JP2005309062A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To correct a large curl amount caused by passing two fixing devices.
SOLUTION: In a fixing device having two or more fixing devices, a detecting means for detecting the direction and amount of the sheet curl is provided on the downstream side in the conveying direction with respect to the fixing device on the most upstream side in the conveying direction. Accordingly, the sheet curl correcting means located downstream in the conveying direction of the detecting means is controlled.
[Selection] Figure 1

Description

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

  The background art will be described with reference to a sectional view of the copying machine 115 in FIG.

  A document (not shown) placed under the pressure plate 100 is read by the document reading unit 101. Then, a latent image is formed on the photosensitive drum 102. The latent image is formed into a toner image by the developing device 103. Further, toner is replenished into the developing device 103 from a predetermined amount of hopper 104 according to a toner remaining amount sensor (not shown) provided in the developing device 103. The transfer paper P placed on the paper feeding device 105 is transported to the transfer / separation unit 107 via the transport path 106. The toner image formed with the image is transferred to the transfer paper P by the transfer / separation unit 107. Then, the toner is conveyed by the conveying unit 108, and the toner is melted and fixed to the transfer paper P by heat and pressure by the first fixing 109. Next, the transfer paper is transported by the transport unit 110, and the second fixing 111 performs the second fixing (see, for example, Patent Document 1 and Patent Document 2). Fixing that performs the fixing operation twice is hereinafter referred to as tandem fixing. There are two reasons for fixing twice.

  The first reason is that fixability may not be obtained depending on the type of transfer paper P. (Especially thick paper or coated paper) There is a limit to the amount of heat and pressure applied to a sheet in a single fixing operation. If you try to fix it by one fixing operation, image deterioration or paper wrinkles will occur during fixing. There is a fear.

  The second reason is that a large amount of gloss is supplied to the transfer paper P by fixing twice in order to improve the gloss on the transfer paper P after fixing. In particular, when copying a photograph on coated paper or the like, this effect is great because the glossy appearance is better.

  After being completely fixed on the transfer paper P by the second fixing 111, the transfer paper P is discharged onto the discharge tray 114 by the drawing roller 112 and the discharge roller 113.

The background art copying machine in FIG. 9 is a black and white copying machine, but a color copying machine can be configured in a tandem fixing manner with a similar structure.
Japanese Patent Laid-Open No. 2002-351237 Japanese Unexamined Patent Publication No. 2002-365967

  In a tandem fixing type copier, the transfer paper P passes through the two fixing devices, so the curl of the transfer paper P may increase. For example, in the case of tandem fixing in which two types of the same fixing devices are arranged, the direction of curl formed by the fixing is the same, so the curl amount may increase. In the case of tandem fixing in which different types of fixing devices (fixing devices having different curl directions) are arranged, curling may increase depending on the environment, paper type, toner amount, and the like.

  As a countermeasure, it is possible to change the fixing condition so that the curl formed by the first fixing is decurled (corrected curl) by the second fixing, but if the second fixing condition is changed for decurling, the tandem fixing is performed. In some cases, the desired fixing property and glossiness cannot be improved.

  Also, using the same fixing device to reduce the cost of the image forming apparatus may reduce the overall cost of the copying machine, so the possibility of tandem fixing using a fixing device of the same configuration is usually better. high.

  As another countermeasure, a configuration in which the curling of the transfer paper P is detected after passing through the second fixing (fixing device on the most downstream side in the conveyance direction) and decurling is performed according to the detected amount is possible. However, in order to provide a detection means for detecting the curl amount of the transfer paper P and a means for decurling after the second fixing, a sufficient distance is required between them, and in order to secure the space, a transfer paper transport path is required. There is a need to lengthen it. In particular, if the distance between the detection means and the decurling means is short, it takes a long time to decur according to the curl of the transfer paper P. Arise.

  In addition, in order to detect the curl (especially the top curl) of the transfer paper P, a sufficient space is required so that the curl can be detected in the vertically upward direction perpendicular to the transfer direction of the transfer paper P. The transport path after the second fixing does not have a vertical space that allows the transfer paper P to be detected.

