JP2010175848A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the occurrence of excessive temperature increase in a fixing section due to electric current application for disconnection detection in a state where a heating element sufficiently gets hot. <P>SOLUTION: This image forming device includes the heating element having a built-in heater, a pressurizing body that pressure-welds to the heating element and forms a nip, the fixing section that has a driving mechanism for rotating the heating element and pressurizing body and fixing a toner image to a recording medium, a temperature detecting section for measuring the temperature of the heating element, and a control section that recognizes the temperature of the heating element based on an output for the temperature detecting section, controls the current application to the heater, performs the current application to the heater, and performs the disconnection detection of the temperature detecting section. When the control section recognizes that the temperature of the heating element is lower than a predetermined temperature, the control section performs the current application to the heater for a predetermined period, then turns off the current application to the heater, detects that there is no disconnection after that, and performs the current application to the heater. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a multifunction machine, a copier, a printer, and a facsimile machine having a fixing unit for fixing a toner image.

  In general, an electrophotographic image forming apparatus (such as a printer or a multifunction peripheral) includes a fixing unit that fixes a toner image formed on a sheet by heating and pressing. Further, the fixing unit includes a heater that generates heat when energized for heating the toner image. In some cases, a temperature sensor or the like is provided for the purpose of preventing overheating or maintaining the temperature of the heating body at a suitable temperature. An example of an image forming apparatus provided with such a fixing unit is described in Patent Document 1.

Specifically, in Patent Document 1, the fixing body, the pressure body, the heating body, the temperature detection body, and the power supply from the power source to the heating body are controlled so that the detected temperature of the temperature detection body becomes a target temperature. In a fixing device for fixing an unfixed image to a recording medium, an abnormality detection means for detecting an abnormality of the heating body and the temperature detection body, and heating time information on heating start and heating stop of the heating body are acquired. Heating time information means, storage means capable of storing abnormality detection and heating time information, real time information is obtained and the elapsed time from heating stop based on the real time information and heating time information is less than a predetermined time length In addition, there is described a fixing device including a prohibiting unit that prohibits power supply from a power source to a heating body for a predetermined period when a detection abnormality is stored in a storage unit. Accordingly, an attempt is made to prevent overheating of the heating body and poor fixing due to disconnection or contact failure of the temperature detection body or the heating body (see Patent Document 1: Claim 1, paragraph [0009], etc.).
JP 2001-242740 A

  First, in order to fix properly and prevent overheating, it is necessary to be able to measure the temperature of the fixing portion (heating body). Therefore, the heater may be energized to check whether a change occurs in the output voltage from the temperature detection unit including the thermistor or the like, and the temperature detection unit may detect the presence or absence of disconnection. If there is a disconnection, the voltage at the output terminal of the temperature detector does not change, and shows a substantially constant value such as 0 V, minimum value, maximum value, and the like.

  Also, in the image forming apparatus, the heater is controlled to be turned on and off so that fixing can be appropriately performed at the time of printing, and the heating body has a substantially constant temperature (for example, about 150 to 200 ° C., such as a toner melting temperature). It is determined in consideration of characteristics, etc. Hereinafter, it is maintained at “fixing control temperature”). Then, the temperature detector has a large change (slope) in the output voltage value with respect to the temperature change in the vicinity of the fixing control temperature so that the heater ON / OFF control can be performed with high accuracy, and the measurement accuracy (sensitivity) is increased. Composed. However, on the other hand, the temperature detector may have a very small change (slope) in the output voltage value with respect to a temperature change in the temperature range of room temperature or room temperature (for example, 25 to 30 ° C. or less). For example, when the temperature detector includes a thermistor, the resistance value of the thermistor differs greatly between the vicinity of the fixing control temperature and a temperature below room temperature. Even if the temperature changes below room temperature, for example, 0V, minimum value, maximum In some cases, the value is almost constant.

  Therefore, when detecting disconnection when the main power is turned on while the image forming apparatus is cold, such as in the morning in winter, the output voltage of the temperature detector shows a substantially constant value even if the heating element is warmed up somewhat. Therefore, generally, the heater continues to be energized until the disconnection detection is completed after the main power is turned on.

  However, if a disconnection has occurred and the user turns off the main power in a resetting manner due to an error, etc., and immediately turns on the main power again, the main power is turned on even though it has already warmed to the fixing control temperature. The heater continues to be energized until disconnection detection is completed, and there is a problem that overheating may occur (for example, a resin member such as a gear that rotates the heating body or the pressure body melts). ). In particular, in recent image forming apparatuses, in order to shorten the time from when the main power is turned on to when the fixing unit is warmed and ready for printing, the heating and pressure bodies are made thinner and smaller, and the heater efficiency is improved. For example, the temperature of the heating body and the pressure body in contact with the heating body tends to increase. Therefore, if the temperature is likely to rise rapidly, there is a side where overheating is likely to occur.

  Here, the image forming apparatus described in Patent Document 1 stops heating, checks the detection value of the temperature sensor to detect an abnormality, and if an abnormality log is stored, power supply from the power source to the heating body is performed. It is forbidden. Therefore, there is a problem that it is not possible to prevent an excessive temperature rise that may occur before abnormality detection (see Patent Document 1: Claims 1, 2, Paragraphs [0038], [0039], FIG. 3, etc.). Further, although it is checked whether the detection value of the temperature sensor has reached a predetermined temperature at a predetermined time set by a timer from the start of heating of the heater, an abnormality is detected (see Patent Document 1: [0041] etc.). Thus, if energization to the heater is continued from the start of heating to a predetermined time, there is a problem that overheating may occur when the main power is turned on again while the fixing unit is warm.

  In Patent Document 1, “predetermined time length”, “predetermined time”, “predetermined temperature”, “predetermined period”, and the like are all “predetermined” in terms of control time, temperature, and the like. Well, there is no definition and there are many unclear points because there is no description of the long / short relationship of each time, specific starting point, end point, specific numerical value, etc.

  In view of the above-described problems of the prior art, the present invention provides an excessive temperature rise in the fixing unit even when a disconnection occurs in the temperature detection unit and power is supplied to detect the disconnection in a state where the heating body is sufficiently warmed. The problem is to prevent the occurrence.

