JP4520726B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet using an intermediate transfer belt.

2. Description of the Related Art Conventionally, in an image forming apparatus that forms an image on a sheet using an intermediate transfer belt, when a sheet conveyed on the belt surface of the intermediate transfer belt is stuck, a claw-like member or the like is attached to the belt surface by a solenoid or the like. There is provided a system in which the sheet is peeled from the belt surface by being pressed against the belt surface. As described above, the sheet adhered on the belt surface may be in close contact without floating. In addition, most of the sheets that are easy to stick to the belt surface as described above are thin with a thickness of about 0.1 mm or less, and when such a sheet is peeled off from the belt surface by a nail member, the belt surface The nail | claw member may be damaged on the top. Such scratches on the belt surface prevent toner adhesion and cause image deterioration. There is a configuration in which the claw member is fixedly disposed in the vicinity of the belt surface without using a solenoid, but in such a configuration, a strict adjustment in manufacturing is required in consideration of the disposition of the claw member. In order to solve such a problem, a configuration is disclosed in which a sensor for detecting a sheet attached to the belt surface is provided, and when the sheet on the belt surface is detected by this sensor, the entire apparatus is stopped. (For example, refer to Patent Document 1).
Japanese Patent Laid-Open No. 11-59962 (pages 4-8, FIG. 1)

  However, the intermediate transfer belt is in contact with a photoreceptor drum (not shown), and even if the entire apparatus is stopped after detecting the sticking of the sheet to the belt surface by the sensor, it is affected by the inertial force due to its own weight. It cannot be stopped instantly. In that case, a sufficient braking force cannot be applied to the sheet, and the sheet does not stop at a desired position and may enter the apparatus while being stuck to the belt surface.

  As described above, when the sheet enters the inside of the apparatus as the belt surface moves, the apparatus may be damaged. Therefore, the entry of the sheet into the apparatus must be avoided as much as possible.

  The present invention has been made to solve the above-described problems, and reliably detects a sheet attached to the intermediate transfer belt with a simple configuration, and allows the sheet to enter the apparatus by the intermediate transfer belt. An object of the present invention is to provide an image forming apparatus that can be avoided.

  In order to solve the above-described problems, an image forming apparatus according to the present invention has a belt surface on which a toner image is formed while moving, and is formed on the belt surface with respect to a sheet conveyed by a conveying unit. An intermediate transfer belt for transferring a toner image, and a transfer position in which the toner image formed on the belt surface is transferred to the sheet in the conveyance direction of the sheet are arranged upstream of the transfer position. A registration operation is performed before being conveyed to a position, and a pair of registration rollers constituting a part of the conveyance unit and a sheet sandwiched by the registration roller pair on the downstream side of the transfer position in the moving direction of the belt surface The sheet moving distance from the position is arranged at a position where the sheet is shorter than the length in the conveyance direction, and the sheet positioned on the belt surface is detected. A sensor belt surface which, when the seat is detected by the belt surface sensor, is characterized in that a control unit for stopping the conveyance of the sheet by the conveying means.

  According to such a configuration, it is difficult to use only a sensor for detecting a jam in the conventional sheet conveyance path, and it is more difficult to remove the sheet attached to the belt surface of the intermediate transfer belt from the regular sheet conveyance path. High-precision detection is possible. That is, it is possible to provide an image forming apparatus that can reliably detect a sheet attached to the intermediate transfer belt with a simple configuration and can prevent the sheet from entering the apparatus by the intermediate transfer belt. . Further, when the belt surface sensor detects a sheet positioned on the belt surface of the intermediate transfer belt, the sheet is still sandwiched between the pair of registration rollers, so that the registration roller with respect to the sheet whose conveyance should be stopped The braking force by the pair can be reliably transmitted and decelerated.

  In the image forming apparatus having the above-described configuration, the control unit detects the sheet by the belt surface sensor after a predetermined time has elapsed from the registration operation start timing by the registration roller pair. It may be configured to stop the conveyance of the sheet.

