JPH11202672A - Heat fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To surely control a fixing roll to be at specified temperature before recording paper passes after a printing instruction is given and to shorten time required before the recording paper passes as much as possible. SOLUTION: This device is provided with a fixing member 2 which is the device to fix an unfixed toner image T on the recording paper and incorporates a heating element 1, a pressing member 3 pressing the recording paper P, a heating degree detecting means 4 measuring the surface temperature H1 of the fixing member 2 and a heating controlling means 5 starting the energizing of the heating element l by waiting for the printing instruction, and also is provided with a cooling degree detecting means 6 measuring the surface temperature P1 of the pressing member 3 when the printing instruction is given, a turning timing deciding means 7 deciding the surface temperature D1 of the fixing member 2 to start the turning of the fixing member 2 and the pressing member 3 by using the temperature P1 measured, a comparing means 8 comparing two kinds of the surface temperature H1 and D1 and a turning controlling means 9 starting the fixing means 2 and the pressing member 3 to turn at the time of judging that the surface temperature H1 is raised to the surface temperature D1 when the surface temperature H1 is lower than the surface temperature D1.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an unfixed toner image transferred on a recording sheet having a toner image formed in an image forming section between a heating and fixing member and a pressing member. More particularly, the present invention relates to an improvement in an apparatus of a type that heats the heat-fixing member after waiting for a print start command to the image forming section after fixing the heat-fixing member on the recording sheet.

[0002]

2. Description of the Related Art Conventionally, as a heat fixing device, a heat fixing roll having a built-in heating element such as a halogen lamp, a pressure roll pressed against the heat fixing roll, Heating control means for controlling the surface temperature of the heat-fixing roll to a predetermined set temperature, and the recording sheet carrying an unfixed toner image is inserted between the heat-fixing roll and the pressure roll, whereby the heating is performed. There is a known configuration in which a toner softened by the surface temperature of a fixing roll penetrates between fibers of a recording sheet, and such an unfixed toner image is firmly fixed to the recording sheet.

By the way, this type of heat fixing device incorporated in an image forming apparatus such as an electrophotographic copying machine or a laser beam printer forms a toner image so that copying or printing can be performed immediately without waiting for a user. Even in a standby state where the image forming unit is not actually operating, as long as the main power supply of the image forming apparatus is turned on, the heat fixing roll is heated to a predetermined fixing control temperature in a mainstream. there were. However, such as printers for small personal computers,
A relatively low-speed and small-sized image forming apparatus is used less frequently, and the standby time is longer than the actual image forming operation. Only wasted power was wasted.

Therefore, in recent years, energization of the heater is started in accordance with a print start command to the image forming unit, and the heating / fixing roll is heated to a predetermined fixing control temperature every time a copy job or a print job is input. A so-called on-demand type heat fixing device is proposed (Japanese Patent Laid-Open No. 5-165368).

In this on-demand type heat fixing device, the heat fixing roll is heated from the time when a print start command is issued to the image forming unit, thereby preventing the occurrence of a defectively recorded image. From the point of view,
When the recording sheet carrying the toner image is actually inserted into the heat fixing device, it is important that the surface temperature of the heat fixing roll is maintained at a predetermined fixing control temperature, and an instruction to start printing is given. From the viewpoint of shortening the waiting time of the user, it is important to insert the first recording sheet into the heat fixing device in as short a time as possible after the power supply to the heater is started.

For this reason, in the heat fixing device disclosed in Japanese Patent Application Laid-Open No. 9-218608, when a print start command is issued to the image forming unit, first, after the power supply to the heater is started, the surface temperature of the heat fixing roll is increased. The transfer timing of the recording sheet in the image forming unit so that the recording sheet can be immediately inserted into the heat fixing device when the heat fixing roll is expected to reach a predetermined fixing control temperature. Was stipulated.

[0007]

However, even if the surface temperature of the heating / fixing roll is steadily rising to a predetermined temperature after the start of energization of the heater, the pressing roll in contact with the heating / fixing roll. Is not heated at all, depending on the surface temperature of the pressure roll at the start of energization, if the rotation of the heat fixing roll and the pressure roll is started before the recording sheet is inserted, the amount of heat on the surface of the heat fixing roll May be taken away by the pressure roll.

For this reason, if the drive start timing of the heat fixing roll and the pressure roll and the conveyance timing of the recording sheet are specified only by taking into account only the temperature rising speed of the heat fixing roll, the rotation of these rolls is started. Immediately after, the surface temperature of the heat fixing roll becomes unstable, for example, the surface temperature of the heat fixing roll suddenly decreases, and when the recording sheet enters the heat fixing device, the surface temperature of the heat fixing roll reaches the fixing control temperature. The worst situation that does not occur occurs.

