Image heating apparatus, image forming apparatus and control method of image forming apparatus

In an image heating apparatus, a region of a recording material, on which an image can be formed, is divided into a boundary region and a non-boundary region so as to correspond to a plurality of heating elements. The boundary region includes a boundary between one heating element out of the plurality of heating elements and an adjacent heating element thereof, and overlap with the one heating element and the adjacent heating element overlap in a predetermined range in the orthogonal direction. The non-boundary region overlaps with the one heating element in a range other than the boundary region. A control target temperature of a heating region that is heated by the one heating element is set to a higher temperature of a first temperature based on information corresponding to the boundary region, and a second temperature based on information corresponding to the non-boundary region.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to an image forming apparatus, such as a printer, a copier and facsimile, using an electrophotographic system or an electrostatic recording system. The present invention also relates to an image heating apparatus, such as a glossing apparatus to improve the gloss of a toner image, by reheating a toner image fixed to a fixing unit or a recording material in the image forming apparatus.

Description of the Related Art

In an image heating apparatus, such as a fixing unit and a glossing apparatus, used for an electrophotographic image forming apparatus (hereafter “image forming apparatus”), such as a copier and a printer, a system to selectively heat an image portion formed on a recording medium was proposed for power saving (Japanese Patent Application Publication H06-95540). According to this system, a plurality of divided heating regions are set in a direction corresponding to the longer direction of the heater (hereafter “longer direction”), which is orthogonal to the transporting direction of the recording material, and a plurality of heating elements which heats the heating regions respectively, are disposed in the longer direction. Then based on the image information on the image that is formed in each heating region, the heating value of the corresponding heating element is controlled. For example, the control temperature for each heating region, where no image exists (hereafter “non-image heating portion”), is set to be lower than the control temperature for a heating region where an image is included (hereafter “image heating portion”).

In the configuration having a plurality of heating regions which are divided in the longer direction, a temperature gradient is generated in the vicinity of a boundary position between a non-image heating portion and an image heating portion adjacent thereto, because of the difference between the control temperatures of these portions. This may generate a fixing failure and a drop in gloss in the vicinity of the edge of the image on the boundary position side.

To solve this problem, Japanese Patent Application Publication No. 2018-4938 discloses an image forming apparatus that changes the temperature of the image heating portion adjacent to the boundary position in accordance with the distance between the boundary position and the edge of the image in the longer direction. This content will be described with reference toFIG. 17. InFIGS. 17, 903-1, 903-2 and 903-3indicate the heating elements divided in the longer direction.910indicates an image where the image910exists only in the region of903-2.903-2is an image heating portion, and903-1and903-3are a non-image heating portion. The image forming apparatus calculates position information of the image, and controls the temperature of903-2, which is an image heating portion, in accordance with the distance (indicated by arrow y inFIG. 17) between the edge of the image of903-2and the boundary position between903-1and903-2, so as to implement both the fixing performance and power saving.

SUMMARY OF THE INVENTION

The control method of Japanese Patent Application Publication No. 2018-4938, however, has the following problem. This problem is related to the method of calculating the position information of the image.FIGS. 18A and 18Cindicate a portion of903-1and903-2inFIG. 17, omitting903-3.FIG. 18Aillustrates a state of the heating elements903-1and903-2, which are divided in the longer direction.FIG. 18Bindicates the position of the images, where image A is an image in the region of903-1, and image B is an image in the region of903-2.FIG. 18Cindicates the temperatures of the heating elements903-1and903-2.

In Japanese Patent Application Publication No. 2018-4938, the image A exists in the region of903-1and the image B exists in the region of903-2, as illustrated inFIG. 18B, hence both903-1and903-2are image heating portions. Therefore, the fixing temperature is the temperature indicated by the dotted line inFIG. 18C(e.g. 200 deg. for both903-1and903-2). However, if the image A is a low print percentage pattern that can be fixed at a temperature lower than the image B, for example, the temperature of903-1may be lower (e.g. 163 deg.).

As indicated by the solid line inFIG. 18C, if there is a temperature difference between903-1and903-2, the temperature changes in the vicinity of the boundary position between903-1and903-2, because of the influence of thermal diffusion. Therefore, even if the temperature of903-1is decreased (e.g. to 150 deg.), the fixing temperature (163 deg.) of the image A can be satisfied. By determining the temperature of903-1like this, in accordance with the distance from the edge of the image, based on a position which considers the temperature change in the vicinity of the boundary position between903-1and903-2, such as a position of the inflection point (e.g. position Z) inFIG. 18C, for example, power can be further saved. In the control method disclosed in Japanese Patent Application Publication No. 2018-4938, the temperature of903-1is determined in accordance with the distance from the edge of the image based on the dividing position of the heating elements of903-1and903-2. Hence the temperature of903-1may be increased in a case where the fixing performance can still be satisfied even if the temperature of903-1is decreased, hence more consideration is required for further power saving.

It is an object of the present invention to provide a technique that implements a further power supply saving effect in a configuration where heating control is performed for a plurality of heating regions independently by a plurality of heating elements disposed in the longer direction, while preventing the generation of a fixing failure and a drop in gloss in a vicinity of the edges of the image.

To achieve the above object, an image heating apparatus that heats an image formed on a recording material according to the present invention includes:

a heater including a plurality of heating elements which are arranged in a direction orthogonal to a transporting direction of a recording material;

a control portion capable of individually controlling power to be supplied to the plurality of heating elements so as to individually control the temperature of a plurality of heating regions which are heated by the plurality of heating elements; and

an acquisition portion that acquires information on an image formed on a recording material, wherein

the control portion

divides a region of a recording material, on which an image is formable, into a boundary region and a non-boundary region which are regions divided in a direction orthogonal to the transporting direction so as to correspond to the plurality of heating elements,

the boundary region is a region which includes a boundary between one heating element, out of the plurality of heating elements, and an adjacent heating element thereof and overlap with the one heating element and the adjacent heating element by a predetermined range in the direction orthogonal to the transporting direction, and

the non-boundary region is a region that overlaps with the one heating element in a range other than the boundary region, wherein

a control target temperature of a heating region that is heated by the one heating element is set to a higher temperature of a first temperature based on information corresponding to the boundary region out of the image information, and a second temperature based on information corresponding to the non-boundary region out of the image information.

