level). Is a period from when the paper 31 is detected by the paper detection sensor 40 until the switching tying is Ta. Further, when the first speed at which the paper 31 is transported is V1, the second speed is V2, and the transport speed of the paper 31 is switched from the first speed V1 to the second speed V2, the period and speed change associated with the speed change can be changed. Since there are few fluctuations in the required distance and period, the speed change period is set to Td and the speed change distance is set to Ld. Further, a period during which the paper 31 is conveyed at the second speed V2 is Tb. In this case, the relationship of the following formula (2) is established in the arrival time T0.

Arrival time T0 = L0 / V0 = Tx + Ta + Tb + Td (2)
The above equation (2) is converted into an equation relating to Tb as in the following equation (3).

Tb = (L0 / V0) -Tx-Ta-Td (3)
Further, when the distance from the sheet detection sensor 40 to the transfer position 34C is L1, the relationship of the following expression (4) is established for the distance L1.

L1 = V2 × Ta + V1 × Tb + Ld (4)
When the above (3) is substituted into the above equation (4) and rearranged as an equation relating to Ta, the following equation (5) is obtained.

画像検知センサ３５によって画像が検知されてから切替タイイングまでをＴｙとした場合、以下の（６）式のようになる。

When Ty is from the detection of the image by the image detection sensor 35 to the switching tying, the following equation (6) is obtained.

ここで、用紙検知センサ４０によって用紙３１が検知されてから切替タイイングまでの期間Ｔｙ−Ｔｘを、例えば、予め定められた周期Ｔｍの基準信号のクロック数を計測することにより計時するものとした場合、クロック数Ｐｄは以下の（７）式より求まる。

Here, when the period Ty-Tx from the detection of the paper 31 by the paper detection sensor 40 to the switching tying is measured, for example, by measuring the number of clocks of a reference signal with a predetermined period Tm. The clock number Pd is obtained from the following equation (7).

よって、第１項、及び第２項、第３項を以下の（８）式（９）式のようにした場合、上記（７）式は以下の（１０）式のようになる。

Therefore, when the first term, the second term, and the third term are represented by the following formula (8) and formula (9), the formula (7) is represented by the following formula (10).

期間Ｔｘは可変であるため、ＰＤ＿ＨＡＲＤは値が変化する。

Since the period Tx is variable, the value of PD_HARD changes.

  On the other hand, PD_SOFT is a fixed value.

  This PD_HARD can be transformed as shown in the following equation (11).

ここで、期間ＴｘをＴｃａｐで割ることにより、Ｔｘ／Ｔｃａｐを求めることができる。このＴｃａｐは、基準信号の周期Ｔｍを（Ｖ２−Ｖ１）／Ｖ１の分周比で分周した分周周期である。

Here, Tx / Tcap can be obtained by dividing the period Tx by Tcap. This Tcap is a frequency dividing period obtained by dividing the period Tm of the reference signal by a frequency dividing ratio of (V2-V1) / V1.

  That is, the clock number Pd can be obtained by measuring the period Tx with the frequency-divided signal having the frequency-divided period Tcap and correcting the measured value with PD_SOFT.

  FIG. 5 shows the configuration of the transport control unit 50 according to the present embodiment.

  The conveyance control unit 50 includes a measurement period control circuit 52, a pre-counter 54, a frequency division ratio register 56, a Tx counter 58, a Pd_SOFT register 60, a subtractor 62, a Pd register 64, and a speed switching timing control circuit. 66.

  The frequency division ratio register 56 and the Pd_SOFT register 60 are connected to the CPU 70 via the CPU bus BUS. The CPU 70 sets the above-described (V2−V1) / V1 as the division ratio in the division ratio register 56 through the CPU bus BUS, and the above-described Pd_SOFT as a correction value in the division ratio register 56 through the CPU bus BUS. Set the value of. Thereby, (V2−V1) / V1 is stored in the frequency division ratio register 56, and the value of Pd_SOFT is stored in the frequency division ratio register 56 as a correction value.

