JP4447985B2 - Image forming apparatus - Google Patents

Description

The present invention is, for example, relate images forming apparatus such as a printer or a copying machine using an electrophotographic method.

Conventionally, in an image forming apparatus such as a printer, a copying machine, and a facsimile using an electrophotographic technology, as a heating device for heating and fixing an unfixed toner image on a recording material (hereinafter referred to as a fixing device), thermal efficiency and safety are high. A good contact heating type heat roller type fixing device is widely known. A heat roller type fixing device has a nip portion between a heating roller (fixing roller) heated to a predetermined temperature and a pressure roller that has an elastic layer and is in pressure contact with the heating roller. The recording material is sandwiched and conveyed to fix the unfixed toner image on the recording material by heating and pressing.

  In recent years, from the viewpoint of promoting energy saving, as a device of high heat conduction efficiency and quick start-up (quick start, on-demand) method, for example, through a fixing film having a small heat capacity as described in Patent Document 1 Attention has been focused on a film heating type heating apparatus that heats the film and has been put to practical use as a fixing apparatus. The fixing device includes a heating body such as a ceramic heater fixedly held on a support member, a heat-resistant fixing film as a flexible member conveyed while being opposed to the heating body, and the fixing A pressure roller as a pressure member that forms a nip portion with a heating body sandwiching the film, and a recording material as a material to be heated is sandwiched and conveyed by the nip portion from the heating body through the fixing film. An unfixed toner image formed on a recording material by heat is heat-fixed.

  Usually, in such a fixing device, recording materials having various widths, lengths, thicknesses, and the like are used as the material to be heated. For example, when a particularly narrow recording material such as an envelope is continuously passed, the difference in heat consumption between the portion where the recording material passes in the fixing device (sheet passing portion) and the portion where it does not pass (non-sheet passing portion). Therefore, a so-called “non-sheet-passing portion temperature rise” occurs in which the temperature rise at the non-sheet-passing portion is large. If this non-sheet passing part temperature rise phenomenon becomes significant, the thermal expansion of the pressure roller of the fixing device will become uneven, causing problems such as rubber breakage or uneven rotation speed of the fixing film and twisting. Will occur. Moreover, the thermal damage of an apparatus structural member is also considered.

  Therefore, in order to prevent such a problem, in a conventional fixing device, when a recording material having a small size such as an envelope (hereinafter referred to as a small size paper) is passed, the recording material is passed per minute. By reducing the number of sheets (throughput) and increasing the sheet passing interval to alleviate temperature non-uniformity, the temperature rise of the non-sheet passing portion is reduced.

  Conventionally, a paper width detection sensor has been used as means for discriminating that a recording material having a narrow width is being passed. An installation example of the paper width detection sensor is shown in FIG. The paper width sensor 51 is disposed on the recording material conveyance path at a position where it can be determined whether the width of the recording material passing therethrough is a normal size such as an A4 size or a narrow size. On the other hand, the top sensor 52 is disposed at a position where it can be detected that recording materials of all sizes pass. In FIG. 8, the paper width sensor 51 is disposed at a position 93 mm from the central paper passage reference, and the top sensor 52 is disposed at the paper reference position. The passing timing of the recording material detected by the top sensor 52, the passing time of the recording material, and the like are reflected in various controls of the apparatus. When the paper width detection sensor 51 does not detect the recording material, it is determined that the recording material is a small size paper of B5 size (width 182 mm length 257 mm) or less, and this is reflected in control such as lowering the throughput.

  This method can reliably detect a narrow recording material, but requires two sensors for detecting the passage of the recording material, which is not preferable in terms of cost reduction of the apparatus. For this reason, a method of easily recognizing a recording material having a short length as a recording material having a narrow width by using the top sensor 52 arranged at the center of paper passing in FIG. 8 is often used. That is, the length of the recording material is determined according to the paper presence detection time of the top sensor 52. For example, when the length of the recording material is 270 mm or more, a normal size recording material, and when the length is less than 270 mm, narrow recording is performed. The material is judged as a material, and control such as a reduction in throughput is performed. This control method has been put to practical use because only one sensor for detecting the passage of the recording material is sufficient, which is advantageous in terms of cost compared to the above method.

  However, in recent years, the types of recording materials used in the fixing device have increased in size, thickness, and the like, and have increased in variety. In some cases, conventional control methods have not been able to cope with them completely.

  For example, a recording material (hereinafter, long narrow paper) having a width as narrow as a business card width (width 55 mm) and a length of A4 size (length 297 mm) or more exists in the market.

  Such a long narrow paper cannot be detected as having a narrow width in an inexpensive apparatus that does not have the paper width detection sensor 51 because it is determined to be larger than the normal size by the length determined by the top sensor 52. For this reason, the long narrow paper is passed at the maximum throughput on the setting of the apparatus, like the normal size such as A4 size. In that case, the non-sheet passing portion of the fixing device is likely to become high temperature, and the temperature of the film guide exceeds the heat resistance temperature when several sheets are continuously passed. Further, if the continuous paper feeding is further continued, the apparatus constituent member may be thermally damaged.

Therefore, in recent apparatuses, a temperature detection element is disposed on a portion of the heating member that becomes a non-sheet-passing portion when a narrow recording material passes, and throughput is improved by detecting the temperature of the non-sheet-passing portion. Control methods such as lowering are often used. This control method will be described with reference to a schematic diagram of component arrangement in the longitudinal direction of the fixing device of the film heating type shown in FIG. Reference numeral 108 denotes a heating body, 101 denotes a film guide for supporting the heating body, 102 denotes a fixing film, and 104 denotes a pressure roller. Reference numeral 61 denotes a main thermistor disposed at a position that always serves as a sheet passing portion regardless of the size of the recording material, and the heating body 108 is maintained by maintaining the detected temperature at a predetermined temperature (hereinafter referred to as temperature control). The amount of heat generated is controlled to obtain an optimum heating amount for the recording material. Reference numeral 62 denotes a sub-thermistor disposed at a position that becomes a non-sheet passing portion when a recording material narrower than the B5 size is passed. The sub-thermistor 62 is not used for temperature control but only for temperature detection of the non-sheet passing portion. In this configuration, when a recording material having a width smaller than the width of the B5 size is continuously passed, the detected temperature of the sub-thermistor 62 is higher than the detected temperature of the main thermistor 62 during the passing of the recording material. . Here, when the sub-thermistor 62 reaches a predetermined temperature, control such as lowering the throughput is performed to mitigate the temperature rise of the non-sheet passing portion to prevent thermal damage of the fixing device. Thus, if the structure which detects the temperature of a non-sheet passing part is used, even if it is an inexpensive structure, the safety | security of an apparatus can be made higher.
JP-A-4-44075

