Image heating apparatus and image forming apparatus

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

Technical Field

[0001] The present invention relates to an image forming apparatus such as a printer or a copier that uses an electrophotographic method. Further, the present invention relates to an image heating device such as a gloss imparting device that improves the glossiness of a toner image by reheating the toner image fixed on a fixing device or a recording material mounted on the image forming apparatus.

Background Art

[0002] As disclosed in Patent Document 1, conventionally, a fixing device that independently drives a heating element arranged by being divided in the longitudinal direction of a heater is known. In such a fixing device, corresponding to the size of a recording material, in the longitudinal direction of the heater, the heating elements are divided into three groups: a central heating element, an intermediate heating element, and an end heating element, and thyristors are independently connected to each heating element group. In such a fixing device, as an example of a safety measure when a thyristor fails and the energization of the heating element by the thyristor cannot be released, it is conceivable to arrange a safety element such as a thermoswitch in each heating element group. However, in this case, since the number of safety elements required is equal to the number of independently driven heating element groups, the cost increases, and there is a concern that a mounting space is required and the fixing device becomes large-sized.

[0003] Furthermore, in the fixing device disclosed in Patent Document 2, as a safety measure in case the triac fails and it becomes impossible to de-energize the heating element by the triac, two printed thermistors are placed on the independently driven heating elements. Even if one of these two thermistors fails, the remaining thermistor will detect the abnormally high temperature of the heating element due to the triac failure, and the relay will turn OFF to stop the power supply. In this fixing device, since two printed thermistors are placed on each heating element as a safety measure, the number of printed thermistors increases as the number of heating element divisions increases, the number of thermistor wirings increases, and the heater board width becomes larger. For this reason, the heating elements at the long ends are not driven independently but are connected in cascaded order to the adjacent heating elements, and only one printed thermistor is placed on the heating elements at the long ends to reduce the number of thermistors and thermistor wirings. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2019-207337 [Patent Document 2] Japanese Patent Publication No. 2018-194682 [Overview of the Initiative] [Problems that the invention aims to solve]

[0005] When two triacs are connected in cascaded order, as described in Patent Document 2, the following problems arise. Specifically, the energized state of the upstream triac A can be controlled by applying a trigger current to its gate terminal. In contrast, when the upstream triac A is in the OFF state, no current flows through the downstream triac B even if a trigger current is applied to the gate terminal of triac B. When triac A is in the ON state, the energization of triac B can be controlled by applying a trigger current to the gate terminal of triac B. In other words, the energized state of triac B is not determined by triac B alone, but is influenced by the energized state of triac A.

[0006] Therefore, the heating element driven by triacs A and B will not be energized even if triac B is controlled to be energized when triac A, the upstream component, is controlled to be energized OFF. For this reason, the energized period of the driven heating element cannot be increased beyond the period when triac A, the upstream component, is energized ON. It was difficult to increase the heat generation by extending the operating period. The temperature gradient during the start-up of the fuser unit tends to be lower at the edges of the heater compared to the center of the heater due to heat dissipation from the edges. In contrast, it was difficult to increase the heat generation at the edges of the heater and make the temperature gradient there similar to that of the center of the heater, making it difficult to shorten the FPOT (First Print Output Time) in order to ensure edge fixing.

[0007] Furthermore, because each independently driven heating element is equipped with two printed thermistors as a safety measure, the number of thermistor wires increases, limiting the reduction in the heater board width.

[0008] The objective of this invention is to provide a technology that enables safety and shortens FPOT (Functional Phase Timeout) in a compact and inexpensive configuration. [Means for solving the problem]

[0009] To achieve the above objective, the image heating apparatus of the present invention is A heater having multiple heating elements arranged in the width direction of the recording material, perpendicular to the transport direction of the recording material, A control unit that controls the power supplied to the plurality of heating elements, Equipped with, An image heating device that heats an image formed on a recording material with the heat of the heater, The aforementioned multiple heating elements are It is positioned in the width direction including the transport reference position of the recording material. The first group of heat-generating elements, They are arranged at different positions in the width direction relative to the first heating element group. It consists of a plurality of heating elements arranged on both sides of the first heating element group in the width direction. The second group of heat-generating elements, Includes, The control unit, A first semiconductor element connected to the first heat-generating group, A second semiconductor element connected to the second heating element group and connected in series with the first semiconductor element, It has, By controlling the first semiconductor element, the power supplied to the first heating element group is controlled. In an image heating device that controls the 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 capable of shutting off the power supply to the first heating element group in response to overheating of the heating elements included in the first heating element group, The second heating element group is characterized in that the maximum possible heat generation per unit length in the width direction is greater than the maximum possible heat generation per unit length in the width direction of the first heating element group. To achieve the above objective, the image forming apparatus of the present invention is An image forming unit that forms an image on the 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 unit is characterized by being the image heating device of the present invention. [Effects of the Invention]

[0010] According to the present invention, it is possible to ensure safety and shorten FPOT with a small and inexpensive configuration.

