JP3781081B2 - Image forming apparatus using endless belt - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as an electrophotographic copying machine or a laser printer, and more particularly to an image forming apparatus that forms an image using an endless belt as an intermediate transfer member.
[0002]
[Prior art]
In an image forming apparatus such as an electrophotographic copying machine or printer, there is a method in which a printed image is obtained by transferring an unfixed toner image formed on a latent image carrier such as a photosensitive drum onto a recording medium such as paper. It is done. As a method for transferring the unfixed toner image to the recording medium, a method for directly transferring the unfixed toner image to the recording medium, and a method for transferring the unfixed toner image formed on the latent image carrier into a drum shape or an endless belt shape. There is known a system in which a primary image is transferred onto an intermediate transfer member made of the above film member, and then an unfixed toner image on the intermediate transfer member is secondarily transferred onto a recording medium to obtain a copy image.
[0003]
FIG. 12 is a schematic diagram illustrating a main configuration of a color printer as an example of an image forming apparatus using a belt-shaped intermediate transfer member. In the figure, the surface of a latent image carrier (hereinafter, described as “photoreceptor drum”) 1 such as a photoreceptor drum is uniformly charged with a predetermined charge by a charger 2, and the laser beam L An electrostatic latent image corresponding to the first color image signal is formed by writing scanning. This electrostatic latent image reaches the position facing the first color developing device of the developing device unit 3 by the rotation of the photosensitive drum 1 in the A direction, and is developed with toner by the first color developing device. The photosensitive drum 1 carries the toner image T and further rotates.
[0004]
In accordance with the toner developing operation, the intermediate transfer belt 4 moves at substantially the same speed as the peripheral speed of the photosensitive drum 1, and the intermediate transfer belt is located immediately below the position where the photosensitive drum 1 and the intermediate transfer belt 4 abut. 4 is applied to the photosensitive drum 1 by a transfer electric field having a polarity opposite to the charging polarity of the toner applied to the primary transfer roll 5 in the primary transfer portion where the primary transfer roll 5 disposed in contact with the primary transfer roll 5 is disposed. The carried toner image T is primarily transferred to the intermediate transfer belt 4. This completes the primary transfer cycle.
[0005]
The toner image primarily transferred to the intermediate transfer belt 4 reaches the secondary transfer portion where the secondary transfer roll 6 is disposed by the circumferential movement of the intermediate transfer belt 4. In the case of a full-color image forming apparatus, the process from the formation of the latent image to the primary transfer of the toner image is repeated for the predetermined colors (generally yellow (Y), magenta (M), cyan (C) and black (Bk)). A color toner image is formed by superimposing multicolor toners on the intermediate transfer belt 4.
[0006]
To form a toner image of each color, a developing device unit 3 yellow developing unit 3 _-1, magenta developing device _3-2, cyan developer 3 _-3 and black developing unit 3 _-4 rotating device consisting of four color developing devices The latent image of each color formed on the photosensitive drum 1 can be sequentially developed.
[0007]
After the first color toner image carried on the photosensitive drum 1 is transferred onto the intermediate transfer belt 4 at the primary transfer portion, the residual toner on the photosensitive drum 1 is removed by the photosensitive cleaner 7 and illustrated. After the charge is neutralized by the static eliminator, the next latent image corresponding to the second color is formed. The electrostatic latent image of the second color is also developed in the same manner as the first color, and the second color toner image is transferred onto the intermediate transfer belt 4 so as to overlap the previously transferred first color toner image. The Thereafter, the third and subsequent colors are similarly transferred to the intermediate transfer belt 4 in the same manner. As a result, a color toner image in which a plurality of unfixed toners are superimposed is formed on the intermediate transfer belt 4.
[0008]
When the intermediate transfer belt 4 on which the toner images of all colors are primarily transferred reaches the secondary transfer position, the recording paper P as a recording medium sent out from the paper feed tray 8 at the appropriate timing is transferred to the secondary transfer position. To be sent to.
