JP6750866B2 - Image forming device - Google Patents

Description

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

In an electrophotographic copying machine or printer, a toner image is formed on an image forming section on a recording material conveyed from a cassette or a tray, and the recording material is heated while being conveyed by a fixing section to fix the toner image on the recording material. To do.

In the above copying machine or printer, when the recording material is not properly set in the cassette or the tray, the recording accuracy may be deteriorated or jam may occur due to the skew of the recording material. Further, in the case of the side-by-side conveyance in which the recording material is conveyed with the center of the recording material being displaced to one side from the conveyance reference position in the width direction orthogonal to the recording material conveyance direction, the recording material of the fixing unit is passed. Not overheated in the non-passage area. In this case, in order to suppress the excessive temperature rise, control is performed to reduce the throughput of the recording material. However, the control of reducing the throughput of the recording material leads to a decrease in print productivity.

An image forming apparatus as described in Patent Document 1 has been proposed as a method for determining such a conveyance failure such as skewing or biasing of the recording material.

In Japanese Patent Laid-Open No. 2004-242242, the temperature difference between the first temperature detecting means and the second temperature detecting means for detecting the excessive temperature rise in the non-passage area that occurs when the small-sized recording material is conveyed in the fixing unit is not less than a predetermined value. There is disclosed a technique of controlling the operation of the apparatus by detecting the deviation of the recording material or the like when the value becomes.

JP, 2011-27885, A

However, in the image forming apparatus described in Patent Document 1, it is difficult to accurately determine skewing or offset of the recording material from the temperature difference between the first temperature detecting unit and the second temperature detecting unit. That is, the temperature difference in the non-passage area that occurs in the fixing portion is not limited to biasing and skewing of the recording material, variation in sensitivity of each temperature detection unit, variation in detected temperature due to deterioration of durability of members, image recording material width. It is caused by various factors such as the density difference in the direction.

Therefore, it is difficult for the determination method of the image forming apparatus of Japanese Patent Laid-Open No. 2004-242242 to accurately determine the one-sided conveyance with a small number of recording materials to be conveyed. It had to be transported. Furthermore, it is extremely difficult to detect the skew of the single-shot recording material in which a small temperature difference does not occur in the width direction orthogonal to the conveying direction of the recording material.

It is an object of the present invention to provide an image forming apparatus capable of accurately detecting a skewed conveyance of a recording material or a conveyance failure such as one-sided conveyance.

In order to achieve the above object, the image forming apparatus according to the present invention,
Image processing means for generating an image signal for image formation from image data;
An image forming unit that forms a toner image on a recording material by the image signal,
A fixing unit that has a fixing rotator and a pressure rotator that forms a nip portion with the fixing rotator, and that fixes the toner image to the recording material while conveying the recording material at the nip portion;
Equipped with
The fixing unit includes a first temperature detecting member and a second temperature detecting member that detect the temperature of the fixing rotating body that passes through both ends in a direction orthogonal to the recording material conveyance direction,
An image forming apparatus including a determination unit that determines a conveyance state of the recording material according to a first detected temperature difference between the first temperature detection member and the second temperature detection member and a second detected temperature difference. At
The image processing means detects the density information of the toner image from the image data, and adjusts the detected temperatures of the first temperature detection member and the second temperature detection member according to the detected density information. Alternatively, the judgment criterion of the judging means is adjusted.

According to the present invention, it is possible to provide an image forming apparatus capable of accurately detecting a skewed conveyance of a recording material or a conveyance failure such as one-sided conveyance.

Sectional view showing a schematic configuration of the image forming apparatus according to the first embodiment. Sectional drawing which shows the schematic structure of a fixing device. Cross-sectional view of the nip portion of the fixing device and the vicinity of the nip portion Diagram of the fixing device of FIG. 2 viewed from the C direction Diagram showing the temperature transition of the thermistor during normal paper transport Diagram showing the positional relationship between the thermistor and paper during normal transport Diagram showing the temperature transition of the thermistor during skew feeding of paper Diagram showing the positional relationship between the thermistor and paper during skew feeding Block diagram showing a control system of the image forming apparatus according to the first embodiment Diagram showing changes in the temperature detected by the thermistor during normal continuous paper transport 3 is a flowchart for explaining a procedure for determining whether the sheet is skewed or biased in the image forming apparatus according to the first embodiment. Sectional drawing which shows schematic structure of the fixing device of the image forming apparatus which concerns on Embodiment 2. FIG. 6 is a flowchart for explaining a procedure for determining whether the sheet is skewed or skewed in the image forming apparatus according to the second embodiment. FIG. 6 is a diagram for explaining a relationship between a thermistor position and a solid image of the image forming apparatus according to the fifth embodiment, and a detection temperature decrease amount of the thermistor. FIG. 5 is a diagram for explaining the relationship between the position of a thermistor and a solid image and the detected temperature decrease amount of the thermistor of the image forming apparatus according to the fifth embodiment. Figure showing the density calculation range of paper Flowchart showing processing from detection of concentration information to correction of temperature detected by the thermistor Diagram for explaining the density information detection area

Hereinafter, embodiments of the present invention will be described with reference to the drawings. Although the preferred embodiment of the present invention is an example of the best embodiment of the present invention, the present invention is not limited to the following examples, and various other configurations within the scope of the idea of the present invention. Can be replaced with.

[Embodiment 1]
<Overall structure of image forming apparatus>
An image forming apparatus 200 according to the present invention will be described with reference to FIG.

FIG. 1 is a sectional view showing a schematic configuration of an example of an image forming apparatus (a full color printer in this embodiment) 200 using an electrophotographic recording technique. The image forming apparatus 200 has a process speed of 240 mm/s and a throughput of 40 ppm (A4 size vertical feed).

In the image forming apparatus 200, the image forming unit 10 that forms a toner image on a sheet P as a recording material has four image forming stations Sa of cyan (C), magenta (M), yellow (Y), and black (K). , Sb, Sc, Sd. Each image forming station cleans the photosensitive drums 2a, 2b, 2c and 2d as image bearing members, the charging members 3a, 3b, 3c and 3d, the developing devices 1a, 1b, 1c and 1d, and the photosensitive drums. The cleaners 5a, 5b, 5c and 5d are included.

Further, the image forming unit 10 includes a laser scanner 6, transfer members 4a, 4b, 4c, and 4d, a belt 7 that carries the toner images transferred from the photosensitive drums by the transfer members, and conveys the belt 7 to the paper P. A secondary transfer member 8 for transferring a toner image. Since the operation of the image forming unit 10 described above is well known, detailed description thereof will be omitted.

Sheets (recording materials) P stored in a cassette (recording material holding unit) 30 in the image forming apparatus main body 201 are fed one by one by rotation of a roller 31. Alternatively, the paper P (not shown) set on the tray (recording material holding unit) 33 is fed one by one by the rotation of the roller 34. The sheet P is conveyed to the secondary transfer nip portion formed by the belt 7 and the secondary transfer member 8 by the rotation of the roller 35. The paper P on which the toner image is transferred at the secondary transfer nip portion is sent to the fixing device (fixing unit) 20, and the toner image is heated and fixed on the paper by the fixing device. The paper P that has exited the fixing device 20 is discharged to the tray 36 by the rotation of the roller 43.

As shown in FIG. 9, the series of operations are controlled by the control unit 100 included in the image forming apparatus 200. The control unit 100 has a CPU (central processing unit) 101, a ROM 102, and a RAM 103 (storage unit), processes information by a predetermined method, and controls the overall operation of the image forming apparatus 200.

<Structure of fixing device>
Next, the fixing device 20 will be described with reference to FIGS. 2 to 4.

FIG. 2 is a sectional view showing a schematic configuration of the fixing device 20. FIG. 3 is a cross-sectional view of the nip portion N of the fixing device 20 and the vicinity of the nip portion. FIG. 4 is a diagram when the fixing device 20 is viewed from the downstream side (the C side in FIG. 2) in the conveyance direction of the paper P.

As shown in FIG. 2, the fixing device 20 includes a tubular film (fixing rotary member) 41, a pressure roller (pressing rotary member) 42, a heater (heating member) 60, and a holder (support member) 61. And a pressure stay (pressure member) 62.

In the width direction orthogonal to the transport direction of the paper P, the holder 61 made of heat-resistant resin supports the heater 60 by the groove provided on the flat surface of the holder. A pressure stay 62 made of metal is placed on the flat surface of the holder 61 opposite to the groove. A flexible heat-resistant film 41 is loosely fitted on a holder 61 supporting the heater 60 and having a pressure stay 628 mounted thereon.

In the film 41, an elastic layer 41b is formed on the outer peripheral surface of a base layer 41a (see FIG. 3) made of metal (SUS in the present embodiment) formed in an endless shape, and an outer peripheral surface of the elastic layer 42b is made of PFA resin. The releasable layer 41c is formed. As the elastic layer 41b, for example, one based on high thermal conductive silicone rubber is used. The film 41 has an outer diameter of 24 mm and a dimension in the width direction orthogonal to the conveyance direction of the paper P is 245 mm.