Brief Description of Drawings

[0011] [Figure 1] Schematic configuration diagram of the heater and control circuit in Example 1 of the present invention [Figure 2] Schematic diagram of the image forming apparatus in Example 1 [Figure 3] Schematic cross-sectional view of the fixing device in Example 1 [Figure 4] Device startup temperature profile during pre-print rotation in Comparative Example and Example 1 [Figure 5] Schematic configuration diagram of the heater and control circuit in Example 2 of the present invention [Figure 6] Schematic diagram of the equivalent circuit of the seven-segment resistance heating element of the heater in Example 1 [Figure 7] Schematic diagram of the equivalent circuit of the seven-segment resistance heating element of the heater in Example 2 [Figure 8] Operation explanatory diagram of a triac [Figure 9] Operation explanatory diagram of a triac [Figure 10] Operation explanatory diagram when triacs are connected in series [Figure 11] Operation explanatory diagram when triacs are connected in series [Figure 12] Table comparing the heater according to Example 1 and the heater according to the Comparative Example

Modes for Carrying Out the Invention

[0012] Hereinafter, with reference to the drawings, modes for carrying out this invention will be exemplarily and specifically described based on examples. Note that dimensions, materials, shapes, relative arrangements, etc. of the components described in this embodiment should be appropriately changed according to the configuration of the apparatus to which the invention is applied and various conditions. That is, the scope of this invention is not intended to be limited to the following embodiments.

[0013] (Example 1) 1. Configuration of the image forming apparatus Figure 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 that utilize electrophotographic or electrostatic recording methods. More specifically, examples of image forming apparatuses include copiers, laser beam printers (LBPs), microfilm reader printers, and recording machines. Examples of recording materials include paper, printing paper, recording material sheets, electrofax sheets, electrostatic recording sheets, OHT sheets, glossy paper, and glossy film. First, an unfixed toner image corresponding to the target image information is formed and supported on the recording surface of the recording material by an image forming process means such as electrophotography, electrostatic recording, or magnetic recording, using a toner made of a heat-meltable resin or the like, either by a direct transfer method or an indirect transfer method. Then, as a fixing process, the unfixed toner image is heat-fixed as a permanently fixed image on the recording material surface on which the image is supported. Here, we will explain the case in which the present invention is applied to a laser beam printer that forms an image on a recording material P such as recording paper using an electrophotographic method.

[0014] When a print signal is generated, the scanner unit 21 emits a laser beam modulated according to the image information and scans the surface of the photosensitive drum (electrophotographic photoreceptor) 19, which has been charged to a predetermined polarity by the charging roller 16. This forms an electrostatic latent image on the photosensitive drum 19, which acts as an image carrier. When toner charged to a predetermined polarity is supplied from the developing roller 17 to this electrostatic latent image, the electrostatic latent image on the photosensitive drum 19 is developed as a toner image (developer image). Meanwhile, the recording material (recording paper) P loaded in the paper feed cassette 11 is fed one sheet at a time by the pickup roller 12 and transported toward the registration roller pair 14 by the transport roller pair 13. Furthermore, the recording material P is transported from the registration roller pair 14 to the transfer position in time 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, which acts as a transfer member. As the recording material P passes through the transfer position, the toner image on the photosensitive drum 19 is transferred to the recording material P. The apparatus configuration responsible for the process of forming the above-described unfixed toner image on the recording material P corresponds to the image forming unit of the present invention.

[0015] Subsequently, the recording material P is heated using the heat from a heater in the fixing device (image heating device) 200, which serves as the fixing unit (image heating unit), and the toner image is heated and fixed to the recording material P. The recording material P, which carries the fixed toner image, is discharged to the output tray 31 at the top of the image forming apparatus 100 by the transport roller pairs 26 and 27.

[0016] The photoreceptor 19 is cleaned by the cleaner 18 to remove any remaining toner from its surface. The paper feed tray (manual feed tray) 28 has a pair of paper regulating plates whose width can be adjusted according to the size of the recording paper P, and is provided to accommodate recording paper P of sizes other than standard sizes. The pickup roller 29 is a roller for feeding the recording paper P from the paper feed tray 28. The motor 30 drives the fuser unit 200, etc. Power is supplied to the fuser unit 200 from the control circuit 400, which is a power supply control unit connected to the commercial AC power supply 401.

