JP2641294B2 - Fixing device - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for heating and fixing a toner image as a developer image on a recording material.

[Related Art] Conventionally, for example, a fixing device used in an image forming apparatus has a configuration as shown in FIG. In FIG. 7, reference numeral 51 denotes a fixing roller which is a metal core 53 made of aluminum, iron, or the like.
A releasable resin layer 54 of PFA, PTFE, or the like is provided thereon, and is heated by a heater 50 provided inside.
The temperature of the fixing roller 51 is detected as a surface temperature of the fixing roller 51 by a temperature detecting element 58 in contact with the fixing roller 51, and the heater 50 is intermittently operated by a temperature control circuit (not shown). The surface temperature is controlled to a predetermined temperature.

On the other hand, 52 is a pressure roller which presses and rotates against the fixing roller 51. An elastic layer such as silicone rubber or fluorine rubber having heat resistance and good releasability is provided on a metal core metal 56 such as iron or stainless steel. 57 are formed.

The recording material 61 carrying the toner image 60 is guided between the fixing roller 51 and the pressure roller 52 by the entrance guide 63, and is fixed by being heated and pressed. Thereafter, the recording material 61 is separated from the fixing roller 51 by the separation claw 55. Further, a temperature detecting element 58 for keeping the temperature of the surface of the fixing roller 51 constant is disposed substantially at the center of the fixing roller 51 in the axial direction.

[Problems to be Solved by the Invention] However, in the case of such a conventional device, since the temperature detecting element is brought into contact with the fixing roller at the center portion,
With the long-term use, the toner or paper powder adheres to the surface of the temperature detecting element, causing the release resin layer on the surface of the fixing roller to be worn, thereby causing a black streak on an image. Was. Therefore, methods for solving the above problem by moving the temperature detecting element to the end of the fixing roller have been proposed in Japanese Utility Model Laid-Open Nos. 59-147168 and 62-084071.

However, in these apparatuses, as shown in FIG. 8, when the temperature is controlled based on the temperature at the end of the fixing roller, when the recording material is continuously fed and the continuous copying operation is performed, the fixing is performed. Since the temperature of the recording material passage area on the roller gradually decreases accordingly, there is a problem that a fixing failure occurs.

The present invention solves the above problem, and by arranging the temperature detecting element at the end of the fixing roller, it is possible to prevent toner and paper dust from adhering to the temperature detecting element and to continuously feed the recording material. It is another object of the present invention to provide a fixing device that does not cause a fixing failure.

[Means for Solving the Problems] According to the present invention, the object is to provide a fixing roller, a pressure roller that forms a nip portion in contact with the fixing roller, a heater that heats the fixing roller, A temperature detecting element for detecting a temperature, and control means for controlling energization to a heater so that the detected temperature of the temperature detecting element maintains a predetermined set temperature. In the fixing device in which the temperature difference between the paper passing area and the non-paper passing area of the fixing roller increases when performing continuous fixing in the nip portion, the temperature detecting element detects the temperature of the non-paper passing area of the fixing roller, The control means is achieved by increasing the set temperature and controlling the power supply when the number of sheets fixed during continuous fixing reaches a predetermined number of sheets.

[Operation] According to the present invention, since the temperature detecting element is disposed outside the recording material passage area of the fixing roller, toner and paper dust do not adhere to the temperature detecting element, and the fixing roller surface is not damaged. Further, since the temperature at the position where the temperature detecting element is disposed is controlled so as to gradually increase with the increase in the number of recording materials fed, the continuous feeding of recording materials is performed. However, the temperature at the center of the fixing roller is maintained at a temperature optimum for fixing.

Embodiment A first embodiment of the present invention will be described with reference to FIGS. 1 to 3 of the accompanying drawings.

In FIG. 1, reference numeral 1 denotes a rotatable fixing roller, and a heater 2 is disposed inside the fixing roller 1. Further, a pressure roller 3 is rotatably disposed on the fixing roller 1 by pressing, and a recording material 4 carrying an unfixed image is nipped and conveyed by the fixing roller 1 and the pressure roller 3 to be undetermined. Fix the received image. Further, a temperature detecting element 5 is in contact with the outside of the recording material passage area C on the fixing roller 1, and the temperature detecting element 5 is connected to a controller 6 shown in FIG. The controller 6 is also connected to the heater 2 and controls the temperature of the fixing roller 1 based on data input by the temperature detecting element 5. The controller 6 is connected to the main control unit 7 and accumulates the number of sheets of the recording material 4 by adding a feed signal of the recording material 4 sent from the main control unit 7 and storing it in the memory 8. It is designed to count.

A method of controlling the temperature of the surface of the fixing roller in the apparatus of the present embodiment as described above will be described with reference to FIG.

