JP2006308788A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent toner from being retransferred from paper to a photoreceptor drum and to make the rush-in posture of the paper to the fixing nip part of a fixing unit stable even when the paper is loosened by frictional resistance between the paper and a pre-transfering conveying guide. <P>SOLUTION: In the image forming apparatus 10, the pre-transfering conveying guide 48 for guiding the paper P to the fixing nip part N of the fixing unit 44 is inclined upward, and the paper P comes into contact with the photoreceptor drum 28 near a destaticizing needle 38C by the frictional resistance between the leading edge P1 of the paper P and the pre-fixing conveying guide 48. Therefore, the toner is prevented from being retransferred from the paper P to the photoreceptor drum 28 by decreasing bias voltage applied to the destaticizing needle 38C while the leading edge P1 of the paper P passes through the pre-transfering conveying guide 48. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that transfers a toner image carried on an image carrier to a recording medium, conveys the recording medium onto which the toner image has been transferred to a fixing device, and fixes the toner image on the recording medium.

  In general, in an image forming apparatus using an electrophotographic method, a photosensitive drum and a transfer charger are opposed to each other with a conveyance path of a recording medium interposed therebetween, and toner is transferred from the transfer charger to the back surface of the recording medium. By applying the polar charge, the toner image carried on the photosensitive drum is transferred to the recording medium. Further, on the downstream side of the transfer charger in the conveyance direction, the separation charger is opposed to the photosensitive drum with the conveyance path of the recording medium in between, and the separation charger removes the charge on the recording medium, The recording medium is separated from the photosensitive drum. Then, the recording medium separated from the photosensitive drum is conveyed to the fixing nip portion of the fixing roll by recording medium conveying means such as a conveying belt to fix the toner.

  At this time, if the tension applied to the recording medium becomes too large, a transfer failure occurs. Therefore, in order to relieve the tension applied to the recording medium, the peripheral speed of the fixing roll may be slower than the conveying speed of the recording medium. is there. However, in this case, on the contrary, the recording medium is slackened, the recording medium comes into contact with the photosensitive drum in the vicinity of the separation charger, and the toner from the recording medium which has been de-charged and loses the electrostatic adsorption force to the photosensitive drum. May be retransferred. For this reason, when the leading edge of the recording medium reaches the fixing nip or a position near the front and back of the fixing nip, the recharging current of the separation charger is reduced to prevent retransfer of toner from the recording medium to the photosensitive drum. It is known to do (see, for example, Patent Documents 1 and 2).

  Here, in the image forming apparatuses described in Patent Documents 1 and 2, a recording medium conveying unit is installed between the transfer position of the photosensitive drum and the fixing nip, and the recording medium conveying unit is a photosensitive unit. Since the conveyance force of the recording medium by the body drum is assisted, the recording medium does not become slack due to the frictional resistance between the recording medium and the conveyance guide until the recording medium reaches the fixing nip portion.

  However, as shown in FIG. 9, the recording medium conveying means is not installed for cost reduction, and the fixing nip portion N of the fixing nip portion N is arranged in order to adjust the entry posture of the recording medium P into the fixing nip portion N of the fixing roll 102. In the case where the ascending pre-fixing conveyance guide 104 is provided in front, the frictional resistance between the leading end portion P1 of the recording medium P and the pre-fixing conveyance guide 104 becomes large, the recording medium P becomes slack, and the separation charger 106. The recording medium P comes into contact with the photosensitive drum 108 in the vicinity of. At this time, since the switching of the discharge current of the separation charger 106 is not performed, the toner is retransferred from the recording medium P to the photosensitive drum 108, and a blank portion P2 is generated in the image.

This problem can be prevented by reducing the discharge current of the separation charger 106 before the recording medium P reaches the fixing nip N of the fixing roll 102, but during this time, the discharge current of the separation charger 106 is reduced. If so, the separation between the recording medium P and the photosensitive drum 108 is deteriorated, and the posture of the recording medium P separated from the photosensitive drum 108 becomes unstable. As a result, there is a problem in that the rush posture of the recording medium P into the fixing nip portion N collapses and a problem such as wrinkles occurs.
JP-A-8-30108 JP-A-9-80921

  The present invention has been made in consideration of the above facts, and prevents retransfer of toner from the recording medium to the image carrier even when the recording medium is slack due to frictional resistance between the recording medium and the pre-fixing conveyance guide. It is another object of the present invention to stabilize the rush posture of the recording medium into the fixing device.