Particularly, in an image forming apparatus having a high copy speed or a high print speed, the peripheral speeds of the heat-fixing roll and the pressure roll are high. The amount of heat taken per unit time from the roll to the pressure roll also increased, and such a problem occurred remarkably.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and it is an object of the present invention until a first recording sheet is inserted after a print start command is issued to an image forming unit. An on-demand type heat fixing device capable of reliably controlling the heat fixing roll to a predetermined fixing control temperature and shortening the time until the recording sheet is inserted as much as possible. It is to provide a device.

[0011]

That is, as shown in FIG. 1, according to the present invention, an unfixed toner image T formed on a recording sheet P in an image forming section (IOT) is heated to fix the unfixed toner image T to the recording sheet P. A fixing device that includes a heating element 1 that rotates with a heating element 1 built therein, a pressure member 3 that rotates with the recording sheet P sandwiched between the heating and fixing member 2, Heating degree detecting means 4 for measuring the surface temperature of 2
And a heating control unit 5 that waits for a print start command to the image forming unit (IOT) and starts energization of the heating element 1.
A cooling degree detecting means 6 for measuring the surface temperature of the pressing member 3 when a printing start command is issued to the image forming section, on the premise of a so-called on-demand type heat fixing device having: A rotation timing determining unit for determining a surface temperature of the heating and fixing member to start rotating the heating and fixing member based on the measurement result of the cooling degree detecting unit; Temperature comparison means 8 for comparing the measurement result of the temperature detection means 4 with the rotation start temperature determined by the rotation timing determination means 7, and the surface temperature of the heat fixing member 2 is lower than the rotation start temperature. In this case, a rotation control means 9 for starting rotation of the heating and fixing member 2 and the pressing member 3 when it is determined that the surface temperature of the heating and fixing member 2 has risen to the rotation start temperature is provided. It is characterized by

In the on-demand type heat fixing device based on the present invention, when a print start command is issued to the image forming unit (IOT), first, the heating control unit 5 is started.
Starts the energization of the heating element 1 and the surface temperature of the heat fixing member 2 gradually rises with this. However, before the recording sheet P is inserted, the heat fixing member 2 and the pressing member 3 Starts rotating, the surface temperature of the heating and fixing member 2 that has been rising until then rapidly decreases, depending on the relative difference between the surface temperature of the heating and fixing member 2 and that of the pressing member 3, Alternatively, there is a case where the temperature rising speed is slow but continues to rise as it is, and the surface temperature of the heat fixing member 2 after the start of the rotation is not stabilized.

However, according to the above-described technical means of the present invention, when a print start command is issued to the image forming section (IOT), the cooling degree detecting means 6 measures the surface temperature of the pressing member 3. Further, it is possible to grasp the decrease or increase in the surface temperature of the heat fixing member 2 after the start of rotation based on the measured value. Therefore, the rotation timing determining means 7 anticipates a decrease or an increase in the surface temperature of the heat fixing member 2 after the start of the rotation, and sets the temperature at which the heat fixing member 2 should start the rotation to a predetermined fixing control temperature. Also determines a higher or lower surface temperature. Then, the temperature comparing means 8 compares the determined rotation start temperature with the actual surface temperature of the heat fixing member 2, and as a result of the comparison, the surface temperature of the heat fixing member 2 falls below the rotation start temperature. If it is determined that the surface temperature has risen to the rotation start temperature, the rotation control means 9 starts rotating the heat fixing member 2 and the pressure member 3 when it is determined that the surface temperature has risen to the rotation start temperature. .

As a result, although the surface temperature of the heating and fixing member 2 changes differently from that before the start of the rotation, it can be substantially stabilized at a predetermined fixing control temperature after a certain period of time has elapsed after the start of the rotation. Thus, after the print start command and before the first recording sheet P is inserted, the surface temperature of the heat fixing member 2 can be reliably set to a predetermined fixing control temperature.

On the other hand, when a plurality of print jobs are continuously executed in the image forming section (IOT), the surface temperature of the heat fixing member 2 is already close to the fixing control temperature at the start of the second and subsequent print jobs. Therefore, even if the timing determination unit 7 determines the rotation start temperature in consideration of the surface temperature of the pressure member 3, the surface temperature of the heating and fixing member 2 already has the rotation start temperature. It is assumed that the situation has been exceeded. This is because, in such a case, the surface temperature of the pressing member 3 is considered to be sufficiently high, and the rotation start temperature is determined to be lower than the fixing control temperature. In such a case, if the heating element 1 is energized in the same procedure as in the case where the surface temperature of the heat fixing member 2 is lower than the rotation start temperature, the surface temperature of the heat fixing member 2 becomes a predetermined value. , A so-called overshoot phenomenon, which rises remarkably beyond the fixing control temperature, occurs, and the toner image T on the recording sheet P peels off from the recording sheet P and sticks to the heat fixing member 2.

