JP2014044381A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress a recording sheet from floating from a conveyance surface of a belt.SOLUTION: An image forming apparatus comprises: a conveyance belt 73 that holds a sheet S with a photoreceptor drum 53 to transfer a developer image to the sheet S while conveying the sheet S; a fixing unit 80 that nips the sheet S by a heating roller 81 and a pressure roller 82 to fix the developer image on the sheet S, in which the conveyance speed of the sheet S is slower than that of the conveyance belt 73, and a nip position is arranged on the photoreceptor drum side with respect to a conveyance surface 73A of the conveyance belt 73; and a control unit that changes the conveyance speed of the sheet S of at least any one of the conveyance belt 73 and the fixing unit 80. When the sheet S to be conveyed is longer than a predetermined value, the control unit reduces a difference between the conveyance speed of the fixing unit 80 and the conveyance speed of the conveyance belt 73 smaller than in the case where the sheet S is shorter than the predetermined value, at least when the conveyance belt 73 conveys a portion around a rear end of the sheet S.

Description

  The present invention relates to an image forming apparatus including a belt for conveying a recording sheet and a fixing device.

  2. Description of the Related Art Conventionally, an electrophotographic image forming apparatus has a belt for transferring a developer image to a recording sheet while conveying the recording sheet, and fixing the developer image on the recording sheet. A device having a slow fixing device is known (for example, see Patent Document 1).

  In the image forming apparatus disclosed in Patent Document 1, the amount of deflection of the recording sheet generated between the belt and the fixing device is changed by changing the difference between the conveying speed of the belt and the conveying speed of the fixing device according to temperature and humidity. Is adjusted.

JP 2005-338562 A

  However, in the above-described technique, when the recording sheet is long, when the conveyance belt is conveying near the rear end portion of the recording sheet, the slack of the recording sheet increases between the belt and the fixing device, and the rear end of the recording sheet. The part may float from the belt surface.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of suppressing a recording sheet from being lifted from a conveying surface of a belt.

In order to achieve the above object, the image forming apparatus of the present invention includes a belt for transferring a developer image to a recording sheet while conveying the recording sheet by sandwiching the recording sheet with a photosensitive drum, and a heating The recording sheet is nipped by the member and the pressure member to fix the developer image on the recording sheet. The recording sheet conveyance speed is slower than the belt, and the position of the nip is arranged on the photosensitive drum side with respect to the conveyance surface of the belt. The fixing unit, the first driving unit for driving the belt, the second driving unit for driving the fixing unit, the first driving unit and the second driving unit, and controlling at least one recording sheet of the belt and the fixing unit. A control unit that changes the conveyance speed.
In this image forming apparatus, when the recording sheet to be transported is longer than the predetermined value, the control unit is at least when the belt is transporting around the rear end of the recording sheet than when the recording sheet is shorter than the predetermined value. It is configured to reduce the difference between the conveyance speed of the fixing device and the conveyance speed of the belt.

  In a configuration in which the conveyance speed of the fixing device is slower than the conveyance speed of the belt, when the recording sheet is pushed from the belt between the belt and the fixing device and the recording sheet is long, when the vicinity of the rear end is being conveyed Looseness may occur. Therefore, the rear end of the recording sheet is lifted from the conveying surface of the belt, and there is a higher risk of electric discharge between the belt and the recording sheet. However, according to the above configuration, when the recording sheet is long, it is more difficult than when the recording sheet is short. Since the difference between the conveyance speed of the belt and the conveyance speed of the fixing device is reduced, the slack of the recording sheet between the portion where the belt and the photosensitive drum sandwich the recording sheet and the fixing device is suppressed, and the trailing edge of the recording sheet Can be prevented from floating from the conveying surface of the belt.

  The image forming apparatus described above can be configured to be able to form an image on the first type of recording sheet and the second type of recording sheet, which is weaker than the first type of recording sheet. In this case, the control unit can be configured to change the conveyance speed of at least one of the belt and the fixing device when the recording sheet to be conveyed is the first type of recording sheet.