  In order to solve the above-described problem, an image forming apparatus according to a first aspect includes a heating body including a heater that generates heat when energized, a pressure body that press-contacts the heating body to form a nip, the heating body, and the heating body. A fixing unit that has a driving mechanism for rotating the pressure body, passes a recording medium on which an unfixed toner image is transferred to the nip, and fixes the toner image on the recording medium, and is provided for measuring the temperature of the heating body And a temperature detector that changes an output voltage according to temperature, recognizes the temperature of the heating body based on the output of the temperature detector, controls energization to the heater, and energizes the heater. And a controller for detecting disconnection of the temperature detector after confirming that the output voltage of the temperature detector has changed, and the controller supplies the heater to the heater for a predetermined time. Heater after energizing OFF the energization, from detection followed by the absence of disconnection, it was decided to perform the energization of the heater.

  In this configuration, the temperature of the entire heating body continues to rise even when the power is turned off by heat conduction from the portion directly heated by the heater of the heating body to the entire heating body. According to this, the control unit performs energization to the heater for a predetermined time at the time of disconnection detection, and then performs disconnection detection after shutting off the energization to the heater. It can be confirmed whether or not. In other words, the control unit recognizes the presence or absence of disconnection without shortening the energization of the heater until the detection of the presence or absence of disconnection is completed, and shortens the energization time to the heater in disconnection detection. Therefore, the disconnection is detected in the state where the fixing unit (heating body, etc.) is already warmed as in the case where the main power supply is turned off and the main power supply is turned on again immediately in the state where the excessive temperature rise cannot be detected due to the disconnection. Even if it is carried out, an excessive temperature rise that does not cause damage to the fixing unit such as melting of a mechanism such as a gear that rotates the heating body or damage of each member of the fixing unit does not occur.

  According to a second aspect of the present invention, in the first aspect of the invention, the predetermined time is a fixing control temperature that is a temperature of the heating body to be maintained during printing when the heater is energized. Therefore, the time required for the temperature to rise to the limit temperature at which any one of the heating body, the pressure body, and the driving mechanism starts to be damaged is determined to be less than the time required. According to this configuration, since the heater energization time at the time of disconnection detection is determined based on the time from the fixing control temperature until reaching the limit temperature at which the member of the fixing unit is damaged, the main power supply is once turned off. Even if the disconnection detection is performed in a state where the fixing unit (heating body or the like) is already warmed as in the case where the main power supply is immediately turned on, the temperature of the fixing unit is not excessively increased.

  According to a third aspect of the present invention, when the control unit recognizes that the temperature of the heating body is lower than a predetermined temperature when the main power is turned on in the first or second aspect of the invention, the disconnection is performed. It was decided to detect. According to this configuration, the disconnection detection is performed only when the temperature measured at the time of turning on the main power is low and the disconnection is occurring or the fixing unit is cooled, and it is not possible to distinguish whether the disconnection is detected. Can do. Therefore, unnecessary disconnection detection is not performed, and the time required for warm-up from when the main power is turned on until the printer is ready for printing can be shortened.

  Note that the “predetermined temperature” is a temperature range in which the temperature measured based on the output voltage of the temperature detection unit hardly changes even if there is a temperature change in the temperature detection unit (for example, 25 to 25). 30 ° C. or lower). In other words, the output voltage of the temperature detector shows a nearly constant value due to disconnection, or because of the temperature detector's characteristics, it is not possible to clearly distinguish whether the temperature change cannot be measured accurately. Temperature.

  According to a fourth aspect of the present invention, in the first to third aspects of the invention, when energized, a commercial power supply is connected to the heater, and the predetermined time is a voltage applied to the heater due to an error. When the heater is energized with the largest output in the tolerance state, the time is less than the time required for the temperature to rise from the fixing control temperature to the limit temperature. The disconnection when the heater is turned on for the predetermined time when the power is turned on and then the heater is turned on with the smallest output due to an error due to the smallest voltage applied to the heater due to an error. After the time required for detection elapses after the main power source is turned on, the heater is turned on again after it is detected that there is no disconnection.

  According to this configuration, assuming that the temperature of the heating element is most likely to rise when the heater is energized, the time for energizing the heater is determined for disconnection detection, and the most heated when the heater is energized. Assuming the case where the temperature of the body is difficult to rise, the time required to confirm the presence or absence of disconnection is taken. Therefore, even if a disconnection occurs in the temperature detection unit, it is possible to prevent the occurrence of excessive temperature rise in the fixing unit, and it is possible to accurately check whether there is a disconnection (disconnection detection).

  As described above, according to the present invention, disconnection detection can be performed accurately, and even if disconnection detection is performed when the main power supply is immediately turned on again in a state where the fixing unit is warm, an excessive rise in the fixing unit is detected. No temperature is generated. Accordingly, it is possible to provide an image forming apparatus that can safely detect disconnection regardless of the temperature of the fixing unit such as a heating roller when the main power is turned on.

1 is a schematic front sectional view showing a schematic configuration of a printer according to an embodiment. FIG. 2 is a block diagram illustrating an example of a hardware configuration of a printer according to an embodiment. It is a circuit diagram which shows an example of the circuit structure for preventing the temperature detection part which concerns on embodiment, and overheating. 6 is a flowchart illustrating an example of control for detecting disconnection of the printer according to the embodiment. 6 is a graph for explaining an example of a temperature rise of a heating roller (fixing unit) in the printer according to the embodiment.

  Hereinafter, embodiments of the present invention will be described with reference to FIGS. However, each element such as configuration and arrangement described in this embodiment does not limit the scope of the invention and is merely an illustrative example.

(Outline of image forming apparatus)
First, an outline of an electrophotographic printer 1 (corresponding to an image forming apparatus) that forms a toner image and fixes the toner image in the fixing unit 2 will be described with reference to FIG. FIG. 1 is a schematic front sectional view showing a schematic configuration of a printer 1 according to an embodiment of the present invention. As shown in FIG. 1, the printer 1 according to this embodiment includes a sheet supply unit 3, a sheet conveyance path 4, an image forming unit 5, a fixing unit 2 and the like from below.

