Patent Grant
9513592
The present invention relates to a heater for heating an image on a sheet, an image heating apparatus including the heater and a manufacturing method of 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 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, the temperature rise to the temperature permitting the performing of the fixing operation is quick.
JPA Hei 6-250539 discloses a structure of a heater including a plurality of electrodes arranged, in a longitudinal direction of a substrate, on a heat generating element (heat generating member) extending in the longitudinal direction. On this heater, the electrodes different in polarity are alternately arranged on the heat generating element, and therefore a current flows through the heat generating elements between adjacent electrodes. Specifically, the electrodes of one polarity are connected with electroconductive lines provided in one widthwise end side of the substrate relative to the heat generating element, and the electrodes of the other polarity are connected with electroconductive lines provided in the other widthwise end side of the substrate relative to the heat generating element. For this reason, when a voltage is applied between these electroconductive lines, the heat generating elements generate heat in an entire region thereof with respect to the longitudinal direction.
Incidentally, the manner of the heat generation of the heat is determined by a resistance of the heat generating element and the magnitude of a current flowing through the heat generating element. The resistance of the heat generating element is determined by a dimension and a value of the resistivity of the heat generating element. In JP-A Hei 6-250539, the heater is caused to generate heat in a desired manner by adjusting the resistance of the heat generating element with respect to an energization direction by a gap between the adjacent electrodes.
However, the heater disclosed in JP-A Hei 6-250539 is susceptible to improvement in terms of durability. The heater disclosed in JP-A Hei 6-250539 has a structure in which the electrodes are laminated on the heat generating element and lower surfaces of the electrodes are connected with the heat generating element. Further, in this heater, between the adjacent electrodes with the gap, the current flows along the longitudinal direction of the heat generating element. The current has such a property that the current tends to flow along a shortest path, and therefore when energization to the heat is made, the current concentratedly flows from an end portion of the electrode toward the heat generating element. Then, by the concentrated current, a part of the heat generating element is locally in an over-heat state, so that the degree of deterioration is accelerated at this part more than another portion. For that reason, the life of the heat decreases.
A principal object of the present invention is to provide a heater whose tendency to shorten its lifespan is suppressed.
Another object of the present invention is to provide an image heating apparatus including a heater whose tendency to shorten its lifespan is suppressed.
A further object of the present invention is to provide a manufacturing method of a heater whose tendency to shorten its lifespan is suppressed.
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. The heater is contactable to the belt to heat the belt. The heater comprises: a substrate; a first electrical contact provided on the substrate and electrically connectable with the first terminal; a plurality of second electrical contacts provided on the substrate and electrically connectable with the second terminal; a plurality of electrode portions including first electrode portions electrically connected with the first electrical contact and second electrode portions electrically connected with the second electrical contacts, the first electrode portions and the second electrode portions being arranged alternately with predetermined gaps in a longitudinal direction of the substrate; and 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. A part of the second electrical contacts is selectably electrically connectable with the second terminal, and the electrode portions are covered with the heat generating portions so as to be positioned between the substrate and the heat generating portions.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
In
In
In
In
In
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 a 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.
[Fixing Device]
The fixing device 40, which is the image heating apparatus used in the printer 1, will be described.
The fixing device 40 is an image heating apparatus for heating the image on the sheet by a heater unit 60 (unit 60). The unit 60 includes a flexible thin fixing belt 603 and the heater 600 as a heating member contacted to the inner surface of the belt 603 to heat the belt 603 (low thermal capacity structure). Therefore, the belt 603 can be efficiently heated, so that quick temperature rise at the start of the fixing operation is accomplished. As shown in
Unit 60 is a unit for heating and pressing an image on the sheet P. The 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 plate-like heating member for heating the belt 603, slidably contacting 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 heater 600 is fixed on the lower surface of the heater holder 601 along the longitudinal direction of the heater holder 601. In this embodiment, the heat generating element 620 is provided on the back side of the substrate 610, which is not in slidable contact with the belt 603, but the heat generating element 620 may be provided on the front surface of the substrate 610, is in slidable contact with the belt 603. However, the heat generating element 620 of the heater 600 is preferably provided on the back side of the substrate 610, by which a uniform heating effect to the substrate 610 is accomplished, from the standpoint of preventing non-uniform heat application to the belt 603. The details of the heater 600 will be described hereinafter.
