JP2006098871A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set a proper heater drive limit time in accordance with use conditions of a thermal fixing unit. <P>SOLUTION: The image forming apparatus is equipped with the thermal fixing unit 19 which has a heat roller 192 with an internal heater 193 and a pressure roller 194, a heater driving part 126 which turns on and off the heater 193, a timer 125 which counts the driving time of the heater 193, and an AC voltage detection part 127 which detects a voltage supplied to the heater 193, and the heater driving control part 1221 sets the heat source driving limit time corresponding to the input voltage value of the heater 193, compares the set heat source driving limit time with the driving time of the heater 193 counted by the timer 125, and makes the heater driving part 126 turns off the heater 193 when the driving time of the heater 193 reaches the heat source driving limit time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus including a heat fixing unit that heats and melts a toner image formed on a recording sheet.

2. Description of the Related Art Image forming apparatuses such as printers, copiers, and facsimile machines are provided with a heat fixing unit for melting toner adhering to a sheet by heat and fixing the toner on the sheet. As a safety device for this heat fixing unit, there are known a temperature sensor that detects the surface temperature of the heat roller in which the heater is incorporated, and a device that stops power supply to the heater when the surface temperature of the heat roller rises above a certain temperature. (For example, Patent Document 1). As another safety device, there is an apparatus in which an upper limit is set for the heater driving time in order to avoid overheating, and the heater driving is stopped when the heater driving time reaches the limit time.
JP 2000-155495 A

  However, when heater drive control is performed according to the surface temperature of the heat roller, the heater may not be stopped at an appropriate timing due to a temperature sensor failure or a time lag due to heat transfer time. On the other hand, when the heater drive control is performed based on the time limit, the rate of temperature increase of the heat fixing unit per hour varies depending on the usage environment such as the supply voltage to the heater, the ambient temperature of the heat fixing unit, and humidity. The time until the heat fixing unit reaches a predetermined temperature varies depending on these conditions. Therefore, considering only the heater driving time as described above, if the heater supply voltage rises rapidly and the thermal fixing unit reaches a predetermined temperature before the time limit elapses, the heater is heated at an appropriate timing. The drive cannot be stopped. In addition, when the heater supply voltage is lower than the target value, the heater is cut off before the heat fixing unit reaches the predetermined temperature, and the fixing process is interrupted even though the heater can be continuously driven. Has occurred.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of setting an appropriate heat source drive time limit in accordance with a use condition of a fixing unit.

  According to a first aspect of the present invention, there is provided an image forming apparatus comprising: a heat roller having a built-in heat source for melting toner on a recording paper; a fixing unit having a pressure roller that presses the recording paper against the heat roller; Heat source driving means for turning on / off the heat source, setting means for setting a heat source driving time limit according to the surrounding environment of the heat source, and measuring the driving time of the heat source from the time when the heat source is turned on by the heat source driving means A time when the heat source drive time reaches the heat source drive time limit by comparing the measurement means, the heat source drive time limit set by the setting means, and the drive time of the heat source measured by the measurement means The heat source driving means includes heat source driving control means for turning off the heat source.

  According to the above configuration, when the heat source is turned on by the heat source driving unit, the measurement of the driving time of the heat source is started by the measuring unit. Then, the heat source drive time limit according to the surrounding environment of the heat source is set by the setting means, and the heat source drive time limit set by the heat source drive control means is compared with the drive time of the heat source measured by the measurement means. When the driving time reaches the heat source drive limit time, the heat source is turned off. Therefore, it is possible to accurately grasp when the temperature of the fixing unit reaches a predetermined temperature according to the surrounding environment of the fixing unit, and to turn off the heat source before overheating occurs, thereby improving safety. In addition, it is possible to avoid inconveniences such as stopping the driving of the heat source before the fixing unit reaches a predetermined temperature and interrupting the fixing process.

  An image forming apparatus according to a second aspect of the present invention is the image forming apparatus according to the first aspect, further comprising: a voltage supply source that supplies a voltage to the heat source; and an input voltage detection unit that detects an input voltage value of the heat source. The setting means includes a storage means for storing a table indicating a heat source drive time limit according to an input voltage value of the heat source, and an input voltage value of the heat source detected by the input voltage means based on the table. And determining means for determining a corresponding heat source drive time limit.