  The image forming apparatus according to claim 1, wherein an image carrier that carries a toner image and a recording medium to be conveyed are disposed to face the image carrier, and a toner image is transferred from the image carrier to the recording medium. Transfer means for transferring, separation means for discharging the recording medium downstream from the transfer means and separating the recording medium from the image carrier, and separation and transportation from the image carrier by the separation means An image forming apparatus comprising: a post-transfer conveyance guide that guides a recording medium; and a pre-fixation conveyance guide that guides the recording medium that has passed the post-transfer conveyance guide ascending from the post-transfer conveyance guide to the fixing device. In addition, there is provided a control unit that reduces the electrical output of the separation unit while the leading end portion of the recording medium passes over the pre-fixing conveyance guide.

  In the image forming apparatus according to claim 1, the image carrier that carries the toner image and the recording medium on which the transfer unit is conveyed face each other, and the toner image is separated from the image carrier by the transfer unit. Transferred to a recording medium. Further, on the downstream side in the transport direction from the transfer means, the separating means removes the charge from the recording medium and separates the recording medium from the image carrier.

  Then, the recording medium separated from the image carrier and conveyed by the separating means passes through the post-transfer conveyance guide while being guided, and is guided to the fixing device by the pre-fixation conveyance guide that is inclined upward from the post-transfer guide. The

  Here, while the leading edge of the recording medium passes over the pre-fixing conveyance guide, the electrical output of the separating means is reduced by the control means.

  For this reason, when the recording medium is loosened in the vicinity of the separating means due to the frictional resistance between the leading edge of the recording medium and the pre-fixing conveyance guide and contacts the image carrier, the toner is electrostatically attracted to the recording medium. The toner can be prevented from being retransferred from the recording medium to the image carrier.

  In addition, the electrical output of the separating means is reduced only while the leading edge of the recording medium passes over the pre-fixing conveyance guide, thereby suppressing the deterioration of the separation between the recording medium and the image carrier. And the collapse of the rush posture of the recording medium into the fixing device can be suppressed.

  An image forming apparatus according to a second aspect is the image forming apparatus according to the first aspect, further comprising medium type identifying means for identifying the type of the recording medium, and the control means is controlled by the medium type identifying means. The electrical output of the separating means is controlled according to the type of the identified recording medium.

  3. The image forming apparatus according to claim 2, wherein the type of the recording medium, that is, the thickness or material of the recording medium is identified by the medium type identifying unit, and the control unit is identified by the medium type identifying unit. Accordingly, the electrical output of the separating means is controlled. That is, the strength of the recording medium differs depending on the type of the recording medium, and the timing at which the slack portion of the recording medium contacts the image carrier and the separation between the recording medium and the image carrier differ. By controlling the timing to reduce the output and the magnitude of the electrical output of the separating means according to the type of the recording medium, retransfer of toner from the recording medium to the image carrier is prevented, and fixing of the recording medium is performed. Stabilize the entry posture into the vessel.

  According to a third aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, further comprising temperature / humidity detecting means for detecting temperature and humidity in the main body of the image forming apparatus, wherein the control means is The electrical output of the separating means is controlled in accordance with the temperature and humidity in the image forming apparatus main body detected by the temperature / humidity detecting means.

  In the image forming apparatus according to claim 3, the temperature and humidity in the image forming apparatus main body are detected by the temperature / humidity detection means, and the control means detects the temperature and humidity in the image forming apparatus main body detected by the temperature / humidity detection means. Accordingly, the electrical output of the separating means is controlled. That is, the strength of the recording medium varies depending on the temperature and humidity in the image forming apparatus main body, and the timing at which the slack portion of the recording medium contacts the image carrier and the separation between the recording medium and the image carrier differ. The toner from the recording medium to the image carrier is controlled by controlling the timing of reducing the electrical output of the separating means, the magnitude of the electrical output of the separating means, etc. according to the temperature and humidity in the main body of the image forming apparatus. Re-transfer is prevented, and the rush posture of the recording medium into the fixing device is stabilized.