  By the way, in the above-described conventional fixing device, when a narrow recording material is passed, even if the temperature of the sub-thermistor exceeds a predetermined temperature (hereinafter referred to as switching temperature) during the passing of the recording material, the recording material is fixed to the fixing device. The temperature of the non-sheet passing portion continues to rise until it passes through. For this reason, the switching temperature has usually been set with a certain margin with respect to the temperature at which the fixing device is thermally damaged (hereinafter, the allowable temperature).

  However, in recent fixing devices, it has become difficult to prevent thermal damage of the fixing device by the conventional method. This point will be described below. In recent years, along with the development of the computer industry, the recording material conveyance speed (hereinafter referred to as process speed) of the image forming apparatus has been increased. Along with this, by increasing the temperature of the heating element (hereinafter referred to as fixing temperature), the amount of heat applied to the recording material and toner is increased, and the degree of fixing of the toner to the recording material (hereinafter referred to as fixing property) is ensured. I have done it.

  As described above, in the fixing device having a high fixing temperature, the detection temperature of the sub-thermistor (hereinafter referred to as the temperature at the time of passing) when the normal size recording material is passed is also high, and the temperature between the passing time and the allowable temperature is increased. The temperature difference is small. Normally, the switching temperature of the sub-thermistor is set between the paper passing temperature and the permissible temperature. If this is set too close to the paper passing temperature, the normal size recording material can be passed. Even when paper is used, the throughput may be reduced due to erroneous detection or the like, and there is a possibility that the specification of the apparatus may be reduced. For this reason, the switching temperature must be set to a value close to the allowable temperature. As described above, since a recent fixing device does not have a sufficient temperature difference between the switching temperature and the allowable temperature, when the above-described conventional method is used, the fixing device has a narrow recording material, in particular, a narrow width and a high length. When a long recording material is passed, the non-sheet passing portion easily exceeds the allowable temperature before the recording material passes through the fixing device, and the fixing device is thermally damaged.

The present invention has been made in order to solve the above-described problems. Even when long narrow paper is used as a recording material, not only the excessive temperature rise in the non-sheet passing area can be suppressed, but also the type of long narrow paper. An object of the present invention is to provide an image forming apparatus capable of performing a suitable fixing process .

In order to achieve the above object, a typical configuration of the superheater according to the present invention is as follows.
An image forming unit for forming a toner image on a recording material;
An endless fixing film; a heater in contact with the inner surface of the fixing film; a pressure roller that forms a fixing nip portion with the heater via the fixing film; and a minimum sheet passing width region through which a recording material of a minimum size passes. The first temperature detecting element for detecting the temperature of the heater, the second temperature detecting element for detecting the temperature of the heater in the area outside the minimum sheet passing width area, and the detected temperature of the first temperature detecting element during the fixing process are control targets. A control unit that controls electric power supplied to the heater so as to maintain the temperature, and a fixing unit that fixes the recording material carrying the toner image at the fixing nip unit;
When the plurality of recording materials are continuously fixed at the fixing nip portion with the control target temperature set to the first control target temperature, the detected temperature of the second temperature detecting element is the first reference temperature. When the temperature is exceeded, the interval until the recording material next to the current recording material passing through the fixing nip portion enters the fixing nip portion is increased more than before, and the temperature detected by the second temperature detecting element is increased. When the temperature exceeds a second reference temperature higher than the first reference temperature, the control target temperature for fixing the current recording material passing through the fixing nip portion is changed from the first control target temperature to the second control temperature. In the image forming apparatus for lowering to the control target temperature,
The second control target temperature is set according to a rising speed of the detected temperature until the detected temperature of the second temperature detecting element reaches the second reference temperature.

According to the present invention, even when long narrow paper is used as the recording material, not only the excessive temperature rise in the non-sheet passing area can be suppressed, but also fixing processing suitable for the type of long narrow paper can be performed .

Reference examples and embodiments of the present invention will be described below with reference to the drawings.
[Reference Example 1]

(1) Example of Image Forming Apparatus FIG. 1 is a schematic configuration diagram of an image forming apparatus in Reference Example 1 . The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process. The standard for conveying the recording material is the central standard. The maximum sheet passing width was letter size (width 216 mm length 279 mm: longitudinal feed), and the minimum sheet passing width was postcard size (width 100 mm length 148 mm: vertical feed).

  A recording material 206 is supplied from the paper cassette 211 through the registration device 213 by the paper supply roller 212 into the apparatus.

  Reference numeral 222 denotes a top sensor disposed at the sheet feeding reference center position of the recording material. The top sensor 222 detects the passing timing and length of the recording material 206, and reflects this in various controls of the image forming apparatus based on this information.

Reference numeral 201 denotes a photosensitive drum as an image carrier, which is rotationally driven in a clockwise direction indicated by an arrow at a predetermined speed. The surface of the photosensitive drum 201 is cleaned by a cleaning device 202 and then charged to a desired polarity / potential by a charging member 203. The uniformly charged surface is subjected to laser beam scanning exposure according to image information by a laser scanner 204 as an exposure device, and an electrostatic latent image corresponding to the image information is formed on the surface of the photosensitive drum 201. The electrostatic latent image is developed as a toner image by the developing device 205. A transfer member 207 contacts the photosensitive drum 201 to form a transfer nip portion. The recording material 206 is supplied to the transfer nip portion by the registration device 213 at a predetermined control timing and is nipped and conveyed. The toner image on the photosensitive drum 201 side is sequentially electrostatically transferred onto the surface of the recording material 206 by the transfer bias applied to the transfer member 207 in the nipping and conveying process.
The photosensitive drum 201, the charging member 203, the exposure device 204, the developing device 205, the transfer member 207, and the like form image forming means (image forming unit) for forming and carrying an unfixed image (unfixed toner image) on the recording material 206. It is.

