JP2013097056A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make the number of signal lines smaller than the number of sensors even if sensors for detecting temperature and the other sensors are provided.SOLUTION: An image forming apparatus comprises: image forming means 1Y, 1M, 1C and 1Bk; a fixing device 16 having a ceramic heater 1104; a thermistor 1040b for detecting the temperature of the ceramic heater 1104 in order to control the temperature of the ceramic heater 1104; a thermistor 1040c for detecting the temperature of the end portion of the ceramic heater 1104; an electric resistance connected to the thermistor 1040c; and CPU521 which controls a power supply amount to the ceramic heater 1104 so that the voltage Vm of the thermistor 1040b is a target voltage and stops heat generation of the ceramic heater 1104 if the voltage Vm is a threshold value or less. If the voltage Vb of 1040c exceeds a predetermined value, CPU521 outputs a signal for accelerating the rotation speed of a pressure roller.

Description

  The present invention relates to temperature control of a fixing heater of an image forming apparatus.

  An electrophotographic image forming apparatus develops an electrostatic latent image formed by exposing a photoreceptor according to an original image using a developer having toner, and transfers the image onto a recording material. A toner image corresponding to the original image is formed. In order to fix the toner image on the recording material, the recording material carrying the unfixed toner image is conveyed to a fixing device.

  The fixing device passes a recording material carrying an unfixed toner image through a fixing nip formed by pressing a pressure roller against a fixing unit having a built-in heater. Is used to melt and fix an unfixed toner image on the recording material. Here, the fixing device is provided with a thermistor for detecting the temperature of the fixing device, and the temperature detected by the thermistor so that the temperature of the fixing nip portion becomes the fixing temperature for fixing the toner image on the recording material. Accordingly, the power supply to the heater is controlled.

  Incidentally, there are some fixing devices that can be attached to and detached from the image forming apparatus main body. In an image forming apparatus having such a fixing device, a sensor such as a photo interrupter that detects the presence or absence of a recording material conveyed to the fixing device is arranged on the fixing device side, so that the sensor has failed or an abnormality has occurred. Even if it is a case, there exists an advantage that a sensor can be replaced | exchanged easily by removing a fixing device. However, in the case of such a configuration, it is necessary to provide a signal line from a photo interrupter in addition to a signal line from a thermistor for detecting the temperature of the heater, which increases the number of signal lines.

  Here, an analog signal corresponding to the temperature of the heater output from a plurality of thermistors is converted into a digital signal, and the digital signal for each thermistor is transmitted to the control device by serial communication using one signal line. It is known (see Patent Document 1). According to Patent Document 1, a digital signal corresponding to the temperature of the heater detected for each thermistor is sequentially transmitted to the control device by serial communication, so that the number of signal lines input to the control device is determined by the thermistor. The number can be reduced.

JP 2004-170841 A

  However, in Patent Document 1, it is necessary to provide a new circuit for performing serial communication, and there is a problem that a circuit for transmitting a signal corresponding to the temperature of the heater to the control device has a complicated configuration. It was. Specifically, the configuration is such that the output signal of each sensor such as a photo interrupter or thermistor is transmitted to the control device in association with each sensor, and from which sensor the signal input to the control device is a signal. A configuration must be provided.

  Accordingly, an object of the present invention is more than the number of sensors without composing a circuit for communicating a signal according to the temperature of the heat source and a signal according to the result of detecting the presence / absence of a recording material. An object of the present invention is to provide an image forming apparatus capable of communication using a small number of signal lines.

  In order to solve the above problems, an image forming apparatus according to claim 1 records an image forming unit that forms a toner image and a toner image formed by the image forming unit that is heated in accordance with supplied power. Detecting the presence or absence of a recording material, a fixing means in which the supplied electric power is controlled so as to achieve a target temperature to be fixed to the material, a temperature detecting element whose resistance value changes according to the temperature of the fixing means, The temperature detection so that a voltage applied to the temperature detection element in a state where a recording material is detected is higher than a voltage applied to the temperature detection element in a state where no recording material is detected by a predetermined value or more. A recording material detecting means connected to the element, a signal line connected to a contact point between the temperature detecting element and the recording material detecting means, and from the voltage applied to the temperature detecting element, the temperature of the fixing means, and the recording With and without materials Determination means for determining, wherein the determination means determines that the recording material has been detected in response to a voltage applied to the temperature detection element increasing within the predetermined time by the predetermined value or more. Features.

  According to the present invention, a signal according to the temperature of the heat source and a signal according to the result of detecting the presence or absence of the recording material can be communicated with a simple configuration and a small number of signal lines.

Schematic sectional view of the image forming apparatus Schematic cross-sectional view of the fuser and diagram showing the thermistor mounting position Thermistor temperature characteristics Perspective view of essential parts of paper ejection sensor Control block diagram The figure which shows the change of the signal value which controls the electric power supply to the ceramic heater The figure which shows the change of the signal value when the paper discharge sensor detects the recording material The figure which shows the change of the signal value when the loop sensor detects the deflection of the recording material The flowchart figure which shows the image formation process of an image forming apparatus Flow chart showing temperature adjustment control of ceramic heater The flowchart figure which shows the recording material detection process of a paper discharge sensor The flowchart figure which shows the deflection | deviation detection process of a loop sensor

  FIG. 1 is a schematic cross-sectional view of an image forming apparatus 100 of the present embodiment. In the present embodiment, an image forming apparatus in which four image forming units 1Y, 1M, 1C, and 1Bk that form toner images of respective color components are arranged in a line is used.

  In each image forming unit, 1Y forms a yellow toner image, 1M forms a magenta toner image, 1C forms a cyan toner image, and 1Bk forms a black toner image.

  Since the image forming units 1Y, 1M, 1C, and 1Bk have the same configuration, the image forming unit 1Y that forms a yellow toner image will be described below, and the other image forming units 1M, 1C, and 1Bk will be described. Omitted. Here, the arrow A direction is a direction in which the photosensitive drums 2a, 2b, 2c, and 2d of the image forming units 1Y, 1M, 1C, and 1Bk rotate.

  The image forming unit 1Y includes a photosensitive drum 2a that carries a toner image of a yellow color component, a charger 3a that charges the photosensitive drum 2a, and a developer that develops the electrostatic latent image formed on the photosensitive drum 2a with toner. It has a developing device 4a that visualizes the toner image using an agent. The electrostatic latent image on the photosensitive drum 2a is formed by exposing the photosensitive drum 2a with light corresponding to the yellow color component from the laser exposure device 7 after the photosensitive drum 2a is charged by the charger 3a. Is done.

  Further, the image forming unit 1Y includes a primary transfer roller 5a that transfers a toner image on the photosensitive drum 2a to an intermediate transfer belt 8 described later, and a drum cleaner that removes toner remaining on the photosensitive drum 2a after the toner image is transferred. 6a.

  The intermediate transfer belt 8 described above can carry a full-color toner image by superimposing and transferring the toner images of the respective color components formed by the image forming portions 1Y, 1M, 1C, and 1Bk. The intermediate transfer belt 8 is wound around a tension roller 11 that rotates the intermediate transfer belt 8 in the direction of arrow B and a secondary transfer counter roller 10. A secondary transfer roller 12 is disposed around the intermediate transfer belt 8 at a position facing the secondary transfer counter roller 10 via the intermediate transfer belt 8.

  The recording material P for transferring the toner image is stored in the paper feeding unit 17 and is formed by the secondary transfer counter roller 10 being pressed against the secondary transfer roller 12 through the conveyance path 18. It is conveyed to the secondary transfer nip portion. Further, the recording material P onto which the toner image has been transferred at the secondary transfer nip portion is conveyed to the fixing device 16 through the conveyance path 34 by the secondary transfer counter roller and the secondary transfer roller 12. The fixing device 16 fixes the toner image on the recording material P to the recording material P, and details thereof will be described later with reference to FIG.

  Next, an image forming operation in which the image forming apparatus 100 according to the present embodiment outputs a printed matter corresponding to image data input from a PC (not shown) or a scanner will be described.

  In the image forming unit 1Y, first, the charger 3a uniformly charges the photosensitive drum 2a, and the laser exposure device 7 irradiates the photosensitive drum 2a with exposure light corresponding to the yellow component of the image data, whereby the photosensitive drum 2a. An electrostatic latent image corresponding to the yellow component of the image data is formed on the top. Next, the electrostatic latent image on the photosensitive drum 2a is developed by the developing device 4a using yellow toner.

