JPH09101719A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To shorten the temperature raising time irrespective of the quality of responsiveness of the thermistor and to prevent the temperature of fixing roll working during temperature raise from exceeding the set fixing temperature drastically. SOLUTION: The temperature raise time till a set fixing temperature is determined from the detected thermistor temperature at the starting time of temperature raise based on a predetermined relation between 'the time required for reaching the target temperature in temperature raise' and 'the fixing roll temperature at the start of temperature raise'. In this case, the target temperature in temperature raise is set in consideration of temperature raise width until the recording paper reaches the fixing section and after the target temperature is reached, the fixing roll is driven to reach the set temperature in temperature raise (steps 401 to 411).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention utilizes the characteristic of the temperature rising time from the temperature of the fixing roll to the set fixing temperature without directly using the temperature detected by the thermistor as a control parameter. The present invention relates to a fixing device that controls temperature.

[0002]

2. Description of the Related Art For example, in the apparatus disclosed in Japanese Patent Laid-Open No. 2-161486, the time from the start of work to the start of fixing is T ₀ , and the time from the start of conveyance of recording material to the start of fixing is T _1. , T ₀ <T ₁ , start work, T ₀ > T
If the value is ₁ , the heating time is driven based on the transfer time to reduce the standby time and power consumption. Generally, the temperature output of the thermistor used as the temperature detecting element of the fixing roll has poor responsiveness when the fixing roll is heated,
There is a considerable temperature difference from the actual fixing roll temperature. Therefore, if the temperature detected by the thermistor is directly used as a control parameter, loss of temperature rise time and overshoot during temperature rise occur. On the other hand, experiments have shown that the time for a stationary fixing roll to reach a certain target temperature depends linearly on the temperature of the fixing roll at the start of temperature rise and not on the ambient temperature. Therefore, it is conceivable to control the fixing roll temperature by utilizing the temperature rising time from the fixing roll temperature to the set fixing temperature.
Further, as a temperature control method after the fixing set temperature is reached, when the temperature is higher than the set temperature, the supplied electric power is set to 0%, and when the temperature is lower than the set temperature, 100% is output.
There is a control method. In this control method, since the applied power is either 0% or 100%, the gradient of the rise or fall of the fixing roll temperature is large and the fluctuation width (ripple) of the fixing roll temperature is large. The temperature gradient of the fixing roll varies depending on whether the fixing roll is driven or not.
In the temperature control of% OR0%, the fluctuation range of the fixing roll temperature becomes large. Further, in the apparatus described in Japanese Patent Laid-Open No. 62-6287, at least three control band widths are provided for each operation mode of the image forming apparatus, and a predetermined energization predetermined for each control band width is provided. By controlling the energization during the fixing period at a rate, good temperature control characteristics are obtained with a simple configuration.

[0003]

In the above prior art, since the temperature output of the thermistor is poor in response when the fixing roll is heated, there is a problem in using the temperature detected by the thermistor directly as a control parameter. is there. Further, when the fixing roll temperature is controlled by utilizing the characteristic of the temperature rising time from the fixing roll temperature to reaching the fixing set temperature, whether the fixing roll temperature at the start of the heating is higher than the target heating temperature. Depending on whether it is lower, it is necessary to set conditions for starting the fixing operation. Further, when the ON / OFF control method is used as the temperature control method after the fixing set temperature is reached, the fluctuation range of the fixing roll temperature is large,
There is a problem that stable fixing properties cannot be obtained when the temperature of the fixing roll is lowered. Further, in the above control method, after the temperature of the fixing roll is raised to the set fixing temperature, the output of the heater is being raised (100%) to when the paper is passing (for example, 50%).
When the temperature around the fixing roll (side plate, drive gear, pressure roll) is low when shifting to the output of 1, the temperature of the fixing roll sharply drops, and there is a possibility that the fixing property at the time of temperature decrease deteriorates. Furthermore, in the above-mentioned conventional technique, no consideration is given to the case where a voltage higher (or lower) than the standard value is applied to the device. For example, when a voltage higher than the standard value is applied to the apparatus, the surface temperature of the fixing roll may run below the fixing setting temperature and run away. When a voltage lower than the standard value is applied to the device, the fixing roll surface temperature does not reach the fixing set temperature,
An unfixed image may be output.