The recording material 206 on which an unfixed toner image that has passed through the transfer nip portion is placed is sent to a fixing device (fixing means) 209 along the conveyance guide 208, and is heated and pressurized in the fixing nip portion, and the toner image is recorded. Fixing (fixing processing) to the material 206 is performed. Thereafter, the recording material 206 is discharged to the paper discharge tray 210 through the paper discharge device 214.

In the image forming apparatus of this example , the process speed was 200 mm / sec. In addition, when the paper length detected by the top sensor 222 is 270 mm or longer, the interval between the trailing edge of the preceding recording material and the leading edge of the succeeding recording material (hereinafter referred to as “paper interval”) is 0.3 seconds. The interval at which the paper roller 212 feeds the recording material is set.

(2) Fixing device 209
FIG. 2 is an enlarged cross-sectional model view of the main part of the fixing device 209. The fixing device 209 is a pressure member driving type and tensionless type film heating type heating device described in JP-A-4-44075. This device uses an endless belt-shaped or cylindrical heat-resistant film as a flexible member, and at least a part of the circumference of the film is always tension-free (a state in which no tension is applied). This is a device that is rotationally driven by a rotational driving force.

  Reference numeral 1 denotes a film guide, which is a heat resistant and rigid member as a heating body holding member and a film guide member. Reference numeral 3 denotes a ceramic heater as a heating body, which is disposed and held on the lower surface of the film guide 1 along the longitudinal direction. Reference numeral 2 denotes an endless (cylindrical) heat-resistant and highly heat-conductive fixing film as a flexible member, which is externally fitted to a film guide 1 including a heating element 3 with a margin in circumference.

The film guide 1 can be composed of a high heat-resistant resin such as polyimide, polyamideimide, PEEK, PPS, or liquid crystal polymer, or a composite material of these resins and ceramics, metal, glass, or the like. In this example , a liquid crystal polymer was used.

The fixing film 2 is made of a single layer film such as PTFE, PFA, FEP or the like having a thickness of 20 μm or more and 100 μm or less, or polyimide, polyamideimide, PFEK, in order to reduce heat capacity and improve quick start properties. A composite layer film in which PTFE, PFA, FEP or the like is coated on the outer peripheral surface of a film such as PES or PPS can be used. The coating on the outer peripheral surface of the fixing film 2 is for ensuring separation of the unfixed toner image and the recording material. It can also be set as the cylinder body of the composite layer structure which has a flexible metal cylinder body and a metal layer. In this example , a polyimide film having a total film thickness of 70 μm coated with PTFE on the outer peripheral surface of the polyimide film was used.

Reference numeral 4 denotes a pressure roller as a pressure member. The pressure roller 4 is film outer surface contact driving means for forming a pressure nip portion (fixing nip portion) N with the fixing film 2 sandwiched between the heating body 3 and rotating the fixing film 2. The pressure roller 4 includes a cored bar 4a, an elastic layer 4b, and an outermost release layer 4c. The fixing film 2 is sandwiched with a predetermined pressing force by a bearing unit and a biasing unit (not shown). It is disposed in pressure contact with the surface of the heating element 3. In this example , the core metal 4a is made of aluminum, the elastic layer 4b is made of silicone rubber, and the release layer 4c is coated with PFA. The outer diameter of the pressure roller 4 was 25 mm, and the thickness of the elastic layer 4b was 3.5 mm.

  The pressure roller 4 is rotationally driven by the drive system M in a counterclockwise direction indicated by an arrow at a predetermined peripheral speed. Due to the rotational driving of the pressure roller 4, a rotational force acts on the fixing film 2 by the frictional force between the pressure roller 4 and the film outer surface at the fixing nip portion N, and the inner surface side of the fixing film 2 is at the fixing nip portion N. While being in close contact with the surface of the heating element 3 and sliding, the outer periphery of the film guide 1 is rotated in the clockwise direction indicated by an arrow at a rotational speed substantially equal to the rotational speed of the pressure roller 4. Sliding grease is applied between the inner surface of the fixing film 2 and the film guide 1 to keep the fixing film 2 slidable. Further, the rotational stability of the fixing film 2 is maintained by the film guide 1.

In the state where the fixing film 2 is rotated by the rotation driving of the pressure roller 4 and the heating body 3 is heated to a predetermined target temperature by energizing the heating body 3 as described later, the fixing nip is adjusted. A recording material 206 carrying an unfixed toner image ta is introduced between the fixing film 2 of part N and the pressure roller 4, and the toner image carrying surface is brought into close contact with the outer surface of the fixing film 2 together with the fixing film 2. by passing through the fixing nip N, the heat of the heating member 3 is unfixed toner image ta is applied to the recording medium 206 via the fixing film 2 is heated and fixed as a solid Chakuzo tb the surface of the recording material 206. a is the conveyance direction of the recording material 206. The recording material 206 that has passed through the fixing nip N is separated from the surface of the fixing film 2 and is discharged and conveyed.

(3) Heating body 3
The heating body 3 is a ceramic heater as means for supplying heat to the recording material 206 via the fixing film 2. 3A is a plan model view of the front surface side (fixing film sliding surface side) of the heating element 3, FIG. 3B is a plan model diagram of the back surface side (back side) of the heating element 3, and FIG. The figure which showed the pattern of the resistance heating element provided in the back surface side of the body substrate, and the electrode part for electricity supply, (d) is an expanded sectional view which follows the (d)-(d) line in (b) figure.