[0017] In this embodiment, a developing unit including a photosensitive drum 19, a charging roller 16, and a developing roller 17, and a cleaning unit including a drum cleaner 18 are configured to be detachably attached to the main body of the image forming apparatus 100 as a process cartridge 15. The image forming apparatus 100 in this embodiment has a maximum paper feed width of approximately 300 mm in the direction perpendicular to the transport direction of the recording material P, and is capable of printing approximately 37 sheets per minute of A4 landscape size [width 297 mm x length 210 mm] plain paper at a transport speed of approximately 160 mm / sec.

[0018] 2. Configuration of the image heating device Figure 3 is a cross-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, a metal stay 204, and a heater holding member 201.

[0019] The fixing member, film 202, is a tubular, multi-layered, high-heat-resistant film 202, also known as an endless belt or endless film, with a base layer made of a heat-resistant resin such as polyimide or a metal such as stainless steel. The surface of film 202 is coated with a release layer made of a high-performance fluororesin such as PFA, which has excellent heat resistance and release properties to prevent toner adhesion. Furthermore, especially in devices that form color images, a high-heat-resistant rubber such as silicone rubber may be formed as an elastic layer between the base layer and the release layer to improve image quality.

[0020] The pressure roller 208 has a core metal 209 made of a material such as iron or aluminum, and an elastic layer 210 made of a highly heat-resistant rubber material such as silicone rubber. With this configuration, the pressure roller 208 is made to have an appropriate hardness, thereby obtaining a fixing nip N corresponding to the fixing device 200.

[0021] The heater 300 is held in a heat-resistant resin heater holder member 201. A thermistor 212 is provided on the back surface of the heater 300 as a temperature sensing means for detecting the temperature of the heater 300. The metal stay 204 receives an applied pressure (not shown) and presses the heater holder member 201 toward the pressure roller 208.

[0022] The control unit 400 drives the motor 30 in response to a print signal input from an external input device such as a PC. The pressure roller 208 rotates in the direction of arrow R1 by receiving rotational driving force from the motor 30. As the pressure roller 208 rotates, a rotational force acts on the film 202 due to the frictional force between it and the outer surface of the film 202, causing the film 202 to rotate in the direction of arrow R2.

[0023] Furthermore, the control unit 400 energizes a triac (see Figure 1), which is a semiconductor element provided as a power supply control means, to turn it ON. As a result, power is supplied from the power supply (see Figures 1 and 2) to the heating element of the heater 300, causing the heater 300 to heat up. The control unit 400 receives the output signal from the thermistor 212 and controls the power supplied to the heater 300 by the triac based on that output signal, thereby controlling the temperature of the heater 300 to a predetermined temperature. Heater 3 When the temperature of 00 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 has been formed is introduced into the fixing nip N. As the recording material P is held and conveyed in the fixing nip N, heat from the heater 300 is applied through the film 202, thereby fixing the unfixed toner image on the recording material P.

[0024] 3. Heater and control circuit used in the image heating device Figure 1 shows an example of the heater 300 and control circuit in Embodiment 1 of the present invention. In this embodiment, the transport reference for the recording material is the central reference, and the recording material P is transported so that its center line in the width direction perpendicular to the transport direction lies along the transport reference position X0.

[0025] The heater 300 has a conductor 301, a resistive heating element 302, and an electrode E on a substrate made of ceramic such as alumina or aluminum nitride, or stainless steel SUS304. When using a metal such as stainless steel SUS304 for the heater substrate, an insulating layer such as a glass coating layer is provided on the metal substrate for insulation, and then the conductor 301, the resistive heating element 302, and the electrode E are formed on top of it.

[0026] The conductor 301 is a conductive pattern that serves as wiring for applying the voltage supplied from electrode E to the resistive heating element, and is formed from a low-resistance, heat-resistant material such as silver paste. The resistive heating element 302 generates Joule heat through the current flowing due to the voltage applied from the conductor 301 and acts as a heating source, and is adjusted to a predetermined resistance value using silver, palladium, ruthenium oxide, etc.

[0027] In this embodiment, multiple resistive heating elements 302 are arranged in seven sections along the longitudinal direction (recording material width direction) of the heater substrate. The longitudinal width of the resistive heating elements 302c-1 and 302c-2 at the longitudinal ends is approximately 39 mm. On the other hand, the longitudinal width of the resistive heating elements 302a-1, 302a-2, 302a-3, 302b-1, and 302b-2, which are arranged inside the longitudinal direction, is approximately 45 mm. Although the spacing between each resistive heating element is approximately 4 mm in the longitudinal direction, the pattern of the resistive heating elements is made slanted at the ends to minimize the effect of uneven heating in the direction of recording material transport.