  The sheet supply unit 3 is provided at the bottom of the printer 1 and accommodates various types of sheets (e.g., A4, B5, etc.) such as copy paper (corresponding to a recording medium). The sheet supply unit 3 is provided with a paper feed roller 31 on the downstream side in the sheet conveyance direction. The uppermost sheet among the stacked sheets comes into contact with the sheet feeding roller 31. During sheet feeding, the sheet feeding roller 31 is rotationally driven by a driving device (not shown) such as a motor to convey the sheets one by one. Send to road 4

  The sheet conveyance path 4 conveys the sheet sent from the sheet supply unit 3 to the discharge tray 41 through the image forming unit 5. Therefore, the sheet conveying path 4 is provided with a conveying roller pair 42 that is rotationally driven by a driving device (not shown), a registration roller pair 43 that sends the sheet to the image forming unit 5 in accordance with the formed toner image, and the like.

  In FIG. 1, the image forming unit 5 is arranged at the center left position in the printer 1, and based on image data such as a document transmitted from the user terminal 100 (see FIG. 2), a toner image of an image to be formed. And transfer to the sheet. The image forming unit 5 includes a photosensitive drum 51, a charging device 52 around the photosensitive drum 51, an exposure device 53, a developing device 54, a transfer roller 55, a cleaning device 56, and the like. The toner image forming process will be described. The photosensitive drum 51 is rotationally driven in a predetermined direction (clockwise in FIG. 1), and the charging device 52 charges the peripheral surface of the photosensitive drum 51. The exposure device 53 irradiates the charged photosensitive drum 51 with light (for example, laser light) based on the image data, scans and exposes the peripheral surface, and corresponds to the image data on the peripheral surface of the photosensitive drum 51. An electrostatic latent image is formed. The developing device 54 charges the toner, supplies the toner to the electrostatic latent image, and develops the electrostatic latent image as a toner image. The transfer roller 55 is rotatably supported and presses against the photosensitive drum 51 to form a nip. When the sheet and the toner image enter the nip, a voltage having a polarity opposite to the charging polarity of the toner is applied to the transfer roller 55, and the toner image is transferred to the sheet. In FIG. 1, the cleaning device 56 is disposed above the photosensitive drum 51, and removes and collects residual toner, dust, and the like on the peripheral surface of the photosensitive drum 51.

  In the present embodiment, the fixing unit 2 includes a heating roller 21 (corresponding to a heating body) including a heater H that generates heat when energized, and a pressure roller 22 (corresponding to a pressure body) that presses against the heating roller 21 to form a nip. ), And a driving mechanism 23 (see FIG. 2) for rotating the heating roller 21 and the pressure roller 22, and the toner image is fixed by passing the sheet with the unfixed toner image transferred to the nip. The heater H extends in the axial direction of the heating roller 21 and can warm the entire peripheral surface of the heating roller 21. The sheet enters the nip between the heating roller 21 and the pressure roller 22, the toner image is pressurized and heated, and the toner image is fixed on the sheet. The sheet after fixing is discharged to the discharge tray 41. A non-contact or contact thermistor TH is provided for detecting the temperature of the heating roller 21 (fixing unit 2) (details will be described later). The drive mechanism 23 is composed of a motor, a gear, and the like, and rotates the heating roller 21 and the pressure roller 22 during printing, warm-up processing after turning on the main power, or the like.

  And the printer 1 of this embodiment has the operation panel 1a in the front upper left side, as shown with a broken line in FIG. The operation panel 1a is provided with a liquid crystal display unit 1b, a plurality of indicators 1c, a plurality of operation keys 1d, and the like. The liquid crystal display unit 1b displays various messages such as a service call (notification of the necessity of inspection / repair by a service person who performs maintenance of the printer 1) and an error. The indicator 1c is composed of a plurality of LEDs, and displays on the status of the printer 1 such as a service call or an error occurrence by lighting or blinking.

(Hardware configuration of printer 1)
Next, an example of the hardware configuration of the printer 1 according to the embodiment of the present invention will be described with reference to FIG. FIG. 2 is a block diagram illustrating an example of a hardware configuration of the printer 1 according to the embodiment of the present invention.

  First, as shown in FIG. 2, the printer 1 of the present embodiment is provided with a control unit 6 for controlling the entire operation of the printer 1. A CPU 61 is provided as a central processing unit of the control unit 6. The control unit 6 (CPU 61) recognizes the temperature of the heating roller 21 based on the output of the temperature detection unit 24 (details will be described later), controls energization to the heater H, and energizes the heater H. After confirming that the output voltage V1 of the temperature detector 24 has changed, the disconnection of the temperature detector 24 is detected.

  The control unit 6 includes a storage unit 62 including a RAM (Random Access Memory), a ROM (Read Only Memory), a flash ROM, an HDD (Hard Disk Drive), and the like. For example, a ROM, a flash ROM, and an HDD store programs and data necessary for performing various controls, and a RAM temporarily develops, for example, control programs and data, image data, and the like. The storage unit 62 stores information for determining the time for energizing the heater H when the disconnection is detected when the main power is turned on, and information for determining the timing for checking the value of the output voltage V1 for disconnection detection. deep. Further, the control unit 6 can be provided with a time measuring unit 63 for measuring time required for various controls.

  The control unit 6 is connected to the sheet supply unit 3, the sheet conveyance path 4, the image forming unit 5, the fixing unit 2, the power supply device 65, and the like by a bus or the like, and performs operation control of each connected unit. In addition, an I / F circuit 64 is attached to or connected to the control unit 6, and the user terminal 100 (for example, a personal computer) and the printer 1 are communicably connected via a network or the like using the I / F circuit 64. Is done. As a result, the printer 1 according to the present embodiment receives image data and print setting data from the user terminal 100 and performs printing.

  As shown in FIG. 2, in the printer 1 of the present embodiment, the fixing unit 2 has a heating circuit 25 for energizing the heater H built in the heating roller 21. The heating circuit 25 is connected to a switch unit 26 that switches ON / OFF of energization to the heater H. A heater control signal line HS from the CPU 61 is connected to the switch unit 26, and the CPU 61 inputs a signal for instructing ON / OFF control of energization to the heater H to the switch unit 26 through the heater control signal line HS. To do. Thereby, the energization to the heater H is turned ON / OFF.

