JP2020007122A - Image formation device - Google Patents

Abstract

To solve the problem that it cannot be determined that a sensor has been replaced with a different kind of one.SOLUTION: An image formation device 100 includes: a conveyance roller R9 for conveying a sheet along a conveyance path; a sheet detection sensor PS9 which has laser scanners 1Y, 1M, 1C and 1Bk, a light emitting element 233 and a light receiving element 234, and detects the sheet on the conveyance path; an EEPROM 302 for storing a time to when the sheet detection sensor PS9 detects the sheet; and a CPU 301 for determining that whether or not the sheet detection sensor PS9 has been replaced. When a main power supply of the device is turned on, the CPU 301 makes the sheet to be conveyed, and makes the sheet detection sensor PS9 detects the sheet, and measures a time Tnow to when the sheet detection sensor PS9 detects the sheet, and, when a difference Tdef of the time Tnow and a time Tbefore is larger than α1 and further smaller than β1, determines that the sheet detection sensor PS9 is replaced.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus having a sensor for detecting a conveyed sheet.

  2. Description of the Related Art Conventionally, an image forming apparatus feeds a sheet from a cassette or a tray, conveys the sheet along a conveyance path, and transfers a toner image to the conveyed sheet to create a product. If the conveyance of the sheet becomes inaccurate, an image is not formed at a desired position on the sheet, and the quality of the product is reduced. Further, when a jam occurs in the apparatus, the sheet may be deformed in a bellows shape. It takes a lot of effort to remove the bellows-shaped jam sheet. Since it takes time to remove the jam sheet, there is a possibility that the downtime during which printing cannot be performed becomes long.

  Therefore, a general image forming apparatus has a plurality of sheet detection sensors arranged on a conveyance path. If the sheet detection sensor does not detect the sheet at a predetermined timing, the image forming apparatus stops conveying the sheet. By controlling in this way, the downtime is prevented from becoming long.

  For example, Patent Literature 1 discloses an image forming apparatus including a reflection-type optical sensor in a transport path. If the reflection type optical sensor has a fast response, the presence or absence of a sheet can be detected with high accuracy even when the image forming apparatus is operated at high speed.

JP-A-2003-306256

  Optical sensors commercialized to detect a sheet often have similar appearances from different manufacturers and different types in order to ensure compatibility of the mounting configuration. In some cases, the image forming apparatus main body has a configuration in which the compatibility of a plurality of optical sensors is ensured so that a low-cost optical sensor can be selectively mounted among them. However, the optical characteristics of these optical sensors often differ, and the detection characteristics of the sensors change. FIG. 9 shows a detection area in the sheet conveyance direction using sensors 400a and 400b having different optical characteristics as an example. The detection area of the sensor 400b is wider than the detection area of the sensor 400a. Therefore, it is faster for the sheet P to reach the detection area of the sensor 400b than to reach the detection area of the sensor 400a. The timing at which the sheet P ends passing through the detection area of the sensor 400b is later than the timing at which the sheet P ends passing through the detection area of the sensor 400a.

  FIG. 10 illustrates a problem in a loop amount control technique for correcting skew of a conveyed sheet in sheet conveyance control of the image forming apparatus. The sensor is replaced from the sensor 400a to the sensor 400b for maintenance or the like. The difference in the amount of skew correction loop immediately after is shown. The loop state of the sheet when the sheet detection sensor 400a is mounted is indicated by a solid line, and the loop state immediately after being replaced by the sheet detection sensor 400b is indicated by a dotted line. The stop timing of the conveyance roller R9 is determined based on the timing at which the sheet detection sensor PS9 detects the leading edge of the conveyed sheet. At this time, since the transport roller R10 has stopped, the sheet is pushed into the nip portion of the transport roller R10. The skew of the sheet generated during the conveyance by the pushing is corrected. When the sensor is replaced with the sensor 400b, the detection timing is advanced as described with reference to FIG. 9, so that the stop timing of the transport roller R9 is also advanced, and the pushing amount to the transport roller R10 is reduced as indicated by the dotted line. As a result, the skew is not sufficiently corrected. The post-process of the transport roller R10 is transfer, and if the skew correction is insufficient, a result is obtained in which an image is formed obliquely to the sheet as shown in FIG.