[0009]
When the recording paper P is nipped and conveyed by the secondary transfer roll 6 and the intermediate transfer belt 4, a transfer electric field formed by a transfer voltage having a polarity opposite to the charging polarity of the toner image applied to the secondary transfer roll 6 is used. The toner image on the intermediate transfer belt 4 is secondarily transferred to the recording paper P. The recording paper P onto which the toner image has been secondarily transferred is sent to the fixing device 9, where the toner image is fixed to the recording paper P by heating and pressurizing processing, and the image forming process is completed.
[0010]
The secondary transfer roll 6 is provided so as to be able to contact and separate in the direction of arrow C with respect to the intermediate transfer belt 4, contacts with the recording paper P entering, and separates with discharge. The secondary transfer roll 6 returns to the retracted position when the secondary transfer ends. Further, the cleaner 10 disposed opposite to the intermediate transfer belt 4 also makes contact with the intermediate transfer belt 4 in the same manner as the secondary transfer roll P in order to clean the toner image that has not been transferred to the recording paper P.・ Separate.
[0011]
The intermediate transfer belt 4 is stretched by a drive roll 11, an idle roll 12, a secondary transfer backup roll 13 and a tension roll 14, and is conveyed in the direction of arrow B by the drive roll 11. The intermediate transfer belt 4 is provided with ribs for regulating the position of each roll in the axial direction, such as the drive roll 11, along the inner circumference of the side end portion. For reinforcement, the intermediate transfer belt is provided with a belt reinforcing tape along the outer periphery of the side end portion.
[0012]
In such a color image forming apparatus using an intermediate transfer belt, a composite toner image (a superimposed image of each color toner image) that has already been multiplex-transferred on the intermediate belt is collectively transferred to a recording medium. There is an advantage that it is possible to effectively prevent the positional deviation between the toner images and the occurrence of image disturbance in the method of sequentially transferring the toner images of the respective colors from the carrier directly to the recording medium.
[0013]
Various configurations have been proposed in the past for rotating the intermediate transfer belt 4 from the viewpoint of preventing breakage of the end of the intermediate transfer belt 4. For example, Japanese Patent Laid-Open No. 5-134556 discloses a transfer belt in which a tape as a reinforcing member is attached to an end portion.
[0014]
[Problems to be solved by the invention]
As described above, since the toners of a plurality of colors are synthesized on the intermediate transfer belt, the reference position on the intermediate transfer belt is accurately set in order to prevent misalignment of these toner colors, that is, color misregistration. Therefore, the operation of each part of the image apparatus must be controlled based on the detection signal of the reference position.
[0015]
Therefore, in order to detect the reference position on the intermediate transfer belt, the marking formed by the paint or tape on the belt or the through hole is read by a reflective sensor, or the rotational position of the belt drive roll is read by an encoder. It is.
[0016]
Among the above detection methods, when marking is performed using a through hole, stress may be concentrated in the hole, which may cause cracks in the intermediate transfer belt. Further, the method of reading the rotation of the drive roll tends to cause an error due to slip between the belt and the drive roll. Therefore, a method of detecting paint or tape on the belt is most advantageous.
[0017]
However, even in this case, in order to reduce the color misregistration of each color on the intermediate transfer belt, it is necessary to devise so that the marking such as the paint or the tape can be detected with extremely high accuracy. For example, when it is desired to suppress the color misregistration to 125 μm, there has been a demand for a marking detection error of 15 μm or less.
[0018]
In order to satisfy such strict accuracy, it is necessary to eliminate many factors that cause detection errors, such as the rotation speed of the intermediate transfer belt, the deflection and vibration generated during the rotation, and the mounting position of the reflective sensor. There is.
[0019]
SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of solving the above-described problems and accurately detecting a reference position on an endless belt and obtaining a good image without color misregistration.
[0020]
[Means for Solving the Problems]
The present invention provides an image forming apparatus having an endless belt as a toner image carrier that holds and conveys a toner image, and belt stretching means comprising a plurality of rolls for stretching and conveying the endless belt. Frame means for supporting the belt device including the belt device, a belt position display mark member provided on the outer peripheral surface of the endless belt, and both ends of the outer peripheral surface of the endless belt for detecting the belt position display mark member. And optical detection means arranged opposite to each other, wherein the optical detection means is fixed to the frame means.
