Patent Application
20160085189
The present invention relates to a heater for heating an image on a sheet and an image heating apparatus including the heater. The image heating apparatus is usable with an image forming apparatus such as a copying machine, a printer, a facsimile machine, a multifunction machine having a plurality of functions thereof or the like.
An image forming apparatus is known in which a toner image is formed on the sheet and is fixed on the sheet by heat and pressure in a fixing device (image heating apparatus). As for such a fixing device, a type of fixing device is proposed (Japanese Laid-open Patent Application (JP-A) Hei 6-250539) in these days in which a heat generating element (heater) is contacted to an inner surface of a thin flexible belt to apply heat to the belt. Such a fixing device is advantageous in that the structure has a low thermal capacity, and therefore, temperature rise for the fixing can be performed quickly.
JP-A Hei 6-250539 discloses a heater including a plurality of electrodes arranged in a longitudinal direction of a substrate so as to connect with heat generating elements extending along the longitudinal direction of the substrate. This is heat includes electroconductor lines extending along the longitudinal direction of the substrate in each of one end side and the other end side of the substrate with respect to a widthwise direction with the heat generating elements as a central portion. These heat generating elements are provided with a plurality of the branch portions with respect to a longitudinal direction of the substrate in order to be connected with a plurality of electrodes provided and arranged in the longitudinal direction of the substrate. Here, the electrodes connected with the electroconductor lines in one end side with respect to a widthwise direction of the substrate and the electrodes connected with the electroconductor lines with respect to the widthwise direction of the substrate are in an alternately arranged relationship with respect to the longitudinal direction of the substrate. For that reason, when a voltage is applied between two electroconductor lines in one end side with respect to the longitudinal direction of the substrate, a potential difference generates between the adjacent electrodes, so that an energized heat generating element generates heat.
The electroconductor lines thus used have a resistance not a little, so that the voltage applied between the electroconductor lines in one end side of the substrate lowers toward the other end side of the substrate. For that reason, the potential of each of the electrodes is a different value depending on a branch position of the electroconductor line connected with the electrode. Therefore, the heater for supplying electric power (energy) to the heat generating elements using the electroconductor lines described above is liable to have a heat generation amount lower in the other end side than in one end side of the longitudinal direction. In the case where the heat generation amount of the heater is different with respect to the longitudinal direction, there is a liability that image defect such as uneven glossiness is caused to generate during fixing of the image on a sheet.
Accordingly, the heater in which electroconductor lines extending from an end portion with respect to a longitudinal direction are branched and electric power is supplied to heat generating elements as disclosed in Japanese Laid-Open Patent Application Hei 6-250539 may desirably be that a temperature non-uniformity due to voltage drop by an electroconductor line resistance with respect to the longitudinal direction is suppressed.
A principal object of the present invention is to provide a heater with suppressed heat generation non-uniformity.
Another object of the present invention is to provide an image heating apparatus including the heater with suppressed lowering in lifetime
According to an aspect of the present invention, there is provided a heater usable with an image heating apparatus including an electric energy supplying portion provided with a first terminal and a second terminal, and an endless belt for heating an image on a sheet, wherein the heater is contactable to the belt to heat the belt, the heater comprising: a substrate; a plurality of electrode portions provided on the substrate and arranged with gaps in a longitudinal direction of the substrate; a plurality of electrical contact portions provided on the substrate and electrically connectable with the energy supplying portion; a plurality of heat generating portions provided between adjacent ones of the electrode portions so as to electrically connect between adjacent electrode portions, the heat generating portions being capable of generating heat by the electric power supply between adjacent electrode portions; and a plurality of electroconductive line portions provided on the substrate and connecting with the electrical contact portions and the electrode portions so that the electrode portions includes first group electrode portions which are connectable with the first terminal and second group electrode portions which are connectable with the second terminal, the first group electrode portions and the second group electrode portions being arranged alternately in the longitudinal direction; wherein the plurality of electroconductive line portions comprise, a main line portion provided on the substrate and extending from the electrical contact portions in the longitudinal direction, a first branch line portion provided on the substrate and branching from the main line portion so as to electrically connect with a first electrode portion of the first group electrode portions, and a second branch line portion provided on the substrate and branching from the main line portion so as to electrically connect with a second electrode portion of the first group electrode portions, wherein the second electrode portion is spaced from the electrical contact portions more than the first electrode portion in the longitudinal direction, and an electric resistance of the first branch line portion is larger than an electric resistance of the second branch line potion.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
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Embodiments of the present invention will be described in conjunction with the accompanying drawings. In this embodiment, the image forming apparatus is a laser beam printer using an electrophotographic process as an example. The laser beam printer will be simply called printer.
As shown in
The photosensitive drum 11 as an electrophotographic photosensitive member is rotated by a driving source (unshown) in the direction indicated by an arrow (counterclockwise direction in
A surface of the photosensitive drum 11 is electrically charged by the charger 12. Thereafter, the surface of the photosensitive drum 11 exposed to a laser beam in accordance with image information by the exposure device 13, so that an electrostatic latent image is formed. The electrostatic latent image is developed into a Bk toner image by the developing device 14. At this time, similar processes are carried out for the other colors. The toner image is transferred from the photosensitive drum 11 onto an intermediary transfer belt 31 by the primary transfer blade 17 sequentially (primary-transfer). The toner remaining on the photosensitive drum 11 after the primary-image transfer is removed by the cleaner 15. By this, the surface of the photosensitive drum 11 is cleaned so as to be prepared for the next image formation.
