JP2005225073A - Image inspection device/method and imaging device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly measure the conveyance rate of oncoming sheet on a conveyor all the time. <P>SOLUTION: The image inspection device inspects a formed image by reading an image formed on oncoming sheet 16 on the conveyor. That is, in the method for inspecting an image, an encoder roller 51 is installed on a conveyance path for the sheet 16 and the sheet conveyance rate is calculated based on the number of pulses detected by the encoder roller 51. On the other hand, a sensor 54 is coaxially mounted with the encoder roller 51 and a change in the roller diameter due to the thermal expansion of the encoder roller 51 following a temperature rise can be monitored from the comparative reference results by comparatively referring to the sheet conveyance rate calculated by the measurement results of the sensor 54 and the sheet conveyance rate calculated by an encoder mechanism 50. Consequently, it is possible to obtain the always correct measurement value by correcting the calculation process of the sheet conveyance rate by the encoder mechanism 50. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus such as a copying machine or a printing machine, and more particularly to inspection of a formed image.

  An image forming apparatus that forms an image on a sheet based on image information is known. In this type of image forming apparatus, there is a demand for confirming or inspecting whether a formed image is formed according to the original image information. As a technique that satisfies such a requirement, for example, in Patent Document 1 below, image information that is the basis of printing is used as reference image information, and this is collated with read image information obtained by reading a formed image. A method is disclosed in which an inspection is performed by looking at a match between image information. In the case of this inspection method, based on the degree of coincidence between the reference image information and the read image information, a threshold value is provided that distinguishes between the case of normal printing and the case of occurrence of an abnormality, and based on this threshold value, The judgment is normal or abnormal.

Japanese Patent No. 2866339

  Incidentally, acquisition of read image information in an image forming apparatus such as a copying machine or a printing machine is generally performed by photographing a sheet conveyed at high speed by an image reading unit such as a CCD camera. The image reading means is provided with a paper conveyance speed detection mechanism for detecting the paper conveyance speed, and it is possible to acquire correct read image information based on the image information acquired by photographing and the detected paper conveyance speed. It has become.

  As a conveyance speed detection mechanism, a method using an encoder roller is generally used, and the sheet conveyance speed is calculated from values such as the number of pulses and the pulse interval detected by the encoder roller, the number of pulses and the rotation time of the encoder roller, and the like. Is possible.

  However, in copiers and printing machines, heat is used to fix the toner on the paper. Therefore, the encoder roller is heated by continuously conveying high-temperature paper, and the roller diameter changes due to thermal expansion. There was a problem of doing so. This is because if the roller diameter of the encoder roller is constantly changing, the correct sheet conveyance speed cannot be obtained, and as a result, correct image inspection becomes impossible.

  The present invention relates to an image inspection apparatus and an image inspection method capable of correctly determining normality / abnormality of an image formed on a sheet even when the sheet having heat is continuously conveyed, An image forming apparatus is provided.

  An image inspection apparatus according to the present invention is an apparatus that inspects a formed image by reading an image formed on a conveyed sheet, and includes an encoder roller installed on the conveyance path of the sheet, An encoder mechanism for calculating a paper conveyance speed based on the number of pulses detected by the encoder roller, and a sensor installed coaxially with the encoder roller, and based on the passage time of the paper detected by the sensor A sensor mechanism for calculating a paper transport speed, and comparing and collating the paper transport speed calculated by the encoder mechanism with the paper transport speed calculated by the sensor mechanism. Changes in the roller diameter due to thermal expansion of the encoder roller are monitored, and the paper transport speed is calculated by the encoder mechanism. Characterized in that so as to correct the physical.

  Another image inspection apparatus according to the present invention is an apparatus that inspects a formed image by reading an image formed on a conveyed sheet, and is installed on the sheet conveyance path and always operates. A first encoder mechanism that includes a first encoder roller and calculates a paper conveyance speed based on the number of pulses detected by the first encoder roller; And a second encoder mechanism that calculates a paper conveyance speed based on the number of pulses detected by the second encoder roller, By comparing and collating the paper conveyance speed calculated by the encoder mechanism with the paper conveyance speed calculated by the second encoder mechanism, Monitoring the change in roller diameter due to thermal expansion of the first encoder roller with a degree increases, characterized in that so as to correct the calculation of the paper conveying speed of the first encoder mechanism.