  The measurement period control circuit 52 receives an image detection signal from the image detection sensor 35 and a paper detection signal from the paper detection sensor 40. Also. The measurement period control circuit 52 is connected to the pre-counter 54. The measurement period control circuit 52 outputs a measurement period signal indicating the measurement period to the pre-counter 54, sets the measurement period signal to high level at the timing when the image detection signal becomes high level, and detects the image detection signal. When the signal becomes high level, the measurement period signal is set to low level.

  For example, a 50 MHz clock signal is input to the pre-counter 54 as a reference signal, and a measurement period signal is input from the measurement period control circuit 52. The pre-counter 54 is connected to the frequency division ratio register 56 and the Tx counter 58. The pre-counter 54 reads the frequency division ratio from the frequency division ratio register 56, and generates a frequency division signal having a frequency division period Tcap obtained by dividing the reference signal by the frequency division ratio while the measurement period signal is at a high level. The generated frequency-divided signal is output to the Tx counter 58.

  The Tx counter 58 measures the clock number of the frequency-divided signal input from the pre-counter 54 and holds the measured clock number. This number of clocks becomes the value of PD_HARD described above.

  The subtractor 62 is connected to the Tx counter 58, the Pd_SOFT register 60, and the Pd register 64. The subtracter 62 reads the value of PD_HARD from the Tx counter 58, reads the value of Pd_SOFT as a correction value from the Pd_SOFT register 60, subtracts the value of Pd_SOFT from the value of PD_HARD, and subtracts the value obtained by the subtraction from the Pd register 64. Output to. The value obtained by this subtraction becomes the value of the clock number Pd described above.

  The Pd register 64 stores and holds the value of the clock number Pd input from the pre-counter 54.

  The reference signal and the paper detection signal from the paper detection sensor 40 are input to the speed switching timing control circuit 66. The speed switching timing control circuit 66 is connected to the Pd register 64 and the motor driver 72. The speed switching timing control circuit 66 reads the value of the clock number Pd from the Pd register 64, starts measuring the number of clocks of the reference signal from the timing when the image detection signal becomes high level, and the measured clock number is the clock number. When the value of Pd is reached, a switching instruction is output to the motor driver 72.

  The motor driver 72 controls the rotational speed of a motor (not shown) that drives the pickup roll 32, the conveyance roller 33, the registration roller 37, the second transfer device 34, the fixing device 36, and the paper discharge roller 38 to rotate. The sheet 31 is conveyed at the second speed V2 in synchronization with the image conveyance by the body belt 18, and when the switching instruction is received from the speed switching timing control circuit 66, the rotation speed of the registration roller 37 is controlled to convey the sheet 31. Is switched to the first speed V1.

  Next, the operation of the image forming apparatus 10 according to the present embodiment will be described.

  For example, when printing image data read from a document by the scanner 11 or image data requested to be printed by an external device, each image forming unit 20 uniformly charges the surface of the photosensitive drum 22 by the charger 24. Then, an electrostatic latent image is formed on the photosensitive drum 22 by irradiating a light beam from the optical scanning device 26 based on the image data. Then, each image forming unit 20 develops the electrostatic latent image formed on the photosensitive drum 22 with the toner of the color each of which forms, thereby forming an image of each color.

  Images of different colors formed on the respective photosensitive drums 22 are transferred onto the intermediate transfer belt 18 so as to overlap each other on the belt surface of the intermediate transfer belt 18. The intermediate transfer belt 18 rotates at a speed V0, and the image transferred to the intermediate transfer belt 18 is conveyed to a transfer position 34C by the second transfer unit 34 as the intermediate transfer belt 18 rotates. The

  When the image detection sensor 35 detects the conveyed image, the image detection sensor 35 outputs a high-level image detection signal.

  The paper 31 stored in the paper feed tray 30 is taken out one by one in synchronization with the conveyance of the image and is conveyed at the second speed V2.

  When the paper detection sensor 40 detects the paper 31 being conveyed, it outputs a high level paper detection signal.

  In the conveyance control unit 50, a period Tx from when the image is detected by the image detection sensor 35 to when the paper 31 is detected by the paper detection sensor 40 is measured with a frequency division period Tcap obtained by dividing the reference signal.

  For example, in the case illustrated in FIG. 6, the number of clocks is 4 as a result of measurement with the frequency division period Tcap.

