JP2000227731A - Fixation device and picture forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To precisely check the presence or the absence of paper winding and thermistor separation by increasing an error detection temperature gradient from a normal one and determining the appropriateness of the temperature gradient while a fixation heater is turned ON after the release of a jam. SOLUTION: A fixation device 1 is heated by a heater 4. A thermistor 5 is arranged to contact with a fixation roller 3 to detect the temperature on the surface of the roller 3. Supply of the power to the heater 4 is controlled by a temperature circuit in accordance with the detected temperature of the thermistor 5 so that the surface temperature of the roller 3 is adjusted to a prescribed heat fixation temperature. In the above, the temperature gradient of the surface temperature of the roller 3 is detected while the heater 4 is turned ON. If the detected gradient is less than the error detection temperature gradient, the heater 4 is forcibly turned OFF. Furthermore, in order to recognize the generation of a jam, the error detection temperature gradient is made steeper than a normal gradient and the appropriateness of the temperature gradient is discriminated while the heater 4 is turned ON after the release of a jam.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a printer, a facsimile, a copying machine, etc., and more particularly to an image forming apparatus for forming and fixing image information on a recording material using a fixing roller, and a fixing device therefor.

[0002]

2. Description of the Related Art Conventionally, in an electrophotographic image forming apparatus, a toner image transferred to a recording material such as a cut sheet is formed by using a toner image.
Fusing and fixing is performed using heat from a heat source such as a halogen lamp.

However, the recording material may be wound around the fixing roller due to poor separation of the recording material or the like, and a paper jam may occur. The wrapping jam occurs when the recording material is to be separated from the fixing roller by a separation claw or the like, but is not satisfactorily separated and wraps around the fixing roller. Is not reached, it is recognized that the paper sensor is not operated, the subsequent sequence is stopped, and the power supply to the fixing roller is cut off. At that time, in a recent high-speed type or the like, the subsequent recording material may reach the fixing device. Therefore, even if the original jammed recording material is removed and the operation is resumed, the subsequent recording material may not be recognized, and the recording material may be wrapped around the fixing roller again.

[0004]

That is, even if it is determined that the jam processing is completed when the wrapping jam occurs, the recording material actually remains on the fixing roller, and the recording material is ignited by the reheating of the fixing roller.・ The danger of smoking remains. When detecting the surface temperature of the fixing roller, it is detected as a temperature lower than the actual surface temperature due to the intervening recording material, and the temperature control is shifted to a higher temperature, and there is a possibility that the fixing device may be damaged. is there.

Further, when removing the wound recording material,
Thermistor, which is a temperature detecting means, is shifted from a predetermined position,
There is also an obstacle to move away from the fixing roller. In such a case, the detected temperature decreases, and accordingly, the temperature control also shifts to a higher level.

SUMMARY OF THE INVENTION In view of the above problems, an object of the present invention is to make it possible to accurately check whether paper is wrapped or the thermistor is separated when a jam occurs while minimizing erroneous detection.

[0007]

An object of the present invention is to provide a fixing heater which uses a detecting means for detecting the surface temperature of a fixing roller.
In a fixing device that performs N / OFF control, a fixing heater O
When a temperature gradient related to the surface temperature of the fixing roller is detected at the time of N, and the detection gradient is smaller than the temperature gradient for error detection, a function of forcibly turning off the fixing heater is provided. The problem can be solved by making the temperature gradient for error detection steeper than the normal one and determining the appropriate temperature gradient when the fixing heater is turned on after the jam is cleared.

A means for updating and storing the normal minimum value of the temperature gradient of the fixing roller surface is provided. When the occurrence of the jam is recognized, the error detecting temperature gradient is compared with the normal error detecting temperature gradient and the normal time. It is even more preferable if the setting is made during the minimum temperature gradient.