First, the surface temperature at the central portion, which is the fixing portion of the fixing roller 1, which was controlled to the standby temperature To ° C., needs to be fixed by the controller 6 which receives the print start signal from the main controller 7 and controls the heater 2. Temperature adjustment is started to reach the temperature Ta ° C. This initial target temperature Ta ° C. is stored in the memory 8 in advance, and the number of recording materials 4 is N
Temperature adjustment is performed at this target temperature until sheets are obtained.
Even while the temperature adjustment is being performed, the controller 6 receives the signal from the main control unit 7 and counts the number of the recording materials 4 cumulatively. Tb ° C, which is the second target temperature higher than Ta ° C, is selected, and the temperature is adjusted at Tb ° C until the number of sheets reaches M.

Since the surface temperature at the center of the fixing roller 1 gradually decreases as the number of recording materials 4 increases, the above-mentioned second target temperature Tb ° C. This is a temperature that compensates for a temperature difference between the position and the central portion of the fixing roller 1. Therefore, even when the temperature is adjusted at the target temperature Tb ° C., the surface temperature at the center of the fixing roller 1 is Ta ° C.
Will be maintained.

If the number of recording materials 4 reaches M, the above Tb ° C
The temperature is adjusted by selecting the third target temperature Tc ° C., which is higher than the third target temperature. Here, the number of sheets M is a sufficient number of sheets so that the temperature does not decrease with the increase in the number of recording materials 4 and the temperature difference between the central portion of the fixing roller 1 and the position where the temperature detecting element is provided becomes constant. Is set as Therefore, temperature adjustment is performed at this Tc ° C. until the end of printing. As above
As a result of gradually increasing the temperature in three stages of Ta ° C., Tb ° C., and Tc ° C., the fixing roller 1 does not generate an offset.
Can maintain the surface temperature at the center of Ta ° C., and good fixability can be obtained. In the present embodiment, the target temperature is set to three levels, but may be increased to a plurality of levels, or the number of recording materials for selecting the target temperature may be appropriately determined according to the thickness of the recording material to be used. Good.

Next, a first experimental example based on the first embodiment will be described. As a first experimental example, the following two experimental examples were performed using two types of fixing rollers. The fixing roller used in the experimental example is obtained by providing an elastic rubber layer on the fixing roller used in the experimental example.

(First experimental example) In this experimental example, the fixing roller 1 has a shaft length of 233 mm and an outer diameter of 30 m.
m, a 3.5 mm-thick aluminum pipe material coated with 25 μm of PFA is used. As the pressure roller 3, a 4 mm sponge layer is attached to the surface of a stainless steel cored bar having an outer diameter of 20 mm, and a solid rubber layer 1 mm is applied to the surface layer. Hardness was measured using an Asker-c hardness tester to 30 degrees. Further, a 750 W halogen lamp was used as the heater 2. Then, a letter-size recording material with a basis weight of 75 g is continuously passed through, the target temperature for the intended printing is 190 ° C, and the target temperature for the 20th to 39th sheets is controlled at a target temperature of 192 ° C. Further, the control was performed at the target temperature of 195 ° C. after the 40th sheet. As a result, the temperature at the center of the fixing roller was maintained at approximately 190 ° C., the fixability was good, and no offset occurred.

Conventionally, a technique of providing a rubber layer having poor heat conductivity on the surface of the fixing roller 1 to improve fixing performance, improve printing quality, or reduce the number of cursors has been actively performed. However, such a roller is particularly susceptible to damage and has a large axial temperature difference compared to PFA due to poor heat conduction in the axial direction. However, by applying the present invention, the temperature at the central portion did not decrease even during continuous printing, good fixability was obtained, and the problem of scratches was eliminated. Next, this experimental example will be described.

As the fixing roller, a roller in which a 0.5 mm silicone rubber layer was attached to an aluminum pipe having the same size and material as in the experimental example and a PFA layer having a surface layer of 30 μm was attached was used. The heater 2 and the recording material 4 were the same as those in the experimental example. The set temperature at the time of the intended printing was 190 ° C., and the control was performed at 195 ° C. from the 20th to 39th sheets. After that, the temperature was controlled at 200 ° C. As a result, the temperature at the center of the fixing roller was maintained at approximately 190 ° C., the fixability was good, and no offset occurred.

As described above, even if the configuration of the fixing roller changes, the control may be changed in accordance with the change, and it is needless to say that the present invention can be applied to various types of rollers.

 Next, a second embodiment will be described.