  In this way, Tx / Tcap can be obtained by counting the period Tx with the frequency dividing period Tcap.

  That is, the T_counter 58 can directly count the value of PD_Hard by generating a frequency-divided signal having a Tcap period with the pre-counter 54 and counting the frequency-divided signal with the Tx counter 58 during the period Tx.

  The conveyance control unit 50 corrects the measured clock number with the value of Pd_SOFT to obtain the clock number Pd, and after the paper 31 is detected by the paper detection sensor 40, a period corresponding to the clock number Pd in the cycle of the reference signal. When the time has elapsed, a switching instruction is output to the motor driver 72.

  When the motor driver 72 receives a switching instruction from the speed switching timing control circuit 66, the motor driver 72 controls the rotational speed of the registration roller 37 to switch the conveyance speed of the paper 31 to the first speed V1.

  As a result, the arrival timing of the paper 31 at the transfer position 34C matches the arrival timing of the image, so that the position of the image transferred to the paper 31 is stabilized.

  In addition, since the frequency division ratio and the value of PD_SOFT can be calculated in advance, the calculation load on the CPU 70 is not affected even in a high load state.

  Also, by storing the value of PD_SOFT in the PD_SOFT register 60, the subtractor 62 can calculate Pd_HARD-PD_SOFT with hardware, so that the calculation load on the CPU 70 is high. In addition, the lead registration correction can be performed stably. Since the conveyance control unit 50 can be realized by a relatively simple circuit such as a counter or a subtracter, it can be configured at low cost.

  On the other hand, for example, after the reference signal is counted by the Tx counter 58 during the period Tx and the period Tx is measured, the CPU 70 performs the above-described calculation of the equation (7) by software control, and the Pd register 64 stores the clock number Pd. As shown in FIG. 7, when the calculation load on the CPU 70 is in a high load state, the calculation period TP becomes long and the setting of the clock number Pd to the Pd register 64 is delayed, as shown in FIG. In some cases, the lead registration correction cannot be performed.

[Second Embodiment]
Since the schematic configuration of the image forming apparatus 10 according to the second embodiment and the schematic configuration inside the apparatus main body 12 are the same as those of the first embodiment, description thereof is omitted here.

  The lead registration correction according to the present embodiment will be described.

  When 0.5 is added to a value having a digit after the decimal point and the decimal part is rounded down, the rounding error is smaller than when the value after the decimal point is truncated as it is.

  Therefore, in the present embodiment, the above-described PD_HARD and PD_SOFT are obtained, for example, to 2 digits after the decimal point, and Pd ′ to 2 digits after the decimal point is obtained from the following equation (12).

Pd ′ = PD_HEAD−PD_SOFT + 0.5 (12)
Then, the number of clocks Pd is obtained by truncating the digits after the decimal point of Pd ′.

  FIG. 8 shows the configuration of the transport control unit 50 according to the present embodiment. The same parts as those in the first embodiment (see FIG. 5) are denoted by the same reference numerals, and description thereof is omitted here.

  The conveyance control unit 50 further includes a division unit 59 and a calculation unit 63.

  In this embodiment, the frequency division ratio is 1 / n times that of the first embodiment described above (n is a natural number of 2 or more), and the frequency division ratio register 56 has (V2−V1) / (V1 × n). ) Is set.

  As a result, the pre-counter 54 generates a frequency-divided signal having a period 1 / n times the frequency-divided period Tcap while the measurement period signal is at a high level, and outputs the generated frequency-divided signal to the Tx counter 58.

  The Tx counter 58 measures the clock number of the frequency-divided signal input from the pre-counter 54 and holds the measured clock number.

  The division unit 59 divides the number of clocks held by the Tx counter 58 by n to obtain up to two digits after the decimal point. In the present embodiment, the value obtained by division becomes the value of PD_HARD.

  The calculation unit 63 reads the PD_HARD value obtained by the division by the division unit 59, and also reads the value of Pd_SOFT as a correction value from the Pd_SOFT register 60, and Pd ′ up to two digits after the decimal point as shown in the above equation (12). And the number of clocks Pd is obtained by truncating digits after the decimal point of Pd ′. The calculation unit 63 outputs the obtained clock number Pd to the Pd register 64.

