JP4034117B2 - Fixing apparatus and image forming apparatus - Google Patents

Description

【００７５】
２）通常湿度範囲（湿度５６％〜７０％）で、厚紙へ印字する場合、下記表２に示すように、加熱ローラ線速を１００％に固定し、印字率の増加に応じて、加圧ローラの線速を減速制御する。厚紙の場合、普通紙よりカール量は総体的に少なく、画像密度の変化に対するカール発生量の変化も少ない。
【００７６】
【表２】

【００７７】
３）湿度範囲（湿度０〜３０％）で、普通紙へ印字する場合、下記表３に示すように、加熱ローラ線速を１００％に固定し、印字率の増加に応じて、加圧ローラの線速を減速制御する。
【００７８】
【表３】

【００７９】
４）湿度範囲（湿度３１〜５５％）で、普通紙へ印字する場合、下記表４に示すように、加熱ローラ線速を１００％に固定し、印字率の増加に応じて、加圧ローラの線速を減速制御する。
【００８０】
【表４】

【００８１】
５）湿度範囲（湿度５６〜７０％）で、普通紙へ印字する場合、下記表５に示すように、加熱ローラ線速を１００％に固定し、印字率の増加に応じて、加圧ローラの線速を減速制御する。
【００８２】
【表５】

【００８３】
６）湿度範囲（湿度７０％〜）で、普通紙へ印字する場合、下記表６に示すように、加熱ローラ線速を１００％に固定し、印字率の増加に応じて、加圧ローラの線速を減速制御する。
【００８４】
【表６】

