JP2019194667A - Image forming apparatus - Google Patents

Abstract

To make it possible to accurately detect a sheet under an environment where dew condensation may occur.SOLUTION: Light output from light-emitting means travels across a conveyance path, is reflected on a reflection member, and enters light receiving means. When a sheet is on the conveyance path, the light is blocked by the sheet. Detection means detects whether the sheet is at a position on the conveyance path across which the light travels on the basis of a detection signal output by the light receiving means according to the quantity of received light. Control means attempts to reduce dew condensation on the reflection member by adjusting at least one of the volume of air and operating time of air blowing means, according to the detection signal output by the light receiving means when the sheet is not at the position on the conveyance path across which the light travels.SELECTED DRAWING: Figure 7

Description

  The present invention relates to an image forming apparatus.

  The fixing device applies heat and pressure to the toner image to fix the toner image on the sheet. A sheet sensor is employed to detect a sheet jam occurring in or near the fixing device. According to Patent Document 1, there is proposed a sheet sensor that detects the presence or absence of a sheet depending on whether light is blocked by the sheet.

Japanese Patent Publication No. 4-15433

  When the sheet passes through the fixing device, water contained in the sheet may evaporate and water vapor may be generated. This water vapor may affect the detection accuracy of the sheet sensor. For example, the sheet sensor described in Patent Document 1 has a configuration in which a light reflected from a light emitting unit is reflected by a reflecting member, and a light receiving unit receives the reflected light. For this reason, when the reflecting member is condensed by water vapor generated from the sheet and the reflectance of the reflecting member is lowered, the detection accuracy of the sheet is lowered. In addition, water vapor generated from the sheet may form water droplets and adhere to the conveyance guide member around the fixing device. If this water droplet adheres to the conveyed sheet, it leads to an image defect. Accordingly, an object of the present invention is to enable accurate detection of a sheet in an environment where condensation can occur.

According to the present invention, for example,
An image forming apparatus,
Light emitting means for outputting light;
A reflecting member that reflects the light output from the light emitting means;
Light receiving means for receiving reflected light from the reflecting member, and receiving the reflected light, which is light that has crossed a conveyance path where the sheet is conveyed at least once from the light emitting means to the light receiving means. A light receiving means for
Detecting means for detecting whether there is a sheet at a position where light crosses the conveyance path based on a detection signal output by the light receiving means according to the amount of received light;
A blowing means for sending air to the reflecting member;
A control unit that adjusts at least one of an air volume and an operating time of the air blowing unit according to a detection signal output by the light receiving unit when there is no sheet at a position where light crosses the conveyance path. A forming apparatus is provided.

  According to the present invention, a sheet can be detected with high accuracy in an environment where condensation can occur.

Schematic sectional view of the image forming apparatus Perspective view of sheet sensor Plan view of sheet sensor Sectional view showing ventilation path for sheet sensor The figure which shows the drive circuit of a ventilation unit, and the detection circuit of a sheet sensor Timing chart showing air flow control Flow chart showing air flow control Flow chart showing air flow control Flow chart showing air flow control Block diagram showing CPU functions Schematic sectional view of the image forming apparatus in Embodiment 1 Diagram explaining parameters related to water vapor volume Plan view showing the ventilation path Flow chart showing air flow control Diagram explaining how to determine working hours Schematic sectional view of the image forming apparatus in Embodiment 5 The perspective view of the sheet sensor in Example 5. Plan view of sheet sensor in embodiment 5 Flow chart showing control of curl correction mechanism The figure explaining the function of CPU The figure explaining the detail of an estimation part

[Example 1]
An electrophotographic color laser beam printer will be described as an example of an image forming apparatus with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. . The image forming apparatus according to the present invention is not limited to a color laser beam printer, but may be another image forming apparatus such as a copying machine or a facsimile.

<Image forming apparatus>
The image forming apparatus 100 shown in FIG. 1 includes process cartridges 5Y, 5M, 5C, and 5K that are detachable from the main body. The letters Y, M, C, and K given to the reference numbers indicate yellow, magenta, cyan, and black toner colors, and will be omitted when matters common to the respective colors are described. The process cartridge 5 includes a toner container 23, a photosensitive drum 1, a charging roller 2, a developing roller 3, a cleaning member 4, and a waste toner container 24. Further, the process cartridge 5 forms an image forming unit 101 together with the exposure unit 7.

  The toner container 23 contains a developer (hereinafter referred to as toner). The photosensitive drum 1 is an image carrier that carries an electrostatic latent image or a toner image. The charging roller 2 uniformly charges the surface of the photosensitive drum 1. The exposure device 7 outputs laser light according to the image information, and forms an electrostatic latent image on the surface of the photosensitive drum 1. The developing roller 3 attaches the toner supplied from the toner container 23 to the electrostatic latent image and develops it to form a toner image.

  An intermediate transfer unit 102, which is an example of a transfer unit, includes an intermediate transfer belt 8, a driving roller 9, a counter roller 10, and a primary transfer roller 6. The primary transfer roller 6 is disposed to face the photosensitive drum 1 and primarily transfers the toner image carried on the photosensitive drum 1 to the intermediate transfer belt 8. The intermediate transfer belt 8 is stretched between a driving roller 9 and a counter roller 10, and is driven by the driving roller 9 to rotate. The intermediate transfer belt 8 rotates in the direction indicated by the arrow A, and conveys the toner image to the secondary transfer unit. The secondary transfer portion is formed by the intermediate transfer belt 8 and the secondary transfer roller 11.

  The paper feed cassette 13 stores a plurality of sheets P. The sheet P is a recording medium (recording material) made of a material that reflects or absorbs light on its surface without transmitting light like paper. The paper feed roller 14 picks up the sheet P and sends it out to the conveyance path. The transport roller 15 transports the sheet P delivered from the paper feed roller 14 further downstream in the transport direction. The registration roller 16 is a conveyance roller that synchronizes the timing at which the sheet P arrives at the secondary transfer portion with the timing at which the toner image arrives at the secondary transfer portion. The toner image is secondarily transferred to the sheet P in the secondary transfer portion. The belt cleaner 21 removes the toner remaining on the intermediate transfer belt 8 and collects it in a waste toner container 22.

  The sheet P to which the toner image has been transferred is conveyed to the fixing device 17. The fixing device 17 includes a heating roller 18 and a pressure roller 19 that apply heat and pressure to the toner image and the sheet P. Inside the heating roller 18, a heat generating unit such as a heater 30 is provided. The heater 30 is provided with a temperature sensor 12 for measuring the temperature of the heating roller 18 or the heater 30. The discharge roller 20 discharges the sheet P on which the toner image is fixed to the outside of the image forming apparatus 100.

  A sheet sensor 31 is provided inside the fixing device 17 and downstream of the heating roller 18 and the pressure roller 19. The downstream refers to the downstream in the conveyance direction of the sheet P. The sheet sensor 31 is a reflective optical sensor. The sheet sensor 31 detects the sheet P conveyed by the heating roller 18 and the pressure roller 19.

  The blower unit 32 has a fan that blows out or sucks air and a motor that drives the fan. The blower unit 32 is provided outside the fixing device 17. The blower unit 32 cools the sheet sensor 31 by sending air, for example, through a ventilation path in the fixing device 17.

  The control board 25 has an electric circuit that controls each part of the image forming apparatus 100. For example, the control board 25 includes a CPU 26 that controls each unit of the image forming apparatus 100 by executing a control program. The CPU 26 controls the drive source (not shown) related to the conveyance of the sheet P, the control related to the sheet sensor 31, the control of the blower unit 32, the control of the drive source (not shown) of the process cartridge 5, the control related to image formation, and the failure detection. You may be responsible for control. The switching power supply 28 converts an AC power supply voltage input from a power cable 29 connected to an external power supply into a DC voltage, and supplies it to the control board 25 and the like.

<Seat sensor>
2A and 2B are perspective views of the sheet sensor 31. FIG. 2A and 2B differ from each other in view of the sheet sensor 31. FIG. In addition, in order to make it easy to understand the orientation of the sheet sensor 31, arrows x, y, and z indicating the directions are given. An arrow z indicates the height direction of the image forming apparatus 100 and is parallel to the conveyance direction of the sheet P in the fixing device 17.

  The first guide 36 is a guide member that is disposed above the pressure roller 19 and guides the sheet P. A cross section of the first guide 36 parallel to the zx plane is substantially U-shaped. That is, one end of the first member 41 is joined to one end of the second member 42. The other end of the second member 42 is joined to one end of the third member 43. The first member 41 has a guide surface for guiding the sheet P.

  The second guide 37 is a guide member that is provided above the heating roller 18 and opposed to the first guide 36 and guides the sheet P. The cross section of the second guide 37 parallel to the zx plane is substantially L-shaped. That is, one end of the fourth member 44 is joined to one end of the fifth member 45. The fourth member 44 has a guide surface that guides the sheet P and is parallel to the first member 41.

  A notch is provided in the center of the first member 41 of the first guide 36. A substrate 35 is fixed to the substrate holding member 46 protruding upward from the second member 42. A light emitting unit 33 and a light receiving unit 34 are mounted on the substrate 35. The light blocking member 47 protruding upward from the second member 42 is provided between the light emitting unit 33 and the light receiving unit 34.

  A notch is also provided in the center of the fourth member 44 of the second guide 37. A reflecting member 38 is fixed to the reflecting member holding portion 48 protruding upward from the fifth member 45. In this example, the reflecting member holding part 48 and the substrate holding member 46 are parallel. The light emitting unit 33, the reflecting member 38, and the light receiving unit 34 are positioned so that the light output from the light emitting unit 33 is regularly reflected by the reflecting member 38 and the reflected light is incident on the light receiving unit 34. In addition, the reflection member 38 should just have the member and reflective film which have the property to reflect light. For example, a mirror or a glossy metal or resin can be used as the reflecting member 38.

  FIG. 3A is a plan view of the sheet sensor 31 when the sheet P is not passing through. FIG. 3B is a plan view of the sheet sensor 31 when the sheet P is passing. As shown in FIG. 3A, the light emitted from the light emitting unit 33 reaches the reflecting member 38 of the second guide 37 across the conveyance path 49. The irradiated light is reflected by the surface of the reflecting member 38 and reaches the light receiving unit 34 across the transport path 49. Accordingly, the light receiving unit 34 outputs a detection signal (for example, a low level signal) indicating that the sheet P is not detected. Alternatively, the light receiving unit 34 does not output a detection signal (eg, a high level signal) indicating that the sheet P is being detected. In this manner, the sheet sensor 31 detects whether or not the sheet P is present at a position where light originating from the light emitting unit 33 crosses in the conveyance path 49.

  As shown in FIG. 3B, when the sheet P is conveyed on the conveyance path 49, the light from the light emitting unit 33 reaches the surface of the sheet P, but the light is blocked by the surface of the sheet P. That is, the light does not reach the reflecting member 38, and the light receiving unit 34 cannot receive the reflected light from the reflecting member 38. Therefore, the light receiving unit 34 outputs a detection signal (eg, a high level signal) indicating that the sheet P is being detected. Alternatively, the light receiving unit 34 does not output a detection signal (eg, a low level signal) indicating that the sheet P is not detected.