Therefore, if the surface temperature of the heating and fixing member 2 has already exceeded the rotation start temperature at the time when the printing start command is issued to the image forming section (IOT), the heating control means 5 will turn on the heating and fixing member. The energization duty to the heating element 1 built in 2 is calculated, and energization to the heating element 1 is performed using the energization duty obtained by the calculation, while the rotation control means 9 issues a print start command. After that, it is preferable that the rotation of the heat fixing member and the pressing member be started immediately (claim 2). With this configuration, it is possible to limit the amount of heat per unit time that the heating element 1 gives to the heating and fixing member 2. Immediately heat fixing member 2
Can be stabilized at a predetermined fixing control temperature.

On the other hand, in the present invention, when the rotation timing determination means 7 determines the rotation start temperature of the heating and fixing member 2, the heating element 1 which has been energized always heats and fixes a predetermined amount of heat per unit time. It is assumed that it is given to the member 2. For this reason, there is no problem in applying the present invention as long as the heating and fixing device is provided with means for constantly supplying power to the heating element 1, but the heating and fixing device mounted on an inexpensive small-sized printer or the like can be used. Since it is difficult to mount such a stabilizing means for the supplied power in the fixing device, when applying the present invention, the heat fixing member 2 is rotated at the rotation start temperature determined by the rotation timing determining means 7.
However, there is a concern that the surface temperature of the heat fixing member 2 does not reach the predetermined fixing control temperature within a certain time even after the rotation of the fixing member starts.

Therefore, when the present invention is applied to a heating and fixing device which does not have a means for stabilizing the power supplied to the heating element 1, a print start command is issued to the image forming unit (IOT). At this time, a heating rate calculating means 10 for calculating a heating rate of the heating and fixing member 2 is provided, and the rotation timing determining means 7 determines the rotation start temperature of the heating and fixing member 2 in consideration of the calculation result. Is preferable (claim 3). With this configuration, the amount of heat given by the heating element 1 to the heating and fixing member 2 per unit time can be predicted, and there is no provision for a means for stabilizing the power supplied to the heating element 1. However, the rotation start temperature of the heat fixing member 2 can be determined with high accuracy.

In providing the heating rate calculating means 10 as described above, if the heating rate of the heating and fixing member 2 is always calculated when the rotation start temperature is determined, the surface temperature of the heating and fixing member 2 may be changed. Is sufficiently higher than at the beginning, the heating and fixing member 2 is turned on after the energization of the heating element 1 is started for calculating the heating rate until the rotation start temperature is determined.
A situation in which the surface temperature exceeds the rotation start temperature is also assumed. Therefore, from this viewpoint, when it is determined that the surface temperature of the heating and fixing member 2 is higher than the predetermined reference temperature, the previous heating rate of the heating and fixing member 2 is not newly calculated, and the previous temperature is not calculated. The heating rate calculated at the time of the printing start command is given to the rotation timing determining means 7,
It is preferable to determine the rotation start temperature of the heat fixing member 2 by using this (claim 4).

Furthermore, even if the surface temperature of the heat fixing member 2 is sufficiently high, if the surface temperature of the pressing member 3 is low,
Since the rotation start temperature is determined to be higher in consideration of the decrease in the surface temperature after the rotation of the heating and fixing member 2, the rotation of the heating and fixing member 2 is always compared with a constant determination reference temperature as described above. If the possibility of calculating the heating rate is determined, the chance of calculating the heating rate is reduced, and it becomes difficult to accurately determine the rotation start temperature of the heat fixing member 2. it is conceivable that.

Therefore, from such a viewpoint, it is preferable that the heating rate calculating means 10 changes the judgment reference temperature based on the surface temperature of the pressing member 3. With this configuration, even when the surface temperature of the heat fixing member 2 is sufficiently high, if the surface temperature of the pressing member 3 is low, the above-described reference temperature is set higher, and the heat fixing member 2 makes it possible to perform the calculation of the heating rate, thereby increasing the chances of performing the calculation of the heating rate as compared with the case where the determination of whether or not the calculation of the heating rate is performed using a certain reference temperature. It is possible to do.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a heat fixing device according to the present invention will be described in detail with reference to the accompanying drawings. FIG. 2 shows a schematic configuration of a laser beam printer to which the heat fixing device of the present invention is applied. In the figure, reference numeral 20 denotes an on-demand type heat fixing device to which the present invention is applied, and reference numeral 3 denotes
Reference numeral 40 denotes an image forming unit (hereinafter, IOT) for forming a toner image corresponding to image information and transferring the toner image to a recording sheet P;
Is a sheet tray that stores the recording sheets P. In this printer, when a print start command is issued to the IOT 2, the recording sheet P is carried out from the sheet tray 40 at a predetermined timing described later, and after the IOT 30 receives the transfer of the toner image corresponding to the image information. The printer is configured to be inserted into the heat fixing device 20 and discharged outside the printer.

