JP2011197155A - Image forming apparatus with fixing device, fixing method, and program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To keep the temperature at which a transfer medium is carried to the nip of a fixing device appropriate.SOLUTION: In an image forming apparatus with a fixing device that heats a fixing heater following light control timing (S101 to S109), when the leading end (or trailing end) of a transfer medium reaches (or passes through) the nip of the fixing device (S109), the lighting control for the fixing heater is exerted regardless of the lighting control timing for the fixing heater. Accordingly, the transfer medium passing through the nip is normally fixed even if the lighting control timing does not match the timing of the reach/passage of the leading end (or trailing end) of the transfer medium to/through the nip.

Description

  The present invention relates to an image forming apparatus, a fixing method, and a program including a fixing device that fixes a toner image on a transfer medium by heating toner carried on the transfer medium as a toner image.

  2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus such as a printer, a copying machine, or a facsimile, a fixing device that fixes an image by heating and melting a toner image formed on a transfer medium such as paper has been used. This fixing device generally detects the temperature by a temperature sensor such as a thermopile or thermistor provided in the fixing heater, and when the detected temperature is lower than the target control temperature according to the difference between the detected temperature and the target control temperature. Is turned on when the heater is energized and turned off when the temperature is higher than the target control temperature to stabilize the temperature of the heating roller in a predetermined temperature range, and control is performed so as to obtain good fixing characteristics.

  As a method for controlling the power supplied to the heater of such a fixing device, a control method is known in which the ratio of lighting the heater is calculated for each heater control period, and the heater is turned on / off based on the ratio. Yes. For example, Japanese Patent Laid-Open No. 2004-228561 calculates the ratio of turning on the heater for each heater control period based on a periodic signal related to conveyance and determines the heater control period, so that the leading edge of a transfer medium such as paper is fixed to the fixing device. A method is disclosed in which the difference between the timing at which the transfer medium reaches the nip portion and the timing at which energization to the fixing heater is started just before that is made constant so that the temperature when the transfer medium reaches the nip portion is kept appropriate. .

By the way, in the control method in which the heater lighting rate is calculated for each heater control cycle (fixed cycle) so far and the heater is turned on / off based on that rate, the heater control cycle and transfer medium conveyance are performed. There are times when the timing is shifted.
However, the temperature change characteristic with respect to the heater control differs depending on whether or not the transfer medium is in contact with the nip portion of the fixing device, so that the transfer medium is in contact with (or in contact with) the nip portion. When the heater control cycle starts and the control cycle ends, that is, before the next heater control cycle, the trailing edge of the transfer medium passes (or the leading edge of the next transfer medium reaches) If the ratio of turning on the heater is calculated, the intended temperature change does not occur and the temperature cannot be maintained properly.
In particular, when transfer media having different lengths are mixed and conveyed, there is a problem that the above-described deviation is likely to occur and a fixing defect occurs.

  In this regard, although the fixing heater control method for the image forming apparatus described in Patent Document 1 determines the timing for controlling the fixing heater in consideration of the transfer medium conveyance timing, transfer media of different lengths are mixed. When the transfer timing of the transfer medium does not reach a certain period, the difference between the timing at which the leading edge of the transfer medium reaches the nip portion of the fixing device and the timing at which energization to the fixing heater is started immediately before that is constant. Can not be. For this reason, the above problem cannot be solved, and fixing failure may occur.

  The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to convey the transfer medium through the nip portion of the fixing device even when the heater control cycle and the transfer medium conveyance timing are deviated. Is to keep the temperature at the right time.

According to the first aspect of the present invention, the toner image formed on the image carrier is transferred to a transfer medium, and the fixing heater is turned on / off at a predetermined lighting control timing to fix the transfer medium. 1st judging means for judging whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device and / or whether or not the trailing edge of the transfer medium has passed the nip portion of the fixing device. Second determining means for determining whether the leading edge of the transfer medium has reached the nip portion of the fixing device, the fixing heater of the fixing heater regardless of the lighting control timing. Lighting control is performed, and when the second determination means determines that the trailing edge of the transfer medium has passed through the nip portion of the fixing device, the fixing heater lighting control is performed regardless of the lighting control timing. Preparative an image forming apparatus according to claim.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the first determination unit determines whether the leading end of the transfer medium has reached the nip portion of the fixing device. The image forming apparatus is characterized in that the arrival time to the nip portion is calculated on the basis of the start of conveyance from the registration rollers.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the first determining means determines whether the leading end of the transfer medium has reached the nip portion of the fixing device, and The image forming apparatus is characterized in that the arrival time to the nip portion is calculated with reference to the start of the writing process.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, a plurality of position detection sensors are provided along the transfer path of the transfer medium to detect the transfer position of the transfer medium, and the first The determination means determines whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device. Among the position detection sensors, the position detection sensor closest to the fixing device is located upstream of the fixing device. The image forming apparatus is characterized in that the arrival time to the nip portion is calculated on the basis of the timing at which the tip is detected.
A fifth aspect of the present invention is the image forming apparatus according to any one of the second to fourth aspects,
When the fixing heater and the nip portion of the fixing device are spaced apart from each other, the first determination unit determines whether or not the leading end of the transfer medium has reached the nip portion of the fixing device. A delay time until the heater-on is reflected in the nip portion is calculated, and it is determined that the transfer medium is subtracted from the calculated arrival time to the nip portion before the delay time. An image forming apparatus.
According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the front end of the transfer medium at the timing reaches the nip portion of the fixing device based on the predetermined lighting control timing. When the calculated time is less than a predetermined time, the lighting control is not performed at the lighting control timing, and the lighting control is performed until the leading edge of the transfer medium reaches the nip portion of the fixing device. An image forming apparatus characterized in that the timing is extended.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first aspect, the second determination unit determines whether or not the rear end of the transfer medium has passed through the nip portion of the fixing device. An image forming apparatus characterized in that it calculates and calculates a time until it passes through a nip portion with reference to a start time of conveyance from a registration roller.
According to an eighth aspect of the present invention, in the image forming apparatus according to the first aspect, the second determining means determines whether or not the rear end of the transfer medium has passed through the nip portion of the fixing device. The image forming apparatus is characterized in that it calculates and calculates the time until it passes through the nip portion with reference to the start of the writing process.
According to a ninth aspect of the present invention, in the image forming apparatus according to the first aspect, a plurality of position detection sensors are provided along the transfer path of the transfer medium to detect the transfer position of the transfer medium. The determination means determines whether or not the rear end of the transfer medium passes through the nip portion of the fixing device, and the position detection sensor closest to the fixing device on the upstream side of the fixing device among the position detection sensors is the transfer medium. The image forming apparatus is characterized in that a time until passing through the nip portion is calculated based on a timing at which the rear end is detected.
According to a tenth aspect of the present invention, in the image forming apparatus according to any one of the seventh to ninth aspects, when the fixing heater and the nip portion of the fixing device are spaced apart from each other, the second determination is performed. The means determines the passage of the rear end of the transfer medium through the nip portion of the fixing device, calculates a delay time until the fixing heater is reflected in the nip portion, and the transfer medium is moved forward by the delay time. In the image forming apparatus, it is determined to subtract from the calculated time until passing the nip portion.
According to an eleventh aspect of the present invention, in the image forming apparatus according to any one of the first or seventh to tenth aspects, with the predetermined lighting control timing as a reference, the rear end of the transfer medium at the timing is a nip portion of the fixing device. When the calculated time is less than a predetermined time, the lighting control at the lighting control timing is not performed, and the trailing edge of the transfer medium passes through the nip portion of the fixing device. The lighting control timing is extended until the image forming apparatus.
According to a twelfth aspect of the present invention, an image forming apparatus for transferring a toner image formed on an image carrier onto a transfer medium and fixing the transfer medium by switching on / off a fixing heater at a predetermined lighting control timing. In the first fixing step of determining whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device and / or the trailing edge of the transfer medium passes through the nip portion of the fixing device. A second determination step for determining whether or not the sheet has passed. In the first determination step, when it is determined that the leading end of the transfer medium has reached the nip portion of the fixing device, the timing of the cycle is set. Regardless of the lighting control of the fixing heater, when the rear end of the transfer medium has passed through the nip portion of the fixing device in the second determination step, the fixed heater is controlled regardless of the lighting control timing. A fixing method and performing lighting control of the heater.
According to a thirteenth aspect of the present invention, there is provided an image forming apparatus for transferring a toner image formed on an image carrier onto a transfer medium and switching the fixing heater on / off at a predetermined lighting control timing to fix the transfer medium. The first determination means for determining whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device and / or whether the trailing edge of the transfer medium has passed the nip portion of the fixing device And determining whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device, the lighting control of the fixing heater is performed regardless of the timing of the cycle. When it is determined that the first determination unit and the rear end of the transfer medium have passed through the nip portion of the fixing device, the second control for controlling the lighting of the fixing heater is performed regardless of the lighting control timing. Is a program for causing to function as a cross section.