<Blower unit>
FIG. 4 is a cross-sectional view of the cooling mechanism of the sheet sensor 31. In FIG. 4, the arrows indicate the flow of air. The exhaust guide 39 guides the air blown from the blower unit 32 to the first guide 36. The exhaust guide 39 and the first guide 36 form a ventilation path 40. As shown in FIG. 4, the substrate 35 is disposed in the ventilation path 40. In addition, a gap is provided between the first member 41 of the first guide 36 and the light emitting unit 33 for air that has entered from the exhaust guide 39 to pass through. The light emitting unit 33 is cooled by the air passing through the gap. Furthermore, the air that has passed through the gap is guided to the reflecting member 38 by a wall that forms part of the light shielding member 47 having a trapezoidal cross section. When air is blown to the reflecting member 38, paper waste or the like hardly adheres to the reflecting surface of the reflecting member 38. Further, when low-humidity air is blown, water vapor in the vicinity of the reflecting member 38 is diffused, and condensation is easily reduced. In this manner, the light from the blower unit 32 disposed outside the fixing device 17 is guided to the light emitting unit 33, whereby the light emitting unit 33 can be cooled and the reflecting member 38 can be cleaned by the blown air.

  The substrate 35 may be sandwiched between the substrate holding member 46 and the light shielding member 47. As a result, the substrate 35 can be positioned stably. Further, the light shielding member 47 can be used not only as an air guiding member but also as a member for holding the substrate 35.

<Description of circuit>
FIG. 5A shows the drive circuit 57 of the blower unit 32. The drive circuit 57 is a step-down converter. The CPU 26 outputs a PWM signal to drive the blower unit 32. The PWM signal is input to the base of the transistor Tr1 via the limiting resistor R1. When the PWM signal becomes Hi level, the transistor Tr1 is turned ON. When the transistor Tr1 is turned on, a voltage generated by dividing the reference voltage Vcc by the resistors R2 and R3 is applied to the base of the transistor Tr2, and the transistor Tr2 is turned on. When the transistor Tr2 is turned on, a charge current flows from the reference voltage Vcc to the electrolytic capacitor C1 through the transistor Tr2 and the coil L1. When the PWM signal becomes low level, the transistor Tr1 is turned off, thereby turning off the transistor Tr2. Thereby, a current flows through the route of the coil L1, the electrolytic capacitor C1, and the regenerative diode D1. By repeating ON / OFF of the PWM signal, a voltage corresponding to the ON duty of the PWM signal is generated at both ends of the electrolytic capacitor C1. This voltage is lower than the reference voltage Vcc. This voltage is applied to the motor in the blower unit 32, and the motor rotates. The number of rotations of the motor is determined according to the voltage applied to the motor.

  The CPU 26 changes the voltage supplied to the blower unit 32 by changing the ON duty of the PWM signal. For example, the CPU 26 outputs the first duty PWM signal to set the air volume of the blower unit 32 to the first air volume. Moreover, CPU26 sets the air volume of the ventilation unit 32 to a 2nd air volume by outputting the PWM signal of a 2nd duty. If the second duty is larger than the first duty, the second air volume is larger than the first air volume.

  FIG. 5B shows the drive circuit 56 of the light emitting unit 33. The CPU 26 outputs a drive signal for driving the light emitting unit 33. The drive signal output from the CPU 26 is smoothed by a smoothing circuit including a resistor R4 and a capacitor C2, and is input to the base of the transistor Tr3. As a result, the transistor Tr3 is turned on. A limiting resistor R5 for limiting current is provided between the collector of the transistor Tr3 and the reference voltage Vcc. The light emitting diode D2 constitutes the light emitting unit 33. The CPU 26 switches light emission / extinction of the light emitting unit 33 by turning on / off the drive signal.

  FIG. 5C shows a detection circuit of the light receiving unit 34. The collector side of the phototransistor Tr4 that receives the light emitted from the light emitting unit 33 is connected to the reference voltage Vcc via the pull-up resistor R6 and also connected to the input port of the CPU 26. The phototransistor Tr4 outputs a detection signal (voltage) at a level corresponding to the amount of received light. Therefore, the voltage input to the input port of the CPU 26 changes between approximately 0V and Vcc. Here, the voltage applied to the input port of the CPU 26 is referred to as the amount of received light. The input port may be an AD port so that the CPU 26 can receive an analog value. When a sufficient amount of light capable of turning on the phototransistor Tr4 is received, a voltage of approximately 0 V is input to the input port of the CPU. On the other hand, when the phototransistor Tr4 cannot receive the reflected light from the reflecting member 38, a voltage substantially equal to the reference voltage Vcc is input to the input port. That is, in this detection circuit, the input voltage (detection voltage) decreases when the amount of received light increases, and the input voltage increases when the amount of received light decreases. In this case, the input voltage increases if the sheet P is present, and the input voltage decreases if the sheet P is not present. Alternatively, a detection circuit may be employed in which the input voltage increases when the amount of received light increases and the input voltage decreases when the amount of received light decreases. In this case, if the sheet P is present, the input voltage decreases, and if there is no sheet P, the input voltage increases.

  The CPU 26 detects the presence or absence of the sheet P based on the voltage input from the input port. For example, the CPU 26 may determine that there is no sheet if the input voltage is less than or equal to the sheet threshold, and the CPU 26 may determine that there is a sheet if the input voltage exceeds the sheet threshold. The resistor R7 is a resistor provided to switch the value of the light receiving gain of the light receiving unit 34. The CPU 26 outputs 0V as an on signal to the gate of the FET 1 to turn on the FET 1. Thereby, FET1 becomes conductive. On the other hand, the CPU 26 outputs Vcc to the gate of the FET 1 as an off signal, thereby turning off the FET 1. When the FET 1 is turned on, the collector side of the phototransistor Tr4 is connected to the reference voltage Vcc via a combined resistance of the pull-up resistor R6 and the resistor R7. When FET1 is turned off, the collector side of the phototransistor Tr4 is connected to the reference voltage Vcc only through the pull-up resistor R6. That is, the CPU 26 switches the light reception gain value of the light receiving unit 34 by outputting an ON signal or an OFF signal to the gate of the FET 1. The CPU 26 sets the light reception gain to the first gain by outputting the ON signal, and sets the light reception gain to the second gain by outputting the OFF signal. For example, a 180 kΩ resistor may be employed as the pull-up resistor R6 and the resistor R7. In this case, when the CPU 26 outputs an ON signal to set the light reception gain to the first gain, the resistance value connected to the reference voltage Vcc is 90 kΩ. On the other hand, when the CPU 26 outputs an off signal to set the light reception gain to the second gain, the resistance value becomes 180 kΩ. That is, the second gain is twice the first gain. When the CPU 26 outputs the off signal, the resistance value connected to the reference voltage Vcc increases. That is, compared with the first gain, the second gain can sufficiently reduce the input voltage to the CPU 26 with a smaller amount of received light.

<Condensation detection>
When the reflecting member 38 is condensed, the reflectance is lowered, the amount of light received by the light receiving unit 34 is reduced, and the detection accuracy of the sheet P is lowered. When the sheet P passes through the fixing device 17, the water adsorbed on the sheet P evaporates to generate water vapor. There is a possibility that the water vapor is condensed on the reflecting member 38. Therefore, when the air blowing unit 32 sends air to the reflecting member 38, it is possible to reduce the water vapor existing around the reflecting member 38 and its surroundings. In this embodiment, the CPU 26 detects the amount of light received by the light receiving unit 34 when the sheet P is not in the sheet sensor 31. Here, it is assumed that the light receiving unit 34 outputs a voltage that is inversely proportional to the amount of received light (negative correlation). When the input voltage exceeds a predetermined threshold, the CPU 26 determines that the amount of received light has decreased (condensation has occurred). When the input voltage does not exceed the threshold, the CPU 26 determines that the amount of received light is greater than a certain level. That is, the CPU 26 may determine that no condensation occurs on the reflecting member 38 or may determine that water vapor is not generated around the reflecting member 38.

<Blower control>
FIG. 6 is a timing chart showing the state of the image forming apparatus 100 and the operation of the blower unit 32. As shown in FIG. 6, power is supplied from the power source at time t0, and the image forming apparatus 100 is activated. That is, at time t0, the image forming apparatus 100 transitions from the power-off state to the standby state. FIG. 7 is a flowchart showing the control executed by the CPU 26.

  In step S <b> 701, the CPU 26 determines whether a print instruction (image formation instruction) is input from the operation unit or an external computer. According to FIG. 7, a print instruction is input at time t1. The state of the image forming apparatus 100 is a standby state waiting for a print instruction from time t0 to time t1. In the standby state immediately after the image forming apparatus 100 is activated, the blower unit 32 does not operate (air volume = 0). Note that the CPU 26 may drive the blower unit 32 so that the air volume is very small. When a print instruction is input at time t1, the CPU 26 advances to S702 to start image formation.

  In step S <b> 702, the CPU 26 controls the image forming apparatus 100 to start printing. Further, the CPU 26 drives the blower unit 32 to start blowing air to the reflecting member 38. Thereby, cooling of the light emission part 33 is also started, and the fall of the emitted light amount accompanying the temperature rise of the light emission part 33 is suppressed. The CPU 26 starts outputting a PWM signal for driving the blower unit 32. Thereby, the drive circuit 57 supplies electric power to the motor of the blower unit 32, the motor rotates the fan, and the air blow to the light emitting unit 33 and the reflecting member 38 is started.

  In step S703, the CPU 26 determines whether printing has ended. The CPU 26 determines whether all print jobs designated by the operation unit or the like have been completed. When printing ends at time t3, the CPU 26 advances to S704.

  In S704, the CPU 26 determines whether or not the elapsed time from the end of printing (time t3) has reached a predetermined time Tx. The CPU 26 measures an elapsed time from the end of printing using a timer or a counter. According to FIG. 6, the elapsed time is the predetermined time Tx at time t4. The predetermined time Tx is a time required until the condensation of the reflecting member 38 is substantially eliminated, and is determined in advance. When the elapsed time reaches the predetermined time Tx, the CPU 26 proceeds to S706. If the elapsed time has not reached the predetermined time, the process proceeds to S705.

  In S <b> 705, the CPU 26 determines whether the amount of light received by the light receiving unit 34 exceeds the dew condensation threshold. When the light receiving unit 34 generates an input voltage that is inversely proportional to the amount of received light, it is determined whether the input voltage is equal to or lower than a voltage threshold value. That is, the CPU 26 may determine the presence or absence of dew condensation on the reflecting member 38 and the state around the reflecting member 38 based on the voltage corresponding to the amount of light received by the light receiving unit 34. Th1 is a dew condensation threshold value used to determine the presence or absence of dew condensation. Thp is a sheet threshold value for determining the presence or absence of the sheet P. Here, Th1> ThP. If the amount of received light exceeds the dew condensation threshold Th1, the CPU 26 determines that the water vapor has been sufficiently reduced and no dew condensation has occurred. If condensation has not occurred, the CPU 26 proceeds to S706 in order to stop the blower unit 32. On the other hand, if the amount of received light does not exceed the condensation threshold Th1 (if the input voltage is equal to or higher than the voltage threshold), the CPU 26 determines that there is a possibility that condensation has occurred. In this case, the CPU 26 proceeds to S704 while maintaining the air volume of the blower unit 32. In addition, when making a transition from S705 to S704, the CPU 26 may wait for a predetermined waiting time. As a result, the processing load on the CPU 26 is reduced.