【００８５】
以上の各表に示すような対応により、画像密度が非常に高い場合であっても、シート材に発生するカールの程度に合わせた補正作用を行うことができるので、コピー後のシート材の後処理作業を容易かつ効果的に行うことができる。
【００８６】
【発明の効果】
以上の説明から明らかなように、本発明は、以下の効果を奏する。
【００８７】
（１）画像密度の検出結果に基づいて設定した周速度差を満たす回転数で、加熱ローラと加圧ローラを回転させるので、シート材に発生するカールの程度に対応した補正を定着部で行うことができるため、画像密度が非常に高い場合であっても、適切な補正を行え、コピー後のシート材の後処理作業を容易かつ的確に行うことができる。
【００８８】
（２）画像密度に加えて湿度をも勘案して設定した周速度差を満たす回転数で、加熱ローラと加圧ローラとを回転させるので、シート材に発生するカールの程度をより高い精度で予測して、定着部で、より適切な補正が可能となるため、画像密度が非常に高い場合であっても、より一層効果的な補正が可能となり、コピー後のシート材の後処理作業をより一層容易かつ的確に行うことができる。
【００８９】
（３）カールを補正する際に、加熱ローラの周速度を固定するので、定着能力を所定の水準に維持することができるため、本来の定着能力の維持が容易となり、制御も容易となり、構成を簡素化することもできる。
【００９０】
（４）画像密度の検出結果等に基づいて設定した周速度差を満たす回転数で、加熱ローラと加圧ローラを回転させるので、シート材に発生するカールの程度に対応した適切な補正を定着部で行うことができ、画像密度が非常に高い場合や、環境条件の変動を伴う場合であっても、コピー後のシート材の後処理作業が容易かつ的確に行え、印字品位も向上する。
【００９１】
（５）算出された画像密度に基づいて設定した周速度差を満たす回転数で、加熱ローラと加圧ローラを回転させるので、シート材に発生するカールの程度に対応した補正を定着部で行うことができるため、画像密度が非常に高い場合であっても、シート材に発生するカールの程度に合わせて適切な補正を行うことができ、コピー後のシート材の後処理作業を容易かつ的確に行え、印字品位も向上する。
【００９２】
（６）算出した画像密度に加えて湿度をも勘案して設定した周速度差を満たす回転数で、加熱ローラと加圧ローラとを回転させるので、シート材に発生するカールの程度をより高い精度で予測して、定着部で、より適切な補正が可能となるため、画像密度が非常に高い場合であっても、より一層効果的な補正が可能となり、コピー後のシート材の後処理作業をより一層容易かつ的確に行え、印字品位もさらに向上する。
【図面の簡単な説明】
【図１】本発明の実施形態に係る定着装置のカール発生原理の説明図である。
【図２】同画像形成装置の構成説明図である。
【図３】同定着装置の斜視図である。
【図４】同カール発生原理を別の観点から説明するための説明図である。
【図５】同定着ローラ対を駆動制御するための制御系統ブロック図である。
【図６】従来の定着装置の斜視図である。
【図７】同画像形成装置の構成の一例を示す説明図である。
【図８】同要部構成図である。
【符号の説明】
１−定着装置
２−加熱ローラ
３−加圧ローラ
５−シート材
３０−制御部、設定部、演算手段
３５−湿度検出手段
３９−駆動部[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fixing device having a curl correction function provided in an image forming apparatus such as a printer or a copying machine, and an image forming apparatus including the fixing device.
[0002]
[Prior art]
In an image forming apparatus such as a printer or a copying machine, toner is attached to an electrostatic latent image formed on a photosensitive drum, and is printed on a transfer material. The transfer material is conveyed to a fixing device provided in the image forming apparatus, and the toner is fixed on the sheet material by melting the toner in the fixing device.
[0003]
For example, as shown in FIG. 6, a fixing device 201 provided in a copying machine includes a heating roller 202 and a pressure roller 203, and the heating roller 202 includes a heater for melting toner therein. The pressure roller 203 presses the sheet material 205 against the heating roller 202, and the heating roller 202 or the pressure roller 203 obtains a driving force from a driving unit (not shown) and is rotationally driven in the direction of the arrow. Then, the other roller is driven to rotate.
[0004]
The illustrated sheet material 205 is conveyed from a paper feeding cassette of a copying machine not shown in FIG. 6, and for example, cut paper that is moisture-proof wrapped every 500 sheets or 1000 sheets is placed in the paper feeding cassette. A predetermined number (for example, about 250 to 500) is set. Then, each time copying is performed, the sheet material 205 is fed out and conveyed one by one from the sheet feeding cassette. After the toner image formed on the photosensitive drum is transferred, the sheet material 205 is conveyed to the fixing device 201.
[0005]
In the fixing device 201, the sheet material 205 is sandwiched between the heating roller 202 and the pressure roller 203, and the toner is fixed to the sheet material 205 by applying heat at a portion where the heating roller 202 is in pressure contact. The pressure roller 203 rotates to fix the toner throughout the sheet material 205 while the sheet material 205 is advanced in the direction of the arrow.
[0006]
However, in the fixing device 201 configured as described above, since the heating roller 202 is at a high temperature, the moisture contained in the sheet material 205 evaporates by different amounts on both the front and back surfaces, causing the sheet material 205 to curl. When the sheet material 205 is curled, it becomes easy to cause trouble in the conveyance of the sheet material 205 from the fixing device 201 to the unillustrated discharge tray, and when the sheet material 205 is discharged to the discharge tray, the sheet material 205 There is also a problem that the loadability of 205 is impaired.
[0007]
Therefore, in order to solve such a problem, conventionally, the fixing device 201 is further curled in the opposite direction on the curled sheet material 205 on the downstream side in the conveying direction of the sheet material 205 from the fixing device 201. The method of canceling the curl generated in the above was adopted.
[0008]
FIG. 7 shows an example of a printing apparatus 200 including a fixing device 201 that employs such a curl erasing method. The printing apparatus 200 includes a fixing device 201 and a curl removing device 100 on the downstream side thereof. The sheet material 205 </ b> A in which the toner is fixed by the fixing device 201 and is curled is conveyed to the curl removing device 100. Then, the sheet material 205A from which the curl is removed by the curl removing apparatus 100 is discharged.
[0009]
Here, FIG. 8A is a schematic front view of the decurling apparatus 100, and FIG. 8B is a schematic cross-sectional view of the decurling apparatus 100. The decurling device 100 includes a paper discharge roller 101, a paper discharge roller 102, and a drive gear 104. The paper discharge roller 101 is for conveying the sheet material 205A by rotating. The paper discharge roller 102 is a driven roller that rotates as the paper discharge roller 101 rotates, and is disposed on the periphery of the paper discharge roller 101. The drive gear 104 is for rotating the paper discharge roller 101 and is driven by a belt (not shown).
[0010]
The decurling apparatus 100 sandwiches the sheet material 205A between the paper discharge roller 101 and the two paper discharge rollers 102, and rotates the paper discharge roller 101 so that the sheet material 205A is wound around the paper discharge roller 101. In this state, the sheet material 205A is curled in the direction opposite to the curl formed by the fixing device 201 shown in FIG.
[0011]
That is, the conventional printing apparatus 200 includes a fixing device 201 and a curl removal device 100 on the downstream side thereof. The curl removal device 100 imparts a reverse curl to the sheet material 205 </ b> A, and the curl generated by the fixing device 201. Was configured to counteract.
[0012]
[Problems to be solved by the invention]
However, the state such as the size and direction of the curl generated by the fixing device 201 varies depending on the type, thickness, size, and the like of the sheet material 205A. Therefore, in the configuration in which the wrapping angle of the sheet material 205A around the paper discharge roller 101 is constant and the same reverse curl is always applied as in the curl removal apparatus 100 having the above configuration, it is based on a general character document. When the image density is relatively low as in the case of copying, the curl generated when the sheet material 205A to which the toner image is transferred passes through the fixing device tends to appear relatively small. Corrections can be made relatively easily.
[0013]
However, when the image density is high, such as a copy based on a photographic document or a graphic document, there is a problem that curl tends to appear greatly, so that a sufficient effect cannot always be obtained.
[0014]
In addition, the curl removal apparatus provided with an adjustment mechanism that adjusts the winding angle of the sheet material around the paper discharge roller has a problem that the configuration of the adjustment mechanism is complicated and difficult to implement. Further, in order to dispose the curl removal device 100 that exclusively performs curl removal as described above, between the fixing device and the paper discharge tray, regardless of the presence or absence of a mechanism for adjusting the winding angle of the sheet material, an extra space is required. There was also a problem of need.