[0021]
According to the above feature, since the endless belt is supported by the frame means and the optical detection means is fixed to the frame means, the positional relationship such as the distance and relative angle with the endless belt can be maintained constant. .
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a color image forming apparatus to which the present invention is applied will be described in detail with reference to the accompanying drawings. Here, the configuration, operation, and the like described with reference to FIG. 12 are used, and description will be made with reference to FIG. 12 as appropriate.
[0023]
FIG. 1 is an enlarged view of a main part showing a manner of attaching a reflective sensor for detecting a reference position on the intermediate transfer belt 4. In the figure, the drive roll 11 is supported by a side frame 18 constituting a belt unit via a shaft 19. The tension roll 14 is supported by a shaft 21 on a bracket 20 pivotally supported by the side frame 18. The intermediate transfer belt 4 is wound around rolls including the drive roll 11, the tension roll 14, the idle roll 12, and the backup roll 13, and a predetermined tension is applied by the tension roll 14.
[0024]
Between the drive roll 11 and the tension roll 14, a reflective sensor 22 that detects the reference position is disposed. The reflective sensor 22 is directly fixed to the side frame 18 so that the distance SD with the intermediate transfer belt 4 does not fluctuate. Further, a sensor backing 23 is disposed at a position facing the reflective sensor 22 on the back side of the intermediate transfer belt 4, that is, the inner peripheral surface side. As shown in FIGS. 15 and 16, the sensor backing 23 has a box shape as a whole, and part of both ends are notched so as to escape a rib 41 (details will be described later).
[0025]
The sensor backing 23 is surely brought into contact with the back surface of the intermediate transfer belt 4 at a position slightly pushed to the outer periphery side of the belt 4 from the surface connecting the outer periphery of the drive roll 11 and the outer periphery of the tension roll 14. Positioned and attached to the side frame 18. In this way, the reflection type sensor 22 for detecting the marking described later is disposed so that the distance from the intermediate transfer belt 4 does not easily fluctuate.
[0026]
For example, the detection error in the traveling direction of the intermediate transfer belt 4 by the reflective sensor 22 is as shown in FIG. As shown in FIG. 4, the total error is determined by each error of measurement repetition, change in power supply voltage, and detection distance. Here, the error due to the detection target, that is, the distance between the marking and the reflective sensor 22 (detection distance) is 3.8 to 11.6 μm when the intermediate transfer belt 4 vibrates by 32 μm. Thus, the influence of the vibration of the intermediate transfer belt 4 on the total error is large.
[0027]
Further, the detection error due to the error in the mounting angle of the reflective sensor 22 is as follows. In FIG. 13, when the distance from the tip of the reflective sensor 22 to the surface of the intermediate transfer belt 4 is H, and the angle between the optical axis and a line perpendicular to the surface of the intermediate transfer belt 4, θ is the intermediate transfer belt 4. Is detected by the following equation when the oscillates up and down hmm. From X / H = x / h to x = h · X / H, the detection error x is obtained by x = h · tan θ (Expression 1). According to (Expression 1), for example, when the angle θ is 5 ° and the intermediate transfer belt 4 vibrates 0.032 mm, the detection error x is 2.8 μm.
[0028]
As described above, the attachment error of the reflective sensor 22 and the marking detection error due to the vibration of the intermediate transfer belt 4 immediately appear as color misregistration. Therefore, it is extremely important to reduce this. In this embodiment, the reflection type sensor 22 is fixed to the side frame 18 that supports the intermediate transfer belt 4 to reduce detection errors, and the sensor backing 23 suppresses vibration of the intermediate transfer belt 4.