  Before a predetermined time elapses after the registration operation is started, the sheet should not have reached the detection position that can be detected by the belt surface sensor. That is, if the conveyance of the sheet by the conveying means is stopped only when the belt surface sensor detects the sheet after a predetermined time has elapsed since the registration operation was started, it is unnecessary due to erroneous detection on the belt surface sensor side. It is possible to avoid stopping the sheet conveyance. In addition, it is possible to detect the sheet attached to the belt surface of the intermediate transfer belt with higher accuracy.

  Further, in the image forming apparatus configured as described above, a sheet moving distance upstream of the transfer position in the sheet conveyance direction and to a detection position by the belt surface sensor is in the sheet conveyance direction. The conveyance path sensor is disposed at a position longer than the length and detects a conveyed sheet, and the control unit detects the sheet simultaneously by both the conveyance path sensor and the belt surface sensor. In some cases, it is preferable not to stop the conveyance of the sheet by the conveying unit.

  According to such a configuration, while the sheet is detected by the conveyance path sensor, even if the sheet is stuck to the intermediate transfer belt, the leading edge of the sheet is not detected by the belt surface sensor. Should not reach.

  That is, the case where both the conveyance path sensor and the belt surface sensor simultaneously detect a sheet is when the belt surface sensor is making some false detection. In such a case, the sheet of the sheet by the conveyance means is detected. By not stopping the conveyance, it is possible to avoid stopping the sheet conveyance unnecessarily. In addition, it is possible to detect the sheet attached to the belt surface of the intermediate transfer belt with higher accuracy.

  In the image forming apparatus having the above-described configuration, the belt surface sensor may be an optical sensor and may be disposed with an inclination of 15 ° to 45 ° with respect to the belt surface.

  As described above in detail, according to the present invention, it is possible to reliably detect the sheet attached to the intermediate transfer belt with a simple configuration and to prevent the sheet from entering the apparatus by the intermediate transfer belt. An image forming apparatus can be provided.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
First, a first embodiment of the present invention will be described.

  FIG. 1 is a configuration diagram for explaining an image forming apparatus according to a first embodiment of the present invention.

  The image forming apparatus according to the present embodiment includes an intermediate transfer belt B, a secondary transfer roller 13 and a registration roller 14 constituting a registration roller pair wound around a plurality of rollers including the roller 12 (other than the roller 12 is not shown). And a registration roller 15, conveyance guides 16 and 17, a CPU (control unit) 18, and a belt surface sensor S1.

  First, a normal sheet conveying operation of the apparatus will be described. Here, since the operation for conveying the sheet on which the toner image is to be formed to the registration roller pair after being supplied to the sheet conveyance path is the same as the conventional configuration, the description thereof is omitted.

  The sheet P conveyed in the sheet conveyance path R and reaching the registration roller pair composed of the registration rollers 14 and 15 is abutted against the nip portion c of the registration roller pair, and performs registration processing such as timing adjustment and skew correction. Is given.

  After completion of the registration operation, the sheet P that has been subjected to timing adjustment and skew correction is conveyed to the transfer position b where the secondary transfer roller 13 and the belt surface of the intermediate transfer belt B abut while being guided by the conveyance guide 17. Is done. The secondary transfer roller 13 is configured to contact and be separated from the belt surface of the intermediate transfer belt B in the x direction.

  A desired toner image T is formed on the belt surface of the intermediate transfer belt B through a developing device (not shown) (a toner image is formed while the belt surface moves), and the toner image T is conveyed to the transfer position b. Then, the toner image is transferred to the sheet P being conveyed while being pressed against the belt surface by the secondary transfer roller 13.

  The sheet P having the transferred toner image T ′ is conveyed through the normal sheet conveyance path R while being guided to the conveyance guide 16, and the toner image T ′ is heated and fixed by a fixing device (not shown).

