JP4750462B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, which forms an image on a recording material using a recording method such as an electrophotographic method, and more particularly, a conductive material made of a metal material or the like as a recording material to be used. The present invention relates to an image forming apparatus provided with foreign matter detection means for preventing in advance a problem that occurs when a sticking foreign matter is attached.

  Conventionally, various image forming apparatuses generally form an image on a sheet-like recording material such as plain paper (transfer paper), postcard, cardboard, sealed letter, OHP plastic thin plate, etc. As typical examples of image forming apparatuses, there are apparatuses such as printers, copiers, and facsimile machines using an electrophotographic system.

  Conventionally, as shown in FIG. 8, the image forming apparatus includes a photosensitive drum 2 as an image carrier that rotates in the direction of an arrow. After the surface of the photosensitive drum 2 is uniformly charged by the charging roller 1, A latent image is formed on the photosensitive drum 2 by exposing the image with an exposure unit 3 such as a laser. Next, this latent image is developed with the toner D of the developing device 4 provided with the developing roller 5a to be visualized as a toner image.

  Further, the toner image on the photosensitive drum 2 is conveyed by the rotation of the photosensitive drum 2 to a transfer nip portion (transfer portion) N formed by the transfer roller 6 and the photosensitive drum 2.

  On the other hand, the recording material 7 such as transfer paper on which an image is recorded is conveyed from the paper supply unit 7a to the transfer nip portion N through the paper supply roller pair 7c and the conveyance roller pairs 7d and 7e. The toner image on the photosensitive drum 2 is transferred to the recording material 7 while the recording material 7 is conveyed by the roller 6.

  Finally, the recording material 7 onto which the toner image has been transferred is conveyed to a fixing device 12 composed of a heating rotator 13 and a pressure rotator 14 that forms a fixing nip H, and is heated and pressurized to be a toner image. Is established.

  As described above, in various image forming apparatuses, a toner image is formed on a recording material, and then the recording material is heated and pressed by a fixing device to melt and fix the toner image. As a fixing method, a contact heating type fixing device having good thermal efficiency and safety is widely known.

  Conventionally, a release layer is mainly formed on the surface of a metal cylindrical core, a heat fixing roller containing a halogen heater inside the cylinder, and an elastic layer made of heat-resistant rubber is formed on the metal core. In recent years, a heat roller fixing device has been used in which a pressure roller formed by forming a pressure-side release layer is pressed and brought into contact therewith. Instead, a fixing film in which a release layer is formed on the surface of a low heat capacity heat-resistant resin film made of a material such as PI (polyimide) is used and heated by contacting a ceramic heater from the inside of the fixing nip portion of the film. A film heating type fixing device has been proposed (see, for example, Patent Documents 1, 2, 3, and 4).

  Further, the film heating type fixing device includes a method of conveying a film between a pressure roller while applying tension using a dedicated conveying roller and a driven roller for conveying the film, and a cylindrical film. There is a method of driving with a conveying force from a pressure roller. The former has an advantage that the film conveying performance can be kept high, and the latter has an advantage that a low-cost fixing device can be realized with a simplified configuration.

  FIG. 9 shows a configuration example of the latter simplified film heating type fixing device.

  The film heating type fixing device 12 includes a heating rotator 13 and a pressure rotator 14, and at least one of the rotators includes a heat-resistant film of 100 μm or less. In the fixing device 12 of this example, the heating rotator 13 includes a fixing film 13a, and the fixing film 13a is rotated by a pressure stay 13f that can be released while being rotatable along a film guide 13e provided inside. The pressure roller 14 is brought into pressure contact with the pressing force.

  The fixing film 13a has a PI base layer 13d, a conductive layer 13c for stabilizing the potential, and a surface release layer 13b, and a ceramic heater 15 is provided inside the film of the fixing nip H. . The pressure roller 14 includes a cored bar 14c, a silicon rubber layer 14b, and a surface release layer 14a.

  Also, in recent years, as a method with higher heating efficiency, a release property is provided on the surface of a film obtained by thinly processing a metal such as SUS into an endless shape instead of a heat-resistant resin having a low heat capacity made of a material such as PI (polyimide). A film heating type fixing device using a fixing film in which a layer is formed has also been proposed.

  In the heating and fixing apparatus as described above, since the recording material is sandwiched in the fixing nip portion and heated while being pressed, if foreign matter enters the recording material, the components of the fixing device depend on the size, hardness and shape of the foreign matter. In particular, the above film heating type fixing apparatus uses a fixing film made of a thin heat-resistant resin or metal material having a thickness of 100 μm or less, so that not only the surface is damaged but also the film itself has a hole. There is a risk that a phenomenon of emptying (hereinafter referred to as “film breakage”) occurs, resulting in a clear fixed image defect and a malfunction of the apparatus itself.

  FIGS. 10 and 11 illustrate an example in which this film breakage occurs when a recording material with staples 16 is fed.

  As shown in FIG. 10, when the recording material 7 with the staple 16 (especially when the end of the needle is exposed on the surface side) enters the fixing nip H, as shown in FIG. The end pierces the surface of the film 13a, is dragged downstream as it is, and after the recording material 7 is discharged, a hole 13g is formed in the film 13a, resulting in partial fixing failure and image disturbance in the subsequent fixed image. At the same time, a crack runs from the hole as it is used, and eventually the film 13a is damaged.

  As described above, foreign matter does not adhere to the recording material in a normal manner. However, in recent years, documents that have been created and circulated have become more and more aware of economic and environmental issues. There is a lot of activity to reuse the unprinted back side without discarding it as it is, and some documents that have been circulated include documents that are closed together with staples and clips. It is. Therefore, when reusing the above documents, if you handle a large amount of documents at once, you may forget to remove some of these staples and clips and print with these metallic foreign objects attached. At that time, the trouble of damaging the film frequently occurs.

  With respect to image forming apparatuses, conventionally, as a countermeasure when foreign matter is mixed in such a recording material, a dedicated metal detection means represented by a magnetic sensor or the like is mainly provided, or a foreign matter is removed by operating a magnet. (See, for example, Patent Documents 5, 6, and 7).