  According to the present invention, even when the control period of the fixing heater is deviated from the transfer timing of the transfer medium, the temperature at which the transfer medium is transferred to the nip portion of the fixing device can be appropriately maintained to prevent fixing failure. it can.

1 is a diagram schematically illustrating a configuration of an engine unit of an image forming apparatus according to an exemplary embodiment. FIG. 2A is a block diagram schematically showing a hardware configuration of an engine control unit that controls the engine unit, and FIG. 2B is an enlarged view of a CPU of an engine main board (EGB). FIG. 6 is a flowchart showing a procedure of a lighting control process of a fixing heater of the fixing device. It is a figure explaining the relationship between lighting control timing and the ON / OFF state of a fixing heater. FIG. 6 is a diagram illustrating a mechanism in which a fixing failure (cold offset) occurs due to a difference between a lighting control timing and a timing at which a leading edge of a transfer medium reaches a nip portion of a fixing device. FIG. 6 is a diagram illustrating a mechanism in which a fixing failure (hot offset) occurs due to a difference between a lighting control timing and a timing at which a rear end of a transfer medium passes through a nip portion of a fixing device. FIG. 7A is a flowchart showing a procedure for performing lighting control when the leading edge of the transfer medium of the present invention reaches the nip portion, and FIG. 7B prevents fixing failure (cold offset) by the lighting control of FIG. 7A. It is a figure explaining a method. FIG. 8A is a flowchart illustrating a procedure for performing lighting control when the trailing edge of the transfer medium of the present embodiment passes through the nip portion. FIG. 8B illustrates a fixing failure (hot offset) due to the lighting control of FIG. 8A. It is a figure explaining the mechanism to prevent. FIG. 10 is a diagram illustrating a method for determining that the leading edge of the transfer medium has reached the nip portion of the fixing device based on the start of conveyance from a registration roller. FIG. 10 is a diagram illustrating a method for determining that the leading edge of the transfer medium has reached the nip portion of the fixing device based on the start of the writing process in the image carrier. FIG. 6 is a diagram illustrating a method for determining that the leading edge of a transfer medium has reached the nip portion of the fixing device in consideration of the structure of the fixing device. FIG. 10 is a flowchart illustrating a procedure of a method for securing a lighting control timing interval for a predetermined time or more in consideration of an electrical problem that occurs when the leading edge of a transfer medium reaches the nip portion of the fixing device. (1) is a diagram for explaining a case where an electrical problem such as flicker occurs, and (2) is a diagram for explaining a case where an electrical problem such as flicker can be prevented by the lighting control of FIG. 12A. FIG. 10 is a diagram illustrating a method for determining that the rear end of the transfer medium has passed through the nip portion of the fixing device based on the position detection sensor being off. FIG. 10 is a diagram illustrating a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device based on the start of conveyance from a registration roller. FIG. 10 is a diagram illustrating a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device based on the start of the writing process in the image carrier. FIG. 6 is a diagram illustrating a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device in consideration of the structure of the fixing device. FIG. 6 is a diagram for explaining a method for securing a lighting control timing interval for a predetermined time or more in consideration of an electrical problem that occurs when the trailing edge of the transfer medium passes through the nip portion of the fixing device 6. (1) is a diagram for explaining a case where an electrical problem such as flicker occurs, and (2) is a diagram for explaining a case where an electrical problem such as flicker can be prevented by the lighting control of FIG. 17A.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments for carrying out the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a diagram schematically illustrating a configuration of the engine unit 100 of the image forming apparatus according to the present embodiment. FIG. 2A is a schematic diagram illustrating a hardware configuration of an engine control unit 200 that controls the engine unit 100. FIG. 2B is an enlarged view of the CPU 231 of the engine main board (EGB) 23.

The image forming apparatus according to this embodiment forms a full color image by superposing four color toners of yellow (Y), cyan (C), magenta (M), and black (K), or black (K) toner. A monochromatic image is formed by using only a known image forming apparatus.
That is, in FIGS. 1 and 2, the engine unit 100 of the image forming apparatus includes an engine control unit 200 that performs control related to the printing process processing, and is a photosensitive drum that is four image carriers adjacent in the horizontal direction. A photoconductor unit 10 having 10a to 10d, and a photoconductor of yellow (C), cyan (C), and magenta (M) other than the black (K) photoconductor drum 10d in contact with the photoconductor unit 10 in parallel. The intermediate transfer member 5 has a contact / separation mechanism with the drums 10a to 10c.

  The photosensitive unit 10 has a charging device (charging unit) 17 that uniformly charges the surface of the photosensitive drum around the photosensitive drum and image information transmitted from the main controller 300 by electrical communication means. Based on this, a writing unit 18 constituted by a polygon mirror motor 14, an exposure device 15 and the like that irradiates a laser beam to form an electrostatic latent image on the surface of the photosensitive drum, and an electrostatic latent image formed by the writing unit 18. Are developed with toner supplied from toner bottles 1 to 4 and a cleaning device 16 that removes post-transfer toner remaining after transfer onto the intermediate transfer member.

  The image developed by the developing device 11 is transferred onto the intermediate transfer member 5 in contact with the photosensitive drums 10a to 10d of each color, and the paper fed by the paper feeding units 9 and 12 as an image in which the respective colors overlap each other. It is transferred to a transfer medium. The image transferred onto the transfer medium is pressed against the transfer medium by the fixing device 6, and the transfer medium is carried out to the paper discharge unit 22 by the paper discharge device 21. In addition, the image forming apparatus includes a duplex unit 7, and a color or monochrome image is printed on both sides of a sheet as a transfer medium.