  The yellow toner image on the photosensitive drum 2a is conveyed to the primary transfer nip N1a where the primary transfer roller 5a presses the photosensitive drum 2a via the intermediate transfer belt 8 as the photosensitive drum 2a rotates in the direction of arrow A. Is done. In the primary transfer nip portion N1a, the yellow toner image on the photosensitive drum 2a is transferred onto the intermediate transfer belt 8 when a primary transfer voltage is applied from the primary transfer roller 5a. The toner remaining on the photosensitive drum 2a is removed by the drum cleaner 6a.

  The toner image transferred to the intermediate transfer belt 8 is conveyed to the secondary transfer nip portion where the secondary transfer roller 12 presses the secondary transfer counter roller 10 via the intermediate transfer belt 8. On the other hand, when the recording material P is adjusted in timing and conveyed to the secondary transfer nip so as to be in contact with the toner image on the intermediate transfer belt 8, the secondary transfer roller 12 to which a secondary transfer voltage is applied is applied. The toner image on the intermediate transfer belt 8 is transferred onto the recording material P. Further, the toner remaining on the intermediate transfer belt 8 without being transferred to the recording material P at the secondary transfer nip portion is removed by a belt cleaner (not shown).

  The recording material P carrying the toner image is conveyed to the fixing device 16, and heat and pressure are applied to the recording material carrying the unfixed toner image in the fixing operation described later, whereby the unfixed toner image is converted to the recording material P. To be melted and fixed.

  Next, the configuration of the fixing device 16 will be described based on the schematic cross-sectional view of the fixing device 16 in FIG.

  FIG. 2A is a schematic sectional view of the fixing device 16. The secondary transfer roller 12 and the secondary transfer counter roller 10 convey the recording material P while sandwiching the recording material P at the secondary transfer nip portion N2.

  The fixing belt 1101 is a cylindrical belt member having high heat resistance, and has an elastic layer on the surface thereof. The fixing belt 1101 is not thermally deformed even at a temperature (for example, 330 [° C.]) higher than the fixing temperature for fixing the toner image. The pressure roller 1102 includes a cored bar part 1102a and an elastic layer rubber part 1102b. The heater holder 1103 is a heat resistant member, and the direction parallel to the axial direction of the pressure roller 1102 is the longitudinal direction. A ceramic heater 1104 as a heat source is attached to the lower surface of the heater holder 1103. In this embodiment, the ceramic heater 1104 and the heated fixing belt 1101 correspond to a fixing unit.

  FIG. 2B is a schematic view of the main part when the ceramic heater 1104 is viewed from the direction of the arrow S in FIG. In the ceramic heater 1104, when the recording material P passes through the fixing nip portion N3, the longitudinal direction is a direction orthogonal to the direction in which the recording material P is conveyed. Further, the length of the ceramic heater 1104 in the longitudinal direction is longer than the width of the maximum size recording material that can be conveyed by the image forming apparatus 100.

  The ceramic heater 1104 is provided with three thermistors 1040 a, 1040 b, and 1040 c as temperature detecting elements for detecting the temperature of the ceramic heater 1104 at different positions in the longitudinal direction of the ceramic heater 1104. As shown in FIG. 2B, the thermistor 1040 b detects the temperature of the central region in the longitudinal direction of the ceramic heater 1104. Here, the central region in the longitudinal direction of the ceramic heater 1104 corresponds to the first position of the heating member. As shown in FIG. 2B, the thermistor 1040a and the thermistor 1040c are within the width of the maximum size recording material that can be transported by the image forming apparatus 100 in the longitudinal direction of the ceramic heater 1104, and the minimum size that can be transported. The temperature of the area outside the width of the recording material is detected. Here, the minimum size recording material allowed to be conveyed by the image forming apparatus 100 corresponds to a predetermined size recording material. In addition, one end of the ceramic heater 1104 corresponds to the second position in a region outside the width of the minimum size recording material.

  In FIG. 2A, the pressure stay 1106 and the pressure spring 1107 press the heater holder 1103 with a uniform pressure along the axial direction of the pressure roller 1102 via the fixing belt 1101, thereby fixing the fixing nip. Part N3 is formed. When the recording material P is conveyed to the fixing nip N3, the recording material P is heated by the ceramic heater 1104 and pressure applied by the pressure stay 1106 and the pressure spring 1107 via the pressure roller 1102. As a result, the unfixed toner on the recording material P is melted and fixed. In FIG. 2A, the arrow C is the recording material conveyance direction, the arrow R 1 is the rotation direction of the fixing belt 1101, and the arrow R 2 is the rotation direction of the pressure roller 1102. The fixing belt 1101 rotates following the driving of the pressure roller 1102 to fix the unfixed toner on the recording material P while conveying the recording material P in the direction of the arrow C in the fixing nip portion N3. Can do.

  The flag 1121 in FIG. 2A is a part of the paper discharge sensor 161 (FIG. 4) that detects the recording material P that has passed through the fixing nip N3. The paper discharge sensor 161 (FIG. 4) is a known photointerrupter composed of a light emitting diode 161a and a phototransistor 161b. The flag 1121 remains at a position (light shielding position) that blocks light emitted from the light emitting diode 161a to the phototransistor 161b by a spring (not shown). The flag 1121 is pushed by the leading end of the recording material P and retracts from the light shielding position. When the trailing end of the recording material P has finished passing, the flag 1121 returns to the light shielding position by the force of a spring (not shown). The paper discharge sensor 161 (FIG. 4) is in a conductive state in which current flows through the phototransistor 161b while the flag 1121 is retracted from the light shielding position and the phototransistor 161b receives light from the light emitting diode 161a. In the present embodiment, when the phototransistor 161b of the paper discharge sensor 161 (FIG. 4) becomes conductive, the value of the voltage Va changes and it is detected that the recording material P has passed the position of the flag 1121. Hereinafter, the position where the flag 1121 detects the recording material P in the conveyance path where the recording material P is conveyed is referred to as a predetermined position of the fixing device 16.

  In the present embodiment, the light emitting diode 161a of the paper discharge sensor 161 corresponds to a light emitting unit, and the phototransistor 161b of the paper discharge sensor 161 corresponds to a light receiving unit.

  The flag 1122 in FIG. 2A is a part of the loop sensor 162 that detects the deflection state of the recording material P. The loop sensor 162 is a well-known photo interrupter including a light emitting diode 162a (FIG. 5) and a phototransistor 162b (FIG. 5). The flag 1122 remains at a position (light shielding position) that blocks light irradiated from the light emitting diode 162a to the phototransistor 162b by a spring (not shown). The flag 1122 is retracted from the light-shielding position when the recording material P is deflected by a predetermined amount or more and pressed from the recording material P, and the deflection of the recording material P becomes smaller than the predetermined amount. When separated, the light is returned to the light shielding position by the force of a spring (not shown). The loop sensor 162 (FIG. 5) is in a conductive state in which current flows through the phototransistor 162b while the flag 1122 is retracted from the light shielding position and the phototransistor 162b receives light from the light emitting diode 162a. In the present embodiment, when the phototransistor 162b of the loop sensor 162 (FIG. 5) becomes conductive, the value of the voltage Vb changes and it is detected that the recording material P is deflected by a predetermined amount or more.

  In the present embodiment, the light emitting diode 162a of the loop sensor 162 corresponds to a light emitting unit, and the phototransistor 162b of the loop sensor 162 corresponds to a light receiving unit.

  In this embodiment, the speed at which the recording material P passes through the fixing nip portion N3 is slower than the speed at which the intermediate transfer belt 8 conveys the toner image. This is because the recording material P is pulled by the difference between the speed at which the secondary transfer counter roller 10 and the secondary transfer roller 12 transport the recording material P and the speed at which the pressure roller 1102 transports the recording material P. This is to prevent the recording material P from being damaged. However, if the speed at which the pressure roller 1102 transports the recording material P is too slow than the speed at which the secondary transfer counter roller 10 and the secondary transfer roller 12 transport the recording material P, the recording material P is transferred at the fixing nip portion N3. This may cause a conveyance failure or reduce the quality of the output image. Therefore, in this embodiment, when the loop sensor 162 detects that the recording material P is bent by a predetermined amount, the rotation speed of the pressure roller 1102 is increased.

  In the present exemplary embodiment, the secondary transfer roller 12 and the secondary transfer counter roller 10 upstream of the fixing belt 1101 and the pressure roller 1102 in the direction in which the recording material P is conveyed corresponds to a conveyance unit.

  Next, changes in resistance values (temperature characteristics) according to the temperatures of the thermistors 1040a, 1040b, and 1040c will be described with reference to FIG.