  The image forming apparatus according to claim 4 is the image forming apparatus according to claim 1, wherein the image forming apparatus includes a resistance detection unit that detects a resistance value of the transfer unit, and the control unit detects the resistance detection. The electrical output of the separating means is controlled in accordance with the resistance value of the transfer means detected by the means.

  In the image forming apparatus according to claim 4, the resistance value of the transfer unit is detected by the resistance detection unit, and the control unit detects the electrical value of the separation unit according to the resistance value of the transfer unit detected by the resistance detection unit. Control the output. Here, the resistance value of the transfer unit changes due to the temperature and humidity in the image forming apparatus main body.

  Therefore, the influence of temperature and humidity in the image forming apparatus main body is controlled by controlling the timing of reducing the electrical output of the separating unit, the magnitude of the electrical output of the separating unit, and the like according to the resistance value of the transfer unit. Regardless of the change in the strength of the recording medium, the retransfer of the toner from the recording medium to the image carrier can be prevented, and the rush posture of the recording medium into the fixing device can be stabilized.

  Since the present invention is configured as described above, even if the recording medium is slack due to the frictional resistance between the recording medium and the pre-fixing conveyance guide, the retransfer of the toner from the recording medium to the image carrier is prevented, and the recording medium The rush posture into the fuser is stabilized.

  Next, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an outline of an image forming apparatus 10 according to an embodiment of the present invention. The image forming apparatus 10 includes an image forming apparatus main body 12, and a two-stage roll loading unit 14 is provided below the image forming apparatus main body 12. Each roll loading unit 14 is rotatably provided with a rotating shaft 16 inserted into a roll core around which the paper P as a recording medium is wound, and a cutter that cuts the paper P unwound from the roll. 18 is provided, and the rotary shaft 16 is rotationally driven so that the paper P is unwound from the roll and fed upward. At that time, the cutter 18 cuts the paper P into a predetermined length.

  Further, a manual feed tray 20 is provided at the center in the height direction of the front side surface (left side in the figure) of the image forming apparatus main body 12. The cut paper P is set on the manual feed tray 20 and is fed into the image forming apparatus main body 12 by a transport mechanism (not shown).

  In addition, a vertical conveyance path 22 is provided above the roll loading unit 14. In the vertical conveyance path 22, a sheet detection sensor 24 and a conveyance roll 26 are provided in order from the upstream side in the conveyance direction.

  An image forming unit 30 is provided on the upper part of the image forming apparatus main body 12. A photosensitive drum 28 is rotatably provided in the image forming unit 30. Around the photosensitive drum 28, a charging roll 32, an exposure head 34, a developing unit 36, a transfer unit 38, a separation claw 40, and a cleaning unit 42 are provided in this order in the rotational direction. The charging roll 32 uniformly charges the photosensitive drum 28, and the exposure head 34 exposes the charging surface of the photosensitive drum 28 to form an electrostatic latent image corresponding to the image data on the photosensitive drum 28. .

  Further, the developing unit 36 includes a cartridge 36A that stores toner of one component or two components, a developing roll 36B that is rotatably supported by the cartridge 36 and faces the photosensitive drum 28, and a stirring unit (not shown). In the developing unit 36, the toner is stirred by the stirring means, a developing bias is applied to the developing roll 36 </ b> B, and the toner is ejected from the developing roll 36 onto the electrostatic latent image on the photosensitive drum 28. As a result, the electrostatic latent image on the photosensitive drum 28 is visualized (developed). In the transfer unit 38, a transfer roll 38 </ b> A that faces the photosensitive drum 28 across the conveyance path of the paper P is rotatably supported by the frame 38 </ b> B and pressed against the photosensitive drum 28. In the transfer unit 38, a transfer bias having a polarity opposite to that of the toner is applied to the transfer roll 38 </ b> A, and the toner on the photosensitive drum 28 is transferred to the paper P. In the transfer unit 38, the static elimination needle 38C is supported by the frame 38B on the downstream side in the transport direction from the transfer roll 38A, and a separation bias is applied to the static elimination needle 38C by the voltage controller 50 (see FIG. 3). The charge on the paper P is removed, and the paper P is separated from the photosensitive drum 28.