However, the provision of metal detection means or the installation of magnets has complicated the apparatus and increased the cost.
JP-A-63-313182 Japanese Patent Laid-Open No. 2-157878 JP-A-4-44075 JP-A-4-204980 Japanese Utility Model Publication No. 4-58526 JP-A-6-56326 Japanese Patent Laid-Open No. 2000-1241

  The present invention has been made in view of the above-mentioned problems, and the object of the present invention is likely to occur as opportunities for reprinting on the back side of documents after use increase with increasing awareness of environmental problems and cost reductions. To provide an image forming apparatus capable of preventing a metal foreign matter such as a staple needle or a clip remaining on a reused recording material from causing a failure of the image forming apparatus at the time of reprinting with a simple configuration at low cost. It is in.

The above object is achieved by the image forming apparatus according to the present invention. In summary, according to one aspect of the present invention,
A conductive conveying member for nipping and conveying the recording material;
While conveying the recording material to form an image on the recording medium, a voltage is applied to the conveying member, the conveying member through the recording medium than the electric resistance is low foreign matter said recording material based on a change in current in images forming apparatus that have a foreign matter detection means detects Ru to stop subsequent image forming process that attached,
An image forming apparatus is provided in which the conveying member is formed of a conductive material having an electric resistance lower than that of the recording material and higher than that of the foreign matter .

According to another aspect of the present invention, a transfer unit that transfers a developer image formed on an image carrier onto a conveyed recording material, and a fixing unit that fixes the developer image on the recording material. In an image forming apparatus having
When the recording material to which foreign matter having a lower electrical resistance than the recording material is transported is conveyed, the foreign matter adheres from the change in the transfer current flowing in the transfer means when the foreign matter-attached recording material enters the transfer process by the transfer means. A transfer current detection type foreign matter detection means for stopping the apparatus before the foreign matter enters the fixing means, and a notification means for notifying that the foreign matter attached recording material is removed by a signal from the detection means, Have
There is a recording material tip passage timing detection means upstream of the transfer step in the recording material conveyance direction, the detection timing t1 by the recording material tip passage timing detection means, the foreign matter detection timing t2 in the transfer step, and the recording of the recording material Between the material tip passage timing detection means and the passage time T between the fixing means,
t2−t1 ≧ T
If the relationship of
The image forming apparatus is characterized in that the notifying unit designates and notifies the recording material removal direction so as to remove the foreign material adhered recording material upstream of the fixing unit in the recording material conveyance direction .

According to another aspect of the present invention, a transfer unit that transfers a developer image formed on an image carrier onto a conveyed recording material, and a fixing unit that fixes the developer image on the recording material. In an image forming apparatus having
When the recording material to which foreign matter having a lower electrical resistance than the recording material is transported is conveyed, the foreign matter adheres from the change in the transfer current flowing in the transfer means when the foreign matter-attached recording material enters the transfer process by the transfer means. A transfer current detection type foreign matter detection means for stopping the apparatus before the foreign matter enters the fixing means,
An image forming apparatus is provided in which the transfer unit is formed of a material having an electric resistance higher than that of the foreign matter.
According to still another aspect of the present invention, a transfer unit that transfers a developer image formed on an image carrier onto a conveyed recording material, a fixing unit that fixes the developer image on the recording material, In an image forming apparatus having
A conductive conveying means for holding and conveying the pre-type recording medium,
Voltage applying means for applying a predetermined voltage to the conductive conveying means;
When the recording material to which foreign matter having a lower electrical resistance than the recording material is transported is detected, the current flowing through the conductive transport means is detected to detect the foreign matter, and before the foreign matter enters the transfer means. Current detection type foreign matter detection means for stopping the device ;
A notification means for notifying the removal of the foreign substance-attached recording material by a signal from the detection means;
Have
Between the recording material leading edge passage detection timing t0 in the conductive transport means, the foreign matter detection timing t2 in the conductive transport means, and the passage time T1 between the conductive transport means and the transfer means,
t2-t0 <T1
If this relationship holds, stop the device,
t2−t0 ≧ T1
If the above relationship holds, the apparatus is stopped, and the notification means designates the removal direction of the recording material so that the foreign material adhered recording material is moved away from the fixing means toward the upstream side in the recording material conveyance direction. Thus , an image forming apparatus is provided.

  According to the present invention, a stapler having a different electrical resistance from that of the recording material can be provided by providing means for detecting the electrical resistance of the recording material at low cost using the basic components in the image forming apparatus without adding new components. By detecting that conductive foreign matter such as a needle is attached to the recording material, the device is stopped, and if necessary, the user is notified of the abnormality and prompting the removal of this foreign matter in an appropriate manner. Problems that occur in images and devices can be prevented. The present invention makes it possible to prevent a film break phenomenon that causes a fatal failure particularly in a fixing type apparatus using a fixing film.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
FIG. 1 shows a schematic configuration of an embodiment of an image forming apparatus provided with a foreign matter detecting means according to the present invention. FIG. 2 is a cross-sectional view illustrating a transfer process of the image forming apparatus according to the present exemplary embodiment, and FIG. 3 is a flowchart illustrating the operation of the image forming apparatus using the foreign matter detection unit.

  First, referring to FIG. 1, the image forming apparatus of this embodiment is an electrophotographic printer.

  In the printer of this embodiment, the surface of the photosensitive drum 2 as the image carrier is uniformly charged to a predetermined polarity by the charging roller 1 as the charging means, and then the photosensitive drum 2 is moved by the exposure means 3 such as a laser. Only the exposed area is neutralized to form a latent image on the photosensitive drum 2.

  This latent image is developed by the developing device 4 including a developing sleeve 5a as a developer carrying member that carries and conveys the developer (toner) T, and is visualized as a toner image.

  That is, the toner D carried on the developing sleeve 5a is frictionally charged to the same polarity as the charging surface of the photosensitive drum 2 between the developing blade 5b as the developer layer thickness regulating member and the developing sleeve 5a. Next, DC and AC voltages are applied in a superimposed manner at the developing gap portion A where the photosensitive drum 2 and the developing sleeve 5a face each other, and the toner D is floated and oscillated by the action of the electric field, and selectively adheres to the latent image forming portion of the photosensitive drum 2. Then, the toner D is conveyed to the transfer nip N formed by the transfer roller 6 and the photosensitive drum 2 by the rotation of the photosensitive drum 2.

  On the other hand, the recording material 7 such as transfer paper on which an image is recorded is fed from the recording material storage box 7a to the vertical conveying roller pair 7d by a feeding roller pair 7c (the lower roller may be a pad). Thereafter, the sheet is transported to the pre-transfer transport roller 7e by the vertical transport roller pair 7d, or is transported from the manual feed tray 7b to the pre-transfer transport roller 7e by the feed roller pair 7c. Be transported.