  Thermistors 1040a, 1040b, and 1040c have a resistance value of 4.7 [kΩ] when the ceramic heater 1104 reaches a target temperature of 230 [° C.], and the resistance value of the thermistor 1040a, 1040b, and 1040c when the ceramic heater 1104 reaches 300 [° C.]. 2.0 [kΩ]. That is, the thermistors 1040a, 1040b, and 1040c have temperature characteristics in which the resistance value decreases as the temperature of the ceramic heater 1104 increases. Here, the fixing belt 1101 of this embodiment can be fixed when the temperature of the ceramic heater 1104 reaches 230 [° C.], and can cause poor fixing when the temperature of the ceramic heater 1104 reaches 330 [° C.].

  Specifically, when the temperature of the ceramic heater 1104 exceeds 330 [° C.], unfixed toner carried on the recording material P conveyed to the fixing nip portion N adheres to the fixing belt 1101. The toner stuck to the fixing belt 1101 may contaminate the recording material when the subsequent recording material passes through the fixing nip N. Therefore, in the present embodiment, when the temperature of the ceramic heater 1104 reaches 300 [° C.], the power supply to the ceramic heater 1104 is forcibly cut off, and the temperature of the ceramic heater 1104 does not rise above 300 [° C.]. It has become.

  Next, the paper discharge sensor 161 of the present embodiment will be described based on the perspective view of the main part of the paper discharge sensor 161 in FIG. FIG. 4A shows a state where the recording material P is detected by the paper discharge sensor 161. FIG. 4B shows a state where the recording material P is not detected by the paper discharge sensor 161.

  The paper discharge sensor 161 includes a light emitting diode 161a, a phototransistor 161b, and an L-shaped flag 1121. When the recording material P passes through the paper discharge sensor 161, the flag 1121 comes into contact with the recording material P and is pushed, so that the light from the light emitting diode 161a is moved to a position where it is received by the phototransistor 161b. On the other hand, when the recording material P finishes passing through the paper discharge sensor 161, the flag 1121 is moved to a position where the light from the light emitting diode 161a is blocked by a spring (not shown). As a result, the phototransistor 161b cannot receive light from the light emitting diode 161a.

  Similarly to the paper discharge sensor 161, the loop sensor 162 causes the flag 1122 to move when the recording material P is bent by a predetermined amount or more, and the bent portion comes into contact with the flag 1122, and the light from the light emitting diode 162a. Is received by the phototransistor 162b. In the loop sensor 162, when the deflection of the recording material P becomes smaller than a predetermined amount, the flag 1122 moves to a position where the light from the light emitting diode 162a is blocked, and the phototransistor 162b cannot receive the light from the light emitting diode 162a.

  Next, the circuit configuration of the present embodiment will be described based on the block diagram of the image forming apparatus in FIG.

  The voltage unit 404 includes a gate-controlled semiconductor switch 510 that controls power supplied to the ceramic heater 1104, a relay circuit 512 and a transistor 511 for cutting off power supply to the ceramic heater 1104.

  The relay circuit 512 is turned on when the Relay signal B is at a high level, and is turned off when the Relay signal B is at a low level. When the relay circuit 512 is turned on, electric power can be supplied to the ceramic heater 1104. When the relay circuit 512 is turned off, electric power cannot be supplied to the ceramic heater 1104.

  When a pulsed heater signal B is input to the gate G, the gate-controlled semiconductor switch 510 adjusts the AC waveform input from the power source according to the timing, and supplies power to the ceramic heater 1104 (power) Supply amount) is controlled. The gate-controlled semiconductor switch 510 supplies power to the ceramic heater 1104 when the relay circuit 512 is on. Thereby, the ceramic heater 1104 generates heat with a heat generation amount corresponding to the power supply amount. Further, the gate-controlled semiconductor switch 510 stops the power supply to the ceramic heater 1104 when the output of the Heater signal is stopped while the relay circuit 512 is on. Thereby, the heat generation of the ceramic heater 1104 is stopped.

  The fixing device 16 includes a ceramic heater 1104 in FIG. 2, a thermistor 1040b for detecting the temperature of the central portion in the longitudinal direction of the ceramic heater 1104, and a thermistor for detecting the temperatures of both ends in the longitudinal direction. 1040a and 1040c are provided. Further, the fixing device 16 is provided with a paper discharge sensor 161 and a loop sensor 162.

  The thermistor 1040b outputs a voltage Vm corresponding to the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 to the controller 403 described later via a signal line. The thermistor 1040b is driven with an input voltage of 3.3 [V] via an electric resistance of 4.7 [kΩ] provided in the controller 403 described later.

  The voltage Vm is 1.65 [V] if the temperature detected by the thermistor 1040b is 230 [° C.], and about 0.98 [V] if the temperature detected by the thermistor 1040b is 300 [° C.]. ].

  The thermistor 1040a is connected in series with an electric resistance of 4.7 [kΩ] through the phototransistor 161b of the paper discharge sensor 161. The contact points of the phototransistor 161b and the thermistor 1040a of the paper discharge sensor 161 are connected to a controller 403, which will be described later, through signal lines. The thermistor 1040a is driven with an input voltage of 3.3 [V].

  Thus, when the phototransistor 161b is turned off, the thermistor 1040a outputs a voltage Va corresponding to the temperature of one end in the longitudinal direction of the ceramic heater 1104 to the controller 403, which will be described later, via the signal line. Here, when the recording material P has not passed the predetermined position of the fixing device 16, the phototransistor 161 b of the paper discharge sensor 161 is blocked by the flag 1121 from the light of the light emitting diode 161 a of the paper discharge sensor 161. It becomes a non-conductive state.

  If the phototransistor 161b is non-conductive, the voltage Va is driven by the thermistor 1040a with an input voltage of 3.3 [V] via an electric resistance of 4.7 [kΩ] provided in the controller 403 described later. It becomes the voltage of the thermistor 1040a at the time. Therefore, the voltage Va is 1.65 [V] if the temperature detected by the thermistor 1040a is 230 [° C.], and about 0.98 if the temperature detected by the thermistor 1040c is 300 [° C.]. [V].

  Further, when the phototransistor 161b becomes conductive, the thermistor 1040a generates a voltage Va having a value higher than the voltage corresponding to the temperature at one end in the longitudinal direction of the ceramic heater 1104 via a signal line. Output to. Here, when the recording material P passes through a predetermined position of the fixing device 16, the phototransistor 161b of the paper discharge sensor 161 becomes conductive by receiving the light of the light emitting diode 161a.

  If the phototransistor 161b of the paper discharge sensor 161 is in a conducting state, the voltage Va is divided by the input voltage of 3.3 [V] by the thermistor 1040a and the combined resistance of 2.35 [kΩ], This voltage is applied to the thermistor 1040a. Note that the combined resistance of 2.35 [kΩ] is a parallel connection of the 4.7 [kΩ] electrical resistance connected to the phototransistor 161 b and the 4.7 [kΩ] electrical resistance provided in the controller 403. Is the combined resistance when connected to.

  Therefore, the voltage Va in a state where the recording material P is detected is higher than a value in a state where the recording material P is not detected by a predetermined value or more. Specifically, if the temperature detected by the thermistor 1040a is 230 [° C.], the voltage Va is about 2.2 [V], and if the temperature detected by the thermistor 1040c is 300 [° C.], the voltage Va becomes approximately 1.52 [V].

  The thermistor 1040c is connected in series with an electric resistance of 4.7 [kΩ] through the phototransistor 162b of the loop sensor 162. Further, the contact points of the phototransistor 162b and the thermistor 1040c of the loop sensor 162 are connected to a controller 403 to be described later by a signal line. The thermistor 1040c is driven with an input voltage of 3.3 [V].

  Thus, when the phototransistor 162b is turned off, the thermistor 1040c outputs a voltage Vb corresponding to the temperature at the other end in the longitudinal direction of the ceramic heater 1104 to the controller 403, which will be described later, via the signal line. Here, when the recording material P is not bent by a predetermined amount or more, the phototransistor 162b of the loop sensor 162 becomes non-conductive because the light of the light emitting diode 162a of the loop sensor 162 is shielded by the flag 1122.

  If the phototransistor 162b is non-conductive, the voltage Vb is driven by the thermistor 1040c with an input voltage of 3.3 [V] through an electric resistance of 4.7 [kΩ] provided in the controller 403 described later. Voltage of the thermistor 1040c at the time. Therefore, the voltage Vb is 1.65 [V] if the temperature detected by the thermistor 1040c is 230 [° C.], and about 0.98 if the temperature detected by the thermistor 1040c is 300 [° C.]. [V].

  Further, when the phototransistor 162b becomes conductive, the thermistor 1040c generates a voltage Vb having a value higher than the voltage corresponding to the temperature at the other end in the longitudinal direction of the ceramic heater 1104 via a signal line. Output to. Here, when the recording material P is bent by a predetermined amount or more, the phototransistor 162b of the loop sensor 162 is turned on by receiving light from the light emitting diode 162a.