  In S <b> 706, the CPU 26 stops the blower unit 32. For example, the blower unit 32 stops outputting the PWM signal or reduces the duty of the PWM signal. Note that the blower unit 32 may not be completely stopped. For example, the duty of the PWM signal may be changed so that the air volume of the blower unit 32 becomes very small.

  According to the present embodiment, the CPU 26 can acquire the dew condensation state of the reflection member 38 and the degree of water vapor generation around it by detecting the amount of received light. For example, in a case where the degree of dew condensation or water vapor generation is not taken into account, the blower unit 32 will always be forcibly driven for a certain period of time. On the other hand, in this embodiment, when it is estimated that the degree of condensation or water vapor is low, the CPU 26 stops the blower unit 32. Thereby, the operation time of the ventilation unit 32 is reduced, and power consumption is also reduced. Further, since the operation time of the blower unit 32 is reduced, the CPU 26 can immediately transition from the print state to the next state (standby state or the like). The condensation threshold Th1 is set to be larger than the sheet threshold Thp. Therefore, the CPU 26 can reliably detect the absence of the sheet P. That is, the accuracy of sheet detection is improved while shortening the operation time of the blower unit 32 and reducing the power consumption.

  In the present embodiment, an example of a sequence for changing the operating time of the blower unit 32 after printing according to the amount of received light is shown. Instead of changing the operating time of the blower unit 32, the CPU 26 may change the air volume of the blower unit 32 in accordance with the amount of received light. For example, the CPU 26 may change the duty of the PWM signal according to the amount of received light. When the image forming apparatus 100 is activated at time t <b> 0, the blower unit 32 is driven to have a first air volume (may be zero). At time t1, the blower unit 32 is driven so that the air volume becomes the second air volume (second air volume> first air volume). From time t3 to time t4, the blower unit 32 continues to blow with the second air volume. At time t4, the air volume of the blower unit 32 is reduced from the second air volume to the first air volume (may be zero). The CPU 26 controls the air volume of the blower unit 32 to zero from time t0 to time t1, controls the air volume to the first air volume (> 0) from time t1 to time t2, and changes the air volume to the second air volume after time t2. (> First air volume) may be controlled. Here, time t2 is a time between time t1 and time t3 in FIG.

  In the present exemplary embodiment, a configuration in which one blower unit 32 is controlled under one condition as the configuration of the image forming apparatus 100 is shown. One blower unit 32 may be controlled under a plurality of conditions. For example, the operation time of the blower unit 32 may be controlled according to the amount of light received by the light receiving unit 34 and the temperature in the fixing device 17. At that time, priority may be given to control based on the amount of received light, or priority may be given to control based on the temperature in the fixing device 17. In the control based on the temperature in the fixing device 17, the temperature detected by the temperature sensor 12 is used. For example, even if the amount of received light exceeds the dew condensation threshold Th1, the CPU 26 may continue the operation of the blower unit 32 as long as the temperature in the fixing device 17 has not decreased below a certain value (temperature priority control). ). Further, even if the temperature in the fixing device 17 has decreased to a certain value or less, the CPU 26 may continue the operation of the blower unit 32 if the light reception amount does not exceed the dew condensation threshold Th1 (light reception amount priority). control). According to this embodiment, the blower unit 32 blows air to the sheet sensor 31, but it may also blow air to the fixing device 17. As described above, the blower unit 32 may cool a plurality of units included in the image forming apparatus 100.

[Example 2]
The second embodiment is an improvement of the first embodiment. When power supply from the power source is started and the image forming apparatus 100 is activated, or when the image forming apparatus 100 returns from the energy saving mode to the normal mode according to the print instruction, the CPU 26 causes condensation on the reflecting member 38. Make sure not. Accordingly, the image forming apparatus 100 can start printing in a state where no condensation occurs on the reflecting member 38. The normal mode is a mode in which the image forming apparatus 100 can form an image and corresponds to the above-described print state. The energy saving mode is a mode in which the image forming apparatus 100 cannot form an image, and corresponds to the above-described standby state.

FIG. 8 is a flowchart showing a method executed by the CPU 26.
In step S <b> 801, the CPU 26 determines whether the image forming apparatus 100 has transitioned from the power-off state to the standby state (power-on state) or has returned from the energy saving mode to the normal mode. This step can be executed, for example, between time t0 and time t1 in FIG. If the image forming apparatus 100 has transitioned from the power-off state to the standby state, the CPU 26 advances to S802. If the image forming apparatus 100 returns from the energy saving mode to the normal mode, the CPU 26 proceeds to S802.
In step S <b> 802, the CPU 26 causes the light emitting unit 33 to emit light through the driving circuit 56. The light output from the light emitting unit 33 is reflected by the reflecting member 38 and received by the light receiving unit 34.
In step S803, the CPU 26 receives the amount of received light acquired by the light receiving unit 34, and determines whether the amount of received light exceeds the dew condensation threshold Thp. S803 is the same process as S705. If the amount of received light exceeds the dew condensation threshold value Thp, no dew condensation that would cause a problem in detecting the sheet P has occurred, and the CPU 26 advances to S805. On the other hand, if the amount of received light does not exceed the dew condensation threshold value Thp, there is a possibility that dew condensation that would cause a problem in detecting the sheet P has occurred, so the CPU 26 advances to S804.
In S804, the CPU 26 drives the blower unit 32 through the drive circuit 57. Thereby, while cooling of the light emission part 33 is started, ventilation to the reflective member 38 is started. For example, the CPU 26 starts outputting a PWM signal for driving the blower unit 32. Thereby, electric power is supplied to the motor of the blower unit 32, the motor rotates the fan, and the air blow to the light emitting unit 33 and the reflection member 38 is started.
In S805, the CPU 26 stops the blower unit 32 through the drive circuit 57. For example, the CPU 26 stops outputting the PWM signal to the blower unit 32. The blower unit 32 does not need to be completely stopped. For example, the CPU 26 may reduce the duty of the PWM signal so that the air volume of the blower unit 32 becomes very small.

  When transitioning from S804 to S803, the CPU 26 may wait for a predetermined waiting time (eg, 5 seconds). The air volume of the air blowing unit 32 may be set to the maximum air volume among the air volumes that can be set in the air blowing unit 32. In this case, water vapor will be reduced in the shortest time. However, this air volume setting is only an example. For example, the CPU 26 may calculate the difference between the received light amount and the dew condensation threshold Th1 and determine the air volume according to the difference. The CPU 26 may determine the air volume according to the power consumption management of the image forming apparatus 100. For example, the CPU 26 sets the first air volume in the blower unit 32 when the image forming apparatus 100 is operating at the first power consumption. The CPU 26 sets the second air volume in the blower unit 32 when the image forming apparatus 100 is operating at the second power consumption. Here, the first power consumption is greater than the second power consumption. The first air volume is greater than the second air volume.

  According to the present embodiment, the CPU 26 can detect the amount of received light before executing image formation, and estimate the dew condensation state of the reflecting member 38 and the degree of water vapor around it based on the amount of received light. Further, when the condensation is sufficiently eliminated or the water vapor is sufficiently reduced, the CPU 26 starts image formation. As a result, the CPU 26 can accurately detect the presence or absence of the sheet P using the sheet sensor 31. As described above, since the water vapor and the condensation are sufficiently eliminated before the printing is started, the necessity of increasing the air volume of the blower unit 32 when the printing is started is reduced. This makes it possible to reduce the total power consumption of the image forming apparatus 100 in the print state. Therefore, according to the second embodiment, the total power consumption of the image forming apparatus 100 is reduced while improving the accuracy of sheet detection.

[Example 3]
In the second embodiment, the CPU 26 estimates that the cause of the decrease in the amount of received light is dew condensation. Other causes for the decrease in the amount of received light include contamination of the light emitting unit 33 and the reflecting member 38 and a decrease in the amount of light emitted from the light emitting unit 33. Thus, when the light amount is reduced due to a cause other than condensation, the accuracy of sheet detection is reduced, and control of the blower unit 32 is wasted. Therefore, in the third embodiment, the CPU 26 distinguishes between a change in light amount due to dirt or component deterioration and a change in light amount due to condensation. Thereby, the presence or absence of condensation is detected accurately.

  The CPU 26 implements various functions by executing a control program stored in the storage device 87. The storage device 87 has a memory such as a RAM or a ROM, and holds a control program, a conversion table, a threshold value, and the like. In the present embodiment, the storage device 87 holds the relationship between the light emission amount of the light emitting unit 33 and the light reception amount of the light receiving unit 34.

FIG. 9 is a flowchart showing a method executed by the CPU 26.
In step S <b> 901, the CPU 26 determines whether the image forming apparatus 100 has transitioned from the power-off state to the standby state (power-on state) or has returned from the energy saving mode to the normal mode. This step can be executed, for example, between time t0 and time t1 in FIG. If the image forming apparatus 100 has transitioned from the power-off state to the standby state, the CPU 26 advances to S902. If the image forming apparatus 100 has returned from the energy saving mode to the normal mode, the CPU 26 advances to S902.
In step S <b> 902, the CPU 26 causes the light emitting unit 33 to emit light through the drive circuit 56. The light output from the light emitting unit 33 is reflected by the reflecting member 38 and received by the light receiving unit 34. Here, the CPU 26 reads the light emission amount stored in the storage device 87 in advance, and generates and outputs a drive signal corresponding to the read light emission amount. The light emission amount stored in the storage device 87 may be, for example, a value determined by a shipping inspection performed at the time of product shipment, or a value determined periodically in a non-condensing state.
In S903, the CPU 26 drives the blower unit 32 through the drive circuit 57. Thereby, while cooling of the light emission part 33 is started, ventilation to the reflective member 38 is started. For example, the CPU 26 starts outputting a PWM signal for driving the blower unit 32. Thereby, electric power is supplied to the motor of the blower unit 32, the motor rotates the fan, and the air blow to the light emitting unit 33 and the reflection member 38 is started. Note that the CPU 26 may start a timer or a counter in order to measure the operating time of the blower unit 32.
In S904, the CPU 26 receives the amount of received light (input voltage) of the light receiving unit 34, and determines whether the amount of received light is within a predetermined range. The amount of received light is a parameter indicating the dew condensation on the reflecting member 38 and the surrounding state of the reflecting member 38. The predetermined range is stored in the storage device 87 in advance. For example, the CPU 26 determines whether the received light amount is within the received light amount range stored in the storage device 87. The received light amount range may be defined by a lower limit value and an upper limit value. In this case, the CPU 26 may determine that the detected amount of received light is not less than the lower limit value and not more than the upper limit value. Alternatively, the predetermined range may be defined based on the reference received light amount that is the center of the predetermined range and ± Δ that is the range parameter. The CPU 26 may determine that the difference between the detected light reception amount and the reference light reception amount is not less than −Δ and not more than + Δ. The parameter that defines the predetermined range can be determined when the image forming apparatus 100 is shipped. For example, the reference light reception amount may be a light reception amount obtained when light is emitted with the above light emission amount at the time of product shipment. Further, the reference light reception amount may be a light reception amount that is periodically acquired in a state without condensation. When the detected amount of received light is within the predetermined range, the reflecting member 38, the light emitting unit 33, and the light receiving unit 34 are not contaminated, and no condensation that causes a problem on the reflecting member 38 occurs. Therefore, the CPU 26 proceeds to S905.
In S905, the CPU 26 stops the blower unit 32.