  Therefore, when a sensor or a unit including a sensor is replaced during service maintenance, if the device does not correctly recognize which sensor is connected, an error occurs in the timing of detecting a sheet, resulting in a decrease in the quality of a printed product and a decrease in conveyance. May cause jam. On the other hand, a method that relies on human beings, such as determining the type of sensor from the external appearance and setting the sensor in the apparatus, has a problem that erroneous setting and omission of setting are likely to occur. In addition, in order to check all the sensors included in the unit, there is a possibility that a work of removing a component constituting the unit may be involved, and there is a possibility that another abnormality may be caused by a work mistake.

  Thus, an object of the present invention is to determine that a sensor of a different type has been replaced.

  In order to solve the above problems, an image forming apparatus of the present invention includes a conveying unit that conveys a sheet along a conveying path, an image forming unit that forms an image on the sheet, a light emitting unit and a light receiving unit, An image forming apparatus comprising: a sensor that detects a sheet on the transport path; a storage unit that stores a time until the sensor detects the sheet; and a determination unit that determines whether the sensor has been replaced. When the main power supply of the image forming apparatus is turned on, the determination unit causes the conveyance unit to convey the sheet, causes the sensor to detect the sheet, and sets a time period until the sensor detects the sheet. When the difference between the measured time and the time stored in the storage means is larger than a first value and smaller than a second value larger than the first value, And judging that the conversion.

  According to the present invention, it can be determined that the sensor has been replaced with a different type of sensor.

Flow chart showing an initial sequence according to the first embodiment. Flowchart showing an initial sequence according to the second embodiment. Sectional view of main part of sheet detection sensor Circuit block diagram of the interface between the sheet detection sensor and the image forming apparatus Control block diagram of control unit Schematic diagram showing transition of the count value of the measurement counter Schematic diagram of measurement time of sheet detection sensors 400a and 400b Schematic sectional view of an image forming apparatus Schematic diagram showing optical characteristics of sheet detection sensors 400a and 400b. FIG. 4 is a schematic diagram showing a change in a sheet loop amount when a sheet detection sensor is replaced. Schematic diagram in which the amount of skew correction changes when the sheet detection sensor is replaced

(1st Embodiment)
Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

  Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings. FIG. 8 is a schematic sectional view of a color digital printer as an example of the image forming apparatus 100 of the present invention.

  First, the image forming unit will be described. The four laser scanners 1Y, 1M, 1C, and 1Bk form electrostatic latent images on four photosensitive drums 2Y, 2M, 2C, and 2Bk, respectively, and form toner images by four developing units 3Y, 3M, 3C, and 3Bk, respectively. I do. The respective color toner images formed on the four photosensitive drums 2Y, 2M, 2C, and 2Bk are transferred onto the intermediate transfer belt 130 by the four primary transfer units 4Y, 4M, 4C, and 4Bk, respectively. As a result, a full-color toner image is formed on the intermediate transfer belt 130. The toner image on the intermediate transfer belt 130 is conveyed to the secondary transfer unit R11 as the intermediate transfer belt 130 rotates.

  The sheet is fed from one of the cassettes CST1 to CST3 by the pickup units PU1 to PU3, and is conveyed toward the registration roller pair R10 by the conveyance roller pairs R5 to R9. Also, when a sheet is fed from the manual feed tray MF, the fed sheet is transported to the registration roller pair R10.

  The registration roller pair R10 controls the sheet feeding timing so that the toner image on the intermediate transfer belt 130 is transferred to a target position on the sheet. The registration roller pair R10 may be configured to control the sheet conveyance speed instead of the conveyance timing. The toner image is transferred to the sheet by the secondary transfer unit R11. Thereafter, the sheet on which the toner image has been transferred is transported to the fixing device UN3. The fixing device UN3 heats and pressurizes the toner image on the sheet to fix the toner image on the sheet. The sheet on which the image is fixed is curled by the decurling unit UN5 from the reversing discharge unit UN4, and is then discharged out of the apparatus main body from the roller pair R15. After printing on the first side during double-sided printing, the sheet is fed again from the reversing and discharging unit UN4 to the registration unit UN1 via the double-sided reversing unit UN6 and the double-sided conveying path UN8, and is similarly printed and discharged.