  The printer 1 also includes a thermistor TH that is disposed in the fixing unit 2 and measures the temperature of the heating roller 21, and a voltage dividing resistor R 1 provided in the substrate of the control unit 6. A temperature detection unit 24 is provided for measuring the temperature of the (fixing unit 2), and the output voltage V1 changes according to the temperature (shown by a broken line in FIG. 2), and the output voltage V1 of the temperature detection unit 24 is provided. Is input to the CPU 61. The CPU 61 A / D converts the output voltage V1 (a separate A / D converter may be provided), and recognizes the temperature of the heating roller 21 (fixing unit 2) based on the magnitude of the output voltage. Therefore, the CPU 61 grasps and monitors the temperature of the fixing unit 2.

  Then, the control unit 6 grasps the current temperature of the fixing unit 2 (the heating roller 21), and after turning on the main power, shifts to a power saving mode (for example, sleep mode) to keep the temperature of the fixing unit 2 low. Except for the case, energization to the heater H is controlled by the heater drive control signal, and the temperature control is performed so that the temperature of the heating roller 21 maintains the fixing control temperature. The “fixing control temperature” is the temperature of the heating roller 21 to be maintained at the time of printing, and is a temperature suitable for fixing the toner image (in the printer 1 of the present embodiment, the temperature is set to about 190 ° C. and below) Explanation).

  For example, if the temperature of the heating roller 21 is too low, the toner will not melt and will not be fixed. On the other hand, if the temperature is too high, the toner adheres to the heating roller 21 and the sheet curls. Therefore, a temperature (fixing control temperature) suitable for fixing the toner image is set for each model of the image forming apparatus in consideration of the toner, the material of the heating roller 21 and the pressure roller 22 and the like in advance through experiments.

  The outline of the control for maintaining the fixing control temperature will be described below. For example, if the temperature of the heating roller 21 is lower than the fixing control temperature when the main power is turned on, the control unit 6 energizes the heater H to turn on the heating roller 21. Warm up. Thereafter, when it is recognized from the output voltage V1 of the temperature detection unit 24 that the temperature of the heating roller 21 has become higher than the fixing control temperature, the control unit 6 instructs the heater H to be turned off. Thereafter, when recognizing that the temperature of the heating roller 21 has become lower than the fixing control temperature, the control unit 6 transmits an instruction to turn on the power to the heater H to the switch unit 26. In this way, the control unit 6 repeats the ON / OFF of the heater H by the switch unit 26 so as to maintain the fixing control temperature.

  The printer 1 of this embodiment is provided with a main switch MS for the user to turn on / off the main power. When the main power is turned on by the main switch MS, a commercial power source is connected to the heater H of the fixing unit 2 when energized, as shown by a two-dot chain line in FIG. Is supplied. In addition, power is supplied from a commercial power source to a power supply device 65 that performs rectification and step-up / step-down in the printer 1 to generate a voltage suitable for each part and supplies power, and the power supply device 65 is supplied to the heater H. Electric power may be supplied from.

(Configuration for measuring the temperature of the heating roller 21)
Next, an example of the circuit configuration of the ON / OFF control of the heater H and the temperature detection unit 24 according to the embodiment of the present invention will be described with reference to FIG. FIG. 3 is a circuit diagram showing an example of a circuit configuration for preventing the temperature detection unit 24 and the excessive temperature rise according to the embodiment of the present invention.

  First, the part which supplies with electricity to the heater H among the structures shown in FIG. 3 is demonstrated. As shown in FIG. 3, the printer 1 of the present embodiment is provided with a heating circuit 25. The heating circuit 25 includes a heater H, an AC power source, a heat sensitive member 27, and the like, which are connected in series. The heater H generates heat by passing an electric current, and the heating roller 21 is heated by receiving the heat. For example, the heater H may be one that uses Joule heat obtained by applying a current to metal (for example, nichrome) or the like, or may be a halogen heater that uses a lamp, as long as the heating roller 21 can be heated. The AC power supply is, for example, a commercial power supply (or the power supply device 65), and applies an AC current (voltage) to the heater H.

  The heat sensitive member 27 is provided as a final measure for preventing the excessive temperature rise when, for example, the CPU 61 runs out of control or a failure occurs in the switch unit 26 or the like and the heat roller 21 is excessively heated. When the temperature of the heating roller 21 (fixing unit 2) exceeds a preset operating temperature (for example, about 300 ° C.), the heat sensitive member 27 forcibly cuts off the power to the heater H. As the heat sensitive member 27, a thermal fuse, a thermal protector, a thermostat or the like can be used. Specifically, when the operating temperature of the heat sensitive member 27 is reached, the heat sensitive member 27 disconnects the heating circuit 25 and interrupts the energization of the heater H. From the viewpoint of safety, in the printer 1 of the present embodiment, the thermal member 27 maintains a disconnected state (does not self-recovery) once it is operated.

  The switch unit 26 turns on / off conduction in the heating circuit 25 based on a control signal transmitted through the heater control signal line HS extending from the port P2 of the CPU 61. Specifically, when a heater control signal for turning on energization is transmitted from the control unit 6 (for example, High), the switch unit 26 closes the heating circuit 25 and energizes the heater H. On the other hand, when a heater control signal for turning off the energization is transmitted from the control unit 6 (for example, Low), the switch unit 26 is opened and becomes a disconnected state. The switch unit 26 only needs to be able to control ON / OFF of the energization of the heating circuit 25 based on the control signal. For example, a photocoupler or the like can be used.

  Next, the temperature detection unit 24 will be described. The temperature detection unit 24 can be configured by, for example, a power source Vcc (positive DC power source), a resistor R1, and a thermistor TH. The thermistor TH is provided in the fixing unit 2 in contact with the heating roller 21 or in a non-contact manner. A power source Vcc is connected to one end of the thermistor TH, and a conductor L for connection to the control unit 6 is provided at the other end. The conducting wire L is routed around the inside of the printer and finally connected to a connector C provided on a control board as the control unit 6.

  A voltage dividing resistor R1 and a port P1 of the CPU 61 are connected to the connector C in parallel on the control board. The resistor R1 is connected to the ground. With these connections, a series circuit is formed as the temperature detector 24 arranged in the order of the power source Vcc, the thermistor TH, the resistor R1, and the ground. Further, the voltage between the thermistor TH and the resistor R1 is taken out as the output voltage V1.