The heater 60 slidingly contacting the inner surface of the film 41 has an elongated substrate 60a. The substrate 60a is a thermally conductive insulating substrate made of ceramic such as alumina or aluminum nitride. A resistance heating element layer (heating element) 60b is provided on the back surface (non-sliding surface of the film) of the substrate 60a opposite to the film 41 along the longitudinal direction of the substrate. Further, a conductive pattern (not shown) electrically connected to the resistance heating element layer, an electrode (not shown) electrically connected to the conductive pattern, and an insulating glass layer 60c are provided on the back surface of the substrate 60a. Has been.

The insulating glass layer 60c overcoats the resistance heating element layer 60b to ensure insulation with an external conductive member, and also has a corrosion resistance function for preventing the resistance value of the resistance heating element layer from changing due to oxidation or the like, and a mechanical resistance. It also has the role of preventing serious damage.

On the other hand, on the film 41 side surface (film sliding surface) of the substrate 60a, a sliding layer 60d is provided in a region where the inner surface of the film 60 of the substrate 60a slides. The sliding layer 60d has a role of ensuring smooth slidability with the inner surface of the film 41.

As shown in FIG. 2, the pressure roller 42 is formed by forming an elastic layer 42b on the outer peripheral surface of a metal cored bar 42a and covering the outer peripheral surface of the elastic layer with a releasable layer 42c. A conductive silicone rubber layer having a thickness of about 3 mm is used as the elastic layer 42b, and a PFA tube having a thickness of about 50 μm is used as the release layer 42c. The pressure roller 42 has an outer diameter of 25 mm and a dimension in the width direction orthogonal to the conveyance direction of the paper P is 230 mm. Both ends of the cored bar 42a of the pressure roller 42 are rotatably supported by the left and right frames FL and FR of the fixing device 20 via bearings 43 in the width direction orthogonal to the conveyance direction of the paper P.

In the width direction orthogonal to the transport direction of the paper P, flanges 63 (see FIG. 4) formed of a heat-resistant resin regulate the track in the rotation direction of the film and the movement of the film at both ends of the film 41. Is fitted to. That is, the left and right flanges 63 regulate the orbit of the film in the rotation direction by sliding the outer peripheral surface 63a of the flanges against the inner surface of the film 41. Further, the left and right flanges 63 restrict the movement of the film by abutting the restricting end surface 63b of the flange when the end portion of the film 41 approaches the width direction orthogonal to the transport direction of the paper P.

The left and right flanges 63 support both ends of the holder 61 and the pressure stay 62 in the width direction orthogonal to the conveyance direction of the paper P. Each of the flanges 63 is pressed by a pair of left and right pressure springs 64 held by the frames FL and FR of the fixing device 20 in the vertical direction orthogonal to the generatrix direction of the film 41.

The pressing stay 62 uniformly presses the holder 61 in the width direction orthogonal to the conveyance direction of the sheet P by the pressing force of the pressing spring 64. As a result, the holder 61 presses the heater 60 against the inner peripheral surface (inner surface) of the film 41 to bring the outer peripheral surface (front surface) of the film into pressure contact with the outer peripheral surface (front surface) of the pressure roller 42. As a result, in the pressure roller 42, the elastic layer 42b of the pressure roller is crushed and elastically deformed to form a nip portion N having a predetermined width between the pressure roller surface and the film 41 surface.

<Temperature detection member>
FIG. 6 shows the positional relationship between the thermistors 51a, 51b and 51c and the paper when the paper P is normally conveyed.

Reference numeral 51c is a thermistor that detects the temperature of the passage area of the heater 60 through which the large size sheet and the small size sheet pass. As shown in FIG. 2, the thermistor 51c supported by the heater holder 61 is in contact with the center of the heater 60 (not shown) in the width direction orthogonal to the conveyance direction of the paper P. The thermistor 51c is intended to control the temperature of the film 41.

51a and 51b are thermistors for detecting the temperature of the non-passage area of the heater 60 where the large size sheet passes and the small size sheet does not pass. As shown in FIG. 2, the thermistor 51a (first temperature detecting member) supported by the heater holder 61 contacts the left end portion of the heater 60 (not shown) in the width direction orthogonal to the conveyance direction of the paper P. ing. As shown in FIG. 2, the thermistor 51b (second temperature detecting member) supported by the heater holder 61 contacts the right end portion of the heater 60 (not shown) in the width direction orthogonal to the transport direction of the paper P. ing. The two thermistors 51a and 51b are intended to detect excessive temperature rise in the non-passage area of the film 41.

The thermistors 51a and 51b are located slightly inside the maximum sheet passing width of the fixing device 20 and in the vicinity of the maximum sheet passing width. That is, the thermistors 51a and 51b are arranged near the positions where both ends of the sheet in the width direction orthogonal to the transport direction of the sheet P pass. Specifically, it is a position 100 mm outside each of the paper transport reference positions in the width direction orthogonal to the paper P transport direction.

In the case of normal conveyance in which LETTER size paper (paper width 216 mm) or A4 size paper (paper width 210 mm) is conveyed in a state where the center in the width direction substantially coincides with the conveyance reference position, the thermistors 51a and 51b are provided with a predetermined size. The detected temperature is almost the same as the fixing temperature (target temperature). On the other hand, when the B5 size paper (paper width 182 mm) smaller than the A4 size paper or the A5 size paper (paper width 148 mm) is continuously conveyed, the thermistors 51a and 51b are overheated (above the predetermined fixing temperature). Temperature rise) is detected. In this case, control for reducing the throughput of the paper P is performed so as to maintain the predetermined fixing temperature.

<Heat fixing processing operation>
The driving force of the motor M (see FIG. 2) is transmitted to the cored bar 42a of the pressure roller 42 via the gear G (see FIG. 4), whereby the pressure roller rotates in the arrow direction shown in FIG. The film 41 rotates in the direction of the arrow shown in FIG. 2 following the rotation of the pressure roller 42 while the inner surface of the film 41 is in sliding contact with the insulating glass layer 60c of the heater 60.

When power is supplied to the electrodes of the heater 60 from a power source (not shown), the resistance heating element layer 60b generates heat and the temperature of the heater rises rapidly. Then, a heater control unit (not shown) controls the amount of electric power supplied to the heater 60 so as to maintain the detected temperature of the film 41 detected by the thermistor 50c at a predetermined fixing temperature.

The recording material P carrying the unfixed toner image T is introduced into the nip portion N. The recording material P is heated by the heat of the heater 60 while being conveyed in the nip portion N. As a result, the toner image T on the recording material is fixed on the recording material.

<Slanting and misalignment of recording materials>
In properly carrying the paper P from the cassette 30 or the tray 33, the user moves a regulation plate (not shown) movable in the width direction orthogonal to the paper carrying direction to hold the paper at a predetermined position. There is a need. However, if the moving operation is insufficient or if the moving operation is forgotten, the regulation plate may not hit the paper P. Alternatively, there is a case in which the amount of paper P exceeds the height of the regulation plate and the paper is not held by the regulation plate in an attempt to set the amount of the paper P larger than the designated amount in the cassette 30 or the tray 33.

At the start of conveyance, the force received by the paper P from the roller 31 or the roller 34 does not always coincide with the conveyance direction. If the position of the regulation plate is displaced, the end portion of the paper is not held and the paper is not held. May begin to skew. As another example, due to overloading of the paper P, the regulation plate does not hold the edge of the paper, and the surface of the paper rubs against an unexpected position, causing the paper to skew. .. For example, if the surface of the sheet P is rubbed and subjected to a load only on one side of the sheet P in the width direction, a force in the rotational direction is applied to the sheet, so that the sheet is skewed.

When the skew amount of the conveyed paper P is small, it is corrected by the roller 35, but the skew correction amount by the roller is limited. If a large skew occurs on the sheet P at the start of transport, the skew is not sufficiently corrected by the roller 35, and the sheet is transported to the secondary transfer nip portion while being inclined with respect to the transport direction, and then the fixing device 20. And is discharged onto the tray 36. When the skew amount is further large, the sheet P is conveyed while extending beyond the area where the sheet originally passes, so that a jam occurs in the conveying path or damage to the edge of the sheet occurs until the sheet P is discharged. It may cause problems such as occurrence.

Alternatively, if the center of the sheet P in the width direction is set so as to be displaced from the transport reference position due to the displacement of the regulation plate, so-called one-sided transport may occur. In the case of the one-sided conveyance, in the width direction orthogonal to the conveyance direction of the sheet P, the temperature rise in the non-passage portion of the film 41 on the side opposite to the side closer to the sheet becomes large, and the throughput unintentionally decreases. There is something to do.