  Another image inspection apparatus according to the present invention is an apparatus connected to an image forming machine that forms an image on a sheet based on reference image information serving as a reference, and the reference image information and the formed image are Inspection is performed by collating the read image information obtained by reading. Such an image inspection apparatus includes an encoder roller installed on the paper conveyance path, an encoder mechanism for calculating a paper conveyance speed based on the number of pulses detected by the encoder roller, and coaxially with the encoder roller. A sensor mechanism that calculates a paper conveyance speed based on the passage time of the paper detected by the sensor, and calculates the paper conveyance speed calculated by the encoder mechanism and the sensor mechanism. By comparing and collating with the sheet conveyance speed, the change in the roller diameter due to the thermal expansion of the encoder roller accompanying the temperature rise is monitored from the collation result, and the calculation process of the sheet conveyance speed by the encoder mechanism is corrected. It is characterized by that.

  Still another image inspection apparatus according to the present invention is an apparatus connected to an image forming machine that forms an image on a sheet based on reference image information serving as a reference, and the reference image information and the formed image The inspection is performed by collating with the read image information obtained by reading. The image inspection apparatus includes a first encoder roller that is installed on the sheet conveyance path and is constantly operating, and calculates a sheet conveyance speed based on the number of pulses detected by the first encoder roller. And a second encoder roller that is installed coaxially with the first encoder roller and operates at a predetermined interval, and based on the number of pulses detected by the second encoder roller A second encoder mechanism that calculates a conveyance speed, and compares and collates the paper conveyance speed calculated by the first encoder mechanism with the paper conveyance speed calculated by the second encoder mechanism. A change in roller diameter due to thermal expansion of the first encoder roller accompanying a temperature rise is monitored from the collation result, and the first encoder mechanism Characterized in that so as to correct the calculation of the paper conveying speed by.

  The image inspection method according to the present invention is a method used when an image inspection apparatus connected to an image forming machine that forms an image on a sheet is operated using a computer based on reference image information serving as a reference. And the inspection process is executed by collating the reference image information with the read image information obtained by reading the formed image. In this image inspection method, a first paper transport speed calculating step for causing a computer to calculate a paper transport speed based on the number of pulses detected by an encoder roller installed on the paper transport path, and the encoder roller Calculated by a second paper transport speed calculating step for calculating a paper transport speed based on a passage time of the paper detected by a sensor installed coaxially with the first paper transport speed calculating step. By comparing and collating the sheet conveyance speed with the sheet conveyance speed calculated in the second sheet conveyance speed calculating step, the amount of change in the roller diameter due to the thermal expansion of the encoder roller accompanying the temperature rise is calculated from the comparison result. The encoder roller diameter calculating step and the encoder roller diameter calculating step. Based on the roller diameter of the by encoder roller, characterized in that to execute a processing including a step of correcting the calculation processing of the paper conveying speed in the first sheet conveying speed calculation step.

  Another image inspection method according to the present invention is used when an image inspection apparatus connected to an image forming machine that forms an image on a sheet is operated using a computer based on reference image information serving as a reference. In this method, an inspection process is executed by comparing the reference image information with the read image information obtained by reading the formed image. In this image inspection method, a first paper transport speed calculation is made to cause a computer to calculate a paper transport speed based on the number of pulses detected by a first encoder roller that is installed on the paper transport path and operates constantly. And a second paper transport for calculating the paper transport speed based on the number of pulses detected by the step and a second encoder roller installed coaxially with the first encoder roller and operating at a predetermined interval By comparing and collating the sheet conveyance speed calculated by the speed calculation step, the first sheet conveyance speed calculation step and the sheet conveyance speed calculated by the second sheet conveyance speed calculation step, from the comparison result An encoder roller for calculating a change amount of a roller diameter due to thermal expansion of the first encoder roller accompanying a temperature rise And a step of correcting the paper conveyance speed calculation process in the first paper conveyance speed calculation step based on the roller diameter of the first encoder roller calculated in the encoder roller diameter calculation step. Processing is executed.