The object of the present invention is to improve such problems and to shorten the temperature raising time regardless of the response of the thermistor. It is an object of the present invention to provide a fixing device that can prevent the occurrence of the above. Further, it is intended to prevent malfunction due to delay in response of the thermistor. Further, in the control for performing the fixing operation by determining the temperature raising time from the fixing roll temperature at the start of the temperature rise, it is possible to perform the constant temperature operation even if the fixing roll temperature is equal to or higher than the temperature raising target temperature. The purpose is to improve the environment. Also, by reducing the temperature ripple width of the fixing roll,
The purpose is to stabilize the fixing property of the toner on the recording paper. It should be noted that the conventional device used for ON / OFF control is also intended to be able to reduce the temperature ripple width of the fixing roll only by changing the control software without electrically changing it. . Further, it is an object of the present invention to maintain the surface temperature of the fixing roll near the preset fixing temperature even when the power supply voltage applied to the apparatus varies greatly.
Another object is to prevent a rapid decrease of the fixing roll and prevent deterioration of the fixing property. Another object is to prevent runaway of the device (or output of an unfixed image) when a voltage higher (or lower) than the standard value is applied to the device.

[0005]

In order to achieve the above object, the invention according to claim 1 provides a fixing roll (19 in FIG. 1).
Including the fixing unit, the thermistor (4 in FIG. 1), the heater (FIG. 1)
16), etc., and the recording paper reaches the fixing unit within a fixed time after the fixing roll is driven, in a fixing device, based on the relationship between the fixing roll temperature and the heater lighting time (see FIG. 3). The heater lighting time is determined from the temperature of the fixing roll detected by the thermistor just before the temperature rise to the preset temperature target temperature in anticipation of the temperature range that rises to the constant fixing set temperature within the above fixed time, and the temperature rise is determined. After the warm target temperature is reached, a control unit that drives the fixing roll (see "1 in FIG. 1").
1, 13 "," steps 401 to 411 of FIG. 4 "). The invention according to claim 2 is
In the invention according to claim 1, when the fixing roll temperature detected from the thermistor immediately before the temperature rise reaches the temperature raising target temperature, the heater lighting time is determined according to the fixing roll temperature and the fixing roll is immediately set. Control means for driving (“11, 13 in FIG. 1”, “Steps 401, 4 in FIG. 4”)
02, 412 to 416 ").
According to a third aspect of the present invention, a fixing unit including a fixing roll, a thermistor, a heater, and the like are provided, and the heater is turned ON / OF based on the magnitude relationship between the fixing roll temperature and the fixing set temperature.
In the fixing device configured to perform the F control, the average power supplied to the heater is changed stepwise to supply power, and the heater output is controlled depending on whether or not the fixing roll is driven. 11, 1 in FIG.
3 ”and“ steps 421 to 427 in FIG. 5 ”). Further, in the invention described in claim 4, in the invention described in claims 1 to 3, when the output mode after the heating of the heater is finished is switched to the mode of sheet passing, the temperature detected by the thermistor reaches the fixing set temperature. Means for controlling the heater output to be gradually reduced until
3 "," steps 417-420 of FIG. 5 "). Further, the invention according to claim 5 is provided with a fixing unit including a fixing roll, a thermistor, a heater, etc., and is configured to control ON / OFF of the heater based on the magnitude relationship between the fixing roll temperature and the fixing set temperature. In the fixing device, a plurality of heater lighting cycle patterns are held in a memory (11a and 13 in FIG. 8), and a heater lighting cycle that matches the electric power supplied to the heater is selected (steps 1001 and 1002 in FIG. 10). Is characterized by. In the invention according to claim 6, in the invention according to claim 5, in the heater lighting cycle used when the fixing roll temperature exceeds a set value, the temperature gradient of the fixing roll monitored by the thermistor is positive. If yes,
The heater lighting cycle is switched so that the electric power supplied to the heater is further reduced (step 1010 in FIG. 10,
1011) is characteristic. In the invention according to claim 7, in the invention according to claim 5, in the heater lighting cycle used when the fixing roll temperature becomes equal to or lower than a set value, the temperature gradient of the fixing roll monitored by the thermistor is negative. If there is, it is characterized by switching to the heater lighting cycle so that the electric power supplied to the heater is further increased (steps 1006 and 1007 in FIG. 10). The invention according to claim 8 is the invention according to claim 6 or 7, wherein temperature gradient detection is performed a plurality of times by a thermistor, and plus / minus is determined from consecutive detection results (steps 1004 to 1006 in FIG. 10).
It is characterized by this.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, a fixing device having a fixing roll incorporating a heater and a thermistor for measuring the temperature of the fixing roll is constructed. In addition, the recording paper reaches the fixing unit from the thermistor detection temperature immediately before the temperature rise based on the relationship between the “time required to reach the temperature rise target temperature” and the “fixing roll temperature at the start of temperature rise” that is obtained in advance. The temperature increase target temperature is set in advance in anticipation of the temperature range that rises to the fixing set temperature within a certain time. When the temperature of the fixing roll is controlled by the controller, the rise time is calculated from the temperature detected by the thermistor immediately before the temperature is raised, the heater FULL output operation is performed, and the fixing roll is driven after the temperature reaches the target temperature. The heater FULL output operation is performed to reach the fixing set temperature by the time the recording paper reaches the fixing unit. If the temperature detected by the thermistor just before the temperature rise has already reached the temperature increase target temperature, the heater is turned on in accordance with the detected temperature.
The LL is turned on, and the recording paper is controlled to reach the fixing set temperature by the time it reaches the fixing unit. Thus, the heater output correction operation is performed until the preset fixing temperature is reached, and the stable fixing operation can be performed at the proper fixing roll temperature by the stepwise heater output operation after the preset fixing temperature is reached. Further, in the present invention, a plurality of heater lighting cycle patterns are held in the ROM, a heater lighting cycle that matches the supplied power supply voltage is selected, and the fixing roll temperature is maintained near the set value. When the fixing roll temperature exceeds the set value, select a heater lighting cycle that suppresses the temperature rise, and in that heater lighting cycle, the fixing roll surface temperature gradient per unit time becomes positive. In such a case, a heater lighting cycle in which the input power is lower than the default value is selected from the ROM to avoid overheating runaway of the device fixing unit. When the fixing roll temperature is below the set value, select a heater lighting cycle that promotes temperature rise, and in that heater lighting cycle, the fixing roll surface temperature gradient per unit time becomes negative. In such a case, the heater lighting cycle is selected such that the input power is increased more than the default value, and the output of the unfixed image is avoided by selecting from the ROM. When the thermistor is used as the temperature detecting element, by adopting the detection result that the same fixing roll surface temperature gradient is obtained several times in succession,
Prevents malfunction due to delayed response of the thermistor.