  Next, an operation when the sheet P is stuck on the belt surface of the intermediate transfer belt B without being conveyed on the regular sheet conveyance path R will be described.

  FIG. 2 is a diagram illustrating a state where a sheet is stuck on the intermediate transfer belt in the image forming apparatus according to the present embodiment.

  The sheet P on which the toner image is transferred at the transfer position b sticks to the belt surface of the intermediate transfer belt B, and the leading end of the sheet P (downstream end in the belt surface movement direction) moves together with the belt surface. When the sensor S1 reaches the detection position a where the sheet on the belt surface is detected, the belt surface sensor S1 detects sticking of the sheet P to the belt surface.

  When the leading edge of the sheet P is detected by the belt surface sensor S1, the CPU 18 stops the conveyance of the sheet P by the conveying unit.

  The conveying means here means means that conveys the sheet P when the leading edge of the sheet P is detected, and includes a conveying roller (not shown) arranged along the sheet conveying path R, or a resist. The rollers 14 and 15, the driving means (not shown) for driving the intermediate transfer belt B, and the like are applicable.

  Specifically, when the leading edge of the sheet P is detected by the belt surface sensor S1, for example, the sheet P is nipped and conveyed by the registration rollers 14 and 15, the intermediate transfer belt B, and the secondary transfer roller 13. If it is, the driving of the registration rollers 14 and 15 and the intermediate transfer belt B is stopped, and the secondary transfer roller 13 pressed against the belt surface is separated from the belt surface. In the present embodiment, the belt surface sensor S1 is downstream of the transfer position b in the moving direction of the belt surface and the sheet moving distance from the sheet nipping position c by the registration roller pair is longer than the length in the sheet conveying direction. Are arranged at a short distance, and are configured to detect a sheet located on the belt surface. As a result, when the belt surface sensor detects a sheet located on the belt surface of the intermediate transfer belt (a sheet attached to the belt surface), the sheet is still held between the pair of registration rollers, and the conveyance is stopped. The braking force by the registration roller pair can be reliably transmitted to the sheet to be caused to efficiently decelerate. Here, the distance from the sheet clamping position c by the registration roller pair to the detection position a by the belt surface sensor S1 is such that the sheet moves during the braking time from when the driving of the registration roller is stopped until the sheet stops. Specifically, the distance is a value obtained by adding a margin considering the sheet detection time by the belt surface sensor and the mechanism variation.

  It is difficult to stop the sheet adhering electrostatically to the belt surface at an early stage by simply stopping the intermediate transfer belt. In the case where the registration rollers 14 and 15 are driven and rotated by a clutch, It is effective to decelerate the sheet by turning off the registration roller clutch and stop the conveyance of the sheet.

  On the other hand, when the registration rollers 14 and 15 are directly driven by the motor, the sheet is quickly decelerated by the holding torque of the motor by stopping the motor. Therefore, the motor that drives the registration rollers 14 and 15. In some cases, it is possible to respond by simply stopping.

  The reason why the secondary transfer roller 13 is separated from the belt surface is to avoid contamination of the secondary transfer roller 13 with residual toner as much as possible. Further, in order to avoid damaging the belt surface, it is desirable to cause the secondary transfer roller 13 to be separated before stopping the driving of the registration roller pair.

  Here, the belt surface sensor S1 is disposed downstream of the transfer position b at which the toner image formed on the belt surface is transferred to the sheet in the moving direction of the belt surface of the intermediate transfer belt B. Thus, the sheet located on the belt surface is detected.

  Specifically, the belt surface sensor S1 is disposed so as to detect a sheet positioned on the belt surface of the intermediate transfer belt B at the detection position a. As described above, the detection position a is disposed at a position where the sheet moving distance from the sheet nipping position c by the registration roller pair is shorter than the length in the sheet conveyance direction, and the leading edge of the sheet is detected by the belt surface sensor S1. Even after stopping the sheet conveying operation of the conveying means (after detecting the sticking of the sheet to the belt surface), the sheet can be easily removed because it is held between the pair of registration rollers and stopped. It is set so that.