  Further, the separation claw 40 is biased toward the photosensitive drum 28, and a pointed tip is brought into contact with the photosensitive drum 28. For this reason, the paper P that has not been separated from the photosensitive drum 28 in the electrical separation step by the static elimination needle 38C is mechanically separated from the photosensitive drum 28 by the separation claw 40.

  The cleaner unit 42 includes a cleaner box 42 </ b> A and a cleaner blade 42 </ b> B supported by the cleaner box 42 </ b> A and having a tip end in contact with the photosensitive drum 28. In the cleaner unit 42, the toner remaining on the photosensitive drum 28 is scraped off by the cleaner blade 42B and collected in the cleaner box 42A.

  Further, a fixing unit 44 is provided on the side of the image forming unit 30 (left side in the drawing) and on the downstream side in the transport direction, and between the fixing unit 44 and the photosensitive drum 28 in order from the upstream side in the transport direction. A post-transfer conveyance guide 46 and a pre-fixation conveyance guide 48 are provided.

  In the fixing unit 44, a heating roll 44A provided on the upper side of the paper P and facing the transfer surface of the paper P, a lower side of the paper P and facing the back surface of the paper P, and pressed against the heating roll 44A. The pressure roll 44B is rotatably supported by the fixing housing 44C, and the paper P is pressurized and heated at the fixing nip N between the heating roll 44A and the pressure roll 44B, so that the toner is fixed to the paper P. .

  Further, the post-transfer conveyance guide 46 extends from the transfer unit 38 to the downstream side in the lateral conveyance direction, and the pre-fixing conveyance guide 48 extends from the post-transfer conveyance guide 46 to the fixing nip portion N in an upward gradient. That is, the post-transfer conveyance guide 46 and the pre-transfer conveyance guide 48 fix the paper P by contacting the back surface of the paper P to which the toner image is transferred and conveyed by the conveyance force between the photosensitive drum 28 and the transfer roll 38A. Guide to nip N.

  A paper discharge tray 49 is provided at the upper part of the front side surface of the image forming apparatus main body 12, and the paper P on which the toner image has been fixed after passing through the fixing unit 44 is discharged to the paper discharge tray 49.

  As shown in FIG. 2, the heating roll 44 </ b> A has a concave flare shape (reverse crown shape) in the center in the axial direction, and the conveyance speed of the paper P at both ends of the fixing nip N is fixed. It is faster than the conveyance speed of the paper P at the center of the nip N. For this reason, in the fixing nip portion N, the paper P is tensioned on both sides in the width direction, and the wrinkles of the paper P due to the difference in the posture of the paper P entering the fixing nip portion N, moisture absorption of the paper P, and the like are generated. Is suppressed.

  Further, the pre-fixing guide 48 has a mountain shape that is curved so that the central portion in the width direction (direction orthogonal to the transport direction) is convex toward the paper P side. For this reason, both end portions in the width direction of the sheet P conveyed to the fixing nip portion N along the pre-fixing guide 48 enter the fixing nip portion N before the center portion in the width direction. The tension on both sides in the width direction is increased, and the generation of wrinkles of the paper P is further suppressed.

  Here, a method of controlling the electrical output of the static elimination needle 38C by the voltage control unit 50 will be described.

  As shown in the timing charts of FIGS. 3 and 4, a bias voltage H is applied to the static elimination needle 38 </ b> C after a predetermined time T <b> 0 elapses after the paper P is detected by the paper detection sensor 24 installed at the point O of the transport path 22. Is done. Here, the predetermined time T0 is a time required until the leading end P1 of the paper P passes through the point O and immediately before reaching the point A above the static elimination needle 38C. The bias voltage H is sufficiently high to separate the paper P from the photosensitive drum 28 and transport it along the post-transfer transport guide 46.

