JPH05297758A - Fixing device - Google Patents

Abstract

PURPOSE:To restrain temperature ripple and overshoot to a minimum and to prevent the unevenness of fixing and the shortening of the life of each part. CONSTITUTION:A microcomputer 13 controls an SSR 12 through a NAND circuit 16 and a buffer 17 based on temperature detected by a thermistor 7 so as to supply power to a resistance heating element 3 by switching the power (200W) at which the temperature of the nip part of an upper roller necessarily rises when the paper of allowable maximum size and maximum basis weight, where toner is stuck all over the surface, passes under the allowable lowest ambient temperature of an image forming device and the power (100W) at which the temperature of the nip part of the upper roller necessarily lowers when the recording paper of allowable minimum size and minimum basis weight, where the toner is not stuck, passes under the allowable highest ambient temperature.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device which is applied to, for example, an electrophotographic copying machine, a printer or the like and heat-fixes a toner image formed on a recording sheet.

[0002]

2. Description of the Related Art Conventionally, an electrostatic latent image formed on a photosensitive conductor is developed with toner, the obtained toner image is transferred to a recording paper, and then thermally fixed by a fixing device to form an image. Photocopiers and printers are used. In the fixing device, a heating element such as a halogen lamp is used as an O
By turning off N and OFF, the fixing temperature is controlled within a predetermined range.

[0003]

However, in the fixing device configured to control the fixing temperature by turning on and off the heating element as described above, the fixing temperature rises sharply when the heating element is turned on. , OFF, the fixing temperature drops sharply. Therefore, there is a problem that the temperature ripple is large, unevenness in the degree of fixing tends to occur, and the temperature overshoot is large, so that the life of each part constituting the fixing device and the like tends to be shortened. It was

In view of the above points, an object of the present invention is to provide a fixing device capable of suppressing temperature ripples and overshoots to prevent uneven fixing and shortening of the life of each part.

[0005]

In order to achieve the above object, the invention of claim 1 is a fixing device for fixing a recording paper on which a toner image is formed by pressing a heating roller against the recording paper to heat the heating roller. Heating means for heating, a power supply means for supplying power to the heating means, and a temperature detection means for detecting the temperature of the recording paper pressure contact portion of the heating roller or the vicinity thereof,
When the temperature detecting means detects the first temperature lower than the predetermined temperature, the power supply means is caused to supply the first electric power, and when the second temperature higher than the predetermined temperature is detected. And a control means for controlling to supply a second electric power, and the first electric power has a maximum allowable size and a maximum basis weight with toner adhered to the entire surface under the minimum allowable environmental temperature. Is set to an electric power that can raise the temperature detected by the detecting means when the paper is passed, the second electric power is an allowable minimum size with no toner adhered under the maximum allowable environmental temperature. Also, when the paper having the minimum basis weight is passed, the electric power is set so that the temperature detected by the detection means can be lowered.

According to a second aspect of the present invention, in a fixing device for fixing a recording paper on which a toner image is formed by pressing a heating roller against the recording paper, a heating means for heating the heating roller and an electric power for the heating means. Power supply means, a temperature detection means for detecting the temperature of the recording paper pressure contact portion of the heating roller or the vicinity thereof, and a power supply means, a predetermined cycle is distributed at a predetermined ratio based on the temperature detected by the detection means. Every hour
It is characterized in that it is provided with control means for controlling so as to alternately supply the first electric power and the second electric power smaller than the first electric power.

[0007]

According to the present invention, the control means allows the power supply means to allow the toner to adhere to the entire surface under the minimum allowable environmental temperature when the first temperature is detected by the temperature detecting means. When the first electric power that can raise the detection temperature of the detection unit is supplied when the paper of the maximum size and the maximum basis weight is passed, and when the second temperature higher than the first temperature is detected. Controlling to supply a second electric power capable of lowering the temperature detected by the detecting means when a sheet of the minimum allowable size and minimum basis weight without toner adhered is passed under the maximum allowable ambient temperature To do.