To achieve the above object, an image forming apparatus according to the present invention includes:

an image forming portion that forms an image on a recording material; and

a fixing portion that fixes an image formed on a recording material to the recording material, wherein

the fixing portion is the image heating apparatus according to the present invention.

To achieve the above object, in a control method of an image heating apparatus that heats an image formed on a recording material according to the present invention includes:

a heater including a plurality of heating elements which are arranged in a direction orthogonal to a transporting direction of a recording material;

a control portion capable of individually controlling power to be supplied to the plurality of heating elements so as to individually control temperatures of a plurality of heating regions which are heated by the plurality of heating elements; and

an acquisition portion that acquires information on an image formed on a recording material, the control method comprising:

a first step where a region of a recording material, on which an image is formable, is divided into a boundary region and a non-boundary region which are regions divided in a direction orthogonal to the transporting direction so as to correspond to the plurality of heating elements, the boundary region is a region which includes a boundary between one heating element, out of the plurality of heating elements, and an adjacent heating element thereof and overlap with the one heating element and the adjacent heating element by a predetermined range in the direction orthogonal to the transporting direction, and the non-boundary region is a region that overlaps with the one heating element in a range other than the boundary region, and a first temperature based on information corresponding to the boundary region out of the image information, and a second temperature based on information corresponding to the non-boundary region out of the image information are acquired; and

a second step where the control target temperature of a heating region that is heated by the one heating element is set to be a higher temperature of the first temperature and the second temperature.

According to the present invention, a further power saving effect is implemented in a configuration where heating control is performed for a plurality of heating regions independently by a plurality of heating elements disposed in the longer direction, while preventing the generation of a fixing failure and a drop in gloss in a vicinity of the edges of the image.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, a description will be given, with reference to the drawings, of embodiments (examples) of the present invention. However, the sizes, materials, shapes, their relative arrangements, or the like of constituents described in the embodiments may be appropriately changed according to the configurations, various conditions, or the like of apparatuses to which the invention is applied. Therefore, the sizes, materials, shapes, their relative arrangements, or the like of the constituents described in the embodiments do not intend to limit the scope of the invention to the following embodiments.

1. Configuration of Image Forming Apparatus

FIG. 1is a configuration diagram depicting an example of an electrophotographic type image forming apparatus according to an embodiment of the present invention. Image forming apparatuses to which the present invention can be applied are a copier and a printer that uses an electrophotographic system or electrostatic recording system, and a case of applying the present invention to a laser printer will be described here.

The image forming apparatus100includes a video controller120and a control unit (control portion)113. The video controller120receives and processes image information and print instructions which are sent from such an external apparatus as a personal computer, as an acquisition portion that acquires information on an image to be formed on a recording material. The control unit113is connected with the video controller120, and controls each component constituting the image forming apparatus100, in accordance with the instruction from the video controller120. When the video controller120receives a print instruction from the external apparatus, the following operation to form the image is executed.

The image forming apparatus100feeds a recording material P using a feed roller102and transports the recording material P toward an intermediate transfer member103. Each photosensitive drum104is rotary-driven counterclockwise by the power of a drive motor (not illustrated) at a predetermined speed and is uniformly charged by a primary charging device105during this rotation process. A laser beam, which was modulated corresponding to an image signal, is outputted from a laser beam scanner106, and selectively scans and exposes the photosensitive drum104so as to form an electrostatic latent image.107indicates a developing device and visualizes the electrostatic latent image as a toner image (developer image) by attaching powder toner, which is a developer, to the electrostatic latent image. The toner image formed on the photosensitive drum104is primarily transferred onto an intermediate transfer member103which rotates in contact with the photosensitive drum104.

The photosensitive drum104, the primary charging device105, the laser beam scanner106and the developing device107are disposed for four colors (cyan (C), magenta (M), yellow (Y) and black (K)) respectively. Four colors of toner images are transferred on the intermediate transfer member103sequentially so as to be superimposed by the same procedure. The toner images transferred onto the intermediate transfer member103are secondarily transferred onto the recording material P by a secondary transfer portion which is constituted of the intermediate transfer member103and a transfer roller108, using the transfer bias applied to the transfer roller108. The configuration related to forming an unfixed image on the recording material P corresponds to the image forming portion according to the present invention. The toner image is then fixed by a fixing apparatus (image heating apparatus)200, which is a fixing portion (image fixing portion) that performs heating and pressing of the recording material P, and the recording material P is discharged from the apparatus as an image forming matter.

The image forming apparatus100of Embodiment 1 supports a plurality of recording material sizes and can print images on various sizes of recording materials which are set in a paper feeding cassette11. The types of recoding materials are, for example, Letter size (about 216 mm×279 mm), Legal size (about 216 mm×356 mm), A4 size (210 mm×297 mm), and Executive size (about 184 mm×267 mm). B5 size (182 mm×257 mm) and A5 size (148 mm×210 mm) are also supported. Irregular sized paper, including DL envelope (110 mm×220 mm) and COM10 envelope (about 105 mm×241 mm) can also be printed. The image forming apparatus100of Embodiment 1 is a laser printer which basically feeds the recording material in the vertical direction (transports the recording material so that the longer side of the recording material is parallel with the transporting direction). The largest (widest) size of the widths of the standard size recording materials (widths of recording materials specified in catalog) that this apparatus supports is about a 216 mm width of Letter size and Legal size paper.