  In the above-described image forming apparatus, the control unit is configured such that when the recording sheet to be conveyed is the first type recording sheet and is longer than a predetermined value, the conveyed recording sheet is the second type recording sheet. The difference between the conveying speed of the fixing device and the conveying speed of the belt is reduced when the belt is conveying at least the vicinity of the rear end of the recording sheet, compared to the case of the sheet, and the conveyed recording sheet is the first sheet. When the recording sheet is of a type and shorter than a predetermined value, the difference between the conveyance speed of the fixing device and the conveyance speed of the belt is made larger than when the recording sheet to be conveyed is the second type of recording sheet. It is desirable.

  When the recording sheet is strong, the present invention is particularly effective because the rear end portion is easily separated from the belt. Also, when the stiffness of the recording sheet is strong and the length (the length in the conveyance direction) is short, the recording sheet is not easily bent between the belt and the fixing device, and the recording sheet is difficult to bend. Easy to leave. Therefore, if the recording sheet is short, the difference between the belt conveyance speed and the fixing device conveyance speed is increased to prevent the recording sheet from being bent and pushed up from the belt conveyance surface. can do.

  In the image forming apparatus described above, the predetermined value can be smaller than 279.4 mm. Further, the predetermined value can be greater than 148 mm and can be greater than 210 mm.

The image forming apparatus described above is on the same side as the photosensitive drum with respect to the conveyance surface, and the discharge tray disposed in the upper part of the apparatus and the recording sheet that has passed through the fixing device are directed upward and then directed horizontally. And a discharge section configured to change direction and carry out to the discharge tray.
In this case, the portion of the recording sheet conveyed through the fixing device that is nipped by the heating member and the pressure member can be inclined by 15 ° or more with respect to the conveyance surface of the recording sheet of the belt.

  As described above, when the portion of the recording sheet conveyed through the fixing device that is nipped by the heating member and the pressure member is inclined by 15 ° or more with respect to the conveying surface of the belt, the conveyance after the fixing device is performed. It is possible to reduce the size of the apparatus by shortening the path. Further, when a strong sheet is conveyed from the belt to the fixing device, it is easy to leave the conveying surface or its extended surface. In such a case, the present invention is particularly effective.

  In the image forming apparatus described above, the control unit can determine the length and stiffness of the conveyed recording sheet based on a signal input by the user. According to such a configuration, control can be executed without providing a separate sensor.

  According to the present invention, when the rear end of the recording sheet is conveyed by the belt, the recording sheet is prevented from slacking between the belt and the fixing device, and the recording sheet is lifted from the conveying surface of the belt. As a result, an undesirable discharge between the belt and the recording sheet can be suppressed, and a good image can be formed.

1 is a cross-sectional view of an image forming apparatus according to an embodiment. It is a block diagram explaining control of the conveyance speed of a conveyance belt and a fixing device by a control part. It is a table | surface which shows the change pattern of the conveyance speed of the fixing device by a control part. It is a flowchart which shows the process by a control part. FIG. 6 is a diagram showing a case where the belt and the fixing device are strong and short (a) when the first half of the paper is being conveyed, and (b) when the second half of the paper is being conveyed. FIG. 4 is a diagram showing a case where the belt and the fixing device are strong and have a long length (a) when the first half of the paper is being conveyed, and (b) when the second half of the paper is being conveyed. This is a comparative example showing a sheet conveyance state when a long sheet is continuously conveyed at the second speed V2. 9 is a table showing a change pattern of a conveyance speed of a fixing device by a control unit in an embodiment according to a modified example. It is a flowchart which shows the process by a control part in embodiment which concerns on a modification.

  Next, an embodiment of the present invention will be described in detail with reference to the drawings as appropriate. In the following description, first, a schematic configuration of the color printer 1 as an example of an image forming apparatus will be described, and then a characteristic part of the present invention will be described in detail.