  If the phototransistor 162b of the loop sensor 162 is in a conducting state, the voltage Vb is obtained by dividing the input voltage of 3.3 [V] by the thermistor 1040c and the combined resistance of 2.35 [kΩ]. The voltage applied to 1040c. Note that the combined resistance of 2.35 [kΩ] is a parallel connection of the 4.7 [kΩ] electrical resistance connected to the phototransistor 162 b and the 4.7 [kΩ] electrical resistance provided in the controller 403. Is the combined resistance when connected to.

  Therefore, the voltage Vb in a state where the recording material P is detected is higher than a value in a state where the recording material P is not detected by a predetermined value or more. Specifically, if the temperature detected by the thermistor 1040c is 230 [° C.], the voltage Vb is about 2.2 [V], and if the temperature detected by the thermistor 1040c is 300 [° C.], the voltage Vb is about 1.52 [V].

  The paper discharge sensor 161 and the electric resistance of 4.7 [kΩ] connected to the paper discharge sensor 161 function as a recording material detection unit that detects the presence or absence of the recording material P. In this embodiment, the phototransistor 161b of the paper discharge sensor 161 is connected between the thermistor 1040a and the electrical resistance. However, the electrical resistance is connected between the thermistor 1040a and the phototransistor 161b. It is good also as composition which has.

  Further, the loop sensor 162 and the electric resistance of 4.7 [kΩ] connected to the loop sensor 162 function as recording material detection means for detecting the presence or absence of the recording material P. Here, in the present embodiment, the phototransistor 162b of the loop sensor 162 is connected between the thermistor 1040c and the electrical resistance, but the electrical resistance is connected between the thermistor 1040c and the phototransistor 162b. It is good also as composition which has.

  The controller 403 is a control board on which a CPU 521 that is a control circuit for controlling the entire image forming apparatus is mounted. The ROM 700 stores a control program for controlling various processes executed by the image forming apparatus. A RAM 800 is a system work memory used by the CPU 521 for processing. Since the image forming units 1Y, 1M, 1C, 1Bk and the laser exposure apparatus 7 have been described with reference to FIG. 1, description thereof will be omitted here. When image data is input from a scanner or a PC, the interface unit 600 transmits the image data to the CPU 521. The display unit 900 is a liquid crystal screen provided in the image forming apparatus 100 and notifies the user of the state of the image forming apparatus.

  The motor 410 is a DC brushless motor that drives the pressure roller 1102, and the motor 411 is a stepping motor that drives the secondary transfer counter roller 10 and the secondary transfer roller 12. The motor 410 can control the voltage applied to the motor 410 by a drive circuit (not shown) in accordance with an acceleration command from the CPU 521, and can control the rotation speed of the motor 410.

  The voltages Vm, Va, and Vb are input to the CPU 521 and the safety circuit 525, respectively.

  The safety circuit 525 includes comparators 522, 523, and 526.

  The comparator 522 outputs a low level signal when the voltage Vm of the thermistor 1040b becomes 0.98 [V] or less. Here, 0.98 [V] is a voltage of the thermistor 1040b when the temperature of the ceramic heater 1104 is 300 [° C.].

  The comparator 523 outputs a low-level signal when the voltage Va at the contact point where the thermistor 1040a and the phototransistor 161b of the paper discharge sensor 161 are connected is 0.98 [V] or less. Here, 0.98 [V] is a voltage value of the thermistor 1040a when the temperature of the ceramic heater 1104 is 300 [° C.].

  The comparator 526 outputs a low-level signal when the voltage Vc at the contact point where the thermistor 1040c and the phototransistor 162b of the loop sensor 162 are connected is 0.98 [V] or less. Here, 0.98 [V] is a voltage value of the thermistor 1040c when the temperature of the ceramic heater 1104 is 300 [° C.].

  The AND circuit 527 outputs a high level signal if both the signal output from the comparator 523 and the signal output from the comparator 526 are high level, and outputs a low level signal otherwise.

  The AND circuit 528 outputs a high-level relay signal B if both the relay signal A output from the CPU 521 and the signal output from the AND circuit 527 are high level, and otherwise outputs a low-level relay signal B. Signal B is output. That is, the AND circuit 528 outputs a low-level Relay signal B when the temperature of the end portion in the longitudinal direction of the ceramic heater 1104 reaches 300 [° C.] or higher, and supplies power to the ceramic heater 1104 by the voltage unit 404 described later. Is prohibited.

  The AND circuit 529 outputs the heater signal A output from the CPU 521 as the heater signal B if the signal output from the comparator 522 is at a high level, and inhibits the output of the heater signal B otherwise. That is, the AND circuit 529 prohibits the output of the heater signal B when the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 becomes 300 [° C.] or higher, and supplies power to the ceramic heater 1104 by the voltage unit 404 described later. Stop.

  Next, a method in which the controller 403 controls power supply to the ceramic heater 1104 will be described based on the timing chart of FIG. In FIG. 6, voltages Vm, Va, and Vb are voltages that are output in a state where the paper discharge sensor 161 and the loop sensor 162 do not detect the recording material P. Further, the power supply amount of the ceramic heater 1104 is the power (power supply amount) supplied from the power supply by inputting the heater signal B (pulse signal) to the gate control type semiconductor switch 510 (FIG. 5) at a predetermined timing. I have control.

  First, when the controller 403 outputs a high-level relay signal B, the relay circuit 512 is turned on, and power supply to the ceramic heater 1104 is enabled. In this state, when the controller 403 drives the gate-controlled semiconductor switch 510 with a power supply amount of 100 [%], the ceramic heater 1104 generates heat with a heat generation amount corresponding to the power supply amount. Here, the power supply amount when the AC voltage from the power source is applied to the ceramic heater 1104 as it is is assumed to be 100 [%]. When the temperature of the ceramic heater 1104 increases, the resistance values of the thermistors 1040a, 1040b, and 1040c decrease, so that the voltage Vm, the voltage Va, and the voltage Vb decrease.

  In the present embodiment, the voltage Vm of the thermistor 1040b is supplied to the ceramic heater 1104 so as to be 1.65 [V] output when the temperature detected by the thermistor 1040b is 230 [° C.]. Power to be controlled. Here, 1.65 [V] corresponds to the first voltage output from the thermistor 1040b when the temperature of the central portion of the ceramic heater 1104 in the longitudinal direction reaches 230 [° C.].

  Next, when the voltage Vm becomes 1.65 [V] or less, that is, the first voltage or less, the controller 403 adjusts the timing of the heater signal B input to the gate-controlled semiconductor switch 510 and sends it to the ceramic heater 1104. Is reduced by a predetermined amount. In addition, when the temperature of the center part in the longitudinal direction of the ceramic heater 1104 becomes 230 [° C.] or more, the voltage Vm becomes 1.65 [V] or less. Here, the predetermined amount is, for example, 10 [%]. After the power supply amount is reduced by a predetermined amount, the controller 403 again reduces the power supply amount by a fixed amount if the voltage Vm is 1.65 [V] or less even after a predetermined time has elapsed. Here, the predetermined time is, for example, 1 [sec].

  When the voltage Vm becomes higher than 1.65 [V] by decreasing the power supply amount by a predetermined amount, the controller 403 determines the timing of the heater signal B input to the gate-controlled semiconductor switch 510. It is adjusted to increase the power supply amount by a predetermined amount. Here, the predetermined amount is, for example, 10 [%].

  When the voltage Vm is stabilized at 1.65 [V] while increasing or decreasing the power supply amount by a predetermined amount, the controller 403 determines that the temperature of the ceramic heater 1104 is stabilized at 230 [° C.], and the discharge sensor 161 and It is assumed that detection by the loop sensor 162 is possible. In the present embodiment, the state in which the temperature of the ceramic heater 1104 is in the range of 230 [° C.] to 235 [° C.] is referred to as a temperature stable region.

  In addition, when one of the voltages Va and Vb becomes 0.98 [V] or less by continuously fixing an image on a small size recording material, the controller 403 outputs a low level Relay signal B. As a result, the relay circuit 512 is turned off. As a result, power supply to the ceramic heater 1104 is interrupted, and heat generation of the ceramic heater 1104 is prohibited. In the present embodiment, the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 230 [° C.] or less, but the temperature of at least one end in the longitudinal direction is 300 [° C.] or more. This case is called edge temperature rise.

  Further, when the CPU 521 goes out of control and the Heater signal A becomes uncontrollable, and the voltage Vm becomes 0.98 [V] or less, the AND circuit 529 prohibits the output of the Heater signal. As a result, power supply to the ceramic heater 1104 is prohibited, and heat generation of the ceramic heater 1104 is stopped.

  Next, a change in the voltage Va when the paper discharge sensor 161 detects the recording material P in the temperature stable region will be described with reference to FIG.