  An image forming apparatus according to the present invention includes an image forming unit that forms an image on a conveyed sheet based on reference image information serving as a reference, and read image information by reading the image formed on the sheet. An image reading means for acquiring the image, and an image inspection means for checking whether the difference between the reference image information and the read image information is within a predetermined range. An encoder roller installed on the conveyance path, an encoder mechanism for calculating the sheet conveyance speed based on the number of pulses detected by the encoder roller, and a sensor installed coaxially with the encoder roller, A paper feed speed calculated by the encoder mechanism, and a sensor mechanism that calculates a paper feed speed based on the passage time of the paper detected by the sensor. And the sheet conveyance speed calculated by the sensor mechanism, the change in the roller diameter due to the thermal expansion of the encoder roller accompanying the temperature rise is monitored from the comparison result, and the sheet conveyance speed is calculated by the encoder mechanism. It is characterized by correcting the processing.

  Another image forming apparatus according to the present invention reads an image forming unit that forms an image on a conveyed sheet based on reference image information serving as a reference, and reads the image formed on the sheet. An image reading means for obtaining image information; and an image inspection means for checking whether the difference between the reference image information and the read image information is within a predetermined range, A first encoder mechanism that is installed on the paper conveyance path and is constantly operated; and a first encoder mechanism that calculates a paper conveyance speed based on the number of pulses detected by the first encoder roller; A second encoder roller that is installed coaxially with the first encoder roller and operates at a predetermined interval; and the number of pulses detected by the second encoder roller And a second encoder mechanism for calculating the paper conveyance speed, and comparing and collating the paper conveyance speed calculated by the first encoder mechanism with the paper conveyance speed calculated by the second encoder mechanism. Thus, the change of the roller diameter due to the thermal expansion of the first encoder roller due to the temperature rise is monitored from the collation result, and the calculation process of the paper conveyance speed by the first encoder mechanism is corrected. And

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic configuration diagram of an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 forms an image on the paper 16 conveyed by the image forming unit 14 based on the reference image information 12. Further, in this apparatus 10, the image formed on the paper 16 is read by the image reading means 18, and the read image (read image information) 20 and the original reference image information 12 are sent to the image inspection means 22. To determine whether image formation has been performed according to the reference image.

  The “paper” used in this specification is a concept including paper, film, OHP sheet, cardboard, postcard, and the like, and indicates all sheet-like recording media to be printed.

  The image forming unit 14 forms a toner image based on the reference image information 12. The image forming unit 14 includes a transfer unit 24 and a fixing unit 26, and the formed toner image is transferred by the transfer unit 24 onto the paper 16 sent from the paper feed tray. The paper 16 to which the toner image has been transferred is sent to the fixing unit 26 along the conveyance path, where the toner is fused and the image is fixed on the paper 16. The image formed on the paper 16 is sent to the image reading means 18. The image reading unit 18 includes a line sensor 28 that reads an image formed on the paper 16, reads the image on the paper 16 that has been conveyed, and sends the read image information 20 to the image inspection unit 22.

  The image inspection unit 22 inspects and determines an image formed on the paper 16 based on the obtained information. That is, the image inspection unit 22 includes a control unit 40 and a collation determination unit 42, and the reference image information 12 and the read image information 20 are compared using these, and the image on the paper 16 is normally formed. It is determined whether or not there is an abnormality. The image inspection apparatus connected to the image forming apparatus 10 can be configured by the image reading unit 18 and the image inspection unit 22.

  In the image forming apparatus 10 that performs inspection / determination as described above, in order to obtain correct read image information 20, for example, an encoder mechanism 50 as shown in FIGS. 2A and 2B is provided in the vicinity of the line sensor 28 that reads image data. Provided.

  The encoder mechanism 50 includes an encoder roller 51, a pressing roller 52, and a pulse detector 53, and is arranged so that the passing paper 16 is sandwiched between the encoder roller 51 and the pressing roller 52. The encoder roller 51 and the pressing roller 52 are set to pressures that do not apply a load to the conveyed paper 16, and the encoder roller 51 rotates without slipping as the paper 16 passes. . The rotation amount of the encoder roller 51 is detected as the number of pulses by the pulse detector 53. Therefore, the encoder mechanism 50 can calculate the sheet conveyance speed from values such as the number of pulses and the pulse interval and the number of pulses and the encoder roller rotation time. The calculation of the sheet conveyance speed may be performed by the control unit 40 connected to the encoder mechanism 50 (not shown).

