JP5927156B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus, and more particularly to a technique for improving the reliability of a fixing apparatus that fixes a toner image on a recording sheet by thermocompression bonding.

  In the electrophotographic image forming apparatus, the fixing device includes a toner that is transferred onto the surface of the recording medium by sandwiching the recording medium onto which the toner image is transferred at a nip portion between a heat roller and a pressure roller that are rotationally driven. The image is heated and pressed to perform a fixing process. Recently, in order to save power and shorten the time from power-on to image output, a fixedly supported heater and a heat-resistant cylindrical film for fixing that is conveyed while being pressed against the heater. A toner image transferred to the surface of the recording medium by applying the heat of the heater to the recording medium through a film. There has been proposed a film heating and fixing device for fixing the image on the surface of a recording medium.

  In the film heating and fixing apparatus, if the pressure roller is always driven to rotate at the same rotational speed, the diameter of the pressure roller changes, so that the rotation speed of the film changes. Therefore, conventionally, the rotation state of the film is detected, the proper rotation state of the pressure roller is maintained to improve the printing accuracy, and the occurrence of abnormal images is prevented (see, for example, Patent Document 1).

JP 2003-76176 A

  In the conventional fixing device, for example, a halogen heater or the like is disposed on the inner peripheral side of the heat roller as a heat source of the heat roller. In order to appropriately fix the toner image on the recording medium, it is necessary to maintain the temperature of the heat roller at an appropriate temperature (fixing temperature) necessary for the fixing. At this time, when the heat roller is rotating in the fixing device, the heat of the heat roller is conducted to the pressure roller or the recording medium to keep the heat roller at an appropriate temperature, but when the heat roller is not rotating, Since the heat conduction becomes insufficient, the threshold temperature at which the heat roller and the pressure roller are welded is lowered. Therefore, in the fixing device, when the temperature of the heat roller becomes equal to or higher than a predetermined temperature, it is necessary to rotate the heat roller.

  The driving of the heat roller is often performed by a configuration in which a main motor that supplies a rotational driving force to the recording medium transport roller is used as power, and the power of the main motor is transmitted to the heat roller using a gear. In this case, in order to prevent the welding, when the main motor is not normally driven, control such as stopping energization of the heater of the heat roller is performed. However, even though the main motor is operating normally, if the power is not transmitted to the heat roller due to gear breakage or assembly failure, the heat roller does not rotate, and its temperature rises and increases with the heat roller. Although there is a risk of welding with the pressure roller, the above control cannot prevent the welding.

  The present invention has been made to solve the above-mentioned problem, and aims to accurately prevent welding between the heat roller and the pressure roller due to a temperature rise of the heat roller without adding a complicated mechanism. To do.

  An image forming apparatus according to an aspect of the present invention has conductivity, a heat roller having an insulating film on a peripheral surface thereof except for a partial region in the circumferential direction, and a pressure roller pressed against the heat roller And a thermistor disposed in the vicinity of the heat roller, and a pull-up resistor connected to the thermistor, and fluctuates according to the electrical resistance value of the thermistor that changes due to temperature changes. The voltage output unit that outputs the voltage between the pull-up resistor and the thermistor, and the rotating roller is in contact with the peripheral surface portion where the insulating film and the partial region are formed, and the partial region The contact between the pull-up resistor and the thermistor via the heat roller, and the voltage output from the voltage output unit is a ground voltage. Based on the time interval becomes, and a determination unit configured to determine whether or not rotating at the heat roller a predetermined reference rotational speed or higher.

  According to the present invention, since the rotation state of the heat roller itself is detected without adding a complicated mechanism, even if the gear transmitting power from the drive source to the heat roller is damaged or there is an assembly failure, It can be reliably detected that the heat roller is not rotating at a predetermined reference rotation speed or higher. This makes it possible to prevent welding between the heat roller and the pressure roller due to the temperature rise of the heat roller.

1 is a front sectional view showing a structure of an image forming apparatus according to an embodiment of the present invention. 2 is a functional block diagram illustrating a main internal configuration of the image forming apparatus. FIG. It is a figure which shows the structure around a fixing | fixed part and a temperature detection part. It is a graph which shows the voltage V1 output from a temperature detection part with progress of time. It is a flowchart which shows the rotational speed detection process of a heat roller.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a front sectional view showing the structure of an image forming apparatus according to an embodiment of the present invention.

  An image forming apparatus 1 according to an embodiment of the present invention is a multifunction machine having a plurality of functions such as a copy function, a printer function, a scanner function, and a facsimile function. The image forming apparatus 1 includes an operation unit 47, an image forming unit 12, a fixing unit (fixing device) 13, a paper feeding unit 14, a document feeding unit 6, a document reading unit 5, and the like in an apparatus main body 11. ing.