Further, in the invention of claim 2, the control means provides the power supply means with the first power at every time when a predetermined cycle is distributed at a predetermined ratio based on the temperature detected by the detection means. The control is performed so that the second electric power smaller than the first electric power is supplied alternately.

[0009]

【Example】

(First Embodiment) As a first embodiment of the present invention, an example of a fixing device applied to an image forming apparatus will be described below with reference to FIGS. In the fixing device, as shown in FIG.
An upper roller 1 made of a cylindrical thin metal roller and a lower roller 2 having an elastic layer made of silicon sponge are provided.

A heat transfer aluminum block 4 is provided on the inner surface side of the nip portion of the recording paper in the upper roller 1, as shown in FIG. The heat transfer aluminum block 4 is biased by a spring 6 provided between the heat transfer aluminum block 4 and a stay 5 attached to a frame (not shown) so as to come into close contact with the inner surface of the upper roller 1. As shown in FIG. 3, a resistance heating element 3 having electrodes 3a, 3a at both ends is attached to the heat transfer aluminum block 4. More specifically, as shown in FIG. 4, the alumite treatment layer 4 is formed on the heat transfer aluminum block 4.
A concave portion 4b having a formed therein is provided, and the resistance heating element 3 is embedded in the concave portion 4b. Since the alumite treatment layer 4a is formed in this manner, the resistance heating element 3
The heat transfer aluminum block 4 and the heat transfer aluminum block 4 are insulated from each other, and the heat resistance therebetween can be suppressed small.

In addition, on the upper part of the heat transfer aluminum block 4,
A thermistor 7 that detects the temperature of the heat transfer aluminum block 4 is attached. The thermistor 7 is not limited to being provided on the upper portion of the heat transfer aluminum block 4, but may be provided near the contact portion of the heat transfer aluminum block 4 with the upper roller 1. The thermistor 7 is connected to the control circuit 11 shown in FIG. 5, and the resistance heating element 3 includes the temperature fuse 8 and the SSR (solid state relay) 1 of the control circuit 11.
It is connected to the power source 9 via 2 and the supplied power is controlled. The temperature fuse 8 is for preventing an excessive temperature rise that may cause mechanical damage.

The control circuit 11 has a terminal 7a of the thermistor 7.
And a microcomputer 13 for outputting a control signal having a predetermined duty ratio in accordance with the potential and the operating state of the image forming apparatus to which the fixing device is applied. Here, since the resistance heating element 3 is used as the heating element as described above, the ON / OFF time of the control signal is less restricted as compared with the case where a halogen lamp is used, and the control can be performed at a desired duty ratio. It's relatively easy.

A safety circuit 14 is provided in the control circuit 11. The safety circuit 14 includes a comparator 15 that compares the potential of the terminal 7a of the thermistor 7 with a predetermined upper limit potential, and a NAND circuit 16 that masks a control signal from the microcomputer 13 according to the output of the comparator 15. The control signal is forcibly made inactive when 13 runs away. The output terminal of the NAND circuit 16 is connected to the gate terminal of the SSR 12 via the buffer 17. As shown in FIG. 6, the SSR 12 is capable of suppressing noise caused by switching by performing a zero-cross operation.

The temperature control operation performed in the fixing device having the above-mentioned structure will be described with reference to FIGS. 7 is a flowchart showing the control operation of the microcomputer 13, FIG. 8 is a time chart showing the operation of the image forming apparatus and the temperature of each part of the fixing device, and FIG. 9 is a time chart showing the relationship between the supplied power and the temperature ripple. ..

In the following description, the upper roller 1
Control temperatures T1 ′ and T1 at the time of standby of the image forming apparatus in the nip part of No. 2 and the thermistor 7 mounting part of the heat transfer aluminum block 4 are 150 ° C. and 200, respectively.
℃, control temperature T2 ', T2 during the fixing operation is 1
It is assumed that the temperature is 80 ° C. and 230 ° C. First,
When the operation instruction of the fixing device is given, the microcomputer 13 outputs a control signal with a duty ratio of 100%,
The SSR12 is continuously turned on, and the resistance heating element 3 receives 40
Electric power of 0 W is supplied (S1).

