Patent Application
20190155202
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electrophotographic printer.
The electrophotographic printer includes an image forming portion for forming an image on a recording material, a fixing portion (fixing device) for fixing the image, formed on the recording material, on the recording material, and a roller pair (discharging member) for discharging the recording material fed from the fixing portion by nipping and feeding the recording material through a nip.
The image forming portion includes a photosensitive drum for carrying the image and a transfer member for forming a transfer nip, in which the recording material is nipped and fed, in cooperation with the photosensitive drum and for transferring the image from the photosensitive drum onto the recording material. The fixing portion includes a rotatable member such as a cylindrical film or a roller, a rotatable pressing member, such as a roller or a cylindrical film, for forming a nip in which the image-formed recording material is nipped and fed, in contact with the rotatable member, and a heater for heating the image-formed recording material in the nip. The recording material on which an unfixed toner image is carried is heated while being nipped and fed through the nip, whereby the toner image is fixed on the recording material.
When the printer is downsized, a recording material feeding path is shortened, so that the case where a single recording material is nipped simultaneously by the nip of the fixing portion and the nip of the rollers occurs. When the single recording material is nipped simultaneously by the two nips provided at two positions, during feeding of the recording material, there is a tendency that a shifting force for shifting the film in a longitudinal direction perpendicular to a recording material feeding direction increases. Particularly, when recording materials are continuously fed in a state in which the recording materials obliquely move, it leads to an increase in shifting force of the film, so that there is a possibility of an occurrence of a film shift such that the film is shifted in the longitudinal direction perpendicular to the recording material feeding direction. In order to suppress the film shift, a countermeasure such that oblique movement of the recording material is detected and then a film shifting force is relaxed may only be required to be taken.
As a method of detecting the oblique movement of the recording material, Japanese Laid-Open Patent Application (JP-A) Hei 7-112849 proposes a method in which sensors are provided inside both ends of a recording material passing region with respect to a longitudinal direction perpendicular to a recording material feeding direction and oblique movement is discriminated depending on a difference in detection time between leading ends of recording materials with respect to the recording material feeding direction.
When this method is used, although the oblique movement of the recording material can be detected, the film shifting force cannot be relaxed.
A principal object of the present invention is to provide an image forming apparatus capable of relaxing a shifting force of shifting a cylindrical rotatable member of a fixing portion.
According to an aspect of the present invention, there is provided an image forming apparatus for forming an image on a recording material, comprising: an image forming portion configured to form the image on the recording material; a fixing portion including a flexible cylindrical rotatable member and a roller configured to form a fixing nip, in which the recording material on which the image is formed is nipped and fed, in press-contact with the rotatable member and configured to fix the image on the recording material; an oblique movement detecting portion configured to detect oblique movement of the recording material; and a control portion, wherein when the oblique movement detecting portion detects the oblique movement of the recording material, the control portion executes control for increasing a feeding interval of the recording material to the image forming portion.
According to another aspect of the present invention, there is provided an image forming apparatus for forming an image on a recording material, comprising: an image forming portion configured to form the image on the recording material; a fixing portion including a flexible cylindrical rotatable member and a roller configured to form a fixing nip, in which the recording material on which the image is formed is nipped and fed, in press-contact with the rotatable member and configured to fix the image on the recording material; a pressure releasing mechanism configured to release pressure exerted on the fixing nip; an oblique movement detecting portion configured to detect oblique movement of the recording material; and a control portion, wherein when the oblique movement detecting portion detects the oblique movement of the recording material, the control portion controls the pressure releasing mechanism so as to execute an operation for lowering the pressure exerted on the fixing nip.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Parts (a), (b), (c) and (d) of
Parts (a) and (b) of
Parts (a), (b) and (c) of
Parts (a) and (b) of
Embodiments of the present invention will be described with reference to the drawings. Although these embodiments are preferred embodiments of the present invention, the present invention is not limited to the following embodiments, but constitutions thereof can be replaced with other various constitutions within a scope of a concept of the present invention.