[0015]
Further, in the above configuration, when the pressing force of the paper discharge roller to the paper discharge roller is increased in order to improve the curl removal effect, there is a problem that the roller material is left on the sheet material and the image quality is deteriorated.
[0016]
Further, in the above configuration, the sheet material is curled by heat of the fixing device, and then conveyed to the curl removing device. After the temperature is lowered and the curl is fixed therebetween, the curl is removed. Therefore, there is a problem that a sufficient curl removal effect cannot be obtained.
[0017]
SUMMARY An advantage of some aspects of the invention is that it provides a fixing device and an image forming apparatus in which curling of a sheet material is removed when a toner image is fixed to the sheet material.
[0018]
[Means for Solving the Problems]
In the present invention, means for solving the above-described problems are configured as follows.
[0019]
(1) A fixing device that includes a fixing roller pair including a heating roller and a pressure roller, and heats and melts a toner image transferred to a sheet material to fix the image on the sheet material.
  A drive unit for independently rotating the heating roller and the pressure roller;
  A setting unit for setting a peripheral speed difference between the heating roller and the pressure roller;
  Image density detecting means for detecting an image density of an image formed on the sheet material;
  A control unit for controlling the drive unit,
  The setting unit predicting curl caused by the fixing operation based on a detection result of the image density detected by the image density detecting unit;
  In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
  The controller isThe peripheral speed of the heating roller and the pressure roller set by the peripheral speed setting meansThe drive unit is controlled to rotate the heating roller and the pressure roller at a rotational speed satisfyingEquipped with meansA fixing device.
[0020]
In this configuration, since the peripheral speed difference is set based on the detection result of the image density, the peripheral speed difference for generating the corresponding reverse curl after accurately predicting the curl that will occur in the sheet material. Can be set with high accuracy.
[0021]
Therefore, by rotating the heating roller and the pressure roller at a rotation speed that satisfies the difference in peripheral speed, correction corresponding to the degree of curl generated in the sheet material can be performed in the fixing unit, so that the image density is extremely high. Even if it is too high, appropriate correction can be performed, and post-processing work of the sheet material after copying can be performed easily and accurately.
[0022]
  Note that the image density basically refers to the degree to which the toner adheres to the sheet material per unit area, but in the present invention, not only binary images but also multi-valued images are targeted. As such, it refers to a broad concept about the adhesion state and degree of toner, which is closely related to the occurrence of curling, including the printing rate, gradation, image density, and the like.
  Further, in this configuration, when the curl is corrected, the peripheral speed of the heating roller is fixed, so that the fixing ability can be maintained at a predetermined level. Accordingly, since the original fixing ability can be easily maintained (as compared with a correction method that involves changing the fixing temperature), the control is facilitated and the configuration can be simplified.
[0023]
(2) A fixing device that includes a fixing roller pair including a heating roller and a pressure roller, and heat-melts a toner image transferred to a sheet material to fix the toner image on the sheet material.
  A drive unit for independently rotating the heating roller and the pressure roller;
  A setting unit for setting a peripheral speed difference between the heating roller and the pressure roller;
  Image density detecting means for detecting an image density of an image formed on the sheet material;
  Humidity detecting means for detecting the humidity in the apparatus;
  A control unit for controlling the drive unit,
  The setting unit predicting curl caused by the fixing operation based on a detection result of the image density detected by the image density detection unit and a detection result of the humidity detected by the humidity detection unit;
  In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
  The controller isThe peripheral speed of the heating roller and the pressure roller set by the peripheral speed setting meansThe drive unit is controlled to rotate the heating roller and the pressure roller at a rotational speed satisfyingEquipped with meansA fixing device.
[0024]
In this configuration, since the peripheral speed difference is set in consideration of humidity in addition to image density, in order to generate a corresponding reverse curl after more accurately predicting the curl that will occur in the sheet material. Can be set with higher accuracy.
[0025]
  Therefore, by rotating the heating roller and the pressure roller at a rotation speed that satisfies the difference in peripheral speed, correction corresponding to the degree of curl generated in the sheet material can be performed in the fixing unit, so that the image density is extremely high. Even if it is very high, more appropriate correction can be performed, and post-processing work of the sheet material after copying can be performed more easily and accurately.
  Further, in this configuration, when the curl is corrected, the peripheral speed of the heating roller is fixed, so that the fixing ability can be maintained at a predetermined level. Accordingly, since the original fixing ability can be easily maintained (as compared with a correction method that involves changing the fixing temperature), the control is facilitated and the configuration can be simplified.
[0028]
(3Claim 1Or 2And a fixing device as described above.
[0029]
In this configuration, since the heating roller and the pressure roller are rotated at a rotational speed that satisfies the peripheral speed difference set based on the detection result of the image density, etc., appropriate correction corresponding to the degree of curl generated in the sheet material Can be performed at the fixing unit, so that even if the image density is very high or the environment conditions fluctuate, post-processing of the sheet material after copying can be performed easily and accurately, and the print quality can be improved. improves.
[0030]
(4A document reading device for reading image information of the document, a calculation unit for calculating the image density of the document based on the data read by the document reading device, and a heating roller according to the image density information calculated by the calculation unit And a setting unit for setting the peripheral speed difference between the pressure roller andA drive unit for independently rotating the heating roller and the pressure roller;
  A control unit for controlling the drive unit,
  The setting unit predicting curl caused by the fixing operation based on the image density information calculated by the calculating unit;
  In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
  The control unit isThe rotational speed satisfying the peripheral speed of the heating roller and the peripheral speed of the pressure roller set by the peripheral speed setting means,The drive unit is controlled to rotate the heating roller and the pressure roller.Equipped with meansIt is characterized by
[0031]