  Here, as shown in FIG. 9, when the period Tx is measured with the frequency division period Tcap, the number of clocks is 4 and the value of PD_HARD is 4 even when it is close to 5 pulses.

  On the other hand, for example, when n = 4 and the period Tx is measured at the frequency of the frequency dividing period Tcap / 4, the number of clocks is 19, and as a result of division by the division unit 59, the value of PD_HARD is 4.75. By adding 0.5 to this value and rounding down after the decimal point, the value of PD_HARD becomes 5.

  Thereby, the error of the lead registration correction is reduced.

  In the second embodiment, the case where the division unit 59 and the calculation unit 63 are provided separately has been described. However, the present invention is not limited to this, for example, an FPGA (Field Programmable Gate Array). For example, it may be configured as one arithmetic unit.

  In addition, the configuration of the image forming apparatus 10 and the schematic configuration inside the apparatus main body 12 (see FIGS. 1 to 3) described in the above embodiments are merely examples, and the scope of the present invention is not deviated. Needless to say, it can be changed as appropriate.

  The configuration of the conveyance control unit 50 described in each of the above embodiments (see FIGS. 5 and 8) is also an example, and it goes without saying that it can be changed as appropriate without departing from the gist of the present invention.

10 Image Forming Apparatus 18 Intermediate Transfer Belt (Image Conveying Unit)
31 paper (recording medium)
33 Conveying roller (recording medium conveying means)
34C Transfer position 35 Image detection sensor (image detection means)
37 Registration roller (recording medium transport means)
40 Paper detection sensor (medium detection means)
50 Conveyance control unit (measuring means, correcting means, switching instruction means)
52 Measurement period control circuit (measurement means)
54 Pre-counter (measuring means)
56 Divider ratio register (measuring means)
58 Tx counter (measuring means)
59 Division (correction means)
62 Subtractor (correction means)
63 Calculation unit (correction means)
66 Speed switching timing control circuit (switching instruction means)
72 Motor driver (recording medium transport means)

Claims (5)

Image conveying means for conveying an image developed by the developer to a transfer position to a recording medium at a predetermined speed;
An image detection means provided on the upstream side of the transfer path of the image from the transfer position and detecting the transferred image;
The conveyance speed can be switched between two stages of a first speed when transferring the image and a second speed higher than the first speed, and the second speed is synchronized with the image conveyance by the image conveying means. A recording medium conveying means for conveying the recording medium and switching the conveying speed to the first speed when a switching instruction is received, and conveying the recording medium to the transfer position;
Medium detection means for detecting the recording medium conveyed, provided upstream of the transfer position in the transport path of the recording medium and closer to the transfer position than the image detection means;
The period from when the image is detected by the image detection means to when the recording medium is detected by the paper passage detection means is a frequency division period obtained by dividing a reference signal having a predetermined period by a predetermined frequency division ratio. Measuring means for measuring;
Correction means for correcting the count value measured by the measurement means with a predetermined correction value;
Switching instruction means for instructing the recording medium conveying means to switch when a period corresponding to the count value corrected by the correcting means has elapsed in the period of the reference signal after the recording medium is detected by the medium detecting means. When,
Image forming apparatus. The correction value is determined in consideration of a speed change period and a speed change distance when the conveyance speed is switched from the second speed to the first speed when a switching instruction is received. Image forming apparatus. The frequency division cycle is a cycle shown in the following equation (A), where Tm is the period of the reference signal, V1 is the first speed, and V2 is the second speed. The image forming apparatus described.

A distance from the image detecting means to the transfer position is L0, a predetermined speed at which the image is conveyed by the image conveying means is V0, and a speed change period from the first speed V1 to the second speed V2 is set. The image forming apparatus according to claim 3, wherein when Td is set and Ld is a speed change distance from the first speed V1 to the second speed V2, the correction value is a value represented by the following equation (B).

The count value and the correction value are predetermined decimal digits,
5. The image forming apparatus according to claim 1, wherein the correction unit performs a correction by adding 0.5 to a value obtained by correcting the count value with the correction value to round off a decimal part. .

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