With reference to
The image forming apparatus 100 includes an image forming portion 10 for forming an image on a recording material and a fixing portion for fixing the image, formed on the recording material, on the recording material (hereinafter, this fixing portion is referred to as a fixing device).
In the image forming portion 10, around an outer peripheral surface of a photosensitive drum 1 as an image bearing member, along a rotational direction (arrow direction) of the photosensitive drum 1, a charging device 2, an exposure device 3 for irradiating a photosensitive drum surface with laser light, a developing device 4, a transfer member 5 and a cleaner 6 are provided in a named order.
First, the photosensitive drum 1 is rotated in the arrow direction, whereby the photosensitive drum surface is electrically charged uniformly to a predetermined polarity and a predetermined potential. Then, on a charged surface of the photosensitive drum 1, an electrostatic latent image is formed by the laser light. This electrostatic latent image is developed with toner by the developing device 4 and thus is visualized as a toner image.
Recording materials P accommodated in a cassette 101 as an accommodating portion provided in an apparatus main assembly 100A are fed one by one by rotation of a roller 102 as a supplying member. The recording material P is supplied by rotation of a roller pair 103 to a transfer nip Nt formed between the photosensitive drum 1 and the transfer member 5. At the transfer nip Nt, the toner image is transferred from the surface of the photosensitive drum 1 onto the recording material P by the transfer member 5 while nipping and feeding the recording material P. The surface of the photosensitive drum 1 after toner image transfer is cleaned by the cleaner 6.
The recording material P on which an unfixed toner image is carried is sent to a fixing device 20 by which the toner image is fixed on the recording material P. The recording material P coming out of the fixing device 20 is fed to a roller pair 105 which is a discharging member through an oblique movement sensor 104 as an oblique movement detecting portion, and is discharged on a tray 106 by rotation of the roller pair 105.
In the image forming apparatus 100, the roller pair 105 has a discharging nip Ne on a side downstream of a fixing nip Nf of the fixing device 20 with respect to a recording material feeding direction. The oblique movement sensor 104 is provided between the fixing nip Nf and the discharging nip Ne. A distance between the transfer nip Nt and the fixing nip Nf is 40 mm, and a distance between the fixing nip Nf and the discharging nip Ne is 30 mm. A display portion 107 such as a display as a notifying portion is provided in the apparatus main assembly 100A. With respect to the recording material feeding direction, a length between the transfer nip Nt and the fixing nip Nf is shorter than a length of a maximum-size recording material (A4-size recording material in this embodiment) usable in the apparatus 100.
A printer control device 200 managing entire control of the apparatus 100 will be described while making reference to
The printer control device 200 roughly includes a controller portion 201 and an engine controller 202.
The controller portion 201 is mutually communicatable with a host computer 300 and the controller 202. The controller portion 201 receives image information and a print instruction from the host computer 300. The controller portion 201 analyzes the received image in formation and converts the image information into bit data. Then, the controller portion 201 sends a print reservation command, a print start command, and a video signal to the controller 202 via a video interface portion 203 for each of the recording materials P.
Further, the controller portion 201 sends the print reservation command in accordance with the print instruction from the host computer 300 and then sends the print start command to the controller 202 at timing when the image forming apparatus 100 is in a printable state.
When the controller 202 receives the print instruction, the controller 202 outputs a TOP signal providing output reference timing of the video signal to the controller portion 201, and executes a printing operation program. The controller portion 201 executed the printing operation program controls a CPU 204 and an image processing portion 205 which are used as control portion through the video interface portion 203. The CPU 204 starts an image forming operation (hereinafter referred to as a printing operation) necessary to the printing operation by controlling the image processing portion 205, a fixing controller 206, a feeding controller 207 and a supply (feeding) controller 208.
In the printing operation, the image processing portion 205 controls an operation of the image forming portion 10, and the fixing controller 206 controls an operation of the fixing device 20. The feeding controller 207 controls rotation of the roller pairs 103 and 105, and the supply controller 208 controls rotation of the roller 102.