On the other hand, the sheet P contained in a feeding cassette 20 or placed on a multi-feeding tray 25 is picked up by a feeding mechanism (unshown) and fed to a pair of registration rollers 23. The sheet P is a member on which the image is formed. Specific examples of the sheet P is plain paper, thick sheet, resin material sheet, overhead projector film or the like. The pair of registration rollers 23 once stops the sheet P for correcting oblique feeding. The registration rollers 23 then feed the sheet P into between the intermediary transfer belt 31 and the secondary transfer roller 35 in timed relation with the toner image on the intermediary transfer belt 31. The roller 35 functions to transfer the color toner images from the belt 31 onto the sheet P. Thereafter, the sheet P is fed into the fixing device (image heating apparatus) 40. The fixing device 40 applies heat and pressure to the toner image T on the sheet P to fix the toner image on the sheet P.
The fixing device 40 will be described.
The fixing device 40 is an image heating apparatus for heating the image on the sheet by a belt unit 60 (unit 60). The unit 60 has a structure in which a flexible thin fixing belt 603 is heated by the heater 600 contacted to the inner surface of the belt 603. Therefore, the fixing device 40 can efficiently heat the fixing belt 603, so that the fixing device is excellent in rising performance during the fixing operation. As shown in
The unit 60 is a unit for heating and pressing an image on the sheet P. A longitudinal direction of the unit 60 is parallel with the longitudinal direction of the roller 70. The unit 60 comprises a heater 600, a heater holder 601, a support stay 602 and a belt 603.
The heater 600 is a member for heating the belt 603, slidably contacting with the inner surface of the belt 603. The heater 600 is pressed to the inside surface of the belt 603 toward the roller 70 so as to provide a desired nip width of the nip N. The dimensions of the heater 600 in this embodiment are 5-20 mm in the width (the dimension as measured in the up-down direction in
The belt 603 is a cylindrical (endless) belt (film) for heating the image on the sheet in the nip N. In this embodiment as the belt 603, a belt prepared by forming on a base material 603a, an elastic layer 603b and a parting layer 603c. Specifically, as the base material 603a, a cylindrical member which is 30 mm in outer diameter and 340 mm in length and 30 μm the thickness and which is formed of a nickel alloy is used. Further, on the base material 603a, as the elastic layer 603b, a silicone rubber layer having a thickness of 400 μm is formed, and on the elastic layer 603b, as a parting layer 603c, fluorine resin tube having a thickness of 20 μm is coated.
A heater holder 601 (holder 601) functions to hold the heater 600 in the state of urging the heater 600 toward the inner surface of the belt 603. The holder 601 has a semi-arcuate cross-sectional shape (the surface of
The support stay 602 is member for supporting the heater 600 by way of the holder 601. The support stay 602 is preferably made of a material which is not easily deformed even when a large load is applied thereto, and in this embodiment, it is made of SUS304 (stainless steel).
As shown in
Between the flange 411 and a pressing arm 414, an urging spring 415 is provided in a compressed state. With such a structure, an elastic force of the urging spring 415 is applied to the heater 600 through the flange 411 and the support stay 602. The fixing belt 603 is pressed against the pressing roller 70 at a predetermined urging force to form the nip N having a predetermined nip width. In this embodiment, the pressure is 156.8 N (16 kgf) at one end portion side and 313.6 N (32 kgf) in total.
A connector 700 is an electric energy supply member electrically connected with the heater 600 for applying a voltage to the heater 600. The connector 700 is detachably provided at one longitudinal end portion of the heater 600.
As shown in
The roller 70 in this embodiment includes a core metal 71 of stainless steel, an elastic layer 72 of silicone rubber foam, and a parting layer 73 of fluorine-containing resin tube. The roller 70 is 25 mm in outer diameter, and 330 mm in length.
As shown in
A themistor 630 shown in
The control circuit 100 is a circuit including a CPU operating for various controls, and a non-volatile medium such as a ROM. Programs are stored in the ROM, and the CPU reads and execute them to effect the various controls. The control circuit 100 is electrically connected with a voltage source 110 so as to control electric power supply (energization) from the voltage source 110.
The control circuit 100 uses the temperature information acquired from the themistor 630 for the electric power supply control for the voltage source 110. More particularly, the control circuit 100 controls the electric power supplied to the heater 600 on the basis of the output of the themistor 630. In this embodiment, a type in which the control circuit 100 carries out a wave number control of the output of the voltage source 110 to adjust an amount of heat generation of the heater 600 is used, so that when the toner image is fixed on the sheet, the heater 600 is maintained at a predetermined temperature.
The structure of the heater 600 used in the fixing device 40 will be described in detail. In
In the illustrations of the heat generation (energization) type shown in
When a voltage V is applied between the electroconductive path A and the electroconductive path B, a potential difference is generated between the adjacent branch paths. As a result, as indicated by arrows in (a) of
In the case that the electric power is supplied individually to the plurality of heat generating elements arranged in the longitudinal direction, it is preferable that the branch paths are disposed so that the directions of the electric current flow alternates between adjacent heat generating elements as described above. As another method of supplying the electric power to the plurality of heat generating elements arranged in the longitudinal direction, it would be considered to arrange the heat generating elements each connected with the branch paths having different polarities at the longitudinal ends thereof, in the longitudinal direction, and the electric power is supplied in the same direction along the longitudinal direction. However, with such an arrangement, two branch paths are required to be provided between adjacent heat generating elements, and therefore there is a liability of generation of short circuit between these branch paths. In addition, the number of required branch paths is large with the result of large non-heat generating portion between the heat generating elements. Therefore, it is preferable to arrange the heat generating elements and the branch paths such that a branch path is made common between adjacent heat generating elements. With such an arrangement, the liability of generation of the short circuit between the branch paths can be avoided, and a space between the branch paths can be eliminated.
In this embodiment, an electroconductive path 640 shown in
As shown in
The substrate 610 determines the dimensions and the configuration of the heater 600 and is contactable to the belt 603 along the longitudinal direction of the substrate 610. The material of the substrate 610 is a ceramic material such as alumina, aluminum nitride or the like, which has high heat resistivity, thermo-conductivity, electrical insulative property or the like. In this embodiment, the substrate is a plate member of alumina having a length (measured in the left-right direction in
On the substrate 610, the heat generating element 620 and the electroconductor pattern are formed by a screen printing method. In this embodiment, as a material for the electroconductor pattern, a low resistivity material such as a silver paste or an alloy paste of silver mixed with palladium in a small amount is used. As a material for the heat generating element 620, a silver-palladium alloy paste mixed to provide a desired resistance value is used. Incidentally, as another material for the heat generating element 620, it is possible to use ruthenium oxide.