  This heating body 3 is a back surface heating type ceramic heater, and includes a heating body substrate 5 and a sliding layer 11 formed almost entirely on the surface side (fixing film sliding surface side) of the heating body substrate 5. A resistance heating element 6 formed on the back surface side (fixing film non-sliding surface side) of the heating element substrate 5, feeding electrode portions 21, 22, and 23 for the resistance heating element 6, and the resistance heating element 6 are provided. The protective layer 10 is provided to be covered, and the main thermistor 8 and the sub-thermistor 81 are provided as first and second temperature sensing elements provided on the upper surface of the protective layer 10.

  The heating body substrate 5 has an elongated shape with the direction perpendicular to the conveying direction a (FIG. 2) of the recording material 206 as the material to be heated as the longitudinal direction. The heating substrate 5 of this example is an aluminum nitride substrate having heat resistance, insulation, and high thermal conductivity, and has a thickness of about 0.5 mm, a width of about 10 mm, and a length of about 300 mm in order to reduce the heat capacity. Used. In FIG. 3, the vertical, horizontal, and thickness dimension ratios of the heating element 3 and the constituent members do not correspond to the dimensions described in the specification.

The sliding layer 10 provided on the surface side of the heating substrate 5 has a function excellent in heat resistance, lubricity, and wear resistance, and has a function of obtaining smooth slidability with the fixing film 2. In this example , 20 μm thick heat resistant glass was used.

The resistance heating element 6 provided on the back surface side of the heating body substrate 5 has Ag / Pd (silver palladium), RuO ₂ , Ta ₂ N on the back surface (non-film sliding surface) of the heating body substrate 5 along the length of the substrate. These are formed by applying an electric resistance material such as a line or a band by screen printing or the like. In this example , a mixture of Ag / Pd and glass was applied by screen printing to a thickness of about 10 μm, a width of 2 mm, and a length of 225 mm. The resistance heating element 6 can obtain a desired resistance value by changing the compounding ratio of Ag / Pd and glass. In this example , the resistance value of the resistance heating element is 13Ω at room temperature.

The power supply electrode portions 21, 22, and 23 are power supply electrodes for supplying power to the resistance heating element 6, and are electrically connected to the ends of the resistance heating element 6 at the longitudinal end portions on the back surface side of the heating body substrate 5. It is made conductive. In this example , the power feeding electrodes 21, 22, and 23 are screen printing pattern layers made of a mixture of Ag / Pd and glass.

The protective layer 10 is a heat-resistant / insulating overcoat layer provided so as to protect the resistance heating element 6. In addition to ensuring insulation from the external conductive member, the protection layer 10 is formed of the resistance heating element 6 due to oxidation or the like. There are anti-corrosion functions for preventing resistance value changes, and further functions for preventing mechanical damage. In this example , a heat-resistant glass having a thickness of about 50 μm was used.

The sliding layer 10 provided on the surface of the heating substrate 5 has a function excellent in heat resistance, lubricity, and wear resistance, and has a function of obtaining smooth slidability with the fixing film 2. In this example , 20 μm thick heat resistant glass was used.

  The heating body 3 is fixedly disposed by holding the back side of the heating body on which the resistance heating element 6 is formed and holding it on the lower surface side of the film guide 1.

The heating element 3 rises in temperature when the resistance heating element 6 generates heat over the entire length by feeding power from the power source 26 to the feeding electrodes 21, 22, 23. The temperature rise is detected by a main thermistor 8 which is a first temperature sensing element (first temperature sensing element) for detecting and controlling the temperature of the heating body 3, and the output of the main thermistor 8 is A / D converted to a control unit. The temperature of the heating element 3 is controlled by controlling the power supplied from the power supply 26 to the resistance heating element 6 by the triac 25 based on the information by phase control, wave number control or the like. The CPU 24 and the triac 25 are energization control means for controlling energization to the heating body 3. That is, the heating element 3 is kept at a constant temperature by controlling the energization so that the heating element 3 is heated when the temperature detected by the main thermistor 8 is lower than a predetermined set temperature, and the temperature is lowered when the temperature is higher than the set temperature. It is. In this example , the energization control is performed using the well-known PI control, and the P term (proportional term) increases the energization amount by 5% when the detected temperature of the main thermistor 8 is 1 deg lower than the predetermined temperature, and conversely when 1 deg is higher. The energization amount was set to be reduced by 5%.

In FIG. 3B, O is a central reference line that is a reference for conveying the recording material. A is the longitudinal dimension of the heating substrate 5 and is 300 mm in this example as described above. B is the longitudinal dimension of the resistance heating element 6 and is 225 mm in this example as described above. C is the maximum sheet passing width, and in this example , as described above, the recording material width of letter size longitudinal feed is 216 mm. E is the minimum sheet passing width (minimum sheet passing width region through which the recording material of the minimum size passes) , and in this example , as described above, the postcard size vertical feeding postcard width is 100 mm. D is a longitudinal feed width of 105 mm of a recording material (long narrow paper) having a width of 105 mm and a length of 355 mm.

Main thermistor 8 is disposed in the sheet passing region of the top Shotsu width E. Sub thermistor 81 is a second temperature detecting element (second thermometry device) is disposed between the end and the end of the resistance heating element 6 of the top Shotsu width E (minimum paper width region outside the region), the heating of the region Detect body (heater) temperature. In this example , the main thermistor 8 is disposed at the sheet passing center position, which is the longitudinal center position of the resistance heating element 6, and the sub-thermistor 81 is disposed at a position 93 mm from the sheet passing center position to the electrode 23 side. The sub thermistor 81 is a temperature detection element disposed at a position different from the main thermistor 8. As described above, the main thermistor 8 is used for temperature control of the heating element 3, while the sub-thermistor 81 is provided for temperature detection in the vicinity thereof. That is, the sub-thermistor 81 detects the temperature of the position that becomes the non-sheet passing portion when the heated material narrower than the predetermined size is conveyed.

(4) Control System Next, a control method of the fixing device of this example will be described. In this example , as described above, the main thermistor 8 is used to control the temperature of the heating element 3 to be constant, and the sub-thermistor 81 is used to detect the temperature in the vicinity thereof.

  Here, a series of operations of the fixing device when the operation is started from room temperature will be described based on the block diagram of the control flow of FIG. This control operation is executed by the CPU 24 which is a control unit.