The control unit113manages the transporting state of the recording material P using a transport sensor114, a resist sensor115, a prefixing sensor116, and a fixed paper discharge sensor117, disposed on the transport path of the recording material P. The control unit113also includes a storage portion that stores a temperature control program and a temperature control table of the fixing apparatus200. Using the later mentioned method, the control unit113controls the temperature of the fixing apparatus200based on the image information received from the video controller120. A control circuit400, which is a heater driving unit connected to the commercial AC power supply401, supplies power to the fixing apparatus200.

2. Configuration of Fixing Apparatus (Image Heating Apparatus)

FIG. 2is a schematic cross-sectional view of the fixing apparatus200according to Embodiment 1. The fixing apparatus200includes: a fixing film202, which is an endless belt; a heater300which contacts an inner surface of the fixing film202; a pressure roller208which forms a fixing nip portion N with a heater300via the fixing film202; and a metal stay204.

The fixing film202is a flexible cylindrical multilayer heat resistant film, of which base layer can be a 50 to 100 μm thick heat resistant resin (e.g. polyimide), or a 20 to 50 μm thick metal (e.g. stainless steel). On the surface of the fixing film202, a release layer is disposed to prevent the attachment of toner and to ensure separation from the recording material P. The release layer is a heat resistant resin which excels in releasability, such as a 10 to 50 μm thick tetra fluoroethylene—perfluoro alkyl vinyl ether copolymer (PFA). In the case of a fixing film that is used for an apparatus to form color images, a heat resistant rubber (e.g. silicon rubber), of which thickness is about 100 to 400 μm and thermal conductivity is about 0.2 to 3.0 W/m·K, may be disposed as an elastic layer between the base layer and the release layer so as to improve image quality. In Embodiment 1, in terms of thermal response, image quality and durability, polyimide, of which thickness is 60 μm, is used for the base layer, silicon rubber, of which thickness is 300 μm and thermal conductivity is 1.6 W/m·K, is used for the elastic layer, and PFA, of which thickness is 30 μm, is used for the release layer.

The pressure roller208includes a core metal209made of iron, aluminum or the like, and an elastic layer210made of silicon rubber or the like. The heater300is held by a heater holding member201made of heat resistant resin and heats the fixing film202. The heater holding member201also includes a guide function which guides the rotation of the fixing film202. The metal stay204receives pressing force from an energizing member (not illustrated), and energizes the heater holding member201toward the pressure roller208. The pressure roller208receives power from the motor30and rotates in the arrow R1direction. By the rotation of the pressure roller208, the fixing film202rotates in the arrow R2direction accordingly. In the fixing nip portion N, the recording material P is held and transported while receiving heat of the fixing film202, whereby the unfixed toner image on the recording material P is fixed.

The heater300is a heater in which heating resistors, which are heating elements disposed on a ceramic substrate305, heat up by energization. The heater300includes a surface protective layer308which contacts the inner surface of the fixing film202, and a surface protective layer307which is disposed on the opposite side (hereafter “back surface side”) of the side where the surface protective layer308is disposed on the substrate305(hereafter “sliding surface side”). On the back surface side of the heater300, electrodes to supply power (electrode E4is indicated here as a representative) are disposed. C4is an electric contact that contacts with the electrode E4, and supplies power to the electrode via this electric contact. The heater300will be described in detail later. A safety element212(e.g. a thermo switch, a thermal fuse), which is activated by overheating of the heater300and shuts the power to be supplied to the heater300OFF, directly contacts the heater300on the back surface side of the heater300, or indirectly contacts the heater300via the heater holding member201.

3. Configuration of Heater

FIG. 3AtoFIG. 3Care diagrams depicting the configuration of the heater300according to Embodiment 1.

FIG. 3Ais a cross-sectional view around the transport reference position X indicated inFIG. 3B. The definition of the transport reference position X is a reference position to transport the recording material P. In Embodiment 1, the recording material P is transported such that the center portion thereof passes through the transport reference position X. In the case of the image forming apparatus according to Embodiment 1, the recording material is transported such that the center portion of the recording material P in the width direction (direction orthogonal to the transporting direction) passes through the transport reference position X. The heater300has a five-layer structure constituted of: the substrate305, two layers on one side (back surface) of the substrate305(back surface layers1and2), and two layers on the other side (sliding surface) of the substrate305(sliding surface layers1and2).

The heater300includes first conductors301(301a,301b) which are disposed on the substrate305on the back surface layer side, along the longer direction of the heater300. The heater300also includes second conductors303(303-4is disposed near the transport reference position X) which are disposed on the substrate305in the longer direction of the heater300, at positions which are different from the first conductors301in the shorter direction (direction orthogonal to the longer direction) of the heater300. The first conductors301are divided into conductors301awhich are disposed on the upstream side in the transporting direction of the recording material P, and conductors301bwhich are disposed on the downstream side thereof. Further, the heater300includes a heating resistor302, each of which is disposed between the first conductor301and the second conductor303, and heats up by power that is supplied via the first conductor301and the second conductor303.

The heating resistors302are divided into heating resistors302a(302a-4is disposed near the transport reference position X) which are disposed on the upstream side in the transporting direction of the recording material P, and heating resistors302b(302b-4is disposed near the transport reference position X) which are disposed on the downstream side thereof. On the back surface layer2of the heater300, an insulating protective layer307(glass in Embodiment 1), that covers the heating resistors302, the first conductors301and the second conductors303(303-4is disposed near the transport reference position X), is disposed so as to avoid electrode portions (E4is disposed near the transport reference position X).

FIG. 3Bis a plan view of each layer of the heater300. On the back surface layer1of the heater300, a plurality of heating blocks (each heating block is constituted of a set of the first conductor301, the second conductor303and the heating resistor302) are disposed in the longer direction of the heater300. The heater300of Embodiment 1 includes a total of seven heating blocks HB1to HB7in the longer direction of the heater300.

The heating blocks HB1to HB7are constituted of heating resistors302a-1to302a-7and the heating resistors302b-1to302b-7, which are formed to be symmetric with respect to the shorter direction of the heater300respectively. The first conductor301is constituted of a conductor301awhich is connected with the heating resistors (302a-1to302a-7) and the conductor301bwhich is connected with the heating resistors (302b-1to302b-7). In the same manner, the second conductor303is divided into seven (conductors303-1to303-7) in order to support seven heating blocks HB1to HB7.