Electrical contacts 645, 655, 665 electrically connected with the voltage source 110 are provided in one end portion side 610a of the substrate 610 with respect to the longitudinal direction. In addition, there are provided the heat generating element 620 and the branch paths (642, 652, 662, 672). The branch paths electrically connect the electroconductor paths 640, 650, 660, 670 with the associated heat generating elements 620, respectively. The heat generating element 620 and the electroconductor pattern are coated with the insulating coating layer of heat-resistant glass, and are electrically protected so as not to generation leakage and short circuit.
The heat generating element 620 (620a-620l) is a resistor capable of generating joule heat by electric power supply (energization). The heat generating element 620 is one heat generating element (member) extending in the longitudinal direction on the substrate 610. The heat generating element 620 in this embodiment has a width (measured in the widthwise direction of the substrate 610) of 3.0 mm, a thickness of 20 μm, and a longitudinal length is 320 mm, in which an entire region of the A4-sized sheet P (297 mm in width) can be heated. A total resistance of the heat generating element 620 is 10Ω.
On the heat generating element 620, seven common branch paths 642a-642g are laminated with regular intervals with respect to the longitudinal direction of the substrate 610. In other words, the heat generating element 620 is partitioned into six sections by the branch paths 642a-642g along the longitudinal direction. The length of each section of the heat generating element 620 is 53.3 mm. On central portions of the respective sections of the heat generating element 620, the six opposite branch paths 662a, 652 (652b-652e), 672 are laminated. In this manner, the heat generating element 620 is divided into 12 sub-sections 620a-620l as a plurality of heat generating elements each positioned between adjacent electrodes. A length of each sub-section is 26.7 mm. A resistance value of each sub-section is 120 Ω.
The resistivity of each of the branch paths 642, 652, 662, 672 is remarkably smaller than the resistivity of the heat generating element 620. For that reason, at a position where branch paths laminate (overlap with each other), the current flowing through the heat generating element 620 becomes small, so that a degree of the heat generation lowers. For that reason, when the width (longitudinal length) of the branch path is large, temperature non-uniformity generates with respect to the longitudinal direction of the heater 600 and the fixing belt 603. When the sheet P is subjected to the fixing process, due to the temperature non-uniformity of the fixing belt 603, there is a liability that glossiness of the image on the sheet P becomes non-uniform. This phenomenon results from a lowering in glossiness of the toner by failure in sufficient heating and melting of the toner on the sheet due to a lowering in temperature of the fixing belt 603 at a portion opposing the branch path. Therefore, as a result of study by the present inventors on this problem, it was turned out that non-uniformity of the glossiness is slight when the width of the branch path is 1.0 mm or less and is not generated when the width of the branch path is 0.5 mm or less. Accordingly, in this embodiment, an upper limit of the branch path is set at 0.5 mm.
The branch paths 642, 652, 662, 672 are a part of the above-described electroconductor pattern. The branch paths 642, 652, 662, 672 are provided along the widthwise direction of the substrate 610 so as to be perpendicular to the longitudinal direction of the heat generating element 620. The branch paths in this embodiment are formed of the same material and with the same width in the entire region thereof. The branch paths 642, 652, 662, 672 are partly provided on the substrate 610 and are partly provided on the heat generating element 620 so that the electroconductor paths 640, 650, 660, 670 described later are electrically connected with the heat generating element 620. In this embodiment, of the branch path, a portion having an overlapping positional relationship with the heat generating element is referred to as an electrode portion.
In this embodiment, of the branch paths connected with the heat generating element 620, odd-numbered branch paths from one longitudinal end of the heat generating element 620 are common branch paths 642, and even-numbered branch paths from the one longitudinal end of the heat generating element 620 are opposite branch paths 652, 662, 672.
That is, the common branch paths and the opposite branch paths are arranged alternately with a predetermined interval with respect to the longitudinal direction of the heat generating element 620.
In the above description, of the plurality of branch paths, the odd-numbered branch paths from the one longitudinal end of the heat generating element 620 and the common branch paths, and the even-numbered branch paths are the opposite branch paths, but the heater is not limited to this constitution. A similar effect can be obtained also in the case where of the plurality of branch paths, the even-numbered branch paths from the one longitudinal end of the heat generating element 620 are the common branch paths, and the odd-numbered branch paths are the opposite branch paths.
The branch path 642 is connected with a terminal 110a of the voltage source 110 in one end side via the electroconductor path 640 and the like described later. That is, the branch path 642 is connected with one terminal side of the voltage source 110.
The branch path 652 is connected with a terminal 110b of the voltage source 110 in the other end side via the electroconductor path 650 described later. The branch path 662 is connected with the other end side terminal 110b of the voltage source 110 via the electroconductor path 660 described later. The branch path 672 is connected with the other end side terminal 110b of the voltage source 110 via the electroconductor path 670 described later. That is, the branch paths 652, 662, 672 are connected with the other end side terminal of the voltage source 110.
The electroconductor paths 640, 650, 660, 670 are a part of the above-described electroconductor pattern, and are electric power supplying lines for connecting electrical contacts with the respective branch paths in order to supply the electric power to the heat generating element.
The electroconductor path 640 is formed along the longitudinal direction of the substrate 610 in one (widthwise) end side 610d of the substrate 610 with respect to the heat generating element 620. The electroconductor path 640 is connected with the branch paths 642 in one end side and is connected with the electrical contact 645 in the other end side. That is, the electroconductor path 640 extends from the electrical contact 645 along the longitudinal direction of the heater.