  Here, in the image forming apparatus 10 illustrated in FIG. 1, heat is used when fixing the toner on the paper 16, so that the high-temperature paper 16 is continuously conveyed. Therefore, there is a problem that the encoder roller 51 is heated and the roller diameter changes due to thermal expansion. If the roller diameter of the encoder roller is constantly changing, the correct paper conveyance speed cannot be measured. Therefore, in order to solve this problem, in this embodiment, the sensor 54 is installed at a position coaxial with the encoder roller 51. The sensor 54 can measure the passage time of the conveyed paper 16, and can calculate the paper conveyance speed from, for example, the paper passage time and the previously recognized paper dimensions. . Note that the calculation of the sheet conveyance speed using the sensor 54 can also be performed by the control unit 40.

  By comparing and collating the paper conveyance speed calculated by the encoder mechanism 50 with the paper conveyance speed calculated based on the detection value of the sensor 54, the change in the roller diameter of the encoder roller 51 with the temperature rise is obtained from the comparison result. It is possible to calculate. That is, the roller diameter of the encoder roller 51 may be calculated from the difference in the sheet conveyance speed. Therefore, based on the calculated roller diameter of the encoder roller 51, the paper conveyance speed calculation processing condition by the control unit 40 is corrected so that the paper conveyance speed calculation processing by the encoder mechanism 50 always has a correct result. Can do it.

  As the sensor 54, any type of sensor such as a transmissive optical sensor can be employed. However, when a reflection sensor is used, the type of paper to be inspected is limited to white paper or the like, which is problematic in terms of versatility. On the other hand, when the reflection sensor is used, it is possible to install the sensor directly under the image reading means 18, and there is an advantage that the restriction on the design in terms of hardware can be eliminated.

  In this embodiment, the case where the sheet conveyance speed calculated by the encoder mechanism 50 and the sheet conveyance speed calculated based on the detection value of the sensor 54 are compared and collated is described as an example. It is obvious that any method can be used as long as it can monitor the roller diameter. For example, by looking at the difference between the rotation amount of the encoder roller 51 (that is, the paper size) and the paper size calculated based on the paper passage time detected by the sensor 54, it is possible to capture the change in the roller diameter.

[Second Embodiment]
In the first embodiment described above, a case where the sensor 54 is installed on the same axis as the encoder roller 51 in order to correct the change in the roller diameter of the encoder roller 51 due to the heat of the conveyed paper 16 will be described as an example. did. In the present embodiment, a case will be described in which an encoder mechanism different from the encoder mechanism 50 is further provided to correct fluctuations in the roller diameter of the encoder roller 51. Note that members that are the same as or similar to those in the first embodiment are denoted by the same reference numerals and description thereof is omitted.

  In the present embodiment, as shown in FIGS. 3, 3A and 3B, a first encoder mechanism 60 installed on the conveyance path of the paper 16 and always operating, and the first encoder mechanism 60 The first encoder roller 61 is provided with a second encoder roller 71 installed coaxially, and a second encoder mechanism 70 is installed so as to operate at a predetermined interval. What is characteristic in the present embodiment is that the second encoder mechanism 70 is set to operate at a predetermined interval with respect to the first encoder mechanism 60 that constantly monitors the sheet conveyance speed. It is that you are. With this configuration, the first encoder mechanism 60 calculates the sheet conveying speed calculated by the second encoder mechanism 70 that can measure the correct conveying speed without being affected by the heat from the sheet 16 at a predetermined interval. By comparing and collating with the sheet conveyance speed to be performed, it is possible to monitor the change in the roller diameter due to the thermal expansion of the first encoder roller 61 accompanying the temperature rise from the collation result.

  As for the second encoder mechanism 70, as shown in FIGS. 3A and 3B, the second encoder roller 71 and the second pressing roller 72 are set at predetermined positions (in the direction of the arrow Y1) when measuring the sheet conveyance speed. It is possible to measure the paper conveyance speed by contacting the paper 16 being conveyed (see FIG. 3A). On the other hand, when the sheet conveyance speed is not measured, the second encoder roller 71 and the second pressing roller 72 are retracted (moved in the direction of the arrow Y2) to avoid the influence of the heat generated by the sheet 16 (FIG. 3B).

  The technical scope of the present invention is not limited to the scope described in the above embodiment, and various modifications or improvements can be added to the above embodiment. It is apparent from the description of the scope of claims that embodiments with such changes or improvements can be included in the technical scope of the present invention.