  On the other hand, in order to prevent the sheet attached to the belt surface from being caught in the apparatus, the sheet conveyance by the conveying means is performed immediately after the belt surface sensor S1 detects the leading edge of the sheet adhered to the belt surface. In order to stop the operation, the belt surface sensor S1 is desirably downstream of the transfer position b and as close as possible to the transfer position b in the moving direction of the belt surface.

  However, considering the convenience of the apparatus configuration and the fact that dust or the like may fly near the transfer position and cause the sensor to malfunction, it is not desirable to be too close to the transfer position b.

  In the present embodiment, in consideration of the above circumstances, the belt surface sensor S1 is disposed behind the conveyance guide 16 that is relatively close to the transfer position b (see FIG. 1), thereby suppressing malfunction of the sensor due to dust or the like. I am trying.

  By the way, in an image forming apparatus that transfers a toner image formed on an intermediate transfer belt to a sheet, not all of the toner image on the belt surface is always transferred to the sheet. Residual toner remaining on the top may occur.

  Since the residual toner exists in a state having a certain thickness on the belt surface as described above, the belt surface sensor S1 may erroneously detect such a thick residual toner as a sheet. Such erroneous detection may cause a wasteful sheet conveyance operation to be stopped, and may affect the processing efficiency of the image forming apparatus.

  Therefore, it is necessary that the belt surface sensor S1 does not detect the residual toner on the belt surface of the intermediate transfer belt B, but only detects the sheet adhered to the belt surface.

  In the present embodiment, a reflective optical sensor is used as the belt surface sensor S1. In such a reflective optical sensor, the object to be detected can be limited by changing the irradiation angle of the irradiated light onto the belt surface.

The following is the relationship between the inclination angle θ with respect to the belt surface of the belt surface sensor S1 obtained by experiments and the detection target. Here, the inclination angle θ means an inclination angle with respect to a normal line on the belt surface in the irradiation direction of the irradiation light from the belt surface sensor S1.
Belt surface of transfer belt 0 ° -8 °
Residual toner 0 ° to 12 °
Thin paper 0 ° to about 75 °
Plain paper 0 ° to about 75 °
FIG. 3 is a table for explaining the arrangement angle of the belt surface sensor S1 in the image forming apparatus according to the present embodiment. This figure shows data relating to an angle range in which the belt surface of the transfer belt can be detected and an angle range in which the sheet can be detected. In the table shown in the figure, the vertical axis represents the sensor detection distance (mm), and the horizontal axis represents the sensor mounting angle (inclination angle θ with respect to the belt surface of the belt surface sensor S1) (°).

  As described above, the belt surface sensor S1 detects a sheet of thin paper or more without detecting the remaining toner by tilting the belt surface sensor S1 with respect to the belt surface in a range of about 13 ° to about 75 °. It is understood that this is possible.

  However, as shown in FIG. 3, when the belt surface sensor is tilted, the distance at which the detection target can be detected changes. If the sensor is too close to the belt surface, the sensor may malfunction due to dust or the like. Furthermore, since the intensity of the reflected light becomes weaker as the arrangement angle of the sensor with respect to the belt surface becomes steeper, it is necessary to make the angle up to a certain degree to maintain the detection accuracy of the sensor. In consideration of these conditions, in the present embodiment, the belt surface sensor S1 is arranged with an inclination angle θ (see FIG. 1) with respect to the belt surface set to 15 ° to 45 °.

