JP2023122238A - Image heating device and image forming apparatus - Google Patents

Abstract

To provide a technique that can ensure safety and shorten FPOT with a small and inexpensive constitution.SOLUTION: In an image heating device, a control portion has a first semiconductor element connected to a first heating element group and a second semiconductor element connected to a second heating element group and connected to the first semiconductor element in series, controls power to be supplied to the first heating element group by controlling the first semiconductor element, and controls power to be supplied to the second heating element group by controlling the first semiconductor element and the second semiconductor element. The control portion has a safety element that can perform the operation for cutting off the supply of power to the first heating element group in response to the overheating of the heating elements included in the first heating element group. The maximum amount of heat generation per unit length in a width direction of the second heating element group is larger than the maximum amount of heat generation per unit length in a width direction of the first heating element group.SELECTED DRAWING: Figure 1

Description

The present invention relates to an image forming apparatus such as a printer and a copier using electrophotography. The present invention also relates to an image heating device such as a gloss imparting device that improves glossiness of a toner image by reheating a toner image fixed on a fixing device or recording material mounted in an image forming apparatus.

2. Description of the Related Art As disclosed in Japanese Patent Laid-Open No. 2002-100000, a conventional fixing device is known that independently drives heating elements that are divided in the longitudinal direction of a heater. In such a fixing device, the heat generating elements are divided into three groups in the longitudinal direction of the heater, corresponding to the size of the recording material, into central heat generating elements, intermediate heat generating elements, and end heat generating elements. , each triac is independently connected. In such a fixing device, a safety element such as a thermoswitch may be arranged in each heat generating element group as an example of a safety measure in the event that the triac fails and the heat generating elements cannot be de-energized by the triac. Conceivable. However, in this case, safety elements are required for the number of heat generating element groups that are independently driven, so there is a concern that the price will be high and the installation space will be required, resulting in an increase in the size of the fixing device.

Further, in the fixing device disclosed in Japanese Patent Application Laid-Open No. 2002-200010, as a safety measure in the case where the triac fails and the power supply to the heat generating element cannot be released by the triac, the print thermistor is connected to the independently driven heat generating element. are placed. Even if one of these two thermistors fails, the remaining one thermistor detects an abnormally high temperature of the heating element caused by the failure of the triac, and turns off the relay to stop power supply. In this fixing device, two printed thermistors are arranged for each heating element as a safety measure. becomes larger. For this reason, the heat generating elements at the longitudinal ends are not driven independently, but are connected in tandem with adjacent heat generating elements, and only one printed thermistor is arranged for the heat generating elements at the longitudinal ends. Therefore, the number of thermistors is reduced, and the thermistor wiring is reduced.

JP 2019-207337 A JP 2018-194682 A

When two triacs are cascade-connected as in Patent Document 2, the following problems occur. That is, the triac A on the upstream side can control the conducting state by applying a trigger current to the gate terminal. On the other hand, no current flows through the triac B on the downstream side even if a trigger current is applied to the gate terminal of the triac B when the triac A on the upstream side is in an OFF state. When the TRIAC A is in the energization ON state, the energization of the TRIAC B can be controlled by applying a trigger current to the gate terminal of the TRIAC B. FIG. In other words, the energization state of the triac B is not determined by the triac B alone, but is affected by the energization state of the triac A.

Therefore, the heat generating element that is subordinately driven by the triac A and the triac B is not energized even if the triac B on the subordinate side is controlled to be energized while the upstream triac A is controlled to be energized OFF. For this reason, the energization ON period of the subordinately driven heating element cannot be increased beyond the energization ON period of the triac A on the upstream side.
It was difficult to increase the calorific value by increasing the period. The temperature gradient at the start-up of the fixing device tends to be lower at the ends of the heater than at the center of the heater due to the influence of heat radiation from the ends. On the other hand, it is difficult to increase the amount of heat generated at the ends of the heater and make the temperature gradient the same as that at the center of the heater. It was difficult.

In addition, since two printed thermistors are arranged as a safety measure for each of the independently driven heating elements, the number of wires for the thermistors increases, and there is a limit to reducing the width of the heater substrate.

SUMMARY OF THE INVENTION An object of the present invention is to provide a technique capable of ensuring safety and shortening FPOT with a compact and inexpensive configuration.

