JPH09212033A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quick start up fixing device at a low cost, capable of surely controlling temperature, having high safety and suitable to save energy. SOLUTION: Provided that D denotes the diameter of a heat roller 1, W denotes the maximum paper passing width, Ts denotes the response time of a pyroelectric non-contact temperature sensor 3 and Th denotes a start-up time of the heat roller 1 from a room temperature to a fixation enabling temperature, the device is set so as to establish 5sec. <=Th<=0.23×-DWsec, and also, 0.01Th<=Ts<=0.08Th. Thus, irrespective of the quick start-up, overshooting and undershooting are kept within the satisfactory extent and the good fixation is maintained. And also, the response speed is very high, but it is unnecessary to use an expensive sensor, so that the cost is suppressed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device for an image forming apparatus using an electrophotographic process, and more particularly to a fixing device using a self-heating type heating roller.

[0002]

2. Description of the Related Art In recent years, there has been a demand for energy saving in image forming apparatuses such as copiers, printers and facsimiles using electrophotography, and one of the measures is to reduce energy consumption.
An on-demand method has been proposed in which the heater of the fixing device is energized only when the fixing operation is performed and the heater is not energized (preheating is not performed) at other times.

As a heating roller of a conventional fixing device, a heater such as a halogen lamp is installed inside a hollow pipe-shaped roller, and the halogen heater is heated to heat the entire roller. In this type of heating roller, an air layer is interposed between the roller and the heater, so that the heating efficiency is poor and it is disadvantageous in energy saving. In order to perform the on-demand method with such a conventional heating roller, it cannot be realized unless the durability is ignored and a heating roller having a small diameter is used, or an unnecessarily large electric power is supplied.

On the other hand, in a self-heating type heating roller in which an electric resistor is attached to the outer surface of the roller and is energized to generate heat, heat is generated in the roller surface layer.
It has high heating efficiency and is suitable for energy saving. The fixing device using the heating roller of this system has better thermal efficiency than the conventional device incorporating a halogen heater and has the advantage of aiming for high-speed startup, and is suitable for the on-demand system. However, in order to immediately start up the apparatus when it is used by the user without performing preheating, it is required to shorten the rising time of the self-heating type heating roller as much as possible.

By the way, the fixing device is provided with a temperature sensor (temperature detecting means) for detecting the temperature of the heating roller, and the temperature of the fixing device is controlled based on the detected temperature. A contact type temperature sensor using a commonly used thermistor conventionally takes a response time of 2 to 3 seconds or more, but a conventional fixing device has a slow rise time of 30 seconds to 40 seconds. The contact temperature sensor used is sufficient. However, when a contact type temperature sensor using a thermistor is used in a fixing device using a self-heating type heating roller, the response time of the temperature sensor is slow. There was a problem that overshoot and undershoot became noticeable. Also, the contact type temperature sensor may wear the release layer due to friction with the release layer on the surface of the heating roller, and when used for a self-heating type heating roller, when the release layer on the surface of the roller deteriorates. However, there is a safety problem in that the heat generating resistance layer on the primary side and the thermistor circuit on the secondary side contact (short-circuit) with each other and damage the device.

In order to improve such a problem, the release layer of the heating roller is thickened or a thick insulating layer is provided between the release layer and the heating resistance layer to protect the heating resistance layer from the outer peripheral side. Measures are taken to provide layers. It is also possible to use an infrared detection type non-contact sensor as the temperature sensor.
No. 0-133328. Then, JP-A-4-159587 and JP-A-58-19206.
Japanese Patent Laid-Open No. 5 (1994) proposes that the temperature of the heating roller is determined based on the change in the resistance value (or current value) of the heating resistor to control the fixing temperature.

[0007]

However, when a protective layer is provided on the outer peripheral side of the heating resistance layer in order to improve the problem of the contact type temperature sensor for the self-heating type heating roller, the rising speed is a side effect. There was a problem that it was a little late. Further, since the infrared detection type non-contact sensor is very expensive, there is a problem in that it cannot be used for an ordinary general-purpose printer in terms of cost.

Further, in the case where the temperature of the heating roller is judged based on the change of the resistance value (or current value) of the heating resistor, the response speed can be improved, but only the average temperature of the entire heating roller is detected. There is a problem that you cannot do it. In a device that has a small heat capacity (the core thickness of the heating roller is as thin as possible) with the aim of shortening the rise time, the heat transfer amount in the axial direction of the heating roller decreases, and if small size paper is continuously fed, the roller A temperature difference occurs in the axial direction. However, if only the average temperature of the heating roller can be detected, this temperature difference in the roller axis direction cannot be detected, and if large size paper is passed immediately after continuous passing of small size paper, fixing failure occurs. May occur.