  As the thermistor TH in the present embodiment, for example, a thermistor whose resistance R1 decreases as the temperature increases is used. Specifically, regarding the output voltage V1 of the temperature detection unit 24, the higher the temperature of the fixing unit 2 (heating roller 21), the smaller the resistance value of the thermistor TH, the current increases, and the output voltage V1 increases. On the other hand, the lower the temperature of the fixing unit 2, the smaller the output voltage V1. For example, if the output voltage V1 is measured in advance according to the temperature of the heating roller 21 and the voltage value for each temperature is stored in, for example, the storage unit 62, the fixing unit depends on the magnitude of the output voltage V1 input to the CPU 61. The temperature of 2 can be recognized.

  In the temperature detection unit 24 of this embodiment, Vcc and ground may be interchanged. In this case, the higher the temperature is, the smaller the output voltage V1 is. However, by measuring the output voltage V1 according to the temperature of the heating roller 21 and storing the voltage value for each temperature in the storage unit 62, There is no difference in that the temperature of the fixing unit 2 can be grasped from the output voltage V1.

(Disconnection detection)
Next, disconnection detection of the temperature detection unit 24 in the printer 1 according to the embodiment of the present invention will be described with reference to FIGS. FIG. 4 is a flowchart illustrating an example of control in disconnection detection of the printer 1 according to the embodiment of the present invention.

<Necessity of disconnection detection>
First, the necessity for disconnection detection of the temperature detection unit 24 will be described. As described with reference to FIG. 3 and the like, the lead wire L is routed from the thermistor TH to the connector C of the control board. A disconnection may occur in the conductive wire L routed over a relatively long distance. If disconnection occurs in the conducting wire L, the voltage V1 input to the port P1 of the CPU 61 becomes substantially constant. Specifically, when the disconnection occurs in the example of FIG. 3, this is the same as that nothing is connected to the connector C, and the voltage input to the port P1 of the CPU 61 except when noise appears on the control board. Becomes almost 0V. Therefore, when disconnection occurs, the control unit 6 cannot measure and recognize the accurate temperature of the heating roller 21.

  If the accurate temperature of the heating roller 21 cannot be measured and recognized, the temperature of the heating roller 21 cannot be maintained properly and an excessive temperature rise cannot be detected. Therefore, in the printer 1 of the present embodiment, disconnection detection is performed to determine the presence or absence of disconnection when the main power is turned on. Note that if the printer 1 is in use and the heating roller 21 is sufficiently warm and the temperature detection unit 24 is disconnected, the voltage V1 input to the port P1 changes abruptly. Can be detected.

<Necessity of energizing the heater H to detect disconnection>
As described above, in the image forming apparatus, it is necessary to maintain the temperature of the heating roller 21 and the like in the vicinity of the fixing control temperature in order to perform fixing appropriately at the time of printing. Accordingly, the thermistor TH of the printer 1 according to the present embodiment is used with high accuracy (sensitivity) in temperature measurement near the fixing control temperature so that the temperature of the heating roller 21 can be accurately measured with the fixing control temperature. . In other words, a thermistor TH having a large change in resistance value with respect to a temperature change near the fixing control temperature and a large change in output voltage V1 with respect to the temperature change near the fixing control temperature is used. Normally, the thermistor used in the image forming apparatus has such characteristics.

  However, as a result of increasing the accuracy (sensitivity) of the thermistor TH in the vicinity of the fixing control temperature, the resistance value is close to the resistance value in the vicinity of the fixing control temperature and the resistance value in the temperature range below room temperature (for example, 25 to 30 ° C. or below). May be very different. In the example of the present embodiment, the resistance value of the thermistor TH is several tens to several hundreds kΩ (for example, 100 kΩ) near the fixing control temperature, but several M to several tens in the temperature range below room temperature. In some cases, the resistance value is MΩ (for example, 10 MΩ or more, assuming that the resistance value near the fixing control temperature is 1, the resistance value in the temperature range below room temperature is 100 or more). As a result, in the circuit configuration of this embodiment, even when a DC power supply Vcc of about several volts is applied, almost no current flows through the series circuit of the thermistor TH and the resistor R1 in the temperature range below room temperature. Therefore, in the circuit configuration of this embodiment, in the temperature range below room temperature, the voltage input to the port P1 of the CPU 61 is almost 0 V, and accurate temperature measurement cannot be performed.

  As described above, the voltage input to the port P1 is almost 0 V even when a disconnection occurs. To detect the presence or absence of disconnection, the heater H is energized when the main power is turned on, etc. It is necessary to raise the temperature of the heating roller 21 to a higher temperature range (for example, higher than 30 ° C.). As a result, whether or not the value of the output voltage V1 input to the port P1 of the CPU 61 is clearly increased from a value of approximately 0 V (for example, 35 ° C. to 50 ° C. or more, for example, the value of the output voltage V1 Is not almost 0V), and disconnection is detected.

<Energization of heater H for disconnection detection>
As described above, in the printer 1 of this embodiment, when the heating roller 21 is cold (for example, 30 ° C. or less) when the main power is turned on, the resistance value of the thermistor TH is too large and is input to the port P1 of the CPU 61. Since the applied voltage V1 is almost 0 V and the temperature cannot be measured accurately, the heater H is energized to check for disconnection. On the other hand, as described above, even when the disconnection occurs, the voltage V1 input to the port P1 of the CPU 61 is almost 0V.

  In order to quickly make the printer 1 ready for use, in the conventional image forming apparatus, energization of the heater H is continued until the disconnection detection for confirming the temperature rise of the heating roller 21 is completed when the main power is turned on. In other words, warm-up processing that continues to warm the heating roller 21 is performed in parallel even during disconnection detection. If the heating roller 21 is cold, for example, when the main power supply of the printer 1 is turned on at the start of winter, regardless of whether or not the conductor L of the temperature detection unit 24 is disconnected, the disconnection detection is performed as in the past. Even if energization of the heater H continues until completion, the presence or absence of disconnection is detected before the excessive temperature rise in the fixing unit 2, and the control unit 6 can detect an abnormality or failure of the printer 1.