  The bias voltage H is lowered to the bias voltage L after a predetermined time T2 has elapsed since the bias voltage H was applied to the charge eliminating needle 38C. Here, the predetermined time T2 is slightly less than the time T1 from when the leading end portion P1 of the paper P reaches the point B which is the boundary between the post-transfer conveyance guide 46 and the pre-fixing conveyance guide 48 after passing the point A. It is time to exceed. The bias L is a value sufficient to electrostatically attract the toner to the paper P.

  Therefore, after a predetermined time T3 has elapsed since the bias voltage H was applied to the charge eliminating needle 38C, the leading end P1 of the paper P reaches the point C on the pre-fixing conveyance guide 48 (downstream in the conveyance direction from the point B), When the paper P comes into contact with the photosensitive drum 28 in the vicinity of the static elimination needle 38C due to the frictional resistance between the leading end portion P1 of the paper P and the pre-fixing conveyance guide 48, the contact portion of the paper P with the photosensitive drum 28 (in the drawing) The state in which the toner is electrostatically adsorbed on the chain line) can be maintained, and the toner can be prevented from being retransferred from the paper P to the photosensitive drum 28.

  Further, by reducing the bias voltage of the static elimination needle 38C while the leading end portion P1 of the paper P passes over the pre-fixing conveyance guide 48, the separation property between the paper P and the photosensitive drum 28 is improved. Deterioration can be suppressed, and collapse of the entry posture of the paper P into the fixing nip N can be suppressed.

  In this embodiment, as a method of changing the electrical output of the static elimination needle 38C, a method of changing the voltage value applied to the static elimination needle 38C is used. However, the method is not limited to this method, and the current value and the resistance value are changed. Various methods can be applied.

  Next, a second embodiment of the method for controlling the electrical output of the static elimination needle 38C by the voltage control unit 60 will be described.

  As shown in the timing charts of FIGS. 5 and 6, the temperature and humidity in the image forming apparatus main body 12 (see FIG. 1) are detected by the temperature / humidity sensor 52, and the voltage control unit 60 is detected by the temperature / humidity sensor 52. In accordance with the detected temperature and humidity, the magnitude of the bias voltage applied to the static elimination needle 38C and the timing for changing the bias voltage applied to the static elimination needle 38C are controlled.

  For example, if the temperature and humidity detected by the temperature / humidity sensor 52 are normal temperature and normal humidity, the bias voltage H is applied to the static elimination needle 38C after a predetermined time T0 has elapsed since the paper P was detected by the paper detection sensor 24. The The bias voltage H is lowered to the bias voltage L after a predetermined time T2 has elapsed since the bias voltage H was applied to the charge eliminating needle 38C.

  On the other hand, if the temperature and humidity detected by the temperature / humidity sensor 52 are high and high, the bias voltage Hl (<H is applied to the static elimination needle 38C after a predetermined time T0 elapses after the paper P is detected by the paper detection sensor 24. , Indicated by a one-dot chain line). Then, after a predetermined time T2s (<T2) has elapsed since the bias voltage Hl was applied to the charge eliminating needle 38C, the bias voltage Hl is lowered to the bias voltage Ll (<L). Here, since the paper P has good separability from the photosensitive drum 28 in a high temperature and high humidity environment, the bias voltage applied to the static elimination needle 38C is lower than that in a normal temperature and normal humidity environment. Further, the sheet P having a large moisture absorption amount and weak is easily loosened due to the frictional resistance with the conveyance guide 48 before fixing, and contacts the photosensitive drum 28 when the leading end P1 reaches the point C1 upstream from the point C. To do. For this reason, in the high temperature and high humidity environment, the timing for lowering the bias voltage applied to the static elimination needle 38C is made faster than in the normal temperature and normal humidity environment.