  According to the above configuration, the input voltage detection unit detects the input voltage value of the heat source, and the determination unit detects the input voltage value based on the table indicating the heat source drive time limit corresponding to the input voltage value of the heat source. The heat source drive time limit is determined according to the input voltage value of the heat source. Thereby, according to the input voltage value of a heat source, a heat source can be drive-stopped at an appropriate timing.

  An image forming apparatus according to claim 3 of the present invention is the image forming apparatus according to claim 1, further comprising: a voltage supply source that supplies a voltage to the heat source; and an input voltage detection unit that detects an input voltage value of the heat source. The setting means includes a storage means for storing an arithmetic expression for obtaining a heat source drive time limit from the input voltage value of the heat source, and an input voltage value of the heat source detected by the input voltage means based on the arithmetic expression. And determining means for determining a corresponding heat source drive time limit.

  According to the above configuration, the input voltage value of the heat source is detected by the input voltage detection means, and the heat source detected by the input voltage detection means is calculated based on the arithmetic expression for obtaining the heat source drive time limit from the input voltage value of the heat source by the determination means. The heat source drive time limit is determined according to the input voltage value. Thereby, according to the input voltage value of a heat source, a heat source can be drive-stopped at an appropriate timing.

  An image forming apparatus according to a fourth aspect of the present invention is the image forming apparatus according to the first aspect, further comprising a temperature / humidity detecting unit that detects an ambient temperature or humidity of the fixing unit, and the setting unit includes the fixing unit. Storage means for storing a heat source drive time limit corresponding to the ambient temperature or humidity of the battery, and heat source drive corresponding to the ambient temperature or humidity of the fixing means detected by the temperature / humidity detection means based on the table And determining means for determining a time limit.

  According to the above configuration, the temperature / humidity detection unit detects the ambient temperature or humidity of the fixing unit, and the determination unit detects the temperature / humidity based on the table indicating the heat source drive time limit according to the ambient temperature or humidity of the fixing unit. The heat source drive time limit is determined according to the ambient temperature or humidity of the fixing means detected by the means. Thus, the driving of the heat source can be stopped at an appropriate timing according to the ambient temperature or humidity of the fixing unit.

  An image forming apparatus according to a fifth aspect of the present invention is the image forming apparatus according to the first aspect, further comprising a temperature / humidity detecting unit that detects an ambient temperature or humidity of the fixing unit, and the setting unit includes the fixing unit. Storage means for storing a heat source drive time limit from the ambient temperature or humidity of the heat source, and heat source drive according to the ambient temperature or humidity of the fixing means detected by the temperature / humidity detection means based on the arithmetic expression And determining means for determining a time limit.

  According to the above configuration, the temperature / humidity detecting unit detects the ambient temperature or humidity of the fixing unit, and the determining unit calculates the heat source drive time limit from the ambient temperature or humidity of the fixing unit based on the arithmetic expression. The heat source drive time limit is determined in accordance with the ambient temperature or humidity of the fixing unit detected by the above. Thus, the driving of the heat source can be stopped at an appropriate timing according to the ambient temperature or humidity of the fixing unit.

  An image forming apparatus according to a sixth aspect of the present invention is the image forming apparatus according to the first aspect, further comprising size receiving means for receiving a selection of a size of the recording paper from outside, wherein the setting means is in accordance with the size of the recording paper. Storage means for storing a table indicating the heat source drive time limit, and determination means for determining a heat source drive time limit according to the size of the recording sheet received by the size receiving means based on the table. And

  According to the above configuration, the recording sheet received from the size receiving unit is received from the outside by the size receiving unit, and based on the table indicating the heat source drive time limit according to the size of the recording sheet by the determining unit. The heat source drive time limit is determined according to the size. Thereby, the driving of the heat source can be stopped at an appropriate timing according to the size of the recording paper.

  An image forming apparatus according to a seventh aspect of the present invention is the image forming apparatus according to the first aspect, further comprising size receiving means for receiving a selection of the size of the recording paper from outside, wherein the setting means determines the heat source from the size of the recording paper. A storage unit that stores an arithmetic expression for obtaining the drive time limit, and a determination unit that determines a heat source drive time limit according to the size of the recording sheet received by the size receiving unit based on the arithmetic expression. And

  According to the above configuration, the selection of the size of the recording sheet is received from the outside by the size receiving unit, and the recording sheet received by the size receiving unit is calculated based on the arithmetic expression for obtaining the heat source drive time limit from the size of the recording sheet by the determining unit. The heat source drive time limit is determined according to the size. Thereby, the driving of the heat source can be stopped at an appropriate timing according to the size of the recording paper.