Further, the CPU 204 controls the fixing controller 206, the supply controller 208 and a display controller 209 on the basis of an output signal of the oblique movement sensor 104.
The fixing device 20 will be described with reference to
The fixing device 20 includes a cylindrical film 21 as a flexible cylindrical rotatable member and a pressing roller 22 as a rotatable pressing member for forming the fixing nip Nf between itself and the film 21. The fixing device 20 further includes a ceramic heater 23 as a heating member for heating the recording material P on which a toner image T is fixed in the fixing nip Nf. The fixing device 20 further includes a holder 24 as a supporting member, a stay 25 as a rigid member, and the flanges 26L and 26R as regulating (preventing) members.
The film 21 is 18 mm in outer diameter in a cylindrical state in which the film 21 is not deformed, and has a multi-layer structure with respect to a film thickness direction. The layer structure of the film 21 includes a base layer 21a for maintaining strength of the film 21 and a parting layer 21b for reducing a degree of deposition of a contaminant on the outer peripheral surface of the film 21.
A material of the base layer 21a needs a heat-resistant property since the base layer 21a receives heat of the heater 23 and also needs strength since the base layer 21a slides with the heater 23, and therefore, as the material of the base layer 21a, metal such as stainless steel or nickel or a heat-resistant resin material such as polyimide may preferably be used. In this embodiment, polyimide was used as the material of the base layer 21a, and a carbon (black)-based filler was added into the polyimide for improving thermal conductivity and strength and then the resultant polyimide was used. As regards a thickness of the base layer 21a, a thinner film is easier to conduct the heat of the heater 23 to the surface of the film 21, but the strength of the film lowers, and therefore, the thickness of the base layer 21a may preferably be about 15 μm-100 μm. In this embodiment, the thickness of the base layer 21a was 52 μm.
As a material of the parting layer 21b, a fluorine-containing resin material such as a tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer (PFA), polytetrafluoroethylene (PTFE), a tetrafluoroethylene-hexafluoropropylene copolymer (FEP) may preferably be used. In this embodiment, a PFA coat excellent in parting property and heat-resistant property in fluorine-containing resin materials was formed in a thickness of 10 μm on an outer peripheral surface of the base layer 21a.
With respect to a longitudinal direction Y of the heater 23 which is a direction perpendicular to a recording material feeding direction X, the holder 24 supports the heater 23 by a groove 24a provided on a flat surface on the pressing roller 22 side. Around the holder 24 supporting the heater 23, the film 21 is loosely fitted. On a flat surface of the holder 24 opposite from the detecting roller 22, the stay 25 made of metal (iron) for imparting strength to the holder 24 is provided.
As a material of the holder 24, a material having a low thermal capacity may preferably be used so that the heat of the heater 23 is not readily taken. In this embodiment, as the material of the holder 24, a liquid crystal polymer which is a heat-resistant resin material was used.
The heater 23 includes an elongated thin substrate 23a made of ceramic. On the substrate 23a, a heat generating resistor 23b is provided along a longitudinal direction of the substrate 23a, and thereon, a protective layer 23c for protecting the heat generating resistor 23b is provided. In this embodiment, as the substrate 23a of the heater 23, a plate member made of alumina and having dimensions of 6 mm with respect to the direction X and 1 mm with respect to a recording material thickness direction 8 was used. Onto the surface of the substrate 23a, a 10 μm-thick heat generating resistor 23b made of silver-palladium was applied by screen printing, and the heat generating resistor 23b was coated with a 50 μm-thick gloss layer as the protective layer 23c.
A dimension of the substrate 23a with respect to the direction Y is 260 mm. A corresponding dimension of the heat generating resistor 23b is 218 mm which is longer than an LTR size by 1 mm on each of left and right sides so that the heater 23 can sufficiently heat a recording material passing region of 216 mm of the LTR size which is a maximum size of the recording material P feedable in the apparatus 100 in this embodiment.