[0029]
Furthermore, in order to improve the detection accuracy by the reflective sensor 22, the following configuration is adopted. FIG. 5 is a cross-sectional view of the intermediate transfer belt 4. A rib 41 is bonded to the inner side of the intermediate transfer belt 4 along the side end. Further, a belt reinforcing tape 42 as a belt reinforcing means is bonded to the outer side of the side end portion of the intermediate transfer belt 4, that is, the outer peripheral portion, along the side end portion. The inner side surfaces of the ribs 41, that is, the surface near the center in the width direction of the intermediate transfer belt 4, abuts and slides against the end surface when passing through the rolls such as the drive roll 11, and the axial direction of the rolls Movement is restricted.
[0030]
The intermediate transfer belt 4 is made of a polyimide resin, and has a thickness of 50 to 100 μm, a volume resistivity of 10 ⁹ to 10 ¹² Ω · cm, and a surface resistivity of 10 ¹¹ to 10 ¹³ Ω / □. It is a sex film. The intermediate transfer belt 4 may be an acrylic resin, a vinyl chloride resin, a polycarbonate resin, or the like as long as it is a semiconductive resin material whose thickness, volume resistivity, and surface resistivity are within the above ranges. A material containing a resistance stabilizing material can be used.
[0031]
A thermosetting resin is suitable for the material of the rib 41. For example, a polyurethane resin having a thickness of 0.5 to 1.5 mm can be used. As an example of the material of the belt reinforcing tape 42, polyethylene terephthalate (PET) having a thickness of 50 to 100 μm can be selected.
[0032]
FIG. 3 is a perspective view of a principal part showing an adhesive state of a reflective tape as a marking affixed to the outer peripheral surface of the intermediate transfer belt 4. The reflective tape 24 is affixed on the belt reinforcing tape 42 in an overlapping manner. The reflective tape 24 is positioned and pasted so as to straddle the gap g generated at the abutting portion of the rib 41. The reason why the reflective tape 24 is disposed across the gap g in this way is as follows.
[0033]
FIG. 5 is an enlarged view of a main part of the rib abutting portion for explaining the detection error. In the figure, when the gap g is generated in the rib 41, the intermediate transfer belt 4 is deformed along the gap g to form a dent. As a result, the surface of the dent acts as a concave lens to reflect the light output from the reflective sensor 22, and the reflective sensor 22 may receive the light and erroneously output a detection signal.
[0034]
On the other hand, when the reflective tape 24 is pasted across the gap g, the following effect is obtained. FIG. 6 is an enlarged view of a main part of the rib abutting portion according to the present embodiment. In the figure, when the intermediate transfer belt 4 moves in the direction of arrow B, the reflective sensor 22 detects the tip of the reflective tape 24. Therefore, even if the reflective tape 24 is recessed due to the gap g, an erroneous received light signal in this recess is immediately after the correct detection signal, and it is relatively easy to distinguish from the correct detection signal.
[0035]
The reflective tape 24 is preferably one that has excellent chemical resistance and heat resistance and generates little static electricity. For example, polyester tape No. 1 manufactured by Sumitomo 3M Limited. A silver color of 850 is preferred. This No. The 850 tape uses an aluminum-deposited polyester film as a base material and uniformly applies an acrylic pressure-sensitive adhesive to form an adhesive portion. No. The physical properties of the 850 tape are shown in FIG. Note that the reflective tape 24 has this No. The present invention is not limited to 850 tapes, and any tape having the same characteristics may be used.
[0036]
Next, a second embodiment will be described. FIG. 7 is a diagram showing the output characteristics of the reflective sensor, with the vertical axis representing the output voltage and the horizontal axis representing the distance to the detection target. In the figure, when the threshold is 1.9 V, the output voltage due to the reflected light from the reflective tape 24 sufficiently exceeds the threshold regardless of whether the reflective tape is an unused product or a used product. Yes. It can be seen that a sufficient output voltage is obtained when the distance to the reflective tape 24 is about 10 mm.