  Sheet detection sensors PS1 to PS23 for detecting the presence or absence of a sheet are arranged on the conveyance path on which the sheet is conveyed. The sheet detection sensors PS1 to PS23 are reflection sensors.

  FIG. 3 is a sectional view of a main part of the sheet detection sensor PS9. The sheet detection sensor is a reflection type optical sensor having a light emitting element 233 and a light receiving element 234. The sheet detection sensor includes a substrate 200 on which the light emitting element 233 and the light receiving element 234 are mounted, a connector 235 mounted on the substrate 200, lenses 230 and 231, and a resin case member 220. The joints 236a and 236b are used to attach the sheet detection sensor to the image forming apparatus. The joints 236a and 236b are attached by a snap fit. Light emitted from the light emitting element 233 is applied to the detection area via the lens 230. Light reflected from the detection area is received by the light receiving element 234 via the lens 231. The light receiving element 234 outputs an output value corresponding to the amount of reflected light (the intensity of the reflected light). The output value is a voltage or current analog value.

  The optical characteristics of the sheet detection sensor are determined in advance by the structures of the light emitting element 233, the light receiving element 234, the lens 230, and the lens 231. The shape of the lenses 230 and 231, the intensity distribution of the light emitting element 233, and the sensitivity characteristics of the light receiving element 234 differ depending on the type of the sheet detection sensor. Therefore, for example, the area of the detection area of the sheet detection sensor is different for each type of the sheet detection sensor.

  FIG. 4 is a circuit block diagram of an interface portion between the sheet detection sensor and the control unit 300. The light emitting unit 201 includes a light emitting element 233 (for example, an LED) and a resistor, and the light receiving unit 202 includes a light receiving element 234 (for example, a photodiode) and an operational amplifier that functions as a comparator. The output voltage of the light receiving unit 202 is input to the transistor of the output unit 203. The control unit 300 includes a CPU 301, an input unit 211 connected to the sheet detection sensor via a cable, and an input / output unit 304 connected to an output terminal of the input unit 211. The input unit 211 has a CR filter for removing a high-frequency component of the output value of the sheet detection sensor. The CPU 301 supplies power to the light emitting unit 201 via the input / output unit 304, and acquires an output value corresponding to a detection result of the sheet detection sensor.

  When a sheet is detected, the operational amplifier of the light receiving unit 202 outputs the voltage Vcc. The voltage Vcc is a voltage value applied to the sheet detection sensor to drive the sheet detection sensor. On the other hand, when no sheet is detected, the output voltage of the operational amplifier of the light receiving unit 202 becomes 0V. An operational amplifier is connected to a base of the transistor of the output unit 203, and a power supply line of the input unit 211 is connected to a collector of the transistor of the output unit 203.

  In the above configuration, when a sheet is detected, the base voltage of the transistor becomes the voltage Vcc, and a current flows between the collector and the emitter. As a result, the voltage of the output terminal of the input unit 211 becomes 0V. That is, when a sheet is detected, a low-level signal is input to the CPU 301 via the input / output unit 304. On the other hand, when no sheet is detected, the base voltage of the transistor becomes 0 V, and no current flows between the collector and the emitter. Therefore, the voltage of the output terminal of the input unit 211 becomes Vcc. That is, when a sheet is detected, a high-level signal is input to the CPU 301 via the input / output unit 304.

  FIG. 5 is a control block diagram of the image forming apparatus 100. The control unit 300 includes an EEPROM 302 and a RAM 303 in addition to the configuration shown in FIG. The image forming apparatus 100 according to the present embodiment has a configuration in which a low-level signal is input to the control unit 300 when a sheet detection sensor detects a sheet, but is not limited to the circuit configuration and the like described here. Absent. For example, the image forming apparatus 100 may be configured such that a high-level signal is input to the control unit 300 when the sheet detection sensor detects a sheet.