An embodiment of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 is a block diagram of a fixing device according to an embodiment of the present invention. In FIG. 1, 11 is a memory for storing a startup time calculation formula, heater lighting time, etc., which will be described later, 4 is a thermistor for measuring the temperature of the fixing roll, and 12 is detection for detecting the measured temperature of the thermistor. Reference numeral 13 denotes a control unit for performing processing such as start-up time calculation and heater output determination / control described later, 14 denotes a heater driving unit, 15 denotes a main motor driving unit, and 16 denotes a halogen lamp heater serving as a heat source for the fixing roller. , 17 is a drive motor for driving the fixing roll and the paper discharge roll, 18 is a paper discharge roll, and 19 is a fixing roll. This fixing roll 1
The configuration of the fixing unit including 9 is as shown in FIG. 2, and the heat roll 2 has a built-in means (heat source 3) capable of heating,
For example, a halogen heater lamp is used. The heat roll 2 is mainly made of a metal material such as aluminum, iron or SUS, and the surface of the pressure roll is covered with silicon rubber or the like. On the surface of the heat roll 2, a toner release layer containing a fluorocarbon-based organic material such as tetrafluoroethylene or trifluoroethylene as a main component is formed. More specifically, the heat roll 2 is 20φ × 0.4t × 2
The pressure roller is 70 L, and the core metal 5 of 10φ is coated with 6 t of silicon rubber (JIS A hardness 16) 1. Pressurization is applied at both ends, and a halogen lamp rated at 700 W is used. A thermistor 4 as a fixing heat roll temperature detecting element is attached to a part of the heat roll 2. In addition to this, a heat roll having a conductive layer formed on the front and back surfaces of a roll made of glass, ceramic, or the like may be used.