  However, when the main power supply is turned off immediately after resetting the main power supply due to an error or the printer 1 being in a function stop state, the heating roller 21 is already warmed. If the lead wire L is disconnected when the main power is turned on again, the voltage V1 input to the port P1 of the CPU 61 is almost 0 V. As described above, the control unit 6 is disconnected. It is not possible to determine whether the heating roller 21 is in a cold state (for example, when the main power supply is turned off once or when a disconnection occurs before the main power supply is turned off).

  Then, when the main power is turned on and off, the controller 6 (CPU 61) energizes the heater H and energizes the heater H until the disconnection detection is completed. If an excessive temperature rise occurs, damage that requires replacement of the fixing unit 2 such as melting of a resin gear (drive mechanism 23) that rotates the heating roller 21 or the pressure roller 22 may occur.

  In particular, in recent image forming apparatuses such as the printer 1, in order to shorten the warm-up process and make the printer 1 ready for use, the thickness of the pressure roller 22 in contact with the heating roller 21, the heater Various measures such as improving the efficiency of H have been repeated. That is, since the temperature of the fixing unit 2 (heating roller 21) is likely to rise, the heater H is energized to detect disconnection when the main power is turned on again while the heating roller 21 is sufficiently warm. Even if it exists, overheating of the fixing unit 2 may occur.

  Therefore, in the printer 1 according to the present embodiment, since it is difficult to distinguish between occurrence of disconnection or whether the fixing unit is cold, the fixing unit is turned on after the main power is turned on in order to prevent overheating of the fixing unit 2 when the main power is turned on again. After the heater H is energized for a predetermined time so that disconnection can be detected by heating the heating roller 21 due to overshoot even if the heater is cold, the heater H is de-energized and then the temperature is excessively increased. There is a feature in the point to avoid. Then, after confirming that no disconnection has occurred, energization of the heater H is resumed. Hereinafter, an example of energization control to the heater H in the warm-up process when the main power is turned on in the printer 1 of the present embodiment will be described with reference to the flowchart of FIG.

  First, the start in FIG. 4 is when the main power is turned on. Thereafter, the control unit 6 rotates the heating roller 21, the pressure roller 22, and the like (step # 1). Then, the control unit 6 confirms the value of the output voltage V1 input to the port P1 of the CPU 61 (step # 2). Next, the control unit 6 confirms whether the temperature of the heating roller 21 is higher than a predetermined temperature based on the value of the output voltage V1 (step # 3). Here, the “predetermined temperature” is a temperature range in which the temperature measured based on the output voltage of the temperature detection unit 24 is almost unchanged even if there is a temperature change in the temperature detection unit 24 (for example, The temperature of the thermistor TH is, for example, a temperature of 25 to 30 ° C. or less which is not more than room temperature), and the resistance value of the thermistor TH is greatly different from the resistance value near the fixing control temperature. . In other words, “predetermined temperature” means that the output voltage of the temperature detection unit 24 indicates a substantially constant value (substantially 0 V in this embodiment) due to disconnection, or the characteristics of the temperature detection unit 24. In addition, the temperature is in a temperature range where it is not possible to clearly distinguish whether the temperature change cannot be measured accurately.

  If it is detected that the temperature is higher than the predetermined temperature (Yes in Step # 3), no breakage occurs in the conductive wire L connecting the control board and the thermistor TH, and to some extent, the fixing unit 2 (the heating roller 21). It can be determined that the main power supply has been turned on again while the Accordingly, it is not necessary to detect disconnection, and the control unit 6 energizes the heater H to warm the heating roller 21 to the fixing control temperature (step # 4). Then, the energization control to the heater H in the warm-up process ends (end), and thereafter, the control unit 6 shifts to temperature maintenance control that repeats ON / OFF of energization to the heater H.

  On the other hand, if it is detected that the temperature is lower than the predetermined temperature (No in step # 3), the control unit 6 controls the switch unit 26 to energize the heater H for a predetermined time ( Step # 5), and then the power supply to the heater H is turned off (step # 6). As described above, in the present invention, when the main power is turned on, the control unit 6 detects disconnection when it recognizes that the temperature of the heating body (heating roller 21) is lower than a predetermined temperature (for example, room temperature or lower). .

  Here, the predetermined time is a gear in a mechanism in which the temperature of the heating roller 21 rotates the rotating body such as the heating roller 21 from the fixing control temperature when the heater H is energized when the main power is turned on again. For example, the time until the temperature rises to a temperature (limit temperature) that damages each member of the fixing unit 2 such as melting can be reduced. That is, when the heater H is energized, any one of the heating roller 21, the pressure roller 22, and the drive mechanism 23 is determined from the fixing control temperature that is the temperature of the heating roller 21 that is to be maintained during printing. The time required for the temperature to rise to the limit temperature at which can begin to be damaged is set to be equal to or less than the time required.

  Further, the predetermined time can be determined on the assumption that the voltage applied to the heater H is maximized and further the output of the heater H is maximized due to tolerance. In other words, it can be determined in consideration of the case where the temperature of the fixing unit 2 is most likely to rise.

  Since the heater H of the present embodiment is connected to a commercial power supply, the magnitude of the voltage applied to the heater H varies from country to country (for example, AC 100 V in Japan). Even when the power supply device 65 supplies power to the heater H, the output voltage of the power supply device 65 has some error. And the voltage of the commercial power supply in each country may have an error of about ± 10% at the maximum (for example, in the case of Japan, 90 to 110 V in AC). Therefore, the maximum voltage applied to the heater H can be assumed to be a value obtained by + 10% of the voltage of the commercial power supply for each country (for example, AC 110 V in Japan).

  The heater H is designed so as to have a predetermined output, but the heater H has a tolerance, and the output has a tolerance of about ± 10 to 20%. For example, if the tolerance is 10%, the heater H of 450 to 550 W can be mounted on the printer 1 if the designed output of the heater H is 500 W.

  In summary, when a commercial power supply is connected to the heater H during energization, the predetermined time is the maximum voltage applied to the heater H due to an error (for example, 110 V AC in Japan). When the current is supplied to the heater H (for example, the designed output + 10%) having the largest output due to tolerance, the time is less than the time required for the temperature to rise from the fixing control temperature to the limit temperature. Is when the heater H is turned on for a predetermined period of time when the main power is turned on, and the heater H having the smallest output due to tolerance is energized with the smallest voltage applied to the heater H due to an error. After the time required for disconnection detection has elapsed since the main power source was turned on, after detecting that there is no disconnection, the heater H can be turned on again. Thereby, when the main power is turned on again, an excessive temperature rise that causes damage to the fixing unit 2 does not occur.