The heater 600 is fixed along the longitudinal direction of the heater holder 601 on a lower surface of the heater holder 601. In this embodiment, the heat generating element 620 is provided in a back surface side (in a side where the heat generating element 620 does not slide with the belt 603) of the substrate 610, but may also be provided in the front surface side (in a side where the heat generating element 620 slides with the belt 603) of the substrate 610. However, in order to prevent generation of non-uniformity of heat supplied to the belt 603 by a non-heat generating portion of the heat generating element 620, it is desirable that the heat generating element 620 is provided in the back surface side, of the substrate 610, where a heat-uniformizing effect of the substrate 610 can be obtained. Details of the heater 600 will be described later.
The belt 603 is a cylindrical (endless) belt (film) for heating the image on the sheet in the nip N. The belt 603 comprises a base material 603a, an elastic layer 603b thereon, and a parting layer 603c on the elastic layer 603b, for example. The base material 603a may be made of metal material such as stainless steel or nickel, or a heat resistive resin material such as polyimide. The elastic layer 603b may be made of an elastic and heat resistive material such as a silicone rubber or a fluorine-containing rubber. The parting layer 603c may be made of fluorinated resin material or silicone resin material.
The belt 603 of this embodiment has dimensions of 30 mm in the outer diameter, 330 mm in the length (the dimension measured in the front-rear direction in
The 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-section (the surface of
The support stay 602 supports 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 high pressure is applied thereto, and in this embodiment, it is made of SUS304 (stainless steel).
As shown in
Between the flange 411a and a pressing arm 414a, an urging spring 415a is compressed. Also, between a flange 411b and a pressing arm 414b, an urging spring 415b is compressed. The urging springs 415a and 415b may be simply called the urging spring 415. With such a structure, the elastic force of the urging spring 415 is applied to the heater 600 through the flange 411 and the support stay 602. The belt 603 is pressed against the upper surface of the 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.
As shown in
As shown in
The roller 70 of this embodiment includes a metal core 71 of steel, an elastic layer 72 of silicone rubber foam on the metal core 71, and a parting layer 73 of fluorine resin tube on the elastic layer 72. Dimensions of the portion of the roller 70 having the elastic layer 72 and the parting layer 73 are 25 mm in outer diameter, and 330 mm in length.
A thermistor 630 is a temperature sensor provided on a back side of the heater 600 (opposite side from the sliding surface side. The thermistor 630 is bonded to the heater 600 in the state that it is insulated from the heat generating element 620. The thermistor 630 has a function of detecting a temperature of the heater 600. As shown in
The control circuit 100 comprises a circuit including a CPU operating for various controls, a non-volatilization medium such as a ROM storing various programs. The programs are stored in the ROM, and the CPU reads and execute them to effect the various controls. The control circuit 100 may be an integrated circuit such as ASIC if it is capable of performing a similar operation.
As shown in
The control circuit 100 uses the temperature information acquired from the thermistor 630 for the electric power supply control for the voltage source 110. More particularly, the control circuit 100 controls the electric power to the heater 600 through the voltage source 110 on the basis of the output of the thermistor 630. In this embodiment, 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. By such a control, the heater 600 is maintained at a predetermined temperature (180 degree C., for example).
As shown in
The motor M is a driving means for driving the roller 70 through the gear G. The control circuit 100 is electrically connected with the motor M to control the electric power supply to the motor M. When the electric energy is supplied by the control of the control circuit 100, the motor M starts to rotate the gear G.
The control circuit 100 controls the rotation of the motor M. The control circuit 100 rotates the roller 70 and the belt 603 using the motor M at a predetermined speed. It controls the motor so that the speed of the sheet P nipped and fed by the nip N in the fixing process operation is the same as a predetermined process speed (200 [mm/sec], for example).
[Heater]
The structure of the heater 600 used in the fixing device 40 will be described in detail.
The heater 600 of this embodiment is a heater using the heat generating type shown in (a) and (b) of
In the case that the electric power is supplied individually to the heat generating elements arranged in the longitudinal direction, it is preferable that the electrodes and the heat generating elements are disposed such that the directions of the electric current flow alternates between adjacent ones. As to the arrangements of the heat generating members and the electrodes, it would be considered to arrange the heat generating elements each connected with the electrodes at the opposite ends thereof, in the longitudinal direction, and the electric power is supplied in the longitudinal direction. However, with such an arrangement, two electrodes are provided between adjacent heat generating elements, with the result of the likelihood of short circuit. In addition, the number of required electrodes 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 electrodes such that an electrode is made common between adjacent heat generating elements. With such an arrangement, the likelihood of the short circuit between the electrodes can be avoided, and a space between the electrodes can be eliminated.