  In the following description, the direction will be described based on the user when the color printer 1 is used. That is, in FIG. 1, the left side toward the paper surface is “front side (front side)”, the right side toward the paper surface is “rear side (back side)”, the front side toward the paper surface is “right side”, and the paper surface is facing. The far side is the “left side”. In addition, the vertical direction toward the page is defined as the “vertical direction”.

<Schematic configuration of color printer>
As shown in FIG. 1, the color printer 1 includes a paper feed unit 3, an image forming unit 4, and a discharge unit 9 in the apparatus main body 2.

  The paper feed unit 3 is provided in the lower part of the apparatus main body 2 and includes a paper feed tray 31 for storing the paper S and a paper feed mechanism 32. The paper S stored in the paper feed tray 31 is supplied to the image forming unit 4 by the paper feed mechanism 32.

  The image forming unit 4 is configured to form an image on the sheet S conveyed from the sheet feeding unit 3. The image forming unit 4 includes an exposure unit 41, four process cartridges 50, a transfer unit 70, and a fixing device 80. I have.

  The exposure unit 41 is provided in the upper part of the apparatus main body 2 and includes a laser light source (not shown), a polygon mirror shown with reference numerals omitted, a plurality of lenses, and a plurality of reflecting mirrors. Laser light emitted from a laser light source based on image data is reflected by a polygon mirror or a reflecting mirror, passes through a lens, and is scanned at a high speed on the surface of each photosensitive drum 53.

  The process cartridge 50 is arranged side by side between the paper feed tray 31 and the exposure unit 41 and includes a photosensitive drum 53, a charger 54, and a developing cartridge 61.

  The developing cartridge 61 includes a developing roller 63, a supply roller and a layer thickness regulating blade that are not shown in the reference numerals, and has a toner storage chamber 66 that stores toner.

  The transfer unit 70 is provided between the paper feed unit 3 and the four process cartridges 50 and includes a driving roller 71, a driven roller 72, a conveyance belt 73, and a transfer roller 74.

  The driving roller 71 and the driven roller 72 are arranged in parallel with a space in the front-rear direction, and a conveyance belt 73 (belt) composed of an endless belt is stretched therebetween. In addition, four transfer rollers 74 that sandwich the conveyor belt 73 between the photosensitive drums 53 are arranged inside the conveyor belt 73 so as to face the photosensitive drums 53. A transfer bias is applied to the transfer roller 74 by constant current control during transfer.

  The fixing device 80 is provided behind the process cartridge 50, and includes a heating roller 81 and a pressure roller 82 that is disposed to face the heating roller 81 and presses the heating roller 81. A conveyance roller 83 that conveys the sheet S toward the discharge unit 9 is provided on the downstream side of the heating roller 81, and the sheet S that has been conveyed on the conveyance belt 73 is disposed on the upstream side of the heating roller 81. In order to guide between the heating roller 81 and the pressure roller 82, a guide 84 is provided which is inclined so as to be positioned upward as it goes backward.

  In the fixing device 80, the portion where the sheet S is nipped is on the side where the photosensitive drum 53 exists, that is, the upper side with respect to the conveyance surface 73 </ b> A of the conveyance belt 73. A portion of the sheet S conveyed by the fixing device 80 that is nipped by the heating roller 81 and the pressure roller 82 is 30 ° or more with respect to the conveyance surface (upper surface) 73A of the conveyance belt 73 (that is, 15 ° or more) In this embodiment, this angle is about 35 °. When this inclination is large, when the strong paper S is transported from the transport belt 73 to the fixing device 80, it easily floats from the transport surface 73A or its extension surface 73B. This is because the stronger the paper S, the more difficult it is to bend, and it deforms with a small curvature when bent. The present invention is particularly effective when the angle of the portion of the sheet S nipped by the heating roller 81 and the pressure roller 82 with respect to the conveyance surface 73A is large. Further, when this angle is large, the size of the apparatus in the front-rear direction can be reduced by conveying the sheet S that has passed through the fixing device 80 directly upward, so that the apparatus main body 2 can be made compact. Can do.