  Further, the recording material 7 is transferred by the transfer roller 6 abutting against the photosensitive drum 2 at an entrance angle defined in advance between the upper transfer guide plate 9a and the lower transfer guide plate 9b by the pre-transfer conveying roller 7e. It is conveyed to the nip portion N.

  Until the recording material 7 is conveyed from the pre-transfer conveyance roller 7e to the transfer nip N, it is used for detecting the leading edge passing timing of the recording material 7 necessary for determining the latent image formation start timing on the photosensitive drum 2. A resist sensor 7f including an arm and a photo interrupter is provided.

  Further, on the downstream side, the neutralizing brush 8 is provided in contact with the back side of the recording material 7 being conveyed and is grounded. Since the surface of the recording material 7 may be charged due to the rubbing with various members that have contacted the recording material 7 before the recording material 7 is conveyed to this region, the static elimination brush 8 performs electrostatic recording. It performs the action of removing unnecessary charging that causes the image to be disturbed.

  In order to electrostatically attract the toner D on the photosensitive drum 2 at the transfer portion N and move it to the recording material 7 side, a high voltage having a polarity opposite to that of the toner D is applied to the transfer roller 6 on the back surface of the recording material 7. The toner D is electrostatically attracted to the back surface of the toner 7 and the toner image is transferred to the recording material 7, and the back surface of the recording material 7 is charged with a polarity opposite to that of the toner D and continues to hold the transferred toner D. Therefore, a transfer charge is applied to the back surface of the recording material 7.

  Finally, the recording material 7 onto which the toner image has been transferred is nipped and conveyed by the transfer roller 8 and the photosensitive drum 2, and is composed of a heating rotator 13 and a pressure rotator 14 that forms a fixing nip H. It is conveyed to the device 12. The nip portion H is temperature-controlled by a heater provided on the heating rotator 13 side so as to maintain a preset fixing temperature, and the recording material 7 is heated and pressed by the nip portion H. The toner image is fixed.

  The fixing device 12 of the present embodiment has the same configuration and function as the conventional fixing device 12 described with reference to FIG. Therefore, in this embodiment, the description of the conventional fixing device 12 described above is used, and the description of the configuration and function of the fixing device 12 of this embodiment is omitted here.

  In addition, since the deposits such as toners having different polarities slightly remain on the surface of the photosensitive drum 2 after the toner image transfer, the surface of the photosensitive drum 2 after passing through the transfer nip portion N is provided in the cleaning device 10. Further, the adhering matter is scraped off by the cleaning blade 10a that is in counter contact with the surface of the photosensitive drum 2. After being cleaned, the photosensitive drum 2 stands by in preparation for the next image formation.

  In the present embodiment, each component of the charging roller 1, the photosensitive drum 2, the developing device 4, and the cleaning device 10 is an integrated cartridge 11, which is detachable from the main body of the image forming apparatus.

  In the present invention, an electric resistance detection type detection unit is employed as a detection unit for the conductive foreign matter adhering to the recording material 7, and in this embodiment, in particular, this is a basic component of an electrophotographic image forming apparatus. A transfer current detection type detection means is used that uses a transfer process section composed of the photosensitive drum 2 and the transfer roller 6 to detect the current flowing through the transfer roller 6 with a current detection means. Therefore, it is not necessary to add a new component, and it can be realized at the lowest cost.

  The transfer portion in this embodiment will be described in more detail.

In this embodiment, the transfer roller 6 constituting the transfer unit is a conductive elastic roller having a medium resistance elastic layer whose volume resistance value is adjusted to 1 × 10 ⁶ to 1 × 10 ¹⁰ Ω · cm. The transfer roller 6 is brought into contact with the photosensitive drum 2, and the recording material 7 is nipped and conveyed at the transfer nip portion N which is a press-contact nip portion formed by the photosensitive drum 2 and the transfer roller 6. Then, a transfer voltage is applied to the transfer roller 6 by the high voltage power source 17. As a result, a charge having a polarity opposite to that of the toner image is applied to the recording material 7 to transfer the toner image on the photosensitive drum 2 onto the recording material 7.

  The transfer roller 6 is an elastic layer whose resistance value is appropriately adjusted, for example, by dispersing inorganic conductive particles such as carbon in rubber or sponge or using ion conductive rubber kneaded with a surfactant or the like. It is well known that the resistance value of the transfer roller 6 changes by an order of magnitude or more due to variations in manufacturing, temperature and humidity, and changes in resistance value due to long-term use (durability).

  In order to always allow the optimum current to flow to the transfer roller 6 whose resistance changes in this way, it is conceivable to apply a transfer voltage to the transfer roller 6 by the “constant current application method”. However, in this case, a small size recording material having a width smaller than the maximum sheet passing width of the apparatus is used, and a non-sheet passing region portion where the photosensitive drum 2 and the transfer roller 6 are in direct contact with each other at the transfer nip portion N is formed. When this occurs, there is a problem that current flows intensively here, current supply to the recording material 7 is insufficient, and transfer failure occurs.

  Therefore, in many image forming apparatuses, the “constant voltage application method” is performed in order to allow an appropriate current to flow regardless of the recording material size. In the constant voltage application method, in order to flow an appropriate current for the resistance value of the transfer roller that changes depending on the manufacturing conditions and environment, a constant current value that flows to the transfer roller during paper feeding is passed to the transfer roller before the transfer operation. A voltage control method (ATCV control method: Act Ive Transfer Voltage Control) applied during transfer while holding the voltage generated in the recording medium or a constant current value before passing the paper is passed through the transfer roller, and the generated voltage at that time can be determined in advance. A voltage control method (PTVC control method: Programmable Transfer Voltage Control) that applies the voltage calculated in the control formula at the time of transfer is detected so that the impedance of the transfer system before passing the paper is detected, and a transfer in which an appropriate range of current flows. A voltage is applied.

  Compared to the ATVC method, which is composed of a dedicated circuit and has only a few voltage values that can be applied, the PTVC control method can perform more precise voltage control and does not require a circuit for voltage control. This is an advantageous voltage control method.