  If the conveying path is lengthened, there arises a problem that the productivity of the image forming apparatus is lowered. Even in the case of tandem fixing, the conveyance path is longer than that of a copier having a single fixing unit, and the productivity of the image forming apparatus is reduced. It becomes a fatal fault. Further, it is necessary to increase the space of the entire image forming apparatus, and there are many problems such as cost increase and power consumption.

  It is not a realistic configuration to detect the curl of the transfer paper P and to decur it after exiting the second fixing due to the problems described above.

  When the curl amount of the transfer paper P is large, the transfer paper at the time of discharging is curled, and there is a problem that the transfer paper P is not stacked well on the tray. Further, when the paper is ejected, the end of the transfer paper may hit the conveyance guide or the like, and a conveyance jam may occur. In addition, the curled transfer paper has a bad impression on the user, which may impair the manufacturer's reliability.

  An object of the present invention is to provide a highly reliable copying machine that minimizes the curling of transfer paper in tandem fixing.

  The fixing device according to the present invention includes a plurality of fixing units that form a nip portion by a heating member and a pressure member, and includes a temperature adjusting unit that controls the temperature of each fixing unit, and is the most in the conveyance direction of the recording material. A deformation amount detecting means for detecting the deformation amount of the recording material is provided downstream of the fixing unit positioned on the upstream side in the recording material conveyance direction, and downstream of the deformation amount detection means in the conveyance direction of the recording material. And a deformation amount correcting means for correcting the deformation of the recording material.

The present invention has the following effects.
(1) It is possible to efficiently suppress deformation of the transfer paper that occurs when the transfer paper is passed through the two fixing devices. According to the configuration of the present invention, it is possible to correct the deformation of the transfer paper in the copying machine with reduced space and cost.
(2) By suppressing the deformation of the transfer paper, the conveyance failure after fixing is drastically reduced, and the conveyance failure in the conveyance unit and the image defect on the transfer paper after fixing can be prevented. As a result, the number of calls to service personnel is reduced, and reductions in service costs can be expected.
(3) The rubbing noise generated when the deformed portion of the transfer paper comes into contact with the conveyance path or the like can be reduced. As a result, the noise of the copying machine main body can be reduced, and the number of complaints from the user can be reduced to improve the reliability.

  Hereinafter, the present invention will be described more specifically with reference to examples. Although these examples are examples of the best mode of the present invention, the present invention is not limited to these examples.

  FIG. 1 is a cross-sectional view of an image forming apparatus equipped with a fixing device embodying the present invention. 2 and 3 are sectional views of a fixing device embodying the present invention. FIG. 4 is a cross-sectional view of the curl correcting means of the fixing device embodying the present invention. FIG. 5 is an electrical block diagram of a fixing device embodying the present invention. FIG. 6 is a flowchart of the fixing device. FIG. 7 shows the curl data detected by the curl detection means in the fixing device, the horizontal axis-time, and the vertical curl amount of the vertical axis. Parts having the same role as in FIG. 9 described in the background art are denoted by the same symbols, and description thereof is omitted.

  A schematic configuration of the present invention will be described with reference to FIGS. As shown in FIG. 2, the surface temperature of the fixing roller 5 is about to be reduced by the amount of heat released from the halogen lamp 6 arranged inside the fixing roller 5 composed of an AL tube whose surface is coated with a PTFE layer. It rises to around 200 degrees. The surface temperature of the fixing roller is a halogen lamp so that the surface temperature of the fixing roller 5 is detected by a thermistor 7 in which a thermocouple contacting the surface of the fixing roller 5 is contained, and the surface of the fixing roller is kept at about 200 ° C. 6 is controlled by a fixing controller (not shown). Under the fixing roller 5, a sponge is disposed on the surface of the iron shaft, and a pressure roller 8 provided with a PTFE layer is disposed on the surface. A nip portion N is provided between the fixing roller 5 and the pressure roller 8 by pressing the pressure roller 8 with a predetermined pressure. By passing the unfixed transfer paper P between the nip portions N, the unfixed toner is fixed to the transfer paper P by heat and pressure. An oil application roller 9 containing silicon oil is provided above the fixing roller 5, and supplies oil to the surface of the fixing roller 5 through a woven fabric 10. This oil is supplied to the surface of the transfer paper P at the time of fixing, and functions to increase the glossiness of fixing and to make the transfer paper P easily peel from the fixing roller 5. If the transfer paper P is wound around the fixed roller 5, the transfer paper P is peeled off from the fixing roller 5 by a separation claw 11 coated with PTFE on a heat resistant resin such as PPS that is in contact with the fixing roller 5 with a predetermined pressure.