  At time t1, when the flag 1121 is retracted from the light shielding position due to contact with the recording material P, and the phototransistor 161b of the paper discharge sensor 161 receives light from the light emitting diode 161a, the voltage Va changes from 1.65 [V] to 2. Increase to 2 [V]. Since the voltage Va has increased by 0.5 [V] or more, the CPU 521 determines that the recording material P has entered a predetermined position of the fixing device 16 of the paper discharge sensor 161, and starts counting by a counter (not shown). In this embodiment, when the voltage Va increases by 0.5 [V] or more, the leading edge of the recording material P reaches a predetermined position of the fixing device 16 in the direction in which the recording material P is conveyed. It was set as the structure judged.

  If paper having a small width and a large basis weight is continuously passed, the temperature of the end of the ceramic heater 1104 will rise above a predetermined temperature. Thereby, although the temperature of the center part of the ceramic heater 1104 is maintained in the temperature stable region, the temperature of the end part of the ceramic heater 1104 rises and the voltage Va becomes 1.65 [V] or less. End up.

  When the flag 1121 returns to the light shielding position again at time t2, the phototransistor 161b of the paper discharge sensor 161 can no longer receive light from the light emitting diode 161a, and the voltage Va changes from 2.0 [V] to 1.3 [V]. Decrease to. The CPU 521 determines that the recording material P has passed the predetermined position of the fixing device 16 because the voltage Va has decreased by 0.5 [V] or more, and ends the counting by a counter (not shown). In this embodiment, when the voltage Va decreases by 0.5 [V] or more, the rear end of the recording material P passes through a predetermined position of the fixing device 16 in the direction in which the recording material P is conveyed. It was set as the structure judged.

  In the present embodiment, it is determined that the recording material P has passed a predetermined position of the fixing device 16 when the voltage Va fluctuates by 0.5 [V] or more. This is because when the toner image is fixed on the recording material P, the recording material P passes through the central portion in the longitudinal direction of the ceramic heater 1104 regardless of the size of the recording material P. When the voltage Va increases by 0.5 [V] or more even though the voltage Vm is in the temperature stable region, the temperature of the end portion in the longitudinal direction of the ceramic heater 1104 decreases to a temperature corresponding to the voltage Va. There is no. That is, the CPU 521 transports the recording material P to the fixing device 16 in order to fix the toner image on the recording material P, so that when the voltage Va increases by 0.5 [V] or more, the recording material P is fixed to the fixing device. It is possible to identify that 16 predetermined positions have been reached. Here, 0.5 [V] corresponds to a predetermined value for identifying that the recording material P has reached a predetermined position of the fixing device 16.

  Further, after the voltage Va is increased by 0.5 [V] or more, the CPU 521 determines that the recording material P is loaded when the voltage Va is decreased by 0.5 [V] or more even though the voltage Vm is in the temperature stable region. It can be identified that a predetermined position of the fixing device 16 has been passed. Here, 0.5 [V] corresponds to a predetermined value for identifying that the recording material P has passed a predetermined position of the fixing device 16.

  In the above description, the CPU 521 can measure the time from when the recording material P enters the predetermined position of the fixing device 16 until it passes through the predetermined position. In the present embodiment, if the time from when the recording material P enters the predetermined position of the fixing device 16 until it passes through the predetermined position is longer than the predetermined time, the recording material P is fixed to the fixing nip of the fixing device 16. It is determined that an abnormality (jam) has occurred while being sandwiched between the portions N3.

  When the voltage Va falls below 0.98 [V] at time t5, the CPU 521 outputs a low-level relay signal A, thereby prohibiting the relay circuit 512 from supplying power to the ceramic heater 1104.

  Even if the CPU 521 goes out of control and continues to output the high level relay signal A, the relay signal 512 is prohibited from being supplied to the ceramic heater 1104 because the relay signal B becomes low level by the AND circuit 528. Thus, even when the end portion temperature rise occurs, the heat generation of the ceramic heater 1104 can be stopped safely.

  Here, a case where the voltage Va falls below 0.98 [V] in a state where the recording material P has reached a predetermined position of the fixing device 16 will be described. In this case, the resistance value of the thermistor 1040c where the end temperature rise is detected is about 1 [kΩ]. When this resistance value is converted into the temperature detected by the thermistor 1040c, it becomes about 330 [° C.]. In the present embodiment, even when the temperature of the ceramic heater 1104 becomes 330 [° C.], the energization to the ceramic heater 1104 can be quickly cut off, so that the temperature before the recording material P reaches a temperature is ignited. The heat generation of the ceramic heater 1104 is safely stopped.

  In the present embodiment, the temperature of the end in the longitudinal direction of the ceramic heater 1104 is detected based on the voltage Va output through one signal line connected to the contact between the paper discharge sensor 161 and the thermistor 1040a. At the same time, it can be detected that the recording material P passes through a predetermined position of the fixing device 16. Therefore, the signal line to which the controller 403 and the paper discharge sensor 161 are connected and the signal line to which the controller 403 and the thermistor 1040a are connected can be used together, and the number of signal lines from these sensors is the number of sensors. Can be less.

  Next, a change in the voltage Vb when the loop sensor 162 detects the recording material P in the temperature stable region will be described with reference to FIG. Note that the pressure roller 1102 of this embodiment has a diameter of 30 [mm], and 140 [rpm] (210 [mm] if the recording material P is not bent more than a predetermined threshold value. / Sec]).

  At time t6, when the flag 1122 is retracted from the light shielding position by contact with the recording material P and the phototransistor 162b of the loop sensor 162 receives light from the light emitting diode 162a, the voltage Vb is changed from 1.65 [V] to 2. Increase to 2 [V]. The CPU 521 determines that the recording material P is deflected by a predetermined amount or more because the voltage Vb has increased by 0.5 [V] or more, and starts counting by a counter (not shown). This is because the speed at which the fixing belt 1101 and the pressure roller 1102 convey the recording material P is slower than the speed at which the secondary transfer counter roller 10 and the secondary transfer roller 12 convey the recording material. When the recording material P is A4 size, after the loop sensor 162 detects that the recording material P is bent by a predetermined amount or more, the rear end of the recording material P in the transport direction is subjected to the secondary transfer. The time until the deflection is eliminated by passing through the nip portion N2 is less than 1 second. Therefore, in this embodiment, the recording material size is larger than A4 if the bending is not eliminated even after 1 second or more has passed since the loop sensor 162 detects that the recording material P is bent by a predetermined amount or more. And the rotation speed of the pressure roller 1102 is increased. Thereby, the state where the recording material P is bent by a predetermined amount or more can be eliminated.

  Here, if a sheet having a small width and a large basis weight is continuously passed, the temperature of the end of the ceramic heater 1104 rises above a predetermined temperature. As a result, the temperature at the end of the ceramic heater 1104 rises and the voltage Vb becomes 1.65 [V] or less, although the temperature at the center of the ceramic heater 1104 is maintained in the temperature stable region. End up.

  At time t7, when the flag 1122 returns to the light shielding position again and the phototransistor 162b of the loop sensor 162 cannot receive light from the light emitting diode 162a, the voltage Vb is changed from 2.0 [V] to 1.3 [V]. Decrease to. At this time, the voltage at the contact point between the loop sensor 162 and the thermistor 1040 c becomes a value corresponding to the temperature of the end of the ceramic heater 1104. The CPU 521 determines that the deflection of the recording material P has been eliminated because the voltage Vb has decreased by 0.5 [V] or more, and ends the counting by a counter (not shown).

  In the present embodiment, it is determined that the recording material P is bent as the voltage Vb increases by 0.5 [V] or more, and the recording material is determined as the voltage Vb decreases by 0.5 [V] or more. It is determined that the bending of P has been eliminated. This is because when the toner image is fixed on the recording material P, the recording material P passes through the central portion in the longitudinal direction of the ceramic heater 1104 regardless of the size of the recording material P. When the voltage Vb increases by 0.5 [V] or more even though the voltage Vm is in the temperature stable region, the temperature of the end portion in the longitudinal direction of the ceramic heater 1104 decreases to a temperature corresponding to the voltage Vb. There is no. That is, the CPU 521 causes the recording material P to bend when the voltage Vb increases by 0.5 [V] or more due to the conveyance of the recording material P to the fixing device 16 in order to fix the toner image on the recording material P. Can be identified. Here, 0.5 [V] corresponds to a predetermined value for identifying that the recording material P is bent by a predetermined amount or more.

  Further, after the voltage Vb is increased by 0.5 [V] or more after the voltage Vb is in the temperature stable region, the CPU 521 determines that the voltage of the recording material P is decreased when the voltage Vb is decreased by 0.5 [V] or more. It can be identified that the deflection has been eliminated. Here, 0.5 [V] corresponds to a predetermined value for identifying that the bending of the recording material P has been eliminated. Thereby, the CPU 521 can count the time during which the recording material P is bent.