On the other hand, when the detected amount of received light is out of the predetermined range, the reflecting member 38, the light emitting unit 33, and the light receiving unit 34 are contaminated with a problem, or condensation that causes a problem on the reflecting member 38 occurs. It may have occurred. Therefore, the CPU 26 proceeds to S906. Here, first, reduction of dew condensation is tried by the blower unit 32 driven in S903.
In S906, the CPU 26 determines whether or not the operating time of the blower unit 32 has exceeded a predetermined time. The predetermined time is a time during which the condensation of the reflecting member 38 can be sufficiently reduced, and is stored in the storage device 87. The blower unit 32 is continuously driven until the operation time exceeds a predetermined time. Thereby, reduction of condensation is tried. If the operating time exceeds the predetermined time, the CPU 26 proceeds to S907. If the operating time does not exceed the predetermined time, the CPU 26 proceeds to S904. In S904, the CPU 26 compares the received light amount with a predetermined range to determine whether or not the condensation has decreased to an allowable range. If the condensation has decreased to an allowable range, the CPU 26 proceeds to S905. If the condensation has not decreased to the allowable range, the CPU 26 proceeds to S906. Thus, if the amount of received light is not within the predetermined range even if the blower unit 32 is operated for a predetermined time, factors other than condensation cause the decrease in the amount of received light.
In S907 and S908, the CPU 26 increases the light emission amount of the light emitting unit 33 or increases the gain of the light receiving unit 34 so that the detected light reception amount falls within a predetermined range. Basically, either increase in light emission amount or increase in gain is adopted. Even if the light emission amount is increased to the maximum light amount that can be set in S907, the light reception amount may not fall within the predetermined range in S908. In this case, the CPU 26 may start increasing the gain in S907. Alternatively, even if the gain is increased to the maximum gain that can be set in S907, the amount of received light may not fall within the predetermined range in S908. In this case, the CPU 26 may start increasing the light emission amount in S907. If it is determined in S908 that the amount of received light is within the predetermined range, the CPU 26 proceeds to S909.
In step S909, the CPU 26 stops the blower unit 32. Thereafter, in S910, the CPU 26 stores the light emission amount of the light emitting unit 33 and the gain of the light receiving unit 34 when the determination condition is satisfied in S908 in the storage device 87. The stored light emission amount and gain are used as initial values.

  According to the present embodiment, condensation or dirt in the image forming apparatus 100 is detected based on the amount of received light, and reduction of condensation by the blower unit 32 is tried. When the decrease in the amount of received light is not eliminated even when the blower unit 32 is operated, the power consumption of the blower unit 32 is reduced, and the light emission amount and the gain are appropriately adjusted. Therefore, the power consumption of the blower unit 32 is reduced while maintaining the accuracy of sheet detection.

<Summary of Examples 1-3>
FIG. 10 shows functions realized by the CPU 26 executing the control program stored in the storage device 87. The CPU 26 functions as a control unit. The technical idea derived from the above embodiment will be described below with reference to FIG. The storage device 87 has a memory such as a RAM or a ROM, and holds a control program, a conversion formula, a conversion table, a threshold value, and the like.

  As shown in FIG. 3A and the like, the conveyance path 49 is an example of a conveyance path for conveying the sheet P. The light emitting unit 33 is an example of a light emitting unit that outputs light that crosses the conveyance path 49. The light amount control unit 50 illustrated in FIG. 10 is an example of a control unit that controls the light amount of the light emitting unit 33. The light quantity control unit 50 turns on the light emitting diode D2 of the light emitting unit 33 through the drive circuit 56 having the circuit shown in FIG. 5B. The reflecting member 38 shown in FIG. 2B or the like is an example of a reflecting member that is provided to face the light emitting unit 33 and reflects the light incident across the conveyance path 49. The light receiving unit 34 is an example of a light receiving unit that receives reflected light from the reflecting member 38 and outputs a level detection signal corresponding to the amount of received light. The light receiving unit 34 is an example of a light receiving unit that receives reflected light that is light that has crossed the conveyance path 49 at least once from the light emitting unit 33 to the light receiving unit 34. The gain control unit 61 changes the voltage generated by the phototransistor Tr4 by controlling the light reception gain in the detection circuit shown in FIG. 5C. The blowing unit 32 is an example of a blowing unit that sends air to the reflecting member 38 or sucks out air so as to promote convection of air around the reflecting member 38. The air volume control unit 51 illustrated in FIG. 10 is an example of a control unit that controls the air volume of the blower unit 32. The air volume control unit 51 controls the air volume of the blower unit 32 through the drive circuit 57. The sheet detection unit 94 is an example of a determination unit that determines the presence or absence of the sheet P based on the amount of reflected light received by the light receiving unit 34. The sheet detection unit 94 is an example of a detection unit that detects whether or not there is a sheet P in the conveyance path 49 based on a detection signal output by the light receiving unit 34 according to the amount of received light. The sheet detection unit 94 may further detect a jam of the sheet P based on the determination result of the presence or absence of the sheet P. As shown in FIGS. 7, 8, and 9, the dew condensation detection unit 53 detects the air volume of the blower unit 32 according to the detection signal output by the light receiving unit 34 when there is no sheet P at the position where the light crosses in the conveyance path 49. And / or adjust the operating time. Therefore, the sheet can be accurately detected even in an environment where condensation can occur. The dew condensation detection unit 53 controls the blower unit 32 through the air volume control unit 51.

  As shown in FIG. 7, the dew condensation detection unit 53 determines whether the level (light reception amount) of the detection signal output from the light receiving unit 34 when the sheet P is not in the conveyance path 49 exceeds the dew condensation threshold Th1. Function as. That is, the dew condensation detection part 53 has a determination means. Here, it is assumed that the light receiving unit 34 outputs a detection signal having a level substantially proportional to the amount of received light. That is, the level of the detection signal only needs to have a positive correlation with the amount of received light. The CPU 26 may convert the input voltage from the light receiving unit 34 into the amount of received light and then compare it with the dew condensation threshold Th1. That is, the input voltage may be inversely proportional to the amount of received light or may have a negative correlation. As described above, the input voltage inversely proportional to the amount of received light may be compared with the voltage threshold. In this case, the magnitude relationship between the amount of received light and the dew condensation threshold Th1 in each determination step is opposite to the magnitude relationship between the input voltage and the voltage threshold. If the amount of received light does not exceed the dew condensation threshold Th1, the dew condensation detection unit 53 increases the air volume of the blower unit 32 or continues blowing by the blower unit 32. This reduces condensation. On the other hand, the dew condensation detection unit 53 reduces the air volume of the blower unit 32 or stops the blown air by the blower unit 32 if the amount of received light exceeds the dew condensation threshold Th1. Thereby, the electric power consumed by the ventilation unit 32 is reduced. In addition, this embodiment has an advantage that a heater for removing condensation can be omitted.

  The timer 52 is an example of a measuring unit that measures the operating time of the blower unit 32. The dew condensation detection unit 53 reduces the air volume of the blower unit 32 if the amount of received light does not exceed the dew condensation threshold Th1 even if the operation time measured by the timer 52 is equal to or longer than the predetermined time, or the blower unit 32 blows air. Stop. Thereby, the electric power consumed by the ventilation unit 32 is reduced.

  As shown in FIG. 7, the dew condensation detection unit 53 may operate the blower unit 32 while the image forming apparatus 100 forms an image on the sheet P. When the image forming apparatus 100 finishes forming an image on the sheet P, the dew condensation detection unit 53 determines the air volume and operating time of the blower unit 32 according to the detection signal output by the light receiving unit 34 when there is no sheet on the conveyance path 49. And at least one of them may be adjusted. As a result, water vapor generated by printing is diffused, so that the dew condensation on the reflecting member 38 is unlikely to occur.

  As shown in FIG. 8, the dew condensation detection unit 53 is brought into a state in which image formation can be performed when power is supplied from a power source and the image forming apparatus 100 is activated or when the image forming apparatus 100 does not perform image formation. When returning, the light emitting unit 33 may output light. Furthermore, the dew condensation detection unit 53 may drive or stop the blower unit 32 according to the detection signal output from the light receiving unit 34. In this way, condensation is reduced when power is supplied from the power source and the image forming apparatus 100 is activated, or when the image forming apparatus 100 returns to a state where image formation can be performed from a state where image formation is not performed. Is done. As a result, it is expected that condensation is sufficiently reduced at the start of printing.

  As shown in FIG. 8, the dew condensation detection unit 53 may start blowing by the blower unit 32 or increase the air volume of the blower unit 32 if the amount of received light does not exceed the dew condensation threshold Th1. Moreover, the dew condensation detection part 53 will reduce the air volume of the ventilation unit 32, or will not perform the ventilation by the ventilation unit 32, if the light-receiving amount exceeds the dew condensation threshold Th1. As a result, the blower unit 32 does not operate unnecessarily, so that power consumption is reduced.

  As shown in FIG. 9, the dew condensation detection unit 53 returns to a state where image formation can be performed when power is supplied from a power source and the image forming apparatus is activated, or when the image forming apparatus does not perform image formation. When this occurs, the light emitting unit 33 is caused to output light. Furthermore, the dew condensation detection part 53 starts the ventilation of the ventilation unit 32. The dew condensation detection unit 53 stops the blower unit 32 according to the detection signal output from the light receiving unit 34 or adjusts the light emission amount of the light emitting unit 33 or the gain of the light receiving unit 34. Therefore, the sheet can be accurately detected even in an environment where condensation can occur.

  If the amount of received light is not equal to or lower than the lower limit value of the predetermined range, the dew condensation detection unit 53 continues the blowing by the blowing unit 32. This attempts to reduce condensation. On the other hand, if the amount of received light is equal to or greater than the lower limit value of the predetermined range, the dew condensation detection unit 53 reduces the air volume of the air blowing unit 32 or stops air blowing by the air blowing unit 32. Thereby, power consumption is reduced.

  As shown in S904 and S906, the dew condensation detection unit 53 increases the light emission amount of the light emitting unit 33 if the light reception amount is not equal to or lower than the lower limit value of the predetermined range even when the operation time measured by the timer 52 is equal to or longer than the predetermined time. Or the gain of the light receiving unit 34 is increased. The dew condensation detection unit 53 controls the light emission amount through the light amount control unit 50. The dew condensation detection unit 53 controls the gain of the light receiving unit 34 through the gain control unit 61. Thereby, even if the amount of received light is reduced due to factors other than condensation, the sheet can be detected with high accuracy.

  The dew condensation detection unit 53 may increase both the light emission amount of the light emitting unit 33 and the gain of the light receiving unit 34, or may increase one of them. The dew condensation detection unit 53 increases the gain of the light receiving unit 34 if the received light amount is not equal to or lower than the lower limit value of the predetermined range even if the light emission amount of the light emitting unit 33 is increased to the maximum value that can be set in the light emitting unit 33. May be. Even if the condensation detection unit 53 increases the gain of the light receiving unit 34 to the maximum value that can be set in the light receiving unit 34, the dew detection unit 53 increases the light emission amount of the light emitting unit 33 if the received light amount is not equal to or lower than the lower limit value of the predetermined range. May be. Note that the dew condensation detection unit 53 may decrease the gain of the light receiving unit 34 when the amount of received light exceeds the upper limit value of the predetermined range. Similarly, the dew condensation detection unit 53 may decrease the light emission amount of the light emitting unit 33 when the light reception amount exceeds the upper limit value of the predetermined range. Thereby, power consumption is reduced.