  According to the present invention, the time when the temperature of the fixing unit reaches a predetermined temperature is accurately determined according to the input voltage value of the heat source provided in the fixing unit, the ambient temperature of the fixing unit, the humidity, or the size of the recording paper. It can be grasped and the heat source can be turned off before overheating occurs, and safety can be improved. In addition, it is possible to avoid inconveniences such as stopping the driving of the heat source before the fixing unit reaches a predetermined temperature and interrupting the fixing process.

(First embodiment)
FIG. 1 is a schematic side view showing a main configuration of a laser printer as an example of an image forming apparatus of the present invention. The laser printer 1 includes an operation panel 10, a power supply unit 11, a printer control unit 12, an exposure unit 13, a photosensitive drum 14, a developing unit 15, a paper cassette 16, a paper feed roller 17, a transfer roller 18, a thermal fixing unit 19, and the like. Is provided. The operation panel 10 is provided with switches for various operations, LED indicators and the like (not shown), and is used for inputting various operation commands and the like. The power supply unit 11 includes an AC voltage source, and generates and supplies a DC voltage necessary for a control system, a drive system, and the like. The printer control unit 12 controls the entire apparatus, and print data including characters and images, the size of characters, and the number of copies from a host computer connected to the laser printer 1 via a network such as a LAN. When a print start instruction signal including such information is received, a video signal corresponding to these pieces of information is generated and output to the exposure unit 13.

  The exposure unit 13 is a semiconductor laser 131, a driving circuit for the semiconductor laser 131, a laser driver 132 for switching on / off of laser light emitted from the semiconductor laser 131 in accordance with a video signal input from a host computer, and a semiconductor laser A rotary polygon mirror 133 that guides the laser light emitted from 131 to the photosensitive drum 14 and a reflecting mirror 134 are provided, and an electrostatic latent image is formed on the photosensitive drum 14 that is charged by a charging device (not shown).

  The developing unit 15 supplies a black developer onto the photosensitive drum 14 and forms a toner image in which the electrostatic latent image formed on the photosensitive drum 14 is visualized.

  The paper feed roller 17 pulls out the recording paper from the paper cassette 16 in which the recording paper is stored, and feeds the recording paper to the transfer roller 18. The transfer roller 18 transfers the toner image on the photosensitive drum 14 to the conveyed recording paper.

  The heat fixing unit 19 includes a heat roller 192 having a heater 193 and a pressure roller 194 in a heat shielding box 191, and heats and presses the recording paper on which the toner image is transferred to fix the toner image on the recording paper. Let The heater 193 of the heat roller 192 is energized when a predetermined voltage is applied from the power supply unit 11. The heat fixing unit 19 includes a temperature sensor 195 that detects the temperature in the heat shielding box 191, and the printer control unit 12 controls on / off of the heater 193 based on temperature information detected by the temperature sensor 195, Control is performed so that the surface of the roller 192 reaches a predetermined temperature at which the fixing process can be performed (hereinafter referred to as “fixing processing temperature”).

  When the temperature in the heat fixing unit 19 reaches the fixing processing temperature, the recording paper stored in the paper cassette 16 is taken into the apparatus by the paper supply roller 17 and supplied to the photosensitive drum 14. The electrostatic latent image formed on the photosensitive drum 14 is visualized by supplying toner from the developing unit 15, transferred to the recording paper conveyed by the transfer roller 18, and then transferred by the heat fixing unit 19. It is fixed on the recording paper.

  FIG. 2 is a block diagram showing the configuration of the printer control unit 12. The printer control unit 12 includes an external device such as a host computer and an image scanner, an I / F unit 121 that transmits and receives print data and control data via a network, a CPU (Central Processing Unit) 122, and data being processed. A RAM (Random Access Memory) 123 for temporarily storing data, a ROM (Read Only Memory) 124 for storing programs for controlling various operations of the laser printer 1 in advance, and a time when the heater 193 is turned on by the heater driving unit 126 A timer 125 that counts the drive time T [Sec] of the heater 193, a heater drive unit 126 that performs on / off control of the heater 193 built in the heat roller 192, and a supply voltage from the power supply unit 11 to the heater 193. And an AC voltage detection unit 127 for detection.