  The operation unit 47 receives instructions such as an image forming operation execution instruction and a document reading operation execution instruction from the operator regarding various operations and processes that can be executed by the image forming apparatus 1. The operation unit 47 includes a display unit 473 that displays operation guidance to the operator.

  When the image forming apparatus 1 performs a document reading operation, the document reading unit 5 optically reads a document fed by the document feeding unit 6 or a document placed on the document placing glass 161, Generate image data. Image data generated by the document reading unit 5 is stored in a built-in HDD or a network-connected computer.

  When the image forming apparatus 1 performs an image forming operation, it is based on image data generated by the document reading operation, image data received from a computer connected to a network, image data stored in a built-in HDD, or the like. The image forming unit (printing unit) 12 forms a toner image on the recording paper P as a recording medium fed from the paper feeding unit 14. When performing color printing, the magenta image forming unit 12M, the cyan image forming unit 12C, the yellow image forming unit 12Y, and the black image forming unit 12Bk of the image forming unit 12 respectively A toner image is formed on the photosensitive drum 121 by charging, exposure, and development processes based on an image composed of each color component constituting data, and the toner image is formed on the intermediate transfer belt 125 by the primary transfer roller 126. Let them transcribe.

  The toner images of the respective colors transferred onto the intermediate transfer belt 125 are superimposed on the intermediate transfer belt 125 with the transfer timing adjusted to form a color toner image. The secondary transfer roller 210 passes the toner image of the color formed on the surface of the intermediate transfer belt 125 from the paper supply unit 14 through the conveyance path 190 at a nip N between the intermediate transfer belt 125 and the driving roller 125a. It is transferred to the recording paper P that has been conveyed. Thereafter, the fixing unit 13 fixes the toner image on the recording paper P to the recording paper P by thermocompression bonding. The recording paper P on which the color image has been formed after completion of the fixing process is discharged to a discharge tray 151.

  The paper feed unit 14 includes a plurality of paper feed cassettes. The control unit 100 (FIG. 3) rotates the pickup roller 145 of the paper feed cassette that contains the recording paper of the size specified by the instruction from the operator, and the recording paper P contained in each paper feed cassette. Is conveyed toward the nip portion N.

  In the case of performing double-sided printing in the image forming apparatus 1, the recording paper P having an image formed on one side by the image forming unit 12 is nipped by the discharge roller pair 159, and then the recording paper P is switched back by the discharge roller pair 159 and sent to the reverse conveyance path 195, and the conveyance roller pair 19 conveys the recording paper P again upstream in the conveyance direction of the recording paper P with respect to the nip portion N and the fixing unit 13. As a result, an image is formed on the other surface of the recording paper by the image forming unit 12.

  FIG. 2 is a functional block diagram showing the main internal configuration of the image forming apparatus 1. The image forming apparatus 1 includes a control unit 10, an operation unit 47, a document feeding unit 6, a document reading unit 5, an image memory 32, an image forming unit 12, a fixing unit 13, a drive motor 70, a facsimile communication unit 71, and a network interface unit. 91, HDD 92, temperature detector 134, and the like.

  The document reading unit (data acquisition unit) 5 includes a reading mechanism 163 (FIG. 1) having a light irradiation unit, a CCD sensor, and the like under the control of the control unit 10. The document reading unit 5 reads an image from the document by irradiating the document with the light irradiating unit and receiving the reflected light with a CCD sensor.

  The image memory 32 is an area for temporarily storing document image data obtained by reading by the document reading unit 5 and temporarily storing data to be printed by the image forming unit 12.

  The facsimile communication unit 71 includes an unillustrated encoding / decoding unit, modulation / demodulation unit, and NCU (Network Control Unit), and performs facsimile transmission using a public telephone network.

  The network interface unit 91 includes a communication module such as a LAN board, and transmits and receives various data to and from the local area or the computer 20 on the Internet via a LAN connected to the network interface unit 91.

  The HDD 92 is a large-capacity storage device that stores document images and the like read by the document reading unit 5.

  The driving motor 70 is a driving source that applies a rotational driving force to each rotating member of the image forming unit 12, the conveyance roller pair 19, the heat roller 131 of the fixing unit 13, and the like.

  In addition, the fixing unit 13 includes a heat roller 131 and a pressure roller 132 (FIG. 3), and a heater 137 provided inside the heat roller 131 and the like to heat the heat roller 131. The control unit 100 performs energization control to the heater 137.