Next, the temperature Temp detected by the thermistor 7
Is lower than the standby control temperature T1 (= 200 ° C.) (S2), and if it is not lower, that is, when the image forming apparatus is turned on again shortly after being turned off, a short If the control temperature T1 during the standby time is reached or exceeded during the time, the process immediately proceeds to (S6). On the other hand, if it is lower than the standby control temperature T1, it is further determined whether or not 20 seconds have elapsed since the operation instruction was given (S3). If 20 seconds have not elapsed, the above (S1) and subsequent steps are repeated, and if 20 seconds have elapsed (A in FIG. 8), (S
Go to 4).

Here, the standby control temperature T1 is a temperature that can be raised to a temperature at which fixing can be performed before the leading edge of the recording paper reaches the fixing device when the image forming operation is started. Good. Further, as long as this condition is satisfied, the warm-up time can be shortened as the temperature is as low as possible. In (S4), a control signal having a duty ratio of 50% is output to supply a power of 200 W in order to suppress the temperature overshoot, and it is determined whether the detected temperature Temp has become equal to or higher than the standby control temperature T1. (S5), after repeating (S4, S5) until the standby control temperature T1 or higher (B in FIG. 8), (S6)
Move to.

In (S6), a "READY" message indicating that the image forming operation is possible is displayed on a display panel (not shown). Next, according to the determination (S7) as to whether the detected temperature Temp is lower than the standby control temperature T1, power of 60 W or 0 W is supplied (S7).
8, S9), it is determined whether or not an image forming instruction has been issued (S10), and the steps from S7 onward are repeated until the image forming instruction is given.

Here, the electric power of 60 W or 0 W is
The power is set to satisfy the following conditions. That is, 60 W is the minimum electric power that the temperature of the nip portion always rises when the upper roller 1 is not driven under the allowable minimum environmental temperature of the image forming apparatus, while 0 W is the maximum allowable environmental temperature. It is electric power that always lowers the temperature of the nip portion when the upper roller 1 is not driven under the temperature.

When it is determined in (S10) that the image forming instruction is given (C in FIG. 8), first, 400 W of electric power is supplied (S11). In this case, the upper roller 1 and the lower roller 2 are rotated by the driving of a main motor (not shown), and the heat amount is taken to a portion where the heat of both rollers is not spread, so that the temperature rise is caused by the operation of the fixing device. Although it becomes slower than when 400 W of electric power is supplied when an instruction is given, it may be raised to a temperature at which fixing is possible in a time period until the leading edge of the recording paper on which the toner image is formed reaches the fixing device. ..

Next, it is determined whether the detected temperature Temp is lower than the image forming control temperature T2 (= 230 ° C.) (S12). If the detected temperature Temp is not lower than the image forming control temperature T2 (D in FIG. 8), The process proceeds to (S16) and the supplied power is reduced to 100W. On the other hand, if the temperature is lower than the image forming control temperature T2, it is further determined whether or not 30 seconds have elapsed since the image forming instruction was issued (S13). If 30 seconds have not elapsed, the above (S11) and subsequent steps are repeated, When 30 seconds have passed, the process proceeds to (S14). Normally, the control temperature T2 during image formation is reached by 30 seconds and the process proceeds to (S16). However, when the thermistor 7 malfunctions, 400 W of electric power is supplied for a long time to adversely affect each part. In order to prevent giving, (S11) ~ (S1
It is designed to get out of the loop of 3).

In (S14) to (S17), the detected temperature T
According to the determination (S14) as to whether the emp is lower than the image formation control temperature T2, the power of 200 W or 100 W is supplied (S15, S16), and it is determined whether the image formation is completed (S17). , And the subsequent steps are repeated until the image formation is completed (S14). When the image formation is completed (E in FIG. 8), the process returns to (S7) and the same control is repeated. When the image formation is continuously performed, when the last image formation is completed (F in FIG. 8),
Return to (S7).

