JPH10207288A - Heater, fixing device, and image forming device - Google Patents

Abstract

(57) Abstract: Provided are a heater having better responsiveness and capable of accurate temperature detection, and a fixing device and an image forming apparatus using the heater. SOLUTION: A heater H for heating a conveyed object to be heated.
, A substrate 17, a heating element 18 provided on one surface side of the substrate 17, which generates heat by energization, and a plurality of temperature detecting elements 20a, 20 for detecting a heating temperature by the heating element 18.
b, and the plurality of temperature detecting elements 20a and 20b are provided on the same surface side on which the heating element 18 is provided.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heater capable of accurately detecting a heating temperature of a heating element, a fixing device using the heater, and an image forming apparatus.

[0002]

2. Description of the Related Art Many printers, copiers and the like form an image by an electrophotographic recording method. In the electrophotographic recording method, a toner image is transferred to a recording medium, and heat and pressure are applied to the recording medium. Is applied to fix the toner image.

As a fixing device for fixing the toner image, a heat roller system has been conventionally used. This method is based on a metal roller with a heater inside and a pressure roller with elasticity that comes into pressure contact with it.
The toner image is heated and pressed and fixed by introducing a recording medium as a member to be heated into the nip portion of the roller pair, nipping, conveying and passing the recording medium.

However, in such a heat roller type fixing device, it takes a very long time to raise the surface of the roller to the fixing temperature because the heat capacity of the roller is large. For this reason, in order to quickly execute the image output operation, there is a problem that the roller surface must be kept at a certain temperature even when the apparatus is not used.

In order to solve the above-mentioned problems, a film heating type heating device for heating and fixing a film has been proposed (JP-A-63-313182;
No. -1557878).

This film heating type fixing device is usually
A heat-resistant film of a book, a heating element (heater) fixedly supported and disposed on one side of the film, and a heater disposed on the other side of the film opposite to the heater via a film. It is composed of a pressure member for bringing the member to be heated into close contact.

When this is used as a fixing device, a recording medium on which a toner image is formed and carried is introduced into a press-contact nip formed by press-contact between a heater and a pressing member with the film interposed therebetween. By passing the recording medium, the surface of the visible image carrier of the recording medium is heated by the heater via the film, heat energy is applied to the unfixed image, the toner is softened and melted, and the image is heated and fixed.

The heater has a resistance heating element that generates heat when energized, and a ceramic substrate having good thermal conductivity on which the resistance heating element is provided. The resistance heating element is provided by an output of a temperature detecting element for detecting the temperature of the substrate. Is controlled.

Conventionally, upon detecting the temperature, a thermistor composed of thermistor beads protected by glass is attached to the back surface of the heating element including the resistance heating element, and the resistance value of the thermistor beads is measured by a lead wire. The temperature of the body is detected and the power applied to the resistance heating element of the heating body is controlled to control the temperature of the heating body to a predetermined value.

[0010] In order to eliminate the variation in the contact state between the thermistor and the heating element and improve the responsiveness, FIG.
As shown in FIG. 1, a heater in which a chip-type thermistor is attached to the back surface of a heater substrate 51 provided with a heating element 50 has been produced. This chip-type thermistor has a thermistor layer 53 and an electrode 54 laminated on a ceramic substrate 52 and a moisture-proof layer 55
Made as a glass coat. Then, the chip-type thermistor is bonded to an electrode 58 provided on the back surface of the heater substrate 51 with a conductive adhesive 56 having high heat resistance.

In order to further improve the assemblability and improve the responsiveness, it has been proposed to form a thermistor 59 directly on the heater substrate 51 by printing as shown in FIG. Since the printing thermistor has no gap with the heater substrate 51 and is printed directly on the substrate 51, the variability of the response is reduced, and more accurate temperature detection becomes possible.

[0012]

In today's image forming apparatuses and the like, with the increase in the process speed, it is required to secure good fixability and to realize a quick start. For that purpose, it is necessary to use a material having high thermal conductivity and low heat capacity for each member of the heat fixing device.

However, when the heat capacity of the heater is reduced,
If the response time of the temperature detecting element is long because the temperature of the heater rises and falls quickly, the temperature ripple becomes large and the control to the target temperature becomes complicated. Therefore, a heater that has a higher responsiveness and that can accurately detect a heating temperature is desired.

SUMMARY OF THE INVENTION The present invention has been made in view of the above points, and has as its object to provide a heater having better responsiveness and capable of accurately detecting a temperature, and a fixing device and an image using the heater. An object of the present invention is to provide a forming apparatus.