The IOT 30 comprises a photosensitive drum 31 which rotates at a predetermined speed in the direction of an arrow, and a charging roll 32 which uniformly charges the photosensitive drum 31 to a predetermined potential.
And a raster scanning unit (ROS) 3 that scans the surface of the photosensitive drum 31 with a laser beam modulated according to image information and forms an electrostatic latent image on the photosensitive drum 31.
3, a developing device 34 for developing the electrostatic latent image with toner to visualize the toner, a transfer roll 35 for electrostatically transferring the toner image formed on the photosensitive drum 31 to the recording sheet P, And a cleaner 36 for cleaning the surface of the photosensitive drum 31 on which the transfer of the image has been completed, and forms a toner image on the photosensitive drum 4 in accordance with image information as the photosensitive drum 31 rotates. The toner image can be transferred to the recording sheet P.

On the other hand, the heat-fixing device 20 includes a heat-fixing roll (heat-fixing member) 21 having a pair of heaters (heating elements) 21a and 21b built therein, and a pressure roll (pressurizing) that presses against the heat-fixing roll 21. Member) 22 and a heating degree detection sensor 23 for measuring the surface temperature of the heating fixing roll 21.
And a cooling degree detection sensor 24 for measuring the surface temperature of the pressure roll 22. The recording sheet P on which the toner image has been transferred is transferred to the heat fixing roll 21 and the pressure roll 22.
And squeezed onto the recording sheet P while melting the toner adhering to the recording sheet P, and fixing the toner image to the recording sheet P. . Reference numeral 25 in the drawing denotes a peeling claw for peeling off the recording sheet P on which the toner image has been fixed from the heat-fixing roll 21, and reference numeral 26 denotes a discharge roll for discharging the recording sheet P out of the printer. It is.

The heat fixing roll 21 is formed by molding an aluminum core material into a hollow cylindrical shape, and has PFA or PTF on its surface to prevent toner from adhering.
A fluorine-based resin such as E is coated with a thickness of several tens of μm. The pair of heaters 21a and 21b built in the heat-fixing roll 21 each output 950 W when an AC voltage of 100 V is applied.
The output is controlled to be W. The pressure roll 22 is formed by covering the periphery of a core material 22a made of SUS or the like with a heat-resistant elastic body 22b such as silicone rubber. It is pressed against the roll. As a result, the elastic body 22b covering the pressure roll 22 is
1, a nip region for sandwiching the recording sheet P with a predetermined width is formed between the heat fixing roll 21 and the pressure roll 22.

FIG. 3 is a block diagram showing a control system of the heat fixing device. Control of various operations of the heat fixing device is performed by a control unit 2 including a microcomputer system.
7 is going. While the control unit 27 receives the temperature detection signals of the heating degree detection sensor 23 and the cooling degree detection sensor 24, the control unit 37 of the IOT also exchanges information regarding the reception of the print start command and the like, and the temperature detection signals and It is configured to generate a drive signal for the heater power supply circuit 28 based on the exchange information. The control unit is also configured to generate a drive signal for a motor 29 that controls the rotation of the heat fixing roll 21 and the pressure roll 22 and send the drive signal to the motor 29 at a predetermined timing described later. Have been. Therefore, the heating control unit, the rotation timing determination unit, the temperature comparison unit, and the rotation control unit of the present invention are realized by the control unit.

The heating / fixing apparatus 20 of this embodiment having the above-described configuration is of a so-called on-demand type, that is, waits for a print start command to the IOT 30 and waits for the heater 1 to start printing.
The power supply to the heaters 1a and 11b is performed. When the printing is completed, the power supply to the heaters 11a and 11b is cut off to suppress wasteful energy consumption.

FIG. 4 is a flowchart showing a first embodiment of a control procedure of the heat fixing device 20 at the time of starting printing in the printer. For example, IOT from computer
When a print start command is transmitted to the control unit 40, the control unit 37 of the heat fixing device 20 receives a notification to that effect from the control unit of the IOT 30 (ST1).
And the surface temperature H1 of the pressure fixing roll 22 is detected by checking the temperature detection signal of the cooling degree detection sensor 24 (ST2). .

Here, the detection of not only the surface temperature of the heat fixing roll 21 but also that of the pressure roll 22 having no built-in heater is performed after the rotation of the heat fixing roll 21 and the pressure roll 22 is started. This is to grasp how much the heat of the fixing roll 21 is taken by the pressure roll 22. That is, as shown in FIG.
The heat-fixing roll 2
In the case where the surface temperature of the pressure roll 22 is low, even if the surface temperature of
When the pressure roll 1 and the pressure roll 22 start rotating, the amount of heat stored in the heat fixing roll 21 rapidly flows out toward the pressure roll 22, and the surface temperature of the heat fixing roll 21 rapidly decreases. . Therefore, after the rotation of the heat fixing roll 21 and the pressure roll 22 starts, the heat fixing roll 2
1 is a fixing control temperature (185 ° in this embodiment).
In order to stabilize the recording sheet P in C) and allow the recording sheet P to be inserted, the surface temperature of the pressure roller 22 is grasped in advance, and the transition of the surface temperature of the heat fixing roller 21 after the start of rotation is predicted. I have to do it.