  This PTVC control method will be described in more detail. The PWM signal (Pulse Width Modulation signal) is increased step by step with a target of a constant current value while the photosensitive drum surface is charged when paper is not passed before printing. Then, a voltage is applied to the transfer roller, and the voltage value reaching the target current value is held as Vt0. From the Vt0 value and a transfer output table or control expression stored in advance in the CPU of the control circuit, a transfer voltage Vt at the time of printing suitable for the Vt0 value is determined (more precisely, the target current and the Vt0 The transfer roller resistance value is determined from the value, and the transfer voltage Vt at which the most appropriate image quality is obtained when the transfer roller having the resistance value is used is selected from the transfer output table stored in advance in the apparatus or substituted into the control expression. This is a control method in which a PWM signal corresponding to the transfer voltage Vt is output and Vt is applied to the transfer roller during printing.

  Thus, by determining the transfer voltage Vt at the time of printing with reference to the generated voltage Vt0 of each transfer roller with respect to a constant current value, the optimum voltage can be applied at the time of printing according to the resistance value of the transfer roller, A good image can be obtained with a transfer roller having a wide range of resistance values.

  This embodiment is characterized in that the metallic foreign matter on the recording material is detected using the transfer current detecting means used for such transfer control as it is.

That is, in this embodiment, as shown in the transfer nip cross-sectional view of FIG. 2, the photosensitive drum 2 whose surface is charged with a negative potential of about −100 v to −600 v depending on the image pattern, and about +6 kv if necessary. A metallic foreign material 16 such as a clip or a staple is attached to the recording material 7 that has entered the transfer nip formed at the contact portion with the transfer roller 6 to which a high voltage is applied by the transfer voltage application circuit 17 that can be applied up to The electrical resistance range of each component,
The volume resistance value of the metallic foreign material 16 is 10 Ω · cm or less. The volume resistance value of one recording material 7 is 10 ¹¹ to 10 ¹⁴ Ω · cm.
The volume resistance value of the transfer roller 6 is 10 ⁶ to 10 ¹⁰ Ω · cm
Assuming that, in the system having such a magnitude relationship of electrical resistance, the current detection means 18 provided in the transfer voltage application circuit,
The maximum current that flows when the recording material 7 is nipped and conveyed between the transfer roller 6 and the photosensitive drum 2 The maximum current that flows when the recording material 7 with a metallic foreign object is nipped and conveyed between the transfer roller 6 and the photosensitive drum 2 The transfer current in both cases is detected, and the result is compared with a reference threshold provided in advance in the CPU 19, and when a current exceeding the threshold flows, it is determined that there is a foreign substance, and the recording material 7 is conveyed immediately. Stop.

At this time, as a threshold value of a transfer current as a judgment criterion,
The transfer current depends on the amount of charge received per unit time at a rate corresponding to the nip area and the conveyance speed from the transfer roller 6 to which a high voltage is applied by the recording material 7 which is almost an insulator in a normal environment.
The contact area between the metal foreign object 16 such as a normal clip or staple, and the surface of the transfer roller 6 and the photosensitive drum 2 is very narrow and moves at a high speed, so that only an instantaneous current change occurs.
For this reason, the amount of change is not simply calculated from the resistance value of each member, but varies depending on the performance and configuration of the apparatus, and also varies greatly depending on the environment such as temperature / humidity.

  In the present embodiment, as a result of evaluation in a 23 ° C./50% temperature / humidity environment using an apparatus capable of printing 45 sheets per minute at a conveyance speed of 266 mm / sec, there is no adhesion of metallic foreign matter. In contrast to the configuration in which a transfer current of 15 μA flows on average, when the paper is passed with a staple or clip, an increase in the transfer current was observed at 22 μA or more, so that the threshold is 1.5 times the normal transfer current. When the above current is detected, the conveyance of the recording material 7 is stopped, so that the metal foreign matter 16 can be prevented from entering the fixing nip portion H.

  As described above, in this embodiment, the foreign matter detection means has a predetermined voltage applied to the transfer roller 6 and the transfer roller 6 made of a conductive material having a lower electrical resistance than the recording material 7 and a higher electrical resistance than the foreign matter. An electric resistance detection type detection means, in particular, a transfer current detection type foreign matter detection means, constituted by a voltage application means 17 for applying a current, a current detection means 18 for detecting a current flowing through the transfer roller 6, and the like.

FIG. 3 shows a flowchart of the image forming process of the apparatus when the above detection and control are incorporated. The image forming process is processed in the following procedure.
First, as soon as the apparatus is turned on, the resistance of the transfer roller 6 is measured while rotating the photosensitive drum 2 and the transfer roller 6 (S1 to S3).
If it is not within the usable resistance range, it is determined as abnormal, the apparatus is stopped, and image formation is terminated (S5, S6). If it is within the usable range, an optimum transfer voltage suitable for the transfer roller resistance is selected, and the process waits until the timing for actually applying the transfer voltage comes (S7).
Here, the transfer voltage application timing is provided for detecting the leading edge of the recording material on the way from the start of feeding the recording material upon receipt of the print signal until the recording material 7 enters the transfer process section. The recording material leading edge passage timing detecting means, that is, the registration sensor 7f notifies the CPU of the time when the leading edge of the recording material has passed through the sensor setting position, and is determined together with the developing bias voltage application timing. As a voltage application timing, if a high transfer voltage is applied when there is no recording material in the transfer nip, unnecessary charging will occur on the surface of the opposing photosensitive drum, which will obstruct the next image formation. It is necessary to set so that the voltage is applied after entering the part.

However, in this embodiment, it is assumed that the metallic foreign matter 16 adheres to the leading end of the recording material. Therefore, if the transfer voltage position is too far from the leading end of the recording material, a short foreign matter such as a staple is attached to the leading end. If this happens, there is a risk of misdetection. For this reason, in this embodiment, the transfer voltage application timing is adjusted so as to be as close as possible to the front end of the recording material, and is set so that the transfer voltage is applied within 2 mm from the front end of the recording material even if it is shifted to the maximum. Yes. (S8-S11).
-In this way, when an abnormal change in transfer current is detected during transfer (in this embodiment, when a current greater than 1.5 times the normal transfer current value is detected), it is determined that foreign matter is attached. The recording material conveyance is stopped at a timing before the foreign matter enters the fixing nip portion, and the image formation is finished (S12, S13). If it is determined that there is no foreign matter attached, the recording material 7 is passed through the fixing nip, and the image formation is completed (S14).
・ At this time, even if there is the ability to detect the foreign matter in the transfer nip as the reaction speed of the device and instantaneously stop the conveyance of the recording material while the foreign matter is still in the nip, Stopping after the toner has come out can avoid the risk of damaging the surface of the photosensitive drum and the transfer roller by an external force applied during the subsequent jam processing.