  As shown in FIG. 2A, the engine control unit 200 includes a CPU 231 for controlling each part of the engine unit 100 such as the charging device 17 and the fixing device 6, a calculation program executed by the CPU 231, and a control for controlling the engine unit 100. An engine main board (EGB) 23 composed of a ROM 232 for storing data and the like, a RAM 233 for temporarily storing calculation results in the CPU 231 and other data, and a power supply unit (PSU) for controlling power and power ) 13 and an input / output management unit (IOB) 24 and the like.

The electric power from the power supply unit (PSU) 13 is input to the input / output management unit (IOB) 24, distributes the electric power in the input / output management unit (IOB) 24, and each unit of the engine unit 100, for example, a toner bottle 1 to 4 memories (memory chips) 241, each motor 242 such as a polygon mirror motor 14, thermistor 243 that is an electric resistor that reacts to a temperature change, each operation unit panel 244, each sensor 245 such as a position detection sensor 8, The load such as the clutch 246 is controlled.
The engine main board (EGB) 23 is connected to and communicates with a main controller 300 that performs interface (I / F) control with an external device and image processing of data input from the external device through a PCI bus 303. .
As shown in FIG. 2B, the CPU 231 of the engine main board (EGB) 23 includes first determination means 231a and second determination means 231b which are function realizing means realized by a program.

Next, the lighting control of the fixing heater according to the fixing method of the fixing device of the image forming apparatus will be described.
FIG. 3 is a flowchart showing the procedure of the lighting control process of the fixing heater of the fixing device 6.
In the fixing device 6, the ratio of lighting the heater is calculated for each control period of the fixing heater (not shown), and the fixing heater is controlled by switching the fixing heater on / off based on the ratio. . Hereinafter, the timing of performing the lighting control of the fixing heater is referred to as a lighting control timing here.

  In FIG. 3, first, the lighting amount D is calculated (S101). The lighting amount D is a ratio (%) of a period during which the fixing heater is turned on during the next period T (ms). The lighting amount D is calculated by a method of D = 100 when the current fixing temperature is lower than the target temperature and D = 0 when the current fixing temperature is higher, or the fixing temperature at the current lighting control timing and the previous lighting control timing. Various methods are known, such as a method of calculating an appropriate lighting amount D from temperature, target temperature, and the like.

Next, appropriate control (fixing heater on / off) is performed based on the calculated lighting amount D (S103 / S107). That is, when “D = 0%” (S102: YES), the fixing heater is turned off (S107), and the next lighting control timing is awaited (S108). When “D ≠ 0%” (S102: NO), the fixing heater is once turned on (S103). When “D ≠ 0%, D = 100%” (S104: YES), the fixing heater is turned on. While continuing, it waits for the next lighting control timing (S108).
On the other hand, when “D ≠ 0%, D ≠ 100%” (S104: NO), the fixing heater off timing is waited (S105: NO), and the fixing device 6 reaches the target temperature and the fixing heater off timing is reached (S105). : YES), the fixing heater is turned off (S106), and the next lighting control timing is awaited (S108).

Here, the time T (on) for turning on the fixing heater is calculated from the next cycle T (ms) and the lighting amount D (%).
T (on) = T × D ÷ 100
The fixing heater is turned off when T (on) = T × D ÷ 100 (ms) has elapsed from the lighting control timing. The period T (off) during which the fixing heater is turned off is expressed by the following equation.
T (off) = T−T (on) = T × (1− (D ÷ 100))

FIG. 4 is a diagram for explaining the relationship between the lighting control timing and the ON / OFF state of the fixing heater.
As shown in FIG. 4, at the first lighting control timing, “D = 100%”, and the fixing heater is continuously turned on during the next control cycle T (ms). At the next lighting control timing, “D = 50%”, and the fixing heater is turned on for the first T / 2 (ms) of the next control cycle T (ms). Further, the fixing heater is turned off for the remaining T / 2 (ms). Further, at the next lighting control timing, “D = 0%”, and the fixing heater is continuously turned off during the next control period T (ms).

FIG. 5 is a diagram for explaining a situation where a fixing failure (cold offset) occurs due to a difference between the lighting control timing and the timing at which the leading edge of the transfer medium reaches the nip portion of the fixing device 6.
Generally, when the transfer medium is not in contact with the nip portion of the fixing device 6, there is no transfer medium that takes away the heat of the fixing device 6.
When the lighting control shown in FIGS. 3 and 4 is performed, there is no dependency between the lighting control timing and the timing at which the leading edge of the transfer medium reaches the nip portion of the fixing device 6, that is, the timings of both are irrelevant. When the lighting control timing and the timing at which the leading edge of the transfer medium reaches the nip portion of the fixing device 6 are greatly deviated, the timing of the two cannot be adjusted and fixing failure may occur.

In other words, FIG. 5 shows an example in which a fixing failure (cold offset) occurs due to excessively low temperature. In FIG. 5, “the leading edge of the transfer medium between the second lighting control timing and the third lighting control timing” is shown. Represents when the nip portion of the fixing device 6 is reached.
As shown in FIG. 5, at the first lighting control timing, since the temperature of the fixing device 6 is lower than the target temperature, the fixing heater is turned on with the lighting amount D = 100%. Since the fixing heater is turned on, the temperature of the fixing device rises.

At the second lighting control timing, since the temperature of the fixing device 6 is higher than the target temperature, the fixing heater is turned off with the lighting amount D = 0%. Since the fixing heater is turned off, the temperature of the fixing device decreases.
Here, when the transfer medium is in contact with the nip portion of the fixing device 6, the temperature is likely to decrease. Therefore, when the transfer medium reaches the nip portion of the fixing device 6, the temperature drop increases.
At the third lighting control timing, since the temperature of the fixing device 6 is lower than the target temperature, the fixing heater is turned on with the lighting amount D = 100%. However, a large temperature drop occurs due to conveyance of the transfer medium before the fixing heater is turned on at the third lighting control timing, and this temperature drop is large, so that a fixing defect (cold offset) occurs.

FIG. 6 is a diagram for explaining a situation in which fixing failure (hot offset) occurs due to a difference between the lighting control timing and the timing at which the trailing edge of the transfer medium passes through the nip portion of the fixing device 6.
When performing the lighting control in FIGS. 3 and 4, there is no dependency between the lighting control timing and the timing at which the trailing edge of the transfer medium passes through the nip portion of the fixing device 6. When the timing at which the end passes through the nip portion of the fixing device 6 is largely deviated, a fixing defect may occur.

  FIG. 6 shows an example in which fixing failure (hot offset) occurs due to the temperature being too high. In the drawing, when the trailing edge of the transfer medium passes through the nip portion of the fixing device 6 between the first lighting control timing and the second lighting control timing, and the second lighting control timing and the third lighting control. This represents the time when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 during the timing.