Therefore, in this embodiment, if the surface temperature P1 of the pressure roll 22 is detected in the above-described ST2, the heating and fixing roll 21 and the rotation of the pressure roll 22 are to be started based on the detected temperature. The surface temperature of the fixing roll 21, that is, the rotation start temperature D1 is calculated (ST
3). The driving start temperature D1 differs depending on the surface temperature P1 of the pressure roll 22, and when the surface temperature P1 of the pressure roll 22 is sufficiently lower than the fixing control temperature,
As shown in FIG. 5, the rotation start temperature D1 is higher than the fixing control temperature. Further, when the surface temperature P1 of the pressure roll 22 is slightly lower than the fixing control temperature, the heat flow from the heat fixing roll 21 to the pressure roll 22 becomes gentle, and even after the rotation starts, the heat Is kept rising, the rotation start temperature D1 is lower than the fixing control temperature. According to an experiment conducted by the inventor of the present application, the amount of temperature change of the heat fixing roll 21 and the surface temperature P
Since there is a certain inverse relationship with 1
By utilizing this relationship, the decrease in the surface temperature of the heat fixing roll 21 after the start of rotation can be ascertained by calculation, and by adding the decrease to the final fixing control temperature, The operation start temperature D1 can be calculated. In this example, the following equation was obtained from an experiment, and the above D1 was calculated from this.

[0031]

(Equation 1)

After calculating the rotation start temperature D1 in ST3 in this manner, the control unit 27
Is compared with the rotation start temperature D1 (ST
4) If the relationship of H1 <D1 is satisfied, energization of the heaters 21a and 21b built in the heat fixing roll 21 is started (ST5). As a result, the surface temperature H1 of the heat fixing roll 21 increases toward the rotation start temperature D1. Thereafter, the control unit 27 checks whether or not the surface temperature H1 of the heat fixing roll 21 has exceeded the rotation start temperature D1 (ST6).
A drive signal is sent to the printer 9 to start driving the heat fixing roll 21 and the pressure roll 22 (ST7).

As a result, the surface temperature of the heat fixing roll 21 is quickly stabilized at the fixing control temperature after the start of rotation, so that the toner image can be fixed to the recording sheet P at an early stage. However, in an image forming apparatus such as a printer, the motor 29 for driving the heat-fixing roller 21 and the pressure roller 22 is often used as a drive motor for the conveyance system of the recording sheet P. In this case, when the rotation of the heat fixing roller 21 is started, the image forming unit 3
0, the conveyance of the recording sheet P is also started.
After a lapse of a predetermined time from the start of the rotation of the heat fixing roller 21, the recording sheet P enters the heat fixing device 20. In this regard, according to the heat fixing device 20 of the present embodiment, when the heat fixing roller 21 starts to rotate, the surface temperature of the roller 21 is quickly stabilized at the fixing control temperature. The surface temperature of the heat-fixing roller 21 is stabilized before is inserted into the heat-fixing device 20, and even if the time from the start of rotation of the heat-fixing roll 21 to the entry of the first recording sheet P is short. Thus, the toner image can be satisfactorily fixed on the recording sheet P.

On the other hand, if it is determined in ST4 that the surface temperature H1 of the heat fixing roll 21 is higher than the rotation start temperature D1 (H1> D1), the control unit 27 should supply the heaters 21a and 21b. Calculate power W (ST
8) A driving signal is transmitted to the heater power supply circuit 28 in accordance with the supplied power obtained as a result of the operation (ST9),
Immediately, the rotation of the heat fixing roll 21 and the pressure roll 22 is started (ST7).

The rotation start temperature D1 is controlled by the heaters 21a and 21a.
It is calculated assuming that the output of b is 850 W,
If the surface temperature of the heat fixing roll 21 detected before the power is supplied to the heaters 21a and 21b exceeds the rotation start temperature D1, the heaters 21a and 21b are output at 850 W as they are.
Is driven, the surface temperature of the heat-fixing roll 21 rises too much, and the surface temperature of the heat-fixing roll 21 when the first recording sheet P is inserted greatly exceeds the fixing control temperature. Therefore, in this embodiment, in such a case, the supply power W to the heaters 21a and 21b is limited, and the amount of change in the surface temperature of the heat fixing roll after the start of rotation is set to ST.
The difference between H1 detected in step 2 and the fixing control temperature was set. In the present embodiment, the following equation was used for the calculation of W.