  FIG. 5 is a control block diagram of the control unit 300. Only parts relevant to the present invention are shown. The CPU 301 controls various sensors and motors based on a program stored in the internal memory in advance, and executes arithmetic processing. The EEPROM 302 is a nonvolatile memory of the image forming apparatus 100. The RAM 303 functions as a system work memory. The input / output unit 304 has an input circuit for receiving signals from the sheet detection sensors PS1 to PS23, and a drive circuit for moving the motors M1 to M11 for driving the transport rollers. An operation unit 305 instructs print setting of the image forming apparatus and start or stop of a print operation. The operation unit 305 includes a power saving button described later.

  Next, the sheet detection sensor identification control in the first embodiment will be described with reference to the flowcharts of FIGS. 1A and 1B. First, an initial sequence including the sensor identification control 1 will be described with reference to FIG. 1A. When the mode is shifted to the normal mode, the CPU 301 reads out the program stored in the EEPROM 302 and executes an initial sequence.

  When the apparatus is activated in step S1001 and power is supplied to the operation unit 305 and the control unit 300, the CPU 301 shifts the processing to step S1002, and determines whether the main power of the image forming apparatus has been turned on or not in the power save mode. Is changed to the normal mode.

  Note that the power save mode is also called a sleep mode. The normal mode is also called a standby mode. In the power save mode, the backlight of the touch panel of the operation unit 305 is turned off, and power supply to some units of the image forming apparatus is stopped. As a result, the power consumption in the power save mode is lower than the power consumption in the normal mode.

  Here, when the power saving key of the operation unit 305 is pressed while the image forming apparatus is controlled to the power save mode, the CPU 301 changes the mode to the normal mode. On the other hand, when the power saving key of the operation unit 305 is pressed while the image forming apparatus is controlled in the normal mode, the CPU 301 determines whether an adjustment operation or a print operation is being performed, and the adjustment operation or the print operation is performed. If not, change the mode to the power save mode.

  When a print job including image data is transferred from an external device while the image forming apparatus is controlled in the power save mode, the CPU 301 changes the mode to the normal mode. Further, if the image forming apparatus does not operate in the normal mode for a predetermined time, the CPU 301 changes the mode to the power save mode.

  Returning to the description of the flowchart of FIG. If the main power supply of the image forming apparatus is turned on in step S1002, the CPU 301 shifts the processing to step S1003 and validates the sensor identification control 1. Normally, when the sheet detection sensor of the image forming apparatus 100 is broken down due to some abnormality and is forced to be replaced, a service person turns off the main power supply of the image forming apparatus 100 and unplugs the power cord to perform the operation. This is because the image forming apparatus 100 is energized in the power save mode. Therefore, the CPU 301 enables the sensor identification control 1 only at the time of startup from the main power supply where the sensor replacement may be performed. Then, the CPU 301 shifts the processing to step S1005 and waits until a print job is started.

  On the other hand, when the mode of the image forming apparatus 100 shifts from the power save mode to the normal mode in step S1002, the CPU 301 shifts the processing to step S1004 and invalidates the sensor identification control 1. Then, the CPU 301 shifts the processing to step S1005 and waits until a print job is started.

  Subsequently, after the print job is started in step S1005, the CPU 301 shifts the processing to step S1006, and determines whether or not the sensor identification control 1 is valid. If sensor identification control 1 is valid in step S1006, the CPU 301 shifts the processing to step S1007 and starts sensor identification control 1. Detailed processing of the sensor identification control 1 will be described later based on the flowchart of FIG. 1B. After the sensor identification control 1 is started in step S1007, the CPU 301 shifts the processing to step S1008 and waits until the sensor identification control 1 ends.

  When the sensor identification control 1 ends in step S1008, the CPU 301 shifts the processing to step S1009, and checks the sensor replacement flag which is the execution result of the sensor identification control 1. If the value of the exchange flag is 1, the CPU 301 shifts the processing to step S1010 and waits until the print job ends.