As shown in FIG. 6, at the first lighting control timing, since the temperature of the fixing device 6 is lower than the target temperature, the fixing heater is turned on with the lighting amount D = 100%. Since the fixing heater is turned on, the temperature of the fixing device 6 rises. When the transfer medium is not in contact with the nip portion of the fixing device 6, the temperature is likely to rise. Therefore, when the rear end of the transfer medium passes through the nip portion of the fixing device 6, the temperature rise is large.
At the second lighting control timing, since the temperature of the fixing device 6 is higher than the target temperature, the fixing heater is turned off with the lighting amount D = 0%. Since the fixing heater is turned off, the temperature of the fixing device 6 decreases. However, since the temperature has increased too much at this time, it takes time until the temperature decreases.
Thereafter, the leading edge of the next transfer medium reaches the nip portion of the fixing device 6, but a fixing failure (hot offset) occurs because the temperature at this time is high.

FIG. 7A is a flowchart showing a procedure for performing lighting control when the leading edge of the transfer medium of the present embodiment reaches the nip portion, and FIG. 7B prevents fixing failure (cold offset) by the lighting control of FIG. 7A. It is a figure explaining the method to do.
In FIG. 7A, first, the lighting amount D is calculated (S101). Here, the lighting amount D is a ratio (%) of a period during which the fixing heater is turned on during the next period T (ms). Next, based on the calculated lighting amount D (S102), appropriate control (fixing heater on / off) is performed (S103, S107). That is, when “D = 0%” (S102: YES), the fixing heater is turned off (S107), waiting for the next lighting control timing (S108), and when the next lighting control timing is reached (S108: Yes), lighting control of the fixing heater is performed.
On the other hand, in step S108, before the next lighting control timing is reached (S108, NO), if the leading edge of the transfer medium reaches the nip portion of the fixing device 6 (S109: YES), lighting control of the fixing heater is performed at that timing. .

When the result of calculation of the lighting amount in step S102 is “D ≠ 0%” (S102: NO), the fixing heater is once turned on (S103), and when “D ≠ 0%, D = 100%”. (S104: YES), while continuing to turn on the fixing heater, wait for the next lighting control timing (S108).
On the other hand, when “D ≠ 0%, D ≠ 100%” in step S104 (S104: NO), the timing of fixing heater off is waited (S105), and when the fixing device 6 reaches the target temperature and the fixing heater is turned off ( (S105: YES), the fixing heater is turned off (S106), the next lighting control timing is awaited (S108), and when the next lighting control timing is reached (S108: YES), the fixing heater lighting control is performed.
In step S105, before the fixing heater is turned off (S105: NO), when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 (S110: YES), the lighting control of the fixing heater is performed at that timing. Do.

  In this lighting control method, when the leading edge of the transfer medium reaches the nip portion of the fixing device 6, lighting control is performed at that timing. Regarding the next lighting control timing when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 and lighting control is performed at that timing, the leading edge of the transfer medium has reached the nip portion of the fixing device 6. Sometimes, the control cycle T (ms) may have elapsed from the lighting control timing performed at that timing, or the control cycle T from the lighting control timing immediately before the leading edge of the transfer medium reaches the nip portion of the fixing device 6. It may be when (ms) has elapsed.

As a result, as shown in FIG. 7B, the lighting control method described in relation to FIG. 7A is performed, so that the lighting control is performed at the timing when the leading edge of the transfer medium reaches the nip portion of the fixing device 6. Since the switch turns on, it is possible to prevent a rapid temperature drop and to prevent the occurrence of fixing failure (cold offset).
7B, when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 between the second lighting control timing and the third lighting control timing in FIG. 5, the lighting control method of FIG. The temperature change when the lighting is performed is indicated by a solid line, and the temperature change when the lighting control method is not performed is indicated by a dotted line.

FIG. 8A is a flowchart illustrating a procedure for performing lighting control when the trailing edge of the transfer medium of the present embodiment passes through the nip portion. FIG. 8B illustrates a fixing failure (hot offset) due to the lighting control of FIG. 8A. It is a figure explaining the method to prevent.
In FIG. 8A, first, the lighting amount D is calculated (S101). Here, the lighting amount D is a ratio (%) of a period during which the fixing heater is turned on during the next period T (ms). Next, based on the calculated lighting amount D (S102), appropriate control (fixing heater on / off) is performed (S103, S107). That is, when “D = 0%” (S102: YES), the fixing heater is turned off (S107), waiting for the next lighting control timing (S108), and when the next lighting control timing is reached (S108: Yes), lighting control of the fixing heater is performed. On the other hand, in step S108, before the next lighting control timing is reached (S108, NO), if the rear end of the transfer medium passes through the nip portion of the fixing device 6 (S109 ′: YES), the lighting control of the fixing heater is performed at that timing. I do.
When the result of calculation of the lighting amount in step S102 is “D ≠ 0%” (S102: NO), the fixing heater is once turned on (S103), and when “D ≠ 0%, D = 100%”. (S104: YES), while continuing to turn on the fixing heater, wait for the next lighting control timing (S108).

On the other hand, if “D ≠ 0%, D ≠ 100%” in step S104 (S104: NO), the timing of fixing heater off is waited (S105), and the fixing device 6 reaches the target temperature and the fixing heater is turned off. (S105: YES), the fixing heater is turned off (S106), the next lighting control timing is awaited (S108), and when the next lighting control timing comes (S108: YES), lighting control of the fixing heater is performed.
In step S105, before the fixing heater is turned off (S105, NO), if the rear end of the transfer medium passes through the nip portion of the fixing device 6 (S110 ′: YES), the fixing heater is turned on at that timing. Take control.

  In this lighting control method, lighting control is performed when the rear end of the transfer medium passes through the nip portion of the fixing device 6. When the lighting control is performed after the rear end of the transfer medium passes through the nip portion of the fixing device 6, the next lighting control timing is as follows when the rear end of the transfer medium passes through the nip portion of the fixing device 6. The control period T (ms) may have elapsed from the lighting control timing performed, or the control period T (ms) has elapsed from the lighting control timing immediately before the trailing edge of the transfer medium passes through the nip portion of the fixing device 6. Sometimes.

As a result, as shown in FIG. 8B, the lighting control method described with reference to FIG. 7A is performed, so that the lighting control is performed at the timing when the rear end of the transfer medium passes through the nip portion of the fixing device 6. Since the heater is turned off, it is possible to prevent an abrupt increase in temperature and to prevent the occurrence of fixing failure (hot offset).
8B, when the trailing edge of the transfer medium passes through the nip portion of the fixing device 6 between the second lighting control timing and the third lighting control timing in FIG. A temperature change when the method is performed is indicated by a solid line, and a temperature change when the lighting control method is not performed is indicated by a dotted line.

FIG. 9 is a diagram illustrating a method for determining that the leading edge of the transfer medium has reached the nip portion of the fixing device 6 based on the start of conveyance from the registration rollers.
FIG. 9 shows a method for determining that the leading edge of the transfer medium shown in FIG. 7A has reached the nip portion of the fixing device 6 based on the start of conveyance of the transfer medium from the registration roller. Since the transfer medium reaches the nip portion of the fixing device 6 without stopping after the transfer from the registration roller is started, the distance from the registration roller to the nip portion of the fixing device 6 is d1 (mm), and the conveyance speed. Is V (mm / ms), the time T1 (ms) from the start of conveyance of the transfer medium from the registration roller to the arrival at the nip portion can be expressed by the following equation.
T1 = d1 ÷ V

  Using the above formula, it is possible to determine whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device 6 in the flowchart of FIG. 7A. That is, the timing when T1 = d1 ÷ V (ms) has elapsed after the transfer medium starts to be conveyed from the registration roller is the timing when the leading edge of the transfer medium reaches the nip portion of the fixing device 6, and lights at this timing. What is necessary is just to implement control.