First, when a print command is input to the apparatus (7A), energization of the resistance heating element 6 is started, and the temperature is adjusted so that the detected temperature th1 of the main thermistor 8 becomes the fixing temperature T (first control target temperature). Control is performed (7B). Next, the recording material 206 is introduced into the fixing device 209 at a predetermined timing (7C), and paper feeding is started. While the recording material 206 is passing (fixing process) , the temperature control is continued so that the detected temperature th1 of the main thermistor 8 becomes the fixing temperature T.

On the other hand, while the recording material 206 is passing (when a plurality of recording materials are continuously fixed to the fixing nip portion) , the detection temperature th2 of the sub-thermistor 81 is monitored, and this is the switching temperature T2 (first reference temperature). ) (7D), the interval of introduction (feeding) of the next recording material 206 ( the recording material next to the current recording material that has passed through the fixing nip portion) into the fixing device 209 is increased. (The interval until the next recording material enters the fixing nip portion is increased as compared with the case .) A setting for lowering the throughput is set (7E). In this example , this paper feed interval is set to 30 seconds regardless of the type of the recording material 206. Once this setting is set, it is held until a series of printing operations are completed (7J described later).

Further, when the detected temperature th2 of the sub-thermistor 81 exceeds the threshold temperature T3 (second reference temperature) (7F), the current recording material passing through the fixing nip portion is fixed while the recording material is passing through (7F). The control target temperature of the main thermistor 8 at the time of processing is switched from T (first control target temperature) to T1 (second control target temperature) (7G).

  The monitoring of the detected temperature th2 of the sub-thermistor 81 is repeated until the recording material 206 finishes passing (7H). If the recording material 206 has been passed and a print command for the next recording material 206 has been input, this operation is repeated from 7B (7I), and if not, a series of operations are terminated (7J). Note that the temperature control is performed so that the detected temperature th1 of the main thermistor 8 becomes T0 different from T during the interval between sheets (between sheets).

In this example , the fixing temperature T when passing paper is 210 ° C., the switching temperature T 2 is 260 ° C., the threshold temperature T 3 is 280 ° C., the control temperature T 1 after switching is 200 ° C., and the control temperature T 0 between papers is 175 ° C. did.

The operation and effect of the fixing device of this example will be described below. FIG. 5 shows the detection temperature time of the main thermistor 8 and the sub-thermistor 81 when four sheets of recording material (hereinafter, long narrow paper) having a width of 105 mm, a height of 355 mm, and a basis weight of 120 g / m ² are passed from room temperature. Showing change. th1 represents the detected temperature of the main thermistor 8, and th2 represents the detected temperature of the sub-thermistor 81. When the long narrow paper is passed, the main thermistor 8 is located at the paper passing portion, and the sub thermistor 81 is located at the non-paper passing portion. FIG. 5 shows a case where four sheets of recording material are passed. The first sheet and the second sheet are arranged in order from the left side, and the rightmost is the fourth sheet. The interval between the third and fourth sheets is much larger than that between the first and second sheets and between the second and third sheets, as will be described later. This is because the interval between the third sheet and the fourth sheet is 30 seconds while the sheet interval is 0.3 seconds.

  First, when a print command is sent to the fixing device, energization of the resistance heating element 6 is started, and the detected temperature th1 of the main thermistor 8 and the detected temperature th2 of the sub-thermistor 81 are rapidly increased. When the detected temperature th1 of the main thermistor 8 reaches the fixing temperature T, the first recording material is introduced into the fixing device at a predetermined timing. During the first sheet passing period, the detected temperature th1 of the main thermistor 8 is temperature-controlled at the fixing temperature T, and thus is maintained at a substantially constant temperature, whereas the sub-thermistor 81 located in the non-sheet passing portion is maintained. It can be seen that the detected temperature th2 continues to rise. In the paper passing portion, the heat generated from the resistance heating element 6 is transmitted to the recording material and carried to the outside of the apparatus. On the other hand, since the recording material does not pass through the non-sheet passing portion, it is generated from the resistance heating element 6. The recorded heat is not taken away by the recording material. Because of this difference in heat consumption, the temperature is high in the non-sheet passing portion. This is the non-sheet passing portion temperature rise.

Here, as described above, in this example , the long narrow paper has a length of 270 mm or more. Therefore, while the detection temperature th2 of the sub-thermistor 81 is lower than the switching temperature T2, both the second and third sheets are set to 0. 0. Paper is fed between 3 seconds of paper. From FIG. 5, even during the second sheet passing, the detected temperature th1 of the main thermistor 8 is controlled by the fixing temperature T. On the other hand, the detected temperature th2 of the sub-thermistor 81 continues to rise and the non-sheet passing portion rises. It can be seen that the temperature is progressing. When the detection temperature th2 of the sub-thermistor 81 reaches the switching temperature T2 near the leading edge of the third sheet, the setting for setting a large gap between the sheets up to the fourth sheet is set in order to follow the control of step (7D → 7E) in FIG. Is done. Further, when the detection temperature th2 of the sub-thermistor 81 reaches the threshold temperature T3 in the middle of the third sheet, the control temperature of the detection temperature th1 of the main thermistor 8 is set to follow the control of step (7F → 7G) in FIG. Change from T to T1.

  Here, in FIG. 5, Td is the allowable temperature of the non-sheet passing portion. When the sub-thermistor detection temperature th2 exceeds the allowable temperature Td, the film guide 1 that supports the heating body 3 is thermally damaged.

As can be seen from FIG. 5, in the fixing device of this example , the detected temperature th2 of the sub-thermistor 81 does not reach the allowable temperature Td. This is because when the control temperature is changed from T to T1, the target temperature for control becomes lower than the detected temperature th1 of the main thermistor 8, so that the amount of current supplied to the resistance heating element 6 is reduced, and the non-sheet passing portion This is because the temperature of the ink drops temporarily and the temperature rise of the non-sheet passing portion is moderated.