  In the image forming unit 4, the surface of the photosensitive drum 53 is uniformly charged by the charger 54, and then exposed by the laser light from the exposure unit 41, thereby electrostatically charging the photosensitive drum 53 based on the image data. A latent image is formed. The toner in the toner storage chamber 66 is supplied to the developing roller 63 via the supply roller, enters between the developing roller 63 and the layer thickness regulating blade, and is carried on the developing roller 63 as a thin layer having a constant thickness. Is done.

  The toner carried on the developing roller 63 is supplied to the photosensitive drum 53 on which the electrostatic latent image is formed, whereby the electrostatic latent image is visualized, and the toner image is formed on the photosensitive drum 53. It is formed. Thereafter, the sheet S supplied from the sheet feeding unit 3 is conveyed while being sandwiched between the photosensitive drums 53 and the conveying belt 73 (the transfer roller 74 to which the transfer bias is applied), so that each of the photosensitive drums 53 is placed on the photosensitive drums 53. The toner images carried on the toner image are sequentially superimposed on the paper S and transferred.

  The sheet S on which the toner image is transferred is conveyed between the heating roller 81 and the pressure roller 82, whereby the toner image is thermally fixed and an image is formed on the sheet S.

  The discharge unit 9 is a part that is provided at the rear of the apparatus main body 2 and carries the paper S that has passed through the fixing device 80 to the discharge tray 95. The discharge tray 95 is on the same side as the photosensitive drum 53 with respect to the conveyance surface 73 </ b> A of the conveyance belt 73, and is disposed on the upper portion of the apparatus main body 2. The discharge unit 9 forms a discharge path 97 by a guide 91 that guides the conveyance direction of the paper S. The guide 91 directs the paper S that has passed through the fixing device 80 upward and then horizontally. It is configured to change direction. A plurality of transport rollers 92 are provided on the discharge path 97, and the sheet S that has passed through the fixing device 80 is transported on the discharge path 97 by the transport rollers 92 and discharged to the discharge tray 95.

  The color printer 1 has a control unit 200 as shown in FIG. 2 in order to control the conveyance speed VF of the fixing device 80 according to the paper S. Specifically, the color printer 1 includes a first driving unit 110 for driving the driving roller 71 of the conveying belt 73 and a second driving unit 120 for driving the heating roller 81, and a control unit. 200 controls the speeds of the driving roller 71 and the heating roller 81 by controlling the first driving unit 110 and the second driving unit 120. The first drive unit 110 includes a motor (not shown) and a plurality of gears, and is connected to the drive roller 71 of the transfer unit 70. The second driving unit 120 includes a motor (not shown) and a plurality of gears independent from the first driving unit 110, and is connected to the heating roller 81. The first driving unit 110 and the second driving unit 120 do not have to be completely independent from each other, and some members such as a motor may be shared.

  The control unit 200 includes a CPU, a ROM, a RAM, and the like, and is configured to receive a signal input by a user and control the first driving unit 110 and the second driving unit 120 according to a program prepared in advance. ing.

  Specifically, the control unit 200 is configured to control the first driving unit 110 so that the conveyance speed VT of the conveyance belt 73 is constant when performing printing. Further, when printing, the control unit 200 acquires the size and type of the paper S, and the strength of the paper S estimated from the length of the paper S and the type of the paper S determined from the size of the paper S. Accordingly, the conveying speed VF of the fixing device 80 is changed. In this embodiment, the description will be made on the assumption that the stiffness of the paper S corresponds to the thickness of the paper S. However, when printing on a recording sheet made of a material different from paper, such as an OHP sheet, the recording sheet is used. It is advisable to store the stiffness in association with the strength of the type.