  Next, the control unit 6 uses the time measuring unit 63 and the like to confirm whether or not the time point for determining the presence or absence of disconnection (the time point when disconnection detection is performed) has been reached (step # 7). In other words, even if the power supply to the heater H is turned off, the temperature of the heating roller 21 continues to rise due to overshoot (heat conduction), so the change in the output voltage V1 such as the temperature of the heating roller 21 becomes higher than room temperature. Wait until it can be clearly detected.

  The standby time from when the power to the heater H is turned off to when it is determined whether or not there is a disconnection is when the voltage applied to the heater H is minimum, and when the output of the heater H is minimum due to tolerances Can be determined.

  When the heater H of the present embodiment is connected to a commercial power source, as described above, the voltage value of the commercial power source in each country may have an error of about ± 10% at the maximum (for example, in the case of Japan, in an alternating current) , 90-110V). Therefore, the minimum voltage applied to the heater H can be a value obtained by -10% of the voltage value of the commercial power supply (for example, AC 90 V in Japan). As described above, the heater H has a tolerance, and the output has a tolerance of about ± 10 to 20%. For example, assuming that the intersection is 10%, if the designed heater H output is 500 W, a 450 W heater H can be mounted on the printer 1.

  When the voltage applied to the heater H is large and the output of the heater H is large, the temperature of the heating roller 21 is likely to rise. Therefore, the time until the temperature of the heating roller 21 becomes higher than room temperature is short. In other words, in the printer 1 according to the present embodiment, when the voltage applied to the heater H is minimum and the output of the heater H is minimum due to tolerance, the temperature of the heating roller 21 is higher than room temperature. Since the disconnection is detected after waiting for a time sufficient to detect a change in the output voltage V1, false detection is reduced. It should be noted that, by experiment or the like, for example, the time when the temperature of the heating roller 21 can be detected statistically due to overshooting may be statistically obtained to determine the waiting time.

  When it is time to determine whether or not there is a disconnection (Yes in step # 7), the control unit 6 confirms whether the value of the output voltage V1 is larger than when the power is turned on (approximately 0V). Then, disconnection detection is executed (step # 8). Thereby, the presence or absence of disconnection of the conducting wire L is confirmed (step # 9). If there is a disconnection (Yes in step # 9), the temperature of the fixing unit 2 cannot be controlled and the printer 1 cannot be used, so the control unit 6 displays an error message indicating that a disconnection has occurred on the operation panel 1a. Then, the warm-up process is interrupted and terminated (step # 10 → end).

  On the other hand, if the output voltage V1 is clearly higher than when the power is turned on and it can be confirmed that there is no disconnection (No in step # 9), the main power is turned on with the fixing unit 2 (heating roller 21) cooled. Since the determination can be made, the process proceeds to step # 4, where the heating roller 21 is warmed to the fixing control temperature, and thereafter, another temperature control is performed. As described above, in the present invention, the control unit 6 turns off the energization to the heater H after energizing the heater H only for a predetermined time, and then detects that there is no disconnection before the heater H Energize H.

(Concrete example)
Next, a specific example of the temperature increase of the heating roller 21 in the printer 1 of this embodiment will be described with reference to FIG. FIG. 5 is a graph for explaining an example of the temperature rise of the heating roller 21 (fixing unit 2) in the printer 1 according to the embodiment of the present invention. In the graph of FIG. 5, the horizontal axis indicates time, and the vertical axis indicates temperature. FIG. 5 shows an example of temperature rise when a commercial power supply of AC 100 V is connected to a heater H of about 500 W built in the heating roller 21.

  First, as shown in the legend, when the graph of the case where only the heater H is energized from when the main power is turned on from the state where the fixing unit 2 is cooled (▲ mark), when the main power is turned on (at time of 0 second) ) To reach the fixing control temperature (set to 190 ° C. in the example of FIG. 5) in about 9 to 10 seconds. For various reasons such as the characteristics of the heater H and the heater H itself being warmed, the temperature increase rate immediately after the main power supply is turned on is small, and the temperature increase rate becomes maximum after about 5 seconds.

Specifically, the time required to increase the temperature at about 5 seconds from about 50 ° C. to 190 ° C. (fixing control temperature) is about 4.5 seconds in the graph of FIG. 5 (TS1 in FIG. 5). As shown). Therefore, the rate of temperature increase when the heater H is energized after about 5 seconds have passed since the main power supply in the example shown in FIG. 5 is as follows.
(190 ° C-50 ° C) ÷ 4.5 seconds ≒ about 30 ° C / second

  Here, the temperature (limit temperature) of the heating roller 21 at which melting of the resin gear or the like for rotating the heating roller 21 or the like starts to cause damage to the fixing unit 2 is set to about 250 ° C., for example. When the main power is turned off and then immediately turned on again, the temperature difference from about 190 ° C., which is assumed to be the highest temperature of the heating roller 21, to the limit temperature (about 250 ° C.) is 60 ° C.

  When the heater H is energized, the time required to increase the temperature by 60 ° C is 60 ° C ÷ 30 ° C / second≈about 2.0 seconds when the previously calculated temperature increase rate is simply used. It becomes. Therefore, considering the case where the main power supply is immediately turned on again, it is necessary to stop the energization of the heater H for detecting disconnection from turning on the main power supply for about 2.0 seconds. In FIG. 5, an example of the temperature rise of the heating roller 21 when the main power supply is turned off and then immediately turned on is indicated by a two-dot chain line, and a time point of about 2.0 seconds is indicated by T1. . Therefore, in the printer 1 of the present embodiment, the heater H can be energized only for about 2.0 seconds as a predetermined time when the main power is turned on.

  Therefore, the temperature of the heating roller 21 is increased when the heater H is energized only for about 2.0 seconds as a predetermined time in the present invention after the fixing unit 2 is cooled, and once the energization to the heater H is turned off. FIG. 5 also shows a graph showing an example of the above (● mark, “ON → OFF → ON” in the legend). In this graph, the heater H is energized from when the main power is turned on until T1. After that, the energization to the heater H is once turned off, and the temperature of the heating roller 21 is warmed to over room temperature (about 25 ° C. to 30 ° C.) by overshoot (heat conduction), and disconnection can be detected. The energization OFF state to the heater H is maintained until the time point T2. That is, when reaching the time of T2 (about 5.5 to 6.0 seconds), the resistance value of the thermistor TH is lowered to the extent that disconnection can be detected, and disconnection can be detected.