The present invention solves the above-mentioned problems in a fixing device using a self-heating type heating roller, reduces a fixing device suitable for energy saving, which has a fast start-up, is capable of reliable temperature control, and is highly safe. The challenge is to provide it at cost.

[0010]

According to the present invention, the above-mentioned problems include a self-heating type heating roller and a temperature sensor for detecting the temperature in a non-contact manner by infrared rays emitted from the heating roller. In the fixing device in which the temperature of the heating roller is controlled based on the output of, the rise time from the room temperature of the heating roller to the fixable temperature is Th,
When the diameter of the heating roller is Dcm, the maximum paper passing width of the heating roller is Wcm, and the response time of the temperature sensor is Ts, 5 (seconds) ≤ Th ≤ 0.23 x DW (seconds) and 0.0
This is solved by 1 Th ≦ Ts ≦ 0.08 Th.

In order to solve the above-mentioned problems, the present invention provides a heating roller, wherein a heating resistor layer is provided on the roller surface layer, and a protective layer for strengthening and insulating is provided on the outer peripheral side of the heating resistor layer. To be formed without.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a fixing device according to an embodiment of the present invention together with its power control system. The fixing device shown in this figure comprises a self-heating type heating roller 1, a pressure roller 2, a non-contact temperature sensor 3 for detecting the temperature of the heating roller 1, a power supply brush 4, and the like. The heating roller 1 is provided with electrode portions 1a at both ends thereof, and the power supply brush 4 is in contact with the electrode portions 1a.

A power source 5 and a control circuit 6 are provided in an electrophotographic apparatus main body (not shown) to which the fixing device is attached. Electric power is supplied from the power source 5 to the heating roller 1 via the power feeding brush 4. Further, the temperature detected by the non-contact temperature sensor 3 is input to the control circuit 6, and the control circuit 6 controls the triac 7 to turn on / off the power from the power source 5.
I do.

Conventionally, as a non-contact type temperature sensor, a thermopile type temperature sensor which has a very fast response speed (usually 0.05 seconds or less) but is expensive is well known. But,
Recently, although the response speed is slightly inferior to the thermopile type, it is cheaper, but a pyroelectric sensor using a chopper or a thermistor-using sensor in which thermistors having different heat capacities are combined has been developed. As the sensor 3, a pyroelectric type sensor or a thermistor type sensor is used.

FIG. 2 is a graph showing the relationship between the heating roller rise time and the overshoot amount depending on the sensor response time when the non-contact temperature sensor is used in the fixing device. In this graph, the horizontal axis represents the rise time and the vertical axis represents the overshoot amount, and the relationship between the two is shown for each sensor response time (written on the graph). The measurement conditions were such that an A3 sheet passing roller having a diameter of 30 mm was used and the heating roller was allowed to rise from room temperature to 180 ° C. The rising time of the heating roller is changed by changing the power consumption. Also, the sensor response time is a general definition,
It is defined as the time during which the sensor output changes to 64% of the saturated output after the temperature change is instantaneously caused.

In the graph of FIG. 2, the overshoot amount of 10 deg is a desirable value for maintaining good fixing property. Therefore, on this graph, if a sensor having a response time capable of achieving an overshoot amount of 10 deg or less at each rising time is used, the fixability can be kept substantially good.

For example, the heating roller rising time is 30
In the case of seconds (S), if the response time of the temperature sensor is 3 seconds, the overshoot amount exceeds 10 deg.
The fixability is not good. However, when the response time of the temperature sensor is 1.6 seconds, 0.8 seconds, and 0.1 seconds, the overshoot amount is 10 deg or less, and the fixability can be kept good.

Further, when the heating roller rise time is 20 seconds (S), the overshoot amount is 10 deg when the sensor response time is 1.6 seconds, which can be said to be a limit for maintaining good fixability. Further, when the heating roller rise time is short and is 10 seconds, the sensor response time is 0.8 seconds as a limit. When the heating roller rise time is 10 seconds or less, the one having a response time of 0.8 seconds is ineligible, and the one having a response time of 0.1 seconds shows good fixing property on the graph.