  FIG. 3 is a table summarizing change patterns of the conveyance speed VF of the fixing device 80 by the control unit 200. As shown in FIG. 3, when the type of the sheet S to be conveyed is thick paper as an example of the first type of recording sheet and longer than a predetermined length (see A4 long), as shown in FIG. The conveyance speed VF of the fixing device 80 is set to the first speed V1. Here, the predetermined length is preferably smaller than 279.4 mm which is the length of the letter size, and is preferably larger than 148 mm which is the postcard size and 210 mm which is the A5 size. In the present embodiment, the predetermined length is 250 mm as an example. Then, the control unit 200 sets the transport speed VF of the fixing device 80 to the second speed V2 when the transported paper S is thick paper and shorter than a predetermined length (see postcard). Further, when the sheet S to be conveyed is plain paper as an example of the second type of recording sheet that is weaker than thick paper (see A4), the control unit 200 sets the conveyance speed VF of the fixing device 80 to the first. 3 speed V3. The first speed V1, the second speed V2, and the third speed V3 are set to be slower than the transport speed VT of the transport belt 73. The first speed V1 is set to be faster than the third speed V3, and the second speed V2 is set to be slower than the third speed V3. That is, these speeds have a relationship of V2 <V3 <V1 <VT.

  As an example, the first speed V1 is 171.7 mm / sec, the second speed V2 is 168.7 mm / sec, the third speed V3 is 170 mm / sec, and the conveyance speed VT of the conveyance belt 73 is 172 mm / sec. It is. That is, the first speed V1, the second speed V2, and the third speed V3 may be different within a range of ± 1% (V1, V2 is within ± 1% of V3).

  In order to change the transport speed as described above, the control unit 200 has a storage unit (not shown) and stores the length corresponding to the size of the paper S. For example, as shown in FIG. 3, this length is 297 mm if the size of the paper S is A4, 148 mm if it is a postcard, 445 mm if it is A4 long, and the like. However, these specific lengths do not have to be stored in the storage unit, and information on whether the paper of these sizes is longer or shorter than a predetermined value is stored in correspondence with the size of the paper. May be.

  With this speed setting, when the transported paper S is thick and longer than a predetermined length, the transport speed VT of the transport belt 73 is higher than when the transported paper S is plain paper. The first speed V1 and the third speed V3 are set so that the difference between the conveyance speed VF of the fixing device 80 and the fixing device 80 becomes small.

  When the transported paper S is a thick paper and shorter than a predetermined length, the transport speed VT of the transport belt 73 and the transport of the fixing device 80 are higher than when the transported paper S is a plain paper. The second speed V2 and the third speed V3 are set so that the difference between the speeds VF becomes large.

The operation of the color printer 1 configured as described above will be described.
As shown in FIG. 4, when a print job is input from a user's computer or the like, the control unit 200 acquires information on the size and type of the paper S included in the print job (S101). The information on the size of the paper S is, for example, “A4”, “postcard”, “A4 long” as shown in FIG. 3, and the length of the paper S is acquired from the storage unit according to this size information. To do.

  Then, the control unit 200 determines from the acquired type of the paper S whether or not it is thick paper (S1022), and when it is not thick paper (when it is plain paper) (S102, No), the conveyance speed VF of the fixing device 80. Is the third speed V3 (S103). On the other hand, if the type of the paper S is thick paper (S102, Yes), it is determined whether the length L is longer than 250 mm (S104). If the length L is not long (S104, No), the conveyance speed is determined. The VF is set to the second speed V2 (S105), and if it is long (S104, Yes), the transport speed VF is set to the first speed V1 (S106).

  Although not shown, the control unit 200 transports the paper S by the transport belt 73 at a predetermined transport speed VT and performs a printing process while transporting the paper S in the fixing device 80 at the set transport speed VF. . Then, after the printing of one sheet S, if the job for the next sheet S remains and the printing is not completed (No in S107), the processing from step S101 is performed, and the job for the next sheet S remains. If the printing is not completed (S107, Yes), the process is terminated.

  With reference to FIGS. 5 to 7, a description will be given of the transport state of the paper S between the transport belt 73 and the fixing device 80 when printing processing is performed on various paper S by the processing of the control unit 200 as described above. .