  The temperature detection unit 134 detects the temperature of the heat roller 131. The temperature detection unit 134 generates a voltage that changes according to the temperature of the heat roller 131, and outputs the voltage to the control unit 100 as a temperature detection signal. The temperature detection unit 134 is an example of a voltage detection unit in the claims.

  The control unit 10 includes a CPU, a RAM, a ROM, a dedicated hardware circuit, and the like, and controls overall operation of the image forming apparatus 1. The control unit 10 includes a control unit 100 and a determination unit 101.

  The control unit 100 includes an operation unit 47, a document feeding unit 6, a document reading unit 5, an image memory 32, an image forming unit 12, a fixing unit 13, a drive motor 70, a facsimile communication unit 71, a network interface unit 91, an HDD 92, and the like. And control each of these parts.

  Further, the control unit 100 controls energization of the heater 137 according to the temperature detection signal output from the temperature detection unit 134. For example, the control unit 100 energizes the heater 137 when the temperature detection signal indicates a temperature lower than a predetermined energization stop temperature (for example, a temperature exceeding a normal reference temperature such as 240 ° C.). The heating roller 131 is heated to a predetermined reference temperature (for example, 180 ° C., for example), while the control unit 100 indicates that the temperature detection signal indicates a temperature equal to or higher than the energization stop temperature. Performs control to stop energization of the heater 137.

  The determination unit 101 determines whether or not the heat roller 131 is rotating at a predetermined reference rotation speed or higher based on a time interval at which the voltage output from the temperature detection unit (voltage output unit) 134 becomes the ground potential. judge. As this reference rotation speed, for example, the peripheral speed at the time of rotation of the heat roller 131 and the pressure roller 132 (FIG. 3) is the same as the peripheral speed at the time of rotation of the transport roller pair 19 that transports the recording paper P. The rotational speed of the roller 131 is used. This reference rotation speed corresponds to a period T described later.

  When the determination unit 101 determines that the heat roller 131 of the fixing unit 13 is rotating at the reference rotation speed or higher, the control unit 100 drives a drive motor 70 that is an example of a drive source of the heat roller 131. The temperature of the heat roller 131 is maintained at the reference temperature by controlling the rotation of the heat roller 131 at the reference rotation speed and energizing the heater 137 (FIG. 3). Further, when the determination unit 101 determines that the heat roller 131 of the fixing unit 13 is not rotating at the reference rotation speed or higher, the control unit 100 stops energization of the heater 137 or the drive motor 70 Control is performed such as stopping driving and stopping rotation of the heat roller 131 and stopping energization of the heater 137.

  Next, the configuration of the fixing unit 13 and the temperature detection unit 134 will be described. FIG. 3 is a diagram illustrating a configuration around the fixing unit 13 and the temperature detection unit 134.

  The fixing unit 13 includes a heat roller 131, a pressure roller 132, and a heater 137.

  The heat roller 131 heats the toner image transferred to the recording medium (recording paper P). The base tube 131a of the heat roller 131 is made of a conductive material, for example, metal. The raw tube 131a is connected to the ground. In addition, a heater 137 made of, for example, a halogen lamp is provided inside the elementary tube 131a. The raw tube 131a heats the recording paper P sandwiched by the nip with the pressure roller 132 while being heated by the heater 137.

  An insulating film 131b is coated on the peripheral surface of the base tube 131a in a non-contact region with the recording paper P in the axial direction thereof in the circumferential direction. However, the insulating film 131b is provided on the peripheral surface of the heat roller 131 in a region excluding the partial region 131c in the circumferential direction. That is, the partial region 131c on the peripheral surface of the element tube 131a becomes a conductive region 131c without being coated with the insulating film 131b, and the element tube 131a is exposed.

  Further, the heat roller 131 is rotated by driving power transmitted from the drive motor 70 (FIG. 3) via a gear (not shown) under the control of the control unit 100.

  The pressure roller 132 is pressed against the heat roller 131 to form a nip portion together with the heat roller 131, and presses the recording paper P between the nip portion.

  The temperature detection unit 134 includes a thermistor 133, a pull-up resistor 135, a contact 136, and a signal line S. Note that the temperature detection unit 134 may include a pull-up power supply V1p.

  The thermistor 133 is connected to the pull-up power source V1p via a pull-up resistor 135. The thermistor 133 is provided in the vicinity of the heat roller 51. The temperature detection unit 134 outputs the voltage V1 between the thermistor 133 and the pull-up resistor 135 that changes according to the temperature change of the heat roller 51 to the control unit 100 and the determination unit 101 of the control unit 10 as a temperature detection signal. . For example, the temperature detection unit 134 connects the connection line between the thermistor 133 and the pull-up resistor 135 (the high potential side of the thermistor 133) to the A / D port of the control unit 10 by the signal line S. A temperature detection signal input from the A / D port to the control unit 10 is processed by the control unit 100 and the determination unit 101. In the present embodiment, an NTC thermistor whose resistance decreases proportionally as the temperature rises is employed, and an example is shown in which the temperature detection unit 134 outputs a voltage that decreases according to the temperature rise. Yes.