  In the above embodiment, the transfer roller 6 as the contact transfer member is a solid (filled meat) or foamed sponge using rubber such as EPDM, silicone, NBR, urethane on a core metal such as iron or SUS. A rubber roller having a medium-resistance elastic layer and having a roller hardness of 25 to 70 degrees (Asker C / total load 9.8 N (1 kg), the same applies hereinafter), the elastic body layer of the transfer roller 6 is 2 after the primary vulcanization. Subsequent vulcanization and then polishing the surface to make the outer diameter shape the desired dimension is used.

  Furthermore, in more detail, the PTVC control method of this embodiment is such that the CPU for controlling the transfer voltage outputs a PWM signal having a pulse width corresponding to the desired transfer output voltage from the OUT terminal. A transfer output table (not shown) corresponding to 1 is stored in the CPU, and this PWM signal is converted to DC by a low pass filter (not shown), amplified by an amplifier (not shown), and transferred to a transfer output voltage. Vt, and a signal corresponding to the current value It flowing at this time is input to the IN terminal of the CPU and detected in the CPU.

  As the current value It, a current value flowing through the transfer high-voltage power supply 17 is detected by a current detection circuit 18, and a value obtained by digital conversion by an A / D converter (not shown) (hereinafter referred to as “transfer AD value”) is sent to the CPU. The input value is used to determine the value of the current flowing through the transfer roller.

  In the above PTVC detection, the output voltage from the high-voltage power supply 17 for transfer is gradually increased, and the voltage value when the transfer current reaches a preset constant current value is held as Vt0. Based on the detection result, the first target value Vt1 of the transfer voltage applied at the time of transfer is determined by the transfer control formula 1 stored in the CPU in advance.

Vt1 = αVt0 + β Equation 1
here,
Vt0: Generated voltages α and β generated when a predetermined detection current is passed through the transfer roller when PTVC is detected. Printing is performed when preparation for image formation is completed after determination of a constant Vt1 preset by the transfer system. The operation is started, and the recording material is fed to the transfer nip portion in synchronization with the toner image on the photosensitive drum.

  In this embodiment, the current detection circuit is used to detect the resistance of the recording material during the transfer process in order to detect the low-resistance metal foreign matter on the recording material. If it is fast and the current change time becomes extremely short, a separate peak hold circuit may be provided, and the output signal of the current detection circuit may be taken into the CPU via the peak hold circuit.

Example 2
Another embodiment of the image forming apparatus provided with the foreign matter detection means according to the present invention will be described. FIG. 4 is a cross-sectional view of the transfer process of the image forming apparatus according to the present embodiment. FIG. 5 uses the electric resistance detection type foreign matter detection means (that is, the transfer current detection type detection means) as in the first embodiment. FIG. 6 is a flowchart for explaining the operation of the image forming apparatus. The image forming apparatus of the present embodiment has the same configuration as that of the image forming apparatus described in the first embodiment, and the description of the first embodiment is used. In this embodiment, members having the same configuration and function as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, as a means for detecting conductive foreign matter adhering to the recording material 7, a transfer process unit including the photosensitive drum 2 and the transfer roller 6 is used as in the first embodiment. There is no need to add it, and it can be realized at the lowest cost.

  The feature of the present embodiment is that the recording material 7 after being stopped according to the attachment position of the foreign matter 16 on the recording material 7 is further different from the first embodiment in which the apparatus is merely stopped when detecting the metallic foreign matter. The function to instruct up to the processing method is added.

  When the recording material 7 is turned over and reset in the image forming apparatus in order to effectively use the back surface of the recording material 7 once printed, the recording material 7 is not always set while clearly recognizing the leading edge and the trailing edge of the recording material 7. In order to print the contents unrelated to the contents recorded on the front side first, it is considered that the mainstream is set with the leading end and the trailing end mixed.

  In this case, as shown in FIG. 4, when the recording material 7 is retransmitted with the metallic foreign material 16 attached to the rear end side with respect to the conveying direction of the recording material 7, the foreign material 16 can be detected and stopped. This is after the formation of most of the image on the recording material. Actually, even if the foreign matter 16 is detected, it stops after exiting the nip, so the apparatus is stopped after all the transfer processes are completed. Will do.

  In this case, although it differs slightly depending on the size of the apparatus and the design of the transfer-fixing distance, most recent apparatuses that do not use a method of transporting the recording material 7 after transfer to the fixing unit by providing another transport means. Then, the first half of the recording material 7 that has already been transferred, at least the tip, has already passed through the fixing nip H.

  When the foreign material 16 is detected at the leading end of the recording material as in the first embodiment, even if the apparatus is stopped, there is no problem if the recording material 7 is removed upstream in the recording material conveyance direction of the apparatus. However, if the leading edge is detected while being detected at the trailing edge as described above and stopped in a state where the leading edge has passed through the fixing nip H, the leading edge of the recording material exposed to the fixing outlet side is indicated unless otherwise specified. It is easy to perform a process of pulling out the part in the paper discharge direction.

  In this case, of course, although the foreign matter 16 is detected and the apparatus is stopped, the foreign matter 16 is caused to pass through the fixing nip H by a manual operation by a human, so that the fixing film is also damaged. In particular, the stress at the time of forcibly pulling out the recording material 7 sandwiched between the fixing portions that are manually stopped in this manner is fed while the film and the roller rotate in the normal fixing process. The damage to the fixing film is larger than the case where it goes on, and the case of film breakage in the actual market is considered to be the mainstream.