  When printing a postcard that is a thick cardboard having a short length, as shown by the solid line in FIG. 5A, when the front end of the sheet S reaches between the heating roller 81 and the pressure roller 82 of the fixing device 80, Due to the stiffness of the sheet S, the sheet S bends with a small curvature and begins to be conveyed relatively far from the extended surface 73B of the conveying surface 73A of the conveying belt 73. When the paper S is a postcard, the transport speed VF of the fixing device 80 is set to the second speed V2 by the operation of the control unit 200 described above, and therefore the transport speed VT of the transport belt 73 and the transport of the fixing device 80. The difference in the speed VF is large, and the sheet S is pushed by the conveyance belt 73 between the fixing device 80 and the conveyance belt 73 (specifically, the portion sandwiched between the photosensitive drum 53 and the conveyance belt 73). As shown in FIG. 5B, when the transport belt 73 and the photosensitive drum 53 are transporting near the rear end of the paper S, the amount that the paper S is separated from the extension surface 73B is small. As described above, when the paper S is a thick paper having a short length, the paper S is transported by the transport belt 73 by increasing the difference between the transport speed VF of the fixing device 80 and the transport speed VT of the transport belt 73. It is possible to suppress floating from the surface 73A.

  When printing plain paper, as shown by the two-dot chain line in FIG. 5A, the paper S is reached when the front end of the paper S reaches between the heating roller 81 and the pressure roller 82 of the fixing device 80. Is curved with a large curvature, and the separation amount of the conveyance surface 73A from the extended surface 73B becomes small. At this time, the transport speed VF of the fixing device 80 is set to the third speed V3 by the operation of the control unit 200, so that the difference between the transport speed VT of the transport belt 73 and the transport speed VF of the fixing device 80 is moderate. The sheet S is pushed in a small amount by the conveyance belt 73 between the fixing device 80 and the conveyance belt 73, and the conveyance belt 73 conveys the vicinity of the rear end of the sheet S as shown in FIG. When the sheet S is, the amount by which the sheet S is separated from the extended surface 73B is small. As described above, when the sheet S is plain paper, the difference between the conveyance speed VF of the fixing device 80 and the conveyance speed VT of the conveyance belt 73 is set to a medium level, so that the sheet S is conveyed on the conveyance belt 73. It is possible to suppress floating from 73A.

  When printing long thick paper, as shown by the solid line in FIG. 6A, when the front edge of the paper S reaches between the heating roller 81 and the pressure roller 82 of the fixing device 80, the paper S The sheet S bends with a small curvature due to the strength of the stiffness, and begins to be conveyed in a state relatively distant from the extended surface 73B of the conveying surface 73A of the conveying belt 73. This state is almost the same as the case of postcard printing. When the sheet S is a long thick sheet, the transport speed VF of the fixing device 80 is set to the first speed V1 by the operation of the control unit 200 described above. The difference in the conveyance speed VF of the fixing device 80 is small, and the sheet S is slightly pushed by the conveyance belt 73 between the fixing device 80 and the conveyance belt 73, and as shown in FIG. When 73 and the photosensitive drum 53 are transporting near the rear end of the sheet S, the amount that the sheet S is separated from the extension surface 73B is slightly reduced. As described above, when the paper S is a long thick paper, the slackness of the paper S is suppressed by reducing the difference between the transport speed VF of the fixing device 80 and the transport speed VT of the transport belt 73. S can be prevented from floating from the conveyance surface 73 </ b> A of the conveyance belt 73.

  If printing of thick paper with a long length is performed with the transport speed VF of the fixing device 80 set to the second speed V2 as in the case of a postcard, the paper S is transported from the front end to the rear end. During this time, the fixing belt 80 and the conveying belt 73 are continuously pushed by the conveying belt 73. Then, as shown in FIG. 7, the sheet S is loosened between the portion sandwiched between the conveyance belt 73 and the photosensitive drum 53 and the portion nipped by the heating roller 81 and the pressure roller 82 of the fixing device 80, and in the vicinity of the rear end. May float from the conveying surface 73A of the conveying belt 73. However, in the color printer 1 according to the present embodiment, when printing on thick paper having a long length as described above, the conveyance belt 73 is moved to the sheet S by setting the conveyance speed VF of the fixing device 80 to the first speed V1. It is possible to reduce the speed of pushing in as compared with the case of thick paper with a short length, and to reduce the possibility of such slack.