  In this configuration, since the heating roller and the pressure roller are rotated at a rotational speed that satisfies the peripheral speed difference set based on the calculated image density, correction corresponding to the degree of curl generated in the sheet material is performed. Therefore, even if the image density is very high, it is possible to make appropriate corrections according to the degree of curling that occurs in the sheet material, and the post-processing work of the sheet material after copying is easy It can be performed accurately and print quality is improved.
  Further, in this configuration, when the curl is corrected, the peripheral speed of the heating roller is fixed, so that the fixing ability can be maintained at a predetermined level. Accordingly, since the original fixing ability can be easily maintained (as compared with a correction method that involves changing the fixing temperature), the control is facilitated and the configuration can be simplified.
[0032]
(5) A document reading device that reads image information of a document, a calculation unit that calculates the image density of a document based on data read by the document reading device, image density information calculated by the calculation unit, and a usage environment A setting unit for setting a peripheral speed difference between the heating roller and the pressure roller according to humidity information detected by the humidity detecting means for detecting humidity;A drive unit for independently rotating the heating roller and the pressure roller;A control unit for controlling the drive unit,
  The setting unit predicting curl caused by a fixing operation based on the image density information detected by the computing unit and the humidity information detected by the humidity detecting unit;
  In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
  The control unit isThe peripheral speed setting meansSetThe circumferential speed of the heating roller and the pressure rollerMeans is provided for controlling the drive unit so as to rotate the heating roller and the pressure roller at a rotational speed satisfying a peripheral speed.
[0033]
  In this configuration, the heating roller and the pressure roller are rotated at a rotational speed satisfying a set peripheral speed difference in consideration of humidity in addition to the calculated image density, so that the degree of curling generated on the sheet is further increased. Predicting with high accuracy, and more appropriate correction is possible at the fixing part, so even more effective correction is possible even when the image density is very high, and after the sheet material after copying Processing operations can be performed more easily and accurately, and the printing quality is improved.
  Further, in this configuration, when the curl is corrected, the peripheral speed of the heating roller is fixed, so that the fixing ability can be maintained at a predetermined level. Accordingly, since the original fixing ability can be easily maintained (as compared with a correction method that involves changing the fixing temperature), the control is facilitated and the configuration can be simplified.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a fixing device and an image forming apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings.
[0035]
An image forming apparatus according to an embodiment of the present invention will be described below with reference to the drawings.
[0036]
(Outline of image forming apparatus and description of operation)
FIG. 2 shows the configuration of an electrophotographic copying machine (image forming apparatus) 1100. The copying machine 1100 includes a platen 1101, optical means 1102, lens 1103, CCD 1104, polygon scanner 1105, photosensitive drum 1106, developer unit. 1107, a cleaner unit 1108, a cassette 1110, a cassette 1111, a pickup roller 1112, a conveyance roller 1114, a registration roller 1115, a conveyance belt 1120, a fixing device (fixing device) 1, and a paper discharge tray 1122.
[0037]
With such a configuration, an image is formed on a sheet material (recording paper) (not shown) as follows. First, image information of a document set on the platen 1101 is imaged on the CCD 1104 via the lens 1103 using the optical unit 1102. Image information on the CCD 1104 is converted into an electrical signal and sent to the polygon scanner 1105, and an image (latent image) is formed on the photosensitive drum 1106 using laser light.
[0038]
Then, the developing unit 1107 develops the latent image on the photosensitive drum 1106 with toner, and the toner contacts and is transferred to the photosensitive drum 1106. As described above, the image forming unit is configured by the developing unit 1107, the cleaner unit 1108, and the like disposed around the polygon scanner 1105, the photosensitive drum 1106, and the photosensitive drum 1106.
[0039]
On the other hand, the sheet material is fed by the pickup roller 1112 from the cassette 1110 or the cassette 1111 in the paper cassette unit. Then, the sheet material is sent to the registration roller 1115 by the conveyance roller 1114. Next, the registration roller 1115 feeds the sheet material to the photosensitive drum 1106 at a timing when the latent image on the photosensitive drum 1106 and the position where the image is formed on the sheet material are aligned, and the toner on the photosensitive drum 1106 is transferred. The The sheet material to which the image has been transferred is conveyed to the fixing device 1 by the conveyance belt 1120. The toner image on the sheet material is fixed by the fixing device 1. Thereafter, the sheet material is discharged onto the discharge tray 1122.
[0040]
(Description of fixing device)
FIG. 3 is a perspective view of the fixing device 1, and this fixing device 1 is for fixing toner (not shown) to the sheet material 5. The fixing device 1 includes a heating roller 2 and a pressure roller 3. The heating roller 2 is for melting toner, has a heater inside, and is rotationally driven (in the direction of the arrow) by a drive unit (not shown). It is press-contacted and is rotationally driven by a drive unit (not shown) at a predetermined speed.
[0041]
As described above, the sheet material 5 is taken out and conveyed one by one from the paper feed cassette 1110 or 1111 (not shown) each time an image is formed, and after the toner image is transferred on the photosensitive drum 1106, the fixing device 1. The fixing device 1 sandwiches a sheet material 5 having a toner image between the heating roller 2 and the pressure roller 3 and applies heat at a portion where the heating roller 2 is in pressure contact with the sheet material 5. Toner is fixed on the toner.
[0042]
  In the fixing device 1 of the present embodiment, the heating roller 2 and the pressure roller 3 rotate together to advance the sheet material 5 and fix the toner over the entire sheet material 5. However, simply a pair of fixing rollers2, 3At the same peripheral speedEvery timeWhen the fixing operation is performed by rotating the sheet material 5, since the heating roller 2 is hotter than the pressure roller 3, the moisture content of the sheet material 5 evaporates by a different amount from one side and the other side of the sheet material 5, for example. As a result, the sheet material 5 may be curled.
[0043]
That is, since the heating roller 2 is hotter than the pressure roller 3, the amount of water evaporation from the sheet surface in contact with the heating roller 2 is larger than the amount of water evaporation from the sheet surface in contact with the pressure roller 3. A difference occurs in the shrinkage amount of the fiber of the sheet material on both sides, and the sheet material 5 is curled toward the heating roller having a large shrinkage amount.
[0044]
  Therefore, in the fixing device 1 of the present embodiment, the fixing roller pair is as follows.2, 3Circumferential speed betweenEvery timeBy providing the difference, a shearing force is generated in the sheet material 5, and the curl generated due to the difference in the amount of heat generated on both surfaces of the sheet material 5 is corrected by the action of the shearing force. Hereinafter, a configuration for correcting curl will be described with reference to the drawings.