[0015]

In order to achieve the above object, a typical configuration according to the present invention is a heater for heating a conveyed object to be heated, which is provided on a substrate and one side of the substrate. And a plurality of temperature detection elements for detecting a heating temperature of the heating element, wherein the plurality of temperature detection elements are provided on the same surface side on which the heating element is provided. It is characterized by.

In the above configuration, since the temperature is detected on the same surface as the heating element, the temperature can be directly and accurately detected regardless of the thickness of the substrate.
In addition, by detecting the temperature with a plurality of temperature detecting elements, by calculating the average value of each detected value,
More accurate temperature detection can be performed.

Therefore, when the fixing device and the image forming apparatus are configured using the heater, it is easy to control the fixing temperature with higher accuracy, and it is possible to obtain a high-quality image.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an image forming apparatus using a fixing device according to the present invention will be described with reference to the drawings.

First Embodiment FIGS. 1 to 5 show a first embodiment. FIG. 1 is an explanatory diagram of a fixing device, FIG. 2 is an explanatory diagram of a heater, and FIG. 3 is a heater. FIG. 4 is an explanatory diagram comparing the temperature ripple by providing a thermistor on the front and back surfaces of the heater substrate, and FIG. 5 is an overall schematic explanatory diagram of the image forming apparatus.

Here, as the order of the description, first, the overall configuration of the image forming apparatus will be described, and then the configuration of the fixing device and the heater used therein will be described.

<< Overall Configuration of Image Forming Apparatus >> This image forming apparatus (laser beam printer) A transmits information light (laser light) based on image information from an optical unit 1 to a drum-shaped image as shown in FIG. A latent image is formed on the photoconductor by irradiating the photoconductor, which is a carrier, and the latent image is developed to form a toner image. Then, in synchronization with the formation of the toner image, a recording medium P, which is a recording medium, is transported by a transport unit,
An image is formed on the recording medium P by an image forming unit.

In the present embodiment, an electrophotographic method is used as an image forming means, and the photosensitive drum 2, which is an electrophotographic photosensitive member, a charging means, a developing means, and a cleaning means (not shown) are formed into cartridges. The cartridge 3 is detachable from the apparatus main body. The image forming unit uniformly charges the surface of the rotating photosensitive drum 2 by the charging unit, and then forms a latent image on the photosensitive drum 2 by irradiating light from the optical unit 1, and this latent image is developed by the developing unit. A visible image is formed by developing the toner. Then, the toner image is transferred to the recording medium P conveyed by the transfer means 4, and the transferred image is fixed by the fixing means 5 which is a fixing device.

On the other hand, a sheet conveying means for conveying the recording medium P separates and feeds one by one from a recording medium cassette 6 mounted on the bottom of the apparatus main body by a pickup roller 7 and a separation claw 6a. 8 and a pinch roller 9 which rotates by being pressed against the sheet, and is conveyed to the image transfer section by U-turn.

By applying a voltage to the transfer roller 4 constituting the transfer means, the recording medium P on which the toner image formed on the photosensitive drum 2 has been transferred is guided by the driving rotation of the transport roller 8 and the transfer roller 4. The sheet is conveyed along the conveyance guide member 10 constituting the means and reaches the fixing means 5. Further, the recording medium P on which the transfer toner image is fixed by applying heat and pressure by the fixing unit 5 is discharged to the discharge roller pair 11, 12.
And discharged to the discharge section 13 in the upper part of the apparatus main body.

{Structures of Fixing Device and Heater} Next, the structure of the fixing means (fixing device) 5 for fixing the toner image transferred to the recording medium P and the structure of the heater used for this will be described.

The fixing means 5 according to the present embodiment is a tensionless type film heating and fixing device. As shown in FIG. 1, the heat-resistant film 14, which is a rotatable cylindrical member, generates heat. It is externally fitted to the support 15 of the heater H which is also a film guide member including the body. The inner peripheral length of the film 14 and the outer peripheral length of the support 15 are the same as those of the film 14,
For example, the film 14 is made larger by about 3 mm.

The film 14 need not have a cylindrical shape, but may have a structure in which the film 14 is sequentially fed from a supply roller to a take-up roller as long as the film 14 moves following the conveyance of the recording medium.