  One end of a contact (contact part) 136 is connected between the thermistor 133 and the pull-up resistor 135 (on the high potential side of the thermistor 133). The other end of the contact 136 is a peripheral surface of the base tube 131a of the heat roller 131 and is in contact with a peripheral surface portion where the insulating film 131b and the conductive region 131c are formed. As a result, the contact 136 connects between the pull-up resistor 135 and the thermistor 133 to the ground via the element tube 131a of the heat roller 131 when contacting the conductive region 131c, and when contacting the insulating film 131b, The pull-up resistor 135 and the thermistor 133 are switched so as not to be connected to the ground.

  For this reason, when the heat roller 131 rotates, in a state where the contact 136 and the conductive region 131c are in contact, the voltage V1 of the ground potential is input from the temperature detection unit 134 to the control unit 10, and the contact 136 and the insulating film In the state where 131b is in contact, the voltage V1 that varies according to the temperature change of the heat roller 131 is input to the control unit 10 from the temperature detector 134. Since the ground potential voltage V1 is input to the control unit 10 every time the heat roller 131 rotates once, it becomes a rotation detection signal of the heat roller 131. Thereby, the temperature detection unit 134 also functions as a rotation detection unit that detects the rotation of the heat roller 131, and enables detection of the number of rotations or the rotation speed of the heat roller 131.

  Although the rotation of the heat roller 131 can be detected even if a rotary encoder is used as a means for directly detecting the rotation of the heat roller 131, the temperature detection unit 134 detects the temperature detection signal and the rotation detection as described above. By sharing one signal line S with a signal, the rotation of the heat roller 131 can be detected with a minimum number of components without adding a complicated mechanism.

  Although the insulating film 131b is coated on the outer circumference of the base tube 131a of the heat roller 131, this is an example of a coating region of the insulating film 131b, and the insulating film 131b is coated on other regions. May be.

  Further, in the above, a configuration is shown in which a part of the peripheral surface (circumference) of the base tube 131a of the heat roller 131 is not coated with the insulating film 131b. A configuration may be adopted in which an electrode that penetrates the insulating film 131 b and contacts the element tube 131 a is provided on a part of the peripheral surface in the direction, and the electrode 136 and the contact 136 are in contact with each other when the heat roller 131 rotates.

  FIG. 4 is a graph showing the voltage V1 output from the temperature detection unit 134 over time.

  With the configuration described above, the temperature detection unit 134 changes the voltage V1 as a temperature detection signal gently according to the temperature of the heat roller 131. For example, as the temperature of the heat roller 131 increases, the value of the voltage V1 decreases. As shown in FIG. 4, when the contact 136 is in contact with the insulating film 131 b, the voltage V <b> 1 that varies according to the temperature change of the heat roller 131 is input to the control unit 10 from the temperature detection unit 134. At the time of contact between the contact 136 and the conductive region 131c, the voltage V1 having the ground potential is input to the control unit 10 at a cycle according to the rotation speed of the heat roller 131. That is, the time interval at which the rotation detection signal that is the ground potential voltage V <b> 1 is input to the control unit 10 indicates the rotation period of the heat roller 131. FIG. 4 shows an example in which the voltage V1 that fluctuates according to the temperature change of the heat roller 131 becomes the ground potential in the period t. In this case, the determination unit 101 is controlled by a timer or the like built in the control unit 10. By measuring the period t at which the ground potential voltage V1 (rotation detection signal) is input, the rotation speed of the heat roller 131 can be detected.

  Next, the rotational speed detection process of the heat roller 131 will be described. FIG. 5 is a flowchart showing the rotation speed detection process of the heat roller 131.

  First, when an image formation execution instruction is input to the control unit 100 by an operation of the operation unit 47 by an operator, the control unit 100 starts energizing the heater 137 and drives the drive motor 70. (S1), the heat roller 131 and the pressure roller 132 are rotated. The control unit 100 causes the image forming unit 12 to start image forming processing by the driving force of the driving motor 70 and causes the pickup roller 145 and the transport roller pair 19 to transport the recording paper P.