As shown in
As regards a clearance between an inner peripheral length of the film 21 and an outer peripheral length of the guiding portions 26Lb and 26Rb, the rotation of the film 21 becomes unstable when the clearance is excessively large, but the film 21 is not readily rotated when the clearance is excessively small. Therefore, there is a need to properly set the clearance by appropriately taking variations or the like in component parts into consideration. In this embodiment, an outer diameter of the guiding portions 26Lb and 26Rb is designed so as to provide the clearance of 1.0 mm.
An outer diameter of the pressing roller 22 is 18 mm. This pressing roller 22 is prepared by providing a 3.5 mm-thick elastic layer (foam rubber) 22b formed with a foam silicone rubber on an outer peripheral surface of a core metal made of iron and having an outer diameter of 11 mm. On another peripheral surface of the elastic layer 22b, as a parting layer, a parting layer 22c made of PFA is provided. The parting layer 22c may also be a layer formed by coating the outer peripheral surface of the elastic layer with a tube or with paint, but in this embodiment, a PFA tube excellent in durability was used.
As regards a surface hardness of the pressing roller 22, a large dimension of the fixing nip Nf with respect to the direction X can be enhanced at a lower (lighter) pressure with a lower surface hardness, but when the surface hardness is excessively low, durability of the pressing roller 22 lowers, and therefore, in this embodiment the surface hardness was 40° as measured in terms of Asker-C hardness (load: 4.9 N).
As shown in
When a motor M (
When electric power is supplied from a power source (not shown) to the heat generating resistor 23b of the heater 23 under control of the fixing controller 206, the heat generating resistor 23b generates heat, so that the heater 23 abruptly increases in temperature. The fixing controller 206 controls an amount of electric power supply (energization) to the heater 23 so that the temperature of the heater 23 is maintained at a predetermined fixing temperature (target temperature), on the basis of a detection temperature outputted from a thermistor 40 (
In
The recording material P carrying an unfixed toner image T is heated in the fixing nip Nf while being nipped and fed through the fixing nip Nf, whereby the toner image is fixed on the recording material P.
A generating mechanism of film shift in the case where the recording material P obliquely moved is fed to the fixing device 20 will be described with reference to
The film 21 is rotated by the pressing roller 22 through the recording material P. The fixing device 20 in this embodiment feeds the recording material P at a speed higher than a recording material feeding speed of the image forming portion 10 by about 1% due to thermal expansion. For that reason, in the case where the recording material P is nipped and fed through the fixing nip Nf and the transfer nip Nt, the recording material P is fed in a state in which a back tension of about several hundred grams is applied to the recording material P by the transfer nip Nt. However, in part (a) of
Part (b) of
The reason why the feeding force F3 becomes small will be specifically described using parts (c) and (d) of
In the case where the recording material P is not obliquely moved, as shown in part (d) of
On the other hand, in the case where the recording material P is obliquely moved, as shown in part (c) of
Further, on the left end side, with advance of the feeding of the recording material P, a non-sheet-passing region where the recording material P does not pass increases, and therefore, overheating is caused in the non-sheet-passing region. For that reason, a region of the pressing roller 22 contacting the film 21 in the non-sheet-passing region is thermally expanded more than that in a normal state, so that the feeding force F1 acting on the film 21 on the left side of the film 21 increases.
The force F1 increases and the force F3 decreases, and therefore, the film 21 is rotated faster on the left end side than on the right end side in the fixing nip Nf, whereby rotation moment shown by an arrow RM of part (b) of
When the film 21 is moved in the left direction L and abuts against the collar portion 26La of the flange 26L, the film 21 receives a reaction force from the flange 26L. When this reaction force is large, there is a liability that the film 21 is deformed so as to be flared out on the left side of the film 21 and a film end portion is broken.