Further, when a temperature difference occurs in the film 41 in the width direction orthogonal to the transport direction of the paper P, a difference in expansion occurs in the elastic layer 41b of the film and the elastic layer 42b of the pressure roller 42. Then, in the width direction orthogonal to the transport direction of the sheet P, the film 41 receives a strong offset force and abuts the flange 63. If such an abutting phenomenon occurs repeatedly, the durability of the base layer 41a of the film 41 may be deteriorated.

In addition, the temperature difference of the film 41 in the width direction orthogonal to the conveyance direction of the paper P also leads to deterioration of the elastic layer 41b of the film and the elastic layer 42b of the pressure roller 42. Due to the deterioration of the elastic layers 41b, 42b, the balance of the transportability of the paper P may be lost in the width direction orthogonal to the transport direction of the paper P, and wrinkles may occur on the paper.

<Diagonal/convergent discriminating method>
A method of discriminating a conveyance failure such as skewing or biasing of the image forming apparatus according to the present embodiment will be described.

In the present embodiment, the non-passage area of the film 41 is indirectly obtained through the detection results of the thermistors 51a and 51b that are in contact with the left end portion and the right end portion of the heater 60 in the width direction orthogonal to the conveyance direction of the paper P. The change in the temperature difference is detected, and skewing or deviation of the sheet P is detected.

FIG. 5 is a diagram showing the transition of the temperature detected by the thermistors 51a and 51b when one sheet of LETTER size P (maximum passage width 216 mm) is correctly set in the tray 33 and is normally conveyed. FIG. 6 shows the positional relationship between the film 41 of the fixing device 20 and the sheet P during sheet conveyance in this case. Since there is no skew in the conveyance of the paper P shown in FIG. 6, the difference between the temperatures detected by the thermistors 51a and 51b is small. ΔTbase and ΔTprint in FIG. 5 will be described later.

Next, in FIG. 7, the LETTER size paper P is also overloaded on the tray 33 and both ends in the width direction of the paper are set in a free state, and the thermistors 51a and 51b when the paper is conveyed obliquely are conveyed. The change of the detected temperature of is shown. FIG. 8 shows the positional relationship between the thermistors 51a, 51b and 51c and the sheet when the sheet P is conveyed in a skewed manner. In addition, as shown in FIG. 8, the skew amount S is defined as an amount in which the trailing edge E2 of the sheet P is closer to the L side than the leading edge E1 of the sheet P. In the illustrated example, the skew amount S is 14 mm.

If there is no skew, the distance X (see FIG. 6) between the side edge E0 (see FIG. 6) of the LETTER size paper P and the thermistor 51a or 51b is 8 mm, as shown in FIG. If a large skew with a line amount S of 14 mm occurs, the sheet is shifted to the L side. Then, in the region Y from the middle of conveyance to the trailing edge of the paper P, the paper P does not take heat of the film 41 at the position of the thermistor 51b on the R side. As a result, the temperature of the film 41 rises on the R side, and a difference ΔT (here, 7.8° C.) occurs in the detected temperature between the thermistors 51a-51b at both ends.

In the above-mentioned Patent Document 1, the skew and the offset of the sheet P are detected based on this temperature difference. However, according to the study by the present inventors, the skew and the skew of the sheet with a high accuracy are obtained. Cannot detect misalignment. The reason will be described below.

FIG. 10 shows, as an example, the transition of the temperature detected by the thermistors 51a and 51b when the fixing device 20 is in a cold state and 160 sheets of paper P are continuously conveyed without skew.

It can be seen that the detected temperature difference ΔT between the thermistors 51a and 51b changes by about 4° C. during the conveyance of only 160 sheets even if the sheet is conveyed without skewing. Here, an example of a change in the detected temperature difference between the thermistors 51a and 51b for a short period in a single continuous paper passing job is shown, but the detected temperature difference between the thermistors 51a and 51b caused by using the device for a long period of time is shown. There are also changes.

The detected temperature difference between the thermistors 51a and 51b is unevenness of excessive temperature rise in the non-passage area of the film 41, deviation of the sensitivity of the thermistor, deviation of the sheet P due to variations in parts and assembly of the image forming apparatus, and deterioration of durability of members. It is caused by various factors such as the fluctuation of the detected temperature due to. In order to accurately detect the skew due to the temperature difference of several degrees Celsius caused by the skew of the sheet P, even if the temperature difference of the non-passage area of the film 41 that occurs during normal conveyance is several degrees Celsius, it cannot be ignored. ..

That is, in order to accurately detect the skew feeding, it is necessary to grasp the state of the fixing device 20 at the start of conveyance, and for that reason, the temperature of the non-passage area of the film 41 at the timing when the leading edge of the paper P reaches the nip portion N. It was decided to measure the difference.

Then, in the present embodiment, skewing/concentration of the sheet P is determined based on the degree of change in the temperature difference in the non-passage area of the film 41 before and after the sheet P is conveyed.

Hereinafter, the method for determining the skewed/converged conveyance of the sheet P in the image forming apparatus 200 according to the present embodiment will be described in detail with reference to the flowchart of FIG.

After the start of printing (S1201), the first detected temperature difference ΔTbase is acquired from the detected temperatures of the thermistors 51a and 51b at the timing when the leading edge of the paper P reaches the nip portion N (S1202).

Next, at the timing when the trailing edge of the paper P passes through the nip portion N, the second detected temperature difference ΔTprint is acquired from the detected temperatures of the thermistors 51a and 51b (S1203).

Here, the timing when the leading edge of the sheet P reaches the nip portion N is the timing before and after the leading edge of the sheet reaches the nip portion, and the influence of the heat of the film being taken off by the sheet at the nip portion is the thermistor as temperature. It indicates the timing before being clearly detected by 51a and 51b.

Similarly, the timing at which the trailing edge of the sheet P exits the nip portion N is the timing before and after the trailing edge of the sheet exits the nip portion, and the influence of the heat of the film being deprived of the sheet is the thermistor 51a, It shows the timing most reflected in the detected temperature of 51b.

In the present embodiment, the timing at which the leading edge of the sheet P reaches the nip portion N is set to a predetermined time before and after the leading edge of the sheet begins to enter the nip portion, for example, 0.3 sec, for a total of 0.6 sec. Meanwhile, using the respective average temperatures TLin and TRin indicated by the thermistors 51a and 51b, the first detected temperature difference ΔTbase, which is the temperature difference between the two thermistors,
ΔTbase=TLin−TRin (Formula 1)
And

Similarly, the timing when the trailing edge of the sheet P leaves the nip portion N is set to 0.9 seconds from 0.3 seconds after the trailing edge of the sheet P leaves the nip portion to 1.2 seconds later. Then, in the meantime, using the respective average temperatures TLout and TRout indicated by the thermistors 51a and 51b, the second detected temperature difference ΔTprint, which is the left-right difference between the two thermistors, is
ΔTprint=TLout−TRout (Formula 2)
It is defined as

In the image forming apparatus 200 of the present embodiment, when the succeeding paper P is printed by continuous conveyance, after the rear end of the paper passes through the nip portion N, the film 41 is rotated about 4 times, that is, about 1.2 sec. It was found that the influence of the temperature rise of the film due to the skewing and biasing was significant during the interval. Therefore, the measurement timing of the second detected temperature difference ΔTprint is set as described above.

In the present embodiment, the first detected temperature difference ΔTbase and the second detected temperature difference ΔTprint are calculated based on the average temperature for a predetermined period, but if the indices represent the temperature difference between the thermistors 51a and 51b, For example, it may be calculated based on other calculated values such as the maximum value of the predetermined period.

Here, in FIG. 5, TL represents the temperature detected by the thermistor 51a, TR represents the temperature detected by the thermistor 51b, and the average temperatures at the timing when the paper P reaches the nip portion N are TLin and TRin. The average temperatures at the timing when the trailing edge of the paper P leaves the nip portion N are TLout and TRout.

Then, the difference |ΔTprint-ΔTbase| of the first detected temperature difference ΔTbase and the second detected temperature difference ΔTprint obtained by the above-described procedure is calculated, and the calculated difference is the detection threshold V which is a preset reference value. The conveyance state is determined by comparing with.

Specifically, the following conditional expression,
|ΔTprint-ΔTbase|≧V (eg, 5° C.)
It is determined whether or not the condition is satisfied (S1204).

In this example, when the detection threshold V is set to 5 (° C.) and the above conditional expression is satisfied, that is, the difference between the first detection temperature difference ΔTbase and the second detection temperature difference ΔTprint is the detection threshold V(5 When the temperature is higher than (° C.), it is determined that the conveyance state of the paper P is abnormal. That is, it is determined that the sheet P is skewed/converged (S1205).

Furthermore, the user is notified that there is a possibility that the setting state of the paper P on the cassette 30 or the tray 33 may not be appropriate, assuming that the sheet is skewed or biased (S1206).

For the notification to the user, a notification signal is output from the control unit 100 shown in FIG. 9 and displayed on the display unit of the control panel 104, for example. However, it is sufficient that the user can be notified, a sound may be emitted, and some kind of notification may be made.