A sheet detecting means is provided downstream of the fixing device in the sheet conveying direction, and the occurrence of a jam is recognized by the sheet detecting means. When the occurrence of the jam is recognized, the image forming operation is stopped, and the error is detected. An instruction is given to change the use temperature gradient from the normal detection level to make it steeper, and an image forming apparatus equipped with a fixing device having the above characteristics also solves the above problem.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on an example shown in the drawings. FIG. 1 shows a main configuration of a fixing device 1 according to the present invention. The fixing roller 3 has a heater 4 such as a halogen lamp built in a hollow metal core. The pressure roller 2 opposed to the fixing roller 3 is pressed against the fixing roller 3 by the action of a pressure spring (not shown).
These rollers rotate so as to convey the paper 7 as a transfer material from right to left in the figure. Fixing device 1 by heater 4
Is heated. A thermistor 5 is disposed so as to be in contact with the fixing roller, and detects the temperature of the roller surface. The power supply to the heater is controlled by a temperature circuit (not shown) according to the temperature detected by the thermistor, and the surface temperature of the fixing roller 3 is adjusted to a predetermined heat fixing temperature. The paper 7 nipped and transported between the rollers is discharged from the fixing device 1 and then sent to the paper discharge rollers 6 to be discharged out of the image forming apparatus. In addition,
Reference numeral 8 denotes a paper ejection sensor.

FIG. 2 shows a circuit configuration relating to the fixing device.
The surface temperature of the fixing roller detected by the thermistor 5 is converted into a digital value by the AD converter 13 in the engine control board 9, and the temperature is recognized by the CPU 10. The set value of the surface temperature is stored in the ROM 11. When the fixing device is started, the power supply to the heater 4 is started, and the temperature of the surface of the fixing roller increases. The temperature detected by the thermistor 5 is ROM
When the temperature becomes higher than the temperature stored in the memory 11, the triac 16 is turned off from the CPU 10 via the I / O 12, and the power supply to the heater 4 is stopped. When the temperature detected by the thermistor 5 becomes lower than the temperature stored in the ROM 11, the triac 1 is transmitted from the CPU 10 via the I / O 12.
6 is turned on to re-energize the heater 4 so that the temperature is controlled to be maintained within a certain range. ON / OF from rising
FIG. 6 shows a state of the temperature of the fixing roller surface by the F control.

In the fixing control, while the control for maintaining the predetermined temperature is performed as described above, the winding of the sheet around the fixing roller and the abnormality detection by the thermistor are checked to improve safety. When a jam occurs in the fixing device, the power supply to the heater is stopped. Then, since the surface temperature decreases while the jammed paper is being removed, power is supplied to the heater after the jam processing. In normal times, that is, when the sheet is not completely wound, the surface of the fixing roller is heated by the temperature gradient shown in FIG. 6, but the sheet is wound or the thermistor 5 is separated from the fixing roller 3. In this case, heat conduction from the roller surface to the thermistor becomes worse, and the gradient of the detected temperature becomes gentler than that in FIG.

In a normal state, in order to avoid erroneous detection due to factors such as noise, a margin of, for example, a dotted line shown in FIG. 7 is used as an error detection level. The detected temperature gradient is
If the inclination is smaller than the inclination of the dotted line, it is recognized that there is an abnormality in the thermistor, and it is recognized as “fixing error”, the machine is stopped, and the information is stored in the EEPROM 15 (FIG. 2). Not to clear. After that, even if the power is turned on, the EEPROM
Since the fixing error information 15 is stored, the fixing heater is not turned on unless a service person or the like clears the information.

As shown in FIG. 3, during printing, if the sheet 7 that has reached the fixing device 1 does not reach the sheet discharge sensor 8 within a predetermined time, processing is performed as a sheet discharge jam. At this time, EEP
The discharge jam flag is set in the ROM 15. In the subsequent fixing check, as shown in FIG. 4, it is detected whether or not the jam has been cleared. If the jam has not been cleared, this control is not performed because the fixing roller is in the OFF state. That is, the routine of FIG. 4 is executed when the jam is cleared. If the jam has been cleared, a jam clearing process is performed. If the jam clearing process has already been performed, no particular process is performed. The discharge jam flag is checked, and when the discharge jam flag is not set, FIG.
The temperature gradient is checked using the dotted line, which is the normal error detection level, as a reference for comparing the temperature gradient. If the output jam flag is set,
Since it is recognized that a paper discharge jam occurs immediately before and the heater has not been started up normally after that, the error detection level is set to a thin line having a slope larger than the dotted line in FIG. 7 (normal temperature gradient and normal error detection comparison). The line between the gradients) is the temperature gradient for comparison, and if less than this gradient, the EEPRO
“Set fixing error” in M. If the detected temperature gradient does not fall on the error level, the paper discharge jam flag is reset. The error detection level indicated by the thin line is previously stored in the ROM 11 together with the one indicated by the dotted line.