With the above-described configuration, it is possible to prevent the sheet attached to the belt surface of the intermediate transfer belt from entering the apparatus outside the sheet conveyance path. In addition, the belt surface sensor is tilted so that the remaining toner and the sheet can be distinguished from each other, thereby preventing a situation in which the remaining toner is erroneously detected as a sheet and stopping the sheet conveying operation (malfunction). can do. Further, the sheet attached to the belt surface of the intermediate transfer belt can be easily removed.
(Second Embodiment)
Next, a second embodiment of the present invention will be described.

The present embodiment is an application of the first embodiment described above. Specifically, a registration switch 19 is added, and a signal from the registration switch 19 is used for a control operation in the CPU. Is different from the first embodiment. Hereinafter, the same parts as those already described in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 4 is a block diagram for explaining an image forming apparatus according to the second embodiment of the present invention.

  As shown in the figure, in the present embodiment, the registration switch 19 is disposed near the upstream side of the registration rollers 14 and 15 in the sheet conveyance direction. The registration switch 19 is turned on by contacting the leading end of the sheet that has reached the pair of registration rollers (the downstream end in the sheet conveying direction).

  The registration roller pair starts a registration operation at a timing based on the ON signal of the registration switch 19.

  Next, the operation of the image forming apparatus according to this embodiment will be described.

  The CPU 18 ′ stops the conveyance of the sheet P by the conveying unit when the belt surface sensor S 1 detects the sheet P after a predetermined time has elapsed from the registration operation start timing by the registration roller pair.

  If the residual toner Tz remains on the belt surface of the intermediate transfer belt B, the residual toner Tz is erroneously detected as a sheet even if the belt surface sensor S1 is inclined depending on the thickness of the residual toner Tz. It can happen.

  Even in such a case, the sheet can be detected by the belt surface sensor S1 before a predetermined time (the time required for the sheet to reach the detection position a from the position of the registration switch 19) has elapsed since the registration switch 19 was turned on. The detection position a should not be reached.

  That is, if the conveyance of the sheet P by the conveying unit is stopped only when the belt surface sensor S1 detects a sheet after a predetermined time has elapsed after the registration switch 19 is turned ON, the residual toner Tz is erroneously detected as a sheet. Thus, it is possible to avoid unnecessarily stopping the sheet conveyance. At this time, if the belt surface sensor S1 detects the sheet within a predetermined time after the registration switch 19 is turned on (that is, it is determined that the sheet is detected), this signal is ignored.

  Here, the predetermined time is determined based on the time when the registration operation is performed by the registration roller pair after the registration switch 19 is turned on, the sheet conveyance speed, the distance from the position of the registration switch 19 to the detection position a, and the like. Is done. Further, although the start timing of the registration operation is determined based on a signal from the registration switch 19, the present invention is not limited to this, and a dedicated switch (sensor) may be provided separately from the registration switch 19.

Further, here, the belt surface sensor S1 detects a sheet by performing a sheet detection operation every 8 milliseconds immediately after a predetermined time has elapsed, for a total of five times. This is because, if the detected object is residual toner, it is rare that the detection result that all sheets are detected by detecting the toner five times at intervals of 8 msec. This is because it should be detected. That is, if all the five detection results are determined to be sheets, the remaining toner is determined to be a sheet when it is determined that there is no sheet even among the five detection results.
(Third embodiment)
Next, a third embodiment of the present invention will be described.

The present embodiment is an application of the above-described first embodiment. Specifically, a conveyance path sensor S2 is added, and a signal from the conveyance path sensor S2 is used for a control operation in the CPU. This is different from the first embodiment. Hereinafter, the same parts as those already described in the above-described embodiment are denoted by the same reference numerals, and description thereof is omitted.

  FIG. 5 is a block diagram for explaining an image forming apparatus according to the third embodiment of the present invention.

  As shown in the figure, in the present embodiment, the sheet moving distance from the transfer position b in the sheet conveyance direction to the upstream side of the transfer position b and the detection position a by the belt surface sensor S1 is the sheet movement distance. It is arranged at a position longer than the size in the transport direction (see FIG. 5). The conveyance path sensor S2 detects a sheet passing near the conveyance path sensor S2 in the sheet conveyance path R.