As shown in FIG. 7, in the present embodiment, when the sheet P is skewed and the skew amount S is 14 mm, ΔTbase=0.6 and ΔTprint=7.8. ,
The difference |ΔTprint-ΔTbase|=7.2° C.,
The skew feeding of the paper P can be detected.

The paper P used here is a paper having a basis weight of 75 g/m ² , manufactured by Xerox Co., Ltd., and a product name “businness Multipurpose 4200”.

In the above description, the skew detection of the sheet P has been described by taking the change in the detected temperature difference between the thermistors 51a and 51b that occurs when the skew amount S is 14 mm as an example. The image forming apparatus according to the present embodiment can detect the skew of the sheet P even when skew of 9 mm or more occurs, and the greater the skew amount S, the higher the frequency of detecting skew of the sheet. ..

<Paper size and criteria>
As described above, the easiness of skew detection depends on the relationship between the position of the edge of the sheet P and the positions of the thermistors 51a and 51b. Therefore, the easiness of skew detection differs depending on the size of the sheet. There is. In the present embodiment, the case of transporting the LETTER size paper has been described, but the effect of being able to accurately detect a transport failure such as skew or bias of the paper P is obtained when a paper of a specific size is passed. It is not limited to.

For example, regardless of the paper size, it is possible to determine the skew of the paper P when the change in the temperature difference in the non-passage area of the film 41 is equal to or larger than a predetermined detection threshold. As an example, with A4 size paper, which is about 6 mm narrower than the LETTER size paper, skew detection was possible even with a skew amount of about 6 mm.

Alternatively, a skew detection value, which is a different reference value, may be set for each sheet size, and skew detection may be performed when the skew amount S is about the same regardless of the sheet size. For example, if the skew detection value for detecting skew of LETTER size paper is 5° C., the skew detection value of A4 size paper is set to 7.5° C., and even for A4 size paper, it is about 9 mm, similar to LETTER size paper. When the skew feeding occurs, the skew feeding of the paper P can be detected.

<Basis weight of paper and judgment criteria>
Further, even with the same skew amount, the change in the temperature difference in the non-passage area of the film 41 varies depending on the basis weight of the paper P. The larger the basis weight, the larger the change, and the smaller the tendency, the smaller the change. The amount of heat required to fix the toner differs depending on factors such as the basis weight and surface property of the paper P. It is general to adjust the process speed of image formation and the control temperature (target temperature) of fixing depending on the basis weight and type of the paper P to secure the fixability of the toner on each paper.

In order to secure the fixability of the paper P having different basis weights at the same process speed, the larger the basis weight, the higher the control temperature is to secure the amount of heat to be given, and the larger the basis weight of the paper. However, the amount of heat supplied per unit area or unit time becomes large.

As a result, when the sheet P is conveyed in a skewed or offset manner, the sheet does not pass to the positions of the thermistors 51a and 51b in the non-passage area of the film 41, so that a sheet having a large basis weight is passed. The higher the temperature, the greater the temperature rise. This is a phenomenon similar to that known in general non-passage part temperature rise.

Therefore, for thick paper having a large basis weight, in which a temperature difference in the non-passage area of the film 41 is likely to occur due to the skew of the paper P, the detection threshold V is set to be larger than that of thin paper in order to prevent erroneous detection. The detection threshold V may be adjusted depending on the basis weight of the paper used.

<Paper surface and judgment criteria>
Similarly, the surface property of the paper P also affects the fixing property of the toner, and the control temperature may be increased for the paper P having a rough surface property. As in the case of the grammage described above, the detection threshold V may be set large for the paper P having a rough surface. The determination of the basis weight and the surface property may be a value set by the user or a detection result of a sheet detection sensor (not shown) of the apparatus.

<Example of control by paper type>
The operation of image forming apparatus 200 in the present embodiment will be described.

The image forming apparatus 200 according to the present embodiment has a normal paper print mode, a thin normal paper print mode, a thick normal paper print mode, and a bond paper print mode, depending on the type of paper P. Normally paper, thin usually paper, the amount of heavy normal paper each assumed basis is, 75~80g / ^{m 2} is usually paper, is a thin usually paper 60 g / ^{m 2} before and after the thick normal paper is 100 g / ^{m 2} before and after.

The control temperature for each print mode is (-15°C) in the thin normal paper print mode and (+15°C) in the thick normal paper print mode, as compared to the normal paper print mode. In the bond paper print mode, the control temperature is (+15°C) as compared with the normal paper print mode.

In the present embodiment, in order to detect the skew feeding with the substantially same skew feeding amount S on the paper P of the same size regardless of the basis weight, the detection threshold value V as a different judgment reference value for each print mode is set. It is configured to have. As described above, the skew detection value in the normal paper print mode is set to 5° C., and the detection threshold value V of each mode is 4° C. in the thin normal paper print mode and 6.5° C. in the thick normal paper print mode. And Further, even in the bond paper print mode, by setting the temperature to 6.5° C., the skew of 9 mm can be detected for the LETTER size paper.

<Measurement Timing of First Detected Temperature Difference ΔTbase>
As described above, the measurement timing of the first detected temperature difference ΔTbase in the present embodiment is the timing at which the temperature control of the heater 60 is performed before and after the timing at which the paper P reaches the nip portion N. The reason is that the temperature difference between the thermistors 51a and 51b is relatively stable. In the present embodiment, the temperature adjustment of the heater 60 is started 0.3 sec before the leading edge of the paper P reaches the nip portion N (approximately one rotation of the film 41), and the first detected temperature difference ΔTbase. Was set as the measurement starting point.

The acquisition end timing of the first detected temperature difference ΔTbase may be the timing at which the front end of the paper P reaches the nip portion N, but it is desirable that the measurement time be long in the range where the temperature of the heater 60 is relatively stable. .. In the image forming apparatus 200 according to the present embodiment, the time when the film 41 makes one rotation after the leading edge of the paper P reaches the nip portion N is set as the measurement end point of ΔTbase.

Heat transfer from the film 41 to the sheet P is locally performed at the nip portion N having a dimension of about 9 mm in the sheet transport direction. The influence of whether or not the heat of the film 41 is transferred to the paper P appears in the temperature detected by the thermistors 51a and 51b approximately after one rotation of the film 41 after the paper reaches the nip portion N. Therefore, the measurement end timing of ΔTbase is set as described above.

<ΔTprint measurement timing>
On the other hand, the measurement timing of the second detected temperature difference ΔTprint is set so that the passage of the sheet P through the nip portion N easily affects the detected temperature of the thermistors 51a and 51b. Since the amount of skewing and biasing of the sheet P is not constant, the timing at which the temperature rise of the film 41 starts to affect the detected temperature of the thermistors 51a and 51b is also not constant.

However, after the paper 41 has passed through the nip portion N and after the film 41 has made one rotation (approximately 0.3 sec), the temperature detected by the thermistors 51a and 51b is affected by the skew and offset of the paper. Further, even when the sheet P to be conveyed next is not skewed or skewed and conveyed, the influence of the temperature rise of the previous sheet conveyance remains while the film 41 makes one rotation. Further, there is a delay due to the thermal conductivity of each member until the temperature rise of the film 41 due to the skew of the sheet P or the one-sided shift is reflected in the detection temperature of the thermistors 51a and 51b.

These characteristics change depending on the configuration of the fixing device 20, the material thereof, and the like. However, the above measurement timing is intended to grasp the change in the first and second detected temperature differences before and after the sheet P passes through the nip portion N. Therefore, the acquisition timings of the first and second detected temperature differences ΔTbase and ΔTprint can be determined according to the configuration, the material, and the like within a range where the purpose can be achieved.

<Control block configuration>
FIG. 9 is a block diagram showing a control system of the image forming apparatus 200. A series of operations based on the flowchart of FIG. 11 is executed by the control unit 100.

The thermistors 51a and 51b are connected to a control unit (discriminating means) 100 that controls the operation of the image forming apparatus 200. Describing the detection of the skew feeding or the one-sided conveyance, the temperature information detected by the thermistors 51a and 51b is subjected to a predetermined calculation by the CPU 101 inside the control unit 100.

The calculation result can be temporarily stored in the RAM 103, and is also compared with a detection threshold value V, which is also stored in advance in the ROM 102 inside the CPU 101 and serves as a reference value for determining skew/deviation. When it is determined that the sheet is skewed or biased, the control unit 100 outputs a signal to the control panel 104 of the apparatus or the PC (personal computer) 105 to notify the user that the sheet setting is not appropriate. be able to. An example of the calculation procedure is as described in the flowchart of FIG. 11 described above, and calculation processing is performed based on the flowchart.

Further, not only the signal is output, but also the skew feed/deviation information can be stored in the PC 105 or the memory inside the image forming apparatus together with the data indicating the generation timing and the usage status of the image forming apparatus 200. ..