A magnitude of the shifting force of the film 21 is largely caused by the recording material P, and therefore, it is not preferable that obliquely moved recording materials with the same throughput as that of recording material which are not obliquely moved are continuously fed to the transfer nip Nt of the image forming portion 10.
When a feeding (supply) interval of the recording materials P to the transfer nip Nt is increased, the position of the film 21 is somewhat returned toward an original position by the reaction force from the flange 26L (or 26R), so that the shifting force is relaxed. In this embodiment, as regards the recording material P having a small size smaller than the A4 size, in order to relax (alleviate) the overheating in the non-sheet-passing region of the film 21, the throughput is lowered by increasing the feeding interval of the recording materials P to the transfer nip Nt. For that reason, even when the oblique movement occurred, a possibility of breakage of the film end portion due to the shift of the film is smaller in the case of the small-size recording materials P than in the case of the A4-size recording materials.
In this embodiment, as the recording material P which is an object to be detected as to the oblique movement, LTR(-size) sheets and A4(-size) sheets are assumed. As regards the LTR sheets and the A4 sheets, these sheets are recording materials having a highest are frequency, and therefore, basically, there is a need to carry out printing with a maximum throughput. The size of the LTR sheet is 279 mm in dimension with respect to the direction X and 216 mm in dimension with respect to the longitudinal direction perpendicular to the direction X. The size of the A4 sheet is 297 mm in dimension with respect to the direction X and 210 mm in dimension with respect to the direction Y perpendicular to the direction X. When the LTR sheet and the A4 sheet are compared with each other, the dimension of the LTR sheet with respect to the direction Y is substantially equal to a dimension of a recording material feeding path of the apparatus 100 in this embodiment.
For that reason, an error is not readily caused to occur when a user accommodates the LTR sheets in the cassette 101 and sets the LTR sheets by bringing regulating plates (not shown) provided in the cassette 101 for regulating left ends (edges) and right ends (edges) of the LTR sheets (recording materials P) into contact with the left ends and the right ends of the LTR sheets, so that oblique movement of the LTR sheets is not readily caused to occur. If the LTR sheets are obliquely moved, with respect to the direction Y, the left and right ends of the LTR sheet contact side plates (not shown) of the recording material feeding path and are liable to be damaged, and therefore, it can be expected that the user notices the oblique movement and rectifies the setting of the LTR sheets.
On the other hand, in the case of the A4 sheets, the A4 sheets are set in some instances in a state in which the regulating plates of the cassette 101 set in contact with the left and right ends of the LTR sheets are left as they are. In such a case, the regulating plates do not function, and therefore, oblique movement of the A4 sheets is liable to occur. The dimension of the A4 sheets with respect to the direction Y is smaller than the dimension of the LTR sheets by about 6 mm, and therefore, even when the A4 sheets are obliquely moved and fed, left and right ends of the A4 sheets do not readily contact the side plates of the recording material feeding path.
For that reason, the case where the A4 sheets are continuously fed to the transfer nip Nt while the user does not notice the oblique movement is assumed. Therefore, it is desirable that the oblique movement of the A4 sheets of the recording materials P fed with the maximum throughput is made detectable.
An oblique movement sensor 104 for detecting the oblique movement of the recording material nipped and fed by the fixing nip Nf and the discharging nip Ne will be described with reference to
The oblique movement sensor 104 is provided, as shown in part (a) of
These sensors 104L, 104R and 104C are provided at positions spaced from a center of the fixing nip Nf with respect to the recording material feeding direction toward the roller pair 105 side by 20 mm and spaced from a center of the discharging nip Ne with respect to the recording material feeding direction toward the fixing device 20 side by 10 mm. The sensors 104L and 104R are disposed at positions of L1=100.5 mm from a recording material feeding reference line Ts toward left and right ends, respectively, of the recording material P. That is, the sensors 104L and 104R are disposed at positions where the oblique movement of the A4-size recording materials P which are most intended to be detected as to the oblique movement.