  At time t8, when the flag 1122 is retracted from the light shielding position again by contact with the recording material P and the phototransistor 162b of the loop sensor 162 receives light from the light emitting diode 162a, the voltage Vb is changed from 1.1 [V] to 1. Increase to 9 [V]. The CPU 521 determines that the recording material P is deflected by a predetermined amount or more because the voltage Vb has increased again by 0.5 [V] or more, and starts counting by a counter (not shown).

  Time t9 is a time after a predetermined time has elapsed since it was determined that the recording material P is bent. Here, in this embodiment, when the state where the recording material P is bent continues for a predetermined time or more, the recording material P sandwiched between the secondary transfer nip portion N2 and the fixing nip portion N3 is bent more than a threshold value. It was set as the structure judged to be.

  At time t9, the voltage Vb is 1.75 [V]. At time t8, since the value when the voltage Vb increases by 0.5 [V] or more is 1.9 [V], the voltage Vb does not decrease by 0.5 [V] or more. In the present embodiment, when the state in which the recording material P is bent continues for a predetermined time or more, it is determined that the recording material P is bent more than a threshold value.

  Therefore, the CPU 521 suppresses the output of a defective image due to the bending of the recording material P by changing the rotation speed of the motor 410 from 140 [rpm] to 150 [rpm]. That is, the CPU 521 reduces the speed difference between the speed at which the secondary transfer counter roller 10 and the secondary transfer roller 12 transport the recording material and the speed at which the fixing device 16 transports the recording material P while fixing the toner image. As described above, the rotation speed of the pressure roller 1102 is increased. Thus, the unfixed toner on the recording material P is prevented from scattering by the bent recording material P coming into contact with the fixing belt or the like.

  When the flag 1122 returns to the light shielding position again at time t10, the phototransistor 162b of the loop sensor 162 cannot receive light from the light emitting diode 162a, and the voltage Vb is changed from 1.7 [V] to 1.0 [V]. Decrease. The CPU 521 determines that the deflection of the recording material P has been eliminated because the voltage Vb has decreased by 0.5 [V] or more, and ends the counting by a counter (not shown). Further, the CPU 521 changes the rotation speed of the motor 410 from 150 [rpm] to 140 [rpm].

  In the above description, if the time during which the recording material P is bent is longer than the predetermined time, the CPU 521 sets the rotation speed of the pressure roller 1102 of the fixing nip N3 that conveys the recording material P to a target speed. Change to a faster speed.

  When the voltage Vb falls below 0.98 [V] at time t11, the CPU 521 outputs a low-level Relay signal A, thereby prohibiting the relay circuit 512 from supplying power to the ceramic heater 1104.

  Even if the CPU 521 runs out of control and the high-level relay signal A continues to be output, the relay circuit 512 prohibits the power supply to the ceramic heater 1104 because the relay signal B becomes low level by the AND circuit 528. Thus, even when the end portion temperature rise occurs, the heat generation of the ceramic heater 1104 can be stopped safely.

  In the present embodiment, the temperature of the end in the longitudinal direction of the ceramic heater 1104 is detected based on the voltage Vb output through one signal line connected to the contact point between the loop sensor 162 and the thermistor 1040c. It is possible to detect that the recording material P is bent by a predetermined amount or more. Therefore, the signal line to which the controller 403 and the loop sensor 162 are connected and the signal line to which the controller 403 and the thermistor 1040c are connected can be used together, and the number of signal lines from these sensors is determined by the number of sensors. Can also be reduced.

  Next, FIG. 9 is a flowchart for explaining the operation of the CPU 521 (FIG. 5) when the image forming apparatus 100 of the present embodiment forms an image. Hereinafter, the image forming process of the ceramic heater 1104 of this embodiment will be described in detail with reference to the block diagram of FIG. 5 and the flowchart shown in FIG. 9 is executed when the CPU 521 reads out a program stored in the ROM 700.

  First, when the main power supply of the image forming apparatus 100 is turned on, the CPU 521 waits until image data is input via the interface unit 600 (S100). In step S100, when image data is input, the CPU 521 starts a temperature adjustment control interrupt process shown in FIG. 10 described later (S101), and waits until the temperature is stable (S102). In step S102, if the temperature stability flag F indicating a temperature stable region in the temperature adjustment control described later is 1, the CPU 521 detects the detection by the paper discharge sensor shown in FIG. 11 described later, and the loop sensor shown in FIG. Is started (S103). Note that 0 is input to the temperature stabilization flag F before the temperature adjustment control is started in step S102.

  Next, the CPU 521 forms an image based on the above-described image forming operation (S104), and determines whether or not the formation of all the images to be formed has been completed (S105). In step S115, when all the images to be imaged are formed, the CPU 521 ends temperature adjustment control shown in FIG. 10 described later (S106). In step S106, the CPU 521 stops the output of the heater signal A and stops the heat generation of the ceramic heater 1104 by setting the relay signal A to a low level.

  Next, the CPU 521 ends detection by a paper discharge sensor shown in FIG. 11 described later and detection by a loop sensor shown in FIG. 12 (S107), and proceeds to step S100.

  If all the images corresponding to the input image data are not formed in step S105, the process proceeds to step S104, and the next image is formed. That is, after all the images corresponding to the image data input through the interface unit 600 are formed, the temperature adjustment control is ended, and the detection of the recording material by the paper discharge sensor and the loop sensor is ended.

  As the interrupt process started in step S101 described above, a temperature adjustment control process performed in parallel with the processes from step S101 to step S106 in FIG. 9 will be described based on the flowchart in FIG. In the present embodiment, the CPU 521 outputs a high level Relay signal A at the timing of starting the temperature adjustment control, and drives the thermistors 1040a, 1040b, 1040c, the paper discharge sensor 161, and the loop sensor 162 to 3.3 [V]. Turn on the power.

  In step S101 of FIG. 9, when the interrupt process is started, the CPU 521 outputs the heater signal A so that the power supply amount becomes 100 [%], and the ceramic heater 1104 generates heat with the maximum heat amount (S200). Next, the CPU 521 waits until the voltage Vm of the thermistor 1040b is 1.65 [V] or less, that is, the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 230 [° C.] or more (S201).

  In step S201, when the temperature of the central portion of the ceramic heater 1104 in the longitudinal direction becomes 230 [° C.] or more, the CPU 521 controls the heater signal A and decreases the power supply amount by 10 [%] (S202). Thereby, the ceramic heater 1104 generates heat with a value smaller than the maximum heat amount.

  Next, the CPU 521 resets the time counter t (S203), and determines whether or not the value of the time counter t is 10 (S204). In the present embodiment, the time counter t is incremented by 1 every 100 [msec]. That is, in step S204, the CPU 521 determines whether or not 1 [sec] has elapsed since the Heater signal A was changed.

  If the value of the time counter t is not 10 in step S204, it is determined whether or not the temperature of the end portion in the longitudinal direction of the ceramic heater 1104 is 300 [° C.] or higher (S205). In step S205, if at least one of the voltage Va and the voltage Vb is 0.98 [V] or lower, the CPU 521 determines that the temperature of the end portion in the longitudinal direction of the ceramic heater 1104 is 300 [° C.] or higher. Identify it. If both the voltage Va and the voltage Vb are 0.98 [V] or more in step S205, the CPU 521 increments the value of the time counter t by 1 (S206), and proceeds to step S204.

  On the other hand, if at least one of the voltage Va and the voltage Vb is 0.98 [V] or less in step S205, the CPU 521 stops the output of the heater signal A (S207) and stops the image forming operation. (S208). Here, 300 [° C.] corresponds to a predetermined temperature higher than the target temperature 230 [° C.], and 0.98 [V] corresponds to the second voltage. In step S207, the CPU 521 stops supplying power to the ceramic heater 1104 when at least one of the voltage Va and the voltage Vb is equal to or lower than the second voltage.

  Further, the CPU 521 invalidates detection of the paper discharge sensor 161 and detection of the loop sensor 162 (S209), notifies the abnormal temperature rise at the end (S210), controls the temperature adjustment of the ceramic heater 1104, and The image forming operation is terminated. In the present embodiment, in step S <b> 210, the CPU 521 notifies the user of the occurrence of the edge temperature rise by displaying a message indicating that the edge temperature rise has occurred on the display unit 900.

  Here, in the present embodiment, the valid flag V is used to determine whether sensor detection is valid in FIGS. 11 and 12 described later. If the valid flag V is 1, the sensor detection is valid, and if the valid flag V is 0, the sensor detection is invalidated. Accordingly, in step S209, the CPU 521 sets 0 to the valid flag V. The valid flag V is set to 0 when the temperature adjustment control is started.