In the present embodiment, the first detected temperature difference ΔTbase and the second detected temperature difference ΔTprint are obtained for each sheet of paper, that is, every time one sheet of paper P is conveyed, and calculation is performed to perform skewing and sheet skewing. The case has been described where the judgment of the conveyance state of the approach is performed. However, the measurement timings of the first and second detected temperature differences and the detection threshold value, which is a reference determination criterion for determining skew/deviation, are set according to the configuration of the apparatus.

Further, the detection threshold serving as the determination reference is not limited to the above value, and may be set so as to further reduce the failure of the determination.

Further, in the present embodiment, the possibility that the setting state of the paper P is not appropriate is notified to the user, but it may be left in the memory of the image forming apparatus 200 without notifying the user. Alternatively, not only the notification but also the printing may be forcibly stopped because there is a risk of a defective image on the paper P or a jam.

<Position relationship between paper size and edge thermistors 51a and 51b>
In the present embodiment, the arrangement position of the thermistors 51a and 51b with respect to the heater 60 is set to the center by a predetermined amount X (for example, 8 mm) with respect to the maximum sheet passing width of the fixing device 20, but the arrangement position is not limited thereto. Absent.

The skew feeding/deviation detection described in the present embodiment is performed in the non-passage portion when the amount of heat of the film is absorbed by the paper at the position where the thermistors 51a and 51b are arranged, or when the paper is displaced from the transport reference position. It is performed based on the temperature difference in the non-passage area of the film caused by the difference in temperature rise. Therefore, from the viewpoint of skew/deviation detection, the detection sensitivity is higher when the target sheet P is closer to the end position in the width direction. That is, the detected temperature difference in the non-passage area of the film 41, which occurs when the sheet P is skewed or biased, becomes large, and skew determination can be performed even if the skew amount is small.

On the other hand, the purpose of arranging the thermistors 51a and 51b is to detect the temperature rise in the non-passing portion during the conveyance of small-sized paper, and the thermistors 51a and 51b are arranged in balance in order to detect the temperature rise in the non-passing portion. It is good to decide the installation position.

In the present embodiment, the thermistors 51a and 51b are arranged closer to the center than the A4 sheet width in order to accurately detect the temperature rise in the non-passing portion when the sheet P having a width smaller than the A4 size is conveyed. .. Since it is difficult to detect the non-passage portion temperature rise in the wide paper P of A4 size or more, the length of the heater 60 is adjusted to secure the fixing property of the end portion in the wide paper P such as A4 or LETTER. At the same time, the temperature rise in the non-passage portion is minimized.

Further, in the present embodiment, the configuration in which the thermistors 51a and 51b are brought into contact with the film non-sliding surface side of the heater 60 has been described, but the arrangement position of the thermistor is not limited to this. The thermistors 51a and 51b may be brought into contact with the inner surface of the film 41, or the temperature of the film may be measured from the surface side of the film 41 without contact.

That is, the present invention is also applicable to a fixing device that uses a heat source other than a ceramic heater, for example, a conventionally known heat roller system that uses a halogen heater, a system that directly heats the outer peripheral surface of the fixing member, or an induction heating system. It is possible to Since the time taken for the temperature of the film 41, the pressure roller 42, etc. to be reflected in the detection temperature of the temperature detection means varies depending on the configuration of the fixing device, the measurement timing may be adjusted for each configuration.

The arrangement of the thermistors 51a and 51b has been described as an example in which they are symmetrical with respect to the conveyance reference position of the sheet P, but if the configuration of the present embodiment that compares the temperature difference before and after the sheet P is conveyed is arranged. The position is not limited to being symmetric, but may be asymmetric.

In the present embodiment, ΔTbase is acquired for each sheet of conveyed paper P, but the temperature of the film 41 may be directly detected, for example. In the case of direct detection, the temperature measurement time of ΔTbase may be shortened, and the measurement of ΔTbase becomes slightly unstable. In such a case, ΔTbase may be the average value of the latest several sheets.

[Second Embodiment]
Next, a second embodiment of the present invention will be described.

In the second embodiment, a procedure in which the difference between the first detected temperature difference and the second detected temperature difference is calculated and held over the continuous conveyance of a plurality of sheets P, and the difference for the plurality of sheets is predetermined. From the difference information obtained by processing in step S1, the conveyance state of the skewed sheet/converged sheet is determined. That is, the difference data obtained by passing a plurality of sheets of paper is acquired and stored, and the skew feeding/deviation of the paper P is performed based on the difference information obtained by calculation by a predetermined method, for example, a statistical method. The transport state is determined, and the user is notified that the sheet set state may not be appropriate.

FIG. 12 is a sectional view showing a schematic configuration of the fixing device 20 according to the second embodiment.

The thermistors 51a and 51b are in contact with the surface of the film 41, and are configured to be able to more directly detect a temperature change in the non-passage area of the film as the sheet P is conveyed. In the present embodiment, the thermistors b51a and 51b are arranged near the end of the maximum sheet passing width of the apparatus so that the scratches on the film surface due to the rubbing between the thermistors 51a and 51b and the film 41 do not affect the image quality. The position is 106 mm from the transport reference position of the paper P.

In other words, even if the LETTER size paper P is passed, since it is controlled so that a normal printed matter is printed with a margin of 5 mm at each end, the image quality is hardly affected. Further, in the image forming process direction, as shown in FIG. 12, it is located at a position apart from the rear end of the nip portion N in the downstream direction by a predetermined angle in the conveying direction of the paper P. In this embodiment, the position is about 40° (=θ). This is a position where the temperature immediately after the downstream side of the nip portion N in the transport direction of the paper P can be measured without hindering the transport of the paper P.

The other device configurations are the same as those in the first embodiment, and the same components are designated by the same reference numerals and description thereof is omitted.

In the second embodiment, the change in the surface temperature of the film 41 is directly and timely measured.

Further, the data obtained by the conveyance of each sheet of paper P is the difference between the first detected temperature difference ΔTprint and the second detected temperature difference ΔTbase (ΔTprint−ΔTbase), as in the first embodiment. It is possible to more accurately determine the set state of the sheets by determining the skewed/converged conveyance state based on the tendency of a plurality of sheets P of paper. According to this method, although it is not possible to detect a single-shot phenomenon, unnecessary notifications to the user due to false detection of skewing or biasing are less likely to occur, so a device with a good balance can be provided for the user. ..

For example, when the state of setting the sheets P on the cassette 30 or the tray 33 is not appropriate, the conveyance state may vary for each sheet. That is, there are sheets that are skewed every time the sheet P is conveyed, and there are sheets that are not skewed. Therefore, in the second embodiment, a method of notifying the user of the possibility that the setting state of the paper P is not appropriate only when the difference |ΔTprint-ΔTbase| exceeds the reference value more than a predetermined frequency is provided. Adopted.

That is, the control unit 100, when the difference |ΔTprint−ΔTbase| becomes equal to or larger than the provisional detection threshold value that is a preset reference value, for each of a plurality of sheets of paper, that is, for each sheet of the conveyed paper P, The transport state is temporarily detected as abnormal. Then, when the number of temporary detections is detected at a frequency equal to or higher than a preset number during the conveyance of the plurality of sheets P, it is determined that the conveyance state is abnormal, that is, skewing/concentration occurs.

Specifically, the provisional detection threshold value V is set to 4° C., and it is determined whether or not the difference |ΔTprint−ΔTbase| is 4° C. or more. If the difference |ΔTprint−ΔTbase| .. When the skew/biased state is tentatively detected at a frequency of three times or more during the most recent 10 sheets or less, the determination of the skewed/biased state is determined, and the abnormal transport state, that is, the temporary skew is detected. It is determined that the line/concentration state has been detected, and the user is notified.

In the present embodiment, it is necessary to grasp the conveyance tendency of a plurality of sheets of paper P, and since the risk of deterioration of usability due to detection failure is lower than that of the first embodiment, the provisional detection provisional threshold value as the reference value is set. It is smaller than the detection threshold value of the first embodiment.

As described above, the image forming apparatus 200 of the present embodiment is different from the first embodiment in the arrangement of the thermistors 51a and 51b. The thermistors 51a and 51b are in contact with the surface of the film 41 immediately after the downstream side of the nip portion N in the transport direction of the sheet P. In this configuration, the time until the thermistors 51a and 51b detect the temperature change of the film 41 is shorter than that in the first embodiment, and therefore the acquisition timings of ΔTbase and ΔTprint are different from those of the first embodiment. ..

The data acquisition timing of the first detected temperature difference ΔTbase in the second embodiment is 0.3 sec before the leading edge of the paper P reaches the nip portion N. The data acquisition timing of the second detected temperature difference ΔTprint is 0.3 seconds immediately after the trailing edge of the sheet P passes through the nip portion N.