  After the print job is completed, the CPU 301 shifts the processing to step S1011 and asks the touch panel (operation screen) of the operation unit 305 whether or not to approve the sensor automatic identification result and a message of “Yes” or “No”. Show action button. If “Yes” is pressed on the operation unit 305, the CPU 301 determines that the sensor automatic identification result has been approved, and shifts the processing to step S1013.

  On the other hand, if “No” is pressed on operation unit 305, CPU 301 shifts the processing from step S1012 to step S1015. When the sensor identification result is approved and the process proceeds to step S1013, the data Tnow measured by the sensor identification control 1 is stored in the EEPROM 302 as the measurement result Tbefore before the power is turned off. Then, in step S1014, the parameters of the transport control are changed. Specifically, in synchronization with the detection timing of the sheet detection sensor PS9, the number of pulses for driving the motor M1 is changed according to the type of the sensor. Thereafter, unless the main power is turned off / on, the sensor identification control 1 is invalidated in step S1015 so that the sensor identification control 1 is not executed, and the processing of the initial sequence ends (S1016).

  If the value of the replacement flag is 0 in step S1009, the CPU 301 determines that the sheet detection sensor has not been replaced, or even if it has been replaced, has a characteristic equivalent to that before power-off. . If the value of the exchange flag is 0, the CPU 301 shifts the processing from step S1009 to step S1015.

  If the sensor identification control 1 is invalid in step S1006, the CPU 301 shifts the processing to step S1016 and ends the processing of the initial sequence. In this case, only the normal print job is executed without executing the sensor identification control 1.

  Next, the processing procedure of the sensor identification control 1 started in step S1007 of FIG. 1A will be described with reference to the flowchart of FIG. 1B. The entire flow measures the time until the sheet detection sensor PS9 detects the leading edge of the sheet, starting from the motor M1 that operates at the start of the print job. Then, the CPU 301 determines whether or not the difference between the measured value Tbefore stored before the main power is turned off and the measured value Tnow measured this time is within a predetermined range. Then, based on whether or not the difference between the measured value Tbefore and the measured value Tnow is within a predetermined range, the CPU 301 determines whether or not the sheet detection sensor PS9 has been replaced with another sensor having different characteristics. Hereinafter, each step will be described. In the present embodiment, a case where sheets are fed from the cassette CST1 is taken as an example.

  In step S1101, the CPU 301 starts rotating the transport roller R10 by the motor M1. When the control of the motor M1 is started, the CPU 301 shifts the processing to step S1102 and starts the counting operation of a measurement timer (not shown). Next, the CPU 301 shifts the processing to step S1103 and waits until the sheet detection sensor PS9 detects a sheet. If the sheet detection sensor PS9 detects a sheet in step S1103, the CPU 301 shifts the processing to step S1104 and stops the measurement timer. The CPU 301 shifts the processing to step S1105 and acquires the measurement result Tnow.

  FIG. 6 is a timing chart showing the counting operation of the measurement timer at this time. The counter starts from 0, and the value of the counter counts up based on a 1 μsec reference clock in the CPU 301. If the count value when the measurement timer stops is n, the measurement result Tnow is n + 1.

  Next, the CPU 301 shifts the processing to step S1106, and reads out the measurement result Tbefore before the power-off stored in the EEPROM 302. The measurement result Tbefore before the power is turned off corresponds to the measurement result of the sheet detection sensor PS9 before replacement. After the measurement result Tbefore is read, the CPU 301 shifts the processing to step S1107, and calculates a difference value Tdef between the measurement results Tnow and Tbefore. The CPU 301 determines in step S1108 whether or not the difference value Tdef calculated in S1107 is within the range of α1 to β1. If the difference value Tdef is within the range, the CPU 301 shifts the processing to step S1109 and sets the sensor replacement flag to 1. Then, the CPU 301 shifts the processing to step S1111 and ends the processing of sensor identification control 1.