Now, the start-up time calculation formula and the heater lighting time stored in the memory 11 of this embodiment will be described. FIG. 3 shows the relationship between the “arrival time to the temperature raising target temperature” of the heat roll 2 and the “fixing roll temperature at the start of temperature raising”. As is clear from FIG. 3, the time (y: temperature rising time) for the stationary fixing roll (heat roll 2) to reach the temperature raising target temperature from a certain temperature is the fixing roll temperature (x ), That is, it is linearly obtained from the input value (° C.) of the thermistor 4. Therefore, in the present embodiment, the apparatus configuration (“material of fixing roll / thickness / roll diameter”, “material of pressure roll / roll diameter / roll length”,
A proper temperature increase target temperature is set in consideration of "a temperature range in which the fixing roll rises during the temperature rise from the start of roll driving to the fixing portion during temperature rise" and "fixing set temperature"), and FIG.
By using the relationship (y = ax + b) shown in (1), the temperature rise time (heater lighting time) from the fixing roll temperature to the temperature rise target temperature at the start of temperature rise or the heater from the temperature rise target temperature to the fixing set temperature Find the lighting time.

First, the control operation when the fixing roll temperature at the start of temperature rise is lower than the temperature rise target temperature will be described. FIG.
In this case (Y in steps 401 and 402)
es), the start-up time is calculated from the start-up time calculation formula (y = ax + b) (step 403), and predetermined power is supplied according to the calculation result (steps 404 to 406).
Set the target temperature for temperature rise. The driving of the fixing roll is started from this target temperature rise (step 407), and a predetermined electric power is supplied until the recording paper reaches the fixing portion (step 4).
08-411). In this way, the fixing roll reaches the fixing set temperature. More specifically, the time required for the recording paper to reach the fixing unit from the start of roll driving is 4.5 seconds (the recording paper conveyance path,
(Limited by the conveyance speed)
When the temperature raising target temperature is set, when the temperature raising target temperature is set to 140 ° C. and the temperature raising target temperature is 140 ° C., a graph of the relationship between the fixing roll temperature immediately before the temperature raising starts and the arrival time to the target temperature is shown in FIG. The constants a and b are determined in advance by raising the temperature from the temperature raising start temperature and obtaining the arrival time from the measured value. When the above roll is used, the constant a: -0.
04503 and a constant b: 5.313275 are obtained. Note that steps 401 to 411 of FIG. 4 correspond to the invention of claim 1.

Next, the control operation when the fixing roll temperature at the start of temperature increase has already reached the temperature increase target temperature will be described. In this case, as shown in FIG.
No. 02), the start-up time is calculated from the start-up time calculation formula (y = cx + d) (step 412), and at that time, the fixing roll is immediately driven (step 41).
3), turning on predetermined power (steps 414-41)
6). More specifically, for example, in the case of a fixing roll that is being driven, the target temperature rise is the fixing set temperature, and even in this case, the fixing roll temperature and the target temperature just before the start of temperature rise as shown in FIG. It is clear that the graph of the arrival time can be obtained from the measured value by actually raising the temperature from each temperature rising start temperature. The above calculation formula (y = ax +
The constants c and d are determined in the same manner as in b). When the above roll is used, the constant c: -0.05031 and the constant d: 10.81579 are obtained. The steps 401, 402, 412 to 416 in FIG. 4 correspond to the invention described in claim 2.