In Embodiment 1, the heating block HB4has a 110 mm width and is used to print DL envelopes and COM10envelopes. The heating blocks HB3to HB5have a 148 mm width and are used to print A5 size, the heating blocks HB2to HB6have a 182 mm width and are used to print B5 size, and the heating blocks HB1to HB7have a 220 mm width and are used to print Letter, Legal and A4 size. In this way, the seven heating blocks HB1to HB7are divided based on the recording material size supported by the image forming apparatus100of Embodiment 1.

Electrodes E1to E7, E8-1and E8-2are used for connecting with electric contacts C1to C7, C8-1and C8-2, which are used to supply power from a later mentioned control circuit400of the heater300respectively. The electrodes E1to E7are electrodes used to supply power to the heating blocks HB1to HB7via the conductors303-1to303-7respectively. The electrodes E8-1and E8-2are electrodes used to connect to a common electric contact, which is used for supplying power to the seven heating blocks HB1to HB7respectively, via the conductor301aand the conductor301b.

In Embodiment 1, the electrodes E8-1and E8-2are disposed on both edges in the longer direction respectively, but only the electrode E8-1may be disposed on one edge (that is, the electrode E8-2is not disposed), or each electrode may be disposed on the upstream and downstream in the recording material transporting direction respectively.

The surface protective layer307on the back surface layer2of the heater300is formed so that the electrodes E1to E7, E8-1and E8-2are exposed. Thereby the electric contacts C1to C7, C8-1and C8-2can be connected to each electrode from the back surface layer side of the heater300, and the heater300can supply power from the back surface layer side. Power to be supplied to at least one heating block of the heating blocks and power to be supplied to the other heating blocks can be controlled independently.

On the sliding surface layer1on the side of the sliding surface (surface that contacts the fixing film) of the heater300, thermistors T1-1to T1-4and thermistors T2-5to T2-7are disposed to detect the temperature of each heating block HB1to HB7of the heater300. Each of the thermistors T1-1to T1-4and the thermistors T2-5to T2-7is made of material having PTC characteristics or NTC characteristics (NTC characteristics in the case of Embodiment 1), which is thinly formed on a substrate. Since each of the heating blocks HB1to HB7includes a thermistor, the temperatures of all the heating blocks can be detected by detecting the resistance value of each thermistor.

In order to energize the four thermistors T1-1to T1-4, conductors ET1-1to ET1-4for detecting the resistance values of the thermistors, and a common conductor EG1of the thermistors, are disposed. By a set of these conductors and the thermistors T1-1to T1-4, a thermistor block TB1is formed. In the same manner, in order to energize the three thermistors T2-5to T2-7, conductors ET2-5to ET2-7for detecting the resistance values of the thermistors, and a common conductor EG2of the thermistors, are disposed. By a set of these conductors and the thermistors T2-5to T2-7, a thermistor block TB2is formed.

On the sliding surface layer2on the side of the sliding surface (surface that contacts the fixing film) of the heater300, a surface protective layer308having sliding characteristics (glass in the case of Embodiment 1) is disposed. The surface protective layer308is formed avoiding both edges of the heater300in order to dispose electric contacts for the conductors ET1-1to ET1-4and ET2-5to ET2-7for detecting the resistance values of the thermistors and the common conductors EG1and EG2of the thermistors. The surface protective layer308is disposed at least on a region sliding with the film202on the surface of the heater300facing the film202, avoiding both edges of the heater300.

As illustrated inFIG. 3C, holes to connect the electrodes E1to E7, E8-1and E8-2and the electric contacts C1to C7, C8-1and C8-2are disposed on the surface of a heater holding member201facing the heater300. Between the stay204and the heater holding member201, the above mentioned safety element212and the electric contacts C1to C7, C8-1and C8-2are disposed. The electric contacts C1to C7, C8-1and C8-2, which connect with the electrodes E1to E7, E8-1and E8-2, are electrically connected to the respective electrode portions of the heater by such a method as energizing by a spring or by welding. Each electric contact is connected to the later mentioned control circuit400of the heater300via such conductive materials as a cable and a thin metal plate, which is disposed between the stay204and the heater holding member201. The electric contacts disposed in the conductors ET1-1to ET1-4and ET2-5and ET2-7for detecting the resistance values of the thermistors, and the electric contacts disposed in the common conductors EG1and EG2of the thermistors, are also connected to the later mentioned control circuit400.

4. Configuration of Heater Control Circuit

FIG. 4is a circuit diagram of the control circuit400of the heater300according to Embodiment 1.401indicates a commercial AC power supply which is connected to the image forming apparatus100. Power of the heater300is controlled by the ON/OFF of a triac411to a triac417. The triacs411to417operate in accordance with FUSER1to FUSER7signals from a CPU420respectively. The drive circuits of the triacs411to417are omitted. The control circuit400of the heater300has such a circuit configuration that the seven heating blocks HB1to HB7can be independently controlled by the seven triacs411to417. A zero cross detection unit421is a circuit to detect a zero cross of the AC power supply401, and outputs a ZEROX signal to the CPU420. The ZEROX signal is used for detecting the timings to control the phases and wave numbers of the triacs411to417.

The temperature detection method of the heater300will be described. For the temperatures detected by the thermistors T1-1to T1-4of the thermistor block TB1, divided voltages using the thermistors T1-1to T1-4and the resistors451to454are detected by the CPU420as Th1-1to Th1-4signals. In the same manner, for the temperatures detected by the thermistors T2-5to T2-7of the thermistor block TB2, divided voltages using the thermistors T2-5to T2-7and the resistors465to467are detected by the CPU420as the Th2-5to Th2-7signals. In the internal processing of the CPU420, power to be supplied is calculated based on the difference between the currently deleted control target temperature of each heating block (each heating region heated by each heating block), and the temperature of the thermistor. For example, the power to be supplied is calculated by the PI control. Further, the power to be supplied is converted into a corresponding control level of the phase angle (phase control) and the wave number (wave number control), and the triacs411to417are controlled under these conditions.