  On the other hand, if the difference value Tdef is out of the range in S1108, the CPU 301 shifts the processing to step S1110, sets the sensor replacement flag to 0, shifts to step S1111 and ends the sensor identification control 1. Here, the difference in measurement time when the sheet detection sensor PS9 is replaced from the sensor 400a shown in FIG. 9 to the sensor 400b having different characteristics from the sensor 400a will be described with reference to a timing chart shown in FIG. Since the sensor 400b has a wider optical detection area than the sensor 400a, the sensor 400b can detect the sheet earlier than the sensor 400a when the sheet reaches a predetermined position. In FIG. 7, the detection result of the sensor 400a before replacement is represented by a measurement time Tbefore, and the detection result of the sensor 400b after replacement is represented by a measurement time Tnow. FIG. 7 shows that the measurement time varies depending on the type of sensor.

  Note that the determination threshold value in step S1108 is set so as not to erroneously determine a difference between a time difference caused by a difference due to a sensor characteristic difference and a measurement time due to a jam. In the present embodiment, the detection areas of the sensors 400a and 400b are 1.0 mm and 3.0 mm, respectively, and a measurement time difference due to a difference in the characteristics of the sensors is about 4 to 6 msec. Therefore, α1 = 3 msec (3000 counts) and β1 = 7 msec (7000 counts). The setting of the threshold value differs depending on the characteristic difference of the sensor, the printing speed, and the like.

  According to the present embodiment, when the absolute value of the difference between the measurement times is larger than the first value and smaller than the second value larger than the first value, it can be determined that the sheet detection sensor has been replaced. Therefore, sheet detection sensors having different characteristics can be automatically determined. Further, according to the present embodiment, the parameters of the motor used to convey the sheet can be automatically changed based on the characteristics of the replaced sensor, so that the trouble of the serviceman manually changing the parameters is reduced. it can.

(2nd Embodiment)
Next, an image forming apparatus 100 according to another embodiment will be described. Hereinafter, portions different from the above-described first embodiment will be described, and description of the same configuration and control will be omitted. The configuration of the image forming apparatus 100 and the control circuit block shown in FIG. 5 are the same, and the processing procedure of the sensor identification control performed by the CPU 301 is different. First, in the first embodiment, the sensor identification control is enabled only when the main power is turned on, and it is determined whether there is a possibility that the sensor replacement has been performed at the time of the first print job. On the other hand, in the present embodiment, a flow is used in which a determination is made using data for a plurality of sheets.

  Now, the processing procedure of the present embodiment will be described with reference to the flowcharts shown in FIGS. In step S2001, the apparatus starts up, and power is supplied to the control unit 300. If it is determined in step S2002 that the activation is not performed from the main power supply, the process advances to step S2004. Here, it is determined whether or not the number of times of the measurement control performed in the sensor identification control 2 has reached 10, and if not, the process proceeds to step S2006, and the sensor identification control 2 becomes effective. If the number of times has reached 10, the process proceeds to step S2007, and the sensor identification control 2 is invalidated. On the other hand, if it is determined in step S2002 that the operation is started from the main power supply, the process proceeds to step S2003. Then, the sensor identification control 2 is made valid. Further, in step S2005, the measurement number counter that counts the number of times the sensor identification control 2 is performed is reset. Then, a print job is started (S2008). In step S2009, it is determined whether or not the sensor identification control 2 is valid. If invalid, the print job is executed as it is, but the sensor identification control is performed. Instead, the process moves to step S2017 and ends. If the sensor identification control 2 is valid in step S2009, the process proceeds to step S2010, and the sensor identification control 2 is started. The specific processing procedure of the sensor identification control 2 will be described later with reference to FIG. 2B. Subsequently, in step S2011, it is determined that the sensor identification control 2 has been completed, and when the print job has been completed (S2012), it is determined in step S2013 whether or not the determination enable / disable flag obtained as a result of the sensor identification control 2 is 1. I do. If the judgment possibility flag is not 1, the flow shifts to step S2017 and ends. If the judgment possible / impossible flag is 1, it is further judged in step S2014 whether or not the sensor replacement flag is 1. If the sensor replacement flag is not 1, the flow shifts to S2017 and ends. If the sensor replacement flag matches 1, the process proceeds to step S2015, and the sensor identification setting for causing the image forming apparatus to recognize the type of sensor is automatically changed. Then, in step S2016, the parameter is changed to a transport control parameter corresponding to the sensor identification result.