[0037]
On the other hand, the output voltage due to the reflected light from the intermediate transfer belt 4 and the belt reinforcing tape 42 adhered on the intermediate transfer belt 4 does not exceed the threshold. In this case, the difference in output voltage between the intermediate transfer belt 4 and the belt reinforcing tape 42 is small. Moreover, although the transparent tape and the black tape were tested as the belt reinforcing tape 42, there was almost no difference in the output voltage in any of them.
[0038]
An example of a circuit for obtaining the output voltage from the detection light by the reflection sensor 22 is shown in FIG. In the figure, when the voltage Vcc is applied, the light emitting diode D1 emits light, and a current i corresponding to the reflected light from the detection object OB flows through the phototransistor Tr1. The comparator COMP detects the output voltage Vout by comparing the terminal voltage of the resistor R2 due to the current i with a reference voltage (divided voltage of the resistors R3 and R4). R1 is a current limiting resistor, and RL is an external connection resistor.
[0039]
As far as the above-mentioned sensor output characteristics are concerned, it seems easy to distinguish the reflective tape 24 from the other by the reflective sensor 22. However, there is a risk of erroneous detection in the following cases.
[0040]
For example, if there is a portion where the belt reinforcing tape 42 and the intermediate transfer belt 4 are not sufficiently bonded, a gap (bubble) may be formed between the portion and the intermediate transfer belt 4 due to repeated use. In particular, when passing through a roll having a large contact angle (lap angle) with the intermediate transfer belt 4 such as the drive roll 11, the deformation of the intermediate transfer belt 4 and the belt reinforcing tape 42 becomes large, so that the stress on the adhesive portion is large. . Similarly, a gap may be formed between the belt reinforcing tape 42 and the intermediate transfer belt 4 in the same manner.
[0041]
FIG. 9A shows a gap SB generated in a portion where the belt reinforcement tape 42 and the intermediate transfer belt 4 are not sufficiently bonded, and FIG. 9B shows a gap formed between the belt reinforcement tapes 42. The gap SB is shown.
[0042]
As described above, when a transparent tape is used as the belt reinforcing tape 42, if a gap including air bubbles is generated between the intermediate transfer belt 4 and the intermediate transfer belt 4, the color of the intermediate transfer belt 4 does not pass through the belt reinforcing tape 42. In addition, the bubble portion looks white. Then, the light of the reflective sensor 22 is reflected by this white portion and input to the reflective sensor 22, and the output voltage may exceed the threshold. That is, an error that outputs a detection signal of the reflective tape 24 occurs in a portion where the reflective tape 24 is not present.
[0043]
Therefore, in the present embodiment, the belt reinforcing tape 42 is made black to successfully prevent the occurrence of the above error. FIG. 10 shows a result of measuring the output voltage of the reflective sensor 22 at a portion where a gap including air bubbles is formed between the belt reinforcing tape 42 and the intermediate transfer belt 4. As shown in the figure, when the belt reinforcing tape 42 is transparent, the output voltage of the reflective sensor 22 exceeds the threshold, but when the belt reinforcing tape 42 is a black tape, the output is also output in the gap portion. The voltage did not exceed the threshold.
[0044]
Next, a third embodiment of the present invention will be described. As shown in FIG. 7, regardless of whether the reflective tape 24 is new or used, if the distance from the reflective sensor 22 is about 12 mm, the reflective sensor 22 has an output voltage higher than the threshold. Indicates.
[0045]
However, it is expected that the reflective tape 24 is heavily soiled and scratched, and it is meaningful to increase the degree of freedom of the attachment position of the reflective sensor 22 by reducing the dirt and scratches of the reflective tape 24 as much as possible.
[0046]
Therefore, in this embodiment, the reflective tape 24 is provided as shown in FIG. In FIG. 11, the reflective tape 24 is disposed between the belt reinforcing tape 42 and the intermediate transfer belt 4. This can prevent the occurrence of dirt and scratches. Further, the side seal that seals the side of the cleaner blade of the belt cleaner 10 slides on the end portion of the intermediate transfer belt 4, but there is an advantage that there is no possibility that the reflective tape 24 is peeled off by such a sliding contact body. is there.