FIG. 10 is a diagram illustrating a method for determining that the leading edge of the transfer medium has reached the nip portion of the fixing device 6 based on the start of the writing process by the writing unit 18 in the image carrier.
FIG. 10 shows a method of determining that the leading edge of the transfer medium in FIG. 7A has reached the nip portion of the fixing device 6 based on the start of the writing process in the image carrier, and the writing start in FIG. The position represents the leading end position of the transfer medium when the writing process is started. The start of the writing process is to start creating an electrostatic latent image on the photosensitive drum.
When the writing process is started, the writing process is not stopped unless an abnormality occurs. Therefore, the distance from the writing start position to the nip portion of the fixing device 6 is d2 (mm), and the conveyance speed is V (mm / ms). Then, the time T2 (ms) from the start of the writing process until the transfer medium reaches the nip portion can be expressed by the following equation.
T2 = d2 ÷ V

Using the above formula, it is possible to determine whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device 6 in the flowchart of FIG. 7A. That is, the timing at which T2 = d2 ÷ V (ms) has elapsed since the start of the writing process is the timing at which the leading edge of the transfer medium has reached the nip portion of the fixing device 6, and lighting control may be performed at this timing. .

  9 and 10 can be used to determine that the leading edge of the transfer medium has reached the nip portion of the fixing device 6, but lighting control is performed at the timing when the leading edge of the transfer medium arrives. It is necessary to accurately determine that the leading edge of the transfer medium has arrived. As a factor that causes the determination to vary, slipping of the transfer medium may be considered. Therefore, in order to increase the accuracy of the determination, it is effective to make a determination based on a position closer to the nip portion of the fixing device 6.

  Further, since the distances d1 and d2 described above vary depending on the configuration of the image forming apparatus, when the distance d1 ≦ d2 (or d1 <d2) is satisfied, the determination based on the start of conveyance from the registration rollers shown in FIG. When the distance d1> d2 (or d1 ≧ d2) is satisfied, the determination based on the start of the writing process in the image carrier shown in FIG. 10 may be used.

FIG. 11 is a diagram illustrating a method for determining that the leading edge of the transfer medium has reached the nip portion of the fixing device 6 in consideration of the structure of the fixing device 6.
In FIGS. 9 and 10 described above, the lighting control is performed when the leading edge of the transfer medium reaches the nip portion of the fixing device 6. However, after the lighting control is performed due to the difference in the structure of the fixing device 6. There may be a delay before it is reflected in the temperature of the nip.

For example, in the example shown in FIG. 11, the fixing device 6 has the heater portion and the nip portion connected by a belt, and the heater portion and the nip portion of the fixing device 6 have a certain distance, so the lighting control is performed. After that, there is a delay from when it is reflected in the temperature of the nip. Assuming that the distance between the heater part and the nip part is d3 (mm), the time T3 (ms) from when the lighting control is performed until it is reflected in the temperature of the nip part is as follows.
T3 = d3 / V
Therefore, in the case of the fixing device 6 having the above-described structure, the time T1 from when conveyance of the transfer medium is started from the registration roller to when lighting control is performed (assuming that the nip portion of the fixing device 6 has been reached). '(Ms) is
T1 '= T1-T3
= (D1-d3) / V
The time T2 ′ (ms) from the start of the writing process until the lighting control is performed (assuming that the nip portion of the fixing device 6 has been reached)
T2 '= T2-T3
= (D2-d3) / V
And it is sufficient.

  FIG. 12A is a flowchart illustrating a procedure of a method for securing a lighting control timing interval for a certain time or more in consideration of an electrical problem that occurs when the leading edge of the transfer medium reaches the nip portion of the fixing device 6. 12B (1) is a diagram illustrating a case where an electrical problem such as flicker occurs, and FIG. 12B (2) is a diagram illustrating a case where an electrical problem such as flicker can be prevented by the lighting control of FIG. 12A.

  In FIG. 7A described above, the lighting control is performed at the timing when the leading edge of the transfer medium reaches the nip portion of the fixing device 6. However, this is performed when the leading edge of the transfer medium reaches the nip portion of the fixing device 6. When the interval between the lighting control and the timing of the lighting control performed immediately before is shortened, an electrical problem such as flicker may occur.

Therefore, when the lighting control is performed at a certain lighting control timing, the time until the leading edge of the next transfer medium reaches the nip portion of the fixing device 6 is calculated, and the calculated time is a predetermined time Tmin (ms). If it is less than this, the above-mentioned problem can be solved by extending the lighting control timing until the leading edge of the transfer medium reaches the nip portion of the fixing device 6 without performing the lighting control at this lighting control timing. it can.
The flowchart of FIG. 12A shows the solution procedure.
Here, the time Tmin (ms) is a value determined in advance based on experiments and evaluations that there is no electrical problem such as flicker, and is stored in the ROM 232 area, for example.

  In FIG. 12A, first, the lighting amount D is calculated (S101). Here, the lighting amount D is a ratio (%) of a period during which the fixing heater is turned on during the next period T (ms). Next, based on the calculated lighting amount D (S102), appropriate control (fixing heater on / off) is performed (S103, S107). That is, when “D = 0%” (S102: YES), the fixing heater is turned off (S107), waiting for the next lighting control timing (S108), and when the next lighting control timing is reached (S108: Yes), the time until the leading edge of the transfer medium reaches the nip portion of the fixing device 6 (that is, the time until the lighting control timing performed when the leading edge of the transfer medium reaches the nip portion of the fixing device 6) is determined in advance. It is determined whether or not the time is less than the predetermined time Tmin (ms) (S111). When the time is less than the predetermined time Tmin (ms) (S111: YES), the lighting control is performed at the next lighting control timing. Without waiting for the leading edge of the transfer medium to reach the nip portion of the fixing device 6 (S109), the lighting control is performed at the timing when the leading edge of the transfer medium reaches the nip portion (S109).

In step S108, before the next lighting control timing (S108, NO), when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 (S109: YES), lighting control of the fixing heater is performed at that timing.
In step S111, when the time of the fixing heater until the leading edge of the transfer medium reaches the nip portion of the fixing device 6 is equal to or longer than a predetermined time Tmin (ms) (S111: NO), lighting control is performed. .

When the result of calculation of the lighting amount in step S102 is “D ≠ 0%” (S102: NO), the fixing heater is once turned on (S103), and when “D ≠ 0%, D = 100%”. (S104: YES), while continuing to turn on the fixing heater, wait for the next lighting control timing (S108).
On the other hand, when “D ≠ 0%, D ≠ 100%” in step S104 (S104: NO), the timing of fixing heater off is waited (S105), and when the fixing device 6 reaches the target temperature and the fixing heater is turned off ( (S105: YES), the fixing heater is turned off (S106), and the next lighting control timing is awaited (S108).
In step S105, before the fixing heater is turned off (S105: NO), when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 (S110: YES), lighting control of the fixing heater is performed at that timing.