  As described above, according to the color printer 1 of the present embodiment, in the configuration in which the conveyance speed VF of the fixing device 80 is slower than the conveyance speed VT of the conveyance belt 73, when the paper S is long, it is shorter than when it is short. Since the difference between the conveyance speed VT of the conveyance belt 73 and the conveyance speed VF of the fixing device 80 is reduced, the looseness of the paper S between the portion where the conveyance belt 73 and the photosensitive drum 53 sandwich the paper S and the fixing device 80 is suppressed. In addition, the trailing edge of the sheet S can be prevented from floating from the conveyance surface 73 </ b> A of the conveyance belt 73.

  The color printer 1 has a difference between the conveyance speed VT of the conveyance belt 73 and the conveyance speed VF of the fixing device 80 when printing a postcard having a thickness larger than that of plain paper and shorter than that of plain paper. Therefore, it is possible to reduce the possibility that the sheet S is lifted from the conveyance surface 73A of the conveyance belt 73 by pushing a large amount of the sheet S between the fixing device 80 and the conveyance belt 73.

  Further, in the color printer 1, the portion of the paper S conveyed through the fixing device 80 that is nipped by the heating roller 81 and the pressure roller 82 is inclined by 15 ° or more with respect to the conveyance surface 73A. The sheet S after exiting the container 80 can be quickly turned up, and the size of the apparatus main body 2 in the front-rear direction can be reduced to reduce the size.

  Since the color printer 1 determines the length and stiffness of the paper S for the above-described control based on information input by the user, it is not necessary to separately provide a sensor or the like, thereby suppressing an increase in cost. Can do.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. About a concrete structure, it can change suitably in the range which does not deviate from the meaning of this invention.

  For example, in the above-described embodiment, when printing thick paper having a long length, the conveyance speed VF of the fixing device 80 is set to the first speed V1 throughout the conveyance of the paper S. However, at least the conveyance belt 73 and the photosensitive drum 53 are used. However, the difference between the conveying speed VF of the fixing device 80 and the conveying speed VT of the conveying belt 73 when the sheet S is being conveyed near the rear end of the sheet S may be made smaller than that when printing a thick sheet having a short length. The speed change pattern table of FIG. 8 is an example showing this case. When printing on A4 long cardboard, the conveyance belt 73 and the photosensitive drum 53 are transporting the first half of the sheet. The transport speed VF is the second speed V2, and the transport speed VF of the fixing device 80 is the first speed V1 when the transport belt 73 and the photosensitive drum 53 are transporting the second half of the sheet.

  At this time, as shown in FIG. 9, after it is determined in step S104 that the length L of the paper S is greater than 250 mm (S104, Yes), the conveyance speed VF of the fixing device 80 is set to V2 (S111). The first half of the sheet is printed while being transported at the transport speed VF. Then, it continues to determine whether or not a predetermined time corresponding to about half of the total length of the paper S has passed (S112), and before the predetermined time has passed (S112, No), printing is performed without changing the transport speed VF. After the predetermined time has elapsed (S112, Yes), the transport speed VF is changed to the first speed V1 (S106), and the printing process is performed until the end of the sheet S.

  According to such a configuration, during printing of thick paper having a long length, while the first half of the paper is being printed, the paper S is prevented from floating from the conveyance surface 73A, as in the case of thick paper having a short length. During printing of the second half of the sheet, the sheet S can be prevented from loosening between the fixing belt 80 and the portion where the conveyance belt 73 and the photosensitive drum 53 sandwich the sheet S.

  In the above-described embodiment, the conveyance speed of the fixing device is changed according to the type and size of the paper to be conveyed. However, the conveyance speed of the conveyance belt is made constant with the conveyance speed of the fixing device being constant. However, it is possible to change only the conveying speed of the fixing device and the conveying belt.