A relay430and a relay440are used to interrupt power to the heater300in the case when the heater300overheats due to a failure. The circuit operation of the relay430and the relay440will be described. When a RLON signal becomes High state, the transistor433turns ON, current is supplied from the power supply voltage Vcc to the secondary side coil of the relay430, and the primary side contact of the relay430turns ON. When the RLON signal becomes Low state, the transistor433turns OFF, the current that is supplied from the power supply voltage Vcc to the secondary side coil of the relay430is interrupted, and the primary side contact of the relay430turns OFF. In the same manner, when the RLON signal becomes High state, the transistor443is turned ON, current is supplied from the power supply voltage Vcc to the secondary side coil of the relay440, and the primary side contact of the relay440turns ON. When the RLON signal becomes Low state, the transistor443is turned OFF, the current that is supplied from the power supply voltage Vcc to the secondary side coil of the relay440is interrupted, and the primary side contact of the relay440turns OFF.

The operation of the safety circuit using the relay430and the relay440will be described. When a temperature detected by any one of the thermistors Th1-1to Th1-4exceeds a predetermined value which is set for each thermistor, a comparison unit431activates a latch unit432, and the latch unit432latches an RLOFF1signal in the Low state. When the RLOFF1signal becomes the Low state, even if the CPU420sets the RLON signal to the High state, the relay430can be kept in the OFF state (safe state) since the transistor443is kept in the OFF state. In the non-latch state, the latch unit432allows the RLOFF1signal to be outputted in the open state. In the same manner, when a temperature detected by any one of the thermistors Th2-5to Th2-7exceeds a predetermined value which is set for each thermistor, a comparison unit441activates a latch unit442, and the latch unit442latches an RLOFF2signal in the Low state. When the RLOFF2signal becomes the Low state, even if the CPU420sets the RLON signal to the High state, the relay440can be kept in the OFF state (safe state) since the transistor433is kept in the OFF state. In this case as well, in the non-latch state, the latch unit442allows the RLOFF2signal to be outputted in the open state.

5. Image Information

Image data from an external apparatus, such as a host computer, is received by the video controller120of the image forming apparatus where image processing is performed. A pixel number of the image forming apparatus of Embodiment 1 is 600 dpi, and the video controller120creates a bit map data (image density data for each CMYK color) accordingly. The video controller120sends the later mentioned three types of image information acquired by the image processing (image information A, image information B, image information C) to the control unit113.

The image information A is image information related to the image density in a region of the heating block, excluding the vicinity of the boundary position. The image information B is image information related to the image density in the vicinity of the boundary position of the heating block. The image information C is image information related to the position of the image in the vicinity of the boundary position of the heating block.

Based on the image information A, image information B and image information C, the control unit113individually controls power supplied to the seven heating blocks HB1to HB7(HBi, i=1 to 7) of the heater300.

The image information A, the image information B and the image information C will be described in detail.

Image Information A

The video controller120analyzes the image density of each color acquired from the CMYK image data received from the host computer using a 1 mm mesh size and calculates the toner amount conversion value for each 1 mm mesh by converting the image density value into a toner amount. As illustrated inFIG. 5, the maximum toner amount conversion value among the toner amount conversion values calculated in each region of A1to A7(Ai, i=1 to 7), is called image information A. A is a region determined by dividing an image formable region of the recording material (image region constituted of an image portion and non-image portion) in the longer direction so as to correspond to each heating block HBi, and is a region overlapping with each heating block HBi(non-boundary region), in a range excluding the later mentioned boundary region. A is a region slightly narrower than each heating block HBiin the longer direction. For example, as illustrated in A4ofFIG. 5, both edges of the region of A4in the longer direction are 4 mm shorter respectively, compared with the region of HB4. The edges of the regions Aiother than A4in the longer direction are also 4 mm shorter respectively, compared with the region of HBi. The reason why both edges in the longer direction are 4 mm shorter like this is to consider preventing the influence of a temperature gradient caused by the difference of the control temperature in the vicinity of the boundary position of the heating block HBi.

A method of calculating the maximum toner amount conversion value of the image information A will be described. From the image data converted into CMYK image data, d(C), d(M), d(Y) and d(K), which are the image density of each dot of each C, M, Y and K color are acquired, and the total value thereof d (CMYK) is calculated. This calculation is performed for all the dots in each region (A1to A7), and these values are converted into the toner amount conversion values. In Embodiment 1, the temperature of the heating block HBiis constant (unchanged) within one page. Therefore, the image information Aiis the maximum value of the toner amount conversion values in one page calculated within each region.

Here the image information in the video controller120is an 8-bit signal, and the image density d(C), d(M), d(Y) and d(K) for each color of the toner is expressed in a range of the minimum density 00h to the maximum density FFh. The total value thereof, d (CMYK), is a 2 byte 8-bit signal. d(CMYK) is a total value of a plurality of toner colors, and the toner amount conversion value may exceed 100%.

Image Information B

As illustrated inFIG. 5, the image information B is information on a vicinity of the boundary position of the heating block HBi, specifically a boundary region that includes a boundary between one heating block HB and an adjacent heating block HB thereof, out of the heating blocks HBi, and that overlaps with these blocks in a predetermined range in the longer direction. This boundary region is disposed to not overlap with the region of Ai. The maximum toner amount conversion values calculated in this boundary region are collectively called the image information B. The method of calculating the maximum toner amount conversion values of the image information B is the same as the above mentioned method of calculating the image information A.

As illustrated inFIG. 5, the image information B on the right side of the heating block HBiis BRi(i=1 to 7), and the image information B on the left side thereof is BLi(i=1 to 7). BLi+1and BRiare exactly the same information, but to simplify description, BRiis used to indicate the image information B on the right side of the heating block HBi, and BLi+1is used to indicate the image information B on the left side of the heating block HBi.