[0028] Of the resistance heating elements arranged in seven sections along the length, resistance heating elements 302a-1, 302a-2, and 302a-3, which are used when feeding small-sized paper with a length of A5 or less, are collectively designated as the first heating element group, heating block A. When feeding paper with a size from A5 vertical feed width to LTR vertical feed width, in addition to heating block A, resistance heating elements 302b-1 and 302b-2 on both sides of the length of heating block A, adjacent to each other, are used as the second heating element group, heating block B. When feeding paper with a size from LTR vertical feed to A3 width, resistance heating elements 302c-1 and 302c-2, which are located adjacent to heating block B on the side away from the transport reference position, are further designated as heating block C.

[0029] Each resistive heating element has a pattern shape that makes approximately two back-and-forth movements in the longitudinal direction of the heater, and is energized from the short direction of the heater (a direction perpendicular to the longitudinal direction) by the conductor 301. Instead of individually and independently driving and controlling all seven resistive heating elements 302, they are divided into three heating blocks and driven and controlled in block units (group units) in order to reduce the number of drive control circuits, thereby making the device cheaper and more compact.

[0030] Electrode E is provided for supplying power to the resistive heating element. An insulating protective glass (see Figure 3) is provided on the surface of the heater substrate on which the conductor 301, resistive heating element 302, and electrode E are mounted (the surface that slides with the film 202), so as to cover the area other than electrode E. The heater 300 is positioned so that its longitudinal direction is perpendicular to the transport direction of the recording material P. The number of heating elements and the number of heat-generating blocks are not limited to those shown in this embodiment.

[0031] The image forming apparatus 100 is connected to a commercial AC power supply 401. The power supply voltage Vcc is a DC power supply generated by an AC / DC converter (not shown) connected to the AC power supply 401. The AC power supply 401 is connected to the heater 300 via relays 430, 440 and triacs 441-443. Triacs 441-443 are turned ON / OFF by control signals FUSER-a-FUSER-c from the CPU 420. The drive circuits for triacs 441-443 are not shown. By selectively controlling the triacs 441-443 as multiple semiconductor elements, the energization of multiple resistive heating elements can be selectively controlled for each heating block, and multiple heating region blocks divided in the longitudinal direction can be selectively heated individually.

[0032] The operation of relay 430 is explained below. When the CPU 420 sets the RLON signal to High, transistor 434 turns ON, current flows from the power supply voltage Vcc to the secondary coil of relay 430, and the primary contact of relay 430 turns ON. When the RLON signal turns Low, transistor 434 turns OFF, the current flowing from the power supply voltage Vcc to the secondary coil of relay 430 is interrupted, and the primary contact of relay 430 turns OFF. Note that resistor 434 is a resistor that limits the base current of transistor 433.

[0033] In the internal processing of the CPU 420, the power to be supplied is calculated, for example, by PI control, based on the set temperature and the temperature detected by thermistors, which are used as temperature sensing means. Multiple thermistors are provided at positions corresponding to each heat-generating block in order 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 ZEROX timing signal, which is synchronized with the zero potential of the AC power supply 401 generated by the zero-cross detection unit 421. Based on the zero-cross timing of the AC power supply 401, the phase angle (phase control) and wavenumber (wavenumber control) corresponding to the power to be supplied are converted into control levels, and the triacs 441 to 443 are controlled according to these control conditions.

[0034] Relays 430 and 440 and the protection circuit will be described below. Relays 430 and 440 are used as means of cutting off power to the heater 300 in the event that the heater 300 overheats due to a malfunction or other reason. In this embodiment, relays 430 and 440 are used as double-pole relays.

[0035] Let's explain the operation of relay 430. When CPU 420 sets the RLON signal to High, transistor 433 turns ON, current flows from the power supply voltage Vcc to the secondary coil of relay 430, and the primary contact of relay 430 turns ON. When the RLON signal turns Low, transistor 433 turns OFF, the current flowing from the power supply voltage Vcc to the secondary coil of relay 430 is interrupted, and the primary contact of relay 430 turns OFF. Since relays 430 and 440 are double-pole relays, relay 440 also turns ON and OFF in conjunction with the ON and OFF operation of relay 430.

[0036] The operation of the safety circuit using relays 430 and 440 will be explained. When the temperature detected by thermistor Th exceeds a set predetermined value, the comparison unit 437 operates the latch unit 436, and the latch unit 436 latches by setting the RLOFF signal to a Low state. When the RLOFF signal is Low, even if the CPU 420 sets the RLON signal to a High state, the transistor 433 remains in the OFF state, so the relay 430 can remain in the OFF state (safe state). In this way, relays 430 and 440 can also be used as a means of cutting off power to the heater 300 in the event that the heater 300 overheats due to a malfunction or other reason.