  Then, by detecting disconnection, the control unit 6 confirms that the conductor L is not disconnected, and then turns on the power to the heater H to warm the heating roller 21 to the fixing control temperature. In summary, in the printer 1 of the present embodiment, after the power is turned on, the heater H is energized for about 2.0 seconds (until time T1), and then the heater H is energized for the time indicated by TS2 in FIG. It is turned off, and disconnection is detected about 5.5 to 6.0 seconds after the power is turned on (at time T2), and then energization to the heater H is resumed. When such control is performed, the time from when the main power is turned on until the fixing control temperature is reached is about 12 to 12.5 seconds as compared with the energization of the heater H by the conventional control (graph of ▲ in FIG. 5). Become slow. However, the delay is only a few seconds, and it is possible to prevent the overheating of the fixing unit 2 from occurring without significantly impairing the convenience for the user.

  Thus, according to this embodiment, even if the energization is turned off by heat conduction or the like from the portion directly heated by the heater H of the heating body (heating roller 21) to the entire heating body, Using the fact that the temperature of the entire heating body continues to rise, the control unit 6 energizes the heater H for a predetermined time at the time of disconnection detection, and then shuts off the energization to the heater H. Since disconnection detection is performed, the presence or absence of disconnection can be confirmed in anticipation of a temperature increase due to overshoot. That is, the control unit 6 recognizes the presence or absence of disconnection without continuing energization to the heater H until the detection of the presence or absence of disconnection is completed, and shortens the energization time to the heater H in disconnection detection. Accordingly, the disconnection detection is performed in the state where the fixing unit 2 (the heating body or the like) has already been warmed as in the case where the main power supply is once turned off and the main power supply is immediately turned on again in a state where the excessive temperature rise cannot be detected due to the disconnection. Even if it is carried out, an excessive temperature rise that does not cause damage in the fixing unit 2 such as melting of the driving mechanism 23 such as a gear for rotating the heating body or damage of each member of the fixing unit 2 does not occur.

  Further, since the energizing time of the heater H at the time of disconnection detection is determined based on the time from the fixing control temperature until reaching the limit temperature at which the member of the fixing unit 2 is damaged, the main power is turned off and the main power is immediately turned off. Even if the disconnection detection is performed in a state where the fixing unit 2 (a heating body or the like) is already warm as in the case where the power is turned on, the temperature of the fixing unit 2 is not excessively increased. In addition, the disconnection detection can be performed to check the presence or absence of disconnection only when the temperature measured when the main power is turned on is low and it is not possible to distinguish whether the disconnection has occurred or the fixing unit 2 is cooled. . Therefore, unnecessary disconnection detection is not performed, and the time required for warm-up from when the main power is turned on until the printer is ready for printing can be shortened.

  Further, assuming that the temperature of the heating element is most likely to rise when the heater H is energized, a time for energizing the heater H for detecting disconnection is determined, and the most heating element when the heater H is energized. Assuming that it is difficult to increase the temperature, the time required to confirm the presence or absence of disconnection is taken. Therefore, even if a disconnection occurs in the temperature detection unit 24, it is possible to prevent the occurrence of excessive temperature rise in the fixing unit 2, and it is possible to accurately check whether there is a disconnection (disconnection detection).

  In the above-described embodiment, the fixing unit including the heating roller and the pressure roller has been described as an example. However, the fixing unit that heats and pressurizes the toner image by incorporating a heater using a belt or a film. The present invention can also be applied to a provided image forming apparatus.

  The embodiment of the present invention has been described above, but the scope of the present invention is not limited to this, and various modifications can be made without departing from the spirit of the invention.

  The present invention is applicable to an image forming apparatus provided with a heater for fixing a toner image.

1 Printer (image forming apparatus) 21 Heating roller (heating body)
22 pressure roller (pressure body) 23 drive mechanism 2 fixing unit 24 temperature detection unit 6 control unit H heater L conducting wire (part of temperature detection unit 24) TH thermistor (part of temperature detection unit 24)
R1 resistance (part of temperature detector 24)

Claims (4)

An unfixed toner in the nip, including a heating body including a heater that generates heat when energized, a pressure body that presses the heating body to form a nip, and a driving mechanism that rotates the heating body and the pressure body. A fixing unit that passes the recording medium on which the image is transferred and fixes the toner image on the recording medium;
A temperature detection unit provided to measure the temperature of the heating body, and the output voltage changes according to the temperature;
Recognizing the temperature of the heating body based on the output of the temperature detection unit, controlling energization to the heater and confirming that the output voltage of the temperature detection unit has changed after energizing the heater And a controller that detects disconnection of the temperature detector,
The controller turns off the power to the heater after energizing the heater for a predetermined time, and then conducts the power to the heater after detecting that there is no disconnection. An image forming apparatus.   The predetermined time is any one of the heating body, the pressure body, and the drive mechanism from the fixing control temperature that is the temperature of the heating body that is to be maintained during printing when the heater is energized. 2. The image forming apparatus according to claim 1, wherein the time is less than a time required for the temperature to rise to a limit temperature at which damage starts.   3. The image forming apparatus according to claim 1, wherein when the main power is turned on, the control unit performs the disconnection detection when recognizing that the temperature of the heating body is lower than a predetermined temperature. 4. . When energized, a commercial power supply is connected to the heater,
The predetermined time is a temperature from the fixing control temperature to the limit temperature when the heater is energized in the state where the voltage applied to the heater is the largest due to an error and the output is the largest on tolerance. Is less than the time it takes to rise,
When the main power is turned on, the control unit turns on the heater for the predetermined time, and then the voltage applied to the heater is the smallest due to an error, and the heater has the smallest output on the tolerance. 4. The heater according to claim 1, wherein the heater is turned on again after detecting that there is no disconnection after the time required for detecting the disconnection when energized has elapsed since the main power source was turned on. 2. The image forming apparatus according to item 1.

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