[0045]
(Action of shear force)
FIGS. 1A and 1B are explanatory views for removing curls. The fixing device 1 shown in FIG. 1 includes an outer peripheral surface 12 of a heating roller 2 having a cross-sectional radius R2 and a pressure roller 3 having a cross-sectional radius R3. The recording paper 5 is sandwiched between the outer peripheral surface 13 and the outer peripheral surface 13. Further, the upper surface S2 of the sheet material 5 shown in FIGS. 1A and 1B is an image surface to which toner is transferred, and the lower surface S3 on the opposite side is a back surface without an image.
[0046]
  In the above configuration, the heating roller 2 and the pressure roller 3 are independently rotated at a peripheral speed V2 and a peripheral speed V3 by a driving unit (not shown). Therefore,FixingrollerversusThe sheet material 5 sandwiched between 2 and 3 receives F2 force (frictional force) from the heating roller 2 on the upper surface S2, and F3 force (frictional force) from the pressure roller 3 on the lower surface S3.TransportProceed at speed V5.
[0047]
The curl removal operation of the fixing device 1 will be described with reference to FIGS. 1A and 1B and FIG. 4. First, in FIG. 1A, the peripheral speed V2 of the heating roller 2 is that of the pressure roller 3. The case where it is set smaller than the peripheral speed V3 is shown. In such a setting, the speed V5 at which the sheet material 5 is transported is set to be equal to the sheet transport speed of the other sheet transport mechanisms, and the relationship between the peripheral speeds V2 and V3 and the transport speed V5 is V3. > V5≈V2 is set to be satisfied.
[0048]
Under the above conditions, the frictional force acting between the sheet material 5 and the heating roller 2 has a relationship of the conveyance speed V5≈the peripheral speed V2, so that a static frictional force such as the frictional force F2 shown in FIG. It has become. On the other hand, the frictional force acting between the sheet material 5 and the pressure roller 3 has a relationship of the conveyance speed V5 <the peripheral speed V3, so that the dynamic frictional force such as the frictional force F3 shown in FIG. It has become.
[0049]
For this reason, a frictional force acts on the sheet material 5 in different directions on the upper surface and the lower surface, and a shearing force is applied to the sheet material 5. By the action of the shearing force, the sheet material 5 is wound around the heating roller 2 that generates a frictional force in the direction opposite to the conveying direction, and curling to the upper surface side is promoted. Such curling toward the recording surface side is called face curling.
[0050]
Next, FIG. 1B shows a case where the peripheral speed V2 of the heating roller 2 is set larger than the peripheral speed V3 of the pressure roller 3. In this setting, the speed V5 at which the sheet material 5 is transported is set to be equal to the sheet transport speed of the other sheet transport mechanisms, and the relationship between the peripheral speeds V2 and V3 and the transport speed V5 is V3 <V2. ≈ It is set to satisfy V5.
[0051]
Under the above conditions, the frictional force acting between the sheet material 5 and the heating roller 2 has a relationship of the conveyance speed V5≈the peripheral speed V2, so that the static frictional force is the frictional force F2 shown in FIG. It has become. On the other hand, since the frictional force acting between the sheet material 5 and the pressure roller 3 has a relationship of the conveyance speed V5> the peripheral speed V3, the frictional force F3 shown in FIG. It is like that.
[0052]
  For this reason, a frictional force acts on the sheet material 5 in different directions on the upper surface and the lower surface, and a shearing force is applied to the sheet material 5. By the action of the shearing force, the sheet material 5 is wound around the pressure roller 3 that generates a frictional force in the direction opposite to the conveying direction, and curling to the lower surface side is promoted. Such curling on the side opposite to the recording surface is called back curl. In the description using FIG. 1 above,FixingLaura pair2, 3ofZhouFocusing only on the speed difference, the pressure roller3The deformation of is not considered.
[0053]
  4A and 4B are diagrams for explaining the occurrence of curling by the above-described configuration. In this case, the circumferential speed of the heating roller 2 is V2, and the circumferential speed of the pressure roller 3 is described. V3 speed, heating roller2Peripheral speedEvery timeV2 ≒ Pressure rollerThreePeripheral speedEvery timeThe relationship of V3 is established. FIG. 4A is a diagram for explaining the same situation as FIG. 1A, and shows a state in which the pressure roller 3 is traveling more than the heating roller 2.
[0054]
Regarding the influence of the nip on the curl, in addition to the surface of the pressure roller 3 biased in the direction of the heating roller 2 being deformed in a concave shape, the sheet is further pushed up in the direction of the heating roller 2 at the nip portion. Thus, curling (positive curl) intensifies along the nip shape direction. And this tendency becomes strong, so that conveyance speed is slow.
[0055]
Regarding the influence of the frictional force on the curl, the pressure roller 3 is set to have a lower surface friction coefficient (for example, covered with a PFA tube) than the heating roller 2, and the toner adhesion surface (electrostatic surface) is Since the heating roller 2 faces the heating roller 2, the heating roller 2 dominates the conveyance of the paper, but the pressure roller 3 is slip-rotated (a state delayed from the progress of the heating roller 2). The frictional force acts, and the sheet material 5 is wound around the pressure roller 3 (reverse curl). Then, as the driven load of the pressure roller 3 is increased, the effect of winding the sheet material 5 around the pressure roller 3 becomes stronger because the heating roller 2 is delayed.
[0056]
FIG. 4B is a diagram for explaining the same situation as FIG. 1B, in which the heating roller 2 is more advanced than the pressure roller 3 so that the sheet material 5 is pulled out. Since it is conveyed, the curl along the nip shape direction is weakened.
[0057]
  As explained above, the peripheral speed is different.FixingWhen the sheet material 5 passes between the roller pair 2 and 3, the conveyance speed of the sheet material 5 depends on the speed of the roller having the higher peripheral speed, and is wound around the roller having the lower peripheral speed. Become.
[0058]
  Therefore, the curl originally generated by the nip effect exists as a positive curl,FixingAdjust the peripheral speed difference between the roller pair 2 and 3 appropriately,FixingrollerversusBy controlling the relationship of the frictional force between the sheet materials 5 and 3 and the sheet material 5, the force applied to the sheet material 5 is set to a force in a direction for promoting the positive curl or a force in a direction for promoting the reverse curl. However, the tendency of the original positive curl can be further strengthened or suppressed.
[0059]
  (Additional heat amount difference on both sides of sheet material)
Fixing roller pair 2,3 is the same peripheral speedEvery timeWhen the fixing operation is performed with the rotation of the sheet material 5, the heating roller 2 is hotter than the pressure roller 3, and therefore, the difference in the amount of water evaporation on both surfaces of the sheet material 5 is large. That is, since the heating roller 2 is hotter than the pressure roller 3, the amount of water evaporation from the sheet surface in contact with the heating roller 2 is larger than the amount of water evaporation from the sheet surface in contact with the pressure roller 3. A difference occurs in the shrinkage amount of the fiber of the sheet material 5 on both surfaces, and the sheet material 5 curls in the direction of the heating roller 2 having a large shrinkage amount.