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. It is a figure for demonstrating the apparatus structure of the encoder mechanism which concerns on 1st Embodiment. It is a figure for demonstrating the apparatus structure of the encoder mechanism which concerns on 1st Embodiment. It is a figure for demonstrating the apparatus structure of the 1st and 2nd encoder mechanism which concerns on 2nd Embodiment. It is a figure for demonstrating operation | movement of the 2nd encoder mechanism which concerns on 2nd Embodiment. It is a figure for demonstrating operation | movement of the 2nd encoder mechanism which concerns on 2nd Embodiment.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Image forming apparatus, 12 Reference | standard image information, 14 Image forming means, 16 Paper, 18 Image reading means, 20 Read image information, 22 Image inspection means, 24 Transfer part, 26 Fixing part, 28 Line sensor, 40 Control part, 42 Collation determination unit, 50 encoder mechanism, 51 encoder roller, 52 pressure roller, 53 pulse detector, 54 sensor, 60 first encoder mechanism, 61 first encoder roller, 70 second encoder mechanism, 71 second encoder Roller, 72 Second pressing roller.

Claims (8)

An image inspection apparatus that inspects a formed image by reading an image formed on a conveyed sheet,
An encoder mechanism installed on the paper transport path, and an encoder mechanism for calculating a paper transport speed based on the number of pulses detected by the encoder roller;
A sensor mechanism that is provided coaxially with the encoder roller, and that calculates a paper conveyance speed based on a passage time of the paper detected by the sensor;
Have
By comparing and collating the paper conveyance speed calculated by the encoder mechanism and the paper conveyance speed calculated by the sensor mechanism, the change in the roller diameter due to the thermal expansion of the encoder roller accompanying the temperature rise is monitored from the comparison result, An image inspection apparatus, wherein the sheet conveyance speed calculation processing by the encoder mechanism is corrected. An image inspection apparatus that inspects a formed image by reading an image formed on a conveyed sheet,
A first encoder mechanism that is provided on the paper conveyance path and is constantly operated; and a first encoder mechanism that calculates a paper conveyance speed based on the number of pulses detected by the first encoder roller;
A second encoder roller that is installed coaxially with the first encoder roller and operates at a predetermined interval is provided, and a sheet conveyance speed is calculated based on the number of pulses detected by the second encoder roller. A second encoder mechanism;
Have
By comparing and collating the paper conveyance speed calculated by the first encoder mechanism with the paper conveyance speed calculated by the second encoder mechanism, the thermal expansion of the first encoder roller as the temperature rises from the comparison result. An image inspection apparatus characterized by monitoring a change in a roller diameter caused by the first encoder mechanism and correcting a paper conveyance speed calculation process by the first encoder mechanism. An image inspection apparatus connected to an image forming machine that forms an image on a sheet based on reference image information serving as a reference, and the read image information obtained by reading the formed image and the reference image information An image inspection apparatus that performs inspection by collating
An encoder mechanism installed on the paper transport path, and an encoder mechanism for calculating a paper transport speed based on the number of pulses detected by the encoder roller;
A sensor mechanism that is provided coaxially with the encoder roller, and that calculates a paper conveyance speed based on a passage time of the paper detected by the sensor;
Have
By comparing and collating the paper conveyance speed calculated by the encoder mechanism and the paper conveyance speed calculated by the sensor mechanism, the change in the roller diameter due to the thermal expansion of the encoder roller accompanying the temperature rise is monitored from the comparison result, An image inspection apparatus, wherein the sheet conveyance speed calculation processing by the encoder mechanism is corrected. An image inspection apparatus connected to an image forming machine that forms an image on a sheet based on reference image information serving as a reference, and the read image information obtained by reading the formed image and the reference image information An image inspection apparatus that performs inspection by collating
A first encoder mechanism that is provided on the paper conveyance path and is constantly operated; and a first encoder mechanism that calculates a paper conveyance speed based on the number of pulses detected by the first encoder roller;
A second encoder roller that is installed coaxially with the first encoder roller and operates at a predetermined interval is provided, and a sheet conveyance speed is calculated based on the number of pulses detected by the second encoder roller. A second encoder mechanism;
Have
By comparing and collating the paper conveyance speed calculated by the first encoder mechanism with the paper conveyance speed calculated by the second encoder mechanism, the thermal expansion of the first encoder roller as the temperature rises from the comparison result. An image inspection apparatus characterized by monitoring a change in a roller diameter caused by the first encoder mechanism and correcting a paper conveyance speed calculation process by the first encoder mechanism. An image inspection method used when an image inspection apparatus connected to an image forming machine that forms an image on a sheet based on reference image information serving as a reference is operated using a computer. An image inspection method for executing an inspection process by collating with read image information obtained by reading the formed image,