As a result, the respective sensors 104L, 104R and 104C are capable of detecting the oblique movement of the recording material P at timing when a leading end side of the recording material P with respect to the recording material feeding direction X is nipped and fed through the discharging nip Ne and a trailing end side of the recording material P with respect to the recording material feeding direction X is nipped and fed through the fixing nip Nf.
Each of the sensors 104L, 104R and 104C includes, as shown in part (a) of
In each of the sensors 104L, 104R and 104C, the lever 104b is swingable about a supporting shaft 104bs. This lever 104b projects to a recording material feeding path Tp at one end portion 104b-1 thereof as indicated by a broken line in part (a) of
Further, when the recording material P fed through the recording material feeding path Tp contacts the one end portion 104b-1 of the lever 104b, the lever 104b is swung about the supporting shaft 104bs by being pushed by the recording material P. As a result, as indicated by a solid line of part (a) of
After the passing of the recording material P through the positions of the levers 104b is ended, the levers 104b are swung and returned to original attitudes, whereby the state of the respective sensors 104L, 104R and 104C is returned to the off state.
Oblique movement detection of the recording material P by the oblique movement sensor 104 will be described with reference to
In the oblique movement sensor 104 of
After the printing operation is started, in the case where the on signals are not inputted from the respective sensors 104L, 104R and 104C in a predetermined time, the CPU 204 discriminates that the recording material P jams in the fixing nip Nf or in the discharging nip Ne. Then, the CPU 204 stops the printing operation by controlling the image processing portion 205, the fixing controller 206, the feeding controller 207 and the supply controller 208.
In the case where the on signals are inputted from the respective sensors 104L, 104R and 104C as shown in part (a) of
In the case where the off signals are inputted from the sensors 104L and 104R and the on signal is inputted from the sensor 104c as shown in part (b) of
Part (c) of
On the basis of input of the on signals from the sensors 104R, 104C and 104L, the CPU 204 discriminates that the recording material is the A4-size recording material P which is obliquely moved, so that the printing operation is performed with the maximum throughput. However, the recording material P is obliquely moved, and therefore, although a time of turned-off of the sensor 104R is close to a time of turned-off of the sensor 104C, the sensor 104L is out of the left end of the recording material P and is turned off during feeding of the recording material P. The CPU 204 compares a time of turning-off of the sensor 104L with the time of turning-off of the sensor 104C and discriminates that the oblique movement occurs when a time difference therebetween (hereinafter referred to as a difference) At exceeds a threshold time S.
In this embodiment, the threshold time S is 600 msec. The recording material feeding speed is 120 mm/sec, so that the CPU 204 discriminates that the oblique movement occurs in the case where the sensor 104L is out of the left end of the recording material P and is turned off at a time earlier than a time when a position of the left end (edge) of the recording material P is 72 mm from the trailing left end of the recording material P with respect to the direction X. That is, in the case where the oblique movement is positioned by the threshold time S, when the recording material P is nipped and fed through the fixing nip Nf and the discharging nip Ne, either one of the sensors 104L and 104R detects absence of the recording material P.
The threshold time S may only be required to be appropriately set depending on an allowable oblique movement amount, but may desirably be set at a value larger than a value obtained by dividing a distance (20 mm) from the fixing nip Nf to the oblique movement sensor 104 by the speed (120 mm/sec) at which the recording material P is nipped and fed. It is preferable that the threshold time S is set at a value larger than 167 msec. In the case where discrimination of the oblique movement detection is made depending on the threshold time S set as described above, the discrimination can be made whether or not the sensor 104L (or 104R) is turned off when the recording material P is nipped and fed through the fixing nip Nf and the discharging nip Ne.
On the recording material leading end side or the recording material trailing end side with respect to the direction X, rigidity of the recording material P is insufficient depending on a kind and a basis weight of the recording material P, and therefore, the recording material P is liable to flap (flutter). When sensor-on timing or sensor-off timing of the sensor 104R or 104L is intended to be discriminated on the recording material leading end side or on the recording material trailing end side, it is difficult to detect the oblique movement of the recording material P with accuracy.