  The storage device 87 is an example of a light emission amount storage unit that stores the light emission amount of the light emitting unit 33 when the light reception amount falls within a predetermined range as an initial value. The dew condensation detection unit 53 sets the initial value stored in the storage device 87 in the light emitting unit 33 when starting the light emission of the light emitting unit 33. Thereby, the time for searching for an appropriate light emission amount is reduced. The storage device 87 is an example of a gain storage unit that stores the gain of the light receiving unit 34 when the amount of received light is within a predetermined range as an initial value. The dew condensation detection unit 53 sets the initial value stored in the storage device 87 in the light receiving unit 34 when the light receiving unit 34 starts to receive light. This reduces the time for searching for an appropriate gain.

  In addition, the dew condensation detection part 53 may function as a detection means which detects dew condensation of the reflective member 38, or may include this. In this case, when the dew condensation detection unit 53 detects dew condensation on the reflecting member 38, the CPU 26 operates the blower unit 32 and tries to reduce dew condensation.

  As described with reference to FIG. 4, a ventilation path 40 is provided to guide the air to the reflecting member 38 so that the air blown from the blowing unit 32 or sucked by the blowing unit 32 blows to the reflecting member 38. May be. By providing such a ventilation path 40, it is possible to efficiently clean the reflecting member 38 and to expel the water vapor generated from the sheet P from the vicinity of the reflecting member 38.

  As shown in FIG. 3A and the like, the first guide 36 and the second guide 37 are examples of a first guide member and a second guide member that are provided to face each other in the conveyance path 49 and guide the sheet P. The light emitting unit 33 and the light receiving unit 34 may be fixed to the first guide 36. The reflecting member 38 may be fixed to the second guide 37. The light shielding member 47 is an example of a light shielding member provided between the light emitting unit 33 and the light receiving unit 34. The light blocking member 47 blocks direct light traveling from the light emitting unit 33 toward the light receiving unit 34. 3B, when the sheet P is transported through the transport path 49, the light from the light emitting unit 33 hardly reaches the reflecting member 38, but reaches the surface of the sheet P. Therefore, depending on the type (surface state) of the sheet P, light may be reflected on the surface of the sheet P and the reflected light may be directed to the light receiving unit 34. When such reflected light is received by the light receiving unit 34, the light receiving unit 34 outputs a detection signal indicating that the sheet P is not detected even though the sheet P is transported through the transport path 49. There is a possibility that. Therefore, the light shielding member 47 may be configured to shield at least part of the reflected light that is reflected on the surface of the sheet P and travels toward the light receiving unit 34. Thereby, the presence or absence of the sheet P will be detected with high accuracy.

  According to FIG. 2A and the like described above, the light output from the light emitting unit 33 enters the reflecting member 38 across the transport path 49, and the reflected light from the reflecting member 38 enters the light receiving unit 34 across the transport path 49. is doing. Thus, although the light output from the light emission part 33 has crossed the conveyance path 49 twice, the frequency | count that light crosses the conveyance path 49 should just be 1 time or more. For example, the light output from the light emitting unit 33 may enter the reflecting member 38 without traversing the transport path 49, and the reflected light from the reflecting member 38 may also enter the light receiving unit 34 across the transport path 49. Further, the light output from the light emitting unit 33 may enter the reflecting member 38 across the transport path 49, and the reflected light from the reflecting member 38 may enter the light receiving unit 34 without crossing the transport path 49. The number of times light crosses the transport path 49 may be one. The light output from the light emitting unit 33 enters the reflecting member 38 across the transport path 49, and the reflected light from the reflecting member 38 also enters the second reflecting member across the transport path 49, and the second reflecting member. The reflected light from the light may enter the light receiving unit 34. In this way, the number of times the light crosses the transport path 49 may be three. By increasing the number of reflecting members, the number of times that the light crosses the conveyance path 49 can be increased. Thus, the light that crosses the transport path 49 may be light that crosses the transport path 49 once or more before being output from the light emitting unit 33 and entering the light receiving unit 34. The timing at which the light output from the light emitting unit 33 crosses the transport path 49 may be before entering the reflecting member 38 or after. In any case, the light emitting unit 33 functions as a light emitting unit that outputs light that crosses the conveyance path. Moreover, the number of the reflection members 38 installed between the light emission part 33 and the light-receiving part 34 should just be one or more. The arrangement of the light emitting unit 33 and the light receiving unit 34 differs depending on the number of times the light crosses the transport path 49. If the number of times that the light crosses the transport path 49 is an even number, as shown in FIG. 2A, the light emitting unit 33 and the light receiving unit 34 are arranged on the same side as viewed from the transport path 49. If the number of times that the light crosses the transport path 49 is an odd number, the light emitting unit 33 and the light receiving unit 34 are disposed on the opposite sides of the transport path 49.

[Example 4]
The optical sheet sensor includes a light emitting element and a light receiving element, and detects the sheet according to whether light is blocked by the sheet. The optical sheet sensor is advantageous in terms of responsiveness as compared to the mechanical flag type sheet sensor, and improves the productivity of the image forming apparatus. The optical sheet sensor increases the manufacturing cost as compared with the mechanical flag type sheet sensor. Therefore, if the optical sheet sensor has other functions in addition to the sheet detection function, the cost effectiveness of the sheet sensor will be improved. Therefore, it will be necessary to improve the cost effectiveness of the sheet sensor.

<Image forming apparatus>
Compared with the image forming apparatus 100 shown in FIG. 1, the image forming apparatus 100 shown in FIG.

  In the single-sided printing mode, the sheet P discharged from the fixing device 17 is conveyed by the flapper 54 toward the discharge roller 20. The conveyance path existing from the flapper 54 to the discharge roller 20 may be called a discharge path. The discharge roller 20 discharges the sheet P to the outside of the image forming apparatus 100.

  In the duplex printing mode, the posture of the flapper 54 is switched so that the sheet P is conveyed toward the reverse roller 27, and the sheet P is conveyed toward the reverse roller 27. The conveyance path from the flapper 54 to the reverse roller 27 may be referred to as a pull-in path. The reversing roller 27 pulls in the sheet P by rotating forward, and further feeds the sheet P into the duplex conveying path 58 by rotating in reverse. At this time, the leading edge of the sheet P is exposed to the outside of the image forming apparatus 100 from the opening 60 of the duplex conveyance path 58, but the trailing edge of the sheet P is not exposed. When the rotation direction of the reverse roller 27 is switched, the leading edge of the sheet P is switched to the trailing edge, and the trailing edge of the sheet P is switched to the leading edge. Thereby, the image forming surface of the sheet P is switched from the first surface to the second surface. The timing of switching from normal rotation to reverse may be determined based on the timing at which the sheet sensor 31 detects the trailing edge of the sheet P. A conveyance guide member 59 is provided between the reverse roller 27 and the blower unit 32 in the double-sided conveyance path 58. A plurality of conveyance rollers 55 provided in the double-side conveyance path 58 conveys the sheet P along the double-side conveyance path 58 and delivers it to the registration rollers 16. The image forming unit 101 forms an image on the second surface of the sheet P, and discharges the sheet P by the flapper 54 and the discharge roller 20.

  The air blower unit 32 is arrange | positioned so that air may be sent toward the double-sided conveyance path 58, for example.

<Water vapor detection algorithm>
The CPU 26 estimates the amount of water vapor generated (water vapor amount) based on the amount of light received by the light receiving unit 34 in the sheet sensor 31. When the sheet P passes through the fixing device 17, the water adsorbed on the sheet P evaporates to generate water vapor. When water vapor is generated in the conveyance path 49, the light irradiated by the light emitting unit 33 crossing the conveyance path 49 is irregularly reflected by the water vapor. Thereby, the amount of light received by the light receiving unit 34 is reduced. That is, the decrease in the amount of received light correlates with the amount of water vapor. Therefore, when the sheet P is not at the detection position of the sheet sensor 31, the CPU 26 outputs light to the light emitting unit 33 and acquires the amount of light received by the light receiving unit 34. The detection position is a position where light crosses the conveyance path 49. Here, it is assumed that the light receiving unit 34 outputs a detection voltage that is inversely proportional (inversely correlated) to the amount of received light. When the detection voltage from the light receiving unit 34 exceeds a predetermined threshold, the CPU 26 estimates that the amount of received light has decreased (the amount of generated water vapor is large). If the detected voltage does not exceed the threshold, the CPU 26 determines that the amount of received light is above a certain level. That is, the CPU 26 estimates that the amount of water vapor generated in the transport path 49 is small.

Here, a result of experimental verification of how the detection voltage of the light receiving unit 34 changes in the moisture absorption state of the sheet P is shown. The experimental conditions assumed a general office environment. Therefore, the image forming apparatus 100 is installed in an environment where the temperature is set to 25 ° C. and the relative humidity is set to 50%. Two types of sheets P having different moisture absorption states were prepared. That is, ten sheets P in the first moisture absorption state and ten sheets P in the second moisture absorption state were prepared. The CPU 26 continuously passed ten sheets P through the fixing device 17 and monitored the detection voltage of the light receiving unit 34. The sheet P is a commonly used plain paper (basis weight: 80 g / m ² ). The ratio of the moisture contained in the sheet P in the first moisture absorption state was 4.3%. The ratio of moisture contained in the sheet P in the second moisture absorption state was 8.3%. When the relative humidity of the conveyance path 49 immediately after the ten sheets P in the first moisture absorption state were passed through the fixing device 17 was measured with a humidity sensor, it was 63%. The relative humidity of the conveyance path 49 immediately after the ten sheets P in the second moisture absorption state were passed through the fixing device 17 was 73%. From this, it can be seen that when the sheet P with a large amount of water is supplied to the fixing device 17, the amount of water vapor staying in the conveyance path 49 or the like is large.

  FIG. 12A shows the voltage output result of the light receiving unit 34. The horizontal axis indicates time. The vertical axis represents the detection voltage of the light receiving unit 34. The lower the detection voltage, the greater the amount of light received (no sheet). The higher the detection voltage, the smaller the amount of light received (with sheet). The reason that the detection voltage fluctuates up and down is that ten sheets P1 to P10 are continuously passed, so that the state where the sheet P is present at the detection position and the state where there is no sheet P are repeated. . The first convex waveform indicates that the first sheet passes through the detection position. The solid line shows the waveform of the detection voltage for the sheet P in the second moisture absorption state with much moisture. The broken line shows the waveform of the detection voltage for the sheet P in the first moisture absorption state with little moisture.