  Thereafter, the transfer paper P is transported by the transport unit 2. When the curl is formed on the transfer paper P by the fixing device 109, the curl amount is detected by the curl amount detection means 12 in the middle of the transport unit 2. The curl amount detection means 12 is provided with a laser light emitting portion and a plurality of light receiving portions, and measures the position up to the transfer paper according to the laser light receiving position. That is, the distance from the transfer paper passing over the curl amount detection means 12 can be measured.

  FIG. 7 shows data on the curl amount detected by the curl amount detection means 12. For example, when the transfer paper P passing over is curled upward, data that gradually decreases with the curl amount at time 0 in FIG. 6 as the maximum value is detected. When the sheet passing above is a lower curl, the curl amount is 0 at time 0, the curl amount increases with time, reaches the maximum value of the curl amount, then decreases, and finally the curl amount becomes 0 . This data processing will be described in detail later.

  Thereafter, the transfer paper P enters the second fixing 3 as shown in FIG. 3, and the second fixing is performed by the second fixing 3. Parts having the same role as the first fixing 109 in the second fixing 3 are denoted by the same symbols as those of the first fixing 109, and description thereof is omitted. By fixing the transfer paper P by the first fixing 109 and the second fixing 3, it is possible to secure the fixability of thick paper or coated paper, which is conventionally difficult to fix with one fixing device. Furthermore, the gloss of the coated paper on the photograph is improved by performing fixing twice, and the appearance is improved.

  In FIG. 2, after the transfer paper P passes through the second fixing 3, the curl correcting means 4 is entered. As shown in FIG. 2, the curl correcting means 4 is composed of one metal roller 14 and sponge rollers 15 and 16 whose centers are biased against the metal roller 14 and whose periphery is covered with a sponge. The sponge rollers 15 and 16 are urged toward the metal roller 14 by a predetermined pressure. As shown in FIG. 3, when the sponge rollers 15 and 16 biased to the metal roller 14 are biased toward the metal roller 14, they are deformed into a concave shape toward the metal roller 14. When the transfer paper P is passed through this recess, the transfer paper P is curled and corrected to the metal roller 14 side. That is, as shown in FIG. 3, when the transfer paper P is passed through the sponge roller 15, the transfer paper P is corrected to a lower curl. On the contrary, if the sponge roller 16 is passed, the curl is corrected. The determination of whether to correct the upper curl or the lower curl will be described later. Depending on the position of the flapper 13, the side of the sponge paper 15 or 16 on which the transfer paper P that has come out of the second fixing 3 is conveyed is changed. Usually, the flapper 13 is urged counterclockwise in the drawing so as to be held at the position shown in FIG. The flapper 13 moves to the position shown in FIG. 3 when the flapper solenoid 35 shown in FIG. 5 is operated. With this configuration, the transfer path of the transfer paper P is changed, and the curl of the transfer paper P is corrected.

  The drive to the curl correction means 4 is transmitted to the metal roller 14 by a drive transmission means (not shown). The drive of the metal roller 14 is transmitted to the sponge rollers 15 and 16 which are driven rollers. The curl correcting means 4 changes its urging force depending on the curl amount of the transfer paper P.

  An example of means for moving the sponge roller 15 is shown in FIG. In FIG. 4, both ends of the metal roller 14 are supported on the side plate 17 by bearings 15 so as to be rotatable. (Only one end is shown in FIG. 4) A gear (not shown) is fixed to the metal roller 14, and the drive is transmitted from the copying machine main body 1. Both ends of the sponge roller 16 are rotatably supported by the side plate 17 by resin bearings 18 such as POM. The resin bearing 18 is fitted into a long hole 17-a formed in the side plate 17 with high accuracy and is slidable in the vertical direction. The vertical movement of the resin bearing 18 is adjusted by rotating a cam 20 made of a resin such as POM fixed to the cam shaft 19. The cam shaft 19 is rotatably supported by bearings 22 arranged on side plates 21 arranged on both outer sides of the side plate 17. A gear 23 is fixed to the end of the camshaft 19 and is configured to transmit the drive of a pulse motor 25 fixed to the side plate 21 by a gear 24.