Image Information C

The image information C indicates the edge positions of the image in the same boundary region as in the case of the image information B, that is, the distance from the non-boundary region to the image portion included in the boundary region in the longer direction. Out of a plurality of boundary regions that are formed corresponding to a plurality of heating blocks HB, the boundary regions formed on the edges in the longer direction (BL1, BR7) have one adjacent non-boundary region respectively (A1, A7) where there is one image information C. In the other boundary regions (BL2to BL7, BR1to BR6), a non-image region adjoins on one side and the other side in the longer direction respectively, hence there are two image information C. InFIG. 5, BL1, BR3(BL4), BR4(BL5) and BR7are enlarged and indicated as examples to describe the image information C.

As illustrated inFIG. 5, the video controller120calculates the image distance, such as the image distance from the right side boundary of BL1is CL1, the image distance from the left side boundary of BR3is CR3, the image distance from the left side boundary of BL4is CL4, and the image distance from the boundary of BR7is CR7. The video controller120also calculates the image distance as the image information C for the other regions that are not illustrated inFIG. 5as well, using the same method. If a plurality of images exist in the region, the distance of an image closest to the boundary is calculated as the image information C, as indicated in CR4and CL5inFIG. 5.

In Embodiment 1, the temperature of the heating block HB, is constant within the page. Therefore, the image information CRiand the image information CLiindicate the minimum distance in the page.

6. Method of Determining Control Temperature

The method of the control unit113, determining the control temperature Ti(i=1 to 7) of the seven heating blocks HBibased on the image information A, image information B and image information C, will be described.FIG. 6is a conceptual diagram of the process of determining the control temperature Ti. For the control temperature Ti, the maximum temperature of three types of required temperatures (TAi, TRi, TLi) is set.

Method of Determining TAi

TAiis a temperature (second temperature) that is required to ensure fixing performance is an area other than the vicinity of the boundary of the heating block HBi. As illustrated inFIG. 6, TAiis determined from the image information Ai.

TAiwill be described with reference toFIGS. 7A and 7B.FIG. 7Ais a diagram of a portion related to the image information A extracted fromFIG. 5.FIG. 7Bis a graph depicting the relationship between the image information Aiand TAi. The image information Aiis a maximum toner amount conversion value in the regions indicated inFIG. 7A, and in Embodiment 1, the temperature must be linearly increased as this value is greater.FIG. 7Bindicates this state.

In the image forming apparatus of Embodiment 1, the toner amount on the recording material P is adjusted so that 1.15 mg/cm2(corresponds to 230% in the case of the toner amount conversion value) is the upper limit. In Embodiment 1, the heat amount required for melting the toner increases as the image density on the recording material P is higher and the toner amount is higher, hence the control temperature must be increased more. As indicated inFIG. 7B, according to Embodiment 1, the temperature of HBimust be 210 deg. if Ai=230% and be 180 deg. if Ai=115%.

Method of Determining TRi, TLi

TRiis a temperature required to ensure the fixing performance in the vicinity of the right side boundary of the heating block HB, (first temperature). As indicated inFIG. 6, TRiis determined based on the image information BRiand the image information CRi.

TRiwill be described with reference toFIGS. 8A to 8C.FIG. 8Ais a diagram for describing the image information B and the image information C, which are image information on the vicinity of the boundary of the heating block HB, and the heating block HBi+1. The contents of the image information B and the image information C are as described inFIG. 5. The image information C is image information in a region that is 8 mm in the longer direction, but for description, the image information C is enlarged in the longer direction here. InFIG. 8A, there are four images, but the distance of an image that is closes to the boundary portion is regarded as the image information C, hence the image distance from the left boundary portion of BRiis CRi, and the image distance from the right boundary portion of BL1+1(BR) is CLi+1.

FIG. 8Bis a graph depicting the image information BRi, and the relationship between the image information CRiand TRi. The 8 mm of the abscissa of the graph and the 8 mm of the image information C in the longer direction illustrated inFIG. 8Aare expressed with a same scale factor. The image information BRiis the maximum toner amount conversion value in the region indicated inFIG. 8A, and in Embodiment 1, the temperature of TRimust be higher as this value BRiis greater.FIG. 8Bis a case when BRi=230%, 150% and 80%, and if CRi=0 mm, that is, if the image exists to the left edge of the region of BRi, TRibecomes 210 deg., 190 deg. and 170 deg. respectively. InFIG. 8B, only three levels of BRiare indicated, but actually a number of BRivalues that are required (230levels in 1% intervals in Embodiment 1) is stored as table values.

The temperature TRican be decreased as the image information CRi, which is a value on the abscissa inFIG. 8B, increases (as the image is more distant from the region of the heating block HBi). This is because in the heating block HBi+1, which is an adjacent zone, the temperature TLi+1, which is required to ensure the fixing performance in the vicinity of the left side boundary, is set.FIG. 8Cis a graph depicting the image information BLi+1and the relationship between the image information CLi+1and TLi+1, and has a form that is symmetrical with the graph inFIG. 8Bwith respect to the boundary between the heating blocks HBiand HBi+1. The graph inFIG. 8Bis determined considering the heat amount supplied from the adjacent heating blocks as well. For the left edge of HB1and the right edge of HB7, which have no adjacent heating blocks, table values higher than the temperature indicated inFIG. 8Bare set.

As described above, the control unit113determines TRiaccording to the relationship inFIG. 8B, based on the image information BRiand the image information CRi, TLi, which is a first temperature that is different from TRi, is also determined based on the image information BLiand the image information CLi.