[0037] The operation of the triac will be briefly explained with reference to Figures 8 and 9. Figure 8 is a simplified circuit diagram showing the power supply control of a heating element by a triac, and Figure 9 shows the operation of the triac from an AC power supply. This figure shows the relationship between the AC voltage applied to the circuit and the voltage applied to the heating element by the triac.

[0038] As shown in Figure 8, the triac is configured to allow current to flow in both directions by connecting two complementary thyristors in antiparallel, making it usable with both DC and AC currents. When a positive voltage is applied to the main electrode T2 of the triac from an AC power source, the triac remains in the 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 to 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 turns ON, and current flows between T2 and T1, causing current to flow to the load and the resistive heating element to heat up.

[0039] As shown in Figure 9, when the AC power supply completes half a cycle, the voltage applied to the triac's main electrode T2 reverses and becomes a negative voltage. As a result, the triac enters the OFF state, no current flows between T2 and T1, and no current flows to the load (resistive heating element). When a trigger current is applied to the triac's gate electrode G, the triac enters the ON state again, current flows between T1 and T2, current flows to the load (resistive heating element), and the resistive heating element generates heat.

[0040] Referring to Figures 10 and 11, the operation of triacs when two triacs are connected in cascade and a load (resistive heating element) is connected to each triac will be explained. Figure 10 is a simplified circuit diagram showing the energization control of two heating elements by two cascade-connected triacs, and Figure 11 is a diagram showing the relationship between the AC voltage applied to the triac from the AC power supply and the voltage applied to the heating element by the triac.

[0041] As shown in Figure 10, even when a positive voltage is applied to terminal T2 of triac A from an AC power source, triac A remains in the OFF state until a trigger current is applied to the gate terminal G of triac A, and no current flows between terminals T2 and T1 of triac A. No current flows to load A (resistive heating element A) connected to triac A, so resistive heating element A does not generate heat during this period.

[0042] During this period, even if a trigger current is applied to the gate terminal G of triac B, which is connected in series with triac A, no voltage is applied to terminal T2 of the downstream triac B because the upstream triac A is in the OFF state. Therefore, no current flows from terminal T2 to T1 of triac B, and no current flows to load B (resistor heating element B) connected to triac B, so resistor heating element B does not generate heat.

[0043] Next, when a trigger current is applied to the gate terminal G of triac A, triac A becomes energized ON, and current flows from terminal T2 to T1 of triac A. As a result, current also flows to load A connected to triac A, and the resistive heating element A generates heat. Also, because the upstream triac A is energized ON, a positive voltage is applied to terminal T2 of the downstream triac B. However, triac B remains energized OFF until a trigger current is applied to its gate terminal G. Therefore, no current flows to load B connected to triac B, and the resistive heating element B does not generate heat.

[0044] When triac A is energized and a trigger current is applied to the gate terminal G of triac B, both triac A and triac B become energized, current flows to the load B connected to triac B, and the resistive heating element B generates heat.

[0045] As shown in Figure 11, half a cycle of the AC power supply has finished, and the terminal of triac A has ended. When a negative voltage is applied to child T2, triac A is turned OFF. In this state, no current flows through triac A regardless of the energized state of triac B, so no current flows through either load A or load B, and neither resistive heating elements A nor B generate heat.

[0046] When a trigger current is applied to the gate terminal G of triac A, triac A becomes energized ON. In this state, triac B remains energized OFF until a trigger current is applied to the gate terminal G of triac B and it becomes energized ON. Therefore, current flows only to load A, and no current flows to load B. When a trigger current is applied to the gate terminal G of triac B, triac B becomes energized ON, so current flows to load B and the resistive heating element B heats up.

[0047] When triacs are connected in cascade in this manner, the energized state of the upstream triac A can be controlled by applying a trigger current to its gate terminal G. In contrast, when the upstream triac A is in the OFF state, no current flows through the downstream triac B even if a trigger current is applied to the gate terminal G of triac B. When triac A is in the ON state, the energization of triac B can be controlled by applying a trigger current to the gate terminal G of triac B. In other words, the energized state of triac B is not determined by triac B alone, but is influenced by the energized state of triac A.

[0048] Referring to Figure 1, the drive configuration using triacs 441 to 443 in this embodiment will be explained. Triacs 441 to 443 are connected to each of the three heat-generating blocks A, B, and C, respectively. Triac 442, which is connected to the adjacent heat-generating block B, is subordinate to triac 441, which drives heat-generating block A. Triac 443, which is connected to heat-generating block C, is further subordinate to triac 442.