  Next, a method for processing the data detected by the curl detecting means 12 and correcting the curl by the curl correcting means 4 will be described in detail. When the paper type, image density, character mode / photo mode, etc. are input in the operation unit 26 (FIG. 5) of the copier 1 shown in FIG. 1, the information is determined in the decision 27 in the flowchart shown in FIG. The information is stored in the storage unit 28. Next, the curl amount detection means 12 shown in FIG. 2 determines whether the curl direction of the transfer paper P is up or down by a judgment 29. If the transfer paper P is determined to be an upper curl by the curl detection means 12, the CPU 30 calculates the upper curl amount of the transfer paper P. (31) Then, the information is input to information 1 (32). If it is determined that the transfer paper P is a lower curl, the CPU 30 calculates the lower curl amount. (33) Then, the information is input to information 1 (32).

  As shown in FIG. 7, whether the transfer paper P is a lower curl or an upper curl is determined as an upper curl if the curl amount is a decreasing function, and as a lower curl if the curling amount is a rising / decreasing function. If the curl amount detection means 12 determines that the curl is upper, the upper curl maximum curl amount shown in FIG. 7 is input as information 1 (32). On the contrary, if it is a lower curl, that information is input to information 1 (32).

  Then, the rotation step angle of the stepping motor 25 is calculated based on the paper type, image mode, and upper (lower) curl amount stored in the information 1, and the sponge rollers 15 and 16 are operated. The movement distance of the sponge rollers 15 and 16 is determined by comprehensively judging the data of the above information 1 and determining the movement distance. The movement distance is stored in advance as a matrix of the movement amount of the sponge rollers 15 and 16 that can correct each paper type, image mode, and upper (lower) curl amount by examination, and the movement amount is determined based on the data.

  If the transfer paper P is an upper curl, the flapper solenoid 35 is operated (36). After the transfer path of the transfer paper P is changed as shown in FIG. 3, the stepping motor 1 (38) is rotated by a predetermined amount (37). Correct the curl of paper P. If the transfer paper P is a lower curl, the stepping motor 2 (25) shown in FIG. 5 is rotated by a predetermined amount (39) and the transfer paper P is conveyed by the path shown in FIG. 2 without operating the flapper solenoid 35 to correct the lower curl. To do.

  Next, calculation of the operation angle of SPM1 in the case of the upper curl and calculation method of SPM2 in the case of the lower curl shown in FIG. 6 will be described.

  In addition to the curl amount of the transfer paper P detected by the curl amount detection means 12 after the first fixing 109, the parameters for determining the curl amount after the transfer paper P passes the second fixing 3 include the following. Moisture absorbed in the transfer paper P, image distribution of the document placed under the pressure plate 100 of the image forming apparatus in FIG. 1, toner characteristics (negative / positive, etc.), temperature distribution on the fixing roller 5 in FIG. , Type of transfer paper P, pressure distribution between the fixing roller 5 and the pressure roller 8. There are many parameters that contribute to curling.

  The type of transfer paper P can be known if the user can input the paper type in the operation unit 26 shown in FIG. Further, a charging roller 120-1 having a high resistance rubber layer and a metal roller 120-2 are arranged in the middle of the conveyance path shown in FIG. 1, and a DC voltage of, for example, +3 kv is applied to the charging roller. The volume resistivity of the paper can be measured by detecting the current flowing to the metal roller 120-2 side. As a result, the thickness and type of the paper can be grasped to some extent. The image distribution of the original can be obtained by providing a toner density detection sensor (not shown) in the longitudinal direction of the photosensitive drum 102 between the developing device 103 and the transfer / separating unit 107 shown in FIG. The developed density can be detected. The toner characteristics can be grasped in advance because one type of toner is normally used for the image forming apparatus 1. Regarding the pressure distribution between the fixing roller 5 and the pressure roller 8, the crown amount of the fixing roller 5 (the outer diameter in the longitudinal direction of the fixing roller 5 is changed in order to prevent wrinkling of the transfer paper P) and the pressure distribution. It depends on the outer diameter of the pressure roller 8 and the hardness of the roller. Therefore, it is possible to grasp in advance before the transfer paper P enters the first fixing 109 by analyzing the stress distribution, the pressure contact area and the shape between the fixing roller 5 and the pressure roller by structural analysis or the like in advance. it can.