  The determination unit 101 determines in advance the rotation speed T of the heat roller 131 in a normal state, that is, the heat roller 131 from the linear velocity of the recording paper P at this time and the diameter of the heat roller 131 (previously held by the determination unit 101). The rotation period T when rotating at the reference rotation speed is calculated (S2). The calculation of the rotation period T by the determination unit 101 may be performed by actual numerical calculation, or the rotation period T stored in advance in the look-up table corresponding to the linear velocity of the recording paper P is read. You may go by.

  At this time, the temperature detection unit 134 determines that the voltage V1 as the temperature detection signal or the ground potential as the rotation detection signal according to the contact of the contact 136 with the insulating film 131b or the conductive region 131c. Output by switching V1.

  The determination unit 101 receives the rotation detection signal from the temperature detection unit 134 until the next rotation detection signal is input, that is, until the voltage V1 becomes the ground potential and then the ground potential. The time required for the period t is measured (S3).

  Here, when T ≧ t (NO in S4), the determination unit 101 determines that the heat roller 131 is rotating at a predetermined reference rotation speed or higher (S5). The control unit 100 continues the drive control of the drive motor 70 started in S1 and energization to the heater 137 (S6).

  On the other hand, when T <t (YES in S4), the determination unit 101 determines that the heat roller 131 does not rotate at a rotation speed equal to or higher than the reference rotation speed but rotates at a rotation speed slower than the reference rotation speed. Determine (S7). At this time, the control unit 100 performs control such as stopping the energization to the heater 137 or stopping the drive motor 70 to stop the rotation of the heat roller 131 and stop the energization to the heater 137. Perform (S8). Thereby, welding with the heat roller 131 and the pressure roller 132 by the temperature rise of the heat roller 131 is prevented.

  Conventionally, since it has been determined whether or not the rotation speed of the heat roller 131 is the reference rotation speed depending on whether or not the drive motor 70 that supplies the rotation drive force to the heat roller 131 is normally driven, the heat roller When the gear for transmitting power to 131 is damaged or there is an assembly failure, it cannot be detected that the heat roller 131 is not rotating at the reference rotation speed or higher. The rotation speed of the heat roller 131 itself can be detected by using the temperature detection unit 134 used for temperature detection of the roller 131, and it can be determined whether or not the rotation speed of the heat roller 131 is the reference rotation speed. For this reason, even if the gear which transmits motive power to the heat roller 131 is damaged or there is an assembly failure, it can be reliably detected that the heat roller 131 is not rotating at the reference rotation speed or higher. Further, according to the present embodiment, it is possible to determine whether or not the rotation speed of the heat roller 131 is equal to or higher than the reference rotation speed without requiring a particularly complicated mechanism. Thereby, it becomes possible to prevent welding of the heat roller and the pressure roller due to the temperature rise of the heat roller accurately and at low cost.

  The present invention is not limited to the configuration of the above embodiment, and various modifications can be made. For example, in the above-described embodiment, the image forming apparatus according to an embodiment of the present invention has been described using a multifunction peripheral. However, this is merely an example, and other electronic devices such as a printer, a copier, a facsimile machine, and the like. Another image forming apparatus such as an apparatus may be used.

  Moreover, in the said embodiment, the structure and process which were shown by the said embodiment using FIG. 1 thru | or FIG. 5 are only one Embodiment of this invention, and are not the meaning which limits this invention to the said structure and process.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 131 Heat roller 131a Element pipe 131b Insulating film 132 Pressure roller 133 Thermistor 134 Heat roller rotation detection part 136 Contact 101 Signal processing part

Claims (3)

A fixing unit having conductivity, a heat roller having an insulating film on a circumferential surface thereof excluding a partial region in the circumferential direction, and a pressure roller pressed against the heat roller;
The thermistor disposed in the vicinity of the heat roller and a pull-up resistor connected to the thermistor, and the pull-up resistor and the ther that vary according to the electrical resistance value of the thermistor that changes due to a temperature change A voltage output unit for outputting a voltage between the misters;
The insulating film and the peripheral surface portion where the partial region is formed are in contact with the rotating heat roller, and the pull-up resistor and the circuit are connected via the heat roller when contacting the partial region. A connection for connecting the mrs to the ground,
And a determination unit that determines whether or not the heat roller is rotating at a predetermined reference rotation speed or higher based on a time interval at which the voltage output from the voltage output unit becomes a ground potential. Image forming apparatus. A heater for heating the heat roller;
The controller according to claim 1, further comprising: a controller that performs control to stop energization of the heater when the determination unit determines that the heat roller is not rotating at the reference rotation speed or more. Image forming apparatus.   The image formation according to claim 2, wherein the control unit uses the voltage output from the voltage output unit as a temperature detection signal of the heat roller, and controls energization to the heater according to the temperature detection signal. apparatus.

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