In this embodiment, as described above, the turning-on and the turning-off of the sensors 104R and 104L can be discriminated at timing when the recording material leading end side is nipped and fed through the discharging nip Ne and the recording material trailing end side is nipped and fed through the fixing nip Nf. The recording material P is nipped and fed through the fixing nip Nf and the discharging nip Ne, and therefore, the rigidity of the recording material P against the sensors 104R and 104L increases, whereby it is possible to reduce a variation in detection result due to the flapping of the recording material P on the leading end side or on the trailing end side. That is, oblique movement detection accuracy of the recording material P can be improved.
Further, in this embodiment, the threshold time S is set so that discrimination of the oblique movement is made in the case where the sensor 104L is out of the left end of the recording material P or in the case where the sensor 104R is out of the right end of the recording material P. For that reason, even when recording material trailing end detection timings between the sensors 104L and 104C or between the sensors 104R and 104C somewhat vary, an influence thereof is small, so that an S/N ratio can be made large. Therefore, the oblique movement detection accuracy of the recording material P can be improved.
In this embodiment, with respect to the A4-size recording material P, where the recording material center line Pc (part (d) of
Further, in this embodiment, the sensors 104L, 104R and 104C are provided on the side downstream of the fixing nip Nf with respect to the recording material feeding direction, and therefore, the oblique movement of the recording material P causing the shifting force to act on the film 21 can be detected with accuracy.
In the case where the oblique movement of the recording material P is detected by the sensors 104L, 104R and 104C, a relaxing operation of the shifting force for shifting the film 21 is performed under control of the CPU 204. In the apparatus of this embodiment, as the relaxing operation, at least one of the following relaxing operations (1) to (4) is set.
When the oblique movement of the recording material P is detected, the CPU 204 controls the supply controller 208, so that rotation start timing of the roller 102 is delayed than that during a normal operation and thus the feeding interval of the recording material P is increased. As a result, a time in which the recording material P is nipped fed through the fixing nip Nf can be ensured, and therefore, the shifting force of the film 21 can be relaxed.
A time of the feeding interval with a maximum throughput when the A4-size recording materials P are continuously fed to the transfer nip Nt in this embodiment is 495 msec which is 59.4 mm when the feeding interval is converted into a distance. In this embodiment, when the above-described relaxing operation is performed after the oblique movement of the recording material P is detected, the time of the feeding interval is set at 7 sec, so that the throughput is reduced (throughput down). This throughput down is carried out in a manner such that when the oblique movement of a preceding single recording material is detected, the feeding interval of a single recording material subsequent to the preceding single recording material is increased. This is because all the subsequent recording materials P causes the throughput down due to unexpected occurrence of the oblique movement.
In this embodiment, the shifting force of the film 21, which is 11.8 N as a maximum (value) can be relaxed to about 9.8 N by the above-described throughput down, so that the reaction force received from the flange 26L or 26R can be reduced.
In this embodiment, as regards the recording material P fed subsequently immediately after the preceding recording material P of which oblique movement has been detected, the printing operation has already been started, and therefore, an operation of increasing the time of the feeding interval of the recording material P subsequent to the preceding recording material P is not in time for the printing operation. For that reason, the time of the feeding interval is delayed for a recording material P subsequent to the subsequent recording material P (subsequent to the preceding recording material P).
When the oblique movement is detected, the CPU 204 controls the image processing portion 205, the fixing controller 206, the feeding controller 207 and the supply controller 208, so that the printing operation is stopped. Then, the CPU 204 sends an oblique movement status to the host computer 300 via the video interface portion 203 and the controller portion 201. The host computer 300 receives the oblique movement status and provides notification to a user so as to check setting of the recording materials P in the cassette 101, and thus prompts the user to rectify (correct) the setting of the recording materials P. By rectifying the setting of the recording materials P, the shifting force for shifting the film 21 can be relaxed.