  FIG. 3 is a block diagram showing a mechanism configuration of the print control unit 12.

  The ROM 124 stores a drive time limit table indicating heater drive time limit TM [Sec] corresponding to various input voltage values V [V] of the heater 193. The heater drive limit time TM is a time expected from the start of driving of the heater 193 until reaching a predetermined temperature lower than a certain temperature at which overheating occurs.

  FIG. 4 is a graph showing the relationship of the heater drive time limit TM [Sec] corresponding to the input voltage value V [V] of the heater 193. When the input voltage value V of the heater 193 is 230 [V], the heater drive limit time TM is 50 [Sec]. On the other hand, when the input voltage value V of the heater 193 is 220 [V], the heat generation amount per hour of the heater 193 is small, and as a result, the heater drive limit time TM is as long as 60 [Sec]. Further, when the input voltage value V is 240 [V], the heat generation amount per hour of the heater 193 increases, and as a result, the heater drive limit time TM becomes as short as 40 [Sec].

  Returning to FIG. 3, the ROM 124 stores a drive time limit table 1241 indicating the heater drive time limit TM with respect to the supply voltage of the heater 193. In the drive limit time table 1241, the heater drive limit time TM is set to 60 [Sec], 50 [Sec], and 40 when the supply voltage of the heater 193 is 220 V or less, 220 V or more and less than 230 V, or 230 V or more, respectively. [Sec]. Here, the value of the heater drive time limit TM with respect to the supply voltage of the heater 193 shown in the drive time limit table 1241 is an example.

  The CPU 122 includes a heater drive control unit 1221 that controls the start or stop timing of the heater 193 and a timer control unit 1225 that controls the start or stop of the operation of the timer 125. The heater drive control unit 1221 refers to the drive time limit table 1241 recorded in the ROM 124, and the time limit determination unit 1222 obtains the heater drive time limit TM from the supply voltage to the heater 193 detected by the AC voltage detection unit 127. A heater state detection unit 1223 that sets a flag indicating that the heater 193 is on when the heater 193 starts driving, cancels the flag when the heater 193 stops driving, and detects on / off of the heater 193; After the heater 193 starts to be driven, the heater driving time T counted by the timer 125 is compared with the heater driving time limit TM determined by the time limit determining unit 1222, and a time determination unit 1224 for detecting the time when the two coincide with each other. With.

  The heater drive control unit 1221 outputs a start signal for starting the drive of the heater 193 to the heater drive unit 126 when the print start instruction is received together with the print data from the host computer, operates the timer 125, and counts by the timer 125. When the heater driving time thus reached reaches the heater driving limit time TM, a stop signal for stopping the driving of the heater 193 is output to the heater driving unit 126. Thereby, the driving of the heater 193 can be stopped before the heat fixing unit 19 reaches the predetermined temperature, and the overheating of the heat fixing unit 19 can be prevented.

  In the above example, every time the supply voltage value of the heater 193 increases by 10 V, the time until the temperature in the thermal fixing unit 19 reaches a predetermined temperature is shortened by 10 [Sec]. When the supply voltage rises by a certain voltage, the heater drive limit time TM is shortened by a certain time. Therefore, the heater drive time limit TM can be obtained from the detected voltage of the heater 193 based on the reference data using the predetermined supply voltage value and the heater drive time limit corresponding to the supply voltage value as reference data. Therefore, instead of the drive time limit table 1241, an arithmetic expression necessary for calculating the heater drive time limit is stored in the ROM 124, and the time limit determination unit 1222 uses this arithmetic expression to detect the AC voltage detection unit 127. The heater drive time limit may be obtained from the voltage.

  FIG. 5 is a flowchart showing drive control of the thermal fixing unit 19 by the printer control unit 12. The drive control of the thermal fixing unit 19 is started when the CPU 122 receives a print start instruction from the host computer. First, the AC voltage detection unit 127 detects the input voltage value V of the heater 193 (step S1), and the time limit determination unit 1222 determines whether the input voltage value V is 220 [V] or more (step S2). ) If the input voltage value V is less than 220 [V] (No in step S2), the process proceeds to step S4, and the heater drive time limit TM is determined to be 60 [Sec].