12B (1) is a diagram illustrating a case where an electrical problem such as flicker occurs, and FIG. 12B (2) is a diagram illustrating a case where an electrical problem such as flicker can be prevented by the lighting control of FIG. 12A.
In FIG. 12B (1), the interval between the timing of the lighting control performed when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 and the timing of the lighting control performed immediately before is T ′ (ms). This is an example.
When the interval T ′ (ms) satisfies the interval T ′ <Tmin, an electrical problem such as flicker may occur.

  In such a case, by performing the lighting control method shown in FIG. 12A, the timing of the lighting control performed when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 as shown in FIG. 12B (2). And the interval from the timing of the lighting control performed immediately before is T + T ′ (ms), so that it is possible to prevent the occurrence of electrical problems such as flicker.

FIG. 13 is a diagram illustrating a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 with reference to the position detection sensor 8 being off.
FIG. 13 shows a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 based on the OFF of the position detection sensor 8 in the flowchart of FIG. 8A. When the distance from the position of the position detection sensor 8 closest to the nip portion to the nip portion is d4 (mm) and the conveyance speed is V (mm / ms). A time T4 (ms) from when the position detection sensor 8 is turned off until it passes through the nip portion can be expressed by the following equation.
T4 = d4 / V

  Using the above equation, it can be determined whether or not the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 in the flowchart of FIG. 8A. That is, at the timing when T4 = d4 ÷ V (ms) has elapsed since the detection of the position detection sensor 8 and the trailing edge of the transfer medium has passed the position detection sensor 8, the trailing edge of the transfer medium is fixed. It is the timing when the nip portion of the device 6 is passed, and the lighting control may be performed at this timing.

FIG. 14 is a diagram illustrating a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 with reference to the start of conveyance from the registration rollers.
In FIG. 13, the method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 with reference to the position detection sensor 8 turned off has been described. However, the position detection sensor 8 is changed from on to off. When a lot of chattering occurs at the time of change, it takes time from when the trailing edge of the transfer medium actually passes the position of the position detection sensor 8 until the detection of the position detection sensor 8 is turned off. It may be impossible to accurately determine that the rear end has passed through the nip portion of the fixing device 6.
In such a case, as shown in FIG. 14, the fact that the trailing edge of the transfer medium as shown in FIG. 8A has passed through the nip portion of the fixing device 6 is based on the start of conveyance of the transfer medium from the registration roller. Judgment can be made.

After the conveyance of the transfer medium from the registration roller is started, the transfer medium passes through the nip portion of the fixing device 6 without stopping. Therefore, the distance from the registration roller to the nip portion of the fixing device 6 is d1 (mm), Assuming that the transfer medium length is x (mm) and the conveyance speed is V (mm / ms), the time T5 (ms) from the start of conveyance of the transfer medium from the registration roller until the trailing edge passes through the nip portion. Can be expressed by the following equation.
T5 = (d1 + x) ÷ V

  Using the above formula, it can be determined whether or not the trailing edge of the transfer medium as shown in FIG. 8A has passed through the nip portion of the fixing device 6. That is, the timing at which T5 = (d1 + x) ÷ V (ms) has elapsed after the transfer medium starts to be conveyed from the registration roller is the timing at which the trailing edge of the transfer medium passes through the nip portion of the fixing device 6. The lighting control may be performed at the timing.

FIG. 15 is a diagram illustrating a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 with reference to the start of the writing process in the image carrier.
The method for determining that the rear end of the transfer medium has passed through the nip portion of the fixing device 6 with reference to the position detection sensor 8 in FIG. When a lot of chattering occurs when changing to OFF, it takes time until the position detection sensor 8 is detected to be off after the trailing edge of the transfer medium actually passes the sensor position. May not accurately determine that the toner has passed through the nip portion of the fixing device.
In such a case, as shown in FIG. 15, in the flowchart of FIG. 8A, the fact that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 indicates that the writing process by the writing unit 18 in the image carrier is started. It can also be judged on the basis of standards.

When the writing process on the image carrier is started, the writing process is not stopped unless an abnormality occurs. Therefore, the distance from the writing start position to the nip portion of the fixing device 6 is d2 (mm), and the transfer medium length is set. When x (mm) and the conveyance speed are V (mm / ms), the time T6 (ms) from the start of the writing process until the trailing edge of the transfer medium passes through the nip portion is expressed by the following equation. Can be represented.
T6 = (d2 + x) ÷ V

  Using the above formula, it can be determined whether or not the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 as shown in FIG. 8A. That is, the timing when T6 = (d2 + x) ÷ V (ms) has elapsed since the start of the writing process is the timing when the trailing edge of the transfer medium passes through the nip portion of the fixing device 6, and lighting control is performed at this timing. do it.

Although any of the determination methods of FIGS. 13 to 15 can be used, it can be determined that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6, but lighting control is performed at the timing when the trailing edge of the transfer medium has passed. In some cases, it is necessary to accurately determine that the trailing edge of the transfer medium has passed. As a factor that causes the determination to vary, slipping of the transfer medium may be considered. Therefore, in order to increase the accuracy of the determination, it is effective to make a determination based on a position closer to the nip portion of the fixing device 6.
When the chattering of the position detection sensor 8 is small, a determination method as shown in FIG. 13 may be used. When the chattering of the position detection sensor 8 is large, the distance to the nip portion is d1 ≦ d2 (or d1 <d2). 14 is used, and when the distance to the nip portion is d1> d2 (or d1 ≧ d2), the determination shown in FIG. 15 may be used.

FIG. 16 is a diagram illustrating a method for determining that the trailing edge of the transfer medium has passed through the nip portion of the fixing device 6 in consideration of the structure of the fixing device 6.
In FIG. 13 to FIG. 15 described above, the lighting control is performed at the timing when the rear end of the transfer medium passes through the nip portion of the fixing device 6. However, the lighting control is performed depending on the structure of the fixing device 6. In some cases, a delay may occur before the temperature is reflected in the nip temperature.

For example, as shown in FIG. 16 (same as the structure described in FIG. 11), the fixing device 6 has a heater portion and a nip portion connected by a belt, and the fixing device 6 has a constant position at the heater portion and the nip portion. Therefore, there is a delay from when the lighting control is performed until it is reflected in the temperature of the nip portion. Assuming that the distance between the heater part and the nip part is d3 (mm), the time T3 (ms) from when the lighting control is performed until it is reflected in the temperature of the nip part is as shown in FIG.
T3 = d3 / V
It becomes.

Therefore, in the case of the fixing device 6 having such a structure, the time T4 from when the position detection sensor 8 is turned off until the lighting control is performed (assuming that the rear end of the transfer medium has passed through the nip portion of the fixing device). '(Ms) is
T4 '= T4-T3
= (D4-d3) / V
And it is sufficient. Also, the time T5 ′ (ms) from the start of conveyance of the transfer medium from the registration roller until the lighting control is performed (assuming that the rear end of the transfer medium has passed through the nip portion of the fixing device 6) is:
T5 '= T5-T3
= (D1 + x-d3) / V
The time T6 ′ (ms) from the start of the writing process until the lighting control is performed (assuming that the rear end of the transfer medium has passed through the nip portion of the fixing device 6)
T6 '= T6-T3
= (D2 + x-d3) / V
And it is sufficient.