Flow of Determining Control Temperature

FIG. 9is a flow to determine the control temperature Tiof the heating block HBi. When the control unit113receives image information from the video controller120and starts calculation of the control temperature (S601), TAiis determined (acquired) from the image information Aiin S602using the relationship inFIG. 7Bas a first step. If the heating blocks for which the control temperature is determined are HB2to HB6(Yes in S603), TRiis determined (acquired) from the image information BRiand the image information CRiin S604using the relationship inFIG. 8Bas a first step. In the same manner, TLiis determined (acquired) from the image information BLiand the image information CLiin S605as the first step. As the second step, TAi, TRiand TLiare compared in S606, and the highest temperature is determined as the control temperature Tiof HBi.

If the heating block for which the control temperature is determined is HB1(Yes in S603, Yes in S607), TL1is determined (acquired) from the image information BL1and the image information CL1in S608using the relationship inFIG. 8Cas the first step. As the second step, TA1and TL1are compared in S609, and the higher temperature is determined as the control temperature T1of HB1. In the case where the heating block is not HB1(No in S607) as well, flow is the same, hence description thereof is omitted. By the above flow, the control temperatures T1to T7of HB1to HB7are all determined, and the control unit113ends the calculation (S612).

7. Effect of Embodiment 1

Power consumption was compared between Embodiment 1 and Comparative Embodiment 1. The power consumption was measured under the following conditions, using the image forming apparatus100. The process speed of the image forming apparatus100according to Embodiment 1 is 210 mm/s, and in the case of Letter size, 40 pages per minute (ppm) of throughput can be implemented in continuous printing. The recording material used here is multipurpose paper (basis weight: 75 g/m2, Letter size) made by HP. The image is a 230% image as illustrated inFIG. 10, which is drawn extending from the region of HB4by 1 mm on both sides in the longer direction, and is uniformly drawn in the transporting direction excluding a 5 mm margin in the front end and the rear end respectively. By comparing the average power consumed by the fixing apparatus200when 100 sheets are continuously printed under the above conditions, the power saving effect of Embodiment 1 with respect to Comparative Embodiment 1 was measured. Table 1 indicates the comparison result.

Comparative Embodiment 1 is a case where the present invention is not used, and HB3and HB5are recognized as image portions. Therefore, the control temperature is set to a same temperature as HB4(210 deg.). In Embodiment 1, on the other hand, the temperature of the HB3is set such that the control temperature be 180 deg. because of the image information BR3=230%, and CR3=3 mm and the above relationship inFIG. 8B. For HB5as well, the control temperature is set to 180 deg. In Embodiment 1, the temperatures of the non-image heating portions, that is, the temperatures of HB1, HB2, HB6and HB7are set to 150 deg. Further, in Embodiment 1, the temperature of the heating block HBiis constant within one page. Hence the image information Aiand the image information Biare the maximum values of the toner amount conversion values within one page calculated in each region, and the image information CRiand the image information CLiare the minimum distances within the one page.

As a result of measuring power under the above conditions, the average power consumed by the fixing apparatus200of Embodiment 1 was 560 W. In the case of Comparative Embodiment 1, on the other hand, the average power was 587 W. Compared with Comparative Embodiment 1, Embodiment 1 can decrease the control temperatures HB3and HB5, therefore a 27 W of power saving effect is implemented.

As described above, in the image forming apparatus that adjusts the heating conditions of a plurality of heating blocks disposed in the longer direction in accordance with the image information, the power saving effect can be improved if Embodiment 1 is applied.

In Embodiment 1, the seven heating blocks are divided based on the recording material sizes supported by the imaging forming apparatus100but may be divided by a different method. A number of heating blocks is seven in the longer direction according to the above description, but a number of heating blocks may be any number that is at least two in the longer direction to apply the setting according to Embodiment 1.

In Embodiment 1, the temperature of the heating block HBiis constant within one page, but the control temperature may be changed if necessary, by updating the image information within one page if necessary. The image information is acquired in units of a 1 mm mesh size, but the mesh size may be changed if necessary.

In Embodiment 1, the recording material P is set so that the center portion of the recording material P passes through the transport reference position X during transporting, but as illustrated inFIG. 11, the recording material P may be set so that one edge of the recording material P passes through the transport reference position X.

The configurations of an image forming apparatus, an image heating apparatus, a heater, and a heater control circuit are the same as Embodiment 1, hence description thereof will be omitted. In Embodiment 2, the control temperature Tiof the heating block HBiis determined by a method different from Embodiment 1. In Embodiment 1, the control temperature Tiof each heating block HBiis determined using the image information A, the image information B, and the image information C. By this method, however, when more detailed information is acquired (e.g. a 1 mm mesh of Embodiment 1 is further divided), processing by the video controller120may not keep up since the information volume of the image is too large.

Image Information and Control Temperature of Embodiment 2

In many cases, an image that is normally outputted is an image that is drawn within a predetermined range of the recording material P, as illustrated inFIG. 12. InFIG. 12, HB3, HB4and HB5, which are disposed at the center portion in the longer direction, are image heating portions where a heating region, of which heating range overlaps with the image of the recording material, is heated. HB1, HB2, HB6and HB7, which are disposed on the edges in the longer direction, are non-image heating portions where a heating region, of which heating range does not overlap with the image of the recording material, is heated.

Further, in many cases, an image that is normally outputted is not an image where such image attributes as text and graphics do not coexist within one page. In this case, the maximum toner amount conversion value in each heating block is not so different from each other, hence the control temperature difference among the image heating portions is not so large. Therefore, a better power saving effect may be expected in some cases by decreasing the control temperature of the non-image heating portions, rather than a power saving effect implemented by determining the control temperatures of the image heating portions using the image information A, the image information B, and the image information C.

Therefore in Embodiment 2, in order to determine the control temperatures of non-image heating portions more accurately, the resolution of the image distance of the image information C related to the control temperatures is made even finer. The resolution is 1 mm in Embodiment 1 but is 0.1 mm in Embodiment 2. Accordingly, the information amount to determine the control temperatures of the image heating portions is decreased as follows. In Embodiment 1, the image information A is a 2 byte 8-bit signal, but in Embodiment 2, the image information A is a 1 byte 3-bit signal, and the maximum toner amount conversion value is expressed in 16 levels, as indicated in Table 2. The image information B and the image information C to determine the control temperatures of the image heating portions do not exist, and the control temperatures of the image heating portions are determined by the image information A alone.