Comparing the voltage waveform in the first moisture absorption state and the voltage waveform in the second moisture absorption state, it can be seen that both of the initial voltages before detecting the first sheet P1 (paper interval t01) are 0.16V. The sheet interval tij is a period corresponding to the distance from the trailing edge of the preceding sheet Pi to the leading edge of the succeeding sheet Pj (j = i + 1). When the leading edge of the first sheet P1 reaches the detection position, the voltage in the first moisture absorption state and the voltage in the second moisture absorption state both rise to 3.1V. Here, the sheet threshold value for determining the presence or absence of the sheet P is set to 2.0V. Therefore, the CPU 26 can detect the presence of a sheet in either moisture absorption state. When the rear end of the sheet P1 reaches the detection position, both the voltage in the first moisture absorption state and the voltage in the second moisture absorption state are reduced to the sheet threshold value or less. In the paper interval t12 between the sheet P1 and the sheet P2, the voltage in the second moisture absorption state was 0.24V, and the voltage in the first moisture absorption state was 0.17V. The concept of the rate of increase of the detection voltage between the sheets with respect to the initial voltage is introduced with reference to the potential difference from 0V to 3.1V.
Increase rate ΔV = ((detection voltage−initial voltage) /3.1) × 100 [%] (1)
The increase rate ΔV in the second moisture absorption state at the paper interval t12 is 2.5%. The increase rate ΔV in the first moisture absorption state at the interval t12 is 0.3%. Therefore, these differences (increase rate differences) are 2.2%.

  FIG. 12B shows the detection voltage and the increase rate difference between the sheets. In FIG. 12B, the left vertical axis indicates the detected voltage [V] between the sheets. In FIG. 12B, the vertical axis on the right side shows the increase rate difference [%]. In all the sheet intervals t01 to t910, the detection voltage for the sheet P having a high moisture content exceeds the detection voltage for the sheet P having a low water content. The average increase rate difference between the papers was about 14%. Here, when the water vapor threshold value for determining the amount of water vapor is set to 0.6 V, as shown in FIG. 12B, the detection voltages for the second and subsequent sheets P with high water content all exceed the water vapor threshold value. Therefore, the CPU 26 can estimate that the second and subsequent sheets P with much moisture are all moisture-rich sheets. The sheet P having a high moisture content refers to the sheet P having a moisture content of 8.0% or more in the sheet P. The water vapor threshold can be arbitrarily changed.

  The above algorithm for estimating the amount of water vapor is only an example. For example, the water vapor amount may be estimated based on the rate of increase instead of the rate of increase. By adopting this estimation method, the effects of component mounting positions and manufacturing variations are reduced. Variations include variations in mounting positions of light emitting elements and light receiving elements, variations in electrical characteristics, variations in the relative positional relationship between the substrate 35 and the reflecting member 38, and the like. These variations cause variations in detection voltage. Therefore, a threshold value may be set in consideration of these variations. There is no need to estimate the water vapor amount for each sheet P, and the water vapor amount may be estimated for each n sheets P. For example, the CPU 26 cumulatively adds n increasing rates acquired for each of n sheets, and when the addition result exceeds a threshold, the sheet P stored in the sheet feeding cassette 13 is added. The sheet P may contain a lot of moisture. By adopting such an estimation method, the estimation accuracy of the moisture absorption state of the sheet P (the amount of water vapor in the conveyance path 49) is improved.

<Blower unit>
The CPU 26 may control the image forming apparatus 100 using the estimation result of the water vapor amount. Here, control of the ventilation unit 32 using the amount of water vapor is exemplified. FIG. 13 is a cross-sectional view of the blower unit 32 and the blower duct 80 that send air into the duplex conveying path 58. In FIG. 13, the arrows indicate the flow of air. The air duct 80 guides the air blown from the air blowing unit 32 to a conveyance guide member 59 that forms a part of the double-sided conveyance path 58. The air blown to the conveyance guide member 59 travels in the opposite direction to the conveyance direction of the sheet P in the double-side conveyance path 58 along the conveyance surface of the conveyance guide member 59. This air is discharged to the outside of the image forming apparatus 100 through the opening 60 provided in the reversing roller 27. The reason for performing such air blowing is to discharge water vapor generated from the sheet P and entering the double-sided conveyance path 58 to the outside of the image forming apparatus 100. Thereby, it is suppressed that water vapor | steam becomes a water droplet and adheres to the double-sided conveyance path 58. FIG. Water droplets adhering to the double-sided conveyance path 58 will also be removed due to the drying effect of the air blowing. If water droplets adhering to the double-sided conveyance path 58 adhere to the second surface of the sheet P, the toner is difficult to be transferred by the water droplets. Therefore, by reducing water droplets, image defects due to water droplets are reduced.

<Blower control>
As shown in FIG. 6, power is supplied from the power source at time t0, and the image forming apparatus 100 is activated. That is, at time t0, the image forming apparatus 100 transitions from the power-off state to the standby state. FIG. 14 is a flowchart showing the control executed by the CPU 26.

  In step S1401, the CPU 26 determines whether a print instruction (image formation instruction) is input from the operation unit or an external computer. According to FIG. 6, a print instruction is input at time t1. The state of the image forming apparatus 100 is a standby state waiting for a print instruction from time t0 to time t1. In the standby state immediately after the image forming apparatus 100 is activated, the blower unit 32 does not operate (air volume = 0). Note that the CPU 26 may drive the blower unit 32 so that the air volume is very small. When a print instruction is input at time t1, the CPU 26 advances to S1402 to start image formation.

  In step S1402, the CPU 26 controls the image forming apparatus 100 to start printing. Furthermore, the CPU 26 drives the blower unit 32 to start blowing air to the conveyance guide member 59. For example, the CPU 26 starts outputting a PWM signal for driving the blower unit 32. As a result, the drive circuit 57 supplies power to the motor of the blower unit 32, the motor rotates the fan, and the blow to the transport guide member 59 is started. As a result, an air flow is formed along the conveyance surface of the conveyance guide member 59, and water vapor is discharged from the opening 60.

  In S1403, the CPU 26 acquires the amount of light received between the sheets from the sheet sensor 31, and estimates the amount of water vapor (water vapor amount) in the conveyance path 49 based on the amount of received light. The estimation of water vapor may be executed at least once during printing. When estimation is performed a plurality of times, an average value of a plurality of estimation results may be employed.

  In step S1404, the CPU 26 determines whether printing has ended. The CPU 26 determines whether all print jobs designated by the operation unit or the like have been completed. If the print job is a job for forming an image on n sheets, it is determined whether or not the image formation on the n sheets is completed. When printing ends at time t3, the CPU 26 advances to S1405.

  In S1405, the CPU 26 determines a predetermined time Tx based on the estimation result of the water vapor amount. As shown in FIG. 6, the predetermined time Tx is an operation time from the timing when printing is finished to the timing when the blower unit 32 is stopped. If the amount of water vapor is large, the predetermined time Tx becomes longer. If the amount of water vapor is small, the predetermined time Tx is shortened.

  In S1406, the CPU 26 determines whether or not the elapsed time from the timing when printing is finished (time t3) has reached the predetermined time Tx. The CPU 26 measures an elapsed time from the end of printing using a timer or a counter. According to FIG. 6, the elapsed time is the predetermined time Tx at time t4. The predetermined time Tx is a time required until water droplet adhesion to the conveyance surface of the conveyance guide member 59 is almost eliminated. The predetermined time Tx varies depending on the moisture absorption state of the sheet P conveyed during printing, the number of conveyed sheets, and the like. When the elapsed time reaches the predetermined time Tx, the CPU 26 proceeds to S1407.

  In S1407, the CPU 26 stops the blower unit 32. For example, the blower unit 32 stops outputting the PWM signal or decreases the duty ratio of the PWM signal. In addition, the ventilation unit 32 does not need to stop. For example, the duty ratio of the PWM signal may be changed so that the air volume of the blower unit 32 becomes very small.

Determination algorithm for the predetermined time Tx The moisture absorption state of the sheet P conveyed during printing is estimated by the water vapor estimation algorithm. The CPU 26 determines a predetermined time Tx based on the estimation result and the number of sheets P conveyed in the immediately preceding print job.

  FIG. 15 is a graph illustrating a determination method for determining the predetermined time Tx. The horizontal axis indicates the number of sheets conveyed during printing. The vertical axis represents the predetermined time Tx. Two straight lines L1 and L2 having different inclinations are straight lines selected according to the amount of water vapor. The straight line L1 is a straight line selected when the amount of water vapor is small. The straight line L2 is a straight line selected when the amount of water vapor is large. When the number n of sheets is 10 and the amount of water vapor is small, the CPU 26 selects the straight line L1 and determines the predetermined time Tx corresponding to 10 sheets as 10 seconds. When the number n of sheets is 10 and the amount of water vapor is large, the CPU 26 selects the straight line L2, and determines the predetermined time Tx corresponding to 10 sheets as 30 seconds. The slope a1 of the straight line L1 is determined based on the time required to reduce water droplets by an experiment performed when the amount of water vapor is small. Similarly, the slope a2 of the straight line L2 is determined based on the time required for reducing the water droplets by an experiment performed when the amount of water vapor is large. Here, a linear function (linear equation) for obtaining the predetermined time Tx from the number n of sheets and the inclination a is employed, but a higher order function may be determined based on experimental results.

  According to the fourth embodiment, the CPU 26 estimates the amount of water vapor (the moisture absorption state of the sheet) according to the amount of light received by the light receiving unit 34. If the operating time (predetermined time Tx) of the blower unit 32 is set without considering the moisture absorption state of the sheet P, the operating time may be excessive or the operating time may be insufficient. If the operation time is insufficient, water droplets will remain on the transport guide member 59. On the other hand, if the operation time becomes excessive, the amount of power consumption increases. Therefore, by determining the operation time according to the amount of water vapor (the moisture absorption state of the sheet), water droplets can be sufficiently reduced and an increase in power consumption can be suppressed. In addition, image defects due to water droplets are unlikely to occur. For the sheet P with less moisture, the operating time of the blower unit 32 can be reduced, and an unnecessary waiting time will not occur.

  In the fourth embodiment, the sequence in which the operation time of the blower unit 32 after the end of the print job is controlled according to the amount of received light is illustrated. Instead of changing the operating time of the blower unit 32, the CPU 26 may change the air volume of the blower unit 32 according to the amount of received light. For example, the CPU 26 may change the duty ratio of the PWM signal according to the amount of received light. When the image forming apparatus 100 is activated at time t <b> 0, the blower unit 32 is driven to have a first air volume (may be zero). At time t1, the blower unit 32 is driven so that the air volume becomes the second air volume (second air volume> first air volume). From time t3 to time t4, the blower unit 32 continues to blow with the second air volume. At time t4, the air volume of the blower unit 32 is reduced from the second air volume to the first air volume (may be zero). The CPU 26 controls the air volume of the blower unit 32 to zero from time t0 to time t1, controls the air volume to the first air volume (> 0) from time t1 to time t2, and changes the air volume to the second air volume after time t2. (> First air volume) may be controlled. Here, time t2 is a time between time t1 and time t3 in FIG. In particular, when the estimation result is confirmed at time t2, the CPU 26 may determine the second air volume based on the estimation result. When the amount of water vapor is large, the second air amount is set relatively large. When the amount of water vapor is small, the second air volume is set relatively small.

  In the fourth embodiment, one estimation result is obtained in one paper interval tij. However, many estimation results may be acquired in one paper interval tij, and the estimation results may be fed back to the control of the image forming apparatus 100. As a result, the control of the image forming apparatus 100 will be finer. The image forming apparatus 100 may include an environmental sensor that can acquire environmental information such as ambient temperature and humidity in real time. The CPU 26 may estimate the water vapor amount with higher accuracy based on the environmental data acquired from the environmental sensor and the received light amount acquired by the sheet sensor 31. For example, the CPU 26 may convert the environmental data into a correction coefficient and correct the estimation result using the correction coefficient.