The data acquisition timing of the first detected temperature difference ΔTbase is a period in which the surface temperature of the film 41 is most stable immediately before the leading edge of the paper P reaches the nip portion N. Further, the data acquisition timing of the second detected temperature difference ΔTprint is set to a timing at which the influence of the paper P passing through the nip portion N on the film 41 can be detected without being disturbed.

Table 1 shows the results of experiments in which the paper P was overloaded on the tray 33 and ten sheets were continuously conveyed.

There is a large skew/deviation that exceeds the judgment reference value on the 2nd, 8th, and 10th sheets, and temporary skew/deviation is shown at a frequency of 3 out of 10 sheets. The line/deviation detection conditions are satisfied. Therefore, the determination of skew/deviation is confirmed, and the user is notified that the setting of the paper P is not appropriate.

Next, the control flow of the control of the second embodiment will be described with reference to the flowchart of FIG. 13, focusing on the differences from the first embodiment.

The image forming apparatus 200 starts to convey the paper P (S1401).

Then, similarly to the first embodiment, the control unit 100 acquires the first detected temperature difference ΔTbase and the second detected temperature difference ΔTprint for each conveyance of each sheet P (S1402, S1403), and the difference |ΔTprint− Calculate ΔTbase|.

A feature of the second embodiment is that the difference |ΔTprint−ΔTbase| obtained in the transportation of the last 10 sheets is held in the RAM 103. Then, with respect to the difference data during 10 paper passages, the number of paper passages having a frequency corresponding to |ΔTprint−ΔTbase|≧4 is counted (S1404).

When the opening (frequency) tentatively detected that skewing/deviation has occurred in the last 10 sheets thus obtained reaches the detection threshold value held in the ROM 102, for example, 3 times (S1405). Then, the abnormality detection is confirmed (S1406), and the user is notified (S1407).

According to this method, although the immediacy is inferior to that of the first embodiment, it is possible to give more accurate information to the user without lowering the detection sensitivity for the conveyance of each sheet P. Become. That is, it is possible to provide the user with an apparatus that is less likely to cause a decrease in usability due to detection failure.

In the present embodiment, the thermistors 51a and 51b are configured to come into contact with the film 41, but if a contact type thermistor is used, the arrangement is limited as described above. If a non-contact type thermopile or the like is used as the temperature detecting means, the cost is increased, but there is no limitation on the position of the temperature detecting means in the non-passage area of the film 41, and the degree of freedom of setting for each device is high. There are merits.

Further, the method of processing the difference data obtained by transporting the plurality of sheets P is not limited to the above. In the present embodiment, the configuration is such that the user is notified when the threshold value is exceeded three or more times during the transportation of the last 10 sheets or less, but since the purpose is to improve the accuracy rather than the determination for each sheet, it is more immediate. In order to obtain the value, it may be performed twice during the transportation of the most recent 5 sheets or less.

In another example, the value of the difference |ΔTprint-ΔTbase| described above is measured and stored over several sheets of paper being conveyed. Then, the standard deviation of the difference |ΔTprint−ΔTbase| may be obtained, and the fact that the setting state of the paper P is not appropriate may be notified from the degree of variation. Further, as another determination condition, the difference |ΔTprint-ΔTbase| may continuously exceed a preset reference value, instead of the frequency in the predetermined number of sheets.

Further, whether or not the total value of the differences |ΔTprint-ΔTbase| measured and stored over the conveyance of a plurality of sheets exceeds a preset reference value may be used as the determination condition.

Also in the present embodiment, as in the first embodiment, the disposition positions of the thermistors 51a and 51b are set slightly toward the center from the end of the paper P that is the target of skew or bias detection, but the end of the paper It may be on the outer side (on the film edge side). Due to skewing or biasing, a difference in heat supply from the film 41 to the sheet at the position where the thermistors 51a and 51b are arranged, or a temperature difference due to the temperature rise in the non-passage portion in the non-passage area of the film occurs. It is possible to detect skew and offset.

[Third Embodiment]
Also in the third embodiment, as in the second embodiment, the difference between the first detected temperature difference and the second detected temperature difference is calculated and held over the continuous conveyance of a plurality of sheets of paper P, and a plurality of sheets of paper P are calculated. 2 is an example of a processing method for determining the transport state from the difference of. The configuration of the device is similar to that of the second embodiment.

In the third embodiment, paying attention to the variation in the conveyance state of the paper, which is a characteristic when the setting of the paper P on the cassette 30 or the tray 33 is not appropriate, and the change in the temperature difference in the non-passage area of the film 41 is changed. The skew is detected by using the average value and the variance of the certain difference. Here, the difference is a value of |ΔTprint−ΔTbase|.

The variance or standard deviation is generally used as a statistic as an index of the data variation. The CPU 101 in the control unit 100 is configured to calculate the variance only in the four arithmetic operations in the present embodiment. This is because it corresponds. The skew detection reference is not limited to the standard deviation or variance as long as it is an index capable of calculating the degree of variation.

When the data follow a normal distribution, it is known that 99.7% of data, that is, almost all values are included in the range of the average value (N)±standard deviation (σ)×3. In this embodiment, as described above, the skew feeding varies due to improper setting of the paper P, and the skew feeding amount shows a normal distribution. Therefore, the difference |ΔTprint−ΔTbase|, which is the amount of change in the detected temperature difference between the thermistors 151a and 151b due to the skew, also has a variation and exhibits a normal distribution.

In the first embodiment, the detection threshold value V as a reference value is set to 5° C., and when the temperature difference in the non-passage area of the film 41 changes by 5° C. or more due to the conveyance of the sheet P, the sheet is skewed or skewed. I showed how to judge that. On the other hand, in the case where the temperature difference does not exceed the threshold value in the conveyance of one sheet of paper P, and the skew and the misalignment are not detected in the first embodiment, as described above, the case where the sheets are not properly set The temperature difference in the non-passage area of the film 41 may vary. In such a case, as shown in the third embodiment, by introducing the standard deviation σ, it is possible to detect the skew and the offset and to predict the set state of the paper P.

Specifically, the range of the difference |ΔTprint-ΔTbase|, which is the data according to the above-described normal distribution, is represented by the average value and standard deviation of the difference data |ΔTprint-ΔTbase| Then, when the maximum value of the data range defined by the average value and the standard deviation exceeds the detection threshold V which is a preset reference value, it is determined that the set state of the paper P is not preferable and the user is notified. can do. Here, the change threshold of the temperature difference in the non-passage area of the film 41 for detecting the skew of the paper P is set to 5° C. as in the first embodiment.

That is, the discriminant is represented by the following equation.
Average value of |ΔTprint−ΔTbase|+3×|standard deviation (σ)≧5 of ΔTprint−ΔTbase| (Equation 3)
However, since the variance σ ² is used instead of the standard deviation σ in the third embodiment as described above, the formula 3 is modified to
Variance (σ ² ) of |ΔTprint-ΔTbase|
≧{(5-|ΔTprint−ΔTbase|average value)/3}^2 (Equation 4)
When, the skew is detected.

Table 2 shows the respective measured values of the difference data |ΔTprint-ΔTbase| when 10 sheets were continuously printed in the case where the skew was not included (A) and the case where the skew was included (B). Here, the data including the skew is the same as that used in the second embodiment.

If there is no problem in setting the paper P,
The average value of the difference data |ΔTprint−ΔTbase| is 0.34, and the variance is 0.54. Since the right side of Expression 4 above is 2.41, it does not meet the skew/bias detection condition.

On the other hand, if there is a problem with the paper setting and skewing or misalignment is included during continuous transport,
The average value of |ΔTprint−ΔTbase| is 2.41 and the variance is 2.49. The right side of Expression 4 becomes 0.75, and as a result, the conditional expression is satisfied, the skew/biasing is detected and the user is notified.

In the third embodiment, the average value and the variance of the difference data |ΔTprint−ΔTbase| are used, but skew detection may be performed using only the variance and the magnitude of the variance. Further, although the case where the variation is ±3σ has been described as an example in the present embodiment, the variation range is not limited thereto, and the variation range can be set according to the purpose.

[Embodiment 4]
In the fourth embodiment, similarly to the second embodiment, the information obtained by the conveyance of the plurality of sheets P is analyzed, and even if the skew or the misalignment cannot be determined by the conveyance of one sheet, the comparison is performed. We will show how to accurately detect skewing and skewing with a relatively small number of conveyed sheets and notify the user.

Conventionally, when the paper P that is offset to the determination standard is transported, it is common to place importance on usability (throughput retention) and continue the transportation without reducing the throughput until a relatively large temperature difference occurs. Met.

However, the film 41 is exposed to a higher temperature than expected by continuing the transportation while the temperature difference in the non-passage area of the film 41 is generated. Further, due to the temperature difference in the non-passage area of the film 41, a biasing force is generated in the film, and the end portion of the film is repeatedly stressed, which may lead to a reduction in fixing life. Therefore, there is an idea that it is better to notify the user that the setting state of the paper P is not preferable at a relatively early stage.