In order to achieve the above object, the image heating apparatus of the present invention comprises:
a heater having a plurality of heating elements arranged in a width direction of the recording material perpendicular to the conveying direction of the recording material;
a control unit that controls power supplied to the plurality of heating elements;
with
An image heating device for heating an image formed on a recording material by heat of the heater,
The plurality of heating elements are
a first heating element group;
a second heating element group arranged at a different position in the width direction with respect to the first heating element group;
including
The control unit
a first semiconductor element connected to the first heating element group;
a second semiconductor element connected to the second heating element group and connected in series to the first semiconductor element;
has
controlling power supplied to the first heating element group by controlling the first semiconductor element;
In an image heating apparatus that controls power supplied to the second heating element group by controlling the first semiconductor element and the second semiconductor element,
the control unit has a safety element operable to cut off power supply to the first heating element group in response to overheating of the heating elements included in the first heating element group;
A maximum possible heat generation amount per unit length in the width direction of the second heat generating element group is larger than a maximum possible heat generation amount per unit length in the width direction of the first heat generating element group. do.
In order to achieve the above object, the image forming apparatus of the present invention includes:
an image forming unit that forms an image on a recording material;
a fixing unit that fixes the image formed on the recording material to the recording material;
In an image forming apparatus having
The fixing section is the image heating device of the present invention.

According to the present invention, it is possible to secure safety and shorten FPOT with a compact and inexpensive configuration.

Schematic configuration diagram of a heater and a control circuit in Embodiment 1 of the present invention Schematic diagram of an image forming apparatus in Embodiment 1 Schematic cross-sectional view of a fixing device in Embodiment 1 Apparatus start-up temperature profile in pre-printing rotation of Comparative Example and Example 1 Schematic configuration diagram of a heater and a control circuit in Embodiment 2 of the present invention Schematic diagram of an equivalent circuit of the 7-part resistance heating element of the heater in Example 1 Schematic diagram of an equivalent circuit of the 7-part resistance heating element of the heater in Example 2 Operational diagram of triac Operational diagram of triac Diagram of operation when triacs are connected in series Diagram of operation when triacs are connected in series Table comparing the heater according to Example 1 and the heater according to the comparative example

BEST MODE FOR CARRYING OUT THE INVENTION A mode for carrying out the present invention will be exemplarily described in detail below based on an embodiment with reference to the drawings. It should be noted that the dimensions, materials, shapes, and relative arrangement of the components described in this embodiment should be appropriately changed according to the configuration of the device to which the invention is applied and various conditions. That is, it is not intended to limit the scope of the present invention to the following embodiments.

(Example 1)
1. Configuration of Image Forming Apparatus FIG. 2 is a schematic cross-sectional view of an image forming apparatus 100 according to an embodiment of the present invention using electrophotographic recording technology. Examples of image forming apparatuses to which the present invention can be applied include copiers and printers using an electrophotographic method or an electrostatic recording method. More specifically, image forming apparatuses include copiers, laser beam printers (LBP), microfilm reader printers, recorders, and the like. Examples of the recording material include paper, printing paper, recording material sheet, electrofax sheet, electrostatic recording sheet, OHT sheet, glossy paper, glossy film, and the like. First, by means of an image forming process such as electrophotography, electrostatic recording, or magnetic recording, the desired image information is transferred onto the recording surface of the recording material by a direct transfer method or an indirect transfer method using a toner made of heat-meltable resin or the like. An unfixed toner image corresponding to is formed and carried. Then, as a fixing process, the unfixed toner image is heat-fixed as a permanently fixed image on the surface of the recording material carrying the image. Here, a case will be described in which the electrophotographic method is applied to a laser beam printer that forms an image on a recording material P such as recording paper.

When a print signal is generated, the scanner unit 21 emits a laser beam modulated according to image information to scan the surface of a photosensitive drum (electrophotographic photosensitive member) 19 charged to a predetermined polarity by the charging roller 16 . As a result, an electrostatic latent image is formed on the photosensitive drum 19 as an image carrier. The electrostatic latent image on the photosensitive drum 19 is developed as a toner image (developer image) by supplying toner charged to a predetermined polarity from the developing roller 17 to the electrostatic latent image. On the other hand, a recording material (recording paper) P stacked in a paper feed cassette 11 is fed one by one by a pickup roller 12 and conveyed toward a registration roller pair 14 by a conveying roller pair 13 . Further, the recording material P is conveyed from the registration roller pair 14 to the transfer position in synchronization with the timing when the toner image on the photosensitive drum 19 reaches the transfer position formed by the photosensitive drum 19 and the transfer roller 20 as a transfer member. be. The toner image on the photosensitive drum 19 is transferred to the recording material P while the recording material P passes the transfer position. The apparatus configuration responsible for the process up to the formation of the unfixed toner image on the recording material P corresponds to the image forming section of the present invention.

After that, the recording material P is heated using the heat of a heater in a fixing device (image heating device) 200 as a fixing section (image heating section), and the toner image is fixed on the recording material P by heating. The recording material P carrying the fixed toner image is discharged to the paper discharge tray 31 above the image forming apparatus 100 by the pair of conveying rollers 26 and 27 .

The photoreceptor 19 is cleaned by removing residual toner and the like from the surface thereof by a cleaner 18 . The paper feed tray (manual feed tray) 28 has a pair of recording paper regulating plates whose width can be adjusted according to the size of the recording paper P, and is provided to handle recording paper P of sizes other than the standard size. It is The pickup roller 29 is a roller for feeding the recording paper P from the paper feed tray 28 . The motor 30 drives the fixing device 200 and the like. Power is supplied to the fixing device 200 from a control circuit 400 as an energization control unit connected to a commercial AC power supply 401 .