  In the fourth embodiment, the blower unit 32 sends air toward the double-sided conveyance path 58, but in addition to this, as described in the first to third embodiments, air may be sent toward the reflecting member 38. Good. In other words, the ventilation path extending from one fan may be divided into two, and one may be directed to the double-sided conveyance path 58 and the other to the reflecting member 38. Alternatively, a fan that simply sends air toward the duplex conveying path 58 and a fan that sends air toward the reflecting member 38 may be arranged one by one.

<Example 5>
In the fifth embodiment, the estimation result of the water vapor amount is fed back to the curl correction mechanism. When the sheet P passes through the fixing device 17, the sheet P may be curled. When the sheet P is curled, the sheet P may be jammed in the double-sided conveyance path 58 or the like. Therefore, the curl correction mechanism is useful.

  FIG. 16 is a cross-sectional view of the image forming apparatus 100 according to the fifth embodiment. The fifth embodiment is different from the fourth embodiment in that a curl correction mechanism is disposed downstream of the fixing device 17. The curl correction mechanism has a decurling roller pair 90. When the sheet P passes through the nip portion of the decurling roller pair 90, curling of the sheet P is reduced.

<Seat sensor>
As shown in FIGS. 17A and 17B, the sheet sensor 31 of the fifth embodiment is a transmissive sheet sensor. The viewpoint with respect to the sheet sensor 31 is different between FIG. 17A and FIG. 17B. The members already described are given the same reference numerals. A light-emitting substrate 70 on which the light-emitting unit 33 is mounted and a light-receiving substrate 72 on which the light-receiving unit 34 is mounted are arranged to face each other across the transport path 49. The light emitting substrate 70 is fixed to a substrate holding member 71 protruding upward from the second member 42. The light emitting unit 33 emits light so that the light crosses the detection position in the conveyance path 49 from the notch provided in the center of the first member 41. The light receiving substrate 72 is fixed to a substrate holding member 73 protruding upward from the fifth member 45. The light emitting substrate 70 and the light receiving substrate 72 are positioned so that light emitted from the light emitting unit 33 passes through a notch provided in the center of the fourth member 44 and enters the light receiving unit 34.

  FIG. 18A is a plan view showing the sheet sensor 31 when the sheet P does not pass through the detection position (conveyance path 49). FIG. 18B is a plan view showing the sheet sensor 31 when the sheet P passes the detection position. As shown in FIG. 18A, the light emitted from the light emitting unit 33 reaches the light receiving unit 34 across the conveyance path 49. Accordingly, the light receiving unit 34 outputs a detection signal (for example, a low level signal) indicating that the sheet P is not detected. Alternatively, the light receiving unit 34 does not output a detection signal (eg, a high level signal) indicating that the sheet P is being detected.

  As illustrated in FIG. 18B, when the sheet P is conveyed on the conveyance path 49, the light from the light emitting unit 33 reaches the surface of the sheet P, but the light is blocked by the surface of the sheet P. That is, light does not reach the light receiving unit 34. Therefore, the light receiving unit 34 outputs a detection signal (eg, a high level signal) indicating that the sheet P is being detected. Alternatively, the light receiving unit 34 does not output a detection signal (eg, a low level signal) indicating that the sheet P is not detected.

  Also in the transmission type sheet sensor employed in the fifth embodiment, the light emitted from the light emitting unit 33 is diffusely reflected by the water vapor generated from the sheet P, and the amount of light received by the light receiving unit 34 is reduced. Therefore, the estimation algorithm related to the water vapor amount described in the fourth embodiment is applicable to the fifth embodiment.

<Curl correction mechanism>
The two rollers constituting the decurling roller pair 90 are soft rollers formed by covering a metal hard roller with rubber over the entire area in the longitudinal direction. When the sheet P passes through the nip portion of the decurling roller pair 90, the decurling roller pair 90 acts on the sheet P so that the curling of the sheet P is corrected. For example, the curl of the sheet P is corrected using a difference in rotational speed between two rollers constituting the decurling roller pair 90. The nip pressure of the decurling roller pair 90 can be changed by an actuator controlled by the CPU 26. Thereby, the curl correction force is adjusted. The CPU 26 corrects the curl correction force by controlling the actuator based on printing conditions such as single-sided printing or double-sided printing.

<Curl correction mechanism control>
FIG. 19 is a flowchart showing the control executed by the CPU 26. 19 is different from FIG. 14 in that S1901 is added between S1403 and S1404. In S1901, the CPU 26 adjusts the curl correction force based on the estimation result of the water vapor amount. For example, when the sheet P with much moisture is conveyed to the fixing device 17, the CPU 26 increases the curl correction force from the reference value. This is because the curl becomes large in the sheet P containing a lot of moisture. On the other hand, when the sheet P with less moisture is conveyed to the fixing device 17, the CPU 26 maintains the curl correction force at the reference value. This is because the curl is reduced in the sheet P having a low water content.

  According to the fifth embodiment, the CPU 26 can adjust the curl correction force based on the estimation result of the water vapor amount (the moisture absorption state of the sheet P). Thereby, it becomes possible to correct the curl of the sheet P appropriately.

<Summary of Examples 4 and 5>
The image forming unit 101 and the intermediate transfer unit 102 are an example of an image forming unit that forms a toner image on a hygroscopic sheet. The fixing device 17 is an example of a fixing unit that applies heat to the toner image formed by the image forming unit and fixes the toner image on the sheet. The conveyance path 49 and the double-side conveyance path 58 are examples of a conveyance path that conveys a sheet that has passed through the fixing unit. The light emitting unit 33 is an example of a light emitting unit that outputs light so as to cross the conveyance path. The light emitting unit 33 is a light emitting element such as an LED. The light receiving unit 34 is an example of a light receiving unit that receives light using the light emitting unit as a light source. The light receiving unit 34 is a light receiving element such as a phototransistor or a photodiode.

  FIG. 20 shows the functions of the CPU 26. FIG. 21 shows the function of the estimation unit 76. All or part of these functions may be realized by the CPU 26 executing a control program, or may be realized by hardware such as ASIC or FPGA. ASIC is an abbreviation for application specific integrated circuit. FPGA is an abbreviation for field programmable gate array. The control program may be stored in the storage device 87.

  The sheet detection unit 94 is an example of a sheet detection unit that detects whether there is a sheet at a position where light crosses the conveyance path based on a light reception result of the light reception unit. For example, the sheet detector 94 detects the presence or absence of a sheet based on the detection voltage output from the detection circuit 93. The estimation unit 76 is an example of an estimation unit that estimates the amount of water vapor in the conveyance path based on the light reception result of the light reception unit acquired when the sheet detection unit does not detect the sheet. For example, the estimation unit 76 estimates the amount of water vapor based on the detection voltage output from the detection circuit 93.

  As described above, the light emitting unit 33 and the light receiving unit 34 are combined with a function of detecting a sheet (sheet sensor) and a function of estimating the amount of water vapor (water vapor amount sensor). Therefore, the cost effectiveness of the sheet sensor is improved. The time when the sheet detection means does not detect the sheet is a period from when the trailing edge of the nth sheet passes the detection position until the leading edge of the (n + 1) th sheet arrives at the detection position. . This period may be referred to as a paper interval.

  As described in relation to FIG. 12B, the estimation unit 76 may estimate whether or not the water vapor amount exceeds the water vapor threshold according to the light reception amount that is the light reception result of the light receiving unit. When the amount of water vapor increases, the amount of received light decreases, and when the amount of water vapor decreases, the amount of received light increases. Therefore, it is possible to accurately estimate the water vapor amount from the received light amount. The water vapor threshold is stored in the storage device 87, for example.

  As described with reference to FIG. 12A, the light receiving means is configured to output a detection voltage inversely correlated with the amount of received light. The estimation unit 76 may estimate that the amount of water vapor exceeds the water vapor threshold when the detected voltage exceeds the voltage threshold. The estimation unit 76 may estimate that the amount of water vapor does not exceed the water vapor threshold when the detected voltage does not exceed the voltage threshold. Thus, the estimation unit 76 may estimate whether the amount of water vapor is large or small.

  The estimation unit 76 is configured to estimate the water vapor amount using a detection voltage acquired when the second and subsequent sheets pass through the fixing unit when a plurality of sheets pass through the fixing unit continuously. May be. This is because the detection voltage acquired when the second and subsequent sheets pass through the fixing unit as shown in FIG. 12B more accurately indicates the water vapor amount. Thus, the estimation unit 76 may ignore the detection voltage acquired when the first sheet passes through the fixing unit.

  The estimation unit 76 may be configured to estimate the water vapor amount based on the rate of increase of the detection voltage with respect to the initial voltage. As shown in FIG. 21, the increase rate calculation unit 81 may calculate the increase rate. As described with reference to FIG. 12B, the initial voltage is a detection voltage output by the light receiving unit before the sheet is passed through the fixing unit. The detection voltage is a detection voltage acquired after the sheet passes through the fixing unit.

  The increase rate calculation unit 81 calculates the increase rate acquired in a period from when the nth sheet passes the position to before the n + 1th sheet passes the position. The increase rate calculation unit 81 calculates the increase rate acquired in a period after the n + 1th sheet passes the position and before the n + 2th sheet passes the position. The adding unit 82 functions as an adding unit that adds these increasing rates. The determination unit 83 may estimate the water vapor amount based on the addition result of the addition unit. For example, the determination unit 83 may determine whether the amount of water vapor is large or small by comparing the detection voltage or the rate of increase with a threshold value.

  The sheet counter 95 is an example of a counting unit that counts the number of sheets that have continuously passed through the fixing unit. The estimation unit 76 may be configured to estimate the water vapor amount when the number of sheets reaches a predetermined number. This is because the estimation result of the water vapor amount is stabilized when the number of sheets reaches a predetermined number.

  As shown in FIG. 17A, the light emitting means and the light receiving means may be arranged so as to face each other across the transport path. As shown in FIG. 3A, a reflection member 38 that reflects the light output by the light emitting means may be further provided. The light receiving means may be arranged to receive the light reflected by the reflecting member 38.

  The jam detection unit 75 shown in FIG. 20 is an example of a jam detection unit that detects a sheet jam in the fixing unit based on the detection result of the sheet detection unit. For example, the jam detection unit 75 determines that a sheet jam has occurred in the fixing device 17 when the trailing edge of the sheet cannot be detected after a predetermined time has elapsed from the timing at which the leading edge of the sheet is detected. The sheet detection result of the sheet detection unit 94 may be used to determine the switching timing of the sheet conveyance direction in the duplex conveyance path 58.

  As shown in FIG. 13, the blower unit 32 is an example of a blower that sends air toward a transport guide member that forms a transport path. The fan control unit 77 shown in FIG. 20 is an example of a control unit that controls at least one of the operation time and the air volume of the blowing unit according to the amount of water vapor. The method for determining the operating time is as illustrated with reference to S1405 and FIG.