When the oblique movement is detected, the CPU 204 controls the image processing portion 205, the fixing controller 206, the feeding controller 207 and the supply controller 208, so that the printing operation is stopped. Then, the CPU 204 controls the display controller 209 so as to cause the display portion 107 to display an oblique movement status and to display such that setting of the recording materials P in the cassette 101 should be checked, and thus provides notification to the user and prompts the user to rectify the setting of the recording materials P. By rectifying the setting of the recording materials P, the shifting force for shifting the film 21 can be relaxed.
When the oblique movement is detected, the CPU 204 controls the image processing portion 205, the fixing controller 206, the feeding controller 207 and the supply controller 208, so that the printing operation is stopped. Then, the CPU 204 controls the fixing controller 206, so that solenoids which are pressure releasing portions 27L and 27R are turned on or an eccentric cam is rotated by a motor. As a result, the stay 25 of the fixing device 20 moves together with the film 21 toward a side opposite from the pressing roller 22 against pressing forces (pressures) of the pressing springs 32L and 32R, so that a press-contact state between the film 21 and the pressing roller 22 is released. As a result, the shifting force for shifting the film 21 is released and thus can be relaxed.
Another embodiment of the image forming apparatus 100 will be described. An image forming apparatus 100 of this embodiment has the same constitution as the image forming apparatus 100 of Embodiment 1 except that an oblique movement sensor is different from the oblique movement sensor in Embodiment 1. In this embodiment, as an oblique movement sensor 104, a non-contact threshold detecting element with the recording material P is used. Part (a) of
Each of oblique movement sensors 104L, 104C and 104R using the same thermopile as the temperature detecting element is provided, as shown in part (a) of
In general, a temperature of the recording material P nipped and fed through the fixing nip Nf reaches a temperature of 100° C. or more. In this embodiment, on the basis of temperature data acquired from the thermopiles, discrimination that the recording material P is present when the temperature is 70° C. or more and that the recording material P is absent when the temperature is less than 70° C. is made. An oblique movement discriminating condition or a relaxing operation of the shifting force for shifting the film 21 is the same as that in Embodiment 1. Therefore, the image forming apparatus 100 of this embodiment is also capable of achieving the same effect as the effect of the image forming apparatus 100 of Embodiment 1.
In this embodiment, temperature information of the recording material P is acquired by the sensors 104L, 104C and 104R and can be fed back to a fixing temperature controlled on the basis of a detection temperature of the thermistor 40. Specifically, when the temperature of the recording material P is high, excessive supply of heat to the recording material P is prevented by setting the fixing temperature at a low value. Thus, the temperature information of the recording material P is fed back to the fixing temperature, whereby unnecessary electric power consumption can be reduced while obtaining a uniform fixing property.
Further, a difference in degree of overheating of the film 21 in non-sheet-passing regions between on the left side and on the right side is predicted depending on a temperature difference between the sensors 104L and 104R, whereby the time of the feeding interval of the recording material P after the detection of the occurrence of the oblique movement is corrected. Specifically, when the temperature difference between the sensors 104L and 104R is 10° C. or more, 1 sec is added to the time of the feeding interval, so that the corrected time of the feeding interval is 8 sec. Thus, by correcting the time of the feeding interval of the recording material P depending on the temperature difference between the sensors 104L and 104R, a degree of an increase in shifting force for shifting the film 21 in the case where a degree of the overheating of the film 21 in the non-sheet-passing regions is large can be reduced.
The fixing device is not limited to the fixing device of the film heating type. The fixing device may also be a fixing device of a heating roller type in which a cylindrical heating roller incorporating a halogen heater is provided on the printing surface side of the recording material and a pressing film unit for forming a nip by bringing a cylindrical film incorporating a pressing member into press-contact with the heating roller is provided on the non-printing surface side.
While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2017-223308 filed on Nov. 21, 2017, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2017-223308 | Nov 2017 | JP | national |