In the one-sided conveyance that occurs when the edge of the paper P is not sufficiently held by the regulation plate, when the one-sided amount is small, the temperature difference in the non-passage area of the film 41 gradually increases, and thus the sheet-by-sheet conveyance is not performed. The state of paper set may not be detected during transportation.

In the fourth embodiment, a method of determining skew or biasing from the tendency of change in the difference (ΔTprint−ΔTbase) will be described.

Unlike the first to third embodiments, the difference between the first detected temperature difference and the second detected temperature difference (ΔTprint−ΔTbase) shows an increasing or decreasing tendency during the conveyance of a plurality of continuous sheets P. In this case, it is determined that there is an abnormality in the sheet conveyance state.

That is, in the one-sided conveyance, it is assumed that the sheet P is set on the cassette 30 or the tray 33 while being shifted to either the left side or the right side in the width direction of the sheet. Therefore, the state where the sign of the difference (ΔTprint−ΔTbase) does not change, that is, the temperature difference in the non-passage area of the film 41 monotonically increases or decreases monotonically is detected, and the one-sided conveyance of the paper P is determined.

In the fourth embodiment, the one-sided conveyance of the sheet is determined by the moving average of the difference (ΔTprint−ΔTbase) between the plurality of sheets P that are continuously conveyed. Specifically, the difference (ΔTprint−ΔTbase) is averaged every time three sheets of paper P are conveyed, and the average value does not change the sign continuously for five times, that is, all five times are positive or all negative. In this case, it is determined that the conveyance is one-sided.

If the sheet P is offset to either the left side or the right side in the width direction of the sheet, the non-passage portion temperature rise is unlikely to occur on the side where the paper sheet approaches, while the non-passage portion temperature increase is large on the side where the paper sheet does not approach. Then, the temperature difference in the non-passage area of the film 41 gradually increases. That is, while the one-sided conveyance continues in this way, the difference data (ΔTprint−ΔTbase) for each conveyance has a substantially positive or negative value.

However, polarity reversal may occur due to factors such as variations in temperature detection. Therefore, in the present fourth embodiment, in order to correctly grasp the increasing tendency of the temperature difference, the statistical average is based on the moving average value of the data. It is configured to make a judgment of one-sided alignment.

Table 3 shows the results when the sheet P is continuously conveyed in a state of being offset by 2 to 3 mm from the conveyance reference position of the sheet P.

In the experiment shown in (A) of Table 3, the value of the difference data (ΔTprint−ΔTbase) tends to show a positive value, but the difference becomes 0 as in the sixth sheet, or negative in another case. In some cases, the value of

However, by measuring the moving average as shown in (B) of Table 3, it is possible to perform highly accurate measurement while suppressing variations in temperature detection. The calculation of the average score and the acquired data is not limited to that of the present embodiment. For example, if the average score is larger, it is easier to understand the tendency. However, since the time required for the one-sided detection becomes longer by increasing the average score, in the present embodiment, the average value of the ΔTprint−ΔTbase values obtained from three sheets of paper is used.

According to the method of the present embodiment, it is possible to determine that the set state of the paper P is not preferable not only for the one-sided conveyance but also for the case where a relatively small skew continues. Further, in addition to the above calculation, by holding a threshold value of the absolute value of the temperature difference in the non-passage area of the film 41 as in Patent Document 1, even if misalignment detection at an early stage cannot be performed, it is as usual. It is possible to detect the misalignment at the timing of. As described above, it is possible to have a configuration in which at least skew and bias are accurately detected by having two determination criteria.

[Fifth Embodiment]
The fifth embodiment is different from the first to fourth embodiments in a method of accurately detecting skew or deviation of the sheet by adjusting the control parameter based on the image information printed on the sheet P. Only explain.

When there is a difference in the toner amount (image density) of the toner image T formed on the paper P in the width direction orthogonal to the conveyance direction of the paper P, when the paper passes through the nip portion N, the width of the paper apparently appears. A difference occurs in the heat capacities in the directions. Therefore, it causes a temperature difference in the non-passage area of the film 41.

In order to solve this problem, a method of acquiring the density information of the image T from the image data, which is a feature of the image forming apparatus 200 according to the present embodiment, and a method of determining whether the sheet is skewed or offset according to the method, will be described below. Will be explained.

The image forming apparatus 200 according to the present embodiment can improve the determination accuracy of skewing/concentration of the sheet P by acquiring the density information from the image data according to the process described below.

First, two experimental results regarding the thermistor 51a and the image position printed on the paper P are shown. The paper P used in all the experiments has a basis weight of 75 g/m ² and is a LETTER size plain paper.

The first experiment investigated the thermistor position and image width. As shown in FIG. 14A, a solid image elongated in the image forming process direction was formed so that the center of the image width direction and the position of the thermistor 51a were overlapped, and one sheet was printed. FIG. 14B shows the relationship between the image width and the amount of decrease in the temperature detected by the thermistor 51a when the same printing is performed for a plurality of image widths.

The detected temperature of the thermistor 51a when the width of the elongated solid image is 0 (no image) is used as the reference temperature. The toner amount of the image in this experiment is 1.00 mg/cm ² .

As can be seen from FIG. 14B, the detected temperature of the thermistor 51a decreases substantially in proportion to the expansion of the image width up to an image width of about 6 mm, and the temperature decreases during the conveyance of one sheet P. The amount was 4.0° C. with an image width of 6 mm. On the other hand, it was found that the image width beyond that is hardly affected by the image width.

Next, the relationship between the image position in the image forming process direction and the amount of decrease in the temperature detected by the thermistor 51a was investigated by the same procedure as in the first experiment. In the experiment, two images shown in FIGS. 15(a)-1 and 15(a)-2 having the same toner amount and different solid image positions were used. The result is shown in FIG.

Also in this second experiment, the toner amount of the image is 1.00 mg/cm ² as in the first experiment. The image width is 6 mm. As shown in FIG. 15B, when the image is in the upstream half area in the image forming process direction, the temperature detected by the thermistor 51a decreases by 1.8° C. during the conveyance of one sheet, and the image is in the image forming process direction. In the downstream half of the above, the decrease amount was 2.2°C, which was about the same amount.

From the above two experiments, the decrease amount of the detected temperature of the thermistors 51a and 51b can be estimated based on the density information within the predetermined range regardless of the position in the image forming process direction. Therefore, by correcting it, the skew detection can be performed. It can be seen that the accuracy can be improved.

Specifically, in the present embodiment, in the vicinity of the thermistors 51a and 51b, specifically, in the range of −103 to −97 mm and +97 to +103 mm from the image forming center in the width direction orthogonal to the transport direction of the paper P. At, the density information is calculated. Here, the density information means an average density, an integrated toner amount, an average toner amount, or the like within two density calculation ranges of −103 to −97 mm and +97 to +103 mm. Then, the temperature detected by the thermistors 501a and 51b is corrected based on the concentration information.

FIG. 16 shows the two density calculation ranges.

As shown in FIG. 16, the two density calculation ranges are referred to as density calculation ranges A and B. Further, in the present embodiment, the average density within the density calculation range is used as the density information. The widths of the density calculation ranges A and B are each 6 mm in the present embodiment, but the width may change depending on the configuration of the device.

Next, a method of acquiring image information according to this embodiment will be described.

When the video controller (image processing means) 106 shown in FIG. 9 receives image data from an external device (not shown) such as a host computer, it sends a print signal to the control unit 100, and at the same time receives the received image data to form an image. To bitmap data for. Then, an image signal for image formation derived from the bit map data is generated, and the control unit 100 causes the laser scanner 6 to scan the photosensitive drums 1a, 1b, 1c, 1d with laser light in accordance with the image signal. ..

Here, the image forming apparatus 200 of the present embodiment acquires the density information of the image to be formed on the paper P from the image data converted into the bitmap data in the video controller 106. More specifically, the density information of each color of C, M, Y, and K is detected in the video controller 106 from the image data converted into CMYK image data.

Hereinafter, the flow from the detection of the concentration information to the correction of the temperature detected by the thermistor will be described with reference to the flowchart shown in FIG.

When detecting the end of the bitmap data conversion in the video controller 106, the video controller 106 starts this control flow from S1801.

In the density information detection of S1802, for example, as shown in FIG. 18, the image printing area to be formed on the paper P is divided into a plurality of areas indicated by broken lines, the density information of the image data is detected for each area, and Repeat for one page of paper without gaps.

In the present embodiment, the density information is detected in the entire area for one page, but the density information may be detected only in the target minimum area. Each of the divided areas has a length y in the conveyance direction of the sheet P and a length x in the width direction orthogonal to the conveyance direction of the sheet. In the present embodiment, x and y are set to 18 dots for 600 dpi pixels. The smaller the size of each area, the more accurate density information can be obtained, but the total calculation time required for density calculation becomes long. Therefore, the values of x and y are appropriately selected according to the capability of the device such as the video controller 106. be able to.