Next, the control for gradually decreasing the heater output in this embodiment will be described. As described above, the actual fixing roll temperature has reached the set fixing temperature, but the output of the thermistor 4 shows a temperature lower than the actual temperature from the response performance. For this reason, in this embodiment, several thermistor detection temperatures for switching the input power are prepared, and the output of the heater is lowered stepwise. After the fixing set temperature is reached as shown in FIG. 4, when the thermistor input value is equal to or lower than the predetermined temperature k as shown in FIG.
o) Repeatedly turning on the power for i seconds until the temperature becomes higher than the predetermined temperature k (step 418), and if it is higher than the predetermined temperature k (Yes in step 417), then whether the thermistor input value is higher than the predetermined temperature l. Check (Step 4)
19). As a result, if the temperature is equal to or lower than the predetermined temperature 1 (No in step 419), the temperature is repeated for j seconds until the temperature becomes higher than the predetermined temperature l (step 420). In this way, the heater output is lowered stepwise (two steps of predetermined temperatures k and l).
More specifically, when the above roll is used, the thermistor detection temperature k: 180 ° C., the thermistor detection temperature l: 1
The temperature is 90 ° C., and the lighting time is i: 11/20 seconds and the lighting time is j: 5/20 seconds. In addition, step 417 of FIG.
420 corresponds to the invention of claim 4.

Next, the control of the heater lighting time during the passage of the recording paper in this embodiment will be described. In this embodiment,
The heater lighting time during the passage of recording paper is finely divided per unit time, and the supplied electric power is changed stepwise to perform more precise control. As mentioned above, the thermistor input value is l
In a larger state (Yes in step 419 of FIG. 5),
Further, it is checked whether the thermistor input value is higher than the fixing set temperature (step 421). As a result, if the thermistor input value is higher than the preset fixing temperature (Yes in step 421) and the fixing roll is being driven (step 42).
2), power is turned on for e seconds (step 42)
3). If the thermistor input value is higher than the preset fixing temperature (Yes in step 421) and the fixing roll is not being driven (No in step 422), the power is turned on for f seconds (step 424). On the other hand, if the thermistor input value is equal to or lower than the preset fixing temperature (No in step 421) and the fixing roll is being driven (Yes in step 425), g
Power is turned on for seconds (step 426). Further, the thermistor input value is equal to or lower than the preset fixing temperature (No in step 421), and the fixing roll is not being driven (step 42).
5), power is turned on for h seconds (step 42).
7). These steps 421 to 427 are repeated until the fixing is completed or an abnormality is detected (step 428) together with the above steps 417 to 420. Such heater lighting time is set by obtaining the relationship between the temperature gradient and the input power as shown in FIG. That is, cases are determined depending on whether or not the fixing roll is driven, the temperature gradient of the fixing roll during the fixing operation of the recording paper is measured, and the lighting time of the heater is determined. In FIG. 6, since the unit time of 1 second is divided into 20, for example, 10/20 seconds, 0.
It is set to turn on the heater for 5 seconds. More specifically, when the above roll is used, lighting time e: 11/20 seconds, lighting time f: 5/20 seconds, lighting time g: 14/20 seconds, lighting time h: 9/20 seconds Set. Note that steps 421 to 428 of FIG. 5 correspond to the invention of claim 3.

FIG. 7 shows the control situation when the fixing operation is performed by the control method of this embodiment. At the start
Although the thermistor output is detected to be lower than the actual fixing roll temperature, it is stabilized at the proper fixing roll temperature by the heater output correction operation until the fixing setting temperature is reached and the stepwise heater output operation after the fixing setting temperature is reached. The fixing operation can be performed. First, regardless of the responsiveness of the thermistor, fixing can be performed at the same time when the set fixing temperature is reached, and the constant temperature operation can be performed even if the fixing roll temperature at the start of temperature increase is equal to or higher than the temperature increase target temperature. In addition, stepwise heater output control (17
/ 20 seconds, taper as shown in 15/20 seconds, 14
/ 20 seconds, continuous increase and decrease as shown in 9/20 seconds)
Thus, the fixing property of the toner on the recording paper can be stabilized. Further, a sharp decrease in the fixing roll temperature can be suppressed, and the fixing property can be prevented from deteriorating. In this embodiment,
The start-up time is calculated according to the thermistor input value using the start-up time calculation formula, and the heater lighting time is determined in consideration of the recording paper arrival time to the fixing section.The thermistor input value and the corresponding heater A control table in which the lighting time is registered may be prepared in advance, and the heater lighting time may be immediately obtained from the thermistor input value.