Here, the power of 200 W or 100 W is power set to satisfy the following conditions.
That is, 200 W is the nip portion of the upper roller 1 when a sheet of the maximum allowable size and the maximum basis weight with toner adhered to the entire surface is passed under the minimum environmental temperature and humidity allowed by the image forming apparatus. While the temperature of the upper roller always increases, 100W is the upper roller when the recording paper of the allowable minimum size and the minimum basis weight with no toner is passed under the allowable maximum environmental temperature and humidity. The electric power is such that the temperature of the nip portion of No. 1 always drops. In particular, the temperature ripple can be suppressed to a small level by setting the above condition to the limit.

With this setting, for example, B / W (black-white ratio) is applied to a recording paper having a basis weight of 80 g / m 2 at room temperature and normal humidity.
When a general document of about 5% is printed, the switching cycle between 200 W and 100 W is about 1 second, and the temperature ripple at the nip portion can be suppressed to about 4 ° C. or less. When the basis weight of the recording paper is small, for example, the temperature ripple becomes large, such as 6 to 7 ° C., but one set of the set electric powers as described above is set in advance in plural numbers, and the basis weight of the recording paper is set. The selection may be made automatically according to the amount or use environment, or by a user operation.

Further, instead of making the determination in (S14) by the threshold temperature, if the supplied power is switched earlier by the predictive control, the control becomes complicated, but the temperature ripple is further suppressed. You can also do so. In the above example, the duty ratio of the control signal is changed to control the supply power, but 200 W and 1
In order to perform only switching to 00W, SSR may be combined to switch between passing the full wave of AC and passing only the half wave of AC as shown in FIG. Further, various elements such as a triac can be used instead of the SSR. (Second Embodiment) A second embodiment of the present invention will be described below with reference to FIG.

In the second embodiment, the mechanical structure of the fixing device and the hardware structure of the control circuit 11 are the same as those in the first embodiment, and the control performed by the microcomputer 13, particularly the control during image formation. Is different. That is, when an image forming instruction is given, first, the image forming control temperature T2 is held as a temporary initial value of the previous temperature T0 for determining the temperature change (S21).

Next, the temperature Tem detected by the thermistor 7
After holding p as the current temperature Te (S22), it is determined whether the temperature is higher than the previous temperature T0 (S23). In accordance with this determination, the times tLO and tHI for supplying electric power of 100 W and 200 W according to the current temperature Te are read from the temperature rising table or the temperature falling table stored in the ROM (not shown) (S24, S2).
5). Here, the total of tLO and tHI is set to be, for example, 1 second.

The values of tLO and tHI held in the temperature rising table and the temperature falling table are
For the same current temperature Te, the temperature rise table is set to have a larger tLO value than the temperature fall table. More specifically, for example, when the current temperature Te is lower than the control temperature T2 at the time of image formation, if the current temperature Te is decreasing, it is continued for 1 second (or for 1 second in order to suppress the undershoot). 200W of electric power is supplied for a sufficiently long time, while 100W of electric power is supplied for a predetermined time within one second in order to suppress overshoot during rising, and this 100W supply time is The current temperature Te is set to increase as it approaches the image forming control temperature T2.
That is, the current temperature Te at which the length of tLO and the length of tHI are reversed is lower when the temperature rises than when it falls.

As described above (S24) or (S2)
When the power supply times tLO and tHI are determined in 5), the powers of 100 W and 200 W are supplied only for the time corresponding to this (S26). Here, which electric power is supplied first may be switched based on the current temperature Te and whether the temperature is currently rising or falling. After that, the current temperature Te is held as the previous temperature T0 (S27), various other processes are performed (S28), it is determined whether the image formation is completed (S29), and the image formation is completed (S29). S
22) and subsequent steps are repeated.

[0030]

As described above, according to the present invention,
By controlling the fixing temperature by switching the electric power in two predetermined steps, the fixing temperature is not abruptly changed. Therefore, temperature ripples and overshoots can be suppressed to a small level to prevent uneven fixing and shorten the life of each part. There is an effect that can be.