  Here, T4 is the time from when the position detection sensor 8 is turned off until the trailing edge of the transfer medium passes through the nip portion (FIG. 13), and T5 starts conveyance of the transfer medium from the registration roller. Is the time from when the trailing edge of the point transfer medium passes through the nip (FIG. 14), and T6 is the time from the start of the writing process until the trailing edge of the transfer medium passes through the nip. (FIG. 15).

FIG. 17A is a diagram for explaining a method of securing a lighting control timing interval for a certain time or more in consideration of an electrical problem that occurs when the trailing edge of the transfer medium passes through the nip portion of the fixing device 6. 17B (1) is a diagram illustrating a case where an electrical problem such as flicker occurs, and FIG. 17B (2) is a diagram illustrating a case where an electrical problem such as flicker can be prevented by the lighting control of FIG. 17A.
In FIG. 8A described above, the lighting control is performed at the timing when the rear end of the transfer medium passes through the nip portion of the fixing device 6. However, the control is performed at the timing at which the rear end of the transfer medium passes through the nip portion of the fixing device 6. When the interval between the lighting control performed and the timing of the lighting control performed immediately before it becomes short, an electrical problem such as flicker may occur.

Therefore, in this embodiment, the time until the trailing edge of the transfer medium passes through the nip portion of the fixing device 6 is calculated at a timing when certain lighting control is performed, and the calculated time is a predetermined time Tmin (ms). If it is less than the above, the lighting control is not performed at this lighting control timing, and the above-mentioned problem is solved by extending the lighting control timing until the leading edge of the transfer medium reaches the nip portion of the fixing device 6. .
The flowchart of FIG. 17A shows the solution procedure.
Here, the time Tmin (ms) is a value determined in advance based on experiments and evaluations that there is no electrical problem such as flicker, and is stored in the ROM 232 area, for example.

  In FIG. 17A, first, the lighting amount D is calculated (S101). Here, the lighting amount D is a ratio (%) of a period during which the fixing heater is turned on during the next period T (ms). Next, based on the calculated lighting amount D (S102), appropriate control (fixing heater on / off) is performed (S103, S107). That is, when “D = 0%” (S102: YES), the fixing heater is turned off (S107), waiting for the next lighting control timing (S108), and when the next lighting control timing is reached (S108: Yes), the time until the rear end of the transfer medium passes through the nip portion of the fixing device 6 (that is, the time until the lighting control timing performed when the rear end of the transfer medium reaches the nip portion of the fixing device 6). It is determined whether or not the time is less than a predetermined time Tmin (s) (S111 ′), and a time until the rear end of the transfer medium passes through the nip portion of the fixing device 6 is determined as a predetermined time Tmin ( If it is less than s) (S111 ′: YES), the lighting control is not performed at the next timing, and the process waits for the rear end of the transfer medium to pass through the nip portion of the fixing device 6 (S109 ′).

In step S111 ′, when the time until the trailing edge of the transfer medium passes through the nip portion of the fixing device 6 is equal to or longer than a predetermined time Tmin (s) (S111 ′: NO), the fixing heater lighting control is performed. I do.
On the other hand, if the rear end of the transfer medium passes through the nip portion of the fixing device 6 (S109 ′: YES) before the lighting control timing is reached in step S108 (S109 ′: YES), the fixing heater lighting control is performed at that timing. I do.

  When the result of calculation of the lighting amount in step S102 is “D ≠ 0%” (S102: NO), the fixing heater is once turned on (S103), and when “D ≠ 0%, D = 100%”. (S104: YES), while continuing to turn on the fixing heater, wait for the next lighting control timing (S108).

On the other hand, if “D ≠ 0%, D ≠ 100%” in step S104 (S104: NO), the timing of fixing heater off is waited (S105), and the fixing device 6 reaches the target temperature and the fixing heater is turned off. (S105: YES), the fixing heater is turned off (S106), and the next lighting control timing is awaited (S108).
In step S105, before the fixing heater is turned off (S105, NO), if the rear end of the transfer medium passes through the nip portion of the fixing device 6 (S110 ′: YES), the lighting control of the fixing heater is performed at that timing. Do.

FIG. 17B (1) shows that an electrical problem such as flicker occurs, and FIG. 17B (2) shows that an electrical problem such as flicker can be prevented by implementing the lighting control method shown in FIG. 17A. FIG. 17B (1) shows the method, and the interval between the lighting control timing performed when the trailing edge of the transfer medium passes through the nip portion of the fixing device 6 and the lighting control timing performed immediately before the timing. Represents an example in which time T ′ (ms) is reached. When this time T ′ (ms) satisfies T ′ <Tmin, an electrical problem such as flicker may occur.
In such a case, by performing the lighting control method of FIG. 17A, the timing of the lighting control performed when the rear end of the transfer medium passes through the nip portion of the fixing device 6 as shown in FIG. Since the interval from the timing of the lighting control performed immediately before is T + T ′ (ms), the occurrence of electrical problems such as flicker can be prevented.

In the embodiment described above, the first determination means for determining whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device 6, and the trailing edge of the transfer medium has passed the nip portion of the fixing device 6. Each of the second determining means for determining whether or not the function is a function realizing means that can be obtained by executing the program by the CPU 231 of the image forming apparatus. The CPU 231 also performs lighting control of the fixing heater as a similar function realizing unit.
When the first determination means determines that the leading edge of the transfer medium has reached the nip portion of the fixing device 6, or the second determination means determines that the trailing edge of the transfer medium is the nip of the fixing device 6. If it is determined that the image has passed through the section, the lighting control of the fixing heater is controlled even if it is not at the timing of the fixing heater control cycle, and the transfer medium is fixed even when the control cycle of the fixing heater deviates from the transfer timing of the transfer medium. The temperature at which the nip portion of the apparatus 6 is conveyed can be kept appropriate.

That is, the determination by the first determination unit or the second determination unit is performed based on the elapsed time from the start of conveyance of the transfer medium from the registration roller or the elapsed time from the start of the writing process on the image carrier. This makes it possible to reliably determine that the leading edge of the transfer medium has reached the nip portion of the fixing device 6 or that the trailing edge of the transfer medium has passed the nip portion of the fixing device 6.
Also, the position detection sensor closest to the fixing device 6 is located upstream of the fixing position (on the paper feeding unit side) in the position detection sensor 8 for detecting the transport position. By performing on the basis of the elapsed time since the detection of the trailing edge of the transfer medium 8, it can be determined more reliably that the trailing edge of the transfer medium has passed the nip portion of the fixing device 6.