In view of this point, in the present embodiment, a system for instructing a recording material processing method in the case where foreign matter adheres to the rear end side according to the flowchart shown in FIG. 5 is added. Go ahead with.
First, as soon as the apparatus is turned on, the resistance of the transfer roller is measured while rotating the photosensitive drum and the transfer roller (S1 to S3).
If it is not within the usable resistance range, it is determined as abnormal, the apparatus is stopped, and image formation is terminated (S5, S6). If it is within the usable range, an optimum transfer voltage suitable for the resistance of the transfer roller is selected and waited (S7).
After starting the feeding of the recording material when receiving the print signal, the registration sensor 7f notifies the CPU of the time when the recording material leading edge has passed through the recording material leading edge detection position, and starts preparation for matching the image formation start timing. At the same time, the passage time t1 is stored in the memory, and at the same time, a timer is activated to start measuring the elapsed time from t1 (S8 to S11).
When the development and transfer steps are advanced (S12, S13), and an abnormal change in the transfer current is detected during the transfer (in this embodiment, a current that is 1.5 times the normal transfer current value or more is detected) In this case, it is determined that foreign matter is attached, and the recording material conveyance is stopped at a timing before the foreign matter portion enters the fixing nip portion, and the time t2 at which the foreign matter is detected is stored in the memory (S14, S15).
The calculation result of t2-t1 or the measurement time of the timer is compared with the recording material front end fixing entry time T calculated in advance from the recording material front end detection position-fixing nip entrance distance and the recording material conveyance speed of the apparatus.
When t2−t1 <T, the apparatus is stopped, and as in the first embodiment, it is determined that foreign matter is attached, and the recording material conveyance is stopped at a timing before the foreign matter portion enters the fixing nip portion. Image formation is terminated (S17).
When t2−t1 ≧ T, the leading edge of the recording material has already entered the fixing nip, and if the leading edge of the recording material is exposed on the recording material discharge side, there is a high risk of being pulled out in the recording material discharge direction. In order to avoid this, after stopping the apparatus, the CPU 19 notifies the user of an error notification and the recording material processing direction of the recording material to the upstream side of the recording material conveyance by the notification means 19a (FIG. 4) provided with a display device or the like. An instruction to pull out is issued, and the image formation ends (S18 to S19).

Normally, the heating rotator 13 and the pressure rotator 14 in the fixing device 12 are pressed against each other by a pressure stay 13f (FIG. 9). Therefore, preferably, the fixing device 12 includes a pressure releasing means (not shown) for releasing the pressure applied by the pressure stay 13f, and when the recording material with foreign matter is detected, the notification means 19a is Then, after the pressure applied by the heating rotator 13 and the pressurizing rotator 14 is released by the pressure release means, the removal of the foreign material recording material is notified.
If it is determined in S14 that there is no foreign matter attached, the recording material 7 is passed through the fixing nip, and the image formation is completed (S20).

  With the above configuration, even if the metallic foreign material 16 is turned over and reprinted while adhering to the rear end portion of the recording material, even if the recording material first half portion has already passed through the fixing nip portion H, an appropriate jam is caused by the apparatus main body. Since the processing method is instructed, it is possible to prevent the film of the fixing unit from being damaged.

  In the above configuration, the timing for turning off the transfer voltage is within 2 mm of the rear end of the recording material on the assumption that metal foreign matter is attached to the rear end of the recording material, as in the case of the recording material front end in Example 1. It is set to cut with

Example 3
Another embodiment of the image forming apparatus provided with the foreign matter detection means according to the present invention will be described. FIG. 6 is a cross-sectional view of the transfer process of the image forming apparatus according to the present embodiment, and FIG. 7 is a flowchart for explaining the operation of the image forming apparatus using the electric resistance detection type foreign matter detection means. The image forming apparatus of the present embodiment has the same configuration as that of the image forming apparatus described in the first embodiment, and the description of the first embodiment is used. In this embodiment, members having the same configuration and function as those of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The feature of the present embodiment is that, as a means for detecting the conductive foreign matter 16 adhering to the recording material 7, a pair of recording material transport rollers 7e and 7e newly positioned upstream in the recording material transport direction in the transfer process is provided with a medium resistance. The recording medium conveying roller voltage applying means 20 and the recording material conveying roller current detecting means 21 are provided.

  In other words, in this embodiment, the foreign matter detection means includes a pair of recording material transport rollers 7e that sandwich and transport the recording material 7 made of a conductive material having a lower electrical resistance than the recording material 7 and a higher electrical resistance than the foreign material. 7e or the like, an electric resistance constituted by a voltage applying means 20 for applying a predetermined voltage to the conductive conveying means, and a current detecting means 21 for detecting a current flowing through the conductive conveying means. Detection type foreign matter detection means, particularly current detection type foreign matter detection means for detecting the current flowing through the recording material transport roller pair.

  In this embodiment, the conveying roller pairs 7e and 7e are collided with the nip portion of the roller pair temporarily stopped before the recording material conveyed before the existing image formation, so that the parallelism of the recording material leading edges is made uniform. By replacing it with a registration roller pair having a function, it can be realized at a low cost, and it can cope with all recording materials of cassette feeding and manual feeding.

  As a feature of the present embodiment, the transfer nip N is further transferred to the transfer nip N in contrast to the first and second embodiments that are configured to prevent the metal foreign matter adhering portion on the recording material from entering the fixing nip H. The foreign matter intrusion prevention function is added.

  When the recording material 7 having a foreign matter 16 such as a clip or a staple is intruded into the transfer nip N, it is nipped and conveyed by the rigid photosensitive drum 2 and the elastic transfer roller 6 and therefore enters the fixing nip H. Although there is no fatal problem such as breakage of the fixing film that makes it impossible to continue use, the possibility of damaging the surface of the photosensitive drum is not zero. It is conceivable that the image remains on the recording material after printing as an image scratch, which is also not preferable.

For this reason, in this embodiment, the metal foreign material 16 can be detected before entering the transfer nip N, and the conveyance of the recording material can be immediately stopped to prevent the foreign material 16 from entering the transfer nip portion N. And Therefore, in the above-described configuration of this embodiment, the volume resistance 10 ⁶ for nipping and transporting the recording material 7 having the volume resistance of 10 ¹¹ to 10 ¹⁴ Ω · cm to which the metallic foreign material 16 having the volume resistance of 10 Ω · cm or less is attached is provided before the transfer process. It is detected based on a difference in electrical resistance between the recording material 7 and the foreign material 16 when the medium resistance roller pair 7e, 7e is composed of 10 to 10 ¹⁰ Ω · cm.

  The specific configuration of this roller pair 7e, 7e is basically the same as that of the transfer roller 6, and the resistance of each roller 7e, 7e is EPDM, silicone, NBR, urethane, etc. on a metal core such as iron or SUS. This is a medium resistance rubber roller with a solid (filled meat) or foamed sponge-like elastic layer made of a rubber of 25 to 70 degrees in hardness (AskerC / total load of 9.8 N (1 kg), the same applies hereinafter) The elastic layer is subjected to secondary vulcanization after primary vulcanization, and then the surface is polished to make the outer diameter shape a desired size. The voltage application power source 20 is actually the transfer high-voltage power source 17. Is diverted.