[0049] Heating block A and triac 441 are the upstream heating block (heating element) and the upstream triac, respectively. From the perspective of triac 442, triac 441 is the upstream triac. From the perspective of heating block B, which is connected to triac 442, heating block A, which is connected to the upstream triac 441, is the upstream heating block (heating element). Conversely, from the perspective of heating block A, heating block B is the subordinate side.

[0050] Similarly, from the perspective of triac 443, triacs 441 and 442 are upstream triacs. From the perspective of heat block C connected to triac 443, heat blocks A and B connected to the upstream triacs 441 and 442 are upstream heat blocks (heating elements). From the perspective of heat block B, heat block C connected to triac 443 is the dependent side.

[0051] In this connection configuration, the upstream heat-generating block A is driven and controlled only by the upstream triac 441. Heat-generating block B is driven and controlled by the triac 441 connected to heat-generating block B and the upstream triac 442. Heat-generating block C is driven and controlled by the triac 443 connected to heat-generating block C and the upstream triacs 441 and 442.

[0052] This section explains whether or not the heat-generating block C remains powered on (a so-called runaway state). Even if the triac 443 connected to the heat-generating block C malfunctions and remains powered on, the heat-generating block C will not be powered unless both the upstream triacs 441 and 442 are powered on. If the drive control of heat-generating block A is performed by a normal triac 441, and the drive control of heat-generating block B is performed by normal triacs 441 and 442, the heat-generating block C will not enter a runaway state.

[0053] Heating block C will malfunction if all triacs 441-443 fail and the power is turned ON. In this case, safety measures such as the activation of safety elements (thermoswitch, thermostat, thermal fuse, etc.) located in heating block A in response to overheating will turn the power OFF.

[0054] Similarly, even if the triac 442 connected to the heat-generating block B malfunctions and remains powered on, the heat-generating block B will not malfunction as long as the upstream triac 441 is functioning correctly.

[0055] Thus, with respect to heating blocks B and C, if the upstream triac 441 is functioning correctly, even if the subordinate connected triacs 442 and 443 fail and remain powered on, a runaway state will not occur. For this reason, it is not necessary to install safety elements (thermoswitches, thermostats, thermal fuses, etc.) or safety circuits with multiple temperature detection means in heating blocks B and C as safety measures against runaway.

[0056] Since the only drive control for heat-generating block A is the triac 441, if the triac 441 malfunctions and remains powered on, heat-generating block A will also remain powered on and enter a runaway state. For this reason, safety measures against runaway operation cannot be reduced for heat-generating block A.

[0057] In this embodiment, a thermoswitch 213 is placed in the heat-generating block A as a safety element. The safety measures against runaway operation of the heat-generating block A are described below. Two examples of cases in which the heat-generating block A may run away are as follows:

[0058] The first case occurs when the triac 441 that drives and controls the heat-generating block A fails, or when the CPU 420 that controls the triac 441 malfunctions, causing the heat-generating block A to remain powered ON (runaway state). In this case, the output of the thermistor 212 (see Figure 3), which is used as a temperature sensing means to detect the temperature of the heat-generating block A, is compared by the comparison unit 437 to see if it has reached a predetermined high temperature, and the latch unit 436 is activated to set the RLOFF signal to Low and latch it. When the RLOFF signal is Low, even if the CPU 420 sets the RLON signal to High, the transistor 433 remains OFF, so the relay 430 can remain OFF (safe state), and power to the heater 300 is cut off.

[0059] In the second case, in addition to the conditions of the first case, the temperature detection means for detecting the temperature of the heat-generating block A fails to function properly, and the comparison unit 437 cannot operate the latch to turn off the relay. In this case, the safety element (thermoswitch, thermal fuse) 213 provided in the heat-generating block A 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.

[0060] In this way, multiple safety measures are in place to prevent runaway operation of the heat-generating block A.

[0061] The ON timing of the triac is generated by the CPU 420 based on the ZEROX timing signal, which is synchronized with the zero potential of the AC power supply 401 generated by the zero-cross detection unit 421. Based on the zero-cross timing of the AC power supply 401, the phase angle (phase control) and wavenumber (wavenumber control) corresponding to the power to be supplied are converted into control levels, and the triacs 441 to 443 are controlled according to these control conditions.

[0062] However, in this embodiment, since triacs 441 to 443 are connected in series, even if the triac on the heating element block side is controlled to ON, the triac upstream of that triac will not turn ON. If all the switches are not turned ON, the heating element block will not be energized.