  Next, the operation of the image forming apparatus according to this embodiment will be described.

  The CPU 18 ″ performs control so as not to stop the conveyance of the sheet by the conveyance unit when both the conveyance path sensor S2 and the belt surface sensor S1 detect the sheet at the same time.

  As described in the second embodiment, when the residual toner Tz remains on the belt surface of the intermediate transfer belt B, the belt surface sensor S1 is inclined and arranged depending on the thickness of the residual toner Tz. Even in this case, the remaining toner Tz may be erroneously detected as a sheet.

  Even in such a case, if the conveyance path sensor S2 is disposed at a position longer than the length of the sheet P conveyed from the detection position a, while the sheet P is detected by the conveyance path sensor S2, Even if this sheet adheres to the intermediate transfer belt B, the leading edge of the sheet should not reach the detection position a.

  That is, in the configuration of the present embodiment, when both the conveyance path sensor S2 and the belt surface sensor S1 simultaneously detect a sheet, the belt surface sensor S1 erroneously detects the remaining toner Tz as a sheet. In such a case, it is possible to avoid stopping the sheet conveyance unnecessarily by controlling the conveyance of the sheet by the conveyance unit so as not to be stopped.

1 is a configuration diagram for explaining an image forming apparatus according to a first embodiment of the present invention; FIG. In the image forming apparatus according to the present embodiment, it is a diagram showing a state where a sheet is stuck to the intermediate transfer belt. 6 is a table for explaining an arrangement angle of a belt surface sensor in the image forming apparatus according to the present embodiment. It is a block diagram for demonstrating the image forming apparatus by the 2nd Embodiment of this invention. It is a block diagram for demonstrating the image forming apparatus by the 3rd Embodiment of this invention.

Explanation of symbols

12 roller, 13 secondary transfer roller, 14, 15 registration roller, 16, 17 conveyance guide, 18 CPU, 19 registration switch, S1 belt surface sensor, S2 conveyance path sensor, B intermediate transfer belt, R sheet conveyance path, T toner image, Tz residual toner, P sheet.

Claims (3)

An intermediate transfer belt having a belt surface on which a toner image is formed while moving, and transferring the toner image formed on the belt surface to a sheet conveyed by a conveying unit;
The toner image formed on the belt surface in the sheet conveyance direction is arranged upstream of a transfer position at which the toner image is transferred to the sheet, and performs a registration operation before the sheet is conveyed to the transfer position. And a pair of registration rollers constituting a part of the conveying means,
The sheet movement distance from the sheet clamping position by the registration roller pair is downstream of the transfer position in the movement direction of the belt surface, and is disposed at a position shorter than the length of the sheet in the conveyance direction, A belt surface sensor for detecting a sheet located on the belt surface;
The sheet moving distance upstream of the transfer position in the sheet conveyance direction and up to the detection position by the belt surface sensor is arranged at a position longer than the length of the sheet in the conveyance direction and conveyed. A conveyance path sensor for detecting a sheet to be detected;
When conveyance of the sheet by the conveying unit is stopped when the sheet is detected by the belt surface sensor, and when the sheet is simultaneously detected by both the conveyance path sensor and the belt surface sensor An image forming apparatus comprising: a control unit that does not stop the conveyance of the sheet by the conveyance unit. The image forming apparatus according to claim 1.
The image forming apparatus that stops the conveyance of the sheet by the conveying unit when the control unit detects the sheet by the belt surface sensor after a predetermined time has elapsed from the registration operation start timing by the registration roller pair. The image forming apparatus according to claim 1.
Sensor wherein the belt surface is a light sensor, the irradiation direction of the irradiation light from the belt surface sensor, inclination angle against the normal line on the belt surface, are arranged so that the 15 ° to 45 ° Image forming apparatus.

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