[0060]
  Therefore, in order to correct the curl in the direction of the heating roller 2, the difference in moisture evaporation between both surfaces of the sheet material 5 is reduced, and the sheet material is reduced.Of 5The circumferential speed of the pressure roller 3 is set so as to increase the amount of heat applied from the pressure roller 3 to the sheet material 5 so as to reduce the difference in the amount of fiber shrinkage between both surfaces.Every timeIs the peripheral speed of the heating roller 2Every timeSlower thanEvery timeSet to the side.
[0061]
In the conventional fixing device, only the image is fixed on the sheet material and conveyed, so the sheet material is curled. However, in the fixing device according to the present invention, as described above, the roller By setting the speed difference between the pair 2 and 3, it is possible to give a reverse curl (from both the shear force balance generated on both sides of the paper and the thermal energy balance), so it simply passes through the fuser. The curling can be suppressed or alleviated by applying the curling in the direction opposite to the curling that occurs.
[0062]
(Control system block diagram)
FIG. 5 shows a control system block diagram of a control device (setting unit, control unit, control means) for controlling the drive unit of the fixing device 1, and the control system includes the fixing device 1 and the control device as shown in the figure. 30, a drive unit 39, a sensor device (humidity sensor, image density detection means, sheet detection means) 34, and an input button 45.
[0063]
  The control device 30 includes a CPU 31, a ROM 32a, a RAM 32b, an input unit 33, and an output unit 38. The drive unit 39 includes a motor driver 40, a heating roller drive motor 41a, and a pressure roller drive motor 41b, and a sensor device. 34 is a heating roller2A temperature sensor 34a for detecting the temperature of the pressure roller, and a pressure roller3A temperature sensor 34b for detecting the temperature of the sensor, a humidity sensor 35, and a set button 37 are provided.
[0064]
In the above configuration, the input unit 33 includes temperature information from the temperature sensor 34 a provided on the heating roller 2 and temperature sensor 34 b provided on the pressure roller 3, humidity information from the humidity sensor 35, and a document of the image forming apparatus. Electrostatic latent image on the photosensitive drum based on the image density information (document information scanned and scanned by the scanning optical system) sent from the reading unit 36a (CCD sensor or the like of the scanning optical system) and passed through the image generation unit. Final data for forming an image) and paper thickness and quality information from a set button 37 provided on the control panel are input. The correction input button 45 provided on the control panel is used to correct data stored in the control device 30, and can input a data correction signal to the memory.
[0065]
As the above-mentioned image density (for example, printing rate) information, in addition to the original reading unit 36a, the original reading data by the external scanner device 36b or the printing from the host PC terminal 36c connected to the image forming apparatus, etc. An instruction may be input.
[0066]
In the control device 30, information for curling correction to the fixing device 1 is transmitted to the drive unit 39 via the output unit 38 based on information from the input unit 33. Here, the setting unit of the control device 30 estimates (predicts) the curl that will occur due to the fixing operation of the fixing device 1 according to the information on the humidity, the sheet thickness, and the image density, and cancels the curl. The peripheral speed difference between the pair of fixing rollers 2 and 3 is set so that it can be performed. The drive unit 39 outputs a drive signal to the motor 41 (the heating roller drive motor 41a and the pressure roller drive motor 41b) that drives the fixing device 1 via the motor driver 40.
[0067]
(Humidity detection means)
A typical humidity detection method will be described below, but the present invention is not limited to this, and other appropriate detection methods can also be applied.
[0068]
1) Humidity sensor
For example, a humidity sensor for detecting the humidity in the paper storage unit may be provided in the paper storage unit (the paper cassette unit) in the image forming apparatus main body. Alternatively, a hygrometer may be arranged at an arbitrary position in the image forming apparatus main body, and information obtained from the hygrometer may be input to the control device.
[0069]
2) Paper moisture content (or paper moisture content)
The humidity in the sheet storage unit and the moisture content of the sheet (or sheet moisture content) show a positive correlation. Therefore, it is possible to detect the paper moisture content (or paper moisture content) and replace it with the humidity in the paper storage unit. Paper moisture content detection means can detect in a short time, that is, change in electrical resistance value due to moisture contained in paper, absorption of infrared rays, microwaves, etc. (paper moisture content when these pass through paper) Therefore, the amount of attenuation may be detected.
[0070]
The paper moisture amount detecting means is disposed at a paper feeding / conveying portion (for example, a pair of registration rollers is formed of a conductive member and is a part of a circuit constituting the paper moisture amount detecting means). The moisture content of the paper passing through the paper may be measured. Alternatively, the moisture content of a sheet placed in the vicinity of the paper cassette in which the paper is stored or the paper feed tray may be measured.
[0071]
(Image density detection means)
The information on the image density can be easily obtained by setting a program for obtaining the image density in the control device 30. Specifically, for example, the semiconductor laser of the image exposure unit is controlled according to the image signal and irradiates the photosensitive member with a laser beam, but emits light for a time corresponding to the pulse width of the signal for each unit pixel. . In the reversal development method, the higher the density pixel, the longer the laser emission time, so the image density can be treated equivalently to the laser beam irradiation time.
[0072]
A document is read by a document reading unit 36a or an external scanner 36b integrated with the image forming apparatus main body, and these have a photoelectric conversion element such as a CCD that converts a document image into an electrical signal. An image signal corresponding to the image information of the document can be output. Accordingly, the relationship between the image signal level and the toner adhesion amount (image density) with respect to the image signal is preliminarily expressed as a data table and stored in the ROM 32a of the control device 30, so that the image signal data is added at the time of prescanning. The total value can be converted into the toner adhesion amount (image density) via the control device 30. It should be noted that the image density can be similarly obtained when a print command output from the host PC terminal 36c or the like externally connected to the image forming apparatus is input to the input unit 33.
[0073]
(Example of linear speed setting for fixing roller pair)
1) When printing on plain paper in the normal humidity range (humidity 56% to 70%), as shown in Table 1 below, the heating roller linear speed is fixed at 100%, and the printing rate (image density) is increased. Accordingly, the linear speed of the pressure roller is controlled to be reduced.
[0074]
[Table 1]