In this embodiment, a common electroconductive line 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
A layer structure will be described using
As shown in
As shown in
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, and is disposed in a region 610c (
The heat generating element 620 is laminated on seven common electrodes 642a-642g arranged in the longitudinal direction of the substrate 610. In other words, a heat generating region of the heat generating element 620 is isolated into six sections by common electrodes 642a-642g along the longitudinal direction. The lengths measured in the longitudinal direction of the substrate 610 of each section are 53.3 mm. On central portions of the respective sections of the heat generating element 620, one of the six opposite electrodes 652, 662 (652a-652d, 662a, 662b) are laminated. In this manner, the heat generating element 620 is divided into 12 sub-sections. The heat generating element 620 divided into 12 sub-sections can be deemed as a plurality of heat generating elements (resistance elements) 620a-620l. In other words, the heat generating elements 620a-620l electrically connect adjacent electrodes with each other. Lengths of the sub-section measured in the longitudinal direction of the substrate 610 are 26.7 mm. Resistance values of the sub-section of the heat generating element 620 with respect to the longitudinal direction are 120Ω. With such a structure, the heat generating element 620 is capable of generating heat in a partial area or areas with respect to the longitudinal direction.
The resistances of the heat generating elements 620 with respect to the longitudinal direction are uniform, and the heat generating elements 620a-620l have substantially the same dimensions. Therefore, the resistance values of the heat generating elements 620a-620l are substantially equal. When they are supplied with electric power in parallel, the heat generation distribution of the heat generating element 620 is uniform. However, it is not inevitable that the heat generating elements 620a-620l have substantially the same dimensions and/or substantially the same resistivities. For example, the resistance values of the heat generating elements 620a and 620l may be adjusted so as to prevent local temperature lowering at the longitudinal end portions of the heat generating element 620. At the positions of the heat generating element 620 where the common electrode 642 and the opposite electrode 652, 662 are provided, the heat generation of the heat generating element 620 is substantially zero. However, there is a heat-uniformizing action of the substrate 610, and therefore by suppressing the thickness of the electrode to less than 1 mm, the influence on the fixing process is a negligible degree. In this embodiment, the thickness of each of the electrodes is less than 1 mm.
The common electrodes 642 (642a-642g) are a part of the above-described electroconductor pattern. The common electrode 642 extends in the widthwise direction of the substrate 610 perpendicular to the longitudinal direction of the heat generating element 620. In this embodiment, each of the common electrodes 642 is formed on the substrate 610 and is coated (covered) with the heat generating element 620. That is, the heat generating element 620 and the common electrode 642 are in a partly overlapping (laminating) positional relationship. The common electrodes 642 are odd-numbered electrodes of the plurality of electrodes connected to the heat generating element 620, as counted from a one longitudinal end of the heat generating element 620. The common electrode 642 is connected to one contact 110a of the voltage source 110 through the common electroconductive line 640 which will be described hereinafter. That is, the common electrode 642 is connected to a one terminal side of the voltage source 110.
The opposite electrodes 652, 662 are a part of the above-described electroconductor pattern. The opposite electrodes 652, 662 extend in the widthwise direction of the substrate 610 perpendicular to the longitudinal direction of the heat generating element 620. Each of the opposite electrodes 652, 662 is formed on the substrate 610 and is coated (covered) with the heat generating element 620. That is, the heat generating element 620 and the opposite electrodes 652, 662 are in a partly overlapping (laminating) positional relationship. The opposite electrodes 652, 662 are the other electrodes of the electrodes connected with the heat generating element 620 other than the above-described common electrode 642. That is, in this embodiment, they are even-numbered electrodes as counted from the one longitudinal end of the heat generating element 620. That is, the common electrode 642 and the opposite electrodes 662, 652 are alternately arranged along the longitudinal direction of the heat generating element. The opposite electrodes 652, 662 are connected to the other contact 110b of the voltage source 110 through the opposite electroconductive lines 650, 660 which will be described hereinafter. That is, the opposite electrodes 652, 662 are connected to the other terminal side of the voltage source 110.