  Further, if the temperature and humidity detected by the temperature / humidity sensor 52 are low and low humidity, the bias voltage Hh (> H, (Shown by a two-dot chain line). Then, after a predetermined time T2l (> T2) has elapsed since the bias voltage Hh was applied to the charge eliminating needle 38C, the bias voltage Hh is lowered to the bias voltage Lh (> L). Here, since the separation of the paper P from the photosensitive drum 28 is poor in a low temperature and low humidity environment, the bias voltage applied to the static elimination needle 38C is higher than that in a normal temperature and normal humidity environment. Further, the sheet P having a small moisture absorption amount and a strong stiffness does not easily loosen due to the frictional resistance with the pre-fixing conveyance guide 48, and contacts the photosensitive drum 28 when the leading end P1 reaches the point C2 downstream from the point C. To do. For this reason, in the low temperature and low humidity environment, the timing for lowering the bias voltage applied to the static elimination needle 38C is delayed compared to the normal temperature and normal humidity environment.

  Next, a third embodiment of a method for controlling the electrical output of the static elimination needle 38C by the voltage control unit 70 will be described.

  As shown in the timing charts of FIGS. 7 and 6, the resistance value of the transfer roll 38 </ b> A is detected by the resistance detection unit 54, and the voltage control unit 70 corresponds to the resistance value detected by the resistance detection unit 54. The magnitude of the bias voltage applied to the static elimination needle 38C and the timing for changing the bias voltage applied to the static elimination needle 38C are controlled.

  Here, the resistance value of the transfer roll 38A relatively changes as the temperature and humidity change. The voltage control unit 70 stores a parameter table in which the resistance value of the transfer roll 38A corresponding to the temperature and humidity in the image forming apparatus main body 12 (see FIG. 1) is preset. The temperature and humidity corresponding to the resistance value detected by the detection unit 54 are read from the parameter table, and the magnitude of the bias voltage and the bias voltages H, Hh, and Hl are respectively determined according to the temperature and humidity environment, as in the second embodiment. The timing to lower the bias voltages L, Lh, and Ll is controlled.

  This makes it possible to control the electrical output of the static elimination needle 38C corresponding to a change in the temperature and humidity environment without installing the temperature and humidity sensor 52.

  Next, a fourth embodiment of a method for controlling the electrical output of the static elimination needle 38C by the voltage controller 80 will be described.

  As shown in the timing charts of FIGS. 8 and 6, the type of the paper P, that is, the thickness and material of the paper P is identified by the paper type identifying unit 56, and the voltage control unit 80 is identified by the paper type identifying unit 56. The magnitude of the bias voltage applied to the static elimination needle 38C and the timing for changing the bias voltage applied to the static elimination needle 38C are controlled according to the identified type of paper P.

  For example, when a paper P having a standard thickness or material is identified by the paper type identification unit 56, the bias voltage H is applied to the static elimination needle 38C after a predetermined time T0 elapses after the paper P is detected by the paper detection sensor 24. Is done. The bias voltage H is lowered to the bias voltage L after a predetermined time T2 has elapsed since the bias voltage H was applied to the charge eliminating needle 38C.

  On the other hand, when the paper type identifying unit 56 identifies the paper P that is thinner or softer than the standard, the bias voltage Hh (> H1) is applied to the static elimination needle 38C after a predetermined time T0 has elapsed since the detection of the paper P by the detection sensor 24. , Indicated by a two-dot chain line). Then, after a predetermined time T2s (<T2) has elapsed since the bias voltage Hh was applied to the static elimination needle 38C, the bias voltage Hh is lowered to the bias voltage Lh (> L). Here, the paper P, which is weak, has poor separation from the photosensitive drum 28. Further, the weak paper P is easily loosened due to the frictional resistance with the pre-fixing conveyance guide 48, and comes into contact with the photosensitive drum 28 when the leading end P1 reaches the point C2 downstream from the point C. For this reason, when the paper P is thinner or softer than the standard, the bias voltage applied to the static elimination needle 38C is made higher than the standard paper P having a thickness or material, and the bias voltage applied to the static elimination needle 38C is lowered. The timing is fast.