Similarly, the electroconductor paths 650, 660, 670 are formed along the longitudinal direction of the substrate 610 in the other (widthwise) end side 610e of the substrate 610 with respect to the heat generating element 620. The electroconductor path 640 is connected with the branch paths 652 (652b-652e) in one end side and is connected with the electrical contact 655 in the other end side. That is, the electroconductor path 650 extends from the electrical contact 655 along the longitudinal direction of the heater. Further, the electroconductor paths 660, 670 are connected with the branch paths 662a, 672f, respectively, and is connected with the electrical contact 665 in the other end side. That is, the electroconductor paths 660, 670 extends from the electrical contact 665 in the longitudinal direction of the heater. Here, the electroconductor paths and the branch paths function as an electroconductor line portion.
The electrical contacts 645, 655, 665 are provided in parallel with each other in one longitudinal end side so as to be positioned outside a region where the heater 600 contacts the fixing belt 603. Here, the electrical contact 645 functions as one electrical contact portion, and the electrical contacts 655, 665 function as the other electrical contact portion.
The electrical contacts 645, 655, 665 are in an exposed state that the electrical contacts are not coated with the insulating coating layer, and are electrically connectable with the connector 700. As described above, in the heater 600 in this embodiment, the voltage source 110 and the heat generating elements 620 are electrically connected with each other via the connector, the electrical contacts, the electroconductor paths and the branch paths.
The connector 700 used with the fixing device 40 will be described in detail.
As shown in
Similarly, the terminal 720 is a member for electrically connecting the electrical contact 665 with a switch C669 described later. The terminal 720 is connected with the switch C669 by a cable 722.
Similarly, the terminal 730 is a member for electrically connecting the electrical contact 655 with a switch B659 described later. The terminal 730 is connected with the switch B659 by a cable 732.
As shown in
In this embodiment, the connector 700 is mounted in the widthwise direction of the substrate 610, but this mounting method is not limiting to the present invention. For example, the structure may be such that the connector 700 is mounted in the longitudinal direction of the substrate.
An electric energy supply method to the heater 600 will be described.
The fixing device 40 of this embodiment is capable of changing a width of the heat generating region of the heater 600 by controlling the electric energy supply to the heater 600 depending on the width size of the sheet P. With such a structure, the heat can be efficiently supplied to the sheet P. In the fixing device 40 of this embodiment, the sheet P is fed with the center of the sheet P aligned with the center of the fixing device 40, and therefore, the heat generating region extend from the center portion. The electric energy supply to the heater 600 will be described in conjunction with the accompanying drawings.
First, the voltage source 110 is a circuit for supplying the electric power to the heater 600. In this embodiment, the commercial voltage source (AC voltage source) of 100V in effective value (single phase AC) is used. The voltage source 110 of this embodiment is provided with a voltage source contact 110a and a voltage source contact 110b having different electric potential. The voltage source 110 may be DC voltage source if it has a function of supplying the electric power to the heater 600.
The control circuit 100 is electrically connected with the switch A649, the switch B659, and the switch C669, respectively to control the switch A649, the switch B659, and the switch C669, respectively. The switch A649 is a switch (relay) provided between the voltage source contact 110a and the electrical contact 641, and connects or disconnects between the voltage source contact 110a and the electrical contact 641 depending on the instructions from the control circuit 100. The switch B659 is a switch provided between the voltage source contact 110b and the electrical contact 655, and connects or disconnects between the voltage source contact 110b and the electrical contact 655 depending on the instructions from the control circuit 100. Similarly, the switch C669 is a switch provided between the voltage source contact 110b and the electrical contact 665, and connects or disconnects between the voltage source contact 110b and the electrical contact 665 depending on the instructions from the control circuit 100.
When the control circuit 100 receives the execution instructions of a job, the control circuit 100 acquires the width size information of the sheet P to be subjected to the fixing process. In accordance with the width size information of the sheet P, turning ON/OFF of the switch A649, the switch B659, and the switch C669 is switched, so that the width size of the heat generation region of the heat generating element 620 is suitable for the fixing process of the sheet P. In this embodiment, the control circuit 100, the voltage source 110, the switches 649, 659, 669 function as an electric energy supplying means.
Next, a method of changing the heat generation region of the heat generating element 620 depending on the size of the sheet P with respect to the widthwise direction will be specifically described.
First, in the case where the sheet P has a large size such as A4-landscape size (widthwise size: 297 mm) of the sheet P, the control circuit 100 effects control so that the heat generating element 620 generates heat with a heat generation width B. Specifically, all the switch A649, the switch B659 and the switch C669 are placed in an ON state, so that the electric power (energy) is supplied to the heater 600. At this time, all of the 12 sub-sections 620a-620l of the heat generating element 620 generate heat. That is, the width of the heat generation region is 320 mm and is a suitable width for performing the fixing process of the toner image on the sheet P having the A4-landscape size.
Next, in the case where the sheet P has a small size such as A4-portrait size (widthwise size: 210 mm) of the sheet P, the control circuit 100 effects control so that the heat generating element 620 generates heat with a heat generation width A. Specifically, the switch A649 and the switch B659 are placed in an ON state and the switch C669 is placed in an OFF state, so that the electric power (energy) is supplied to the heater 600. At this time of the 12 sub-sections, 8 sub-sections 620c-620j of the heat generating element 620 generate heat. That is, the width of the heat generation region is 213 mm and is a suitable width for performing the fixing process of the toner image on the sheet P having the A4-portrait size.
The fixing device 40 is capable of changing the width size of the heater in the heat generation region depending on the width size of the sheet P, and therefore temperature rise of the heater 600 in a non-passing region of the sheet P can be suppressed. In addition, by suppressing the heat generation in the non-passing region of the sheet P, it is possible to suppress waste of electric power.
Resistances of the branch paths 642, 652, 662, 672 will be described.