[0063] To increase the power supplied to the heating element block, it is necessary to increase the ON time (by increasing the phase angle in phase control or increasing the ON wavenumber in wavenumber control). However, in this embodiment, since the triacs are connected in series, it is not possible to increase the ON time beyond the ON time of the upstream triac.

[0064] Figure 6 shows the equivalent circuit of the seven-segment resistor heating element of Example 1 shown in Figure 1. Figure 10 shows a table comparing the resistance values ​​of each heating block in the comparative example and Example 1. Figure 10 also shows the calculation results for the comparative example and Example 1.

[0065] As shown in Figure 10, in the comparative example heater, the resistance of each resistive heating element (302a-1 to 302a-3) constituting the heating block A is 80.7Ω each, so the combined resistance is 80.7Ω / 3 = 26.9Ω. Since the length of each resistive heating element (302a-1 to 302a-3) constituting the heating block A is 45mm each, the resistance value per unit length of the heating block is 26.9Ω / (45*3mm) = 0.20Ω / mm.

[0066] Next, when 100V is applied and the device is 100% ON, the heat generated by heating block A is 100V^2 / 26.9Ω = 371.74W. Therefore, the heat generated per unit length of heating block A (maximum possible heat generation) is 371.74W / (45*3mm) = 2.75W / mm.

[0067] Similarly, when calculating for heating blocks B and C, the amount of heat generated per unit length when 100V is applied and they are 100% ON is the same as for heating block A, which is 2.75 W / mm.

[0068] Figure 4(a) shows the temperature rise curve of the film 202 in the fixing device at this time. Compared to the temperature rise curve in the center, the temperature rise curve at the edges may have a lower slope than the temperature rise curve in the center due to the influence of heat dissipation from the edges. For this reason, it is not possible to shorten the pre-print rotation time in order to satisfy the edge fixing performance during the first print, and it becomes difficult to shorten the so-called FPOT. In the comparative example, it was necessary to extend the pre-print rotation until the film temperature at the edges reached approximately the same temperature as the center, and the FPOT was approximately 9 seconds.

[0069] As shown in Figure 10, the resistance values ​​of each heating block in Example 1 are as follows. Specifically, although the total resistance value of heating block A is 26.9Ω, the same as the comparative example, the total resistance values ​​of heating block B and heating block C are configured to be lower than those of the comparative example, thereby increasing the amount of heat generated by heating block B and heating block C compared to the comparative example. Specifically, the total resistance value of heating block B is 16.5Ω in Example 1 compared to 40.4Ω in the comparative example, and the total resistance value of heating block C is 18.3Ω in Example 1 compared to 46.6Ω in the comparative example. Methods for changing the resistance value of the heating blocks include changing the pattern width and thickness of the resistive heating element, changing the pattern length of the resistive heating element, and changing the resistance value of the paste used in the pattern of the resistive heating element.

[0070] Figure 4(b) shows the film rise curve in this embodiment 1. Since the heat generation of heating blocks B and C can be made greater than that of heating block A, the current supply ratio of heating blocks B and C to heating block A was adjusted as needed to reduce longitudinal temperature unevenness. As a result, the temperature unevenness between the center and the edges can be reduced, ensuring edge adhesion of the first print, thus shortening the pre-print rotation time and shortening the FPOT. In embodiment 1, compared to the comparative example, the time it takes for the film edge temperature to become approximately the same as the center temperature is shortened, and the pre-print rotation time can be shortened, so the FPOT is approximately 8 The time was reduced to seconds compared to the comparative example.

[0071] Furthermore, in a configuration where multiple triacs are connected in cascading order to drive and control multiple heat-generating blocks, if any of the upstream triacs are operating normally, the heat-generating blocks will not enter a runaway state, thus enhancing safety.

[0072] (Example 2) The image heating apparatus according to Embodiment 2 of the present invention will now be described. In Embodiment 2, the same components as in Embodiment 1 will not be described. Matters not specifically described here in Embodiment 2 are the same as in Embodiment 1.

[0073] Figure 5 shows an example of the heater 300 and control circuit in Embodiment 2 of the present invention. Figure 7 shows a schematic diagram of the equivalent circuit of the 7-segment resistor heating element of the heater in Embodiment 2.

[0074] In Example 2, the connection configuration of triacs 441 to 443 differs from that of Example 1. In Example 1, triacs 441 to 443 were connected in series (triac 442 was connected to triac 441 as a subordinate, and triac 443 was connected to triac 442 as a subordinate). In contrast, in Example 2, triacs 442 and 443 are each connected as subordinates to triac 441. In other words, in Example 1, triac 443 was connected as a subordinate to triac 442, whereas in Example 2, triac 443 is connected as a subordinate to triac 441.