  When the time limit determining unit 1222 determines that the input voltage value V is 220 [V] or more (Yes in step S2), it is further determined whether or not the input voltage value V is 230 [V] or more. When the input voltage value V is less than 230 [V] (No in step S3), the heater drive time limit TM is determined to be 50 [Sec] (step S5), and the input voltage value V is If it is 230 [V] or more (Yes in step S3), the heater drive time limit TM is determined to be 40 [Sec] (step S6).

  Next, the heater state detection unit 1223 determines whether or not the heater 193 is in an on state (step S7). If the heater 193 is in an off state, the process returns to step S1. If the heater 193 is on, the timer control unit 1225 resets the timer 125 (step S8), and then the timer 125 starts counting the heater driving time T (step S9).

  The time determination unit 1224 determines whether or not the heater driving time T is equal to or longer than the heater driving time limit TM (step S10). If the heater driving time T is less than the heater driving time limit TM (No in step S10). ) The heater state detection unit 1223 determines whether or not the heater 193 is in an off state (step S11). If the heater 193 is in an off state, the process returns to step S1. If the heater 193 is on, the process returns to step S10. If the heater drive time T is equal to or longer than the heater drive limit time TM (Yes in step S10), the heater 193 is forcibly turned off by the heater drive unit 126 (step S12).

  As described above, in the present embodiment, since the heater drive time limit TM corresponding to the supply voltage V of the heater 193 is obtained from the drive time limit table 1241, the time when the temperature of the heat fixing unit 19 reaches a predetermined temperature is accurately grasped. The heater 193 can be turned off before overheating occurs, and safety can be improved. In addition, it is possible to avoid inconveniences such as stopping the driving of the heater 193 before the heat fixing unit 19 reaches a predetermined temperature and interrupting the fixing process.

(Second Embodiment)
FIG. 6 is a block diagram showing the configuration of the printer control unit 12. In the figure, the same reference numerals as those in FIG. 2 and FIG. The ambient temperature detection unit 20 is provided in the vicinity of the thermal fixing unit 19 and detects the ambient temperature of the thermal fixing unit 19.

  FIG. 7 is a graph showing the relationship of the heater drive time limit TM [Sec] with respect to the ambient temperature T [° C.] of the heat fixing unit 19. When the ambient temperature T of the thermal fixing unit 19 is 15 [° C.], the heater drive time limit TM is 60 [Sec], and when the ambient temperature T is 25 [° C.], the heater drive time limit TM is 50 [Sec]. When the ambient temperature T is 35 [° C.], the heater drive limit time TM is 40 [Sec].

  The ROM 124 stores a drive time limit table 1242 indicating the heater drive time limit TM with respect to the ambient temperature of the heat fixing unit 19. In the drive limit time table 1242, for example, when the ambient temperature of the thermal fixing unit 19 is less than 15 ° C., 15 ° C. or more and less than 25 ° C., and 25 ° C. or more, the heater drive limit time TM is set to 60 [Sec. ], 50 [Sec], and 40 [Sec]. Here, the value of the heater drive time limit TM with respect to the ambient temperature of the thermal fixing unit 19 indicated by the drive time limit table 1242 is an example.

  The time limit determination unit 1226 refers to the drive time limit table 1242 recorded in the ROM 124 and obtains the heater drive time limit TM from the ambient temperature of the thermal fixing unit 19 detected by the ambient temperature detection unit 20.

  In the above example, every time the ambient temperature of the thermal fixing unit 19 increases by 10 ° C., the time until the temperature in the thermal fixing unit 19 reaches a predetermined temperature is shortened by 10 [Sec]. When the temperature rises by a certain temperature, the heater drive limit time TM is shortened by a certain time. Accordingly, the heater drive time limit TM can be obtained from the ambient temperature of the heat fixing unit 19 based on the reference data, using the predetermined ambient temperature and the heater drive time limit for the ambient temperature as reference data. Therefore, instead of the drive time limit table 1242, an arithmetic expression necessary for calculating the heater drive time limit time is stored in the ROM 124, and the time limit determination unit 1226 uses the arithmetic expression to calculate the ambient temperature detection unit 20. The heater drive time limit may be obtained from the detected temperature.

  FIG. 8 is a flowchart showing drive control of the thermal fixing unit 19 by the printer control unit 12. First, the ambient temperature T of the thermal fixing unit 19 is detected by the ambient temperature detector 20 (step S51), and the time limit determining unit 1226 determines whether or not the ambient temperature T is 15 [° C.] or higher (step S52). ) If the ambient temperature T is less than 15 [° C.], the heater drive limit time TM is determined to be 60 [Sec] (step S54).