In this embodiment, the developing unit including the photosensitive drum 19, the charging roller 16 and the developing roller 17, and the cleaning unit including the drum cleaner 18 are detachably attached to the main body of the image forming apparatus 100 as the process cartridge 15. It is The image forming apparatus 100 of the present embodiment has a maximum paper passing width of about 300 mm in the direction perpendicular to the conveying direction of the recording material P, and passes A4 horizontal size plain paper [width 297 mm x length 210 mm] at a speed of about 160 mm/sec. It is possible to print about 37 sheets per minute at the transport speed.

2. Configuration of Image Heating Device FIG. 3 is a sectional view of the fixing device 200 of this embodiment. The fixing device 200 includes a fixing film (hereinafter referred to as film) 202 , a heater 300 that contacts the inner surface of the film 202 , a pressure roller 208 that forms a fixing nip N together with the heater 300 via the film 202 , and a metal stay 204 . , has a heater holding member 201 .

The film 202, which is a fixing member, is a multi-layer highly heat-resistant film 202 formed in a tubular shape, which is also called an endless belt or an endless film, and has a base layer made of a heat-resistant resin such as polyimide or a metal such as stainless steel. . The surface of the film 202 has excellent heat resistance and is coated with a highly functional fluororesin such as PFA to prevent adhesion of toner. Further, particularly in an apparatus for forming color images, a highly heat-resistant rubber such as silicone rubber may be formed as an elastic layer between the base layer and the release layer in order to improve image quality.

The pressure roller 208 has a metal core 209 made of iron, aluminum, or the like, and an elastic layer 210 made of a highly heat-resistant rubber material such as silicone rubber. With such a configuration, the pressure roller 208 has an appropriate hardness, thereby obtaining a fixing nip N suitable for the fixing device 200 .

The heater 300 is held by a heater holding member 201 made of heat-resistant resin. A thermistor 212 is arranged on the rear surface of the heater 300 as a temperature detecting means for detecting the temperature of the heater 300 . The metal stay 204 receives pressure (not shown) and presses the heater holding member 201 toward the pressure roller 208 .

The control unit 400 drives the motor 30 in accordance with a print signal input from an external input device such as a PC. The pressure roller 208 receives a rotational driving force from the motor 30 and rotates in the direction of arrow R1. As the pressure roller 208 rotates, a rotational force acts on the film 202 due to the frictional force with the outer surface of the film 202, and the film 202 is driven to rotate in the direction of arrow R2.

The control unit 400 also energizes a triac (see FIG. 1), which is a semiconductor element provided as energization control means, to turn it on. As a result, the heating element of the heater 300 is energized from the power supply (see FIGS. 1 and 2), and the heater 300 generates heat. The control unit 400 takes in the output signal of the thermistor 212, controls the electric power supplied to the heater 300 by the trackac based on the output signal, and controls the temperature of the heater 300 to a predetermined temperature. heater 3
00 temperature is controlled to a predetermined temperature, and the rotational peripheral speed of the film 202 is stabilized at a predetermined speed by the rotation of the pressure roller 208, the recording material P on which the unfixed toner image is formed is moved to the fixing nip N. introduced into The recording material P is nipped and conveyed in the fixing nip N, and the unfixed toner image on the recording material P is fixed by heat from the heater 300 being applied through the film 202 .

3. 1. Heater and Control Circuit Used in Image Heating Apparatus FIG. 1 shows an example of a heater 300 and a control circuit in Embodiment 1 according to the present invention. The conveyance reference of the recording material in this embodiment is the center reference, and the recording material P is conveyed so that the center line in the width direction perpendicular to the conveyance direction is along the conveyance reference position X0.

The heater 300 has a conductor 301, a resistance heating element 302, and an electrode E on a substrate made of ceramic such as alumina or aluminum nitride or stainless steel SUS304. When a metal such as stainless steel SUS304 is used for the heater substrate, an insulating layer such as a glass coat layer is provided on the metal substrate for insulation, and then the conductor 301, the resistance heating element 302, and the electrode E are formed.

The conductor 301 is a conductor pattern as wiring for applying the voltage supplied from the electrode E to the resistance heating element, and is formed of a material such as silver paste that has a low resistance value and heat resistance. The resistance heating element 302 acts as a heating source by generating Joule heat by means of a current that flows due to voltage applied from the conductor 301, and is adjusted to a predetermined resistance value with silver, palladium, ruthenium oxide, or the like. .