  The conveyance guide member 59 is a double-sided conveyance path that reverses the image forming surface of the sheet from the first surface to the second surface in order to form a toner image on the second surface of the sheet having the toner image formed on the first surface. 58 may be a part. The conveyance guide member 59 reverses the image forming surface of the sheet from the first surface to the second surface in order to form a toner image on the second surface of the sheet having the toner image formed on the first surface. It may be. The reverse roller 27 is an example of a reverse roller provided in the reverse conveyance path. The opening 60 is an example of an opening provided in the reverse conveyance path and communicating with the outside of the image forming apparatus. The blower unit 32 is arranged so that the air sent by the blower is discharged from the opening to the outside of the image forming apparatus. As a result, water vapor generated inside the image forming apparatus 100 can be discharged to the outside.

  The fan control unit 77 controls the blower unit 32 via the drive circuit 57. The fan control unit 77 may start the timer 88 when the print job ends. The fan control unit 77 stops the blower unit 32 when the elapsed time reaches the operating time Tx. Further, the fan control unit 77 may determine at least one of the operation time and the air volume of the blowing unit according to the amount of water vapor and the number of sheets that have passed through the fixing unit continuously. The coefficient selection unit 84 may select a coefficient such as a slope according to the water vapor amount. As shown in FIG. 15, the selection of the coefficient can correspond to the selection of a linear equation for determining the predetermined time Tx. The operating time determination unit 85 may determine the predetermined time Tx based on the number n of sheets acquired by the sheet counter 95 and the selected coefficient. Thereby, the operation time of the air blowing unit 32 will be appropriately controlled. As shown in FIG. 6, the operation time Tx may be the time from the end of the print job for a plurality of sheets until the blower is stopped. Since water vapor is always generated from the sheet during execution of the print job, the air blowing unit 32 discharges the water vapor to the outside of the image forming apparatus 100. When the print job is finished, water vapor may not be sufficiently discharged. Therefore, the blower unit 32 may operate even after the print job is completed. However, if the air blowing unit 32 is operating even after the water vapor has been sufficiently discharged, power is wasted. Therefore, the operation time Tx is determined according to the amount of generated water vapor.

  The decurling roller pair 90 is an example of a curl correcting unit that corrects curl generated on the sheet by passing through the fixing unit. The decurling control unit 78 may adjust the curl correction amount Fx of the decurling roller pair 90 by controlling the actuator 79 according to the amount of water vapor. The correction amount determination unit 86 determines the amount of curl correction by the curl correction means according to the amount of water vapor.

  Although the reflective sheet sensor is employed in the fourth embodiment, the transmissive sheet sensor described in the fifth embodiment may be employed instead of the reflective sheet sensor. Further, although the transmissive sheet sensor is employed in the fifth embodiment, the reflective sheet sensor described in the fourth embodiment may be employed instead of the transmissive sheet sensor.

  DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 49 ... Conveyance path, 26 ... CPU, 38 ... Reflecting member, 34 ... Light-receiving part, 33 ... Light-emitting part, 32 ... Blower unit

Claims (27)

Light emitting means for outputting light;
A reflecting member that reflects the light output from the light emitting means;
Light receiving means for receiving reflected light from the reflecting member, and receiving the reflected light, which is light that has crossed a conveyance path where the sheet is conveyed at least once from the light emitting means to the light receiving means. A light receiving means for
Detecting means for detecting whether there is a sheet at a position where light crosses the conveyance path based on a detection signal output by the light receiving means according to the amount of received light;
A blowing means for sending air to the reflecting member;
Control means for adjusting at least one of the air volume and operating time of the air blowing means according to a detection signal output by the light receiving means when there is no sheet at a position where light crosses the conveyance path. An image forming apparatus. The control means includes
If the level of the detection signal does not exceed the dew condensation threshold, increase the air volume of the blowing means, or continue blowing by the blowing means,
2. The image forming apparatus according to claim 1, wherein when the level of the detection signal exceeds the dew condensation threshold, the air volume of the air blowing unit is reduced or the air blowing by the air blowing unit is stopped. It further has a measuring means for measuring the operating time of the blowing means,
The control means, if the level of the detection signal does not exceed the dew condensation threshold even if the operating time measured by the measurement means is a predetermined time or more, or reduces the air volume of the blower means, or The image forming apparatus according to claim 2, wherein the blowing by the blowing unit is stopped.   The control means operates the air blowing means while the image forming apparatus forms an image on a sheet, and when the image forming apparatus finishes image formation on the sheet, a position where light crosses in the conveyance path 4. The apparatus according to claim 1, wherein at least one of an air volume and an operation time of the air blowing unit is adjusted according to a detection signal output by the light receiving unit when there is no sheet. 5. The image forming apparatus described in 1.   The control unit emits the light when the power is supplied from a power source and the image forming apparatus is activated, or when the image forming apparatus returns to a state where image formation can be performed from a state where image formation is not performed. The image forming apparatus according to claim 1, wherein the image forming apparatus causes the light to be output to the device, and the air blowing device is driven or stopped in accordance with a detection signal output from the light receiving device. The control means includes
If the level of the detection signal does not exceed the dew condensation threshold, start blowing by the blowing means, or increase the air volume of the blowing means,
6. The image forming apparatus according to claim 5, wherein when the level of the detection signal exceeds the dew condensation threshold, the air volume of the blowing unit is decreased or the blowing by the blowing unit is not executed.   The control unit emits the light when the power is supplied from a power source and the image forming apparatus is activated, or when the image forming apparatus returns to a state where image formation can be performed from a state where image formation is not performed. The light is output to the means and the air blower starts to blow, and the air blower is stopped according to the detection signal output from the light receiving means, or the light emission amount of the light emitting means or the gain of the light receiving means The image forming apparatus according to claim 1, wherein the image forming apparatus is adjusted. The control means includes
If the level of the detection signal is not greater than or equal to the lower limit of the predetermined range, continue blowing by the blowing means,
The image formation according to claim 7, wherein when the level of the detection signal is equal to or higher than a lower limit value of the predetermined range, the air volume of the blowing unit is decreased or the blowing by the blowing unit is stopped. apparatus. It further has a measuring means for measuring the operating time of the blowing means,
The control means increases the light emission amount of the light emitting means if the level of the detection signal is not equal to or higher than the lower limit value of the predetermined range even if the operation time measured by the measuring means is equal to or longer than a predetermined time. 9. The image forming apparatus according to claim 8, wherein a gain of the light receiving unit is increased.   The control means increases the gain of the light receiving means when the level of the detection signal is not equal to or lower than the lower limit value of the predetermined range even when the light emission amount of the light emitting means is increased to a maximum settable value. The image forming apparatus according to claim 9.   The control means increases the light emission amount of the light emitting means when the level of the detection signal is not equal to or lower than the lower limit value of the predetermined range even if the gain of the light receiving means is increased to a maximum settable value. The image forming apparatus according to claim 9. A storage means for storing the light emission amount of the light emission means when the level of the detection signal falls within the predetermined range as an initial value;
The image forming apparatus according to claim 9, wherein the control unit sets an initial value stored in the storage unit in the light emitting unit when starting the light emission of the light emitting unit. A storage means for storing the gain of the light receiving means when the level of the detection signal falls within the predetermined range as an initial value;
The image forming apparatus according to claim 9, wherein the control unit sets an initial value stored in the storage unit in the light receiving unit when starting light reception of the light receiving unit.   2. The air passage according to claim 1, further comprising a ventilation path that guides the air to the reflection member so that the air blown from the air blowing unit or sucked by the air blowing unit is blown to the reflection member. 14. The image forming apparatus according to any one of items 13 to 13. A first guide member and a second guide member that are provided opposite to each other in the conveyance path and guide the sheet;
The light emitting means and the light receiving means are fixed to the first guide member,
The image forming apparatus according to claim 1, wherein the reflecting member is fixed to the second guide member.   The image forming apparatus according to claim 1, further comprising a light shielding member provided between the light emitting unit and the light receiving unit. A conveyance guide member that forms the conveyance path;
The image forming apparatus according to claim 1, wherein the blowing unit sends air to each of the reflection member and the conveyance guide member.   The conveyance path is a reversal conveyance path that reverses the image forming surface of the sheet from the first surface to the second surface in order to form an image on the second surface of the sheet having an image formed on the first surface. The image forming apparatus according to claim 17, wherein the image forming apparatus is provided. A reverse roller provided in the reverse conveyance path;
An opening provided in the reverse conveyance path and communicating with the outside of the image forming apparatus;
The image forming apparatus according to claim 18, wherein the air blowing unit is arranged so that the air blown by the air blowing unit is discharged from the opening to the outside of the image forming apparatus. Image forming means for forming an image on a sheet;
Fixing means for applying heat to the image formed by the image forming means to fix the image to the sheet;
A conveyance guide member that forms a conveyance path through which the sheet that has passed through the fixing unit is conveyed;
Light emitting means for outputting light;
A light receiving means for receiving the light output from the light emitting means, the light receiving means for receiving the light that has crossed the transport path at least once from the light emitting means to the light receiving means;
Detecting means for detecting whether or not there is a sheet at a position where light crosses in the conveying path based on a detection signal output by the light receiving means according to the amount of received light;
A blowing means for sending air to the conveyance guide member;
Control means for adjusting at least one of the air volume and operating time of the air blowing means according to a detection signal output by the light receiving means when there is no sheet at a position where light crosses the conveyance path. An image forming apparatus.   21. The image forming apparatus according to claim 20, wherein the light emitting unit and the light receiving unit are arranged to face each other with the conveyance path interposed therebetween. A reflection member that reflects the light output by the light emitting means;
The image forming apparatus according to claim 20, wherein the light receiving unit is arranged to receive reflected light from the reflecting member.   The conveyance path is a reversal conveyance path that reverses the image forming surface of the sheet from the first surface to the second surface in order to form an image on the second surface of the sheet having an image formed on the first surface. 21. The image forming apparatus according to claim 20, wherein the image forming apparatus is provided. A reverse roller provided in the reverse conveyance path;
An opening provided in the reverse conveyance path and communicating with the outside of the image forming apparatus;
24. The image forming apparatus according to claim 23, wherein the air blowing unit is arranged so that air sent by the air blowing unit is discharged from the opening to the outside of the image forming apparatus.   The control means adjusts at least one of the operating time and the air volume of the blowing means according to the detection signal output from the light receiving means and the number of sheets that have passed through the fixing means continuously. The image forming apparatus according to claim 20, wherein the image forming apparatus is an image forming apparatus. Image forming means for forming an image on a sheet;
Fixing means for applying heat to the image formed by the image forming means to fix the image to the sheet;
A conveyance guide member that forms a conveyance path through which the sheet that has passed through the fixing unit is conveyed;
Light emitting means for outputting light;
A light receiving means for receiving the light output from the light emitting means, the light receiving means for receiving the light that has crossed the transport path at least once from the light emitting means to the light receiving means;
Detecting means for detecting whether or not there is a sheet at a position where light crosses in the conveying path based on a detection signal output by the light receiving means according to the amount of received light;
Curl correcting means for correcting curl generated in the sheet by passing through the fixing means;
An image forming apparatus, comprising: a control unit that controls the curl correcting unit according to the detection signal output by the light receiving unit when there is no sheet at a position where light crosses the conveyance path.   27. The image forming apparatus according to claim 26, wherein the control unit adjusts a curl correction amount by the curl correction unit in accordance with the detection signal output from the light receiving unit.

Images