  In the embodiment, the control unit determines the length and stiffness of the paper S based on the information input by the user. However, the sensor that detects the length of the paper S or the sensor that detects the thickness is used. And the control unit may determine the length and stiffness of the paper S based on the outputs of these sensors. Further, the information input by the user may be information input by an operation button from the operation panel of the apparatus main body instead of a print job.

  In the embodiment described above, for the understanding of the invention, the postcard and the A4 long are assumed to have the same stiffness. The actual paper strength varies slightly depending on the paper, but papers with slightly different stiffness may be treated as the same stiffness in the image forming apparatus.

  In the embodiment, a color printer is shown as an example of the image forming apparatus. However, the image forming apparatus may be a monochrome type, a copier, or a multifunction machine.

DESCRIPTION OF SYMBOLS 1 Color printer 2 Apparatus main body 3 Paper feed part 4 Image formation part 9 Ejection part 41 Exposure unit 50 Process cartridge 53 Photosensitive drum 71 Drive roller 73 Conveyance belt 73A Conveyance surface 74 Transfer roller 80 Fixing device 81 Heating roller 82 Pressure roller 83 Conveyance Roller 91 Guide 92 Conveying roller 95 Discharge tray 110 First drive unit 120 Second drive unit 200 Control unit S Paper

Claims (8)

A belt for transferring the developer image onto the recording sheet while conveying the recording sheet by sandwiching the recording sheet with the photosensitive drum;
The recording sheet is nipped by the heating member and the pressure member to fix the developer image on the recording sheet, the recording sheet conveyance speed is slower than that of the belt, and the position of the nip is relative to the conveyance surface of the belt. A fixing device arranged on the drum side;
A first drive unit for driving the belt;
A second driving unit for driving the fixing unit;
A control unit that controls the first driving unit and the second driving unit, and changes a conveyance speed of at least one recording sheet of the belt and the fixing device,
When the recording sheet to be conveyed is longer than a predetermined value, the control unit is configured so that the fixing unit is at least when the belt is transporting at least the vicinity of the rear end of the recording sheet, as compared with the case where the recording sheet is shorter than the predetermined value. The image forming apparatus is characterized in that the difference between the belt conveyance speed and the belt conveyance speed is reduced. The image forming apparatus is capable of forming an image on a first type of recording sheet and a second type of recording sheet that is weaker than the first type of recording sheet,
The control unit is configured to change the conveyance speed of at least one of the belt and the fixing device when the conveyed recording sheet is the first type of recording sheet. The image forming apparatus according to claim 1. The controller is
When the recording sheet to be conveyed is the first type recording sheet and is longer than the predetermined value, at least the recording sheet than the case where the recording sheet to be conveyed is the second type recording sheet. When the belt is transporting near the rear end of the belt, the difference between the transport speed of the fixing device and the transport speed of the belt is reduced,
When the recording sheet to be conveyed is the first type of recording sheet and shorter than the predetermined value, the fixing device is more than when the recording sheet to be conveyed is the second type of recording sheet. The image forming apparatus according to claim 2, wherein a difference between the conveyance speed of the belt and the conveyance speed of the belt is increased.   The image forming apparatus according to claim 1, wherein the predetermined value is smaller than 279.4 mm.   The image forming apparatus according to claim 1, wherein the predetermined value is larger than 148 mm.   The image forming apparatus according to claim 1, wherein the predetermined value is greater than 210 mm. A discharge tray disposed on the same side as the photosensitive drum with respect to the conveying surface and on the upper part of the apparatus;
A discharge section configured to turn the recording sheet that has passed through the fixing device upward, and then turn the recording sheet to the horizontal direction and carry it out to the discharge tray;
A portion of the recording sheet conveyed through the fixing device that is nipped by the heating member and the pressure member is inclined by 15 ° or more with respect to the recording sheet conveyance surface of the belt. The image forming apparatus according to claim 1.   8. The image formation according to claim 1, wherein the control unit determines the length and stiffness of a conveyed recording sheet based on a signal input by a user. 9. apparatus.

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