In this embodiment, a plurality of resistance heating elements 302 are arranged in seven divisions in the longitudinal direction of the heater substrate (printing material width direction). The longitudinal width of the resistance heating elements 302c-1 and 302c-2 at the ends in the longitudinal direction is approximately 39 mm. On the other hand, the longitudinal width of the resistance heating elements 302a-1, 302a-2, 302a-3, 302b-1, and 302b-2 arranged on the inner longitudinal side is about 45 mm. The resistance heating elements are spaced about 4 mm apart in the longitudinal direction, but the pattern of the resistance heating elements has a slanting shape at the end so that the effect of uneven heat generation in the conveying direction of the recording material is less likely to occur. .

The resistance heating elements 302a-1, 302a-2, and 302a-3, which are used when small-size paper with a vertical feed width of A5 or less is fed, are grouped together into a first A heat generating block A is a heat generating element group. When paper of size from A5 longitudinal feed width to LTR longitudinal feed width is passed, in addition to the heating block A, the resistance heating elements 302b-1 and 302b-2 on both longitudinal sides of the heating block A are set to the second It is used as a heating block B which is a heating element group. When the LTR longitudinal feed to A3 width size paper is passed, the resistance heating elements 302c-1 and 302c-2 arranged adjacent to the heating block B on the side away from the conveyance reference position are further connected to the heating element block. Use as C.

Each resistance heating element has a pattern shape that reciprocates about two times in the longitudinal direction of the heater, and is energized from the short side direction (perpendicular to the longitudinal direction) of the heater by a conductor 301 . Rather than independently driving and controlling all of the resistance heating elements 302 divided into seven parts, the drive control is performed in block units (group units) in three heat generating blocks. This is because

The electrode E is provided for power supply to the resistance heating element. On the surface of the heater substrate on which the conductor 301, the resistance heating element 302, and the electrode E are mounted (the surface on which the film 202 slides), insulating protective glass (see FIG. 3) is applied to the area other than the electrode E. is provided to cover the The heater 300 is arranged so that its longitudinal direction is orthogonal to the conveying direction of the recording material P. As shown in FIG. The number of heating elements and the number of heating blocks are not limited to those shown in this embodiment.

A commercial AC power supply 401 is connected to the image forming apparatus 100 . The power supply voltage Vcc is DC power generated by an AC/DC converter (not shown) connected to the AC power supply 401 . AC power supply 401 is connected to heater 300 via relays 430 and 440 and triacs 441-443. The triacs 441 to 443 are turned on/off by control signals FUSER-a to FUSER-c from the CPU 420 . Driving circuits for the triacs 441 to 443 are omitted from the drawing. By selectively controlling the triacs 441 to 443 as a plurality of semiconductor elements, it is possible to selectively control the energization of the plurality of resistance heating elements for each heating block, and to form a plurality of heating regions divided in the longitudinal direction. The blocks can be selectively heated individually.

The operation of relay 430 will be described. When the CPU 420 sets the RLON signal to a high state, the transistor 434 is turned on, the secondary coil of the relay 430 is energized from the power supply voltage Vcc, and the primary contact of the relay 430 is turned on. When the RLON signal goes low, the transistor 434 is turned off, the current flowing from the power supply voltage Vcc to the secondary coil of the relay 430 is cut off, and the primary contact of the relay 430 is turned off. A resistor 434 is a resistor that limits the base current of the transistor 433 .

In the internal processing of the CPU 420, the electric power to be supplied is calculated by PI control, for example, based on the set temperature and the temperature detected by the thermistor as temperature detection means. A plurality of thermistors are provided at positions corresponding to the heat generating blocks so as to individually detect the temperature of each heat generating block. The ON timing of the FUSER-a to c signals is generated by the CPU 420 based on the timing signal ZEROX synchronized with the zero potential of the AC power supply 401 generated by the zero-cross detector 421 . Based on the zero cross timing of the AC power supply 401, the phase angle (phase control) and the wave number (wave number control) corresponding to the power to be supplied are converted into control levels, and the triacs 441 to 443 are controlled according to the control conditions.

The relays 430, 440 and protection circuits will be described. The relays 430 and 440 are used as means for cutting off power to the heater 300 when the temperature of the heater 300 rises excessively due to failure or the like. In this embodiment, the relays 430 and 440 are used as a two-way relay.

The operation of relay 430 will be described. When the CPU 420 sets the RLON signal to a high state, the transistor 433 is turned on, the secondary coil of the relay 430 is energized from the power supply voltage Vcc, and the primary contact of the relay 430 is turned on. When the RLON signal is brought to the Low state, the transistor 433 is turned off, the current flowing from the power supply voltage Vcc to the secondary coil of the relay 430 is interrupted, and the primary contact of the relay 430 is turned off. Since the relays 430 and 440 are both switching relays, the relay 440 is also turned ON/OFF in conjunction with the ON/OFF operation of the relay 430 .