Further, the determination by the first determination means or the second determination means is performed in consideration of the structure of the fixing device 6, that is, when the positions of the fixing heater and the nip portion are different. Is performed assuming that the leading edge of the transfer medium has reached the nip portion of the fixing device 6, or before the trailing edge of the transfer medium passes through the nip portion of the fixing device 6. The fixing device having a structure in which there is a possibility that there is a delay from the time when the lighting control is performed until the temperature change is reflected in the nip portion of the fixing device 6 by assuming that the nip portion of the fixing device 6 has passed. 6, the temperature change at the timing when the lighting control is performed is the timing when the leading edge of the transfer medium reaches the nip portion of the fixing device 6 and the timing when the trailing edge of the transfer medium passes through the nip portion of the fixing device 6. Reflect Rukoto can.
Also, the position detection sensor closest to the fixing device 6 is located upstream of the fixing position (on the paper feeding unit side) in the position detection sensor 8 for detecting the transport position. By performing based on the elapsed time after the trailing edge 8 detects the trailing edge of the transfer medium, it can be reliably determined that the trailing edge of the transfer medium has passed the nip portion of the fixing device 6.

  Further, when the lighting control time interval is shorter than a certain time interval, the lighting control immediately before the leading edge of the transfer medium reaches the nip portion of the fixing device 6 or the trailing edge of the transfer medium is the nip portion of the fixing device 6. By not performing the lighting control immediately before passing through, it is possible to prevent the occurrence of electrical problems such as flicker.

  DESCRIPTION OF SYMBOLS 1-4 ... Toner bottle, 5 ... Intermediate transfer body, 6 ... Fixing device, 7 ... Duplex unit, 8 ... Position detection sensor, 9 ... Paper feed part, 10 ... Photosensitive unit, 11 ... developing device, 12 ... feeding unit, 13 ... PSU, 14 ... polygon mirror motor, 15 ... exposure device, 16 ... cleaning device, 17. ..Charging device, 18... Writing unit, 21.

JP 2004-198535 A

Claims (13)

In an image forming apparatus that transfers a toner image formed on an image carrier to a transfer medium, and switches the fixing heater on / off at a predetermined lighting control timing to fix the transfer medium.
First determination means for determining whether the leading edge of the transfer medium has reached the nip portion of the fixing device and / or determining whether the trailing edge of the transfer medium has passed through the nip portion of the fixing device A second determination means for
When the first determination unit determines that the leading edge of the transfer medium has reached the nip portion of the fixing device, the second determination unit performs lighting control of the fixing heater regardless of the lighting control timing. When it is determined that the rear end of the transfer medium has passed through the nip portion of the fixing device, the lighting control of the fixing heater is performed regardless of the lighting control timing. The image forming apparatus according to claim 1,
The first determination means determines whether the leading edge of the transfer medium has reached the nip portion of the fixing device, and calculates the arrival time to the nip portion based on the start of conveyance of the transfer medium from the registration roller. And an image forming apparatus. The image forming apparatus according to claim 1,
The first determination means determines whether the leading edge of the transfer medium has reached the nip portion of the fixing device by calculating the arrival time to the nip portion based on the start of the writing process in the image carrier. An image forming apparatus. The image forming apparatus according to claim 1,
Provided with a plurality of position detection sensors installed along the transfer path of the transfer medium to detect the transfer position of the transfer medium;
The first determination means determines whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device. Among the position detection sensors, a position detection sensor closest to the fixing device is located upstream of the fixing device. An image forming apparatus comprising: calculating an arrival time to a nip portion based on a timing at which a leading edge of a transfer medium is detected. The image forming apparatus according to claim 2,
When the fixing heater and the nip portion of the fixing device are spaced apart from each other, the first determination unit determines whether or not the leading end of the transfer medium has reached the nip portion of the fixing device. A delay time until the heater-on is reflected in the nip portion is calculated, and it is determined that the transfer medium is subtracted from the calculated arrival time to the nip portion before the delay time. Image forming apparatus. The image forming apparatus according to any one of claims 1 to 5,
Based on the predetermined lighting control timing, a time until the leading edge of the transfer medium reaches the nip portion of the fixing device at the timing is calculated, and when the calculated time is less than a predetermined time, the lighting control timing The image forming apparatus is characterized in that the lighting control timing is extended until the leading edge of the transfer medium reaches the nip portion of the fixing device without performing the lighting control in the above. The image forming apparatus according to claim 1,
The second determination means determines whether or not the rear end of the transfer medium has passed through the nip portion of the fixing device, and the time until the transfer medium passes through the nip portion based on the start of conveyance from the registration roller. An image forming apparatus characterized in that the calculation is performed. The image forming apparatus according to claim 1,
The second determination means determines whether or not the rear end of the transfer medium has passed through the nip portion of the fixing device by calculating a time until the nip portion passes through the writing process on the image carrier. An image forming apparatus. The image forming apparatus according to claim 1,
Provided with a plurality of position detection sensors installed along the transfer path of the transfer medium to detect the transfer position of the transfer medium;
The second determination means determines whether or not the rear end of the transfer medium has passed through the nip portion of the fixing device, and among the position detection sensors, a position detection sensor closest to the fixing device is located upstream of the fixing device. An image forming apparatus characterized in that it calculates and calculates a time until it passes through a nip portion based on a timing at which a trailing edge of a transfer medium is detected. The image forming apparatus according to any one of claims 7 to 9,
When the fixing heater and the nip portion of the fixing device are spaced apart from each other, the second determination means determines whether or not the rear end of the transfer medium has passed through the nip portion of the fixing device. A delay time until the heater-on is reflected in the nip portion is calculated, and it is determined that the transfer medium is subtracted from the calculated time until it passes through the calculated nip portion before the delay time. An image forming apparatus. The image forming apparatus according to any one of claims 1 and 7 to 10,
Based on the predetermined lighting control timing, a time until the trailing edge of the transfer medium passes through the nip portion of the fixing device at the timing is calculated, and when the calculated time is less than a predetermined time, the lighting control is performed. An image forming apparatus characterized in that the lighting control timing is extended until the trailing edge of the transfer medium passes through the nip portion of the fixing device without performing the lighting control at the timing. A fixing method in an image forming apparatus that transfers a toner image formed on an image carrier onto a transfer medium, switches a fixing heater on / off at a predetermined lighting control timing, and fixes the transfer medium.
A first determination step for determining whether or not the leading edge of the transfer medium has reached the nip portion of the fixing device and / or whether or not the trailing edge of the transfer medium has passed the nip portion of the fixing device Including a second determination step,
In the first determination step, when it is determined that the leading edge of the transfer medium has reached the nip portion of the fixing device, lighting control of the fixing heater is performed regardless of the timing of the cycle, and the second determination is performed. In the process, when it is determined that the rear end of the transfer medium has passed through the nip portion of the fixing device, the lighting control of the fixing heater is performed regardless of the lighting control timing. A computer of an image forming apparatus that transfers a toner image formed on an image carrier to a transfer medium, switches the fixing heater on / off at a predetermined lighting control timing, and fixes the transfer medium.
First determination means for determining whether the leading edge of the transfer medium has reached the nip portion of the fixing device and / or determining whether the trailing edge of the transfer medium has passed through the nip portion of the fixing device A second judging means for
When it is determined that the leading edge of the transfer medium has reached the nip portion of the fixing device, the first determination unit that performs lighting control of the fixing heater regardless of the timing of the cycle;
When it is determined that the rear end of the transfer medium has passed through the nip portion of the fixing device, the transfer medium functions as the second determination unit that performs lighting control of the fixing heater regardless of the lighting control timing. Program to do.

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