  Next, a case where the value of the time counter t becomes 10 in step S204 will be described. In step S204, if the value of the time counter t is 10, the CPU 521 determines whether or not the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is higher than 235 [° C.] (S211). In step S211, the CPU 521 determines that the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is higher than 235 [° C.] if the voltage Vm is lower than 1.6 [V].

  In step S211, if the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is higher than 235 [° C.], the CPU 521 sets the temperature stabilization flag F to 0, and the temperature of the central portion in the longitudinal direction of the ceramic heater is 300 [° C.]. It is determined whether or not this is the case (S212). In step S212, if the voltage Vm is higher than 0.98 [V], the CPU 521 identifies that the temperature of the central portion in the ceramic heater longitudinal direction is lower than 300 [° C.], and proceeds to step S202. That is, if the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is higher than 235 [° C.] and lower than 300 [° C.], the CPU 521 controls the heater signal A to reduce the amount of heat of the ceramic heater 1104. Therefore, the amount of power supply is reduced.

  Here, a case where the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 235 [° C.] or less in step S211 will be described. In step S211, the CPU 521 determines whether the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 230 [° C.] or more if the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 235 [° C.] or less. Is determined (S213). In step S213, if the voltage Vm is 1.65 [V] or less, the CPU 521 identifies that the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 230 [° C.] or more and 235 [° C.] or less. It determines with it being a stable area | region (S214). In step S214, if the CPU 521 determines that the temperature is in the temperature stable region, the temperature stable flag F is set to 1, and the processing after step S103 of the image forming process in FIG. 9 described above is started.

  Next, the CPU 521 enables the detection of the paper discharge sensor 161 and the loop sensor 162 (S215), and proceeds to step S203. In step S215, the CPU 521 sets 1 to the valid flag V.

  Here, a case where the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is lower than 230 [° C.] in step S213 will be described. In step S213, if the voltage Vm is higher than 1.65 [V], the CPU 521 sets the temperature stability flag F to 0, and disables detection of the paper discharge sensor 161 and detection of the loop sensor 162 described later ( S216). In step S216, the CPU 521 sets 0 to the valid flag V.

  Next, the CPU 521 controls the heater signal A to increase the power supply amount by 10 [%] (S217), and proceeds to step S203. That is, when the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is lower than 230 [° C.], the CPU 521 increases the power supply amount in order to increase the heat amount of the ceramic heater 1104 by controlling the heater signal A. Yes.

  On the other hand, when the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 300 [° C.] or higher in step S212, that is, when the voltage Vm is 0.98 [V] or lower, the CPU 521 The output is stopped (S218). Next, the CPU 521 stops the image forming operation by the image forming units 1Y, 1M, 1C, and 1Bk and the laser exposure device 7 (S219), and disables detection of a paper discharge sensor 161 and detection of a loop sensor 162 described later. (S220). In step S220, the CPU 521 sets 0 to the valid flag V.

  Next, the CPU 521 notifies the user that the ceramic heater 1104 is abnormally heated (S221), and ends the temperature adjustment control of the ceramic heater 1104 and the image forming operation. In the present embodiment, in step S221, the CPU 521 displays a message on the display unit 900 indicating that the temperature of the central portion in the longitudinal direction of the ceramic heater 1104 is 300 [° C.] or higher, thereby abnormally increasing the user. The generation of temperature is informed.

  As the interrupt process started in step S103, the recording material P detection process of the paper discharge sensor 161 performed in parallel with the process from step S103 to step S107 in FIG. 9 will be described based on the flowchart in FIG.

  In step S103 of FIG. 9, when the interrupt process is started, the CPU 521 detects the voltage Va (S300) and waits until the sensor detection becomes valid (S301). In step S301, the CPU 521 identifies that the sensor detection is valid if the valid flag V described in the above temperature adjustment control is set to 1.

  In step S301, if the valid flag V is set to 1, the CPU 521 detects the voltage Va (S302). Next, the CPU 521 determines whether or not the voltage Va detected in step S302 has increased by 0.5 [V] or more than the voltage Va detected in step 300 (S303). In step S303, if the voltage difference has not increased by 0.5 [V] or more, the process proceeds to step S301. In the present embodiment, the processing from step S301 to step S303 is repeated every 500 [msec].

  On the other hand, if the voltage Va increases by 0.5 [V] or more in step S303, the CPU 521 sets the value of the paper discharge counter Ca to 0 (S304) and waits until the sensor detection becomes valid. (S305). In step S303, the phototransistor 161b of the paper discharge sensor 161 and the electrical resistance connected to the phototransistor 161b increase the voltage Va by a predetermined value or more when the recording material P reaches a predetermined position of the fixing device 16. . Thereby, the CPU 521 detects that the recording material has passed the predetermined position. Here, the CPU 521 functions as identification means for identifying that the recording material has been detected. In step S305, the CPU 521 identifies whether or not 1 is set in the valid flag V, as in step S301.

  In step S305, if the valid flag V is set to 1, the CPU 521 detects the voltage Va (S306). Next, the CPU 521 determines whether or not the voltage Va detected in step S306 has decreased by 0.5 [V] or more than the voltage Va detected in step 302 (S307). In step S307, if the voltage Va is decreased by 0.5 [V] or more, the CPU 521 determines that the recording material P has been retracted from the predetermined position of the fixing device 16, and proceeds to step S301.

  On the other hand, if the voltage Va does not decrease by 0.5 [V] or more in step S307, the CPU 521 increases the value of the paper discharge counter Ca by 1 (S308), and the value of the paper discharge counter Ca is 10 or more. It is determined whether or not (S309). If the value of the paper discharge counter Ca is smaller than 10 in step S309, the process proceeds to step S305. The processing from step S304 to step S309 is performed at 100 [msec], for example.

  On the other hand, if the value of the paper discharge counter Ca is 10 or more in step S309, the CPU 521 determines that 1 [sec] has elapsed with the recording material P remaining at a predetermined position of the fixing device 16 by the paper discharge sensor 161. The output of the heater signal A is stopped (S310). In step S <b> 310, if the voltage Va does not decrease more than the predetermined value within the predetermined time even after 1 [sec] has elapsed after the voltage Va increases by the predetermined value or more within the predetermined time, the CPU 521 proceeds to the ceramic heater 1104. It functions as a control means for stopping the power supply.

  Next, the CPU 521 stops the image forming operation (S311), notifies the discharge abnormality (S312), detects by the discharge sensor 161, detection by the loop sensor 162, temperature adjustment control of the ceramic heater 1104, and image forming operation. End. In step S312, when the voltage Va does not decrease by a predetermined value or more after 1 [sec] has elapsed since the voltage Va has increased by a predetermined value or more, the recording material P has a discharge abnormality (jam). It functions as an informing means for informing that it has occurred.

  As the interrupt process started in step S103 described above, the recording material P detection process of the loop sensor 162 performed in parallel with the processes from step S103 to step S107 of FIG. 9 will be described based on the flowchart of FIG.

  In step S103 of FIG. 9, when the interrupt process is started, the CPU 521 detects the voltage Vb (S400) and waits until the sensor detection becomes valid (S401). In step S401, the CPU 521 identifies that the sensor detection is valid if the valid flag V described in the above temperature adjustment control is set to 1.

  If 1 is set in the valid flag V in step S401, the CPU 521 detects the voltage Vb (S402). Next, the CPU 521 determines whether or not the voltage Vb detected in step S402 has increased by 0.5 [V] or more than the voltage Vb detected in step 400 (S403). In step S403, if the voltage difference has not increased by 0.5 [V] or more, the process proceeds to step S401. Here, as described with reference to FIG. 8, the loop sensor 162 increases the voltage Vb by 0.5 [V] or more when it is detected that the recording material P is bent and bent by a predetermined amount. In the present embodiment, the processing from step S401 to step S403 is repeated every 500 [msec].

  On the other hand, if the voltage Vb has increased by 0.5 [V] or more in step S403, the CPU 521 sets the value of the loop counter Cb to 0 (S404) and waits until the sensor detection becomes effective (S404). S405). In step S403, the phototransistor 162b of the loop sensor 162 and the electrical resistance connected to the phototransistor 162b increase the voltage Vb by 0.5 [V] or more when the recording material P bends by a predetermined amount or more. Thereby, the CPU 521 identifies that the recording material is bent by a predetermined amount or more. Here, the CPU 521 functions as identification means for identifying that the recording material has been detected. In step S405, the CPU 521 identifies whether the valid flag V is set to 1 as in step S401.