The temperature gradient at the time of the actual temperature rise of the fixing roller has some variation as shown by a range indicated by a double arrow in FIG. Therefore, the temperature gradient having the minimum value (the dashed-dotted line in FIG. 8 on the gentle slope) is always recognized as the normal temperature gradient. Therefore, necessary updating is performed according to the flow shown in FIG. That is, in the normal state,
When a gradient smaller than the temperature gradient stored in the ROM is detected, the contents of the EEPROM are updated. In this case, the post-jam detection level is affected by the content of the normal temperature gradient.
(FIG. 2). Calculation is performed so as to be between the normal temperature gradient minimum level and the normal error detection level (the hatched portion in FIG. 8) and stored in the RAM. EEPR as much as possible
If the inclination close to the minimum level stored in the OM is the error detection level after the jam (the thin line in FIG. 8), it is possible to more strictly check whether the paper is wrapped or the thermistor is separated.

[0016]

According to the present invention, when the fixing heater is turned on, a temperature gradient relating to the surface temperature of the fixing roller is detected, and when the detected gradient is smaller than the error detecting temperature gradient, the fixing heater is forcibly turned off. In addition, when the occurrence of a jam is recognized, the error detection temperature gradient is steeper than that at the normal time, and the appropriate temperature gradient when the fixing heater is turned on after the jam is released is determined, whereby the erroneous detection is performed. It is possible to accurately check whether the paper is wrapped or the thermistor is separated when a paper jam occurs, while keeping it as small as possible.

A means for updating and storing the normal minimum value of the temperature gradient of the fixing roller surface is provided. When the occurrence of the jam is recognized, the error detecting temperature gradient is compared with the normal error detecting temperature gradient. If the temperature gradient is set between the minimum temperature gradients, it is possible to correctly determine whether the paper is wrapped or the thermistor is separated when a jam occurs, and the error detection temperature gradient to be changed and set is the normal time By approaching the minimum value as much as possible, more severe checks can be performed.

[Brief description of the drawings]

FIG. 1 is a schematic front sectional view of a fixing device according to the present invention.

FIG. 2 is a diagram illustrating a circuit configuration related to a fixing device.

FIG. 3 is a flowchart for checking whether or not a paper output jam has occurred;

FIG. 4 is a flowchart regarding handling of a detection level of a fixing error when a paper output jam occurs.

FIG. 5 is a flowchart for updating a fixing temperature gradient in a normal state.

FIG. 6 is a graph related to control of the surface temperature of the fixing roller.

FIG. 7 is a graph illustrating a gradient between a normal error detection level and a post-jam error detection level in the configuration according to claim 1;

FIG. 8 is a graph illustrating a minimum temperature gradient, a normal error detection level, and a post-jam error detection level in the configuration according to claim 2;

[Explanation of symbols]

 3 Fusing roller 4 Heater 5 Thermistor 8 Discharge sensor

Claims (3)

[Claims] In a fixing device for performing ON / OFF control of a fixing heater by using a detecting unit for detecting a surface temperature of a fixing roller, a temperature gradient related to a surface temperature of the fixing roller is detected when the fixing heater is turned on. It has a function to forcibly turn off the fixing heater when the temperature gradient is smaller than the error detection temperature gradient. When the occurrence of a jam is recognized, the error detection temperature gradient is steeper than the normal one and the jam is released. A fixing device for judging a proper temperature gradient when a fixing heater is turned on later. Means for updating and storing the normal minimum value of the temperature gradient of the surface of the fixing roller, wherein when the occurrence of the jam is recognized, the temperature gradient for error detection is replaced with the temperature gradient for normal error detection and the normal temperature gradient. The fixing device according to claim 1, wherein the setting is performed during a temperature gradient of a minimum value at the time. 3. A sheet detecting means is provided downstream of the fixing device in the sheet conveying direction, and the occurrence of a jam is recognized by the sheet detecting means. When the occurrence of the jam is recognized, the image forming operation is stopped. 3. The image forming apparatus having the fixing device according to claim 1, wherein the error detecting temperature gradient is changed from a normal detection level to give an instruction to increase the steepness.