[0075]
2) When printing on cardboard in the normal humidity range (humidity 56% to 70%), as shown in Table 2 below, the heating roller linear speed is fixed at 100% and the pressure is increased according to the increase in the printing rate. Reduces the linear speed of the roller. In the case of thick paper, the curl amount is generally smaller than that of plain paper, and the change in the amount of curl with respect to the change in image density is also small.
[0076]
[Table 2]

[0077]
3) When printing on plain paper in the humidity range (humidity 0 to 30%), as shown in Table 3 below, the heating roller linear speed is fixed at 100%, and the pressure roller is increased as the printing rate increases. The line speed is controlled to be reduced.
[0078]
[Table 3]

[0079]
4) When printing on plain paper in the humidity range (humidity 31 to 55%), as shown in Table 4 below, the heating roller linear speed is fixed at 100%, and the pressure roller is increased according to the increase in the printing rate. The line speed is controlled to be reduced.
[0080]
[Table 4]

[0081]
5) When printing on plain paper in the humidity range (humidity 56-70%), as shown in Table 5 below, the heating roller linear speed is fixed at 100%, and the pressure roller is increased according to the increase in the printing rate. The line speed is controlled to be reduced.
[0082]
[Table 5]

[0083]
6) When printing on plain paper in the humidity range (humidity 70% ~), as shown in Table 6 below, the heating roller linear speed is fixed at 100%, and the pressure roller Reduces the linear speed.
[0084]
[Table 6]