  However, regarding the amount of moisture absorbed in the transfer paper P and the temperature distribution in the longitudinal direction on the fixing roller 5, when the transfer paper P passes through the first fixing 109, the data cannot be grasped in advance. The amount of moisture absorbed by the transfer paper P varies depending on the timing when the transfer paper P is put in the cassettes 105 and 106 shown in FIG. 1 and the external temperature and humidity environment, etc., but the transfer paper P is put in the cassettes 105 and 106. It is difficult to identify and detect the time. However, after the transfer paper P is fixed by the first fixing 109, the moisture content of the transfer paper P is also evaporated by the heating at the time of fixing, and almost disappears when fixing by the second fixing 3. Therefore, the amount of moisture absorbed on the transfer paper P cannot be predicted when fixing with the first fixing 109, but the amount of moisture absorbed on the transfer paper P can be predicted when fixing with the second fixing 3.

  As for the temperature distribution on the fixing roller 5, the surface temperature of the fixing roller 5 is lowered due to moisture absorbed inside the transfer paper P when the first fixing 109 fixes, and as a result, the temperature of the fixing roller 5. Uneven distribution occurs. Therefore, it is difficult to grasp the temperature distribution of the fixing roller 5 of the first fixing 109 in advance. However, when fixing with the second fixing 3, most of the moisture inside the transfer paper P evaporates, and the temperature distribution of the fixing roller 5 hardly becomes uneven. Therefore, the temperature distribution on the fixing roller 5 cannot be predicted when fixing by the first fixing 109, but the temperature distribution on the fixing roller 5 can be predicted to some extent when fixing by the second fixing 3.

  As described above, when the transfer paper P is fixed by the first fixing 109, the moisture content of the transfer paper P and the temperature distribution on the fixing roller 5 cannot be predicted. As a result, the transfer paper after the first fixing 109 is predicted. It is difficult to predict the curl amount of P. However, for the curl of the transfer paper P after the second fixing, the moisture content of the transfer paper P and the temperature distribution on the fixing roller 5 can be predicted for the reason described above, and therefore the curl amount of the transfer paper P can be predicted. it can. Therefore, the curl detection means 12 is arranged after the first fixing 109 in which the curl amount of the transfer paper P cannot be predicted, and the curl amount of the transfer paper P is detected. Then, the second fixing 3 that can predict the curl amount of the transfer paper P is performed for the second time, and the curl amount of the transfer paper P after exiting the second fixing 3 is predicted. Based on the result, the curl correction means 4 is controlled.

  The curl amount of the transfer paper P when exiting from the second fixing 3 can be predicted based on the results detected and analyzed in this way. Then, the rotation angles of SPM1 (38) and SPM2 (25) shown in FIG. 5 are calculated. For example, if the curl of the transfer paper P detected by the curl amount detection means 12 is an upper curl +5 mm, this +5 mm is input to the formula constituted by the above parameters, and the rotation angle of SPM1 (38) or SPM2 (25) is set. calculate. Since mathematical formulas are difficult to obtain with theoretical formulas, calculations are made using empirical formulas based on each parameter.

  In this embodiment, the sponge rollers 15 and 16 are operated by the stepping motors 1 (38) and 2 (25). However, the stepping motors 1 (38) and 2 (25) are not used, and FIG. Needless to say, the cam shaft 19 may be rotated stepwise using a spring clutch (not shown), a solenoid (not shown), etc., transmitted from the main motor (not shown) of the copying machine 1 shown in FIG. Yes.

  In this embodiment, only the first fixing 109 and the second fixing 3 are used, but it goes without saying that three or more fixing structures may be used.