In this embodiment, in order to suppress the electric power consumption, as a material for these branch paths, a paste material principally comprising silver having low resistivity is used. However, these electroconductor paths have a resistance not a little, and therefore an applied voltage is described depending on a path length of the electroconductor path.
A resistance Ra of the electroconductor path from the electrical contact to the branch path is calculated from the following formula. In the formula, a width of the electroconductor path is Wa (widthwise direction of the substrate 610), a height is Ha, a resistivity is pa, and a distance from the electrical contact to the branch path is La.
Ra=ρa×La/(Wa×Ha) (1)
That is, it is understood that the resistance value Ra becomes large in proportional to the distance from the electrical contact to the branch path.
A resistance Rb from a contact point of the branch path with the electroconductor path to a terminal is calculated from the following formula, in the formula, a width (longitudinal direction of the substrate 610) of the branch path is Wb, a height is Hb, a resistivity is ρb, and a length of the branch path is Lb.
Rb=ρb×Lb(Wb×Hb) (2)
Accordingly, a total resistance Rall which is a resistance from the electrical contact to an end portion (terminal) of the branch path is calculated from the following formula.
Rall=Ra+Rb=ρa×La/(Wa×Ha)+ρb×Lb/(Wb×Hb) (3)
That is, the total resistance Rall is larger with the path having a larger distance from the point to the heat generating element. Accordingly, the voltage applied to the electroconductor path 640 lowers with distance from the electrical contact 645. For that reason, in the case where if all of the resistances of the branch paths 642 are the same, the voltage applied from the branch paths 642 to the heat generating element 620 becomes smaller with a decreasing distance from the other end with respect to the longitudinal direction of the substrate 610. Similarly, the voltage applied to the electroconductor path 650 lowers with distance from the electrical contact 655, and the voltage applied to the electroconductor paths 660, 670 lowers with distance from the electrical contact 665. For that reason, in the case where if all of the resistances of the branch paths 652, 662, 672 are the same, the voltages applied from the branch paths 652, 662, 672 to the heat generating element 620 become smaller with a decreasing distance from the other end with respect to the longitudinal direction of the substrate 610.
Accordingly, the heat generation amount every section of the heat generating element 620 when the voltage is applied to the heater 600 gradually lowers with an increasing distance from one end, i.e., a decreasing distance to the other end with respect to the longitudinal direction of the substrate. That is, the heat generation amount of the heat generating element 620a located at a position closest to the electrical contact is largest, and the heat generation amount of the heat generating element 6101 located at a position remotest from the electrical contact is smallest. For that reason, the belt 603 heated by the heater 600 is higher in temperature toward one end side (a contact side of the heater 600 with the electrical contact) and is lower in temperature toward the other end side (a side opposite from the contact side).
Therefore, in this embodiment, the resistance is changed every branch path so that the voltages applied to the respective sections of the heat generating element 620 becomes uniform. That is, the resistance of each branch path is adjusted so that the total resistance from each of the electrical contacts to the associated one of the branch paths of the heat generating element 620 is the same for any path. Specifically, in this embodiment, the resistance of each branch path is adjusted by changing a branch path width every branch path. In this embodiment, in order to further enhance an effect of resistance adjustment varying depending on the width of the branch path, as a material for the branch path, a material having a higher resistivity than the electroconductor path is used.
By the above-described constitution, in the respective electric power supplying paths using the branch paths 642 (642a-642g) of the heater 600, values of the total resistance Rall are substantially the same. Further, in the respective electric power supplying paths using the branch paths 652 (652b-652f), 662a, 672g of the heater 600, values of the total resistance Rall are substantially the same. For that reason, in this embodiment, it is possible to uniformly apply the voltage to the respective sections of the heat generating element 620, so that the heat generation amounts of the respective sections of the heat generating element can be made substantially equal. This will be described specifically using the drawings.
A resistor r8 represents a resistor of the electroconductor path 660. Further, resistors r9-r12 represent resistors of the electroconductor path 650. Specifically, the resistor of the electroconductor path 660 extending from the electrical contact 665 to branch to the branch path 652b is r8. The resistor of the electroconductor path 650 extending from the electrical contact 655 to the branch path 652a is r9. Further, in the electroconductor path 650, the resistor of the electroconductor line between the branch path 652b and the branch path 652c is r10. The resistor of the electroconductor line between the branch path 652c and the branch path 652d is r11. The resistor of the electroconductor line between the branch path 652d and the branch path 652e is r12.
A resistor r13 represents a resistor of the electroconductor path 670. A resistor r642a represents a resistor of the branch path 642a. Similarly, resistors r642b-r642g represent resistors of the branch paths 642b-642g, respectively. A resistor r662a represents a resistor of the branch path 662a. Resistors r652b-r652e represent resistors of the branch paths 652b-652e, respectively. A resistor r672f represents a resistor of the branch path 672f.
According to
According to Table 1, it is understood that a magnitude of the resistance (path resistance) between the electrical contact and the branch path varies depending on the respective branch paths. This is attributable to a difference in length of the path between the electrical contact and the branch path. A difference in resistance for each of the paths leads to a difference in voltage drop for each of the paths, and therefore the difference in path resistance causes the energization non-uniformity of the heat generating element 620, so that there is a liability that heat generation non-uniformity of the heat generating element 620 is caused to generate.
Therefore, in this embodiment, the resistance of each branch path is adjusted so that the voltage applied to the associated section of the heat generating element becomes uniform. Specifically, the width Wb of the branch path short in path length is made narrow and the width Wb of the branch path long in path length is made broad so that values of the total resistance from the electrical contacts to terminals (end points) of the branch paths are the same for any paths.
For example, the resistance of the branch path 642a which is an example of a first branch line is larger than the resistance of the branch path 642g which is an example of a second branch line. Further, the resistance of the branch path 652b which is an example of a third branch line is larger than the resistance of the branch path 652e which is an example of a fourth branch line.