  Note that a broken line G in FIG. 5 indicates a change over time in the detected temperature th2 of the sub-thermistor 81 when the conventional control method is used. In the conventional control method, even if the detection temperature th2 of the sub-thermistor 81 reaches the threshold temperature T3, the control temperature T is not lowered. Therefore, the temperature rise of the non-sheet passing portion is continued, and the detection temperature th2 of the sub-thermistor 81 is the allowable temperature. It can be seen that Td is greatly exceeded. In such a conventional control method, the fixing device is thermally damaged.

  Next, when the trailing edge of the third sheet is completely removed from the fixing device, as described above, there is a 30-second gap between the fourth sheet and the first sheet. Between the sheets, the temperature control of the temperature detection th1 of the main thermistor 8 is controlled at T0 lower than T. Also, it can be seen that the detected temperature th2 of the sub-thermistor 81 is also lowered and is substantially the same as the detected temperature th1 of the main thermistor 8. Since the recording material is not passed between the sheets, there is no difference in the amount of heat consumption between the sheet passing part and the non-sheet passing part, and the temperature difference generated during the sheet passing is equalized. For this reason, the detected temperature th2 of the sub-thermistor 81 is substantially the same as the detected temperature th1 of the main thermistor 8.

  Subsequently, when the fourth sheet is introduced into the fixing device, the detected temperature th1 of the main thermistor 8 is raised to the fixing temperature T during sheet passing. During the fourth sheet passing, the detected temperature th1 of the main thermistor 8 is temperature-controlled at the fixing temperature T during the sheet passing, while the detected temperature th2 of the sub-thermistor 81 continues to rise. However, the detection temperature th2 of the sub thermistor is lowered between the third and fourth sheets, and the temperature rise of the non-sheet passing portion is mitigated, so that the detection of the sub thermistor 81 is performed during the fourth sheet passing. Although the temperature th2 rises, it can be seen that there is a sufficient margin up to the allowable temperature Td.

As described above, by using the fixing device according to this example , when the long narrow paper is passed, the excessive temperature rise of the non-sheet passing portion, which has conventionally occurred, is prevented, and the fixing device is prevented from being broken. I knew it was possible.

Next, the amount of decrease from the control temperature T to T1 will be described. As in this embodiment, lower control temperature during the sheet passing, the amount of heat that can be imparted to the recording material is reduced, the solid deposition degree of the toner to the recording medium (hereinafter, fixability) decreases. On the other hand, as described above, unless the control temperature is lowered, the temperature of the non-sheet passing portion exceeds the allowable temperature. Table 1 shows the relationship between the temperature of T1 and the fixing temperature after switching the control temperature to T1 in this example , and the temperature reached by the detection temperature th2 of the sub-thermistor 81.

  Here, the fixability shown in Table 1 was determined according to the following criteria. The printed character pattern is lightly rubbed 5 times with the index finger and the middle finger through Sylbon paper. When the character pattern after rubbing could be read, it was determined to be OK, and when it could not be read, it was determined to be NG.

As can be seen from Table 1, when T1 is 205 ° C., that is, when the control temperature is lowered by 5 deg, the fixing property can be secured, but the detection temperature th2 of the sub-thermistor 81 in the non-sheet passing portion exceeds the allowable temperature Td. I understand that. When T1 is 195 ° C., that is, when the control temperature is reduced by 15 deg, the detection temperature th2 of the sub-thermistor 81 in the non-sheet passing portion can be suppressed to the allowable temperature Td or less, but sufficient fixability is obtained. It turns out that it cannot be obtained. Further, it can be seen that by setting T1 to 200 ° C., the detection temperature th2 of the sub-thermistor 81 in the non-sheet passing portion can be suppressed to the allowable temperature Td or less while ensuring sufficient fixing property. That is, it can be seen that by setting T1 to 200 ° C., it is possible to prevent good fixing properties and excessive temperature rise in the non-sheet passing portion. Therefore, in this example , the temperature of T1 was set to 200 ° C.

As described above, by using the control method of this example , when long narrow paper is passed, excessive temperature rise of the non-sheet passing portion and thereby failure of the fixing device are prevented, and the recording material is excellent. It was found that it was possible to achieve both securing of fixing property.
[Example 1]

An embodiment of an image forming apparatus according to the present invention will be described. In the first embodiment , since the schematic configurations of the image forming apparatus and the fixing device are exactly the same as those of the first reference example , the description thereof will be omitted.

Hereinafter, the control method of the present embodiment will be described. Here, as in Reference Example 1 , a series of operations of the fixing device when the operation is started from room temperature will be described with reference to the control flow block diagram of FIG. This control operation is executed by the CPU 24 which is a control unit. The process speed and the paper interval were the same as in Reference Example 1, and were set to 200 mm / sec and 0.3 seconds, respectively.

When a print command is input to the apparatus (8A), first, energization of the resistance heating element 6 is started, and temperature control is performed so that the detected temperature th1 of the main thermistor 8 becomes the fixing temperature T (8B). At a predetermined timing, the recording material 206 is introduced into the fixing device 209 (8C). While the recording material passes through the fixing device (paper passing), the main thermistor 8 is continuously controlled in temperature so that the detected temperature th1 becomes the fixing temperature T. While the recording material is being fed, the detected temperature th2 of the sub-thermistor 81 is monitored. If this temperature exceeds the switching temperature T2 (8D), the interval of introduction (feeding) of the next recording material to the fixing device is set. Open and set the setting to lower the throughput (8E). In this embodiment, as in the reference example , regardless of the type of recording material, this paper feed interval is set to 30 seconds, and once this setting is set, a series of printing operations are completed (8J described later). To do. Up to this point, the control method is exactly the same as that of the reference example 1 . Further, when the detected temperature th2 (first reference temperature) of the sub-thermistor 81 exceeds the threshold temperature T3 (second reference temperature) (8F), the detected temperature th2 of the sub-thermistor 81 during the recording material passing is determined. The rising speed (the rising speed of the detected temperature until the detected temperature of the second temperature detecting element reaches the second reference temperature) is calculated, and the control target temperature of the main thermistor 8 in the recording material passing according to this rising speed Is switched from T to T1 (8G). In this embodiment, the rising speed of the detection temperature th2 of the sub-thermistor 81 is determined based on the detection temperature th2a of the sub-thermistor 81 when the leading end of the recording material enters the fixing device, and the sub-thermistor after the leading end of the recording material enters the fixing device. Assuming that time until the detected temperature th2 of 81 reaches T3 is τ,
th2 rising speed = (T3−th2a) ÷ τ [deg / sec]
The calculation formula represented by is used.