Now, taking a printer as an example, it takes about 5 seconds from the exchange of data and the feeding of paper to the fixing device, and the heating roller rise time is set shorter than 5 seconds. Does not mean much. Therefore, considering the response time of the temperature sensor, in reality, even the sensor with the fastest response speed should be able to handle the heating roller with a rise time of 5 seconds. That is, it is only necessary to achieve an overshoot amount of 10 deg or less when the heating roller rising time is set to 5 seconds, and the temperature sensor satisfying this condition can maintain good fixability even in a fixing device with a quick rise. Looking at the graph in FIG. 2, the heating roller rise time 5
At the time of 2 seconds, the one having a response time of 0.1 seconds has an overshoot amount of 10 deg or less, and maintains a sufficiently good fixing property. Of course, when the heating roller rise time is long, there is a margin in the sensor response time, and it is possible to use a sensor with a longer response time. The undershoot is considered to be the same as the overshoot.

And what can be seen from the graph of FIG.
This means that if a sensor having a response time shorter than that obtained by multiplying (multiplying) the heating roller rise time by 0.08 is used, good fixability can be maintained. For example, when the heating roller rise time is 20 seconds, 20 seconds × 0.08 = 1.
It takes 6 seconds, and a sensor having a response time of 1.6 seconds or less may be used. Looking at the graph, the sensor with a response time of 1.6 seconds has an overshoot amount of 10 deg.
Those with response times of 0.8 seconds and 0.1 seconds have smaller overshoot amounts. When the heating roller rise time is 10 seconds, 10 seconds × 0.08 = 0.
It becomes 8 seconds, and if a sensor with a response time of 0.8 seconds or less is used, an overshoot amount of 10 deg or less can be achieved.

However, as described above, since the non-contact type temperature sensor having a response time of 0.05 seconds or less is expensive, it is necessary to use a sensor having a response time of 0.05 seconds or more in the present invention. This sensor response time of 0.05 seconds is set as the heating roller rise time in the shortest time of 5 seconds (the rise time does not have to be 5 seconds or less as described above). Time x 0.01. That is, 5 seconds × 0.01 = 0.05 seconds. Therefore, in this embodiment, as the non-contact temperature sensor 3, a sensor having a response time of heating roller rising time × 0.01 or more and heating roller rising time × 0.08 or less is used. When this is expressed by a mathematical expression, the response time of the non-contact temperature sensor is Ts, and the heating roller rise time is Th.
Is as follows. The heating roller rise time is the rise time from room temperature to the fixable temperature. 0.01Th ≦ Ts ≦ 0.08Th ... FIG. 3 is a graph in which the horizontal axis of the graph of FIG. 2 is normalized by the heating roller rise time, that is, the horizontal axis of the graph is the temperature related to the heating roller rise time. It is the response time of the sensor. As shown in this graph, the sensor response time is 0.08 Th and the overshoot amount is 10 deg. It can be seen that a sensor having a response time shorter than this can maintain good fixing property.

For reference, when the temperature sensor having a response time of 0.8 seconds is used for the self-heating type heating roller having a rise time of 10 seconds, the heating roller temperature change characteristic at the time of rising is shown in FIG.
Similarly, when a temperature sensor having a response time of 3 seconds is used for a self-heating type heating roller having a rise time of 10 seconds,
FIG. 5 shows the temperature change characteristic of the heating roller at the time of rising, and FIG. 6 shows the temperature change characteristic of the heating roller at the time of rising when a temperature sensor having a response time of 3 seconds is used in the conventional fixing device. In the graphs of the respective figures, the horizontal axis represents the time after the heater is turned on, and the vertical axis represents the heating roller temperature. The set temperature of the heating roller was 180 ° C. In addition, the time from when the roller temperature reaches the set temperature to when the overshoot ends is the response time of each sensor.
It is the time including the time lag from detection to the actual processing. This time lag varies depending on the control system, but is usually about 0.05 to 0.5 seconds.

Comparing FIG. 4 and FIG. 5, the heating roller has the same rise time, but the sensor response time + time lag time is short due to the difference in response time of the temperature sensor.
It can be seen that the sample No. 1 has less overshoot and undershoot around the set temperature. Further, the conventional method shown in FIG. 6 is not suitable for the on-demand method (energy saving) because the rising time is long. However, since the heat capacity of the heating roller is larger than that of the self-heating type, the overshoot amount and the undershoot amount do not become so large even when the sensor response time is 3 seconds.

By applying the heating roller rise time of 10 seconds to the equation, 0.1 second ≦ Ts ≦ 0.
It is 8 seconds, and it can be seen that the good fixing property can be maintained within the range of the sensor response time of 0.1 seconds to 0.8 seconds. In the example shown in FIG. 4, the response time of the temperature sensor is 0.8 seconds, and
As can be seen from the range of 1 second to 0.8 seconds, it can be said that good fixability is maintained. Further, in the example shown in FIG. 5, the response time of the temperature sensor is 3 seconds, and
Since it is not in the range of seconds to 0.8 seconds, it cannot be said that good fixability is maintained. This can also be understood from the fact that the overshoot amount and the undershoot amount are large in the figure.