FIG. 7 shows a flowchart when performing metallic foreign object detection using this embodiment.
First, as soon as the power source of the apparatus is turned on, a predetermined voltage is applied from the high voltage power source 20 while rotating the conductive transport rollers 7e and 7e, and the current is measured by the current detection means 21, thereby measuring the upper and lower transport rollers 7e, The combined resistance of 7e is measured (S1 to S3).
If the resistance range of the transport rollers 7e and 7e is determined in advance based on the same standard as that of the transfer roller 6 and is not within the usable resistance range using a reference table stored in the storage means in the apparatus. It is determined that there is an abnormality, the apparatus is stopped, and image formation is terminated (S4 to S6). If it is within the usable range, the same reference table as that of the transfer roller 6 is used to select the optimum applied voltage suitable for the resistance of the conductive transport roller. Since there is no, there is a standby while applying this voltage.
The feeding of the recording material is started when the print signal is received, and at this time, the high resistance predicted in advance at the moment when the recording material 7 enters the pair of conductive transport rollers 7e and 7e and the leading edge of the recording material passes. The current decrease change occurrence time due to the recording material 7 is stored in the memory as t0, and at the same time, the timer is started to start measuring the elapsed time from t0 (S8 to S11).
Next, in step 14 (S14), when an abnormal change in the current flowing in the high voltage circuit of the conductive roller pair is detected during this conveyance after t0 (in this embodiment, 1.5 times the normal transfer current value) When the above current is detected), it is determined that foreign matter has adhered, and the recording material conveyance is stopped at the timing before the foreign matter portion enters the fixing nip portion H, and the time t2 at which the foreign matter is detected is stored in the memory. (S14, S15). Steps 12 and 13 (S12 and S13) and steps 20 and 21 (S20 and S21) will be described later.
The calculation result of t2-t0 or the measurement time of the timer is compared with the recording material front end transfer entry time T1 calculated in advance from the distance between the conductive roller pair-fixing nip entrance position and the recording material conveyance speed of the apparatus (S16). ).
When t2−t0 <T1, the apparatus is stopped, it is determined that foreign matter is attached, the conveyance of the recording material is stopped at a timing before the foreign matter portion enters the transfer nip portion N, and the image formation is finished ( S17).
When t2−t0 ≧ T1, the leading end of the recording material has already entered the transfer nip portion N, and the apparatus is stopped before the foreign matter enters the transfer nip portion N, and the recording material conveyance is stopped (S18). At this time, the photosensitive drum forming the transfer nip portion is fixed to the main unit separately from the main unit on the assumption that it is to be replaced before the main unit life in the current mainstream devices, or is durable equivalent to the main unit life. In the former case, when the recording material stops and remains in the transfer nip portion, in the former case, the photosensitive drum is removed from the main body. In this case, the drum fixed to the main body releases the contact state of the transfer nip portion and removes the photosensitive drum from the main body opening formed at that time. Since it is configured to be able to be separated from the recording material conveyance path, it is mainstream to remove the recording material upstream from the main body opening formed in this separated state. For this reason, usually, after the apparatus is stopped in such a case, the user is notified that the recording material remains in the transfer nip portion, and at least the photosensitive drum is separated from the transfer drum. It is only necessary to instruct to take out the recording material from the opening, and it is not necessary to specify the removal direction of the recording material. However, in a small device with a relatively short transfer-fixing distance, if a relatively long recording material is used and metal foreign matter adheres to the trailing edge of the recording material, transfer may occur depending on the combination of the device and the recording material. Even if the conveyance of the trailing edge of the recording material is stopped before, the leading edge of the recording material does not necessarily enter the fixing nip portion and is not exposed to the recording material outlet side. In such a case, that is, when the leading end of the recording material passes through the fixing nip and is detected by the paper discharge detection sensor while stopping the trailing end of the recording material before the transfer nip, If the leading end of the recording material is exposed, there is a high risk of being pulled out in the recording material transport direction. To avoid this, the apparatus is stopped (S18), and then the user is notified of the error by the notification means 19a. At the same time, an instruction is given to pull out the recording material processing direction of the recording material to the upstream side of the recording material conveyance (S19).

  Note that steps 12 and 13 (S12 and S13) and steps 20 and 21 (S20 and S21) can be added to the above procedure.

That is, if the metallic foreign material 16 is attached to the pole tip of the recording material 7, it is difficult to detect a slight current decrease with respect to the current flowing through the conductive roller pairs 7e, 7e. When the recording material leading edge passing time t1 is detected by the recording material leading edge passing timing detecting means provided on the downstream side, that is, the registration sensor 7f, the distance between the positions of the conductive roller pair 7e, 7e-registration sensor 7f and the recording of the apparatus. Compare the recording material tip registration sensor entry time T2 calculated in advance from the material conveyance speed (S12, S13),
If t1−t0 <T2, it is considered that the metallic foreign material 16 has adhered to the pole tip of the recording material 7, and the apparatus is immediately stopped (S20). An instruction is given to pull out and remove the recording material from the downstream side of the sensor (S21).
In the case of t1-t0 ≧ T2, the process is performed according to the procedure after step 14 (S14), and the conveyance is continued until the t2 is detected.

  In this embodiment, similarly to the previous embodiment, by using the conductive recording material conveying roller pair 7e, 7e, the apparatus is stopped before the metal foreign matter enters the transfer nip, and the photosensitive drum and the transfer roller are stopped. Can be prevented from being damaged.

1 is a schematic configuration diagram of an embodiment of an image forming apparatus including a foreign matter detection device according to the present invention. FIG. 5 is a diagram illustrating foreign matter intrusion into a transfer nip portion of the image forming apparatus of the present invention. FIG. 6 is a flowchart illustrating an example of the operation of the image forming apparatus of the present invention. FIG. 5 is a diagram illustrating foreign matter intrusion into a transfer nip portion of the image forming apparatus of the present invention. FIG. 10 is a flowchart illustrating another example of the operation of the image forming apparatus of the present invention. It is a schematic block diagram of the other Example of the image forming apparatus provided with the foreign material detection apparatus of this invention. FIG. 10 is a flowchart illustrating another example of the operation of the image forming apparatus of the present invention. It is a figure which shows the structure of the conventional image forming apparatus. FIG. 10 is a diagram illustrating a configuration of a fixing device of a conventional image forming apparatus. FIG. 10 is a diagram illustrating foreign matter intrusion into a fixing device of a conventional image forming apparatus. FIG. 6 is a diagram illustrating damage to a fixing film due to entry of foreign matter into a fixing device of a conventional image forming apparatus.