(Second Embodiment) In the control method shown in the first embodiment (specifically, steps 421 to 428 in FIG. 5), the ripple width of the fixing roll temperature is suppressed to a low level.
When the fluctuation of the power supply voltage applied to the fixing device is large, the fixing roll temperature may not be maintained at the fixing set temperature in the pair of heater lighting cycles. In view of this, the present embodiment shows a control method in which a plurality of heater lighting cycles are held in a memory and a heater lighting cycle that matches the power supply voltage applied to the device is selected. The structure of the fixing unit including the fixing roll in the fixing device of this embodiment is the same as that of the first embodiment (FIG. 2). The configuration of the fixing device of this embodiment is as shown in FIG.
The ROM 11a stores a plurality of heater lighting cycle values. The heater lighting cycle value currently in use is stored in the RAM 11b. Further, the control unit 13 includes a temperature gradient calculation / determination function, a ROM 1
1a has a function of appropriately selecting a heater lighting cycle and a function of writing the selected heater lighting cycle in the RAM 11b.

As the heater lighting cycle stored in the ROM 11a, for example, a unit time of 1 second is divided into 10 units, and 10 heater lighting times within the unit time of 1 second are prepared. More specifically, "10/10 seconds: continuous lighting, 9 /
10 seconds: 0.9 seconds on, 0.1 seconds off, ..., 1 /
10 seconds: 0.1 seconds on, 0.9 seconds off, 0/10
10 seconds of "second: continuous light off" is set. The unit time, the division method, the set time, the set number, etc. may be arbitrary. Further, the relationship between the heater lighting cycle and the temperature gradient on the surface of the fixing roll 19 when the reference voltage is applied to the fixing heater 16 is as shown in FIG. In addition, the heater lighting cycle and the temperature gradient of the fixing roll surface temperature are determined by the device configuration (fixing roll material, fixing roll thickness, roll diameter, roll length, pressure roll material, pressure roll thickness, roll diameter, Since the roll length, the heater rating, etc.) are different, it is necessary to measure in advance at each unit to understand the relationship between the heater lighting cycle and the fixing roll surface temperature gradient.

Here, the fixing roll temperature control method of this embodiment will be described with reference to FIG. In the present embodiment, when the thermistor detection temperature exceeds the set value (fixing set temperature) (step 1001 and above), the fixing roll surface temperature is lowered (so that the fixing roll surface temperature gradient fluctuates in the negative direction). The heater lighting cycle is switched to the dedefault heater stored in the RAM 11b (step 1003). When the temperature detected by the thermistor is lower than the set value (less than step 1001), the default stored in the RAM 11b is set so as to increase the surface temperature of the fixing roll (so that the surface temperature gradient of the fixing roll swings positive). Switch to the heater lighting cycle (step 100)
2). For example, "4/10 seconds: 0.4 seconds in 1 second,
If the fixing roller temperature detected by the thermistor 4 is lower than the fixing roll set temperature when the heater lighting cycle of "0.6 second off" is selected, then "8/10 seconds: 0.8 seconds in 1 second" The heater lighting cycle of "lighting, turning off for 0.2 seconds" is selected. The above is one embodiment of the invention described in claim 1.

Next, the temperature gradient is detected 3 times per unit time (for example, 0.5 seconds) after the heater lighting cycle is switched.
The operation is repeated (steps 1004, 1005, or steps 1008, 1009), and when the same result is continuously obtained, the process proceeds to the next step. The number of times the fixing heater surface temperature gradient is detected depends on the response performance of the thermistor 4. The above is one embodiment of the invention described in claim 4.

Further, if the result of the determination in step 1001 is "above the set fixing temperature" and the result of the determination in step 1010 is positive, the heater lighting cycle is set so that the power input becomes lower than the default value. If the switch (step 1011) is negative, the heater lighting cycle is left at the default (step 10).
12). More specifically, in step 1010,
The thermistor detection temperature before and after the unit time (for example, 0.5 seconds) after switching is compared by the control unit 12 to obtain the temperature change rate. The unit time for detecting the surface temperature gradient of the fixing roll is determined from the rate of temperature change when the default voltage is applied, and is, for example, the time from when the lighting cycle of the heater is switched to when it falls below the fixing set temperature. 1/10 of the above. If the rate of temperature change is positive, the setting value on the ROM 11a is set to 1 from the default value.
The heater lighting cycle in which the step output decreases is selected, and the writing heater lighting cycle is switched to the control RAM 11b. For example, the default of the RAM 11a is 4/10
If it is seconds, rewrite to 3/10 seconds. After the switching, if the temperature gradient does not change to a negative value, the above control is repeated until the gradient becomes negative.
In step 1010, if the temperature change rate is negative, the default setting value is used. The above is one embodiment of the invention described in claim 2.