On the computer,
A first paper transport speed calculating step for calculating a paper transport speed based on the number of pulses detected by an encoder roller installed on the paper transport path;
A second paper transport speed calculating step for calculating a paper transport speed based on a passage time of the paper detected by a sensor installed coaxially with the encoder roller;
By comparing and collating the paper conveyance speed calculated by the first paper conveyance speed calculation step and the paper conveyance speed calculated by the second paper conveyance speed calculation step, the collation results in accordance with the temperature rise. An encoder roller diameter calculating step for calculating a change amount of the roller diameter due to thermal expansion of the encoder roller;
Correcting the paper conveyance speed calculation process in the first paper conveyance speed calculation step based on the roller diameter of the encoder roller calculated in the encoder roller diameter calculation step;
An image inspection method characterized by causing a process including: An image inspection method used when an image inspection apparatus connected to an image forming machine that forms an image on a sheet based on reference image information serving as a reference is operated using a computer. An image inspection method for executing an inspection process by collating with read image information obtained by reading the formed image,
On the computer,
A first paper transport speed calculating step for calculating a paper transport speed based on the number of pulses detected by a first encoder roller installed on the paper transport path and always operating;
A second paper conveyance speed calculating step for calculating a paper conveyance speed based on the number of pulses detected by a second encoder roller that is installed coaxially with the first encoder roller and operates at a predetermined interval. When,
By comparing and collating the paper conveyance speed calculated by the first paper conveyance speed calculation step and the paper conveyance speed calculated by the second paper conveyance speed calculation step, the collation results in accordance with the temperature rise. An encoder roller diameter calculating step for calculating a change amount of the roller diameter due to thermal expansion of the first encoder roller;
Correcting the paper conveyance speed calculation process in the first paper conveyance speed calculation step based on the roller diameter of the first encoder roller calculated in the encoder roller diameter calculation step;
An image inspection method characterized by causing a process including: An image forming unit that forms an image on a conveyed sheet based on reference image information serving as a reference;
Image reading means for acquiring read image information by reading an image formed on the paper;
An image inspection means for verifying whether the difference between the reference image information and the read image information is within a predetermined range;
In an image forming apparatus having
An encoder mechanism installed on the paper transport path, and an encoder mechanism for calculating a paper transport speed based on the number of pulses detected by the encoder roller;
A sensor mechanism that is provided coaxially with the encoder roller, and that calculates a paper conveyance speed based on the passage time of the paper detected by the sensor;
Have
By comparing and collating the paper conveyance speed calculated by the encoder mechanism and the paper conveyance speed calculated by the sensor mechanism, the change in the roller diameter due to the thermal expansion of the encoder roller accompanying the temperature rise is monitored from the comparison result, An image forming apparatus, wherein the paper feed speed calculation processing by the encoder mechanism is corrected. An image forming unit that forms an image on a conveyed sheet based on reference image information serving as a reference;
Image reading means for acquiring read image information by reading an image formed on the paper;
An image inspection means for verifying whether the difference between the reference image information and the read image information is within a predetermined range;
In an image forming apparatus having
A first encoder mechanism that is provided on the paper conveyance path and is constantly operated; and a first encoder mechanism that calculates a paper conveyance speed based on the number of pulses detected by the first encoder roller;
A second encoder roller that is installed coaxially with the first encoder roller and operates at a predetermined interval is provided, and a sheet conveyance speed is calculated based on the number of pulses detected by the second encoder roller. A second encoder mechanism;
Have
By comparing and collating the paper conveyance speed calculated by the first encoder mechanism with the paper conveyance speed calculated by the second encoder mechanism, the thermal expansion of the first encoder roller as the temperature rises from the comparison result. The image forming apparatus is characterized in that the change in the roller diameter due to is monitored and the calculation process of the paper conveyance speed by the first encoder mechanism is corrected.

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