The common electrode 642 and the opposite electrode 652, 662 function as electrode portions for supplying the electric power to the heat generating element 620. In this embodiment, the odd-numbered electrodes are common electrodes 642, and the even-numbered electrodes are opposite electrodes 652, 662, but the structure of the heater 600 is not limited to this example. For example, the even-numbered electrodes may be the common electrodes 642, and the odd-numbered electrodes may be the opposite electrodes 652, 662.
In addition, in this embodiment, four of the all opposite electrodes connected with the heat generating element 620 are the opposite electrode 652. In this embodiment, two of the all opposite electrodes connected with the heat generating element 620 are the opposite electrode 662. However, the allotment of the opposite electrodes is not limited to this example, but may be changed depending on the heat generation widths of the heater 600. For example, two may be the opposite electrode 652, and four maybe the opposite electrode 662.
The common electroconductive line 640 is a part of the above-described electroconductor pattern. The common electroconductive line 640 extends along the longitudinal direction of the substrate 610 toward the one end portion side 610a of the substrate in the one end portion side 610d of the substrate. The common electroconductive line 640 is connected with the common electrodes 642 (642a-642g) which is in turn connected with the heat generating element 620 (620a-620l). The common electroconductive line 640 is connected to the electrical contact 641 which will be described hereinafter. In this embodiment, the electroconductor patterns connecting the electrodes with the electrical contacts are called the electroconductive lines.
The opposite electroconductive line 650 is a part of the above-described electroconductor pattern. The opposite electroconductive line 650 extends along the longitudinal direction of substrate 610 toward the one end portion side 610a of the substrate 610 in the other end portion side 610e of the substrate. The opposite electroconductive line 650 is connected with the opposite electrodes 652 (652a-652d) which are in turn connected with heat generating elements 620 (620c-620j). The opposite electroconductive line 650 is connected to the electrical contact 651 which will be described hereinafter.
The opposite electroconductive line 660 (660a, 660b) is a part of the above-described electroconductor pattern. The opposite electroconductive line 660a extends along the longitudinal direction of substrate 610 toward the one end portion side 610a of the substrate 610 in the other end portion side 610e of the substrate. The opposite electroconductive line 660a is connected with the opposite electrode 662a which is in turn connected with the heat generating element 620 (620a, 620b). The opposite electroconductive line 660a is connected to the electrical contact 661a which will be described hereinafter. The opposite electroconductive line 660b extends along the longitudinal direction of substrate 610 toward the one end portion side 610a of the substrate 610 in the other end portion side 610e of the substrate 610. The opposite electroconductive line 660b is connected with the opposite electrode 662b which is in turn connected with the heat generating element 620. The opposite electroconductive line 660b is connected to the electrical contact 661b which will be described hereinafter.
The electrical contacts 641, 651, 661 (661a, 661b) are a part of the above-described electroconductor pattern. Each of the electrical contacts 641, 651, 661 preferably has an area of not less than 2.5 mm×2.5 mm in order to assure the reception of the electric power supply from the connector 700 which will be described hereinafter. In this embodiment, the electrical contacts 641, 651, 661 has a length of about 3 mm measured in the longitudinal direction of the substrate 610 and a width of not less than 2.5 mm measured in the widthwise direction of the substrate 610. The electrical contacts 641, 651, 661a, 661b are disposed in the one end portion side 610a of the substrate beyond the heat generating element 620 with gaps of about 4 mm in the longitudinal direction of the substrate 610. As shown in
When voltage is applied between the electrical contact 641 and the electrical contact 651 through the connection between the heater 600 and the connector 700, a potential difference is produced between the common electrode 642 (642b-642f) and the opposite electrode 652 (652a-652d). Therefore, through the heat generating elements 620c, 620d, 620e, 620f, 620g, 620h, 620i, 620j, the currents flow along the longitudinal direction of the substrate 610, the directions of the currents through the adjacent heat generating elements being substantially opposite to each other. The heat generating elements 620c, 620d, 620e, 620f, 620g, 620h, 620i as a first heat generating region generate heat, respectively. When voltage is applied between the electrical contact 641 and the electrical contact 661a through the connection between the heater 600 and the connector 700, a potential difference is produced between the common electrode 642a and the opposite electrode 662a. Therefore, through the heat generating elements 620a, 620b, the currents flow along the longitudinal direction of the substrate 610, the directions of the currents through the adjacent heat generating elements being opposite to each other. The heat generating elements 620a, 620b as a second heat generating region adjacent the first heat generating region generate heat.
When voltage is applied between the electrical contact 641 and the electrical contact 661b through the connection between the heater 600 and the connector 700, a potential difference is produced between the common electrode 642f and the opposite electrode 662b through the common electroconductive line 640 and the opposite electroconductive line 660b. Therefore, through the heat generating elements 620k, 620l, the currents flow along the longitudinal direction of the substrate 610, the directions of the currents through the adjacent heat generating elements being opposite to each other. By this, the heat generating elements 620k, 620l as a third heat generating region adjacent to the first heat generating region generate heat.
In this manner, on the heater 600, a part of the heat generating elements 620 can be selectively energized.
Between the one end portion side 610a of the substrate and the other end portion side 610c, there is a middle region 610b. More particularly, in this embodiment, the region between the common electrode 642a and the electrical contact 651 is the middle region 610b. The middle region 610b is a marginal area for permitting mounting of the connector 700 to the heater 600 placed inside the belt 603. In this embodiment, the middle region is 26 mm. This is sufficiently larger than the distance required for insulating the common electrode 642a and the electrical contact from each other.
[Connector]
The connector 700 used with the fixing device 40 will be described in detail.
As shown in
Similarly, the contact terminal 720a functions to contact the electrical contact 661a with the switch SW663 which will be described hereinafter. The contact terminal 720a is provided with the electrical contact 721a for connection to the electrical contact 661a and a cable 722a for connection to the switch SW663.
Similarly, the contact terminal 720b functions to contact the electrical contact 661b with the switch SW663 which will be described hereinafter. The contact terminal 720b is provided with the electrical contact 721b for connection to the electrical contact 661b and a cable 722b for connection to the switch SW663.
Similarly, the contact terminal 730 functions to contact the electrical contact 651 with the switch SW653 which will be described hereinafter. The contact terminal 730 is provided with the electrical contact 731 for connection to the electrical contact 651 and a cable 732 for connection to the switch SW653.
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.
[Electric Energy Supply to Heater]
An electric energy supply method to the heater 600 will be described. The fixing device 40 of this embodiment is capable of changing the width of the heat generating region of the heater 600 by controlling the electric energy supply to the heater 600 in accordance with 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.
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.
As shown in
Switch SW643 is a switch (relay) provided between the voltage source contact 110a and the electrical contact 641. The switch SW643 connects or disconnects between the voltage source contact 110a and the electrical contact 641 in accordance with the instructions from the control circuit 100. The switch SW653 is a switch provided between the voltage source contact 110b and the electrical contact 651. The switch SW653 connects or disconnects between the voltage source contact 110b and the electrical contact 651 in accordance with the instructions from the control circuit 100. The switch SW663 is a switch provided between the voltage source contact 110b and the electrical contact 661 (661a, 661b). The switch SW663 connects or disconnects between the voltage source contact 110b and the electrical contact 661 (661a, 661b) in accordance with 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, a combination of ON/OFF of the switch SW643, switch SW653, switch SW663 is controlled so that the heat generation width of the heat generating element 620 fits the sheet P. At this time, the control circuit 100, the voltage source 110, switch SW643, switch SW653, switch SW663 and the connector 700 functions as an electric energy supplying means for supplying the electric power to the heater 600.
When the sheet P is a large size sheet (an introducible maximum width size broader than a predetermined width size), that is, when an A3 size sheet is fed in the longitudinal direction or when the A4 size is fed in the landscape fashion, the width of the sheet P is 297 mm. Therefore, the control circuit 100 controls the electric power supply to provide the heat generation width B (
When the size of the sheet P is a small size (a width size narrower than the introducible maximum width size), that is, when an A4 size sheet is fed longitudinally, or when an A5 size sheet is fed in the landscape fashion, the width of the sheet P is 210 mm. Therefore, the control circuit 100 provides a heat generation width A (
[Heater Layer Step]
A layer structure of the heater 600 will be described.
First, a manufacturing method of a ceramic heater using a thick film printing method (screen printing method) will be described.
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 the conventional example, the heater is manufactured by a procedure as shown in
A cross-section, taken along A-A line (
In such a heater 600, in the case where a voltage is applied between adjacent electrodes, a current concentratedly flows through a portion, of the heat generating element 620, adjacent to lower surface end portions of the electrodes. Then, the heat generating element 620 locally causes abnormal heat generation, so that deterioration is accelerated. For that reason, there was a risk that the connecting portion of the heat generating element 620 peels off from the electrodes.
Therefore, in this embodiment, the heater 600 is manufactured by a procedure as shown in
Then, the heat generating element 620 is formed on the substrate 610 so as to coat (cover) the electrodes 642, 652, 662 (S12) ((b) of
Then, on the substrate 610 on which the electroconductor pattern and the heat generating element are placed, an insulating coat layer 680 for effecting electrical, mechanical and chemical protection is formed (S13) ((c) of
A cross-section, taken along A-A line (
In such a heater 600, in the case where a voltage is applied between adjacent electrodes, a current principally flows through the heat generating element 620 from an entire region of the electrode side surfaces providing a minimum current path, and in addition, the current flows through the heat generating element 620 from the electrode upper surface. That is, in this embodiment, current concentration at the connecting portion between the heat generating element 620 and the electrodes is suppressed. For that reason, in the heat generating element 620 in this embodiment, the local abnormal heat generation is suppressed, so that deterioration is suppressed. For that reason, compared with the conventional example, the risk that the connecting portion between the heat generating element and the electrodes is peeled off is low.
Further, as in the conventional example, in the method in which the electrodes are laminated on the heat generating element, in the case where the substrate 610 is formed of AlN (aluminum nitride) and a paste obtained by mixing a material for the heat generating element 620 with ruthenium oxide and glass particles is used, the following problem can occur. The problem is such that air bubbles generated between the electrodes and the heat generating element during the baking of the electrodes and then these manufactures are peeled off from each other. However, as in this embodiment, in the method in which the heat generating element is laminated on the electrodes, such a problem does not occur.
Further, in the heater 600 in the conventional example, after the manufacturing step S21, the printing non-uniformity of the heat generating element 620 is checked by measuring the resistance of the heat generating element 620 at a plurality of positions to check the resistance distribution. By performing this checking step, it is possible to manufacture the heater 600 for which a temperature distribution during energization is stabilized (i.e., temperature non-uniformity is suppressed). However, with respect to the heater 600 in this embodiment, the electroconductor pattern printing step S11 is performed before the step S11 of printing the heat generating element 620, and therefore it is difficult to measure the resistance distribution of the heat generating element 620. Therefore, in this embodiment, a checking step using a thermocamera is performed. Specifically, energization to the manufactured heater 600 is made, so that the heater 600 is heated to 200° C. Then, the temperature distribution is measured using the thermocamera, so that the state in which there is no difference of 5° C. or more between a minimum temperature and a maximum temperature is checked. By performing such a checking step, also in this embodiment, it is possible to manufacture the heater 600 with the stabilized temperature distribution (i.e., the suppressed temperature non-uniformity). In the checking step in this embodiment, the thermocamera is used, but another method may also be used if the method is capable of measuring the temperature distribution of an entire longitudinal region of the heat generating element 620. For example, a method in which the heater 600 is scanned with a non-contact thermistor in the longitudinal direction to detect a portion where abnormality in temperature may also be used.
A heater 600 in Embodiment 2 will be described.
In the conventional example, the heater is manufactured by a procedure as shown in
Then, on the substrate 610 on which the heat generating element 620 is formed, an electroconductor pattern (electrode, electroconductive wire) of a silver paste is formed (S32) ((b) of
Then, the heat generating element 620 is formed as an upper layer on the substrate 610 (S33) ((c) of
Then, on the substrate 610 on which the electroconductor pattern and the heat generating element 620 are placed, an insulating coat layer 680 for effecting electrical, mechanical and chemical protection is formed (S34) ((d) of
A cross-section, taken along A-A line (
In the case where a voltage is applied between adjacent electrodes, a current principally flows through the heat generating element 620 from an entire region of the electrode side surfaces providing a minimum current path, and in addition, the current flows through the heat generating element 620 from the electrode upper and lower surface. That is, in this embodiment, current concentration at the connecting portion between each of the heat generating elements 620 and the electrodes is suppressed. For that reason, in each of the heat generating elements 620 in this embodiment, the local abnormal heat generation is suppressed, so that deterioration is suppressed. For that reason, compared with the conventional example, the risk that the connecting portion between each of the heat generating elements and the electrodes is peeled off is low.
(Current Density Simulation)
In each of the heaters 600 in Embodiment 1, Embodiment 2 and the conventional example, the state of a distribution of the ease of a flow of the current through the heat generating element 620 was checked by simulation.
The result of the simulation made in a state in which the electrodes (electrode portions) and the heat generating element are arranged by following a positional relationship between adjacent electrodes (e.g., the electrodes 642a and 662a) arranged with a gap in the cross-section taken along the A-A line (
In the simulation of the heater in the conventional example, a voltage of 60 V is applied between the left and right electrodes. In the simulation of the heater in Embodiment 1, a voltage of 36 V is applied between the electrodes so that the heat generation amount of the heat generating element between the electrodes is similar to that in the simulation of the heater in the conventional example. In the simulation of the heater in Embodiment 2, a voltage of 26 V is applied between the electrodes so that the heat generation amount of the heat generation element between the electrodes is similar to that in the simulation of the heater in the conventional example.
The difference among these applied voltages results from a difference in resistance of the heat generating element generated due to a difference in manner of lamination of the electrodes and the heat generating element.
In each of the simulations, a result of parameters of the blocks where the current density becomes high is shown in Table 1.
As shown in
In the simulation in Embodiment 1, as shown in
Of the blocks (J1 to J6, J50 to J55, K6 to T6, K50 to T50) at the connecting portions adjacent to the left and right electrodes of the heat generating element, the maximum degree of the ease of the current flow is shown at the blocks K6 and K50. A value thereof is 1.57, which is about 0.9 times the degree (1.7) of the ease of the current flow at the blocks of the position of 28 in the abscissa.
In the simulation in Embodiment 2, as shown in
From the above results, it was understood that in Embodiments 1 and 2, the current concentration is alleviated compared with the conventional example. Particularly, it was understood that in Embodiments 1 and 2, the current concentration is alleviated at the connecting portion of the heat generating element with the electrodes.
(Heat Cycle Test)
A heat cycle test was conducted using ten heaters in each of embodiment 1, Embodiment 2 and the conventional example. In this test, each heater is caused to generate heat by being energized so that the heater temperature becomes 250° C., and the heater is cooled to 50° C. (one cycle). This cycle was repeated 300×103 times. A result is shown in Table 2.
As shown in Table 2, in the conventional example, of the 10 heaters, 2 heaters were incapable of achieving the heat cycle of 300×103 times. Of the 2 heaters, one heater generated partial peeling off at the connecting portion between the common electrode 642g and the heat generating element 620l at the time of the heat cycle of 270×103 times, and the other heater generated partial peeling-off at the connecting portion between the opposite electrode 662a and the heat generating element 620b at the time of the heat cycle of 250×103 times. On the other hand, in each of Embodiments 1 and 2, all of the 10 heaters were capable of achieving the heat cycle of 300×103 times.
As described above, with respect to the heater 600 in each of Embodiments 1 and 2, the common electrode 642 and the opposite electrodes 652 and 662 are covered with the heat generating element 620. The spaces each between the adjacent electrodes are filled with the heat generating element 620. For that reason, it is possible to connect, by the heat generating element, the shortest path connecting the adjacent electrodes. For that reason, the current flow does not readily generate a by-pass, so that the current concentration is not readily generated. The contact area between the electrodes and the heat generating element 620 is increased, so that the path of the current flowing from the electrodes to the heat generating element 620 is dispersed, and thus the current concentration is suppressed. For that reason, with respect to the heater 600 in each of Embodiments 1 and 2, the generation of local overheating of the heat generating element due to the current concentration is suppressed. Accordingly, according to Embodiments 1 and 2, thermal deterioration of the heater 600 due to local heat generation of the heat generating element 620 (particularly at the connecting portion of the heat generating element 620 with the electrode) can be suppressed, and therefore, it is possible to provide the heater having a long lifetime.
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 that 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 satisfy the condition 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 number of patterns of the heat generating region of the heater 600 is not limited to two. For example, three or more patterns may be 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.
Further, in the fixing device 40 in Embodiment 1, by the constitution in which all of the electrical contacts are disposed in one longitudinal end portion side of the substrate 610, the electric power is supplied from one end portion side to the heater 600, but the present invention is not limited to such a constitution. For example, a fixing device 40 having a constitution in which electrical contacts are disposed in a region extended from the other end of the substrate 610 and then the electric power is supplied to the heater 600 from both of the end portions may also be used.
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 may be used, 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 the necessary device, equipment and casing structure.
The image heating apparatus is not limited to the apparatus 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 the glossiness and/or the 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. 2014-183707 filed on Sep. 9, 2014, which is hereby incorporated by reference herein in its entirety.
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