On the other hand, the judgment result of step 1001 is "fixing temperature or less", and the judgment result of step 1006 (in this embodiment, the temperature gradient is judged three times in succession).
If is positive, the heater lighting cycle is left at the default (step 1012), and if negative,
The heater lighting cycle is switched so that the electric power supplied increases from the default value (step 100).
7). More specifically, in step 1006, the thermistor detection temperature before and after the unit time (for example, 0.5 seconds) after switching is compared by the control unit 12, and if the temperature change rate is positive, the default setting value is set. To use. If the rate of temperature change is negative, the heater lighting cycle in which the output is increased by one step from the default value is selected from the set value on the ROM 11a, and the lighting heater lighting cycle is switched to the control RAM 11b. For example, RAM1
If the default on 1b is 7/10 seconds, rewrite to 8/10 seconds. If the temperature gradient does not change to a positive value after switching in this manner, the above-described control gradient is repeated until it becomes a positive value. The unit time for detecting the surface temperature gradient of the fixing roll is set in the same manner as described above. The above is one embodiment of the invention described in claim 3.

[0020]

According to the present invention, the temperature rise time up to the fixing set temperature is determined by the detected temperature at the start of temperature rise regardless of the response of the thermistor. It is possible to prevent the actual fixing roll temperature from significantly exceeding the fixing set temperature during the temperature rise, while fixing can be performed at the same time when the set temperature is reached. Further, according to the present invention, in the control for performing the fixing operation by deciding the temperature rising time from the fixing roll temperature at the start of temperature increase, the fixing roll temperature range in which the fixing operation can be started can be from room temperature to just before the fixing set temperature. The restriction that the constant temperature operation cannot be performed at the temperature increase target temperature or higher is eliminated, and the user's environment for using the apparatus is improved. Further, according to the present invention, the fixing property of the toner on the recording paper can be stabilized by reducing the temperature ripple width of the fixing roll. Further, also in the device used in the conventional ON / OFF control, the temperature ripple width of the fixing roll can be reduced only by changing the control software without electrically changing it. Further, according to the present invention, it is possible to prevent a sharp decrease in the fixing roll temperature and prevent the fixing property from deteriorating. Further, according to the present invention, by holding the heater lighting cycle in a plurality of memories, it is possible to select the heater lighting cycle that matches the power supply voltage applied to the apparatus, and set the fixing roll surface temperature to the fixing setting. It can be maintained near the temperature. Further, according to the present invention, even when the power supply voltage applied to the apparatus is higher than the standard value, heating runaway of the fixing apparatus can be prevented in advance. In addition, a stable fixing property can always be obtained against the fluctuation of the power supply voltage. Further, even when the specifications of the power supply are different (for example, 220V system and 240V system), it can be dealt with without changing the hardware of the device, so that the manufacturing cost can be reduced. Further, according to the present invention, even when the power supply voltage applied to the apparatus is smaller than the standard value, an unfixed image is not output, and stable fixability can always be obtained against fluctuations in the power supply voltage. Further, even when the specifications of the power source are different, it is possible to deal with the apparatus without changing the hardware, so that the manufacturing cost can be reduced. Further, according to the present invention, since the judgment is made on the basis of the temperature detection results obtained by the thermistor continuously, it is possible to prevent malfunction.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a configuration of a fixing device according to an exemplary embodiment of the present invention.

FIG. 2 is a diagram illustrating a configuration of a fixing unit according to an exemplary embodiment of the present invention.

FIG. 3 is a diagram showing a relationship between a fixing roll temperature at the start of temperature increase and an arrival time to a temperature increase target temperature in one embodiment of the present invention.