Further, by switching the electric power in two stages for each time distributed at the ratio according to the temperature detected by the detecting means, there is an effect that temperature ripple and the like can be further suppressed.

[Brief description of drawings]

FIG. 1 is a perspective view illustrating a configuration of a fixing device according to a first exemplary embodiment.

FIG. 2 is a sectional front view showing the configuration of the fixing device.

FIG. 3 is a plan view showing the structure of the resistance heating element.

FIG. 4 is a perspective view showing a detailed structure of the heat transfer aluminum block.

FIG. 5 is a circuit diagram showing a configuration of a control circuit of the same.

FIG. 6 is an explanatory diagram showing a switching waveform of supplied power.

FIG. 7 is a flowchart showing a control operation of the microcomputer.

FIG. 8 is a time chart showing the operation of the image forming apparatus and the temperature of each part of the fixing device.

FIG. 9 is a time chart showing the relationship between supplied power and temperature ripple.

FIG. 10 is an explanatory diagram showing a switching waveform of supplied power in a modified example.

FIG. 11 is a flowchart showing the control operation of the microcomputer in the second embodiment.

[Explanation of symbols]

 1 Upper Roller 2 Lower Roller 3 Resistance Heating Element 3a Electrode 4 Heat Transfer Aluminum Block 4a Alumite Treatment Layer 4b Recess 5 Stay 6 Spring 7 Thermistor 7a Terminal 8 Thermal Fuse 9 Power Supply 11 Control Circuit 12 SSR 13 Microcomputer 14 Safety Circuit 15 Comparator 16 NAND circuit 17 buffer

 ─────────────────────────────────────────────────── ─── Continuation of front page (72) Inventor Kenki Oka 2-3-13 Azuchi-cho, Chuo-ku, Osaka Inside Osaka Kokusai Building Minolta Camera Co., Ltd. (72) Inventor Keno Kubota 2-chome, Azuchi-cho, Chuo-ku, Osaka 3-13 No. 13 Osaka International Building Minolta Camera Co., Ltd.

Claims (3)

[Claims] 1. A fixing device for fixing a recording paper on which a toner image is formed by pressing a heating roller against the recording paper, the heating means for heating the heating roller, and a power supply means for supplying electric power to the heating means. Temperature detecting means for detecting the temperature of the heating roller at or near the recording paper pressure contact portion, and when the temperature detecting means detects a first temperature lower than a predetermined temperature, first power is supplied to the power supply means. And a control means for controlling to supply the second electric power when the second temperature higher than the predetermined temperature is detected while the electric power is supplied. The temperature is set to an electric power capable of increasing the detection temperature of the detection unit when a sheet of the maximum allowable size and the maximum basis weight with toner adhered to the entire surface is passed under the temperature. Power is the highest allowed It is characterized in that it is set to an electric power capable of lowering the detection temperature of the detection means when a sheet of the allowable minimum size and the minimum basis weight without toner is passed under the boundary temperature. Fixing device. 2. A fixing device for fixing a recording paper on which a toner image is formed by pressing a heating roller against the recording paper, and heating means for heating the heating roller, and power supply means for supplying electric power to the heating means. A temperature detection means for detecting the temperature of the heating roller at or near the recording paper pressure contact portion; and a power supply means for each time when a predetermined cycle is distributed at a predetermined ratio based on the temperature detected by the detection means. Power of
A fixing device comprising: a control unit that controls to alternately supply a second electric power that is smaller than the first electric power. 3. The first electric power is used to detect the temperature detected by the detecting means when a sheet having an allowable maximum size and a maximum basis weight with toner adhered to the entire surface is passed under the allowable minimum environmental temperature. While the power is set to increase, the second
The power of is set to the power that can lower the detection temperature of the detection means when the paper of the allowable minimum size and the minimum basis weight with no toner is passed under the maximum allowable ambient temperature. The fixing device according to claim 2, wherein