The operation of the safety circuit using relays 430 and 440 will be described. When the detected temperature of the thermistor Th exceeds a set predetermined value, the comparison section 437 operates the latch section 436, and the latch section 436 latches the RLOFF signal in the Low state. When the RLOFF signal becomes Low, even if the CPU 420 changes the RLON signal to High, the transistor 433 is kept OFF, so the relay 430 can be kept OFF (safe state). In this manner, the relays 430 and 440 are also used as means for cutting off power to the heater 300 when the temperature of the heater 300 is excessively increased due to failure or the like.

The operation of the triac will be briefly described with reference to FIGS. 8 and 9. FIG. FIG. 8 is a circuit diagram simply showing the energization control of the heating element by the TRIAC, and FIG. 9 shows the relationship between the AC voltage applied from the AC power supply to the TRIAC and the voltage applied to the heating element by the TRIAC. FIG. 4 is a diagram showing;

As shown in Fig. 8, a triac has a configuration in which two complementary thyristors are connected in anti-parallel, making it possible to pass current in both directions, making it possible to use not only direct current but also alternating current. It is. When a positive voltage is applied to the main electrode T2 of the TRIAC from an AC power supply, the TRIAC is in an operation OFF state until a trigger current is applied to the gate electrode G. Therefore, no current flows between T2 and T1, and no current flows through the load (resistive heating element) connected to the triac. When a trigger current is applied to the gate electrode G of the TRIAC, the TRIAC is turned on and a current flows between T2 and T1, so that a current also flows through the load and the resistance heating element generates heat.

As shown in FIG. 9, when 1/2 cycle of the AC power supply is completed, the voltage applied to the triac main electrode T2 is reversed to become a negative voltage. Therefore, the triac is in an operation OFF state, no current flows between T2 and T1, and no current flows through the load (resistive heating element). When a trigger current is applied to the gate electrode G of the triac, the triac is turned on again, current flows between T1 and T2, current also flows through the load (resistive heating element), and the resistive heating element generates heat.

With reference to FIGS. 10 and 11, the operation of the triac when two triacs are connected in series and a load (resistive heating element) is connected to each triac will be described. FIG. 10 is a circuit diagram simply showing the energization control of two heating elements by two cascaded triacs, and FIG. FIG. 10 is a diagram showing the relationship between the applied voltage and the applied voltage;

As shown in FIG. 10, even if a positive voltage is applied to the terminal T2 of the TRIAC A from the AC power supply, the TRIAC A is in the conduction OFF state until the trigger current is applied to the gate terminal G of the TRIAC A. No current flows between terminals T2-T1 of A. Since no current flows through the load A (resistance heating element A) connected to the triac A, the resistance heating element A does not generate heat during this period.

During this period, even if a trigger current is supplied to the gate terminal G of the triac B connected in series with the triac A, since the upstream triac A is in the OFF state, the terminal T2 of the downstream triac B has No voltage is applied. Therefore, no current flows from the terminals T2 to T1 of the triac B, and no current flows through the load B (resistive heating element B) connected to the triac B, so the resistive heating element B does not generate heat.

Next, when a trigger current is applied to the gate terminal G of the triac A, the triac A is turned ON, and current flows from the terminals T2 to T1 of the triac A. Therefore, the load A connected to the triac A also A current flows and the resistance heating element A generates heat. In addition, since the triac A on the upstream side is turned ON, a positive voltage is applied to the terminal T2 of the triac B on the downstream side. B is in the energization OFF state. Therefore, no current flows through the load B connected to the triac B, and the resistance heating element B does not generate heat.

When a trigger current is applied to the gate terminal G of the triac B while the triac A is in the energized ON state, the triac B is also energized in addition to the triac A, and current flows through the load B connected to the triac B, causing the resistance heating element B to flow. heats up.

As shown in FIG. 11, when the AC 1/2 cycle of the AC power supply is completed and a negative voltage is applied to the terminal T2 of the triac A, the triac A is turned off. In this state, no current flows through the triac A regardless of the energized state of the triac B, so no current flows through the loads A and B, and the resistance heating elements A and B do not generate heat.

When a trigger current is applied to the gate terminal G of the triac A, the triac A is turned on. In this state, until the trigger current is applied to the gate terminal G of the TRIAC B and the TRIAC B is turned ON, the TRIAC B is in the energization OFF state. When a trigger current is applied to the gate terminal G of the triac B, the triac B is turned ON, so that a current also flows through the load B and the resistance heating element B generates heat.

When the triacs are connected in cascade in this way, the triac A on the upstream side can control the conduction state by applying a trigger current to the gate terminal G. FIG. On the other hand, in the triac B on the downstream side, current does not flow through the triac B even if the trigger current is applied to the gate terminal G of the triac B when the triac A on the upstream side is in the OFF state. When the TRIAC A is in the energization ON state, the energization of the TRIAC B can be controlled by applying a trigger current to the gate terminal G of the TRIAC B. FIG. In other words, the energization state of the triac B is not determined by the triac B alone, but is affected by the energization state of the triac A.