[0047]
In the above-described embodiment, the intermediate transfer belt has been described as an example of the endless belt. However, the present invention is not limited to this, and the present invention can also be applied to an image forming apparatus that uses a photoreceptor belt instead of the photoreceptor 1.
[0048]
【The invention's effect】
As is apparent from the above description, according to the present invention, the endless belt is supported by the frame means, and the optical detection means is fixed to the frame means, so that the positional relationship with the endless belt is maintained constant. be able to. Therefore, an error in detection accuracy due to an error in the detection distance and detection angle can be reduced, and the reference position on the endless belt can be detected accurately. As a result, color misregistration can be minimized.
[Brief description of the drawings]
FIG. 1 is an enlarged view of a main part of an intermediate transfer belt according to an embodiment of the present invention.
FIG. 2 is a cross-sectional view of an intermediate transfer belt.
FIG. 3 is a perspective view of a main part of an intermediate transfer belt showing a position of a reflective tape.
FIG. 4 is a diagram illustrating the magnitude of a total detection error of a reflection type sensor.
FIG. 5 is an enlarged view of a main part showing a rib joint part of a conventional device.
FIG. 6 is an enlarged view of a main part showing a rib joint part according to the embodiment.
FIG. 7 is a diagram showing output characteristics of a reflective sensor.
FIG. 8 is a circuit diagram of a reflective sensor.
FIG. 9 is an essential part enlarged view showing a gap formed between a reinforcing tape and an intermediate transfer belt.
FIG. 10 is a diagram showing output characteristics of a reflective sensor.
FIG. 11 is a perspective view showing an example in which a reflective tape is disposed between an intermediate transfer belt and a reinforcing tape.
FIG. 12 is a schematic diagram illustrating a main configuration of a color printer.
FIG. 13 is a diagram for explaining a detection error due to the attachment accuracy of the reflective sensor.
FIG. 14 is a characteristic diagram of the reflective tape.
FIG. 15 is a perspective view of a main part of a belt backing member.
FIG. 16 is a cross-sectional view of a main part of a belt backing member.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 4 ... Intermediate transfer belt, 11 ... Drive roll, 14 ... Tension roll, 18 ... Side frame, 22 ... Reflective sensor, 23 ... Backing, 41 ... Rib, 42 ... Belt reinforcement tape

Claims (8)

In an image forming apparatus having an endless belt as a toner image carrier for holding and transporting a toner image, and a belt stretching means comprising a plurality of rolls for stretching and transporting the endless belt,
A rib member provided along both ends of the inner peripheral surface of the endless belt, including a butted portion at the end;
A belt position indicating mark member disposed on the outer peripheral surface of the endless belt and straddling the butted portion;
An image forming apparatus using an endless belt, comprising: a light reflection type sensor disposed opposite to an outer peripheral surface of the endless belt for detecting the belt position display mark member. Further comprising an endless belt reinforcing tape provided along both ends of the outer peripheral surface of the endless belt;
The belt position indicating mark member, an image forming apparatus using an endless belt according to claim 1, characterized in that it is arranged on the endless belt reinforcing the tape. 3. An image forming apparatus using an endless belt according to claim 2, wherein the endless belt reinforcing tape has a black color. 3. The image forming apparatus using an endless belt according to claim 2, wherein the endless belt reinforcing tape has the same color as the endless belt. 3. The endless belt according to claim 2, wherein the endless belt reinforcing tape is a transparent tape, and the belt position indication mark member is disposed between the endless belt and the endless belt reinforcing tape. An image forming apparatus using a belt. The endless belt in contact with the back surface of the endless according to claim 1, characterized by including a belt backing member disposed in the width direction region of endless belt including at least the light reflection type sensor and a position facing An image forming apparatus using a belt. 7. The image forming apparatus using an endless belt according to claim 6 , wherein the belt backing member is fixed to the frame means. 7. An image forming apparatus using an endless belt according to claim 6, wherein the belt backing member is formed with a relief so as not to contact a rib provided on an inner periphery of the end portion of the endless belt. .

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