Further, the width of the branch path 642a which is an example of a first branch line is broader than the width of the branch path 642g which is an example of a second branch line. Further, the width of the branch path 652b which is an example of a third branch line is broader than the width of the branch path 652e which is an example of a fourth branch line.
In this embodiment, a high-resistivity material is used for the branch paths so that a resistivity ρb of each branch path is higher than a resistivity ρa of the associated electroconductor path. By employing such a constitution, enlargement in size of the branch path is suppressed. With this, heat generation non-uniformity of the heater 600 and the belt 603 with respect to the longitudinal direction due to lamination between the heat generating element and the branch paths is suppressed. As described above, in order to satisfy uniformity in glossiness of the image, the width of the branch paths may desirably be 0.5 mm or less. Further, from the viewpoint of a limit of manufacturing accuracy in the screen printing, the width of the branch paths may desirably be 0.1 mm or more.
Therefore, selection of the materials is made so that the width of the branch path 642a for which a largest resistance is required and the width of the branch path 642g for which a smallest resistance is required fall within the above-described range. For that reason, as the material for the branch paths, the material having a larger resistivity than the material for the electroconductor paths. In this embodiment, as the material for the branch paths, a paste in which silver is mixed with palladium so that the resistivity thereof is 2.8×10−7 Ω·m which is about 17.5 times the resistivity ρa of the electroconductor paths is used. The height Hb of each branch path is 35 μm which is equal to that of the height Ha of each electroconductor path. Constitutions of the respective branch paths based on the above description in this embodiment are shown in Table 2. In Table 2, a resistance 1 represents a resistance of the branch path resistances, of a portion which is in non-contact with the heat generating element 620. Further, a resistance 2 represents a resistance, of the branch path resistances, of a portion (energization layer) which is in contact with the heat generating element 620.
Here, in order to verify an effect of this embodiment, a compression between this embodiment and Comparison Example is made. In Comparison Example, all of the branch paths are 0.2 mm in width Wb and 35 μm in height Ha. Further, the branch paths are 1.6×10−8 (Ω) in resistivity ρb and are formed of the same material as that for the electroconductor paths.
First, between this embodiment and Comparison Example, the total resistance Rall of the path from the electroconductor path to the heat generating element will be compared. In
In
On the other hand, in this embodiment, as the material for the branch path, the material having a larger resistivity than the material for the electroconductor path, and the width of the branch path is made narrower with a position closer to the electrical contact. For that reason, as shown in (a) of
First, a manufacturing method of a ceramic heater using a thick film printing method (screen printing method) will be described. In
In a step of subjecting the substrate 610 to the screen printing, a plate (mesh plate, metal mask plate, as shown in (a) to (c) of
In this embodiment, the heater 600 is manufactured by a procedure as shown in
Then, on the substrate 610 on which the above-described electroconductor patterns and the heat generating element are formed, the branch paths 642, 652, 662, 672 are formed (S13) ((c) of
Incidentally, in this embodiment, after the heat generating element 620 is formed on the substrate 610 (S11), the electroconductor lines are formed on the substrate (S12) and thereon, the branch paths are formed (S13), but the manufacturing procedure of the heater is not limited thereto. For example, the branch paths are formed (S13), the electroconductor lines are formed (S12), and then the heat generating element may also be formed (S11). That is, the steps (S11-S13) may also be in no particular order.
Next, between this embodiment and Comparison Example, a temperature distribution of the fixing belt 603 with respect to the longitudinal direction will be compared.
According to
According to
Accordingly, according to this embodiment, it is possible to suppress non-uniformity of the energization to the heat generating element 620 generating due to the difference in length of the electroconductor path having the resistance. Further, heat generation non-uniformity of the heater 600 with respect to the longitudinal direction can be suppressed. Accordingly, it is possible to suppress the uneven glossiness of the image when the image on the sheet is heated in the fixing device 40.
In this embodiment, the resistivity of the branch path is made larger than the resistivity of the electroconductor path and the widths of the branch paths are made different from each other, but a method of adjusting the resistances of the branch paths is not limited. If a method is capable of adjusting the branch path resistance, the method may also be used. For example, the branch path resistance may also be adjusted only by a change in width of the branch path while the resistivity of the branch path and the resistivity of the electroconductor path are kept in an equal state. When this method is used, the branch paths and the electric power supplying lines can be printed in the same step, and therefore the number of steps can be reduced. However, from the viewpoint that the enlargement in size of the branch path can be suppressed, the heater 600 may desirably employ the constitution in this embodiment. Further, from the viewpoint that a local temperature lowering of the heat generating element 620 due to the lamination between the heat generating element 620 and the branch path can be suppressed, the heater 600 may desirably employ the constitution in this embodiment.
For example, the branch resistance may also be adjusted by changing the branch path length. However, in order to increase the branch path length between the heat generating element and the electroconductor path, there is a need to arrange these members so that the branch path detours around these members, so that a large space is required. Accordingly, it is desirable that the heater 600 employs the constitution in this embodiment from the viewpoint that the enlargement in size of the branch path can be suppressed.
For example, a modified example in which the branch path resistance is adjusted by changing the resistivity of the respective branch paths while keeping the width of the branch paths at a constant level may also be used. In
In this embodiment, the widths of the branch paths arranged in the longitudinal direction of the substrate are changed every branch path, but the constitution of the heater 600 is not limited thereto. When the branch paths include the branch path closer to the electrical contact and having a large resistance and the branch path remoter from the electrical contact and having a small resistance are provided so that the energization non-uniformity of the heat generating element 620 can be suppressed, the branch paths may also be used. For example, the widths of the branch paths may also be changed every two branch paths. Specifically, such a constitution that the branch paths 652b and 652c have the same width and the branch paths 652d and 652e have the same width which is broader than the width of the branch paths 652b and 652c may also be employed.