  Table 2 shows the relationship between the rising speed of the detection temperature th2 of the sub-thermistor 81 and T1 in this embodiment. When the ascending rate is less than 10 deg / sec, the control temperature T1 after switching is set to 205 ° C., and when it is 10 deg / sec or more, it is set to 200 ° C. If the recording material has been passed and a print command for the next recording material has been input, this operation is repeated (8G), and if not, a series of operations are terminated (8H). Note that the temperature control is performed so that the detected temperature th1 of the main thermistor 8 becomes T0 different from T during the interval between sheets (between sheets).

  In this embodiment, the fixing temperature T at the time of paper passing is 210 ° C., the switching temperature T 2 is 260 ° C., the threshold temperature T 3 is 280 ° C., and the control temperature T 0 between papers is 175 ° C.

  Below, the effect of a present Example is described. First, long narrow paper (hereinafter referred to as normal / long narrow paper) composed of plain paper with a smooth surface and long narrow paper (hereinafter referred to as rough / long narrow paper) composed of bond paper with irregularities on the surface are not fixed. The temperature rise of the paper passing section will be described.

  Table 3 summarizes the relative relationship between the fixability, power consumption, and non-sheet passing temperature rise of normal / long narrow paper and rough / long narrow paper. Normal long narrow paper has a smooth surface, so when it passes through the fixing nip, it efficiently removes heat from the fixing film and pressure roller, so it has good fixability and consumes a lot of power. . The power consumed is large because it is located in the paper passing area and the temperature of the main thermistor 8 used for energization control to the resistance heating element tends to decrease, and the amount of energization to the resistance heating element 6 is increased to compensate for this It is. Further, when the power consumption is large, the temperature rise rate at the non-sheet passing portion is large. On the other hand, rough and long narrow paper has irregularities on its surface, so that the contact area between the fixing film 2 and the pressure roller 4 is small, and heat cannot be efficiently taken when passing through the fixing nip N. . For this reason, compared with normal long narrow paper, fixing property is bad and power consumption is also small. For this reason, the temperature rise rate of the non-sheet passing portion is smaller than that of normal / long narrow paper.

Actually, when the temperature rise rate of the non-sheet passing part of the normal long long narrow paper and the rough long narrow paper with a width of 105 mm and the length of 355 mm was measured, the long narrow paper with a basis weight of 120 g / m ² Rough and long narrow paper having a basis weight of 14 deg / sec and a basis weight of 105 g / m ² was 8 deg / sec.

  Based on the above, it is possible to determine whether the long narrow paper to be passed is normal / long narrow paper or rough / long narrow paper by evaluating the speed of temperature rise in the non-sheet passing portion. I knew it was possible.

  As described above, rough / long narrow paper has poor fixability compared to normal / long narrow paper, so that fixing failure occurs if the control temperature during paper passing is too low.

  Table 4 shows the relationship between the value of T1 and the fixability and the temperature reached by the detection temperature th2 of the sub-thermistor 81 when the above-mentioned rough / long narrow paper is passed.

From Table 4, it can be seen that when the T1 is set to 200 ° C. with respect to the rough long narrow paper, the fixing property cannot be sufficiently secured. In addition, when T1 is set to 210 ° C., that is, when the temperature is not lowered, it can be seen that the temperature th2 of the non-sheet passing portion exceeds the allowable temperature Td. Then, it can be seen that by setting T1 to 205 ° C., it is possible to prevent good fixability and excessive temperature rise in the non-sheet passing portion.

  Therefore, it can be understood that the optimum temperature as the control temperature after switching is 205 ° C. for rough / long narrow paper.

Regarding the normal long narrow sheet is exactly the same as in Reference Example 1, as described in Reference Example 1, the optimum temperature as the control temperature after switching is 200 ° C..

  As described above, when the detection temperature th2 of the sub-thermistor 81 exceeds the threshold temperature T3 as in the present embodiment, the temperature rise rate of the non-sheet passing portion in the recording material passing is calculated and the paper is passed. By predicting whether long-narrow paper is normal / long-narrow paper or rough / long-narrow paper, it becomes possible to select the optimum switching temperature for each.

Therefore, by using the control method of the present embodiment, it was possible to ensure good fixability while maintaining the safety of the fixing device for more types of long narrow paper.
[Reference Example 2]

Reference Example 2 will be described. In this example, since the schematic configurations of the image forming apparatus and the fixing device are exactly the same as those in the above-described Reference Example 1 and Example 1, the description thereof will be omitted.

Hereinafter, the control method of this example will be described. Here, as in Reference Example 1 and Example 1 , a series of operations of the fixing device when the operation is started from room temperature will be described with reference to the control flow block diagram of FIG. This control operation is executed by the CPU 24 which is a control unit. The process speed and the paper interval were the same as those in Reference Example 1 and Example 1, and were set to 200 mm / sec and 0.3 seconds, respectively.

When a print command is input to the apparatus (10A), first, energization of the resistance heating element 6 is started, and temperature control is performed so that the detected temperature th1 of the main thermistor 8 becomes the fixing temperature T (10B). At a predetermined timing, the recording material 206 is introduced into the fixing device 209 (10C). While the recording material passes (passes through) the fixing device, the temperature control of the main thermistor 8 is continued so that the detected temperature th1 becomes T. While the recording material is being fed, the detection temperature th2 of the sub-thermistor 81 is monitored. If this temperature exceeds the switching temperature T2 (10D), the interval of introduction (feeding) of the next recording material to the fixing device is set. Open and set the setting to lower the throughput (10E). In this example as well, as in Reference Example 1 and Example 1 , regardless of the type of recording material, this paper feed interval is set to 30 seconds, and once this setting is set, a series of printing operations ends (described later). 10J).