  When the time limit determining unit 1226 determines that the ambient temperature T is 15 [° C.] or higher, it is further determined whether or not the ambient temperature T is 25 [° C.] or higher (step S53). If T is less than 25 [° C.], the heater drive limit time TM is determined to be 50 [Sec] (step S55). If the ambient temperature T is 25 [° C.] or more, the heater drive limit time TM is 40 [Sec] is determined (step S56).

  Next, the heater state detection unit 1223 determines whether or not the heater 193 is on (step S57). If the heater 193 is off, the process returns to step S51. When the heater 193 is on, the timer control unit 1225 resets the timer 125 (step S58), and then the timer 125 starts counting the heater driving time T (step S59).

  The time determination unit 1224 determines whether or not the heater drive time T is equal to or longer than the heater drive limit time TM (step S60). If the heater drive time T is less than the heater drive limit time TM, the heater state detection unit. Whether or not the heater 193 is in an off state is determined by 1223 (step S61). If the heater 193 is in an off state, the process returns to step S51. If the heater 193 is on, the process returns to step S60. On the other hand, when the heater driving time T is equal to or longer than the heater driving limit time TM, the heater 193 is forcibly turned off by the heater driving unit 126 (step S62).

  As described above, in the present embodiment, the heater drive time limit TM corresponding to the ambient temperature T of the heat fixing unit 19 is obtained from the drive time limit table 1242, so that the time when the temperature of the heat fixing unit 19 reaches a predetermined temperature can be accurately grasped. In addition, the heater 193 can be turned off before overheating occurs, and safety can be improved. In addition, it is possible to avoid inconveniences such as stopping the driving of the heater 193 before the heat fixing unit 19 reaches a predetermined temperature and interrupting the fixing process.

(Other embodiments)
In the present embodiment, the heater drive time limit is determined based on the supply voltage value of the heater 193 or the ambient temperature of the heat fixing unit 19, but the heater depends on other use conditions of the other heat fixing units 19. The drive time limit may be determined. For example, the higher the humidity around the heat fixing unit 19 is, the more heat is consumed by the heater 193 for evaporating the water contained in the paper and toner, and thus the heater drive limit until the heat fixing unit 19 reaches a predetermined temperature. The time will be longer. Accordingly, the image forming apparatus according to the present invention is provided near the heat fixing unit 19, a hygrometer that detects the ambient humidity of the heat fixing unit 19, and driving that defines the heater drive time limit with respect to the ambient humidity of the heat fixing unit 19. A ROM that stores a time limit table in advance, and a time limit determination unit that refers to the drive time limit table and determines a heater drive time limit corresponding to the ambient humidity of the thermal fixing unit 19 detected by the hygrometer. A configuration in which the time determination unit determines the heat source drive time limit according to the ambient humidity of the heat fixing unit 12 detected by the hygrometer based on the drive time limit table may be employed.

  Further, since the heat consumption of the heater 193 increases as the size of the recording paper increases, the heater drive limit time until the heat fixing unit 19 reaches a predetermined temperature becomes longer. Therefore, an image forming apparatus according to the present invention includes a size receiving unit that receives a selection of a recording paper size from a host computer, a ROM that preliminarily stores a driving time limit table that defines a heater driving time limit for the recording paper size, A time limit determination unit that determines a heater drive time limit corresponding to the size of the recording sheet received by the size receiving means with reference to the drive time limit table, and the time limit determination unit determines the size based on the drive time limit table. A configuration for determining the heat source drive time limit according to the size of the recording sheet received by the receiving unit can also be adopted.

  In this embodiment, the heater drive time limit according to various use conditions (heater supply voltage value, ambient temperature) of the heat fixing unit 19 is obtained using the drive time limit tables 1241 and 1242. Data of an arithmetic expression for obtaining the heater drive time limit from the 19 various use conditions may be stored in the ROM 124 in advance, and the heater drive time limit may be obtained using the arithmetic expression data.

  In this embodiment, the image forming apparatus according to the present invention is described as a laser printer. However, the image forming apparatus is not limited to this, and has a copying machine, a facsimile machine, a copy function, a printer function, or a fax function. It may be a multifunction machine.