As illustrated inFIG. 12, in Embodiment 2, the image information R and the image information L are used. The image information R is a distance from the right edge of the heating block HB7located as the right end position of the image in one page, and the image information L is a distance from the left edge of the heating block HB1located at the left end position of the image in the one page. As illustrated inFIG. 12, in Embodiment 2, an image in a region from the heating block HB3to the heating block HB5is drawn.

FIGS. 13A to 13Bare diagrams depicting determination of the control temperatures of the heating blocks HB6and HB7based on the image information R using the image inFIG. 12as an example. Further, the control temperatures of the heating blocks HB1and HB2are determined based on the image information L. The description of the determination of the control temperatures based on the image information L, however, will be omitted, since the procedure is the same as the case of the image information R.

FIG. 13Ais a diagram extracting a portion related to the image information B fromFIG. 5.FIG. 13BandFIG. 13Care enlarged views of the portion near the right edge of the image inFIG. 12.FIG. 13Bis a case when the right edge of the image, that is, the image information R, is not in a region of BR5which is in the vicinity of the boundary position between HB5and HB6, but inside the image heating portion HB5(Case1).FIG. 13Cis a case when the right edge of the image, that is, the image information R, is in a region of BR5which is in the vicinity of the boundary position between HB5and HB6(Case2).

In Case1inFIG. 13B, the control temperature 150 deg. is set for the heating blocks HB6and HB7as the non-image portion temperatures. The temperature of the heating block HB6can be decreased because the image is not in the vicinity of the boundary position between HB5and HB6, and the fixing performance in the right edge of the image can be ensured even if the temperature of HB6is not high. The temperatures of the heating blocks HB3, HB4and HB5, which are image heating portions, are determined by the relationship inFIG. 7Bbased on the image information A3, A4and A5, just like Embodiment 1. However, as mentioned above, the signal of the image information A has been compressed more than Embodiment 1, as mentioned above. Therefore, the control temperature of Case1has the distribution indicated in Case1inFIG. 14.

In Case2inFIG. 13C, the control temperature 150 deg. is set for the heating block HB7as the non-image portion temperature, which is the same as Case1. The temperature of the heating block HB6, on the other hand, is determined by the relationship inFIG. 7Bbased on the image information BL6and the image information CL6, just like Embodiment 1, in order to ensure the fixing performance in the right edge of the image in the vicinity of the boundary position with HB5. The resolution of the distance of the image CRi, however, is finer than Embodiment 1, as mentioned above. The control temperature of Case2has the distribution indicated in Case2inFIG. 14. In Case2, the control temperatures of HB2and HB6are higher than Case1, in order to ensure the fixing performance of the image in the vicinity of the boundary position with HB3or HB6.

Effect of Embodiment 2

Power consumption was compared among Embodiment 2, Comparative Embodiment 2, and Embodiment 1. The power consumption was measured under the same conditions as Embodiment 1, using the image forming apparatus100. The image of Embodiment 2 is a 230% image and a 185% image, as illustrated inFIG. 15, which are uniformly drawn in the transporting direction, excluding 5 mm margins in the front end and the rear end. By comparing the average power consumed by the fixing apparatus200when 100 sheets are continuously printed under the above conditions, the power saving effect of Embodiment 2 with respect to Comparative Embodiment 2 and Embodiment 1 was measured. Table 3 indicates the comparison result.

Comparative Embodiment 2 is a case where the present invention is not used, and HB2and HB6are recognized as image portions. Therefore, the control temperature of HB2is set to a same temperature as HB3(210 deg.), and the control temperature of HB6is set to a same temperature as HB5(199 deg.).

Just like the relationship inFIG. 7B,FIG. 16Aindicates that the control temperature is determined based on the image information Aiin the image heating portions of Embodiment 1 and Embodiment 2. In Embodiment 1, A5=185% and the control temperature of HB5is set to 199 deg., as indicated inFIG. 16A. In Embodiment 2, on the other hand, data is in 16 levels, as indicated in Table 2 above, hence A5=195% and the control temperature of HB5is set to 201 deg., as indicated inFIG. 16A.

Just like the relationship inFIG. 8B,FIG. 16Bindicates that the control temperature is determined based on the image information CRiin the non-image heating portions adjacent to the image heating portions of Embodiment 1 and Embodiment 2. InFIG. 16B, only the state when CRi=230% is indicated as a representative example. In Embodiment 1, the actual image position is CR2=2.8 mm, since the resolution of the distance of the image information CRiof Example 1 is 1 mm, but is regarded as CR2=2 mm. In Embodiment 1, the control temperature of HB2is set to 198 deg. based on the image information of BR2=185% and CR2=2 mm, and the relationship inFIG. 16B. In Embodiment 2, on the other hand, the control temperature of HB2is set to 191 deg. based on the image information of BR2=195% and CR2=2.8 mm, and the relationship inFIG. 16B. In the same manner, the control temperature of HB6in Embodiment 1 and in Embodiment 2 are also set.

As a result of measuring power under the above conditions, the average power consumed by the fixing apparatus200of Embodiment 2 was 609 W. On the other hand, the average power was 632 W in the case of Comparative Embodiment 2 and was 616 W in the case of Embodiment 1. Embodiment 2 can decrease the control temperatures of HB2and HB6than Comparative Embodiment 2 and Embodiment 1, although the temperature of HB5is slightly higher, and therefore a power saving effect is implemented.

As described above, in the image forming apparatus that adjusts the heating conditions of a plurality of heating blocks disposed in the longer direction in accordance with the image information, a power saving effect can be improved if Embodiment 2 is applied.

Configurations of the above embodiments may be combined as much as possible.

This application claims the benefit of Japanese Patent Application No. 2018-218910, filed on Nov. 22, 2018, which is hereby incorporated by reference herein in its entirety.