Referring to FIG. 1, the driving configuration by triacs 441 to 443 in this embodiment will be described. Triacs 441 to 443 are connected to the three heating blocks A, B, and C, respectively. A triac 442 connected to an adjacent heat generating block B is cascade-connected to the triac 441 that drives the heat generating block A. As shown in FIG. The triac 443 connected to the heating block C is further subordinately connected to the triac 442 .

The heating block A and the triac 441 are the most upstream heating block (heating element) and the most upstream triac. When viewed from the triac 442, the triac 441 is the triac on the upstream side. When viewed from the heat generating block B connected to the triac 442, the heat generating block A connected to the upstream triac 441 is the upstream heat generating block (heat generating element). Conversely, when viewed from the heat generating block A, the heat generating block B is on the dependent side.

Similarly, when viewed from triac 443, triac 441 and triac 442 are upstream triacs. When viewed from the heat generating block C connected to the triac 443, the heat generating blocks A and B connected to the upstream triacs 441 and 442 are upstream heat generating blocks (heat generating elements). When viewed from the heat generating block B, the heat generating block C connected to the triac 443 is the subordinate side.

With this connection configuration, the most upstream heating block A is driven and controlled only by the most upstream triac 441 . The heating block B is driven and controlled by a triac 441 connected to the heating block B and an upstream triac 442 . The heat generating block C is driven and controlled by the triac 443 connected to the heat generating block C and the upstream triacs 441 and 442 .

A description will be given of whether or not the heating block C is in a state of being energized (a so-called runaway state). Even if the triac 443 connected to the heat generating block C fails and remains energized, the heat generating block C is not energized unless both the upstream triacs 441 and 442 are energized. If the normal triac 441 controls the drive of the heat generating block A and the normal triacs 441 and 442 controls the drive of the heat generating block B, the heat generating block C will not run out of control.

The heat generating block C goes into a runaway state when all of the triacs 441 to 443 fail and the power is turned on. In this case, the power supply is turned off by safety measures such as activating safety elements (thermo switch, thermostat, thermal fuse, etc.) arranged in the heating block A in response to overheating.

Similarly, even if the TRIAC 442 connected to the heat generating block B fails and remains ON, the heat generating block B will not run out of control if the TRIAC 441 on the upstream side is normal.

As described above, if the triac 441 on the upstream side is normal, the heat generating blocks B and C will not go into a runaway state even if the triacs 442 and 443 on the sub-connection side are faulty and remain ON. Therefore, in the heating blocks B and C, there is no need to provide a safety element (thermo switch, thermostat, thermal fuse, etc.) or a safety circuit with a plurality of temperature detection means as a safety measure against runaway.

As for the heat generating block A, only the triac 441 is driven and controlled. Therefore, if the triac 441 fails and the power remains ON, the heat generating block A is turned ON and falls into a runaway state. It will be. Therefore, safety measures against runaway cannot be eliminated in the heating block A section.

In this embodiment, a thermoswitch 213 is arranged as a safety element in the heating block A portion. Safety measures against runaway of the heating block A will be described below. Examples of the cases where the heating block A runs out of control include the following two cases.

In the first case, the triac 441 that drives and controls the heat generating block A fails or the CPU 420 that controls the triac 441 malfunctions, leaving the heat generating block A energized (runaway state). In this case, the comparator 437 compares the output of the thermistor 212 (see FIG. 3) as a temperature detecting means for detecting the temperature of the heat generating block A to see if it is at a predetermined high temperature, and the latch 436 is operated. , the RLOFF signal is set to the Low state and latched. When the RLOFF signal becomes Low, even if the CPU 420 changes the RLON signal to High, the transistor 433 is kept OFF. Power is interrupted.

In the second case, in addition to the conditions in the first case, the temperature detection means for detecting the temperature of the heat generating block A has a disconnection failure, and the comparator 437 operates the latch to turn off the relay. It is not possible. In this case, the safety element (thermo switch, thermal fuse) 213 provided in the heat generating block A section reacts to the high temperature caused by the runaway of the heat generating block A, and cuts off the power supply to the heater 300 .

In this manner, multiple safety measures are provided against runaway of the heat generating block A. FIG.

The ON timing of the triac is generated by the CPU 420 based on the timing signal ZEROX synchronized with the zero potential of the AC power supply 401 generated by the zero-cross detector 421 . Based on the zero cross timing of the AC power supply 401, the phase angle (phase control) and wave number (wave number control) corresponding to the power to be supplied are converted into control levels, and the triacs 441 to 443 are controlled according to the control conditions.

However, in this embodiment, since the triacs 441 to 443 are connected in series, even if the triac on the heating element block side is turned on, if all the triacs on the upstream side of the triac are not turned on, the heating element The block is not energized.