[0075] Therefore, in Example 1, the heating block C to which the triac 443 is connected could not be energized except when both triacs 441 and 442 were energized ON. In contrast, in Example 2, heating block B and heating block C can be independently controlled for heating, regardless of whether the triac 442 is energized ON or OFF.

[0076] In other words, in Example 1, when heating block C is powered on and generating heat, both heating blocks A and B are powered on and generating heat. In contrast, in Example 2, when heating block C is powered on and generating heat, heating block A is always powered on and generating heat, but heating block B does not necessarily need to be powered on and generating heat. Therefore, compared to Example 1, Example 2 makes it possible to reduce the power fluctuations (so-called flicker) of the entire fixing device.

[0077] Except for the connection configuration of triacs 441-443 described above, the other configurations of the heater in Example 2 are the same as those of the heater in Example 1 shown in Figure 12. [Explanation of Symbols]

[0078] 200…Fusing device, 202…Fusing film (fixing material), 208…Pressure roller, 212…Thermistor, 213…Safety element (thermoswitch, thermal fuse), 300…Heater, 301…Conductor, 302…Resistive heating element, E…Electrode, 400…Control unit, 401…AC power supply, 420…CPU, 421…ZEROX circuit (zero-crossing detection circuit), 430, 440…Relay, 433…Transistor, 434…Resistor, 436…Latch unit, 437…Comparison unit, 441~443…Triac (semiconductor element), N…Fusing nip, P…Recording material

Claims

1. A heater having multiple heating elements arranged in the width direction of the recording material, perpendicular to the transport direction of the recording material, A control unit that controls the power supplied to the plurality of heating elements, Equipped with, An image heating device that heats an image formed on a recording material with the heat of the heater, The aforementioned multiple heating elements are A first group of heating elements is positioned in the width direction including the transport reference position of the recording material, A second heating element group comprising a plurality of heating elements arranged at different positions in the width direction relative to the first heating element group, and arranged on both sides of the first heating element group in the width direction, Includes, 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 with the first semiconductor element, It has, By controlling the first semiconductor element, the power supplied to the first heating element group is controlled. In an image heating device that controls the 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 capable of shutting off the power supply to the first heating element group in response to overheating of the heating elements included in the first heating element group, An image heating device characterized in that the maximum possible heat generation per unit length in the width direction of the second heating element group is greater than the maximum possible heat generation per unit length in the width direction of the first heating element group.

2. The system further includes temperature detection means for 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, respectively. The control unit, based on the temperature detected by the temperature detection means, controls the first heating element glue The image heating device according to claim 1, characterized in that it controls the power supplied to the power source and the power supplied to the second heating element group, respectively.

3. The aforementioned multiple heating elements are The system further includes a third group of heating elements positioned at different locations in the width direction relative to the first group of heating elements and the second group of heating elements, The control unit, The third semiconductor element is connected to the third heating element group and is connected in series with the first semiconductor element and the second semiconductor element. By controlling the first semiconductor element, the second semiconductor element, and the third semiconductor element, the power supplied to the third heating element group is controlled. The image heating device according to claim 1 or 2, characterized in that the maximum possible heat generation per unit length in the width direction of the third heating element group is greater than the maximum possible heat generation per unit length in the width direction of the second heating element group.

4. The aforementioned multiple heating elements are The system further includes a third group of heating elements positioned at different locations in the width direction relative to the first group of heating elements and the second group of heating elements, The control unit, The third semiconductor element is connected to the third heating element group and is connected in series with the first semiconductor element, By controlling the first semiconductor element and the third semiconductor element, the power supplied to the third heating element group is controlled. The image heating device according to claim 1 or 2, characterized in that the maximum possible heat generation per unit length in the width direction of the third heating element group is greater than the maximum possible heat generation per unit length in the width direction of the first heating element group.

5. The image heating device according to claim 3 or 4, characterized in that the third heating element group is composed of a plurality of heating elements arranged in the width direction on a side away from the transport reference position of the recording material relative to the second heating element group.

6. The image heating device according to any one of claims 1 to 5, characterized in that the safety element is a thermostat, a thermoswitch, or a thermal fuse.

7. A cylindrical film in which the heater is arranged on the inside, A roller that contacts the outer surface of the film, Furthermore, The heater and the roller form a nip between the film and the roller that holds the recording material. The image heating device according to any one of claims 1 to 6, characterized in that an image formed on a recording material held between the nip is heated by the heat of the heater.

8. An image forming unit that forms an image on the 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 characterized in that the fixing unit is an image heating device according to any one of claims 1 to 7.

Images