[0036]

(Equation 2)

According to an experiment conducted by the inventor of the present invention, the amount of change in the surface temperature of the heat fixing roll 21 after the start of rotation is proportional to the power supplied to the heaters 21a and 21b, and this relationship is used. By doing
The power supply to the heaters 21a and 21b suitable for the target amount of change in the surface temperature of the heat fixing roll 21 can be calculated. Thereby, in the present embodiment, the heaters 21a, 2
Even when the surface temperature H1 of the heating / fixing roll 21 before the energization to 1b is higher than the rotation start temperature D1, the surface temperature of the heating / fixing roll 21 is quickly stabilized at the fixing control temperature. Is what you can do.

FIG. 6 is a flowchart showing a second embodiment of the control procedure of the heat fixing device 20 at the start of printing by this printer. As described above, the amount of change in the surface temperature of the heating and fixing roll 21 after the start of rotation of the heat fixing roll 21 is proportional to the power supplied to the heaters 21a and 21b. To do so, it is necessary to know the amount of heat given by the heaters 21a and 21b to the heat fixing roll 21 per unit time. For this reason, the control procedure of the first embodiment is based on the assumption that the output of each heater 21a, 21b is stabilized at 850W. However, in the case of copiers and printers of a general type that require a reduction in production cost, means for stabilizing the heater output, for example, detecting the output voltage and stabilizing the output voltage based on the result. Some of the image forming apparatuses do not include a circuit or the like for performing the above-described operation, and it becomes difficult to accurately calculate the rotation start temperature in such an image forming apparatus.

Therefore, in the control procedure of the second embodiment,
The heating rate of the heating / fixing roll 21 when the heaters 21a and 21b are energized is calculated, and the heaters 21a and 21b use the heating / fixing roll 21 per unit time based on the heating rate.
It was configured to grasp the amount of heat to be given.

That is, as shown in FIG. 6, when the control section 37 of the heat fixing device 20 receives a print start command from the control section of the IOT 30 (ST101), first, it checks the temperature detection signal of the heating degree detection sensor 23. Thereby, the surface temperature H1 of the heat fixing roll 21 is detected, and the surface temperature P1 of the pressure roll 22 is detected by checking the temperature detection signal of the cooling degree detection sensor 24 (ST1).
02). Up to this point, the control procedure is the same as in the first embodiment.

Next, the control unit 27 checks whether or not the detected surface temperature H1 of the heat fixing roll 21 is lower than a predetermined judgment reference temperature (50 ° C. in this example) (ST103). If it is determined that the temperature is low, the heaters 21 a and 2
1b is energized (ST104). The reason why the surface temperature H1 of the heat fixing roll 21 is compared with the above-described reference temperature will be described later. Thereafter, the control unit 27 controls the heating and fixing roll 2 based on the temperature detection signal of the heating degree detection sensor 23.
1 is calculated (ST105), and further, the rotation start temperature D1 of the heat fixing roll 21 is calculated using the temperature increase speed TR1 and the surface temperature P1 of the pressure roll 22 detected in ST102. (ST106).

In the calculation of the temperature rise rate TR1 in ST105, one cycle from the start of energization to the heaters 21a and 21b is performed.
The surface temperature of the heat fixing roll 21 after a lapse of second was detected, and the surface temperature after one second was detected. The amount of change in the surface temperature was directly used as the temperature rise rate TR1. The reason why the heating rate TR1 is not calculated based on the surface temperature of the heating and fixing roll 21 at the start of energization is that the heating rate of the heating and fixing roll 21 is not stable immediately after the start of energization, and an accurate heating rate can be calculated. Because there is no. In this embodiment, the heater 21
The heating rate of the heating fixing roll 21 is calculated using the detection signal of the heating degree detection sensor 23 used for the control of a and 21b. In view of the fact that the heating rate is calculated, a temperature detection sensor dedicated to the low temperature range used for calculating the heating rate may be provided for the heating fixing roll 21.

After calculating the rotation start temperature D1 in ST106 as described above, the control unit 27 compares the surface temperature H1 of the heat fixing roll 21 with the rotation start temperature D1 (ST107). Since the power supply to the heaters 21a and 21b has already been started, the surface temperature H1 of the heat fixing roll 21 is rising toward the rotation start temperature D1 at this point. When it is determined that the surface temperature H1 of the heat fixing roll 21 has exceeded the rotation start temperature D1, the driving progress is sent to the motor 29 to start driving the heat fixing roll 21 and the pressure roll 22. (ST108). Thus, similarly to the case of the control procedure in the first embodiment, the heat fixing roll 21
After the roll 21 starts rotating, the surface temperature of the roller 21 is quickly stabilized at the fixing control temperature. Note that the following equation obtained by an experiment was used for the calculation of D1.