Explanation of symbols

2 Photosensitive drum (image carrier)
6 Transfer roller 7 Recording material 7e Pre-transfer conveying roller pair (conductive roller pair)
7f Registration sensor (recording material tip passage detection means)
12 Fixing device 16 Stapler needle (conductive foreign matter)
17, 20 High voltage power supply 18, 21 Current detection means 19 CPU
19a Notification means

Claims (15)

A conductive conveying member for nipping and conveying the recording material;
While conveying the recording material to form an image on the recording medium, a voltage is applied to the conveying member, the conveying member through the recording medium than the electric resistance is low foreign matter said recording material based on a change in current in images forming apparatus that have a foreign matter detection means detects Ru to stop subsequent image forming process that attached,
The image forming apparatus , wherein the conveying member is formed of a conductive material having an electric resistance lower than that of the recording material and higher than that of the foreign matter .   The image forming apparatus according to claim 1, further comprising a notification unit configured to notify the removal of the foreign material adhered recording material by a signal from the detection unit. Before Kikoto object detection means,
Voltage applying means for applying a predetermined voltage to the conveying member ;
Current detecting means for detecting a current flowing through the conveying member ;
The image forming apparatus according to claim 1, further comprising: The conveying member, the image forming apparatus according to any one of claims 1-3, wherein the recording material is a conductive Russia over roller pair for nipping and conveying the. The volume resistance value of the recording material is 10 ¹¹ to 10 ¹⁴ Ω · cm, the volume resistance value of the foreign matter is 10 Ω · cm or less, and the volume resistance value of the conveying member is 10 ⁶ to 10 ¹⁰ Ω · cm. The image forming apparatus according to claim 1, wherein the image forming apparatus is cm. A transfer means for transferring the developer image formed on the image carrier onto the conveyed recording material;
6. The image according to claim 1, wherein when detecting that the foreign matter is attached to the recording material, the apparatus is stopped before the foreign matter enters the transfer unit. Forming equipment. Fixing means for fixing a developer image on the recording material;
The image forming apparatus according to claim 6, wherein the fixing unit includes a heating rotator and a pressure rotator, and at least one of the rotators includes a heat-resistant film having a thickness of 100 μm or less. . In an image forming apparatus comprising: a transfer unit that transfers a developer image formed on an image carrier onto a conveyed recording material; and a fixing unit that fixes the developer image on the recording material.
When the recording material to which foreign matter having a lower electrical resistance than the recording material is transported is conveyed, the foreign matter adheres from the change in the transfer current flowing in the transfer means when the foreign matter-attached recording material enters the transfer process by the transfer means. A transfer current detection type foreign matter detection means for stopping the apparatus before the foreign matter enters the fixing means, and a notification means for notifying that the foreign matter attached recording material is removed by a signal from the detection means, Have
There is a recording material tip passage timing detection means upstream of the transfer step in the recording material conveyance direction, the detection timing t1 by the recording material tip passage timing detection means, the foreign matter detection timing t2 in the transfer step, and the recording of the recording material Between the material tip passage timing detection means and the passage time T between the fixing means,
t2−t1 ≧ T
If the relationship of
The image forming apparatus according to claim 1, wherein the notifying unit designates and notifies the recording material removal direction so as to remove the foreign material adhered recording material upstream of the fixing unit in the recording material conveyance direction . In an image forming apparatus comprising: a transfer unit that transfers a developer image formed on an image carrier onto a conveyed recording material; and a fixing unit that fixes the developer image on the recording material.
When the recording material to which foreign matter having a lower electrical resistance than the recording material is transported is conveyed, the foreign matter adheres from the change in the transfer current flowing in the transfer means when the foreign matter-attached recording material enters the transfer process by the transfer means. A transfer current detection type foreign matter detection means for stopping the apparatus before the foreign matter enters the fixing means,
The image forming apparatus, wherein the transfer unit is formed of a material having an electric resistance higher than that of the foreign matter. The image forming apparatus according to claim 9 , further comprising a notification unit configured to notify the removal of the foreign material adhered recording material by a signal from the detection unit. The transfer means, the image forming apparatus according to any one of claims 8-10, which is a conductive roller. Said fixing means comprises a heating rotary member and the pressure rotating body, at least one of said rotary member, of any one of claims 8 to 11, characterized in that it comprises the following heat-resistant film thickness of 100μm The image forming apparatus described in the item. The volume resistance value of the recording material is 10 ¹¹ to 10 ¹⁴ Ω · cm, the volume resistance value of the foreign matter is 10 Ω · cm or less, and the volume resistance value of the transfer means is 10 ⁶ to 10 ¹⁰ Ω · cm. the image forming apparatus according to any one of claims 8 to 13, which is a cm. In an image forming apparatus comprising: a transfer unit that transfers a developer image formed on an image carrier onto a conveyed recording material; and a fixing unit that fixes the developer image on the recording material.
A conductive conveying means for holding and conveying the pre-type recording medium,
Voltage applying means for applying a predetermined voltage to the conductive conveying means;
When the recording material to which foreign matter having a lower electrical resistance than the recording material is transported is detected, the current flowing through the conductive transport means is detected to detect the foreign matter, and before the foreign matter enters the transfer means. Current detection type foreign matter detection means for stopping the device ;
A notification means for notifying the removal of the foreign substance-attached recording material by a signal from the detection means;
Have
Between the recording material leading edge passage detection timing t0 in the conductive transport means, the foreign matter detection timing t2 in the conductive transport means, and the passage time T1 between the conductive transport means and the transfer means,
t2-t0 <T1
If this relationship holds, stop the device,
t2−t0 ≧ T1
If the above relationship holds, the apparatus is stopped, and the notification means designates the removal direction of the recording material so that the foreign material adhered recording material is moved away from the fixing means toward the upstream side in the recording material conveyance direction. The image forming apparatus is characterized in that notification is made . A recording material tip passage timing detection means on the downstream side in the recording material conveyance direction of the conductive conveyance means;
Between the recording material tip passage detection timing t1 in the recording material tip passage timing detection means, and the passage time T2 between the conductive transport means and the recording material tip passage timing detection means,
t1-t0 <T2
The image forming apparatus according to claim 14, wherein the apparatus is stopped when the above relationship is established.

Images