The image information in the video controller 106 is an 8-bit signal, and the density data per toner single color is expressed in the range of the minimum density 00h to the maximum density FFh.

Next, in order to calculate the average density of each of the density calculation ranges A and B described above, the density average value (hereinafter referred to as Ave-d) of each area included in each range is calculated for each color.

When these operations are completed for the entire area of the image (S1803), the average density Ave-d of each color is calculated in each density calculation range of the recording material P in S1804 and added (C(Ave-d)+M(Ave-d)). +Y(Ave-d)+K(Ave-d)), and the total value thereof is the D value. This D value is a 2-byte 8-bit signal. Then, in S1805, the D value is transmitted to the control unit 100.

The processing from S1801 to S1805 up to this point is the control flow in the video controller 106, and the processing from S1806 to S1810 is the control flow in the control unit 100.

In step S1806, the D value transmitted from the video controller 106 is converted from the 8-bit signal into a value (D' value) handled as density information by the control unit 100. Specifically, the minimum density 00h per toner single color is 0%, and the maximum density FFh is 100%. The value of this% correlates with the actual amount of toner on the paper P, and in this embodiment, the amount of toner on the paper is 0.50 mg/cm ² =100%.

The D value is the sum of average density values of a plurality of toner colors. Therefore, the D′ value may exceed 100%, but in the image forming apparatus 200 of the present embodiment, the toner amount on the paper P is 1.00 mg/cm ² for all solid images (corresponding to 200% for the D′ value). ) Is the upper limit.

Subsequently, in step S1807, the temperature of the detection temperature of the thermistors 51a and 51b used for skewing/deviation detection of the sheet P according to the average densities D'(A) and D'(B) of the density calculation ranges A and B. Determine the correction amount. When the average density is 0%, the correction temperature is 0° C., and when the average concentration is 200%, the correction temperature is +4.0° C. to perform temperature correction, and the correction temperature between 0 and 200% is linearly interpolated. This operation is repeated while printing continues, and when it is determined in S1808 that the next page is not printed, the flow ends (S1809).

As described above, in the configurations described in the first to fourth embodiments, if the detected temperatures of the thermistors 51a and 51b corrected by the method described in the present embodiment are used, an image printed on the paper P is formed. Regardless of this, it is possible to detect skewing and offset of the sheet with high accuracy.

In the present embodiment, the case where the detected temperature of the thermistors 51a and 51b is corrected based on the image information has been described as an example, but not the detected temperature of the thermistor, but the detection threshold value for detecting the skewing/deviation of the paper P. The (determination criterion) may be corrected.

In the present embodiment, the temperature change when one sheet of paper P is conveyed has been described as an example, but when the sheets are continuously conveyed, the number of sheets and the warming state of the fixing device 20 may be determined. Accordingly, the correction amount of the detected temperature of the thermistors 15a and 15b may be further adjusted.

As the image information, the correction of the detected temperature of the thermistors 51a and 51b based on the density information has been described, but the information is not limited to the above description as long as the information has a correlation with the density. For example, in the present embodiment, the average density D value (image data) of the image information handled by the video controller 106 is converted into the density information D′ handled by the control unit 100, but the present invention is not limited to this, and the image information D is not changed. It may be used as density information.

Further, the skew/deviation detection of the sheet based on the change in the temperature difference between the detected temperatures of the thermistors 51a and 51b before and after the conveyance of the sheet P has been described above, but the present embodiment can more simply describe the temperature difference of the thermistor. The present invention can also be applied to the detection of skewed or skewed sheets based on the above.

In the image forming apparatus 200, in which the sensitivity variations of the thermistors 51a and 51b and the temperature difference in the width direction due to the deterioration of the durability of the film 41 are small, it is possible to determine the conveyance state of the sheet based on the temperature difference detected by the thermistor. .. That is, in such an apparatus, it is not necessary to detect the temperature difference change in the non-passage area of the film 41 as described in the first to fourth embodiments. However, even in such an apparatus, the detection temperature of the thermistors 15a and 15b is lowered according to the amount of toner on the paper P, so that the detection temperature of the thermistor is corrected based on the image information to achieve higher accuracy. It is possible to judge the skew and the misalignment of the paper.

The image forming apparatus according to the present invention is not limited to the image forming apparatus (full-color printer) described in the first to fifth embodiments, but may be an image forming apparatus including the fixing device 20, such as a fax machine, a monochrome printer, a copying machine, or a multifunction machine. It is widely applicable.

10 image forming part, 20 fixing device, 30 cassette, 33 tray, 41 tubular film, 42 pressure roller, 51a, 51b thermistor, 60 heater, 101 CPU, 106 video controller, N nip part, P paper, ΔTbase 1 detection temperature difference, ΔTprint 2nd detection temperature difference

Claims (19)

Image processing means for generating an image signal for image formation from image data;
An image forming unit that forms a toner image on a recording material by the image signal,
A fixing unit that has a fixing rotator and a pressure rotator that forms a nip portion with the fixing rotator, and that fixes the toner image to the recording material while conveying the recording material at the nip portion;
Equipped with
The fixing unit includes a first temperature detecting member and a second temperature detecting member that detect the temperature of the fixing rotating body that passes through both ends in a direction orthogonal to the recording material conveyance direction,
An image forming apparatus including a determination unit that determines a conveyance state of the recording material according to a first detected temperature difference between the first temperature detection member and the second temperature detection member and a second detected temperature difference. At
The image processing means detects the density information of the toner image from the image data, and adjusts the detected temperatures of the first temperature detection member and the second temperature detection member according to the detected density information. Alternatively, the image forming apparatus is characterized in that the judgment standard of the judging means is adjusted. The image forming apparatus according to claim 1, wherein the determination unit determines the transport state for each of the transported recording materials. The determination means determines that the transport state is abnormal when a difference between the first detected temperature difference and the second detected temperature difference reaches a preset reference value. Item 2. The image forming apparatus according to item 2. The determination means calculates and holds the first detected temperature difference and the second detected temperature difference over the continuous conveyance of the plurality of recording materials, and the first detection in the plurality of recording materials. The image forming apparatus according to claim 1, wherein the conveyance state is determined from difference information obtained by processing a temperature difference and the second detected temperature difference in a predetermined procedure. The discriminating means sets the conveyance state when the difference between the first detected temperature difference and the second detected temperature difference becomes equal to or more than a preset reference value for each of the plurality of recording materials. An abnormality is provisionally detected, and the conveyance state is determined to be abnormal when the provisional detection is detected at a frequency of a preset number of times or more when conveying the plurality of recording materials. Item 4. The image forming apparatus according to item 4. 5. The discriminating means discriminates the carrying state from information indicating a variation in the difference between the first detected temperature difference and the second detected temperature difference in the plurality of recording materials. The image forming apparatus according to item 1. The information indicating the variation is a data range defined by an average value of the differences between the first detected temperature difference and the second detected temperature difference, and a standard deviation, and a maximum value of the data range is predetermined. The image forming apparatus according to claim 6, wherein it is determined that the conveyance state is abnormal when the reference value exceeds the reference value. The image forming apparatus according to claim 7, wherein the standard deviation is replaced with a variance of the standard deviation. When the difference between the first detected temperature difference and the second detected temperature difference shows an increasing or decreasing tendency when the plurality of sheets of the recording material are continuously conveyed, The image forming apparatus according to claim 4, wherein the image forming apparatus determines that the conveyance state of the recording material is abnormal. The determination of the increasing or decreasing tendency of the difference between the first detected temperature difference and the second detected temperature difference is performed by determining the difference between the first detected temperature difference when transporting the plurality of recording materials in succession. The image forming apparatus according to claim 9, wherein the determination is performed by a moving average of a difference from the second detected temperature difference. The image forming apparatus according to claim 3, wherein the reference value varies depending on a basis weight of the recording material that is conveyed. The image forming apparatus according to claim 3, wherein the reference value varies depending on a size of the recording material that is being conveyed. The image forming apparatus according to claim 3, wherein the reference value varies depending on a surface property of the recording material being conveyed. The recording material holding unit holds the recording material, and the determining unit determines that the recording material holding unit may not hold the recording material properly when the recording material is determined to be in an abnormal conveyance state. The image forming apparatus according to claim 1, wherein a notification signal for notifying is output. The image forming apparatus according to claim 1, wherein the fixing unit has a heating body for heating the fixing rotating body. The image forming apparatus according to claim 15, wherein the first temperature detection member and the second temperature detection member detect the temperature of the fixing rotating body. The image forming apparatus according to claim 15, wherein the first temperature detecting member and the second temperature detecting member detect the temperature of the heating body. The fixing rotator is a tubular film, and is brought into pressure contact with the pressure rotator by the heating body that is in sliding contact with the inner surface of the film. The image forming apparatus described. The first temperature detecting member and the second temperature detecting member detect an excessive temperature rise in a non-passage area of the fixing rotating body where the recording material does not pass in the nip portion. The image forming apparatus according to any one of claims 1 to 18.