  FIG. 8 is a sectional view of the fixing device of the second embodiment. The feature of this embodiment is that the curl correcting means is the fans 40 and 41 provided after the second fixing 3. The fans 40 and 41 are so-called axial fans that can generate an air flow, and correct the curling of the transfer paper P by blowing the wind on the upper and lower surfaces of the transfer paper P that has come out of the second fixing.

  Generally, when the wind is blown from the lower side of the transfer paper P like the fan 41, the lower curl of the transfer paper P is corrected, and when the wind is blown from the upper side like the fan 40, the upper curl is corrected. Is done.

Also in the second embodiment, the curl direction and the curl amount of the transfer paper P differ depending on the paper type, density, environment, and the like of the transfer paper P as in the first embodiment. As in the first embodiment, which fan 40 or 41 is to be driven is determined based on the curl information of the transfer paper P obtained by the curl detection means 12 of the transfer paper P. Further, according to the study by the present inventor, it has been found that the amount of curl correction differs depending on the amount of air blown by the fans 40 and 41. For example, when a 10% image density original is copied at 60g / m ^{2 ·} A4 horizontal feed, a transfer paper with a lower curl of 26mm blows a fan air volume of 3.0m / min from the bottom immediately after fixing. The lower curl was reduced to 5 mm.

  In this way, the curl correction data of the transfer paper is stored under various conditions, and which of the fans 40 and 41 is activated according to the curl direction, curl amount, image density, paper type, transport direction, etc. A CPU (not shown) calculates what to do with the air volume. The fan air volume is changed by changing the fan drive voltage.

1 is a cross-sectional view of a copying machine main body in a first embodiment. 1 is a cross-sectional view of a fixing device according to a first embodiment. 1 is a cross-sectional view of a fixing device according to a first embodiment. Sectional drawing of the curl correction means of the fixing device in the first embodiment. FIG. 3 is an electrical block diagram of the fixing device in the first embodiment. FIG. 3 is a flowchart of the fixing device in the first embodiment. The time-dependent data of the curl amount detected by the curl detection means of the fixing device in the first embodiment. Sectional drawing of the fixing device in 2nd Example. Sectional drawing of the copying machine main body in background art.

Explanation of symbols

3 Second fixing unit (second fixing)
4 Curl correction means (deformation amount correction means)
6 Heating member (halogen lamp)
7 Temperature control means (Thermistor)
8 Pressure member (Pressure roller)
12 Curling amount detection means (deformation amount detection means)
N nip 109 First fixing unit (fixing device)

Claims (6)

In a fixing device in which a plurality of fixing units that form a nip portion by a heating member and a pressure member are arranged,
Deformation amount detecting means for detecting the deformation amount of the recording material is provided downstream of the fixing unit located on the most upstream side in the recording material conveyance direction in the recording material conveyance direction,
A fixing device comprising: a deformation amount correcting means for correcting deformation of a recording material downstream of the deformation amount detecting means in a conveyance direction of the recording material.   The deformation amount detecting means is located between a fixing device located on the most upstream side in the conveyance direction of the recording material and a fixing device located on the most downstream side in the conveyance direction of the recording material. Item 1. The fixing device according to Item 1. When the fixing device located on the most upstream side in the conveyance direction of the recording material is defined as the first fixing, the fixing device on the downstream side thereof is defined as the second fixing and the third fixing in order,
3. The fixing device according to claim 2, wherein the deformation amount detecting means is located between the first fixing and the second fixing.   4. The fixing device according to claim 1, further comprising a control unit that controls a deformation amount of the transfer paper by the deformation amount correcting unit based on information of the deformation amount detecting unit.   The deformation amount correcting means includes a pair of metal rollers and a sponge roller that is in contact with the metal roller at a predetermined pressure, and the sponge roller is set according to the deformation amount of the recording material detected by the deformation amount detecting means. 5. The fixing device according to claim 1, wherein the pressure applied to the metal roller is controlled.   The deformation amount correcting means has a correction position that differs depending on whether the transfer paper is convexly convex upward or when the transfer paper is convexly convex downward, and the transport path that changes the transport path to the correction position by the deformation amount detecting means. 6. The fixing device according to claim 1, further comprising a control unit that includes a changing unit and controls driving of the transport path changing unit.

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