In order to increase the power to the heating element block, it is necessary to increase the energization ON time (increase the phase angle in phase control, and increase the ON wave number in wave number control). However, since the triacs are connected in series in this embodiment, the ON time cannot be increased beyond the ON time of the triac on the upstream side.

FIG. 6 shows an equivalent circuit of the 7-divided resistance heating element of Example 1 shown in FIG. FIG. 10 shows a table comparing the resistance value and the like of each heating block in the comparative example and the first example. FIG. 10 also shows the calculation results of the comparative example and the first embodiment.

As shown in FIG. 10, in the heater of the comparative example, the resistance of each resistance heating element (302a-1 to 302a-3) constituting the heating block A is 80.7Ω, so the combined resistance is 80.7Ω. /3=26.9Ω. Since the longitudinal width of each resistance heating element (302a-1 to 302a-3) constituting the heating block A is 45 mm, the resistance value per unit length of the heating block is 26.9Ω/(45*3mm). = 0.20Ω/mm.

Next, when 100 V is applied and 100% ON, the heat generation amount of the heat generation block A is 100 V^2/26.9 Ω = 371.74 W, so the heat generation amount per longitudinal unit length of the heat generation block A (maximum possible heat generation amount ) becomes 371.74 W/(45*3 mm)=2.75 W/mm.

Similarly, when the heat generation blocks B and C are calculated, the heat generation amount per longitudinal unit length when the heat generation blocks B and C are 100% ON when 100 V is applied is 2.75 W / mm, which is the same as the heat generation block A. .

FIG. 4A shows the temperature rise curve of the film 202 of the fixing device at this time. The slope of the temperature rise curve at the ends may be lower than that of the temperature rise curve at the center due to the influence of heat radiation from the ends. For this reason, it is impossible to shorten the pre-printing rotation time in order to satisfy the edge fixability at the time of printing the first sheet, and it becomes difficult to shorten the so-called FPOT. For the comparative example, a longer pre-rotation was required until the film temperature at the edges reached about the same temperature as the center, and the FPOT was about 9 seconds.

As shown in FIG. 10, the resistance value of each heating block in Example 1 is as follows. That is, although the total resistance value of the heating block A is 26.9Ω, which is the same as in the comparative example, the total resistance values of the heating blocks B and C are lower than those in the comparative example, The amount of heat generated by the heat generating block B and the heat generating block C is increased compared to the comparative example. Specifically, the total resistance value of the heating block B is 40.4Ω in the comparative example, whereas it is 16.5Ω in Example 1, and the total resistance value of the heating block C is 46.6Ω in the comparative example. In contrast, Example 1 is set to 18.3Ω. Methods for changing the resistance value of the heating block include methods such as changing the pattern width and thickness of the resistance heating element, changing the pattern length of the resistance heating element, and changing the resistance value of the paste used for the pattern of the resistance heating element. .

FIG. 4(b) shows the film start-up curve in the first embodiment. Since the amount of heat generated by the heat generating blocks B and C can be made larger than that of the heat generating block A, the energization ratio of the heat generating blocks B and C with respect to the heat generating block A is appropriately adjusted so as to reduce the longitudinal temperature unevenness. Therefore, it is possible to reduce the temperature unevenness between the central portion and the edge portion, and it is possible to secure the edge fixability of the first printed sheet, so that the pre-printing rotation time can be shortened, and the FPOT can be shortened. can do. In Example 1, the time required for the edge temperature of the film to reach approximately the same temperature as the center temperature is shorter than in the comparative example, and the pre-rotation time can be shortened.
Seconds could be shortened from the comparative example.

Further, in a configuration in which a plurality of triacs are connected in cascade to drive and control a plurality of heat generating blocks, if any of the triacs on the upstream side of a given triac are operating normally, the heat generating block will not enter a runaway state. Therefore, safety can be improved.

(Example 2)
An image heating apparatus according to Embodiment 2 of the present invention will be described. In the second embodiment, descriptions of the same components as in the first embodiment are omitted. Matters not specifically described here in the second embodiment are the same as those in the first embodiment.

FIG. 5 shows an example of a heater 300 and a control circuit in Example 2 of the present invention. Also, FIG. 7 shows a schematic diagram of an equivalent circuit of the 7-divided resistance heating element of the heater in the second embodiment.

The second embodiment differs from the first embodiment in the connection configuration of the triacs 441-443. In the first embodiment, the triacs 441 to 443 are connected in series (the triac 442 is subordinately connected to the triac 441, and the triac 443 is subordinately connected to the triac 442). On the other hand, in the second embodiment, the triac 442 and the triac 443 are subordinately connected to the triac 441 . In other words, while the triac 443 is subordinately connected to the triac 442 in the first embodiment, the triac 443 is subordinately connected to the triac 441 in the second embodiment.