[0044]

(Equation 3)

On the other hand, if it is determined in ST103 that the surface temperature H1 of the heat fixing roll 21 is higher than a predetermined reference temperature (50 ° C. in this example), the control unit 27 determines Heating rate TR1
Is not read out, and the heating rate TR2 of the heat fixing roll calculated in the previous print job is read out from the memory (S
T109), the rotation start temperature D2 of the heat fixing roll 21 is calculated using the temperature increase rate TR2 (ST110).

As described above, when the surface temperature H1 of the heat fixing roll 21 is higher than a predetermined judgment reference temperature, the heating rate T
The reason why the calculation of R1 is not performed is that the heaters 21a and 21b are energized for calculating the heating rate TR1 (ST104).
When power is supplied to the heaters 21a and 21b in a state where the surface temperature of the heat fixing roll 21 is high, ST10
This is because it is highly probable that the surface temperature H1 of the heat-fixing roll 21 is higher than the calculated rotation start temperature D1 before the rotation start temperature D1 is calculated in Step 6. Therefore, the surface temperature H1 of the heat fixing roll 21 is
Is higher than the predetermined reference temperature, it is not possible to calculate the heating rate of the heat fixing roll 21 again so that the energization of the heaters 21a and 21b can be started after the rotation start temperature D2 is calculated. Instead, the rotation start temperature D2 is calculated using the temperature increase rate TR2 calculated in the previous print job. In addition, the following formula obtained by experiment was used for the calculation of D2.

[0047]

(Equation 4)

The subsequent steps are exactly the same as ST4 to ST9 of the first embodiment. That is, the control unit 27 compares the surface temperature H1 of the heat fixing roll 21 with the rotation start temperature D2 (S
T111) If the relationship of H1 <D2 holds, a drive signal is sent to the heater power supply circuit 28 to
After the power supply to the a and 21b is started (ST112), if it is determined that the surface temperature H1 of the heat fixing roll 21 has exceeded the rotation start temperature D1 (ST113), a drive signal is sent to the motor 29. The driving of the heat fixing roll 21 and the pressure roll 22 is started (ST108).

On the other hand, in ST111, the surface temperature H1 of the heat fixing roll 21 is higher than the rotation start temperature D2 (H
When it is determined that 1> D2), the control unit 27 supplies the power to the heaters 21a and 21b with the energization duty D.
T is calculated (ST114).
The power supply to a and 21b was limited. In the case of an AC voltage having a frequency of 50 Hz, one cycle of the voltage change is 20 msec. Therefore, the energization time of the heaters 21a and 21b is determined so that the energization time during 500 msec is a multiple of 20 msec. Then, a drive signal is sent to the heater power supply circuit 28 in accordance with the energization duty DT obtained as a result of the calculation (ST115), and the rotation of the heat fixing roll 21 and the pressure roll 22 is started immediately (ST10).
8). The above DT is the energization time in 500 msec, and the following equation obtained by experiment was used for the calculation.

[0050]

(Equation 5)

FIG. 7 is a flowchart showing a third embodiment of the control procedure of the heat fixing device 20 at the start of printing by this printer. In the second embodiment described above, ST
At 103, it is checked whether or not the surface temperature H1 of the heat fixing roll 21 is lower than a predetermined reference temperature (50 ° C.).
1 was calculated. Since it takes about 3 seconds from the start of energization to the heaters 21a and 21b to calculate the heating rate, it is necessary that the surface temperature of the heat-fixing roll 21 does not reach the rotation start temperature D1 during the three seconds. The determination reference temperature of ° C is a value set with a sufficient margin for the fluctuation of the rotation start temperature D1.

However, since the rotation start temperature D1 fluctuates according to the surface temperature P1 of the pressure roll 22 as described above, the reference temperature for determining whether to calculate the temperature increase rate TR1 is also determined by the pressure roll. When the temperature is changed in accordance with the surface temperature P1, the chance of calculating the heating rate TR1 increases, and the accuracy of calculating the rotation start temperature is improved.

Therefore, in this embodiment, after the judgment reference temperature HS is calculated in advance using the surface temperature P1 of the pressure roll 22, the judgment reference temperature HS obtained by the calculation is compared with the surface temperature H1 of the heating fixing roll 21. Then, it is configured to determine whether or not to calculate the heating rate TR1 of the heat fixing roll 21 based on the comparison result. That is, as shown in FIG. 7, in ST202, the surface temperature H of the heat fixing roll 21 is increased.
1 and the surface temperature P1 of the pressure fixing roll, the reference temperature HS is calculated using the above P1, and ST204.
In the first embodiment, it is checked whether or not the surface temperature H1 of the heat fixing roll is lower than the reference temperature HS. still,
The following equation obtained by experiments was used for the calculation of HS.