In this embodiment, the energization is effected from one longitudinal end side of the substrate 610 by using the constitution in which all the electrical contacts are disposed in one longitudinal end side of the substrate 610, but the constitution of the fixing device 40 is not limited thereto. In a constitution in which the energization is effected from a longitudinal end portion side, heat generation non-uniformity can generate in the heat generating element 620 due to the voltage drop of the electroconductor lines.
A heater in Embodiment 2 will be described.
A constitution of the fixing device 40 in this embodiment is similar to a constitution in Embodiment 1 except that a constitution regarding the branch paths of the heater 600. For that reason, constituent elements similar to those in Embodiment 1 are represented by identical reference numerals or symbols and will be omitted from detailed description.
As shown in
In this embodiment, the resistance between the electrical contact and the heat generating element 620 is calculated in the following manner.
First, a resistance value Ra of the electroconductor path from the electrical contact to the branch portion is calculated from the formula (1) similarly as in Embodiment 1. That is, the resistance Ra of the electroconductor path increases in value in proportional to the distance from the electrical contact to the branch portion.
A resistance Rb1 of each of the branch portions is calculated from the following formula. In the formula, a width (longitudinal direction of the substrate 610) of the branch portion is Wb1, a height is Hb1, a resistivity is ρb1, and a length of the branch portion is Lb1.
Rb1=ρb1×Lb1/(Wb1×Hb1) (4)
A resistance Rb2, of each of the connecting portions, from a contact point of the branch portion with the connecting portion to another terminal of the connecting portion is calculated from the following formula. In the formula, a width (longitudinal direction of the substrate 610) of the connecting portion is Wb, a height is Hb2, a resistivity is ρb2, and a length of the connecting portion is Lb2.
Rb2=ρb2×Lb2(Wb2×Hb2) (5)
Accordingly, a total resistance Rall which is a resistance from the electrical contact to an end portion (terminal) of the connecting portion is calculated from the following formula.
Rall=Ra+Rb1+R=ρa×La/(Wa×Ha)+ρb1×Lb1/(Wb1×Hb1)+ρb2×Lb2/(Wb2×Hb2) (6)
In this embodiment, as the material for the connecting portion, the same low-resistance material as the material for the electroconductor path is used, and is 1.6×10−8 (Ω) is resistivity ρb2. Thus, the heater 600 in this embodiment uses the low-resistance material as the material for the connecting portion, and therefore a difference in potential between the contact point of the branch portion with the connecting portion and another end of the connecting portion is small. For that reason, the heat generation distribution of the heat generating element 620 with respect to the widthwise direction easily becomes uniform compared with the heater in Embodiment 1. Further, the temperature distribution of the heat generating element 620 easily broadens on the basis of the neighborhood of the widthwise central portion. Incidentally, in this embodiment, in the neighborhood of the widthwise central portion of the heat generating element 620, the heater 600 stably contacts the fixing belt 603 with a large contact force. For that reason, in this embodiment, heat can be stably supplied to the fixing belt 603. The width Wb2 of the connecting portion is uniformized as 0.2 mm. This width is sufficient narrow for suppressing the temperature non-uniformity of the heater 600 during the energization due to the lamination between the heat generating element 620 and the branch path. The length Lb2 of the connecting portion is 3 mm which is equal to the widthwise width of the heat generating element 620m and the height Hb2 of the connecting portion is 35 μm which is equal to the height of the electroconductor path. Accordingly, the resistance of each connecting portion is 0.015 Ω.
On the other hand, in order to uniformize the path from the electrical contact to the connecting portion for each of the paths, the resistances of the respective branch portions are adjusted by changing widths of the branch portions. In this embodiment, in order to effectively adjust the resistances of the respective branch portions, the material having a larger resistivity than the material for the electroconductor path is used for each branch portion. In this embodiment, as the material for the branch portions 642a1-642g1, a paste in which silver is mixed with palladium in an amount providing the resistivity of 2.7×10−6 Ω·m is used. In addition, as the material for the branch portions 652b1-652e1, 662a1, 672a1, a paste in which silver is mixed with palladium in an amount providing the resistivity of 3.3×10−6 Ω·m is used.
In this embodiment, the width of the branch portions is broader with an increasing distance (larger path) from the electrical contact. This is because and difference is provided between the resistances of the respective branch paths. However, in view of a manufacturing limit by the screen printing, there is a need to provide the branch portion with the width of 0.1 mm or more. For that reason, the width of the branch portion 642a1 closest to the electrical contact 645 is 0.1 mm as a reference, and then the width of other branch portions 642b1-642g1 are determined.
Further, the width of the branch portion 662a1 closest to the electrical contacts 665, 655 is 0.1 mm as a reference, and then other branch portions 652b1-652e1, 672f1 are determined.
Constitutions of respective branch portions designed on the basis on the above description are shown in Table 3.
Between this embodiment and Comparison Example, the total resistance Rall of the path from the electroconductor path to the heat generating element will be compared. In
In
On the other hand, in this embodiment, as the material for the branch path, the material having a larger resistivity than the material for the electroconductor path, and the width of the branch path is made narrower with a position closer to the electrical contact. For that reason, as shown in (a) of
In the case of this embodiment, the heat generation amounts of the respective sections of the heat generating element 620 of the heater 600 are uniform, and therefore the temperature of the fixing belt 603 is uniform at 195° C. with respect to the longitudinal direction. For that reason, in the case where the image is fixed using the fixing belt 603 heated by the heater 600 in this embodiment, it is possible to output a high-quality image for which the uneven glossiness is suppressed.
Accordingly, according to this embodiment, it is possible to suppress non-uniformity of the energization to the heat generating element 620 generating due to the difference in length of the electroconductor path having the resistance. Further, temperature non-uniformity of the heater 600 with respect to the longitudinal direction can be suppressed. Accordingly, it is possible to suppress the uneven glossiness of the image when the image on the sheet is heated in the fixing device 40.