For this reason, in Example 1, the heat generating block C to which the triac 443 is connected could not be energized except when both the triacs 441 and 442 were energized. On the other hand, in the second embodiment, the heat generation of the heat generating block B and the heat generating block C can be controlled independently of each other regardless of whether the triac 442 is ON/OFF.

That is, in the first embodiment, when the heat generating block C is energized and heats up, both the heat generating blocks A and B are energized and heat is generated. On the other hand, in the second embodiment, when the heat generating block C is energized and heats up, the heat generating block A is always energized and generates heat, but the heat generating block B is always energized and generates heat. You don't have to. Therefore, compared to the first embodiment, in the second embodiment, it is possible to reduce power fluctuation (so-called flicker) of the entire fixing device compared to the first embodiment.

Except for the connection configuration of the triacs 441 to 443 described above, other configurations of the heater of the second embodiment are the same as those of the heater of the first embodiment shown in FIG.

200... Fixing device 202... Fixing film (fixing member) 208... Pressure roller 212... Thermistor 213... Safety element (thermo switch, temperature fuse) 300... Heater 301... Conductor 302... Resistance heating element , E... electrode, 400... control unit, 401... AC power supply, 420... CPU, 421... ZEROX circuit (zero cross detection circuit), 430, 440... relay, 433... transistor, 434... resistor, 436... latch unit, 437... Comparative portion 441 to 443: triac (semiconductor element), N: fixing nip, P: recording material

Claims (9)

a heater having a plurality of heating elements arranged in a width direction of the recording material perpendicular to the conveying direction of the recording material;
a control unit that controls power supplied to the plurality of heating elements;
with
An image heating device for heating an image formed on a recording material by heat of the heater,
The plurality of heating elements are
a first heating element group;
a second heating element group arranged at a different position in the width direction with respect to the first heating element group;
including
The control unit
a first semiconductor element connected to the first heating element group;
a second semiconductor element connected to the second heating element group and connected in series to the first semiconductor element;
has
controlling power supplied to the first heating element group by controlling the first semiconductor element;
In an image heating apparatus that controls power supplied to the second heating element group by controlling the first semiconductor element and the second semiconductor element,
the control unit has a safety element operable to cut off power supply to the first heating element group in response to overheating of the heating elements included in the first heating element group;
A maximum possible heat generation amount per unit length in the width direction of the second heat generating element group is larger than a maximum possible heat generation amount per unit length in the width direction of the first heat generating element group. image heating device. the first heating element group is arranged at a position including a conveyance reference position of the recording material in the width direction;
2. An image heating apparatus according to claim 1, wherein said second heating element group comprises a plurality of heating elements arranged on both sides of said first heating element group in said width direction. further comprising temperature detection means for respectively detecting the temperature of the heating elements included in the first heating element group and the temperature of the heating elements included in the second heating element group;
The control unit controls power supplied to the first heating element group and power supplied to the second heating element group based on the temperature detected by the temperature detection means. 3. An image heating apparatus according to claim 1 or 2. The plurality of heating elements are
further comprising a third heating element group arranged at different positions in the width direction with respect to the first heating element group and the second heating element group;
The control unit
a third semiconductor element connected to the third heating element group and connected in series to the first semiconductor element and the second semiconductor element;
controlling power supplied to the third heating element group by controlling the first semiconductor element, the second semiconductor element, and the third semiconductor element;
A maximum possible heat generation amount per unit length in the width direction of the third heat generating element group is larger than a maximum possible heat generation amount per unit length in the width direction of the second heat generating element group. The image heating apparatus according to any one of claims 1 to 3. The plurality of heating elements are
further comprising a third heating element group arranged at different positions in the width direction with respect to the first heating element group and the second heating element group;
The control unit
a third semiconductor element connected to the third heating element group and connected in series to the first semiconductor element;
controlling power supplied to the third heating element group by controlling the first semiconductor element and the third semiconductor element;
A maximum possible heat generation amount per unit length in the width direction of the third heat generating element group is larger than a maximum possible heat generation amount per unit length in the width direction of the first heat generating element group. The image heating apparatus according to any one of claims 1 to 3. The third heat generating element group is composed of a plurality of heat generating elements arranged in the width direction on a side away from the reference conveying position of the recording material with respect to the second heat generating element group. 6. An image heating apparatus according to claim 4 or 5. 7. An image heating apparatus according to claim 1, wherein said safety element is a thermostat, a thermoswitch, or a thermal fuse. a cylindrical film in which the heater is arranged;
a roller in contact with the outer surface of the film;
further comprising
the heater and the roller form a nip between the film and the roller for sandwiching a recording material;
8. The image heating apparatus according to claim 1, wherein an image formed on the recording material sandwiched by said nip is heated by heat of said heater. an image forming unit that forms an image on a recording material;
a fixing unit that fixes the image formed on the recording material to the recording material;
In an image forming apparatus having
An image forming apparatus, wherein the fixing section is the image heating device according to any one of claims 1 to 10.

Images