[0054]

(Equation 6)

When it is determined that the temperature is low, the temperature rise speed TR1 is calculated and then the rotation start temperature D1 is calculated (ST205 to ST209). The calculation is stopped, and the rotation start temperature is calculated using the temperature increase rate TR2 used in the previous print job (ST210 to ST216). still,
ST205 to ST209 correspond to ST104 to S of the second embodiment.
At T108, ST210 to ST216 correspond to S of the second embodiment.
Since it corresponds to T109 to ST115, a detailed description thereof will be omitted here.

In each of the above embodiments, the rotation start temperature D
1, the power supplied to the heaters 21a and 21b, the reference temperature H
S and the like may be configured to derive an arithmetic expression based on data collected by experiments and calculate based on this arithmetic expression. However, a numerical value table is formed based on the collected data, and this numerical value table is The configuration may be such that the determination is made with reference to.

[0057]

As described above, according to the heat fixing apparatus of the present invention, but according to the above-mentioned technical means of the present invention, when a print start command is issued to the image forming section, the pressure is increased. Based on the surface temperature of the member, grasp the change in the surface temperature of the heating and fixing member after the start of rotation of the member,
Since the temperature at which the rotation of the heat fixing member is to be started is determined, the surface temperature of the heat fixing member is substantially stabilized at a predetermined fixing control temperature after a certain period of time has elapsed after the start of the rotation. After the print start command, the surface temperature of the heat fixing member can be quickly set to a predetermined fixing control temperature, so that the time until the first recording sheet is inserted is reduced as much as possible, It is possible to prevent the generation of the recording sheet.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a heat fixing device of the present invention.

FIG. 2 is a schematic view showing an embodiment of a laser beam printer equipped with the heat fixing device of the present invention.

FIG. 3 is a block diagram illustrating a control system of the heat fixing device according to the embodiment.

FIG. 4 is a flowchart showing a first embodiment of a control procedure of the heat fixing device of the present invention.

FIG. 5 is a graph showing a change in the surface temperature of the heat fixing roll in the control procedure of the first embodiment.

FIG. 6 is a flowchart illustrating a control procedure of the heat fixing device according to a second embodiment of the present invention.

FIG. 7 is a flowchart showing a third embodiment of the control procedure of the heat fixing device of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Heating element, 2 ... Heat fixing member, 3 ... Pressurizing member, 4 ... Heating degree detecting means, 5 ... Heating control means, 6 ... Cooling degree detecting means, 7 ... Rotation timing determining means, 8 ... Temperature comparing means ,
9: rotation control means, 10: heating rate calculation means, IOT ...
Image forming unit, P: recording sheet, T: toner image

Claims (5)

[Claims] 1. A heating and fixing device for fixing an unfixed toner image formed on a recording sheet in an image forming section to the recording sheet, the heating and fixing member having a built-in heating element and rotating, A pressure member that rotates while sandwiching a recording sheet between the fixing member, a heating degree detecting unit that measures the surface temperature of the heating and fixing member, and a heating unit that waits for a print start command for the image forming unit and Heating control means for starting the energization of, further, cooling degree detecting means for measuring the surface temperature of the pressurizing member when a printing start command is issued to the image forming unit,
Rotation timing determining means for determining the surface temperature of the heating / fixing member at which rotation of the heating / fixing member is to be started based on the measurement result of the cooling degree detecting means, and measurement of the heating degree detecting means Temperature comparison means for comparing the result with the rotation start temperature determined by the rotation timing determination means; and, when the surface temperature of the heat fixing member is lower than the rotation start temperature, the surface temperature of the heat fixing member. A rotation control means for starting rotation of the heat fixing member and the pressing member when it is determined that the temperature has risen to the rotation start temperature. 2. The heat fixing device according to claim 1, wherein
As a result of the comparison by the temperature comparing unit, when the surface temperature of the heat fixing member is higher than the rotation start temperature,
The heating control means calculates an energization duty to the heating element based on the comparison result, and energizes the heating element using the energization duty, while the rotation control means immediately rotates the heating and fixing member. A heat fixing device, characterized by starting. 3. The heat fixing device according to claim 1, wherein
A heating rate calculating means for calculating a heating rate of the heating and fixing member when a print start command is issued to the image forming unit; A heat-fixing device for determining a rotation start temperature of the heat-fixing device. 4. The heat fixing device according to claim 3, wherein
If the temperature increase speed calculating means determines that the measured surface temperature of the heat fixing member is higher than a predetermined determination reference temperature, the temperature increase speed calculating means calculates the temperature increase speed of the heat fixing member again without newly calculating the temperature increase speed of the heat fixing member. A heating fixing device characterized in that a heating rate calculated at the time of a start command is given to a rotation timing determining means. 5. The heat fixing device according to claim 4, wherein
The heating and fixing device according to claim 1, wherein the temperature increasing speed calculating means changes the reference temperature based on a surface temperature of the pressing member.