[0085]
Because of the correspondence shown in the above tables, even if the image density is very high, it is possible to perform a correction operation according to the degree of curl occurring in the sheet material, so that after the sheet material after copying Processing operations can be performed easily and effectively.
[0086]
【The invention's effect】
As is clear from the above description, the present invention has the following effects.
[0087]
(1) Since the heating roller and the pressure roller are rotated at a rotational speed satisfying the peripheral speed difference set based on the detection result of the image density, correction corresponding to the degree of curling occurring in the sheet material is performed in the fixing unit. Therefore, even when the image density is very high, appropriate correction can be performed, and post-processing work of the sheet material after copying can be performed easily and accurately.
[0088]
(2) Since the heating roller and the pressure roller are rotated at a rotational speed satisfying a circumferential speed difference set in consideration of humidity in addition to image density, the degree of curling generated in the sheet material can be improved with higher accuracy. Predicting and making it possible to make more appropriate corrections at the fixing unit, even when the image density is very high, even more effective correction is possible, and post-processing work for sheet material after copying is possible. This can be done more easily and accurately.
[0089]
(3) Since the peripheral speed of the heating roller is fixed when correcting the curl, the fixing ability can be maintained at a predetermined level, so that the original fixing ability can be easily maintained and controlled easily. Can also be simplified.
[0090]
(4) Since the heating roller and the pressure roller are rotated at a rotational speed satisfying the peripheral speed difference set based on the detection result of the image density, an appropriate correction corresponding to the degree of curl generated in the sheet material is fixed. Even if the image density is very high or the environmental conditions are fluctuating, the post-processing work of the sheet material after copying can be performed easily and accurately, and the print quality is improved.
[0091]
(5) Since the heating roller and the pressure roller are rotated at a rotational speed satisfying the peripheral speed difference set based on the calculated image density, correction corresponding to the degree of curling occurring in the sheet material is performed in the fixing unit. Therefore, even if the image density is very high, appropriate correction can be performed according to the degree of curl generated on the sheet material, and post-processing work of the sheet material after copying can be performed easily and accurately. And print quality can be improved.
[0092]
(6) Since the heating roller and the pressure roller are rotated at a rotational speed satisfying a set peripheral speed difference in consideration of humidity in addition to the calculated image density, the degree of curling generated in the sheet material is higher. Predicting with accuracy, more appropriate correction is possible at the fixing unit, so even more effective correction is possible even when the image density is very high, and post-processing of the sheet material after copying The work can be performed more easily and accurately, and the printing quality is further improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a curl generation principle of a fixing device according to an embodiment of the present invention.
FIG. 2 is a configuration explanatory diagram of the image forming apparatus.
FIG. 3 is a perspective view of an identification wearing apparatus.
FIG. 4 is an explanatory diagram for explaining the curl generation principle from another viewpoint;
FIG. 5 is a block diagram of a control system for driving and controlling the identification roller pair.
FIG. 6 is a perspective view of a conventional fixing device.
FIG. 7 is an explanatory diagram illustrating an example of a configuration of the image forming apparatus.
FIG. 8 is a configuration diagram of the main part.
[Explanation of symbols]
1-Fixing device
2-heating roller
3-Pressure roller
5-sheet material
30-control unit, setting unit, calculation means
35-Humidity detection means
39-Driver

Claims (5)

A fixing device comprising a fixing roller pair comprising a heating roller and a pressure roller, wherein the toner image transferred to the sheet material is heated and melted and fixed to the sheet material,
A drive unit for independently rotating the heating roller and the pressure roller;
A setting unit for setting a peripheral speed difference between the heating roller and the pressure roller;
Image density detecting means for detecting an image density of an image formed on the sheet material;
A control unit for controlling the drive unit,
The setting unit predicting curl caused by the fixing operation based on a detection result of the image density detected by the image density detecting unit;
In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
The control unit controls the drive unit to rotate the heating roller and the pressure roller at a rotational speed satisfying the circumferential speed of the heating roller and the pressure roller set by the peripheral speed setting unit. fixing apparatus characterized by comprising a. A fixing device comprising a fixing roller pair comprising a heating roller and a pressure roller, wherein the toner image transferred to the sheet material is heated and melted and fixed to the sheet material,
A drive unit for independently rotating the heating roller and the pressure roller;
A setting unit for setting a peripheral speed difference between the heating roller and the pressure roller;
Image density detecting means for detecting an image density of an image formed on the sheet material;
Humidity detecting means for detecting the humidity in the apparatus;
A control unit for controlling the drive unit,
The setting unit predicting curl caused by the fixing operation based on a detection result of the image density detected by the image density detection unit and a detection result of the humidity detected by the humidity detection unit;
In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
The control unit controls the drive unit to rotate the heating roller and the pressure roller at a rotational speed satisfying the circumferential speed of the heating roller and the pressure roller set by the peripheral speed setting unit. fixing apparatus characterized by comprising a. An image forming apparatus comprising the fixing device according to claim 1 . A document reader for reading image information of the document;
Arithmetic means for calculating the image density of the document based on the data read by the document reader;
A setting unit for setting a peripheral speed difference between the heating roller and the pressure roller in accordance with the image density information calculated by the calculation unit;
A drive unit for independently rotating the heating roller and the pressure roller;
A control unit for controlling the drive unit,
The setting unit predicting curl caused by the fixing operation based on the image density information calculated by the calculating unit;
In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
The controller is configured to rotate the heating roller and the pressure roller at a rotational speed satisfying a circumferential speed of the heating roller and a circumferential speed of the pressure roller set by the circumferential speed setting unit. An image forming apparatus comprising means for controlling the image. A document reader for reading image information of the document;
Arithmetic means for calculating the image density of the document based on the data read by the document reader;
Image density information calculated by said arithmetic means, a setting unit and humidity information detected by the humidity detecting means for detecting the humidity of the usage environment, in accordance with the set peripheral speed difference between the heating roller and the pressure roller ,
A drive unit for independently rotating the heating roller and the pressure roller;
A control unit for controlling the drive unit,
The setting unit predicting curl caused by a fixing operation based on the image density information detected by the computing unit and the humidity information detected by the humidity detecting unit;
In order to cancel the curl predicted by the predicting means, a peripheral speed setting means is provided that fixes the peripheral speed of the heating roller and controls the peripheral speed of the pressure roller to be decelerated compared with the peripheral speed of the heating roller. ,
The controller is configured to rotate the heating roller and the pressure roller at a rotational speed satisfying a circumferential speed of the heating roller and a circumferential speed of the pressure roller set by the circumferential speed setting unit. An image forming apparatus comprising means for controlling the image.

Images