In the first embodiment, the printer enters the standby state immediately after printing is completed, and prints the number of recording materials 4 stored in the memory 8. However, in this method, when printing is started again immediately after printing is completed, the first target temperature of the fixing roller 1 is set to the initial Ta ° C., and the heater 2 is turned on until the temperature at the position where the temperature detecting element 5 is disposed drops to Ta ° C. In this case, the temperature at the center of the fixing roller 1 was lowered to Ta ° C. or lower, and fixing failure occurred. Therefore, in this embodiment, after printing is completed, the number of recording materials stored in the memory 8 is stored for a certain period of time, and when printing is started again within that time, a target corresponding to the number of sheets stored in the memory 8 is used. The temperature control is started from the temperature, and the number of recording materials is added cumulatively to the contents stored in the memory 8. By doing so, even if printing is started again immediately after printing is completed, it is possible to prevent occurrence of a fixing failure.

The configuration of the apparatus of this embodiment is the same as that of the first embodiment, and a timer 9 is connected to the controller 6 as shown in FIG. The controller 6 sends a print end signal to the main controller 7.
, The timer 9 is started with the target temperature of the fixing roller 1 in a standby state. When the timer 9 reaches a predetermined time, the contents of the number of recording materials stored in the memory 8 are reset. When printing is started again within this predetermined time, the number of recording materials at the end of printing is stored in the memory 8, so printing is started from the target temperature corresponding to the number. Therefore, the temperature at the central portion of the fixing roller 1 does not drop temporarily, and therefore, fixing failure does not occur. FIG. 4 shows a change in the temperature of the fixing roller when this control is performed.

This shows a state in which printing is restarted within a predetermined time after printing is completed on the Mth sheet. Immediately after printing is restarted, the fixing roller 1 is heated to the target temperature Tb ° C. corresponding to the (M + 1) th sheet. ing. Here, the predetermined time is determined from the temperature decrease speed during the natural cooling of the fixing device, and is set within the time required to decrease from the target temperature of the M-th sheet to the target temperature during standby.

Next, a second experimental example based on the second embodiment will be described.

(Second experimental example) The device configuration of this experimental example is the same as that of the first experimental example.
When printing was started at the same time when printing was completed, and the number of recording materials stored in the memory 8 was reset after 30 seconds, fixing failure did not occur immediately after printing was restarted.

As an improvement of this embodiment, there is also an effect of subtracting the stored contents from the number of recording materials stored in the memory 8 in accordance with the speed at which the temperature of the fixing roller decreases after printing is completed. With this method, the temperature at the center of the fixing roller can be brought to the printing temperature Ta ° C. more quickly when printing is resumed.

 Next, a third embodiment of the present invention will be described.

In this embodiment, the width of the recording material is considered. Ninth
The figure shows the axial temperature distribution of the fixing roller 1 when 30 sheets of two types of recording materials having different widths are passed. Here, the size A recording material is narrower than the size B recording material.
The temperature difference between the central part and the end part is different. Also,
The finally generated central portion of the fixing roller 1 and the temperature detecting element 5
The temperature difference between the arrangement positions of the recording materials having a smaller width is also larger. This embodiment solves this problem. FIG. 5 shows a change in the surface temperature of the fixing roller 1 when a small-sized recording material is passed according to the present embodiment. In this embodiment, the target temperature is switched at an earlier number of sheets than in the first embodiment shown in FIG. Switching from Ta ° C. to Tb ° C. is performed on the N ′ (<N) th sheet, and switching from Tb ° C. to Tc ° C. is performed on the M ′ (<M) sheet. Further, the set temperature is set to Td ° C. on the K-th sheet. On the other hand, for a recording material having a large size, control is performed as shown in FIG.

The target temperature and the reference number for switching the target temperature can be changed according to the type of recording material used. A known method may be used as a method for detecting the size of the recording material by attaching a cassette (not shown) for supplying the recording material to the image forming apparatus.

Next, a third experimental example based on the third embodiment will be described.

(Third Experimental Example) This experimental example apparatus is the same as the first experimental example except that the means 10 for detecting the recording material width is connected to the controller 6, and uses a B5 size recording material having a basis weight of 75 g. Was. In this case, the set temperature was switched to 195 ° C. after the 15th print after the start of printing, to 200 ° C. after the 30th print, and to 205 ° C. after the 45th print. As a result, the temperature at the center of the roller could be maintained at 190 ° C., and no fixing failure occurred. Also, at this time, when using a recording material of A4 size with a basis weight of 75 g, the method of the first embodiment was used as it was, so that the fixability was good even in A4 size.

 Next, a fourth embodiment of the present invention will be described.

In the first to third embodiments described above, the recording material is fed at equal time intervals. However, the interval at which the recording material enters the fixing roller 1 is actually random because printing is started by a signal from the main control unit 7. In the first to third embodiments, while the main control unit 7 continues to output a signal to maintain the printing state, the image forming apparatus determines that continuous recording is being performed and sets the temperature to the printing temperature. I have. Then, when the interval at which the recording material is fed is long, the temperature is gradually increased in spite of the fact that the temperature difference in the axial direction of the fixing roller 1 is reduced due to heat conduction, and the temperature at the center of the fixing roller 1 is increased. Offset may occur due to too long. This embodiment solves this problem.