In this example , when the detected temperature th2 of the sub-thermistor 81 exceeds the threshold temperature T3 (10F), the control target temperature of the main thermistor 8 during the recording material passing is switched from T to T1, and the recording material The conveyance speed (process speed) is reduced to 150 mm / sec (10 G). Monitoring of the detection temperature th2 of the sub-thermistor 81 is repeated until the recording material is finished passing (10H). When the recording material is passed, if the print command for the next recording material has been input, the process speed is returned to the original 200 mm / sec and this operation is repeated from 10B (10I). The operation is terminated (10J). It should be noted that the temperature control is performed so that the detected temperature th1 of the main thermistor 8 becomes T0 different from T between the paper passes (paper interval), and the recording material conveyance speed is returned to 200 m / sec.

The effects of this example are described below. First, the relationship between the recording material conveyance speed (process speed) and the fixing temperature will be described. In general, in order to obtain sufficient fixability, it is necessary to increase the fixing temperature as the process speed increases. This is because as the process speed increases, the time for the recording material to pass through the fixing nip N is shortened, and it becomes necessary to supply a larger amount of heat instantaneously from the heating element 3 to the recording material 206. Conversely, if the process speed is slowed down, sufficient fixability can be obtained without increasing the fixing temperature.

In this example , when the detection temperature th2 of the sub thermistor 81 exceeds the threshold temperature T3, the process speed is lowered. For this reason, after the process speed is lowered, sufficient fixability can be secured at a lower fixing temperature as compared with the case where the process speed is not lowered. In addition, the temperature of the non-sheet passing portion can be made lower than when the fixing temperature is high.

Table 5 shows the relationship between the temperature of T1 and the fixability and the temperature reached by the detection temperature th2 of the sub-thermistor 81 in this example . In Table 5, “normal” and “rough” represent the normal long narrow paper and the rough long narrow paper described in Example 1 , respectively.

From 1) and 2) of Table 5, in this example , regardless of the type of long narrow paper, the detection temperature th2 of the sub-thermistor 81 is suppressed to the allowable temperature Td or lower by setting T1 to 195 ° C. and good It can be seen that excellent fixing properties can be obtained. 3) and 4) in Table 5 are extracted from Table 1 described in Reference Example 1 . Comparing 1) and 3) and 4) in Table 5, in this example , good fixability can be obtained at 195 ° C. for normal long narrow paper, whereas in Reference Example 1 , 200 ° C. is required. It can be seen that T1 can be lowered by 5 degrees by using this example . Table 5-5) is extracted from Table 4 shown in Example 1 . By comparing 2) and 5) in Table 5, it can be seen that in this example , good fixability can be obtained at a lower fixing temperature even for rough and long narrow paper. As described above, by using this example , T1 can be set to a lower temperature, and by setting only one type, the sub-thermistor 81 can be stably detected for more types of long narrow paper. It has been found that the temperature th2 can be suppressed to Td or lower, and good fixability can be obtained.

As in this example , when the detected temperature th2 of the sub-thermistor 81 exceeds the threshold temperature T3, the control temperature is changed and the control speed after the change is lowered by lowering the recording material conveyance speed. Can be. In addition, by providing only one type of T1, it is possible to secure a good fixing property while suppressing the temperature rise of the non-sheet passing portion and ensuring the safety of the apparatus for a larger number of types of long narrow paper. I was able to.

2 is a schematic cross-sectional view of an example of an image forming apparatus in Reference Example 1. FIG. 2 is a schematic cross-sectional view of a fixing device (heating device) in Reference Example 1. FIG. 5 is a configuration explanatory diagram of a heating body in Reference Example 1. FIG. 6 is a block diagram illustrating a fixing device control method in Reference Example 1. FIG. FIG. 6 is a diagram illustrating a change over time in detected temperatures of a main thermistor and a sub-thermistor of a fixing device in Reference Example 1 . FIG. 3 is a block diagram illustrating a control method of the fixing device according to the first exemplary embodiment . 10 is a block diagram illustrating a fixing device control method in Reference Example 2. FIG. It is a figure showing the paper width detection sensor which concerns on a prior art example. It is a component arrangement | positioning figure of the longitudinal direction of the fixing apparatus of the film heating system which concerns on a prior art example.

  DESCRIPTION OF SYMBOLS 1 ... Film guide, 2 ... Fixing film, 4 ... Pressure roller, N ... Fixing nip part, 8 ... Main thermistor (first temperature sensing element), 81 ... Sub thermistor (second temperature sensing element) ), 206 ... Recording material, th1 ... Detection temperature of the main thermistor 8, th2 ... Detection temperature of the sub-thermistor 81

Claims (1)

An image forming unit for forming a toner image on a recording material;
An endless fixing film; a heater in contact with the inner surface of the fixing film; a pressure roller that forms a fixing nip portion with the heater via the fixing film; and a minimum sheet passing width region through which a recording material of a minimum size passes. The first temperature detecting element for detecting the temperature of the heater, the second temperature detecting element for detecting the temperature of the heater in the area outside the minimum sheet passing width area, and the detected temperature of the first temperature detecting element during the fixing process are control targets. A control unit that controls electric power supplied to the heater so as to maintain the temperature, and a fixing unit that fixes the recording material carrying the toner image at the fixing nip unit;
When the plurality of recording materials are continuously fixed at the fixing nip portion with the control target temperature set to the first control target temperature, the detected temperature of the second temperature detecting element is the first reference temperature. When the temperature is exceeded, the interval until the recording material next to the current recording material passing through the fixing nip portion enters the fixing nip portion is increased more than before, and the temperature detected by the second temperature detecting element is increased. When the temperature exceeds a second reference temperature higher than the first reference temperature, the control target temperature for fixing the current recording material passing through the fixing nip portion is changed from the first control target temperature to the second control temperature. In the image forming apparatus for lowering to the control target temperature,
2. The image forming apparatus according to claim 1, wherein the second control target temperature is set according to a rising speed of the detected temperature until the detected temperature of the second temperature detecting element reaches the second reference temperature.