  In step S405, if 1 is set in the valid flag V, the CPU 521 detects the voltage Vb (S406). Next, the CPU 521 determines whether or not the voltage Vb detected in step S406 has decreased by 0.5 [V] or more than the voltage Vb detected in step S402 (S407). In step S407, if the voltage Vb has decreased by 0.5 [V] or more, the CPU 521 determines that the deflection of the recording material P has been eliminated, and proceeds to step S401.

  On the other hand, if the voltage Vb has not decreased by 0.5 [V] or more in step S407, the CPU 521 increases the value of the loop counter Cb by 1 (S408), and whether or not the value of the loop counter Cb is 10 or more. Is determined (S409). If the value of the loop counter Cb is smaller than 10 in step S409, the process proceeds to step S405. The processing from step S404 to step S409 is performed, for example, at 100 [msec].

  On the other hand, in step S409, if the value of the loop counter Cb is 10 or more, the CPU 521 determines that the recording material P is bent by the loop sensor 162 or more and the rotation speed of the motor 410 is 150 [rpm]. (S410). In step S410, when the rotation speed of the motor is changed from 140 [rpm] to 150 [rpm], the CPU 521 increases the rotation speed of the pressure roller 1102 rotated by the motor 410 by a predetermined amount. Here, the increment of the rotational speed is, for example, 15 [mm / sec]. That is, in step S410, the motor 410 determines the speed at which the secondary transfer counter roller 10 and the secondary transfer roller 12 transport the recording material P and the speed at which the fixing belt 1101 and the pressure roller 1102 transport the recording material P. The speed difference is reduced, and the deflection of the recording material P is suppressed.

  Next, the CPU 521 waits until the sensor detection becomes valid (S411). In step S411, the CPU 521 identifies whether the valid flag V is set to 1 as in steps S401 and S405.

  In step S411, if the valid flag V is set to 1, the CPU 521 detects the voltage Vb (S412). Next, the CPU 521 determines whether or not the voltage Vb detected in step S412 has decreased by 0.5 [V] or more than the voltage Vb detected in step S402 (S413). If the voltage Vb has decreased by 0.5 [V] or more in step S413, the CPU 521 changes the rotation speed of the motor 410 to 140 [rpm] (S414), and proceeds to step S401.

  In the present embodiment, when the recording material P is bent by a threshold value or more, the rotation speed of the pressure roller 1102 is increased, and when the bending of the recording material P identified by the loop sensor 162 is eliminated, the rotation speed is increased. Control to return to the original speed.

  Further, in the paper discharge sensor 161 of the present embodiment, if the time for which the recording material P passes through a predetermined position of the fixing device 16 is longer than a predetermined time, an abnormal discharge (jam) of the recording material P has occurred. However, the present invention is not limited to this configuration. For example, if the paper discharge sensor 161 cannot detect the arrival of the recording material P at the timing when the recording material P should reach a predetermined position of the fixing device 16, the image forming apparatus 100 detects a conveyance abnormality (jam) of the recording material P. It may be configured to detect the occurrence. In this configuration, the count number from when the image forming operation is started until the recording material P reaches a predetermined position of the fixing device 16 is stored, and the voltage Va is maintained even when the stored count number is reached. If it does not fluctuate more than a predetermined value within a predetermined time, it may be detected that an abnormality has occurred.

  In the present embodiment, the value of the voltage Va increasing within a predetermined time is sufficiently larger than the increase in the voltage Va due to the temperature drop of the ceramic heater 1104 due to natural heat dissipation. Therefore, when the voltage Va increases by 0.5 [V] or more within a predetermined time after the temperature of the ceramic heater 1104 is controlled to the target temperature, the CPU 521 causes the paper discharge sensor 161 to bring the recording material P to a predetermined position. It is good also as a structure which determines with having detected having arrived.

  Further, in the present embodiment, the value of the voltage Vb that increases within a predetermined time is sufficiently larger than the increase in the voltage Vb due to the temperature drop of the ceramic heater 1104 due to natural heat dissipation. Therefore, after the temperature of the ceramic heater 1104 is controlled to the target temperature, the CPU 521 causes the recording material P to be bent by a predetermined amount or more by the loop sensor 162 when the voltage Vb increases by 0.5 [V] or more within a predetermined time. It is good also as a structure which determines with having detected.

  As described above, in the present embodiment, the controller 403 side does not have a complicated configuration even when it has a plurality of sensors that detect the temperature of the ceramic heater 1104 and a sensor that detects the presence or absence of the recording material P. In addition, the number of signal lines can be reduced from the number of sensors.

1Y Yellow image forming unit 1M Magenta image forming unit 1C Cyan image forming unit 1Bk Black image forming unit 16 Fixing device 1040a Thermistor 1040b Thermistor 1040c Thermistor 1104 Ceramic heater 1121 Paper discharge sensor 1122 Loop sensor 521 CPU

Claims (10)

An image forming means for forming a toner image;
A fixing unit that is heated in accordance with the supplied power and that controls the supplied power so as to reach a target temperature for fixing the toner image formed by the image forming unit on a recording material;
A temperature detecting element whose resistance value changes according to the temperature of the fixing unit;
The voltage applied to the temperature detection element while detecting the presence or absence of the recording material and the state where the recording material is detected is more predetermined than the voltage applied to the temperature detection element when the recording material is not detected. Recording material detection means connected to the temperature detection element so as to be higher than the value,
The temperature of the fixing unit or the recording material is connected to a contact point between the temperature detecting element and the recording material detecting unit by a signal line and is applied to the temperature detecting element detected via the signal line. Determination means for determining the presence or absence of a recording material by the detection means,
The determination means detects the recording material in response to a voltage applied to the temperature sensing element detected via the signal line increasing by the predetermined value or more within a predetermined time. And an image forming apparatus.   The determination means indicates that the voltage represents the temperature of the fixing means until the voltage applied to the temperature detection element detected via the signal line increases within the predetermined time by the predetermined value or more. Determining that if the voltage applied to the temperature detecting element detected via the signal line decreases by more than the predetermined value within a predetermined time, it is determined that the voltage represents the temperature of the fixing unit. The image forming apparatus according to claim 1, wherein:   The image forming apparatus further stops supplying power to the fixing unit when the voltage applied to the temperature detection element detected via the signal line becomes a voltage corresponding to a predetermined temperature higher than the target temperature. The image forming apparatus according to claim 2, further comprising a stopping unit that stops the operation.   The image forming apparatus according to claim 1, wherein the recording material detection unit detects a recording material conveyed to the fixing unit.   The image forming apparatus further applies the recording material on which the toner image is formed by the image forming unit to the temperature detection element detected via the signal line even when the recording material should reach the fixing unit. The image forming apparatus according to claim 4, further comprising a notifying unit that notifies a recording material conveyance abnormality if the voltage does not increase by a predetermined value or more within a predetermined time.   The image forming apparatus further includes a time required for the recording material to pass through the fixing unit after a voltage applied to the temperature detection element detected via the signal line has increased by the predetermined value or more within a predetermined time. If the voltage applied to the temperature detection element detected via the signal line does not decrease by the predetermined value or more within a predetermined time even after the elapse of time, the supply of power to the fixing unit is stopped. The image forming apparatus according to claim 4, further comprising a unit.   The image forming apparatus further includes a time required for the recording material to pass through the fixing unit after a voltage applied to the temperature detection element detected via the signal line has increased by the predetermined value or more within a predetermined time. If the voltage applied to the temperature sensing element detected via the signal line does not decrease by the predetermined value or more within a predetermined time even after the elapse of time, an error that the recording material cannot be ejected is notified. The image forming apparatus according to claim 4, further comprising a notification unit configured to perform notification. The image forming apparatus is further provided upstream of the fixing unit in a direction in which the fixing unit conveys the recording material, and the recording unit is fed to the fixing unit at a speed faster than a speed at which the fixing unit conveys the recording material. Having a transport section to transport,
The image forming apparatus according to claim 1, wherein the recording material detection unit detects that the recording material is bent by a predetermined amount or more between the fixing unit and the transport unit.   The fixing unit and the conveying unit may be configured to detect the signal even if a predetermined time has elapsed after a voltage applied to the temperature detection element detected via the signal line has increased by the predetermined value or more within a predetermined time. If the voltage applied to the temperature detection element detected via the line does not decrease by the predetermined value or more within the predetermined time, the fixing unit conveys the recording material, and the conveying unit uses the recording material. The image forming apparatus according to claim 8, wherein a speed difference from a conveying speed is reduced. The recording material detection means includes a light emitting unit that emits light, a light receiving unit that receives light from the light emitting unit, and an electrical resistance connected to the light receiving unit,
9. The voltage applied to the temperature detection element by the electrical resistance increases by the predetermined value or more while the light receiving unit receives light from the light emitting unit. The image forming apparatus according to one item.

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