  Now, the processing procedure of the sensor identification control 2 started in step S2010 will be described with reference to the flowchart of FIG. 2B. The entire flow measures the time until the sheet detection sensor PS9 detects the leading edge of the sheet, starting from the motor M1 that operates at the start of the print job. The processing so far is the same as in the first embodiment. The present embodiment is different from the first embodiment in that, when the number of times of measurement reaches ten, the measurement result is statistically processed and then calculated from the past ten times of data before the main power is turned off. The CPU 301 of the present embodiment determines whether the difference between the measured value TaveBefore stored in the EEPROM 302 and the measured value TaveNow calculated from the current ten data is within a predetermined range or not. Is replaced with another sensor having different characteristics.

  Now, description will be given along each step. In step S2101, when the control of the motor M1 for driving the transport roller R10 is started, the process proceeds to step S2102, and the counting operation of the measurement timer inside the CPU 301 is started. When the sheet detection sensor PS9 detects a sheet in step S2103, the process proceeds to step S2104, and the measurement timer is stopped. In step S2105, the measurement result Tnow is obtained. Here, it is determined in step S2106 whether the number of times of measurement has reached 10 times, and if not, in step S2108, a determination enable / disable flag indicating whether or not sensor identification determination is possible is set to 0, and the process ends. (S2116). When the number of times reaches 10 in step S2106, the process proceeds to step S2107, where the determination enable / disable flag is set to 1, and the sensor identification determination is enabled. Then, an average value of eight measurements excluding the maximum and minimum data from the ten measurement data is calculated (S2109). A difference value TaveDef between the previous average value TaveBefore stored in the EEPROM 302 and the current average value TaveNow is calculated (S2111). In step S2112, it is determined whether the difference value TaveDef is within a predetermined range from α2 to β2, and if it is within the range, the process proceeds to step S2113 to set the sensor replacement flag to 1. If it is out of the range, the flow shifts to step S2114 to set the sensor replacement flag to 0. Then, the current TakeNow is stored in the EEPROM 302 as a SaveBefore, and the process ends (S2116).

  According to the present embodiment, when the absolute value of the difference between the measurement times is larger than the first value and smaller than the second value larger than the first value, it can be determined that the sheet detection sensor has been replaced. Therefore, sheet detection sensors having different characteristics can be automatically determined. Furthermore, according to the present embodiment, the parameters of the motor used to convey the sheet can be automatically changed based on the characteristics of the replaced sensor, so that the trouble of manually changing the parameters by the service person is reduced. it can.

R5 to R11, R15 Transport rollers 1Y, 1M, 1C, 1K Laser scanner PS1 to PS23 Sheet detection sensor 301 CPU
302 EEPROM

Claims (4)

Conveying means for conveying the sheet along the conveying path,
Image forming means for forming an image on the sheet,
A sensor having a light emitting unit and a light receiving unit, and detecting a sheet on the conveyance path;
Storage means for storing a time until the sensor detects the sheet,
A determination unit for determining whether the sensor has been replaced, and
When the main power supply of the image forming apparatus is turned on, the determination unit causes the conveyance unit to convey the sheet, causes the sensor to detect the sheet, and measures a time until the sensor detects the sheet. If the difference between the measured time and the time stored in the storage means is larger than a first value and smaller than a second value larger than the first value, it is determined that the sensor has been replaced. An image forming apparatus comprising: The transport unit has a roller and a motor that rotates the roller,
The image forming apparatus according to claim 1, wherein the determination unit measures a time from when the motor starts rotating the roller to when the sensor detects the sheet. The transport unit has a roller and a motor that rotates the roller,
And a controller configured to change a parameter of the motor used for controlling the roller based on the measured time when it is determined that the sensor has been replaced. 3. The image forming apparatus according to 2.   The determination means causes the conveyance means to convey a plurality of sheets, causes the sensor to detect the plurality of sheets, measures the time in each of a plurality of sheets, and stores an average of a plurality of measured times and the storage. 4. The sensor according to claim 1, wherein when the time difference stored in the means is larger than the first value and smaller than the second value, it is determined that the sensor has been replaced. Item 10. The image forming apparatus according to item 1.

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