The film 14 has a heat capacity of 100 μm or less, preferably 50 μm or less and preferably 20 μm or more and has a heat resistance of PTFE (polytetrafluoroethylene) to reduce the heat capacity and improve the quick start property of the apparatus. P
FA (tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer), FEP (tetrafluoroethylene-hexafluoropropylene copolymer) monolayer,
Alternatively, it is preferable to use a composite film such as polyimide, polyamideimide, PEEK (polyetheretherketone), PES (polyethersulfone), or PPS (polyphenylenesulfide), which is coated with PTFE, PFA, FEP, or the like on its outer peripheral surface. . In the present embodiment, a polyimide film having an outer peripheral surface coated with PTFE is used.

Reference numeral 16 denotes a rotating member which forms a nip N with the heater H sandwiching the film 14, presses the recording medium P against the film 14, and applies a conveying force to the recording medium P. It is a pressure roller. This pressure roller 16
In FIG. 1, a heat-resistant rubber roller portion 16b having good releasability such as silicone rubber is integrally provided on a cored bar 16a, and a driving force is transmitted to a gear (not shown) attached to an end of the cored bar 16a. It is driven and rotated in the direction of arrow A. As a result, the recording medium P is transported in the direction of arrow B, and
Rotates in the direction of arrow C.

A heater H for heating the film 14 is attached to the support 15, and by heating the recording medium P passing through the nip N, the toner image transferred by the image forming means is permanently applied to the recording medium P. Establish.

Here, the structure of the heater H will be described. As shown in the schematic diagram in the longitudinal direction of the heater in FIG.
Heating element made of electric resistance material such as Pd (silver palladium)
18 is applied by screen printing or the like to a thickness of about 10 μm and a width of 1 to 3 mm, and a protective layer 19 is coated thereon with glass, fluororesin or the like. Further, in order to detect the heating temperature by the heating element 18 for controlling the temperature of the heater, the temperature
Thermistors 20a and 20b as temperature detecting elements are attached.

The thermistors 20a and 20b are printed on the substrate 17 on the same surface side on which the heating elements 18 are provided and in the vicinity of the heating elements 18 (inside the fixing nip) by printing. To form a protective layer 19 on the upper surface.
It is configured by coating. Then, one of the thermistors 20a is connected to the recording medium P which is a heating target rather than the heating element 18.
And the other thermistor 20b is located downstream of the heating element 18 in the recording medium transport direction (hereinafter simply referred to as “downstream side”).
It is arranged on a straight line parallel to the upstream thermistor 20a in the transport direction.

In FIG. 2, reference numeral 22 denotes an AC electrode for supplying power to the heating element 18, and reference numeral 23 denotes an electrode pattern 21.
a, 21b are the DC electrodes connected to each other.

The detection of the heating temperature by the heater H is performed by
The number of thermistors 20a and 20b is determined based on the values detected. That is, as shown in FIG. 3, the detected temperatures of the thermistors 20a and 20b are read as voltages Va and Vb, and the difference voltage V is output by the comparator 24 and input to the comparator 25. This comparator 25
The comparison voltage Vref is compared with the output voltage V, and the result is input to the CPU 27 through the A / D converter 26, and the control temperature of the heating element 18 is determined. The CPU 27 controls the heater driver 28 to maintain A
The power supply to the heating element 18 from the C power supply 29 is controlled. Further, when the control temperature is switched, a new comparison voltage is output from the CPU 27 and is used by the D / A converter 30 for comparison by the comparator 25 as a new comparison voltage Vref.

In this way, the heating temperature of the heating element 18 is controlled in accordance with the detected temperature difference between the thermistors 20a and 20b arranged on the upstream and downstream sides of the heating element 18.

The temperature control is performed by controlling the temperature of the heating element 18 in the fixing nip and the thermistor 20 as the process speed increases.
Are required to have no error in the detected temperature, to have good responsiveness, and to have small variations in temperature ripple. Here, the fixing temperature is controlled by using a heater provided with a thermistor on the surface of the heater substrate (on the same side as the heating element), and when the image is formed, the fixing is performed using the heater provided with the thermistor on the back surface of the heater substrate. The experimental results in the case of controlling the temperature to form an image (process speed 50 mm / sec) are shown.

The table shown in FIG. 4A shows the actual surface temperature of the heating element in the fixing nip with respect to the thermistor output (temperature control temperature) of a heater having a thermistor on the back surface of the heater substrate. Indicates the value of the temperature ripple ΔT at that time.