  When the paper type identification unit 56 identifies a paper P that is thicker or harder than the standard, the bias voltage Hl (<<) is applied to the static elimination needle 38C after a predetermined time T0 elapses after the paper P is detected by the paper detection sensor 24. H1, indicated by a dashed line). Then, after a predetermined time T2l (> T2) has elapsed since the bias voltage Hl was applied to the charge elimination needle 38C, the bias voltage Hl is lowered to the bias voltage Ll (<L). Here, the strong paper P has good separation from the photosensitive drum 28. Further, the strong paper P is not easily loosened due to the frictional resistance with the pre-fixing conveyance guide 48, and comes into contact with the photosensitive drum 28 when the leading end P1 reaches the point C2 downstream from the point C. For this reason, when the paper P is thicker or harder than the standard, the bias voltage applied to the static elimination needle 38C is made lower than that of the standard paper P having a thickness or material, and the bias voltage applied to the static elimination needle 38C is lowered. The timing is delayed.

  Note that there are various known methods for identifying the type of the paper P, such as a method for recognizing the type of the paper P input by the user on the touch panel or a personal computer, and a method for detecting the thickness of the paper P with an ultrasonic sensor. Various methods are applicable.

1 is a schematic view of an image forming apparatus according to an embodiment of the present invention. FIG. 3 is a front view illustrating a fixing unit and a pre-fixing conveyance guide of the image forming apparatus according to the exemplary embodiment of the present invention. FIG. 2 is an enlarged side view showing an image forming unit to a fixing unit of the image forming apparatus according to the first embodiment of the present invention. It is a timing chart for demonstrating 1st Embodiment of the control method of the electrical output of a static elimination needle. FIG. 10 is an enlarged side view illustrating an image forming unit to a fixing unit of an image forming apparatus according to a second embodiment of the present invention. It is a timing chart for demonstrating 2nd thru | or 4th embodiment of the control method of the electrical output of a static elimination needle. FIG. 10 is an enlarged side view illustrating an image forming unit to a fixing unit of an image forming apparatus according to a third embodiment of the present invention. FIG. 10 is an enlarged side view illustrating an image forming unit to a fixing unit of an image forming apparatus according to a fourth embodiment of the present invention. FIG. 9 is an enlarged side view illustrating an image forming unit to a fixing unit of a conventional image forming apparatus.

Explanation of symbols

10 Image Forming Device 28 Photosensitive Drum (Image Carrier)
38C Static elimination needle (separation means)
44 Fixing unit (fixing device)
46 Post-transfer conveyance guide 48 Pre-fixation conveyance guide 50 Voltage control unit (control means)
52 Temperature / humidity sensor (temperature / humidity detection means)
54 Resistance detection unit (resistance detection means)
56 Paper type identification unit (medium type identification means)
60 Voltage control unit (control means)
70 Voltage control unit (control means)
80 Voltage control unit (control means)
P paper (recording medium)

Claims (4)

An image carrier for carrying a toner image;
A transfer unit facing the image carrier with a recording medium conveyed therebetween, and transferring a toner image from the image carrier to the recording medium;
Separating means for discharging the recording medium downstream from the transfer means in the transport direction to separate the recording medium from the image carrier;
A post-transfer conveyance guide that guides a recording medium that is separated and conveyed from the image carrier by the separation unit;
An image forming apparatus comprising: a pre-fixing conveyance guide that guides a recording medium that has passed through the post-transfer conveyance guide ascending from the post-transfer conveyance guide to the fixing device;
An image forming apparatus comprising: a control unit that reduces an electrical output of the separation unit while a leading end of a recording medium passes over the pre-fixing conveyance guide. A medium type identifying means for identifying the type of the recording medium;
The image forming apparatus according to claim 1, wherein the control unit controls an electrical output of the separating unit according to a type of the recording medium identified by the medium type identifying unit. It has temperature and humidity detection means for detecting the temperature and humidity in the image forming apparatus body,
3. The control unit according to claim 1, wherein the control unit controls an electrical output of the separation unit according to a temperature and humidity in the image forming apparatus main body detected by the temperature and humidity detection unit. Image forming apparatus. Having a resistance detection means for detecting a resistance value of the transfer means;
The image forming apparatus according to claim 1, wherein the control unit controls an electrical output of the separating unit according to a resistance value of the transfer unit detected by the resistance detecting unit.

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