The method of temperature control according to the present embodiment will be described with reference to the flowchart of FIG.

First, when a print signal is input, temperature control is started (10
0), the memory S is reset to 1 (101), the timer t is set to 0 (102), and the printing operation is performed (10).
3). After the printing is completed, it is determined whether or not there is a next print start signal (104).
It is determined whether or not it is smaller than the above. If it is smaller, a print start signal is waited for (105 → 104). Here, t1 is a time required for the temperature drop generated in the fixing roller 1 by printing one sheet to return to the original state. Here stops the timer t when the print signal has been entered (106), the timer value t _x at that time in the memory S adds the value t0 / t _x obtained by dividing the t0 (107). Here, t0 is the time required for printing one sheet when continuous printing is performed at the maximum speed, and is obtained by dividing the sum of the length of the recording material and the interval between the recording materials by the transport speed. Then, the next printing operation is performed again. Also, if the timer t has a print signal becomes higher t1 (108) when the you the timer value t _x when there signal, from the memory _{S (t x -t1) / (} t1-t0) Subtract (109
→ 110). This indicates that the temperature drop gradually decreases after t1 and approaches the temperature of the immediately preceding print.
If there is no print signal even when the timer t becomes t1 or more (111), it is checked whether or not the timer t is t2 or less. When the timer t becomes larger than t2, it is determined that the printing is not continuous printing, the memory S is reset (112), and the temperature control is stopped (11).
3).

In this way, even when the interval between the recording materials changes, the target temperature for the number of recording materials is set in consideration of the heat conduction. The occurrence was prevented.

 Next, a fourth embodiment based on this embodiment will be described.

(Fourth embodiment) The configuration of the present experimental example apparatus was the same as that of the first experimental example. In the first embodiment, a letter-size recording material was printed at a speed of 16 sheets per minute, and the interval at which the recording material was sent was constant. When printing was performed eight times per minute with the recording material feeding interval being random, the temperature at the center of the fixing roller reached 198 ° C. at the 40th sheet in the first to third embodiments, causing an offset. Was. However, in the present embodiment, when the control was performed with t0 = 3.75 sec, t1 = 6.00 sec, t2 = 30 sec, the temperature of the center of the fixing roller did not rise above 195 ° C. and did not drop below 185 ° C. No offset occurred.

[Effects of the Invention] As described above, the temperature detecting element is disposed at the end of the fixing roller outside the recording material passage area to prevent the occurrence of black stripes in the image due to the flaw of the fixing roller and to prevent the end of the fixing roller By gradually increasing the target temperature at the arrangement position of the temperature detecting element according to the number and width of the recording materials, it was possible to prevent the occurrence of defective fixing and offset even in continuous printing.

[Brief description of the drawings]

1 is a perspective view of the apparatus of the first embodiment of the present invention, FIG. 2 is a schematic configuration diagram showing a control portion of the apparatus of FIG. 1, and FIG. 3 is a temperature change on the surface of the fixing roller of the apparatus of the first embodiment. FIG. 4
FIG. 5 is a diagram showing a temperature change on the surface of the fixing roller of the second embodiment, FIG. 5 is a diagram showing a temperature change on the surface of the fixing roller of the third embodiment, and FIG. FIG. 7 is a longitudinal sectional view of the conventional device, FIG. 8 is a diagram showing a temperature change of the fixing roller surface of the conventional device, and FIG. 9 is a diagram showing a temperature distribution of the fixing roller surface of the conventional device. is there. DESCRIPTION OF SYMBOLS 1 ... Fixing roller 2 ... Heater 3 ... Pressure roller 4 ... Recording material 5 ... Temperature detection element

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-88134 (JP, A) JP-A-63-95484 (JP, A) JP-A-2-42473 (JP, A) JP-A-54-88 29650 (JP, A) JP-A-54-33040 (JP, A) JP-A-53-55036 (JP, A) JP-A-53-129052 (JP, A) Shokai Sho 62-84071 (JP, U)

Claims (1)

(57) [Claims] A fixing roller, a pressure roller for forming a nip portion in contact with the fixing roller, a heater for heating the fixing roller, a temperature detecting element for detecting a temperature of the fixing roller,
Control means for controlling the power supply to the heater so that the temperature detected by the temperature detecting element maintains a predetermined set temperature, and when a plurality of recording materials carrying unfixed images are continuously fixed in the nip portion, the fixing is performed. In the fixing device in which the temperature difference between the paper passing area and the non-paper passing area of the roller increases, the temperature detecting element detects the temperature of the non-paper passing area of the fixing roller, and the control unit performs the fixing in the continuous fixing. A fixing device, wherein when the number of sheets reaches a predetermined number, the set temperature is increased to control the energization.