FIG. 4 is a part of a flowchart showing a fixing roll temperature control method according to an embodiment of the present invention.

FIG. 5 is a part of a flow chart showing a fixing roll temperature control method in one embodiment of the present invention.

FIG. 6 is a diagram showing an applied power and a temperature gradient of a fixing roll in one embodiment of the present invention.

FIG. 7 is a diagram showing a state change during fixing roll temperature control in one embodiment of the present invention.

FIG. 8 is a diagram showing a configuration of a fixing device according to an exemplary embodiment of the present invention.

FIG. 9 is a diagram showing a fixing roll surface temperature gradient in each heater lighting cycle when a reference voltage is applied in one embodiment of the present invention.

FIG. 10 is a flowchart showing a fixing roll temperature control method according to an embodiment of the present invention.

[Explanation of symbols]

1: Silicone rubber, 2: Heat roll, 3: Heat source, 4:
Thermistor, 5: pressure roll core metal, 11: memory, 1
2: detection unit, 13: control unit, 14: heater drive unit, 1
5: main motor drive unit, 16: halogen lamp heater, 17: drive motor, 18: paper discharge roll, 19: fixing roll.

Claims (8)

[Claims] 1. A fixing unit including a fixing roll, a thermistor arranged in contact with a part of the fixing roll, and a heater for raising the temperature of the fixing roll, and recording within a fixed time after driving the fixing roll. In the fixing device configured so that the paper reaches the fixing unit, based on the relationship between the fixing roll temperature and the heater lighting time, from the fixing roll temperature detected by the thermistor immediately before the temperature rise,
A control means for determining the heater lighting time up to the preset temperature raising target temperature in anticipation of the temperature range that rises to the constant fixing set temperature within the fixed time, and driving the fixing roll after reaching the temperature raising target temperature. A fixing device having. 2. When the temperature of the fixing roll detected by the thermistor just before the temperature rise reaches the target temperature of the temperature rise, the heater blinking time is determined according to the temperature of the fixing roll and the fixing roll is immediately driven. The fixing device according to claim 1, further comprising a control unit. 3. A fixing unit including a fixing roll, a thermistor arranged in contact with a part of the fixing roll, and a heater for raising the temperature of the fixing roll. ON / OFF of heater based on relationship
In the fixing device configured to control, the average electric power supplied to the heater is changed stepwise to supply electric power, and the fixing device has means for controlling the output of the heater depending on whether or not the fixing roll is driven. Fixing device characterized by. 4. A means for controlling so that the output of the heater is stepwise reduced until the temperature detected by the thermistor reaches a fixing set temperature when the output mode after the heating of the heater is finished is switched to the mode of paper passing. The fixing device according to claim 1, 2 or 3, further comprising: 5. A fixing unit including a fixing roll, a thermistor arranged in contact with a part of the fixing roll, and a heater for raising the temperature of the fixing roll. ON / OFF of heater based on relationship
In the fixing device configured to control, the storage unit for holding the pattern of the plurality of heater lighting cycles corresponding to the fixing roll temperature and the heater lighting cycle corresponding to the fixing roll temperature detected by the thermistor are And a control unit that selects from a storage unit. 6. When the fixing roll temperature exceeds a fixing set temperature, a predetermined heater lighting cycle is selected from the storage means, and the temperature gradient of the fixing roll temperature detected by the thermistor in the heater lighting cycle is selected. However, if it is positive, the fixing means for switching to the heater lighting cycle is set so that the electric power supplied to the heater is lower than that of the heater lighting cycle. apparatus. 7. When the fixing roll temperature becomes equal to or lower than the fixing set temperature, a predetermined heater lighting cycle is selected from the storage means, and the temperature gradient of the fixing roll temperature detected by the thermistor in the heater lighting cycle is selected. If the value is negative, the fixing means for switching to the heater lighting cycle is set so that the electric power supplied to the heater is increased more than the heater lighting cycle. apparatus. 8. When the temperature gradient of the fixing roll temperature detected by the thermistor is obtained, the temperature gradient is detected a plurality of times in succession, and a control means for making a determination based on the continuous detection result is provided. The fixing device according to claim 6, wherein: