JP5479075B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.

  As a fixing device mounted on a copying machine or a printer, there is an apparatus having an endless belt, a ceramic heater that contacts an inner surface of the endless belt, and a pressure roller that forms a fixing nip portion with the ceramic heater via the endless belt. . When small-size paper is continuously printed by an image forming apparatus equipped with this fixing device, a phenomenon (temperature increase of the non-sheet passing portion) occurs in which the temperature of the region where the paper does not pass in the longitudinal direction of the fixing nip portion gradually increases. If the temperature of the non-sheet passing part becomes too high, the parts in the device will be damaged, or if printing on large size paper with the non-sheet passing part temperature rise, the non-sheet passing part of small size paper The toner may be offset at a high temperature in a region corresponding to.

  As one of the methods for suppressing the temperature rise of the non-sheet passing portion, a heating resistor on the ceramic substrate is formed of a material having a positive resistance temperature characteristic, and the short direction of the heater (recording paper) with respect to the heating resistor. It is considered that two conductors are arranged at both ends of the substrate in the short direction so that a current flows in the direction of the sheet. When the temperature of the non-sheet-passing part rises, the resistance value of the heating resistor in the non-sheet-passing part rises, and the current flowing through the heating resistor in the non-sheet-passing part is suppressed, thereby suppressing the heat generation in the non-sheet passing part. This is the idea. The positive resistance temperature characteristic is a characteristic in which the resistance increases as the temperature rises, and is hereinafter referred to as PTC (Positive Temperature Coefficient).

  However, the material of PTC has a very low volume resistance, and it is very difficult to set the total resistance of the heating resistor of one heater within a range that can be used with a commercial power source. In view of this, the PTC heating resistor formed on the ceramic substrate is divided into a plurality of heating blocks in the longitudinal direction of the heater, and each heating block is configured so that a current flows in the short direction of the heater (the conveyance direction of the recording paper). The two conductors are arranged at both ends of the substrate in the short direction. Further, Patent Document 1 discloses a configuration in which a plurality of heat generating blocks are electrically connected in series. This document also discloses that a plurality of heating resistors are electrically connected in parallel between two conductors to form a heating block.

JP 2005-209493 A

  However, with the shape of the heat generating block disclosed in Patent Document 1, even when large-size paper that does not cause the temperature rise of the non-paper passing portion described above is passed, a region that generates heat in the longitudinal direction of the heater and heat generation It was found that there was a region that did not. If there are areas that generate heat and areas that do not generate heat, uneven fixing of the image will occur.

  In addition, when one heating block has a structure in which a plurality of heating resistors are electrically connected in parallel between two conductors, the position of the heating resistor in the heating block and the non-sheet passing portion rise It has been found that the effect of suppressing the temperature rise at the non-sheet passing portion is reduced unless the positional relationship of the end portions of the recording material for which the temperature is to be suppressed is accurately defined.

The present invention for solving the above-described problems includes an image forming unit that forms an unfixed image on a recording material, an endless belt, a heater that contacts an inner surface of the endless belt, and the heater via the endless belt. A fixing unit that heats and fixes an unfixed image onto a recording material while sandwiching and transporting a recording material carrying an unfixed image at the nip portion, the heater However, the substrate, the first conductor provided on the substrate along the longitudinal direction of the substrate, and the first conductor on the substrate along the longitudinal direction at different positions in the lateral direction of the substrate. A second conductor provided, and a plurality of heating resistors having positive resistance temperature characteristics and electrically connected in parallel between the first conductor and the second conductor; And the heating resistor is provided Having a fixing portion which has a structure of the heating block having a plurality of heating resistors is farthest outermost portion is the parallel connection from the recording material conveyance reference in the longitudinal direction of the substrate in the region where there In the image forming apparatus, the plurality of heat generating resistors are in the longitudinal direction and the heat generating resistors are overlapped in the longitudinal direction with respect to adjacent heat generating resistors in the longitudinal direction. A recording material of at least one specific size of a size smaller than the largest size among the standard recording material sizes which are arranged obliquely with respect to the recording material conveyance direction and which the apparatus supports. when passing through the nip, the side of the end portion in the longitudinal direction of the recording material, prior to the two ends in the heating block the are arranged on the outermost end portion So as to pass between the area where the heating resistors are arranged, and the plurality of heating resistors are arranged.

  According to the present invention, it is possible to suppress the temperature rise of the non-sheet passing portion when a recording material of a specific size is passed while suppressing unevenness in heat generation.

Sectional view of a fixing device mounted in the image forming apparatus of the present invention Heater configuration diagram of Example 1 The figure which showed the relationship with the paper size of the heater of Example 1. Explanatory drawing of the non-paper passing portion temperature rise suppression effect of the heater of Example 1 Heater control flowchart of Example 1 Sectional view of the image forming apparatus of the present invention Heater configuration diagram of Example 2 Heater configuration diagram of Example 3 Heater configuration diagram of Example 4

  FIG. 6 is a sectional view of a laser printer (image forming apparatus) using an electrophotographic recording technique. When the print signal is generated, the scanner unit 21 emits a laser beam modulated according to the image information, and scans the photoconductor 19 charged to a predetermined polarity by the charging roller 16. As a result, an electrostatic latent image is formed on the photoreceptor 19.

  Toner is supplied from the developing unit 17 to the electrostatic latent image, and a toner image corresponding to image information is formed on the photoreceptor 19.

  On the other hand, the recording material (recording paper) P loaded in the paper feeding cassette 11 is fed one by one by the pickup roller 12 and conveyed toward the registration roller 14 by the roller 13. Further, the recording material is conveyed from the registration roller 14 to the transfer position in accordance with the timing at which the toner image on the photoconductor 19 reaches the transfer position formed by the photoconductor drum 19 and the transfer roller 20. The toner image on the photoconductor 19 is transferred to the recording material P while the recording material P passes through the transfer position.

  Thereafter, the recording material P is heated by the fixing unit 100, and the toner image is heat-fixed on the recording material P. The recording material P carrying the fixed toner image is discharged to a tray above the printer by rollers 26 and 27. Reference numeral 18 denotes a cleaner for cleaning the photoconductor 19, and 28 denotes a paper feed tray (manual feed tray) having a pair of recording material regulating plates whose width can be adjusted according to the size of the recording material.

  The paper feed tray 28 is provided to cope with recording materials having a size other than the standard size. A pickup roller 29 feeds the recording material from the paper feed tray 28, and a motor 30 drives the fixing unit 100 and the like. The photosensitive member 19, the charging roller 16, the scanner unit 21, the developing device 17, and the transfer roller 20 described above constitute an image forming unit that forms an unfixed image on a recording material.

  The printer of this example is an A4 size (210 mm × 297 mm) compatible printer corresponding to the LETTER size (about 216 mm × 279 mm). In other words, it is a printer that basically feeds A4 size paper vertically (conveys so that the long side is parallel to the carrying direction), but it is designed so that LETTER size paper that is slightly wider than A4 size can also be fed vertically. It is.

  Accordingly, the largest (largest width) size among the standard recording material sizes (corresponding paper sizes on the catalog) supported by the apparatus is the LETTER size.

  FIG. 1 is a cross-sectional view of a fixing device (fixing unit) 100. The fixing device 100 includes a cylindrical film (endless belt) 102, a heater 200 that contacts the inner surface of the film 102, and a pressure roller (nip portion forming member) that forms a fixing nip portion N together with the heater 200 via the film 102. 108). The material of the base layer of the film is a heat resistant resin such as polyimide, or a metal such as stainless steel. The pressure roller 108 includes a cored bar 109 made of iron or aluminum and an elastic layer 110 made of silicone rubber or the like.

  The heater 200 is held by a holding member 101 made of heat resistant resin. The holding member 101 also has a guide function for guiding the rotation of the film 102. The pressure roller 108 receives power from the motor 30 and rotates in the direction of the arrow. As the pressure roller 108 rotates, the film 102 is driven and rotated.

  The heater 200 includes a ceramic heater substrate 105, a heating line A (first row) and a heating line B (second row) formed on the substrate 105 using a heating resistor, and heating lines A and B. An insulating (covering glass in this embodiment) surface protective layer 107 is provided. A temperature detection element 111 such as a thermistor is in contact with the sheet passing area of the minimum size paper (envelope DL: 110 mm width in this example) set on the back side of the heater substrate 105 and used in the printer. .

  The electric power supplied from the commercial AC power source to the heat generation line is controlled according to the detected temperature of the temperature detecting element 111. The recording material (paper) P carrying the unfixed toner image is heated and fixed while being nipped and conveyed by the fixing nip N.

  A safety element 112 such as a thermo switch that operates when the heater is abnormally heated and shuts off the power supply line to the heat generation line is also in contact with the back surface side of the heater substrate 105. Similarly to the temperature detecting element 111, the safety element 112 is also in contact with the paper passing area of the minimum size paper. Reference numeral 104 denotes a metal stay for applying a spring pressure (not shown) to the holding member 101.

  FIG. 2 is a view for explaining the structure of the heater. 2A is a plan view of the heater, FIG. 2B is a sectional view of the heater, and FIG. 2C is an enlarged view showing one heat generation block A1 in the heat generation line A. The heating resistor in the heating line A and the heating resistor in the heating line B are both PTC.

  The heat generation line A (first row) has 20 heat generation blocks A1 to A20, and the heat generation blocks A1 to A20 are connected in series. The heat generation line B (second row) also has 20 heat generation blocks B1 to B20, and the heat generation blocks B1 to B20 are also connected in series.

  The heat generation line A and the heat generation line B are also electrically connected in series. Electric power is supplied to the heat generation lines A and B from electrodes AE and BE connecting the power feeding connectors. The heat generation line A is provided along the longitudinal direction of the substrate at a position different from the conductive pattern Aa (first conductor of the heat generation line A) provided in the longitudinal direction of the substrate and the conductive pattern Aa in the lateral direction of the substrate. The conductive pattern Ab (second conductor of the heat generation line A) is provided. The conductive pattern Aa is divided into 11 (Aa-1 to Aa-11) in the longitudinal direction of the substrate.

  The conductive pattern Ab is divided into ten (Ab-1 to Ab-10) in the longitudinal direction of the substrate. Since the structure of the heat generation line B is the same as that of the heat generation line A, description thereof is omitted.

  FIG. 2B shows a sectional view of the heater 200. When manufacturing the heater 200, first, the heating resistors A and B are formed on the heater substrate 105, the conductive patterns Aa, Ab, Ba, and Bb are then formed, and finally the surface protective layer 107 is formed. .

  Because of this order of formation, when the cross section of the heater is viewed as shown in FIG. 2B, the conductive pattern covers the heating resistor (FIG. 2B shows the heater of FIG. 1). The layer to be formed later is shown below).

  If the conductive pattern is formed on the heater substrate 105 before the heating resistor, a part of the heating resistor is covered on the conductive pattern, and the cross-sectional shape of the heating resistor is deformed. The resistance value of the heating resistor is proportional to the length and inversely proportional to the width. However, when the cross-sectional shape is deformed, the region in which the current flows in the heating resistor changes, and the size of the heating resistor (of FIG. 2B) The resistance value as shown in the area viewed from the arrow L direction may not be shown. Therefore, it becomes difficult to set the resistance value of the heating resistor as designed.

  However, if the heating resistor is formed prior to the conductive pattern as in this example, the sectional shape of the heating resistor does not change, so that the resistance value of the heating resistor can be easily set as designed. is there.

  FIG. 2C shows a detailed view of the heat generation block A1. As shown in FIG. 2C, a plurality (eight in this example) are formed between the conductive pattern Aa-1 which is a part of the conductive pattern Aa and the conductive pattern Ab-1 which is a part of the conductive pattern Ab. ) Heating resistors (A1-1 to A1-8) are electrically connected in parallel to form a heating block A1. The size (line length (a−n) × line width (b−n)), layout (interval (c−n)), and resistance value of each heating resistor in the heat generation block A1 are shown in FIG. It is as follows.

  As shown in FIG. 2, each heating resistor is disposed obliquely (angle θ) with respect to the longitudinal direction of the substrate and the recording material conveyance direction. As shown in FIG. 2C, the heating block length c is the length in the heater longitudinal direction from the center of the short side of the heating resistor at the left end to the center of the short side of the heating resistor at the right end. Define as

  In the heater 200, the heating resistor intervals c-1 to c-8 are equally spaced not only in the heat generation block A1 but also in other heat generation blocks, and all the intervals are set to c / 8. The heat generation block A1 improves the uniformity of the heat generation amount of the heat generation resistors A1-1 to A1-8 by changing the line width of the heat generation resistors in order to make the heat distribution in the heater longitudinal direction of the heat generation block uniform. Yes.

  The heating block A1 has a lower resistance value as the heating resistor (A1-4, A1-5) in the center portion and a higher resistance value as the heating resistor (A1-1, A1-8) in the end portion. The line width b-n of each heating resistor is set. The table shown in FIG. 2C shows the sizes and resistance values of the eight heating resistors in the heating block A1.

  Here, the length (ann: a-1 to a-8) and the interval (cn: c-1 to c-8) of the heating resistor are constant, and the line width (bn: b-1). ˜b-8) is changed so that the heat generation distribution of the heat generation block A1 becomes uniform. Since the resistance value of the heating resistor is proportional to the length / line width, the resistance value of the heating resistor may be adjusted by changing the length of the heating resistor in the same manner as the line width. Also, as shown in FIG. 2C, the current distribution flowing in the heating resistor can be made more uniform by making the heating resistor shape rectangular.

  For example, if the heating resistor is made into a parallelogram, a large amount of current flows through the shortest path of the resistor, so the current distribution flowing through the heating resistor may be biased. It becomes easier for the current to flow uniformly through the entire resistor.

  However, the effect of suppressing the temperature rise of the non-sheet passing portion can be obtained even when a parallelogram heating resistor is used, and the shape of the heating resistor is not limited to a rectangle. Further, as shown in FIG. 2C, in one heating block, the shortest current path of each of the plurality of heating resistors is in the longitudinal direction with respect to the outermost current path of the heating resistors adjacent in the longitudinal direction of the substrate. The plurality of heating resistors are arranged obliquely with respect to the longitudinal direction and the recording material conveyance direction so as to have an overlapping positional relationship.

  This positional relationship is such that the outermost heating resistor in one heating block (for example, the rightmost heating resistor A1-8 in the heating block A1) and the outermost heating resistor in the adjacent heating block (for example, The same applies to the leftmost heating resistor A2-1) in the heating block A2. Since the heating resistor of this example has a rectangular shape, the entire region of one heating resistor is the endmost current path.

  In this example, as shown in FIG. 2C, the central portion of the rectangular short side of one heating resistor overlaps the central portion of the rectangular short side of the adjacent heating resistor in the longitudinal direction of the substrate. Thus, the respective heating resistors are arranged.

  FIG. 3 is a diagram for explaining the temperature rise of the non-sheet passing portion of the heater 200. This heater is arranged so that the central portion of the region (heat generation line length) where the heating resistor is provided in the longitudinal direction of the substrate matches the recording material conveyance reference X of the printer. In this example, A4 size (210 mm × 297 mm) paper is fed vertically (when the 297 mm side is fed in parallel with the carrying direction), and the center of the 210 mm side of A4 size paper is shown as an example. The paper feed cassette 11, the paper feed tray 28, various transport rollers, a fixing unit, and the like are arranged so that the value matches the reference X.

  As shown in FIGS. 2 and 3, a plurality of regions in which the heating resistors are provided (= the heating line length) that are farthest from the recording material conveyance reference X in the longitudinal direction of the substrate are connected in parallel. It has a heat generating block structure (A1 (B1) and A20 (B20)) having a heat generating resistor. In order to be able to print LETTER size paper (approximately 216 mm × 279 mm) in the longitudinal direction, the heating line length of the heater is 216 mm.

  As described above, the printer of this example is compatible with the LETTER size, but is basically a printer compatible with A4 size paper. Therefore, it is a printer for users who use A4 size paper most frequently. However, since it supports LETTER size, when A4 size paper is printed, a non-sheet passing region is generated by 3 mm at both ends of the heat generation line. During the fixing process, the power supplied to the heater is controlled so that the detected temperature of the temperature detecting element 111 that detects the heater temperature near the recording material conveyance reference X maintains the control target temperature. Therefore, since heat is not deprived of paper in the non-sheet passing portion, the temperature of the non-sheet passing portion rises compared to the sheet passing portion. In this example, the LETTER size is the maximum size and the A4 size is the specific size.

  FIG. 4 shows the relationship between the heating resistor formed on the heater substrate and the recording material end passage position (FIG. 4A), and the circuit diagram of the heater used for the simulation of the temperature rise of the non-sheet passing portion (FIG. 4). FIG. 4B is a diagram (FIG. 4C) showing a simulation result of the passing position of the recording material and the heat generation distribution of the heater.

  FIG. 4A shows the positional relationship between the heat generation blocks A1 and B1 and the end of the recording material. The positions of the end portions of the recording material are D1 (0 mm), D2 (1.0 mm), D3 (2.0 mm), D4 (9.5 mm), D5 (10.4 mm), respectively, from the left ends of the heat generation lines A and B. D6 (11.4 mm).

  In the case of this example, the position D1 is a position through which the end of the paper passes when the LETTER size paper is transported according to the reference X. Further, the positions D2 and D5 are cases where the end of the recording material passes through the heat generating resistors (A1-1, A1-8, B1-1, B1-8) at the extreme ends of the heat generating blocks A1 and B1. Assumed. Position D3 and position D4 assume a case where the end of the recording material does not pass through the heating resistors (A1-1, A1-8, B1-1, B1-8) at the extreme ends of the heating blocks A1 and B1. ing.

The simulation result in FIG. 4C assumes a state in which the heater is controlled at a control target temperature of 200 ° C. and the non-sheet passing region is heated to 300 ° C. That is, when the non-sheet passing region is 300 ° C., the power supplied to each heating resistor is calculated and converted into a heat generation amount. In addition, the resistance temperature coefficient of the heating resistor of this example is 1000 ppm, and the resistance value of the heating resistor heated to 300 ° C. is increased by 10% with respect to the heating resistor at 200 ° C.

  FIG. 4B is a simulation circuit diagram in which the conditions are simplified. The sheet resistance value of the conductive pattern is calculated as 0.005Ω / □, and the sheet resistance value of the heating element paste is calculated as 0.75Ω / □ (at 200 ° C.). The resistance values of the heat generation patterns A1-1 and A1-8 included in the heat generation block A1 are 2.23Ω, the resistance values of the heat generation patterns A1-2 and A1-7 are 2.06Ω, and the heat generation patterns A1-3 and A1-6 The resistance value is 1.95Ω, and the resistance values of the heat generation patterns A1-4 and A1-5 are 1.89Ω.

  When both ends of adjacent heat generation patterns in the heat generation block are connected by a conductive pattern having a line length of 1.35 mm and a line width of 1 mm, the resistance value r of the conductive pattern connecting the heat generation patterns is 0. .007Ω. The description of the heat generation block B1 is omitted because it matches the heat generation block A1. In FIG. 4B, the heat generation blocks other than A1 and B1, which are necessary for explanation, are simply shown as a combined resistance value R.

  When the heat generation pattern temperature of the non-sheet-passing portion reaches 300 ° C. or more, the heat resistance of the heat-resistant rubber elastic body 110, the film 102, the film guide 101, etc. of the pressure roller 108 becomes a limit and the fixing device is damaged. Since there is a possibility, the temperature of non-sheet passing portion temperature rise is set to 300 ° C. The set temperature is not particularly limited because it varies depending on the material and the configuration. Further, in practice, there is a continuous temperature distribution in the non-sheet-passing area or the edge of the sheet-passing area, but for simplification, D1 in FIG. 4A, which is the boundary between the non-sheet-passing area and the sheet-passing area. The simulation was performed with the temperature rising to 300 ° C. in the non-sheet passing region and the temperature in the sheet passing region being 200 ° C. with ˜D6 as a boundary. Since the conductive pattern has a low resistance value and is less affected by a change in resistance due to a temperature rise, this simulation does not consider the change in resistance of the conductive pattern due to temperature.

  FIG. 4C is a simulation result showing the heat generation distribution of the heater 200 under the above conditions. From the simulation results, it can be seen that when the end positions of the recording material are D3 and D4, the amount of heat generated in the non-sheet passing area is suppressed compared to the sheet passing area. It can be seen that when the end position of the recording material is D6, there is no difference in the amount of heat generated between the sheet passing area and the non-sheet passing area, and the effect of reducing the amount of heat generated in the non-sheet passing area cannot be obtained. When the end position of the recording material is located at the gap position D6 of the heat generating block, the plurality of heat generating blocks are electrically connected in series, so that the heat generating blocks A1 and B1 as a whole are heated by the non-sheet passing portion temperature rise. This is because the resistance value increases.

  When the end of the recording material is at position D1, the end of the heat generation line coincides with the end of the sheet, and there is no non-sheet passing area. It can be seen that when the end positions of the recording material are D2 and D5, the effect of suppressing the temperature rise of the non-sheet passing portion is reduced as compared with the end positions D3 and D4.

  Therefore, the heat generation pattern and the heat generation block are formed so that the end of the small size paper (A4 paper) passes through the inside of the heat generation pattern at both ends of the heat generation block (between D3 and D4 in FIG. 4A). Thus, the effect of suppressing the temperature rise of the non-sheet passing portion of the heater 200 can be effectively obtained.

  In the above simulation, the amount of heat generated when the temperature of the non-sheet passing portion region reaches 300 ° C. is explained, but the end portion of the specific size paper passes between D3 and D4 in FIG. In fact, the temperature rise in the non-sheet passing area can be suppressed. In the heater 200, when the temperature rises in the non-sheet-passing area, the amount of heat generated in the non-sheet-passing area can be suppressed as shown in FIG.

  As described with reference to FIG. 4, it is desirable to form both the heat generation line A and the heat generation line B so that the end of the small-size paper passes inside the heat generation pattern at both ends of the heat generation block. When the lengths of the heat generation lines A and B in the substrate longitudinal direction are different, the above effect can be obtained if the shape of the heat generation block at the end of the longer heat generation line is designed in consideration of specific size paper. .

  By the way, particularly when feeding paper from the paper feed tray 28, one of the long sides of the A4 size paper is moved along the recording paper restriction plate while the recording paper position restriction plate is accidentally widened to the LETTER size interval. It is also possible to feed them together. That is, this is a case of feeding A4 size paper without matching the recording material conveyance reference X, that is, a so-called side-by-side paper case. In this case, a non-sheet passing region of 6 mm is generated on one side of the heat generation line. This misaligned paper can also occur when paper is fed from the paper feed cassette 11. For example, this occurs in a case where after the paper is set in the paper cassette 11, the paper cassette is returned to the image forming apparatus main body without restricting the paper position by the paper position restriction plate in the paper cassette. obtain.

  It is preferable to design the shape of the heating resistor in consideration of such an irregular case. In the heater having the heat generation line length of 216 mm, the non-sheet passing area width is 3 mm when the A4 size paper is fed in the vertical direction (small size paper 210 mm) with reference to the center portion, and one side of the heat generation line. When the paper is passed in a state of being justified, the width of the non-sheet passing area is 6 mm, since the end of the paper passes between D3 to D4 of the heater 200, so that the A4 size paper is based on the center of the heater 200. The effect of suppressing the temperature rise of the non-sheet passing portion can be obtained when the paper is passed through the paper and when the paper is fed away.

  Although the present embodiment has been described with the A4 size (210 mm × 297 mm) compatible printer corresponding to the LETTER size (about 216 mm × 279 mm), for example, A3 for SRA3 size (A3 stretch size) longitudinal feed (width 320 mm). The present invention can also be applied to a size vertical feed (width 300 mm) printer and an A3 vertical feed (300 mm) printer compatible with LETTER size horizontal feed (279 mm).

  FIG. 5 is a flowchart illustrating a control sequence of the fixing device 100 by a control unit (CPU) (not shown). In the first embodiment, an image forming apparatus capable of printing indefinite form paper fed from the manual paper feed tray 28 using two paper sizes of Letter and A4 as standard form papers is described.

  The maximum processing speed of this printer is 42 ppm. In step S501, it is determined whether a print start request is generated. When the request is generated, the process proceeds to step S502. In step S <b> 502, it is determined whether the standard paper print fed from the paper feed cassette 11 or the irregular paper print fed from the manual paper feed tray 28 is used. In the case of standard paper printing, the process proceeds to S503, and the size of the recording material set in the paper feed cassette 11 is detected. In S504, it is determined whether the size of the recording material is LETTER size. When the size of the recording material is the LETTER size, the process proceeds to S506 and the counter is set to N = 9999.

  This counter indicates the number of sheets that are allowed to be continuously printed at the maximum processing speed. In the case of the LETTER size, no non-sheet passing portion is generated, so N = 9999 (= infinite) is set. That is, it can be output infinitely at a rate of 42 ppm. In S505, it is determined whether the size of the recording material is A4 size. When the size of the recording material is A4 size, the process proceeds to S507 and the counter is set to N = 500.

  In the case of A4 size, the maximum number of sheets allowed to be continuously printed at the maximum processing speed (42 ppm) is 500 sheets. If the shape of the heating resistor is not considered in consideration of A4 size paper as described above, the counter value in the case of A4 size paper must be set small. When the paper set in the paper feed cassette 11 is less than A4 size, or when printing indeterminate paper fed from the manual paper feed tray 28, the process proceeds to S508, and the counter is set to N = 10. In S509, “N = N−1” is subtracted. In S510, it is determined whether the counter N is 0 or less. When the counter N is not 0 or less (that is, 1 or more), the process proceeds to S511, and a normal image forming step is performed.

  In S511, the print processing is performed with the control target temperature (fixing target temperature) of the heater 200 set to 200 ° C. and the process speed set to the full speed (processed at a speed of 42 ppm). When the counter N is 0 or less in S510, the process proceeds to S512, the control target temperature (fixing target temperature) of the heater 200 is lowered to 170 ° C., the throughput of the image forming apparatus is lowered, and the process speed is reduced to half speed (21 ppm). Print processing as speed). If the process speed is set to half speed, the paper moving speed in the fixing nip is halved, so that the fixing property can be secured even at a lower heater temperature than the full speed. Further, since the fixing target temperature is lowered, the temperature of the non-sheet passing portion can also be suppressed.

  The above processing is repeated in S513 until there is no remaining print job, and the throughput of the image forming apparatus, the image forming process speed, and the fixing target temperature are set. When the paper size is LETTER size, the heat generation line length of the heater 200 is designed to be optimized to LETTER size, so even if the maximum continuous print number of the image forming apparatus is continuously passed, the non-sheet passing portion Little temperature rise occurs.

  For this reason, the counter value is set to N = 9999, so that the number of continuous prints is not limited. When the paper size is A4, the non-sheet-passing portion temperature rises. However, since the effect of suppressing the non-sheet-passing portion temperature increase described in FIG. 4 can be obtained, the process speed is full speed and the fixing target temperature is 200 ° C. Even if 500 sheets are printed continuously, the fixing device is not damaged. When the paper size is undetermined paper, the effect of suppressing the non-sheet passing portion temperature rise may be reduced as described with reference to FIG. Therefore, the number of sheets that can be continuously printed at the full speed (42 ppm) is limited to 10. In a normal printer, paper sizes other than LETTER and A4 are set as standard paper. For standard sizes other than the LETTER size and the A4 size, the counter value, the throughput of the image forming apparatus, the process speed of the image forming apparatus, the fixing target temperature, etc. can be individually set so as to prevent the temperature rise of the non-sheet passing portion for each size. It ’s fine.

  Further, in an image forming apparatus having a thermistor as a second temperature detection element in the vicinity of both ends of the heat generation line of the heater 200, when the detected temperature of the end thermistor reaches a predetermined threshold, the throughput of the image forming apparatus. The image forming process may be half speed and the fixing target temperature may be controlled to 170 ° C.

  Further, the predetermined threshold value for reducing the throughput may be set lower in the case of non-standard paper than the standard paper. By performing the control shown in the flowchart shown in FIG. 5, it is possible to obtain a more appropriate non-sheet-passing portion temperature rise suppression effect.

As described above, 1. In the region where the heating resistors are provided, the endmost portion farthest from the recording material conveyance reference in the longitudinal direction of the substrate has a structure of a heating block having a plurality of heating resistors connected in parallel. Yes. 2. The plurality of heating resistors are inclined obliquely with respect to the longitudinal direction and the recording material conveyance direction so that the heating resistors are in a positional relationship overlapping with each other in the longitudinal direction. Are arranged. 3. When at least one recording material of a specific size out of the largest recording material sizes of the standard recording material sizes supported by the device passes through the nip portion, the side of the end in the longitudinal direction of the recording material but so as to pass between the area where the heating resistors at both ends of the inside of the heating block located endmost component is arranged, a plurality of heating resistors are placed, the structure of that heater By using the image forming apparatus, it is possible to provide an image forming apparatus capable of suppressing the temperature rise of the non-sheet passing portion when the recording material having a specific size is passed while suppressing unevenness in heat generation.

  Next, a second embodiment in which the heater mounted on the fixing unit of the image forming apparatus is changed will be described. The description of the same configuration as in the first embodiment is omitted.

  FIG. 7 is a diagram illustrating a configuration of the heater 700 according to the second embodiment. The heater 700 has a configuration in which the heat generation line A (first row) and the heat generation line B (second row) can be independently driven by two heater driving circuits. For this purpose, the electrode CE is connected to the heater 200 of the first embodiment. It is added between the heat generation lines A and B. The heat generation line A is supplied with electric power through the electrodes AE and CE, and the heat generation line B is supplied with electric power through the electrodes BE and CE. The configuration is the same as the heater 200 except that the electrode CE is added. Thus, the present invention can also be applied to a heater having a configuration in which the heat generation lines A and B can be controlled independently.

  Next, a description will be given of a third embodiment in which the heater mounted on the fixing unit of the image forming apparatus is changed. The description of the same configuration as in the first embodiment is omitted.

FIG. 8 is a schematic view for explaining a heater 800 used in this embodiment. FIG. 8A shows a heat generation pattern and a conductive pattern of the heater 800. The heater 800 has a heat generation line A. The heat generation line A is divided into 20 heat generation blocks, and each heat generation block is connected in series. The heater 800 supplies power to the heat generation line A from the electrodes AE1 and AE2. FIG. 8B shows a detailed view of the heat generation block A1.

  The heat generation block A1 has a heat generation pattern A1-8 with a line length a-8, a line width b-8, and a slope θ-8, from a heat generation pattern A1-1 with a line length a-1, a line width b-1, and a slope θ-1. Up to eight lines are arranged at intervals c-1 to c-8, and are connected in parallel via the conductive pattern. The heat generation block A is characterized in that the density of the heat generation patterns 1 to 8 is increased toward the center of the heat generation block by changing the heat generation pattern interval and the inclination in order to make the heat generation distribution in the heater longitudinal direction of the heat generation block uniform. The present invention can also be applied to the case of using a heater shown in FIG. 8 that does not have a plurality of heat generation lines (only one heat generation line).

  FIG. 9 is a diagram illustrating a configuration of the heater 900 according to the fourth embodiment. As shown in FIG. 9A, the heating blocks A1, A2, B1, and B2 similar to the heater 200 of the first embodiment are provided at both ends of the heater 900 in the longitudinal direction. Between the heat generation block A1 and the heat generation block A2 of the heat generation line A, a heat generation pattern AP made of one heat generation resistor is connected in series with the heat generation blocks A1 and A2. The heat generation line B has the same configuration as the heat generation line A. As described above, the heating block of each row of the heater 900 is provided at the end in the longitudinal direction of the substrate, and one heating block is provided on the paper passing reference side (in this example, the central side in the longitudinal direction of the substrate). A heating pattern made of a heating resistor is connected.

  FIG. 9B shows an enlarged view of a part of the heat generation block A1 representing the four heat generation blocks and the heat generation pattern AP connected to the heat generation block A1. In the heat generation block A1, eight rectangular heat generation patterns having a line length a and a line width b are arranged and connected in parallel via the conductive patterns Aa-1 and Ab-1. The heat generation blocks A2, B1, and B2 have the same configuration. The pattern width of the heat generation pattern AP is k.

  In the heater of FIG. 9, the heat generating paste used for the heat generating blocks A1, A2, B1, and B2 and the heat generating paste used for the heat generating pattern AP have different sheet resistance values. In order to adjust the heat generation amount per unit length in the substrate longitudinal direction of the heat generation block A1 and the heat generation pattern AP, a heat generating paste having a sheet resistance value lower than that of the heat generation block A1 is used for the heat generation pattern AP. As described above, the present invention can be applied to the heater having the heat generation block described in the first embodiment only at both ends of the heat generation line.

100 Fixing device 200 Line A (first row)
B Heat generation line B (second row)
A1 to A20 Heat generation block of heat generation line A B1 to B20 Heat generation block of heat generation line B Aa, Ab Conductive pattern of heat generation line A Ba, Bb Conduction pattern of heat generation line B A1-1 to A20-8, B1-1 to B20- 8 Heating resistor

Claims (4)

An image forming unit for forming an unfixed image on a recording material;
An endless belt, a heater that contacts an inner surface of the endless belt, and a nip portion forming member that forms a nip portion together with the heater via the endless belt, and carries a non-fixed image at the nip portion. A fixing unit that heats and fixes an unfixed image on a recording material while nipping and conveying the material, wherein the heater includes a substrate, a first conductor provided on the substrate along a longitudinal direction of the substrate, A second conductor provided on the substrate at a position different from the first conductor in the lateral direction of the substrate along the longitudinal direction; a positive resistance temperature characteristic; and the first conductor A plurality of heating resistors electrically connected in parallel between the second conductors, and from the recording material conveyance reference in the longitudinal direction of the substrate in the region where the heating resistors are provided the most distant top end portion A fixing unit which has a structure of the heating block with a heat generating resistor of the plurality of which are the parallel connection,
In an image forming apparatus having
Wherein the plurality of heating resistors, said to be a positional relationship overlapping in the longitudinal direction relative to the heating resistor adjacent in the longitudinal direction, the plurality of heating resistors in the longitudinal direction and the recording material conveyance direction At least one recording material having a specific size out of the largest size among the standard recording material sizes supported by the device and passing through the nip portion is disposed obliquely with respect to the device. When this is done, the side of the end of the recording material in the longitudinal direction passes between the regions where the heat generating resistors at both ends of the heat generating block disposed at the endmost portion are disposed. The image forming apparatus further comprising the plurality of heating resistors.   2. The heater according to claim 1, wherein the heater has a structure of the heat generating block in a portion other than a portion farthest from the recording material conveyance reference, and the heat generating blocks are electrically connected in series. Image forming apparatus. The image forming apparatus according to claim 1, wherein the heater has a plurality of rows in the recording material conveyance direction in which the heating resistor is provided . The apparatus further includes a paper feed tray having a pair of recording material restricting plates movable in the longitudinal direction according to the size of the recording material, and the recording material of the specific size is in a state where the restricting plate is most widened. If the fed paper side of the longitudinal ends in contact with one of said regulating plate and the edge in contact with the regulating plate of the recording material is disposed on the opposite side edges in the top end min 4. The heating element according to claim 1, wherein the plurality of heating resistors are arranged so as to pass between regions where the heating resistors are arranged at both ends of the heating block. The image forming apparatus according to claim 1.

Images