As described above, when the response time of the temperature sensor is shown in relation to the heating roller rise time, by using the temperature sensor satisfying the formula, good fixing property can be obtained on the heating roller having the rise time ( It was found that it can be maintained (at low cost). However, it was mentioned above that the on-demand system cannot be realized with a heating roller having a slow rise time. Therefore, it is necessary to use a heating roller that rises to some extent. Less than,
What kind of heating roller is used to meet the purpose of realizing energy saving and how to apply the conditions of the formula to the heating roller will be described.

Looking at the relationship between the diameter and width of the heating roller and the rise time, the rise time naturally becomes longer when the roller diameter is large and the width is wide. Therefore, if the roller diameter is made smaller and the width is made narrower, the rise time can be shortened. To some extent, the conventional method (method with a built-in halogen heater, etc.) can be achieved, but to shorten the rise time above a certain level, the conventional method can be achieved. Then it is impossible. In the conventional method, it is necessary to apply more power than necessary or to make the roller core metal wall thickness extremely thin. This is not realistic because it results in deterioration of durability, wasteful power consumption, cost increase due to large-capacity power supply, and deterioration of roller workability.
Limit level (rise time) in such a conventional method
Is expressed as the relationship between the roller diameter and the roller width, 0.23 × DW
(Seconds). Where D: heating roller diameter (cm),
W: Maximum paper width (cm). For example, A with a diameter of 30 mm
0.2 for rollers for 3 sizes (paper width 297 mm)
3 × DW = 0.23 × 3 × 29.7≈20.5 seconds.

However, with the self-heating type heating roller, the rise time of 0.23 × DW (seconds) or less can be reasonably achieved. Therefore, 0.23 x DW
The range of (seconds) or less is defined as a region where the self-heating type heating roller has an advantage. Therefore, although a heating roller having a rising time of 0.23 × DW (seconds) or less is used, it is meaningless to set the heating roller rising time to 5 seconds or less as described above. In the present invention, a heating roller having a rise time of 0.23 × DW (second) for a second or more is used. This condition is expressed by the following equation. The heating roller rising time is Th. 5 (seconds) ≦ Th ≦ 0.23 × DW (seconds) Therefore, in the present embodiment, the heating roller 1 that meets the condition of the expression is used, and the above-mentioned expression is used as the non-contact temperature sensor 3. Use what you are satisfied with. As a result, it is possible to achieve an overshoot amount of 10 deg or less in a fixing device using a self-heating type heating roller having a quick rise time which is difficult to achieve in the conventional method. Therefore, the overshoot and the undershoot can be kept within a good range and the fixability can be kept good even though the fixing device starts up quickly. Further, since the non-contact temperature sensor is used, there is no safety problem as in the contact type sensor and no adverse effect on the rising speed (due to the thick release layer or the insulating layer provided). Further, since the temperature of the heating roller is directly detected (the average temperature of the heating roller is not obtained from the resistance value of the heating resistor), reliable temperature detection does not cause fixing failure. Further, the response speed is very fast, but it is not necessary to use an expensive sensor, so that the cost can be suppressed. Of course, since the heating roller used is quick to start up, it is possible to save energy by the on-demand method.

FIG. 7 is a sectional view showing the structure of the heating roller of this embodiment. As shown in this figure, the heating roller 1 has a layered structure in the order of a release layer, a heat generating layer, an insulating layer and a cored bar from the outer periphery thereof. The core metal is inside the heating layer,
Further, since there is no thick insulating layer (of the reinforced insulation level when the contact type temperature sensor is used) on the outside of the heat generating layer, the heating roller 1 realizes a high-speed rising. Further, since the non-contact type temperature sensor is used, there is no danger of exposure of the heat generating layer and safety is secured. An insulating layer or a protective layer may be thinly provided between the first release layer and the second heat generating layer.

FIG. 8 is a graph comparing the rise time of the heating roller 1 of this embodiment shown in FIG. 7 with the rise time of the conventional heating roller shown in FIG. The heating roller 11 of the conventional example shown in FIG. 9 has a release layer, a core metal, an insulating layer, and a heat generating layer from the outer periphery thereof, and the core metal is outside the heat generating layer. In the present embodiment, the heat generating layer is arranged outside the cored bar and the thick insulating layer is formed outside the heat generating layer by fully utilizing the merit that the roller surface is not worn by using the non-contact type temperature sensor as the temperature sensor. There are no layers. Therefore, as shown in FIG. 8, the heating roller of this embodiment is
The rise time is shorter than that of the conventional example of FIG. Therefore, it is possible to realize a more energy-saving fixing device that rises faster and is excellent in heat supply to paper.