A manufacturing method of a ceramic heater using a thick film printing method (screen printing) will be described. In
In the steps of subjecting the substrate 610 to the screen printing, plates (mesh plates, metal masks plates) as shown in
The plate 813 is a member for printing the branch portions 6421, 6521, 6621, 6721, on the substrate. The plate 813 is provided with passing holes through which the material paste is passable so that the branch portions 6421, 6521, 6621, 6721 are printed in desired shapes. The plate 814 is a member for printing the coat layer 680 on the substrate. The plate 814 is provided with a passing hole through which the material paste is passable so that the coat layer 690 is printed in a desired shape.
In this embodiment, the heater 600 is manufactured by a procedure as shown in
Then, the branch portions 6421, 6521, 6621, 6721 are formed on the substrate 610 on which the electroconductor patterns and the heat generating element 620 are formed (S33) ((c) of
Then, on the substrate 610 on which the various printing steps are performed, an insulating coat layer 680 for effecting electrical, mechanical and chemical protection is formed (S34) ((d) of
In this embodiment, the resistivity of the branch portion is made larger than the resistivity of the electroconductor path and the widths of the branch portions are made different from each other, but a method of adjusting the resistances of the branch portions is not limited. If a method is capable of adjusting the branch portion resistance, the method may also be used. For example, the branch portion resistance may also be adjusted only by a change in width of the branch portion while the resistivity of the branch portion and the resistivity of the electroconductor path are kept in an equal state. However, from the viewpoint that the enlargement in size of the branch portion can be suppressed, the heater 600 may desirably employ the constitution in this embodiment.
For example, the branch portion resistance may be adjusted by changing the resistivity of the respective branch paths while keeping the width of the branch paths at a constant level. However, in the case where materials different in resistivity are used for the respective branch portions, in the manufacturing method using the screen printing, the number of steps increases. Specifically, it is required that the masks are prepared corresponding to the number of the different resistance materials and then printing of the branch portions is made in separate steps. For that reason, from the viewpoint that the heater can be manufactured using the same material for the respective branch portions 642a-642g, in the same step, the constitution in this embodiment may desirably be employed. Similarly, from the viewpoint that the branch portions 652b-652e, 662a, 672f can be printed using the same material in the same step, the constitution in this embodiment may desirably be employed.
In this embodiment, the widths of the branch portions are changed every branch path, but the constitution of the heater 600 is not limited thereto. When the branch paths include the branch path closer to the electrical contact and having a large resistance and the branch path remoter from the electrical contact and having a small resistance are provided so that the energization non-uniformity of the heat generating element 620 can be suppressed, the branch paths may also be used. For example, the widths of the branch paths may also be changed every two branch paths. Specifically, such a constitution that the branch paths 652b and 652c have the same width and the branch paths 652d and 652e have the same width which is broader than the width of the branch paths 652b and 652c may also be employed.
In this embodiment, as the material for the connecting portions 4622, 6522, 6622, 6722, the same low-resistance material as the material for the electroconductor paths and the like is used, but similarly as in the case of the branch portions 6421, 6521, 6621, 6721, the medium-resistance material may also be used. That is, the connecting portions and the branch portions may also be integrally printed using a mask provided with passing holes so that the connecting portions are narrower than the branch portions.
The present invention is not restricted to the specific dimensions in the foregoing embodiments. The dimensions may be changed properly by one skilled in the art depending on the situations. The embodiments may be modified in the concept of the present invention.
The heat generating region of the heater 600 is not limited to the above-described examples which are based on the sheets P are fed with the center thereof aligned with the center of the fixing device 40, but the sheets P may also be supplied on another sheet feeding basis of the fixing device 40. For that reason, e.g., in the case where the sheet feeding basis is an end(-line) feeding basis, the heat generating regions of the heater 600 may be modified so as to meet the case in which the sheets are supplied with one end thereof aligned with an end of the fixing device. More particularly, the heat generating elements corresponding to the heat generating region A are not heat generating elements 620c-620j but are heat generating elements 620a-620e. With such an arrangement, when the heat generating region is switched from that for a small size sheet to that for a large size sheet, the heat generating region does not expand at both of the opposite end portions, but expands at one of the opposite end portions.
The heater 600 is not limited to the heater having only the structure in which the branch paths are laminated on the heat generating element 620. For example, the branch paths may also be formed on the substrate and thereon, the heat generating element 620 may also be formed.
In the heaters in Embodiments 1 and 2, a constitution in which only two regions consisting of the heat generating regions A and B are provided is employed, but the applied range of the present invention is not limited to the constitution. The present invention is also applicable to a constitution in which heat generating regions have three or more patterns are provided.
The number of the electrical contacts limited to three or four. For example, five or more electrical contacts may also be provided depending on the number of heat generating patterns required for the fixing device.
The belt 603 is not limited to that supported by the heater 600 at the inner surface thereof and driven by the roller 70. For example, so-called belt unit type in which the belt is extended around a plurality of rollers and is driven by one of the rollers. However, the structures of Embodiments 1 and 2 are preferable from the standpoint of low thermal capacity.
The member cooperative with the belt 603 to form of the nip N is not limited to the roller member such as a roller 70. For example, it may be a so-called pressing belt unit including a belt extended around a plurality of rollers.
The image forming apparatus which has been a printer 1 is not limited to that capable of forming a full-color, but it may be a monochromatic image forming apparatus. The image forming apparatus may be a copying machine, a facsimile machine, a multifunction machine having the function of them, or the like, for example, which are prepared by adding necessary device, equipment and casing structure.
The image heating apparatus is not limited to the fixing device for fixing a toner image on a sheet P. It may be a device for fixing a semi-fixed toner image into a completely fixed image, or a device for heating an already fixed image. Therefore, the image heating apparatus may be a surface heating apparatus for adjusting a glossiness and/or surface property of the image, for example.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2014-191456 filed on Sep. 19, 2014, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2014-191456 | Sep 2014 | JP | national |