As can be seen from the values shown in FIGS. 4 (a) and 4 (b), the actual heater surface temperature when monitoring the temperature on the back surface of the heater and controlling the temperature indicates a temperature higher than the thermistor output.
Temperature ripple ΔT on the front surface rather than temperature ripple ΔT on the back surface
Is larger.

In the experiment, the temperature of the heater of this embodiment was set such that the same fixing property as that of the heater having the thermistor on the back surface of the heater substrate was obtained. Temperature control temperature 200 ℃, 190
℃ and 180 ℃, whereas the heater of this embodiment
0 ° C, 200 ° C, and 190 ° C. FIG. 4C shows the temperature ripple at this time, and it can be seen that the ripple of the heater surface temperature is clearly smaller than that of FIG. 4B.

Therefore, in this embodiment, the thermistors 20a,
Since the heating element 20b is disposed in the fixing nip on the same surface as the heating element 18, the temperature of the heating element 18 in the actual fixing nip and the temperature of the thermistor 20 are lower than when the thermistor is provided on the back side of the substrate 17.
Is suppressed, and the response is improved. For this reason, even with a high-speed apparatus, it is possible to accurately control the fixing temperature, and it is possible to obtain a good image free from defective fixing, offset, and uneven gloss.

In this embodiment, one of the two thermistors 20a and 20b is a heating element.
Since it is on the upstream side of 18, the temperature to be detected becomes lower due to the influence of the temperature of the film 14, the recording medium P and the pressure roller 15 before heating. On the other hand, the temperature of the downstream thermistor 20b is increased due to the temperature of the film 14, the recording medium P and the pressure roller 15 after the heating.

Therefore, in the present embodiment, for example, when the detected temperature difference between the two thermistors 20a and 20b is 40 ° C. or more, the control temperature of the heater is 165 ° C. as viewed from the thermistor 20b.
When the temperature difference is less than 40 degrees and 30 degrees or more, the temperature is controlled to 155 degrees C. When the temperature difference is less than 30 degrees and 20 degrees or more, the temperature is controlled to 145 degrees C. Control to 140 ° C.

In this way, by controlling the heater temperature in accordance with the temperature difference between the upstream and downstream sides of the heating element 18, it is possible to reliably prevent an offset or a fixing defect and fix an image. Further, in the above configuration, the control temperature can be changed with respect to the heat capacity and temperature of the recording medium P, which is the object to be heated, so that environmental friendliness and the degree of freedom of the medium can be increased. Further, by using the average value of the thermistors 20a and 20b, the heater temperature at the center of the nip can be accurately known.

[Second Embodiment] In the above-described first embodiment, an example is shown in which two thermistors are arranged on the upstream and downstream sides of the heating element. However, the second embodiment conveys the smallest recording medium conveyed. FIG. 6 shows an example in which thermistors are arranged in the area and the non-transport area. The members having the same functions as those of the first embodiment are denoted by the same reference numerals.

In the fixing device, when a small-sized recording medium is continuously conveyed, the temperature of the heating element 18 in the non-conveying area is greatly increased, and the life of the heating element 18 is shortened. There is a possibility that the film 14 is unbalanced due to thermal expansion in the transfer region.

Therefore, the heater H according to this embodiment is the same as that shown in FIG.
As shown in FIG. 5, one of the two thermistors 20a and 20b is arranged in a conveyance area of a recording medium having a minimum size for conveying, and the other thermistor 20b is arranged in a non-conveyance area. Then, the outputs of the two thermistors 20a and 20b are compared by the difference circuit (FIG. 3) described in the first embodiment, and for example, the conveying interval of the recording medium is widened according to the temperature difference. When the difference becomes equal to or higher than a certain temperature, heat is diffused by stopping the apparatus or the like, thereby suppressing an excessive rise in temperature in the non-transport region.

That is, while the temperature difference is small, the conveying interval is shortened as in the case of the recording medium having a large size, and the temperature in the non-conveying region increases as the temperature difference increases. It is configured so that there is a transport interval.

For example, when the temperature difference is less than 10 ° C., the conveyance interval is set to 50 mm, which is the same as that for a large-sized recording medium. When the temperature difference is 10 ° C. or more and less than 30 ° C., the conveyance interval is increased to 60 mm. If the temperature is between 50 ° C. and 50 ° C., the conveyance interval is extended to 80 mm.

As described above, by increasing the transport interval as the temperature difference increases, it is possible to suppress excessive temperature rise in the non-transport area due to thermal diffusion during the interval.