FIG. 10 is for supplementary explanation of the response time of the non-contact type temperature sensor in the fixing device of the present invention, and shows the output of the pyroelectric temperature sensor usable in the fixing device of the present invention. It is a graph which shows what averaged it. When a pyroelectric temperature sensor is used as the non-contact temperature sensor, noise is often added to the output as shown in FIG. This noise is conspicuous when the speed of the sensor is increased to some extent to reduce the cost of the sensor and a circuit for protecting against noise or a circuit for preventing generation of noise is omitted. In order to improve this, by averaging the output signal of the temperature sensor several times, as shown in FIG.
Noise removal can be performed as shown in (b).
When the averaging process of the output signal is performed, the sensor response time is substantially delayed, but in the present invention, the time including this noise removal (averaging process) is set as the sensor response time as the sensor response time. Of course, also in the above embodiment,
The substantial response time including the averaging process of the output signal is the response time of the temperature sensor.

[0031]

As described above, according to the fixing device of the present invention, the rising time of the heating roller is Th, the heating roller diameter is Dcm, the maximum paper passing width of the heating roller is Wcm, and the response time of the non-contact temperature sensor. Let Ts be 5 (seconds) ≤ T
h ≦ 0.23 × DW (seconds) and 0.01 Th ≦ Ts ≦
Since it is 0.08 Th, overshoot and undershoot can be kept within a good range and good fixability can be maintained without using an expensive temperature sensor in a quick-starting fixing device. In addition, there is no safety problem or adverse effect on the rising speed when using the contact sensor. Further, since the temperature of the heating roller is directly detected, fixing temperature and the like will not be caused by reliable temperature detection.

According to the second aspect of the present invention, since the heat generating layer is arranged outside the core bar and there is no protective layer outside the heat generating layer, the fixing device is faster in rising and excellent in heat supply to the paper, and is more energy saving. Can be realized.

[Brief description of drawings]

FIG. 1 is a perspective view showing a fixing device according to an embodiment of the present invention together with its power control system.

FIG. 2 shows a case where a non-contact temperature sensor is used in a fixing device,
7 is a graph showing the relationship between the heating roller rise time and the overshoot amount depending on the sensor response time.

FIG. 3 is a graph in which the horizontal axis of the graph of FIG. 2 is normalized by the heating roller rising time.

FIG. 4 is a graph showing a temperature change characteristic of a heating roller at the time of rising when a self-heating type heating roller having a rising time of 10 seconds and a temperature sensor having a response time of 0.8 seconds are used.

FIG. 5 is a graph showing a temperature change characteristic of a heating roller at the time of rising when a temperature sensor having a response time of 3 seconds is used for a self-heating type heating roller having a rising time of 10 seconds.

FIG. 6 is a graph showing a temperature change characteristic of a heating roller at the time of rising when a temperature sensor having a response time of 3 seconds is used in a conventional fixing device.

7 is a cross-sectional view showing the structure of a heating roller of the fixing device shown in FIG.

FIG. 8 is a graph comparing rise times of the heating roller and a heating roller of a conventional example.

FIG. 9 is a sectional view showing the structure of an example of a conventional heating roller.

FIG. 10 is a graph showing an output of a pyroelectric temperature sensor usable in the fixing device of the present invention and an averaged output thereof.

[Explanation of symbols]

 1,11 Heating roller 1a Electrode part 2 Pressure roller 3 Non-contact temperature sensor 4 Power supply brush 5 Power supply 6 Control circuit 7 Triac

Claims (2)

[Claims] 1. A self-heating heating roller, and a temperature sensor for detecting the temperature of the heating roller in a non-contact manner by infrared rays emitted from the heating roller, and the temperature of the heating roller is controlled based on the output of the temperature sensor. In the fixing device described above, when the rising time from the room temperature to the fixable temperature of the heating roller is Th, the diameter of the heating roller is Dcm, the maximum sheet passing width of the heating roller is Wcm, and the response time of the temperature sensor is Ts. 5 (seconds) ≦ Th ≦ 0.23 × DW
(Sec) and 0.01 Th ≤ Ts ≤ 0.08 Th. 2. The heating roller is characterized in that a heating resistor layer is provided on a roller surface layer, and a protective layer for strengthening and insulating is not provided on an outer peripheral side of the heating resistor layer. The fixing device according to claim 1.