1 is a schematic side view showing a main configuration of a laser printer as an example of an image forming apparatus of the present invention. FIG. 2 is a block diagram illustrating a configuration of a printer control unit according to the first embodiment. FIG. 2 is a block diagram illustrating a detailed configuration of a print control unit. It is a graph showing the relationship of the heater drive time limit with respect to the input voltage value of a heater. 6 is a flowchart showing drive control of a thermal fixing unit by a printer control unit in the first embodiment. It is a block diagram which shows the structure of the printer control unit in 2nd Embodiment. It is a graph showing the relationship of the heater drive time limit with respect to the ambient temperature of a heat fixing unit. 10 is a flowchart illustrating drive control of a thermal fixing unit by a printer control unit according to a second embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Laser printer 10 Operation panel 11 Power supply unit 12 Printer control unit 121 Interface part 122 CPU
1221 Heater drive control units 1222 and 1226 Time limit determination unit 1223 Heater state detection unit 1224 Time determination unit 1225 Timer control unit 123 RAM
124 ROM
1241, 1242 Drive time limit table 125 Timer 126 Heater drive unit 127 AC voltage detection unit 13 Exposure unit 14 Photosensitive drum 15 Development unit 16 Paper cassette 17 Paper feed roller 18 Transfer roller 19 Heat fixing unit 192 Heat roller 193 Heater 194 Pressure Roller 195 Temperature sensor 20 Ambient temperature detector

Claims (7)

A fixing roller having a heat roller with a built-in heat source for melting toner on the recording paper, and a pressure roller that presses the recording paper against the heat roller;
Heat source driving means for turning on / off the heat source;
Setting means for setting a heat source drive time limit according to the ambient environment of the heat source;
Measuring means for measuring the driving time of the heat source from the time when the heat source is turned on by the heat source driving means;
The heat source drive time limit set by the setting means and the heat source drive time measured by the measurement means are compared, and when the heat source drive time reaches the heat source drive time limit, the heat source drive time Heat source drive control means for causing the means to turn off the heat source;
An image forming apparatus comprising: A voltage supply source for supplying a voltage to the heat source;
An input voltage detecting means for detecting an input voltage value of the heat source;
The setting means includes
Storage means for storing a table indicating a heat source drive time limit according to an input voltage value of the heat source;
The image forming apparatus according to claim 1, further comprising: a determination unit that determines a heat source drive time limit according to an input voltage value of the heat source detected by the input voltage unit based on the table. A voltage supply source for supplying a voltage to the heat source;
An input voltage detecting means for detecting an input voltage value of the heat source;
The setting means includes
Storage means for storing an arithmetic expression for obtaining a heat source drive time limit from an input voltage value of the heat source;
The image forming apparatus according to claim 1, further comprising: a determining unit that determines a heat source drive time limit corresponding to an input voltage value of the heat source detected by the input voltage unit based on the arithmetic expression. A temperature / humidity detecting means for detecting the ambient temperature or humidity of the fixing means;
The setting means includes
Storage means for storing a table indicating a heat source drive time limit according to the ambient temperature or humidity of the fixing means;
2. The image according to claim 1, further comprising a determining unit that determines a heat source drive time limit according to an ambient temperature or humidity of the fixing unit detected by the temperature / humidity detecting unit based on the table. Forming equipment. A temperature / humidity detecting means for detecting the ambient temperature or humidity of the fixing means;
The setting means includes
Storage means for storing an arithmetic expression for obtaining a heat source drive time limit from the ambient temperature or humidity of the fixing means;
2. The determining unit according to claim 1, further comprising: a determining unit configured to determine a heat source drive time limit according to an ambient temperature or humidity of the fixing unit detected by the temperature / humidity detecting unit based on the arithmetic expression. Image forming apparatus. A size receiving means for receiving a selection of the size of the recording paper from outside;
The setting means includes
Storage means for storing a table indicating the heat source drive time limit according to the size of the recording paper;
2. The image forming apparatus according to claim 1, further comprising a determining unit that determines a heat source drive time limit according to the size of the recording sheet received by the size receiving unit based on the table. A size receiving means for receiving a selection of the size of the recording paper from outside;
The setting means includes
Storage means for storing an arithmetic expression for obtaining the heat source drive time limit from the size of the recording paper;
The image forming apparatus according to claim 1, further comprising: a determining unit that determines a heat source drive time limit according to the size of the recording sheet received by the size receiving unit based on the arithmetic expression.

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