[Third Embodiment] The heater H shown in FIG.
Of the two thermistors, this is the transport area for the smallest sized recording medium that transports one thermistor 20a, upstream of the heating element 18 and the non-transport area for the smallest sized recording medium that transports the other thermistor 20b. This is arranged downstream of the heating element 18. In this case, members having the same functions as those in the first embodiment are denoted by the same reference numerals.

In the heater H shown in FIG. 7, the above-described temperature control of the first embodiment and the control of the transport interval of the second embodiment are simultaneously performed based on the detected temperatures of the thermistors 20a and 20b. It is possible to obtain the combined effect of the first and second embodiments.

[Other Embodiments] In the above-described embodiment, an example is shown in which two thermistors for detecting temperature are provided. However, three or more thermistors may be provided. In this case, more accurate temperature detection becomes possible.

[0053]

The present invention is constructed as described above.
Since the temperature is detected on the same surface as the heating element, the temperature can be directly and accurately detected regardless of the thickness of the substrate. Further, the temperature can be detected by a plurality of temperature detecting elements, and the average value of the respective detected values is obtained, whereby more accurate temperature detection can be performed.

Therefore, when the fixing device and the image forming apparatus are configured using the heater, it is easy to control the fixing temperature with higher accuracy, and it is possible to obtain a high-quality image.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a configuration of a fixing device.

FIG. 2 is a diagram illustrating a configuration of a heater.

FIG. 3 is an explanatory diagram of a heating temperature detection circuit using a heater.

FIG. 4 is an explanatory diagram in which a thermistor is provided on a front surface and a back surface of a heater substrate to compare temperature ripples.

FIG. 5 is an overall schematic diagram of the image forming apparatus.

FIG. 6 is an explanatory diagram of a heater in which a thermistor is arranged in a transport region and a non-transport region of a recording medium.

FIG. 7 is an explanatory diagram of a heater in which a thermistor is disposed in a transport region and a non-transport region of a recording medium, and is disposed upstream and downstream of a heating element.

FIG. 8 is an explanatory diagram of a configuration of a heater for detecting a temperature by a thermistor chip provided on a back surface of a heater substrate.

FIG. 9 is a diagram illustrating a configuration of a heater that detects a temperature using a printing thermistor provided on the back surface of a heater substrate.

[Explanation of symbols]

 H ... heater P ... recording medium 1 ... optical means 2 ... photosensitive drum 3 ... process cartridge 4 ... transfer means 5 ... fixing means 6 ... recording paper cassette 6a ... separation claw 7 ... pickup roller 8 ... transport roller 9 ... pinch roller 10 ... Conveying guide member 11 ... Discharge roller pair 12 ... Discharge roller pair 13 ... Discharge part 14 ... Film 15 ... Support 16 ... Pressurizing roller 16a ... Core metal 16b ... Roller part 17 ... Substrate 18 ... Heating element 19 ... Protective layer 20a ... Thermistor 20b ... Thermistor 21a ... Electrode pattern 21b ... Electrode pattern 22 ... AC electrode 23 ... DC electrode 24 ... Comparator 25 ... Comparator 26 ... A / D converter 27 ... CPU 28 ... Heater driver 29 ... AC power supply 30 ... D / A converter

Claims (5)

[Claims] 1. A heater for heating a conveyed object to be heated, comprising: a substrate; a heating element provided on one surface side of the substrate for generating heat by energization; and a plurality of sensors for detecting a heating temperature of the heating element. And a temperature detecting element, wherein the plurality of temperature detecting elements are provided on the same surface side on which the heating element is provided. 2. The heater according to claim 1, wherein the temperature detecting elements are arranged on an upstream side and a downstream side in a conveying direction of the heated object conveyed across the heating element. 3. The heater according to claim 1, wherein the temperature detecting elements are arranged in a transport area and a non-transport area of a minimum heated object to be transported. 4. A fixing device for heating and fixing an image transferred to a recording medium, comprising: a film member that moves following the conveyance of the recording medium; and a recording medium that is pressed against the film member and conveyed to the recording medium. 4. A rotating member that applies a force, and a heater that conveys the recording medium through the film member, wherein the heater is used as the heater.
A fixing device characterized by using the heater described in (1). 5. An image forming apparatus for transferring an image to a recording medium, heating and fixing the image, a conveying unit for conveying the recording medium, an image forming unit for transferring the image to the recording medium, An image forming apparatus comprising: a fixing unit for fixing a transferred image to a recording medium; and wherein the fixing device according to claim 4 is used as the fixing unit.